Papers by Keyword: Polymer Pyrolysis

Abstract: Carbon/carbon composite of various density were synthesized via chemical vapor infiltration process, and the sedimentary process of pyrolytic carbon were also researched. The density of the sample increased with the extension of growth time. Density change rate of the samples were various at different stages of the growth process, namely pyrolytic carbon of different densities formed at the different stages. It was found that pyrolytic carbon filled the pores of carbon fiber preform, which can help to relieve the interface stress between the fiber and the ceramic substrate. In order to improve the performance of the composite, SiC and ZrC ceramics were introduced into the carbon/carbon composite via polymer infiltration and pyrolysis (PIP) process. The ability of high temperature resistance and oxidation resistance of the composite were strengthened by the PIP process. The bending strength, tensile strength and compressive strength were also increased with the extension of PIP cycle. The C/C-SiC-ZrC composites were obtain through this process, which are useful in various areas.

Abstract: SiC nanopowder, polycarbosilane and divinylbenzene mixed slurries were prepared for viscosity measurement, which were used as matrix source of ceramic matrix composites. Results showed that apparent viscosity of the slurries increased with the increase of the content of SiC particles. The slurries with 50 nm SiC particles showed a low viscosity as compared with those slurries with 20 nm or 120 nm SiC particles at the same content of SiC. In particular, when the viscosity of slurry was higher than 30 mPa•s, the slurry could not be used in the test. Three-dimensional carbon fiber (3D-C_f) preforms were infiltrated with the aforementioned slurries. Addition of the nanoSiC powder as the inert filler in the slurries led to reduce the porosity and the infiltration–curing–pyrolysis cycles to manufacture 3D-C_f/SiC composites by the subsequent polymer impregnation and pyrolysis (PIP) process. Characterizations of the composites showed that the maximum flexural strength of specimen in the composites was 326 MPa and its fracture toughness was 10.5 MPa•m^1/2.

Abstract: Because of its combined characteristics of metals and ceramics, such as low density, high Young’s modulus, thermal and chemical resistance with low hardness, high electrical and thermal conductivity, it was expected that the introduction of Ti3SiC2 to fiber reinforced ceramic matrix can make the composite own some unique properties. In the present research, Ti3SiC2 powders used as inert fillers were fabricated by the in-situ reaction between Ti and polycarbosilane mixtures. The purity of Ti3SiC2 powders analyzed by XRD was determined by RIR method, which is a semi-quantitative XRD analysis. The results showed that the purity of Ti3SiC2 powders is about 96%. Cf/Ti3SiC 2-SiC composites are obtained by polymer infiltration and pyrolysis process using Ti3SiC2 powders as the inert fillers. The bending strength of Cf/Ti3SiC2-SiC composites was about 160 MPa.

Abstract: Stitched carbon fiber cloth reinforced zirconium carbide composite (C/ZrC) was prepared by polymer infiltration and pyrolysis (PIP) process. C/ZrC-SiC composite was obtained by further introduction of SiC with PIP process in order to improve anti-oxidation property. The results show that 1.9vol% SiC addition improves the mechanical and anti-oxidation properties of C/ZrC composite. The flexural strength of C/ZrC is 247.9MPa, while that of C/ZrC-SiC is 273.1MPa. After oxidation in a muffle furnace at 1200°C for 30 minutes, the mass loss rate was reduced from 30.6% (C/ZrC) to 20.1% (C/ZrC-SiC), and the flexural strength and elastic modulus of C/ZrC were 56.7MPa and 5.7GPa, respectively, while those of C/ZrC-SiC were 122.9MPa and 17.2GPa, respectively.

Abstract: By using the active filler controlled polymer pyrolysis, new and cost-effective composite materials can be obtained. In this work, ceramic matrix composites were prepared by using this precursor route, using a polysiloxane network filled with metallic niobium and aluminum powders as active fillers. The mixtures were blended, uniaxially warm pressed, and pyrolyzed in flowing argon at 1400 °C. Porous ceramic preforms were infiltrated with a LZSA glass material, in order to improve the density of a porous composite material. The properties of the pyrolyzed composite material and the effect of the LZSA infiltration on the Al2O3-NbC-SiOC ceramic composite material were investigated. The results have showed that the infiltration processes has improved the physical and mechanical properties of the composite material.

Abstract:
The formation, microstructure and electrical property of conductive ceramic composites derived from polymer pyrolysis were investigated. Methylpolysiloxane was mixed with TiH2 as a filler and pyrolyzed in nitrogen, argon and vacuum atmosphere at a temperature of 1600oC for 1 hour after the preheat treatment at 850oC in N2 atmosphere. Depending on the atmosphere conditions, TiN and Ti5Si3 phases were formed by reaction of TiH2 as reactive filler and atmospheric gas or pyrolytic product such as SiO2. Consequently, the microstructures of the ceramic composites with 70 vol.%TiH2 pyrolyzed at 1600oC for 1 hour in vacuum were composed of TiN and Ti5Si3 particles. The density and electrical conductivity of the ceramic composites were 97.3 TD% and 6200 ohm-1⋅cm-1, respectively. These composites pyrolyzed by polymer were considered as superior conductive material with a value of 103 ~ 104 in log scale at room temperature.

Abstract: In this work, ceramic matrix composites (CMC) were prepared by AFCOP process, using a polysiloxane network filled with metallic niobium and aluminum powders as active fillers. The liquid polysiloxane precursor was loaded with a suitable polymer/filler ratio in relation to stoichiometric Nb : C and Al : O molar ratios. Changing Al for a-Al2O3, which acted as an inert filler, non-stoichiometric conditions were obtained. The mixtures were blended, uniaxially warm pressed, and pyrolysed in flowing argon at 800, 1000 and 1200 °C. Thermogravimetry was used to follow the weight changes during the pyrolysis process. X-ray diffraction was used to identify the formation of new crystalline phases, such as Al2O3, NbC, Nb2C and Al3Nb in the composites. Sintered specimens were also characterized by SEM and EDS. The results indicated good potential for this system to obtain multiphasic composite material in the Al-Nb system at lower temperatures.