A few centuries ago, there were just a few widely used materials: wood, brick, iron, copper, gold and silver. Today’s material diversity is astounding. A chip in your smartphone, for instance, contains 60 different elements. Our lives are so dependent on these materials that a scarcity of a handful of elements could send us back in time by decades.
If we do ever face such scarcity, what can be done? Not a lot, according to Thomas Graedel of Yale University and his colleagues who decided to investigate the materials we rely on. He chose to restrict his analysis to metals and metalloids, which could face more critical constraints because many of them are relatively rare.
The authors’ first task was to make a comprehensive list of uses for these 62 elements. This is a surprisingly difficult task. Much of the modern use of metals happens behind closed doors of corporations, under the veil of trade secrets. Even if we can find out how certain metals are used, it may not always be possible to determine the proportions they are used in. Their compromise was to account for the use of 80% of the material that is made available each year through extraction and recycling.
The next task was to determine if there were any substitutes for these uses. But, as Graedel writes, “the best substitute for a metal in a particular use is not always readily apparent.” Elemental properties are quite unique and substitution will often reduce the performance of the product. But it can be done.
Two examples stand testament to that. In the 1970s, cobalt was commonly used in magnets. When a civil war in Zaire caused scarcity of cobalt, scientists at General Motors and elsewhere were forced to develop magnets that used no cobalt. More recently, a shortage of rhenium, which is used in superalloys for gas turbines, forced General Electric to develop alternatives that use little or no rhenium.
Graedel’s analysis of substitutes involved ploughing through scientific literature and interviewing product designers and material scientists. The results are a sobering reminder of how critical some metals are. On seeing the data, Andrea Sella of University College London said, “This is an important wake up call.”
None of the 62 elements have substitutes that perform equally well. And some of those have no substitutes at all (or if there are substitutes, then they are inadequate). They include: rhenium, rhodium, lanthanum, europium, dysprosium, thulium, ytterbium, yttrium, strontium and thallium.
Economists have long assumed that a shortage of anything will promptly lead to the development of suitable substitutes, an attitude fostered in part because there have been successful substitutions in the past, such as the cobalt and rhenium examples. But metals are special, Graedel said: “We have shown that metal substitution is very problematic. Substitution would need to mimic these special properties – a real challenge in many applications.”
“The clarity of Graedel’s thinking is impressive,” said Sella. “No one has analysed metal criticality in such detail.” One of Graedel’s biggest contributions has been developing a visual way of understanding how critical metals are. They created a 3D map, where the three axes represent supply risk, environmental implications and vulnerability to supply restriction.
The Yale analytical framework for determining metal criticality. PNAS
The scarcity of metals came to public attention in 2010 when China suddenly decided to restrict its export of a group of metals called the rare earths. Prices of these metals shot up by as much as five times and caused companies around the world to consider reopening their rare earth mines. This had knock-on effects on the prices of everything from gadgets to wind turbines.
Some comfort may be drawn from the fact that consumptions of some metals can peak. For example, the use of iron has reached saturation in many countries. And, in the US, this seems to have happened for aluminium too. This, however, is the case only for bulk metals. Scarcer metals, even with superior recycling, may never reach saturation.
Apart from China, a handful of countries, including the US, South Africa, Australia, Congo, and Canada, hold the most diverse and largest metal reserves. “A national disaster or extended political turmoil in any of them would significantly ripple throughout the material world in which we live,” said Graedel.
In a rare double, another Nobel Prize has gone to scientists who build models. The 2013 Nobel Prize in Chemistry was awarded to Martin Karplus, Michael Levitt and Arieh Warshel for their work that enables modelling complex chemical reactions on computers.
Scientists build models to understand the world. Those models that survive experiments get widely used. The 2013 Physics Nobel Prize recognised one such feat, where the Higgs boson helped prove that the best-known Standard Model works. Many physicists will be quick to point out that Peter Higgs and François Englert did this by using merely a paper and pen.
To develop their theories, physicists can treat subatomic particles in isolation and then generalise their calculations. Developments in quantum mechanics, the science of the microscopic, mean the behaviour of these particles is quite well-understood. Chemists, however, have to deal with the messiness of the real world, where the number of atoms and the particles within them is large. That is why they rely on computers to do their calculations.
Chemical reactions involve the movement of electrons as atoms interact. Applying quantum mechanics to the reactions of small molecules (containing a handful of atoms) is possible using current computational power. Researchers who developed methods to do that received a Nobel Prize in 1998. But if the molecules that need to be modelled become larger, like proteins which contain thousands of atoms, even current computational power is not up to the task.
This year’s prize went to researchers for making that process easier. They developed methods to deal with the growing complexity of reactions of bigger molecules. They achieved this by marrying two different methods of understanding molecules: quantum mechanics (QM) and molecular mechanics (MM).
MM is based on the classical physics developed by Isaac Newton. It works to explain how large molecules behave (bend, move, vibrate or rotate). In the 1970s, at the Weizmann Institute of Science in Israel, Warshel and Levitt had worked to develop computer programs to use classical physics to model these big molecules.
Then, on completing his PhD, Warshel started working with Karplus at Harvard University. So far Karplus had been dealing with small molecules using QM, but with Warshel he started developing programs to combine the two methods.
They found that a hybrid method improved accuracy without stretching computational power to its limits. Dominic Tildesley, president-elect of the Royal Society of Chemistry, explained: “Computer experiments now combine the quantum mechanics of making and breaking bonds with the classical mechanics of the movement of proteins. Their programs modelled the active parts of a molecule (where the reaction took place) more accurately using QM and the rest with MM. This marriage led to what is commonly known as the QM/MM approach.
“Today QM/MM is very widely used,” Jeremy Harvey at the University of Bristol, said. “Chemists, biochemists, geochemists and chemical engineers all use it.” Its application has helped develop better drugs, improve environmental models and understand the oceans. Since the 1980s, incremental developments to programs and vastly improved computing power has led to the explosion of the use of QM/MM.
But models are only good if they reflect reality. “That is why computational chemists and experimental chemists talk to each other regularly,” Harvey said, “feeding into each others work.” Thirty years ago this did not happen. The prize recognises how researchers ushered chemistry into the computer age.
Eric Drexler may get the credit for popularising the idea of nanotechnology in his books of the 1980s, but chemists have been dreaming of manipulating molecules to do their bidding ever since they found out that all matter is made of atoms. While Drexler’s self-assembling molecular machines may remain a dream, in the last decade chemists have already achieved a more practical version of that dream. Nanoparticles have found use in manufacturing, materials, energy, electronics and medicine. Now, a newly emerging field is using them to do two things at once diagnose and treat diseases.
Microbes are principally used by industry to turn larger organic compounds into smaller, more useful ones – fermenting corn sugars to produce ethanol, for instance. More desirable, though, is direct conversion of carbon dioxide into organic compounds. But current methods that use blue-green algae are not attractive.
Now US researchers have engineered a heat-loving microbe to produce a bulk chemical from carbon dioxide and hydrogen. Their results may provide a viable industrial alternative to blue-green algae, which have a much lower efficiency for such chemical transformations.
X-ray crystallography has shaped modern chemistry. It is arguably the most powerful tool for molecular structural analysis. But it suffers from one big drawback: it can only analyse materials that form well-defined crystals. This may now be about to change. Researchers in Japan have used ‘crystal sponges’ to hold molecules that can’t be crystallised, allowing them to be analysed using x-ray crystallography.
Clouds turn to rain when water droplets and ice crystals that make them up get too big to resist the pull of Earth’s gravity. This is often caused by particles that disturb the maelstrom of droplets and crystals to become seeds around which cloud matter coalesces. Once this happens, the seeds grow rapidly and eventually fall to the ground.
The seeds can be caused by the passage of exotic things like cosmic rays. More often, though, they are dust particles lofted high into the air. A study in 2009 showed that dust from Taklimakan desert in China, whisked above 5,000 metres, circumnavigated the globe in just 13 days. Because dust needs large horizontal distances to attain sufficient altitude, it might then cause rainfall half-way across the world.
For example, the Rocky Mountains in America push water vapour to higher altitudes that help form clouds. At that point, the theory goes, the clouds run into particles swept in from Africa and Asia. To find if that is indeed what happens Kaitlyn Suski and her colleagues at the University of California, San Diego, examined dust and clouds in Californian skies, to the Rockies’ west. They report their findings in Science.
Ms Suski needed to confirm that dust particles reached heights of about 3,000 metres or more to be able to intercept rain clouds. She also had to verify that they originated in Asia and Africa. She collected samples in an aeroplane equipped with a mass spectrometer, which can accurately determine the dust’s chemical composition. These chemical signatures were then compared with those found in Asian and African deserts. As a cross-check, Ms Suski used data from satellites like CALIPSO, which tracks dust particles’ atmospheric peregrinations.
Perhaps more interesting, Ms Suski also found that rain clouds contained bacteria, though it proved impossible to pin down their origins. Tiny living organisms can float in the atmosphere for a long time, feeding on trace carbon and any other nutrients they bump into. They can also act as cloud seeds.
In 2010 researchers in Norway concluded that bacteria are not as important to rainfall as dust is. But calculations by Ms Suski and her colleagues suggest that their rainmaking powers are amplified when they mingle with desert dust. Deserts may be some of the harshest places on the planet to live, but, if Ms Suski is right, they may be the enablers of life everywhere else.