Department of Physics

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IIT Jodhpur

The paper describes the synthesis and characterisation of a composite of Fe-Co with copolymer of aniline formaldehyde by chemical processing. The resulting material was studied by XRD, X-ray microradiography, TEM, Mossbauer effect and magnetisation measurements. Uniform dispersion of spherical shaped nano-sized particles of spinel magnetic oxide in polymer matrix is inferred.

World University root node

Journal De Physique. IV : JP

Preparation and study of finely dispersed magnetic oxide in polymer matrix

Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively. Dehydration of CAH10 and C2AH8 (where H=H2O) occur - at 160-180°C and 200-280°C respectively. These two phases are unstable and ultimately get transformed to AH3 and C3AH6. Dehydration of AH3 and C3AH6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH3 and C2AH6 phases has been found to be 107.16 and 35.58 kJ mol-1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA2, ultimate strength has been attained in 14 days and in C12A7 in 1 day. DSC results have been correlated with the rate of strength developments. © 1996 Akadémiai Kiadó.

Journal of Thermal Analysis

Thermal analysis of hydrated calcium aluminates

Magnetic hysteresis and Barkhausen emissions have been measured for amorphous Fe82B10Si8 samples with positive magnetostriction of λs = 27 × 10-6 under tensile stress of up to 35 MPa. The root mean square voltage of the Barkhausen signal and the number of events per cycle increased monotonically with the applied stress. The results are explained in terms of a theory which includes a stress-dependent hysteresis model and a stochastic process model for the Barkhausen emissions.

Journal of Magnetism and Magnetic Materials

Effects of tensile stress on magnetic Barkhausen emissions in amorphous Fe-Si-B alloy

Conducting polymers are materials of recent origin. They are obtained by polymerisation of simple organic monomers and doping with electron acceptor or donor species and show conductivity ranging from that of a semiconductor to that of metal. These materials are now available with unique electronic and optical properties of metals and semiconductors in combination with the attractive mechanical and processable advantages of polymers. The field has progressed to a level of maturity consistent with a new set of opportunities to develop wide range of applications based upon conducting polymers as materials for industrial products. Examples include: static charge dissipation, EMI shielding, flexible light emitting diodes, transparent electrodes, batteries, gas sensors, gas separators, etc. Many of the conducting polymers and devices based on them are now available commercially.

Defence Science Journal

Conducting polymers : Emerging commercial materials

When materials possessing long range magnetic order (e.g., ferromagnetism, antiferromagnetism and ferrimagnetism) are reduced in size they can show unique properties as compared with bulk materials. One of the ways to reduce the size of the ordered magnetic regions is to isolate them inside non-magnetic species. The present paper describes in-situ room temperature synthesis of composites of fine magnetic particles in the polymer matrix of aniline-formaldehyde and their characterization using Mössbauer spectroscopy.

Proceedings of SPIE - The International Society for Optical Engineering

Synthesis and characterization of composites of fine magnetic particles with copolymers of aniline

A study of the magnetic Barkhausen effect emissions in 2605 CO amorphous alloys has been made. These emissions, which appear as magnetization pulses in the material, can be detected by a pick-up coil and analyzed in a variety of ways. In this study the Barkhausen effect signals were found to be dependent on both magnetic field and applied tensile stress. This dependence was in accordance with a theoretical model of the Barkhausen effect developed previously. The analysis and modeling of the resulting behavior was found to be particularly simple because amorphous alloys have no crystalline anisotropy, and therefore the effects of stress on the Barkhausen emissions were not masked by competing effects. © 1995 IEEE

IEEE Transactions on Magnetics

Effects of Tensile Stress on the Magnetic Barkhausen Effect in 2605 CO Amorphous Alloy

Phase transformation studies carried out on Mn-Al-C permanent magnet alloy employing DSC and electrical resistivity measurements, are reported and discussed. The transformation of the hexagonal Mn-Al phase (disordered and non-magnetic) to the ferromagnetic fct phase proceeds via the formation, in at least two stages, of the ordered orthorhombic phase. The activation energy for the formation of the fct phase is ≈34.65 kcal/mol. Microstructural changes occurring at various stages of the transformation are also studied. © 1995 Akadémiai Kiadó.

Journal of Thermal Analysis and Calorimetry

Phase transformation studies on Mn-Al-C alloy, by DSC and electrical resistivity measurements

The loss of ductility of a longitudinally welded steel pipe, brought about by hydrogen ingress during exposure to simulated sour environments, was investigated. The material was found to be very prone to hydrogen induced cracking (HIC). The presence of hydrogen-induced cracks were not necessarily detrimental to the ductility as demonstrated by ex-situ straining. It was concluded that mobile lattice hydrogen was responsible for ductile loss, while trapped hydrogen was responsible for HIC. © 1995.

Corrosion Science

Investigation on the mechanical degradation of a steel line pipe due to hydrogen ingress during exposure to a simulated sour environment

Magnetic hysteresis and micromagnetic Barkhausen parameters were measured in base and weld metals of a service exposed CrMo steel. Although the coercivity was higher in the welds, the difference in hysteresis parameters between welds and base metals was small. Hence, hysteresis parameters were not suitable to distinguish service exposed weld and base metals. However, a significant variation in Barkhausen activity was most prominent at low magnetizing fields. The results of this study have been correlated with the microstructure of the samples. © 1995.

NDT and E International

Nondestructive magnetic measurements in weld and base metals of service exposed CrMo steel

The magnetic properties of a process heater tube were determined to evaluate the structural integrity of its use in the oil industry. Carbon diffusion inside the tube during processing of petroleum is a cause of concern in the oil industry because it leads to brittle fracture. Both magnetic hysteresis and magneto-acoustic emission (MAE) parameters were determined for three specimens made from virgin, laboratory-aged and service-exposed materials. It was expected that the coercivlty would be a good damage parameter by which to assess the servie-exposed material because it increased with carbon concentration. However, the observed insignificant difference in coercivity between service-exposed material and the virgin one ruled out the possibility of using coercivity as a suitable damage parameter. The present study indicated that saturation induction could be used to find the extent of carbon deposition inside the material. The RMS voltage (Kins) of the MAE signal signal at low field was found to be higher in the laboratory-aged specimen due to greater interparticle distances which allowed domain walls to move longer distances before encountering a pinning centre. At high field, Vms in the virgin specimen was found to be higher than that in laboratory-aged and service-exposed materials. That was attributed to the presence of higher anisotropy in the virgin sample, originating from the metallurgical processing. © 1995 IOP Publishing Ltd.