Showing papers on "Thermogravimetric analysis published in 2002"
TL;DR: In this article, a mesoporous molecular sieve of MCM-41 type (MCM41-PEI) has been used as a CO2 adsorbent.
Abstract: The objective of the work presented here is to develop a nanoporous solid adsorbent which can serve as a “molecular basket” for CO2 in the condensed form Polyethylenimine (PEI)-modified mesoporous molecular sieve of MCM-41 type (MCM-41-PEI) has been prepared and tested as a CO2 adsorbent The physical properties of the adsorbents were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, and thermogravimetric analysis (TGA) The characterizations indicated that the structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the molecular sieve The CO2 adsorption/desorption performance was tested in a flow system using a microbalance to track the weight change The mesoporous molecular sieve had a synergetic effect on the adsorption of CO2 by PEI A CO2 adsorption capacity as high as 215 mg-CO2/g-PEI was obtained with MCM-41-PEI-50 at 75 °C, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure
967 citations
TL;DR: In this article, a Pechini sol−gel process combined with soft lithography was used to fabricate nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a pechini sol-gel process.
Abstract: Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) show...
638 citations
TL;DR: Phenomenological thermodynamic predictions of the size dependence of the melting point of gold agree with the experimental observation, and implications to the self-diffusion coefficient of gold in the nanoparticles are discussed, especially as they relate to the spontaneous alloying of core-shell bimetallic particles.
Abstract: We report on the size dependence of the melting temperature of silica-encapsulated gold nanoparticles. The melting point was determined using differential thermal analysis (DTA) coupled to thermal gravimetric analysis (TGA) techniques. The small gold particles, with sizes ranging from 1.5 to 20 nm, were synthesized using radiolytic and chemical reduction procedures and then coated with porous silica shells to isolate the particles from one another. The resulting silica-encapsulated gold particles show clear melting endotherms in the DTA scan with no accompanying weight loss of the material in the TGA examination. The silica shell acts as a nanocrucible for the melting gold with little effect on the melting temperature itself, even though the analytical procedure destroys the particles once they melt. Phenomenological thermodynamic predictions of the size dependence of the melting point of gold agree with the experimental observation. Implications of these observations to the self-diffusion coefficient of gold in the nanoparticles are discussed, especially as they relate to the spontaneous alloying of core-shell bimetallic particles.
534 citations
TL;DR: In this article, a thermogravimetric analyzer coupled with a differential scanning calorimeter (DSC) and mass spectrometer (MS) was used to pyrolyze materials such as cellulose, pectin, and xylan.
473 citations
TL;DR: In this paper, the authors showed that multiwalled nanotubes (MWNTs) annealed at 2200 to 2800 °C are more air stable than as-produced MWNTs.
Abstract: Thermogravimetric analysis (TGA) has demonstrated that multiwalled nanotubes (MWNTs) annealed at 2200 to 2800 °C are more air stable than as-produced MWNTs, diamond, graphite, and annealed diamond. The annealed MWNTs are similar in stability to annealed graphite. Defect sites along the walls and at the ends of the raw MWNTs facilitate the thermal oxidative destruction of the nanotubes. Thermal annealing removes these defects, thereby providing MWNTs with enhanced air stability.
449 citations
TL;DR: In this paper, nanocomposites of poly(e-caprolactone) (PCL) were prepared by melt blending the polymer with natural Na + montmorillonite and montminillonite modified by hydrogenated tallowalkyl (HTA)-based quaternary ammonium cations, such as dimethyl 2-ethylhexyl HTA ammonium and methyl bis bis(2-hydroxyethyl) ammonium.
407 citations
TL;DR: In this paper, date pits, a low-cost agricultural byproduct, was tested as a precursor for the production of porous carbons in a chemical scheme using phosphoric acid.
386 citations
TL;DR: In this article, the morphology and thermal properties of polylactide (PLA)/clay nanocomposites and microcomposites were compared with unfilled PLA, keeping the same thermomechanical history.
Abstract: Polylactide (PLA)/clay nanocomposites loaded with 3 wt % organomodified montmorillonite and PLA/clay microcomposites containing 3 wt % sodium montmorillonite were prepared by melt blending. We investigated the morphology and thermal properties of the nanocomposites and microcomposites and compared them with unfilled PLA, keeping the same thermomechanical history. The influence of the processing temperature on the structural characteristics of the investigated systems was determined. The investigations were performed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), size exclusion chromatography (SEC), and polarized light microscopy (LM). XRD showed that the good affinity between the organomodified clay and the PLA was sufficient to form intercalated structure in the nanocomposite. The microcomposite featured a phase-separated constitution. DSC and LM studies showed that the nature of the filler affected the ordering of the PLA matrix at the molecular and supermolecular levels. According to TGA, the PLA-based nanocomposites exhibited improvement in their thermal stability in air. Reduced flammability, together with char formation, was also observed for nanocomposites, compared to the microcomposites and pure PLA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1497–1506, 2002
348 citations
TL;DR: In this article, a review on recent results on characterisation of layered double hydroxides (LDHs) prepared by conventional coprecipitation methods is reported, focusing on the application of few experimental methods for characterising structural properties of these compounds.
345 citations
01 Jan 2002
TL;DR: In this paper, the authors present a model for sample-controlled thermal analysis using thermogravimetric analysis with dynamic Vapour Sorption (DTA) and temperature-modulated DSC.
Abstract: Nomenclature Thermogravimetric Analysis Dynamic Vapour Sorption DTA and DSC Temperature-Modulated DSC Isothermal Microcalorimetry Isothermal Reaction Calorimetry and Adiabatic Calorimetry TMA and DMA Dielectric Spectroscopy Micro-TA Hot-stage Microscopy Simultaneous Techniques Sample-controlled Thermal Analysis.
344 citations
TL;DR: In this article, a spray pyrolysis technique was employed to deposit nickel oxide (NiO) thin films from hydrated nickel chloride salt solution on to glass substrates, and the effect of the volume of sprayed solution on structural, optical and electrical properties was studied using X-ray diffraction (XRD), infrared (IR), optical absorption, electrical resistivity and thermoelectric power (TEP) techniques.
TL;DR: Very high purity single-walled carbon nanotubes (SWNTs) were obtained from HiPco SWNT samples containing Fe particles by a two-step purification process.
TL;DR: In this paper, a novel magnetic nano-adsorbent has been developed using Fe3O4 nanoparticles (13.2 nm) as cores and polyacrylic acid (PAA) as ionic exchange groups.
Abstract: A novel magnetic nano-adsorbent has been developed using Fe3O4 nanoparticles (13.2 nm) as cores and polyacrylic acid (PAA) as ionic exchange groups. The Fe3O4 magnetic nanoparticles were prepared by co-precipitating Fe2+ and Fe3+ ions in an ammonia solution and treating under hydrothermal conditions. PAA was covalently bound onto the magnetic nanoparticles via carbodiimide activation. Transmission electron micrographs showed that the magnetic nanoparticles remained discrete and had no significant change in size after binding the PAA. The X-ray diffraction patterns indicated the magnetic nanoparticles were pure Fe3O4 with a spinel structure, and the binding of PAA did not result in a phase change. Magnetic measurement revealed the magnetic nanoparticles were superparamagnetic, and their saturation magnetization was reduced only slightly after PAA binding. Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analyses, and X-ray photoelectron spectroscopy confirmed the binding of PAA to the magnetic nanoparticles, suggested a binding mechanism for the PAA, and revealed the maximum weight ratio of PAA bound to the magnetic nanoparticles was 0.12. In addition, the ionic exchange capacity of the resultant magnetic nano-adsorbents was estimated to be 1.64 mequiv g−1, much higher than those of commercial ionic exchange resins. When the magnetic nano-adsorbents were used for the recovery of lysozyme, the adsorption/desorption of lysozyme was completed within 1 min due to the absence of pore-diffusion resistance. Also, the adsorption/desorption efficiency could reach almost 100% under appropriate conditions, and the recovered lysozyme retained 95% activity.
TL;DR: The degradation of chitosan by hydrogen peroxide was studied in this article, where the degradation was monitored by gel permeation chromatography (GPC) and the molecular weight distribution of partially degraded products from homogeneous reaction displayed a single-modal curve whereas that from heterogeneous reaction was bimodal.
TL;DR: In this article, the results were interpreted assuming progressive evolution of the random coil regions forward the more stable β-sheet conformation, as induced by the different applied preparation conditions or treatment.
Abstract: Films of silk fibroin cast from fibroin-water solutions at different casting temperatures and untreated or treated after casting with methanol, were characterized by differential scanning calorimetry (DSC), under static and dynamic mode, thermogravimetric analysis and dynamic mechanical thermal analysis. DSC revealed the presence of a lower temperature endothermic phenomenon centered at about 70 °C for the as-prepared room temperature cast film, and other typical material thermal parameters - glass transition, crystallization, and thermal degradation - more or less pronounced depending on the specific preparation procedure and thermal or solvent treatment. These results were interpreted assuming progressive evolution of the random coil regions forward the more stable β-sheet conformation, as induced by the different applied preparation conditions or treatment. The low temperature endothermic transition observed in DSC (30-120 °C) corresponded in the dynamic mechanical analysis to a quite anomalous behavior, with a sharp decrease and immediate increase of E'. Conditions producing modifications of the thermal and dynamic mechanical curves, as well as analogies with the thermogravimetric analysis findings, were analyzed and discussed.
TL;DR: In this article, a scalable method for purification of single-wall carbon nanotubes (SWNTs) by using microwave heating in air is developed, where microwaves couple to the residual metal catalyst, raising significantly the local temperature leading to both the oxidation and rupturing of the carbon passivation layer over the metal catalyst particles.
Abstract: A new scalable method for purification of single-wall carbon nanotubes (SWNTs) by using microwave heating in air is developed. The microwaves couple to the residual metal catalyst, raising significantly the local temperature leading to both the oxidation and rupturing of the carbon passivation layer over the metal catalyst particles. With this protective carbon coating weakened or removed, a mild acid treatment is then sufficient to remove most of the metal in the sample, leaving the nanotubes in tact. Using microwave processing and 4 M HCl acid reflux for 6 h we were able to remove residual metal (Ni, Y) in arc-discharge SWNTs to a level lower than 0.2 wt % (∼0.04 at. %). Results from transmission and scanning electron microscopy, Raman spectroscopy, and thermogravimetric studies were discussed.
TL;DR: In this article, a support for the grafting of thin films of molecularly imprinted polymers (MIPs) was used as a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity.
Abstract: Silica particles containing surface-bound free radical initiators have been used as supports for the grafting of thin films of molecularly imprinted polymers (MIPs). This technique offers a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity in chromatographic or sensor applications. Thus prepared MIPs imprinted with l-phenylalanine anilide, have been characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis, fluorescence microscopy, and scanning electron microscopy (SEM), providing evidence concerning the reproducibility in each step and the quantity and quality of the grafted films. The chromatographic properties of the materials have been investigated with respect to the average layer thickness of the polymer on the surface, the solvent, the support pore diameter, the cross-linker concentration, and the composition of the mobile phase. For the porous particles, the column efficiency depend...
TL;DR: The synthesis of cerium containing MCM-41 mesoporous molecular sieves was carried out using different hydrothermal methods as mentioned in this paper, and the syntheses were mainly prepared by refluxing the gel mixture at atmospheric pressure under stirring (∼600 rpm).
TL;DR: In this article, a micro-structural characterization of cement pastes modified with EVA copolymer was performed, where the pastes were submitted to two different curing conditions, and analyzed at 28 days old, and thermal analyses (differential thermal analysis [DTA] and thermogravimetric [TG] analysis), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) tests were performed, which permitted the evaluation of the EVA effects on the cement hydration.
TL;DR: In this paper, a nanocomposite of conducting polyaniline (PAN) with inorganic Na+−montmorillonite (MMT) clay was synthesized by the emulsion polymerization method.
Abstract: Nanocomposites of conducting polyaniline (PAN) with inorganic Na+−montmorillonite (MMT) clay were synthesized by the emulsion polymerization method. The dodecylbenzenesulfonic acid (DBSA) was used for both dopant and emulsifier. Analyses of X-ray diffraction patterns demonstrated that conducting PAN-DBSA was intercalated between inorganic clay layers at the nanoscale level (<10 A). We observed that the clay induced more disordered state in PAN-DBSA/clay nanocomposites. From the temperature-dependent dc conductivity [σdc(T)] experiments, we investigated charge transport mechanism of the PAN-DBSA and PAN-DBSA/clay systems. The interaction between the intercalated PAN-DBSA and the clay layers was observed by FT-IR spectra. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed the improved thermal stability of the nanocomposite materials. The σdc of these systems was 101−10-2 S/cm at room temperature, varying with dopant molar ratio. The σdc(T) of the nanocomposite...
TL;DR: In this article, the results at 1200 °C by use of hydrogen as fuel are presented, and the features of the reactions are discussed based on the analyses of the composition of the exhaust gas.
TL;DR: In this paper, the cationic surfactant (cetyltrimethylammonium bromide, CTAB) and the hydrous metal chlorides (ZnCl2·2H2O, NiO, and SnO2) were used to obtain nanocrystalline metal oxide powders.
TL;DR: In this article, the authors used the Brunauer-Emmett-Teller method to evaluate the specific surface area of nanocrystalline LiFePO 4 and showed very good electrochemical performance delivering about the full theoretical capacity (170 Ah kg -1 ) when cycled at the C/10 rate.
Abstract: Nanocrystalline LiFePO 4 was obtained by heating amorphous nanosized LiFePO 4 . The amorphous material was obtained by lithiation of FePO 4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O and NH 4 H 2 PO 4. using hydrogen peroxide as the oxidizing agent. The materials were characterized by chemical analysis, thermogravimetric and differential thermal analysis, X-ray powder diffraction, and scanning electron microscopy. The Brunauer- Emmett-Teller method was used to evaluate the specific surface area. Nanocrystalline LiFePO 4 showed very good electrochemical performance delivering about the full theoretical capacity (170 Ah kg -1 ) when cycled at the C/10 rate. A capacity fade of about 0.25% per cycle affected the material upon cycling.
TL;DR: In this paper, polystyrene (PS)/clay nanocomposites were synthesized by emulsion polymerization of styrene in the presence of sodium ion-exchanged montmorillonite (Na+-MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers.
Abstract: Polystyrene (PS)/clay nanocomposites were synthesized by the emulsion polymerization of styrene in the presence of sodium ion-exchanged montmorillonite (Na+-MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers. The nanocomposites were examined by means of X-ray diffraction, transmission electron microscopy, thermogravimetric analysis. The rheological properties of the PS/Na+-MMT nanocomposites were also studied to exhibit more pronounced shear thinning behavior with increasing clay content.
TL;DR: In this paper, a mixture of N-methyl-2-pyrrolidinone (NMP) and polyimide/organoclay mixture was used to achieve fully exfoliated nanocomposites, which were characterized by differential scanning calorimetry, dynamic thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thin film tensile properties.
TL;DR: In this paper, molecular motion and thermal stability in two series of nanophase-separated polyimide-silica (PI-SiO2) hybrid materials with chemically bound components were studied.
Abstract: Molecular motion and thermal stability in two series of nanophase-separated polyimide–silica (PI–SiO2) hybrid materials with chemically bound components were studied. The hybrids were synthesized from p-aminophenyltrimethoxysilane-terminated poly(amic acid)s as PI precursors and tetramethoxysilane as a silica precursor via a sol–gel process. The hybrids differed in their PI chemical structure and chain length (number-average molecular weight = 5.000, 7.500, or 10.000) and in their SiO2 content, which ranged from 0 to 50 wt %. Differential scanning calorimetry, laser-interferometric creep rate spectroscopy, and thermally stimulated depolarization current techniques were used for studying the dynamics from 100 to 650 K and from 10−3 to 10−2 Hz. Comparative thermogravimetric measurements were also carried out from 300 to 900 K. Silica nano- or submicrodomains that formed affected PI dynamics in two opposite directions. Because of the loosening of the molecular packing of PI chains confined to nanometer-scale spaces between silica constraints, an enhancement of small-scale motion, mostly at temperatures below the β-relaxation region, occurred. However, a partial or total suppression of segmental motion could be observed above the β-relaxation temperature, drastically so for the shortest PI chains at elevated silica contents and within or close to the glass-transition range, because of the covalent anchoring of chain ends to silica domains. Large changes in thermal stability, including a 2.5-fold increase in the apparent activation energy of degradation, were observed in the hybrids studied. A greater than 100 °C rise in long-term thermal stability could be predicted for some hybrids with respect to pure PI. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1056–1069, 2002
TL;DR: A series of polymer-clay nanocomposite (PCN) materials that consisted of emeraldine base of poly( o -ethoxyaniline) (PEA) and layered montmorillonite (MMT) clay were prepared by effectively dispersing the inorganic MMT clay platelets in organic PEA matrix via in situ oxidative polymerization as discussed by the authors.
TL;DR: In this article, a methyl methacrylate (MMA) copolymer with pentavalent phosphorus-containing monomers is copolymed with PMMA and the flame retardance of the resulting copolymers has been assessed by limiting oxygen indicies (LOI) and cone calorimetry experiments.
TL;DR: In this article, three ammonium salts, hexadecylallyldimethyl ammonium chloride (Allyl16), hexadecylvinylbenzyldimmethyl ammonium (VB16), and hexadecylvinylbenzylbenzine methyl ammonium compound (Bz16), were synthesized and ion exchanged onto montmorillonite and characterized by X-ray diffraction and transmission electron microscopy.
TL;DR: In this paper, the thermal properties of epoxy resins containing flame retardants based on silicon, phosphorus, and melamine, were investigated with thermogravimetric analysis (TGA).