Studies of changes of pH, H ÷ ion limiting current, conductivity and temperature during sol-gel processes in a TMOS system

Two gasotight cells with appropriate electrodes were constructed of transparent polypropyletle and kep! at con,ltalll temperature in a water bath. Simultaneous measuren)ents o1' pH, conductivity and temperature as a function of time were can*ted out in the first cell containing a solutiolt with the molar ratio (TMOS:H,O:HCI) of 1:4:10 '~ or 1:4:11) ~ 4. The H' ion limiting current was ~riodically determined by linear vollammetry on a Pt microelectn~de in the second cell with the same solution. The measurements were made in deoxygenated solutions, at 25°C. 40°C or 50°C and extended to a point alter gelation until the contact between the respective electrode and the gel broke down. A significant temperature change was found to occur in the first 20 min after mixing. Strong fluctuations of pH and conductivity were observed in this period. The subsequent changes with time of temperature, pH. conductivity and limiting current were small. The results are discussed in relation to other .studies. ~3 1997 Elsevier Science S.A.