共查询到20条相似文献,搜索用时 31 毫秒
1.
Huan-ping Wang Shi-qing Xu Shui-qin Lu shi-long Zhao Bao-ling Wang 《Ceramics International》2009,35(7):2715-2718
The effects of B2O3 additives on the sintering behavior, microstructure and dielectric properties of CaSiO3 ceramics have been investigated. The B2O3 addition resulted in the emergence of CaO–B2O3–SiO2 glass phase, which was advantageous to lower the synthesis temperature of CaSiO3 crystal phase, and could effectively lower the densification temperature of CaSiO3 ceramic to as low as 1100 °C. The 6 wt% B2O3-doped CaSiO3 ceramic sintered at 1100 °C possessed good dielectric properties: r = 6.84 and tan δ = 6.9 × 10−4 (1 MHz). 相似文献
2.
Akira Morikawa Koichi Kikuta Akihiko Suda Hirofumi Shinjo 《Applied catalysis. B, Environmental》2009,88(3-4):542-549
Oxygen storage capacity (OSC) of CeO2–ZrO2 solid solution, CexZr(1−x)O4, is one of the most contributing factors to control the performance of an automotive catalyst. To improve the OSC, heat treatments were employed on a nanoscaled composite of Al2O3 and CeZrO4 (ACZ). Reductive treatments from 700 to 1000 °C significantly improved the complete oxygen storage capacity (OSC-c) of ACZ. In particular, the OSC-c measured at 300 °C reached the theoretical maximum with a sufficient specific surface area (SSA) (35 m2/g) after reductive treatment at 1000 °C. The introduced Al2O3 facilitated the regular rearrangement of Ce and Zr ions in CeZrO4 as well as helped in maintaining the sufficient SSA. Reductive treatments also enhanced the oxygen release rate (OSC-r); however, the OSC-r variation against the evaluation temperature and the reduction temperature differed from that of OSC-c. OSC-r measured below 200 °C reached its maximum against the reduction temperature at 800 °C, while those evaluated at 300 °C increased with the reduction temperature in the same manner as OSC-c. 相似文献
3.
Wear properties and microstructures of alumina matrix composite ceramics used for drawing dies 总被引:1,自引:0,他引:1
The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al2O3/TiC, Al2O3/(W,Ti)C and Al2O3/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al2O3/TiC and Al2O3/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die. 相似文献
4.
Chih-Hung Chu Chih-Peng Lin Shaw-Bing Wen Yun-Hwei Shen 《Ceramics International》2009,35(8):3455-3461
Aluminum nitride (AlN) ceramics, prepared with Y2O3 and CaO sintering additives, have been densified in an Al2O3 crucible at temperatures of up to 1650 °C and 1700 °C using a conventional MoSi2 heating element furnace. The results of this study show that relative densities in excess of 99% of theoretical and a relatively high-thermal conductivity of 147 W m−1 K−1 have been achieved for feedstock materials prepared with combined addition of 1 wt.% Y2O3 and 1 wt.% CaO. All of the phases in sintered samples have been shown to be crystalline AlN and minor amount of secondary phases, were detected such as enriched Y- and Ca-aluminates by the XRD patterns, back-scattered imagery and microprobe analysis. The advantage of using the particular experimental system and sintering condition is considered to be amenable to lower production cost and enhance the feasibility of mass production. Critical temperature for AlN densification to obtain the highest density is about 1650 °C. 相似文献
5.
Amir Javad Nikkhah Omid Torabi Reza Ebrahimi-Kahrizsangi Sanaz Naghibi Amin Jamshidi 《Ceramics International》2014
Alpha-alumina–boron nitride (α-Al2O3–BN) nanocomposite was synthesized using mixtures of aluminum nitride, boron oxide and pure aluminum as raw materials via mechanochemical process under a low pressure of nitrogen gas (0.5 MPa). The phase transformation and structural evaluation during mechanochemical process were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential thermal analysis (DTA) techniques. The results indicated that high exothermic reaction of Al–B2O3 systems under the nitrogen pressure produced alumina, aluminum nitride (AlN), and aluminum oxynitride (Al5O6N) depending on the Al value and milling time, but no trace of boron nitride (BN) phases could be identified. On the other hand, AlN addition as a solid nitrogen source was effective in fabricating in-situ BN phase after 4 h milling process. In Al–B2O3–AlN system, the aluminothermic reaction provided sufficient heat for activating reaction between B2O3 and AlN to form BN compound. DTA analysis results showed that by increasing the activation time to 3 h, the temperature of both thermite and synthesis reactions significantly decreased and occurred as a one-step reaction. SEM and TEM observations confirmed that the range of particle size was within 100 nm. 相似文献
6.
A number of nano-gold catalysts were prepared by depositing gold on different metal oxides (viz. Fe2O3, Al2O3, Co3O4, MnO2, CeO2, MgO, Ga2O3 and TiO2), using the homogeneous deposition precipitation (HDP) technique. The catalysts were evaluated for their performance in the combustion of methane (1 mol% in air) at different temperatures (300–600 °C) for a GHSV of 51,000 h−1. The supported nano-gold catalysts have been characterized for their gold loading (by ICP) and gold particle size (by TEM/HRTEM or XRD peak broadening). Among these nano-gold catalysts, the Au/Fe2O3 (Au loading = 6.1% and Au particle size = 8.5 nm) showed excellent performance. For this catalyst, temperature required for half the methane combustion was 387 °C, which is lower than that required for Pd(1%)/Al2O3 (400 °C) and Pt(1%)/Al2O3 (500 °C) under identical conditions. A detailed investigation on the influence of space velocity (GHSV = 10,000–100,000 cm3 g−1 h−1) at different temperatures (200–600 °C) on the oxidative destruction of methane over the Au/Fe2O3 catalyst has also been carried out. The Au/Fe2O3 catalyst prepared by the HDP method showed much higher methane combustion activity than that prepared by the conventional deposition precipitation (DP) method. The XPS analysis showed the presence of Au in the different oxidation states (Au0, Au1+ and Au3+) in the catalyst. 相似文献
7.
Xu Li Guanzhong Lu Yanglong Guo Yun Guo Yanqin Wang Zhigang Zhang Xiaohui Liu Yunsong Wang 《Catalysis communications》2007,8(12):1969-1972
A novel solid superbase catalyst of Eu2O3/Al2O3 was prepared and its basic strength reached 26.5 measured by indicators according to Hammett scale. The catalytic activity of Eu2O3/Al2O3 was evaluated for the transesterification of soybean oil with methanol to biodiesel in the fixed bed reactor and under atmospheric pressure. The results show that Eu2O3/Al2O3 is an excellent catalyst for the transesterification of soybean oil, and the conversion of soybean oil can reach 63.2% at 70 °C for 8 h. 相似文献
8.
The acid-base properties of -Al2O3 and alumina-supported B2O3, Ga2O3 and In2O3 have been determined by microcalorimetry of ammonia and sulfur dioxide adsorption. From the adsorption of NH3, it was found that the addition of B2O3 on alumina leads to an increase of the number of acid sites, while Ga2O3 and In2O3 additives caused a decrease in the acidity of alumina. Using SO2 as a probe molecule to study the basicity, the number of surface basic sites on alumina was found to be strongly decreased by the addition of boron oxide, while it was only slightly affected by the addition of gallium oxide and decreased by the addition of indium oxide. The differential heats of adsorption are discussed as a function of the coverage by the probe molecules. The electronic properties of the oxides are examined in order to explain the acid-base properties of the supported oxides. 相似文献
9.
On investigating the possibility of using alumina whisker reinforced 3 mol% Yttria stabilized Tetragonal Zirconia (TZ-3Y) composite for bioceramic applications, presented here is the influence of varying whisker concentration (2, 5, 10, 15 and 20 wt%) on flexural strength of the composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina during sintering. It was found that with addition of alumina whiskers, strength was increased and reached a maximum value of 1212±60 MPa and 1325±65 MPa, in pure and 1 wt% CTAB added samples respectively, at a concentration of 10 wt% Al2O3 whiskers. The strength values of the synthesized composite can compete well with commercially available materials for dental applications. 相似文献
10.
Jos Escobar María C. Barrera Jos A. Toledo María A. Corts-Jcome Carlos Angeles-Chvez Sara Núez Víctor Santes Elizabeth Gmez Leonardo Díaz Eduardo Romero Jos G. Pacheco 《Applied catalysis. B, Environmental》2009,88(3-4):564-575
Phosphorous-doped NiMo/Al2O3 hydrodesulfurization (HDS) catalysts (nominal Mo, Ni and P loadings of 12, 3, and 1.6 wt%, respectively) were prepared using ethyleneglycol (EG) as additive. The organic agent was diluted in aqueous impregnating solutions obtained by MoO3 digestion in presence of H3PO4, followed by 2NiCO3·3Ni(OH)2·4H2O addition. EG/Ni molar ratio was varied (1, 2.5 and 7) to determine the influence of this parameter on the surface and structural properties of synthesized materials. As determined by temperature-programmed reduction, ethyleneglycol addition during impregnation resulted in decreased interaction between deposited phases (Mo and Ni) and the alumina carrier. Dispersion and sulfidability (as observed by X-ray photoelectron microscopy) of molybdenum and nickel showed opposite trends when incremental amounts of the organic were added during catalysts preparation. Meanwhile Mo sulfidation was progressively decreased by augmenting EG concentration in the impregnating solution, more dispersed sulfidic nickel was evidenced in materials synthesized at higher EG/Ni ratios. Also, enhanced formation of the so-called “NiMoS phase” was registered by increasing the amount of added ethyleneglycol during simultaneous Ni–Mo–P–EG deposition over the alumina carrier. That fact was reflected in enhanced activity in liquid-phase dibenzothiophene HDS (batch reactor, T = 320 °C, P = 70 kg/cm2) and straight-run gas oil desulfurization (steady-state flow reactor), the latter test carried out at conditions similar to those used in industrial hydrotreaters for the production of ultra-low sulfur diesel (T = 350 °C, P = 70 kg/cm2, LHSV = 1.5 h−1 and H2/oil = 2500 ft3/bbl). 相似文献
11.
Kalle Arve Jos R. Hernndez Carucci Kari Ernen Atte Aho Dmitry Yu. Murzin 《Applied catalysis. B, Environmental》2009,90(3-4):603-612
The effect of longer paraffins on the mechanism of the HC-SCR reaction over a 1.91 wt.% Ag/alumina catalyst was investigated by kinetic studies. Hexadecane (C16H34) was chosen as a model compound as it is also a representative molecule for a second generation biodiesel consisting of only long-chain paraffins. The kinetic behaviour of the catalytic reduction of NOx was examined at steady-state conditions in the temperature range 250–550 °C (50 °C ramping) and by using the following gas concentrations: PNO = 100, 250, 500, 750 or 1000 ppm, Phexadecane = 31, 94, 188, 281 or 375 ppm and PO2=1.5, 3, 4.5, 6 or 9 vol.%. Results showed that in the temperature range 250–425 °C high hexadecane concentration had an inhibiting effect on the NO reduction. At temperatures above 350 °C the apparent reaction orders for hexadecane with respect to hexadecane increased to close or above 1. Reaction orders towards NO were close to 0.55 indicating that NO adsorption on the catalyst surface is stronger than hexadecane adsorption. Based on the experimental data it is proposed that small clusters alone cannot be the active sites for HC-SCR over Ag/Al2O3 but the important requirement for high activity over the catalyst is the local concentrations of hydrocarbon and NO on the interface of silver and the support. 相似文献
12.
In this study, mixed hydride/alanate nano powders in the Al–Mg system were used as the interlayer for low temperature diffusion bonding of dense alumina parts. Decomposition of hydride nanopowders at bonding temperatures in-situ formed metals and alloys nano particles with oxide free surfaces and high sinter-ability in the interlayer. Nano powders sintering behavior in the interlayer and formation of compounds in the reaction layer during diffusion bonding were studied. Mixture of 50–50 M ratio of AlH3 and Mg(AlH4)2, as the interlayer improved bond strength of the joints. Diffusion bonding products were formed in the MgO–Al2O3 spinel system with different stoichiometries. Bond strength improved up to 202 MPa by induction hot pressing alumina parts at low bonding temperature of 400 °C under pressure of 20 MPa during 30 min bonding period. 相似文献
13.
Jaroslav Sedl
ek Duan Galusek Peter van
rek Ralf Riedel Alan Atkinson Xin Wang 《Journal of the European Ceramic Society》2008,28(15):2983-2993
The response of Al2O3, Al2O3–SiC–(C) and Al2O3–C nanocomposites to grinding was investigated in terms of changes of quality of ground surfaces and of the weight losses with time. The study used monolithic polycrystalline aluminas as references, and alumina-based composites with nanosized SiC and C inclusions and with alumina matrix grain size varying from submicrometer to approximately 4 μm. The studied materials can be roughly divided into two groups. Materials with submicrometer alumina matrix grains (Group 1) wear predominantly by plastic deformation and grooving. Coarse-grained materials (Group 2) wear by mixed wear mechanism involving crack initiation and interlinking accompanied by grain pull-out, plastic deformation and grooving. The wear rate of composites increases with increasing volume fraction of SiC. The Group 2 materials wear much faster then those with submicron microstructure. In all cases (with one exception) the wear resistance of composites was higher than that of pure aluminas of comparable grain sizes used as reference materials. 相似文献
14.
Nitikon Wongwaranon Okorn Mekasuwandumrong Piyasan Praserthdam Joongjai Panpranot 《Catalysis Today》2008,131(1-4):553
Nanocrystalline α-Al2O3 and Ni-modified α-Al2O3 have been prepared by sol–gel and solvothermal methods and employed as supports for Pd catalysts. Regardless of the preparation method used, NiAl2O4 spinel was formed on the Ni-modified α-Al2O3 after calcination at 1150 °C. However, an addition of NiO peaks was also observed by X-ray diffraction for the solvothermal-made Ni-modified α-Al2O3 powder. Catalytic performances of the Pd catalysts supported on these nanocrystalline α-Al2O3 and Ni-modified α-Al2O3 in selective hydrogenation of acetylene were found to be superior to those of the commercial α-Al2O3 supported one. Ethylene selectivities were improved in the order: Pd/Ni-modified α-Al2O3–sol–gel > Pd/Ni-modified α-Al2O3-solvothermal ≈ Pd/α-Al2O3–sol–gel > Pd/α-Al2O3-solvothermal Pd/α-Al2O3-commerical. As revealed by NH3 temperature program desorption studies, incorporation of Ni atoms in α-Al2O3 resulted in a significant decrease of acid sites on the alumina supports. Moreover, XPS revealed a shift of Pd 3d binding energy for Pd catalyst supported on Ni-modified α-Al2O3–sol–gel where only NiAl2O4 was formed, suggesting that the electronic properties of Pd may be modified. 相似文献
15.
T. Chrska J. Hostomský M. Klementov J. Dubský 《Journal of the European Ceramic Society》2009,29(15):3159-3165
Crystallization kinetics of amorphous alumina–zirconia–silica ceramics was studied by nonisothermal differential scanning calorimetry (DSC). Different amorphous materials were produced by plasma spraying of near-eutectic Al2O3–ZrO2–SiO2 mixtures. Phase composition and microstructure of the amorphous materials and nanocrystalline products were analyzed. All of the investigated materials show an exothermic peak between 940 and 990 °C in the DSC experiments. The activation energies calculated from DSC traces decrease with increasing SiO2 concentration. Values of the Avrami coefficients together with results of the microstructural observations indicate that tetragonal zirconia crystallization from materials containing more than 10 wt.% SiO2 proceeds by a diffusion-controlled mechanism with nucleation occurring predominantly at the beginning of the process. In contrast, material with almost no SiO2 exhibited a value of the Avrami exponent consistent with the crystal growth governed by processes at the phase boundary. 相似文献
16.
Na-Ra Park Dong-Mok Lee In-Yong Ko Jin-Kook Yoon In-Jin Shon 《Ceramics International》2009,35(8):3147-3151
Nano-powders of Ni–Fe and Al2O3 were made from NiO and FeAl powders by high-energy ball milling. Nanocrystalline 5Ni0.6Fe0.4–Al2O3 composite was consolidated by high frequency induction heated sintering (HFIHS) method within 2 min from mechanically alloyed powders of Al2O3 and Ni–Fe. The average grain size and mechanical properties of the composite were investigated. 相似文献
17.
This paper presents some important results of the studies on preparation and catalytic properties of nanodispersed Au/Al2O3 catalysts for low-temperature CO oxidation, which are carried out at the Boreskov Institute of Catalysis (BIC) starting from 2001. The catalysts with a gold loading of 1–2 wt.% were prepared via deposition of Au complexes onto different aluminas by means of various techniques (“deposition-precipitation” (DP), incipient wetness, “chemical liquid-phase grafting” (CLPG), chemical vapor deposition (CVD)). These catalysts have been characterized comparatively by a number of physical methods (XRD, TEM, diffuse reflectance UV/vis and XPS) and catalytically tested for combustion of CO impurity (1%) in wet air stream at near-ambient temperature. Using the hydroxide or chloride gold complexes capable of chemical interaction with the surface groups of alumina as the catalyst precursors (DP and incipient wetness techniques, respectively) produces the catalysts that contain metallic Au particles mainly of 2–4 nm in diameter, uniformly distributed between the external and internal surfaces of the support granules together with the surface “ionic” Au oxide species. Application of organogold precursors gives the supported Au catalysts of egg shell type which are either close by mean Au particle size to what we obtain by DP and incipient wetness techniques (CVD of (CH3)2Au(acac) vapor on highly dehydrated Al2O3 in a rotating reactor under static conditions) or contain Au crystallites of no less than 7 nm in size (CLPG method). Regardless of deposition technique, only the Cl-free Au/Al2O3 catalysts containing the small Au particles (di ≤ 5 nm) reveal the high catalytic activity toward CO oxidation under near-ambient conditions, the catalyst stability being provided by adding the water vapor into the reaction feed. The results of testing of the nanodispersed Au/Al2O3 catalysts under conditions which simulate in part removal of CO from ambient air or diesel exhaust are discussed in comparison with the data obtained for the commercial Pd and Pt catalysts under the same conditions. 相似文献
18.
An investigation was conducted of noble metal and metal oxide catalysts deposited on Al2O3. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO2, CoO, Ag2O, In2O3, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In2O3/Al2O3 catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al2O3 oxidation and metal oxide combined catalyst system was also studied. Pt/Al2O3 and In2O3/Al2O3 combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C. 相似文献
19.
Bo-Hyuk Jang Tae-Hun Yeon Hyun-Sik Han Yong-Ki Park Jae-Eui Yie 《Catalysis Letters》2001,77(1-3):21-28
Barium-containing NO
x
storage catalyst showed serious deactivation under thermal exposure at high temperatures. To elucidate the thermal deterioration of the NO
x
storage catalyst, four types of model catalyst, Pt/Al2O3, Ba/Al2O3, Pt–Ba/Al2O3, and a physical mixture of Pt/Al2O3 + Ba/Al2O3 were prepared and their physicochemical properties such as BET, NO TPD, TGA/DSC, XRD, and XPS were evaluated while the thermal aging temperature was increased from 550 to 1050°C. The fresh Pt–Ba/Al2O3 showed a sorption capacity of 3.35 wt%/g-cat. but the aged one revealed a reduced capacity of 2.28 wt%/g-cat. corresponding to 68% of the fresh one. It was found that this reduced sorption capacity was directly related to the deterioration of the NO
x
storage catalyst by thermal aging. The Ba on Ba/Al2O3 and Pt–Ba/Al2O3 catalysts began to interact with alumina to form Ba–Al solid alloy above 600°C and then transformed into stable BaAl2O4 having a spinel structure. However, no phase transition was observed in the Pt/Al2O3 catalyst having no barium component, even after aging at 1050°C. 相似文献
20.
Dense Ti3AlC2/TiB2 composites were successfully fabricated from B4C/TiC/Ti/Al powders by spark plasma sintering (SPS). The microstructure, flexural strength and fracture toughness of the composites were investigated. The experimental results indicate that the Vickers hardness increased with the increase in TiB2 content. The maximum flexural strength (700 ± 10 MPa) and fracture toughness (7.0 ± 0.2 MPa m1/2) were achieved through addition of 10 vol.% TiB2, however, a slight decrease in the other mechanical properties was observed with TiB2 addition higher than 10 vol.%, which is believed to be due to TiB2 agglomeration. 相似文献