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In this paper, we report the preparation of a B4C/ZrB2 composite powder material via boron carbide reduction of zirconium oxide in the presence of carbon nanofiber as a carbon reducing agent. The material was synthesized in the temperature range 1200–1900°C in 20 min. The optimal synthesis temperature was 1650°C, independent of the starting-mixture composition. We have studied characteristics of the composite powders containing 10–30 mol % ZrB2. The 50% particle size of the composite powders with the compositions studied does not exceed 9.5 μm. The powders consist of aggregated particles of the B4C and ZrB2 phases up to 10 and 40 μm in size, respectively. Visual analysis of micrographs of the powders showed that the mixtures containing 20–30 mol % ZrB2 had a uniform modifying additive distribution over the B4C particles and that the content of large and medium inclusions did not exceed 15 vol %. The specific surface area of the samples ranged from 1.3 to 2.1 m2/g. The zirconium diboride particles were uniformly distributed over the boron carbide matrix. Increasing the ZrB2 content of the composite powder material from 10 to 30 mol % improved the thermal stability of the material in an oxidizing medium. The composite material is potentially attractive for ceramic fabrication. [ABSTRACT FROM AUTHOR]

Microcracks and surface/subsurface damage are easily generated in engineering ceramics grinding. Fracture toughness is an important mechanical property that affects the grinding performance of engineering ceramics, and dynamic fracture toughness accurately reflects the mechanism of crack generation and propagation mechanism in different grinding conditions. Considering the dynamic fracture toughness and grinding process parameters for zirconia ceramics with different grain sizes (50 nm/500 nm/5000 nm) in this paper, the critical grinding force and maximum subsurface damage depth models for the crack generation were established and verified by grinding experiments. The effects of dynamic fracture toughness on the material removal mechanism during the ductile–brittle transition with different process parameters were analyzed, and the influence of different grain sizes on grinding force, workpiece surface roughness, surface cracking rate, and subsurface damage depth were discussed. Experiment results showed that the dynamic fracture toughness values range from 13.0 to 15.0 Mpam1/2 with grain size 50 nm, 9.8 to 11.3 Mpam1/2 with grain size 500 nm, and 6.1 to 6.8 Mpam1/2 with grain size 5000 nm in the experimental process parameters. The relative error of the dynamic maximum subsurface damage depth is respectively 15.77%, 11.65%, and 18.36%. And the subsurface damage depth of zirconia ceramics is respectively 27 μm, 31 μm, and 40 μm with the grain size of 50 nm, 500 nm, and 5000 nm in the 5th group process parameters, which showed that the small grain size exhibited excellent grinding quality. But the influence of grain size on dynamic fracture toughness was weaker than that of grinding process parameters. [ABSTRACT FROM AUTHOR]

The present paper is devoted to the problem of sintering ceramics based on yttria-stabilized zirconia (Y-TZP). In this paper, we studied the effect of two obtaining methods (co-precipitation and technical hydrolysis) on sintering kinetics of Y-TZP nanopowders. We used the constant rate of heating (CRH) method at different heating rates for determining the sintering mechanisms. The basic mechanism and activation energy ( Q) of diffusion at the initial sintering stage were estimated using the sintering rate equations that are applicable to the CRH data. We found that nanopowder 3Y-TZP produced by the co-precipitation method (DIPE) was sintered according to the volume diffusion mechanism ( n = 1/2) and nanopowder TZ-3Y (TOSOH) produced by the technical hydrolysis was sintered according to the grain boundary diffusion mechanism ( n = 1/3). [ABSTRACT FROM AUTHOR]

This paper describes an efficient method of fabricating high-performance ceramic (HPC) parts by using solvent-based slurry stereolithography (3S) and sintering. In this study, zirconia was used as the structural material, methyl alcohol was used as the solvent, a waterborne inorganic pigment was used as the dispersant, and a visible-light-curing resin was used as the organic binder for forming the slurry. The slurry was photocured using a visible-light projector for layer-by-layer deposition in an enclosed cabinet to form a three-dimensional object. The obtained green part was sintered at high temperatures (up to 1600 °C) so that it densified and formed a rigid body. Thus, an HPC part with high material strength could be produced. A complete system was developed for producing complex zirconia ceramic parts with a high level of precision without the necessity of generating support structures for the overhang features. The system was determined to achieve a very fine-detailed shape (30 μm). The mechanical properties of the obtained zirconia parts, such as flexural strength, density, and average roughness, were also investigated in this study. [ABSTRACT FROM AUTHOR]

The 0.2Li2ZrO3-0.8MgO (Li2Mg4ZrO7) ceramics were prepared by conventional solid-state reaction method. The effects of lithium fluoride (LiF) addition on the microstructure, sintering temperature and microwave dielectric properties of Li2Mg4ZrO7 ceramics were investigated. The experimental results demonstrated a typical single phase existed in Li2Mg4ZrO7-LiF ceramics, in which LiF was proved to be an effective sintering aid for the Li2Mg4ZrO7 ceramic. LiF obviously lowed the optimum sintering temperature of Li2Mg4ZrO7 ceramic from 1500 to 1050 °C and improved the sintering ability of the matrix. In this paper, the microwave dielectric properties were strongly dependent on the amount of LiF additions and the sintering temperature. Optimum microwave dielectric properties (εr = 12.95, Q·f = 180,011 GHz and τf =− 23.51 ppm/°C) were obtained in Li2Mg4ZrO7-4 wt% LiF ceramics sintered at 1050 °C. [ABSTRACT FROM AUTHOR]

In dentistry, all ceramic restorations were widely used because of perfect esthetic, especially the zirconia ceramic. Now in digital dentistry, zirconia dental restorations are mostly made from digital manufacturing system such as the computer-aided design and computer-aided manufacturing (CAD/CAM) or three-dimension printing (3DP). After producing, the sintering process is indispensable due to the increase in the mechanical properties. Notably, the side effect of shrinkage of the sintering process is difficult to predict or control and cannot be studied deeply. Reflecting the accurate of zirconia restoration is lower, especially the most important factor of restoration fitness. So the poor fitness of restoration easily leads to secondary caries or micro leakage that the tooth will decay again and the remaining teeth will need to be removed completely. In this paper, the 3DP is the target manufacturing process to avoid the high cost of CAD/CAM processing; the 3DP product needs to be of high precision after the sintering process. However, the shrinkage of the 3DP product is difficult to predict and cannot be studied deeply. Therefore, different shrinkage rates of experimental pieces following the manufacturer's instructions of the sintering process are first predicted in CAE analysis, experimental design, and regression analysis. The results are then applied in the manufacture of incisor restoration to verify the shrinkage. This can make the restoration fit in the patient's mouth properly and reduce the medical operation time. It helps the 3DP to successfully apply the dentures. [ABSTRACT FROM AUTHOR]

This paper presents the micro-shot peening of zirconia (ZrO)-advanced ceramics applicable for bio-medical, dental, automotive and aerospace sectors. A ZrO-advanced ceramic was micro-shot blasted with selected parameters as a first-step investigation focused on the topography, microstructure, surface hardness and the surface fracture toughness ( K) characteristics. A new technique of micro-blasting was conducted using a portable shot blaster. A white-light interferometer, scanning electron microscopy and Vickers indentation technique were employed for the analysis. This was followed by determining the K using an empirical equation. Surface roughness was improved by 34 % after micro-shot blasting treatment. No surface cracking was present which generally exists due to the brittle nature of the ceramic. The hardness, however, reduced by 5.6 % with a reduction in the Vickers crack length of 9 %. This improved the K by 3 % when comparing the micro-shot peened surface to the original, as-received surface. It is difficult to conclude if the ZrO-advanced ceramic has undergone plastic deformation and the movement of dislocations increased to strengthen the ZrO ceramic at this stage. However, based on the results, it can be predicted that a level of surface compression was induced beneath the micro-shot peened layer as indicated from the result of the surface topography and integrity. This would justify the hardness modification and the enhancement in K. [ABSTRACT FROM AUTHOR]

The paper discusses structure investigations of the zirconium oxide-multiwalled carbon nanotube composite produced by electrophoretic codeposition of the components. Thermal analysis, Raman spectroscopy, and TEM analysis have revealed the strong influence of multiwalled carbon nanotubes on the sintering kinetics of zirconium oxide, as well as the structure and phase composition of sintered ceramics. [ABSTRACT FROM AUTHOR]

Two-component micropowder injection molding allows two different materials and, hence, two different functions to be integrated in one microdevice. This requires both components to be matched precisely. Therefore, high dimensional accuracy is essential in the successful development of a two-component micropart. This paper is about studies of the accuracy of the diameters of the inner hole of a gear wheel to be used as the first component of a shaft-to-collar connection. Diameters were measured in two defined directions, oriented 90° relative to each other. Items discussed are the size accuracy of green bodies and sintered specimens as well as the effects of different gating concepts. Sometimes, the inner hole is eccentric, depending on the gating concept employed. It was shown that a point-shaped gate can exert pressure on the feedstock nearby, thus causing deformation and reducing the diameter in these areas compared to the diameter in areas far from the gating system. The results also show that the eccentricity of the inner hole after sintering differs from that measured on green bodies, which is an indication of anisotropy in sintering. Moreover, the types of powder were seen to have an effect. [ABSTRACT FROM AUTHOR]

In this paper, the densification of a ceramic powder matrix that contained large macropores of the size much larger than the average grain size of the matrix was studied. The grain-boundary diffusion controlled sintering models of ceramic matrix contained large macropores were first established. A sintering potential associated with the macropores was also verified and introduced into the models. The experimental data were collected for the sintering of porous 8 mol% yttria-stabilized zirconia system with 20 vol% large pores. The predictions of the model were found in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

The processing of yttria-stabilised zirconia (Y-ZrO2)-based ceramic nanocomposites by means of pulsed electric current sintering (PECS) is described. A nanometer-sized electrically conductive secondary TiCN phase was added to the insulating zirconia matrix in order to make the composite electrically conductive. The paper focuses on the importance of processing conditions and highlights the benefits of the PECS method as compared to more traditional hot pressing. The mechanical and microstructural properties of the ZrO2–TiCN composites have been determined, and the benefits of using an electrical current to densify these composites were explained in terms of the evolution of the electrical properties of the densifying powder compact. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells are currently constructed using a yttria stabilised zirconia electrolyte membrane. However, zirconia has a number of disadvantages associated with its use, such as the high operational temperatures required for it to exhibit acceptable levels of ionic conductivity. Alternative ceramics such as doped cerium oxide show promise as electrolytes capable of operating at reduced temperatures, but introduce additional problems such as electronic conduction and inferior mechanical properties. This paper describes the manufacture and characterisation of a number of prototype electrolytes consisting of a mixture of yttria stabilised zirconia and gadolinium doped ceria. Traditional ceramic processing techniques were used to produce the samples, which were then examined using dilatometry, impedance spectroscopy and X-ray diffraction. Results show a lowering of the ionic conductivity of zirconia with the addition of doped ceria. X-ray diffraction patterns obtained from the samples suggested that this effect could be attributed to the formation of a solid solution of ceria in zirconia. [ABSTRACT FROM AUTHOR]

The present paper discusses the complications that can arise in using in the core melt trap of the European nuclear reactor being designed a sacrificial material of 40% FeOx–60% SiO2 composition. The investigation of the interaction of zirconium dioxide ceramics with the sacrificial material has permitted the conclusion that at a local baring of the refractory layer its destruction can occur. The addition of neodymium oxide to the melts lowers erosion and excludes regeneration of the ceramics structure. [ABSTRACT FROM AUTHOR]

Zirconia ceramics are widely used in aerospace, optical, bio-medical, electronics, and other industries for better physical and mechanical properties. However, the poor processability and reliability become a bottleneck restricting its industrialization. This study introduced multidimensional ultrasonic vibration-assisted electrolytic in-process dressing (UVA-ELID) grinding to overcome this bottleneck and improve the processing effect. Firstly, the implementation of multidimensional UVA-ELID grinding was demonstrated. Secondly, the kinematic analysis of a single abrasive grain was performed for the one-, two-, and three-dimensional UVA-ELID grinding. Finally, the multidimensional UVA-ELID grinding experiment was conducted to obtain the effect of processing parameters on the grinding force and surface roughness. It was found that the maximum reduction of grinding forces Fn and Ft in the 3D case can be reduced by 36.8 and 37.5%, 55.4 and 51.5%, 38.1 and 30.7%, and 31.1 and 30.7%, respectively, compared to those in the 1D with the variation of spindle speed, feed rate, grinding depth, and duty cycle, and the surface roughness could be maximally reduced by 53.5, 51.5, 54.1, and 45.7%. The results of this study can provide a reference for UVA-ELID grinding of zirconia ceramics and other hard brittle materials. [ABSTRACT FROM AUTHOR]

Ceramics and other hard-and-brittle materials are very effectively processed by longitudinal-torsional coupled rotary ultrasonic machining (LTC-RUM), which cutting force evolution and the effects of processing parameters on the material removal mechanism need to be optimized. This study introduced the LTC-RUM cutting force model of zirconia ceramics based on the brittle material removal mechanism. Firstly, the kinematic analysis of a single abrasive grain was performed, with further consideration of the material removal volume, the effective contact time, and the impact force per one ultrasonic vibration cycle. Then, the longitudinal-torsional coupled vibration of the core tool was analyzed from the wave energy conversion standpoint. The analytical model was finalized and experimentally verified by LTC-RUM tests, which results closely correlated with the ones predicted via the proposed model. With the spindle speed, feed rate, and ultrasonic power variation, the maximum discrepancies between the predicted and experimental cutting forces are 15.51, 13.24, and 8.3%, respectively. The results obtained are considered instrumental in predicting the effects of processing parameters on the cutting force during LTC-RUM of ceramics and their further optimization. [ABSTRACT FROM AUTHOR]

Parts made of zirconia ceramics have been used in various high-end fields, and some of these parts exhibit complex styles with various curved surfaces. As a prominent machining technique for manufacturing zirconia ceramic parts, tangential ultrasonic-assisted grinding has mainly been employed in improving the processing efficiency and simultaneously ensuring the surface quality. With the aim of further improving the processing performance of tangential ultrasonic-assisted curved surface grinding, the effects of the grinding paths with α = 0°, α = 45°, and α = 90° on the surface quality and profile of a workpiece were studied for a specific curved surface, and the wear of the grinding wheel with different paths was analyzed. In addition, the material removal mechanisms were discussed for single diamond grit grinding tests. The obtained results demonstrated that (1) the surface roughness Sa was different at different grinding paths, i.e., at different values of α, and the surface finish mainly depended on the ultrasonic amplitude. (2) The profile error of the curved work-surface was different at different values of α. (3) The wear of the grinding wheel at α = 45° was the most serious, and at α = 0° and α = 90°, the abrasive grain wear was slight. These tendencies agreed with the case of the work-surface quality. (4) The material removal mechanism was different with and without ultrasonics, which resulted in the differences in the work-surface finish. [ABSTRACT FROM AUTHOR]

The effect of the diamagnetic ZrO2 addition on the microstructure and magnetic properties of LiTiZn ferrite ceramics, including the shape and parameters of the temperature dependence of the initial permeability, has been investigated. The defect structure of ferrite ceramic samples is assessed according to our earlier proposed method based on the mathematical treatment of the experimental temperature dependencies of the initial permeability. It was found that the defect structure of ferrite ceramics increased by 350% with an increase in the concentration of the ZrO2 additive in the range of (0–0.5) wt.%. In this case, for the same samples, the increase in the true physical broadening of diffraction peaks is only 20%, and the coercive force by 50%. Simultaneously, the maximum of the experimental temperature dependence of the initial permeability dropped by 45%. The microstructure of all samples is characterized with a similar average grain size according to the SEM data. However, samples with 0.5 wt.% of ZrO2 are characterized by the formation of conglomerates. A linear relationship was obtained between the defect structure and the width of the diffraction peaks, which indicates that this parameter is related to the elastic stress of ferrite ceramics. These results suggest that the high sensitive proposed method can be recommended for impurity and defect monitoring of soft ferrite products. [ABSTRACT FROM AUTHOR]

Zirconia ceramics have been used in the field of smartphone manufacturing, especially for the phone shells. To improve the machining efficiency and simultaneously obtain a mirror-surface quality on the curved surface made by zirconia ceramics, the tangential ultrasonic-assisted grinding (TUAG) was proposed, in which the ultrasonic vibrations of the grinding wheel are always in the direction tangential to the work surface at the grinding point. To reveal the fundamental grinding characteristics of the TUAG on the zirconia ceramic curved surface, the processing principle and according experimental setups were given out at first. The effects of the proposed method on the surface morphology and surface roughness were investigated experimentally and analyzed numerically under different process parameters for plane workpieces. Finally, a curved surface was successfully processed by the novel method with the optimized experimental conditions. The obtained results demonstrated that (1) typical sinusoidal cutting traces appeared on the work surface, which implied that the surface morphology was affected significantly by the ultrasonic vibrations; (2) the surface roughness was distinctly affected by the amplitude of the grinding wheel, and a higher efficiency was attained on the surface quality enhancement when the larger amplitude was applied, e.g., Ra was reduced by 58.3% when an amplitude of Ap–p = 4.66 μm was imposed; and (3) the Ra value in the direction vertical to the wheel feed direction on the curved surface decreased to 39.5 nm, implying that a mirror curved surface can be obtained by TUAG with the appropriate process conditions. [ABSTRACT FROM AUTHOR]

Zirconia-based ceramic has generated considerable interest in specialist structural/engineering ceramics. Among current available additive manufacturing methods for fabrication of ceramic components, the conventional material jetting systems are able to create local deposition of thin layers, dense green bodies, and complex shapes. However, this method is mainly limited to low viscous ceramic inks (mostly in the range of 20–40 mPa/s) with often less than 25 vol% solid loading which has restricted the widespread adoption of this technique. In this work, we employed a novel in-house developed hybrid drop-on-demand material jetting system (DODMJ) to deposit a highly viscous paste (up to 72 wt% solid content, a viscosity of 2100 mPa/s) of yttria-stabilized-zirconia (YSZ), with approximately 20 times higher speed than the current material jetting methods, for the first time. For this study, tetragonal zirconia polycrystal containing 8 wt% Y2O3 (5Y-TPZ), which is commonly used to produce dental restorations by subtractive manufacturing, was utilized. The printability of several visible light–curable zirconia pastes was studied in terms of the rheology, paste composition, solid content, and printing parameters. The density and porosity measurements as well as a two-stage sintering process to achieve fully dense and crack-free parts were carried out. The microstructure and internal features of the printed parts were also explored by X-ray nano-computed tomography (CT) scanning and scanning electron microscopy (SEM). In this work, standard test methods were also utilized to study the Vickers hardness and fracture toughness of the sintered 5Y-TPZ parts for the first time. The results showed that specimens produced with the paste containing 62.3 wt% solid loading yielded a relative density of 99.5% and presented an average fracture toughness and micro-hardness of 5.62 MPa/m0.5 and 1516 HV, respectively. Overall, the outcomes presented in this work confirmed that the novel DODMJ technique adopted for this study has great potential in the development of a feasible, high-speed, and cost-effective manufacturing system to produce zirconia ceramic parts with adequate mechanical and structural properties that meet the demanding requirements for various applications such as dental crowns restoration. [ABSTRACT FROM AUTHOR]

During the manufacturing of ceramic components, grinding is an important manufacturing step. It influences the workpiece quality and the operational reliability. Thermomechanical loads during grinding can influence the lifetime and operational reliability of ceramics by modifying their bending strength and subsurface properties. Therefore, it is necessary to consider the influence of the grinding forces and mechanical loads on the strength of the ceramics in order to design a suitable grinding process. In this investigation, a quick-stop device is used to interrupt the grinding process of the newly developed mixed oxide ceramic SHYTZ (strontium hexaaluminate/yttria-toughened zirconia) and the market-established ceramic ATZ (alumina-toughened zirconia). Subsequently, an analysis of the occurring material removal phenomena, the number of active abrasive grains, and the real thermomechanical loads is carried out. It was found that the number of active grains and the material removal phenomena are influenced by the tool specifications. Besides that, the experimentally determined number of active grains was found to be up to 14 times higher than predicted by an analytical model given in literature. Consequently, the calculated single grain chip thickness was found to be up to 12.1% lower than analytically predicted. The investigation of the process forces and thermal loads showed up to 52% higher loads for ATZ than for SHYTZ. The subsequent analysis of the resulting bending strength of the ceramics revealed a lower influence of the grinding process on the strength of SHYTZ than for ATZ. Furthermore, a correlation between the used tool bonding and the resulting thermomechanical loads, bending strength, and residual stresses could be observed. [ABSTRACT FROM AUTHOR]

BiFeZrO ( x = 0.00-0.30) ceramics were synthesized using solid state reaction method followed by rapid liquid phase sintering, and the microstructure, electrical and magnetic properties of the synthesized ceramics were systematically investigated. The XRD patterns show that no impurity phases exist in Zr doped samples; Zr doping induces the crystal structure distortion when x ≤ 0.10, and a structural phase transition occurs when the content of Zr varies from 0.10 to 0.20. SEM observations indicate that the average grain size is remarkably decreased by Zr doping. Positron annihilation lifetime spectra results indicate that cation vacancy-type defects exist in all samples, the cation vacancy concentration increases with increasing Zr content from 0.00 to 0.20, and then decreases with further increase of Zr content. Electrical and magnetic measurements show that enhanced leakage, ferroelectric and magnetic properties are observed in Zr doped ceramics. The analysis of microstructure and properties show that the cation vacancy defect plays an important role in modulating the electrical and magnetic properties of BiFeO. [ABSTRACT FROM AUTHOR]

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions (<38 vol%). The sintered structures were able to retain the original morphologies with >94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability. [ABSTRACT FROM AUTHOR]

The development of advanced ceramics such as zirconia has gained importance because of their desirable properties. However, the engineering applications of ceramics are still limited by the ability to develop cost-efficient machining techniques. To achieve the cost-efficient production of zirconia parts, laser irradiation was introduced as a step before grinding. In this study, this hybrid process was investigated by measuring the grinding force and the specific grinding energy in grinding tests. The results confirmed significant decreases in the grinding force and specific grinding energy. The decreases suggest that the hybrid process can be an economical and efficient way to overcome the limitation of the high specific energy required for grinding advanced ceramics. Scratch tests were performed to obtain a fundamental understanding of the decreases in the grinding force and energy, and the scratch morphology and crack types beneath the scratch tracks were observed. The transition of crack types and the chip-forming mechanism was confirmed. It was noted that the scratch hardness of ceramics reduced after laser irradiation, which explains the reduction in the grinding force. In addition, micro-debris and lateral cracks were induced by scratching on the surface with laser irradiation, which contributed to the decrease in the specific grinding energy. [ABSTRACT FROM AUTHOR]

Zirconia (ZrO) ceramics are being considered as a candidate material for thermal insulating barriers in pressure tubes used in the supercritical water (SCW) nuclear reactors. However, the literature suggests that zirconia may undergo a detrimental phase transformation which is accelerated in aqueous environments. In this research, 8 mol% Yttria-Stabilized Zirconia (YSZ) ceramics with the addition of 5 and 10 mol% NdO were manufactured via spark plasma sintering (SPS) process and subsequently subjected to a SCW environment. The weight losses and microstructural evolutions of these materials during SCW exposure were studied. The results suggest that doping YSZ with NdO significantly decreased the degradation rate of the YSZ ceramic and improved its structural stability. X-ray diffraction studies revealed that after degradation testing, the NdO helped to retain the desirable cubic phase of YSZ matrix. In the case of pure YSZ ceramic, a phase change of the matrix toward the monoclinic lattice was observed and likely contributed to the ceramic's disintegration in SCW environment. [ABSTRACT FROM AUTHOR]

The (SmGd)(CeZr)O oxides were prepared by solid-state reaction, and their phase compositions, microstructures, and thermophysical properties were investigated. Results of x-ray diffraction reveal that pure (SmGd)(CeZr)O oxides with fluorite structure are successfully synthesized in the current study. The thermal expansion coefficient decreases with increasing content of ZrO, which is higher than that of 7 wt.% yttria-stabilized zirconia (YSZ). The substitution of Zr for Ce reduces the thermal conductivity of SmCeO oxide. The thermal conductivity decreases from 1.69 W/m K ( x = 0) to 1.22 W/m K ( x = 0.3) at 1000 °C. The composition with x = 0.3 exhibits the lowest thermal conductivity at all temperatures, and the thermal conductivity of (SmGd) (CeZr)O ceramics was obviously lower than those of fully dense 7 wt.% YSZ. These results suggested promising potential applications of the (SmGd) (CeZr)O ceramics for high-temperature thermal barrier coatings. [ABSTRACT FROM AUTHOR]

A synthesis technology for ceramics based on a tetragonal solid solution of zirconia in ZrO-YO-CeO and ZrO-YO-AlO systems with a high degree of tetragonality (∼1.436) and an average crystal size of 45-70 nm has been developed; it can be recommended for producing bioceramics in restorative dentistry. [ABSTRACT FROM AUTHOR]

Porous yttria-stabilized zirconia (ZrO2-8 mol% Y2O3, YSZ) ceramics with ultra-low thermal conductivity (as low as 0.06 W/mK) could be fabricated by tert-butyl alcohol (TBA)-based gel-casting process with low solid loadings of 10 and 15 vol%. High porosity (52–76%) and fine pores with average pore size of 0.7–1.8 μm formed after sintering at 1350–1550 °C. These air-containing pores were believed to affect the through-thickness heat transfer propagation, resulting in low thermal conductivity. The thermal conductivity of porous YSZ ceramics with different porosities fits well with computed values derived from Effective Medium Theory (EMT). [ABSTRACT FROM AUTHOR]

Zirconium dioxide (ZrO2)-based composites with WC addition are demonstrated to be suitable for electrical discharge machining (EDM) in deionized water. ZrO2-based composites with 40 vol. % WC, obtained from distinctive WC powder sources, were produced in order to derive correlations between material removal rate (MRR), surface finish, wire EDM parameters and material properties. Dry reciprocating sliding experiments on wire-electrical discharge machined ZrO2-WC composite samples against WC-Co cemented carbide, performed using a pin-on-plate testing rig, revealed a significant influence of the microstructure of the secondary WC-phase on wire EDM behavior and frictional characteristics. [ABSTRACT FROM AUTHOR]

Capability of the recycling of high strength and high fracture toughness yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) sintered body utilizing “low-temperature annealing degradation” phenomenon was investigated. Hydrothermal treatment was employed to induce the phase transformation from tetragonal to monoclinic zirconia and to disintegrate the Y-TZP sintered body. 3 mol% Y2O3–ZrO2 specimens sintered at 1,550 °C and more were disintegrated without leaving the original appearances when the treatment temperature was between 200 °C and 400 °C. The size of the disintegrated fragments of Y-TZP sintered body was much affected by hydrothermal treatment conditions. Only with hydrothermal treatment and simple ball milling, the sintered body was pulverized into the primary particle level. This technique is expected to apply to a sustainable recycling system for the zirconia ceramics, which restrains an energy consumption compared to crushing zirconia using mechanical procedures. [ABSTRACT FROM AUTHOR]

This article discusses the ageing effects of sub-micrometric 3mol% yttria-stabilized zirconia (3Y-TZP) ceramics on its nanoindentation response. Yttria-stabilized zirconia ceramics are used as prosthesis material in hip replacement. 3Y-TZP was obtained starting from two commercial powders. The zirconia ceramics were used as a function of ageing time and peak load. The general hardness decreased with the ageing time should be ascribed to the increase of monoclinic phase content.

High temperature creep of a metal–ceramic composite consisted of yttria tetragonal zirconia polycrystals (YTZP) with a certain amount of nickel grains (Ni–YTZP, 2.5% vol.) has been studied. The average grain size of YTZP grains was 0.20 μm, whereas that of the Ni grains was 50–70 nm. This work reports the mechanical response under creep of such composite materials. It is found that the activation energy for creep is significantly higher than that reported in similar systems with much larger nickel grains. This fact has been explained in terms of the chemical nature of the metal–ceramic interfaces. [ABSTRACT FROM AUTHOR]

Ceramic monolithic and multilayered composites were produced by stacking water based green ceramic cast tapes. Two different mixtures of composites within the Al2O3/YTZP, system were investigated. The difference in the coefficient of thermal expansion (CTE) between the composites fabricated, resulted in the development of residual stresses when the same compositions were combined in a multilayered structure. The magnitude and the distribution of these residual stresses were assessed by the piezo-spectroscopic technique. The stress within the layers varied with a parabolic trend, with the highest values at the interfaces and a reduction toward the centre of the layers. The influence of symmetry of the multilayered laminate on the magnitude and distribution of the residual stresses within the structure are discussed. [ABSTRACT FROM AUTHOR]

Dense nanocrystalline ZrO2-3 wt% Y2O3 ceramics with grain sizes ranging between 23 to 130 nm were tested by ultrasonic pulse echo and Vickers hardness. The elastic modulus and hardness results were corrected for the residual porosity and the phase content. The corrected elastic moduli exhibited continuous decrease with decrease in the grain size. In contrast no correlation was found between the corrected hardness and grain size. The percolative composite model was used to describe the changes in the elastic moduli in terms of percolation of the elastic wave through the intercrystalline phase at the percolation threshold. The absence of correlation with the hardness results was explained due to the other energy absorbing mechanisms such as microcracking beneath the indenter. [ABSTRACT FROM AUTHOR]

A high performance 500 nozzle in-line piezoelectric drop-on-demand print-head mounted on a linear table with z-axis control was used to prepare arrays of fine ceramic pillars. Such structures may find applications in miniature heat exchangers, catalyst supports, for cell up-regulation in prosthetics or in polymer-ceramic piezoelectric 1–3 composites. The ink conveyed 14 vol% fine zirconia and deposited a wax-based suspension in an octane-alcohol mixture. The dried ink contained 63 vol% zirconia. [ABSTRACT FROM AUTHOR]

ZrO2 and SiC ceramic thin films and their bilayer have been successfully prepared by a newly developed electrostatic atomization technique. This technique can generate fine spray of ceramic suspensions in a micrometer sized range with a narrow size distribution which is crucial for preparation of uniform thin films of these ceramic materials. Compared to some other thin film deposition techniques, such as Chemical vapour deposition (CVD), physical vapour deposition (PVD) and plasma spray (PS) etc. the thin film deposition process using electrostatic atomization is not only cheap but also controllable. The prepared ZrO2 and SiC thin films were investigated using scanning electron microscopy (SEM) and energy dispersion analysis (EDA) techniques. These thin films were observed to be homogenous with a particle size less than 10 μm. The ZrO2-SiC bilayer was found to have an abrupt interface, implying that the deposition process is controllable and also that functionally graded ceramic/ceramic materials can be prepared in this way if the thickness of each layer is accurately controlled. [ABSTRACT FROM AUTHOR]

Effect of YNbO4 addition on the fracture toughness and stress-strain characteristics of ZrO2(3Y) ceramics was investigated using micro-indentation, X-ray diffractometry and in-situ compression-diffraction techniques in the present work. X-ray diffraction patterns show that sintering of YNbO4 and ZrO2(3Y) mixture results in formation of a solid solution, and the tetragonality of ZrO2(3Y) ceramics increases with the content of YNbO4. The ratio of 002t to 200t peak intensity in X-ray diffraction spectra of the specimens changes significantly after a grinding process at low fractions of YNbO4 (less than 5 mol%) and approaches to a constant value as the content of YNbO4 is higher than 5 mol%, implying that the addition of YNbO4 reduces the domain switchability of the ZrO2(3Y) ceramics. Fracture toughness of modified-ZrO2(3Y) specimens with the same heat treatment conditions could be greatly enhanced by an appropriate addition of YNbO4. In addition, stress-strain curves of YNbO4-modified ZrO2(3Y) specimens exhibit an extraordinary elastic behavior. Data of in-situ loading-diffraction experiment show that an unidentified stress-induced transformation occurs and the peak intensity varies with the stress conditions. Analysis of the stress-strain characteristics and X-ray diffraction results suggest that the fracture toughness of the specimens cannot be simply attributed to the t-to-m phase transformation. [ABSTRACT FROM AUTHOR]

In this study, a slip casting method was used for the production of tensile specimens for superplastic deformation from zirconia powders containing 3 and 8 mol% yttria. It was seen that the slip casting process allowed the production of complex, net-shape and economical production of a relatively small number of individual shapes. The factors affecting the casting characteristic of the slip system, namely, solid content, slip viscosity, dispersing agent concentration and moulding conditions were investigated and optimum values for the above were determined. The effect of shaping process on superplastic deformation was also investigated for slip-cast and die-pressed specimens. It was seen that superplastic ductility obtained from slip-cast specimen was higher than that of die-pressed one. The reason for ductility enhancement was due to the homogeneous dispersion of the powder and elimination of agglomerates in slip-cast specimen, compared to die-pressed specimen in which agglomeration caused non-homogeneous sintering leaving crack-like voids responsible for early fracture. [ABSTRACT FROM AUTHOR]

The crystal structure of compositionally homogeneous, nanocrystalline ZrO2 - X mol% Y2O3 ( X = 2.8, 4, 5, 6, 7, 8, 9, 10, 11, and 12) powders synthesized by a nitrate-citrate gel-combustion process has been studied by X-ray diffraction. By applying the Rietveld method, it was found that all the powders presented the tetragonal phase ( P42/ nmc space group). The axial ratio c/ a f decreased with increasing Y2O3 content and became almost unity at 9 mol% Y2O3. However, powders in the compositional range of ZrO2 - 9 to 12 mol% Y2O3 exhibited the oxygen atoms displaced from their ideal sites of the cubic phase along the c axis, which is known as the t′′-form of the tetragonal phase. A conjunct analysis of crystallite size and microstrain of all the powders is also presented. [ABSTRACT FROM AUTHOR]

Indentation fatigue testing is carried out for four kinds of zirconia ceramics; 6Y-FSZ, 3Y-TZP, Mg-PSZ and Ce-TZP; which have different strengthening-toughening mechanisms one another. Each material shows different indentation fatigue behavior. Large sized surface chipping is produced easily in early cycles for non-toughened 6Y-FSZ, while 3Y-TZP toughened by anelasticity has high resistance against chipping. There is a possibility that anelastic characteristic works as resistance against indentation fatigue damage. Stress induced phase transformation also improves fatigue damage, but this effect depends on the extent of transformation and/or occurrence of microcracking. [ABSTRACT FROM AUTHOR]

The zirconia particles in zirconia-containing ceramics have a size distribution similar to Gaussian distribution. The spontaneously martensitic start temperature (Ms) of different particles are not the same. The larger the particle, the higher its Ms. On cooling from high temperature to a value lower than the macro Ms of the materials, the stress-induced and spontaneous transformation will happen, so that the toughness of the materials increases at first, then gradually drops to a value slightly higher than that of the matrix. The size distribution plays an important role in affecting the toughness of the materials. When the average particle size increases, the maximum toughening (ΔKc)max and the temperature (Tmax) at which (ΔKc)max happens will all increase. The toughness at given temperature will increase at first and then drop also to a value slightly higher than that of matrix with increasing of average particle size. The stronger concentration of the size distribution, the higher (ΔKc)max will be. The weaker concentration for size distribution (either the range of zirconia particle sizes becomes wider or the scale parameter of the distribution increases), the lower (ΔKc)max, but the range of temperature in which the toughness is larger than certain value will become wider. Some suggestions of designing ceramics with high toughness at different temperatures are given. [ABSTRACT FROM AUTHOR]

The mechanical strength of ceramic multilayers for use in solid oxide fuel cell stacks was examined. The multilayers consist of a substrate, made of yttria stabilised zirconia (YSZ), with a NiO/YSZ composite coating on both faces. Under some processing conditions the mechanical strength of the multilayers was similar to that of pure YSZ, while a much lower strength was found for other processing conditions. Inspections of the fracture surfaces revealed markedly different appearances, suggesting that a transition in failure mode had occurred. Fracture mechanics models for thin films on substrates were used to interpret the observed fracture modes, providing insight to the underlying failure mechanisms. [ABSTRACT FROM AUTHOR]

Abstract  The possibilities of preparing ceramics from a zirconia nanopowder have been investigated. A ceramic material with a fine-grained (of the order of 2–3 µm) structure is synthesized. A ceramic material with zircon predominant is produced using a silica nanopowder (tarkosil). The properties of the initial nanopowder and the ceramic material synthesized are investigated using transmission electron and scanning electron microscopies. The microhardness and strength of the ceramics are determined. [ABSTRACT FROM AUTHOR]

Alumina and zirconia ceramics joints were made by diffusion bonding through platinum and palladium gaskets in air at temperatures between 1300 and 1550°C. The instrumentation and the procedure for these joints manufacturing are described. The effects of temperature, pressure and exposition time on 3-pt bending strength of resulting joints were established. The maximum bending strength of the samples reached 500 MPa. During thermal resistance testing the samples withstood several hundreds of thermal cycles at temperatures up to 800°C in air. [ABSTRACT FROM AUTHOR]

We have developed a technique for obtaining soldered joints of ZrO2 ceramics in air with the help of solders of the copper-silver-oxygen system. We used different methods of the preliminary application of a layer of copper-oxide onto the surface of ZrO2 ceramics (with burn-in and without it) with subsequent soldering in a mixture of silver and CuO powders and also with the help of Ag-22Cu alloy. The bending strength of these joints is about 300 MPa. Soldered joints possess a high corrosion resistance and can be used for operation in air at a temperature up to 700°C. [ABSTRACT FROM AUTHOR]

Examines the thin-layer activation of silicon nitride and zirconium dioxide ceramics. Sensitivity of the method in analyzing the wear of ceramics; Running-in performance of the bearings; Aspects associated with the effects of the irradiation on the properties of the material that govern the wear resistance; Comparison of measurements for irradiated and unirradiated ceramic specimens with a PMT-3 microhardness tester.