Making light of metals
Key text
This topic is sponsored by the Australian Research Council Centre of Excellence for Design in Light Metals.
The light metals aluminium, titanium and magnesium are taking a load off transport and other everyday objects.
Bikes are changing
Look at the frame of your bicycle. It will be made of metal tubing, strong enough to carry your weight but light enough so you can carry its weight if you have to. It also needs to resist rusting and be affordable. In most bikes that metal is steel, which meets all these requirements, other than the rusting one (and painting and proper care can deal with that). But increasingly, ‘high-end’ bikes are being made of other, more exotic metals, alloys containing aluminium or magnesium, or even titanium. As time goes by, more ‘everyday’ bikes will be made the same way, and other goods as well. Why? Read on.
metals like magnesium. (Image: Paketa Bikes)
The metal miracle
Modern life would be impossible without metals. We can date the start of civilisation pretty much from the time our ancestors found out how to extract first copper and then iron and fashion those metals into tools, weapons and everyday items. The Industrial Revolution of the last 200 years, which created today’s world, was founded on iron and its alloy steel, letting us manufacture powerful, durable machines and build skyscrapers, bridges and railway tracks.
But these traditional metals have their drawbacks. Iron and steel are strong and cheap but they can rust and weigh a lot. Copper resists corrosion but is expensive and relatively soft. Now research is finding replacements, particularly for steel. We have known about aluminium, magnesium and titanium for a hundred years or more. We recognised that they are strong but relatively light and that they don’t rust. But for a long time they were too expensive for everyday use (much as steel was until the late 19th century).
That is now changing, and changing fast. Through advances in production and processing, these ‘light metals’ are becoming cheaper and more versatile. We are starting to see them in everyday items: in cars, aircraft, bicycles, the cases for laptops, mobile phones and even iPods. And Australian scientists are helping in this transformation of light metals.
Why light metals?
Industry is excited by light metals because they combine many of the traditional advantages of metals (Box 1: The magic of metals) with the virtue of being much lighter than the iron and steel we have used for so long. By replacing steel in things like cars and aircraft with lighter metals, they become more efficient, consuming less fuel and producing fewer greenhouse gases – big pluses in today’s world.
Everyday objects like mobile phones, cookware and soft drink cans, or exotic objects like medical implants, can be made both more convenient and more durable by using light metals. They are also readily recyclable. In fact, extracting metals from their ores usually takes so much energy it can be much cheaper to recycle them than to use a newly produced metal.
Light metal researchers have two big challenges if they want to make their metals more competitive and more widely used. They have to cut the cost and environmental impact of extracting the metals from their ores. They also need to find new ways to process the metals once extracted, so they can be produced in more useful and versatile forms. Some of these forms will be alloys, where other metals or non-metals are added to improve the properties of the metal. (Box 2: Changing metals: Alloys).
There is a good reason why Australian researchers are very active in this field. Australia has some of the world’s largest deposits of aluminium, magnesium and titanium ores. The more uses that are found for these metals, the more Australia will benefit.
And there is more. Rather than exporting mostly unprocessed ore, by developing and applying the new technology here at home we could add huge value to our resources. Exporting magnesium alloys could earn us up to 100 times more per tonne than the unprocessed magnesium ore. Components made from that alloy would be worth three times more again. At the moment, we make and export a lot of aluminium metal, but no pure magnesium or titanium. We have a long way to go.
Aluminium
Aluminium was the first of the light metals to hit the big time. We have been using it for decades in niche products; drink cans, cooking foil, planes and building materials. We are using it increasingly in other applications like iPod cases and cars, where its lightness and resistance to rusting is appealing. But it still can’t compete everywhere with the alternatives, largely because it costs too much.
There is no shortage of aluminium. It is the most plentiful metal in the crust of the Earth. We extract it by electrolysis from alumina, which in turn is produced by removing the impurities from bauxite.
Australia has immense deposits of bauxite, in northern Queensland, the Northern Territory and Western Australia. We are the world’s largest producer of the stuff. We also produce 30 per cent of the planet’s alumina, and a lot of that alumina is turned into aluminium metal in big smelters, at the cost of a lot of electricity. Australian scientists are working on reducing the cost of producing aluminium, to make it more competitive with other materials like steel. And the costs aren’t just financial. Like other metals, mining and processing aluminium has an environmental cost. But operators of today’s mines are careful not to repeat the environmental blunders of the past. Mining sites these days are carefully managed to minimise their impact, and after the ore has been extracted, the sites are remediated to return them as close as possible to their natural state.
Life cycle assessment shows that aluminium production produces more greenhouse gases than steel production. But when used in vehicles, aluminium’s lighter weight leads to better fuel efficiency, and so reduces greenhouse gas emissions from transport.
Better aluminium alloys are being developed and tested for a host of applications. We may be flying in some of them before long. Through an agreement with the second largest producer of alumina in the world, Monash University scientists are working on lighter, stronger aluminium alloys for Chinese-built commercial aircraft.
Magnesium
Everyone recalls magnesium from school as the metal that burnt with a blinding white light. However, in larger and thicker shapes magnesium is much less susceptible to burning. And when alloyed with aluminium, magnesium can be made even safer and more useful. Magnesium alloys are being used in motor vehicles, planes, and casings for mobile phones and laptops. It is an impressive metal, one third lighter than aluminium, stronger (kilo for kilo) than steel and resistant to shock and impact.
Unlike aluminium, magnesium can be extracted from several different minerals, as well as from sea water and even fly ash. Australia’s magnesium resources are in the form of magnesite. Extracting the metal requires conversion to magnesium chloride, then electrolysis to separate the magnesium and chlorine. This process takes a lot of energy, pushing up the price. As with aluminium, Australian scientists are looking into ways of cutting the energy needs and costs involved in producing magnesium.
Meanwhile, work will go on to develop even more sophisticated magnesium alloys, alloys that are stronger, cheaper, more ductile, able to stand higher temperatures, more resistant to corrosion, as well as better techniques to cast and shape those alloys into useful products. And magnesium is proving its worth, with alloys developed in Australia being tested in car engines in Europe and the US in the hope that they will produce lighter, more fuel-efficient cars.
Titanium
The major source of titanium is black ’beach sand’ which we often see on today’s beaches, but which can also be found in vast deposits from ancient beaches often many kilometres from the sea. Australia has the world’s biggest deposits of these titanium ores.
medical implants and sporting goods. (Image: Stockxpert)
Beach sands are a mixture of compounds, one of which can be rutile. When separated and purified, it becomes the brilliant white pigment titanium dioxide, much used in paint, paper making and plastics. Extraction using chlorine (the Kroll Process) yields titanium metal, but consumes magnesium along the way. Titanium costs a lot, mostly because it can be made only in batches rather than continuously. Australia mines more than half of the world’s rutile supply, but produces only 4 per cent of the pigment and no titanium metal at all.
The appeal of titanium is its high strength-to-weight ratio. Popular uses are in the aerospace industry (the Boeing 787 Dreamlineris 15 per cent titanium), medical implants or sporting goods where the need to reduce weight overcomes the problem of price. With its high melting point, titanium is particularly well suited to high temperature components in jet engines and spacecraft. Its resistance to corrosion makes it good for use in desalination plants and in the human body. Titanium is often alloyed with other metals to change its properties.
Although titanium is light, strong, and doesn’t corrode, its use is limited by its relatively high cost. Australian researchers are on a mission to lower the production and processing costs of titanium to allow it to be more widely used. The use of titanium powder technology is just one way they hope to achieve their goal, with scientists at CSIRO suggesting they could halve production costs.
Australian research reducing the load
Through advances in production and processing, light metals are becoming cheaper, more versatile and able to compete with traditional metals like iron and steel in a wide range of applications. That trend is sure to continue. You will see more titanium, aluminium and magnesium in your lives in future years, and enjoy the benefits. And much of the research into these metals, which is changing our future, is Australian.
Boxes
1. The magic of metals
2. Changing metals: Alloys
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Posted December 2009, edited August 2012.