Ionic Transport in PbO–SiO₂‐Melts (I). Tracerdiffusion and Chemical Interdiffusion

Abstract

Tracerdiffusion coefficients of Si and Pb in PbO‐SiO2‐melts are determined at 850°C between 0.1 < Xsio2 < 0.6. In addition, the temperature dependence of DPb is measured at the metasilicate composition. The chemical interdiffusion coefficient is determined at the same temperature in the quasibinary system PbO‐SiO2 between 0.3 < Xsio2 < 0.6. Theoretical relations are deduced that relate tracerdiffusion and interdiffusion for quasibinary silicate melts. The measured diffusion data show that the cross coefficients Lik (i ≠ k) cannot be neglected in the interpretation of interdiffusion. Also, they indicate a change in the diffusion mechanism between the metasilicate and the orthosilicate composition.

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

“…As we mentioned in the Introduction, measured selfdiffusion coefficients for silicon (D Si ) and lead (D Pb ) ions [8][9][10] are available for lead metasilicate liquid, supercooled liquid, and glass. Here we extend the range of available D Pb using impedance measurements and the Nernst-Einstein relation,…”

“…In this paper, we focus on the lead metasilicate composition (PbSiO 3 , abbreviated as PS). To the best of our knowledge, apart from pure SiO 2 , PS is the only other known stoichiometric oxide glass-forming composition for which experimentally measured diffusion coefficients of network former cations (silicon and lead) are available in a wide temperature range, [8][9][10] above and below T g . The diffusivities of silicon and/or oxygen species could be used as proxies of melt viscosity in silicate systems.…”

The Electrochemical Behavior of Platinum and Iridium in Lead Orthosilicate Melts

“…Using thermodynamic data obtained from the literature, the Nernst potential for the PtI[~-PtO2 equilibrium relative to the PblPbO (in melt) equilibrium can be calculated. For the equilibrium reaction 2Pb(1) + PtO2 ,~ Pt(s) + 2PbO (1) [4] E = +0.535V assuming unit activities for all components except PbO (apbo = 0.287 relative to a liquid PbO standard state). The lack of a distinct oxidation peak in the voltammograms suggests that the reaction proceeds at higher potentials where detail is lost in the exponentially rising current due to 02 production.…”

“…Upon insertion of the electrodes into the melt, but before any experiments were conducted, a rest potential was measured between the working and reference electrodes. This corresponded to the cell IrlPb(1) + 2PbO 9 SiO2(1)ICSZI2PbO -SiO2(1)lIr:O2(g) [1] reference electrode working electrode which is related to the oxygen partial pressure in the argon gas, Po~, and the equilibrium activities of the reference cell, apb and apbo such that E = -(RT/4F) 9 in [apbo.r/(apb.r" ao2.w)]. Here, the activity of molecular oxygen ao2 ~ (Po2/P~ where P~ 2 is the standard oxygen partial pressure.…”

“…Investigations of electrical and electrochemical properties of molten silicates often utilize metal electrodes such as platinum and iridium. This is particularly the case with studies on lead silicate melts where platinum and iridium have been used for ac conductivity measurements, thermodynamic and transference number measurements (1)(2)(3)(4). Despite their use, little attention has been given to the possible reactions that might occur between the melt and the electrode.…”