Counter-Flow Liquid Injection Plasma Synthesis (CF LIPS) of Spinel Fine Powders
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COUNTER-FLOW LIQUID INJECTION PLASMA SYNTHESIS (CF LIPS) OF SPINEL FINE POWDERS T.W. Or, Z.P. Lu, L. Stachowicz, P. Kong, and E. Pfender. Dept. of Mech. Engr., University of Minnesota, Minneapolis, MN 55455 USA ABSTRACT Fine powders of aluminate, ferrite, and chromite spinels were successfully produced by a novel Counter-Flow Liquid Injection Plasma Synthesis (CF LIPS) method using a DC plasma jet. CF LIPS has been demonstrated to be an excellent method to produce fine ceramic powders with a narrow particle size distribution. The spinels produced by this techniques, both magnetic and non-magnetic, have a very similar particle size distribution. The powders produced were spherical, non-agglomerating and dispersable with average sizes of 1 pLm. INTRODUCTION There has been a growing interest in the processing of fine ceramic powders. The fine ceramic powders find applications in their original powder as well as their sintered form. Many spinels are used in their fine powder form in applications such as magnetic recording and as catalysts. The sintered form of these powders are used in the fabrication of optical apparatus and permanent magnets. Liquid injection plasma synthesis has been proven to be a promising method to produce these fine ceramic powders [1-6]. The advantages of liquid precursors over gaseous and solid precursors are: 1) The availability of liquid precursors for ceramics is extensive, 2) the reaction is essentially gas phase, fast and complete, 3) the time required for complete evaporation of liquid droplets is substantially shorter than that for solids, 4) complete control of the molar concentrations of liquid reactants results in products with precise chemical compositions. The spinel liquid precursors are nitrate solutions with the metal cations in their theoretical mole ratios. In liquid injection plasma synthesis, the precursor solutions are atomized and then sprayed into the plasma jet either with or against the plasma flow. The method employed in this study is the Counter-Flow Liquid Injection Plasma Synthesis (CF LIPS) [7-10]. The advantages of CF LIPS over the conventional parallel-flow injection are: 1) heat transfer is substantially higher, 2) longer residence time for reactant droplets (> 100 ms) ensures complete evaporation and a gas phase reaction, 3) large recirculation zones in the reaction chamber enhance mixing and longer time for particle nucleation and growth, 4) a long high temperature ridge (> 2500 K) exists in the reactor. Typical spinels powders produced are spherical and smooth with an average particle diameter of 1 g.m and standard deviations of 0.5 to 1 pgm. Diagnostics included X-ray diffraction, XPS, SEM, X-ray mapping, EDXS, BET particle surface area measurement, particle size distribution by centrifugal sedimentation and vibrating sample magnetometer (VSM) for the magnetic spinels. The powders produced will be used for plasma sintering studies in the future. EXPERIMENTAL PROCEDURE The experimental setup is shown schematically in Fig. 1. The setup consists of a high power
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