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Journal of Thermal Analysis and Calorimetry
Authors:
J. C. J. Bart
,
A. Bossi
,
P. Perissinoto
,
A. Castellan
, and
N. Giordano

The thermal degradation of H6TeO6 in air has been evaluated critically. Evidence is presented for a decomposition mechanism involving step-wise dehydration of H6TeO6 via non-stoichiometric amorphous solids to polymetatelluric acid and up to a composition corresponding to pyrotelluric acid. No morphological changes were observed during these structural variations and no evidence was found for the formation of allotelluric acid. Further dehydration is accompanied by reduction, which, depending upon the experimental conditions accounts for the considerable variety of results reported previously. Crystalline Te(VI)-Te(IV) oxides are obtained at about 550‡ from which TeO2 is formed by additional calcination at about 620‡.

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Journal of Thermal Analysis and Calorimetry
Authors:
S. Meenakshisundaram
,
S. Parthiban
,
G. Bhagavannarayana
,
G. Madhurambal
, and
S. Mojumdar

Abstract  

It was observed that the addition of a very small quantity (5·10−3 M L−1) of an organic solvent, benzene (C6H6) in the aqueous growth medium (pH ∼5.9) of tristhioureazinc(II)sulphate (ZTS) markedly influences the SHG efficiency. The measurements using Nd:YAG laser source reveal that second harmonic generation (SHG) conversion efficiency which is one of the most important nonlinear optical (NLO) properties is enhanced by benzene dopant by a factor of nearly 1.5 times. The crystalline perfection of the grown crystals was evaluated by high-resolution X-ray diffractometry (HRXRD). The full width at half maximum (FWHM) of the diffraction curve (which gives an estimate for the degree of crystalline perfection) for undoped and benzene doped specimen crystals are 26 and 15 arc sec, respectively. The reduction in FWHM due to the benzene solvent indicates the significant improvement in crystalline perfection. This very much suggests that the dissolution of trace impurities in the presence of benzene prevents the entry of impurities into the crystal lattice and at the same time enhances the growth promoting effect (GPE). Not much variation is observed in XRD, FTIR and TG-DTA of ZTS in the presence and absence of benzene in the aqueous growth medium.

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Abstract  

This paper presents a study for the preparation of CoxFe3−xO4 (x = 0.02, 0.2, 0.5, 0.8, 1.0, 1.1, 1.5) nanoparticles, starting from metal nitrates: Co(NO3)2·6H2O, Fe(NO3)3·9H2O and ethylene glycol (C2H6O2). By heating the solutions metal nitrates-ethylene glycol, the redox reaction took place between the anion NO3 and OH–(CH2)2–OH with formation of carboxylate anions. The resulted carboxylate anions reacted with Co(II) and Fe(III) cations to form coordinative compounds which are precursors for cobalt ferrite. XRD and magnetic measurements have evidenced the formation of cobalt ferrite for all studied molar ratios. The average diameter of the cobalt ferrite crystallites was estimated from XRD data and showed values in the range 10–20 nm. The crystallites size depends on the annealing temperature. The magnetization of the synthesized samples depends on the molar ratio Co/Fe and on the annealing temperature.

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Abstract  

The synthesis and characterization of lanthanide(III) citrates with stoichiometries 1:1 and 2:3; [LnL·xH2O] and [Ln2(LH)3·2H2O], Ln=La, Ce, Pr, Nd, Sm and Eu are reported. L stands for (C6O7H5)3− and LH for (C6O7H6)2−. Infrared absorption spectra of both series evidence coordination of carboxylate groups through symmetric bridges or chelation. X-ray powder patterns show the amorphous character of [LnL·xH2O]. The compounds [Ln2LH3·2H2O] are crystalline and isomorphous. Emission spectra of Eu compounds suggest C 2v symmetry for the coordination polyhedron of [LnL·xH2O] and C 4v for [Ln2(LH)3·2H2O]. Thermal analyses (TG-DTG-DTA) were carried out for both series. The thermal analysis patterns of the two series are quite different and both fit in a 4-step model of thermal decomposition, with lanthanide oxides as final products.

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Journal of Thermal Analysis and Calorimetry
Authors:
K. Kafarska
,
D. Czakis-Sulikowska
, and
W. Wolf

Abstract  

New metal(II) complexes with empirical formulae Co(ibup)2·4H2O, Cd(ibup)2·3H2O, Co(nap)2·H2O, Cd(nap)2·3H2O (where ibup=(CH3)2CHCH2C6H4CH(CH3COO) and nap=CH3O(C10H6)CH(CH3COO)) were isolated and investigated. The complexes were characterized by elemental analysis, molar conductance, IR spectroscopy and thermal decomposition. The thermal behavior was studied by TG, DTG, DTA methods under non-isothermal conditions in air atmosphere. The hydrated complexes lose water molecules in first step. All complexes decompose via intermediate products to corresponding metal oxides CoO and CdO. A coupled TG-MS system was used to detect the principal volatile products of thermolysis and fragmentation processes of Co(nap)2·H2O. The IR spectra of studied complexes revealed also absorption of the carboxylate group. Principal concern with the position of asymmetric, symmetric frequencies. The value of their separation allow to deduce about type of coordination these groups.

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Abstract  

It is proposed to use 14 MeV neutrons tagged by the associated particle neutron time-of-flight technique (APnTOF) to identify the fillers of unexploded ordnances (UXO) by characterizing their carbon, nitrogen and oxygen contents. To facilitate the design and construction of a prototype system, a preliminary simulation model was developed, using the Geant4 toolkit. This work established the toolkit environment for (a) generating tagged neutrons, (b) their transport and interactions within a sample to induce emission and detection of characteristic gamma-rays, and (c) 2D and 3D-image reconstruction of the interrogated object using the neutron and gamma-ray time-of-flight information. Using the modeling, this article demonstrates the novelty of the tagged-neutron approach for extracting useful signals with high signal-to-background discrimination of an object-of-interest from that of its environment. Simulations indicated that an UXO filled with the RDX explosive, hexogen (C3H6O6N6), can be identified to a depth of 20 cm when buried in soil.

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Abstract  

4-Chloro-2-methoxybenzoates of light lanthanides(III) were obtained as mono-, di-or trihydrates with metal to ligand ratio of 1:3 and general formula Ln(C8H6ClO3)3·nH2O, where n=1 for Ln=Ce, Pr, n=2 for Ln=Nd, Sm, Eu, Gd and n=3 for Ln=La. The complexes were characterized by elemental analysis, IR spectra, thermogravimetric studies, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical bidentate, chelating ligand. All complexes seem polycrystalline compounds. Their thermal stabilities were determined in air. When heated they dehydrate to form anhydrous salts which next are decomposed to the oxides of the respective metals. The solubilities of light lanthanide(III) 4-chloro-2-methoxybenzoates in water at 293 K are of the order of 10−5 mol dm−3. The magnetic moments were determined over the range of 77–300 K. They obey the Curie-Weiss law. The values of μeff calculated for all compounds are close to those obtained for Ln3+ by Hund and Van Vleck. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature.

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Abstract  

A flow microcalorimeter has been used to determine excess enthanlpies (H E) at 298.15 K for binary mixtures of dimethylsulfoxide (1)+alkylbenzenes (benzene, methylbenzene, ethylbenzene, n-propylbenzene and sec-propylbenzene, n-butylbenzene, sec-butylbenzene and tert-butylbenzene) or tetrachloromethane, trichloromethane, tetrachloroethane, dichloromethane and monochloroalkanes (1-chloropropane, 1-chlorobutane, 1-chloropentane, 1-chlorohexane) (2). These data with the data available in the literature on the molar excess enthalpies (H E), molar excess Gibbs energies (G E), activity coefficients at infinite dilution, γi , liquid-vapour equilibria (LVE) and liquid-liquid equilibria (LLE) for dimethylsulfoxide (DMSO)+n-alkanes, cyclohexane, benzene or alkylbenzenes (mono-, dialkyl-and trialkyl-) or tetrachloromethane, trichloromethane, dichloromethane and monochloroalkanes are treated in the framework of DISQUAC, an extended quasi-chemical group contribution theory. The systems are characterized by three types of contact surfaces: sulfoxide (S=O group), aliphatic (CH3, CH2, CH groups), cycloaliphatic (c-CH2 group), aromatic (C6H6, C6H5 groups) and chlorine (C1 group). Using a set of adjusted contact interchange energies parameters, structure dependent, the model provides a fairly consistent description of the thermodynamic properties as a function of concentration. The model may serve to predict missing data.

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Journal of Thermal Analysis and Calorimetry
Authors:
W. Ferenc
,
A. Dziewulska-Kułaczkowska
,
J. Sarzyński
, and
B. Paszkowska

Abstract  

4-Chloro-2-methoxybenzoates of heavy lanthanides(III) and yttrium(III) were obtained as mono-, di-, tri-or tetrahydrates with metal to ligand ratio of 1:3 and general formula Ln(C8H6ClO3)3·nH2O, where n=1 for Ln=Er, n=2 for Ln=Tb, Dy, Tm, Y, n=3 for Ln=Ho and n=4 for Yb and Lu. The complexes were characterized by elemental analysis, FTIR spectra, TG, DTA and DSC curves, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical bidentate chelating ligand. All complexes are polycrystalline compounds. The values of enthalpy, ΔH, of the dehydration process for analysed complexes were also determined. The solubilities of heavy lanthanide(III) 4-chloro-2-methoxybenzoates in water at 293 K are of the order of 10−4 mol dm−3. The magnetic moments were determined over the range of 76–303 K. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature.

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Abstract  

The paper presents the conditions under which compounds of the commercial herbicides, 2,4-dichlorophenoxyacetic acid (2,4D; C8H6O3Cl2) and 2-(2,4-dichlorophenoxy)-propionic acid (2,4DP; C9H8O3Cl2), with lead(II) and cadmium(II) are formed and the results of the examination of their properties.On the basis of the elemental analysis and Pb and Cd determination, the following molecular formulae for the obtained compounds were proposed: Pb(C8H5O3Cl2)2.H2O, Cd(C8H5O3Cl2)2.2H2O, Pb(C9H7O3Cl2)2·H2O and Cd(C9H7O3Cl2)2·H2O. Water solubility of the synthesized complexes at room temperature was examined. X-ray powder analysis was carried out. The discussion of IR spectra and conductivity data is presented. Thermal decomposition of these compounds in air was studied by TG/MS methods.

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