Reaction of Silicate Glasses and Mullite with Hydrogen Gas

The increasing order of corrosion resistance to H₂ gas flowing fast enough to ensure that the reaction is the slow step is fused silica, aluminosilicate glass, and mullite at T =1300° to 1500° C; the activation energies are 347.3, 358.6, and 389.1 kj/mol (83.0, 85.7, and 93.0 kcal/mol), respectively. No detectable reaction with a-Al₂O₃ was observed. Addition of a small amount of CaO to the glass reduced its activation energy (283.7 kj/mol (67.8 kcal/mol)) and made its reactivity with H₂ similar to that of mullite at high temperatures. The reaction product for the glasses consisted of a porous zone composed of an intermediate layer close to mullite in composition and an outer layer of a-AI₂O₃. The reaction product for mullite consisted of a porous a-Al₂O₃ residue layer.