Development of Techniques to Produce Nickel Coated Composite Materials as well as Hollow Nickel Fibres and Kinetic Study of the Process Involved

Sammanfattning: The present thesis was mainly to study the preparation of nickel composite materials by chemical plating process. Nickel coated boron nitride particles, nickel coated spherical silica particles and nickel viscose composite fibres were prepared. Both experiment and model development were carried out to study the kinetics of the processes. Preparation of hollow nickel fibres was also investigated.NiSO4-(NH4)2SO4-NH3·H2O-N2H4·H2O was found a suitable system for nickel plating. This system could be employed in preparing nickel coating layer on surface of boron nitride particles, spherical silica powder and viscose fibres. The main factors which could affect the plating process were investigated. The optimum conditions were suggested for different substrate materials based on the experimental results.It was found that Pd on the surface of substrate materials acted as an active center for nickel deposition at the initial stage of the process. Thereafter, Ni itself would act as an active center to catch Ni from the solution through the reaction: Ni2+ + 2H' ad ? Ni + 2H+. The rate of the process was found to be controlled by the reaction at the interface under the present experimental conditions. A kinetic model was developed on the basis of the mechanism study. The model predictions were found to be in agreement with the experimental data for different substrate materials. Since the kinetic model does not have any parameters related to the shape and surface area of the substrate, it could be used as a general model to describe the processes controlled by interface reaction with growing interface area.Hollow nickel fibers were prepared by thermal decomposition method from nickel viscose composite. The experiments showed that viscose filling could be removed by heat treatment in air atmosphere. Experiments showed that hollow nickel fiber could be prepared by direct thermal decomposition in air flow at low temperature, e.g. 573 K. But slight surface oxide is inevitable. Decomposition of the viscose filling could also be carried at higher temperature. However, serious oxidation of nickel would also take place during the decomposition. To remove nickel oxide, reduction by hydrogen gas could be applied.Preliminary effort was made to extend the application of the present method to prepare copper viscose composite fibres. Promising result was obtained. More detailed study is required to confirm the applicability of the technique.