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1.
《武汉理工大学学报(材料科学英文版)》2018,(6)
The effect of thermal wave at the initial stage for non-conductive Al_2 O_3 powders compact in field assisted sintering technique(FAST) was investigated. The Lord and Shulman type generalized thermoselastic theory was introduced to describe the influence of thermal-mechanical interaction, as well as the heat transport and thermal focusing caused by thermal wave propagation. The expression of vacancy concentration difference of the particles was deduced by considering transient thermal stress. Subsequently, the relationship between activation energy and vacancy concentration difference was obtained. The mechanism of surface diffusion, volume diffusion, simultaneous surface and volume diffusion was analyzed. The numerical simulations indicate that low sintering temperature can obtain high local temperature by the superposition effect of thermal wave. Vacancy concentration differences were improved during FAST compared with hot-pressure and pressureless sintering, thereby decreasing the sintering time. By contrast, the activation energy declined with the decrease of vacancy concentration difference in the neck growth process. 相似文献
2.
Composite powders of nanocrystalline WC-10Co (15wt%),Y2O3 (8mol%) stabilized nanocrystalline ZrO2 (30wt%),industrial cobalt powder (4.5wt%) and submicron Al2O3 (55wt%) composite powders were fabricated by high-energy ball-milling process.The nanocomposite powders were consolidated by microwave sintering process at temperature ranged 1300℃-1550℃ for 15min,respectively.The optimum consolidation conditions,such as temperature,were researched during microwave sintering process.Vickers Hardness of the consolidated cermets was measured by using a Vickers indentation test,and density of specimens was also determined by Archimedes’ principle.Microwave sintering process could not only increase the density of Al2O3-ZrO2-WC-Co cermets and reduce the porosity,but also inhibit abnormal grain growth. 相似文献
3.
The structure and properties of the glass-ceramics were tested with X-ray diffraction testing instrument,correlative software,and other modern testing means.Then the effect of Al2O3 content on internal stresses in CaO-Al2O3-SiO2 glass-ceramics was studied deeply.In order to study the relationship of Al2O3 to the residual stress of CaO-Al2O3-SiO2 glass-ceramics,X-ray diffraction "sin2ψ" was used.The means utilized the x radial incidence produced from cathode radial tube,and took the space between crystals as measurement of strain.When the stresses produced,the space between crystals changed and the diffraction peak moved during Bragg diffraction.The magnitude of movement is related to the stresses.The experimental results show the residual stress is considerably high and Al2O3 can influence the mechanical properties of this material hugely. 相似文献
4.
艾桃桃 《武汉理工大学学报(材料科学英文版)》2009,24(5):732-735
Al2O3/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO2 and Nb2O5, and the microstructure and mechanical properties were investigated. The results indicate the fine Al2O3 particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb2O5 content. The bending strength and fracture toughness reach to a maximum when Nb2O5 content is 6 wt%, under 642 MPa and 6.69 MPa·m1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al2O3 particles. 相似文献
5.
By means of transient plastic phase process, the Al2O3-SiC-Me composites were produced throungh adding metal aluminium and silicon-powder to Al2O3-SiC materials. Under the condition of the same content of silicon and aluminium mixed-powder, the effect of silicon powder
addition on properties of Al2O3-SiC-Me composites was studied by means of XRD and EPMA analyses in the temperature range of 300°–1600°C. The results indicated
that the content of metal phase in the sample at 1600°C increases with increasing silicon powder content. At the same time,
when the temperature is lower than 1100°C, the strength of samples gradually increases with increasing temperature. However
when the temperature is higher than 1100°C, the strength of samples gradually decreases with increasing temperature, and this
change is very small. The results also indicated that at the same sintering temperature, the sample with 6% silicon powder
has the maximum strength.
Supported by the Chen Yunbo Academician Fund (Grant No. 2007CY021) 相似文献
6.
HEFeng NIUFeng LOUGuang-hui DENGZhi-guo 《武汉理工大学学报(材料科学英文版)》2004,19(3):51-53
The erosion resistance tests were used to research the erosion wear behavior of CaO-Al2O3-SiO2 system glass-ceramic. With the orthogonal test method, the factors thai affect the erosion wear of CaO-Al2O3-SiO2 system galss-ceramic such as pacticles property, impact angle, impact time, size of particles were discussed. The results show that erosion rate rises along a straight line at the early period of erosion wear. With the impact time increased, the erosion rate deviates from original staight line, tendency of the erosion rate increases, With the size of paricle increased , it will have more kinetic energy, the erosion rate of the surface of glass-ceramics ploate rises. 相似文献
7.
吴顺华 《武汉理工大学学报(材料科学英文版)》2010,25(5):730-733
The effect of ZnO-B2O3(ZB) glass addition on the sintering behavior, microstructures and microwave dielectric properties of BaO-Nd2O3-TiO2-Bi2O3 (BNTB) system was investigated with the aid of X-ray diffraction, scanning electron microscopy and capacitance meter. It
is found that the ZB glass addition, acting as a sintering aid, can effectively lower the sintering temperature of BNTB system
to 850 °C. The dielectric constant of BNTB-ZB ceramics increases with the increase of soaking time and the value of dielectric
loss decreased with increasing soak time. The optical dielectric properties at 1 GHz of ɛ=74, tan δ=4×10−4, and TCC=25 ppm/°c were obtained for the BNTB system doped with 25 wt% ZB glass sintered at 850 °C for 2 h, representing
that the BNTB-ZB ceramics could be promising for multilayer low temperature co-fired ceramics applications. 相似文献
8.
王茂祥 《武汉理工大学学报(材料科学英文版)》2009,24(5):721-724
The fabrication process of Cu/Al2O3/MgF2/Au double-barrier metal/insulator/metal junction (DMIMJ) was introduced, and more stable light emission from this junction
was successfully observed. The light emission physical mechanism of the junction was discussed. Results show that light emission
spectrum of this structure locates at wavelength of 250–700 nm with two peaks at around 460 nm and 640 nm, which moves towards
shorter wavelength region in comparison with that of the Al/Al2O3/Au junction. The light emission efficiency of this junction ranges from 0.7×10−5–2.0×10−5, which is 1 to 2 orders higher than that of the single-barrier Al/Al2O3/Au junction. The improved properties of this structure should be due to the electrons resonant tunneling effect in the double-barrier. 相似文献
9.
The investigated low temperature Co fired ceramics(LTCC) composite of 60wt% CaO-Al2O3-B2O3-SiO2 glass and 40wt% α-Al2O3 as a filler is a non-reactive system, which is a critical part of the low temperature Co fired ceramics process. Through a study on densification process, the phase transformation and microstructure can be revealed. Its composites typically consist of CaO-Al2O3-B2O3-SiO2 glass and α-Al2O3 powders of average particle size (D50=3.49 mm). The sintering behavior, phase evaluation, sintered morphology, and microwave dielectric properties were investigated. In the fire range of 800 to 900 ℃, the composites were crystallized after completion of densification. It is found that the composites start to densify at 825 ℃, simultaneously, the dielectric constant (εr) reaches its maximum. With increasing heat-treatment temperatures, due to the loose microstructure of the material, tanδ increases slightly. The last of the sintered samples were identified as partly Anorthite at 850 ℃. At that temperature it has εr of 7.9 and tanδ less than 1×10-3, and can be used as a promising LTCC material. 相似文献
10.
Al2 O3/Al composite was fabricated by the reaction between SiO2 and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The
formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably
by the reaction temperature, reaction time and the quantity of SiO2. The morphologies of Al2O3 have different features, depending on the reaction temperature. The composite has equaxed Al2O3 grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al2O3 grains and aluninum. The composite has a frame-shaped Al2O3 microstructure at the reaction temperature of above 1250°C.
CHENG Xiao-min: Born in 1964
Funded by the National Natural Science Foundation of China (No. 91522) 相似文献
11.
FAN Jinpeng ZHAO Daqing XU Zening & WU Minsheng . Department of Mechanical Engineering Tsinghua University Beijing China . Key Laboratory for Advanced Manufacturing by Materials Processing Technology Tsinghua University Beijing China 《中国科学E辑(英文版)》2005,48(6):622-631
Since their discovery by Iijima[1], carbon nanotubes (CNTs) have been the focus in novel materials research. Theoretical and experimental studies show[2-9] that CNTs have extraordinary mechanical and electrical properties. Krishnan et al.[2] have reported that the mean value of Young’s modulus of single-wall nanotubes (SWNTs) is 1.25 TPa. Yu et al.[3] measured Yang’s modulus of multi-wall nanotubes (MWNTs) between 270 and 950 GPa and breaking strength between 11 and 63 GPa. The ele… 相似文献
12.
王启岁 《武汉理工大学学报(材料科学英文版)》2018,33(1):97-101
To improve the cyclic stability at high temperature and thermal stability, the spherical Al2O3-modified Li(Ni0.5Co0.2Mn0.3)O2 was synthesized by a modified co-precipitation method, and the physical and electrochemical properties were studied. The TEM images showed that Li(Ni0.5Co0.2Mn0.3)O2 was modified successfully with nano-Al2O3. The discharge capacity retention of Al2O3-modified Li(Ni0.5Co0.2Mn0.3)O2 maintained about 99% after 200 cycles at high temperature (55 °C), while that of the bare one was only 86%. Also, unlike bare Li(Ni0.5Co0.2Mn0.3)O2, the Al2O3-modified material cathode exhibited good thermal stability. 相似文献
13.
Three series of Al2O3/Al laminated ceramic matrix composites,named SPA,SPV and HP,were fabricated by different methods.SPA and SPV were prepared using Al2O3 slices and Al slurry via screen printing and subsequent heat treatment in air or vacuum.HP samples were made by hot pressing the layered stack of Al foils and Al2O3 slices.SEM and XRD were applied to analyze the microstructure and the interlayer crystal phase.The bending strength,fracture toughness and fracture work of the samples made by the three methods were measured and compared.The results show that the composites have much better toughness and higher fracture work than the Al2O3 slice.Among the samples made by the three methods,the samples made by hot pressing have the optimum mechanical performance.The displacement-load curves and fracture mechanism were analyzed. 相似文献
14.
The oxidation behavior of Al2O3/TiAl in situ composites fabricated by hot-pressing technology was investigated at 900° in static air. The results indicate that the mass
gains of the composites samples decrease gradually with increasing Nb2O5 content and the inert Al2O3 dispersoids effectively increase the oxidation resistance of the composites. The higher the Al2O3 dispersoids content, the more pronounced the effect. The primary oxidation precesses obey approximately the linear laws,
and the cyclic oxidation precesses follow the parabolic laws. The oxidized sample containing Ti2AlN and TiAl phases in the scales exhibits excellent oxidation resistance. The oxide scale formed after exposure at 900°C
for 120 h is multiple-layered, consisting mainly of an outer TiO2 layer, an intermediate Al2O3 layer, and an inner TiO2+Al2O3 mixed layer. From the outer layer to the inner layer, TiO2+Al2O3 mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer. Near the substrate, cross-section micrograph
shows a relatively loose layer, and micro- and macro-pores remain on this layer, which is a transition layer and transferres
from Al2O3+TiO2 scale to substrate. The thickness of oxide layer is about 20 μm. It is also found that continuous protective alumina scales
can not be observed on the surface of oxidation scales. Ti ions diffuse outwardly to form the outer TiO2 layer, while oxygen ions transport inwardly to form the inner TiO2+Al2O3 mixed layer. Under long-time intensive oxidation exposure, the internal Al2O3 scale has a good adhesiveness with the outer TiO2 scale. No obvious spallation of the oxide scales occurs. The increased oxidation resistance by the presence of in situ Al2O3 particulates is attributed to the enhanced alumina-forming tendency and thin and dense scale formation. Al2O3 particulates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface, thereby the TiO2 growth rate decreases, which is also beneficial to improve the oxidation resistance. Moreover, the multi-structure of the
TiO2+Al2O3 mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance
of the as-sintered composites.
Supported by the Special Program for Education Bureau of Shaanxi Province, China (Grant No. 08JK240) and Scientific Research
Startup Program for Introduced Talents of Shaanxi University of Technology, China (Grant No. SLGQD0751) 相似文献
15.
何峰 《武汉理工大学学报(材料科学英文版)》2016,31(6):1267-1271
Influence of aluminum addition on the structures and properties of SiO2-B2O3-Al2O3-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10-6 °C-1, respectively. 相似文献
16.
Thermal energy storage is an attractive option for effectiveness since it gives flexibility and reduces energy consumption and costs. New composite materials for storage and transformation of heat of NaCl-Al2O3 composite materials were synthesized by one-step synthesis method. The chemical composition, morphology, structure, and thermal properties were investigated by XRD, EDS, SEM, and DSC. The results show that NaCl can be absorbed by Al2O3 particle from 800 to 900 °C for Al2O3 particle surface is rich active structure. The results also indicate that the leakage of NaCl when the phase change can be prevented by Al2O3 particles and the enthalpy of phase change of NaCl-Al2O3 material is 362 J/g. The composites have an excellent heat storage capacity. Therefore, this study contributes to one new thought and method to prepare high temperature heat storage material and this material can be applied in future thermal engineering. 相似文献
17.
The influence of Mo on the microstructure, bending strength and HV of Ti/Al2O3 composite was studied, and the influence mechanism was analyzed. The results indicate that after the addition of Mo, the
composite organization is finer and phases distribution is better-proportioned which make the microstructure denser, the bending
strength and HV of composite are also increased to a degree. But the bending strength increases first then decreases with
the increasing of Mo content, so the appropriate Mo content for the Ti/Al2O3 composite is to be further confirmed.
WANG Zhi: Born in 1962
Funded by Natural Science Foundation of China (No. 50232020) and Natural Science Foundation of Shandong Province (No. 2002F21) 相似文献
18.
The glass forming region of Bi2O3-B2O3-BaO ternary system was investigated. A serial of glass samples with high Bi2O3 content in Bi2O3-B2O3-BaO system were prepared by using conventional melting and quenching meld, and the refractive indexes and absorption spectra
of samples were measured. It is found that the refractive index of samples as well as the UV absorption increase with the
increase of BaO content. According to the Tauc law, optical band gap E
opg which is assumed to be the effective energy band gap E
g is calculated and decreases with the increasing BaO content, and the ratio of E
g/E
opg is 1.3. 相似文献
19.
A n-Hexyl NH3Sr2Nb3O10 is obtained by the stepwise ion-exchange reaction, then is dispersed in aqueous solution of trinuclear acetato-hydroxo iron
(III) nitrate, [Fe3(OCOCH3)7OH·2H2O]NO3, and the interlayer potassium cations of the perovskite niobate are exchanged with the partially hydrolyzed trinuclear acetato
complex ions. On heating, the exchanged complex ions are converted into iron oxide pillars which keep the perovskite sheets
apart. The product is characterized by XRD, SEM, EDAX and surface area measurement respectively.
Zhang Hui: Born in 1970
Funded by the National Natural Science Foundation of China (No. 50002007), Major Program of Ministry of Education (No. 0201)
and Open Foundation of State Key Lab of Advanced Tech. for Materials Synthesis and Processing. 相似文献
20.
Yuan Xi-ming Xu Yong-sheng Yu Jiang-bo Wang Yong-qian Wang Hong-mei 《武汉理工大学学报(材料科学英文版)》2003,18(1):41-43
Nano fluorescent powder of Y4Al2O9: Eu3+ was synthesized by sol-gel method. The XRD shows that the product prepared at 900°C is pure-phase Y4Al2O9: Eu3+. The Y4Al2O9 powder is nano-size crystal testified by BF and ED analysis of TEM. The grain diameter of Y4Al2O9 is in the range between 20 and 50nm, and its average is 30 nm. The luminescent spectra show that Eu3+ ious occupy two kinds of sites in Y4Al2O9 crystal lattice. One is in the strict inversion center, and the other is in off lying inversion center. When excited with
UV light (λ=254nm), Y4Al2O9: Eu3+ exhibits an orange emission bond at λ=590 nm due to the5Do→7F1 transition and a red emission band at λ=610 nm due to5Do→7F2 transition.
YUAN Xi-ming: Born in 1951
Funded by Key Scientific and Technological Project of Hubei Province (2001 AA102A03) 相似文献