Consumable cathode selection in the production of neodymium-iron alloys via molten salt electrolysis
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MATTHEW R. EARLAM, Senior Research Engineer, is with the Texas Inorganic Research and Development, Magnesium Group, Dow Chemical Company, Freeport, TX 77541. Manuscript submitted October 18, 1989. METALLURGICAL TRANSACTIONS B
one end. The pot was 25.4-cm long and weld-clad with INCO* 182 weld metal, with a single loop of 9 - m m HASTELLOY** C-276 tubing silver soldered around the top of the pot. The internal diameter of the pot was machined to fit a COORS*** 10.16-cm alumina tube which *INCO is a trademark of Inco Alloys International, Inc., Huntington, WV. **HASTELLOY is a trademark of Stoody Deloro Stellite Inc., Industry, CA. ***COORS is a trademark of Coors Ceramics, Inc., Golden, CO.
was inserted to a depth of 7 cm. The alumina tube was cemented in place with a magnesium cell mortar. This gave a working volume of the pot of 1500 cc. A type k thermocouple was imbedded into this joint to monitor temperature. The cell was joined to the glove box through an O-ring flange. A forced air system was used to keep these joints cool since the VITON* O-ring material has a temperature service limit *VITON is a trademark of Du Pont Co., Inc., Wilmington, DE.
of 225 ~ The alumina/pot joint was kept below 435 ~ above this temperature, the difference in expansion of the two materials will cause the cell to leak. A sketch of this is shown in Figure 1. Since it is necessary to maintain the glove box at a positive pressure, the argon gas (Big Three welding grade) and the anode gases from the cell were pulled through a H A L O C A R B O N * oil series 56 bubbler. The off-gases *HALOCARBON is a trademark of Halocarbon Products Corp., Hackensack, NJ.
were discharged under 4.8 cm of oil, thus a 9.4-cm water head could be maintained on the system. Argon was flowed through the box at 28 l / m i n at 20 ~ and 1 atm. The off-gases were scrubbed. Current was supplied by a SORENSEN* 40-50 rectifier, and the load was measured by the voltage across a shunt which gives an analog of current; cell voltage and temperature of the electrolyte were also measured. Electrode shields, thermowells, and collecting crucibles were made of alumina. Cathodes were --51-cm-long x 6.35-mm-diameter rods; commercial steels, consolidated electrolytic iron flake (Atlantic Equipment Engineers, a division of Micron Metals, Inc., Bergenfield, N J), and high-purity iron supplied by ESPI** were used. Anodes *SORENSEN is a trademark of Raytheon Co., Lexington, MA. **ESPI is a trademark of Electronic Space Products International, Inc., Westlake Village, CA.
were made of electrode grade graphite and were - 5 1 cm in length x 12.7 m m in diameter. The bath chosen was developed by Seon et al.,Is} and the composition was 53 pct LiC1, 22 pet LiF, and 25 pct NdC13. Lithium chloride and lithium fluoride of purified grade were obtained from Fischer Scientific, Pittsburgh, PA. The neodymium chloride hexahydrate was obtained from Rhone-Poulenc Inc., Monmouth Junction, NJ. It was certified as 95 pct NdC13"6H20, 2 pct LaC13.6HzO, 2 pct PrC13.6H20, and 1 pct other rare earths. T
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