Controlling solute channel formation using magnetic fields

Solute channel formation introduces compositional and microstructural variations in a range of processes, from metallic alloy solidification, to salt fingers in ocean and water reservoir flows. Applying an external magnetic field interacts with thermoelectric currents at solid/liquid interfaces generating additional flow fields. This thermoelectric (TE) magnetohydrodynamic (TEMHD) effect can impact on solute channel formation, via a mechanism recently drawing increasing attention. To investigate this phenomenon, we combined in situ synchrotron X-ray imaging and Parallel-Cellular-Automata-Lattice-Boltzmann based numerical simulations to study the characteristics of flow and solute transport under TEMHD. Observations suggest the macroscopic TEMHD flow appearing ahead of the solidification front, coupled with the microscopic TEMHD flow arising within the mushy zone are the primary mechanisms controlling plume migration and channel bias. Two TE regimes were revealed, each with distinctive mechanisms that dominate the flow. Further, we show that grain orientation modifies solute flow through anisotropic permeability. These insights led to a proposed strategy for producing solute channel-free solidification using a time-modulated magnetic field

Thermoelectric magnetohydrodynamic control of melt pool flow during laser directed energy deposition additive manufacturing

Melt flow is critical to build quality during additive manufacturing (AM). When an external magnetic field is applied, it causes forces that alter the flow through the thermoelectric magnetohydrodynamic (TEMHD) effect, potentially altering the final microstructure. However, the extent of TEMHD forces and their underlying mechanisms, remain unclear. We trace the flow of tungsten particles using in situ high-speed synchrotron X-ray radiography and ex situ tomography to reveal the structure of TEMHD-induced flow during directed energy deposition AM (DED-AM). When no magnetic field is imposed, Marangoni convection dominates the flow, leading to a relatively even particle distribution. With a magnetic field parallel to the scan direction, TEMHD flow is induced, circulating in the cross-sectional plane, causing particle segregation to the bottom and side of the pool. Further, a downward magnetic field causes horizontal circulation, segregating particles to the other side. Our results demonstrate that TEMHD can disrupt melt pool flow during DED-AM

Arsenic(V) removal in wetland filters treating drinking water with different substrates and plants

Constructed wetlands are an attractive choice for removing arsenic (As) within water resources used for drinking water production. The role of substrate and vegetation in As removal processes is still poorly understood. In this study, gravel, zeolite (microporous aluminosilicate mineral), ceramsite (lightweight expanded clay aggregate) and manganese sand were tested as prospective substrates while aquatic Juncus effuses (Soft Rush or Common Rush) and terrestrial Pteris vittata L. (Chinese Ladder Brake; known as As hyperaccumulator) were tested as potential wetland plants. Indoor batch adsorption experiments combined with outdoor column experiments were conducted to assess the As removal performances and process mechanisms. Batch adsorption results indicated that manganese sand had the maximum As(V) adsorption rate of 4.55 h−1 and an adsorption capacity of 42.37 μg/g compared to the other three aggregates. The adsorption process followed the pseudo-first-order kinetic model and Freundlich isotherm equations better than other kinetic and isotherm models. Film-diffusion was the rate-limiting step. Mean adsorption energy calculation results indicated that chemical forces, particle diffusion and physical processes dominated As adsorption to manganese sand, zeolite and gravel, respectively. During the whole running period, manganese sand-packed wetland filters were associated with constantly 90% higher As(V) reduction of approximate 500 μg/L influent loads regardless if planted or not. The presence of P. vittata contributed to no more than 13.5% of the total As removal. In contrast, J. effuses was associated with a 24% As removal efficiency

Effects of egg and vitamin A supplementation on hemoglobin, retinol status and physical growth levels of primary and middle school students in

Lack of protein and vitamin A influences the growth of student in impoverished mountain areas. The aim of the study was to assess the effects of egg and vitamin A supplementation on hemoglobin, serum retinol and anthropometric indices of 10-18 years old students of a low socioeconomic status. A total number of 288 students from four boarding schools were randomly selected by using cluster sampling method in Chongqing, and they were assigned into supplement group and control group non-randomly. Students in supplement group received a single 200,000 international units vitamin A and 1 egg/day (including weekends) for 6 months. The control group did not receive any supplementation. We measured hemoglobin, serum retinol and height and weight at baseline and after supplementation. The supplementation increased the mean hemoglobin concentration by 7.13 g/L compared with 1.38 g/L in control group (p<0.001), the mean serum retinol concentration by 0.31 μmol/L compared with 0.09 μmol/L in the control group (p=0.005), the mean height-for-age z score by 0.05 compared with 0.03 in the control group (p=0.319), the mean weight-for-age z score by 0.05 compared with -0.12 in the control group (p<0.001). Our results revealed that egg and vitamin A supplementation is an effective, convenient, and practical method to improve the levels of hemoglobin, serum retinol and prevent the deterioration of growth in terms of weight for primary and middle school students from outlying poverty-stricken areas. Our intervention did not have a beneficial effect on linear growth

Magnetic Field Control of Melt Pool Flow and Keyhole Dynamics during Additive Manufacturing

Metal additive manufacturing (AM), also known as metal 3D printing, is revolutionising our manufacturing industries. However, there are several major concerns with process instability developing during AM, including a complex and intensive flow appearing within the melt pool and keyhole instability. Developing methods to control process instability has been a priority in the AM community. This work investigates the potential use of a magnetic field to control process instability in AM, with a specific focus on using in situ synchrotron X-ray imaging to reveal the magnetic field control mechanisms. Firstly, the results demonstrated that the application of a static magnetic field (0.12 T) to the directional solidification (DS) of a Ga-In alloy can disrupt and potentially prevent solute channel formation through the thermoelectric magnetohydrodynamic (TEMHD) effect. Then, by applying a static magnetic field (0.2 T) to laser directed energy deposition (DED) process of a nickel-based superalloy, the Marangoni flow within the melt pool was observed to be disrupted, and the flow direction was dependent on the magnetic field orientation, which indicates that the TEMHD effect can dominate flow patterns. Furthermore, a magnetic field of 0.6 T was applied to the laser powder bed fusion (LPBF) of Al alloys under keyhole conditions. The findings showed that the keyhole appeared more stable and there was a reduction in keyhole porosity, which can be attributed to the thermoelectric effect stabilising the keyhole when a static magnetic field is applied. These observations and the underlying physics revealed in this research offer a new pathway for using an external magnetic field to control process instability in multiple metal solidification processes, including directional solidification and additive manufacturing. By employing this approach, the microstructure can be tailored, and pores can be minimised during the solidification process

Grain Refinement of a Powder Nickel-Base Superalloy Using Hot Deformation and Slow-Cooling

A pre-hot-deformation process was applied for a polycrystalline nickel-base superalloy to active deformation twins and dislocations, and subsequent slow cooling treatment was used to achieve grain refinement and microstructure homogenization. The microstructural evolution of the alloy was investigated, and the corresponding underlying mechanism was discussed. It was found that twinning mainly occurred in large grains during pre-hot-deformation owing to the stress concentration surrounding the large grains. High density dislocations were found in large grains, and the dislocation density increased approaching the grain boundary. The average grain size was refined from 30 μm to 13 μm after slow cooling with a standard deviation of grain size decreasing from 10.8 to 2.8, indicating a homogeneous microstructure. The grain refinement and microstructure homogenization during cooling process could be achieved via (i) static recrystallization (SRX), (ii) interaction of twin tips and γ’ precipitates, and (iii) grain coarsening hindered by γ’ precipitates in grain boundaries

Adsorptive performance of chromium-containing ordered mesoporous silica on volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) are the primary poisonous emissions into the atmosphere in natural gas exploitation and disposing process. The adsorption method has been widely applied in actual production because of its good features such as low cost, low energy consumption, flexible devices needed, etc. The commonly used adsorbents like activated carbon, silicon molecular sieves and so on are not only susceptible to plugging or spontaneous combustion but difficult to be recycled. In view of this, a new adsorbent (CrSBA15) was made by the co-assembly method to synthesize the ordered mesoporous silica materials with different amounts of chromium to eliminate VOCs. This new adsorbent was characterized by small-angle-X-ray scattering (SAXS), nitrogen adsorption/desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its adsorption performance to eliminate VOCs (toluene, benzene, cyclohexane and ethyl acetate used as typical pollutants) was also tested systematically. Research results indicate that this new adsorbent of CrSBA-15(30), with the silicon/chromium ration being 30, owns the maximum micropore volume, and shows a higher adsorption performance in eliminating toluene, benzene, cyclohexane and ethyl acetate. Besides, it is cost-effective and much easier to be recycled than the activated carbon. In conclusion, CrSBA-15(30) is a good adsorbent to eliminate VOCs with broad application prospects. Keywords: Mesoporous materials, Silicon dioxide, Synthesis, Adsorption, Volatile organic compounds (VOCs), Recyclability, Energy savin

Preparation of a mesoporous Cu-Mn/TiO2 composite for the degradation of Acid Red 1

Heterogeneous catalysts which show high catalytic performance, structural stability, and low toxicity, are greatly required to efficiently degenerate organic pollutants in waste water in advanced oxidation processes (AOPs). In this paper, a mesoporous Cu-Mn/TiO2 composite heterogeneous catalyst was successfully prepared, which has a stable crystalline TiO2 mesostructure as the support, and well-dispersed Cu-Mn oxides as the catalytic active sties. Its Cu, Mn content is measured to be 5.7 and 6.0 wt%, and the BET surface area is measured to be 97 m2 g-1 with a pore size of approx. 6.0 nm and pore volume of 0.15 cm3 g-1. Using the prepared Cu-Mn/TiO2 composite as an AOPs catalyst for the degeneration of Acid Red 1, it can efficiently (\u3e99%) degenerate the model pollutant in water within only 90 min. Compared with homogeneous catalysts, it can retain its catalytic performance over a wide pH range (3-9) and can be recycled for at least five times while still possessing the decolorization efficiency of 89%. By analyzing the catalytic process, a possible catalytic procedure for the degradation of Acid Red 1 has been proposed. Furthermore, using bulk Cu-Mn oxides, Cu-Mn/P25, and Cu-Mn/SBA-15 as reference catalysts, we propose that the excellent catalytic performance of Cu-Mn/TiO2 could be ascribed to the anatase mesoporous TiO2, which not only offers a stable matrix with high surface area for Cu-Mn catalysts, but also serves as a type of catalytic promoter for the synergistic catalytic degeneration of Acid Red 1

Electrospun Conductive Nanofiber Yarn for a Wearable Yarn Supercapacitor with High Volumetric Energy Density

One-dimensional, flexible yarn-shaped supercapacitors for woven cloth have the potential for use in different kinds of wearable devices. Nevertheless, the challenge that supercapacitors face is low energy density. In this paper, we present a low-cost and large-scale manufacturing method to construct a supercapacitor yarn with high power and high energy density. To construct the novel and flexible poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)–polyacrylonitrile (PDEOT: PSS-PAN)/Ni cotton (PNF/NiC) capacitor yarn, an electrospinning technique was initially used to wrap the polyacrylonitrile (PAN) nanofibers around the core Ni-coated yarn. The PEDOT: PSS–PAN nanofiber composite electrode was created using in situ deposition and H3PO4/PVA was used as a gel electrolyte. This electrode material has a yarn/nanofiber/PEDOT: PSS nanoparticle hierarchical structure, providing a high specific area and enhanced pseudocapacitance. The electrode demonstrated a high volumetric capacitance of 26.88 F·cm−3 (at 0.08 A·cm−3), an energy density of 9.56 mWh·cm−3, and a power density of 830 mW·cm−3. In addition, the PNF/NiC capacitor yarns are lightweight, highly flexible, resistant to bending fatigue, can be connected in series or parallel, and may be suitable for a variety of wearable electronic products