Hot isostatic pressing (hipping) can be used for upgrading castings, densifying presintered components, consolidating powders, and interfacial bonding. It involves the simultaneous application of a high pressure and elevated temperature in a specially constructed vessel. The pressure is applied with a gas (usually inert) and, so, is isostatic. Under these conditions of heat and pressure, internal pores or defects within a solid body collapse and diffusion bond. Encapsulated powder and sintered components alike are densified to give improved mechanical properties and a reduction in the scatter band of properties. In this article, the basic science of sintering and hipping is summarized and contrasted. The current state of understanding and modeling of hipping is then reviewed. Models can be classified either as microscopic or macroscopic in their approach. In the microscopic approach, the various mechanisms of densification are analyzed in terms of a single particle and its surroundings. In the macroscopic approach, the compact is treated as a continuous medium. In hipping, although the pressure is isostatic, shrinkage is not generally isotropic, particularly if containment is used. However, the shrinkage can now be well predicted, provided that the material and container properties are accurately known.

Fundamental aspects of hot isostatic pressing: An overview

On the basis of the analysis of key engineering factors predominating in a reactive precipitation process, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high-gravity conditions, is presented here for the massive production of nanoparticles. A rotating packed-bed reactor was designed to generate acceleration higher than the gravitational acceleration on Earth. The syntheses of nanoparticles of CaCO3, aluminum hydroxide, and SrCO3 were employed to demonstrate the advantages and industrial potentials of this technology, where the typical gas−liquid−solid, gas−liquid, and liquid−liquid multiphase reaction systems were involved. Experimental results show that the mean size of CaCO3 particles can be controlled and adjusted in the range of 17−36 nm through the change of operation conditions such as high-gravity levels, fluid flow rates, and reactant concentrations. Nanofibrils of aluminum hydroxide of 1−10 nm in diameter and 50−300 nm in le...

Synthesis of Nanoparticles with Novel Technology: High-Gravity Reactive Precipitation

Microstructure and mechanical properties of spark plasma sintered zirconia-hydroxyapatite nano-composite powders

Theory of high pressure/low temperature sintering of bulk nanocrystalline TiO2

The production and the supply of high quality laboratory animals have fundamental importance for the accomplishment of vanguard scientific research, with reproducibility and universality. The quality of those animals depends, largely, of the available facilities for their production and lodging, to assure the demanded sanitary control and animals’ welfare, in agreement with the ethical principles that control the activity. The facilities also have to fill out other requirements, such as: the functionality of the environments to make possible the suitable and efficient handling of the animals, facilitating the execution of the routine activities; the respect to ergonomic principles to provide a safe environment and the operators’ well being. The facilities design is of vital importance so that the mentioned requirements can be reached. The project of the Nuclear and Energy Research Institute (IPEN) Animal House Facilities was accomplished in the year of 1964. However, by that time there were not the current recommendations with respect to the sanitary, genetic and environmental controls. The facility was planned with the objective of being a production unit and a local for keeping of defined animals from sanitary, genetic and environmental point of view. Nevertheless, the original unit drawing presents an unsuitable distribution of the area where animals are stocked and also different activities are performed. The Animal House Facilities occupy an area of 840 m, with one pavement, where the production areas and the stock of original animal models of the own Institution are distributed, as well as the maintenance of animals from other national or foreigner institutions. It supplies rats and mice for biological tests of radiopharmaceutical lots, produced in IPEN, before they be sent to hospitals and clinics spread out in Brazil, for use in Nuclear Medicine. It also supplies rats and mice for tests of odontological materials, for tests with growth hormones and for researches of new pharmaceuticals and radiopharmaceuticals, among others applications. Many of the animals models produced in IPEN are unique in Brazil and they constitute, therefore, an important patrimony that should be preserved. This paper describes the activities that have been executed in Animal House Facilities of IPEN, including the refurbishment project and the adaptation of the facilities.

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Instituto de Pesquisas Energéticas e Nucleares

Al2O3 composite ceramics containing 10 vol% SiC nanoparticles were prepared by pressureless sintering. SiC particles < 150 nm detach from the matrix grain boundaries during grain growth and are predominantly observed in intragranular positions, whereas larger SiC particles retain intergranular positions. Thermal expansion mismatch causes local residual tensile stresses in the matrix grains, giving rise to strain contrasts in TEM imaging; occasionally microcracking around intragranular inclusions ≥ 100 nm is observed in thin TEM foils. It appears that the volume fraction of intragranular SiC particles in the size range 100 < d < 150 nm should not exceed ≈ 0.5% in high strength/high toughness Al2O3-SiC nanocomposites. The interaction between propagating cracks and internal stress fields around intragranular inclusions forces a transgranular fracture mode. Grain boundary pinning by large intergranular SiC particles, in combination with solute drag inhibits matrix grain growth, while the presence of an amorphous phase at Al2O3 grain boundaries and Al2O3-SiC phase boundaries assists in densification. Excess liquid phase is exuded from the interfaces during consolidation and accumulates in large pores, stabilized by the accidental agglomeration of large SiC particles.

https://publikationen.sulb.uni-saarland.de/bitstream/20.500.11880/24635/1/sm199804.pdf

Microstructural characterization of Al2O3-SiC nanocomposites

Prediction of deformation behaviour during hipping is often difficult because data on complex material properties are required but are not usually available from the literature. From the present work, measurement of the deformation of a single sphere is proposed as a direct and simple method of predicting hipping behaviour. For C1018 steel, copper, and API nickel superalloy, the predictions made from deformation experiments with single spheres were in good agreement with measured hipping behaviour at hipping densities <93% theoretical. In addition, the creep parameters, such as the exponent n for the power law creep relation, of the powder material itself were measured during single sphere deformation. During hipping of C1018 in the density range above 90%, the use of lower pressures, which is favoured for economic reasons, showed that microstructural development and densification during the final stage of hipping are determined by relatively large pores. These large pores may result from irregul...

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Mesut Aslan

Papers

Microstructural characterization of Al2O3-SiC nanocomposites

Microstructural development and densification during hipping of ceramics and metals

Observations on Microstructural Development and Densification during Hiping of Ceramics and Metals