Synthesis of Zirconium Carbide in a Triple Torch Plasma Reactor Using Liquid Organometallic Zirconium Precursors
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Synthesis of Zirconium Carbide in a Triple Torch Plasma Reactor Using Liquid Organometallic Zirconium Precursors Z. P. Lu,
T.
W. Or, L. Stachowicz, P. Kong and E. Pfender Department of Mechanical Engineering University of Minnesota Minneapolis, Minnesota 55455, U. S. A.
Zirconium carbide has been synthesized using (RO)4Zr, a liquid organometallic precursor in a newly developed Triple Torch Plasma Reactor. Thermodynamic equilibrium simulations indicate that in the temperature range of 1,800 - 3,800 K, zirconium carbide can be formed by plasma pyrolysis. The calculation results also suggest that by adding a certain amount of C02 into the plasma, the excess carbon can be removed. The product is characterized with X-ray powder diffraction, SEM and BET. X-ray powder diffraction profiles support the results predicted by the equilibrium calculations. The product powder is porous and spherical. The 2 specific area of the powder measured by BET is 140 m /gram.
INTRODUCTION Zirconium carbide is a promising material because of its refractory properties and its extraordinary mechanical strength and hardness [1]. However, it has not been studied as much as other transition metal carbides such as tungsten carbide or titanium carbide. There are several routes for the preparation of zirconium carbide. Solid phase reaction between metallic zirconium and graphite has been used for preparing bulk materials or single crystals [1]. To obtain fine powders for sintering [2-3], reduction of zirconium chloride or very fine zirconia by magnesium or other reducing metals in the presence of carbon was used [4-7]. The method of reduction of zirconia tends to leave oxide or reducing metal residues in the final product. Both are harmful to the properties of the carbide. For example, in a recent study, it has been shown that during the sintering process, oxide residues react with carbide to form zirconium oxycarbide which has a low oxidation resistance [8]. In the present study, zirconium carbide powder has been synthesized using a liquid zirconium butoxide precursor in a DC thermal plasma reactor. Equilibrium calculations have been carried out to predict the reaction behavior over the temperature range from 1000 to 6000 K with temperature increments of 100 K. Various C02 atmospheres have been postulated in the computer calculations in an attempt to control the excess carbon formation in the final product. Experiments have been conducted in a Triple Torch Plasma Reactor at 1 atm with liquid organometallic precursors jet-atomized into the temperature valley formed by the three coalescing plasma jets. The product has been characterized with X-ray powder diffraction, SEM and BET. Rapid quenching 15 . . . . which is characteristic for this process should prevent the possible oxidation 14 Zr(Cno 0)4 + 0 COA
in the lower temperature range.
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THERMODYNAMIC
10 9 8 7 6
CALCULATIONS
Equilibrium calculations were performed using a computer program, SOLGASMIX-PV [9], which has been modified in the High Temperature Lab at the University of Minnesot
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