“Rhenium?”, you might ask, “what’s that?”. It’s among the more obscure elements in the periodic table, but not for lack of utility; indeed, rhenium is highly desired as a high-performance material in jet engines as well as rocket engines. Why? Because high temperatures are involved, and rhenium is a refractory element, meaning it has a very high melting point and boiling point, in addition to it being corrosion- and oxidation-resistant; where other metals will melt, deform, or rust under the heat of high-speed flight or engine operations, rhenium will stay strong, solid, and pure. It’s not particularly light for its strength, like for instance titanium, but for high-temperature operations its properties are unmatched by any metal. So why don’t we see it everywhere? Well…because it’s very rare in the Earth’s crust as well as in the universe in general.
In a timeline like the one I write my stories in, supersonic jets, rocket travel, nuclear pulse propulsion, nuclear reactors, and all manner of high-temperature, high-energy, high-speed operations are many orders of magnitude more common and intense than in our world, and already in our world the rhenium supply is scarce, hence its high price. Yes, substitutes can be found, but in these realms there is no other element that works quite as well. Which in my view makes rhenium an ideal candidate for mass production via nuclear transmutation, the harnessing of nuclear processes to change one chemical element into another element.
Transmutation most prominently occurs in stars (the forging of hydrogen into helium by nuclear processes is what generates most of the sunlight we know and love on Earth…), but it’s also the essence of nuclear fission, as in the reactors that generate much electricity. Transmutation also occurs by various other processes, but also by “neutron capture”. Certain heavier elements when exposed to the heavy neutron flux of a nuclear fission reactor will be transmuted as they capture new nucleons. It so happens that rhenium can be produced in this fashion; take a rod of tungsten (a rather common, cheap element), dunk it in a reactor pool long enough, and you’ll eventually see it turns into rhenium.
In my sci-fi setting, nuclear fission reactors producing suitable neutron fluxes are ubiquitous, and so my world’s economy can just make as much rhenium as desired. Modern-day alchemy! So with the chains of cosmic rarity removed, what would rhenium be used for? Turns out it’s rather versatile stuff, since, unsurprisingly, a strong conductive metal that can withstand high temperatures without corroding or oxidizing much is actually quite useful.
The applications for jet and rocket engines are obvious; in the high-temperature realm of spaceflight or supersonic travel, rhenium-heavy alloys enable far more efficient and effective operations, to the point of single-stage-to-orbit rocketships becoming feasible. Forges where carbon nanotubes, graphene, or exotic metal alloys are worked could be cheaply lined with rhenium-based material, enabling fabrication well beyond what existing common ceramics would permit. Nuclear reactor parts could be made much more robust. Even maglev trains could see enhanced performance, since much higher temperatures could be withstood by the components. Wiring could be much more durable as well; rhenium is moderately conductive, after all.
Where it gets really fancy is that applications of cheap abundant rhenium aren’t just limited to industry, they also extend to the household. You could see cookware that never oxidizes, never scratches, and never warps, even at searingly hot temperatures, knives that never dull, cooking devices that operate at ultra-high heat for their size. Really, with rhenium-based alloy, anything that normally wears out because of heat, oxidation, or stress essentially becomes indestructible by our standards, which upgrades…uh, a lot.
In my sci-fi universe automobiles usually run on jet engines (not as far-fetched as you might think since Chrysler was working on it in the 1960s; yes, really), so even the jet-engine-parts applications are rather broad. In my timeline, by default titanium is the go-to metal for automobile frames, since it’s strong and light…but by the 21st century on-board nuclear reactors become the norm, so rhenium will see a prominent place inside car power plants too…and perhaps even in the frame of the vehicle. It’s heavy compared to titanium, but even a small on-board reactor will imply vehicles massing in the hundreds of tons or even heavier…to the point one wonders if any kind of conventional tires would be capable of spreading the weight onto the pavement. Of course, if you used magnetic levitation for the vehicles it wouldn’t really matter how heavy they were, and an element like rhenium is useful here too. Even unto the pavement, which might be made out of what we’d consider an exotic metallic base rather than concrete or asphalt. Very classic sci-fi.
Also classic sci-fi would be the metals in common use having a brassy or better yet coppery aesthetic in terms of their color. Alas, rhenium is a depressingly generic silvery-grey color…in its pure form. But rhenium trioxide, conveniently, is a striking reddish color, and can, thanks to abundant reactor heat in the dark satanic mills of the rhenium forges, be diffused into pure rhenium metal to create a material that’s comparably desirable in its properties to pure rhenium but with a color resembling but clearly distinct from copper. Very futuristic. You could have kitchens and pipes that look copper-like, but behave like some far-out alien metal that never melts, never warps, never corrodes, and is quite heavy and strong.
And speaking of the abundant reactor heat, I’m considering that pipes could look very different in my universe. In our timeline we extract water from sources that are already “fresh” and then go to great lengths to treat it with chlorine and filters and so forth. This is usually not questioned, but when you interrogate it, it’s a very inconvenient way to obtain drinking water…we only do it because it’s less energy-intensive than the alternatives. There’s plenty of water in the air you can extract and process. There’s an even better source in the oceans: all the water you’d ever want! Only it’s salty. Well…apply reactor heat to the seawater to the point of boiling, and you get steam that you can condense into distilled water and then send on through to the households. In a world with cheap abundant energy this would be trivial to do anywhere next to the ocean, we just don’t do it because energy is far too expensive.
But would condensing the steamwater on-site even be optimal? Consider that the higher the temperature is and the longer it’s sustained, the more assuredly sterile the water becomes, which is optimal. It’s also optimal to not take the slightest chance of pathogens and so forth being introduced from the piping itself. So in principle, it would be optimal to boil the water to a very high temperature at the water plant and then send it still at sterile boiling temperatures through the pipes to the household, and then condense it at the household. Naturally this would demand pipes that can handle water at high temperatures, and while copper is horrendous for this purpose, rhenium would hold up perfectly well…and my timeline is one where rhenium is an abundant cheap metal.
If you wanted to get really fancy about it, it would actually be optimal to send out the water in supercritical phase, which is not a phase of water where any known life (i.e. contamination) can survive; the “critical point” for water is 705 degrees Fahrenheit in temperature and 218 atmospheres of pressure, above which it will be neither liquid nor gas but rather a fluid with properties of both. Cool and depressurize the supercritical water when it reaches the household, and out comes pure distilled water. Water hardeners can be installed to reintroduce beneficial minerals for human consumption, but machinery can enjoy the benefits of fully soft water whether at the industrial or household level.
Naturally hundreds of degrees and hundreds of atmospheres demands very high-performance material, and rhenium alloys fit the bill. Another interesting consequence of this energy-intensive but simple and effective process is that the optimal pipe would be one where the water flows much more slowly than is the case today; at such extreme pressures vibration and mechanical stress start to be a concern, and the same nuclear technology makes tunneling trivial, since you can just apply reactor heat to melt rock and evacuate a cavity of the desired shape and size. So why not make the pipes big? Big enough for a man and his machine to inspect and repair while on the inside, ideally. So again, we see classic sci-fi vibes, but for sound reasons that have fallen into obscurity; perhaps, in certain science-fictional universes, they don’t have huge plumbing for the hell of it, but rather because of the economics of tunneling and the properties of the materials they’re using. Fascinating, isn’t it?
Rhenium oxides, especially with diffusion being easily accomplished due to abundant energy (in our world it’s a pain for metallurgy to employ such methods, again owing to the energy-intensity), could be used for artistic purposes. In my universe I envision, due again to abundant energy, home forges similar to our 3D printers but hot enough to work metal, so applying different diffusions of rhenium oxides to make objects that are not only tough but beautiful would be commonplace. So trivial would this be that it might even be a common technique in infrastructure such as the aforementioned rhenium pipes, maybe even jet engine parts and the like. Rhenium oxides can even be used in glassworking as well to create particularly striking reds and oranges beyond what our go-to techniques can achieve.
And as if that wasn’t enough, the fastest known semiconductor is a chemical compound that heavily uses…rhenium. Specifically a molecule that consists of 2 parts chlorine, 8 parts selenium, and 6 parts rhenium. How fast? Up to a million times as fast as silicon-based electronics. That’s enough to take a laptop to the level of performance that now is the preserve of the very largest supercomputers. Abundant electricity from nuclear power is already enough of a superpower…now we see that nuclear reactors can help make material that makes the use of said electricity a million times more efficient? Forget AI…that’s where the real breakthrough lies. I’ve always been impressed with rhenium, as a bit of a nerd (okay, more than a bit), but in my research on what people in my sci-fi universe would use rhenium for, I come away feeling like “holy smokes…what wouldn’t they use this stuff for?”.
Well…one answer would be skyscrapers, since for a tall building you want materials that are not only strong but also light…but even then the cheap abundant energy means refining large quantities of ore into titanium is trivial, and with titanium frames the constraints on the height of a tower are much more forgiving than for steel or for current forms of concrete. Then you have carbon nanotubes, boron nitrides, even…when you open up the periodic table with abundant heat and energy to work processes both chemical and nuclear, it’s like the universe opens up to you for the first time. And in a way that’s delightfully reminiscent of the best of old-timey science fiction, an angle that I’m intent on exploring further.