Al_2O_3-SiO_2系焼結体とカルシウムカーバイドとの反応  [in Japanese] Reaction of Al_2O_3-SiO_2 Ceramics with Calcium Carbide  [in Japanese]

カルシウムカーバイド系溶銑脱硫剤による耐火物の損傷機構を明らかにするため, カルシウムカーバイドとAl2O3-SiO2系ち密質焼結体との反応を検討した. 組成の異なる3種の焼結体をカルシウムカーバイド粉末中に埋め込み, 還元雰囲気中で1200°-1400℃で反応させた.SiO2含有量の多いムライト質焼結体の場合, 明りような反応層を形成し, その厚さは時間の平方根に比例して増大する. 反応層の酸素濃度は原セラミック層のそれより小さく, 金属シリコンの析出が認められる. 反応層と原セラミック層との間には, 主としてAl2O3単味で構成される薄い界層が存在する. ムライト質焼結体とCaC2との反応は次のような過程により進行するものと推定される. まず, CaC2が反応層と境界層を拡散して原セラミック層に達し, ムライトの分解を促進境するとともに, 生成したSiO2を還元してSiOガスを生成する. SiOガスは境界層を移動して反応層に達し, ここで更にCaC2によって還元されSiを生成する.

Severe wear of lining refractories in torpedo car occurs when injection of desulphurizing agent containing calcium carbide is done to desulphurize molten pig iron. To make clear the corrosion mechanism of the refractories, reactions between calcium carbide and Al2O3-SiO2 ceramics were studied. Three kinds of mullite and corundum disks were embeded in calcium carbide powder, and heated at 1200°-1400°C in a reducing atmosphere. Mullite ceramics formed a reacted zone, leaving metallic silicon particles in it. The thickness of the reacted zone is proportional to the square root of time. Thin boundary zone, which is mainly consisted of alumina, is formed between the reacted and the original ceramic zones. On the other hand, corundum ceramics did not form any reaction zone.From these results, SiO2 component in the mullite ceramics is considered to be reduced by CaC2, forming metallic silicon, calcium oxide, and carbon monoxide or carbon. The reaction would proceed by the following steps:(1) Transportation of CaC2 through the reacted zone and the boundary zone.(2) Decomposition of mullite: 3Al2O3⋅2SiO2→3Al2O3+2SiO2(3) Reduction of SiO2 by CaC2: 3SiO2+CaC2→3SiO(g)+CaO+2CO(4) Transportation of SiO gas through the boundary zone(5) Reduction of SiO by CaC2: 3SiO+CaC2→3Si+CaO+2COThe rate of the reaction is considered to be controlled by transportation of CaC2 through reacted zone and boundary zone.