Hydrothermal Heat Research Articles

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•− play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Enhanced dopamine detection using Ti3C2Tx/rGO/Pt ternary composite synthesized via microwave-assisted hydrothermal method

A novel electrochemical sensing platform for dopamine (DA) detection was developed by fabricating the ternary composite of Ti3C2Tx MXene (M) and reduced graphene oxide (rGO) with platinum nanoparticles (Pt NPs) through microwave-assisted hydrothermal heating. The exceptional electrical conductivity and rich surface chemistry of MXene provide abundant active catalytic sites for electrochemical reactions, while the large surface area of rGO facilitates ion and electron pathways. The integration of rGO in the MXene sheet, forming MXene-rGO (M_rGO) heterostructure composite, imparts long-term stability to the 2D heterostructure while providing additional electron pathways and significantly enhancing conductivity. Pt NPs synergistically increased the electrocatalytic activity of the electrochemical sensor's performance. Ternary nanocomposites were fabricated with different weight percentages (wt.%) of Pt NPs, ranging from 5 to 20. Characterizations of the samples (rGO, M, M_rGO, and 5–20 wt% Pt@M_rGO) were conducted through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RAMAN), and X-ray spectroscopy (XPS). Electrochemical evaluations of the samples were investigated in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analyses. The analysis revealed that the ternary composite with 5 wt% of Pt NPs (5% Pt@M_rGO) exhibited a uniform well-distribution of Pt NPs and the highest oxidation peak for DA oxidation in CV studies. The presence of metal nanoparticles, aided by the synergistic effects between the MXene and rGO, resulted in an excellent DA sensor with a 0.147 μM detection limit from 1 to 14 μM linearity range. The sensor demonstrated outstanding selectivity, reproducibility (RSD values of 8.10%), repeatability (RSD value of 2.46%) and, excellent stability over 14 days. In human urine samples, the sensor exhibited excellent DA recovery (88.62–110.65%). This study significantly advances the development of electrochemical sensors for DA detection by introducing a rapid, facile and, efficient method for fabricating ternary composites. The fabricated sensor exhibited high sensitivity, excellent selectivity, and robust electrochemical performance, offering valuable insights into human and behavioral health advancements.

Automated monitoring of natural parameters of renewable energy production systems

The paper discusses the urgent issues of the need to automate the monitoring of natural parameters of renewable energy production systems. Monitoring involves the collec- tion and analysis of various parameters of the natural environment that affect the efficiency and environmental friendliness of systems powered by renewable energy. Based on analytical materials and practical work related to techno-economic and ecological studies concerning the assessment of water reserves in indi- vidual wells, the study focused on the development of technologies and technical means for monitoring. It was found that, in practice, hydrogeological research on groundwaters use outdated methods and technical means for measuring and storing data. A local automated system for monitoring well parameters was developed and constructed. It ensures the operation of the hydrothermal heat pump system at the experimental site of the Institute of Renewable Energy of the National Academy of Sciences of Ukraine. This system was tested in our research. The benefits of this study are revealing the need to create an intelligent monitoring system with the possibility of automated decision-making regarding the management of renewable energy generation systems, depending on changes in the am- bient parameters. A network automated system for monitoring natural parameters was developed, consisting of several wireless sensor subsystems that communicate with each other via wireless connection and transmit information to the gateway. The gateway, in turn, is connected to the computer with a graphical interface for interaction with the system. The results of work indicate that the proposed structures for automated water monitoring are simple and easy to implement. Consequently, the study revealed that one of the prospects is the development of automated monitoring systems with intelligent features, capable of making optimal individual decisions regard- ing the management of renewable energy generation systems under variable environmental parameters. As a result, the data obtained from this study have significant scientific and practical implications for advancing the design methodology of geothermal heat pump wells, focusing on long-term forecasts and assessments of their ecological and economic efficiency.

Facile synthesis of MWCNT hexagonal needles grown on interconnected honeycombs like MnCo2O4/MnO2 nanoporous electrode for high-performance asymmetric supercapacitor

The construction of a honeycomb-like structure composed of MnCo2O4/MnO2was effectively achieved using a combination of hydrothermal processing and heat treatment. The whole surface of the MnCo2O4/MnO2 honeycomb is coated with neatly arranged hexagonal nano needles made of MWCNT, leading to a substantial enhancement in the specific surface area. At 1 A/g, the supercapacitor electrode composed of MnCo2O4/MnO2@MWCNT composite exhibited an exceptional specific capacitance of around 1539 F/g. Furthermore, it maintained approximately 95.5 % of its capacity even after undergoing 10,000 cycles. The asymmetric capacitor device, with MnCo2O4/MnO2@MWCNT and AC electrode, has a power density of 1537.8 W kg−1 and an energy density of 48.78 Wh kg−1. The MnCo2O4/MnO2composite exhibits exceptional rate performance, significant capacitance, and excellent cycle performance due to the synergistic effect between MnCo2O4/MnO2 and MWCNT, as well as the high specific surface area and unique structure. Consequently, it presents a viable option for the advancement of high-efficiency electrochemical super capacitors in the next generation.

Hydrothermal extraction of ulvans from Ulva spp. in a biorefinery approach

A simple cascade process based on the hydrothermal fractionation of Ulva spp. biomass was proposed. Considering the overall extraction yields (50 %), ulvan recovery (23 %), and ulvan composition, structural, mechanical and cytotoxic properties, the selected optimal final heating temperature was 160 °C. Ethanol precipitation provided the highest ulvan recovery yields but choline chloride precipitated ulvans showed stronger mechanical properties, G´ moduli 1.5·104 Pa and 3·104 Pa for ethanol and for choline chloride, respectively. Both products were safe on NCTC 929 mouse fibroblasts and after a cooling stage, formed films without requiring any additives. From the ulvan-free liquid fraction, one product with 43 % (wt, d.b.) phenolics and moderate antiradical properties and a byproduct containing nutrients and minerals were separated. The methane potential of the corresponding residual solids was influenced by the hydrothermal heating temperature and was doubled compared to than for the untreated seaweed biomass (60 mL/g VS). This scheme could be also applied to the wet algal biomass, in a chemical free alternative to provide ready to use ulvan biopolymers, bioactives, nutrients, salts and biogas, conforming a biorefinery approach.

Impacts of finned rotating cylinder on hydrothermal flow of hybrid nanofluids in a vented cavity based on dynamic mesh approach

This study aims to explore and enhance the understanding of how finned rotating cylinders impact mixed convection of the hydrothermal flow and heat transfer of hybrid nanofluids in a vented cavity. The significance of this study contributes to the advancement of increasingly efficient and productive thermal control mechanisms in diverse industrial sectors employing rotating cylinders. Simulations employ a dynamic mesh approach to model the flow domain and boundary motion of the rotating bladed cylinder based on the finite volume technique. The presented results underwent a rigorous comparison with existing related works in the open literature. The chosen working fluid is a Newtonian hybrid nanofluid composed of SiO2-Al2O3 suspended in water. Various configurations of cylinder locations and sizes are examined, alongside a broad spectrum of associated variables with certain ranges. These parameters with defined ranges are; Reynolds numbers (2 × 102 ≤ Re ≤ 1 × 103), cylinder radius (0.1 ≤ R≤0.3), cylinder locations (0.25 ≤ δ ≤ 0.75), spinning speeds (− 3 ≤ Ω ≤ 3), and nanoparticle concentrations (0 ≤ φ1 ≤ 0.03 and 0 ≤ φ2 ≤ 0.03). The results indicate significant impacts of Reynolds numbers (Re), Grashof numbers (Gr), cylinder radius (R), location (δ), spinning speed (Ω), and the number of blades on the hydrothermal characteristics. The major finding states that the cylinder radius of 0.3 for Case 5 with five fins provides the greatest enhancement of mixed flow and relatively maximum heat transfer rate. Furthermore, increasing concentrations of nanoparticles (φ) of hybrid nanofluids further improves the thermal performance.

Microwave synthesis of composite of AgInS2 quantum dots and zeolitic imidazolate framework-8 for application in white light emitting diodes

Preparation of AgInS2 quantum dots (AIS QDs) with high photoluminescence quantum yield (PLQY) and thermal stability remains an important challenge. In this paper, AIS QDs were successfully introduced into zeolitic imidazolate framework-8 (ZIF-8) by microwave-assisted hydrothermal method. Due to the effective isolation of the ZIF-8, the AIS QDs avoid the concentration quenching when they were assembled into white light emitting diodes (WLEDs) devices as color conversion materials. More importantly, the generation of ZnS layer between the interfaces of AIS QDs and ZIF-8 can efficiently improve the optical performance of AIS QDs, resulting in the fluorescence lifetime extended to 470.05 ns. Meanwhile, the PLQY of AIS/ZIF-8 composite reached up 34.30 % when microwave hydrothermal heating at 120 °C for 60 min with AgIn/Zn=1/3, which was higher than that of the pristine AIS QDs as 25.30 %. Finally, the WLED devices were fabricated by combining AIS/ZIF-8 composite fluorescent powder with (Ba, Sr)Si2O2N2:Eu2+ phosphors and blue LED. At 20 mA, the AIS/ZIF-8 based WLED shows the luminous efficiency (LE) of 44.54 lm/W, correlated color temperature (CCT) of 4242 K and color rendering index (CRI) of 89.1. Moreover, the Commission International de L'Eclairage (CIE) was (0.36, 0.35), indicating the WLED emited warm white light. The present strategy aims at enhancing the optical performance of AIS QDs, which also may trigger the development of QDs-based WLED.

Mesoporous carbon particles by biomass waste based on sulfonation and copper oxide functionalization as efficient and stable electrode material for supercapacitor.

Here, the hierarchical mesoporous-activated carbon particles obtained by KOH activation from pistachio shell wastes are modified by both the sulfonation process and CuO doping by hydrothermal heating (CuO@S-doped PSAC) for use as a supercapacitor. It is predicted that the electrochemical performance of the porous carbon electrode material obtained by such CuO doping and sulfonation process will be significantly increased with increased Faradaic capacitance. The electrochemical performance of CuO@S doped PSAC composite is systematically investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge/discharge (GCD) in the presence of 1M H2SO4, 1M Na2SO4, and 1M NaOH as electrolytes. The CuO@S doped PSAC-based electrode shows excellent stability with high specific capacitance up to 397.16 F/g at 0.1 A/g and 92.64% retention. Furthermore, FTIR, SEM, XRD, EDS, and nitrogen adsorption/desorption analyses are used for the characterisation of the obtained composites. Based on a significant supercapacitor performance, the synthesis strategy of carbon-based electrode material containing sulfonation and CuO modifications derived from agricultural biomass waste material is predicted to be a valuable example.

Graphene-loaded nickel−vanadium bimetal oxides as hydrogen pumps to boost solid-state hydrogen storage kinetic performance of magnesium hydride

To modify the thermodynamics and kinetic performance of magnesium hydride (MgH2) for solid-state hydrogen storage, Ni3V2O8-rGO (rGO represents reduced graphene oxide) and Ni3V2O8 nanocomposites were prepared by hydrothermal and subsequent heat treatment. The beginning hydrogen desorption temperature of 7 wt.% Ni3V2O8-rGO modified MgH2 was reduced to 208 °C, while the additive-free MgH2 and 7 wt.% Ni3V2O8 doped MgH2 appeared to discharge hydrogen at 340 and 226 °C, respectively. A charging capacity of about 4.7 wt.% H2 for MgH2 + 7 wt.% Ni3V2O8-rGO was achieved at 125 °C in 10 min, while the dehydrogenated MgH2 took 60 min to absorb only 4.6 wt.% H2 at 215 °C. The microstructure analysis confirmed that the in-situ generated Mg2Ni/Mg2NiH4 and metallic V contributed significantly to the enhanced performance of MgH2. In addition, the presence of rGO in the MgH2 + 7 wt.% Ni3V2O8-rGO composite reduced particle aggregation tendency of Mg/MgH2, leading to improving the cyclic stability of MgH2 during 20 cycles.

Catalytic hydrothermal carbonization of corn and rice straws with citric acid: Implications for charcoal production and combustion performance

Hydrothermal carbonization represents a promising environmental approach for converting biomass into high-quality biochar fuel. Despite extensive discourse, limited research has focused on fuel properties and combustion performances of biochar as well as reaction mechanisms under catalysts. This study scrutinized properties of biochar from citric acid-catalyzed carbonization. Straw (corn/rice) was hydrothermally carbonized in 5 % citric acid solution with a solid-liquid ratio of 1:10 g/mL at 190–250 °C for 3 h. Results revealed an increase in C and a decrease in O with elevated temperature and citric acid concentration. The calorific values for corn and rice straw biochar ranged from 23.53 MJ/kg to 29.81 MJ/kg and from 23.14 MJ/kg to 26.98 MJ/kg, respectively. This study highlighted diverse impacts of hydrothermal reaction temperature and citric acid concentration on biochar attributes, calorific value, energy density, mass yield, energy yield, and thermal stability. It elucidated the influence of citric acid concentration on biochar burnout temperature and the role of hydrothermal reaction temperature and heating rate in biochar combustion characteristics. Citric acid effectively reduced biochar activation energy in low-temperature areas and prolonged the biochar combustion reaction time, achieving highly favorable comprehensive combustion characteristics at 47.56×10−7. The findings present the potential for biochar production with enhanced performance for integrating and co-firing with conventional fuels.

Study on Effects of Hydrothermal Heat Treatment Method on Fertilizer Efficiency of Biomass Waste

This study explores a new way of utilizing biomass waste as fertilizer based on the hydrothermal heat treatment method. Hydrothermal heat treatment was carried out on common biomass waste, including corn stalks, livestock manure, and vegetable waste. by heating them to 120°C and then to 240°C respectively, while measuring the contents of organic matter, total nutrients, and humus in hydrothermal solid products. The experimental results are as follows. With the increase in temperature, the pH of three kinds of biomass waste hydrothermal products is reduced to different degrees. The content of organic matter in the solid products of corn stalk increased with the increase of temperature, the content of organic matter in the hydrothermal products of vegetable waste was opposite to that of corn stalk, and the content of organic matter in the hydrothermal solid products of pig manure was higher than 30% at different temperatures. The total nutrient content of the hydrothermal product of corn stalk decreased first and then increased with the increase of temperature, and reached the minimum value of 10.12 g/L at 180°C. The total nutrient content of the solid product of vegetable waste showed a negative correlation with temperature, and the total nutrient content of the raw material of pig manure was 60.55 g/kg. The total nutrient content of solid products after different hydrothermal temperature treatments was 41.8–59.03 g/kg, which was lower than that of raw materials. With the increase of temperature, the humic acid content of the solid product of corn stalk first increased and then decreased, the humic acid content of hydrothermal product of pig manure continued to increase with the increase of temperature, and the humic acid content of hydrothermal product of vegetable continued to increase with the increase of temperature. At 210°C, the contents of humic acid and fulvic acid reached the maximum, and the humification rate reached the maximum of 0.856.

Three accelerated methods based on microwave, hydrothermal and conventional heating in the green synthesis of selenium nanoparticles using garlic aqueous extract: Screening and characterization

Selenium nanoparticles (Se NPs) have unique biological characteristics, including anticancer, antioxidant and antimicrobial activities. Furthermore, the green synthesis of Se NPs using plant extracts, due to their natural reductant and stabilizer molecules, can intensify the process with minimal toxic effects on the human body and the environment. Se NPs have been synthesized using an aqueous extract of garlic and three accelerated heating methods based on microwave (800 W for 2.5 min), hydrothermal (temperature and pressure of 121 ºC and 1.5 atm, for 15 min) and conventional (at 150 ºC for 1 h) heating using a heater with stirring. Solution mixtures containing 20 mL of the prepared extract and 5 mL of sodium selenite solution (10 mM) were exposed to these three mentioned heating methods. Fourier transform infrared spectroscopy, UV-Vis spectrophotometry, dynamic light scattering analysis and transmission electron microscopy were used to assess characteristics of the formed Se NPs. The results showed that the fabricated Se NPs via microwave, autoclave and conventional heating methods had minimum particle size (107 nm) and polydispersity index (0.155), and maximum zeta potential (-38.7 mV) values. Furthermore, the spherical formed Se NPs using garlic extract and under microwave, conventional and autoclave heating methods had antioxidant activity of 44.2, 34.8 and 32.6 %, respectively. The formed Se NPs also indicated high antibacterial activity toward Escherichia coli and Staphylococcus aureus bacteria strains.

Ensemble learning for predicting average thermal extraction load of a hydrothermal geothermal field: A case study in Guanzhong Basin, China

Accurate prediction of the average thermal extraction load (ATEL) in hydrothermal heating systems optimizes energy recovery, though numerical models are constrained by modeling accuracy and computational time costs. Data-driven modeling can efficiently screen alternative production plans and enhance daily operational decisions. However, ensemble learning applications for forecasting ATEL lack comprehensive comparisons and appropriate algorithm selection. This study evaluates six ensemble learning algorithms: random forest (RF), adaptive boosting (AdaBoost), gradient boosting decision trees (GBDT), extreme gradient boosting (XGBoost), light gradient boosting machine (LightBGM) and categorical boosting (CatBoost) on 1159 data points from a homogeneous thermal-hydraulic coupling numerical model. The superior performance of the CatBoost is characterized by the highest accuracy (with the lowest root mean square error (RMSE) of 150.6 kW–170.7 kW, minimal mean absolute percentage error (MAPE) of 0.66%–0.73%, and exceptional R2 values of 0.999), commendable stability, reasonable computational cost and low uncertainty. LightGBM, XGBoost, and GBDT are identified as suitable substitutes, whereas RF is a possible substitute. Moreover, the production rate is identified as the most significant factor contributing to the ATEL, followed by the well spacing and injection temperature. While perforation depth has the least influence on heat recovery.

RGO/In2O3 heterostructures based gas sensor for efficient ppb-level n-butanol detection

The real-time and effective detection of n-butanol gas is particularly important in production and daily life due to its flammability, toxicity, and potential hazards to the environment. This article reports the preparation of hollow indium oxide spheres and rGO/In2O3 composites through a simple hydrothermal and subsequent heat treatment method. Test results indicate that the gas sensitivity of n-butanol can be significantly improved through rGO composites. The prepared hollow indium oxide spheres are composed of nanosheets with a diameter of probably 500 nm. After combination by rGO, the specific surface area and the proportion of adsorbed oxygen of the material are increased, both of which are advantageous for enhancing gas sensitivity abilities. At the optimum operating temperature of 160 °C, the response value of rGO/In2O3 complex sensor is 51–50 ppm of n-butanol, which is 3.6 times the response of pure In2O3. Gas sensors composed of rGO/In2O3 exhibit ultra-fast response time and low detection limit. Even for ppb grade (100 ppb) n-butanol gas, the response value is still 2.3. These characteristics make rGO/In2O3 a promising material for the preparation of high-performance n-butanol gas sensors. Besides, the gas-sensitive mechanism of the enhanced n-butanol sensing performances is also analyzed.

Light-assisted room temperature ammonia gas sensor based on porphyrin-coated V2O5 nanosheets

This study explores the gas-sensing capabilities of light-activated porphyrin-coated V2O5 nanosheets for ammonia detection. The nanosheets were synthesized via a hydrothermal method, heat treatment, and solution dispersion. They were then coated with thin layers of Zn-porphyrin and Cu-porphyrin derivatives. The gas-sensing performance of the porphyrin/V2O5 sensor was evaluated under dark and visible light conditions. The combination of materials significantly improves the sensor's performance compared to pure V2O5 nanosheets sensor. The study also investigated selectivity, temporal stability, and proposed a mechanism for ammonia detection based on the interaction between photo-excited charge carriers and adsorbed gas molecules. With such performance, compact size, cost-effectiveness, and low energy consumption, this sensor holds substantial promise for monitoring freshness and spoilage along food supply chains.

Microencapsulation of Al-Si-Fe alloys for high-temperature thermal storage with excellent thermal cycling performance

Metal-based phase change heat storage materials have become a potent candidate to regulate supply and demand of thermal energy due to their high conductivity, latent heat and stability. With the development of high-efficiency energy storage systems, materials with higher phase change temperatures are in demand urgently for more effective energy storage, which had not been achieved. Herein, the industrial Al-Si-Fe alloy with phase change temperature of 869 °C was chosen as heat storage material in this research. Furthermore, to prevent the alloy from the inherent problems such as liquid leakage, oxidation and corrosion at high temperature, a new and simple strategy was developed to micro-capsulate the alloy. The prepared process of microcapsules involved two steps: pre-coated of aluminum hydroxide along with hydrothermal carbon and heat treatment in nitrogen atmosphere. The composition, morphology, and thermal performance of the microcapsules were characterized by XRD, SEM, TEM, and TG-DSC. The results indicated the shell below 1 μm was composed of α-Al2O3 strengthened by network AlN fibers formed through the V-S mechanism. The latent heat of microcapsules reached 187.6 J·g−1 which was 82.9 % relative to raw material. Moreover, the total latent heat of the microcapsules did not change much after 300 cycles between 500 and 900 °C, although the phase transition behavior was altered. Overall, this research provides a novel idea for the encapsulation technology and the application of thermal energy storage materials from preparation and structure, which is conducive to promote the application of high-temperature phase change materials.

Binary blends of normal corn starch and cow cockle starch for the slow-thickening behavior upon pasting

Corn starch with slow thickening property may facilitate more efficient heat transfer and safety of corn starch-thickened foods. Partial substitution of normal corn starch (NCS) with slow-pasting behavior of cow cockle starch (CCS) was hypothesized to impart binary starch blend with slow-thickening effect during hydrothermal heating. To test hypothesis, a series of starch blend dispersions (with weight ratios of CCS to NCS = 75:25, 50:50, 25:75) were prepared at various starch concentrations (6 %, 8 %, 10 %, and 12 %) and subjected to the Rapid Viscosity Analysis (RVA). RVA viscographs of starch blends were compared with that of NCS, suggesting that nearly all starch blends at various concentrations showed longer time span of pasting and lower pasting rate. Although CCS and NCS blend gels exhibited lower Young's modulus and hardness based on textural profile analysis, the sensory panels revealed that 6 % and 8 % starch blend gels (with weight ratio of CCS to NCS = 25:75) showed the mouthfeel analogous to NCS gel. These findings highlight a viable non-chemical modification strategy that enables binary blends of CCS and NCS as a novel gelling agent with slow-pasting property and may aid in safety and high-quality processing of hydrogel foods.

Unveiling the inherent physical-chemical dynamics: Direct measurements of hydrothermal fluid flow, heat, and nutrient outflow at the Tagoro submarine volcano (Canary Islands, Spain)

Tagoro is one of the few submarine volcanoes in the world that has been monitored since its early eruptive stage in 2011 to present day. After six multidisciplinary oceanographic cruises conducted between 2014 and 2023 to gather a comprehensive dataset of georeferenced video-imagery and in situ measurements of hydrothermal flow velocities and hydrothermal fluid samples, we provide a robust characterization of the ongoing hydrothermal fluid velocity, heat flux, and nutrient release, along with an accurate delimitation of the hydrothermal field area. Our results reveal that Tagoro hydrothermal system extends from the main hydrothermal crater up to the summit, covering an area of 7600 m2. This hydrothermal field comprises thousands of small individual vents, displaying diverse morphologies such as crevices and delicate chimney-like structures, irregularly scattered across the dominant diffuse venting surface. Hydrothermal fluid temperatures and velocities at the substratum level reveal a clustered spatial distribution, ranging from 21.0 to 33.3 °C and 1.6–26.8 cm min−1, respectively. Furthermore, our findings indicate a discernible correlation between hydrothermal fluid temperature and vent density, while significant differences were observed between velocities from diffuse and focused areas. Additionally, heat fluxes exceed 200 MW across the entire active region, with heat flux values ranging from 6.06 to 146.87 kW m−2 and dissolve inorganic nutrient concentrations exhibit significant enrichments, comparable to the magnitude of important nutrient sources in the area as upwelling systems or mesoscale structures.

Energy Efficiency of the Carbonate Hydroxyapatite Nanoparticle Synthesis Using Microwave Heating Treatment and Its Effect on Material Characteristics

This work aimed to study the energy efficiency of the synthesis process of carbonated hydroxyapatite (CHA) nanoparticles using microwave heating treatment and its effect on material characteristics. Microwaves can provide heat quickly, so it is expected to increase the efficiency of CHA synthesis through the heat provided. The CHA nanoparticles were synthesized using precipitation and heated using a microwave oven. The unheated and hydrothermal-heated precipitation methods were also conducted for comparison purposes. The microwave-heated precipitations were done at 270 W for 0.05, 0.10, and 0.15 h, while the hydrothermal-heated precipitations were done at 100 °C for 1, 2, and 3 h. The CHA materials were characterized using an infrared spectrophotometer, X-ray diffractometer, and electron microscope. The X-ray diffractogram and infrared spectra confirmed that the synthesized materials had a hydroxyapatite crystal phase with a CO32− functional group in their spectra. Microscopic images revealed that the materials were nanometer-sized grain aggregates. The heat treatment and duration increased the material characteristics, i.e., crystallinity, crystallite, and grain size. The CHA with microwave heat treatment had the highest crystallinity and crystallite size. The electrical energy calculation revealed microwave heating had better energy efficiency than hydrothermal heating.

How Hydrothermal Cooling and Magmatic Sill Intrusions Control Flip‐Flop Faulting at Ultraslow‐Spreading Mid‐Ocean Ridges

Abstract“Flip‐flop” detachment mode represents an endmember type of lithosphere‐scale faulting observed at almost amagmatic sections of ultraslow‐spreading mid‐ocean ridges. Recent numerical experiments using an imposed steady temperature structure show that an axial temperature maximum is essential to trigger flip‐flop faults by focusing flexural strain in the footwall of the active fault. However, ridge segments without significant melt budget are more likely to be in a transient thermal state controlled, at least partly, by the faulting dynamics themselves. Therefore, we investigate which processes control the thermal structure of the lithosphere and how feedbacks with the deformation mechanisms can explain observed faulting patterns. We present results of 2‐D thermo‐mechanical numerical modeling including serpentinization reactions and dynamic grain size evolution. The model features a novel form of parametrized hydrothermal cooling along fault zones as well as the thermal and rheological effects of periodic sill intrusions. We find that the interplay of hydrothermal fault zone cooling and periodic sill intrusions in the footwall facilitates the flip‐flop detachment mode. Hydrothermal cooling of the fault zone pushes the temperature maximum into the footwall, while intrusions near the temperature maximum further weaken the rock and promote the formation of new faults with opposite polarity. Our model allows us to put constraints on the magnitude of two processes, and we obtain most reasonable melt budgets and hydrothermal heat fluxes if both are considered. Furthermore, we frequently observe two other faulting modes in our experiments complementing flip‐flop faulting to yield a potentially more robust alternative interpretation for existing observations.