This story was originally published by cabling and appears here as part of the climatic table collaboration.
Consider for a moment the electrical cord, a ubiquitous technology that is extremely easy to forget. Coiled inside our devices, wrapped around our walls, strung along our streets, millions of tons of thin metallic threads do the job of electrifying the world. But his work is benign and so naturalistic that it doesn’t really feel like technology at all. Wires move electrons simply because that’s what metals do when supplied with a current: they conduct.
But there is always room for improvement. Metals conduct electricity because they contain free electrons that are not tied to any particular atom. The more electrons flow, and the faster they go, the better a metal will conduct. So to improve that conductivity—crucial for preserving energy produced in a power plant or stored inside a battery—materials scientists typically seek more perfect atomic arrangements. Its main objective is purity: to remove any bits of foreign material or imperfections that interrupt the flow. The more gold a lump of gold is, the more copper a copper wire is, the better it will conduct. Anything else gets in the way.
“If you want something really highly conductive, then you have to go pure,” says Keerti Kappagantula, a materials scientist at the Pacific Northwest National Laboratory. That’s why she considers her own investigation to be quite “clumsy”. Her goal is to make metals more conductive by making them less pure. It will take a metal like aluminum and add additives like graphene or carbon nanotubes to it, producing an alloy. Do it the right way, Kappagantula discovered, and the extra material can have a strange effect: It can push the metal past its theoretical conductivity limit.
The goal, in this case, is to create aluminum that can compete with copper in electrical devices, a metal that is almost twice as conductive, but also costs twice as much. Aluminum has advantages: it is much lighter than copper. And as the most abundant metal in the earth’s crust, a thousand times more abundant than copper, it’s also cheaper and easier to dig up.
Copper, on the other hand, is getting harder to come by as the world transitions to greener energy. Although it has long been ubiquitous in wiring and motors, demand is increasing. An electric vehicle uses about four times as much copper as a conventional car, and even more will be needed for the electrical components of renewable power plants and the cables that connect them to the grid. Analysts at Wood Mackenzie, an energy-focused research firm, Estimate that offshore wind farms it will require 5.5 megatons of the metal over 10 years, mainly for the massive system of cables inside the generators and to transport the electrons produced by the turbines to the coast. In recent years, the price of copper has skyrocketed and analysts project a growing deficit for the metal. Goldman Sachs recently declared it “the new oil.”
Some companies are already swapping it for aluminum where they can. In recent years, there has been a multi-million dollar change in the components of everything from air conditioners to auto parts. High-voltage power lines already use aluminum wires, because they are cheap and light, allowing them to run longer distances. That aluminum is typically in its purest, most highly conductive form.
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But this conversion has slowed recently, in part because the switch has already been made for applications where aluminum makes the most sense, says Jonathan Barnes, senior analyst for copper markets at Wood Mackenzie. For use in a broader range of electrical applications, conductivity is the primary limit. That’s why researchers like Kappagantula are trying to redesign the metal.
Engineers often design alloys to improve other qualities of a metal, such as strength or flexibility. But these concoctions are less conductive than the pure stuff. Even if a particular additive is especially good at carrying electricity (which is the case with the carbon-based materials Kappagantula works with), the electrons within the alloy often have trouble jumping from one material to another. The interfaces between them are the trouble spots.
It is possible to design interfaces where that is not the case, but this must be done with care. The usual ways of making aluminum alloys are not enough. Metallic aluminum has been produced for over a century by processes that may sound familiar if you remember your high school chemistry textbook: the Bayer process for extracting aluminum oxide from bauxite (the sedimentary rock in which it is found). mainly the element), followed by the Hall-Héroult process to melt the material into aluminum metal.
As the world turns to electric vehicles and renewable energy, molecular tweaks to aluminum could improve its conductivity.
That second process involves heating the metal to nearly 1,000°C to melt it, a not-so-environmentally friendly procedure that goes a long way toward explaining why it takes about four times as much energy to make aluminum as it does to make copper. . And at these temperatures problems arise in making properly nuanced alloys. It’s too hot for an additive like carbon, which will lose its carefully designed structure and end up unevenly distributed throughout the metal. The molecules of the two substances realign to form what is known as an intermetallic, a hard, brittle material that acts as an insulator. Electrons cannot jump from one side to the other.
Instead, the PNNL researchers turned to a process called solid-phase fabrication, which uses a combination of shear and frictional forces at lower temperatures to layer the new carbon material into the metal. The key is to do this at a temperature that is high enough for the aluminum to become flexible, in the so-called “plastic” state, but not molten. This allows Kappagantula to carefully control the distribution of the materials, which are then verified with computer simulations that model the atomic structures of the new alloys.
It will be a long process to get those materials out of the lab. The team’s first step has been to produce cables made from the new alloys, first a few inches long and then a few meters. Next, they’ll create bars and sheets that can be run through a variety of tests to make sure they’re not only more conductive, but also strong and flexible enough to be useful for industrial purposes. If it passes those tests, they will work with manufacturers to produce larger volumes of the alloy.
But for Kappagantula, it’s worth reinventing the two-century-old aluminum-making process. “We need a lot of copper, and soon we’re going to have a shortage,” he says. “This research tells us that we are on the right track indeed.”