Advances in the theory and practice of hard chromium plating.

A consideration of pertinent aspects of general electro- chemistry and electrodeposition was followed by a review of the relevant literature relating to hard chromium plating technique and understanding (and problems and proposed improvements therein). Following the establishment and evaluation (using a Standard Solution at 55 0 C) of a reproducible technique for the measurement of (low current density) partial cathodic polarization data during plating, the Tafel regions of the resulting curves were analysed using the relationship - dn Cp -2.303 kT to provide an indication as to the nature of the rate-determining step in the plating and hydrogen evolution (cathodic) reactions. Information thus generated was used with a modified Arrhenius- type expression and further (experimentally determined) data to provide values of the thermodynamic constants of activation for the plating reaction. A series of experiments were undertaken to determine the effects upon various (physical) plate and plating parameters of three new inorganic additions (at selected concentrations) to a Standard Solution at 55 0 C. The results of these tests were commented upon with regard to potential industrial applications. The electrochemical investigative techniques referred to earlier were then employed with each new solution tested to determine the effect (if any) of the new additions upon those aspects of the deposition mechanism yielded, and to relate these effects to the observed (corresponding) changes in plate and plating parameters. The new additions were found to have profound effects upon a number of (physical) plate and plating parameters, and upon experimentally determined theoretical aspects of the deposition mechanism (the relationship between the two is discussed). Whilst no definite conclusion has been reached with regard to the precise mechanism of chromium plating, the techniques employed and the data generated have been used to provide significant pointers with regard to the direction future investigations might take.