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1997 TMS Annual Meeting: Wednesday Abstracts


Sponsored by: LMD Aluminum Committee
Program Organizer: Robin Conger, Pacific Northwest National Laboratory, P.O. Box 999, K8-11, Richland, WA 99352

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Room: 232B

Session Chairperson: Larry Boxall, Fluor Daniel/C107I, 100 Fluor Daniel Drive, Greenville, SC 29607-2762

2:00 pm

DEGASSING LIQUID ALUMINUM ALLOYS BY ARGON IN CLOSED CIRCUIT: Robert A. Rapp, L.S. Fan, Ohio State University, Department of Material Science and Engineering, 116 W. 19th Ave., Columbus, OH 43210

The large reduction in the solubility of dissolved hydrogen in aluminum as it is solidified to form ingots, strip, sheet or cast products necessitates that the liquid metal is degassed prior to casting. Pure argon is frequently injected into the liquid alloy through a submerged lance or bubbler, so that dissolved hydrogen enters the argon bubble prior to discharge into the environment. This work introduces a proprietary concept to achieve the same argon degassing of liquid aluminum alloys, with recirculation of the argon in a closed loop such that the cost of the argon is saved. In practice, the hydrogen entrained by the argon from the liquid alloy would be oxidized to form H2O() by reaction with a fixed bed of copper oxide pellets and the H2O() product would be extracted by a desiccator bed. When the reactant bed of copper oxide is mostly reduced to copper and the desiccator approaches saturation, a relay is activated, causing a redirection of the gas flow which replaces the spent reactants with newly regenerated ones.

2:30 pm

CLOSED-LOOP NITROGEN-CHLORINE DEGASSING/FLUXING OF LIQUID ALUMINUM ALLOYS: L.S. Fan, Robert A. Rapp, Ohio State University, Department of Material Science and Engineering, 116 W. 19th Ave., Columbus, OH 43210

The need to degas liquid aluminum alloys to reduce dissolved hydrogen prior to solidification to form any product is indigenous to all aluminum processing plants. Likewise, to produce aluminum sheet and some other products, dissolved sodium and calcium must be fluxed by reaction with chlorine. Today, the combined degassing and fluxing is often achieved by the bubbling of a nitrogen-chlorine gas mixture into the melt, with release of the product HCl and unreacted Cl2 into the environment. This work introduces a proprietary concept to accomplish the degassing/fluxing of aluminum melts by the usual nitrogen-chlorine gas mixture, but with recirculation of the chlorine within a closed-loop system so that it is not released to the environment. Reaction of HCl and Cl2 from the degassing product gases with copper oxide pellets in a fixed bed lead to their conversion to copper chlorides, and the H2O() product is safely vented to the environment. Ambient air is used to regenerate the reactant copper oxide from the product copper chloride.

2:50 pm


A novel method of producing ceramic degassing components through freeze-casting and injection molding is employed to manufacture components used in the production of recycled aluminum metal, where contaminant levels are higher than normal, resulting in lower than normal grade metals. Recycled aluminum degassing operations based on today's standard practice are inadequate for the task, requiring either costly rotary components which require high maintenance, and operating costs, or large pore ceramic porous plugs which fail to deliver the necessary fine gas bubble pattern reliably and continually.

3:10 pm BREAK

3:30 pm

EVALUATION OF A NEW MATERIAL FOR HALL-HEROULT CELL CATHODES: Thomas J. Mroz, Advanced Refractory Technologies, Inc., 699 Hertel Avenue, Buffalo, NY 14207

A new, non-oxide material has recently been identified which exhibits electrical resistance 2 orders of magnitude less than graphite, and which can be formed by reaction hot pressing or sintering at relatively low temperatures. Additionally, this material is easily machined, and exhibits good oxidation resistance and excellent thermal shock resistance. It appears to be a good candidate for Hall cell cathode applications. Additionally, there appears to be an opportunity to inexpensively surface treat this material to obtain TiB2 integral coatings. We will evaluate the corrosion resistance of this material with and without the TiB2 coating and further evaluate the parameters required to produce the TiB2 coating.

3:50 pm

DISPOSAL OF HALL-HEROULT CELL POT-LINING: J.R. Divine, ChemMet, Ltd., P.O. Box 4068, West Richland, WA 99353-2309

The proposed disposal process provides an energy efficient mechanism for recovering salts from the pot-lining and disposing of the carbonaceous liner itself. The proposed method is to grind the spent pot-liner into small particles and then oxidize them. The method which appears most likely to be successful is to grind to about 1 mm diameter, heat to about 1300 K in an "inert" atmosphere of CO2, and then react with steam. The resulting mixture of CO and H2 can be used as fuel in a boiler to generate steam, preheat the spent pot-liner, or provide co-generation for feeding electrical power back into the grid or into the aluminum process.

4:10 pm

AN ALUMINA CONCENTRATION SENSOR: James Oxley, Oxley Research Inc., 25 Science Park, New Haven, CT 06511

This work concerns development of a novel electroanalytical sensor to monitor the depletion in alumina concentration which occurs during electrowinning of aluminum from molten cryolite-alumina baths. The concept relies on the use of an inert indicator electrode which responds directly to variations in dissolved alumina concentration. The electrical signal thus produced can be used in a control algorithm to enable the automatic feeding of alumina to the bath, thereby avoiding the occurrence of "anode effect".

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