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.