Serpentine Type Research Articles

Investigation of Liquid Water Distribution under Temperature Gradient in PEFC Using in-situ X-ray Visualization

Polymer electrolyte fuel cells (PEFCs) are expected to be applied in wider range of applications including automobiles, and the operation at higher current density has been required. However, in the operation at high current densities, the performance of PEFCs is degraded due to liquid water accumulation in the gas diffusion layers (GDLs) which prevents the supply of oxygen to the catalyst. Furthermore, heat is generated in catalyst layer due to electrochemical reaction, leading temperature rise inside PEFCs. Since liquid water accumulation is closely related to temperature distribution, it is expected that temperature distribution alters the spots of liquid water accumulation. Therefore, it is necessary to understand the relationships between the liquid water distribution and the temperature distribution in the GDLs to improve the performance at high current density. This study intended to investigate the effects of temperature distribution on liquid water accumulation by in-situ X-ray visualization.Liquid water distribution of 60, 70, and 80 ℃ cell temperature cases were measured by X-ray radiography, and current density was kept 1.5 A/cm2 in all cases. We used a serpentine type cell with ribs and flow channels of 300 µm width with 1.5 x 3.0 mm2 active area. As for GDLs, SIGRACET 29BC was used. The humidity of hydrogen in the anode was fixed at 100%. While, the humidity of air in the cathode was adjusted so that the gap between water vapor pressure and saturation pressure becomes 4.0 kPa.Fig. 1 (a), (b) and (c) shows the liquid water distribution of the 60 ℃, 70 ℃, 80 ℃ cases. It is shown that the liquid water distribution in a region near the MPL/substrate boundary is clearly altered by the cell temperature. This effect is also observed in the averaged profiles of liquid water volume under rib areas (Fig. 1(d)). In Fig. 1(d), liquid water volume in the region near the MPL/substrate boundary (the region between 50 µm to 80 µm) of the 70 and 80 ℃ cases are clearly reduced compared to the 60 ℃ case. Since the overvoltage of each case is almost the same, the resultant temperature gradient inside GDLs due to the heat production is considered to be the same. Meanwhile, the saturated vapor pressure increases more abruptly at higher temperature, since the saturated vapor pressure is more affected by the initial cell temperature. The saturated vapor pressure of the 80 ℃ case is much larger than the other cases, therefore it is suggested that the lower amount of liquid water accumulation of the 80 ℃ case is caused by the larger saturated vapor pressure. Figure 1

Characterization of T-shaped magneto-rheological brake

Serpentine flux T-shaped magneto-rheological brake (MRB) featuring a single coil has been proposed for reducing the needs of coil that usually implemented in conventional T-shape MR brake. Here, the use of serpentine type magnetic flux flow is the key to coil reduction. The prototype was designed and fabricated in the laboratory. The design covers analytical torque prediction, magnetic circuit simulation, and workshop drawing. While the fabricated prototype was characterized using MRB test rig equipped with torque and angular velocity sensors. The experimental work was carried out in constant speed and constant current. The torque using the analytical approach and experiment result respectively was 1.51 Nm and 1.91 Nm at 1 A current supplied. Based on the comparison between prediction and experiment results, it could be seen that the highest difference was about 20.

Mineralogy and geochemistry of the Berong Ni-Co laterite deposit, Palawan, Philippines

Intense weathering of the serpentinized peridotite resulted in the formation of the Berong Ni-Co laterite deposit in Palawan (Philippines). The studied laterite profiles are divided from base to top into: (i) serpentinized bedrock, (ii) saprolite horizon, and (iii) limonite horizon. Olivine in the peridotite contains a significant amount of Ni (average 0.38 wt% NiO), thus representing the main source of the ore in the laterite horizons. Six types of Ni-bearing serpentines (up to 6.65 wt% NiO) in the saprock are discriminated based on their textures and Raman signatures. Garnierite (a mixture of serpentine-, kerolite- and sepiolite-like clays) typically occurs as coatings or fracture fillings in the saprock and is characterized by strikingly high NiO content up to 34.86 wt%. Goethite and Mn-oxy-hydroxides (i.e. lithiophorite-asbolane intermediates) are the principal hosts of Ni in the limonite (up to 2.15 wt% NiO and 23.89 wt% NiO, respectively) with the latter also being the main Co carriers (up to 12.59 wt% CoO). The whole-rock XRF data show typical trends observed in other Ni laterite deposits, where Mg and Si are depleted toward the surface, and the transition metals (i.e. Fe, Al, Ni, Co, and Mn) are retained in the weathered horizons. The saprolite horizon is particularly enriched in Ni, while the lower section of the limonite horizon is enriched in Co. The mildly acidic environmental condition (pH ≤ 6.57) in the limonite horizon was found to enhance the mobilization and re-distribution of Ni from the limonite towards the lower section of the profiles. Geological observations, coupled with mineralogical and geochemical data, show that the Berong Ni-Co laterite deposit formed in two weathering processes: (i) development of the saprolite and the limonite horizons, and (ii) late precipitation of secondary phyllosilicates (i.e. garnierite), Mn-oxy-hydroxides and silica.

Possibility of using different types of Egyptian serpentine as fine and coarse aggregates for concrete production

This work is the first attempt to study the possibility of incorporating three different types of Egyptian serpentine aggregates (antigorite, lizardite and chrysotile) with different serpentinization grades as fine and coarse aggregates for normal concrete production. The results of physical and mechanical tests for each type of aggregate were compared to the others. In addition, the effect of serpentinization grade on their mineralogical composition, physico-mechanical and morphological properties of was evaluated and compared. The results were analyzed by using sophisticated tools such as X-ray diffraction, thermogravimetry/differential thermogravimetry and scanning electron microscopy. The results revealed that the physical, mechanical and microstructural properties of serpentine-based concretes were negatively influenced by the progress of serpentinization and deformation processes. The antigorite aggregate showed the lowest serpentinization grade compared to the others (i.e. lizardite and chrysotile). Thus, the antigorite-based concrete revealed better physical and mechanical properties as well as a condensed interfacial transition zone than those of lizardite- and chrysotile-based. Therefore, the results of this study indicated that antigorite is the most appropriate serpentine aggregate to be used in normal concrete production, however, more tests on the durability of such concrete are needed.

Ni-Co Mineralization in the Intex Laterite Deposit, Mindoro, Philippines

The Intex laterite deposit in Mindoro, Philippines is derived from the weathering of the ultramafic rocks under a tropical climate. This study investigates the several types of serpentines and the effect of the degree of chemical weathering of ultramafic rocks and laterites on the enrichment of Ni in the deposit. The five types of serpentines are differentiated based on their textural features and Raman spectral data. Type I, type II, type III, and type IV serpentines contain a low amount of NiO (average 0.15 wt%), and their formation is linked to the previous exhumation of the ultramafic body. Conversely, type V serpentines show the highest NiO contents (average 1.42 wt%) and have the composition of serpentine-like garnierites, indicating a supergene origin. In the limonite horizon, goethite is the main ore mineral and shows high NiO contents of up to 1.68 wt%, whereas the Mn-oxyhydroxides (i.e., asbolane and lithiophorite–asbolane intermediate) display substantial amounts of CoO (up to 11.3 wt%) and NiO (up to 15.6 wt%). The Ultramafic Index of Alteration (UMIA) and Index of Lateritization (IOL) are used to characterize the different stages of weathering of rocks and laterites. The calculated index values correspond to a less advanced stage of weathering of the Intex laterites compared with the Berong laterites. The Berong deposit is a Ni-Co laterite deposit in the Philippines, which is formed from the weathering of the serpentinized peridotite. The less extreme degree of weathering of the Intex laterites indicates less advanced leaching, and thereby the re-distribution of Ni, Si, and Mg from the limonite towards the saprolite horizon may have resulted in the poor precipitation of talc-like (kerolite-pimelite) and sepiolite-like (sepiolite-falcondoite) phases in the studied saprolite horizon. Nickel in the Intex deposit has undergone supergene enrichment similar to other humid tropical laterite deposits.

Investigation of formability of metallic bipolar plates via stamping for light-weight PEM fuel cells

Bipolar plates (BPs) are one of the main members which constitute a significant percentage of a fuel cell system in terms of cost, weight and structural strength. Although frequently used graphite BPs have low density, high conductivity and corrosion resistance, machining the desired flow channels on the graphite plates is an important issue. On the other hand, metallic BPs can be considered a reasonable alternative material to graphite in the view of the material cost, fabrication of flow channels and some post-processes in which the large-scale manufacturing of graphite BPs is more complex compared to cutting and stamping processes for metal ones. This study offers a comparison of the formability of four different metals with four flow channel depths as bipolar plates formed by stamping. 304 Stainless Steel (SS 304), pure Titanium - Grade2 (CP–Ti) and Aliminium (Al 6016 and Al 3104) are chosen as the BP materials. A serpentine type flow channel with two different channel widths are formed on to 0.1 mm thick sheets. The channel width is chosen as 1.2 mm and 1.8 mm for the channel depths of 0.36 mm–0.55 mm, and 0.54 mm–0.82 mm, respectively. The stamping processes of the BPs materials are simulated via commercially available eta/Dynaform v5.9.4. software and formability characteristics are obtained for sixteen various cases. As a result, it is determined that SS 304 is the more appropriate material in the view of the formability for such a complex form.

Numerical investigation of hydrogen absorption in a metal hydride reactor with embedded embossed plate heat exchanger

In this paper, a Metal Hydride (MH) reactor integrated with an Embossed Plate Heat Exchanger (EPHX) was studied for the first time for its hydrogen absorption rate and thermal performance. A detailed numerical analysis of the various flow-field designs in the EPHX such as parallel-type, pin-type, and serpentine types (vertical and horizontal) was performed. The serpentine flow-field EPHX presented better heat transfer and faster hydrogen storage ability. Also, it showed more uniform temperature distribution in the bed compared with parallel and pin-type flow-fields. Next, the vertical-serpentine flow-field EPHX was compared with the most commonly used Helical Coil Heat Exchanger (HCHX) and the outcomes were discussed. Although, EPHX showed slightly lower overall heat removal from the reactor, it presented similar hydrogen absorption rate and remarkable uniformity in temperature distribution in the reactor.

Fabrication of wavy micromixer using soft lithography technique

Microfluidic devices are enormously used in different engineering applications such as biological, chemical, electronics, mechanical, etc. Manufacturing of microfluidic devices becomes one of the emerging areas of research in the current times. Manufacturing of microfluidic devices is a challenging issue via general fabrication technologies. Several types of materials and methods are in use for fabricating microfluidic devices for different kinds of uses. Micromixer is an essential component to integrate any microfluidic device. In this paper, a fast process for the fabricating of micromixer with poly-di-methyl-siloxane (PDMS) is presented and elaborated. Two types of wavy micromixers, namely raccoon, and serpentine are fabricated. The complete fabrication process of the micromixer has been conducted with major two steps, namely, mold preparation, and fabrication. Initially, the mold of the micromixer of raccoon, and serpentine type with proper dimensions is produced using CO2 assisted laser machining on poly-methyl-meth-acrylate (PMMA), and then using these molds, micromixer of PDMS is prepared by soft lithography technique. Micromixer with accurate and precious dimensions as per the required design can be fabricated using the proposed process for different purposes. This article may be helpful for the researchers to get the proper knowledge related to the fabrication of wavy micromixer in a fast and cost-effective way.

Glucose oxidase immobilized biofuel cell flow channel geometry analysis by CFDsimulations

Glucose oxidase was covalently immobilized to a porous electrode, which was developed by using ferrocene functionalized polyethyleneimine, multiwall carbon nanotubes, and carbon cloth for biofuel cell applications in our recent studies. The kinetics parameters (i.e. k$_{M}$, V$_{max})$ and other parameters required for the modeling study were determined experimentally. Fuel cell flow channel geometry was analyzed by a computational fluid dynamics modeling approach. Substrate flow rate and mass transfer for each proposed channel type were considered in the simulations. The results showed that serpentine type flow channels are advantageous over pin type or parallel flow channels to acquire sufficient performance from the immobilized enzyme electrode at lower substrate flow rates. On the other hand, a disadvantage of using serpentine type channels was observed as higher pressure drops. However, such pressure drops were accepted as reasonable for the considered flow rates for suitable biofuel

A Reply to the Comment by Kostrovitsky, S. and Yakovlev, D. on ‘Was Crustal Contamination Involved in the Formation of the Serpentine-free Udachnaya-East Kimberlite? New Insights into Parental Melts, Liquidus Assemblage and Effects of Alteration’ by Abersteiner et al. (J. Petrology, 59, 1467–1492, 2018)

The Comment by Kostrovitsky & Yakovlev aims to demonstrate that Abersteiner et al. (2018) ‘presented erroneous statements regarding the genesis’ of the mineralogically and geochemically unique Serpentine-Free Udachnaya-East (SFUE) kimberlite (Russia) as it contradicts the views presented by Kostrovitsky et al. (2013). Furthermore, these authors reassert that ‘the supposition that surfaces salts and sulphates represent the main source for Na–Cl–S mineralization of kimberlites with unaltered olivine (Kostrovitsky et al., 2013) is still valid’ and ‘the mantle origin of salts is doubtful’. Numerous hypotheses are presented in both Kostrovitsky & Yakovlev (Comment) and Kostrovitsky et al. (2013) advocating a crustal brine origin for salts in the SFUE kimberlite. However, we find these interpretations to be poorly substantiated by empirical evidence and often contradictory. It is, therefore, important to revisit the earlier publication by Kostrovitsky et al. (2013) that is used to support the Comment by Kostrovitsky & Yakovlev. Here we address some of the erroneous and contradictory points presented by Kostrovitsky et al. (2013), which render their interpretations tenuous and misleading: Presence of evaporites in country rocks: Kostrovitsky et al. (2013) contradict themselves by suggesting that evaporites in the country rocks are both present and absent at the Udachnaya-East kimberlite. These authors stated that the Udachnaya-East kimberlite ‘does not intersect massive evaporites’ (p. 77), but later claimed that ‘...the highest (8 vol %) abundance of halite is restricted to depth levels of southern diatremes (Mir, Udachnaya, and International’naya) where they cut through halite-rich evaporite’, (p. 84) and ‘The absence of all textural types of serpentine in SFUE kimberlite is easily explained by the model of the evaporite country rock contamination’ (p. 88). The published and unpublished reports for parametric and geotechnical drill holes [figures 1 and 2 of Kamenetsky et al. (2014)] showed no evidence of sedimentary evaporite beds in or around the Udachnaya-East kimberlite. The composition of the putative kimberlite melt: The composition of the melt that is supposedly parental to Udachnaya-East was suggested by Kostrovitsky et al. (2013) to have resulted from ‘assimilation of evaporite xenoliths at relatively high, magmatic temperatures producing hybrid melt with elevated contents of Na, K, Cl, and S’, (p.88) and that ‘the hybrid residual kimberlite that digested evaporite xenoliths had lower H2O activity due to increased halogen and alkali abundances’ (p. 88). However, these authors also stated that ‘the contents of H2O, Na2O, and, by inference, the mode of halite are thus controlled only by the spatial position of the kimberlite specimen, rather than by the composition of the kimberlite melt’. Again, Kostrovitsky et al. (2013) did not present a consistent view as to whether salt was controlled by assimilation of alleged ‘evaporites’ or by the spatial position of the kimberlite rock. Primary versus secondary enrichment in Na and Cl: (Kostrovitsky et al., 2013) again presented conflicting views on the origin of Na and Cl mineralisation. On the one hand, these authors considered Na and Cl to be primary magmatic: ‘Na-rich kimberlite compositions are not solely restricted to unserpentinized kimberlites and that groundmass serpentine does not replace primary alkali- and chlorine-bearing minerals’. (p. 84), and ‘...alkali-, sulfur-, and chlorine-rich minerals may have crystallized from this late hybrid melt and may be comagmatic with kimberlite’ (p.88), but on the other hand they pushed for their secondary origin: ‘the strongest evidence for the secondary origin of Na-, Cl-, and S-rich minerals in the Udachnaya-East kimberlite... is the regional correlation between the geology and hydrogeology of the local country rocks and the mineralogy of Yakutian kimberlites’ (p.86). With this preface, we discuss below the Comment by Kostrovitsky & Yakovlev, and emphasise that previous data and interpretations by Abersteiner et al. (2018b) and other works are still valid and concordant with a magmatic origin of alkalis and halogens in the SFUE kimberlite.

Single serpentine flow fields design and sub-rib convection analysis for a PEM fuel cell

In a polymer electrolyte membrane fuel cell (PEMFC), transport of reactant gases through a bypass convection mechanism established between two adjacent channels along the gas diffusion layer (GDL) under the serpentine type flow field of a bipolar plate can enhance the fuel cell performance by reducing the power losses. In this paper, three different serpentine type flow field models for bipolar plates of a PEM fuel cell unit have been designed, with different channel width/rib width ratios of 1, 1.05 and 1.2, and different pressure loses have been evaluated. An analytical model for bypass sub-rib convection, based on two adjacent flow channels and a serpentine in contact with a GDL layer was used here. This model established the influence of bypass convection in the form of Peclet number Pe for the flow field models, by modifying the GDL thickness t (mm) and active channel length L (mm). The optimal combination of thickness t, porosity ε and permeability k for a series of commercial GDL materials from the perspective of sub-rib convection was established for SigracetTM GDL 35 BC, with highest Pe number modified along the channel.

Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia

In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS2) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.

HYDRODYNAMICS, DISTRIBUTION OF FLOWS AND THERMAL EFFICIENCY OF COIL HEAT EXCHANGERS IN UNITS OF HEAT-USING APPARATUS OF TUBE FURNACES

The theoretical foundations of construction, mathematical description and engineering calculation of heat exchangers of the serpentine type in blocks of heat-using equipment of tube furnaces and other types of reactors designed for carrying out endothermic reactions (in particular, reforming of natural gas with water vapor) are considered. It is shown that the thermal efficiency of heat exchangers of the coil type is significantly affected by the correct choice of parameters ensuring a uniform distribution of energy flows over the surface of heat-resistant heat exchange tubes. This technological problem is solved by compiling the heat balance and selecting the system of the corresponding equations, which allows to calculate the temperature contour of the coil heat exchanger, its hydrodynamic characteristics and the distribution of mass and heat flows through the heat exchange tubes. The use of the tensor form of the Boussinesq hypothesis is considered, with which the Reynolds equation describing a turbulent flow is transformed to a partial differential equation for a single unknown function and its averaged form is obtained. In relation to the problem under consideration, the correctness of the chosen approach was confirmed both theoretically and experimentally. It is shown that in the core of a turbulent flow with an intense suction or injection, the liquid behaves almost as ideal and the well-known Helmholtz – Friedmann theorem holds with the necessary accuracy. From the aforementioned averaged equation, expressions are obtained that are suitable for describing heat fluxes in channels with suction or injection. According to this theoretical model, thermal calculations of coil-type heat exchangers were carried out, a more accurate assessment of the temperature of the heated medium in each coil tube was made, and the temperature gradient of the external heat carrier over the cross section of the gas duct was found. For the first time in the practice of calculations when choosing the parameters of coils, a number of boundary conditions were taken into account, such as the condition of the coil layout, the necessary heat exchange surface, permissible restrictions on hydraulic resistance, etc.

Examination of Materials Supply from the Side of Channel in Product

This research is on the development of a new extrusion method of a fuel cell separator with an orthogonal channel. Separators are successfully produced separators by this new extrusion method. It is important to determine the most suitable extrusion condition to enable stable continuous production. We decided to attempt the production of a fuel cell separator with a serpentine channel, which is a complicated shape. However, its formation has so far been impossible by the method of supplying material from the upper surface of the separator with the serpentine channel. Supplying the material from the side of the product channel was proposed as a new extrusion method for separators like the serpentine type. The flow of the material at the time of product formation was observed and the flow of the material required to achieve stable production was controlled by the position and geometry of the front guide at the position from which the product is extruded.

Performance investigation of salt gradient cylindrical solar pond integrated and nonintegrated with evacuated tube solar collectors

In this study, the energetic and exergetic efficiencies of a salt gradient cylindrical solar pond (SGCSP) that integrated and nonintegrated evacuated tube solar collectors (ETSCs) are investigated to improve daily heat preservation performance of the heat storage zone (HSZ). The integrated system is consisted of an SGCSP and four ETSCs. The SGCSP has a surface area of 2 m2, a depth of 1.65 m, salty water layers at different densities, and HSZ in which the cylindrical serpentine type heat exchanger (CSHE) is located. Thus, the daily effects of the heat storage performance of both the ETSCs and the SGCSP in the winter season was determined experimentally. The analysis of the data regarding the efficiencies of the system is investigated separately by means of experimental studies where the SGCSP is integrated and nonintegrated with the ETSCs. The number of ETSCs integrated with SGCSP is increased to 1, 2, 3, and 4, respectively, and each of the five different experimental systems is performed separately. The temperature distributions of the integrated system are measured by a data acquisition system on 11 different points per hour. The efficiencies are calculated using the data obtained from these studies. Consequently, the energetic and exergetic efficiencies of the SGCSP are obtained without collectors as 10.4% and 4.3% and with one collector as 12.83% and 6.15%, with two collectors 14.88% and 8.25%, with three collectors 16% and 9.35%, and finally with four collectors 16.94% and 10.3%, respectively. Furthermore, the theoretical efficiencies are found to be consistent with the experimental results obtained by increasing the collector numbers.

Modeling polymer electrolyte fuel cells: A high precision analysis

In this paper, a computational model is used to study the distributions of several key parameters and the performance of a fuel cell with an active area of 200 cm2. The results reveal that the model is capable of predicting the overall behavior in good agreement with experimental data and with superior resolution. Polarization curves are compared and cell voltage prediction deviations are within 43mV of experimental values. The predicted current density distribution is very close to both the experimentally measured results and a volume-average approach based on rate equations. Local variations of current density, oxygen, and water mole fraction change significantly from under-rib regions to under-channel regions. The serpentine type flow path leads to greater pressure gradients, but is beneficial to gas bypassing through the gas diffusion layers. This type of flow path helps to redistribute the species and current density distributions. Never before has it been possible to construct computational models capable of predicting fine-scale details in local current density; details which were not captured neither by previous models nor by present-day experiments.

Characterization of Weda Bay nickel laterite ore from Indonesia

The association of fine grained MgNi silicates with oxy-hydroxides in laterites and saprolites represents challenges for ore processing, in particular, in nickel enrichment. The Weda Bay nickel deposit in Indonesia is a typical example of these complex ores, where clays such as nontronites develop on polyphase serpentinite as protolith. Thus, ores at Weda Bay have a very fine textured and complex mineralogy, which requires a comprehensive mineralogical identification through the use of a series of different types of analytical approaches (i.e. macroscopic and microscopic methods including SEM equipped with energy dispersive X-ray spectrometry (EDS), Raman spectroscopy, Infrared and X-ray fluorescence spectroscopy, and QEMSCAN® mapping). Nickel rich saprolites were found to be principally composed of several types of MgNi serpentines, quartz, clays (nontronite in particular) and little amounts of iron hydroxides. Besides, some parts of the deposit were characterized by the development of nontronites at the interface between the saprolite and the limonite zone. Above this zone, the limonite zone is dominated by iron hydroxides as expected, which replace all earlier silicates including serpentine, and contains a significant amount of nickel. The representative composite ore sample contains several nickel bearers with variable nickel grade of 2 to 3%. Exceptionally richer phases such as polygonal Fe (Ni)-rich serpentine were also found with nickel grade of 5 to 10%. Serpentine types as well as other newly formed silicates such as Fe-Mg-(Ni) smectites, are intimately mixed, preventing any mineral separation. Therefore, the only phases which can be separated are quartz and magnetite. This complicates the upgrading of nickel in Weda Bay laterite ore.

Study on rectangular-to-circular waveguide mode converter for KSTAR LHCD transmission line

A major upgrade of KSTAR LHCD system to 4 MW is planned for 2021. The system will be composed of eight 5-GHz 500-kW klystrons, low loss transmission lines with oversized circular waveguides, and a passive active multijunction launcher. Circular TE01 mode will be adopted for transmission lines longer than 50 m because it has extremely low loss in oversized waveguide, but mode converters from rectangular TE10 to circular TE01 mode are not easy to design. Mock-ups of two types of mode converters were developed. One is serpentine type, and the other is symmetric sidewall coupling type. The TE01 mode purities were demonstrated by measuring the transmission efficiencies between two identical mode converters at various angles between symmetric planes. A sidewall coupling mode converter with a refined design, which showed better circular symmetry and higher transmission efficiency than serpentine type, is under fabrication for prototype. The prototype mode converter is calculated to have 99.5% transmission efficiency, with 0.16% diffraction loss and 0.35% resistive loss, according to the simulation.

Global and gene-specific DNA methylation effects of different asbestos fibres on human bronchial epithelial cells

Inhalation exposure to asbestos is associated with lung and pleural diseases in humans and remains a major public health issue worldwide.Human bronchial epithelial cells (16HBE) were exposed to UICC amosite, crocidolite and chrysotile. Cytotoxicity, genotoxicity, global DNA methylation on cytosine residues (using LC-MS/MS) were investigated at different doses (2.5–100 μg/ml). Gene-specific DNA methylation alterations at the whole genome were investigated using a microarray that interrogates >450 thousand CpG sites. Subsequently, gene functional analyses (KEGG pathway, Gene Ontology and functional classification) were performed on genes with differentially methylated gene promoters.At non-cytotoxic doses, global DNA methylation was altered after 24 h exposure to amosite and crocidolite (>2.5 μg/ml). Exposure to amosite and crocidolite (amphibole type asbestos) induced both hypomethylation and hypermethylation at single CpG site and gene promoter levels whereas exposure to chrysotile (serpentine type asbestos) induced hypomethylation at the gene promoter level.Gene functional classification analyses revealed that all types of asbestos fibres induce alterations on GO-clusters i.e. on regulation of Rho-protein signal transduction, nucleus, (e.g. homeobox genes), ATP-binding function and extracellular region (e.g. WNT-group of genes). These differentially methylated genes might contribute to asbestos-related diseases in bronchial cells.

An Isotopic Exchange Kinetic Model to Assess the Speciation of Metal Available Pool in Soil: The Case of Nickel.

In this study an innovative approach is proposed to predict the relative contribution of each mineral phase to the total metal availability in soils, which, in other words, could be called the available metal fractionation. Through the use of isotopic exchange kinetics (IEK) performed on typical Ni bearing phases (i.e., two types of serpentines, chlorite, smectite, goethite, and hematite) the isotopic exchange and metal-solid interaction processes are connected, considering both the thermodynamic and kinetic aspects. Results of Ni IEK experiments on mineral phases are fitted with a pseudo-first order kinetic model. For each Ni bearing phase, this allows to (i) determine the number and size of exchangeable pools (ENi(i)), (ii) assess their corresponding kinetic constants (k(i)), and (iii) discuss the mechanism of Ni isotopic exchange at mineral surfaces. It is shown that all the phases investigated, with the only exception of hematite, present at least two distinct reactive pools with significantly different k(i) values. Results suggest also that metal involved in outer-sphere complexes would display isotopic exchange between 100 and 1000 times faster than metal involved in inner-sphere complexes, and that the presence of high and low affinity sites may influence the rate of isotopic exchange up to 1 order of magnitude. Moreover, the method developed represents a tool to predict and estimate Ni mobility and availability in natural soil samples on the basis of soil mineral composition, providing information barely obtained with other techniques.