LiNO3 NaNO3 Research Articles

Local Structure and Molecular Mobility in Ternary System LiNO3–NaNO3–H2O at Room Temperature, According to Data from Molecular Dynamics Simulation

Local Structure and Molecular Mobility in Ternary System LiNO3–NaNO3–H2O at Room Temperature, According to Data from Molecular Dynamics Simulation

The Effect of In Situ Synthesis of MgO Nanoparticles on the Thermal Properties of Ternary Nitrate.

The multiple eutectic nitrates with a low melting point are widely used in the field of solar thermal utilization due to their good thermophysical properties. The addition of nanoparticles can improve the heat transfer and heat storage performance of nitrate. This article explored the effect of MgO nanoparticles on the thermal properties of ternary eutectic nitrates. As a result of the decomposition reaction of the Mg(OH)2 precursor at high temperature, MgO nanoparticles were synthesized in situ in the LiNO3–NaNO3–KNO3 ternary eutectic nitrate system. XRD and Raman results showed that MgO nanoparticles were successfully synthesized in situ in the ternary nitrate system. SEM and EDS results showed no obvious agglomeration. The specific heat capacity of the modified salt is significantly increased. When the content of MgO nanoparticles is 2 wt %, the specific heat of the modified salt in the solid phase and the specific heat in the liquid phase increased by 51.54% and 44.50%, respectively. The heat transfer performance of the modified salt is also significantly improved. When the content of MgO nanoparticles is 5 wt %, the thermal diffusion coefficient of the modified salt is increased by 39.3%. This study also discussed the enhancement mechanism of the specific heat capacity of the molten salt by the nanoparticles mainly due to the higher specific surface energy of MgO and the semi-solid layer that formed between the MgO nanoparticles and the molten salt.

Thermodynamic evaluation and optimization of LiNO3–KNO3–NaNO3 ternary system

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.

Application of geometric models for calculation of viscosity and density of LiNO3 and CsNO3 based ternary nitrate salt systems

Determining the thermophysical properties of ternary molten salt systems accurately is a challenging task as it incorporates experimentation at high temperatures, cost of running the experiments, and complexity due to material interactions. Modelling of these properties can overcome most of these difficulties. In this paper, various geometric models were used for determining the density and viscosity of two ternary nitrate salt systems viz. LiNO3–NaNO3–KNO3 and CsNO3–NaNO3–KNO3. On comparison, it was observed that the General Solution Model (GSM) developed by K.C. Chou predicts better results for both density and viscosity of the salts. The density prediction of the salt systems using GSM recorded an error less than 2%, while the prediction of viscosity showed a variation of 17–20%.

Preparation and thermal characterization of LiNO3–NaNO3–KCl ternary mixture and LiNO3–NaNO3–KCl/EG composites

Phase change material (PCM) has important applications in the field of thermal energy storage due to its characteristic that the temperature is basically unchanged during the endothermic and exothermic processes. At the same time, it helps to achieve heat supply/demand balance and reasonable energy distribution. Nitrates are widely used as mid-temperature phase change material, but they have relatively low phase change latent heat than chlorine salt. In order to get a kind of material with high phase change latent heat, 50 wt% LiNO3–45 wt% NaNO3–5 wt% KCl (LNK) ternary mixed molten salt is prepared with static mixing melting method. Meanwhile, LNK/expanded graphite (EG) composite phase change materials are prepared with ultrasound smashing method. The experimental results show that the addition of KCl changes the performance. The melting temperature of LNK reduces 20.6 °C and its phase change latent heat increases 19.9 J/g, compared with 43 wt% NaNO3–57 wt% LiNO3 binary nitrate mixture. The thermal properties and thermal stability of the materials are tested and analyzed. The experimental results show that both the ternary phase change material and the composite phase change materials have high phase change latent heat and chemical stability. EG has greatly increased the heat conductivity of the composite phase change materials. The thermal conductivity of 85 wt% LNK/15 wt% EG composite phase change material increases by 778% compared to LNK at 20 MPa forming pressure.

Novel key parameter for eutectic nitrates based nanofluids selection for concentrating solar power (CSP) systems

A high-performance heat transfer fluid (HTF) plays a crucial role in the overall performance and efficiency of concentrating solar power (CSP) systems for utilizing solar energy. Molten salt-based nanofluids, which may offer a promising solution to help reduce the size and cost of CSP systems, have attracted increasing attention. However, there is still no comprehensive assessment strategy that considers the conflictive effects of adding nanoparticles in HTFs, such as the compromise between energy storage capacity increase and pumping cost increase. In this work, a methodology for nanofluids screening and selection is proposed and a novel parameter (R) is determined to assess the conflictive effect. The parameter (R) considers the ratio between the relative pumping power and the relative energy stored of the nanofluid compared to its base fluid. Three promising eutectics nitrate based nanofluids (NaNO3–KNO3, LiNO3–NaNO3–KNO3, LiNO3–NaNO3–KNO3–Ca(NO3)2) doped with 0.5 wt.% and 1 wt.% silica nanoparticles were selected and evaluated by the proposed methodology. As a result, adding nanoparticles into binary salts always present a negative effect (R = 1.03–1.22) when considering the ratio between the relative pumping cost and the relative energy stored. For ternary salt, adding 1 wt.% silica nanoparticles would be more preferable with a decrease of the parameter (R = 0.89–0.97, R < 1). In terms of quaternary, adding nanoparticles into quaternary does not change the parameter significantly (R = 0.96–1.04).

Chemical Transformation for 5-Hydroxymethylfurfural Production from Saccharides Using Molten Salt System

Herein, we have demonstrated using a eutectic ternary LiNO3–NaNO3–KNO3 (LSP) molten salt melt under mild conditions for chemical transformation of 5-hydroxymethylfurfural (HMF) production directly from biomass-derived saccharides, such as fructose, glucose, cellobiose, starch, and cellulose. In addition, 2-sec-butylphenol (SBP) was used for enhancing HMF production through efficient extraction from LSP salt melts. Notably, LSP salt can be recovered and reused without compromising activity, which could make this chemical transformation sustainable. Moreover, a simple vacuum distillation system can be employed for easy separation of HMF while processing. The aforementioned chemical transformation through LSP molten salt melts could be attributed to the intrinsic unique acid–base pair and saccharide molecule perturbation by small cations present in molten salt melts.

Size effect of nanoparticle on specific heat in a ternary nitrate (LiNO3–NaNO3–KNO3) salt eutectic for thermal energy storage

In this study we investigate the effect of nanoparticles on the specific heat of ternary nitrate salt eutectic doped with nanoparticles. Four different sizes of SiO2 nanoparticles were tested: 5nm, 10nm, 30nm, and 60nm. They were doped into ternary nitrate salt eutectic (LiNO3–NaNO3–KNO3) at 1% concentration by weight. Ternary nitrate salt eutectic has been considered as advanced thermal energy storage material due to its lower melting point and high thermal stability. Enhancing the specific heat of ternary nitrate salt eutectic can greatly increase its thermal storage density. This can not only reduce the material cost but also the size of pipe and storage tanks and, therefore, energy storage cost can be significantly reduced. A modulated differential scanning calorimeter was employed to measure the specific heat of ternary nitrate salt eutectic before and after doping with nanoparticles. According to the conventional specific heat model (density weighted rule), the specific heat of ternary nitrate salt eutectic should slightly decrease after doping with nanoparticles since the concentration of nanoparticles is very small (∼1% by weight) and the specific heat of nanoparticles is lower than that of ternary nitrate salt eutectic. However, the specific heat of the mixture was measured to be enhanced by 13–16% and no significant variation in specific heat was observed with nanoparticle size. From subsequent material characterization study, we observed a large amount of nanometer-sized structure formed by the salt compound around nanoparticles. Nanostructure has extremely large specific surface area. This can amplify the effect of surface energy on the effective specific heat (which was often negligible on a macroscale) and can be primarily responsible for the enhanced specific heat with doping nanoparticles.

Form-stable LiNO3–NaNO3–KNO3–Ca(NO3)2/calcium silicate composite phase change material (PCM) for mid-low temperature thermal energy storage

In this paper, a novel form-stable LiNO3–NaNO3–KNO3–Ca(NO3)2/calcium silicate composite PCM was developed by cold compression and sintering. The eutectic quaternary nitrate is used as PCM, while calcium silicate is used as structural supporting material. X-ray Diffraction (XRD) shows the PCM and the supporting material have good chemical compatibility. This composite PCM has a low melting point (103.5°C) and remain stable without decomposition until 585.5°C. Moreover, this composite shows excellent long term stability after 1000 melting and freezing cycles. Thermal conductivity of the composite was measured to be 1.177Wm−1K−1, and that could be increased by adding thermal conductivity enhancers into the composite. Meanwhile, microstructure of the composite PCM is observed by scanning electron microscopy (SEM). Latent heat and heat capacity of the composite are measured by differential scanning calorimetry (DSC). This composite PCM with low melting temperature, high thermal conductivity and excellent stability could be used as a new PCM for mid-low temperature thermal energy storage (TES) system.

High-temperature corrosion of Cr–Mo steel in molten LiNO3–NaNO3–KNO3 eutectic salt for thermal energy storage

This study investigated the effects of adding chromium on the high-temperature corrosion behavior of Cr–Mo steels in contact with the molten salt used for thermal energy storage. Corrosion testing was performed by immersing Cr–Mo steels with various chromium contents (0, 2.25, 5, 9, 12wt% Cr) in static molten LiNO3–NaNO3–KNO3 eutectic salt at 550°C for 250, 500 and 1000h under nitrogen cover gas. Our results revealed that the corrosion behavior of the steels was governed by oxidation as well as lithiumization. Weight gains in the various forms of steel were positively correlated to corrosion time but negatively correlated to chromium content. Analysis of the microstructure of the corroded steels revealed an outer LiFeO2 and an inner (Fe,Cr)3O4 layers in the corrosion scales found on the steel. In addition, the thicknesses of the corrosion scales and the descaled weight losses of the steels decreased with an increase in chromium content. Our results confirm that the corrosion resistance of steel exposed to molten salt can be dramatically improved by the addition of chromium (9wt%).

Preparation and thermal properties of porous heterogeneous composite phase change materials based on molten salts/expanded graphite

Three kinds of porous heterogeneous composite phase change materials were synthesized from expanded graphite (EG) and binary molten salts (LiNO3–KCl, LiNO3–NaNO3 and LiNO3–NaCl) through solution impregnation method. Binary molten salt content in the composite phase change materials was calculated to be between 77.8% and 81.5% and high encapsulation efficiency was calculated to be between 72.8% and 78.8%. The thermal conductivity of binary molten salts was enhanced by 4.9–6.9 times after impregnation with EG. SEM photographs showed that the prepared composites were more homogeneous in comparison to other salt/EG composites prepared by infiltration or compression. Phase change properties of the porous heterogeneous composite phase change materials showed great thermal stability, which was maintained after 100 cycles.

Czochralski growth of NaNO3–LiNO3 solid solution single crystals using axial vibrational control technique

T-x diagram of LiNO3–NaNO3 quasi-binary system has been improved using an original technique based on Raman measurements of condense phase. (LiNO3)x(NaNO3)1−x solid solution single crystal has been grown at different regimes of axial vibrational control (AVC) technique. Significant difference in segregation coefficient behavior between AVC-CZ and conventional CZ grown crystals has appeared: with AVC intensity increase the segregation coefficient (SC) raises for light molecular weight elements, SC reduces for medium molecular weight elements, and SC remains practically unchangeable for heavy molecular weight elements. Effect of vibrational intensity on vibron and optical characteristics, microhardness of AVC-CZ (LiNO3)x(NaNO3)1−x solid solution single crystals has been studied. For the AVC-CZ crystals has been observed increases in microhardness as well as in optical transmission up to 10rel% compare to conventional CZ grown crystals.

Thermodynamic modeling of eutectic point in the LiNO3–NaNO3–KNO3–NaNO2 quaternary system

A novel model based on the thermodynamic principles is developed to predict the eutectic temperature and composition in molten salt systems. In pursuit of novel low melting point molten salt mixtures with high thermal storage density for concentrating solar power generation, a new quaternary eutectic system comprising of lithium nitrate, sodium nitrate and potassium nitrate and sodium nitrite was developed. The thermodynamic model based on regular solution approximation was used to predict the eutectic composition and temperature in the LiNO3–NaNO3–KNO3–NaNO2 quaternary salt system. The result obtained for eutectic point of the LiNO3–NaNO3–KNO3–NaNO2 quaternary system was T=98.6°C and XLiNO3=0.215, XNaNO3=0.142, XKNO3=0.424, and XNaNO2=0.219. The calculated eutectic composition obtained from the thermodynamic model was verified experimentally for the eutectic temperature using the Differential Scanning Calorimetry (DSC) technique. Melting temperature of 99.02°C was obtained from the heating cycles. The experimentally determined melting temperature of the eutectic composition was in excellent agreement with that of calculated eutectic temperature of the system.

Thermophysical Properties of LiNO3–NaNO3–KNO3 Mixtures for Use in Concentrated Solar Power

One of the major challenges preventing the concentrated solar power (CSP) industry from occupying a greater portion of the world's energy portfolio are unattractive start up and operating costs for developers and investors. In order to overcome these reservations, plant designers must be able to achieve greater efficiencies of power production. Molten salt nitrates are ideal candidates for CSP heat transfer fluids and have been proposed to offer significant performance advantages over current silicone based oil heat transfer fluids. Ternary molten salt nitrates offer high operating temperatures while maintaining low freezing temperatures. However, a shortage of important thermophysical property data exists for these salts. Previous work has shown the ternary compositions of LiNO3–NaNO3–KNO3 salts offer the widest possible temperature range for use in a CSP system. The present work contains data for the viscosity, specific heat, and latent heat of some mixtures of these salts at various temperatures, providing vital information for plant designers to optimize power generation and attract future investment to CSP systems.

Solubility Prediction and Measurement of the System KNO3–LiNO3–NaNO3–H2O

A Pitzer–Simonson–Clegg model has been applied to calculate the isotherms of the system KNO3–LiNO3–NaNO3–H2O and its subsystems. The model parameters are fitted against experimental solubility and water activity in the sub-binary and sub-ternary systems of the titled quaternary system. The solubility of the system KNO3–LiNO3–NaNO3–H2O at 298.1 and 308.5 K and its subsystems KNO3–LiNO3–H2O at 283.1 K and LiNO3–NaNO3–H2O at 323.1 K are elaborately measured for verifying the reliability of the model prediction. Comparisons indicated that the calculated values are in agreement with our experimental data and literature data.

LiNO3–NaNO3–KNO3 salt for thermal energy storage: Thermal stability evaluation in different atmospheres

The thermal stability of the eutectic LiNO3–NaNO3–KNO3 salt was investigated by simultaneous differential scanning calorimetry, thermogravimetry and mass spectrometry (DSC/TG–MS). The work was carried out between room temperature and 1000°C in blanket gas atmospheres of argon, nitrogen, oxygen and air. The stability of the salt, as measured by the gases evolving from the melt, was influenced by the atmosphere. Evolution of the main gaseous species NO was detected at 325°C in an atmosphere of argon, at 425°C in an atmosphere of nitrogen, at 475°C in an atmosphere of air and at 540°C in an atmosphere of oxygen. Prior to melting, the eutectic underwent endothermic (α/β) solid–solid type transformation at 87°C. The melting point was 121°C, and the solidification point 98°C. Under-cooling of the salt coincided with the onset of the (α/β) solid–solid transformation upon heating. At a temperature of 500°C in air, TG analysis showed that the long-term stability of the salt was limited and this was confirmed by DSC. Uncertainty analysis indicated that the measurement of temperature is accurate to ±2.7°C.

Thermodynamic properties of LiNO3–NaNO3–KNO3–2KNO3·Mg(NO3)2 system

A novel low melting eutectic salt was predicted in the LiNO3–NaNO3–KNO3–2KNO3·Mg(NO3)2 quaternary system using thermodynamic modeling. The melting point of the eutectic salt was predicted to be 374.90K. Differential scanning calorimetry (DSC) was used to experimentally determine the melting point and specific heat capacity of the quaternary system. The mixture was measured to be completely melted at 373.90±0.78K which is in an excellent agreement with the predicted value. The measured heat capacity data as function of temperature are fit to polynomial function. Subsequently, the thermodynamic properties such as enthalpy, entropy and Gibbs energies of this novel quaternary eutectic salt were deduced as function of temperature.

Testing method of phase change temperature and heat of inorganic high temperature phase change materials

An analytical temperature model and an enthalpy difference function, based on lumped parameter method and assumption of rectangular effective specific heat, are presented in this study, which can measure the enthalpy change of inorganic salt high temperature. It is easy to carry out in practicable test, because an automated test equipment is designed to measure and record the T-history curves of the PCMs and “Valley, Bottom, and peak” and “Peak, Top, and Valley” criteria are proposed to select the starting temperature of phase-changing process (TS), the ending temperature of phase-changing process (TE) and the melting point (Tm) of the PCMs. The binary eutectic LiNO3–NaNO3 (5.5:4.5, mass ratio), LiCl–NaCl (7:3, mass ratio) and Li2CO3–Na2CO3 (4:6, mass ratio) are tested, whose melting point and heat of fusion are (198.9°C, 255kJ/kg), (559°C, 460kJ/kg) and (499°C, 374kJ/kg). The maximum deviation between measurements and the values from DSC and references is less than 8%. It can be seen that with this method it is possible to obtain both melting point and heat of fusion in a simple way which will be of great help in selecting heat storage material in solar-energy and industrial waste heat utilization and in the subsequent design of a thermal energy storage system.

Thermal conductivity of the ternary eutectic LiNO3–NaNO3–KNO3 salt mixture in the solid state using a simple inverse method

Low melting point eutectic salt mixtures are developed as potential candidate for thermal energy storage applications. Thermal conductivity of the ternary eutectic LiNO3–NaNO3–KNO3 salt mixture in the solid state was determined using a simple inverse method. The inverse method was verified for two metal alloys and a HITEC® heat transfer salt, and the thermal conductivities were in excellent agreement with those of the literature data. Thermal conductivity of the ternary eutectic salt mixture in the solid state showed a non-linear behavior with temperature.

Thermal stability of the eutectic composition in LiNO3–NaNO3–KNO3 ternary system used for thermal energy storage

The new eutectic composition in the LiNO3–NaNO3–KNO3 ternary salt system has a very low melting point (118°C) and is a potential candidate for use in parabolic trough solar power generation. The short and long-term thermal stabilities and reliability of the eutectic composition in this ternary system were determined using the Thermogravimetric Analyzer (TGA) and Differential Scanning Calorimetry (DSC), respectively. The system demonstrates excellent short-term thermal stability and reliability during thermal cycling. However, the system showed 8% weight loss during long-term thermal stability test. Long-term isothermal stepwise study reveals that below 435°C the weight change is minimal and this temperature is taken as the upper limit of thermal stability of the system. The eutectic composition in the ternary system was characterized by XRD and SEM techniques before and after the thermal stability experiments to identify the morphology and compositions of the phases. From the present study it can be concluded that the major contributor to the weight loss is the dissociation of lithium nitrate to lithium oxides.