Preparation of FexOy/SiO2 nanocomposites by thermal decomposition of some carboxylate precursors formed inside the silica matrix

In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in the redox reaction between Fe(NO₃)₃ and diol. We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO₃)₃·9H₂O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe₂O₃/50% SiO₂. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO₃)₃-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors took place up to 300°C.     

CoFe2O4/SiO2 nanocomposites by thermal decomposition of some complex combinations embedded in hybrid silica gels

The study reports the preparation of CoFe₂O₄/SiO₂ nanocomposites by a new modified sol–gel method starting from cobalt nitrate, iron nitrate, and diols: 1,2-ethanediol (EG), 1,3-propanediol (1,3PG), and tetraethylorthosilicate (TEOS), for final compositions of 30 %CoFe₂O₄/70 %SiO₂ and 50 %CoFe₂O₄/50 %SiO₂. The method is based on the formation of a Co(II), Fe(III)—carboxylate precursors mixture, during the redox reaction between the NO ₃ ^? ion and the diol (~140 °C) within the silica gels. The thermal decomposition of these complex combinations takes place at ~300 °C leading to the corresponding amorphous metal oxides within the pores of the hybrid gels. Depending on the subsequent thermal treatment, CoFe₂O₄ can be obtained as single phase or in a mixture with Co₂SiO₄. The CoFe₂O₄ crystallites sizes are in the nanometer range (3–10 nm). The obtained nanocomposites have a hard magnet behavior, as a result of the high anisotropy of CoFe₂O₄ having large hysteresis cycles.     

About compensation effect by thermal decomposition of some catalyst precursors

Summary In order to obtain catalysts, the thermal decomposition of the precursors is a compulsory step. However, kinetic analysis of the decomposition data obtained under non-isothermal conditions lead very seldom to the intimate reaction mechanism. There is also a lack of information because in non-isothermal kinetics, the compensation effect, is rather a rule and unfortunately a source of debate. In order to discriminate between these processes, and the influence of conversion, respectively temperature on the reaction rate, the NPK (non-parametric kinetic - Sempere and Nomen) method was used. This method is based on the singular value decomposition algorithm (SVD) applied on the matrix of reaction rate at corresponding conversion and temperature. This method allows a less speculative determination of the conversion functions and of the kinetic parameters.     

Mössbauer studies of thermal decomposition of metal(II) hexacyanoferrates(II)

The thermal decompositions of metal(II) hexacyanoferrates(II) (Co, Ni and Zn) were studied in air with Mössbauer, infrared, thermal analysis and magnetic susceptibility techniques. Dehydration is almost complete at 200° and decomposition starts at 250° in the cases of cobalt and nickel hexacyanoferrates(II), and at 300° for zinc hexacyanoferrates (II). Finally, ferrites are formed as decomposition products.     

A thermal decomposition study of some nickel(II)thioureachloride complexes

TG/DTA and Thermal Degradation Mass spectrometry (TDMS) data are presented for a series of nickel(II)thiourea chloride complexes: NiL₄Cl₂:L=thiourea or methyl-, dimethyl-, tetramethyl-, di-n-butyl, naphthyl-, ethylene- or allylthiourea. Two different thermal decomposition mechanisms are proposed for these complexes, and it is apparent that the thermal decomposition mechanism adopted by a particular complex depends on the structure of the relevant thiourea ligand and not on the nature of the halide ligand or on the existence of geometrical isomerism for these complexes.

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Zusammenfassung Durch TG, DTA und thermodegradative Massenspektrometrie (TDMS) von Nickel(II)-thioharnstoff-chlorid-Komplexen, NiL₄Cl₂ (L=Thioharnstoff oder Methyl-, Dimethyl-, Tetramethyl-, Di-n-butyl-, Naphthyl-, Vinyl- oder Allylharnstoff), erhaltene Daten werden angegeben. Zwei verschiedene Mechanismen werden für die thermische Zersetzung vorgeschlagen. Es ist offensichtlich, daß der Mechanismus, nach der die thermische Zersetzung eines gegebenen Komplexes verläuft, von der Struktur des relevanten Thioharnstoffliganden und nicht von der Natur des Halidliganden oder vom Vorliegen einer geometrischen Isomerie abhängt.

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/ - NiL₄Cl₂, L= , -, -, -, ---, -, - . . , .

     

热解单源前驱体方法可控制备纳米金属硫化物

本文简要综述了本研究组近年来在利用热解单源前驱体合成方法制备纳米金属硫化物方面的相关工作．通过采用不同的反应前驱体,改变反应时间、反应温度,选择不同的表面配体分子及反应溶剂等手段实现了对纳米金属硫化物形貌、尺寸、组成和晶相的精确调控．除了对合成方法和过程进行介绍外,本文还简要讨论了具有特定形貌的金属硫化物的形成机理,并对几类典型硫化物的应用研究进行了总结．     

Mössbauer study of the thermal decomposition of some iron(III) dicarboxylates

The thermal decomposition of iron(III) succinate, Fe₂(C₄H₄O₄)₂(OH)₂ and iron(III) adipate pentahydrate, Fe₂(C₆H₈O₄)₃·5 H₂O, has been investigated at different temperatures for different time intervals in static air atmosphere using Mössbauer spectroscopy and nonisothermal techniques (DTG-DTA-TG). The reduction of iron(III) to iron(II) species has been observed at 533 K and 563 K in the case of iron(III) succinate and iron(III) adipate, respectively. At higher temperatures, α-Fe₂O₃ is formed as the final thermolysis product.     

Synthesis and thermal conversions of unsaturated nickel(II) dicarboxylates as precursors of metallopolymer nanocomposites

Nickel(II) dicarboxylates of unsaturated carboxylic acids (maleic (MalA), itaconic (ItA), acetylenedicarboxylic (ADCA), allylmalonic (AlMalA), glutaconic (GlutA), cis,cis-muconic (MucA) acids) were synthesized and characterized by thermal analysis and IR spectroscopy. The synthesized dicarboxylates were subjected to thermolysis, and the obtained nanocomposites were studied by transmission and scanning electron microscopy and X-ray diffraction. The synthesized metallopolymer nanocomposites were NiO and metallic Ni nanoparticles distributed over a stabilizing matrix. The formation enthalpy of dicarboxylates (ΔН_r^°) was calculated by the PM3 semi-empirical quantum-chemical method. The nanoparticle size was determined, and a relationship between the average nanoparticle diameter (d_avg) and ΔН_r^° was established. The microstructure and magnetic characteristics of the obtained nanocomposites, namely, the maximum and residual magnetization and the coercive force, were studied.     

Mössbauer studies of thermal decomposition of metal(III) hexacyanoferrates(II)

The thermal decomposition of metal(III) hexacyanoferrates(II) (Al, As, Sb, Bi) was studied up to 700° in air by employing Mössbauer, infrared spectroscopy and thermal analysis techniques. With the exception of the bismuth compound, the isomer shift of these hexacyanoferrates(II) increases on dehydration at 200°. Dehydration is complete at 200°, decomposition into the ferrite at 300°, and formation of-Fe₂O₃ from aluminium and bismuth hexacyanoferrates(II) and Fe₃O₄ from antimony and arsenic hexacyanoferrates(II) at 700°.

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Zusammenfassung Die thermische Zersetzung von Metall(III)ferrocyaniden (Al, As, Sb, Bi) wurde bis zu 700° in Luft unter Anwendung der Mössbauer und Infrarotspektroskopie, sowie thermoanalytischer Techniken untersucht. Die Isomerverschiebung dieser Ferrocyanide nimmt mit der Dehydratisierung bei 200° zu, mit Ausnahme des Wismuts. Die Dehydratisierung ist bei 200° abgeschlossen, die Zersetzung zum Ferrit bei 300° und die Bildung von-Fe₂O₃ aus Aluminium- und Wismutferrocyanid, von Fe₃O₄ aus Antimon- und Arsenferrocyanid bei 700°.

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Résumé On a étudié dans l'air jusqu'à 700°, la décomposition thermique des ferrocyanures de métaux trivalents (Al, As, Sb, Bi), par spectroscopies Mössbauer et infrarouge, ainsi que par les techniques d'analyse thermique. Le déplacement des isomères de ces ferrocyanures augmente lors de la déshydratation à 200°, à l'exception du bismuth. La déshydratation est complète à 200°, la décomposition en ferrite à 300°, la formation d'-Fe₂O₃ à partir des ferrocyanures d'aluminium et de bismuth ainsi que du Fe₃O₄ à partir des ferrocyanures de l'antimoine et de l'arsenic à 700°

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-, , — Al, As, Sb, Bi- 700° . , , 200°. 200°, 300° -Fe₂O₃. 700° Fe₃O₄.

     

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Peculiarities of thermal transformations of metal-containing monomers and polymers prepared by various synthetic routes are analyzed. It is shown that the thermal stability of metalcarboxylate groups is determined by the spatial organization of the nearest environment and the microstructure of polymer chains formed as a result of thermal transformations. Main paths of thermal transformations of studied compounds are considered. Qualitative and quantitative compositions of the gaseous and solid-phase products at the end of transformations and some properties of forming polymer-metal nanocomposites are studied.60th communication from Preparation and Reactivity of Metal-Containing Monomers series. For 59th communication see [1].Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 57–69. Original Russian Text Copyright © 2005 by Rozenberg, Dzardimalieva, Chukanov, Pomogailo.     

Kinetics and reaction mechanism for the thermal decomposition of some even chain lead(II) carboxylates

The kinetics of the thermal decomposition of lead(II) dodecanoate, tetradecanoate and octadecanoate have been studied thermogravimetrically in the temperature range 298–1073 K by the modified method of Freeman and Carroll. The thermogravimetric curves show that while the octadecanoate decomposes in one single step to lead oxide, the dodecanoate and tetradecanoate decompose in two stages to lead oxide. The kinetic results show all the reactions, except the second step breakdown of dodecanoate (which is nearly unity), to be of zero order. Activation energy values are presented for the desorption of carbon dioxide and the diffusion controlled rate of formation of a degradative intermediate identified as a ketone. Tentative mechanisms are advanced to explain the degradative route of these compounds.     

Evaluation of cation influence on the formation of M(II)Cr2O4 during the thermal decomposition of mixed carboxylate type precursors

This paper reports an investigation regarding the influence of the cation M(II) (M = Zn, Ni, Mg) on the formation of MCr₂O₄ by thermal decomposition of the corresponding M(II),Cr(III)-carboxylates (precursors) obtained by redox reaction between the corresponding metal nitrates and 1,3-propanediol. The decomposition products at different temperatures have been characterized by FT-IR spectroscopy and thermal analysis. Thus, we have evidenced that by thermal decomposition of the studied precursors in the range 250–300 °C, different amorphous oxidic phases mixtures form depending on the nature of metalic cation: (Cr₂O_3+x + ZnO) (Cr₂O_3+x + Ni/NiO) and (Cr₂O_3+x+MgO). In case of M = Zn, around 400 °C when the transition Cr₂O_3+x to Cr₂O₃ takes place, zinc chromite nuclei form by the interaction ZnO with Cr₂O₃. In case of M = Ni, due to the partial reduction of Ni(II) at Ni(0) during the thermal decomposition of the precursor the formation of nickel chromite by the reaction NiO + Cr₂O₃ is shifted toward 500 °C, when Ni is oxidized at NiO. The thermal evolution of the mixture (MgO + CrO₃) is different due to the formation as intermediary phase of MgCrO₄, which decomposes to MgCr₂O₄ around 560 °C. In order to investigate the chromites formation mechanism, we have studied the mechanical mixtures of single oxides obtained from the corresponding carboxylates. These mixtures (MO + Cr₂O₃) have been annealed at 400, 500, and 600 °C to study the evolution of the crystalline phases. It results in the prepared mixture behaving different from the mixtures obtained by thermal decomposition of the binary M(II),Cr(III)-carboxylates, recommending our synthesis method for obtaining binary oxides.     

Mössbauer studies of the thermal decomposition of iron(II) ammonium sulphate hexahydrate

The thermal decomposition of binary copolymers of acrylonitrile with variable amounts of -methylstyrene (2–40%) has been studied atp=10^–2–10^–4 torr andT=0–600°. The decomposition products (solids, liquids and gases) have been characterized by IR and UV spectroscopy, gas chromatography, vapor pressure osmometry and elemental analysis. The decomposition mechanism has been ascertained on the basis of the obtained results.

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Zusammenfassung Die thermische Zersetzung der binären Kopolymere von Akrylnitril mit verschiedenen Mengen von -Methylstyrol (2–40%) wurde beip=10^–2–10^–4 Torr undT=0–600° untersucht. Die Zersetzungsprodukte (Festkörper, Flüssigkeiten und Gase) wurden durch IR- und UV-Spektroskopie, Gaschromatographie, Dampfdruck-Osmometrie und Elementaranalyse charakterisiert. Der Zersetzungsmechanismus wurde an Hand der erhaltenen Ergebnisse bestätigt.

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Résumé On a étudié la décomposition thermique des copolymères binaires de l'acrylonitrile avec des quantités variables d'-méthylstyrène (2–40%), àp=10^–2–10^–4 torr etT=0–600°. Les produits de décomposition (solides, liquides et gaz) ont été caractérisés par spectroscopie IR et UV, Chromatographie en phase gazeuse, osmométrie sous pression de vapeur et analyse élémentaire. Le méchanisme de décomposition a été établi à partir des résultats obtenus.

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(2–40%) - p=10^–2–10^–4 =0–600°. (, ) - - , , . .

     

Structural characterization and thermal decomposition of layered double hydroxide/poly(p-dioxanone) nanocomposites

Nanocomposites based on layered double hydroxides (LDH) and poly(p-dioxanone) (PPDO) were prepared by melt processing using dodecylbenzene sulfonate (DBS) and 4-hydroxybenzene sulfonate (HBS) as organic modifiers. The incorporation of organic anions in LDH was demonstrated by wide-angle X-ray scattering (WAXS) and Fourier transform infrared (FTIR). The dispersion degree of the organically modified LDHs in the PPDO matrix was analyzed by WAXS, indicating that only the LDH modified with HBS was exfoliated. The effect of the organically modified LDHs on the thermal stability of PPDO was studied using thermogravimetric analysis (TGA). The thermal stability of PPDO matrix was enhanced by the incorporation of the LDH modified with HBS due to the shielding effect of the exfoliated layers. In contrast, the LDH modified with DBS produced a decrease of the thermal stability of PPDO, probably due to hydrolytic decomposition of ester group. The thermogravimetric analysis also showed that the organo-modified LDH did not modify the thermal decomposition mechanism of the polymer, but had an effect on the thermal stability.     

Enhancement of properties of polyimide/silica hybrid nanocomposites by benzimidazole formed hydrogen bond

Polyimide/silica hybrid nanocomposites were prepared by sol–gel method without coupling agent. A novel diamine with a benzimidazole group, 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ), was introduced to copolymerize with 4,4'‐oxydianiline (ODA) and pyromellitic dianhydride (PMDA) to synthesize polyimide (PI) matrix. The compatibility between PI and silica was improved by hydrogen bonds formed between silica phase and the –NH– group on benzimidazole of the new diamine. Highly transparent hybrid films were obtained when silica content reached as high as 30 wt%. SEM results show that silica particles with sizes much smaller than that in PMDA‐ODA/silica system disperse homogeneously in the PI matrix. Differing from most hybrid systems without coupling agent, the tensile strength of PABZ system increases from 152 MPa to 165 MPa with silica content increasing from 0 to 20 wt%, while, it decreases linearly in PMDA‐ODA system. DMA analysis shows that the introduction of PABZ largely increases the glass transition temperature (Tg) for all silica contents, which is suggested to be due to the more rigid structures and stronger interaction between the two phases. Meanwhile, the decomposition temperature and char yields at 800 °C are both higher than that of pure PIs. The structures of the hybrid films were identified by FTIR spectra, which indicate that different silica morphologies are developed, resulted from the hydrogen bonds between benzimidazole and silica phase. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxidising properties of MgO formed by thermal decomposition of Mg(OH)2

To clarify whether trans-cis photoisomerization can be induced by an infrared laser in low temperature matrices, argon matrices of trans-2-butene and rans-1,2-dichloroethylene were irradiated with a TEA CO₂ laser. The results were negative, indicating that the multiple-photon absorption is suppressed in low-temperature matrices.     

Synthesis and thermal properties of aminopyrimidine Ge(II) precursors for CVD/ALD technology

Derivatives of aminopyrimidine had been used as ligands in various metals complexes but not as precursors for PRAM. A series of aminopyrimidine Ge(II) precursors has been synthesized for the first time. The diamine germanium (II) precursors were tested by TG and demonstrated excellent volatilization.     

The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

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Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.

     

New method for the synthesis of trans-hydroxotetraamminenitrosoruthenium(II) dichloride and its characterization

A procedure for the synthesis of mpa h c-[Ru(NO)(NH₃)₄(OH)]Cl₂ in a nearly quantitative yield (～95%) comprising treatment of a solution of (NH₄)₂[Ru(NO)Cl₅] with ammonium carbonate at t ～80°C was developed. It was found that [Ru(NO)(NH₃)₄(H₂O)]Cl₃·H₂O and trans-[Ru(NO)(NH₃)₄Cl]Cl₂ formed in the reaction of [Ru(NO)(NH₃)₄(OH)]Cl₂ with hydrochloric acid at various temperatures most often contain some initial hydroxy complex. The former compound is unstable, even at room temperature, it slowly eliminates water and HCl. A procedure for preparing the latter compound in a pure state in 85–90% yield was proposed. The acidity constant of the complex trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺ at room temperature (K _a = (4 ± 1) × 10^?2) was estimated by ¹⁴N NMR spectroscopy.