Hot Pressure HP Sintering

Since then, HP became a widely used technique to prepare transparent spinel ceramics. For example, HP process was used to fabricate MgAl204 transparent ceramics, with a nearly 100 % densification [44]. Spinel powders for the production of transparent polyciystalline ceramic windows were produced by using both the traditional ceramic solid-state reaction and solgel methods. Among them, the powders produced from the reaction of organomagnesium compounds with surface modified boehmite precursors were best to produce high-quality transparent spinel ceramics. The powder synthesis method allowed fine control over the particle size. 

I I MgAljO spinel sample I i Metal capsule Boron nitride I I Mica 

I I Cesium chloride saturated zirconia Molybdenum cunent lead aThermocouple 

Similar process was also used to develop yttrium aluminum garnet (Y3AI5O12, YAG) transparent ceramics with nanosized grains [52], In this study, a high-pressure cell was used, where disk samples were placed in a capsule made of NaCl, both to ensure the quasi-hydrostatic compression of the sample and prevent its contact with the graphite heater. The whole structure was then contained in the pyrophyllite high-pressure cell. The sample temperature in the high-pressure cell 

Hot isostalic pressing (HIP) is a fabrication process that is used to reduce the porosity of metals and increase the density of various ceramic materials [70-74]. The HIP process subjects a component to both elevated temperature and isostatic gas pressure in a high-pressure containment vessel. The chamber is heated, causing the pressure inside the vessel to increase. Many systems use associated gas 

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Figure 16.11 Effect of lattice oxygen content on the thermal resistivity of Si3N4 fabricated by gas-pressure sintering (filled circles) and hot-pressing (HP squares). The thermal...

Hot pressed (HP) SisNa, preformed mixtures of a and j8 polymorphs sintered to high density using high pressures. 

HP Hot-pressing HHP High-pressure hot-pressing HIP Hot-isostatic pressing GPS Gas-pressure sintering. 

While REPEL or conventionally sintered (CS) materials are the common forms, hot pressed material (HP) of almost theoretical density is also available. The HP artifacts are usually obtained at 2100°C and 50 MPa pressure with either aluminum or boron carbide, B4C, added as a sintering aid. Hot pressing with up to 1.5% aluminum produces equiaxed microstructures with grains about 2 /im in diameter, but a different microstnicture, with elongated grains 20-40 fim long, is produced in the presence of B4C. 

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