Sol-Gel Synthesis of B2O3-Doped Anorthite and its Characteristics

Pure anorthite was prepared by calcination of a gel formed by mixing boehmite, silica sols with Ca(NO3)2⋅4H2O solution at 1050°C. Doping of this sol with B2O3 lowered the crystallization temperature of anorthite to less than 950°C depending on the dopant content. B2O3-doped anorthite powders were sintered at temperatures below 1000°C. The sintering was promoted by the formation of a B2O3-rich glassy phase around the grains. The dielectric constant of pure anorthite was 8.5 and decreased to 7.2 with the addition of 2.8wt% B2O3. Doping of B2O3 decreased the thermal expansion coefficient, whereas the mechanical properties were only little affected.