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In nature, diamonds form deep within the Earth over billions of years. This process requires exceptionally high pressure environments and temperatures above 1,000 ℃.
Our international team created two different types of diamonds at room temperature and in minutes. It is the first time that diamonds have been successfully produced in a laboratory without added heat.
Our findings are published in Small magazine.
There is more than one diamond shape
Carbon atoms can bond together in different ways to form different materials, including soft black graphite and hard transparent diamond.
There are many well-known forms of carbon with graphite-like bonds, including graphene, the thinnest material ever measured. But did you know that there is also more than one type of carbon-based material with a diamond-like bond?
In a normal diamond, the atoms are arranged in a cubic crystal structure. However, it is also possible to arrange these carbon atoms so that they have a hexagonal crystal structure.
This different shape of diamond is called Lonsdaleite, named after Irish crystallographer and Royal Society member Kathleen Lonsdale, who studied the structure of carbon using X-rays.
There is a lot of interest in Lonsdaleite, as it is predicted to be 58% harder than regular diamond, which is already considered the hardest natural material on Earth.
It was first discovered in nature at the Canyon Diablo meteorite crater site in Arizona. Tiny amounts of the substance have since been synthesized in the laboratory by heating and compressing graphite, using a high-pressure press or explosives.
Our research shows that both lonsdaleite and normal diamond can be formed at room temperature in a laboratory setting by simply applying high pressures.
The many ways to make a diamond
Diamonds have been synthesized in the laboratory since 1954. Then, General Electric’s Tracy Hall created them using a process that mimicked the natural conditions within the earth’s crust, adding metal catalysts to accelerate the growth process.
The result was high-pressure, high-temperature diamonds similar to those found in nature, but often smaller and less perfect. These are still produced today, mainly for industrial applications.
The other main method of diamond manufacturing is through a gas-chemical process that uses a small diamond as a “seed” to grow larger diamonds. Temperatures of around 800 ℃ are required. Although growth is quite slow, these diamonds can be enlarged and relatively free from defects.
Nature has provided suggestions for other ways to form diamonds, including during the violent impact of meteorites on Earth, as well as in processes such as high-speed asteroid collisions in our solar system – creating what we call “extraterrestrial diamonds.”
Scientists have been trying to understand exactly how extraterrestrial or impact diamonds are formed. There is some evidence that, in addition to high temperatures and pressures, sliding forces (also known as “shear” forces) could play an important role in triggering their formation.
An object hit by shear forces is pushed in one direction up and in the opposite direction down.
An example would be pushing a deck of cards left up and right down. This would force the deck to slide and the cards to scatter. Hence, the shear forces are also called “sliding” forces.
Making diamonds at room temperature
For our work, we designed an experiment in which a small fragment of graphite-like carbon was subjected to both extreme shear forces and high pressures, to help diamond formation.
Unlike most previous work on this front, no additional heating was applied to the carbon sample during compression. Using advanced electron microscopy, a technique used to acquire very high resolution images, the resulting sample was found to contain both normal diamond and Lonsdaleite.
In this never-before-seen arrangement, a thin diamond “river” (about 200 times smaller than a human hair) was surrounded by a “sea” of Lonsdaleite.
The arrangement of the structure is reminiscent of the “shear bands” seen in other materials, in which a small area undergoes intense and localized stress. This suggests that cutting forces were critical to the formation of these diamonds at room temperature.
Resistant nuts to break
The possibility of making diamonds at room temperature, in a few minutes, opens up numerous production possibilities.
In particular, making Lonsdaleite “harder than diamond” in this way is exciting news for industries where extremely hard materials are needed. For example, diamond is used to coat tips and blades to extend the life of these tools.
The next challenge for us is to lower the pressure required to form diamonds.
In our research, the lowest pressure at room temperature where diamond formation was observed was 80 gigapascals. This is the equivalent of 640 African elephants on the toe of a dance shoe!
If both diamond and lonsdaleite could be produced at lower pressures, we could make more, faster, and cheaper.
Images used courtesy of Pexels / Leah Kelley
This article was republished by The Conversation under a Creative Commons license. Read the original article.
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