Surfactant-assisted hydrothermal synthesis of chains self-assembled by cobalt microspheres

Magnetic cobalt chains, self-assembled by microspheres of hexagonal-phase cobalt, have been synthesized at 100 °C via a hydrothermal reduction route in the presence of cobalt chloride, the surfactant sodium dodecylsulfate (SDS) (or cetyltrimethylammonium bromide CTAB) and the complex reagent sodium tartrate. As-synthesized, the chains are 100–300 μm in length and the cobalt microspheres, which consist of nanosheets with an average thickness of about 60 nm, are 5–10 μm in diameter. The magnetic hysteresis loops at 5 K and 300 K of the chains of microspheres show ferromagnetic characteristics. The morphologies of the microspheres can be controlled by adjusting the concentrations of the surfactant and the complex reagent and also the reaction temperature.     

Preparation of spherical silica in emulsion systems using the co-precipitation technique

Silica powders with particles of spherical shape and a low tendency to agglomeration of primary particles have been prepared by precipitation from sodium metasilicate and hydrochloric acid via the emulsion technique. The organic phase of the emulsion system was cyclohexane while a non-ionic surfactant was applied as an emulsifier. In the course of silica precipitation three alternative ways of dispersion induction were applied: the top stirrer, homogenization and ultrasounds. The precipitation was performed at three temperatures (25 °C, 40 °C and 60 °C), using different variants of dosing schemes of the emulsion and the aqueous solutions of substrates. Homogenization of the reactive system yielded silica of spherical particles of the lowest mean particle diameter and the most uniform character. The only appropriate mode of dosing the reagents to the emulsion was the introduction of alkaline emulsion to acidic emulsion. A decreased tendency for silica particles agglomeration could be achieved by increasing the volume of the organic phase in the emulsions prepared. The optimum temperature for the precipitation reaction was 25 °C. The procedure permitted obtaining in SiO₂ particles of the optimum diameter (<1 μm) and particles of spherical shape. Moreover, the silica adsorbents obtained manifested high activity. Their surface area reached values in the 340–390 m² g^?1 range.     

Wavelet packet analysis of particle response to turbulent fluctuation

The fluid–particle synchronous measurements in a boundary layer wind tunnel were conducted to determine the particle concentration response to turbulent velocity fluctuation. Three groups of natural sand samples (diameter of 300–500, 100–125 and 63–80 μm) were employed in the experiments. Consecutive instants of saltating particles were recorded by using a high-speed digital camera at 2000 frames per second and a constant-temperature hot-wire anemometer was used to measure the turbulent fluctuation simultaneously. The particle concentration in the saltation layer was calculated by the dynamic-threshold binarization algorithm. The results confirm that the concentration fluctuation is a fairly typical stochastic process, and the low-frequency variation of particle concentration is closely related to the turbulent fluctuation. Moreover, a method was developed to apply wavelet packet transform to two-phase data analysis from the viewpoint of frequency-domain energy structure. Further analysis shows that the concentration fluctuation is predominant in the low frequency band less than 250 Hz. In addition, the particle concentration response to the turbulent fluctuation is significantly correlated with the particle diameter. For the fine particles (63–80 μm), medium particles (100–125 μm) and coarse particles (300–500 μm), the highest response frequencies of particle concentration variation to the turbulent fluctuation are 60, 40 and 30 Hz, respectively, which demonstrates that an appropriate sampling rate is crucial in saltation measurement. These qualitative and quantitative results are beneficial to understand the fluid–particle interaction mechanism.     

Microwave-assisted hydrothermal synthesis of Ni(OH)2 architectures and their in situ thermal convention to NiO

The Ni(OH)₂ architectures with flower-like morphology assembled from nanosheets have been successfully synthesized through a microwave-assisted hydrothermal method using urea as a hydrolysis-controlling agent and polyethylene glycol (PEG) as a surfactant. The NiO architectures with similar morphology were obtained by a simple thermal decomposition process of the precursor Ni(OH)₂. The as-obtained products were well characterized by XRD, TG-DTA, SEM, TEM, FTIR and UV–Vis. The experimental results shown that flower-like Ni(OH)₂ architectures with a diameter of 2.5–4.0 μm are assembled from nanosheets with a thickness of 10–20 nm and width of 0.5–1.5 μm. The UV–Vis experimental results shown that the absorption edge of the NiO architectures have a blue-shift with the increasing of the calcination temperature.     

Formation of cobalt hollow nanospheres via surfactant-assisted hydrothermal progress

In the paper we present the synthesis of Co hollow nanospheres by surfactant-assisted hydrothermal method at mild condition. The XRD pattern indicates the sample is hexagonal close-packed (hcp) Co with cell constants a = 2.512 Å and c = 4.102 Å. The Co hollow nanospheres have the outer diameter of about 50–200 nm with the thin wall of 10–20 nm. Room temperature magnetic measurement of the Co hollow nanospheres demonstrates its enhanced ferromagnetic property. The surfactant CTAB might play a vital role in the formation of the hollow Co nanospheres, and simply adapting different reaction temperatures can control the size of these hollow nanospheres. The possible formation mechanism was also discussed.     

Preparation and characterization of a novel microcapsule-type latent curing agent for epoxy resin

A novel spherical latent curing agent microcapsule with the diameter ranging from 6 to 30 μm has been prepared by encapsulating butyl glycidyl ether modified 2-ethyl-4-methyl imidazole (BGE-M-2E4MZ) with polyetherimide (PEI) as the shell material through emulsion/solvent evaporation method. The microcapsule-type latent curing agent was characterized by a Fourier transformation infrared spectrometer, an optical microscope, and an environmental scanning electron microscope. The optimal parameters were obtained through experiments, and the influences of different process parameters on the formation of microcapsules were studied. When the prepared microcapsule-type latent curing agent was mixed with epoxy resin, there were few curing reactions occurred after storage for 100 days at 25 °C, however this latent curing agent could be released and curing reaction of the epoxy resin could be finished within 3 h at 100 °C. In the process of curing, this agent could not be released uniformly in the resin due to the restriction of microcapsule shell, so the resin could not be cured 100%, causing a sharp decrease of mechanical properties of E-51/Mic-2E4MZ casting.     

Synthesis and characterization of nano-hydroxyapatite at ambient temperature using cationic surfactant

Hydroxyapatite (HAP) nanorods were successfully prepared by co-precipitation method using cationic surfactant template, at ambient temperature and pressure. The preparation was done in the customary environment by a process which eliminates the temperature control. The structure of the prepared HAP was confirmed by the FTIR and XRD. HAP rods with diameter ~ 20 nm and length in the range of 100–120 nm were confirmed by FESEM and TEM while the SAED pattern established the crystalline nature of particles. The cytotoxicity studies show IC₅₀ of HAP in 3T3 cell line in the range 850 ± 10 μM for 24 h and 650 ± 10 μM for 48 h treatment.     

Formation of ZnS nano- and microparticles from thiourea solutions

Effects of temperature, concentration of thiourea and reaction conditions (thermal heating and microwave irradiation) on morphological properties of ZnS particles obtained by sedimentation from 0.01, 0.1 and 1 М zinc nitrate solutions are studied. It is found that ZnS particles of two shapes are formed from thiourea solutions at a thermal heating (70–90 °С): agglomerated particles of the spherical shape with the dimensions of agglomerates 50–100 nm (particle size in agglomerates of 3–5 nm) and hexagonal columns in length up to 2 μm and diameter of 80–100 nm. At the microwave heating conditions (90 °С), irrespective of thiourea concentration formation of spherical ZnS particles with the size 0.6–1.2 μm is observed.     

Photovoltaic performance of dye sensitized solar cell based on rutile TiO2 scaffold electrode prepared by a 2 step bi-layer process using molten salt matrices

Dye sensitized solar cells were made on TiO₂ scaffold anodes of rutile particles. These TiO₂ scaffold anodes were grown from rutile seeds by using a molten salt synthesis technique. Different thickness coatings of mixed amorphous titanium hydroxide and NaCl–KCl eutectic salt mixture on the rutile seeds were heat treated at different temperatures. The rutile whiskers of different aspect ratios were grown depending on the growth temperature. The best photovoltaic performances were obtained for the device made from the scaffold of 20–50 nm diameter and 0.5–1 μm length nanowhiskers obtained at 700 °C for 5 h of treatment.     

Fabrication of partially crystalline TiO2 nanotube arrays using 1, 2-propanediol electrolytes and application in dye-sensitized solar cells

We report the fabrication of self-organized partial crystalline TiO₂ nanotube arrays in 1, 2-propanediol containing fluoride ion. The influence of anodization parameters including NH₄F concentration, water content, anodization voltage and time on the morphology, diameter and length of TiO₂ nanotube were investigated in detail. The prepared TiO₂ nanotube has diameter in 30–120 nm and length in 0.6–3 μm. TiO₂ nanotube arrays are used as photoanode for the application in dye-sensitized solar cell and the photovoltaic performance of 1.91% is achieved with a TiO₂ nanotube sample of 2.2 μm in length combining with N719 dye, and the corresponding photovoltaic parameters of 3.6 mA cm^?2 in short circuit photocurrent density, 840 mV in open circuit potential, and 63.2% in fill factor.     

Experimental investigation of heat transfer through porous media in superfluid helium

An experimental investigation of heat transfer through porous media in superfluid helium has been conducted in the framework of the development of porous electrical insulations for superconducting magnet cables cooled by superfluid helium. Several types of porous media with different characteristics were tested and, in particular, samples with pore size diameters of 0.1 μm, 1 μm, 2 μm, 10 μm and 20 μm. Temperature and pressure were measured between an insulating inner bath and the cryostat bath, communicating only through the porous medium. The cryostat bath is held constant all along the measurement and, for each sample, the tests are performed for bath temperature from 1.4 K to 2.1 K with 0.1 K increment. Depending on the porous medium average pore size diameter, different flow regimes are observed: for porous media with a pore diameter of 0.1 and 1 μm, only the Landau regime is observed whereas for porous media with a pore diameter of 2 μm, we observed the Landau regime and the Gorter-Mellink regime. For samples with a pore diameter of 10 and 20 μm, measurements only permitted to detect the Gorter-Mellink regime. In the laminar regime, the permeability of the samples was determined and it was found that the permeability is constant for bath temperature above 1.9 K whereas it increases as the bath temperature decreases from 1.8 K to 1.4 K. For samples with a pore size diameter of 10 and 20 μm, measurement permits only to observe the turbulent regime and the analysis exhibits a constant average tortuosity for each samples, independently of the bath temperature.     

Obtaining ultra-long copper nanowires via a hydrothermal process

Ultra-long and uniform copper nanowires with controllable diameters of 30–100 nm, length up to several millimeters (aspect ratio >10⁵) and tunable crystallinity were obtained by hydrothermal processing the complex emulsion of copper (II) chloride and ODA at 120–180 °C. Both XRD pattern and EDX spectrum indicated that the products were pure copper without any observable impurities. It is observed by FESEM that the diameters and aspect ratios of the synthesized copper nanowires were influenced by the concentration of ODA and reaction temperature. HRTEM images and SAED patterns revealed that the crystallinity of copper nanowires were strongly dependent on the synthesis temperatures. Poly- and single-crystal copper nanowires were obtained at 120 °C and 180 °C, respectively.     

Eggshell- and fur-like microstructures of yttrium silicate film prepared by laser chemical vapor deposition

Yttrium silicate (Y–Si–O) films with eggshell- and fur-like microstructures were prepared by laser chemical vapor deposition using a Nd:YAG laser, and tetraethyl orthosilicate (TEOS) and yttrium dipivaloylmethane (Y(dpm)₃) precursors. Amorphous Y–Si–O films were prepared at deposition temperature below 1200 K. The crystalline Y–Si–O films with mixtures of Y_4.67(SiO₄)₃O and α-Y₂Si₂O₇ phases were obtained at deposition temperature above 1200 K. y-Y₂Si₂O₇ and X1-Y₂SiO₅ minor phases were also formed at a higher deposition temperature. At deposition temperature ranging between 1285 and 1355 K, a dome-like structure covered with fine fur-like projections was formed under a total pressure of 3.5 kPa, whereas an eggshell-like structure 200–300 μm in diameter and 10–20 μm in shell thickness was formed at 7.5 kPa. The deposition rate for the Y–Si–O films with fur- and eggshell-like microstructures reached 300 and 1000 μm h^?1, respectively.     

Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.     

A simple process for magnetic nanocrystalline porous Co–Fe alloy hollow microfibers

A simple process has been developed to fabricate the magnetic nanocrystalline porous Co–Fe alloy microfibers with a hollow structure by the sol–gel and phase transformation at a low temperature. The alloy microfibers consisting of nanoparticles about 30 nm are characterized with a fiber diameter around 0.5 μm, a ratio of the hollow diameter to the fiber diameter about 1/2 and pore sizes of 50 to 300 nm. These nanocrystalline porous Co–Fe alloy hollow microfibers have a good magnetic property, with the specific saturation magnetization of 212.8 A m² kg^?1and coercivity of 15.6 kA m^?1 at room temperature.     

Hard X-ray imaging by a spherical compound refractive lens

Hard X-ray imaging by a spherical compound refractive lens is presented. The lens is composed of 123 biconcave microlenses with a size of 200 μm in diameter. Each microlens was formed by the epoxy between two bubbles, which were injected into an epoxy-filled glass capillary. The focal length of the lens is 114 mm at 8.05 keV. The light source was obtained by using a copper anode X-ray tube without a filter. The lens can be achieved a spatial resolution of 5 μm with field of view of about 700 μm, and 1–3 μm resolution may be obtainable by using monochromator and diaphragm.     

Silanized polymeric nanoparticles for DNA isolation

The aim of this study is to prepare silanized polymeric nanoparticles for DNA isolation. Polymeric p(HEMA)-IMEO-PBA nanoparticles around 85.7 nm diameter, was obtained by surfactant free emulsion polymerization for DNA isolation. Synthesized nanoparticles for characterization studies were realized scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Zeta-size. Surface area, average particle size and size distribution were also performed. The surface area of synthesized silanized polymeric nanoparticles was 2460 m²/g. Synthesized polymeric nanoparticles were silanized with 3-(2-imidazoline-1-yl)propyl (triethoxysilane) (IMEO). After that, phenylboronic acid (PBA) which is DNA specific ligand were covalently binded to silanized polymeric nanoparticles. The amount of DNA adsorbed onto the p(HEMA)-IMEO-PBA nanoparticles first increased and then reached a saturation value at around 14.0 mg/mL of DNA concentration. The maximum adsorption was 672.41 mg/g silanized polymeric nanoparticles in the optimum adsorption medium. The maximum DNA adsorption was achieved at 4 °C. The overall recovery of DNA was calculated as 95%. In repetitive adsorption–desorption circles, it is observed not being important decrease in DNA adsorption capacities. The results were shown that silanized polymeric nanoparticles can be a good alternative for DNA isolation.     

Wear characteristics of mechanically milled TiO2 nanoparticles incorporated in electroless Ni–P coatings

Nanosized TiO₂ particles have been prepared by top down approach using mechanical milling with high energy planetary ball mill at 250 rpm for different extents of time (5, 10, 20, 30 and 40 h). Electroless (EL) Ni–P–TiO₂ nanocomposite coatings were developed using alkaline bath containing milled TiO₂ nanoparticles (4 g/l). The results show that, the morphology of TiO₂ particles milled for 40 h exhibit irregular shape with a particle diameter in the range of 33–45 nm. Wear studies of the coatings with 30 μm thickness were investigated using 1, 1.5 and 2 N loads with 0.1 and 0.2 m/s rotation speeds. The Ni–P–TiO₂ nanocomposite coatings exhibit the enhanced hardness and wear resistance as compared to that of Ni–P alloy coatings. Also the composite after heat treatment at 400 °C for 1 h in argon atmosphere showed improved hardness (1010 VHN) and wear resistance (1.5e-06 mm³/N m).     

Blending effect of sucrose and surfactant templating agents on silica mesostructure

We report the blending effect of surfactant and sucrose as a nonsurfactant templating agent on the silica mesostructure. The CTAB/sucrose-templated mesoporous silica (SCS) was compared with CTAB-templated MCM-41. The MCM-41 showed spherical morphology with a particle diameter of 1.1–1.5 μm, and gave a bimodal size distribution, centered at 2.1 nm and 8.9 nm, which is assigned to hexagonally-arrayed cylindrical pores and interparticle-pores between small MCM-41 clusters, respectively. SCS gave unique and extraordinary morphology in which two different mesostructures have grown with both of them facing each other. The ordered MCM-41 pore structure clung to silica nanosphere-framed wormlike mesostructure, resulting in a bimodal pore size distribution centered at 2.1 nm and 7.0 nm. It was revealed that both of CTAB and sucrose act independently as a surfactant and a nonsurfactant template.     

Flower-like hierarchical nickel microstructures: Facile synthesis,growth mechanism,and their magnetic properties

Flower-like hierarchical nickel microstructures were prepared by a facile chemical reduction method requiring 4 h at temperature of 85 °C without any template or external magnetic field. Nickel (II) sulfate hexahydrate was used as nickel source and hydrazine hydrate acted as the reducing agent. XRD study confirmed the highly crystalline with face-centered cubic (fcc) phase. SEM images revealed that the individual flower-like microstructures have an average diameter of 1–2 μm and are composed of sword-like nanopetals growing radially from the core of the spherical particles. HRTEM image and SAED pattern of the single petal show that the lattice spacing is 0.203 nm corresponding to the (1 1 1) plane of fcc nickel and the growth orientation is along [0 1 1] direction. A rational formation process of nickel micro-flowers was proposed. Magnetic hysteresis measurements revealed that the hierarchical nickel microstructures possess ferromagnetic behavior with an enhanced coercivity value of about 203.3 Oe.