In some respects, material science is a new discipline since university departments bearing this name only originated in the middle of the 20th century. On the other hand, material science can be said to be the oldest branch of science of all. As far back as prehistoric times, men and women have explored ways in which to use the materials around them to facilitate their everyday lives.
This has included the use of rocks, such as flints, to fashion arrow-heads for the purposes of hunting and self-defence during the aptly named Stone Age. It was also realised very early that certain minerals would give up extremely useful metals when suitably heated with coal. In modern parlance the element carbon is capable of reducing metallic oxides, meaning it is capable of removing the oxygen to leave the uncombined metal. Among the first metals to have been extracted in this way were copper and tin. When blended together, these two metals make an alloy known as bronze, a discovery, which also served to name another pre-historic time period – The Bronze Age, which began around 3300 BC and lasted until around 1200 BC. This was followed by the Iron Age, brought about by the extraction of the stronger metal iron. This period, spanning roughly between 1200 and 700 BC included the accidental discovery of steel, or iron with a diminished carbon content and a corresponding large increase in tensile strength.
The Middle Ages brought numerous discoveries of materials and processes based upon them, including tin-glazing of ceramics, porcelain, improved forms of steel and other metal alloys. In the early modern period clear glass was perfected and made possible the making of telescopes, microscopes and reading glasses. The Italian genius Galileo published the first quantitative analysis of the strength of various materials. According to some, material science properly begins here with Galileo. Moving swiftly to the 19th century we see the discovery of cement, vulcanised rubber and photographic film, to name just some of the many materials that have revolutionised people’s lives.
Key 20th and 21st-century discoveries
But I want to concentrate on a few key discoveries in the 20th and 21st centuries, some of which have yet to reach their full promise. Such is their potential that huge teams of scientists in all parts of the world are engaged in trying to make further improvements upon the initial findings. For example, superconductivity, the ability of some materials to conduct an electric current with essentially zero resistance, was discovered in 1911. The only problem is that this phenomenon only occurs at extremely low temperatures which requires a vast expenditure of resources to achieve. Then in the 1980s it was suddenly found that the temperature at which some materials became superconductors could be as high as 100K, which, relatively speaking, is a huge bonus (fig 1). These days there is an intensive search on the part of material scientists to improve upon this in order to eventually achieve superconductivity at room temperature. If this were possible, levitating trains, which already run along superconducting rails, could be driven at a fraction of the cost.
Figure 1. Superconductivity was discovered in mercury in 1911 at a temperature of 4 K. The temperature at which materials behave as superconductors has risen steadily ever since (green points and triangles), except in the 1980s when there was a sharp increase in certain materials as shown by blue data points. In 2006 another class of high temperature superconductors was discovered (yellow points).
In the 1960s a number of chemists happened upon the existence of a new form of carbon, which occurs in flames, for example. They discovered a remarkable molecule which consists of precisely 60 carbon atoms that form an exact replica of a soccer ball consisting of pentagons and hexagons all stitched together to form an almost spherical shape (fig 2). They quickly found that there were entire families of such structures named buckyballs and in addition that one could form tubes and sheets from such materials and all with promising optical and electrical properties.
Figure 2. The C60 or buckminsterfullerene molecule discovered in 1985 by Kroto, Curl and Smalley. They were awarded the 1996 Nobel Prize in chemistry for this work.
Chemists have also been involved in the discovery and exploitation of a unique set of metals, most of which are situated in the lower parts of the iconic periodic table. They are the rare earth elements, which as it happens, are not especially rare but are nonetheless extremely difficult to extract and process. They include metals such as cerium, neodymium, samarium, gadolinium, holmium and ytterbium. They have unique optical and magnetic properties and have found countless applications in modern technologies including computers, cell phones and electric cars. For example, neodymium magnets are far stronger than the traditional ones made of iron and as a result less material can be used. Loudspeakers can be miniaturised with an improvement in their sound quality using them.
I have left the best till last. The really big buzz in material science these days lies in the area of nanotechnology. It has been found that familiar materials, such as gold for example, can behave in a totally unexpected manner depending on the size of the particles involved. The name nano-science derives from the fact that interest is being increasingly focused on materials at the scale of a nanometer or one-thousandth of a micrometer. In a similar way to rare earth elements, these nano-materials have unique biological, electronic, optical and mechanical properties and have already produced some novel applications.
It emerges that gold nanoparticles are able to kill certain types of cancer cells when appropriately administered. When gold nanoparticles are attached to cancer cells they become selectively labelled and can be easily detected using a simple microscope due to their enhanced light scattering properties. The nanoparticles can also strongly absorb light and can rapidly convert this energy into heat, thus allowing the destruction of cancer cells at laser energies that are too low to harm surrounding healthy cells.
The future of material science
What about the future of material science? How will that look? It is certainly safe to say that accidental discoveries will continue to contribute to the discovery of new materials just as they did in the case of buckyballs and high temperature superconductors. But one new aspect of modern research is that technology advances, and especially the use of density functional theory, are making it possible to calculate the properties of materials without needing to carry out every possible combination of substances in every possible proportion. This option is bound to accelerate the rate of discovery of new materials to an even higher level than before.
Dr. Eric Scerri teaches chemistry at UCLA in Los Angeles and has authored several popular science books www.ericscerri.com