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Abstract: Metal materials show poor lifetime behavior under high‐temperature conditions and aggressive atmospheres. An alternative solution is the use of ceramic material, e.g., silicon carbide ceramics. These ceramics cannot be processed and joined like metal materials. For this reason, the simple geometry of a heat pipe can be used as a basic design for ceramic heat exchanger systems in the high‐temperature process technology for industrial and power plant applications. Heat pipes are hermetically sealed tubes filled with a working fluid. By transferring heat to one side and by releasing heat from the other side a two‐phase cycle is set up. For these apparatuses a numerical calculation model for a more exact determination of the working behavior of large units under high‐temperature conditions is introduced, considering both convective and radiative heat transfer. [ABSTRACT FROM AUTHOR]

Polycrystalline Ba1.5Sr1.5Co2Fe24O41 ceramics were prepared by the sol-gel method with clear grains and grain boundaries having been identified by the scanning electron microscopy. High-temperature colossal dielectric response has been observed and studied through a series of dielectric and impedance measurements. The electrode effect was also studied and the measurement findings reveal that the colossal dielectric permittivity at low frequency is ascribed to the extrinsic effect of Maxwell Wagner polarization. Dielectric relaxation was identified and investigated by the impedance spectra, which is attributed to the thermally activated model. The complex impedance data is simulated with an equivalent electric circuit and the result suggests that the electric response originates from both the grains and grain boundaries. The activation energies of the grains and grain boundaries are calculated which are 0.62 and 0.67 eV, respectively. The comparable activation energies obtained from the complex impedance spectra and DC conductivity indicates that the relaxation may result from the conduction process. Besides, scaling behaviors are observed below 550 K suggesting that the relaxation time is temperature independent. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of temperature on the friction and wear of rice bran (RB) ceramics, a hard porous carbon material made from rice bran, sliding against alumina, stainless steel, and bearing steel balls under dry conditions. Friction tests were performed using a ball-on-disk-type friction tester wherein a ceramic heater was installed in the rotational stage. The surface temperature of the RB ceramic disk specimens was controlled at 20, 100, 150, or 200°C. The normal load was 1.96 N, sliding velocity was 0.1 m/s, and number of cycles was 20,000. The effect of surface temperature on the friction and wear of RB ceramics substantially differed among the ball material types. The friction coefficient for the RB ceramics sliding against an alumina ball decreased with increasing temperature and exhibited an extremely low value (0.045) at 200°C. The friction coefficient in the case of the RB ceramics sliding against a stainless steel ball exhibited a stable value as the temperature was increased to 150°C and slightly decreased as the temperature was increased further, reaching a low value of 0.122 at 200°C. The friction coefficient for the RB ceramics sliding against bearing steel ball drastically increased with increasing temperature, reaching 0.381 at 200°C. The specific wear rate of the RB ceramics increased with increasing temperature; it was lowest when sliding against alumina and highest when sliding against bearing steel. The wear of the alumina ball was the lowest and that of the bearing steel ball was the highest under all investigated temperature conditions. On the basis of these results, we concluded that alumina is a promising counterpart material for RB ceramics sliding at high temperatures (≤200°C). [ABSTRACT FROM AUTHOR]

A series of methyltriethoxysilane-based silica aerogel monoliths were prepared by ambient pressure drying with various volume ratios of water to ethanol ( R). The pore volumes and average pore sizes of silica aerogels were obtained by Barrett-Joyner-Halenda (BJH) method from nitrogen adsorption-desorption isotherms. The stress-strain curves of the cylindrical aerogel specimens were measured by performing uniaxial compressive tests. The particle size distributions and the average particle sizes of silica aerogels were also evaluated based on scanning electron microscopic observations. The experimental data revealed that the average particles size increased from 0.115 to 3.08 μm as R varied from 0.7 to 1.5, and that the silica aerogels exhibited two characteristic types of the compressive stress-strain responses. By proposing a multiscale structural model to describe microstructures of silica aerogels, a structural parameter, defined as the slenderness L/ D of the cube column length L and the average particle diameter D, was related to the specific volume and the BJH volume of the silica aerogel monoliths, as well as the specific volume of silica. Accordingly, the two types of the compressive stress-strain responses may be distinguished by the critical value ( L/ D). [ABSTRACT FROM AUTHOR]

This work is meant to study the electrocaloric effect in 0.9(0.75Pb(Mg Nb)O-0.25PbTiO)-0.1PbSnO (0.9(PMN-PT)-0.1PS) ferroelectric ceramics. The adiabatic temperature change (Δ T) of 0.9(PMN-PT)-0.1PS ceramic, due to the application or withdrawal of an electric field, were calculated through the thermodynamic relation. The temperature change increases with an increase in the applied electric field and reaches a maximum of 0.66 K in a 30 kV/cm electric field shift near the morphotropic phase boundary transition, ferroelectric-paraelectric, at 373 K; that is, the electrocaloric coefficient is 0.220 × 10 m K/V, this obtained value is at high temperature, which limits its potential as the next generation solid state cooling devices. [ABSTRACT FROM AUTHOR]

Bi2((Zn1/3Nb2/3)1-xTix)2O7weberite ceramics with 0.3≤x≤0.45 were synthesized using solid-state reaction method. Except Bi2((Zn1/3Nb2/3)0.7Ti0.3)2O7with single body-centered orthorhombic weberite phase, the orthorhombic weberite phase of the other compositions changes with sintering temperatures. End-centered orthorhombic weberite is the phase of the ceramics sintered at lower temperatures. With increasing sintering temperature, the end-centered orthorhombic weberite phase transforms into body-centered orthorhombic weberite phase gradually. Although the crystal structures are sensitive to the chemistries and synthesizing conditions, the dense ceramics of Bi2((Zn1/3Nb2/3)1-xTix)2O7show similar dielectric permittivity ϵ of ∼160. Their temperature coefficients of capacitance TCC vary from −150 to −280 ppm/°C with increasing Ti content. High ϵ, low tanδ (<0.003) and low sintering temperature (∼950°C) make the Bi2((Zn1/3Nb2/3)1-xTix)2O7ceramics are competitive candidates for multiplayer ceramics capacitors and low-temperature co-fired ceramics materials. [ABSTRACT FROM PUBLISHER]

(Na0.525K0.443Li0.037)(Nb0.883Sb0.08Ta0.037)O3+ 0.3wt% Bi2O3+ 0.4wt% Fe2O3lead-free ceramics were prepared by conventional soild-state sintering process and the effect of sintering temperature on microstructure, piezoelectric and dielectric properties were investigated. The outstanding physical properties of d33= 343 pC/N, kp= 0.520, Qm= 56.1 and ϵr= 1473 were obtained for specimens sintered at 1040°C for 3h. These results show that the sintering temperature of the ceramics plays an important role in piezoelectric properties of the ceramics. [ABSTRACT FROM PUBLISHER]

The ZnFeNiMnO ceramic materials with different sintering temperatures are synthesized by homogeneous co-precipitation method. The effects of different sintering temperatures on the structure, electrical properties and stability of the ceramic materials are characterized by X-ray diffraction, scanning electron microscope, electrical measurement and impedance analysis. The results show the ceramic powders calcined at 800 °C can form a single cubic spinel structure NiFeO phase, which exhibits great stability at sintering temperature from 1150 to 1300 °C. The values of B constant, ρ and Ea of ZnFeNiMnO ceramic samples at different sintering temperatures are in the range of 3786-3881 K, 84-134 KΩ cm and 0.327-0.335 eV, respectively. The values of relative resistance drift ( ΔR/R ) are in the range of 0.58-0.78 % and have a minimum at 1300 °C after aging test at 125 °C for 600 h. The ZnFeNiMnO ceramic materials are desirable for high stability thermistor applications. [ABSTRACT FROM AUTHOR]

A densification process called reactive hydrothermal liquid-phase densification ( rHLPD), based on principles of hydrothermal reaction, infiltration, reactive crystallization, and liquid-phase sintering, is presented. rHLPD can be used to form monolithic ceramic components at low temperatures. The densification of barium titanate-titania composite monoliths was studied to demonstrate proof of concept for this densification model. Permeable, green titania (anatase) compacts were infiltrated with aqueous barium hydroxide solutions and reacted under hydrothermal conditions in the temperature range 90°C-240°C. The effects of reaction time and temperature on the conversion of titania (anatase) into barium titanate were studied. Utilizing a 72 h reaction at 240°C between l.0 M Ba( OH)2, an anatase (TiO2) powder compact, and a corresponding Ba/Ti ratio of 1.5, it was possible to crystallize a composite 95 wt% (88 mol%) BaTiO3 and 5 wt% (12 mol%) TiO2. The composite had a relative density of ~90% with a compressive strength of 172 ± 21 MPa and a flexural strength of 49 ± 4 MPa. [ABSTRACT FROM AUTHOR]

The effect of firing temperature in the range 800 - 1600°C and heat treatment duration (60 h at 1350 - 1400°C) on shrinkage and growth indices, porosity, and strength for specimens based on HCBS of composite composition (bauxite and VFQG), and also with added clay, is studied. Depending on specimen composition there is low shrinkage within the limits of 0.4 - 1.15% in the range 1100 - 1200°C and significant growth (2.0-.27%) as a result of secondary mullite formation occurring at 1300 - 1500°C. [ABSTRACT FROM AUTHOR]

In this work, to formulate piezoceramic systems such as PbZr0.52Ti0.48O3 ( PZT) for low-temperature co-fired ceramic ( LTCC)-based devices, liquid-phase sintering approach is demonstrated. ZnO-B2O3 ( ZB) binary glass system is used as sintering aid. X-ray diffraction ( XRD) study confirms the formation of morphotropic phase boundary ( MPB; tetragonal + rhombohedral) in PZT prepared by hydrothermal route. ZB is found to induce change in tetragonal/rhombohedral ratio in MPB of PZT. 1% ZB in PZT is found to raise the tetragonality from 71% to 92% in MPB region of PZT. ZB addition in PZT has reduced the sintering temperature from 1250 to 825°C for relative density about 91% with sustaining MPB phase. 1% ZB content is optimal percentage to enhance sinterability and relative density. Uniform dispersion of glass in PZT matrix is confirmed by SEM images. ZB content in PZT is found to controlling grain growth during sintering. Highest dielectric constant and lowest dielectric loss with low sintering temperature (825°C) of 1% ZB among all glass added in PZT exhibit technical suitability of 1% ZB + PZT to use as LTCC-based energy storage devices. [ABSTRACT FROM AUTHOR]

ZrC and ZrN ceramics are of interest in the application of materials in extreme high temperature environments, particularly for nuclear applications in generation IV reactors. These materials demonstrate desirable characteristics such as high thermal and electrical conductivities along with high hardness and melting temperatures. Data reported in the literature often suffer from scatter due to differences in processing techniques and difficulty determining stoichiometry, which will significantly affect thermophysical properties. This article reviews the current available data for the properties of ZrC, ZrN and mixed carbonitrides phases and identifies causes of scatter in the literature and areas requiring further research. [ABSTRACT FROM AUTHOR]

The effect of temperature on ferroelectric and piezoelectric behaviour of multiferroic ceramics (1 mol% Mn-doped 0.75BF-0.2BT) was investigated under an electric field at various temperatures (30 to 200°C). The polarization hysteresis loop and strain loop of ceramics were investigated at various temperatures. The effect of temperature was represented by the change of polarization hysteresis loop, strain loop and dielectric properties with various temperatures. The results showed that the remanant polarization and remanant strain of ceramics were improved with increasing temperature. The improving of these properties could be attributed to the greater domain switch ability at high temperature. [ABSTRACT FROM AUTHOR]

Bi3TiNbO9(BTN) is an important member of the Aurivillius bismuth layer-structured ferroelectric compounds, consisting of [Bi2O2]2+layers between which [BiTiNbO7]2-layers are inserted. Ho3+and Yb3+co-doped Bi3TiNbO9(BTN) ceramics were synthesized by a conventional solid state reaction method and their up-conversion (UC) luminescence and the ferroelectric properties were investigated. A strong green emission band centered at 547 nm, two weak red emission bands centered at 657 nm and 758nm were obtained under a 980 nm laser excitation at room temperature. With the increasing of Yb3+content, the intensity of the up-conversion luminescence increased initially and then decreased due to concentration quenching. The fluorescence intensity ratio of green UC emission centered at 547 nm and red UC emission centered at 657 nm was studied as a function of temperature in a range of 123 - 573K, and the result showed a quite good linear variation of the two emissions with temperature, which indicates that Ho3+/Yb3+co-doped Bi3TiNbO9multifunctional ceramic is a promising candidate for applications in optical temperature sensors. [ABSTRACT FROM AUTHOR]

Influence of NaCl/LiF additives (with molar ratio of 0.58:0.42) on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of (K0.5Na0.5)NbO3ceramics has been studied. Intensification of the sintering process and a decrease in the unit cell parameters were proved. Enhancement of ferroelectric properties and an increase in the Curie temperature value stimulated by the additives were revealed using the Dielectric Spectroscopy and Second Harmonic Generation methods. [ABSTRACT FROM AUTHOR]

The behavior and mechanism of NiCr-HfB cermet coating oxidation at 1,000, 1,100 and 1,200 °C in pure oxygen were investigated using thermogravimetric equipment, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Analyses of the oxidation kinetics confirmed that the parabolic rate law was followed at each temperature and the activation energy of oxidation was 284 kJ/mol. The oxidation layers were detected to be composed of NiO, NiCrO, CrO. The cross-sectional morphologies indicated that the oxidation layer consisted of three parts: Ni-rich oxide layer, spinel NiCrO layer and a thin layer of CrO. The oxidation process was controlled by the outward diffusion of the oxide-forming elements Ni, Cr and inward penetration of oxygen, by which the interaction mechanisms between the microstructures was clarified. On the basis of the experimental results and fundamental analyses, the NiO/NiCrO/CrO multi-layer oxidation mechanism was accordingly established to illustrate the oxidation behaviors. [ABSTRACT FROM AUTHOR]

The microstructures and microwave dielectric properties of (1 − x)MgSiO- xCaSrTiO ( x = 0.05-0.08) composite ceramics, prepared via a conventional solid-state ceramic route, were investigated. As expected, an increase in sintering temperature effectively promoted densification and enhanced the dielectric properties of the (1 − x)MgSiO- xCaSrTiO ceramics used in this study. As the amount of CaSrTiO increased, temperature coefficient of resonant frequency ( τ) increased; with a near-zero τ obtained for samples where x = 0.06. The optimal microwave dielectric properties, a dielectric constant ( ε) of 8.01, high quality factor ( Q × f) of 58,389 GHz (at 14.6 GHz) and a τ of −3.62 ppm/°C, were obtained for 0.94MgSiO-0.06CaSrTiO sintered at 1,440 °C for 3 h. [ABSTRACT FROM AUTHOR]

A novel microwave dielectric ceramics LiMg(WO) (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the LiMg(WO) ceramics were investigated. The optimal sintering temperature of dense LiMg(WO) ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε = 7.72, Q × f = 29,600 GHz ( f = 6.0 GHz), and τ = −15.5 ppm/°C. Moreover, the LiMg(WO) ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application. [ABSTRACT FROM AUTHOR]

Lead-free (BaCa)(ZrTi)O- xmol% ( x = 0-1.6) cobalt ceramics (BCZT- xCo) have been fabricated by the traditional solid-state reaction technique and the effects of Co and sintering temperature on ferroelectric, dielectric and piezoelectric properties of (BaCa)(ZrTi)O lead-free ceramics have been studied systematically. The orthorhombic-tetragonal ( T) transition shift towards lower temperature with increasing Co addition, while Curie temperature ( T) remained at relatively high value of 107 °C. And the Main piezoelectric parameters are optimized at x = 0.8 mol% with a high piezoelectric coefficient ( d = 330 pC/N), a planar mode electromechanical coupling factor ( k = 46.7 %), a high dielectric constant ( ε = 2,675) and a low dielectric loss ( tanδ = 0.90 %) at 1kHZ. Besides these, high remnant polarization ( P) and low coercive field ( E) of 11.5 μC/cm, 0.31 kV/cm are also obtained at (BaCa)(ZrTi)O-0.8 mol%Co lead-free ceramics. Furthermore, greatly enhanced temperature stability of the piezoelectric properties was obtained in the temperature range from 20 to 90 °C. The above results indicate that BCZT-Co ceramics are promising lead-free materials for practical applications. [ABSTRACT FROM AUTHOR]

The influence of synthesis parameters, such as calcination temperature and sintering temperature, on the microstructure, phase composition, and electrical properties of NiMnO negative temperature coefficient (NTC) ceramics was systematically investigated. The NiMnO NTC ceramics were synthesized via solid-state coordination reaction. With increasing sintering temperatures, the relative density increased, whereas the porosity decreased. Single-phase, cubic spinel ceramic was obtained following sintering at 900 and 1,050 °C, whereas a secondary phase, i.e., NiO, was detected when the sintering temperature was higher than 1,100 °C. High-density ceramics were obtained when the sintering temperature was higher than 1,100 °C, and featured the lowest room temperature resistivity of 2,924 Ω cm and thermal constant B of 3,429 K. The latter parameter reflects the temperature sensitivity of the NTC ceramics. Variations of the electrical property were because of increases in density and onset of decomposition. [ABSTRACT FROM AUTHOR]

Gelcasting was employed to fabricate SiN/SiC whisker (SiCw) composite ceramics, and the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers and SiCw content on microwave dielectric properties were studied. Compared with pure SiCw of spherical structure obtained at temperature of 1,750 °C(Ar), pure SiCw treated at 1,600 °C(Ar) showed rod-like structure, higher dielectric properties and more evenly distribution in SiN/SiCw composite ceramics. Both the real (ε′) and imaginary (ε″) permittivity of SiN/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised owing to the interface and SiCw playing a role of dipole in the frequency range of 8.2-12.4 GHz. In addition, comparing the ceramics with lower content of SiCw, the reflectivity of the composite ceramics moved to a lower frequency; the maximum absorption peak reached −22.4 dB at the whisker content of 15 wt%. [ABSTRACT FROM AUTHOR]

Ba[SnZnNb]O ceramics were sintered at different temperatures by conventional solid-state sintering method so as to clarify the effects of the sintering temperatures on vibrational modes, crystal structures and dielectric properties. Lattice vibrational spectra, obtained by Raman spectroscopy and Fourier transform far-infrared reflection (FTIR) spectroscopy, show the relationship among polar phonon modes, crystal structures and dielectric properties in Ba[SnZnNb]O ceramics as a function of sintering temperatures. Raman and FTIR active modes were indicated according to the group theory. The results demonstrate that dielectric constant and temperature coefficient of capacitance are closely related to Raman modes at 480 cm; dielectric loss values are closely connected with full width at half-maximum of A(Nb) and E(O) active modes with increasing temperatures, which can also be proved by FTIR. [ABSTRACT FROM AUTHOR]

The effects of copper oxide (CuO) on the microstructure and electric properties of nonstoichiometric compound terbium dioxide (TbO) ceramics were investigated. Results included a reduction in the sintering temperature to 1,100 °C, a grain size of 4.2 μm, and a density of 96.2 %, which are larger than the values in previous investigation for TbO ceramics (grain sizes between 0.4 and 1.0 µm). Among the sintered ceramics, the sample doped with 10.0 wt% CuO showed the maximum nonlinear coefficient α = 43.5, which is obviously greater than α = 3.03 of the pure sample. Doping with 10.0 wt% CuO also exhibited nonlinearity α = 2.14 even at 1,123 K. In addition, the impedance spectra of the sample doped with 5.0 mol% CuO showed the largest grain boundary semicircle; 0 and 20 % samples showed both inductive and capacitive reactance. [ABSTRACT FROM AUTHOR]

Various instruments for measuring the temperature in brick raw materials are analyzed and a method of setting up optimal control of the process of drying a ceramic brick to reduce the energy costs of an industrial enterprise by means of new Celsius heat sensors is proposed. It is shown that the device is universal and will be effective for the needs of enterprises for which monitoring of the thermodynamic parameters is the basis of the technological process. [ABSTRACT FROM AUTHOR]

CaNdCoO polycrystalline thermoelectric ceramics with small amounts of Nd have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Nd has been incorporated into the CaCoO and CaCoO phases and no Nd-containing secondary phases have been produced. Apparent density measurements have revealed that all samples are very similar, with densities around 70 % of the theoretical one. Electrical resistivity decreases in all Nd-doped samples, compared with the pure one, while Seebeck coefficient remains constant for all samples. The improvement in resistivity leads to higher power factor values than the obtained for the undoped samples. [ABSTRACT FROM AUTHOR]

Bulk ceramic compounds of formula xPZT + (1 − x)PFW, where PZT = Pb(Zr0.575Ti0.425)O3 and PFW = Pb(Fe2/3W1/3)O3, for x = 0.15; 0.20; 0.25; 0.37; 0.50; 0.60; 0.65; 0.70 and 0.80, were synthesized. In these single phase perovskites a change from rhombohedral to cubic structure is observed as the proportion of PFW increases. Magnetic investigations including zero-field cooled and field-cooled magnetization versus temperature measurements, magnetic hysteresis loops measurement and ac susceptibility measurements were performed. At high temperatures a clear antiferromagnetic (AFM)-like transition was observed for high PFW concentrations. The low temperature behaviour indicated spin freezing and thermal activation of magnetic moments and measurements confirmed the existence of a barrier maximum for x = 0.37. Competition between the long-range AFM order and short-range magnetic ordering of small nano-sized regions with finite magnetic moments was observed in the studied system. [ABSTRACT FROM AUTHOR]

The temperature dependence of the generalized Wien displacement law is investigated. For determining the true temperature of a $$\text{ ZrB }_{2}$$ -SiC-based ultrahigh-temperature ceramic, the experimental values of the position of the maximum of the spectral density power are needed. Thermodynamics of the thermal radiation of $$\text{ ZrB }_{2}$$ -SiC is constructed by using the temperature dependence of the generalized Stefan-Boltzmann law. The calculated values of the normal total emissivity for $$\text{ ZrB }_{2}$$ -SiC at different temperatures are in good agreement with experimental data. The total radiation power emitted from a surface of $$\text{ ZrB }_{2}$$ -SiC specimens at different temperatures is calculated. The temperature dependences of the Helmholtz free energy, entropy, heat capacity at constant volume, pressure, enthalpy, and internal energy of the thermal radiation of $$\text{ ZrB }_{2}$$ -SiC are obtained. For determining the true temperature, experimental values of either the normal total emissivity or the normal total energy density are needed. The uncertainty in the determination of the true temperature is no greater than 1 %. A new universality class of bodies with a new relationship between the temperature $$T$$ and the position of the spectral energy density maximum is established. [ABSTRACT FROM AUTHOR]

In order to develop dielectric ceramics with temperature-stable permittivity characteristics, perovskite BaTiO-Bi(ZnTi)O-NaNbO ceramic solid solutions were investigated with a particular focus on effects of BaTiO and NaNbO contents on the dielectric properties of ternary compounds. Keeping the ratios of the other two constituents constant, decreasing the BaTiO content leads to a broadening of the temperature-dependent permittivity maximum and a decrease in the overall permittivity. For compositions of constant BaTiO content, replacing Bi(ZnTi)O with NaNbO shifts the temperature of the maximum permittivity to lower temperatures (e.g., to −103 °C for a composition of 70BT-5BZT-25NN) while maintaining a broad permittivity peak with temperature, which for the 50BT-25BZT-25NN composition also satisfies the X9R standard. Thus, the investigation of BT-BZT-NN compounds resulted in promising dielectric properties with broad temperature ranges of high permittivity, which is of interest for advanced capacitor applications. [ABSTRACT FROM AUTHOR]

In this article, pollucite ceramic with high relative density and low coefficient of thermal expansion (CTE) was prepared from Cs-based geopolymer using synthetic metakaolin. Crystallization and sintering behavior of the Cs-based geopolymer together with thermal expansion behavior of the resulted pollucite ceramic were investigated. On heating at 1200 °C for 2 h, the amorphous Cs-based geopolymer completely crystallized into pollucite based on crystal nucleation and growth mechanism. Selected area diffraction analysis and XRD results confirmed the resulted pollucite ceramic at room temperature was pseudo-cubic phase with superlattice structure. Compared with Cs-based geopolymer using natural metakaolin, geopolymer using synthetic metakaolin in this article showed a much lower viscous sintering temperature range, which started at 800 °C, reached a maximum value of −7.47 × 10-4/°C at 1121.9 °C, and ended at 1200 °C. Cesium volatilization appeared only when temperature was above 1250 °C. Therefore, densified pollucite ceramic can be prepared from Cs-based geopolymer using synthetic metakaolin without cesium volatilization. Abnormal thermal shrinkage of pollucite ceramic was observed at temperature range from 25.3 to 54.6 °C because of pseudo-cubic to cubic phase transition, and its average CTE was 2.8 × 10-6/°C from 25 to 1200 °C. [ABSTRACT FROM AUTHOR]

Ca2CuO3ceramics were synthesized by the traditional solid-state sintering method. Its dielectric properties were studied in the frequency range from 102Hz to 106Hz and in the temperature range from 100 K to room temperature. The activation energy was calculated by the Arrhenius Equation. The analysis for XPS spectrum and the fitting value of the activation energy (Q= 0.17 eV) indicated that the dielectric response in Ca2CuO3might be governed by the electron hopping between the Cu ions. The experimental result revealed a relaxation process for the polarization mechanism. Given the relationship between relaxation time and temperature, the dielectric properties of Ca2CuO3can be perfectly described by the Cole-Cole model. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics (1-x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3-xSrTiO3(abbreviated as KNLNS-xST) were sintered by the conventional method. The effects of SrTiO3content on the structure, the electrical properties and the temperature stability of ceramics were investigated. The X-ray diffraction patterns revealed that all the ceramics have a perovskite structure, and the SEM micrographs revealed that the grain size of the ceramics was decreased with the increase of SrTiO3content.The partial substitution of SrTiO3decreased the Curie temperature (Tc) and shifted the orthorhombic–tetragonal phase transition temperature (TO–T) to below room temperature. It was found that the ceramics with x = 0.008 possess optimum piezoelectric properties (d33= 250 pC/N, kp= 51.7%, ϵr∼1143 and tanδ ∼ 4.45%), and the ceramics with x = 0.015 exhibit improved temperature stability, due to the shift of TO-Tto below room temperature. These results indicate that these materials are promising candidates for lead-free piezoelectric ceramics for practical applications. [ABSTRACT FROM AUTHOR]

The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) as a basis for presenting the temperature-dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR to allow it to operate at higher power levels. The GCT's operating conditions place severe constraints on the choice of material. An electrically-insulating material is required with a high-thermal conductivity, low-dielectric loss factor, and high-thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this article is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically determined temperature-dependent and room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young's, bulk and shear moduli, Poisson's ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient, and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon, and silicon nitride. [ABSTRACT FROM AUTHOR]

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics have been investigated in a wide temperature range from 300 to 433 K. It is observed that remnant polarization, saturation polarization, and coercive field are increasing with an increase of the temperature in a low-field region and decreasing in a high-field region. Such behavior is explained by the competition between switching and backswitching mechanisms. A three-stage dependence of the logarithm of the hysteresis loop area on the logarithm of the electric field is identified. The temperature dependence of backswitching properties has been studied. The obtained results indicate that the temperature dependence of the polarization backswitching can be well described by the Arrhenius law. The activation energy for the domain switching determined from the fitting results exhibits decreasing tendency with the increase of the electric field. [ABSTRACT FROM AUTHOR]

A modified resonant cavity method was developed to measure the dielectric properties of ferroelectric ceramics at microwave frequencies, which were difficult to be evaluated accurately because of the high dielectric constant and high dielectric loss. With the aid of low-loss reference ceramic, the dielectric constant and dielectric loss of the small-sized ferroelectric ceramic sample could be measured accurately from the difference between the resonant peaks (TE01δ mode) with and without introducing the to-be-determined sample. The microwave dielectric properties of Pb(Zr0.52Ti0.48)O3, Ba0.5Sr0.5Nb2O6, and BaTiO3 ferroelectric ceramics were measured between 3.4 and 4.9 GHz using this method, together with the temperature dependence. [ABSTRACT FROM AUTHOR]

The thermal properties of zirconium diboride ( ZrB2) ceramics with carbon additions of up to 3 wt% were characterized up to 2000°C. Carbon contents were selected to produce ZrB2 that was nominally pure, contained dissolved carbon, or contained carbon inclusions. The microstructure and density changes that resulted from the carbon additions affected the thermal behavior of ZrB2 at room and elevated temperatures. Thermal diffusivity at 200°C increased from 0.150 cm2/s for nominally pure ZrB2 to 0.175 cm2/s for ZrB2 with 3 wt% carbon. The thermal diffusivity decreased with increasing temperature, reaching a value of 0.143 cm2/s at 2000°C for ZrB2 with 3 wt% carbon. In addition, thermal diffusivity changed irreversibly during the first thermal cycle after densification due to changes in the microstructure that started between 1550°C and 1650°C. Heating resulted in the formation of a new phase, growth of ZrB2 grains, changes in the morphology of carbon inclusions, and migration of W impurities from the ZrB2 matrix into the new phase. Heat capacity, unlike thermal diffusivity, did not change during thermal cycling. Thermal conductivity, which was calculated from thermal diffusivity, heat capacity, and density, was as high as 64.2 W·(m·K)−1 at 2000°C for ZrB2 with 3 wt% carbon. The phonon contribution to thermal conductivity decreased to nearly zero with the addition of 3 wt% carbon due to the presence of elongated carbon inclusions around ZrB2 grains. [ABSTRACT FROM AUTHOR]

High temperature flexural strength of ZrB2-20 vol% SiC ceramics ( ZS) up to 1600°C in high purity argon atmosphere was significantly improved by adding 5 vol% WC, but degraded when 5 vol% ZrC was added. ZrB2-20 SiC-5 WC ceramic ( ZSW) has a very high strength (mean ± SD) of 675 ± 33 MPa at 1600°C, and also an elastic and transgranular fracture mode was observed. According to the analysis of the fracture modes and crack origins in ZSW ceramics, the improvement in strength above 1000°C was attributed to the removal of the oxide impurities from grain boundaries. [ABSTRACT FROM AUTHOR]

LaFeO3 nanoparticles were prepared by a sol-gel method and chosen as the precursor for the preparation of LaFeO3 ceramics. A series of ceramic samples were fabricated by annealing at different temperatures from 800 to 1300 °C and was immersed in ethanol for 1 h afterward, so as to study the effect of sintering temperature and ethanol on the dielectric response at room temperature. As sintering temperature increases, the grain becomes larger, while the degree of porosity is reduced as revealed by FE-SEM. The effect of sintering temperature on dielectric permittivity is dependent on the measuring frequency, while the effect on the loss is less frequency-dependent and is mainly determined by its stronger influence on the whole resistance. Owing to the influence of ethanol on the MW polarization at electrode-sample interface and grain boundaries, both dielectric permittivity and loss were increased by different extent after immersing in ethanol for all the samples. The effect is more obvious with smaller grain size and higher degree of porosity, and the highest values and variations of dielectric permittivity and loss were obtained by LaFeO3 ceramics sintered at 800 °C with the smallest grain size and highest degree of porosity. [ABSTRACT FROM AUTHOR]

The X-band electromagnetic interference (EMI) shielding properties of nano-layered Ti3SiC2 ceramics were evaluated from room temperature up to 800°C in order to explore the feasibility of Ti3SiC2 as efficient high temperature EMI shielding material. It was found that Ti3SiC2 exhibits satisfactory EMI shielding effectiveness (SE) close to 30 dB at room temperature and the EMI SE shows good temperature stability. The remarkable EMI shielding properties of Ti3SiC2 can be mainly attributed to high electrical conductivity, high dielectric loss and more importantly the multiple reflections due to the layered structure. [ABSTRACT FROM AUTHOR]

A correction to the article "Temperature dependence of self-consistent full matrix material constants of lead zirconate titanate ceramics" by Liguo Tang and Wenwu Cao, that was published in the previous issue is presented.