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1.
S. K. RHEE 《Journal of the American Ceramic Society》1970,53(7):386-389
The wettability of AlN, TiB2 , TiN, and TiC by liquid aluminum was investigated by the sessile drop technique at 2×10-7 torr or less. The contact angle decreased linearly with increasing temperature in all cases. Variation of the contact angle with temperature is correlated with the surface tension of the drop, and the Zisman-type relation is established. The critical surface tensions (Rγc ) of AlN, TiB2 , TiN, and TiC are 664, 700, 713, and 725 dynes/cm, respectively. These values are correlated with the melting point of the ceramics. The Zisman relation is discussed and applied to calculation of the work of adhesion. The surface tension of liquid aluminum varies linearly with temperature: γLv (dynes/cm) = 948–0.202 T (°K). 相似文献
2.
S. K. RHEE 《Journal of the American Ceramic Society》1972,55(3):157-159
Wetting of TaC0.97±0.01 by liquid Cu and liquid Ag was studied by the sessile drop method. The cosine of the contact angle increased linearly with increasing temperature in both systems. The critical surface energy for spreading was 1098 ergs/cm2 at 1605°C for Cu and 688 ergs/cm2 at 2160°C for Ag. The work of adhesion, which was 1759 ergs/cm2 at the melting point for Cu and 321 ergs/cm2 at the melting point for Ag, increased parabolically with increasing temperature in both systems. The surface energy of TaC0.97±0.01 was estimated to be 1804±706 ergs/cm2 . 相似文献
3.
S. K. RHEE 《Journal of the American Ceramic Society》1971,54(8):376-379
According to Zisman and co-workers, in organic systems the cosine of the contact angle of a sessile drop increases with the decreasing surface tension of the drop at room temperature. The applicability of the Zisman relation to liquid metal-ceramic systems is discussed using the systems (Al-Mg)/graphite and (Cu-O)/sapphire. Also discussed is the significance of the critical surface tension for spreading, γc , in the systems where the surface tension of the liquid is greater than that of the solid substrate; γc is 230 dynes/cm for graphite at 720°C and 440 dynes/cm for sapphire at 1230°C. 相似文献
4.
S. K. RHEE 《Journal of the American Ceramic Society》1972,55(6):300-303
Based on the wetting properties of a -Al2 O3 , and pyrolytic graphite by liquid metals, the critical surface energy for spreading was determined and compared with the surface energy of the ceramics. The surface energy γ-8 (ergs/cm2 ) of the (0001) surface of a -Al2 O3 is estimated to be 892–0.12 T (°C), that of the c plane of pyrolytic graphite 1139–0.13 T (°C), and that of the a plane of pyrolytic graphite 1300–0.17 T (°C). Also, the liquid-solid interfacial energies were calculated and found compatible with the values reported in the literature. The surface energy of liquid Ag or liquid Cu is not significantly affected by carbon. 相似文献
5.
Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors 总被引:1,自引:0,他引:1
Corinna L. Czekaj Michael L. J. Hackney William J. Hurley Jr. Leonard V. Interrante Gary A. Sigel Paul J. Schields Glen A. Slack 《Journal of the American Ceramic Society》1990,73(2):352-357
Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me3 Si)0.80 ((CH2 =CH)MeSi)1.0 (MeHSi)0.35 ] n (VPS) or [MeHSiCH2 ] n (MPCS) with [R2 AlNH2 ]3 , where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et2 AlNH2 ]3 . In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu2 AlNH2 ]3 yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed. 相似文献
6.
AlN, Al2 OC, and the 2 H form of SiC are isostructural. Both SiC–AlN and AlN–Al2 OC form homogeneous solid solutions above 2000° and 1950°C, respectively. The kinetics of phase separation in the two systems, however, are quite different. Interdiffusion in both SiC–AlN and AlN-Al2 OC systems was examined in the solid-solution regime in an attempt to elucidate differences in the kinetics of phase separation that occur in the two systems when annealed at lower temperatures. Diffusion couples of (SiC)0.3 (AlN)0.7 /(SiC)0.7 (AlN)0.3 and (AlN)0.7 (Al2 OC)0.3 /(AlN)0.3 (Al2 OC)0.7 were fabricated by hot pressing and were annealed at high temperatures by encapsulating them in sealed SiC crucibles to suppress loss due to evaporation. Interdiffusion coefficients in (SiC)0.3 -(AlN)0.7 /(SiC)0.7 (AlN)0.3 diffusion couples were measured at 2373, 2473, and 2573 K, and the corresponding activation energy was determined to be 632 kJ/mol. (AlN)0.7 (Al2 OC)0.3 / (AlN)0.3 (Al2 OC)0.7 samples were annealed at 2273 K. The interdiffusion coefficient measured in the AlN–Al2 OC system was much larger than that in the SiC–AlN system. 相似文献
7.
Edwin Kroke Lars Loeffler Fred F. Lange Ralf Riedel 《Journal of the American Ceramic Society》2002,85(12):3117-3119
Aluminum nitride (AlN) powders were prepared from the oxide precursors aluminum nitrate, aluminum hydroxide, aluminum 2-ethyl-hexanoate, and aluminum isopropoxide (i.e., Al(NO3 )3 , Al(OH)3 , Al(OH)(O2 CCH(C2 H5 )(C4 H9 ))2 , and Al(OCH(CH3 )2 )3 ). Pyrolyses were performed in flowing dry NH3 and N2 at 1000°–1500°C. For comparison, the nitride precursors aluminum dimethylamide (Al(N(CH3 )2 )3 ) and aluminum trimethylamino alane (AlH3 ·N(CH3 )3 ) were exposed to the same nitridation conditions. Products were investigated using XRD, TEM, EDX, SEM, and elemental analysis. The results showed that nitridation was primarily controlled by the water:ammonia ratio in the atmosphere. Single-phase AlN powders were obtained from all oxide precursors. Complete nitridation was not obtained using pure N2 , even for the non-oxide precursors. 相似文献
8.
Experimental Method for Determining Surface Energy Anisotropy and Its Application to Magnesia 总被引:2,自引:0,他引:2
David M. Saylor Darren E. Mason Gregory S. Rohrer 《Journal of the American Ceramic Society》2000,83(5):1226-1232
An experimental technique has been developed to determine the surface energy anisotropy of crystalline solids. The technique is based on atomic force microscopy measurements, which are used to quantify the geometry of thermal grooves, and electron backscattered diffraction pattern measurements, which are used to specify crystallographic orientations. Observations are made at circumferential thermal grooves, where it is assumed that Herring's local equilibrium condition for a triple junction holds and that the grain-boundary energy is independent of its boundary plane. A truncated double Fourier series is used to approximate the surface energy, and the unknown coefficients of the series are determined by fitting the observations to the local equilibrium condition. The method, which should be applicable to most polycrystalline materials, has been tested on magnesia that has been thermally grooved at 1400°C in air. The maximum of the best-fit surface energy function is at (111) and the minimum is at (100). The relative surface energies of the low-index planes are γ110 /γ100 = 1.040 ± 0.008 and γ111 /γ100 = 1.072 ± 0.010. 相似文献
9.
The surface tension of a 62ZrF4 .33BaF2 .5LaF3 (mol%) glass was measured by a solidified pendant drop technique. The surface tension at 550°C is 0.174 ± 0.005 J/m2 . 相似文献
10.
L. N. GROSSMAN 《Journal of the American Ceramic Society》1963,46(6):264-267
Thermal conductivity ( k ), electrical resistivity ( p ), total hemispherical emittance (εt ), and normal spectral emittance (ε0.65μ ) of dense, arc-cast uranium monocarbide (5.3 wt % total carbon) were measured in the temperature range 1150° to 2050°K. The results were as follows: k , 0.057 cal/sec-cm-deg, 1200° < T < 2050°K, probable error ± 0.002; p, 20.4 × 10−6 + 114.8 T × 10−9 ohm-cm, 1175° < T < 2050°K, probable error ± 1.7 × 10−6 ; εt 0.42, 1250° < T < 1980°K, probable error ± 0.02; ε0.65 0.539 – 0.02 T × 10−3 1150° < T < 1890°K, probable error ± 0.02. Experimental methods are discussed and error sources are analyzed. Uranium monocarbide exhibited typical metallic behavior in its thermophysical properties. 相似文献
11.
SiO2 -Al2 O3 melts containing 42 and 60 wt% A12 O3 were homogenized at 2090°C (∼10°) and crystallized by various heat treatment schedules in sealed molybdenum crucibles. Mullite containing ∼78 wt% A12 O3 precipitated from the 60 wt% A12 O3 melts at ∼1325°± 20°C, which is the boundary of a previously calculated liquid miscibility gap. When the homogenized melts were heat-treated within this gap, the A12 O3 in the mullite decreased with a corresponding increase in the Al2 O3 content of the glass. A similar decrease of Al2 O3 in mullite was observed when crystallized melts were reheated at 1725°± 10°C; the lowest A12 O3 content (∼73.5 wt%) was in melts that were reheated for 110 h. All melts indicated that the composition of the precipitating mullite was sensitive to the heat treatment of the melts. 相似文献
12.
The microstructure, thermal expansion, mechanical property, and ionic conductivity of samaria-doped ceria (SDC) prepared by coprecipitation were investigated in this paper. The results revealed that the average particle size ranged from 10.9±0.4 to 13.5±0.5 nm, crystallite dimension varied from 8.6±0.3 to 10.7±0.4 nm, and the specific surface area distribution ranged from 62.6±1.8 to 76.7±2.2 m2 /g for SDC powders prepared by coprecipitation. The dependence of lattice parameter, a, versus dopant concentration, x , of Sm3+ ion shows that these solid solutions obey Vegard's rule as a ( x )=5.4089+0.10743 x for Ce1− x Sm x O2−1/2 x . For SDC ceramics sintered at 1500°C for 5 h, the bulk density was over 95% of the theoretical density; the maximum ionic conductivity, σ800°C =(22.3±1.14) × 10−3 S/cm with minimum activation energy, E a =0.89±0.02 eV, was found in the Ce0.80 Sm0.20 O1.90 ceramic. A dense Ce0.8 Sm0.2 O1.9 ceramic with a grain size distribution of 0.5–4 μm can be obtained by controlling the soaking time at 1500°C. When the soaking time was increased, the microhardness of Ce0.8 Sm0.2 O1.9 ceramic increased, the toughness slightly decreased, which was related to grain growth with the soaking time. 相似文献
13.
Tomohiro Yamakawa Junichi Tatami Toru Wakihara Katsutoshi Komeya Takeshi Meguro Kenneth J. D. MacKenzie Shinichi Takagi Masahiro Yokouchi 《Journal of the American Ceramic Society》2006,89(1):171-175
Aluminum nitride (AlN) powders were synthesized by gas reduction–nitridation of γ-Al2 O3 using NH3 and C3 H8 as the reactant gases. AlN was identified in the products synthesized at 1100°–1400°C for 120 min in the NH3 –C3 H8 gas flow confirming that AlN can be formed by the gas reduction–nitridation of γ-Al2 O3 . The products synthesized at 1100°C for 120 min contained unreacted γ-Al2 O3 . The 27 A1 MAS NMR spectra show that Al–N bonding in the product increases with increasing reaction temperature, the tetrahedral AlO4 resonance decreasing prior to the disappearance of the octahedral AlO6 resonance. This suggests that the tetrahedral AlO4 sites of the γ-Al2 O3 are preferentially nitrided than the AlO6 sites. AlN nanoparticles were directly formed from γ-Al2 O3 at low temperature because of this preferred nitridation of AlO4 sites in the reactant. AlN nanoparticles are formed by gas reduction–nitridation of γ-Al2 O3 not only because the reaction temperature is sufficiently low to restrict grain growth, but also because γ-Al2 O3 contains both AlO4 and AlO6 sites, by contrast with α-Al2 O3 which contains only AlO6 . 相似文献
14.
Shuichi Kawano Junichi Takahashi Shiro Shimada 《Journal of the American Ceramic Society》2003,86(9):1609-1611
Nano-sized TiO2 powders were prepared by controlled hydrolysis of TiCl4 and Ti(O-i-C3 H7 )4 solutions and nitrided in flowing NH3 gas at 700°–1000°C to form TiN. Nano-sized TiN was densified by spark plasma sintering at 1300°–1600°C to produce TiN ceramics with a relative density of 98% at 1600°C. The microstructure of the etched ceramic surface was observed by SEM, which revealed the formation of uniformly sized 1–2 μm grains in the TiCl4 -derived product and 10–20 μm in the Ti(O-i-C3 H7 )4 -derived TiN. The electric resisitivity and Vickers micro-hardness of the TiN ceramics was also measured. 相似文献
15.
Akira Kato Hisao Yamashita Hiroshi Kawagoshi Shimpei Matsuda 《Journal of the American Ceramic Society》1987,70(7):157-C
Mixtures of La2 O3 and Al2 O3 with various La contents were prepared by co-precipitation from La(NO3 )3 and Al(NO3 )3 solutions and calcined at 800° to 1400°C. The addition of small amounts of La2 O3 (2 to 10 mol%) to Al2 O3 gives rise to the formation of lanthanum β-alumina (La 2 O3 ·11–14Al2 O3 ) upon heating to above 1000°C and retards the transformation of γ-Al2 O3 to α-Al2 O3 and associated sintering. 相似文献
16.
Phase relations in the system Bi2 O3 -WO3 were studied from 500° to 1100°C. Four intermediate phases, 7Bi2 O3 · WO3 , 7Bi2 O3 · 2WO3 , Bi2 O3 · WO3 , and Bi2 O3 · 2WO3 , were found. The 7B2 O · WO3 phase is tetragonal with a 0 = 5.52 Å and c 0 = 17.39 Å and transforms to the fcc structure at 784°C; 7Bi2 O3 · 2WO3 has the fcc structure and forms an extensive range of solid solutions in the system. Both Bi2 O3 · WO3 and Bi2 O3 · 2WO3 are orthorhombic with (in Å) a 0 = 5.45, b 0 =5.46, c 0 = 16.42 and a 0 = 5.42, b 0 = 5.41, c 0 = 23.7, respectively. Two eutectic points and one peritectic exist in the system at, respectively, 905°± 3°C and 64 mol% WO3 , 907°± 3°C and 70 mol% WO3 , and 965°± 5°C and 10 mol% WO3 . 相似文献
17.
Tentative phase relations in the binary system BnOa-A12 O3 are presented as a prerequisite to the understanding of the system Li2 O-B2 O3 -Al2 O3 . Two binary compounds, 2A12 O3 .B2 O3 and 9A12 O3 .-2B2 O3 , melted incongruently at 1030° f 7°C and about 144°C, respectively. Two ternary compounds were isolated, 2Li2 O.A12 O3 .B2 O3 and 2Li2 O. 2AI2 O3 . 3B2 03 . The 2:1:1 compound gave a melting reaction by differential thermal analysis at 870°± 20° C, but the exact nature of the melting behavior was not determined. The 2:2:-3 compound melted at 790°± 20° C to Liz O.-5Al2 O3 and liquid. X-ray diffraction data for the compounds are presented and compatibility triangles are shown. 相似文献
18.
Takayuki Nagano Hidezumi Kato Fumihiro Wakai 《Journal of the American Ceramic Society》1991,74(9):2258-2262
The deformation behavior of an Al2 O3 /30 wt% TIC composite in uniaxial tension was evaluated under vacuum over the temperature range of 1300° to 1550°C. The Al2 03 /TiC composite exhibited the maximum elongation of 66% at an initial strain rate of 1.19 X l0-4 s-1 at 1550°C. The stress exponent calculated from peak stresses of true stress-true strain curves at 1500O C was 3.8, which was in good agreement with that obtained by changing the crosshead speed during the tension test. The apparent activation energy at 20 MPa was 853 kJ/mol. In addition the deformation of the Al2 O3 /TiC composite in uniaxial tension at elevated temperature was accompanied by cavitation. 相似文献
19.
Mechanical-Activation-Triggered Gibbsite-to-Boehmite Transition and Activation-Derived Alumina Powders 总被引:2,自引:0,他引:2
Mechanical activation of monoclinic gibbsite (Al(OH)3 ) in nitrogen led to the formation of nanocrystalline orthorhombic boehmite (AlOOH) at room temperature. The boehmite phase formed after merely 3 h of mechanical activation and developed steadily as the mechanical-activation time increased. Forty hours of mechanical activation resulted in essentially single-phase boehmite, together with α-alumina (α-Al2 O3 ) nanocrystallites 2–3 nm in size. The sequence of phase transitions in the activation-derived boehmite was as follows: boehmite to γ-Al2 O3 and then to α-Al2 O3 when flash-calcined at a heating rate of 10°C/min in air. γ-Al2 O3 formed at 520°C, and flash calcination to 1100°C led to the formation of an α-Al2 O3 phase, which exhibited a refined particle size in the range of 100–200 nm. In contrast, the gibbsite-to-boehmite transition in the unactivated gibbsite occurred over the temperature range of 220°–330°C. A flash-calcination temperature of 1400°C was required to complete the conversion to α-Al2 O3 phase, with both δ-Al2 O3 and θ-Al2 O3 as the transitional phases. The resulting alumina powder consisted of irregularly shaped particles 0.4–0.8 μm in size, together with an extensive degree of particle agglomeration. 相似文献
20.
Anthony C. Sutorik Siew Siang Neo David R. Treadwell Richard M. Laine 《Journal of the American Ceramic Society》1998,81(6):1477-1486
Flame spray pyrolysis of a polymeric precursor is used to prepare ultrafine powders that, when sintered, convert to essentially pure phase lithium-doped sodium β"-alumina. The precursor Na1.67 Al10.67 Li0.33 [N(CH2 CH2 O)3 ]10.67 -[OCH2 CH2 O]·x(HOCH2 CH2 OH) has been synthesized from stoichiometric amounts of metal hydroxides and tri-ethanolamine (N(CH2 CH2 OH)3 , TEA) in excess ethylene glycol. The precursor is dissolved in ethanol, and an atom-ized spray of the solution is combusted in a specially con-structed flame spray apparatus. Combustion occurs at ∼2000°C, followed by immediate quenching. This proce-dure provides for a measure of kinetic control over the process. The resulting nanopowder particles are 50–150 nm in diameter and exhibit powder X-ray diffractometry pat-terns similar to β"-alumina. Heating the nanopowder at 30°C/min to 1200°C with a 1 hisotherm converts it to pure β"-alumina. In preliminary sintering studies, green powder compacts (∼65% theoretical density) sintered at 1600°C for 12 min densify to 3.0 ± 0.1 g/cm 3 (∼92% theoretical density) with minimal loss of Na2 O. This procedure offers several processing and cost advantages over conventional β"-alumina syntheses. 相似文献