Hydrate Phase Research Articles

Identifying dehydration-induced shear velocity anomaly in the Earth's core-mantle boundary.

The steep temperature gradient near the bottom of the mantle is known to generate a negative correlation between the shear wave velocity (V S ) and the depth in most regions of the D″ layer, as detected by seismological observations. However, increasing V S with depth is observed at the D″ layer beneath Central America, where the Farallon slab sinks, and the origin of this anomaly has not been well constrained. Here, we calculate the thermoelastic constants and obtain the elastic wave velocities of hydrous phase H with various Al contents and cation configurations, which may act as a water carrier to the D″ layer. We find its V S to be substantially lower than the post-perovskite-type bridgmanite. The dehydration of Al-enriched phase H and the redistribution of Al from the hydrous component to dry silicates would gradually raise the V S below the top of the D″ layer. The presence of 3.5 wt% water is sufficient to compensate for the thermal effects to match the seismic anomaly at the bottom of the mantle beneath Central America. The positive slope of V S versus depth in the D″ layer may fingerprint deep water recycling.

Enhancement of phosphogypsum’s water stability in early hydration phase as embankment fill with lime-ground granulated blast-furnace slag

Enhancement of phosphogypsum’s water stability in early hydration phase as embankment fill with lime-ground granulated blast-furnace slag

Granite Dust and Silica Fume as a Combined Filler of Reactive Powder Concrete.

By volume, cement concrete is one of the most widely used construction materials in the world. This requires a significant amount of Portland cement, and the cement industry, in turn, causes a significant amount of CO2 emissions. Therefore, the development of concrete with a reduced cement content is becoming an urgent problem for countries with a significant level of production and consumption of concrete. Therefore, the purpose of this article is to critically investigate the possibility of using inert granite dust in combination with highly active silica fume in reactive powder concrete. The main physical and mechanical properties, such as the compressive strength at different curing ages and the water absorption, were studied using mathematical planning of experiments. The consistency and microstructure of the reactive powder concrete modified with granite dust in combination with silica fume were also analyzed. Mathematical models of the main properties of this concrete are presented and analyzed, and the graphical dependencies of the influence of composition factors are constructed. A more significant factor that affects the compressive strength at all curing ages is the silica fume content, increases in which to 50 kg/m3 lead to a 25-40% increase in strength at 1 day of age, depending on the granite dust content. In turn, an increase in the amount of granite dust from 0 kg/m3 to 100 kg/m3 in the absence of silica is followed by an increase in strength of 8-10%. After 3 days of curing, the effect of granite dust becomes more significant. Increases in the 28-day strength of 25%, 46% and 56% were obtained at a content of 50 kg/m3 of silica fume and 0 kg/m3, 100 kg/m3 and 200 kg/m3 of granite dust in concrete, respectively. It is shown that the effect of inert granite dust is more significant in combination with silica fume at its maximum content in the range of variation. The pozzolanic reaction between highly active silica and Ca(OH)2 stimulates the formation of hydrate phases in the space between the grains and causes the microstructure of the cement matrix to compact. In this case, the granite dust particles act as crystallization centers.

Black oat, rye, and wheat cereals: kinetics and changes during hydrothermal processing

The grain hydration process is fundamental in cereal processing but can modify their physical and chemical properties. However, there is a gap in understanding the principles of mass transport (water) and its changes during the hydration phases, especially in rye, which has yet to be studied. A kinetic study was carried out to investigate moisture transfer and changes in starch during oats, rye, and wheat hydration. During the process it was observed that the mass transfer was directly affected by the system's temperature, which indicates changes in the absorption capacity over time. The tracer pigment indicated that water entered the grains by diffusion through the grain coating and capillarity through the fissures. Thermal analyses revealed that the starch remained unchanged at hydration temperatures below 50°C. Mathematical models describe the moisture gain in the different conditions studied, while the generalized model allows the experimental moisture to be predicted. This study contributes to understanding the time/temperature relationship in cereal hydration by presenting a kinetic model and examining changes in starch. This provides valuable insights to optimize the industrial operation of this stage and guides new project development.

Mechanism and Kinetics of Hydration of CuSO4·H2O in the Presence of an Intermediate Step.

The hydration of salt hydrates is often described as a solution mediated nucleation and growth mechanism, occurring between a reagent and a product in thermodynamic equilibrium with each other. If a system possesses more than one hydrate phase, the kinetic pathway may involve additional mechanisms due to the formation of intermediate hydrate species. We elected CuSO4 as our model system and analyzed the pathway leading from CuSO4·H2O (C1H) to CuSO4·5H2O (C5H), while CuSO4·3H2O (C3H) being a possible intermediate. We found that C1H hydration is mediated by the formation of C3H and that C5H does not nucleate directly from C1H, at the studied conditions. The hydration pathway therefore is characterized by the same mechanism occurring twice, nucleation and growth of C3H and nucleation and growth of C5H. Analysis of the hydration kinetics of C1H revealed that C5H nucleates rapidly from C3H, as if the metastability of C3H was reduced when starting from C1H. Therefore, we concluded that the hydration kinetics of C1H are probably controlled by the growth process of C5H. Despite being controlled by a single reaction process, we show that a single front 1D diffusion model is insufficient to describe the reaction kinetics at the tablet level. Understanding of these complex transformations is necessary to evaluate the suitability of these reactions for application, in particular with respect to the achieved power output.

Advances, Applications, and Perspectives of Machine Learning Approaches in Predicting Gas Hydrate Phase Equilibrium

Advances, Applications, and Perspectives of Machine Learning Approaches in Predicting Gas Hydrate Phase Equilibrium

Study on the gas composition of hydrate phase and unreacted liquid phase for hydrate-based gas separation

Hydrate-based gas separation (HBGS) method is an environment-friendly gas separation technique. At the end of the hydrate formation stage, the system usually consists of gas phase, hydrate phase and residual unreacted liquid phase. The separation efficiency of HBGS is usually determined by measuring the gas composition of gas phase before and after hydrate formation. It is currently unclear the gas composition of hydrate phase and residual unreacted liquid phase, and how they will affect the gas separation efficiency of HBGS separately. This work developed a novel method for efficiently separating the hydrate phase and the unreacted liquid phase, making it possible to directly measure the gas composition in the hydrate phase and residual unreacted liquid phase for the gas mixture hydrate system. The influence factors, such as operation conditions, gas composition of feed gas and types of guest gas on the gas composition of liquid and hydrate phases were studied. The experimental results show the mole fraction of CO2 in both hydrate phase and liquid phase are higher than that in the feed gas. The increase of system pressure and the mole fraction of CO2 in feed gas will obviously lead to the increase of the mole fraction of CO2 in hydrate phase, while slightly affect the mole fraction of CO2 in the liquid phase. When the mole fraction of CO2 in feed gas exceeds 80 %, the mole fraction of CO2 in the water phase will reach over 96 %, resulting in other influence factors being negligible. The mole fraction of N2 in hydrate phase is higher than that of H2, while the mole fraction of N2 in water phase is close to H2.

Machine Learning Potential for Serpentines

AbstractSerpentines are layered hydrous magnesium silicates (MgOO) formed through serpentinization, a geochemical process that significantly alters the physical property of the mantle. They are hard to investigate experimentally and computationally due to the complexity of natural serpentine samples and the large number of atoms in the unit cell. We developed a machine learning (ML) potential for serpentine minerals based on density functional theory calculation with the SCAN meta‐GGA functional for molecular dynamics simulation. We illustrate the success of this ML potential model in reproducing the high‐temperature equation of states of several hydrous phases under the Earth's subduction zone conditions, including brucite, lizardite, and antigorite. In addition, we investigate the polysomes of antigorite with periodicity = 13–24, which is believed to be all the naturally existent antigorite species. We found that antigorite with larger than 21 appears more stable than lizardite at low temperatures. This ML potential can be further applied to investigate more complex antigorite superstructures with multiple coexisting periodic waves.

Elasticity of Nacrite: Implications for Subduction Zone Dynamics

AbstractSubduction zones exhibit heterogeneities in composition due to different mineral assemblages transported into the mantle by the descending slabs, thus affecting the seismic properties of the region. These minerals are typically rich in alumina and silica and often contain hydrous phases. Nacrite, Al2Si2O5(OH)4, a mineral consisting of these components, forms in basaltic crust through hydrothermal alteration and is frequently overlooked due to its structural alikeness with its polytypes, making it hard to distinguish by traditional methods. Its occurrence in oceanic sediments and altered basaltic crust significantly impacts the subduction process by facilitating the transport of water into deeper mantle regions. In this study, we investigate the equation of state and elasticity of nacrite using first‐principles calculations based on density functional theory corrected for dispersive forces over its pressure stability range. Anomalous behavior of elastic coefficients are suggestive of a polytypic transformation, evidenced by anomalous softening in the shear modulus and a decrease of approximately 3% in shear wave velocity observed at low pressures ( 2 GPa). Our studies indicate that nacrite exhibits a significantly lower shear wave velocity compared to the surrounding mantle, resulting in very high VP/VS ratios. These findings emphasize the role of nacrite in the subduction zones of Japan and Alaska, particularly in the formation of low‐velocity layers. We propose that nacrite's presence is a significant factor explaining these observations, alongside other hydrous minerals like lawsonite, glaucophane, etc., contributing to the low‐velocity layers in these regions.

An assessment of the pozzolanic potential and mechanical properties of Nigerian calcined clays for sustainable ternary cement blends

This study investigates the potential of calcined clays from Nigerian deposits as supplementary cementitious materials. Clay materials were obtained from three sites namely: Ikpeshi, Okpilla and Uzebba. The raw clay samples were then calcined at 700°C and 800°C. Chemical and mineralogical compositions were determined for the raw and calcined clay samples using XRF and XRD respectively. The chemical composition by XRF confirmed these clays as potential pozzolans with SiO2, Al2O3, and Fe2O3 collectively exceeding 70%. XRD analysis identified kaolinite and quartz as major mineral phases in the raw clays, which transformed into metakaolin upon calcination. Thermo Gravimetric Analysis (TGA) indicated varying lime consumption levels among the clays, with Ikpeshi clay displaying the highest pozzolanic reactivity and Uzebba clay the least. Compressive strength investigation on mortar cubes prepared with 50% substitution of Portland cement with the calcined clay and limestone, showed that Ikpeshi clay at 800°C had the best strength performance, with strength activity index of 0.92 (at age 28 days), demonstrating superior pozzolanic potential. Strength development was more significant between 7 and 28 days, indicating the pozzolanic reaction's contribution to long-term strength. However, initial strength at 3 days was lower than the reference Portland cement due to a delayed pozzolanic reaction. XRD analysis of blended pastes revealed typical phases of hydration like portlandite, calcium silicate hydrate phase, strätlingite, and ettringite, with the calcined clay blends showing reduced portlandite content, indicating absorption by the pozzolan's alumina phase.

Agro-industrial waste utilization in air-cured alkali-activated pavement composites: Properties, micro-structural insights and life cycle impacts

This study investigates the development and performance of agro-industrial waste-based air-cured alkali-activated composites (AC) for sustainable high-strength pavement applications. The calculated amount of Na2SiO3 and NaOH were employed with water to generate alkaline activator solution. Locally sourced materials, including blast furnace slag, construction and demolition (C&D) waste, and sugarcane bagasse ash (SBA), were utilized to examine mechanical properties, micro-structural behaviour, and life cycle impacts. Optimized AC mixes containing 50% recycled aggregates (RCA) and 15% SBA demonstrated superior compressive, tensile, and flexural strength, while significantly reducing embodied energy and carbon emissions. Microstructural analysis through XRD, SEM, EDAX, and TGA confirmed the formation of stable alumino-silicate hydrate phases, contributing to enhanced superior-strength. The life cycle analysis results indicated considerable environmental benefits compared to traditional OPC pavement concretes. This research presents a sustainable solution for pavement infrastructure, aligning with circular economy principles by promoting the reduction of resource consumption and greenhouse gas emissions.

Electrically driven nucleation for enhanced control of salt hydrate hydrogel heat release in long-term thermal storage applications

Sodium acetate trihydrate (SAT) is a well-known salt hydrate phase change material (PCM) with large energy density and a high degree of supercooling, making it suitable for long-term thermal storage. However, effectively discharging heat from the supercooled SAT remains a challenge. This study delves into optimizing the electrical nucleation process in an SAT-based PCM, beginning with the validation of electrode pre-treatment and concluding with initiation under various conditions. The research identifies the optimal voltage and electrode spacing for nucleation. The crucial role of diffusion field interactions from growing crystals at different sites is highlighted, noting that their convergence creates a complex concentration gradient profile that hampers crystallization efficiency. Additionally, an increase in electrode pairs correlates with a more uniform heat distribution. Findings revealed that through material modification and nucleation strategy optimization, the theoretical crystallization time for SAT-based PCMs can vary significantly, ranging from 44 to 252 s. This variability, offering up to a 472.73 % extension in discharge time, underscores the PCM's adaptability for customized applications, especially in fields requiring variable discharge rates, such as residential heating and electronic thermal management.

Influence of magnesium oxychloride cement mortar with different strength grades: Fly ash as compensation material

Magnesium oxychloride cement (MOC) is widely used due to its high solid waste utilization efficiency. However, the demand for cement raw materials (MgO and MgCl2) in the lower strength gradation remains low, leading to excessive sand particles in the slurry, thus reducing the working performance of the MOC mortar. Fly ash (FA) has been used in the construction industry to improve the workability of the slurry. The focus and innovation of this work involved using FA as a compensation material to produce MOC mortar materials with different strength levels. In this study, FA was used as compensation material to form MOC mortar with different strength grades, and the effects of FA on the MOC mortar flow performance, setting time, hydration heat release, strength development, phase composition, pore structure, and micromorphology were investigated. Combined with the experimental analysis and referring to the strength grade law of silicate concrete, the grade classification of MOC mortar with FA as the compensation material could be simply divided by adding 20 %, 30 %, 40 %, and 50 % FA, which could serve as a reference for the use design of MOC in different environments.

Modulating the highland barley hordein/glutelin ratio can improve reconstituted fermented dough characteristics to promote Chinese Mantou quality

To improve the defective processing of barley fermented dough, this study constructed barley model dough using reconstituted hordein/glutelin ratios (75:25, 50:50, and 25:75) and elucidated its regulatory roles and potential mechanisms. SEM and CLSM results showed that increasing the hordein ratio improved the continuity and completion of the reconstituted gluten network compared to Control, thus allowing the gluten to stretch and elongate during fermentation. Also, LF-NMR revealed that the water distribution of the reconstituted system tended to shift from a free to a bound state, contributing to water retention during the dough hydration phase. Rheological determination indicated that the 75H-25G sample exhibited maximum tan δ (G′/G″) with optimal viscoelastic solid behavior. Although the reconstituted system is homogeneous in composition, a moderate increase in the hordein ratio can improve the lack of barley dough textural properties, which agrees with the stress-relaxation results. Further analysis revealed that an increased hordein ratio results in a gluten-free sulfhydryl content decrease, SDS extractability rate increase, and λmax redshift; this is due to the ionic and hydrogen bonding weakening as well as hydrophobic interactions enhancement within its system. Furthermore, conformational relationship analysis revealed that free sulfhydryl, intermolecular forces, and protein secondary and tertiary structures were the characteristic indicators influencing the reconstituted barley dough and Mantou. The obtained results are expected to provide new insights into the quality improvement of barley dough during fermentation; in the future, attention towards blending strategies with other cereal flours should be focused on facilitating the barley gluten network deficiencies, thus promoting the flourishing of cereal products.

Natural gas storage in hydrates in the presence of thermodynamic hydrate promoters: Review and experimental investigation

Natural gas (NG), the cleanest fossil fuel, is playing an increasingly important role in the current energy supply. However, the safe storage and transportation of flammable NG is a long-standing challenge. Furthermore, NG emission has a stronger per molecule greenhouse effect on the environment than CO2. Therefore, efficient and effective methods of NG storage and transportation are needed. Storing NG in the form of gas hydrate offers advantages over common compression or liquefaction methods, but the thermodynamic conditions required for gas hydrate formation hinder the large-scale application of solidified natural gas (SNG) technology. This work presents a review of phase equilibrium conditions of gas hydrates formed by greenhouse gases including CH4, CO2 and NG in the presence of thermodynamic hydrate promoters. This study uses available thermodynamic software to calculate gas hydrate phase equilibrium using different Equations of State (EoS). We include an experimental investigation using a 2 L autoclave reactor to evaluate the effect of mass transfer, the presence of cyclopentane as a thermodynamic promoter, and the level of subcooling on the NG hydrate formation kinetics. The results show that: 1) Tetrahydrofuran and cyclopentane generally have the strongest thermodynamic-promoting effect; 2) Thermodynamic promotion of cyclopentane on NG hydrate is validated experimentally; 3) NG hydrate formation kinetics is greatly influenced by mechanical stirring (mass transfer), cyclopentane as a co-former and its concentration and subcooling; 4) At high subcooling, cyclopentane-promoted systems show a significantly improved gas storage capacity than the baseline sample; and 5) NG hydrate particles have a size distribution of hundreds of microns under current experimental conditions. This study offers new insight into NG hydrate formation thermodynamics and kinetics that has application to SNG technology.

Hydrate phase equilibrium of hydrogen with THP, DCM, TBAB+THF and sulfur hexafluoride +TBAB aqueous solution systems

Experimental hydrogen hydrate dissociation data with single thermodynamic additive: tetrahydropyran (THP, with oxygen-containing functional group) or dichloromethane (DCM, with halogen group), and thermodynamic additive mixtures: tetrahydrofuran (THF) + tetrabutylammonium bromide (TBAB) system and sulfur hexafluoride (SF6) +TBAB system were reported with temperature range from 275.33 to 282.98 K and pressure range from 1.65 to 12.63 MPa. Other experimental data were collected from the literature. The compared results showed that the oxygen-containing or halogen functional group can significantly affect the hydrogen bonding between water molecules, which present great promoting effects on hydrogen hydrates formation. Also, the promoting effects of mixture additives on the phase equilibrium of hydrogen hydrates were investigated. The results indicated that the combination of thermodynamic additives showed better promoting effects on hydrate formation compared to the individual ones. And the results obtained in this work would provide useful information to select suitable and effective thermodynamic additives for hydrate-based hydrogen storage technology.

Evaluation of stratigraphic adaptability for hydrate-based CO2 sequestration in marine clay-containing reservoirs

Geological sequestration of carbon dioxide (CO2) in solid hydrate state beneath seafloor is an attractive option for mitigating global warming. However, as a representative geological factor in marine sediment, clay mineral still plays an ambiguous role in hydrate depositional behaviors and reservoir structural evolution, which provides an obstacle to accurately assessing the potential and security of marine CO2 sequestration. In this work, spatiotemporal hydrate distribution and sedimentary structure evolution in the presence of two typical clay minerals with different structures and properties were investigated by low-field nuclear magnetic resonance (LNMR) technique. There was an inextricable interaction between clay-fluid migration and hydrate phase transition in porous sediments. Pore plugging owing to migration, agglomeration, and redeposition of unstable kaolinite (KIT) particles weakened final CO2 storage capacity by 10.3% and exacerbated heterogeneous hydrate distribution. CO2 storage capacity in montmorillonite (MMT) system was significantly improved with a water conversion of 82.7% for the high interaction potential between clay particles and favorable mass transfer conditions within the reservoir. However, clay minerals accelerated CO2 hydrate destabilization and disrupted the initial water distribution and pore structure. Migration of MMT fluid with high viscosity and gel property during hydrate phase transition resulted in a complex pore evolution and irreversible sedimentary skeleton deformation, providing an effective warning for field implementation of geological carbon sequestration. The findings expand the understanding of pore-scale interaction between clay minerals and gas hydrates, and provide valuable support for stratigraphic adaptability evaluation of CO2 sequestration in marine sediments.

Liquidus of SiO2 in the Li2O‐SiO2, Na2O‐SiO2, and K2O‐SiO2 systems

AbstractThe phase equilibria in the SiO2‐rich region of the Li2O‐, Na2O‐, and K2O‐SiO2 systems at 1550°C to 1650°C were experimentally studied to determine accurate liquidus of SiO2 in the systems. A classical equilibration/quenching method was used, and the equilibrated samples were analyzed by X‐ray diffraction (XRD) and electron probe microanalysis (EPMA). Samples were contained in sealed Pt crucibles and held at the target temperatures for 7–21 days to reach equilibrium condition. Sealed Pt crucibles were employed to avoid the volatile loss of alkali oxides during high temperature phase equilibration and hydration upon quenching. Accurate liquidus of SiO2 in alkali‐silicate systems was determined for the first time, and the results were analyzed using the limiting slope rule in order to understand the dissolution behavior of alkali oxides in SiO2 melt. It was confirmed that alkali oxide dissolves in SiO2 melt by producing Li+, Na+, and K+ cationic species rather than Li22+, Na22+ and K22+ species.

Characterisation of Fault-Related Mn-Fe Striae on the Timpa Della Manca Fault (Mercure Basin, Southern Apennines, Italy)

The Quaternary Mercure basin is a complex fault structure located in the Pollino region of the southern Apennines (Italy). A persistent seismic gap makes the Mercure basin structure one of Italy’s highest seismic risk zones. The southernmost termination of the Mercure basin is the Timpa della Manca fault. The fault’s mirror is characterised by distinctive, lineated, black-coloured striae decorating a cataclasite made of carbonate clasts. These black-coloured striae consist of a mixture of Mn phases, including hollandite, todorokite, birnessite, and orientite, which are associated with goethite and hematite along with minor amounts of phyllosilicates (chlorite, muscovite), quartz, and sursassite. This mineral association and their phase stability suggest that hydrothermal circulating fluids may have mobilised and re-precipitated low-temperature Mn hydrous phases within the shear zone, leaving remnants of higher-temperature minerals. Oceanic crust remnant blocks within the Frido Unit appear to be the most likely source of the Mn. The uniqueness of the Mn striae on the Timpa della Manca fault offers intriguing insights into fluid circulation within the Mercure basin tectonic system, with potential implications for the seismotectonic characteristics of the Pollino region.

High-performance superhydrophobic fly ash based geopolymers with graphene oxide reinforcement for enhanced durability and repellency

While high-performance fly ash geopolymers offer a demonstrably reduced carbon footprint in the construction industry, their inherent affinity for water (hydrophilicity) can facilitate the accumulation of moisture within the material matrix, potentially leading to the initiation and propagation of internal corrosion. The implementation of hydrophobic functionalization strategies on fly ash geopolymers demonstrably enhances their resistance to corrosive degradation. Nevertheless, a crucial challenge persists in the form of mitigating potential declines in mechanical strength. This investigation endeavors to attenuate the deleterious effects exerted by the hydrophobic aluminosilicate hydrate phase on the material's mechanical properties, while concurrently preserving its superhydrophobic character. Our approach involved the incorporation of a novel composite modifier, wherein polymethylhydrosiloxane (PMHS) served as the principal hydrophobic component. Graphene oxide (GO) was strategically introduced to achieve efficient pore filling, owing to its exceptional dispersibility. Furthermore, the presence of GO reinforces the mechanical performance of the composite due to its inherent superior mechanical properties. Additionally, the well-dispersed GO portion forms nano hydrophobic particles by covalently grafting hydrophobic groups, further enhancing the overall hydrophobicity of the composite. This synergistic interplay between PMHS and GO facilitated the successful development of a high-performance fly ash geopolymer composite characterized by exceptional mechanical strength, three-dimensional superhydrophobicity, and enhanced chemical stability. The graphene oxide reinforced high-performance three-dimensional superhydrophobic hybrid hydrogel geopolymer composites maintained high compressive strength while achieving a water contact angle of 153 ° and a water absorption rate of only 1.7 %. Remarkably, the geopolymer retains its high hydrophobicity even after 24 hours in an acid-base solution, with a contact angle exceeding 140° and water absorption rates lower than 4 %.