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Arrhenius plot for the exothermic peaks of the DSC curves for Al 2 O 3 - PTFE.
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The dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give...
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... thermodynamic calculations (THERMO software, ISMAN) of reaction (1) give an adiabatic temperature of T ad =1420K. For this calculation, the enthalpy of 817.5 kJ/mol for Teflon in solid state was used [7]. To study the heating rate impact on the reaction of Al 2 O 3 - PTFE, the thermo-calorimetric analysis was guided by 3 different heating rates: 20, 80 and 150 °C/min, in argon flow of 100 ml/min. DTA/TG curves of Al 2 O 3 -PTFE mixture at 20 °C/min heating rate are plotted in Figure 1, (left). The DTA result presents a clear endothermic peak at 320 °C, which represents the melting of PTFE with 27.7 J/g of latent heat. At 500 °C starts decomposition of PTFE with endothermic energy utilization of 289 J/g with 59.4 % of a weight loss. According to reaction stoichiometry, 59.5% of the mixture is the PTFE, so this indicates the complete decomposition and removal of PTFE. There is no reaction between Al 2 O 3 and PTFE at the heating rate of 20 °C/min. For the heating rate of 80°C/min, the DTA/TG curves are shown in Figure 1, (center). At 320°C appeared PTFE melting. For the TG curve 53% of a weight loss demonstrates that more than 6% of PTFE remains in system and reacts with Al 2 O 3 . DTA curve also shows a trend of a broad exothermic peak corresponding to PTFE decomposition. Finally, at heating rate of 150 °C/min (Figure 1, right) the TG curve shows a well- developed exothermic peak with maximum of 658 °C. Under such high heating rate PTFE melting is unnoticeable. The weight loss at the system is ~44 % so more than 15 % of the PTFE remains in the mixture and reacts with Al 2 O 3 . The broad exothermic peak is almost covering the endotherm of PTFE decomposition (a little curve at the top of the peak). Therefore it is evident that heating rate affects the reaction mechanism of Al 2 O 3 - PTFE. More precisely, at the fast heating rates PTFE remains in the system and reacts with Al O . 1. The DTA-DTG curves for Al 2 O 3 - PTFE at heating rate of (left) 20 C/min; (center) 80 o C/min; and (right) 150 C/min in argon. We estimated the activation energy from the DSC data by using the isoconversional method suggested by Starink [8,9], which was shown in (Ref. [10]) to provide a more accurate value than the Kissinger and Ozawa methods. The Starink method determines the activation energy from the equation: (2) where E a is the apparent activation energy (in kJ/mol), β the heating rate in thermal analysis (in K/min), T is the peak temperature of the exothermic curve (in K), and R the universal gas 1.8 constant. E a is estimated from the slope of the graph of ln(T / β ) vs. 1/T shown in Figure 2. The activation energy for Al O – PTFE was estimated to be 265 kJ/mol. Al 2 O 3 -PTFE system: In the thermogram (Figure 3, left) received for Al 2 O 3 -PTFE system at a heating rate of 780 °C/min, there is an endotherm in temperature ~360 °C which is corresponding to the melting of PTFE. According to the HSTS data, the PTFE decomposition takes place at about 640 °C close to the Al melting point (Figure 3, right). In the system Al 2 O 3 PTFE the decomposition of PTFE and the reaction between Al O and PTFE occur almost in the same temperature range, which is around 800 °C (Figure 4). As can be seen from Figure 3, (left), the interaction between Al 2 O 3 and PTFE is exothermic enough and the temperature rise on the thermogram was about 80 °C at heating rate of 780 °C/min. Table 1 summarizes the characteristic temperatures and heating rates for the samples of Al-PTFE, Al 2 O 3 -PTFE, and ...
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... The aim of this work is twofold: (i) to develop Ni-based catalyst on a mesoporous network of highly aligned alumina nanofibers (MAN) by wet-combustion method; and (ii) to study the effect of fuel on the combustion mechanism and as-synthesized product by High-Speed Temperature Scanning (HSTS) technique. The HSTS allows fast heating the samples (up to 10 4 ᵒ/min) up to real solid-state combustion conditions, which is reported to be around 10 2 ᵒ/min, and studying mechanism of the process [14][15][16]. However, there is no attempt to study the mechanism of liquid based processes; particularly, solution combustion method. ...
Mesoporous networks with a special distribution of functional centers are an important class of high performance materials for catalysts, bioscaffolds, energy conversion and storage systems. Methods of fabrication allowing to control over special distribution of the functional sites of required phases and designed morphology are still of a great challenge. Here, we report a wetcombustion method for functionalization of the
mesoporous network of alumina nanofibers with a single fiber diameter of 7 ± 2 nm by Ni-based nanoparticles. The second-scale duration of the combustion process developing high flame temperature (>1000 °C) allows fabrication of mesoporous functional networks with tailored size, morphology and homogeneity of the dopants in a single-stage. The mechanism of the combustion process are studied by in situ high-speed temperature scanner, which continuously records the temperature history and applied power
during the process. It readily allows quenching of the samples at a specified point, demonstrates the critical effect of a fuel on the decomposition temperature, combustion enthalpy, functional group, and pH. As a result of the wet-combustion synthesis, aligned double core-shell NiONiAl2O4-Al2O3 fibers or NiO nanoparticles deposited onto alumina nanofibers can be formed.
... In this paper are thoroughly outlined the results of investigation of the mechanism and kinetics of tungsten and copper oxides joint reduction by Mg ? C mixture at programmed and high heating rates by thermal analysis method, utilizing the so-called high-speed temperature scanner (HSTS) developed by our research group [23][24][25]. At the last stage of the work, experiments performed at various heating rates (V h = 100-5200°C min -1 ) allow to calculate the kinetic parameters (effective values of activation energy) for magnesiothermic reduction stage for the binary, ternary and quaternary systems. ...
The mechanism and kinetics of tungsten and copper oxides joint reduction by Mg + C combined reducer was studied at high heating rates by thermal analysis method utilizing high-speed temperature scanner. The effective values of activation energy for magnesiothermic reduction stage for the binary (WO3–Mg, CuO–Mg), ternary (WO3–Mg–C, CuO–Mg–C, WO3–CuO–Mg) and quaternary (WO3–CuO–Mg–C) systems were determined in a new and wide range of heating rates (Vh = 100–5200 °C min⁻¹). It was shown that for all the systems under study the increasing of heating rate shifts T* values toward to high-temperature area and unlike the low heating rates (Vh = 5–20 °C min⁻¹, DTA/DTG studies) at high heating rates Mg always participates in molten state. In addition, by varying heating rates of reagents it was possible to separate the main stages and analyze intermediate compounds, making useful tool for the exploration of interaction mechanism in the complex systems. On the other hand, the tendency of merging of metals reduction stages at higher heating rates has an essential practical interest. That is, simultaneous reduction in metals is very prominent for obtaining metal composites with more homogeneous microstructure.
... There are a few techniques which allow monitoring the kinetics of chemical reactions under such conditions, including the so called electrothermographic [6,7] and electro thermal explosion analyses [8,9]. In this work, a new thermographic method based on the use of high speed temperature scanner (HSTS) [10][11][12][13] was used to investigate the kinetics of chemical reactions in the 1 The article is published in the original. Ni-Al system. ...
... Assuming that y 1, the following approximation to (7) can be obtained: (8) The assumption y 1 seems reasonable because for the majority of solid state reactions 15 < y < 60. By taking the logarithm of Eq. (6) and using (8) one may obtain: (9) And at constant extent of conversion η, we have: (10) which is exactly the formula (1) described above. According to this equation, the ln( /V) -1/T f plot should represent a straight line with a slope equal to E/R. ...
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A new electrothermographic method, viz. high-speed temperature scanning, was applied to kinetic studies of reactions taking place in the Ni-Al system, including those after mechanical activation in a planetary ball mill. Treatment of the temperature profiles taken at different heating rates in terms of the Kissinger-Akahira-Sunose (KAS) approximation gave activation energy E for non-activated mixtures: E = 155 kJ/mol (for temperature range 650–850°C). But for mechanically activated mixtures, the characteristic points (reaction onset temperature, temperature of maximum reaction rate) were found to decrease with increasing heating rate, which makes the KAS method inapplicable to these compositions. It has been concluded that mechanical treatment leads to significant changes in the reaction kinetics, possibly due to splitting the reaction route into two stages the first of which has very low activation energy.
... These formulations are well-known energetic materials and are the subject of extensive investigation (Dlott 2006;Kubota and Serizawa 1987;Martirosyan 2011;McGregor and Shuterland 2004). Moreover, fluorocarbons in thermite compositions may increase the reaction rate of metalfluorocarbons (Hobosyan et al. 2013), even if the concentration of fluorocarbons is less than 2% by weight, by reducing oxide thickness on the metal surface. ...
It is widely recognized that future exploration missions to the Moon will include construction of permanent lunar bases to support long-term lunar missions. The lunar in situ resource utilization concept to produce superior construction materials is a vital part of exploration missions. This paper presents a novel approach for consolidation of lunar regolith with activated thermite reactions using aluminum or magnesium-polytetrafluoroethylene (PTFE) systems to produce superior ceramic materials for potential construction purposes on the Moon. Thermodynamic analysis of reactive systems was used to predict the adiabatic temperature and equilibrium product concentrations. It was demonstrated that PTFE up to 2% by weight is sufficient to achieve regolith consolidation and reduce aluminum (magnesium) content to 15% by weight with utilization of more than 80% by weight regolith. Testing of fabricated materials shows that consolidated ceramics can have up to 60% porosity, which significantly improves thermal insulation up to 0.1∈∈W/mK. The hardness value of the material - approximately 850 in the Knoop scale - confirms that consolidated regolith can accomplish the construction requirements on the Moon.
