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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]

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]

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]