. 24/7 Space News .
Physicists 'undiscovered' technetium carbide
by Staff Writers
Moscow, Russia (SPX) Apr 01, 2016

Tetrahedral (blue) and octahedral (red) voids in a two-layer packing and their position in the unit cell (bottom). Image courtesy MIPT's press office. For a larger version of this image please go here.

An international team of scientists led by Artem Oganov, Head of Computational Materials Discovery Lab at MIPT, has proven that technetium carbide does not exist - it was pure technetium that was mistakenly considered as such. This is important from the view point of chemistry of transition metal carbides which are in many ways considered as promising substances. The article was published in RSC Advances.

Transition metals are elements whose electrons responsible for forming chemical bonds are located in a specific position within the atom: they sit on d-orbitals. The list of such metals also includes well-defined iron and copper, as well as radioactive technetium, which the scientists managed to synthesize only in the mid-20th century using accelerators, and later extracted from radioactive waste.

Compounds of transition metals with carbon are called carbides, they are usually hard, heat-resistant substances, with a varying ratio of carbon and metal content: there are, for example, a chromium carbide CrC2 and a chromium carbide Cr23C6.

An important question is what carbides can be synthesized in principle, which intrigues not just the theorists, but also engineering professionals and chemical technology specialists. While engineers strive for strong and heat resistant coatings for cutting tools, the chemists are attracted by carbides of transition metals for their ability to act as chemical catalysts similar to expensive platinum plates.

There is no universal and simple way to predict the existence of certain chemical compounds to date, this is why the substance thought to be technetium carbide turned out to be a controversial one: some researchers claimed that they managed to synthesize it, others doubted the correctness of the published data.

Using an available USPEX algorithm, a group of scientists headed by Artem Oganov (Professor of Skoltech and the State University of New York, and Head of Lab at MIPT, Professor of the Russian Academy of Sciences) including Dr.Qinggao Wang (MIPT and Anyang Normal University, Anyang, People's Republic of China) have modeled a number of transition metal carbides and convincingly demonstrated that carbide technetium cannot be obtained.

What was done and how
To find out whether low-carbon carbides (containing much fewer carbon atoms then metal atoms) are stable, the authors succeeded in calculating the two key parameters: the energy of metal atoms' mutual interconnection (ECoh) and the energy for introducing carbon into a transition metal (EC-dis) - that is, the energy required to insert carbon in the crystal lattice.

Whenever the EC-dis value is negative (which means that carbon insertion is favorable), carbon atoms occupy the octahedral voids (internodal space) in the metal lattice. In such metals as ruthenium or osmium both values are too great, and these metals are too inert to form more or less stable compounds: they cannot form carbides in principle.

To assess the stability of high-carbon compounds, the authors have calculated the energy required to form monocarbide (ETMC). Some of ETMC values were negative, meaning that the formation of such monocarbides was energetically favorable, and they must be stable when actually synthesized.

Among the metals that can be successfully fused with carbon are titanium, vanadium, zirconium, niobium, hafnium and tantalum. For them, the monocarbide formation energy and the carbon insertion energy are both negative, i.e., these processes are energetically favorable, which means monocarbides of these metals exist and are stable.

Iron, chromium, magnesium and technetium belong to the Green Group, having positive formation energy for FeC, CrC, MnC and TcC, therefore, these monocarbides are unstable. In addition, the energy of carbon insertion is also greater than zero, therefore having it in the lattice is energy-inefficient: it turns out that the previously "discovered" technetium monocarbide stumbles at the fundamental laws of nature, therefore one can only synthesize Tc10C , Tc8C and Tc6C.

This is the outcome of USPEX simulation algorithm, and it is perfectly consistent with the findings of researchers who have actually obtained these compounds.

False trail
Physicists have also been able to explain the data that was previously interpreted in favor of technetium monocarbide. Previously, the key evidence was represented by a radiograph showing two indicative peaks.

The X-ray Phase Identification Method is based on the fact that different substances have different interplanar spacing (atom balls of various substances have different diameters, and hence the thickness of layers that they form). Therefore, every substance produces a unique line pattern on a radiograph. By analyzing the location and intensity of the lines it is possible to draw a conclusion about how much of a certain substance is contained in the sample.

However, when they modeled the x-ray scattering process in pure technetium, scientists saw a very similar picture: therefore, the previous group might have mistakenly assumed the pure element's trace for that of technetium carbide. Not only "undiscovery" of the disputed compound allows to answer the question about an exotic substance, but it also systematizes our knowledge about transition metal carbide prospects in general.

"Chemistry of transition metal carbides is controversial - there may be different articles on the same material arguing - some 'for', and others 'against' - the possibility of its existence. In this paper we added a modicum of clarity as to the causes of the formation of these compounds, and created a foundation for future research and quest for new carbides useful in practical applications.

Besides, sometimes an "undiscovery" of a substance such as TcC at the right moment can help save time and efforts of contemporary and future researchers in the field," Oleg Feya, the study co-author and a Computational Materials Discovery Lab fellow, commented.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only


Related Links
Moscow Institute of Physics and Technology
Space Technology News - Applications and Research

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
A new model for how twisted bundles take shape
Amherst MA (SPX) Mar 28, 2016
In the current issue of Nature Materials, polymer scientists Greg Grason, Douglas Hall and Isaac Bruss at the University of Massachusetts Amherst, with Justin Barone at Virginia Tech, identify for the first time the factors that govern the final morphology of self-assembling chiral filament bundles. They also report experimental results supporting their new model. At the molecular level, G ... read more

Moon Mission: A Blueprint for the Red Planet

The Moon thought to play a major role in maintaining Earth's magnetic field

The Lunar Race That Isn't

Earth's moon wandered off axis billions of years ago

Martian winds slowly build enormous mounds over billions of years

'Mixed Reality' Technology Brings Mars to Earth

Opportunity moves to new locations to the southwest

NASA: Manned mission to Mars still 'long way' off

New DNA/RNA Tool to Diagnose, Treat Diseases

ASU to develop the next generation science education courseware for NASA

Space-Related Budget Requests for FY17

NASA Selects American Small Business, Research Institution Projects for Continued Development

Has Tiangong 1 gone rogue

China's 1st space lab Tiangong-1 ends data service

China's aim to explore Mars

China to establish first commercial rocket launch company

Russia launches cargo ship to space station

Cargo ship reaches space station on resupply run

Unmanned Cygnus cargo ship launches to ISS on resupply run: NASA

Cygnus Set to Deliver Its Largest Load of Station Science, Cargo

Roscosmos Says Reports on Sea Launch Project Sale Might Be True

Water System Tested on Crew Access Arm at KSC

NASA's 'Spaceport of the Future' Reaches Another Milestone

India to launch 22 satellites by single rocket in May

Map of rocky exoplanet reveals a lava world

Instrument Team Selected to Build Next-Gen Planet Hunter

NASA's Spitzer Maps Climate Patterns on a Super-Earth

'Smoothed' light will help search for Earth's twins

Students learn astrophysics through mixed-reality computer simulation

For the first time scientists can observe the nano structure of food in 3-D

A new model for how twisted bundles take shape

More efficient system for the synthesis of organic compounds

The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.