Study On Preparation Of Nanometer Zirconium Phosphate By Freeze-drying Method And Its Lubrication Performance

With the development of nanotechnology,various kinds of nanomaterials are applied to different fields.Nano?-ZrP is widely used on surface coating,flame retardant,medical and the other fields due to its stable molecular structure,diverse morphology and diverse properties.In recent years,nano?-ZrP has attracted extensive attention in in the field of friction lubrication and related fields.As a lubricant additive,it can improve the tribological performance of lubricating oil.However,the particle size of nano?-ZrP obtained by traditional method is large.In addition,there are few studies about the influence of different microstructure and particle size on the lubrication performance.In this study,nano?-ZrP was prepared by freeze-drying method.SEM,TEM and XRD were used to observe the microstructure of freeze-drying nano?-ZrP.Different particle size and microstructure(granular,lamellar and rod-like)nano?-ZrP are obtained by controlling the experimental conditions of additive concentration,such as reaction time,freezing time,stirring time and stirring speed.L9(3~3)orthogonal experiment was used to optimize the process parameters,reaction temperature,material tray area and freezing mode,which have great influence on nano?-ZrP particle size.The results show that the main factor of influencing particle size is freezing speed,material tray area and reaction temperature.The particle size is small when the process parameters(reaction temperature 98°C,material tray area 80mm~2and vacuum freezing)is selected.The particle size of nano?-ZrP obtained by vacuum-freezing is small,it can be frozen without cold source in general vacuum freeze-drying equipment,which is convenient and saves energy.However,the freezing temperature and freezing rate in vacuum-freezing process cannot be accurately controlled,so it is seldom used.A theoretical model of vacuum freezing process is established based on the basic principle of phase change heat and mass transfer and the equilibrium equation of gas state.The model is solved by recursive method.The relationship between freezing temperature and freezing rate and three macroscopically controlled process parameters,such as gas extraction rate,evaporation area and material thickness,is obtained.The theoretical calculation results are basically the same as the experimental results.The theoretical results can provide a theoretical basis for controlling the freezing temperature and freezing rate in the vacuuming freezing process.The friction test was carried out on a ball-on-disk reciprocating tribometer.When the concentration of nano?-ZrP particle was 2%,the friction coefficient decreased by 34.6%and the wear depth was-0.6?m.The roughness parameters Sa=0.185,Sq=0.257 and Sz=2.542 can be achieved,showing good lubrication performance.The particle size has a great influence on the friction coefficient.When the particle size decreases,the friction coefficient decreases correspondingly.When the particle size is about 20nm,the friction coefficient decreases to 0.08.The frictional tests of nano?-ZrP with different morphologies(granular,lamellar and rod)were carried out.The results show that the granular nano?-ZrP has better lubrication performance than the other two crystal types.The tribological experiments of lamellar nano?-ZrP and granular nano?-ZrP were carried out under different loads and speeds.The results show that the tribological properties for nano?-ZrP samples with different morphologies are different.At high speed and light load(5.35×10~8Pa,1.44m/s),the wear depth and roughness index of granular nano?-ZrP are smaller than that of lamellar nano?-ZrP.At low speed and heavy load(7.72×10~8Pa,0.36m/s),the wear depth and roughness index of lamellar nano?-ZrP are smaller than that of granular nano?-ZrP.Granular nano?-ZrP is suitable for high speed and light load,while lamellar nano?-ZrP is more suitable for low speed and heavy load.