- Alternative route for the preparation of CoSb3 and Mg 2Si derivatives
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An alternative manufacturing route has been developed for cobalt triantimonide and magnesium disilicide derivatives. Elemental powders were mixed in stoichiometric proportions, cold pressed into cylindrical preforms and heated in oxygen-free environment to initiate the exothermic reaction. According to DTA/TG measurements and observations under high-temperature microscope, the onset of reaction occurred at a temperature not exceeding the melting point of the more volatile component, i.e. antimony in the case of CoSb3 and magnesium in the case of Mg2Si. The reaction products were additionally heat treated to secure homogenization. Dense sinters were obtained by hot uniaxial pressing of the obtained powders in moderate temperature-and-pressure conditions. Several advantages were identified in the proposed technology: absence of liquid phases, relatively short time of the synthesis, possibility of in-situ or ex-situ doping and grain size control.
- Godlewska,Mars,Zawadzka
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- Thermoelectric Properties and Transport Mechanism of Pure and Bi-Doped SiNWs-Mg2Si
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Through the use of nano-Si wires as additive, a significant improvement in the thermoelectric (TE) properties of Mg2Si is achieved. SiNWs-Mg2Si materials are prepared by a wet etching method followed by field activated pressure assisted synthesis (FAPAS). The results show that the presence of SiNWs successfully decouples the relationship between the electrical resistivity and the Seebeck coefficient of Mg2Si. The effect of doping with Bi is also investigated. The results show that the addition of Bi changed the scattering mechanism, and a zT value of 0.47 is determined at 800 K for Mg2Si0.99Bi0.01-0.005SiNWs. The presence of MgO as an impurity and its effect on zT are discussed.
- Yang, Xiaomeng,Chen, Shaoping,Zhang, Hua,Lv, Feng,Fan, Wenhao,Wang, Wenxian,Munir, Zuhair A.
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- Electrochemical characteristics of intermetallic phases in aluminum alloys : An experimental survey and discussion
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This paper presents a survey of corrosion potentials, pitting potentials, and electrochemical characteristics for intermetallic particles commonly present in high-strength aluminum-based alloys. Results from relevant pure metals and solid solutions are also presented. It is seen that corrosion potentials and pitting potentials vary over a wide range for various intermetallics. Elaboration of the results reveals that the electrochemical behavior of intermetallics is more detailed than the simple noble or active classification based upon corrosion potential or estimated from the intermetallic composition. Intermetallics capable of sustaining the largest cathodic current densities are not necessarily those with the most noble Ecorr, similarly those with the least noble Ecorr will not necessarily sustain the largest anodic currents. The data herein was collected via the use of a microcapillary electrochemical cell facilitating electrode investigations upon intermetallic particles in the micrometer-squared range. This survey may be used as a tool for clarification of localized corrosion phenomena in Al alloys.
- Birbilis,Buchheit
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- Nanoporous silicon prepared through air-oxidation demagnesiation of Mg2Si and properties of its lithium ion batteries
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Nanoporous silicon has been prepared through the air-oxidation demagnesiation of Mg2Si at 600 °C for 10 hours (Mg2Si + O2 → Si + MgO), followed by HCl washing. Mg2Si was prepared from 200 mesh commercial Si at 500 °C for 5 h in an autoclave. The as-prepared Si exhibits a reversible capacity of 1000 mA h g-1 at 36 A g-1 and ~1200 mA h g-1 at 1.8 A g-1 over 400 cycles. This journal is
- Liang, Jianwen,Li, Xiaona,Hou, Zhiguo,Guo, Cong,Zhu, Yongchun,Qian, Yitai
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- A metathesis reaction route to obtain fine Mg2Si particles
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We have developed a novel synthetic route for the production of fine Mg2Si particles (2, and Na. Mg2Si was suggested to be formed by a solid-state metathesis reaction, in which MgCl2 reacts with Na to form Mg and NaCl, and then Mg reacts with NaSi.
- Itahara,Yamada,Oh,Asahi,Imagawa,Yamane
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- Structural, electronic, and hydriding properties of Li2MgSi
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An investigation of Li2MgSi, with particular emphasis on its potential as a hydrogen storage material, is reported. A cubic P over(4, ?) 3 m crystal structure, differing from previous determinations, is established. We find that the material reversibly sorbs ~2.8 mass% hydrogen at T ~ 300 °C according to the reaction Li2MgSi + H2 ? 1/2Mg2Si + 2LiH + 1/2Si. Electronic structure calculations indicate that Li2MgSi is a semiconductor with a small, indirect gap of ~0.2 eV.
- Herbst,Meyer
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- Mill setting and microstructural evolution during mechanical alloying of Mg2Si
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The mechanical alloying behaviour of magnesium and silicon to form the intermetallic compound Mg2Si and the optimum setting of a planetary ball mill for this task, were examined. For the ductile-brittle magnesium-silicon system it was found that the efficiency of the mill is mostly influenced by the ratio of the angular velocity of the planetary wheel to that of the system wheel and the amount of load. The examination of the kinetics inside the planetary ball mill for different mill settings showed that a ratio of angular velocities of at least 3 is necessary to compensate the reduction of efficiency due to slip. The optimum powder load for the 500 ml vial was found to be 10-20 g. The milling process starts with elemental magnesium and silicon bulk particles. During the milling, the silicon pieces are rapidly diminished and together with the constantly forming Mg2Si they act as an emery powder for the magnesium bulk pieces. Simultaneous to the diminution of the magnesium, alloying occurs.
- Riffel,Schilz
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- Thermoelectric properties of Bi-doped Mg2Si semiconductors
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The thermoelectric properties of Bi-doped Mg2Si (Mg 2Si:Bi=1:x) fabricated by spark plasma sintering process have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 900 K. Bi-doped Mg2Si samples are n-type in the measured temperature range. The electron concentration of Bi-doped Mg2Si at 300 K ranges from 1.8×1019 cm -3 for the Bi concentration x=0.001 to 1.1×1020 cm-3 for x=0.02. The solubility limit of Bi in Mg2Si is estimated to be about 1.3 at% and first-principles calculation revealed that Bi atoms are expected to be primarily located at the Si sites in Mg2Si. The electrical resistivity, Seebeck coefficient, and thermal conductivity are strongly affected by the Bi concentration. The sample of x=0.02 shows a maximum value of the figure of merit, ZT, is 0.86 at 862 K.
- Tani, Jun-Ichi,Kido, Hiroyasu
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- Combined effect of high-intensity ultrasonic treatment and Ca addition on modification of primary Mg2Si and wear resistance in hypereutectic Mg-Si alloys
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The combined effect of high-intensity ultrasonic treatment (HIUST) and 0.3 wt.%Ca addition on modification of primary Mg2Si and wear resistance in the hypereutectic Mg-5 wt.%Si alloy has been investigated. The results show that without treatmen
- Moussa,Waly,El-Sheikh
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- Synthesis of a low-density Ti-Mg-Si alloy
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A low-density titanium alloy was synthesized from blended elemental powders of TiH2, Mg, and Si by mechanical alloying and/or heat treatment. The titanium hydride was used in place of titanium. Phase transformations occurring in the system during heating at a constant rate were studied with the use of DTA and XRD. During heating of the blended elemental powders decomposition of titanium hydride occurred in the temperature range 550-750 °C and some silicon went into solid solution in titanium while the majority of the silicon reacted exothermically with magnesium at about 500 °C producing an intermetallic phase Mg2Si. This phase was stable on heating up to 950 °C, where a eutectic component of this phase began to melt leading to formation of a liquid solution of magnesium in silicon, followed by a reaction of the liquid silicon with titanium and formation of a Ti5Si3 phase. A third reaction in the system was detected at about 1100 °C due to formation of MgO, so that after annealing at 1150 °C three stable phases, Ti(Si), Ti5Si3, and MgO, were present in the alloy. No decomposition of the Ti5Si3 phase or formation of Mg2Si were detected either during subsequent cooling or a second heating of the alloy. Completely different kinetics of the phase reactions occurred in the mechanically alloyed powders. Magnesium and silicon dissolved in the titanium hydride during mechanical alloying. Decomposition of the titanium hydride occurred at 320-600 °C, the Mg2Si phase was formed after heating to 450 °C, and the Ti5Si3 phase was detected after heating to 570 °C. The Mg2Si decomposed completely at a temperature of 650 °C with the formation of MgO and Ti5Si3. After heating to 1150 °C, three stable phases, TiN0.3, Ti5Si3, and MgO, were present in the alloy. A discussion of the results is given.
- Senkov,Cavusoglu,Froes
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- Thermoelectric properties of Al-doped Mg2Si1-xSnx (x ≦ 0.1)
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The thermoelectric properties of Al-doped Mg2Si1-xSnx (x = 0.0-0.1) [Mg2Si1-xSnx:Al = 1:y (0.00 ≦ y ≦ 0.02)] fabricated by spark plasma sintering have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), the Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 900 K. Al-doped Mg2Si1-xSnx samples are n-type in the measured temperature range. By Al-doping, electron concentration is controlled up to 5.3 × 1019 cm-3 in the composition range 0.0 ≦ x ≦ 0.1. Al-doped Mg2Si0.9Sn0.1 shows a maximum value of the figure of merit ZT of 0.68 at 864 K, which is 6 times larger than that of nondoped Mg2Si0.9Sn0.1.
- Tani, Jun-ichi,Kido, Hiroyasu
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- Si-particle-size dependence of Mg2Si powders directly produced by liquid-solid synthesis method
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The synthesis and powder processing of compounds in an Mg2Si system are difficult to achieve. These processes require a multi-step procedure that involves melting, crushing, grinding, and sieving in order to obtain Mg2Si powders from the Mg and Si starting materials. This may lead to the oxidation of Mg and contamination of the obtained powders with impurities. In this study, we developed a direct technique for synthesizing Mg2Si particles using a liquid-solid reaction. Si powders of various particle sizes (20-38, 38-53, 53-75, 75-106, 106-150, and 150-250 μm) were employed in the synthesis. The resulting powders were identified as single phase of Mg2Si by both XRD and EDX analyses. The optimal heat treatment temperature was between the two eutectic temperatures, 911 K and 1218 K. After heat treatment at 1143 K for 4 h, Si powders with particle sizes of less than 53 μm did not yield Mg2Si powders. In contrast, after heat treatment at 973 K for 10 h, all the Si powders produced Mg2Si powders. The Mg2Si powder particles were larger than the starting Si particles; for example Si particles with sizes of 53-75 μm produced Mg2Si powders with sizes ranging from 75 to 106 μm. The yields of Mg2Si powder reached approximately 90%.
- Isoda,Tada,Shioda,Shinohara
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- Altering hydrogen storage properties by hydride destabilization through alloy formation: LiH and MgH2 destabilized with Si
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Alloying with Si is shown to destabilize the strongly bound hydrides LiH and MgH2. For the LiH/Si system, a Li2.35Si alloy forms upon dehydrogenation, causing the equilibrium hydrogen pressure at 490?°C to increase from approximately 5 ?? 10-5 to 1 bar. For the MgH 2/Si system, Mg2Si forms upon dehydrogenation, causing the equilibrium pressure at 300?°C to increase from 1.8 to >7.5 bar. Thermodynamic calculations indicate equilibrium pressures of 1 bar at approximately 20?°C and 100 bar at approximately 150?°C. These conditions indicate that the MgH2/Si system, which has a hydrogen capacity of 5.0 wt %, could be practical for hydrogen storage at reduced temperatures. The LiH/Si system is reversible and can be cycled without degradation. Absorption/desorption isotherms, obtained at 400-500?°C, exhibited two distinct flat plateaus with little hysteresis. The plateaus correspond to formation and decomposition of various Li suicides. The MgH2/Si system was not readily reversible. Hydrogenation of Mg2Si appears to be kinetically limited because of the relatively low temperature, 150?°C, required for hydrogenation at 100 bar. These two alloy systems show how hydride destabilization through alloy formation upon dehydrogenation can be used to design and control equilibrium pressures of strongly bound hydrides.
- Vajo, John J.,Mertens, Florian,Ahn, Channing C.,Bowman Jr., Robert C.,Fultz, Brent
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- Non-isothermal crystallization kinetics of Mg60Zn30Ti5Si5amorphous alloy prepared by mechanical alloying
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Mg60Zn30Ti5Si5amorphous alloy was prepared via mechanical alloying (MA) and heat treated in different way. X-ray diffractometer (XRD) was used to detect the phases of alloy. The crystallization characteristics a
- Chen,Yang,Gao,Li,Yu,Ma,Yuan
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- Fast synthesis of nanocrystalline Mg2Si by microwave heating: A new route to nano-structured thermoelectric materials
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The ultra fast synthesis of nanocrystalline Mg2Si was carried out using microwave radiation. The elemental precursors were first milled together under dry conditions to get fine particles. The resulting mixture of powders of Mg and Si was cold pressed before being heated by microwave irradiation. Precursors and products were analyzed by X-ray diffraction and scanning electron microscopy. The high energy ball milling parameters utilized to prepare the reactive powders have quite an influence on the behavior of the mixture under irradiation. Moreover, SEM imaging demonstrates that the power and time of irradiation are crucial for the grain growth of the Mg2Si and must be adequately controlled in order to avoid the decomposition of the phase. Our results show that we successfully managed to easily and quickly synthesize homogeneous nanocrystalline Mg2Si with particle size smaller than 100 nm using a microwave power of only 175 W for two minutes on powders ball milled for two hours. The Royal Society of Chemistry 2010.
- Savary, Etienne,Gascoin, Franck,Marinel, Sylvain
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- Inverse Perovskite Oxysilicides and Oxygermanides as Candidates for Nontoxic Infrared Semiconductor and Their Chemical Bonding Nature
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We have synthesized inverse-perovskite-type oxysilicides and oxygermanides represented by R3SiO and R3GeO (R = Ca and Sr) and studied their characteristics in the search for nontoxic narrow band gap semiconductors. These compounds exhibit a sharp absorption edge around 0.9 eV and a luminescence peak in the same energy range. These results indicate that the obtained materials have a direct-band electronic structure, which was confirmed by hybrid DFT calculations. These materials, made from earth abundant and nontoxic elements and with a relatively light electron/hole effective mass, represent strong candidates for nontoxic optoelectronic devices in the infrared range.
- Ohashi, Naoki,Mora-Fonz, David,Otani, Shigeki,Ohgaki, Takeshi,Miyakawa, Masashi,Shluger, Alexander
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- Metallurgical Synthesis of Mg2FexSi1- x Hydride: Destabilization of Mg2FeH6 Nanostructured in Templated Mg2Si
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Magnesium-based transition-metal hydrides are attractive hydrogen energy materials because of their relatively high gravimetric and volumetric hydrogen storage capacities combined with low material costs. However, most of them are too stable to release the hydrogen under moderate conditions. Here we synthesize the hydride of Mg2FexSi1-x, which consists of Mg2FeH6 and Mg2Si with the same cubic structure. For silicon-rich hydrides (x 2Si phase is observed by X-ray diffraction, and M?ssbauer spectroscopy indicates the formation of an octahedral FeH6 unit. Transmission electron microscopy measurements indicate that Mg2FeH6 domains are nanometer-sized and embedded in a Mg2Si matrix. This synthesized metallographic structure leads to distortion of the Mg2FeH6 lattice, resulting in thermal destabilization. Our results indicate that nanometer-sized magnesium-based transition-metal hydrides can be formed into a matrix-forced organization induced by the hydrogenation of nonequilibrium Mg-Fe-Si composites. In this way, the thermodynamics of hydrogen absorption and desorption can be tuned, which allows for the development of lightweight and inexpensive hydrogen storage materials.
- Asano, Kohta,Dam, Bernard,Doi, Masaaki,Fujita, Asaya,Isobe, Shigehito,Kim, Hyunjeong,MacHida, Akihiko,Maejima, Naoyuki,Nakamura, Yumiko,Sakaki, Kouji,Schreuders, Herman,Wang, Yongming,Watanuki, Tetsu,Westerwaal, Ruud J.
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- Synthesis and properties of new multinary silicides R5Mg 5Fe4AlxSi18-x (R = Gd, Dy, Y, x ≈ 12) grown in Mg/Al flux
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Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1 Mg/Al mixed flux produce well-formed crystals of R5Mg5Fe4Al xSi18-x (x ≈ 12). These phases have a new structure type in tetragonal space group P4/mmm (a = 11.655(2) A, c = 4.0668(8) A, Z = 1 and R1 = 0.0155 for the Dy analogue). The structure features two rare earth sites and one iron site; the latter is in monocapped trigonal prismatic coordination surrounded by silicon and aluminum atoms. Siting of Al and Si was investigated using bond length analysis and 27Al and 29Si MAS NMR studies. The magnetic properties are determined by the R elements, with the Gd and Dy analogues exhibiting antiferromagnetic ordering at TN = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic behavior with varying field.
- Ma, Xiaowei,Chen, Banghao,Latturner, Susan E.
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- Synthesis and crystal structure of RMgSi2 compounds (R=La, Ce, Pr, Nd), a particular example of linear intergrowth
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A new series of rare earth compounds with stoichiometry RMgSi2 (R=La, Ce, Pr, Nd) is reported. The single crystal X-ray diffraction showed that CeMgSi2, which melts congruently at 1200 °C, crystallizes in a new tetragonal structure t
- Wrubl,Pani,Manfrinetti,Rogl
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- Strain-induced suppression of the miscibility gap in nanostructured Mg2Si-Mg2Sn solid solutions
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Solid solutions of Mg2Si and Mg2Sn are promising thermoelectric materials owing to their high thermoelectric figures-of-merit and non-toxicity, but they may undergo phase separation under thermal cycling due to the presence of miscibility gaps, implying that the thermoelectric properties could be significantly degraded during thermoelectric device operation. Herein, this study investigates the strain-induced suppression of the miscibility gap in solid solutions of Mg2Si and Mg2Sn. Separately prepared Mg2Si and Mg2Sn powders were made into (Mg2Si)0.7(Mg2Sn)0.3 mixtures using a high energy ball-milling method followed by spark plasma sintering. Afterwards, the phase evolution of the mixtures, depending on thermal annealing and mixing conditions, was studied experimentally and theoretically. Transmission electron microscopy and X-ray diffraction results show that, despite the presence of a miscibility gap in the pseudo-binary phase diagram, the initial mixture of Mg2Si and Mg2Sn evolved towards a solid solution state after annealing for 3 hours at 720 °C. Thermodynamic analysis as well as phase-field microstructure simulations show that the strain energy due to the coherent spinodal effect suppresses the chemical spinodal entirely and prevents phase separation. This strategy to suppress the miscibility gap induced by lattice strain through non-equilibrium processing can benefit the thermoelectric figure-of-merit by maximizing phonon alloy scattering. Furthermore, stable solid solutions by engineering phase diagrams have the potential to facilitate the reliable long term operation of thermoelectric generators under continuous thermal loads.
- Yi, Su-In,Attari, Vahid,Jeong, Myunghwan,Jian, Jie,Xue, Sichuang,Wang, Haiyan,Arroyave, Raymundo,Yu, Choongho
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- A magnesiothermic reaction process for the scalable production of mesoporous silicon for rechargeable lithium batteries
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Mesoporous, 3-D, nanocrystalline Si has been synthesized via the magnesiothermic reduction of SiO particles at a peak temperature of only 500 °C in a scalable flow-through reactor setup. Such 3-D porous Si as an anode material exhibited high, reversible capacities (i.e., >900 mA h g -1 after 160 charge-discharge cycles at 1000 mA g-1).
- Xing, An,Zhang, Jing,Bao, Zhihao,Mei, Yongfeng,Gordin, Ari S.,Sandhage, Kenneth H.
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- Enhanced thermoelectric performance of high pressure synthesized Sb-doped Mg2Si
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n-type Mg2Si1-xSbx compounds were prepared within a short duration by using high pressure synthesis followed by spark plasma sintering. The structural and compositional characterizations indicated highly densified single-phase products with no obvious oxidation or volatilization of Mg. High pressure synthesized samples showed greatly enhanced thermoelectric performance compared with ambient-pressure synthesized ones. For the optimal Mg2Si0.985Sb0.015, the power factor reached 3300 μWm?1K?2 at 773 K meanwhile the lattice thermal conductivity was suppressed to 1.0 Wm?1K?1 at temperatures higher than 700 K. As a result, the highest ZT of 0.94 was achieved at 873 K. High pressure synthesis thus provides us an alternative and effective pathway to synthesize magnesium silicide based thermoelectric materials.
- Li, Jianghua,Li, Xiaopu,Cai, Bowen,Chen, Chen,Zhang, Qian,Zhao, Zhisheng,Zhang, Long,Yu, Fengrong,Yu, Dongli,Tian, Yongjun,Xu, Bo
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- Significant enhancement of flux pinning in MgB2 superconductor through nano-Si addition
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Polycrystalline MgB2 samples with 10 wt.% silicon powder addition were prepared by an in situ reaction process. Two different Si powders, one with coarse (44 μm) and the other with nano-size (a significantly improved field dependence of the critical current over a wide temperature range compared with both undoped samples and samples with coarse-Si added. Jc is as high as 3000 A/cm2 in 8 T at 5 K, one order of magnitude higher than for the undoped MgB2. X-ray diffraction results indicated that Si had reacted with Mg to form Mg2Si. Nano-particle inclusions and substitution, both observed by transmission electron microscopy, are proposed to be responsible for the enhancement of flux pinning in high fields. However, the samples made with the coarse-Si powders had a poorer pinning than the undoped MgB2.
- Wang,Zhou,Qin,Munroe,Soltanian,Liu,Dou
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- Investigation on the microstructure, mechanical properties and corrosion behavior of Mg-Sb and Mg-Sb-Si alloys
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In the present research work, the microstructure, mechanical properties as well as corrosion behavior of newly designed Mg-Sb (2, 4, 6, and 8?wt %) and Mg-4Sb-Si (2, and 4?wt %) alloys were investigated. The results showed that the microstructure of binary alloys were composed of α-Mg and Mg3Sb2whereas that of ternary Mg-4Sb-Si (2, 4?wt %) alloys consisted of α-Mg, Mg3Sb2and Mg2Si intermetallic phases. Mg-4Sb-4Si alloy exhibited superior tensile, creep and corrosion properties in comparison to that of other studied alloys. The significant improvement in tensile properties at ambient temperature was associated with the dendrite refinement and presence of optimum amount of Mg3Sb2intermetallics along with Mg2Si intermetallics. Moreover, the presence of thermally stable Mg3Sb2and Mg2Si intermetallic phases in the ternary alloys restricted the grain boundary sliding and dislocation movement at high temperature and thus improved the creep resistance. The intermetallics played a key role in corrosion behavior of Mg alloys. Increase the volume of Mg3Sb2in Mg-Sb alloys reduced the corrosion resistance of the alloys whereas Mg2Si intermetallics improved the corrosion resistance of the Mg-Sb-Si alloys.
- Rajeshkumar,Jayaraj, Jithu,Srinivasan,Pillai
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- Thermoelectric properties of Sc- and Y-doped Mg2Si prepared by field-activated and pressure-assisted reactive sintering
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Sc- and Y-doped-Mg2Si samples were reactively sintered by the field-activated and pressure-assisted synthesis (FAPAS) method. The incorporation of these rare-earth elements in this silicide resulted in an n-type semiconductor. The addition of Sc and Y had no discernable effect on the lattice constant of Mg2Si. The average grain size of the Y-doped Mg2Si was about 2 μm, which was smaller than that of the sintered pure Mg2Si. The power factor of samples doped with 2500 ppm Sc was consistently higher than that of pure Mg2Si in the temperature range of 300-550 K. Similarly, the power factor of 2000 ppm Y doped Mg2Si samples was higher than that of pure Mg2Si over the temperature range of 300-675 K; the highest value being about 2.2 × 10-3 W m-1 k-2 at 468 K. This value is about two times that of the undoped Mg2Si at the same temperature. The thermal conductivity of Mg2Si doped with 2000 ppm Y was 80% of that of pure Mg 2Si. The highest figure of merit (ZT) for the Y doped (2000 ppm) samples was 0.23 at 600 K which was higher by a factor of 1.6 than the corresponding value of pure Mg2Si at the same temperature. The results demonstrate the benefits of doping of Mg2Si with Sc and Y in enhancing its thermoelectric properties.
- Meng,Fan,Chen,Munir
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- Silicon oil: A cheap liquid additive for enhancing in-field critical current density in Mg B2
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In this work, the authors report on significant flux pinning enhancement in Mg B2 that has been easily obtained using a liquid additive, silicon oil. Mg B2 bulk samples with 0 up to 30 wt % silicon oil added were prepared by an in situ reaction. Results showed that the Si and C released from the decomposition of the silicon oil formed Mg2 Si and substituted into B sites, respectively. Increasing the amount of the Si oil up to 15 wt % has resulted in the reduction of the lattice parameters, as well as Tc and R (300 K) R (Tc) values, accompanied by a significant enhancement of Jc (H), Hirr, and Hc2.
- Wang,Cheng,Dou
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- Selflating synthesis of silicon nanorods from natural sepiolite for high-performance lithium-ion battery anodes
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Nanostructured silicon is an attractive anode material for next-generation lithium-ion batteries, but its commercialization remains a challenge owing to the energy-intensive, costly, and complex preparation of nanostructured silicon. Herein, one-dimensional (1D) silicon nanorods (SNRs) have been synthesized from natural sepiolite by a simple selflating synthesis method. The intrinsic crystal structure and chemical composition of sepiolite allow for the maintenance of 1D structures during magnesiothermic reduction without any additional templates and heat scavengers. The as-prepared SNRs showed a large specific surface area (~122 m2 g-1) and hierarchical porous structure (i.e., macro- A nd meso-pores). As anodes for lithium-ion batteries, SNRs exhibited a high reversible capacity of 1350 mA h g-1 at 1.0 A g-1 after 100 cycles, and 816 mA h g-1 at 5.0 A g-1 after 500 cycles (with a capacity retention of 98%). With a low-cost precursor and facile approach, this strategy for synthesizing 1D nanostructured Si would be promising in practical production of high-performance anode materials for lithium-ion batteries.
- Chen, Qingze,Zhu, Runliang,Liu, Shaohong,Wu, DIngcai,Fu, Haoyang,Zhu, Jianxi,He, Hongping
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- Improved cyclic stability of Mg2Si by direct carbon coating as anode materials for lithium-ion batteries
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High-crystalline Mg2Si/C composites with uniform carbon layer were successfully synthesized by the decomposition of C2H2 gas onto the surface of pre-synthesized Mg2Si. The Mg 2Si/C composites with a carbon content of 1.19% delivered a discharge capacity of 320 mA h g-1 after 100 cycles and a stable Coulombic efficiency over 95% after the first cycle, which is better than the bare Mg 2Si. The uniform carbon layer could enhance the electronic conductivity, buffer the volume change and reduce the pulverization during the charge/discharge process, which might be responsible for the enhanced cyclic performance. The results indicate that the chemical vapor deposition (CVD) of the carbon layer with low carbon content can distinctly enhance the cyclic stability of Mg2Si, which can be extended to other anode materials.
- Xiao, Chengmao,Du, Ning,Zhang, Hui,Yang, Deren
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- Thermoelectric performance of Mg2-xCaxSi compounds
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Thermoelectric materials Mg2-xCaxSi (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1) compounds have been prepared by vacuum melting followed by hot-pressing. Effects of the substitution of Ca for Mg on phase structures and the thermoelectric pro
- Zhang,Zhao,Yin,Zhu
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- Synthesis and Characterization of the Mg2SixGe 1-x Solid Solution
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The Mg2SixGe1-x solid solution was prepared by heating stoichiometric amounts of elemental Mg, Si, and Ge in an argon atmosphere. Both microprobe and X-ray diffraction analysis of the reaction products suggest that homogeneous alloys can be made by heating the elements to 1200 °C, a temperature roughly 100 °C in excess of the melting temperatures for pure Mg2Si and Mg2Ge. 29Si solid-state nuclear magnetic resonance was used to characterize the Mg2SixGe1-x solid solution. The 29Si isotropic chemical shift changes consistent with the band gap in these materials while the line width increases with local disorder.
- Ratai, Eva,Augustine, Matthew P.,Kauzlarich, Susan M.
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- Electrical, thermal, thermoelectric and related properties of magnesium silicide semiconductor prepared from rice husk
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Polycrystalline, 10 μm size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited at room-temperature (30°C) thermoelectric power of 565 μVK-1 and an electrical resistivity of 35 Ω cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3 × 10-3 cal s-1cm-1K-1 (2.6 Js-1m-1K-1. These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology of large-scale production of silanes (SiH4) can be developed using this Mg2Si which could be prepared in large quantities by a simple and low-cost process.
- Bose, S.,Acharya, H. N.,Banerjee, H. D.
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- Correlation between the magnetic and thermoelectric properties in Mg2?xMnxSi
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Single crystals of Mg2?xMnxSi (x?=?0, 0.1, 0.2, 0.3, and 0.4) were prepared using a vertical Bridgman method. The formation of desired materials was confirmed using single-crystal and powder X-ray diffraction. The thermoelectric and magnetic properties were investigated for various Mn contents in the temperature range between 2 and 300?K and in magnetic fields up to 70?kOe. For various x values, Mg2?xMnxSi with x?=?0.2 possesses the highest figure of merit. The experimental results revealed that the substitutional Mn atoms exhibit mixed valences of?+3 (majority) and?+2, giving rise to dramatic changes of carrier density and magnetic interaction. At the same time, the Seebeck coefficient and magnetic susceptibility show a sudden change at the same temperature. These results imply that the thermoelectric properties are correlated with the magnetic properties in the Mg2?xMnxSi crystals.
- Kim, Chungman,Kim, Soohyun,Hong, Yang-Ki,Oh, Min-Wook,Jung, Myung-Hwa
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- Combustion synthesis of silicon by magnesiothermic reduction
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Magnesiothermic reduction of silica is a powerful method for producing silicon owing to its simplicity, low reduction temperature and low production cost. However, the inevitable formation of magnesium silicide (Mg2Si) limits the use of this method. A new approach was developed in this research to prevent the formation of Mg2Si by using alumina as a consumer of gaseous magnesium. Utilizing this approach, highly pure silicon was produced by firstly purifying the silica regent by acid-leaching. It was then subjected to magnesiothermic reduction regimes in order to optimize the power input and molar Mg/SiO2 ratio to minimize Mg2Si production. Silicon products were analyzed by X-ray powder diffraction (XRD) and quantitative Rietveld refinement. Optimum electrical power and molar ratio were found to be 3.75?kW and 2.25:1, respectively. The silicon product was examined by glow discharge mass spectrometry which indicated that its purity was 99.96%, with 0.10?ppm of B and 0.15?ppm of P, making it an attractive material for solar cell generation.
- Haouli, Saida,Boudebane, Said,Slipper, Ian J.,Lemboub, Samia,G?bara, Piotr,Mezrag, Samiha
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- Synthesis of alkyl-terminated silicon nanoclusters by a solution route
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We describe the synthesis and characterization of alkyl-capped nanocrystalline Si (R-n-Si) prepared by the reaction of SiCl4 with Mg2Si in ethylene glycol dimethyl ether (glyme) and surface-terminated with various alkyl groups, R-n-Si (R = methyl, ethyl, n-butyl, and n-octyl). This reaction produces crystalline nanoparticles with surfaces that can be chemically modified. The resultant crystalline nanoparticles can be suspended in organic solvents or isolated as a powder. The nanoclusters were characterized by transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, UV-vis absorption, and photoluminescence spectroscopy. The average cluster size depends on the reflux time of Mg2-Si with SiCl4, which provided nanoclusters with an average size of 2-5 nm. HRTEM confirms the presence of crystalline nanoclusters, and SAED is consistent with diamond-structured silicon. FTIR spectra are consistent with alkyl surface termination and show very little or no evidence for oxygen on the surface of the nanoclusters, depending on the surface alkyl group. The alkyl termination can be removed by reaction in air at 450 °C, and a Si-O stretch is observed in the FTIR spectra. EPR spectroscopy is consistent with crystalline Si nanoclusters and shows no signal at 4 K. The optical absorption spectra show an absorption edge between 260 and 240 nm, depending on the surface alkyl group, while a strong UV-blue photoluminescence between 315 and 520 nm is observed.
- Yang, Chung-Sung,Bley, Richard A.,Kauzlarich, Susan M.,Lee, Howard W. H.,Delgado, Gildardo R.
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- Effect of high-intensity ultrasonic treatment on modification of primary Mg2Si in the hypereutectic Mg-Si alloys
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The effect of high intensity ultrasonic treatment (HIUST) on modification of primary Mg2Si in the hypereutectic Mg-5 wt.%Si alloy have been studied. Various resulted microstructures were produced in this alloy by employing ultrasonic vibrations during solidification process at different pouring temperatures and for different application times. The results showed clearly that in the absence of HIUST, the dendrites of primary Mg2Si were coarser and non-uniform in size. Upon HIUST of the alloy during solidification process, nearly uniform and polyhedral shape of primary Mg 2Si with a network of Mg phase segregated along the grain boundaries were obtained. Interestingly, the average size of primary Mg2Si decreased significantly with increasing the pouring temperature and the vibration time of HIUST reached a minimum at 800 °C and 90 s. After that the average size of primary Mg2Si increased slightly with further increasing the pouring temperature and the ultrasonic vibration time. Modification mechanism resulting in the development of microstructure is also investigated.
- Moussa,Waly,El-Sheikh
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- Intense vortex pinning enhanced by semicrystalline defect traps in self-aligned nanostructured MgB2
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The semicrystalline defect wells in self-aligned nanostructured MgB2 were analyzed. It was shown that these aperiodic regions trap numerous crystal defects migrating along nanodomain boundaries during self alignment. The results show that the d
- Li,White,Laursen,Tan,Sun,Dong,Li,Zho,Horvat,Dou
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- Enhancement of thermoelectric performance of Mg2Si via co-doping Sb and C by simultaneous tuning of electronic and thermal transport properties
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Thermoelectric power generation using distributed waste heat energy has received attention as a long-life, environmentally friendly power supply. The intermetallic compound Mg2Si is a lightweight, mid-temperature thermoelectric material that contains no toxic elements, and its thermoelectric performance has been enhanced by various methods such as impurity doping, nanostructuring, and alloying. In this study, we examined the influence of the influence of co-doping with Sb and dilute amounts of the isoelectronic impurity C on the thermoelectric properties of Mg2Si. We fabricated dense polycrystalline specimens of Mg2CxSbySi using the melting process and subsequent plasma-activated sintering. Doping Mg2Si with Sb increased the electrical conductivity ~102 times. Further co-doping with isoelectronic C did not significantly change the electrical conductivity; however, it did reduce the thermal conductivity independently of the electrical properties. Consequently, the specimens co-doped with Sb and C achieved higher thermoelectric performance than specimens of Mg2Si single-doped with Sb. The dimensionless figure of merit ZT of the co-doped specimens reached 0.79 at 873 K over the temperature range 323–873 K.
- Shiojiri, Daishi,Iida, Tsutomu,Kakio, Hiroki,Yamaguchi, Masato,Hirayama, Naomi,Imai, Yoji
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- Synchronous synthesis of a Si/Cu/C ternary nano-composite as an anode for Li ion batteries
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Commercial micron-sized bulk Si is chemically converted into a nano-sized Si/Cu/C ternary composite. The Si particles, Cu crystals, and amorphous carbon are generated synchronously and mixed uniformly. As an anode, the Si/Cu/C exhibits a capacity of 1560 mA h g-1 after 80 cycles at 0.5 mA g-1, long-term cycling stability with a capacity of 757 mA h g-1 at 2 A g-1 after 600 cycles, and fine rate capability.
- Lin, Ning,Zhou, Jie,Zhou, Jianbin,Han, Ying,Zhu, Yongchun,Qian, Yitai
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supporting information
p. 17544 - 17548
(2015/09/01)
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- Thermodynamic destabilisation of MgH2 and NaMgH3 using Group IV elements Si, Ge or Sn
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The addition of Group IV elements of Si, Ge or Sn to Mg-based hydrides has led to the successful destabilisation of MgH2 or NaMgH3, resulting in hydrogen release at lower temperatures. This is the first time a direct comparison has b
- Chaudhary, Anna-Lisa,Paskevicius, Mark,Sheppard, Drew A.,Buckley, Craig E.
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p. 109 - 116
(2015/02/19)
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- Low temperature chemical reduction of fusional sodium metasilicate nonahydrate into a honeycomb porous silicon nanostructure
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Honeycomb porous silicon (hp-Si) has been synthesized by a low temperature (200 °C) magnesiothermic reduction of Na2SiO3· 9H2O. This process can be regarded as a general synthesis method for other silicide materials. Significantly, hp-Si features excellent electrochemical properties after graphene coating. the Partner Organisations 2014.
- Liang, Jianwen,Wei, Denghu,Lin, Ning,Zhu, Youngchun,Li, Xiaona,Zhang, Jingjing,Fan, Long,Qian, Yitai
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supporting information
p. 6856 - 6859
(2014/06/23)
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- Phase selection during calcium silicide formation for layered and powder growth
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Phase selection during Ca silicide formation was discussed using the chemical potential and the effective heat of formation (ΔH′) models. The compositional analyses of Ca silicides were experimentally carried out in detail for both the layered and powder
- Wen, Cuilian,Kato, Akihiko,Nonomura, Tomomi,Tatsuoka, Hirokazu
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p. 4583 - 4587
(2011/04/22)
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- Reactivity of MgB2 with common substrate and electronic materials
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The reactivity of MgB2 with powdered forms of common substrate and electronic materials is reported. Reaction temperatures between 600 and 800°C, encompassing the range commonly employed in thin-film fabrication, were studied. The materials tes
- He,Cava,Rowell, John M.
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p. 291 - 293
(2008/10/08)
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