Metal-sulfur combustion

A number of metal-sulfur compounds have been synthesized in the present investigation aa self-propagating, high-temperature synthesis (SHS) process. Equilibrium calculations indicate that a large number of metals react with sulfur energetically, yielding adiabatic flame temperatures sufficiently high to support self-sustained flame propagation. To permit the combustion process to proceed entirely in the condensed phase, the pressure of the environment has to be kept at elevated levels (1-20 MPa) for most of the metal-sulfur mixtures studied. Computed adiabatic flame temperatures of some of the metal-sulfur reactions exceed 5000 K (Ca-S, Sr-S, Ba-S). The present experimental investigation was carried out to verify the equilibrium calculations. Seven metals have been studied (i.e., Mg, Si, Ti, Mn, Cr, Zn, and Mo). Samples are prepared by melting the metal-sulfur precursor mixture, which eliminates any trapped gas so that the density of the sample approaches the theoretical value. X-ray diffraction analysis of the products shows that the synthesized samples have a high purity and that the reactions are close to completion. Ignition temperatures for the metal-sulfur mixtures were found to be in the range of 350-600 degrees C. Flame speeds measured for several of the metal-sulfur mixtures ranged from 5 to 10 mm/s. The large-energy-release, low-ignition temperatures and high adiabatic flame temperatures associated with metal-sulfur combustion make this process also promising for a variety of "energetic" applications.