The results of a study on the temperature dependence of differential capacity in alkali nitrites, perchlorates and thiocyanates are given. The adsorption of carbamide, phthalimide and benzidine sulphate on platinum electrodes in a thiocyanate melt was studied by impedance method. A faradaic process has been detected at equilibrium potential in the thiocyanate melt.
Most studies on the double-layer capacity in melts have been carried out on halides. The structure of the double-layer under the conditions of organic substance adsorption on a solid electrode was also studied in the low-melting 2Al, Na/Cl chloride electrolyte. This paper analyses the results of a study of the doublelayer capacity in molten systems containing a complex anion.
Some information on the double-layer structure in molten nitrates was obtained from an analysis of ditrerential capacity curves, taken on mercury[ l] and silver[2] electrodes, and is reported in literature. There is no complete agreement between the results obtained by different authors; however, it follows from all papers that nitrate systemsdo not obey the general rule of proportional relation between double-layer capacity and temperature in melts, which was derived and confirmed for various halogen melts. It was interesting to make clear whether the results obtained are specific to nitrate ion or are regular for all oxygencontaining melts or for the whole of melts with complex anion. Figure 1 shows C-rpcurves, which were obtained at three temperatures in potassium and lithium nitrite melts. As is seen from the figure, the double-layer capacity rises with temperature, and the minimum region decreases with temperature like the regularities observed in molten halides. The doublelayer capacity in potassium and lithium perchlorates increases by 3pF/deg with temperature (see Fig. 2). A similar increase in double-layer capacity is observed on a platinum electrode in the K, Na/SCN melt. Consequently, the observed anomaly is specific to NO, and is not common for oxygen-containing salts. The C-rp curves for NO, taken by us on platinum and gold electrodes, show on the whole the same regularity as on mercury and silver electrodes. The explanation of it is to be sought in the structure of molten nitrates, and one should use structural chemistry methods in addition to electrochemical methods.
The study of the adsorption of organic substances was of qualitative nature in molten nitrates due to the dticulty to treat C-cp curves in a pure solvent (K, Na/NOs); organic additives were not added to the nitrate and perchlorate melts because of possible