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1.
Hans Wohlfromm Pilar Pena José S. Moya Joaquín Requena 《Journal of the American Ceramic Society》1992,75(12):3473-3476
Al2 TiO5 formation in Al2 O3 /TiO2 multilayer composites obtained by slip casting has been studied in the temperature interval ranging from 1200° to 1450°C. It has been found that nucleation plays a fundamental role in Al2 TiO5 formation. Furthermore, it has been observed that initial growth of Al2 TiO5 is substantially enhanced when in contact with TiO2 . 相似文献
2.
In the system TiO2 —Al2 O3 , TiO2 (anatase, tetragonal) solid solutions crystallize at low temperatures (with up to ∼ 22 mol% Al2 O3 ) from amorphous materials prepared by the simultaneous hydrolysis of titanium and aluminum alkoxides. The lattice parameter a is relatively constant regardless of composition, whereas parameter c decreases linearly with increasing Al2 O3 . At higher temperatures, anatase solid solutions transform into TiO2 (rutile) with the formation of α-Al2 O3 . Powder characterization is studied. Pure anatase crystallizes at 220° to 360°C, and the anatase-to-rutile phase transformation occurs at 770° to 850°C. 相似文献
3.
Byong-Taek Lee Rajat Kanti Paul Hyun-Jin Hong Kap-Ho Lee 《Journal of the American Ceramic Society》2009,92(4):911-915
Using a multipass extrusion process, continuous porous Al2 O3 body (∼41% porosity) was produced and used as a substrate to fabricate continuous porous TiO2 /Al2 O3 composite membrane. The diameter of the continuous pores of the porous Al2 O3 body was about 150 μm. The TiO2 nanopowders dip coated on the continuous pore-surface Al2 O3 body existed as rutile and anatase phases after calcination at 520°C in air. However, after aging of the fabricated continuous porous TiO2 /Al2 O3 composite membrane in 20% NaOH at 60°C for 24 h, a large number of TiO2 fibers frequently observed on the pore surface. The diameter of the TiO2 fibers was about 150 nm having a high specific surface area. However, after 48-h aging period, the diameter of the TiO2 fibers increased, which was about 3 μm. Most of the TiO2 fibers had polycrystalline structure having nanosized rutile and anatase crystals of about 20 nm. 相似文献
4.
Subsolidus phase relationships in the Ga2 O3 –Al2 O3 –TiO2 system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO2 (rutile), Ga2−2 x Al2 x O3 ( x ≤0.78 β-gallia structure), Al2−2 y Ga2 y O3 ( y ≤0.12 corundum structure), Ga2−2 x Al2 x TiO5 (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga4−4 x Al4 x Ti n −4 O2 n −2 ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work. 相似文献
5.
Alumina–aluminum titanate–titania (Al2 O3 –Al2 TiO5 –TiO2 ) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al2 O3 –TiO2 nanocomposite, while at a higher temperature (1300°C) an Al2 O3 –Al2 TiO5 –TiO2 nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties. 相似文献
6.
Heromichi Okamura Eric A. Barringer H. Kent Bowen 《Journal of the American Ceramic Society》1986,69(2):22-C-
An unagglomerated, monosized Al2 O3 TiO2 composite powder was prepared by the stepwise hydrolysis of titanium alkoxide in an Al2 O3 dispersion. Particle size was controlled by selecting the particle size of the starting Al2 O3 powder; TiO2 content was determined by the amount of alkoxide hydrolyzed. A composite-powder compact containing 50 mol% TiO2 , when fired at 1350°C for 30 min, showed nearly theoretical density with aluminum titanate phase formation. 相似文献
7.
Reaction kinetics in a coarse equimolar powder mixture were slow enough to allow for the different stages to be identified, notably in the lower and higher temperature ranges, respectively. In the former ( T ≤ 1600 K), Al2 TiO5 nucleation was hindered by the strain energy contribution to the overall driving force. The setting up of metastable layer sequences Al2 TiO5 /TiO2 /Al2 O3 was found to occur generally during subsequent growth. The high Al mobility in the TiO2 provided a rapid aluminum transport from the metastable Al2 O3 /TiO2 interface to the TiO2 /Al2 TiO5 front. At temperatures above ∼1700 K the Al2 O3 /TiO2 interface was very rapidly sealed off by Al2 TiO5 formation. Reactant transport across the Al2 TiO5 was slow because of the low mobilities in the product phase. Therefore, much lower product growth velocities were observed at higher temperatures than at lower temperatures. 相似文献
8.
Compatible phases in the system Li2 O-Al2 O3 -TiO2 at various temperature levels were determined mainly by solid-state reactions for the portion of the ternary system bounded by Li2 O Al2 O2 , Li2 O.TiO2 , Al2 O, and TiO2 . The existence of a ternary compound, Li2 O.Al2 O3 .4TiO2 , and nine joins was established. The ternary compound has a lower limit of stability at 1090°± 15°C. and dissociates and recombines rapidly at 1380°± 15°C. 相似文献
9.
Mark I. Pownceby Keri K. Constanti-Carey Michael J. Fisher-White 《Journal of the American Ceramic Society》2003,86(6):975-980
Subsolidus phase equilibria in the system Fe2 O3 –Al2 O3 –TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3 O5 solid solution series between end members Fe2 TiO5 and Al2 TiO5 , (b) a miscibility gap along the Fe2 O3 –Al2 O3 binary, (c) an α-M2 O3 ( ss ) ternary solid-solution region based on mutual solubility between Fe2 O3 , Al2 O3 , and TiO2 , and (d) an extensive three-phase region characterized by the assemblage M3 O5 +α-M2 O3 ( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe2 O3 –Al2 O3 –TiO2 system shows considerable discrepancy. 相似文献
10.
Daniele Mazza Mario Vallino Guido Busca 《Journal of the American Ceramic Society》1992,75(7):1929-1934
A morphous solids belonging to the systems Al2 O3 –Me2 O (Me = Na, K) and Al2 O3 –B2 O3 were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850° to 900°C for the compositions Al6 Mex O(9+0.5 x ) ( x ≅ 1; Me = Na, K) and Al6- x B x O9 (1 x 3). The resultant solids were stable only within a difinite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na+ , K+ ) or (2) substitution of B for Al in some of the tetrahedral positions. 相似文献
11.
High-purity polycrystalline MgO and Al2 O3 were thermally grooved at 1500° and 1600°C. Accurate techniques were developed for following the growth of a single groove. For high-purity samples growth kinetics were essentially similar to those reported in the literature but were determined to be controlled by volume diffusion. Specimens for thermal grooving were prepared from Al2 O3 to which transition metal oxides (Fe2 O39 , MnO, and TiO2 ), which are known to accelerate shrinkage and sintering of Al2 O3 powder compacts, had been added; the rate of groove growth was increased remarkably by minor amounts of these additives. Control of partial pressure indicated that Fe2+ and Ti4+ are the species active in promoting groove growth. Substantial evidence was found for volume diffusion as the mechanism controlling groove formation. 相似文献
12.
J. P. COUTURES 《Journal of the American Ceramic Society》1985,68(3):105-107
A tentative phase diagram for the system Al2 03 -Nd2 O3 is presented. Three compounds were obtained: a β -A12 O3 -type compound, the perovskite NdAlO3 , and Nd4 Al2 O9 . The perovskite melts congruently (mp 2090°C), and the two other compounds exhibit incongruent melting behavior: β -Nd/Al2 O3 , mp 1900°C; Nd4 Al2 O9 , mp 1905°C. Two eutectics exist with the following compositions and melting points: 80 mol% Al2 O3 , 1750°C; 23 mol% Al2 O3 ,1800°C. Nd4 Al2 O9 decomposes in the solid state at 1780°C. 相似文献
13.
A liquid phase in the Al2 O3 -1 mol% TiO2 -0.5 mol% NaO1/2 composition is confirmed at ±1300°C by an electrical conductivity measurement. The ease of the method led to a study of the Al2 O3 -2 mol% CuO-2 mol% TiO2 system and to the geologically important detection of eutectics (peritectics) in rock materials. 相似文献
14.
Susumu Nishigaki Shinsuke Yano Hiroshi Kato Takami Hirai Toshio Nonomura 《Journal of the American Ceramic Society》1988,71(1):11-C-
Microwave ceramic resonators composed of BaO-TiO2 -WO3 were developed. The effect of WO3 addition on the system of BaO·xTiO2 ·(1+x)yWO3 (x=4 and 4.5, y=0 to 0.04) was studied. The ceramics of this system are composed of crystallines including Ba2 Ti9 O20 , BaTi4 O9 , BaWO4 , and TiO2 . At y=0.02, the BaO·4TiO2 ·0.1WO3 ceramic was found to have excellent microwave properties such as ε=35, Q=8400 at 6 GHz, and nearly 0 ppm/°C of τf . 相似文献
15.
Adam J. G. Ellison Paul C. Hess Gerald C. Naski 《Journal of the American Ceramic Society》1998,81(12):3215-3220
The saturation surface of cassiterite, SnO2 , was determined for liquids in the system K2 O–Al2 O3 –SiO2 as a function of bulk composition and temperature. At fixed K2 O/Al2 O3 cassiterite solubility varies weakly with SiO2 concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f O 2 ) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K2 O/Al2 O3 lessthan equal to 1 (peraluminous liquids). As K2 O/Al2 O3 increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K2 O in excess of Al2 O3 . It is proposed that potassium in excess of aluminum combines with Sn4+ to form quasi-molecular complexes with an effective stoichiometry of K4 SnO4 . 相似文献
16.
HIROSHI HIRASHIMA KOTA NISHII TETSURO YOSHIDA 《Journal of the American Ceramic Society》1983,66(10):704-708
The dc conductivities (σ) of V2 O5 -P2 O5 glasses containing up to 30 mol% TiO2 were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 106 Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V2 O5 -P2 O5 glass. The temperature dependence of σ was exponential with σ = σ0 exp(-W/kT ) in the high-temperature range. When part of the P2 O5 was replaced by TiO2, σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO2 content. 相似文献
17.
The system TiO2 -P2 O5 was investigated in the compositional range TiO2 .P2 O5 to 100% TiO2 . Two compounds exist, TiO2 .P2 O5 and 5TiO2 .-2P2 O5 . TiO2 .P2 O5 begins to lose P2 O5 at 1400°C. and both fusion and vaporization proceed rapidly at 1500°C. 5TiO2 .2P2 O6 melts congruently at 1260°± 3°C. to a glass which can be retained in substantial quantities at room temperature. Physical properties of certain compositions are described. 相似文献
18.
This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li2 O·9Al2 O3 ·38 TiO2 ·39P2 O5 glass–ceramic and polyethylene. The processing involved tape casting of 14Li2 O·9Al2 O3 ·38TiO2 ·39P2 O5 glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 950°–1100°C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150–350 μm thick membranes were characterized and are discussed in this paper. The crystallites of the glass–ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO4 at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity. 相似文献
19.
Adiabatic bulk modulus, Bs , of polycrystalline MgO and Al2 O3 was measured from 298° to 1473°K using the resonance technique. The Grüneisen constant, calculated from the measured bulk modulus, was constant over the whole temperature range (1.53 for MgO and 1.34 for Al2 O3 ). Another important parameter, , is constant at high temperature and is 3.1 for MgO and 3.6 for Al2 O3 . The Poisson's ratio increases linearly with temperature for MgO and Al2 O3 . To describe the change of bulk modulus with temperature a theoretical equation was verified by using the foregoing constants. A practical form of this theoretical equation is where Bs 0 is the adiabatic bulk modulus at 0°K, δ is the quantity , γ is the Grüneisen constant, H is the enthalpy. The experimental data are described very well by this equation, which is equivalent to the empirical equation suggested by Wachtman et al., Bs T = Bs 0 - CT exp (-Tc /T) , where C and Tc are empirical constants. 相似文献
20.
Koji Takahashi Masahiro Yokouchi Sang-Kee Lee Kotoji Ando 《Journal of the American Ceramic Society》2003,86(12):2143-2147
Al2 O3 reinforced by SiC whiskers (Al2 O3 /SiC-W) was hot-pressed to investigate the crack-healing behavior. Semielliptical surface cracks of 100 μm in surface length were introduced using a Vickers indenter. The specimens containing precracks were crack-healed at temperatures between 1000° and 1300°C for 1 h in air, and their strengths were measured by three-point bending tests at room temperature and elevated temperatures between 400° and 1300°C. The results show that Al2 O3 /SiC-W possesses considerable crack-healing ability. The surface cracks with length of 2 c = 100 μm could be healed by crack-healing at 1200° or 1300°C for 1 h in air. Fracture toughness of the material was also determined. As expected, the SiC whiskers made their Al2 O3 tougher. 相似文献