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      Volume 26, Issue 6

      October 2003,   pages  569-654

    • Anisotropic behaviour of semiconducting tin monosulphoselenide single crystals

      T H Patel Rajiv Vaidya S G Patel

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      Single crystals of ternary mixed compounds of group IV–VI in the form of a series, SnS𝑥Se1-𝑥 (where 𝑥 = 0, 0.25, 0.50, 0.75 and 1), have been grown using direct vapour transport technique. The grown crystals were characterized by the X-ray diffraction analysis for their structural parameter determination. All the grown crystals were found to be orthorhombic. The microstructure analysis of the grown crystals reveals their layered type growth mechanism. From the Hall effect measurements Hall mobility, Hall coefficient and carrier concentration were calculated with all crystals showing 𝑝-type nature. The d.c. electrical resistivity measurements perpendicular to 𝑐-axis (i.e. along the basal plane) in the temperature range 303–453 K were carried out for grown crystals using four-probe method. The d.c. electrical resistivity measurements parallel to 𝑐-axis (i.e. perpendicular to basal plane) in the temperature range 303–453 K were carried out for the same crystals. The electrical resistivity measurements showed an anisotropic behaviour of electrical resistivity for the grown crystals. The anisotropic behaviour and the effect of change in stoichiometric proportion of S and Se content on the electrical properties of single crystals of the series, SnS𝑥Se1-𝑥 (where 𝑥 = 0, 0.25, 0.50, 0.75 and 1), is presented systematically.

    • Studies on POM/graphite/Ekonol composites

      Chun-Guang Long Wen-Xian Liu Xia-Yu Wang

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      POM/graphite/Ekonol composites were prepared by the Torque Rheometer mixing and compression molding, and their hardness, compressive and impact strengths have been tested. The tribology behaviour was also investigated by the friction and wear experiment. The worn surface of the composite was studied by SEM technique, and on its basis, the wear mechanism was analysed. Results show that it was possible to prepare POM/graphite/Ekonol composites of high tribology performance and good mechanical properties by the Torque Rheometer mixing and compression molding. With the rise of Ekonol content, the wear mechanism was changed from adhesion plus plough to fatigue wear plus abrasive wear.

    • Role of PET in improving wear properties of PP in dry sliding condition

      Somit Neogi S A R Hashmi Navin Chand

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      The sliding wear of isotactic polypropylene (PP), polyethylene terephthalate (PET) and their blends was evaluated as a function of applied pressure and composition against a stainless steel counter face in dry condition. Wear rate decreases with the addition of PET in the blend. The wear was observed in two stages, the moderate wear and high wear while increasing the applied pressure on test samples. The addition of PET in PP helps in increasing the limit of moderate wear towards the high-pressure side. Microstructure and worn surfaces of samples were observed by scanning electron microscope. The wear phenomenon has been discussed based on wear losses and worn surfaces.

    • Nanoindentation and AFM studies of PECVD DLC and reactively sputtered Ti containing carbon films

      A Pauschitz J Schalko T Koch C Eisenmenger-Sittner S Kvasnica Manish Roy

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      Amorphous carbon film, also known as DLC film, is a promising material for tribological application. It is noted that properties relevant to tribological application change significantly depending on the method of preparation of these films. These properties are also altered by the composition of the films. In view of this, the objective of the present work is to compare the nanoindentation and atomic force microscopy (AFM) study of diamond like carbon (DLC) film obtained by plasma enhanced chemical vapour deposition (PECVD) with the Ti containing amorphous carbon (Ti/𝑎-C : H) film obtained by unbalanced magnetron sputter deposition (UMSD). Towards that purpose, DLC and Ti/𝑎-C : H films are deposited on silicon substrate by PECVD and UMSD processes, respectively. The microstructural features and the mechanical properties of these films are evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nanoindentation and by AFM. The results show that the PECVD DLC film has a higher elastic modulus, hardness and roughness than the UMSD Ti/𝑎-C : H film. It also has a lower pull off force than Ti containing amorphous carbon film.

    • Material characterization of ancient Indian copper

      A Srivastava R Balasubramaniam

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      A chalcolithic (2350–1800 BC) copper chisel from Balathal has been characterized by X-ray diffraction, microstructural and electrochemical methods. The surface patina was composed of sulfates and oxysulfates in the outer layers while the inner layers were rich in copper oxides. The chisel exhibited smaller grain sizes near two of the surfaces while the structure in the interior was equiaxed. The deformed grains and inclusions near the surfaces and variation in the microhardness of the sample from different faces proved that the copper chisel was processed by cold deformation after initial casting of the square cross-section chisel. The electrochemical behaviour of chalcolithic Cu has been compared with that of a modern Cu sample by potentiodynamic polarization studies. The corrosion rate of chalcolithic Cu in aerated 3.5% NaCl solution was only marginally higher than that of modern Cu. The higher rate of corrosion has been attributed to the presence of second phase sulfide inclusions. The excellent condition of preservation of the 3800-year-old copper object, with no indications of stress corrosion cracking, suggests that pure copper or copper-based materials can be seriously considered as candidate canister materials for long-term underground storage of nuclear wastes in underground repositories.

    • Influence of degree of deformation in rolling on anneal hardening effect of a cast copper alloy

      Svetlana Nestorovic Desimir Markovic Ljubica Ivanic

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      This paper reports results of investigations carried out on a cast copper alloy containing 8 at.% Al. The alloy, and pure copper for the sake of comparison, were subjected to cold rolling with a final reduction of 30, 50 or 70%.

      The cold rolled copper and copper alloy samples were isochronally and isothermally annealed up to the recrystallization temperature. The hardness, strength and electrical conductivity were measured and X-ray and DSC analyses performed.

      Anneal hardening effect was observed in the alloy in the temperature range 180–300°C, followed by an increase in the electrical conductivity. The amount of strengthening increases with increasing degree of prior cold work. The X-ray analysis shows a change in the lattice parameter during annealing when anneal hardening effect was observed. The DSC analysis shows the exothermic character of this effect.

    • Corrosion of reinforcement induced by environment containing chloride and carbon dioxide

      Vladimír Živica

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      Reinforced concrete structures during their exploitation may be exposed to the common action of carbonation and chlorides causing corrosion of steel reinforcement. Therefore, the related data seem to be interesting and important when the evaluation of the service life of the structures is the object of interest. This fact was a motivation for the present experimental study on the sequence of action of chloride solutions and carbonation of the embedding concrete. The results obtained show that carbonation of concrete foregoing the action of chloride solutions may intensify the process of corrosion of steel reinforcement in comparison to the converse sequence of the action of mentioned media. At the same time the natrium chloride solution has been shown as a more aggressive medium opposite to the calcium and magnesium chloride solutions.

    • Corrosion behaviour of amorphous Ti48Cu52, Ti50Cu50 and Ti60Ni40 alloys investigated by potentiodynamic polarization method

      A Dhawan S Roychowdhury P K De S K Sharma

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      Potentiodynamic polarization studies were carried out on virgin specimens of amorphous alloys Ti48Cu52, Ti50Cu50 and Ti60Ni40 in 0.5 M HNO3, 0.5 M H2SO4 and 0.5 M NaOH aqueous media at room temperature. The value of the corrosion current density (𝐼corr) was maximum for Ti48Cu52 alloy in all the three aqueous media as compared to the remaining two alloys. The value of 𝐼corr for the alloy Ti48Cu52 was maximum (𝐼corr = 2.6 × 10-5 A/cm2) in 0.5 M H2SO4 and minimum (𝐼corr = 3.5 × 10-6 A/cm2) in 0.5 M NaOH aqueous solutions. In contrast, the alloy Ti60Ni40 exhibited the least corrosion current density in 0.5 M HNO3 (𝐼corr = 4.0 × 10-7 A/cm2) and in 0.5 M NaOH (𝐼corr = 5.5 × 10-7 A/cm2) aqueous media as compared to those for Ti–Cu alloys, while its value in 0.5 M H2SO4 was comparable to that for Ti50Cu50. It is suggested that the alloy Ti60Ni40 is more corrosion resistant than the alloys Ti48Cu52 and Ti50Cu50 in all the three aqueous media.

    • Space charge limited conduction in CdSe thin films

      Pradip Kr Kalita B K Sarma H L Das

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      The current (𝐼)–voltage (𝑉) characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 Å and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study of 𝐼–𝑉 curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage (𝑉𝑡) from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the ln 𝐼 vs 103/T plots are found to be within 0.60–0.37 eV. Using the relevant SCLC theory, the carrier concentration, 𝑛0, total trap concentration, 𝑁t, and the ratio of free charge to trapped charge, 𝜃 , have been calculated and correlated with ambient temperature and intensity of illumination.

    • Dielectric properties of Na1–𝑥K$_x$NbO3 in orthorhombic phase

      Vijendra Lingwal B S Semwal N S Panwar

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      Pellets of ceramic, Na1–𝑥K𝑥NbO3 (𝑥 = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz–1 MHz, and in the temperature range from 50–250°C for 𝑥 = 0.2 and 0.5,and between 50 and 480°C for 𝑥 = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.

    • Orthorhombic rational approximants for decagonal quasicrystals

      S Ranganathan Anandh Subramaniam

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      An important exercise in the study of rational approximants is to derive their metric, especially in relation to the corresponding quasicrystal or the underlying clusters. Kuo’s model has been the widely accepted model to calculate the metric of the decagonal approximants. Using an alternate model, the metric of the approximants and other complex structures with the icosahedral cluster are explained elsewhere. In this work a comparison is made between the two models bringing out their equivalence. Further, using the concept of average lattices, a modified model is proposed.

    • Synthesis and characterization of conducting poly (1-aminonaphthalene), poly (2-aminonaphthalene) and poly (aniline-co-1-aminonaphthalene)

      Bidhan C Roy Maya Dutta Gupta Leena Bhowmik Jayanta K Ray

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      Poly (1&2)-aminonaphthalene and poly (aniline-co-1-aminonaphthalene) have been synthesized in high yields by chemical oxidative polymerization method. The polymers are soluble in polar solvents such as DMSO, NMP etc. In PNA-2 as head-to-tail coupling cannot occur, the electrical conductivity is lower than PNA-1. The copolymer exhibits distinct morphology, higher viscosity, characteristic exciton peak, appreciable thermal stability and electrical conductivity compared to PNA-1.

    • Optical properties of lead–bismuth cuprous glasses

      P T Deshmukh D K Burghate V S Deogaonkar S P Yawale S V Pakade

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      The optical transmission and absorption spectra in UV–VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO)𝑥(PbO)50–𝑥(Bi2O3)50 (𝑥 = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (𝛼), optical energy gap (𝐸opt), refractive index (𝑛D), optical dielectric constant ($\varepsilon_{\infty}^{′}$), measure of extent of band tailing (𝛥 𝐸), constant (𝛽) and ratio of carrier concentration to the effective mass (𝑁/𝑚*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.

    • Modified technique of using conventional slider boat for liquid phase epitaxy of silicon for solar cell application

      D Majumdar S Chatterjee U Gangopadhyay H Saha

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      Epitaxial layers of silicon are grown on single crystal Si-substrate from a solution of silicon in indium using conventional graphite slider boat technique. The important problems of natural convection due to lower density of silicon compared to indium, poor wetting of substrate due to high angle of contact of indium solution on silicon substrate resulting in poor nucleation, melt removal from the growth substrate and saturation wafer associated with LPE in this technique are practically eliminated using sandwich method with simple modifications of the boat and the method of growth. Some experimental studies on the effect of different surface preparations of growth substrate are also reported. Growth results are shown and discussed. Further, improvization of slider boat to facilitate better study of growth parameters is suggested in the line of modification already carried out.

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