Showing papers on "Thermogravimetric analysis published in 2003"

Amine-Grafted MCM-48 and Silica Xerogel as Superior Sorbents for Acidic Gas Removal from Natural Gas

Abstract: In an effort to develop selective solid sorbents for acidic gas (CO2 and H2S) removal from natural gas mixtures, we synthesized amine-surface-modified silica xerogel and MCM-48 materials. With large amounts of basic amine groups on the surface, the sorbents are able to selectively bind the acidic gases CO2 and H2S. High adsorption capacities and adsorption rates were obtained for both gases. The adsorption−desorption isotherms of the gases and thermogravimetric analysis of the sorbents showed that these sorbents can be regenerated completely under mild conditions such as those used in pressure swing or temperature swing adsorption processes. We have also investigated the effect of moisture on the adsorption of CO2 and H2S by TPD-MS and infrared spectroscopy. The results indicated that the presence of water vapor doubled the amount of CO2 adsorbed and barely affected the H2S adsorption.

Nitric Acid Purification of Single-Walled Carbon Nanotubes

Abstract: We report a systematic evaluation of the use of refluxing nitric acid as a purification treatment for electric arc-produced single-walled carbon nanotubes (SWNTs), by using a combination of thermogravimetric analysis (TGA) and near-infrared (NIR) spectroscopy. Nitric acid is the standard reagent for purification of SWNTs and has traditionally constituted the first step in many different purification schemes. It has been suggested that nitric acid removes the transition metal catalyst that is used in the production of the SWNTs together with amorphous carbon. Under all conditions, we find that nitric acid destroys SWNTs to produce amorphous carbon while reducing the amount of transition metal catalyst remaining in the sample. Thus, nitric acid is suitable for removing the catalyst from SWNT samples, but only at the expense of a significant destruction of the SWNTs.

OH Surface Density of SiO2 and TiO2 by Thermogravimetric Analysis

Abstract: Thermogravimetric analysis (TGA) is investigated for determination of the OH surface density (OH/nm2) and carbon content of silica and titania powders made by flame aerosol and sol−gel processes. It is shown that it is possible to distinguish between physically adsorbed and chemically bound water and to rapidly determine the OH surface density even of small powder samples (<0.2 g) by TGA calibrated with LiAlH4 titration data. The high accuracy of the OH surface density determination by TGA is confirmed further with additional LiAlH4 titration data of silica powders and by comparison with the specifications of commercially available silica Aerosil and titania P25 powders. Furthermore, by connecting a CO2 sensor or a mass spectrometer to the TGA balance, it is possible to verify the carbon content and determine other components (organic residues) of the powders. Thereby, it is shown that flame-made powders have high purity while the preparation conditions of sol−gel powders greatly affect their purity. At a...

S2-Glass/Epoxy Polymer Nanocomposites: Manufacturing, Structures, Thermal and Mechanical Properties

Abstract: This paper is primarily focused in studying the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials. Basic correlations between polymer morphology, strength, modulus, toughness, and thermal stability of thermoset nanocomposites were investigated as a function of layered silicate content. S2-glass/epoxy-clay nanocomposites were manufactured through an affordable vacuum assisted resin infusion method (VARIM). The nanocomposites are formed during polymerization when the adsorbing monomer separates the clay particles into nanometer scales. Transmission electron microscopy (TEM) and wide angle X-ray diffraction(WAXD) were used to characterize the morphology of the dispersed clay particles. The thermal properties such as onset of decomposition and glass transition temperatures were determined by Thermo Gravimetric Analysis (TGA) and Dynamic Modulus Analyzer (DMA). Mechanical properties such as interlaminar sh...

Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical applicability.

Abstract: Previous studies shown that thermoplastic blends of corn starch with some biodegradable synthetic polymers (poly(e-caprolactone), cellulose acetate, poly(lactic acid) and ethylene-vinyl alcohol copolymer) have good potential to be used in a series of biomedical applications. In this work the thermal behavior of these structurally complex materials is investigated by differential scanning calorimetry (DSC) and by thermogravimetric analysis (TGA). In addition, Fourier-transform infrared (FTIR) spectroscopy was used to investigate the chemical interactions between the different components. The endothermic gelatinization process (or water evaporation) observed by DSC in starch is also observed in the blends. Special attention was paid to the structural relaxation that can occur in the blends with poly(lactic acid) at body temperature that may change the physical properties of the material during its application as a biomaterial. At least three degradation mechanisms were identified in the blends by means of using TGA, being assigned to the mass loss due to the plasticizer leaching, and to the degradation of the starch and the synthetic polymer fractions. The non-isothermal kinetics of the decomposition processes was analyzed using two different integral methods. The analysis included the calculation of the activation energy of the correspondent reactions.

Reactivity of some metal oxides supported on alumina with alternating methane and oxygen - Application for chemical-looping combustion

Abstract: Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel. Two reactors are used in the process: (i) a fuel reactor where the metal oxide is reduced by reaction with the fuel, and (ii) an air reactor where the reduced metal oxide from the fuel reactor is oxidized with air. The possibility of using oxides of Cu, Co, Mn, and Ni as oxygen carriers was investigated. Particles were prepared by deposition of the metal oxides on γ-Al2O3 particles by so-called dry impregnation. The reactivity of the oxygen carrier particles was evaluated in a thermogravimetric analyzer (TGA), where the alternating atmosphere which an oxygen carrier encounters in a CLC system was simulated by exposing the sample to alternating reducing (10% CH4, 5% CO2, 10% H2O) and oxidizing (10% O2) conditions at temperatures between 750 and 950 °C. The particles ...

Mechanism of high-temperature CO2 sorption on lithium zirconate.

Abstract: Lithium zirconate (Li2ZrO3) is one of the most promising materials for CO2 separation from flue gas at high temperature. This material is known to be able to absorb a large amount of CO2 at around 400-700 degrees C. However, the mechanism of the CO2 sorption/desorption process on Li2ZrO3 is not known yet. In this study, we examined the CO2 sorption/desorption mechanism on Li2ZrO3 by analyzing the phase and microstructure change of Li2ZrO3 during the CO2 sorption/desorption process with the help of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. Li2ZrO3 powders were prepared from lithium carbonate (Li2CO3) and zirconium oxide (ZrO2) by the solid-state method, and the CO2 sorption/desorption property was examined by TGA. It was shown that pure Li2ZrO3 absorbs a large amount of CO2 at high temperature with a slow sorption rate. Addition of potassium carbonate (K2CO3) and Li2CO3 in the Li2ZrO3 remarkably improves the CO2 sorption rate of the Li2ZrO3 materials. DSC analysis for the CO2 sorption process indicates that doped lithium/potassium carbonate is in the liquid state during the CO2 sorption process and plays an important role in improving the CO2 uptake rate. XRD analysis for phase and structure change during the sorption/desorption process shows that the reaction between Li2ZrO3 and CO2 is reversible. Considering all data obtained in this study, we proposed a double-shell model to describe the mechanism of the CO2 sorption/desorption on both pure and modified Li2ZrO3.

Structural Characteristics and Thermal Properties of PE-g-MA/MgAl-LDH Exfoliation Nanocomposites Synthesized by Solution Intercalation

Abstract: Exfoliated nanocomposites (PE-g-MA/MgAl-LDH) were synthesized by solution intercalation of polyethylene-grafted-maleic anhydride (PE-g-MA) into the galleries of organo-modified MgAl layered double hydroxide (OMgAl-LDH) under reflux in xylene. Their structural elucidation and thermal characterization were carried out by X-ray diffraction (XRD), Fourier transfer infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The molecular dispersion of OMgAl-LDH layers within the PE-g-MA matrix has been verified by the disappearance of d001 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The OMgAl-LDH layers of about 70-nm length or width show a disordered phase in PE-g-MA matrix. The SAED pattern demonstrates that the MgAl hydroxide sheets of about 0.48-nm thickness have a hexagonal crystal structure with a = 0.305 nm. TGA profiles of the PE-g-MA/MgAl-LDH nanocompo...

Urea thermolysis and NOx reduction with and without SCR catalysts

Abstract: Urea–selective catalytic reduction (SCR) has been a leading contender for removal of nitrogen oxides (deNOx) from diesel engine emissions Despite its advantages, the SCR technology faces some critical detriments to its catalytic performance such as catalyst surface passivation (caused by deposit formation) and consequent stoichiometric imbalance of the urea consumption Deposit formation deactivates catalytic performance by not only consuming part of the ammonia produced during urea decomposition but also degrading the structural and thermal properties of the catalyst surface We have characterized the urea thermolysis with and without the urea-SCR catalyst using both spectroscopic (DRIFTS and Raman) and thermal techniques (thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)) to identify the deposit components and their corresponding thermal properties Urea thermolysis exhibits two decomposition stages, involving ammonia generation and consumption, respectively The decomposition after the second stage leads to the product of melamine complexes, (HNCNH)x(HNCO)y, that hinder catalytic performance The presence of catalyst accompanied with a good spray of the urea solution helps to eliminate the second stage In this work, kinetics of the direct reduction of NOx by urea is determined and the possibility of using additives to the urea solution in order to rejuvenate the catalyst surface and improve its performance will be discussed

Surface Passivation of Bare Aluminum Nanoparticles Using Perfluoroalkyl Carboxylic Acids

Abstract: Surface passivation of unpassivated Al nanoparticles has been realized using self-assembled monolayers (SAMs). Nanoscale Al particles were prepared in solution by catalytic decomposition of H3Al·NMe3 or H3Al·N(Me)Pyr by Ti(OiPr)4 and coated in situ using a perfluoroalkyl carboxylic acid SAM. Because the Al particles are prepared using wet chemistry techniques and coated in solution, they are free of oxygen passivation. This SAM coating passivates the aluminum and appears to prevent the oxidation of the particles in air and renders the composite material, to some extent, soluble in polar organic solvents such as diethyl ether. Characterization data including scanning electron microscopy , transmission electron microscopy, thermogravimetric analysis, and attenuated total reflectance-Fourier transform infrared spectroscopy of prepared materials are presented.

Thermal stability of lithium nickel oxide derivatives. Part I: LixNi1.02O2 and LixNi0.89Al0.16O2 (x = 0.50 and 0.30)

Abstract: The thermal degradation mechanism of LixNi1.02O2 and LixNi0.89Al0.16O2 (x = 0.50 and 0.30) was studied by in situ X-ray diffraction correlated with thermal gravimetric analysis coupled with mass spectrometry. The degradation mechanism appears to be the same for both types of samples. It consists of two steps: the first step, corresponding to the lamellar to pseudo-spinel transformation, is accompanied by an oxygen loss only for compounds with an initial (Li + M)/O ratio (M = Ni, Al) smaller than 3/4. The second step corresponds to the progressive transformation to a NiO-type structure, with an oxygen loss for both initial lithium compositions. The thermal stabilization obtained by partial aluminum substitution for nickel can be explained by the stability of the Al3+ ions in tetrahedral sites, which disrupts the cationic migrations necessary for the phase transformations observed upon increasing temperature to occur.

Catalysis of intumescent flame retardancy of polypropylene by metallic compounds

Abstract: Divalent and multivalent metallic compounds catalyze the flame retardancy performance of intumescent systems based on ammonium polyphosphate (APP) and pentaerythritol (petol) in poly(propylene) (PP). The catalytic effect is shown by increases in the oxygen index (OI) and UL-94 ratings. The effect is exerted by small concentrations of the metallic compounds in the range of 0.1–2.5 wt% of the compositions. The effect increases with the concentration of the catalyst until a maximum is reached. At higher concentrations of the catalyst a decrease in the flame retardancy parameters is observed, accompanied in several cases by a degradation and discoloration of the composition. The catalyst replaces melamine in intumescent systems. Catalytic effectiveness is defined and calculated for a number of compounds. Thermogravimetric parameters, such as initial decomposition temperature, temperature of the transition point and residue-after-transitions (RAT) change in parallel with the catalytic effect of the metal compound concentration. Metal compounds investigated include oxides, acetates, acetyl acetonates, borates and sulfates of Mn, Zn, Mg, Al, Ca, Ba, V, Co, Ni, Cu, Mo, Zr, and Cr. Mechanistic considerations on the activity of the catalysts are presented. Copyright © 2003 John Wiley & Sons, Ltd.

Hyperbranched Poly(phenylenesilolene)s: Synthesis, Thermal Stability, Electronic Conjugation, Optical Power Limiting, and Cooling-Enhanced Light Emission

Abstract: Silole-containing hyperbranched polyphenylenes (1) are synthesized, which exhibit high thermal stability, extended electronic conjugation, excellent optical power limiting performance, and novel cooling-enhanced photoluminescence. The homopolycyclotrimerization of 1,1-diethynyl-2,3,4,5-tetraphenylsilole (2) and its copolycyclotrimerizations with 1-octyne catalyzed by TaCl5−Ph4Sn proceed smoothly at room temperature and produce completely soluble polymers in high yields (up to ∼85%). The molecular structures of 1 are characterized by spectroscopic analyses. The thermal stability of 1 is evaluated by thermogravimetric analyses, which detect virtually no weight losses when the polymers are heated to ∼300 °C. The hyperbranched polyphenylenes are electronically conjugated, as suggested by their strong absorption in the visible spectral region (λmax ∼ 520 nm). Because of this extended electronic conjugation, polymers 1 are nonlinear optically active and strongly attenuate the optical power of intense laser puls...

Supercritical Fluid Extraction of a Nonionic Surfactant Template from SBA-15 Materials and Consequences on the Porous Structure

Abstract: SBA-15 mesoporous materials were synthesized using the method reported by Zhao et al. Surfactant was removed from as-made materials by means of different techniques: thermal treatment under air atmosphere, solvent washing at different temperatures, and supercritical CO2 extraction in the presence and absence of cosolvents. The structure of resulting materials was characterized using conventional techniques: nitrogen and argon adsorption measurements, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), and 29Si MAS NMR. The efficiency of surfactant removal using CO2 under supercritical conditions is similar to that obtained by means of solvent washing under reflux but shows some improvements in the presence of cosolvents. Mesoscopic properties of mild-temperature solvent extracted SBA-15 materials depend on the efficiency of the surfactant removal and the use of supercritical CO2 as solvent. Likewise, the size and volume of the complementary microporosity dete...

Structure of the silica phase extracted from silica/(TPA)OH solutions containing nanoparticles

Abstract: Subcolloidal particles of a few nanometers in diameter are observed during the clear-solution synthesis of silicalite-1. These nanoparticles (3−5 nm) can be synthesized at room temperature starting from tetrapropylammonium (TPA) hydroxide, tetraethyl orthosilicate (TEOS), and water, and they have been reported to have a uniform structure identical to that of zeolite ZSM-5 (called nanoblocks or nanoslabs). To study their structure, we followed the extraction procedure proposed in the literature to obtain a dry powder of the particles. These dried particles were analyzed with powder X-ray diffraction (XRD), solid-state NMR spectroscopy, FTIR spectroscopy, thermogravimetric analysis, and N2 adsorption isotherms. The results are compared with those obtained for colloidal size silicalite-1, amorphous silica, and the mesoporous silicate SBA-15. To obtain a better idea of the shape and structure of the particles, we conducted simulated annealing modeling to fit the particle shape to the fractions of Qn obtained ...