The search for new diamonds

Diamonds are formed in the planet’s deep layers, under high pressures and temperatures. However, for industrial use, the first choice is to use more accessible artificial diamonds. Developed in laboratories, artificial diamonds have many applications.

Agência FAPESP – Diamonds are a girls’s best friend, as immortalized in Marilyn Monroe’s famous movie Gentlemen Prefer Blondes. Diamonds are formed in the planet’s deep layers, under high pressures and temperatures.

However, for industrial use, the first choice is to use more accessible artificial diamonds. Developed in laboratories, artificial diamonds have many applications, from cutting tools to rock drilling for oil extraction in the pre-salt layer.

Investigating potential applications and gaining new knowledge about artificially produced diamonds—in addition to nanotubes, another carbon derivative—are the main objectives of the Thematic Project entitled “New materials, studies and applications of CVD diamond, diamond-like-carbon (DLC) and nanostructured carbon obtained by chemical vapor deposition,” funded by FAPESP.

Coordinated by Evaldo José Corat, a researcher at the National Space Institute’s (INPE) Associated Laboratory of Sensors and Materials, the project involves three different areas that share a common point: they are all carbon materials produced through chemical vapor deposition.

The process, known internationally as CVD, involves the activation of a gas, which can be performed by altering the temperature, generating plasma or, in the case of diamonds, through the use of a heated filament.

The reactive gas causes materials to be deposited on surfaces, a process known as “growth” that is used to produced CVD diamonds (different than those used to make jewelry), DLC (diamond-like carbon) and carbon nanotubes.

Researchers have known about CVD since the 1950s. In the INPE studies, the CVD process involves a mixture of gases with a low methane concentration. The mixture is placed in a hot filament reactor—the equipment used for the research uses tungsten filaments—at temperatures of over 2,300°C. When the gas is activated, the diamond is deposited on a substrate, forming a diamond film.

Even though the process sounds simple, producing diamonds in laboratories takes time. “The growth rate is from 2-4 microns per hour. We can grow diamonds that are very thin until relatively thick ones,” said Corat.

In a previous project involving the use of CVD diamonds in soil drilling bits, the researchers grew diamonds with a diameter of 2 millimeters, a process that took over a month.

Diamond is known to be the hardest material existing in nature, and the specimens produced in laboratories maintain this characteristic. These diamonds are also excellent heat conductors and are transparent in the part of the electromagnetic spectrum ranging from X-ray to far-infrared wavelengths.

These characteristics can be exploited in the protection of the surfaces of space equipment, microelectronic devices and cutting tools. CVD diamond films can be used as anti-friction layers in automotive and aeronautic motors to protect surfaces in aggressive environments and in glass and ceramic materials processing.

CVD diamonds can also be used in the fields of medicine and dentistry as dental drill bits or in ultrasound equipment, in implant connectors and as electrodes for runoff and water treatment. 

Corat and his team of researchers have taken on the challenge of increasing the growth of CVD diamond tubes around thin tungsten wires. “We are scheduling production to obtain relatively large quantities. We want to get abrasive tools, including high-durability drill bits for perforating rock and hopefully also for drilling oil wells. The challenge is to make production economically viable,” he explained.

Another important objective of the project is the development of interfaces for the deposition of CVD diamond on steel and tool materials. The studies showed that an interface of vanadium carbide and of iron borides obtained through a thermodiffusion process (diffusion produced by heat) is able to promote the growth of high-quality diamond. Another application being studied involves the use of diamond as an electrode for electrochemistry that could be used, for example, in the treatment of water. 

The group coordinated by Corat is also researching the process of growing nanodiamonds for potential use with a new concept involving solar cells that convert heat directly into electricity, offering solar energy at a lower cost than is possible with silicon cells. This line of basic research was performed by a group that is coordinated by INPE. This research involves calculations for the growing process and identification of the material and seeks to understand how and why nanodiamonds grow.

Nanotubes

In the Thematic Project, the researchers study the growth of carbon nanotubes in an aligned shape over a surface (usually nanotubes are presented in dust form). The main application was in structural compositions or, in other words, to make in-line nanotube deposits on carbon fiber.

“We are performing studies for tiering the process, still only on the laboratory scale for our own use,” explained Corat. The researchers are seeking to make their process as fast and agile as possible to make larger composite samples to aid in their studies.

Another area of work being undertaken is the development of techniques for making surfaces of aligned nanotubes hydrophobic (water-repellant) and hydrophilic (water-attractant).

Using the oxygen plasma technique, the researchers transformed the surfaces of aligned carbon nanotubes into a super-hydrophilic material. Moreover, using a laser treatment that evaporates part of the nanotubes, these researchers made the surface super-hydrophobic. One possible application is filtering water and oil for possible use in oil platform filters. However, the study involving carbon nanotubes to which Corat calls the most attention is the one investigating the interaction of nanotubes with cells.

“We grew cells and hydroxyapatite crystals on nanotubes, which improved the cell growth process. It’s a line we intend to continue investing in,” he said. Hydroxyapatite is an important mineral for bones and teeth.
 
Vladimir Airoldi, a principal investigator in the Thematic Project, was the winner of the 2011 FINEP Innovation Prize.