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Molybdenum (Mo) is a transition element and improves strength, toughness, hardenability and weldability of cast iron and steel. Commercially molybdenum production involves two staged hydrogen reduction which has some disadvantages. An alternative way to produce Mo metal powder is electrochemical production process, however, molten salt electrolysis is not suitable to produce Mo powder due to its high melting point. Moreover, FFC Cambridge process is also not applicable for production of molybdenum because of Mo loss during the process. An alternative electrochemical process was searched to produce Mo metal powder in this study. CaMoO4 (calcium molybdate) and MoS2 (molybdenum disulphide) were used as raw materials for reduction process. CaMoO4 was not successfully reduced, because solubility of CaMoO4 was observed during experiments. Complete reduction of MoS2 to Mo was achieved and CaS was observed as a by-product at 750oC under argon gas flow. CaS was removed by a dilute acid washing to obtain Mo metal powder.

Silicon plays an important role in fabrication of solar cells and solar chips.  Metallurgical grade silicon (98 to 99 % Si) demands further purification such as zone refining [1, 2], metallothermic reduction [3] and Siemens process [4] to convert it to solar grade. A promising method, based on direct electrochemical reduction of oxides by FFC Cambridge Process [5], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2–NaCl salt mixture [6]. The contamination of silicon powder by iron and nickel originating from stainless steel cathode was reported to disqualify the product from solar applications. SiO2 pellets, sintered at 1300oC for 4 hours, were sandwiched between pure silicon wafer plates to minimize contamination of silicon. The promising results indicated a potential alternative method of direct solar grade silicon production for expanding solar energy industry. [1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239. [2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004). [3] K. Yasuda, T.H. Okabe, “Solar-grade silicon production by metallothermic reduction”, JOM,62 (12) (2010), 94-101. [4] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956 [5] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364. [6] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.

Molybdenum (Mo) is a refractory metal and mostly used as an alloying agent in cast iron, steels and superalloys to enhance hardenability, strength, toughness and corrosion resistance. It also finds other uses either in the form of a pure metal or an element in, for example, lubricants and catalysts. Traditional metal production methods are not suitable for molybdenum because pure molybdenum has very high melting point and has a tendency to get oxidized at low temperatures. Hydrogen reduction of molybdenum oxide is a very common way for Mo production but, it has two stages during process. At the second stage, the reduction process needs very high temperatures, therefore, high energy consumption and special equipment requirement is essential. FFC Cambridge process [1] based on electrochemical reduction of solid compounds was considered as an alternative way to produce molybdenum at relatively low temperatures. Similar to reduction of WO3 [2], loss of molybdenum as molybdenum oxychloride from MoO3 in CaCl2 containing molten salts is inevitable [3]. MoS2 powder pressed and sintered at 400oC to form pellets were used as starting material for electrochemical formation of pure Mo in molten CaCl2-NaCl salt mixture under argon gas at 800oC. A constant voltage in the range 1 to 3.0V was applied between MoS2 cathode and graphite anode. When the process was terminated at a prescribed time, the cathode was removed from the molten salt, cooled in argon, washed with water in air to dissolve the solidified salt, and then dried at about 100oC in vacuum before further analysis employing XRD, SEM and EDS. [1] G.Z. Chen, D. J. Fray, T. W. Farthing, Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride, Nature, 407 (2000), 361-364. [2] M. Erdoğan, İ. Karakaya, Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder, Metallurgical and Materials Transactions B, 41B (2010), 798-804. [3] W.T. Thompson, C.W. Bale, and A.D. Pelton: Facility for the Analysis of Chemical Thermodynamics (FACT), McGill University Montreal, Royal Military College of Canada in Kingston, E´cole Polytechnique, Montreal, Canada, 1985.

Nowadays, Silicon is the most critical element in solar cells and/or solar chips. Silicon having 98 to 99% Si as being metallurgical grade, requires further refinement/purification processes such as zone refining [1,2] and/or Siemens process [3] to upgrade it for solar applications. A promising method, based on straightforward electrochemical reduction of oxides by FFC Cambridge Process [4], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2-NaCl salt mixture [5]. It was reported that silicon powder contaminated by iron and nickel emanated from stainless steel cathode, consequently disqualified the product from solar applications. SiO2 pellets sintered at 1300oC for 4 hours, were placed in between pure silicon wafer plates to defeat the contamination problem. Encouraging results indicated a reliable alternative method of direct solar grade silicon production for expanding solar energy field. [1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239. [2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004). [3] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956 [4] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364. [5] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.