MMTA member Molymet, a major molybdenum processor and the world’s largest producer of rhenium, with headquarters in San Bernardo, Chile has launched production of highly spheroidised powders of rhenium, molybdenum and their alloys.
Having completed its trial run at Molymet Nos facilities,the equipment, which uses plasma speroidisation, is now in operation.
Spherical powders can be densely compacted, minimisingimpurities, and are optimised for advanced manufacturing technologies including additive manufacturing (AM0), metal injection moulding (MIM), thermal spray (TS), cold and hot
isostatic pressing (CIP and HIP), some of which are commonly termed 3D Printing. As well as eliminating most of the metal waste associated with subtractive manufacturing techniques such as forging, these technologies offer greater flowability and allow for small, complex and custom parts to be made.
Powder metallurgy opens up a number of new and growing applications, particularly for rhenium, a rare meal with a niche market mainly tied to the power engineering — high pressure turbine blades for aerospace engines and industrial gas turbines — and to petrochemical catalysts.
“We will try to take rhenium to new markets, such as medical implants and the space industry,” Mario Lama, Business Development and By-Product Sales Executive Manager tells the MMTA. “Rhenium is used in satellite thrusters — and a lot of our rhenium goes into satellites, for launch companies such as Blue Origin, and SpaceX, etc.
“We are looking also at the high-end watches and jewellery, where rhenium could replace platinum, because it is greener and its production requires much less CO2.,” Lama adds. Molymet currently features in the top 5% of Dow Jones Sustainability Index for mining and metals companies. Rhenium is30-40 times cheaper than platinum, which requires labour -intensive and costly deep-pit extraction, but it is still a very rare, exclusive metal, associated with aviation and space.
At this time, rhenium jewellery is only a concept for what could become a niche application. Whereas space vehicle propulsion, with rhenium alloy used in iridium-coated thrusters, is a current and growing one. Etymology sees this as a large part of the powder market expected to take up about 5t of its rhenium production per year, over the next 5 years.
The US and China are major consumers of rhenium for space vehicle thrusters, Lama said, while Europe is not yet active in this market. Having stepped up its satellite launches in recent years, China has been buying more rhenium, although it is hard to estimate how much is used in which specific application, based on import figures alone (10-20t/year).
Meanwhile medical implants are another growing market for rhenium. This market would be particularly well aided
by the launch of Molymet molybdenum-rhenium alloy spheroidised powders that enable this material to be 3D
printed into custom designs.
Molybdenum-rhenium (Mo-50Re, 52.5% Mo and 47.5% Re) alloy can be used to fabricate a variety of implants, e.g. for spinal cord surgery, ankle, hip and knee replacement joints, dental implants and coronary stents. Mo-50 Re wins against more traditional implant materials, such as cobalt-chromium on biocompatibility and titanium alloy Ti-6Al-4V (a.k.a. Grade 5 Ti) on strength. Even compared with the highly corrosion resistant and biocompatible titanium, the Mo-50Re alloy has less ion release. Tests have shown that the rate of bone growth around the implant is similar between titanium and moly-rhenium.
As the alloy is denser, implants can be made smaller in moly-rhenium, Lama explains, requiring less invasive surgery. Mo 50Re so strong that is promises to last a lifetime. Whereas titanium implants eventually start to show wear and may need to be replaced after 10-15 years, moly-rhenium looks likely to stay the course, reducing the need for repeat surgery.
Recently, the US Food and Drug Administration (FDA) approved the use of Mo-50Re for manufacturing stents, mesh implants that are used to expand constricted arteries. These had been previously manufactured using meshes made from stainless steel, cobalt–based or titanium-based alloys, or from Nitinol, a nickel-titanium alloy. Against stainless steel and nickel in particular, because of risk of allergies associated with nickel, the moly-rhenium alloy wins as the biocompatible alternative. The alloy is also completely non-magnetic (comparable or even better than pure titanium), so the presence of an implant (e.g. cardiac stent) would not interfere with MRI scans (or metal detectors). Another advantage of Mo-50Re is its high ductility (ability to change shape without fracturing), thanks to twinning induced plasticity (TWIP), a grain microstructure characteristic found particularly in advanced steels. This makes Mo-50Re highly plastic opening it up to cold-working, making it perfect for manufacturing the ultra-fine meshes used in stents.
So here is a perfect combination of Molymet, the world’s largest rhenium producer with its own R & D innovation centre and spheroidised powder technology, and ongoing scientific advances that favour powder metallurgy, moly and rhenium.
