Surface Layer Research Articles

Investigating the salinity distribution using field measurements in the semi-arid region of southern Ethiopia

This study investigated the distribution of salinity and sodicity in the irrigated areas of Abaya Chamo. Representative water and soil samples were collected from different soil depths (0–30 cm and 30–60 cm). Sodium absorption ratio (SAR), electrical conductivity (Ec), pH, exchange sodium, magnesium, calcium, and potassium cations, and exchange sodium percentage (ESP) of the sampled sites were analyzed for soil salinity classification and severity analysis. The spatial analysis revealed predominant strongly saline (72%) and sodic (71.1%) conditions in the surface layer (0–30 cm), intensifying very strongly saline (78.7%) and sodic (71.9%) conditions at 30–60 cm depth. Combined saline-sodic conditions dominated both layers, increasing from 91.2% at the surface to 97.1% in the deeper layer, indicating severe agricultural limitations. The results show that soil in the catchments of Lakes Abaya and Chamo suffer from different salinity and sodium content classes. Therefore, appropriate remedial measures based on soil salinity and sodium content should be developed to achieve better reclamation, agricultural production, and land sustainability.

The Laser Processing of the Stainless-Steel Surface Layer of a Heat Exchanger Membrane in Order to Enhance Its Heat Transfer Coefficient

Research on temperature regulation is essential for ensuring thermal comfort and optimizing machine performance. Effective cooling systems are critical in industrial processes and everyday electronic devices in order to prevent overheating. Laser-modified heat exchangers can enhance heat dissipation without increasing weight, addressing the need for energy-efficient solutions in the market. The main aim of this experimental research was to establish an efficient method for altering the surface layer of AISI 316L stainless steel with laser pulses and to determine the effectiveness of the laser alterations to the surface layer in the context of intensifying the convective heat transfer. A series of laser-texturing processes was performed on the surface layer of AISI 316L steel using a Nd: YAG pulse laser. Selected samples were subjected to a series of measurements using a recuperator-type heat exchanger. Based on the measurements’ results, the heat transfer coefficients, α, obtained from the modified surfaces were determined. The results were compared with other data from the existing literature and those obtained from unmodified reference samples. The intensification of the convective heat transfer was achieved for 43% of the modifications conducted with a pulsed laser. The highest observed average increase in the heat transfer coefficient, α, was 16.53%. However, the effective intensification of the convective heat transfer, in some cases, was only observed for a certain range of temperatures or flow dynamics parameters.

How Amino Acids Intercalate in CaFe Layered Double Hydroxides: A Combined RIXS and NEXAFS Study.

Two-dimensional layered double hydroxides (LDHs) are ideal candidates for a large number of (bio)catalytic applications due to their flexible composition and easy to tailor properties. Functionality can be achieved by intercalation of amino acids (as the basic units of peptides and proteins). To gain insight on the functionality, we apply resonant inelastic soft x-ray scattering and near edge x-ray absorption fine structure spectroscopy to CaFe LDH in its pristine form as well as intercalated with the amino acids proline and cysteine to probe the electronic structure and its changes upon intercalation. We observe the activation of pristine LDH defect states by soft x-rays and their passivation by the intercalated molecules. The nitrogen at the amino amino is found to form C=NH+ bonds and thus generating positive charge at the amino group, moving it away from the positively charged LDH layers. The carboxyl group in cysteine is deprotonated and thus in zwitterionic state after intercalation. This negative charge is used to compensate the positive layer charge. For intercalated proline the spectral signature of a protonated carboxyl group is observed, however, we find orbital overlap to defects at the layer surfaces indicating strong interaction with the carboxyl groups.

Release of PAHs from reclaimed asphalt mixtures into the water environment after passivation by cold in-place recycling technology.

The paper deals with an analysis of the amount of 16 polycyclic aromatic hydrocarbons (PAHs (Polycyclic aromatic hydrocarbons-16 defined by US EPA.)) released from reclaimed asphalt mixtures used in base layers of road surfaces and in binder layers in road construction using cold in-place recycling. For the ten samples tested, the sum of 16 PAHs was determined directly for the crushed asphalt mixture and for its 24-h leachate. The crushed asphalt samples were used to make cylindrical asphalt specimens of the cold recycling mixture. The asphalt specimens were prepared to simulate as realistically as possible the use of the mixtures in road reconstructions implementing the cold in-place recycling technology, which should ensure the passivation of PAHs. The asphalt specimens were subjected to a dynamic leaching test under laboratory conditions with regular replacement of the leaching liquid. The results showed that the concentration of PAHs released into the water environment from the test specimens (passivated material) was approximately 40-50% lower than the amount of PAHs released from the asphalt mixtures in the 24-h leaching test. When compared to the input PAH concentrations in the asphalt mixtures (36-1323mg.kg-1), on average, only 0.15% of PAHs is released from the passivated material. Dynamic leaching test has shown that the wrapping of the original asphalt mixture with a new binder and its subsequent compaction leads to the preservation of PAHs in the original material at such a level that their total concentrations are reduced by two orders of magnitude.

Research on the optimal laser preparation process parameters of groove-shaped micro-texture on the mill roll surface

Laser micro-texture preparation technology significantly excels in micro-texture processing, yet there has been scant reported research on utilizing this technology for micro-texture processing and texture morphology control on the surface of wheat mill rolls. The aim was to ascertain the ideal laser preparation process parameters for the creation of groove-shaped micro-textures on the surface of the chilled alloy cast iron, serving as the surface layer material of the wheat mill roll. An experiment was conducted using a nanosecond pulsed fiber laser to explore the impact of laser power, scanning times, scanning velocity, and pulse frequency on the morphology and dimensions of the groove-shaped micro-textures. It was found that with laser power set at 7 W, 15 scanning times, a pulse frequency of 35 kHz, and a scanning speed of 500 mm/s, the desired microgroove can be successfully fabricated on the surface of the mill roll. The findings of this study offer insights for the surface modification of critical components in grain and oil machinery and equipment through the application of laser micro-texturing technology.

Single Particle Dynamics at the Free Surface of Imidazolium-Based Ionic Liquids.

In this work, we carry out a systematic computer simulation investigation of the single particle dynamics at the free surface of imidazolium-based room temperature ionic liquids by applying intrinsic surface analysis. Besides assessing the effect of the potential model and temperature, we focus in particular on the effect of changing the anion type, and, hence, their shape and size. Further, we also address the role of the length of the cation alkyl chains, known to protrude into the vapor phase, on the surface dynamics of the ions. We observe that the surface dynamics of ionic liquids, being dominated by strong electrostatic interactions, is about 2 orders of magnitude slower than that for common molecular liquids. Furthermore, the free energy driving force for exposing apolar chains to the vapor phase "pins" the cations at the surface layer for much longer than anions, allowing them to perform noticeable lateral diffusion at the liquid surface during their stay there. On the other hand, anions, accumulated in the second layer beneath the liquid surface, stay considerably longer here than in the surface layer. The ratio of the mean surface residence time of the cations and anions depends on the relative size of the two ions: larger size asymmetry typically corresponds to larger values of this ratio. We also find, in a clear contrast with the bulk liquid phase behavior, that anions typically diffuse faster at the liquid surface than cations. Finally, our results show that the surface dynamics of the ions is largely determined by the apolar layer of the cation alkyl chains at the liquid surface, as in the absence of such a layer, cations and anions are found to behave similarly with respect to their single particle dynamics.

Intensification of sediment flux by wind-induced residual currents in a heavily contaminated, micro-tidal bay.

Wind-induced currents are the major forces responsible for sediment resuspension and transport in micro-tidal bays. To reveal the impact of wind-induced residual currents on the sediment flux, in-situ measurements using acoustic Doppler current profilers (ADCPs) were conducted at two mooring stations in a heavily contaminated, micro-tidal Onsan Bay. During the mooring period, the suspended sediments at both stations were transported seaward (landward) at the surface (bottom) layer mainly through the residual currents (mean-flow flux Fmean: > 70% of the total flux). Under northerly winds, the landward bottom residual currents at both stations strengthened, resulting in the "intensification" of landward Fmean. This suggests that the northerly winds might be a primary factor intensifying the landward sediment fluxes, potentially resulting in the increased sediment deposition into the bay. The findings provide insights into managing sedimentation in contaminated coastal bays and highlight the importance of wind effects on sediment transport in micro-tidal bays.

Structure and properties of pure copper surface layers after reverse-polarity plasma cutting

Structure and properties of pure copper surface layers after reverse-polarity plasma cutting

Lattice Oxygen Redox Dynamics in Zeolite-Encapsulated CsPbBr3 Perovskite OER Electrocatalysts.

Understanding the oxygen evolution reaction (OER) mechanism is pivotal for improving the overall efficiency of water electrolysis. Despite methylammonium lead halide perovskites (MAPbX3) have shown promising OER performance due to their soft-lattice nature that allows lattice-oxygen oxidation of active α-PbO2 layer surface, the role of A-site MA or X-site elements in the electrochemical reconstruction and OER mechanisms has yet to be explored. Here, it is demonstrated that the OER mechanism of perovskite@zeolite composites is intrinsically dominated by the A-site group of lead-halide perovskites, while the type of X-site halogen is crucial for the reconstruction kinetics of the composites. Using CsPbBrxI3- x@AlPO-5 (x = 0, 1, 2, 3) as a model OER catalyst, it is found that the CsPbBr3@AlPO-5 behaves oxygen-intercalation pseudocapacitance during surface restructuring due to absence of halogen-ion migration and phase separation in the CsPbBr3, achieving a larger diffusion rate of OH- within the core-shell structure. Moreover, distinct from the single-metal-site mechanism of MAPbBr3@AlPO-5, experimental and theoretical investigations reveal that the soft lattice nature of CsPbBr3 triggers the oxygen-vacancy-site mechanism via the CsPbBr3/α-PbO2 interface, resulting in excellent OER performance. Owing to the variety and easy tailoring of lead-halide perovskite compositions, these findings pave a way for the development of novel perovskite@zeolite type catalysts for efficient oxygen electrocatalysis.

Influence of Laser Shock Peening on the Bobbin Tool Friction Stir-Welded AW6060 Alloy.

Friction stir welding (FSW) is a solid-state welding process that uses a rotating tool to soften and stir the base metal, thereby joining it. A special type of tool that has attracted the interest of researchers is the so-called bobbin tool (BTFSW), which, unlike conventional tools with one shoulder, features two shoulders that envelop the base metal from both the top and bottom sides. As a result, significant tensile stresses develop on both sides of the weld, caused by the action of both tool shoulders. In this paper, this issue was addressed by applying laser shock peening (LSP), aiming to introduce compressive stresses, which can be useful as a post-processing technique for BTFSW on both weld sides. It was found that this process completely alters residual stresses in the treated area, from tensile to compressive, through shock waves that impart plastic deformation in the surface layer. It was shown that the LSP effect is more pronounced as the accumulated energy is higher. As a consequence, the microhardness values were significantly increased in the surface and subsurface layers, reaching a maximum depth of 480 to 780 µm for the lowest and highest accumulated laser energy, respectively, while surface roughness increased. While increasing compressive stresses and microhardness in the surface layer is beneficial from the point of view of fatigue resistance, increased roughness has a detrimental effect. Accumulated energy was hereby shown to have a higher effect compared to the maximal energy applied to the specimens.

Reverse osmosis membrane fouling caused by typical surfactants in the integrated circuit industry: Fouling mechanism and control strategies.

In the integrated circuit manufacturing process, reverse osmosis (RO) membranes are widely used for wastewater reclamation. However, fouling by typical surfactants significantly reduces membrane efficiency and lifespan. This study investigates the fouling mechanisms of typical surfactants-cetyl trimethyl ammonium bromide (CTAB, cationic), sodium dodecyl sulfate (SDS, anionic), and polyoxyethylene octyl phenyl ether (TX, nonionic)-on RO membranes. Quartz crystal microbalance analysis results show that CTAB and TX exhibit significantly stronger adhesion to RO membranes than SDS. The order of adsorption mass on the membrane surface is CTAB > TX > SDS, with CTAB causing the most severe fouling. Molecular dynamics (MD) simulations indicate that unclustered CTAB molecules contribute to severe fouling by inserting into the membrane surface. As surfactant concentration increases, clustered CTAB is less likely to enter the membrane's surface layer. A comparison of oxidative technologies-continuous dual-wavelength ultraviolet (VUV/UV), intermittent VUV/UV, and intermittent VUV/UV with chlorine, ozone alone, chlorine alone, and ozone combined with chlorine (ozone/chlorine)- reveals that pre-treating surfactants with ozone/chlorine (simultaneous dosing at 10 mg/L each) before membrane filtration effectively controls fouling. After 30 min of treatment, 29 % of CTAB and 86 % of TX were degraded, respectively. Ozone/chlorine oxidation significantly alleviates membrane fouling, increasing the normalized steady-state permeate flux (Jpss) of CTAB and TX by 245 % and 151 %, respectively. The extended Derjaguin-Landau-Verwey-Overbeek theory calculations and MD simulations show that oxidation weakens the adhesion of CTAB and TX to RO membranes, reducing fouling. Ozone/chlorine treatment also effectively mitigates membrane fouling in actual wastewater from the electronics industry. Post-oxidation, the flux ratio (J/J0) increased from 0.28 to 0.52, resulting in a 116.7 % improvement in the Jpss. This study combines experimental data, theoretical calculations, and MD simulations, highlighting the significance of molecular clustering in surfactant-induced fouling before and after oxidation.

Historical reconstruction of PFAS discharge into the Cooum River - Before and after the great Chennai flood in 2015.

Despite widespread research on PFAS, less is known in developing countries like India. PFAS levels in sediment core samples from the Cooum River of Chennai City (India) in 2014 and 2016 were estimated to evaluate the effect of the major flood event in 2015. Among 22 target PFAS in this study, 11 and 12 of them were detected in the 2014 and 2016 samples, respectively. Total PFAS concentrations were 70-1402pg/g dw (average: 503pg/g dw) in 2014 and 188-3629pg/g dw (average: 1103pg/g dw) in 2016. PFBS, N-EtFOSA, and 6:2 FTUCA, which were not detected in any layers in 2014, exhibited a dramatic increase in DFs in 2016, showing 50%, 50%, and 88%, respectively. Hierarchical cluster analysis revealed that the subsurface to bottom sediment layers for both years were similar in PFAS pollution, suggesting originating from the same sources. In contrast, the PFAS pollution in the surface layers in 2014 (0-18cm) was statistically different from that in 2016 (0-23cm), likely due to significant disturbance of the sediment profile caused by a major flood event in 2015. Correlation matrix analysis indicates the industrial uses of C8-based PFAS and shorter-chain alternatives near the studied area can be the major source of PFAS in the sediment near the studied area. The present study evidenced the ongoing production and use of PFAS in India, warranting and recommending further environmental monitoring of PFAS. To our knowledge, this is the first report about the effect of a major flood event in India on historical reconstruction of PFAS dynamics in Cooum river.

Formation of Directed Wave Fields on Surface of Deformable Layer Under Impulse Load

Formation of Directed Wave Fields on Surface of Deformable Layer Under Impulse Load

In Situ Growth of Metal-Organic Layer on Polyoxometalate-etching Cu2O to Boost CO2 Reduction with High Stability.

Low-cost Cu2O with a suitable band gap holds great potential for solar utilization. However severe photocorrosion and weak CO2 capture capability have significantly hindered their application in artificial photosynthesis. Herein, polyoxometalate (POM)-etching and in situ growth of metal-organic framework (MOF) can simultaneously incorporate electron-sponge and HKUST protective layer into Cu2O. The resulting ternary composites Cu2O@POM@HKUST-n (POM = PMo12O40 and PW12O40) with dual hetero-interfaces can efficiently convert CO2 to HCOOH with 5226 µmol g-1 yield, over 5 and 55 times higher than that of Cu2O (1010 µmol g-1) and Cu2O@HKUST (95.02 µmol g-1). In situ XPS and DFT studies reveal that Cu mainly existed in the form of Cu2O and Cu-MOF, while a unique Cux+ (1< x ≤2) surface layer formed upon the Cu2O matrix surrounding POMs for CO2 absorption and activation. Systematic investigations demonstrate that the electron-sponge can efficiently capture electrons from excited Cu2O to promote the generation of a Cux+ surface layer, while the closely surface-coating metal-organic layer can act as protective layer and CO2 adsorbent. This dual function concurrently contributes to promote photocatalysis and prevent Cu2O degradation. Remarkably, the ternary composites exhibit much enhanced photochemical stability and can be used for over 60 h without noticeable activity loss.

Hardening of stainless steel surface layers by non-vacuum electron beam cladding

Hardening of stainless steel surface layers by non-vacuum electron beam cladding

Multifunctional Siloxane Additive Enabling Ultrahigh-Nickel Lithium Battery with Long Cycle Life at 30 and 60°C.

Ultrahigh-nickel layered oxide cathodes (≥90% nickel) possess exceptionally high discharge capacities, which can significantly improve the energy density of lithium-ion batteries and alleviate the driving range anxiety of electric vehicles. However, the high interfacial reactivity of ultrahigh-nickel cathodes, especially the detrimental side reactions with harmful acidic species like HF in the electrolyte, can deteriorate the battery interface and reduce the cycle life, hindering their practical application. In this study, 3-isocyanatopropyltrimethoxysilane (PTTS-NCO) is introduced as the electrolyte additive, which can effectively scavenge the harmful acidic species in the electrolyte and form a protective surface layer at the electrode/electrolyte interface, thereby enhancing the electrochemical performance of the battery (NCM90/Li). Specifically, the most effective battery based on the PTTS-NCO additive can maintain 70.3% of its capacity after 500 cycles at 30°C. Even under a high cathode loading (3.0mAhcm-2), it can retain 86.2% of its capacity after 300 cycles, far exceeding the base battery. Furthermore, it exhibits good performance under the harsh high-temperature environment, maintaining over 70.3% capacity retention in the NCM90/Li battery up to 350 cycles at 60°C. This work demonstrates the great potential of multifunctional siloxane additive in lithium batteries based on ultrahigh-nickel cathode.

Responses of fungal communities at different soil depths to grazing intensity in a desert steppe.

Grazing can alter the physicochemical properties of soil and quickly influence the composition of microbial communities. However, the effects of grazing intensity on fungal community composition in different soil depth remain unclear. On the Inner Mongolia Plateau, we studied the effects of grazing intensity treatments including no grazing (NG), light grazing (LG), moderate grazing (MG), heavy grazing (HG), and over grazing (OG) on the physicochemical properties and fungal community composition of surface (0-20 cm) and subsurface (20-40 cm) soil layers. The α-diversity of fungi in subsurface soil decreased under the influence of grazing. The relative abundance of Ascomycota in the subsoil was higher than that in the topsoil, while the situation of Basidiomycota was the opposite. This was caused by the differences in the soil carbon (C) environment for the growth of oligotrophic and copiotrophic fungi. In the subsoil, grazing affected nutrient contents such as soil organic matter (SOM) and total nitrogen (TN), resulting in significantly lower relative abundance of Ortierellomycota under LG, HG, and OG than in the NG. HG showed much higher relative abundance of Glomeromycota. Results of a multiple regression tree (MRT) analysis revealed that TN and nitrate nitrogen affected the fungal α-diversity in top- and subsoils, respectively; the main driving factor regulating fungal community changes was soil water content (SWC) in the topsoil, while it was ammonium nitrogen and nitrate nitrogen in the subsoil. The results of our study indicate that grazing changes the soil environment by changing TN, SWC, nitrate nitrogen, ammonium nitrogen, and affects the diversity and community structure of soil fungi. This provides empirical support for coping with the impact of grazing on soil microbiomes in desert steppes.

Etching Ceramic Samples with Fast Argon Atoms

A new approach to stripping surface layers from ceramics with fast atoms is proposed. The existing beam sources do not allow for a stripping rate of more than a few µm/h to be achieved. Usually, an increase in the etching rate is associated with growing flux density and energy of fast atoms, which can heat the parts of the beam source up to an inadmissible temperature. In the present work, the etching rate was significantly increased at permanent flux density and energy due to an increase in the angle of incidence of fast atoms on the product surface. An increase in the angle of incidence from zero to 80° resulted not only in an increase in the etching rate by several times but also in simultaneous polishing of the surface to a high finishing class.

A Novel Protocol for Reconstructing Depositional Histories of Anthropogenic, Sedimentary Records: the Case of the Holocene-Deep Kirkhellaren Cave Deposits in Coastal Arctic Norway

ABSTRACT This paper presents a novel protocol for reconstructing formation processes of archaeological depositional sequences, applied to Holocene-wide cave deposits located on a remote coastal island in Arctic Norway as a case study. Extensive GPR surveying is correlated with geochemical analysis and in situ environmental deposit monitoring for sedimentary fingerprinting and forecasting of future preservation of organic remains. Subsurface deposit characteristics are integrated with a high-precision, laser-based 3D-reconstruction of the cave, enabling triangulation with historic photos and local informant knowledge that facilitate modeling and quantification of erosional history. The results showcase detrimental depletion of critical organic heritage, accelerated by the removal of protective surface layers after the a.d. 1930s. Critically, subsurface deposits are trending towards overshooting a threshold for accelerated in situ degradation. The results act as a direct validation of the methodology. Measures for future protection of similar archaeological deposits are discussed and an outline of the general applicability of the protocol.

Distribution of microbial taxa and genes degrading halogenated organic pollutants in the mangroves.

Anthropogenic activities have led to serious contamination of halogenated organic pollutants (HOPs), such as PCBs, PBDEs, and HBCDs, in the mangrove wetland. Biodegradation of HOPs is generally driven by environmental microorganisms harboring dehalogenase genes. However, little is known if HOPs can affect the distributions of HOPs-degrading bacteria and dehalogenase genes in the mangrove wetlands. Historical data suggested that HOPs contamination has been persistent and even deteriorated in the mangrove wetlands in China. We found that the organohalides-respiring bacteria Dehalococcoidia and reductive dehalogenase genes were more prevalent in the subsurface layer sediments (20-30 cm depth; 1.935-9.876 % relative abundance; 71-286 contigs) than the surface layer (0-5 cm depth; 0.174-2.020 % relative abundance; 7-130 contigs). While the genes of haloacid and haloalkane dehalogenases were more abundant in the surface layer (30-100 and 18-138 contigs) than the subsurface layer (22-56 and 50-101 contigs). The abundance of HOPs-degrading genes of reductive dehalogenase, haloacid dehalogenases, AtzA, AtzB, TrzA, TrzN, PcpB, were determined by GeoChip 5.0. Their total abundance ranged from 444.760 to 880.909. Their distributions were mainly associated with the contamination levels of HOPs and strength of anthropogenic activities around the mangrove wetlands. Therefore, the distribution of bacterial taxa and genes involved in HOPs degradation was related to the depth of sediments and affected by the selective stress from HOPs.