[downer91]

Alright, so here are some of the most common applications, although I'm not sure about the chemistry behind them...

Rhenium: High performance super alloys, particularly when mixed with tungsten, mostly useful in turbine jet engines and heat exchangers. Also used as a catalyst in petroleum cracking when distilling crude oil. Isotopes are used as radiation sources.

Rhodium: A non-reactive metal with characteristic shine, mostly used as beads in automotive catalytic converters. Also used for jewelry and decorative purposes. Also as an good electrical conductor included in alloys for niche wiring applications and as a fiberglass additive.

Lanthanum: Commonly used as gas lamp mantles, but many other uses include acting as a cathode ray source, neutron and gamma ray detector, glass additive, alloy additive, all rare earths in the lanthanide series are useful as catalysts for petroleum cracking when distilling crude oil, and finally potential use in hydrogen fuel cells to sequester hydrogen.

Europium: Flourescent lamps, red phosphors in cathode ray tubes, anti-counterfeiting agent due to unique flourescent properties.

Dysprosium: Mostly magnetic applications. Can be used as a neodymium substitute with unique magnetic properties for niche applications, such as improving conductivity is solenoids for high performance electric motors, and in magnetic media such as hard disk platters.

Thulium: Very rare and expensive, but useful as a safe low-intensity x-ray source, also used in solid state lasers, and due to rarity as an anti-counterfeiting substance with unique flourescant properties.

Ytterbium: Miniscule vitrified sampled are bombarded by lasers as the time keeping component in high quality atomic clocks. Radioactive isotopes can be bombarded with neutrons to produce gamma rays.

Yttrium: Red phosphors in CRT monitors, emits white light from LEDs, semicondoctor doping agent, and lots more.

Strontium: Mostly mixed into glass to shield against x-ray emissions from cathode ray tubes.

Thallium: Mixed with glass to provide special properties, regarding hardness, optical effects and infrared effects. Also used as semiconductor doping agent.

Magnesium: Mostly used as a component of alloys, mixed with other metals to fabricate durable lightweight parts. Comparable to aluminum.

Manganese: An important metallurgical component in steel production, both when refining raw iron ore, and as a component of high quality steel alloys.

I guess it's a pretty wide mix, since many of the elements come from all across the board, on the periodic table. Recurring themes are alloys, glass additives, semiconductors, and chemical catalysts.

[lewispollard]

How come Rhenium is in the list of metals without substitutes, but also given as an example of a metal that was successfully substituted by General Electric? Is it just that it serves a different purpose in smartphones that nothing else can be adequately used for?

[downer91]

Wikipedia's article seems to point to the idea that recently, super alloy applications are placing high demand on a supply chain that was not prepared for such a change in market trends.

I think rhenium diboride seems to be a useful substitute for tungsten carbide in places where tungsten carbide is useful for its hardness. Apparently rhenium is used heavily in the production of tungsten alloys, so there's an association, in that industrial pipelines involving tungsten tend to have a lot of rhenium on hand too.

Meanwhile the super alloys which involve high use of rhenium are nickel-rhenium alloys. Apparently GE has produced a series of super alloys named Rene alloys, and the compositions vary among each memeber of the series, some don't involve rhenium. Given that they seem to be proprietary products with military applications (mostly high temperature rocket engine nozzles) details are somewhat scarce.

Maybe the demand directly relates to how many rockets are being launched, and how many fighter jets are serviced for replacement parts or lost in crashes?