Volume diffusion of I– anions in the near surface region of copper has been studied by radiotracer technique. The diffusion coefficients were determined for different I– coverages on copper employing the Gruzin method of measuring the residual activity. Diffusion annealing was carried out between 303 and 673 K. The distribution of the I– species in the diffusion-annealed sample was monitored by noting the residual activity of the specimen upon subjecting it to successive acid-etchings. The simultaneous evaporation losses from the I– deposit are reduced by securely holding the sample coupon in between two blank copper coupons using a metal clip.
Volume diffusion coefficients of I– anions in the near surface region of silver have been determined using131I. The distribution of the labelled ions with depth is determined by acid etching and counting the residual activity. The coefficient of diffusion is determined for surface layers of three different thicknesses over the temperature range 373–823 K. The mechanism proposed assumes the dissociation of Ag+I– in surface layer and the diffusion of I– into the interstitial free space immediately beneath the surface. This process is found to be accompanied by a small negative entropy change.
Authors:K. P. Sharma, R. S. B. Reddi, and R. N. Rai
The phase diagram of 1,4-dibromobenzene (DBB) with pyrogallol (PG) shows the formation of a monotectic and a eutectic alloys at 0.12 and 0.99 mol fractions of DBB, respectively. The phase equilibrium shows the large miscibility gap region with the upper consolute temperature 159.0 °C at 0.55 mol fraction of DBB. Growth kinetics of pure compounds and their monotectic and eutectic at different undercooling (ΔT) obey Hillig–Turnbull's equation: v = u (ΔT)n. Thermodynamic parameters such as enthalpy of mixing, entropy of fusion, interfacial energy, roughness parameters and excess thermodynamic functions were computed based on enthalpy of fusion values obtained from DSC studies. The Cahn wetting condition is applicable for monotectic alloy. The optical microphotographs of binary alloys show lamellar and dendritic features.