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Showing papers by "Wuhan University of Technology published in 1997"


Journal ArticleDOI
TL;DR: According to a space charge theory analysis, the space-charge potential of the Y 2O 3 and Al 2 O 3-codoped ZrO 2 is negative, which is the result of an Al′ Zr segregation and a V ǫ depletion in the space charge layers.

43 citations


Journal ArticleDOI
TL;DR: In this article, the effect of porosity on the thermal-electric properties of porous Al-doped SiC ceramics by hot pressing and pressureless sintering methods is reported.
Abstract: Silicon carbide has being used in many practical applications because of its many excellent properties, such as extreme hardness, excellent thermal and mechanical properties and high thermal shock resistance. There are many reports in the literature on silicon carbide. Recently, as high-temerature thermoelectric materials, silicon carbide ceramics have attracted much attention in the literature [1±6]. Koumoto et al. [1] reported that porous SiC ceramics showed high ®gures of merit for thermoelectric energy conversion. Since then, the thermoelectric properties of porous SiC ceramics fabricated by using different starting SiC powders (e.g. synthesized by carbothermal reduction of silica contained in rice hull ash [2] and the gas-phase reaction method [3]) and different processing routes (e.g. sintering in nitrogen or argon atmosphere [4] and reaction sintering [5]) have been investigated. Despite efforts to investigate the porous SiC thermoelectric ceramics, the effect of porosity on the thermoelectric properties is still unclear. In this letter, the effect of porosity on the thermal-electric properties of porous Al-doped SiC ceramics by hot pressing and pressureless sintering methods is reported. Commercial a-SiC powders (grain size ,10 im, purity .98.5%) were ball milled with different contents of Al powder (400 mesh, purity .99%) for 24 h. The samples were prepared in two different ways: (i), pressureless sintering (PS) under argon for 1 h at 1770 8C after the mixtures were cold isostatic pressed at 200 MPa and (ii) hot-pressing (HP) under argon at 20 MPa and 1900 8C for 0 h or 1 h in highstrength graphite dies. During the sintering, graphite end-caps were bonded to the silicon carbide cylinders, which facilitated attachment of thermocouples and electrical leads for Seebeck coef®cient and electrical conductivity measurements. The relative density of the ceramic samples, measured by the liquid displacement method, is shown in Fig. 1. The porosity of the samples decreased with Al dopant concentration, which is supported by scanning electron microscope (SEM) observation. X-ray diffraction (XRD) analyses showed that there existed only a single SiC phase and no other new phase. The average grain size was around 8 im from SEM. Electrical conductivity measurements were carried out under argon by a two-probe a.c. method. Two platinum lines were sealed on two platinum slices, which were pressed to ®rmly attach to the polished graphite electrodes on the two ends of the samples. The electrical conductivity was obtained from two resistance values measured under two opposite current directions (biased at about 0.2 V a.c. voltage). Fig. 2 shows the electrical conductivity of the 4 wt % Al-doped SiC ceramics with different densities. It is clear that the electrical conductivity increases with the decrease of porosity, as expected. The thermal conductivity was measured using a

41 citations


Journal ArticleDOI
TL;DR: In this article, an engineering geology evaluation method based on an artificial neural network (AN 2 EGEM) is presented, which eliminates the defects of traditional evaluation methods, which rely excessively on experience and are difficult to quantify.

39 citations


Journal ArticleDOI
TL;DR: In this article, up to 1.5 mol% Nb 2 O 5 was added to 9 mol% Y 2 O 3 -stabilized ZrO 2, and the resistances were measured by the complex impedance approach in air.

35 citations


Journal ArticleDOI
TL;DR: Several methods of manufacturing γ-aluminium oxynitride spinel (ALON) powder are discussed in this article, including the carbothermal reduction process and reaction sintering process.
Abstract: Several methods of manufacturing γ-aluminium oxynitride spinel (ALON) powder are discussed in this paper In the carbothermal reduction process, ALON is an intermediate compound, and powders with a high ALON content may be produced in flowing nitrogen below 1650 °C if process parameters are carefully controlled In addition, ALON may be produced when Al2O3/C mixtures are heated in a coke powder bed above 1650 °C In the reaction sintering process, ALON is unlikely to form below 1600 °C in a flowing nitrogen atmosphere or in a coke powder bed, owing to the instability of ALON and the fact that the solid–solid reaction does not readily occur unless additives, eg MgO, MgAl2O4, are employed

35 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method to improve the quality of the data collected by the data collection system of the Internet.Abstracts are not published in this journal. But
Abstract: Abstracts are not published in this journal

28 citations



Journal ArticleDOI
TL;DR: In this paper, single crystal X-ray diffraction was used to confirm that the C11A7 · CaF2 is cubic, with a = 11.981 A, space group I43d, Z = 2 and D X = 2.

13 citations


Journal ArticleDOI
TL;DR: In this paper, a volume-weighted averaging procedure was introduced to estimate the effect of particle size distribution on deformation in the case of both no damage and including particle fracture, and the difference between the deformation, secant and the incremental, tangent modulus approaches chosen for EMA modeling was addressed.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the heating effect of the system in the microwave field, which was influenced by several factors including dielectric properties of synthesis system and thermal insulate structures, was discussed in detail.
Abstract: Microwave equipment at 2 450 MHz was employed to prepare BaTiO3. The heating effect of the system in the microwave field, which was influenced by several factors including dielectric properties of synthesis system and thermal insulate structures, was discussed in detail. The heating rates of the synthesis system were mainly determined by BaCO3 and TiO2 at low temperature and by TiO2 and BaTiO3 at high temperature. The results show that the heating effects in microwave field are greatly different from those in conventional furnace. The reaction of BaCO3 and TiO2 only lasts for 3 min at 1 100°C, and the fine, narrow-distributed and well-crystallized powders were prepared.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the authors showed that the reaction dynamics in microwave is suitable for the Carter equation and that the activity energy for reaction of BaCO3 and TiO2 in the microwave field was 4226 kj/mol, which was only one fifth of the conventional reaction.
Abstract: The difference of intermediate products, microstructure and element concentration in the particles between microwave synthesized samples and conventional samples was responsible for the existence of non-thermal effect in the microwave field The diffusions of Ba2+, Ti4+ in the microwave field were enhanced, so that the diffusion of Ti4+ could not be neglected as in the conventional solid state reactions The influences of the microwave field were mainly expressed as diffusion coefficient and the driving force of ionic motion The intermediate phase Ba2TiO4 which occurred in the conventional solid reaction was not found during microwave syntheses The quantity analyses based on XRD experimental data show that the reaction dynamics in microwave is suitable for the Carter equation The activity energy for reaction of BaCO3 and TiO2 in the microwave field was 4226 kj/mol, which was only one fifth of the conventional reaction

Journal ArticleDOI
TL;DR: In this paper, the effects of the sample geometry and the TiC side surface state on the cyclic thermal shock behavior were investigated, together with thermal stresses under steady-heating conditions.
Abstract: Cyclic thermal shock tests on three TiC/Ni3AI FGM specimens were carried out under simulated large temperature-difference conditions. The effective thermal conductivity was measured and the variation of microstructure was observed. The effects of the sample geometry and the TiC side surface state on the cyclic thermal shock behavior were investigated, together with thermal stresses under steady-heating conditions. The relation between the variation of effective thermal conductivity and crack propagation was also investigated. The damage which occurred in these FGMs was mainly caused by excessive inplane compressive stresses on the surface of the TiC side during the cyclic thermal shock tests.


Journal ArticleDOI
TL;DR: In this article, a DC voltage of 8 V at 600°C in air was applied to codoped ZrO2 specimens, and electrons were injected from the cathode into the ZRO2, thus colour centers were formed.

Journal ArticleDOI
TL;DR: In this paper, the effects of quenching treatment in terms of the phase present, microstructure and electrical properties for doped V2O3 system were examined in the presence of PM phase.
Abstract: The effects of quenching treatment are examined in terms of the phase present, microstructure and electrical properties for doped V2O3 system, in this paper. The results indicate that the specimens transform to the PM phase and show microcracks in the structure after quenching. The room temperature (RT) resistivities become low and the resistivity ratios increase remarkably. There are optimum values for the RT resisitivity and resisitivity ratio under a certain quenching time. The electrical properties of quenched specimens containing Fe metal phase become stable after subsequent thermal cycles.




Book ChapterDOI
01 Jan 1997
TL;DR: In this article, a density functionally graded materials (DFGM) was hot-pressed by powder stacking with adjusting soaked temperature, load interval and pressure, and quasi-continuous density variation along the thickness direction.
Abstract: To lower the temperature-enhancement inside the target material and achieve higher pressure and velocity is important in dynamic high-pressure technology. It can be realized through quasi-isentropic loading by density functionally graded materials (DFGM). A kind of Al-Cu DFGM was hot-pressed by powder stacking with adjusting soaked temperature, load interval and pressure et al. The FGM has quasi-continuous density variation along the thickness direction.

Journal ArticleDOI
TL;DR: In this paper, the microstructure of (Nb,Ti)C-35Ni (Y 2 O 3 ) cermet prepared via hot isostatic pressing (HIP) was observed by transmission electron microscopy (TEM).

Journal Article
TL;DR: A preview compensating algorithm for the foreknown external-disturbances with the help of the theory on preview control is presented and it is shown that this algorithm can get rid of the disturbances on the system only if selecting appropriate preview information.
Abstract: There are various external-disturbances on the position servo system,but some of these can bepreviewed This paper presents a preview compensating algorithm for the foreknown external-disturbanceswith the help of the theory on preview control The practical simulation of numerical value and the analysis ofexperiments show that this algorithm can get rid of the disturbances on the system only if selectingappropriate preview information Therefore the algorithm is effective and feasible

Book ChapterDOI
01 Jan 1997
TL;DR: In this article, the analysis model for the response of ceramic-metal FGMs under dynamic thermal loading is investigated, focusing on the effects of residual stress, thermal- mechanical coupling and hardening.
Abstract: The analysis model for the response of ceramic-metal FGMs under dynamic thermal loading is investigated Emphasis is put on the effects of the residual stress, thermal- mechanical coupling and hardening model for the materials It is shown that the three effects are significant when the materials’ response is inelastic and should carefully be considered in constructing the analysis model

Journal ArticleDOI
TL;DR: In this paper, the Raman and IR spectra of LnTPPTS·10H2O [Ln=La,Sm, TPPTS=P(m-C6H4SO3) 3 3− ] complexes are reported.
Abstract: The Raman and IR spectra of LnTPPTS·10H2O [Ln=La,Sm, TPPTS=P(m-C6H4SO3) 3 3− ] complexes are reported. Based on the observed Raman and IR characteristic frequencies, a vibrational assignments has been made for these complexes. Coordination induces a lengthening of the S−O bonds and a shortening of the C−S bond. The C−S stretching frequencies should therefore increase while the position of the\(v_{(SO_3 )} \) should move to a lower wavenumber. Vibrational modes of metal-oxygen polyhedron V (La-O) at 146, 168,253 cm−1 are the structural charactrization for coordinate bond of LnTPPTS complexes.

Book ChapterDOI
01 Jan 1997
TL;DR: In this article, a finite element finite-element finite-grain fabrication (FEMFGM) was used for the first wall materials of thermonuclear experimental reactors, and the residual thermal stresses during fabrication were calculated by finite element inethod.
Abstract: TiC/Ni3Al-Ni system was chosen for the potential use as the first wall materials of thermonuclear experimental reactors. The residual thermal stresses during fabrication were calculated by finite element inethod. Based on the consideration of minimum stress, minimum ratio of stress to fracture strength and proper distribution of thermal stress in pure TiC side, the optimum design with the distribution exponent P = 1.6 was reached. According to the design result, TiC/Ni3Al-Ni FGM samples were then successfully fabricated.

Journal ArticleDOI
TL;DR: In this article, a diphasic oriented polar glass (DOPG)-ceramic (Sr2TiSi2O8 and SrTiO3) is first prepared, which shows the piezoelectric property of Sr2TiNiSi 2O8 crystal and the high dielectric properties of SrinTiO 3 crystal.
Abstract: A new kind of the oriented polar glass—ceramics i.e. the diphasic polar glass—ceramic (Sr2TiSi2O8 and SrTiO3) is first prepared. This unique material shows the piezoelectric property of Sr2TiSi2O8 crystal and the high dielectric property of SrTiO3 crystal.

Book ChapterDOI
01 Jan 1997
TL;DR: In this paper, a very thin gradient layer and wide range concentration distribution of FGMs were prepared by SHS/QP and heat treating, which showed that the thickness of the gradient layer is decided by the heat treatment to a great extent.
Abstract: SHS/QP is an efficient method for preparing FGM. But in synthesis process, high temperature and high velocity may result in some results not expected by us, which as a consequence will affect the FGM’s performance. A1 so, repeatability of the concentration distribution is not good. In this work, FGMs were prepared by SHS/QP and heat treating, which had very thin gradient layer and wide range concentration distribution. The manufacturing was carried out as following: the pellet including mixture-metal layers was processed by SHS/QP, and then the product was treated longer than two hours at 700 °C ~ 1200 °C. Quantitative and qualitative analyses were carried out to different points in the gradient layer. The result indicates that the thickness of the gradient layer is decided by the heat treatment to a great extent. The chemical and phase composition, and the connection between grains show no great change.

Journal ArticleDOI
TL;DR: Some Harnack type inequalities for analytic operator functions have been obtained in this paper, for analytic functions with respect to analytic functions and analytic operators with analytic functions only; see Section 2.1.