The　effects　of　CaB6 on　the　properties　of　MgO-C　bricks　and　the　behavior　of　CaB6 have　been　investigated． 　The　addition　of　CaB6 together　with　metalic　Al，Al-Mg　powder　increases　markedty　the　hot　modulus　of　rupture　without decreasing　the　spalling　resistance．　And　the　abrasion　resistance　is　improved　with　increasing　hot　strength． 　CaB6　reacts　with　CO（g）　and　formes　CaB2C2，CaC2　and　B2O3、CaB2C2　and　CaC2　cause　the　bonding．Since　B2O3（l），that　exisits　on　the　surface　of　CaB6，or　B2O3（g）　catches　Al（g）and　Mg（g），the　formation　of　MgO・Al2O3　is　accelated．And　MgO・Al2O3　formed　is　filled　in　gaps　between　particles　and　sintered　with　B2O3　liquid．So　the　expansion　of　bricks　is　controHed．It　is　considered　that　the　increasing　of　hot　strength　due　to　the　secondary　bonding　formatlon　and　the　accelation　of　MgO・ Al2O3　formation．

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