• Philip Kurian

      Articles written in Bulletin of Materials Science

    • Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

      M R Anantharaman K A Malini S Sindhu E M Mohammed S K Date S D Kulkarni P A Joy Philip Kurian

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      Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.

    • Evaluation of a.c. conductivity of rubber ferrite composites from dielectric measurements

      S Sindhu M R Anantharaman Bindu P Thampi K A Malini Philip Kurian

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      The effect of frequency, composition and temperature on the a.c. electrical conductivity were studied for the ceramic, Ni1–𝑥Zn𝑥Fe2O4, as well as the filler (Ni1–𝑥Zn𝑥Fe2O4) incorporated rubber ferrite composites (RFCs). Ni1–𝑥Zn𝑥Fe2O4 (where 𝑥 varies from 0 to 1 in steps of 0.2) were prepared by usual ceramic techniques. They were then incorporated into a butyl rubber matrix according to a specific recipe. The a.c. electrical conductivity (𝜎a.c.) calculations were carried out by using the data available from dielectric measurements and by employing a simple relationship. The a.c. conductivity values were found to be of the order of 10–3 S/m. Analysis of the results shows that 𝜎a.c. increases with increase of frequency and the change is same for both ceramic Ni1–𝑥Zn𝑥Fe2O4 and RFCs. 𝜎a.c. increases initially with the increase of zinc content and then decreases with increase of zinc. Same behaviour is observed for RFCs too. The dependence of 𝜎a.c. on the volume fraction of the magnetic filler was also studied and it was found that the a.c. conductivity of RFCs increases with increase of volume fraction of the magnetic filler. Temperature dependence of conductivity was studied for both ceramic and rubber ferrite composites. Conductivity shows a linear dependence with temperature in the case of ceramic samples.

    • Enhanced microactuation with magnetic field curing of magnetorheological elastomers based on iron–natural rubber nanocomposites

      M P Vasudevan P M Sudeep I A Al-Omari Philip Kurian P M Ajayan T N Narayanan M R Anantharaman

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      The incorporation of nanoparticles of iron in a natural rubber matrix leads to flexible magnetorheological (MR) materials. Rod-shaped MR elastomers based on natural rubber and nanosized iron have been moulded both with and without the application of an external magnetic field during curing. These MR elastomer rods and filler material were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. Magnetic properties were investigated by using vibrating sample magnetometry. Microactuation studies were carried out by employing a laser Doppler vibrometer. It is seen that microactuation of field cured samples have been enhanced by two times when compared with that of zero field cured samples. The effect of alignment of magnetic particles during field-assisted curing was also studied by using a dynamic mechanical analyzer. A plausible model is put forwarded to explain the observed enhancement of actuation for field cured samples.

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