A new preparation method of CaF2@SiO2 nano solid lubricant and analysis of its coating mechanism

Abstract

The microstructure of materials is the basic factor affecting their properties. In order to reduce the influence of adding solid lubricant on the performance of ceramic cutting tools, a new preparation method was adopted to prepare CaF2@SiO2 solid lubricant. Firstly, uniformly dispersed CaF2 nanoparticles were obtained by precipitation and azeotropic distillation, and then SiO2 was coated on the surface of CaF2 by using the hydrolytic condensation effect and heterogeneous nucleation effect of TEOS, so as to prepare CaF2@SiO2 solid lubricant with core-shell structure. The effects of process parameters on the microstructure and surface morphology of coated nanoparticles were analyzed. The results show that TEOS titration speed, pH value, temperature and azeotropic distillation have great influence on the quality of nano-silica powder. The optimum preparation parameters are: pH 8.5, TEOS dropping rate 0.4 mL/min, reaction temperature 40 °C and azeotropic distillation. The formation process and surface coating modification mechanism of CaF2@SiO2 nanoparticles were analyzed. Owing to heterogeneous nucleation theory, SiO2 can be adsorbed on the surface of CaF2 stably, and the interaction between SiO2 and CaF2 can form a stable adsorption interface. And the driving force of nucleation changes with the process parameters. By changing different process parameters, the controllable preparation of coating can be realized, and the optimal thickness of coating is about 10 nanometers.