Growth of silicides in Ni-Si and Ni-SiC bulk diffusion couples

In this work, the integrated diffusion coefficient, D'-int' is used to describe the growth kinetics of silicides in Ni -Si and Ni-SiC diffusion couples. The integrated diffusion coefficients are determined from planar diffusion couple experiments for all intermetallic phases of the binary Ni-Si system between 1073 and 1173 K. For the growth of NisSi2 'an activation energy of 180 ± 30 kJjmol (1.9 ± 0.3 eV) was found. The position of the Kirkendall plane revealed that Ni is the only diffusing species in Ni3 Si and NisSi2. In NiSi2, Ni and Si are equally mobile. The activation energy for the interdiffusion in the Ni(Si) solid solution, measured between 1093 and 1423 K, is 250 ± 10 kJjmol (2.6 ± 0.1 eV) and is independent of the Si-concentration

Phase relations in the Ag-Fe-Ti system at 1123 K

Abstract Phase equilibria in the Ag-Fe-Ti system at 1123 K were determined by using polyphase diffusion couples and equilibrated alloys. The experimental observations are in agreement with a thermodynamic evaluation performed on this system. No ternary phases are present on the Ag-Fe-Ti isotherm at 1123 K. The solubility of iron in the binary intermetallic compounds Ti2Ag and TiAg as well as the solubility of silver in FezTi are negligible. The maximum silver content in FeTi was estimated as =0.5 at.%, while nearly 6 at.% of silver can be dissolved in the /3-Ti(Fe) based solid solution at this temperature

Absorption of water and corrosion performance of a clear and pigmented epoxy coating on Al-2024 alloy

The corrosion performance of Al-2024 substrates coated with an epoxy clear coating and a pigmented epoxy coating was investigated. The absorption of water in the pigmented coating was high compared to the clear coating. The clear coating provided a good barrier which is stable beyond 120 days of immersion in a 0.5 M NaCl solution. The shape of the Nyquist plot of the pigmented coating changed with immersion time and reveals the existence of physico-chemical processes in the coating and/or at the interface. Its impedance magnitude at low frequencies remained very high (~ 109 .cm2) after 72 days of immersion in sodium chloride solution. Both coatings exhibited good dry adhesion on Al-2024. The wet adhesion of the clear coating was poor while the stress (~ 9 MPa) required in a pull off adhesion test of the wet pigmented coating remained high

Abiotic ammonium formation in the presence of Ni-Fe metals and alloys and its implications for the Hadean nitrogen cycle

Experiments with dinitrogen-, nitrite-, nitrate-containing solutions were conducted without headspace in Ti reactors (200°C), borosilicate septum bottles (70°C) and HDPE tubes (22°C) in the presence of Fe and Ni metal, awaruite (Ni80Fe20) and tetrataenite (Ni50Fe50). In general, metals used in this investigation were more reactive than alloys toward all investigated nitrogen species. Nitrite and nitrate were converted to ammonium more rapidly than dinitrogen, and the reduction process had a strong temperature dependence. We concluded from our experimental observations that Hadean submarine hydrothermal systems could have supplied significant quantities of ammonium for reactions that are generally associated with prebiotic synthesis, especially in localized environments. Several natural meteorites (octahedrites) were found to contain up to 22 ppm Ntot. While the oxidation state of N in the octahedrites was not determined, XPS analysis of metals and alloys used in the study shows that N is likely present as nitride (N3-). This observation may have implications toward the Hadean environment, since, terrestrial (e.g., oceanic) ammonium production may have been supplemented by reduced nitrogen delivered by metal-rich meteorites. This notion is based on the fact that nitrogen dissolves into metallic melts