A Novel, Inexpensive, and Rugged Probe for Measuring Gas Bubbles in Liquid Metals: Part I. Mathematical Modeling and Lab
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eloping and improving technologies for processing liquid metals, there is sometimes a need to be able to determine the distribution of bubbles in the molten metal. One example from the aluminum industry is determining the distribution of bubbles in a ‘‘gas fluxing’’ unit. Such units are used for removal of impurities or unwanted alloying elements, e.g., in recycled metal, by injection of a gas, such as an argonchlorine mixture, intended to react with the metal. Dispersion of the injected gas throughout the liquid volume may be important in full use of the fluxing unit volume. It is possible to use X-ray machines for this purpose,[1] but this technique is restricted to small melt volumes in the laboratory because of the strong absorption of X-rays by metals and the safety issues of powerful X-ray machines in an industrial setting. Of course, some information can be gleaned by visual or photographic examination of the top surface of the melt, but there can be no certainty that gas well dispersed across the surface means gas well distributed in the liquid bulk. PIERO MARCOLONGO, Graduate Student, JAMES W. EVANS, Professor of Metallurgy, and DANIEL A. STEINGART, Postdoctor, are with the Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA. Contact e-mail: [email protected] Manuscript submitted: September 12, 2006. Article published online May 23, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
Various probes have been used to measure gasses in liquid metals or in model fluids such as water. In many cases, these probes measure the frequency with which bubbles arrive at a particular location in the melt. In other cases, additional variables, such as the bubble rise velocity and bubble size, may be obtained by a probe. Perhaps the most widely used probe has been the ‘‘electroresistivity’’ probe of Brimacombe and co-workers.[2] This probe has an electrically conducting tip connected to one side of an electric circuit with the other side connected to the melt. When no bubbles are present, there is electrical connection through the metal; when a bubble rises to engulf the tip, the circuit is broken and the break is recorded by some suitable electronic circuit. Brimacombe’s group worked mostly in water with a few measurements in mercury. Iguchi and colleagues were able to use such a probe in molten iron.[3] However, the use of these probes in high-temperature liquid metals is limited by the need to make the tip conductive, which limits the material choices to metals, carbon, or conductive ceramics, all of which dissolve in or are attacked by most liquid metals of industrial interest. For example, liquid aluminum will dissolve steel, copper, or most other common metals and react with carbon. One form of probe that does not require contact of a conductive tip with the liquid metal is the ‘‘capacitance probe’’ described by Fu and Evans.[4] This probe consists of two wires passing down through a twin bore VOLUME 38B, JUNE 2007—389
alumina tube. At the end of the probe, the tube bores
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