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In this study, tantalum network nanoparticles are prepared from a Ta 2 O 5 + k Mg system via a liquid magnesium-controlled combustion reaction. Super-stoichiometric amounts of magnesium are used in the preparation of a reaction mixture to produce a liquid magnesium pool capable of lowering the combustion temperature and leading to the formation of Ta network structures. The heat transfer kinetics from the hot reaction zone of 'cold' Mg particles is determined using heat transfer-coupled fluid dynamics simulation software. The formation of network structures is characterized through SEM, TEM, XRD, and BET analysis techniques. The mechanism of network formation is explained based on solid particle collisions in liquid media. Our method is able to produce Ta network structures in which the size of individual particles ranges between 50 and 700 nm. [ABSTRACT FROM AUTHOR]

Abstract A lot of efforts being invested into producing efficient thermoelectric devices based on Bi 0.5 Sb 1.5 Te 3 materials for room temperature applications. Key research achievements of these efforts that incorporation of oxide nanoparticles into Bi 0.5 Sb 1.5 Te 3 materials exhibit higher thermoelectric performance in nano-composite form. Here, we prepared Bi 0.5 Sb 1.5 Te 3 nanocomposite incorporated with TeO 2 nanoparticles (NPs) by high energy ball milling and spark plasma sintering, where in-situ Sb 2 O 3 phase and triple functional interfaces were developed. The formation mechanism of in-situ Sb 2 O 3 phase in the Bi 0.5 Sb 1.5 Te 3 /TeO 2 composites was explored by the thermodynamic calculations; microstructural features and material composition in the bulk samples were investigated using high-resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray spectroscopy (EDS). The formation of interfaces between in situ senarmontite Sb 2 O 3 nanophase and Bi 0.5 Sb 1.5 Te 3 matrix causes an enhanced Seebeck coefficient by ∼20% due to increase of carrier energy filtering and significant reduction of thermal conductivity by ∼77% ascribed to intensified phonon scattering or trapping at 350 K. As a result, an improved dimensionless figure of merit (ZT) of 1.07 at 350 K was achieved in a Bi 0.5 Sb 1.5 Te 3 /3 wt%TeO 2 composites. The proposed in-situ reaction and interface formation mechanisms are expected to open the possibility of further increases in ZT. Graphical abstract Image 1 Highlights • Formation of in-situ Sb 2 O 3 phase in the Bi 0.5 Sb 1.5 Te 3 /TeO 2 composites was explored. • Sb 2 O 3 phase is obtained by in-situ reaction of Sb with TeO 2 during milling and SPS. • The Seebeck coefficient was enhanced owing to increase of energy filtering effect. • Thermal conductivity was reduced (77%) due to phonon scattering at interfaces. [ABSTRACT FROM AUTHOR]

A melt-assisted solid flame synthesis approach was applied to synthesize boron nanoparticles in argon gas and air atmospheres. For this purpose, we investigated the characteristics of a thermally induced combustion wave in B 2 O 3 + α Mg mixtures ( α = 1.0–1.5 mol) in argon and air atmospheres. Utilizing stoichiometrically insufficient amounts of magnesium ensured that a large portion of molten B 2 O 3 remained in the sample, which reduced the combustion parameters and favored the formation of boron nanoparticles. Under these conditions the combustion temperature and burning velocity were controlled in the range of 1300–1580 °C and 0.065–0.18 cm/s, respectively, and boron nanoparticles in a ∼20–200 nm size range were obtained. The characteristics of boron nanoparticles (morphology, purity, specific surface area, oxidation activity, etc.) were analyzed and a reaction pathway leading to boron nanoparticles synthesis was proposed. [ABSTRACT FROM AUTHOR]

Amorphous boron nanoparticles were synthesized by heating a B 2 O 3 + 3 Mg + k NaCl ( k is the number of moles of NaCl) exothermic mixture in a laboratory oven at 800 °C under argon flow. NaCl was used as inert material to decrease the maximum combustion temperature of the reaction mixture when it was self-ignited after the melting of Mg at 650 °C. The size of the boron nanoparticles extracted from the final product by acid leaching ranged between 30 and 300 nm for k values ranging from 1 to 5. Moreover, increasing the value of k from 1 to 5 resulted in an increase in the specific surface area of the nanoparticles from 40 to 74 m 2 g −1 . However, at k = 10, a decrease in the specific surface area to 47.56 m 2 g −1 was recorded due to incomplete reduction of B 2 O 3 . The ignition point of boron nanoparticles in air as estimated using a thermocouple was approximately 300 °C. Digital camera recording of the combustion process of boron nanoparticles in air revealed that the burning speed of the nanoparticles increased significantly from 0.3 to 15 cm/s when k increased from 1 to 5. [ABSTRACT FROM AUTHOR]

Tantalum nitride nanoparticles were produced from a (K2TaF7 +5NaN3) exothermic mixture under the combustion regime. The effects of the K2TaF7/NaN3 ratio and KF and NH4F concentrations on the combustion parameters, product composition, and size of the tantalum nitride particles were studied. Depending on the synthesis conditions, the combustion temperature was maintained in the 700–1200°C range, resulting in hexagonal ε-TaN, TaN0.8, and Ta2N phases. The dominant phases were TaN and TaN0.8 in the 1000–1200°C range, whereas only the Ta2N phase was present in the 700–100°C range. Pure-phase cubic tantalum nitride (δ-TaN) was produced with 4.0mol of NH4F at a combustion temperature of ~800°C. Under controlled reaction conditions, the size of the tantalum nitride particles was about 10–50nm. We also found that during the synthesis, the stainless steel tube located inside of the reaction mixture was partially coated with fine TaN crystals. The mechanism of the combustion process is discussed in regards to the experimental results. [ABSTRACT FROM AUTHOR]