The high potential energy release of boron makes it a prime candidate for a high enthalpy fuel or as a fuel additive to solid propellant formulations, as well as a prospective additive for tailoring energy release rates of explosive grains. The problem of long ignition delays at atmospheric and lower pressures, caused by a combination of factors which include the necessity to remove a combustion-retarding oxide layer from the particles, a high vaporization temperature for the pure boron substrate, and slow condensation kinetics, have generally precluded the use of boron for energetic fuel applications at these pressures. This report summarizes experiments which measure an order of magnitude shorter ignition delays than previously published 1 atm data, for pure and reduced oxygen and oxygen mixtures with water vapor and fluorine compounds (H, HF) over 8.5 to 34 atm and 2000 to 3000 K. Ignition delays in the 300 to 500 microsecond range are observed in a shock tube, decreasing with increasing temperature, and increasing twofold when oxygen concentrations are reduced to 5% in Ar. Fluorine, from dissociated 1% SF6 in O2, is seen to decrease ignition delays by a factor of 1.7 compared to pure oxygen. A combustion chamber is used at a peak pressure of 157 atm and temperature in excess of 2800 K to study ignition delays at higher pressures than are possible in the shock tube. Endwall emission spectra of BO2 are recorded for comparison with boron ignition models.

Boron-Based Fuel-Rich Solid Rocket Propellant Technology is a professional book that systematically introduces the latest research progress for boron-based fuel-rich solid propellants. It covers surface modifications, coating and agglomerating techniques, granulation, and characterization of amorphous boron powders, and its application to fuel-rich solid rocket propellants. Technologies for controlling the processing methods and combustion performance of fuel-rich propellants are examined, and the book concludes with a summary of the research progress in boron-based fuel-rich solid propellants and a look forward to the foreseeable development trends of military applications.

Combustion of single boron particles, about 75 microns in diameter, from a crystalline powder sample has been studied. Particles were ignited by being dropped through a focused laser beam in several oxidizing gases over a range of pressures. In pure oxygen, in air, and in O2/Ar(20/80), particles were merely preheated to a temperature about 2000K; ignition took place spontaneously after a measurable induction period. Quantitative values of both the induction period and the subsequent self-sustained combustion period are listed. It was shown that the classical theory of ignition and combustion can account for all three observed burning modes: metastable surface reaction during the preignition period, rapid self-sustained diffusion-combustion, and decaying combustion. Previously reported reaction-rate and ignition-limit data were used for quantitative estimates of parameters pertaining to the three regimes. (Author).

Experimental and theoretical studies are reported which provide basic information concerning the ignition and combustion processes of amorphous, crystalline, gamma-irradiated, and LiF coated single boron particles. All studies were conducted at ambient pressure with particles or particle agglomerates between 30 and 50 microns in diameter. Boron particles were suspended in a levitation cell and ignited using a pulsed neodymium-doped laser. The burning processes were recorded in either self-light or shadowgraph. Within experimental error the burning time for amorphous boron and spherodized crystalline boron are the same indicating that the initial particle character has a minor effect on the liquid droplet burning time combustion process. Analytical studies were made concerning the unsteady heating of boron particles subjected to high flux rates. The theory of nonequilibrium thermodynamics is explored and it is demonstrated that engineering calculations based on the equilibrium hypothesis may predict mass flux rates 50 to 100 percent in error. (Author).

Single particles of pure crystalline boron were injected into streams of hot oxidizing gases, generated by a gas-burner, at atmospheric pressure. Two powder samples, having average diameters of 34.5 and 44.2 microns respectively, were studied. Gas temperatures were varied from 1800 to 2900K, mole fractions of oxygen from 0.08 to 0.37, and mole fractions of water from 0 to 0.21. Qualitative photographic and spectroscopic observations of the particle combustion process are described. Ignition temperatures of boron particles, 1850 to 2000K, were found to be independent of particle size and of gas temperature, but affected by the composition of ambient gases. Burning times, ranging from 10 to 40 msec, were found to be inversely proportional to the mole fraction of oxygen in the gas, to decrease slightly with increasing gas temperature, and to decrease substantially with addition of water vapor. Experimentally determined burning rates are correlated with diffusion rates of gaseous oxidants to the surface of the burning particle. (Author).