The effect of nano-particles on the bubble absorption performance in a binary nanofluid

The objectives of this paper are to examine the effect of nano particles on the bubble type absorption by experiment and to find the optimal conditions to design highly effective compact absorber for NH₃/H₂O absorption system. The initial concentrations of NH₃/H₂O solution and the kinds and the concentrations of nano particles are considered as key parameters. The results show that the addition of nano particles enhances the absorption performance up to 3.21 times. Moreover, the absorption rate increases with increasing concentration of nano particles and the nano particles are more effective for lower absorption potential solution. The potential enhancement mechanism for binary nanofluid is suggested. The experimental correlations of the effective absorption ratio for each nano particles, Cu, CuO, and Al₂O₃, are suggested within ±10% error-band.     

A new barium molybdate phase

A new barium molybdate phase (Ba₈Mo₂₀O₆₅(OH)₆.12H₂O) was prepared from the reaction of barium nitrate on the layered sodium bronze Na_0.5 MoO₃ nH₂O. Extensive characterisation of the new phase has been performed using complementary techniques, including wet chemical analysis, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, infrared spectroscopy and thermogravimetric analysis. The results indicate a discrete new phase not reported previously in the literature.     

Crystallization of mixed rare earth (didymium) molybdates in silica gel

Experiments on the growth of mixed rare earth (didymium—a combination of La, Nd, Pr and Sm) molybdates in silica gel medium are reported. The optimum conditions conducive for the growth of these crystals are described and discussed. Concentration programming is reported to enhance the size of crystals by two-fold; the maximum size obtained being about 1 mm³. EDAX results suggest the crystals to be heptamolybdates of type R₂Mo₇O₂₄, bearing composition La_1.23Nd_0.43Pr_0.29 Sm_0.05Mo₇0₂₄. The didymium molybdate crystals assume morphologies corresponding to those of spherulites, platelets, cuboids and coalesced crystals. Twinned structure in didymium molybdate crystals are also reported. It is explained that spherulitic morphologies result from aggregates of crystals joining in a spherical envelope. It is suggested that the crystals of didymium molybdates grow by two-dimensional spreading and piling up of layers.     

Synthesis,characterization and welding property of micro-spherical molybdenum-ruthenium particles

Molybdenum-ruthenium powder is widely used as high-temperature brazing filler material. In this study, micro-spherical Mo-Ru particles were synthesized by spray drying combined with calcination technique from commercial (NH₄)₆Mo₇O₂₄ and (NH₄)₂RuCl₆ powders. Micro-spherical (NH₄)₆Mo₇O₂₄ and (NH₄)₂RuCl₆ mixture particles were achieved by spray drying treatment. The influences of calcination temperature on crystallization, morphology and size of as-synthesized Mo-Ru particles were investigated. The composition of as-synthesized Mo-Ru particles were Mo_0.3124Ru_0.6876 alloy and elemental Mo. Porous tungsten cylinders and molybdenum cylinders were welded together using the as-synthesized Mo-Ru powder. There was no any cracks around the welding region. The average tensile strength of welding samples was 76.65 ± 1.15 MPa. The results show that this is an excellent method to prepare molybdenum-ruthenium powder by spray drying combined with calcination. It should be noted that the powder technology in this study can be applied to synthesize other alloy powders (binary, ternary and more) with high-performance requirements.     

Microwave dielectric properties of low temperature sinterable RE2Mo4O15 (RE = Nd, Sm) ceramics for LTCC applications

The present paper investigates the structure and microwave dielectric properties of novel low temperature sinterable RE₂Mo₄O₁₅ (RE = Nd, Sm) ceramic system. Phase pure ceramics were prepared through solid state ceramic method. The powder X-ray diffraction patterns show that these materials have triclinic crystal structure with space group Pī. The title compounds are well densified around 690 °C. The Scanning Electron Microscopic image reveals dense microstructure for the well sintered ceramic compacts. Nd₂Mo₄O₁₅ ceramic exhibits a dielectric constant of 11.1, an unloaded quality factor of 5,123 at 12 GHz, and a temperature coefficient of resonant frequency (τ_f) of ?44 ppm/ °C. Whereas Sm₂Mo₄O₁₅ samples possess a dielectric constant of 10.7, unloaded quality factor of 5,468 at 11.6046 GHz together with a temperature coefficient of resonant frequency (τ_f) of ?50 ppm/°C. Both the ceramic systems under study show good chemical compatibility with silver electrode.     

Crystallinity enhancement of flame-made LiCo0.25Ni0.75O2 nanoparticles by heat-treatment

LiCo_0.25Ni_0.75O₂ nanoparticles of 22.8 nm in geometric mean diameter were synthesized by flame spray pyrolysis from aqueous droplets of nitrate compounds of lithium, cobalt and nickel. The crystallinity of the as-prepared LiCo_0.25Ni_0.75O₂ particles was enhanced by post-heat-treatment at various conditions, such as temperature, duration, and atmospheric gas with different flow rates. The effect of heat-treatment on the particle morphology and crystallinity was investigated systematically. Higher heat-treating temperature under normal air atmosphere improved hexagonal ordering and sufficient O₂ flow during the heat-treatment reduced the cation mixing problem.     

Impact of Zr/Ti ratio in the PZT on the photoreduction of silver nanoparticles

Silver nanoparticle deposition from an aqueous solution of silver nitrate onto the surface of PZT thin films of stoichiometric compositions PbZr_0.3Ti_0.7O₃ and PbZr_0.52Ti_0.48O₃ has been investigated. The impact of Zr/Ti ratio on the photochemical properties of PZT is shown by the preferential growth of silver nanoparticles onto the surface. Photoreduction of silver occurs on both c⁺ and c⁻ domains on PbZr_0.52Ti_0.48O₃ whereas it occurs only on c⁺ domains on a PbZr_0.3Ti_0.7O₃ surface. The difference in deposition pattern is attributed to difference in magnitude of spontaneous polarization, effective hole concentration and band gap of the two samples which impacts shape and width of space charge layer in the two samples resulting in a change in band bending at the surface.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

Synthesis and photoelectrochemical properties of thin bismuth molybdates film with various crystal phases

Bismuth molybdate films with various phase structures including α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, γ-Bi₂MoO₆, and γ′-Bi₂MoO₆ are fabricated on the indium-tin oxide glass substrates from an amorphous heteronuclear complex via the dip-coating method by appropriate adjustment of the reaction conditions. α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, and γ-Bi₂MoO₆ film can be obtained at 400 °C, 500 °C, and 500 °C for 1 h, respectively. At 500 °C, γ′-Bi₂MoO₆ can be obtained for 4 h. Film formation process is proposed based on the experimental results. Thin γ-Bi₂MoO₆ films exhibit high photoresponse under visible light irradiation. Incident photon to current conversion efficiency of thin γ-Bi₂MoO₆ film starts to increase near 450 nm. And, it can reach 4.1% at 400 nm. The top of the valence band and bottom of the conduction band are roughly estimated to be − 0.71 and 1.69 eV, respectively. In contrast, γ′-Bi₂MoO₆ generated weak photocurrent; α-Bi₂Mo₃O₁₂ and β-Bi₂Mo₂O₉ film has no photoresponse under visible light irradiation. The reason for the difference in the visible light response was discussed.     

Big to Small: Ultrafine Mo2C Particles Derived from Giant Polyoxomolybdate Clusters for Hydrogen Evolution Reaction

Due to its electronic structure, similar to platinum, molybdenum carbides (Mo₂C) hold great promise as a cost‐effective catalyst platform. However, the realization of high‐performance Mo₂C catalysts is still limited because controlling their particle size and catalytic activity is challenging with current synthesis methods. Here, the synthesis of ultrafine β‐Mo₂C nanoparticles with narrow size distribution (2.5 ± 0.7 nm) and high mass loading (up to 27.5 wt%) on graphene substrate using a giant Mo‐based polyoxomolybdate cluster, Mo₁₃₂ ((NH₄)₄₂[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]·10CH₃COONH₄·300H₂O) is demonstrated. Moreover, a nitrogen‐containing polymeric binder (polyethyleneimine) is used to create Mo? N bonds between Mo₂C nanoparticles and nitrogen‐doped graphene layers, which significantly enhance the catalytic activity of Mo₂C for the hydrogen evolution reaction, as is revealed by X‐ray photoelectron spectroscopy and density functional theory calculations. The optimal Mo₂C catalyst shows a large exchange current density of 1.19 mA cm^?2, a high turnover frequency of 0.70 s^?1 as well as excellent durability. The demonstrated new strategy opens up the possibility of developing practical platinum substitutes based on Mo₂C for various catalytic applications.     

Rapid synthesis of Mo2N and Mo2C nanoparticles using non-toxic nitrogen sources in air atmosphere

This study demonstrated a simple and inexpensive route to synthesize molybdenum nitride (Mo₂N) and molybdenum carbide (Mo₂C) in a normal air atmosphere. Sodium molybdate (Na₂MoO₄) and dicyandiamide (C₂N₄H₄) were selected as the reagent precursors. X-ray diffraction (XRD) results revealed that Na₂MoO₄ reacted with dicyandiamide to form Mo₂N in the temperature range of 450–700 °C, whereas Mo₂C formed at a higher temperature. Pure and highly crystalline Mo₂N and Mo₂C were obtained after washing the calcinated products with water. Transmission electron microscopy (TEM) results illustrated the size of Mo₂N nanoparticles to be in the range of 3–10 nm. In comparison to conventional synthesis procedures, our method provides a better cost-effective alternative.     

Synthesis of ceramics by sol–gel method in molybdenum,silicon and carbon containing systems. Thermogravimetric studies

The results of investigations on synthesis of ceramics in nanometric systems containing molybdenum compounds, silicon compounds and active carbon have been presented. As precursors ammonium molybdatetetrahydrate ((NH₄)₆Mo₇O₂₄ 4H₂O) and tetraethyl orthosilicate (Si(OC₂H₅)₄) were used. The samples for analysis were obtained by sol–gel method. The course of the process was investigated by thermogravimetric method. The gaseous products were analysed by mass spectrometry. X’ray diffraction (XRD) method was used for identification of solid phases, and morphology of the samples was studied by scanning electron microscopy (SEM). The process proceeded in the following way. At temperature t ⩽ 673 K (NH₄)₆Mo₇O₂₄ 4H₂O decomposes into MoO₃. Then at temperature range of 1046 ⩽ t ⩽ 1065 K MoO₃ is reduced into MoO₂ (or also into Mo). Synthesis of Mo₂C proceeds at temperature in the order of 1273 K. Before the carbothermal reduction of SiO₂ and synthesis of compounds containing molybdenum and silicon we have the Mo₂C–SiO₂-active carbon mixtures. In one stage, at temperature of 1523 K in argon, the synthesis of SiC and the synthesis of compounds containing molybdenum and silicon takes place. In the wide range of initial compositions of the mixtures Mo_4.8Si₃C_0.6 was obtained as the main phase.     

Effect of process parameters on synthesis of aluminum nitride powder prepared by chemical vapor deposition

Ultrafine aluminum nitride (AlN) powders were obtained by the chemical vapor deposition (CVD) process via the AlCl₃-N₂-NH₃ system operated at various temperatures and different mixing modes of AlCl₃ and NH₃ gases. X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR), transmission electron microscope (TEM) and electron diffraction (ED) were utilized to study the effect of process parameters on the synthesis and characterization of the AlN powders. It had been shown that all of the obtained powders were exclusively identified to be the single phase AlN and were indifferent to the different mixing modes AlCl₃ and NH₃ gases. The yield of synthesized AlN powder was affected by the entries mixing position of the reacting gases of AlCl₃ and NH₃.The yield increased from 13% to 82% where the mixed position was shifted from the front edge to middle point of the quartz tube. On the other hand, the yield increased from 5% to 82% as the reaction temperature increased from 600°C to 1050°C. The morphology of the AlN powders was affected by the diameter of a feeding nozzle and mixing mode of AlCl₃ and NH₃ gases.     

Morphology and size-controllable preparation of silver nanostructures through a wet-chemical route at room temperature

In this letter a simple wet-chemical route was developed to prepare silver nanostructures. The formation of the silver nanostructures occurs in a single process, carried out by mixing an AgNO₃ aqueous solution and a para-phenylenediamine solution at room temperature without the introduction of other reducing agents and morphology controlling agents. It is found that both the morphology and the size of such silver nanostructures can be facilely controlled by the molar ratio and concentration of the reactants as well as the solvent that was used to dilute para-phenylenediamine aqueous solution. As-formed silver nanostructures were examined by scanning electron microscopy.     

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10⁻² and 2.4 × 10⁻² S/cm at 700 °C and 800 °C respectively.     

Thermal expansion studies of Gd2Mo3O12 and Gd2W3O12

Simultaneous thermogravimetric/differential thermal analysis of Gd₂Mo₃O₁₂ showed an irreversible phase transition at 1178 K where as Gd₂W₃O₁₂ showed reversible phase transition at 1433 K, which were confirmed by powder X-ray diffraction. The thermal expansion behavior of α-Gd₂Mo₃O₁₂ (room temperature phase), β-Gd₂Mo₃O₁₂ (phase obtained by heating Gd₂Mo₃O₁₂ at 1223 K) and Gd₂W₃O₁₂ have been investigated using high temperature X-ray diffractometer. The cell volume of α-Gd₂Mo₃O₁₂, β-Gd₂Mo₃O₁₂ and Gd₂W₃O₁₂, fit into polynomial expression with respect to temperature, showed positive thermal expansion up to 1073, 1173 and 1173 K, respectively. The average volume expansion coefficients for α-Gd₂Mo₃O₁₂, β-Gd₂Mo₃O₁₂ and Gd₂W₃O₁₂ are 39.52 × 10⁻⁶, 21.23 × 10⁻⁶ and 37.96 × 10⁻⁶ K⁻¹, respectively.     

Room temperature mechanical properties and high temperature oxidation behavior of MoSi2 matrix composite reinforced by adding La2O3 and Mo5Si3

MoSi₂ matrix composites containing 0.8 wt.%La₂O₃ and different volume fractions of Mo₅Si₃ were synthesized by self-propagating high temperature synthesis. The room temperature mechanical properties and high temperature oxidation behavior at 1200 °C were studied. Results showed that La₂O₃ and Mo₅Si₃ caused the grain size to decrease of the MoSi₂ matrix composite. The flexure strength and fracture toughness are improved compared with pure MoSi₂. The strengthening mechanism of La₂O₃–Mo₅Si₃/MoSi₂ is fine-grain strengthening, and its toughening mechanisms are fine-grain toughening, crack deflection, crack branching and crack bridging. With an increase in Mo₅Si₃ content, the oxidation resistance gradually decreased. This is attributed to the poor oxidation resistance of Mo₅Si₃, grain refinement and relative density decrease of the composites. In this experiment, a La₂O₃–Mo₅Si₃/MoSi₂ composite was found to have optimal mechanical properties and high temperature oxidation resistance after adding 0.8 wt.%La₂O₃ and 16.3 wt.% Mo₅Si₃.     

Holey Reduced Graphene Oxide Coupled with an Mo2N–Mo2C Heterojunction for Efficient Hydrogen Evolution

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small‐sized Mo₂N–Mo₂C heterojunction (Mo₂N–Mo₂C/HGr). The method includes the first immobilization of H₃PMo₁₂O₄₀ (PMo₁₂) clusters on graphite oxide (GO), followed by calcination in air and NH₃ to form Mo₂N–Mo₂C/HGr. PMo₁₂ not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH₃ simultaneously react with the Mo species to form an Mo₂N–Mo₂C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H₂SO₄) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm^?2). The good activity of Mo₂N–Mo₂C/HGr is ascribed to its small size, the heterojunction of Mo₂N–Mo₂C, and the good charge/mass‐transfer ability of HGr, as supported by a series of experiments and theoretical calculations.     

Molten salt solvent synthesis of La2Mo2O9 nano-wires by controlling the subsequent calcinations process

Large amounts of La₂Mo₂O₉ nano-wires have been produced using molten-salt synthesis method. The powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy are used to investigate structure and morphological features of the obtained products. The formed nano-wires have an average diameter of about 100 nm and a length in the range from ten to several tens of micrometers. The analyses of the high resolution transmission electron microscopy and the selected area electron diffraction results show that the nano-wires are single crystalline and grow along the [0 0 1] direction. A growth mechanism of La₂Mo₂O₉ nano-wires is also proposed in this report. It implies that the temperature, chloride ions and cation lattice in β-La₂Mo₂O₉ might be related to the particles morphologies transition.     

A Forceful “Dendrite-Killer” of Polyoxomolybdate with Reusability Effectively Dominating Dendrite‑Free Lithium Metal Anode

In this work, a series of Mo-containing polyoxometalates (POMs) modified separators to inhibit the growth of lithium dendrites, and thus improving the lifespan and safety of the cells is proposed. When the deposited lithium forms dendrites and touches the separator, the optimized Dawson-type POM of (NH₄)₆[P₂Mo₁₈O₆₂]·11H₂O (P₂Mo₁₈) with the stronger oxidizability, acts like a “killer”, is more inclined to oxidize Li⁰ into Li⁺, thus weakening the lethality of lithium dendrites. The above process is accompanied by the formation of Li_x[P₂Mo₁₈O₆₂] (x = 6–10) in its reduced state. Converting to the stripping process, the reduced state Li_x[P₂Mo₁₈O₆₂] (x = 6–10) can be reoxidized to P₂Mo₁₈, which achieves the reusability of P₂Mo₁₈ functional material. Meanwhile, lithium ions are released into the cell system to participate in the subsequent electrochemical cycles, thus the undesired lithium dendrites are converted into usable lithium ions to prevent the generation of “dead lithium”. As a result, the Li//Li symmetrical cell with P₂Mo₁₈ modified separator delivers exceptional cyclic stability for over 1000 h at 3 mA cm⁻² and 5 mAh cm⁻², and the assembled Li–S full cell maintains superior reversible capacity of 600 mAh g⁻¹ after 200 cycles at 2 C.