Search

Abstract The barium aluminosilicate glass ceramic (BAS) is a potential material for high temperature application due to its high melting point and low thermal expansion coefficient. However, the low mechanical performance has limited its widely using in industry. A lot of effort has been made to reinforce the BAS matrix by incorporating carbon fibers, but the enhancement is limited by the strong interface bonding. In this work, the Fe3+ was employed to promote graphization of carbon fibers and increase mechanical properties by weakening the interface bonding. The evolution of carbon fibers with Fe3+ doping and effects on the mechanical properties of C f /BAS composites were investigated. The results indicate that the incorporation of 1.35 wt.% Fe3+ could increase the flexural strength and fracture toughness of the composites by 28.11% and 37.10%, respectively. This is attributed to the formation of brick micro-crystalline graphite interface layer and carbon nano-sized grains in the matrix. When Fe3+ doping content is higher than 1.35 wt.%, the mechanical performance of composites undergo a gradually decrease, resulting from the excessive erosion of carbon fiber, accompanied by the growth of carbon nanofiber on the fiber surface. The mechanisms of the evolution of carbon fiber and the effects on mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

Abstract The constitutive relation of micro-cracked ultra-high temperature ceramics deduced by energy method and the temperature-dependent critical energy release rate of ceramics were demonstrated in this paper. Taking advantage of the constitutive relation and temperature-dependent critical energy release rate, the thermal shock behavior of Al 2 O 3 had been simulated firstly with finite element method. Results showed that the crack patterns of simulation approximated in the experiments. That confirmed the accuracy of our model. The ZrB 2 -based ceramic was then used as an example to study the effects of the temperature dependence of crack propagation criterion on the evaluation of thermal shock resistance of ultra-high temperature ceramics. In addition, given that the cracks forming during thermal shock lead to discontinuities in the ceramic material and influence thermal conduction. The interaction between thermal shock cracks evolution and thermal conduction, and the corresponding effects on the thermal shock behavior of ultra-high temperature ceramics were studied for the first time. Results indicated that the thermal shock crack patterns and temperature fields were significantly different while the thermal conductivities at the cracks were different for identical thermal shock conditions. Therefore, in order to improve the accuracy of simulation and the evaluation of thermal shock resistance of ultra-high temperature ceramics, the temperature dependence of the crack propagation criterion and the interaction between the cracks evolution and thermal conduction must be taken into consideration. Graphical abstract Image 1 Highlights • A temperature-dependent constitutive relation of micro-cracked ultra-high temperature ceramics. • Temperature-dependent critical energy release rate. • The interaction between thermal shock cracks evolution and thermal conduction. [ABSTRACT FROM AUTHOR]

Lead-free 0.955K 0.5 Na 0.5 NbO 3 -0.045Bi 0.5 Na 0.5 ZrO 3  + 0.6%MnO (KNN-0.045BNZ + Mn0.6) ceramics have been prepared by a conventional solid-state sintering method in air. All the samples sintered at different temperatures possess a coexisting phase boundary (CPB) between rhombohedral (R) phase and tetragonal (T) phase. The increase of sintering temperature ( T s ) increases the phase fraction of T phase in CPB region. Mn 2+ , Mn 3+ and Mn 4+ ions coexist in all the KNN-0.045BNZ + Mn0.6 ceramics sintered at 1110 °C to 1190 °C. High sintering temperature can induce a transformation from M n N b ' ' defects to M n N b ' defects. The samples with fine grain show stable octahedral structure. The KNN-0.045BNZ + Mn0.6 ceramics with fine grain possess excellent temperature stability of d 33 * due to the wide phase transition region. The increase of sintering temperature induces the (R-T) phase transition temperature to move to room temperature. [ABSTRACT FROM AUTHOR]

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]

Room temperature static and cyclic fatigue of ZrB 2 -32 vol% SiC and ZrB 2 -45 vol% SiC particulate ceramic composites has been studied. It was established that the presence of grain bridging plays an important role in the lifetime and time dependent mechanical performance of ZrB 2 -SiC composites. It was also established that the cohesive strength of grain boundaries of the composites was a determining factor if grain bridging would occur during crack growth, as the grain boundaries strength would determine the pathway of the moving crack. Grain bridging was limited in ZrB 2 -32 vol% SiC leading to the absence of a cyclic fatigue effect, while grain bridging indeed occurred in ZrB 2 -45 vol%SiC contributing to a cyclic fatigue effect which limits the lifetime of the composite. Such differences were responsible for the occurrence of R-curve behavior in ZrB 2 -SiC ceramic composites. [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]

Low temperature cofired ceramics technology (LTCC) has been widely studied and used in wireless communication because of their outstanding capability for device miniaturization and integration. However, many commercial microwave dielectric materials have high sintering temperatures that pose challenge for cofiring with inner electrodes. Herein, two brannerite vanadate LiMVO 6 (M = Mo, W) ceramics with intrinsically low sintering temperatures were prepared. Dense and stable LiMVO 6 (M = Mo, W) ceramics could obtained at 640 °C for LiMoVO 6 and 700 °C for LiWVO 6 . Favorable microwave dielectric properties were also obtained with ε r = 13.3, Q × f = 12,460 GHz, and τ f = +101.0 ppm/°C for LiMoVO 6 and ε r = 11.5, Q × f = 13,260 GHz, and τ f = +163.8 ppm/°C for LiWVO 6 . Moreover, the relationship between crystal structure and microwave dielectric properties was studied by means of packing fraction, bond valence, and octahedral distortion. Their chemical compatibility with the metal electrodes were confirmed. [ABSTRACT FROM AUTHOR]

This paper aims to study the effects of heat treatment temperatures on the aging degradation of piezoelectric properties, i.e. piezoelectric coefficient ( d 33 ) and planar electromechanical coupling factor ( k p ), in soft and hard PZT ceramics. Aging degradations of d 33 and k p of the samples were measured for 192 h prior to heat treatments. The samples were then treated at various temperatures equivalent to 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 times of the materials' Curie temperatures. Aging degradations of d 33 and k p of the heat-treated samples were observed continuously for 1128 h. The piezoelectric properties of the un-treated samples gradually decreased with aging time. Attenuation of d 33 and k p in the samples immediately after heat treatment increased with increasing heat treatment temperature. Moreover, aging degradation rate and relaxation time of the samples measured after heat treatments increased with increasing heat treatment temperature. Comparing to hard PZT ceramics, soft PZT demonstrated greater change of d 33 and k p immediately after heat treatments. Soft PZT also showed greater aging rate and aging time than those of hard PZT. From the overall results, it can be concluded that both material type and heat treatment temperature have effects on aging behaviors of PZT materials. Aging degradation was more pronounced in soft PZT and the samples treated at high temperatures. The observed aging behaviors of PZT materials were explained by the interaction between domains and defects of oxygen vacancies that leads to volume, domain and grain boundary effects. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the thermoelectric response of porous Ca 3 Co 4 O 9 (CCO) samples. The porosity in the CCO samples was increased by introducing wood particles in the material followed by a high-temperature sintering to completely burn off the wood. The density of the resulting samples was found to decrease gradually with increase in porosity. Structural and chemical characterization of the samples was performed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. All these characterization experiments showed that, except for an increase in the ratio of the relative concentration of Co 3+ and Co 4+ , increasing porosity did not coincide with any change in phase or elemental composition of the material. The increase in the ratio of Co 3+ /Co 4+ , did serve to enhance the value of Seebeck coefficient of the more porous samples. Porosity also caused a reduction in the thermal conductivity due to increased phonon scattering, thereby enhancing the figure of merit, ZT , of the sample. A ZT value of 0.19 at 800 K was obtained for the CCO sample with optimum porosity of 47%. These promising results coming from materials prepared by an eco-friendly process give a path to a new era of porous materials for practical applications in thermoelectric modules. [ABSTRACT FROM AUTHOR]

In this study, sintering effects on microstructural behavior of bovine derived hydroxyapatite doped with powder mullite are considered in the temperature range between 1000 °C and 1300 °C. Results show that maximum values of both compressive strength and microhardness are achieved in the samples sintered at 1200 °C for all mullite additions of 5, 7.5, 10 and 12.5 wt%. Moreover, above 1000 °C, decomposition of HA and new phase formations such as whitlockite and gehlenite play a major role in both compressive strength and microhardness properties which increase up to 10 wt% mullite reinforcement. [ABSTRACT FROM AUTHOR]

Variants of SNNV (Sr 0.2 Na 0.8 Nb 1−x V x O 3 , X = 0.1–0.3) ceramic oxides were synthesized via wet chemical method. SNNVs show high electronic conductivity of >100 S/cm when reduced in hydrogen at a relatively low temperature of 650 °C. In particular, 30% V-doped SNNV exhibited the highest conductivity of 300 S/cm at 450 °C. In order to investigate the fuel cell performance, Gd 0.1 Ce 0.9 O 2−δ (GDC) based electrolyte-supported fuel cells were prepared to study the anode characteristics. Sr 0.2 Na 0.8 Nb 0.9 V 0.1 O 3 (SNNV10)-GDC composite was used as an anode and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF)–GDC as a cathode. Both electrodes were porous and sintered at 1050 °C for 2 h in air. The anode side of the fuel cell was infiltrated with 10 wt% GDC/Ni-GDC precursor to activate the anode for fuel oxidation. I-V characteristics were determined in gas conditions such as dry/humidified hydrogen and methane at 650 °C. With the infiltration Ni-GDC, peak power density (PPD) of 280 mW/cm 2 and 220 mW/cm 2 in dry H 2 and CH 4 , respectively, were obtained at 650 °C, which is higher than GDC alone as infiltrate. The high resistances in the humidified conditions are attributed to the lower conductivity of SNNV10 in high P O2 atmospheres. [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 paper examines the thermo-mechanical volume change behaviour of Opalinus Clay in relation to different stress conditions and overconsolidation ratio (OCR) values and evaluates the impact of temperature on some hydro-mechanical properties of this material. To this aim, a focused experimental campaign consisting in high-temperature/high-pressure oedometric tests has been carried out. The results show that the thermo-mechanical volume change behaviour of Opalinus Clay is heavily affected by the OCR: thermal expansion is found when the heating is carried out at high OCR, whereas irreversible thermal compaction is observed when heat is applied at a vertical effective stress that is sufficiently close to the vertical effective yield stress. The study of the thermal cyclic behaviour shows that expansive irreversible strains can occur upon first heating at high OCR and that a reversible behaviour follows during subsequent thermal cycles. The experimental results reveal an impact of temperature on yielding: a decrease in the yield threshold is detected when compression is applied at high temperature with respect to the yield threshold found at low temperature. Compressibility and swelling indexes are not significantly influenced by thermal changes, as well as the oedometric modulus and the secondary compression coefficient, whereas consolidation processes are found to occur faster at high temperature. The obtained results are presented in this paper together with a description of the testing device and experimental procedure employed. [ABSTRACT FROM AUTHOR]

During high-temperature compression tests on intermetallic Mo 5 SiB 2 , the dislocation microstructures vary with increasing temperature and strain rate. At 1400 °C, an increasing tendency exists for slip planes to be of an unexpected type (e.g., {143) and {523)) as a function of the decreasing strain rate and increasing strain that originates from a dislocation climb. As the temperature increases to 1600 °C, the internal strain rate of 6.07 × 10 − 3 s − 1 from the dislocation climb at 4% strain exceeds the applied value of 1.67 × 10 − 3 s − 1 , and thus, the climb mainly controls the plastic strain, as evidenced by a strength that is lower than that at 1200 °C under the same conditions. [ABSTRACT FROM AUTHOR]

Rock-like materials like ceramic refractories, in working conditions may be subject to large temperature variations. To simulate practical applications, bespoke constitutive modelling is required. In this work a general, thermodynamically consistent framework, able to incorporate key micromechanical features of the material behaviour, and applicable to a wide range of geomaterials, is formulated and validated. Different thermodynamic potentials are proposed to deal with both reversibility and irreversibility. A key advantage of this approach is the ability to freely choose the thermal dependency interpolation functions. Extensive model validation is provided by correctly reproducing both reversible and irreversible experimental trends of different materials under different loading conditions. It is found that even for simple materials, if a sample is subject to a large stress level, its thermal and mechanical responses become unexpectedly coupled. The proposed modelling framework is not limited to refractories and can be easily adapted to different types of rock-like materials. [ABSTRACT FROM AUTHOR]

The development of thermal stresses inside refractory ceramics experiencing severe thermal shock is studied. The present analysis departs from the linear theory of thermal stresses as it accounts for temperature dependent thermal and mechanical material properties. Radiation surface heat exchange between the refractory component and its surroundings is included. A Finite Element Procedure is presented and a MATLAB code is developed. The nonlinear heat equation is solved for the temperature field and this solution is subsequently used in order to determine the stress field evolution. The finite element code is validated and used for the thermal shock estimation of a refractory brick. Material properties corresponding to Al 2 O 3 are selected. A thermal cycle consisting of a heating stage followed by cooling down is simulated. The results are compared with those predicted by the linear thermal stresses theory and significant deviations are observed for the examined values of the Biot number. [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 study the effect of the sintering temperature (1200-1300 °C) on V2O5 doped ZnO- Bi2O3-Sb2O3-MnO2 (ZBSM) based varistor ceramics from 0 to 0.4 mol% was investigated for electrical and microstructural properties. The materials was processed using a conventional solid-state method and the finished samples were characterized using XRD, SEM and EDX techniques. The measured leakage current density was 1?10-4 mA/cm2 when the barrier height was 1.38 eV, which gave the highest nonlinear coefficient around 12.18 at 0.20 mol%. The analyses related to those quoted in the literatures confirmed the presence of Zn7Sb2O12, MnVO4, BiVO4 and Zn3(VO4)2 polymorphs as the secondary phase with ZnO as the primary phase. The Zn3(VO4)2 polymorphs resided at the triple point junctions or were embedded in ZnO grains. Henceforth, the results showed that V2O5 doping can facilitate the sintering process of the varistor ceramics, particularly in the phase formation. This contributed to better electrical properties, especially to 0.2 mol%. The density of the sintered ceramic decreased from 5.32 to 5.06 g/cm³ and the average grain size increased in the range of 11.02 to 31.39 µm with an increased of sintering temperature from 1200 to 1300 °C, respectively. [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]

High temperature flexural and oxidation behavior of hot-pressed B 4 C–ZrB 2 ceramics with various ZrB 2 addition amounts was measured and analyzed in the temperature range of 1000 to 1600 °C in ambient air atmosphere. The high temperature flexural strength is a strong function of temperature. With the temperature increasing, the high temperature flexural strength decreases. The oxidation behavior was investigated in detail, and the oxidation mechanism was summarized. The purpose of this study is to give fundamental understanding of the high temperature behavior of B 4 C based ceramics. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effects of grinding with diamond burs and low-temperature aging on the mechanical behavior (biaxial flexural strength and structural reliability), surface topography, and phase transformation of a Y-TZP ceramic for monolithic dental restorations. Disc-shaped specimens (Zirlux FC, Ivoclar Vivadent) were manufactured according to ISO 6872 (2008) and divided in accordance with two factors: “grinding — 3 levels” and “LTD — 2 levels”. Grinding was performed using a contra-angle handpiece under constant water-cooling with different grit-sizes (extra-fine and coarse diamond burs). LTD was simulated in an autoclave at 134 °C, under a pressure of 2 bar, over a period of 20 h. Surface topography analysis showed an increase in roughness based on surface treatment grit-size (Coarse > Xfine > Ctrl), LTD did not influence roughness values. Both grinding and LTD promoted an increase in the amount of m-phase, although different susceptibilities to degradation were observed. According to existing literature the increase of m-phase content is a direct indicative of Y-TZP degradation. Weibull analysis showed an increase in characteristic strength after grinding (Coarse = Xfine > Ctrl), while for LTD, distinct effects were observed (Ctrl < Ctrl LTD; Xfine = Xfine LTD and Coarse = Coarse LTD). Weibull moduli were statistically similar between all tested groups. Within the limits of this current study, it was feasible to notice that both aging in autoclave for 20 h (LTD) and grinding showed not to be detrimental to the mechanical properties of Zirlux FC Y-TZP ceramic. [ABSTRACT FROM AUTHOR]

To improve the sintering properties and the thermal shock resistance of magnesium matrix ceramic, this work used micron-sized MgO as the main raw material and nano-Al 2 O 3 and SiO 2 as additives. Magnesium matrix ceramic was doped with different amounts of Al 2 O 3 and SiO 2 (Al 2 O 3 and SiO 2 at a molar ratio of 1:2) and sintered under standard atmospheric conditions. The effect of Al 2 O 3 /2SiO 2 doping amounts on sintering properties, thermal shock resistance, phase composition, and microstructure of composite ceramic materials were investivigated. The results suggested that introducing Al 2 O 3 /2SiO 2 could improve the sintering properties of magnesium matrix ceramic. The grain boundary migration of its periclase phase could be hindered by the magnesium aluminate spinel and forsterite formed by solid reaction including Al 2 O 3 , SiO 2 addition, and the MgO itself. Furthermore, according to the mechanism of thermal expansion mismatching, with increasing Al 2 O 3 /2SiO 2 addition, thermal shock times increased significantly, the number of ceramic internal micro-cracks increased after the thermal shock and the material fracture surface energy was improved. It is found that the way of transgranular combining intergranular fractures can decrease the stress concentration at the crack tips and hinder crack propagation. The secondary phase particles deflected matrix internal micro-cracks and the crack propagation path length thus increased, residual stress field were subjected to interference and energy dissipation mechanisms improved. Meanwhile, thermal shock times for the material were enhanced and the degree of densification increased with increasing sintering temperature. [ABSTRACT FROM AUTHOR]

Ceramic hollow spheres were produced by a sacrificial template technique with subsequent sintering under temperatures ranging from 1100 °C to 1250 °C. The effect of the sintering temperature on the structure of the ceramic hollow spheres was investigated by optical and scanning electron microscopy, and a gas adsorption method. The results show that the structure of the ceramic hollow spheres can be controlled, with the retention of the hollow spherical shape, by variation of the sintering temperature. Increase of the sintering temperature from 1100 °C to 1250 °C decreased the outer diameter of the ceramic hollow spheres by 14 percent, the shell thickness by 18 percent, and the void area ratio of the shell surface by 9.2 times; both of the specific surface area and the total pore volume of ceramic hollow spheres decreased by 60 percent. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the effect of sintering temperature on the properties of nanostructured spinel (MgAl 2 O 4 )fabricated by Spark Plasma Sintering (SPS). The starting material was a pure spinel (MgAl 2 O 4 ) nanopowder. The sintering was carried out at T =1300 °C, 1350 °C and 1400 °C under a pressure of 73 MPa.The samples sintered at 1300 °C exhibit a finer microstructure (mean grain size is about ~250 nm) than those sintered at 1350 °C and 1400 °C. The relative density is about 99.93% at 1300 °C, 99.63% at 1350 °C and 99.58% at 1400 °C due to the presence of some porosity in the fabricated samples. Samples sintered at 1300 °C have a good transmittance (70% at 550 nm and 78% at 1100 nm) compared to those sintered at 1350 °C and 1400 °C. Due to their high density and fine grain size, samples sintered at 1300 °C exhibit a Vickers micro-hardness Hv=18 GPa, elastic modulus E =228 GPa relatively more important than those measured on samples sintered at 1350 °C (Hv=15 GPa, E =172 GPa,) and at 1400 °C (Hv=12 GPa, E =136 GPa). They present the reverse behavior for fracture toughness k IC (1.05 MPa √m for samples sintered at 1300 °C, 1.43 MPa √m for samples sintered at 1350 °C and 2.23 MPa √m for that sintered at 1400 °C). The tribological behavior of the MgAl 2 O 4 ceramic was equally studied: the friction coefficient µ is measured and increases with sintering temperature µ =0.06, µ =0.13, µ =0.18, respectively for sintering temperature of 1300 °C, 1350 °C and 1400 °C. The wear behavior is also examined and the mass loss increases with increasing sintering temperature. [ABSTRACT FROM AUTHOR]

Slip-cast ceramic samples of the system (100 −x ) (ZrO 2 –3.5 mol% Y 2 O 3 )– x Al 2 O 3 (abridged as (100− x ) 3.5 YSZ/ x Al 2 O 3 composite, where x is expressed in wt%) were examined using dilatometry, isothermal sintering and electron microscopy methods. The shrinkage in the range 1100–1300 °C was found to be higher for the (100− x ) 3.5 YSZ/ x Al 2 O 3 samples with prevailing fraction of PSZ than for the composites with a corundum matrix. When the weight fraction of corundum was increased, the relative shrinkage of the (100− x ) 3.5 YSZ/ x Al 2 O 3 samples decreased and the open porosity of the ceramic materials grew. The effect of -Al 2 O 3 impurity on the sintering process and linear dimensions of ceramics is shown. Heat treatment of (50–40) 3.5 YSZ/(50–60) Al 2 O 3 composites at 1300 °C are proposed as the optimum conditions for porous diaphragm formation. [ABSTRACT FROM AUTHOR]

This work deals with structural and electrical investigations for different ZnO nanoparticles annealed at 300, 400 and 500 °C. The ac conductivity increases with temperature following the Arrhenius law, with single apparent activation energy for conduction process. The frequency dependence of the electric conductivity follows a simple power law behavior, in accord to the relation σ ac ( T , ω ) = A ( T ) ω s ( T , ω ) , where s is smaller than 1. Electrical conductivity measurements revealed semiconducting behavior and the variation of the universal exponent s with temperature designates the presence of correlated barrier hopping mechanism in these nano-materials. The impedance spectra were analyzed in terms of equivalent circuits involving resistors, capacitors and constant phase elements (CPE). The contribution of grain boundary resistance to the total resistance of the system is remarkable. The Nyquist diagrams of our nano-materials were used to identify an equivalent circuit and the fundamental parameters of the circuit are specific at different temperatures with the aim to study the contributions of the grains and boundary grains to the conductivity. [ABSTRACT FROM AUTHOR]

Microcracking in illite-based ceramic bodies and its influence on their bulk properties were investigated by means of the acoustic emission (AE) technique during the cooling stage of firing up to different maximum temperatures (800–1200 °C). Because of the mismatch of the thermal expansion coefficients between the glassy phase and the quartz particles, radial microcracking around quartz grains began to occur at ∼750 °C (temperature of glass transition). At ∼573 °C, where the β → α transformation of quartz takes place, a non-monotonic behavior of the Young’s modulus and a temporary cessation of the AE activity occurred. Below this temperature, the AE signals appeared again, reflecting the formation of circumferential cracks around the particles. The presence of circumferential microcracks was also confirmed by the use of scanning electron microscopy. [ABSTRACT FROM AUTHOR]

X2-RE 2 SiO 5 orthosilicates are promising candidate environmental/thermal barrier coating (ETBC) materials for silicon-based ceramics because of their excellent durability in high-temperature environments and potential low thermal conductivities. We herein present the mechanical and thermal properties of X2-RE 2 SiO 5 orthosilicates based on theoretical explorations of their elastic stiffness and thermal conductivity, and experimental evaluations of the macroscopic performances of dense specimens from room to high temperatures. Mechanical and thermal properties may be grouped into two: those that are sensitive to the rare-earth (RE) species, including flexural strength, elastic modulus, and thermal shock resistance, and those that are less sensitive to the RE species, including thermal conductivity, thermal expansion coefficient, and brittle-to-ductile transition temperature (BDTT). The orthosilicates show excellent elastic stiffness at high temperatures, high BDTTs, very low experimental thermal conductivities, and compatible thermal expansion coefficients. The reported information provides important material selection and optimization guidelines for X2-RE 2 SiO 5 as ETBC candidates. [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]

Copyright of Science of Sintering is the property of National Library of Serbia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Silicon carbide (SiC) is being used increasingly as a room temperature structural material in environments where moisture cannot always be excluded. Unfortunately, there have been almost no reports on slow crack growth (SCG) in SiC at room temperature. To address this gap, SCG in SiC was studied using constant stress rate and double torsion tests in water. SiC based materials were produced with a wide range of grain boundary chemistries and microstructures, which may affect their slow crack growth behaviour. To clarify the role of chemistry and microstructure respectively, solid state (SS) sintering with carbon and boron along with liquid phase (LP) sintering using oxides additives were used to produce materials with fine and coarse grains. The LP-SiC was three times more sensitive to SCG than SS-SiC materials. Moreover, the larger grained material with a higher toughness was less sensitive to SCG than the materials with fine grains. [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]

The response of carbonate-rich illitic clay heated up to 1200°C was investigated by means of electron paramagnetic resonance (EPR) in order to define the factors influencing the shape of the resonance signals and to establish whether this method can be used for evaluation of firing temperature for clay-based ceramic objects. The results show that the dominating hyperfine sextet, at g≅2, due to Mn2+, is replaced over 700°C by a large signal, mainly due to Fe3+. Oxidation of Mn2+ (EPR active) to Mn3+ (EPR silent) or Mn4+, and Fe2+ (EPR silent) to Fe3+ (EPR active) respectively, combined with changes in their environment produce the resonance signals. The destruction of the carriers such as Fe-oxihydroxides, clinochlore, calcite, dolomite, altered biotite, illite and muscovite, as well as the formation of new minerals and glass are the main mineralogical processes influencing the width of the resonance signals. The results of this study can be used in conjunction with mineralogical and microstructural data for the investigation of technological conditions such as firing temperature and atmosphere related to archaeological ceramic objects. Data gathered from other methods may also help to constrain the EPR signal shape. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report the red-shift of absorption edge for Yb:YAG ceramic with rising Yb content. [•] We report the preferred emission at 1030nm for lower doping Yb:YAG ceramic. [•] We report the influence of temperature on both emission peak and thermal diffusivity. [ABSTRACT FROM AUTHOR]