The phase diagram of LiNO3–KNO3

doi:10.1016/S0040-6031(01)00704-3

Thermochimica Acta

Volume 385, Issues 1–2, 25 March 2002, Pages 81-84

https://doi.org/10.1016/S0040-6031(01)00704-3 Get rights and content

Abstract

The binary phase diagram of LiNO₃–KNO₃ are studied by means of differential scanning calorimeter (DSC). The convincing evidence for the identification of new phase has been presented. The phase diagram indicates an intermediate compound KLi(NO₃)₂, which melts congruently at 428 K. The coordinates of two eutectic points are 420 K, 47 mol% KNO₃ and 410 K, 54 mol% KNO₃.

Introduction

The system of LiNO₃–KNO₃ is usually regarded as a simple eutectic one [1], [2], although some researchers [3] have noted that in addition to the eutectic point at x(Li⁺)=0.41, there was another discontinuity at x(Li⁺)=0.45 which was tentatively attributed to an intermediate incongruently melting compound. This observation seems to have been neglected by some investigators using the liquid mixtures of LiNO₃–KNO₃ [2], [4]. No further thermal measurements have been attempted to explore the origin of the discontinuity. Raman spectroscopic studies [5], [6] indicated that a congruently melting compound KLi(NO₃)₂ was formed. The new compound can be prepared from quenched samples.

In this work, we determined the phase diagram of LiNO₃–KNO₃ by differential scanning calorimetry and calculated their phase diagram.

Section snippets

Experimental

The thermal analyses were carried out on a Perkin-Elmer DSC-7 differential scanning calorimeter. The calibration of the instrument was made by high purity indium and zinc as standard samples.

Reagent grade potassium nitrate and lithium nitrate were recrystallized from redistilled water and dried in the oven at approximately 378 K for 3 days. The dried chemicals were weighed at definite ratios, mixed well in a mortar and transferred to quartz crucibles. The mixtures were dried for 3 days, first at

Thermodynamic relationships

For equilibrium between a solid and a liquid phase in a binary system with components A and B, the Gibbs energy of fusion of A may be expressed as $− Δ_{fus} G_{A} =RT ln x_{A} (ℓ) x_{A} (s) +G_{A}^{E} (ℓ)−G_{A}^{E} (s)$ where x_A(ℓ) and x_A(s) are the mole fractions of A on the liquidus and solidus at temperature T respectively, and R is the gas constant. G_A^E(ℓ) and G_A^E(s) are the partial excess Gibbs energies of A in the liquid and solid. In this system the excess entropy S^E(ℓ) and S^E(s) were set to equal zero. So G^E=H^E. The partial

Results and discussion

Fig. 1 shows the DSC profiles for the salt mixtures of the LiNO₃–KNO₃ system. The DSC profile of 1:1 mixture (mole fraction of KNO₃, x=0.5) shows the typical of the congruently melting compound KLi(NO₃)₂. To determine the eutectic composition, the sharpness of the DSC peaks (expressed by the ratio of peak height to half the width) were compared from sample to sample in the composition range x=0.4–0.6 at 1% intervals. The sharpest peaks were observed for the sample of x=0.47 and x=0.54. The

Conclusions

The convincing evidence for the identification of new phase has been presented in our work. This studies suggested that a congruently melting compound KLi(NO₃)₂ was formed in the system of LiNO₃–KNO₃ formerly regarded as a simple eutectic system, and the KLi(NO₃)₂ forms eutectic mixtures with the end members. This result is identical with thermodynamic calculation.

Acknowledgements

The authors would like to acknowledge the financial support by the Natural Science Foundation of Gansu Province.

References (12)

M.J Maeso et al.
Thermochim. Acta
(1993)
C Vallet
J. Chem. Thermodyn.
(1972)
K Xu
J. Phys. Chem. Solid
(1999)
K Xu et al.
J. Phys. Chem. Solid
(1999)
N.K. Voskresenskaya (Ed.), Handbook of Solid–Liquid Equilibria in Systems of Anhydrous Inorganic Salts, Vol. I, Kete...
M.H Brooker et al.
J. Electroanal. Chem.
(1987)

There are more references available in the full text version of this article.

Cited by (30)

Low-energy consumption LiCl–LiBr–KBr–CsBr electrolyte for high-energy thermal battery application
2024, Ceramics International
The activation of thermal batteries requires plentiful heat to melt the ambient solid electrolyte into an ionic conductor with high ionic conductivity for large current discharge. The process necessitates massive heating powder to provide heat, severely reducing the effective specific energy of the thermal battery. To decrease energy consumption, we developed the LiCl–LiBr–KBr–CsBr molten salt with low melting point of 239 °C, fusion enthalpy at 59.08 J/g, specific heat capacity of 0.38 J/K·g and 0.88 J/K·g in the solid and liquid states, correspondingly, which takes 44% less heat to reach the operating temperature (generally 500 °C) compared to the commonly used LiF–LiCl–LiBr electrolyte. These reductions not only enable the battery to discharge across a broad temperature range, but also lessens the quantity of pyrotechnic heating pellets and enhances the thermal battery's overall specific energy and safety.
Exploring nanoengineering strategies for the preparation of graphitic carbon nitride nanostructures
2023, FlatChem
Graphitic carbon nitride (g-C₃N₄) is a metal-free semiconductor that has drawn considerable attention due to its remarkable photoactivity under visible light irradiation, becoming one of the most promising photocatalytic materials in recent years. However, the photocatalytic performance of bulk g-C₃N₄ is quite limited due to its irregular morphology, low surface area, and rapid recombination of photogenerated charge carriers. Several strategies have been developed to overcome these drawbacks, where morphological control has played a crucial role. In this review, novel nanoengineering strategies for the synthesis of well-defined g-C₃N₄ nanostructures are explored and discussed in detail. Strategies such as exfoliation of bulk material, ionic-liquid assisted synthesis, confinement of nitrogen-rich organic precursors in inorganic salts, use of dynamic gas templates, and design of supramolecular precursors, lead to nano and micrometric morphologies that exhibit outstanding photocatalytic properties. Finally, summary comments and a future perspective on the design of novel g-C₃N₄ morphologies are noted. This review is expected to provide a comprehensive and timely summary of the morphological control of graphitic carbon nitride, leading to a better rational design that improves its performance in photocatalytic processes.
Chemical and mechanical stability of an ion-exchanged lithium disilicate glass in artificial saliva
2023, Journal of the Mechanical Behavior of Biomedical Materials
Multi-component lithium disilicate (LD) glasses were ion-exchanged in a pure or mixed nitrate salt bath. The surface morphologies, mechanical properties, chemical stability and ion leaching of ion-exchanged LD glasses before and after storage in artificial saliva for 21 days were investigated. It can be found that chemical stability of ion-exchanged LD glass was temperature-dependent. The residual compressive stress induced by ion-exchange increased the chemical potential of alkali ions in glass, and the ion-exchanged LD glass, especially 235 °C/64 h group, chemical stability in artificial saliva for 21 days were deteriorated. Back-exchange treatment could relax the stress on the outermost layer of the ion-exchanged LD glass without deteriorating its strengthening effect, and back-exchanged LD glass presented good chemical and mechanical stability in artificial saliva. The results might help to enhance the service stability of ion-exchanged LD glass-ceramics in the oral condition.
Calorimetric characterization and simplified modeling of mixtures of nitrates of the first group elements
2022, Inorganica Chimica Acta
Citation Excerpt :
In Table 5 calculated and experimental data relative to the eutectic temperature and composition are shown. Our data are in better agreement with Vallet [34] and Zang [32], the theory of regular solution is able to correctly calculate both composition and melting temperature of the eutectic and of the liquidus curve while the ideal solution theory differs a lot. The ternary system lithium–sodium-potassium nitrates has been extensively studied and a complete phase diagram is present in the literature [6].
With the aim of finding new heat transfer fluids with high operating temperature (>400 °C) while maintaining low melting point, for use in concentrating solar power plants, new mixtures of nitrate salts have been experimentally characterized and modeled. A simplified model derived from the theory of regular solutions, with interaction parameters optimized on experimental binary data, was implemented to define the starting points for the experimental work on ternary and quaternary mixtures. The model and the experimental procedure were verified on the well-known NaNO₃-KNO₃ and LiNO₃-NaNO₃-KNO₃ mixtures. Substitution and addition of different amounts of cesium to these mixtures have been analyzed. Ternary mixtures with cesium did not show lower melting temperature than known nitrate ternary systems, on the contrary several quaternary mixtures with composition around Li-Na-K-CsNO₃ = 0.29–0.14–0.33–0.24 mol showed a melting temperature of 92–93 °C.
Experimental investigation and thermodynamic evaluation of the CsNO<inf>3</inf>-LiNO<inf>3</inf>-NaNO<inf>3</inf> ternary system
2021, Journal of Alloys and Compounds
The alkali nitrate mixtures are promising phase change materials (PCMs) in the temperature range (373−573) K for the development of thermal storage systems. In this context, their thermochemical properties and phase diagrams which provide useful thermal information are needed for their better use. In the present paper, the mixtures based on cesium nitrate, lithium nitrate, and sodium nitrate are studied by both experimental and optimization techniques. Thus, a critical analysis of thermodynamic data from literature sources of the phases in the CsNO₃-LiNO₃-NaNO₃ ternary system including the pure components is performed. Therefore, reliable phase change data (enthalpy and temperature) of pure nitrates CsNO₃, LiNO₃ and NaNO₃ are proposed. In addition, by means of differential thermal analysis (DTA), the binary CsNO₃-LiNO₃ system and two vertical sections ( $X_{C s N O_{3}} / X_{L i N O_{3}}$ = 1 and $X_{N a N O_{3}}$ = 0.2) in the ternary CsNO₃-LiNO₃-NaNO₃ system are investigated. X-ray diffraction (XRD) technique is also used to analyze phases in the CsNO₃-LiNO₃ binary system at room temperature. The CsNO₃-LiNO₃ binary system is characterized by a congruent equimolar compound Cs_0.5Li_0.5NO₃ which appears at (334 ± 2) K. Two eutectic reactions are found at (445 ± 2) K and (435 ± 2) K, respectively. The system exhibits also a plateau at (427 ± 2) K corresponding to the polymorphic transition of CsNO₃. The CsNO₃-LiNO₃-NaNO₃ ternary system shows two ternary eutectic reactions at (408 ± 2) K and (405 ± 2) K, respectively. Combining our results with experimental data available in the literature, an optimization of the thermodynamic parameters in the ternary system is performed with the help of Calphad approach. A reasonable agreement between the calculated results and the experimental data is obtained.
Thermodynamic evaluation and optimization of LiNO<inf>3</inf>–KNO<inf>3</inf>–NaNO<inf>3</inf> ternary system
2020, Calphad: Computer Coupling of Phase Diagrams and Thermochemistry
Citation Excerpt :
As shown in Fig. 2-II, an obvious liquidus peak was measured at 157.58 °C, which indicates that KNO3·LiNO3 is an incongruent compound. Zhang [11] reported a single peak for the compound KNO3·LiNO3 and considered it to be a congruent compound. However, a small peak can be found at the end of the main peak from the DSC profile [11], which means that KNO3·LiNO3 is probably not a congruent compound.
The phase diagram of LiNO₃–KNO₃ system was investigated with differential scanning calorimetry. Phase transitions data of LiNO₃–KNO₃ system were obtained. Using the measured phase equilibrium data as well as other available phase equilibrium and thermodynamic data in literature, the thermodynamic optimization of parameters for all phases and compounds in the LiNO₃–NaNO₃–KNO₃ system was performed. The Modified Quasichemical Model was applied for the liquid phase, and Compound Energy Formalism was used for the NaNO₃–KNO₃ solid solutions. The compound KNO₃·LiNO₃ was treated with Neumann-Kopp rule. The optimized parameters were used to predict the phase diagram of LiNO₃–NaNO₃–KNO₃ ternary system and the predicted ternary invariant points were experimentally verified.

View all citing articles on Scopus

View full text

The phase diagram of LiNO3–KNO3

Abstract

Introduction

Section snippets

Experimental

Thermodynamic relationships

Results and discussion

Conclusions

Acknowledgements

Thermochim. Acta

J. Chem. Thermodyn.

J. Phys. Chem. Solid

J. Phys. Chem. Solid

J. Electroanal. Chem.

The phase diagram of LiNO₃–KNO₃