Uncovering secret structure to safer explosives

October 18, 2018, Lawrence Livermore National Laboratory
Supercomputer simulations of shock-induced explosive reactions suggest that the microstructure of heterogeneous solid explosive materials impact performance and safety. Credit: Lawrence Livermore National Laboratory

A team of scientists at Lawrence Livermore National Laboratory (LLNL) has shown that the structure of microscopic pores in high explosive materials can significantly impact performance and safety. These findings —  published recently as the cover article in the journal Propellants, Explosives, Pyrotechnics —  open the door to the possibility of tuning high explosives by engineering their microstructure.

"The funny thing about explosives is that they have these little defects and pores and holes," said research scientist Keo Springer, lead author on the paper and researcher at LLNL's High Explosives Applications Facility. "It turns out that that's an important part of what makes them work. Explosive performance, in a broad sense, isn't just a chemistry question, it's a microstructure question."

In most high explosives, detonation is initiated through a process where pores get compressed by a shockwave. When a collapses, it creates a hotspot capable of initiating a chemical reaction in the microscopic crystalline grains of explosive material. This research focused on an explosive compound called HMX, which is known to be more sensitive and more dangerous to work with than other explosives. The fundamental question at the root of this study was whether it makes a difference if the pores are located in the interior of the grains or on their surface.

"We found out that when pores are at the surface, they speed up the reaction," Springer said. "We also discovered that if a shockwave hits a number of surface pores at once, they bootstrap each other. It's an explosive party, and they party well together."

In addition to pore location, the team examined whether it makes a difference if the porosity is distributed across many small pores or across fewer larger pores. While they showed that many small pores can work together to accelerate one another's burning, they also were able to identify a threshold where pores become so small that the reaction is extinguished.

This examination was conducted in a series of numerical simulations on LLNL supercomputers with the multi-physics code, ALE3D. Next steps for the research team—Springer, along with LLNL scientists Sorin Bastea, Al Nichols, Craig Tarver and Jack Reaugh—include verifying that the numerical simulations capture the real physical and chemical processes. A direct way to do that is to conduct micro-scale experiments to quantify pore collapse mechanisms and reactivity.

"Validation is the tough part," Springer said. "Ideally, we would need a really good magnifying glass and the ability to stop time. We're talking about sub-micron resolution with a shutter speed on the order of nanoseconds. What's neat is that the research community is starting to work on this.

"If we can engineer initiation properties into the microstructure of explosives, it would be a game changer for industry and for the safety of the nuclear stockpile. But we have a long way to go to realize that vision. This type of research is very important, but just one of the first steps."

Explore further: Simulations improve understanding of crystalline HMX explosives

More information: H. Keo Springer et al. Modeling The Effects of Shock Pressure and Pore Morphology on Hot Spot Mechanisms in HMX, Propellants, Explosives, Pyrotechnics (2018). DOI: 10.1002/prep.201800082

Related Stories

Army's new find lowers accidental stockpile detonation

May 1, 2018

Scientists at two major national laboratories have demonstrated a new method for testing explosives stored in weapons stockpiles, a step they say will help reduce accidental detonation and ensure the weapons perform as expected.

Imaging high explosive detonators

March 8, 2017

Lawrence Livermore National Laboratory (LLNL) scientists and collaborators at Los Alamos National Laboratory (LANL) for the first time have taken 3-D snapshots of operating high explosive detonators.

Recommended for you

Asteroids, hydrogen make great recipe for life on Mars

March 26, 2019

A new study reveals asteroid impacts on ancient Mars could have produced key ingredients for life if the Martian atmosphere was rich in hydrogen. An early hydrogen-rich atmosphere on Mars could also explain how the planet ...

Cool Earth theory sheds more light on diamonds

March 26, 2019

A QUT geologist has published a new theory on the thermal evolution of Earth billions of years ago that explains why diamonds have formed as precious gemstones rather than just lumps of common graphite.

New cellulose-based material represents three sensors in one

March 26, 2019

Cellulose soaked in a carefully designed polymer mixture acts as a sensor to measure pressure, temperature and humidity at the same time. The measurements are completely independent of each other. The ability to measure pressure, ...

Physicists discover new class of pentaquarks

March 26, 2019

Tomasz Skwarnicki, professor of physics in the College of Arts and Sciences at Syracuse University, has uncovered new information about a class of particles called pentaquarks. His findings could lead to a new understanding ...

Study finds people who feed birds impact conservation

March 26, 2019

People in many parts of the world feed birds in their backyards, often due to a desire to help wildlife or to connect with nature. In the United States alone, over 57 million households in the feed backyard birds, spending ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.