•Distribution of iron impurity is calculated with fluctuant growth rate.•High fluctuant distribution of impurity in silicon ingot is explained.•Effect degree of production accident can be evaluated by the model.•Process parameters can be design and optimization by the model.•Maximum yield for different impurity concentration of raw silicon can be evaluated.A theoretical model to determine distribution of iron impurity during silicon purification by directional solidification with fluctuant crystal growth rate is proposed in this paper. The crystal growth rate is fluctuant usually and it has profound effect on the distribution of iron impurity in practical production. The model validation by the distribution of iron impurity during silicon purification by directional solidification in industrial production and the results show that the calculation agrees with existing experimental results. The results also indicate that distribution of iron impurity is directly correlated with the instantaneous value of crystal growth rate. The high fluctuant distribution of iron impurity during silicon purification by directional solidification can be well explained. Many potential applications of the model in practical production are found, such as predicting the distribution of iron impurity with fluctuant crystal growth rate, evaluating the effect degree of production accident, design and optimization of the process parameters and evaluating of maximum yield for raw silicon with different impurity concentration. Silicon purification with low energy consumption is possible based on the research in this paper.

•Nickel-based superalloy was refined by electron beam smelting (EBS).•The segregation of alloy elements is weak during solidification after EBS.•Ni, Ti, Mo and Al show positive segregation; Cr, Co and W show negative segregation.•The segregation degree of Co shows little change with the increasing of smelting power and time.The segregation behavior of alloy elements in nicked-based superalloy ingots during electron beam smelting was investigated. Three series of experiments were carried out with different parameters. The micromorphology of the cross section of the ingot and the distribution of alloy elements in the ingot were analyzed. The results show that the melt solidified at the bottom and formed a region of equiaxed grain at the beginning of solidification; the columnar crystal is formed in the middle of ingot with the proceeding of solidification; the region with large grains is formed at the end of the solidification. The segregation of alloy elements is weak during solidification after the nickel-based superalloy is smelted for 10 min with a power of 9 kW. That is, Ni, Ti, Mo and Al show positive segregation with effective segregation coefficient value of 0.994, 0.982, 0.995 and 0.884, respectively; Cr, Co and W show negative segregation with effective segregation coefficient value of 1.051, 1.005 and 1.013, respectively. With the increasing of smelting power and time, the segregation degree of Ni, Cr, Ti, W and Mo is increased, the segregation degree of Al is decreased and the segregation degree of Co shows little change in the ingot.

•We achieved continuous electron beam melting of silicon powder by prefabricating a molten silicon pool for the first time.•The characteristic of electron beam melting of silicon powder was revealed.•The feasibility of continuous silicon powder melting was analyzed in basic theory of convective heat transfer.•The most appropriate powder feeding rate was determined by considering various factors in this experiment.•Compared with the melting of silicon block, this continuous powder feeding process was confirmed to be more cost saving.We successfully achieved the continuous melting of silicon powder in a vacuum electron beam melting system. The characteristic of electron beam melting of silicon powder was revealed by comparing the three different approaches to prefabricate the molten silicon pool. The application of silicon block can be regarded as the most efficient method to prefabricate a stable molten silicon pool. Afterward, the silicon powder was added into the molten silicon pool at different rates by a spiral silicon powder feeding device. Finally, all of the silicon powder was melted completely. Although the P removal efficiency decreases with increasing powder feeding rate during the powder feeding process, an appropriate increase in the powder feeding rate is not only beneficial to improve the melting efficiency of silicon powder but also conductive to the improvement in uniformity of the obtained silicon ingot. Therefore, the powder feeding rate of 10 g/min was the best option in this study. Compared with the melting of silicon block, which has been wildly applied, this continuous powder feeding process can be beneficial to saving smelting time and the total cost.

A multicrystalline silicon ingot with columnar and irregular grains was obtained from metallurgical-grade silicon (MG-Si) by directional solidification. The segregation behaviors of substitutional and interstitial impurities in different grain morphologies have been studied. The concentration distribution of substitutional impurities (B and Al) in the silicon ingot was accord with the Scheil's equation, which depended on the grain morphology. However, the concentration distribution of interstitial impurities (Fe, Ti, Cu, and Ni) was only accord with the Scheil's equation under the columnar grains growth condition. The difference lattice sites of the impurities will result in the disparate segregation behavior of impurities for columnar and irregular grains growth, which leads to the diverse concentration distribution of substitutional and interstitial impurities in the silicon ingot. Furthermore, the transport mechanism of interstitial and substitutional impurities in front of the solid-liquid interface boundary has been revealed.

•Polymer based graphite felts PGF and RGF are evaluated as electrodes for ICRFB.•Bismuth deposition on the negative electrodes can improve the ICRFB performance.•RGF and PGF have different crystallite structures in radial and basal planes.The performances of rayon (RGF) and polyacrylonitrile (PGF) based graphite felts as electrodes are compared in the iron-chromium redox flow battery (ICRFB). The essential differences in structure between RGF and PGF are also characterized in this study. The results show that the RGF electrode displays excellent electrochemical performance for negative redox couple (Cr3+/Cr2+), resulting in the cell with higher charge efficiency and slower capacity decay. However, due to the high degree of graphitization and electrochemical activity for positive redox couple (Fe2+/Fe3+) in PGF, the cell using PGF has higher voltage efficiency and energy efficiency, as well as lower area surface resistance than the cell with RGF. The fundamental difference between RGF and PGF is the crystallites structure in radial direction and basal plane of the fiber. PGF with the core-rim structure has better graphitization stacked in radial direction of the fiber. Further, PGF has more defective carbons exposed in the basal planes, while the surface of RGF exhibits a higher concentration of oxygen functional groups. The role of catalysts in the ICRFB has also been studied by introducing bismuth (Bi) into RGF and PGF used as negative electrodes. The electrocatalytic activities of RGF and PGF before and after modification with Bi are investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Bismuth deposition on the negative electrode is found to improve the negative reaction in ICRFB.

A full domain control model is established for impurity transportation in the liquid phase, gas–liquid interface and gas phase of silicon to analyze the dynamic mechanics of impurity removal. The results show that the overall mass transfer coefficient mainly depends on the temperature and the chamber pressure. Its value increases with the increase of temperature or the decrease of chamber pressure. Under the same melting condition, the order of the overall mass transfer coefficients for P, Al and Ca is kP > kAl > kCa, indicating that P is easier to remove by evaporation. Mass transfer in the gas phase is the rate-controlling step for volatile impurity removal at the temperature above the melting point of silicon. The rate-controlling step transits to evaporation on the gas–liquid interface then to mass transfer in the liquid boundary layer as the temperature increases. During electron beam melting, the removal of P is controlled by both evaporation on the gas–liquid interface and mass transfer in the liquid boundary layer, and the removal of Al and Ca is controlled by evaporation on the gas–liquid interface.

•Inconel 718 superalloy was refined firstly by electron beam smelting.•The mole fraction of Fe in Inconel 718 superalloy was found little change at different temperature.•The relationship of Cr > Ni > Fe can be found for evaporation rates during experiments.•The theoretical mass loss rates of Ni, Cr and Fe are in good agreement with the experiments.The electron beam smelting (EBS) technology was employed in refining the Inconel 718 superalloy for the first time. The evaporation behavior of Ni, Cr and Fe in Inconel 718 superalloy during the smelting process was investigated, which would facilitate the controlling of alloy composition. The Inconel 718 superalloy was smelted by three groups of different power in the experiments; the volatile regularity of Ni, Cr and Fe in Inconel 718 superalloy was studied theoretically by calculating the element volatile of Ni-Cr-Fe ternary alloy. The experimental results show that the mole fraction of Fe remains constant before and after the experiment, while for Ni and Cr, the mole fraction are found to be above and below the level of raw material respectively. The smelting power of 9 kW, 10.5 kW and 12 kW correspond to the average temperatures of 1530.1 K, 1552.4 K and 1553.5 K, respectively, for the melt surface. The theoretical calculation and experimental results of Ni, Cr and Fe mass loss rates are in good agreement, the model employed in calculation shows its significance in theoretical guidance for the preparation of Inconel 718 superalloy and other nickel based superalloys.

Inconel 718 superalloy was fabricated by electron beam smelting (EBS) technique. The effect of solution heat treatment on the precipitation behavior and mechanical properties of EBS 718 superalloys were studied, the strengthening mechanisms were analyzed and related to the mechanical properties. The results indicate that the optimized microstructures can be acquired by means of EBS, which is attributed to the rapid cooling rate of approximately 280 ℃/min. The solution heat treatment shows a great impact on the microstructures, precipitation behavior and mechanical properties of EBS 718 superalloy. The γ`` phase shows an apt to precipitate at relatively lower solution temperatures followed by aging, while the γ` precipitates are prone to precipitate at higher temperatures. When solution treated at 1150 ℃, the γ` precipitates are dispersively distributed in the matrix with size and volume fraction of 8.43 nm and 21.66%, respectively, a Vickers hardness of approximately 489 HV0.1 is observed for the aged superalloy. The precipitation strengthening effect of EBS 718 superalloy could be elucidated by considering the interaction between the dislocations and γ``/γ` precipitates. The shearing of γ` is resisted by the coherency strengthening and formation of antiphase boundary (APB), which shows equal effect as weakly coupled dislocation (WCD) model. And for γ``, the strengthening effect is much more prominent with the primary strengthening mechanism of ordering. Moreover, it is interestingly found that the strengthening mechanism of stacking fault (SF) shearing coexists with APB shearing, and SF shearing plays a major role in strengthening of EBS 718 superalloy.

•Electron beam smelting, a new method, was used to prepare the Inconel 740 superalloy.•The EBS 740 shows higher strengthening effect than 740 made in traditional method.•The EBS 740 shows better oxidation resistance than traditional 740.•It shows application prospect of EBS technology in preparing Ni-base superalloys.A novel method, namely electron beam smelting (EBS) technology was used to prepare the Inconel 740 superalloy. The microstructures, hardness and oxidation behavior were characterized and compared with the traditionally prepared Inconel 740 superalloy. The results imply that the solution treatment gives rise to the coarsening of γ′ precipitates, with further aging treatment, the γ′ precipitates with size of less than 30 nm are distributed dispersively in the matrix, leading to a decreasing of the lattice parameters and an increasing of the misfit. The γ′ precipitates result in shearing mechanism of weakly pair coupling. The EBS 740 superalloy produces better properties than that prepared in the traditional method in both precipitation strengthening effect and oxidation resistance.

•Electron beam smelting, a novel method, was used to prepare the Inconel 740 superalloy.•The average size of the γ′ precipitates after aging treatment is < 30 nm.•The shearing mode generates a stronger strengthening effect than the traditional 740.•At low Zener-Hollomon parameter, the EBS 740 shows higher flow stress than 740H.Electron beam smelting (EBS) has been used to fabricate the Inconel 740 superalloy. Microstructures, hardness, and deformation characteristics of the alloy are studied. It is observed that carbides and fine secondary phase nuclei are distributed in the hot worked EBS 740 superalloy. The Ostwald ripening occurs during solution treatment and leads to aggregation of the γ′ precipitates, the size of γ′ precipitates varies from several nanometers to more than one hundred nanometers as a result. The average size of the secondary phase is < 30 nm after aging treatment and the average Vickers hardness is measured to be about 370. The critical shear stress is calculated to be 0.627 GPa with governing mechanism of shearing, causing a stronger strengthening effect than the traditionally prepared Inconel 740 superalloy. The compression behavior indicates that the EBS 740 superalloy shows higher flow stress than 740H at low Zener-Hollomon parameter, which may arise from the undissolved γ′ precipitates and higher activation energy Q. The tensile results show that the fracture surface exhibits a ductile fracture pattern, in contrast to no obvious plastic deformation on the macroscopic fracture. Crack propagation proceeds in a transgranular fracture mode with facets and voids presented on the fracture surface.Electron beam smelting (EBS) has been used to fabricate the Inconel 740 superalloy. Microstructures, hardness, and deformation characteristics of the alloy are studied. The average size of the secondary phase is < 30 nm after aging treatment and the average Vickers hardness is measured to be about 370. The critical shear stress is calculated to be 0.627 GPa with governing mechanism of shearing, causing a stronger strengthening effect than the traditionally prepared Inconel 740 superalloy. The EBS 740 superalloy shows higher flow stress than 740H at low Zener-Hollomon parameter, which may arise from the undissolved γ′ precipitates and higher activation energy Q. The EBS technology shows encouraging potential in preparation of nickel-based superalloys.Morphologies of γ′ precipitates and Vickers hardness as well as hot compression curves for electron beam smelting 740 superalloy.

•Crystal growth rate and solidified height Si purification by directional solidification is investigated.•Relationship between temperature of melt surface and graphite heater was found.•Crystal growth rate can be designed or predicted by controlling temperature of graphite heater.•Distribution of impurity during silicon purification by directional solidification can be designed or predicted.A theoretical model for investigating the crystal growth rate and the solidified height during silicon purification by directional solidification is proposed. The growth rate is not constant usually and it has profound effects on the distribution of metal impurity in production process. The crystal growth rate and the solidified height, based on thermal equilibrium on the melt–crystal interface, were discussed. The relationship between the surface temperature of silicon melt (T1) and temperature of graphite heater (TC′1) was found. The result shows that the value of T1 has an approximate linear relationship with the TC′1. The theoretical model can be used to design or predict the crystal growth rate by controlling the TC1 according to the different request. Then, the distribution of metal impurity during silicon purification by directional solidification can be calculated according to the crystal growth rate. Thus, the theoretical model can be used to design the growth rate and predict the distribution of impurity to the silicon purification process by directional solidification. The experiments proved that the calculation agreed well with the existing experimental results.

•Directional solidification of silicon was achieved by electron beam with exponential decreasing power.•The removal efficiency of aluminum was improved by this method.•The loss of silicon was reduced by more than 52%.•The energy consumption was reduced by more than 54%.Aluminum is one of the main impurities in silicon, which can be separated and eliminated by electron beam melting. However, high removal efficiency can be obtained only by increasing melt temperature or extending refining time, resulting in high energy consumption. In this work, the directional solidification of silicon was achieved by electron beam with exponential decreasing power, considering that aluminum has both characteristics of segregation and evaporation. The distributions of aluminum show increasing trend from the bottom to the top of the electron beam melted silicon ingot, which is the same as that after traditional directional solidification. The removal efficiency is improved by the coupling of segregation and evaporation. Compared with traditional electron beam melting, the loss of silicon reduced by more than 52% and the energy consumption reduced by more than 54%. This method is more effective to remove aluminum from silicon with low energy consumption.

•Electron beam smelting, a new method, was used to prepare the Inconel 740 superalloy.•The effect of solution heat treatment on electron beam smelting 740 was investigated.•TiNiSi phase’s content changes exponentially with solution temperature increasing.•γ′ precipitates coarsening occurs at 1150 °C, higher temperature cause their solution.•γ″ phase transformed into Nb0.03Ni3Ti0.97 phase at 1210 °C.Electron beam smelting (EBS) was used to prepare the Inconel 740 superalloy. The microstructure and hardness of Inconel 740 were investigated both under hot working condition and followed by solution heat treatment under high temperature ranging from 1120 to 1210 °C for 30 min. The results show that fine γ′ nucleus and primary MC carbides exist in the hot working superalloy. With increasing temperature of solution treatment, TiNiSi phase is gradually solutionized into the matrix, whose volume fraction decreases exponentially. γ′ precipitates coarsening occurs at 1150 °C, while higher temperature solution treatment leads to the solution of γ′ precipitates. γ″ phase has been found keeping a stringent coherent relationship with Nb0.03Ni3Ti0.97 phase at 1180 °C, and utterly transformed into Nb0.03Ni3Ti0.97 phase at 1210 °C. The hardness of the solution-treated superalloy is lower than that of hot working, the value decreases at first and then increases with increasing of solution temperature, which is attributed to dislocations interaction and localized shear stress caused by γ′ precipitates and local stress fields.

•Carbon behavior in electron beam melted silicon was investigated for the first time.•Special morphology of SiC gathered to ingots' top surface after electron beam melting.•Electron beam melting can be a possible way to separate SiC from silicon scraps.The behavior of carbon in multicrystalline silicon scraps by electron beam melting was investigated in this study. It was found that the process favors nucleation of SiC on Si3N4. Furthermore, carbon tends to gather to top surface of the ingots with increasing melting time, and the reaction between oxygen and carbon favors carbon migration. The melt convection and temperature gradient caused by electron beam are employed to be the dominate reason the phenomenon occurs. The results can provide guidance in silicon recycling.

•Volatile metal impurities' behavior in Si was studied under low vacuum condition.•Distribution of Na depends on the effect of the low vacuum condition.•A evaporation model is constructed to calculate the mass transfer coefficient.•The directional solidification of Cu and Mn was modeled by the Scheil's equation.A multicrystalline silicon ingot was obtained from metallurgical-grade silicon after directional solidification under low vacuum condition. The concentration distributions of metal impurities such as copper (Cu), manganese (Mn) and sodium (Na) along the growth direction of the ingot were investigated. The result shows that the concentration of Cu and Mn decrease respectively from 28.56 ppmw and 10.53 ppmw to about 0.1 ppmw and 0.01 ppmw in below 80% of the ingot height, which are in good agreement with the value calculated by the Scheil's equation. The concentration of Na decreases from 1096.91 ppmw to about 0.2 ppmw in the whole ingot, due to the evaporation effect. The evaporation model of Na under low vacuum condition is proposed and the mass transfer coefficient of Na is also calculated.

•Solid-state back-diffusion of impurity was controlled to improve the Si purity.•Zn addition was designed to separate Si from Si–Al alloy.•Zn addition favors more Si precipitation with low B content.During solidification refining of Si, the eutectic alloy ultimately solidifies and becomes enriched with impurity elements according to their small segregation coefficients, which may contaminate the primary Si through the cooling process. Combined with analysis of the morphology of the primary Si, the contamination mechanism was verified for a Si–63.8 wt%Al alloy using various cooling rates in the final cooling stage (873–293 K). By a quenching treatment, the B content in Si was decreased from the initial content of 14.8 to 1.4 ppmw, which is quite close to the value predicted by Scheil’s equation. Si cooled down at a rate of 1 K/min showed an increase in impurity content (e.g., B: 4.2 ppmw) owing to solid-state back-diffusion. In order to prevent such contamination, Zn was added to the Si–Al melt at 873 K, which decreased the eutectic temperature and separated Si from the alloy. A final Si amount of 94.1 wt% was recycled without further contamination.

Silicon is widely used as a raw material for production of solar cells. As a major impurity in silicon, phosphorus must be removed to 1 × 10−5 wt.%. In the present study, based on the distribution of phosphorus in a silicon ingot obtained by vacuum refining and directional solidification, the mechanism for removal of phosphorus from silicon is investigated. The results show that the distribution is controlled not only by segregation at the solid–liquid interface but also by evaporation at the gas–liquid interface, showing some deviation from Scheil’s equation. A modified model which considers both segregation and evaporation is used to simulate the distribution, matching quite well with the experimental results. The temperature and solidification rate are two important parameters that affect the overall mass transfer coefficient and the effective segregation coefficient and thus the distribution of phosphorus. A high removal efficiency and a homogeneous distribution can be obtained by adjusting these two parameters.

•Impurity behavior in Si was experimentally studied during refining and solidification process.•The vacuum induction melting process was analyzed based on basic evaporation theory.•The directional solidification was modeled by modified Scheil's equation, considering the effect of evaporation.•The impurity distribution depends on the effect of segregation and evaporation.A multicrystalline silicon ingot was obtained from metallurgical-grade silicon by vacuum induction melting and directional solidification. Based on the concentration distributions of aluminum and calcium along the growth direction, the removal mechanism of such impurities with both high saturated vapor pressures and low segregation coefficients is investigated. The results show that the removal of this type of impurities only depends on evaporation during vacuum induction melting process, thus their contents decrease significantly due to the strongly evaporation under the high temperature and high vacuum conditions. During subsequent directional solidification process, a model including both segregation and evaporation is used to simulate the concentration distribution. The results show that the impurity distribution is controlled by both two mechanisms in the initial stage of solidification and is mainly determined by segregation in the end stage due to the decrease of the diffusibility and evaporability of the impurity atoms.

•Al behavior in liquid Si was experimentally studied during electron beam refining, followed by solidification.•The refining process of Al was modeled based on basic evaporation model and experimental results.•The model was extended by a solidification step, which modeled the experimental results fairly well.•The removal efficiency in most area of electron beam melted Si ingot was more than 97%.The purification of metallurgical grade silicon, especially the removal of aluminum, was investigated by electron beam melting and solidification. Small amounts of silicon raw materials were melted in an electron beam furnace with same melting time and different solidification time to obtain the distribution of Al in silicon ingot. The removal mechanisms in different stages were also discussed. The results show that the removal of Al during melting process only depends on evaporation and that during solidification process depends on both segregation and evaporation. The distribution of Al shows an obvious increasing trend from the bottom to the top of the silicon ingot when solidification time is 600 s. The removal efficiency in most area is close to that in the ingot solidified instantaneously, but the energy consumption is less, which is considered to be an effective way for the purification of silicon.

Solidification rate has a significant influence on purification of silicon due to segregation of impurities at a liquid–solid interface of a solidifying silicon ingot. A mathematical model is developed to evaluate time-dependent position of the liquid–solid interface and solidification rate of electron beam melted ingots. A series of solidification experiments with different cooling rates are conducted to measure position of a line which separates directionally grown columnar crystals visible in cross-sections of the solidified ingots. Results show that not the whole ingot solidifies directionally when the reduction rate of the beam current is larger than 1.67 mA/s. The position of the dividing line depends on cooling rate and the experimental trend is consistent with that resulted from theoretical simulations. Modeling shows that the solidification rate changes fast when the beam current reduces linearly that is detrimental for segregation of impurities. It also predicts that an exponential reduction of the beam current leads to a uniform solidification rate which is beneficial to segregation of impurities, though not all exponential current reductions lead to this kind of solidification behavior.Highlights► Solidification rate of electron beam melted silicon ingots is examined. ► Directional growth doesn't occur in the whole ingot if reduction rate is too large. ► The solidification behavior of silicon ingots depends on the cooling mode. ► The solidification rate can be controlled by adjusting the electron beam current.

According to the traditional metallurgical theory, the evaporation process of phosphorus and silicon during silicon refining by electron beam melting (EBM) is discussed and a theoretical model is established to obtain the loss rate of silicon, the removal efficiency of phosphorus and the corresponding energy consumption. The results show that phosphorus can be removed from silicon melt efficiently and quickly by EBM. There is a one-to-one correspondence between the loss of silicon and the removal efficiency of phosphorus, indicating that they have obvious effect on each other, whereas the EB power has little influence on the loss rate of silicon. If the EB power is increased from 9 kW to 21 kW, the melting time can be shortened by 68%, the loss of silicon increased by only 0.1% and the energy consumption decreased by 25%. Based on the theoretical and experimental results, a high-power EBM method is considered to be a better way for the removal of phosphorus with high efficiency and low energy consumption under such experiment conditions.Highlights► An EBM model is established to analyze the evaporation of P and Si. ► The removal efficiency of phosphorus is obtained by experiments and calculation. ► The EBM power has no obvious influence on the loss rate of Si. ► Energy consumption decreases with the increasing of EBM power under experiments.

In this paper a mathematical model is developed to investigate the removal of volatile impurities in molten silicon by electron beam melting (EBM) with a high efficiency and low energy consumption. The temperature distribution of molten silicon is obtained using the commercial software FLUENT. Based on the temperature distribution, the vaporization behaviors of phosphorus and silicon are investigated by Langmiur's vaporization theory. The results show that the evaporation rate of silicon during EBM increases exponentially with the increase of beam power, while, it decreases with the increase of scanning radius. The optimal parameters are discussed from the aspect of efficiency and energy saving. The energy consumption decreases with the decrease of scanning radius and with the increase of the beam power. The optimum values are consider to be with a scanning radius of 0.0339 m and a beam power of 23.4 kW for 0.5 kg silicon when phosphorus is removed from 1.44 × 10−2 to 1 × 10−5 (wt.%).Highlights► A model is developed for energy utilization optimization during Si purification by EBM. ► The surface temperature and area of the molten pool are calculated. ► The vaporization behaviors of Si and P are discussed. ► The relationship between energy consumption and melting parameters is obtained. ► The melting parameters are optimized from the aspect of efficiency and energy saving.

Aluminum nitride (AlN) ceramics were prepared by hot-pressing with Y(NO3)3·6H2O as sintering additive. The mechanical properties including flexural strength, Vickers’ hardness, and fracture toughness were studied. The relative density and mechanical property of the monolithic AlN were improved by adding Y(NO3)3·6H2O, which decreased the porosity. At 2 wt% Y2O3, the AlN ceramic exhibited the highest strength of 383 MPa, the highest hardness of 15.39 GPa, and the highest fracture toughness of 3.1 MPa m1/2. However, doping with more additive, the strength, hardness, and toughness of AlN ceramics decreased because of the weak interfacial bonding between AlN matrix and the yttrium aluminates phase.Highlights► Y(NO3)3·6H2O was used to prepare AlN ceramics as sintering additive. ► The residual stress was discussed in sintered AlN ceramics. ► The interfacial bonding of AlN and yttrium aluminates phase was discussed.

The fibers of AlN were synthesized by carbothermal reduction and nitridation of precursor fibers obtained by electrospinning. XRD result indicated that the wurtzite AlN phase had been successfully synthesized in fibers. The SEM and TEM analysis indicated that the hollow fibers with an out-diameter of about 500 nm and a wall thickness of about 100 nm were obtained and the crystal in fibers was hexagonal after calcination. The fibers were further characterized by TG–DTA, FT-IR and UV–vis absorption spectra. The formation mechanism of hollow structure was proposed based on our understanding and characterizations.

The processing and mechanical behavior of Al2O3 composites with 1–20 wt.% nano-/micro-sized SiC particles was investigated. The composites were densified by hot-pressing. The mechanical properties of nano-/micro-sized SiC/Al2O3 composites including hardness, fracture toughness and flexural strength were investigated. It was found that the fracture strength and fracture toughness of the nano-/micro-sized SiC/Al2O3 composites were significantly improved in comparison with the monolithic Al2O3. 7.6 MPa m1/2 was the highest fracture toughness and was found in the composite with 5% SiC, while the 20% SiC composite exhibited the highest flexural strength. The toughening and strengthening mechanisms of the ceramic composites were discussed.

•Novel octopus like carbon nanostructures are synthesized using pure Cu film through CVD.•The morphology of nanostructures vary from edge towards center of substrate.•The effect of methane gas, Cu film thickness, and supporting substrates are studied.•A mechanism is proposed for the growth of carbon nanostructures.Growth of novel carbon nanomaterials has been of great interest for researchers due to their potential applications in nano-devices. In the current work, we reported radial growth of novel octopus-like carbon nanostructures (OCNS) by chemical vapor deposition (CVD), using methane as carbon precursor gas, and Cu film sputtered on Si/SiO2 substrate as the catalyst. Annealing at high temperature transforms Cu thin film to catalytic copper nanoparticles (CuNPs), which on exposure to methane results in the radial growth of carbon nanofibers (CNFs) departing from the central CuNPs. The size of OCNS and morphology vary as a function of Cu film thickness, precursor gas concentration, and growth time. High methane concentration boosts up growth kinetics, resulting in long carbon fibers in addition to OCNS, with fiber length varying from a few hundred nanometers to several hundred microns. Effect of substrate on the morphology of carbon nanostructures is also studied using Cu film sputtered on silicon, quartz, and Si/SiO2 substrates. The branch like morphology of OCNS exhibits large surface/contact area for their applications in electronic and electrochemical devices.

•Silicon ingots with and without magnetic field under industrial system are obtained.•The concentration of impurities are decreased due to addition of magnetic field.•The thickness of the diffusion layer is reduced by the alternating magnetic field.•The effective segregation coefficient are also reduced.Multicrystalline silicon ingots without and with alternating magnetic field during directional solidification process under industrial system were obtained from metallurgical grade silicon (MG-Si). The concentrations and normalized concentrations of metal impurities in the two silicon ingots were studied. The result shows that the concentrations and normalized concentrations in high-purity area of the silicon with alternating magnetic field are lower than those of the ingot without alternating magnetic field. The transport mechanism for metal atoms in the diffusion layer area has been changed due to the alternating magnetic field. Alternating magnetic field introduces a convection to reduce the thickness of diffusion layer in the molten silicon, which results in a decreased effective segregation coefficients. Enhancing transport driving force of metal atoms in molten silicon is the effective way to improve the removal rate of metal impurities.