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1.
《Carbon》2013
Carbon/carbon(C/C) composites infiltrated with Zr–Ti were prepared by chemical vapor infiltration and reactive melt infiltration. Their microstructure and ablation behavior at different temperatures and time were investigated. The results show that C/C composites infiltrated with Zr–Ti have good interface cohesion between carbon fibers, pyrocarbon and carbide. Compared with C/C composites and C/C–ZrC composites, the synthesized sample with Zr0.83Ti0.17C0.92 and Ti0.82Zr0.18C0.92 exhibits better ablation resistance at 2500 °C due to the newly formed protective layer composed of ZrTiO2 pinned by ZrO2 grains after ablation. The ablation resistance of the sample with Zr0.57Ti0.43C1.01 increased gradually with the decrease of temperature from 3000 °C to 2000 °C, whereas the ablation resistance of the sample with Zr0.83Ti0.17C0.92 and Ti0.82Zr0.18C0.92 first increased obviously and then decreased slightly. In addition, the work indicates that surplus particles or liquid phases of oxides cannot protect the matrix, and that the liquid oxides may even cause severe ablation. Furthermore, a protective layer of oxides tends to be formed with the increase of ablation time. 相似文献
2.
C/C–ZrC–SiC composites with continuous ZrC–SiC ceramic matrix were prepared by a multistep technique of precursor infiltration and pyrolysis process. Ablation properties of the composites were tested under an oxyacetylene flame at 3000 °C for 120 s. The results show that the linear ablation rate of the composites was about an order lower than that of pure C/C and C/C–SiC composites as comparisons, and the mass of the C/C–ZrC–SiC composites increased after ablation. Three concentric ring regions with different coatings appeared on the surface of the ablated C/C–ZrC–SiC composites: (i) brim ablation region covered by a coating with layered structure including SiO2 outer layer and ZrO2–SiO2 inner layer; (ii) transition ablation region, and (iii) center ablation region with molten ZrO2 coating. Presence of these coatings which acted as an effective oxygen and heat barrier is the reason for the great ablation resistance of the composites. 相似文献
3.
Zhigang Zhao Kezhi Li Wei Li Qing Liu Gang Kou Yulei Zhang 《Ceramics International》2018,44(7):7481-7490
ZrC precursor was synthesized by a solution approach using ZrOCl2·8H2O, acetylacetonate, glycerol and boron-modified phenolic resin. A ZrC yield of ~ 40.56 wt% was obtained at 1500 °C in the C/Zr molar ratio of 1:1. C/C-ZrC-SiC composites were fabricated by a combined processes of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) using the synthesized ZrC precursor. For comparison, C/C-SiC composites were prepared by CVI. Thermogravimetric analysis showed that C/C-ZrC-SiC composites exhibited better oxidation resistance than C/C-SiC composites. After oxyacetylene torch ablation, the mass ablation rate of C/C-ZrC-SiC composites was 9.23% lower than that of C/C-SiC composites. The porous ZrO2 skeleton in the ablation center was prone to be peeled off by the flame flow, resulting in the higher linear ablation rate of C/C-ZrC-SiC composites. The oxide layers of ZrO2 and SiO2 were formed on the transition and brim region of C/C-ZrC-SiC composites and acted as effective heat and oxygen barriers. For C/C-SiC composites, the C-SiC matrix was severely depleted in the ablation center and the formed SiO2 layer in the brim region could protect the matrix against further ablation. 相似文献
4.
《Ceramics International》2015,41(4):5976-5983
Cf/ZrC composites were fabricated by reactive melt infiltration at 1200 °C, Low melting Zr7Cu10, ZrCu and Zr2Cu alloys were used as infiltrators and the effect of Cu on ablation properties of the composites was investigated. The results show that the Cf/ZrC composites exhibit excellent anti-ablative properties affected apparently by the Cu contents. With the increase of Cu in infiltrators, the linear recession rates decrease from 0.0019±0.0006 to −0.0006±0.0002 mm s−1, whereas the mass loss rates increase from 0.0006±0.0003 to 0.0047±0.0009 g s−1. The formation of a dense ZrO2 protective layer and the evaporation of residual Cu are in favor of their ablation resistance. 相似文献
5.
《Carbon》2013
In this study, C/C–SiC–ZrC composites coated with SiC were prepared by precursor infiltration pyrolysis combined with reactive melt infiltration. The pyrolysis behavior of the hybrid precursor was investigated using thermal gravimetric analysis-differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy techniques. The microstructure and ablation behavior of the composites were also investigated. The results indicate that the composites exhibit an interesting structure, wherein a ceramic coating composed of SiC and a small quantity of ZrC covers the exterior of the composites, and the SiC–ZrC hybrid ceramics are partially embedded in the matrix pores and distributed around the carbon fibers as well. The composites exhibit good ablation resistance with a surface temperature of over 2300 °C during ablation. After ablation for 120 s, the mass and linear ablation rates of the composites are 0.0026 g/s and 0.0037 mm/s, respectively. The great ablation resistance of the composites is attributed to the formation of a continuous phase of molten SiO2 containing SiC and ZrO2, which seals the pores of the composites during ablation. 相似文献
6.
《Carbon》2013
C/C–ZrC–SiC composites were prepared by precursor infiltration and pyrolysis process using a mixture solution of organic zirconium-containing polymer and polycarbosilane as precursors. Porous carbon/carbon (C/C) composites with density of 0.92, 1.21 and 1.40 g/cm3 were used as preforms, and the effects of porous C/C density on the densification behavior and ablation resistance of C/C–ZrC–SiC composites were investigated. The results show that the C/C preforms with a lower density have a faster weight gain, and the obtained C/C–ZrC–SiC composites own higher bulk density and open porosity. The composites fabricated from the C/C preforms with a density of 1.21 g/cm3 exhibit better ablation resistance with a surface temperature of over 2400 °C during ablation. After ablation for 120 s, the linear and mass ablation rates of the composites are as low as 1.02 × 10−3 mm/s and −4.01 × 10−4 g/s, respectively, and the formation of a dense and continuous coating of molten ZrO2 solid solution is the reason for their great ablation resistance. 相似文献
7.
Lei Guo Zheng Yan Jianxing Yu Chenglong Zhang Mingzhu Li Fuxing Ye Vincent Ji 《Ceramics International》2018,44(1):261-268
3.5 mol% Yb2O3 stabilized zirconia (YbSZ) doped with 10 mol% TiO2 (Ti-YbSZ) was produced, and its hot corrosion behavior exposed to Na2SO4 + V2O5 molten salt was investigated. The as-fabricated ceramic mainly consists of metastable tetragonal (t′) phase. When exposed to the molten salt at 700 °C, 800 °C, 900 °C and 1000 °C for 2 h and 10 h, YbVO4 and m-ZrO2 formed as corrosion products due to chemical reactions between the ceramics and the salt. Ti4+ in Ti-YbSZ solid solution keeps stable during the hot corrosion tests, which acts as a stabilizer for ZrO2, preventing total decomposition of the t′ phase. After the hot corrosion tests, Ti-YbSZ has an apparently lower m phase content than Y2O3 doped Zirconia and YbSZ, indicative of better corrosion resistance. The hot corrosion mechanism of Ti-YbSZ is proposed based on Lewis acid-base rule, phase diagrams and thermodynamics. 相似文献
8.
《Ceramics International》2016,42(6):6720-6727
3D Cf/ZrC–SiC composites were prepared by a combination process of slurry infiltration and reactive melt infiltration. ZrO2 powders and ZrSi2 alloy, both of which reacted with amorphous carbon, were used as pore-making agent and infiltrator, respectively. After carbothermal reduction at 1650 °C, X-ray diffraction analysis revealed that ZrO2 powders were completely converted into ZrC by reacting with amorphous carbon, and an in-situ formed submicron porous configuration was observed at the areas containing ZrO2. Results showed that the matrix in composites mainly consisted of SiC, ZrC and a small quantity of residual metal. SEM and TEM images revealed the formation of ZrC or SiC intergranular particles in the matrix and the characteristic around the residual resin carbon. The composites had a bending strength of 94.89±16.7 MPa, fracture toughness of 11.0±0.98 MPa m1/2, bulk density of 3.36±0.01 g/cm3, and open porosity of 4.64±0.40%. The formation mechanisms of ZrC–SiC dual matrix and intrabundles׳ structure were discussed in the article. 相似文献
9.
A high performance and low cost C/C–ZrC composite was prepared by chemical vapor infiltration combined with zirconium–silicon (Zr: 91.2 at.%; Si: 8.8 at.%) alloyed reactive melt infiltration. The density of the as-received composite is 2.46 g/cm3 and the open porosity is 5%. Due to the reaction between the pyrolytic carbon and Zr–Si alloy in the composite, ZrC and Zr2Si phases were formed, the formation and distribution of which were investigated by thermodynamics and phase diagram. The as-received C/C–ZrC composite, with the flexural strength of 239.5 MPa, displayed a pseudo-ductile fracture behavior. Ablation properties of the C/C–ZrC composite were tested by a pulse laser. The linear ablation rate was 0.028 mm/s. A ZrO2 barrier layer was formed on the ablation surface and the composite presented excellent ablation resistance. 相似文献
10.
Daren Wu Geng Huangfu Dong Wang Boxin Wei Yujin Wang Yu Zhou 《Ceramics International》2018,44(1):246-253
ZrC-TaCx composites synthesized via Displacive Compensation of Porosity method 1300 °C using porous TaC preforms and Zr-Cu binary melts (Zr2Cu, ZrCu and Zr14Cu51) are presented in this work. Effect of Zr content in the infiltration on microstructure is investigated by XRD, FE-SEM and TEM analysis. The results indicate that ZrC and platelet-like Ta2C formed during the reactive infiltration of Zr-Cu melts into TaC preforms. The nano precipitations in TaCx/ZrC grains and Ta atoms dissolved in ZrC suggests a probable dissolution-precipitation mechanism of the reaction between Zr-Cu melts and TaC. The ZrC-TaCx composite exhibits a flexural strength of 142 MPa and a fracture toughness of 5.34 MPa m1/2. The platelet-like Ta2C phase has toughening effect by crack deflection and bridging. 相似文献
11.
《Ceramics International》2015,41(6):7359-7365
A soluble polymer precursor for ultra-fine zirconium carbide (ZrC) was successfully synthesized using phenol and zirconium tetrachloride as carbon and zirconium sources, respectively. The pyrolysis behavior and structural evolution of the precursor were studied by Fourier transform infrared spectra (FTIR), differential scanning calorimetry, and thermal gravimetric analysis (DSC–TG). The microstructure and composition of the pyrolysis products were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, scanning electron microscope (SEM) and element analysis. The results indicate that the obtained precursor for the ultra-fine ZrC could be a Zr–O–C chain polymer with phenol and acetylacetone as ligands. The pyrolysis products of the precursor mainly consist of intimately mixed amorphous carbon and tetragonal ZrO2 (t-ZrO2) in the temperature range of 300–1200 °C. When the pyrolysis temperature rises up to 1300 °C, the precursor starts to transform gradually into ZrC, accompanied by the formation of monoclinic ZrO2 (m-ZrO2). The carbothermal reduction reaction between ZrO2 and carbon has been substantially completed at a relatively low temperature (1500 °C). The obtained ultra-fine ZrC powders exhibit as well-distributed near-spherical grains with sizes ranging from 50 to 100 nm. The amount of oxygen in the ZrC powders could be further reduced by increasing the pyrolysis temperature from 1500 to 1600 °C but unfortunately the obvious agglomeration of the ZrC grains will be induced. 相似文献
12.
Solid state reaction using m-ZrO2 and high alumina cement as starting materials was studied. Various compositions containing different proportions of calcium aluminate cement (5–50 mol% CaO in ZrO2) were reaction sintered at 1300–1500 °C. Crystalline phase formation and densification of Ca stabilized ZrO2 composites was investigated by X-ray diffraction analysis, density and shrinkage measurements. Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy was used to examine the microstructure. The main crystalline phases formed are related to the expected with the equilibrium phase diagram of the ZrO2–CaO–Al2O3 system. Stabilized c-ZrO2 is formed with the composition of Ca0.15Zr0.85O1.85. The sintering of the mixtures leads to porous composites materials. Textural properties were analyzed considering the initial composition and the present crystalline phases. 相似文献
13.
Zhan-Guo Liu Jia-Hu Ouyang Yu Zhou Xiao-Liang Xia 《Journal of the European Ceramic Society》2009,29(11):2423-2427
Gd2Zr2O7 ceramic was prepared by solid state reaction at 1650 °C for 10 h in air, and exhibited a defect fluorite-type structure. Reaction between molten V2O5 and Gd2Zr2O7 ceramic was investigated at temperatures ranging from 700 to 850 °C using an X-ray diffractometer (XRD) and scanning electron microscopy (SEM). Molten V2O5 reacted with Gd2Zr2O7 to form ZrV2O7 and GdVO4 at 700 °C; however, in a temperature range of 750–850 °C, molten V2O5 reacted with Gd2Zr2O7 to form GdVO4 and m-ZrO2. Two different reactions observed at 700 °C and 750–850 °C could be explained based on the thermal instability of ZrV2O7. 相似文献
14.
Yulin Zhu Song Wang Hongmei Chen Wei Li Jinming Jiang Zhaohui Chen 《Ceramics International》2013,39(8):9085-9089
Carbon fiber-reinforced zirconium carbide matrix composites (Cf/ZrC) were prepared by vacuum infiltrating porous carbon/carbon preforms with molten Zr2Cu alloy at 1200 °C. X-ray diffraction, scanning electron microcopy and transmission electron microscopy analysis were used to characterize the composition and microstructure of the final composites. It was found that the matrix of the composites were composed of the Cu–Zr–C amorphous phase dispersed with either single- or polycrystalline ZrC. Based on the microstructural analysis, the formation mechanism of the matrix was proposed to be a solution-precipitation and grain coalescence process. The influence of the heat treatment at 1800 °C was also investigated. Results indicated that at very high temperature the volatilization of residual metal somewhat deteriorated the flexural strength and the elastic modulus, but the fracture toughness of the composites was improved due to the sintering of ZrC grains. 相似文献
15.
To improve the ablation resistance of carbon/carbon composites at the temperature above 2000 K, a ZrB2-SiC-ZrC ultra-high temperature ceramic coating was prepared by combination of supersonic atmosphere plasma spray (SAPS) and reaction melt infiltration. The micro-holes in ZrB2-Si-ZrC coating prepared by SAPS were effectively filled and the compactness and interface compatibility between the coating and C/C composites was improved through the reaction melt infiltration process. The ultra-high temperature ceramic coating exhibited good ablation resistance under oxyacetylene torch ablation above 2000 K. After ablation for 120 s, the mass and linear ablation rates of the ZrB2-SiC-ZrC coated C/C samples were only ?0.016 × 10?3 g/s and 1.30 µm/s, respectively. Good ablation resistance of the ultra-high temperature ceramic coating is mainly attributed to the dense coating structure and the improvement of interface compatibility between the coating and C/C composites. 相似文献
16.
Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized using the conventional solid-state reaction method. In order to increase the vacancy concentration, La3+ was doped on the Sr2+ site. Crystal structures of doped samples were characterized by X-ray diffraction. Except, perovskite-type Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0, 0.05, 0.10, 0.15) samples were fabricated by heat treatment at 1250 °C, 1275 °C, 1275 °C and 1275 °C, respectively, for 15 h. Lattice sizes decreased with the increase of doping amounts because of the smaller ion radius of La3+ compared to that of Sr2+. Ionic conductivities of the samples were measured by AC impedance spectroscopy. The results showed that the ionic conductivity increases at first and then decreases with raising doping amounts and sintering temperatures. So the optimized composition Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0.05) sintered at 1275 °C was selected with the highest total conductivity of 3.33 × 10?5 S cm?1at 30 °C and an activation energy of 0.27 eV. Additionally, potentiostatic polarization test was used to evaluate the electronic conductivity. The optimal composition Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 (x = 0.05) as a possible Li-ion conducting solid electrolyte has an electronic conductivity of only 8.39 × 10?9 S cm?1. 相似文献
17.
《Ceramics International》2016,42(11):12756-12762
Three-dimensional (3D) Cf/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the Cf/ZrC–SiC composites without and with a thin PyC interlayer of 0.15 µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2 µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2 µm. The highest flexural strength of 272.3±29.0 MPa and fracture toughness of 10.4±0.7 MPa m1/2 were achieved for the composites with a 1.2 µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the Cf/ZrC–SiC composites slightly and the ZrO2 scale acts as an anti-ablation component during the testing. 相似文献
18.
Jianli Gai Erqing Zhao Furui Ma Deye Sun Xiaodi Ma Yongcheng Jin Qingliu Wu Yongjie Cui 《Journal of the European Ceramic Society》2018,38(4):1673-1678
The elements Nb and Y were simultaneously substituted to the Zr sites of an Li7La3Zr2O12 (LLZO) electrolyte to improve its Li-ion conductivity and air stability. Samples of Li7La3Zr2-2xNbxYxO12 were fabricated using a solid-state reaction method. The results show that the introduction of Nb and Y can stabilise cubic-phase LLZO. The total conductivity of Li7La3ZrNb0.5Y0.5O12 electrolyte can reach 8.29 × 10?4 S cm?1 at 30 °C when sintered at 1230 °C for only 15 h. Surprisingly, the conductivity of Li7La3ZrNb0.5Y0.5O12 can be maintained at 6.91 × 10?4 S cm?1 after exposure to air for 1.5 months, indicating excellent air stability. Furthermore, a LiFePO4/Li7La3ZrNb0.5Y0.5O12/Li cell displayed stable charge/discharge and cycling performance at ambient temperature, suggesting there is potential to use Li7La3ZrNb0.5Y0.5O12 electrolyte in Li-ion batteries. Additionally, the effects of varying the co-doping amount and dwelling time on the Li-ion conductivity of Li7La3Zr2-2xNbxYxO12 were investigated. 相似文献
19.
《Ceramics International》2016,42(5):6221-6227
Ultrafine powders of pyrochlore-type La2Zr2O7 were synthesized via a simple molten salt mediated process using zirconium oxide and lanthanum oxide as raw materials, and sodium chloride, potassium chloride and sodium fluoride to form a reaction medium. The effects of reaction temperature, salt/reactant ratio and salt type on the La2Zr2O7 formation were investigated. Among the three attempted salt assemblies (KCl–LiCl, Na2CO3–K2CO3, and NaCl–KCl–NaF), NaCl–KCl–NaF showed the best accelerating effect on the La2Zr2O7 formation. At a given temperature, the La2Zr2O7 content in the final products increased with the increase in the salt amount. Phase pure submicron sized La2Zr2O7 ultrafine powders were obtained after 3 h firing at 1100 °C with the salt/reactant weight ratio of 5:1 or at 1200 °C with salt/reactant weight ratio of 3:1. The synthesis temperature (1100 °C) was much lower than that required by the conventional solid-state mixing method or a wet chemical method. The “dissolution–precipitation” mechanism had dominated the synthesis process. 相似文献
20.
《Ceramics International》2017,43(11):8525-8530
Commercial Y2O3 powder was used to fabricate Y2O3 ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO2 and La2O3 as sintering aids. One group with different contents of La2O3 (0–10 mol%) with a fixed amount of 1 mol% ZrO2 and another group with various contents of ZrO2 (0–7 mol%) with a fixed amount of 10 mol% La2O3 were compared to investigate the effects of co-doping on the microstructural and optical properties of Y2O3 ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La2O3 exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO2 and La2O3 co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO2 and La2O3 single-doped samples. It was proved that the grain growth suppression caused by ZrO2 overwhelms the acceleration by La2O3. Meanwhile, 1 mol% ZrO2 acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y2O3 ceramic (1.2 mm in thickness) with 3 mol% of ZrO2 and 10 mol% of La2O3 sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm. 相似文献