Tuning of ferrimagnetic nature and hyperfine interaction of Ni2+ doped cobalt ferrite nanoparticles for power transformer applications

Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni²⁺ substitution effect in Co_1-xNi_xFe₂O₄ (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni²⁺ concentration. The M-H loops reveals that saturation magnetization(M_s), coercive field(H_c) remanence magnetization(M_r) and magnetron number(η_B) decreases significantly with increasing Ni²⁺ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(H_c) is found strongly dependent on the concentration of Ni²⁺ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni²⁺ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application.     

Investigations on mechanical behavior of hot rolled Al7075/TiO2/Gr hybrid composites

In the present work, influence of titanium dioxide (TiO₂) and graphite (Gr) hybrid reinforcement on microstructure and mechanical behavior of Al7075 alloy is studied. Al7075 and its hybrid composite samples were fabricated by using stir-casting and hot rolling technique. Hot rolling was carried out at a temperature of 450 °C with a reduction-ratio of 90%. Microstructure examination showed a good dispersion of titanium dioxide and graphite reinforcement particles with excellent bond with Al7075 matrix alloy. In case of hot rolling, both the reinforcements were found to be aligned in the direction of rolling. The microhardness and tensile strength of hybrid composites were remarkably improved in case of hot rolling compared to that of cast composites.     

A new approach for filtering of surface profiles using morphological operations

Among different filtering approaches used to remove waviness and obtain roughness, envelope and motif techniques are considered to be suitable for functional characterization. Morphological filtering being closely related to envelope technique can be used for filtering of surfaces. This paper discusses a new approach combining morphological operations namely closing and opening with circle as structuring element in a unique way to generate the reference profile representing waviness. The reference profile generated by this method is smooth without any slope discontinuities and robust against deep valleys present in the profile. Analysis of the proposed method for robustness and form-approximation capabilities is presented in this paper. Comparison is also made with envelope and morphological closing filters as well as Gaussian regression filter to bring out the effectiveness of this approach.     

Fitting of robust reference surface based on least absolute deviations

Engineering surfaces comprise shape deviations namely form, waviness and roughness. For characterization of roughness, form and waviness are separated from the measured surface by establishing a reference surface that represents these deviations. This paper presents a new approach of simultaneously separating form and waviness deviations by fitting a reference surface that remains robust against the outliers such as deep grooves. A second degree polynomial and a set of sinusoidal functions are taken as basis functions to represent form and waviness respectively. A criterion of minimization of sum of absolute deviations (L₁-norm) is considered as against the commonly used least squares (L₂-norm) criterion and the reference surface obtained is found to be robust against outliers such as deep valleys in the measured surface. The superiority of the proposed fitting scheme is brought out by testing on different surfaces and comparing with the least squares method of fitting and the robust Gaussian regression filtering.     

Structural,Microstructural, Infrared,and Mössbauer Spectroscopy Study of LuFeO3 Prepared by Solution Combustion Method

Journal of Superconductivity and Novel Magnetism - In the present work, we investigate the electronic structural microstructure and spectroscopic characteristics of LuFeO3. Sample is prepared by...     

From waste to wealth: recycling the secondary resource from steel ladle as a flux in Si-killed steelmaking process

With the regulations pertaining to the environment and waste disposal becoming stringent day by day, the steelmaking industry is being compelled to adopt a zero-waste-policy for sustainability. As a consequence, 3R (reduce, reuse and recycle) technique of waste handling has become the most favoured option among the industries. This paper focuses on recycling of slag generated after secondary refining process. Trials were conducted in two stages, namely (a) prevention of dusting phenomenon of Al-killed steel ladle slag to generate lump slag by suitably selecting the ladle covering compound and chemically modifying the slag, and (b) utilisation of the lump slag as a 100% replacement of synthetic slag in Si-killed steel ladles, leading to a reduction in its specific consumption from 1.2?kg/TLS to zero. As a process requirement, specific power consumption, arcing time and degree of desulphurisation were considered as the major parameters for comparing the results using hypothesis test statistical tool.     

Microstructural development and austempering kinetics of ductile iron during thermomechanical processing

A new method of refining the microstructure of austempered ductile iron (ADI) by thermome chanical processing is investigated. Refinement of microstructure is effected by grain refinement of parent austenite by hot deformation in the austenitizing temperature range, before the austempering treatment. The effects of austenite deformation on the kinetics of austempering reaction and the microstructure development were studied using metallography and X-ray diffraction (XRD), at different austempering temperatures and deformations. The process window for optimum microstructure was determined in terms of the parameters involved. Deformation of 40 to 60 pct could be imparted in the temperature range 900 °C to 1025 °C, resulting in a reduction in the prior austenite grain size by 35 to 50 pct and ferrite size in ausferrite by 70 to 75 pct. The effects of austenitization temperature on the austempered microstructure were also studied.     

Optical properties of bismuth tellurite glasses doped with holmium oxide

The study of polarizability, optical basicity, and electric susceptibility carried out on the new and very rare set of bismuth - tellurite glasses doped with Ho³⁺ ions were fabricated by the conventional melt quenching process. The non-crystalline nature was confirmed by X-ray diffractometer measurements. Physical properties such as rare earth ion concentration, interionic distance, polaron radius, and average tellurium - tellurium separation were investigated by appropriate formulae. By UV absorption spectra, optical properties of Ho³⁺ ions doped glasses were found in the wavelength limit from 400 to 700 nm. The optical properties like optical dielectric constant, electronic polarizability, metallization criterion, electronegativity, optical basicity, and electric susceptibility were measured with appropriate mathematical relations. The impact of Ho³⁺ ions on nonlinearity in optical parameters discloses bismuth tellurite glass as a new applicant for holmium doped fiber amplifier applications.     

Studies on the influence of process parameters on the AISI 316L resistance spot-welded specimens

Energy saving and improving product performance are long-term concerns in extrusion process. Therefore, this paper proposes a novel extrusion process called alternate extrusion (AE). The proposed process uses split punches alternately instead of the overall structure to apply the downward load, but receives an unexpected load-saving and grain refinement effect. Experimental and finite element method (FEM) methods were used to investigate the effects of different extrusion ratios on microstructure and mechanical properties. Results indicate that load value is significantly reduced, grain size is considerably refined, and tensile strength and elongation of material are improved after AE processing. The fractography shows that the fracture mode of AZ31 magnesium alloy changes from brittle to ductile. Although the actual extrusion ratio decreases in AE process, additional shear forces produced by different punch-alternating loads at the interface improve microstructure and mechanical properties. Therefore, AE can achieve grain refinement and load saving and improve strength and plasticity of magnesium alloys.