The refining effect of Ar/Ar-H2 plasma arc melting (PAM) was investigated and the purity of Ta metals was evaluated by glow discharge mass spectrometry (GDMS). Most impurities in the Ta metals were removed by Ar/Ar-H2 PAM, down to a few mass ppm levels, and the purities of respective Ta metals refined by Ar/Ar-20% PAM were improved up to 5N5 (99.9995 %) and 5N7 (99.99972 %). It was also found that the deoxidation reaction under hydrogen plasma condition is enhanced by a remarkable decrease in the oxygen concentration of the Ta metal refined by Ar-H2 PAM.

Purity evaluation of Ta metal refined by Ar/Ar−H2 plasma Arc melting

Tantalum is a rarely occurring transition metal which is chiefly used to manufacture capacitors for electronic appliances such as mobile phones. The demand for tantalum is expected to show an annual growth rate of about 5%; however, tantalum produced in the Democratic Republic of Congo is considered a conflict mineral due to illegal mining which is accelerating the extinction of lowland gorillas. Although tantalum recycling is desirable, the recycling technology has been poorly developed. Phase separation was applied to recover tantalum. It was expected that a copper phase could absorb tantalum, but tantalum was slightly transferred into an iron-rich phase in the Cu-Fe-C system. When ferric oxide was applied as an auxiliary, the tantalum was concentrated as precipitate on the surface of the iron-rich phase. In terms of practical application, a theoretical prediction suggests that the addition of a reductant will make it possible to recover tantalum as a high-purity powder. Since conflict, illicit exploration and hunting (bush-meat trade) have caused a decline in the population of wild animals, it is considered that a feasible tantalum recycling system will be helpful in solving such problems.

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Preliminary Information of Laboratorial Tantalum Recovery and Considerations for a Potential Solution for Conflict Mineral and Wildlife Conservation

Structure refinement for tantalum nitrides nanocrystals with various morphologies

Niobium powder was fabricated by sodiothermic reduction process using K 2 NbF 7 as the raw materials, KCl and KF as the diluents and Na as the reducing agent. The apparatus for the experiment was designed and built specifically for the present study. Varying properties of niobium powder depending on reaction temperature and excess of reducing agent were analyzed. The niobium particle size increased significantly as the reduction temperature increased from 993 to 1093 K. The particle size was fairly uniform at a given reaction temperature, varying from 0.2 μm to 50 nm, depending on the reaction temperature. The yield of niobium powder increased from 58 to 83% with a increasing a reaction temperature. The average particle size of niobium powder is improved from 70 nm to 0.2 μm with a increasing amount of sodium excess. And the yield ratio of Nb powder was 82% in the 5% excess sodium.

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Characteristic Variation of Niobium Powder Produced under Various Reduction Temperature and Amount of Reductant Addition

Niobium powder was fabricated by sodiothermic reduction process using K 2 NbF 7 as a raw materials, KCl and KF as the diluents and sodium as a reducing agent. The apparatus for the experiment was designed and built specifically for the present study. Varying properties of niobium powder depending on reaction temperature and excess of reducing agent were analyzed. The niobium particle size increased significantly as reduction temperature increased from 993 to 1093 K. The particle size was fairly uniform at given reaction temperature, varying from 0.2 μm to 50 nm depending on the reaction temperature. The yield of niobium powder increased from 58% to 83% with a increase in reaction temperature. The average particle size of niobium powder was improved from 70 nm to 0.2 μm with increase in the amount of sodium excess. In addition, the yield of niobium powder was 82% in the 5% sodium excess.

The fabrication of niobium powder by sodiothermic reduction process

Tantalum powder was made from potassium heptafluorotantalate (K2TaF7) using sodium as a reductant based on the Hunter metallothermic reduction method. The apparatus for the experiment was designed and built specifically for the present study. The tantalum particle size greatly decreased as the reduction temperature decreased from 860 to 740°C. The particle size was fairly uniform, varying from 2–3 μm to submicron sizes depending on the reaction temperature. Holding the reactants for more than 10 minutes after the completion of a sodium feeding caused irregular particle growth, thereby affecting particle size uniformity. It was found to be possible to agglomerate the powder to tens of micrometers in size by a vacuum heat treatment at 1350°C. The formation of Ta2C during the heat treatment shows that care must be taken to prevent contamination from the furnace environment.

Seong Man Jeong

Papers

Making of tantalum powder using the hunter process