This project focuses on developing high performance basalt fibre, enhancing the technical value of fibre material with an innovative concept.
Did you know there is a type of rock you can turn into fibres strong enough to weave into a fabric? No, I’m not spinning a yarn: basalt, the substance that more than 90% of all volcanic rock is made from, can be melted and processed into fibres.
There was a brief spat of interest into basalt fibre materials in the 1960s, centred around basalt-rich regions of the USA and the Soviet Union. It was thought that these weavable strands made from rock could be used as reinforcement for plastics, significantly enhancing the performance of corresponding composites. But by the 1970s interest had waned, and basalt fibre was all but abandoned in favour of fibreglass and carbon fibre.
This fibre has seen a revival in recent years, due to its superior mechanical properties compared to fibreglass, and its low price compared to carbon fibre, and also its environmental benignity. It is no surprise then that basalt fibre has found various applications in transportation, construction, and other fields, most commonly as a reinforcing material in plastic and concrete. Basalt fibre also boasts green manufacturing and easy recycling, high resistance to chemicals, and a wide working temperature making it suitable as a safe replacement for asbestos.
Despite recent interest, studies aiming to enhance the properties of basalt fibres are hardly numerous compared to the wealth of information surrounding its counterparts: glass and carbon fibre materials. A research team led by Professor Peng-Cheng Ma at the Xinjiang Technical Institute of Physics and Chemistry at the Chinese Academy of Sciences is one of the research groups driving progress in this field.
One of the unknowns regarding basalt fibre is how to control its tensile strength. Manufactured basalt fibre tends to have a lower tensile strength than it theoretically should. This effect is thought to be because of defects, like microscopic scratches, crystals, and voids, but what causes these defects to form?
In 2019, Professor Ma’s team published a paper which established links between the chemical composition of basalt fibres and their mechanical properties. By comparing samples from seven different basalt fibres produced by Chinese manufacturers, the team discovered that the chemical composition was actually the dominating effect in the tensile strength.
Because basalt fibres are made directly from basalt rock, regulating this is as simple as carefully sourcing basalt with the right composition. Basalt can vary in composition but is largely made from a mixture of oxides of silicon, iron, aluminium, calcium, and magnesium. Ma’s team found that basalt with a higher Al2O3 content resulted in fibres with a higher tensile strength. They also found that fibres with more Fe2+ and less Fe3+ had better properties, which can be controlled by performing the manufacturing process in an inert atmosphere. In both cases, it was possible to observe the microstructural defects of these compositional changes using electron microscopy.
The team also discovered that the sizing – a substance applied to the fibres after manufacture – can protect the structures by literally filling in the micro-scale scratches and cracks on the surface of these fibres, thus enhancing the strength of the basalt fibre.
Professor Ma’s team have also made valuable contributions to some of the more unique properties of basalt fibre. In a 2017 study, they deposited a thin layer of carbon-based nanocomposites on the surface of basalt fibres using a chemical vapour deposition process. Basalt fibre is normally electrically insulating, but by depositing a thin layer of carbon onto the surface of a basalt fibre strand and embedding the strand into a polymer, Ma’s team discovered that the carbon layer allowed the strand to conduct electricity.
This material also exhibited an effect known as piezoresistance – that is, the resistance of material was changing as the material was placed under strain, thought to be the result of fibres breaking in the material. This intriguing property may mean that carbon-coated basalt fibres could both reinforce and be used to monitor structural damage in composites.
In another study, Ma’s team developed a method to grow carbon nanotubes directly on the surface of woven basalt fibre fabric. By layering the resulting material and curing the layers into a multi-layered fabric, the team created a material with excellent electromagnetic shielding properties.
Carbon nanotubes constitute the majority of the electromagnetic shielding, but nanotubes on their own are notoriously difficult to disperse evenly across a polymer because they tend to clump together. By synthesising the nanotubes directly onto basalt fibres, Prof Ma and his team were able to overcome this problem: because the nanotubes are fixed to the large basalt fibres, they cannot re-agglomerate during the processing of nanocomposites.
“Now the team is looking at a more ambitious application of basalt fibre for the construction of a lunar base.”
Another study in 2019 by the team confirmed the ability to create a superhydrophilic substance from basalt fibre. Superhydrophilic materials are characterised by the way they interact with water: when water meets their surface instead of a droplet forming, the water spreads out into a thin film. These materials are therefore very desirable for separating oil-water mixtures. The material was created by coating basalt fibres in a natural product extracted from konjac glucomannan, a water-soluble material derived from the roots of the elephant yam that is used to make tofu.
Underwater, this material was shown to be superoleophobic, meaning it repels oils very effectively, whilst soaking up water. The material was furthermore not affected by corrosive acid or alkaline liquids, meaning it could operate in harsh conditions — potentially even as a barrier material used to contain and clean up oil spills. Best of all, this material is both economical and ecological: it’s much cheaper than the pricy nanoparticle-based alternatives, and is made from plants and rocks.
Most recently, the team has been looking at more ambitious applications for basalt fibre materials. Given the high cost of sending materials into space, it is very desirable to be able to build from local materials if humans ever manage to set up permanent residence on the moon. Given that basalt is found all across the moon, Professor Ma’s team was interested to know if it would be possible to process moon rock to create a continuous basalt fibre for use in construction of a moon base.
The team used a lunar soil simulant which they confirmed had a similar chemical composition to basalt found on the Earth. By melting and spinning the lunar soil simulant, the team confirmed that lunar soil can be converted efficiently into continuous fibre with a tensile strength of more than 1,400 MPa, comparable with that of the commercial basalt fibres found on the Earth.
Which industries stand to gain the most from improvements in basalt fibre materials?
Basalt fibre has been used in transportation, building, and composite industries. It is expected to be an ideal material for the construction of a multi-functional lunar/Mars base for deep-space exploration.
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