Showing papers on "Thermogravimetric analysis published in 1995"

Synthesis, characterization, and properties of microemulsion-mediated nanophase TiO2 particles

Abstract: Nanophase Ti02 particles, with typical particle sizes in the range of 20-50 nm, have been synthesized using a microemulsion-mediated process. In this process, the aqueous cores ofwater/TritonX-100/exanol/ cyclohexane microemulsions have been used as constrained microreactors for the precipitation of precursor titanium hydroxide. The hydroxide particles thus formed were separated, dried, and calcined at different temperatures to form nanoparticles of TiO2. In order to see the phase transition temperature, thermogravimetric analysisldifferential thermal analysis studies were performed on the precursor hydroxide particles. The average particle size ofthese particles was determined by transmission electron microscopy, BET surface area and line broadening by X-ray diffraction. Phase transformation of these particles was confirmed by X-ray diffraction. The attenuation of ultraviolet radiation increased as the particle size decreased. As a catalyst for the photodegradation ofphenol, only the anatase form ofTiO2 showed significant degradation of phenol, whereas the rutile form of Ti02 was totally inactive for this reaction.

Thermal Properties of Polyaniline and Poly(aniline-co-o-ethylaniline)

Abstract: Block copolymers of aniline (r 1 1) can readily be formed by acid-catalyzed oxidation. These copolymers have enhanced solubility in common solvents, compared to polyaniline. For example, while a 47 mol % o-ethylaniline copolymer is 2-7 times more soluble in ethanol, methanol, and acetone than polyaniline, the solubility of the copolymer in tetrahydrofuran increases by more than 20 times. Thermal effects on the properties of polyaniline and poly(aniline-co-o-ethylaniline) in their emeraldine base forms have been studied by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electron paramagnetic resonance (EPR), four-probe conductivity, UV-vis, and FT-IR spectroscopies. Upon heating, the number of free electrons in the polymer, as determined by EPR, increases by up to 10 times. An irreversible exothermic transition was observed by DSC, which is believed to be an indication of cross-linking. The electron-donating character of the ethyl group appears to help stabilize the intermediates during the cross-linking reaction. Complete characterization of the copolymer is given.

Synthesis and Characterization of Degradable Poly(anhydride-co-imides)

Abstract: A series of poly(anhydride-co-imides) based on trimellitylimidoglycine (TMA-gly), pyromellitylimidoalanine (PMA-ala), sebacic acid (SA), or 1,6-bis(carboxyphenoxy)hexane (CPH) were synthesized by condensation polymerization. Monomers and polymers were characterized by NMR and IR spectroscopy, elemental and thermogravimetric analyses, and thermal transition temperatures. Contact angle, intrinsic viscosity, and compressive strength measurements were also performed on the polymers. For all polymer systems, the molecular weights decreased as the amount of imide in the backbone increased. Polymers containing CPH are more hydrophobic, have higher compressive strengths, have higher glass transition and decomposition temperatures relative to polymers containing SA, and exhibit no melting transitions. The mechanical and thermal stability of the materials are increased by the incorporation of imide groups in the polymer backbone. The selection of imide monomers, TMA-gly vs PMA-ala, can significantly affect the resulting polymer characteristics. Both imide monomers affect the hydrophobicity of the resulting polymers in similar ways, with the materials becoming more hydrophilic as the imide content is increased. However, polymers containing PMA-ala have thermal transition temperatures that are higher than the corresponding polymers with TMA-gly.

Structural characterization of plasma-sprayed hydroxylapatite coatings

Abstract: Plasma-sprayed hydroxylapatite coatings, widely used on metallic surgical implants to improve their adhesion to bone, are formed by rapid quenching of molten, or partly molten, particles which impact the substrate at high velocity. the performance of these coatings in the body depends upon their structure, which is not well understood. Coatings prepared under a range of spraying conditions have been studied by X-ray diffraction (XRD). differential thermal analysis (DTA), thermogravimetric analysis (TGA) and solid-state nuclear magnetic resonance spectroscopy (NMR). The results suggest that particles partly melt and lose combined water at lower plasma torch input powers forming a glass, by quenching of the liquid phase, and an OH-depleted hydroxylapatite residual crystalline phase. At higher power inputs an increasing amount of P2O5 is also lost and the coatings contain CaO and Ca4P2O9. Heat treatment of coatings in air at 600°C results in crystallization of the glass phase and reaction with water vapour to form hydroxylapatite. The results show that XRD is relatively insensitive to some of the structural details of hydroxylapatite coatings which may be significant to their performance. NMR provides more structural information and is a significant tool for coating characterization.

Synthesis, structure, and thermal properties of epoxy‐imide resin cured by phosphorylated diamine

Abstract: New phosphorylated epoxy-imide polymer was obtained using diimide-diepoxide (DIDE) cured with bis(3-aminophenyl)methylphosphine oxide (BAMP). In addition, composition of the synthesized diimide-diepoxide (DIDE) with common curing agents, e.g., 4,4′-diaminodiphenylether (DDE) and 4,4′-diaminodiphenylsulfone (DDS), were used for making a comparison of its curing reactivity, heat and flame retardation with that of bis(3-aminophenyl)methylphosphine oxide. The reactivity of those curing agents toward epoxy-imide, as measured by differential scanning calorimetry (DSC), was of the order DDE > BAMP > DDS. Through the evaluation of thermal gravimetric analysis (TGA), the new phosphorylated epoxy-imide polymer demonstrated excellent thermal properties as well as a high char yield. © 1995 John Wiley & Sons, Inc.

Thermal degradation of foamed polystyrene

Abstract: The thermal degradation of foamed polystyrene patterns in the expendable pattern casting (EPC) process has been studied. Various physical transitions that may occur during the degradation of the polymer have been determined with scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The effects of polymer density and bead structure on the degradation characteristics have been investigated. The results indicate that, when exposed to elevated temperatures, the polymer beads collapse at about 110–120 °C. The collapsed beads melt at 160 °C, and start to vaporize at temperatures greater than about 275 °C. Complete volatilization occurs in the temperature range 460–500 °C. The heat of degradation of expanded polystyrene has been estimated to be at the order of 912 Jg−1.

Characterization of chromia/alumina catalysts by X-ray photoelectron spectroscopy, proton induced X-ray emission and thermogravimetric analysis

Abstract: Chromia/alumina catalysts with different metal loading were characterized using X-ray photoelectron spectroscopy (XPS), proton induced X-ray emission (PIXE) and thermogravimetric (TG) techniques to elucidate the surface structure of these catalysts XPS studies on calcined samples show a sharp increase of the Cr/Al ratio at calcination temperatures up to 500°C while the ratio remains relatively unchanged at higher calcination temperature The surface state of chromium shows predominantly Cr6+ At calcination temperatures higher than 500°C, calcination-induced reduction is observed of the Cr6+ to Cr3+, where the fraction of chromia in Cr3+ oxidation state increases with increasing temperature A progressive increase of the intensity of the peak due to Cr 2p of the Cr3+ oxidation state is also observed with increasing amount of metal loading The calcination-induced reduction of the alumina-supported chromia was found to be less than the corresponding reduction of bulk CrO3 Also, the size of the spin-orbit splitting of the Cr 2p level of chromia catalysts which had undergone calcination-induced reduction was found to be smaller than would be expected for bulk Cr3+ The XPS spectra of chromium on the Cr/Al catalysts were found to be time dependent Photoreduction of Cr6+ on Cr/Al samples was found for irradiation times longer than 40 min It was found from PIXE analysis that at higher calcination temperature, the Cr/Al atomic ratio approaches the values obtained by XPS For all samples, the chromium particles were found to be homogeneously distributed on the alumina support for calcination temperatures up to 800°C Thermogravimetric results on uncalcined bulk CrO3 agree well with the XPS observation as to the fact that the main phase transformation of Cr6+ compounds occurs at about 500°C, resulting in reduction to Cr3+

Synthesis and physicochemical properties of cobalt aluminium hydrotalcites

Abstract: Cobalt aluminium hydrotalcites with different compositions were prepared by a coprecipitation method under low supersaturation conditions. The compounds were characterized by X-ray diffraction (XRD), infrared absorption (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and BET surface area measurements. XRD and IR studies revealed that all the compounds are single-phase crystallized under a hydrotalcite-like network. Hydrothermal treatments given to the aged sample increased the crystallinity of the samples. TG studies showed two stages of weight loss, the first due to the removal of interlayer water and the second ascribed to the removal of water molecules from the brucite sheet and CO2 from the interlayer carbonate anion, whose transition temperature depends on the Co/Al atomic ratio. Thermal calcination of these materials results in the formation of high surface area non-stoichiometric spinel phase whose crystallinity increases with increase in the calcination temperature attributed to the sintering of the particles.

Controlling the particle size of amorphous iron nanoparticles

Abstract: A method for controlling the particle size of amorphous iron, which was prepared by the sonication of iron pentacarbonyl [Fe(CO)5], is reported in this paper. The sonolysis was performed on neat Fe(CO)5 and its solutions in decane whose concentrations were 4 M, 1 M, and 0.25 M. The iron nanoparticles were subjected to TEM (Transmission Electron Micrograph), ESR (Electron Spin Resonance), TGA (Thermogravimetric Analysis), DSC (Differential Scanning Calorimctry), and Quantum Design SQUID magnetization measurement. The measured properties demonstrated a strong dependence on the concentration of the solution, e.g., particle size.

Dynamic mechanical analysis of epoxy composites plasticized by water : artifact and reality

Abstract: The plasticization of a glass/epoxy unidirectional composite by water has been investigated by Dynamic Mechanical Thermal Analysis (DMTA). The analysis of the thermomechanical spectra of the water aged material revealed the appearance of a splitting of the tan 6 peak associated with the α transition. This splitting was found to be dependent on the experimental conditions, i.e., the temperature scan rate, the straining frequency, and the initial water content on the composite. A thermogravimetric analysis (T.G.A.) of the wet specimens has shown that this effect could be attributed to an enhanced drying of the specimens above the glass transition, during the DMTA temperature scan. A differential plasticization of the epoxy network at the aging temperature can therefore not be invoked from the appearance of a splitting of the DMTA spectra. In conditions where the sample drying was minimized, plasticization effects on the thermomechanical properties of the composite were found to be temperature independent and reversible after re-drying of the aged material. Owing to the filling of hygrothermally induced cracks with water, the composite sensitivity to plasticization can be underestimated significantly at elevated aging temperature.

An Epoxy‐Silane Approach to Prepare Anode Materials for Rechargeable Lithium Ion Batteries

Abstract: A series of carbonaceous materials containing silicon and oxygen have been synthesized via pyrolysis of epoxy-silane composites prepared from hardened mixtures of epoxy novolac resin and epoxy-functional silane. Chemical composition of the pyrolyzed materials has been determined to be C{sub 1{minus}y{minus}z}Si{sub z}O{sub y} by a combination thermogravimetric analysis, Auger electron spectroscopy, carbon, hydrogen, and nitrogen analyses, and wet chemical analyses. Pyrolysis of the epoxy novolac resin gives pure carbon made up predominantly of single graphene sheets having lateral dimension of about 20 {angstrom} which are stacked like a house of cards. Pyrolysis of the pure epoxy-functional silane gives C{sub 0.50}Si{sub 0.19}O{sub 0.31} with a glassy structure. X-ray diffraction and electrochemical tests show that pyrolyzed materials prepared from mixtures initially containing less than 50% (by weight) silane are mixtures of the carbon single-layer phase and the glassy phase, while those initially with greater than 50% silane show predominantly the glassy phase. The reversible specific capacity of these materials increases from about 500 mAh/g for the pure disordered carbon up to about 770 mAh/g in the material which contains the most silicon and oxygen. However, the voltage profile develops hysteresis of about 1 V and the irreversible capacity associated with the firstmore » reaction within lithium increases as the silicon and oxygen contents are increased. Further work is needed to eliminate these drawbacks.« less

Perfluorocyclobutane aromatic ether polymers. II. Thermal/ oxidative stability and decomposition of a thermoset polymer

Abstract: The results of thermal and oxidative stability studies are reported for one perfluorocyclo-butane aromatic ether thermoset polymer. The polymer was prepared from 1,1,1-tris (4-trifluorovinyloxyphenyl)ethane by the thermal cyclodimerization of the trifluorovinyl either functionality, resulting in a network polymer comprising alternating perfluorocy-clobutane and aromatic either groups. The results of isothermal and dynamic thermal gravimetric analysis (TGA) studies are reported with kinetic approximations for de-composition in nitrogen, along with FTIR studies of the oxidative process in air and TGA/mass spec determination of the gasses evolved from decomposition in air. Based on these results, thermal and oxidative decomposition mechanisms are proposed. © 1995 John Wiley & Sons, Inc.

Synthesis of α-silicon nitride powder from a polymeric precursor

Abstract: Methylcyclosiloxanes and methylcyclosilazanes prepared using dichloromethylsilane have been reacted together to prepare a copolymer which was pyrolysed to give a ceramic powder. The copolymer was characterized using proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infra-red spectroscopy (FT-IR). Thermogravimetric analysis of the pyrolysis process and reactions which could occur during conversion of the copolymer to the ceramic are discussed. The product, which was found to be amorphous, was also studied using FTIR, crystallized by re-heating and characterized using FT-IR, X-ray techniques and scanning electron microscopy. It was identified as α-silicon nitride and its characteristics are compared with a conventionally prepared, widely used, commercially available grade of silicon nitride. The α-silicon nitride synthesised in the present work contains a wide range of particle morphologies, varying from needles (500 nm in length and 100 nm in width) to equiaxed agglomerates (200–500 nm in size with a substructure in the size range 50–120 nm).