Molten Alkali Nitrates Research Articles

Flux crystal growth of rubidium–iron silicates and germanates and their ion-exchange using alkali nitrate salts

Single crystals of two new rubidium ferrites, RbFeSiO4 and RbFeGeO4, were grown out of a eutectic RbCl–RbF melt. Both compounds crystallize in the noncentrosymmetric orthorhombic space group Ima2 and exhibit a three-dimensional porous framework structure composed of statistically disordered (Fe/T)O4 (T = Si, Ge) tetrahedra that corner-share to generate large channels running down the c-axis. These channels are occupied by Rb ions to maintain charge balance. RbFeSiO4 can also be prepared via a solid-state reaction by mixing and heating stoichiometric amounts of Rb2CO3, Fe2O3 and elemental Si; however, a similar approach for preparing RbFeGeO4 yielded a mixture of RbFeGeO4 and RbFeGe2O6. Powder second harmonic generation (SHG) measurements of RbFeSiO4 determined that the material is SHG-active with an intensity of 0.5 times of α-SiO2. First principles calculations in the form of density-functional theory indicated that it would be possible to ion exchange the Rb cation for other alkali metal cations. Applying a molten alkali nitrate salt-bath treatment at low soak temperatures of 350 °C–450 °C and short soak times of ∼16 h resulted in the almost complete replacement of rubidium with potassium and the partial replacement of rubidium with cesium, yielding K0.92Rb0.08FeSiO4, K0.91Rb0.09FeGeO4, and Cs0.48Rb0.52FeGeO4. No ion-exchange was observed when RbFeSiO4 was soaked in molten CsNO3; however, it was possible to force the exchange by using a CsCl melt at 680 °C to yield Cs0.13Rb0.87FeSiO4.

Assessment of bismuth oxide-based electrolytes for composite gas separation membranes

Oxide + salt composites can be used in CO2 and NOx separation membranes, where high oxide-ion conductivity is crucial to improve performance. Pursuing this goal, the stability of three different bismuth oxide-based electrolytes (Cu + V, Y and Yb-doped) against molten alkali carbonates (Li, Na, K) or nitrates (Na, K) was tested firing them in the 450–550 °C temperature range, and with endurance tests up to 100 h. A well-known ceria-based composite was used as reference (CGO - Ce0.9Gd0.1O1.95). Oxides and composites were studied by X-ray diffraction, scanning electron microscopy and impedance spectroscopy (in air, 140–650 °C temperature range). Bi2Cu0.10V0.90O5.35 easily reacts with molten salts. Bi0.75Y0.25O1.5 and Bi0.75Yb0.25O1.5 have higher stability against molten carbonates and complete stability against molten nitrates. The Y-doped oxide stability against the molten carbonates was enhanced changing the molten salt composition (Y2O3 additions) and using lower firing temperatures. Above all, composites based on Y or Yb-doped Bi2O3 with molten alkali nitrates showed impressive 6× or 3× higher electrical conductivity at 290 °C, in air (4.88 × 10−2 and 2.41 × 10−2 S cm−1, respectively) than CGO-based composites (7.72 × 10−3 S cm−1), qualifying as promising materials for NOx separation membranes.

Material aspects of Solar Salt for sensible heat storage

For sensible thermal energy storage (TES) in liquids in the temperature range from 250°C to 550°C, a mixture of 60wt% sodium nitrate (NaNO3) and 40wt% potassium nitrate (KNO3), known as Solar Salt, is commonly utilized. At the time of writing, TES technology for concentrating solar power is the major application. Although commercial systems have been demonstrated, there are still several material aspects to be investigated. In this paper we address thermophysical properties and metallic corrosion, as well as thermal decomposition processes. The paper reviews temperature dependent thermophysical properties of Solar Salt. Deviations among the authors of these properties were small for the density (±1.5%), medium for the heat capacity (±7%) and large for thermal diffusivity and thermal conductivity values (±15%). The paper gives an overview of the various aspects of steel corrosion in molten alkali nitrate salts. From literature data, four steel type categories mainly depending on the temperature range are defined. The paper presents thermal stability examinations of Solar Salt and NaNO3 by isothermal lab-scale tests and thermal analysis measurements. Salt analysis in the isothermal test showed a steadily increasing oxide level at a constant nitrite to nitrate ratio. The result shows that there are kinetic differences in the first decomposition process with nitrite formation and the second decomposition process with oxide formation. The impact of the partial oxygen pressure on the decomposition temperature was examined by thermogravimetric measurements. Measurements show an improved stability limit for higher partial oxygen pressures.

Synthesis of mullite precursors in molten salts. Influence of the molten alkali nitrate and additives

Silica gel and aluminium salt, in the stoichiometric ratio for mullite (Al/Si=3), have been used to prepare the mullite precursor by reaction in molten alkali nitrates at 450°C. The influence of the nitrate (NaNO 3, KNO 3 or mixture NaNO 3–KNO 3) and the additives (Ca 2+, Ba 2+, Bi 3+) on the phase transformations has been followed between 1000 and 1400°C. It appears that molten NaNO 3 favours the crystallization of cristobalite and α-Al 2O 3 whereas KNO 3 inhibits the formation of silica and mullite. The mixture NaNO 3–KNO 3 seems to be the best choice. Addition of foreign cations improves the mullite formation and favours the synthesis of θ-Al 2O 3, especially in the case of Bi 3+. But the crystallization temperature of mullite is not changed.

Mixing Properties of Molten Alkali Nitrates Based on the Law of Corresponding States

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMixing Properties of Molten Alkali Nitrates Based on the Law of Corresponding StatesYutaka Tada, Setsuro Hiraoka, Takashi Achiwa, and Seung-Tae KohCite this: Ind. Eng. Chem. Res. 1995, 34, 4, 1461–1470Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/ie00043a055RIGHTS & PERMISSIONSArticle Views71Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (837 KB) Get e-Alerts Get e-Alerts

The Frequency Dependence of the Dynamical Conductivity of Molten Alkali Nitrates in the Microwave and Millimetre Wave Range

AbstractMeasurements are reported of the dynamical conductivity of the alkali nitrates in the molten state near their melting points Tm (1 < T/Tm < 1.2) in the microwave and millimetre‐wave range. The conductivity of KNO3, RbNO3 and CsNO3 shows no dispersion up to the far‐infrared whereas in LiNO3 and NaNO3 it passes through a shallow minimum in the millimetre‐wave range. The temperature dependence of the conductivity indicates that it is due to activated processes up to the millimetre‐wave region. The shallow minimum in LiNO3 and NaNO3 indicates a high frequency limit of the diffusive response at about 50 GHz.

Local Structure and Okada's Empirical Relation for the Internal Mobility of Cations in Molten Alkali Nitrates

The empirical relation bi = (V - FOi)-1 Ai exp(- Ei/RT) for the internal mobility bi of cations i in mixtures of molten alkali nitrates, where V is the molar volume of the mixture, is compared with MD simulations. For pure LiNO3 and NaNO3 it is found that (V-Voi)-1 is proportional to the concentration of oxygens in the first coordination shells of the cations i.

Ultrasonic and Hypersonic Spectroscopy of Alkali Nitrate Single and Binary Melts

Sound propagation in the molten alkali nitrate single salts, LiNO3, NaNO3, RbNO3 and CsNO3 and the binary melts, NaNO3–LiNO3, −RbNO3 and −CsNO3, have been studied over the frequency range of 5–25 Mhz and 3–8 GHz by means of pulse and Brillouin scattering methods, respectively. A dispersion of sound propagation is observed at the frequency between ultra- and hyper-sound region for KNO3, RbNO3 and CsNO3. The thermodynamic properties derived from the sound velocity are approximately additive for the binary melts investigated. The bulk viscosity, ηB was derived from the absorption coefficient determined. The value of ηB/dT is negative and temperature dependence of ηB/ηS is insignificant for the molten alkali nitrate single salts. The bulk viscosity of the binary melt decreases rapidly with the addition of the component having smaller bulk viscosity in pure salt.

Ultrasonic Absorption and Relaxation Phenomena in Molten Nitrate Mixtures

An optical device based on the Debye-Sears effect is developed to determine the ultrasonic absorption and velocity in molten alkali nitrate + silver nitrat mixtures. RbNO3 + AgNO3 and CsNO3 + AgNO3 are investigated in the total composition range between 480 K and 580 K within a frequency interval from 10 MHz to 35 MHz. In the concentration range of high ultrasonic absorption we find dispersion and a frequency dependent step in the absorption curve caused by relaxation. The relaxation time of the structural relaxation in the molten salt mixtures investigated here is in the order of 10-8 s. The volume viscosity, the adiabatic constant, and the compressibilities are calculated.

Raman, Visible and Ultra-violet Spectral Studies of Ionic Interactions in Molten Alkali Nitrate and Nitrite Systems

Abstract The interaction between the various ions in the molten systems NaNO3-NaNO2, LiNO3-NaNO2 and NaNO3-KNO2 has been investigated by Raman, visible and ultraviolet absorption spectroscopy. It is concluded that the interaction between the anions is very weak and that the cations Na+ and K+ are randomly distributed around the nitrate and nitrite anions. The empty orbital level of Na+ (434 nm) in NaNO3-NaNO2 relative to the π level of NO2 - is estimated. When small amounts of Li+ are added to the binary sodium melt, an anomalous spectroscopic result is obtained.

Diffusion Measurements with the Gravimetric Method in Solutions and in Molten Alkali Nitrates

Abstract The gravimetric method of interdiffusion measurement from a quartz frit is developped into an accurate general method. It is applied to a number of electrolyte solutions; for iodides and bromides a correction for the adsorption is applied. For the molten alkali nitrate systems (K-Cs)NO3 at the molar fractions xCs = 0.0 and xCs = 0.1, (Na-Cs)NO3 at xCs = 0.0 and xCs = 0.1. (Na-Rb)NO3, at xRb = 0.0 and xRb = 0.1 and (Na-K)NO3 at ,xNa = 0.0, xNa = 0.3 and xNa = 1.0 the interdiffusion coefficient is determined over the temperature range of 600-723 K. The values obtained here are discussed in comparison to those from literature.

Oxide Ion Chemistry and Corrosion in Molten Alkali Nitrates and Nitrites

Oxide Ion Chemistry and Corrosion in Molten Alkali Nitrates and Nitrites

ChemInform Abstract: Precipitation of Lead Oxides in Molten Alkali Nitrates.

AbstractDie Fällung von Pb‐oxiden aus Pb(NO3)2‐Lösungen in Alkalimetallnitratschmelzen wird unter Luftausschluß untersucht.

Precipitation of lead oxides in molten alkali nitrates

The precipitation of lead oxides from solutions of lead nitrate in molten alkali nitrates and in the absence of air is investigated. Lead oxides are never produced in lithium nitrate while these compounds spontaneously settle in molten potassium nitrate. In the case of sodium nitrate, the precipitation needs the addition of alkaline oxides.The nature of the solid product is temperature dependent. The precipitation of PbO or of the basic salt 5 PbO . Pb (NO3 )2 takes place below 325 °C while Pb3 O4 is formed at higher temperatures. This latter compound seems to be replaced by PbO2 beyond 475°C. In the case of mixtures of nitrates and nitrites (25 M %), the production of PbO only is observed independently on the temperature of the melt.These phenomena are explained by differences in the acidic properties of the cations of the investigated melts and by the temperature dependence of the oxidizing power of molten nitrates.

Solubility of carbon dioxide in molten alkali halides and nitrates and their binary mixtures

Solubility of carbon dioxide in molten alkali halides and nitrates and their binary mixtures

ChemInform Abstract: ELECTROCHEMISTRY OF HYDROGEN IN IONIC SOLVENTS‐ RDE CURRENT‐POTENTIAL CURVES FOR THE SYSTEM (PLATINUM)WATER HYDROGEN, HYDROXYL ION IN MOLTEN ALKALI NITRATES

Chemischer InformationsdienstVolume 9, Issue 5 Physical Inorganic Chemistry ChemInform Abstract: ELECTROCHEMISTRY OF HYDROGEN IN IONIC SOLVENTS- RDE CURRENT-POTENTIAL CURVES FOR THE SYSTEM (PLATINUM)WATER HYDROGEN, HYDROXYL ION IN MOLTEN ALKALI NITRATES E. DESIMONI, E. DESIMONISearch for more papers by this authorF. PALMISANO, F. PALMISANOSearch for more papers by this authorP. G. ZAMBONIN, P. G. ZAMBONINSearch for more papers by this author E. DESIMONI, E. DESIMONISearch for more papers by this authorF. PALMISANO, F. PALMISANOSearch for more papers by this authorP. G. ZAMBONIN, P. G. ZAMBONINSearch for more papers by this author First published: January 31, 1978 https://doi.org/10.1002/chin.197805030AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume9, Issue5January 31, 1978 RelatedInformation

P–V–T studies on molten alkali nitrates. Part 1.—Thermal pressure coefficients and compressibilities

The p–V–T relationships of the molten alkali nitrates (Li, Na, K, Rb and Cs) were determined using a gas-pressurised, externally-heated pressure vessel. The cells were the pyknometer type with a long capillary barrier between the pressurising gas and the bulk of the liquid. Data, over a range of temperature from 500 to 800 K and a range of pressure to 1400 bar, were plotted in the form of isochores and used to determine densities and compressibilities of the liquids.

Hydrogen Behavior in Molten Alkali Nitrates

Hydrogen Behavior in Molten Alkali Nitrates

Growth of oxide layers on platinum electrodes in molten alkali nitrates

The formation of oxide layers on Pt anodes and on Pt cathodes in each of the molten alkali nitrates, LiNO 3, NaNO 3 and KNO 3, has been investigated under galvanostatic and potentiostatic conditions at 340°C. The coverage by oxygen on the anode increased with the polarization potential and time and reached a limiting value of about 2·6 oxygen atoms per apparent surface platinum atom. No cation effect on the anodic formation of the oxide film was observed. Thick multilayer oxide films grew very rapidly on the “cathode” in the KNO 3 melt and slowly on that in the NaNO 3 melt. In the KNO 3 melt and also in the NaNO 3 melt, the growth rate of the multilayer oxide reached a maximum at −1.65 V ( vs a Ag 0.1 M Ag + in 1 kg KNO 3 reference electrode) and rapidly fell at more negative potentials because of the dissolution of the oxide into the melt. Above −2.0 V, neither the formation of the multilayer oxide nor corrosion of the electrode was observed. In the LiNO 3 melt, no multilayer oxide film was formed at any potentials.

Chemical and electrochemical studies of the oxide ion-oxygen reaction in equimolar sodium nitrate+potassium nitrate

Manometric and potentiometric studies of the oxide ion+oxygen reaction in molten alkali nitrate are reported. Sufficient oxygen was found to be absorbed by alkali nitrate melts after addition of Na 2O to convert virtually all of the added O 2− ion to O 2 2− and O 2 − ions. The equilibrium constant and the temperature dependence of the reaction 2 O 2 −=O 2+O 2 2− was determined over a temperature range of 250–400°C. The value of the equilibrium constant determined by the method used was found to depend on whether Na 2O, Na 2O 2, or NaO 2 was used as the starting material. Stabilized zirconia tubes were studied for use as oxide ion probes in these melts. In oxygen-containing melts the zirconia/melt interface was shown to respond to added Na 2O or NaO 2 in a manner similar to the response of a platinum wire dipped into the melt. This response is shown to be the expected one, for the cells studied. When nickel chloride was added to oxygen-saturated melts which contined Na 2O, a reaction was found to occur which resulted in the effective loss of two oxide ions from the melt for each nickel ion which was added.