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Same Site, Different Look. Spex SamplePrep is now Cole-Parmer.


Some of the most frequently asked questions we get are listed below.
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What are your hours of operation?
Our normal business hours are from 8:30AM - 5PM EST.

What warranty comes with Cole-Parmer Products?

Cole-Parmer guarantees its products against defects of materials and workmanship for three years from the date of original shipment. Repairs, replacements, or parts provided under warranty are guaranteed for 30 days or for the remaining original warranty period (whichever is greater) Items not produced by Cole-Parmer carry the manufacturer's warranty only. The warranty excludes wear parts: parts that wear out through use and have to be replaced periodically for proper operation. Accessories and consumable products are also excluded from warranty coverage. The customer pays return freight for warranty claims but Cole-Parmer will pay for return freight to the customer if the claim is valid. Cole-Parmer reserves the right to judge whether a malfunction is due to defects in materials or workmanship, or to wear, negligence, or misuse. This warranty shall not apply to any components subjected to misuse due to common negligence, adverse environmental conditions, or accident, not to any components, which are not operated in accordance to the printed instructions in the operation manual. Nor does this warranty apply to any product, which has been altered, damaged, tampered with, or subjected to misuse or abuse including substituting parts or accessories of other manufacturers without the written consent of the Seller. Minor adjustments are not covered by warranty. Labor, materials, and expenses shall be billed to the Buyer at the rates then in effect for any repairs or replacements not covered by this warranty. This warranty shall not apply to any Cole-Parmer manufactured components that have been repaired, altered or installed by anyone not authorized Cole-Parmer in writing. We reserve the right to determine if there has been any misuse of our equipment. Complete warranty details are provided in Cole-Parmer's Terms and Conditions , which are supplied with product quotes and purchase, or upon request

Do you offer a demo program for your products?
Yes we do! In fact we allow companies just like yourself to try our products for a demonstration period of one week. This will allow your staff the opportunity to use our products first-hand. You only have to pay for the cost to ship the product. For more details please visit our demo program page or contact us for more details.

Cole-Parmer is not in my country, how do I find a local distributor?

You can find a local distributor by viewing our distributor list or by contacting customer service.

I just placed my order, when should I expect this to ship?

Shipments of in stock consumable and accessory items will typically ship out within 2-3 business days.  Equipment and out of stock items may take longer to ship.  Please call customer service for exact lead times on your product of interest.

What do I do if I need my items faster?
If you require expedited shipping please let us know at the time of order. You must upgrade to overnight or next day shipping to have your order expedited.

Tissue Homogenization and Cell Lysis

What are the applications for the Geno/Grinder®?
The SPEX SamplePrep 2010 Geno/Grinder® was originally designed as a titer plate shaker for extracting DNA from seeds and plant tissue. This involved shaking two sealed, 96-well titer plates with plant tissue, buffer, and a steel grinding ball in each well. Over the years, the versatility of the Geno/Grinder design has enabled it to accommodate a wider variety of sample containers and sample types. Not only can it be used for high-throughput tissue homogenization, DNA/RNA and protein extraction, it can also be used for lysing bacteria and yeast. Most recently it has been used to increase sample throughput for pesticide residue analysis using the QuEChERS method. A wide range of Application Notes are available which discuss the various Geno/Grinder® applications in more detail.
What are the advantages of the Geno/Grinder® over other tissue homogenizers?
Unlike other tissue homogenizers which clamp titer-plates on their side and move in a "figure-eight motion", the 2010 Geno/Grinder® uses a vertical shaking motion - a much more efficient grinding process. This ensures that the grinding media impacts the sample each and every time and ultimately results in higher yields. Another benefit of the vertical grinding action is that titer-plates and vials are kept in their upright position, eliminating potential well-to-well contamination. The Geno/Grinder is also able to accommodate a larger quantity and variety of sample formats including micro-centrifuge and PCR tubes, titer-plates, vial sets, and conical bottom centrifuge tubes. The list of Geno/Grinder accessories has been greatly expanded making it possible to grind a much wider range of samples. Cryo-Blocks® and related Kryo-Tech® accessories preserve temperature sensitive samples and can be used for extracting RNA and proteins from both plant and animal tissue.
What are the benefits of grinding at low temperatures?
Most samples become embrittled at low temperatures, making them easier to grind. When working with nucleic acids, grinding at low temperatures can also result in higher yields.
Can I use third party titer plates, vials, and centrifuge tubes?
While most titer plates and vials can be used in the 2010 Geno/Grinder, the titer plates and vial sets sold by SPEX SamplePrep were specifically chosen for their durability. They have been tested extensively with various samples and have been shown to resist perforation by steel grinding balls even at high clamp speeds. Standard conical bottom centrifuge tubes may be used when grinding at room temperature with the 2196 Foam Holder for 50 mL Centrifuge Tubes and the 2197 Foam Holder for 15 mL Centrifuge Tubes. However, when grinding cryogenically with the 2664 Cryo-Block for 50 mL Centrifuge Tubes or 2661 Cryo-Block for 15 mL Centrifuge Tubes, SPEX SamplePrep's Cryovials MUST be used. Cryovials are specifically designed to withstand the low temperatures and they include the 2252-PC-30 15 mL Polycarbonate Cryovial, 2253-PC-12 50 mL Polycarbonate Cryovial, and 2254-PE-12 50 mL Polyethylene Cryovial.
Which formats will the Geno/Grinder® accommodate?
The 2010 Geno/Grinder®, in combination with the 2195 Large Clamp Assembly, accommodates a wide variety of formats including but not limited to: •Micro-centrifuge and PCR tubes •96-well titer plates •48-well titer plates •24-well titer plates •5ml Vial Sets •15 ml Vial Sets •15 mL centrifuge tubes and Cryovials •50 mL centrifuge tubes and Cryovials
How many samples can I process at one time?
The number of samples you can process at one time in the 2010 Geno/Grinder® depends on which clamp assembly is used. The standard clamp assembly that is supplied with the Geno/Grinder can accommodate two titer plates, vial sets or Cryo-Blocks. The 2195 Large Clamp Assembly (sold separately) can hold four titer plates or vial sets and can also accommodate conical bottom centrifuge tubes and CryoVials™. The Geno/Grinder® Sample Throughput Chart details the different options that are available.
What type of samples can I process in the Geno/Grinder®?
The 2010 Geno/Grinder® can be used for a variety of samples including plant tissues like soybeans, sugar beet leaves, fungi, and seeds. It also grinds animal tissues like liver and fat and can lyse yeast and bacterial cells.

What is the maximum weight of all samples that the Geno/Grinder can shake without breaking down?

To maintain proper functionality of the Geno/Grinder, the maximum recommended total sample load in the clamp assembly is 4 lb. (1.8 kg).  The total sample load includes sample, vials (or titer plates), grinding media, holders (or cryo-blocks), and nesting trays.  For Sample loads exceeding 2 lb. (0.9 kg), the maximum recommended operating rate is 1500 rpm.  Sample loads less than 2 lb. can be run at rates up to the maximum of 1750 rpm.  Dynamic loads greater than 2 lb. can create a rate error.  When stacking 4 or 6 titer plates, do not add more than five 4 mm steel balls to a single titer plate well.

Operating with loads that exceed the recommended maximum rate and weight limits can result in damage to the Geno/Grinder.  Therefore, warranty restrictions or invalidation may apply.

Milling and Grinding

How do I choose a Mixer/Mill®?
Which SPEX SamplePrep Mixer/Mill is best for your application can best be determined through three criteria: 1. The weight/volume of the sample to be ground. 2. The number of samples per day. 3. The preferred grinding container material. 5100 Mixer/Mill - The smallest of the SPEX SamplePrep Mixer/Mills has the capacity for running three ½ in. (12.7 mm) diameter x 1 in. (25.4 mm) long or two ¾ in. (19 mm) diameter x 2 in. (50.8 mm) long grinding vials. The weight of typical samples for this mill is around 0.5 g for the smaller vials and 1 g for the larger ones. 8000M Mixer/Mill® and 8000D Dual Mixer/Mill - The larger SPEX SamplePrep Mixer/Mills typically grind samples in the 10 g range. Both mills use the same vials but 8000D has a dual clamp and thus twice the output of the single clamp 8000M. The smaller capacity vials traditionally used in the 5100 can also be used in the 8000M and 8000D with a special adapter.
What is the difference between the 8000M Mixer/Mill® and the 8000D Mixer/Mill®?
The SPEX SamplePrep 8000 Series Mixer/Mills are efficient compact laboratory mills capable of pulverizing one or two samples in the 10-gram range. There are two versions: the classic 8000M Mixer/Mill with one clamp, and the 8000D Dual Mixer/Mill with two clamps. The single clamp 8000M (previously the 8000) is known simply as "the SPEX Mill" to thousands of users and has been in service for over forty years. The clamp mechanism has changed little since the earliest versions, simply because it has proven extremely durable. Many of the earliest 8000 Mixer/Mills are still in service. Now the wind-up timer has been replaced by an electronic 100-minute timer (extended timer available 39450 Chip for Extended Running Time) and the mill's safety features have been improved. The dual-clamp 8000D Mixer/Mill combines two clamps on one shaft with an electronic 100-minute timer (extended timer available). As the two clamps move in balance, vibration is reduced and component life extended. A fan keeps the clamps and motor cool during operation.
What types of grinding vials are available for the 8000M Mixer/Mill® and 8000D Dual Mixer/Mill®?
8000 Series grinding vials are 2 1/4 in. (5.7 cm) wide and up to 3 in. (7.1 cm) long. They have an internal volume of 50-60 mL with a grinding capacity of about 10 mL and a blending capacity of 25 mL. They are available in hardened and stainless steel, tungsten carbide, alumina ceramic, zirconia ceramic, silicon nitride, agate, and methacrylate. We recommend that vials for the 8000D Dual Mixer/Mill be purchased and used in pairs to maintain the balanced motion of the clamps. If only one sample needs to be ground, the second similar vial should be clamped in place without the sample or grinding ball.
What are the principles behind the grinding action in the 8000M Mixer/Mill® and 8000D Dual Mixer/Mill®?
The SPEX SamplePrep 8000 Series Mixer/Mills are functionally described as shaker mills or high-energy ball mills. They shake one or two containers back and forth several thousand times a minute. In each clamp, the vial, which contains a sample and one or more balls, is shaken in a complex motion which combines back-and-forth swings with short lateral movements, each end of the vials describing a "figure-eight". The length of that swing is the same as the internal length of the vial, about two inches (5.08 cm). With each swing the balls impact against one end of the vial, simultaneously milling the sample to a powder and blending it. Due to the amplitude and velocity of the clamp's swing, each ball develops fairly high G-forces, enough to pulverize the toughest rocks, slags, and ceramics.

How much Liquid Nitrogen (LN) does the Freezer/Mill use and can it be operated without LN?

The Freezer/Mills use several liters of LN for the initial cool down, then use several liters per hour of operation.  Exact amounts depend on the ambient temperature and the amount of sample being ground.  Due to its unique design using electromagnetic coils to power the impactor, the Freezer/Mills cannot be operated without LN.

What are the SPEX SamplePrep laboratory mills designed for?
SPEX SamplePrep mills are intended for the analytical laboratory. They are not for batch or production milling, but for rapid, efficient grinding of analytical samples ranging in amounts from less than one gram up to approximately 100 grams. The hallmark SPEX SamplePrep Freezer/Mills, Mixer/Mills and Shatterbox all have separate grinding containers for individual samples, so after use the container is cleaned and not the mill. SPEX SamplePrep mills were designed for spectroscopists who were concerned not only about reducing samples to uniform homogeneous powders, but also about what was added to the samples during processing.
How do I use my choice of grinding container to minimize sample contamination?
Processing a sample always contaminates it. Successful analysis depends on recognizing the sources of contamination and controlling them. When the contaminants are known and can be quantified, analytical results can be refined accordingly. As the grinding container is the major source of contamination, its selection is critical. In general, one's objective should be to minimize contamination levels while avoiding elements which will interfere with analysis. An example is the grinding of steel slags in a tungsten carbide container: tungsten carbide grinds rapidly, and the expected low-level contaminants of tungsten, carbon, and cobalt are not generally looked for in these slags. SPEX SamplePrep's selection of grinding container materials gives you maximum flexibility in choosing the best approach for your samples and analytical aims. Major, minor, and trace elements predictably found in SPEX SamplePrep grinding containers are listed in the SPEX SamplePrep Grinding Container Material Selection Chart. However, strictly speaking, almost no two grinding containers will have exactly the same elemental profile. There are many different steels, carbides, and ceramics, each with specific compositions. Often the formulas are proprietary, so that a type of tungsten carbide engineered to have specific properties will have a different makeup from two different manufacturers. In addition, there are inevitable variations from batch to batch of the same material, both in the exact proportions of the major elements and in trace element composition. Because of these variations in grinding container composition, we strongly recommend determining the exact elemental profile of your individual grinding containers, preferably with your own analytical equipment and techniques. The simplest approach is to grind samples of known composition and see what is added by grinding. Lacking known samples, one may grind portions of a single sample for increasing lengths of time, and check to see which elements increase in proportion to grinding time. Once the contributed impurities and their proportions are known for a grinding container, the resulting profile can be fitted to the analytical results, regardless of the actual contamination level. (While this level is important, it clearly will vary with the composition and condition of the grinding container, the size, hardness, and toughness of the sample, and grinding time).
How can I prevent my sample from caking during grinding?
When samples agglomerate or "cake" during grinding, further particle size reduction is inhibited. Caking can result from moisture, heat, static charge accumulation, the fusing of particles under pressure, and other causes. Many of the techniques which make sample preparation an "art" are devoted to getting around caking, and we can only hint at the possibilities. Slurry grinding is one approach; if particles remain in suspension during grinding, they are unlikely to cake. Water, alcohol, or other liquids are added to the sample before grinding, and removed afterwards. Although slurry grinding is a reasonably reliable way of grinding a sample to micron-sized particles, it is sloppy and time consuming, requires a leak proof grinding container, and adds extra steps to one's sample preparation procedure. Dry grinding is simpler and quicker, but requires much more careful matching of the technique to the sample. If the caking is due to moisture, as in many soils and cements, the sample can be dried before grinding. Other samples can be successfully ground with a variety of additives. Dry soaps/detergents are lubricants, and some also include an abrasive; graphite is an anti-static agent as well as a lubricant; there are many proprietary grinding aids as well, which may contain an abrasive, a lubricant and a binding agent. Other grinding aids include polyvinyl alcohol, phenyl acetate and aspirin.
Can the Mixer/Mill® be used for mechanical alloying?
Mechanical alloying, also referred to as reactive milling, is a process originally developed for the production of oxide dispersion strengthened superalloys. Today, mechanical alloying is often used as a solid-state powder processing technique that generates powders with unique microstructures. A high-energy ball mill can be used to accomplish this. Over the past few decades, the SPEX SamplePrep Mixer/Mill, widely known as the "SPEX Mill", has become the industry standard for mechanical alloying applications. The high energy of the milling action, and the durability of the motor, allow running for extended periods. The SPEX SamplePrep 8000M Mixer/Mill® and 8000D Dual Mixer/Mill® are equipped with a timer that is factory set for a 100-minute time range. However, mechanical alloying requires significantly longer grinding times. For these applications, SPEX SamplePrep offers an optional chip (39450 Chip for Extended Running Time) to extend the timer range to 1,000 or 10,000 minutes. This chip is available as either a factory-installed or user-installed option. Due to the extreme wear that can occur on the Mixer/Mill from extended running times, installation of this chip will change the warranty terms (consult SPEX SamplePrep sales or service). Additionally, in order to prevent the mill from breaking down prematurely, a routine schedule of preventative maintenance is strongly suggested.
What is the typical cryogenic grinding technique?
Cryogenic grinding presents unique challenges for designers of laboratory mills, as the low temperatures required are very hard on mechanical equipment. The 6770 Freezer/Mill® and 6870 Large Freezer/Mill® impel a steel impactor magnetically while the sample vial is immersed in liquid nitrogen. Once chilled, samples can be pulverized quickly; grinding times rarely exceed a few minutes with either mill. A typical milling program involves pre-cooling the sample. Chilling times vary with the mill and the insulating ability of the sample but can range from 10 minutes to 30 minutes or more. This is followed by one or more grinding cycles, each of which consists of a grinding period followed by a pause for re-cooling. An example is 15 minutes of precooling followed by three 2-minute grinds with two-minute rests in between each grinding period. The optimum volume, weight, grinding time, and impact frequency for any sample ground in a SPEX SamplePrep Freezer/Mill are determined by experimentation, the experience of the operator, and the requirements of the analyst. As a rule of thumb, the smaller the sample and the longer it is ground, the finer the particle size will be. In cryogenic grinding, temperature also affects the outcome: the colder a sample, the more finely it can be ground. We strongly suggest submitting samples for test grinding if there is any question about the suitability of our mills and techniques for your application.
What type of controls do the Freezer/Mills® have?
The 6770 Freezer/Mill® and the 6870 Large Freezer/Mill® feature LCD touch-screen displays used for programming and manual control. A typical milling program involves pre-cooling the sample. This is followed by one or more grinding cycles, each of which consists of a grinding period followed by a pause for re-cooling. An example is 15 minutes of precooling followed by three 2-minute grinds with two-minute rests in between each grinding period. With these new Freezer/Mill models such a cycle can be programmed and it is possible to store up to ten grinding programs. The LCD touch-screen display is incorporated in a detachable control module located on the lid of the mill. The control module can be detached for remote use via a cable. This is ideal for operating the mill in a glove box or under sterile conditions.
What safety features are the Freezer/Mills® equipped with?
Both the 6770 Freezer/Mill® and the 6870 Large Freezer/Mill® include latch-down lids with a lid sensor that prevents the mill from being operated when the lid is open. A liquid nitrogen sensor detects the level of liquid nitrogen in the mill and will not allow operation if the liquid nitrogen level is too low. The 6870 Large Freezer/Mill® has an auto-fill option that eliminates direct handling of liquid nitrogen. Both Freezer/Mill models are CE Approved.
How do the Freezer/Mills® aid in the screening of asbestos-containing materials (ACMs)?
Typically the floor tiles, ceiling tiles, and pipe insulation being checked for harmful asbestiform minerals are composite materials which are both flexible and tough. The challenge is first to free the mineral fibers from their matrix and then to determine whether they are among the species most damaging to human health. Freezer/ Mills are useful not only to break up the matrix and free included fibers for polarized-light microscopy, but also to grind those fibers finer for X-ray diffraction analysis. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
Who uses the Freezer/Mills® and what are their applications?
SPEX SamplePrep Freezer/Mills are incredibly versatile instruments. They are used by polymer chemists, forensic experts, environmental biologists, geneticists, botanists, doctors and dentists, geologists and mineralogists, and many others. Applications include DNA and RNA extraction, polymer structure studies, trace element monitoring, food analysis, mineral diffraction research, implant surgery, drug testing, textile identification and more. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.

Can the Freezer/Mills® be used to grind samples for RoHS/WEEE compliance testing?

The Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) Directives of the European Union were introduced to minimize the accumulation of hazardous waste in landfills from the disposal of electrical and electronic equipment. The concentrations of hazardous substances such as lead, cadmium, mercury, chromium VI, polybrominated diphenylethers (PBDEs), and polybrominated biphenyls (PBBs) are restricted in electrical and electronic products and/or components. RoHS/WEEE states that if the component can be mechanically separated, then each component is subject to the RoHS limits. The definition of exactly what this means is an ongoing process. However, one thing is certain; in order to get an accurate analytical result, these products and components must be reduced to homogenous, representative samples. Many components such as circuit boards, wire, solder, polymers and resins are difficult if not impossible to grinding using traditional methods. Cryogenic grinding in the 6770 Freezer/Mill® and the 6870 Large Freezer/Mill® is often the easiest way to homogenize these materials. The end plugs and impactor of the standard Freezer/Mill® grinding vials are made of 440C stainless steel. This type of steel contains 16-18% Cr metal which could potentially contaminate the samples. This poses an issue because Chromium VI (a restricted substance) cannot be distinguished from Cr metal by XRF, ICP, and other common analytical techniques. Hence the new Cr-Free Grinding Vials, whose end plugs and impactor are made from chromium-free steel, were designed to insure that any Cr found in a sample originated there, and not in the grinding vial. A detailed Application Note describing the use of the Freezer/Mill® for RoHS/WEEE is available.

What is the procedure for using Vertrel® XF as a grinding aid?
3650 Vertrel® XF, a DuPont product sold as a cleaning fluid, is finding increased acceptance as a grinding aid. A fluorocarbon fluid, it prevents sample caking during grinding, and quickly evaporates from an open grinding container without leaving any residue. Our experience is that the "grindability" of almost any sample is enhanced by the use of Vertrel XF, contamination is lowered, and the grinding container is easier to clean. Typical XRF samples such as cement, rock, clinker, and similar material can be routinely ground below 10 microns. Vertrel XF also lowers contamination levels from the grinding container. The technique that follows was pioneered by John Anzelmo and colleagues at Bruker AXS and is here adapted for SPEX SamplePrep equipment: In an 8501 Hardened Steel Grinding Container load together 10 grams of sample, 2.5 grams of 3642 Cellulose Binder or 3644 Ultrabind®, and 7 mL of 3650 Vertrel® XF. Grind in an 8530 Enclosed Shatterbox for 2.0 minutes then open the grinding container in a hood until the Vertrel XF has evaporated. Prepare a 3614 40mm Evacuable Pellet Die Set with a flared 3617 38 mm Spec-Cap®, and transfer the ground sample/binder powder to the die. Press at 20 tons for 0.3 minutes in a 3635 Automated X-Press. Reference Anzelmo, John; Seyfarth, Alexander; and Arias, Larry (2001). Approaching a Universal Sample Preparation Method for XRF Analysis of Powder Materials. Advances in X-ray Analysis, Vol. 44, JCPDS - International Centre for Diffraction Data, Newtown Square PA.
What publications reference the Mixer/Mill® for mechanical alloying?
Over the years nearly one hundred articles have been published in refereed scientific journals regarding the SPEX SamplePrep Mixer/Mill and its use for mechanical alloying. This includes mechanical alloying techniques, evaluations of grinding vial materials, and numerous other topics. The following publication list is intended to highlight the more recent publications that we are aware of and is not intended to be comprehensive. If you are considering the Mixer/Mill for your own mechanical alloying application, we strongly encourage you to do your own search for applicable publications and references. Effect of the heating rate on crystallization behavior of mechanically alloyed Mg50Ni50 amorphous alloy. Aydinbeyli, N., Nuri Celik, O., Gasan, H., Aybar, K. International Journal of Hydrogen Energy, Vol. 31, Issue: 15, December, 2006. pp. 2266-2273. Effect of ball milling on simultaneous spark plasma synthesis and densification of TiC-TiB2 composites. Locci, A.M., Orru, R., Cao, G., Munir, Z.A. Materials Science and Engineering A, Vol. 434, Issue: 1-2, October 25, 2006. pp. 23-29. Temperature of the milling balls in shaker and planetary mills. Takacs, L., McHenry, J. S. Journal of Materials Science, Vol. 41, Issue: 16, August 2006. pp. 5246 - 5249. Modeling of comminution processes in Spex Mixer/Mill. Concas, A., Lai, N., Pisu, M., Cao, G. Chemical Engineering Science, Vol. 61, Issue: 11, June, 2006. pp. 3746-3760. Effect of mechanical alloying conditions on the microstructure evolution and electrode characteristics of Mg63Ni30Y7. Khorkounov, B., Gebert, A., Mickel, Ch., Schultz, L. Journal of Alloys and Compounds, Vol. 416, Issue: 1-2, June 8, 2006. pp. 110-119. A study of mechanical alloying processes using reactive milling and discrete element modeling. Ward, T.S., Chen, W., Schoenitz, M., Dave, R.N., Dreizin, E.L. Acta Materialia, Vol. 53, Issue: 10, June, 2005. pp. 2909-2918. Microstructural evolution during mechanical alloying of Mg and Ni. Rojas, P., Ordonez, S., Serafini, D., Zuniga, A., Lavernia, E. Journal of Alloys and Compounds, Vol. 391, Issue: 1-2, April 5, 2005. pp. 267-276. Mechanical milling of magnesium powder. Hwang, S., Nishimura, C., McCormick, P.G. Materials Science and Engineering: A, Vol. 318, Issue: 1-2, November, 2001. pp. 22-33. Formation of supersaturated solid solutions by mechanical alloying. Huang, B.-L., Perez, R.J., Lavernia, E.J., Luton, M.J. Nanostructured Materials, Vol. 7, Issue: 1-2, January 2, 1996. pp. 67-79. Synthesis of nanocrystalline Fe-B-Si powders. Perez, R.J., Huang, B.-L., Crawford, P.J., Sharif, A.A., Lavernia, E.J. Nanostructured Materials, Vol. 7, Issue: 1-2, January 2, 1996. pp. 47-56.
Why is the Mixer/Mill® considered a high-energy ball mill?
SPEX SamplePrep Mixer/Mills are a variant of the ball mill or jar mill, which grinds samples by placing them in a container along with one or more grinding elements, and imparting motion to the container. The containers are usually cylindrical; the grinding elements are most often balls, as is the case with the Mixer/Mills, but may be rods, cylinders, or other shapes. Generally the containers and grinding elements are made from the same material. As the container is rolled, swung, vibrated, or shaken, the inertia of the grinding elements causes them to move independently, into each other and against the container wall, grinding the sample. Variations of the "ball mill" range from laboratory mills with a sample capacity of a gram or less to large industrial mills with a throughput of tons per minute. SPEX SamplePrep Mixer/Mills can be described as laboratory scale, high-energy ball mills. They are designed to pulverize a sample rapidly while mixing it homogeneously—an approach long known to be effective in preparing samples for emission spectroscopy and XRF spectrometry. SPEX SamplePrep Mixer/Mills are also widely used for blending powders and making emulsions. Due to its high-energy action the SPEX SamplePrep 8000 Series Mixer/Mills have recently become indispensable for nanomilling and mechanical alloying
What types of controls and safety features is the 5100 Mixer/Mill® equipped with?
The 115 V/60 Hz version of the 5100 Mixer/Mill has a pushbutton, resettable 30-minute timer. The 230 V/50 Hz version has a push-button, resettable 72-minute timer. The rugged construction of the 5100 Mixer/Mill ensures a long life of heavy work. The steel housing protects the entire clamp mechanism and vials and the lid is equipped with a locking latch.
How to I choose a laboratory mill?
If your samples can be pulverized by impact at room temperature, you have a choice of several proven SPEX SamplePrep laboratory mills. The 8530 Enclosed Shatterbox® and 8500 Shatterbox® are ring-and-puck mills that are ideal for rapid grinding of samples up to approximately 100 grams, in 5 minutes or less. The 8000M Mixer/Mill® and 8000D Dual Mixer/Mill® are high-energy ball mills that not only pulverize samples in the 10 gram range but are suitable for blending powders and making emulsions up to approximately 50 mL. The 5100 Mixer/Mill® is a smaller high-energy ball mill, with about 10% the sample capacity of the 8000-series Mixer/Mills. All these mills have multiple-sample capacity with smaller samples, and a wide choice of grinding container sizes and materials, for maximum on-the-job flexibility over a wide rangeof applications. Soft, brittle materials and flexible samples that can be ground by shearing as well as impact may be suitable for the 5200 Micro Hammer-Cutter Mill, which uses revolving hammers in a chamber with a serrated lining. Product particle size is controlled by perforated screens in the bottom of the grinding chamber. This is the only "flow-through" mill sold by SPEX SamplePrep, and has proven useful for a comparatively narrow range of samples. The 6770 Freezer/Mill® and 6870 Freezer/Mill® are unique cryogenic mills that can grind almost any "ungrindable" sample, including all plant and animal tissue, most polymers, and countless other samples that are resistant to room-temperature milling. Freezer/Mills require liquid nitrogen for chilling the sample, and maintaining cryogenic temperatures in the vial during grinding. Forty years after its introduction the Freezer/Mill remains the most widely used and most effective cryogenic mill in the world. Finally, the 2010 Geno/Grinder® is a high-throughput tissue homogenizer with an adjustable clamp that accommodates a variety of formats ranging from deep-well titer plates to centrifuge tubes. It is specifically designed for rapid cell disruption, lysis, and tissue homogenization while preserving temperature sensitive samples. To discuss any SPEX SamplePrep laboratory mills and their suitability for your applications, feel free to contact our product specialists. We also offer test-grinding of your samples in our applications lab, or we can loan you a mill for short-term trials in your own lab. The more you know about SPEX SamplePrep laboratory mills, the more confident you can be that they will do the job you need to get done.
How do I choose a grinding container?
Your selection of appropriate grinding and mixing containers is as important as your choice of a mill. The proper grinding vial or dish will greatly enhance analytical accuracy. The grinding container is generally harder than the material to be ground and should be of a substance whose presence in the sample will not interfere with analysis. SPEX SamplePrep's containers have been selected with care to offer optimum capability in the lab. The following is a brief description of the pros and cons of each grinding container material. Please keep in mind that not all materials are available for each of SPEX SamplePrep's laboratory mills. Methacrylate and polystyrene vials and balls are ideal for pulverizing soft, brittle materials and for mixing and storing powders. With these vials only traces of organic impurities are added to your sample. Hardened steel is durable and tough, suitable for general-purpose grinding; it's the workhorse of the lab. When hard substances are ground in steel containers, some Fe and Cr contamination can be expected. Stainless steel is less subject to chemical attack, but contributes Ni as well. Cr-free steel rusts easily but can be used to grind samples for RoHS/WEEE testing. Halide-releasing compounds corrode steel and should be ground in tungsten carbide, alumina, agate, zirconia, or silicon nitride containers. Tungsten carbide vials and dishes are the most effective and versatile of all. Because tungsten carbide is substantially harder and heavier than steel, grinding is faster and contamination is minimal. Other than tungsten, cobalt (a binder) is the major contaminant. If cared for, tungsten carbide containers will last indefinitely. They're recommended as a long-term "best buy" for grinding almost anything. Alumina ceramic is ideal for extremely hard samples or in cases where steel and tungsten carbide contaminants are objectionable. All SPEX SamplePrep alumina components are 99.5% pure aluminum oxide, with some silicon, calcium, and magnesium present. It is lightweight and brittle but very abrasion-resistant. Necessary for an important minority of samples, alumina ceramic vials are a helpful addition to any lab's grinding armory. Agate is harder than steel, and chemically inert to almost anything except HF. It's also brittle and must be handled with care. Agate vials are for the grinding and mixing of samples when organic and metallic contamination are equally undesirable. Agate is 99.9% silica and is extremely wear-resistant. Silicon nitride is a tough space-age material with remarkable wear characteristics, and hardness superior to agate and zirconia. If it is important to have a container whose only major contaminant is silicon, consider SPEX SamplePrep silicon nitride. It is extremely durable compared to agate, and while it contains some yttria and alumina, overall contamination levels will be very, very low. Zirconia is a ceramic which in many ways approaches the ideal grinding medium. Since it is both hard and tough it wears very slowly, adding little contamination. It is about one and one-half times as dense as alumina, grinding almost as fast as steel. And because it is mostly zirconium oxide with low percentages of magnesium oxide and hafnium oxide, the contamination SPEX SamplePrep zirconia ceramic does contribute is often not important to the analyst.
What is the procedure for using propylene glycol as a grinding aid?
Howard Kanare of Construction Technology Laboratories, Inc. has publicized the use of propylene glycol (one drop for up to ten grams of sample, roughly 0.3 wt.%) for laboratory fine grinding of Portland cement and many minerals. In a swing mill such as the SPEX SamplePrep Shatterbox, oven-dried samples can be ground quickly to less than ten microns without agglomeration or sticking to the mill walls. Propylene glycol must be used safely, after consulting the material safety data sheet; it is available as a PrepAid product (see pages 68 and 76).

What are the benefits of cryogenic grinding?

While cryogenic grinding has long been a vital sample preparation tool for the analytical chemist, it rarely receives publicity. Many analytical samples which are too flexible or sensitive to be impact-ground at room temperature can be embrittled by chilling, and then pulverized. These include polymers, rubber, textiles, cereal grains, hair, fingernails, skin, bone, and muscle tissue. There are also many samples which degrade in various ways during normal grinding, but whose critical properties are preserved by chilling. Coal, for example, can be cryogenically ground to retain its more volatile components, and clay minerals may be pulverized for XRD study without distorting their crystal structure. Bone, fingernails, and other biological materials can be cryogenically ground in preparation for nucleic acid extraction without damaging DNA and even RNA through heating.

What is the recommended procedure for cleaning Mixer/Mill® Grinding Vials and Shatterbox® Grinding Containers?
Grinding vials and containers should be cleaned between sample runs to avoid cross-contamination, and the procedure can be as simple or as complex as your analytical objectives warrant. In some applications a simple wipe down with ethanol may suffice; another practical approach is to brush out a container, then briefly grind an expendable portion of the next sample and discard it. For more thorough cleaning one may grind one or more batches of pure quartz sand, and then wash the container thoroughly. In extreme cases, such as the plating of container walls with a malleable metal, chemical cleaning or multiple grinds with quartz may be necessary. An effective single-step grinding procedure for most grinding containers is to grind pure quartz sand together with hot water and detergent, then rinse and dry the container. Drying is speeded by the use of a blow-dryer or similar appliance. A safety advantage of this cleaning method is that it controls respirable airborne dust. A cleaning procedure is easily evaluated by grinding and analyzing a known sample, or even by checking the impurities appearing in successive batches of ground quartz sand. It should be noted that grinding containers become more difficult to clean with age because of progressive pitting and scratching of the grinding surfaces. Hardened steel and even stainless steel containers can rust. While iron oxide coatings can be removed by warm dilute oxalic acid solution or abrasive cleaning, we recommend that steel containers be thoroughly dried after cleaning and, if stored, kept in a plastic bag with a desiccating agent.

What is the recommended procedure for cleaning Freezer/Mill® Grinding Vials?

All of the Freezer/Mill® Grinding vials may be superficially cleaned quickly and easily by placing them under running hot water. If the vial is cold a coating of ice will form on the steel parts, but will melt quickly as the water runs. All of the basic grinding vials have polycarbonate center cylinders. The Poly-Vial has polycarbonate center cylinders and end caps. While this polymer is very tough at low temperatures, it is sensitive to alcohol and other organic solvents, and should be cleaned only with soap and water. A mild bleach solution will control organic contamination. Polycarbonate can be autoclaved, but this will weaken it. Before re-using polycarbonate cylinders, always inspect them for cracks. They may last for dozens or hundreds of samples, but as soon as they begin to crack they should be discarded. If sample adheres to the steel end plugs and impactor, they can be cleaned with water and soap or detergent, or even with organic solvents. If they must be disinfected or cleaned of any organic residue, they can be washed with bleach or chemical cleaners or autoclaved, but should always be dried immediately after use. The steel parts in the basic grinding vials are made out of a so-called "magnetic stainless steel", which is corrosion-resistant but will rust if left in contact with water. Surgical-grade stainless steel, which is truly rustproof, is nonmagnetic and cannot be used for Freezer/Mill end-plugs and impactor. Rust on steel Freezer/Mill parts can be removed by scrubbing them with steel wool or an abrasive cleanser.

Is respiratory protection required during grinding?
The general objective of sample grinding is, of course, to convert an inhomogeneous solid to a fine, homogeneous powder. Inevitably, some of this powder is released into the environment, usually during the emptying or cleaning of the grinding container. We strongly recommend the wearing of an approved dust-mask during this procedure, and suggest the use of a laboratory fume hood. Even harmless rock and cement samples can become potentially harmful to the respiratory system when finely pulverized.
How are Mixer/Mills® used to prepare infrared mulls?
KBr pellets and Nujol mulls are quickly prepared with SPEX SamplePrep Mixer/Mills using small plastic (3111 2.5 mL Polystyrene Vial with Slip-On Cap), agate (3118 Agate Grinding Vial Set, 1.6 mL) and steel vials (3114 Stainless Steel Grinding Vial Set, 2.5 mL). The polystyrene spectrum appears as a constant background and can easily be subtracted. Steel and agate produce no IR background.
What types of samples can be cryogenically ground?
Nearly every naturally occurring material of biological origin can be cryogenically ground, usually to a fine particle size: hair, muscle tissue, bone, wood, plant stems and roots, seeds, cotton fiber, etc. Polymers in general can be ground, but their physical form is important. Many flexible plastics which can routinely be milled in pellet form are difficult to grind as thin fibers and films, which remain flexible even at -200°C. For the same reason, polymers in general cannot be ground to as fine a particle size as biological samples. As the particles become smaller they become more flexible, and progressively more difficult to grind. Many silicone compounds remain elastic and hard-to-grind in any form. The behavior of metals and metal alloys during cryogenic milling is highly variable. For example, impure copper as well as many copper alloys can be ground without much trouble, while pure copper remains malleable. Metal samples as a rule should be test-ground. When a sample initially resists grinding, it may not be because it is "ungrindable." Many such samples respond to the strategies of reducing the sample volume, increasing grinding time, and even lengthening the pre-cooling period to 30 minutes or so. Successes have also been scored by using "filler" grinding agents such as detergent and quartz sand.

What are the limits of cryogenic grinding? 

As with samples ground at room temperature, those processed cryogenically vary enormously in their "grindability," and it is difficult to predict the optimum sample size, chilling time, or grinding time. In addition, a given sample material may exist in several forms, some of which are easy to grind while others are very difficult. For example, polypropylene is supplied to molders as small pellets, but can be made into thin films or fibers; the pellets grind fairly easily, as they become rigid when chilled, but the films and fibers may remain flexible and become difficult to grind cryogenically. Not every substance which is difficult to grind at room temperature can be pulverized by cryogenic milling. For this reason SPEX SamplePrep recommends that you discuss your samples and grinding requirements with one of our specialists before selecting a mill. If there is any question about whether a sample can be ground in a Freezer/Mill we will request that a portion be submitted for test-grinding.

What type of grinding vials are offered for the Freezer/Mills®?

SPEX SamplePrep Grinding Vials are now available in four different sizes. Microvials have a sample capacity of 0.1 - 0.5 grams; Small Grinding Vials have a capacity of 0.5 - 4.0 grams. Mid-Size Grinding Vials have a sample capacity up to 25 grams and the Large Grinding Vials can accommodate up to 100 grams. The basic grinding vials include the 6751 Small Grinding Vial Set, 6881 Mid-Size Grinding Vial Set, and the 6801 Large Grinding Vial Set. They all consist of a steel impactor and end plugs with a polycarbonate center section. Steel is ideal for the impactor and end plugs as it is the only magnetic material that is easily manufactured and holds up well at liquid nitrogen temperature. The polycarbonate center section is surprisingly durable, and has two practical advantages: when chilled it forms a tight seal with the end plugs, and it allows visual inspection of the ground sample. Stainless steel center sections are available for cases where contamination with polycarbonate is not acceptable. The Microvial Set is ideal for grinding smaller samples. Each individual microvial consists of an impactor, center cylinder, and end plugs all made of steel. A microvial holder, positions three microvials in the Freezer/Mill. Poly-Vials include the 6761 Small Poly-Vial Set and the 6885 Mid-Size Poly-Vial Set. They consist of polycarbonate end plugs and center cylinder with a Teflon-encapsulated steel impactor. They are used for milling delicate plant and animal tissues with no metallic contamination. Low Chrome Vials are designed for RoHS/WEEE testing of electronic components. They include the 6771 Small Vial Set, 6883 Mid-Size Vial Set, and the 6871 Large Grinding Vial Set. They consist of a polycarbonate center cylinder with end plugs and an impactor made of low chrome steel.

What is the sample capacity of the Freezer/Mill's® grinding vials?
The 6770 Freezer/Mill® with the 6751 Small Grinding Vial Set has a sample volume limit of about 5 mL; bulkier samples may restrict movement of the impactor. For efficient grinding, typical sample volume is 1 to 2 mL, corresponding to weights of 1 to 2 grams for polymers and 2 to 4 grams for bone. Specialized grinding vials with similar capacity are the 6761 Small Poly-Vial Set for metal-free grinding of delicate samples, and the 6771 Small Cr-Free Vial Set for grinding electronic components without adding chromium. The 6753 Microvial Set includes three 6753V Microvials. Each Microvial can hold a small amount of sample, typically between 0.1 - 0.5 grams. The 6870 Large Freezer/Mill® with the 6801 Large Grinding Vial Set has at least 50 mL maximum sample capacity, 10 times that of the 6770 Freezer/Mill®. Typical sample volumes are 10 to 20 mL, equivalent to weights of 10 to 20 grams for polymers and 20 to 40 grams for bone. The new line of Mid-Size Vials has about half the capacity of the 6801 vial, and includes the 6885 Mid-Size Poly-Vial Set, the 6883 Mid-Size Cr-Free Grinding Vial Set, as well as the standard 6881 Mid-Size Vial Set. The 6870 Large Freezer/Mill® can also hold up four 6751, 6761, and 6771 vials for simultaneous grinding of multiple smaller samples. Can the Freezer/Mills® be used to grind samples for RoHS/WEEE compliance testing? The Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) Directives of the European Union were introduced to minimize the accumulation of hazardous waste in landfills from the disposal of electrical and electronic equipment. The concentrations of hazardous substances such as lead, cadmium, mercury, chromium VI, polybrominated diphenylethers (PBDEs), and polybrominated biphenyls (PBBs) are restricted in electrical and electronic products and/or components. RoHS/WEEE states that if the component can be mechanically separated, then each component is subject to the RoHS limits. The definition of exactly what this means is an ongoing process. However, one thing is certain; in order to get an accurate analytical result, these products and components must be reduced to homogenous, representative samples. Many components such as circuit boards, wire, solder, polymers and resins are difficult if not impossible to grinding using traditional methods. Cryogenic grinding in the 6770 Freezer/Mill® and the 6870 Large Freezer/Mill® is often the easiest way to homogenize these materials. The end plugs and impactor of the standard Freezer/Mill® grinding vials are made of 440C stainless steel. This type of steel contains 16-18% Cr metal which could potentially contaminate the samples. This poses an issue because Chromium VI (a restricted substance) cannot be distinguished from Cr metal by XRF, ICP, and other common analytical techniques. Hence the new Cr-Free Grinding Vials, whose end plugs and impactor are made from chromium-free steel, were designed to insure that any Cr found in a sample originated there, and not in the grinding vial. A detailed Application Note describing the use of the Freezer/Mill® for RoHS/WEEE is available.

What are the principles behind the grinding action used in the Freezer/Mills®?

SPEX SamplePrep Freezer/Mills are cryogenic mills that utilize liquid nitrogen as a coolant. The Freezer/Mill technology has been field proven since the 1960's. Chilling materials in liquid nitrogen (at temperatures approaching - 200°C) has two important consequences for sample preparation: it embrittles flexible samples so they can be pulverized by impact milling, and it preserves structural and compositional aspects usually damaged or lost during room-temperature grinding. The Freezer/Mill incorporates an insulated tub into which liquid nitrogen is poured. The grinding mechanism is a magnetic coil assembly suspended in the liquid nitrogen bath. Each sample is placed in a closed grinding vial along with a steel impactor, and the vial is then inserted in the coil assembly and lowered into the liquid nitrogen. When the sample is thoroughly chilled - usually a few minutes - grinding begins. The magnetic coil shuttles the impactor rapidly back and forth, pulverizing the sample against the end plugs of the vial at speeds up to 30 impacts per second. When the grinding cycle is complete, the vial is removed from the Freezer/Mill, emptied, and cleaned.

How have the Freezer/Mills® been used in the field of medical research?
Medical schools and research hospitals have long used Freezer/ Mill technology in a variety of unconventional projects. One is the pulverizing of fresh, sterilized bone to use as a cement in joint-replacement surgery. The tiny bone fragments act as growth nuclei to stimulate the formation of bone around prosthetic implants. Another is the homogenizing of heart tissue to smear on slides as a culture medium. Freezer/Mills have even been used to grind implant materials to a fine powder which can be injected into live subjects for allergy and toxicity testing. At dental schools cryogenic grinding is used to pulverize fresh teeth without degrading them through heating. The overall possibilities in the medical field seem endless. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
How can the Freezer/Mills® be used in the recovery of volatile compounds?
Coal, petroleum shale, waxes, and many other organic materials contain light-molecular-weight fractions which are quickly driven off when their matrix is pulverized at room temperature. Grinding these materials in Freezer/Mills insures the retention of volatile components, which can be concentrated later by heating the ground sample in a gas trap. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
How can the Freezer/Mills® been used for mineralogical studies?
The structures of certain minerals, notably clays, micas, and fibrous amphiboles, can be difficult to distinguish by X-ray diffraction because they are subject to matting and preferred orientation when pulverized by normal means, with unusually soft minerals there can also be distortion of the crystal lattice due to impact. When chilled during grinding in SPEX SamplePrep Freezer/Mills, these minerals can often be broken up more completely, exhibiting more nearly random orientation of grains and maintaining greater structural integrity. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
How are the Freezer/Mills® beneficial for pharmaceutical testing and drug analysis?
The complex molecules present in drugs, and their metabolites, are of considerable interest to both pharmaceutical researchers and crime labs. There are many cases where it is important to be able to distinguish between different closely related isomers. Unfortunately, many such compounds are quickly degraded by the pressure and heat accompanying room-temperature milling. Preparation of key samples, whether the compounds themselves or tissues which may contain them, is greatly facilitated by cryogenic grinding in SPEX SamplePrep Freezer/Mills. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
How can the Freezer/Mills® be used for trace metal analysis?
Low levels of toxic heavy metals such as cadmium, chromium, and mercury are known to have profound effects on human health, whether present in substances we ingest or in paint, fabric, plastic, and other materials with which we (or our food and water) have contact. Many such samples, from fish scales and bovine liver to the plastics used in food packaging and children's toys, have to be prepared for analysis; grinding with SPEX SamplePrep Freezer/Mills is often the simplest way. Medical examiners, pathologists, and even anthropologists may be concerned with clues such as the concentration of chromium in bones or the accumulation of arsenic in hair and fingernails; here again, cryogenic milling is often the best way of pulverizing such samples for extractions, dissolutions, or direct analysis. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
What landmark studies have used the Freezer/Mills® for DNA and RNA extractions?
Human bones and teeth, especially when fresh, are difficult to pulverize with normal mills. However, skeletal material can be ground cryogenically and DNA extracted from the powder, whether the remains are recent or very old. Forensics labs use Freezer/Mills to isolate the DNA of crime victims or war casualties when medical and dental records are inadequate. Recently this approach was used to help identify the bones of Russia's Czar Nicholas II and his family. Paleoarchaeologists are beginning to plot the DNA of more ancient human remains, again using cryogenic grinding and PCR (polymerase chain reaction) amplification. A SPEX SamplePrep Freezer/Mill was employed to prepare bone fragments from the 5300-year-old "Ice Man" found in the Alps in 1991. RNA in fresh plant tissue is degraded or destroyed by grinding at room temperature. However, Freezer/Mills preserve RNA for analysis by keeping it below -70° C during grinding. A wide range of Application Notes which discuss the various Freezer/Mill® applications in more detail are available.
What are the applications for the 5100 Mixer/Mill®?
The 5100 Mixer/Mill® is ideal for grinding small amounts of brittle samples such as minerals, rocks, or glass. It has even been used for grinding gallstones. The 5100 Mixer/Mill® can also be used for mixing powders and slurry grinding and is commonly used to blend samples with KBr for IR analysis.
What types of grinding vials are available for the 5100 Mixer/Mill®?
The 5100 Mixer/Mill's continuously adjustable jaws accept vials from 1 in. (25.4 mm) to 21/2 in. (63.5 mm) long and up to 3/4 in. (19 mm) in diameter without adapters. It holds three 1/2 in. (12.7 mm) diameter or two 3/4 in. (19 mm) diameter vials. Vials are available in plastic (polystyrene and polycarbonate), hardened and stainless steel, agate, and tungsten carbide. All of the vials except for the agate are able to accommodate slurry grinding.
What are the principles behind the grinding action used in the 5100 Mixer/Mill®?
The high grinding and mixing efficiency of the 5100 Mixer/Mill is a result of its three-dimensional action. A one-inch (25.4 mm) component of motion along the axis of the vial is complemented by two motions at right angles to the vial axis: a 3/16 in. (4.8 mm) horizontal movement and a 1/4 in. (6.35 mm) vertical oscillation. The resulting action is consistent with the general shape and size of the vials. That is, at every stroke there is an impact at the end of the vial - over 100 per second - to crush the material rapidly and reproducibly.
What are the applications for the 8000M Mixer/Mill® and 8000D Dual Mixer/Mill®?
8000 Series Mixer/Mills have been used for pulverizing rocks, minerals, sand, cement, slag, ceramics, catalyst supports, and hundreds of other brittle, often hard samples. Early on, the Mixer/Mill was used to grind samples, and then blend them with graphite for arc/spark spectroscopy. Now similar samples are ground and then blended with binder before being pressed into samples disks for XRF. The vigorous motion of the clamp is also excellent for making emulsions such as paints, inks, and pharmaceuticals. The 8000M Mixer/Mills have also achieved notoriety for their ability to mechanically alloy small quantities of materials.
What type of safety features are the 8000M Mixer/Mill® and 8000D Mixer/Mill® equipped with?
The 8000 Series Mixer/Mill's rugged and durable construction is the reason why many of the original mills are still in use. A steel cabinet protects the entire clamp mechanism and vials. Both of the 8000 Series Mixer/Mills are equipped with safety interlocks so that they cannot be operated with the lid open. Each clamp has a lock nut to prevent it from loosening while the mill is running. The motors are also equipped with a thermal overload protector and both of the 8000 Series Mixer/Mills are CE Approved.
What is the difference between the 8530 Shatterbox® and the 8500 Shatterbox®?
The full-sized 8530 Enclosed Shatterbox is CE-Approved and has a soundproof enclosure to help reduce noise levels. It also features a safety interlock system, LCD display with a push button membrane switch, and lockable casters. The 8530 Enclosed Shatterbox is ideal for labs concerned with minimizing noise and maximizing safety. The 8500 Shatterbox, offers the same grinding performance as 8530 but without the timer and cabinet. Instead, it has a perforated metal skirt to provide ventilation for continuous operation, and a rubber cover protects against dust. It also includes an anti-skid wood/rubber floor mount. The 8500 Shatterbox was the original SPEX SamplePrep swing mill. It was developed for cement plants and steel mills with open, noisy lab conditions and is still used in many locations where the working environment requires a rugged, simple mill.
What are the applications for the Shatterbox®?
Shatterboxes typically grind cement mix, rocks, slags, soils, ceramics, and ores, but have been used for hundreds of other materials including sulfur pellets, dried marsh-grass, and pharmaceuticals.
What types of grinding containers are available for the Shatterbox®?
The standard grinding containers, with a nominal volume of about 100 mL, is available in hardened steel (8501), tungsten carbide (8504), alumina ceramic (8505), and zirconia ceramic (8506). Typical grinding loads for samples such as cement, rock, or slag are 50 grams for the steel and tungsten carbide containers and 30 grams for the ceramic containers. Note that the actual capacity of the containers is much higher, and (for example) the steel container has been used for as little as 4 grams and as much as 100 grams. However, grinding efficiency decreases as the container becomes more tightly packed. There are also small grinding containers made of hardened steel (8507) and tungsten carbide (8508), which can be run either one or three at a time with the 8507R Rack. These grinding containers have about a fifth the capacity of the standard grinding containers and a typical sample size of 10 grams. An oversize steel grinding container (8521) is also available and has approximately a 150 mL capacity. This corresponds to a typical sample size of 75-100 grams. The 8525 Transporter can be used to move the heavier grinding containers (8501, 8504, 8521) in and out of the Shatterbox.
What are the principles behind the Shatterbox® grinding action?
The Shatterbox swings a dish-shaped grinding container in a tight, high-speed horizontal circle. Inside the container are the sample, a puck, and (in most containers) a ring. As these grinding elements swing free inside the container, the sample is rapidly crushed between the walls of the container, puck, and ring, and further reduced by the millstone-like action of the puck and ring against the container floor. Grinding times are usually between two and five minutes, with resultant particle size well below 200 mesh (approximately 50 microns). With grinding aids, smaller samples can be reduced below 10 microns.
What type of controls does the Shatterbox® have?
The 8500 Shatterbox® can be plugged into a standard lab timer that is not included with the mill. The 8530 Enclosed Shatterbox® features a new LCD display with an environmentally safe, push-button membrane switch. Electronic controls allow programmed running times up to 10 minutes. As the Shatterbox runs, the timer display counts down the minutes and seconds remaining. A "pause" function allows interruption of a grinding cycle.
What type of safety features is the Shatterbox® equipped with?
The 8500 Shatterbox contains a motor protected by a perforated shield to allow ample air-cooling for continuous running, and a rubber "skirt" shields the drive mechanism but is easy to move aside when the drive belts need to be replaced. It is shipped with a rubber matted plywood base to prevent it from "walking" during operation. The old screw-down clamp has been replaced with the cam-activated clamp to accommodate all SPEX SamplePrep grinding containers. The 8530 Enclosed Shatterbox includes a sound-insulated steel cabinet with lockable casters, with which the mill can be moved about the lab and then fixed in place. Safety features include a safety interlock and gas cylinders for the lid. The interlock holds the lid closed whenever the mill is running, and the cylinders control movement of the lid when it is closed or opened.

Mixing and Blending

What type of controls does the 8000M Mixer/Mill® and 8000D Dual Mixer/Mill® have?
The electronic timer of the 8000 Series Mixer/Mills displays the programmed running time in minutes and seconds. While the mill is operating, the timer also counts down the amount of time left in the run. Push-button controls include start, stop and pause functions as well as timed programming. The timer is factory-set for a maximum of 100 minutes but this may be extended to 1,000 or 10,000 minutes for special applications such as mechanical alloying with the installation of a special chip (39450 Chip for Extended Running Time). Prolonged continuous operation of Mixer/Mills requires special maintenance and warranty restriction may apply. Contact SPEX SamplePrep for details.

What are non-wetting agents (NWA)?
Non-wetting agents (NWA) are iodides and bromides which can be added in small quantities to a fusion so the molten flux will not stick to the crucible or mold. The visible effect of a non-wetting agent is to increase the surface tension of the melt. A fused disk with too little NWA will have a concave upper surface and may be difficult to remove from the mold, whereas a molten flux bead with excessive NWA will ball up when poured and not form a complete disk. SPEX SamplePrep offers LiBr solution for quick addition of a non-wetting agent to a flux (FF-0711 Lithium Bromide, 25% m/v Solution).
What are fluidizers and oxidizers?
Lithium fluoride can be used as a fluidizer, lowering the melting point of a flux and making it flow far more easily. At 10% by weight, it lowers a flux's melting point by about 100° C. Oxidizers such as lithium nitrate and sodium nitrate can be useful in eliminating unoxidized components from a sample that will not fuse. Graphite, often present in cement mix, is relatively harmless but can leave a black film on a glass disk or even cause it to crack. Graphite can be oxidized to CO2. Other sample components such as phosphides and sulfides may be corrosive enough to damage or wreck a crucible in a single fusion. If they are oxidized to phosphates and sulfates they will be comparatively harmless, and their cations will be present in the fused glass disk for analysis. As oxidizers have much lower melting points then borate fluxes, any fusion including them should proceed at a low temperature until oxidation is complete.
How do I use a non-wetting agent?
When glass disks for XRF are being made, a non-wetting agent is mixed with the flux and the sample before fusion starts. Typically the amount of NWA is about 0.2% of the weight of the flux, e.g. 12 mg of NWA for 6 grams of flux. Certain samples such as iron ores, which greatly increase the "stickiness" of a melt, require additional NWA. As non-wetting agents gradually volatize during a fusion, somewhat longer fusions (as for some technical ceramics) may also need greater amounts of NWA. The ideal amount of NWA for a specific procedure is usually determined by experiment. When making solutions by pouring the molten flux into a dilute mineral acid, it is desired to have complete transfer from the crucible to the beaker. This can require a much higher proportion of non-wetting agent than is necessary to pour a glass disk. A quantity of flux plus sample not exceeding 2 grams might require 50 to 100 mg of NWA. Lithium iodide and lithium bromide are popular non-wetting agents because they do not add an impurity to the flux. However lithium bromide is hydroscopic, so it is usually made into a saturated solution and added to the flux from a dropper bottle. Lithium iodide, sodium iodide, and cesium iodide are somewhat more air-stable, and easier to use as solids. While it is simpler to add a drop or two of a liquid NWA than it is to weigh out 10 or 20 mg of a solid, liquid NWA cannot be added to a hot crucible while a fusion is in progress. Note that non-wetting agents should be used with care when copper bearing samples are being fused, as copper halides are extremely volatile.

Pressing and Pelletizing

How fine do I need to grind my sample prior to XRF analysis?
It is impossible to say a priori how fine to pulverize a given sample. It has been known for many years that the X-ray fluorescence intensity from a sample will increase as the particle size of the sample is decreased. This is due to the reduction in the size and extent of the voids in the sample. By the same reasoning, as the particle size of one of two sample components is decreased, it will yield a higher intensity relative to the component of fixed particle size. Further, if the particle size of both components is decreased, their respective intensities may increase or decrease depending on their relative absorption coefficients. Fortunately, when the particle size becomes small enough, the intensities stabilize. In practice, the limiting particle size is often determined empirically by grinding the sample for a given length of time, measuring the particle size, analyzing the sample, then repeating at longer grinding times until the intensities reach a plateau. SPEX SamplePrep offers laboratory mills and grinding vials that are ideal for this procedure.
How do I remove the pressed sample disk from the pellet die?
When the sample disk has been formed, and the die taken out of the press, the disk must then be removed from the die. In some cases this can be done by inverting the die and standing it on the plunger, removing the base, and pressing down on the edge of the die barrel with the heels of the hands. As the die barrel moves down, the plunger pushes the polished pellets and sample disk up. If hand pressure will not budge the plunger, the knock-out ring (supplied with each SPEX SamplePrep Pellet Die Set) should be used. The knock-out ring is a tube which fits into the recess in the lower end of the die barrel. With the die base removed and the knock-out ring in place, mechanical force can be applied to the die, easing the polished pellets and the sample disk out of the die without damaging them. Whether the sample disk is extracted by hand, or with the press and knockout ring, the die barrel and plunger should be kept in an inverted position to minimize the risk of damaging the sample disk during extraction. The use of lubricants in the die usually makes it possible to extract the sample disk by hand, as well as minimizing the chances of the sample disk jamming or sticking in the die bore. Consult the section on How can I prevent the pressed sample disk from sticking to the die bore and polished pellets? for additional information.
How can I prevent the pressed sample disk from sticking to the die bore and polished pellets?
In commercial molding operations, whether of plastics, metals, or other materials, releasing agents are often necessary to effect the easy removal of the product from the mold. This is the case with XRF sample disk preparation, but releasing agents are not widely used because of concerns about sample contamination. Even samples which are not inherently sticky can become somewhat adhesive when forced against a steel plate by 25 tons of ram pressure, and in general it is difficult to remove a pressed sample disk from a die by hand pressure alone. The use of the press together with the die's knock-out ring is common practice, and as long as the disk does not bind to the die bore or the polished pellets, the knock-out ring approach works well enough. However, the use of a lubricant in the bore of the die does not have to contaminate the face of the sample if that lubricant is carefully applied, and the sample disk is carefully handled during and after removal from the die. For example, there is a fluoropolymer spray which can be squirted into the bore of a die before the die is loaded. After application, the volatile carrier evaporates, leaving a thin coating of fluoropolymer on the die bore. When the die is then loaded and the sample pressed, the sample disk and the polished pellets should have lubricant only along their edges, and should be easy to remove from the die. Even so, any such lubricant should be thoroughly tested before it is incorporated in a pressing procedure. Every XRF analyst knows the anguish of having a sample disk emerge from the die firmly attached to the polished pellet; at best the disk is ruined. This may be due to the pellet being damaged or poorly cleaned, but it is more likely that the sample is at fault. While spraying the polished pellet with lubricant will prevent sample adhesion, it will also contaminate the face of the sample disk with lubricant. The simplest non-contaminating approach is to place a piece of thin plastic film between the polished pellet and the sample before pressing. SPEX SamplePrep 3516 Mylar® Window Film is recommended because of its 0.12 mil thinness. After the sample powder is added to the die and leveled, a piece of film can be placed over the bore, and the upper polished pellet pushed down on top of it. (A more elegant approach is to cut circles of film the size of the die bore. When the pressed sample disk has been removed from the die, the film is peeled off and discarded).
How do I prepare powdered samples for XRF analysis?
X-ray fluorescence spectrometry often requires the sample to be in a homogeneous powdered form with a planar surface. Although this can be accomplished by spreading the powder on the window film of a cell designed for liquid samples (such as a SPEX SamplePrep X-Cell), compression of the powder in a pellet die yields a denser, flatter surface that provides greater analytical accuracy and sensitivity, especially for wavelength XRF. There are many different procedures for preparing powdered samples for XRF analysis. Typically, however, a representative quantity of the sample is first pulverized, and then split to obtain enough powder for an XRF sample disk, usually 6 to 10 grams. That powder is blended with a binder if necessary, and placed in a pellet die (with or without a Spec-Cap) to be pressed into a sample disk which will hold together and has a flat, compositionally uniform surface. This disk is then placed in the sample holder of the XRF spectrometer. An alternate technique, particularly useful when only a small amount of sample is available, incorporates a thin layer of sample on a disk of binder. The SPEX SamplePrep Sleeve-and-Plunger set, used with the appropriate pellet die, makes this procedure easy. In the end, an exact procedure must be developed for each type of sample. The sampling method and the amount of sample to be ground, the type of mill and the grinding time, what size of die and what pressure to use, whether to include a binder or press the disk in a Spec-Cap, all these details may vary and must be worked out by the analyst to suit his or her samples, equipment, and analytical requirements. Running a series of standards or known samples will help to confirm that your chosen procedure results in accurate, reproducible data. Reproducibility is a cardinal virtue in sample preparation. SPEX SamplePrep Laboratory Pellet Presses and Evacuable Pellet Die Sets ensure production of uniform sample disks, whatever the sample or analytical technique.
What are the recommended pressure, holding time, and bleed time for pressing a sample disk?
In pressing samples for XRF, the loaded pellet die is placed in a hydraulic press, and the pressure raised to a level that will cause the sample or sample/binder mixture to cohere into a stable sample disk. A basic pressing sequence consists of raising the pressure to a specific level, holding it there for a certain length of time, and then releasing it, preferably slowly. The maximum pressure for a given task varies considerably, depending on the size of the die and the nature of the sample. Obviously maximum pressures should not exceed the load limits of the die. The 13 mm die has a 10-ton limit, so some care must be exercised, but 31 mm and larger dies usually have load limits higher than either the capacity of the press or the pressure required to form a sample disk. Typical pressures for a 31 mm disk are from 20 to 25 tons; for a 35 mm disk, from 22 to 30 tons; and for a 40 mm disk, from 25 to 35 tons. Some samples cohere adequately at low pressures, but uniform high pressure is recommended. As "infinite depth" is very shallow for XRF analysis of most elements, a matter of microns, compaction of the sample decreases pore space and increases analytical accuracy. Holding time and bleed time are both important. If a sample is simply brought to maximum pressure, and the pressure is abruptly released, the sample disk often does not hold together. This may be due to elastic rebound of gases trapped in the sample, because a binder may take time to completely penetrate the sample, or for other reasons. A holding time at maximum pressure of at least 30 seconds is recommended. Some analysts hold pressure for 5 minutes or more. During holding time the pressure should be maintained as well as possible. An advantage of the 3636 Automated X-Press is that it turns on the pump if the pressure drops more than 1 ton during the holding period. A gradual release of pressure after the hold period is perhaps even more important than prolonged holding time. A minimum bleed time of 15 seconds is recommended. For samples that do not bind well, several minutes may be appropriate. A slow, careful bleed period can be difficult to accomplish with manual presses, as the pressure release control is often not sensitive, but it is still never a good idea to dump pressure abruptly in any pelletizing procedure. Another significant advantage of the 3636 Automated X-Press is that lengthy hold times and precisely controlled pressure release can be programmed in, and will remain the same, sample after sample. The overall uniformity of the sample disks (and hence of the analytical results) will inevitably be greater.
How do I choose a pellet die set?
The choice of pellet die is generally determined by the requirements of the analytical instrument. SPEX SamplePrep offers dies to make four standard sizes of sample disks: 3613 13 mm Evacuable Pellet Die Set for IR spectrometers, 3623 31 mm Evacuable Pellet Die Set for most OES and XRF instruments, and 3616 35mm Evacuable Pellet Die Set and 3614 40 mm Evacuable Pellet Die Set for newer XRF spectrometers. Dies are clearly labeled with bore size and maximum safe load.
What is included with the purchase of a SPEX SamplePrep Evacuable Pellet Die Set?
Each SPEX SamplePrep die set is sold as a complete unit. Made of hardened stainless steel for durability and extra wear, the SPEX SamplePrep die includes a body with detachable base, a plunger, and two polished steel pellets. Sample material is pressed in the die bore between the polished pellets, yielding a compact sample disk ready for the spectrometer's sample holder. A convenient "knock-out ring" allows easy extraction of the steel pellets and sample disk from the die. Each precision-machined SPEX SamplePrep die set also incorporates a vacuum hose attachment. This allows evacuation of gases, volatiles, and moisture during pressing, assisting compaction and preventing possible sample disk rupture under vacuum-path conditions. XRF Accessories such as Spec-Caps® and PrepAid® Binders are sold separately.
How do I set up and load a pellet die set?
Most evacuable pellet dies operate in the same way, by pressing the analytical sample between two polished pellets of steel or tungsten carbide. The simplest way of loading the die is to assemble the die barrel and die base; insert the lower polished pellet, polished side up, into the bore; pour the sample into the bore, level it, and add the upper polished pellet, polished side down; then insert the plunger, and place the assembled die in the press. This approach works well if the sample coheres well under pressure and is neither abrasive nor adhesive. Once the sample disk is pressed, it should be fairly easy to remove it from the die, either by hand or with the use of the knockout ring supplied with each SPEX SamplePrep Evacuable Pellet Die Set. When the sample does not hold together well after pressing, or sticks to the die or scratches it, there are various pelletizing aids available. These include Spec-Caps®, PrepAid® Binders, Sleeve-and-Plunger sets, and various anti-sticking agents.
When should I use a vacuum during the pressing of a sample disk?
All SPEX SamplePrep evacuable pellet dies have a vacuum hose attachment, which enables a vacuum pump to be hooked up to the die before and during a pressing operation. Most samples contain gases, moisture, and pore space, and removal or reduction of these can in fact affect the stability and uniformity of the sample disk. In the case of 13 mm dies, which are primarily used to produce KBr disks for infrared spectrometry, the use of a vacuum is necessary to draw moisture out of the KBr. Most XRF analysts do not bother to evacuate their 31 mm, 35 mm or 40 mm dies during pressing, but in fact the withdrawal of air and moisture from the sample can improve disk compaction and quality. Troublesome samples will often benefit from this technique. When evacuating a die, it is advisable to make sure both the upper and lower O-rings are in place and in good condition.
How do I properly handle and clean a pellet die set?
The SPEX SamplePrep evacuable pellet die is a precision tool which must be handled carefully and diligently maintained for proper operation. Although in design and function such dies are very simple, precise fit of the working parts is absolutely necessary, and easily jeopardized. A pellet die in good condition will produce thousands of sample disks without difficulty; a damaged or heavily worn die is likely to produce frustration, delays, and chipped or broken sample disks. Any damage to the polished pellets or the bore of a pellet die should be corrected immediately. In handling the pellet die, some simple rules should be kept in mind: keep the die clean, and always treat it as the precision tool it is. Pellet dies should be cleaned after every use, to avoid both sample cross-contamination and the possibility of disk jamming or sticking from sample build-up. In cleaning the polished pellets, treat them like glass; in other words, use the same cleaning technique you would for a glass lens or mirror. Steel has a hardness similar to glass, and it is important to avoid scratching the polished surface. Remember that the polished pellets are the most critical parts of the die, and the most easily damaged. When inserting the polished pellets into the bore of the die, take extra care that they do not jam; the fit is so precise that a very slight tilt will cause them to stick. When this happens, free the pellet gently. Above all, do not push it down further and make the situation worse, as this can cause the pellet to chip, and quite possibly ruin the die. A simple technique for inserting the polished pellet into the die bore is to hold the trailing edge of the pellet lightly with the finger-tips, and rotate it gently in the mouth of the bore to make sure it is properly lined up. When a polished pellet is placed in the die bore, it should move freely. If it does not, careful corrective action should be taken immediately.
How do I test a pellet die set to make sure it's in good working condition?
In a pellet die in proper condition, the polished pellets should pass smoothly through the die bore without binding, but their fit should be so precise that the pulverized sample will not "leak" around the pellet edges. A good test is to assemble the die bore and base, seal the evacuation port with a fingertip, and place a polished pellet (polished side up) in the bore. It should remain at or near the top of the bore, and spring back when pushed down lightly, due to compression of the air inside the die. When the evacuation port is unsealed, the pellet should drop smoothly to the bottom of the bore. If the polished pellet sinks immediately with the evacuation port sealed, it is either a loose fit, or the seal between the die body and base is damaged.
How do I repair a damaged pellet die and how does the damage affect my analytical accuracy?
Polished pellets are made with close tolerances and sharp edges so that a sample powder will not "feather" into the gap between the pellet and the bore. (When this happens, the sample disk may have a raised, crumbly lip and the disk and upper polished pellet may be difficult to remove from the die). The edges of these pellets are by far the most vulnerable part of a die, as they can be dented or chipped by dropping them even a short distance onto a hard surface. Such dents are extremely dangerous to the integrity of the die. Not only can they cause the pellets to bind in the die, but also, under the high pressures of pelletizing, the stressed edge of the pellet can spall off. The resulting chip can be dragged through the bore, scarring it deeply, and potentially jamming the plunger and ruining the die. Minor damage to the polished pellets and die bore should be immediately corrected with a fine-grained (e.g. 600 grit) emery paper. If after this the pellet will still pass smoothly through the die bore, and its leading edge is not significantly chipped, the pellet and die can continue in service. (A badly chipped pellet should be retired, as sample can wedge into the space left by the chip, making it difficult to extract the pellet from the die. In addition, further chipping is likely to occur under pressure). A lightly scarred die bore, properly smoothed, can continue in use. Damage to the polished face of the pellet should also be avoided, but will probably not affect the functioning of the die. Analytical accuracy is what suffers. Scratches on the order of 20-30 microns can cause shielding effects in the sample disk, and overall abrasion of the polished pellet face can very slightly change the geometry and distance in the critical relationship between X-ray tube, sample disk, and detector. Obviously if analytical results are being distorted because of the condition of the polished pellets, it is time to replace them, but the degree to which such distortion is tolerable will vary considerably from user to user. A simple way to check polished pellets is to press two sample disks of identical material, one with a pristine polished pellet and the other with the worn pellet, and compare the analytical data.
How does the preparation of powdered samples for XRF differ from that of OES, IR, and spark ablation?
Analytical spectroscopic methods such as XRF, OES, and IR often require samples in the form of round, flat-surfaced disks. Although sample disks can be cast from a fusion melt, they often begin as a powder and are pressed to shape in a pellet die. The basic principles of forming sample disks are the same for XRF, OES, IR, spark ablation, etc. The major differences are the diameters of the disks, and the nature of the binders or additives. IR disks are 13 mm across and consist largely of pure potassium bromide (KBr) with the pulverized sample blended in; no Spec-Cap® jacket is used, as the sample disk must be able to transmit infrared light. OES and spark ablation systems generally use 31 mm disks. As the disk must be electrically conductive for these techniques, most samples are blended with 50% pelletizing-grade graphite, and often pressed in an aluminum Spec-Cap®. The diameter of XRF sample disks is dependent on the size of the spectrometer sample holder, which may be 31 mm, 35 mm, 40 mm, or even larger. XRF disks do not require a binder or Spec-Cap if the sample coheres under pressure, but most analysts use a binder or a Spec-Cap or both. The prime requirement for an XRF binder is that it does not contribute impurities. XRF binders include cellulose, paraffin, graphite, orthoboric acid, polyvinyl alcohol, and proprietary products with special properties, e.g. Ultrabind. SPEX SamplePrep offers a variety of XRF Accessories specifically design for the preparation of pressed power samples. Reproducibility is a cardinal virtue in sample preparation. SPEX SamplePrep Laboratory Pellet Presses and Evacuable Pellet Die Sets ensure production of uniform sample disks, whatever the sample or analytical technique.
How do particle size effects affect the XRF analysis of a pelletized sample disk?
As an X-ray enters a pelletized sample disk the exciting radiation is absorbed by the matrix. When a particle within the matrix absorbs radiation, the resulting fluorescence is also absorbed, in whole or in part, by the matrix. Hence there is a limit to the depth to which the existing radiation can penetrate and result in fluorescence emitted from the sample. This depth is usually called the critical or infinite thickness. As particle size becomes small relative to the critical thickness, fluorescence intensities emitted from different sample components approach stable values. This is shown graphically below. In case A, the average penetration of the X-ray is of the same order of magnitude as the large particles, and a change in the size of these particles would have a substantial effect on the fluorescent intensity. This results from the filling of the voids by components with smaller particle sizes. In case B, since the average penetration depth covers many particles of many components, changing the particle size should have little or no effect.
What tools and materials do I need to press a sample disk?
To make a sample disk, you need a sufficient quantity of homogeneous powder, often a mixture of thoroughly pulverized sample material and an appropriate binder; a pellet die set, including two pellets of polished steel or other hard, smooth material for sandwiching the sample powder; and a laboratory pellet press for exerting the necessary pressure on the powder. An optional aluminum cup such as the SPEX SamplePrep Spec-Cap® contains the powder, protects the die bore against abrasive samples during pressing, and subsequently protects the pellet against chipping or breaking. An alternate technique, which yields a durable disk of solid binder with a thin layer of sample on one side, involves the use of a sleeve-and-plunger set with a pellet die. In pressing samples for XRF, the loaded pellet die is placed in a hydraulic press, and the pressure raised to a level that will cause the sample or sample/binder mixture to cohere into a stable sample disk. Manual and motorized hydraulic presses are available for this task: SPEX SamplePrep offers the 35-ton 3635 Automated X-Press, the 25-ton 3628 Air-Actuated Bench-Press, the 25-ton 3622 Carver® Model M Manual Press and the 12-ton 3621 Carver® Model C Manual Press. Any SPEX SamplePrep Pellet Die Set will fit these presses. SPEX SamplePrep also offers the 3626 Carver® Mini-C Manual Press, a 12-ton bench top press ideal for pressing sample pellets for IR. This press is only compatible with the 3613 13 mm Pellet Die Set.
How should pressed sample disks be handled and stored?
For maximum precision in XRF analysis, the surface of the sample disk should be very flat and very clean. It follows that these disks should be handled carefully, to avoid both surface contamination and damage. Sample disks should be handled only by their edges, and preferably not with bare skin; sweat, skin oils, and incidental contaminants are easily transferred to the analytical surface of the sample disk. Physical damage to the disk surface also affects accuracy: scratches, chips, pits, and swelling or curving should all be watched for and guarded against. As a general rule, it is best to analyze a sample disk as soon as possible after it is pressed. If it must be kept as a reference sample or standard, it should be preserved in a desiccator. Most pressed powders will absorb moisture with time, and swell. Some samples exhibit a kind of elastic rebound shortly after pressing. (Flatness can be checked by holding a sample disk against a polished pellet). Sample disks can also be degraded by X-rays. Even the heat produced by the X-ray beam can cause small flakes or particles to break loose from the face of the disk, leaving the disk with an irregular and possibly non-representative sample surface, and contaminating the spectrometer. There can be sample disks which, after the use of binders and the most careful pressing procedures, will still degrade in the spectrometer. The most common remedy is to place a piece of XRF window film (e.g. SPEX SamplePrep 3525 Ultralene® Window Film) where it will protect the spectrometer; one ingenious solution has been to place a pressed 31 mm sample disk inside a SPEX SamplePrep 3527 40 mm Closed X-Cell. If a pressed sample disk is to be used as a standard, it is advisable to have that standard made in duplicate, with the spare disk carefully preserved. The standard in daily use should be periodically compared with the standard kept in reserve. Often the first symptom of sample disk degradation is a decline in analytical accuracy.
How do I choose a laboratory pellet press?
Your choice of a laboratory pellet press will depend primarily on the amount of pressure required, the need for uniformity, and the number of samples you press per day. The diameter of the pellet to be pressed and the nature of the sample material and binder determine the necessary pelletizing pressure, which may vary from two tons to thirty-five tons. Motorized presses will provide greater convenience, yield more sample uniformity and increase sample throughput as compared to manual presses. SPEX SamplePrep offers a wide variety of laboratory pellet presses, one of which is sure to meet your needs. 3635 Automated X-Press® 35-ton (31.8 metric ton) hydraulic laboratory pellet press that accepts 13 mm, 31 mm, 35 mm, and 40 mm pellet die sets. Automatic and fully programmable. Ideal for repetitive pressing of sample pellets for XRF, IR, and other analytical techniques. Typical samples include cement, rocks, minerals, soils, ceramics, and pharmaceuticals. 3628 Air-Actuated Bench-Press® 25-ton (22.7 metric ton) air-actuated laboratory pellet press that accepts 13 mm, 31 mm, 35 mm, and 40 mm pellet die sets. Manually controlled. Ideal for repetitive pressing of sample pellets for XRF, IR, and other analytical techniques. Typical samples include cement, rocks, minerals, soils, ceramics, and pharmaceuticals. 3622 Carver® Model M Manual Press Full-size 25-ton (22.7 metric ton) Carver hydraulic laboratory pellet press that accepts 13 mm, 31 mm, 35 mm, and 40 mm pellet die sets. Manually controlled. Ideal for pressing sample pellets for XRF, IR, and other analytical techniques. Typical samples include cement, rocks, minerals, soils, ceramics, and pharmaceuticals. 3621 Carver® Model C Manual Press Full-size 12-ton (10.9 metric ton) Carver hydraulic laboratory pellet press that accepts 13 mm, 31 mm, 35 mm, and 40 mm pellet die sets. Manually controlled. Ideal for pressing sample pellets for XRF, IR, and other analytical techniques. Typical samples include cement, rocks, minerals, soils, ceramics, and pharmaceuticals. 3626 Carver® Mini-C Manual Press Bench top 12-ton (10.9 metric ton) Carver hydraulic laboratory pellet press that accepts 13 mm pellet die sets. Manually controlled. Ideal for pressing sample pellets for IR.