Experiments in space

Materials World magazine
,
19 Dec 2018

New alloys could be developed from an experiment to be carried out on the International Space Station in 2021, as Ellis Davies reports.

An experiment looking into complex fluids will be one of three carried out on the International Space Station (ISS) in 2021. Researchers at Strathclyde University, UK, will carry out work in the micro gravity environment of the ISS to create new alloys and medicines that cannot be made on Earth. The two other experiments will be on age-related loss of muscle mass by the University of Liverpool, and spaceflight-induced muscle loss by the Universities of Nottingham and Exeter, all in the UK.

Complex fluids are binary mixtures that coexist between two phases – a liquid with dispersed solid particles, bubbles or droplets of another immiscible liquid. The fluids are applicable to a wide range of fields, including mechanics, chemicals, petrochemicals, nuclear, energy, and inorganic and organic materials.

Many alloys, before solidifying, pass through a liquid or fluid state, which involves particles dispersed in an external liquid. The ability to control the dispersed phase in alloys is regarded, according to researchers, as crucially important to the improvement of industrial processes. It is also relevant to nanotechnologies and related products.

Dr Marcello Lappa, of the Department of Mechanical and Aerospace Engineering at Strathclyde University, told Materials World, ‘The performance of many materials is linked to their microscopic structure. Their electrical and/or mechanical properties can be ascribed to characteristics such as high disorder, caging and particle networking. Acquiring the ability to precisely control the distribution of particles will lead to new inorganic materials with improved electrical and mechanical properties.’ Lappa also points out that similar concepts can be applied to organic materials, such as crystals of proteins, which can be used in the development of new drugs and medicines.

Into space

On Earth, gravity causes sedimentation – in heavy particles – or flotation – in light particles – in the dispersion, which separates this phase from the fluid matrix. This causes a concentrated layer of particles to form on the bottom or top of the container, which can prevent the production of materials with the desired properties. This can be overcome using inertial and thermovibrational effects. The latter can force particles initially dispersed in the liquid to self-assemble and form highly ordered, high-resolution structures. The thermovibrational effect is produced every time a fluid is subjected to vibrations in non-isothermal conditions, such as applying a temperature difference to the fluid container.

‘By properly tuning the frequency of applied vibrations and their direction with respect to the applied temperature difference, it is possible to drive the particles to specific sub-regions of the container, where they accumulate to form well-defined geometric objects resembling the perfection of the typical quadrics of projective geometry – open or compact surfaces such as cylinders, paraboloids, ovoids and conical surfaces,’ Lappa explained. These shapes are regarded as more stable and give more desirable properties.

The gravitational effect prevents performing these experiments in normal conditions. Therefore, the micro gravity environment of the ISS is ideal. ‘Simulating microgravity conditions on Earth is extremely difficult, or impossible in many cases,’ said Lappa. ‘Even though fluid motion induced by gravity could be minimised by reducing the size of the fluid container, there is no way to prevent particles from undergoing sedimentation. In the future we plan to attempt a possible application of this technique in normal gravity conditions, at very small scales.’

Forming a knowledge of planets

Lappa also mentioned that these experiments could shed some new light on the mechanisms at play in the early stages of formation of asteroids and planets. ‘For decades, theorists have had problems elaborating models to explain the growth of asteroids and planets starting from a population of dust grains in a protoplanetary gas-dust disk,’ he said.

‘A crucial step in planet formation is the growth of solid bodies in the sub-millimetre to metre size range – too large to condense directly from the gas and too small to interact meaningfully through mutual gravitation. The existence of planets in our solar system demands that some growth process once operated in that size regime, but the underlying cause-and-effect relationships have not been clarified yet. We think that the thermovibrational effect may contribute to support asteroid and planet formation.’

Over the next two years, researchers will be working on three different tasks in the build-up to the launch. Firstly, they will undertake a series of numerical simulations to determine which experiments will be performed in space, including determining precise information about the duration of each single experiment and its power requirements power. Researchers will also perform tests and experiments to identify the ideal visualisation techniques to be used in space to monitor the particle accumulation phenomena.

Lappa says particles will be illuminated using a laser beam, and related images will be transferred from the ISS to Earth. Finally, the team will monitor the hardware manufacturing process. This hardware will be launched at the end of 2021, and installed in a microgravity science glovebox already onboard the ISS. As soon as the hardware is ready, it will be powered up and the experiments will start.