Influence of annealing temperature on the microstructure and mechanical properties of MgB2

We have investigated the effect of annealing temperature on the microstructure, magnetic and mechanical properties of MgB2 superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), ac susceptibility and Vickers microhardness measurements. XRD patterns and SEM micrographs are used to obtain information about lattice parameters and grain size, respectively. These measurements indicate that MgB2 grain size, lattice parameters, and critical temperature are increased, and grain connectivity is improved, with increasing the sintering temperature up to 850°C. It is also observed that the Vickers microhardness of the samples is dependent of the sintering temperature and applied load. In addition, we calculate the load dependent mechanical properties of MgB 2 samples such as the Young's modulus, yield strength, and fracture toughness. The possible reasons for the observed improvements in microstructure, superconducting and mechanical properties due to annealing temperature are discussed. © 2009 IOP Publishing Ltd

Thermal expansion and Vickers hardness measurements on Bi1.6Pb0.4Sr2Ca2-xSmxCu3Oy superconductors

Ozturk, Ozgur/0000-0002-0391-5551WOS: 000239286300004In this work, Bi1.6Pb0.4Sr2Ca2-SmxCu3Oy (x = 0.0000, 0.0005, 0.0010, 0.0050, 0.0100, 0.1000, 0.5000, 1.0000, 1.5000) superconductors were prepared by conventional solid-state reaction method. The effect of the substitution of Sm for Ca in the high-T-c phase Bi-2223 was investigated by DTA, thermal expansion coefficient, Vickers microhardness, XRD and SEM analysis. The lattice constants and volume fractions are estimated from XRD analysis. The thermal expansion coefficient, the microhardness, the volume fraction, and the lattice constants strongly depend on the Sm content of the samples. XRD data show that the high-Tc phase decreases and the low-T-c phase increase as the Sm substitution changes from x = 0.0 to 1.5. The coefficients of thermal expansion (in the range of 30-800 degrees C) of the pure (x = 0.0) and high doped (x = 1.5) samples were 7.90 x 10(-7) and 5.70 x 10-7 degrees C-1, respectively. The results of Vickers hardness measurements varied between 0.254 and 0.623 GPa as increasing the Sm concentration. (c) 2006 Elsevier B.V. All rights reserved

Human Paraoxonase-1 Activity in Children with Acute Bronchiolitis

INTRODUCTION: Human paraoxonase-1 (PON1) is one of the endogenous antioxidant molecules working against oxidative stress. We aimed to investigate serum PON1 activity in children with acute bronchiolitis

Journal of Physics Conference Series

We investigated the effect of cooling rates on the microstructure and mechanical properties of Bi(1,6)Pb(0,4)Sr(2)Ca(2)Cu(3)Oy superconductors prepared by standard solid state reaction methods. The samples were annealed under identical condition and cooled with different cooling rates. The investigations consisted of Vickers microhardness, SEM and XRD measurements. XRD examination of the samples showed that high percentage of Bi-2212 phase was observed and low-T(c) phase increased with increasing the cooling rates. From SEM analysis, flake-like grains were more pronounced with increasing cooling rates. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. We calculated Vickers hardness, Young's modulus, yield strength, fracture toughness values. These mechanical properties of the samples were found to be load and cooling rate dependent. In addition, we calculated the load independent microhardness, Young's modulus, and yield strength and fracture toughness of the samples using different models. The possible reasons for the observed changes in microstructure and mechanical properties of the samples due to cooling rates were discussed