• Volume 27, Issue 4

August 2004,   pages  323-394

• Growth features of ammonium hydrogen 𝑑-tartrate single crystals

Ammonium hydrogen 𝑑-tartrate (𝑑-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail.

• On the growth of calcium tartrate tetrahydrate single crystals

Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride. The role played by formate–formic acid on the growth of crystals is discussed. The grown crystals were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction analysis (XRD), microhardness measurement, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA). The results obtained are compared with the previous work.

• Bridgman growth and defects of Nd3+ : Sr3Ga2Ge4O14 laser crystals

Nd3+ : Sr3Ga2Ge4O14 crystals have been grown by the modified Bridgman method. The growth defects, such as striations, scattering particles and dislocations were investigated. Some featherlike striations were observed in as-grown crystals. EPMA analysis suggested that these inclusions were caused by the segregation of Nd2O3 from the melt. Chemical etching results showed that the dislocation density was in the range of 103 ∼ 105/cm2.

• X-ray analysis of 2-aniline benzo(2,3-𝑏) cyclopentane-1,3-dione

The molecular and crystal structure of 2-aniline benzo(2,3-𝑏) cyclopentane-1,3-dione has been determined by X-ray crystallographic techniques. This compound crystallizes in the orthorhombic space group 𝑃212121 with unit cell parameters: 𝑎 = 5.467(1), 𝑏 = 10.657(3), 𝑐 = 19.602(6) Å; 𝑉 = 1142.01(5) Å3, 𝑍 = 4. The crystal structure has been resolved up to an 𝑅-factor 0.050 for 1129 reflections. All the three rings in the structure are planar. However, the dihedral angle between the phenyl ring and the moiety comprising of a five-membered and six-membered ring is 92.4°. The oxygen atom O1 acts as a trifurcated acceptor and is involved in the formation of three intermolecular interactions.

• Corrosion behaviour, microstructure and phase transitions of Zn-based alloys

This paper is aimed at investigating the corrosion behaviour, microstructure and phase transitions of Zn-based alloys with different compositions. The corrosion tests are carried out both in acidic medium using 1 N HCl solution and in temperature dependence of thermogravimetric analysis (TGA). In the two different media, in particular, the corrosion behaviour of Zn-based alloys with respect to Al and Si contents is examined, and microstructure in acidic and TGA and phase transformations in TGA are also studied. Corrosion mechanism in TGA is also examined in terms of oxidation parameters and activation energies. The study reveals that corrosion behaviour of Zn-based alloys in acidic medium shows sometimes an increase and sometimes a decrease with time due to Al content which assists in delaying the corrosion by forming a oxide layer on the surface of Zn-based alloys. This property does not appear in temperature dependence of TGA. Further, Si content appears to remain in main matrix without being affected by acidic solution. On the other hand, it is observed that in microstructure, AlO(Al2O3), ZnO oxides and Zn–Cu phase precipitations are formed in main matrix, grain boundaries and partially inside the grains.

• Oxidation behaviour of the near α-titanium alloy IMI 834

Oxidation behaviour of the near 𝛼-titanium alloy IMI 834 was investigated over a range of temperatures, from 600–800°C, in air. Specimens were solution-treated in the 𝛼 + 𝛽 and 𝛽 phase fields for 1 h and 1/2 h, respectively and cooled in air to room temperature. The solution treated samples were subjected to stabilization treatment at 700°C for 2 h, followed by cooling in air. Oxidation behaviour of these samples was studied from 600–800°C in air, for 50 h. The morphology of the scales formed was examined by SEM and the phases present in the scales were characterized by X-ray diffraction. While there was little oxidation at 600°C, the rate of oxidation increased at higher temperatures. In general, the rate of oxidation was found to be more in the 𝛼 + 𝛽 treated condition than that in the 𝛽 treated one. The results are discussed in terms of the characteristics of the oxide film formed under different conditions.

• Oxidative leaching of chromium from layered double hydroxides: Mechanistic studies

The layered double hydroxide (LDH) of Zn with Cr on treatment with a hypochlorite solution releases chromate ions as a result of oxidative leaching by a dissolution–reprecipitation mechanism. The residue is found to be 𝜀-Zn(OH)2. The LDH of Mg with Cr on the other hand is resistant to oxidative leaching. In contrast, a X-ray amorphous gel of the coprecipitated hydroxides of Mg and Cr yields chromate ions. These results suggest that the oxidation potential of Cr(III) in LDHs is determined by the nature of the divalent ion and the crystallinity of the phase while being unaffected by the nature of the intercalated anions.

• Low temperature Mössbauer studies on magnetic nanocomposites

Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of 𝛾-Fe2O3 of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of 𝛾-Fe2O3 in the matrix.

• Synthesis of Er3+ and Er3+ : Yb3+ doped sol–gel derived silica glass and studies on their optical properties

Er3+ and Er3+ : Yb3+ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol–gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er3+ doped samples clearly revealed the absorption due to Er3+ ions. On the other hand Yb3+ : Er3+ doped samples showed enhanced absorption due to ${}^{2}F_{7/2} \rightarrow {}^{2}F_{5/2}$ transition. The absorption and emission crosssection for ${}^{2}F_{7/2} \leftrightarrow {}^{2}F_{5/2}$ of Yb3+ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm-1. The 960 cm-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.

• Effective thermal conductivity of real two-phase systems using resistor model with ellipsoidal inclusions

A theoretical model has been developed for real two-phase system assuming linear flow of heat flux lines having ellipsoidal particles arranged in a three-dimensional cubic array. The arrangement has been divided into unit cells, each of which contains an ellipsoid. The resistor model has been applied to determine the effective thermal conductivity (ETC) of the unit cell. To take account of random packing of the phases, non-uniform shape of the particles and non-linear flow of heat flux lines in real systems, incorporating an empirical correction factor in place of physical porosity modifies an expression for ETC. An effort is made to correlate it in terms of the ratio of thermal conductivities of the constituents and the physical porosity. Theoretical expression so obtained has been tested on a large number of samples cited in the literature and found that the values predicted are quite close to the experimental results. Comparison of our model with different models cited in the literature has also been made.

• Stone fragmentation by ultrasound

The presence of kidney stone in the kidney causes discomfort to patients. Hence, removal of such stones is important which is commonly done these days, non-destructively, with lithotripters without surgery. Commercially, lithotripters like extra-corporeal shock wave lithotripters (ESWL) made by Siemens etc are in routine use. These methods are very cumbersome and expensive. Treatment of the patients also takes comparatively more time because of more number of sittings. Some delicate nerves and fibres in the surrounding areas of the stones present in the kidney are also damaged by high ultrasonic intensity used in such systems. In the present work, enhancement of the kidney stone fragmentation by using ultrasound is studied. The cavitation bubbles are found to implode faster, with more disintegration efficiency of the lithotripters, which give better treatment to the patients.

• Microstructure evolution and fracture behaviour for electron beam welding of Ti–6Al–4V

The effect of microstructural characteristics on fracture behaviour mechanism for electron beam welding of Ti–6Al–4V was investigated. The results indicated that the welded microstructure composed of coarse needle 𝛼 + 𝛽 phases presenting disordered and multidirectional short needle morphology to make fracture mechanism complex. The coarse grains in weld seam with microhardness 536 HV were easy to be fractured in the region where welding heat input was ≥ 68.8 kJ/m. There exists flat curves of Ti, Al and V, Fe concentration distribution fluctuation to cause microstructural amplitude-modulated decomposition to increase the joint ductility and cleavage strength. The uneven distribution of the partial micropores located at the interior of the specimen acting as crack initiation sites lead to non-linear branch propagating path. The 𝛼 + 𝛽 interlaced structure results in the fracture location near 𝛼/𝛽 interface. The existence of stacking fault structure caused pile-up of dislocation to produce micropores to be new fracture initiation sites.

• Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10-8 Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 1013 ions/cm2 and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.

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