I Nyoman Sudiana

The microwave effects on the properties of alumina at high frequencies of microwave sintering

Microwave sintering of materials has attracted much research interest because of its significant advantages (e.g. reduced sintering temperatures and soaking times) over the conventional heating. Most researchers compared processes that occurred during the microwave and conventional heating at the same temperature and time. The enhancements found in the former method are indicated as a `non-thermal effect` which is usually used for explaining the phenomena in microwave processing. Numerous recent studies have been focused on the effect to elucidate the microwave interaction mechanism with materials. Moreover, recent progress on microwave sources such as gyrotrons has opened the possibility for processing materials by using a higher microwave frequency. Therefore, the technology is expected to exhibit a stronger non-thermal effect. This paper presents results from a series of experiments to study the non-thermal effect on microwave sintered alumina. Sintering by using a wide rage of microwave frequencies up...

Structure Formation of a Double Sintered Nanocrystalline Silica Xerogel Converted From Sago Waste Ash

In the present study, double sintered nanocrystalline silica xerogel (NSX) bulk material has been produced from amorphous silica xerogel (ASX) powders extracted from sago waste ash. The ASX powders have been sintered at 1200°C, milled, pressed and then re-sintered at temperatures ranging from 1200° to 1600°C. The crystallization process of the NSX has been examined by thermal analysis (DSC/TGA) and X-ray diffraction (XRD), while the functional groups and the structure have been identified by infrared and Raman spectroscopy, respectively. From the DSC analysis it has been found that the tetragonal phase of α-cristobalite transforms to the stable phase of SiO2, namely cubic β-cristobalite in the samples re-sintered at 1600°C. This observation has been corroborated by an analysis of the XRD patterns, infrared and Raman spectra. The obtained data suggest that such novel material could be considered as an appropriate alternative for deposition of ceramic coatings on various machine and tool parts, e.g. components of gas-turbine engines.

Dilute Acid Hydrolysis of Lignocellulose Fiber Sago Pretreated by Microwave Heating

The dilute acid hydrolysis of fiber sago with cloride acid was undertaken in a microwave reactor system. The glucose and morphology analysis were performed after cellulose and hemi-cellulose hydrolysis. The hydrothermal condition was setup in a microwave furnace at microwave power of 800 W for 30-60 min. Scanning electron microscopy (SEM) analysis were utilized to confirm the microstructural changes after pretreatment. The results show that by using microwave energy, hydrolysis is not only can work in lower temperature than that of hot plate hydrolysis but also give a higher yield. There also found that the pretreatment optimum conditions for fiber sago hydrolysis is at 5% chloride acid solution and applied microwave power of 800 watt for 45 minutes. At that condition, there was found that sugar degradation occurred at acid concentrations greater than 30.15%. Microstructure evaluation from SEM photos shows that the disruption of the structure of the cell wall increases the accessibility of cellulase to lignocellulose. This results suggest that microwave technology is appropriate technology for holocellulose (cellulose and hemi-cellulose) hydrolysis.

Characterization of Silica Extracted from Rice Husk Ash Wastes Doped by Tin Dioxide for Wave Guide Material

A series of experiments is made to produce silica, mixing with tin dioxide (SnO2), and characterizing for application of waveguide device. Silica xerogels (SX) are prepared from raw materials derived from rice husks ash (RHA), which abundant in South East Sulawesi. The synthesis conditions have been optimized to obtain the ash of rice husks with the maximum silica content. SnO2 are prepared from a commercial powder. The ceramic waveguide materials are produced by mixing SX and SnO2 with various composition. The mixtures are molded to form the rectangular shape of 20 mm, 40 mm, and 5 mm in size. The samples will be sintered at different level of temperatures (from 300°C to 1200°C) by using microwave heating system as well as electric furnace. The microstructural of sintered samples were characterized on the basis of the experimental data obtained using densification measurement method (Archimedes method), crystallization (X-ray diffraction, XRD), microstructure (Scanning electron microscope, SEM). Optical and related properties such as the functional groups, structure, and absoption were characterized by using FTIR, Infrared and Raman Spectroscopy and absorption (UVVis). The permittivity and permeability will be calculated from S-parameters determined by using Vector Network Analyzer (VNA). Characterization results are presented in this paper and the others are will be published in another separated papers. Furthermore, the relationship between properties with SnO2 content and sintering temperature is also studied.

Banana peel reductant for leaching medium grade manganese ore in sulfuric acid solution

In this investigation, manganese has been produced from medium grade manganese ore from Karangnunggal mine (West Java, Indonesia). The effects of weighed amount of banana peels on the structural and leaching properties have been studied. The material’s properties have been characterized on the basis of the experimental data obtained using X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier transforms infrared (FTIR) spectroscopy. It has been found that an increase of the weighed amount of banana peels up to 4 g leads to an increase of the leaching efficiency of manganese from manganese ore. Above 4 g, however, the leaching efficiency does not change significantly. The analysis based on the interpretation of both XRD patterns and FTIR spectrum allows one to explain the increase in the leaching efficiencies of manganese by the reduction of MnO2 minerals and by the removal of hemicelluloses groups of banana peel in the samples.

High thermal behavior of a new glass ceramic developed from silica xerogel/SnO2 composite

In this investigation, a new glass ceramics have been produced by mixing SnO2 and amorphous silica xerogel (ASX) extracted from sago waste ash. The composition has been prepared by adding 10 mol% of SnO2 into SX. The samples have been dry pressed and sintered in the temperature range between 800 °C and 1500 °C. The effects of temperature on the crystallization of silica xerogel after adding SnO2 and their relationship to bulk density have been studied. The crystallization process of the silica xerogel/SnO2 composite has been examined by an X-ray diffraction (XRD) and the bulk density has been characterized on the basis of the experimental data obtained using Archimedes′ principle. It has been found that an addition of SnO2 confers an appreciable effect on the grain and from the interpretation of XRD patterns allow one to explain the increase in the density by an increased crystallite size of SnO2 in the composite.

Effect of High-Frequency Microwaves on the Microhardness of Alumina Ceramic

Microwave processing of ceramics has attracted much research interest because of its significant advantages over the conventional one. Most researchers compared processes that occurred during the microwave and conventional heating at the same temperature and time. The enhancements found in the former method are indicated as a microwave effect which is usually used for explaining the phenomena in microwave processing. Numerous recent studies have been focused on the effect to elucidate the microwave interaction mechanism with materials. This paper will present effect of very high microwave frequency to hardness of sintered alumina. The sintering results were taken from a series of experiments to study the microwave effect on properties of alumina. Microwave sintering was performed by using the 300 GHz microwave sintering system. Some possible physical mechanisms are also discussed.

Structural Characterization of a Glass Ceramic Developed from TiO2 and a Novel Material-Silica Xerogel Converted from Sago Waste Ash

In this paper, we present the synthesis procedure and the results of an investigation of a novel silica xerogel (SX) glass ceramic developed from an amorphous SX derived from sago waste ash that incorporates TiO2 as an additive. The studied compositions have been prepared by adding of either 20% or 80 wt% of TiO2 into SX, respectively. The samples have been dry pressed and sintered in the temperature range between 900°C and 1500°C. Their properties have been characterized on the basis of the experimental data obtained using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet-visible (UV-Vis) spectroscopy. It has been found that an increase of the content of SX in the composition leads to an increase of the shift of the bandgap energy of TiO2. The analysis based on the interpretation of both XRD patterns and FTIR spectrum allows one to explain the shift in the bandgap energy by an enlargement of the crystallite size of TiO2 and by forming of more Si–O–Ti bonds in the samples with a smaller loading of TiO2.