珪藻土からの窒化ケイ素ウイスカの合成における還元剤の効果

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Carbothermal reduction and nitridation of di atolnaceous earth were carried out in a flow of nitro gen containing various reducing gases (NH_3, H_2, CO, and CH_4) at 1350℃. Addition of 75 mol% NH_3 to N_2 brought about a marked effect upon the inside and out side whisker formation. The ability of the various reducing agents in the reduction of SiO_2 was investigat ed, and found that a carbon plate or methane, can reduce Si0_2 in diatonraceous earth, but that neither H_2 nor CO can reduce SiO_2 at 1350℃. The reduction rate in the presence of both the carbon plate and H_2 was higher than that for either one of them. The formation of CH_4 in a blank experiment using no diatolnaceous earth suggests that the CH_4 formed from NH_3 and the carbon plate plays all iurportant role in the reduction of SiO_2 into SiO (g) . Next, the effect of addition of pow dered carbon to diatomaceous earth was studied. Since an excess amount of powdered carbon accelerates the reduction and nitridation of Si0_2 and SiO(g) , the yields of inside and outside whiskers decreased with in creasing amount of powdered carbon added. On the other hand, the yield of Si_3N_4 powder increased with in creasing carbon content in the starting materials up to 20 wt%. SiC was also obtained in the Si_3N_4 powder at carbon contents>20 wt% . When only methane was used as a reducing agent, the maximum yield of inside whiskers was about 28% at 1.0 vol% CH_4 in N_2. On the other hand, the yield of the outside whiskers was lower over the CH_4 concentration examined.
社団法人日本セラミックス協会の論文
1994-07-01

珪藻土からの窒化ケイ素ウイスカの合成における還元剤の効果

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