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.

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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.

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.

In the present investigation, nanocrystalline silica xerogel (NSX) powders were produced from an amorphous silica xerogel (ASX) extracted from sago waste ash. The NSX powders have been calcined at 1200oC, milled and then annealed at temperatures ranging from a room temperature to 1200oC. Their properties (and most notably the size of the particles) have been characterized on the basis of the experimental data obtained using thermal analysis (DSC/TGA), X-ray diffraction (XRD), Infrared and Raman spectroscopy. For the crystalline silica xerogel powders the results show a narrow distribution of the particle sizes centered around an average value of 636  67 nm. The DSC analysis of NSX indicates that in the temperature range from a room temperature to 300oC five distinct stages of the crystallization process take place, which are delimited by the transition temperature of 38oC, 92oC, 129oC, 168oC, and 246oC, respectively. Above 300oC, the crystalline phase is similar to an amorphous silica xerogel (ASX), i.e. cristoballite-like and tridymite-like crystalline silica phases confirmed by the XRD analysis. It has been observed that the characteristic band of cristoballite is strongly dependent on the thermal history and the NSX transforms into a stable form at a temperature of 1200oC. Both the Raman and the FTIR spectra elucidate the bonding system of the constituent atoms and groups (such as Si, O and OH) and throw light on their underlying structure. The obtained results are important for optimization of the parameters of the technological processes for production of nanocrystalline silica glass ceramics used as a host matrix for luminescence materials, each of which requires a specific porosity and structure.

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