Showing papers on "Thermogravimetric analysis published in 2000"

Characterization of the Porous Structure of SBA-15

Abstract: SBA-15 ordered mesoporous silicas were synthesized using the method reported by Zhao et al. The structures of these materials were characterized using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nitrogen adsorption. The samples were found to exhibit structural properties similar to those reported earlier. Our study confirmed that the size of primary mesopores of SBA-15 can be tailored by the choice of synthesis temperature and that SBA-15 exhibits a significant amount of disordered micropores and small mesopores. The volume and size of these complementary pores were found to be dependent to some extent on the synthesis/aging temperature. It was shown that the washing of as-synthesized SBA-15 in water or ethanol was accompanied by an appreciable structural shrinkage and led to the removal of a significant part of the polymeric template. Therefore, washing needs to be avoided if one wants to isolate SBA-15 without appreciable loss of the template. It was confirmed that water-washed...

Thermal stability of polyurethanes based on vegetable oils

Abstract: A series of polyurethanes from polyols derived from soybean, corn, safflower, sunflower, peanut, olive, canola, and castor oil were prepared, and their thermal stability in air and nitrogen assessed by thermogravimetric analysis, FTIR, and GC/MS. Oil-based polyurethanes generally had better initial thermal stability (below 10% weight loss) in air than the polypropylene oxide-based polyurethane, while the latter was more stable in nitrogen at the initial stage of degradation. If weight loss at a higher conversion is taken as the criterion of stability, then oil polyurethanes have better thermal stability both in air and in nitrogen. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1723–1734, 2000

Sonochemical synthesis and characterization of pure nanometer-sized Fe3O4 particles

Abstract: Sonochemical synthesis of pure nanometer-size Fe3O4 powder with particle size of ca 10 nm is reported in this article. Fe3O4 can be simply synthesized by sonication of iron(II)acetate in water under an argon atmosphere. The properties of pure nanometer-size Fe3O4 particles were characterized by X-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA) with an external magnetic field, and quantum design SQUID magnetization measurements. The prepared Fe3O4 nanoparticles are superparamagnetic and its magnetization at room temperature is very low (

Layered double hydroxides with the hydrotalcite-type structure containing Cu2+, Ni2+ and Al3+

Abstract: Layered double hydroxides (LDHs) with the hydrotalcite-like structure have been prepared containing different amounts of Ni2+, Cu2+ and Al3+ in the brucite-like layers by a coprecipitation method. The samples have been characterized by elemental chemical analysis, powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis, FT-IR and UV–VIS diffuse reflectance spectroscopies, temperature-programmed reduction, and specific surface area and porosity assessment by N2 adsorption at −196 °C. The nature of the phase obtained, crystallinity of the HT-like phase and thermal behaviour of these materials were influenced by MII/Al atomic composition and concentration of bivalent metal ion. Calcination at 500 °C leads to mostly amorphous solids containing NiO, and also CuO (tenorite) for large Cu2+ contents (Cu/Ni molar ratio equal to 4). When the calcination temperature is increased to 850 °C, crystallization of well defined phases (NiO, CuO and NiAl2O4, depending on the relative amounts of Ni, Cu and Al) takes place. Reduction of Cu2+ species in these samples takes place at a lower temperature than that for Ni2+, while the temperature of reduction of nickel is increased with an increase in aluminium and copper content of the samples.

Bioactivity of a CaO−SiO2 Binary Glasses System

Abstract: Five glasses in the CaO−SiO2 binary system with different silica content (50−90% in mol) have been prepared by the sol−gel method. The referred glasses have been characterized by thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) showing clear differences in composition and specific surface and porosity between those glasses with low SiO2 content (50−70% in mol) and those with high SiO2 content (80−90% in mol). The in vitro bioactivity study of all glasses prepared were carried out by soaking in a simulated body fluid (SBF) at 37 °C. The FTIR, XRD, SEM, and EDS analysis of the surface of these glasses after the in vitro assays reveal the formation of a hydroxycarbonate apatite (HCA) layer. The formation process of this layer on the glass is a function of the glass composition. The rate of formation increases in those glasses with lower SiO2 (50−70...

Synthesis and Thermal Behavior of Novel Si−B−C−N Ceramic Precursors

Abstract: Several boron-modified polysilazanes of general type {B[C2H4Si(R)NH]3}n (C2H4 = CHCH3 or CH2CH2) were synthesized and their thermal behavior studied. In contrast to the known derivatives with R = alkyl or aryl, we describe ceramic precursors in which the bulky moieties R are substituted with lower weight groups and/or reactive entities. Reactive units enable further cross-linking of the polymeric framework and therefore minimize depolymerization during ceramization. The polymer-to-ceramic conversion of all synthesized polymers was monitored by thermogravimetric analysis. Both low molecular weight substituents and/or cross-linking units increase the ceramic yield from 50% (R = CH3) to 83−88%. High-temperature thermogravimetric analysis in an inert gas atmosphere indicates the ceramics obtained are stable up to ∼2000 °C. XRD studies of the fully amorphous materials point out that, with increasing temperature, formation of α-SiC or α-SiC/β-Si3N4 crystalline phases occurs at 1550−1750 °C, depending on the mat...

Metal−Support Interactions in Co/Al2O3 Catalysts: A Comparative Study on Reactivity of Support

Abstract: Co/Al2O3 catalysts have been prepared with conventional impregnation and sol−gel methods to vary the chemical reactivity of the alumina support. The material system has been investigated with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance Fourier transform spectroscopy (DRIFT), Brunauer−Emmett−Teller (BET) method, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) (with thermogravimetric analysis (TGA) and differential thermal analysis (DTA)), and gas chromotography (GC) for the catalytic oxidation of CO. It had been found that the reactivity of the support changes the surface structure and chemical composition of catalysts significantly. When the metal−support interaction is weak, Co3O4 is a predominant surface phase (which is interfaced by a “cobalt surface phase”). With an increase in support reactivity, CoO and CoAl2O4 are found to be present on the surface. The cobalt content on the surface decreases upon the increase in suppor...

Thermal and Fire Studies on Polystyrene-Clay Nanocomposites

Abstract: Nanocomposites of polystyrene and several organophilic clays have been prepared by a bulk polymerization technique. The resulting polymers have an intercalated structure and show enhanced thermal stability, as measured by thermogravimetric analysis and cone calorimetry, relative to virgin polystyrene, even when as little as 0.1% of clay has been added.

Thermogravimetric Measurement of Hydrogen Absorption in Alkali-Modified Carbon Materials

Abstract: We have prepared Li-doped multiwall carbon nanotubes and Li- and K-intercalated graphite and measured their hydrogen storage properties using a thermogravimetric analyzer (TGA). In a flowing H2 atmosphere Li-doped nanotubes and Li-intercalated graphite both exhibit a cyclable weight gain between 200 and 400 °C and weight loss between 400 and 500 °C characterized by a distinct and unusual temperature profile. We find, however, that neither H2 nor carbon is required to generate this TGA feature; we observe it even in Li-containing samples measured in flowing Ar without H2 and in LiOH samples measured in either H2 or Ar. Potassium-intercalated graphite shows mass cycling with a different thermal character between 40 and 250 °C, but as with Li, observation of a large cyclable feature does not rely on the presence of H2. In both cases we identify the cycling mass to be absorption/desorption of H2O present as an impurity in the TGA atmosphere. The temperature signatures we observe are strikingly similar to thos...

Gas-Phase Purification of Single-Wall Carbon Nanotubes

Abstract: A gas-phase purification method for raw nanotube material has been developed which incorporates a chlorine, water, and hydrogen chloride gas mixture to remove unwanted carbon. The evolved gases can be easily monitored by infrared spectroscopy to follow the cleaning process. The quality of the final material was verified by SEM (scanning electron microscopy), TGA (thermogravimetric analysis), and UV−vis (ultraviolet and visible absorption spectroscopy). The yield of ∼15 wt % indicates a uniquely selective carbon surface chemistry that prevents etching of the nanotubes, which are generally more reactive due to their larger curvature. Although the technique's usefulness for large-scale purification was not determined, the ability to purify single-wall nanotubes by a gas-phase method has been demonstrated, and a mechanism proposed.

Thermosetting polymers from cationic copolymerization of tung oil: Synthesis and characterization

Abstract: The cationic copolymerization of tung oil with the divinylbenzene comonomer initiated by boron trifluoride diethyl etherate produces promising plastics. The gel times are largely dependent on the relative composition and the reaction conditions and vary from a few seconds to 1 h. Controlled reactions producing homogeneous materials can be obtained by (1) lowering the reaction temperature or (2) decreasing the initiator concentration to less than 1 wt % or (3) adding a certain amount of a less reactive oil, such as soybean oil, low saturation soybean oil (LoSatSoy), or conjugated LoSatSoy to the reaction. The resulting polymers are rigid and dark brown in color. The weight % of the starting materials converted to the crosslinked polymer is ∼85–98% as determined by Soxhlet extraction with methylene chloride. The structure of the bulk product is that of a crosslinked polymer network plasticized by a small amount of low molecular weight oil. The chemical composition of the bulk polymers varies with the original composition of the tung oil system. Dynamic mechanical analysis shows that the resulting products are typical thermosetting polymers with densely crosslinked structures. The modulus of the plastics is approximately 2.0 × 109 Pa at room temperature. One broad glass transition is observed at approximately 100°C. Thermogravimetric analysis shows that the tung oil polymers are thermally stable below 200°C with a 10% weight loss in air around 430°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1044–1056, 2000

Synthesis and properties of phosphorus-containing advanced epoxy resins. II

Abstract: A series of advanced epoxy resins with various epoxy equivalent weights were synthesized from a reactive phosphorus-containing diol, 2-(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-1,4-dihydroxy phenylene and diglycidyl ether of bisphenol A and then cured with 4,4′-diaminodiphenyl sulfone, phenol novolac, or dicyandiamide. The parameters of the polymerization reaction (such as reaction time, catalyst) are discussed in this article. Thermal properties of cured epoxy resins were studied using differential scanning calorimetry, dynamic mechanical analysis, and thermal gravimetric analysis. The flame retardancy of cured epoxy resins was tested by limiting oxygen index. The relations between thermal properties, flame retardancy, and epoxy equivalent weights were also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 429–436, 2000

Thermal degradation of nylon polymers

Abstract: This paper is concerned with the processes of thermal degradation of nylon 6 and nylon 6,6, which lead to crosslinking and the production of involatile char. The techniques used in this study include thermogravimetric analysis (TG), differential scanning calorimetry (DSC), hot-stage Fourier transform infrared spectroscopy (hot-stage FTIR) and solution viscosity. TG results showed that nylon 6 and nylon 6,6 produce involatile char during thermal degradation. The formation of char lead to a deviation from first order kinetics of thermal degradation, and the amount of char yielded decreased with increasing temperature. Thermal degradation lead to a decrease in the amount of crystallinity attainable on cooling from the melt, which was considered to be due to crosslinking, and was accompanied by an increase in molecular weight and formation of colour. Hot-stage FTIR results showed that thermal degradation lead to the formation of an aromatic-conjugated structure, which may contain keteneimine groups.

The effect of thermal treatment on some of the physicochemical properties of a bentonite

Abstract: A white calcium bentonite (CaB) from the Kutahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. % Ca-rich montmorillonite (CaM). Samples were heated at various temperatures between 100–1300°C for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtained. The change in the d (001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol−1, respectively. The average deformation enthalpies, in the respective temperature intervals between 200–700°C and 700–900°C, were estimated to be 25 and 205 kJ mol−1 using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a “zig zag” variation with increasing temperature to 700°C, but decrease rapidly above this temperature. The S and V values were 43 m2 g−1 and 0.107 cm3 g−1, respectively, for untreated bentonite. They reach a maximum at 500°C and are 89 m2 g−1 and 0.149 cm3 g−1, respectively. The XRD data clearly show that, at 500°C, where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.

Production of hard and heat-resistant coatings on aluminium using a plasma micro-discharge

Abstract: Oxide structures were synthesized on aluminium alloy surfaces as the anode under plasma discharges conditions. Aqueous solutions containing ions of an organic acid were used as electrolytes. It was ascertained that the amorphous coatings obtained have a significant microhardness and heat-resistance up to 870°C. On the basis of experimental data obtained by thermogravimetric analysis, X-ray analysis and laser mass-spectroscopy methods, conclusions about the formed oxide layer compositions were made.

Preparation, characterisation and applications of thin films for gas sensors prepared by cheap chemical method

Abstract: The physical properties of pure and doped (Ni, Os, Pd and Pt) SnO 2 thin films, prepared by using a chloride-based inorganic sol–gel route, have been reported. These properties were investigated by using differential scanning calorimetry and thermogravimetric (DSC/TG), FTIR, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. Microsensors for gas detection were also fabricated and tested in various atmospheres (nitrogen oxide, carbon monoxide, ethanol, methanol and methane). The dopants affected the coating properties depending on the formation of nanoparticles. Furthermore the gas-sensing properties towards reducing and oxidising gases were found to be dependent on the nature of doping element. An array consisting of the manufactured sensors has been arranged and examples of applications for “electronic nose” are given.