Densification process for spherical glass powders with the same particle size by hydrothermal hot pressing

Abstract

Low-temperature sintering of spherical glass powders with the same particle size was attempted by hydrothermal hot pressing at 260 ~ The microstructure of densified bodies was observed by scanning electron microscope and the existence of water in the surface reaction layer was confirmed by Fourier transform infrared spectroscopy. The reaction layer was formed on the surface of spherical glass particles after hydrothermal hot pressing. The thickness of the layer increased with reaction time. The layer was deformed and layers stuck together by mechanical compression. The reaction layer contained much molecular water. The kinetics of the formation rate of the reaction layer was agreed with Kondo's equation, [1 -(1 -X) 1/3] N= kt where t= reaction time, X= reaction ratio of glass, and N= a constant. N is 1 at the initial stage and 2 at the secondary stage. These values show that hydration on to the surface at the initial stage, and diffusion of water in the reaction layer at the secondary stage, are the rate determining steps.

Synthesis and Evaluation of Bulky Y‐Zeolites by Hydrothermal Hot‐Pressing Method

“…These processes are quite similar to the liquid sintering mechanism of ceramics. Hence, the successful syntheses of bulks of zeolites are thought to be due to the cementation by dissolution of solution of sodium silicate as a mechanism of solidification, although we cannot neglect the solution/precipitation process as well as other previous results of oxide during HHP 11–22 . Further detailed works are now under investigation.…”

“…Previous papers suggested that the bulk prepared by HHP was solidified by dissolution and precipitation processes 11–22 . Especially, the results of densification of glass powder suggested that shrinkage proceeded by viscous flow mechanism 11,12 . In the HHP process, the zeolite polycrystalline surface was dissolved in NaOH solution on HHP and then dissolved zeolitic gel was made to flow at voids in bulks and finally recrystallized.…”

“…The hydrothermal hot‐pressing (HHP) method is a unique method to obtain a solidified bulk body by compressing uniaxially under a hydrothermal condition. Studies on solidification of some inorganic materials such as glass powder, hydroxyapatite, phosphate salt, CaCO 3 , bioactive glass, silica, titania, and high‐level radioactive wastes 12–22 by HHP methods have been reported, in which their solidifications were achieved by squeezing out water existing between particles and connecting particles under hydrothermal conditions. However, no research of zeolite bulks using the HHP method has been carried out.…”

Mechanical Properties of Glass-Based Geopolymers Affected by Activator and Curing Conditions under Optimal Aging Conditions

“…When the curing duration is shorter than the optimal curing duration, an increase in the curing temperature or curing duration causes OH − to bond with additional Si and Al, which are required for geopolymer formation. However, if the curing duration exceeds the optimal curing duration, water molecules and OH − ions may diffuse to the surface of undissolved glass particles and corrode them [34]. The higher the AE%, the more severe this corrosion.…”

Use of Slag Containing Water as a Lubricant in High Straining Rolling for Ultrafine-grained Steels

“…The schematic of the autoclave, composed of a stainless tube, pistons, packing and an electric heater, for hydrothermal hotpressing [13][14][15] is shown in Fig. 1.…”