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Aluminum oxide (alumina, Al 2 O 3) is one of the most widely used ceramic materials owing to its excellent dielectric, chemical resistance, and low cost. In contemporary semiconductor fabrication processing, in particular, Al 2 O 3 plays a key role in high-value processing components, such as an electrostatic chuck. Here, we report for the first time a novel densifying technique for Al 2 O 3 that can be referred to as the powder metallurgy hot isostatic press (PM-HIP) process. Unlike the conventional HIP process, our PM-HIP process can directly convert Al 2 O 3 powders into fully densified ceramics via a one-step process. More importantly, during the PM-HIP process, thermomechanical energy can easily be transferred to each of the particles simultaneously, which facilitates the sinter process (i.e., necking and diffusion) and the clipping of lattice planes. As a result, highly dense dislocation arrays are embedded within the entire volume of the sintered body. This correlates with unique material properties-processing relationships in the Al 2 O 3 ceramics sintered via PM-HIP. The Al 2 O 3 ceramics sintered by PM-HIP exhibited unique mechanical and electrical properties, highlighting its potential for use in electrostatic chucks. [ABSTRACT FROM AUTHOR]

In this work, MgAl 2 O 4 : Cr3+ transparent ceramics have been synthesized by the hot press sintering techniques, and the effect of the sintering aid Gd 2 O 3 and its content on the densification, microstructure, and optical, photoluminescence was studied and discussed. The relative density reached 99.29% with 0.8 wt% Gd 2 O 3 as a sintering aid, and the optical transmittance at 686 nm and 1446 nm were approximately 76%. As Gd 2 O 3 content continued to increase, the grain size of the ceramics became smaller and uniform, accompanied by some pores with the size of ～1 μm. The ceramics with 4.0 wt% Gd 2 O 3 showed a higher transmittance, of 82% at 1446 nm. Additionally, Gd 2 O 3 was helpful for Cr3+ in the sites of octahedral symmetry, which increased the quantum yield. The quantum yield of MgAl 2 O 4 : Cr3+ with 0.8 wt% Gd 2 O 3 was about 0.175, which was 36% higher than that of ceramic without Gd 2 O 3. In short, the sintering aid Gd 2 O 3 not only contributed to improving the densification, homogenizing the grain size, and heightening the optical transmittance but also enhanced the quantum yield of Cr3+. [ABSTRACT FROM AUTHOR]

Geopolymers are attracting attention in the field of concrete building materials from the viewpoint of reducing CO 2 emissions. This study demonstrates the effects of the addition of silica fume in the warm press method on the densification and mechanical properties of a geopolymer. First, geopolymer products hardened by conventional slurry curing, using fly-ash and sodium hydroxide solution as starting materials, were prepared. The hardened geopolymer products were then pulverized into small grains. Subsequently, various amounts of silica fume were mixed into the fine geopolymer particles to form the starting powder mixtures. A series of these mixtures (10 mass% water added) were placed into a steel mold, which was then inserted into a warm press device. An uniaxial pressure of 240 MPa was applied at room temperature and then the temperature was raised from 80 to 180 °C. When the warm press temperature was set at 80 °C, the compressive strength of the hardened bodies increased in line with the amount of added silica fume. Particularly, in the case of a hardened body with 30 wt% silica fume, the compressive strength reached 195 MPa, which was about three times that of a hardened body with 0 wt% silica fume. The added silica fume was found to improve the fine stacking of starting geopolymer particles in the early stages of warm pressing and help form objects with tightly packed voids between the original geopolymer particles. In contrast, for heat treatment at a warm press temperature of 180 °C, the compressive strength of the hardened bodies with 30 wt% silica fume decreased compared to those for the hardened bodies with 0, 10 and 20 wt% silica fume. From the results of nuclear magnetic resonance analysis, this decrease in strength was considered to be due to an increase in the silica-rich phase. [ABSTRACT FROM AUTHOR]

Ta 2 O 5 nanoparticles were synthesized by thermal decomposition of tantalum (V) ethoxide, and Ca 3 Co 4 O 9 /Ta 2 O 5 composites were fabricated by ball milling. The volume percentage of Ta 2 O 5 nanoparticles in the composites was controlled as 0, 2%, 4%, and 6% in four samples. The existence and dispersion of Ta 2 O 5 nanoparticles in the composites were confirmed by electron microscopies. The Ca 3 Co 4 O 9 /Ta 2 O 5 composite particles were hot-pressed into pellets and sintered for thermoelectric property measurement. The impacts of the Ta 2 O 5 volume percentage on the lattice/electronic thermal conductivity, Seebeck coefficient, electrical conductivity, and thermoelectric Figure of Merit (ZT) of the Ca 3 Co 4 O 9 /Ta 2 O 5 composites were investigated. The results indicated that an increased Ta 2 O 5 volume percentage resulted in decreased electrical conductivity and thermal conductivity. When the Ta 2 O 5 was 4 vol %, the highest Seebeck coefficient, and maximum ZT were observed in the Ca 3 Co 4 O 9 /Ta 2 O 5 composite. [ABSTRACT FROM AUTHOR]

The objective of this research was to evaluate the impact of the morphology of SiC additive on the microstructure development, sintering behavior, hardness, and fracture toughness of TiB 2 -based ceramics. For this purpose, three different samples were produced via the hot-pressing method at 1950 °C under 25 MPa for 120 min. Subsequently, the samples were characterized by XRD, SEM, and optical microscopy. The samples containing SiC particles (SiC p) reached their theoretical densities. XRD results manifested the formation of an in-situ TiC during the hot-pressing. Thermodynamical investigation and SEM fractographs revealed the role of a liquid phase in boosting the sintering behavior of as-sintered ceramics. The SEM images also confirmed the in-situ generation of B 4 C in the specimens doped with SiC whiskers (SiC w). Finally, the most significant Vickers hardness (28.9 GPa) and fracture toughness (6.4 MPa m1/2) was secured for the sample toughened by 30 vol% SiC w , whereas the lowest values, namely a Vickers hardness of 18.1 GPa and a fracture toughness of 5.1 MPa m1/2, were obtained for the composites doped with 30 vol% SiC p , and 15 vol% SiC w + 15 vol% SiC p , respectively. [ABSTRACT FROM AUTHOR]

The densification and microwave dielectric properties of H 3 BO 3 ceramics prepared by dry pressing at room temperature were studied. The results show that pressure is the key factor of densification of H 3 BO 3 ceramics. No second phase appears in all the as-fabricated H 3 BO 3 ceramic samples. A dense H 3 BO 3 ceramic (relative density~97.6%) was obtained by uniaxial compression of 384 MPa for 300s and the optimal microwave dielectric properties are ε r = 2.83, Q × f = 59,400 GHz (f = 16 GHz), τ f = −91 ppm/°C, which make it as a prospective candidate for microwave and millimeter-wave devices such as substrates for 5G communication technology. [ABSTRACT FROM AUTHOR]

Yttria-stabilized dental zirconia ceramic powders were synthesized by chemical precipitation method and then sintered at 1350 °C. 3 wt% and 5 wt% PVA were added as a binder. Chemical, phasic, thermogravimetric, and differential thermal and grain size, as well as distribution analyses were performed on synthesized and commercial dental ceramic powders. The synthesized and commercial samples containing different binder ratios were molded using different cold isostatic presses (200, 300, and 400 MPa). Final sintering was performed at 1450 °C for 2 h. Density, microhardness, and fracture toughness analyses were performed on all the block samples. In addition, the fracture behavior of sintered blocks was evaluated by electron microscopy. The results showed that the molding force of 400 MPa with 3% binder content was sufficient to achieve the desired mechanical value, and this sample had 6.02 g/cm3 density, 10.44 GPa hardness, and 6.34 MPa m1/2 fracture toughness. As the molding force increased, the density and mechanical values of the synthesized powder also increased, yet no marginal changes were observed in the commercial sample. [ABSTRACT FROM AUTHOR]

Abstract The goal of the present contribution is to show what is the effect of Ag addition on in vitro bioactivity and degradation characteristics of hydroxyapatite (HAP) in simulated body fluid (SBF), Dulbecco's Modified Eagle's medium (DMEM) and phosphate buffer solution (PBS) over a period of immersion at 37 ± 0.5 °C ranged from 1 to 21 days. Also, the corrosion investigations in all three media were carried out at 37 ± 0.5 °C. The results showed that the coatings behaviour is modulated with respect to the testing media and indicated that the Ag addition into hydroxyapatite has enhanced the general behaviour of HAP by either preventing and/or reducing dissolution of the HAP in SBF and DMEM solutions, while in PBS media the Ag addition contributed to a very slow degradation of hydroxyapatite. Thus, it can be said that the Ag addition into HAP enhances the overall chemical stability and behaviour in acellular media. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

This paper studies the microstructure and mechanical properties of hot pressed submicron TiB 2 powders obtained from a special carbon coated precursors method. With the hot press temperature increasing from 1500 °C to 1800 °C, the relative density increases and the sample maintains a single TiB 2 phase. The powders are able to be sintered to a relative density of ~94.5% at the temperature of 1800 °C. For the first time, unique elongated platelike grain structure, which has only been observed from transient liquid phase or reaction sintered borides, also forms at the sintering temperature of 1800 °C. In addition, the sample sintered at 1800 °C has a fine microstructure (elongated grain of ~0.3–3 µm) and high mechanical properties (hardness of ~27.6 ± 2.3 GPa, flexural strength of ~560 ± 49 MPa, and fracture toughness of ~6.5 ± 0.2 MPa m −1/2 ). Correlations between mechanical properties and microstructure are further discussed. [ABSTRACT FROM AUTHOR]

The processing parameters have been optimized to achieve highly pure and fully dense pellets of calcium cobalt oxide (Ca 3 Co 4 O 9 ) from solid-state ball milled calcium carbonate and cobalt oxide mixtures, calcined at optimized temperature and time, and consolidated by hot-pressing. The microscopic, spectroscopic, and thermal analysis suggest samples with longer ball-milling time require less calcination time for synthesizing highly pure crystalline phases of Ca 3 Co 4 O 9 , and provide 99.2 ± 0.5% relative density. [ABSTRACT FROM AUTHOR]

Nanocrystalline alumina powder with an average crystallite size of ≤50 nm has been consolidated by spark plasma sintering (SPS) and hot pressing (HP) with a view to achieving dense, fine grained alumina bodies that display transparency. When as-synthesised powder was densified directly, excessive grain growth resulted from both the SPS and HP techniques and hence a large final grain size was observed. Attempts to improve the uniformity of the green microstructure prior to densification were unsuccessful when spray freeze dried granules were used, whether pre-pressed into a compact or not. The use of 53% dense slip cast green compacts, however, enabled final density of ~99.96% and a mean grain size of ~0.32 µm to be achieved when SPS conditions of 1200 °C and 500 MPa were applied for 20 min. These samples offered in-line transmittance values of up to ~80% and microhardness values of 22 GPa. [ABSTRACT FROM AUTHOR]

The effects of hot-pressing (HP) and spark plasma sintering (SPS) methods on the grain size, microstructural features, and mechanical behaviour of graphene nanoplatelet/carbon nanotubes (GNTs) reinforced Al 2 O 3 nanocomposites were comprehensively studied. Different graphene nanoplatelet to carbon nanotube ratios were selected as the overall reinforcement content of composites prepared using HP and SPS. Highly densified samples (>98%) were obtained at 1650 °C under 40 MPa in Ar atmosphere, with dwell times of 1 h and 10 min for HP and SPS respectively. Both types of sample showed a mixture of inter- and transgranular fracture behaviour. A 50% grain size reduction was observed for samples prepared by HP compared to SPS samples. Both types of samples achieved a high flexural strength and fracture toughness of >400 MPa and 5.5 MPa m 1/2 , whilst SPS samples peaked at relatively lower GNT contents than those for the HP samples. Based on analyses of the morphology, grain sizes and fracture mode, similar toughening mechanisms for both types of sample were observed, involving the complex characteristics of the combined GNT fillers. [ABSTRACT FROM AUTHOR]

This article concerns a hot-press sintered Sialon ceramic using Si 3 N 4 and AlN as raw materials, Y 2 O 3 and La 2 O 3 as additives. The influences of AlN adding amount (5~30 wt.%) on the sintered densification, phase compositions and microstructures are discussed. Results showed that the β-Sialon ceramic could be obtained by hot-press sintering of 95~80 wt.% Si 3 N 4 , 5~20 wt.% AlN and extra 5 wt% Y 2 O 3 -La 2 O 3 additives, while the excess of 25 wt.% AlN would lead to the transformation from β-Sialon to α-phase. The relationships of AlN contents with bending strength and thermal conductivity of the sintered composites were also involved in the study. For the composition of 80 wt.%Si 3 N 4 -20 wt.%AlN, the sintered sample showed the fracture strength of 408 MPa and the highest thermal conductivity of 34 W/(m·K) which is 44.7% higher than that of the sample at an adding AlN content of 5 wt.%. [ABSTRACT FROM AUTHOR]

Abstract: Sodium zirconium phosphate and calcium zirconium phosphate, two potential radioactive wasteforms, were treated with fluoride, and different methods of sintering were evaluated. Different compositions were prepared by adding calcium fluoride to sodium zirconium phosphate and sodium fluoride to calcium zirconium phosphate. These mixtures were calcined in a microwave furnace and then sintered. The increase in densification of the samples sintered in a hot isostatic press were observed to be nearly uniform, while other samples that were sintered in a microwave and in a resistance furnace were inhomogeneous. The concentration of inhomogeneities was higher in fluorinated samples prepared under closed conditions in a hot press than samples prepared under microwave conditions in air. [Copyright &y& Elsevier]

Abstract: This research explores the use of a variety of carbon nanostructures as reinforcing agents for Si3N4 matrix composites. We have chosen highly promising families of carbon materials: multiwall, singlewall carbon nanotubes (MWCNTs, SWCNTs), graphene, carbon black nanograins and graphite micrograins for use as fillers. These materials were dispersed with a concentration of 3wt% in silicon nitride matrices. A high efficiency attritor mill has also been used for effective dispersion of second phases in the matrix. In the present work the development of sintering processes (hot isostatic pressing (HIP) and spark plasma sintering (SPS)) has been performed to consolidate and tailor the microstructure of Carbon nanotube (CNT)-reinforced silicon nitride-based ceramic composites. The silicon nitride nanocomposite systems retained the mechanical robustness of the original systems. Elastic modulus measurements and micro-indentation investigations of the hardness and fracture toughness have been performed as well as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction in order to characterize the composites produced by the two sintering methods. [Copyright &y& Elsevier]

Abstract: Sintering behavior of nanocrystalline zinc oxide (ZnO) powder compacts using hot pressing method was investigated. The sintering conditions (temperature and total time) and results (density and grain size) of two-step sintering (TSS), conventional sintering (CS) and hot pressing (HP) methods were compared. The HP technique versus CS was shown to be a superior method to obtain higher final density (99%), lower sintering temperature, shorter total sintering time and rather fine grain size. The maximum density achieved via HP, TSS and CS methods were 99%, 98.3% and 97%, respectively. The final grain size of samples obtained by HP was greater than that of TSS method. However, the ultra-prolonged sintering total time and the lower final density (88ks and 98.3%) are the drawbacks of TSS in comparison with the faster HP (17ks and 99%) method. [Copyright &y& Elsevier]