Inorganics2014, 2(3), 396-409; doi:10.3390/inorganics2030396 (doi registration under processing) - published online 31 July 2014 Show/Hide Abstract
Abstract: The spray-pyrolysis of borazine at 1400 °C under nitrogen generates boron nitride (BN) nanoparticles (NPs). The as-prepared samples form elementary blocks containing slightly agglomerated NPs with sizes ranging from 55 to 120 nm, a Brunauer-Emmett-Teller (BET)-specific surface area of 34.6 m2 g−1 and a helium density of 1.95 g cm−3. They are relatively stable in air below 850 °C in which only oxidation of the NP surface proceeds, whereas under nitrogen, their lower size affects their high temperature thermal behavior in the temperature range of 1450–2000 °C. Nitrogen heat-treated nanostructures have been carefully analyzed using X-ray diffraction, electron microscopy and energy-dispersive X-ray spectroscopy. The high temperature treatment (2000 °C) gives hollow-cored BN-NPs that are strongly facetted, and after ball-milling, hollow core-mesoporous shell NPs displaying a BET-specific surface area of 200.5 m2·g−1 and a total pore volume of 0.287 cm3·g−1 were produced. They have been used as host material to confine, then destabilize ammonia borane (AB), thus improving its dehydrogenation properties. The as-formed AB@BN nanocomposites liberated H2 at 40 °C, and H2 is pure in the temperature range 40–80 °C, leading to a safe and practical hydrogen storage composite material.
Abstract: This manuscript summarizes the failure mechanisms found in inorganic fullerene-type tungsten disulfide (IF-WS2) nanoparticles treated with diverse pressure loading methods. The approaches utilized to induce failure included: the use of an ultrasonic horn, the buildup of high pressures inside a shock tube which created a shock wave that propagated and impinged in the sample, and impact with military rounds. After treatment, samples were characterized using electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and surface area analysis. The microstructural changes observed in the IF-WS2 particulates as a consequence of the treatments could be categorized in two distinct fracture modes. The most commonly observed was the formation of a crack at the particles surface followed by a phase transformation from the 3D cage-like structures into the 2D layered polymorphs, with subsequent agglomeration of the plate-like sheets to produce larger particle sizes. The secondary mechanism identified was the incipient delamination of IF-WS2. We encountered evidence that the IF-WS2 structure collapse initiated in all cases at the edges and vertices of the polyhedral particles, which acted as stress concentrators, independent of the load application mode or its duration.
Abstract: Recent studies have clearly indicated the favorable effect of lead as a growth promoter for MX2 (M = Mo, W; X = S, Se) nanotubes using MX2 powder as a precursor material. The experimental work indicated that the lead atoms are not stable in the molybdenum oxide lattice ion high concentration. The initial lead concentration in the oxide nanowhiskers (Pb:Mo ratio = 0.28) is reduced by one order of magnitude after one year in the drawer. The initial Pb concentration in the MoS2 nanotubes lattice (produced by solar ablation) is appreciably smaller (Pb:Mo ratio for the primary samples is 0.12) and is further reduced with time and annealing at 810 °C, without consuming the nanotubes. In order to elucidate the composition of these nanotubes in greater detail; the Pb-“modified” MX2 compounds were studied by means of DFT calculations and additional experimental work. The calculations indicate that Pb doping as well as Pb intercalation of MoS2 lead to the destabilization of the system; and therefore a high Pb content within the MoS2 lattice cannot be expected in the final products. Furthermore; substitutional doping (PbMo) leads to p-type semiconducting character; while intercalation of MoS2 by Pb atoms (Pby/MoS2) should cause n-type semiconducting behavior. This study not only sheds light on the role of added lead to the growth of the nanotubes and their role as electron donors; but furthermore could pave the way to a large scale synthesis of the MoS2 nanotubes.
Abstract: This paper reports about a new synthesis method for preparing Mg2Si in an efficient way. The intermetallic Mg2Si-phase forms gradually from a mixture of Mg and Si fine powder during exposure to hydrogen atmosphere, which reacts in a vacuum vessel at 350 °C. The resulting powder has the same particle size (100 µm) compared with commercial Mg2Si powder, but higher reactivity due to large surface area from particulate morphology. Both types of powders were compacted by spark plasma sintering (SPS) experiments at 627, 602, 597, and 400 °C for 600 s with a compaction pressure of 80 MPa. The thermoelectric characterization was performed with low and high temperature gradients of ΔT= 10 K up to 600 K. The results confirmed a Seebeck coefficient of −0.14 mV/K for specimens sintered from both powders. The small difference in total performance between purchased and produced power is considered to be due to the effect of impurities. The best values were obtained for n-type Mg2Si doped with 3% Bi yielding a Seebeck coefficient of −0.2 mV/K, ZT = 0.45) and electric output power of more than 6 µW.
Abstract: The adsorption of glycine (Gly) both in gas-phase conditions and in a microsolvated state on a series of zig-zag (n,0) single-walled boron nitride nanotubes (BNNTs, n = 4, 6, 9 and 15) has been studied by means of B3LYP-D2* periodic calculations. Gas-phase Gly is found to be chemisorbed on the (4,0), (6,0) and (9,0) BNNTs by means of a dative interaction between the NH2 group of Gly and a B atom of the BNNTs, whose computed adsorption energies are gradually decreased by increasing the tube radius. On the (15,0) BNNT, Gly is found to be physisorbed with an adsorption driving force mainly dictated by p-stacking dispersion interactions. Gly adsorption in a microsolvated environment has been studied in the presence of seven water molecules by progressively microsolvating the dry Gly/BNNT interface. The most stable structures on the (6,0), (9,0) and (15,0) BNNTs present the Gly/BNNT interface fully bridged by the water solvent molecules; i.e., no direct contact between Gly and the BNNTs takes place, whereas on the (4,0) BNNT the most stable structure presents a unique direct interaction between the COO− Gly group and a B atom of the nanotube. Further energetic analyses indicate that the (6,0), (9,0) and (15,0) BNNTs exhibit a low water affinity, which favors the Gly/water interactions upon BNNT coadsorption. In contrast, the (4,0) BNNT has been found to show a large water affinity, bringing the replacement of adsorbed water by a microsolvated glycine molecule as an unfavorable process.
Abstract: This manuscript demonstrates the design, modification and initial investigation of a rotary furnace for the manufacturing of inorganic fullerene WS2 nanoparticles. Different preparation methods starting with various precursors have been investigated, of which the gas-solid reaction starting with WO3 nanoparticles was the most efficient technique. Furthermore, the influence of temperature, reaction time, and reaction gases etc. on the synthesis of inorganic fullerene WS2 nanomaterials was investigated, and these parameters were optimised based on combined characterisations using XRD, SEM and TEM. In addition, the furnace was further modified to include a baffled tube, a continuous gas-blow feeding system, and a collection system, in order to improve the batch yield and realise continuous production. This technique has improved the production from less than 1 g/batch in a traditional tube furnace to a few tens of g/batch, and could be easily scaled up to industry level production.