D. Arivuoli

Size and shape dependence on melting temperature of gallium nitride nanoparticles

The study of variation of the size and shape effect on the melting property of gallium nitride nanoparticles with their spherical and cylindrical geometrical feature is theoretically explored. A numerical thermodynamical model has been devoted for the study. A comparative investigation is made between the two shapes, at the range of ∼3 nm dia. The cylindrical GaN nanoparticles, whose melting point has been reported to decrease with decreasing particle radius, become larger than spherical-shaped nanoparticles. The melting temperature obtained in the present study is in line with the function of radius of curvature.

In vitro corrosion behaviour of plasma nitrided Ti–6Al–7Nb orthopaedic alloy in Hanks solution

Abstract Titanium alloy (Ti–6Al–7Nb) used for orthopaedic applications was nitrided using a conventional dc plasmatechnique. Load-dependent microhardness measurements exhibit a hardness of 2087 Hv at 25 g load for the alloy nitrided at 900 8C for 8 h. Cyclic polarization measurement in Hanks solution show maximum corrosion rate and minimum areaof repassivation for the alloy nitrided for 8 h at 900 8C. Electrochemical impedance measurements show an increase in charge transfer resistance and decrease in double layer capacitance when compared to untreated alloy.

Microhardness studies of doped and undoped strontium tartrate tetrahydrate single crystals

The study of the microhardness of undoped and doped crystals and the way in which this parameter is connected with the dislocation density is of great interest for transducer applications involving mechanical vibrations [1, 2]. Microhardness gives information about the deformation resistance near the surface, anisotropy in the crystals, evidence for multiphase in the crystals, etc. Tartrates of calcium and strontium crystallize in the orthorhombic system with space group P212121 [3-5] showing ferroelectric properties [6]. Growth of these crystals doped with cobalt, nickel, etc., has drawn considerable interest recently [7, 8]. We carried out microhardness studies on both doped and undoped strontium tartrate tetrahydrate single crystals, using a diamond pyramid indentor. Crystals of strontium tartrate tetrahydrate were grown in silica gel medium [9, 10] in pure form and with chromium, iron, cobalt, nickel and cadmium as dopants. Sodium metasilicate gel of density 1.04 gem -3 was prepared and acidified with tartaric acid. The gel was allowed to set in test tubes of length 20 cm and diameter 2.5 cm. After gelation, 1 M aqueous solution of SrC12 was poured on top and allowed to diffuse into the gel. Strontium tartrate tetrahydrate crystals were found to grow in the gel. The best results were obtained for a gel density of 1.04 gcm -3, pH 4.2, 1 M tartaric acid and 1 ~ SrC12. To grow the doped crystals, an aqueous solution of the chloride of the dopant was used together with the outer reactant SrCI2. The detailed experimental procedure was reported elsewhere [11]. Doped and undoped crystals of strontium tartrate tetrahydrate of size about 8 m m × 4 mm × 2 mm (Fig. 1) were used for microhardness study. Before indentation the crystals were carefully lapped and polished to avoid surface effects which influence the hardness value strongly. Indentations were made using a Vickers pyramidal indentor for various loads from 5 to 100 g. The distance between two indentation points were more than three times the pit diagonal length, in order to avoid any mutual influence of the indentations. The diagonals of the impressions were measured using a Leitz Metallux II microscope with a calibrated ocular at magnification ×500. The measurements were made at room temperature and the indentation time was 10 s. To maintain uniformity between samples, the microhardness was measured on the dominant (1 1 0) face

Electrochemical behaviour and characterisation of plasma nitrided Ti-5Al-2Nb-1Ta orthopaedic alloy in Hanks solution

Abstract The present investigation deals with the study of the corrosion behaviour of glow discharge nitrided orthopaedic Ti–5Al–2Nb–1Ta alloy, using electrochemical techniques in Hanks solution. Potentiodynamic cyclic polarisation measurements show that the pit repassivation potential was higher in the case of nitrided alloy than the untreated alloy. The maximum pit repassivation potential was obtained for the alloy nitrided at 900 °C for 8 h. The electrochemical impedance spectroscopic (EIS) measurements showed an increased charge transfer resistance (Rct) and decreased double layer capacitance (Cdl) for nitrided alloys.

Growth of some group V-VI-VII compounds from the vapour

Crystals of bismuth oxyiodide (BiOI), bismuth oxychloride (BiOCI) and bismuth seleno-iodide (BiSeI) have been successfully grown from the vapour. The BiOCI platelets are transparent, while BiOI and BiSeI platelets exhibit mirror like faces with metallic lustre. These crystals are semiconductors with highly anisotropic properties due to the layer structure. Interesting morphological features of the crystals were studied by optical and scanning electron microscopy. Optical interferograms of BiOCI crystals were analysed. Dielectric studies of BiSel crystals showed a new phase transition at 410 K.

Growth of oxide crystals : effect of change in melt depth

Abstract The present investigation deals with the effect of the change in the melt depth in the crucible (during pulling) on the temperature distribution in the melt and on the critical crystal rotation rate, and hence on the growth of Bi12SiO20, Bi12GeO20, Bi4Si3O12 and TeO2 oxide crystals. The need to terminate the growth before a critical value of the melt depth is reached and the difficulty in getting good quality crystals beyond this point is reported.

Growth of bismuth silicon oxide and bismuth germanium oxide crystals by the Czochralski technique and their characterization

Photorefractive single crystals of bismuth silicon oxide (Bii2SiO2o) and bismuth germanium oxide (Bi12GeO2o) have been grown using the Czochralski technique. The experimental results are explained with the existing theoretical models. The grown crystals are characterized by x-ray, differential thermal analysis, scanning electron microscopy, IR transmission spectrum, and electron-probe microanalysis.

Some aspects of growth and characterisation of BSO and BGO crystals

Abstract Bismuth silicon oxide (BSO) and bismuth germanium oxide (BGO) crystals were grown by the Czochralski technique and the various parameters such as crystal rotation rate, pulling rate and growth temperature have been optimised for bubble free growth.

Microscopy observations of Cz-grown BSO (Bi12SiO20) crystals

Abstract The effect of the seed rotation rate on the morphology of Bi 12 SiO 20 (BSO) crystals has been investigated. The grown crystals were investigated by optical and scanning electron microscopy. The factors responsible for core formation, precipitates, microcracks and faceting are discussed.

Dendritic structures of brushite in silica gel

Abstract The results of growth of the brushite dendrites by the gel method are presented. The effect of impurities on the growth of the dendrites is also reported.