Inner surface potential at (111) fluorite/aqueous electrolyte solution interface

Abstract

Za svrhu određivanja površinskog potencijala (111) kristalografske plohe fluorita konstruirane su dvije fluoritne monokristalne elektrode novog dizajna. Izrađenim monokristalnim elektrodama ispitana je stabilnost odziva te ponovljivost mjerenja. Potenciometrijskim titracijama istraţio se utjecaj pH sustava, ionske jakosti otopine, koncentracije Ca2+ iona te koncentracije F− iona na površinski potencijal (111) plohe fluorita. Fluorit je slabo topljiv u vodenim otopinama pa se topografskim mjerenjima mikroskopom atomskih sila proučio utjecaj otapanja (111) plohe fluorita na morfologiju njezine površine. Istražena je kinetika otapanja (111) plohe fluorita praćenjem koncentracije Ca2+ i F− iona u otopini tijekom 24 sata otapanja fluorita in situ mjerenjima s fluoridnom i kalcijevom ionski selektivnom elektrodom. Na temelju rezultata navedenih mjerenja predložen je model elektriĉnog međupovršinskog sloja i model površinskih reakcija za međupovršinu (111) fluorit/vodena otopina elektrolita.For the purpose of determining the inner surface potential of (111) fluorite plane two fluorite single-crystal electrodes of the new design were constructed. The reproducibility and sensitivity of the constructed single-crystal electrodes were tested. A series of potentiometric titrations was carried out to examine the surface potential of (111) fluorite plane as a function of pH, ionic strength and concentrations of Ca2+ and F− ions. Due to the fact that fluorite is a semisoluble salt in aqueous solutions the topographic measurements were done by atomic force microscope to examine the influence of dissolving (111) fluorite plane on the morphology of its surface. The kinetics of dissolving (111) fluorite plane was investigated by monitoring the concentrations of Ca2+ and F− ions in solution for 24 hours of dissolution by in situ measurements with fluoride and calcium ion-selective electrode. Based on the results of the above mentioned measurements, a model of the electrical interfacial layer and a surface complexation model for the (111) fluorite/NaCl solution interface was proposed