Preparation Of Diamond@CeO₂ And Diamond@SiO₂ Composite Abrasives And Their Effect On SiC Polishing Performance

Single crystal silicon carbide（Si C）has high hardness and high brittleness.During chemical mechanical polishing,there are problems of low material removal efficiency and easy surface damage,so it is difficult to achieve ideal planarization of the plane.Diamond has the characteristics of high mechanical removal rate due to its high hardness,houwever it is easy to cause scratches on the machined surface;Cerium oxide（CeO₂）has good chemical activity,Silicon dioxide（SiO₂）has good dispersibility,and the two abrasives have low hardness.It has good polishing quality itself,and the surface quality of workpiece is better when used for chemical mechanical polishing.In this paper,ultrafine diamond（UFD）produced by crushing method is used as the core,and CeO₂ and SiO₂ are coated on the surface by homogeneous chemical precipitation method and Stober method,respectively,to synthesize new UFD@CeO₂ and UFD@SiO₂ composite particles.The structural characteristics,dispersion stability and anti-oxidation properties of two kinds of composite abrasive particles were studied.The effect of two kinds of composite abrasive particles on the chemical mechanical polishing performance of Si C was investigated by configuring the composite abrasive particle polishing liquid.The main research contents are as follows:1.Preparation and characterization of UFD@CeO₂ composite abrasive particles.The mean particle size of diamond particles（0.05μm,0.25μm and 1.5μm,respectively）,the precursor Ce（NO₃）₃?6H₂O content（corresponding to 10%,20%,30%and 40%of CeO₂ coating）and the dispersion of the coating effect of CeO₂ on the diamond surface by type and amount of the agent.Using the mixture of water and ethanol as the dispersion system,coating 20%CeO₂ on the ultrafine diamond particles of 0.25μm has the best effect.Scanning Electron Microscopy（SEM）,Transmission electron microscopy（TEM）,X-ray diffraction analysis（XRD）,Fourier transform infrared spectroscopy（FT-IR）,Raman spectroscopy（Raman）and X-ray photoelectron spectroscopy（XPS）to study.the structure and morphology of UFD@CeO₂ composite particles.The results show that the CeO₂ particles of 5-10 nm are uniformly distributed on the diamond surface to form a particle-deposited core-shell structure.The shell CeO₂is a cubic fluorite structure,but contains a certain proportion of Ce³⁺,which may be oxygen vacancies.The dispersibility and thermal stability of the composite particles were studied by laser particle size analysis,Zeta potential and comprehensive thermal analysis（TG-DSC）.The results showed that the existence of the CeO₂ shell significantly increased the Zeta value of UFD and improved its the dispersibility,particle size distribution shows that there are no agglomerated secondary particles in UFD@CeO₂,the initial oxidation temperature of UFD particles is 548°C,and the initial oxidation temperature of UFD@CeO₂-10%and UFD@CeO₂-30%composite particles is increased to 602°C,617°C.2.Preparation and characterization of UFD@SiO₂ composite particles.The process conditions such as dispersant,TEOS dosage,ammonia water dosage,and reaction time were optimized.When the amount of TEOS added was 3 m L/100 m L,the amount of ammonia water was 4 m L/100 m L,and the reaction time was 12 h,the synthesis was performed with a controllable thickness and a package.The composite particles with uniform coating and no free SiO₂,SEM,TEM,XRD and FT-IR analysis results show that the UFD@SiO₂ composite particles have a core-shell structure,and the SiO₂ shell layer on the UFD surface has a uniform thickness and an amorphous structure;The distribution shows that there are no agglomerated particles in the UFD@SiO₂ composite particles,and the absorbance of the supernatant of the suspension is significantly higher than that of UFD at different times,indicating that the existence of the SiO₂ shell can improve the dispersion and stability of UFD particles in aqueous solution TG-DSC test results found that different shell thicknesses of SiO₂can increase the initial oxidation temperature of UFD by 20°C-50°C.3.The polishing performance of UFD@CeO₂ and UFD@SiO₂ composite abrasives on single crystal Si C.UFD,CeO₂,UFD@CeO₂ and UFD@SiO₂ composite abrasives were respectively configured into polishing liquid,and the appropriate polishing process was selected to polish single crystal silicon carbide.The surface morphology of Si C was observed by atomic force microscope（AFM）and the surface roughness and removal rate.After polishing with UFD,UFD@CeO₂ and UFD@SiO₂polishing liquids,the surface roughness of Si C is 1.45 nm,0.83 nm and 0.71 nm,respectively,and there are obvious scratches and adhered particles after UFD polishing;Si C surface curve profile changes are±2 nm,±1 nm,and±0.5 nm;material removal rates for Si C were 316 nm/h,290 nm/h,and 332 nm/hn,respectively.The results show that while maintaining the high polishing rate of diamond particles,the surface quality of Si C after processing is significantly improved,which is expected to be applied to high-efficiency and high-quality polishing of silicon carbide,and achieves the research goal of preparing composite abrasive particles with good polishing performance.Innovation point:UFD@CeO₂ and UFD@SiO₂ composite abrasive particles that can be used to polish hard and brittle substrate materials such as Si C are prepared for the first time.