Synthesis and characterization of high-density B₂O₃-added forsterite ceramics

Boria (B₂O₃)-added forsterite (Mg₂SiO₄) ceramics were synthesized and their properties were characterized. The addition of B₂O₃ was aimed to produce high density forsterite ceramics at a low sintering temperature. The raw materials were purified silica sand and commercial magnesia powders. Fosterite powder was produced from a solid reaction between the raw powders at 1100 °C prior to addition of B₂O₃, uniaxial pressing and sintering at 1200 °C. The amount of added B₂O₃ varied between 0%, 4%, and 8% by weight. Elemental analysis was performed by X-ray fluorescence (XRF) spectroscopy on the purified silica powder, whereas phase analyses were obtained from X-ray diffraction (XRD) data. Characterization of the ceramics included diameter shrinkage, density-porosity, thermal expansion, Vickers hardness, and dielectric constant. The results showed that the silica powder contained 98.7 at% Si with minor impurities, including 0.5 at% Ti, but the only identified crystalline phase was quartz. Further phase analysis of the ceramics showed that the addition of B₂O₃ reduced the amount of formed forsterite and increased the amount of cristobalite, proto- and clino-enstatite (MgSiO₃) as well as suanite (Mg₂B₂O₅). The highest forsterite content was found in B₂O₃-free ceramics, approximately 88.1 wt%. Moreover, the addition of B₂O₃ also reduced the diameter of the sample by more than 21%, resulting in a very dense ceramic with an apparent porosity of only 0.3%. The Vickers hardness significantly increased from 0.3 GPa for the B₂O₃-free ceramic to 10.9 GPa for the 4% B₂O₃ sample. The dielectric constant of the B₂O₃-added forsterite ceramics was improved by approximately 2–6 times that of the B₂O₃-free ceramic, which was primarily attributed to the loss of porosity in the samples.