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

Nickel-rich layered oxide cathode materials with the chemical formula of LiNi0.8Co0.1Mn0.1O2 (NCM) are increasingly utilized in the electric vehicle industry owing to their high energy density and high capacity. Although increasing the nickel concentration would enhance the chemical reaction between the surface layer and Li+/Ni2+ cationic mixing, the structural and thermal stability of the cathode material would be degraded. The single crystallization strategy of the particles can improve the structural stability and electrochemical performance of the cathode materials; however, their mechanism is not well understood yet. In this research, a computational model was proposed to show that by reducing the pH and controlling the amount of supersaturation, the nucleation rate of hydroxide particles and consequently the number of formed nuclei would decrease. Based on the results of this model, the numbers of hydroxide nuclei formed at the end of co-precipitation synthesis at pH 11.5, 11, and 10.5 were, respectively, 5.73, 4.3, and 2.27 times the number of nuclei formed in co-precipitation synthesis at pH 10. According to the observations, by reducing the pH during the synthesis process from 11.5 to 10, the fine particles produced in the system will be completely transformed into larger crystals, thus tending to become single crystals. As a result, the problems of the cathode/electrolyte intermediate layer will be minimized. The results of this model can justify the experimental results obtained by other researchers who synthesized single-crystal cathode materials.

Cathode is an important component in the performance of Li-ion batteries. Various compounds have been used as cathodes in Li-ion batteries, among which NCA (LiNi0.8Co0.15Al0.05O2) has attracted a lot of attention due to its high specific capacity and capacity retention. However, the applied reversible capacity is lower than the theoretical value, which is because of the migration of Ni cation to the Li layer (cation mixing). Therefore, proper synthesis of this structure can help to increase the capacity and battery lifetime

In this research, the precursor of Ni0.8Co0.15Al0.05(OH)2 were synthesized by co-precipitation method using ammonia as complexing agent at the temperature and pH of 60˚C and 12 and then NCA cathode powder was obtained by solid state method and calcination and sintering at 550 and 800˚C respectively, under oxygen atmosphere. For comparison, the synthesis of Ni0.8Co0.15(OH)2 and then addition of aluminum hydroxide by solid state method was done. The effects of synthesis method and time were studied.

Results showed that in the sample with a synthesis time of 4 days and then 2 sintering stages, anodic and cathodic peaks in cyclic voltammetry can be seen clearly. Besides, better capacity and capacity retention, lower charge resistance, and higher Li diffusion were achieved.

Results indicate that ammonia as a complexing agent in co-precipitation synthesis is suitable for the Al ion. Moreover, increasing the synthesis time helps to have complete layered structures, which is followed by better capacity. Two times sintering is also effective in reducing the cation mixing.

Cobalt ferrite is a magnetic material with a spinel structure. nano particles of Cobalt ferrite is attractive because of medium supersaturation, magnetic anisotropy,optical properties which causes to wide range applications such as drag delivery, cancer diagnosis and treatment, magneto-sensor, optical fibers and magneto-optical devices. In this investigation, the effect of reaction temperature on structure and magnetic properties of co-precipitated cobalt ferrite nanoparticles was studied. The nanoparticles were synthesized at 80, 90,100 and 110 C. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibration sample magnetometer (VSM) were used to charactization of nano particls. The results showed that cobalt ferrite nanoparticles was synthesized at all the reaction temperatures and supersaturation of non-calcination samples was noticeable. According to the results, by increasing the reaction temperature, crystallite size increased from 32 nm to 90 nm and also the magnetic supersaturation increased from 32 from 71.5 emu/g. besides, The purity of cobalt ferrite increased with increasing reaction temperature.

Zinc-cobalt ferrite nanoparticles (NPs) were synthesized using co-precipitation method. In the present process, NPs precipitated at various pHs, then calcined at 750°C for 2 h. X-ray diffraction (XRD) analysis confirmed single phase of ZnCo ferrite phase in all of the samples. Williamson-Hall calculations showed that the strain value in the microstructure of specimen prepared at pH= 8 is equal to -7*10-4. This content for pHs of 11 and 14 increased to 10-4 and 10-3, respectively. Therefore, the highest crystallite diameter was obtained as 51.35 nm for prepared NPs at pH= 14. Field emission scanning electron microscopy (FESEM) showed a relatively uniform distribution of particles with average size of 9.38, 50.1 and 30.7 nm for prepared powders at pHs equal to 8, 11 and 14, respectively. Vibrating sample magnetometer (VSM) measurements revealed that saturation magnetization (MS), anisotropic constant (K) and Bohr magneton (nB) characteristics are different at various pHs. So that, these parameters were obtained as 95.48 emu/g, 14.614*103 and 4.06, respectively for prepared powders at pH= 8, while at pH= 11 increased to 100.34 emu/g, 15.358*103 and 4.27, then changed to 81.98 emu/g, 11.712*103 and 3.49 at pH= 14. It was found different conditions of particles precipitation have a remarkable role on the properties of produced NPs.

Electromagnetic energy converters have been used as electrical energy suppliers. The use of solid magnets in these devices, for producing of magnetic induction, has produced difficulties for the design and application of these systems in various forms and frequencies. Magnetic fluids as a substitute for solid magnets have recently been considered for the use of these devices in low frequency ranges and different designs. In this study, a simple vibrational energy converter was designed using magnetite ferrofluid. For this purpose, the nanoparticles of magnetite were synthesized by co-precipitation method and surface modified by oleic acid. The XRD, FTIR, VSM testes and SEM studies were done to investigate properties of the samples. The nano magnetite particles had the average size of 70 nm and the saturation magnetization of 41.63 emu/gr. Three types of fluid including water, kerosene and brake oil were used to make magnetite stable ferrofluid. The most stable ferrofluid was brake oil based ferrofluid. The fabricated energy converter converted mechanical vibrations to induction voltage and voltage increased with frequency of vibration and applied magnetic field.

This study aimed to compare the phase changes and morphology of yttria-stabilized zirconium oxide powders (YSZ) synthesized by co-precipitation and molten salt methods. Ammonia precipitating agent was used for the synthesis of YSZ powder by co-precipitation method and a mixture of sodium carbonate and potassium carbonate salts was used as a molten salt in the molten salt method. Samples were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC) analysis. The results showed that only the sample prepared with zirconium oxychloride and yttrium nitrate by co-precipitation method had a single phase of yttria-stabilized zirconium oxide with tetragonal crystal lattice and particle size distribution in the range of 30 to 55 nm. The powder synthesized by the molten salt method contained a mixture of zirconia with monoclinic crystal lattice and yttria stabilized zirconia with tetragonal crystal lattice and particle size of 200 nm.

Hematite iron oxide (α-Fe2O3) is used in military industries as a main component of thermite mixtures, burning rate catalyst of composite propellants and pyrotechnic igniter systems. Catalytic and oxidation activity of this mineral combination increases strongly with reduction of particle size. In this research, nanoparticles of hematite iron oxide was synthesized by a new co-precipitation method by using iron (III) nitrate monohydrate in alkaline environment (pH=11). In order of completion of oxidation, hydrogen peroxide 35% was added in the final step. Product was analyzed by SEM, TEM, FT-IR and XRD techniques after separation and drying at 60 °C. SEM and TEM images indicated that the product is rodshape by mean diameter of 40 nm and length of 150 nm. Afterward, this product was applied in incendiary thermite formulation. Results showed that the thermite formulation containing nano 𝐹𝑒2𝑂3 has more intense ignition effects compared to the same composition containing micronized 𝐹𝑒2𝑂3. Burning time of these formulations were 3 and 4 sec respectively. Furthermore, the hole diameter created in steel target increased about 23% by using nano-iron oxide.

In this study, ZnWO4 nanoparticles were synthesized through co-precipitation method with sodium tungstate dehydrate (Na2WO4.2H2O) and zinc nitrate hexahydrate (Zn (NO3)2.6H2O) as starting materials. In order to optimize the conditions for obtaining smallest mean particle size, Central Composite Design (CCD) was used and three parameters of temperature, weight ratio of precursors, and pH value were studied in five levels. The obtained ZnWO4 nanoparticles were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), powder x-ray diffraction (XRD), thermal gravimetric- differential scanning calorimetry (TG-DSC) and photoluminescence (PL). The results showed that optimal conditions for smallest mean nanoparticles with particle size of 37.3 6.9 nm were temperature =83 , weight ratio of precursor equal to 1.1, and pH=6. The resulting ZnWO4 nanoparticles were dry- pressed to green compact pellets with a diameter of 11mm and thickness of 1.5 nm at the compaction pressure of 500 MPa. The densification of nanoparticles compacts was carried out by a pressure less sintering at 950 for 2 hours in air atmosphere. Scintillation properties of pellets were determined by means of Gama-rays spectroscopy. The results showed that manufactured ZnWO4 pellets illustrated counting sensitivity to Cs137 and Am241 irradiation sources and couldn’t detect energy of Gama-rays emitted from this two source.