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1.
Physical properties of advanced ceramics are influenced by impurities produced in the forming process. The forming compacts produced by slip casting using gypsum molds contain calcium and sulfur in green bodies. Therefore, a porous Al2O3-glass mold was produced and slip casting was performed in the present study. Porous Al2O3 ceramics as casting molds were examined in comparison with gypsum mold from viewpoints of free energy for wettability and rate of filter cake buildup. The sintered compact of Al2O3 produced by slip casting using the porous Al2O3-glass mold was compared with those using the gypsum mold. Transmittance of the sintered Al2O3 compacts using the porous Al2O3-glass molds was increased in comparison with that using the gypsum mold. 相似文献
2.
Shih-Cheng Chuang Cheng-Tzu Kuo Chi-Ting Ho Al-Kang Li 《Journal of Materials Science》1992,27(22):6213-6218
In situ formation of TiB2 in Al2O3 matrix through the reaction of TiO2, boron and carbon has been studied. In hot-pressed samples, in addition to TiB2, TiC and Al2TiO5 were also found to be dispersed phases in Al2O3 matrix. However, in the case of pressureless-sintered samples, pure Al2O3/TiB2 composite with > 99% relative density can be obtained through a preheating step held at 1300°C for longer than 30 min and then sintering at a temperature above 1500°C. Pressureless-sintered composite containing 20vol% TiB2 gives a flexural strength of 580 MPa and a fracture toughness of 7.2 MPa m1/2. 相似文献
3.
Equimolar Al2O3-TiO2 composite powders were prepared via controlled hydrolysis of organometallic precursors, sometimes in the presence of submicrometre commercial-Al2O3 or anatase-TiO2 particles. Variations in the chemical procedures were used aimed at different submicrostructures within the resulting powders. Heating such powders in air shows that structural behaviour is influenced by the micromorphology of the composite particle. Transformation temperatures of the titania phases seem to depend upon some size parameter which would represent their morphology within the powders. Studies performed on a series of non-equimolar Al2O3-TiO2 composite powders showed that the temperature of -Al2O3 formation may be decreased by 210° C possibly due to a seeding effect of rutile. Pseudobrookite Al2TiO5 was never detected at 1300° C in air. 相似文献
4.
Novel biomaterials are of prime importance in tissue engineering. Here, we developed novel nanostructured Al2TiO5–Al2O3–TiO2 composite as a biomaterial for bone repair. Initially, nanocrystalline Al2O3–TiO2 composite powder was synthesized by a sol–gel process. The powder was cold compacted and sintered at 1300–1500 °C to develop nanostructured Al2TiO5–Al2O3–TiO2 composite. Nano features were retained in the sintered structures while the grains showed irregular morphology. The grain-growth and microcracking were prominent at higher sintering temperatures. X-ray diffraction peak intensity of β-Al2TiO5 increased with increasing temperature. β-Al2TiO5 content increased from 91.67% at 1300 °C to 98.83% at 1500 °C, according to Rietveld refinement. The density of β-Al2TiO5 sintered at 1300 °C, 1400 °C and 1500 °C were computed to be 3.668 g cm?3, 3.685 g cm?3 and 3.664 g cm?3, respectively.Nanocrystalline grains enhanced the flexural strength. The highest flexural strength of 43.2 MPa was achieved. Bioactivity and biomechanical properties were assessed in simulated body fluid. Electron microscopy confirmed the formation of apatite crystals on the surface of the nanocomposite. Spectroscopic analysis established the presence of Ca and P ions in the crystals. Results throw light on biocompatibility and bioactivity of β-Al2TiO5 phase, which has not been reported previously. 相似文献
5.
Heguo Zhu Yaling Jiang Jinzhu Song Jianliang Li Paul Munroe Zonghan Xie 《Journal of Materials Science》2013,48(2):929-935
A hierarchically structured α-Al2O3/Al3Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO2. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti2O3, and γ-Al2O3, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO2 occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al2O3/Al3Ti composites. 相似文献
6.
Hideyuki Yoshimatsu Koji Kawabata Akiyoshi Osaka Yoshinari Miura Hitoshi Kawasaki 《Journal of Materials Science》1996,31(18):4975-4980
Organic precursors containing Al and Zr atoms were synthesized from an aluminium chelate compound and zirconium n-butoxide. A ZrO2-Al2O3 composite powder was prepared by the thermal decomposition of these precursors. An amorphous phase exists to higher temperatures for this ZrO2-Al2O3 powder than for a comparable powder prepared from aluminium sec-butoxide and zirconium n-butoxide. In addition the tetragonal ZrO2 phase was stabler in this ZrO2-Al2O3 powder than in a comparison powder. The ZrO2 grains were 50–500 nm in diameter and were homogeneously dispersed in the Al2O3 matrix after heating at 1400 °C. 相似文献
7.
The sintering characteristics of SiO2-36.6 wt % Al2O3 powder, prepared by condensation from high frequency plasma, have been studied and microstructural changes occurring during sintering followed by transmission electron microscopy The as-prepared amorphous powder showed evidence of spinodal decomposition into an Al2O3-rich and SiO2-rich glass consistent with the position of a previously reported metastable miscibility gap in the SiO2-Al2O3 system. Mullite crystallized on an extremely fine scale at 1000° C and gradually coarsened at higher temperatures. Sintering occurred above 1100° C by a viscous flow mechanism with activation energy 87 kcal mol–1 which corresponds to the activation energy for viscous flow of SiO2-Al2O3 glass containing approximately 17 wt % Al2O3. 相似文献
8.
The morphology and phase constitution of sub-micron Al2O3-TiO2 powders prepared by oxidation of mixtures of Al2Br6 and TiCl4 in an oxygen-argon high-frequency plasma have been studied. The particle size and distribution were consistent with formation of liquid particles by rapid nucleation and surface reaction followed by growth by coalescence of droplets. The particle size of the powders is related to the concentration of reactants in the gas stream and the temperature difference between condensation and solidification. A metastable solution of TiO2 in -Al2O3 was formed in the range 0 to 7 wt% TiO2, at higher TiO2 concentrations particles consisted of a dispersion of rutile particles (~ 10 nm) within single crystals of -Al2O3. A metastable phase identified as 3Al2O3·TiO2 was also formed in powder with compositions in the range 14 to 40 wt% TiO2. Over the composition range 40 to 80 wt% TiO2 the powder consisted predominantly of crystals with a two-phase Al2TiO5-rutile structure. Pure TiO2 consisted largely of anatase and the addition of Al2O3 resulted in the formation of rutile as the major phase. The phase constitution of the powders is interpreted in terms of the nucleation kinetics of the various phases. 相似文献
9.
M. Kobayashi T. Meguro K. Komeya T. Yokoyama J. Funahashi T. Kameda 《Journal of Materials Science》2000,35(16):4129-4136
The effect of TiO2 content on the oxidation of sintered bodies from the conventional Si3N4-Y2O3-Al2O3-AlN system was investigated. Sintered specimens composed of Si3N4, Y2O3, Al2O3, and AlN, with a ratio of 100 : 5 : 3 : 3 wt% and containing TiO2 in the range of 0 to 5 wt% to Si3N4, were fabricated at 1775 °C for 4 h at 0.5 MPa of N2. Oxidation at 1200 to 1400 °C for a maximum of 100 h was performed in atmospheres of dry and wet air flows. The relation between weight gain and oxidation time was confirmed to obey the parabolic law. The activation energies decreased with TiO2 content. In the phases present in the specimens oxidized at 1300 °C for 100 h in dry air, Y3Al5O12 and TiN, which had existed before oxidation, disappeared. Alpha-cristobalite and Y2O3·2TiO2 (Y2T) appeared in their place and increased with increasing TiO2 content. In those oxidized at 1400 °C, -cristobalite was dominant and very small amounts of Y2O3·2SiO2 and Y2T were contained. There was a tendency for more -cristobalite to form in oxidation in wet air than in dry air. Therefore, moisture was confirmed to affect the crystallization of SiO2 formed during oxidation. Judging from the lower activation energy, the crystallization, and the pores formation, we concluded that the addition of TiO2 decreases oxidation resistance. 相似文献
10.
Gong HongyuYin Yansheng Li AijuLiu Yingcai Zhen YuhuaLi Chunsheng 《Materials Research Bulletin》2002,37(9):1603-1611
The (AlN, TiN)-Al2O3 composites were fabricated by reaction sintering powder mixtures containing 10-30 wt.% (Al, Ti)-Al2O3 at 1420-1520°C in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the Al, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (Al, Ti)-Al2O3 powder in nitrogen in 1520°C for 30 min yields (AlN, TiN)-Al2O3 composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa m1/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of Al2O3. The AlN identified by XRD was not directly observed, but probably resides at the Al2O3 grain boundary. The fracture mode of these composites was observed to be transgranular. 相似文献
11.
An investigation has been made of the constitution of laser-processed ceramics from the SiO2-Al2O3 system. Samples were produced in the form of pellets a few millimetres in diameter by pulsed laser melting of mixtures of silica and alumina powders containing 40, 60 and 70 mol % Al2O3. X-ray diffraction identified the main crystalline phases as Al2O3 in the pellets produced from the 70 mol % Al2O3 mixture and mullite from the 60 and 40 mol % Al2O3 mixtures. The proportion of glassy phase present increased with increasing SiO2 content. Microstructural observations on the 60 mol % Al2O3 pellet showed primary mullite crystals and a lamellar structure interpreted as a eutectic of Al2O3 and mullite. Pellets prepared by melting kaolin powder consisted essentially of a glassy phase and much porosity. Cladding of an alumina substrate, carried out using a continuous powder feed into a laser-generated melt pool, was carried out using the same silica-alumina mixtures as those employed for pellet production. A clad layer was also produced by preplacing a kaolin coat on the alumina substrate prior to laser processing. The effects of traverse speed over the range 3.7 to 7.4 mm s?1 inclusive, power density (44.4 and 111 W mm?2) and powder flow rate (0.13 to 0.47 g s?1 inclusive) were investigated. It was found that the phases present in the clad layer depended on the composition of the precursor powder and the processing conditions. Microstructural examination of the clad layers produced from SiO2-60 mol % Al2O3 and kaolin that had completely melted during processing exhibited various growth morphologies. 相似文献
12.
Wen-Cheng Tzou Sang-Li ChangCheng-Fu Yang Ying-Chung Chen 《Materials Research Bulletin》2003,38(6):981-989
The microwave characteristics and the microstructures of 0.88Al2O3-0.12TiO2 with various amounts of MgO-CaO-SiO2-Al2O3 (MCAS) glass sintered at different temperatures have been investigated. The sintering temperature can be lowered to 1300 °C by the addition of MCAS glass. The densities, dielectric constants (εr) and quality values (Q×f) of the MCAS-added 0.88Al2O3-0.12TiO2 ceramics decrease with the increase of MCAS glass content. The temperature coefficients of the resonant frequency (τf) are shifted to more negative values as the MCAS content or the sintering temperatures increase. The change of the crystalline phases of Al2TiO5 phase and rutile-TiO2 phase has profound effects on the microwave dielectric properties of the MCAS-added Al2O3-TiO2 ceramics. As sintered at 1250 °C, 0.88Al2O3-0.12TiO2 ceramics with 2 wt.% MCAS glass addition exists a εr value of 8.63, a Q×f value of 9578 and a τf value of +5 ppm/°C. 相似文献
13.
V. Buscaglia M. Alvazzi Delfrate M. Leoni C. Bottino P. Nanni 《Journal of Materials Science》1996,31(7):1715-1724
The formation of Al2(1–x)Mg
x
Ti(1+x)O5 solid solutions from Al2O3-TiO2-MgAl2O4 powder mixtures of 1 m particle size and moderate purity has been studied at 1300°C for different final composition values: x=0 (pure Al2TiO5), 10–3, 10–2 and 10–1. Analysis of the kinetic data and microstructural observation indicates that MgAl2O4 affects the mechanism of Al2TiO5 formation by providing active nuclei for the growth of the new phase. These nuclei are probably constituted by Mg0.5AlTi1.5O5, i.e. the equimolar Al2TiO5-MgTi2O5 solid solution, and are formed by reaction between MgAl2O4 and TiO2 at temperatures above 1150 °C. As the value of x increases, the number of titanate particles per unit volume accordingly increases and the conversion of the original oxides is faster. At values of x10–2, the prevailing mechanism is the nucleation and growth of Al2TiO5 nodules for fractional conversion up to 0.8. Further conversion of the residual Al2O3 and TiO2 particles dispersed into the titanate nodules is slower and controlled by solid-state diffusion through Al2TiO5. At x=0.1, a large number of nucleation sites is present, and solid-state diffusion through Al2TiO5 becomes important even in the initial stage of reaction, as the diffusion distances are strongly reduced. The study of Al2TiO5 formation under non-isothermal conditions in the temperature range 1250–1550°C shows that reaction proceeds between 1300 and 1350 °C for x=0.01 and between 1250 and 1300 °C for x=0.1. Densification of the titanate becomes important at temperatures above 1300°C for x=0.1, but only above 1450 °C for x=0.01. 相似文献
14.
The effect of calcination on the characteristics and sintering behaviour of zirconia-toughened alumina (ZTA) composite powders has been investigated. TiO2 was selected as an additive to promote the sinterability of ZTA powders. The starting materials were Al2O3 powder, Zr(OC3H7)4 and Ti(OC3H7)4, and homogeneous ZTA powder containing Zr-O-Ti bonding was prepared. Calcination affected the tetragonalmonoclinic phase transformation temperature of ZrO2 crystallizing from the gels. Calcination improved the densification rate of ZTA powder compact during sintering, which was attributed to the optimal ZrO2 particle size and distribution on the surface of alumina. A ZTA specimen with high bulk density and high tetragonal ZrO2 content was obtained under the conditions of 850°C/1 h calcination and 1500°C/1 h sintering. 相似文献
15.
《Virtual and Physical Prototyping》2013,8(4):371-381
ABSTRACTAl2O3-based composite ceramics have excellent high temperature performance and are ideal materials for preparing hot end components. However, poor fracture toughness and thermal shock resistance limit its applications. Based on the excellent low thermal expansion characteristics and thermal shock resistance of Al2TiO5 ceramic, different composition ratios of Al2O3/Al2TiO5 composite ceramics were prepared by directed laser deposition (DLD) technology. Effects of TiO2 doping amount on microstructure and properties of the composite ceramics were investigated. Results show that α-Al2O3 phase is discretely distributed in the continuous aluminum titanate matrix when TiO2 doping amount between 2 and 30?mol%. With the increase of TiO2 doping amount, content of Al2O3 gradually decreases and its morphology changes from cellular to dendritic. When TiO2 doping amount reaches 43.9?mol%, the microstructure transforms into fine Al2TiO5/Al6Ti2O13 eutectic structure. Property test results show that Al2O3/Al2TiO5 composite ceramics have good comprehensive mechanical properties when TiO2 doping amount between 2 and 6?mol%. 相似文献
16.
Nanostructured, γ-Al2O3/TiO2 composite powder was fabricated via an in situ, sol–gel reaction of titanium iso-propoxide in a self-assembled, polyelectrolyte multilayer (PEM) formed on the surface of high-specific-area, polycrystalline, γ-Al2O3 lamellas. The infiltration of the titanium precursor into the PEM, followed by the hydrolysis and condensation reactions with the water absorbed in the PEM after annealing, resulted in the formation of a nanostructured TiO2 layer on the surface of the γ-Al2O3 lamellas. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were employed to evaluate the morphology, the chemical composition and the crystallinity of the γ-Al2O3/TiO2 particles of the composite powder. The as-formed, nanostructured, γ-Al2O3/TiO2 composite powder exhibited a 2.7-times-higher photo-activity in the near-UV region compared to commercially available TiO2 (Degusa P25), as monitored by the photo-decomposition of a methylene blue (MB) dye. 相似文献
17.
High-energy milling was used for production of Cu–Al2O3 composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al2O3 powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al2O3 particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al2O3 particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al2O3 particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al2O3 composites. 相似文献
18.
SiO2-Al2O3 binary glass powders with Al2O3 contents up to 50 wt% have been synthesized by the sol-gel process. The starting solution (sol) consisted of 1 mole of tetraethoxysilane, 50 moles of water containing aluminum nitrate, 10 moles of ethyl alcohol and 0.02 moles of HCl catalyst. The sol was converted into gel by heating at 85°C and suction by running water. The sintering process was analysed by DTG thermal analysis. The fired powders were examined by XRD. It was confirmed that the gels were converted into the glass structure without crystallization. The measurements of refractive index and powder size of fired powders revealed that these powders could be used as refractive-index-adjustable fillers for dental composite resins. The other potential usage of the SiO2-Al2O3 powders obtained might be in the production of powders for dental cements.To whom correspondence should be addressed at Osaka University, Faculty of Dentistry, Department of Dental Technology, 1-8 Yamadaoka, Suita, Osaka 565, Japan. 相似文献
19.
The effect of various preparative parameters, such as the size and form of alumina and also the time of sintering, on the electrical conductivity of the Li2SO4-Al2O3 composite system has been investigated. The sintering time appears to be an insignificant preparative parameter. The role of different phases of Al2O3 on the electrical conductivity of the composite clearly establishes that the maximum enhancement is achieved for γ-Al2O3. The 50 m/o Al2O3 composition was found to exhibit the highest conductivity, an enhancement of three orders of magnitude at 500°C. The experimental data indicates higher conduction in the space charge layer near the surface to be the possible mechanism of conductivity enhancement. 相似文献
20.
In this paper, the TiO2/Al2O3 composite nanoparticles were prepared by a hydrothermal method and in situ modified with acrylic acid. It was found that the mean particle size of modified TiO2/Al2O3 composite nanoparticles was about 80 nm with a uniform distribution by the particle size analysis. The modified TiO2/Al2O3 composite nanoparticles can disperse in lubricating oil homogenously for several weeks. The dispersion stabilization of modified TiO2/Al2O3 composite nanoparticles in lubricating oil was significantly improved in comparison with the as-prepared nanoparticles, which was due to the introduction of grafted polymers by surface modification. The formation of covalent bands was identified by Fourier transform infrared spectrum. Under an optimized concentration of 0.1 wt%, the averaged friction coefficient was reduced by 14.75%, when the modified TiO2/Al2O3 composite nanoparticles were used as lubricating oil additivities. 相似文献