Accession Number : ADA332794

Title :   Shock-Induced and Shock-Assisted Reaction Synthesis of Materials.

Descriptive Note : Final rept. 1 Mar 93-30 Aug 97,

Corporate Author : GEORGIA INST OF TECH ATLANTA

Personal Author(s) : Thadhani, Naresh ; Royal, Tyrus ; Lee, Jong-Heon ; Counihan, Partrick ; Namjoshi, Shantanu

PDF Url : ADA332794

Report Date : 24 NOV 1997

Pagination or Media Count : 25

Abstract : The beneficial effects of shock-compression of powders and solid-state chemical reactions were utilized to synthesize Ti-Si and Ti-A1 intermetallics, Ti-B and Ti-C ceramics, and Ti-Si:Ti-A1 composites. Time-resolved stress measurements provided evidence for shock-initiation of reactions in 53% dense Ti-Si powders, based on increased wave speed and volume expansion (due to formation of intermetallic product with higher elastic modulus) measured at shock-pressures exceeding 1.5 GPa. These measurements combined with controlled recovery experiments, revealed the effect of powder morphology and the influence of property differential between reactants on the reaction threshold, demonstrating the dominant role of mechanochemical processes on shock-initiation of chemical reactions. Shock-synthesis was applied to form beta-phase C3N4 compound using cyano group precursors mixed with azides and iodides. The post-shock reaction behavior of shock-densified Ti-C and Ti-Si powder mixtures was observed to reveal enhanced kinetics with activation energies for diffusion of reactants being lowered by four-to-six times. It was also demonstrated that the shock-activated dense-packed state of powders (elemental reactants or compounds) can be used as an intermediate step for fabrication of net-shaped TiC ceramics, nanocrystalline Ti5Si3 intermetallics, and compositionally-graded composites.

Descriptors :   *COMPOSITE MATERIALS, *SHOCK, *SOLID STATE CHEMISTRY, STRESSES, VELOCITY, RECOVERY, REACTION KINETICS, POWDERS, PRECURSORS, THRESHOLD EFFECTS, MODULUS OF ELASTICITY, CERAMIC MATERIALS, RESPONSE, CHEMICAL REACTIONS, INPUT OUTPUT DEVICES, CYANIDES, AZIDES, ACTIVATION ENERGY, IODIDES, MORPHOGENESIS.

Subject Categories : Physical Chemistry
      Ceramics, Refractories and Glass

Distribution Statement : APPROVED FOR PUBLIC RELEASE