Papers by Keyword: Solid State Diffusion

Abstract: Sulfidation of undoped and aluminum doped zinc oxide materials has been performed by TGA under a H₂S atmosphere in order to evaluate the impact of the doping element on sulfidation reaction kinetics and mechanism. The presence of aluminum seems to slow-down the reaction kinetics. This phenomenon might be explained by a modification of the solid state diffusion processes involved in ZnO sulfidation reaction and the related ZnS outward growth, assuming the presence of aluminum atoms inside ZnO and ZnS phases. In order to determine solid state diffusion mechanisms controlling the reaction kinetics, molecular dynamics simulations were performed using a Coulomb-Buckingham potential. Firstly, the diffusion of the different elements (Zn, O, S) was simulated for both the oxide and sulfide phases considering a vacancy mechanism. Secondly, simulations of the oxide phase doped by a trivalent cation were also performed. The results obtained in this preliminary work are presented and compared to the literature.

Abstract: The structure of Nb3Sn-based, bronze-processed Ti-doped multifilamentary superconducting wires has been studied by TEM and SEM after the first (5750C,100 h) and the second (6500C,100 h) stage of the diffusion annealing. The Nb3Sn layers formation in all the composites proceeds by one and the same mechanism and starts with nucleation of particles and very fine grains of this phase in Nb filaments where Sn diffuses from the bronze matrix. Ti, inserted both in the bronze matrix, or Nb filaments, diffuses into the growing superconducting layer and promotes its more active formation. At the first stage of annealing (5750C, 100 h) Nb3Sn grains have an average size of 40 nm, and at the second stage (6500C, 100 h) they increase by a factor of 1.5 and the grain size distribution gets wider. After the two-stage annealing the amount of the residual niobium is small, and some Nb filaments, especially in doped composites, almost completely transform into Nb3Sn. In the Nb3Sn layers of a zone of columnar grains is adjacent to the residual Nb.

Abstract: In2O3(ZnO)3 layered compound was synthesized by 2.45 GHz microwave heating in a solid state reaction. Microwave-processed samples were obtained at low temperature by the enhancement of solid state diffusion and sublimation of the powder bed. Plate-like grain microstructures formed on the bottom part of the pellet, and vicinity of the surface was dense. The plate-like grain was oriented in the ab-plane direction. Compared with a conventional heated sample, the electrical conductivity increased and the band gap energy decreased. In the case of deposition on a silica substrate by microwave heating, the plate-like grain film was synthesized.

Abstract: The primary factors that effect solid state diffusion during solidification are described and binary solute redistribution equations that permit estimation of the significance of solid state diffusion are discussed. Model calculations suggest that solid state diffusion of substitutional alloying elements in FCC alloys is insignificant under most processing conditions, while that of interstitial alloying elements is likely to be complete. Experimental data that supports these results are presented. Several cases that highlight the practical importance of microsegregation on performance of engineering alloys are described as well as methods for avoiding or minimizing microsegregation for improved properties. A solute redistribution model for handling the limiting cases of solute diffusion in ternary alloys is presented and model calculations are reviewed to reveal the strong influence diffusion can have on the solidification path and resultant microstructure.