Influence of dislocations on diffusion kinetics in solids with particular reference to the alkali halides
01 Jan 1961-Transactions of The Faraday Society (The Royal Society of Chemistry)-Vol. 57, pp 1191-1199
About: This article is published in Transactions of The Faraday Society.The article was published on 1961-01-01. It has received 859 citations till now. The article focuses on the topics: Halide.
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TL;DR: In this article, diffusion measurements were performed on chromia layers grown on the model alloys Fe-20Cr and Fe- 20Cr-12Ni in order to consider effects of small amounts of dissolved alien cations in Cr2O3.
Abstract: Diffusion of the cations Cr, Fe, Mn, and Ni in Cr2O3 has been investigated at 1173 K. The diffusion measurements were performed on chromia layers grown on the model alloys Fe-20Cr and Fe-20Cr-12Ni in order to consider effects of small amounts of dissolved alien cations in Cr2O3. The samples were diffusion annealed in H2-H2O at an oxygen partial pressure close to the Cr2O3/Cr equilibrium. For all tracers the lattice-diffusion coefficients are 3–5 orders of magnitude smaller than the grain-boundary diffusion coefficients. The lattice diffusivity of Mn is about two orders of magnitude greater than the other lattice-diffusion coefficients, especially in Cr2O3 grown on Fe-20Cr-12Ni. The values of the diffusion coefficients for Cr, Fe, and Ni are in the same range. Diffusion of the tracers in Cr2O3 grown on different alloys did not show significant differences with the exception of Mn.
309 citations
TL;DR: In this article, the diffusion coefficients of Co, Cr, Fe and Mn tracers were determined in polycrystalline CoCrFeNi and CoCr FeMnNi HEAs using the radiotracer method in the temperature interval of 1073-1373 K.
283 citations
Cites methods from "Influence of dislocations on diffus..."
...A distinct grain boundary contribution to the penetration profile under the present conditions corresponds to the B-type kinetic regime after Harrison's classification [22], which can be analyzed using Le Clair's functional form [23],...
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TL;DR: The product of the grain boundary diffusion coefficient and width, D′δ, has been measured directly for the diffusion of 63Ni along grain boundaries in high-purity NiO as discussed by the authors.
Abstract: The product of the grain boundary diffusion coefficient and width, D′δ, has been measured directly for the diffusion of 63Ni along grain boundaries in high-purity NiO. These measurements have been made at an oxygen pressure of 1 atm in the temperature range 500–800°C, and also at an oxygen pressure of 7 × 10−6 atm at 700°C. At po 2 = 1 atm, D′δ is given by D′δ = 3·0× 10−8 exp {−1.78(eV)/kT} cm3 S−l. The width of the boundary, δ, is estimated to be 7 × 10−8 cm and in this region near the boundary the concentration and mobility of Ni vacancies are greater than in the bulk. The measured values of D’δ confirm quantitatively that the rate of oxidation of Ni to NiO at 500–800°C is controlled by the diffusion of Ni along grain boundaries in the NiO scale.
269 citations
TL;DR: Important considerations for in situ characterization and new reactor designs that may enable researchers to better understand the physical growth mechanisms and to optimize the synthesis of CNTs are illustrated, thus contributing to make carbon nanotubes a manufacturing reality.
Abstract: Carbon nanotubes (CNTs) have been extensively investigated in the last decade because their superior properties could benefit many applications. However, CNTs have not yet made a major leap into industry, especially for electronic devices, because of fabrication challenges. This review provides an overview of state-of-the-art of CNT synthesis techniques and illustrates their major technical difficulties. It also charts possible in situ analyses and new reactor designs that might enable commercialization. After a brief description of the CNT properties and of the various techniques used to synthesize substrate-free CNTs, the bulk of this review analyzes chemical vapor deposition (CVD). This technique receives special attention since it allows CNTs to be grown in predefined locations, provides a certain degree of control of the types of CNTs grown, and may have the highest chance to succeed commercially. Understanding the primary growth mechanisms at play during CVD is critical for controlling the properties of the CNTs grown and remains the major hurdle to overcome. Various factors that influence CNT growth receive a special focus: choice of catalyst and substrate materials, source gases, and process parameters. This review illustrates important considerations for in situ characterization and new reactor designs that may enable researchers to better understand the physical growth mechanisms and to optimize the synthesis of CNTs, thus contributing to make carbon nanotubes a manufacturing reality.
269 citations
01 Feb 1999-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: An overview of boundary diffusion theory with emphasis on the interpretation of concentration profiles measured in diffusion experiments is given in this article, where the authors consider the most important situations encountered in boundary diffusion experiments, such as diffusion in the B and C regimes.
Abstract: Grain boundary (GB) diffusion often controls the evolution of structure and properties of engineering materials at elevated temperatures. A knowledge of diffusion characteristics of GBs and deep fundamental understanding of this phenomenon are critical to many materials applications. In this paper we give an overview of boundary diffusion theory with emphasis on the interpretation of concentration profiles measured in diffusion experiments. We consider the most important situations encountered in boundary diffusion experiments, such as diffusion in the B and C regimes and diffusion in the presence of segregation. We also discuss the recent progress in the atomistic interpretation of GB diffusion. We conclude with an outlook for future research in this area.
226 citations