Magnesiothermal Reduction Research Articles

Role of Crystalline Si and SiC Species in the Performance of Reduced Hybrid C/Si Gels as Anodes for Lithium-Ion Batteries.

In recent years, the research on lithium-ion batteries (LIBs) to improve their lifetime, efficiency and energy density has led to the use of silicon-based materials as a promising anode alternative to graphite. Specifically, crystalline silicon (cSi) and silicon carbide (SiC) obtained from deposition or reduction processes (e.g., magnesiothermal reduction) stand out for their electrochemical properties. However, the synthesis routes proposed until now have limitations that make them difficult to afford or operate on a large scale. For this reason, in this work, carbon-silicon (C-Si) hybrid materials synthesized through an efficient route are evaluated as the potential precursor for the obtention of both cSi and SiC species in a single material. The feasibility and influence of the magnesiothermal reduction process were evaluated, and materials with 10 wt.% of reduced Si and 10-26 wt.% of SiC were obtained. Both species play a role in the improvement of the performance of silicon-based materials as anodes in lithium-ion batteries. In comparison with materials obtained by the reduction of silica gels and composites, the reduced C-Si hybrid gels stand out thanks to the homogeneous distribution and stability of the species developed.

Rice husk-derived silicon nanostructured anode to enhance power generation in microbial fuel cell treating distillery wastewater

The present study aims to utilize rice husk as a source of silica to prepare rice husk derived silicon nanoparticles (RH-Si) and demonstrate its ability as an anode modifier in a two-chambered H-shaped microbial fuel cell (MFC). The silicon nanoparticles synthesized by magnesiothermal reduction process were spherical in shape and ranged in size from 15 to 60 nm. The anode modified with silicon nanoparticles of 0.50 mg cm−2 recorded the maximum power and current density of 190.5 mW m−2 and 1.5 A m−2 corresponding to 7.6-fold and 3-fold increase as compared to the control . The modified anode also recorded a COD removal and coulombic efficiency of 74% and 49%, respectively in MFC operated with combined distillery and domestic wastewater at a HRT and OLR of 72 h and 59.2 gCOD L−1 d−1, respectively. The results evidence that RH derived silicon NPs are good anode modifiers and effective in enhancing bioelectricity generation and COD removal in MFCs.

New magnesio-thermal reduction technique to produce high-purity crystalline nano-silicon via semi-batch reactor

Abstract The production of high-purity crystalline nano-silicon from natural sources is one of the most difficult tasks due to the complexity of the process and its expense. In the present investigation, high-purity crystalline nano-silicon was produced from rice husk via a modified magnesiothermic technique. In this technique, a stainless steel semi-batch reactor was constructed to carry out the reduction process. The reduction was achieved at different reaction temperatures (i.e., 600, 700 and 800 °C) under a continuous flow of argon gas. The obtained powder was leached with HCl, HF: CH3COOH, and HF solutions. The structural properties of the obtained silicon nanoparticles (SiNPs) were analyzed and measured by X-ray fluorescence (XRF) and X-ray diffraction (XRD), while the size of the obtained particles was calculated using atomic force microscopy (AFM). The XRF results indicated that the best reduction temperature for the production of high-purity nano-silicon was 800 °C, which showed a purity of 99.923%. While at 600 °C and 700 °C the purity was 98.471 and 99.908, respectively. Also, the purity of the produced silica by the precipitation method was 99.9%. Furthermore, the results indicated that the leaching processes with HCl and HF: CH3COOH solutions played a key role in determining the quality of the final prepared nano-silicon. The prepared nano-silicon had a high-purity polycrystalline structure with a particle size of 95.4 nm. Finally, this cost-effective technique synthesized a high-purity nano-silicon with simple operation in a semi-batch reactor.

NiO reduction by Mg + C combined reducer at high heating rates

The mechanism and kinetics of nickel oxide reduction by Mg + C combined reducer at non-isothermal conditions in a wide range of high heating rates (100–1200 °C min−1) were studied by high-speed temperature scanner technique. It was shown that both the magnesiothermal and magnesiocarbothermal reduction processes, unlike low heating rates (5–20 °C min−1, DTA/DTG method), start beyond the melting point of magnesium and proceed via solid + liquid scheme. It was found out that the utilization of Mg + C combined reducer allows to significantly lower the reduction temperature (by about 200–400 °C) of nickel oxide as compared with exclusively magnesium or carbon reducers evidencing on the synergetic effect of combined reducers in the ternary mixture. The effective values of activation energy (Ea) for the NiO + Mg and 2NiO + Mg + C reactions were determined to be 185 ± 15 kJ mol−1 and 195 ± 15 kJ mol−1, respectively.

Magnesiothermal Synthesis and Consolidation of the Multicomponent Powder Ceramics in the Zr–Si–Mo–B System

This work is devoted to the fabrication of ZrB2–ZrSi2–MoSi2-based composite powder ceramics by self-propagating high-temperature synthesis (SHS) according to the scheme of magnesium thermal reduction from oxide feedstock and its subsequent hot-pressing (HP) consolidation. The combustion of reaction mixtures has rather high adiabatic temperatures in a range of 2060–2120 K and burning rates in a range of 8.3–9.4 g/s. The end product yield of the magnesiothermal reduction is 34–38%. The resulting powder contains 13–47% ZrB2, 21–70% ZrSi2, 2–32% ZrSi, and 10–18% MoSi2, depending on the composition of the initial reaction mixture; has high structural homogeneity; and consists of composite polyhedral particles with an average size on the order of 8 μm. The structure of ceramics consolidated by HP from the SHS powder is homogeneous and includes needle ZrB2 grains distributed in the ZrSi2 matrix, MoSi2 inclusions of various morphologies, and inclusions of ZrSiO4 silicate distributed over the ZrSi2 grain boundaries. The HP-formed samples have a high degree of homogeneity of the chemical composition and residual porosity of 2.5–7.4%.

Synthesis of silica nanoparticles from sugarcane bagasse ash and nano-silicon via magnesiothermic reactions

Nanoparticles of SiO2 were synthesized via sol-gel route using sugarcane bagasse ash as a silica source. The influence of the synthesis operational conditions, as well as, the use of different purification methods, such as chemical treatments, on morphological, structural and chemical properties of the synthesized nanoparticles were evaluated. The results showed that the sol-gel synthesis is a feasible alternative method for obtaining silica xerogel using ashes with high impurities contents, such as iron and aluminum oxide. Amorphous SiO2 nanoparticles with an average size of ~10 nm were obtained by controlling the main synthesis variables (pH, temperature and SiO2/H2O molar ratio). The purification methods investigated allowed to obtain nanosilica with different levels of purity, greater than 96%. The combined morphological features, i.e., large specific surface and pore volume, allow these materials to have applications in several technological fields, such as optical, electronics and biomedical and additionally, as a source of nano-silicon via magnesiothermal reduction.

Magnesiothermal synthesis and consolidation of multicomponent powder ceramics in the Zr–Si–Mo–B system

The work aims to obtain composite powder ceramics based on ZrB2–ZrSi2–MoSi2 by the self-propagating high-temperature synthesis (SHS) according to the scheme of magnesium thermal reduction from oxide raw materials, as well as its subsequent consolidation by hot pressing (HP). The combustion of the reaction mixtures is characterized by rather high adiabatic temperatures in the range of 2060 to 2120 K and burning rates in the range of 8,3 to 9,4 g/s. The yield of the end product with magnesiothermal reduction is 34–38 %. The resulting powder contains 13–47 % ZrB2, 21–70 % ZrSi2, 2–32 % ZrSi, and 10–18 % MoSi2 depending on the composition of the initial reaction mixture. It is characterized by high structural homogeneity and consists of composite particles of polyhedral shape with an average about 8 microns in size. The structure of ceramics consolidated by the HP method from SHS powder is homogeneous and includes ZrB2 needle grains distributed in a ZrSi2 matrix, MoSi2 inclusions of various morphology and ZrSiO4 silicate, distributed along the grain boundaries of ZrSi2. The samples obtained by HP are characterized by a high degree of homogeneity of the chemical composition and a residual porosity of 2,5–7,4 %.

Synthesis of Si/SiOx from talc and its characteristics as an anode for lithium-ion batteries

A mixture of silicon (Si) and silicon suboxide (SiOx, x<2) phases is prepared from talc by magnesio-thermal reduction and acid etching processes. Talc is a clay mineral composed of hydrated magnesium silicate and is one of the most abundant minerals on earth. The reduced Si/SiOx nanoparticles are found to be porous after acid etching and are closely connected. The Si/SiOx particles are supported on a carbon layer which imparts them with electronic conductivity and improved durability towards stresses associated with the volume change of Si/SiOx during cycling. The structural, physical, and electrochemical properties of these electrodes are analyzed through X-ray diffraction, scanning electron microscopy, Fourier transform-infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, electrochemical impedance spectroscopy and galvanostactic charge-discharge tests. The initial discharge capacity of the carbon-coated Si/SiOx obtained from talc is measured to be 842mAh/g at 1C (1500mA/g) which decreases to 470mAh/g after 300cycles, showing a much higher capacity retention (~55.8%) than pure Si nanoparticles. This superior cycling stability may be attributed to the porous network structure of the magnesio-thermally reduced Si/SiOx and its endurance towards volume changes during cycling.

Synthesis of nanosized SiC by low-temperature magnesiothermal reduction of nanocomposites of functionalized carbon nanotubes with MCM-48

Silicon carbide synthesis by a magnesiothermal method was investigated using MCM-48 as the silica source mechanically mixed with carbon nanotubes (CNTs) as the carbon source, and nanocomposites of MCM-48/functionalized CNTs (CNTF). SiC syntheses were carried out with different molar ratios of MCM-48, carbon and magnesium at 700 °C in argon. The MCM-48 and carbon nanotube starting materials and the SiC products were characterized by BET, XRD, FESEM, EDX and TEM. The effect of the carbon content and the type of CNTs (either functionalized or unfunctionalized) on the SiC synthesis was studied. The results show that an improved yield of SiC is obtained when the carbon nanotubes are functionalized, producing a better contact with the MCM-48. This improved contact between the reactants ensures a good degree of reaction in a stoichiometric mixture of silicon and carbon, with no improvement in product formation being achieved by the use of additional carbon. These findings suggest that the degree of contact between reactants is an important factor in the magnesiothermal synthesis of SiC. The SiC products from magnesiothermal synthesis of the functionalized nanocomposite precursors were shown by TEM and FESEM to have unusual nanofiber morphologies mimicking the morphology of the CNTF nanotubes.

Synthesis of mesoporous Si/SiC with three-dimensional structure derived from C/silicalite-1 via magnesiothermic reduction

C/silicalite-1 composites were successfully synthesized by using industrial silica sol as silica source and multiwalled carbon nanotube (MWCNTs) as carbon source under hydrothermal method. Then, C/silicalite-1 composites were transformed into mesoporous Si/SiC through magnesiothermal reduction at relatively low temperature (650 °C). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and Brunauer–Emmett–Teller analysis (BET). The XRD patterns and TEM micrographs exhibit that C/silicalite-1 composites are transformed into Si/SiC. The SEM images exhibit that Si/SiC keeps the three-dimensional structure of silicalite-1. BET analysis shows that the specific surface areas and mesoporous distribution of Si/SiC are 274 m2/g and 4.69 nm, respectively.

Fabrication of high-alloy powders consisting of spherical particles from ultradispersed components

It is shown that powders of a model high alloy consisting of spherical particles 25–50 μm in size can be synthesized from a starting ultradispersed powder, which is made of a mixture of the alloy components and is fabricated by the magnesiothermal reduction of metal chlorides in the potassium chloride melt. The synthesis includes the stages of microgranulation of an ultradispersed powder, heat treatment of microgranules, classification of the microgranules with the separation of microgranule fraction of 25–50 μm, spheroidization of the separated fraction in a thermal plasma flow, and classification with the separation of a fraction of micro- and submicrometer-sized particles.

Particles of porous silicon formed from silica powders of plant origin and their structural properties

In this paper, we present the results on study of formation regularities, morphology, composition and photoluminescence of porous silicon particles fabricated by the magnesiothermal reduction of different samples of biogenic silicon dioxide based on rice husk, bamboo husk and bamboo joints at 650 °C at argon atmosphere.

Synthesis of Silicon Microspheres

The synthesis of silicon microspheres is of outmost importance, especially for the production of optical and electrical devices due to their unique properties displayed by this material. In this paper, we review the research on the synthesis of silicon microspheres, including one physical method, the drop method and several chemical methods, such as vapor-phase reaction, vapor-solid reaction, liquid phase reaction and magnesio-thermal reduction method. The formation mechanisms for silicon microsphere particles are also summarized.

Biotemplated Silica and Silicon Materials as Building Blocks for Micro- to Nanostructures

Silicon is essential in several energy-related devices, including solar cells, batteries, and some electrochemical systems. These devices often rely on micro- or nanostructures to function efficiently, and require patterning of metallic surfaces. Currently, constructing silicon features at the micro- and nanoscale requires top-down energy-intensive processes, such as e-beam lithography, chemical etching, or anodization. While it is difficult to form silicon in aqueous solution, its oxide, silica, can easily be synthesized using sol–gel chemistry and nucleated onto templates with diverse shapes to create porous or continuous architectures. Here, we demonstrate that novel silica nanostructures can be synthesized via biomineralization, and that they can be reduced to silicon using magnesiothermal reduction. We selected three biotemplates to create silica structures with various aspect ratios and length scales. First, we use diatomaceous earth as a model silica material to optimize our process, and we also biomineralize silica onto two microorganisms, the high aspect ratio M13 bacteriophage, and the helical Spirulina major algae. During our process, the shape of the materials is preserved, resulting in silicon nanowires, nanoporous networks, spirals, and other micro- and nanostructures with high surface area. Our method provides an alternative for the creation of silicon nanostructures, using preformed silica synthesized in solution. The process could be extended to a broader range of microorganisms and metal oxides for the rational design of on-demand micro- and nanostructured metals. In addition, we show that the intrinsic composition of the biotemplates as well as their growth medium can introduce impurities that could potentially be used as dopants in the final silicon structures, and that could allow for tuning the composition of n-doped or p-doped biotemplated silicon for use as semiconducting building blocks.

Graphene-like carbide derived carbon for high-power supercapacitors

Two graphene-like carbide derived carbons (CDC-Gs) were produced by chlorination of SiC nanosheets obtained by magnesio-thermal reduction at moderate temperature of silica/graphene oxide nanocomposites. These CDC-Gs were evaluated as supercapacitor electrode materials in an organic electrolyte. Starting from a low SiO2/GO ratio in the precursor, the resulting CDC-G nanosheets are composed of a few layers of graphite, partially coated with microporous CDC. In contrast, a high SiO2/GO ratio leads to micropores generated on the basal plane of individual carbon nanosheets. The latter CDC-G shows a remarkable high power capability with 76 % of retention of the initial capacity at scan rates up to 3Vs−1. Notably, the equivalent series resistance (ESR) and time constant of the cell were found to be extremely low at 0.45Ω·cm2 and 0.4s, respectively, thanks to the unique 2D open surface and enhanced access to micropores. These features were attributed to the unique nanostructure of the microporous graphene.

Synthesis of nanostructured SiC by magnesiothermal reduction of silica from zeolite ZSM-5 and carbon: The effect of carbons from different sources

Nanostructured SiC was synthesized by magnesiothermal reduction of silica derived from zeolite ZSM-5 with a Si/Al ratio of about 80 and four carbons from different sources. The carbons were carbon black and three carbons synthesized by impregnating furfuryl alcohol or sucrose into three porous templates (ZSM-5, clinoptilolite and MCM-48). Magnesiothermal reduction was carried out by reacting mixtures of silica, carbon and magnesium powder at 600–800°C in a flowing argon atmosphere. The starting materials and final products were characterized by X-Ray diffraction, thermogravimetric analysis, scanning electron microscopy and BET analysis. The results indicated that the synthesis of nanostructured SiC is influenced by the chemical nature of the carbon and its surface area.

Silicon carbide with tunable ordered mesoporosity

Tunable mesoporous silicon carbides (SiCs) are synthesized by magnesio-thermal reduction of homogeneous composites of silica and carbon precursors. Two triblock copolymers, P123 and F127, are used as structuring agents leading to composites showing an hexagonal mesoporous pattern which is kept by the final SiC thanks to the relatively low temperature of the magnesio-thermal reduction. Two series of mesoporous SiCs are obtained with uniform pore sizes ranging from 6.0nm to 2.5nm (P123 used as structuring agent) and 11.0–3.5nm (F127) depending on the carbon/silica molar ratio in the pristine composite. In each series, SiC polytype transforms from 6H–SiC to 3C–SiC in pace of increasing the carbon content in the composite precursor. A multi step growth mechanism is proposed to account for the composite precursor to final carbide characteristics.

Ordered mesoporous silicon carbide-derived carbon for high-power supercapacitors

Micro/mesoporous carbon was prepared by chlorination of ordered mesoporous silicon carbide derived from magnesio-thermal reduction of templated carbon-silica precursors. These materials were then used as active materials for electrochemical capacitors and characterized in 1.5M NEt4BF4/AN. The electrodes showed outstanding rate capability (90% of capacity retention at 1V/s and time constant of 1s) with high specific areal capacitance (0.5F/cm2 of electrode), that makes such hierarchical porous carbons promising for high power and energy density supercapacitors.