EML: Thermolab and NEQUISOL

Experiments using a levitation device in space will tell scientists more about the properties of metals. Eliminating the effects of gravity helps build a more accurate picture of a material’s fundamental nature, its structure and how it forms. This information can then be used to design new materials with useful properties – stronger, for example, or lighter, better at conducting heat or electricity.

The Electromagnetic levitator (EML) is a furnace used for studying metals on the International Space Station, in the European Space Agency’s (ESA) Columbus laboratory.

It heats metals up to 2100°C and rapidly cools them – this is essentially what blacksmiths have been doing for centuries, creating steel tools by heating, hammering and quenching in water. This process sets the steels structure and causes it to be hard and stay sharp.

Using the EML, this age-old process is given a space age update: creating molten metals without gravity, or a container to hold them: the liquid metal is levitated, fixed in position, either in a vacuum or a gas, and its changes during heating and cooling are measured by high speed cameras and other sensors.

The physics underlying the process of heating, melting and solidification of metals and metallic alloys is highly complex and affected by many factors – but removing gravity and the container holding the metal from the equation, you can observe the fundamental properties of different metals, alloys, rates of cooling and so on much more accurately. This data can then be used to design new materials with specific useful properties: strong, lightweight, conductive, pliable or rigid.

There are two experiments using the EML with significant UK involvement: NEQUISOL and Thermolab.

Thermolab

Traditionally, trial and error was used to test new alloys – creating a batch and testing its properties. Increasingly, largely thanks to improvements in processing power, computers can model and predict the properties of new alloys. However, before they can do so, they need to have reliable data on the properties of the constituent materials.

Thermolab is delivering these parameters, investigating the temperatures and physical properties of industrial alloys. This will help scientists improve models of industrial processes for the aerospace, automotive and consumer electronics industries – ultimately leading to materials produced more quickly, cheaply and with less waste – good both for the environment and for companies’ bottom line.

Professor Koulis Pericleous at the University of Greenwich is a member of the international Thermolab team. His team has studied the stability of the EML, making sure that the forces induced by the coils are balanced, to give measurements to the required degree of accuracy.

NEQUISOL

Non-equilibrium Solidification of Industrial Alloys (NEQUISOL) is looking at the rapid solidification of industrially important alloys. Cooling these alloys quickly, to below their freezing point, causes dendrites to form as they solidify – dendrites are ‘tree-shaped’ crystal structures, much like you might see in ice on your windscreen. The NEQUISOL project is analysing this process in comparison with ground-based studies. To date, mostly Nickel-Aluminium alloys have been used, but Aluminium-Silicon alloys and Silicon-Germanium materials will now be studied too. These materials may give a variety of advantages in industrial applications – ultimately leading to more efficient processing and lower energy requirements in many different settings.

Professor Andy Mullis, Director of the Institute for Materials Research at the University of Leeds, will lead ground-based studies against which the space experiments will be compared. A 6.5 metre ‘drop-tube’ at Leeds simulates the microgravity experienced in space, dropping objects and studying them in free-fall – after all, everything in orbit around the Earth is essentially just in an extended free fall.

Professor Mullis’ team will also be conducting simulations of the expected solidification morphologies, using a technique called phase-field modelling. The Leeds group is world-leading in using such simulations with unprecedented spatial resolution.

Why these materials

Nickel-aluminides (Ni-Al) are potential materials for high temperature structural materials, particularly for applications such as in gas turbines, where lightweight, high temperature operation can deliver much greater energy efficiency.
Al-Ni catalysts are used extensively in industrial hydrogenation reactions (everything from pharmaceuticals to margarine) but are attracting a lot of attention in applications such as H-fuel cells, where the Ni-catalysts can replace platinum at vastly lower cost.

Aluminium-silicide (Al-Si) is one of the main classes of light weight structural alloys, with Al-alloys being used extensively in aerospace applications. It is a material that has been around for a long time and is relatively well understood – however, Al- and Al-Mg alloys with very small (0.1-0.2%) additions of scandium can dramatically improve modulus and stiffness. NEQUISOL will study a 0.2% Sc alloy (and a reference Al-Si alloy without Sc additions) to help elucidate the strengthening mechanism of this ‘magic ingredient’.

Silicon-Germanium

The interest in Si-Ge is as a thermoelectric material for energy harvesting – i.e. converting ‘waste’ heat into power. This strand of the project is being strongly industrially led, with the industrial partner specifying the material composition.