High-Purity Chromium Metal Supply Issues for Gas-Turbine Superalloys (1995) / Chapter Skim
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4 ALTERNATIVE TECHNOLOGIES FOR CHROMIUM-METAL PRODUCTION
4 ALTERNATIVE TECHNOLOGIES FOR CHROMIUM-METAL PRODUCTION
Pages 39-44
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From page 39... ...
The two processes of electrolytic deposition, discussed in the previous chapter, and aluminothermic reduction have evolved over time as more efficient than such other processes as carbon and silicon reduction (Sully, 19541. Both the electrolytic and the alummothermic processes have been successfully improved over time to result in lower levels of impurities so that the requirements of high-punty applications have continued to be met, even though purity specifications have become increasingly stringent over time.
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From page 40... ...
ALI) MINUM REDUCTION METHOD FOR PRODUCING CHROMIUM METAL The aluminothermic process is a batch process usually carried out in a steel cylindrical container with a basic or neutral refractory lining.
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From page 41... ...
Carbon and silicon have also been used as reducing agents, but heat must again be supplied to the process. The availability of aluminum with its highenergy investment, the stability of Al2O3 as a reaction product, and the autogenous nature of the process have made the aluminothermic process the second major engineering method of choice for the reduction of chromium metal.
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From page 42... ...
However, as also stated in Chapter 2, while aluminothermic material of equivalent quality to the electrolytic material may now be available, changes in such critical applications as rotor-grade materials must be mutually acceptable to producer and user and would have to be subject to extensive qualification studies involving production and testing of alloys, test specimens, final cast and forged products, and possibly the engines containing them. Overall, the aluminothennic chromium-metal industry does not currently appear to be producing at full capacity.
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From page 43... ...
The obvious difficulty is to obtain appropriate consumable electrodes from the above sources to run the process. Processes utilizing powder metallurgy, the chloride route, or chemical vapor deposition methods could be adapted to making electrodes.
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From page 44... ...
The committee considers it possible that a process based on induction plasma technology could use a chromium powder to produce satisfactory electrodes for remelt processing. Induction plasma methods, as opposed to arc plasma methods, can have inherently lower process-induced contamination.
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