共查询到20条相似文献,搜索用时 15 毫秒
1.
Augusto O. Kunrath Ivar E. Reimanis John J. Moore 《Journal of the American Ceramic Society》2002,85(5):1285-1290
A microstructural analysis of compounds produced by combustion synthesis coupled with hot pressing, for reactions between titanium, chromium, and carbon, was conducted. The reactions were aimed to produce composites of Cr3 C2 and TiC at three different volume fractions of each carbide (25/75, 50/50, and 75/25). Large amounts of chromium and carbon were found to be in solution in the B1 rock-salt structure of TiC. The materials with 25 and 50 vol% of Cr3 C2 consisted of 100% (Ti,Cr)Css solid solution, while the composition with 75 vol% Cr3 C2 was formed by Cr3 C2 + (Ti,Cr)Css . Some precipitation of Cr3 C2 was achieved by annealing, but a minimum of 20 wt% was always in solution. The 50 vol% Cr3 C2 –50 vol% TiC composition was the most affected by the heat treatments. Discontinuous and general precipitation were observed, depending on the annealing conditions. A TTT-type diagram was plotted for this material. 相似文献
2.
Porous Cr3 C2 grains (∼300 to 500 μm) with ∼10 wt% of Cr2 O3 were prepared by heating a mixture of MgCr2 O4 grains and graphite powder at 1450° to 1650°C for 2 h in an Al2 O3 crucible covered by an Al2 O3 lid with a hole in the center. The porous Cr3 C2 grains exhibited a three-dimensional network skeleton structure. The mean open pore diameter and the specific surface area of the porous grains formed at 1600°C for 2 h were ∼3.5 (μm and ∼6.7 m2 /g, respectively. The present work investigated the morphology and the formation conditions of the porous Cr3 C2 grains, and this paper will discuss the formation mechanism of those grains in terms of chemical thermodynamics. 相似文献
3.
Cr3C2和VC对Ti(C,N)基金属陶瓷中环形相的价电子结构和性能的影响 总被引:11,自引:0,他引:11
根据固体与分子经验电子理论,计算了Ti(C,N)基金属陶瓷中界面环形相的价电子结构,讨论了其价电子结构与塑性间的关系。当材料晶体结构相同时,Σna可用来比较其塑性的相对高低。Cr在环形相(Ti,Mo)(C,N)中的固溶,可使其塑性增强,V在环形相中的固溶将使其塑性变差。在计算的基础上进行实验,实验结果表明:Cr3C2的适量加入确实有利于提高金属陶瓷的强度,最终所制备出金属陶瓷的强度比典型成分体系材料的提高了1倍以上;尽管VC的加入能使材料的晶粒得到有效地细化,但它使环形相塑性降低,使金属陶瓷的抗弯强度略有增加。 相似文献
4.
Ki-Woong Chae Koichi Niihara Doh-Yeon Kim 《Journal of the American Ceramic Society》1996,79(12):3305-3308
The densification behavior and mechanical properties of SiC-30TiC (in volume percent) composites prepared with Cr3 C2 additive were investigated. By hot-pressing a SiC-30TiC-lCr3 C2 specimen at 1950°C, 98.5% of theoretical density was achieved and the specimen exhibited a fracture strength of 750 MPa. For the SiC-30TiC-10Cr3 C2 specimen, (β-α transformation of SiC was observed to occur during hot-pressing and in situ growth of elongated α-SiC grains resulted in an increase of fracture toughness. Micro-structural observations using high-resolution TEM indi-cated that no liquid phase was present at the interfaces. 相似文献
5.
Wu-bian Tian Pei-ling Wang Guo-jun Zhang Yan-mei Kan Yong-xiang Li 《Journal of the American Ceramic Society》2007,90(5):1663-1666
Dense and predominantly single-phase samples of Cr2 AlC, together with a trace amount of Cr7 C3 , were fabricated by hot pressing of a mixture of chromium, aluminum, and graphite powders at 1400°C for 1 h. The hardness, Young's modulus, flexural strength, and compressive strength of Cr2 AlC samples were 5.2, 288 GPa, 483±29, and 1159±23 MPa, respectively, which are comparable with those of Ti3 AlC2 and Nb2 AlC. The material exhibits good damage tolerance. For indentation loads up to 50 N, the post-indentation flexural strengths decrease by approximately 10% and by 31% for a load of 100 N. The flexural strengths of Cr2 AlC samples quenched from 300°C to room temperature decrease from 483 to 455 MPa, while the retained strengths decrease quickly to 199 MPa when the quench temperature increases to 500°C. A further increase in quench temperature to 700°, 900°, and 1100°C results in a small reduction of strength. 相似文献
6.
The effect of Al8 B4 C7 used as an antioxidant in MgO–C refractories and the behavior of Al8 B4 C7 in CO gas were investigated in the present study. Al8 B4 C7 was found to react with CO gas, to form Al2 O3 ( s ), B2 O3 ( l ), and C( s ), at temperatures >1100°C. The Al2 O3 reacts with MgO to form MgAl2 O4 near the surface of the material. At the same time, B2 O3 ( l ) evaporates and reacts with MgO, to form a liquid phase, at >1333°C, the eutectic point between 3MgO·B2 O3 and MgO. The coexistence of the liquid and MgAl2 O4 makes the protective layer more dense, thus inhibiting oxidation of the refractory. At >1333°C, the process apparently is controlled by oxygen diffusion, whereas it is controlled by chemical reaction when the temperature is <1333°C. 相似文献
7.
The quenching method has been used to determine approximate phase relations in the system iron oxide-Cr2 O3 in air. Only two crystalline phases, a sesquioxide solid solution (Fe2 O3 –Cr2 O3 ) with corundum structure and a spinel solid solution (approximately FeO ·Fe2 O3 –FeO – Cr2 O3 ), occur in this system at conditions of temperature and O2 partial pressure (0.21 atm.) used in this investigation. Liquidus temperatures increase rapidly as Cr2 O3 is added to iron oxide, from 1591°C. for the pure iron oxide end member to a maximum of approximately 2265°C. for Cr2 O3 . Spinel(ss) is the primary crystalline phase in iron oxide-rich mixtures and sesquioxide (ss) in Cr2 O3 –rich mixtures. These two crystalline phases are present together in equilibrium with a liquid and gas (po2 = 0.21 atm.) at approximately 2075°C. 相似文献
8.
The conditions necessary for synthesizing Al4 SiC4 from mixtures of aluminum, silicon, and carbon and kaolin, aluminum, and carbon, as starting materials, were examined in the present study. The standard Gibbs energy of formation for the thermodynamic reaction SiC( s ) + Al4 C3 ( s ) = Al4 SiC4 ( s ) changed from positive to negative at 1106°C. SiC and Al4 C3 formed as intermediate products when the mixture of aluminum, silicon, and carbon was heated in argon gas, and Al4 SiC4 then formed by reaction of the SiC and Al4 C3 at >1200°C. Al4 C3 , SiO2 , Al2 O3 , SiC, and Al4 O4 C formed as intermediate products when the mixture of kaolin, aluminum, and carbon was heated under vacuum, and Al4 SiC4 formed from a reaction of those intermediate products at >1600°C. 相似文献
9.
P. L. ROEDER F. P. GLASSER† E. F. OSBORN 《Journal of the American Ceramic Society》1968,51(10):585-593
Liquidus phase equilibrium data are presented for the system Al2 O3 -Cr2 O3 -SiO2 . The liquidus diagram is dominated by a large, high-temperature, two-liquid region overlying the primary phase field of corundum solid solution. Other important features are a narrow field for mullite solid solution, a very small cristobalite field, and a ternary eutectic at 1580°C. The eutectic liquid (6Al2 O3 -ICr2 O3 -93SiO2 ) coexists with a mullite solid solution (61Al2 O3 -10Cr2 O3 -29SiO2 ), a corundum solid solution (19Al2 O3 -81Cr2 O3 ), and cristobalite (SO2 ). Diagrams are presented to show courses of fractional crystallization, courses of equilibrium crystallization, and phase relations on isothermal planes at 1800°, 1700°, and 1575°C. Tie lines were sketched to indicate the composition of coexisting mullite and corundum solid solution phases. 相似文献
10.
Cr2 O3 and ZrO2 were mixed in various ratios and pressed to form compacts, which were then sintered in carbon powder. Compacts with >30 wt% Cr2 O3 were sintered to densities >98% of true density at 1500°C. This method of sintering in carbon powder can be used to prepare very dense Cr2 O3 -ZrO2 ceramics at a relatively low temperature, (∼1500°C) without additives. 相似文献
11.
The phase diagrams in the Al2 O3 –Cr2 O3 and V2 O3 –Cr2 O3 systems have been assessed by thermodynamic modeling with existing data from the literature. While the regular and subregular solution models were used in the Al2 O3 –Cr2 O3 system to represent the Gibbs free energies of the liquid and solid phases, respectively, the regular solution model was applied to both phases in the V2 O3 –Cr2 O3 system. By using the liquidus, solidus, and/or miscibility gap data, the interaction parameters of the liquid and solid phases were optimized through a multiple linear regression method. The phase diagrams calculated from these models are in good agreement with experimental data. Also, the solid miscibility gap and chemical spinodal in the V2 O3 –Cr2 O3 system were estimated. 相似文献
12.
Koichiro Fukuda Satoshi Mori Shinobu Hashimoto 《Journal of the American Ceramic Society》2005,88(12):3528-3530
The crystal structure of Zr2 Al3 C4 was refined by the Rietveld method from conventional X-ray powder diffraction data. The structure was hexagonal (space group P 63 mc , Z =2) with a =0.334680(6) nm, c =2.22394(3) nm, and V =0.215731(6) nm3 , being isomorphous with that of U2 Al3 C4 . The final reliability indices were R wp =8.57%, R p =6.06%, and S =1.32. The crystal showed an intergrowth structure with NaCl-type ZrC slabs separated by Al4 C3 -type Al3 C2 layers. 相似文献
13.
Shingo Hirano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1996,79(1):171-176
In the ZrO2 -Cr2 O3 system, metastable t -ZrO2 solid solutions containing up to 11 mol% Cr2 O3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr2 O3 content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t (ss)→ t (ss) + m + Cr2 O3 → m + Cr2 O3 . Above 11 mol% Cr2 O3 addition, c-ZrO2 phases are formed in the presence of Cr2 O3 . The t -ZrO2 solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15–30 nm) showing thin platelike morphology. Dense ZrO2 (3Y)-Cr2 O3 composite ceramics (∼99.7% of theoretical) with an average grain size of 0.3 μm have been fabricated by hot isostatic pressing for 2 h at 1400°C and 196 MPa. Their fracture toughness increases with increased Cr2 O3 content. The highest K Ic value of 9.5 MPa·;m1/2 is achieved in the composite ceramics containing 10 mol% Cr2 O3 . 相似文献
14.
Thermal and X-ray studies show that there is complete solid solution between MgO.Cr2 O3 and MgO.Al2 O3 and that the spinel solid solutions are stable with no exsolution down to temperatures as low as 510°C. There is no solid solution of excess Cr2 O3 in MgO.Cr2 O3 nor of MgO.Cr2 O3 in Cr2 O3 . The join MgO.Cr2 O3 –Al2 O3 is found to be nonbinary; compositions along that join yield mixtures of a chromium oxide-alumina solid solution and a spinel solid solution on firing to temperatures high enough to promote solid-state reaction. Chromium oxide loss by volatilization increases at higher temperature. At a given temperature, chromium oxide loss is found to vary directly with the partial pressure of oxygen in the furnace atmosphere and with the ratio of MgO to SiO2 in the charges heated. 相似文献
15.
Mats Carlsson Mats Johnsson Mats Nygren 《Journal of the American Ceramic Society》1999,82(8):1969-1976
Ta0.33 Ti0.33 Nb0.33 C and Ta0.33 Ti0.33 Nb0.33 C x N1− x whiskers were synthesized via a carbothermal vapor-liquid-solid growth mechanism in the temperature range 900°-1450°C in Ar or N2 . The optimum temperature was 1250°C. Whiskers were obtained in a yield of 70-90 vol%. The whiskers were 0.5–1 µm in diameter and 10–30 µm in length. The starting materials that produced the highest whisker yield were: TiO2 , Ta2 O5 , Nb2 O5 , C, Ni, and NaCl. C was added to reduce the oxides, and Ni to catalyze whisker growth. NaCl was used as a source of Cl for vapor-phase transportation of Ta and Nb oxochlorides and Ti chlorides to the catalyst. The catalyst metal was recycled several times during the synthesis and was transported as NiCl2 ( g ) according to thermodynamic calculations. The rate of formation and the chemical composition of the whiskers depended on the synthesis temperature, the choice of catalyst, and the atmosphere. At low temperatures, the whiskers were enriched in Nb and Ta, whereas the Ti content increased with increased synthesis temperature. 相似文献
16.
Refractory bodies of 65 wt% Al2 O3 were prepared from a mixture of calcined alumina and raw kaolin with the addition of Cr2 O3 up to 15 wt%. The Cr2 O3 addition effectively enhances slag resistance and reduces mullite formation. Petrographic analysis of the refractories after the slag test suggests that Cr2 O3 increases the viscosity of both the glassy phase in the refractory as well as the slag, thereby retarding slag penetration and reaction at elevated temperature. 相似文献
17.
The weight loss of Cr2 O3 in oxidizing environments (Po2 = 1 to 10−3 atm) at 1200°C was measured. Both hot-pressed and sintered Cr2 O3 pellets were investigated in O2 /Ar gas mixtures, and the dependence of the weight loss on the O2 partial pressure, the gas flow rate, and the total pressure was determined independently. The experimentally determined O2 partial pressure dependence (rate ∝ PO2 3/4 ) corresponds to that expected for the reaction Cr2 O3 (s)+3/2O2 ⇌2CrO3 (g). The flow rate and total pressure dependencies show that mass transport through a gaseous boundary layer is the rate-controlling step in the oxidation/vaporization of Cr2 O3 . Evaporation coefficients for the loss of CrO3 (g) under the experimental conditions were <0.01. 相似文献
18.
JONG-HEE PARK WAYNE E. KING STEVEN J. ROTHMAN 《Journal of the American Ceramic Society》1987,70(12):880-885
The cation diffusivities in the lattice and along dislocations and grain boundaries have been measured on sintered polycrysals of Cr2 O3 ; and Cr2 Cr2 O3 -0.09 wt% Y2 O3 at1100°C and at the pO2 corresponding to that of Cr/Cr2 O3 equilibrium at that temperature. Results for lattice and dislocation diffusivities in pure Cr2 O3 are in good agreement with previous work. The present results indicate that yttrium additions have negligible effect on lattice and dislocation diffusion. However, grain-boundary diffusion in pure Cr2 O3 is significantly slower than grain-boundary diffusion in Cr2 O3 -0.09 wt% Y2 O3 . The results are discussed in terms of their implications for the reactive-element effect in high-temperature oxidation of chromium-containing alloys. 相似文献
19.
Compositions on the join A14 C3 ·2AIN-A14 C3 .2SiC were investigated using X-ray diffraction and thermal analysis of hot-pressed bodies prepared from materials of various purities. The quaternary phase A14 C3 · AIN · SiC was observed in samples prepared from the high-purity elements, but the ternary phases A14 C3 ·2AIN and A14 C3 ·2SiC were observed only in samples containing significant impurities. A projection onto the base triangle at 1860°C for the pseudoternary system Al4 C3 -AlN-SiC was constructed using X-ray diffraction, thermal analysis, and existing information in the literature. 相似文献
20.
Masahiro Yoshimura Manikpurage Jayaratna Shigeyuki Smiya 《Journal of the American Ceramic Society》1982,65(10):c166-c168
The pseudoternary system ZrO2 -Y2 O3 -Cr2 O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3 , was observed on the Y2 O3 −Cr2 O3 join. ZrO2 and Y2 O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2 , Cr2 O3 , and YCrO3 three-phase region was located at =17 mol% Y2 O3 (83 mol% ZrO2 ). Below 17 mol% Y2 O3 , ZrO2 solid solution coexisted with Cr2 O3 . Cr2 O3 appears to be slightly soluble in ZrO2 (ss). 相似文献