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

Abstract

The formation of TaC and Ta2C 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 (Ta2C phase as an intermediate. In the synthesis of Ta2C, the reaction proceeds directly to the product with no discernible 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 Ta2C 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 Ta2C is a factor of two faster than that of TaC.

Burning velocities in catalytically assisted self-propagating high-temperature combustion synthesis systems

“…Experimental results of catalytically assisted and unassisted SHS as a function of pressure for the Ta/C system, where i is the mole fraction of transport agent i in the combustion chamber (mole basis of gas-phase species). The results of Shkiro et al [17] and Larson et al [16] are results of unassisted Ta/C SHS studies. Error bars denote the uncertainty in the determinations of burning velocity in the current work.…”

“…2 and 4. Larson et al [16] examined SHS of Ta/C using in situ X-ray diffraction at pressures of approximately one atmosphere. The authors also examined two different size tantalum particles (Ta ϭ 2 m and Ta Ͻ 1 m) and found an increase in the Fig.…”

“…Experimental results of the effects of gas-phase transport agents on burning velocities for the catalytically assisted Ta/C SHS system. The data of Larson et al [16] are the results of a study of an unassisted Ta/C SHS system. 969 CATALYTICALLY ASSISTED SHS burning velocity with decreasing Ta particle size.…”

New Entropic Routes for Nano‐Bands and Nano‐Particles

“…Several time-resolved X-ray studies have been carried out and reported [24,26,27,29,32,46,60,61,[78][79][80][81] which indicate the occurrence of the intermediates during micropyretic synthesis of NiAl compound. The list of reactants, intermediates, and products reported in different studies at different time intervals from time-resolved X-Ray diffraction patterns are shown in Table 2 [4,26,27,29,46,60,61,80,81].…”

In-Situ Chemical Dynamics and Phase Mapping Under Steep Thermal Gradients Using Time-Resolved and Spatially Resolved X-Ray Diffraction

“…In fact, it has been suggested that the rate controlling step in the combustion reactions of Ta and C is the diffusion of carbon into the tantalum particles [14][15][16] . Secondly, Ta and its compounds are strong xray scatterers which in turn enable short scan time of each diffraction pattern down to tens of milliseconds with good signal-to-noise ratios 17 . …”