Diamonds richly valuable to developing new materials, say Army research scientists

March 18, 2014

Diamonds are more than "a girl's best friend," as the saying goes. U.S. government researchers have proposed with them for years in research projects and have had explosive results ... literally.

Today, the U.S. Army Research Laboratory uses diamonds as part of a 10-year effort to investigate innovative approaches that enable revolutionary advances for the protection of Soldiers and their equipment, particularly in dynamic environments, where extremely high pressure and high temperatures commonly exist.

An ARL research team lead by Dr. Jennifer Ciezak-Jenkins uses the diamond anvil cell technique, an experimental method, to subject small amounts of material to very high pressures when squeezed between two diamonds. Ciezak-Jenkins, a research scientist, leads the Diamond Anvil Cell research laboratory.

"It's a brave new world in materials science," Ciezak-Jenkins said, "in which the material properties can be tailored to meet the specific needs of the Army system or Soldier in the field."

Dr. John Beatty agrees. He manages ARL's Materials in Extreme Dynamic Environments Collaborative Research Alliance. Under his watch, this alliance will build the capability to design revolutionary materials for protecting Soldiers. He said "No longer will we take materials 'off the shelf' to put into armor systems. Instead materials will become an integral part of the design process itself."

ARL is conducting experiments with the diamond anvil cell that exert pressure at 300 gigapascals and above, ". . . which is in the range of pressures seen when a high-explosive material detonates, or when an armor system gets hit in the field," explained Beatty.

The interest in high-pressure science grew out of the laboratory's mission to study material behavior at conditions similar to those experienced during detonations. Over the past few years, the research has broadened to include a wider variety of materials because under extreme conditions material behavior does not always follow the conventional chemistry and physics rules learned in high school. For example, nitrogen gas, the primary component of the Earth's atmosphere, transforms into a structure very similar to diamond at 140 GPa and 4220 °F and it has been proposed that hydrogen transforms into a metal at conditions still being explored.

"At the bottom of the Marianna's trench, the deepest part of the ocean, the pressure is about 0.1 GPa so we're 3,000 times more than that. But it's not enough to just expose materials to the pressure, we also have to understand how the material properties are changing in response to the extreme conditions," Beatty said.

He said because the diamond anvil is transparent, ARL researchers can use several methods to examine the material while it is subjected to high pressure and/or high temperature such as laser-based spectroscopies and various forms of x-ray spectroscopy.

"The analysis from these experiments allows us to understand the changes occurring at the atomic level in response to these conditions. Armed with this information, we can then explore routes to stabilize these materials at lower pressures as well as techniques to synthesize the material without the pressure or temperature as is needed for larger scale production," said Ciezak-Jenkins.

From this technique, researchers can understand a great deal about the material and how it may be beneficial to Army systems.

"We can use this information to validate models that are built-up from quantum mechanics to describe these materials. It's a very important step in our quest to design materials to perform well when subjected to these extreme environments in the field," said Beatty.

Diamond anvils are diamonds that have been polished flat by a laser-guided process. Besides withstanding high pressure, they're strong and hard, and they're good electrical insulators and heat conductors. Diamond anvil cells have been used to simulate the high pressure in a variety of extreme environments, like the high pressures at the Earth's core, or even the pressures that exist at inception on a nuclear blast.

Although it has advanced and evolved since, this experimental technique became popular in the late 1950s with researchers at the National Standards Board, now known as NIST, the National Institute of Standards and Technology. Also growing during that time was a new field of study slowly embraced by industry and academia that would become the seed for future Army materiel: Materials Science. It's the scientific study of the properties and applications of materials and how those properties are determined by the material's composition and structure, both macroscopic and microscopic.

Besides the diamond anvil cell, ARL uses another experimental apparatus, the Kolsky bar, to understand the behavior of material under high pressure and strain, or impact.

"In armor systems, protection materials are struck with a lot on energy in a small spot. Our enemies hope that that energy can basically go right through the armor system and damage the innards, and yes, that also means wounding or killing our Soldiers inside. So we need to be able to examine materials when we load them up with energy real fast!"

"In a Kolsky bar, we send a high-stress pulse down a solid metal bar, then smash a sample between that bar and another one, and then examine the stress pulses that result. And those stress pulses tell us a lot about what happened to the material we were smashing," said Beatty.

To improve that insight, ARL has changed how the Kolsky bar is used.

"Until recently, the systems we used were kind of limited into how fast they could deform or smash the materials we were looking at." He said an ARL team led by Dr. Dan Casem has worked to modify the instrumentation used on the bars, which are typically as big around as the handle on a baseball bat. With the new optical instrumentation from ARL, the bars can now be made as thin as some human hairs. By making the bars smaller, "we can actually smash them in a way to get even higher deformation rates, at orders of magnitude greater than before, making the extreme environment during the test much more realistic."

ARL's work with Johns Hopkins University and Argonne National Lab is also utilizing similar high strain-rate tests with even more advanced diagnostics. They're using the Department of Energy's beam line to produce short pulse, high energy x-rays during these experiments.

"These x-rays will allow us to take snapshots of many things going on inside the materials we are testing, such as phase changes, defect changes, etc.," Beatty said. These experiments are needed to peer inside these materials during the experiments to validate the multiscale models that the ARL team is building from the atomic level up.

"We need these advanced techniques to both discover what we need to model, as well as to validate those models, to make sure they are real. Experiments matter and are critical to expanding our abilities to design materials," said Beatty, "and the experimental capabilities of the Army's Rodman Materials Laboratory at Aberdeen Proving Ground will be critical in achieving our goals."

This is the second of a two-part series based on the article "Designing Materials" that appeared in the March/April 2014 edition of the RDECOM Army Technology Magazine.

 

Last Update / Reviewed: March 18, 2014