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  • Author or Editor: K. Chandra x
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Abstract  

Zinc(II), cadmium(II) and mercury(II) complexes of o-vanillin oxime have been synthesized and characterized by different physicochemical techniques. All the complexes have been subjected to non-isothermal decomposition studies in nitrogen atmosphere using thermogravimetry. The kinetic parameters for the decomposition of these complexes were evaluated using different methods and comparatively better results were obtained by these different methods. It has also been found that the decomposition processes of all these complexes follow first order kinetics.

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Abstract  

Transition metal dithiocarbamate complexes, [M(S2CN(C2H5)(CH2CH2OH)] (M=Co, Ni, Cu, Zn and Cd) have been prepared and characterized by elemental analysis and infrared spectra. Thermal decomposition of all the complexes occurs in two or three stages. The first stage in all the complexes is always fast with 65-70% mass loss. In all cases the end product is metal oxide except in the case of cobalt complex which gives Co metal as an end product. During decomposition of copper complex, first CuS is formed at ~300C which is converted into CuSO4 and finally CuO is formed. However, decomposition in helium atmosphere yields CuS. SEM studies of transition metal dithiocarbamates reveal needle shape crystalline phase at room temperature and formation of metal sulphide/oxide at higher temperatures. The activation energy varies in a large range of 33.8-188.3 kJ mol-1, being minimum for the Cu complex and maximum for the Zn complex possibly due to d 10 configuration. In the case of Ni, Zn and Cd complexes the order of reaction is two suggesting bimolecular process involving intermolecular rearrangement. However, in other cases it is a unimolecular process. Large negative values of ΔS # for all the complexes suggest that the decomposition process involves rearrangement.

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Summary A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the & max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsakó, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (< 60 kJ mol-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).

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A new gall-inducing and lirellate lichenicolous fungus, Plectocarpon diedertzianum Y. Joshi, Upadhyay et Chandra, is described from Kumaun Himalayan regions of India colonising thallus of various parmelioid lichens (Flavoparmelia caperata, Myelochroa aurulenta, Parmotrema crinitum, P. melanothrix, P. reticulatum, Punctelia subrudecta). The new species is characterised by black, epruinose rounded to lirellate ascomata with a carbonised surface and a ±thalline pseudomargin, as well as a carbonised, sterile stromatic tissue, 4-spored asci and 3-septate hyaline ascospores.

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Abstract

Two aluminate spinel materials (ZnAl2O4 and NiAl2O4) were synthesized by the citrate precursor method. The citrate precursors consisting of coprecipitated citrates of Zn2+ or Ni2+ and aluminum were first subjected to thermal analysis (TG-DSC) for determining the optimum temperature for annealing. Two step decomposition was observed incorporating dehydration and formation of the aluminate. The second step gives an endo peak (−2937 J/g) at 356 °C in the DSC curve of the coprecipitated nickel(II) citrate–aluminum citrate gel in O2 atmosphere. Kinetic/mechanistic analysis of the TG data has also been carried out and values of E a, ΔS #, ΔG #, and A were approximated. On the basis of the findings, 450 °C has been chosen for annealing of the gels. Annealing has also been done at 650 °C for 1 h in muffle furnace in an attempt to obtain nanometric particles of aluminates (MAl2O4) {M = Ni, Zn} and to find out their magnetic properties which could render them useful for chemical sensing applications, etc. The TG-DSC curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N2 atmosphere. NiAl2O4 and ZnAl2O4 spinels (particle size 17 and 34 nm, respectively) are obtained in pure crystalline phase at 650 °C. ZnAl2O4 prepared this way shows coercivity values of 470 and 58.37 G and NiAl2O4, 107 and 23.24 G when annealed at 450 and 650 °C, respectively. ZnAl2O4 prepared by a polymer precursor method and annealed at 1000 °C, has earlier been reported to have coercivity value of 469 G. Thus, the citrate precursor method is good for the synthesis of ZnAl2O4, producing single phase nanocrystalline powder of high quality and crystallinity. The value of magnetization was found to be small in the present case for the NiAl2O4 spinel obtained at 450 °C.

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Journal of Thermal Analysis and Calorimetry
Authors: Gurdip Singh, A. K. Shrimal, Inder Pal Singh Kapoor, Chandra Prakash Singh, Dinesh Kumar and Manan S. Mudi

Abstract

Three transition metal perchlorate complexes of general formula [M(dah)2)](ClO4)2 (where M = Zn, Cu, and Ni; dah = 1,6-diaminohexane) have been prepared, and characterized by elemental analysis, infrared spectroscopy (IR), and gravimetric method. The thermal decomposition has been studied by thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). Kinetics parameters of their thermolysis were evaluated by model-fitting and isoconversional methods using isothermal TG data. Model-fitting method has given the single value of activation energy (E) whereas; isoconversional method yields a series of E values which vary with the extent of conversion. Further ignition delay of these complexes was measured to see the response toward rapid heating with varying amounts. The thermal stability of the complexes decreases in the order as: [Zn(dah)2)](ClO4)2 > [Cu(dah)2)](ClO4)2 > [Ni(dah)2)](ClO4)2

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