Impact of Co doping on physical,structural, microstructural and magnetic features of MgZn nanoferrites for high frequency applications

Cobalt (Co) doped MgZn spinel nanoferrites with composition Mg_0.5Zn_0.5Co_x Fe_2-xO₄ at x = 0.0, 0.10, 0.20, 0.30, 0.40, 0.50 were prepared using sol-gel auto ignition method. The characterizations techniques such as FESEM, FTIR, XRD and VSM were used to determine the morphology, force constants, phase, structure and magnetic features of the samples. Lattice parameters, FWHM, d-spacing, crystallite size, micro strains and volume were investigated using high score plus software. Materials analysis using diffraction (MAUD) software was also used to study the Rietveld refinement properties of the Co doped MgZn ferrites. Physical properties such as porosity, X-ray and bulk density were also determined. Force constants of their respective absorption bands were calculated from FTIR of the Co doped MgZn nanoferrites. Single phase structure with cubic phase were observed for MgZn and Co doped MgZn at x = 0.0 whereas second phase was observed at higher Co concentrations respectively. FESEM show regular shape of the particles at low Co concentrations whereas agglomerations were observed at higher Co concentrations respectively. The magnetic properties of the Co doped MgZn ferrites were also investigated from VSM study. Magnetic remanence, coercivity, initial permeability, saturation magnetization, Bohr magneton and anisotropy constant were determined from VSM analysis. The coercivity, saturation magnetization, remanence, anisotropy constant and initial permeability were enhanced with the doping of ‘Co’ in MgZn nanoferrites. Response of the Co doped MgZn nanoferrites at high frequency regime was also evaluated. It can be seen that the response from all the Co doped MgZn nanoferrites was 2.84 GHz–5.96 GHz respectively and suggested the use of these nanoferrites for the operation of nanodevices in the X-band high frequency regime.     

On processing of Ni-WC based functionally graded composite clads through microwave heating

Present study focuses on the development of four layered functionally graded clads (FGC) of Ni-WC based composite material on AISI 304 substrate through microwave heating route. Experimental trials were conducted inside a microwave applicator of domestic type at frequency range of 2.45?GHz. The optimal exposure time of 900?W microwave power was varied with compositional gradient and it was from 300 to 360?s. The mechanism of FGC formation through microwave heating was explained and developed FGC was subjected to mechanical and microstructure characterizations. The results of micro-structural analysis revealed that the FGC of ～1.8?mm thickness was produced and was free from any type of interfacial cracks and visible porosity. It was observed that WC particles were randomly dispersed in the nickel matrix. XRD study revealed the formation of inter-metallics, such as NiW₄, NiSi, and Cr₂₃C₆. Maximum value of microhardness was observed in the top FGC layer and was 880?±?30?HV.     

Synthesis of Novel Tetra(µ3-Methoxo) Bridged with [Cu(II)-O-Cd(II)] Double-Open-Cubane Cluster: XRD/HSA-Interactions,Spectral and Oxidizing Properties

A new double-open-cubane core Cd(II)-O-Cu(II) bimetallic ligand mixed cluster of type [Cl₂Cu₄Cd₂(NNO)₆(NN)₂(NO₃)₂].CH₃CN was made available in EtOH/CH₃CN solution. The 1-hydroxymethyl-3,5-dimethylpyrazole (NNOH) and 3,5-dimethylpyrazole (NNH) act as N,O-polydentate anion ligands in coordinating the Cu(II) and Cd(II) centers. The structure of the cluster in the solid state was proved by XRD study and confirmed in the liquid state by UV-vis analysis. The XRD result supported the construction of two octahedral and one square pyramid geometries types around the four Cu(II) centers and only octahedral geometry around Cd(II) two centers. Interestingly, NNOH ligand acts as a tetra-µ³-oxo and tri-µ²-oxo ligand; meanwhile, the N-N in NNH acts as classical bidentate anion/neutral ligands. The interactions in the lattice were detected experimentally by the XRD-packing result and computed via Hirschfeld surface analysis (HSA). The UV-vis., FT-IR and Energy Dispersive X-ray (EDX), supported the desired double-open cubane cluster composition. The oxidation potential of the desired cluster was evaluated using a 3,5-DTB-catechol 3,5-DTB-quinone as a catecholase model reaction.     

Experimental investigation on high temperature wettability and structural behaviour of SAW fluxes using MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system

To establish the relationship between wettability and structure with the change in SAW flux composition, the contact angle measurement study was performed at 1700 K. For MgO–TiO₂–SiO₂ and Al₂O₃–MgO–SiO₂ flux system the wetting behaviour was studied by evaluating the contact angle as well as surface tension properties. Sessile drop method was used to determine the wetting properties of SAW fluxes. Twenty-one SAW fluxes were designed & developed by applying mixture design approach of design of experiments. Chemical, phase and structural properties of SAW fluxes were measured using modern techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD) & Fourier Transform Infra-red spectroscopy (FTIR). As per the calculated contact angle value, different surface tension values for MgO–TiO₂–SiO₂ and Al₂O₃–MgO–SiO₂ flux system was calculated using Young's & Boni's equations. Using Dupre's equation the adhesion energy for twenty-one basic fluxes was also calculated. Measured contact angle value increased with increase in the TiO₂/MgO & TiO₂/Al₂O₃ flux ratio. Lower contact angle gives higher wettability between the flux and the heating substrate. With increase of TiO₂/SiO₂ ratio up to 1.5 to 2.0 the calculated surface tension value is decreasing while after that it is increased with increase in TiO₂/SiO₂ ratio.     

Study of residual stress variation with depth of friction stir welded aluminium plates with different thicknesses

ABSTRACT

The residual stress may greatly vary through thickness due to the large temperature gradients and severe plastic deformation in depth for thick section friction stir welded plates. AA 2024-T351 plates with 6.5, 12 and 20?mm thicknesses were joined by friction stir welding to investigate the differences of residual stress variations with depth between thin and thick plates. The surface residual stresses were compared between the X-ray diffraction and contour measurements. Significant variations of stress peaks, root central residual stresses and widths of ‘M’ profiles were observed along the thickness for thick plates. The origins of the aggravated variations with depth were investigated from the temperature gradients and material flow variations through thickness.     

Preparations and tailoring of structural,magnetic properties of rare earths (REs) doped nanoferrites for microwave high frequency applications

Rare earths (Res) doped Mn spinel nanoferrites with nominal composition MnR_0.2Fe_1·8O₄ (REs = Tb, Pr, Ce, Y and Gd) were synthesized using sol gel method. FTIR, XRD and FESEM were employed to evaluate the structure, phase, vibrational bands, morphology, grain size and microstructure respectively. VSM was employed to investigate the magnetic features of the Mn nanoferrite and REs doped Mn nanoferrites. XRD confirmed the single-phase cubic structure of Mn nanoferrite whereas tetragonal phase was observed for all REs doped Mn nanoferrites. Unit cell software was used to determine the structural features such as lattice parameter, cell volume, ‘da’, ‘db’, ‘dc’ and ‘dv’ respectively. FTIR results demonstrated the absorption peaks of Mn and REs doped Mn ferrite at 647-674 cm⁻¹. FESEM results depicted the irregular shapes of the particles with large agglomerations in the prepared samples. The grain size evaluated by LIM (line intercept method) found in the range of 94 to 213 nm respectively. Saturation magnetization was increased from 1.332 to 38.097 emu/g whereas remanence was increased from 1.096 to 25.379 emu/g respectively. In addition, other magnetic parameters such as initial permeability, magnetic anisotropy and magnetic moments were also increased. Moreover, Y–K angles showed significant response with REs doping in Mn ferrites. Furthermore, high frequency response and switching field distribution (SFD) of Mn ferrite and REs doped Mn ferrites were also determined. It is found that Y doped Mn ferrite depicted better high frequency and SFD response as compared to Mn ferrite and REs doped Mn ferrites. The coercivity of all these pure Mn ferrite and rare earth's substituted Mn ferrites (425–246 Oe) was higher as compared to the pure Mn and yttrium substituted Mn ferrite (107–217 Oe. Therefore, it was suggested that Y doped Mn ferrite was more suitable candidate for switching, and high frequency absorption applications in microwave regime.     

Role of Nd-Ni on structural,spectral and dielectric properties of strontium-barium based nano-sized X-type ferrites

The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu_2?xNi_xNd_yFe_28?yO₄₆ (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd³⁺) as compared to (Fe³⁺), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (ų). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm^?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd³⁺ ions at octahedral site impedes the valence alternation of Fe³⁺; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)^?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc).     

Strength of pure alumina ceramics above 1 GPa

Up to now, commercially available alumina ceramics were claimed to have strength between 400 and 550 MPa. However, our study shows strength ~ 2 times higher for commercially available alumina than commonly believed. The average and characteristic strength, measured on 31 pure alumina ceramic discs by ball on three balls (B3B) test, were 1205 ± 93 MPa and 1257 MPa, respectively, with a Weibull modulus of m = 11.8. Tested specimens were in form of discs with a diameter of 5 mm and thickness 0.5 mm. The grain size distribution of the alumina is bimodal with an average grain size of ~ 850 nm measured at the surface. The fracture reveals a mixed transgranular / intergranular failure mode. To avoid incorporation of additional flaws, the discs were tested as sintered. The characteristic flexural strength measured in B3B was recalculated according to Weibull theory for standard 4-point bending bars of size 3 × 4 × 45 mm as bend 856 MPa. The measured strength of nearly 900 MPa shows the potential of strength for high purity alumina ceramics.     

Mullite-bonded SiC-whisker-reinforced SiC matrix composites: Preparation,characterization, and toughening mechanisms

A novel mullite-bonded SiC-whisker-reinforced SiC matrix composite (SiCw/SiC, SiC whisker-to-SiC powder mass ratio of 1:9) was designed and successfully prepared. Before preparing the composite, the inexpensive lab-made SiCw was first modified by an oxidation/leaching process and then coated with Al₂O₃. The kinetics results indicate that the oxidation process can be described by improved shrinking-cylinder models. The aspect ratio of SiCw improved after modification. Subsequently, raw materials with a SiC–SiO₂–Al₂O₃ triple-layered structure were obtained after the Al₂O₃-coating process and used as feedstocks during the subsequent hot-pressing sintering. Finally, the characterization of the composites indicates that the mullite-bonded sample performs better (relative density of 93.8?±?1.4%, flexural strength of 533.3?±?18.2?MPa, fracture toughness of 13.6?±?2.1?MPa?m^1/2, and Vickers hardness of 20.6?±?2.5?GPa) than the reference sample without the mullite interface. The improved toughness could essentially be attributed to the moderately strong interface bonding and effective load transfer effects of the mullite interface.