Voltage anomalies of the glass electrode and the chemical durability of the glass

Abstract

Additional ,,·o rk ha been done on the correspondence between voltage departures (errors) of elecl rodes p repared fr om Com ing 01 5 g lass and t he change in t he chemical durabili ty of the g lass . The results con firm and extend t he earli er findin gs that voltage depart ures of the elcetrod e arc accompanied by durabili ty chan ges of t he glass. Th e pronoullced voltage departures in the a lkaline region an d in h ydrofluoric acid solution s are accompanied by conspie uou attack of the glass. Dilu te solu t ions of acids that do not form so luble compounds of s ilica cause swell ing of the glass. Th is s,,·el li ng is repressed as the concent ralion of lhe solution s is in creased . As i to be expected from the di stribution Jaw and Donnan membran e conside rations, th is repression of swellin g was also br ought aQout by high CQJ1cent rations of orga ni c acids and salts as well as b y the so-called "stro ng" a ids.The attac k of Corning 01 5 glass by alkaline solutions of different ion s was found to be in the orde r, Na+> Li+> K +> Ba++> NH.+, ,,"hich is the same order dicta ted for these ions by the voltage depar t ure data.

Heterogeneous equilibria at the glass electrode-solution interface

“…S uch results arc at least compatible with the predic tions based on Donnan membrane equilibri a. Swelling h as been found to occur for so m an~· sili cate glasses in acid buffers th at one is inclined to conclude that swelling always takes place in the earlier stages of attack excep t for solutions form ing soluble silicate or other solu ble silicon compounds [5,8) . (1) Effect oj Concentration.…”

“…Full-strength ammoni a was used in every case because of its minimal attack on the silica-rich layer as indicated by previous experiments on voltage departures of the glass electrode [7) and th e ch emical durability of glasses [5,8). By taking advantage of th e differe nces in solubility products of silver iodide, silver bromide, and silver chloride (approximate values 10-16 , 8 X 10-13 , and 10 -10 , respectively) , the silver" bromide was precipitated and purified by the addition of silver nitrate to a solution containing an exccs of potassium bromide.…”

“…[3,8,18], (2) alteration of the physical and chemIcal ~ature of th e smface of the electrode [5 , 8], (3) operatlOn of the glass as a "water electrode" [3 19,20, 22], and (4) alteration of the interfacial volt~ age in accor~ with the above .equation [1,2]. If any ?n~ of th em IS correct, any dIsagreement as to which It IS can merely center about agreement on which member of the list is th e cause and which ones are the effects.…”

Effect of annealing and other heat treatments on the pH response of the glass electrode

“…Upon being heated near 550 0 C and cooled according to the previous annealing schedule, these electrodes lost much of their electrode function (table 1, curves -B , fig . 1) and behaved similarly to electrodes prepared from a glass of low hygroscopicity [18,19]. The values for voltage departure plotted in these curves are those shown by the electrodes after 72 hours conditioning in distilled water.…”

pH response of nonhygroscopic glasses

“…Voltage or polarization effects induced by the presence of hydrogen gas are presumably the reason for these high spurious resistances. It is interesting to note that the large drop in these apparent resistance values appears near 50 percent CH.COOH, the same concentration at which marked repression in the rate of swelling had appeared in chemical-durability measurements [22]. In spite of its shortcomings, the Voltohmyst may often give more reliable readings than the resistance bridge because its low-voltage operation minimizes electrolysis and polarization.…”