Showing papers on "Thermogravimetric analysis published in 1989"

Thermal analysis of chemically synthesized polyaniline and effects of thermal aging on conductivity

Abstract: Thermal characteristics of chemically synthesized polyaniline with various dopants have been studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared spectroscopy, gel-permeation chromatography (GPC), and chemical titration. The HCl-doped polyaniline shows three major weight losses at around 100, 200, and 500°C which are assigned to removal of H2O and HCl, and decomposition of the polymer, respectively. Thermal aging of the HCl-doped polyaniline performed at 100, 150, and 200°C for various periods of time results in a decrease in conductivity. After the thermal treatments, the polymer can be re-doped with HCl to partially recover the conductivity. However, both the conductivity and the doping level cannot be restored to the level of the original materials owing probably to changes in morphology, crosslinking, or other chemical reactions.

Effect of oxides on binder burnout during ceramics processing

Abstract: The burnout of poly (vinyl butyral) from green bodies of oxide ceramics was studied by thermogravimetric analysis and infrared spectroscopy. The decomposition of the polymer to release butyraldehyde, in air or in argon, was enhanced by the presence of the oxide powders. The degree of enhancement was much greater in the presence of oxygen. Ceria gave rise to a separate oxidation process at lower temperatures. The concentration of carbon remaining after treatment to 1000° C was correlated with surface activity.

Thermogravimetric analysis of cellulose: Effect of the molecular weight on thermal decomposition

Abstract: Cellulose fractions of different molecular weights were subjected to dynamic thermogravimetric analysis in a nitrogen atmosphere. From the experimental data, activation energies and reaction orders were obtained following the Freeman–Carroll and Broido methods. The thermal stabilities of the samples were estimated taking into account the values of Ti, Tmax, and Ea. The results show that thermal stability increases as the molecular weight increases. It was also found that the cellulose pyrolisis process cannot be described as having a single value of Ea over the entire pyrolisis range. The dependence of Ea. The dependence of Ea on molecular weight is also discussed.

Thermal decomposition of butylindium thiolates and preparation of indium sulfide powders

Abstract: Thermal properties of organoindium thiolates were investigated by means of thermogravimetric (TG) and differential thermal (DT) analysis. Dibutyl-indium propylthiolates (Bun2InSPrn, Bun2InSPri, Bui2InSPrn and Bui2InSPri) decomposed up to 280°C along with an exothermic DT peak and gave indium(I) sulfide (InS) powders. Although the arylthiolate Bun2InSPh also afforded InS powders, it decomposed at a slightly higher temperature. In contrast, the dithiolate and the dithiocarbamate complexes [BunIn(SPri)2 and In (S2CNBu2)3] gave indium(III) sulfide (In2S3) powders.

Chemical energy storage by the reaction cycle CuO/Cu2O

Abstract: The cyclic decomposition of cupric oxide followed by the oxidation of cuprous oxide in air was studied, in order to investigate the potential use of this reaction cycle for chemical energy storage. Isothermal and non-isothermal thermogravimetric method was used to study the kinetics of these reactions. The activation energy of the forward reaction (decomposition) is 313.0 kJ mol−1 in the temperature range 760–910°C, while that for the backward reaction is 76.5 kJ mol−1 in the temperature range 400–500°C. The reaction reactivity was found to be essentially unchanged for up to 20 cycles. This was explained as due to the swelling of the CuO particles and the development of a highly porous structure on repeated cycling.

The preparation, characterization and electrical properties of copper manganite spinels, CuxMn3−xO4, 0 ⩽x ⩽ 1

Abstract: Single-phase copper manganite spinels CuxMn3−xO4 with 0⩽x⩽1 were prepared by a careful thermal processing of copper-manganese co-precipitated hydroxide precursors. Powder X-ray diffraction (XRD) analysis of these spinels revealed the presence of a tetragonally distorted single spinel phase, with tetragonal distortionc/a > 1 which decreases with copper content. Thermogravimetric analysis (TGA) curves, run in an oxygen atmosphere for all the compositions studied, are characterized by a stability step up to 250 to 300° C, followed by a domain of oxidation between 300 and 900° C and finally a domain of reduction that restores the initial stoichiometry of the samples. The oxidation is observed to occur in two successive steps. The phenomenon appearing at the low temperature is due to the oxidation of Cu+ ions, while that at higher temperature corresponds to the oxidation of Mn2+ ions in tetrahedral sites. Further, electrical resistivity measurements confirm the presence of Cu+ ions on the tetrahedral sublattice of spinel. Correlation of the results obtained by XRD, TGA and electrical resistivity measurements permits one to infer the cation distribution, given by Cux+Mn1−x2+[Mn2−x3+Mnx4+] O42−.

Thermal stability and degradation studies of polyester resins

Abstract: Thermal behavior and degradation mechanisms of three polyester resins, namely bisphenol A based, isophthalic acid based, and general purpose were studied. These resins were cured with styrene in the presence of benzoyl peroxide (BPO) and methyl ethyl ketone peroxide (MEKP) as initiators. The cured resins were studied by thermogravimetric analysis and mass spectrometry. From the thermogravimetric data it was observed that the cured bisphenol-A-based polyester resin was thermally more stable than the cured isophthalic acid-based and general purpose polyester resins. It was also observed that polyester resins cured with MEKP are thermally more stable than benzoyl peroxide-cured products. Thermogravimetric analysis data shows that there are two first-order degradation reactions during thermal degradation in nitrogen atmosphere. The first degradation step involves the scission of cross-links/weak links with the liberation of free linear chains. The second step involves a random scission of the free linear chains into smaller fragments. The framentation patterns of the polyester resins were identified by mass spectrometery. Possible mechanisms for the degradation of the cured polyesters accounting for the experimental observations are discussed.

Surface Area, Adsorption, and Desorption Studies on Indoor Dust Samples

Abstract: Adsorption by dust samples from homes was studied to evaluate the extent to which household dust particles could act as carriers of vapors into the lower respiratory tract. The dust samples were examined for volatilizable and combustible materials via thermogravimetric analysis as well as for specific surface area and surface characteristics by nitrogen and formaldehyde adsorption and desorption isotherms. Particle morphology and size were examined by scanning electron microscopy (SEM) and elemental composition by energy dispersive x-ray analysis (EDXA). Thermogravimetric analysis (TGA) demonstrated marked differences between samples from different homes. The volatilizable material removed by heating dust samples in argon to 500°C ranged from 32% to 69%. The residue not combustible in oxygen at 700°C, presumably minerals, ranged from 11% to 58%. In most cases, differences between samples from the same borne were small. SEM of the samples demonstrated the presence of many fibers and of irregularly shaped p...

Rapidly quenched Bi-containing high T c superconducting oxide compositions

Abstract: Twin roller quenching from the melt at cooling rates of ∼107 K s−1 was used on several Bi-containing high Tc compositions. Pure glass was obtained in most compositions and the route of crystallization was studied by differential thermal and thermogravimetric analysis, x-ray diffraction, and magnetic measurements. Heating of the glasses produced poorly crystallized short-range-order-only as determined by x-ray diffraction, despite passing through several exotherms, some of which were very strong. This anomalous behavior deserves further investigation. On heating to higher temperatures the expected double-copper-oxide-layer high Tc phase formed sluggishly via intermediate CuBi2O4 and/or single-copper-oxide-layer Bi2(Sr, Cu)2CuO4 phases. Considerable oxygen absorption of about 0.5 O per Cu occurs during these steps, peaking at about 680 °C; some of this oxygen is lost again by the time the high Tc phase forms just below the melting point.

Polyamides containing arylene sulfone ether linkages

Abstract: dibenzoyl chloride (SMCl), and arylene sulfone ether diamines (SED), by solution and interfacial polymerization techniques. In solution polymerization, the effect of various acid acceptors such as propylene oxide (PO), lithium chloride (LiCl)/lithium hydroxide (LiOH), and triethylamine (TEA) on molecular weight of the polyamides was studied. The effect of methyl substituted and unsubstituted aromatic sulfone ether diamines on molecular weight and thermal properties of polyamides was also studied. The polyamides prepared were characterized by solution viscoSity, elemental analysis, thermal gravimetric analysis, differential scanning calorimetry, and x-ray diffraction. Physical and thermal properties of polyamides prepared from SPCl and SED were compared with the polyamides prepared from SMCl and SED.

Cellulose pyrolysis kinetics in a simulated solar environment

Abstract: The instrumentation and methods required to study rapid, radiative decomposition of highly reactive biopolymers are described and used to determine the kinetic parameters for the pyrolysis of Avicel PH105 microcrystalline cellulose. Experiments were carried out at heating rates greater than 2 K/s in a specially fabricated thermogravimetric analyzer system which employed a 30-kW e /2-kW th downward-facing beam, arc-image furnace as a heat source. The thermogravimetric data were interpreted assuming a simple, single-step reaction mechanism and using a nonlinear least-squares kinetic analysis

Study of the formation of silicoaluminates by the sol-gel method, by means of IR, DTA and TGA

Abstract: Silicoaluminates were synthesized from aluminum and silicon alkoxides with varying water content. The obtained solids were studied by infrared spectroscopy (IR), Thermal Differential Analysis (DTA) and Thermogravimetric Analysis (TGA). The results show a positive water effect in the rate of polymerization and in the number of Si tetrahedral functional groups (OR) substituted by the aluminum. This type of material has high surface area, suitable to act as a catalyst support.

Arylidene Polymers IV. Synthesis, Characterization and Morphology of New Polyesters of Diarylidenecyclohexanone:

Abstract: New polyesters prepared by the intefacial polycondensation of 2,6-bis(4- hydroxybenzylidene )cyclohexanone (I) and 2,6-bis(4-hydroxy-3-methoxybenzylidene)- cyclohexanone (II) with 4,4'-diphenic, isophthalolyl, terephthaloyl, adipoyl and sebacoyl dichlorides have been produced The yield and the values of reduced viscosity of the polyesters were found to be affected by the kind of organic phase, the quantitative ratio of organic to aqeuous phase, concentration of hydrogen chloride acceptor, rate of acid chloride addition, contribution of benzyltriethylammonium chloride as a catalyst and the temperature of the polycondensation reactionIn order to characterize these polymers the necessary model compounds were prepared from I or II and benzoyl chloride The resulting polyesters were characterized by IR, elemental analyses, viscometry, DTA, DSC measurements and thermogravimetric analy sis The crystallinity of all polyesters was examined by X-ray analysis In addition the electrical properties of the polyeste

Synthesis, characterization, and thermal stability of bismaleimides derived from maleimido benzoic acid

Abstract: Bismaleimides containing ester, amide, urethane, and imide groups in the backbone were synthesized from maleimido benzoic acid via its acid chloride or isocyanate with 4,4′-dihydroxy-diphenyl-2,2-propane, 3,3′-diamino diphenyl sulfone, and 3,3′,4,4′-benzophenone tetracarboxylic acid anhydride by simple condensation or addition reaction. The new bismaleimides are characterized by IR, 1H-NMR, and elemental analysis. DSC studies of these bismaleimides indicated a curing exotherm in the temperature range 150–270°C with heat of polymerization 30–50 J/g. Thermogravimetric analysis of the uncured resins showed high thermal stability and char yield for imide containing bismaleimide. The observed char yields of the bismaleimide resins are in accordance with the calculated C/H ratios.

Adsorption of Dispersants on Zirconia Powder in Tape‐Casting Slip Compositions

Abstract: This paper reports the extension of the more fundamental work of Tormey et al. on the effectiveness of a common dispersant (menhaden fish oil) and a model system (glycerol trioleate) to tape-casting slip formulation. The adsorption isotherms of the two adsorbates on doped zirconia from methyl ethyl ketone—ethanol solutions were measured by thermogravimetric analysis of solutions equilibrated with the powder surface. Viscosity decreased while sintered density increased in tape-cast samples prepared to dispersant concentrations corresponding to points along the adsorption isotherm in a way which follows the isotherm if binder competition for surface sites is considered.

Very high heat thermoplastic polyetherimides containing aromatic structure

Abstract: The present invention relates to a wholly aromatic polyetherimide further containing sulfur containing groups in the backbone of the polyetherimide The polyetherimide is characterized by extremely high glass transition temperatures, high chemical resistance and thermogravimetric stability

Kinetic analysis of thermogravimetric data on some nickel(II) N-alkyldithiocarbamates

Abstract: Thermogravimetric and derivative thermogravimetric curves of some complexes [Ni(S2CNHR)2] (R=Me, Et, Pri, Bui, But, Bz,p-MePh,p-MeOPh,p-ClPh,p-NO2Ph) in a dynamic nitrogen atmosphere were studied to determine their modes of decomposition. All these complexes show similar TG profiles. The weight losses in the main decomposition stages indicate conversion of the nickel(II) dithiocarbamates to sulphide. Reaction orders were estimated via the shape characteristics of the corresponding derivative thermogravimetric curves and kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern and Horowitz-Metzger methods.

Laboratory screening of engine lubricants for high temperature performance

Abstract: Key properties of lubricants designed to operate in future high temperature engine applications are their oxidation stability, volatility and thermal stability. Isothermal differential scanning calorimetry (DSC) and temperature programmed thermogravimetric analysis (TGA) are rapid and convenient ways to assess these properties. These techniques were employed to evaluate the performance of a range of mineral and synthetic base fluids containing the same additive system. This revealed a strong influence of basestock structure on oxidation performance, with pentaerythrityl tetra (linear acid) esters showing the best performance of the structures tested. The behavior of DSC induction period with temperature has been examined for different lubricants and the energies of activation derived from the Arrhenius relationship are discussed in relation to the mechanism of inhibited autoxidation

Electrical, optical and ESR study of thin films of plasma polymerized acrylonitrile

Abstract: Thin films of plasma-polymerized acrylonitrile (PPAN) were deposited by glow discharge polymerization and were made semiconducting by the process of pyrolysis. Electrical and optical measurements along with electron spin resonance (ESR) measurements were used to study the extent of conjugation in the pyrolysed system. The onset and building up of conjugation due to the structural remodifications was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and infrared (IR) spectroscopy. A major structural transition was observed at around 550 K which is responsible for the drastic reduction in the electrical resistivity and optical band gap. ESR studies revealed that pyrolysis causes conjugation and generation of free radicals in PPAN, thereby enhancing the electrical conductivity The mechanism of conduction was observed to be dominated by the variable-range hopping.

Study of the kinetics of decomposition of goethite in vacuo and pore structure of product particles

Abstract: The kinetics of decomposition ofα-goethite were investigated, under vacuum conditions, in the temperature range 170–250° C. The experimental thermogravimetric traces were interpreted according to the shrinking core model for cylindrical particles. The Arrhenius plot of InK (kinetic constant) against 1/T yielded an activation energy of 119±9 kJ mol−1 at 210° C. The highest specific area,S BET=118.4±5.5 m2 g−1, of the reaction productα-hematite, was obtained by decompsition at 225° C. Information about the formation of micropores and their evolution with temperature was also obtained.