T,p-Dependence of intradiffusion in binary fluid mixtures with ammonia as one component

Abstract

Intradiffusion coefficients D_ii were measured for four binary systems with ammonia as one component by the pulsed field gradient NMR technique. The second components are: benzene, acetonitrile, 1-pentanol and methanol. The studies are limited at the low temperature side by the onset of crystallisation. They are extended to a maximum pressure of 200 MPa. The concentration dependence of D_ii in the mixtures containing methanol, shows at constant T and p at lower temperatures a pronounced minimum in the D_ii s. x curves. This minimum becomes deeper with increasing pressure. This can only be explained by the formation of transient hydrogen bonded networks in which the ammonia molecules participate as donors and acceptors. The data for the ammonia/methanol system are analysed by the mode coupling- and the VTF-models. Both show significant anomalies in the mole fraction range of ammonia x(NH₃)≈0.7.