Sulfides such as CaS，K2SO4，etc．are formed in the dolomite refractories used in　burning　zone　of　cement　kiln． 　　 In this paper，conditions for formation of the compounds such as the sulfides were clarified thermochemically，and atmosphere in the burning zone was estimated in　the　case　of 1700K　as　follows； 　　 Partial pressure of oxygen was in －6・636＞log PO2＞8・82．　Main gas species were CO2（g），CO（g）， H2O（g），SO2（g），H2（g），S2（g）・K2SO4（g），etc．and　each　partial　pressure　was　obtained．

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　　Refractories　containning　silicon　carbide　are　used　in　industry　as　special　ceramics　and　these　refractories　usually　contaln　a　large　amounts　of　silicates　or　silicon　nitride　as　a　bonding　materials　in　grain　boundaries　in　order　to　proceed　sintering．A　new　technique　is　eagerly　expected　to　produce　silicon　carbide　refractories　with　a　high　quality．The　present　paper　will　describe　an　application　of　a　thermal　plasma　technique　to　sintering　problems　of　silicon　carbide．The　following　parameters　are　 considered　here　as　a　major　factors　in　plasma　sintering　of　silicon　carbide：out－put　power　of　radio　frequency，gaseous　pressure　and　flow　rate　of　plasma　working　gas，sintering　duration，and　additive　amounts　of　boron　and　carbon． 　　The　experimental　results　show　that　an　optimum　condition　existed　for　each　parameters．The　reasons　of　the　exist　of　optimum　points　will　also　be　discussed．Silicon　carbide　could　be　sintered　to　the　theotrtical　denslty　by　a　plasma　sintering，according　to　the　experimental　results　obtained　here．The　data　analysis　of　the　present　experimental　results　revealed　that　an　interaction　between　plasma　and　a　sample　is　tremendously　important　as　well　as　plasma　temperature　（gaseous　temperature）．

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