Use of armor ceramics by the U.S. military is rapidly increasing. The manufacture of armor ceramics requires extensive use of energy, raw materials, processing, capital equipment, and consumables. The environmental impact of processing these materials is considerable in terms of greenhouse gases produced, release of volatile organic compounds (VOC), and consumption of natural resources. Industry needs to identify which steps in the processing route can be modified to prevent pollution without affecting the function of the materials. The non-oxide ceramics have shown significant promise for these applications.
The objective of this project was to use the principles of surface chemistry, ceramic processing, and ballistic testing to develop new processing methods that eliminate the use of VOCs in the manufacture of non-oxide armor ceramics. These new processing techniques were assessed in terms of chemistry, microstructure, mechanical properties, and ballistic performance, which must be similar to that of conventionally processed material of the given composition.
Non-oxide armor ceramics are generally made from powders that are mixed/milled, formed, and densified. Many factors are important in their processing such as particle size of the powder, type and amount of sintering aid, temperature and pressure during densification, and methods of mixing and blending. The performance of armor ceramics has been shown to vary greatly with different processing methods, starting powders, and sintering additives. Among the factors believed to be of importance to ballistic behavior is the grain boundary phase in the final material. In this project, new methods of processing non-oxide ceramics were developed to significantly reduce the use of VOCs. Maintaining and controlling the oxygen content of powders in these processes was studied. Ballistic tests using threats of appropriate caliber were performed to determine the effect of process changes on ballistics.
In this project, it was shown that both Cercom pressureassisted- densified (PAD) boron carbide (B4C) and Cercom PAD silicon carbide (SiC) can be produced by water-based processing and that their properties are similar to that of the same materials processed with organic liquids (i.e., VOCs). Ballistic screening tests on water-processed PAD B4C and PAD SiC were performed using threats envisioned for future body armor. The water-processed material passed the screening test and was comparable to conventionally processed PAD B4C and PAD SiC. More extensive ballistic testing needs to be performed to confirm these results and to determine the effects of different flaw populations. In addition, further tests using different threats need to be conducted.
Eliminating or reducing the use of VOCs without affecting ballistic performance in the production of non-oxide ceramics will reduce the environmental impact of manufacturing these materials. The release of VOCs into the atmosphere produces ozone, which is a significant environmental problem. The technology also can ease the transition to forming methods that are near net-shape, which are of particular importance due to difficulties in machining armor ceramics. (SEED Project Completed - 2004)