Corrosion Mechanism of Alumina-magnesia Dry Materials for Smelting Manganese/chromium Steel in Coreless Medium Frequency Induction Furnaces

Alumina-magnesia dry materials are widely used in induction furnace linings, but they show different kinds of damage when melting different kinds of alloy steel. In this paper, the chemical composition, phase composition, and microstructure of the post-use dry materials for the working liners melting different kinds of steel were evaluated. Furthermore, the corrosion mechanism of the steel on the furnace lining materials was comprehensively analyzed. The findings reveal a significant ability of the Mn element in the molten steel to diffuse and penetrate into the refractories. Mn oxidizes to form MnO at the steel-refractory interface, and then forms a liquid phase with Al_(2)O_(3). The Cr element is dissolved into corundum and spinel of the refractories, resulting in lattice defects and structural damage of the materials. TiO2reacts with Al_(2)O_(3) to form Al_(2)TiO_(5), which plays a crucial role in preventing crack formation and propagation. Part of Ti4+dissolves into magnesia-alumina(MA), densifying the materials. TiO2also slows down the reaction between the Cr element and refractory components, further improving the corrosion resistance of the materials.

Structure and Mechanical Properties of CrN Thick Films Deposited by High-Rate Medium-Frequency Magnetron Sputtering

A home-made electron source assisted medium-frequency （MF） magnetron sputter- ing system was used to deposit thick CrN films on silicon and tungsten carbide substrates at various nitrogen flow rates with a fixed total pressure （0.3 Pa） and MF power （11.2 kW）. Result from scanning electron microscopy showed that the deposited CrN films have clear columnar struc- ture, and X-ray diffraction revealed a preferred orientation of CrN （200） for samples prepared at a rate of N2/（N2＋Ar） below 60%, whereas those prepared at higher N2/（N2＋Ar） rate are dom- inated by Cr2N. Deposition rates up to 12.5 μm/h were achieved and the hardness of the CrN coatings were in a range of 11 GPa to 18 GPa.

Study on the Reversible DC-DC Converter as Interface between Low and Medium Voltage DC Networks

This paper introduces an isolated reversible DC-DC converter with a particular topology, which benefits from both the NPC （neutral point clamped） structure and the series-parallel connection of converters. The key property of the proposed topology is the output voltage elevation above the blocking capabilities of each switch, without taking to a delicate synchronization of series-connected semiconductors. The converter is composed by two identical cells, each containing a full bridge, a medium frequency transformer and an NPC converter, connected in parallel at the input and in series at the output. The operation principle of each cell, into which a trapezoidal modulation was implemented, is similar to a DAB （dual active bridge）. A new model improves the dynamic performance of the controller. Simulation and experimental results verify the proposed topology, its control and start-up strategy.

Fabrication and photoluminescence characteristics of nonuniform Yb-Er codoped films

The nonuniform Yb-Er Codoped Al2O3 films were prepared on SiO2/Si substrates using a medium frequency magnetron sputtering system. Two asymmetry targets in the system were introduced to realize the nonuniform dopant. Some curves of Photoluminescence （PL） peak intensity were obtained by adjusting the deposition parameters, such as, the pillar number of erbium and ytterbium in the mixed target and the distance between a sample table and targets. Typically, the curve of PL peak intensity against the offset distance was approximately linear. The ratio of the PL intensity at the two ends of the same sample was 12.6 and the slope was 71.83/mm when the pillar numbers of the erbium and ytterbium in the mixed target are 5 and 60, respectively, and the distance between targets and the sample table is 2.9 cm.

Observation of therapuetic effect on cervical spondylosis treated mainly with electroacupuncture

Objective To observe the clinical effects of cervical spondylosis treated with electroacupuncture （EA）, cupping and TDP irradiation. Methods Ninety cases of mixed cervical spondylosis were randomized into 3 groups. Of which, in the treatment of observation group （30 cases）, the acupoints included Fengchi （风池 GB 20）, Jianjing （肩井GB 21）, Tianzong （天宗SI 11）, etc. EA, cupping and TDP irradiation were provided in combination. Two control groups were divided. In control group 1 （30 cases）, cervical traction was adopted in treatment. In control group 2 （30 cases）, stimulation with medium frequency was provided. In all of 3 groups, 5 treatments were given each week. 10 treatments made one course. The therapeutic effects of 3 groups were compared one course of treatment later. Resuits The total effective rate was 93.3% in observation group, 70.0% in control group 1 and 66.7% in control group 2. Significant differences were presented statistically in comparison between observation group and 2 control groups （both P〈0.05）. Conclusion The treatment with EA, cupping and TDP irradiation achieves quite satisfactory therapeutic effect on cervical spondylosis in clinical application.

The Averaged-value Model of a Flexible Power Electronics Based Substation in Hybrid AC/DC Distribution Systems

The concept of a flexible power electronics substation(FPES)was first applied in the Zhangbei DC distribution network demonstration project.As a multi-port power electronics transformer(PET)with different AC and DC voltage levels,the FPES has adopted a novel topology integrating modular multilevel converter(MMC)and four-winding medium frequency transformer(FWMFT)based multiport DC-DC converter,which can significantly reduce capacitance in each sub-module(SM)of a MMC and also save space and cost.In this paper,in order to accelerate speed of electromagnetic transient(EMT)simulations of FPES based hybrid AC/DC distribution systems,an averaged-value model(AVM)is proposed for efficient and accurate representation of FPES.Assume that all SM capacitor voltages are perfectly balanced in the MMC,then the MMC behavior can be modeled using controlled voltage sources based on modulation voltages from control systems.In terms of the averaged current transfer characteristics among the windings of the FWMFT,we consider that all multiport DC-DC converters are controlled with the same dynamics,a lumped averaged model using controlled current and voltage sources has been developed for these four-port DC-DC converters connected to the upper or lower arms of the MMC.The presented FPES AVM model has been tested and validated by comparison with a detailed IGBT-based EMT model.Results show that the AVM is significantly more efficient while maintaining its accuracy in an EMT simulation.