Banded structures in unstable combustion synthesis

Li, H. P.

doi:10.1557/jmr.1995.1379

Cited by 18 publications

(11 citation statements)

References 18 publications

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“…17, Zr-Al-CuNi multilayers develop a regular, banded microstructure after reaction. This structure is similar, in several respects, to products formed in bulk materials that undergo pulsating SHS reactions [197]. The banded product microstructure of this foil is composed of dark and light phases, with the former having a larger grain size.…”

Section: -D (Oscillatory) Instabilitiessupporting

confidence: 52%

Reactive multilayers fabricated by vapor deposition: A critical review

2015

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a b s t r a c t a r t i c l e i n f o Available online xxxxReactive multilayer thin films are a class of energetic materials that continue to attract attention for use in joining applications and as igniters. Generally composed of two reactants, these heterogeneous solids can be stimulated by an external source to promptly release stored chemical energy in a sudden emission of light and heat. In this critical review article, results from recent investigations of these materials are discussed. Discussion begins with a brief description of the vapor deposition techniques that provide accurate control of layer thickness and film composition. More than 50 reactive film compositions have been reported to date, with most multilayers fabricated by magnetron sputter deposition or electron-beam evaporation. In subsequent sections, we review how multilayer ignition threshold, reaction rate, and total heat are tailored via thin film design. For example, planar multilayers with nanometer-scale periodicity exhibit rapid, self-sustained reactions with wavefront velocities up to 100 m/s. Numeric and analytical models have elucidated many of the fundamental processes that underlie propagating exothermic reactions while demonstrating how reaction rates vary with multilayer design. Recent, time-resolved diffraction and imaging studies have further revealed the phase transformations and the wavefront dynamics associated with propagating chemical reactions. Many reactive multilayers (e.g., Co/Al) form product phases that are consistent with published equilibrium phase diagrams, yet a few systems, such as Pt/Al, develop metastable products. The final section highlights current and emerging applications of reactive multilayers. Examples include reactive Ni(V)/Al and Pd/Al multilayers which have been developed for localized soldering of heat-sensitive components.

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Section: -D (Oscillatory) Instabilitiessupporting

confidence: 52%

Reactive multilayers fabricated by vapor deposition: A critical review

2015

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“…Nevertheless, it is likely that many of the same factors influencing spin behavior during powder SHS 19,[53][54][55][56][57][58] are germane. Previous works explain that unsteady propagation can result from the differences in rates of heat conduction and mass transport.…”

Section: Modes Of Propagationmentioning

confidence: 99%

Rare-earth transition-metal intermetallic compounds produced via self-propagating, high-temperature synthesis

et al. 2010

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Several binary intermetallic compounds-each containing a rare-earth (RE) element paired with a transition metal (TM)-were prepared by self-propagating, high-temperature synthesis (SHS). Thin multilayers, composed of alternating Sc or Y (RE element) and Ag, Cu, or Au (TM), were first deposited by direct current magnetron sputtering. Once the initially distinct layers were stimulated and caused to mix, exothermic reactions propagated to completion. X-ray diffraction revealed that Sc/Au, Sc/Cu, Y/Au, and Y/Cu multilayers react in vacuum to form single-phase, cubic B2 structures. Multilayers containing Ag and a RE metal formed cubic B2 (RE)Ag and a minority (RE)Ag 2 phase. The influence of an oxygen-containing environment on the reaction dynamics and the formation of phase were investigated, providing evidence for the participation of secondary combustion reactions during metal-metal SHS. High-speed photography demonstrated reaction propagation speeds that ranged from 0.1-40.0 m/s (dependent on material system and foil design). Both steady and spin-like reaction modes were observed.

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“…38 Further, unsteady modes are predicted to become more likely with decreasing propagation velocity. 39 Self-propagating reactions of Al/Zr foils were studied by time-resolved x-ray phase contrast imaging. The technique has previously been used to study the mechanism of exothermic W/Si reactions, 25 but in this study we are particularly interested in the evolution of the reaction front.…”

Section: A Unsteady Propagation Modesmentioning

confidence: 99%

Self-propagating reactions in Al/Zr multilayers: Anomalous dependence of reaction velocity on bilayer thickness

Barron

Kelly

Kirchhoff

et al. 2013

Journal of Applied Physics

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Effect of varying bilayer spacing distribution on reaction heat and velocity in reactive Al/Ni multilayers J. Appl. Phys. 105, 083504 (2009); 10.1063/1.3087490Modeling of the self-propagating reactions of nickel and aluminum multilayered foils Deposition and characterization of a self-propagating CuO x / Al thermite reaction in a multilayer foil geometry High temperature, self-propagating reactions are observed in vapor-deposited Al/Zr multilayered foils of overall atomic ratios 3 Al:1 Zr and 2 Al:1 Zr and nanoscale layer thicknesses; however, the reaction velocities do not exhibit the inverse dependence on bilayer thickness that is expected based on changes in the average diffusion distance. Instead, for bilayer thicknesses of 20-30 nm, the velocity is essentially constant at $7.7 m/s. We explore several possible explanations for this anomalous behavior, including microstructural factors, changes in the phase evolution, and phase transformations in the reactant layers, but find no conclusive explanations. We determine that the phase evolution during self-propagating reactions in foils with a 3 Al:1 Zr stoichiometry is a rapid transformation from Al/Zr multilayers to the equilibrium intermetallic Al 3 Zr compound with no intermediate crystalline phases. This phase evolution is the same for foils of 90 nm bilayer thicknesses and foils of bilayer thicknesses in the range of 27 nm to 35 nm. Further, for foils with a bilayer thickness of 90 nm and a 3 Al:1 Zr overall chemistry, the propagation front is planar and steady, in contrast to unsteady reaction fronts in foils with 1 Al:1 Zr overall chemistry and similar bilayer thicknesses. V C 2013 AIP Publishing LLC. [http://dx.

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Banded structures in unstable combustion synthesis

Cited by 18 publications

References 18 publications

Reactive multilayers fabricated by vapor deposition: A critical review

Reactive multilayers fabricated by vapor deposition: A critical review

Rare-earth transition-metal intermetallic compounds produced via self-propagating, high-temperature synthesis

Self-propagating reactions in Al/Zr multilayers: Anomalous dependence of reaction velocity on bilayer thickness

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