Rapid Sintering of Silica Xerogel Ceramic Derived from Sago Waste Ash Using Sub-millimeter Wave Heating with a 300 GHz CW Gyrotron

Abstract

In this paper, we present and discuss experimental results from a microwave sintering of a silica-glass ceramic, produced from a silica xerogel extracted from a sago waste ash. As a radiation source for the microwave heating a sub-millimeter wave gyrotron (Gyrotron FU CW I) with an output frequency of 300 GHz has been used. The powders of silica xerogel have been dry pressed and then sintered at temperatures ranging from 300°C to 1500°C. The influence of the sintering temperature on the technological properties such as porosity and bulk density was studied in detail. Furthermore, X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy have been used in order to study the structure of the produced silica glass-ceramics. It has been found that the silica xerogel crystallizes at a temperature of 800°C, which is about 200°C lower than the one observed in the conventional process. The silica xerogel samples sintered by their irradiation with a sub-millimeter wave at 900°C for 18 minutes are fully crystallized into a silica glassceramic with a density of about 2.2 g/cm 3 and cristobalite as a major crystalline phase. The results obtained in this study allow one to conclude that the microwave sintering with sub-millimeter waves is an appropriate technological process for production of silica glass-ceramics from a silica xerogel and is characterized with such advantages as shorter times of the thermal cycle, lower sintering temperatures and higher quality of the final product.

Formation and Particle Growth of TiO2 in Silica Xerogel Glass Ceramic During a Sintering Process

“…The detailed extraction procedures are described elsewhere (Affandi et al, 2009;Aripin et al, 2011;. High-purity amorphous silica amounting to 98.8% has been observed (Aripin et al, 2011).…”

“…Therefore, SiO 2 production from these sources on an industrial scale is not technologically or economically viable. In our study, SiO 2 in the form of silica xerogel was prepared using a sago waste ash (Aripin et al, 2011;Aripin et al, 2012) as a starting powder and was used to produce TiO 2 -SiO 2 composites by mixing 20 wt% and 40 wt% of TiO 2 into SiO 2 . It was found that, at 900°C, the size of the anatase crystallites are 26.3 nm and 21.4 nm for 20 wt% and 40 wt% of TiO 2 , respectively.…”

High Purity Mode CW Gyrotron Covering the Subterahertz to Terahertz Range Using a 20 T Superconducting Magnet

“…The same requirement is imposed also by many other technologies that utilize gyrotrons as sources of powerful sub-THz and THz waves, for example, materials treatment (e.g. sintering of advanced ceramics, development of new functional materials) [23]- [25], biological and medical applications [26]- [28], just to name a few. Additional features demanded by some of the above-mentioned applications are frequency and amplitude modulation and stabilization, as well as frequency tunability.…”

Multiphysics Model of Iron Powder Compacts for Efficient Microwave Processing

“…For sintering of various materials such as ceramic, metal matrix composites and metal powder compacts, there is lots of interest nowadays to use the microwave energy as it offers several advantages such as the volumetric and selective heating, improved product quality, energy savings, self cooling system, better precision in controlling the process of energy deposition, and reduction in manufacturing costs, over the conventional heating methods [1,2]. In recent years, the iron powders are widely investigated for their applicability in many fields such as for various strategic applications, magnetic applications, in electronic industry as RF transformers, EMI filters, switch mode power supplies, and absorbent fillers.…”