简介概要

Template growth mechanism of spherical Ni(OH)2

来源期刊:中南大学学报(英文版)2007年第3期

论文作者:彭美勋 沈湘黔

文章页码:310 - 314

Key words:spherical Ni(OH)2; microstructure; Ostwald ripening; growth mechanism; crystallization

Abstract: The microstructures and growth process characteristics of spherical Ni(OH)2 particles synthesized by the aqueous precipitation-crystallization method were investigated by SEM, TEM and XRD, and their growth mechanism was discussed. With the reaction beginning and continuing, amorphous Ni(OH)2 nano-crystallites grow up to spherical micron-particles with radially arranged crystallites. The nucleation, crystallization and re-crystallization led by Ostwald ripening simultaneously take place through the whole growth processes. With the course from reversible aggregation to irreversible agglomeration, the Ni(OH)2 particles tend to grow according to the template growth model: the growth on the crystallite templates stretching in the radius directions is free and quick, while the growth rate for crystallites in other directions is confined due to lower monomers concentration and tends to dissolve. So it is only the radially arranged crystallites that predominate in the particle and lead to characteristic microstructures.

基金信息:the National Natural Science Foundation of China



详情信息展示

J. Cent. South Univ. Technol. (2007)03-0310-05

DOI: 10.1007/s11771-007-0061-9               

Template growth mechanism of spherical Ni(OH)2

PENG Mei-xun(彭美勋)1,2, SHEN Xiang-qian(沈湘黔)2,3

(1. School of Geoscience and Environmental Engineering, Central South University, Changsha 410083, China;

2. Changsha Research Institute of Mineral and Metallurgy, Changsha 410012, China;

3. College of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China)

                                                                                                 

Abstract: The microstructures and growth process characteristics of spherical Ni(OH)2 particles synthesized by the aqueous precipitation-crystallization method were investigated by SEM, TEM and XRD, and their growth mechanism was discussed. With the reaction beginning and continuing, amorphous Ni(OH)2 nano-crystallites grow up to spherical micron-particles with radially arranged crystallites. The nucleation, crystallization and re-crystallization led by Ostwald ripening simultaneously take place through the whole growth processes. With the course from reversible aggregation to irreversible agglomeration, the Ni(OH)2 particles tend to grow according to the template growth model: the growth on the crystallite templates stretching in the radius directions is free and quick, while the growth rate for crystallites in other directions is confined due to lower monomers concentration and tends to dissolve. So it is only the radially arranged crystallites that predominate in the particle and lead to characteristic microstructures.

Key words: spherical Ni(OH)2; microstructure; Ostwald ripening; growth mechanism; crystallization

                                                                                                            

1 Introduction

Spherical Ni(OH)2 have been widely used as the active materials for the nickel electrodes in Ni-MH batteries due to an appropriate packing density and high electrochemical performances. In the last two decades, a lot of investigations have been carried out to explain electrochemical processes for Ni-MH batteries by modeling Ni(OH)2 active materials’ microstructures and the electrode processes[1-2], because the microstructures of spherical Ni(OH)2 particles work on the electrochemical performance for the nickel electrodes in Ni-MH batteries. Many sophisticated methods therefore have been advanced to correlate the chemical composition-processing-microstructure-electrochemical performance of the materials[3-5]. Although the precipitation-crystallization processes of spherical Ni(OH)2 has been used in industry for many years[6-7], it is hard to produce spherical Ni(OH)2 with an appropriate particle size distribution, required precise chemical compositions and microstructures to meet the demand of high performances from the development of advanced mobile power technologies as the formation processing of spherical Ni(OH)2 is not completely understood, and it results in the product quality instable and the electrochemical performance disparity.

In this paper the formation of the microstructures and the growth mechanism of the spherical Ni(OH)2 synthesized with aqueous precipitation-crystallization method in a continuous stirring-tank reactor(CSTR) was studied.

2 Experimental

2.1 Synthesis of spherical Ni(OH)2

The required amounts of NiSO4, NaOH and NH4?H2O solutions were continuously fed into the CSTR at temperature of 50-55 ℃ and pH value of 11.0-11.5. The temperature and pH value were digitally responded and automatically controlled by adjusting the heater and reagents pumping speed automatically. The precipitate was sampled from the reactor at different times from the reaction beginning to the equilibrium state for the system to examine the particle characteristics with reaction time. The nickel hydroxide precipitates were washed with distilled water, then filtered and dried in an oven at    105 ℃.

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