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Abstract  

A substoichiometric analytical method, using a carrier-free radioisotope, is developed for the accurate and precise determination of yttrium. The method is applied to yttrium determination in high-Tc superconducting oxide ceramics. The error of the analytical results is estimated to be within 1%.

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Abstract  

A kinetic model for the reaction sintering of oxide ceramics in the system Al2O3–SiO2–ZrO2 using mixtures of intermetallic compounds is presented. A 2D finite-difference model is developed to describe the exothermic gas-solid reactions taking place during the firing of ZrAl3/ZrSi2 powder compacts. The model accounts for the oxidation kinetics of the powder particles, as well as the consumption and diffusion of gaseous oxygen through the porous matrix. Additionally, possible changes in the pore structure of the green body due to the oxidation reactions and sintering effects are incorporated in the model. The resulting differential equations are coupled with a two-dimensional Fourier heat balance equation leading to a system of nonlinear partial differential equations, which is solved by the numerical method of lines. The influence of different processing parameters like sample composition and heating cycle on the reaction sintering process is investigated and the model-predicted reaction behaviour is compared to experimental results.

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The interfacial energies between solid oxide ceramic and liquid metals have been investigated for a number of systems. At the metal melting point: (1) the interfacial energies between a given oxide ceramic and various metals vary by less than 10%:γ SL=2.538±0.139 J/m2 for Al2O3-liquid metals;γ SL=1.599+0.064 J/m2 for ZrO2-liquid metals;γ SL=1.676±0.142 J/m2 for UO2-liquid metals; (2) the respective contact angles (Φ>90°) idicate no wettability. Linear temperature functions of the interfacial energies in oxide ceramic-liquid metal systems have been derived. By extrapolation, temperature coefficients of interfacial energies can be estimated for oxide ceramic-liquid metal systems that have not yet been measured. The interfacial energies, together with the surface energies of the materials concerned, also provide the work of adhesion for all Al2O3- and ZrO2-liquid metal combinations considered.

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Abstract  

The polycrystalline ceramic samples of general formula Pb1−XCaXTiO3 with X = 0.00, 0.1, 0.2 and 0.3 have been synthesized by standard high temperature solid state reaction method using high purity oxide and carbonates. The formation of the single phase compounds have been checked by X-ray diffraction technique. The Modulated Differential Scanning Calorimetry has been used to investigate the effect of substitution on the phase transition temperature and the corresponding change on the enthalpy and other thermal parameters of the substituted compound/solid solutions. It was observed that the phase transition temperature (T c) decreases linearly with the increase of substitution concentration. The linear decrease in T c with increase of substitution concentration may be useful for the eventual functionality of the materials for different ferroelectric devices. The results are discussed in detail.

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Ageing of wet-synthesized oxide powders

Role of surface carbonation, effect on sintering, restoration

Journal of Thermal Analysis and Calorimetry
Authors: Laura Montanaro, K. Belgacem, P. Llewellyn, F. Rouquerol, F. Merlo, and Paola Palmero

Abstract  

Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained from aged precursors can reach a very low final density with respect to the theoretical value. A large degree of the original sintering properties can be recovered after washing the aged powders with ethanol in a basic medium.

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Journal of Thermal Analysis and Calorimetry
Authors: M Yasuoka, Y Nishimura, T Nagaoka, and K Watari

Abstract  

The ceramic industry uses enormous amounts of energy to produce products at high temperatures. Energy-saving measures based on sintering process improvements are examined. Oxide ceramics were irradiated by two different methods during microwave sintering: intermittent use of the same high power levels (time-control method) and continuous use of lower, increasing levels of power (power-control method). We found that: 1) the power consumption and efficiency of the time-control method were lower than those of the power-control method; 2) the power-control method gave more precise control of temperature under our experimental conditions; 3) sample densification did not differ greatly between the two methods; and 4) grain growth did not differ greatly between the two methods.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Viorel Chihaia, Karl Sohlberg, M. Scurtu, S. Mihaiu, M. Caldararu, and M. Zaharescu

Abstract

Tin and cerium based oxide ceramics, due to their peculiar properties, are good candidates for using as sensors, solid electrolytes in fuel cells, and catalysts. In the present work, Sn–Ce–O powders with the composition of interest for catalysis applications were obtained by solid state reactions and by thermal decomposition of the different tin and cerium precursors. The structural characterization of the resulted samples was performed by X-ray diffraction. Morphological characteristics were evaluated from X-ray microstructural parameters and BET surface areas measurements. Surface evolution of the studied powders was investigated by electrical measurements in various atmospheres in the 25–400 °C temperature range. The samples studied behave as a n-type semiconductor. The catalytic activity for CO oxidation was measured in gas flow between 25 and 400 °C. The conversion degree depends on the preparation method of the samples. Magnetic susceptibility measurements at room temperature of the samples before and after catalytic test indicated a paramagnetic behavior. Higher values of magnetic susceptibility of the samples after catalytic test compared to initial ones could indicate the influence of CeO2 on the catalytic activity.

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Journal of Thermal Analysis and Calorimetry
Authors: Abdelhamid Harabi, Djamel Belamri, Noureddine Karboua, and Fatima-Zohra Mezahi

. Janney MA , Kimrey HD . Materials research society symposium proceedings: diffusion-controlled processes in microwave fired oxide ceramics . In: Snyder WB, Sutton WH Jr, Iskander MF, Johnson DL, editors. Microwave processing of

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Resolution and Discovery
Authors: Taťána Fenclová, Zdeněk Jonšta, Miroslav Hnatko, Josef Kraxner, and Pavol Šajgalík

acceptance, and application possibility as powder form. The most commonly used ceramic materials in orthopedics are oxide ceramics (Al 2 O 3 and ZrO 2 ), due to their excellent biocompatibility. However, among the biocompatible materials was Si 3 N 4

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known that diffusion rate in oxide ceramics under such low temperatures is extremely small. TG researches have shown that the powder ferrite mass remained practically a constant at heating from 300 up to 700 K. Therefore, it is impossible to analyze the

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