The purpose of this article is to investigate the effect of compaction pressure on the sintering of PTFE moldings. The major factor of this process are both compaction pressure and dwell time, which lead to high compactability of moldings. Bulk density of the moldings compacted at a lower pressure increases by sintering due to coalescence of particles by viscous flow. On the other hand, there is no change of the density by sintering in higher compacted moldings, since the coalescence of particles has been already finished in the pre-forming process and sintering does not eliminate inter-particle cavities. In this case, even if the moldings are sintered in shorter times nearly at the melting temperature, their bulk density reaches a constant value.
Pressure-Volume-Temperature (PVT) properties of polymers are very important data for polymer processing, especially, injection molding. The coefficients of thermal expansion in polymers are much larger than those of metals and inorganic materials. So the changing of specific volumes in polymers is very large under processing, i. e., for changes of temperature and pressure. In this paper we describe the relationship between PVT behavior and processing in polymers.
Understanding the properties of polymeric materials under high pressure is of great importance in polymer processing. This is because high pressure has a large effect on the behavior of the resin (such as flow, crystallization, compatibility, etc. ) during the molding processes, and thus strongly influences the quality of the molded products. In this review, we report on measurements of the various properties of polymeric materials under high pressure which have been recently carried out. Examples include: (1) specific volume of resins under high pressure and rapid cooling rate corresponding to the actual molding conditions. (2) the pressure dependence of thermal conductivity, Young's modules and Poisson's ratio measured by modified PVT apparatus. (3) the pressure dependence of viscosity.
This article deals with the polymer behavior within the mold cavity during the packing-holding process of injection-molding from the viewpoint of pressure transmission. The packing-holding process is used to be adopted in the practical injection-molding of polymeric materials to reduce the generation of molding failure due to shrinkage of polymer melt, but sometimes the packing-holding process may induce another type of failure such as residual strain and birefringence. The author revealed the behavior of polymer melt in the mold cavity by using visualization techniques, and the reduction mechanism of molding failure due to the packing-holding process was discussed on the basis of P-V-T characteristics of the polymer material.
Microcellular plastics are a unique cellular material in which voids, smaller than the natural flaw size pre-existing in polymers, are nucleated: this process results in material costs savings without significant reductions and sometimes improvements in mechanical properties. They are characterized by average cell diameter sizes on the order of 0. 1 to 10 μm, cell densities on the order of 109 to 1015 cells/cm3, and specific density reductions (relative to the unfoamed plastic) from 5 to 95 percent. In this paper, the basic concept of foaming for microcellular plastics is described and the process technology of microcellular plastics based on that concept is introduced. The effect of pressure in processing of microcelullar plastics is discussed.
Hydrophilicity of aluminosilicate materials is an important characteristics as an index of the degree of hydrothermal reaction and hydration of starting materials. Heat of immersion of amorphous aluminosilicate after hydrothermal treatment have been studied to clarify the meaning of the leading time of hydrothermal reaction. The heat of immersion and specific surface area are compared with structural data, XRD, DTA-TG, and IR. The hydrothermal reaction is divided into two stages: (1) hydration of amorphous aluminosilicate for the first stage and (2) crystallization of kaolinite for the second stage. The leading time of hydrothermal reaction is attributed to the hydration period of starting material.
The techniques for applying an optical liquid high pressure cell are described. The optical cell described enables visual observation at high pressures up to about 1 GPa. Its advantages over the diamond anvil cell are the larger sample volume, the higher accuracy of pressure measurement (about ± 1 MPa), and the higher reliability of pressure control. The cell has been applied in the fields of chemistry, biology, physics, chemical engineering, and etc. Recently, we show here how it is applied to the observation of crystal growth at high pressure.
Special attention has been given to ZrO2-based ceramics, such as partially stabilized ZrO2 (PSZ), tetragonal ZrO2 polycrystal (TZP), and ZrO2-toughened Al2O3 (ZTA), to improve the mechanical properties of ceramic materials. Hot isostatic pressing (HIP) is applied to fabricate dense ZrO2-based ceramics from solid solution powders developed by sol-gel techniques. This paper reviews recent research trends and progresses related to the solid solution and composite ceramics focussing on the microstructures, strength and fracture toughness, and ionic conductivity.
A direct weighing densimeter was newly developed for the measurement of densities for compressed liquids. The density of 1, 1, 1, 2-tertrafluoroethane was measured by means of the new apparatus at 283 to 353 K and from near the saturated line to pressures up to 20 MPa. It is confirmed that an uncertainty of density is ± 0. 15 % in the high density region.