Kazuo Muraishi

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.

Thermal decomposition of bivalent transition metal malonates in various atmospheres

Abstract The thermal decomposition of the malonates of bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn) was investigated by mainly TG-DTA, X-ray diffraction analysis and evolved gas analysis in atmospheres of N 2 , CO 2 and O 2 and in the air. It was shown that CO 2 has an inhibiting effect on the decomposition whereas O 2 and air have the accelerating effects on the basis of N 2 . The decomposition of the salts investigated can be classified into three groups from solid decomposition products: Mn and Zn malonates gave the metal oxides including 1–1.5 moles of elementary carbon, while Cu and Ni malonates gave the metals with 1–1.5 moles of the carbon. Fe and Co malonates in the last group gave once the metal oxides with 1-0.5 moles of the carbon and the oxides produced were subsequently reduced to the metals by the carbon. A possible reaction mechanism for the malonates was discussed and compared with those of the corresponding oxalates and succinates.

Preparation of Superconducting Y?Ba?Cu?O and Bi?Pb?Sr?Ca?Cu?O Compounds by Chelating Method

Superconducting Y?Ba?Cu?O (YBCO) and Bi?Pb?Sr?Ca?Cu?O (BPSCCO) compounds were prepared by a chelating method with various chelating agents, such as nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA) and ethylenediaminetetraacetic acid (EDTA). Above 600?C, the precursors YBCO and BPSCCO turned into a mixture of metal oxides and BaCO3, which finally transformed into the almost single phase of YBCO at 850?930?C and into the high-Tc phase of BPSCCO at 840?C. The critical current densities of YBCO and BPSCCO in blocks of 1*4*15 mm3 were estimated to be as high as 350 and 500 A/cm2 at 77 K, respectively.

Thermal decomposition of Fe(II) carboxylates: Comparison of decomposition processes between the formate and malonate

Abstract The thermogravimetric curves of Fe(II) formate dihydrate, Fe(for)2 · 2H2O, and Fe(II) malonate dihydrate, Fe(mal) · 2H2O, in an argon atmosphere were obtained. The products at each decomposition stage were determined by Mossbauer spectroscopy, IR, powder X-ray analysis and gas chromatography. The dehydration of Fe(for)2 · 2H2O took place in two steps to form an anhydrous salt in the crystalline state, while Fe(mal) · 2H2O lost 2 mole of H2O in one step to form an anhydrous salt in the amorphous state. The decomposition processes of Fe(for)2 and Fe(mal) were represented as Fe(for)2→Fe3O4→FeO and Fe(mal)→FeO→α-Fe, respectively.

The thermal behaviour of dicarboxylic acids in various atmospheres

Abstract The thermal decomposition of anhydrous dicarboxylic acids was studied systematically in atmospheres of Ar, CO2 and air by means of thermogravimetry (TG) and differential thermal analysis (DTA). For all the acids, it was shown that CO2 has an inhibiting effect on the decomposition, whereas air has an accelerating effect, with respect to the behaviour in Ar. Except for oxalic acid, plots of the initial decomposition temperatures Ti and the DTA peak temperatures Tm versus the number of CH2 groups in the acids have a saw-tooth or periodic pattern. It is assumed that their properties depend on the zig-zag structures of the dicarboxylic acids.

Thermal behaviour of dicarboxylic acids. Determination of melting points by DTA

Abstract The melting points of dicarboxylic acids HOOC(CH 2 ) n COOH have been determined using DTA. The melting points obtained, except that for fumaric acid, are in close agreement with the literature values. All the acids are anhydrous; the decomposition of the acids with n = 0–2 in an air atmosphere takes place in two steps and that of the other acids ( n = 3–8 and maleic and fumaric acids) involves a single step.

Thermal dehydration reactions of Na1, K1, Rb1 and Cs1 malonate hydrates in the solid state

Abstract The thermal dehydration of alkali metal malonate hydrates was studied by means of thermogravimetry, differential thermogravimetry, differential thermal analysis and X-ray diffraction analysis, mainly in a nitrogen atmosphere. The reaction order of dehydration obtained by the TG method is found to be 2 3 for all the salts examined; the values of activation energy E a and frequency factor A for all the salts examined in the first step were 68–96 kJ mol −1 and 10 10 –10 13 s −1 , and these values for rubidium and caesium salts in the second step were 185–194 kJ mol −1 and 10 20 –10 22 s −1 respectively. The dehydration temperature reflecting the strength of the metal-OH 2 bond is lower in sodium and potassium malonate hydrates than in rubidium and caesium malonate hydrates.

Thermal decomposition of alkali metal malonate anhydrides in various atmospheres

Abstract The thermal decomposition of malonic acid and alkali metal malonate anhydrides has been studied using TG-DTA and IR spectroscopy. Malonic acid is anhydrous and its decomposition in a nitrogen atmosphere takes place in a single step. In the same atmosphere, the thermal decomposition of Li malonate occurs in four stages and that of other alkali metal malonates occurs in three stages. A comparison of the initial decomposition temperature values leads to the stability order: Cs > Rb > K > Li > Na. DTA was used to follow the process of melting and the decomposition of the malonates. The DTA curves of K, Rb, and Cs malonates indicate a complicated behaviour with the appearance of many small exothermic peaks between 340 and 400, 385 and 410, and 370 and 450°C, respectively. The activation energy values decrease regularly in Group I of the periodic system from Li to Cs. It was shown that CO 2 has an inhibiting effect on the decomposition whereas the oxidising atmospheres O 2 and air have an accelerating effect, compared with N 2 . In fact it was not possible to obtain the thermograms in static air for Na and K malonates because they decomposed explosively above 298 and 295°C, respectively.

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.

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.