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The production and use of carbon nanotubes (CNTs) have become extremely wide within the last decade. Hence, the high interest in producing non-expensive and quality CNTs has motivated many research projects. This research considers the design and development of new technology for producing MWCNTs by electrolysis in molten salts using non-stationary and stationary current regimes. The electrolysis is simple, ecological, economical, and flexible, and it offers possibilities for accurate control of various parameters, such as applied voltage, current density, or temperature. We infer the underlying relationship between the parameters and the quality of the experimentally produced MWCNTs by using explainable tree-based Machine Learning (ML) models. We train several models in a supervised manner, whereas in model covariates, we use the parameters of the MCWNTs, and as a target variable, the quality of the produced MWCNT. Domain experts label all the experimental examples in our data set. Controlling these parameters enables high-yield production and, particularly important, obtaining MWCNTs, which are up to ten times cheaper than other existing technologies.

Mosquitoes are a great threat to human health to date and are a subject of interdisciplinary research involving scientists from many areas. Recently much attention has been put to novel approaches to mosquito repellent products that involve the use of novel materials, such as carbon nanomaterials, where it is essential to determine their properties. This research discusses the full molecular characterization of carbon nanotubes (CNTs) produced by electrolysis in molten salts. Each CNT has its mathematical representation due to its hexagonal lattice structure. Multi-wall carbon nanotubes (MWCNTs) are considered. The focus is on determining their structural parameters: innermost and outermost diameters, chiral indices m and n, number of walls, and unit cell parameters. Corresponding frequency parts of Raman spectra of four experimentally produced CNTs are elaborated, and Python programming and Mathematica are employed for the most accurate (m,n) assignment. Determining the chirality of these samples enables the calculation of other structural properties, which are performed now, including their graph representation. The latter enables the evaluation of different distance-based topological indices (Wiener, Balaban, Sum-Balaban, Harary index, etc.) to predict some index-related properties of the molecules.

High-resolution nano X-ray computed tomography (nano-XCT) was used to investigate the process of infiltration of a Molten Carbonate Fuel Cell (MCFC) matrix by liquid electrolyte. A ceramic matrix made of a LiAl 2O3 powder was infiltrated by a liquid electrolyte during the start-up process of the MCFC. Nano-XCT extends the state-of-the art techniques for characterizing the morphology of the ceramic matrix and for the study of the penetration kinetics with electrolyte. Quantitative morphology analysis using high-resolution nano-XCT provides 3D information for each MCFC component nondestructively. The spatially resolved volume fraction of the molten electrolyte calculated from the 3D XCT data is used for simulation and to improve MCFC performance. Based on the results obtained, a new start-up procedure is proposed for a single MCFC. This procedure is consistent with the morphology changes which occur during the melting process inside the ceramic matrix.

This work focuses on the development of a comprehensive numerical methodology for the study of natural circulation systems using molten salts as working fluid, in particular for its application in the design of passive safety systems for Molten Salt Reactors (MSRs).The goal of the methodology is to evaluate the performance of possible 3D natural circulation configurations through the description of their dynamic behavior, with a focus in the identification of bifurcation phenomena and performing a stability analysis. The numerical tool implementing this methodology is based on a CFD-based MATLAB-OpenFOAM coupling and has been evaluated against a numerical benchmark of a differentially heated cavity, showing good agreement with literature results. For a first assessment of the performance of the tool a simple 2D case of a simple natural circulation configuration known as Rayleigh-Bénard convection has been used. This configuration results from a 2D enclosure heated and cooled from the bottom and top surfaces respectively. The dynamic states of this system have been studied for a large range of both geometric and physical parameters, showing both steady state and oscillating solutions. A bifurcation diagram is produced, showing the transition between the different solutions. In the vicinity of certain bifurcation points hysteresis phenomenon has been observed. The numerical tool developed for the evaluation of natural circulation systems has shown a good performance both for the description of the thermal-hydraulic system as well as for the stability analysis. The complexity and variety of the possible solutions for this first assessment illustrates the need of a robust and systematic methodology for the considered applications which in practice will involve more complex geometries and additional underlying phenomena.

Химическим анализом установлено, что при электрохимическом восстановлении в расплавах MWO -WO (M - Li, Na, K, Cs,Tl) образуются оксидные вольфрамовые бронзы различного состава и структуры. Изучена зависимость изменения равновесных потенциалов катодных продуктов от температуры и состава расплава. Установлено, что с увеличением содержания щелочного металла в вольфраматных расплавах число зародышей кристаллов уменьшается. Снижение температуры расплава и увеличение катодной плотности тока также приводит к уменьшению размеров зерен катодных осадков, что позволяет получать порошки оксидных вольфрамовых бронз контролируемой дисперсности. Методами рентгеноэлектронной спектроскопии и каналирования были исследованы структура конденсированных в среднем вакууме тонких пленок, а также монокристаллы натрийвольфрамовых бронз электрохимически циклированных в анодном и катодном режимах для получения информации о толщине окрашивающего слоя. Chemical analysis established that during electrochemical reduction in MWO - WO (M - Li, Na, K, Cs,Tl) melts, tungsten oxide bronzes of various compositions and structures are formed. The dependence of the change in the equilibrium potentials of cathode products on the temperature and composition of the melt has been studied. It was found that with an increase in the content of alkali metal in tungsten melts, the number of crystal nuclei decreases. A decrease in the melt temperature and an increase in the cathode current density also lead to a decrease in the grain size of the cathode deposits, which makes it possible to obtain powders of tungsten oxide bronzes of controlled dispersion.

In this paper, the author describes several new electrochemical reactions in molten salts (MSs) and ionic liquids (ILs), which includes the development of new ILs, and their applications. First, the electrochemical reduction of solid SiO2 to Si in molten CaCl2 at 1123 K is mentioned. The author explains the mechanism how the insulating SiO2 is electrochemically reduced to silicon. A new production method of solar grade silicon (SOG-Si) is introduced as one of the promising applications of the electrochemical reduction of SiO2. The author also mentions another new production method of SOG-Si which utilizes a liquid Si–Zn cathode in molten CaCl2. Secondly, the author describes the electrodeposition of silicon and titanium from water-soluble KF–KCl MSs. Compact crystalline Si films are electrodeposited from molten KF–KCl–K2SiF6 at 923 K. When K2TiF6 and Ti are added in molten KF–KCl, Ti(III) ions are produced by the proportionation reaction between Ti(IV) and Ti(0), in which compact Ti films can be electrodeposited. Thirdly, the author describes the binary and ternary mixtures of M[TFSA] (M = Li, Na, K, Rb, and Cs; TFSA = bis(trifluoromethylsulfonyl)amide) ILs as a new class of electrolytes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) operating in the intermediate temperature range. Fourthly, the development of binary and ternary mixtures of M[FSA] (M = Li, Na, K, Rb, and Cs; FSA = bis(fluorosulfonyl)amide) ILs and their applications for NIBs are mentioned; the binary and ternary mixtures of M[FSA] are unique in the points that they are inorganic compounds and have low melting temperatures. Finally, the author explains the development of several binary mixtures of M[FSA]–[Ocat][FSA] (M = Li, Na, and K; Ocat = organic cations) ILs which can be used for LIBs, NIBs, and KIBs (K-ion batteries). As a typical application of the M[FSA]–[Ocat][FSA] ILs, the development of practical NIB with a capacity of 27 Ah is described.

Next generation concentrated solar power (CSP) plants promise a higher operating temperature and better efficiency. However, new issues related to the corrosion against protection of the construction alloys need to be solved. In this work, two different duplex stainless steels grades, namely 2205 (DS2205) and 2507 (DS2507), were evaluated for their compatibility with the eutectic molten salt mixture of Li2CO3-K2CO3-Na2CO3 at 500 °C in air for thermal energy storage applications. Corrosion tests combined with complementary microscopy, microanalysis and mechanical techniques were employed to study the oxide scales formed on the surface of the duplex steels. The corrosion tests evidenced that the attack morphology in both duplex steels was a uniform oxidative process without localized corrosion. DS2507 presented a better corrosion resistance than DS2205, due to the formation of thinner, compact and continuous oxide layers with higher compositional content in Cr, Ni and Mo than DS2205. The oxide scales of DS2507 showed more remarkable mechanical integrity and adhesion to the metallic substrate.

The interaction between UN and CdCl2 in the LiCl-KCl molten eutectic was studied at 773 K.The reaction was controlled by sampling the melt, as well as by analysis of the resulting precipitate. The process was shown to proceed according to several parallel reactions. The summary reaction was determined to have two stages: a fast one and a slow one. The 19–53% UN → UCl3 conversion was obtained for the molar ratio of CdCl2/UN = 1.22–14.9. The rest of UN converts into the precipitate of complex composition (UNCl + U2N3 + U4N7 + UN2). The increase in the CdCl2/UN molar ratio from 1.22 to 14.9 resulted in the decrease in duration of the first “fast” stage of the process from 18 h to 1 h. Keywords: Spent nuclear fuel, Nitride nuclear fuel, Chlorination, Pyrochemistry, UN, UNCl, Molten salts

Molten chloride salts are promising advanced high-temperature (400–800 °C) thermal energy storage (TES) and heat transfer fluid (HTF) materials in next generation concentrated solar power (CSP) plants for higher energy conversion efficiencies. However, severe corrosion of structural materials in contact with molten chloride salts is one of the most critical challenges limiting their applications at elevated temperatures. In this work, two corrosion mitigation strategies are investigated to alleviate the hot corrosion of structural materials in molten chloride salts: (1) adding corrosion inhibitor and (2) using a Fe-Cr-Al alloy with a protective alumina layer on the surface after pre-oxidation. Three commercial high temperature Fe-Cr-Ni alloys (SS 310, Incoloy® 800 H and Hastelloy® C-276) were exposed to molten MgCl2-NaCl-KCl (60–20–20 mol%) mixed salts with 1 wt% Mg as corrosion inhibitor, for 500 h at 700 °C under inert atmosphere. By addition of the Mg inhibitor, the corrosion rates of the studied alloys were found to be significantly reduced, more precisely by ~ 83% for SS 310, ~ 70% for In 800 H and ~ 94% for Ha C-276 compared with the exposure tests without Mg addition. The corrosion mitigation mechanism of Fe-Cr-Ni based alloys in molten chloride salts by adding Mg is discussed based on corrosion thermodynamics. To assess the second mitigation strategy two pre-oxidized alumina forming Fe-Cr-Al alloys were exposed to the same molten chloride salts without Mg corrosion inhibitor under the same conditions. It is observed that the adherent alumina scales can effectively inhibit the dissolution of Cr and Fe and the bulk penetration of corrosive impurities. Overall, both strategies offer enormous potential for enhancing the expected lifetime of commercial alloys in molten chloride salts.

International audience; In situ high temperature NMR spectroscopy was used to characterize the NaF-ScF3 melt over a wide range of compositions. 19 F, 23 Na, and 45 Sc NMR spectra were acquired in NaF-ScF3 melts of up to 70 mol% of ScF3. The interpretation of all experimental results obtained in situ in the melt is significantly enhanced by the contribution of Molecular Dynamics (MD) calculations. A new interatomic potential for the molten NaF-ScF3 system was developed by using a Polarizable Ion Model (PIM). The potential parameters were obtained by force-fitting to density functional theory (DFT) reference data. MD simulations were combined with further DFT calculations to determine NMR chemical shifts for 19 F, 23 Na, and 45 Sc. The agreement between the experimental NMR data and the corresponding calculated data from our applied computational protocol indicated the polymerization and network formation in the melt. Additionally, the density and the electrical conductivity in the molten state were calculated from the statistical analysis of ionic trajectories obtained through MD simulations.

The industrial sector is a major source of wealth, producing about one-quarter of the global gross product. However, industry is also a major emitter of CO2 and it represents a key challenge towards achieving the worldwide CO2 emission reduction targets. Nowadays, about 22 % of the overall energy demand is heating for the industrial sector, generating about 40 % of the global CO2 emissions. Solutions to decarbonize the industrial sector are needed. This work presents the techno-economic assessment of molten salt based power-to-heat solution aiming at decarbonizing the industrial sector, requiring medium temperature heat (150–450 ◦C). The system is studied under different electric markets considering electricity prices of 2021, future electricity market price modifications are assessed via sensitivity analyses. Dispatch strategies and system sizing are identified to ensure optimal techno-economic performance. The main performance indicators investigated are the Levelized cost of heat, the operational expenditure, and the attainable savings with respect to traditional solutions. The system scalability and sizing criteria are investigated accounting for different typical industrial load profile curves and nominal thermal power demands. The results highlight that nominal levelized cost of heat as low as55 €/MWhth are attainable in cheap electricity markets (i.e. Denmark) and 80 €/MWhth in more expensive scenarios (i.e. United Kingdom). The proposed system can provide operational cost savings between 0.5 and 3M€/y against traditional non-flexible electric boilers and even wider benefits if fossil fuels-based boilers are considered. Future electricity markets, subjected to higher renewable penetration causing cheaper average electricity prices and higher price volatility, could lead to further reductions of the levelized cost of heat of more than 20 % achieving values below 45 €/MWhth in markets such as Denmark. This study sets the ground for further power-to-heat techno-economic investigations addressing different industrial sectors and identifies main system design strategies. QC 20221201 RIHOND - Renewable Heat on Demand

Understanding molten salt chemistry is essential in ongoing research of the molten salt nuclear reactor (MSR). In this context, detailed understanding of the mechanisms underlying selective oxidation of metal species, such as Cr, is required to guide the design of effective corrosion mitigation strategies in molten salts. An important starting point for such mechanistic understanding is knowledge of the solvation structure and its role in controlling metal speciation. In this work, we use ab initio molecular dynamics simulations to study the short-range (on the scale of the nearest-neighbor bond lengths) and medium-range (over length scales of several neighbor spacings) structure in three different fluoride melts with and without Cr addition; namely, 2KF-NaF, 2LiF-BeF2, and 3LiF-AlF3. We find that Cr0,Cr2+,Cr3+ can each be coordinated by different numbers of F-, with the variance in coordination number decreasing as oxidation state increases, and that these coordination geometries are largely independent of solvent. The manner by which Cr changes the medium-range structure, however, is found to be solvent-dependent. While 2KF-NaF melts show short and medium range order that is highly dynamic, 2LiF-BeF2 and 3LiF-AlF3 are characterized by molecular associates that are relatively long-lived that organize into oligomer structures on larger length scales. Rather than being solvated by F- ions alone, we find that Cr can incorporate into and be solvated within this oligomer structure. Fluoroacidity, alone, may therefore prove too simple a metric for assessing the corrosivity of molten fluorides. As our work suggests, the ability of Cr to solvate must be understood in the context of the short- and medium-range structure of the solvent.

In this study, two modified MCrAlY-type coatings were prepared by the same arc ion plating process. ‘Gradient annealing’ and ‘gradient annealing plus preoxidation’ were adopted as post-treatments for the two coatings. A two-layer scale of a mixed oxide layer and a pure alumina layer with the alumina next to the substrate was formed on the latter coating. A cyclic hot corrosion test was carried out on them with a conventional MCrAlY-type coating as a reference. The kinetics and evolution of the microstructure showed them to have greater hot corrosion resistance at 900 °C. The preformed inner alumina scale by preoxidation retarded the occurrence of internal oxidation–sulphidation to some extent. Additionally, the internal sulphidation–oxidation model is elucidated and extended.

Molten-salt assisted solid-state synthesis is considered a promising method in obtaining layer-structured cathodes for lithium-ion batteries with homogeneous elemental distribution and controllable morphologies. However, drawbacks like resource wasting which have arisen from redundant salt removal after sintering greatly hinder the broader application of this technique. In this paper, a closed-loop utilization of molten salts is proposed for the first time with specific electrochemical properties of the products studied. Results confirm the feasibility of this strategy, and that with only replenishing LiOH, the recycled LiOH-LiCl molten salts can be successfully reused into another LiNi0.5Co0.2Mn0.3O2 synthesis, which exhibits almost equal electrochemical performance to the product using fresh molten salts. We believe this research can provide significant insight in guiding green and environmental-friendly preparation methods involving molten salts.

[EN]A multi-objective and multi-parametric optimization of a Pumped Thermal Electricity Storage system based on Brayton cycles is presented by the calculation of different Pareto fronts and the associated Pareto optimal sets for energetic and design analysis, respectively. A large range of internal and external irreversibilities and the thermodynamic properties of the storage media are taken into account. The analysis shows that the heat capacity of the working fluid and the heat capacity of the storage media should be the same in the contact with the hot reservoirs and in the contact with the cold reservoir in the heat pump, but in the contact with the cold reservoir for the heat engine the ratio should be 0.33, this offers information regarding the mass flow increasing significantly the achievable values for the round-trip efficiency, power output and the heat engine efficiency in the discharge process. Optimal values are given in terms of the degree of irreversibilities in the system and a comparison is made with extreme cases of infinite and minimum sizes for the storage system. Round-trip efficiencies in the so-called optimum scale/mass-flow-ratio design point exhibits noticeably larger values compared to previously reported results including the so-called endoreversible limit, where no internal irreversibilities are considered and where the improvement can achieve 49% over the endoreversible case in the most ideal scenario. Explicit numerical values of the maximum round trip efficiency, power output, and efficiency are given for a broad range of both internal and external irreversibilities., Agencia Nacional de Investigación e Innovación (ANII): Fondo Sectorial de Energía (Uruguay), under contract FSE-1-2018-1-153077 Universidad de Salamanca, Spain, under contracts 18.KB.YF/463A.C.01 and 0218463AB01.

Исследована зависимость интенсивности массопереноса у поляризованного жидкого металлического электрода в хлоридных расплавах, характеризуемая величиной коэффициента массопереноса, от вида структур, возникающих у межфазной границы электрода с электролитом. Установлено, что зависимости плотности тока и коэффициента массопереноса от перенапряжения имеют максимум, при этом перенапряжения, соответствующие максимумам плотности тока и коэффициента массопереноса, не совпадают. Приведено обоснование этого факта., The dependence of the intensity of mass transfer at a polarized liquid metal electrode in chloride melts, characterized by the value of the mass transfer coefficient, on the type of structures appearing at the interface between the electrode and the electrolyte has been investigated. It was found that the dependences of the current density and the mass transfer coefficient on the overvoltage have a maximum, while the overvoltages corresponding to the maximums of the current density and the mass transfer coefficient do not coincide. The substantiation of this fact is given.

The Al coatings achieved via electrodeposition on a Cu electrode from AlCl3-NaCl-KCl (80–10–10 wt.%) molten salts electrolyte with Tetramethylammonium Chloride (TMACl) and Sodium Iodide (NaI) additives is reported. The effect of the two additives on electrodeposition were investigated by cyclic voltammetry (CV), chronopotentiometry (CP), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results reveal that compact and smooth Al coatings are obtained at 150 °C by the electrodeposition process from the electrolyte with 1% TMACl and 10% NaI. The Al coatings exhibit great corrosion resistance close to that of pure Al plate, with a corrosion current of 3.625 μA. The average particle size is approximately 2 ± 1 μm and the average thickness of the Al layer is approximately 7 ± 2 μm. The nucleation/growth process exhibits irrelevance with TMACl or NaI during the electrodeposition of Al. TMACl cannot affect and improve the electrodeposition effectively. However, the addition of TMACl and NaI can intensify the cathodic polarization, producing an inhibition of Al deposition, and contribute to form uniform Al deposits. This can increase the conductivity and facilitate in refining the size of Al particles, contributing to forming a continuous, dense and uniform layer of Al coating, which can be used as effective additives in molten salts electrolyte.

Nowadays, the incorporation of nanoparticles into thermal fluids has become one of the most suitable strategies for developing high-performance fluids. An unconventional improvement of thermo–physical properties was observed with the addition of 1% wt. of nanoparticles in different types of fluids, such as molten salts, allowing for the design of more thermally efficient systems using nanofluids. Despite this, there is a lack of knowledge about the effect that nanoparticles produce on the thermal stability and the decomposition kinetics of the base fluid. The present study performs IR- and UV-vis spectroscopy along with thermogravimetric analysis (TGA) of pure nitrate and nitrate based nanofluids with the presence of SiO2 and Al2O3 nanoparticles (1% wt.). The results obtained support that nanoparticles accelerate the nitrate to nitrite decomposition at temperatures below 500 °C (up to 4%), thus confirming the catalytic role of nanoparticles in nanofluids.

The eutectic mixture Li2CO3-Na2CO3-K2CO3 is investigated as a high temperature heat transfer fluid and storage medium alternative for molten salt solar thermal power plants. This salt has an operating temperature range of 400–700 °C, enabling the use of higher temperature/efficiency power cycles. However, this carbonate mixture is known to thermally decompose in air. This study evaluates the thermal stability of the salt mixture under different cover gases: air, nitrogen, carbon dioxide, and an 80/20 carbon dioxide/air mixture. Initial characterization is performed through thermogravimetric analysis (TGA), followed by larger scale testing in a custom-made reactor to simulate conditions closer to its practical use. The results show improved thermal stability with a CO2 atmosphere. The decomposition kinetics under different cover gases are estimated from TGA data. However, larger-scale, longer duration experiments show much slower decomposition rates compared to the classical TGA approach. These findings indicate that the main contribution to mass loss in TGA is due to vaporization rather than thermal decomposition. Thus, a proper evaluation of the molten salt´s thermal stability can only be obtained from reactor experiments where vaporization is inhibited. Very long induction periods (of the order of days) are observed, suggesting that the kinetic decomposition mechanism is a nucleation and growth type. Other considerations for future plants incorporating these high temperature salts are discussed., This project was funded through the Spanish Center for Industrial Development (CDTI) under grant CDTI – Feder- Innterconecta ITC-20131017 “Avanza2: Nuevo concepto de planta de torre con fluidos a muy alta temperatura y mayor rendimiento de ciclo respect a las actuales”.

A comparative study of the metal emulsion-based synthesis of Sn-based materials in two different types of molten salts (namely LiCl–KCl–CsCl and LiNO3-NaNO3-KNO3 eutectics) is presented, and the properties of Sn, Sn-Cu and Sn-Cu-Zn microsphere phase change materials prepared in chloride salts are evaluated by differential scanning calorimetry (DSC) to understand the effect of element doping. Despite a high ultrasonic power (e.g., 600 W or above) being required for dispersing liquid Sn in the chloride system, well-shaped Sn microspheres with a relatively narrow size range, e.g., about 1 to 15 µm or several micrometers to around 30 µm, can be prepared by adjusting the ultrasonic power (840–1080 W), sonication time (5–10 min) and the volume ratio of salts to metal (25:1–200:1). Such a method can be extended to the synthesis of Sn-based alloy microspheres, e.g., Sn-Cu and Sn-Cu-Zn microspheres. In the nitrate system, however, a very low ultrasonic power (e.g., 12 W) can be used to disperse liquid Sn, and the particles obtained are much smaller. At low ultrasonic power (e.g., 12 W), the particle size is generally less than 10 or 4 µm when the sonication time reaches 2 or 5 min, and at high ultrasonic power, it is typically in the range of hundreds of nanometers to 2 µm, regardless of the change in ultrasonic power (480–1080 W), irradiation time (5–10 min), or volume ratio of salts to metal (25:1–1000:1). In addition, the appearance of a SnO phase in the products prepared under different conditions hints at the occurrence of a reaction between Sn droplets and O2 in situ generated by the ultrasound-induced decomposition of nitrates, and such an interfacial reaction is believed to be responsible for these differences observed in two different molten salt systems. A DSC study of Sn, Sn-Cu, and Sn-Cu-Zn microspheres encapsulated in SiO2 reveals that Cu (0.3–0.9 wt.%) or Cu-Zn (0.9 wt.% Cu and 0.6% Zn) doping can raise the onset freezing temperature and thus suppress the undercooling of Sn, but a broad freezing peak observed in these doped microspheres, along with a still much higher undercooling compared to those of reported Sn-Cu or Sn-Cu-Zn solders, suggests the existence of a size effect, and that a low temperature is still needed for totally releasing latent heat. Since the chloride salts can be recycled by means of the evaporation of water and are stable at high temperature, our results indicate that the LiCl–KCl–CsCl salt-based metal emulsion method might also serve as an environmentally friendly method for the synthesis of other metals and their alloy microspheres.

High carbon ferromanganese is used as a starting material to prepare pure ferromanganese by electrorefining in molten salts. High carbon ferromanganese was applied as the anode, molybdenum was the cathode and Ag/AgCl was the reference electrode. The anodic dissolution was investigated by linear polarization in molten NaCl-KCl system. Then potentiostatic electrolysis was carried out to produce pure ferromanganese from high carbon ferromanganese. The cathodic product was determined to be a mixture of manganese and iron by x-ray diffraction (XRD). The content of carbon in the product was analyzed by carbon and sulfur analyzer. The post-electrolysis anode was characterized by scanning electron microscope (SEM). The mechanism of the anode dissolution and the distribution of the main impurity of carbon and silicon after electrolysis were discussed.

This paper focuses on the thermodynamic modelling and parametric optimization of an Organic Rankine Cycle (ORC) which recovers the heat stored in a thermal energy storage (TES). A TES with two molten-salt tanks (one cold and one hot) is selected since it is able to operate in the temperature range useful to recover heat from different sources such as exhaust gas of Externally Fired Gas Turbine (EFGT) or Concentrating Solar Power (CSP) plant, operating in a network for Distributed Generation (DG). The thermal storage facilitates a flexible operation of the power system operating in the network of DG, and in particular allows to compensate the energy fluctuations of heat and power demand, increase the capacity factor of the connected plants, increase the dispatchability of the renewable energy generated and potentially operate in load following mode. The selected ORC is a regenerative cycle with the adoption of a Heat Recovery Vapour Generator (HRVG) that recovers heat from molten salts flowing from the Hot Tank to the Cold Tank of the TES. By considering the properties of molten salt mixtures, a ternary mixture able to operate between 200 and 400 °C is selected. The main ORC parameters, namely the evaporating pressure/temperature and the evaporator/condenser pinch point temperature differences, are selected as variables for the thermodynamic ORC optimization. An automatic optimization procedure is set up by means of a genetic algorithm (GA) coupled with an in-house code for the ORC calculation. Firstly, a mono-objective optimization is carried out for two working fluids of interest (Toluene and R113) by maximization of the cycle thermal efficiency. Afterwards, a multi-objective optimization is carried out for the fluid with the best performance by means of a Non-dominated Sorting Genetic Algorithm (NSGA) in order to evaluate the cycle parameters which maximize the thermal efficiency and minimise the heat exchanger surface areas. Toluene results able to give the best trade-off between efficiency and heat exchanger dimensions for the present application, showing that by with respect to the best efficiency point, the heat exchange area can be reduced by 36% with only a penalty of 1% for the efficiency.

RESUMEN Con el reciente auge de las energías amigables con el medio ambiente, surge la demanda de materiales capaces de resistir a ciertas condiciones de trabajo que exigen estos procesos, por ejemplo, la obtención de energía a partir de luz solar, en la cual el almacenamiento térmico es vital en el transcurso del funcionamiento de la planta. En el presente trabajo se evaluó la reacción que presenta el acero AISI 316L en contacto con sales fundidas de nitratos (Ca(NO3)2+NaNO3+KNO3 y LiNO3+KNO3+NaNO3), para ello se realizaron pruebas gravimétricas, con dos tipos de sales ternarias de nitratos a una temperatura de 600°C, evaluando la ganancia de masa en el acero, a su vez se realizaron estudios metalográficos, con el fin de evaluar el daño de la microestructura. Por medio de SEM y micrografías ópticas se observó la morfología de la capa y el daño del acero. La superficie donde se evidenció la mayor agresividad de daño por parte de la sal ternaria en el acero es la superficie del acero expuesta a la sal de litio. Los resultados de DRX arrojaron Fe0,612Ni0,388 y CrNi, como principales productos de corrosión del acero, demostrando así que la sal fundida con el componente de calcio es menos corrosiva para el acero usado en este proyecto. ABSTRACT With the recent boom of environmentally friendly energies, the demand for materials capable of resisting certain working conditions demanded by these processes arises, for example, the obtaining of energy from sunlight, in which the Thermal storage is vital during the operation of the plant. In the present work, the reaction of AISI 316L steel in contact with molten nitrate salts (Ca (NO3)2 + NaNO3 + KNO3 and LiNO3 + KNO3 + NaNO3) was evaluated, gravimetric tests were carried out with Two types of ternary salts of nitrates at a temperature of 600°C, evaluating the gain of mass in the steel, in turn, were carried out metallographic studies, in order to evaluate the damage of the microstructure. By means of SEM and optical micrographs, the morphology of the layer and the damage caused to the steel was observed. The surface where the greater aggressiveness of damage by the ternary salt in the steel was evidenced is the surface of the steel exposed to the lithium salt. The results of DRX yielded Fe0.612Ni0.388 and CrNi, as the main steel corrosion products, demonstrating that the salt fused with the calcium component is less harmful to the steel used in this project.

El protagonisme creixent de la tecnologia solar termoelèctrica entre el ventall de les energies renovables es centra en la seva capacitat d’adaptar la seva producció a la demanda energètica exigida. La gestionabilitat d’aquest tipus de centrals s’ha aconseguit amb la integració de sistemes d’emmagatzematge tèrmic en les mateixes. La major part dels sistemes d’emmagatzematge tèrmic, ja sigui els que s’utilitzen a nivell comercial com aquells que es troben en fase de desenvolupament proposen l’ús de sals inorgàniques foses com a medi d’emmagatzematge. Aquestes sals presenten l’inconvenient de la seva alta corrosivitat a altes temperatures. Per un costat, s’han analitzat els fenòmens de corrosió associats a les sals solars utilitzades a la planta pilot TES-PS10 mitjançant la instal·lació de racks de testimonis de corrosió als tancs de sals. A més, al finalitzar l’operació de la instal·lació pilot s’ha dut a terme un estudi post-mortem dels seus. Finalment, amb l’objectiu d’abaratir el cost de l’inventari de sals, s’ha analitzat a nivell de laboratori la corrosivitat de diferents mescles de nitrats de baixa puresa. El segon bloc de la tesi es centra en els sistemes d’emmagatzematge tèrmic en calor latent. Concretament, s’analitza la corrosió associada a la mescla peritèctica 46% LiOH-54% KOH proposta com a material de canvi de fase en un mòdul d’evaporació d’instal·lacions termoelèctriques de generació directa de vapor. D’aquesta forma, s’han dut a terme una sèrie d’assajos a nivell de laboratori amb l’objectiu d’avaluar el comportament envers la corrosió de diferents materials en contacte amb aquests hidròxids. El creciente protagonismo de la tecnología solar se centra en su capacidad para adaptar su producción a la demanda energética exigida. La gestionabilidad de este tipo de centrales se ha conseguido mediante la integración de sistemas de almacenamiento térmico en sales fundidas. El uso de sales fundidas en sistemas de almacenamiento térmico presenta el hándicap de su corrosividad a alta temperatura. El primer bloque de la Tesis analiza los fenómenos de corrosión asociados a las sales solares en la planta piloto TES-PS10 mediante la instalación de racks de corrosión en los tanques de sales. Además, se ha llevado a cabo un estudio post-mortem de componentes de la instalación. Finalmente, se ha analizado a nivel de laboratorio la corrosividad de distintas mezclas de nitrato de baja pureza. El segundo bloque de la tesis se centra en los sistemas de almacenamiento en calor latente. En concreto, se analiza la corrosión asociada a la mezcla peritéctica 46% LiOH-54% KOH propuesta como material de cambio de fase en el módulo de evaporación en plantas de generación directa de vapor. De este modo, se han llevado a cabo ensayos de corrosión a nivel de laboratorio para evaluar el comportamiento a corrosión de distintos materiales en contacto con los hidróxidos. The growing of concentrated solar power (CSP) within the different renewable energies is due to its ability to adapt the production to the required energy demand. The dispatchability of this type of plants has been achieved through the integration of molten salts thermal storage systems (TES). Molten salts have a handicap associated to their corrosiveness at high temperature. First block of this Thesis analyzes the corrosion phenomena associated with solar salts used in TES-PS10 pilot plant by installing corrosion racks in the salt tanks. Moreover, a postmortem study of different components was performed after facility shut down. Finally, in order to reduce the cost of the salt inventory in TES systems, the corrosivity of different low purity nitrates mixtures has been analyzed at laboratory scale. The second block of the Thesis focuses on latent heat storage systems. Specifically, it has been analyzed the corrosion associated with the proposed 46% LiOH-54% KOH peritectic mixture as a phase change material in the evaporation module of direct steam generation (DSG) CSP plants. Thus, corrosion tests have been performed at laboratory level to evaluate the corrosion performance of several materials in contact with such hydroxides.

High temperature heat storage is an active field of research, especially for addressing the intermittency issues of solar power. [...]

Interest in luminescent materials has been continuously growing for several decades, looking for the development of new systems with optimized optical properties. Nowadays, research has been focused on the development of materials that satisfy specific market requirements in optoelectronics, radioelectronics, aerospace, bio-sensing, pigment applications, etc. Despite the fact that several efforts have made in the synthesis of organic luminescent materials, their poor stability under light exposure limits their use. Hence, luminescent materials based on inorganic phosphors are considered a mature topic. Within this subject, glass, glass-ceramics and ceramics have had great technological relevance, depending on the final applications. Supposing that luminescent materials are able to withstand high temperatures, have a high strength and, simultaneously, possess high stability, ceramics may be considered promising candidates to demonstrate required performance. In an ongoing effort to find a suitable synthesis method for their processing, some routes to develop nanostructured luminescent materials are addressed in this review paper. Several ceramic families that show luminescence have been intensively studied in the last few decades. Here, we demonstrate the synthesis of particles based on aluminate using the methods of sol-gel or molten salts and the production of thin films using screen printing assisted by a molten salt flux. The goal of this review is to identify potential methods to tailor the micro-nanostructure and to tune both the emission and excitation properties, focusing on emerging strategies that can be easily transferred to an industrial scale. Major challenges, opportunities, and directions of future research are specified.

Metals : open access journal 11(7), 1053 (2021). doi:10.3390/met11071053 special issue: "Special Issue "Advances in Understanding of Unit Operations in Non-ferrous Extractive Metallurgy" / Special Issue Editors Dr. Srecko Stopic, Prof. Dr. Bernd Friedrich", Published by MDPI, Basel

Unprecedented interest for clean and sustainable energy innovation has recently stimulated a return of attention on molten alkali carbonate salts not only for traditional use as electrolyte and high temperature reaction media but also as innovative energetic material for advanced applications in hybrid fuel cell systems and high-temperature CO2 gas separation processes. The main focus of this literature review is on examining novel and emerging molten carbonate applications in energy sectors beyond the well-assessed and mature domain of the Molten Carbonate Fuel Cells. In general, a number of advanced processes and highly functional materials are currently under investigation involving molten carbonates in a key role, suggesting a high potential of these salt systems for the future development of sustainable energy technologies. Current research activities can be grouped into three main energy research areas related to generation/conversion/storage of energy, materials and manufacturing processes, hot gas processing and gasification technologies. As already analyzed in Part I of this work, notable features of molten carbonates include their chemical stability, safety and optimal performance under a wide range of moderate (500–600 °C) and moderate-to-high temperature (600–800 °C) conditions. Thanks to these peculiar aspects, molten carbonate processes can be ideally integrated with solar energy sources for maximum sustainable level of use and with broad development prospects in the storage of solar energy and solar-to-chemical conversion systems. This view is confirmed, for example, by a series of extensive studies that has recently investigated novel solar-to-chemical energy conversion strategies based on a molten carbonate electrolysis process for solar production of fuels and other important chemical products, including iron and cement. In the last part of this work, several directions and opportunities for future research and studies on molten carbonates are suggested. © 2016 Hydrogen Energy Publications LLC

Hot corrosion of Inconel 625 in sodium chloride, potassium chloride, magnesium chloride, calcium chloride and their mixtures with different compositions is conducted at 900°C to investigate the effects of cations in chloride salts on corrosion behavior of the alloy. XRD, SEM/EDS were used to analyze the compositions, phases, and morphologies of the corrosion products. The results showed that Inconel 625 suffers more severe corrosion in alkaline earth metal chloride molten salts than alkaline metal chloride molten salts. For corrosion in mixture salts, the corrosion rate increased with increasing alkaline earth metal chloride salt content in the mixture. Cations in the chloride molten salts mainly affect the thermal and chemical properties of the salts such as vapor pressure and hydroscopicities, which can affect the basicity of the molten salt. Corrosion of Inconel 625 in alkaline earth metal chloride salts is accelerated with increasing basicity.

Flue dust produced by copper flash smelting causes problems by forming corrosive melts on the walls of heat recovery boiler used to recover the process heat value and to separate flue dust from SO2-rich gas, derived from smelting sulphidic copper ore, before manufacture of sulphuric acid. The corrosion phenomena of molybdenum containing low and high nickel stainless steels AISI 316 and Sanicro 28 were studied by simulating the conditions prevailing in the heat recovery boiler in laboratory in the temperature range of 250–350°C. ZnCl2 in copper smelter flue dust resulted in partial melting of the deposit containing sulphates and oxides of copper, zinc, arsenic, iron and lead, which increased the rate of corrosion dramatically. Chlorination of the steel was the dominant corrosion mechanism. The high nickel steel corroded more than low nickel steel due to reactivity of nickel under molten sulphates.

Hot corrosion behavior of three nickel-based single crystal superalloys with different key alloying elements (including Re, Cr, Al and Ti) contents in molten Na2SO4 salt at 900 °C was investigated. Comparative study of hot corrosion resistance was conducted on two Re-free superalloys with 12 wt% Cr and different content of Al and Ti. By further adding Re, the experimental alloy with moderate Cr content (8.5 wt%) and Al/Ti > 1 in the present research also exhibited excellent hot corrosion resistance. The influence mechanism of Re on promoting hot corrosion resistance was attempted to be explored in combined with first-principle calculation. In addition, the potential design space of new-developed single crystal superalloys was also proposed.

[EN]A thermodynamic model for a steady state pumped heat energy storage in liquid media is presented: it comprises a coupled Brayton-like heat pump and heat engine cycles connected to a cryogenic liquid and a hot molten salt by counter-flow heat exchangers. The model considers non-isothermal heat transfers between the working fluid and the liquid media and explicitly includes a set of parameters accounting for the main internal and external losses, heat leak, and pinch point effects for both the heat pump (charge) and heat engine (discharge) modes. Specific expressions for the main magnitudes in the charge (as the input power and coefficient of performance) and discharge (as power output and efficiency) modes and the global round trip efficiency have been analytically derived in terms of isentropic efficiencies of the compressor and turbine, pressure losses in the heat exchange processes, effectivenesses of the external counter-flow heat exchangers, and coupling between the working fluid and the storage and cryogenic liquid media. Round trip efficiencies around of 35 − 40% have been obtained, internal losses being those with main negative influence on the calculated values. The strong constraints imposed by the pinch point effects and liquid media have been analyzed. The model provides a thermodynamic assessment of the main involved processes and their interplay for a selected arrangement (molten salts, cryogenic fluid, and the charge and discharge power blocks) in order to check parametric strategies for thermodynamic optimization and design. These strategies are based on a reduced set of parameters of the overall installation and without the high computational costs of dynamical models., (ANII); Fondo Sectorial de Energía, Uruguay; contract FSE-1-2018-1-153077.

Raw syngas conditioning using molten salts was carried out in a fixed-bed reactor. The effects of the reaction conditions, including temperature, gas velocity, bubble diameter, molten salt static liquid heights, and inlet gas composition, on the composition of the syngas product and the properties of the spent molten salts were investigated. The molten salt absorbed CO2 in all of the experiments (at temperatures from 350 &deg, C to 500 &deg, C) and decreased its concentration down to 1%. The H2/CO increased from 0.94 to a maximum of 11.0, which may meet most of the synthetic process&rsquo, requirements. The temperature, gas velocity, and molten salt static liquid heights had significant effects on the H2 and CO concentrations in the gas product. Molten salt raw syngas conditioning can be a suitable follow-up procedure for gasification and pyrolysis.

The ‘Solar salt’ (60% NaNO3-40% KNO3, wt. %) is the most used heat transfer and storage material in high temperature CSP systems. The main drawback is its high melting temperature of 228 °C, which requires extra-energy to keep it in the liquid state and avoid damage to pipes at low temperatures. Multi-component salts are combinations of different cations and anions. The difference in size of the ions hinders the crystallization of the material and provides lower melting temperatures. Multi-component salts are considered in this study to replace simpler combinations, such as binary and ternary eutectic mixtures. Herein, we report on two novel six-component nitrates with a melting temperature of 60–75 °C and a thermal stability up to ~500 °C under a linear heating program in N2 atmosphere. Properties such as the thermal conductivity in solid and molten state, heat capacity and vibrational spectra were evaluated. The study of the thermal behaviour of these materials using differential scanning calorimetry was insufficient, hence alternative and complementary techniques were used, such as: the three-omega technique, optical transmission and Raman spectroscopy. Multi-component salts were found to solidify as amorphous solids even at slow cooling rates and water was found to behave as a catalyst of crystallization., The Catalan Institute of Nanoscience and Nanotechnology (ICN2) acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2017-0706) and funding from the CERCA Programme/Generalitat de Catalunya. Funding from the Spanish Ministry MINECO/FEDER: FIS2015-70862-P PHENTOM and MAT2015-68394-R NaCarFLOW are also acknowledged. M.-C. L acknowledges support from the Ministry of Science and Technology in Taiwan, MOST 104-2221-E-009-147-MY3.

The use of molten salt-based nanofluids as heat transfer fluids or thermal energy storage materials to increase the efficiency of Concentrated Solar Power plants has gained attention due to the use of the renewable energies against Global Warming. One of the issues of interest is the colloidal stability of the nanoparticles dispersed in ionic media like molten salts. In this work a new experimental set-up to measure the particle size distribution of molten salt-based nanofluids by means of Dynamic Light Scattering was developed. The colloidal stability of silica and Al/Cu nanoparticles dispersed in solar salt (NaNO3-KNO3) was experimentally measured for the first time. Silica nanoparticles were dispersed in water, calcium nitrate tetrahydrate and solar salt, and the formation of micrometrical agglomerates was observed when molten salts were used as base fluid due to the high ionic strength of the medium and the reduced Debye length. The influence of the nanoparticle composition was proved to be also important. For the Al/Cu metal alloy nanoparticles the agglomerates formed were smaller than for silica. Besides, even though both nanoparticles settle after 4 h in static conditions, only Al/Cu nanoparticles recover the initial particle size distribution when they are mechanically redispersed

We report on surface investigations of cesium and tetraphenylphosphonium bis(trifluoromethylsulfonyl)imide (Cs[Tf2N], [PPh4][Tf2N]) molten salts and their mixtures. Depending on composition, these ionic compounds combine low melting points with exceptionally high thermal stability, and thus, exhibit considerably enlarged thermal operation windows compared to conventional ionic liquids. To elucidate their liquid-solid transition behavior in the near-surface region, temperature-dependent angle-resolved X-ray photoelectron spectroscopy (ARXPS) investigations were performed using our unique laboratory electron spectrometer DASSA (“Dual Analyzer System for Surface Analysis”), dedicated for investigations of macroscopic liquid samples. We followed temperature-induced changes in bulk and surface composition within the first nanometers of the neat salt melts and of Cs[Tf2N] : [PPh4][Tf2N] = 3:1 and 1:3 mixtures. In the mixtures, pronounced surface enrichment of Cs+ on expense of the bulky [PPh4]+ ions was found in the liquid state at temperatures close to the liquid-solid transition. In the solid state of Cs[Tf2N]-rich mixtures, [PPh4]+ completely vanishes from the near-surface region probed by XPS.

Los fluidos de transferencia de calor, y en particular los nanofluidos, se pueden considerar un elemento esencial en diversos sectores industriales y su rendimiento es clave para una adecuada aplicación en tecnologías que van desde la gestión térmica y la refrigeración, a la generación de energía solar térmica y eléctrica mediante el uso de intercambiadores de calor. Estas industrias necesitan fluidos de transferencia de calor con un rango de temperatura del líquido más amplio y mejores prestaciones en la transferencia de calor que los fluidos convencionales. Todos los fluidos parecen beneficiarse de la dispersión de nanopartículas sólidas, tanto aquellos usados en aplicaciones de baja temperatura y temperatura ambiente, como aquellos que funden a más alta temperatura (p. ej. sales fundidas). La dispersión de nanopartículas conduce a la obtención de nanofluidos que con frecuencia presentan mejores conductividades térmicas y/o calores específicos en comparación con los fluidos base. Sin embargo hay algunas excepciones. En la bibliografía podemos encontrar resultados contradictorios acerca de la mejora de las propiedades térmicas en nanofluidos, lo cual hace que sea necesario un estudio de estos materiales en mayor profundidad. Por otra parte, la naturaleza líquida de estos materiales plantea un verdadero desafío, tanto desde el punto de vista experimental como en relación al marco conceptual. El trabajo que se presenta en esta tesis ha abordado dos retos diferentes relacionados con los fluidos de transferencia de calor y los nanofluidos. En primer lugar, se llevó a cabo un estudio riguroso y sistemático de las propiedades térmicas, morfológicas, reológicas, de estabilidad, acústicas y vibracionales de nanofluidos de grafeno en disolventes orgánicos. Observamos un gran aumento de la conductividad térmica de hasta un 48% y un aumento del 18% en la capacidad calorífica de los nanofluidos de grafeno en N,N-dimetilacetamida (DMAc). También se observó una mejora significativa en los nanofluidos de grafeno en N,N-dimetilformamida (DMF) del orden del 25% y 12% para la conductividad térmica y la capacidad calorífica, respectivamente. El desplazamiento de varias bandas del espectro Raman de DMF y DMAc hacia altas frecuencias (máx. ~ 4 cm-1) al aumentar la concentración de grafeno, sugirió que éste tiene la capacidad de afectar a las moléculas de disolvente a larga distancia, en términos de energía vibracional. En paralelo, las simulaciones numéricas basadas en la teoría funcional de la densidad (DFT) y dinámica molecular (MD) mostraron una orientación paralela de DMF hacia el grafeno, favoreciendo la interacción π-π y contribuyendo a la modificación de los espectros de Raman. Además, se observó un orden local de las moléculas de DMF alrededor del grafeno, lo que sugiere que tanto este tipo especial de interacción como el orden local inducido pueden contribuir a la mejora de las propiedades térmicas del fluido. También se realizaron estudios similares en nanofluidos de grafeno disperso en 1-metil-2-pirrolidona, sin embargo, no se observó ninguna modificación de la conductividad térmica o de los espectros de Raman. Todas estas observaciones juntas sugieren que existe una correlación entre la modificación de los espectros vibracionales y el aumento de la conductividad térmica de los nanofluidos. En vista de los resultados, se discutieron y descartaron algunos de los mecanismos propuestos para explicar la mejora de la conductividad térmica en nanofluidos. La segunda línea de investigación se centró en el desarrollo y caracterización de nuevas formulaciones de sales fundidas con baja temperatura de fusión y alta estabilidad térmica. Con este propósito, se sintetizaron dos nuevas formulaciones de seis componentes basadas en nitratos con una temperatura de fusión de 60-75 °C y una estabilidad térmica de aprox. 500 °C. Por otro lado, la complejidad de las muestras llevó a establecer una serie de métodos experimentales que se proponen para la detección del punto de fusión de estos materiales como una alternativa a la calorimetría convencional, estas técnicas son: espectroscopia Raman, técnica 3ω y transmisión óptica. Heat transfer fluids and nanofluids constitute an important element in the industry and their performance is key to the successful application in technologies that go from heat management and cooling to heat exchangers in thermal-solar energy and electricity generation. These industries demand heat transfer fluids with a wider liquid temperature range and better thermal performance than the conventional fluids. From low-temperature fluids to high-temperature molten salts, these fluids seem to benefit from the dispersion of solid nanoparticles, leading to nanofluids which frequently feature improved thermal conductivities and/or specific heats as compared with the bare fluids. However, there are some exceptions. Contradictory reports make it necessary to study these materials in greater depth than has been usual. Yet, the liquid nature of these materials poses a real challenge, both from the experimental point of view and from the conceptual framework. The work reported in this thesis has tackled two different challenges related to heat transfer fluids and nanofluids. In the first place, a careful and systematic study of thermal, morphological, rheological, stability, acoustic and vibrational properties of graphene-based nanofluids was carried out. We observed a huge increase of up to 48% in thermal conductivity and 18% in heat capacity of graphene-N,N-dimethylacetamide (DMAc) nanofluids. A significant enhancement was also observed in graphene-N,N-dimethylformamide (DMF) nanofluids of approximately 25% and 12% for thermal conductivity and heat capacity, respectively. The blue shift of several Raman bands (max. ~ 4 cm-1) with increasing graphene concentration in DMF and DMAc nanofluids suggested that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. In parallel, numerical simulations based on density functional theory (DFT) and molecular dynamics (MD) showed a parallel orientation of DMF towards graphene, favoring π–π stacking and contributing to the modification of the Raman spectra. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the thermal properties of the fluid. Similar studies were also performed in graphene-N-methyl-2-pyrrolidinone nanofluids, however, no modification of the thermal conductivity or the Raman spectra was observed. All these observations together suggest that there is a correlation between the modification of the vibrational spectra and the increase in the thermal conductivity of the nanofluids. In light of these results, the mechanisms suggested in the literature to explain the enhancement of thermal conductivity in nanofluids were discussed and some of them were discarded. The second line of research focused on the development and characterization of novel molten salts formulations with low-melting temperature and high thermal stability. In this regard, two novel formulations of six components based on nitrates with a melting temperature of 60-75 °C and a thermal stability up to ~ 500 °C were synthesized. Moreover, the complexity of the samples led to establish a series of experimental methods which are proposed for the melting temperature detection of these materials as an alternative to conventional calorimetry. These methods are Raman spectroscopy, three-omega technique, and optical transmission.

In this review, we summarise the current status and new trends in concentrating solar power (CSP) technology, analysing the technology cost and their evolution during the last years, with special focus on thermal storage. Moreover, we have carried out a comprehensive review of the molten salts used and proposed in CSP commercial plants. Nitrates, nitrites, chlorides, and carbonates are presented, including their corrosion aspects with common alloys as well as the different possibilities available in the literature to replace them (ternary and quaternary nitrate molten salt) or improve them (addition of nanoparticles). Finally, we have proposed the key factors for a successful new generation of CSP plants, with special focus on high-temperature molten salts (carbonates and chloride blends) and the main important materials requirements for CSP system components. The research leading to these results has received funding from the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors thank the Catalan Government for the quality accreditation given to their research group GREiA (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. Angel G. Fernández acknowledges the financial support provided by CONICYT/FONDAP 15110019 “Solar Energy Research Center” SERC-Chile. Dr. Aran Solé thanks Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI-2015-25741. Dr. Eduard Oró thanks Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva IJCI-2016-30568. This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office, Concentrating Solar Power. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Commercial buildings or shopping malls are characterized by large thermal and electrical energy consumptions with high variability of energy demand. Therefor e, there is a large interest to explore novel renewable energy generation systems for these applications. A novel flexible configuration of biomass - fired CHP system with organic Rankine cycle (ORC) is here proposed and applied to the case study of Sainsbur y’s supermarkets in the UK . The proposed configuration adopts a molten salt (MS) circuit to transfer heat from the biomass furnace to the ORC plant. A thermal Energy Storage (TES) is proposed to improve the flexible operation of the plant and reduce the si ze of the biomass boiler . Molten salts have been preferred to thermal oil as they have no fire risks and low environmental impact and can be used as medium for a Two Tank TES with a “direct heating” scheme. Th e plant has been analysed using real input dat a of biomass boiler installed, conversion efficiency and heat demand from the store. The model is informed by hourly energy costs and electricity feed in tariff in order to d efine optimal size and operation of the bottoming ORC for the specific case study of large commercial energy end user in the UK. The results show that the use of thermal storage in a biomass - fired ORC plant can improve the boiler efficiency and reduce the biomass consumption in thermal - load following operating mode and increase the inve stment profitability.

A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD simulations. This study aims at identifying the convective flows produced within the melted phase by temperature gradients and gravity. Simulations were carried out on experimental devices for applications to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat transfer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is examined by solving the unsteady Navier-Stokes equations for HTF and PCM and conduction for the tube. In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about 30% the time needed to charge the heat storage. A detailed description of the convective motion in the melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the mushy zone constant is also investigated. © 2015 Elsevier Ltd.

En esta investigación se evaluó la oxidación del acero ASTM A335 P92 en una mezcla de sales 40% K2SO4 - 60% NaCl a temperaturas de 500°C a 700°C, a intervalos de 50°C con tiempos de exposición de 1, 3, 10, 30, 100 y 150 horas, utilizando la norma estandarizada por la Federación Europea de Corrosión. Se realizó análisis metalográfico y de dureza antes y después del ensayo para identificar el posible cambio estructural; se realizan pruebas de difracción de rayos X (drx), microscopía electrónica de barrido (SEM-EDS), para determinar los productos de corrosión presentes en el acero. Se demuestra con el análisis SEM-EDS que las especies corrosivas como el Cl-, SO4- no reaccionan con los elementos de aleación del acero. También se observó que las capas de óxido formadas muestran una buena estabilidad y adherencia, lo cual confirma la protección de estos óxidos sobre el metal. Las curvas de ganancia de peso por deposición de sales muestran un comportamiento parabólico, propio de los materiales utilizados a temperatura alta. In this research the oxidation of ASTM A335 P92 steel and the effect of 40% K2SO4 - 60% NaCl salt mixture at temperatures of 500°C to 700°C in intervals of 50°C with exposure times of1,3,10, 30,100 and 150 hours were evaluated using the standard standardized by the European Federation of Corrosion. Metallographic analysis and hardness analysis were performed before and after the test to identify the possible structural change; evidence of x-ray diffraction (xrd) and scanning electron microscopy (SEM-EDS) were performed to determine the corrosion products present in the steel. By SEM-EDS analysis it is shown that corrosive species such as Cl~, SO4- do not react with the alloying elements of steel. It was also noted that the oxide layers formed showed stability, and good adhesion which confirms the oxides protection on the metal. The "gained weight by salts deposition" curves showed a parabolic behavior, typical of high temperature materials.

A novel Solar-Gas Hybrid Receiver (SGHR) that combines the function of a solar receiver and a gas boiler in a single device is presented. This concept requires less equipment and maintenance compared to the Solar Gas Hybrid (SGH) concept, in which the boiler and the solar receiver (SR) are independent devices. The economic benefit is attributed to the increased sharing of infrastructures. Additionally, it has less thermal stress, cycles and shocks, which reduce the failure risk. However, the additional benefit in the reliability of these receivers has not been analyzed so far. In this work, a mathematical model of SGHR is presented. It determines the stress in steady state which is used to estimate the allowable transient stress in order to achieve the required 30 years life design. The results show that the SGHR is exposed to lower thermal stress due to much better temperature distribution. Moreover the higher absorber heat flux of SGHR is translated in a higher mechanical stress with could jeopardizes the durability. However the reduced number of cycles and the lower thermal stress of a SGHR allows higher transient stresses than the conventional tube type solar receiver, which lead to more reliable and efficient designs.

Several forms of renewable energy have in the last decade achieved a remarkable technological improvement and cost effectiveness, including Solar Energy. Photovoltaic systems (PV) are reaching grid parity in the sunniest regions of Europe. Apart from PV, a promising technology is Concentrated Solar Power (CSP) with thermal storage, because it enables higher power plant availability throughout the year as well as dispatchability, a highly important and valuable feature for a power plant. However significant cost reductions are still to be achieved, for CSP to be competitive with conventional electricity production and with PV. In this paper a few technological improvements are described and a proposal is made to combine them in a system that is more efficient and has, simultaneously, the potential of being cheaper. The goal is to show the potential for advanced LFR concepts in combination with high temperature molten salt mixtures and energy storage as being also important contenders to the objective of bringing STE- Solar Thermal Electricity to the market in a competitive way. The concept presented and developed includes a higher ΔT of the heat transfer fluid (HTF), a particular storage strategy and a new optical concept based on a new Linear Fresnel Concentrator (LFR XX SMS-Simultaneous Multiple Surface, Fig.1,2, [1] enabling an important increase in the overall yearly solar to electricity conversion efficiency and generating an important potential for electricity cost reduction. It is shown that values approaching 10eurocents/kWh, for a 50MW plant with 7 hours storage capacity are possible in Southern Europe.

Renewable energies are main players to ensure the long-term energy supply. Solar power plants with thermal energy storage (TES) are one of the available renewable technologies which have more potential. Nowadays, there are still several aspects in the design and operation of these power plants which need to be improved, such as the correct operation of some specific instrumentation, the compatibility between TES materials and storage tanks materials, and operational process strategies. This paper presents the acquired experience during the design, start-up, and operation of a kWh scale pilot experimental facility built at the University of Lleida (Spain) together with Abengoa Research (Spain) in 2008. The versatility of this facility has allowed simulating real working conditions and therefore testing different TES systems, TES materials, solar power plant components, and operational strategies focused on TES for temperatures up to 400 °C. In the present paper, the authors show the lessons learnt at pilot and present the main problems and limitations encountered, and give advices of this experimental set-up to extrapolate the data to real plant, to provide solutions to technical problems and reduce the cost of commercial plants. The authors want to thank specially to Dr. Eduard Oró (today at Institut de Recerca d’Energies de Catalunya, Spain) and Dr. Antoni Gil (today at Massachusetts Institute of Technology, USA) for their help in the design, start-up and operation of the pilot plant facility. The research leading to these results has received funding from Spanish government through CDTI granted projects (Fondo tecnológico IDI-20090393, ConSOLida CENIT 2008-1005) and from Abengoa Solar NT. The work is partially funded by the Spanish government (ENE2008-06687-C02-01/CON, ENE2011-22722, ULLE10-4E-1305, and ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group GREA (2014 SGR 123). GREA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement NºPIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). Laia Miró would like to thank the Spanish Government for her research fellowship (BES-2012-051861). Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017FI_B1 00092).

We herein describe a straight forward procedure to increase the performance of platinum-on-alumina catalysts in methanol steam reforming by applying an alkali hydroxide coating according to the “solid catalyst with ionic liquid layer” (SCILL) approach. We demonstrate by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed desorption (TPD) studies that potassium doping plays an important role in the catalyst activation. Moreover, the hygroscopic nature and the basicity of the salt modification contribute to the considerable enhancement in catalytic performance. During reaction, a partly liquid film of alkali hydroxides/carbonates forms on the catalyst/alumina surface, thus significantly enhancing the availability of water at the catalytically active sites. Too high catalyst pore fillings with salt introduce a considerable mass transfer barrier into the system as indicated by kinetic studies. Thus, the optimum interplay between beneficial catalyst modification and detrimental mass transfer effects had to be identified and was found on the applied platinum-on-alumina catalyst at KOH loadings around 7.5 mass %.

Herein, we report the synthesis of a new type of porous Mo 2 C/C composite by using luffa sponge-derived carbon template and ammonium molybdate ((NH 4 ) 6 Mo 7 O 24 •4H 2 O) in molten NaCl–KCl salt media. The product exhibits a higher specific surface area and three-dimensional porous structure, including macrochannels, micropores and mesopores. The desirable porous structure results from the carbon template structure and Mo 2 C coating formed.

The use of solar thermal power plants is considered a cost-effective alternative to produce renewable energy. Unlike other energy installations, in this type of plants the transfer and storage of energy has been solved by using molten salts. These salts run between two tanks through the steam generation system that feeds the turbine. Although the use of salts as a heat transfer fluid is considered an adequate solution, they are not without problems. One of them is the formation of blockages in the pipes due to a partial solidification of the salt, which leads to the shutdown of the installation, with the consequent economic losses. Fast location of these blockages in a minimally intrusive way is the objective pursued in this work. The method to achieve this is based on the use of a new magnetostrictive sensor that simplifies previous designs.