Nano technology marches on
December 6, 2011
- Engineers at Picatinny Arsenal have forged sintered objects from nanopowders.
- Engineers use Field Assisted Sintering Technology (FAST) to dramatically reduce forging time.
A year ago, engineers at Picatinny Arsenal were busy processing and refining nanomaterials.
This year, they have made the next logical step in their ongoing work by forging objects from those nanopowders.
Objects they have created include rounded plates.
These objects can be used in creating prototypes of new equipment and devices or, alternatively, pieces can be cut from these basic shapes for use as components in other systems now under development.
"Typically, in everyday use, a pile of powder is somewhat useless," said Joseph Paras, a materials engineer at Picatinny Arsenal. "The powder must be converted into a useful form."
Given the mission focus at Picatinny Arsenal, possible future applications for nanomaterials may include enhanced lethality for current and future weapons systems, such as better penetrators for large and small caliber projectiles and warhead liners, Paras said.
"Because the technology is not material limited, things like nanostructured boron carbide as a SAPI (Small Arms Protective Insert) plate and transparent ceramics for missile domes are also possible," Paras suggested.
The powder is converted into solid objects through a process called sintering. The traditional method of sintering exposes the materials to high temperatures for a long period of time.
"During that time, the grains of the material will tend to grow," said Paras. "Smaller particles will be absorbed into larger ones."
As the nanoparticles consolidate into larger chunks during the traditional sintering process, they lose their novel properties, thus defeating the purpose of refining the materials into nanopowders in the first place.
To counteract this dilemma, Picatinny engineers use a novel technique dubbed as the Field Assisted Sintering Technology (FAST).
"The power of FAST is that the sintering times are drastically reduced and the (nanopowder) grains are not given enough time to grow significantly."
Nanopowder is placed in a die in the shape of the final object. Then the die with the nanopowder is placed into the sintering machine.
The machine runs an electric current through the material while subjecting it to extreme pressure with a ram and anvil.
The temperature that the nanopowders are subjected to can vary depending on the type of material being worked on and the desired properties of the final object, but, according to Paras, the FAST system can operate at temperatures as high as 2400 degrees Celsius.
In their research, Picatinny engineers use nanopowders made from common metals and other basic substances.
The allure of working and conducting research with nanomaterials is that elements and compounds that are well understood display novel properties in their nanoparticle state.
Some differences include a change in color, strength, transparency, and conductivity. Not all of the properties of the elements are known when they are in their nano form and basic research into nanomaterials continues in universities and laboratories worldwide.
Nanomaterials are engineered from naturally occurring elements and compounds.
The raw material is fed either as a liquid or a conventionally sized powder into a plasma flame where it is completely vaporized and then rapidly cooled with a cold quench gas.
The resulting nanopowder is the same as what went in but it is now a collection of ultrafine particles that range in size from 10-200 nanometers.
Nanopowders are collections of these ultrafine particles that can be as small as 100 atoms in diameter.
"To put in perspective, the average diameter of a human hair is approximately 100 microns," said Paras.
At around 100 atoms in diameter, the nanoparticles are roughly 10,000 times smaller.