Materials and Methods of Quartz Powder

The process involves preparing the potassium silicate solution, ion exchange, gelation, freezing, thawing, drying, cleaning, and sintering. First, 500 g of potassium silicate solution was prepared by mixing with six wt% fumed silica, 2.4 wt% KOH, and 91.6 wt% deionized water. The solution was poured into polypropylene (PP) bottles and placed on hotplates at 80 °C for 24 h under 300 rpm mechanical stirring via a magnetic stirrer. The experiment for the dependency of dissociation of fumed silica on the weight percent of KOH and fumed silica determined the mixing ratio among fumed silica, KOH, and deionized water. For the ion exchange process, 300 g of strongly acidic cation exchange resin was put into a PET cartridge, and 500 g of the potassium silicate solution was ion exchanged through the cartridge at a flow rate of 188 mL/min. The potassium silicate solution was changed to SiO2 sol state via the ion-exchange process and then gel state through heating on a hotplate at 60 °C for three h. Two gel samples in PP bottles were prepared to investigate the effect of the pulverizing process on the morphology and crystallinity of the quartz powder. One of the samples was preceded by pulverizing via the bottle-shaking method, and the other was not. Then, two gel samples were frozen at −25 °C for 16 h, followed by thawing at 80 °C for 4.5 h, and were turned into quartz powder form through the decantation and drying process. In addition, the experiments on the dependency of forming as-synthesized powders were carried out after the freezing and thawing process on gelation time ranging from 0 to 5 h.

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