Preparations, Structures And Properties Of Triphenylethynylsilane Resins And Their SiC/C (TiN/C) Composite Woodceramics

The purpose of our investigation is to prepare polytri(phenylethynyl)]silane resin with highthermal stability and char yield, then using this resin as matrix to synthesize SiC/C(TiN/C)composite woodceramics, which was prepared in virtue of nature structure of fir by Sol-Gelimpregnation method via thermal treatment. Furthermore, the studies of structure and properties ofresin and ceramics provide theoretical and experimental foundation for the industrialization of SiC/C(TiN/C) composite woodceramics.The major creative works are listed as following:1) Using vinyltrichlorosilane and phenyltrichlorosilane as raw materials, phenylethynylmagnesium as Grignard reagent, vinyl tri(phenylethynyl)silane〔(ph-C≡C)3-Si-C=CH2〕(VTPES) andphenyl tri(phenylethynyl)silane〔(ph-C≡C)3-Si-ph〕(PTPES) were synthesized by Grignard reaction.Their molecular structures were characterized by means of nuclear magnetic resonance (1H-NMR,13C-NMR,²⁹Si-NMR), Fournier transform infrared (FT-IR). The corresponding kinetic parameters,such as activation energy (Ea), pre-exponential factor (A) and the order of the reaction (n), were alsoobtained according to the Kissinger method by differential scanning calorimetry (DSC). The resultsshow that their melting points of VTPES and PTPES were84℃and116℃, and their curing peaktemperatures were285℃and336℃, respectively, which indicated that the two monomers had botha wide processing window over200℃. The activation energy was114.25kJ/mol and153.89kJ/mol,and the order of the reaction (n) was0.92and0.93. The curing reaction rates were consistent with afirst-order kinetic equation. TGA showed that the decomposed temperature of the two polymers wasabout550℃and the char yield was beyond75%at800℃.2) Catalytic graphitization of poly [vinyl tri(phenylethynyl)]silane resin (PVTPES) with ironoxide and nickel between900℃and1590℃under nitrogen atmosphere was investigated. Theeffects of the catalyst content and the heat treatment temperature (HTT) on the graphitization werestudied. The structural change in the graphitization process was also characterized by X-raydiffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and laser Raman(LR). The XRD results show that the (002) diffraction angle increased from25.95°to26.50°, andthe graphitization degree was also beyond86%when the HTT increased from900℃to1590℃,which indicated that the two catalysts had excellent catalytic effect at low temperature. The (002)diffraction angle closed to26.50°and the graphitization degree closed to86%when the catalystcontent increased from3%to15%. HRTEM images indicate that the graphitic carbon materialspossessed a high graphitization with coil, rod and capsule morphology.Comparative analysis of catalytic effect of Ni and Fe2O3was investigated at1590℃. The (002)diffraction angle changed between26.40°and26.42°with increasing the catalyst content, and thecorresponding R (ID/IG) value was1.03. While the diffraction angle closed to the26.56°using ironoxide as catalyst and the corresponding R value was0.51, which indicated that iron oxide was moreeffective than nickel at1590℃.3) The effects of solvent polarity, HTT and particle size on relative crystallinity index (Ic) andthermal stability of fir powder were investigated by XRD, thermal gravity analysis (TGA),derivative thermogravimetry (DTG) and FT-IR. The results show that the percentage of extractionincreased from3.75%to7.22%when the solubility parameter varied from7.3to12.1, and the Icalso increased from46.5%to52.9%. On the contrary, the decomposed temperature decreased from319℃to304.7℃. When the HTT was at below170℃, the Ic was increased from46.9%to50%as the increase of temperature. Beyond200℃, the crystalized cellulose began to melt, resulting in adecrease of thermal stability. The Ic slightly decreased from46.8%to42.6%and the thermalstability decreased from329.5℃to293.4℃as the particle sizes decreased from400μm to35μm.4) Catalytic graphitization of fir powder with iron oxide and nickel between900℃and1590℃under nitrogen atmosphere was investigated. The effects of the catalyst content, the HTT andholding time on the graphitization were analyzed, and the structural change was also studied byXRD, HRTEM and LR. XRD results show that the (002) diffraction angle increased from26.04°to26.50°, and the graphitization degree was also beyond95%when the HTT increased from900℃to1590℃. Noticeably, the iron oxide reacted with carbon to form metal carbide and the graphiticcarbon was formed by carbide formation-decomposition mechanism. While the nickel waschemically stable in the experiments and the catalytic graphitic mechanism were carbondissolution-precipitation mechanism. The (002) diffraction angle closed to26.56°and thegraphitization degree was also increased from50%to100%when the catalyst content increasedfrom3%to15%. Comparative analysis of catalytic effect of Ni and Fe2O3showed that nickel wasmore effective than iron oxide at1400℃. But the R values were both0.6when the holding timewas6h at1590℃, which indicated that the two catalysts had the same catalytic effect when the heattreated time was long enough.5) Using tetraethylorthosilicate (TEOS) as precursor, SiO₂/charcoal hybrid materials withinterpenetrating network were fabricated by Sol-Gel method. The results show that the weight addedto145.2%when the impregnation times repeated nine times. In the course of carbonization of hybridmaterials from800℃to1590℃, SiO₂particles transformed from amorphous into crystalline and theSiO₂reacted with carbon to form SiC particles or whiskers by solid-solid or solid-liquid reaction,resulting in the formation of SiC woodceramics.The direct impregnation of Titanium n-butoxide (TNBT) show that the TiO₂particles obtainedby condensation of TNBT transformed from amorphous to crystalline at low800℃accompany withthe reaction with N2which acted as protection atmosphere to form TiN particles. When thetemperature arrived at1200℃, the reaction finished and the TiN woodceramics was composed ofamorphous carbon, graphitic carbon and TiN crystal. While the TiN crystal was chemical stabilityand the ceramics only transformed from amorphous carbon to graphitic carbon when HTT increasedto1590℃. The N2adsorption and desorption isotherm showed that the pore of the TiNwoodceramics consisted of two parts: one was the original pore structure of fir charcoal with4nm,although the impregnation of TNBT decreased the pore volume, the effect of TNBT on porediameter was slight; another was the pore of TiN crystal with12nm.The SiC/C (TiN/C) composite woodceramics were prepared by impregnating the VTPESmonomer in Si (Ti) woodceramics at ambient temperature, then cured and carbonized at designedtemperature. Experimental investigation was conducted on the friction and wear properties of SiC/C(TiN/C) composite woodceramics. The results showed that the wear percentage closed to a certainvalue with increasing the impregnation times and carbonized temperature due to the lubrication ofgraphitic carbon grain.