Kinetic analysis of non-isothermal thermogravimetric analyser results using a new method for the evaluation of the temperature integral and multi-heating rates

A technique using non-isothermal thermogravimetric analyser results was developed for the validation of reaction rate models together with associated parameters suitable for chemically controlled gas-solid reactions. The solution of the temperature integral which occurs in the calculation is achieved by numerical integration with respect to a dimensionless activation energy variable, y=E/RT, following a transformation of the temperature integral equation. The evaluation of the validity of the kinetic model and determination of all the constants is accomplished with a two-step regression procedure with experimental results from several thermogrammes with different linear heating rates. The technique was validated by comparing results obtained for the combustion of two coal-chars with corresponding isothermal results using a shrinking core model with a nth order surface reaction.     

Preparation,microstructure, and improved dielectric and nonlinear electrical properties of Na1/2La1/2Cu3Ti4O12 ceramics by sol–gel method

Na_1/2La_1/2Cu₃Ti₄O₁₂ (NLCTO) ceramics were prepared by the sol–gel method (SG) and solid-state method (SS), and the effect of sintered temperature on microstructure and dielectric and nonlinear electrical properties has investigated. The experimental results indicated that NLCTO-SG ceramics sintered at 1090 °C for 10 h showed larger grain size, higher density and more homogeneous microstructure, especially higher dielectric constant up to ca 1.3–1.8 × 10⁴, lower dielectric loss of about 0.057 and better temperature stability than NLCTO-SS counterparts. However, the good low-voltage varistor behavior and the third kind of dielectric relaxation behavior could not be observed from the NLCTO-SS ceramics. The higher dielectric constant of the NLCTO-SG ceramics may be due to the stronger internal barrier layer capacitor (IBLC) effect. Two values of grain activation energy were obtained above room temperature for the first time. The transition temperature of two values was basically coincident with that of sudden changes of the dielectric properties.     

A thermogravimetric and FT-IR study of the reduction by H2 of sulfated Pt/CexZr1−xO2 solids

The nature, concentration and reducibility by H₂ of sulfate species formed from SO₂ oxidation were studied over a range of Pt/Ce_xZr_1−xO₂ catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H₂ first occurred at the Ce_xZr_1−xO₂ surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction.     

COMPARISON AMONG TECHNIQUES TO RETRIEVE KINETIC PARAMETERS FROM THERMOGRAVIMETRY DATA

A statistical comparison of methods used to retrieve kinetic information from thermogravimetric analysis (TGA) data was done. The objective of this work was to try to establish if there is a difference between the kinetic parameters predicted using: Coats and Redfern (1964), and its modifications: Fischer, el al. (1987), Chen and Nuttal (Nutall et al. 1983), Reich and Stivala (1980), and Horowitz and Metzger (1963). All these methods were tested using data obtained by numerical integration of a first order irreversible reaction under typical TGA conditions, and to study the effects of experimental error in parameter estimation these data were perturbed by introducing a random error variation in the numerical data. From the results, the first three methods are statistically similar, while the last two produce significantly erroneous values even with no error present in the data     

桑蚕茧的热分解动力学和反应机理的研究

本文用热重分析法(TGA)研究了桑蚕茧的热分解动力学和反应机理。根据四个不同升温速率的热重分析谱图,求得热分解百分数为5、10和15时的热分解活化能分别为410.8,376.7和324.0 kJ/mol.又根据热分解的气体产物和固体残留物的红外光谱图,推出了热分解反应的机理。     

TG–DTA approach for designing reference methods for moisture content determination in food powders

There is no systematic procedure described in the literature to establish a robust and accurate reference method for determining the moisture content in any solid food product. In this paper, we are proposing a new approach based on simultaneous thermogravimetry and differential thermal analysis (TG–DTA), with data for several amorphous food powders that result from spray-drying, freeze-drying or extrusion. In the first step, by heating a representative sample of about 20 mg at 2 °C/min we would detect the temperature and the mass loss at the inflection point that characterises, if there is an inflection, the end of the drying and the onset of chemical reactions. In cases of not too much sensitive products, the mass loss at the inflection may be considered as a good estimation of the moisture content. At 2 °C/min heating rate, the inflection temperature T_i is an indicator that allows estimating the optimal isothermal drying temperature T_d about 15–30 °C below T_i, depending on the product sensitivity to heat treatments and the kinetics of water molecule diffusion through the amorphous matrix. Then, a series of three isothermal drying are performed at about T_d−12 °C, T_d and T_d+8 °C, and a simple multilinear model allows calculating the best oven temperature to achieve the optimal moisture content determination in 2 h. This procedure is described and results are shown for several dehydrated food products: milk, coffee, cereal and pet food. This fast procedure may be applied either for establishing optimal oven conditions for most amorphous new products or for revising conditions that have been established in the past but are not robust enough for several ones.     

Preparation and Properties of Barium Titanate Nanopowder/Epoxy Composites

This article is focused on the preparation of barium titanate nanopowder/epoxy composites and studying the effect of barium titanate nanopowder on improving mechanical and thermal characteristics of the epoxy polymer. Composites are prepared by dispersing barium titanate nanopowder in epoxy resin and, subsequently, cross-linking by using diamino diphenyl methane (DDM) curing agents. Synthesis of barium titanate nanopowder/epoxy composites is carried out for different concentrations (1, 3, and 5 by weight) of barium titanate nanopowder at high temperature. High-temperature curing (HTC) involves mixing the resin-nanopowder solution followed by DDM hardener and curing at 120°C. Tensile, flexure, and impact results showed a maximum value of 72.7 MPa, 2.98 GPa, and 2 J/cm, respectively. DSC analysis revealed that curing occurs at low temperature in the presence of barium titanate nanopowder. Thermogravimetry analysis (TGA) showed the increased thermal stability in the nanoparticle filled epoxy composites as compared with the pure epoxy counterparts. Dynamic mechanical analysis (DMA) revealed, maximum storage modulus of 6400 MPa and glass transition temperature of 154°C for 3 wt% barium titanate nanopowder.     

Thermogravimetry Studies Concerning the Synergism of Antimony Trioxide-Tin(II)Chloride Dihydrate on the Flame-Retardancy of a Cotton Fabric

The synergistic effect between antimony trioxide and tin(II)chloride dihydrate on the flame-retardancy of a cotton fabric (woven construction massing 150 g/m²) was studied in this investigation. The laundered bone-dried massed specimens were impregnated with appropriate concentrations of individual aqueous antimony trioxide suspensions or tin(II)chloride dihydrate suspensions, and some bunches were impregnated with suitable admixed solutions of both chemicals. An acceptable synergistic effect was then experienced by using an admixed bath containing 0.06 formal antimony trioxide and 0.06 formal tin(II)chloride dihydrate suspensions for impartation of flame-retardancy to a cotton fabric. By using a vertical flame spread test the optimum mass of the mixture needed to impart flame-retardancy was obtained to be about 10.38 g anhydrous additives per 100 g fabric. Thermogravimetry (TG/DTG) outcomes of untreated and the supported cotton fabrics at the optimum addition were put in practice and their curves were compared and commented. The results comply with flame-retardancy theories.     

Thermochemical treatment of E-waste from small household appliances using highly pre-heated nitrogen-thermogravimetric investigation and pyrolysis kinetics

The EU directive on waste of electrical and electronic equipment (WEEE) 2002/96/EC has set a goal of recovering 70–80% in terms of materials and energy. Nowadays, thermal cracking (pyrolysis) of such waste streams is receiving renewed attention, due to the energy and material recovery that can be achieved and therefore the sustainable waste management. However, it still lacks the kinetic background which is of great importance for a successful design of thermochemical processes. In this study the kinetic parameters of WEEE (originating from small household appliances) pyrolysis using highly pre-heated nitrogen under six different heating rates (1–2.5 K/s) have been estimated using a combination of model-free and model fitted methods. Even though WEEE is heterogeneous material, similar behavior at each of the six different heating rates applied was observed. The activation energy of the pyrolysis process determined with two different model-free methods gave comparable results. Pre-exponential factor and reaction order were determined using the Coats-Redfern method. The estimated kinetic parameters for the WEEE pyrolysis are: E = 95.54 kJ/mol, A = 1.06 × 10⁸ and n = 3.38.     

热重法高炉喷吹煤粉燃烧性的研究

采用热重法对高炉喷吹煤粉的燃烧性进行了研究,通过对单煤、混煤燃烧时的热力学分析,发现混煤的燃烧率大于组成该混煤的纯煤燃烧率的加权平均值。结果表明,混煤喷吹有利于提高煤粉的燃烧率,扩大高炉喷吹量和降低喷煤成本。