Mg2Si Nanoparticles Research Articles

Strengthening of the magnesium matrix composites hybrid reinforced by chemically oxidized carbon nanotubes and in situ Mg2Sip

Aggregation and weak interfacial bonding limit the superior strengthening potential of the carbon nanotubes (CNTs) in the metal matrix composites. To overcome these challenges, in situ Mg2Si nanoparticles (Mg2Sip) have been hybridized with surface modified CNTs through chemical oxidization. The synergistic strengthening was enhanced by tailoring the volume ratios of CNTs to Mg2Sip in the Mg matrix through powder thixoforming technology. Herein, when 0.3CNTs-1.2Mg2Sip was added, a yield strength, ultimate tensile strength, and elongation of 213 MPa, 271 MPa, and 6.3%, respectively, were obtained, which were 18.3%, 16.8%, and 3.3% higher than those of the 0.75CNTs-0.75Mg2Sip/Mg composites, respectively. The strengthening effects of the CNTs-Mg2Sip reinforcements were more effective than those of the individual 1.5CNTs and 1.5Mg2Sip owing to the effective thermal mismatch and load transfer strengthening mechanisms. In this study, we propose an effective approach to harness the superior performances of the hybrid reinforcements for enhancing the composites.

Effect of Al3(Sc, Zr) and Mg2Si precipitates on microstructure and tensile properties of selective laser melted Al-14.1Mg-0.47Si-0.31Sc-0.17Zr alloy

A novel Al-14.1Mg-0.47Si-0.31Sc-0.17Zr alloy with a low density of 2.54 g/cm3 and a high tensile strength of 510 MPa was manufactured using selective laser melting (SLM) at 200 W and 500 mm/s. The SLM-processed alloy has the comprehensive characteristics of the 5xxx and 6xxx series Al alloys due to its optimized composition. The formation of equiaxed grains occurred during the SLM process, and the mean grain size was 2.97 μm2 in the as-printed (AP) condition. With a heat treatment (HT) of 325 °C for 4 h, the grain size was nearly unchanged (3.45 μm2), and the tensile strength increased to 571 MPa with the formation of Al3(Sc, Zr) and Mg2Si nanoparticles. This new AlMgSiScZr alloy has promising prospects for replacing some specialized titanium parts in the future.

Microstructure and synergistic strengthening mechanisms of carbon nanotubes and Mg2Si nanoparticles hybrid reinforced Mg matrix composites prepared by powder thixoforming

AZ91D Mg-based composites containing carbon nanotubes (CNTs), magnesium silicide (Mg2Sip) nanoparticles, or CNTs-Mg2Sip hybrid reinforcements were synthesized via powder thixoforming using blending and pressing procedures in powder metallurgy, followed by partial remelting and thixoforming technology. The thixoformed microstructure of the CNTs-Mg2Sip hybrid reinforced Mg composite consisted of spheroidal primary α-Mg particles, intergranular secondary solidified structures (SSSs), and hybrid reinforcements homogeneously dispersed within the SSSs. A yield strength of 180 MPa was achieved in the Mg matrix composite reinforced by 0.75CNTs-0.75Mg2Sip hybrids, which was 26% and 12% higher than those of composites reinforced with individual 1.5CNTs and 1.5Mg2Sip, respectively (143 and 161 MPa, respectively). This was attributed to the in situ-synthesized Mg2Sip around the CNTs, which not only restricted the aggregation and pulling out of CNTs but also facilitated the synergistic strengthening effect of the CNTs. This work presents a promising strategy for the synthesis of metal matrix composites with impressive mechanical properties by employing hybrids of CNTs and Mg2Sip as reinforcements.

Modulating Hypoxia via Nanomaterials Chemistry for Efficient Treatment of Solid Tumors.

The common existence of hypoxia in solid tumors has been heavily researched because it renders tumors more resistant to most standard therapeutic methods, such as radiotherapy (RT), chemotherapy, and photodynamic therapy (PDT), and is associated with a more malignant phenotype and poor survival in patients with tumors. The development of hypoxia modulation methods for advanced therapeutic activity is therefore of great interest but remains a considerable challenge. Since the significant development of nanotechnology and nanomedicine, functionalized nanomaterials can be exploited as adjuvant "drugs" for these oxygen-dependent standard therapies or as hypoxia initiators for advanced new therapies to solid tumors. In this Account, we summarize our recent studies on the design and synthesis of nanomaterials with a set of desired chemistry benefits achievable by modulating hypoxia, suggesting a valid therapeutic option for tumors. The investigated strategies can be categorized into three groups: The first strategy is based on countering hypoxia. Considering that O2 deficiency is the major obstacle for the oxygen-dependent therapies, we initially developed methods to supply O2 by taking advantage of the hypoxia-responsive properties of nano-MnO2 or nanomaterials' photothermal effects for increased intratumoral blood flow. The second approach is to disregard hypoxia. Possible benefits of nanoagents include reducing/eliminating reliance on O2 or making O2 replacements as adjuvants to standard therapies. To this end, we investigated a nano-upconversion/scintillator with the capacity toup-/down-convertnear-infrared light (NIR)/X-ray to luminescence in the ultraviolet/visible region fortype-I PDT with minimized oxygen-tension dependency or developed Fe-based nanomaterials for chemodynamic therapy (CDT) without external energy and oxygen participation for efficient free radical killing of deep tumors. The third strategy involves exploiting hypoxia. The unique biological characteristics of hypoxia are exploited to activate nanoagents for new therapies. To address the discrepancy between the nanoagents' demand and supply within the hypoxia region, a smart "molecule-nano" medicine that stays small-molecule-like in the bloodstream and turns into self-assembled nanovesicles after entry into the hypoxia region was constructed for hypoxia-adaptive photothermal therapy (PTT). In addition to traditional anti-angiogenesis therapy, we prepared Mg2Si nanoparticles by a special self-propagating high-temperature synthesis approach. These nanoparticles can directly remove the intratumoral oxygen via the oxidation reactions of Mg2Si and later efficiently block the rapid reoxygenation via tumor blood vessels by the resultant SiO2 microsheets for cancer starvation therapy. Taken together, these findings indicate that nanomaterials will assume a valuable role for anticancer exploration based on either their properties to make up oxygen deficiency or the use of hypoxia for therapeutic applications.

Mg2Si Nanoparticle Synthesis for High Pressure Hydrogenation

The Mg–Si–H system is economically favorable as a hydrogen storage medium for renewable energy systems while moving toward sustainable energy production. Hydrogen desorption from MgH2 in the presence of Si is achievable, forming magnesium silicide (Mg2Si). However, absorbing hydrogen into Mg2Si remains problematic due to severe kinetic limitations. The objective of this study is to reduce these kinetic limitations by synthesizing Mg2Si nanoparticles to limit the migration distance for magnesium atoms from the Mg2Si matrix to produce MgH2 and Si, thus improving the reversibility of the Mg–Si–H system. Mg2Si nanoparticles were synthesized using a reduction reaction undertaken by solid–liquid mechanochemical ball milling. Particle size was controlled by adding a reaction buffer (lithium chloride) to the starting reagents to restrict particle growth during milling. The reaction buffer was removed from the nanoparticles using tetrahydrofuran and small-angle X-ray scattering revealed an average Mg2Si particle s...

Formation and characterization of semiconductor Ca2Si layers prepared on p-type silicon covered by an amorphous silicon cap

Formation of calcium silicide on three types of templates: Si(111)7 × 7, 2D Mg2Si, and 3D Mg2Si, was studied during Ca deposition at 120 °C in situ by Auger and electron energy loss spectroscopy, and by differential optical reflectance spectroscopy. A continuous Ca2Si layer is formed on 2D and 3D Mg2Si templates; but, on an atomically clean silicon surface (Si(111)7 × 7), a mixture of Ca2Si with another Ca silicide was found. The growth of a Si cap layer over the Ca silicide layers at about 100 °C studied by in situ methods demonstrated the full embedding of Ca silicide in amorphous silicon, independent of the used template. Transmission electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, and electrical characterization of Schottky junctions revealed the Ca2Si and Mg2Si nanoparticles and the redistribution of Mg and Ca during the silicon cap growth and its effect on the electronic properties of the structures. Reproduction of the experiments on higher doped and better purity substrates is needed to understand better the role of Mg- and Ca-related defects, and defects of silicon generated by the growth process.

Spark plasma sintering of fine Mg2Si particles

Nanostructuration is an efficient way to improve thermoelectric properties. In this paper, the densification of micro and nanocrystalline Mg2Si is studied using Spark Plasma Sintering process. It seems very problematic to successfully sinter Mg2Si nanoparticles because the nano-size promotes oxidation at grain boundaries and prevent obtaining high green densities of the compacts. The in situ synthesis of Mg2Si under reductive atmosphere, during SPS process, has not led to dense samples, demonstrating that the grain size is the key factor in densifying magnesium silicide powders. Moreover, the sintering of micronic Mg2Si grains has been successfully carried out confirming this assumption. Our results show that mixing powders made of small and large particles give access to 95% dense composite materials with a large amount of fine grains homogeneously distributed in the large grain matrix.

Preparation and Thermoelectric Characteristics of SiO<sub>2</sub>/Mg<sub>2</sub>Si<sub>0.8</sub>Sn<sub>0.2</sub> Bulk Nanocomposite

In the present study, Mg2Si nanoparticles of high purity were successfully synthesized through low-temperature reaction by using MgH2and Si powders as rawmaterials. The size of Mg2Si particles is about 50nm. The bulk nanocomposites xSiO2/Mg2Si0.8Sn0.2(x = 0, 0.1, 1 and 2wt. %) were followed by field-Activated and pressure-assisted synthesis (FAPAS). The effects of SiO2addition on the microstructure and thermoelectric properties of Mg2Si0.8Sn0.2were studied. The field emission scanning electron microscopy shows that the nanometer-sized SiO2particles disperse homogeneously in Mg2Si0.8Sn0.2matrix. Among all of the samples, 1wt. % SiO2/Mg2Si0.8Sn0.2exhibits the best figure of merit (ZT = 0.25 at 573 K), which is 24% higher than that of the sample without SiO2, indicating that the thermoelectric properties of Mg2Si0.8Sn0.2can be enhanced effectively by the dispersion of nanometer-sized SiO2.

Conflicting Effects of SiC Doping on the Properties of Mechanically Alloyed Bulk ${\rm MgB}_{2}$

The influence of micro- and nano-scaled SiC on the phase formation, the structural properties, and the superconductivity of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bulk samples was studied. Mechanical alloying was applied to prepare a nanocrystalline precursor powder with SiC additions up to 10 wt.%. The data implies that, in contrast to previously reported results in literature, the use of SiC as a dopant in MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> shows a conflicting effect. Although a certain carbon substitution was observed and, therefore, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> was enhanced, an often reported increase of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was only obtained for low SiC concentrations. Beyond that, a strong decline of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was observed, coming from an accumulation of SiC and Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si nanoparticles at the grain boundaries which decouples the grains and thereby decreases the connectivity and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

The effect of Cu addition on the sintering process and superconductive properties of μm-SiC-doped MgB2 bulks

Based on the phase identification and microstructural observation, it is found that the Cu addition in the μm-SiC-doped samples could depress the reaction between Mg and SiC and thus decrease the amount of both C substitution for B and the Mg2Si nanoparticles. As a result, compared to the only μm-SiC-doped MgB2 sample, the T c of the Cu and μm-SiC multi-doped MgB2 sample is improved and the J c in high fields is deteriorated.