Showing papers in "Journal of Thermal Analysis and Calorimetry in 2013"

Thermal conductivity and specific heat capacity measurements of CuO nanofluids

Abstract: A study of thermal properties of CuO dispersed in water and ethylene glycol as a function of the particle volume fraction and at temperatures between 298 and 338 K has been performed. Thermal conductivities have been studied by the steady-state coaxial cylinders method, using a C80D microcalorimeter (Setaram, France) equipped with special calorimetric vessels. Heat capacities have been measured with a Micro DSC II microcalorimeter (Setaram, France) with batch cells designed in our laboratory and the “scanning or continuous method.” Results for thermal conductivities can be well justified using a classical model (Hamilton–Crosser), and experimental measurements of heat capacities can be justified with a model of particles in thermal equilibrium with the base fluid.

Application of PCM thermal energy storage system to reduce building energy consumption

Abstract: The building sector is known to make a large contribution to total energy consumption and CO2 emissions. Phase change materials (PCMs) have been considered for thermal energy storage (TES) in buildings. They can balance out the discrepancies between energy demand and energy supply, which are temporally out of phase. However, traditional PCMs need special latent storage devices or containers to encapsulate the PCM, in order to store and release the latent heat of the PCM. The proper design of TES systems using a PCM requires quantitative information and knowledge about the heat transfer and phase change processes in the PCM. In Korea, radiant floor heating systems, which have traditionally been used in residential buildings, consume approximately 55% of the total residential building energy consumption in heating. This article reviews the development of available latent heat thermal energy storage technologies and discusses PCM application methods for residential building using radiant floor heating systems with the goal of reducing energy consumption.

Ozawa’s kinetic method for analyzing thermoanalytical curves

Abstract: By reviewing the history of thermal analysis and its application to the kinetic analysis of the solid-state processes, we investigate the theoretical basis and historical perspective of Ozawa’s kinetic method for analyzing thermoanalytical curves. Ozawa’s nonisothermal kinetic method is demonstrated using thermoanalytical data for the thermal decomposition of sodium hydrogencarbonate and the crystallization of anhydrous magnesium acetate glass as examples. Through investigating recent theoretical advancements in nonisothermal kinetic analysis in view of the theoretical fundamentals of Ozawa’s kinetic method, it is indicated that they are in line with Ozawa’s kinetic theory. On the basis of the above investigations, we discuss the role of Ozawa’s kinetic theory in advancing the analysis of complex reaction kinetics.

Applicability of Fraser–Suzuki function in kinetic analysis of complex crystallization processes

Abstract: A modified peak-deconvolution procedure for complex crystallization processes was introduced. The method is based on the constrained curve-fitting technique using the Fraser–Suzuki (FS) function, where the FS asymmetry parameter a 3 correlates with the value of the Johnson–Mehl–Avrami (JMA) kinetic parameter m. The correlation was verified for an extensive number of theoretically simulated JMA curves; in addition, the dependencies of the a 3 parameter on other kinetic variables (E, A, q +) were quantified. The suggested deconvolution procedure was tested on two glassy systems with different overlay degree of the involved overlapping surface and bulk crystallization processes. In both cases, the kinetic analysis of deconvoluted data provided reasonable, consistent and accurate results. However, certain level of knowledge and experience was needed in order to correctly recognize and consequently account for all deviations from the theoretical behavior caused by thermal gradients or imperfections of the data acquisition process. As the input data for the fitting procedure can be in any form equivalent to the dα/dT temperature dependence, the method seems to be highly universal and may be applied to data obtained by various TA techniques.

Study on thermal properties of organic ester phase-change material embedded with silver nanoparticles

Abstract: This study investigates the thermal properties of new silver nano-based organic ester (SNOE) phase-change material (PCM) in terms of latent heat capacity, thermal conductivity and heat storage and release capabilities experimentally Spherical-shaped surface-functionalized crystalline silver nanoparticles (AgNP) prepared were embedded in mass proportions of 01 through 50 wt% into the pure (base) PCM Experimental results reveal that dispersion of AgNP into PCM was effective, only physical and no chemical interaction between AgNP and PCM has been exhibited; thereby phase-change temperature of SNOE PCMs were acceptable These are essential characteristics for SNOE PCMs which signified their thermal and chemical stability on long term Test results suggest that while compared to pure PCM, degree of supercooling was reduced by 117–68 % for aforesaid mass proportions of AgNP, whereas latent heat capacities decreased by 788 % in freezing and 891 % in melting The interdependencies between thermophysical properties in improving nucleation and growth rate of stable SNOE PCM crystals were signified and discussed Thermal conductivity of SNOE PCMs were enhanced from 0284 to 0765 W m−1 K−1 which was expected to be a 10–67 % increase for the above mass loading of AgNP Furthermore, for SNOE PCMs enhancement span in freezing and melting cycles was improved by 41 and 456 %, respectively Similarly, cooling and melting times were reduced by 308 and 113 %, respectively Embedded AgNP helps to achieve improved thermophysical and heat storage characteristics for SNOE PCMs, which in turn can be considered as a potential candidate for cool thermal energy storage applications

Kinetic approach to partially overlapped thermal decomposition processes

Abstract: Practical usefulness of the kinetic deconvolution for partially overlapped thermal decomposition processes of solids was examined by applying to the co-precipitated basic zinc carbonate and zinc carbonate. Comparing with the experimental deconvolutions by thermoanalytical techniques and mathematical deconvolutions using different statistical fitting functions, performance of the kinetic deconvolution based on an accumulative kinetic equation for the independent processes overlapped partially was evaluated in views of the peak deconvolution and kinetic evaluation. Two-independent kinetic processes of thermal decompositions of basic zinc carbonate and zinc carbonate were successfully deconvoluted by means of the thermoanalytical measurements in flowing CO2 and by applying sample controlled thermal analysis (SCTA). The deconvolutions by the mathematical curve fittings using different fitting functions and subsequent formal kinetic analysis provide acceptable values of the mass-loss fractions and apparent activation energies of the respective reaction processes, but the estimated kinetic model function changes depending on the fitting functions employed for the peak deconvolution. The mass-loss fractions and apparent kinetic parameters of the respective reaction processes can be optimized simultaneously by the kinetic deconvolution based on the kinetic equation through nonlinear least square analysis, where all the parameters indicated acceptable correspondences to those estimated through the experimental and mathematical deconvolutions. As long as the reaction processes overlapped are independent kinetically, the simple and rapid procedure of kinetic deconvolution is useful as a tool for characterizing the partially overlapped kinetic processes of the thermal decomposition of solids.

Thermal characteristics of the combustion process of biomass and sewage sludge

Abstract: The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min−1 in 40 mL min−1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.

Study of kinetic parameters of thermal decomposition of bagasse and sugarcane straw using Friedman and Ozawa–Flynn–Wall isoconversional methods

Abstract: Pyrolysis process of sugarcane bagasse and sugarcane straw was studied with the objective of determining the kinetic parameters activation energy (E), logarithm of pre-exponential factor (log A) in agreement with converted fraction (α). The determination of kinetic parameters was done through software thermokinetics by NETZSCH, which associated “Model Free” package enabled the determination of these parameters by Friedman and Ozawa–Flynn–Wall isoconversion models and a probable mechanism that describes the thermal decomposition process of these materials. The thermal degradation of sugarcane bagasse and sugarcane straw was carried out in the range of 303–1073 K under nitrogen flow and the heating rate used was 5, 10, 15, and 20 K min−1. The obtained results showed that the most appropriate kinetic model to describe the thermal decomposition of sugarcane bagasse was the autocatalytic reactions model in three parallel stages (F n C n C n model) and for sugarcane straw was also the autocatalytic reactions model for two parallels reactions (F n C n model).

Dehydration characteristics of struvite-K pertaining to magnesium potassium phosphate cement system in non-isothermal condition

Abstract: Struvite-K (KMgPO4·6H2O) is the main hydration product of magnesium potassium phosphate cement. Its thermal stability is critical to the properties of magnesium potassium phosphate cement. Therefore, in this study, the dehydration behavior of struvite-K was investigated at N2 atmosphere in non-isothermal condition. The process was conducted and controlled in a simultaneous TG/DTA analyzer, at heating rates of 2, 5, 10, 15, and 20 K min−1. The residual mass was always around 58.5% of the initial one, regardless of the heating rate, which corresponds to the dehydration reaction through one step, KMgPO4·6H2O → KMgPO4. The activation energy (Ea) corresponding to the dehydration of struvite-K was evaluated by non-isothermal kinetic analysis based on the application of isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods). The calculated results show that Flynn–Wall–Ozawa has slightly higher values of activation energy (Ea) and correlation coefficients (R2). Both methods have been proved to be suitable for analyzing dehydration behavior of struvite-K.

Thermogravimetric analysis of co-combustion of biomass and biochar

Abstract: The co-combustion of biomass and biochar was investigated by thermogravimetric analysis. Several thermal parameters and mean reactivity index (R M) for different blends were used to evaluate co-combustion features. As the biomass content increased from 30 to 90 mass%, volatile releasing temperature (T v), burnout temperature (T b), and the temperature at the maximal peak (T max) generally reduced, while average mass loss rates (R a) and R M increased, the maximum mass loss rate (R max) initially decreased and then increased. Results showed that biochar additions enhanced biomass fuel reactivity over weighted average in main combustion region. Besides, blends with 10–30 mass% of biochar behaved better than those with higher biochar ratio. Synergy exists between the two components and better combustibility is feasible by co-firing biochar with biomass.

Calcium carbonate decomposition

Abstract: Calcium carbonate decomposes under well-defined conditions giving CaO (solid) and CO2 (gas). The process kinetics are known to be strongly influenced by the CO2 partial pressure and temperature. In dynamic conditions, as in thermogravimetric analysis (TG) and differential thermal analysis (DTA), kinetics influence the observed heat effect and mass losses, as was shown in semi-static studies by Hyatt et al. (J Am Ceram Soc 41:70–74, 1). However, differing DTA and TG curve shapes are reported in the literature even under supposedly comparable conditions. The differences are attributed in part to the design of the equipment and in part to differing crystalline states of the precursor calcium carbonate. To resolve these uncertainties, the TG has been performed at different heating rates and at different but controlled partial pressures of CO2. The results are reported and critically evaluated in the light of the data obtained, and the kinetic parameters as reported by Hyatt et al. (J Am Ceram Soc 41:70–74, 1) are re-evaluated.

Practical remarks concerning phase diagrams determination on the basis of differential scanning calorimetry measurements

Abstract: Phase diagrams of binary systems at constant pressure are representations of oneand two-phase regions with their boundaries being functions of temperature and concentration. The most popular techniques used in determination of phase diagrams are thermal analysis (TA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The first of them, based on recording of cooling curves, has no significant meaning nowadays; however, it is still used, especially in didactics. Actually DTA and DSC are widely used in phase diagrams determination. DSC has an advantage over DTA, because in addition to temperature it gives precise value of enthalpy of thermal effect. Two types of DSCs must be distinguished: the heat flux DSC and the power compensation DSC. The characteristic feature of all DSC measuring systems is the twin-type design and the direct in-difference connection of the two measuring systems which are of the same kind. It is the decisive advantage of the differential principle that, in first approximation, disturbances such as temperature variations in the environment of the measuring system and the like, affect the two measuring systems in the same way and are compensated when the difference between the individual signals is formed [1]. The differential signal is the essential characteristic of each DSC. Another characteristic—which distinguishes it from most classic calorimeters—is the dynamic mode of operation. The DSC can be heated or cooled at a preset heating or cooling rate. A characteristic common to both types of DSC is that the measured signal is proportional to a heat flow rate (in opposition to classical calorimeters where heat flow is measured). This fact—directly measured heat flow rates—enables the DSC to solve problems arising in many fields of application [1]. In the heat flux DSC a defined exchange of the heat to be measured takes place via a thermal resistance. The measurement signal is the temperature difference; it describes the intensity of the exchange and is proportional to the heat flow rate. There are two main types of the heat flux DSC: the disc-type measuring system with solid sample support (disc) and the cylinder-type measuring system with integrated sample cavities. Heat flux DSCs with a disctype measuring system are available for temperatures between -190 and 1,500 C [1]. In the heat flux DSC with a cylindertype measuring system, the outer surfaces of each sample container are in contact with a great number of thermocouples connected in a series between the container and furnace cavity. The thermocouples bands or wires are the dominating heat conduction path from the furnace to samples. Both sample containers are thermally decoupled; heat exchange takes place only with parts of the massive furnace. These apparatuses are available for temperature range between -190 and 1,500 C [1]. The power compensation DSC belongs to the class of heat-compensating calorimeters. The heat to be measured is compensated with electric energy, by increasing or decreasing an adjustable Joule’s effect. The measuring temperature range extends from -175 to 725 C [1]. Differential scanning calorimetry is a relative technique. Because of its dynamic temperature characteristics, the measurements are not made in thermal equilibrium. The relative data must be converted to absolute values by a calibration procedure requiring the employment of standards whose property values and their associated uncertainties are known and established following a metrological procedure [2]. Practical remarks concerning phase diagrams determination on the basis of DSC measurements are illustrated by numerous examples of binary lanthanide halide–alkali halide systems.

Preparation and thermal properties of fatty acids/CNTs composite as shape-stabilized phase change materials

Abstract: A series of fatty acids/carbon nanotubes (CNTs) composite shape-stabilized PCMs were prepared through infiltration method by using the eutectic mixture of capric acid, lauric acid, and palmitic acid as phase change materials, multi-walled CNTs as a supporting material. Nitrogen adsorption–desorption curves and SEM images of composite shape-stabilized PCMs indicate that the eutectic mixture was effectively absorbed into the porous structure of the CNTs. DSC thermograms show that the composite fatty acids/CNTs possess good phase change behavior. And the latent heat of the sample absorbed with 80 wt% fatty acids can achieve 101.6 J g−1 in the melting process and its phase change temperatures and latent heat almost remain unchanged in 30 times of thermal cycling. Moreover, the thermal conductivity of the composite materials are significantly improved (up to 0.6661 W m−1 k−1) due to the addition of the highly thermal conductive CNTs.

Effect of addition of nano-magnetite on the hydration characteristics of hardened Portland cement and high slag cement pastes

Abstract: In this investigation the effect of addition of magnetite nanoparticles on the hydration characteristics of both ordinary Portland cement (OPC) and high slag cement (HSC) pastes was studied. The cement pastes were prepared using a water/solid (W/S) mass ratio of 0.3 with addition of 0.05, 0.1, and 0.3 % of magnetic fluid Fe3O4 nanoparticles by mass of cement. An aqueous stable magnetic fluid containing Fe3O4 nanoparticles, with a mean diameter in the range of super-paramagnetism, was prepared via co-precipitation method from ferrous and ferric solutions. The admixed magnetite-cement pastes were examined for compressive strength, chemically combined water content, X-ray diffraction analysis, and differential scanning calorimetry. The results of compressive strength revealed that the hardened pastes made from OPC and HSC admixed with different amounts of magnetic fluid have higher compressive strength values than those of the neat cement OPC and HSC cement pastes at almost all ages of hydration. The results of chemically combined water content for the admixed cement pastes showed almost the same general trend and nearly comparable values as those of the neat cement pastes. From the XRD diffractograms obtained for the neat OPC and HSC cement pastes, the main hydration products identified are calcium silicate hydrates, portlandite, and calcium sulfoaluminate hydrates. Addition of magnetic fluid nanoparticles to both of OPC and HSC did not affect the main hydration products of the neat OPC or HSC cement in addition to one main basic difference, namely, the formation of calcium iron hydroxide silicate as a new hydration product with a reasonable hydraulic character.

Thermogravimetric analysis of selected layered double hydroxides

Abstract: Thermogravimetric analysis (TG) and powder X-ray diffraction (PXRD) were used to study some selected Mg/Al and Zn/Al layered double hydroxides (LDHs) prepared by co-precipitation. A Mg/Al hydrotalcite was investigated before and after reformation in fluoride and nitrate solutions. Little change in the TG or PXRD patterns was observed. It was proposed that successful intercalation of nitrate anions has occurred. However, the absence of any change in the d(003) interlayer spacing suggests that fluoride anions were not intercalated between the LDH layers. Any fluoride anions that were removed from solution are most likely adsorbed onto the outer surfaces of the hydrotalcite. As fluoride removal was not quantified it is not possible to confirm that this has happened without further experimentation. Carbonate is probably intercalated into the interlayer of these hydrotalcites, as well as fluoride or nitrate. The carbonate most likely originates from either incomplete decarbonation during thermal activation or adsorption from the atmosphere or dissolved in the deionised water. Small and large scale co-precipitation syntheses of a Zn/Al LDH were also investigated to determine if there was any change in the product. While the small scale experiment produced a good quality LDH of reasonable purity; the large scale synthesis resulted in several additional phases. Imprecise measurement and difficulty in handling the large quantities of reagents appeared to be sufficient to alter the reaction conditions causing a mixture of phases to be formed.

Thermal properties and applications of low molecular weight polyhydroxybutyrate

Abstract: The properties of the low molecular weight polyhydroxybutyrate (LMWPHB) and LMWPHB plasticized polyhydroxybutyrate (PHB) are studied using differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), mechanical, and biodegradation tests. The results of DSC, WAXD, and POM indicate that LMWPHB has a lower glass transition temperature (T g), crystallinity, crystallization rate, melting temperature (T m), and crystal size than PHB due to its much smaller molecular weight. The tensile strength, T g, T m, crystallinity, crystallization rate, and thermal stability of LMWPHB plasticized PHB decrease, while the flexibility and biodegradation rate increase with the increasing content of the added LMWPHB. It is confirmed that LMWPHB can be used to improve the brittleness and control the biodegradation rate of PHB.

Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities

Abstract: Differential scanning calorimetry (DSC) has become a popular tool to investigate thermal transitions in food ingredients such as gelatin. Upon heating commercial gelatin samples beyond glass transition (T g) and melting (T m) temperatures, a relatively large endothermic transition (T i) can be observed. We have observed that both the peak temperature and the enthalpy of the T i transition are influenced by the integrity of the seal of the DSC pans used for the analysis. This study shows that escape of moisture from the DSC pan appears to be responsible for this effect. The effect of different types of DSC pans, as well as technique of sealing them on the T i transition were evaluated using DSC, SDT, and TG–MS.

The effect of carbon nanotubes on epoxy matrix nanocomposites

Abstract: The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (Tg) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in Tg was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity.

Combustion characteristics and kinetic analysis of Turkish crude oils and their SARA fractions by DSC

Abstract: In this study, two Turkish crude oils from southeastern part of Turkey and their saturate, aromatic, resin fractions were analyzed by differential scanning calorimetry (DSC). The experiments were performed at three different heating rates (5, 10, 15 °C min−1) under air atmosphere. Two different reaction regions were observed from DSC curves due to the oxidative degradation of crude oil components. In the first reaction region, it was deduced that the free moisture, volatile hydrocarbons were evaporated from the crude oils, light hydrocarbons were burned, and fuel was formed. The second reaction region was the main combustion region where the fuel was burned. From DSC curves, it was observed that as the sample got heavier, the heat of the reaction increased. Saturates gave minimum heat of reaction. As the heating rate increased, shift of peak temperatures to high values and extended reaction region intervals were observed. The kinetic analysis of the crude oils and their fractions were also performed using ASTM E-698 and Borchardt and Daniels methods, respectively. Activation energy values of the crude oil samples and the fractions’ high-temperature oxidation region were close to each other and varied between 67 and 133 kJ mol−1 in ASTM and 35 and 154 kJ mol−1 in Borchardt and Daniels methods, respectively.

Thermal studies of chitin–chitosan derivatives

Abstract: New poly(azo) amino-chitosan compounds were obtained from the azo coupling reaction of N-benzyl chitosan and diazonium salts. The thermal behavior of these compounds was studied by thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), TG coupled with a Fourier-transform infrared, and differential scanning calorimetry (DSC). TG/DTG curves of chitin–chitosan polymer showed two thermal events attributed to water loss and decomposition of the polysaccharide after cross-linking reactions. Thermal analysis of the poly(azo) amino-chitosan compounds showed that the decomposition temperatures decreased when compared to the starting chitin–chitosan and N-benzyl chitosan. DSC results showed an agreement with the TG/DTG analyses. Thermal behavior of poly(azo) amino-chitosans suggest that these compounds could be considered as potential thermal sensors.

Non-isothermal kinetics of thermal degradation of chitin

Abstract: Thermogravimetric studies of chitin in air atmosphere were carried out at six rates of linear increase of the temperature. The kinetics and mechanism of the thermal decomposition reaction were evaluated from the TG data by iso-conversional calculation procedure of Kissinger–Akahira–Sunose recommended from ICTAC kinetics committee, as well as 27 mechanism functions. The comparison of the results obtained showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect, the iso-conversion calculation procedure turned out to be the most appropriate one. In the present work, the values of the apparent activation energy E, pre-exponential factor A in Arrhenius equation, as well as the changes of entropy ΔS ≠, enthalpy ΔH ≠, and Gibbs free energy ΔG ≠ for the formation of the activated complex from the reagent are calculated. All the calculations were performed using programs compiled by ourselves.

The thermodynamic method for selecting oxygen carriers used for chemical looping air separation

Abstract: Chemical looping air separation (CLAS) has been suggested as a new and energy saving method for producing oxygen from air. The selection of suitable oxygen carriers is the key issue for CLAS system. This paper shows a comprehensive thermodynamic method for selecting oxygen carriers used for CLAS through studying the properties of 34 different oxygen releasing reactions referring to 18 elements at different temperatures. The research mainly includes analysis of oxygen releasing capacity by calculating the Gibbs free energy change (ΔG) and the equilibrium partial pressure of oxygen of the reduction or oxidation reaction at different temperatures. Oxygen content and transport capacity were calculated. The spontaneous reaction temperatures for oxygen releasing reactions were presented to determine the operating temperatures. Also, the minimum demand of the steam for the reduction reaction was discussed. On the basis of the comprehensive thermodynamic study, the oxide systems of CrO2/Cr2O3, PbO2/Pb3O4, PbO2/PbO, Pb3O4/PbO, MnO2/Mn2O3, and Ag2O/Ag have been found suitable for the CLAS process in low temperatures (500–800 K). The systems of PdO2/PdO, PdO2/Pd, PdO/Pd, MnO2/MnO, and MnO2/Mn3O4 were suitable for medium temperatures (800–1100 K) CLAS process. And Co3O4/CoO, CuO/Cu2O, Mn2O3/Mn3O4, and OsO2/Os systems only worked successfully in high temperatures (1100–1400 K). In addition, the CaO2/CaO system was not suitable for CLAS because of the reaction with steam. The various binders such as SiO2, TiO2, Al2O3, Y2O3, ZrO2, and YSZ which have been used for CLC could also be the supports for CLAS oxygen carriers.

The effect of crystal structure on the thermal reactivity of CL-20 and its C4 bonded explosives (I): thermodynamic properties and decomposition kinetics

Abstract: The crystal structure, thermal behavior, and decomposition kinetics of e-CL-20, RS-e-CL-20, α-CL-20, e-CL-20/C4, and RS-e-CL-20/C4 were investigated by nonisothermal FTIR, TG, and DSC techniques. It was found that the thermal decomposition of α-CL-20, e-CL-20/C4, and RS-e-CL-20/C4 could be considered as a two-step process and the initial step is partly controlled by crystal structure. However, the crystal structure could only affect the initial step of decomposition and the total heat release, and the heat release of RS-e-CL-20 is the highest compared with α- and normal e-CL-20. In addition, the activation energy of studied materials was calculated by Kissinger method and modified KAS method, which was compared with the results obtained by other researchers. It was indicated that the obtained activation energy of e-CL-20 by Kissinger method is about 176.0 kJ mol−1, which is almost the same with the results from the literatures by STABIL and Noniso-TG methods. It was noticed that the crystal structure has significant effect on the initial activation energy distribution of CL-20, while in case of second stage (α = 0.30–0.85) this effect is relatively small, resulting in identical decomposition mechanism. Moreover, the kinetic compensation effects show that the studied materials could be divided into two groups, one including e-CL-20, RS-e-CL-20, α-CL-20, and e-CL-20/C4 which decompose at solid state and another including e-CL-20/Formex and RS-e-CL-20/C4 which decompose at partial liquid state, resulting in different kinetic compensation effects. It reveals that the C4 base could affect the distribution of activation energy of e-CL-20 and RS-e-CL-20 in a totally different way.

Thermal characterization of dried extract of medicinal plant by DSC and analytical techniques

Abstract: The increased search for herbal products has generated an increasing interest in improving the quality control of dried extracts by pharmaceutical industry since these are raw materials of great importance by their quality and versatility. This work aimed at the application of various analytical techniques (thermal analysis, X-ray diffraction, scanning electron microscopy, and infrared Fourier transform spectroscopy) in the characterization of dried extracts of two plants from the Brazilian semiarid region with medicinal properties. The DSC curves for the dried extracts of Ximenia americana L. and Schinopsis brasiliensis Engl. showed that thermal processes occur between 33.50 and 118.58 °C and between 39.17 and 126.14 °C. The X-ray powder diffraction revealed high degree of amorphization, but the dried extract of X. americana L. showed some diffraction peaks of high intensity. The IR spectra showed high variety of metabolites in the extracts dried. Through this study it was possible to verify the feasibility of applying these techniques in the characterization of raw materials from medicinal plants for use in the herbal medicines production.

Hydrogen sorption–desorption studies on ZrCo–hydrogen system

Abstract: The ZrCo–H2 system was investigated in this study owing to its importance as a suitable candidate material for storage, supply, and recovery of hydrogen isotopes. Desorption hydrogen pressure-composition isotherms were generated at six different temperatures in the range of 524–624 K. A van’t Hoff plot was constructed using the plateau pressure data of each pressure-composition isotherms and the thermodynamic parameters were calculated for the hydrogen desorption reaction of ZrCo hydride. The enthalpy and entropy change for the desorption of hydrogen were found to be 83.7 ± 3.9 kJ mol−1 H2 and 122 ± 4 J mol−1 H2 K−1, respectively. Hydrogen absorption kinetics of ZrCo–H2 system was studied at four different temperatures in the range of 544–603 K and the activation energy for the absorption of hydrogen by ZrCo was found to be 120 ± 5 kJ mol−1 H2 by fitting kinetic data into suitable kinetic model equation.

Instrumental evidence for biodegradation of tannery waste during vermicomposting process using Eudrilus eugeniae

Abstract: Animal fleshing (ANFL) is the main solid waste generated during manufacturing leather, which should be disposed friendly to the environment. The effect of epigeic earthworm Eudrilus eugeniae (with and without addition) to transform fermented ANFL in solid state (SSF) and submerged state (SmF) mixed with cow dung and leaf litter into value added product was studied in a vermibioreactor at low residence period (25 days). The products were characterised for pH and C:N ratio and the results were declined at the end of the treatment process with significant reduction in earthworm processed product. The maturity and the chemical changes of the final products were determined using spectroscopic analysis as UV–Visible Spectroscopy in which worm products (vermicompost) reached >5; this indicated that they were well humified. The FT-IR analyses results confirmed the complete mineralisation of polypeptides, polysaccharides, aliphatic methyl groups and lignin, and formation of a deep nitrate band in worm product compared to without worm processed product. Thermogravimetry (TG) and differential scanning calorimetry analyses were carried out in the initial mixture and final products to identify the mass loss and quantitative and qualitative information regarding physical and chemical changes occurred during composting process. The overall results indicated that the maturity of vermicompost (with worms) was in the order SSF > SmF > control. The results indicate that the combination of both fermentation and bacterial/vermicomposting (without worms/with worms) reduced the overall time required for production of well humified organic manure especially with worms.

Mechanism of thermal decomposition of yttrium nitrate hexahydrate, Y(NO3)3·6H2O and modeling of intermediate oxynitrates

Abstract: The thermal decomposition of yttrium nitrate hexahydrate Y(NO3)3·6H2O is a complex condensation process generating a tetramer arrangement Y4O4(NO3)4 formed by alternating yttrium and oxygen atoms. The anions NO3 − attach themselves to the yttrium atoms. The tetramer gradually loses N2O5 and, through the formation of Y4O5(NO3)2, is transformed into yttrium oxide. The bond lengths and bond angles of intermediate oxynitrates calculated using the molecular mechanics method rendered data compatible with the results of X-ray diffraction for related compounds.

Chemical modification of activated carbon monoliths for CO2 adsorption

Abstract: The development of materials with potential application for CO2 capture is a topic of great scientific interest. Activated carbons (AC) can be conveniently used as CO2 adsorbents thanks to their microporous structure and tunable chemical properties. In this work, two AC honeycomb monoliths were synthesized starting from African palm stones through activation either with H3PO4 or with ZnCl2 solution. Surface functionalization was performed in order to add nitrogen groups, aiming at an enhancement of CO2 adsorption capacity. This chemical modification was performed either with ammonia in gas phase or a with 30 % ammonium hydroxide aqueous solution on both AC monolith samples. The original and modified monoliths were characterized by N2 adsorption at 77 K, infrared spectroscopy, Boehm titration, and immersion calorimetry in benzene and water. CO2 adsorption on both raw and functionalized AC monoliths was evaluated in volumetric equipment at a temperature of 273 K and until 1 bar, and adsorption capacity ranging between 120 and 220 mgCO2 g AC −1 was obtained. The experimental results indicated that both methods of chemical modification determined an increase in the content of superficial nitrogen groups and thus an increase in CO2 adsorption capacity, the treatment with ammonium hydroxide being slightly preferable.

Thermal degradation and evolved gas analysis of epoxy (DGEBA)/novolac resin blends (ENB) during pyrolysis and combustion

Abstract: The thermal degradation of epoxy (DGEBA) and phenol formaldehyde (novolac) resins blend was investigated by using thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy and mass spectroscopy. The results of TGA revealed that the thermal degradation process can be subdivided into four stages: drying the sample, fast and second thermal decomposition, and further cracking process of the polymer. The total mass loss of 89.32 mass% at 950 °C is found during pyrolysis, while the polymer during the combustion almost finished at this temperature. The emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, etc., while aromatic products, are emitted at higher temperature during combustion and pyrolysis. It was observed that the intensities of CO2, CO, H2O, etc., were very high when compared with their intensities during pyrolysis, attributed to the oxidation of decomposition product.

Thermal and flame retardant properties of novel intumescent flame retardant polypropylene composites

Abstract: Novel intumescent flame retardant polypropylene (PP) composites were prepared based on a char forming agent (CFA) and silica-gel microencapsulated ammonium polyphosphate (Si-MCAPP). The thermal and flame retardancy of flame retardant PP composites were investigated by limiting oxygen index, UL-94 test, cone calorimetry, thermogravimetric analysis, scanning electron micrograph, and water resistance test. The results of cone calorimetry show that the flame retardant properties of PP with 30 wt% novel intumescent flame retardants (CFA/Si-MCAPP = 1:3) improve greatly. The peak heat release rate and total heat release decrease, respectively, from 1,140.0 to 156.8 kW m−2 and from 96.0 to 29.5 MJ m−2. The PP composite with CFA/Si-MCAPP = 1:3 has the excellent water resistance, and it can still obtain a UL-94 V-0 rating after 168 h soaking in water.