Study of crystallization process of soda lead silicate glasses by thermal and spectroscopic methods

The crystallization process of some glasses in the ternary Na₂O–SiO₂–PbO system with good chemical stability that can be used for waste inertization was studied using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and scanning electron microscopy. The parent glasses were characterized by XRD and FT-IR, and their vitreous state was determined. DTA measurements evidenced glass transition (T _g) and crystallization temperatures (T _c). The thermal treatments were conducted at vitreous transition temperature (400 °C) and at highest effect of crystallization (650 °C). XRD evidenced the lead and sodium silicate crystalline phases in samples treated at 650 °C for 12 h. Micrometer crystallites dispersed in the glass matrices have affected the transparence of glasses and made them opaque after treatment at 650 °C. The influence of oxide quantities in compositions on the crystallization tendency was revealed. A PbO higher content than that of SiO₂ as well as lower Na₂O content decreased the tendency of crystallization.     

Influences of temperature and atmosphere on thermal stability of BaCrO4

In this article, the influences of temperature and atmosphere on thermal stability of BaCrO₄ were investigated. BaCrO₄ powders with an orthorhombic structure were synthesized by a facile aqueous solution route. The synthesized BaCrO₄ products were then heat treated at different atmospheres to evaluate their thermal stability by differential thermal analysis–thermogravimetry (DTA–TG), X-ray photoelectron spectroscopy and X-ray diffraction. BaCrO₄ has a good thermal stability and does not decompose in air up to 1,400 °C. However, the decomposition of BaCrO₄ in vacuum depends mainly upon a two-stage chemical reaction. BaCrO₄ is finally decomposed into BaCr₂O₄ with trivalent Cr³⁺ cations and Ba₃(Cr⁶⁺ Cr⁵⁺)₂O_9?x with both pentavalent Cr⁵⁺ and hexavalent Cr⁶⁺ cations after heat treatments in vacuum.     

Thermal stability of quaternary ammonium hexafluorophosphates and halides

Thermal decomposition of hexafluorophosphates of short-chain tetraalkylammonium salts of the general formula R₃R’NPF₆, where R₃ = R’ = CH₃, C₂H₅, C₄H₉; R₃ = C₂H₅, R’ = CH₂C₆H₆ or CH₂CH=CH₂, was studied by thermal gravimetric analysis. Measurements were performed in air in the temperature interval 20–500°C. The thermal stability of halides with the same cations in the same temperature interval was studied for comparison. The effect of cation on the thermal stability of the halides and hexafluorophosphates was examined. The mechanism of thermal decomposition of quaternary ammonium hexafluorophosphates was suggested.     

Luciferase-streptavidin fusion proteins: Preparation and properties

We constructed plasmids encoding genes of fusion proteins of a thermostable mutant of Luciola mingrelica firefly luciferase (Luc) and streptavidin (SA) with the polyhistidine sequence (His₆) at the N- or C-terminus of the protein: SA-Luc-His₆, His₆-SA-Luc, Luc-SA-His₆. Fusion proteins were produced and purified; their composition, luciferase activity, thermal stability, bioluminescence spectra, and biotin-binding capacity were investigated. Streptavidin introduction does not affect the bioluminescence spectra, but it decreases the thermal stability twofold at 47°C. It was shown by size-exclusion chromatography that, depending on the plasmid structure, the fusion proteins were expressed as dimers, tetramers, and larger oligomers, which differ in luciferase activity and biotin-binding capacity. The His₆-SA-Luc fusion protein demonstrated the most optimal properties.     

Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites

Increasing the thermal stability of organically-modified layered silicates is one of the key points in the successful technical application of polymer-layered silicate nanocomposites on the industrial scale. To circumvent the detrimental effect of the lower thermal stability of alkyl ammonium-treated montmorillonite, a series of alkyl-imidazolium molten salts were prepared and characterized by elemental analysis, thermogravimetry (TGA) and thermal desorption mass spectroscopy (TDMS). The effect of counter ion, alkyl chain length and structural isomerism on the thermal stability of the imidazolium salts was investigated. Alkyl-imidazolium-treated montmorillonite clays were prepared by ion exchange of the imidazolium salts with Na-montmorillonite. These organically-modified clays were characterized by X-ray diffraction (XRD), TDMS and thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and compared to the conventional quaternary alkyl ammonium montmorillonite. Results indicate that the counter ion has an effect on the thermal stability of the imidazolium salts, and that imidazolium salts with PF₆⁻, N(SO₂CF₃)₂⁻ and BF₄⁻ anions are thermally more stable than the halide salts. A relationship was observed between the chain length of the alkyl group and the thermo-oxidative stability; as the chain length increased from propyl, butyl, decyl, hexadecyl, octadecyl to eicosyl, the stability decreased. The results also show that the imidazolium-treated montmorillonite has greater thermal stability compared to the imidazolium halide. Analysis of the decomposition products by FTIR provides an insight about the decomposition products which are water, carbon dioxide and hydrocarbons.     

The role of alkali content in the devitrification mechanisms of SiO2–Fe2O3–Na2O–PbO SYSTEM

Three batch compositions of pure oxides (SiO₂, Fe₂O₃, PbO, Na₂O) with equivalent SiO₂, Fe₂O₃ and PbO contents and a gradually increased Na₂O content were vitrified through heating in a high temperature electric furnace and subsequent quenching. The resulting vitreous products were thermally treated in order to study the devitrification behaviour, under conditions designated from differential thermal analysis experiments. Depending on the Na₂O content, crystal phase separation gave rise to the growth of acmite and hematite or maghemite. A uniformly phase separated glass-ceramic material, with crystallites of similar size and population density, was produced from devitrification of the vitreous product with the higher Na₂O content.     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of temperature on the structural behaviour of sodium tri- and hexa-titanates and their protonated forms

The thermal stability of Na₂Ti₃O₇ and Na₂Ti₆O₁₃, together with that of their protonated forms was investigated. The influence of temperature on the structural behaviour of tri- and hexa-titanates was studied using DTG, XRD, FTIR and FT-Raman. These results were correlated with the nature of the exchangeable cations using elemental analysis and N₂-sorption. The tunnel structure of Na₂Ti₆O₁₃ revealed a higher thermal stability compared to the layered structure of Na₂Ti₃O₇ that shows traces of dimerisation above 800 °C. The sodium forms were observed to be more thermally stable compared to their protonated forms. However, analysis show that ‘H₂Ti₆O₁₃’ is much more thermally stable than the layered H₂Ti₃O₇ which go through structural changes above 250 °C and suffer a complete structural collapse into anatase/rutile above 800 °C. It was obvious that thermal stability was significantly influenced by the nature of the exchangeable cations and the degree of ion-exchange.     

Synthesis, characterization and thermal behaviour of solid-state tartrates of heavy trivalent lanthanides and yttrium(III)

Solid state Ln₂-L₃ compounds, where Ln stands for heavy trivalent lanthanides (terbium to lutetium) and yttrium, and L is tartrate [(C₄H₄O₆)^?2] have been synthesized. Simultaneous thermogravimetry and differential thermal analysis, differential scanning calorimetry, X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results provided information concerning the stoichiometry, crystallinity, ligand??s denticity, thermal stability and thermal behaviour of these compounds.     

Thermal behaviour study of some sol-gel TiO2 based materials

Among the great number of sol-gel materials prepared, TiO₂ holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO₂ nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO₂ matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO₂ crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.     

Simultaneous thermoanalytical investigations of (C6H5)4AsCl and (C6H5)4PCl under air and argon atmospheres

The thermoanalytical curves of (C₆H₅)₄AsCl (I) and (C₆H₅)₄PCl (II) were generated simultaneously by using a Netzsch simultaneous thermal analyser 409 under static air and dynamic argon atmospheres. The ranges of thermal stability of I and II were found to be 145–310°C and 137–365°C, respectively, and their melting points to be 261 and 278°C. The DTA profiles of I and II differ and can be used for their distinction.     

Thermal behavior of some uranyl bis-(1,3-diketonate) complexes

Thermal gravimetric (TG) and differential thermal (DTA) analyses were performed to characterize the thermal behavior and the stoichiometry of uranyl bis-1,3-diketonate complexes (R₁COCR₂COR₃)₂ UO₂ x H₂O, where R_1,3=CH₃; C₂H₅; C₆H₅; CF₃; pNO₂−C₆H₄; pCl−C₆H₄; pMe−C₆H₄; NH−C₆H₅; R₂=H, C₆H₅ andx=1; 2. Based on the data obtained, a thermal degradation mechanism for each complex was proposed. The final degradation product for all studied complexes was U₃O₈ oxide. The temperature of the first organic fragment rupture including the U-O (ligand) bond was taken as criterion for the thermal stability of the metal-oxygen donor bond in these complexes. The observed stability order is in good agreement with the IR determined constant force values,k, of the U-O (ligand) bond.     

Polymerization of Methyl Propiolate with Palladium Chloride,Triphenylphosphine, and Palladium Chloride Triphenylphosphine Complex

Some results of the bulk polymerization of methyl propiolate in the presence of PdCl₂, triphenylphosphine, and [(C₆H₅)₃P]₂.PdCl₂ complex are presented. From the polyconjugated polymers obtained, fractions based on their solubility in various solvents were separated. Subsequently, these products were characterized by IR and ¹H NMR spectroscopies and by thermal analysis. The data obtained indicate that polymerization assisted by [(C₆H₅)₃P]₂.PCl₂ proceeds faster, giving products with a lower cyclic oligomers content. The polymers possess good thermal stability and semiconducting properties.     

Double Tetrametaphosphates Ca2-xMx IIP4O12

Abstract

The thermal synthesis of Ca₂-_xM_x ^IIP₄O₁₂ (M^II=Mn, Co; x=0,5 -1,5) starts from a mixture of carbonates of the respective metals and phosphoric acid. Formation of the products has been followed by TA (thermal analyses) under quasi-isothermal-isobaric conditions and compared with that of simple tetrametaphosphates at the same conditions (Refs 1,2). Distinct effect of water vapour pressure on the condensation reaction course is indicated; enhanced pressure retards the reactions and shifts them to higher temperatures, but it favours formation of the desired condensation intermediates and, especially, increases the yield of the double tetrametaphosphate. Monoclinic structure of the microcrystalline products obtained has been confirmed. The lattice parameters have been determined, and their shift to lower values with increasing x has been observed. The TA methods have been used to follow thermal stability of the products and to determine the temperatures of melting and of reversible transition to higher linear phosphates (polyphosphates). For these vitreous products we have determined their softening temperatures, and temperature, heat, and energy of the recrystallization connected with reverse formation of the double tetrametaphosphates. The reversible transition is also used for synthesis of the pure products (Ref. 3) which appear to be promissing as special inorganic pigments (Ref. 4).     

The block copolymers and polymer blends of nylon 6 with poly(4,4′-diphenylsulfone terephthalamide). I. Preparation and thermal properties

In this study, the flexible nylon 6 was reinforced by the rigid-chain aromatic polyamide, poly(4,4′-diphenylsulfone terephthalamide) (PSA). Various high molecular weight block copolyamides were synthesized by solution polymerization using 4,4′-diisocyanatodiphenylmethane (MDI) or p-aminophenylacetic acid (p-APA) as a coupling agent, respectively. Their thermal properties had shown that block copolyamides exhibited higher T_g and T_m, and better thermal stability, especially those using p-APA as a coupling agent. Decrease in thermal stability of block copolyamides based on MDI coupling agent was due to its urea linkage which been explained and proved by the infrared spectra data. On the other hand, the PSA molecules could act as “nucleating agents” among the nylon 6 matrix in the polymer blends, and accelerated the growth rate of crystallization of nylon 6 molecules, even though high molecular weight of PSA was used.     

Synthesis and characterization of Li1.05Co1/3Ni1/3Mn1/3O1.95X0.05 (X = Cl,Br) cathode materials for lithium-ion battery

In order to improve the thermal stability and dynamic performance of LiCo_1/3Ni_1/3Mn_1/3O₂ materials, Cl-doped and Br-doped materials were synthesized via the co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by environment scanning electron microscopy (ESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), charge–discharge cycling and differential scanning calorimetry (DSC). Results show that all materials had a stable layered structure with α-NaFeO₂ and that Cl-doping slightly increased the size of grains. Both Cl-doping and Br-doping improved the high rate of discharge capacity, cycle-life performance and thermal stability, but Cl-doping was better than Br-doping in improving the material structure stability, dynamic performance and thermal stability.     

Use of thermal analysis techniques for evaluation of the stability and chemical properties of papaya biodiesel (<Emphasis Type="Italic">Carica Papaya</Emphasis> L.) at low temperatures

Solid state Ln₂–L₃ compounds, where Ln stands for light trivalent lanthanides (lanthanum to gadolinium), except promethium, and L is folate (C₁₉H₁₇N₇O₆), have been synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy (FTIR), TG coupled to FTIR, elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results provided information concerning the stoichiometry, crystallinity, ligand’s denticity, thermal stability, thermal behaviour and identification of the gaseous products evolved during the thermal decomposition of these compounds.     

Thermal behaviour of fumaric acid, sodium fumarate and its compounds with light trivalent lanthanides in air atmosphere

Characterization, thermal stability and thermal decomposition of light trivalent lanthanide fumarates, as well as, the thermal behaviour of fumaric acid and its sodium salt were investigated employing simultaneous thermogravimetry and differential thermal analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), TG?CFTIR techniques, elemental analysis and complexometry. On heating, sublimation of fumaric acid is observed, while the thermal decomposition of the sodium fumarate occurs with the formation of a mixture of sodium carbonate and carbonaceous residue. The thermal decomposition of light trivalent lanthanide fumarates occurs in consecutive and/or overlapping steps with the formation of the respective oxides: CeO₂, Pr₆O₁₁, and Ln₂O₃ (Ln?=?La, Nd, Sm, Eu, Gd).     

Dicationic Bis-Pyridinium Hydrazone-Based Amphiphiles Encompassing Fluorinated Counteranions: Synthesis,Characterization, TGA-DSC,and DFT Investigations

Quaternization and metathesis approaches were used to successfully design and synthesize the targeted dicationic bis-dipyridinium hydrazones carrying long alkyl side chain extending from C8 to C18 as countercation, and attracted to halide (I^-) or fluorinated ion (PF₆^-, BF₄^-, CF₃COO^-) as counteranion. Spectroscopic characterization using NMR and mass spectroscopy was used to establish the structures of the formed compounds. In addition, their thermal properties were investigated utilizing thermogravimetric analyses (TGA), and differential scanning calorimetry (DSC). The thermal study illustrated that regardless of the alkyl group length (Cn) or the attracted anions, the thermograms of the tested derivatives are composed of three stages. The mode of thermal decomposition demonstrates the important roles of both anion and alkyl chain length. Longer chain length results in greater van der Waals forces; meanwhile, with anions of low nucleophilicity, it could also decrease the intramolecular electrostatic interaction, which leads to an overall interaction decrease and lower thermal stability. The DFT theoretical calculations have been carried out to investigate the thermal stability in terms of the T_onset. The results revealed that the type of the counteranion and chain length had a substantial impact on thermal stability, which was presumably related to the degree of intermolecular interactions. However, the DFT results illustrated that there is no dominant parameter affecting the thermal stability, but rather a cumulative effect of many factors of different extents.     

Analysis of thermodynamic and kinetic stabilities in the thermal decomposition of the trinuclear μ-oxoacetates Fe 2 III MIIO(CH3OO)6(H2O)5, with M=Mn,Fe, Co or Ni

The thermal analysis of acetate clusters of general formula [Fe ₂ ^III M^IIO(CH₃COO)₆(H₂O)₃]·2H₂O, with M=Mn, Fe, Co or Ni, was performed in dynamic and quasi-isothermal regimes. The thermal decompositions of these compounds proceed in the interval 40–310° and consist of two endothermic and three exothermic stages. Dependence on the nature of the transition metal M is evidenced most explicitly in the parameters of the second stage, proceeding in the interval 103–170°. For this stage the sequences of thermodynamic stability and kinetic stability were established. The effect of the nature of the metal on the thermodynamic and kinetic parameters of the thermal decomposition processes involving the heteronuclear acetates was analyzed. Mechanisms for the first two stages of thermal decomposition are suggested.