Available Forms,Cost and Manufacturing Process Of Rhenium

Elemental Re appears silvery-white with a metallic luster. Its usual commercial form is powder, but it can also be consolidated by pressing and resistance sintering in a vacuum or hydrogen atmosphere.Chemically, Re is available mainly as a metal powder, perrhenic acid (HReO4), or ammonium perrhenate (NH4ReO4). Re has become one of the ten most expensive metals following its rapid price increase during 2007 and 2008. While ammonium perrhenate was priced at 8.2 – 10.6 $/g, the metal powder was priced between 9.0 – 11.9 $/g in 2008.

The two principal manufacturing processes for Re-based items are powder metallurgy (P/M) and chemical vapor deposition (CVD). Although the latter is currently the major process for deposition of Re, it is an expensive, complex, and energy intensive process. Electroplating at near-room temperature using aqueous, non-toxic bath chemistries may become a successful alternative and allow the production of uniform Re coatings on complex shapes. Electrodeposition of Re and its alloys has also recently been reviewed by Eliaz and Gileadi.Rhenium belongs to a group of metals that are difficult to produce by electrolysis of their aqueous solutions, mainly because of its very low overpotential for hydrogen evolution.It has recently been reported that electroplating of pure Re was associated with low Faradaic efficiency(FE ≤7%) and poor coating quality. However, by adding a suitable nickel (Ni) salt to the bath,coatings with a Re content as high as 93 atomic percent (at.%), a FE as high as 96%, and a thickness as high as 25 μm were obtained. In addition, the Vickers hardness number (VHN) of the as-deposited coating was high: 928 ± 60 (approximately 68 Rockwell hardness C (HRC)). As the nickel ion concentration in the bath was increased, the FE and the partial current densities of both Ni and Re increased, whereas the Re content in the deposit decreased.It was proposed that the mechanism by which addition of nickel to the solution enhanced the rate of deposition of Re was through a unique type of electroless plating, in which the reducing agent was metallic Ni formed in situ.