Showing papers in "Journal of Thermal Analysis and Calorimetry in 2009"

Kinetics of thermal degradation of polymers

Abstract: The thermal degradation of polymers has been studied quite extensively using thermogravimetric measurements. For the kinetic description, most of the times single rate heating data and model-fitting methods have been used. Since the thermal degradation of the polymers is a very complex reaction, the choice of a reliable model or a combination of kinetic models is very important. The advantages or the disadvantages of using a single heating rate or multiple heating rates data for the determination of the kinetic triplet have been investigated. Also, the activation energy has been calculated with the isoconversional and model-fitting methods. The reaction model was determined with the model-fitting method. The limits of all these procedures were investigated with experimental data of the thermal degradation of the poly(ethylene adipate) (PEAd).

Characterization of sugarcane and coconut fibers by thermal analysis and FTIR

Abstract: Pyrolysis of sugarcane bagasse and coconut fiber was studied by thermal analysis in order to characterize their thermal behavior and to identify their constituents by the aid of their thermogravimetric curves and to determine their heat capacity by means of DSC. The Fourier Transform Infrared Spectrum (FTIR) was used to determine the main constituents present in both residues. The thermal degradation of sugarcane bagasse and coconut fiber presents two mass loss steps attributed to the release of humidity and to the decomposition of organic material (hemicellulose, cellulose and lignin). It was expected that the results of DSC analysis were almost the same for both types of biomasses.

Thermal degradation of poly(lactic acid) measured by thermogravimetry coupled to Fourier transform infrared spectroscopy

Abstract: Thermal decomposition of poly(lactic acid) (PLA) has been studied using thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA-FTIR). FTIR analysis of the evolved decomposition products shows the release of lactide molecule, acetaldehyde, carbon monoxide and carbon dioxide. Acetaldehyde and carbon dioxide exist until the end of the experiments, whereas carbon monoxide gradually decreases above the peak temperature in that the higher temperature benefits from chain homolysis and the production of carbon dioxide. A kinetic study of thermal degradation of PLA in nitrogen has been studied by means of thermogravimetry. It is found that the thermal degradation kinetics of PLA can be interpreted in terms of multi-step degradation mechanisms. The activation energies obtained by Ozawa–Flynn–Wall method and Friedman’s method are in good agreement with that obtained by Kissinger’s method. The activation energies of PLA calculated by the three methods are 177.5 kJ mol−1, 183.6 kJ mol−1 and 181.1 kJ mol−1, respectively.

Dissociation enthalpies and phase equilibrium for TBAB semi-clathrate hydrates of N2, CO2, N2 + CO2 and CH4 + CO2

Abstract: Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N2 and CO2 and gases mixtures such as N2 + CO2 and CH4 + CO2 were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N2 for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26.

Effects of MWNTs on phase change enthalpy and thermal conductivity of a solid-liquid organic PCM

Abstract: The effects of multi-walled carbon nanotubes (MWNTs) on the phase change enthalpy (ΔH) and the thermal conductivity (κ) of a solid-liquid phase change materials (PCM), palmitic acid (PA), have been investigated. The results showed that both the ΔH and the κ of the composite were lower than that of PA when the loading of MWNTs was small. As the concentration of MWNTs in the composites increased, the ΔH of the composites was slightly improved and then decreased linearly. However, the κ of the composites was monotonously increased from the minimum value. When the loading of MWNTs increased to 5% and no surfactant was added, the κ of the composite was enhanced to be 26% higher than that of PA. The κ of the composite could be enhanced by CTAB instead of SDBS when the loading of MWNTs was small, as SDBS showed no obvious effect on the κ of the composites. Furthermore, the effects of surface modification of MWNTs on the ΔH and the κ of the composites have also been investigated.

Thermal properties of poly(lactic acid)/organo-montmorillonite nanocomposites

Abstract: Poly(lactic acid)/organo-montmorillonite nanocomposites were prepared by melt intercalation technique. Maleic anhydride-grafted ethylene propylene rubber (EPMgMA) was added into the PLA/OMMT in order to improve the compatibility and toughness of the nanocomposites. The samples were prepared by single screw extrusion followed by compression molding. The effect of OMMT and EPMgMA on the thermal properties of PLA was studied. The thermal properties of the PLA/OMMT nanocomposites have been investigated by using differential scanning calorimeter (DSC) and thermo-gravimetry analyzer (TG). The melting temperature (Tm), glass transition temperature (Tg), crystallization temperature (Tc), degree of crystallinity (χc), and thermal stability of the PLA/OMMT nanocomposites have been studied. It was found that the thermal properties of PLA were greatly influenced by the addition of OMMT and EPMgMA.

THERMAL PROPERTIES OF POLYLACTIDES Effect of molecular mass and nature of lactide isomer

Abstract: A thermal analysis of a series of polylactides (PLA) was carried out based on the number of average molecular mass (Mn), and the nature of isomer (D, L and DL). It is confirmed that the glass transition temperature (Tg) of PLA increased as a function of molecular mass irrespective of isomer type except sample with a high polydispersity index. The melting temperature (Tm) and enthalpy of crystal fusion (ΔHf) of L-isomer increased as the Mn was increased from 1100 to 27500. The degree of crystallinity (χc%) increased as a function of molecular mass. However no crystallization peak was detected in the lower molecular mass range (550–1400). The non-isothermal crystallization behavior of the PLA melt was significantly influenced by the cooling rate. Both D and L isomers exhibited insignificant difference in thermal properties and DL lactides exhibited amorphous behavior at identical molecular masses. Change in microstructure showed significant difference between two isomers. Analysis of the FTIR spectra of these PLA samples in the range of 1200–1230 cm−1 supported DSC observation on crystallinity.

Thermo-kinetics study of orange peel in air

Abstract: Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis. According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas products were mainly CO2, CO, and CH4. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H2O was also detected. The Eα on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds. These results could explain the non-autocatalytic character of the reactions during the decomposition process.

Design of liposomes containing photopolymerizable phospholipids for triggered release of contents.

Abstract: We describe a novel class of light-triggerable liposomes prepared from a photo-polymerizable phospholipid DC(8,9)PC (1,2- bis (tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) and DPPC (1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine). Exposure to UV (254 nm) radiation for 0-45 minutes at 25 degrees C resulted in photo-polymerization of DC(8,9)PC in these liposomes and the release of an encapsulated fluorescent dye (calcein). Kinetics and extents of calcein release correlated with mol% of DC(8,9)PC in the liposomes. Photopolymerization and calcein release occurred only from DPPC/DC(8,9)PC but not from Egg PC/DC(8,9)PC liposomes. Our data indicate that phase separation and packing of polymerizable lipids in the liposome bilayer are major determinants of photo-activation and triggered contents release.

Fire retardancy mechanisms of arylphosphates in polycarbonate (PC) and PC/acrylonitrile-butadiene-styrene

Abstract: The pyrolysis of polycarbonate (PC) and PC/acrylonitrile-butadiene-styrene (PC/ABS) with and without arylphosphates (triphenylphosphate TPP, resorcinol-bis(diphenyl phosphate) RDP and bisphenol A bis(diphenyl phosphate) BDP) is investigated by thermal analysis as key to understanding the flame retardancy mechanisms and corresponding structure–property relationships. The correspondence between the decomposition temperature range of arylphosphates and PC is pointed out as prerequisite for the occurrence of the reaction between arylphosphate and structures that are typical for the beginning of PC decomposition. Resulting cross-linking enhances charring in the condensed phase and competes with the alternative release of phosphate in the gas phase and thus flame inhibition. Flame inhibition was identified as the main flame retardancy mechanism. The additional condensed phase mechanisms optimise the performance.

Thermal degradation and flame retardancy of epoxy resins containing intumescent flame retardant

Abstract: Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants (IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0. The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry (DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and R max, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol−1 while it becomes 193.8 kJ mol−1 for EP containing IFR, decreased by 36.6 ...

Determination of the glass transition temperature: methods correlation and structural heterogeneity

Abstract: The definition of the glass transition temperature, Tg, is recalled and its experimental determination by various techniques is reviewed. The diversity of values of Tg obtained by the different methods is discussed, with particular attention being paid to Differential Scanning Calorimetry (DSC) and to dynamic techniques such as Dynamic Mechanical Thermal Analysis (DMTA) and Temperature Modulated DSC (TMDSC). This last technique, TMDSC, in particular, is considered in respect of ways in which the heterogeneity of the glass transformation process can be quantified.

Thermal analysis, effect of dopants, spectral characterisation and growth aspects of kap crystals

Abstract: Potassium acid phthalate (KAP) which is also known as potassium hydrogen phthalate (KC8H5O4), a semi-organic compound was grown from its aqueous solution only by slow evaporation method at room temperature. The effect of metallic salts HgCl2 and PbCl2 as dopants in the growth aspects, thermal properties and SHG efficiency of KAP were determined using UV-VIS, FTIR spectral studies, thermal (TG and DTA) analysis and NLO test. There is only one significant mass loss step on TG curve of pure and doped KAP crystal. DTA curve exhibit a higher peak temperature in case of doped KAP crystal compared to those of pure KAP crystals.

Kinetic analysis of wheat straw pyrolysis using isoconversional methods

Abstract: The pyrolysis of wheat straw has been carried out by means of thermogravimetric analysis in inert atmosphere. The samples were heated over a range of temperatures that includes the entire range of pyrolysis with three different heating rates of 5, 10 and 20 K min−1. The activation energy values as a function of the extent of conversion for the pyrolysis process of wheat straw have been calculated by means of the Flynn–Wall–Ozawa isoconversional method, the Vyazovkin–Sbirrazzuoli isoconversional method and an iterative isoconversional method presented in this article. The results have showed that there are small differences between the activation energy values obtained from the three methods, and the pyrolysis process reveals a dependence of the activation energy on conversion and have indicated the validity of the iterative integral isoconversional method. The effective activation energy for the pyrolysis of wheat straw is 130–175 kJ mol−1 in the conversion range of 0.15–0.85. Furthermore, the prediction of the pyrolysis process under isothermal conditions from the dependence of the activation energy on the extent of conversion has been presented.

Microstructure development in mixes of calcium aluminate cement with silica fume or fly ash

Abstract: The most widely identified degradation process suffered by calcium aluminate cement (CAC) is the so-called conversion of hexagonal calcium aluminate hydrate to cubic form. This conversion is usually followed by an increase in porosity determined by the different densities of these hydrates and the subsequent loss of strength. Mixes of calcium aluminate cement (CAC) and silica fume (SF) or fly ash (FA) represent an interesting alternative for the stabilization of CAC hydrates, which might be attributed to a microstructure based mainly on aluminosilicates. This paper deals with the microstructure of cement pastes fabricated with mixtures CAC-SF and CAC-FA and its evolution over time. Thermal analysis (DTA/TG), X-ray diffraction (XRD) and mid-infrared spectroscopy (FTIR) have been used to assess the microstructure of these formulations.

Thermogravimetric analysis of combustion characteristics and kinetic parameters of pulverized coals in oxy-fuel atmosphere

Abstract: Temperature programmed combustions (TPC) of Yang-Quan anthracite, Liao-Cheng lean coal and Li-Yan bituminous coal in oxy-fuel atmosphere were conducted in a thermogravimetric analyzer and characteristic parameters were deduced from the TG-DTG curves. The results showed that combustion got harder to progress as the coalification degree increasing. Within range of 40%, effect of heightening O2 concentration favored the combustion process, but beyond this zone, the effect leveled off. The model-fitting mathematical approach was used to evaluated the kinetic triplet (f (α), E, A) through Coats–Redfern method. The calculation showed that D 3-Jander was the proper reaction model and the evaluations of E and A validated the experimental results.

Thermal decomposition of hydrotalcites with variable cationic ratios

Abstract: Thermal analysis complimented with evolved gas mass spectrometry has been applied to hydrotalcites containing carbonate prepared by coprecipitation and with varying divalent/trivalent cation ratios. The resulting materials were characterised by XRD, and TG/DTG to determine the stability of the hydrotalcites synthesised. Hydrotalcites of formula Mg4(Fe,Al)2(OH)12(CO3)·4H2O, Mg6(Fe,Al)2(OH)16(CO3)·5H2O, and Mg8(Fe,Al)2(OH)20(CO3)·8H2O were formed by intercalation with the carbonate anion as a function of the divalent/trivalent cationic ratio. XRD showed slight variations in the d-spacing between the hydrotalcites. The thermal decomposition of carbonate hydrotalcites consists of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal oxides and spinels, including MgO, MgAl2O4, and MgFeAlO4.

Kinetic and thermodynamic studies of MgHPO4 · 3H2O by non-isothermal decomposition data

Abstract: The thermal decomposition of magnesium hydrogen phosphate trihydrate MgHPO4 · 3H2O was investigated in air atmosphere using TG-DTG-DTA. MgHPO4 · 3H2O decomposes in a single step and its final decomposition product (Mg2P2O7) was obtained. The activation energies of the decomposition step of MgHPO4 · 3H2O were calculated through the isoconversional methods of the Ozawa, Kissinger–Akahira–Sunose (KAS) and Iterative equation, and the possible conversion function has been estimated through the Coats and Redfern integral equation. The activation energies calculated for the decomposition reaction by different techniques and methods were found to be consistent. The better kinetic model of the decomposition reaction for MgHPO4 · 3H2O is the F 1/3 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the decomposition reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous without connecting with the introduction of heat.

[1]Benzofuro[3,2- c ]pyridine synthesis and coordination reactions

Abstract: (E)-3-(1-Benzofuran-2-yl)propenoic acid (1) was prepared from 1-benzofuran-2-carbaldehyde under the Doebner’s conditions. The obtained acid was converted to the corresponding azide 2, which was cyclized by heating in diphenyl ether to [1]benzofuro[3,2-c]pyridine-1(2H)-one (3). This compound was aromatized with phosphorus oxychloride to chloroderivative 4 which was reduced with zinc and acetic acid to the title compound 5. [1]Benzofuro[3,2-c]pyridine-2-oxide (6) was synthesized by reaction of 5 with 3-chloroperoxybenzoic acid in dichloromethane. Treatment of 6 with benzoyl chloride and potassium cyanide (Reissert-Henze reaction) was shown to produce the corresponding [1]benzofuro[3,2-c]pyridine-1-carbonitrile (7). The title compound was used for preparation of complexes Cu2(ac)4(bfp)2 (8) and CoCl2(bfp)2 (9), where ac=CH3CO 2 − and bfp=[1]benzofuro[3,2-c]pyridine. Both oxygen atom of carboxylate ions is used in the coordination to Cu(II). Thermal properties of the complexes 8 and 9 have been studied by TG and DTA and both complexes exhibited high thermal stability while complex 9 are thermally more stable than complex 8.

Lubricant properties of Moringa oil using thermal and tribological techniques

Abstract: The increasing application of biobased lubricants could significantly reduce environmental pollution and contribute to the replacement of petroleum base oils. Vegetable oils are recognized as rapidly biodegradable and are thus promising candidates for use as base fluids in formulation of environment friendly lubricants. Although many vegetable oils have excellent lubricity, they often have poor oxidation and low temperature stability. Here in, we report the lubricant potential of Moringa oil, which has 74% oleic acid content and thus possess improved oxidation stability over many other natural oils. For comparison, Jatropha oil, cottonseed oil, canola oil and sunflower oil were also studied. Among these oils, Moringa oil exhibits the highest thermo-oxidative stability measured using PDSC and TG. Canola oil demonstrated superior low temperature stability as measured using cryogenic DSC, pour point and cloud point measurements. The friction and wear properties were measured using HFRR. Overall, it was concluded that Moringa oil has potential in formulation of industrial fluids for high temperature applications.

Dissolution kinetic and structural behaviour of natural hydroxyapatite vs. thermal treatment

Abstract: The dissolution kinetic and structural behaviour of natural hydroxyapatite (N-HA) and synthetic hydroxyapatite (S-HA) was studied vs. sintering temperature and using ‘in vitro’ experiments. Obtained results highlight the chemical stability of N-HA. Any structural modification was observed until 1200°C. In the fact S-HA undergoes some modifications. XRD diagrams show the tricalcium phosphate (TCP) phase formation between 800 and 1100°C and tetracalcium phosphate (TetCP) phase formation at 1200°C. The ‘in vitro’ assay shows that the dissolution was occurred more in N-HA than in S-HA. The formed TCP activated the dissolution kinetic and then the precipitation phenomena when a continuous dissolution of TetCP leaded to slow down the kinetic precipitation.

Thermogravimetric analysis of selected group (II) carbonateminerals — Implication for the geosequestration of greenhouse gases

Abstract: The precursors of carbonate minerals have the potential to react with greenhouse gases to form many common carbonate minerals. The carbonate bearing minerals, magnesite, calcite, strontianite and witherite, were synthesised and analysed using a combination of thermogravimetry and evolved gas mass spectrometry. The DTG curves show that as both the mass and the size of the metal cationic radii increase, the inherent thermal stability of the carbonate also increases dramatically. It is proposed that this inherent effect is a size stabilisation relationship between that of the carbonate and the metal cation. As the cationic radius increases in size, the radius approaches and in the case of Sr2+ and Ba2+ exceeds that of the overall size of the carbonate anion. The thermal stability of these minerals has implications for the geosequestration of greenhouse gases. The carbonates with the larger cations show significantly greater stability.

Thermal degradation of CTAB in as-synthesized MCM-41

Abstract: Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal surfactant degradation outside and inside pores were identified at various temperatures using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and 13C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41 synthesis on molecular level.

TG-FTIR coupling to monitor the pyrolysis products from agricultural residues

Abstract: Thermogravimetry has been widely used for the characterization of several biomasses but the most useful information given by this technique has been normally concerned to the relative amounts of humidity, hemi-cellulose, cellulose and lignin present in the biomass. TG-FTIR has been used to yield qualitative data about the pyrolysis products, in an exploratory way, by some authors. In the present paper, this technique was employed to reach comparative data about the products of pyrolysis of biomasses that are potentially available at economic bases for the production of biofuels. Agricultural residues such as coconut shell, sugarcane bagasse, corn stalks and peanut shell were chosen to be investigated. For all samples, the thermogravimetric curves showed a mass loss between 35 and 400 °C changed up to 73%, while that the loss between 400 and 800 °C changed up to 26%. TG-FTIR indicated tendencies in the rate of the formation of important species during the pyrolysis process of the four biomasses studied. The interpretation of the spectra allowed the proposition of characteristic absorbance ratios and the comparison of these values allowed inferences about the relative abundances of components formed in the pyrolysis of the biomasses. As an example of the possible inferences reached, among the species formed in the pyrolysis condensate, called bio-oil, the formation of carboxylic acids has to be specially considered due to their corrosivity. Thus, the data produced indicated that a bio-oil derived from peanut shell should be a little less acidic while the one derived from sugarcane bagasse should be showed more acidic among the biomasses studied.

Synthesis and thermal properties of nanoparticles of bioactive glasses containing silver

Abstract: Calcium phosphate bioactive glasses (BG) and some ceramics are candidates for implantation due to their excellent bonding to bone. Silver is a bactericidal element and can be easily introduced in glasses and ceramics. In this work, nanometer-sized bioactive glass particles doped with silver were produced and characterized by Thermal Gravimetric analysis (TG), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). Water hygroscopy was reduced with increasing silver content. The increase in the amount of silver caused an increase in quartz and metallic silver crystallization while reducing the BG transformation into hydroxyapatite. It was observed the silver reduction leading to metallic silver formation for bioactive glasses containing high amount of silver.

Influence of pH on nanosized Mn–Zn ferrite synthesized by sol–gel auto combustion process

Abstract: Sol-gel auto combustion process was employed to synthesize nanosized Mn-Zn ferrite at different pH values (\1, 5, 6, 7, 8 and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective com- bustion was observed at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH \ 1 showed localized burning. Thermogravimetric (TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air) of powders P1 and P6 synthesized at pH \ 1 and pH 6 were also determined. B-H loop results showed that calcined powder C6 was more ferromagnetic than C1 due to fully developed spinel phase and larger par- ticle size.

Characterization of microbial activity in soil by use of isothermal microcalorimetry

Abstract: Isothermal microcalorimetry is now established as a useful technique for the characterization of the microbial activity in soil. A brief summary of publications from this field and of instruments used in such work is presented. Several experimental parameters that can form important sources for systematic errors are discussed and it is suggested that further method work is made in this area. In most isothermal microcalorimetric investigations on the microbial activity in soil, the samples are amended with glucose. It is proposed that cellulose also will be used.

Processing and characterization of aluminum-based nanothermites

Abstract: During the past several years, a significant effort has been on investigation of reaction front propagation and the rate of energy release in heterogeneous systems consisting of nanopowder reactants. Substantial size reduction of each reactant powder (e.g. from micro- to nano-size) leads to increase of reaction front propagation in some systems under unconfined conditions by approximately two to three order of magnitude. This paper presents key challenges associated with processing and use of nanothermite materials and characterization of nanoreactants. Reaction constants, such as activation energies and frequency factors were determined using DSC technique for several nanothermite systems based on nanosize aluminum and iron oxide, bismuth trioxide, and molybdenum trioxide. Experimental data of ignition delay times for different nanothermite systems using laser energy source were compared well to those predicted by proposed mathematical model.

Thermal decomposition kinetics of some aromatic azomonoethers Part IV. Non-isothermal kinetics of 2-allyl-4-((4-(4-methylbenzyloxy)phenyl) diazenyl)phenol in air flow

Abstract: Thermal analysis of 2-allyl-4-((4-(4-methylbenzyloxy)phenyl)diazenyl)phenol dye was performed in air flow. The compound thermal behavior was investigated using TG, DTG and DSC techniques, under non-isothermal linear regime. Kinetic parameters of the two decomposition steps were obtained by means of multi-heating rates methods. Isoconversioanl methods (KAS and FWO), Invariant Kinetic Parameters method and Perez-Maqueda et al. criterion (by means of CR and FW equations) were used.

Kinetic analyses of biomass tar pyrolysis using the distributed activation energy model by TG/DTA technique

Abstract: Biomass tar pyrolysis behavior was investigated in absence and presence of catalyst-dolomite (10% mass) with different heating rates of 10, 20, 30 K min−1 under nitrogen atmosphere. Different kinetic methods such as distributed activation energy model (DAEM), Coats–Redfern method were used to analyze the TG/DTA data to identify reaction parameters. For Coats–Redfern method, first reaction order (n = 1) and two stages (volatilization and pyrolysis) reaction model was selected to calculate the kinetics parameters; for DAEM model, three different heating rates (10, 20, 30 K min−1) were selected to obtain the activation energy distribution (Ea). The peak values of Ea curves for biomass tar volatilization process are nearly 250 and 200 kJ mol−1 in absence and presence of dolomite, whereas, the value of Ea for pyrolysis stage gradually increase and varied from 70 to 200 and 40 to 100 kJ mol−1 with the mass loss, respectively, in absence and presence of dolomite. The application of the new DAEM model can show the variation trend of activation energy for the whole pyrolysis process.