Preparation and crystallization of forsterite fibrous gels

Transparent forsterite fibrous gels were prepared from the hydrolysis of alkoxide precursor sols with acetic acid and water, and the crystallization process of gel fibers was studied after heat treatments up to 1500 °C. Appropriate amount of acetic acid not only promoted the formation of spinnable linear-type polymeric species, but also enhanced the chemical homogeneity and reduced the crystallization temperature of the resultant gels. On heating, fibrous gels started to crystallize into forsterite at 550 °C as investigated by infrared spectrum, X-ray diffraction and thermal analysis. Single phase forsterite fiber thus could be obtained up to 1500 °C when the amount of hydrolysis water was limited. However, fibrous gel derived from the high-water-content sol displayed a few secondary phases of the magnesia (MgO) and protoenstatite (MgSiO3) following heating at 1000 and 1400 °C, respectively; similarly, xerogels derived from without or with insufficient amount of acetic acid also revealed the segregation of second phases on heating. The synthesized forsterite fibers displayed nanocrystalline structure up to 1100 °C. On heating to 1300 °C, fired fibers exhibited grain growth into around 0.3–0.5 μm in size, with the room temperature dielectric constants of around 6.8–7.2 (at 1 MHz).