Interface reaction between alloys and submerged entry nozzle controlled by an electric current pulse

To solve the limitations of clogging and erosion of the submerged entry nozzle (SEN) for the production of high-quality special steel, the chemical reactivity between different alloys and the SEN and the interface reaction between alloys and the SEN controlled by an electric current pulse (ECP) were examined in this study. Results revealed that the chemical reactivity between different alloys and the SEN is different. For example, the reactivity between rare-earth metal and the SEN was strong, while that between Al and the SEN was extremely weak. At the same time, some differences between the clogging and interface reaction by ECP control were observed. Typically, at the positive electrode of the SEN, when a stable and dense clogging layer is formed, the internal SEN was effectively protected. However, at the negative electrode of the SEN, the decarburization rate of the SEN was accelerated by ECP, probably leading to a vicious circle of accelerated clogging and erosion of the SEN. Therefore, in the future, issues of clogging, erosion, infiltration, and decarbonization between active alloys and the SEN in the casting process may be solved and regulated by using the positive electric field of ECP. Meanwhile, the gain effect of ECP also helped to promote the homogenization of molten steel.     

Thermally stable Ni MOF catalyzed MgH2 for hydrogen storage

The poor kinetics is the main issue hindering MgH₂ for practical hydrogen storage application. In this work, the tricarboxybenzene was used to construct the stable Ni MOF (Ni-BTC300) as the catalyst for MgH₂. The prepared MOFs maintained their chemical structure after 300 °C calcining and doped to MgH₂ by ball milling. The dispersed, uniformly bonded Ni atoms can improve the kinetics of the composites, which could desorb 5.14 wt% H₂ within 3 min at 300 °C. And the stable MOF structure leading to good cycle stability in both kinetics and capacity, with retention of 98.2% after 10 cycles.     

多氢酸酸化反应特征及动力学

利用自制多氢酸液XS-1进行静态岩粉溶蚀与岩心流动实验,通过SEM、ICP等实验考察了多氢酸的缓速性与预防二次沉淀性能,并研究了多氢酸与岩心反应动力学特性。结果表明,XS-1多氢酸液具有良好的缓速与预防二次沉淀性能,反应后残酸的极限浓度为0.296 1 mol/L,酸液有效作用时间为6~7 h。在该多氢酸体系下岩心渗透率提高至4.15倍,在此条件下以酸岩反应动力学参数模型建立动力学方程,反应速率比同条件下普通酸液小,进一步证明多氢酸具有一定的缓速性。     

Kinetic Monte Carlo simulation of GaN epitaxy

A chemical reaction mode about GaN epitaxy in MOCVD is presented. We simulate the growth process of GaN in the vertical-spray MOCVD system on this mode using the KMC mothod. The result shows that adductive reaction mostly occurs at a lower temperature and pyrolytic reaction mostly occurs at a high temperature. And the growth rate increases with increasing temperature. This feature determines the surface morphology of the material. We also include the diffusion and desorption process of the reaction particle by the KMC method. These processes depend mostly on temperature and ultimately affect the surface morphology of the GaN material.     

Reinforced and hardened three-phase-foams

Currently and in the past several lightweight materials were evolved focusing on different applications. Many developments are based on biomimetic approaches to reach material and cost savings with a simultaneous combination of thermal insulation and sustainability, for example. The desire of needed high porosity and lower density lead to less strength of the materials. Thus, applications are limited. One way to solve this problem is the creation of foams based on three phases. A new approach is the implementation of nanotubes and further chemical treatment of the inorganic foams to avoid further energy consuming thermal treatment for strengthening. Three-phase-foams consist of pozzolanic active nanomaterials as a third phase, which can be varied and surface treated. The resulting materials can be combined with other binders to further improve their properties or used as self-contained materials.Aided by chemical treatment a hardening of the foams has been achieved. Implementation of prefabricated and synthesized nanotubes as a nanoreinforcement were successfully done and properties of the foams investigated. Results based on studies of the microstructure and phase formation will be illustrated and discussed.     

Influence of two-step ball-milling condition on electrical and mechanical properties of TiC-dispersion-strengthened Cu alloys

TiC-dispersion-strengthened Cu alloys were prepared by a two-step ball-milling (BM) process followed by sparks plasma sintering (SPS), heat treatment and hot rolling in sequence. The two-step BM process is composed of a pre-ball-milling (pre-BM) on both Ti and graphite powders as well as a subsequent homogenizing by BM together with Cu powder. Microstructure evolution analysis was performed to evaluate the effects of BM conditions on the electrical and mechanical properties of Cu-based alloys. The X-ray results revealed that titanium carbide (TiC) formed from Ti and C under high impact energy BM. Moreover, the formation of TiC during the SPS and heat treatment processes was found to more beneficial in enhancing the mechanical properties of alloy. The residual Ti in Cu matrix was found to be the predominant factor lowering the electrical conductivity of Cu–Ti–C alloys.     

Detection of unapproved genetically modified potatoes in Korea using multiplex polymerase chain reaction

Several genetically modified (GM) potato cultivars with improved traits such as increased amylopectin levels, decreased asparagine levels, and reduced incidence of black spot have been developed. In this study, we describe a multiplex polymerase chain reaction (PCR) method specific for four GM potato events (EH92-527-1, AM04-1020, PH05-026-0048, and E12) that are unauthorized in Korea. The UDP-glucose pyrophosphorylase (UGPase) gene was used as the endogenous reference gene. The specificity of the primer sets was evaluated using GM potatoes and other GM crops. The limit of detection in the developed multiplex PCR was confirmed to be approximately 0.04% (w/w). Thirty-three commercial products containing potato ingredients were tested by the multiplex PCR assay, and GM potato event E12 was found in one of the 33 samples. This result suggested that the developed PCR method could be used to effectively identify unauthorized GM potatoes in Korea.     

DFT study of the oxygen reduction reaction on iron,cobalt and manganese macrocycle active sites

The best performing non-precious metal based catalysts for polymer electrolyte membrane fuel cells are manufactured by incorporation of nitrogen into a carbon structure in the presence of iron and cobalt. Herein, density functional theory (DFT) calculations have been performed to investigate the oxygen reduction reaction on catalyst active sites modelled as transition metal macrocycles with iron, cobalt or manganese central atoms. The effects of the transition metal and macrocycle structure have been investigated. The structure of the most promising active sites has been proposed, and the detailed potential energy profiles of the oxygen reduction reaction have been obtained over the active sites, including all intermediate steps with corresponding activation barriers. The efficiency of the active sites depends primarily on the transition metal nature, and the central iron atom accounts for the higher catalytic activity than cobalt and manganese. The central manganese atom can favour the two-electron oxygen reduction pathway and thus yielding hydrogen peroxide.     

Intensify the application of ZnO-based nanodevices in humid environment: O2/H2 plasma suppressed the spontaneous reaction of amorphous ZnO nanowires

In this work, we have demonstrated that amorphous ZnO nanobranches (a-ZnO NBs) could spontaneously react from the crystalline ZnO NWs (c-ZnO NWs) at specific humid environment. The spontaneous reaction mechanism and result can be analyzed by humidity controlling and optical microscope (OM)/scanning electron microscope (SEM)/Kelvin probe force microscopy (KPFM)/transmission electron microscopy (TEM) system. We can make the c-ZnO NWs spontaneous reaction happen at different humid environments and suppress the a-ZnO NBs spontaneous reaction by oxygen/hydrogen plasma surface passivation. The hydrogen plasma surface treatment also can improve the UV sensing sensitivity more than twofold. This work provides the mechanism and methods of the a-ZnO NBs spontaneous growth and offers the passivation treatment for strengthening and enhancing ZnO-based nanodevice application in humid environment and UV light detection, respectively.     

Enhanced catalytic activity of nanoshell carbon co-doped with boron and nitrogen in the oxygen reduction reaction

The use of carbon cathode catalysts in polymer electrolyte fuel cells instead of the current platinum catalysts is attracting increasing attention. We claim that two factors are important for enhancing the activity of carbon cathode catalysts in the oxygen reduction reaction (ORR): the formation of a nanoshell structure and co-doping with boron and nitrogen. Herein, we investigate the preparation and characterization of active ORR carbon catalysts that combine the above factors. Boron and nitrogen (BN)-doped nanoshell-containing carbon (BN-NSCC) was prepared by carbonizing a mixture of poly(furfuryl alcohol), cobalt phthalocyanine, melamine, and a trifluoroborane–methanol complex at 1000 °C. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed the formation of nanoshell structures with distorted graphitic layers and the introduction of boron and nitrogen atoms, respectively. The ORR activity was evaluated in oxygen-saturated 0.5 mol dm^?3 H₂SO₄ using Koutecky–Levich analysis. The BN-NSCC showed an eight to ten times higher ORR activity than undoped NSCC, with an increased number of electrons participating in the reaction. Tafel analysis revealed a change in the rate-determining step caused by BN-doping. Thus, the combination of a nanoshell structure and co-doping with boron and nitrogen was found to improve the ORR activity of carbon catalysts.