Increased chemical reactivity of the surface compared with that in the bulk volume of britton-robinson universal buffers

Abstract

A direct comparison of the chemical r ea ctivi ty at t he surface with t.h at in t~e bulk volume of buffer solutions over the r ange pH 7 t o pH 11.8 was m ade, u s~ng Cornll1~ 01 5 glass as the indicator. By observing in terferometrically the surface alteratIOns of opt ically flat sp ecimen s brought a bout by exposures to a q.u eous buffer solutIOns und ercontr~ll e~ conditions of t ime temperature, and pH it was possible to eva luate, at least semlquantltatlvely, t he difference b etween the che mica l react ivity of t he s urface a nd the bulk volume of the solutions. For t he buffer a t pH 7 t he surfa ce reactivity appeared to corres pond to a h ydrogen ion activity o f pH 9.4. Th e a ppare nt concentra tion different ial between th e s urfa ce a nd bulk volume falls off sharply for buffer s of in creased pH, a moun tlllg t o only 0.2 pH Ul1I t for the buffer at pH 11.0, a nd becomes nondetectable at pH 11.~. U nfo r~un a tel y t he chemical dura bili ty ch ar acteri stics of t he glass were such that no d iff erentiatio n COUld. be ma de between t he h ydrogen ion activ ity of t he surface a nd the bulk volumc III solutIOns more a cid t ha n pH 7.

Use of micro-reactors to obtain new insights into the factors influencing tricalcium silicate dissolution

“…Further work is ongoing in our group to better understand the underlying mechanisms behind the effect of aluminum observed here. Another point to consider in understanding the effect of aluminum is that pH at a micro-reactor surface is likely different from the bulk pH values presented in the text due to reactions taking place at these surfaces [34]. It may be possible to determine micro-reactor surface pH using nano-pH sensors [35] or interferometrically [36] but this is out of the scope of the current work.…”