ISSN:
1436-5073
Schlagwort(e):
silicon nitride
;
contamination
;
clean room processing
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract This work investigates the uptake of impurities during processing of Si3N4 and describes an analytical scheme for detecting sources of contamination. For this purpose a process as simple and short as possible was chosen, using commercial starting materials with a high standard of purity and reproducibility. The uptake of non-metallic and metallic contaminants was investigated by choosing elements which were specific for individual processing steps. This was difficult in the determination of metallic impurities in a powder consisting of Si3N4 with Y2O3/Al2O3 additives, because the powder mixture and the sources of contamination (milling balls, attritor disk, wall materials) were similar in composition and the available analytical methods were not precise enough to detect the small increase in concentration that occurred. Therefore pure Si3N4 powders were milled in order to get an indication of the kind and concentration of impurity introduced by the individual milling materials and steps. These elements can then be used as monitor elements to trace sources of contamination and to optimize processing parameters. Experience with the processing of Si3N4 with Y2O3/Al2O3 additives by cyclic milling, spray drying, burn-out and isopressing are reported. Contamination by carbon is unavoidable. Its concentration during the process is relatively high, as it is added in the form of processing aids (deflocculants, binders), but temporary, as it can be completely burned out. Oxygen is predominantly taken up during milling. Good deflocculation reduces the milling time and thus limits the uptake of oxygen. As a consequence of these findings the processing parameters could be optimized. Thus the uptake of metallic impurities, e.g. Fe could be limited to 10 μg/g and the uptake of oxygen was found to be less than 0.2 wt%.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01245102
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