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Silicon dioxide(SiO2) ultrafine powders were synthesized by sol-gel method using tetraethoxysilane as the silica source, absolute ethanol as the solvent, deionized water and a certain proportion of catalyst. The effects of different initial conditions (water consumption, catalyst, sintering temperature) on the morphology, crystal size and crystallinity of SiO2 powder were studied. The following conclusions were obtained:

Effect of water content on the morphology, crystal size and crystallinity of silicon dioxide(SiO2) powder. With the increase of water consumption, the aging time needed to form gel is prolonged, and the grain size of the powder is also increased, meanwhile, the particle size of the powder increases. After the sintering at 1400 ℃, the amount of water used has little effect on the crystal form of powder. Therefore, we should choose V (H2O) / V (TEOS) as 1: 1 for the preparation of SiO2 powder with small particle size and short time consuming.

Effect of catalyst on the morphology, crystal size and crystallinity of silicon dioxide(SiO2) powder. Gel time studies have shown that gelatin can be prepared in a relatively short time by using a mixture of saturated ammonium acetate and acetic acid, hydrochloric acid or nitric acid as a catalyst. SEM analysis shows that the mixture of saturated ammonium acetate and acetic acid, ammonia or nitric acid can be used as the catalyst to obtain the powder with better particle size distribution and less agglomeration. XRD analysis showed that the powders with smaller crystal size could be obtained by using hydrochloric acid or nitric acid as catalysts. After sintering at 1200 ℃, the crystallinity of the powders was greatly affected by the catalyst, while when the sintering temperature rose to 1400 ℃, the catalyst had little influence on the crystal form of the powders.

Effect of sintering temperature on the surface morphology, crystal size and crystallinity of silicon dioxide(SiO2) powders. After sintering at 1000 ℃, the powders did not undergo the obvious crystallization and the phase transformation was still amorphous. After sintering at 1200 ℃, the SiO2 started to change from amorphous state to crystalline state, and its crystal phase was basically cristobalite, only a small amount of phosphorus quartz, but the crystal transformation is still incomplete, at 1400 ℃ after sintering all the crystal phase of quartz, indicating that the sample crystal transformation is basically complete. Therefore, to prepare high purity quartz crystal, sintering temperature should be selected above 1400 ℃. The higher the sintering temperature, the more complete the crystallization, but with the sintering temperature of the powder increases, the grain size and grain size of the powder are obviously larger, and the agglomeration of the powder becomes serious.

 

 

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