| Popis: |
The process of electrochemical deposition of gold in citrate solution containing Thallium is studied on the rotating disc electrode using cyclic voltametry. Obtained data for different rotational rates could be analyzed in accordance to the well knowm Levich equation. For the first order kinetics, with respect to the reacting ions Au(CN)2- the current density could be expressed in linearized form. Limiting current dansity is defined by the mass transfer coefficient derrived from criterial equation Sh = f(Pe). For constant physical characteristics of an electrolyte, during experiments, i.e. D and V as well as for constant concentration of reacting ions, in the bulk of an electrolyte, a relationship between current density and rotation speed may be written in reduced form as: i-1 = ik-1 + K w-0.5 Accordingly to the equation, a plot of i-1 vs. w-0.5 should give stright lines for various electrode potentials, were the intercepts are ik-1 values and the slopes are K values.The straight lines are not quite paralell as they have to be in accordance to equation. This especially relates indicating a possible change in the number of transferred change, since the other variables constituting the term K kept constant. In this case, at higher potentials, the number of electrons per Au(CN)2- ion increases, as well as the K value, indicating a mixed of even pure kinetic reaction control. Equation may also be applied for the solution in which thallium ions were added. The effect of temperature is significant. At elevated temperature the slopes of the linesdecreases, tending to reach a zero value, corresponding to kinetic kontrol meaning that both D and v changes their values with temperature oppositely each other leading to a certain decrease in lines slopes but also the reaction mechanism changes. |
