Showing papers on "Thermogravimetric analysis published in 2004"

Selection of Oxygen Carriers for Chemical-Looping Combustion

Abstract: Chemical-looping combustion (CLC) has been suggested as an energetically efficient method for capture of carbon dioxide from the combustion of fuel gas. This technique involves the use of an oxygen carrier that transfers oxygen from the air to the fuel, preventing direct contact between them. The oxygen carrier is composed of a metal oxide as an oxygen source, and an inert as a binder for increasing the mechanical strength of the carrier. In this work, 240 samples composed of 40−80% of Cu, Fe, Mn, or Ni oxides on Al2O3, sepiolite, SiO2, TiO2, or ZrO2 were prepared by mechanical mixing as cylindrical extrudates. The samples were sintered at four temperatures between 950 and 1300 °C. The effects of the chemical nature and composition of the carrier and the sintering temperature were investigated by reactivity tests in a thermogravimetric analyzer using CH4 as fuel, and the mechanical strength of the solids. On the basis of these properties, the most promising carriers to be used in a CLC system were selecte...

Preparation and characterization of nano-structured silica from rice husk

Abstract: Uniformly sized ultrafine silica powder can be obtained by nonisothermal decomposition of rice husk in an oxidizing atmosphere. The properties of reactant and product including morphology, particle size, surface area, pore volume and pore distribution, have been investigated by TEM, SEM, XRD, FTIR, ICP-MS, and EA. At a heating rate of 5 K/min, the specific surface area of the silica powder was 235 m 2 /g, the average pore diameter was 5.4 nm, and the average particle size was 60 nm. The products obtained from various heating rates were all amorphous. By using a thermogravimetric analysis technique, a mechanism including two reaction stages was observed for the thermal decomposition of rice husk in air. The activation energy was found to be 166±10 kJ/mol. This method can conveniently provide preparation of silica of high surface area and nanometer grade.

β-Nickel Hydroxide Nanosheets and Their Thermal Decomposition to Nickel Oxide Nanosheets

Abstract: Powders of single-crystalline β-nickel hydroxide (β-Ni(OH)2) nanosheets with the hexagonal structure have been successfully synthesized by the hydrothermal method at 200 °C using nickel acetate as the nickel source and aqueous ammonia as both an alkaline and complexing reagent The yields of β-Ni(OH)2 nanosheet powders were higher than 924% This method is simple and low-cost for large-scale production of powders of single-crystalline β-Ni(OH)2 nanosheets Single-crystalline nickel oxide (NiO) nanosheets have been synthesized by thermal decomposition method at 400 °C for 2 h using single-crystalline β-Ni(OH)2 nanosheets as the precursor The sheet shape of β-Ni(OH)2 was sustained after thermal decomposition to NiO The as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TG)

Structure of organoclays—an X-ray diffraction and thermogravimetric analysis study

Abstract: X-ray diffraction has been used to study the changes in the surface properties of a montmorillonitic clay through the changes in the basal spacings of montmorillonite (SWy-2) and surfactant-intercalated organo-clays. Variation in the d-spacing was found to be a step-function of the surfactant concentration. High resolution thermogravimetric analysis (HRTG) was used to study the thermal decomposition surfactant modified SWy-2-MMTs modified with the surfactant octadecyltrimethylammonium bromide. High resolution thermogravimetry shows the decomposition takes place in 4 steps. A mass loss step is observed at room temperature and is attributed to dehydration of adsorption water. A second mass loss step is observed over the 87.9 to 135.5 degrees Celsius temperature range and is also attributed to dehydration of water hydrating metal cations such as Na+ . The third mass loss occurs from 178.9 to 384.5 degrees Celsius and is assigned to a loss of surfactant. The fourth mass loss step is ascribed to the loss of OH units through dehydroxylation over the 556.01 to 636.35 degrees Celsius temperature range.

Thermogravimetric analysis of rice husk flour filled thermoplastic polymer composites

Abstract: The thermal degradation and thermal stability of rice husk flour (RHF) filled polypropylene (PP) and high-density polyethylene (HDPE) composites in a nitrogen atmosphere were studied using thermogravimetric analysis. The thermal stability of pure PP and HDPE was found to be higher than that of wood flour (WF) and RHF. As the content of RHF increased, the thermal stability of the composites decreased and the ash content increased. The activation energy of the RHF filled PP composites increased slowly in the initial stage until α=0.3 (30% of thermal degradation region) and thereafter remained almost constant, whereas that of the RHF filled HDPE composites decreased at between 30 and 40 mass% of RHF content. The activation energy of the composites was found to depend on the dispersion and interfacial adhesion of RHF in the PP and HDPE matrix polymers.

Hyperbranched fluoropolymer and linear poly(ethylene glycol) based amphiphilic crosslinked networks as efficient antifouling coatings: An insight into the surface compositions, topographies, and morphologies

Abstract: Polymer coatings with features of differing hydrophilicity, mobility, and topography, distributed across a substrate in microscopic and nanoscopic patches were designed as complex materials equipped with sufficient variability in composition, structure, and dynamics to inhibit interactions associated with biomacromolecular fouling. These complex polymer coatings were prepared by the in situ phase separation and crosslinking of mixtures of hyperbranched fluoropolymer (HBFP) and diamino-terminated poly(ethylene glycol) (PEG), for which the degree of crosslinking, compositions, topographies, and morphologies were varied by alteration of the PEG/HBFP stoichiometries (14, 29, 45, and 55 wt % PEG). This article examines the physicochemical details of HBFP–PEG network coatings prepared on glass substrates, functionalized by 3-aminopropyltriethoxysilane, as characterized by atomic force microscopy (AFM), contact-angle measurements, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and thermogravimetric analysis. Upon incubation in water or artificial seawater, the surfaces underwent reconstruction, which was believed to be driven by the swelling of the PEG domains and the energetic favorability offered by the segregation of PEG to the solid–water interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6193–6208, 2004

Polystyrene- and poly(3-vinylpyridine)-grafted magnetite nanoparticles prepared through surface-initiated nitroxide-mediated radical polymerization

Abstract: Polymer-grafted magnetite (Fe3O4) nanoparticles (diameter about 10 nm) were prepared through a direct polymer grafting reaction from their surfaces. The chemisorbed initiator (TEMPO-based alkoxyamine) for nitroxide-mediated radical polymerization with a phosphoric acid group gave controlled polystyrene (PS) and poly(3-vinylpyridine) (P3VP) graft layers on the surface. The graft densities of polymers on the surfaces of magnetite particles were estimated at 0.12−0.20 chains/nm2 by thermogravimetric analysis (TGA). The improvement in the dispersibility of PS-modified magnetite in good solvents was verified by ultraviolet−visible (UV−vis) absorption spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). In the case of P3VP-modified magnetite, the particles were stably dispersed in good solvents, by protonation, in acid solution, and by quarternization with iodomethane, in neutral aqueous solution. The magnetic response of the polymer-grafted magnetite against an external mag...

On the effects of moisture in a polyurethane shape memory polymer

Abstract: It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (Tg) of polyurethane. Accompanying the decrease of Tg, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between Tg and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.

Acid dye removal: comparison of surfactant-modified mesoporous FSM-16 with activated carbon derived from rice husk

Abstract: Cetyltrimethylammonium bromide (CTAB)-modified mesoporous molecular sieve FSM-16, prepared by a hydrothermal process (373 K, 3 days), was tested as an adsorbent for acid dye (acid yellow, AY, and acid blue, AB) removal in comparison with as-prepared FSM-16 and activated carbon (AC) derived from rice husk (50 vol% H 3 PO 4 , 773 K, 2.5 h). The adsorption isotherms, sorption kinetics, and pH effects upon acid dyes sorption on the adsorbents were thoroughly investigated. The structures of different adsorbents were characterized by XRD, FTIR spectroscopy, N 2 adsorption measurements, and thermogravimetric (TG) analysis. It was found that the ultimate capacity of the adsorbents varied in the order FSM-16 > modified FSM-16 > AC and followed first-order rate kinetics. The adsorption isotherm of acid dyes on FSM-16 is of type IV, according to the IUPAC classification, drastically different from that of CTAB/FSM-16, which showed a type I isotherm. The latter sample had better adsorption performance at low concentration of acid dyes than the former. As compared to activated carbon of microporous character, the CTAB/FSM-16 sample achieved higher performance at low concentrations. This was due to the successful narrowing of the pore opening of FSM-16 using CTAB with maintenance of a considerable portion of the pore volume. Powder XRD and N 2 adsorption studies of the CTAB/FSM-16 material indicated that the textural properties of the support were preserved during the hydrothermal synthesis and that the channels remained accessible, despite a significant reduction in surface area (ca. 26%). TG studies, on the other hand, confirmed that the modified material presented a higher hydrophobicity than that of the CTAB-free FSM-16 sample.

Organic-Inorganic Hybrid Membrane: Thermally Stable Cation-Exchange Membrane Prepared by the Sol-Gel Method

Abstract: Organic−inorganic hybrid membranes based on poly(vinyl alcohol)−SiO2 were prepared under acidic and basic conditions, in which sulfonic acid groups were introduced at the inorganic segment. These membranes were extensively characterized for their morphology, intermolecular interactions, thermal and mechanical stability, and physicochemical properties using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and water uptake studies. Schematic models for acid-catalyzed linear weakly polymeric clusters and for base-catalyzed highly branched polymeric clusters were proposed. A higher ion-exchange capacity, permselectivity, and conductivity for the acid-catalyzed hybrid membranes than for the base-catalyzed membranes with the same composition indicated that the former route is suitable for the preparation of ion-exchange membranes. The electro...

Nanocomposite Polymer Electrolytes Based on Poly(oxyethylene) and Cellulose Nanocrystals

Abstract: Lithium-conducting nanocomposite polymer electrolytes based on high molecular weight poly(oxyethylene) (POE) were prepared from high aspect ratio cellulosic whiskers and lithium imide LiTFSI salt. The thermomechanical behavior of the resulting films was investigated by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The ionic conductivity and the electrochemical stability of the nanocomposite polymer electrolytes are quite consistent with the specifications of lithium batteries. The ionic mobilities were determined by pulsed magnetic field gradient NMR, and it was shown that the reinforcement does not affect the lithium transference number. High performance nanocomposite electrolytes based on tunicin whiskers were obtained. Indeed, the filler provides a high reinforcing effect, while a high level of ionic conductivity is retained with respect to unfilled polymer electrolytes.

Intumescent paints: fire protective coatings for metallic substrates

Abstract: This study investigates the role of the binder in an intumescent paint. In fact, it is generally known that acid source, carbon source and blowing agent are the main ingredients of such a paint. However, since the binder may react with these ingredients, it is also a very important component of an intumescent paint. To begin with, the effect of the nature of the monomers composing the polymeric binder, on the chemical reactivity between the binder and the intumescent additives is investigated using thermogravimetric analysis, solid state NMR and FTIR analysis. It is found that the thermal stability increases when the copolymer is based on substituted styrene. Subsequently, the efficiency of protective behaviour of the intumescent coatings is evaluated varying the nature of the binder resin. It is found that the thermal insulation is greatly improved when using a mixture of a linear copolymer presenting a good reactivity with the acid source and a cross-linked copolymer as binder in the intumescent paint.

Synthesis and characterization of diperfluorooctyl-substituted phenylene-thiophene oligomers as n-type semiconductors. Molecular structure-film microstructure-mobility relationships, organic field-effect transistors, and transistor nonvolatile memory elements

Abstract: A new series of mixed phenylene−thiophene oligomers with terminal n-perfluorooctyl groups has been synthesized These compounds are 2,5-bis(4-n-perfluorooctylphenyl)thiophene (DFO−PTP, 1), 5,5‘-bis(4-n-perfluorooctylphenyl)-2,2‘-bithiophene (DFO−PTTP, 2), 5,5‘ ‘-bis(4-n-perfluorooctylphenyl)-2,2‘:5‘,2‘ ‘-terthiophene (DFO−PT3P, 3), 5,5‘ ‘‘-bis(4-n-perfluorooctylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DFO−PT4P, 4), and 1,4-bis[5-(4-n-perfluorooctylphenyl)-2-thienyl]benzene (DH−PTPTP, 5) These systems have been characterized by 1H and 19F NMR, elemental analysis or HRMS, optical absorption and emission spectroscopies, differential scanning calorimetry, and thermogravimetric analysis Vacuum-deposited films were characterized by optical absorption and emission spectroscopy, X-ray diffraction, scanning electron microscopy, and field effect transistor measurements As thin films, all of the fluorinated compounds are n-type semiconductors with carrier mobilities ranging from ∼10-6 to ∼ 01 cm2 V-1 s-1

Adsorption and Thermal Condensation Mechanisms of Amino Acids on Oxide Supports. 1. Glycine on Silica

Abstract: Glycine was adsorbed on the surface of a well-defined silica from aqueous solutions of variable concentrations and pHs. The adsorbed molecules were characterized using middle-IR and UV−vis−NIR spectroscopies. Except at the lowest pH (2.0), they were predominantly present on the surface as zwitterions. Two successive deposition mechanisms were evidenced with increasing glycine concentration. At low concentrations, glycine is specifically adsorbed on silica surface sites, probably through its NH3+ moiety. The pH dependence suggests that these sites may be silanolate groups (≅Si−O-). At higher concentrations, specific adsorption sites are saturated and surface-induced precipitation of β-glycine is observed. The thermal reactivity of adsorbed/deposited glycine was then investigated by thermogravimetric analysis, in situ diffuse reflectance IR spectroscopy, and thermoprogrammed desorption coupled with mass spectrometry. Adsorbed glycine molecules react to form peptide bonds at a temperature considerably lower ...