Scanning Electron Microscope Imagery Research Articles

Effect of spinning solution concentration of high DP and high S-diad PVA polymer on the structural properties of high-strength and high-modulus PVA fiber

To address the challenge of enhancing the mechanical properties of polyvinyl alcohol (PVA) fiber, constrained by the spinning process limitations, this study introduces a PVA/DMSO spinning solution. The solution, with concentrations ranging from 21.0 wt%, utilized PVA polymer (DP of 7499 and S-diad of 53.7 %) as the raw material. This approach facilitated the production of high-strength and high-modulus PVA fibers through a consistent dry-wet spinning method. The viscosity of the spinning solution was determined using a viscometer, while the PVA fibers underwent comprehensive characterization through various testing methodologies. Fourier Transform Infrared (FTIR) spectroscopy analysis revealed an initial increase followed by a decrease in the hydrogen bonding within PVA fibers as the spinning solution concentration increased. Scanning Electron Microscope (SEM) imagery indicated that the surfaces of the PVA fibers were smooth. Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and X-Ray Diffraction (XRD) analyses demonstrated that the melting temperature, thermal decomposition temperature, and crystallinity of the PVA fibers exhibited a similar trend of initial increase and subsequent decrease with rising concentrations of the spinning solution. In addition, mechanical tester indicated that when spinning solution concentration was 22.5 wt% the PVA fibers process best mechanical property, and the breaking strength and elastic modulus reached 15.02 ± 0.5 cN/dtex and 357.12 ± 9.4 cN/dtex, respectively.

An experimental investigation on feasibility of submerged ultrasonic spot welding of thermoplastics

Although conventional methods such as mechanical fastening, adhesive bonding and hot air welding have proven effective in dry conditions, they exhibit diminished efficacy in submerged environments. Hence, a thermoplastic welding technique with minimal dependence on surrounding media is essential. Ultrasonic spot welding (USW) represents a promising approach to thermoplastic joining, offering high efficiency and low operating costs. In this study, we investigate the efficacy of water-submerged ultrasonic spot welding (S-USW) for joining amorphous polyvinyl chloride (PVC) to PVC and semi-crystalline polypropylene (PP) to PP under submerged conditions. Our experimental results show that S-USW leads to a remarkable 39% and 21% increase in lap-shear strength for PVC/PVC and PP/PP welds, respectively, as compared to traditional USW techniques. We corroborate these findings with additional metrics such as Shore-D hardness tests, optical microscopy and scanning electron microscopy imagery, which collectively confirm the improved efficacy of S-USW over USW for joining PVC and PP.

Optoelectronic and Dielectric Properties of Tenorite CuO Thin Films Sprayed at Various Molar Concentrations

The work in hand presents the elaboration of CuO thin films using a home-made spray pyrolysis technique at room atmosphere. The films were synthesized on preheated glass substrate at 450 °C. The source solution molarity was varied from 0.025 to 0.1 mol/L. The films were characterized by employing X-Ray Diffraction technique, UV-Vis-NIR spectrophotometry, Scanning Electron Microscope imagery, Energy Dispersive Spectroscopy, and four-points probe techniques. The X-ray diffraction analysis confirmed that all films are polycrystalline with a preferred orientation along the plane (−111) of the monoclinic crystal structure phase of tenorite (CuO). The SEM images showed a homogeneous and smooth surface. Crystallinity and grain size were improved. The rise of solution concentration induced a reduction of transmittance and reflectance in the visible region. The energy gap, the absorption coefficient, the extinction coefficient, refractive index, dielectric constant (ԑr and ԑi) and loss energy were estimated from transmittance and reflectance data. The gap energy decreases from 2.72 to 2.56 eV. The film deposited for 0.025 mol/L exhibits the highest real part of the dielectric constant (ԑr ~ 17). The film resistivity which is in order of 102 Ω cm decreases with the increase of molar concentration. The estimated dielectric constant indicated that the resulting CuO thin films could be used as dielectric layers for optoelectronic devices working in Vis-NIR region of radiation. Furthermore, the relatively high band gap, high absorption coefficient and high conductivity of the film obtained at 0.075 mol/L, make them good candidates as absorption layers in solar cells applications.

Comparative analysis of bamboo-based (<i>Bambusa vulgaris</i>) activated carbon produced through trioxonitrate (V) acid and potassium hydroxide

ABSTRACT: Activated carbon (AC) is one of the numerous cost-effective inputs for treating wastewater in an efficient and cost-effective manner, and several materials have been used to produce AC with diverse results. One such material with a large potential is African Bamboo (Bambusa vulgaris), especially due to its availability. In this study, bamboo was carbonized and then activated using trioxonitrate (V) acid (HNO3) and potassium hydroxide (KOH) as activating agents. The AC was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) technologies at 50 μm, 80 μm, 100 μm, and 200 μm magnification. The SEM imagery results at 50 μm and 1500x magnification showed that the AC produced using KOH had the largest and most well-developed pore spaces hence maximum capacity to absorb contaminants compared to HNO3's AC and inactivated carbonated charcoal. The FTIR spectra peak analysis results also confirmed that KOH's AC had the highest number of functional groups on its surface and, therefore, enhanced its adsorption capacity.

The influence of basalt fiber filament length on shear strength development of chemically stabilized soils for ground improvement

In recent years, adding fiber reinforcements into chemically stabilized weak soils to resolve brittleness at the post-peak shear strength state is becoming an increasingly popular research area. However, there is little to no research investigating the shear developments initiated through the hybridization of ground improvement techniques using high-strength basalt fibers and sustainable chemical stabilizers such as rice husk ash (RHA). This study investigated how different basalt fiber filament lengths can reinforce and consequently influence shear response in such chemically stabilized soils. A series of triaxial compression tests, scanning electron microscopy (SEM), and X-ray powder diffraction (XRD), considering curing periods, were carried out on fiber-reinforced and unreinforced chemically stabilized specimens containing: weak clay soil, varied lengths of basalt fibers filaments, RHA, and cement in their specified combinations. Based on the results, an increment in basalt fiber filaments length significantly increased the deviatoric stresses, increasing cohesion and angle of internal friction by 81% and 63%, respectively. SEM imagery showed a highly reinforced soil composite at the microstructural level. At the same time, XRD analysis justified the presence of solid calcium aluminosilicate hydrate bonds, a product of pozzolanic activity. The fiber reinforcing mechanism through interfacial contacts between basalt fiber filaments and the new stabilized soil composite was investigated and validated to form a new construction material for use as a base course during ground improvement.

Parameters, Properties, and Process: Conditional Neural Generation of Realistic SEM Imagery Toward ML-Assisted Advanced Manufacturing

The research and development cycle of advanced manufacturing processes traditionally requires a large investment of time and resources. Experiments can be expensive and are hence conducted on relatively small scales. This poses problems for typically data-hungry machine learning tools which could otherwise expedite the development cycle. We build upon prior work by applying conditional generative adversarial networks (GANs) to scanning electron microscope (SEM) imagery from an emerging advanced manufacturing process, shear-assisted processing and extrusion (ShAPE). We generate realistic images conditioned on temper and either experimental parameters or material properties. In doing so, we are able to integrate machine learning into the development cycle, by allowing a user to immediately visualize the microstructure that would arise from particular process parameters or properties. This work forms a technical backbone for a fundamentally new approach for understanding manufacturing processes in the absence of first-principle models. By characterizing microstructure from a topological perspective, we are able to evaluate our models’ ability to capture the breadth and diversity of experimental scanning electron microscope (SEM) samples. Our method is successful in capturing the visual and general microstructural features arising from the considered process, with analysis highlighting directions to further improve the topological realism of our synthetic imagery.

Fractal analysis of pore structures in transitional shale gas reservoirs in the Linxing area, Ordos Basin

Studying complex pore structures and fractal characteristics of gas shale provides significant guidance for clarifying the mechanism of shale gas accumulation and realizing its efficient development. In this paper, 12 samples of Taiyuan Formation shale are used as the research object, and the fractal theory is combined with mercury intrusion porosimetry and N2 adsorption technology to innovatively solve the problem of splicing point selection, which can reveal the full-scale pore size distribution of shale. The results demonstrate that the most common types of pores in the chosen samples are pores between or within clay minerals, micropores and mesopores inside organic matter, and microfractures, based on scanning electron microscopy imagery analyses. The pores of shale samples have fractal geometries. The fractal dimension DM1 values in the mercury intrusion porosimetry experiments range from 2.3060 to 2.6528. Two fractal dimensions, DN1 and DN2, may be obtained using the Frenkel-Halsey-Hill fractal method. DN1 values vary from 2.4780 to 2.6387, whereas DN2 values range from 2.5239 to 2.7388. Most macropores in shale samples have a size range of about 0.2 mm, with a wide pore size distribution, and the largest peak of the micro-mesopore volume is generally about 50 nm. The fractal dimension correlates positively with the corresponding pore volume, although the correlation between volume and composition is weak. The relatively strong correlation between fractals and the basic compositions of shale proves the fractal theory’s relevance in defining pore inhomogeneity. This study would contribute to the development of a fractal perspective-based method for pore splicing while also expanding our understanding of pore morphology and structure in transitional shale.

Diatom influence on the production characteristics of hydrate-bearing sediments: Examples from Ulleung Basin, offshore South Korea

The Ulleung Basin Gas Hydrate field expeditions in 2007 (UBGH1) and 2010 (UBGH2) sought to assess the Basin's gas hydrate resource potential. Coring operations in both expeditions recovered evidence of gas hydrate, primarily as fracture-filling (or vein type) morphologies in mainly silt-sized, fine-grained sediment, but also as pore-occupying hydrate in the coarser-grained layers of interbedded sand and fine-grained systems. A commonality across many of these occurrences is the presence of diatoms in the fine-grained sediment. Here we tested fine-grained sediment (median grain size <12.5 μm) associated with hydrate occurrences at four UBGH2 sites (UBGH2-2-2, UBGH2-3, UBGH2-6 and UBGH2-11) to investigate potential impacts of diatoms on efforts to extract methane from hydrate, or to tap hydrocarbon reservoirs beneath hydrate-bearing sediment. Two key considerations are: the extent to which diatoms control sediment mechanical properties, and the extent to which pore-water freshening, which occurs as gas hydrate breaks down during resource extraction, alters the diatom control on sediment mechanical properties. We conducted experiments to measure sediment index properties, sedimentation behavior and compressibility to address these considerations. We relied on scanning electron microscope (SEM) imagery and X-ray powder diffraction (XRD) to characterize the sediment mineralogy. Our high-level findings are that at the ∼20–45% (by volume) diatom concentrations observed at these UBGH2 sites, sediment compressibility increases with diatom content, but diatoms only appear to increase porosity and permeability at the highest diatom concentration (∼45%). Our measurements suggest in situ compression indices of 0.35–0.55 and permeabilities on the order of 0.01milliDarcies (1 × 10−17 m2) can be anticipated at these sites. Importantly, these properties are not expected to vary significantly upon pore water freshening that accompanies gas hydrate dissociation during production.

Bacterial Cadmium-Immobilization Activity Measured by Isothermal Microcalorimetry in Cacao-Growing Soils From Colombia

In cacao farms, the presence of cadmium (Cd) is a major issue for commercialization, particularly for countries such as Colombia. Cadmium-tolerant bacteria (CdtB) are an important functional group of microorganisms with a potential for bioremediation strategies. Cd immobilization activity by CdtB can be accurately measured by isothermal microcalorimetry (IMC). In this study, the metabolic capacity of an entire CdtB community in cacao farm soils from three cacao-producing districts of Colombia, with and without the addition of Cd was measured using IMC. The differences between the observed peaks in metabolic activity related to Cd immobilization were analysed to determine whether activation of CdtB populations occurred when Cd content was increased. The thermograms from Santander soil samples have a major metabolic activity of the CdtB community compared to peaks of maximal heat-flow in the samples from Antioquia and Arauca. IMC showed differences in Cd immobilization ratios of the soil samples of 0.11–0.30 mg kg−1 h−1 at 25°C over 12 days of thermal monitoring. Furthermore, the amplicons of cadA and smt genes from the soil samples allow elucidation of possible metabolic mechanisms used by CdtB soil populations. The gene amplification confirmed the existence of CdtB populations related to both bioweathering and biochelating metabolic capacities. Scanning electron microscope (SEM) images supported the existence of otavite biologically induced by CdtB naturally. A Pearson correlation analysis was made between kinetical growth parameters and thermodynamic data. Besides, a PCA was performed between CdtB cadA gene copies, soil pH and SOM indicating the effect of CdtB in Cd translocation. Thus, it is concluded that the combination of Cd immobilization ratios obtained using isothermal microcalorimetry, the molecular basis of metabolic immobilization, and SEM imagery could act as a useful toolkit to identify CdtB populations for bioremediation strategies in contaminated cacao farms. The research importance of this study is the use of combined tools for quantitative IMC measurements to identify and assess Cd metabolic capacities of CdtB populations in soil, in situ, as a new proxy for CdtB assessment in cacao-growing soils.

Scanning electron microscopy (SEM) and macroscopic analysis of immature human permanent molar immersion in hydrochloric acid (HCL, 38%)

Recent literature indicates the destruction of human remains using hydrochloric acid (HCl, 38%) is often attempted to obscure the identity of victims or as a disposal method. Dentition are informative in an investigation where acid is used as a means of body disposal, as teeth are more likely to survive intact. Importantly, researchers studying acid immersion have not observed immature dentition, nor have they analyzed immature acid-treated teeth using scanning electron microscopy (SEM). This study analyzes the effects of HCl on immature human molars, with two goals: understanding the timing and nature of physical changes to immature molars caused by HCl immersion, and aiding in the identification and age determination of dental tissues partially or nearly completely destroyed using HCl.Our results indicated that immature human molars immersed in HCl follow a pattern of physical changes and decrease in weight as they dissolve similar to mature molars, although the timing of dissolution is affected by their smaller size and incompletely developed roots in a predictable way. With less root material present and an open root tip, we observed that HCl can more quickly penetrate the pulp cavity of immature molars. The mobile SEM images indicated immature and mature molars immersed in HCl exhibit similar changes at the microscopic level. Immature molars treated with HCl for over 18 h exhibited cracking features similar to those visible on mature molars that were difficult to differentiate from similar features on untreated teeth (both mature and immature) when images were taken at 3,000x or less. The appearance of features such as peeling layers and lamination at high magnification (6000x) were visible on both acid-treated mature and immature molars, but were not visible on untreated molars at the same level of magnification.By observing changes in the enamel and pulp cavity, it was possible to determine whether third molars were immature until approximately 18 h immersed in acid. At 42 h, it was no longer possible to determine whether the molars were immature. However, they were still easily identifiable as human teeth. In situations where teeth may no longer be identifiable macroscopically, we found that the laminating and peeling features observed on high magnification SEM imagery can be useful in characterizing acid treatment even on very small fragments of dental remains, potentially allowing investigators to determine if acid was used as a disposal method.

Applications of Scanning Electron Microscopy Using Secondary and Backscattered Electron Signals in Neural Structure.

Scanning electron microscopy (SEM) has contributed to elucidating the ultrastructure of bio-specimens in three dimensions. SEM imagery detects several kinds of signals, of which secondary electrons (SEs) and backscattered electrons (BSEs) are the main electrons used in biological and biomedical research. SE and BSE signals provide a three-dimensional (3D) surface topography and information on the composition of specimens, respectively. Among the various sample preparation techniques for SE-mode SEM, the osmium maceration method is the only approach for examining the subcellular structure that does not require any reconstruction processes. The 3D ultrastructure of organelles, such as the Golgi apparatus, mitochondria, and endoplasmic reticulum has been uncovered using high-resolution SEM of osmium-macerated tissues. Recent instrumental advances in scanning electron microscopes have broadened the applications of SEM for examining bio-specimens and enabled imaging of resin-embedded tissue blocks and sections using BSE-mode SEM under low-accelerating voltages; such techniques are fundamental to the 3D-SEM methods that are now known as focused ion-beam SEM, serial block-face SEM, and array tomography (i.e., serial section SEM). This technical breakthrough has allowed us to establish an innovative BSE imaging technique called section-face imaging to acquire ultrathin information from resin-embedded tissue sections. In contrast, serial section SEM is a modern 3D imaging technique for creating 3D surface rendering models of cells and organelles from tomographic BSE images of consecutive ultrathin sections embedded in resin. In this article, we introduce our related SEM techniques that use SE and BSE signals, such as the osmium maceration method, semithin section SEM (section-face imaging of resin-embedded semithin sections), section-face imaging for correlative light and SEM, and serial section SEM, to summarize their applications to neural structure and discuss the future possibilities and directions for these methods.

Predicting carbon nanotube forest attributes and mechanical properties using simulated images and deep learning

Understanding and controlling the self-assembly of vertically oriented carbon nanotube (CNT) forests is essential for realizing their potential in myriad applications. The governing process–structure–property mechanisms are poorly understood, and the processing parameter space is far too vast to exhaustively explore experimentally. We overcome these limitations by using a physics-based simulation as a high-throughput virtual laboratory and image-based machine learning to relate CNT forest synthesis attributes to their mechanical performance. Using CNTNet, our image-based deep learning classifier module trained with synthetic imagery, combinations of CNT diameter, density, and population growth rate classes were labeled with an accuracy of >91%. The CNTNet regression module predicted CNT forest stiffness and buckling load properties with a lower root-mean-square error than that of a regression predictor based on CNT physical parameters. These results demonstrate that image-based machine learning trained using only simulated imagery can distinguish subtle CNT forest morphological features to predict physical material properties with high accuracy. CNTNet paves the way to incorporate scanning electron microscope imagery for high-throughput material discovery.

The Mg/Ca proxy for temperature: A Uvigerina core-top study in the Southwest Pacific

The Mg/Ca ratio of the infaunal benthic foraminifer Uvigerina peregrina is a commonly used proxy for reconstructing bottom water paleotemperatures because it is hypothesized to be insensitive to changes in bottom water carbonate chemistry. This study presents core-top U. peregrina samples from the southwest Pacific from 0.6 to 4.4 km water depth, corresponding to water temperatures of 1–9 °C. Samples from New Zealand’s Bay of Plenty and Chatham Rise were compared to previous calibrations to assess Mg/Ca temperature sensitivity. Published core-top temperature sensitivies can explain U. peregrina Mg/Ca at a majority of our study sites, with the exception of sites at intermediate depths of ~2.4–3.3 km, where the Mg/Ca ratios are substantially higher than expected from these calibrations, possibly reflecting diagenetic or non-thermal effects. Stable isotope measurements (δ18O and δ13C), laser ablation analyses, and scanning electron microscope imagery complement trace element measurements to assess variables potentially affecting U. peregrina Mg/Ca at these sites. Morphotype variability, contamination, dissolution, and recrystallization all failed to provide satisfactory explanations for anomalously high Mg/Ca observations. We infer that a non-temperature control, perhaps related to carbonate chemistry, may be affecting the Mg incorporation in some U. peregrina specimens, though no factor has yet been clearly identified. It is unclear whether the factor affecting these sites is constant through time or could vary. For this reason, we recommend that Mg/Ca of recent specimens at each core site should be checked against established calibration curves prior to pursuing down-core paleotemperature reconstructions using U. peregrina. Where possible, paleotemperature estimates should also be validated using other independent proxies. Existing core-top calibrations effectively predict U. peregrina Mg/Ca at the majority of our study sites, but our findings underscore the need for a more thorough understanding of non-temperature factors that can influence Mg/Ca in U. peregrina.

Preparation and Performance Evaluation of Platinum Barium Hexaaluminate Catalyst for Green Propellant Hydroxylamine Nitrate Thrusters.

Spacecraft have monopropellant thruster systems for attitude control in the vacuum of space. Hydroxylamine nitrate is a green propellant that has high performance and low toxicity. Owing to the high adiabatic decomposition temperature of the hydroxylamine nitrate propellant, it is necessary to develop a catalyst with high thermal stability. We used a platinum barium hexaaluminate catalyst for green propellant hydroxylamine nitrate thrusters. Barium hexaaluminate support was prepared by a wet impregnation method and heat treatment. Platinum, the active material, was coated on catalyst supports. The Brunauer–Emmett–Teller specific surface was also investigated. X-ray diffraction and scanning electron microscope imagery were used to confirm the formation of barium hexaaluminate. A hydroxylamine nitrate propellant blended with methanol was used for performance evaluation via firing tests of the thruster. The catalytic decomposition performance of each test was evaluated by calculating the characteristic velocity efficiency using the pressure of the chamber at the end of the catalyst bed and the mass flow rate of the propellant. As the catalyst bed was preheated to 350 °C, the characteristic velocity efficiency was 71.9%. Test results revealed that the platinum barium hexaaluminate catalyst is feasible for a hydroxylamine nitrate thruster.

Synthesis and preliminary gas permeation properties of vitreous composite clinoptilolite membranes

In this study, we communicate our initial findings regarding the development of novel inorganic composite clinoptilolite membranes. The membranes were formed from natural clinoptilolite microparticles sintered together using specialty glass atop a porous Al2O3 porous disk that was used as a support. Fourier transform infrared spectroscopy and x-ray diffraction analysis was used to confirm that the natural clinoptilolite used in this study maintains its overall structural conformation following heat treatment as high as 1073 K. Surface and cross-sectional scanning electron microscopy imagery of the prepared membranes showed the formation of a porous clinoptilolite – glass composite layer and a mostly glass layer with lesser porosity. Single gas He, CO2, CH4, and N2 permeation experiments were carried out to evaluate the initial performance parameters of the membranes. Single gas membrane permeation decreased with increasing amount of glass, and ranged from 2 × 10−7 mol/m2s Pa for the membrane prepared with 30 wt. % clinoptilolite as filler to as high as 4 × 10−6 mol/m2s Pa for the 50 wt. % clinoptilolite membrane. The ideal selectivity was calculated from the single gas permeance for potential natural gas or biogas CH4/N2 and CO2/CH4 separations. These values were the highest at 1.7 ± 0.2 and 1.9 ± 0.1 for the membranes prepared with 40 wt. % and 30 wt. % clinoptilolite, respectively. Considerable refinements to this technique are necessary in order to minimize the presence defects before it may be used as an alternative to inorganic membranes or mixed matrix membranes as an approach when zeolite crystallization is difficult to achieve.

Recycling of high quantities of wastepaper sludge ash for production of blended cements and alternative materials

Among low cost and widely available raw materials, wastepaper sludge ash is of key interest as potential construction material. These materials come from the paper recycling industry. In present study, wastepaper sludge ash (WSA) retrieved from UPM Chapelle Darblay Company located in the south of Rouen, France, were subjected to preliminary physicochemical characterization by X-ray fluorescence, laser granulometry and scanning electron microscope (SEM) imagery for particles morphology. Afterwards, the WSA considered as mineral addition was blended with cement, lime, and calcined kaolin for the highest possible dosages in WSA. The effects of reactivity were evaluated by means of mechanical strength measurements. Cylindrical samples were prepared with WSA mixtures and air-cured for 7, 14 and 28 days at ambient room temperature. WSA content ranged from 30%–95%. The samples obtained were subjected to unconfined compressive strength to verify the occurrence of reactivity and resistance. The results indicated that the strength increased along the curing time for all mixtures except for the reference sample in which 100% of WSA was used. The lime addition does not impact the unconfined compressive strength. As main results, on one hand, WSA and cement based mixtures with a weight ratio of 95/5 develop 2 MPa compressive strength and more during the curing time which suit for construction materials. On the other hand, with only 5% of calcined kaolin, a value of 9 MPa was attained after 28 days indicating that mixtures with calcined kaolin can be effectively used for building materials such as bricks or blocks. • Possible implementation of high volume of wastepaper sludge ash (WSA) in mixtures blended with cement and/or lime, or with calcined kaolin. • Wastepaper sludge ash and cement based mixtures with a weight ratio of 95/5 developed an unconfined compressive strength (UCS) more than 2 MPa after 28 days. • WSA and calcined kaolin based mixtures can also be employed for building materials. Their UCS strength was nearly 9 MPa after 28 days when only 5% of calcined kaolin was added.

Freeze–thaw processes degrade post‐fire water repellency in wet soils

AbstractWildfires are a cause of soil water repellency (hydrophobicity), which reduces infiltration whilst increasing erosion and flooding from post‐fire rainfall. Post‐fire soil water repellency degrades over time, often in response to repeated wetting and drying of the soil. However, in mountainous fire‐prone forests such as those in the Western USA, the fire season often terminates in a cold and wet winter, during which soils not only wet and dry, but also freeze and thaw. Little is known about the effect of repeated freezing and thawing of soil on the breakdown of post‐fire hydrophobicity. This study characterized the changes in hydrophobicity of Sierra Nevada mountain soils exposed to different combinations of wet–dry and freeze–thaw cycling. Following each cycle, hydrophobicity was measured using the Molarity of Ethanol test. Hydrophobicity declined similarly across all experiments that included a wetting cycle. Repeated freezing and thawing of dry soil did not degrade soil water repellency, but freeze–thaw cycles decreased hydrophobicity in wet soils. Total soil organic matter content was not different between soils of contrasting hydrophobicity. Macroscopic changes such as fissures and cracks were observed to form as soil hydrophobicity decayed. Microscopic changes revealed by scanning electron microscope imagery suggest different levels of soil aggregation occurred in samples with distinct hydrophobicities, although the size of aggregates was not clearly correlated to the change in water repellency due to wet–dry and freeze–thaw cycling. A 9‐year climate and soil moisture record from Providence Critical Zone Observatory was combined with the laboratory results to estimate that hydrophobicity would persist an average of 144 days post‐fire at this well‐characterized, typical mid‐elevation Sierra Nevada site. Most of the breakdown in soil water repellency (79%) under these climate conditions would be attributable to freeze–thaw cycling, underscoring the importance of this process in soil recovery from fire in the Sierra Nevada.

Sediment deformation and production beneath soft-bedded Palaeozoic ice sheets

The expansion of ice sheets over soft, sandy substrates was widespread in the Early Palaeozoic, during the Late Ordovician glaciation of North Africa and Arabia. Similarly, large parts of southern Africa were glaciated by soft bedded ice sheets in the Late Palaeozoic Ice Age. An unanswered question is the extent to which subglacial deformation involved the passive recycling of unconsolidated materials, or the active production of new sediment through erosion and shearing. Here, we compile thin section data dovetailed with scanning electron microscope imagery from sandy subglacial substrates from South Africa, Algeria and Libya. Six samples were collected from soft-sediment striated pavements, i.e., surfaces that were sheared and deformed subglacially in an unconsolidated state. The samples show a considerable variation in deformation style but a unifying trait is the occurrence of striated and facetted quartz sand grains. These textural features testify to grain-grain attrition, and the potential production of sediment in the subglacial environment.

Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic

Hydrogenetic ferromanganese crusts are likely to be exploited as resources for critical metals in the near future, yet the processes controlling where and how they grow are poorly understood. Using detailed mapping of seafloor outcrop and well constrained hydrographic modelling alongside scanning electron microscope imagery of samples from the Tropic Seamount, a star-shaped guyot located in the Tropical East Atlantic, we investigate the relationship between currents, ferromanganese crustal texture and the locations and intensity of crustal erosion. Here, we report the distribution of FeMn crusts and explore factors controlling their growth and erosion. We find that just over 35% of the summit plateau of the guyot exposes some form of ferromanganese crust mineralisation, with the rest variably covered by plains of mobile sediment and slim cliff exposures of carbonate. The steep flanks of the guyot largely expose ferromanganese crust both in situ and as debris flows. The strongest currents are located on the upper flanks of the guyot, the central part of its eastern limb, and across the summit plateau. Three categories of surface morphologies are identified; from pristine botryoidal surfaces to flat areas that have been completely polished by the erosive action of currents and sediment. The relationship between the outcrop of crusts, their erosional states and the hydrographic current regime to which they are exposed is complicated. There is a general correlation between the degree of erosion and location across the seamount, with the least eroded being found on the flanks below 2000 m water depth and the most heavily eroded crusts largely restricted to the summit area. Furthermore, the pristine samples all reside in areas that rarely experience current magnitudes over 0.2 m/s, suggesting that above this the currents have the ability to erode ferromanganese crust. However, there is a strong overlap between the measured current magnitudes at the locations of partially and completely eroded crusts, as well as partial overlap with the current magnitudes measured at pristine crust locations. This complexity is likely due to the presence of cliffs and plateaus increasing current magnitudes and turbidity at a scale smaller than the model resolution.

Aerosol extraction and direct laser ablation ICP-MS analysis of the fine and ultrafine fractions of regolith

The &lt;10, &lt;4, &lt;2.5 and &lt;1 µm fractions of eight regolith samples have been extracted as aerosols, then analysed for more than 60 elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Precision and accuracy rivals that of conventional digestion and ICP-MS analysis for most elements, but the aerosol extraction and ablation approach can be completed within 30 min, avoids compromising the sample by screening, column settling, fusion and/or digestion, and includes data for elements such as Br, Cl, I and Se that are conventionally analysed by individual procedures. Major element chemistry and scanning electron microscope (SEM) imagery show that the aerosol fractions of regolith are dominated by kaolinite, with quartz in aeolian regolith. The aerosol fractions of Si- and Ca-rich regolith have higher trace element concentrations than the coarser fraction (0.45–2 mm), but chalcophile elements are depleted in the aerosols of Fe-rich regolith relative to the coarser fraction. Improvements in in-field analytical technology coupled with aerosol extraction mean that fine and ultrafine fraction chemistry can be used to guide mineral exploration programmes in close to real time.Supplementary material: The results of the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of filter papers are available at https://doi.org/10.6084/m9.figshare.c.4562807