Concerning oxygen anions in a nitrate melt

Burke, J.D.; Kerridge, D.H.

doi:10.1016/0013-4686(74)85075-9

Cited by 38 publications

(5 citation statements)

References 21 publications

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“…Thermodynamic calculations support the conclusions regarding the important role of the cation in reactions involving molten nitrates. Considering, for example, the reaction M20(s) + MNOs(1)~ M202(s) + MNO2(1) [12] the standard free-energy change, AG o, at 350~ is estimated to be about 10.2 kcal/mole in LiNOs, 1.8 kcal/mole in NaNO3, and --3.4 kcal/mole in KNOs from available data (14,(52)(53)(54). These values show that Li20 is quite stable, thermodynamically, in LiNO8 at 350~ and that the stability of the metal oxide in its corresponding nitrate melt decreases with increasing size of the cation involved.…”

Section: Discussionmentioning

confidence: 99%

“…Oxide ions are produced by the electrochemical reduction of molten alkali metal nitrates (2)(3)(4)(5) MN'Oa + 2e-~ MNO2 + O-- [1] The role of the oxide ion produced by this reaction has been a controversial ghost which has haunted the chemistry of fused nitrates (6,7). A variety of studies (8)(9)(10)(11)(12)(13)(14)(15)(16)(17), however, support the conclusions that the oxide ion in nitrate melts is an unstable species due to the following reactions O = + NO~-~ NO2-+ 02 = [2] 02 = + 2NO~-~ 2NO2-+ 202- [3] in which the oxide is converted to peroxide or superoxide (6,18,19). Most of the previous studies were conducted in molten NaNOs-KNO3 mixtures at about 230~ with very little consideration given to the role of the metal cation.…”

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confidence: 99%

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Cation Effects on the Electrode Reduction of Molten Nitrates

Miles

Fletcher

1980

J. Electrochem. Soc.

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Cyclic voltammetric, potentiostatic, and galvanostatic methods were used to investigate the electroreduction of molten alkali metal nitrates at 350°C on a platinum electrode. The cation of the nitrate salt plays a major role in the reduction reaction as well as in determining the ultimate fate of the oxide ion produced. Nitrate reduction occurs most readily in LiNO3 melts, and the Li2O formed appears to be relatively stable. Overvoltages for nitrate reduction increase with increasing size of the metal cation involved and the oxide ions produced by the reaction become more prone to oxidation to form peroxides or superoxides. The rate of water removal by purging the nitrate melt with helium gas was monitored by the water‐wave on platinum. Surprisingly, no water‐wave was detected using a nickel electrode. The solubilities of several substances were determined in LiNO3 and KNO3 and compared with ideal solubility calculations.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Cation Effects on the Electrode Reduction of Molten Nitrates

Miles

Fletcher

1980

J. Electrochem. Soc.

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“…Platinum was chosen in order to avoid the effect of silica as an acid (12)(13)(14). The platinum crucible was itself contained in a Pyrex glass cell.…”

Section: Experimental Section Technicalmentioning

confidence: 99%

“…For each experiment, 100g of the nitrate-nitrite mixture thus prepared were introduced into a cylindrical platinum crucible. Platinum was chosen in order to avoid the effect of silica as an acid (12)(13)(14). The platinum crucible was itself contained in a Pyrex glass cell.…”

Section: Experimental Section Technicalmentioning

confidence: 99%

Acidity and Thermochemical Stability of Molten Sodium Nitrate and Nitrite Mixtures

Picard

Flament

Trémillon

1985

J. Electrochem. Soc.

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The influence of acidity on the thermochemical stability of molten sodium nitrate-nitrite mixtures used as heattransfer fluids (as in the case of the French electrosolar power system called Themis) has been demonstrated by considering the potential-pO 2-diagram relative to redox systems corresponding to these mixtures and been established from thermochemical data. The importance of fixing the pO 2-value with a buffer has been clarified. The couple H20(g)/ OH-, whose acid-base constant was previously determined, appears as the most efficient for this purpose. The potential-pO 2-diagram could be set up experimentally by studying the disproportionation of nitrite ion into nitrate and nitrogen monoxide and by determining the standard potential of the electrochemical system NO3-/NO2-by means of potentiometric measurements with a platinum electrode and with an yttria-stabilized zirconia membrane electrode indicator of pO 2-. This diagram has allowed us to specify, as a function of temperature, the boundary values of pO 2-which should not be gone beyond in order to avoid the decomposition of the mixtures as a result of the nitrite disproportionation.Molten alkali nitrate-nitrite mixtures are known for their high heat capacities and their low melting points, which have led to their use as heat-transfer fluids at temperatures not greater than 723 K. The use of the mixture called HITEC [KNO~53-NaNO240-NaNO37 weight percent (w/o)] in the French electrosolar power system Themis, built by Electricit6 de France, makes necessary that this liquid can circulate in a thermal loop where the extreme working temperatures are 523 and 773 K. In view of this use, we have decided to study the chemical factors influencing the thermal stability of molten NaNO~-NaNO2 mixtures.The thermochemical decomposition of nitrates (1, 2) and nitrites (3-5) has been the subject of many studies, but the authors do not agree about the reactions which take place. It seems, nevertheless, well established that decomposition is accompanied by the release of nitrogen, nitrogen oxides, and oxygen, with the production of alkali oxide. Because of the complexity of these reactions, we have undertaken a preliminary study based on the existing thermochemical data (6). Reactions in these media put into play the redox systems of nitrogen which depend on the oxide anion activity. So, the results have been expressed in the form of a potential-(oxo)acidity diagram. This sort of presentation has already been used for alkali nitrates and for alkali nitrites by Conte and Casiado (7), Marchiado and Arvia (8), and by Haan and Van Der Porten (9), but not for their mixtures.The calculated diagram has subsequently been specified by experimental determinations, and the results obtained have. finally permitted the definition of the conditions which would be favorable to the thermochemical stability of the heat-transfer fluid.We present here a part of our investigation concerning the effect of acidity, in studying especially the sodium nitrate-sodium nitrite-nitrogen monoxide syst...

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“…The reaction of 2 with 2,3-dimethylbutadiene also yielded a dienic adduct (16) along with the expected products (14 and 15). The formation of dienes 13 and 16 14 (46%) 15 (26%) 16 (28%) can be considered to occur via a hydrogen atom transfer reaction in an initially formed diradical intermediate (eq 2).…”

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confidence: 99%

Oxygen electrodes in nitrate melts

Schlegel¹

1975

J. Am. Chem. Soc.

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Concerning oxygen anions in a nitrate melt

Cited by 38 publications

References 21 publications

Cation Effects on the Electrode Reduction of Molten Nitrates

Cation Effects on the Electrode Reduction of Molten Nitrates

Acidity and Thermochemical Stability of Molten Sodium Nitrate and Nitrite Mixtures

Oxygen electrodes in nitrate melts

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