جستجوی مقالات مرتبط با کلیدواژه « co » در نشریات گروه « مواد و متالورژی »

In this paper, the structural and electronic properties of MoS2 and MoS2 compounds doped with cobalt in two nonmagnetic and magnetic states are investigated in the framework of the density functional theory with the Espresso quantum computing code in two exchange approximations of the generalized slope correlation and the local density of the constant charge type. The lattice constants were calculated and compared and were consistent with the results. The band structure and density of states for the MoS2 compound showed semiconducting properties. The band structure and density of states for the cobalt-doped MoS2 compound in the non-magnetic state showed metallic properties. The band structure and density of states for the cobalt-doped MoS2 composite in the magnetic state with cobalt showed weak ferromagnetism and metallic nature. The density of partial states for the composition of MoS2 shows the role of d orbital of molybdenum atom and p orbital of sulfur atom, and for MoS2 doped with cobalt, it shows the role of d orbital of cobalt atom, d orbital of molybdenum atom and p orbital of sulfur atom, which is consistent with the results of others. To compare the structural properties of the two structures, the MoS2 compound changes from the hexagonal structure to the tetragonal structure after doping with cobalt. The results are consistent with previous works.

Crofer 22 APU ferritic stainless steel has been evaluated as one of the favorable materials for utilization in Solid oxide fule cell (SOFC) interconnects. However, there are difficulties in utilizing these metallic interconnects, including the quick  decrease of their electrical conductivity and evaporation of Cr species. To overcome the above problems, the application of protective coatings has been proposed. In this work, Co/Y2O3 composite coatings were deposited onto Crofer 22 APU stainless steels by direct current electrodeposition method. Oxidation and electrical properties of uncoated and coated steels were evaluated. Surface and cross-section of the bare and coated steels were characterized using scanning electron microscopy and X-ray diffraction techniques. Results showed that oxidation rate of the coated specimen was reduced by about 4 times, as compared to the uncoated one after 500 h isothermal oxidation in air at 800˚C. Formation of Co3O4 and MnCo2O4 spinel compositions improved electrical conductivity of the coated sample. After 500 h of isothermal oxidation at 800˚C, ASR value of the Co/Y2O3-coated and uncoated steels was 15.8 mΩ·cm2 and 25.9 mΩ·cm2 , respectively.

In this research (PANI/CNT) core/shell nanocomposite were synthesized via in situ chemical oxidative seeding polymerization‚ the results of SEM indicated the structure of synthesized nanocomposite. TEM‚ FTIR‚ UV-Vis‚ XRD analyses of samples showed that this nanocomposite is decorated with (Ni‚ Co) oxide nanoparticles. The VSM test of as prepared and annealed nanocomposite exhibited the saturated magnetization of 0.93‚ 1.96 emu/g, respectively; the coercivity values were also 26.5‚ 1200 Oe, respectively. The reflection loss characteristics of (Ni‚ Co) oxide- Pani- CNT core/shell nanocomposite were also investigated with a vector network analyzer‚ in the 12.4–18 GHz range (Ku band). The maximum absorption increases with enhancement of the dispersed nanoparticles percent in polyurethane matrix from 1 to 10%. The value of the maximum reflection loss in the absorption samples with 1% and 10% of nanoparticles is -3.84 dB at 15.80 GHz and -7.3 dB at 17.5 GHZ, respectively.

In this research¡ the wear behavior of commercial grades of WC-10wt%Co (H10F)¡ WC-40vol%Co and WC40vol%FeAl-B composites with different amounts of boron from zero to 1000 ppm has been investigated by the pin on disk test method at high temperature. The wear tests were done under load of 40 N¡ a distance of 100 m and at ambient temperature¡ 200
̊ C and 300
̊ C. Wear surfaces were examined by scanning electron microscopy. The results showed that the wear resistance of all composites decreased with increasing temperature. The boron free WC-40vol%FeAl composite showed the lowest wear resistance at all ranges of temperature. In the presence of boron up to 500 ppm in iron-aluminide matrix¡ the high temperature wear resistance of these composites improves and the wear mechanisms changes from particle pullout into abrasive state. The toughness enhancement of these composites and plasticity enhancement of iron aluminide in the presence of boron¡ leads to better link of the interface of FeAl matrix and tungsten carbide particles¡ and thus increases the wear resistance of these composites. WC-40vol% FeAl-500ppmB composite has a higher wear resistance at high temperature than WC-40vol% Co and commercial WC-10wt% Co.

In this study, creation of a silicon aluminide coating on IN738LC nickel-based superalloy has been investigated, using co-deposition process. Thermochemical calculations indicated the possibility of obtaining a silicon aluminide with NH4Cl activated pack powder at 900°C, in order to achieve coating with desirable structures. Two powder mixtures with nominal compositions of 7Si-14Al-(1-3) NH4Cl-Al2O3 (wt. %) and 16Si-4Al-(1-3) NH4Cl-Al2O3 (4 and 0.5 Si/Al ratios, respectively) were used. According to the results, both coatings showed multi-layered structures containing AlNi2Si as dominant phase. In coating created by pack powder with Si/Al ratio of 0.5, a porous and brittle layer of NiSi was formed on the surface which deteriorated the mechanical properties of coating to some extent. It was found that inward diffusion of Al was dominant at the first stage, while afterward, inward diffusion of Si led to conversion of NiAl phase to AlNi2Si and, finally, to NiSi phase. Eventually, the sample coated by Si/Al=4, showed superior microstructural characteristics, containing desirable AlNi2Si phase without undesirable brittle NiSi phase.

The present study aimed to investigate the synthesis, microstructural and mechanical properties of alumina/zirconia-cobalt composite. The compositions containing 5, 10, 20 Vol.% of the sum of ZrO2 and Co were studied. The composite powders were prepared through mixing of alumina powder with partially stabilized zirconia and cobalt sulfate powders followed by calcination treatment at 1100 for 3h and reduction of cobalt by aluminum powder additive, in carbon bed at 950 for 3h. The XRD analysis showed the presence of Al2O3, t-ZrO2, Co and a little m-ZrO2. In order to investigate the properties of Al2O3/ZrO2-Co composite, composite powders were pressed uniaxial followed by Cold Isostatic Pressing (CIP) at 400MPa. The prepared discs were sintered in carbon bed at 1550 1600 , 1650 for 5h. The alumina specimen was also prepared with the same procedure. The final results showed that the highest relative density value was 83.9% obtained for the specimen with the composition containing 5vol.% ZrO2 and 5vol.% Co densified at 1650 for 5h. The bending strength and hardness of this specimen was 322MPa and 11.95MPa.m1/2 respectively. So 20.15% increment of bending strength and 15.96% decrease of hardness was observed compare to monolithic alumina. The decrease of hardness was due to the lower hardness of metallic phase and the increase of bending strength is occurred because of presence of zirconia and cobalt particles which prevent of alumina grains growth.

In this research, ZnxNi1-x(OH)2 nanostructured layered double hydroxide active materials were successfully synthesized by a chemical co-precipitation route using polyethylene glycol as the structure-directing reagent. Structural characterizations were performed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), and morphology of materials was obtained by Field Emission Scanning Electron Microscopy (FESEM). The results show that the as-prepared materials have a porous structure with nanoscale walls and their crystal structure was mainly ?-phase. Electrochemical experiments using cyclic voltammetry, galvanostatic charge-discharge and cyclability show that Zn0.33Ni0.67(OH)2 active material has the highest initial specific capacitance of 926 F g-1 at a current density of 1 A g-1 and a capacity retention of about 98% after 100 charge-discharge cycles.

Nanoparticles of Mg–Co–Ti substituted strontium hexaferrite with nominal composition of SrFe12-2x(Mg,Co)0.5x TixO19 (x=0-2.5) were synthesized by a co-precipitation method. The structural, magnetic and electromagnetic properties of samples were studied as a function of x by thermal gravimetric (TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analysis. It was found that the synthesis temperature increases with an increase in Mg–Co–Ti substitution and hence the particle size decreases. The XRD results showed that whole samples had good crystallinity and with an increase incations, the impurity phase of Fe2O3 appears. The results of hysteresis loops indicated that the saturation of magnetization of ferrite decreases from 40 emu/g to 19 emu/g with an increase in x. The Mössbauer spectroscopy showed that the cations are substituted in the 12k site of magnetoplumbite structure. Vector network measurements showed that the doped samples had much more effective reflection loss values than those of undoped ferrites. As a result, Mg–Co–Ti doped Sr-hexaferrites with x=2 can be proposed as suitable absorbers for applications in microwave technology with a good deal of consistency.

In this research, the wear behavior of commercial grade of WC-10wt%Co (H10F), WC-40vol%Co and WC-40vol%FeAl-B composites with different amount of boron from zero to 1000ppm was investigated by the pin on disk test method. The wear tests were done in ambient temperature, under load of 40 N and a distance of 100 m. Wear surfaces were examined by scanning electron microscopy (SEM). The results showed that among samples, the WC-40vol%FeAl composite without boron has the lowest wear resistance due to higher brittleness and lack of suitable continuity between iron-aluminide matrix and tungsten-carbide particles. This behavior leads to the separation of the reinforcer particles from matrix. In the presence of boron up to 500 ppm in iron-aluminide matrix, the wear behavior of these composites improved and the wear mechanism of these composites changed in to abrasive state. In ambient temperature the wear resistance of WC-40vol%FeAl-500ppmB composite was close to commercial WC-10wt%Co although has lower WC percent.

The present work deals with the process of electrochemical deposition of cobalt–tungsten /polychlorotrifluoroethylene (Co-W-PCTFE) nanocomposite coatings in the tartrate bath and electrochemical corrosion behavior in 3.5 wt.% NaCl solution. Surface morphology and composition of the composite coatings are characterized by energy dispersive X-ray (EDX), scanning electron microscopy (SEM). Corrosion behavior of coatings is carried out applying opencircuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS) and polarization techniques in 3.5 wt.% NaCl solution. The study reveals reduce in corrosion current density, important substitute in corrosion potential towards the positive direction with the incorporation of PCTFE particles in the Co-W matrix. Therefore, the significant improvement in corrosion resistance observed for Co-W-PCTFE nanocomposite coatings (7.587kΩ cm2) compared to Co-W (2.325kΩcm2). The results of SEM images indicated to changing morphology of alloys coatings in the presence of PCTFE particle sizes from micrometric to nanometeric sizes. The EDX analyzes confirmed the forming of Co-W-PCTFE nanocomposite coatings.

Ni–SiC composite coatings are successfully employed as a protective coating in the inner walls of engine cylinders. In this study, Ni-SiC, Ni-SiC-MoS2 and Ni-SiC-Gr composite coatings were prepared from a sulfamate bath. Both mechanical and ultrasonic stirring were used simultaneously during the process. Taking into account the working temperature of engine cylinders, the wear behavior of coatings was evaluated at 25 to 300 ºC and the high temperature tribological properties of the coatings were investigated. Based on the results obtained from the wear tests, all three coatings showed almost good friction coefficient values at 25 and 100 ºC, which were close to each other. By increasing the temperature to 200-300 °C, the friction coefficient and weight loss values strongly increased. However, addition of solid lubricants caused the values to decrease. The Ni-SiC-Gr coating at all temperatures showed a good and stable behavior.

Nano-composite coating of Ni+RuO2 was prepared in acidic media by sol-gel technique and then heat treated at 350 -400 oC. Electrochemical activity, surface properties and stability of the coating was investigated, considering the effect of alcohol adiition, by linear sweep voltametry (LSV), cyclic voltametry (CV) and chronopotentiometry, respectively. According to the LSV results, addition of Isobutyl alcohol to the sol solution having Ni+RuO2 resulted in a significant increase in exchange current density up to 0.61 mA/ cm2 and a large decline in Tafel slope down to 39 mV/ decade. The cyclic voltamograms obtained showed that the activity of the cathode coating did not decrease with time. The study of electrochemical stability of the coating by chronopotentiometry revealed that the sol-gel derived coating proved to be a suitable electrocatayst for hydrogen evolution reaction in alkaline media.

In this research, uniform LaF3 nanoparticles have been successfully synthesized via co-precipitation route in which ethylenediaminetetraacetic acid (EDTA) was used as an effective size-controlled chelating agent. The appropriate analyses were carried out to characterize final nano-crystallites such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results revealed that the nanoparticles were well-crystallized with hexagonal structure and were coated with an organic additive. From the scanning electron microscopy (SEM) micrographs, the spherical particles in the presence of EDTA were more uniform with higher detectable boundary phase. The dynamic light scattering (DLS) results showed that the mean diameter for samples with and without EDTA is 66.1 and 106 nm, respectively. Furthermore, from up-conversion luminescence (UCL) spectrum under excitation at 980 nm, the La0.85Yb0.12Er0.03F3 nanoparticles exhibit the bright orange emission photo-physically originated from separate transitions: 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 at 520, 538 and 658 nm, respectively. Consequently, as prepared LaF3:Yb,Er with relatively bright up-conversion luminescence can be a promising candidate for use as bio-labels.

In this research paper the crystallinity-index and physical-mechanical properties of Co-based self-fluxing thermal spray coatings produced using APS and HVOF on low-carbon steel substrates were investigated. Advanced characterization methods such as XRD, SEM and TEM as well as DSC thermal analysis were used to evaluate the evolution of phase transformation during thermal spraying processes. The phase analysis results show that the main phase of the thermal spray coatings was α-Co solid solution with FCC crystal structure as well as amorphous phase that produced during rapid solidification of particles over the course of flying on impacting to the substrate. The Crystallinity-index for APS and HVOF coatings was computed around 75% and 80% respectively. The existence of amorphous phase in the matrix was yielded to increase the hardness of the coatings. The average microhardness was estimated around 800 and 500 Vickers for HVOF and APS coatings respectively. In addition the porosity content percentage was calculated about 2.12±0.11 for HVOF and 5.52±0.73 for APS coatings. The adhesion strength test showed that for the APS coating fracture was happened in the interface of the coating / substrate in the form of adhesive, however, for HVOF coating fracture was occurred in glue or the interface of the glue / substrate.

Co-P electrodeposites are appropriate substitute for hard chromium coatings due to their suitable properties. In this study, nano-crystalline and amorphous Co-P coatings were deposited on plain carbon steel substrates using a direct current and their morphology was examined. The effect of pH on morphology, current efficiency, phosphorus content, hardness and preferred orientation of the coatings were investigated. Moreover, the effect of heat treatment on microstructure and hardness of the nano-crystalline and the amorphous coatings was studied. The results showed that, phosphorus content and hardness of the coatings were decreased by increasing the pH from 1 to 4 in spite of an enhancement in the current efficiency up to 98%. Preferred orientation and morphology of the coatings were also changed by increasing of pH values. Hardness numbers of the amorphous and the nano-crystalline coatings, deposited at the optimum condition, were about 750 and 600 HV, respectively. These values were increased and reached 1090 and 760 HV by heat treatment.