Measurement of silicon carbide in respirable dusts

Status:

completed 05/2004

Aims:

Silicon carbide (SiC) is generally used in a range of fractions as a grinding and blasting abrasive, and for the manufacture of ceramic materials. Exposure of employees to SiC can be anticipated during the manufacture of SiC itself, during its use for the manufacture of various products, and in various applications of the material. No recognized method has been available to date for measurement of workplace air SiC concentration. A method was to be developed by means of which the SiC concentration can be measured in combination with fine dust sampling on membrane filters.

Activities/Methods:

X-ray diffraction was employed for measurement of the silicon carbide. Analyses were performed with thin surface samples in order to minimize the influence of different mass absorption coefficients of other sample components. A suitable quantity of dust sample was charged for this purpose on a silver membrane filter, which is used for powder diffraction analysis. SiC is a polytypic substance, which may occur in different crystal structures or structure variations with the same chemical composition. This had to be taken into consideration in the selection of suitable standards. For this purpose, different SiC products were examined by means of x-ray diffraction for differences in the characteristic x-ray reflections. Calibration series were produced by means of representative SiC samples. Test measurements were performed in the development phase on samples obtained from practical applications in order to identify disturbance factors or cross-sensitivities.

Results:

X-ray diffraction is a suitable method for the measurement of SiC in respirable dusts. Cellulose membrane filters are employed for sampling. Following measurement of the respirable dust concentration, the samples can be prepared in the same way for quartz and SiC measurements, permitting measurement in parallel. A selection of industrial SiC materials should be available in respirable form for calibration purposes, since analysis of different SiC variants can be expected to yield differences in the position and intensity of the peaks in the x-ray diffractogram owing to the polytypic properties of SiC. For SiC in typical industrial form, the absolute detection limit is 50 µg. For two-hour sampling with a personal sampler (volumetric flow of 10 l/min), this results in a relative detection limit of 0.04 mg/m³. A material sample should be supplied of the SiC employed in the working area. Should the diffractogram of this material show it to differ in terms of the polytypic variants which it contains, the SiC standard provided should be used in place of the standard calibration. The method has been employed as a standard method in the BGMG hazardous substance measurement system since 15 June 2004.

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