Computer modelling of the non-isothermal crystallization kinetics of electroless nickel-phosphorus deposits

Non-isothermal differential scanning calorimetry (DSC) data of electroless nickel-phosphorus (EN) samples with three different phosphorus contents (9, 12 and 16 wt%) has been used in the computer modelling of crystallization kinetics based upon the Johnson-Mehl-Avrami (JMA) theory. The major crystallization processes of the EN samples are complex and could involve multiple reactions, as indicated by the corresponding DSC curves obtained at the heating rates of 5-50 °C/min. The degrees of transformation for major crystallization process of the samples were calculated from those DSC experimental data. Computer simulations of the degree of transformation as well as the corresponding DSC curves were performed using the JMA models, and the results were compared to those from the experiments. It was found that the JMA models could perform within the experimental accuracy of the samples with high (12 and 16 wt%) phosphorus contents. However, satisfactory application of the model to a sample with medium (9 wt%) phosphorus content was not achieved, probably due to the presence of crystalline phase in the deposit prior to crystallization process. The derived JMA kinetic exponents (n) are compared and discussed upon their kinetic interpretation to the non-isothermal crystallization processes of the samples.