Fabrication And Properties Study Of SiC Hollow Micospheres

Silicon carbide?SiC?is a binary solid compound of IV-IV family.SiC is expected to be an important target in laser inertial confinement fusion?ICF?physical experiments for its distinct properties,such as excellent mechanical properties,stable chemical properties,high thermal conductivity and great thermal stability.Generally,SiC hollow microspheres for ICF were prepared by dry-gel method.However,limited to its preparation principle,this method can not prepare high-quality SiC hollow microspheres with large diameter?mm?,adjustable diameter and controllable wall thickness.With the continuous development of ICF physical experiments,the demand for large-diameter?mm?SiC hollow microspheres is increasingly urgent.New preparation methods have to be explored.Therefore,plasma enhanced chemical vapor deposition?PECVD?-pyrolysis method was initially explored in this paper.The surface roughness,density and other properties were optimized.Our work provides experimental and technical basis for the preparation of SiC hollow microspheres with large diameter?mm?,adjustable diameter and controllable wall thickness required for ICF experiment.In this paper,the silicon doped glow discharge polymer?Si-GDP?was first deposited on poly??-methylstyrene??PAMS?shells,using TMS+T₂B+H₂ as precursor gases.Then,SiC hollow microspheres were successfully fabricated by mandrel degradation and pyrolysis.The effects of Si-GDP preparation parameters?TMS flow and pressure?and Si-GDP heat treatment parameters?temperature and holding time?on the structure and properties of SiC hollow microspheres were investigated.The chemical composition and structure of SiC hollow microspheres prepared under different parameters were analyzed and discussed by XPS.The crystallinity of microspheres was studied by XRD.The surface morphology and roughness of SiC hollow microspheres were studied by using scanning electron microscope?SEM?,atomic force microscope?AFM?and white light interferometer?WLI?.The sphericity and wall thickness uniformity of SiC hollow microspheres were tested by X-ray camera.The transition process and transformation mechanism of Si-GDP to SiC was studied by using TG-DTG synchronous heat analyzer.The weight of SiC hollow microspheres was measured by analytical balance,and the influence of heat treatment parameters on the density of microspheres was studied.Through the research of the above contents,we have made the following progresses and regular cognitions.?1?The influence of TMS flow on the structures and properties of SiC hollow microspheres.The results show that SiC microspheres are amorphous with a small amount of carbon.With the increase of TMS flow,the content of carbide element decreases while the content of Silicon element increases,that is,C/Si atomic ratio gradually decreases.The surface root mean square roughness?Rq?of SiC hollow microspheres firstly decreases then increases with the increase of TMS flow.Comparing with the Si-GDP before heat treatment,the diameter and wall thickness of the SiC hollow microspheres have a large shrinkage,and the shrinkage rate gradually decreases as the TMS flow increases.The spherical degree of SiC microspheres is not significantly affected by the large shrinkage,and the spherical degree of the microspheres under different TMS flow is above 99%.The wall thickness uniformity of the microspheres prapred with TMS flow of 0.1,0.25,0.3 sccm is almost equal and better than that of 0.4 sccm.When TMS flow is 0.3 sccm,the sphericity degree and the wall thickness uniformity of the microspheres are better,and the shrinkage of the diameter and wall thickness is appropriate.?2?The influence of working pressure on the structure and properties of SiC hollow microspheres.The results show that pressure has little effect on the composition of SiC microspheres.C/Si atomic ratio slightly firstly increases then decreases with the increase of pressure.Rq of SiC microspheres firstly decreases and then increases as pressure increases.With the increase of pressure,the spherical degree of the microspheres has little change and all of them are better than 97%.The wall thickness uniformity of SiC microspheres firstly increases then decreases with the pressure increasing.When the pressure is 10Pa,the surface roughness and the wall thickness uniformity of the SiC microspheres are better.At the same time,the cotent of the Si-C bond is higher and the deposition rate is larger.?3?The influence of temperature during heat treatment process on the structures and properties of SiC hollow microspheres.The results show that the weightlessness of Si-GDP mainly occurres at 300-600°C and the weightlessness rate firstly increases then decreases.When temperature is 450°C,the weightlessness rate is the largest.The MRS roughness of the microspheres fluctuates greatly with the increase of temperature.When the heat treat temperature is 900°C,the surface of microspheres is the smoothest and the RMS roughness?47.52 nm?is the smallest.During the heat treatment process,diameter and wall thickness exist a large shrinkage,and shrinkage rate presents an increasing trend.When temperature is above 600°C,the increase of shrinkage rate is greatly reduced.As temperature increases,the microspheres become denser and denser,and the density increases from 1.04 g/cm³ to 2.75g/cm³.?4?The influence of holding time during heat treatment process on the structures and properties of SiC hollow microspheres.The results show that the content of C-Si bond in the microspheres increases with the increase of the holding time at 450°C.As holding time increases,the number of protuberance on the surface of the microspheres gradually decreases,the surface becomes smoother and smoother,and the RMS roughness decreases from 43.37 nm to35.66 nm.The density of the microspheres is also effectively improved from2.19 g/cm³ to 2.46 g/cm³ by prolonging the holding time.