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  • Author or Editor: S. C. Mojumdar x
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Abstract

The information on heat of oxidation–reduction reactions is important for the heat balance and optimization of the autoclave design in the hydrometallurgical industry in ore processing. Pyrite (FeS2) is a gangue mineral that presents with nickel-containing pentlandite, and copper-containing chalcopyrite minerals. The presence of pyrite impacts to the overall heat of leaching process. This study has been performed on a differential scanning calorimeter (DSC80, Setaram) with a commercial mixing cell to study the thermal behaviour of pure pyrite FeS2 (Valdenegrillos, Spain) mineral particles during oxidative pressure leaching at 150 °C and partial oxygen pressure of 3.4 MPa. A calorimetric method for determining the enthalpy of leaching of sulphide minerals at high temperatures and oxygen pressures has been used to evaluate the enthalpies of oxidation of freshly ground pyrite and pyrite stored for a year in contact with air (stored pyrite) under conditions relevant to pressure oxidation operations. Ground pyrite stored over time has long since been known to result in greater heat evolution during oxidative leaching. A likely mechanism for this phenomenon was uncovered: formation of ferrous sulphate and sulphuric acid during storage in contact with air influencing greater heat evolution at the outset of the reaction. Two mass loss steps on TG curve of stored pyrite, attributed to the elimination of atmospheric moisture and H2O molecule from FeSO4·H2O, is absent on TG curve of freshly ground pyrite.

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Abstract

Thermal comfort is condition of an organism, when there is no sweating and the mean skin temperature is in the range from 32 to 34 °C (Hes, Measurement of comfort, What can textile III, 2009). Thermal comfort is closely connected with the following characteristics: thermal resistivity and thermal conductivity. Related properties are: resistance against the penetration of water vapor, air permeability, and porosity. The thermal resistivity R (W−1 K m2) and thermal conductivity K (W K−1 m−1) of knitted fabrics containing PP fiber were measured. Measurements were realized on three different types of devices. The experimental results were compared with simple mechanistic model for prediction of thermal conductivity K for textile structures.

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Synthesis growth and characterization of l-valine nickel (II) chloride

A novel semiorganic nonlinear optical crystal

Journal of Thermal Analysis and Calorimetry
Authors:
M. K. Sangeetha
,
M. Mariappan
,
G. Madhurambal
, and
S. C. Mojumdar

Abstract

A new semi organic nonlinear optical crystal, l-valine nickel chloride has been synthesized and good optical quality single crystals were grown by slow evaporation technique. The growth conditions of the crystals are studied and the grown crystals are confirmed by powder X-ray diffraction studies. The grown crystal was characterized by using powdered XRD, FT-IR, UV–Vis–NIR, EDAX, and TG–DTA. The crystalline nature and its various planes of reflections were observed by the powder XRD. The presence of various functional groups was confirmed by FT-IR spectroscopic technique. The UV–Vis–NIR spectrum indicates that the crystal has very good absorption in the entire visible and near IR region spectrum suggesting the suitability of the material for NLO applications. The decomposition temperatures and mass loss have been estimated from the thermogravimetric analysis.

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Abstract

Single crystal of tris thiourea chromium(III) sulphate was grown by slow evaporation technique at 303 K. The structural properties of the grown crystals were characterized by FTIR spectroscopy, UV spectroscopy and powder X-ray diffraction analysis. FTIR and UV spectra provide information about the presence of functional groups. Thermal analysis confirms that the crystal is thermally stable up to 163.48 °C. The TG curve presented a two-step mass loss on heating the compound at 0–1,200 °C.

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Abstract

Single crystal of bisthiourea iron(II) sulphate was grown by slow evaporation technique at 303 K. The structural properties of the grown crystals were characterized by FTIR spectroscopy, UV spectroscopy and powder X-ray diffraction. FTIR and UV spectra provide information about the presence of functional groups. Thermal analysis confirms the crystal is thermally stable up to 167.02 °C.

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Abstract

A single crystal of cinnamic acid–urea was grown by slow evaporation of methanol solution at room temperature. In this research, many analytical methods such as FTIR, second harmonic generation, NMR, and TG–DTA were used. The presence of title compound in the crystal lattice has been qualitatively determined by FTIR analysis. Thermal stability of the grown crystals was evaluated by TG-DTA. Incorporation of urea increases the thermal stability insuring the suitability of material for possible non-linear optical application up to 180 °C.

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Abstract

Mixed crystals of various proportions of urea thiourea were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized using thermogravimetry–differential thermal analysis (TG–DTA) and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two-stage mass loss between 175 and 750 °C. In this temperature range, DTA curves show exothermic peaks supporting the formulated decomposition pattern. The FTIR spectra show the characteristic absorption, vibration frequencies due to urea thiourea. Detailed structural analysis of the compound is under progress.

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Abstract

Thiourea Urea Zinc (II) Chloride (TUZC), a new semiorganic non-linear optical material has been synthesized. The solubility studies have been carried out at room temperature. Single crystals of different proportions of TUZC have been grown by slow evaporation of saturated aqueous solution at room temperature. The FTIR and UV spectral bands have been compared with urea, thiourea and bis Thiourea Zinc Chloride (BTZC). The TG curve showed a two steps mass loss on heating the compound between 30 and 800 °C corresponding to two exothermic DTA peaks at 181–183 and 250–252 ºC.

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Journal of Thermal Analysis and Calorimetry
Authors:
S. C. Mojumdar
,
G. Madhurambal
,
M. Mariappan
, and
B. Ravindran

Abstract

The induction period of various proportion of urea–thiourea zinc chloride crystal in water has been measured experimentally using the visual observation method. The induction period, which is inversely proportional to the nucleation rate, has been used to estimate the interfacial tension between the urea–thiourea zinc chloride and water; hence, the nucleation parameters like critical radius (r∗), number of molecules in the radius (r∗) and Gibbs free energy change for the formation of a critical nucleus (ΔG∗) have been calculated.

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