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1.
Phase Relations and Reaction Sintering of Transparent Cubic Aluminum Oxynitride Spinel (ALON) 总被引:4,自引:0,他引:4
A new isobaric, condensed phase diagram in the region of stability of cubic aluminum oxynitride spinel (ALON) along the pseudobinary AI2 O3 -AIN composition join is presented, deduced primarily from various analytical measurements and microstructural observations. It is shown that cubic aluminum oxynitride spinel melts incongruently at ≊2050°C and is compositionally centered at ≊35.7 mol% AIN, which is equivalent to the following stoichiometric composition: AI23 O27 N5 or 5AIN·9AI2 O3 . Single-phase ALON material sintered to nearly full density exhibits transparency in visible light. 相似文献
2.
A phase diagram of the system A12 O3 -A14 C3 is proposed. Two intermediate oxycarbides, A14 O4 C and A12 OC, were established. Eutectic melting between alumina and A14 O4 C occurred at 1840° C. No other low melting was observed. The alumina phase was not corundum but was similar to delta-alumina. Because of the high reactivity of aluminum carbide and all the intermediate compounds with moisture and oxygen, use of refractories based on the system A12 O3 -A14 C3 must be limited to applications where these agents are excluded. The behavior of high-alumina refractories in the presence of carbon is explained. 相似文献
3.
Elastic Properties of Polycrystalline Aluminum Oxynitride Spinel and Their Dependence on Pressure, Temperature, and Composition 总被引:1,自引:0,他引:1
EARL K. GRAHAM W.C. MUNLY JAMES W. McCAULEY NORMAN D. CORBIN 《Journal of the American Ceramic Society》1988,71(10):807-812
The isotropic elastic moduli of four specimens of nitrogen-stabilized cubic aluminum oxide (ALON) were measured using pulse superposition interferometry. Experiments were carried out as a function of both pressure (ambient to 1 GPa) and temperature (0° to 25°C) for specimens of 30.0 and 35.7 mol% AlN. The second-order moduli results were corrected for porosity using the "self-consistent-scheme" approach. Pertinent ambient results for isotropic pore-free ALON are K = 226.3 GPa and G = 132.0 GPa for the 30.0 mol% AlN material, and K = 229.8 GPa and G = 135.5 GPa for 35.7 mol% ALON ( K and G denote the bulk and shear moduli, respectively). The estimated uncertainties in these values are about 2%. The second-order elastic properties of ALON, as well as their pressure and temperature derivatives, fall midway between spinel (MgAl2 O4 ) and corundum (Al2 O3 ), indicating the excellent potential of this material for structural engineering purposes. 相似文献
4.
L. G. VAN UITERT W. H. GRODKIEWICZ E. F. DEARBORN 《Journal of the American Ceramic Society》1965,48(2):105-108
An improved flux consisting of PbO-PbF2 and B2 O3 was developed for the growth of garnets. Rare-earth aluminum garnet crystals weighing in excess of 100 g and modified yttrium aluminum garnet crystals weighing up to 60 g were obtained using this flux. Lead contamination was reduced to noncritical levels in these crystals by working with large excesses of A12 O3 in the melt. Excellent optical quality has been produced as indicated both by visual examination and by outstanding laser performance. 相似文献
5.
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
6.
Yucong Wang Tetsuro Fujimoto Hiroshi Maruyama Kazunori Koga 《Journal of the American Ceramic Society》2000,83(4):933-936
Al2 O3 ceramics with magnesium aluminum spinel dispersion particulates were produced by a precipitation treatment of Al2 O3 -matrix solid solution, (Al1—2x ,Ti x ,Mg x )2 O3 . We successfully constructed the precipitation process for synthesizing the nanocomposite, using the solubility dependence of titanium and magnesium in Al2 O3 on the valence of titanium. Changing of the valence of titanium from 4+ to 3+ was accomplished by controlling the heating atmosphere, and, thereby, magnesium precipitation was promoted. The precipitation behavior was characterized using X-ray diffractometry, and the microstructure was observed using transmission electron microscopy. We confirmed that magnesium aluminum spinel nanosized particulate were precipitated in the Al2 O3 grain. 相似文献
7.
Microstructure and Mechanical Properties of Porous Alumina Ceramics Fabricated by the Decomposition of Aluminum Hydroxide 总被引:3,自引:0,他引:3
Zhen-Yan Deng Takayuki Fukasawa Motohide Ando Guo-Jun Zhang Tatsuki Ohji 《Journal of the American Ceramic Society》2001,84(11):2638-2644
The mechanical properties of Al2 O3 -based porous ceramics fabricated from pure Al2 O3 powder and the mixtures with Al(OH)3 were investigated. The fracture strength of the porous Al2 O3 specimens sintered from the mixture was substantially higher than that of the pure Al2 O3 sintered specimens because of strong grain bonding that resulted from the fine Al2 O3 grains produced by the decomposition of Al(OH)3 . However, the elastic modulus of the porous Al2 O3 specimens did not increase with the incorporation of Al(OH)3 , so that the strain to failure of the porous Al2 O3 ceramics increased considerably, especially in the specimens with high porosity, because of the unique pore structures related to the large original Al(OH)3 particles. Fracture toughness also increased with the addition of Al(OH)3 in the specimens with higher porosity. However, fracture toughness did not improve in the specimens with lower porosity because of the fracture-mode transition from intergranular, at higher porosity, to transgranular, at lower porosity. 相似文献
8.
Carbothermal Synthesis of Aluminum Nitride Using Sucrose 总被引:2,自引:0,他引:2
Youngmin Baik Kartik Shanker Joseph R. McDermid Robin A. L. Drew 《Journal of the American Ceramic Society》1994,77(8):2165-2172
Several aluminum oxides (α-Al2 O3 , θ-Al2 O3 , and AIOOH) were examined to study the differences in reaction behavior and powder characteristics during carbothermal nitrida-tion to AIN using sucrose and carbon black. The reaction conditions investigated were carbon-to-alumina ratio, reaction temperature, and time. Carburized sucrose resulted in Full conversion to AIN and produced a uniform powder morphology using a near-istoichiometric ratio of C:Al2 O3 while carbon black required higher C:Al2 O3 ratios (i.e., >4:1) for full conversion and led to agglomeration of the AIN powder. The most favorable reaction temperature was 1600°C, with the reaction time to full conversion being dependent on the type of Al2 O3 . The particle and agglomerate size of the AIN powders did not change significantly with reaction time. However, the particle size and morphology were strongly dependent on that of the initial AI2 O3 with sucrose, whereas agglomeration of the AIN occurs when using carbon black. A solid–solid reaction mechanism is proposed. 相似文献
9.
Calcium hexa-aluminate (CaO·6Al2 O3 ) has been prepared from calcium nitrate and aluminum sulfate solutions in the temperature range of 1000°–1400°C. A 0.3 mol/L solution of aluminum sulfate was prepared, and calcium nitrate was dissolved in it in a ratio that produced 6 mol of Al2 (SO4 )3 ·16H2 O for each mole of Ca(NO3 )2 ·4H2 O. It was dried over a hot magnetic stirrer at ∼70°C and fired at 1000°–1400°C for 30–360 min. The phases formed were determined by XRD. It was observed that CaO·Al2 O3 and CaO·2Al2 O3 were also formed as reaction intermediates in the reaction mix of CaO·6Al2 O3 . The kinetics of the formation of CaO·6Al2 O3 have been studied using the phase-boundary-controlled equation 1 − (1 − x )1/3 = K log t and the Arrhenius plot. The activation energy for the low-temperature synthesis of CaO·6Al2 O3 was 40 kJ/mol. 相似文献
10.
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
11.
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
12.
CHOWDARI R. KORIPELLA FERDINAND A. KRÖGER 《Journal of the American Ceramic Society》1986,69(12):888-896
High-temperature dc electrical conductivity and emf of oxygen concentration cells with A12 O3 as the electrolyte were studied. The defect structure of α-Al2 O3 doped with Fe and Y was investigated to test an explanation proposed for the favorable effect of Y addition to super alloys (Fe, Cr, Ni, Al) which leads to well-adherent and nonconvoluted A12 O3 oxide scales. Results indicate that Y is a singly ionizable donor in Al2 O3 and Y additions are effective in compensating Fe acceptors in A12 O3 at iron concentrations up to the solubility limit of Y. At higher acceptor concentrations leading to a decrease in [ V "'Al ] and an increase in [Al… i ], incorporation of Y leads to a small increase in the concentration of V'" Al . This suggests that the mechanism proposed for the prevention of oxide scale spallation based on the Y donor action to suppress the bulk diffusion of aluminum interstitials created by the Fe acceptors cannot explain the effect. Energy level positions of Fe and Y in A12 O3 are estimated, and values for electron and hole mobility at 1500°C are derived. 相似文献
13.
Zhizhan Chen Erwei Shi Wenjun Li Yanqing Zheng Nanchun Wu Weizhuo Zhong 《Journal of the American Ceramic Society》2002,85(12):2949-2955
Nanosized CoAl2 O4 and ZnAl2 O4 powders with particle sizes of 67 and 6.5 nm are synthesized under hydrothermal conditions at 245°C for 20 h. The precursors are reacted at different temperatures to provide intermediate phase transformations using X-ray diffraction (XRD), infrared (IR) spectra, and thermal gravity and differential thermal analysis (TG-DTA). XRD patterns and IR spectra demonstrate that the CoAl layered double hydroxide structure (CoAl-LDHs) is more stable than ZnAl layered double hydroxide structure (ZnAl-LDHs) when they are hydrothermally treated. The different thermal stability of the CoAl- and ZnAl-LDHs results in the different aluminum source, e.g., β-Al(OH)3 for ZnAl2 O4 vs γ-AlO(OH) for CoAl2 O4 , when the aluminate spinels are formed. The different aluminum sources lead to the particle size difference. The phenomenon is reasonably expounded based on the nucleation theory from the microscopic scale. 相似文献
14.
Inger-Lise Tangen Yingda Yu Tor Grande Ragnvald Høier Mari-Ann Einarsrud 《Journal of the American Ceramic Society》2004,87(9):1734-1740
AlN–AlN polytypoid composite materials were prepared in situ using pressureless sintering of AlN–Al2 O3 mixtures (3.7–16.6 mol% Al2 O3 ) using Y2 O3 (1.4–1.5 wt%) as a sintering additive. Materials fired at 1950°C consisted of elongated grains of AlN polytypoids embedded in equiaxed AlN grains. The Al2 O3 content in the polytypoids varied systematically with the overall Al2 O3 content, but equilibrium phase composition was not established because of slow nucleation rate and rapid grain growth of the polytypoid grains. The polytypoids, 24 H and 39 R , previously not reported, were identified using HRTEM. Solid solution of Y2 O3 in the polytypoids was demonstrated, and Y2 O3 was shown to influence the stability of the AlN polytypoids. The present phase observations were summarized in a phase diagram for a binary section in the ternary system AlN–Al2 O3 –Y2 O3 parallel to the AlN–Al2 O3 join. Fracture toughness estimated from indentation measurements gave no evidence for a strengthening mechanism due to the elongated polytypoids. 相似文献
15.
Microstructure and Properties of Co2+ : ZnAl2 O4 /SiO2 Nanocomposite Glasses Prepared by Sol–Gel Method
Xiu-Lan Duan Duo-Rong Yuan Xiu-Feng Cheng Hai-Qing Sun Zhi-Hong Sun Xin-Qiang Wang Zeng-Mei Wang Dong Xu Meng-Kai Lv 《Journal of the American Ceramic Society》2005,88(2):399-403
Transparent bulk Co2+ : ZnAl2 O4 /SiO2 nanocomposites containing nanocrystalline Co2+ : ZnAl2 O4 dispersed in silica glass matrix were obtained by the sol–gel method. The gels of composition 89SiO2 –6Al2 O3 –5ZnO− x CoO ( x =0.2, 0.4, 0.6, 0.8, 1.0) (mol%) were prepared at room temperature by using two different aluminum salts, aluminum nitrate and aluminum alkoxide (aluminum-iso-propoxide, Al(OPri )3 ), as starting materials. The transparent gels were converted to the crystalline phase of gahnite by heating above 900°C. The microstructural evolution of gels was characterized. The effect of Co2+ concentration on spectroscopic properties was also discussed. Co2+ : ZnAl2 O4 nanocrystals dispersed in the SiO2 -based glass are formed at lower heat-treatment temperature and shorter heating time by using Al(OPri )3 as raw material. 相似文献
16.
Formation of Titanium Carbide/Aluminum Oxide Nanocomposite Powder by High-Energy Ball Milling and Subsequent Heat Treatment 总被引:1,自引:0,他引:1
The preparation of titanium carbide/aluminum oxide (TiC/Al2 O3 ) nanocomposite powders from a mixture of titanium, carbon, and Al2 O3 powders via a high-energy ball milling process and subsequent heat treatment was investigated. The microstructure development of the powder mixtures was monitored by X-ray diffraction and transmission electron microscopy. The ball milling of an elemental carbon, titanium, and Al2 O3 powder mixture at ambient temperature resulted in the formation of TiC within 15 h of milling. With further milling of up to 25 h, the resulting powder mixture was composed of nanosized TiC particles and nanocrystalline carbon, titanium, and Al2 O3 . The nanocrystalline titanium and carbon were transformed into nanosized TiC particles after subsequent heat treatment. The final product was composed of nanosized TiC and microcrystalline Al2 O3. Most of the nanosized TiC particles were located within Al2 O3 grains. 相似文献
17.
Shinichi Kikkawa Naoya Hatta Takashi Takeda 《Journal of the American Ceramic Society》2008,91(3):924-928
Spinel-type AlON, Al2.75 □0.25 O3.74 N0.26 , was obtained by ammonia nitridation of an oxide precursor prepared by peptizing a glycine gel with aluminum nitrate. To achieve crystallization, the nitrided product had to be annealed at 1500°C for 10 min in flowing nitrogen. The use of glycine instead of citric acid was important for obtaining a white product without residual carbon. A similar preparation method was used for adding small amounts of europium below 10 mol%. A strong blue emission was observed for products ranging from 0.5 to 3.0 mol% Eu doping. The product with 0.5 mol% doping had a maximum emission intensity at 400 nm for an excitation of 254 nm. The products with 1 and 3 mol% doping showed double maxima at 475 and 520 nm. These three emissions were due to the presence of divalent europium in the EuAl12 O19 magnetoplumbite-like aluminum oxynitride impurity mixed with the AlON spinel major phase. The 1 mol% Eu-doped product exhibited expanded hexagonal lattice parameters ( a =0.5591 and c =2.236 nm) compared with the values for EuAl12 O19 magnetoplumbite itself, observed in the 7.7 mol%-doped product without any strong emission. The above spectrum change was discussed in relation to the coordination around Eu2+ . 相似文献
18.
A. C. D. CHAKLADER 《Journal of the American Ceramic Society》1961,44(4):175-180
The effect of additions of 0.22, 0.44, 0.88, and 1.76% A12 O3 (Si4+ /A13+ ratio of 200:1, 100:1, 50:1, and 25:1) on the transformation of Brazilian quartz to cristobalite was studied at 1500°, 1530°, and 1570°C. The smaller percentages of A12 O3 (0.22 and 0.44%) catalyzed the transformation of quartz and the formation of cristobalite considerably. The rates of transformation of quartz with 0.88 and 1.76% A12 O3 were slower than with 0.22 or 0.44%, indicating a critical A13+ /Si4+ ratio where the catalytic effect was found to be maximum. This appeared to occur at about 0.5% A12 O3 . The transformation rate of quartz indicated that the reaction was first order. Cristobalite, however, showed two different rates; the initial rapid growth was followed by a slower rate. The point of changeover was found to be at about 30 ± 5% cristobalite. The critical nature of the A13− /Si4+ ratio at about 0.01 (or A12 O3 /SiO2 ± 0.005) may have some bearing on the properties of silica refractories with more or less than 0.5% A12 O3 . 相似文献
19.
Examination of mixtures of extremely pure silica and alumina shows that the greatest reactivity is not encountered with stoichiometric ratios to form mullite with the formula 3Al2 O3 . 2SiO2 but rather with the formula 2A12 O3 -SiO2 , and that reactivity also depends on the crystalline modification of alumina. A sharp exothermic differential thermal peak at 980°C. is attributed to three simultaneous reactions dependent on the silica-alumina ratio of the mixture: (1) the crystallization of gamma alumina, (2) the crystallization of a hydrogen aluminum spinel (HAl5 O5 ), and (3) the reaction of silica with the hydrogen aluminum spinel to form mullite. 相似文献
20.
Haiyan Liu Morris E. Fine H. S. Cheng Alan L. Geiger 《Journal of the American Ceramic Society》1994,77(1):179-185
Lubricated rolling wear studies of SiC-whisker (SiCw ) reinforced A12 O3 composites and monolithic A12 O3 against M2 tool steel were conducted using a cylinder-on-cylinder apparatus. The composites wore considerably less than A12 O3 . The wear of the tool steel against the composites was also considerably less than against A12 O3 . Microfracture occurred on a smaller scale in the composites than in the Al2 O3 . This was attributed to the differences in microstruc-ture and fracture toughness. The worn surfaces of the steel and the composites were polished, possibly due to fine, hard wear debris circulating with the lubricant to the contact area. 相似文献