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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]

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]

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]

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]