Study of the thermal decompositions of some transition metal perchlorates

The thermal decompositions of nickel(II), copper(II), cobalt(II) and manganese(II) perchlorates were studied by thermal analysis and kinetic measurements. Anhydrous perchlorates could not be prepared by heating and outgassing the samples in vacuum; oxides were obtained as the main solid decomposition products. In the case of cobalt and manganese perchlorates, oxidation of the metal ions was observed during the decomposition. In most cases the decompositions of the perchlorates followed the Avrami-Erofeyev kinetics. A correlation was found between the stabilities of the perchlorates and the effective field strengths of the cations.

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Zusammenfassung Die thermische Zersetzung von Nickel(II), Kupfer(II)-, Kobalt(II)- und Mangan(II)-perchloraten wurde mittels Thermoanalyse und kinetischer Messungen untersucht. Durch Erhitzen und Entgasen der Proben im Vakuum konnten keine wasserfreien Perchlorate hergestellt werden; Oxide wurden als feste Hauptzersetzungsprodukte erhalten. Im Falle der Perchlorate von Kobalt und Mangan wurde die Oxidation der Metallionen während der Zersetzung beobachtet. In den meisten Fällen verlief die Zersetzung der Perchlorate nach der Kinetik von Avrami-Erofeyev. Eine Korrelation wurde zwischen den Stabilitäten der Perchlorate und der tatsächlichen Feldstärke der Kationen gefunden.

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Résumé La décomposition thermique des perchloartes de nickel(II), de cuivre(II), cobalt(II) et de manganèse(II) a été étudiée par analyse thermique et mesures cinétiques. Les perchlorates anhydres n'ont pas pu être préparés par chauffage et traitement sous vide de échantillons; les oxydes ont été obtenus comme produits solides principaux de décomposition. Dans le cas des perchlorates de cobalt et de manganèse, l'oxydation des ions métalliques a été observée pendant la décomposition. Dans la plupart des cas, la décomposition des perchlorates a suivi la cinétique d'Avrami-Erofeyev. Une corrélation a été trouvée entre la stabilité des perchlorates et les intensités effectives des champs des cations.

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The thermal decompositions of some transition metal acrylates and polyacrylates

The thermal behaviours of zinc, cobalt, nickel and copper acrylates and their polymers were investigated. It was found that the decompositions of these compounds are complex processes. The main decomposition of the monomer was preceded by thermal polymerization. The thermal effect of this reaction was greater for zinc acrylate than for the other salts. The reaction orders and activation energies of decomposition of the monomers and the polymers were calculated and the differences discussed.

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Zusammenfassung Das thermische Verhalten der Acrylate von Zink, Kobalt, Nickel und Kupfer und das der entsprechenden Polymere wurde untersucht. Es wurde festgestellt, dass die Zersetzung dieser Verbindungen komplexe Prozesse sind.Der Zersetzung der Monomeren ging eine thermische Polymerisation voraus. Der thermische Effekt dieser Reaktion war im Falle des Zinkacrylats grösser als bei den anderen Salzen. Die Reaktionsordnungen und Aktivierungsenergien der Zersetzung der Monomeren und Polymeren wurden berechnet und die Unterschiede diskutiert.

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Synthesis,characterization and thermal behaviour of some metal indigodisulphonates

Some indigodisulphonates of Cr(III), Cu(II), Ag(I), An(II) and Cd(II) have been prepared in aqueous medium and characterized on the basis of elemental analyses, diffuse reflectance infrared spectra and magnetic measurements.The thermal behaviours of these salts were studied by TG, DTG and DSC techniques. Cr(III), Cu(II), Zn(II) amd Cd(II) indigodisulphonates contain 12, 2, 2 and 2 molecules of crystallization water, respectively. The end-products of thermal decomposition have been verified by infrared spectroscopy and X-ray diffraction. Values of dehydration enthalpies have been calculated from the DSC curves.

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Zusammenfassung Einige Indigodisulphonate von Cr(III), Zn(II), Ag(I), Zn(II) und Cd(II) wurden in wäßrigem Medium dargestellt und durch Elementaranalyse, diffuse Reflektions-IR-Spektren und magnetische Messungen charakterisiert. Das thermische Verhalten dieser Salze wurde mittels TG, DTG und DSC untersucht. Die Indigodisulphonate von Cu(II), Zn(II) und Cd(II) kristallisieren mit 2 Molekülen Kristallwasser, die von Cr(III) mit 12 Molekülen. Die Endprodukte der thermischen Zersetzung wurden infrarotspektroskopisch und röntgendiffraktometrisch identifiziert. Die Werte der Dehydratisierungsenthalpien wurden aus den DSC-Kurven berechnet.

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The thermal decomposition of some heteropolytungstates with transition metal ions

The thermal behaviour of some heteropolytungstates of the 2:11 series was studied by means of T.G. and D.T.A. measurements, I.R. spectrometry and X-ray powder analysis (DEBYE -SCHERRER method).     

A comparative study on the thermal decomposition of some transition metal carboxylates

Thermal decomposition of transition metal malonates, MCH₂C₂O₄?xH₂O and transition metal succinates, M(CH₂)₂C₂O₄?xH₂O (M=Mn, Fe, Co, Ni, Cu, Zn) has been studied employing TG, DTG, DTA, XRD, SEM, IR and Mössbauer spectroscopic techniques. After dehydration, the anhydrous metal malonates and succinates decompose directly to their respective metal oxides in the temperature ranges 310–400 and 400–525°C, respectively. The oxides obtained have been found to be nanosized. The thermal stability of succinates have been found to be higher than that of the respective malonates.     

Study of the thermal behaviours of some metal acrylates

The thermal behaviours of Na, Ca, Mg and Zn acrylates were investigated by TG and DTA. It was found that the anhydrous acrylates were subject to thermal polymerization processes, which preceded the main decomposition. The presence of oxygen influences the decomposition of the organic part of the molecule very strongly, but it does not markedly affect the extent of polymerization or the type of the resulting solid products. Metal carbonates or oxides make up the major proportion of the residue obtained after the decomposition of the metal acrylates, similarly as in the case of other low molecular monocarboxylic acid salts.

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Zusammenfassung Das thermische Verhalten von Na, Ca, Mg und Zn-Akrylaten wurde mittels TG und DTA untersucht. Es wurde festgestellt, daß die wasserfreien Akrylate einen termischen Polymerisierungsproze erleiden, der der Hauptzersetzung vorangeht. Die Gegenwart von Sauerstoff wirkt sich sehr stark auf die Zersetzung des organischen Teils des Moleküls aus, beeinflut jedoch das Ausma der Polymerisierung und den Typ der entstandenen festen Produkte nicht besonders. Die bei der Zersetzung von Metallakrylaten erhaltenen Substanzen bestehen größtenteils aus Metallkarbonaten oder -oxiden, analog wie bei anderen Salzen von niedermolekularen Monokarbonsäuren.

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Résumé Etude du comportement thermique des acrylates de Na, Ca, Mg et Zn par thermogravimétrie et par analyse thermique différentielle (TG et ATD). On observe que les acrylates anhydres subissent un processus de polymérisation thermique qui précède la décomposition principale. La présence d'oxygène exerce une forte influence sur la décomposition de la partie organique de la molécule mais elle n'affecte pas de manière importante le degré de polymérisation ni la nature des produits solides formés. La majeure partie du produit obtenu après la décomposition des acrylates métalliques est constituée de carbonates et d'oxydes métalliques comme c'est le cas pour les autres sels d'acides monocarboxyliques à faibles poids moléculaires.

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TG Na, , Mg Zn. , , . , . , , , .

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The authors thank Mr. J. Bobinski for his help in translating this paper into English.     

Study of thermal behaviour of some edible mushrooms

This paper is aimed to analyse the thermal behaviour in air of edible mushrooms through nonisothermal (TG, DTG, DTA) and calorimetric (Berthelot calorimeter) methods. The studied mushrooms were Pleurotus ostreatus spontaneously grown and from culture and Agaricus bisporus from culture, currently used in alimentation but insufficiently investigated from this point of view. The analysis of TG–DTG–DTA curves has indicated that the degradation mechanism is complex and characteristic to every species and major differences between the cap and the stipe of investigated mushrooms have not been recorded. These species are thermally stable in the range of 30–160 °C. The thermal stability in terms of initial degradation temperature (T _i °C) and the temperature corresponding to the conversion grade (T _α=0.03 °C) indicate that the stipe has a thermal stability close to the cap one and that the cultivated mushrooms are more thermally stable than those spontaneously grown. The obtained results concerning the combustion of the sample using Berthelot calorimeter are in accordance with the TG–DTG–DTA analysis. The residue obtained is a measure of the mineral content and is quantitatively close.     

Study of the thermal decomposition of cellulose-hyphan and its complexes with some transition and indium metal ions

The studied complexes formed by the chelating ion exchanger were characterized by reflectance and infrared spectrometry. The thermal degradation of pure cellulose-hyphan (CH) and its complexes with Hg²⁺, In³⁺, Cr³⁺, Mo⁴⁺ and Mn²⁺ under an atmosphere of air has been studied using thermal gravimetry (TG) and differential thermal analysis (DTG). The results showed that four different stages are accompanying the decomposition of (CH) and its complexes with the studied metals. These stages were found to be affected by the presence of the investigated metal ions. On the bases of the applicability of a non-isothermal kinetic equation it was found to be a first-order reaction with the rate of degradation,k, ranging from 8.3·10^?5 to 6.2·10^?3 for (CH) and from 1.7·10^?5 to 6.6·10^?3 s^?1 for its complexes. The activation energy,E _a, the entropy change, ΔS°, the enthalpy change, ΔH° and Gibbs free energy, ΔG° are calculated by applying the rate theory of the first-order reaction. The effect of the different central metal ions on the calculated thermodynamic parameters is discussed.     

Kinetics of thermal dehydration of some bis-salicylato-diaquo complexes of transition metal ions

The kinetics of thermal dehydration of bis-salicylato-diaquo complexes of VO(II), Cu(II), Ni(II), Co(II), Fe(II), Mn(II) and Zn(II) were studied. The activation energies and other kinetic parameters were evaluated. The observed kinetic parameters indicate first-order reactions. The activation energy of the thermal dehydration decreases in the sequence VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > Fe(II) > Mn(II), which is also the sequence for the difference in carboxyl group IR frequency.

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Zusammenfassung Die Kinetik der thermischen Dehydratisierung von Bis-salicylato-diaquo-Komplexen von VO(II), Cu(II), Ni(II), Co(II), Fe(II), Mn(II) und Zn(II) wurden untersucht. Aktivierungsenergien und andere kinetische Parameter wurden bestimmt. Die beobachteten kinetischen Parameter weisen auf Reaktionen erster Ordnung hin. Die Aktivierungsenergie der thermischen Dehydratisierung nimmt in der Reihenfolge VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > > Fe(II) > Mn(II) ab. In der gleichen Reihenfolge ändert sich auch die IR-Frequenz der Carbonylgruppe.

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-- , , , , , . , . VO(II) > Cu(II) > Zn(II) > Co(II) > Ni(II) > Fe(II) > Mn(II). .

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The authors express their sincere thanks to the late Dr. M. D. Karkhanawala (then Head, Chemistry Division, BARE, India), for providing the facilities for TG and DTA, and also to the UGC (India) for research fellowships to the authors (BDH and SMA).     

Preparation, characterization and thermal studies of some transition metal ternary complexes

Ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nitrilotriacetic acid as a primary ligand and glycine as secondary ligand were prepared in slightly acid medium. Their molecular masses were determined by acid-base titration against standard potassium hydroxide solution. Their molecular structures were found to be [M (HNTA)(glyH)(2H₂O)]. Thermogravimetric analysis confirmed this structure and that the water present is coordinated to the central metal atom. UV-Vis spectra showed that the complexes have octahedral symmetry. IR spectra suggested the presence of intermolecular hydrogen bonding. This phenomenon was supported by mass spectra. The ionization constants of these complexes, as diprotic acids, were determined.     

Synthesis,spectroscopic characterization,electrochemical behaviour and thermal decomposition studies of some transition metal complexes with an azo derivative

Complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a novel heterocyclic azo derivative, formed by coupling diazotized 2-amino-3-carbethoxy-4,5-dimethylthiophene with acetylacetone were synthesized and characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility measurements, UV–vis, IR, ¹H NMR and EPR spectral data. Spectral studies revealed that the ligand existed in an internally hydrogen bonded azo-enol form rather than the keto-hydrazone form and coordinated to the metal ion in a tridentate fashion. Analytical data revealed that all the complexes exhibited 1:1 metal–ligand ratio. On the basis of electronic spectral data and magnetic susceptibility measurements, suitable geometry was proposed for each complex. The nickel(II) complex has undergone facile transesterification reaction when refluxed in methanol for a long period. The ligand and the copper(II) complex were subjected to X-ray diffraction study. The electrochemical behaviour of copper(II) complex was investigated by cyclic voltammetry. The thermal behaviour of the same complex was also examined by thermogravimetry.     

Study of the thermal behaviour of several metal acrylates and methacrylates

The thermal behaviour of several metal acrylates and methacrylates was investigated and the temperature characteristics were determined. The main decomposition of the monomer was preceded by thermal polymerization. The values of the peak temperatures of this effect do not correlate either with the thermal stabilities or with theQ values of the Alfrey-Price scheme of the monomers. The thermal resistance of the salts depends on the type of cations present, but there is no simple relationship. Divalent metal acrylates are thermally more stable than the corresponding methacrylates.     

A comparative study on the thermal decomposition of some transition metal maleates and fumarates

Thermal decomposition of M(mal/fum)·xH₂O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C employing TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320–360°C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than maleates.     

Ligational behaviour of a tetradentate NONS donor ligand towards some transition metal ions

Summary The synthesis and characterization of Cr^II, Mn^II, Fe^II, Co^II, Ni^II, Pd^II, Cu^II, Zn^II, Cd^II and UO ₂ ²⁺ complexes of 1-meotinoyl-4-phenyl-3-thiosemicarbazide (H₂NTS) are reported. I.r. spectral data show that the ligand behaves in a bidentate and/or tetradentate manner. An octahedral structure is proposed for the Cr^II, Fe^II and Ni^II complexes; a tetrahedral structure for the Mn^II, Co^II and Cu(NTS)·2H₂O complexes; and a square planar structure for the Pd^II and Cu(HNTS)Cl·H₂O complexes. The i.r. data suggest that the Fe^II complex contains a hydroxo bridge.     

Preparation and thermal behaviour of divalent transition metal complexes of pyromellitic acid with hydrazine

Hydrazine forms two different types of complexes with divalent metal ions and pyromellitic acid (H₄pml) in aqueous medium: (i) hydrazinium complexes of formulae, (N₂H₅)₂M(pml)·xH₂O, where x = 3 for M=Ni and x = 4 for M=Co or Zn, and (N₂H₅)₂Mn(H₂pml)₂, at pH 4.5, (ii) neutral hydrazine complexes with formulae, M₂(pml)(N₂H₄) _n ·xH₂O where M=Co or Ni when n = 4 and x = 5 or 4 and M=Zn or Cd when n = 2, and x = 4 or 3 at pH 7, and M(H₂pml)(N₂H₄)·xH₂O where x = 4; M=Cu and x = 0; M=Hg, at pH 3, 7.5, respectively. All the complexes are insoluble in water, alcohol and ether. The N–N stretching frequency (990–1,007 cm⁻¹ for coordinated hydrazinium ion and 956–985 cm⁻¹ for bridged neutral hydrazine) indicates the nature of hydrazine present in the complexes. Simultaneously TG-DTA analysis indicates that hydrazinium complexes undergo dehydration and dehydrazination in a single step endothermally in the range of 289–300 °C whereas neutral hydrazine complexes undergo endothermic dehydration (~100 °C) followed by exothermic dehydrazination in the temperature range, 253–332 °C. The anhydrous metal carboxylates further decompose exothermally to leave the respective metal oxides or metal carbonates except zinc, which gives its oxalate as the end product. X-ray powder patterns indicate that even the complexes with the same formulation possess no isomorphism.     

A comparative study of the thermal reactivities of some transition metal oxalates in selected atmospheres

A comparative investigation has been made of the nonisothermal, solid-state thermal decompositions of the oxalates of six divalent transition metals (cations: manganese, iron, cobalt, nickel, copper and zinc) in alternative flowing atmospheres, inert (N₂, CO₂), reducing (H₂) and oxidizing (air). Derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) response peak maxima, providing a measure of reaction temperatures, have been used to determine salt reactivities and thus to characterize the factors that control the relative stabilities of this set of chemically related reactants. Two trends were identified. Trend (1): in the inert and reducing atmospheres, the decomposition temperature (salt stability) increased with rise in enthalpy of formation of the divalent transition metal oxide, MO. It is concluded that the rupture of the cation-oxygen (oxalate) bond is the parameter that determines the stability of salts within this set. Trend (2): the diminution of decomposition temperatures from values for reactions in inert/reducing atmosphere to those for reactions in an oxidizing atmosphere increased with the difference in formation enthalpy between MO and the other participating oxide (MO_3/2 or MO_1/2). The change of cation valence tended to promote reaction, most decompositions in O₂ occurred at lower temperatures, but the magnitude of the effect varied considerably within this set of reactants. Observed variations in stoichiometric and kinetic characteristics with reaction conditions are discussed, together with the mechanisms of thermal decompositions of these solid oxalates.This approach to the elucidation of crystolysis reaction mechanisms emphasizes the value of comparative investigations within the group of chemically related reactants. Previous isothermal kinetic studies had been made for each of the reactants selected here. From these, much has been learned about the form of the (isothermal) solid-state yield-time curves, often interpreted to provide information about the geometry of interface development for the individual rate processes. However, identification of the controls of reactivity, reaction initiation (nucleation) and advance (nucleus growth), is much more difficult to characterize and less progress has been made towards elucidation of the interface chemistry. The trends of reactivity changes with salt compositions, identified here, offer a complementary approach to that provided by the study of single salts. Much of the recent literature on thermal decompositions of solids has been concerned with individual reactants, but many results and conclusions are not presented in the widest possible perspective. Comparisons between systematically related reactants are identified here as providing a chemical context for the elucidation of the chemical steps that participate in interface reactions. The article advocates the use of a more chemical approach in investigations of crystolysis (solid-state chemical) reactions.     

Study of the thermal dehydration of some fibrillar alkali metal trimolybdates

The dehydration process of the fibrillar potassium, rubidium and cesium isopolytrimolybdates was investigated by thermogravimetry and X-ray diffractometry. The dehydration took place in one step and the trimolybdates of general formula X₂Mo₃O₁₀ (whereX=K, Rb or Cs) were obtained.     

Superconductivity of some transition metal compounds

Single crystals of niobium carbonitride were made by zone melting growth methods and single crystals of γ-NbN and δ-NbN by zone annealing crystal growth. The crystals are nonstoichiometric in contrast to the niobium carbonitride or niobium nitride prepared in reaction with nitrogen gas and niobium-niobium carbide mixtures and niobium metal, respectively. The transition temperature for superconductivity (T_c) decreases with increasing deviation from stoichiometry, and a determination of T_c is a nondestructive determination of this deviation. An instrument using the Wheatstone bridge principle is described and T_c values are listed for some nonstoichiometric single crystals of niobium carbonitride and niobium nitride.     

Mutual-diffusion of some transition metal halides

The diffusion of some zinc and cobalt salts in water have been measured using an improved version of the capillary technique. In this technique, diffusion proceeds in the absence of stirring in the bulk solution. The amount of diffusing substance which remains in the capillary is analyzed after a chosen time. Nanis' solution for three-dimensional diffusion from a capillary has been used to calculate the experimental values. The values of diffusion coefficient of zinc iodide, cobalt bromide and cobalt iodide have been obtained with a diffusion run time of four hours. A comparison has been made between the experimental and theoretical values obtained from Onsager-Fuoss theory. An attempt has also been made to explain the deviation between the experimental and theoretical values over the concentration range studied.