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The redox reaction M (x+n) + n/2O ?2 + M x+ + n/4O₂ of multivalent ions in glass melts influences the melting process and final properties of the glass including the fining (removal of bubbles), infrared absorption and homogenization of melts, reaction between metal electrodes and melts or refractory and melts, and transmission and color of glass. In this review paper, the redox behaviors that occur frequently in the glass production process are introduced and the square wave voltammetry (SWV) is described in detail as an in situ method of examining the redox behavior of multivalent ions in the melt state. Finally, some voltammetry results for LCD glass melts are reviewed from the practical viewpoint of SWV.

The dependence of sulfur redox behavior and its diffusivity on temperature and composition was studied in mixed alkali silicate melts by means of square wave voltammetry (SWV) at different frequencies in a temperature range of 1000℃ to 1400℃. The voltammograms showed two reduction peaks at high frequency but only one peak at low frequency. Irrespective of K₂O/(Na₂O+K₂O), each peak potential due to reduction of S?? to S⁴? and S⁴? to S? moved toward a negative direction with temperature decrease, and the peak current showed a strong dependence on frequency at a constant temperature. However, the compositional dependence of the peak potential showed an inconsistent behavior with an increase of K₂O. The mixed alkali effect was not observed in sulfur diffusion. This inconsistency of both peak potential and diffusion for compositional dependence may be derived from the strong volatilization of sulfur in melts.

Redox investigation of Sn and S ion was attempted in alkaline earth borosilicate glass melts with only 1 mol% Na₂O by means of Square Wave Voltammetry (SWV). According to voltammograms, there was only one peak due to Sn 4+ /Sn 2+ in melt doped with SnO₂. The calculated standard enthalpy and entropy of the reduction of Sn 4+ to Sn 2+ were 116kJ/mole and 62 J/mol K, respectively. The determined redox ratio, [Sn 2+ ] / [Sn 4+ ] in the temperature range of 1300~1600oC was in 0.4~2.1. On the contrary, in the voltammogram of melt doped with BaSO₄ there was no peak due to S 4+ /S? but shoulder that might be attributed to the adsorption of sulfur at the electrode. The absence of the peak related with S4+/S? was discussed from the view-point of the thermal decomposition behavior of BaSO₄ in the glass batch.

Redox behavior was observed in alkali alkaline earth silicate PDP (Plasma Display Panel) glass melts doped with sulfate and sulfide by square wave voltammetry (SWV). According to voltammograms produced at a temperature range of 1100 to 1400℃ and frequency range of 5 to 1000 ㎐, both melts showed the same behavior in which there is one reduction peak at low frequency but another peak at an increase of frequency. Based on the frequency dependence of the peak current, self diffusivity of S 4+ was determined. Based on the temperature dependence of the peak potential, standard enthalpy (ΔH?) and standard entropy (ΔS0) for the reduction of S 4+ to S? were calculated.

The oxygen gas behavior in PDP (Plasma Display Panel) glass melts doped with sulfate (SO₄?²) or blast furnace slag (BFS, S²?) or both by means of yttria-stabilized zirconia (YSZ) electrodes was observed after the first fining. The temperature dependence of oxygen equilibrium pressure (P O2 ) in each melt showed typical behavior, namely P O2 decreased as temperature decreased. This suggests that an oxidation of S⁴? to S?? took place. However, the P O2 -value at constant temperature increased in the following order: BFS＜sulfate+BFS＜sulfate. Of particular note, the P O2 of the melt doped with sulfate+BFS was much lower than that of the melt with only sulfate, although only 10% of sulfur was added by the BFS. This behavior can be explained by the redox reaction between sulfide ions in the BFS and dissolved oxygen ions in the melt during the first fining.

In this study, flint glass batches with blast furnace slag (BFS) were prepared and the contribution of the BFS to the fining of melts was studied through investigations of the melting and fining characteristics. Additionally, a sulfur redox reaction for BFS-doped melts was examined by square wave voltammetry (SWV). The results of the melting & fining test showed that BFS improved the fining of the melts. In a voltammogram of BFS-doped melts, two reduction peaks were shown at high frequencies while only one peak appeared at low frequencies. The peaks were located at a potential that was similar to those of melts fined by sulfate. From those results it was concluded that sulfide (S²?) in BFS has effects in glass melts that are identical to those of sulfate (SO₄²?).

After observing the alkali-silica reaction of the mortar that contains glass abrasive sludge, when evaluating it by a mineral or chemical point of view, it contained reactive silica (59~67%) and R₂0 elements (4.3~9.8%). Also, when evaluated by the mortar bar method, an addition of 5 wt% of CRT glass abrasive sludge is judged harmless. However when adding more, there appear severe contractions, thus carefulness is needed while using. Less than 0.10% of expansion was measured when adding up to 30wt% of flat glass abrasive sludge. However, after 30 days of the measurement, more than 0.1% rate of expansion was measured when adding more than 5 wt%. Therefore, more detailed experiments are needed in case of more than 5 wt%.

The behavior of oxygen gas participating in fining was observed in CRT (Cathode Ray Tube) glass melts doped with Sb₂O? or CeO₂ by means of a yttria-stabilized zirconia (YSZ) electrode. The temperature dependence of the oxygen equilibrium pressure (P O2 ) or the activity in both melts showed typical behavior corresponding to a theoretical redox reaction. In other words, the P O2 value of melts with CeO₂ was lower than that of melts with Sb₂O? above 1250℃. The result implies that Sb₂O? is more efficient as a fining agent compared to CeO₂. On the other hand, melts from a batch containing Sb₂O? and KNO₃ showed much higher P O2 values compared to melts without KNO₃ above 1350℃. It is suggested that the addition of KNO₃ to a CRT glass batch contributes partly to the first fining of the melts.

With aids of square wave voltammetry (SWV) the redox behavior for various combination of polyvalent ions (Sb+Fe, Sb+Zn, Sb+Ce+Ti+Zn) was investigated in alkali-alkaline earth-silica CRT (Cathode Ray Tube) glass melts. The current-potential curve so called voltammogram was produced at temperature range of 1400 to 1000℃ under the scanned potential between 0 and ?800 ㎷ at 100 ㎐. In the case of the Sb+Fe and Sb+Zn doped melts, peak for Sb³?/Sb? shown voltammogram was shifted to negative direction comparing to the only Sb doped melts. However, according to voltammogram of Sb+Ce+Ti+Zn doped melt, Ti and Ce except Zn had hardly any influence on the redox reaction of Sb. Based on the temperature dependence of the peak potential, standard enthalpy (?H?) and standard entropy (?S?) for the reduction of Fe³? to Fe²?, Sb³? to Sb0, Zn²? to Zn? and Ti²? to Ti? in each polyvalent ion combination of CRT glass melts were calculated.

Fining and homogenization of melts during batch melting is closely related to the redox reaction of polyvalent element M (M:Sb, As etc), M (x+n)+ +n/2O 2? → M x+ +n/4O₂. In this study, square wave voltammetry (SWV) measurements were performed to examine the redox behavior of an antimony ion in cathode ray tube (CRT) glass melts. According to results, well-separated two peaks are shown at low temperature while only one peak is shown at high temperature in voltammograms, which reveals that redox reaction of antimony consist of two steps: Sb 5+ /Sb 3+ and Sb 3+ /Sb?, depending on the temperature. Based on the peak potential shown in the voltammogram, the thermodynamic data and the redox ratio for two redox couple were determined.

For self-developed alkali-alkaline earth-silicate and commercial glass melts for plasma display panel substrate, the corrosion behavior of fused casting refractory consisting of Al₂O₃-ZrO₂-SiO₂ was examined at the temperature corresponding to 10²dPa·s of melt viscosity by static finger methode. The corroded refractory specimens showed a typical concave shape due to interfacial convection of melts at their flux line. However, the corrosion thickness by commercial glass melts was 6~10 times comparing to that by the self-developed melts. From the view point of the glass composition and the role of alkaline earth in glass network, it was discussed the effect of alkali/alkaline earth diffusion and temperature on the refractory corrosion.

For substrate glass applied to PDP (Plasma Display Panel), it has been developed many glass compositions that have to not only meet the specifications of PDP but also satisfy the float process as production technology. In the present work, several compositions with no deformation at PDP processing temperature and thermal expansion coefficient of 83~90 × 10 -7 /K were designed. Based on viscosity at high temperature and liquidus temperature for those compositions, three candidate compositions named T-2, T-4, T-6 were selected finally. It was examined additionally that thermal shrinkage at PDP processing temperature and visible transmittance. The properties of T-series were compared with those of commercial glasses and discussed from the view point of PDP device and glass production.

In order to examine the process parameters for the vitrification of Low and Intermediate Level radioactive Waste (LILW) generated from nuclear power plants, measurements of several melt properties was performed for four selected glasses containing simulated waste. Electrical conductivity and viscosity were determined at temperatures ranging from 1123 to 1673℃. The temperature dependences of both properties in the molten state showed a similar behavior in which their values decrease as the temperature increases. The values of the electrical conductivity and viscosity at a temperature of 1423 K adopted in an induction cold crucible melter process were 0.27~0.42 S/cm and 9.8~42 dPas, respectively.

The influence of spindle immersion depth on the determination of glass melt viscosity was examined in rotating cylinder method. The exact adjustment of spindle immersion depth into soda lime silicate standard glass melts could be performed by self-constructed electric system. The results showed a slight dependence of viscosity value on the immersion depth change of spindle shaft. The viscosity error per unit length of spindle was 0.4%/mm under the present cylinder dimension.