History of Rhenium and Alloys
Rhenium was an unknown element when the periodic table was introduced in 1870. The properties predicted for an element of atomic #75 turned out to be in general agreement of those of rhenium when it was discovered in 1925. W. Noddack and O. Berg were the first to locate it in platinum ores such as columbite and tungstate. J.G.F. Druce discovered it independently in manganese sulphate. The ores from which rhenium was first extracted commercially came from the region of the river Rhine (Latin: Rhenus) hence the name rhenium was born.
Rhenium’s melting point of 3180º C is second only to tungsten. Only osmium, iridium, and platinum exceed its density of 21.04 g/cc. Because of its high melting point, rhenium is a refractory metal. In that classification, rhenium is unique. It is the only refractory metal that does not form carbides. Its crystal structure is hexagonal close-packed (hcp), while other refractory metals have a body centered cubic (bcc) structure. Rhenium also does not have a ductile-to-brittle transition temperature it maintains its ductility from absolute zero all the way to its melting point and also has a high modulus of elasticity. This means that structures made of rhenium will have very good stability and rigidity.
A high re-crystallization temperature is a pre-requisite for good creep resistance and among refractory metals, rhenium is the highest. At temperatures up to 2800º C and high stresses, the rupture life of rhenium is longer than tungsten. The metal also accommodates wide swings in temperature – large thermal expansions and contractions – without incurring mechanical damage.
Rhenium is distributed in extremely minute quantities throughout nature but does not exist as a separate mineral. Approximately 4 parts per billion of the earths crust contain rhenium and no ore contains more than 1 part per billion. Most rhenium today is produced as a by-product of the copper mining industry. It is found in those copper ores contaminated with molybdenum. When they purify the copper the rhenium is extracted with the molybdenum in the form of sulfurous sludge. The high temperature roasting of the sludge to form molybdenum oxide releases the rhenium and it is collected and concentrated in special units. The next step is to make a medium purity ammonium salt containing rhenium called ammonium perrhenate (APR). This APR is sold around the world to various metal traders and catalyst manufacturers.
Arc melting of rhenium in an inert atmosphere or vacuum is possible but the metal produced tends to have coarse grain size and may have segregation of rhenium oxides at the grain boundaries. These issues are a problem for further fabrication and powder metallurgy is the preferred answer to the problem. Rhenium powder is consolidated at pressure to a density of approximately 60% of the theoretical density of solid rhenium.
The pressed compacts are then presintered in a hydrogen atmosphere to facilitate handling before final sintering. Rhenium alloys are produced by the same production methods as used for rhenium. Proper choice of powder sizes, careful blending and adequate sintering times and temperatures produce bars of hi yield and small grain size with the same homogeneity attainable by electron beam or arc melting. Subsequent fabrication is performed by swaging, rolling, forging and drawing with intermediate annealing. Some of these operations may have to be conducted at elevated temperatures. The optimum sequence of these operations varies for rhenium ad it alloys and depends on the final end form.
- Additive to tungsten and molybdenum-based alloys to increase ductility at higher temperatures
- Filaments for mass spectrographs and ion gauges
- Rhenium-molybdenum alloys become super-conducting at 10K
- Electrical contact material, as it has good wear resistance and withstands arc corrosion
- Thermocouples made of Re-W are used for measuring temperatures up to 2200° C
- Rhenium wire is used in flash lamps for photography
H. Cross Company can supply your rhenium needs in two grades, the standard 99.98% minimum purity and for spectrographic filaments or applications requiring the highest purity a 99.999% zone refined rhenium. We can supply wire, rod, sheet, foil, strip or ribbon in the standard grade product and foil, ribbon or strip in the zone refined product. Thickness down to .0004″, diameters down to .002″ and widths up to 3″ are available with tolerances to meet the most demanding applications. Call or email us for more information on your specific needs.
In addition to pure rhenium H. Cross Company also produces a 50/50 (48% rhenium by analysis) rhenium molybdenum alloy that combines the strength of molybdenum and rhenium’s ductility. This product is available in all the same forms and sizes as pure rhenium at lower cost due to the lower rhenium percentage. We can also supply rhenium alloyed with tungsten at 3%, 5% and 25% rhenium content that greatly improves tungsten’s ductility after exposure to elevated temperatures. These material’s are available in wire, ribbon and strip forms only. For comparisons of the properties for each alloy see our Typical Dimensions and Tolerances page where there are data tables and charts for more information.
All H. Cross Company products are delivered in packaging specifically designed for the product’s application. As an example, wire is furnished on returnable plastic reels containing a single length of wire.
If required, H. Cross Company can adopt standard packaging methods or develop new ones for your special needs.