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1.
The presence of TiC or TiN paritcles in an Al2 O3 matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤ T ≤ 1100°C. At low temperatures ( T < 900°C), the oxidation follows a phase-boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO2 rutile crystals that subsequently grow and coalesce. When a continuous TiO2 rutile layer is formed ( T ≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O2 through a thick TiO2 layer is proposed as the governing step. 相似文献
2.
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
3.
Auger Electron Spectroscopy Analysis of Cross-Section Surface of Oxidized Titanium Carbide Single Crystal 总被引:2,自引:0,他引:2
Alessandra Bellucci Daniele Gozzi † Takashi Kimura Tetsuji Noda Shigeki Otani 《Journal of the American Ceramic Society》2003,86(12):2116-2121
A TiC monocrystal was heated by three thermal cycles with isotherm at 1108 K while exposed to Ar/O2 mixtures respectively with O2 contents of 239, 1.0, and 324 ppm. The reactivity was detected with a homemade device based on two identical solid electrolyte oxygen sensors connected to a quadrupole mass spectrometer (QMS). The oxidized sample was cleaved by impact bending under high vacuum and the cross section investigated by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) techniques. Both area and profile AES spectra were acquired by using a 70 nm diameter beam. Spectral changes have been analyzed to identify chemical species present at the TiC/TiO2 interface. A model for high-temperature oxidation of TiC has been proposed. It implies oxygen diffusion through a protective TiO2 layer and the existence of two inner interfaces: TiC/TiC1− x O x and TiC1− x O x /TiO2 . 相似文献
4.
Yong Ming Luo Shu Qin Li Jian Chen Rui Gang Wang Jian Qiang Li Wei Pan 《Journal of the American Ceramic Society》2002,85(12):3099-3101
In the present study, the room-temperature properties of Al2 O3 -Ti3 SiC2 composites with different Ti3 SiC2 contents are determined. The composites are prepared by attrition milling Al2 O3 and Ti3 SiC2 mixture powders followed by spark plasma sintering (SPS) under vacuum. From a closer examination of the dependencies of the electrical conductivity on compositions in this system, we determined the percolation threshold at which an interconnected network of electrically conductive phase arises. Since the hardness of Ti3 SiC2 is lower than that of Al2 O3 , the Vickers hardness decreased with the increasing of Ti3 SiC2 content while the fracture toughness and the strength increased. The maximum strength (673 MPa) and the maximum toughness (9.3 MPa·m1/2 ) were reached in the pure Ti3 SiC2 material. 相似文献
5.
The phase domain of Ti3 O5 –Ti2 O3 –Ti(CO) at 1580 K was determined from the formation energies of Ti(C x O y ), as calculated via the Gibbs–Duhem equation. An extensive Ti(CO) domain is attributed to the high affinity between TiC and TiO. The phase domain of Ti3 O5 –Ti2 O3 –Ti(CN) was obtained at 1673 K using the formation energies of Ti(C x N y ). This study shows that the stable region for Ti2 O3 is significantly small in the Ti3 O5 –Ti2 O3 –Ti(CN) phase domain. It demonstrates the absence of TiO and Ti2 O3 in the normal syntheses of TiC and Ti(CN) from TiO2 , respectively. 相似文献
6.
Photoluminescence Probing of the Formation of Titanium Dioxide Sols from a Titanium Peroxide Solution 总被引:1,自引:0,他引:1
Photoluminescence spectroscopy was used to probe the formation of colloidal TiO2 sols from a titanium peroxide solution, which were prepared by reaction of H2 O2 and titanium hydrate gel that was precipitated from acidic TiOCl2 solution neutralized by NH4 OH, during aging at 100°C for 0–64 h. Emission spectra revealed broad band luminescence which is interpreted as the superposition of a multiple photoluminescence process involving TiO2 precursors. The maximum peak position of the luminescence band was shifted to a shorter wavelength by the generation of the dominant emission peak as aging time increased, and a peak at ∼390 nm, indicating the anatase phase, was observed after aging for >48 h. However, sols aged for 2 h already were of the anatase phase, according to X-ray diffraction analysis. It was deduced that the interfacial layers between the particles and the liquid in an aqueous solution caused luminescence quenching or accelerated sink. 相似文献
7.
Dmitri Brodkin Antonios Zavaliangos Surya R. Kalidindi Michel W. Barsoum 《Journal of the American Ceramic Society》1999,82(3):665-672
Ambient- and high-temperature properties of a class of titanium carbide-titanium boride composites that have been produced by transient plastic phase processing are presented. The composites produced are comprised of Ti3 B4 , TiB2 , and TiC0.65 at their equilibrium composition (34.5, 30.5, and 34.9 vol%, respectively), and the Ti3 B4 phase in these composites occurs either as equiaxed grains or as platelets, depending on the starting mixture composition. Measurements of the ambient- and high-temperature flexure strength and fracture toughness, thermal shock susceptibility, oxidation resistance, and wear resistance of this class of composites are presented. The role of various microstructural parameters—such as the morphology of the Ti3 B4 phase, the length scale of the microstructure, and the volume fraction of borides—on these properties has been identified. 相似文献
8.
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
9.
Interstitial titanium-chromium oxynitrides in the solid solution series Ti1− z Cr z (O x N y ) ( z = 0.2, 0.4, 0.5, 0.6, 0.8) have been obtained by ammonolysis of the TiO2 /Cr2 O3 precursors resulting from the coprecipitation method. The precursors and the resulting oxynitrides were characterized by auger electron spectroscopy, X-ray diffraction analysis, electron probe microanalysis, transmission electron microscopy, and BET surface area techniques. Compounds in the Ti1− z Cr z (O x N y ) series are prepared as single phases by nitridation at 1073 K for 8 h. The as-synthesized oxynitride powders contain only Ti1− z Cr z (O x N y ) with cubic structure and the particle size is in the nanometer scale. 相似文献
10.
Tian D. Xia Zuhair A. Munir Yan L. Tang Wen J. Zhao Tian M. Wang 《Journal of the American Ceramic Society》2000,83(3):507-512
Structure formation in the combustion synthesis of Al2 O3 –TiC composites from TiO2 , Al, and graphite powders was investigated using cylindrical samples and cone-shaped "quenching samples." It is shown that the phases Ti and Ti3 Al exist as intermediates in the combustion synthesis process. Titanium carbide forms in a secondary step through reactions between graphite and liquid Ti or Ti3 Al, then nucleates from a liquid mixture of the three phases Ti, Ti3 Al, and alumina. The nucleated particles grow in the postcombustion stage. Liquid alumina, containing TiC as a dissolved phase, solidifies into corundum grains in the postcombustion stage. Moreover, it is shown that the temperature gradient in the postcombustion stage markedly affects the microstructures of the products. Higher-temperature gradients, typical at the surface of the samples, give rise to the formation of corundum whiskers and TiC agglomerates. In contrast, lower gradients, typical in the center of the samples, lead to the formation of relatively large TiC particles and corundum grains. 相似文献
11.
Dopants in Flame Synthesis of Titania 总被引:2,自引:0,他引:2
Srinivas Vemury Sotiris E. Pratsinis† 《Journal of the American Ceramic Society》1995,78(11):2984-2992
The effect of dopants on the characteristics of titania particles made by oxidation of TiCl4 in a laminar diffusion flame reactor is presented. Introduction of dopant SiCl4 inhibits the transformation of anatase to rutile, due to the formation of interstitian solid solution of SiO2 and TiO2 . Silica decreases the sintering rate of titania and decreases the primary particle size, and, as a result, the specific surface area increases. Intruduction of SnCl4 enhances the transformation of anatase to rutile, due to the similar crystalline structure of SnO2 and rutile titania. However, the presence of SnO2 and rutile titania. However, the presence of SnO2 does not affect the primary particle size or the specific surface area of titania particles. Introduction of AICI3 enhances the transformation of anatase to rutile, due to the formation of excess oxygen vacancies as Al2 O3 and TiO2 form a substitutional solid solution. 相似文献
12.
Y. C. Zhou D. T. Wan Y. W. Bao J. Y. Wang D. T. Wan 《International Journal of Applied Ceramic Technology》2006,3(1):47-54
Ti3 SiC2 has many salient properties including low density, high strength and modulus, damage tolerance at room temperature, good machinablity, and being resistant to thermal shock and oxidation below 1100°C. However, the low hardness and poor oxidation resistance above 1100°C limit the application of this material. The poor oxidation resistance at temperatures above 1100°C was because of the absence of protective layer in the scale and the presence of TiC impurity phase. TiC impurity could be eliminated by adding a small amount of Al to form Ti3 Si(Al)C2 solid solutions. Although the high-temperature oxidation resistance was significantly improved for the Ti3 Si(Al)C2 solid solutions, the strength at high temperatures was lost. One important way to enhance the high-temperature strength is to incorporate hard ceramic particles like SiC. In this article, we describe the in situ synthesis and simultaneous densification of Ti3 Si(Al)C2 /SiC composites using Ti, Si, Al, and graphite powders as the initial materials. The effect of SiC content on high-temperature mechanical properties and oxidation resistance were investigated. The mechanisms for the improved high-temperature properties are discussed. 相似文献
13.
Masanori Hirano Keisuke Ota Takaharu Ito 《Journal of the American Ceramic Society》2005,88(12):3303-3310
Anatase-type TiO2 powder containing sulfur with absorption in the visible region was directly formed as particles with crystallite in the range 15–88 nm by thermal hydrolysis of titanium(III) sulfate (Ti2 (SO4 )3 ) solution at 100°–240°C. Because of the presence of ammonium peroxodisulfate ((NH4 )2 S2 O8 ), the yield of anatase-type TiO2 from Ti2 (SO4 )3 solution was accelerated, and anatase with fine crystallite was formed. Anatase-type TiO2 doped with ZrO2 up to 9.8 mol% was directly precipitated as nanometer-sized particles from the acidic precursor solutions of Ti2 (SO4 )3 and zirconium sulfate in the presence and the absence of (NH4 )2 S2 O8 by simultaneous hydrolysis under hydrothermal conditions at 200°C. By doping ZrO2 into TiO2 and with increasing ZrO2 content, the crystallite size of anatase was decreased, and the anatase-to-rutile phase transformation was retarded as much as 200°C. The anatase-type structure of ZrO2 -doped TiO2 was maintained after heating at 1000°C for 1 h. The favorable effect of doping ZrO2 to anatase-type TiO2 on the photocatalytic activity was observed. 相似文献
14.
Effect of Particle Dispersion on the Mechanism of Combustion Synthesis of Titanium Silicide 总被引:1,自引:0,他引:1
The combustion synthesis (SHS) of titanium silicide (Ti5 Si3 ) was investigated. The main combustion reaction (thermal explosion) occurs in the presence of a liquid phase and is usually preceded by a relatively small reaction in the solid state. The influence of Ti particle size on the dominance of each of these types of reactions was investigated. SEM observations and X-ray diffraction analyses indicate that the combustion synthesis of Ti5 Si3 proceeds according to the following sequence: TiSi2 → TiSi → Ti5 Si4 → Ti5 Si3 . 相似文献
15.
Enhancing Effect of Iron Chlorides on the Anatase-Rutile Transition in Titanium Dioxide 总被引:5,自引:0,他引:5
Fabiana C. Gennari Daniel M. Pasquevich 《Journal of the American Ceramic Society》1999,82(7):1915-1921
The effect of solid Fe2 O3 and gaseous iron chlorides on the anatase-rutile phase transition was investigated in the temperature range of 750°-950°C via X-ray diffractometry and scanning electron microscopy. In both cases, iron diffusion in the anatase lattice decreased the transition temperature and increased the anatase-rutile transformation rate, in comparison with that in TiO2 fired in air. The enhancement effect of iron on the anatase-rutile transition is understood on the basis of oxygen-vacancy formation, which favors rutile nucleation. Solid-state iron diffusion between the contact points of TiO2 and Fe2 O3 particles and vapor mass transport through gaseous chlorides were the primary mechanisms of iron mass transport to the TiO2 surface in the presence of both Fe2 O3 and gaseous iron chlorides, respectively. The transformation rate at a given reaction temperature increased in the following order of reaction conditions: pure TiO2 in air, TiO2 in the presence of Fe2 O3 in air, TiO2 in the presence of Fe2 O3 in chlorine, and TiO2 in the presence of gaseous iron chlorides. 相似文献
16.
The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2 Si2 O11 -Na2 Ti2 Si2 O9 . Both narsarukite (Na2 TiSi4 O11 ) and lorenzenite (Na2 Ti2 Si2 O9 ) melt incongruently. Narsarsukite melts at 911°±°C to SiO2 +liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13 +liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C. 相似文献
17.
Samples of the titanium oxides with O/Ti ratios between 0.5 and 1.67 were prepared by heating mixtures of Ti and TiO2 in high vacuum to 1500°C and annealing them in silica ampuls at 900° to 1100°C. Results of chemical and X-ray analyses are combined with previously published data to form a complete phase diagram. The melting points of Ti2 O3 and Ti3 O5 were 1839°° 10°C and 1774°° 10°C, respectively. 相似文献
18.
Preparation of Titanium Nitride: Microwave-Induced Carbothermal Reaction of Titanium Dioxide 总被引:3,自引:0,他引:3
Ramesh D. Peelamedu Mary Fleming Dinesh K. Agrawal Rustum Roy 《Journal of the American Ceramic Society》2002,85(1):117-122
Carbothermal reduction and nitridation of TiO2 was performed in a 2 kW, 2.45 GHz microwave furnace. Carbon, generally added for the removal of oxygen from TiO2 lattice also served as the low-temperature susceptor in these experiments. At temperatures >1200°C, the mixtures started reacting vigorously (self-burn), which was never observed with the respective pure compounds. In the self-burning state, the minimum duration required for complete titanium nitride transformation was ∼20 min with stoichiometric amounts of carbon. With excess C, the transformation duration dropped to just 1 min. CO removal and subsequent Ni fixation occur more directly in microwave-induced reactions than in conventional nitridation procedures. Intermediate formation of successive Magneli phases (Ti2 n O2 n −1 ) was not found in the microwave-induced reactions. The combination of microwave processing and combustion makes this route of economical interest. 相似文献
19.
Al2 O3 -TiN composites varying from 60 to 66.6 mol% TiN were prepared by an in situ reaction between TiO2 and AlN. N2 or O2 evolution takes place, depending on the composition selected. A pseudobrookite (PB) phase appears in the reaction product, the amount decreasing as the TiO2 :AlN ratio becomes poor in AlN. The in situ reaction product can be pressureless sintered to 94% to 97% theoretical density at 1600°C in N2 . The four-point flexural strength varies from 280 to 430 MPa at room temperature. The fracture toughness is 3 to 4.7 MPa.m1/2 . Oxidation of a 94% dense TiN-Al2 O3 composite in the temperature range 710° to 1050°C was also studied. A layer of TiO2 (rutile) protects the composite at 710°C from further oxidation with a weight gain of 0.08 mg/cm2 in 90 min. In the temperature range 820° to 1050°C, the initial oxidation kinetics are parabolic, with an activation energy of 216.5 kJ/mol. Linear oxidation kinetics with an activation energy of 113.7 kJ/mol pertain at longer times. 相似文献
20.
Dong-Wan Kim Kyung Hyun Ko Do-Kyun Kwon Kug Sun Hong 《Journal of the American Ceramic Society》2002,85(5):1169-1172
(1− x )ZnNb2 O6 · x TiO2 ceramics were prepared using both anatase and rutile forms of TiO2 . At a composition of x = 0.58, a mixture region of ixiolite (ZnTiNb2 O8 ) and rutile was observed and the temperature coefficient of resonant frequency (τf ) was ∼0 ppm/°C. We found that although ɛr and τf were comparable, the quality factor ( Q × f , Q ≈ 1/ tan δ, f = resonant frequency) of 0.42ZnNb2 O6 ·0.58TiO2 prepared from anatase and rutile was 6000 and 29 000, respectively. The origin of the difference in Q × f of both samples was investigated by measuring electrical conductivity and by analysis of the anatase–rutile phase transition. The anatase-derived sample had higher conductivity, which was related to the reduction of Ti4+ . It is suggested that the increase of dielectric loss originates from an increase in Ti3+ and oxygen vacancies due to an anatase–rutile phase transition. 相似文献