Cobalt Segregation Research Articles

Cobalt intergranular segregation in WC-Co composites

Interfaces between carbide grains in the tungsten carbide-cobalt composite have been considered. Different techniques, such as transmission electron microscopy and energy dispersive X-ray analysis have been used to characterize the orientation relationship, the nature of the planes and the chemical composition of the grain boundaries.The cobalt concentration at WC-WC grain boundaries was determined by X-ray energy selective analysis in the TEM. Cobalt profiles were performed across low-angle grain boundaries, coincidence and general grain boundaries. Cobalt segregation was found whenever dislocations were imaged in the grain-boundary plane of a low-energy grain boundary. The segregation value was compared with the segregation ratio measured in special grain boundaries characterized by a coincidence site lattice.

Oxygen adsorption on the Co50Ni50(111) surface

Oxygen adsorption on the Co50Ni50(111) surface at RT has been studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The uptake rate and the work function variations show the different stages of linear initial adsorption, oxide nucleation and oxide thickening. Chemisorption of oxygen induced a segregation of cobalt. Heating at 327°C caused a further cobalt segregation which reduced Ni2+ to Ni0 and finally islands of cobalt oxide were formed.

ChemInform Abstract: Cobalt Segregation in Nickel Electrodes During Nickel Hydrogen Cell Storage.

AbstractStorage of Ni‐electrodes in a hydrogen gas environment at potentials near that of the alkaline hydrogen electrode is found to result in a segregation of cobalt additives from the active material of the Ni‐electrode.

Cobalt Segregation in Nickel Electrodes during Nickel Hydrogen Cell Storage

Storage of nickel electrodes in a hydrogen environment can result in significant changes in the performance of these electrodes in nickel hydrogen battery cells. Such performance changes appear to be associated with the formation of cobalt oxides from the cobalt additives incorporated in the active materials of the nickel electrode. In this study the microscopic location of these cobalt oxides has been mapped using scanning electron microscopy. The cobalt additive in the active material was found to be depleted around the nickel metal particles comprising the sintered current‐collector matrix. The cobalt‐containing oxides found in chemical analyses of these electrodes were re‐deposited in areas several microns or more distant from the sinter particles. A mechanism is proposed for cobalt segregation in nickel electrodes that involves the reaction of the active material with hydrogen gas at low potentials to initiate the segregation process, which then proceeds through a dicobaltite ionic intermediate when the potential of the cell is eventually brought back to its normal operating level.

Atom‐Probe analysis of grain boundary segregation

AbstractAtom‐probe micronalysis has a very high spatial resolution and equal detectivity for all elements, including the lightest. It is therefore well suited for the study of grain boundary segregation. In this paper the accuracy and spatial resolution of atom‐probe analysis are discussed, as well as the advantage of and limitations to the method. Specimen preparation methods are descibed, in particular controlled preparation using electron microscopy and pulse electropolishing. Three examples of atom‐probe studies of grain boundary segregation are given: cobalt segregation to carbide grain boundaries in cemented carbide materials; boron grain boundary segregation in austenitic stainless steels; and nickel segregation to grain boundaries in tungsten.

Investigation of the Cobalt Segregation and the Structure of a Grain Boundary in Silicon

Investigation of the Cobalt Segregation and the Structure of a Grain Boundary in Silicon

High temperature surface segregation on cobalt-rhodium alloys using Auger electron spectroscopy

Abstract Surface segregation measurements were made on three Co-Rh alloys (19.3, 47.8 and 84.7 at% Rh) in the temperature range 623–1123 K using AES. Cobalt segregation occurred on the Co-84.7Rh alloy with a heat of segregation of −3.7 ± 7 kJ mol −1 while rhodium enrichment was observed on the Co-19.3Rh alloy with a heat of segregation of 1 ± 1 kJ mol −1 . No variation from the bulk composition could be conclusively demonstrated on the surface of the Co-47.8Rh alloy. There is good quantitative agreement between these results and the combined bond breaking and lattice strain theories of segregation.

High temperature surface segregation on cobalt-rhodium alloys using Auger electron spectroscopy

Surface segregation measurements were made on three Co-Rh alloys (19.3, 47.8 and 84.7 at% Rh) in the temperature range 623–1123 K using AES. Cobalt segregation occurred on the Co-84.7Rh alloy with a heat of segregation of −3.7 ± 7 kJ mol −1 while rhodium enrichment was observed on the Co-19.3Rh alloy with a heat of segregation of 1 ± 1 kJ mol −1. No variation from the bulk composition could be conclusively demonstrated on the surface of the Co-47.8Rh alloy. There is good quantitative agreement between these results and the combined bond breaking and lattice strain theories of segregation.

Edge plane segregation in cobalt-doped MoS 2 crystals

Single crystals of cobalt-doped MoS 2 have been examined by Auger spectroscopy. Segregation of cobalt to growth steps (edge planes) of the faceted crystals has been detected. Edge planes are preferred sites for oxygen adsorption. Some evidence has been obtained that oxygen adsorption enhances cobalt segregation. These findings are consistent with the pseudo-intercalation model of segregation in MoS 2 crystals.

In-situ measurements of cobalt segregation in CsCdCl 3

A novel method is reported for studying dopant segregation by continuous monitoring of the dopant concentration in the liquid phase. The cobalt concentration in Co-doped CsCdCl 3 melts was determined by measuring the absorption of a He-Ne laser beam and the distribution coefficient was calculated from a series of measurements during crystal growth by directional solidification.