Showing papers on "Thermogravimetric analysis published in 2001"

Evidence for Bilayer Assembly of Cationic Surfactants on the Surface of Gold Nanorods

Abstract: The surface structure of gold nanorods (NRs) capped with cationic surfactants in water was studied by FTIR, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). For gold nanorods, the FTIR results show the formation of new bands, which indicate binding of the surfactant headgroup to the surface of the NR. These bands are stable at temperatures as high as 350 °C. For a surfactant mixture (used as capping material), TGA shows a weak weight loss peak at 235 °C and a strong peak at 298 °C assigned to the surfactant molecules in monomer and aggregated forms, respectively. For gold nanorods, three weight loss peaks at about 230, 273, and 344 °C are observed. For gold nanospheres (NSs), TGA shows a strong mass loss at 225 °C and two weak mass loss peaks at 255 and 288 °C. The released material after combustion in the TGA process was analyzed by FTIR spectroscopy and found to be CO2. Our results suggest the following for both NRs and NSs: (1) There are two different binding modes for the...

Fire Properties of Polystyrene-Clay Nanocomposites

Abstract: Polystyrene−clay nanocomposites have been prepared using a bulk polymerization technique. Three new “onium” salts have been used to prepare the nanocomposites, two are functionalized ammonium salts while the third is a phosphonium salt. By TGA/FTIR, both ammonium and phosphonium treatments have been shown to degrade by a Hofmann elimination mechanism at elevated temperatures. TGA/FTIR showed that the phosphonium treatment is the most thermally stable treatment when compared to the two ammonium salts. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, strength and elongation at break, as a measure of the mechanical properties, thermogravimetric analysis, and cone calorimetry. The onset temperature of the degradation is increased by about 50 °C and the peak heat release rate is reduced by 27−58%, depending upon the amount of clay that is present. The mass loss rates are also significantly reduced in the presence of the clay.

Studies on the Mechanism by Which the Formation of Nanocomposites Enhances Thermal Stability

Abstract: Polystyrene-clay and polystyrene-graphite nanocomposites have been prepared and used to explore the process by which the presence of clay or graphite in a nanocomposite enhances the thermal stability of polymers. This study has been designed to determine if the presence of paramagnetic iron in the matrix can result in radical trapping and thus enhance thermal stability. Nanocomposites were prepared by bulk polymerization using both iron-containing and iron-depleted clays and graphites, and they were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and cone calorimetry. The presence of structural iron, rather than that present as an impurity, significantly increases the onset temperature of thermal degradation in polymer-clay nanocomposites. Intercalated nanocomposites show an iron effect, but this is less important for exfoliated systems. Polymer-graphite nanocomposites show no difference between iron-free and iron-containing nanocomposites, presumably because the iron is not nanodispersed in the graphite.

Anchoring of Phosphonate and Phosphinate Coupling Molecules on Titania Particles

Abstract: Titanium oxide particles were treated using six organophosphorus compounds chosen as model coupling molecules: phenylphosphonic and diphenylphosphinic acids, their ethyl esters, and their trimethylsilyl esters. The ability of all of these coupling molecules to modify the surface of the TiO2 particles was demonstrated by elemental analysis, thermogravimetric analysis, and nitrogen adsorption. The bonding modes on the surface were investigated by means of diffuse reflectance IR Fourier transform (DRIFT) and 31P solid-state MAS NMR spectroscopy. Upon irradiation in water, a marked trend to the photooxidative degradation of the anchored organophosphorus groups was evidenced, especially in the case of phosphinate groups.

Sonochemical Proparation and Characterization of Nanocrystalline Copper Oxide Embedded in Poly(vinyl Alcohol) and its Effect on Crystal Growth of Copper Oxide

Abstract: Uniformly dispersed copper oxide nanoparticles in poly(vinyl alcohol) (CuO−PVA) have been synthesized by the sonochemical method. The properties of the as-prepared composite material are characterized by XRD, DSC, thermogravimetric analysis (TGA), TEM, and diffuse reflection spectroscopy (DRS). A band gap of 2.1 eV is estimated from DRS measurements. The controlled crystal growth of copper oxide has been studied by using the as-prepared CuO−PVA composite as seed for the crystal growth of copper oxide. Well-shaped crystals of 1 μm in length were grown.

Synthesis of Nanosized α-Nickel Hydroxide by a Sonochemical Method

Abstract: Nanosized α-nickel hydroxide with an interlayer spacing of 7.2 A has been synthesized with the aid of ultrasound radiation. This method was found to be a simple and convenient method to produce α-nickel hydroxide. The synthesized hydroxide was found to possess good stability in KOH medium and the material might be interesting from the application point of view in secondary alkaline batteries. The α-nickel hydroxide has been characterized by powder X-ray diffraction, transmission electron microscopy, DSC, thermogravimetric analysis, FT-IR spectroscopy, and elemental analysis.

Direct Synthesis of Periodic Mesoporous Organosilicas: Functional Incorporation by Co-condensation with Organosilanes

Abstract: Mesoscopic organosilicas were synthesized with bis(triethoxysilyl)ethane (BTSE) and cetyltrimethylammonium chloride (CTAC) under basic conditions. Further functionalization was achieved by co-condensation with trialkoxyorganosilanes. Surfactant extraction produced periodic mesoporous organosilicas (PMO's) functionalized with the respective organosilane pendent groups. Organosilanes used in this study include: 3-aminopropyltrimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 2-(trimethoxysilylethyl)pyridine, n-(3−triethoxysilylpropyl)-4,5-dihydroimidazole, phenethyltrimethoxysilane, and benzyltriethoxysilane. These materials have been characterized by nitrogen gas adsorption, powder X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), elemental analysis (EA), and high-resolution thermogravimetric analysis (TGA). The effect of organosilane incorporation on the porous structure of these materials is examined.

Surface modification of inorganic oxide particles with silane coupling agent and organic dyes

Abstract: The silane coupling agent 3-glycidoxypropyl trimethoxylsilane (GPS) was grafted onto the surface of silica gel, P2 glass beads and TiO2 oxide particles. FT-IR, thermogravimetric and elemental analysis were used to characterize the modified particles. The effects of various factors on the GPS grafting efficiency such as catalyst, GPS concentration, reaction temperature and time were studied. After modification with GPS, the xanthene dye rhodamine B and azo dyes 4-phenylazophenol and 4-phenylazoaniline, respectively, were grafted on to the particles, which were then used as pigment fillers. The colors of the pigments were adjusted by changing the kind of dyes, the concentration, the pH and the reaction solvents. Copyright © 2001 John Wiley & Sons, Ltd.

Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1 − xZrxO2 (x = 0–1) solid solutions

Abstract: Ce1 − xZrxO2 solid solutions are produced continuously by hydrolysis of mixtures of cerium ammonium nitrate and zirconium acetate in near-critical water at ca. 300 °C and 25 MPa using a flow reactor. Rapid hydrothermal coprecipitation leads to nano-particulate Ce1 − xZrxO2 (x = 0–1), the composition of which is largely determined by the initial relative concentrations of Ce4+ and Zr4+ ions in the starting solution. The freshly prepared materials are crystalline, possess very small particle sizes, and have high surface areas. The effects of calcining the products in air at high temperature have been studied. Apart from the 1∶1 Ce∶Zr solid solution, the phases of Ce1 − xZrxO2 remain stable on calcining to 1000 °C, but the particles sinter and the surface areas decrease significantly. The materials have been characterised by Powder X-ray Diffraction (PXD), IR and Raman Spectroscopy, microanalysis, Thermogravimetric Analysis (TGA), X-ray Fluorescence (XRF) and BET (surface area measurements). In selected cases, high resolution Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images were recorded to examine the particle morphology.

Thermal and carbothermic decomposition of Na 2 CO 3 and Li 2 CO 3

Abstract: In order to elucidate the decomposition mechanism of Na2CO3 and Li2CO3 in mold-powder systems employed in the continuous casting of steel, decompositions of Na2CO3 and Li2CO3 were investigated using thermogravimetric (TG) and differential scanning calorimetric (DSC) methods at temperatures up to 1200 °C, under a flow of argon gas. For the case of pure Na2CO3, the thermal decomposition started from its melting point and continued as the temperature was increased, but at a very slow rate. For Li2CO3, however, the decomposition occurred at much faster rates than that for Na2CO3. When carbon black was added to the carbonate particles, the decomposition rates of both Na2CO3 and Li2CO3 were significantly enhanced. From mass-balanced calulations and X-ray diffraction (XRD) analyses of the reaction products, it is concluded that decompositions of Na2CO3 and Li2CO3 with carbon black take place according to the respective reactions of Na2CO3 (1) + 2C (s) = 2Na (g) + 3CO (g) and Li2CO3 (l) + C (s) = Li2O (s) + 2CO (g). It was found that liquid droplets of Na2CO3 were initially isolated due to carbon particles surrounding them, but, as the carbon particles were consumed, the liquid droplets were gradually agglomerated. This effected a reduction of the total surface area of the carbonate, resulting in a dependence of the decomposition rate on the amount of carbon black. For the case of Li2CO3, on the other hand, hardly any agglomeration occurred up to the completion of decomposition, and, hence, the rate was almost independent of the amount of carbon black mixed. The apparent activation energies for the decomposition of Na2CO3 and Li2CO3 with carbon black were found to be similar and were estimated to be 180 to 223 kJ mole−1.

Pore-Size Control of Cobalt Dispersion and Reducibility in Mesoporous Silicas

Abstract: The effect of porosity in a wide range of mesopore diameters (dp = 20−330 A) on the dispersion and reducibility of cobalt species in mesoporous silicas is examined using nitrogen adsorption, X-ray diffraction, thermogravimetric analysis, and in situ X-ray absorption. It is shown that modification of mesoporous silicas by cobalt via aqueous impregnation results in small Co3O4 crystallites located in the pores of silicas. The sizes of these crystallites increase with increasing mesopore diameters. In situ X-ray absorption and thermogravimetric analyses show that the reduction of Co3O4 crystallites in hydrogen leads to CoO and Co metal particles. The porous structure of the supports strongly affects the extent of cobalt reduction. It is found that smaller particles in the narrow pores (20−50 A) are much more difficult to reduce to metal species than larger ones situated in the broad pores (>50 A) of mesoporous silicas.

Baseline Studies of the Clay Minerals Society Source Clays: Thermal Analysis

Abstract: Thermal analysis involves a dynamic phenomenological approach to the study of materials by observing the response of these materials to a change in temperature. This approach differs fundamentally from static methods of analysis, such as structural or chemical analyses, which rely on direct observations of a basic property of material ( e.g. crystal structure or chemical composition) at a well-defined set of conditions ( e.g. temperature, pressure, humidity). Clay minerals are highly susceptible to significant compositional changes in response to subtle changes in conditions. For example, changes in the fugacity of water affect the stability of interlayer H2O in a clay mineral (see below). Therefore, care must be taken that all experimental conditions are known with accuracy and precision. Differential thermal analysis (DTA), thermal gravimetric analysis (TG or TGA), and derivative thermal gravimetric (DTG) analysis are reported for each of the eight Source Clay minerals using commonly available commercial instruments. The DTA curves show the effect of energy changes (endothermic or exothermic reactions) in a sample. For clays, endothermic reactions involve desorption of surface H2O ( e.g. H2O on exterior surfaces) and dehydration ( e.g. interlayer H2O) at low temperatures (<100°C), dehydration and dehydroxylation at more elevated temperatures, and, eventually, melting. Exothermic reactions are related to recrystallization at high temperatures that may be nearly concurrent with or after dehydroxylation and melting. Discriminating between desorption and dehydration or dehydration and dehydroxylation may be problematic. The TG curves ideally show only weight changes during heating. The derivative of the TG curve, the DTG curve, shows changes in the TG slope that may not be obvious from the TG curve. Thus, the DTG curve and the DTA curve may show strong similarities for those reactions that involve weight and enthalpy changes, such as desorption, dehydration and dehydroxylation reactions. In …

Structure and Reactivity of Ni−Au Nanoparticle Catalysts

Abstract: We discuss the design of a Ni−Au nanoparticle catalyst system, which is based on the detailed experimental and theoretical understanding of the alloying and the chemical reaction processes on single-crystal surfaces. The alloy formation and structure of Ni−Au catalysts supported on SiO2 and on MgAl2O4 are simulated by Monte Carlo schemes as well as experimentally studied by a combination of in situ X-ray absorption fine structure, transmission electron microscopy, and in situ X-ray powder diffraction. On-line mass spectrometry is used to follow the reactivity of the catalyst and thermogravimetric analysis provided information on the deposition rate of carbon during steam reforming of n-butane. The simulations and the experiments give evidence for the formation of a Ni−Au surface alloy on the Ni particles for both supports. The Ni−Au catalysts exhibiting the surface alloy are active for steam reforming and are more resistant toward carbon formation than the pure Ni catalyst. Blocking of highly reactive Ni ...

High-yield Carbonization of Cellulose by Sulfuric Acid Impregnation

Abstract: The carbonization of cellulose with sulfuric acid impregnation was studied by thermogravimetric analysis and scanning electron microscopy. The mass yield of carbon after 800°C treatment in nitrogen increased to 2–3 times by addition of small amounts of sulfuric acid. The sulfuric acid is considered to work as dehydration catalyst, thus suppressing the release of volatile organic substances. The shrinkage of the sample during carbonization was also significantly reduced by the addition of sulfuric acid.

Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate

Abstract: In this work, we studied the mechanism of the fire retardancy of ammonium polyphosphate (APP) in polyurethane (PU). Indeed, according to the limiting oxygen index test, the efficiency of APP in PU coating was proven. On the one hand, thermogravimetric analyses showed that the addition of APP to PU accelerates the decomposition of the matrix but leads to an increase in the amount of high-temperature residue, under an oxidative or inert atmosphere. This stabilized residue acts as a protective thermal barrier during the intumescence-fire retardancy process. On the other hand, spectroscopic analysis of the charring materials using infrared spectroscopy, MAS NMR of the solid state, and ESR enables better understanding of the carbonization process and, consequently, of the intumescence phenomenon. It has been shown that the char resulting from PU consists of an aromatic carbonaceous structure which condenses and oxidizes at high temperature. In the presence of APP, a reaction between the additive and the polymer occurs, which leads to the formation of a phosphocarbonaceous polyaromatic structure. Moreover, this char is strongly paramagnetic. The presence of large radical species, such as a polyaromatic macromolecule trapping free radicals, was demonstrated. Both of these characteristics help to explain the fire-retardant performance of PU/APP.

Amine-Functionalized Periodic Mesoporous Organosilicas

Abstract: Ordered mesoporous materials have been synthesized by co-condensation of bis(triethoxysilyl)ethane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS) under basic conditions with supramolecular templates of cetyltrimethylammonium chloride as structure-directing agents Incorporation of the templates into the mesoscopic composite was followed by surfactant extraction to form periodic mesoporous organosilicas These materials have been characterized by powder X-ray diffraction, nitrogen gas sorption, metal ion adsorption, elemental analysis, and high resolution thermogravimetric analysis The effects of AAPTS concentration in the initial solutions on the chemical and structural properties of the final products are examined