MULLITE JOINING BY THE OXIDATION OF MALLEABLE, ALKALINE-EARTH-METAL-BEARING BONDING AGENTS

Metallic Ba-Al-Si bonding agents have been used to produce all-ceramic , BaO-Al2O3-SiO2 bonds between plates of mullite (Al6Si2O13). Ba-Al-Si tapes (200 mu m thick) were fabricated by compaction and rolling of m echanically alloyed powder. The Ba-Al-Si tapes were placed between mul lite plates and then oxidized by heating to a peak temperature of 1230 degrees C in air. The oxidized tapes strongly adhered to the mullite plates at 25 degrees and 1000 degrees C, as indicated by the fracture morphologies obtained from compressive shear tests. Electron microscop y (EPMA, TEM) revealed that the bulk of the oxidized Ba-Al-Si tapes (a way from the interfaces with mullite) consisted largely of the compoun d BaAl2Si2O8, along with some BaSiO3 and an amorphous, barium-rich alu minosilicate. The interface between the oxidized bonding agent and bul k mullite consisted of a mixture of BaAl2Si2O8, Al6Si2O13, Al2O3, BaAl 2O4, and an amorphous, barium-bearing aluminosilicate.