SBIR-STTR Award

Boron has significant potential as a high energy density ingredient in ramjet propellants and fuels. This is due to boron's high heat of combustion and low atomic weight. For a ramjet ducted rocket, theoretical volume specific impulses of 1600- 1800 sec g cm-3 have been reported for a fuel rich boron solid propellant, 45 % greater than the best hydrocarbon composition. Boron's high ignition temperature and surface oxide layer make it difficult to ignite and sustain combustion. Magnesium treating boron employing MACH I's proprietary reactive milling technology should improve the ignition and combustion characteristics and realize this potential. Magnesium will be present as a surface coating and penetrated into the bulk particle as magnesium-boron inter-metallic compounds. Magnesium readily ignites due to its lower ignition temperature vs. boron. It should also improve the combustion characteristics since magnesium will remove the boron oxide layer (which inhibits boron combustion) by reducing it to elemental boron. Ignition temperature and combustion properties will be studied as a function of magnesium level. Dr. Edward Dreizin of the New Jersey Institute of Technology will employ his previously developed hotwire ignition measurement technique and constant volume explosion apparatus. The minimum required magnesium level (maximum energy density) will be determined

Boron has significant potential as a high energy density fuel in munitions and propellants. Its superior energy density makes it attractive as a fuel component in conventional solid propellants, as well as fuel slurries for ramjet applications. For a ramjet ducted rocket, theoretical density impulses of 1600-1800 sec-g/cm3 have been reported, 45% higher than the best hydrocarbon formulation. Boronís potential has not been realized because it is difficult to ignite and resists complete combustion. Our Phase I project demonstrated that boron ignition and combustion were dramatically improved by magnesium coating to form MgB composites. Magnesium ignites at a lower temperature and facilitates boron ignition by heating the boron particle to its ignition temperature. Ignition temperature improved from 1800 to 1000K as determined by our Phase I partner, Dr. Edward Dreizin of the New Jersey Institute of Technology. Under the same conditions, pure boron did not ignite at all. Magnesium also promotes sustained combustion of boron by removing boron oxide, which inhibits combustion, as it is formed. Another advantage of MgB is the dramatic reduction of viscosity, compared with pure boron, when used to form mixes with hydroxy-terminated polybutadiene, thus permitting the use of higher levels of boron in fuel mixes. MgB composites were provided to Mark Mason and Mark Swett of NAVAIR Weapons Division, China Lake, CA, and to Talley Defense Systems (TDS). Mr. Swett found composite performance in enhanced blast munitions was superior to competitive materials. The results were positive to the point of considering whether the data should be secured in an interim secrecy order. This determination is in progress. More information can be provided by Mr. Swett subject to security considerations. Dr. Mason has confirmed these enhanced blast observations and has observed ìa profound affect on the ballistic properties of solid rocket propellantsî as well as improved ignition and combustion. TDS also confirms this in enhanced blast testing, finding increased thermal output for MgB compared to pure boron. Swett, Mason, and Talley all evaluated 10 atom % MgB. Phase I results show higher Mg levels significantly improve combustion vs.10% and should be evaluated in the proposed Phase II program to achieve boronís potential in enhanced blast munitions and propellants.

Keywords:
Boron, Magnesium, Enhanced Blast Munitions, High Impulse Propellants