A time-resolved diffraction study of the Ta--C solid combustion system

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Journal of Materials Research; (United States)

DOI:https://doi.org/10.1557/JMR.1993.1533· OSTI ID:5447163

Larson, E M; Wong, J; Holt, J B; Waide, P A; Nutt, G; Rupp, B; Terminello, L J ^[1]

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1. Lawrence Livermore National Laboratory, University of California, P.O. Box 808, Livermore, California 94551 (United States)

The formation of TaC and Ta[sub 2]C by combustion synthesis from their elemental constituents has been studied by time-resolved x-ray diffraction (TRXRD) using synchrotron radiation. The reactions have been followed with a time resolution down to 50 ms. Since the adiabatic temperatures for both reactions are well below any liquidus temperature in the Ta--C phase diagram, no melting occurs and these combustion reactions occur purely in the solid state. The phase transformations associated with these reactions are followed by monitoring the disappearance of reactant and appearance of product powder diffraction peaks in real time as the reaction front propagates through the combusting specimen. In the synthesis of TaC, the results show the formation of the subcarbide (Ta[sub 2]C) phase as an intermediate. In the synthesis of Ta[sub 2]C, the reaction proceeds directly to the product with no discernable intermediate Ta--C phase within a 50 ms time frame. The chemical dynamics associated with the combustion synthesis of TaC may be described by an initial phase transformation to hexagonal Ta[sub 2]C arising from carbon diffusion into the Ta metal lattice. As more carbon is available this intermediate subcarbide phase, which has one-half of its octahedral interstices occupied by the carbon, further transforms to the cubic TaC final product, in which all octahedral sites are now occupied. The time-resolved data indicate that the rate of formation of Ta[sub 2]C is a factor of two faster than that of TaC.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5447163
• Journal Information: Journal of Materials Research; (United States), Journal Name: Journal of Materials Research; (United States) Vol. 8:7; ISSN JMREEE; ISSN 0884-2914
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201* -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
BREMSSTRAHLUNG
CARBIDES
CARBON COMPOUNDS
CHEMICAL REACTIONS
COHERENT SCATTERING
COMBUSTION
DIFFRACTION
ELECTROMAGNETIC RADIATION
OXIDATION
PHASE TRANSFORMATIONS
RADIATIONS
REFRACTORY METAL COMPOUNDS
RESOLUTION
SCATTERING
SYNCHROTRON RADIATION
SYNTHESIS
TANTALUM CARBIDES
TANTALUM COMPOUNDS
THERMOCHEMICAL PROCESSES
TIME RESOLUTION
TIMING PROPERTIES
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION