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

Abstract

The effect of annealing and other heat treatments on the pH response of electrodes prepared f,:o m Corning 015 glass has been studied and a comparison made with the accompanying changes in hygroscopicity of the glass. New, unleached electrodes continued to give t he correct pH respon se after being annealed near t he cri tical temperature as indicated by the expan sion curve for Cornin 17 01 5 glass . Electrodes t hat were leached in 0.1 N HCI at SO° C lost much of thei r pH fun ction when given identical heat treatments. The pH respon se of a typical glass electrode, held 10 minutes at 500° C after being leached in 0.1 N Hel for 6 hou rs at SOO C, was reduced from 59 millivolts per pH (the theoretical value at 25° C) to 22 millivolts per pH. A few seconds in hydrofluoric acid solution restored the pH function of these "dead" electrodes, showing that the inhibiting effect was confined to the outer surface of the electrode bulbs. Evidence obtained by the in te rferometer indicated that the t hi ckness of this inhibiting layer was less than 5.SX 10-6 centimeter. Hygroscopicity determination s made on leached samples of t he powdered glass showed t hat the "sorption" power was greatly reduced by heat t reatment, whereas for unleached specimens this property was much less affected. From the evidence obtain ed it seem s reasonable to in terpret the loss in pH funct ion shown by glass electrodes on heat t reatm ent as being due to the formation of a thin non hygroscopic silica-rich layer. T he resulting electrodes behaved in a manner similar to electrode prepared from glasses of low h yg roscopicity.

Effects of surface initial condition on aqueous corrosion of glass—A study with a model nuclear waste glass

“…Annealing, however, has been utilized to remove internal stresses arising from unsuitable cooling condition during manufacturing process or defects created during polishing. The effects of heat treatment on chemical durability of some glasses have been shown by several studies …”

Some properties of a glass used in paper manufacture

“…The additional strength may have been brought about by initial stages of fluxing the fibers to each other or to the bentonite filler. For other glasses, heating after leaching is known to improve the chemical durability, decrease the hygroscopicity of the surface layer, and greatly lower th e vol tage response of glass electrodes to hydrogen ion activity of aqueous solu tions [21] . The increase in density of the paper at 600 0 C would be accompanied by normal increase in density that is observed to take place in glasses upon being altered from the "quenched" to the annealed condition [22] .…”