Effects of sintering additives on microstructure and dielectric properties of calcium borosilicate glass-ceramics

The effects of additives P₂O₅and ZnO on the sintering process, phase composition, microstructures and dielectric properties of CaO-B₂O₃-SiO₂ (CBS) glass-ceramics were investigated. The results show that without additives, the crystal grains of the samples sintered at 1000°C are large, ranging from 1 to 3 μm, and the structure is rough. With the combined additives of 2% (mass fraction, the same below) P₂O₅ and 0.5% ZnO, the crystal phases of the sample sintered at 850°C are β-CaSiO₃, α-SiO₂ and CaB₂O₄, the grains are fine (around 0.5 μm) and uniformly distributed. Some glassy phase exists in the sample, and the structure is dense. The dielectric constant ε_r and dielectric loss tan δ of the material obtained by adding the additives are 6.38 and 0.0018 respectively at 10 MHz. The sintering temperature of CBS glass powders can be lower than 900°C with P₂O₅ and ZnO additives, and co-firing with Ag and Cu is possible. The effect of the combined additives can be attributed to the following advantages of each additive: P₂O₅ can promote the formation of low melting point glass phase and lower the sintering temperature, and ZnO can improve the viscosity of low melting point glass, widen the sintering temperature range, make the crystal grains fine and prevent distortion of glass-ceramics.