David P. Adams, Ph.D.
The Materials Science Center
Sandia National Laboratories
Host: Prof. Jerry Floro
Talk Title: Reactive Multilayer Thin Films that Exhibit Self-propagating, High temperature Formation Reactions
Date: Monday, September 14, 2015
Time: 4:00 to 5:00
Room: Wilsdorf 101
Refreshments: 3:30 to 4:00
Reactive, bimetallic multilayer thin films are a class of energetic materials that continue to attract attention for use as heat sources 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. Reactive multilayers fabricated with a nanometer-scale periodicity exhibit rapid, self-propagating reactions with tailored wavefront velocities up to 100 m/s.
With this presentation, I describe recent experiments and supporting model simulation predictions that probe a few key properties of reactive multilayers. First, we explore the requirements for multilayer ignition and the processes that underlie the start of reactions. Studies of point ignition involve single pulse laser irradiation, wherein laser pulse duration is varied from millisecond to femtosecond duration in order to access a range of local heating rates. A highlight of this study is the demonstration that reactant melting is not required for initiating reactions; high temperature reactions can initiate through solid-state diffusion. In addition, recent high-speed optical imaging, thermometry and time-resolved transmission electron microscopy studies of self-propagation reaction waves are described. These experiments explore the wavefront dynamics and phase transformations associated with propagating chemical reactions and how these vary with multilayer design. Of note, highly exothermic reactive multilayers, with DHo ~ -70 to -110 kJ/mol at., undergo steady reactions characterized by a single propagation speed. Moderately exothermic multilayers, such as Co/Al and Ni/Ti, are characterized by 2-d (spin) wavefront instabilities. A phenomenological model is presented to explain the large temperature variations near an unsteady reaction front.
BIO: David Adams received a B.A. in Physics from the University of Virginia in 1989 and a Ph.D. in Materials Science & Engineering from the University of Michigan in 1994. He held a postdoctoral position at Sandia National Laboratories in Albuquerque, NM, from 1994 to 1997 under the guidance of Dr. T.M. Mayer. In 1997 he joined Sandia National Laboratories as a Senior Member of the Technical Staff, where he worked in the Thin Films, Vacuum and Electronic Packaging Department. David Adams is currently a member of Sandia’s Materials Science Center. He is an active member of AVS and MRS.
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