Mixed alkali effect in sodium thiocyanate–potassium thiocyanate – acetamide melt systems

Abstract

Electrical conductivity and molar volume of the 0.25[xNaSCN + (1 -x)KSCN] + 0.75CH3CONH, systems were measured as functions of temperature (~293.15-358.15 K) and composition (x = 0.0 -1 . O mol fraction). Temperature dependence of the electrical conductivity was non-Arrhenius in nature and has been analysed by using the Vogel-TammannFulcher (VTF) equation. Molar volume data were fitted to an equation similar to the VTF equation based on the free volume model. Molar volumes and intrinsic volumes were found to be additive in nature. Electrical conductivity isotherms deviate from linearity in different fashion for different temperature regions. The onset of the mixed alkali effect is governed by the anion polarization effect, by a contribution of the auto-dissociated molten acetamide, and by polymeric-type solvated ions.

Electrical Conductivity, Viscosity, and Sound Velocity of Lithium Bromide + Lithium Nitrate + Acetamide Melt Systems

“…On the other hand, K + has a structure breaking property and acetamide in the liquid state exhibits a water-like nature (Kerridge, 1988). As a result we have observed deviation in both conductivity and viscosity isotherms (Mahiuddin, 1996;Kalita et al, 1988c). In the present systems (i.e., a common cation with different anions) unlike mixed alkali system Li + form a rigid polymeric type solvated ion with low mobility and NO 3and Brgovern the conductivity process.…”

“…From Figure 2 it is apparent that the conductivity iso-therms showed significant negative deviation (∼11-15%) and may be considered as the onset of the mixed anion effect, whereas viscosity isotherms (Figure 3) do not show any detectable mixed anion effect as lithium nitrate is progressively replaced by lithium bromide. In our earlier mixed Na/K thiocyanates in acetamide medium (Mahiuddin, 1996;Kalita et al, 1998c) we reported both positive (∼4.6% in K + rich region) and negative (∼27% in Na + rich region) deviations in electrical conductivity isotherms and ∼27-55% negative deviation in the viscosity isotherms. Plowiec et al (1985) reported that Na + in acetamide melt medium form a polymeric type solvated ion.…”

“…Both LiNO 3 and LiBr (E. Merck, >99%) were recrystallized twice from the conduc-tivity water and dried over P 2 O 5 in a vacuum desiccator. Details of the purification of acetamide (Loba, >99%), preparation of the samples, and the temperature control unit to maintain the temperature of the measurements to (0.02 K are given elsewhere (Mahiuddin, 1996). Density Measurements.…”

Viscosity and Molar Volume of Potassium Thiocyanate + Sodium Thiocyanate + Acetamide Melt Systems

“…In the scope of investigating the mixed alkali effect (Day, 1976;Moynihan, 1979;Ingram, 1987;Sangma et al, 1984;Mahiuddin, 1994Mahiuddin, , 1996a in the ternary system, we reported earlier on the electrical conductivity of sodium + potassium thiocyanates in acetamide melt medium (Mahiuddin, 1996a). We observed a pronounced mixed alkali effect (MAE), i.e., both positive and negative deviation from the linearity in the electrical conductivity isotherms in the different temperature ranges of the study.…”

“…In the mixed alkali metal ion systems, both electrical conductivity and viscosity isotherms generally exhibit either positive or negative deviation from linearity. In our earlier paper, we reported the electrical conductivity in an alternating electric field of 1.5 kHz (Mahiuddin, 1996a); perhaps the aggregates/rigid polymeric type solvated ions (Płowiec et al, 1985), which predominate below 333.15 K and in the Na + ion rich region, practically do not move, and the conductivity is due to the jumps of the ions. As a result, we observed both maxima above 333.15 K and minima below 333.15 K in the electrical conductivity isotherms.…”