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.
Recent research has been significantly increased our fundamental understanding of microwave interactions with materials. Thermal absorption has been demonstrated to result from simultaneous action of multiple dissipation mechanisms during processing. In addition, it has been conclusively established that strong microwave fields exert a non-thermal driving force during sintering. This force acts as an additional driving force for atomic transport. For strong electric fields, the force can enhance diffusion rates during ceramic sintering. This paper describes recent research on microwave sintering of two oxide ceramics, a silica xerogel ceramic produced from rice husk ash (RHA) and a high purity alpha alumina. A millimeter waves (MMW) heating system with a 28 GHz gyrotron is applied for microwave sintering experiment. The ceramics were also sintered by using an electric furnace where served as comparison. Effect of microwave energy on the porosity reduction of the ceramics was investigated. Some possible physical mechanisms were discussed.
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.
In this feasibility study a novel prospective electrode material for electric double layer capacitors (EDLC) has
been investigated. This promising material is activated carbon (AC) film produced using sago waste as a precursor.
Important parameters of the technological process are the KOH to charcoal ratio and the content of the
polytetrafluoroethylene (PTFE) binder. The influence of these parameters on the microtexture and pore structure and on
the electrochemical characteristics of the AC films has been studied in detail. The measured specific surface area (SSA) of
the samples is in the range from 212 to 1498 m2/g. It has been found that the presence of micropores increases the specific
capacity while the presence of the mesopores acts in the opposite direction, because these mesopores are too wide in
diameter for aqueous electrolyte. The specific capacitance of the studied samples has been found to be in the range from
16 to 64 F/g.
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