Influence of silicon on the microstructures, mechanical properties and stretch-flangeability of dual phase steels

Uniaxial tension tests and hole-expansion tests were carried out to determine the influence of silicon on the microstructures, mechanical properties, and stretch-flangeability of conventional dual-phase steels. Compared to 0.03wt% silicon, the addition of 1.08wt% silicon induced the formation of finer ferrite grains （6.8μm ） and a higher carbon content of martensite （Cm≈ 0.32wt%）. AS the silicon level increased, the initial strain-hardening rate （n value） and the uniform elongation increased, whereas the yield strength, yield ratio, and stretch-flangeability decreased. The microstructures were observed after hole-expansion tests. The results showed that low carbon content martensite （Cm ≈ 0.19wt%） can easily deform in coordination with ferrite. The relationship between the mechanical properties and stretch-flangeability indicated that the steel with large post-uniform elongation has good stretch-flangeability due to a closer plastic incom- patibility of the ferrite and martensite phases, which can effectively delay the production and decohesion of microvoids.

The model developed for stress-induced structural phase transformations of micro-crystalline silicon films

The nanoindentations were applied to island-shaped regions with metal-induced Si crystallizations. The experimental stress-strain relationship is obtained from the load-depth profile in order to investigate the critical stresses arising at various phase transitions. The stress and strain values at various indentation depths are applied to determine the Gibbs free energy at various phases. The intersections of the Gibbs free energy lines are used to determine the possible paths of phase transitions arising at various indentation depths. All the critical contact stresses corresponding to the various phase transitions at four annealing temperatures were found to be consistent with the experimental results.

Electromagnetic separation of primary iron-rich phases from aluminum-silicon melt

The difference of conductivity between primary iron-rich phases and aluminum melt has been used to separate them by electromagnetic force (EMF) which is induced by imposing a direct electric current and a steady magnetic field in molten Al-Si alloy. Theoretical analysis and experiments on self-designed electromagnetic separation indicates that primary needle-like β phases are difficult to separate; while primary α iron-rich phases can be separated by electromagnetic separation. Primary iron-rich phases have been removed from the melt successfully when the molten metal flows horizontally through separation channel. The iron content is reduced from 1.13% to 0.41%.

Determination of Triclocarban, Triclosan and Methyl-Triclosan in Environmental Water by Silicon Dioxide/Polystyrene Composite Microspheres Solid-Phase Extraction Combined with HPLC-ESI-MS

This paper developed a sensitive and efficient analytical method for triclocarban (TCC), triclosan (TCS) and Methyl-triclosan (MTCS) determination in environmental water, which involves enrichment by using silicon dioxide/polystyrene composite microspheres solid-phase extraction and detection with HPLC-ESI-MS. The influence of several operational parameters, including the eluant and its volume, the flow rate and acidity of water sample were investigated and optimized. Under the optimum conditions, the limits of detection were 1.0 ng/L, 2.5 and 4.5 ng/L for TCC, TCS, and MTCS, respectively. The linearity of the method was observed in the range of 5-2000 ng/L, with correlation coefficients (r2) >.99. The spiked recoveries of TCC, TCS and MTCS in water sampleswereachieved in the range of 89.5% -96.8% with RSD below 5.7%. The proposed method has been successfully applied to analyze real water samples and satisfactory results were achieved.

Preparation and Characterization of CA-MA Eutectic/Silicon Dioxide Nanoscale Composite Phase Change Material from Water Glass via Sol-Gel Method

This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon dioxide（nano-SiO_2） serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, Fourier-transform infrared（FT-IR） spectroscopy and polarizing microscopy（POM）. It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA） measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m^（-1）·K^（-1） by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.

Thermodynamic behaviors of SiCl_2 in silicon deposition by gas phase zinc reduction of silicon tetrachloride

The modified Siemens process,which is the major process of producing polycrystalline silicon through current technologies,is a high temperature,slow,semi-batch process and the product is expensive primarily due to the large energy consumption.Therefore,the zinc reduction process,which can produce solar-grade silicon in a cost effective manner,should be redeveloped for these conditions.The SiCl2 generation ratio,which stands for the degree of the side reactions,can be decomposed to SiCl4 and ZnCl2 in gas phase zinc atmosphere in the exit where the temperature is very low.Therefore,the lower SiCl2 generation ratio is profitable with lower power consumption.Based on the thermodynamic data for the related pure substances,the relations of the SiCl2 generation ratio and pressure,temperature and the feed molar ratio（n（Zn）/n（SiCl4） are investigated and the graphs thereof are plotted.And the diagrams of Kpθ-T at standard atmosphere pressure have been plotted to account for the influence of temperature on the SiCl2 generation ratio.Furthermore,the diagram of Kpθ-T at different pressures have also been plotted to give an interpretation of the influence of pressure on the SiCl2 generation ratio.The results show that SiCl2 generation ratio increases with increasing temperature,and the higher pressure and excess gas phase zinc can restrict SiCl2 generation ratio.Finally,suitable operational conditions in the practical process of polycrystalline silicon manufacture by gas phase zinc reduction of SiCl4 have been established with 1200 K,0.2 MPa and the feed molar ratio（n（Zn） /n（SiCl4）） of 4 at the entrance.Under these conditions,SiCl2 generation ratio is very low,which indicates that the side reactions can be restricted and the energy consumption is reasonable.

Determination of Particle Sizes and Crystalline Phases on Colloidal Silicon Nanoparticle Suspensions

Particle size and crystallinity of silicon nanoparticles were determined by analyzing the optical extinction spectra of colloidal suspensions. Experimental results from these colloids were anaiyzed using Mie theory in connection with effective medium theory, in order to determine particle sizes and their internal structure with the simple technique of optical transmission spectroscopy. By modeling an effective refractive index for the particles, the crystalline volume fraction can be extracted from extinction spectra in addition to information about the size. The crystalline volume fraction determined in this way were used to calibrate the ratio of the Raman cross sections for nanocrystalline and amorphous silicon, which was found to be σc./σa = 0.66

Preparation of Porous Silicone Resin Sheet with Phase Inversion in Parallel with Non Solvent Induced Phase Separation and Application to Hollow Particle Formation

We have tried to prepare the porous silicone resin sheet with the phase inversion method in parallel with the non solvent induced phase separation method. In the experiment, ethyl acetate and water were adopted as a good solvent and a poor solvent for silicone resin, respectively and ethyl alcohol as an amphiphilic solvent was used to increase the solubility of ethyl acetate in water and decrease the interfacial tension by mass transfer from water to ethyl acetate. The concentration of silicone resin in ethyl acetate and the oil soluble surfactant species were changed. Increasing the concentration of silicone resin could depress coalescence between the water droplets in the (W/O) dispersion and increase the porosity and pore number density of silicone resin sheet. Span 80 among the oil soluble surfactant species made the porosity and pore number density larger. The effect of physical proparties of liquids concerned on the porosity and pore number density was discussed on the basis of dispersing behavior of liquid droplets in the liquid-liquid dispersion. The hollow silicone resin particles could be prepared by applying the preparation method presented here.

Liquid Phase Sintering (LPS) and Dielectric Constant of α-Silicon Nitride Ceramic

The spark plasma sintering （SPS） was applied to prepare α-Si3 N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The mechanism of liquid phase sintering （LPS） wus discussed and the factors influencing the density of the prepared samples were analyzed. The dielectric constant of sintered samples was tested. The experimental results show that the density can be controlled from 2.48 g/ cm^3 to 3.09 g/ cm^3 while the content of the sintering aids and the sintering temperature alter and the dielectric constant is closely dependent on the density of obtained samples.

Effect of Additives on the Sintering of Amorphous Nano-sized Silicon Nitride Powders

Amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering. The influences of the additives of Y2O3 and Al2O3 prepared by two different ways, the polyacrylamide gel method and the precipitation method, were investigated. The grain sizes of the additives prepared by the first method were finer than those of prepared by the latter method. When sintered at the same temperature, 1700 ℃, the average grain size of the silicon nitride is 0.3 um for the sample with the former additives, which is much finer than the one with the latter additives. The density of additives prepared by precipitation method is clearly lower than those of prepared by polyacrylamide gel method.

Effects of CaO and Na2CO3 on the Reduction of High Silicon Iron Ores

The effects of CaO and Na2CO3 on the reduction of high silicon iron ores at 1 250 ℃ were studied. The experimental results showed that the metallization rate was significantly hindered by the addition of CaO and Na2CO3, particularly at the early stage of roasting, compared to the rate without additives. In the absence of additives, iron oxides were quickly reduced to metallic iron, and fayalite was difficult to form. When CaO and Na2CO3 were added, the low reducible iron-containing silicate compounds formed and melted, subsequently retarding the metallization process. The inhibition of Na2CO3 was more noticeable than that of CaO, and higher Na2CO3 doses resulted in stronger inhibition of the increased metallization rate. However, when Na2CO3 was added prior to CaO, the liquid phase formed, which facilitated the growth of the metallic phase. To reinforce the separation of the metallic phase and slag, an appropriate amount of liquid phase generated during the reduction is necessary. It was shown that when 10% CaO and 10% Na2CO3 were added, a high metallization rate and larger metallic iron particles were obtained, thus further decreasing the required Na2CO3 dosage.

Evolution of Phase Composition and Microstructure of Al_2O_3-Si-Al Composite at High Temperatures in Reducing Atmosphere

Al2 O3-Si-Al composite specimens with the size of 25 mm × 25 mm × 125 mm were prepared using fused alumina （as aggregates and fines）,ultra-fine α-Al2O3,Si and Al powders as starting materials,liquid phenol formaldehyde resin as the binder,pressing and heating at 800-1 500 ℃ for 3 h under carbon embedded condition.Evolution of phase composition and microstructure of Al2 O3-Si-Al composite during heating from 800 to 1 500 ℃ under carbon embedded condition were studied.The results show that：（1） Al4 C3,AlN and SiC are initially formed at 800-900 ℃ due to reactions of Al and Si with C or CO and N2 ; （2） at 1 000-1 300 ℃,the amounts of Al4C3,AlN and SiC increase with temperature rising and their crystals grow; （3） at 1 400-1 500 ℃,Al4 C3 and AlN disappear,and minor SiAlON crystals are observed; the nonoxide crystals develop well and they are interlaced in the corundum skeleton structure,which creates strengthening and toughening

Fabrication of solid-phase-sintered Si C-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.

Time Sequential and Phase-resolved Measurement and Analysis of Corona Discharge in Air and Streamer Discharge in Insulating Liquid

Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.

Monte Carlo study on abnormal growth of Goss grains in Fe-3%Si steel induced by second-phase particles

The selective abnormal growth of Goss grains in magnetic sheets of Fe-3%Si （grade Hi-B） induced by second-phase particles （AlN and MnS） was studied using a modified Monte Carlo Ports model. The starting microstructures for the simulations were generated from electron backscatter diffraction （EBSD） orientation imaging maps of recrystallized samples. In the simulation, second-phase particles were assumed to be randomly distributed in the initial microstructures and the Zener drag effect of particles on Goss grain boundaries was assumed to be selectively invalid because of the unique properties of Goss grain boundaries. The simulation results suggest that normal growth of the matrix grains stagnates because of the pinning effect of particles on their boundaries. During the onset of abnormal grain growth, some Goss grains with concave boundaries in the initial microstructure grow fast abnormally and other Goss grains with convex boundaries shrink and eventually disappear.

Thermodynamic Calculation for Silicon ModifiedAISI M2 High Speed Tool Steel

During high speed tool steel production up to 0.2 wt % silicon is added, primarily to react with oxygen e.g. silicon acts as a de-oxidizer. If more than 0.2 wt % silicon is added, it serves to improve the deep hardening properties. An addition up to ~1 wt % silicon provides hardness and improves temper-stability but reduces the ductility. At high concentration, silicon causes embrittlement. Alloying with silicon raises the solubility of carbon in the matrix and hence the as-quenched hardness. It has virtually no influence on the carbide distribution, but it promotes the formation of M6C type carbides. The many essential alloy additions to iron (C, W, Mo, V, Cr, Si) make the high speed tool steel, HSS a complex multi-component system. Its complete experimental investigation would require enormous time and effort. Instead, the CALPHAD method has been successfully used for computation of phase equilibrium the multi-component HSS system. In the present work, the Thermo-Calc program has been applied to the system Fe-C-Cr-W-Mo-V-Si with the thermodynamic information contained in the solid-solution-database of the TCFE. In the present work, some temperature-concentration diagrams for silicon modified AISI M2 steel are presented by calculated quantities (melting and transformation temperatures, amount and compositions of phases). Calculated data are compared with standard AISI M2 high speed tool steel.

过共晶铝硅合金中硅相细化的研究进展

过共晶铝硅合金因其耐磨性能良好而受到关注,但组织中含有粗大的初晶硅和针状的共晶硅,限制了其进一步广泛使用。本文综述了当前过共晶铝硅合金中硅相细化的一些方法,如合金化、变质处理和改进制备工艺等。其中重点介绍了合金化对过共晶铝硅合金中组织的作用;然后对各种变质剂的细化效果进行了对比分析;并讨论了改进制备工艺对硅相尺寸和形貌的影响;最后指出未来的研究方向应集中开发出适用于广泛使用的新型复合变质剂,并通过变质和改进制备工艺相结合,获得性能更加优异的过共晶铝硅合金。

Dynamic study in partial transient liquid phase bonding of Si_3N_4

Dynamics in partial transient liquid phase bonding (PTLP bonding) of Si_3N_4 ceramic with Ti/Cu/Ti multi-interlayer was systematically studied through micro-analysis of joint interfaces. The results show that growth of reaction layer and isothermal solidification procession do at the same time. Growth of reaction layer and moving of isothermal solidification interface obey the parabolic law governed by the diffusion of participating elements during the PTLP bonding. Coordination of the above two dynamics process is done through time and temperature. When reaction layer thickness is suitable and isothermal solidification process is finished, the high bonding strength at room temperature and high temperature are obtained.

Temperature Induces Self-assembly of Silicon Nano/Micro-structure based on Multi-physics Approach

A three-dimensional dynamic model for nano/micro-fabrications of silicon was presented. With the developed model, the fabrication process of silicon on nothing（SON） structure was quantitatively investigated. We employ a diffuse interface model that incorporates the mechanism of surface diffusion. The mechanism of the fabrication is systematically integrated for high reliability of computational analysis. A semi-implicit Fourier spectral scheme is applied for high efficiency and numerical stability. Moreover, the theoretical analysis provides the guidance that is ordered by the fundamental geometrical design parameters to guide different fabrications of SON structures. The performed simulations suggest a substantial potential of the presented model for a reliable design technology of nano/micro-fabrications.