A new combination of materials was developed that can prevent weaknesses in body armor. By adding a tiny amount of silicon to boron carbide (a material commonly used for making body armor) bullet-resistant gear can be made substantially more resilient to high-speed impacts.
Boron carbide, dubbed “black diamond,” is a manmade material that ranks second below another synthetic material called cubic boron nitride for hardness. Unlike cubic boron nitride, however, boron carbide is easier to produce on a large scale. Also, boron carbide is harder and lighter than other armor materials like silicon carbide, making it an ideal choice for protective gear, particularly ballistic vests.
Despite boron carbide’s many desirable qualities, its main shortfall is that it can damage very quickly upon high-velocity impact. Boron carbide is very good at stopping bullets traveling less than 900 meters per second, so it can block bullets from most handguns quite effectively; however, above this critical speed, boron carbide suddenly loses its ballistic performance and is not as effective.
Scientists know high-speed jolts cause boron carbide to have phase transformations — a phenomenon where a material changes its internal structure such that it is in two or more physical states, like liquid and solid, at the same time. The bullet’s impact thus converts boron carbide from a crystalline state where atoms are systematically ordered to a glass-like state where atoms are haphazardly arranged. This glass-like state weakens the material’s integrity at the site of contact between the bullet and boron carbide.
Previous work using computer simulations predicted that adding a small quantity of another element, such as silicon, had the potential to make boron carbide less brittle. To simulate the initial impact of a high-speed bullet, the researchers made well-controlled dents on boron carbide samples with a diamond tip with a width smaller than a human hair. Then, under a high-powered electron microscope, they looked at the microscopic damage that was formed from the blows. They found that even with tiny quantities of silicon, the extent of phase transformation went down by 30%, noticeably reducing the damage from the indentation.
Although silicon serves well to enhance boron carbide’s properties, more experiments need to be done to know if other elements, like lithium and aluminum, could also improve boron carbide’s performance. In the near future, these stronger cousins of pure boron carbide will find other non-military applications such as in nuclear shields. Using a touch of silicon in boron carbide changes the spacing between atoms and the empty spaces created might be good sites to absorb harmful radiation from nuclear reactors.