Effect Of C₃H₆/C₂H₂Mixtures On The C/C Composites Prepared By CVI

The microstructure of pyrocarbon is crucial to the performance of C/C composites, changing the parameter to acquire right structure of pyrocarbon and increase the efficiency is one of the hot subjects both domestic and international research. There are many factors influencing the microstructure of pyrolytic carbon. The effect of different carbon sources on the densification process and the microstructure of matrix prepared by methods of CVI were investigated. The following aspects were studied:the effects of different carbon sources(C3H6and C3H6/C2H2mixtures) on the carbon yield,density distribution and the microstructure of C/C composites prepared by CVI, in the condition of constant pressure and temperature; the effects of propylene/acetylene mixtures at different concentrations on the carbon yield, density distribution and the microstructure of C/C composites prepared by CVI, in the same condition of constant pressure and temperature; the effects of different temperature on the carbon yield, density distribution and the microstructure of C/C composites prepared by CVI, using propylene/acetylene mixtures(v/v about2:1) as carbon sources. The following results were obtained.1. When the temperature is980℃, the pressure is0.6kPa, the yields ratio and the degree of orientation of pyrolytic carbon prepared by C3H6/C2H2mixtures are higher than by C3H6only, the density grads in the inside and outside of sample prepared by C3H6/C2H2mixtures is smaller.2.When the temperature is1080℃, the pressure is1.4kPa, as the v/v of propylene/acetylene mixtures ringing range from about2:1to1:2, the density grads in the inside and outside of sample decreased as the v/v of C3H6/C2H2mixtures changed from2:1to1:1, then increased as the v/v of C3H6/C2H2mixtures changed from1:1to1:2. as the v/v of C3H6/C2H2mixtures ringing range from about2:1to1:2, the yields ratio of pyrolytic carbon increased as the v/v of propylene/acetylene mixtures ringing range from about2:1to1:2, which was higher than that obtained from C2H2only. The pyrocarbon in the C/C composites which were prepared by C3H6/C2H2mixtures are all belong to SL, but the degree of orientation of pyrolytic carbon prepared by C3H6/C2H2mixtures(v/v about1:1) is higher than the others.3.When the v/v of the C3H6/C2H2mixtures is about2:1, as the temperature varied from1000℃to1080℃, after40h deposition, the density of sample increased from1.309g/cm3to1.526g/cm3, as the temperature reached1120℃, the density of sample decreased from1.526g/cm3to1.417g/cm. The average density grads in the inside and outside of the sample which were prepared at1080℃is lowest and the total yields ratio of pyrolytic carbon is higher than the others.