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.     

The influence of exchangeable cation on thermal behaviour of ground vermiculite

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal resistance of hardened cement pastes containing vermiculite and expanded vermiculite

The durability and thermal stability of hardened Portland cement pastes containing vermiculite (V) and expanded vermiculite (EV) exposed to high temperatures were studied. Different mixtures were prepared using 2.5, 5, and 10 wt% of both types of V. Each mixture, after 28?days of hydration, was heated at 300, 600, and 800?°C for 3?h. Two modes of cooling were used; gradual cooling in air and rapid cooling in cold water. The percentage of residual strength, chemically combined water content, change in phase composition, and the thermal stability of the heated specimens were studied. The specimens cooled in water showed greater loss in strength than the air-cooled specimens. The presence of V improved the heat resistance of ordinary type I Portland cement (OPC) pastes. 5 wt% replacement revealed the best performance at all heating temperatures. The EV showed better thermal resistance than the nonexpanded one. Addition of silica fume (SF) with V in OPC pastes lead to superior performance. This can be explained as result of the combined effects of insulation properties of V and pozzolanic reactivity of SF which accounts for the notable increase in the residual strength for these mixes.     

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 characterization of polypropylene/vermiculite composites

Vermiculite clay (VMT) was organically modified with a quaternary organic salt and added to polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder. The morphology of the composites was investigated through wide-angle X-ray diffraction (WAXD). The WAXD results suggested that exfoliation phenomena were found for the composites with modified clay. The thermal properties of the obtained composites were studied by means differential scanning calorimetry (DSC) and thermogravimetry (TG) measurements. A variation in the crystallinity of PP was found. A significant increase of the thermal stability of PP was achieved in the presence of the modified VMT.     

Thermal behaviour of citric acid and isomeric aconitic acids

Thermal decomposition of citric acid, trans- and cis-aconitic acid has been studied using the TG-MS, TG-FTIR and DSC techniques. The measurements were carried out in an argon atmosphere over a temperature range of 293–673 K. The influence of the acid structures and configurational geometry on stability of the transition products and pathways of thermal transformations of the studied compounds studied is discussed.     

Thermal behaviour of hydrated lanthanide complexes with heptanedioic acid

The multi-step dehydration and decomposition of trivalent lanthanum and lanthanide heptanediate polyhydrates were investigated by means of thermal analysis completed with infrared study. Further more, X-ray diffraction data for investigated heptanediate complexes of general stoichiometry Ln₂(C₇H₁₀O₄)₃.nH₂O (wheren=16 in the case of La, Ce, Pr, Nd and Sm pimelates,n=8 for Eu, Gd, Tb, Dy, Er and Tm pimelates,n=12 for Ho, Yb and Lu pimelates) were also reported.

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Zusammenfassung Mittels TG, DTG, DTA wurde in Verbindung mit IR-Methoden der mehrstufige Dehydratations- und der Zersetzungsvorgang der Polyhydrate der PimelinsÄuresalze von dreiwertigem Lanthan und dreiwertigen Lanthanoiden untersucht. Röntgendiffraktionsdaten der untersuchten Heptandiat-Komplexe mit der allgemeinen Formel Ln₂(C₇H₁₀O₄)₃ nH₂O (mitn=16 für Ln=La, Ce, Pr, Nd und Sm,n=8 für Ln=Eu, Gd, Tb, Dy, Er und Tm sowien=12 für Ln=Ho, Yb und Lu) werden ebenfalls gegeben.

     

Thermal behaviour of lanthanide complexes of 1,3-propanediamine- tetramethylenephosphonic acid

1,3-propanediaminotetramethylenephosphonic acid (PDTMP, H₈L) was prepared and its complexes with some lanthanide ions (La(III), Eu(III), Gd(III) and Sm(III)) were isolated. The IR spectra and thermal stabilities of PDTMP and its complexes were studied. All the complexes contain physically and coordinately bound water molecules, which are released from the solid samples below 370°C. On heating PDTMP decomposes to phosphorus oxides, while its anhydrous complexes decompose to lanthanide oxides, and cyclic and linear polyphosphates between 400 and 1000°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal degradation behaviour of radiation grafted FEP-g-polystyrene sulfonic acid membranes

The thermal degradation behaviour and the gaseous products of FEP-g-polystyrene sulfonic acid membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films and the subsequent sulfonation were studied using thermal gravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR). The membranes were found to have a three-step degradation behaviour due to water removal, elimination of sulfonic acid groups and decomposition of the FEP matrix. The evolving gaseous products were identified using FTIR analysis. The degree of grafting was found to have a strong effect on the weight loss in the membranes, whilst the degradation temperatures of the individual membrane components were shown to be independent of the degree of grafting.     

Thermal behaviour of some derivatives of malic acid with calcium and strontium

Results are presented on the thermal behaviour of two derivatives of malic acid. The decomposition intermediates obtained at about 400?C were identified as derivatives of malonic acid. For some individual thermal decomposition steps, the values of the non-isothermal kinetic parameters were determined.     

Studies on manganese nodule leached residue 4. Physicochemical characterization and catalytic activity of acetic acid treated manganese nodule leached residue

The catalytic activity of water-washed manganese nodule leached residue (WMNLR) samples improved by treating with acetic acid. The effects of acetic acid treatment on the physicochemical properties and catalytic activity of manganese nodule leached residue have been studied. The surface area, surface oxygen, surface hydroxyl groups, surface acidity, electron donating properties, etc., increase gradually with acid treatment up to 0.5 M and thereafter show a decreasing trend. The rate constant of H2O2 decomposition, catalytic activity of CO oxidation, and esterification of acetic acid also show a similar trend to that of surface properties.     

Thermal behaviour of thallium(I) fatty acid salts,II

The electrical conductivity (EC) changes of thallium(I) salts of fatty acids, which possess liquid crystalline phases, were investigated as a function of temperature. It was found that sharp EC jumps are associated with the phase transitions. The EC of the liquid crystalline phases depended not only on the temperature, the molecular weight and the geometry of the measuring cell, but also very sensitively on the heat treatment conditions which affect the relative magnitude of the EC in the mesophases.Study of these dependences revealed a memory effect. An explanation is given for this phenomenon.

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Zusammenfassung Die Änderungen der elektrischen Leitfähigkeit (EC) von Fettsäure-Thalium(I)-Salzen mit flüssig-kristallinen Phasen wurden als Funktion der Temperatur untersucht. Es wurde festgestellt, daß den Phasenübergängen scharfe EC-Sprünge entsprechen. Die EC der flüssig-kristallinen Phase hängt nicht nur von der Temperatur, dem Molekulargewicht und der Geometrie der Meßzelle ab, sondern auch — in sehr empfindlicher Weise — Phasen bestimmen.Die Untersuchung dieser Zusammenhänge führte zur Beobachtung eines »Memorieeffektes« Eine Erklärung dieser Erscheinung wird gegeben.

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Résumé On a étudié les variations de la conductibilité électrique (EC) des sels de thallium(I) des acides gras possédant des phases cristallines liquides, en fonction de la température. On a établi que les variations brusques d'EC correspondent aux transitions de phases. L'EC des phases cristallines liquides dépend non seulement de la température, de la masse molaire et de la géométrie de la cellule de mesure, mais aussi, et d'une manière très sensible, des conditions du traitement thermique qui affectent l'amplitude relative de l'EC dans les mésophases.Un «effet de mémoire» a été observé lors de l'étude de ces phénomènes, dont on donne une explication.

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(I) , , . , . - , , , . « ». .

     

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.     

Equilibrium behaviour of exchange of [Coen3]3+ on vermiculite

Summary The cation exchange data of tris ethylene diamine cobaltic ion on H-vermiculite fit in with theLangmuir equation. The exchange of [Coen₃]³⁺ by different cations are in the order: Li < Na < NH₄ < K < Rb < H < Cs for the monovalent, Mg Ca < Ba for the bivalent and (C₂H₅)₄N < (CH₃)₄N CTA < CP for monovalent organic ions. Quaternary cations such as (C₂H₅)₄N⁺ exchange less than (CH₃)₄N⁺. This may be ascribed to the larger size of the former and also to the limitedc-axis expansion of vermiculite. By use of the equation ofKielland, thermodynamic equilibrium constants and standardGibbs free energy change have been evaluated. The plots of log (selectivity coefficient) vs. hydrated ionic radius and the reciprocal of theDebye Hückel parametera ⁰, suggest that the parametera ⁰ rather than the hydrated ionic radius may be found to correlate with the relative affinities of univalent cations for the vermiculite surface.     

Thermal behaviour of riboflavin

From the thermal decomposition curves of riboflavin at various heating rates in static air atmosphere, the stages of thermal decomposition of this compound were established. The following kinetic parameters were calculated for the first decomposition stage of this process: activation energy (E _a ), reaction order (n), preexponential factor (A) and reaction rate constant (k). A mechanism of the changes is proposed.

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Zusammenfassung Die Stadien der thermischen Zersetzung von Riboflavin wurden aus den Kurven der thermischen Zersetzung in Luftatmosphäre bei verschiedenen Aufheizgeschwindigkeiten ermittelt. Für den ersten Zersetzungsschritt dieses Prozesses werden die Werte für die Aktivierungsenergie (E _a ), die Reaktionsordnung (n), den präexponentiellen Faktor (A) und die Reaktionsgeschwindigkeitskonstante (k) berechnet. Für die Umwandlungen wird ein Mechanismus vorgeschlagen.

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, , . , (E _a ), (n), (A) (k). .

     

Thermal behaviour or thallium(I) fatty acid salts,I

We have studied the thermal behaviours of the fatty acid (C₁-C₉, C₁₂, C₁₄, C₁₆ and C₁₈) thallium(I) salts.Investigating the dependence of the thermal decomposition reactions on the experimental conditions, we established that they decompose differently depending on the atmosphere, and on the shape and material of the sample holders.We also determined the heat-stable temperature ranges of the compounds in which they can be investigated without any thermal decomposition.The temperatures and enthalpy changes of the polymorphic and phase changes were measured and the corresponding entropy changes were calculated.

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Zusammenfassung Das thermische Verhalten der Thallium(I)-Salze der Fettsäuren mit C₁ bis C₉, C₁₂, C₁₄ und C₁₈ wurden untersucht. Die Temperaturen und Enthalpien der einzelnen polymorphen und Phasenänderungen, sowie die thermische Stabilität der Verbindungen wurden bestimmt. Es wurde festgestellt, daß die zu Ketonen und Gemischt-Ketonen führende thermische Zersetzung in der Schmelzphase von Destillationsprozessen begleitet wird, welche von der Molekülstruktur und von zahlreichen Versuchsbedingungen abhängig sind.

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Résumé Etude du comportement thermique des sels de thallium(I) d'acides gras (de C₁ à C₉, C₁₂, C₁₄ et C₁₈). L'étude de la décomposition thermique en fonction des conditions expérimentales a permis d'établir que les sels étudiés se décomposent différemment suivant l'atmosphère utilisée, ainsi que suivant la forme et la nature des supports échantillons. Détermination des domaines de température où ces composés restent thermiquement stables. Mesure des températures et des variations d'enthalpie des transitions de phase et des transitions polymorphiques et calcul des variations d'entropie correspondantes.

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(I) C₁-C₉, C₁₂, C₁₄, C₁₆, C₁₈. , . , , , .

     

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 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.