C. W. Won

Self-propagating high-temperature synthesis of nano-sized titanium carbide powder

The combustion process of a titanium–carbon system with sodium chloride as an inert diluent was investigated. The combustion laws and microstructure of final products according to diluent content were obtained. It was shown that sodium chloride not only decreases combustion temperature but also makes effective protective shells around primary carbide crystals and keeps this ultrafine structure up to the end of combustion. As a result, nano-sized titanium carbide powders were successfully obtained.

Preparation of tungsten powder by the combustion of CaWC4/Mg

Tungsten powder was prepared by a Self-Propagating High-Temperature Synthesis(SHS) Process of a CaWO4-Mg mixture. Mg vapor was discovered to significantly affect such combustion parameters as the combustion temperature(Tc), the combustion velocity(U), the relative mass change(δm) and the relative elongation(δh) of the sample. These effects could be reduced by decreasing the internal Ar pressure, sample density and reducing agent content. The oxygen content in tungsten was decreased by using 5% excess Mg; the carbon content was diminished when the combustion process occurred under PAr=0.1 MPa. The MgO and CaO in the product was leached with an HC1 solution. Such parameters as combustion temperature(Tc), U, Am, and milling time(τ) were found to affect the tungsten particle size and morphology.

Structure and properties of rapidly solidified Mg-Al alloys

Three binary Mg-Al alloys containing nominally 5, 15, and 30 at % Al were prepared in the ingot and rapidly solidified flake conditions using the twin roll technique. The microstructure, mechanical properties, and electrochemical behavior of the extruded alloys in both the conditions were investigated. The hardness, tensile strength, and corrosion resistance increased with increasing Al content. Further, the hardness, tensile strength, and corrosion resistance of the rapidly solidified alloys were superior to the ingot-metallurgy alloys and this is attributed to the microstructural refinement and increased homogeneity in the rapidly solidified alloys.

Preparation by sol-gel method of SiO2 and mullite (3Al2O3, 2SiO2) powders and study of their surface characteristics by inverse gas chromatography and zetametry

Abstract Silica and mullite powders have been prepared by the sol-gel method and their surface characteristics studied by inverse gas chromatography (IGC) and zetametry. The optimum conditions were defined using two different catalysts (HCl and 2,4-pentanedione). The dispersive component of the surface energy γd of the mullite samples measured by IGC shows a minimum for the molecular ratio Al 2 O 3 SiO 2 = 1.14 , indicating high modifications of the surface where the apolar component becomes low. Zetametry measurements reveal that a segregation phenomenon of the Si and Al elements takes place at the mullite surface with an enrichment of the surface with silicon during the syntheses. Our results have to be considered when substrates are coated with such alumino-silicates in catalyst preparation.

Synthesis of Al2O3-WC composite powder by SHS process

Al2O3-WC composite powder was synthesized by self-propagating high-temperature synthesis using Al powder as a reducing agent. WC, W2C and Al2O3 were concurrently formed in WO3-Al-C system. It was found that the complete reaction was achieved with excessive addition of carbon and appropriate processing parameters such as degree of dilution, particle size of aluminum, pellet compaction pressure and carbon source. The final product which was leached by 50% 1 : 4 HNO3 + HF diluted solution was consisted of Al2O3-55wt%WC having 2–3 μm of mean particle size.

Simultaneous synthesis and densification of NiAl and Ni3Al by pressure-assisted combustion

Simultaneous synthesis and densification of NiAl and Ni3Al from elemental powders of Ni and Al was investigated. Combustion synthesis was carried out under the uniaxial compressive pressure and preheating of die. It was shown that both the compressive pressure and preheating of die strongly affect the density, the grain size and the hardness of NiAl and Ni3Al product. A high relative density of NiAl and Ni3Al products as much as 99.8% was achieved under compressive pressure of 275 MPa and preheating temperature of 600°C.

Interfacial microchemistry and microstructure of Al-Mg-Si alloy matrix composites reinforced with Al2O3 particulates

In discontinuously reinforced metal matrix composites produced by ingot metallurgy, the ceramic particles are introduced in the molten alloy which provides adequate opportunity for reactions to quickly occur between the particles and the molten alloy. Similar reactions, although less rapid, can occur in composites produced by powder metallurgy routes. Using transmission electron microscopy (TEM) and X-ray spectroscopy, matrix and interfacial microchemistry can be analyzed in the metal matrix composites and correlated with the observed characteristics. In this study, the microstructure and the microchemistry of Al-Mg-Si alloy matrix composite reinforced with 10 vol.% Al{sub 2}O{sub 3} were characterized in order to examine the effect of the reinforcements on the distribution of alloying elements.

The self-propagating high-temperature synthesis (SHS) of ultrafine high-purity TiC powder from TiO2+Mg+C

The self-propagating high-temperature synthesis (SHS) method has been applied to the preparation of TiC powder from mixtures of TiO2, Mg, and C. The TiC/MgO product is leached by hydrochloric acid to remove the MgO. The optimum mixing ratio was TiO2∶Mg∶C=1∶2.2∶1.5. The final product TiC had > 99.9% purity and relatively uniform particle size of 0.3–0.4 μm.

Size control of tungsten powder synthesized by self-propagating high temperature synthesis process

Abstract Tungsten powder was prepared by self-propagating high temperature synthesis (SHS) from a mixture of WO 3 and Mg. The MgO in the product was leached with an HCl solution. The complete reduction of WO 3 required a 33% excess of magnesium over the stoichiometric molar ratio Mg/WO 3 of 3. The tungsten product had a purity of 99.98%, which was higher than that of the reactants. The high purity resulted because the impurities in the reactants were volatilized during the highly exothermic reaction and dissolved during leaching of the product. Size distribution and the shape of the tungsten particles produced was affected by compaction pressure on the green pellet.

Preparation of nickel-coated alumina composite powder by an aqueous-phase reduction process

A nickel coating on the surface of alumina particles, used as a reinforcement in metal-ceramic composite materials, substantially improves their wettability by molten metals. Nickel was deposited on alumina particles by reducing nickel ions from a solution under hydrogen pressure in the presence of ammonia as a complexing agent. It was found that the addition of Fe2+ ions and anthraquinone was necessary for forming an adequate nickel coating on the alumina surface. The optimum conditions were the [NH3]/[Ni2+] ratio of 1.6, 2760 kPa hydrogen pressure, 175 °C, and an anthraquinone addition of 0.04 g l−1.