共查询到20条相似文献,搜索用时 0 毫秒
1.
Guy Ann Kim Vanmeensel Bram Neirinck Omer Van der Biest Jef Vleugels 《Journal of the European Ceramic Society》2006,26(16):3531-3537
Stable suspensions based on methylethylketone (MEK), n-butylamine and nitrocellulose were developed for the electrophoretic deposition (EPD) of Al2O3 and ZrO2 powder. Deposits with a high green density, smooth surface and high deposition yield were obtained upon adding 10–15 vol.% n-butylamine in combination with 1 wt.% nitrocellulose. The influence of the reaction between MEK and n-butylamine, forming water and imines, on the electrophoretic deposition behaviour was investigated. Experimental results revealed that the zeta potential is not a straightforward indication of the stability of these suspensions, since the maximum absolute zeta potential did not correspond with a maximum suspension stability, due to the additional electrosteric stabilisation of the adsorbed charged nitrocellulose. 相似文献
2.
The phase diagram of the Al2O3–ZrO2–Nd2O3 system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd2O3·11Al2O3 + F-ZrO2 + NdAlO3. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al2O3–ZrO2–Nd2O3 system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. 相似文献
3.
The system Al2O3–ZrO2 was studied by differential thermal analysis in inert atmosphere and in vacuum. The eutectic was located at 1866°C and 40% mass of ZrO2. Zirconia solid solution at the eutectic temperature is up to 1.1±0.3% mass of Al2O3. Enthalpy of melting of this eutectic is 1080±90 J/g. Pure ZrO2 transforms from monoclinic to tetragonal at 1162±7°C, but the saturated solid solution of ZrO2, with 0.7±0.2% mass Al2O3 at this temperature, transforms at 1085±5°C. Inverse transitions occur with hysteresis correspondingly at 1055±5 and 995±5°C. Enthalpy of transformation of pure ZrO2 from monoclinic to tetragonal phase is 42±5 J/g (5.2±0.6 J/mol) but only 30±5 J/g for a ZrO2 saturated solid solution. 相似文献
4.
The effect of Al2O3 on mechanical properties of Ti3SiC2/Al2O3 composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti3SiC2/Al2O3 composite can reach 10.28 GPa, 50% higher than that of pure Ti3SiC2. However, slight decrease in the other mechanical properties was observed with Al2O3 addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al2O3 in the composite. 相似文献
5.
M. L. Guevara-Franco S. Robles-Andrade R. García-Alamilla G. Sandoval-Robles J. M. Domínguez-Esquivel 《Catalysis Today》2001,65(2-4):137-141
Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr2O were synthesized by means of sol–gel methods. The catalysts were sulfated with H2SO4 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N2-adsorption at 78 K, and SEM. The catalytic properties of the Al2O3–ZrO2 series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al2O3–ZrO2 solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane. 相似文献
6.
Processing of ultrafine ZrO2 toughened WC composites 总被引:1,自引:0,他引:1
Olivier Malek Bert Lauwers Yeczain Perez Patrick De Baets Jef Vleugels 《Journal of the European Ceramic Society》2009,29(16):3371-3378
The interrelationships between the dispersion of the secondary ZrO2 phase and the material properties of WC-based composites with up to 10 vol% of ZrO2 are investigated. The homogeneity of the ultrafine WC–nanometric ZrO2 powder mixtures was optimized by means of multidirectional milling and bead milling. In an alternative route, zirconium butoxide was used as a ZrO2 source. The composites were fully densified by means of pulsed electric current sintering (PECS), also known as spark plasma sintering, within a few minutes at 1700 °C allowing to maintain an ultrafine grained microstructure combining a hardness of 2600 kg/mm2 with an indentation toughness of 6 MPa m1/2. The ZrO2 content and Y2O3 stabilization were found to strongly influence the mechanical properties and especially strength of the WC–ZrO2 composites. 相似文献
7.
Bikramjit Basu Jef Vleugels Omer Van der Biest 《Journal of the European Ceramic Society》2005,25(16):3629-3637
In this paper, a strategy is described to develop high toughness yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) composites reinforced with hard TiB2 particles. The experimental results revealed that fully dense Y-TZP composites with 30 vol.% TiB2 can be obtained with a moderate hardness of 13 GPa, a high strength up to 1280 MPa and an excellent indentation toughness up to 10 MPa m1/2 by hot pressing in vacuum at 1450 °C. The toughness of the composites can be tailored between 4 and 10 MPa m1/2 by varying the yttria stabiliser content of the ZrO2 matrix between 3 and 2 mol%. An optimum composite toughness was achieved for a ZrO2 matrix with an overall yttria content of 2.5 mol%, obtained by mixing pure monoclinic and 3 mol% Y2O3 co-precipitated ZrO2 starting powders. An important observation is that the thermal residual tensile stress in the ZrO2 matrix due to the TiB2 addition, needs to be taken into account when optimising the transformability of the ZrO2 matrix in order to develop high toughness Y-TZP composites. 相似文献
8.
Surface-phase ZrO2 on SiO2 (SZrOs) and surface-phase La2O3 on Al2O3 (SLaOs) were prepared with various loadings of ZrO2 and La2O3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH4/CO2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al2O3 and Pt/SiO2 catalysts. CO2 or CH4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.
The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
9.
P. Lommens C. De Meyer E. Bruneel K. De Buysser I. Van Driessche S. Hoste 《Journal of the European Ceramic Society》2005,25(16):3605-3610
In this work, a ceramic composite of ZrW2O8 and ZrO2 was synthesized, in order to investigate the possibility of compensating the positive thermal expansion of ZrO2 with the negative thermal expansion (NTE) compound ZrW2O8, tailoring the thermal expansion of these composites. The NTE material was mixed with varying amounts of ZrO2. The thermal expansion coefficients of this series of composites decrease with increasing amounts of ZrW2O8. Nevertheless, a negative deviation from the values expected by the rule of mixtures was found to be most pronounced in the middle of the compositional region. 相似文献
10.
Stefan Kbel Juliane Plüschke Ulrich Vogt Thomas J. Graule 《Ceramics International》2004,30(8):2105-2110
Al2O3–MoSi2 composites with MoSi2 volume fractions between 16 and 40% were fabricated from commercial ceramic Al2O3 and intermetallic MoSi2 powders by granulation, cold isostatic pressing and vacuum-sintering. The addition of MoSi2 had only a slight influence on the densification of the composites, with sintered densities of 98% for samples with 16 vol.% MoSi2 and 94% for samples with 40 vol.% MoSi2. Composites with MoSi2 contents of 20 vol.% and higher were electroconductive due to the formation of a three-dimensional percolating network of the conductive MoSi2 phase. 相似文献
11.
Enzhao Cui Jun Zhao Xuchao Wang Jialin Sun Xiantong Huang Chao Wang 《Ceramics International》2018,44(12):13538-13543
To toughen the Al2O3 matrix ceramic materials, Al2O3/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2?wt% GNPs were markedly improved by about 35.3% (~ 7.78?MPa?m1/2) and 49% (~ 608.54?MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22?GPa. However, the mechanical properties degrade with the further increase of GNPs’ content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs. 相似文献
12.
A process using metal-organic chemical vapor infiltration (MOCVI) conducted in fluidized bed was employed for the preparation of nano-sized ceramic composites. The Cr-species was infiltrated into Al2O3 granules by the pyrolysis of chromium carbonyl (Cr(CO)6) at 300–450 °C. The granulated powder was pressureless sintered or hot-pressed to achieve high density. The results showed that the dominant factors influencing the Cr-carbide phases formation, either Cr3C2 or Cr7C3, in the composite powders during the sintering process were the temperature and oxygen partial pressure in the furnace. The coated Cr-phase either in agglomerated or dispersive condition was controlled by the use of colloidal dispersion. The microstructures showed that fine (20 –600 nm) CrxCy grains (≤8 vol.%) located at Al2O3 grain boundaries hardly retarded the densification of Al2O3 matrix in sintering process. The tests on hardness, strength and toughness appeared that the composites with the inclusions (Cr3C2) had gained the advantages over those by the rule of mixture. Even 8 vol.% ultrafine inclusions have greatly improved the mechanical properties. The strengthening and toughening mechanisms of the composites were due to grain-size reduction, homogenous dispersion of hard inclusions, and crack deflection. 相似文献
13.
Hao-Tung Lin Sheng-Chang Wang Jow-Lay Huang Shin-Yun Chang 《Journal of the European Ceramic Society》2007,27(16):4759-4765
Nanosized particles dispersed uniformly on Al2O3 particles were prepared from the decomposition of precursor Cr(CO)6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr2O3, CrC1−x, and C. A solid solution of Al2O3–Cr2O3 and an Al2O3–Cr2O3/Cr3C2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al2O3–Cr2O3/Cr-carbide (Cr3C2 and Cr7C3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr3C2 and Al2O3 is non-coherent, while the interface between Cr7C3 and Al2O3 is semi-coherent. 相似文献
14.
Yun Guo Guanzhong Lu Zhigang Zhang Liangzhu Jiang Xiaohong Wang Shuben Li Bing Zhang Jianzhong Niu 《Catalysis Today》2007,126(3-4):441-448
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO2/Al2O3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO3)2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO2 is highly dispersed on the surface of Al2O3 up to 10 wt.% ZrO2, beyond this value tetragonal ZrO2 is formed. The presence of a small amount of ZrO2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO2, but it does not accelerate the activity of 0.2% Pd/ZrO2/Al2O3 for methane combustion. 0.2% Pd/ZrO2/Al2O3 dried at 120 °C shows highest activity for CH4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH4 combustion. 相似文献
15.
Wenguang Zhang Weimin Liu Chengtao Wang 《Journal of the European Ceramic Society》2002,22(16):2869-2876
Thin films of Al2O3 and doped Al2O3 were prepared on a glass substrate by dip coating process from specially formulated ethanol sols. The morphologies of the unworn and worn surfaces of the films were observed with atomic force microscope (AFM) and scanning electron microscope (SEM). The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of obtained thin films sliding against Si3N4 ball were evaluated and compared with glass slide on a one-way reciprocating friction tester. XPS results confirm that the target films were obtained successfully. The doped elements distribute in the film evenly and exist in different kinds of forms, such as oxide and silicate. AFM results show that the addition of the doped elements changes the structure of the Al2O3 films, i.e., a rougher and smoother surface is obtained. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, the doped films exhibit better tribological properties due to the improved toughness. Sever brittle fracture is avoided in the doped films. The wear of glass is characteristic of brittle fracture and severe abrasion. The wear of Al2O3 is characteristic of brittle fracture and delamination. And the wear of doped Al2O3 is characteristic of micro-fracture, deformation and slight abrasive wear. The introduction of ZnO is recommended to improve the tribological property of Al2O3 film. 相似文献
16.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
17.
Toughening alumina with silver and zirconia inclusions 总被引:4,自引:0,他引:4
Both silver and zirconia inclusions are added into an alumina matrix, the strength and toughness of the composites are determined. The toughening agents prohibit the grain growth of the matrix, the strength of alumina is, therefore, enhanced. The addition of two toughening agents also enhances the toughness of alumina. The presence of Ag inclusions raises the transformation ability of ZrO2; however, the toughness increase of the Al2O3–ZrO2–Ag composites is slightly lower than the sum of the toughness increase of Al2O3–ZrO2 and of Al2O3–Ag composites. The present study demonstrates that the toughening effects contributed by a transformation toughening agent and a ductile toughening agent can interact with each other; nevertheless, such interaction depends strongly on the microstructure of the composites. 相似文献
18.
19.
Chunlei Shi Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1997,14(3-4):175-188
Dispersing La2O3 on δ- or γ-Al2O3 significantly enhances the rate of NO reduction by CH4 in 1% O2, compared to unsupported La2O3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La2O3 precursor used, the pretreatment, and the La2O3 loading. The most active family of catalysts consisted of La2O3 on γ-Al2O3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m2) occurred between the addition of one and two theoretical monolayers of La2O3 on the γ-Al2O3 surface. The best catalyst, 40% La2O3/γ-Al2O3, had a turnover frequency at 700°C of 0.05 s−1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La2O3/Al2O3 catalysts exhibited stable activity under high conversion conditions as well as high CH4 selectivity (CH4 + NO vs. CH4 + O2). The addition of Sr to a 20% La2O3/γ-Al2O3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO=4 to the latter Sr-promoted La2O3/Al2O3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La2O3. Dispersing La2O3 on SiO2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La2O3. This is presumably due to water sensitivity and silicate formation. The La2O3/Al2O3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
20.
Yohei Harada Naofumi Uekawa Takashi Kojima Kazuyuki Kakegawa 《Journal of the European Ceramic Society》2008,28(10):1973-1978
Homogeneous-eutectic microstructure of Y3Al5O12–Al2O3 system without coarse primary crystals was formed at an off-eutectic composition. This method utilizes a low migration rate in an amorphous phase. A mixture of Y2O3 and Al2O3 having the off-eutectic composition was melted and quenched rapidly to form an amorphous phase. A heat-treatment of the amorphous phase at 1000 °C and 1300 °C for 30 min formed Y3Al5O12 and Al2O3 phases. SEM observation of this material, which was formed from the amorphous phase at 1300 °C for 30 min, showed homogeneous eutectic-like microstructure. The formation of the primary crystals (coarse Al2O3), which are always observed in the off-eutectic compositions by ordinary method, was completely suppressed. 相似文献