Showing papers on "Thermogravimetry published in 1993"
TL;DR: The residual alkali elements issuing from the precipitating agents induce variations on the final state of the solid as discussed by the authors, and the residual elements can be used to obtain a better calcination at high temperatures (1073 K).
Abstract: Cerium hydroxide samples prepared with different precipitating agents (NaOH, KOH, NH[sub 4]OH) have been studied by thermogravimetry, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The untreated samples are a mixture of CeO[sub 2] and Ce(OH)[sub 4] with a small quantity of Ce(OH)[sub 3] present in the bulk of the solid. A part of the Ce[sup 3+] species remains stable even after calcination at high temperatures (1073 K) under air. The residual alkali elements issuing from the precipitating agents induce variations on the final state of the solid. 38 refs., 7 figs., 1 tab.
192 citations
191 citations
150 citations
126 citations
TL;DR: In this paper, a stoichiometric proton transfer from the bridging hydroxyl Bronsted acid site to the physisorbed water has been demonstrated for the H 3 O + oxonium ion in C s or C 1 symmetry.
Abstract: Diffuse reflectance infrared spectroscopy, combined with thermogravimetry, of progressively dehydrated (up to 550 o C) silicoaluminophosphate (SAPO-34) reveals that, at room temperature, there is a stoichiometric proton transfer from the bridging hydroxyl Bronsted acid site to the physisorbed water. All six predicted infrared vibrations for the H 3 O + oxonium ion in C s or C 1 symmetry are identified. In a typical sample there are 10.0×10 20 H 3 O + ions g -1
108 citations
TL;DR: In this article, the thermal degradation of poly(N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200-600°C under nitrogen and oxygen atmospheres at various heating rates.
Abstract: The thermal degradation of poly(N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200–600°C under nitrogen and oxygen atmospheres at various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in N2, whereas in the presence of oxygen, two trends may be considered: At relatively low temperatures (200–400°C) and degrees of conversion, α, lower than 0.5, we obtained an average value of 199 kj/mol, whereas in the temperature interval 400–600°C with degrees of conversion higher than 0.5, the value of Ea was 306 kj/mol. Isothermal experiments carried out in N2 in the interval 350–400°C gave an average value of Ea = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in N2 as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. © 1993 John Wiley & Sons, Inc.
105 citations
TL;DR: In this paper, the authors reported the chemical synthesis of an N -substituted water-soluble polyaniline derivative, which was characterized by a wide range of techniques including visible absorption, FT i.r.m. and 1 H n.c.
86 citations
TL;DR: In this paper, the thermal decomposition of three lignosulphonates, three sodium salts of a spruce milled wood lignin (MWL) and a mixture of MWL and NaCl was studied by thermogravimetry/mass spectrometry (TG/MS).
74 citations
TL;DR: In this article, the thermal decomposition of divalent metal alginate gel compounds has been studied using thermogravimetry (TG) and differential thermal analysis (DTA).
70 citations
TL;DR: In this article, a phase of approximate composition SbVO4 has been reported in the literature as a key component in new catalysts for the ammoxidation of propane to acrylonitrile.
67 citations
TL;DR: In this article, the non-isothermal decomposition of nickel acetate tetrahydrate was studied by means of thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry(DSC) from ambient temperature up to 500°C.
TL;DR: In this paper, the reaction of the precursor powders necessary for the formation of the final Bi(2223) phase was investigated with and without the presence of an Ag sheath by means of differential thermogravimetry (DTA/DTG).
Abstract: The reaction of the precursor powders necessary for the formation of the final Bi(2223) phase was investigated with and without the presence of an Ag sheath by means of differential thermogravimetry (DTA/DTG). The nature of the endothermic peaks observed by DTA as well as the influence of Ag on their positions are discussed. By means of X-ray diffraction and energy dispersive X-ray analysis (EDX) on oil-quenched Ag-sheathed tapes it is shown that the Bi(2212) phase originally present in the precursor powders undergoes a structural modification which can be associated with the dissolution of Pb. This transformation occurs at a temperature near 836 degrees C in Ag-sheathed tapes. This work has been essentially focused on the role of Pb and its effects on the Bi(2212) phase in the first stages of transformation.
TL;DR: In this paper, phase equilibrium in the binary PbO-Ag and CuO−Ag systems has been investigated using differential thermal analysis (DTA), thermogravimetry (TG), and X-ray diffractometry (XRD) techniques.
Abstract: Silver has played a critical role in the fabrication of metal/ high-Tc superconductor composites. Phase equilibrium in the binary PbO–Ag and CuO–Ag systems has been investigated using differential thermal analysis (DTA), thermogravimetry (TG), and X-ray diffractometry (XRD) techniques. Composition versus temperature diagrams have been established for these systems in air. Eutectic reactions CuO + Ag = L at a composition of Ag = 98.6 mol% and 932°± 3°C for the CuO–Ag system and PbO + Ag = L at a composition of Ag = 8.3 mol% and 825°± 3°C for the PbO–Ag system have been detected. The CuO–Ag system has two immiscible liquid phases in the composition regime of Ag = 30.6–98 mol%, and there are two immiscible liquid phases at the composition range of Ag = 11.7–95.7 mol% in the PbO–Ag system.
TL;DR: In this article, the effect of extraction on the thermal behaviour and chemical-physical properties of chars and activated products was studied, and the FT-IR spectra of the carbonized and activated carbon displayed absorption bands compatible with the presence in the materials of surface olefinic C�C double bonds, aromatic rings, and oxygen functional groups.
TL;DR: In this article, the chemical compositions of the ultrafine amorphous transition metal-boron (TM-B, TM = Co, Ni, Fe) powders have been prepared, under identical experimental conditions, by chemical reduction of Co2+, Ni2+, and Fe2+ ions with potassium borohydride in aqueous solution.
Abstract: Ultrafine amorphous transition metal-boron (TM-B, TM = Co, Ni, Fe) powders have been prepared, under identical experimental conditions, by chemical reduction of Co2+, Ni2+, and Fe2+ ions with potassium borohydride in aqueous solution. The chemical compositions of the samples are close to TM60B40. The particles have a spheroidal shape with diameters ranging from 10 to 100 nm. X-ray diffraction and transmission electron microscopy investigations show that the Co-B and Ni-B samples are fully amorphous while in a few particles of the Fe-B sample the presence of I±-iron microcrystallites are observed. Crystallization of the samples has been investigated by differential scanning calorimetry. Under anaerobic conditions the Co-B sample evolves toward t-Co2B accompanied by a minor quantity of o-Co3B; in the Ni-B and Fe-B samples, crystallization gives rise to a metallic component plus boride phases. A significant decrease of the boride phases and a corresponding increase of the metallic component are obtained in all samples when the thermal treatment is performed in the presence of traces of oxygen.
TL;DR: In this article, the high-temperature stability of highly cross-linked cyclotetrasiloxane glasses, derived from (Me(Vi)SiO) 4 and Me(H) SiO 4, was investigated using TGA/MS and 29 Si NMR Results show that the cyclosiloxanes network remains largely intact after heating at 400°C for 1 h Decomposition of the siloxane network does not occur until greater than 525°C
Abstract: The high-temperature stability of highly cross-linked cyclotetrasiloxane glasses, derived from (Me(Vi)SiO) 4 and (Me(H)SiO) 4 , was investigated using TGA/MS and 29 Si NMR Results show that the cyclosiloxane network remains largely intact after heating at 400°C for 1 h Decomposition of the siloxane network does not occur until greater than 525°C
TL;DR: In this paper, a simple and convenient method for the synthesis of YBa2Cu3O7−x powder is described, which involves autoignition of a citrate-nitrate gel resulting from a thermally induced oxidation-reduction reaction to yield an ash that upon calcination produces the desired compound.
Abstract: A simple and convenient method for the synthesis of YBa2Cu3O7−x powder is described. The technique involves autoignition of a citrate-nitrate gel resulting from a thermally induced oxidation-reduction reaction to yield an ash that upon calcination produces the desired compound. The resulting powder is pure, homogeneous, and possesses a reasonably fine particle size. The autoignition is restricted to a particular range of citrate-nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good potential for large-scale production.
TL;DR: Two doubly hyphenated, thermogravimetry-based analytical techniques, viz.
Abstract: Two doubly hyphenated, thermogravimetry-based analytical techniques, viz. TG/GC/MS and TG/ GC/IR, are described. A valveless, quartz, heated sample path between TG furnace and GC column minimizes losses of products. Furthermore, combination of a pulsed automated vapor sampling inlet and a transfer line type GC column permits high-speed GC identification of individual TG products while maintaining sufficiently high temporal resolution with the ∼1-min sampling interval to provide kinetic information about the underlying reaction mechanisms. Example analyses on poly(α-methylstyrene), a styrene-isoprene block copolymer, and wood demonstrate the techniques' capability for monitoring specific minor products and isomers
TL;DR: In this paper, the thermal decomposition of 1-methyl-5-aminotetrazole and 1,5-diaminotetaxole has been studied using thermogravimetry, differential scanning calorimetry and thermal volumetric analysis.
TL;DR: In this article, solid state Ln-DMBP compounds, where Ln represents trivalent lanthanides (except for promethium) and yttrium, and DMBP is 4-dimethylaminobenzylidenepyruvate, were prepared.
TL;DR: In this paper, the thermal degradation of poly(furfuryl methacrylate) was studied by means of dynamic thermogravimetric analysis (TGA) in the temperature range 100-600°C under nitrogen and oxygen atmospheres at various heating rates, and the apparent activation energy for the interval 230-340°C corresponding to the first degradation step was determined.
TL;DR: In this paper, an anisotropic degradation method based on the unreacted core principle was proposed to account for the effect of carbon fiber-reinforced polymeric composites in air.
Abstract: The weight loss of carbon fiber-reinforced polymeric composites in air has been found to depend on the sample surface characteristics such as fiber orientation with respect to the exposed surfaces This phenomenon can be attributed to the diffusion of oxygen through the sample and the dependence of diffusion rate on fiber orientation Recently, an anisotropic degradation methodolgy was proposed, based on the unreactedcore principle, commonly used in catalysis, as extended to account for the anisotropic effects In this work, these anisotropic diffusion effects were also identified for small thermogravimetric (TGA) samples Isothermal TGA experiments were performed in air at 310°C using samples weighing 10–163mg Weight loss was found to be a strong function of fiber orientation The anisotropic degradation methodology successfully predicted the weight loss of all samples, although some deviation attributed to the sample edge effects was observed When samples were examined by optical microscopy, a degraded zone was observed on the sample surfaces The thickness of this layer depended on the type of exposed surface, validating the anisotropic degradation methodology © 1993 John Wiley & Sons, Inc
TL;DR: In this paper, the effects of oxidant/monomer ratio and metanilic acid/aniline ratio on the physicochemical properties of the copolymers are investigated and comparisons are made with the self-doped polymer obtained from the sulfonation of polyanilines.
TL;DR: In this paper, two different methods for preparing electrochromic nickel hydroxide films are tested: thermal hydrolysis of [Ni(NH 3 ) 6 ] 2+ complex and thermal decomposition of a mixture of urea and NiSO 4.
TL;DR: A new copper diammine divanadate Cu(NH 3, H 2 O and VO 3 ) 2 has been synthesized and structurally characterized in this article, where the unit cell is monoclinic, space group Pc, a = 5616(2) A, b = 5591(1) A, c = 11331(2), A, β = 9091(2 )°, V = 3557(3) A 3, Z = 2, Z = 0.
TL;DR: In this article, spherical gel particles have been prepared by the digestion of rice husk with concentrated HNO3, and the organic composition of the husk and residue were analysed by chemical methods.
Abstract: Spherical gel particles have been prepared by the digestion of rice husk with concentrated HNO3. The colloidal portion of the digestion product was washed, dried and aged at standard conditions to initiate particle formation. The organic composition of the husk and residue were analysed by chemical methods. Thermal decomposition of the gel has been investigated by thermogravimetry (TG) and isothermal heating. The observed thermal behaviour of the gel is characteristic decomposition of cellulose and hemicellulose which are believed to be the main components of the gel. Morphological features of the gel before and after heating were examined by scanning electron microscopy. The crystallinity of the gel was determined by X-ray diffraction analysis.