The use of Cryogenic grinding to comply with the RoHS/WEEE Directive

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. 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 grind using traditional methods. Cryogenic grinding in the SPEX SamplePrep  Freezer/Mill®  is  the  easiest  way  to  homogenize  these  materials.  Using cryogenic grinding to chill samples until they are brittle, and thenbreak them up through impact, crushing, or shearing allows the toughest samples to be ground.

Consider analyzing circuit boards: (Fig. 1) A small piece taken from a board at random would not be representative of the whole board. Sampling many boards, and homogenizing them, assures that the sample used for analysis is representative of the batch.

 The sample is cut into manageable pieces, these are then placed in the appropriately sized Chromium-Free Grinding Vial (Cat. No. 6771, 6871, or 6883). This vial also contains a magnetically driven Cr-free  impactor. The vial is then loaded into the  Freezer/ Mill and  immersed  in  liquid  nitrogen  until the contents are thoroughly chilled, usually a matter of 10-15 minutes. For high throughput applications, up to 3 additional vials can be chilled in the pre-cool chamber inside the mill. The sample inside the vial is then pulverized, and because the sample   is isolated in a closed grinding vial, cross- sample  contamination  is  easily controlled and sample integrity is maintained. Grinding time can vary depending on the type of sample but a grinding time of approximately 10 minutes can be expected. The resultant fine, uniform powder (Fig. 2) can then be used for XRF, ICP or other types of analysis.

For further information, please request our study entitled “Evaluation of sampling methods for compliance with RoHS/WEEE analysis”