The Application Of Diatomite Purification And Nano-SiO 2 Fiber Preparation And Si 2 N 2 O Synthesis

Silicon oxynitride?Si₂N₂O?is a promising structural material and refractory material for high-temperature applications.In this study,purified diatomite and nano SiO₂ fiber are used as silicon source,and the carbothermal reduction nitridation process is used under the follow conditons: the ration of raw materials is m?silicon source?: m?carbon source?= 1 : 1;reaction temperature in the range of 1300-1450 ?,and the reaction time is 2-4 h.Experimental results show that the XRD spectra of samples from different silicon sources showed the similar characteristics.A small amount of Si₂N₂ O phase has been appeared when sintered at 1350 ? for 4 h;But the phase of ?-cristobalite has been disappeared when sintered at 1450 ? for 4 h.The major phases of sample are Si₂N₂ O and SiC,and the morphology is spherical but a large number of lamellar small grains are distributed in its interspace.In this investigation,the phase of SiC appeared in atmosphere of H2,but the phases of Si₂N₂ O and SiC appeared in atmosphere of N2 under similar conditions.In addition,when Si₂N₂ O synthesized through carbothermal reduction nitridation process,graphite cannot play a role of carbon source.Diatomite is a type of biologic sedimentary rock which composed of fossilized skeletons of diatoms.Diatomite resources are abundant in China,but the vast majority of diatomite is low or moderate quality,which limit some performance of it.In this research,acid leaching purification process is utilized,and nature diatomite powders from region of Baishan areas in China are used as raw materials.The effects of purification in the range of 110-140 ? and time in the range of 2-12 h on leaching rates of Al₂O₃ and Fe₂O₃ are respectively discussed in the following conditions: initial concentration of HCl as 11.64 mol/L,ratio of liquid to solid as 200 ml : 100 g.The experimental data indicated that leaching rate of Al₂O₃ increased from 38.05% to 77.60% and leaching rate of Fe₂O₃ increased from 68.77% to 79.68% when temperature is raised from 110 ? to 140 ? and that the reaction time is kept at 4 h.With temperature increasing,the acid leaching rate of Al₂O₃ and Fe₂O₃ reached saturation ahead of time,but also the leaching rate constant of Al₂O₃ is always larger than that of Fe₂O₃.These data of purification kinetics summarized that the leaching processes of Al₂O₃ and Fe₂O₃ follows unchanged shrinking core model,the apparent activation energy is 2.96 kJ/mol and 6.41 kJ/mol respectively.Through exploring the morphologies and surface properties of diatomite before and after purification specimens,it is done to vertify the success of this approach in producing highly purity diatomite and in maintaining the integrity of porous structure of diatom skeletons.Purification did not change the type of adsorption/desorption isotherms.Palygorskite is a high surface area clay mineral containing channels of molecular dimensions.In this investigation,acid leaching process is utilized;the samples of nano SiO₂ fiber are synthesized through the raw palygorskite from the region of Jiangsu and Anhui province in China.The effects of dissolution octahedron cations of Al³⁺ and Mg²⁺ follow the conditions of initial concentration of HCl as 8 mol/L;ratio of liquid to solid as 200 ml ? 100 g.Experimental results show that the reaction is endothermic,the content of SiO₂ is increased from 62.27% to 98.74%,the content of Al₂O₃ is decreased from 12.64% to 0.66% and the content of MgO is decreased from 7.91% to 0.11% after treated.The component unit of sample is [SiO4],but six ring heights are distorted.These data of kinetics are summarized that leaching processes of Al₂O₃ and Fe₂O₃ follows unchanged shrinking core model,the apparent activation energy is 3.35 kJ/mol and 7.13 kJ/mol respectively.