bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Performance of Alkaline Niobate-Based Ceramics Manufactured by Two-Step Sintering
Authors: Fang Jian , Wang Xiao Hui , Li Long Tu
Published: June 2012

In this paper, a typical Li- and Ta/Sb- modified alkaline niobate-based ceramics are prepared by conventional sintering and two-step sintering respectively. The ceramics sintered by two-step sintering exhibit better electrical properties than the samples prepared by conventional sintering. The related mechanisms are also discussed in terms of phase-structures and microstructures. Results show that two-step sintering can restrain the volatilization of alkali elements and compositional segregation during the process of sintering dense alkaline niobate-based ceramics, and enhance the electrical properties accordingly. Therefore, two-step sintering is a promising approach to achieve high performance alkaline niobate-based ceramics.
Effects of Sintering Process on the Properties of Ti3SiC2/Cu Composite
Authors: Lu Jin Rong , Zhou Yang , Zheng Yong , Li Shi Bo , Huang Zhen Ying , Zhai Hong Xiang
Published: June 2012

In this paper, a new type of Ti3SiC2/Cu composites with the volume fractions of 30% Ti3SiC2 particle was prepared by hot pressing and vacuum sintering respectively. The effects of sintering temperature and holding time on the density, resistance and Vickers hardness of Cu-30vol%Ti3SiC2 composite were investigated. The results show that the mechanical properties of the composites prepared by hot pressing are better than that prepared by vacuum sintering. The relative densities of Cu-30vol% Ti3SiC2 composites are rather high in suitable sintering conditions. It achieved 100% for the composites prepared by hot pressing at 930°C for 2h, and 98.4% for the composites prepared by vacuum sintering at 1250°C for 1h. At the same time, the maximum Vickers hardness reached 1735MPa at 900°C by hot pressing. The resistance and Vickers hardness of the composites decreased with an increase in sintering temperature, whereas the density increased. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) were used to observe the microstructure of the composites. The relationship between microstructure and mechanical properties was discussed.
Direct Write Assembly of 3-Dimensional Structures with Aqueous-Based Piezoelectric Inks
Authors: Li Ya Yun , Li Bo , Sun Jing Bo , Cai Kun Peng , Zhou Ji , Li Long Tu
Published: June 2012

A kind of aqueous based suspensions of lead lanthanum zirconnate titanate (PLZT) was developed for direct ink writing (DIW) assembly. Piezoelectric ceramic woodpile structures with diameter of 315-470μm were fabricated from these inks by using DIW. The preparation of aqueous based piezoelectric inks, the principle of DIW and the sintering process were systematically discussed. The ink with solids volume fraction over 70% by 1 day aging reveals shear-thinning behavior and proper viscoelastic properties, which ensures a feasible extrusion in the whole shaping process. The PLZT samples sintered at varying temperatures between 1150 oC and 1250 oC for 2h or 4 h in either air or a lead-rich atmosphere yielded various microstructures observed by scanning electron microscopy (SEM). Choosing the optimum sintering condition, the sintered products were densified with relative density exceed 98%. The test of X-ray diffraction (XRD) analysis reveals that the main phase of sintered samples is rhombohedral Pb0.93La0.07(Zr0.65Ti0.35)0.9825O3. The direct ink writing technique has advantages of good design ability and rapid forming capability, which opens up a potential route for the design and fabrication of piezoelectric devices.
Superplastic Forming of Oxide Ceramic Composite
Authors: Chen Guo Qing , Zu Yu Fei , Luo Jun Ting , Fu Xue Song , Zhou Wen Long
Published: June 2012

The paper mainly focused on the two issues that restricted the practical application of superplastic ceramics, which were the low strain rate in superplastic forming as well as resulted severely cavitation in deformed materials. The alumina-based composites Al2O3-ZrO2(3Y) and Al2O3-30mol%ZrO2(3Y)-30mol%MgAl2O4(AZ30S30) were selected as research materials. The nano-sized composite powders were synthesized by heating of ethanol-aqueous salt solutions method. The superplastic forming tests under the compressive stress state were carried out to evaluate the superplastic formability of the as-sintered materials. The results demonstrate that the following conditions are the essentials for attaining high-strain-rate superplastic forming in alumina based ceramic composites: reduction in the initial grain size by second phase dispersion and insurance of a homogeneous microstructure, enhanced diffusivity by co-doped certain elements, suppressed dynamic grain growth in deformation, as well as provide new rate-controlling accommodation process in superplastic forming. The results also indicate during the superplastic forming the cavitation damage was eliminated because of compression stress state, which ensured the mechanical properties after deformation. Therefore, the postdeformation mechanical properties after superplastic forming were enhanced in some extent.
Prediction of Critical Pressure in the Preparation of Composites by Vacuum - Pressure Infiltration Process
Authors: Huang Ming Tao , Wang Yang Wei , Wang Fu Chi , Gao Ju Bin
Published: June 2012

The SiC3D/Al composite with high SiC content were prepared by vacuum– pressure infiltration process, and the prediction model of infiltration pressure threshold involving capillary pressure and viscous resistance was established. The effects of model parameters on the critical infiltration pressure were analyzed. The results show that the main factors are the permeability coefficient of SiC performs and the temperature of molten aluminum alloy. Temperature affects the melt viscosity and the wetting angle between SiC and molten alloy. The ingiltration pressure threshold of the specific infiltration system had been calculated by this model, which is in agreement with experimental results.
Zirconia Fiber Memberance Prepared by Electrospinning
Authors: Gao Fang , Liu Kai , Li Hai Jian , Qi Jian Mei
Published: June 2012

Electrospinning is an effective appoach to get one-dimensional nano structured materials.Thin PVA/zirconium oxychloride and yttrium nitrate composite fibers were prepared by using precurssor solution and electrospinning technique. Influence factors in PVA content and concentration of inorganic salts on nanofibers were discussed in this paper.After calcinations of the above precursor fibres, ZrO2 nanofibres could be successfully obtained.The fibres were characterized by SEM, XRD, respectively.
Elastic Properties of Spark Plasma Sintered (SPS) ZrB2/SiC-Sm2Zr2O7 Composites
Authors: Yan Zhen Yu , Zhu Shi Zhen , Xu Qiang , Liu Ying
Published: June 2012

Due to extremely low oxygen transportation at elevated temperature, samarium zirconate (Sm2Zr2O7) with pyrochlore structure was introduced into ZrB2-based functional gradient composites as oxygen insulation. The elastic properties of composites with different phase ratio were investigated in this study. A series of nearly-fully dense ZrB2-based composites with different Sm2Zr2O7 content was consolidated by spark plasma sintering (SPS) technology. The microstructure and phase compositions were characterized by scanning electronic microscope (SEM) and X-ray diffraction respectively. The dynamic elastic properties were obtained by resonance method at room temperature. The results revealed that the addition of Sm2Zr2O7 can significantly improve its densification for the refractory diboride, which mainly caused by the high sintering activity of Sm2Zr2O7. Young’s modules of the series of composites obviously decreased with the increasing content of Sm2Zr2O7. The low Young’s modulus of Sm2Zr2O7 was the main reason. The Young’s modules of the series of composites were calculated theoretically. The experimental results matched the theoretical data well. A little deviation appeared due to the continuous structure of Sm2Zr2O7 in the composites.
The Gibbs Energy Description of Nd:YAG System
Authors: Cui Xiao Jin , Pan Wei
Published: June 2012

Sublattice model is used to describe the complex system, Neodymium-doped yttrium aluminum garnet (Nd:YAG), and then Gibbs energy function of Nd:YAG system is seriously evaluated, mainly focusing on the instability of NAG, which has a direct effect on the Gibbs energy of NAG as well as Nd:YAG. Incorporating the selected literature thermochemical data of Nd:YAG system with the reevaluated parameters in Gibbs energy function according to a method utilized for defining the instability of NAG, the Gibbs energy function is well described. Trying to be more convincible, the method utilized for defining compounds stability and reevaluating the parameters has been test in Al2O3-Nd2O3, Al2O3-Y2O3, Al2O3-Gd2O3, Al2O3-Sm2O3 systems, achieving a satisfying agreement.
Preparation of Mullite Nanocomposites Powders by the Hydrothermal Crystallization Method from Coal Gangue
Authors: Tong Ling Xin , Li Jin Hong , Liu Fang
Published: June 2012

Mullite nanocomposites powders have been successfully synthesized from pretreated coal gangue via hydrothermal crystallization process. The mullite nanocomposites powders are investigated and charactered by laser particle size analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) analysis, selected area electron diffraction (SAED) analysis and energy-dispersive X-ray (EDX) analysis. Moreover, the reaction mechanism of this process is speculated according to MAS-NMR results. It is indicated that mullite nanocomposites powders can be prepared at 80-90 °C for 3 h with NaOH concentration of 2-4 mol/L and L/S ratio (liquid/solid ratio in mass) of 10 mL/g by using calcined coal gangue as precursor. The agglomerate powder size of D50 is about 3.83-4.71 mm. Furthermore, some imperfective puncheon-shaped crystals exist among a large number of whole puncheon-shaped crystals which are about 30-70 nm in length and about 10-20 nm in diameter. MAS-NMR analysis indicates that the nano-size mullite grow around the central atom-Al, Si of [AlSi]O4 tetrahedral and the growth unit Al[OH]4- exist in this process definitely.
Effect of Different Composite Additives on Thermal Conductivity of Corundum Ceramics
Authors: Gu Xing Yong , Wu Shao Ling , Zhang Ai Hua , Luo Ting , Chen Yun Xia
Published: June 2012

To improve the thermal conductivity of alumina ceramics, different inorganic materials such as AlN, BN, Si3N4 and SiC which own high thermal conductivity were integrated with 96% alumina ceramic. The effect of addition of AlN, BN, Si3N4 and SiC on water absorption, flexural strength and thermal conductivity of the as-prepared alumina-based composite ceramics were investigated. Field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) were employed to characterize the microstructure and phase compositions of the composites. The results showed that sintering temperature of 96% alumina ceramic matrixes were improved in varying degree due to adding AlN, BN, SiC and Si3N4. A small quantity of Al6Si2O13 crystals were formed in the case of adding Si3N4 and SiC, which is due to the oxidation of Si3N4 and SiC into SiO2 in the air and the subsequent reaction with alumina. At appropriate firing temperature, the flexural strength of the composites with the addition of AlN is the best and higher than corundum matrixes. Meanwhile, the thermal conductivity of the composites with AlN has 110% improvement. It is obvious that AlN with high thermal conductivity is suitable for improving the thermal conductivity of corundum ceramics.
Corrosion Behavior of Al2O3 Ceramics in the Acid and Alkaline Solutions
Authors: Huang Long , Luo Shan Shan , Li Wen Kui
Published: June 2012

Al2O3 materials were used in a very wide range due to its good mechanical properties and relative low manufacture cost. The corrosion resistance of Al2O3 materials in acid, alkaline and sea water solutions gained more and more attention because many application situations are severe and the working life is shorten due to the corrosion. In this paper, the corrosion behavior of Al2O3 based materials in acid and alkaline solutions was studied and effect of corrosion time on the corrosion behavior of Al2O3 materials was investigated. The microstructure of as prepared Al2O3 materials was characterized by SEM. Possible corrosion process and mechanism was discussed in details. The results reveal that the as prepared Al2O3 materials show better corrosion resistance in alkaline solution than in acid solutions. In both acid and alkaline conditions, the corrosion mainly occurs in the grain boundary. Mass loss increased with increasing corrosion time, while the corrosion rate was decreased.
Research the Performance of Alumina Insulation Material by Freeze-Drying
Authors: Yang Dao Yuan , Wei Guang Hui
Published: June 2012

The traditional method of preparation alumina insulation material includes the addition of pore-forming agent, direct foaming, foam impregnation and gel-casting. In this experiment, α-alumina as raw material, silica fume as an additive, Combination freeze-drying method, add pore-forming agent and direct foaming successfully prepared low-density, high strength, low thermal conductivity of alumina insulation material. Change the particle size of pore-forming agent can be get different properties of the sample. The SEM photograph was clearly observed that the hole wall dense uniform, α-alumina particles sufficient contact, no significant ice sublimation hole left. There are also the reasons of the sample with higher value of bending strength and compressive strength. This can make a control of porosity, as well as pore size, pore shape and pores space topology of alumina insulation material.
The Effects of Density on Thermal Conductivity of Al2O3 Fiber Composite Papers
Authors: Zhang Shi Chao , Chen Yu Feng , Shi Xing , Wu Wei , Sun Hao Ran , Wang Guang Hai
Published: June 2012

In this study, Al2O3 fiber composite papers with a certain strength and flexibility were prepared by pressure filtration. Microstructure and pore size of the composite papers with different density were investigated and thermal conductivities were measured by plane table thermo-conductivity meter at 600°C to 1200°C. Then the relationship between density ρ and thermal conductivity λ was studied, and the optimum density of Al2O3 fiber composite papers at different temperature was determined.
3D Interconnetive Porous Silica Ceramics Prepared by Gel Casting with Egg White Protein as a Foaming Agent
Authors: Xu Hai , Liu Jia Chen , Zhao Ying Na , Hou Zhen Guang
Published: June 2012

Highly porous silica ceramics were produced by gel casting with egg white protein (EWP) as a foaming agent and evaluated by measuring the porosity, mechanical strength and microstructure. After drying, the green bodies were debindered and sintered at 1300°C for 4 h. The influences of the EWP content on the open porosity as well as the strength were investigated. The porosity of the obtained porous silica ceramics was within 70.2%-86.1%, the bending strength decreased from 6.81 MPa to 5.48 MPa. It was found that the strength dependence of the porosity was well described by a modified exponential relation of the form σ=σ0exp(-BP), where P is the porosity and B is a constant (B = 1.37 was obtained by fitting the experimental data). This finding is in agreement with other literature data and seems to indicate a common feature of all porous ceramics.
Effect of Pyrophyllite on the Mullite Generation in Ternary Porcelain System
Authors: Pee J.H. , Kwak A.N. , Kim Jong Young , Kim Yoo Jin , Kim Kyung Ja
Published: June 2012

Promoting of mullite generation has been studied by replacing kaolinite with pyrophyllite because of mullite has excellent strength and thermal shock resistance. Effects of promoting of mullite generation and vitrification by replacing kaolinite with pyrophyllite on the mechanical and thermal properties were investigated. Addition of 45-55% pyrophyllite as a replacement of kaolinite (pyrophyllite (45-55%)-feldspar (30%)-clay (20%)) could vitrify samples (water absorption: 0.05%, bulk density: 2.66g/cm3) and improve the strength (122MPa) of samples fired at 1280°C. In ternary porcelain system, pyrophyllite-feldspar-clay, mullite generation of samples with 50% pyrophyllite reaches about 78.7% and thermal expansion coefficient is 5.4×10-6/K. Beyond 50% pyrophyllite addition, quartz and cristobalite phases increased. And thermal expansion coefficient of samples decreased with increasing of mullite amount.
Reinforcement of Porcelain by Mullite Fiber for Power Applications
Authors: Chen Lei , Qiao Li
Published: June 2012

Porcelain insulator has a long history of being used in power transmission and distribution due to the good strength, chemical resistance capacity and mature manufacturing technology. However, there are some disadvantages of porcelain materials which could be the barrier for the development of porcelain insulators such as brittleness, which could lead to severe hurt to personnel and power station after a burst failure. In this paper, mullite fibers are used in order to improve the mechanical properties of porcelain material and further enhance the anti-burst behavior of porcelain insulators. The samples were prepared by traditional wet method for ceramic materials and several material characterization methods including XRD, SEM were employed to evaluate the reinforcement effect. The test result showed that with the addition of mullite fibers both the bending strength and the fracture toughness of porcelain materials have been largely improved. The investigation provided a meaningful pathway for further development not only for porcelain insulators but also for the power industry.
Rare Earth and Perovskite Composite Ceramics Applied for the Thermistor with Wide Temperature Range
Authors: Zhang Bo , Zhao Qing , Chang Ai Min , Zhao Peng Jun , Guan Fang
Published: June 2012

Different compositions (aY2O3+bCeO2)-0.4YCr0.5Mn0.5O3 (a+b=0.6) were prepared via a conventional solid-state reaction at 1200°C, and sintered under air atmosphere at 1600°C. XRD patterns analysis has revealed that for 0<a<0.6, the major phases present in the calcined bodies are Y2O3, CeO2 and orthorhombic perovskite YCr0.5Mn0.5O3 phase, respectively. SEM and EDAX observations confirm the obtaining of three-phased composite ceramics. The brighter regions are the Y2O3 and CeO2 phase, whereas the darker are perovskite phase. All the NTC thermistors prepared show a similar linear relationship between the ln of the resistance and the reciprocal of the absolute temperature, indicative of NTC characteristics. For 0≤a≤0.6, the plotting curves of resistance- temperature characteristic are none linear on the wide temperature range, exhibit two branches. The obtained B25/150 and B700/1000 constants of the thermistors are in the range 3600-4400K and 6700-12000K. The magnitude order of the resistivity at 25°C is of 106-107Ωcm and activation energies vary from 0.313 to 1.029 eV at low and high temperatures, respectively. These compounds, having good NTC characteristics in a wide range of temperatures, could be applied as potential candidates for NTC thermistors from ambient to 1100°C.
Synthesis and Characterization of Double Pore Size Multiphase Materials from Waste Aluminum Slag and Activated Carbon
Authors: Chen Yan Qing , Wu Ren Ping
Published: June 2012

A new type of double pore size activated alumina/activated carbon multiphase material was made by using waste aluminum slag and activated carbon as main raw materials. The microstructures and pore size distribution of the new material were characterized by SEM and BET techniques. Iodine adsorption value was used to evaluate the adsorption performance of the multiphase materials, and the benzene adsorption capability was also measured. The results show that the specific surface area of the activated alumina/activated carbon multiphase materials is 261.95m2/g, pore volume can reach 0.25m3/g, and the iodine adsorption value is 381.97mg/g. BET pore size distribution shows that micropores and mesopores both exist in the composite material. The micropores range from 0.6 to 1.4nm, and the mesopores range from 3.0 to 7.0nm. The benzene adsorption capability of this new material is excellent, with a saturated adsorption capacity of 241.00 mg/g, much better than pure activated alumina or activated carbon.
Mineral Compositions and Textures of Jadeite Orebody and its Country Rock in Nammaw, Myanmar
Authors: Yang Hui Xuan , An Mei , Ye Dong , Zu En Dong
Published: June 2012

This paper studies the mineral compositions and textures of seven rock specimens from jadeite orebody and its country rock in Nammaw, Myanmar through XRD and observation of hand specimens and thin sections. The jadeite orebody is mainly composed of jadeite and minor zeolite minerals. Phlogopite schist and chromite-bearing amphibolite occur between the orebody and its country rock. The country rock is antigorite serpentinite. Outside of serpentinite is schist consisting of chlorite, hastingsite and polylithionite. The specimens of jadeite orebody show mainly following texture types: radiation texture, inequigranular crystalloblastic texture, granular-prismatic crystalloblastic texture, metasomatic texture and mylonitic texture. These textures indicate that the formation of the orebody is related to the intrusion of some fused mass or hydrothermal solution and then the orebody underwent dynamical metamorphism and hydrothermal metamorphism.
Evaluation of Firing Temperature of the Bangsan Porcelain
Authors: Pee Jae Hwan , Lee E.M. , Kim G.H. , Kim Y.J. , Kim Kyung Ja , Gang G.I. , Jung D.S. , Katsuki H.
Published: June 2012

Thermal expansion behavior method in reheating process was used to evaluate firing temperature of white porcelains excavated in Yanggu area, Jangpyung-Ri No.1 (J1, 17~20 centuries) and Songhyun-Ri No.5 (S5, 14~15 centuries). For standard specimen used for evaluation of the firing temperature, we used starting materials (YC) that have similar chemical composition of J1 and S5 and then they were fired at various temperatures from 800 to 1300°C. Starting temperature of shrinkage and shrinkage rate were measured in thermal expansion behavior in reheating process of the of 1st fired specimens and the base line for original firing temperature was set based on the results from the measurement of the standard specimens. Effects of particle size of starting materials for standard specimens on the thermal expansion behavior in reheating process were also investigated and the base lines were also set. As a result, we found that difference in particle size for starting materials could cause different shrinkage rate and starting temperature of shrinkage in reheating process even with the same original firing temperature.
Microstructures, Properties and Fracture Behavior of Solidified TiC-TiB2 Composites with Increasing Content of TiB2
Authors: Huang Xue Gang , Zhang Long , Zhao Zhong Min , Pan Chuan Zeng
Published: June 2012

By adjusting the mole ratio of C and B elements in combustion system, solidified TiC-TiB2 composites with different TiB2 mole fraction were achieved by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that with increasing TiB2 content, the matrix of TiC-TiB2 composite ceramics transformed a number of fine TiB2 platelets from the TiC spherical grains, and fine-grained even ultrafine-grained microstructures were achieved in solidified TiC-50mol% TiB2 due to eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 simultaneously reached the maximum values of 21.5 ± 1.5 GPa and 860 ± 35 MPa , whereas TiC-66.7mol%TiB2 presented the maximum fracture toughness of 13.5 ± 1.5 MPa • m0.5. FESEM fractography analyses of the ceramics exhibited a mixed mode of transcrystalline fracture of TiC spherical grains and intercrystalline fracture of TiB2 platelets, and the tendency of intercrystalline fracture was obviously enhanced with increasing TiB2 content to be 66.7 mol%, resulting in enhanced toughening mechanisms of crack deflection, crack-bridging and pull-out by fine TiB2 platelets, thus, the highest flexural strength was achieved in TiC-50mol%TiB2 due to the achievements of both fine-grained microstructures and high fracture toughness in the full-density solidified ceramics.
Tailoring Plate-Like Grained ZrB2 Ceramic via a Strong Magnetic Field Alignment Method Followed by Spark Plasma Sintering
Authors: Hu Chun Feng , Huang Qing , Zhang Guo Jun , Sakka Yoshio
Published: June 2012

Through strong magnetic field alignment (SMFA) method followed by spark plasma sintering (SPS), dense tailored ZrB2 ceramic could be prepared using the plate-like grains as initial material. The measured Lotgering orientation factor f(00l) on the textured top surface (TTS) was high as 0.62 and f(hk0) on the textured side surface (TSS) was 0.65. Vickers hardness measurement showed the anisotropic mechanical property of textured sample. On the TTS, the hardness was 13.4 ± 0.9 GPa, while on the TSS the hardness was 12.0 ± 0.9 GPa.
Effect of BN Short Fiber Content on Mechanical Properties of ZrB2-SiC UHTCs
Authors: Zhou Chang Ling , Wang Yan Yan , Cheng Zhi Qiang , Wang Chong Hai , Liu Rui Xiang
Published: June 2012

ZrB2-20%volSiC ceramic composites with different volume of BN short fiber were fabricated by the hot-pressing sintering under 2000°C. The content of BN short fiber changed from 0 to 15vol%. The density, flexural strength, fracture toughness and thermal expansions coefficient were studied. The microstructures of the samples were observed by scanning electron microscopy. The results show that the introducing of BN short fiber into the ZrB2-20%volSiC lead to a serious of change to the mechanical properties of the ceramic. When the content of the BN short fiber is 10vol%, the flexural strength and fracture toughness reach 422.1MPa and 6.15 MPa•m 1/2 respectively. And the mechanism of the increasing toughness was studied.
Synthesis of Amorphous Al2O3-ZrO2 Powders Prepared by Citric Acid Gel Process
Authors: Wang Yi , Liu Jia Chen
Published: June 2012

AmorphousAl2O3ZrO2powders were synthesized by citric acid gel process. The effects of molar ratio of citric acid to total metal ions concentration and the calcined powders with CA/M=2:1 were investigated through XRD and SEM analysis. Thermal behavior of the dried gel with CA/M=2:1 was studied by DSC/TG. Amorphous Al2O3-ZrO2 powders with particle size of about 3μm were obtained.
Effect of Adding Phase on the Properties of ZrB2 Based Ultra-High-Temperature Ceramics
Authors: Song Jie Guang , Wang Fang , Xu Ming Han , Li Shi Bin , Ji Gang Chang
Published: June 2012

ZrB2 belongs to a class of ceramics defined ultra-high-temperature ceramics with extremely high melting temperatures, but ZrB2 ceramics is difficultly sintered and easily oxidized. To make ZrB2 ceramics possess the high relative density and the better oxidation resistance. The effects of adding phase on the sintering and oxidation resistance mechanism of ZrB2 based high-temperature multi-phase ceramics were investigated. YAG and Al2O3 help for the densification of ZrB2 based ceramics. The oxidation layer thickness of sintered ceramics adding YAG or YAG-Al2O3 phase is thinner than that of sintered pure ZrB2 ceramics under the same oxidation condition, the oxidation layer thickness of sintered ceramics adding YAG-Al2O3 phase is thinner than that of sintered ceramics adding YAG phase, the oxidation layer thickness of sintered ceramics is decreased with an increased Al2O3 content.
A Multilayer Coating Method to Prepare Borosilicate Glass-Aluminum Composite Coating on Cubic Boron Nitride Particle
Authors: Guo Huan Huan , Fan Bing Bing , Li Jian , Zhang Rui
Published: June 2012

CBN particles coated with borosilicate glass-aluminum composite coating (Glass-Al-CBN) were prepared by a multilayer coating method. The coated composite particles were sintered at 800°C for 2h. XRD, DTA-TG, SEM techniques were used to characterize the samples. It was found that AlN was formed by the reaction of Al and CBN. The mechanical properties and the oxidation resistance of the composite was improved due to the presence of the glass coating and alumina.
Influence of Adding β-SiС on the Performance of α-SiС Pressureless Sintering Ceramics
Authors: Deng Li Rong , Lu Shu He , Wang Xue Ying , Wang Jia Bo , Liu Ying Bo , Wang Xiao Gang , Yang Xin Ling
Published: June 2012

βThe B4C and phenolic resin were used as sintering additives to study the different β-SiC（cubic silicon carbide) addition to the performance of α-SiC pressureless sintering ceramics in this paper, and the optimum sintering temperature and the best β-SiC addition amount were determined. By XRD, SEM,density testing and other tests showed that, all the β-SiC transform 6Hα-SiC during the sintering process ,the ceramics have a Vickers hardness of 18.04 GPa,a frature toughness of 4.51MPa ,a density of 3.13g/cm3 by adding 15wt% β-SiC powders.
Improved Oxidation Resistance of SiС-Based Ceramic Matrix Composites by In Situ Reaction with Si3N4 Filler
Authors: Wu Bin , Wang Zhen , Dong Shao Ming
Published: June 2012

SiC-Si3N4 powders and modified SiC-based ceramic matrix composites (CMCs) were fabricated using polycarbosilane (PCS), divinylbenzene (DVB) and Si3N4 filler. Si3N4 was introduced into CMCs fabricated through polymer infiltration and pyrolysis (PIP) to lower down the carbon content by in-situ carbothermal reaction, which derived from pyrolyzed PCS-DVB. The oxidation resistance and three point bending strength of modified C/SiC composites were effectively enhanced. The phase composition, microstructure of SiC-Si3N4 powders and modified C/SiC composites were investigated by XRD, SEM and TEM.
The Dispersion of SiC Nanopowders in Ethanol
Authors: Hou Yang , Hu Ping , Han Wen Bo
Published: June 2012

The dispersion of SiC nanopowders in ethanol solution was studied by sedimentation test, particle size measurement and TEM analysis. The dispersion behavior of SiC nanopowders in ethanol solution was strongly dependent on the pH values, types and amounts of dispersant. PEI was found to be effective for the dispersion of SiC nanopowders in ethanol solution. With the addition of PEI, the isoelectric points of SiC nanopowders in ethanol solution were at pH 9.5, and shift to pH 12.3. The stability of SiC suspension increased with the dispersant content increasing until reached 2.5 wt% PEI. The suitable pH value for the dispersion of SiC nanopowders should lower than 10.
Mechanical Properties of Short Carbon Fiber-Reinforced SiC-Matrix Composites and Correlation to Fibers
Authors: Guo Shu Qi , Nishimura Toshiyuki , Kagawa Yutaka
Published: June 2012

PAN and Pitch short carbon fiber-reinforced SiC matrix composites were fabricated by using a melting infiltration technique. The microstructure of the composites was characterized by scanning electron microscopy. The flexural strength of the composites was measured at room and high temperatures. The thermal conducitivity of the composites were evaluated. Effects of fibers on mechanical properties and thermal conductivity were assessed. The experimental results showed that the silicification of fibers during siliconizing was prevented due to the presence of barrier layer on the surface of fiber. Also, flexural strength and thermal conductivity depended on fibers used and content of fibers.
Microstructures and Mechanical Properties of SiC-TiB2 Composite Prepared by Pressureless Sintering
Authors: Yue Xin Yan , Wang Jian Jun , Sun Qi , Ru Hong Qiang
Published: June 2012

SiC-TiB2 composite was prepared at 2298 K by using pressureless sintering. The microstructures and mechanical properties of the SiC-TiB2 composite were investigated. The SiC-TiB2 composite with 5 mass % B4C-C showed the optimized comprehensive properties. The volume density, hardness, flexural strength and fracture toughness of that were 3.43 g/cm3, 18.5 GPa, 353 MPa and 4.67 MPa•m1/2, respectively. The excessive B4C-C content might decrease the mechanical properties of the composite.
Porous Si3N4 Fabricated Using Benzoic Acid as Pore-Forming Agent
Authors: Wang Hong Sheng , Liu Kai , Wang Chong Hai , Liu Jian , Liao Rong , Gao Fang , Liu Rui Xiang
Published: June 2012

In this study, porous Si3N4 ceramics with interconnected pores were prepared by cold isostatic pressing using benzoic acid as a pore-foring agent. The pore-forming agent of green bodies was sublimation rapidly below 200°C without carbon remained. Mechanical Properties were tested by universal testing machine, and the microstructures of the specimen were observed by scanning electron microscopy (FEI Sirion 200). The resulting shows, many fibrous β-Si3N4 grains grown from the internal wall of the round pores, and the porous distribution uniform in the matrix. By changing the content of benzoic acid, the silicon nitride ceramics with different porosity was fabricated. As the acid content decreased from 15wt% to zero, the porosities decreased from 57.6% to 48.0%, flexural strength increased from 36.8MPa to 141.2MPa. Both the grains and suitable interfacial bonding strength contributes to the high fracture strength.
Electric Conductive Si3N4/TiN Composite Ceramic Manufactured by Liquid-Qhase Sintering
Authors: Jiang Yong , Wu Lan Er , Huang Zhen Kun
Published: June 2012

Si3N4 based electric conductive ceramics were fabricated by pressureless liquid phase sintering with La2O3-AlN and TiN as sintering and conductive additives. The Si3N4 powder was synthesized by SHS (self-propagation high-temperature synthesis) method. The bulk density, mechanical properties and electrical conductivity of the sintered samples were studied. Microstructure and phase composition were analyzed by SEM and XRD. The results show that the density of the samples is above 96%. The sintered samples consist of β-Sialon and the conductive phase. β-Sialon grains shows elongated and the conductive phase granular which formed electric conductive network. The sintered samples have good mechanical properties and its electric resistivity is from 1012 Ω•cm above drop to 1 Ω•cm below.
Porous Nitride Ceramic Composites with Low-Dielectric Properties
Authors: Liao Rong , Wang Chong Hai , Liu Jian , Wang Hong Sheng , Wei Qi Hong
Published: June 2012

The influences of the mullite hollow balls content on selected properties of Si3N4-BN matrix ceramics were investigated.The experiment showed that the apparent densities and the porosity of the nitride ceramic composites decreased as the mullite hollow balls contents increased.The strength of the porous nitride ceramic composite was greatly improved, and the dielectric constant decreased with a small addition of the mullite hollow balls. SEM micrographs showed that the mullite hollow balls became one flesh with the nitride ceramic composites.Many large pores appeared in the whole materials. The properties of the nitride ceramic composites were effectively improved.
Dielectric and Mechanical Properties of Porous Si3N4-BN Ceramic Composites
Authors: Dou Jian Peng , Liu Xiao Lin , Ma Jing Tao , Lin Xu Ping
Published: June 2012

Recently, ceramic composites with low dielectric constant, low loss tangent, high flexural strength and high thermal shock resistance have received a considerable attention as candidate materials for certain high speed radome. In this paper, Si3N4-BN ceramic composites were fabricated by dry-press processing and cold isostatic pressing, with α-Si3N4 and BN as starting powder, Al2O3 and Yb2O3 as sintering additives, PMMA as pore-forming agenSubscript textt. After sintering for 2 h at 1750°C, porous Si3N4-BN ceramic composites with a three-point bending strength of 50~120MPa and a dielectric constant of 3.2~4.4 at 7~18 GHz frequency were obtained. The sintered body was mainly β-Si3N4 grains; BN was dispersed in the grains. The formation of β-Si3N4 grains was demonstrated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. Furthermore, the influence of the BN content on the dielectric and mechanical properties was also studied. The porous Si3N4-BN ceramic composites showed a lower dielectric constant and shrinkage. For above excellent properties, Si3N4-BN ceramic composites have been became one of the most hopeful candidate materials for high speed radome.
Synthesis and Characterization of Spinel-Type NiCr2O4 Nanocrystalline
Authors: Hu Zhi Qiang , Liu Xian Qing , Huang De Feng , Gao Hong , Liu Jing Xiao
Published: June 2012

In this article, spinel–type NiCr2O4 Nanocrystalline were prepared by the citrate method. After doping it into P25 (degussa, TiO2), NiCr2O4/TiO2 thin film photoanode were prepared by screen printing process on the surface of Fluorine Tin Oxide (FTO) Glass. And then they were assembled into Dye sensitized TiO2 Nanocrystalline solar cells (DSSC). The as–prepared NiCr2O4 powders were characterized by differential thermal analysis/thermo gravimetry (DTA/TG), X–ray diffraction (XRD) and ultraviolet visible (Uv–Vis) diffuse spectra. The properties of the solar cells were investigated by Solar Simular and Keithley Sourcemeter, respectively. The results showed that the grain size of the NiCr2O4 particles obtained at optimum synthesis temperature (1000 °C) was about 40.23 nm and the band gap was 1.8ev. The cell properties increased when the doping amount of NiCr2O4 was 1wt%. The open–circuit voltage (Voc) of Dye Sensitized TiO2 Nanocrystalline Solar Cell was from 0.71V up to 0.73V, The short–circuit photocurrent (Jsc) of DSSC increased from 5.21mA·cm-2 to 6.95mA·cm-2. The photoelectric conversion efficiency (η) was from 2.40% up to 3.14%, which was 30.8% higher than the pure TiO2 thin film photoanode.
The Influence of Sintering Temperature on Properties and Microstructure of TiN/Si3N4 Composite
Authors: Wu Lan Er , Jiang Yong
Published: June 2012

Electrical discharge machining can be used easily for the materials which has good conductivity. In order to improve conductivity of Si3N4 based ceramics, TiN/Si3N4 composite was sintered by adding TiN into Si3N4 powder. In the present research, influence of sintering temperature (1535-1925°C, 8 temperatures) on properties and microstructure of the TiN/Si3N4 composite were investigated with La2O3, AlN as sintering additives, liquid phase pressure less sintering used. Densities of the sintered sample were measured. Bending strength, hardness, fracture toughness and electrical resistively of the sample were tested. Phase composition and microstructure of the samples were analyzed by XRD, SEM and EDX. The results showed that the density and fracture toughness of the sintered bodies reached maximum at temperature of 1760°C (relative density of 97.9%; fracture toughness of 8.5 MPa•m1/2) in the sintering temperature range of 1535~1925°C. With increasing of temperature, the bending strength and hardness of the samples kept raising, reached maximum at temperature of 1925°C (bending strength of 634MPa and Vickers hardness of 1869). But the weight lost at the highest temperature was the severe. Microstructure and EDX showed that crystals of the Si3N4 transferred into complete β phase from α + β both phases. The grain of Si3N4 grew up into long columnar from equiaxial fine particles. The fine grain of TiN grew up also. The comprehensive performances of the samples are better at sintering temperature of 1760°C. The long columnar β-Si3N4 grains interweaved with conductive TiN particles, formed conductive nets through sintering. At this sintering temperature, the bending strength of TiN/Si3N4 sintered body was 560MPa，Vickers hardness 1708MPa. The conductivity of the sintered bodies was irregular with the difference of temperature. The minimum of the conductivity is 20Ω.
Effect of MgO and NH4OH on Formation of 5Mg(OH)2·MgSO4·3H2O Whiskers
Authors: Yu Ri , Pee Jae Hwan , Kim Hyung Tae , Kim Kyung Ja , Kim Young Woong , Kim Yoo Jin
Published: June 2012

The Magnesium hydroxide sulfate hydrate whiskers (5Mg(OH)2.MgSO4.3H2O, abbreviated 513MHSH) have attracted much attention due to its practical applications as filler and reinforcement. However, it is difficult to produce high quality MHSH because plate-like Mg(OH)2 impurities were formed in high concentrations of OH- and interaction between Mg2+ and OH-. In this work, to reduce formation Mg(OH)2, molar ratio ofSuperscript text magnesium oxide (MgO) and magnesium sulfate (MgSO4.7H2O) were controlled. As a result, when low concentration of SO42-, MHSH whiskers co-existed with hexagonal plate Mg(OH)2. The molar ratio of MgSO4.7H2O/MgO was high, uniform MHSH whiskers were formed without Mg(OH)2. In addition, appropriate amount of NH4OH has affected formation of high quality MHSH. Their morphologies and structures were determined by powder X-ray diffraction (XRD) scanning electron microscopy (SEM) and thermo-gravimetric analyzer (TGA)
TiCN-Based Cermets Strengthened with SiC Nano-Whiskers by Spark Plasma Sintering
Authors: Peng Ying , Peng Zhi Jian , Ren Xiao Yong , Rong Hui Yong , Wang Cheng Biao , Fu Zhi Qiang , Qi Long Hao , Miao He Zhuo
Published: June 2012

TiCN-based cermets with different amounts of SiC nano-whiskers were prepared by spark plasma sintering. The microstructure and mechanical properties of the as-prepared cermets were investigated. X-ray diffraction revealed that there were no SiC peaks detected, turning out some peaks of new carbide and silicate hard phases. Scanning electron microscopy indicated that there were more and more pores in the cermets with increasing amount of SiC whisker added, and the fracture mechanism of the cermets was mainly inter-granular fracture. With increasing addition amount of nano-SiC whisker, the hardness and flexural strength of the cermets increased first and decreased then, presenting the highest hardness (2170 HV) and flexural strength (750 MPa), respectively, when the addition content of nano-whiskers is 2.5 wt%.
Preparation and Characterization of Amorphous SiO2 Coating SiCp/Cu Composites
Authors: Ren Xiang Qian , Fan Bing Bing , Han Qian Fei , Wang Peng Hui , Zhang Rui
Published: June 2012

Hybrid sol–gel process was used to fabricate the precursor particles of amorphous SiO2 coating at the composites of SiCp⁄Cu, and then formed by Vacuum hot-pressed method. Various methods were used to measure the sintered compacts of different SiC volume fraction. The results showed that the densities, bending strength and conductivity were decreased slightly with the increases in the amounts of SiC, and the vickers hardness were increased first and then decreased. The techniques of DTA–TG, SEM–EDS and XRD were used to characterize the phases and the morphologies of the composite particles and composites. It was inferred that the formation of SiO2–Cu2O eutectic mixture in this system and the viscous interaction of amorphous SiO2 improved the interfacial modification of the composites of SiCp⁄Cu.
Two Fracture Dynamics Problems of Fiber Reinforced Ceramics
Authors: Lü Nian Chun , Cheng Yun Hong , Ji Jin Li
Published: June 2012

After fiber reinforced ceramics occur a crack, its bridging fibers must engender, moreover the crack usually runs in the format of similarity. In order to analyze easily dynamic problems of fiber reinforced ceramics, bridging fiber segment is substituted for loads. When a crack moves at high speed, its fibers will break continuously. By application of the built dynamic model and the ways of self-similar functions, analytical solutions of the displacements, stresses and dynamic stress intensity factors under the action of a running increasing force Px2/t2 and a motive unit step load, respectively, can be gained, and it is also used to attain the concrete solution by means of superposition theorem.
Impedance Analysis on the Percolation Mechanism of the Nickel/Calcium Copper Titanate/Polyvinylidene Fluoride Composite
Authors: Yang Wen Hu , Yu Shu Hui , Sun Rong , Du Ru Xu
Published: June 2012

The composites composed of micro-sized calcium copper titanate (CCTO) and nano-sized metallic nickel (Ni) fillers in the polyvinylidene fluoride (PVDF) matrix (Ni/CCTO/PVDF) were prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60 %. The impedance spectra and a serial equivalent circuit model consisting three RC units were used to investigate the behaviors of the Ni/CCTO/PVDF three-phase composite system near the percolation threshold. The real (Z′) and imaginary (Z″) parts of the impedance dramatically decreased as the Ni content was increased from 22% to 24% indicating a transition from an insulating to a conducting state. This transition process has been realized by the changes in the capacitance derived from the model, and the investigation has been carried out to clarify the release mechanism of the entrapped electrons at the interfaces.
Carbon Nanotube/Polymer Nanocomposites: Improved or Reduced Thermal Stabilities?
Authors: Li Zhuo , Wilkins Stewart J. , Moon Kyoung Sik , Wong C.P.
Published: June 2012

The effects of carbon nanotubes (CNTs) on the thermal stability of CNT/polymer nanocomposites are discussed using CNT/silicone composites as a model compound. Pristine CNTs can improve the thermal stability of polymer composites due to the high thermal stability of CNTs, their network structure and free radical scavenging capabilities. However, impurities such as metal catalyst residues and defects such as carboxylic acid functional groups in CNTs can lead to decreased thermal stability of CNT/silicone nanocomposites. Acid purification is an efficient way to remove metallic impurities and can enhance free radical scavenging capabilities. However, controlling the amount of oxidation is important to avoid acid catalyzed thermal degradation induced by carboxylic acid groups on CNT surfaces.
Luminous Chitosan-Dye Nanocomposite Particles with Enhanced Lifetime and Stability
Authors: Wong Ka Wai , Li Xing Hua , Lam Novem C. Y. , Chan Kimmy Mui
Published: June 2012

Nanoparticular chitosan-dye nanocomposites were prepared by a facile ionotropic gelation, which show a much improved stability against UV and ozone attack. The nanocomposites do not contain any toxic material. Also, as natural occurring biopolymeric chitosan is used as the matrix material, the nanocomposite is biocompatible and biodegradable with high bioaffinity. After suitable bioconjugation, the developed luminous chitosan-dye nanocomposites can be used as target biolabels in various medical and biomedical applications.
Rapid Toolpath Correction for Five-Axis High Efficiency Machining Based on Image Analysis
Authors: Zhang Li Qiang , Wang Da Zhong
Published: June 2012

Five-axis high speed machining can improve the efficiency and accuracy obviously, but the machining errors and tool interference are likely to happen due to the complexity of tool motion. So the collision detection and verification of tool path are very important and necessary before machining the part. Using a combination of process simulation and collision detection based on image analysis, a rapid detection approach is developed in this research. The geometric model provides the cut geometry for the collision detection and records a dynamic geometric information for in-process workpiece. For the precise collision detection, a strategy of image analysis method is developed in order to make the approach efficient and maintian a high detection precision. An example of five-axis machining propeller is studied to demonstrate the proposed approach.
Study on Surface Roughness in Ultrasonic High-Speed Milling of SiCp/Al Composites
Authors: Xiang Dao Hui , Yue Guang Xi , Liu Hai Tao , Zhao Bo
Published: June 2012

The orthogonal analysis and single factor analysis were used to analyze the roughness of SiCp/Al metal matrix composites (SiCp/Al MMCs) with ultrasonic high-speed milling and high-speed milling. The influences of milling speed, feed and milling depth on the roughness were studied. The research indicates that the roughness in ultrasonic high-speed milling is lower than that in high-speed milling under the same condition, at the same time the optimal parameters of ultrasonic high-speed milling are obtained, this has a guiding significance for finish machining of SiCp/Al composites.