The Determination Of Transference Numbers Of Aqueous Electrolytes By Electromotive Force Measurements Of Concentrations Cells Using Mortar (cement,sand) Membranes

Abstract

The transport and :!.on-exc.hange propert ies of mortar (cement-sand) membranes have been experimentally investigated by determining the transferenc..e numb er s of sodium chloride (Na.C'l) through such membranes. The transferenc.e phenomena of sodium c.hloride was studied due to the deleterious elfec.ts of c.hloride (CI-) ions on imbedded steel 1n rejnforc.ed mortar/concrete struc.tures exposed to m~rine environments. This was done by setting up conc.entration cells of the type 1 'mortar ' , Ag/AgCI NaCIC ) mb INaCIC- ) AgCI/Ag aq,c1 me rane dq,C2 c1>c2' using diffe~~e.Rtmembrane thicknesses and ,.,. concentrations "i and •.c,2. The measured emf of the various cells with the corresponding equilib rium chloride ion concentrations were used for the computation of the transference numbers. Th8 pH values of the solutions from both cell cornpa rt meu t s were also measured until a constant value of about 12 was achieved. The chloride ion constituent ~ransference number was found to vary between 0.8028 and 0.8104' while that of the sodium ion constituent (iv) was found to vary between 0.1896 and 0.1972 for a fixed merrb r ane thic.kness (5mm) and a concentration range of O.05M to O.5M. The transference numbers were however found to be' invariant with different rnembrarie thicknesses (4mm, 5mm and Gmm) for a constant set of external electrolyte concentration, and we ref 0un d to bet C1- :=0 O. 806 an d t Na + = O. 19 3 (to 3 dec. placEs). The ion exchange capacity of the mort ar merrbr arie s 1'1 as found to increase with increasing rnembr an c thickness, as depieted from the quantity 01 chloride ions retained in - the mernbr ane matrix with increasing membrane thickness. The investigation has shown that a mort ar membrane can act as an an i.on exchange -.....- - .- ., mernbrane, and the experiment ally determined transference nurrb eTS u s i.ng the mort ar membr ane s were in very good agreement with the empirical formula E = 2 tN + a RT F used for the comput ation of trans ference nuirb ers.