Study On The Structure And Electrical Properties Of Pyrolytic Carbon Prepared By MICVD Method

Pyrolytic carbon(PyC)with excellent mechanical,physical and biological properties,has been widely used in nuclear energy,aerospace,power and biomedical engineering.In this study,the thermoelectric properties of carbon composites with different dimensions are researched.It is found that the structure of PyC is important to the thermoelectric properties.Therefore,it is great significance to research the relationship of the microstructure and thermoelectric properties of PyC.Based on the former research on microwave chemical vapor infiltration technology,we design and proposed microwave constant temperature chemical vapor deposition(MICVD)strategy for the synthesis PyC by microwave heating process;the deposition apparatus was designed by ourselves,the microstructure and electrical properties of PyC was studied under different preparation conditions,further investigate the relationship of PyC microstructure,electrical transport properties,growth mechanism and process parameters of the PyC.The main contents of this paper are as follows:The morphology and microstructure of PyC prepared by MICVD process were researched.The variety of micro texture PyC can be prepared by controlling the process parameters,such as deposition temperature,carbon source partial pressure ratio,total cavity pressure and residence time.The structure of PyC was characterized by polarized light microscopy(PLM),X ray diffraction(XRD)and scanning electron microscopy(SEM).The results show,when the micro texture order of PyC gradually decreased(followed by high texture,medium texture,low texture and amorphous carbon),PyC,La and Lc in the graphite crystallite size decreases and the interlayer spacing of d002 increases gradually,the orientation change worse.The effect of deposition time on PyC structure was researched.The results showed that the deposition time had no effect on PyC structure.Base on analysis and research of the microstructure,morphology of PyC,and the growth process of PyC prepared by MICVD,we proposed the island layered growth model of PyC.Under the condition of 1200? and the total pressure of 50 KPa,the high texture of PyC was obtained,and the maximum deposition rate was up to 108 m/h.The electrical transport properties of PyC with different structures were studied by using a thermoelectric performance tester(ZEM)and an integrated physical property measurement system(PPMS).The results show that the hole as the main charge carrier of PyC as the conductivity.While the ordered of PyC increases,the carrier concentration,mobility and conductivity also increase gradually,but the Holzer coefficient in magnetic resistance decreases,the Seebeck coefficient decreases initially and then increases,the high textured of PyC has the best electrical transport properties.The carbon microtubes were prepared by MICVD technology,using porous silicon carbide ceramic as matrix.The diameter of carbon microtubes is about 5 ?m,and the wall thickness is about 500 nm,the microstructure of PyC is high texture,specific surface area is 1.5483 m2/g and the capacity is 40 F/g and showed a certain capacitance characteristics.