Showing papers on "Thermogravimetric analysis published in 1997"

Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres: Part I Fibre characterization

Abstract: The microstructure, thermal and mechanical properties of flax and wheat straw fibres have been examined with a view to using these natural fibres as reinforcing additives for thermoplastics. In this regard, the fibres were characterized prior to incorporation into the polymer, using a range of techniques, including SEM, image analysis, thermogravimetric analysis and micro-mechanical tensile testing, at room and elevated temperatures. The thermal and mechanical properties obtained have been discussed in relation to the measured composition and structural form of the fibres.

Carbothermal synthesis of titanium carbide using ultrafine titania powders

Abstract: The synthesis of titanium carbide (TiC) by the carbothermal reduction of carbon coated titanium dioxide (TiO2), a novel synthesis process, and titanium dioxide (TiO2) mixed with carbon black was investigated. A high surface area (64 m2g-1) TiO2 powder consisting of anatase and rutile phases was used for starting powders. The carbon coated method is a two-step process that utilizes a precursor derived from decomposing propylene (C3H6) and depositing carbon on the TiO2 particles. TiO2 powders were also mechanically mixed with carbon black for comparison. Both starting precursors and mixtures were reacted in a tube furnace for 2 and 4 h at temperatures of 1100°C to 1550°C under 1 l min-1 flowing argon. The TiC powders were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analyser, chemical analysis (oxygen and carbon) and transmission electron microscopy (TEM). The carbon coating process provides high contact area between the reactants which results in a TiC product with lower oxygen content (0.6 wt%), finer particle size (0.1 μm), and uniform shape when synthesized at 1550°C for 4 h.

Synthesis of pure amorphous Fe2O3

Abstract: A method for the preparation of pure amorphous Fe2O3 powder with particle size of 25 nm is reported in this article. Pure amorphous Fe2O3 can be simply synthesized by the sonication of neat Fe(CO)5 or its solution in decalin under an air atmosphere. The Fe2O3 nanoparticles are converted to crystalline Fe3O4 nanoparticles when heated to 420 °C under vacuum or when heated to the same temperature under a nitrogen atmosphere. The crystalline Fe3O4 nanoparticles were characterized by x-ray diffraction and M¨ossbauer spectroscopy. The Fe2O3 amorphous nanoparticles were examined by Transmission Electron Micrography (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Quantum Design SQUID magnetization measurements. The magnetization of pure amorphous Fe2O3 at room temperature is very low (<1.5 emu/g) and it crystallizes at 268 °C.

Infrared and thermogravimetric study of high pressure consolidation in alkoxide silica gel powders

Abstract: High density, transparent, crack-free and hard compacts of silica gel were produced by compaction under nearly hydrostatic environment at 4.5 GPa, at room temperature. The starting material was used three days after synthesis by hydrolysis of alkoxides without additional treatment. Fourier transform infrared spectroscopy (FTIR), using the KBr technique and a high vacuum cell at temperatures up to 450°C, and thermogravimetric analysis (TGA) up to 900°C was conducted. A reduction up to 60% in the adsorbed water content of the compacted silica gel was observed. Changes in the 3000 to 3800 cm−1 region indicate that the surface silanol groups became bridged, which promotes condensation reactions of dehydroxylation. Those results suggest that the mechanism for consolidation under high-pressure, is ‘cold sintering’ process, where silanol groups at the surface of the nanoparticles condense to form siloxane bonds between the particles and water, resulting in a stiff body with closed nanopores containing trapped water.

Characterization of sonochemically prepared unsupported and silica-supported nanostructured pentavalent molybdenum oxide

Abstract: We describe the preparation and characterization of unusual pentavalent molybdenum oxide stabilized by water molecules, Mo2O5·2H2O. Ultrasound irradiation of a slurry of molybdenum hexacarbonyl, Mo(CO)6, in Decalin for 3 h under ambient air yields blue-colored Mo2O5·2H2O. Infrared (FT-IR) spectrum analysis of the resulting blue product reveals that the Mo ions possess molybdenyl bonds (MoO) and Mo−O character and also shows the presence of hydrogen-bonded, as well as coordinated, water molecules. The DSC profile of the blue oxide shows the presence of two endothermic peaks at around 100 °C and 140 °C, corresponding to the elimination of hydrogen-bonded and coordinated water molecules, respectively. The amount of water molecules was determined by thermogravimetric analysis (TGA). Characterization using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) shows the amorphous nature of the blue product. The TEM picture shows that the blue ox...

Preparative Parameters, Magnesium Effects, and Anion Effects in the Crystallization of Birnessites

Abstract: Na-birnessites (Na4Mn14O27·9H2O) have been prepared by aging MnOx gels, whose composition can be represented as MnA·wMgA·xKMnO4·yNaOH·zH2O (A is any of the anions of chloride, nitrate, sulfate, and acetate) The effects of aging time, aging temperature, basicity, the amount of water, the addition of Mg2+, the ratios of MnO4-/Mn2+, and types of anions on the crystallization of birnessite, the phase transformations of intermediate phases, the morphology, the ion-exchange properties, and the thermal stability have been investigated XRD (X-ray diffraction), SEM (scanning electronic microscope), EDX (energy dispersive X-ray), IR (Infrared), DSC (differential scanning calorimetry), and TGA (thermogravimetric analysis) techniques have been used The preparative parameters such as composition and temperature have been optimized Three stages are observed in the crystallization process of birnessite on increasing the crystallization time: an induction period, a fast crystallization period, and a steady-state per

The relative physical and thermal properties of polyurethane elastomers: Effect of chain extenders of bisphenols, diisocyanate, and polyol structures

Abstract: Polyurethane elastomers based on polyols such as polycaprolactone diol of molar mass 2000 and polytetramethylene glycol of molar mass 2000; diisocyanantes such as diphenyl methane 4,4′ diisocyanate and dicyclohexyl methane 4,4′ diisocyanate; and chain extenders such as bisphenol-A, bisphenol-S,bisphenol-AF, and their brominated derivatives were synthesized. The effects of polyol, diisocyanate, and chain extender on the physical and thermal properties were also studied. The polyurethane elastomers were investigated by X-ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Their limiting oxygen indexes (LOIs), solubilities, tensile strengths, hardnesses, and elongations were also determined. XRD analyses revealed that all of the polyurethanes were semicrystalline. However, the addition of bromine atoms in the polyurethanes markedly decreased their degrees of crystallinity. The brominated polyurethane elastomers have good flame retardancy, as indicated by large LOIs. All of the unbrominated polyurethanes showed good mechanical properties and high thermal stabilities. Polyurethanes based on bisphenol-S had lower solvent resistance caused by the dipolar nature of sulfonyl groups in the polymer chains. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1251–1265, 1997

Adsorption and Thermogravimetric Studies of Silica-Based Amide Bonded Phases

Abstract: Moreover, adsorption energy distribution functions were calculated from submonolayer adsorption data using the regularization method. It was estimated that about 40% of the available surface silanols were converted to amine groups and about 60% of amines were converted to amides. It was shown that although the chemical modification of the surface does not significantly alter the porous properties of the starting silica, it significantly affects the interaction of nitrogen probe molecules with the surface. Moreover, it was demonstrated that nitrogen adsorption is quite sensitive to the presence or absence of various functional groups on the silica surface and that the information obtained from the adsorption measurements can be utilized for the characterization of silica-based materials used in chromatographic applications.

Self-Assembled Monolayer Coatings on Amorphous Iron and Iron Oxide Nanoparticles: Thermal Stability and Chemical Reactivity Studies

Abstract: Self-assembled coatings of long chain thiols on nanoparticles of amorphous iron as well as on amorphous Fe2O3 were formed. The thermal stability of these coatings was investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the particles and by mass spectrometric analysis of the molecules desorbed from the surface by heating the amorphous substrates. The results showed a sharp weight loss centered at about 200 °C for the thiol-coated particles. The mass spectrometric study of the molecules removed from the surface of the amorphous iron revealed the formation of a dialkyl thioether. For the amorphous Fe2O3 surfaces, a dialkyl disulfide was removed from the surface. The desorptions from the Fe2O3 surface occurred at higher temperatures than those for the amorphous iron. The different mechanisms responsible for these desorption reactions are discussed.

Synthesis and characterization of molybdenum disulphide formed from ammonium tetrathiomolybdate

Abstract: An investigation has been carried out into the possibility of in situ formation of MoS2 within porous anodic films on aluminium, to improve subsequent tribological behaviour, by re-anodizing in thiomolybdate electrolyte. Acidification of thiomolybdate was employed to simulate the conditions for formation of the sulphide at the anodic film/electrolyte interface, followed by appropriate vacuum heat treatments to study possible temperature effects on the sulphide due to either friction or Joule heating during anodizing. The products of both acidification and heat treatment, characterized by X-ray powder diffraction and scanning electron microscopy, were compared with those formed by direct thermal decomposition of ammonium tetrathiomolybdate crystals. The precipitate formed by acidification was mainly amorphous molybdenum trisulphide (MoS3), which on heat treatment at 450 and 850°C yielded 3R-MoS2. 3R-MoS2 also formed by the thermal decomposition of thiomolybdate crystals. Thermogravimetric and differential thermal analyses showed that the decomposition of MoS3 to MoS2 occurred in the range 220–370°C and revealed the sequence of reaction steps. The findings suggest that mainly amorphous MoS3 is formed as a consequence of changes in the pH of the film/electrolyte interface during re-anodizing but the product is relatively easily transformed to crystalline MoS2 on moderate heating which may occur during wear processes.

Thermogravimetric analysis on global mass loss kinetics of rice hull pyrolysis

Abstract: Pyrolyses of rice hulls were performed in a thermogravimetric analyzer from room temperature to 1173 K at heating rates of 10, 30, 60, and 100 K/min. The global mass loss during rice hull pyrolysis was modeled by a combination of the volatile evolutions of four independent parallel lumps: one for moisture and the other three for nonmoisture volatiles. The decomposition of each lump was characterized by a single reaction, first-order with respect to the amount of volatile yet to evolve. The moisture lump evolves mainly at low temperatures with an activation energy of 48 kJ/mol. The activation energies for the evolution of the nonmoisture volatile lumps, which are attributed to the decompositions of hemicellulose, cellulose, and lignin, are 154, 200, and 33 kJ/mol, respectively. Excellent agreement between the experimental data and model predictions was found.

Characterization and catalytic performance of mesoporous molecular sieves Al-MCM-41 materials

Abstract: Mesoporous Al-MCM-41 materials of different Si/Al ratios have been synthesized and characterized by X-ray powder diffraction, 27Al and 29Si MAS NMR, differential thermogravimetric analysis, N2 adsorption measurements, FT-IR and catalytic cracking of alkanes. The experimental results show that the incorporation of aluminium into the framework of MCM-41 has a great effect on the degree of long-distance order, the surface acidities and the mesoporous structures of the materials. With increase of the aluminium content, the amounts of tetrahedral framework aluminium and the acid sites on the samples increase, but the acid strength decreases. Al-MCM-41 materials exhibit high activity for n-C160 cracking and good selectivity for producing low carbon alkylenes, particularly for i-C4=.

Synthesis and Characterization of Silazane‐Based Polymers as Precursors for Ceramic Matrix Composites

Abstract: The goal of this investigation was to optimize the synthesis of silazane-based polymers for processing fibre-reinforced ceramic matrix composites (CMCs). Liquid oligomeric silazanes were synthesized by ammonolysis of chlorosilanes and characterized spectroscopi- cally (FTIR, NMR) as well as by elemental analysis. The silazanes were obtained in high yield and purity. Different functional groups (system S1: Si—H, Si—CH3, Si—CH=CH2) and different degrees of branching in the Si—N backbone [system S2; Si(NH)3, Si(NH)2] were realized in order to study the properties of the silazanes that are dependent on the molecular structure. For processing ceramics via pyrolysis of pre-ceramic oligomers, molecular weight, rheological behaviour, thermosetting and ceramic yield were investigated systematically and correlated with the molecular structure of the silazanes. Low molecular weights (500–1000 g mol−1) as well as low viscosity values (0.1–20 Pa s) enable processing of the silazanes in the liquid phase without any solvent. Due to the latent reactivity of the functional groups, curing of the polymers via hydrosilylation is achieved. Structural changes and weight loss during polymer curing as well as the organic/inorganic transition were monitored by FTIR spectroscopy and differential thermogravimetric analysis. With increasing temperature (room temperature to 800 °C) the hydrogen content decreases from 7 to < 0.5 wt% due to the formation of gaseous molecules (NH3, CH4, H2). High ceramic yields up to 80% were reached by branching the oligomers, thus reducing the amount of volatile precursor fragments. Up to 1300 °C, ceramic materials remained amorphous to X-rays. At higher temperatures (1400–1800 °C) either SiC or SiC/Si3N4 composites were selectively crystallized, depending on the pyrolysis conditions. The utility of the optimized precursors for CMCs has been demonstrated by infiltration of fibre preforms and subsequent pyrolysis. © 1997 by John Wiley & Sons, Ltd.

Steam reforming of methanol on binary CuZnO catalysts: Effects of preparation condition upon precursors, surface structure and catalytic activity

Abstract: Precursors for CuZnO catalysts, with CuZn molar ratios in the range from 1000 to 0100, were prepared by two coprecipitation methods These methods differ by the addition rate of a mixed Cu(NO3)2Zn(NO3)2 solution to a NaHCO3 solution Characterisation by powder X-ray diffraction (PXRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), FT-IR and UV/VIS spectroscopies indicated that the structure of precursors with CuZn ratios in the range of 3070 to 7030 depends greatly upon the addition rate of the mixed solution Amorphous copper hydroxycarbonate and sodium zinc carbonate were formed prior to the various precursors such as malachite, aurichalcite and hydrozincite The uZnO catalysts subsequently formed from the precursors showed the activity for steam reforming of methanol to vary with its composition Based on the results of temperature programmed oxidation (TPO) with N2O and an infrared spectra of CO chemisorption, the TOF of the reaction is proposed to be associated with the surface of metallic Cu