SYNTHESIS, STRUCTURE AND CONDUCTIVITY OF NEW QUATERNARY CHALCOGENIDE SNBI4TE4SE4

The new quaternary chalcogenide SnBi4Te4Se4 has been prepared by reaction among the elements at 900-degrees-C. The material is then characterized by X-ray diffraction, diffuse reflectance spectroscopy, EDAX and electrical conductivity. The compound exhibits a lower resistivity in the range of 0.07 to 0. 14 OMEGA cm at room temperature and with a carrier concentration 1.5 to 2.36 x 10(16) cm-3. ac susceptibility against temperature shows a weak diamagnetic response over a large temperature interval from 70 to 93 K

Electrochemical studies of kerosene-pyrolysed carbon films

Polycrystalline thin films of conducting carbon are deposited on alumina substrates by the pyrolysis of kerosene vapour at 1000 degrees C for 2 h in argon atmosphere. Preliminary structural analysis is done by XRD, laser-Raman, FTIR and SEM studies. The electrochemical behaviour of as-grown conducting carbon films was investigated in various electrolytes at different pH and the performance was compared with that of platinum and glassy electrodes. The electrochemical window of the kerosene carbon electrode in 100 mM H2SO4 was found to be 2.91 V which is greater than that of glassy carbon (2.79 V) and platinum (2.02 V). Cyclic voltammetry reveals that Pt electrode has almost an equal tendency towards hydrogen and oxygen evolution, whereas glassy carbon favours hydrogen evolution and kerosene carbon favours oxygen evolution. It is suggested that the kerosene carbon electrode can be used as an oxygen electrode more efficiently. Unlike diamond films or glassy electrodes, kerosene carbon thin films are of low cost and good stability; they are also easy to grow on various ceramic substrates of any size. Moreover, these electrodes are very economical and promising for application in chlor-alkali industry

Synthesis of conducting fibers, nanotubes, and thin films of carbon from commercial kerosene

Commercial kerosene, commonly used as a cheap fuel for cooking or lighting in underdeveloped areas, has for the first time been found capable of producing conducting fibers, nanotubes, and thin films of carbon. The process of synthesis involves simple pyrolysis of kerosene vapor at 1000 degrees C in argon atmosphere. Various kinds of conducting fibers were obtained, viz., 6-7-cm-long straight fibers (70-75 mu m phi), flexible hair-like fibers (2 mu m phi), soft wool-like fibers (60-250 nm phi), tiny earthworm-like fibers (50 nm phi), rough bitter-gourd-like fibers (3 mu m phi), and uniform hollow fibers (nanotubes of inner and outer diameters of 30 and 80 nm, respectively). Formation of these kerosene-pyrolyzed products and their interrelation are discussed on the basis of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies. X-ray diffraction (XRD) analyses of these nanocarbon materials suggest that they have a novel structure, not matching that of known forms of carbon. This conclusion is supported by FTIR and laser-Raman analyses. Thin film of conducting carbon was found to possess an electrochemical potential window as wide as 2.91 V and was effectively used to electrolyte 30% brine solution at a current density of 300 mA cm(-2) at 3 V. It is suggested that the kerosene-pyrolyzed carbon electrodes can be used in the chloro-alkali industry. (C) 1999

Study of camphor-pyrolysed carbon electrode in a lithium rechargeable cell

Pure camphor pyrolysed at 900 degrees C fur 2 h in different gaseous environments yields graphite-like carbons which were used as a negative electrode in rechargeable carbon/Li cells. These cells were continuously cycled at a constant current of 300 mu A cm(-2) for 10-20 days and reversible Li+ intercalation capacities of 0.45-0.61 were observed. Kinetic analysis of such a cell was studied by complex impedance spectroscopy and current interruption. After initial irreversible passivation during the first discharge, fully reversible intercalation capacity was observed for subsequent charge-discharge cycles. This property makes the camphor-pyrolysed carbon (CPC) a promising electrode material for further investigation for making a rechargeable lithium battery. A CPC/Li cell model is proposed. The structural properties of the camphor-pyrolysed electrode material is discussed on the basis of SEM, TEM, XRD and FTIR analyses. (C) 2000 Elsevier Science S.A.

Lithium-ion intercalation into carbons derived from pyrolysis of camphor

Carbon electrodes prepared from the pyrolysis of camphor at 1000 degrees C in argon atmosphere have been found to facilitate Li-ion intercalation similar to that observed with carbons generally prepared at temperatures well above 2000 degrees C. An irreversible intercalation capacity of these carbon/lithium half cells during the initial discharge was measured to be 0.34, after which fully reversible Li-ion intercalation takes place right from the 1st to the 20th charge-discharge cycle, with a constant intercalation capacity of 0.61. Camphor-pyrolyzed carbon thus appears as a promising candidate for investigation as a lithium battery electrode material

Carbon fibers from kerosene

Different kinds of carbon fibers (3 - 4 mu m phi) were grown from the pyrolysis of commercial kerosene at 1000 degrees C for 2 h in argon atmosphere. These products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) analyses. Kerosene-pyrolyzed fibers differ from those obtained from other precursors. To our knowledge, this is the first time that (i) carbon fibers are produced from kerosene and (ii) conducting carbon fibers as long as 7 cm are produced from the pyrolysis of any hydrocarbon. The method is very simple and inexpensive, compared with conventional techniques for carbon fiber fabrication

Semiconducting carbon films from a natural source: camphor

Thin films of carbon have been grown on alumina substrates by the pyrolysis of camphor at 900 degrees C for 2h in an argon atmosphere, followed by sintering for various time periods. The effect of sintering time on the surface morphology, conductivity, carrier concentration, mobility and bandgap of camphor-pyrolyzed films is discussed. Structural characterizations are performed on the basis of XRD and SEM analyses. Electrical conductivity measurements of these films, as a function of temperature, suggest them to be semiconductors. Hall-effect study of the as-grown films shows their carrier concentrations to be of the order of 10(17) cm(-3). The Hall mobilities of these films are found to vary from 1702 to 10263 cm(2) V-1 s(-1). The thermal bandgaps of these films are found to decrease with increasing sintering time. Thus, by controlled sintering of camphor-pyrolyzed carbon films, it is possible to obtain a semiconductor with the desired bandgap. Therefore, camphor-pyrolyzed semiconducting carbon films seem to be a promising material to develop a photovoltaic solar cell. (C) 1999 Elsevier Science S.A. All rights reserved

Evaluating the thermal damage resistance of graphene/carbon nanotube hybrid composite coatings

We study laser irradiation behavior of multiwalled carbon nanotubes (MWCNT) and chemically modified graphene (rGO)-composite spray coatings for use as a thermal absorber material for high-power laser calorimeters. Spray coatings on aluminum test coupon were exposed to increasing laser irradiance for extended exposure times to quantify their damage threshold and optical absorbance. The coatings, prepared at varying mass % of MWCNTs in rGO, demonstrated significantly higher damage threshold values at 2.5 kW laser power at 10.6 μm wavelength than carbon paint or MWCNTs alone. Electron microscopy and Raman spectroscopy of irradiated specimens show that the coating prepared at 50% CNT loading endure at least 2 kW.cmˉ² for 10 seconds without significant damage. The improved damage resistance is attributed to the unique structure of the composite in which the MWCNTs act as an efficient absorber of laser light while the much larger rGO sheets surrounding them, dissipate the heat over a wider area