F. D. Gnanam

Synthesis of gamma ferric oxide by direct thermal decomposition of ferrous carbonate

Abstract Ferrous carbonate was precipitated from the reaction of ferrous sulfate and sodium carbonate in an aqueous medium. The precipitate was calcined at different eating rates (2, 5 and 10 °C/min, respectively) up to 500 °C and the iron oxides produced were found to be magnetic. X-ray diffraction studies indicated the presence of gamma ferric oxide as a major phase in all the cases. It was found that wet precipitates, faster heating rate and short residence time in the furnace produced gamma ferric oxides with better magnetic properties (coercivity of around 360 Oe and saturation magnetization of 64 emu/g). The effect of aging time of ferrous carbonate precipitates on the magnetic properties was also studied.

Electrical and magnetic properties of Ni0.8Zn0.2Fe2O4/silica composite prepared by sol-gel method

Ultrafine Ni0.8Zn0.2Fe2O4 particles dispersed in silica (SiO2) matrix are produced by sol-gel method. The powders were subjected to X-ray diffraction to confirm the formation of crystalline phases. The physical properties such as bulk density, true density, % of porosity and % of linear shrinkage were studied. The magnetic permeability as the function of frequency from 1 kHz to 13 MHz and temperatures from room temperature to 300°C were studied for samples sintered at temperature 1250°C. The AC electrical resistivity as the function of frequency and DC electrical resistivity as the function of temperature were studied. The AC-resistivity of the order of ≥105 Ωcm and DC-resistivity ≥108 Ωcm were obtained at room temperature. Microstructural features of sintered samples show the presence of ferrite grains of 1–2 μm size.

Dielectric behavior of Ni1−xZnxFe2O4 prepared by flash combustion technique

Abstract The frequency dependence of dielectric properties such as dielectric constant, e ′, and dielectric loss factor, tan δ , has been studied for a series of Ni 1− x Zn x Fe 2 O 4 ferrite samples prepared by flash combustion technique. The experimental results indicate that the dielectric constant values are quite low when compared to Ni–Zn ferrites prepared by conventional solid state mixing of oxides and it decreases with increasing the frequency. The results of the present study indicate that these ferrites are suitable for high frequency applications.

Growth and microhardness studies on NH4Sb3F10 single crystals

Abstract Ammonium fluoride NH 4 F and antimony triflouride SbF 3 from many stoichiometric compounds, such as NH 4 SbF 4 , (NH 4 ) 2 SbF 5 , NH 4 Sb 2 F 7 , (NH 4 ) 3 Sb 2 F 9 , NH 4 Sb 3 F 10 , etc. Since (NH 4 ) 2 SbF 5 exhibits superionic conductivity and undergoes phase transitions, an attempt has been made to grow other stoichiometric compounds of this group. In this report, we deal with the growth and microhardness studies of NH 4 Sb 3 F 10 single crystals. Crystals of size 60 × 25 × 35 mm 3 were grown in a period of two months. Microhardness studies have been carried out using a Vickers diamond pyramid indenter. To study the anisotropy of this material, specimens cut in different orientations such as (001), (010), (100), (101), (μ01) have been subject to microhardness studies. The results show strong anisotropy in the work-hardening coefficient for different orientations. This anisotropy is explained on the basis of a plastic deformation model.

Revert and direct type liesegang phenomenon of silver iodide

Abstract The experimental conditions for Liesegang phenomenon of silver iodide in agar gel columns, and particularly the transition from revert to direct type of periodic precipitations, have been investigated. The theoretically derived Mathurs spacing law, which suits both revert and direct type of Liesegangs rings, has been experimentally verified. An attempt has been made to explain the mechanism of revert and direct type and of the transition of revert to direct type of periodic precipitation on the basis of adsorption on the precipitated silver iodide and of flocculation. The dependence of the transition point on the concentrations of the outer and inner electrolytes has been studied. The time law of Morse and Pierce has been verified. The dependence of the velocity constant ( K = x n t n 1 2 ) on the concentrations of the outer and inner electrolytes has been studied.

Direct current resistivity studies of Ni1−xZnxFe2O4 prepared through flash combustion and citrate-gel decomposition techniques

Abstract The room temperature direct current (DC) resistivity of Ni 1− x Zn x Fe 2 O 4 ( x =0.2, 0.3, 0.4 and 0.5) prepared by the non-conventional flash combustion and citrate-gel decomposition techniques have been studied. The high resistivity ( ρ dc ) of the order of 10 9 Ω cm is obtained and it has been found that there is reduction in resistivity with increase in zinc content and sintering temperature. The high resistivity values observed in the present work confirm that the dielectric constant of the samples should be low.

Effect of medicinal plants on the crystallization of cholesterol

Abstract One of the least desirable calcifications in the human body is the mineral deposition in atherosclerosis plaques. These plaques principally consist of lipids such as cholesterol, cholesteryl esters, phospholipids and triglycerides. Chemical analysis of advanced plaques have shown the presence of considerable amounts of free cholesterol identified as cholesterol monohydrate crystals. Cholesterol has been crystallized in vitro. The extracts of some of the Indian medicinal plants detailed below were used as additives to study their effect on the crystallization behaviour of cholesterol. It has been found that many of the herbs have inhibitory effect on the crystallization such as nucleation, crystal size and habit modification. The inhibitory effect of the plants are graded as Commiphora mughul > Aegle marmeleos > Cynoden dactylon > Musa paradisiaca > Polygala javana > Alphinia officinarum > Solanum trilobatum > Enicostemma lyssopifolium.

Growth of bismuth sulpho-iodide single crystals from vapour

Bismuth sulpho-iodide single crystals were grown from the vapour phase for various temperature gradients. When the temperature gradient was kept at 2° C cm−1 in a horizontal furnace a large polycrystalline boule was obtained. The boule consisted of thick platelets at the top and needles at the bottom. When the temperature gradient was decreased to 1° C cm−1 very good needles of length 2 cm and thickness varying from 0.5 to 2 mm were obtained. They grew as hollow needles in a vertical furnace. The grown crystals were of length 1.5 cm and thickness ranging from 0.5 to 1 mm.

Growth of antimony sulphoiodide in gel

Abstract The conditions for growing single crystals of SbSI in sodium silicate gel at room temperature have been investigated in detail. The SbSI crystals grow in the needle shape. The effect of pH on the growth of SbSI has also been discussed.

Growth and spectroscopic characterization of NdAl3(BO3)4 crystals grown using BaO-B2O3 flux

Caracterisation de NdAl 3 (BO 3 ) 4 par microanalyse par sonde electronique, spectrometrie IR et Raman