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Notes: Abstract The (001)-oriented, single crystalline thin films of Cu-3% Ni, Cu-4.6% Ni, and Cu-50% Ni alloy were prepared by vapor deposition onto (001) NaCl substrates. The films were subsequently annealed at around 1100°K and oxidized at 725°K at an oxygen partial pressure of 5×10−1 N · m−2 (5× 10−6 atm). High-resolution transmission electron microscopy was employed to observe the changes in situ. For all the alloy concentrations Cu2O and NiO were observed to nucleate and grow independently; no mixed oxides were noted. The shape and growth rates of Cu2O nuclei were similar to those found in previous work on pure copper films. For low-nickel alloy concentrations the NiO nuclei were larger and the number density of NiO was less when compared to the oxidation of pure nickel films. For the Cu-50% Ni films the shape and growth rates of NiO were identical to those for the oxidation of pure nickel films. Low nickel concentrations exhibited a reduced induction period for Cu2O when compared to pure copper films. Cu-50%Ni films showed surface precipitation and growth of NiO first, followed by Cu2O in a typical through -thickness growth after a prolonged induction period. The results are consistent with the previously established oxidation mechanisms of pure copper and pure nickel films.

Notes: Abstract The sulfidation of 310 stainless steel was studied over the temperature range from 910 to 1285° K. By adjusting the ratio of hydrogen to hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39 N·m−2, 1.4×10−2 N·m−2, and 1.5×10−4 N·m−2. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer0 (OL-I), nearest the subscale, contained Fe-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. Two different phases were observed in OL-II depending on the temperature and sulfur potential. Below 1065°K OL-II is composed of a mixture of monosulfides of iron and nickel (Fe Ni)1−xS and pentlandite (Fe4.5Ni4.5S8) with the pentlandite phase exsolved as lamellae upon cooling. At temperatures higher than 1065°K only the pentlandite phase was formed, which melted above 1145°K at sulfur potentials greater than 10−2 N·m−2, yielding metal-rich iron-nickel-sulfur. Above 1145°K, and at sulfur potentials less than 10−2 N·m−2, OL-II ceased to exist (this temperature is termed transition temperature). Below the transition temperature, where OL-II exists, OL-I could be represented by the general composition (Fe, Cr)1−xS. This phase on cooling transformed into an array of structures differing in Fe∶Cr ratio. These substructures, however, were not observed in quenched samples. Above the transition temperature OL-I changed to a chromium-rich sulfide composition and was associated with a sudden decrease in reaction rate. Subscale formation was found to be due to the dissociation of OL-I at the scale-metal interface, and the extent of subscale growth was found to depend on the temperature and the sulfur potential, as well as the composition of OL-I. At a given temperature and sulfur potential the weight-gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39 N·m−2 did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at a sulfur potential below 2 × 10−2 N·m−2, however, did show a break at 1145°K. This break was found to be associated with the changes which had occurred in the Fe∶Cr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kJ · mole−1. Above the transition temperature the rate of sulfidation decreased with temperature but depended on the Fe∶Cr ratio in the ironchromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed in which the diffusion of cations through OL-I is the rate-controlling step. Below the transition temperature the diffusion of Fe and Ni through OL-I contributes to the scale formation, whereas above the transition temperature the diffusion of Cr through OL-I controls the scale formation. Existing literature on the Fe-Ni-S system is compared with the present results.

Notes: Abstract single-crystalline thin films of copper were oxidized at an isothermal temperature of 425°C and at an oxygen partial pressure of 5×10−3 Torr in situ in a high-resolution electron microscope. The specimens were prepared by epitaxial vapor deposition onto polished {100} and {110} faces of rocksalt and mounted in a hot stage inside an ultra-high-vacuum specimen chamber of the microscope. Large amounts of sulfur, carbon, and oxygen were detected by Auger electron spectroscopy on the surface of the as-received films and were removed in situ by ion-sputter etching immediately prior to the oxidation. The nucleation and growth characteristics of Cu2O on Cu were studied. The predominantly observed crystallographic orientations of Cu2O on {100} and {110} copper films were epitaxial, parallel {100} and {110} orientations, respectively. In addition, a Cu2O {111} orientation with Cu2O 〈770〉//Cu 〈110〉 was found frequently on {100}-oriented copper films. The distinct particle shapes observed most frequently were square and hexagonal, representing {100} and {111} orientations, respectively. An induction period of about 30 min was found, which did not depend on the film thickness but did depend strongly on the oxygen partial pressure and the oxygen exposure prior to the oxidation. Neither stacking faults nor dislocations were found to be associated with the Cu2O nucleation sites. The growth of Cu2O nuclei was found to be linear with time. The experimental findings, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving (a) the formation of a surface-charge layer, (b) oxygen saturation in the metal and formation of a supersaturated zone near the surface, and (c) nucleation, followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Notes: The (A) C3v and (B) C2v structures for LiAlF4(g) have been discussed in the literature. The present work indicates strong evidence in favour of the structure (B) by means of different approaches which, include spectral and thermodynamical measurements.