Solid NaCl Research Articles

Sublimation rate of solid NaCl powders and evaporation rate of liquid NaCl upon heating in vacuum and air

The volatilization of sodium chloride (NaCl) is important for multiple applications, such as energy storage, manufacturing porous parts, and purification and recycling of composites. Until now, only limited information on this feature has been published. To expand the knowledge in this field, we investigated the sublimation and evaporation of two NaCl powders by thermal gravimetry in vacuum and air. The study has shown that the volatilization kinetics of powders with different shapes and sizes are identical. The volatilization of NaCl powders in vacuum occurs mainly by sublimation before melting. In contrast, the volatilization of NaCl in the air is preferentially caused by the evaporation of the melt. In a vacuum, the evaporation of NaCl powder after melting is significantly slower than the sublimation before melting, because of a drastic decrease in the volatilization area. The Hertz-Knudsen relation with an appropriate fitting coefficient satisfactorily describes the mass loss by volatilization in vacuum and air.

NaCl aerosol filtration over filter media with intrafiber porosity: can filtrate capacity be increased by wicking into this pore volume?

This paper investigates a novel fiber-based filter media wherein a NaCl filtrate is collected and reservoired not only onto the surfaces of the fibers and within their inter-fiber voidage but also within the internal porosity of high pore volume nanoporous fibers or vapor grown carbon nanofibers (VGCF) floc used to fabricate the media. This transport process is shown to occur through a NaCl dissolution into the water-filled nanopores of the fiber and a subsequent intra-fiber wicking phenomenon. The study further elucidates two distinct NaCl accommodation mechanisms which are uniquely available to filter media containing nanoporous intrafiber porosity: (1) wicking and capillary condensation of liquid NaCl aerosols directly into the intrafiber pores at high RH, and (2) dissolution of otherwise solid NaCl aerosols deposited onto fiber surfaces (at low RH) into the interior nanopores of the fiber because these pores (when hydrophilic) are saturated with water (even at low RH). To investigate these two mechanistic regimes, various media were fabricated possessing multiscale porosity in the form of: (i) embedded flocs of VGCFs (4.108 cm3gm-1pore volume), (ii) hydrophilic and high pore volume activated carbon fibers (ACFs, 0.950 cm3gm-1) and (iii) solid graphite fibers. These media were then comparatively evaluated toward NaCl aerosol filtration at different relative humidities. Pressure drop measurements versus filtrate accumulation and SEM-EDAX VGCF demonstrated the location and transport of NaCl into the intrafiber voidage. Media containing both VGCF floc and ACF accumulated 1200% more NaCl at low RH (and a specified pressure drop) than similar media prepared from non-porous graphite fibers, with an additional 315% increase from low to high RH. A Gibbs free energy driving force model is provided to illustrate the driving forces favoring water condensation into the nanopores and solid NaCl aerosol dissolution into the water phase. Filtration efficiency and quality factor assessments for the various media are also systematically evaluated to demonstrate the observed mechanistics.

Iodine-induced self-depassivation strategy to improve reversible kinetics in Na-Cl2 battery

Rechargeable sodium-chlorine (Na-Cl2) batteries show high theoretical specific energy density and excellent adaptability for extreme environmental applications. However, the reported cycle life is mostly less than 500 cycles, and the understanding of battery failure mechanisms is quite limited. In this work, we demonstrate that the substantially increased voltage polarization plays a critical role in the battery failure. Typically, the passivation on the porous cathode caused by the deposition of insulated sodium chloride (NaCl) is a crucial factor, significantly influencing the three-phase chlorine (NaCl/Na+, Cl-/Cl2) conversion kinetics. Here, a self-depassivation strategy enabled by iodine anion (I-)-tuned NaCl deposition was implemented to enhance the chlorine reversibility. The nucleation and growth of NaCl crystals are well balanced through strong coordination of the NaI deposition-dissolution process, achieving depassivation on the cathode and improving the reoxidation efficiency of solid NaCl. Consequently, the resultant Na-Cl2 battery delivers a super-long cycle life up to 2000 cycles.

Corrosion behavior of low melting glass modified potassium silicate coating under the synergy of solid NaCl deposit and water vapor at 700 °C

The effects of LMG (SiO2–BaO–Al2O3–TiO2–Na2O–K2O–ZnO) modification on the performance of potassium silicate coatings on Ti–6Al–4V alloy during tests of either H2O/O2- or NaCl/H2O/O2- corrosion were investigated at 700 °C for 500 h using thermogravimetric, SEM, EPMA, and XRD. Adding 10-30 wt% LMG particles into the potassium silicate solution did not impair the intact and the surface roughness of the coatings and improved the resistance of the coatings against humid oxygen corrosion and NaCl/H2O/O2-induced corrosion. For the humid oxygen corrosion, the improvement was enhanced when the amounts of LMG was increased. However, the LMG10 coating with 30 vol% LMG had the most excellent corrosion resistance, the formation of titanate was prohibited; the coatings with more LMG additions were less protective than LMG10 though better than the coating without LMG.

Corrosion Behavior of Pre-oxidized GH4169 Alloy with Solid NaCl Deposited in a Wet Oxygen Flow at 600 °C

Corrosion Behavior of Pre-oxidized GH4169 Alloy with Solid NaCl Deposited in a Wet Oxygen Flow at 600 °C

Corrosion mechanism of potassium silicate coating on Ti–6Al–4V alloys under solid NaCl deposit at 700 °C

A potassium silicate coating cured by calcium hydrogen phosphate was prepared on Ti–6Al–4V, and its protection behavior against NaCl-induced corrosion was investigated at 700 °C for 500 h by the means of thermogravimetry, SEM, EMPA, XRD and TEM. The bare Ti–6Al–4V alloy suffered severe corrosion as the thickness of corrosion production layer exceeded 2 mm after 500 h. The major corrosion production was TiO2, and sodium titanates was observed within 100 h while disappeared after long-term tests. Accordingly, a novel model for NaCl-induced corrosion of Ti alloys at high temperatures was proposed. That is, the porosity of the corrosion product is strongly correlated with the reaction between water vapor in air and sodium titanates at high temperatures. The coating exhibited excellent protection as the corroded substrate layer, which is Ti5Si3 resulted from coating-substrate reaction, is ∼6.6 μm only, and no oxide scale was formed. Dissolution of Na in the coating was identified and is believed to be associated with the protective mechanism of the potassium silicate coating, i.e. this dissolution avoids chlorination-oxidation of Ti alloy.

Fretting fatigue damage mechanism of Ti6Al4V dovetail joint specimens at high temperature treated with salt layer

Salt layer preparation on the contact surface of Ti6Al4V dovetail joint specimens using solid NaCl and Na2SO4 deposition, the effect of hot salt layer on fretting fatigue properties of Ti6Al4V alloy at high temperature was studied. The maximum stress load and temperature are 10 kN and 500 °C, respectively. The results show that the average fatigue life of the base metal dovetail joint sample (BM sample) is 9.93×104, and the average fatigue life of the hot salt dovetail joint sample (HS sample) is increased to 69.9×104. The increase in fatigue life stems from the fact that the hot salt layer promotes the generation of thicker loose oxides on the surface of the Ti6Al4V alloy, besides, the lubricating effect of the oxide with higher hardness and the wear debris alleviates the fretting damage between the dovetail joint sample and the contact surface of the fretting pad. Fracture analysis shows that the hot salt layer does not change the crack initiation mechanism, and all of them show single crack source propagation and ductile fracture mechanism. Analysis of crack formation zone by electron back-scattered diffraction (EBSD), it is found that the presence of less dislocation distribution in the HS sample relative to the BM sample. The dislocations are more concentrated on the crack propagation paths and the fretting fatigue contact surfaces. This indicates that the BM sample produced more significant plastic deformation in the crack formation zone, accelerating crack initiation. The contact surface plastic deformation of the HS sample is small and the fretting fatigue life is enhanced.

Corrosion behavior of Ti powder enhanced potassium silicate coating with solid NaCl deposit in wet oxygen at 500 °C

The potassium silicate coatings modified with various contents of Ti powders were prepared on the surfaces of Ti-6Al-4V alloy. The corrosion tests of NaCl coated specimens were conducted in wet oxygen at 500 °C for 50 h. The corrosion depth of the bare Ti-6Al-4V alloy was deeper than 60 μm while the mass gain reached to about 1.9 mg/cm2. All the coatings exhibited excellent protection against corrosion as corrosion products have been hardly detected. The main roles of the Ti powders in the coatings are believed to be prohibiting formation of micro-pores and oxygen permeation through the coatings.

Drying system via solar energy and heat accumulator for almond's cocoa

The traditional method of drying cocoa almonds occurs through barges: wooden or masonry structures where almonds are placed and drying takes place by direct solar incidence. During the night period or in instances of low solar incidence, burning fuels are employed to produce heat for the drying process. Nevertheless, this burning generates residues that contaminate the almonds, reducing their commercial value and their acceptance in the market. The objective of this work was to develop a system that captures solar energy through a series of semi-cylindrical mirrors and transfers the heat to an accumulator tank containing solid NaCl. The accumulated thermal energy is used to heat airflow during the night period, which will conduct a uniform drying and clean of the cocoa almonds. The simulations of the system were performed using COMSOL Multiphysics ® software and showed that for the average solar incidence of Ilhéus-BA. Six semi-cylindrical mirrors of 0.30 m in diameter and 1.00 m in length are required, sequentially arranged, to heat and maintain the temperature around 50°C during the daytime, demonstrating that this system can adequately provide the necessary thermal energy for almond drying within the ideal temperature range.

Supersonic nozzle performance prediction considering the homogeneous-heterogeneous coupling spontaneous non-equilibrium condensation

Supersonic nozzles are widely applied in steam turbines and other industrial fields. Condensation occurs due to rapid expansion of steam flowing through a sonic nozzle. The process is affected by the presence of steam impurities. The primary purpose of this study is to investigate the impact of different heterogeneous particles (solid particles, tiny droplets and NaCl particles) at different concentrations on the non-equilibrium condensing flow, and to classify and calculate condensation losses and total static isentropic efficiency resulting from the non-equilibrium condensation phenomenon. First, the proposed non-equilibrium condensation model is estimated numerically using the Barschdorff nozzle, and the model accuracy is validated by comparing the results with existing experimental data. Second, the effect of different particle concentrations on several condensing flows is studied using the Barschdorff nozzle. The results show that homogeneous condensation will get weaker with an increase in the particle concentration in the vapour condensing flow with solid particles and NaCl particles. Moreover, homogeneous condensation will be slightly enhanced first and then weakened with an increase in the particle concentration in the vapour condensing flow with tiny droplets. The steam condensing flow with different heterogeneous particles at the same particle concentration and the process of pure steam condensation are analysed. The results show that impurity particles in steam have a significant impeding effect on the process of homogeneous condensation. The losses are classified in the Barschdorff nozzle, and the magnitude of the losses and the flow total static isentropic efficiency are estimated. As the particle concentration increases from 1014[1/kg] to 1015[1/kg], the total static isentropic efficiency of solid particles and tiny droplets increases by 12.8 % and 9.6 %, respectively, while the total static isentropic efficiency of NaCl particles decreases by 27.2 %. This indicates that an appropriate increase in the particle concentration can effectively reduce condensation losses and improve total static isentropic efficiency. The paper describes the effect of heterogeneous particles on the steam condensing flow, providing a reference for future research on heterogeneous condensation processes.

Effects of solid NaCl and water vapour on hot corrosion behaviour of Inconel 718 superalloy and its aluminide coating

The corrosion behaviour of Inconel 718 alloy and its aluminide coating was studied at 750 °C in air + NaCl, and air + NaCl + water vapour environments. The results indicate that the substrate shows poor corrosion resistance in both corrosive environments, with less protective NiO and Fe2O3 as main corrosion products. In contrast, the aluminide coating greatly improves the corrosion resistance of the substrate, with α-Al2O3 forming on the coating surface during corrosion. Besides, in air + NaCl + water vapour environment, the corrosion attack suffered by the aluminide coating is mitigated than that in air + NaCl environment.

Effect of NaCl-rich environment on internal corrosion for Ti60 alloy at 600 °C

The morphologies and compositions of internal oxides on Ti60 alloy after corrosion under solid NaCl in H2O+O2 at 600 °C have been studied by TEM. The results show that microstructure has an effect on the internal corrosion process. The partial pressure of Cl2 was found to be higher inside the β strip and at the β phase/α platelet boundary, which promotes the corrosion process in αs grains located inside the β strip. Our results confirm that the internal oxides do not originate from the oxidation of chlorides. Titanium depletion caused by the Cl attack promotes oxidation of the matrix.

AI-based analysis of in-line process endoscope images for real-time particle size measurement in a continuous pharmaceutical milling process

This paper presents a case study on the first in-line application of AI-based image analysis for real-time pharmaceutical particle size measurement in a continuous milling process. An AI-based imaging system, which utilises a rigid endoscope, was tested for the real-time particle size measurement of solid NaCl powder used as a model API in the range of 200–1000 µm. After creating a dataset containing annotated images of NaCl particles, it was used to train an AI model for detecting particles and measuring their size. The developed system could analyse overlapping particles without dispersing air, thus broadening its applicability. The performance of the system was evaluated by measuring pre-sifted NaCl samples with the imaging tool, after which it was installed into a continuous mill for in-line particle size measurement of a milling process. By analysing ∼100 particles/s, the system was able to accurately measure the particle size of sifted NaCl samples and detect particle size reduction when applied in the milling process. The Dv50 values and PSDs measured real-time with the AI-based system correlated well with the reference laser diffraction measurements (<6% mean absolute difference over the measured samples). The AI-based imaging system shows great potential for in-line particle size analysis, which, in line with the latest pharmaceutical QC trends, can provide valuable information for process development and control.

Effect of oxygen doping on the corrosion behavior of nanocrystalline coating under the synergy of solid NaCl deposit and water vapor

Nanocrystalline coating with the same chemical composition as the nickel-based superalloys was proved to possess high resistance to oxidation and scale spallation, meanwhile avoid notable elements interdiffusion. It opens up a new direction for the development of protective coatings. However, in a worse environment containing chlorine and water vapor, the ultrafine grains act like a double-edged sword, which can promote the formation of a protective scale of Al2O3 or Cr2O3, but also favor the inward diffusion of Cl and H2O to accelerate corrosion. In order to solve this problem, moderate amount of oxygen was doped into nanocrystalline coating during magnetron sputtering. Then, corrosion behavior of the two nanocrystalline coatings with or without oxygen doping was studied in the O2 + 38% H2O environment with solid NaCl deposit. Results indicated that the doped oxygen can attract active elements of Ti and Al to form TiO2 and θ-Al2O3, which pinned at grain boundaries to keep the ultrafine grains stable at high temperature while prevent inward diffusion of the corrosive media. Accordingly, a dense and pure chromia scale was formed quickly at surface, ensuring that the oxygen-doped nanocrystalline coating provided the highest corrosion resistance under the synergy of solid NaCl deposit and water vapor. In contrast, the coating without oxygen doping suffered from severe internal corrosion.

Refreshing the liquid-gas reaction interface to provoke the zincothermic reduction of SiCl4 to prepare lithium-storage nano silicon

Many heterogeneous reduction reactions are hampered by the generated intermediate products located at the interface of reactants, resulting in reducing the reaction area or slowing down the mass transfer and thereby shutting off or slowing down the reaction. Thus, removing the unwanted intermediate products from the reaction interface is key to enabling a rapid and sufficient reduction rate and rationally mediating the product sizes and structures. Herein, we employ solid NaCl to absorb the intermediate molten ZnCl2 generated at the liquid Zn-SiCl4 gas interface, making the reaction happen continuously and sufficiently at a relatively low temperature of below 450 °C. In addition to refreshing the reaction interface, NaCl acts as a buffer to absorb the reaction heat, ensuring the production of hollow Si inherited from the spherical liquid Zn template. As a result, the yield of Si reaches over 95% within 2 h and the Si particle size is below 200 nm. Further, the obtained Si anode has an initial Coulombic efficiency of 86.7% and delivers a capacity of 1580 mAh g−1 at 3 A g−1 after 350 cycles with a capacity retention of 90.6%. Overall, this paper provides an effective strategy for engineering the reaction interface and revalorizing waste SiCl4 for making Li-storage Si anodes.

Feasibility of using quantitative 1H-NMR spectroscopy and ultra-microbalances for investigation of a PET microplastic reference material

Here, we report on the feasibility of using quantitative NMR and ultra-microbalances for additional measurements of the mass of poly-ethylene terephthalate (PET) particles in a reference material (RM). The microplastic (MP) PET particles were immobilised in solid NaCl following freeze-drying of a 1-ml NaCl suspension. The particles ranged from 30 to about 200 µm (Feretmin). In a 3-day process, more than 500 such units of PET particles in the NaCl carrier were prepared and later used in a large-scale inter-laboratory comparison. The homogeneity of PET in the salt carrier over these 500 units had previously been evaluated with respect to the mass of PET using an ultra-microbalance. In addition to the original results obtained by weighing, two independent results of quantitative 1H-NMR have been obtained for further investigation of this reference material together with one additional set of weighing data. The NMR data were used for confirmation of the weighed amount of PET (as weighing is non-specific for PET). Average masses of 0.293 ± 0.04 mg and 0.286 ± 0.03 mg of PET were obtained using two different ultra-microbalances (14% RSD for n = 14 and 9% RSD for n = 4, respectively). The corresponding 1H-NMR data was 0.300 ± 0.02 mg of PET (6.7% RSD for n = 5) and 0.345 ± 0.04 mg of PET (12.5% RSD for n = 14), respectively. The average mass of PET obtained by 1H-NMR measurements was in agreement with the weighed amounts within their standard deviations. A mean value of 0.306 mg PET with an expanded uncertainty of 0.058 mg (± 19% relative) was calculated, and it is traceable to the SI system of measurements. Measurement of PET by quantitative 1H-NMR spectroscopy is also reported for a water sample. The PET contained in one RM sample was transferred to 1 L of water to mimic a drinking water sample for microplastics.Graphical abstract

Effects of solid NaCl deposit and water vapor on corrosion resistance of K452 superalloy and aluminized coating

Aluminized coating was prepared on K452 superalloy by chemical vapor deposition (CVD) technique. The oxidation/corrosion behavior of alloy and coating were investigated at 750 ℃ in air, air with solid NaCl deposit and moist air with solid NaCl deposit, respectively. The microstructure and composition of samples were characterized by SEM/EDS and XRD techniques. The results demonstrated that aluminized coating exhibited better oxidation/corrosion resistance than K452 alloy in the three environments above. And the main oxidation and corrosion products of alloy were Cr2O3 and NiO, respectively. This indicated that Ni participated in the corrosion process due to the depletion of Cr during accelerated corrosion. Therefore, the established corrosion scale was non-protective, which could not protect underlying alloy from accelerated corrosion. Contrarily, the main oxidation and corrosion products of coating were protective Al2O3, which acted as a barrier to separate coating from NaCl and oxygen, interrupting the self-sustainable accelerated corrosion. Additionally, the presence of water vapor was beneficial in reducing the spallation of corrosion products within a short time. The mechanisms of K452 alloy and aluminized coating in the three environments above were discussed in detail.

Effect of the ultrasonic surface rolling process and plasma electrolytic oxidation on the hot salt corrosion fatigue behavior of TC11 alloy

The effects of the ultrasonic surface rolling process (USRP), plasma electrolytic oxidation (PEO), and their combined treatment (USRP + PEO) on the hot salt corrosion fatigue (HSCF) behavior of TC11 alloy are comparatively studied. The mechanism of improving the HSCF performance of TC11 alloy through the above surface strengthening techniques is revealed by analyzing the surface integrity and microstructure of the modified layer. The results show that the TC11 alloy exhibits high HSCF sensitivity, and fatigue limit reduces by 27.78 % under the condition of 0.1 mg/cm2 solid NaCl deposition at 500 °C compared to the sample without salt deposition. The mechanism of HSCF is that corrosion pits promote the initiation of fatigue cracks by causing local stress concentration on the sample’s surface. Meanwhile, hydrogen and hydride generated by hot salt corrosion also promote fatigue crack propagation. Compared with the base material (BM) sample under the condition of 0.1 mg/cm2 NaCl deposition, the HSCF limit increases by 10.26 % by USRP treatment. This is due to the combination of an increase in dislocation density, a decrease of β-phase content, and the introduction of compressive residual stress (CRS), improving the high-temperature fatigue resistance, corrosion resistance, and hydrogen damage resistance of TC11 alloy. PEO treatment increases HSCF resistance of TC11 alloy, and the HSCF limit increases by 47.44 % compared with the BM sample. This is mainly because the dense barrier layer (DBL) could effectively inhibit erosion by the chloride medium and inhibit hydrogen damage, which significantly improve the crack initiation resistance. The HSCF limit of the TC11 alloy further increases by 64.10 % by the USRP + PEO treatment, and the effect of improving the HSCF resistance is better than that of USRP or PEO treatment alone. This is attributed to the fact that USRP pretreatment increases the alloy’s erosion resistance to a corrosive medium by increasing the thickness of the DBL. Meanwhile, the synergistic effect of stable CRS and gradient nanostructure introduced by USRP significantly increases the crack initiation and propagation resistance of HSCF for TC11 alloys.

Feasibility of volumetric expansion of molten chlorides by conventional pushrod dilatometry

This study is a short communication on progress made in the adaptation of conventional push-rod dilatometry for the measurement of volumetric expansion of liquid salts up to 1300 K. A new crucible design is offered as a practical solution for measurement of liquid salts by this method. Proof-of-concept measurements of the volumetric expansion of sodium chloride (NaCl) are compared to the available data in literature. Measurement of the coefficient of thermal expansion (CTE) of solid NaCl compared favorably to the available data in literature, confirming both magnitude and trend. The average CTE of NaCl (solid) was overline{alpha }_{{{text{NaCl}};{text{Solid}}}} = 5.63 cdot 10^{ - 5} {raise0.7exhbox{1} !mathord{left/ {vphantom {1 K}}right.kern-nulldelimiterspace} !lower0.7exhbox{K}}. The volumetric expansion of liquid NaCl was measured as beta_{{{text{NaCl}};{text{Liquid}}}} approx 3.96 cdot 10^{ - 5} 1/K and is essentially constant from the melt point to 1300 K. The volumetric expansion produced by this method is in reasonable agreement with the available published data and previous measurements made by the authors by neutron radiographic technique.

Corrosion behavior of Ti60 alloy under continuous NaCl solution spraying at 600 °C

• The corrosion rate of Ti60 alloy in NaCL spray is lower than that under NaCL film. • A mixed corrosion including classical oxidation and active oxidation happened. • The mixed corrosion delayed active oxidation and formed dense Ti oxides scale, both of which decreased corrosion rate. The corrosion behavior of Ti60 alloy was investigated under continuous NaCl solution spraying at 600 °C. Results indicate that the corrosion rate of the Ti60 alloy is lower than that obtained with the solid NaCl deposit film in H 2 O + O 2 . The outer corrosion products are compact layers mainly containing Na 2 TiO 3 and nanocrystalline TiO 2 . The inner layer is mainly composed of Ti 2 O, TiO and SnO 2 . Ti 2 O has a lamellar structure, and TiO has a strip-shaped structure. A mixed corrosion mechanism including classic oxidation and active oxidation occurred under NaCl solution spraying environment: the first stage was controlled by the classic oxidation mechanism with the promotion by the active oxidation following parabolic curves, and the second stage was controlled by the active oxidation mechanism following a linear rise in the mass gain curve. The mixed corrosion mechanism between classic oxidation and active oxidation produced a relatively dense Ti oxides scale, which decreased the corrosion rate.