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Title: The effect of crystal defects on the chemical properties of selected metals
Author: Pearce, Clive Edwin
ISNI:       0000 0001 3480 4750
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1971
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It is well known that cold working of a crystalline solid leads to high concentrations of dislocations in the lattice. In this state, the solid contains residual microstrains and is usually observed to have enhanced chemical reactivity when compared with the annealed condition. The residual strain energy, due to the strain fields around the dislocations, increases the free energy of the solid; this has two effects on the reactivity of the solid:- (1) The increased chemical free energy results in an increased thermodynamic tendency for chemical reaction to occur. (2) The increase in free energy results in a decrease in the activation energy for chemical reactions involving the solid. As a consequence, reactions may occur at faster rates. The work presented in this thesis is a quantitative study of the effects of crystal defects on the chemical reactivities of both cold worked and chemically prepared copper and nickel. It has been shown that residual microstrains affect the electrode potential of cold worked copper in the form of wire or powder. The relationship between the strain energy and the change in electrode potential, relative to the annealed state, is linear. Changes of electrode potential have been thermodynamically related to changes of surface chemical free energy, which result from the residual microstrain energy. A polarographic technique has been developed to measure the rates of electrode processes of cold worked copper and nickel wires. It has been shown that residual microstrains affect the rates of anodic dissolution. An extension to standard electrochemical theory has been proposed, which relates the anodic exchange current density with the change in activation energy for dissolution which results from residual microstrains. Experiments have been carried out on cold worked aluminium oxide powder to compare chemisorption and BET adsorption particle sizes with crystallite size. It has been demonstrated that ball-milling caused a change of surface free energy in aluminium oxide powder. This was found to give rise to a change of electrode potential of the milled powder relative to that of the annealed powder. X-ray line broadening has been used to measure crystallite sizes, microstrains and stacking fault probabilities in Raney copper and Raney nickel catalysts, and also in platinum catalysts. The defect concentrations in technically useful Raney nickel catalysts, of high catalytic activities, are considerably higher than those found in the relatively inactive catalysts which had been studied by previous workers Measurements have been made of defect concentrations in catalysts of various activities, prepared by different methods. A relationship has been established between the catalyst structure and the temperature and time period used for digestion of Raney alloy. A similar relationship has been shown for platinum catalyst, prepared by ignition of a platinum salt at various temperatures. In addition, the aging processes occurring in a highly active Raney nickel have been followed by X-ray line broadening. These experiments show that catalysts with high defect concentrations are of high catalytic activity but of low stability, since they are subject to crystallite growth and strain relief at room temperature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available