In　order　to　prevent　structural　spalling　of　MgO－based　basic　refractories　for　steel－ladle，slag　penetration　into　the　refractories　was　studied　and　new　type　of　a　basic　refractory　has　been　developed．Results　obttained　are　as　follows； 　Both　diissolution　rate　of　the　refractories　into　slag　and　diffusion　rate　in　the　slag　of　chemical　components　of　the　refractories　are　high．Even　if　aids　such　as　SiO2，Al2O3，CaO　or　others　are　added　to　MgO－based　basic　refractories，composition　of　the　slag　which　penetrates　into　pores　of　the　refractories　is　saturated　with　MgO． 　In　the　case　of　the　refractories　which　ars　easily　wetted　by　the　slag，slag　penetration　speed　is　high．Because　viscosity　of　the　slag　saturated　with　MgO　is　low．The　value　of　several　cm/h　was　measured　at　the　first　stage　of　penetration． 　It　is　difficult　to　prevent　slag　penetration　into　the　basic　refractories　that　are　easily　wetted　by　the　slag．To　prevent　the　slag　Penetration　into　the　refractories，it　is　essential　for　the　refractories　to　be　not　easily　weetted　by　the　slag． 　Even　in　the　case　in　which　the　refractories　are　not　easily　wetted　by　the　slag，the　slag　can　be　pushed　into　pores　by　static　pressure　of　molten　steel．Critical　pore　radius，below　which　no　slag　Penetration　occurs，is　inversely　propotional　to　the　static　pressure．For　a　given　static　pressure，decreasing　the　pore　size　of　the　refractories　is　effective　to　decrease　the　slag　penetrati　on　volume． 　Basic　castable　refractory　that　was　not　easily　wetted　by　the　slag　and　whose　pore　size　was　decreased　has　been　developed，and　used　at　250t　steel－ladle．Only　slight　spalling　was　observed，and　life　of　the　refractory　was　67 heats　without　repair．

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Wettability　of　solid　oxides （alumina　and　mullite） by　molten　Fe－Mn　alloys　has　been　investigated　using　the　sessile　drop　method． Main　results　are　as　follows： 1）Surface　tension　of　molten　Fe　decreased　with　increasing　of　Mn　content　in　molten　Fe． 2）Contact　angle，work　of　adhesion．and　interfacial　free　energy　between　molten　Fe－Mn　alloy　and　solid　oxides　depended　on　a　partial　oxygen　pressure　in　the　atmosphere　used．Small　contact　angle，low　　interfacial　free　energy　and　large　work　of　adhesion　were　obtained　when　the　partial　oxygen　pressure　was　low． 3）The　contact　angle　and　interfacial　free　energy　between　molten　Fe－Mn　alloy　and　the　mullite　were　always　smaller　than　those　between　molten　Fe－Mn　alloy　and　alumina．This　can　be　caused　by　the　reactivity　of　solid　oxides．

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