Synthesis of CaF Nanoparticles Coated by SiO for Improved AlO/TiC Self-Lubricating Ceramic Composites.

In order to reduce the influence of CaF addition on the mechanical properties of self-lubricating ceramic tools, we applied a silicon dioxide (SiO) coating on calcium fluoride (CaF) nanoparticles through hydrolysis and condensation reactions using the tetraethoxysilane (TEOS) method. The powder was dried by the azeotropic method, so that it acquired a better dispersibility. The resulting composite powders were characterized using XRD (X-ray diffraction) and TEM (transmission electron microscopy), showing that the surface of CaF was coated with a layer of uniform and compact SiO. SiO shells with different thicknesses could be obtained by changing the amount of TEOS added, and the thickness of the SiO shells could be controlled between 1.5 and 15 nm. At the same time, a ceramic material containing CaF nanoparticles and CaF@SiO-coated nanoparticles was prepared. It had the best mechanical properties when CaF@SiO-coated nanoparticles were added; its flexural strength, fracture toughness, and hardness were 562 ± 28 MPa, 5.51 ± 0.26 MPa·m, and 15.26 ± 0.16 GPa, respectively. Compared with the ceramic tool containing CaF nanoparticles, these mechanical properties were increased by 17.57%, 12.67%, and 4.88%, respectively. The addition of CaF@SiO-coated nanoparticles greatly improved the antifriction and wear resistance of the ceramic material, and the antifriction and wear resistance were balanced.