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Homogeneous Precipitation of Nickel Hydroxide Powders.

DE2004822049

Publication Date	2003
Personal Author	Mavis, B.
Page Count	130
Abstract	Precipitation and characterization of nickel hydroxide powders were investigated. A comprehensive precipitation model incorporating the metal ion hydrolysis, complexation and precipitation reactions was developed for the production of the powders with urea precipitation method. Model predictions on Ni(sup 2+) precipitation rate were confirmed with precipitation experiments carried out at 90 C. Experimental data and model predictions were in remarkable agreement. Uncertainty in the solubility product data of nickel hydroxides was found to be the large contributor to the error. There were demonstrable compositional variations across the particle cross-sections and the growth mechanism was determined to be the aggregation of primary crystallites. This implied that there is a change in the intercalate chemistry of the primary crystallites with digestion time. Predicted changes in the concentrations of simple and complex ions in the solution support the proposed mechanism. The comprehensive set of hydrolysis reactions used in the model described above allows the investigation of other systems provided that accurate reaction constants are available. the fact that transition metal ions like Ni(sup 2+) form strong complexes with ammonia presents a challenge in the full recovery of the Ni(sup 2+). On the other hand, presence of Al(sup 3+) facilitates the complete precipitation of Ni(sup 2+) in about 3 hours of digestion. A challenge in their predictive modeling studies had been the fact that simultaneous incorporation of more than one metal ion necessitates a different approach than just using the equilibrium constants of hydrolysis, complexation and precipitation reactions. Another limitation of using equilibrium constants is that the nucleation stage of digestion, which is controlled mainly by kinetics, is not fully justified. A new program released by IBM Almaden Research Center (Chemical Kinetics Simulator(trademark), Version 1.01) lets the user change the order of kinetic components of a reaction which was set to stoichiometric constant with which the species appear in the reaction in KINSIM by default. For instance, in the case of LDH precipitation, the new program allows to change the order of species in the reactions associated with Al(sup 3+) and let the Ni(sup 2+) reactions take over. This could be carried on iteratively until a good fit between the experimental data and the predictions were observed. However for such studies availability of accurate equilibrium constants (especially for the solubility products for the solid phase) is a prerequisite.
Keywords	Kinetics Urea Decomposition Theses Simulations Hydroxides Mathematical models Equations Nichol Chemical analysis
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Iowa State Univ., Ames.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200503

Homogeneous Precipitation of Nickel Hydroxide Powders.

Homogeneous Precipitation of Nickel Hydroxide Powders.
DE2004822049

Publication Date	2003
Personal Author	Mavis, B.
Page Count	130
Abstract	Precipitation and characterization of nickel hydroxide powders were investigated. A comprehensive precipitation model incorporating the metal ion hydrolysis, complexation and precipitation reactions was developed for the production of the powders with urea precipitation method. Model predictions on Ni(sup 2+) precipitation rate were confirmed with precipitation experiments carried out at 90 C. Experimental data and model predictions were in remarkable agreement. Uncertainty in the solubility product data of nickel hydroxides was found to be the large contributor to the error. There were demonstrable compositional variations across the particle cross-sections and the growth mechanism was determined to be the aggregation of primary crystallites. This implied that there is a change in the intercalate chemistry of the primary crystallites with digestion time. Predicted changes in the concentrations of simple and complex ions in the solution support the proposed mechanism. The comprehensive set of hydrolysis reactions used in the model described above allows the investigation of other systems provided that accurate reaction constants are available. the fact that transition metal ions like Ni(sup 2+) form strong complexes with ammonia presents a challenge in the full recovery of the Ni(sup 2+). On the other hand, presence of Al(sup 3+) facilitates the complete precipitation of Ni(sup 2+) in about 3 hours of digestion. A challenge in their predictive modeling studies had been the fact that simultaneous incorporation of more than one metal ion necessitates a different approach than just using the equilibrium constants of hydrolysis, complexation and precipitation reactions. Another limitation of using equilibrium constants is that the nucleation stage of digestion, which is controlled mainly by kinetics, is not fully justified. A new program released by IBM Almaden Research Center (Chemical Kinetics Simulator(trademark), Version 1.01) lets the user change the order of kinetic components of a reaction which was set to stoichiometric constant with which the species appear in the reaction in KINSIM by default. For instance, in the case of LDH precipitation, the new program allows to change the order of species in the reactions associated with Al(sup 3+) and let the Ni(sup 2+) reactions take over. This could be carried on iteratively until a good fit between the experimental data and the predictions were observed. However for such studies availability of accurate equilibrium constants (especially for the solubility products for the solid phase) is a prerequisite.
Keywords	Kinetics Urea Decomposition Theses Simulations Hydroxides Mathematical models Equations Nichol Chemical analysis
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Iowa State Univ., Ames.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200503