Isothermal diffusion studies of water-potassium chloride-hydrogen chloride and water-sodium chloride-hydrogen chloride systems at 25.deg.

Abstract

Time-of-flight measurements have been made on the flux of molecules from the surface of ammonium salts vaporizing under vacuum. As expected with ammonium halides and ammonium bisulfate the TOF distributions correspond to equimolar fluxes of ammonia and the corresponding acid. In the case of ammonium perchlorate the vapor subliming from a single crystal surface comprised ammonia and perchloric acid. When the source was compressed powder the vapor was a mixture of lower molecular weight species. This result seems best explained in terms of decomposition of the vapor after dissociative sublimation in the subsurface interstices of the pressed material.

An eigenvalue method for determination of multicomponent diffusion coefficients. Application to NaOH + NaCl + H2O mixtures

“…This mechanism accounts for the increased diffusivity of the NaOH component in aqueous NaCl as well as the large negative values of Dm?, (the cross-diffusion coefficient measuring coupled flow of NaCl produced per unit concentration gradient in NaOH). Similar diffusional behavior has been observed for HCI + NaCl + H 2 0 and other acid-containing mixed electrolytes (6,8,21). In those systems, the electric field generated by diffusion of highly mobile protons produces counterflow of cations.…”

“…Let Y represent the refractive index (4)(5)(6)(8)(9)(10)(11)(12)(13), conductance (1 4 , 2 I), density (26), optical absorbance (27), or another concentration-dependent property measured along the path of diffusion during an experiment. For initial concentration differences Aci(0) across a sharp diffusion boundary, the corresponding difference in Y is " n [7] …”

“…In many cases the diffusivity of a solute in a multicomponent mixture is significantly different from its binary diffusivity, especially if the solutes are electrolytes or they react chemically (3)(4)(5)(6)(7)(8). Moreover, because diffusional flows interact, multicornponent diffusion of a component produces countercurrent or cocurrent flows of other components in the mixture.…”

“…This system was chosen in order to test recent predictions (21) that aqueous hydroxides diffuse much more rapidly in supporting electrolytes than in pure water. Another purpose of the study was to determine whether or not pH gradients produced by hydroxide gradients, like pH gradients produced by acid gradients (6)(7)(8), can generate large coupled flows of salts. Coupled transport driven by pH gradients has applications to separation technology and plays vital roles in biological systems (22-24).…”

General Linearized Matrix Theory of Electrochemical Mass Transfer With Applications to Electrode Processes and Ion Exchange

“…(5) can be determined from the Stefan-Maxwell diffusivities using relations described below or estimated directly using relations described by Miller (1967) and Kim et al (1973).…”