NaCl Salt Mixture Research Articles

Hot salt corrosion behavior of the Ti-44Al-4Nb-1.5Mo-(B,Y) alloy in the temperature range of 750–950 °C

Hot salt corrosion behavior of TNM alloy (Ti-44Al-4Nb-1.5Mo-(B, Y) (at.%)) was investigated in cyclic conditions at 750 °C, 850 °C and 950 °C for 100 h in the 75 wt% Na2SO4 + 25 wt% NaCl salt mixture. The hot salt corrosion resistance of γ、α2 and β phase in the alloy was studied by short-term quasi-in-situ hot corrosion experiments. Results show that the hot salt corrosion resistance of the three phases decreases in the following order: γ、α2、β. The weight changes of TNM alloy after hot salt corrosion at 750 °C, 850 °C and 950 °C for 100 h are 13.8 mg/cm2, -19.6 mg/cm2 and -26.7 mg/cm2. Under the condition of hot salt corrosion at 750 °C, the corrosion scales are mainly composed of a mixed corrosion scale of TiO2 and Al2O3, Al2O3 scale, and Al depletion zone, similar to the morphology of a high-temperature oxidation scale. The corrosion scales are seriously peeled off and destructive transverse cracks are generated inside the corrosion scales under the conditions of hot salt corrosion at 850 °C and 950 °C. The acid-base corrosion dissolution of oxides in the corrosive medium and the formation of volatile chlorides are the main causes of cracks in the TiO2 and Al2O3 scales. In addition, the Nb element in the TNM alloy is mainly enriched beneath the corrosion scales to form a NaNbO3 layer, which can inhibit the decomposition and penetration of the corrosive medium. Mo element reacts with the S element to form MoS2, which anchors the S element to a certain extent.

Multi-cationic molten salt electrolyte of high-performance sodium liquid metal battery for grid storage

Multi-cationic molten chloride salt mixtures such as LiCl–KCl–NaCl are promising molten salt electrolytes for sodium liquid metal batteries (Na-LMBs). In this work, the melting temperature of LiCl–KCl–NaCl was determined with Differential Scanning Calorimetry (DSC), assisted by FactSage™ simulation and confirmed by a melting point apparatus OptiMelt™. It is founded that the eutectic LiCl–KCl–NaCl can be considered as a pseudo-binary system with LiCl–KCl eutectic (59.2–40.8 mol.%) as the solvent and NaCl as the solute. When NaCl is not more than 9 mol.%, the eutectic LiCl–KCl–NaCl salt mixture has a melting temperature of ∼350 °C as that of LiCl–KCl eutectic. In addition, the exchange reactions between anode Na metal with LiCl–KCl–NaCl molten salt electrolyte were studied at the temperature of 400–500 °C quantitatively. The equilibrium constants of the exchange reactions were determined by chemical analysis on the salt and metal phases with Ion Chromatography (IC). A one ampere-hour (Ah) Na-LMB test cell shows promising energy storage performance. Moreover, the phenomena in the cell test can be explained convincingly, combining the results of exchange reactions and the pseudo-binary-system theory. The findings on the multi-cationic molten salt electrolytes for Na-LMBs in this work could support further development of other liquid metal batteries.

Simulation-Assisted Determination of the Minimum Melting Temperature Composition of MgCl2–KCl–NaCl Salt Mixture for Next-Generation Molten Salt Thermal Energy Storage

Molten chloride mixtures such as MgCl2–KCl–NaCl are potential thermal energy storage (TES) materials and heat transfer fluids (HTFs) for next-generation concentrating solar power (CSP) systems due to their high operation temperatures (>700°C) and low costs. This ternary MgCl2–KCl–NaCl salt mixture with a low material cost (<0.35 $/kg) is a promising salt for high-temperature TES/HTF applications, for example, it could enable next-generation CSP plants to have significant power cycle efficiency and lower levelized cost of electricity (LCOE). In this study, the minimum melting temperature composition for the MgCl2–KCl–NaCl mixture was estimated by FactSage simulation, while the binary and ternary phase diagrams of the MgCl2–KCl–NaCl salt system, including their phase transitions, were studied. Five different eutectic compositions of the MgCl2–KCl–NaCl mixture from literature and simulations were selected to determine the minimum melting temperature composition by the differential scanning calorimetry technique. Results show agreement between experiments and simulations of the melting temperature and its composition. Hence, values of the exact and reliable minimum melting temperature and salt composition in mol% and wt% are given. Based on the determined melting temperature, the minimum operating temperature of MgCl2–KCl–NaCl is recommended according to the safety margin for CSP applications.

Hot corrosion behaviour of constant and pulsed current welded Hastelloy X in Na2SO4, V2O5, and NaCl salt mixture at 900 °C

The high-temperature corrosion behavior of constant current gas tungsten arc (GTA) and pulsed current gas tungsten arc (PCGTA) welded Hastelloy X with different filler wires (C263 and ERNiCr-3) are studied for 50 cycles at 900 °C. Molten salt I (MS I) (75% Na2SO4 + 25% V2O5) and molten salt II (MS II) (75% Na2SO4 + 20% V2O5 + 5% NaCl) were coated on the welded specimens. MS II coated substrate shows the highest weight gain than MS I with a parabolic constant for GTA ERNiCr-3 as 21.440 × 10–6 mg2/(cm4.s). Whereas PCGTA C263 welded sample with MS I, revealed parabolic constant (lowest) of 0.008 × 10–6 mg2/ (cm4.s). Based on the results, an increasing pattern of hot corrosion resistance of substrates is arranged as GTA ERNiCr-3 < GTA C263 < PCGTA C263 < PCGTA ERNiCr-3. PCGTA shows more refined grains, higher grain boundary volume, better corrosion resistance, and more protective phases like Cr2O3, NiO, NiCr2O4, CoCr2O4, Al2O3, NiFe2O4, NbO than GTA weldment. But phases such as Fe2O3, MoO3, and Cr2S3 (non-protective phases) decrease corrosion resistance due to acid fluxing of alloying elements that promote the oxide scale exfoliation, spallation, chipping, and cracking. This study observed that PCGTA with C263 filler in MS I and MS II environment provides good corrosion resistance at high temperatures.

Comparative investigation of oxidation behavior and hot corrosion behavior in NaCl–Na2SO4 mixture for a Ti2AlNb based alloy at 1023 K

Oxidation behavior of a Ti2AlNb based alloy (Ti–22Al–23Nb (at.%)) and hot corrosion behavior of this alloy coated with a salt mixture of NaCl–Na2SO4 at 1023 K were comparatively investigated. The results showed that the alloy possessed relatively good oxidation resistance while suffered severe hot corrosion attack. The mass gain of the hot-corroded alloy was much larger than that of the oxidized alloy. The oxide scale was mainly composed of TiO2. During the oxidation, the oxide scale could keep intact. In the corrosion product scale, TiO2 + Al2O3 layers and NaNbO3 layers existed alternately and Al2O3 was distributed in the lower parts of the TiO2 + Al2O3 layers. The formation of the TiO2 + Al2O3 layer and the NaNbO3 layer should promote each other by altering the acidity/basicity of the salt film, and thus the growth of the scale was accelerated. The escape of the gaseous chlorides, the fast growth of the scale and the coefficient of thermal expansion (CTE) mismatch between TiO2 and NaNbO3 resulted in serious cracking and spalling of the scale.

Hot corrosion behavior of electrodeposited SiO2 coating on TiAl alloy

To improve the hot corrosion resistance, thickness controllable SiO2 coating was electrodeposited on TiAl alloy. The hot corrosion behavior of the specimens contaminated with 75 wt.% Na2SO4 + 25 wt.% NaCl salt mixture was investigated at 700 °C. Results showed that the generation of compact amorphous SiO2 embedded with Na2Si4O9 and cristobalite was responsible for the enhanced hot corrosion resistance. Moreover, the SiO2 coating does not only act as a diffusion barrier to sulfur and chlorine but also decreases the oxygen partial pressure at the coating/alloy interface, therefore promoting the selective oxidation of Al to form protective Al2O3 layer.

The effect of Nb and Si on the hot corrosion behaviors of TiAl coatings on a Ti-6Al-4V alloy

Hot corrosion behaviors of TiAl coatings with different Nb and Si additions in a Na2SO4 + NaCl salt mixture at 800 °C were investigated. Corrosion kinetics was evaluated based on mass change measurements. The corrosion products and morphologies of the corrosion scales were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The adhesion strength of the corrosion scales was evaluated by acoustic emission (AE). High Si addition on its own and a co-addition of a high content of Si and an appropriate content of Nb improved the hot corrosion resistance of the coatings.

Effect of Mg dissolution on cyclic voltammetry and open circuit potentiometry of molten MgCl2–KCl–NaCl candidate heat transfer fluid for concentrating solar power

Molten chloride salts have recently gained attention for application to heat transfer and thermal energy storage in concentrating solar power (CSP) plants. In this study, we studied the electrochemical effect of addition of hydroxide ions and/or dissolved metals added to MgCl2–KCl–NaCl salt mixture. Open circuit potentiometry indicated that the salt's redox potential increased with addition of hydroxide ions and decreased with the addition of soluble magnesium metal. Cyclic voltammetry indicated that a reduction peak associated with hydroxides vanished with addition of Mg0. Hydrogen gas was evolved when a mixture of Mg metal and MgCl2–KCl–NaCl containing NaOH was heated to 650 °C. These results demonstrate the benefit and mechanism for redox potential control in this salt using dissolved Mg metal.

Preparation, characterization and formation mechanism of single-crystal zirconia micro-sheets

Zirconia micro-sheets were prepared by molten salt method using the salt mixture of NaCl and NaF. FE-SEM, TEM, EDS, DTA-TG, XRD, Raman and FT-IR techniques were employed to characterize the morphology, phase composition and formation mechanism of the ZrO2 micro-sheets. The obtained monoclinic ZrO2 microsheets with exposed {100} facets show an average thickness of 0.2 ?m. The growth of the ZrO2 micro-sheets is proved to be assisted by the addition of fluoride. On the one hand, the addition of fluoride promotes the mass transfer of zirconia through the formation of zirconium fluoride complexes (ZrF 3-7). On the other hand, fluoride adsorbed on the surface of zirconia stabilizes {100} facets and lead to the exposure of {100} facets in the final product.

Seedling stage salt stress response specific characterization of genetic polymorphism and validation of SSR markers in rice.

Salt tolerance status at early seedling stage in 30 rice varieties including two tolerant (Pokkali and CSR-36) and two susceptible (IR-29 and IR-64) checks was assessed under different levels of salinity (0, 4, 8 and 16dSm-1) created by salt mixture of NaCl, CaCl2, Na2SO4 in 7:2:1 ratio. Overall salinity tolerance indices clearly reflected that 17 varieties including the two tolerant checks were highly tolerant, seven varieties exhibited moderately tolerant, whereas six varieties including the two susceptible checks had highly susceptible response to salt stress. Molecular profiling of 13 tolerant and 5 susceptible rice varieties by using 24 SSR markers revealed 8.5 alleles per primer with altogether 114 shared and 91 unique allelic variants. Considering the allele number, polymorphism information content and polymorphism percent, SSR primers RM 302, RM 8094, RM 10665, RM 10694, RM 10748 and RM 10825 appeared to be highly polymorphic and comparatively more informative. Hierarchical classification and spatial distribution patterns based on amplification profiles dependent similarity indices unambiguously discriminated these 18 varieties in accordance with their salt tolerance response. Sequential exclusion of primers in further analysis led to validation of RM 140, RM 1287, RM 3412, RM 10745, RM 10764 and RM 10772 for their efficiency to distinguish salt tolerant varieties from susceptible ones. A specific combination of either four (RM 1287, RM 3412, RM 10764 and RM 10772) or even two markers (RM 1287 and RM 3412) also seemed to be equally effective in discrimination of entries according to their salt stress responsiveness. Principal coordinate analysis completely corroborated hierarchical classification of the varieties. Salt tolerance donors identified and SSR primers validated in the present study may be further utilized in the development of salt stress tolerant varieties of rice.

Design and statistical analysis of plasma coatings on superalloy for gas turbine applications

The Influence of plasma sprayed NiCr–Cr2O3 and Al2O3–40% TiO2 (A40T) coatings on Inconel 617 are investigated at 900 and 1000 °C under mixed salt environment for gas turbine applications. The results revealed that the plasma coated alloy exhibits lower mass change than bare alloy in the Na2SO4 and NaCl salt mixture with and without V2O5. The response to the experimental analysis is statistically evaluated using 23 factorial design. Further the exposed samples were analyzed by means of optical image, SEM, EDS and XRD results. The EDS and XRD analysis revealed that the oxides are rich in Ni and Mo on the surface of the samples. The coated samples exhibited better corrosion resistance in A40T when compared to NiCr–Cr2O3 coatings than bare alloy.

In Search of an Alternative Solar Grade Silicon Production By Electrochemical Reduction of SiO2

Silicon plays an important role in fabrication of solar cells and solar chips. Metallurgical grade silicon (98 to 99 % Si) demands further purification such as zone refining [1, 2], metallothermic reduction [3] and Siemens process [4] to convert it to solar grade. A promising method, based on direct electrochemical reduction of oxides by FFC Cambridge Process [5], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2–NaCl salt mixture [6]. The contamination of silicon powder by iron and nickel originating from stainless steel cathode was reported to disqualify the product from solar applications. SiO2 pellets, sintered at 1300oC for 4 hours, were sandwiched between pure silicon wafer plates to minimize contamination of silicon. The promising results indicated a potential alternative method of direct solar grade silicon production for expanding solar energy industry. [1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239. [2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004). [3] K. Yasuda, T.H. Okabe, “Solar-grade silicon production by metallothermic reduction”, JOM,62 (12) (2010), 94-101. [4] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956 [5] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364. [6] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.

Oxidación a alta temperatura de un acero ASTM A335 P92 en contacto con una mezcla de sales de K2 SO4 – NaCl

In this research the oxidation of ASTM A335 P92 steel and the effect of 40% K2SO4 - 60% NaCl salt mixture at temperatures of 500oC to 700oC in intervals of 50°C with exposure times of 1,3,10, 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.

Study on formation of unstable clathrate-like water molecules at freezing/melting temperatures of water and salty water

Having performed simulations for the pure water and water–NaCl salt mixture at several temperatures, we reveal new aspects of the formation of unstable clathrate-like water molecules in coexistence with ice molecules. Interestingly, the maximum numbers of water molecules in clathrate hydrate phase are recorded at freezing/melting points of the pure water and water–salt mixture. In the presence of NaCl salt, the number of water molecules in the unstable formed clathrate phase decreases. We first perform molecular dynamics simulations using the coarse-grain model to study the freezing/melting behavior of the pure water and 14% water–salt mixture at several temperatures. For both systems, the freezing/melting behavior of water molecules is studied using some qualities such as density, number of ice molecules, coordination number, and liquid fraction. From the results of our study, we also show that calculating the coordination numbers of water, sodium and chloride ions at different temperatures can serve as a useful method for determining the freezing/melting temperature for the pure water and salty water, and also for the brine rejection process for water–salt mixture. In the pure water, large changes occur at the freezing/melting point for the coordination numbers both for the first and higher coordination shells.

Hot Corrosion Behavior of Superalloy IN718 at 550 and 650 °C

This investigation was undertaken to evaluate oxidation and hot corrosion behavior of the Fe-Ni-based superalloy IN718, at 550 and 650 °C, to explore its performance as turbine engine components under marine environment. Uncoated and different salt-coated samples (100 wt.% NaCl, 75 wt.% Na2SO4 + 25 wt.% NaCl, and 90 wt.% Na2SO4 + 5 wt.% NaCl + 5 wt.% V2O5) were exposed in air at 550 and 650 °C under cyclic heating and cooling for 100 h. Weight gain was studied for both uncoated and salt-coated samples. X-ray diffraction, scanning electron microscopy, and electron dispersive spectroscopy were used to characterize the oxidation and corrosion products. A possible mechanism of corrosion, based on the corrosion compounds, is discussed. The variation in weight gain with time showed a parabolic growth of oxides. Coating with NaCl was found to be detrimental both at 550 °C as well as 650 °C. On the other hand, the salt mixture of NaCl and Na2SO4 had no effect at 550 °C; however, it was detrimental at higher temperature of 650 °C. Coatings of salt mixture of Na2SO4, NaCl, and V2O5 caused very slow oxidation at both the temperatures. Increase in thickness of salt coating was observed to enhance the rate of hot corrosion. Among the three types of salt coatings, the coating of NaCl was found to be most damaging both at 550 and 650 °C.

Influence of saline environment on creep rupture life of Nimonic-263 for marine turbine application

The present paper highlights the effect of Na2SO4 and NaCl salt mixture on creep rupture properties of Nimonic-263 alloy at 800 and 850°C. Results revealed that for short duration tests, the rupture life is not much affected by the corrosive action of the salt mixture at both the temperatures. Whereas for long term creep tests, salt mixture affects the creep rupture properties of the material catastrophically. Minimum creep rate increases marginally for salt deposited sample compared to the bare alloy. Fractographic features of the ruptured salt deposited and bare samples have been discussed.

Electrochemical decomposition of SiO2 pellets to form silicon in molten salts

▶ Increasing temperature or decreasing SiO 2 particle size increased the reduction rate. ▶ Addition of NaCl to the electrolyte decreased the reduction rate. ▶ Complete reduction of SiO 2 pellets was achieved after 16 h of electrolysis. ▶ The brown color of silicon may be the result of nanometer-scale crystallite size. ▶ Higher purity of Si may be obtained by advancement of cell component materials. Direct electrochemical reduction of porous SiO 2 pellets in molten CaCl 2 salt and CaCl 2 –NaCl salt mixture was investigated by applying 2.8 V potential. The study focused on the effects of temperature, particle size of SiO 2 powder starting material and the behavior of cathode contacting materials during electrochemical reduction process. The starting materials and the electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy mainly. The studies showed that smaller particle sizes and higher temperatures had slightly positive effects in increasing the reduction rate within the ranges covered in this study. The results were interpreted from variations of current and accumulative electrical charge that passed through the cell as a function of duration of electrochemical reduction under different conditions. Microstructures and compositions of the reduced pellets were used to infer that electrochemical reduction of SiO 2 in molten salts may become a method to produce silicon that could be used in solar energy utilization. Furthermore, X-ray diffraction analysis results indicated that the silicon produced at the cathode reacts with contacting materials; nickel, and iron in stainless steel to form Ni–Si and Fe–Si compounds due to very reactive nature of silicon especially at high temperatures.

Pesticide Multiresidue Analysis in Cereal Grains Using Modified QuEChERS Method Combined with Automated Direct Sample Introduction GC-TOFMS and UPLC-MS/MS Techniques†

The QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation method was modified to accommodate various cereal grain matrices (corn, oat, rice, and wheat) and provide good analytical results (recoveries in the range of 70-120% and RSDs <20%) for the majority of the target pesticides (about 180 analytes). The method consists of a 1 h shaking of a milled sample (2.5-5 g) in 20 mL of 1:1 (v/v) water/acetonitrile (or 25 mL of 1.5:1 water/acetonitrile in the case of rice) to provide simultaneous matrix swelling and analyte extraction. Then, a MgSO(4)/NaCl salt mixture (4:1, w/w) is added to the extract to induce phase separation and force the pesticides into the upper acetonitrile layer, a 1 mL aliquot of which is subsequently cleaned up using dispersive solid phase extraction with 150 mg of PSA, 50 mg of C(18), and 150 mg of MgSO(4). GC-amenable pesticides were analyzed using gas chromatography combined with time-of-flight mass spectrometry (GC-TOFMS) and the automated direct sample introduction technique for a large volume injection of the extracts. Ultraperformance liquid chromatography coupled to triple-quadrupole tandem mass spectrometry (UPLC-MS/MS) was employed for the analysis of LC-amenable pesticides. This method was implemented in a routine laboratory, providing about 3-fold increased sample throughput, 40-50% reduction in the cost of disposable materials and in the operation costs, 1:100 solvent waste reduction, and increased scope of the analysis versus the traditional approach based on the Luke method.

Hot corrosion of glass coating on nickel base superalloy

Hot corrosion behaviour of BaO–MgO–SiO 2 based glass coating on nickel base superalloy was studied using 80 wt.% Na 2SO 4 + 20 wt.% NaCl salt mixture, which melts at about 700 °C. In one set of experiments the glass coated superalloy substrates were immersed in the molten salt wherein in the other samples were suspended in the salt vapour at 1000 °C. During the test, mass loss per unit surface area was observed to be higher for specimens suspended in the salt vapour. The phase composition and microstructure of the corroded coating were investigated by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) in association with energy dispersive X-ray (EDX) analysis.

Effects of osmotic potential on virulent and hypovirulent strains of the chestnut blight fungus

Mycelial growth and conidial germination of two virulent and four isogenic hypovirulent strains of Cryphonectriaparasitica (Murr.) Barr were monitored on cornmeal agar media osmotically adjusted with NaCl, KCl, sucrose, or a salt mixture of NaCl–KCl–Na2SO4 of 5:3:2. Mycelial growth generally was not inhibited on KCl or sucrose adjusted media with an osmotic potential above −2.0 MPa. Mycelial growth generally was inhibited at this osmotic potential, however, on those media that contained sodium in the osmoticum. While conidial germination was more sensitive than mycelial growth to sodium, conidia were more tolerant than mycelia to osmotic potentials less than −2.0 MPa when media were adjusted with KCl or sucrose. Conidia of all strains germinated on media adjusted to −6.0 MPa with these two osmotica after incubation for 48 h but not 24 h at 25 °C. Hypovirulent strains generally reacted similarly to their isogenic virulent strains with regard to reduced osmotic potential. Because the lowest osmotic potential of chestnut (Castaneadentata (Marsh.) Borkh.) bark observed in monthly samples was −2.0 MPa (see companion paper), it appears that water stress has little direct impact on the pathogen during pathogenesis.