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High temperature thermal diffusivity of combustion synthesized samples Dominique Vrel CNRS-LIMHP, UPR 1311, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse, France Nikhil Karnatak, Ellen M. Heian, Sylvain Dubois, Marie-France Beaufort, Benoît Cochepin CNRS-LMP, UMR 6630, Bât. SP2MI, Bd M. & P. Curie, BP 30179 86962 Futuroscope-Chasseneuil du Poitou Cedex, France
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vrel@limhp.univ-paris13.fr2 Modeling studies Equation in 1D with the following approximation : Importance in modeling before scaling-up; in determination of kinetic parameters such as use of Boddington model (thermal profile analysis, TPA)
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vrel@limhp.univ-paris13.fr3 Measuring thermal diffusivity Impossible at high temperature on reactants Easy at low temperature on reactants and products Not possible during reaction (coupled equations with kinetics) … Not practically possible on products at high temperature: re-crystallization, sintering, stress relaxation, homogenization of structure and composition (long time at high temperature) We need to find a way to determine thermal diffusivity as fast as possible, just after reaction
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vrel@limhp.univ-paris13.fr4 A weird sample
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vrel@limhp.univ-paris13.fr5 IR streak image - principle
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vrel@limhp.univ-paris13.fr6 IR streak image - result Reference frame Igniter is on Reaction propagates Reaction pauses Reaction re-starts – Hot spot
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vrel@limhp.univ-paris13.fr7 TRXRD – no second reaction XRD, 25 pps Left shift = temperature increase 2d sin = if d 1 reaction only 1 re-heating can be used to estimate thermal diffusivity
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vrel@limhp.univ-paris13.fr8 Hot spot diffusion i for the space step; n for the time step 77 space steps (77 pixels on the IR image) 25 time steps per second 2 unknowns: and
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vrel@limhp.univ-paris13.fr9 Golden section search To determine the unknowns, starting from an experimental temperature profile, we model the evolution of temperature with arbitrary values of and , and then minimize the sum of differences between the final calculated profile and the final experimental profile
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vrel@limhp.univ-paris13.fr10 Flow chart
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vrel@limhp.univ-paris13.fr11 Modeling results
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vrel@limhp.univ-paris13.fr12 Thermal diffusivity – results
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vrel@limhp.univ-paris13.fr13 Weaker hot spots with nickel with finer C
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vrel@limhp.univ-paris13.fr14 Finer C particles
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vrel@limhp.univ-paris13.fr15 Calculated thermal diffusivity
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vrel@limhp.univ-paris13.fr16 And before reaction ? Noisy data Calculated value of thermal diffusivity sets the lower limit for the real value : method measures only the part of the heat flowing through the sample that contributes to the temperature increase and neglects the part that contributes to the heat losses. System might reach equilibrium, where the heat flowing through the sample only compensate the heat losses
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vrel@limhp.univ-paris13.fr17 Results before reaction
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vrel@limhp.univ-paris13.fr18 Summary
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vrel@limhp.univ-paris13.fr19 Conclusions Method is easy and seems trustworthy References Dominique Vrel, Nikhil Karnatak, Marie-France Beaufort, Sylvain Dubois, In-situ measurement of high-temperature thermal diffusivity in a combustion-synthesized ceramic, European Physical Journal B 33 (2003), 31-39. Dominique Vrel, Nikhil Karnatak, Ellen M. Heian, Sylvain Dubois and Marie-France Beaufort, Measurement of thermal diffusivities during self-propagating high temperature synthesis, submitted, International Journal of Self-Propagating High- Temperature Synthesis. Should be applied with care Cannot be used on any sample; needs instability Could be improved by a « controlled hot spot ».
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