Papers by Keyword: Ni-Fe

Abstract: In nickel laterite agglomerates from rotary kiln of RKEF process the phases lizardite and/or chrysotile, clinochlore, quartz and hematite were identified. The product contain SiO₂ (32.67%), Fe₂O₃ (24.68%), MgO (21.81%) and NiO (3.30%) as principal components. When thermal treatment were carried out weight differences can be observed where the adsorbed water removed during drying, without phase changes in temperatures ranging from 60°C to 100°C, indicated influence of mineral assemblage. Phase changes and weight loss was observed in calcination with clear crystalline restructuring of the serpentines and clinochlore at 500°C. Above this temperature new phases are crystallized until 820°C, when is formed forsterite and enstatite, provably trevorite and remaining unchanged quartz. There were identified nickel minerals. The nickel occurs in bearing phases as Mg-Ni ion substitution in the crystal structure. On the analyzed conditions might infer that these new phases formed can affect the pyrometallurgical process of reduction.

Abstract: The microstructure of a Ni–18 wt.% Fe electrodeposits having a banded structure is described in detail. The aim is to investigate the influence of the banded structure on grain growth behaviour and texture and to elucidate if there are other mechanisms operative in the stabilization of nanocrystalline electrodeposits. Spectroscopy techniques have been used to characterize the variations in alloy/impurity concentration perpendicular to the growth direction. The influence of these chemical variations on the microstructural evolution has been monitored by in-situ annealing treatments in the TEM. Local texture of the annealed material has been determined by use of the electron backscatter diffraction (EBSD) technique. SEM and TEM investigations have shown that the banded structure is not related to phase changes and that grain growth is not affected by the banded structure, i.e. there is no preferred growth along bands. The first grown grains have <100>, <112> and <111> orientations with the growth direction and upon further grain growth a <111> fibre texture with respect to the growth direction of the electrodeposits is formed. The banded structure seems not to affect the general behaviour of nanocrystalline electrodeposits.

Abstract: Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Fe electrodeposit revealed the existence of a banded structure perpendicular to the growth direction. To evaluate if the banded structure is affecting grain growth and texture development, EBSD orientation maps were obtained after annealing for 30 min at 300, 350, and 400°C. Grown grains were found to be random in shape and no preferential sites for grain growth were observed. The texture of the grown grains is changing upon annealing and the final fibre texture parallel to growth direction of the electrodeposit can be obtained from texture components found at lower annealing temperatures when performing one or two consecutive twinning operations.