Oxidation Zone Research Articles

Crab bioturbation drives coupled iron-phosphate-sulfide cycling in mangrove and salt marsh soils

Coastal wetlands sequestering abundant blue carbon in soils are biogeochemical hotspots and critical habitats for benthic animals like invertebrate fiddler crabs. Here, we reveal how crab bioturbation (i.e., burrowing activity) drives the redox geochemistry of ferrous iron (Fe(II)), phosphate (PO43-), and sulfide (S(-II)) under contrasting vegetation types and hydrological conditions. We used in-situ approaches of diffusive gradients in thin films to perform detailed mm-scale burrow observations in two subtropical wetlands with a vegetation gradient of mudflat-salt marsh-mangrove. Burrow flushing caused a top-down hydrologic connectivity through the crab burrows and thus created a deep depth for the occurrence of Fe(III) reduction and sulfate reduction which were accompanied by P mobilization. The burrow oxidation zone, indicated by lower concentrations of Fe(II), PO43- and S(-II), were shallower in mudflats and salt marshes than in mangroves due to the unique respiratory roots of mangrove plants. The redox of Fe(II), PO43- and S(-II) in crab burrow was insensitive to the convection flow-induced input of dissolved oxygen through the surrounding soil matrix, indicating the burrow soil is an independent microenvironment. Crab burrowing activities favored Fe-S coupling which is conductive the formation of pyrite and alkalinity generation. Overall, our in-situ high-resolution observations and porewater hydraulic dynamics revealed spatially variable soil geochemistry, active coupled cycling of Fe-P-S in crab burrows, and mm-scale hotspots of redox cycling within burrows.

Evolution of the Tepeoba porphyry-skarn Cu-Mo-Au deposit, NW Turkey: New mineralogical and geochemical findings

This study recently investigates the evolution of the Tepeoba porphyry Cu-Mo-Au deposit (Cu ∼ 3 wt%, Mo ∼ 0.16 wt%, Au ∼ 10 ppm) with associated skarn prospects in the Biga Peninsula (NW Turkey) using the geochemical and mineralogical data. Ore-related alteration types which include biotite (±muscovite)-K-feldspar at the center of the mineralization zone, actinolite-albite alteration, and outer chlorite-epidote-calcite mineral facies, are observed in the Tepeoba mine area along the southern contact between the Karakaya Complex (mainly hornfels at the mine area) and porphyry Eybek intrusion. Porphyry style alteration pattern has been detected recognized in the porphyritic microgranite host rock. On the other hand, the calcareous and carbonate as well as the mineralized hornfels refer to the skarn style alteration pattern associated with a porphyritic felsic stock. Sulfide-rich stockwork and mineralized brittle brecciated, and fracture zones are associated with these hydrothermally altered wallrocks. Ore mineralogy includes chalcopyrite, molybdenite, pyrrhotite, pyrite, subordinate cubanite and native gold. These minerals are replaced by marcasite, hematite, and goethite in the oxidized cap rocks. EPMA data of the alteration and sulfide minerals revealed that Cu-, Fe-, Mo-sulfides partially replace biotite ± muscovite-K-feldspar/actinolite-albite and chlorite-epidote-calcite alteration facies. The estimated ore formation conditions returned wide range of temperatures of 546–471 °C (biotite thermometry) to 340–264 °C (chlorite thermometry), at which sulfides had most likely precipitated while the oxygen fugacity of the magmatic-hydrothermal ore fluids was gradually lowered and developed during the stage of retrograde metasomatic reactions. Chalcopyrite and cubanite was likely to have formed via un-mixing of intermediate solid solution (iss) under oxidizing hydrothermal conditions. Under these conditions, thiosulfide complexes could have been responsible for the transport and deposition of gold. This also refers to native gold, which could have been liberated from sulfide ores (i.e., pyrite) in the oxidation zone due to the processes of supergene enrichment.

On the role of stress in microstructure evolution during thermo-chemical surface engineering

<h2>Abstract</h2> Thermochemical surface engineering of metals is the deliberate and targeted modification of the (sub-)surface region of metals, with the aim to improve materials performance. Generally, thermochemical surface engineering is understood in terms of thermodynamics and diffusion kinetics to describe the evolution of the microstructure during chemical modification at elevated temperature. Associated with the change in composition, strains and stresses are introduced. These strains/stresses affect the thermodynamics and the kinetics of microstructure evolution. This contribution illustrates several examples from activities in the authors' research group. The following examples are covered:<ul><li>•The dissolution of nitrogen (N) or carbon (C) into austenitic stainless steels and high entropy alloys at temperatures below 725 K for N and below 825 K for C. Strong supersaturation with interstitials of the austenite leads to lattice expansion which is accommodated elasto-plastically and residual stresses of several GPas.</li><li>•Oxidizing of ZrCuAl-based bulk metallic glass (BMG) below the glass transition temperature leads to an internal oxidation zone (IOZ), consisting of nano-crystalline ZrO₂. Compressive residual stresses induce outward diffusion of "noble" elements, as for example Ag (if present) and Cu, which segregate at free surfaces. This segregation leads to crystalline metallic regions, which can provide a mechanism for self-healing of cracks.</li></ul>

Corrosion behavior of T91 steel in liquid lead-bismuth eutectic at 550 °C: Effects of exposure time and dissolved oxygen concentration

Long-term corrosion behavior of T91 steel was investigated in 550 °C static liquid lead-bismuth eutectic (LBE) at different dissolved oxygen (DO) concentration. It was found that the oxide film formed in the oxygen-saturated LBE consists of iron-lead composite oxide, Fe3O4, Fe-Cr spinel and an inner oxidation zone (IOZ). The IOZ is composed of matrix and FeCr2O4 which follows orientation relationships with the matrix. The thickness of oxide film significantly reduces at DO= 1.26 × 10−6 wt %. Dissolution corrosion and intergranular penetration of Pb-Bi were observed at DO≤ 1.41 × 10−8 wt %. The corrosion mechanism of T91 steel in liquid LBE is discussed.

Investigation of Spontaneous Combustion Zones and Index Gas Prediction System in Goaf of “Isolated Island” Working Face

Studies show that accurate division of spontaneous combustion (SC) zones in the goaf and the determination of the prediction system of the SC index are of great significance to prevent spontaneous and unwanted combustions in the goaf. Aiming at resolving the problem of coal SC in the goaf of an “isolated-island” fully mechanized caving face, a multiphysics model coupled with gas flow field and gas concentration field was established in the present study. Taking the 8824 working face of Nanzhuang coal mine as the research object and the oxygen concentration as the division index, coal SC was simulated in the goaf. The obtained results show that the ranges of heat dissipation zone, oxidation zone, and the asphyxia zone on the air inlet side are around 0–107 m, 107–239 m, and beyond 239 m, respectively. Moreover, the ranges of the three zones on the return air side are 0–13 m, 13–189 m, and beyond 189 m, respectively. The ranges of the three zones in the middle of goaf are 0–52 m, 52–213 m, and beyond 213 m, respectively. The performed analyses demonstrate that the obtained simulation results are consistent with the experimental data. Meanwhile, the coal programmed temperature rise experiment was carried out to improve the prediction index gas system of SC. It was found that CO and C2H4 can be used as early warning indices of SC in the goaf, while C2H6, C3H8, and C2H4/C2H6 are auxiliary indices to master the coal SC.

The Mushiston Sn deposit in Tajik Tien Shan as the type locality for stannite-cassiterite-hydrostannate mineralization: New mineral chemistry data and genetic constraints

The Mushiston Sn deposit is located in Hercynian South Tien Shan fold and thrust belt on the territory of Tajikistan. Unique features of the deposit include sulphide-dominated composition of the primary ore with stannite being the main ore mineral, and a thick oxidation zone where stannite is replaced by various hydrostannate minerals. Therefore, the Mushiston deposit is a rare example of stannite-cassiterite-hydrostannate mineralization and the type locality where several new hydrostannate minerals such as mushistonite, natanite and vismirnovite were first described. The structure of the deposit is characterized by a series of subvertical, generally NE-trending mineralized veins crosscutting the limbs of the large submeridional anticline composed of Paleozoic sedimentary strata. The primary ore mainly consists of a quartz-stannite group minerals – cassiterite mineral assemblage with other subordinate sulfides and minor sulfosalts. A 200–400 m thick zone of supergene oxidation is developed in the upper part of the deposit. New mineral chemistry data reveal compositional variations of the stannite group minerals, sphalerite and sulfosalts. The chemical compositions of co-existing stannite group minerals and sphalerite indicate extensive mutual substitution between Fe and Zn. The use of stannite-sphalerite geothermometry constrains the temperature for the main stage of the primary ore formation in the range of 257–308 °C. The tetrahedrite geothermometry yields temperatures in the range of 170–200 °C, which is in agreement with geological evidence for the late crystallization of sulfosalts at lower temperatures. The geological and mineralogical features of the Mushiston Sn deposit correspond to the mesothermal hydrothermal vein system mainly developed under intermediate sulfidation conditions. The proposed genetic model for the Mushiston deposit suggests formation of brittle fractures in the thermal aureole above the concealed causative granitoid intrusion, by regional analogue of Permo-Carboniferous age, where magmatic fluids mixed with meteoric water to form the hydrothermal system responsible for deposition of cassiterite-sulfide ore.

Oxidation Behavior of Intermetallic Phase and Its Contribution to the Oxidation Resistance in Fe-Cr-Zr Ferritic Alloy

Oxidation resistance of the ferritic Fe-Cr-W-Zr alloy with dispersed Fe2Zr phase were investigated in stagnant air and in static oxygen-saturated liquid Pb-Bi eutectic separately considering the service environment in the advanced generation IV nuclear reactors. A duplex structure including an outer Fe2O3 layer and an inner (Fe,Cr,Zr)2O3 layer is developed after oxidation in air, while a three-layered structure consisting of outer magnetite layer, inner Fe-Cr spinel layer, and internal oxidation zone is formed after oxidation in liquid Pb-Bi eutectic. The dispersed Fe2Zr phase shows delayed oxidation with respect to the α-Fe in air and in liquid Pb-Bi eutectic, which significantly affects the oxidation behaviors of the alloy. After oxidation in air at 923 K, the incorporated Fe2Zr phase in the scale would obstruct the diffusion of metal/oxygen across the scale, resulting in the nonuniform oxidation behavior. After oxidation in static oxygen-saturated liquid Pb-Bi eutectic at 823 K, a reduction in the Fe supply to the magnetite/Fe-Cr spinel interface is present adjacent to the Fe2Zr phase, which might lead to the creation of cavities in the outer magnetite layer with prolonged oxidation time.

Improved computational fluid dynamics modelling of coal spontaneous combustion control and gas management

Computational fluid dynamics (CFD) is an effective methodology that has been widely used for decades to solve engineering problems involving spontaneous combustion and abnormal gas emissions. However, most of the previous CFD modelling focused on qualitative rather than quantitative analysis, and the factors influencing spontaneous combustion control and gas management are numerically under-researched. The onset of spontaneous heating in the goaf area is dictated by many operational and environmental parameters, including mining method, ventilation and geology. Based on field data from a real mine site, extensive CFD modelling was conducted and analyzed qualitatively and quantitatively to investigate the impact of ventilation design and operational measures on the management and control of spontaneous combustion and gas exceedance. Real-time gas monitoring data was utilized for model validation, and a good agreement between simulation results and monitoring data was reached. The tightness of goaf seals described by permeability was quantitatively investigated, revealing that the permeability should be smaller than 10−9 m2 to prevent air leakage effectively. Goaf inertisation parameter optimization is crucial to minimize the risk of spontaneous combustion. The systematic study revealed that the oxidation zone area (OZA) was the largest for nitrogen injection (29706 m2), followed by boiler gas (28396 m2), while it was the smallest for carbon dioxide (11902 m2), which produced the best goaf inertisation performance. Injection flow rate is another significant factor influencing the effectiveness of heating prevention. The simulation results indicated that a critical injection rate of 1750 m3/h was determined, and the ratio of the OZA to the goaf area (GA) fluctuated around 7% once the injection rate was beyond this critical value. The installation location of curtains and brattices both on the longwall face and tailgate end was also simulated and optimized. Noticeable methane reduction at the tailgate end was observed with optimal configurations of brattices and curtains. Results from the modelling will shed light on improving current practices to effectively contain goaf heating in the longwall goaf areas and mitigate methane exceedance on the longwall face.

Effect of film-forming regulation of the self-formed compound layer on the oxidation inhibition capacity of HfB2-SiC coating

To heighten the oxidation inhibition capacity of HfB2-SiC coating, film-forming regulation of the self-formed compound layer was utilized to enhance the dynamic stability and the oxygen hindering capacity of the coating. The oxidation process of the HfB2-SiC coating in air from room temperature to 1700 °C can be divided into the lower temperature oxidation zone, the medium temperature protection zone and the high temperature corrosion zone. The oxidation activity of the coatings was significantly weakened in the medium temperature oxidation protection zone from 1100 °C to 1400 °C, which was selected as the film-forming regulation temperature region to ensure the lower film-forming wastage of the coatings. When the film-forming temperature was 1200 °C, the coating was uniformly covered by the glass layer with fewer defects. The values of active factor and inerting factor of the HfB2-SiC coating after film-forming at 1200 °C were 0.151 and 0.953 × 10−6 g cm−2 s−1, respectively, which show the lowest film-forming wastage of the coating. With further ascending the film-forming temperature, a large number of pores and cracks generated on the glass layer owing to the evaporation and release of the gaseous byproducts, which destroyed the structure of the glass layer and aggravated the oxidation wastage of the coating. With increasing the film-forming time at 1200 °C for 360 min, the protection efficiency of the HfB2-SiC coating increased to 99.13%, the oxygen permeability and carbon loss rate decreased by 79.6% and 67.8%, respectively, which slowed down the oxidation activity and improved the dynamic stability of the coating during oxidation.

Effects of surface treatments and temperature on the oxidation behavior of 308L stainless steel cladding in hydrogenated high-temperature water

The properties of the oxide films grown on 308 L SS cladding with various surface treatments and temperatures in simulated PWR primary water are studied. The thickness of the inner oxide layer increases with the decrease of the surface roughness. The high oxidation resistance of the ground surface is due to the thicker fine-grained layer with high dislocations density and subgrain boundaries in the near-surface. The ferrite-affected oxidation zone (FAOZ) expands with the increase in temperature, resulting from the thermally activated self-diffusion of Cr in ferrite. The effects of surface states, ferrite and temperature on oxidation performance of 308 L SS cladding are discussed.

Study on Spontaneous Combustion "Three Zones" of the Distribution Law and Integrated Fire Prevention Technology in Mined-Out Area of Lingquan Mine.

To determine the risk range of remaining coal in the goaf of the higher slice on the seventh mining and fifth face of Lingquan Mine, the beam tube monitoring system was adopted to supervise the temperature and gas content changes in the goaf during the normal mining period of the working face. As per the principle of dividing spontaneous combustion “three zones” (SCTZ), numerical simulation of the distribution of SCTZ in the goaf of the work face was performed. The O2 content and index gas in the goaf were measured and analyzed, and combined with the in-situ measurement outcomes, the distribution of SCTZ in the goaf was determined through the FLUENT numerical modeling program. The outcomes show that the distribution pattern of SCTZ in the goaf of fully mechanized mining face is: the heat dissipation zone is 0–41 m, the oxidation zone is 41–97 m, the suffocation zone is more than 97 m away from the work face, and the increment of temperature is 0.7/°C. Based on the judgement result of SCTZ, the minimum recovery rate of work face is above 3.7 m/d. The use of new polymer materials validly solves the problem of excessive CO in the return air corner of the goaf and prevents self-ignition accidents in the goaf.

Effect of Silicon on Dynamic/Static Corrosion Resistance of T91 in Lead-Bismuth Eutectic at 550 °C.

The 9–12% Cr ferritic–martensitic heat-resistant steel is the main candidate structural material for the Lead-cooled Faster Reactor. The lower Gibbs free energy change of Si oxide can promote the formation of a stable oxide layer, which can improve the corrosion resistance of the material. Therefore, it is of great significance to study the effect of silicon (Si) on the corrosion resistance of T91 steel in lead–bismuth eutectic (LBE). The corrosion resistance of T91 steel with Si contents of 0.5 wt.%, 1.3 wt.%, and 2.0 wt.%, both in dynamic and static LBE at 550 °C, was investigated. The microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), while the oxide films were characterized by electron probe microanalysis (EPMA). Results show that the addition of Si is conducive to improving the corrosion resistance of T91 steel in LBE. T91 steel with high Si content has a thinner and more stable oxide film. The change of Si content can change the contact angle between the steel and LBE, and the contact angle is the largest when the Si content is 1.3 wt.%. The Si-rich oxide layer is usually located in the inner oxide layer, which promotes the formation of a Cr oxide layer located in the internal oxidation zone (IOZ). Si will not enter the precipitated phase, but only change the ferrite content. The oxidation model of T91 steel containing Si in LBE was also proposed.

Studi Gasifikasi Pengembangan Tongkol Jagung dengan Jerami Padi Menggunakan Reaktor Downdraft Dengan Dua Masukan Udara Tekan

The production of corn and rice produced by farmers in East Java has the potential to cause agricultural waste, therefore corn cobs are waste that requires special processing in order to be used optimally. Agricultural waste corn cobs and rice straw can be converted into gas fuel (Syngas). The purpose of this study was to determine the performance of gasification seen from the temperature distribution and composition of combustible gases such as CO, H2 and CH4. The downdraft gasifier type is used and applies the AR and E.R ratio to the temperature. For the pyrolysis and oxidation regions, the intake air varies (AR pir-oxi ) 80%; 70%; and 0% at 14.5 air intake; 19.3; and 24.1 Nm 3 /hour from E.R 0.3, 0.4, and 0.5. Air intake in the adjust area using a valve. Temperature measurement using the type K thermocouple. The results show that the maximum temperature using ARpir-oks = 80%, the drying zone temperature is 187°C, the pyrolysis zone is 488°C, the oxidation zone is 895°C and the reduction zone is 585°C. Meanwhile, the highest production of CO gas is 20.50% and H 2 gas is 14.55% using an ER of 0.4. Meanwhile, CH4 decreased for all ER values using ARpir-oks = 80% .

Evaluation of Ni-Fe base alloys as inert anode for low-temperature aluminium electrolysis

• Oxidation behaviors of Ni-Fe-Cr alloys with different Cr content were investigated in air at 800 °C and 900 °C °. • A multilayer oxide structure with an inner Cr 2 O 3 , a middle (Ni,Fe,Cr) 3 O 4 , and an outer (Ni,Fe) 3 O 4 /Fe 2 O 3 layers was formed on Ni-Fe-15Cr alloy. • Increasing of oxidation temperature or Cr content for Ni-Fe-Cr alloys not only accelerates to form Cr 2 O 3 inner layer, but also reduces Fe 2 O 3 content. • The (Ni,Fe) 3 O 4 /(Ni,Fe,Cr) 3 O 4 /Cr 2 O 3 layered scale was highly oxidation/corrosion resistant in molten alumina-cryolite at 800 °C. Isothermal oxidation behaviors of Ni–Fe (wt.%) and of the same alloy with additions of 10 and 15%Cr alloys in the air at 800 °C and 900 °C and their anodic behaviors in aluminum electrolysis system at 800 °C were evaluated. The composition morphologies of oxide scales were characterized by XRD, SEM, and EDS. Results show that the scales formed on Ni–Fe alloy at both temperatures consisted of an inner (Ni,Fe) 3 O 4 layer and an outer Fe 2 O 3 layer. For Ni–Fe–10Cr alloy, an external (Ni,Fe) 3 O 4 /Fe 2 O 3 layers and an internal oxidation zone were formed at 800 °C, while a continuous Cr 2 O 3 layer forms at the internal oxidation zone/substrate interface at 900 °C. A multilayer structure oxide of Cr 2 O 3 /(Ni,Fe,Cr) 3 O 4 /(Ni,Fe) 3 O 4 /Fe 2 O 3 was formed on Ni–Fe–15Cr alloy at 800 °C, while at 900 °C the Fe 2 O 3 becomes discontinuous disperses in the (Ni,Fe) 3 O 4 layer close to the surface. Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner Cr 2 O 3 layer and simultaneously reduce Fe 2 O 3 content. After 4 h of electrolysis at an anode current density of 0.25 A cm −2 , the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.

New insight into proactive goaf inertisation for spontaneous combustion management and control

Spontaneous heating in the active goaf area during normal mining processes poses increased threats to mine productivity and safety, as evidenced in events induced by spontaneous combustion of coal. To control and mitigate this engineering problem, there is a need to gain critical knowledge of spontaneous combustion in the longwall goaf area, which can be achieved through a combination of field tests and numerical modeling. This paper introduces the spontaneous combustion management system widely used in Australia and presents Computational Fluid Dynamics (CFD) models for the simulation of gas flow dynamics in the goaf area, based on the site conditions of an underground coal mine where coal seam gas is predominantly comprised of carbon dioxide. The models were validated with gas monitoring data and used to conduct parametric studies for proactive goaf inertisation optimization. Qualitative and quantitative analysis of simulation results indicated that better goaf inertisation could be achieved when nitrogen was injected via cut-through at 250 m on the maingate (MG) side and surface boreholes at 100 m and 700 m on the tailgate (TG) side, with a total injection rate greater than 1750 l/s. The oxygen concentration on the MG and TG side dropped below 5% at distances of 120 m and 75 m behind the longwall face, with an oxidation zone area of 35375 m2, which was approximately one-third of the oxidation zone area of the scenario without inert gas injection. Simulation results help shed light on improving current goaf inertisation practices to effectively reduce the risk of heating in goaf areas and improve mining process safety based on Australian conditions and practices.

Effect of Hydrogen on the Internal Oxidation of a Pd–Cr Alloy in Dual-Atmosphere Conditions

The effect of hydrogen on oxygen permeability has been studied in a diluted Pd–Cr alloy in dual- and single- atmosphere conditions between 600 and 950 °C. The 0.3 mm thick Pd–1.5Cr foil was exposed in dry and humid air as well as in dual-atmosphere conditions, with one sample surface being exposed to air and one to hydrogen, as encountered in solid oxide fuel cells. At all temperatures, Cr oxidized internally forming internal oxidation zones which were measured in metallographic cross sections. Below 800 °C, an external layer of PdO formed on the surface decreasing the internal oxidation kinetics. No measurable effect of hydrogen on the internal oxidation of Cr in Pd has been detected.

Effect of Cr and W addition on the oxidation behavior of Ni–8%Al alloy at 1000 °C

The effect of (6 wt%) Cr and (6 wt%) W on the oxidation behavior of Ni–8%Al alloy at 1000 °C in air was investigated. The oxidation-affected zones of Ni–8%Al–6%Cr/W alloys consist of outer oxidation zone (NiO layer) and mixed internal oxidation zone. The addition of Cr promotes the formation of the intermediate Ni(Al, Cr)2O4 layer and internal Al2O3 in internal oxidation zone, which provides a blocking effect and reduces the oxidation rate of Ni–8%Al–6%Cr alloy. However, the addition of W element facilitates the development of non-protective NiO and NiWO4 oxides, which accelerates the oxidation of alloy. As a result, Ni–8%Al–6%W alloy shows poor oxidation performance.

Aquifer remediation using surfactant-enhanced gas sparging applied to target the contaminant source

The surfactant-enhanced gas sparging process designed to specifically target the source zone of an organic contaminant in an aquifer with minimal usage of injected additives was investigated using a physical model. Aqueous solutions of the anionic surfactant Sodium dodecylbenzne sulfonate (SDBS) and/or the thickener Sodium carboxymethylcellulose (SCMC) were applied in a contaminated horizontal layer in the simulated laboratory aquifer model followed by gas sparging. Fluorescein sodium salt (FSS) was added to the SDBS/SCMC solutions and represented the organic contaminant. Air and ozone were injected to generate gas sparging. A modified surfactant-enhanced ozone sparging method was also tested by applying additional air venting ports installed in the aquifer above the gas injection zone. Both non-aqueous phase liquid (NAPL) and water-dissolved TCA were applied to the SDBS-applied region to evaluate the removal of contaminants during gas sparging. A significant expansion of the de-saturated zone for the SDBS-applied region was observed during air sparging. During ozone sparging, the fluorescence by FSS in the SDBS-applied layer disappeared over a much wider range than that of the control experiment. SCMC application enhanced the performance of the SDBS-applied gas sparging process. The TCA mass removed by volatilization during air sparging from the SDBS-applied layer was 2.3 times the application in the absence of SDBS. Among five regions of injected NAPL contamination located above the single gas injection port, and during 2 h of ozone sparging, with SDBS applied, more than 50% of fluorescence in the NAPL was removed, whereas under the same conditions with no SDBS applied, less than 30% was removed. Diverted gas flow through the venting ports installed in the aquifer model induced a horizontally expanded oxidative reaction zone during ozone sparging. This study demonstrates enhanced gas sparging performance for the removal of contaminants from the aquifer with limited usage of additives applied specifically to the source zone.

Reduced methane emissions in former permafrost soils driven by vegetation and microbial changes following drainage.

In Arctic regions, thawing permafrost soils are projected to release 50 to 250 Gt of carbon by 2100. This data is mostly derived from carbon‐rich wetlands, although 71% of this carbon pool is stored in faster‐thawing mineral soils, where ecosystems close to the outer boundaries of permafrost regions are especially vulnerable. Although extensive data exists from currently thawing sites and short‐term thawing experiments, investigations of the long‐term changes following final thaw and co‐occurring drainage are scarce. Here we show ecosystem changes at two comparable tussock tundra sites with distinct permafrost thaw histories, representing 15 and 25 years of natural drainage, that resulted in a 10‐fold decrease in CH4 emissions (3.2 ± 2.2 vs. 0.3 ± 0.4 mg C‐CH4 m−2 day−1), while CO2 emissions were comparable. These data extend the time perspective from earlier studies based on short‐term experimental drainage. The overall microbial community structures did not differ significantly between sites, although the drier top soils at the most advanced site led to a loss of methanogens and their syntrophic partners in surface layers while the abundance of methanotrophs remained unchanged. The resulting deeper aeration zones likely increased CH4 oxidation due to the longer residence time of CH4 in the oxidation zone, while the observed loss of aerenchyma plants reduced CH4 diffusion from deeper soil layers directly to the atmosphere. Our findings highlight the importance of including hydrological, vegetation and microbial specific responses when studying long‐term effects of climate change on CH4 emissions and underscores the need for data from different soil types and thaw histories.

The effect of grain size on the internal oxidation of Sm2Co17-type permanent magnets

This work has examined the influence of grain size in sintered Sm2(Co,Fe,Cu,Zr)17-type permanent magnets on the growth of an internal oxidation zone (IOZ). Two magnets of similar composition but with average grain sizes of 46 μm and 170 μm respectively, were exposed to temperatures of 500 °C in air for times up to 1000 h. Overall, the smaller grained magnet showed a reduced growth rate of the IOZ (∼39.01 μm2h−1) compared to the larger grained magnet (∼48.95 μm2h−1) and a smaller irredeemable loss in Br (3.11%) after 1000 h. However, growth rate of the IOZ is shown to depend on the growth direction, in respect to the crystallographic c-axis of the matrix phase. The smaller grain size was shown to be most effective at retarding the growth of IOZ under surfaces parallel to the c-axis. It is proposed therefore, that a smaller grained sintered magnet may be the microstructure of choice for use in demanding, high temperature applications, where a protective coating is not always a possibility, such as a high-performance electrical machine with a surface mount PM rotor. Orientation of the exposed face must also be considered to minimise the resultant magnetic induction loss caused by oxidation.