J.S. Zhang

Physical simulation of the effect of sample volume on ignition temperature in the thermal explosion synthesis of Ti+3Al→TiAl3

Abstract Semenovs theory of a spontaneous ignition was applied to study the sample geometrical dependence of ignition temperature ( T cr ) of thermal explosion synthesis in Ti–75at.%Al cylinder sample in various sizes. By linear-fitting of 2ln T cr +ln(1/ r +1/ h )∼−1/ RT cr plot, the apparent activation energy of ignition process is obtained 169±15 kJ/mol. The kinetic mechanism of the ignition process was also provided.

DSC Research on Critical Temperature in Thermal Explosion Synthesis Reaction Ti+3Al→TiAl3

AbstractThe critical furnace chamber temperature (T′ign) of the thermal explosion synthesis reaction Ti+3Al→TiAl3 is studied by isothermal and non-isothermal DSC. The reaction product is characterized by using the X-ray powder diffraction. The value of T′ign is between 740 and 745°C obtained from the isothermal DSC observations, and 729°C obtained from non-isothermal DSC curves. It shows that these two values have a good consistency. With the help of the apparent activation energy of the reaction obtained by Friedman method and the value of T′ign0 by the multiple linear regression of the T′igns at different heating rates (β), the critical temperature (Tb) of thermal explosion for Ti–75at%Al mixture is estimated to be 785°C.

Corrosion of intermetallic compound Fe40Al in molten LiCl and LiCl-Li2O

A lithium reduction technique has been developed for the spent nuclear fuel management [1]. In this process the oxide (UO2) is reduced to metallic form by the reaction with lithium dissolved in the molten LiCl at 750 ◦C. The strong basic Li2O formed during the reduction process is soluble in salt. Thus, the accelerated corrosion of alloys resulting form the Li2O in molten LiCl cause a serious problem in containment materials, resulting in the delay of the application of the new technique. To date, only a few reports have been published on the corrosion of materials in molten LiCl-Li2O, with the main objective to find a material that can be used to improve the vessel longevity for this new technology [1– 3]. In these studies, corrosion behaviors of many ironbase and nickel-base alloys with good high-temperature oxidation resistance have been investigated in molten LiCl-Li2O under air. Unfortunately, all these alloys experience serious corrosion in the melt. Fe40(at%)Al-base intermetallics in presence of molten salts present better corrosion resistance when comparing them with common alloys [4]. Accordingly, this work was conducted to investigate the corrosion behavior of Fe40Al in molten LiCl and LiClLi2O mixture by immersion experiments. Fe40Al was prepared by vacuum induction melting and casting into an ingot. The ingot was cut into specimens of 10 mm × 8 mm × 2 mm. All the specimens were finely ground and polished. Immersion experiments were carried out at 750 ◦C in molten LiCl or LiCl-3 wt%Li2O. The concentration of Li2O in the molten mixture was chosen to be 3 wt% which corresponded to approximately 100% theoretical UO2 reduction [1]. LiCl and the mixture of LiCl and Li2O, contained in alumina crucibles were dried at 350 ◦C for 24 h, and then held in the molten state at 750 ◦C. For every group of experiments, 25 g salt was contained in an alumina crucible of 25 ml. After a selected period of time, the corroded specimens were rinsed with distilled water, dipped in a solution containing hydrochloric acid and tetrabutylammonium iodide to strip corrosion products, dried and weighted by microbalance. Fig. 1 shows the weight loss curves for the corrosion of Fe40Al in molten LiCl and LiCl-Li2O at 750 ◦C in air. The presence of Li2O significantly accelerates the corrosion of Fe40Al. In molten LiCl, the weight loss increased linearly with test time in the initial stage, and then increased parabolically after about 5 h. Similarly, in molten LiCl-Li2O, a large weight loss is first obtained at short exposure times (about 1 h), and then the 0 5 10 15 20 25 0 20 40 60 80 100 120

Corrosion study of NiAl-28Cr-5.8Mo-0.2Hf alloy in molten LiCl-10 wt.%Li2O

Corrosion of the reduction vessel induced by molten LiCl-Li2O is an important problem in the lithium reduction technique for the spent nuclear fuel management. This study investigates the corrosion of NiAl-28Cr-5.8Mo-0.2Hf alloy in the molten LiCl-10 wt.%Li2O at 750 degreesC by immersion experiments. The alloy is mainly composed of NiAl(beta) phase and Cr(Mo) phase. The corrosion scale is composed of LiCrO2 and LiAlO2. The NiAl(beta) phase is corroded slowly because of the depletion of Al near the phase boundaries, but the Cr(Mo) phase undergoes fast corrosion, which results in that the corrosion of Cr(Mo) phase is preceded over that of the NiAl(beta) phase in the molten LiCl-10 wt.%Li2O. The corrosion kinetic curve shows a linear pattern, which is mainly attributed to the fast corrosion of Cr(Mo)