Tawat Chanadee

Self-Propagating High-Temperature Synthesis of Si-SiC Composite Powder

Silicon-silicon carbide (Si-SiC) composite powders were synthesized by in-situ self- propagating high-temperature synthesis using rice husk ash (RHA)/carbon/Mg as precursors in argon atmosphere. The as-SHS powders were leached by two leaching steps. The microstructure and chemical composition of the obtained Si-SiC composite powders were examined using scanning electron microscope (SEM) and x-ray diffractometer (XRD), respectively.

Influence of Ar Pressure on Product Characteristics of Self-Propagating High-Temperature Synthesis from WO3/B2O3/Al Reactant System

nfluence of Ar gas pressure on the SHS reaction products from WO3/B2O3/Al system has been investigated. The pressure of Ar gas has a significant effect on the phase separation and microstructures of SHS products. Increase in Ar gas pressure has a effect on the phase compositions of SHS products and results in the increase of the amount of W2B. Furthermore, the crystalize sizes of W2B increase with the increase of Ar gas pressure from 0.3 to 0.5 MPa, respectively.

Effect of Ar Gas Pressure on Phase Separation of Tungsten Silicides Intermetallic Compound In Situ Self-Propagating High Temperature Synthesis-Casting Process

Tungsten silicides intermetallic compound (WSi2) was synthesized in-situ by self-propagating high temperature synthesis-casting of WO3-Si-Al system in Ar gas environment. It is proposed that the extent of phase separation between oxide ceramic and intermetallic compound depends on the reaction temperature that made a lower viscosity and longer lifetime of the melted. The effects of inert gas pressure on densification of the intemetallic product were investigated.

Synthesis of WSi2-W5Si3 Intermetallic Alloy via Self-Propagating High Temperature Synthesis

Intermetallic alloy of tungsten silicide (WSi2-W5Si3) was synthesized by self-propagating high temperature synthesis (SHS) from the reactant of tungsten oxide (WO3) and silicon lump (Si) using magnesium (Mg) as fuel. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the possible reacting species. The as-SHS products were characterized by X-ray diffraction (XRD) technique. The magnesiothermic reaction process successfully synthesized dense of WSi2-W5Si3 intermetallic alloy. According to the experimental results, it can be proposed that the reaction also promotes the phase separation between alloy and oxide slag of the product.

Extraction and Characterization of Silica Powders from Natural Waste for Environmental Remediation

The present work describes the preparation and characterization of silica powder from the natural waste materials stink bean pod, Barbados pride pod, banana leaves, coconut shell, sugar palm shell and groundnut shell. Ash was produced by incineration of the natural wastes at 650 °C for 1, 3 and 5 h in atmospheric air. Silica was then extracted from the natural waste ash using 1 M sodium hydroxide solution to produce a sodium silicate solution from which silica was precipitated by adding 5 M hydrochloric acid solution. The results showed that the low content of residual carbon from the natural waste was incinerated at the optimal condition of 650°C for 5 h. FT-IR indicated that the as-prepared silica had Si-O-Si and Si-OH functional groups consistent with the XRF analysis, which detected SiO2 content between 73.76 and 95.72 wt%. In analysis of XRD and SEM, the as-prepared silica exhibited an amorphous, irregular shape and particle sizes in a range from 1 to 2 μm. The results obtained by the reported method proved that natural waste materials can be used for the production of valuable silica.

SHS synthesis of Si-SiC composite powders using Mg and reactants from industrial waste

Si-SiC composite powders were synthesized by self-propagating high-temperature synthesis (SHS) using reactants of fly ash-based silica, sawdust-based activated carbon, and magnesium. Fly ash-based silica and sawdust-based activated carbon were prepared from coal mining fly ash and Para rubber-wood sawdust, respectively. The work investigated the effects of the synthesis atmosphere (air and Ar) on the phase and morphology of the SHS products. The SHS product was leached by a two-step acid leaching processes, to obtain the Si-SiC composite powder. The SHS product and SHS product after leaching were characterized by X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectrometry. The results indicated that the SHS product synthesized in air consisted of Si, SiC, MgO, and intermediate phases (SiO2, Mg, Mg2SiO4, Mg2Si), whereas the SHS product synthesized in Ar consisted of Si, SiC, MgO and a little Mg2SiO4. The SiC content in the leached-SHS product was higher when Ar was used as the synthesis atmosphere. As well as affecting the purity, the synthesis atmospheres also affected the average crystalline sizes of the products. The crystalline size of the product synthesized in Ar was smaller than that of the product synthesized in air. All of the results showed that fly ash and sawdust could be effective waste-material reactants for the synthesis of Si-SiC composite powders.

Investigations of Tungsten Based Intermetallic Alloys by Self Propagating High Temperature Synthesis from Metal Oxide Precursors

The in-situself propagating high temperature synthesis technique were used to synthesis tungsten based intermetallic alloys from WO3/SiO2/Al and WO3/B2O3/Al reactant mixture system. The reaction was carries out in a SHS reactor under static argon gas at the pressure of 0.5 MPa. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the reacting species. The microstructure and phase distribution of the SHS reaction products were characterized by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX), respectively. The results indicate that complete reaction of precursors to yield Al2O3-WSi2 and Al2O3-WB as product composites with clearly separation between Al2O3 and WB.