Time-Resolved X-Ray Diffraction Study of Solid Combustion Reactions

• Published in: Science (American Association for the Advancement of Science) 1990-09, Vol.249 (4975), p.1406-1409
• Main Authors: Wong, Joe, Larson, E. M., Holt, J. B., Waide, P. A., Rupp, B., Frahm, R.
• Format: Article
• Language: English
• Subjects: 360100 - Metals & Alloys; 400201 - Chemical & Physicochemical Properties; 400800 - Combustion, Pyrolysis, & High-Temperature Chemistry; Alloys; CHEMICAL REACTIONS; Chemistry; COBALT; COHERENT SCATTERING; COMBUSTION; Combustion research; Combustion. Flame; DATA; DIFFRACTION; ELEMENTS; Exact sciences and technology; EXPERIMENTAL DATA; Flame propagation; Gases; General and physical chemistry; High temperature; INFORMATION; Innovations; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MATERIALS SCIENCE; METALS; NICKEL; NUMERICAL DATA; OXIDATION; PHASE TRANSFORMATIONS; Reactants; SCATTERING; Synchrotron radiation; Synchrotrons; THERMOCHEMICAL PROCESSES; TITANIUM; TRANSITION ELEMENTS; Wave diffraction; Wave fronts; X ray diffraction
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.249.4975.1406

Real-time synchrotron diffraction has been used to monitor the phase transformations of highly exothermic, fast self-propagating solid combustion reactions on a subsecond time scale down to 100 milliseconds and in some instances to 10 milliseconds. Three systems were investigated: Ti + C → TiC; Ti + C + xNi →TiC + Ni-Ti alloy; and Al + Ni → AlNi. In all three reactions, the first step was the melting of the metal reactants. Formation of TiC in the first two reactions was completed within 400 milliseconds of the melting of the Ti metal, indicating that the formation of TiC took place during the passage of the combustion wave front. In the Al + Ni reaction, however, passage of the wave front was followed by the appearance and disappearance of at least one intermediate in the afterburn region. The final AlNi was formed some 5 seconds later and exhibited a delayed appearance of the (210) reflection, which tends to support a phase transformation from a disordered AlNi phase at high temperature to an ordered CsCl structure some 20 seconds later. This new experimental approach can be used to study the chemical dynamics of high-temperature solid-state phenomena and to provide the needed database to test various models for solid combustion.