Preparation And Thermophysical Properties Characrazision Of Ultrafine Potassium Nitrate

Energy storage is the premise and guarantee of energy security and sustainable development.From the current classification of energy structure,heat energy is one of the most important form of energy.The storage and utilization of thermal energy have a great impact on social life.The storage of thermal energy is mainly latent heat storage,sensible heat storage and chemical reaction heat storage.As the latent heat storage energy storage density,storage and heat process is similar to the isothermal process,simple operation control,so it has become the main mean of heat storage.The key of heat storage technology is heat storage material,so research and development of new high performance phase change heat storage material has important strategic significance and application prospect.The ultrafine potassium nitrate powders in this paper belong to molten salt phase change heat storage material.In this paper,nano-SiO₂ and nitrate as raw materials,the dispersion of nano-SiO₂ in nitrate is analyzed,and then the nano-SiO₂ induced crystallization to produce superfine potassium nitrate powder;then anti-solvent method is used to produce ultra-fine ammonium dihydrogen phosphate powder,and the method applied to the crystallization of potassium nitrate.Specific work is as follows:1.The effects of nano-SiO₂ concentration,nitrate concentration and dispersant on the dispersion of nano-SiO₂ in nitrate solution were studied.The results show that when the concentration of nanoparticles in the four salts reaches the aggregation threshold need the corresponding salt concentration is in the order of K⁺<Na⁺<Li⁺<NH₄⁺.The increase of the nanoparticle concentration is not conducive to the dispersion of the nanoparticles.The dispersant sodium hexametaphosphate promotes The dispersion of nano,SiO₂.2.Nano-silica induces potassium nitrate to form fibrous micro-nano crystals.The effects of different dispersion methods,such as concentration of nano-silica,concentration of potassium nitrate,pH,dispersant and solvent on the formation of fibrous micro-nano-structured potassium nitrate crystals were studied.The optimum conditions as follows:dispersing with ultrasonic crusher,the concentration of nano-silica is 0.05 wt%?the concentration of potassium nitrate is 1 wt%.From the polarizing microscope and scanning electron microscope?SEM?,it was found that the minimum diameter of the crystal fiber was about 2?m.The average solid and liquid specific heat capacity of the fibers are 22.3%and 41.4%higher than those of the pure potassium nitrate powder,respectively.3.The conditions for the formation of ammonium dihydrogen phosphate and potassium nitrate micro-nano-particles by anti-solvent method were studied.The effects of initial concentration of salt solution,solvent-antisolvent volume ratio,ultrasonic power and ultrasonic time on the size and morphology of salt crystals were studied.The optimum condition for the formation of ultrafine ammonium dihydrogen phosphate was obtained:the initial concentration of ammonium dihydrogen phosphate is 0.1 mol/L,the ultrasonic time is 4min,the volume ratio of solvent to antisolvent is 2:8,the ultrasonic power is 9%.Under these conditions,nanometer fluid with particle size of about 500 nm can be prepared,but after centrifugation and drying,the solid particle size of the ammonium dihydrogen phosphate ultrafine powder is 2?3 pm.The optimum conditions for the preparation of potassium nitrate ultrafine powder by ultrasonic solvent crystallization was obtained:the initial concentration of ammonium dihydrogen phosphate solution is 0.75 mol/L,the ultrasonic time is 4 min,the solvent-antisolvent volume ratio 2:8 and the ultrasonic power 9%,the nano-fluid with particle diameter about 187 nm can be prepared.However,after centrifugation and drying,the solid ultrafine powder size is about 3 ?m.How to reduce the size of the growth process in the subsequent need for further study.How to reduce the growth of particle size during the subsequent centrifugation and drying process of ultrasound still needs further study.