Browsing by Author "Hilger, Jean-Pierre"
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- ItemElectrochemical measurement of oxygen activity in Iead glass by means of a stabilized ZrO2 sensor Part 1. Qualitative aspect(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) El Harfoui, Mohammed; Hilger, Jean-PierreA zirconia-based electrochemical cell has been developed to measure the oxygen potential in glass with respect to the following parameters: time, temperature, composition of the glass and the nature of the redox system. After melting the raw materials, the glass is very oxidized and the electromotive force grows up to a maximum before diminishing to a level of equilibrium with the surrounding atmosphere. Two opposing kinetically different systems exist: the appearance of oxygen through shifting of the redox equilibrium to the reduced state, and the disappearance of oxygen so as to come back to equilibrium with the surrounding atmosphere. The amplitude of the electromotive force variation with the temperature is based on the constitution of the glass as well as of the redox system.
- ItemElectrochemical measurement of oxygen activity in lead glass by means of a stabilized ZrO2 sensor Part 2. Determination of the equilibrium constants in the redox systems arsenic and antimony(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Lafroukhi, Omar; Hertz, Jean; Hilger, Jean-Pierre; Cornier, GérardThe influence of the redox systems Sb3+/Sb5+ and As3+/As5+ on the lead glass refining is shown. This is achieved through the determination of the equilibrium constant, K, and the thermodynamic standard quantities, ΔG^0, ΔH^0, ΔS^0, by means of chemical analysis as well as electrochemical measurement. A discussion of the results yields the thermodynamic standard quantity ΔH^0 as determined by electrochemical measurement and the transition temperature, T, as determined by chemical analysis, in turn resulting in ΔS^0 = ΔH^0/T. For the redox system As2O3/As2O5 the following thermodynamic standard quantities are determined: ΔH^0 = - 193 kJ/mol, ΔS^0 = - 112 J/(mol K) with T = 1725 K. The respective quantities for the system Sb2O3/Sb2O5 are: ΔH^0 = - 325 kJ/mol, ΔS^0 = - 226 J/(mol K) with T = 1435 K.
- ItemElectrochemical measurement of oxygen activity in lead glass by means of a stabilized ZrO2 sensor Part 3. Measurement of the diffusion coefficient of oxygen(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Hilger, Jean-Pierre; Lafroukhi, OmarThe diffusion coefficient of oxygen is determined with respect to the evolution of the oxygen potential measured at one point of a glass column in the electrochemical cell as well as with respect to time and temperature; subsequently Fick's equation is solved. The measurements are made an the same glass, first with a refining agent, then without one. The results are compared with the values estimated from Eyring's model of viscosity. Different values are found; this would prove the existence of two diffusing species and two distinct diffusion mechanisms as other researchers have recently shown. By applying Eryring's model the diffusion coefficient can be measured according to the relation: lg D* = - 5.40 - 9740/T. By the same way, a glass without a refining agent is investigated by the electrochemical method according to the equation: lg D = - 5.54 - 6548/T. The electrochemical study of a glass with a refining agent shows the following relation: lg D= - 5.56 - 5852/T.