Papers by Keyword: Spinel

Abstract: In recent time, interest to ferrite magnetic nanomaterials has considerably grown mainly due to their much promising medical and biological applications. The spinel ferrite powder samples having high heat generation ability in AC magnetic field was studied for application to hyperthermia treatment of cancer tumor. These properties of ferrites are strongly depending on their chemical composition, ion distribution, spin orientation and method of preparation in general and crystal structure in particular nature of the material. In this study, several samples of ferrite magnetic structures were investigated by neutron diffraction. The explanation of the mechanism to occurs the heat generation ability in the magnetic materials and the electronic and magnetic states of ferrite-spinel – type structures were theoretically defined by the first-principles calculations within the framework of DFT.

Abstract: The paper focuses on the determination of how in-situ formed magnesia-alumina spinel (MA spinel) content in corundum refractory castables influences the final properties and pore size distribution of no-cement refractory castables. The motivation for this research was the continued pressure on increasing the utility properties of refractory castables, namely their corrosion resistance to blast-furnace slag. The influence of MA spinel content was observed in vibration-compacted refractory castables (three mixtures). The corrosion test was performed to determine the dependence of the size of the slag-penetrated area on MA spinel content in the specimen. The pore structure of a slag-penetrated NCC and an unaffected castable was described.

Abstract: The phase equilibrium in the Fe-Ge-O system is investigated by measuring EMF of galvanic elements with solid oxygen-conductive electrolytes. The samples for investigation were prepared by the solid phase reaction at 900 °C. The samples were analyzed to determine the total and phase composition. The gross composition of the samples was refined by chemical analysis. The iron content was determined by the standard method of bichromatometric titration, while that of germanium was determined by the photometric method, which is based on measuring the optical density of the colored colloid solution of germanium phenyl fluoronate, which is formed upon the interaction of germanium dioxide with phenylfluorone in the acidic medium. The phase composition was established using X-ray diffractometry and electron probe microanalysis using a DRON-3 diffractometer and a JEOL JSM-6460LV computer controlled scanning (raster) microscope. The experimental function of EMF galvanic elements of temperature is formulated. After processing the obtained data, the equilibrium oxygen pressures over the samples were calculated, the solubility of germanium in iron monoxide (wustite) was determined, the phase composition of the regions bordering the wustite region was established, the isothermal sections of the state diagram of the system were constructed at 1173 and 1273 K in the equilibrium region of the wustite solution with metallic and spinel phases

Abstract: A ferritic stainless steel (FSS) AISI 430 coated by (Mn_xCo_1-x)₃O₄ spinel has been intensively studied for its potential in application as an interconnect of a solid oxide fuel cell (SOFC). In this study, in order to develop fabrication of (Mn_xCo_1-x)₃O₄ coatings, Mn-Co coatings on AISI 430 by an electrodeposition technique was adopted. The electric direct current (DC) and alternative current (AC) modulated DC (AC+DC) signals were utilized to drive voltage levels for electrodeposition. By varying the duty of the AC+DC signals from 25 % to 50 %, the ratio of Mn and Co composition in the coating changed, consequently by this technique it is possible to adjust the composition of binary alloy coating. The fabricated coatings also exhibited different morphologies indicating nucleation and grain growth process of various oxide scales of Mn-Co. The oxidation behavior is also investigated to evaluate the quality of the coatings.

Abstract: In this paper, the Fe-containing phases in BOF slag were identified before and after oxidized with atmospheric air. XRD and SEM with EDS results showed that The element Fe existed in slag in the form of calcium ferrite, wustite solid solution and hematite. Mg solid solute in wustite. After oxidized, magnetite became the major mineral phase in slag and Mg ⁺ replace the Fe²⁺ of magnetite crystal to form spinel.

Abstract: The paper focuses on the determination of how periclase content in the raw material influences the final properties of no-cement refractory castables. The motivation for this research was the continued pressure on increasing the utility properties of refractory castables, especially their corrosion resistance. The influence of MgO was observed in vibration-compacted refractory castables; the mixtures were made so that the consistency of each one was the same. There were only minimal differences in the water content of the mixtures. The mineral composition of the raw materials used in the manufacturing of the refractory castables was determined and the influence of the firing temperature on their compressive strength, flexural strength, apparent porosity, mineralogy and pore structure was described. The corrosion resistance was determined by means of the crucible test according to CSN P CEN/TS 15418 (726022) Method of test for dense refractory products – Guidelines for testing the corrosion resistance of refractories caused by liquids.

Abstract: In work investigated effects of zirconium oxide (ZrO₂), spinel (MgAl₂O₄) and mullite (Al₆Si₂O₁₃) nanosized powders on the base oil tribological properties. The nanosized (30-40nm) powders manufactured by plasma chemical synthesis method. Tribological experiments used on ball-on-disc type tribometer, measured coefficient of friction and determined metalic disc wear. Base oil used selectively purified mineral oil (conform SAE-20 viscosity) without any functional additives. Nanosized powders dispersed in base oil at 0.5; 1.0; 2.0; wt.%. At work cocluded, that the adition nanoparticles in base oil, possible reduced friction pair wear and friction coefficient. As the main results include spinel (MgAl₂O₄) nanoparticles 0.5 and 1.0 wt. % concentration ability reduced friction coeffiecient value.

Abstract: This work developed a ceramic material for dental application, spinel-base (MgAl₂O₄), a ceramic material with recognized translucency. Spinel powders were uniaxially pressed at 100 MPa and pre-sintered in order to obtain porous ceramic blocks. The pre-sintered blocks were characterized and indicated 80% of relative density. X-ray diffraction (XRD) only showed MgAl₂O₄ phase. Samples with 15 x 15 x 1 mm were submitted to infiltration using glass rich in lanthanum (La). The products were characterized by scanning electron microscopy (SEM) and mechanical properties, as hardness and fracture toughness. Results were compared to the commercial product VITA-InCeram Spinell. Relative densities exceeding 92%, hardness around 900 HV and high toughness 2.5 MPa.m^1/2 were obtained for both examined systems.

Abstract: We synthesized polycrystals of cobaltite spinels LiCo₂O₄, ZnCo₂O₄, and their mixed crystal (Li_1-xZn_x)Co₂O₄, and performed the magnetic susceptibility and specific heat measurements. LiCo₂O₄ with the Weiss temperature Θ_W ~ -114 K exhibits an antiferromagnetic transition at T_N ~ 30 K. On the other hand, ZnCo₂O₄ with the Weiss temperature Θ_W ~ -90 K exhibits the absence of magnetic phase transition down to low temperature (2 K), indicating the presence of strong frustration. Taking into account the absence of magnetic phase transition in the orbital-degenerate ZnCo₂O₄, it is suggested that the antiferromagnetic transition in the charge-orbital-degenerate LiCo₂O₄ is driven by the charge degree of freedom. Furthermore, the magnetic properties of (Li_1-xZn_x)Co₂O₄ suggest that the antiferromagnetic transition in LiCo₂O₄ is sensitively suppressed by diluting the charge degeneracy.

Abstract: The paper presents the comparative analysis of phase formation in NiO-CuO-Fe₂O₃-Cr₂O₃ system at salt decomposition reactions. Spinel phase formation is proven for each material. Synthesized materials are examined with X-ray phase analysis, low temperature nitrogen absorption, electronic microscope scanning. Highly dispersed spinel samples are proven to be obtained through synthesis at organic precursor presence. High catalytic activity of synthesized materials in the process of methyl orange oxidative destruction at hydrogen peroxide presence is determined. The fact is extremely useful for industrial sewage water treatment materials development for enterprises that employ organic pigments or colorants at their production process.