Effects of Added Kaolinite on Sintering of Freeze‐Cast Kaolinite–Silica Nanocomposite I. Microstructure and Phase Transformation

Abstract

In our previous study, the effects of added kaolinite on the microstructure and strength of freeze‐cast composites of kaolinite platelets and silica nanoparticles were reported. This current article details the results of an investigation into the effects of the kaolinite on the microstructure and phase transformation of these materials during sintering. It is found that upon sintering at 1000°C, grain growth and phase transformation of the silica nanoparticles in the silica/kaolinite composites are hindered, and even completely inhibited, at sufficient concentrations of added kaolinite. Nonetheless, reduction in the size of the nanoparticles suggests that diffusion from silica nanoparticles to kaolinite platelets is occurring. Upon increasing the sintering temperature to 1250°C, boundaries between the two species completely disappear and new peaks are observed in the X‐ray diffraction pattern of the composite that are not present in the patterns of either silica‐only or kaolinite‐only samples. These findings indicate that a transitioning interfacial phase forms at higher temperatures.

Effects of Rod‐like Particles on the Microstructure and Strength of Porous Silica Nanoparticle Composites

“…(2) Increased Strength from Rods In previous work, it was found that adding relatively large kaolinite platelets to a silica nanoparticle suspension led to a significant increase in the mechanical strength of both the freeze-cast and sintered composites created from the suspension. 24,36,37 The suggested reason for this increase was that the platelets were capable of distributing any applied stress over a larger portion of the sample, which would reduce the likelihood of stress being concentrated at any one point.…”

Positioning growth of scalable silica nanorods on the interior and exterior surfaces of porous composites

“…31,32 In brief, Ludox TMA, kaolinite powder, and NaOH were dispersed/dissolved in water with a total solids loading at 18 vol%. 31,32 In brief, Ludox TMA, kaolinite powder, and NaOH were dispersed/dissolved in water with a total solids loading at 18 vol%.…”

Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting

“…The solids content determines the volume of the porosity and the pore size. 6,7,9,21,22 There is an optimal range of suspension concentrations required to obtain a handling solid and to avoid microstructure collapse if the solid content is very high.…”

“…8 The most important parameters involved in the process are the freezing temperature, the rate and manner of cooling and the solids content. [6][7][8][9][16][17][18][19][20][21][22][23] Cooling temperatures ranging from -20/-80 °C down to liquid nitrogen temperature (-196 °C) are normally used. The solids content determines the volume of the porosity and the pore size.…”