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TEM

Case Study

Identification of fibre mats in catalytiCatalytic converterc converters

The Problem

Catalytic converters are manufactured in all shapes and sizes, with the primary aim of reducing the volatile organic compounds (VOCs), carbon monoxide and nitrous oxides emitted from vehicle exhaust gas. Some catalytic converters and diesel particulate filters are known to contain supporting insulation mats made from refractory ceramic fibres (RCF).

RCF is classified as a Category 1B carcinogen and end of life catalytic converters should therefore be treated as hazardous waste. RCF are also covered by the Registration, Evaluation, Authorisation, restriction of Chemicals regulations (REACH 2006) and Classification, Labelling and Packaging of substances (CLP 2009). This means that suppliers and users must be aware that products contain RCF when selling on or sending for re-cycling. Appropriate packaging and labelling must also be used.

However, catalytic converters are also manufactured with poly-crystalline wools (PCW) or alkali earth wools (AEW), neither of which is classified as a carcinogen. PCWs and AEWs are visually very similar in appearance to RCF's and it is therefore impossible to differentiate between these fibre types by visual inspection.

The catalytic converter manufacturers and suppliers will typically replace the existing stock of new customers with their own products. As a result large numbers of RCF containing converters are either sent for recycling (extraction of precious metals) or sold on to third parties.

The morphology and chemistry of RCF and PCW's are very similar and therefore can be difficult to differentiate. The chemistry of AEW is sufficiently different to RCF and PCW to allow easy differentiation.

How We Can Help

Using transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX), we can use morphology and elemental composition to differentiate between RCFs and AEWs. Electron diffraction (ED) can then be used to determine crystallinity and differentiate between RCFs and PCWs.

TEM of RCF fibresEDX spectrum from RCF fibre

TEM image of RCF fibres    and    EDX spectrum from RCF fibre

ED patternCatalytic converter

Above ED pattern from PCW showing concentric ring pattern

Right-hand Image shows a cross-section of a catalytic converter (left) and a close up of the recyclable honeycomb structure (right) which contains the precious metals.  The recyclable part is shown in yellow in the cross-section, surrounded by the white fibre matting which may contain F's.

 

Outcome/Benefits

The identification of fibre type within catalytic converter fibre mats will identify which contain RCF and which contain unregulated PCW and AEW. This allows provide significant cost savings by identifying which converters require segregation and special treatment due to the presence of RCFs and which do not. Worker health is also protected by preventing accidental exposure to RCF during disposal and recycling.

HSL is UKAS accredited (ISO 17025) for the identification of inorganic fibres by TEM/EDX.

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