Sharif Digital Repository

WC-Co cemented carbides, including small angular tungsten carbides particles, are used extensively to improve wear resistance. Some additives can affect mechanical and wear properties of these materials. In this study, the effect of VC and (Ta, Nb)C content on wear of WC- 10Co were considered. The tests were performed at normal load of 230 N and sliding distance of 800 m up to 3200 m. Wear tests were carried out using dry sand/rubber wheel apparatus. Wear rate, standard and modified wear coefficients were calculated. The microstructures of prepared specimens were examined by optical microscopy. The morphological analysis of the worn surfaces was made by SEM. The results show that VC content... 

To attain superior energy density concurrently with high power density, high-performance supercapacitors have been developed. Herein an innovative strategy has been adopted to fabricate unique binder-free electrodes composed of a unique porous structure of binary metal carbonate hydroxide nanomace-decorated hydrothermal porous carbon spheres (PCSs). Hierarchical nickel-cobalt carbonate hydroxide (NiCOCH) nanomaces, directly grown on PCSs, are used as positive electrodes for supercapacitors fabrication. Furthermore, Fe2O3@PCS composites, having benefits of highly reversible redox reaction in the negative potential window and highly porous structure, are employed as the negative electrode in... 

To attain superior energy density concurrently with high power density, high-performance supercapacitors have been developed. Herein an innovative strategy has been adopted to fabricate unique binder-free electrodes composed of a unique porous structure of binary metal carbonate hydroxide nanomace-decorated hydrothermal porous carbon spheres (PCSs). Hierarchical nickel-cobalt carbonate hydroxide (NiCOCH) nanomaces, directly grown on PCSs, are used as positive electrodes for supercapacitors fabrication. Furthermore, Fe2O3@PCS composites, having benefits of highly reversible redox reaction in the negative potential window and highly porous structure, are employed as the negative electrode in... 

The MgO-supported Fe-Co-Mn catalysts, prepared using co-precipitation procedure, were tested for production of light olefins via CO hydrogenation reaction. The effect of a range of drying conditions including drying temperature and drying time on the structure and catalytic performance of Fe-Co-Mn/MgO catalyst for Fischer-Tropsch synthesis was investigated in a fixed bed micro-reactor under the same operational conditions of T = 350 °C, P = 1 bar, H2/CO = 2/1, and GHSV = 4500 h-1. It was found that the catalyst dried at 120 °C for 16 h has shown the best catalytic performance for CO hydrogenation. Furthermore, the effect of drying conditions on different surface reaction rates was also... 

Aromatic and cyclic organic compounds such as nitrobenzene (NB) are widely used in various industries and are present in their wastewater. In addition, the photocatalytic process has received considerable attention due to its lower chemical consumption and more efficient degradation of refractory pollutants. In this study, a CoFe2O4-ZnO (CFZ) composite was prepared and evaluated its efficiency in the degradation of NB from aqueous solution under UV light. The optical, structural, and physicochemical properties of catalysts were characterized using PL, UV–vis DRS, XRD, TEM, FESEM-EDS, and VSM techniques and then discussed in detail. It was found that not only does the use of CF facilitate the... 

In the present investigation, different agricultural solid wastes namely: eggplant hull (EH), almond green hull (AGH), and walnut shell (WS), that are introduced as low cost adsorbents, were used for the removal of heavy metals (cobalt, strontium and mercury ions) from aqueous solutions. Activation process and/or chemical treatments using H 2O 2 and NH 3 were performed on these raw materials to increase their adsorption performances. The effectiveness of these adsorbents was studied in batch adsorption mode under a variety of experimental conditions such as: different chemical treatments, various amounts of adsorbents, initial metal-ion concentrations, pH of solutions, contact times, and... 

In this paper we study graphs all of whose star sets induce cliques or co-cliques. We show that the star sets of every tree for each eigenvalue are independent sets. Among other results it is shown that each star set of a connected graph G with three distinct eigenvalues induces a clique if and only if G = K1, 2 or K2, ..., 2. It is also proved that stars are the only graphs with three distinct eigenvalues having a star partition with independent star sets. © 2008 Elsevier Inc. All rights reserved  

In this work, we have studied single-texture formation of CoSi2 layer in heat-treated Co/Ta0.7W0.3/Si(100) structure. Moreover, self-encapsulation process of the CoSi2 layer and surface roughness of the encapsulated layer, as a contact layer, has been examined. A direct current magnetron co-sputtering technique was employed to deposit a 10 nm Ta0.7W0.3 alloy intermediate layer. After growth of the layer on the Si substrate, a 25 nm Co layer was deposited using thermal evaporation method. Post-annealing process of the films was treated in an N2(80%) + H2(20%) ambient in a temperature range from 400 to 1000 °C for 60 min. X-ray diffraction analysis showed that a single-texture CoSi2 layer with... 

Epitaxial formation of CoSi2 nanolayer by solid state reaction of Co-Si in refractory metal intermediate-layer and cap-layer systems was investigated. Thin films of Ta and W, as the refractory metal intermediate or cap layers of the Co film, were deposited on Si(100) substrate and then heat-treated. The both interlayers resulted in formation of epitaxial CoSi 2 with (100) crystallographic orientation at 900°C. However, in the Ta intermediated system, the grown CoSi2 layer was thermally unstable at 1000°C, unlike the W system with a stable silicide layer. We found that use of W cap-layer cannot yield an epitaxial CoSi2 phase. But, a Ta cap-layer resulted in formation of epitaxial CoSi2(100)... 

In this investigation, the crystalline structure of a nanometric CoSi 2 layer, formed in heat treated Co/W x Ta (1-x) /Si(1 0 0) systems, has been studied by XRD analysis. Careful measurements of the diffraction intensities revealed that temporary formation of a metastable diamond cubic structure of CoSi 2 phase, rather than its usual CaF 2 structure, was occurred. It has been shown that formation of this metastable structure depends on the kind of the applied interlayer in addition to the annealing temperature. Among the studied systems with x = 0, 0.25, 0.5, 0.75 and 1, the second and the last systems resulted in growing a (1 0 0) single-texture CoSi 2 layer with the preferred usual CaF 2... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were... 

Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co1+xSmxFe2-2xO4 at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the... 

The electrochemical oxidation of sumatriptan on the surface of carbon paste electrode modified with multi-walled carbon nanotube and cobalt methyl-salophen complex is studied by using cyclic voltammetry and polarization studies. The results indicate that the drug is irreversibly oxidized in a one electron oxidation mechanism. It was found that the peak potential shifted negatively with increasing pH, confirms that H + participate in the oxidation process. The electrode is shown to be very effective for the detection of sumatriptan in the presence of other biological reductant compounds. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of... 

In this work, V, Co-codoped TiO2(B) samples are synthesized through a hydrothermal method, and used as negative electrode materials for lithium ion batteries. The amount of dopants is varied in order to investigate their influence on electrochemical properties. The formation of V, Co-codoped TiO2(B) nanobelts with widths of 20 and 60 nm is demonstrated using X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma–optical emission spectrometry and field-emission scanning electron microscopy analyses. In addition, the electrochemical properties of the samples are tested by cyclic voltammetry, charging/discharging, and cyclic performance techniques. Compared to other... 

Kinetic modeling of CO hydrogenation over Fe-Co-Mn catalyst was investigated; a ternary catalyst was prepared using incipient wetness impregnation. The kinetic parameters were determined from experiments carried out in a fixed bed micro-reactor under the following process conditions: T = 523.15-533.15 K, P = 1-10 bar, H2/CO = 1/1-3/1 and space velocity = 4500 h-1. Seventeen rate expressions were derived from five different mechanisms according to Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) mechanisms and were tested against the experimental data. Non-linear regression method was used to estimate different kinetic parameters; according to the obtained experimental results... 

The present work is comprised of two main parts. In part 1 the Co-Ni/γ-Al2O3 catalyst was prepared using a sol-gel procedure. Then the effect of calcination variables including the calcination temperature and time on the catalytic performance for production of light olefins was investigated and optimized. The obtained results have shown that the catalyst which was calcined at 550 °C for 6 h has revealed the better catalytic performance for production of light olefins. In part 2 the effect of process conditions including the reaction temperature, H2/CO feed ratio and total reaction pressure on the catalytic performance (CO conversion%, (C2-C4) selectivity% and C5+ selectivity%) was... 

Herein, a novel sensing platform based on NiCo layered double hydroxide (LDH) nanosheets/graphene nanoribbons (GNRs) modified glassy carbon electrode is presented for sensitive non-enzymetic determination of glucose. In the first step, nanoflower-like NiCo LDH nanosheets were grown on the surface of ZIF-67 dodecahedron nanocrystals which used as sacrificial template and were further characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and FTIR. In the next step, in order to fabricate a mechanically stable modified electrode, the as-prepared nanosheets were mixed with... 

Synthesis of efficient, low-cost, and stable bifunctional electrocatalysts with earth-abundant resources for electrochemical water electrolysis is a challenging subject for large-scale energy conversion processes. Herein, we report a high-performance electrocatalyst based on vanadium oxysulfide/cobalt-cobalt sulfonitride (VOS/Co-CoSN) for oxygen and hydrogen evolution reaction (OER and HER). The Co-CoSN film was synthesized on a copper sheet (CS) by a facile electrodeposition method. Then, VOS was electrochemically grown onto the Co-CoSN@CS electrode at various deposition times. At the optimal deposition time (300 s), the obtained VOS-300/Co-CoSN catalyst was studied for OER and HER in... 

Synthesizing efficient electrode materials for water splitting and supercapacitors is essential for developing clean electrochemical energy conversion/storage devices. In the present work, we report the construction of a ruthenium cobalt oxide (RuCo2O4)/Ti3C2Tx MXene hybrid by electrophoretic deposition of Ti3C2Tx MXene on nickel foam (NF) followed by RuCo2O4 nanostructure growth through an electrodeposition process. Owing to the strong interactions between RuCo2O4 and Ti3C2Tx sheets, which are verified by density functional theory (DFT)-based simulations, RuCo2O4/Ti3C2Tx MXene@NF can serve as a bifunctional electrode for both water splitting and supercapacitor applications. This electrode...