Papers by Keyword: Structural Investigation

Abstract: In this paper will be presented experimental researches on development advanced alloys with amorphous structures based on Ni and Cu for resistance brazing joints. The main advantages of these amorphous alloys in shape of ribbons are their ductility and flexibility. These ribbons are obtained by ultra-rapid cooling of the melt. Using resistance brazing process, were obtained brazing joints of stainless steel and copper strips. The joints were mechanical and structural analysed. It was performed mechanical shear test on the brazed joints to establish the shear strength of the joints, and also it was performed structural investigation to emphasize the microscopic structure and the structural transformations that take place in the base material and brazing alloys during the brazing process.

Abstract: It Has Been Reported that the Metal Hydride, Ymn2hy (y ≤ 4.5), Wherein the Hydrogen Atoms Are Located into the Interstitial Sites, Transformed into a Complex Hydride, YMn₂H₆, Containing Complex Anions, [MnH₆]^5-. We Investigated the Possibility of Synthesizing the Complex Hydride, Y(Mn_1-xFe_x)²H₆ (x ≤ 0.3), where Mn Atoms Were Partially Substituted by Fe. As a Result, the Transformation into the Complex Hydride, Y(Mn1-Xfex)2H6, Was Successfully Realized for x ≤ 0.10 upon the Hydrogenation of the Metal Hydride, Y(Mn_1-xFe_x)₂H_y (y = 4.4 and 4.5), under 50 Mpa H₂, much Lower than the Previously Reported Value of 1 GPa. Our Structural Investigation Suggested that the Fe Substitution in Y(Mn_1-xFe_x)₂H₆ (x ≤ 0.10) Resulted in the Form of Complex Anions, I.e., [MnH₆]^5- Were Partially Substituted by [FeH₆]^4-.

Abstract: Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid by using two different type of milling method (attrition milling and ball milling). According to the analysis, the attrition milling resulted nanosize HAp even after milling, while the ball milling process provided HAp only after a 400oC, 2 h long heat treatment. The grain size in both cases were approximately preserved during the heat treatment. The effect of temperature on stoichiometry, morphology and crystallinity of HAp powders were investigated. The structures of the HAp were characterized by X-ray diffraction and Scanning Electron Microsopy.

Abstract: Solid-state Nuclear Magnetic Resonance (NMR) has been used for a detailed structural analysis of different amorphous calcium phosphate (ACP) and hydroxyapatite (HAp) samples. For ACP the NMR data reveal the presence of hydrogenphosphate units in much larger quantities as known previously also showing differences between the samples. Furthermore, phosphate units close to water and a third group (yet unknown) are found in the spectra. A novel proposal has been established to explain the Ca-deficiency in nanocrystalline HAp. It consists of a crystalline core of stoichiometric composition which contains only 50% of the total phosphate amount. The residual phosphate is contained in a disordered surface layer with about 1 nm thickness. Most importantly, this surface layer contains hydrogenphosphate groups to a large extend and carbonate units. A Ca/P ratio of 1.52 is obtained from the NMR data which is very close to the value of 1.51 of the chemical analysis. Thus, NMR allows the investigation of the disordered mineral-protein interface and first examples concerning bone and nacre are presented and discussed.