New record set for world's most heat resistant material

December 22, 2016 by Caroline Brogan
Discovery paves the way for new types of heat shields. Credit: NASA

Researchers have discovered that tantalum carbide and hafnium carbide materials can withstand scorching temperatures of nearly 4000 degrees Celsius.

In particular, the team from Imperial College London discovered that the melting point of hafnium carbide is the highest ever recorded for a material. Being able to withstand temperatures of nearly 4000°C could pave the way for both materials to be used in ever more extreme environments, such as in heat resistant shielding for the next generation of hypersonic space vehicles.

Tantalum carbide (TaC) and hafnium carbide (HfC) are refractory ceramics, meaning they are extraordinarily resistant to heat. Their ability to withstand extremely harsh environments means that refractory ceramics could be used in thermal protection systems on high-speed vehicles and as fuel cladding in the super-heated environments of nuclear reactors. However, there hasn't been the technology available to test the of TaC and HfC in the lab to determine how truly extreme an environment they could function in.

The researchers of the study, which is published in the journal Scientific Reports, developed a new extreme heating technique using lasers to test the heat tolerance of TaC and HfC. They used the laser-heating techniques to find the point at which TaC and HfC melted, both separately and as mixed compositions of both.

They found that the mixed compound (Ta0.8Hf0.20C) was consistent with previous research, melting at 3905°C, but the two compounds on their own exceeded previous recorded melting points. The compound TaC melted at 3768°C and HfC melted at 3958°C.

Space race

The researchers say the new findings could pave the way for the next generation of hypersonic vehicles, meaning spacecraft could become faster than ever.

Dr Omar Cedillos-Barraza, who is currently an Associate Professor at the University of Texas - El Paso, carried out the study while doing his PhD at Imperial's Department of Materials.

Dr Cedillos-Barraza said: "The friction involved when travelling above Mach 5 – – creates very high temperatures. So far, TaC and HfC have not been potential candidates for hypersonic aircraft, but our new findings show that they can withstand even more heat than we previously thought - more than any other compound known to man. This means that they could be useful materials for new types of spacecraft that can fly through the atmosphere like a plane, before reaching hypersonic speeds to shoot out into space. These materials may enable spacecraft to withstand the extreme heat generated from leaving and re-entering the atmosphere."

Examples of potential uses for TaC and HfC could be used in nose caps for spacecraft, and as the edges of external instruments that have to withstand the most friction during flight.

Currently, vehicles going over Mach 5 speeds do not carry people, but Dr Cedillos-Barraza suggests it may be possible in the future.

Dr Cedillos-Barraza added: "Our tests demonstrate that these materials show real promise in the engineering of space vehicles of the future. Being able to withstand such extreme temperatures means that missions involving hypersonic spacecraft may one day be manned missions. For example, a flight from London to Sydney may take about 50 minutes at Mach 5, which could open a new world of commercial opportunities for countries around the world."

Explore further: Scientists create a ceramic resistant to extreme temperatures

More information: Omar Cedillos-Barraza et al. Investigating the highest melting temperature materials: A laser melting study of the TaC-HfC system, Scientific Reports (2016). DOI: 10.1038/srep37962

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antialias_physorg
3.7 / 5 (3) Dec 22, 2016
hypersonic space vehicles.

This phrase always strikes me as vaguely ridiculous. What exactly is the speed of sound in space?
Mark Thomas
5 / 5 (4) Dec 22, 2016
Importantly, these materials might make excellent nuclear thermal rocket engine parts. This is because the thrust and efficiency of a rocket engine are determined in large part by its temperature. The higher the temperature, the better. While their high density is a drawback, it is possible they could be used as coatings. An investigation of the Hf-Ta-C system suggests more work remains to be done to find the most heat resistant material.

http://journals.a...2.020104
mangaba12000
5 / 5 (2) Dec 22, 2016
"...For example, a flight from London to Sydney may take about 50 minutes at Mach 5...
I think that are something wrong here
London to Sydney about 17000 km
Mach 5 about 6200 km/h
javjav
not rated yet Dec 22, 2016
@antialias I agree the article is a bit vague, but the key is when it says "like a plane" . In this context, "Hypersonic space vehicles" means vehicles that can use oxygen from the atmosphere in their transition to space, rather than bringing the oxidizer with them. That could make a huge difference in weight, opening the door to much cheaper -- even single stage- launchs. What I miss is a mention to previous temperature records to compare. I believe heat shield materials in real production (that you can buy) can withstand around 2000 degrees, with the latest lab prototypes being around 3000. Then, this material seems to be very remarkable. 4000 degrees would be a huge advance
Mark Thomas
5 / 5 (1) Dec 22, 2016
javjav, these materials have been known for a long time, but are very difficult to work with. For example, injection molding isn't going to work because no mold can hold them in liquid form.

I was a little surprised the HfC had the higher melting temperature as opposed to the HfC mixed with TaC, which previously was thought to hold the record.
Coolbreeze
5 / 5 (2) Dec 23, 2016
Mark Thomas ( it is possible they could be used as coatings.)
Hafnium was used in the lunar lander's descent engine nozzle during the Apollo missions.
antialias_physorg
not rated yet Dec 23, 2016
I agree the article is a bit vague, but the key is when it says "like a plane"

Yeah...it was more of a tongue-planted-firmly-in-cheeck comment.

Funnily it turns out you *can* calculate the speed of sound in space (since space is not a perfect vacuum). In our local neighborhood (solar system and thereabouts) the speed of sound in space currently comes out to about 9000m/s (or about 32000km/h). So by a pedantic definition even the speeds mentioned in the article wouldn't make them hypersonic (not even supersonic) 'space planes'.

http://physics.st...in-space
tblakely1357
not rated yet Dec 23, 2016
Hmm, the denser the medium the faster the speed of sound. Sound travels much faster in water than in the air. I doubt you could even measure the speed of sound in space since even if there are stray atoms floating around there isn't enough of them close enough together to transmit sound.
antialias_physorg
not rated yet Dec 23, 2016
Speed of sound goes up with the temperature. The 'gas' in the solar system is pretty 'hot'.
You can measure sound in any medium - even not-quite-empty space. The sound waves are just very low frequency. The laws are the same as for a denser gass (probabilistic interaction between 'neighboring' atoms).
http://www.scienc...-hear-it
The site has a video that models the sound right after the big bang (which to this day is still ongoing, but at a very, very, very low pitch by now)
In space the interaction probabilities are very low. But with large volumes you do get wave propagation (which is basically what sound is)

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