Atmospheric Pressure Conditions Research Articles

Synthesis of nitrogen-doped crystalline Ga2O3 thin films via trimethylgallium doped NH3/H2/N2/O2 premixed stagnation flames

This study presents a novel and cost-effective technique for fabricating nitrogen-doped crystalline α-Ga2O3 and β-Ga2O3 thin films under atmospheric pressure conditions through flame synthesis for the first time. We employ metal–organic ammonia (NH3)-assisted flame synthesis (MO-NAFS) in a quasi-one-dimensional trimethylgallium (TMG) doped NH3/H2/N2/O2 flat flame to achieve a one-step deposition of Ga2O3 onto c-plane α-Al2O3 substrates. We found that hydrogen (H2) addition directly impacts the crystallinity of the Ga2O3 thin film. When only NH3 is employed as the fuel, a thin-film single-crystal nitrogen-doped β-Ga2O3 was observed. Blending the NH3 with 5 % of H2 yields a single-crystal nitrogen-doped α-Ga2O3, while a further increase of H2 fraction up to 10 % results in a mixture of both α-Ga2O3 and β-Ga2O3 crystals. Remarkably, the nitrogen doping through MO-NAFS was found to persistently result in an N/O atomic ratio as high as 1.12, as determined by the XPS analysis. This approach paves the way to a simple and scalable means for producing crystalline nitrogen-doped Ga2O3 thin films with potential control of crystal phase composition through parameter adjustments.

Suppression effects of different extinguishing agents on vent gases fires from lithium-ion batteries after thermal runaway: A comprehensive experimental and numerical study

During the thermal runaway process of lithium-ion batteries, the release of vaporized electrolyte and combustible gases can lead to the formation of a jet flame, posing a significant fire or explosion risk. In order to deal with the threat of lithium-ion battery vent gas fires to the safety of energy storage power stations, it's crucial to identify effective fire extinguishing agents for lithium-ion battery systems. This study employs a combination of experimental and numerical simulation methods to assess the suppression capabilities of CO2, N2, and HFC-227ea on vent gas/air premixed flames originating from lithium-ion batteries with various cathode materials. Laminar flame speed of vent gas/air/extinguishing agent premixed flames at specific equivalence ratios were measured using a Bunsen burner device under ambient temperature and atmospheric pressure conditions. Additionally, numerical calculations of laminar flame speed and adiabatic flame temperature were conducted using CHEMKIN-Pro, accompanied by an analysis of the chemical inhibition mechanism of HFC-227ea. The findings reveal that although HFC-227ea may slightly elevate the adiabatic flame temperature at lower equivalence ratios, its overall fire extinguishing efficacy surpasses that of CO2 and N2. These results offer valuable insights for selecting appropriate fire extinguishing agents for energy storage power stations, thereby enhancing the safety standards of energy storage systems.

Quantitative three-dimensional reconstruction of cellular flame area for spherical hydrogen-air flames

The cellular flame area continues to increase with the development of cells on the spherical flame surface, which will greatly promote the flame burning rate and propagation speed. This work mainly focuses on a new three-dimensional (3D) reconstruction method of the cellular structure on the flame surface, attempting to quantitatively characterize the real flame area. Initially, the visualization investigation of hydrogen-air premixed spherical flames within a constant volume vessel was conducted using the Schlieren optical technique under room temperature and atmospheric pressure conditions. In parallel, the Cellpose 2.0 graphical user interface was used for the preliminary training of the cell segmentation model. Subsequently, this pre-trained model was applied in the image post-processing, enabling the quantitative characteristics extraction of the cellular structure, such as the cells number, area, and the flame radius, etc. Additionally, a concept of peak height h on the flame profile was proposed to characterize the fluctuation degree of flame profile. A new flame equivalent radius ru was defined by the average value of valid distance from flame centroid to flame profile pixel by pixel. Based on the comparison of cell equivalent radius r and average peak height h¯, an innovative 3D reconstruction concept was proposed for the quantitative characterization of flame area. Finally, cellularity factor ξ was introduced to evaluate the cellularization degree on spherical flames surface. Results show that the appearance of secondary cracks marks the formal onset of flame cellularization, accompanied by an increase in the h¯. In the later stages of flame development, cellularization will eventually tend to a stable value of about 0.4, indicating the occurrence of “saturated state”. After 3D reconstruction, the average cell area stable at around 26 mm2 in this stage. The results of this study provide data support for the construction of combustion models in the field of premixed hydrogen-air combustion.

Analysis of Ozone and VOCs Pollution Characteristics, Sources, and Abatement Control Strategies in Hebi

In order to control the increasing ozone （O3） pollution in Hebi, Henan Province, clarifying the pollution characteristics of ozone and its precursors is vital. Therefore, we conducted a comprehensive analysis of O3 pollution utilizing the OFP-PMF-EKMA method combined with online hourly resolution monitoring data of conventional pollutants and volatile organic compounds （VOCs） in the summer of 2022 （June-September）. Ozone formation potential （OFP） was used to identify the key VOCs species, and the PMF model was used to identify the VOCs emission sources, whereas EKMA curves and scenario analysis were used to identify the main ozone control area in Hebi and to determine the reduction ratio of VOCs and NOx in a scientifically refined way. In 2022, Hebi had persistent O3 pollution, with the highest concentration in June. Conditions of high temperature, low humidity, and low atmospheric pressure contributed to the O3 accumulation. Aromatic and oxygenated volatile organic compounds （OVOCs） contributed significantly to the OFP and VOCs fraction, which were the dominant active substance and concentration dominant species. The results of the VOCs source analysis indicated that vehicle exhaust sources （25.3%） were the main source of atmospheric VOCs, followed by process sources （17.7%） and biomass combustion sources （17.6%）. Thus, emission sources associated with the combustion of fossil fuels and industrial production emissions were the most urgent sources of atmospheric VOCs to be controlled in Hebi. The O3 generation in Hebi occurred in the VOCs-sensitive zones, and the emission reduction results showed that a synergistic emission reduction of VOCs and nitrogen oxide （NOx） could effectively control O3 pollution with a 75% reduction in VOCs and a 10% reduction in NOx.

Solubility of codeine phosphate in ethylene glycol + N-methyl-2-pyrrolidone mixtures at different temperatures

ABSTRACT The primary objective of the present study is to systematically investigate the solubility data and thermodynamic properties associated with codeine phosphate within mixtures comprising ethylene glycol (EG) and N-methyl-2-pyrrolidone (NMP) under atmospheric pressure conditions within the temperature range of 293.2–313.2 K. The analysis reveals a discernible positive correlation with both temperature and the ratio of EG. Mathematical models are employed for the purpose of correlating the obtained data, and the reliability of these models is rigorously assessed through the computation of mean relative deviations for back-calculated values. Additionally, the density values of codeine phosphate saturated mixtures are meticulously measured and subsequently correlated utilising the Jouyban-Acree model. Furthermore, the apparent thermodynamic properties governing the solubilisation process of codeine phosphate, including standard enthalpy, entropy and Gibbs free energy, are computed through the application of Gibbs and van’t Hoff equations, and the obtained results are comprehensively documented.

Kinetic modeling of arabinoxylan extraction from Brewers’ spent grain using alkaline pretreatment at atmospheric pressure

This study evaluated the kinetic modeling of arabinoxylan (AX) extraction from Brewers’ spent grain (BSG) by alkaline pretreatment at atmospheric pressure, considering severe (low concentration of NaOH and high temperature) and moderate (high concentration of NaOH and low temperatures) process conditions. The effects of NaOH concentration and temperature on yield extraction were studied over time, as well as the concentration of weak acids and phenolic compounds at the end of the pre-treatment. The AX yield extraction varied from 41.2 % (1 M, 90 °C) to 64.8 % (4 M, 40 °C) after 1 h and 16 h, respectively. Acetic acid ranging from 420 ppm to 1020 ppm was released, while ferulic acid was the phenolic compound produced at the highest concentration ranging from 78.3 ppm to 224.1 ppm. In addition, rates of chemical reactions were correlated mathematically from the experimental data with a good fit, and a sensitivity analysis was performed to understand the kinetic behavior. The first-order kinetic model demonstrates that increasing AX extraction requires both low temperatures (between 30 and 40 °C) and low NaOH concentration, but at the same time, this effect increases the time required (16 h) to obtain the maximum AX yield (64.8 %).

Mechanism of synthesis ammonia over atomically dispersed Ni/BCN catalyst under atmospheric pressure and low-temperature conditions

In industry, ammonia synthesis process typically requires high temperatures (400 ∼ 500 °C) and high pressures (20 ∼ 40 MPa), resulting in high energy consumption and high carbon emissions. Exploring the direct ammonia synthesis with N2 and H2 under mild conditions without the assistance of electrochemical or photochemical energy, represents a promising approach. In this study, atomically dispersed Ni loaded on B-doped CN catalyst (Ni/BCN) was prepared by a liquid phase one-pot method, which achieved efficient ammonia synthesis under mild conditions of 101.3 kPa and 80 °C, with an ammonia yield of 114 μmol h−1 gcat-1 after 10 h. Further experimental studies combined with the characterization of catalyst morphology, bulk phase structure, and surface chemical state reveal the mechanism of ammonia synthesis under mild conditions. The appearance of nitrogen vacancies on Ni/BCN can promote the electron delocalization of stable N≡N bonds in N2, facilitating the activation of N2. B, C and N bond with each other to form a hybrid BCN carrier, which promotes the electron transfer on the surface. Our findings suggest a general approach to engineer catalysts that can drive critical reactions pertinent to energy conservation, low-carbon, and sustainability.

Leaching behaviour of limonite ores from Lapaopao, Southeast Sulawesi, Indonesia: Effect of mineralogy and acid types

An atmospheric leaching study of limonite ores from Lapaopao, Southeast Sulawesi, using hydrochloric acid (HCl), nitric acid (HNO<sub>3</sub>), and sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) has been performed. The objectives of this study were to analyze the effect of ore mineralogy and acid types on the dissolution behavior of minerals and the leaching rate of Ni and Co at atmospheric pressure conditions. Mineralogical analysis was carried out using optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometry (XRD), while the ore's chemical composition was determined by using X-ray fluorescence spectrometry (XRF) and atomic absorption spectrophotometry (AAS). Mineralogically, the limonite ores are dominated by goethite, followed by gibbsite, talc, and lizardite, with less amounts of hematite and quartz. Analysis results of solid residues revealed that mineral dissolution order was determined as follows: goethite > lizardite > gibbsite> hematite > talc> quartz. The results of the leaching experiment exhibited that the order of leaching rates of Ni in the three ores samples using three different acids were found as follows: Ore-1 > Ore-2 > Ore-3. Comparison of HCl, HNO<sub>3</sub>, and H<sub>2</sub>SO<sub>4</sub> as the lixiviants for the leaching of limonite ores demonstrated that HCl was the most reactive acid, followed by HNO<sub>3</sub> and then H<sub>2</sub>SO<sub>4</sub>. This might be due to the differences in mineralogical nature and reactivities of acids during the leaching process.

A study on thermophysical properties of binary mixtures of n-hexane with benzene and some alkyl-substituted benzenes within temperature range (293.15–323.15) K: Experimental and modeling approach

The current work reports densities and sound speeds, and related thermodynamic excess properties, namely excess molar volumes and excess isentropic compressibilities, measured at temperatures from (293.15 to 323.15) K and under atmospheric pressure conditions for binary mixtures of n-hexane with benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene. Redlich-Kister polynomial correlated the thermodynamic excess properties to test the quality of experimental data. Excess properties contributed to understanding molecular interactions between involved molecules and the peculiarities of their packing in the mixture. The Jouyban-Acree model was used to correlate the mixtures' experimental densities, sound speeds, and their related derived properties, namely isobaric thermal expansivities and isentropic compressibilities. The average absolute percentage deviation of the correlated values from the experimental ones was better than 0.036 %, 0.058 %, 0.040 %, and 0.146 % for density, sound speed, isobaric thermal expansivity, and isentropic compressibility, respectively, attesting to the robustness of the Jouyban-Acree correlations. Additionally, the Perturbed Chain Statistical Associating Fluid Theory Equation of State modeled the densities of the current mixtures. Schaaff's Collision Factor Theory and Nomoto's relation were compared for their ability to model the sound speeds of the mixtures. The efficacy of these models was tested by computing the average absolute percentage deviations between experimental and computed values. The modeled densities are reasonably concordant with experimental data, with an overall deviation of 0.02 %. Notably, Nomoto's relation exhibited superior performance over Schaaff's theory in modeling sound speeds of current mixtures, with an overall deviation of 0.33 %. The current findings underline the efficacy and versatility of the used models for thermodynamic modeling in systems of varying complexity.

Rates of air flow in and out of closed atmospheric-pressure plasma jet system affected surface properties of treated polysulfone membrane

The cold plasma jet works in an atmospheric-pressure condition, and is used to modify polymer membranes by creating hydrophilic functional groups on the membrane surface. Since it can be used without a pressure-reducing system, treatment time and cost are reduced. However, the plasma jet has a narrow beam which limits the area of the membrane surface that can be activated. In this study, a plasma jet was generated in a closed system with controllable rates of air flow in and out of the system. The plasma discharge was recorded with a camera and analyzed by optical emission spectroscopy (OES). Polysulfone membrane surfaces were treated with various conditions of plasma discharge, and the induced membrane hydrophilicity was assessed from water contact angle (WCA) and surface energy (SE) measurements. Atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and WCA contour mapping were respectively employed to study surface roughness, functional groups, and WCA distribution on the treated membrane surfaces. The airflow had distinctly different effects on the plasma characteristics. The inflow rate condition affected the width of the plasma beam, and the outflow rate condition affected the diffusion of the plasma beam. Water flux was changed according to the plasma characteristic, and an air outflow rate of 6 L/min was the optimum condition for this experiment.

Ultrasonic enhanced liquid-liquid interfacial reaction for improving the synthesis of Iron-doped carbon dots (Fe-CDs) for achieving superior photocatalytic performance

The precise and controllable preparation of carbon nanomaterials under mild conditions poses a great challenge, especially for metal-catalysed multiphase preparation. This work proposes an efficient method that utilizing high-density ultrasound to enhance the liquid-liquid interfacial reaction system. Iron-doped carbon dots (Fe-CDs) are successfully synthesized in such a normal temperature and atmospheric-pressure reaction condition. It is shown that transient cavitation provides a high-temperature and high-pressure microenvironment for the preparation of Fe-CDs. Moreover, the size of the reactant droplets is reduced from 200.0 ± 17.3 μm to 8.1 ± 2.9 μm owing to the acoustic flow and cavitation effects, which increases the specific surface area of the two reacting phases and improves the mass transfer coefficient by more than 252.0 %. As a result, the yield increases by more than an order of magnitude (from 0.7 ± 0.1 % to 11.9 ± 0.2 %) and the Fe doping rate reaches 20.9 %. The photocatalytic oxidation conversion of 1,4-Dihydropyridine (1,4-DHP) using the obtained Fe-CDs is as high as 98.2 %. This research gives a new approach for the efficient and safe production of Fe-CDs, which is promising for industrial applications.

CO2-Based Stable Porous Metal-Organic Frameworks for CO2 Utilization.

The transformation of carbon dioxide (CO2) into functional materials has garnered considerable worldwide interest. Metal-organic frameworks (MOFs), as a distinctive class of materials, have made great contributions to CO2 capture and conversion. However, facile conversion of CO2 to stable porous MOFs for CO2 utilization remains unexplored. Herein, we present a facile methodology of using CO2 to synthesize stable zirconium-based MOFs. Two zirconium-based MOFs CO2-Zr-DEP and CO2-Zr-DEDP with face-centered cubic topology were obtained via a sequential desilylation-carboxylation-coordination reaction. The MOFs exhibit excellent crystallinity, as verified through powder X-ray diffraction and high-resolution transmission electron microscopy analyses. They also have notable porosity with high surface area (SBET up to 3688 m2 g-1) and good CO2 adsorption capacity (up to 12.5 wt %). The resulting MOFs have abundant alkyne functional moieties, confirmed through 13C cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectra. Leveraging the catalytic prowess of Ag(I) in diverse CO2-involved reactions, we incorporated Ag(I) into zirconium-based MOFs, capitalizing on their interactions with carbon-carbon π-bonds of alkynes, thereby forming a heterogeneous catalyst. This catalyst demonstrates outstanding efficiency in catalyzing the conversion of CO2 and propargylic alcohols into cyclic carbonates, achieving >99% yield at room temperature and atmospheric pressure conditions. Thus, this work provides a dual CO2 utilization strategy, encompassing the synthesis of CO2-based MOFs (20-24 wt % from CO2) and their subsequent application in CO2 capture and conversion processes. This approach significantly enhances overall CO2 utilization.

Study on the difference in subcooling flow boiling of materials in a vertical rectangular channel at a low flow rate

Alloy materials with excellent properties are widely used in different industrial fields. Conducting flow boiling studies on alloy surfaces will help explore their applications in flow boiling, especially in heat exchange equipment. Five alloys were selected, including 304SS, Inconel600, Monel400, Zr4 and FeCrAl. Bubble dynamics in a vertically upward-flowing rectangular channel were observed using a high-speed camera under the condition of atmospheric pressure, 400 kg·m^-2·s^-1 mass flowrate and 5 K inlet subcooling. Results show that roughness and wettability cannot individually define material-sensitive heat transfer coefficient (HTC) and critical heat flux (CHF). Thermal effusivity shows a linear relationship to HTC. Material-sensitive CHF seems to be a power-law function of the nondimensional parameter of the product of the maximum nucleation site density and the minimum bubble nucleation area.

A Numerical Study on the Influence of External Magnetic field on Hydrogen Electric Arc Flow

We present a 3D numerical model capable of simulating hydrogen electric arc. The numerical model couples the electromagnetic field with hydrogen plasma arc dynamics (flow and heat transfer). Electric arc operates under the conditions of atmospheric pressure using direct current (DC) in the presence of external magnetic field. It is found that arc instabilities emerge spontaneously near the cathode before propagating downwards along the arc jet. Also, spontaneous splitting into several arcs is observed before merging again into one arc. The horizontal magnetic field induces arc skewing and directional flow perpendicular to the applied magnetic field. However, the axial magnetic field induces a rotational flow and arc swirling.

Characterization of centrifugal compressors operating in FRIB’s sub-atmospheric compression system

Helium cryogenic systems operating below the normal boiling point (of 4.22 K) are required for many modern high-energy particle accelerators to achieve the necessary performance criteria. Temperatures below the normal boiling point are established by lowering saturation pressure below atmospheric conditions using vacuum equipment. FRIB operates a multi-stage string of cryogenic compressors (or ‘cold-compressors’) to achieve the sub-atmospheric pressures required (30 mbar) for the accelerator operating conditions of approximately 2 K. Housed within a vacuum insulated vessel (i.e., the sub-atmospheric cold box), the cold-compressor system re-pressurizes the helium from approximately 30 mbar to above atmospheric pressure condition before injecting the flow back into the helium refrigerator. Despite the implementation of cold-compressors in several existing large-scale cryogenic systems, openly available literature is insufficient to provide the information necessary for a general characterization of the performance and stability for these cold compressors. A one dimensional steady-state model to predict the performance of cryogenic centrifugal compressors has been developed. This model enables performance prediction by using optimally selected enthalpy loss correlations and basic impeller and diffuser geometrical data. The present work provides an initial comparison of the estimated performance of the individual and string of cryogenic centrifugal compressors to the operational / test data. With appropriate validation, the model is anticipated to allow assessment and prediction of optimal operational envelops that ensure stable and efficient operation at different operating conditions.

Thermal-hydraulic phenomena and heat removal performance of a passive containment cooling system according to exit loss coefficient

The natural circulation system has been widely studied for use in various applications because of its inherent advantage. However, it has a key weakness called flow instability that makes the system unstable. Through massive previous research, the mechanisms of flow instability were analyzed, but there was an ambiguous aspect related to the effect of experimental parameters on the phenomenon. Particularly, there has been no report on the heat transfer performance of the system when flow instability phenomena were present. In this study, thermal-hydraulic phenomena of a two-phase natural circulation system that functions as a passive containment cooling system (PCCS) was investigated according to experimental parameters, namely, the temperature boundary (120–158 °C) and exit loss coefficient (0–34.5) under atmospheric pressure conditions. The experimental results showed five different flow types in the loop. The flow modes that occurred by the interaction between flashing and boiling were classified by referring to the mass flow rate, void fraction, and visualization data. The system was more unstable when the temperature boundary conditions increased, but it was more stable when the exit loss coefficient increased. These results have only been confirmed in our research. The reason for the results is that the flow conditions are located on the boundary between Density Wave Oscillation I and the stable flow region, and that boundary does not have clear criteria. In addition, comparing the heat transfer performance of a system by heat rate can confirm the effect of flow instability on the thermal performance of the passive cooling system. As a result, the high exit loss coefficient stabilizes the system better than the low case and has similar heat removal performance.

Optimisation of cationic dye dyeing process of Porel fabrics using response surface methodology

AbstractPolyethylene terephthalate (PET) fibre, widely utilised across diverse industries, suffers from inherent drawbacks such as inadequate moisture absorption, limited hydrophilicity, and susceptibility to static electricity. To address these limitations, Porel fibre has emerged as a novel modified polyester fibre that incorporates flexible aliphatic polyester into its macromolecular chain. This innovative design not only overcomes the deficiencies of PET fibre but also enables it to be dyed using cationic dyes or disperse dyes under atmospheric pressure conditions. However, the investigation of the dyeing process of cationic dyes on Porel textiles remains relatively scarce. In this work, response surface methodology (RSM) was used to optimise the dyeing process of Porel fabrics with C.I. Basic Blue 162. The effects of dyeing temperature, dyeing time, and dye concentration on exhaustion percentage and colour strength (K/S value) were investigated using the Central Composite Design (CCD) method. The optimal dyeing process condition was as follows: a dyeing temperature of 96°C, a dyeing time of 51 min, a dye concentration of 3.6% owf, a dye solution pH value of 4–5, and a liquor ratio of 1:20. Under the optimal dyeing process conditions, the Porel fabrics achieved an exhaustion percentage of 96.2% and a K/S value of 36.0. The aforementioned efforts endow Porel fibre with high‐quality dyeing capabilities and broaden the application prospects of polyester textiles.

Nix/TiO2 catalysts for enhancing the selectivity of methylcyclohexane dehydrogenation

The dehydrogenation of methylcyclohexane (MCH) is a widely used hydrogen storage technology, but nowadays, precious metal catalysts such Pt are used for this reaction and non-precious metal catalysts suffer from low selectivity and instability problems. Two catalysts, Ni20/TiO2 and Ni20/Al2O3, were prepared through the improved co-precipitation method and their dehydrogenation performance of MCH was compared. It was found that the application of TiO2 carrier could significantly reduce the acidity of the catalysts, and the nickel particles could be stably dispersed on the carriers, which could effectively improve the selectivity of the target product (toluene). In addition, the influences of different Ni contents, reaction temperatures, and weight hourly space velocity (WHSV) on the performance of the catalysts were also evaluated, and the results showed that the catalyst with 17.16 % Ni content exhibited high activity with up to 86.48 % conversion of MCH and 96.51 % selectivity of toluene, under atmospheric pressure condition with the reaction temperature of 375 °C and WHSV of 1.9 h−1, while 96.03 % and only 42.64 %, respectively, for the Ni20/Al2O3 catalyst. In addition, the catalyst exhibited excellent anti-coking ability, indicating that it has a promising future for industrial applications.

Investigation on the rock-breaking performance of specially-shaped PDC cutter under confining pressure conditions

Cutter shape has a significant influence on the rock-breaking performance of drill bit. Compared with conventional Polycrystalline Diamond Compact (PDC) cutter, the emergence of specially-shaped PDC cutters (SSPCs) with different geometric shapes is of great benefit to solve the problems of low rate of penetration (ROP) and rock-breaking efficiency in deep hard and hot dry rock formations. However, the high confining pressure and high in-situ stress (HCHS) have a significant influence on the rock-breaking performance of PDC cutter which cannot be ignored. Given that the above facts, this paper selects five kinds of PDC cutters with different cutter shapes, and implements a series of cutting experiments of granite under confining pressure conditions (CPCs) and atmospheric pressure condition (APC) using a true triaxial rock cutting device. The influence of cutter profile on the rock-breaking performance of PDC cutter was studied from the perspective of cutting force, mechanical specific energy (MSE), cuttings, coarseness index (CI) and fractal dimension. The results show that the rock breaking under CPC is more difficult than that under APC, resulting in the increased cutting force and MSE. Moreover, the cuttings obtained under CPC are smaller in size and the cutting grooves are smoother. Cutter shape has a great influence on the rock-breaking efficiency of PDC cutter, the rock-breaking efficiency of axe-shaped cutter is higher, while that of stinger cutter is lower. Moreover, PDC cutters with different shapes have different sensitivities to confining pressure, and stinger cutter has the lowest sensitivity to confining pressure, in other words, confining pressure has little influence on the rock breaking process of stinger cutter. What is more, the distribution of cuttings is characterized by the fractal dimension and particle size distribution parameter from the perspective of cuttings morphology and size respectively, and they present completely opposite changing trends. The obtained results are of great significance to the optimization of cutter profile, the design of bit cutter arrangement and the drilling of deep formation.

Spontaneous Degradation of the "Forever Chemicals" Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) on Water Droplet Surfaces.

Because of their innate chemical stability, the ubiquitous perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been dubbed "forever chemicals" and have attracted considerable attention. However, their stability under environmental conditions has not been widely verified. Herein, perfluorooctanoic acid (PFOA), a widely used and detected PFAS, was found to be spontaneously degraded in aqueous microdroplets under room temperature and atmospheric pressure conditions. This unexpected fast degradation occurred via a unique multicycle redox reaction of PFOA with interfacial reactive species on the droplet surface. Similar degradation was observed for other PFASs. This study extends the current understanding of the environmental fate and chemistry of PFASs and provides insight into aid in the development of effective methods for removing PFASs.