The Effects of Fuel Type Above Magnetic Properties of the Nickel Ferrite Nanoparticles Synthesized with Microwave Method

The synthesis of nickel ferrite nanoparticles was used various fuel substances such as glycine, urea and citric acid. The mixture prepared in stoichiometric rates was put in to the kitchen type microwave oven. In the end of reaction time was obtained a brown-black solid. The obtained solid was characterized with X-Ray Powder Diffraction and Scanning Electron Microscopy. The results of this analysis showed that all of the obtained particles have got nano-size particle size distribution. To determine the magnetic properties of the nanoparticles were analyzed by using a vibrating sample magnetometer. Fuel type used in synthesis is quite effective on the magnetic properties of NiFe2O4 nanoparticles. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3527

The Effects of Fuel Type Above Adsorbtive Properties of the Nickel Ferrite Nanoparticles synthesized with Microwave Method

In this study, we were able to develop a new and practical method for the synthesis of the NiFe2O4 nanoparticles. The synthesis of nickel ferrite nanoparticles was used various fuel substances such as glycine, urea and citric acid. The synthesis mixture prepared in stoichiometric rates was put in to the kitchen type microwave oven. In the end of reaction time was obtained a brown-black solid. The obtained solid was characterized with X-Ray Powder Diffraction and Scanning Electron Microscopy. The results of this analysis showed that all of the obtained particles has got nano-size particle size distribution. Later, the nanoparticles were analyzed by using a surface area analyzer and their adsorptive properties were investigated such as surface area and average pore size. We observed that the nanoparticles prepared with urea has the highest surface area. However, fuel type used in synthesis is quite effective on the surface properties of NiFe2O4 nanoparticles. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3527

The Effect of Calcination Temperature in NiFe2O4 Nanoparticles Synthesis with Microvawe Combustion Method

Magnetic ferrites are a group of technologically important magnetic materials. Synthesis of nanocrystalline spinel ferrite has been investigated intensively in recent years due to their potential applications in high-density magnetic recording, microwave devices, and magnetic fluids In this study, NiFe2O4 nano particles were prepared with microvawe combustion methods. In experiments, samples obtained by microvawe method were calcined at various temperatures. The structural and morphological properties of NiFe2O4 nano particles was determined by X-ray powder diffraction (XRD) and Scanning Electron microscopy (SEM). Results showed that increasing calcination temperature contributed to cyristallinity of NiFe2O4 nanoparticles. But also average particle size increased. As a result, average particle size calculated by using Debye-Scherrer Formula as aproximately 30 nm. However, this results was confirmed with SEM analysis. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3502

Investigation of the Effects of Reaction Temperature in NiFe2O4 Nanoparticles Synthesis by Hydrothermal Method

In this experimental study was investigated the effect of reaction temperature in NiFe2O4 nanoparticles synthesis with hydrothermal method. An appropriate ratio of solutions nickel nitrate and ferric nitrate were dissolved in deionized water and poured into a crucible. Later, polyethylene glycol 600 (PEG 600) was added to this mixture. Samples were adjusted to pH 11 values using NaOH solution. Accordingly, experiments were made at 180, 200 and 250 oC, respectively. The other parameters, were fixed as reaction time 24 h and pH value 11. The structural and morphological properties of NiFe2O4 nanoparticles were determined by X-ray powder diffraction (XRD) and Scanning Electron microscopy (SEM). Results showed that increasing calcination temperature contributed to cyristallinity of NiFe2O4 nano particles. But also average particle size increased. As a result, average particle size was calculated by using Debye-Scherrer Formula as approximately 30 nm. However, this results was confirmed with SEM and TEM analysis. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3502

The Effect of pH in Nickel Ferrite Nanoparticles Synthesis by Hydrothermal Method

In this study, NiFe2O4 nano particles was prepared with aqueous solutions of nickel nitrate and ferric nitrate salts. An appropriate ratio of solutions nickel nitrate and ferric nitrate were dissolved in deionized water and poured into a crucible. Later, polyethylene glycol 600 (PEG 600) was added to this mixture. Samples were adjusted to various pH values. In experiments, samples obtained by hydrothermal method were heat treated at 700 oC for 8 h to enhance their crystallinity and remove the residual organic materials. The structural and morphological properties of NiFe2O4 nano particles were determined by X-ray powder diffraction (XRD) and Scanning Electron microscopy (SEM). Results showed that increasing calcination temperature contributed to cyristallinity of NiFe2O4 nano particles. But also average particle size increased. As a result, average particle size was calculated by using Debye-Scherrer Formula as aproximately 30 nm. However, this results was confirmed with SEM analysis. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3502

Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods

AGB stars are responsible for producing a variety of elements, including carbon, nitrogen, and the heavy elements produced in the slow neutron-capture process ($s$-elements). There are many uncertainties involved in modelling the evolution and nucleosynthesis of AGB stars, and this is especially the case at low metallicity, where most of the stars with high enough masses to enter the AGB have evolved to become white dwarfs and can no longer be observed. The stellar population in the Galactic halo is of low mass ($\lesssim 0.85M_{\odot}$) and only a few observed stars have evolved beyond the first giant branch. However, we have evidence that low-metallicity AGB stars in binary systems have interacted with their low-mass secondary companions in the past. The aim of this work is to investigate AGB nucleosynthesis at low metallicity by studying the surface abundances of chemically peculiar very metal-poor stars of the halo observed in binary systems. To this end we select a sample of 15 carbon- and $s$-element-enhanced metal-poor (CEMP-$s$) halo stars that are found in binary systems with measured orbital periods. With our model of binary evolution and AGB nucleosynthesis, we determine the binary configuration that best reproduces, at the same time, the observed orbital period and surface abundances of each star of the sample. The observed periods provide tight constraints on our model of wind mass transfer in binary stars, while the comparison with the observed abundances tests our model of AGB nucleosynthesis.Comment: 18 pages, 20 figures, accepted for publication on A&

Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-ss stars

Many observed CEMP stars are found in binary systems and show enhanced abundances of $s$-elements. The origin of the chemical abundances of these CEMP-$s$ stars is believed to be accretion in the past of enriched material from a primary star in the AGB phase. We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-$s$ stars were formed. For this purpose we compare a sample of $67$ CEMP-$s$ stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-$s$ stars in three groups based on the observed abundance of europium. In CEMP$-s/r$ stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP$-s/nr$ stars. No measurement of europium is currently available for CEMP-$s/ur$ stars. On average our models reproduce well the abundances observed in CEMP-$s/nr$ stars, whereas in CEMP-$s/r$ stars and CEMP-$s/ur$ stars the abundances of the light-$s$ elements are systematically overpredicted by our models and in CEMP-$s/r$ stars the abundances of the heavy-$s$ elements are underestimated. In all stars our modelled abundances of sodium overestimate the observations. This discrepancy is reduced only in models that underestimate the abundances of most of the $s$-elements. Furthermore, the abundance of lead is underpredicted in most of our model stars. These results point to the limitations of our AGB nucleosynthesis model, particularly in the predictions of the element-to-element ratios. Finally, in our models CEMP-$s$ stars are typically formed in wide systems with periods above 10000 days, while most of the observed CEMP-$s$ stars are found in relatively close orbits with periods below 5000 days.Comment: 23 pages, 8 figures, accepted for publication on Astronomy & Astrophysic

The Structure of Close Binaries in Two Dimensions

The structure and evolution of close binary stars has been studied using the two-dimensional (2D) stellar structure algorithm developed by Deupree (1995). We have calculated a series of solar composition stellar evolution sequences of binary models, where the mass of the 2D model is 8Msun with a point-mass 5Msun companion. We have also studied the structure of the companion in 2D, by considering the zero-age main-sequence (ZAMS) structure of a 5Msun model with an 8Msun point-mass companion. In all cases the binary orbit was assumed to be circular and co-rotating with the rotation rate of the stars. We considered binary models with three different initial separations, a = 10, 14 and 20Rsun. These models were evolved through central hydrogen burning or until the more massive star expanded to fill its critical potential surface or Roche lobe. The calculations show that evolution of the deep interior quantities is only slightly modified from those of single star evolution. Describing the model surface as a Roche equipotential is also satisfactory until very close to the time of Roche lobe overflow, when the self gravity of the model about to lose mass develops a noticeable aspherical component and the surface time scale becomes sufficiently short that it is conceivable that the actual surface is not an equipotential.Comment: 22 pages, 10 figures, accepted by Ap