Engineers with the U.S. Army’s Picatinny Arsenal in New Jersey are developing a new paint formula that will tell soldiers if their ammunition is safe to use just by looking at the color.
‘Thermal Indicating Paints’ uses thermochromic polymers to detect temperature ranges that ammunition was exposed to during transport or storage, much like a mood ring changing color in response to the body temperature of the wearer.
The thermochromic element changes the wavelength of light when it is exposed to different temperatures, but Picatinny’s challenge is ensuring the color change is permanent.
“We have formulas that change color within the designated temperature ranges, but our biggest challenge is maintaining long-term stability of a coating,” says James Zunino, project Officer/materials engineer, Armament Research, Development and Engineering Center (ARDEC). “We have to develop a paint that will survive in military operating conditions, including harsh temperatures and wind blasts.”
EXPOSURE TO EXTREME TEMPERATURES
Ammunition is often exposed to extreme temperatures during transport, storage and pre-positioning. Tests showed that Middle East combat operations temperatures inside munition containers can exceed 190°F, which can compromise the integrity and performance of the round and increase safety risks for the soldier.
When ammo is exposed to high temperatures for extended periods, it can rapidly deplete the propellant stabilizer, which creates a potential for auto-ignition. Zunino says there have been documented incidents of failures caused by thermal exposures during Operation Desert Storm and recent conflicts in Iraq and Afghanistan.
“Thermal indicating paints can help prevent warfighters from using ammo that may have been compromised by exposure to environmental conditions outside of design limits,” he says. “It could reduce the amount of accidents that could happen, it can reduce the logistical burden of transporting and storing munitions, and it gives increased survivability to the soldier.”
ARDEC uses in-house testing equipment at Picatinny to test various formulations of the paints. The team is partnering with the New Jersey Institute of Technology to develop a formula that can provide an irreversible, permanent color change to indicate specific temperature ranges on munitions.
WORKING CLOSELY TOGETHER
“Working with NJIT has been exceptional,” says Giuseppe Di Benedetto, ARDEC technical lead / chemical engineer. “We work very closely with one another and we’re actively meeting with them.”
The team is developing cost effective and commercially available formulations that can detect four heat ranges in Fahrenheit: 145-164, 165-184, 185-200, and above 200. The first round to be tested will likely be the 30mm high explosive round.
The paint coating has potential to cost less, as in pennies per application compared to costly temperature gauges the Army now uses on its larger caliber ammunition stocks.
“We’re starting with the 30mm family of ammo because they aren’t expensive enough rounds to deem the use of a costly temperature gauge or monitor. The savings are bigger because it’s low value, high volume assets,” says Zunino, adding that the team plans to have a formula ready for trial testing within the year.
Thermal indicating paints are just one of many “smart” coatings the Picatinny team is developing for military applications. The team started working on thermal indicating coatings in 2008 and has made considerable progress.
The team is also exploring non-military applications for thermal-indicating paints that can help firefighters, law enforcement personnel and first responders to emergencies.