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1.
Al2O3:ZrO2 ceramics have been prepared from physically mixed pure oxide powders. The results indicate that careful processing of the
starting powders and a two-stage sintering process can avoid expensive processing methods like hot pressing/hot isostatic
pressing used for achieving high densification. The mechanical properties were measured and the resultant microstructure studied
to explain the toughening behaviour of this material. 相似文献
2.
《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
3.
《Materials at High Temperatures》2013,30(1):71-77
AbstractThe 1,200°C oxidation behavior of NiAl was examined at various levels of sulfur and zirconium dopants to test the possibility of a critical S/Zr ratio required for adhesion. Cyclic furnace testing for 200 1-h cycles and interrupted testing for 500 h were used as screening tests. Pure NiAl and NiAl(Zr) with 0.14 at. % Zr were chosen as model base compositions; they exhibited normal, slow-growing scales (3 mg/cm2) with excellent adhesion for the Zr-doped alloys. NiAl with about 120 ppma S exhibited a substantial weight loss (?20 mg/cm2) in cyclic tests and a very large weight gain (+60 mg/cm2) in interrupted tests. The major surface phase remained as α-Al2O3. Sulfur doping the NiAl(Zr) alloy caused massive weight gains of 80–100 mg/cm2, swelling, cracking, and nearly complete conversion into NiAl2O4 and α-Al2O3. The initial objective of determining critical S/Zr ratios for adhesion was therefore unattainable. Initiation of the catastrophic attack was examined after a 10 h exposure, revealing a few sites of broad, raised, and cracked ridges. In cross-section, the ridges appeared as nodular intrusions, with a complex, fractal, oxide–metal interface. They were primarily alumina (with occasional entrapped islands of NiAl2O4 or pure Ni metal). They possessed a unique microstructure consisting of 0.3 μm lamellae, separated by 0.1 μm open channels. This allowed for rapid growth controlled by gaseous diffusion. The microstructure is discussed in terms of SO2 evolution and a sulfur-driven depassivation process. 相似文献
4.
The effect of TiO2 addition (0–4.0 wt%) on the sintering behavior and mechanical properties of an ultrafine (150 nm) alumina–5 wt% zirconia powder has been investigated. TiO2 is a beneficial additive, resulting in lower sintering temperature and higher sintered density. The grain growth is shown to be enhanced simultaneously after TiO2 addition. At higher amounts of TiO2 addition and at higher sintering temperature, the formation of secondary phases of ZrTiO4 or Al2TiO5, which has lower elastic moduli compared with alumina, reduces the hardness of the sintered bulk from 19.3 to 17.9 GPa. The lager grain size and the transition of fracture mode to fully intergranular due to the TiO2 addition seem to improve the toughness from 4.4 to 5.2 MPa m1/2. 相似文献
5.
S.C. Farmer 《Engineering Fracture Mechanics》2002,69(9):1015-1024
Al2O3-ZrO2(Y2O3) eutectic materials possess good fracture strengths and creep resistance. Increased Al2O3 content is one means to further improve creep resistance. The objective of this study is to examine fracture strength of Al2O3-rich (hypoeutectic) compositions at varying Y2O3 contents. Fibers 160-220 μm in diameter with 68 m/o Al2O3 and 1.1-7.6 m/o Y2O3 (30.5 to 16 m/o ZrO2) were directionally solidified at 0.11 mm/s using the laser-heated float-zone process. Defect populations increased in size and severity with higher Y2O3 contents. However, fibers maintained 1 GPa fracture strength in the presence of numerous pores and shrinkage cavities, which extend with crack-like morphology along the fiber axis. 相似文献
6.
Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue) 总被引:1,自引:0,他引:1
Lanthanide ions (La3+, Nd3+, Sm3+, Eu3+, Gd3+, and Yb3+)/doped TiO2 nanoparticles were successfully synthesized by sol–gel method. Their photocatalytic activities were evaluated using Direct Blue dye (DB53) as a decomposition objective. The structural features of TiO2 and lanthanide ions/TiO2 were investigated by XRD, SEM, UV-diffuse reflectance, and nitrogen adsorption measurements. Our findings indicated that XRD data characteristic anatase phase reflections and also XRD analysis showed that lanthanides phase was not observed on Lanthanide ions/TiO2. The results indicated that Gd3+/TiO2 has the lowest bandgap and particle size and also the highest surface area and pore volume (Vp) as well. Lanthanide ions can enhance the photocatalytic activity of TiO2 to some extent as compared with pure TiO2 and it was found that Gd3+/TiO2 is the most effective photocatalyst. The photocatalytic tests indicate that at the optimum conditions; illumination time 40 min, pH ∼4, 0.3 g/L photocatalyst loading and 100 ppm DB53; the dye removal efficiency was 100%. Details of the synthesis procedure and results of the characterization studies of the produced lanthanide ions/TiO2 are presented in this paper. 相似文献
7.
Fracture behavior under mixed-mode loading of ceramic plasma-sprayed thermal barrier coatings at ambient and elevated temperatures 总被引:2,自引:0,他引:2
The fracture behavior under modes I and II loading of ceramic plasma-sprayed thermal barrier coatings was determined in air at 25 and 1316 °C in asymmetric four-point flexure. The mode I fracture toughness was found to be KIc = 1.15 ± 0.07 and 0.98 ± 0.13 MPa , respectively, at 25 and 1316 °C. The respective ‘nominal’ mode II fracture toughness values were KIIc = 0.73 ± 0.10 and 0.65 ± 0.04 MPa . The empirical mixed-mode fracture criterion best described the coatings’ fracture behavior under mixed-mode loading. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. 相似文献
8.
The presence of Fe(3)O(4)-CoO/Al(2)O(3) can improve degradation efficiency significantly during the ozonation of the herbicide 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP). The main factors affecting degradation efficiency, such as pH, the catalyst concentration and addition of the scavenger, were investigated. The kinetics of the catalytic ozonation are also discussed. The results indicate that two factors, the oxidation after adsorption of 2,4-DP and the oxidation of hydroxyl radicals (OH), lead to a great enhancement in ozonation efficiency during the catalytic ozonation of 2,4-DP in the presence of Fe(3)O(4)-CoO/Al(2)O(3), in which the oxidation of the OH plays an important role. Under controlled conditions, the apparent reaction rate constants for the degradation of 2,4-DP were determined to be 2.567 × 10(-4)s(-1) for O(3) and 1.840 × 10(-3)s(-1) for O(3)/Fe(3)O(4)-CoO/Al(2)O(3). The results from the analysis of the reaction kinetics using the relative method showed that O(3)/Fe(3)O(4)-CoO/Al(2)O(3) possessed a larger R(ct) (R(ct) is defined as the ratio of the ·OH exposure to the O(3) exposure, R(ct) = ∫C(t)(OH) dt/C(t)O(3)dt) than O(3), indicating that O(3)/Fe(3)O(4)-CoO/Al(2)O(3) produced more hydroxyl radicals. 相似文献
9.
Jagos Puric 《Vacuum》2010,85(5):555-562
Material processing using nano-technology is now advancing towards a more precise and controllable “smart” stage and plasma systems with high performance are being required for advanced thermal processing. One such unique plasma generator, a high speed plasma accelerator is capable of generating high energy plasma flows of required composition within a large range of plasma parameters. Another gas tunnel type plasma system also exhibits high energy density and high efficiency. Its application to the plasma spraying of ceramics proved that the characteristics of these ceramic coatings are superior to conventional ones. Various types of plasma accelerators are described here with emphasis on a MagnetoPlasma Compressor of Compact Geometry (MPC-CG) which was used to investigate plasma flow interaction with solid silicon surfaces. Different types of submicron structure were obtained due to the compression plasma flow action? The plasma produced by a gas tunnel type plasma source was used for the surface modification of Titanium, TiN films being formed in a relatively short time of 5 s. Plasma sprayed ZrO2/Al2O3 coatings were also investigated, and the results showed that the ZrO2/Al2O3 composite system has the possibility for the development of high functionally graded thermal barrier coating (TBC), which exhibits excellent mechanical properties and oxidation resistance. 相似文献
10.
Stefan Wiechmann 《Thin solid films》2009,517(24):6847-1504
The direct measurement of the thermo-optic coefficients of aluminium oxide, tantalum pentoxide and titanium dioxide thin films is presented. Using ellipsometry on monolithically integrated permutations of the layers of silicon, silicon dioxide and the material under test, allows the direct measurement of the overall thermo-optic coefficient accounting for thermally induced changes in the dielectric permittivity and density of the materials as well as the elasto-optic effect due to the non-matching thermal expansion coefficients of the different materials. 相似文献
11.
The Nd2O3 modified ZrO2 was synthesized using two methods of co-precipitation (Nd-ZrO2) and wet impregnation (Nd/ZrO2). The surface and bulk crystalline phases of Nd2O3 modified ZrO2 were investigated by using UV Raman spectroscopy, visible Raman spectroscopy, and X-ray diffraction (XRD). It is observed that the tetragonal phase in the surface region of Nd-ZrO2 was not effectively stabilized by Nd2O3, as Nd2O3 is mainly present in the bulk of Nd-ZrO2. However, in Nd/ZrO2, it is found that with the impregnation of 0.5 mol% Nd2O3 on ZrO2, the surface tetragonal phase of Nd/ZrO2 can be stabilized even after calcination at 700 °C. The UV Raman results indicate that a disordered structure, or intermediate structure, which is involved in the transition from the tetragonal to the cubic phase, is formed at the surface region of Nd/ZrO2. The formation of the aforementioned intermediate structure inhibits the phase transition from tetragonal to monoclinic in the surface region of Nd/ZrO2. Furthermore, it is observed that the mixed tetragonal and monoclinic phases in the surface region of ZrO2 which has been impregnated with Nd2O3 can also be stabilized after calcination at 700 °C. This work provides a simple method for controlling the surface phase of ZrO2 at high temperatures. 相似文献
12.
Xue-Yang 《Thin solid films》2010,518(22):6441-6445
In this study, the etching characteristics of ALD deposited Al2O3 thin film in a BCl3/N2 plasma were investigated. The experiments were performed by comparing the etch rates and the selectivity of Al2O3 over SiO2 as functions of the input plasma parameters, such as the gas mixing ratio, the DC-bias voltage, the RF power, and the process pressure. The maximum etch rate was obtained at 155.8 nm/min under a 15 mTorr process pressure, 700 W of RF power, and a BCl3 (6 sccm)/N2 (14 sccm) plasma. The highest etch selectivity was 1.9. We used X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface. Auger electron spectroscopy (AES) was used for the elemental analysis of the etched surfaces. 相似文献
13.
《Materials at High Temperatures》2013,30(3):253-259
AbstractThe examination of high temperature (HT) oxide scale growth mechanisms was performed using secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS), in conjunction with 16O2/18O2 HT oxidation experiments. Cr2O3, NiO, ZrO2 and Al2O3 were studied because they constitute excellent representative thermally grown oxide scales: they grow by cationic diffusion (Cr2O3, NiO), anionic diffusion (ZrO2) or mixed anionic-cationic diffusion (Al2O3). The oxidation tests were performed first in 16O2 and subsequently in 18O2 at several temperatures (600–1000°C for NiO, 600°C for ZrO2, 1000°C for Cr2O3 and 1100°C for Al2O3). The oxygen isotope distribution observed by SIMS and SNMS profiles are discussed and related with the HT oxidation mechanisms proposed in the literature. 相似文献
14.
The present study is targeted on the effect of pH on solar photocatalytic removal of metal ions from wastewater. Photoreductive deposition and dark adsorption of metal ions Cu(II), Ni(II), Pb(II) and Zn(II), using solar energy irradiated TiO(2), has been investigated at pH values 2, 4, 7, 8 and 10. Modeling of metal species at the studied pH values has been performed and speciation is used as a tool for discussing the photodeposition. The decreasing order of metal deposition at pH 2 and 4 was found to be Pb(II)>Cu(II)>Ni(II) congruent with Zn(II). In the neutral and alkaline pH conditions (pH 7, 8 and 10) the order was Cu(II)>Zn(II)>Ni(II)>Pb(II). 相似文献
15.
《Materials at High Temperatures》2013,30(4):507-517
AbstractAdvanced and baseline thermal barrier coatings (TBCs) were thermal cycle tested in air at 1163°C until delamination or spallation of the ceramic top coat. The top coat of the advanced TBC’s consisted of ZrO2 with various amounts of Y2O3, Yb2O3, Gd2O3, or Nd2O3 dopants. The composition of the top coat of the baseline TBC was ZrO2-8wt.%Y2O3. All top coats were deposited by air plasma spraying. A NiCrAlY or NiCoCrAlY bond coat was deposited by low pressure plasma spraying onto a single-crystal, Ni-base superalloy. The TBC lifetime for the baseline coatings was approximately 190 cycles (45 minutes at 1163°C per cycle) while the lifetime for the advanced coatings was as high as 425 cycles. The fracture surfaces and sample cross sections were examined after TBC failure by SEM and optical microscopy, and the top coats were further examined by X-ray diffraction. These post-test studies revealed that the fracture path largely followed splat boundaries with some trans-splat fracture. However, there were no obvious distinguishing features which explained the difference in TBC lifetimes between some of the advanced and baseline coatings. 相似文献
16.
The hollow spheres of anatase TiO2 with higher photocatalytic activity have been fabricated by spherical CaCO3 nanoparticles as a template, and titanium sulfate (Ti(SO4)2) as a precursor, and the CaCO3 templates were dissolved subsequently in dilute HNO3 solution. The TiO2 hollow spheres samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption-desorption isotherms. The characterization results indicate that as prepared TiO2 hollow spheres sample was transformed to anatase phase in calcined at 400 °C, and the anatase TiO2 hollow spheres have a higher specific surface area and show much better photocatalytic activity than commercial P25 in the photodegradation of Rhodamine B under the UV irradiation. 相似文献
17.
Naoomi Yamada Taro Hitosugi Ngoc Lam Huong Hoang Shoichiro Nakao Yasushi Hirose Toshihiro Shimada Tetsuya Hasegawa 《Thin solid films》2010,518(11):3101-3104
Transparent conducting Nb-doped anatase TiO2 (TNO) epitaxial films were sputtered from TiO2-, Ti2O3-, and Ti-based targets at various oxygen partial pressures (Po2). Using the TiO2- and Ti2O3-based targets, highly conductive films showing a resistivity (ρ) of ~ 3 × 10− 4 Ω cm could be formed without postdeposition treatment. In the case of the TNO films formed from the Ti-based target, reductive annealing had to be carried out at a temperature of 600 °C to achieve similar resistivity values. Thus, the use of oxide targets is preferable to obtain as-grown transparent conducting TNO films. In particular, the Ti2O3-based target is practically advantageous, because it offers a wide range of optimal Po2 values at which ρ values of the order of 10− 4 Ω cm are achievable. 相似文献
18.
Pragyan Mohanty Sankar Mohapatra Jyoshnarani Mohapatra S. K. Singh Payodhar Padhi 《Materials and Manufacturing Processes》2016,31(10):1311-1317
Fine powders of (Al2O3)100–x(SiC)x (0 ≤ x ≤ 50) composites were prepared by chemical route (named as pyrophoric technique) to achieve a uniform mixture of SiC in an alumina matrix. The chemically synthesized fine SiC/Al2O3 composite powders were sintered to form composites at 1450°C which is well below the sintering temperature of SiC. Sintering was performed in an argon atmosphere. Highly dense SiC/Al2O3 microstructures were achieved. An improvement in bulk density and hardness has been achieved for SiC/Al2O3 composites with 20 wt% of SiC. Hexagonal-shaped grains have been obtained in (Al2O3)50(SiC)50 composite with well-connected grain boundaries. The peak position of alumina in SiC/Al2O3 composites shifts toward lower wavenumbers in Fourier transform infrared spectroscopy and higher wavenumbers in Raman spectroscopy due to the incorporation of SiC in the composites. The optical band gap decreases with the addition of SiC and the composite behaves more like a semiconductor rather than an insulator. These properties make SiC/Al2O3 composites attractive for various industrial applications. 相似文献
19.
A novel method for preparing Al2O3/ZrO2 (Y2O3) eutectic was developed by combining combustion synthesis with melt-casting under ultra-high gravity (CSMC-UHG). The application of UHG = 800 g resulted in a high relative density of 99.8%, and an orientation-growth along the UHG direction. The microstructure was composed of aligned growth regimes containing a triangular dispersion of orderly ZrO2 rods in Al2O3 matrix with a spacing of 300 nm. The eutectic had a high fracture toughness up to 17.9 MPa·m1/2, which was mainly attributed to the nanostructure and the elastic bridge effects of the aligned ZrO2 rods. 相似文献
20.
Phase transformation and morphology evolution of ZrO2/Al2O3/ZrO2 laminate induced by the post-deposition NH3 annealing at 480 °C were studied and the effect on the electrical property of the TiN/ZrO2/Al2O3/ZrO2/TiN capacitor module was evaluated in dynamic random access memory cell. Experimental results indicated N could indeed be incorporated into the dielectric laminate by the low-temperature NH3 annealing, resulting in tetragonal-to-cubic phase transformation and small crystallites in the ZrO2 layers. The C residue and Cl impurity in the ZrO2/Al2O3/ZrO2 laminate, which derived from the dielectric film formation and capping TiN layer deposition, respectively, could also be reduced by the nitridation process. As a result of the better surface morphology and less impurity content, lower dielectric leakage current and longer reliability lifetime were observed for the nitrided ZrO2/Al2O3/ZrO2 capacitor. This study demonstrates the low-temperature NH3 annealing on ZrO2/Al2O3/ZrO2 dielectric can be applicable to the metal-insulator-metal capacitor structure with nitride-based electrode, which brings advantages over mass production-wise property improvements and extends the practical applicability of the ZrO2/Al2O3/ZrO2 dielectric. 相似文献