Hiroko Yokobayashi

Systematics on the thermal reactions of lanthanide malonates Ln2(C3H2O4)3 · nH2O in the solid state

Abstract The thermal reactions of the lanthanide malonates in the solid state were investigated systematically by means of TG/DTA, and X-ray, IR and elemental analyses. The onset temperatures of the dehydration ( t h ) and decomposition ( t d ), which can measure relative stabilities of the hydrated and anhydrous malonates, respectively, varied systematically with some physical parameters of the lanthanides and lanthanide malonates.

Spectrophotometric and thermal analytical studies on the dehydration of copper(II) sulfate and its double salts

Abstract Spectrophotometric (diffuse reflection) and TG-DTA data on the dehydration of CuSO 4 · 5H 2 O, Na 2 Cu(SO 4 ) 2 · 2H 2 O, M 2 Cu(SO 4 ) 2 · 6H 2 O(M + = K + , Rb + , Cs + and NH + 4 ) and Co 2 Cu(SO 4 ) 3 · 18H 2 O are given. Although complete dehydration of CuSO 4 · 5H 2 O brings about a striking color change from blue to white, it was found that there is only a slight decrease in the v max. of its d-d band in the course of this change, and the total light absorption in the visible-UV region increases at the same time. The dehydration of the alkali metal and ammonium double salts, most of which contain [Cu(OH 2 ) 6 ] 2+ aquo ions (in contrast to the [Cu(OH 2 ) 4 ] 2+ in CuSO 4 · 5H 2 O), occurs generally more easily than that of CuSO 4 - 5H 2 O, and their v max. increases slightly in the change, leading to blue or green anhydrous products, although the formation of a white modification was observed with the potassium salt. It was also found that the v max. of the Cu 2+ ion in the dehydrated cobalt(II) double salt is still lower than that in anhydrous CuSO 4 , i.e., the ligand field and/or tetragonality around it is decreased by the presence of Co 2+ ions.

Effects of heating rate (1–300° h−1) on the non-isothermal thermogravimetry of CuSO4 · 5 H2O

Abstract The course of the reaction CuSO4 · 5 H2O − CuSO4 · H2O + 4 H2O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h−. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h−, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h−; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h−. This can reasonably be compared with the phase diagram of copper sulfate.

Comparative studies between the thermal decomposition reactions of lanthanide(III) oxalates and malonates: Part I. The reaction processes of Eu2ox3 ·10H2O and Eu2mal3·6H2O

Abstract TG-DTA analyses of Eu2ox3·10H2O and Eu2mal3·6H2O [ox and mal = (COO−)2 and CH2(COO−)2, respectively] were carried out in N2, O2 and CO2 atmospheres. The products at each TG stage were determined on the basis of the IR spectra. X-ray diffractograms, evolved gas analyses and elemental analyses. In N2, the decomposition processes of EU2ox3 and Eu2mal3 were very similar and proceeded through the intermediate formation of Eu(II), which, in the case of Eu2ox3, was confirmed to be in the form of EuCO3. In CO2, on the other hand, the decomposition processes of the two salts were different; that of Eu2ox3 is represented as follows: Eu2ox3 → EuCO3 → Eu2O2CO3 → Eu2O3, while that of Eu2mal3 may tentatively be formulated as follows: Eu2mal3 → EuCH(COO)2 → Eu2O(CO3)2 → Eu2O2CO3 → Eu2O3.

Thermal analytical study on coordination in tetramethylene sulfoxide and dimethyl sulfoxide complexes of tervalent lanthanoid perchlorates

Abstract TG-DTA analyses of [Ln(tmso) 8 ](ClO 4 ) 3 (Ln=tervalent ions of the lanthanoid series; tmso=tetramethylene sulfoxide) were carried out in a nitrogen atmosphere and under vacuum. The observed values of the characteristic temperatures show systematic changes along the series, owing to the affects of the “lanthanoid contraction”. The corresponding dimethyl sulfoxide complexes were also investigated by the same method.

Kinetic compensation effect for the thermal solid state reactions of lanthanide oxalate, malonate and succinate hydrates and their anhydrides

Abstract The kinetic parameters of the thermal reactions of lanthanide oxalate, malonate and succinate hydrates and their anhydrides have been derived by means of the Coats and Redfern method on the basis of the TG runs. The kinetic compensation effect was observed between the activation energies (E a ) and the pre-exponential factors ( A ). The plots of E a , vs . lgA, except for the decomposition of the succinates, showed two linear portions for the light and the heavy lanthanides as a reflection of the double periodicity between the former and latter half of the lanthanide sequence.

Kinetic analysis of superconducting YBa2O7, by thermogravimetry in high vacuum

Abstract Superconducting YBa 2 Cu 3 O 7 , was subjected to high vacuum thermogravimetry (TG) at various heating rates in the range from room temperature to 1000°C. Two distinct weight-loss steps, each of which corresponds to the evolution of almost 1/20 2 , were observed on the TG curve. The product following the first step was apparently the non-stoichiometric compound YBa 2 Cu 3 O 7-δ . The rate equation for the first step was dδ/d t = k (1-δ); the corresponding specific rate constant, k , was 1.8 × 10 −3 s −1 at 490°C, the activation energy, E a , was 75 kJ mol −1 and the frequency factor, A , was 3.0 × 10 2 s −1 .