(Digital Presentation) Mechanistic Understanding of Rhenium Electrodeposition

The electrodeposition of rhenium (Re) has received renewed attention in the past decade for a wide range of applications in aerospace, nuclear, catalysis, biomedical and electrical fields. Rhenium has unique and superior properties when compared with other refractory metals, making it attractive as an engineering material. It has a very high modulus of elasticity and superior tensile strength and creep-rupture strength over a wide temperature range. Re also is very resistant to highly corrosive environments, possesses a very high melting point, and enhanced wear resistance properties. However, Re is difficult to deposit by electrolysis of their aqueous solutions due to its very low over potential for hydrogen evolution. The electrodeposition of rhenium has been demonstrated in the literature with approaches ranging from simple acidic solutions, induced codepostion with iron group metals, and water-in-salt electrolytes. However, these coatings are generally deposited at low Faradaic efficiency, are brittle, and limited in the obtainable thickness (sub-micron) due to absorbed hydrogen and formation of oxide phases. Herein, we present systematic studies progressing towards the development of stable and efficient electrolytes to enable the electrodeposition of thick (100+ microns) Re coatings. Examples from both simple acidic solutions and water-in-salt electrolytes will be presented. Specifically, we correlate nucleation and growth mechanisms of Re with the ability to produce thick coatings. Pulse/pulse reverse electroplating was applied to manipulate the obtained grain structure. Correlations between electrolyte composition and pulse parameters with observed morphology will be discussed. The ultimate goal of this project is the electrodeposition of rhenium-cobalt (Re-Co) graded density samples of millimeter thickness. Thus, understanding how to transition from a coating of pure metallic rhenium to a graded composition of Re-Co as a function of dynamic processing conditions will be presented. Towards this end, we are using a combination of electrochemical techniques with in situ measurements (atomic force microscopy, Raman, optical microscopy) to isolate variables controlling nucleation and growth which lead to the grain structure of the deposit. LA-UR-21-31694