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A series of double-perovskite oxides Sr2Sr1-xCaxTeO6 (0 ≤ x ≤ 1) samples have been prepared in order to study the effect of composition on phase formation and the related optical properties. The objective of this work is to study the possibility of calcium insertion with different percentages since calcium in known to enhance the electrical properties. In this work a well detailed structure and phase transitions investigation of the compounds were conducted and probed by X-ray diffraction and Raman spectroscopy techniques at room temperature. Both Rietveld refinements and Raman studies revealed that two phase transitions took place as the calcium amount x increases; a first from a triclinic to a hexagonal in the range 0.1 < x < 0.25 and a second from the hexagonal to a monoclinic structure in the range 0.5 < x < 0.6. The optical absorption α(λ) was also determined as a function of calcium content in the series samples using UV-vis analysis. It was revealed that a remarkable change occured in the cut-off wavelength, confirming the sequence of phase transitions C1 → R 3 ¯ m → P21/n. The optical band gap measurements showed that the triclinic Sr3TeO6 and the monoclinic Sr2CaTeO6 phases have band gap values of 2.75 and 2.81 eV, respectively. When the calcium increased to x = 0.25 (Sr2.75Ca0.25TeO6), remarkable decrease of the band gap value was observed, with Eg = 2.627 eV. [ABSTRACT FROM AUTHOR]

This study shows the effects of heat treatment on the manganese steel which microstructure consists essentially of 18.447% of manganese, 0.745% of chromium, and 1.169% of carbon. The techniques used are: X-ray diffraction, optical microscope, scanning electron microscope.After heat treatment at 600 °C and 1050 °C for 30 minutes, metallurgical analysis will connect the microstructural changes occurring during the temperature maintenance to the mechanical behavior of the material. The characterization of the microstructures and the surface morphology of the alloy before and after the heat treatment determine that this treatment process favors the dispersion of carbides in the austenitic matrix and the appearance of precipitates which causes structural hardening. [ABSTRACT FROM AUTHOR]

The superalloy Hastelloy G30 (trademark of Haynes International, Inc.) is an alloy with a high proportion of nickel, characterized by a high corrosion resistance in environments containing extra oxidizing acids. The alloy consists essentially of 43% of nickel with a proportion of chromium which varies from 28 to 31.5% and from 13 to 17% for iron. Its matrix is austenitic and its structure is face-centered cubic. The objective of this work is to treat the alloy G30 thermally at 4 different temperatures 700 °C, 800 °C, 900 °C and 1000 °C for 3 hours. Indeed, we followed the progression of structural and mechanical properties. The micro structural evolution influence slightly on the mechanical properties of the alloy G30: hardness of the alloys treated at 700 °C and 800 °C is equal to 46 HRF and that of the alloys treated at 900 °C and 1000 °C is 46.25 HRF. The images obtained by optical microscopy revealed the presence of carbides at the joints and inside the grains .The X-ray diffraction spectra obtained after the isothermal treatments showed the presence of peaks of the precipitates and the peaks of the austenite phase. [ABSTRACT FROM AUTHOR]