• Volume 26, Issue 5

August 2003,   pages  461-568

• Preparation, characterization and dielectric behaviour of some yttrium doped strontium stannates

Samples of Sr$_{(1–3x/2)}$Y$_x$SnO3 are prepared by usual solid state reaction route. X-ray diffraction studies confirm the formation of single cubic perovskite single phase. The dielectric constant and dielectric loss at 1 kHz were measured in the temperature range from room temperature up to ≅ 150°C. The dielectric constant decreases and losses increase with increased yttrium content in the samples. The percentage porosity and unit cell parameters are also calculated for the samples.

• Performance characteristics of a gelled-electrolyte valve-regulated lead-acid battery

12 V/25 AH gelled-electrolyte valve-regulated lead-acid batteries have been assembled in-house and their performance studied in relation to the absorptive glass-microfibre valve-regulated and flooded-electrolyte counterparts at various discharge rates and temperatures between –40°C and 40°C. Although the performance of the gelled-electrolyte valve-regulated battery is similar to both the absorptive glass-microfibre valve-regulated and flooded-electrolyte lead-acid batteries at temperatures above 0°C, it is superior to both the flooded-electrolyte and absorptive glass-microfibre valve-regulated lead-acid batteries at temperatures between 0°C and -40°C. The latter characteristic is attractive for expanding the application regime of valve-regulated lead-acid batteries. The corrosion rate for the positive grids in the gelled-electrolyte is also lower than both the flooded-electrolyte and absorptive glass-microfibre configurations.

• Influence of 𝑤/𝑐 ratio on rate of chloride induced corrosion of steel reinforcement and its dependence on ambient temperature

The permeability of the embedding cement material for the rate of chloride induced corrosion when the ambient temperature is increased has found a dominant position. The importance of the given permeability in the process is based on the fact that it represents a factor conditioning the possibility of the escaping of the unambiguous reaction partners, oxygen and water vapour, from the system embedding cement material-steel, as the ambient temperature is increased. The resulting effect is a slowing down of the corrosion rate when the 𝑤/𝑐 ratio over the value 0.6 and the ambient temperature over the value 40°C are increased.

Due to the similarity of the chemism of the corrosion process of steel reinforcement, independent of the action of aggressive species, the found relationships are generally valid, e.g. for the corrosion due to carbonation.

• Effects of partial crystallinity and quenched-in defects on corrosion of a rapidly solidified Ti–Cu alloy

Rapid solidification by planar flow casting has been found to have introduced deficiencies, viz. partial crystallinity, air pockets and compositional difference in the ribbons of rapidly solidified Ti42.9-Cu57.1 alloy. In order to investigate the effects of these deficiencies on the corrosion of rapidly solidified Ti42.9-Cu57.1 alloy ribbons, electrochemical behaviour of alloy ribbons has been investigated in the acidic chloride environments at room temperature by taking into consideration each side of the alloy ribbon separately. The alloy displayed passivity followed by pitting corrosion. In the as-solidified condition, air pockets appear to be the most detrimental defect from the viewpoint of corrosion resistance of the alloy ribbons.

• Alloy design of ductile phosphoric iron: Ideas from archaeometallurgy

Alloy design criteria to produce ductile phosphoric irons have been proposed based on a detailed microstructural study of ancient Indian irons. The alloy design aims at avoiding phosphorus segregation to the grain boundaries by

1. soaking the phosphoric iron at high temperatures within the ferrite + austenite region to precipitate austenite allotriomorphs,

2. utilizing a critical amount of carbon to segregate to grain boundaries, and

3. precipitation of some of the phosphorus in solid solution in the ferrite matrix as fine coherent phosphide precipitates.

• A.c. susceptibility study of CaCl2 doped copper–zinc ferrite system

Polycrystalline soft ferrites, Zn$_x$ Cu$_{1–x}$ Fe2O4 (𝑥 = 0.30, 0.50, 0.70, 0.80 and 0.90), doped with controlled amount of calcium chloride (CaCl2) were prepared by standard ceramic route and studied for a.c. susceptibility. X-ray diffraction studies of the compositions reveal formation of single-phase cubic spinel. The values of lattice constant increase as doping percentage of CaCl2 increased from 0.01% to 0.05% and afterwards decrease slightly. The presence of chlorine ions is confirmed by absorption peak in far IR spectra near 650 cm-1 for all the samples. The variation of a.c. susceptibility with temperature shows the existence of single domain structure for 𝑥 = 0.3 and exhibits transition from single domain to multidomain structure with increased Ca2+ contents from 0.01 to 0.1%. The composition, 𝑥 = 0.5, shows multidomain structure independent of Ca2+ content. The samples for 𝑥 = 0.70, 0.80 and 0.90 show paramagnetic behaviour at and above room temperature.

• Development of low-power loss Mn–Zn ferrites using microwave sintering method

Microwave sintering (MS) method has been successfully used for densifying Mn–Zn ferrites used for high frequency applications. This method needs only a short time to obtain high density when compared to conventionally sintered (CS) Mn–Zn ferrites. The lowest power loss was also achieved at 100 kHz and 200 mT condition for the microwave sintered samples. Conductor-embedded ferrite transformers were constructed using CS and MS samples and output power, efficiency, and surface rise of temperature were measured at sinusoidal voltage of 25 V with frequency, 1 MHz. The efficiency and surface rise of temperature of transformer were found to be high and low, respectively.

• Mössbauer studies of Sn4+/Nb5+ substituted Mn–Zn ferrites

At room temperature, Mössbauer spectra of Sn4+/Nb5+ substituted Mn–Zn ferrites have been taken to understand the site occupancy of substituted ions. The results indicate that both the substituted ions occupy tetrahedral (A) site only at lower concentration of substitution while at higher concentration they occupy both tetrahedral and octahedral sites. At higher concentration of Nb substitution a doublet has been observed besides sextets. The possibility of canting existence on octahedral sites has been discussed. The observed variations of the hyperfine fields, isomer shift, line widths and B/A peak area ratio with the ferrite composition are interpreted.

• Mössbauer effect studies and X-ray diffraction analysis of cobalt ferrite prepared in powder form by thermal decomposition method

Cobalt ferrite (Co$_x$Fe$_{3–x}$O4) is prepared in powder form by thermal decomposition of iron and cobalt salts and is analysed by X-ray diffraction and Mössbauer spectroscopic techniques. The variation of Mössbauer parameters, lattice parameters and crystallite size of the products formed with variation in the composition of Fe and Co ratios are studied. The studies confirm the formation of nano-size cobalt ferrite particles with defect structure and it is found to be maximum for the Fe : Co = 60 : 40 ratio of the initial precursor oxides.

• Structural and magnetic properties of Co$_{1+y}$Sn$_y$Fe$_{2–2y–x}$Cr$_x$O4 ferrite system

The samples of the series Co$_{1+y}$Sn$_y$Fe$_{2–2y–x}$Cr$_x$O4 ferrites with 𝑥 = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 𝑦 = 0.05, were prepared by the usual double sintering ceramic technique. The single-phase spinel structure of the samples was confirmed by using X-ray diffractometry technique. The lattice parameter 𝑎’ with an accuracy of ± 0.002 Å were determined using Bragg peaks of XRD pattern. The lattice parameter 𝑎’ decreases with concentration, 𝑥, which is due to the difference in the ionic radii of Cr3+ and Fe3+ ions. The X-ray intensity calculations were carried out in order to determine the possible cation distribution amongst tetrahedral (A) and octahedral [B] sites. The X-ray intensity calculations show Cr3+ ions occupying B site. The saturation magnetization, $\sigma_{s}$, and magneton number, $n_B$ (the saturation magnetization per formula unit), measured at 300 K determined from high field hysteresis loop technique decrease with increase in concentration, 𝑥, suggesting a decrease in ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility measurements from room temperature to about 800 K exhibits almost normal ferrimagnetic behaviour and the Curie temperature, $T_C$ determined from a.c. susceptibility data decreases with increase in 𝑥.

• Heat-deproteinated xenogeneic bone from slaughterhouse waste: Physico-chemical properties

Xenogeneic bone procured from the slaughterhouse waste was deproteinated by heat treatment method intended for use as a bone substitute. The effect of heat treatment was investigated by thermal analysis and by physico-chemical methods such as X-ray powder diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. The heat treatment temperatures for the bovine bone samples were predetermined by thermogravimetric (TG) analysis. The XRD results revealed that the process of heat treatment promoted the crystallinity of bone samples, particularly at 700 and 900°C. There was no secondary phase transformation detected for heat-deproteinated bone except the presence of the hydroxyapatite (HA) phase, which indicated its phase purity even at a higher temperature. The FTIR spectra of raw bone and bone heated at 300°C indicated the presence of organic macromolecules whereas these disappeared in the samples heated at 500, 700 and 900°C, which suggested the removal of antigenic organic matters around 500°C. The same results were also confirmed quantitatively by calculating the amount of collagen using hydroxyproline estimation. There was no significant change in the TG-thermogram of bone heated at 500, 700 and 900°C, which indicated their thermal stability. These findings implied that the heat treated bone at 500°C had properties similar to carbonated HA with low crystallinity, while 700 and 900°C samples had the same with higher crystallinity. As low temperature treatment does not alter morphological and structural properties, we propose that the 500°C heat treated xenogeneic bone may act as an excellent osteogenic bone substitute.

• Charge dynamics in conducting polyaniline–metal oxalate composites

Polyaniline (Pani) and its metal oxalate composites (∼ 10 wt.%) of trivalent metal ions of Cr, Fe, Mn, Co and Al were synthesized by chemical oxidative polymerization technique with potassium perdisulphate oxidant in aqueous sulphuric acid medium. These materials were characterized by UV–VIS and EPR spectral techniques. Their d.c. electrical conductivities at room temperature and also as a function of temperature (307–453 K) were measured by four-probe technique. Presence of radical cation/polaron transition was indicated by UV–VIS absorption peak and EPR signals. Further, a close correlation existed between the conductivities and EPR parameters such as line width and peak ratio, which demonstrated that both mobile and fixed spins are involved in these composites. The dependence of conductivity on temperature, when analysed graphically by VRH, GB and TC mechanisms, pointed out that VRH is the predominant charge transport mechanism in these materials.

• Photoplastic effect in polycarbonate using microhardness measurements

Vickers microhardness indentation technique has been employed to detect the photoplastic effect in the transparent polycarbonate specimens in darkness and under mercury illumination. For low applied loads, the hardening of specimens under illumination confirms the positive photoplastic effect that causes illumination-induced increase of crosslinking (in polymer). For high applied loads the positive photoplastic effect decreases as the level of microhardness decreases.

• Kinetics of Ge20Se80–𝑥As𝑥 (𝑥 = 0, 5, 10, 15 and 20) in glass transition region

The results of differential scanning calorimetric (DSC) measurements on Ge20Se80–𝑥As𝑥 (𝑥 = 0, 5, 10, 15 and 20) system with the specific aim of investigating the effect of heating rate and composition on glass transition temperature have been discussed. The results indicate that the glass transition temperature (𝑇𝑔) is dependent both on the heating rate and composition. The glass transition activation energy (𝐸𝑡) and heat absorbed in glass transition region (𝛥𝐻) are higher for Ge20Se65As15 as compared to the values of other compositions of arsenic. An effort has also been made to develop an empirical model for the composition dependence of 𝛥𝐻. A good agreement has been observed between the experimental values and the results of model calculation.

• Crystallization study of Te–Bi–Se glasses

Crystallization studies are carried out under non-isothermal conditions with samples heated at several uniform rates. The dependence of the glass transition temperature (𝑇𝑔), the crystalline temperature (𝑇𝑐) and the peak temperature of crystallization (𝑇𝑝) on the composition and heating rate (𝛽) has been studied. For a memory/switching material, the thermal stability and ease of glass formation are of crucial importance. The glass transition temperature, 𝑇𝑔, increases slightly with the variation of Bi content. From the heating rate dependence of 𝑇𝑔, the activation energy for glass transition (𝐸𝑡) has been evaluated. The results are discussed on the basis of Kissinger’s approach and are interpreted using the chemically ordered network model (CONM).

• Devitrification of rapidly quenched Al–Cu–Ti amorphous alloys

X-ray diffraction, transmission electron microscopy and differential scanning calorimetry were carried out to study the transformation from amorphous to icosahedral/crystalline phases in the rapidly quenched Al50Cu45Ti5 and Al45Cu45Ti10 alloys. In the present investigation, we have studied the formation and stability of amorphous phase in Al50Cu45Ti5 and Al45Cu45Ti10 rapidly quenched alloys. The DSC curve shows a broad complex type of exothermic overlapping peaks (288–550°C) for Al50Cu45Ti5 and a well defined peak around 373°C for Al45Cu45Ti10 alloy. In the case of Al50Cu45Ti5 alloy amorphous to icosahedral phase transformation has been observed after annealing at 280°C for 73 h. Large dendritic growth of icosahedral phase along with 𝛼-Al phase has been found. Annealing of Al50Cu45Ti5 alloy at 400°C for 8 h results in formation of Al3Ti type phase. Al45Cu45Ti10 amorphous alloy is more stable in comparison to Al50Cu45Ti5 alloy and after annealing at 400°C for 8 h it also transforms to Al3Ti type phase. However, this alloy does not show amorphous to icosahedral phase transformation.

• Synthesis and mesomorphic behaviour of lithocholic acid derivatives

A series of liquid crystalline derivatives of lithocholic acid were prepared using simple chemical reactions involving the terminal functional group—hydroxyl at C-3 and/or carboxyl at C-24. Thus methyl -3-(3-carboxy propionyl) lithocholate (I), 3-(3-carboxy propionyl) lithocholic acid (II), 3-acetyl lithocholic acid (III), 3-propionyl lithocholic acid (IV), 3-benzoyl lithocholic acid (V), 3-(4-nitrobenzoyl) lithocholic acid (VI), 3-cinnamoyl lithocholic acid (VII), methyl-3-(4-nitrobenzoyl) lithocholate (VIII) and 1,4-bis [cholan-24-methoxy carbonyl-3-oxycarbonyl] butane (IX) were prepared in good yields and characterized by IR, NMR and polarizing optical microscopy. Compounds (I) and (IX) exhibited monotropic behaviour while the others were enantiotropic. Some of the compounds also showed a high tendency of super cooling. Compounds (V), (VI) and (IX) formed cholesteric phase while the remaining compounds displayed smectic phase.

• Linear heating system for measurement of thermoluminescence using 8031/51 microcontroller

A linear heating system is developed using a 8031/51 microcontroller for the measurement of thermoluminescence (TL) in alkali halides and other related compounds. This system also measures the temperature and the amount of light emitted by the sample for TL studies.

• # Bulletin of Materials Science

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