Salt Crystals Research Articles

Modelling the flux decline induced by gypsum scaling in direct contact membrane distillation

Scaling has been a major technical challenge in the membrane distillation (MD) process, hindering the broader application of MD processes. Despite the increasing number of studies on MD scaling, there are limited prediction tools to describe the scaling process and help make informed decisions about the experimental conditions to prevent scaling and its irreversible damage. In this paper, a semi-analytical model was developed based on the classical nucleation theory and crystal growth to model the membrane area reduction caused by the deposition of inorganic salt crystals on the membrane surface, which is equivalent to the decrease in permeate flux resulting from scaling. The model was developed using calcium sulphate, a model scalant. The model was validated and verified with available literature data, and it has been proved that the model has the capability to produce reasonable predictions on the onset of flux decline and the declining rate with respect to the experimental data with the coefficient of determination (R2) ranging from 0.74 to 0.96. The sensitivity analysis was applied on the model, which revealed that flux decline would happen earlier in the case of higher feed temperature, higher feed velocity, and higher initial feed concentration.

Analysis of Surface Damage on the Mural Painting in Josadang Shrine of Buseoksa Temple in Yeongju Using Reflectance Transformation Imaging Technology

In this study, we examined the effectiveness of RTI(Reflectance Transformation Imaging) method as a digital imaging technology that can accurately and three-dimensionally record the damaged state of mural heritage. For this purpose, major damage types were classified on the mural painting in Josadang shrine of Buseoksa temple in Yeongju, and an RTI was conducted on areas with highly damaged areas. According to the results by the type of damage to the murals, salt weathering damage (58.9-18.2%), painting layer damage (37.9-13.0%), past reinforcement area (9.8-4.2%), biological damage and other contamination (19.8-2.5%), exposed damage to the finishing layer (19.7∼0.7%), past fixative area (2.5∼0.0%), and cracks (0.5∼0.3%) were found to have a high share of damaged area. From the RTI investigation for each damage type, image data was constructed to visually identify the degree of damage. In particular, in the case of microscope-based RTI, it was confirmed that it can be used as an accurate recording technology because it can identify color layer exfoliation, pigment particle shape, and salt crystal shape that are difficult to see in general microscope images. This is a research method that has not been attempted in existing RTI or mural research, and is expected to be applicable in the future not only to murals but also to the field of cultural heritage with painting layers.

Study of direct drinking water production and sea salt recovery from photothermal conversion based on MWCNTs

The use of solar desalination is expected to solve the problem of water scarcity. Based on this, MWCNTs were loaded on filter paper and assembled into a MWCNTs disc evaporator using cotton threads as water channels in this paper. MCED with different loadings were prepared, and the photothermal conversion performance of MCED was evaluated through experiments. The results showed that the evaporation rate of 0.7-MCED at one solar intensity could reach 1.3134 kg/m2 h; the efficiency of solar separation of vapor and salt was 77.63 %. Meanwhile, after a 7-day evaporation cycle of 0.3-MCED, salt crystallizes at the edge of MCED under light and is recovered by gravity shedding during darkness, and the freshwater collection rate and salt recovery rate are 0.82 kg m−2 h−1 and 38.24 g m−2 h−1, realizing efficient and continuous water collection and salt recovery. In addition, MCED can generate voltage through water evaporation. This work demonstrates a solar evaporator that can be used for continuous seawater desalination as well as salt recovery and power generation, and provides a new direction for the design of photothermal modulation of MWCNTs and solving the salt crystallization problem for solar desalination.

Plant-growth promotion by halotolerant black yeast Hortaea sp. strain PMGTC8 associated with salt crystals from solar saltern of Goa, India.

Plant-growth-promoting microbes are sustainable alternative to improve the soil fertility and plant-growth facilitating the nutrients uptake in normal and stressed environmental conditions. Among these, halotolerant and halophilic microorganisms with plant- growth-promoting ability are better candidates that could be exploited as bioinoculants in salinity affected agriculture soils. Considering this, the current study aimed to isolate, characterize and determine the plant-growth-promoting potential of the culturable halotolerant black yeast associated with salt crystals from the solar saltern of Goa, India. The results revealed 1.3 × 104CFU/g of viable number of colonies on 25% NaCl Tryptone Yeast Extract (NTYE) agar after 30-45days incubation. Among ten morphologically distinct isolates, a black pigmented strain PMGTC8 was characterized as yeast-like and appeared two celled with average size of 4.30 ± 0.14µm under scanning electron micrograph. Based on phylogenetic analysis using internal transcribed spacer (ITS) marker, the isolate showed maximum similarity to genus Hortaea. Interestingly, Hortaea sp. strain PMGTC8 (OR527117) exhibited plant-growth-promoting characteristics and caused significantly (p < 0.01) higher germination rate (93.33%), vigor index (964.22), shoot (3.95cm) and root length (6.38cm), and fresh weight (0.039g) of Oryza sativa var. Korgut. This halotolerant black yeast may play a role in nutrition of the plants growing in saline soils. Conclusively, the current findings report for the first time the plant-growth-promoting potential of Hortaea sp. strain PMGTC8 associated with salt crystals of solar saltern, Goa, India for its possible use as bio-fertilizers in saline agriculture soils.

Impact of secondary ice in a frozen NaCl freeze-concentrated solution on the extent of methylene blue aggregation

Freezing and lyophilization have been utilized for decades to stabilize pharmaceutical and food products. Freezing a solution that contains dissolved salt and/or organic matter produces pure primary ice crystal grains separated by freeze-concentrated solutions (FCS). The microscopic size of the primary ice crystals depends on the cooling conditions and the concentration of the solutes. It is generally accepted that primary ice crystals size influences the rate of sublimation and also can impact physico-chemical behaviour of the species in the FCS. This article, however, presents a case where the secondary ice formed inside the FCS plays a critical role. We microscoped the structures of ice-cast FCS with an environmental scanning electron microscope and applied the aggregation-sensitive spectroscopic probe methylene blue to determine how the microstructure affects the molecular arrangement. We show that slow cooling at −50 °C produces large salt crystals with a small specific surface, resulting in a high degree of molecular aggregation within the FCS. In contrast, fast liquid nitrogen cooling yields an ultrafine structure of salt crystals having a large specific surface area and, therefore, inducing smaller aggregation. The study highlights a critical role of secondary ice in solute aggregation and introduces methylene blue as a molecular probe to investigate freezing behaviour of aqueous systems with crystalline solute.

Thermodynamic modeling of calcium or magnesium chloride, chlorate, and perchlorate ternary mixtures deliquescence at Mars-relevant temperatures

The definition of habitability on Mars is intimately linked to the stability of liquid water on the surface or near sub-surface. Brines provide the best pathway to stabilize liquid water, and form through deliquescence where a solid salt crystal transitions into an aqueous solution when exposed to a humid atmosphere. In a typical brine controlled by temperature and water relative humidity, ternary mixtures represent the best potential liquid brines. Here we modeled the deliquescence relative humidity (DRH) and the eutonic relative humidity (RH) of ternary salt mixtures. Chloride, chlorate, and perchlorate were modeled with either calcium or magnesium as the cation at temperatures ranging from 223 to 273 K. For the calcium ternary mixtures, the main salt composition precipitating at the DRH was dominated by calcium chloride, and by magnesium perchlorate in the magnesium ternary system. The hydration state of the precipitating salts systematically increased as temperature decreased. The eutonic RH for the calcium mixtures ranged from 14.24% at 273 K and increased to 43.54% by the coldest temperature of 223 K. The eutonic RH for the magnesium mixtures was significantly higher than the calcium counterpart, at 49.76% at 273 K and increased to 53.09% by 223 K. Calcium perchlorate was the predominate eutonic precipitate for the calcium mixtures, and magnesium chlorate for the magnesium mixtures., This study shows that ternary mixtures bring a slight improvement to the stability of brines on Mars compared to single salts or binary mixtures.

Ordinary light induced polarization zones in Tutton salt crystal

Ordinary light wave passing through a low symmetry crystal along an off optic -axis direction gets split into ordinary and extra-ordinary waves. If the beam size is large, the two polarized waves could overlap covering a large volume within the medium. It is realized that overlapping ordinary and extra-ordinary waves, result in creation of alternate polarization regions with different fluctuating crystalline fields inside a low - symmetry hydrated crystal. If suitable ions are doped in an experimental crystal, their optical absorption spectra could reflect the effect of alternate polarization fields and creation of ordinary light induced periodic polarization (OLIPP) effect inside a low symmetry hydrated crystal.

Experimental study on particle deposition of Fe3O4 in supercritical heat exchange tube

Particle deposition poses a significant challenge to the economics and safety of supercritical boilers. Understanding the deposition behavior of particles on the steam-water side wall is essential. A supercritical particle deposition system was designed and build according to the actual conditions. The effects of fluid thermal state, flow rate and exposure time on particle morphology, deposition layer morphology and deposition distribution were investigated. The results showed that FeCl2 was oxidized to micron sized Fe3O4 particle, and the salt crystals had a redissolution behavior in supercritical water. The particle deposition layer was a three-layer structure, possibly related to the gas-like fluid clusters and turbulence. The deposition distribution was related to the flow state, and there was a forward shift of the peak point with exposure time. Our results help to understand the particle deposition behavior in supercritical heat exchangers.

Cellulose Isolation and Characterization of Green Seaweed C. Lentillifera from Halmahera, Indonesia

Caulerpa lentillifera or known as sea grapes is a type of green seaweed which is rich of nutritional components and widespread in the tropical regions in Asia, including Indonesia. Moreover, C. lentillifera contains of polysaccharides, such as cellulose which has the potential to various applications. In this study, C. lentillifera collected from Halmahera, Indonesia was determined for its chemical compositions (moisture, ash, extractives, hemicellulose, α-cellulose contents) and was extracted to obtain cellulose. Isolation of cellulose from C. lentillifera was done by soxhlet extracted using ethanol-benzene solvent to remove extractives, boiling to increase the amount of cellulose extracted, H2O2 bleaching to eliminate any remaining pigments and other contaminants, and freeze drying to get coarse powder of cellulose. The moisture content, ash, extractives, hemicellulose, α-cellulose of C. lentillifera were 11.94%, 31.62%, 11.53%, 35.57%, and 7.95%, respectively. The yield of cellulose obtained was 31.13% based on seaweed dry weight. FE-SEM (Field Emission-Scanning Electron Microscopy) analysis of C. lentillifera showed colonies of diatoms in elliptical shapes. FTIR (Fourier Transform Infrared) measurements indicating cellulose purity after extraction process. X-Ray Diffraction (XRD) analysis resulted some peaks of salt crystals in C. lentillifera and cellulose of C. lentillifera in amorphous form. After extraction, the crystallinity index of cellulose obtained was 37.3%.

The influence of weathering processes on microtopographic changes of sandstone under simulated upper intertidal conditions from hourly to weekly scales

Micro-scale surface changes of bedrock on shore platform have been monitored with micro-erosion meters (MEMs) and show significant downwearing over several (≥2) years. At short-term temporal scale of hours to days, rock surface behaviors are reversible and do not generate net surface lowering. Therefore, there is a temporal gap between the two temporal scales of surface behaviors over which grain detachment must occur. In this study, an upper intertidal zone (2-h immersion with subsequent 2-week exposure) was simulated in the laboratory to investigate the fast erosion rate at high elevation identified from the Otway coast in south-eastern Australia using MEMs.During the experiments, the microtopography of rock surface was monitored 2-hourly during the daytime period (0−12 h) on Day 1 (beginning), 8 (middle) and 14 (end) of the 14-day simulation to understand the cumulative effect of short-term surface changes on rock weathering and erosion at longer timescales in order to provide insights into the role of rock surface dynamics in shore platform evolution. Through manipulation of the salt content of water as well as temperature and humidity in the controlled measures, the experiment was also designed to test the primary weathering process in driving short-term surface changes at this particular tide level. Results show the primary role of temperature-induced salt crystal volume change in generating the short-term rock surface movements on high tidal to supratidal rock. Although the cumulative effect of short-term surface behaviors on rock microtopography appeared to be observed over longer timescales, it still remains uncertain if this drives rock decay at the weekly scale. Future studies are required to monitor the rock surface over a sufficiently long period (up to months) to determine the temporal threshold of erosion and understand the linkage between short-term surface changes and rock decay.

A Simple Laser-Induced Breakdown Spectroscopy Method for Quantification and Classification of Edible Sea Salts Assisted by Surface-Hydrophilicity-Enhanced Silicon Wafer Substrates.

Salt, one of the most commonly consumed food additives worldwide, is produced in many countries. The chemical composition of edible salts is essential information for quality assessment and origin distinction. In this work, a simple laser-induced breakdown spectroscopy instrument was assembled with a diode-pumped solid-state laser and a miniature spectrometer. Its performances in analyzing Mg and Ca in six popular edible sea salts consumed in South Korea and classification of the products were investigated. Each salt was dissolved in water and a tiny amount of the solution was dropped and dried on the hydrophilicity-enhanced silicon wafer substrate, providing homogeneous distribution of salt crystals. Strong Mg II and Ca II emissions were chosen for both quantification and classification. Calibration curves could be constructed with limits-of-detection of 87 mg/kg for Mg and 45 mg/kg for Ca. Also, the Mg II and Ca II emission peak intensities were used in a k-nearest neighbors model providing 98.6% classification accuracy. In both quantification and classification, intensity normalization using a Na I emission line as a reference signal was effective. A concept of interclass distance was introduced, and the increase in the classification accuracy due to the intensity normalization was rationalized based on it. Our methodology will be useful for analyzing major mineral nutrients in various food materials in liquid phase or soluble in water, including salts.

Interacting density fronts in saturated brines cooled from above

When a saturated brine layer is cooled from above, both a convective temperature front as well as a front of sedimenting salt crystals can form. We employ direct numerical simulations to investigate the evolution and interaction of these two density fronts. Depending on the ratio of the temperature front velocity and the crystal settling velocity, which is governed by a dimensionless parameter in the form of a Rayleigh number, we find that either two separate fronts exist for all times, two initially separate fronts combine into a single front after some time or a single front exists at all times. We furthermore propose approximate scaling laws for the propagation of the thermal and crystal fronts in each regime and compare them with the simulation data, with generally good agreement.

Structural Phase Transitions in the Double Salts (NH4)2PO3F·NH4NO3 and (NH4)2XO4·3NH4NO3 (X = Se, Cr)

In the context of investigating isostructural relationships between sulfates and monofluorophosphates, crystals of the double salts (NH4)2PO3F·NH4NO3 (AFP·AN) and (NH4)2XO4·3NH4NO3 (AX·3AN; X = Se, Cr) were grown from aqueous solutions and structurally characterized using X-ray diffraction and thermal analysis. Whereas the high-temperature forms of the two AX·3AN double salts are in fact isostructural with the sulfate analogue, AFP·AN crystallizes with a reduced amount of NH4NO3 and thus has a unique crystal structure. Both AFP·AN and the two AX·3AN compounds exhibit reversible structural phase transitions. Upon cooling, the monofluorophosphate double salt transforms from the monoclinic room-temperature polymorph (I; P21/n, Z = 4) to the intermediate triclinic polymorph (II; P1, Z = 4) that in turn transforms to the monoclinic low-temperature polymorph (III; P21/n, Z = 4). The two phase transitions (I) → (II) and (II) → (III) are characterized by a significant increase of the unit cell volumes upon cooling. The two AX·3AN double salts transform upon cooling from a disordered monoclinic crystal structure (P21, Z = 2) to a monoclinic polymorph with a doubled unit cell (P21/c, Z = 4). Such a phase transition is not observed for the sulfate analogue. All molecular moieties are fully ordered at −93 °C for the selenate double salt, whereas one of the nitrate anions remains disordered for the chromate double salt even at −173 °C. In all AFP·AN and AX·3AN crystal structures, the nitrate anions play a crucial role during the phase transitions, and an extensive network of N–H···O hydrogen-bonding interactions is responsible for the cohesion of the crystal.

Formation-water evaporation and salt precipitation mechanism in porous media under movable water conditions in underground gas storage

Underground gas storage (UGS) plays an important role in large-scale energy (natural gas) storage, while salt deposition may affect the storage and production capacity of UGS. However, salt precipitation mechanism of UGS under movable water conditions is not clear. This work aims at understanding salt precipitation on rock properties of an UGS in porous media under movable water conditions. Firstly, core flooding experiments are performed to establish the relationship between dynamic petrophysical properties and the amount of salt crystals. The dynamic process of salt precipitation at the pore-scale is further captured by microscopic visualization experiments, and the location and morphology of salt crystals at micro-scale are also observed using scan electron microscope (SEM). Results indicate that formation-water evaporation and salt precipitation improve the formation properties when the amount of deposited salt is less than 39 mg/g. After the amount of deposited salt is more than 48 mg/g, formation porosity and permeability can be reduced. The size of salt crystals under movable water (>40 μm) is much larger than that under irreducible water conditions (1 μm–5 μm). This work offers a methodology for analyzing the effect of salt precipitation on the UGS in porous media under movable water conditions.

Harvesting of aerial humidity with natural hygroscopic salt excretions.

Plants and animals that thrive in arid regions utilize the diurnal changes in environmental temperature and humidity to optimize their water budget by combining water-harvesting mechanisms and morphophysiological traits. The Athel tamarisk (Tamarix aphylla) is a halophytic desert shrub that survives in arid, hypersaline conditions by excreting concentrated solutions of ions as droplets on its surface that crystallize into salt crystals and fall off the branches. Here, we describe the crystallization on the surface of the plant and explore the effects of external conditions such as diurnal changes in humidity and temperature. The salt mixtures contain at least ten common minerals, with NaCl and CaSO4·2H2O being the major products, SiO2 and CaCO3 main sand contaminants, and Li2SO4, CaSO4, KCl, K2Ca(SO4)2·H2O, CaMg(CO3)2 and AlNaSi3O8 present in smaller amounts. In natural conditions, the hanging or sitting droplets remain firmly attached to the surface, with an average adhesion force of 275 ± 3.5 µN measured for pure water. Rather than using morphological features of the surface, the droplets adhere by chemical interactions, predominantly by hydrogen bonding. Increasing ion concentration slightly increases the contact angle on the hydrophobic cuticle, thereby lowering surface wettability. Small amounts of lithium sulfate and possibly other hygroscopic salts result in strong hygroscopicity and propensity for deliquescence of the salt mixture overnight. Within a broader context, this natural mechanism for humidity harvesting that uses environmentally benign salts as moisture adsorbents could provide a bioinspired approach that complements the currently available water collection or cloud-seeding technologies.

Metal casting into NaCl molds fabricated by material extrusion 3D printing

Aluminum die casting is a well-established industrial process for mass producing aluminum parts with complex shapes, but design restrictions exclude some features like undercuts and hollow structures from being produced with this method. Water-soluble casting molds offer a promising solution to overcome those restrains, for example by hot pressing of salt cores or 3D printing of NaCl molds. Presently, 3D printing techniques available for NaCl are limited to direct ink writing (DIW) and photopolymerization. This study presents an approach to prepare NaCl parts by thermoplastic material extrusion (MEX) 3D printing. Firstly, a 3D printable feedstock is developed consisting of an organic binder, which is usually used for ceramic injection molding, and sodium chloride (NaCl) salt crystals. Various molds are then printed on a granulate-fed MEX printer. After thermal debinding and sintering at 690 °C, the 3D printed parts consist of pure NaCl. Furthermore, the same NaCl feedstock is used for injection molding. The bending strength of 3D printed samples with and without post-treatment are measured and compared to injection molded test specimens. Finally, metal casting in 3D printed NaCl molds is shown with tin or aluminum and the metal demonstrator parts with complex geometries such as gyroid structures and turbine wheels are released by dissolving the NaCl molds in water.

Design of High-Performance Organic Nonlinear Optical and Terahertz Crystals by Controlling the van der Waals Volume.

In the development of new organic crystals for nonlinear optical and terahertz (THz) applications, it is very challenging to achieve the essentially required non-centrosymmetric molecular arrangement. Moreover, the resulting crystal structure is mostly unpredictable due to highly dipolar molecular components with complex functional substituents. In this work, new organic salt crystals with top-level macroscopic optical nonlinearity by controlling the van der Waals volume (VvdW ), rather than by trial and error, are logically designed. When the VvdW of molecular ionic components varies, the corresponding crystal symmetry shows an observable trend: change from centrosymmetric to non-centrosymmetric and back to centrosymmetric. All non-centrosymmetric crystals exhibit an isomorphic P1 crystal structure with an excellent macroscopic second-order nonlinear optical response. Apart from the top-level macroscopic optical nonlinearity, new organic crystals introducing highly electronegative fluorinated substituents with strong secondary bonding ability show excellent performance in efficient and broadband THz wave generation, high crystal density, high thermal stability, and good bulk crystal growth ability.

Damage on asphalt surfaces caused by ionic solution erosion and salt crystallization at molecular scale

The damage mechanism of severe salt corrosion on asphalt surfaces should be revealed at molecular scale. This study utilized molecular dynamics (MD) and density functional theory (DFT) simulations to investigate damage degree and mechanism of ionic solution erosion and salt crystallization on asphalt surfaces. Various asphalt-solution and asphalt-salt interfaces models were built, while interfacial interaction, diffusion, adhesion, and electronical properties were calculated. The electrostatic interaction played a critical role both in solution-asphalt and crystal-asphalt systems, particularly between anions and asphalt. All ions adsorbed onto unaged asphalt surfaces and eroded into unaged asphalt interiors while only cations penetrated into aged asphalt due to electronical repulsions between anions and SO/CO, indicating cation erosion contributed more to salt damage during aging. Salt crystals participated and expanded on asphalt surfaces, resulting in micro-cracks and micro-voids. Sulfates adhered asphalt more than chlorides because sulfates had closer interval distance and larger free volumes with asphalt. Asphalt molecules with high polarity and more charge were more susceptible to interact by ions. The salt damage on asphalt mainly included solution perpetration and crystal adhesion. The order of salt damage of cations to asphalt is: Mg2+ > Na+ > Ca2+, and of anions is: SO42− > Cl−.

Highly Precise Laser-Induced Breakdown Spectroscopy Analysis of Major Mineral Nutrients in Edible Salts Using Miniaturized Salt Ponds and Alternating Laser-Ablation Data Sampling.

In this work, we applied a hydrophilicity-enhanced solid substrate and an alternating laser-ablation data sampling (ALADS) scheme to improve laser-induced breakdown spectroscopy (LIBS) measurement precision and demonstrated the performance in analyzing K, Mg, Ca, and S contained in commercially available edible salt products. Five edible salt products from Australia, Bolivia, France, and South Korea were dissolved in water and a tiny volume of each solution was dropped on the solid substrate, that is, a miniaturized salt pond. After being dried, the residual salt crystals distributed still inhomogeneously, but the homogeneity could be significantly improved in comparison with that from typical drop-and-dry methods. The ALADS scheme was applied to extract three precise measurements from 9798 single-shot LIBS spectra covering the entire salt pond. The measurements obtained by ALADS were found to agree well with one another regardless of the inhomogeneous distribution of salt crystals. As a result, the measurement precision was proved remarkably. Limits of detection for K, Mg, Ca, and S were estimated to be 0.64, 1.7, 14, and 530 mg/kg, respectively, which are enough to analyze those elements contained in salts typically at the level of 100 parts per million (ppm) to ∼3 wt% for the purpose of salt quality assessment.

Growing recyclable and healable piezoelectric composites in 3D printed bioinspired structure for protective wearable sensor

Bionic multifunctional structural materials that are lightweight, strong, and perceptible have shown great promise in sports, medicine, and aerospace applications. However, smart monitoring devices with integrated mechanical protection and piezoelectric induction are limited. Herein, we report a strategy to grow the recyclable and healable piezoelectric Rochelle salt crystals in 3D-printed cuttlebone-inspired structures to form a new composite for reinforcement smart monitoring devices. In addition to its remarkable mechanical and piezoelectric performance, the growth mechanisms, the recyclability, the sensitivity, and repairability of the 3D-printed Rochelle salt cuttlebone composite were studied. Furthermore, the versatility of composite has been explored and applied as smart sensor armor for football players and fall alarm knee pads, focusing on incorporated mechanical reinforcement and electrical self-sensing capabilities with data collection of the magnitude and distribution of impact forces, which offers new ideas for the design of next-generation smart monitoring electronics in sports, military, aerospace, and biomedical engineering.