Papers by Keyword: Nanostructured Materials

Abstract: Thin Mo films in the thickness range between 1 and 164 nm have been deposited on high-quality quartz and Corning glass substrates by Radio Frequency (RF) magnetron sputtering under high vacuum (base pressure ~ 3 × 10^-7 mbar). The sputtering target was metallic Mo. Subsequent short annealing of Mo at temperatures between about 400 °C - 600 °C in a muffle furnace in air produced MoO₃ thin films. Heating even to 400°C resulted in significant growth of crystal size. Surprisingly, films thinner than about 50 nm could not be heated at higher temperatures due to the evaporation of the oxide. Ultraviolet – visible light absorption spectroscopy experiments were employed for the determination of the optical band gap. The results for direct and indirect allowed transitions are discussed.

Abstract: Severely-deformed high-strength brasses were investigated by leveraging high-pressure torsion (HPT) processing in order to obtain more enhanced mechanical properties of copper alloys. Pure copper, binary Cu-Zn solid-solution alloys and high-strength brasses including aluminum and manganese additions were selected for experiments. For comparison of these materials, zinc equivalent parameter was used. These materials were subjected to the HPT processing, followed by hardness tests and tensile tests. The maximal hardness value of the nanostructured high-strength brass with β phase matrix was reached 420 HV. The HPT processed high-strength brass with β phase matrix showed significant increase in the yield stress and tensile strength with sacrificing ductility. The tensile specimen of the high-strength brass with β phase matrix was fractured before initiation of necking. It was found that utilizing β phase matrix is also beneficial for controlling enhanced strength of high-strength copper alloys for not only casting process but also severe plastic deformation.

Abstract: In order to study the electrochemical sensor of nanometer mechanism materials to realize the high sensitive detection of different chemical molecules, in this research, the preparation methods of molybdenum dioxide nanomaterials, molybdenum dioxide/metal particles (Au, Pt, Au@Pt) composites and the preparation of molybdenum dioxide nanomaterials, molybdenum dioxide /Au composite nanomaterials, molybdenum dioxide /Pt composite nanomaterials and molybdenum dioxide /Au @Pt composite nanomaterials were introduced. Then the electrochemical behavior of several modified electrodes, electrochemical behavior in catechol system, scanning and pH were applied to the modified electrode. Finally, the electrode p-catechol system was detected by differential pulse voltammetry and the actual samples were analyzed. The results showed that compared with unmodified electrode materials, the electrode modified by molybdenum dioxide nanomaterials, molybdenum dioxide /Au composite nanomaterials, molybdenum dioxide /Pt composite nanomaterials and molybdenum dioxide /Au @Pt composite nanomaterials has better electrocatalytic performance and the detection of catechol has a good effect. Among them, the electrochemical sensor constructed by MoS₂-Au@Pt composite has the best detection performance for catechol. The results have a good guiding significance for the performance improvement of electrochemical sensor.

Abstract: Superconductivity in nanostructured ceramics offers significant advantages over the conventional coarse-grained materials in view of miniaturization of superconducting electronic devices. In this paper, we report the formation of four morphologies of superconducting YBa₂Cu₃O_7-δ (YBCO) nanostructures by electrospinning technique using polymeric polyvinyl pyrrolidone (PVP) solutions of different molecular weight and altering the total content of the metallic precursors. The morphologies prepared using this strategy are nanorods (NRs), nanogarlands (NGs), nanohierarchical (NH), and nanoparticles (NPs). Alternating current susceptibility measurements showed high critical temperatures (T_C ~90 K) for the NH YBCO synthesized using PVP of the lowest molecular weight; whereas the YBCO NRs synthesized using a higher molecular weight polymer showed the lowest T_C (82 K). A relationship between the particulate properties and T_C was also observed – the lower is the pore size the higher is the T_C. The YBCO NGs showed the highest specific surface area (7.06 m²/g) with intermediate T_C (88 K). Electrospinning process appears an effective and controllable technique to produce different nanomorphologies with intrinsic properties suitable for practical applications.

Abstract: In this work, a low-cost method to produce ZnO nanostructured materials for the treatment of water polluted with model organic pollutants (e.g. dyes) is presented. Zinc and silver-coated Zn (Ag/Zn) films, fabricated via sputtering method were naturally oxidized via a simple, low-temperature, scalable thermal process. During oxidation, Ag/ZnO nanorods were grown on Zn foils after treating their surface with various agents (e.g. acids) and annealing in an oven at temperatures 385-400 °C. The ZnO and Ag/ZnO films on Zn were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. The cationic dye Methylene Blue (MB) was selected as model pollutant dissolved in water, and a batch photo-reactor was fabricated and used to to study the adsorption capacity and photocatalytic performance of films. The transient varation of MB concentration in aqueous solutions was measured with UV-Vis spectroscopy. Ag/ZnO demonstrated a strong MB adsorbion capacity in dark conditions, and a satisfactory MB photocatalytic degradation under UV light irradiation.The optimized doping of Ag in Ag/ZnO film enhanced its photocatalytic activity, and seems well-promising for the potential scale-up of Ag/ZnO films, and use in large-scale systems for water purification under UV light irradiation.

Abstract: Nanocrystalline structure of CuFeCo (50:25:25 wt%) alloy has been obtained by high energy mechanical milling from elemental metal powder mixture during large hours of work. Phase transformations and diffusion in the system subjected to heat treatment are discussed. Thermal stability at high temperatures is analysed and considered of importance for several applications. The nanostructure was studied by employing X-Ray diffraction and electron microscopy. It has been determined the reduction in crystallite size and the induced microstrain by the milling time. The solid solution achievement through the increment of defect density was confirmed by Mössbauer analysis. Magnetic behaviour was analysed through magnetization technique entailing their soft ferromagnetic behaviour related to the microstructural changes.

Abstract: The results of experimental studies show that the use of composite powders (WC-Co) in combination with the modification by the additives of ceramic nanoparticles allows controlling the parameters of the microstructure and increasing the strength of the binder and the level of physical and mechanical properties of the hard metal in general. The coating of carbide particles with a layer of a binder is an effective starting method that allows to obtain a bulk compound that preserves the unique properties of the initial nanopowders and ensures a uniform distribution of the phases (WC, Co, Al₂O₃). Such multiphase fragmentary nanostructured composite is characterized by additional heterogeneity, determined by the differences in size and elastic properties of the phases. By combining the sizes and properties of the phase components in such heterogeneous composite, it is possible to increase the fracture energy (i.e. Palmqvist fracture toughness) up to 20 - 22 MPa∙m^1/2 as a result of inhibition on inclusions of nanoparticles the stress relaxation and change in the trajectory of the intergranular crack. Based on the proposed stereological models and experimentally established relationships between composition and microstructure parameters, the required volume concentrations of nanoparticles’ additives and composite powders (WC-Co) were determined.

Abstract: A relevant technology issue in lost foam casting is preventing the metal penetration appearance on steel and cast-iron mouldings. As a result of the research the appropriate parting model paint compositions with the use of recycling and nanostructured materials were developed. The basic technological characteristics of the developed parting model paint compositions are: relative stickiness due to VZ-6 18...25 s; residual moisture content 1...1.5 %, permeability to gases 40...50 ea. The parting paint effectiveness is determined by defect reduction of the castings on the core blow, uncertainty in geometry, metal penetration, and also the use of available and environmentally friendly molding materials in their composition, that makes the product to be highly competitive.

Abstract: A new simple universal form of the Kelvin equation that can be used even near the gas-liquid phase transition critical point is shown. The correction of the chemical potential, pressure, and density outside the porous medium is presented and taken into account for the CO₂ meniscus curvature radius calculation at capillary condensation in mesoporous silica MCM-41, known [1] for its wide range of applications.

Abstract: This paper introduces a new concept of coated fine carbides modified by nanoparticles Al₂O₃, ZrO₂ (inhibitors) as the starting method for improved hardmetals. The study involved computational and experimental methods to determine functional relationships between the parameters of microstructure, sizes, volume content of additives of nanoparticles and properties (transverse rupture toughness, hardness, fracture toughness) of the heterophase hardmetal composites. Factors having a positive influence on the structure of hardmetals are the decrease in the average size and contiguity of carbide grains due to SPS-consolidation and ultrasonic activation during mixing. The study of microstructural parameters by scanning electron microscopy in a combination with x-ray phase analysis indicates high statistical homogeneity of the relative distribution of nanoparticles (inhibitors) in the cobalt binder between carbide grains and the formation of nanostructured inclusions in hardmetal composites.