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.
In this paper, we present and discuss experimental results from a microwave sintering of silica glass-ceramics, produced from amorphous silica xerogel extracted from sago waste ash. As a radiation source for a microwave heating a sub-millimeter wave gyrotron (Gyrotron FU CW I) with an output frequency of 300 GHz has been used. The powders of the amorphous silica xerogel have been dry pressed and then sintered at temperatures ranging from 300°C to 1200°C. Microwave absorbing properties of the sintered samples were investigated by measuring the dielectric constant, the dielectric loss, and the reflection loss at different frequencies in the interval from 8.2 to 12.4 GHz. Furthermore, the characteristics of the formation process for producing silica glassceramics were studied using a Raman Spectroscopy and a Scanning Electron Microscopy (SEM). The results indicate that the samples sintered at 1200°C are characterized by lower reflection losses and a better transparency due to the formation of a fully crystallized silica glass-ceramic at sufficiently high temperature.
A novel type of ceramic material was produced by mixing sago waste ash from
the sago processing industry in Indonesia with clay. The composition was
prepared by adding 50 %wt amount of sago waste into the clay, then a series
of samples was milled for 6 h, 12 h, 24 h and 48 h, respectively. The samples
were dry pressed and sintered at temperatures ranging from 800?C to 1200?C.
The influence of the sintering temperature and the milling time on bulk
density, firing shrinkage, water adsorption, and hardness was studied in
detail. The results demonstrate that the low water absorption of less than
0.5% and the highest hardness of 5.82 GPa were obtained for the sample
sintered at 1100?C and milled for 48 h. The investigation of the absorptive
properties of such ceramics indicates that they could be recommended as a
promising material for manufacturing of unglazed floor tiles.
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