Department of Physics

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Ferromagnetic properties of plastically deformed AISI 304ss have been studied using magnetic hysteresis and Barkhausen emissions methods. The present study has been concentrated on low volume fraction of martensite, i.e., below 58 pct, as compared to the available literature for a higher percentage of martensite. In measured materials, the coercivity increased with deformation and had a tendency to go toward saturation value. A linear increase in remanence with the deformation was observed. A large number of small amplitude of Barkhausen emissions were found at low percentage of martensite, indicating that magnetization rotation took place within a small region. However, large amplitude Barkhausen emissions were observed with the increase of deformations. Angular variation of Barkhausen emissions indicated the formation of rolling texture within the materials. A model has been proposed to explain the results. At the initial stage, small martensite clusters are formed, which grow with the deformation, and the intracluster exchange interaction becomes predominant. With the increase of deformation, martensite volume fraction increases. In this process, existing clusters grow and new clusters are formed. As a result, martensite clusters come closer and intercluster exchange interaction becomes important.

World University root node

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Ferromagnetic properties of deformation-induced martensite transformation in AISI 304 stainless steel

Low alloy steel such as 1.25Cr-0.50 Mo steel is widely used in thermal power plants, petro-chemical industries and fertiliser plants. In recent years considerable attention has been paid to estimate the remaining life of a service-exposed component for effective utilising such components beyond the design life. Although these steels are heat treated to obtain a stable microstructure, microstructural changes such as carbide coarsening, increasing inter lamella spacing, formation of more stable carbides, dissolution of carbides, etc. take place due to prolong service exposure at elevated temperatures. This paper describes the systematic investigation on microstructural changes, changes of composition on carbides and their effect on the magnetic Barkhausen emission parameters. The materials were heat-treated at different temperatures (500-700 °C) for various duration of time (0-1000 h) to get wide variation in microstructure. RMS voltage and pulse height distributions of Barkhausen emissions signal were calculated. A good correlation between MBE parameters and microstructural changes has been found. The study will be useful for the non-destructive evaluation of microstructural degradation of in-service 1.25Cr-0.5Mo steel structure. © 2003 Elsevier Ltd. All rights reserved.

NDT and E International

Magnetic Barkhausen emissions and microstructural degradation study in 1. 25 Cr-0.50 Mo steel during high temperature exposure

Multi-colour emitting doped ZnS nanocrystals surface capped with pyridine (P-ZnS) or polyvinyl pyrrolidone (PVP-ZnS) have been synthesized by wet chemical methods. The photoluminescence studies show that the dopant related emission from P-ZnS nanocrystals are caused by the energy transfer from band-to-band excitation of the host lattice. However, in the case of PVP capped ZnS, considerable enhancement in the emission intensity was observed and the corresponding excitation spectra appeared dramatically broadened due to the presence of multiple excitation bands with peak maxima at 235, 253, 260, 275, and 310 nm. The bands from 235 to 275 nm are assigned to the electronic transitions in the chemisorbed PVP molecules whereas the excitation maximum around 310 nm corresponds to the band-to-band transition within the nanocrystalline ZnS host. The presence of PVP related energy bands in the excitation spectrum indicates the process of energy transfer from the surface adsorbed PVP molecules to dopant centers in ZnS nanocrystals. This study brings out a heterogeneous sensitizer-activator relation between organic surface adsorbate and doped semiconducting nanocrystals. © 2003 Elsevier Ltd. All rights reserved.

Solid State Communications

Energy transfer from organic surface adsorbate-polyvinyl pyrrolidone molecules to luminescent centers in ZnS nanocrystals

Strange stars (ReSS) calculated from a realistic equation of state (EOS), that incorporate chiral symmetry restoration as well as deconfinement at high density [Phys. Lett. B 438 (1998) 123; Phys. Lett. B 447 (1999) 352, Addendum; Phys. Lett. B 467 (1999) 303, Erratum; Indian J. Phys. B 73 (1999) 377] show compact objects in the mass radius curve. We compare our calculations of incompressibility for this EOS with that of nuclear matter. One of the nuclear matter EOS has a continuous transition to ud-matter at about five times normal density. Another nuclear matter EOS incorporates density dependent coupling constants. From a look at the consequent velocity of sound, it is found that the transition to ud-matter seems necessary. © 2004 Elsevier B.V. All rights reserved.

Fulltext

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Incompressibility of strange matter

Low voltage ac electroluminescence from Cu+-Al3+ and Cu+-Al3+-Mn2+ doped ZnS nanophosphors was demonstrated. By controlling the defect chemistry and doping concentrations, the EL emission color was varied from blue to orange-red.

Applied Physics Letters

Multicolor electroluminescent devices using doped ZnS nanocrystals

The functional integral formalism is used to provide a unified treatment of the effect of squeezing of the bath and frequency modulation of the system-bath coupling on the decoherence and dissipation properties of an open quantum system. The system chosen is a standard one consisting of a particle in a harmonic oscillator potential interacting with a bath of harmonic oscillators by a coupling of the position-position kind. Using an Ohmic bath and the high-temperature limit, the coefficients of the master equation describing dissipation and decoherence are obtained and analyzed. © 2004 Elsevier B.V. All rights reserved.

Physica A: Statistical Mechanics and its Applications

Decoherence and dissipation of an open quantum system with a squeezed and frequency-modulated heat bath

We report on the laser ablation of Si in vacuum, and in the presence of helium ambient at 1 and 10 Torr, respectively. The silicon nanoparticles were deposited on silicon substrate at room temperature by ablating silicon wafer in ambient atmosphere of helium at 1 Torr. The mean cluster size ranging from 1.8 to 4.4 nm is observed depending on the laser intensity. Optical emission spectroscopy and images of the plume are used to study the spatial and temporal variation of the silicon plasma. The electron density, measured by the Stark-broadening of Si I transition 3p 21 S-4s 1 P 0 at 390.55 nm and temperature, assuming thermal equilibrium, were found to be 1.2 × 10 18 cm -3 and 2 eV, respectively. The temporal variation of Si I transition 3p 2 1 S-4s 1 P 0 at 390.55 nm showed a shift in peak position attributed to collisions at an early stage of plasma formation. The relative concentration of Si II/Si I estimated by using the Saha-Boltzmann relation showed abundance of Si I. Time resolved images of the plume were used to investigate the dynamics of the expanding plasma plume, estimating the vapor pressure, vapor temperature, velocity, and stopping distance of the plume. The photoluminescent spectra of the Si thin films showed three distinct emission bands at 2.7, 2.2 and 1.69 eV, the origin of these bands is attributed to defects and quantum confinement. © 2003 Elsevier B.V. All rights reserved.

Applied Surface Science

Emission spectroscopy of laser-ablated Si plasma related to nanoparticle formation

The effect of structural and surface morphological developments on the soft magnetic properties of Fe 71 Nb 3.7 Cu 1 Al 3 Mn 0.8 Si 13.5 B 7 alloy was investigated. AFM studies showed that the material, which was amorphous in the as-cast state indicated segregates in the form of Cu atoms seated within the holes in the surface topography. With an increase in annealing temperature, nucleation and subsequent growth of α-Fe phase from the adjoining matrix on these nucleating Cu atoms was manifested in the form of magnetic softening. At optimum temperature Si and Al dissolved from adjoining matrix on these α-Fe phase indicating relatively low surface roughness and ultrasoft magnetic properties. The correlation between the surface morphology and magnetic properties were explained by nucleation and growth model. At elevated temperatures formation of strongly magneto-crystalline anisotropic crystalline phases like Fe-borides and Fe 7 Nb 6 deteriorated the soft magnetic properties. The occurrence of these phases in the form of multiple protrusions increased surface roughness. © 2004 Elsevier B.V. All rights reserved.

AFM surface morphology and magnetic properties of nanocrystalline Fe 71 Nb 3.7 Cu 1 Al 3 Mn 0.8 Si 13.5 B 7 ribbons

The structural and magnetic properties of Fe62Co9.5Gd3.5Si10B15 alloy in as-spun and annealed states have been investigated. The presence of a nanocrystalline (Fe,Co)3Gd phase together with an amorphous phase in the as-spun ribbon was recognized. The primary crystallization of the amorphous phase occurred at 928 K. In spite of the presence of (Fe, Co)3Gd nanoparticles, the materials in the as-spun state exhibited a low coercivity of 2.74 A m-1 and the coercivity further reduced to 2.45 A m-1 after annealing at 773 K. The Curie temperature also increased with increasing annealing temperature. Excellent ac magnetic properties were also observed in the annealed specimen. The results indicate that the materials may be used for high frequency application. The good soft magnetic nature of the materials significantly deteriorated after annealing at temperatures above 823 K because of the precipitation of highly anisotropic B-rich phases.

Journal of Physics D: Applied Physics

Magnetic properties of melt-spun and annealed Fe62Co9.5Gd3.5Si10B15 alloy

Synthesis of nanoparticles of Ni-Zn ferrite dispersed in aniline formaldehyde copolymer using a room temperature route and the effect of heat treatment on these samples were studied using XRD, FTIR spectroscopy, 57Fe Mössbauer spectroscopy and TEM microscopy. The results show the formation of nanosized particles of Ni-Zn ferrite in the polymer matrix at room temperature. On pyrolysis, the Ni-Zn ferrite phase persists up to 500 °C. However, heating of composites to 700 °C results in the partial reduction of the spinel ferrite leading to the formation of Ni-Fe alloy under ambient conditions and complete reduction of the alloy on heating in inert atmosphere. © 2003 Elsevier B.V. All rights reserved.