Thermal decompositions of complexes of metal ions with riboflavin

Two kinds of complexes of riboflavin with Zn(II), Co(II), Cu(II), Fe(III), Mg(II) and Ca(II) were synthesized, having metal: ligand molar ratios of 11 and 21. When heated, these complexes first lose water. Their thermal degradation in static air atmosphere starts at temperatures higher than, equal to, or lower than that observed for free riboflavin degradation. The rates and stages of pyrolysis were related to the structures of the complexes.

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Zusammenfassung Es wurden zwei verschiedenartige Komplexe von Riboflavin mit Zn(II), Co(II), Cu(II), Fe(III), Mg(II) und Ca(II) mit einem molaren Metall-Ligandenverhältnis von 11 und 21 dargestellt. Beim Erhitzen geben diese Komplexe zuerst Wasser ab. Ihre thermische Zersetzung beginnt in unbewegter Luftathmosphäre bei einer Temperatur, die entweder mit der für die Zersetzung freien Riboflavins übereinstimmt, größer oder kleiner als diese ist. Die Abschnitte und Geschwindigkeit der Pyrolyse werden mittels der Struktur der Komplexe erläutert.

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, , , : 11 21. . , . .

     

Thermal behaviour of melamine

Melamine undergoes condensation on heating with elimination of ammonia and formation of insoluble products. Thermogravimetry and infrared characterisation show that two products of successive condensation can be reproducibly obtained upon heating atT}<500 °C and then at 600 °C. Above 620 °C, the melamine condensate undergoes thermal degradation with quantitative formation of volatile products.

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Zusammenfassung Melanin geht beim Erhitzen eine Kondensation unter Abgabe von Ammoniak und Bildung unlöslicher Produkte ein. Durch Thermogravimetrie und Infrarotspektroskopie wird gezeigt, daß beim Erhitzen zwei Produkte von aufeinanderfolgenden Kondensationsreaktionen beiT}<500 °C undT= 600 °C reproduzierbar erhalten werden. Oberhalb 620 °C wird das Melaminkondensat vollständig unter Bildung flüchtiger Produkte thermisch zersetzt.

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. , . , 500°, — 600°. 620° .

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The authors wish to thank Dr. N. Del Fanti of Mantefluos, Italy for most helpful discussion.

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This work has been supported by the Consiglio Nazionale delle Ricerche through the Progetto Finalizzato Chimica Fine e Secondaria.     

Thermal behaviour of cardanol-based benzoxazines

A novel benzoxazine monomer (Bz-C) based on agrochemical renewable resource—cardanol (by-product of cashew nut tree, Anacardium occidentale) was synthesized. Bz-C, a liquid monomer, was used as reactive diluent for the solventless synthesis of bisphenol-A benzoxazine monomer (Bz-A). Benzoxazine monomer based on cardanol and bisphenol-A in 3:1, 1:1 and 1:3 blend ratio were prepared by this method. The resins had Brookfield viscosity at 316 K in the range of 145–81,533 mPa s. The resins were characterized by ¹H-NMR, FTIR and elemental analysis. Curing characteristics were studied by DSC analysis. Thermal stability of cured resins was found to improve with increase in Bz-C content in the blends.     

Thermal behaviour of thallous perchlorate

Thermal decomposition characteristics of thallous perchlorate are investigated in nitrogen and in air using TG and DTA techniques. Isothermal studies at 380°, 400°, 420° and 440° in air and in nitrogen showed that the relative amounts of the decomposition products, namely, thallic oxide and thallous chloride, depend upon both the temperature and the atmosphere around the sample. At low pressures (5×10^–1 mm/Hg) there is volatilization of thallous perchlorate even at 200°.

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Zusammenfassung Die thermischen Zersetzungscharakteristika von Thallium(I)-perchlorate wurden in Stickstoff und in Luft unter Anwendung der TG- und DTA-Techniken untersucht. Isotherme Studien bei 380°, 400°, 420° und 440° in Luft und in Stickstoff zeigten, daß die relativen Mengen der Zersetzungsprodukte, Thallium(III)oxid und Thallium(I) Chlorid, sowohl von der Temperatur als auch von der das Muster umgebenden Atmosphäre abhängen. Bei niedrigen Drücken (5×10^–1 mm/Hg) verflüchtigt sich Thallium(I)perchlorat bei 200°.

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Résumé On a étudié par TG et ATD les caractéristiques de la décomposition thermique du perchlorate de thallium(I) dans l'azote et dans l'air. Des études isothermes à 380, 400, 420 et 440°C dans l'air et dans l'azote ont montré que les taux relatifs de produits de décomposition, c'est-à-dire l'oxyde de thallium(III) et le chlorure de thallium(I), dépendent de la température ainsi que de l'atmosphère autour de l'échantillon. Sous faible pression (5 · 10^–1 torr) le perchlorure de thallium(I) se volatilise même à 200°.

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. , 380°, 400°, 420°, 440° , , , , , . (5 · 10^–1 . .) 200°.

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One of us (A.S.G.) is thankful to the Council of Scientific and Industrial Research, India for the award of a fellowship.     

Thermal behaviour of zinc phenoxyacetate

The thermal behaviour of solid zinc phenoxyacetate was investigated by DSC and TG techniques. The results obtained showed that this compound is a dihydrate and that the water molecules are differently bonded. The compound melts and then decomposes in two steps, with the formation of ZnCO₃ and ZnO, respectively. The thermodynamic parameters associated with the thermal processes were evaluated.

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Zusammenfassung Mittels DSC und TG wurde das thermische Verhalten von festem Zinkphenoxyazetat untersucht. Die Ergebnisse zeigen, daß diese Verbindung ein Dihydrat ist, in dem die beiden Wassermoleküle unterschiedlich gebunden sind. Die Verbindung schmilzt und zersetzt sich anschließend unter der Bildung von ZnCO₃ und ZnO in zwei Schritten. Die thermodynamischen Parameter der thermischen Prozesse wurden bestimmt.

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. , . , , . .

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We thank the Italian Public Education Minister for financial support.     

Thermal behaviour of lyocell fibres

Fourier-transform infrared (FTIR) spectroscopy has been applied in combination with wide-angle X-ray diffraction and measurements of strength, fluidity, yellowness, birefringence, and moisture regain to detect microstructural changes in lyocell fibres, a regenerated cellulose fibre, subjected to direct heat and annealing treatments. TMA, and SEM were used to show the effect of direct heat and annealing on lyocell fibres. The FTIR spectroscopy results show that a decrease in intermolecular hydrogen bonding occurs at 70 and 80 °C for annealed and directly heated samples, respectively. The results demonstrate increase of the intensity of O–H stretching vibrations, this associated with hydrogen bonds reforming around 130 °C. Lyocell fibres shrink with direct heating in the temperature range 130–160 °C. The crystallinity decreases gradually with increasing temperature. There is no significant change in colour of the samples annealed up to 150 °C. A continuous increase in the fluidity occurs for the annealed samples in the range 150–230 °C. The tenacity and breaking extension of heated samples decrease with increasing temperature. The lower annealing temperatures cause no observable change in the smooth and void-free surface, but in the annealing temperature range 170–230 °C, substantial non-uniformity is apparent on the surface of the fibres.     

Thermal behaviour of modified faujasites

A derivatograph was used to follow the modification of the skeleton structure and thermal stability of zeolites in sodium and ammonium forms. Analogous investigations were carried out by independent methods such as IR and X-ray. Comparison showed good agreement between the results. The controlled dealumination of the Y-type zeolite enhanced the thermal stability     

Thermal behaviour of some minerals

Thermal behaviour of some minerals (kaolinite, halloysite, two montmorillonites, quartz and calcite) for different sample amounts and heating rates has been investigated using differential thermal analysis. On the basis of the DTA analysis carried out, the PA curves of each mineral have been obtained for different heating rates. These diagrams can be employed in the semiquantitative evaluation of identical substances contained in uncharacterized polymineral samples.     

Thermal behaviour of polyacrylamidoxime-copper chelates

The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime-copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.     

Thermal behaviour of urea nitrate

The thermal decomposition under argon of the boracites M₃B₇O₁₃X (M=divalent metal ion, X=halogen ion or OH^?) has been studied by thermogravimetry (TG) and differential thermal analysis (DTA) for the compositions MgCl, MgOH, CrC1, CrBr, CrI, MnCl, MnBr, MnI, FeCl, FeBr, FeI, CoCl, CoBr, CoI, NiCl, NiBr, NiI, CuCl, CuBr, ZnCl, ZnBr, ZnI, CdCl, CdBr and CdI. The lithium boracites Li₄B ₇O₁₂X, with XCl and Br, have also been studied. The stability of the boracites systematically decreases in the order MCI>MBr>MI. The most stable boracite is CrCl (1% weight loss at 1242°C) and the least stable one studied here is MgOH (1% weight loss at 717°C).     

Thermal behaviour of ground vermiculite

Thermal behaviour of natural vermiculite (Santa Olalla, Huelva, Spain) was investigated by TG, DTA, emanation thermal analysis (ETA) and high temperature XRD on heating in the temperature range from 30 to 1100°C before and after vibratory mill grinding. Microstructure changes of natural and ground vermiculite samples were characterized by using ETA under in situ conditions of heating. By comparing the ETA and XRD results it was demonstrated that a decrease of radon release rate measured by ETA characterized the decrease in the interlayer spacing of the vermiculite samples that followed the dehydration. Dedicated to the memory of Professor Dr. Ferenc Paulik who passed away on October 12, 2005.     

Thermal behaviour of rigid polyurethane foams

The effects of P- and Cl-containing reactive antipyrenes with different compositions and structures on the mechanism and kinetics of the total thermal decomposition of rigid polyurethane foams, together with the possibility of evaluating their effectiveness as combustion inhibitors, were studied by means of a combined thermal analysis technique. It is shown that dynamic thermal analysis can register the changes resulting in the mechanisms and kinetics of the thermal decompositions of the investigated polyurethanes from comparatively low concentrations and differences in the concentrations and from differences in the chemical compositions and structures of the antipyrenes. The most sensitive characteristics associated with the influence of antipyrenes in this case were the coke residue determined at 850? in an inert medium and the areas of exothermic peaks I and II in the DTA curve in air medium.     

Thermal behaviour of hydrated dodecatungstosilicic acid

The thermal behaviour of H₄SiW₁₂O₄₀·24.8H₂O (SiW₁₂) was investigated by using DTA, TG and FTIR. Endothermic effects were observed at 40, 98 and 217°C, corresponding to the fusion of SiW₁₂ in its own crystallization water, boiling of the solution and decomposition of the remaining tetrahydrate into anhydrous SiW₁₂, respectively. The mass of the sample remained constant on heating from about 250 to 400°C. Subsequently, it slowly decreased and reached a constant value at about 500°C. At 526°C a DTA peak appeared. There was an abrupt change in the FTIR spectrum of the sample heated to 550°C. The typical spectrum of the Keggin unit vanished and new bands at 807.5 and 1030 cm^?1 indicated the presence of free WO₃ and SiO₂, respectively.     

Thermal behaviour of some sugar alcohols

The glass transition of isomalt and its components, the enthalpy of solution (crystalline state, glassy state) and the enthalpy of melting are reported. From the measured data (solution enthalpy, enthalpy of fusion and heat capacities) a cycle like the BORN-HABER cycle can be constructed. It is possible to calculate the amounts of amorphous isomalt from measured solution enthalpies; however, the values obtained do not agree with those provided by X-ray powder diffraction studies.This study was supported by Südzucker AG, Mannheim/Ochsenfurt. We thank Dr. M. Kunz and G. Witte of Südzucker AG for discussions.     

Thermal behaviour of composites aluminosilicate-calcium phosphates

A new type of aluminosilicate matrix calcium phosphate crystallites composites (ACPC) was synthesized and studied for osseous bone applications. The room temperature synthesis of the aluminosilicate matrix and composites was described. Thermal treatments of compounds allowed the adaptability of some parameters (pH, porosity and mechanical properties). Structure of heat treated composites were characterized by XRD and FTIR. The influence of thermal treatment on the mechanical properties, the porosity and the pH was studied for two temperatures (250 and 500°C). Results evidenced the ability to control the pH, the high level of porosity (»70%) and the good mechanical properties, allowing to consider that ACPC are potential biomaterials for osseous bone application.     

Thermal behaviour of gypsum based composites

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.     

Thermal behaviour of melt crystallized phenylbutazone

In the DSC curves, the melting point of phenylbutazone Form A was affected by the heating rate (first heat cycle). The DSC curves of the melt crystallized phenylbutazone (second heat cycle) showed the endothermic peaks of both Form C and Form A. The change in the first heat cycle of either the heating rate, the upper temperature limit, or the isothermal hold period at the upper temperature limit affected the value of the area ratio between the endothermic peaks of the two polymorphs in the DSC curves of the melt crystallized phenylbutazone. It was therefore suggested that the value of the area ratio is related to the energy supplied to the melt phenylbutazone in the first heat cycle. According to this hypothesis, the energy level that the melt should reach to crystallize as the metastable Form C should be higher than the essential one to crystallize as the stable Form A.

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Zusammenfassung Bei der Aufname der DSC-Kurven wird der Schmelzpunkt von Phenylbutazon Form A durch die Aufheizgeschwindigkeit beeinflusst (erster Aufheizzyklus). Die DSC-Kurven des aus der Schmelze kristallisierten Phenylbutazon (zweiter Aufheizzyklus) zeigt beide endothermen Peaks der Form C und Form A.Eine Veränderung der Aufheizgeschwindigkeit, der oberen Temperaturgrenze oder der isothermen Wartezeit auf der oberen Temperaturgrenze des ersten Aufheizzyklus beeinflussen das Verhältnis der Flächen der endothermen Peaks der beiden polymorhen Formen in der DSC Kurve des aus der Schmelze kristallisierten Phenylbutazons. Es wird angenommen, daß der Wert für das Verhältnis der Flächen eine Funktion der im ersten Aufheizzyklus für das geschmolzene Phenylbutazon aufgewendeten Energie ist. In Übereinstimmung mit dieser Hypothese müßte das Energieniveau, welches die Schmelze erreichen muß, um als metastabile Form C zu kristallisieren, höher liegen als jenes, bei der sie als stabile Form A kristallisiert.

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This work was possible by a grant of the Ministero della Pubblica Istruzione, Rome, Italy.