SYNTHESIS, CHARACTERIZATION AND HIGH TEMPERATURE CORROSION OF GLASS-CERAMICS IN THE B_2O_3-SiO_2-Al_2O_3 SYSTEM

摘要

Glass coatings containing boron oxide are used to limit the oxidation of non-oxide ceramic composites for applications under oxidant atmosphere. Nevertheless in wet oxidant environment, boron oxide reacts with gaseous water to produce volatile boric acids. The glass protection is then rapidly damaged by volatilization. In this study, the stabilization of boron oxide were achieved by addition of aluminium oxide and silicon oxide in the glass protection. Aluminium borate crystals (2Al_2O_3.B_2O_3 and 9Al_2O_3.2B_2O_3) embedded in a glass matrix and a borosilicate glass were synthesized after a heat treatment at 900℃. Corrosion tests with synthesized glass-ceramics at 900℃ and 1200℃ show the reduction of the boron oxide weight loss. So, the 2Al_2O_3.B_2O_3 and 9Al_2O_3.2B_2O_3 compounds are able to entrap boron oxide through their stability in water vapour at high temperature. The addition of silica also inhibits the volatilization of boron oxide by the formation of Si-O-B bonds with an increased viscosity.