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Synthesis and properties of beryllium iodates IV

Thermal and calorimetric investigations of Be(IO3)2·2HIO3·6H2O

Journal of Thermal Analysis and Calorimetry
Authors: M. Maneva and M. Georgiev
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Abstract  

Methods of DTA, TG, X-ray phase analysis and IR spectroscopy were used to study the thermal dehydration and decomposition of Ni2+ and Zn2+ peroxotitanates to the corresponding metatitanates. The course of the process was established and the intermediate phases were identified. The information obtained was utilized to determine the optimum temperatures of heating the initial peroxotitanates for conversion to metatitanates with a fairly high degree of crystallinity (for ZnTiO3 the optimum temperature is 600C, while for NiTiO3 it is 550C).

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Abstract  

DTA and DSC were used to study the thermal behaviour of Ca(NO3)2·4H2O, Cd(NO3)2·4H2O, Mg(NO3)2·6H2O and their deuterated analogues. Evidence was found concerning the process of melting of the initial hydrates and deuterates, followed by a one-stage dehydration of the melt to vield the respective anhydrous salt. T m, ΔH m o , ΔS m o and ΔH deh o were determined and the ΔH f o values for the investigated hydrates were calculated from the ΔH deh o data.

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Abstract  

The thermal dehydration and decomposition of M(IO3)2·2H2O (M 2+=Ni2+ and Zn2+) and their deuterates were investigated by DTA and DSC methods. The data obtained confirm their onestage dehydration and their decomposition to the respective oxides. Ni(IO3)2·2H2O and Ni(IO3)2·2D2O, were more stable than Zn(IO3)2·2H2O and Zn(IO3)2·2D2O. A considerable isotope effect was observed in relation toT deh for Ni(IO3)2·2H2O and Ni(IO3)2·2D2O, which was explained by the presence of structural changes well differentiated from the dehydration process for the deuterate. The data obtained for both pairs of dihydrates were used to determine ΔH f o for Ni(IO3)2·2H2O and Ni(IO3)2·2D2O.

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The percentage of thermal dehydration and decomposition of ordinary and deuterated hydrates of barium acetate (tri- and monohydrates) were studied with a derivatograph and by DSC method. The observed phase transitions were identified and their corresponding enthalpy changes determined. The latter were compared with those estimated on thermodynamic data. The conclusions made on the dehydration process in correlation with IR spectra were used as information about the structure of the dehydrated water in the compounds investigated. The end product was also identified as barium carbonate.

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Abstract  

Methods of DTA, TG, DSC, IR spectroscopy and X-ray phase analysis were used to study the thermal dehydration and decomposition of Ca2+ and Sr2+ peroxotitanates to the corresponding metatitanates. The stages of the process and the intermediate phases were identified. The information obtained was utilised to determine the optimum temperatures of heating of the initial peroxotitanates to yield metatitanates with a fairly high degree of crystallinity (for CaTiO3 680C, and for SrTiO3 650C).

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Abstract  

A DTA and DSC study was made of the thermal dehydration and decomposition of Mg(IO3)2·4H2O and Mg(IO3)2·4D2O. The data obtained show that the dehydration takes place in one stage. The ΔH deh o obtained were used to calculate ΔH f o , and comparisons were made with the literature data. It was confirmed that the thermal decomposition passes through an intermediate Mg5(IO6)2, which is unstable and immediately decomposes to MgO. An isotope effect is observed in both DTA and DSC curves. Thermogravimetric data on Mg(IO3)2·10H2O are also presented.

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The kinetics and mechanism of thermal dehydration of Sr(NO3)2.4H2O and its deuterated analogue were studied by means of DTA, TG and DSC. The temperatures, enthalpies and weight losses of phase transitions were measured. The dehydration occurs in a stepwise manner, and the composition of the intermediate depends on the rate of thermal decomposition. The kinetic parameters (E * andZ) for the two steps of dehydration at a heating rate of 5 deg min−1 were calculated. A correlation was found between the dispersity of the end-product of the thermal decomposition (SrO) and the conditions of its preparation.

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