Preparation And Properties Of ZrC_xO_y Ceramic And Composites

Based on the demand of aerospace science and technology for high-temperature thermal-structure material,ZrC_xO_y ceramics and its composites were prepared by organic precursor method.The ceramic and composites might be of good heat resistance,oxidation resistance and low thermal conductivity.The crosslinking and minerallization process of ZrC_xO_y ceramic precursor,high temperature evolvement of ZrC_xO_y ceramic,the properties of mechanical,thermal physical,high temperature,anti-oxidation and anti-ablation of C/ZrC_xO_y composite were investigated.To further improve the anti-oxidation performance of composites,C/SiZrOC compsites modified with SiOC ceramics were prepared and evaluated comparatively.The precursor of ZrC_xO_y ceramic was designed with zirconium n-butoxide（Zr（OBu）4）and divinyl benzene（DVB）as the source of zirconium and carbon respectively.The cross-linking and pyrolysis process of the precursor were investigated.The high temperature properties of ZrC_xO_y ceramic were evaluated.The precursor could be heat cross-linked at above 110℃and the cross-linked yield was 46.3% at 150℃.After thermal pyrolysis at 1200℃,a ceramic compound composed with ZrO₂ and C was obtained,which had a ceramic yield of 23%.The carbo-thermal reaction between ZrO₂ and C occurred when the pyrolysis ceramic was post heat-treated above 1400℃ and the ZrC_xO_y phase appeared.With the increasing of heat treatment temperature and time,the carbo-thermal reaction was aggravated.The product of carbo-thermal reaction was ZrC_0.84O_0.07,with a lattice parameter of 4.688 nm.C/ZrC_xO_y composites were prepared by precursor infiltration pyrolysis method.Densification process and mechanical properties of composites were investigated.The bending strength and compression strength of composites increased with the density.The composites with a density of 2.43g/cm3 had the best mechanical properties.The composites had a bending strength of 123 Mpa,a compression strength of 164 MPa and a fracture toughness of 13.1MPa·m1/2.The thermo-physical properties of C/ZrC_xO_y composites were characterized from RT to 1200℃.The heat capacity increased from 0.56J·g-1·K-1 at RT to 1.18J·g-1·K-1 at 1200℃,independent of the density.The thermal diffusion coefficient and the thermal conductivity increased with the increasing of the density.When the composites had a density of 2.43 g/cm3,the thermal diffusion coefficient and the thermal conductivity were 1.23mm2/s and 2.99W/m·K.The high temperature properties of C/ZrC_xO_y composites were investigated.The bending strength remained unchanged basically after the composites were heat-treated at under 1400℃,but declined after heat-treatment at 1500℃.When the heat treating temperature was elevated to 1600 ℃,the properties of the composites damaged obviously,and the mass retention rate and strength retention rate of the composites were only 86.4% and 21.6%.Loosing of the matrix and damage of the carbon fiber due to the carbo-thermal reaction between ZrO₂ matrix and carbon martrix or carbon fiber were the main reasons for the damage of the composites.The anti-oxidative and anti-ablative performance of C/ZrC_xO_y composites at short time were studied.After oxidation in air for 150 s at 1600℃,the mass retention rate and strength retention rate of composites were 92.4% and 23.1%,respectively.The ablation test of composites was performed in oxyacetylene flame.After tested for 30 s,the mass ablation rate and the linear ablation rate were 0.016g·s-1 and 0.105mm·s-1,respectively.To improve the anti-oxidative performance of C/ZrC_xO_y composites,C/SiZrOC composites modified with SiOC ceramics were designed and fabricated by precursor infiltration pyrolysis method.Densification process and mechanical properties of C/SiZrOC composites were studied.The bending strength and compression strength of composites increased with the increasing of the density.When the composites had a density of 2.04g/cm3,the bending strength and compression strength were 197.1MPa and 210.6MPa,and the fracture toughness was 13.1MPa·m1/2.The thermo-physical properties of C/SiZrOC composites had the same law with C/ZrC_xO_y.When the composites had a density of 2.04g/cm3,the thermal diffusion coefficient,the heat capacity and the thermal conductivity of the composites were 1.196 mm2/s,0.639 J·g-1·K-1 and 1.55 W/m·k,respectively.The high temperature properties of C/SiZrOC composites were investigated.The bending strength remained unchanged basically after the composites were heat-treated at under 1400℃,but declined after heat-treatment at 1500℃,as same as the C/ ZrC_xO_y composites.When the heat treating temperature was elevated to 1600℃,the mass retention rate and strength retention rate of the composites was only 62.5% and 13.1%.Compared to C/ZrC_xO_y,C/SiZrOC has lower high-temperature mechanical properties.The anti-oxidative and anti-ablative performance of C/SiZrOC composites at short time were studied.After oxidation in air for 150 s at 1600℃,the mass retention rate and strength retention rate of composites were 83.5% and 42.3%,respectively.After ablation in oxyacetylene flame for 30 s,the mass ablation rate and the linear ablation rate were 0.025g·s-1 and 0.133mm·s-1,respectively.The introduction of the Si OC had not improved the anti-ablative performance of the C/ ZrC_xO_y composites.