EFFECTS OF FIRING ATMOSPHERE AND V2O5 ADD ITION ON SINTERED AND MECHANICAL-PROPERTIES OF MULLITE

High-purity mullite was sintered in oxidizing (air) and reducing (N-2= H-2=50%) atmospheres, and effects of the firing atmosphere and V2O5 ad dition on the sintering behavior and bending strength of mullite ceram ics were investigated. The firing atmosphere did not affect the bulk d ensity of the undoped mullite ceramics sintered at below 1650 degrees C. SiO was formed by the reaction between mullite and H-2 in the reduc ing firing. Higher bulk densities of the undoped mullite ceramics sint ered at 1700 degrees C in the reducing atmosphere than those sintered in the oxidizing atmosphere were assumed to be caused by the formation of glass phase in pores from the reaction between SiO and H2O. Additi on of 0.1 mass% V2O5 yielded mullite ceramics with the highest bulk de nsity irrespective of the sintering atmosphere. High-temperature bendi ng strength of the undoped mullite ceramics sintered in the reducing a tmosphere showed a maximum at a lower temperature than that in the eas e of the ceramics sintered in the oxidizing atmosphere probably becaus e of the presence of the glass phase.