Oxide Ion Titrations in Molten NaCl with the Zirconia Electrode

Stern, Kurt H.

doi:10.1149/1.2129427

Cited by 8 publications

(8 citation statements)

References 9 publications

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“…10 -~ for Na20 in NaC1 (21). Solubility products from the French school (23,24) are perhaps of uncertain significance since activity ~ concentration as pointed out by Stern (25). In the present case for the oxide CaO, where K~p = ac,+ +ao2-equality of activities does not imply equality of concentrations, the aca2+ being governed by the thermodynamics of the CaC12:KC1 system, where ao2-depends on that of the metal oxide-metal chloride system.…”

Section: Resultsmentioning

confidence: 64%

Voltammetric Investigations of CaCl2 : KCl Melts at 700°C

Brookes

Inman

1988

J. Electrochem. Soc.

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Oxyspecies in molten CaC12:KC1 (73:27 mole percent) at 700~ were monitored voltammetrically using a Au flag electrode. Hydroxide and moisture were shown to be rapidly converted to oxide in the melt. The nature of the oxyspecies present depends on the purity of the blanketing gas used and an oxide ~ peroxide equilibrium pertains with the peroxide ion being stable in the melt. Gold indicator electrodes proved unsatisfactory for quantitative monitoring of oxide itself, probably because oxidative dissolution of gold occurs at potentials close to the presumed oxide oxidation potential. A yttria stabilized zirconia electrode was used to monitor changes in [O-] potentiometrically~ The effects of oxide, peroxide, oxygen, moisture, and hydroxide additions were examined. The evidence suggests that the following reactions predominate in the melt at 700~ C1-+ H20 ~HC1 + OH rapidly displaced to the right 2 OH--~ O = + H20 displaced to the right 02 + 2 O = ~ 2 O22-rapidly displaced to the right Voltammetric evidence for the following reversible redox processes was obtained OH-+ e ~ O = + 1/2 HdAu) Oz 2-+2e ~20 zOz + 2e ~ O2 zSpent nuclear fission material can be reprocessed by converting certain metal oxides to the metal by reduction in molten calcium chloride as redox solvent. Most molten calcium chloride contains oxysPecies which significantly reduce the efficiency of the redox processes concerned. This investigation involves an electrochemical characterization of oxyspecies in CaC12:KC1 [73:27 mole percent (m/o)] at 700~Polarographic waves obtained at Pt on CaO addition to CaC12:NaCI melts were interpreted (1) in terms of the reversible reaction CaO ~ Ca 2+ + 1/2 02 + 2e and anodic voltammetry at Pt was proposed as a means of oxide determination in these melts. An unexplained anodic peak was observed which increased in size as the CaO content increased, and was somehow related to the surface preparation of the Pt electrode, varying from one electrode to another. Addition of water to the melt (2) produced some irreversible electrode process, whereas NaOH addition produced no effect. Complex formation between water and CaC12 melts was proposed.Additions of H20, HC1, and Mg(OHh to MgC12:KC1 melts (3) gave a voltammetric response at Pt interpreted as passivation of the Pt due to formation of insoluble MgO on the Pt surface. No such passivation occurred at W.Reversible two electron oxidation of O-in LiC1-KC1 melt (4), and one electron transfers to H20 and OH-, were proposed at Pt at 390~ In this instance, however, W electrodes gave irreproducible results. Delarue (5) in contrast found~ at Pt, that addition of hydroxide to LiC1-KCt at 400~ produced the same wave as addition of oxide, which conclusion was confirmed by Polart and Degobert (6). Efforts to develop a reversible oxygen electrode in chloride melts have produced uncertain results with several workers unable to decide if O-or 022-were active species in

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Section: Resultsmentioning

confidence: 64%

Voltammetric Investigations of CaCl2 : KCl Melts at 700°C

Brookes

Inman

1988

J. Electrochem. Soc.

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“…Neutron activation analysis is a precise elemental analysis technique for trace quantities of analyte. Trace amounts of elemental oxygen can be determined using the interaction of fast neutrons with oxygen: 16 O ( nf ,p ) 16 N, using a gamma ray detector to quantify the 6 MeV γ ray [12]. Though neutron activation analysis isprecise, it is cumbersome and requires a research reactor with a fast neutron beam and a few days' analysis time for irradiation, cooling, detection and data processing.…”

Section: Fast Neutron Activationmentioning

confidence: 99%

A Review of Electrochemical and Non-Electrochemical Approaches to Determining Oxide Concentration in Molten Fluoride Salts

2018

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The design of reactor core and heat transfer systems for molten salt reactors (MSRs) and fluoride-salt cooled high temperatures reactors (FHR) necessitates a precise understanding of oxide contribution to thermophysical and chemical properties of the molten salt medium [1]. The dissolved oxide content in the melt can vary during reactor operation due to transmutation or migration to/from outside the core. Therefore, it is important to develop capabilities to quantify the oxide concentration at reactor conditions such as temperatures exceeding 500 o C. As part of the oxide sensor design process, a literature review of electrochemical and non-electrochemical approaches to determining oxide concentration in molten fluoride salts was conducted and an evaluation of various methodologies is presented here. This evaluation was the basis for selecting electrochemistry as the most promising technique with which to develop an oxide sensor.

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“…The indicator electrode is Ni/NiO/ SZ. (SZ = stabilized zirconia) which is specifically reversible only to 02- (7)(8)(9)(10)(11). The entire cell can be written as Ni/NiO/SZ/FLINAK Melt/BN/NiF2(sat)/Ni [A] where BN is the boron nitride envelope containing the reference electrode.…”

Section: Wo42-+ 02-= Wo54-[6]mentioning

confidence: 99%

“…In aM2o [8] in dilute oxide melts activity coefficients are constant and can also be absorbed into E ~ Equation [8] then becomes…”

Section: Wo42-+ 02-= Wo54-[6]mentioning

confidence: 99%

“…It has been reported that 10 -~ mol/cm 2 (approximately 5 monolayers) is the smallest amount of RuO2, deposited on Nb (7), that will exhibit a measurable electrocatalytic effect for the chlorine evolution reaction. Additional reports show that electrocatalytic activity of RuO2-modified TiO2 remains high even when RuO2 at the electrode surface is depleted beyond the limits of Auger detection (8).…”

Section: Introductionmentioning

confidence: 99%

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Potentiometric Studies of Some Oxyanions in Molten Fluorides

Stern

1989

J. Electrochem. Soc.

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The dissociation of several oxyanions: WO42-, SiO32-, TaO3 , TiO32-, and M0042-in molten FLINAK has been studied potentiometrically with a stabilized zirconia electrode. The interaction of these melts with 02. has similarly been studied. All of these ions appear to be stable in FLINAK, but SiO32-and TaO3 take up O 2-to form higher oxides, probably SiO44and TaO43-, respectively. The behavior of the Pt electrode in these melts is quite complex. Its potential varies with ln[O2-], the slope being RT/F or larger. It is therefore not suitable as either reference or 02-indicator electrode.

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Oxide Ion Titrations in Molten NaCl with the Zirconia Electrode

Cited by 8 publications

References 9 publications

Voltammetric Investigations of CaCl2 : KCl Melts at 700°C

Voltammetric Investigations of CaCl2 : KCl Melts at 700°C

A Review of Electrochemical and Non-Electrochemical Approaches to Determining Oxide Concentration in Molten Fluoride Salts

Potentiometric Studies of Some Oxyanions in Molten Fluorides

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