NiO Dissolution Research Articles

Polymorphic transformation of t′ phase in Yttria partially stabilized zirconia

Plasma-sprayed yttria partially stabilized zirconia (5 mol.% Y 2O 3) with and without 10 mol.% additions of NiO source precursor were fired at temperatures between 1200 and 1600°C, and studied by X-ray diffraction and electron microscopy. The samples free of NiO underwent metastable tetragonal to metastable cubic (t′−c′) transformation above a critical aging temperature T 0 between 1400 and 1500°C, and then decomposed to equilibrium cubic (c) and tetragonal (t) assemblages. At 1600 °C, the t′−c′ transformation of NiO-free specimens was complete within 1 h and the subsequent decomposition to c+t assemblages took about 16 h. The dissolution of NiO in zirconia enhanced the formation of equilibrium c phase above 1400°C.

Effect of NiO dissolution on the transformation of plasma-sprayed Y-PSZ

Plasma-sprayed Y-PSZ (5 mol.% Y 2O 3) with and without 10 mol.% additions of NiO-source precursor was fired at temperatures between 1200 and 1500 °C to study the dissolution effect of NiO on the transformation behaviour of zirconia. Postsintering heat treatment at 1200 and 1300 °C caused significant dissolution of NiO in Y-PSZ, as indicated by the increasing c/a ratio of tetragonal (t-) or non-transformable t′-zirconia and the contraction of the cubic (c) and monoclinic (m) lattices. The NiO dissolution enhanced the decomposition of t′ phase to c + t zirconia phases, but suppressed the subsequent t → m transformation. The effect of NiO dissolution on the properties of the plasma-sprayed coating of Y-PSZ is discussed.

Factors Determining the Rate of Dissolution of Metal Oxides in Acidic Aqueous Solutions

AbstractEmpirical rules governing the dissolution rates of oxides of the transition metals in acidic solutions containing redox systems are exemplified by the dissolution of CoO. Deviations from these rules shown during the dissolution of NiO (and partly of CuO) are discussed. The presence of organic complexing agents in the solution enhances in general the rate of dissolution of metal oxides. In the case of the iron oxides, induction periods of slow dissolution have been observed. An interpretation of these induction periods is based on a particular formation mechanism of metal chelates. The combined action of redox potential and complexing agent in the solution leads to a decrease of the dissolution rates, due possibly to a blocking of crystal surface sites by constituents of the redox couple and the complexing agent.

Summary Abstract: Temperature effects on NiO growth and dissolution on Ni(100)

Summary Abstract: Temperature effects on NiO growth and dissolution on Ni(100)

Effect of solid state impurities on the dissolution of Nickel oxide

The influence of two dopants: Li2O and Cr2O3 on the dissolution of NiO has been investigated using dilute sulfuric acid solutions at 60 °C. The dissolution rate is decreased by chromium additions of up to 1.0 mol pct Cr2O3, but the addition of 1 mol pct Li2O dramatically increases the dissolution rate. The results are interpreted in terms of the modification of the defect structure of NiO (p-type semiconductor with metal vacancies) by the dopants. It is proposed that Li+ doping increases the surface concentration of Ni3+ and that subsequent strong Ni3+-SO42− interaction enhances NiO dissolution. The NiO-SO42− surface interaction is confirmed with electrophoretic mobility measurements. A similar, though less pronounced, trend is observed when perchloric acid is used instead of sulfuric acid as the dissolution reagent. The difference in the behavior of the acids is attributed to differences in their affinities for the oxide surface.

Role of Lattice Defects in the Anodic Dissolution of NiO

Role of Lattice Defects in the Anodic Dissolution of NiO

On the dissolution behavior of NiO

The dissolution of NiO in dilute H 2SO 4 has been investigated with particular referenceto the effect of small amounts of foreign ions on the dissolution rate. The rate is affected remarkably by the O 2 pressure prevailing during preparation of specimen, storing period and atmosphere after preparation, and by the nature and concentration of ions in the solution. These effects can be ascribed to the adsorption of reducing molecules or ions on the defect sites of the NiO surface. If a small amount of reducing ions, such as Fe 3+ or I −, is present in the solution, they will adsorb preferentially at the defect sites and thus hinder initiation of dissolution. Even 1 ppm of these ions shows a conspicuous effect on the dissolution rate, and the order of magnitude of effect by each ion is in accordance with that of their standard redox potential. This can be explained by similar consideration on the depletive adsorption of gas on p-type semiconductors.