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1.
Mechanical Properties of Silicon Oxycarbide Ceramic Foams 总被引:6,自引:0,他引:6
Paolo Colombo John R. Hellmann David L. Shelleman 《Journal of the American Ceramic Society》2001,84(10):2245-2251
The mechanical properties of ceramic foams obtained through a novel process that uses the direct foaming and pyrolysis of preceramic polymer/polyurethane solutions were investigated. The elastic modulus, flexural strength, and compressive strengths were obtained for foams in the as-pyrolyzed condition; values up to 7.1 GPa, 13 MPa, and 11 MPa, respectively, were obtained. The strength of the foam was virtually unchanged at temperatures up to 1200°C in air; however, long-term exposure at 1200°C led to a moderate degradation in strength, which was attributed to the evolution of intrastrut porosity during the oxidation of residual free carbon, as well as devitrification of the foams struts. 相似文献
2.
Thermal Shock Behavior of Porous Silicon Carbide Ceramics 总被引:1,自引:0,他引:1
Using the water-quenching technique, the thermal shock behavior of porous silicon carbide (SiC) ceramics was evaluated as a function of quenching temperature, quenching cycles, and specimen thickness. It is shown that the residual strength of the quenched specimens decreases gradually with increases in the quenching temperature and specimen thickness. Moreover, it was found that the fracture strength of the quenched specimens was not affected by the increase of quenching cycles. This suggests a potential advantage of porous SiC ceramics for cyclic thermal-shock applications. 相似文献
3.
Jihong She Jian-Feng Yang Daniel Doni Jayaseelan Naoki Kondo Tatsuki Ohji Shuzo Kanzaki Yoshiaki Inagaki 《Journal of the American Ceramic Society》2003,86(4):738-40
The thermal shock behavior of isotropic and anisotropic porous Si3 N4 was evaluated using the water-quenching technique. The critical temperature difference for crack initiation was found to be strongly dependent on the ratio of fracture strength to elastic modulus. Because of a very high strain-to-failure, anisotropic porous Si3 N4 showed no macroscopic cracks and was able to retain its strength even at a quenching-temperature difference of ∼1400°C. 相似文献
4.
Jihong She Jian-Feng Yang Daniel Doni Jayaseelan Shunkichi Ueno Naoki Kondo Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2003,86(9):1619-1621
A water-quenching technique was used to evaluate the thermal-shock strength behavior of silicon nitride (Si3 N4 ) ceramics in an air atmosphere. When the tensile surface was shielded from air during the heating and soaking process, the quenched specimens showed a gradual decrease in strength at temperatures above 600°C. However, the specimens with the air-exposed surface exhibited a ∼16% and ∼29% increase in strength after quenching from 800° and 1000°C, respectively. This is because of the occurrence of surface oxidation, which may cause the healing of surface cracks and the generation of surface compressive stresses. As a result, some preoxidation of Si3 N4 components before exposure to a thermal-shock environment is recommended in practical applications. 相似文献
5.
Marco Antonio Schiavon Christel Gervais Florence Babonneau Gian Domenico Soraru 《Journal of the American Ceramic Society》2004,87(2):203-208
Homogeneous silicon boron oxycarbide (Si-B-O-C) glasses based on SiO x C4– x and BO y C3– y mixed environments were obtained by pyrolysis under inert atmosphere of sol–gel-derived precursors. Their high-temperature structural evolution from 1000° to 1500°C was followed using XRD, 29 Si and 11 B MAS NMR, and chemical analysis and compared with the behavior of the parent boron-free Si-O-C glasses. The XRD study revealed that, for the Si-O-C and the Si-B-O-C systems, high-temperature annealing led to the crystallization of nanosized β-SiC into an amorphous SiO2 -based matrix. NMR analysis suggested that the β-SiC crystallization occurred with a consumption of the mixed silicon and boron oxycarbide units. Finally, by comparing the behavior of the Si-O-C and Si-B-O-C glasses, it was shown that the presence of boron increased the crystallization kinetics of β-SiC. 相似文献
6.
The thermal shock behavior of an alumina monolith and two alumina–iron ceramic-matrix composites has been investigated by superimposing the measured K R -curves of the materials onto the theoretically generated curves of the thermally induced stress intensity factor. Predictions of the critical-temperature differentials and retained strengths after quenching are in good agreement with the experimental data. The inclusion of metallic particles into an alumina matrix improves the thermal shock resistance, although the increase in toughness is not solely responsible for this improvement. There is a decrease in thermal stress-intensity factor that is generated for the composites; this decrease is due to a reduction in the Young's modulus and/or Biot modulus. However, the increased toughness for large crack lengths may offer increased damage resistance for severe thermal shock treatments. 相似文献
7.
Thermal Shock Behavior of Open-Cell Ceramic Foams 总被引:2,自引:0,他引:2
Specimens of heated, open-cell ceramics were thermally shocked by immersion in water or oil. It was found the strength retained after thermal shock underwent a gradual decrease with increasing quench temperature, indicative of a cumulative damage mechanism which manifests itself with increasing thermal stress. This damage could also be monitored using measurements of the elastic constants before and after quenching. The thermal shock resistance of the open-cell materials was found to be strongly dependent on cell size (increased with increasing cell size) and weakly dependent on density (increased with increasing density). Two possible sources of thermal stress were considered; one was associated with the temperature gradient across the microscopic struts and the other with the heating of the quenching medium as it infiltrates the cellular structure. Such heating was confirmed and it was concluded that this was the dominant source of thermal stress in this particular study, controlling the thermal stress in this particular study, controlling the thermal shock resistance of the open-cell ceramics. 相似文献
8.
Chemical Durability of Silicon Oxycarbide Glasses 总被引:2,自引:0,他引:2
Gian Domenico Sorarù Stefano Modena Emanuel Guadagnino Paolo Colombo James Egan Carlo Pantano 《Journal of the American Ceramic Society》2002,85(6):1529-1536
Silicon oxycarbide (SiOC) glasses with controlled amounts of Si—C bonds and free carbon have been produced via the pyrolysis of suitable preceramic networks. Their chemical durability in alkaline and hydrofluoric solutions has been studied and related to the network structure and microstructure of the glasses. SiOC glasses, because of the character of the Si—C bonds, exhibit greater chemical durability in both environments, compared with silica glass. Microphase separation into silicon carbide (SiC), silica (SiO2 ), and carbon, which usually occurs in this system at pyrolysis temperatures of >1000°–1200°C, exerts great influence on the durability of these glasses. The chemical durability decreases as the amount of phase separation increases, because the silica/silicate species (without any carbon substituents) are interconnected and can be easily leached out, in comparison with the SiOC phase, which is resistant to attack by OH− or F− ions. 相似文献
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10.
Fracture toughness behavior, stress–strain behavior, and flaw resistance of pressureless-sintered Si3 N4 -BN ceramics are investigated. The results are discussed with respect to the reported thermal shock behavior of these composites. Although the materials behave linear-elastic and exhibit no R -curve behavior, their flaw resistance is different from that of other linear-elastic materials. Whereas the critical thermal shock temperature difference (Δ T c ) is enhanced by adding BN, the content of BN has no influence on the strength loss during severe thermal shocks. 相似文献