Synthesis of ultrafine nickel aluminide particles by the hydrogen reduction of vapor-phase mixtures of NiCl 2 and AlCl 3
- PDF / 333,347 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 215 Views
Welcome
MATERIALS RESEARCH
Comments
Help
Synthesis of ultrafine nickel aluminide particles by the hydrogen reduction of vapor-phase mixtures of NiCl2 and AlCl3 H. Y. Sohn and S. PalDey Department of Metallurgical Engineering, University of Utah, Salt Lake City, Utah 84112-0114 (Received 4 August 1997; accepted 22 January 1998)
Fine particles of nickel aluminides were synthesized for the first time by reducing mixtures of AlCl3 1 NiCl2 vapors by hydrogen. A thermodynamic equilibrium calculation was carried out in the Ni–Al–H–Cl–Ar system to evaluate the effect of the reactant partial pressures and temperature on the formation of intermetallic phases. A single intermetallic phase was found to be feasible only in a very narrow range of the reactant partial pressures. For all other conditions the predicted solid product was a mixture of two phases. Experimentally, Ni3 Al was formed along with metallic Ni. Though the coreduction of NiCl2 and AlCl3 by H2 to form Ni3 Al is thermodynamically favorable at 1100 ±C, it did not happen experimentally under the conditions of this work. However, with a small addition of aluminum vapor, the coreduction reaction proceeded as expected by thermodynamics. The effects of reactant partial pressures and temperature were studied. The content of Ni3 Al was maximized to 52 mol % at 1050 ±C under the partial pressures of H2 , AlCl3 , and NiCl2 at 57, 1.5, and 0.5 kPa, respectively. The product particles, as observed by TEM, were very fine, but usually agglomerated. The electron diffraction analysis identified the particles of NiAl and NiAl3 along with Ni3 Al and metallic Ni. I. INTRODUCTION
The search for new high-temperature structural materials has stimulated much research on intermetallic compounds. Nickel aluminides have low densities, relatively high melting points, and good high-temperature strength properties. They show an increase, rather than a decrease, in yield strength with increasing temperature.1 The major shortcomings of these intermetallics are their inherent brittleness at room temperature when they are in polycrystalline form. For much the same reason, the conventional casting of intermetallics is difficult. Ingot metallurgy and powder metallurgy are two other processing techniques. The first technique is quite energy consuming. In powder metallurgy, the powders of metals and alloys are consolidated in near net shape and then subjected to secondary processing. It would, therefore, be advantageous if intermetallic compounds can be produced in fine powder form from inexpensive raw materials, using less energy. There are published articles on the preparation of ultrafine particles (UFP) of metals and refractory metal compounds, but little has been reported on the particles of intermetallic compounds. Several methods have been practiced to produce UFP of metals. One of those is the preparation of UFP from vapor-phase reduction of metal chlorides. A reaction between a metal halide and hydrogen can in general be written as follows: MXn sgd 1 0.5nH2 sgd Mssd 1 nHXsgd , 306
Data Loading...
