Electroanalytical Chemistry in Molten Salts—A Review of Recent Developments

Fung, Kin Wah; Mamantov, G.

doi:10.1007/978-1-4757-0662-8_4

Cited by 15 publications

(15 citation statements)

References 170 publications

(77 reference statements)

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“…The volatilization of titanium tetrafluoride from the melt was confirmed in a separate experiment in a closed stainless steel vessel provided with a cold trap; the volatile product collected was identified as TiF4 by x-ray diffraction. These observations are not too unexpected since the formation of TiF4 may occur in this fluoride-deficient melt at 500~ by virtue of the following reactions TiF6(l)~-+ 2ZrFx(1) 4-x ~ 2ZrFx+l(D 3-x + TiF4(g) [4] TiF6(D 2-+ ZrFx(D 4-x ~ ZrFx+2(*) 2-x -5 TiF4(g) [5] Since TiF4 volatilizes at 284~ (42), its removal from the melt serves as a driving force to shift the above equilibrium reactions to the right even if TiF4 were to be a stronger Lewis acid than ZrFx 4-x.…”

Section: Electrochemical Studies Of Titanium(ill) In Molten Lif-bef2-...mentioning

confidence: 63%

“…Reagent grade NaBF4 was obtained from the Harshaw Chemical Company and was further purified by a recrystallization procedure described previously (4). The procedure involved a double recrystallization from O.12M HF (aqueous) solution, air-drying at ll0~ crushing, and redrying.…”

Section: Methodsmentioning

confidence: 99%

“…The status of this subject through 1968 has been summarized by Mamantov (I). Recent reviews of molten salt electrochemistry (2)(3)(4) contain much more information pertaining to molten fluorides than did earlier reviews on the same topic (5)(6)(7)(8).…”

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Electrochemical Studies of Titanium in Molten Fluorides

Clayton¹,

Mamantov²,

Manning³

1973

J. Electrochem. Soc.

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The electrochemical reduction of Ti(IV) in molten LiF-NaF-KF [46.5-11.5-42.0 mole per cent (m/o)] at 500~ was studied by means of linear sweep voltammetry, chronopotentiometry, and chronoamperometry. The reduction of Ti(IV) to Ti(III) was found to proceed reversibly at both platinum and pyrolytic graphite electrodes; further reduction of Ti(III) to the metal was shown to be a reversible process involving alloy formation with the platinum electrode. Standard electrode potentials for the processes, Ti(IV) + e-Ti(III) and Ti(III) + 3e = Ti, are-0.058 and-1.798V, respectively (both vs. a unit mole fraction Ni (II)/Ni electrode). The electrochemical oxidation of Ti(III) at unsheathed platinum and sheathed glassy carbon electrodes was studied in molten LiF-BeF~-ZrF4 (65.6-29.4-5.0 m/o) at 500~ Evidence for a reversible electrode reaction was obtained from voltammetric and chronopotentiometric studies. A standard potential of +0.197V (vs. a unit mole fraction Ni(II)/Ni electrode) was determined for the process Ti(III) : Ti(IV) + e. The more anodic value of the standard potential of the Ti(IV)/Ti(III) couple in LiF-BeF2-ZrF4 in comparison to LiF-NaF-KF reflects the higher acidity (Lewis concept) of the LiF-BeF2-ZrF4 melt.

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Section: Electrochemical Studies Of Titanium(ill) In Molten Lif-bef2-...mentioning

confidence: 63%

Section: Methodsmentioning

confidence: 99%

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Electrochemical Studies of Titanium in Molten Fluorides

Clayton¹,

Mamantov²,

Manning³

1973

J. Electrochem. Soc.

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“…Lower oxidation states of certain metals are known to be stabilized in chloroaluminate melts with high aluminum chloride contents, e.g., Cd22+, Pb + Sn2 + (80), and Hg32+ (31). Possible reasons for this stabilization have been discussed by Anders (32), Skala (18), and Mamantov (33). These include, firstly, steric factors and charge densities of anions which affect the stability of low valent cations and, secondly, increased stabilization is expected to occur as the solvent media are made increasingly acidic in the Lewis sense.…”

Section: Table II Anodic Stripping Efficiency Variation With Current ...mentioning

confidence: 99%

Investigation of Subvalent Ion Effects During Aluminum Anodization in Molten NaCl-AlCl[sub 3] Solvents

Gale

Osteryoung

1974

J. Electrochem. Soc.

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Anode current yield variations with current density have been measured in the nominal I: 1 and I: 2 molar NaCI-A/CI3 molten electrolytes by an anodic stripping procedure. In the range of apparent current densities 0.03-6.30 mA cm -2, the brutto electrode reaction was found to be a faradaic three-electron oxidation. Subvalent ion effects could not be positively established. Experimental difficulties in removing final traces of impurities limit the precision of coulometric determinations in these systems; however, the anodic stripping procedure does provide a sensitive means of detecting corrosion losses of aluminum.It has recently been reported (1, 2) that the anode current yields for aluminum dissolution in molten NaC1-A1Cls solvents are appreciably higher at low current densities than required for the three-electron oxidation reactionAs early as 1857 (3), high current yields for the anodic dissolution of aluminum were recorded, and they have since been observed for a variety of electrolytes; aqueous (4, 5), organic (6-8), and nonaqueous (1,2,9). In general, the alternative explanations to account for these deviations from a faradaic three-electron oxidation are (i) the formation of subvalent aluminum ions, (ii) spallation or electrophoretic removal of colloidal aluminum particles, and (iii) chemical corrosion, i.e., direct electrolyte or impurity attack on the anode surface.Delimarskii et al. (1) found that the anode current yields in the NaC1-A1CI3 (l:2M) electrolyte at 160~ were dependent on the anodic current densities for the range 10-150 mA cm -2 and, for all experiments, the anode current efficiencies were usually >100% and exceeded the cathode current efficiencies (weight losses corresponding to faradaic three-electron oxidation of aluminum are 100%). From studies in the equimolar NaC1-A1Cls melt at 300~ Storozhenko (2) determined current yields >100% for the anodic dissolution of annealed aluminum anodes and, similarly, the current yields increased with decreasing anodic current densities, to reach a value 230% at the minimum investigated current density of 0.11 mA cm -2. Delimarskii and co-workers considered that chemical corrosion or losses from spallation were unable to explain the magnitude of their anode current yields, whereas the results of Storozhenko are stated to have been corrected for losses due to chemical corrosion. Accordingly, both sets of data were interpreted by the assumption that considerable quantities of univalent aluminum ion are formed under the conditions of anodization, especially at current densities of 10 mA cm -2 and lower.It was of interest to examine this phenomenon in more detail as the presence of free or complex univalent aluminum ion in larger than trace quantities might have significant consequences in many of the chemical or electrochemical studies, in particular 9 Electrochemical Society Active Member. Key words: fused salts, NaC1-A1CI~ melt, aluminum electrode, subvalent aluminum, Al(I) ion. chloroaluminate solvents, e.g., materials corrosion in aluminum deposition ...

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“…The electroanalytical chemistry of the molten ni-trates and nitrites has been investigated in detail recently. Such studies have been mainly concerned with the salt decomposition reactions and the effect of various additions to the melt on these reactions (1). Passivation and oxidation studies on iron, nickel, and mild steel in these melts have also been reported (2,3).…”

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confidence: 99%