Microstructural Properties of Air Plasma Sprayed Coating Consisting of Tungsten Carbide and Yttria‐Stabilized Zirconia

Thermal Spraying technologies are proven to be capable of producing composite materials and structures. In the present work, an innovative composite coating was produced to achieve high wear and thermal resistant properties in a single‐step process using air plasma spraying (APS) technique. Tungsten carbide has shown high wear resistance and zirconia coatings exhibited excellent tribological and insulation properties. It is speculated that a composite material consisting of zirconia and tungsten carbide exhibits excellent thermomechanical properties. A powder mixture of 50wt% WC‐10wt% Ni (WC‐Ni) and 50wt% ZrO₂‐8wt% Y₂O₃ (YPSZ) was deposited on a low carbon steel substrate using APS technique. Important microstructural properties of WC‐Ni/YPSZ coating such as splat boundaries, pore and grain morphology, microcracks, phase composition, elemental distribution of coatings, and lattice parameters of the crystals were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X‐ray (EDS), and X‐ray diffractometry (XRD). A good adhesion was observed between different phases in tungsten carbide mixed with zirconia coatings. Decarburization process which occurred during APS process resulted in formation of tungsten hemi‐carbide (W₂C) phase in plasma sprayed samples. The calculated crystal size for APS‐deposited coating was smaller than those of feedstock powder.     

Effects of Heat Treatment on Microstructural Modification of As-Cast Gamma-TiAl Alloy

Effects of normalizing and annealing treatments on the microstructure of Ti-48Al-2Cr-2Nb (at.%) were investigated. Normalizing processes were done at 1385 ± 5 °C in α-phase domain with the heating rate of 10 °C/min, the average cooling rate of 30 °C/min, and the holding times of 5, 10, 15, 20, and 25 min. The annealing process was done at the same temperature and heating rate, the holding time of 15 min, and the average cooling rate of 2 °C/min. Microstructures, phases, and hardness levels were studied by optical and field emission electron microscopic observations, x-ray diffractometry (XRD), and microhardness testing, respectively. Also, crystallographic texture variations were analyzed by means of texture coefficient and XRD results. Experimental results showed a linear direct relationship between treatment time and grain size, up to 15 min. A linear reversed behavior was observed for longer times. The untreated alloy consisted of γ and α₂ phases with a columnar morphology with the length of about 300 μm. A near-lamellar microstructure with equiaxed gamma grains, Widmansttäten, and laminar γ + α₂ colonies was obtained by the normalizing process. The maximum reduction of the grain size was about 70%, as achieved by normalizing with the 15 min holding time. A texture-free microstructure was acquired by normalizing treatment in comparison with strong texture of the as-cast and annealed alloys.     

Preparation of Ni-metal organic framework-74 nanospheres by hydrothermal method for SO<Subscript>2</Subscript> gas adsorption

In this investigation hierarchical nanospheres-like Ni-MOFs were successfully synthesized with hydrothermal method. These MOFs samples were characterized with electron microscopy (SEM and TEM) for crystal structure, X-ray diffraction for phase structure, and nitrogen adsorption (BET) for pore textural properties. The experimental results showed that Ni-MOF samples synthesized by the hydrothermal method had a smaller particle size with relatively more uniform particle size distribution. Based on high roughness, crystallinity, and unreported type of FTIR spectrum, a new structure of Ni-MOF structure was proposed.     

Different effects of process conditions on PA6/nanoclay composites at nanoclay contents above and below percolation threshold: Rheological,thermo‐dynamical,and thermal properties

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co‐rotating twin‐screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion‐controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 22:259–266, 2016. © 2014 Society of Plastics Engineers     

Effect of electrospinning on the ionic conductivity of polyacrylonitrile/polymethyl methacrylate nanofibrous membranes: optimization based on the response surface method

A novel fibrous polymer electrolyte membrane was produced based on polymethyl methacrylate/polyacrylonitrile (PMMA/PAN) blend. This was achieved through optimization in the loadings of the two polymers and electrospinning method. Consequently, the effect of PMMA on the ionic conductivity was assessed. A quantitative relationship between ionic conductivity and the important parameters including voltage, solution concentration, and PMMA content was determined. The response surface method (RSM) was employed to obtain the quantitative relationship and to determine the ion conductivity of PAN/PMMA electrospun membrane. Analysis of variance technique was used to study the importance of parameters and their interactions. A regression model was applied to determine the most influential factors on the ionic conductivity and to find the maximum ionic conductivity of the electrolyte membrane as an optimal result. The average fiber diameter was in the range of 206–367 nm, and the membranes were associated with high porosities between 50 and 91 %, and the electrolyte uptakes were in the range of 285–460 %. For all samples, the ionic conductivity of gel polymer electrolytes at 25 °C was above the 1 mS/cm. The ionic conductivity changed with the voltage directly and with the solution concentration inversely. According to the results, the ionic conductivity showed its dependency with the PMMA content, increasing with the PMMA content up to 50 % and smoothly decreasing with PMMA further increases. Some important interactions between the parameters were also detected.     

The chemical composition of the seeds of Iranian pumpkin cultivars and physicochemical characteristics of the oil extract

Four Iranian pumpkin seed cultivars were evaluated for their chemical composition and physicochemical characteristics of the extracted oils. Moisture content of seeds was quite low and ranged from 4.7 to 5.4%. The samples showed high level of protein (28.8–35.5%) and oil content (36.9–47.8%) in which the highest amount belonged to Postekaghazi cultivar. In regard to oil properties, due to the high level of oleic acid (52.7%) followed by linoleic acid (28.1%), Khoreshti cultivar was much different from other samples (in which linoleic acid is predominant: 46.5–56.1%). Moreover, relatively high content of phenolic compounds led to high‐oxidative stability index (OSI) of 16.63 h for Khoreshti oil compared to other samples (6.99–10.54 h). Furthermore, cluster analysis confirmed the data obtained in this study. The results showed that pumpkin seed oils were nutritionally valuable and refined oil might be suitable to use as salad or cooking oil.     

Solvothermal Synthesis and Characterization of Hollow Sphere-Like ZnS/ZnAl2S4 Nanocomposites

In this investigation, hollow sphere-like ZnS/ZnAl₂S₄ nanocomposites have been successfully synthesized by solvothermal process in propylene glycol as solvent. To study the effect of sulfur source on the morphology of ZnS/ZnAl₂S₄ nanocomposites, thioacetamid and thiourea were applied. In the all experiments, Al(NO₃)₃·9H₂O and Zn(OAc)₂ were used as aluminium and zinc precursors, respectively. The as-synthesized products were characterized by XRD, SEM, FT-IR, TEM, PL, and EDS. According to SEM images, it was found that the type of sulfur source, capping agent and reaction time had a great influence on the morphology of ZnS/ZnAl₂S₄ nanocomposites. The novelty of this investigation is related to the synthesis hollow and hierarchical microspheres of ZnS/ZnAl₂S₄ by using thiourea as sulfur source in the absence and presence of sodium dodecyl sulfate as capping agent, respectively.     

An exact solution for stresses and displacements of pressurized FGM thick-walled spherical shells with exponential-varying properties

Exact closed-form solutions have been derived for stresses and the displacements in thick spherical shells made of functionally graded materials with exponential-varying properties subjected to internal and external pressure. Poisson’s ratio is assumed to be constant. The obtained results show that the inhomogeneity properties of FGMs have a significant influence on the displacement and stresses distribution along the radial direction. A numerical solution using finite element method is also presented and good agreement was found between the analytical solutions and the solutions carried out through the FEM. The values used in this study are arbitrarily chosen to demonstrate the effect of inhomogeneity on displacements and stresses distributions.     

Effects of Fat Replacers and Sweeteners on the Time-Dependent Rheological Characteristics and Emulsion Stability of Low-Calorie Pistachio Butter: A Response Surface Methodology

The effect of three fat replacers (xanthan gum, Reihan seed gum, and Balangu seed gum) and two sweeteners (sucrose and isomalt) on time-dependent rheological properties of low-calorie pistachio butter were analyzed using response surface methodology. The steady shear behavior of all samples was shear thinning (n = 0.156–0.6175), and power law model was fitted the upward and downward curves properly (R ² = 0.847–0.998). Balangu seed gum (0.01–0.04 wt.%), Reihan seed gum (0.01–0.023 wt.%), xanthan gum (0.06–0.1 wt.%), isomalt (0–1 wt.%), and sucrose (0.25–1 wt.%) were the levels investigated. A central composite design was used to develop models for the responses. The obtained experimental data were fitted to a second-order polynomial equation and also analyzed by appropriate statistical methods. In most cases, increasing the sweetener level led to a significant decrease in consistency coefficients. However, the effect on the flow behavior index was not significant. The effect of gum concentration on the rheological parameters was not significant (p ≤ 0.1), except for formulas prepared using Balangu seed gum. All formulas studied were stable on shelf.     

Simple Pathway to Predict the Power of High Energy Materials

A new method has been introduced to predict the power of important classes of energetic compounds including nitroaromatics, acyclic and cyclic nitramines, nitrate esters and nitroaliphatics. In this method, the predicted specific impulse and the corrected heat of detonation on the basis of H₂O‐CO₂ arbitrary decomposition, have been used to calculate the power of an explosive with the molecular formula C_aH_bN_cO_d as determined by the Trauzl test. The predicted results show good agreement with respect to the measured values for both pure and mixture of explosives. The calculated volume expansions of pure energetic compounds have a root mean square (rms) deviation of 33 cm³ from 73 measured values (corresponding to 58 molecules). For 9 explosive mixtures, the predicted volume expansions have an rms deviation of 39 cm³ from the experimental results.