共查询到20条相似文献,搜索用时 62 毫秒
1.
Daniel P. Riley Erich H. Kisi Thomas C. Hansen Alan W. Hewat 《Journal of the American Ceramic Society》2002,85(10):2417-2424
In situ neutron diffraction at 0.9 s time resolution was used to reveal the reaction mechanism during the self-propagating high-temperature synthesis (SHS) of Ti3 SiC2 from furnace-ignited stoichiometric 3Ti + SiC + C mixtures. The diffraction patterns indicate that the SHS proceeded in five stages: (i) preheating of the reactants, (ii) the α→β phase transformation in Ti, (iii) preignition reactions, (iv) the formation of a single solid intermediate phase in <0.9 s, and (v) the rapid nucleation and growth of the product phase Ti3 SiC2 . No amorphous contribution to the diffraction patterns from a liquid phase was detected and, as such, it is unlikely that a liquid phase plays a major role in this SHS reaction. The intermediate phase is believed to be a solid solution of Si in TiC such that the overall stoichiometry is ∼3Ti:1Si:2C. Lattice parameters and known thermal expansion data were used to estimate the ignition temperature at 923 ± 10°C (supported by the α→β phase transformation in Ti) and the combustion temperature at 2320 ± 50°C. 相似文献
2.
Adrish Ganguly Michel W. Barsoum Roger D. Doherty 《Journal of the American Ceramic Society》2007,90(7):2200-2204
In this work, we report on the interdiffusion of Ge and Si in Ti3 SiC2 and Ti3 GeC2 , as well as that of Nb and Ti in Ti2 AlC and Nb2 AlC. The interdiffusion coefficient, D int , measured by analyzing the diffusion profiles of Si and Ge obtained when Ti3 SiC2 –Ti3 GeC2 diffusion couples are annealed in the 1473–1773 K temperature range at the Matano interface composition (≈Ti3 Ge0.5 Si0.5 C2 ), was found to be given by
Dint increased with increasing Ge composition. At the highest temperatures, diffusion was halted after a short time, apparently by the formation of a diffusion barrier of TiC. Similarly, the interdiffusion of Ti and Nb in Ti2 AlC–Nb2 AlC couples was measured in the 1723–1873 K temperature range. The D int for the Matano interface composition, viz. ≈(Ti0.5 ,Nb0.5 )2 AlC, was found to be given by
At 1773 K, the diffusivity of the transition metal atoms was ≈7 times smaller than those of the Si and Ge atoms, suggesting that the former are better bound in the structure than the latter. 相似文献
D
At 1773 K, the diffusivity of the transition metal atoms was ≈7 times smaller than those of the Si and Ge atoms, suggesting that the former are better bound in the structure than the latter. 相似文献
3.
The effect of vacuum annealing on the thermal stability and phase transition of Ti3 SiC2 has been investigated by X-ray diffraction (XRD), neutron diffraction, synchrotron radiation diffraction, and secondary ion mass spectroscopy (SIMS). In the presence of vacuum or a controlled atmosphere of low oxygen partial pressure, Ti3 SiC2 undergoes a surface dissociation to form nonstoichiometric TiC and/or Ti5 Si3 C x that commences at ∼1200°C and becomes very pronounced at ≥1500°C. Composition depth profiling at the near surface of vacuum-annealed Ti3 SiC2 by XRD and SIMS revealed a distinct gradation in the phase distribution of TiC and Ti5 Si3 C x with depth. 相似文献
4.
Véronique Gauthier Benoît Cochepin Sylvain Dubois Dominique Vrel 《Journal of the American Ceramic Society》2006,89(9):2899-2907
Ti3 SiC2 is synthesized by self-propagating high-temperature synthesis (SHS) of elemental titanium, silicon, and graphite powders. The reaction paths and structure evolution are studied in situ during the SHS of the 3Ti+Si+2C mixture by time-resolved X-ray diffraction coupled with infrared thermography. The proposed reaction mechanism suggests that Ti3 SiC2 might be formed from Ti–Si liquid phase and solid TiC x . Finally, the effect of the powders starting composition on the Ti3 SiC2 synthesis is studied. For the investigated initial mixtures, TiC x is always formed as a major impurity together with the Ti3 SiC2 phase. 相似文献
5.
José M. Córdoba María J. Sayagués María D. Alcalá Francisco J. Gotor 《Journal of the American Ceramic Society》2007,90(3):825-830
Titanium silicon carbide (Ti3 SiC2 ) and Ti3 SiC2 -based composite powders were synthesized by isothermal treatment in an inert atmosphere as a function of initial compositions (mixtures). A high content of TiC was obtained in the final product when the initial mixtures contained free carbon. The use of TiC as a reagent was unsuccessful in obtaining Ti3 SiC2 . High Ti3 SiC2 conversion was found for the initial mixtures containing SiC as the main source for silicon and carbon. An initial mixture with a large excess of silicon, 3Ti/1.5SiC/0.5C, was needed to obtain high-purity Ti3 SiC2 . A reaction mechanism, where Ti3 SiC2 nucleates on Ti5 Si3 C crystals and grows by long-range diffusion of Ti and C, is proposed. The reaction mechanism was proposed to be based on silicon loss during the formation of Ti3 SiC2 . 相似文献
6.
Jing-Feng Li Toshiro Matsuki Ryuzo Watanabe 《Journal of the American Ceramic Society》2002,85(4):1004-1006
Mechanical alloying (MA) has been used to synthesize Ti3 SiC2 powder from the elemental Ti, Si, and C powders. The MA formation conditions of Ti3 SiC2 were strongly affected by the ball size for the conditions used. MA using large balls (20.6 mm in diameter) enhanced the formation of Ti3 SiC2 , probably via an MA-triggered combustion reaction, but the Ti3 SiC2 phase was not synthesized only by the MA process using small balls (12.7 mm in diameter). Fine powders containing 95.8 vol% Ti3 SiC2 can be obtained by annealing the mechanically alloyed powder at relatively low temperatures. 相似文献
7.
Zhe-Feng Zhang Zheng Ming Sun Hitoshi Hashimoto Toshihiko Abe 《Journal of the American Ceramic Society》2003,86(3):431-436
Ti/Si/2TiC powders were prepared using a mixture method (M) and a mechanical alloying (MA) method to fabricate Ti3 SiC2 at 1200°–1400°C using a pulse discharge sintering (PDS) technique. The results showed that the Ti3 SiC2 samples with <5 wt% TiC could be rapidly synthesized from the M powders; however, the TiC content was always >18 wt% in the MA samples. Further sintering of the M powder showed that the purity of Ti3 SiC2 could be improved to >97 wt% at 1250°–1300°C, which is ∼200°–300°C lower than that of sintered Ti/Si/C and Ti/SiC/C powders using the hot isostatic pressing (HIPing) technique. The microstructure of Ti3 SiC2 also could be controlled using three types of powders, i.e., fine, coarse, or duplex-grained, within the sintering temperature range. In comparison with Ti/Si/C and Ti/SiC/C mixture powders, it has been suggested that high-purity Ti3 SiC2 could be rapidly synthesized by sintering the Ti/Si/TiC powder mixture at relatively lower temperature using the PDS technique. 相似文献
8.
Sui Lin Shi Wei Pan Ming Hao Fang Zhen Yi Fang 《Journal of the American Ceramic Society》2006,89(2):743-745
Ti3 SiC2 /HAp composites with different Ti3 SiC2 volume fractions were fabricated by spark plasma sintering (SPS) at 1200°C. The effects of Ti3 SiC2 addition on the mechanical properties and microstructures of the composites were investigated. The bending strength and fracture toughness of the composites increased with increasing of Ti3 SiC2 content, whereas the Vickers hardness decreased. The bending strength and fracture toughness reached 252±10 MPa and 3.9±0.1 MPa·m1/2 , respectively, with the addition of 50 vol% Ti3 SiC2 . The increases in the mechanical properties were attributed to the matrix strengthening and interactions between cracks and the Ti3 SiC2 platelets. 相似文献
9.
Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba 6−3 x Sm8+2 x Ti18 O54 solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τf ) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba6−3 x Sm8+2 x (Ti1− z Snz )18 O54 -based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm2 O4 and Sm2 (Sn,Ti)2 O7 appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τf . Excellent microwave dielectric properties were achieved in Ba6−3 x (Sm1− y Nd y )8+2 x (Ti1− z Sn z )18 O54 ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τf =+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value. 相似文献
10.
P. Mogilevsky Tai-Il Mah T. A. Parthasarathy C. M. Cooke 《Journal of the American Ceramic Society》2006,89(2):633-637
Composites in the SiC–TiC–Ti3 SiC2 system were synthesized using reactive hot pressing at 1600°C. The results indicate that addition of Ti3 SiC2 to SiC leads to improved fracture toughness. In addition, high microhardness can be retained if TiC is added to the material. The best combination of properties obtained in this study is K I c =8.3 MPa·m1/2 and H v =17.6 GPa. The composition can be tailored in situ using the decomposition of Ti3 SiC2 . Ti3 SiC2 decomposed rapidly at temperatures above 1800°C, but the decomposition could be conducted in a controlled manner at 1750°C. This can be used for synthesis of fully dense composites with improved properties by first consolidating to full density a softer Ti3 SiC2 -rich initial composition, and then using controlled decomposition of Ti3 SiC2 to achieve the desired combination of microhardness and fracture toughness. 相似文献
11.
Haibin Zhang Yanchun Zhou Yiwang Bao Meishuan Li 《Journal of the American Ceramic Society》2008,91(2):494-499
The thermal stability of bulk Ti3 SiC2 in high-purity nitrogen was investigated. It was surprising to observe that Ti3 SiC2 underwent rapid and catastrophic disintegration above 1300°C, although this material was thermally stable below this temperature. This degradation was unexpected and extremely serious, and has been termed "Ti3 SiC2 pest." This phenomenon was related to the volume change associated with the formation of mixtures of TiC x , Ti(C, N) x , and TiN, which caused internal tensile stresses and cracked the resulting layers. "Ti3 SiC2 pest" could be prevented by increasing oxygen partial pressure in nitrogen. 相似文献
12.
Bouchaib Manoun Surendra K. Saxena Hanns-Peter Liermann Michel W. Barsoum 《Journal of the American Ceramic Society》2005,88(12):3489-3491
We measured the volume thermal expansion of Ti3 SiC2 from 25° to 1400°C using high-temperature X-ray diffraction using a resistive heated cell. A piece of molybdenum foil with a 250 μm hole contained the sample material (Ti3 SiC2 +Pt). Thermal expansion of the polycrystalline sample was measured under a constant argon flow to prevent oxidation of Ti3 SiC2 and the molybdenum heater. From the lattice parameters of platinum (internal standard), we calculated the temperature by using thermal expansion data published in the literature. The molar volume change of Ti3 SiC2 as a function of temperature in °C is given by: V M (cm3 /mol)=43.20 (2)+9.0 (5) × 10−4 T +1.8(4) × 10−7 T 2 . The temperature variation of the volumetric thermal expansion coefficient is given by: αv (°C−1 )=2.095 (1) × 10−5 +7.700 (1) × 10−9 T . Furthermore, the results indicate that the thermal expansion anisotropy of Ti3 SiC2 is quite mild in accordance with previous work. 相似文献
13.
Tamer El-Raghy Michel W. Barsoum Antonios Zavaliangos Surya R. Kalidindi 《Journal of the American Ceramic Society》1999,82(10):2855-2860
In this article, the second part of a two-part study, we report on the mechanical behavior of Ti3 SiC2 . In particular, we have evaluated the mechanical response of fine-grained (3–5 μm) Ti3 SiC2 in simple compression and flexure tests, and we have compared the results with those of coarse-grained (100–200 μm) Ti3 SiC2 . These tests have been conducted in the 25°–1300°C temperature range. At ambient temperature, the fine- and coarse-grained microstructures exhibit excellent damage-tolerant properties. In both cases, failure is brittle up to ∼1200°C. At 1300°C, both microstructures exhibit plastic deformation (>20%) in flexure and compression. The fine-grained material exhibits higher strength compared with the coarse-grained material at all temperatures. Although the coarse-grained material is not susceptible to thermal shock (up to 1400°C), the fine-grained material thermally shocks gradually between 750° and 1000°C. The results presented herein provide evidence for two important aspects of the mechanical behavior of Ti3 SiC2 : (i) inelastic deformation entails basal slip and damage formation in the form of voids, grain-boundary cracks, kinking, and delamination of individual grains, and (ii) the initiation of damage does not result in catastrophic failure, because Ti3 SiC2 can confine the spatial extent of the damage. 相似文献
14.
In this article, the first part of a two-part study, we report the reaction path and microstructure evolution during the reactive hot isostatic pressing of Ti3 SiC2 , starting with titanium, SiC, and graphite powders. A series of interrupted hot isostatic press runs have been conducted as a function of temperature (1200°–1600°C) and time (0–24 h). Based on X-ray diffractometry and scanning electron microscopy, at 1200°C, the intermediate phases are TiC x and Ti5 Si3 C x . Fully dense, essentially single-phase samples are fabricated in the 1450°–1700°C temperature range. The time-temperature processing envelope for fabricating microstructures with small (3–5 μm), large (∼200 μm), and duplex grains, in which large (100–200 μm) Ti3 SiC2 grains are embedded in a much finer matrix, is delineated. The microstructure evolution is, to a large extent, determined by (i) the presence of unreacted phases, mainly TiC x , which inhibits grain growth; (ii) a large anisotropy in growth rates along the c and a directions (at 1450°C, growth normal to the basal planes is about an order of magnitude smaller than that parallel to these planes; at 1600°C, the ratio is 4); and (iii) the impingement of grains. Ti3 SiC2 is thermally stable under vacuum and argon atmosphere at temperatures as high as 1600°C for as long as 24 h. The influence of grain size on the mechanical properties is discussed in the second part of this study. 相似文献
15.
Formation of titanium silicon carbide (Ti3 SiC2 ) by mechanical alloying (MA) of Ti, Si, and C powders at room temperature was experimentally investigated. A large amount of granules less than 5 mm in size, consisting of Ti3 SiC2 , smaller TiC particles, and other silicides, have been obtained after ball milling for only 1.5 h. The effect of excess Si in the starting powders on the formation of Ti3 SiC2 was studied. The formation mechanism of Ti3 SiC2 was analyzed. It is believed that a mechanically induced self-propagating reaction is ignited during the MA process. A possible reaction mechanism was proposed to explain the formation of the final products. 相似文献
16.
The reciprocal salt pair Sr2 SiO4 -Sr2 GeO4 -Ba2 GeO4 -Ba2 SiO4 was investigated using X-ray powder diffraction and DTA. Unlimited solubility in the low-K2 SO4 structure type (α') occurs throughout the system above 85°C. The nonlinear changes of some lattice constants of the solid solutions are discussed. A stable monoclinic low-temperature (β) form of Sr2 SiO4 was found which converts reversibly to the high-temperature α'-modification at 85°C. The enthalpy of the β-α' transition is 51 cal/mol. In the reciprocal salt pair the β-form solid solutions occur in a very narrow region below 85°C. 相似文献
17.
Da Chen Kiroshi Shirato Michel W. Barsoum Tamer El-Raghy Robert O. Ritchie 《Journal of the American Ceramic Society》2001,84(12):2914-2920
The cyclic fatigue and fracture toughness behavior of reactive hot-pressed Ti3 SiC2 ceramics was examined at temperatures from ambient to 1200°C with the objective of characterizing the high-temperature mechanisms controlling crack growth. Comparisons were made of two monolithic Ti3 SiC2 materials with fine- (3–10 μm) and coarse-grained (70–300 μm) microstructures. Results indicate that fracture toughness values, derived from rising resistance-curve behavior, were significantly higher in the coarser-grained microstructure at both low and high temperatures; comparative behavior was seen under cyclic fatigue loading. In each microstructure, Δ K th fatigue thresholds were found to be essentially unchanged between 25° and 1100°C; however, there was a sharp decrease in Δ K th at 1200°C (above the plastic-to-brittle transition temperature), where significant high-temperature deformation and damage are first apparent. The substantially higher cyclic-crack growth resistance of the coarse-grained Ti3 SiC2 microstructure was associated with extensive crack bridging behind the crack tip and a consequent tortuous crack path. The crack-tip shielding was found to result from both the bridging of entire grains and from deformation kinking and bridging of microlamellae within grains, the latter forming by delamination along the basal planes. 相似文献
18.
Yi Li Xiang Ming Chen † Ni Qin YaoWu Zeng 《Journal of the American Ceramic Society》2005,88(2):481-484
Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3 x Nd8+2 x Ti18 O54 ( x =1/2, 2/3, and 3/4) ceramics. A small amount ( z <0.1) of Sn substitution resulted in Ba6−3 x Nd8+2 x (Ti1− z Sn z )18 O54 solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Q f value significantly, while, due to the formation of secondary phases, the Q f value degraded sharply for larger Sn content. The relative dielectric constant (ɛr ) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τf ) generally decreased, although an obvious fluctuation was observed for x =3/4. 相似文献
19.
Fei Zhao Zhenxing Yue Jing Pei Hao Zhuang Zhilun Gui Longtu Li 《Journal of the American Ceramic Society》2007,90(8):2461-2466
Microwave dielectric ceramics with the composition of Ba[Ti1− x (Ni1/2 W1/2 ) x ]O3 ( x =0.4–0.6) were prepared by a solid-state reaction method. The evolution of the crystalline phases was investigated by X-ray powder diffraction analysis. A cubic-to-hexagonal phase transition occurred between 1000° and 1300°C. The phase transition is irreversible; thus, the hexagonal phase remains stable at room temperature. The X-ray powder diffraction data for x =0.5 were refined using the Rietveld method. It was identified as a h -BaTiO3 -type hexagonal perovksite with the space group of P 63 / mmc . It also reveals that random occupancy of Ti4+ and W6+ ions occurs in the B-site substructures, whereas Ni2+ ions exclusively occupy the octahedral site in the corner-sharing octahedron. The dielectric properties of dense-sintered ceramics were characterized at microwave frequencies. With an increase in x from 0.4 to 0.6, the Q × f value increased from 26 700 to 42 000 GHz, whereas ɛr decreased from 29.8 to 20.0, and τf from +6.5 to −9.9 ppm/°C. 相似文献
20.
Mari Lou Balmer Fred F. Lange Vikram Jayaram Carlos G. Levi 《Journal of the American Ceramic Society》1995,78(6):1489-1494
Aqueous mixtures of zirconium acetate and aluminum nitrate were pyrolyzed and crystallized to form a metastable solid solution, Zr1- x Al x O2− x /2 ( x < 0.57). The initial, metastable phase partitions at higher temperatures to form two metastable phases, viz., t −ZrO2 +γ-Al2 O3 with a nano-scale microstructure. The microstructural observations associated with the γ- →α-Al2 O3 phase transformation in the t -ZrO2 matrix are reported for compositions containing 10, 20, and 40 mol% A12 O3 . During this phase transformation, the α-Al2 O3 grains take the form of a colony of irregular, platelike grains, all with a common crystallographic orientation. The plates contain ZrO2 inclusions and are separated by ZrO2 grains. The volume fraction of A12 O3 and the heat treatment conditions influence the final microstructure. At lower volume fractions of A12 O3 , the colonies coarsen to single, irregular plates, surrounded by polycrystalline ZrO2 . Interpenetrating microstructures produced at high volume fractions of A12 O3 exhibit very little grain growth for periods up to 24 h at 1400°C. 相似文献