Thermal Analysis of a Hydrated Silica–Sodium Thiosulfate–Sulfur System

A system formed by concerted action of orthosilicic acid gelation and decomposition of sodium thiosulfate to afford highly dispersed elemental sulfur was studied by simultaneous methods, DTA, TG and DTG. A typical curve has been found to be an outcome of thermal processes associated with desorption of physically adsorbed water, condensation of surface silanol groups and thermal degradation of sodium thiosulfate. A large loss in mass over the lower temperature range was assigned to the loss of physically adsorbed water and condensation of silanol groups of the gel as indicated by accompanying strong endothermic effects. Subsequent strong exothermic effects were attributed to combustion of elemental sulfur embedded in the gel. Experiments were also conducted to control the extent of decomposition of the thiosulfate and generation of elemental sulfur by varying pH of thesilicic acid solution. These have shown that acidification of the silicic acid - sodium thiosulfate system with sulfuric acid fostered decomposition of the thiosulfate and raised the quantity of elemental sulfur. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of purification process of single-walled carbon nanotubes by thermoanalytical techniques

The thermal behaviour of commercial Carbolex single-walled carbon nanotubes (SWCNTs) both as-received and after purification by a novel method has been studied by thermogravimetric/derivative thermogravimetric/difference thermal analysis (TG/DTG/DTA). Purification from metal catalysts (Ni and Y) has been successfully obtained using 0.1 M I₂ in iso-propanol instead of the usual concentrated HNO₃. The final residues of thermal analysis have been characterised by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The gathered results showed that the as-received SWCNTs burns out in a one-step between 573 and 923 K, whereas the SWCNTs treated with HNO₃ become highly hygroscopic. The I₂-iso-propanol-treated SWCNTs showed three overlapped exothermic peaks between 500 and 973 K in the DTA curve, which allowed separating amorphous carbon from SWCNTs by air-thermal treatment at 573 K. The graphite-like compounds, which are present in both untreated and treated SWCNTs, does not burn up to 1173 K.     

New view on the oxidation mechanisms of crude oil through combined thermal analysis methods

In the previous study, the oxidation behavior of four Chinese crude oils (Oil 1 to 4) in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques and oxidation tube experiments. The present work investigates the thermal behavior of these oils by combining DTG–DTA method. First, we conducted comparative analysis about mass loss rate from DTG curves and endothermic/exothermic phenomenon from DTA curves attempting to clarify the endothermic or exothermic mechanism in crude oil low-temperature oxidation. Finally, we combined the thermal analysis method with low-temperature oil oxidation tube experiment in porous media to ascertain, whether the two methods are consistent in the aspect of low-temperature oxidation mechanism of crude oil by O₂ consumption rate and CO₂ generating rate (carbon bond stripping reaction rate). Results show that crude oils undergo an endothermic oxidation behavior during low-temperature oxidation stage, suggesting the decomposition of hydrocarbon components. Clay can play a catalytic effect on low-temperature oil oxidation. The results of DTG–DTA tests can also better reflect oil oxidation mechanism under real conditions.     

Thermal characterization of the poultry fat biodiesel

Chemical composition of oils and fats used in the biodiesel synthesis can influence in processing and storage conditions, due to the presence of unsaturated fatty acids. An important point is the study of the biodiesel thermal stability to evaluate its quality using thermal analysis methods. In this study the thermal stabilities of the poultry fat and of their ethyl (BEF) and methyl (BMF) biodiesels were determined with the use of thermogravimetry (TG/DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), in different atmospheres. The TG/DTG curves of the poultry fat in synthetic air presented three decomposition steps while only one step was observed in nitrogen (N₂) atmosphere. The DSC results indicated four exothermic enthalpic transitions in synthetic air and an endothermic transitions in N₂ atmosphere attributed to the combustion process and to the volatilization and/or decomposition of the fatty acids, respectively. For both biodiesels the TG/DTG curves in air indicated two mass loss steps. In the DSC curves four exothermic transitions were observed in synthetic air besides an endothermic one in N₂ atmosphere.     

Studies on thermal decomposition of electrochemically oxidized glass-like carbon

Glass-like carbon (GC) tiles were electrochemically oxidized in 1 mol·dm^?3 H₂SO₄ solution at a potential of 2.3 V/SCE. The surfaces of the oxidized samples were examined by scanning electron microscopy (SEM). The solid oxidation products were studied by derivatographic (TG, DTG and DTA) and elemental analyses. The solid products of electrochemical oxidation of GC, with the general formula C₈O_4.2H_2.3 were thermolabile and revealed properties similar to those of graphite oxide. They are hydrophylic and their thermal decomposition proceeds in three steps: (i) evaporation of-chemisorbed water (320–400 K), (ii) exothermic decomposition of graphite oxide (370–430 K), and (iii) gradual decomposition of the oxidation products (>430 K).     

Study of thermal behaviour of some edible mushrooms

This paper is aimed to analyse the thermal behaviour in air of edible mushrooms through nonisothermal (TG, DTG, DTA) and calorimetric (Berthelot calorimeter) methods. The studied mushrooms were Pleurotus ostreatus spontaneously grown and from culture and Agaricus bisporus from culture, currently used in alimentation but insufficiently investigated from this point of view. The analysis of TG–DTG–DTA curves has indicated that the degradation mechanism is complex and characteristic to every species and major differences between the cap and the stipe of investigated mushrooms have not been recorded. These species are thermally stable in the range of 30–160 °C. The thermal stability in terms of initial degradation temperature (T _i °C) and the temperature corresponding to the conversion grade (T _α=0.03 °C) indicate that the stipe has a thermal stability close to the cap one and that the cultivated mushrooms are more thermally stable than those spontaneously grown. The obtained results concerning the combustion of the sample using Berthelot calorimeter are in accordance with the TG–DTG–DTA analysis. The residue obtained is a measure of the mineral content and is quantitatively close.     

SiO2-PEG凝胶体系的热物理化学特征

用程序升温热重法分析了SiO2及SiO2-PEG干凝胶的热物理化学行为,结果表明：采用不同的环境气氛对SiO2-PEG干凝胶进行热处理,聚乙二醇（PEG）表现出不同的热稳定性,并由此影响干凝胶的织构性质;通过对氮气气氛中得到的DTG曲线进行处理,得到不同温度段的表现活化能,说明SiO2干凝胶脱羟反应表现出动力学控制,而SiO2-PEG干凝胶随着温度的升高则表现出动力学控制逐步向表面羟基的扩散控制转变．     

TG–DTA, UV and FTIR spectroscopic studies of urea–thiourea mixed crystal

A mixed crystal of urea–thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized by thermogravimetric–differential thermal analysis (TG–DTA), UV and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage weight loss between 200 and 750 °C. In this temperature range DTA curve shows exothermic peaks supporting the formulated decomposition pattern. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea–thiourea mixed crystals. Detailed structural analysis of the compound is under progress.     

Investigation of thermal decomposition of rice husk

Studies on the thermal decomposition of untreated rice husk and that treated with HCl and H₂SO₄ of various concentrations were carried out by TG, DTG and DTA. The mass loss occurred in three distinct stages, namely, removal of moisture, release of volatile matter and burning of combustible material. The corresponding temperature ranges for untreated husk were 40–150, 215–350 and 350–690°C. The final temperature of combustion decreased with acid-treatment of the husk. The thermal decomposition of the husk was found to be an exothermic process.     

A study of the compounds present in the three-component system Dy2O3-SeO2-H2O at 100°C

The solubility isotherm of the system Dy₂O₃-SeO₂-H₂O at 100°C was studied and drawn. The selenites present in the system were identified and isolated. A thorough TG, DTG and DTA analysis was made. By modelling the conditions of TG, DTG and DTA analysis, the phases of the thermal decomposition were isolated and identified. The chemistry of the reaction was described.     

Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and NiL₂ (L^?=diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL₂, DTG 250–350°, DTA 300–320° and for NiL₂, DTG 290–390°, DTA 360–400°. Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

     

Study by thermal methods on some new cyclic ylides and derivatives

The study is devoted to the characterization by TG, DTG, DTA, both in air and N₂ atmosphere, of three cyclic ylides as well as two spirane derivatives, to the purpose of elucidating the correlation between structure, thermostability and thermal degradation mechanism. Thermal analysis data indicated that the degradation mechanism is characteristic for every sample, and the consequences of structural peculiarities are discussed. The thermostability series of the samples is correlated to their structure. The quantitative TG-DTG-DTA analysis allowed some considerations on the thermal degradation mechanism, subsequently confirmed by mass spectrometry. The melting points obtained by DTA and Boetius measurements along with the initial degradation temperatures from TG-DTG-DTA curves indicates the temperature range for the use and storage of these compounds, considering that some derivatives of cyclic ylides show biological activity and potential medical applications.     

Thermal behavior of modified urea–formaldehyde resins

The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO₂ was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3.     

Thermal and FTIR spectral studies in various proportions of urea thiourea mixed crystal

Mixed crystals of various proportions of urea thiourea were grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized using thermogravimetry–differential thermal analysis (TG–DTA) and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two-stage mass loss between 175 and 750 °C. In this temperature range, DTA curves show exothermic peaks supporting the formulated decomposition pattern. The FTIR spectra show the characteristic absorption, vibration frequencies due to urea thiourea. Detailed structural analysis of the compound is under progress.     

Thermal stability of the amorphous system Ge20As14(SexS1−x)52I14

Results of thermal investigations of the amorphous five-component chalcogenide system Ge₂₀As₁₄(Se_xS_1?x)₅₂I₁₄ are presented. Differential thermal analysis (DTA), derivative differential thermal analysis (DDTA), and dilatometry were employed to determine the temperatures of softening and partial crystallization of the samples. Thermal treatment of the samples at 1000°C and recording of the corresponding thermogravimetric (TG) and derivative thermogravimetric (DTG) curves allowed an elucidation of the full mechanism of their decomposition, which proceeds via seven characteristic phase transitions.     

Thermal behaviour of lignins extracted from different raw materials

The thermal degradation of lignins extracted from bagasse, rice straw, corn stalk and cotton stalk, have been investigated using the techniques of thermogravimetric analysis (TG) and differential thermal analysis (DTA), between room temperature and 600°C. The actual pyrolysis of all samples starts above 200°C and is slow. The results calculated from TG curves indicated that the activation energy, Efor thermal degradation for different lignins lies in the range 7.949–8.087 kJ mol^?1. The DTA of all studied lignins showed an endothermic tendency around 100°C. In the active pyrolysis temperature range, thermal degradation occurred via two exothermic process at about 320 and 480°C, and a large endothermic pyrolysis region between 375 and 450°C. The first exothermic peak represents the main oxidation and decomposition reaction, the endothermic effect represents completion of the decomposition and the final exothermic peak represents charring.     

Synthesis and Characterization of Na And Mg Containing Carbonatefluorapatites

Abstract

The apatites were precipitated in an aqueous NH₄OH-NH₄NO₃ solution with pH 9–10 at temperatures 20°C and 80°C. The synthesized materials were studied by chemical and thermal analyses (TG/DTG/DTA, TG/ETIR-EGA), IR-spectroscopy, XRD-powder analysis and specific area measurements.     

Caracterisation par analyse thermique de la lignine,de la cellulose et de quelques uns de ses derives etherifies

Cellulose and its derivatives (methyl cellulose, sodium carboxymethyl cellulose, hydroxymethyl cellulose and hydroxypropyl cellulose) used as excipients in pharmaceutical industry can be characterised by simultaneous thermoanalytical (DTA and TG) methods, based on the temperatures of exothermic peaks. Lignine cellulose can be identified by taking into account the difference in temperature between the first exothermic DTA peak and the corresponding DTG peak.

     

Thermal decomposition of ammonium copper chromate: effect of the addition of barium

The influence of the addition of barium (as barium chromate) to ammonium copper chromate on its thermal decomposition has been investigated by TG, DTG and DTA in the temperature range 303–1273 K. The solid products formed in the decomposition at different temperatures were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and also by measuring their specific surface area. The addition of BaCrO₄ at different concentrations (0–19.8%) was found not to change the general trend in the decomposition of ammonium copper chromate (which occurs in four distinct steps), except small changes in the temperature corresponding to DTG and DTA peaks. However, the sintering (or crystal growth) of the solid product is largely reduced by the presence of BaCrO₄.     

A new crystal engineering approach for the synthesis of {[K.18-Crown-6]I3}n as a nanotube-Like and recyclable catalyst for the chemoselective silylation of alcohols

Reaction of 18-crown-6 with KI in ethanol solution followed by addition of iodine (I₂) afforded a unique triiodide salt with a nanotube-like structure ({[K.18-Crown-6]I₃}_n). It is shown that this reagent may be used for the chemoselective trimethylsilylation of alcohols. The synthesis of the crystalline reagent is a good example of crystal engineering. Reagent was recycled and reused.