It's time to talk about... "the materials basis of modern society."

Over half a century ago, the global economy largely depended on just ten or so different materials. Most important products were made out of wood, brick, iron, copper, gold, silver or a few plastics — and that was about it.

Nice elements you got there. Shame if anything should happen to 'em. (Ashley Pon/BLOOMBERG) Nice elements you got there. Shame if anything should happen to 'em. (Ashley Pon/BLOOMBERG)

Things are wildly different today. A huge chunk of modern-day technology, from hybrid cars to iPhones to flat-screen TVs to radiation screens, use dozens of different metals and alloys. A computer chip typically involves more than 60 different elements that are specifically selected to optimize performance, like europium or dysprosium.

And that's long raised a concern: What would happen if we run short of any of these valuable metals? Say there's a war. Or unrest in a crucial mining region. Or China decides to lock up its strontium deposits. Could we easily come up with substitutes? Or is modern society vulnerable to a materials shortage?

Here's the case for vulnerability: A fascinating recent paper in The Proceedings of the National Academies of Science looks at 62 different metals that are widely used in modern-day industry. For a dozen metals, potential substitutes are either inadequate or flat-out unavailable. And there are no "excellent" substitutes for any of the 62 metals. A shortage of any of them could do some damage.

Here's that conclusion in periodic table form: The truly irreplaceable elements here, in red, are manganese, magnesium, yttrium, rhodium, rhenium, thallium, as well as a handful of "rare earth" metals (lanthanum, europium, dysprosium, thulium, and ytterbium):

So how did the authors reach this conclusion? The researchers, led by Thomas Graedal of Yale's Center for Industrial Ecology, first tried to figure out the major industrial uses for the 62 metals highlighted above — a time-consuming task.

They note that many modern products are exquisitely fine-tuned, mixing in a careful combination of elements to optimize performance. The "superalloy" metals used in aircraft turbine blades are an example. Take out any one element and engine efficiency would suffer.

The authors then had to sift through potential substitutes for each of the different metals. Sometimes, when an element becomes scarce, engineers can figure out a substitute. In the 1970s, a civil war in Zaire triggered a shortage of cobalt. So researchers at General Motors developed magnets that didn't need cobalt. Likewise, a recent rhenium shortage forced engineers at GE to develop alloys for gas turbines that used little or no rhenium.

A man works at the site of a rare earth metals mine in Nancheng County, China. (Reuters) A man works at the site of a rare earth metals mine in Nancheng County, China. (Reuters)

But the authors of the PNAS paper wanted to see if this sort of market adaptation was the rule or an exception. It's a tricky question to tackle: "The best substitute for a metal in a particularly use is not always readily apparent," they write. So they sifted through the scientific literature and interviewed product designers and materials scientists for each individual element. The full results are here.

Situations vary widely. Some elements do have easy substitutes. For instance, 54 percent of the world's palladium is used as a catalyst to control emissions from vehicle exhaust. But if we ran short of palladium, we could still swap in platinum and get similar results. Or: Roughly 88 percent of the world's titanium is used to create white pigment for paints, plastics, and paper. But in a pinch, we could use talc instead.

Other metals, however, have no ready substitutes. Rhodium is used as a catalyst to control nitrogen-oxide emissions from cars. Right now, there's no alternative in the event of a shortage. Likewise, about 90 percent of the world's supply of manganese is used as a deoxidizing and desulfurizing agent in steel production. Again, no good alternative on hand.

That's not to say it's impossible to imagine a substitute — materials scientists are clever and markets are good at adjusting to shortages. Never say never. The study notes that there's plenty of ongoing research into things like "advanced composite materials." But substitution can be a slow process and performance can suffer in the meantime.

That's troubling, they note, because the risks of materials disruptions are real — even if they're often only temporary. "No country or region, in fact, has substantial deposits of everything; platinum comes largely from South Africa and Russia, copper from Chile and the United States, strontium from China and Spain, and so on." Case in point: China now dominates the supply of "rare earth" metals — when it throttled back on exports, other countries had to scramble to adjust (although, eventually, they did).

"The consequence," the authors conclude, "is that modern technology is dependent on resources from every continent other than Antarctica, a situation that increases the potential for geopolitical machinations as far as resources."

Further reading:

-- Here's an earlier post on how China created a stranglehold over the world's rare earths supply. And here's a follow-up post on how the rest of the world adjusted after China imposed a rare earth shortage — other countries began mining, and researchers in Japan began the frantic search for substitutes. That suggests that optimism may be warranted in some cases.

-- Note that some politicians are starting to focus on this situation: There's a bill floating around the Senate that would designate a list of up to 20 "critical minerals" and spend $60 million to conduct an assessment of their scarcity, speed up domestic mining if need be, and fund research into alternatives. And here's an argument from John Kemp of Reuters that the situation is best left to markets rather than government oversight.