Experimental Study On Thermophysical And Corrosion Properties Of ZnO-Molten Salt Nanocomposites

Carbonate and chloride molten salts have great development potential in the medium and high temperature heat storage of solar thermal power stations in the future because of their wide working temperature range,low steam pressure and low cost.However,there are still many problems to be solved in its practical application,including the further improvement of key thermal performance parameters such as specific heat capacity,and the prevention and control of metal corrosion by molten salt.The preparation of molten salt nanocomposites by dispersing a small amount of nanoparticles in molten salt is an effective way to solve the above problems.Therefore,the improvement of specific heat capacity and corrosion properties of carbonate and chloride molten salts and their molten salt nanocomposites were studied in this paper.In this paper,ternary carbonate（31Li₂CO₃-34Na₂CO₃-35K₂CO₃,wt%）and ternary chloride molten salt（25KCl-27Ca Cl₂-48Mg Cl₂,wt%）with low eutectic ratio were prepared and slected according to the phase diagram.Nano ZnO particles of 30,60 and 90 nm were dispersed into the target base salt by two-step aqueous solution method for the first time,and ZnO-molten salt composites were prepared.The melting point,melting latent heat and specific heat capacity of molten salt nanocomposites were measured and analyzed by differential scanning calorimetry（DSC）;The chemical composition,crystal structure and micro morphology of molten salt nanocomposites were characterized by Fourier infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The corrosion behavior of molten salt nanocomposites on 201,304 and 316L stainless steel was studied by static immersion method,and the surface morphology and corrosion kinetics were analyzed.The main conclusions of the experiment are as follows:（1）The binary and ternary carbonate/chloride molten salts with low eutectic point selected according to the phase diagram can form composite molten salts with single melting point.The actual melting point of the sample is measured by DSC experiment and compared with the reference value of the phase diagram.The preferred ternary molten salt has significantly lower melting point,and is more suitable as the base salt of molten salt nanocomposites.（2）The specific heat capacity of molten salt nanocomposites is effectiv ely improved compared with the base salt,and the increase range is related to the particle size and mass concentration of ZnO.When 1.0wt%of 30nm ZnO is added,the enhancement effect of the specific heat capacity of ternary carbonate is the best,in which the liquid specific heat capacity is 2.231 J·g^-1·℃^-1,which is 21.61%higher than that of base salt;When adding 1.0wt%60nm ZnO,the enhancement effect of the specific heat capacity of ternary chloride molten salt is the best,in which the liquid specific heat capacity is 1.083 J·g^-1·℃^-1,which is 18.98%higher than that of the base salt.FT-IR test showed that there was no new chemical bond formation in molten salt nanocomposites after the addition of ZnO.XRD test showed that crystal doping occurred in the composite and ZnO was successfully introduced.SEM characterization shows that special nanostructures formed in molten salt nanocomposites may play a positive role in improving their specific heat capacity.（3）After adding ZnO nanoparticles,the corrosion of carbonate and chlori de molten salt nanocomposites to metals was improved.The total corrosion weight gain of 201,304 and 316L stainless steel samples in carbonate nanocomposites decreased by 19.1%,27.4%and 7%respectively compared with the base salt;The average corrosion rate decreased by 18.7%,25.8%and 6.5%respectively.The total weight loss of 304,57%and 316,7%of the three kinds of chloride in the stainless steel matrix decreased by 1.57%respectively;The average corrosion rate decreased by56.4%,57.0%and 54.3%respectively.