Using Electrospinning Technique for Preparation of Cobalt Hydroxide Nanoparticles

Cobalt hydroxide or cobaltous hydroxide or cobaltous hydrate, has attracted increasing attention in recent years because of its novel electric and catalytic properties and important technological applications, for examples in advanced batteries, supercapacitors, solar cells, electrochromics, as an oil additive, it can improve tribological properties [1,2], etc. Cobalt hydroxide nanoparticles were prepared via in-situ electrospinning. Thus, electrospinning of polyethylene oxide solution with different cobalt nitrate concentrations were carried out in gaseous ammonia atmosphere. The reaction of cobalt nitrate with ammonia produces cobalt hydroxide. The reaction occurs during fiber formation. Transmission Electron Microscopy (TEM) showed that cobalt hydroxide Co(OH)2 nanoparticles were formed on the produced nanofibers of 100-600 nm in diameter. The existence of the formed Co(OH)2 was also proven by X-ray Diffraction (XRD) analysis and it showed that the Co(OH)2 nanoparticles were produced. Thermogravimetric Analysis (TGA) results also confirmed the presence of Co(OH)2 within the fibers. Experimental Section Co(NO3)2.6H2O (supplied by Merck Chemical Co.) with different concentrations was dissolved in 100 mL distilled water to produced Co+2 solution. Then, the following seven experiments (Exp. G1, G2, G3, G4, G5 (collectively called G-series in this article), P, and N) were carried out. G-series: 4.0 g of polyethylene oxide (with weight average molecular weight of 600,000 g/mol and supplied by Acros Organics Co.) was added to 100 mL of above mentioned cobalt nitrate solution with different concentrations (given in Table I) and left for two nights to obtain a homogenous PEO solution having cobalt ions. The polymer solution was put into a hypodermic syringe. A syringe pump (Stoelting Co., USA) was used to feed the polymer solution into a metallic needle with an inner diameter of 0.7 mm. A grounded aluminum foil as collector was placed at a fixed distance of 18 cm from the needle. The metallic needle and the collector were enclosed in a polymethyl metacrylate box (40?50?60 cm). The feed rate of the syringe pump was fixed at 0.7 mL/h. A positive potential of 18 kV was then applied to the polymer solution using a high-voltage power supplier (HV35P series, Fnm Co., IR) with a maximum voltage of 35 kV. During electrospinning, gaseous ammonia (from a cylinder purchased from Merck Chemical) was purged into the box with a rate of 10 L/min. Electrospun nanofibers were collected on the surface of the grounded aluminum foil. Results and Discussion A comparison of the appearance (color change) of the mats obtained from G-series with that of the P fiber mat suggested that the cobalt ions in the jet traveling the distance between the needle and the collector could precipitate in the gaseous ammonia atmosphere to produce cobalt hydroxide. In other words, in this process, one reaction occurs during fiber formation: the reaction of Co+2 ions with NH3 which produces Co(OH)2 nanoparticles on the nanofibers. Cobalt (II) hydroxide is obtained as a precipitate when an alkaline hydroxide is added to an aqueous solution of cobalt (II) salt. Since the reaction of nanoparticle formations occurs during fiber formation in electrospinning process, the precipitated nanoparticles have special morphology and crystalline structures (due to the applied voltage, elongation, etc.). Figure 1 displays the TEM images of fibers obtained from Exp. G1 (electrospinning of polyethylene oxide solution having 2.5% Co+2 based on PEO, in ammonia atmosphere) and as it shows, dark spots of Co(OH)2 are heterogeneously dispersed on the fibers. These TEM images suggest that in the Exp. G1, Co(OH)2 nanoparticles were heterogeneously synthesized on fibers through the reaction of cobalt ions with NH3. Fig.1 TEM images of nanofibers obtained from Exp. G1. Ref. Zhang, L.; Dutta, A.K.; Jarero, G.; Stroeve, P. Nucleation and growth of cobalt hydroxide crystallites in organized polymeric multilayers. Langmuir, 2000, 16, 7095. Patnaik, P.; Handbook of Inorganic Chemicals, McGraw-Hili, New York, 2002.qscienc

Multiple parts process planning in serial–parallel flexible flow lines: part II—solution method based on genetic algorithms with fixed- and variable-length chromosomes

Multiple parts process planning (MPPP) is a hard optimization problem that requires the rigor and intensity of metaheuristic-based algorithms such as simulated annealing and genetic algorithms. In this paper, a solution method for this problem is developed based on genetic algorithms. Genetic algorithms solve problems by exploring a given search space. To do this, a landscape over which the search traverses is constructed based on a number of algorithm choices. Key algorithm choices include (a) type of chromosome representation, which affects the efficiency of an algorithm, and (b) type and form of genetic operators, which affect the effectiveness of an algorithm. More specifically, the suitability of a variable-length chromosome (VLC) representation for encoding a solution to a MPPP problem is investigated. The effectiveness and efficiency of implementing the VLC algorithm is analyzed and compared with: (a) the commonly used fixed-length chromosome representation, (b) a variant of the simulated annealing algorithm, and (c) a knowledge-informed simulated annealing algorithm. The scalability of the algorithms is analyzed and their effectiveness demonstrated by experimental results based on four problem sizes. Obtained results show that, although there are variances in performances, all algorithms investigated are capable of obtaining good solutions. In addition, variances were observed for different aspects of the MPPP problem. The results indicate that the VLC algorithm is effective in solving MPPP problems that consider multiple aspects in the search for optimal process planning solutions

Effect of Ca Addition on the Microstructural and Mechanical Properties of AZ51/1.5 A12O3 Magnesium Nanocomposite

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Hierarchical honeycomb auxetic metamaterials

Most conventional materials expand in transverse directions when they are compressed uniaxially resulting in the familiar positive Poisson’s ratio. Here we develop a new class of two dimensional (2D) metamaterials with negative Poisson’s ratio that contract in transverse directions under uniaxial compressive loads leading to auxeticity. This is achieved through mechanical instabilities (i.e., buckling) introduced by structural hierarchy and retained over a wide range of applied compression. This unusual behavior is demonstrated experimentally and analyzed computationally. The work provides new insights into the role of structural organization and hierarchy in designing 2D auxetic metamaterials, and new opportunities for developing energy absorbing materials, tunable membrane filters, and acoustic dampeners

PS/TiO2 (polystyrene/titanium dioxide) composite nanofibers with higher surface-to-volume ratio prepared by electrospinning: Morphology and thermal properties

Polystyrene (PS)/Titanium dioxide (TiO2) composite nanofibers were prepared by electrospinning of PS/TiO2 solution in N,N-dimethylformamide (DMF). The effect of PS and TiO2 concentration on the morphology and thermal properties of the fibers was investigated. The resultant fibers were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology and thermal properties of PS nanofibers with and without TiO2 were compared. The composite fibers had a size range of about 400–1200 nanometer in diameter with jaggy morphology which increases its surface-to-volume ratio. Different aspects of thermal properties including thermal decomposition temperatures, glass transition temperature, and residue in PS/TiO2 composite fibers at different TiO2 loading of electrospun fibers are evaluated.Wiley Online librar