| Quartz is one of the most of minerals in the Earth’s crust. Because of its excellent performance, they are both an important basic raw materials of many traditional industries and very important structural and functional materials of high-tech areas such as defence, aerospace and electronics. When be used in advanced technology areas, it has strict requirements in quartz crystal’s properties of purity, particle size and microstructure.This research uses hydrothemal method, takes polysilicon by-product SiCl4hydrolysis as precursor, the experiment is basee on the following conditions:water temperature100-270℃, precursor concentration0.5-2mol/L, respectively with Na2CO3and NaOH for mineralizer, pH value8.5-12.5. After setting up the best hydrothemal technology’s conditions, alpha quartz are produced, the finished products have size between1-15μm, with axial prism grows and ideal appearance. The properties of precursor and products are expressed by XRD, SEM, EDS and FTIR, and the relationship between water temperature, precursor concentration, pH and chemical phase, particle size, microstructure are researched by XRD, SEM, EDS and FTIR. In addition, the phase transition of quartz crystals is analysised through heat treatment.In this paper, precursor were prepared by SiCl4hydrolyzing in hartshorn slow, and the precursor’s properties are analysised by XRD, SEM,and FTIR. XRD results show that it is no crystal peaks appear in the precursor, FTIR shows precursor contain silicon dioxide groups, SEM showed that precursor reunited for very small irregular-shaped powder. In following conditions:water temperature270℃, precursor concentration1mol/L, Na2CO3as mineralizer, pH10.5, depthratio80%, soaking time30h. Quartz crystal are produced for the first time.the finished products have size5μm approximately, with axial prism grows.When pH value and precursor concentration are not to change, reaction temperature have a big impact on the product. The experiment results shows, the particles size of quartz crystal is maximum in220℃, crystal morphology is ideal appearance. When reaction temperature is low, due to phase transition drive force is insufficient, atomic diffusion more slow, result in growth rate more slow, grain get smaller; and when reaction temperature rise, activation energy of nucleation reduced, led to nucleation rate is rising, crystal growth is limited.When water temperature and pH value is unchanging, precursor concentration have a big impact on the appearance and size of product. The experiment results shows, the particles size of quartz crystal is maximum in1.2mol/L. when precursor concentration is too high, led to less concentration fluctuation, higher nucleation temperatureand shorter nucleation time, result in smaller smaller particles size; when precursor concentration is too low, quartz crystals is flawed and cannot continue to grew up because of lacking of raw materials.When reaction temperature and precursor concentration value is unchanging, pH values influence on solution solubility of precursor in aqueous solution, the solubility of the precursor impact on nucleation and grew up of quartz crystal. Experiment results show that particles of quartz crystal is Larger when the pH value of10.5.To sum up, getting the better hydrothemal technology’s conditions of quartz crystal growth, reaction condition as follows:the water temperature220℃, precursor concentration1.2mol/L, Na2CO3as mineralizer, pH=10.5, depthratio80%. The finished quartz crystals have ideal crystal morphology, and average size of quartz is about11μm. EDS results show that it only have the Si and O elements, it explain that artificially synthesized quartz crystal was purely grow up.Finally, Researched phase transition of synthesized quartz crystals. The results explained that high-purity quartz crystal don’t transform into a-tridymite in870℃but directly transform into a-cristobalite through overheating1000℃. |
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