水蒸気濃度の異なる窒素水素混合ガス雰囲気中で焼成したケイ素粉末成形体の組織と結晶

Abstract

The objective of this work is to investigate the effect of water vapor content in a mixed gas consisting of nitrogen and hydrogen for firing atmosphere on the micro structure and crystal phase of fired silicon powder compact. In consequence of the firing test, crystal of α-silicon nitride, α-cristobalite and α-quartz were formed in order as water vapor content grows higher and fibrous or network shaped micro structures were formed in all range. From XRD and SEM observations of the fired specimens and from phase diagram of Si-SiO2 system, the following mechanism of silicon oxide formation was suggested. At the time of the firing, first melted layer consisting of silicon and oxigen was formed on the surface of the specimen. Secondly an oxigen content of the melted layer increased further. Lastly an amorphous silicon oxide precipitated from there. By keeping on the specimen at the firing temperature, precipitation of amorphous silicon oxide and dissolution of silicon and oxigen proceeded concurrently in the melted layer. Finally silicon was completly transformed into silicon oxide.