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

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 (sa.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 sa.c. increases with increase of frequency and the change is same for both ceramic Ni1–xZnxFe2O4 and RFCs. sa.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 sa.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

Processability, hardness, andmagnetic properties of rubber ferrite composites containingmanganese zinc ferrites

Rubber ferrite composites have the unique advantage of mouldability, which is not easily obtainable using ceramic magnetic materials. The incorporation of mixed ferrites in appropriate weight ratios into the rubber matrix not only modi es the dielectric properties of the composite but also imparts magnetic properties to it. Mixed ferrites belonging to the series of Mn(1 – x )Znx Fe2O4 have been synthesised with diVerent values of x in steps of 0·2, using conventional ceramic processing techniques. Rubber ferrite composites were prepared by the incorporation of these pre-characterised polycrystallineMn(1 – x )Znx Fe2O4 ceramics into a natural rubber matrix at diVerent loadings according to a speci c recipe. The processability of these elastomers was determined by investigating their cure characteristics. The magnetic properties of the ceramic llers as well as of the rubber ferrite composites were evaluated and the results were correlated. Studies of the magnetic properties of these rubber ferrite composites indicate that the magnetisation increases with loading of the ller without changing the coercive eld. The hardness of these composites shows a steady increase with the loading of the magnetic llers. The evaluation of hardness andmagnetic characteristics indicates that composites with optimummagnetisation and almost minimum stiVness can be achieved with a maximum loading of 120 phr of the ller at x=0·4. From the data on the magnetisation of the composites, a simple relationship connecting the magnetisation of the rubber ferrite composite and the ller was formulated. This can be used to synthesise rubber ferrite composites with predetermined magnetic properties

Spectroscopic and photoluminescence studies on optically transparent magnetic nanocomposites based on sol–gel glass: Fe3O4

Sol–gel glasses with Fe3O4 nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated in the porous network of silica resulting in nanocomposites having both optical and magnetic properties. Spectroscopic and photoluminescence studies indicated that Fe3O4 nanocrystals are embedded in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The optical absorption edge of the composites red shifted with increasing concentration of Fe3O4 in the silica matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe3O4 except that the intensity of the peak is decreased. The unique combinations of magnetic and optical properties are appealing for magneto–optical applications.

On the dielectric dispersion and absorption in nanosized manganese zinc mixed ferrites

The temperature and frequency dependence of dielectric permittivity and dielectric loss of nanosized Mn1−xZnxFe2O4 (for x = 0, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The impact of zinc substitution on the dielectric properties of the mixed ferrite is elucidated. Strong dielectric dispersion and broad relaxation were exhibited by Mn1−xZnxFe2O4. The variation of dielectric relaxation time with temperature suggests the involvement of multiple relaxation processes. Cole–Cole plots were employed as an effective tool for studying the observed phenomenon. The activation energies were calculated from relaxation peaks and Cole–Cole plots and found to be consistent with each other and indicative of a polaron conduction

Dielectric andmechanical properties of rubber ferrite composites

Rubber ferrite composites (RFCs) containing powdered nickel zinc ferrite (Ni1 – xZnxFe2O4 ) in a natural rubber matrix have been prepared and their mechanical and dielectric properties have been evaluated. Variations in the relative permittivity of both the ferrite ceramics and RFCs have been studied over a range of frequencies, ceramic compositions, ceramic ller loadings, and temperatures, and the results have been correlated. Appropriate mixture equations have been formulated to calculate the dielectric permittivity of the composite from the dielectric permittivity of its constituents. Values calculated using these equations have been compared with experimental data on relative permittivity, and the two have been found to be in good agreement. In the present investigationit was also observed that for x=0·4 and for the maximum ferrite loading, the composite sample exhibits maximum magnetisation and optimum exibility

A microwave absorber based on strontium ferrite–carbon black–nitrile rubber for S and X-band applications

Flexible and thin single layer microwave absorbers based on strontium ferrite–carbon black–nitrile rubber composites have been fabricated employing a specific recipe and their reflection loss characteristics were studied in the S (2–4 GHz) and X-bands (8–12 GHz). The incorporation of carbon black not only reinforces the rubber by improving the mechanical properties of the composite but also modifies the dielectric permittivity of the composite. Strontium ferrite when impregnated into a rubber matrix imparts the required magnetic permeability to the composite. The combination of strontium ferrite and carbon black can then be employed to tune the microwave absorption characteristics of the resulting composite. The complex dielectric permittivity and permeability were measured by employing a cavity perturbation technique. The microwave absorption characteristics of composites were modelled in that an electromagnetic wave incident normally on the metal terminated single layer absorber. The influence of filler volume fraction, frequency, absorber thickness on the bandwidth of absorption are discussed and correlated

Sequential interactions of Silver-silica nanocomposite (Ag-SiO2NC) with cell wall, metabolism and genetic stability of Psedomonas aeruginosa, a multiple antibiotic resistant bacterium

The study was carried out to understand the effect of silver-silica nanocomposite (Ag-SiO2NC) on the cell wall integrity, metabolism and genetic stability of Pseudomonas aeruginosa, a multiple drugresistant bacterium. Bacterial sensitivity towards antibiotics and Ag-SiO2NC was studied using standard disc diffusion and death rate assay, respectively. The effect of Ag-SiO2NC on cell wall integrity was monitored using SDS assay and fatty acid profile analysis while the effect on metabolism and genetic stability was assayed microscopically, using CTC viability staining and comet assay, respectively. P. aeruginosa was found to be resistant to β-lactamase, glycopeptidase, sulfonamide, quinolones, nitrofurantoin and macrolides classes of antibiotics. Complete mortality of the bacterium was achieved with 80 μgml-1 concentration of Ag-SiO2NC. The cell wall integrity reduced with increasing time and reached a plateau of 70 % in 110 min. Changes were also noticed in the proportion of fatty acids after the treatment. Inside the cytoplasm, a complete inhibition of electron transport system was achieved with 100 μgml-1 Ag-SiO2NC, followed by DNA breakage. The study thus demonstrates that Ag-SiO2NC invades the cytoplasm of the multiple drug-resistant P. aeruginosa by impinging upon the cell wall integrity and kills the cells by interfering with electron transport chain and the genetic stability