Showing papers in "Journal of Thermal Analysis and Calorimetry in 2016"

Measurement of thermal conductivity of ZnO–TiO 2 /EG hybrid nanofluid

Abstract: The hybrid nanofluids are novel nanofluids and can be prepared by suspending various kinds of nanoparticles in base fluid. In this paper, an experimental investigation on the effects of temperature and nanoparticles concentration on the thermal conductivity of ZnO–TiO2/EG hybrid nanofluids is presented. The experiments were implemented at temperature ranging from 25 to 50 °C and solid volume fraction range of 0–3.5 %. Experiments indicate that the thermal conductivity enhances with increasing the solid volume fraction and temperature. It was found that the variation of thermal conductivity enhancement of nanofluids with solid volume fraction at higher temperatures is greater than that at lower temperature. Moreover, it can be also seen that the variation of thermal conductivity enhancement of nanofluids with temperature at higher solid volume fraction is more than that at lower solid volume fraction. Finally, based on experimental data, in order to predict the thermal conductivity ratio of ZnO–TiO2/EG hybrid nanofluids, a correlation was proposed. Deviation analysis of the thermal conductivity ratio was also performed. Comparison between experimental data and the proposed correlation outputs revealed that this correlation has a good accuracy.

Physicochemical properties of microcrystalline nitrocellulose from Alfa grass fibres and its thermal stability

Abstract: The conventional cellulose nitrate (NC), used in many applications such as coating agent, main charge of propellant, museum artefacts, biofilter material, solid-phase immobilization supports for proteins, was mainly prepared from wood or cotton. The conventional NC presents many drawbacks such as low density, high friability and low combustion temperature. One approach to improve these shortcomings is the modification of the structure of the NC precursor (cellulose). In this work, microcrystalline cellulose nitrate was successfully produced from an inexpensive and easily renewable source which is Alfa grass. Fourier transform infrared spectroscopy indicates some modifications in the peak positions and intensities, suggesting that a significant difference between conventional and microcrystalline cellulose nitrate samples exists. According to X-ray diffraction results, microcrystalline cellulose nitrate samples were more crystalline than the conventional cellulose nitrate samples, where the increase of the crystallinity is 22 %. The morphology was investigated using scanning electron microscopy, showing a compact structure and a rough surface. In comparison with the commercial nitrocellulose material, the microcrystalline cellulose nitrate particles have good thermal stability, low viscosity, high nitrogen content and important quantity of gas released. Besides on these results, Alfa microcrystalline cellulose nitrate showed tremendous potential use as a propellant and gas generator component or other high value-added applications.

Effect of volume concentration and temperature on viscosity and surface tension of graphene–water nanofluid for heat transfer applications

Abstract: In the present study, the effect of volume concentration (0.05, 0.1 and 0.15 %) and temperature (10–90 °C) on viscosity and surface tension of graphene–water nanofluid has been experimentally measured. The sodium dodecyl benzene sulfonate is used as the surfactant for stable suspension of graphene. The results showed that the viscosity of graphene–water nanofluid increases with an increase in the volume concentration of nanoparticles and decreases with an increase in temperature. An average enhancement of 47.12 % in viscosity has been noted for 0.15 % volume concentration of graphene at 50 °C. The enhancement of the viscosity of the nanofluid at higher volume concentration is due to the higher shear rate. In contrast, the surface tension of the graphene–water nanofluid decreases with an increase in both volume concentration and temperature. A decrement of 18.7 % in surface tension has been noted for the same volume concentration and temperature. The surface tension reduction in nanofluid at higher volume concentrations is due to the adsorption of nanoparticles at the liquid–gas interface because of hydrophobic nature of graphene; and at higher temperatures, is due to the weakening of molecular attractions between fluid molecules and nanoparticles. The viscosity and surface tension showed stronger dependency on volume concentration than temperature. Based on the calculated effectiveness of graphene–water nanofluids, it is suggested that the graphene–water nanofluid is preferable as the better coolant for the real-time heat transfer applications.

Erratum to: Study on thermal conductivity of water-based nanofluids with hybrid suspensions of CNTs/Al2O3 nanoparticles

Abstract: The aim of this work was to investigate the effects of temperature and solid volume fraction on thermal conductivity of CNTs–Al2O3/water nanofluids. Both Al2O3 nanoparticles and CNTs are dispersed in the base fluid with equal solid volume. Experiments were conducted with various solid volume fractions of 0.02, 0.04, 0.1, 0.2, 0.4, 0.8 and 1.0 % and various fluid temperatures of 303, 314, 323 and 332 K. Measured data reveal that the thermal conductivity of nanofluid highly depends on the solid volume fraction. Also, temperature may play an important role in enhancing thermal conductivity of CNTs–Al2O3/water, especially at high solid volume fractions. Based on experimental data, correlations are proposed for different temperatures by nonlinear regression. These correlations are able to predict thermal conductivity of nanofluid with high precision. Besides, a general correlation of thermal conductivity with function of temperature and solid volume fraction was proposed.

Investigation of magnetite nanoparticles stability in air by thermal analysis and FTIR spectroscopy

Abstract: Magnetic iron oxides were prepared by precipitation of Fe(II) hydroxide using different precipitation agents: ammonia, benzylamine and sodium hydroxide, followed by oxidation with the oxygen dissolved in water. Thermal analysis, coupled with FTIR spectroscopy, has evidenced the formation of a mixture of magnetite and maghemite, with a higher content of magnetite in case of the powder synthesized with benzylamine. The stability of magnetite at oxidation by air during storage at room temperature and 60 °C was investigated by means of TG/DSC simultaneous thermal analysis, FTIR spectroscopy and X-ray diffractometry. Thermal analysis evidenced an exothermic process with mass gain in temperature range 100–190 °C, corresponding to magnetite oxidation process, but due to the superposition of other processes it could not offer quantitative information. FTIR spectroscopy has provided, especially through the first and second derivatives of FTIR spectra, the most valuable information regarding the evolution of magnetite to maghemite, due to their different characteristic bands. XRD technique has evidenced a slight shift of the main diffraction peaks at higher 2-theta values during the evolution of magnetite to maghemite. According to thermal analysis data, the powder synthesized with ammonia was completely oxidized after 15 days, while the other two powders, synthesized with benzylamine and sodium hydroxide, were completely oxidized after 110 days of keeping in air at room temperature. For a temperature of 60 °C, the oxidation was much faster; the oxidation process of the powder synthesized with benzylamine disappeared from TG/DSC curves after 1 day. All final powders were formed from nanoparticles with diameters up to 25 nm, with magnetic properties characteristic to nanometric maghemite.

Designing artificial neural network on thermal conductivity of Al2O3–water–EG (60–40 %) nanofluid using experimental data

Abstract: The main purpose of this research was to investigate the efficiency of artificial neural networks in modeling thermal conductivity data of water–EG (40–60 %) nanofluid with aluminum oxide nanoparticles (with average diameter of 36 nm). The measured data as modeling input data are in six volume fractions from 0 to 1.5 % and different temperatures from 20 to 60 °C. In order to optimize the network, different numbers of neurons with different transfer functions have been tested and after preprocessing and normalizing the data, the optimum network structure with one hidden layer and six neurons was obtained. This structure simulated the experimental data with very high precision. The measured thermal conductivity was compared with the two models that calculated thermal conductivity for mixtures. The results indicated that Hamilton–Crosser and Lu–Lin models failed in estimating the thermal conductivity of Alumina–water–EG nanofluid in different temperatures and concentration. Finally, a new correlation was presented based on experimental data with regression coefficient of 0.9974.

Using artificial neural network to predict thermal conductivity of ethylene glycol with alumina nanoparticle Effects of temperature and solid volume fraction

Abstract: The correlations of thermal conductivity of alumina nanoparticle dispersed in pure ethylene glycol were proposed by neural network modeling using experimental data. The required input and target data have been taken from the experimental measurement to train artificial neural network (ANN). The temperatures were changed within 24–50 °C. Levenberg algorithm was used to train the ANN. Results showed that the thermal conductivity of nanofluid had a significant increase with increasing solid volume fraction of nanoparticles. The results also revealed that the ANN model can predict the thermal conductivity of Al2O3–EG nanofluid accurately with maximum deviation of 1.3 % and high correlation coefficient (R > 0.998).

Preparation and thermal properties of stearic acid/diatomite composites as form-stable phase change materials for thermal energy storage via direct impregnation method

Abstract: Stearic acid/diatomite composite form-stable phase change materials (PCMs) have been prepared by using a direct impregnation method without vacuum treatment. The surface morphology, chemical compatibility, thermal properties and thermal stability were characterized by scanning electron microscopy, Fourier transform infrared spectrometer and X-ray diffraction (XRD), differential scanning calorimeter and thermogravimetric analysis (TG), respectively. The results show that there are only physical interactions between stearic acid and diatomite in composite PCM. XRD analysis reveals that crystal type is not affected by composite technology of SA/diatomite composite form-stable PCM with decrease in crystal size due to the limited pores in diatomite. The melting and freezing temperatures of stearic acid/diatomite composite, respectively, are 52.3 and 48.4 °C. The latent heat of SA/diatomite composite reaches 57.1 J g−1, potential to be used in a practical application. TG result indicates that the decomposition of SA/diatomite composite starts at 192 °C, implying that the SA/diatomite has a good thermal stability.

Second law analysis of a nanofluid-based solar collector using experimental data

Abstract: The present study deals with the entropy generation analysis of a flat-plate solar collector using SiO2/ethylene glycol–water nanofluids. For this purpose, available experimental data on the performance of a flat-plate solar collector are exploited for estimating the entropy generation in the system. Ethylene glycol–water (EG–water) and EG–water-based nanofluids having three different nanoparticle volume fractions including 0.5, 0.75, and 1 % are considered as the working fluids. The results are presented in terms of exergy efficiency, entropy generation parameter, and Bejan number for three different mass flow rates and various solar radiation intensities. It is found that when nanofluid concentration increases from 0 to 1 %, exergy efficiency enhances up to 62.7 % for a mass flow rate of 1 L min−1, whereas the corresponding increases in mass flow rates of 1.75 and 2.5 L min−1 are 45.2 and 39.7 %, respectively. The results also elucidate that entropy generation parameter, which is a function of entropy generation, ambient temperature, and solar radiation, reduces with increasing the nanofluid concentration.

Thermal stability of imidazolium-based ionic liquids investigated by TG and FTIR techniques

Abstract: Thermal stability and thermal decomposition kinetics of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) were investigated using isothermal and non-isothermal thermo-gravimetric analysis. The results indicated that isothermal test in the air showed that after storage at 180 and 300 °C both for 10 h, the conversion rate of [bmim]BF4 was 1.28 and 2.57 %, respectively. When stored at less than 300 °C, all bands of IR spectra are nearly unchanged. It suggests that [bmim]BF4 basically is stable. When isothermal stored at 350 °C for 2 h, the ATR–FTIR spectra show that the relative intensity of BF 4 −1 anion near band of 1058 cm−1 fell by 36.7 %. Due to the intensity of the absorption band declined significantly in the range of 300–350 °C, the anion of BF 4 −1 was possibly dissociated by the action of air and heat; thus, at the time [bmim]BF4 is not stable. The average apparent activation energy of thermal degradation obtained by multiple scanning methods is 105.6 kJ mol−1. Moreover, mass spectrometric analysis also shows that the z/m of [bmim+] is 139.1; in the thermal degradation process, the possibility of generating a dimer between imidazolium cation exists.

Long-term thermal and chemical reliability study of different organic phase change materials for thermal energy storage applications

Abstract: The purpose of this experimental study is to determine the thermal and chemical reliability of organic phase change materials (O-PCMs) viz. paraffin, palmitic acid, and myristic acid for 1500 accelerated melt/freeze. The differential scanning calorimeter (DSC) was used to measure the melting temperature and the latent heat of fusion at zeroth cycle and after 100th, 500th, 1000th, and 1500th thermal cycles. The DSC results show the gradual changes in the value of thermophysical properties of all the tested PCMs. The changes in melting temperature of paraffin, palmitic acid, and myristic acid have been found in the range of +0.72 to +3.27, −0.29 to +1.76, and −2.09 to +1.5 °C, respectively, and the latent heat of fusion in −9.8 to 14.2, 3.3 to 17.8, and 0.9 to 9.7 %, respectively. The Fourier transform and infrared spectroscopy (FT-IR) technique was used to investigate the changes in the compositional/functional group of the O-PCMs before and after thermal cycles. The FT-IR spectrum confirms the chemical stability during the thermal cycle test. The experimental results show that these organic PCMs possess a good thermal reliability in terms of melting temperature and the latent heat of fusion and chemical stability during thermal cycle testing.

Physicochemical characterization and kinetic study of pine needle for pyrolysis process

Abstract: The present study concerns physicochemical characterization and pyrolysis kinetics of pine needle. The physiochemical properties of pine needle were analyzed to examine the potential for pyrolysis. The physiochemical properties such as proximate analysis, ultimate analysis, lignocellulosic composition, heating values and FTIR spectroscopy of pine needle were investigated. The pyrolysis experiments were conducted in a non-isothermal thermogravimetric analyzer (TG) under an inert atmosphere and operated at different heating rates (5, 10 and 20 °C min−1) to understand the thermal degradation behavior. The kinetic parameters such as activation energy, pre-exponential factor and reaction order were evaluated by using iso-conversional methods proposed by Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW) and Coats–Redfern using TG data. The average activation energy of pine needle derived from KAS and OFW models is found to be 70.97 and 79.13 kJ mol−1, respectively. The degree of conversion of pine needles on heat treatment by using the kinetic parameters of the proposed model is found to be in good agreement with experimental data. Maximum error limit between experimental data and proposed model data is 9.8, 6.8 and 10.6 % for 5, 10 and 20 °C min−1, respectively. Analysis of the results proves the suitability of pine needle as a potential feedstock for pyrolysis.

Thermodynamic performance of forced convection solar air heaters using pin–fin absorber plate packed with latent heat storage materials

Abstract: In this work, the thermodynamic performance of a forced convection solar air heater (FCSAH) was evaluated using two different absorber plate configurations, namely a flat absorber plate and a pin–fin absorber plate packed with latent heat storage material (paraffin wax). The experiments were carried out under the meteorological conditions of Coimbatore city in India. The parameters such as outlet air temperature, thermo-hydraulic efficiency and exergy efficiency were evaluated with reference to solar intensity, ambient temperature and ambient wind velocity. An artificial neural network (ANN) model was developed to simulate the thermodynamic performance of a FCSAH using flat absorber plate and pin–fin absorber plate packed with paraffin wax to have a realistic performance comparison. The ANN-predicted results are found to be closer to the experimental values with a maximum fraction of absolute variance, minimum root-mean-square errors and minimum coefficient of variance. The results showed that the pin–fin absorber plate packed with paraffin wax has additional heat storage for the period of 3 h with 2–5 °C enhanced outlet air temperature when compared to the flat absorber plate. The FCSAH using pin–fin absorber plate packed with paraffin wax has 3–35 % higher thermo-hydraulic efficiency with 2–15 % higher exergy efficiency when compared to the flat absorber plate. The results confirmed that pin–fin absorber plate packed with paraffin is a good option to enhance the thermodynamic performance of a FCSAH.

Investigation on thermal properties of capric–palmitic–stearic acid/activated carbon composite phase change materials for high-temperature cooling application

Abstract: Based on the theory calculation, the capric–palmitic–stearic (CA–PA–SA) ternary eutectic mixture was prepared with melting and freezing temperature of 19.93 and 16.84 °C, respectively. Regarding CA–PA–SA as phase change materials (PCMs), and activated carbon (AC) as the additive, the CA–PA–SA/AC composites can be prepared by physical blend method which can be applied to high-temperature cooling application in solar cooling systems, radiant cooling systems, etc. A comprehensive study of the structure, thermal properties, thermal stability, thermal durability and thermal storage-release characteristic of CA–PA–SA/AC composites was conducted through the FT-IR, DSC, TG, accelerated thermal cycling test and melting–freezing experiments. The results show that, with the increase in AC content, the melting temperature of CA–PA–SA/AC composites decreases gradually, whereas the freezing temperature increases. And the addition of AC can enhance the thermal stability, the thermal durability and the thermal storage-release rate of PCM: the thermal stability of PCM1–PCM4 is much greater than that of pure mixture, and its storage time was reduced by 37, 31, 23 and 9 %, respectively, while its release time was reduced by 67, 58, 48 and 43 % respectively.

Phosphorus–nitrogen compounds

Abstract: The salicylic acid salts of fully substituted mono(4-fluorobenzyl)spirocyclotriphosphazenes (10–15) were prepared. The structures of these phosphazenium salts (10a–15a) were determined by elemental analyses, FTIR and 1H, 13C{1H}, 31P{1H} NMR techniques. The crystal structure of 14a was verified by X-ray diffraction analysis. The thermal properties of the salts were investigated using TG/DTA and DSC instruments. The results obtained from DSC indicated that the melting temperatures and latent heats of the compounds were in the ranges of 107.76–143.04 °C and 41.64–69.73 J g−1, respectively. The thermal stabilities of the phosphazenium salts (10a–15a) are found to be different, but they have a similar decomposition mechanism. The compounds 14a and 15a exhibit noticeable cytotoxic activity against DLD-1 cancer cells, and they seem to be good candidates for being anticancer agents. All of the compounds have an antimicrobial effect on bacterial and yeast strains within the ranges of 312–625 µM (bacterial strains) and 19.5–312 µM (yeast strains). It is found that compounds 13a–15a were most effective against yeast strains. Moreover, interactions between the salts and pBR322 plasmid DNA show that 14a and 15a cleave the DNA and decrease the intensity of form I. BamHI and HindIII digestion results demonstrate that the compounds are not bound with G/G and A/A nucleotides, respectively.

The effects of temperature and volume fraction on the thermal conductivity of functionalized DWCNTs/ethylene glycol nanofluid

Abstract: An experimental study on the effects of temperature and volume fraction of double-walled carbon nanotubes (DWCNTs) on the thermal conductivity of ethylene glycol (EG) was performed. In this way, the thermal conductivity of samples of nanofluid was examined at temperature ranging from 27 to 52 °C and concentrations range of 0.02, 0.05, 0.075, 0.1, 0.25, and 0.6 %. The results showed that the thermal conductivity of nanofluids enhances strangely with increase in volume fraction and temperature. Moreover, attempts were made to provide a new correlation for predicting the thermal conductivity of functionalized DWCNTs/EG nanofluid at different temperatures and concentrations. Finally, a deviation of margin analysis of the correlation revealed that there is a good agreement between experimental data and correlation outputs.

Effect of side substituents on thermal stability of the modified chitosan and its nanocomposites with magnetite

Abstract: Three different novel chitosan derivatives for medical or biotechnological applications have been successfully obtained by chemical modification of reactive amino and hydroxyl groups in chitosan chain. The modification has led to incorporation of different amount (one to three) of long-distanced amino and imine groups into each repeating unit. These highly functionalized chitosan derivatives were used as a matrix for magnetite nanoparticles. The thermal stability of all obtained chitosan materials has been determined using thermogravimetric analysis in oxidative and inert atmosphere. Chitosan containing two side substituents behaves differently from the other two, which is caused by the significant water uptake. Magnetite causes decrease in thermal stability of studied chitosan derivatives. The highest stability is observed for the nanocomposite obtained from chitosan with three side groups. The changes in the structure of the magnetite core have been observed above 600 °C in nitrogen. Due to the different competitive reactions occurring in the modified chitosan, the proposed mechanism of thermal degradation is very complex.

Experimental investigation of the rheological behavior and viscosity of decorated multi-walled carbon nanotubes with TiO2 nanoparticles/water nanofluids

Abstract: The effects of temperature and concentration on the flow behavior and viscosity of nanofluids containing TiO2 nanoparticles, pristine MWCNTs, oxidized MWCNTs and decorated MWCNTs with TiO2 nanoparticles are experimentally investigated. The results of rheological characteristics of nanofluids revealed that nanofluid of TiO2 nanoparticle and MWCNT–TiO2 exhibits shear thickening or dilatant behavior. In contrast, nanofluids containing pristine and oxidized MWCNTs depict the shear thinning or pseudoplastic behavior. Also results demonstrated that the rheological characteristics of nanofluids are functions of temperature and concentration, whereas the viscosity of all prepared nanofluids decreases with increasing the temperature and decreasing the concentration. In addition, the results show that the oxidation of MWCNTs in nitric acid leads to the reduction in viscosity. The rheological behavior of decorated MWCNTs illustrates that viscosity decreases by increasing the attached TiO2 nanoparticles. TEM results show that TiO2 nanoparticles successfully attached to the outer surface of oxidized MWCNTs.

Heat of hydration of low-clinker cements: Part I. Semi-adiabatic and isothermal tests at different temperature

Abstract: The hydration heat evolution of low clinker cements is studied in a dependence on the testing method and temperature. Four substitution rates of ordinary Portland cement by ground granulated blast furnace slag or siliceous fly ash were used—10, 30, 50 and 70 %. In all cases, the water/binder ratio of the cement paste was 0.5. The heat evolution and the heat evolution rate were monitored over 72 h with the use of two testing methods. The isothermal measurements were carried out with the use of TAM Air isothermal calorimeter at 20 and 50 °C. The heat evolution was also determined with the use of a semi-adiabatic calorimeter. Part I of the paper presents the results of the experimental tests and discussed the influence of mineral additives on the hydration heat evolution.

Influence of Fe 2 O 3 on smoke suppression and thermal degradation properties in intumescent flame-retardant silicone rubber

Abstract: This article examines the feasibility of intumescent flame retardant (based on phosphorus acid, melamine, and pentaerythritol) as a flame retardant and Fe2O3 as a smoke suppression agent in silicone rubber (SR) composites Smoke suppression of Fe2O3 on intumescent flame-retardant SR composites was investigated using smoke density test and cone calorimeter test (CCT) And, the flammability of SR composites was characterized using CCT at an incident heat flux of 50 kW m−2 The test results further revealed that Fe2O3 could increase smoke suppression efficiency and thermal degradation temperature Fe2O3 can promote early cross-linking of polymer during decomposition to increase char formation The silica ash layer integrity governs the efficiency of diffusion barrier that restricts the diffusion of fuels into combustion zone and access of oxygen to the unburned fuels

Bio-polyamides based on renewable raw materials

Abstract: Structural characterization of a series of novel bio-polyamides based on renewable raw materials—PA 4.10, PA 6.10, PA 10.10, and PA 10.12—was performed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). Infrared spectra and the WAXD patterns indicate the coexistence of different crystalline forms, α- and γ-triclinic and β-pseudohexagonal. Thermal properties in the glass transition (T g) and melting region were then investigated using temperature-modulated DSC (TOPEM® DSC). The melting point (T m) was found to increase with increasing amide/methylene ratio in the polymer backbone, which is consistent with the increase in linear density of hydrogen bonds. Studies on the molecular dynamics by dynamic mechanical analysis show three distinct regions associated with the γ- and the β-relaxation and the dynamic glass transition. TOPEM® DSC data reveal that at low frequency/long timescales, the materials with significantly different amide/methylene ratios have similar segmental dynamics.

Elaborated studies on nano-sized homo-binuclear Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) complexes derived from N2O2 Schiff base, thermal, molecular modeling, drug-likeness, and spectral

Abstract: A series of new homo-binuclear nano Mn(II), Fe(III), Co(II), Ni(II), and Cu(II) complexes were synthesized using a Schiff base ligand derived by condensation of p-phenylenediamine with 2-hydroxy-1-naphthaldehyde The prepared complexes were characterized using elemental, thermal analyses, FTIR, 1HNMR, 13CNMR, UV–Vis, XRD, SEM, molar conductance, and magnetic moment measurements FTIR spectral studies revealed the interaction of the ligand as bi-negative tetra-dentate towards Mn(II) and Fe(III) atoms, whereas the ligand molecule coordinates in neutral tetra-dentate mode towards Co(II), Ni(II), and Cu(II) ions The geometries proposed are mainly octahedral configuration surrounds the central atoms referring to the electronic spectral data and magnetic measurements The calculations abstracted from XRD patterns propose the nano-sized complexes The SEM images show the nano-sized appearance of the particles except for the Ni(II)-complex Thermo-gravimetric analysis was used to ensure the nature of the presence of solvent molecules attaching to the complexes Molecular modeling was performed to assert the structural formula proposed for the ligand and some of its complexes Also, drug-likeness was theoretically estimated to display the probable biological activity of the free ligand through a theoretical comparison with known drugs

Spontaneous combustion in six types of coal by using the simultaneous thermal analysis-Fourier transform infrared spectroscopy technique

Abstract: Using simultaneous thermal analysis-Fourier transform infrared spectroscopy, we analyzed the oxidation and exothermic behaviors of six types of coal based on various factors, such as characteristic temperature, heat release, and gas release, to establish a foundation for prevention and control of spontaneous combustion in six types of coal in China. According to the experimental results, a decrease in the metamorphic grade of coal causes an increase in the amount of volatile matter, the heat release rate, and the total heat released. The apparent exothermic onset temperature and initial temperature for the release of H2O, CO2, CO, and CH4 during the nonisothermal oxidation process of coal took place earlier, indicating that the oxidation reaction occurred more easily in lower-grade coal, increasing the hazards of spontaneous combustion. Moreover, when decomposing, coal releases large amounts of CH4, which may cause gas explosions in coal mines. Therefore, technology facilitating the detection of CH4 and prevention of explosions should be developed for use in the coal industry.

Thermal decomposition of ammonium molybdates

Abstract: The thermal behavior of ammonium molybdates, i.e., (NH4)6Mo7O24·4H2O (1) and (NH4)2MoO4 (2), was studied in inert (N2) and oxidizing (air) atmospheres by TG/DTA-MS, XRD, FTIR and SEM. The thermal decomposition sequence of 2 had similarities to 1; however, there were significant differences as well. When both of them were annealed, NH3 and H2O were released parallel, and in air the as-evolved NH3 was burnt partially into NO and N2O. In both atmospheres, while 1 decomposed in four steps, the thermal decomposition of 2 involved 5 steps. In the case of 1, the intermediate products were (NH4)8Mo10O34, (NH4)2Mo4O13 and h-MoO3. In contrast, the decomposition intermediates of 2 were (NH4)2Mo3O10, (NH4)2Mo2O7, (NH4)2Mo4O13 and h-MoO3. By both 1 and 2, the final product was dominated by o-MoO3, accompanied with small amount of Mo4O11 in N2, which was absent in air. Most decomposition steps were endothermic, except for the last step around 400 °C, where crystallization from the residual amorphous phase had an exothermic heat effect. In addition, the combustion of NH3 also changed the DTA curve into exothermic in some cases. The morphology of the final products was characterized by 1–5 μm sheet-like particles, except for annealing 2 in N2, when 0.5- to 1-μm-thick and 5- to 10-μm-long needle-shaped particles were detected.

The research for crumb rubber/waste plastic compound modified asphalt

Abstract: Crumb rubber (CR)/waste plastic compound modified asphalts were prepared by the addition of CR and waste plastic including waste polypropylene, low-density polyethylene, linear low-density polyethylene (LLDPE). The physical properties of each modified asphalt were studied and compared, and LLDPE was confirmed as the right modifier in enhancing the high-temperature performance. Meanwhile, dioctyl phthalate (DP) as a plasticizer was used further in improving low-temperature properties. On the basis of the optimal proportion of CR/LLDPE/DP modified asphalt, rheological tests were used to study the high- and low-temperature properties and structural characteristics of modified binder. Fourier transform infrared spectroscopy was used to investigate the modification mechanism of each modifier. Morphology observation was used to study the effect of modifier and ageing on the morphological characteristics of asphalt. Thermal analysis was adopted to study the thermodynamic characteristics and constituents of each modified binder.

Wood biomass characterization by DSC or FT-IR spectroscopy

Abstract: The wood biomass obtained from four tree species: spruce, beech, willow and alder was studied. Sawdust obtained by sawing of wood was dried in a convective dryer at 80 °C, without drying-agent flow. The measurements taken with oven-drying method covered determination of initial moisture and its detailed changes during entire drying process. Both DSC curves and spectral data from infrared spectra registered in the classic MIR range were also used to monitor change in water content in studied samples within entire drying process. Results obtained suggest that the DSC curves can be efficiently used as a discriminant to distinguish dry and wet biomass samples, as significant differences within courses of specific DSC curves of woody biomass before and after drying process occurred. Calorimetrically measured values of enthalpy of evaporation of water and water content in studied biomass samples were directly proportional to high determination coefficient, i.e. 0.9653. Statistical analysis proved quantitative directly proportional correlation between content of water measured with oven-drying method and IR spectral data of studied samples.

Thermal stability of cellulose nanomaterials and their composites with polyvinyl alcohol (PVA)

Abstract: This study investigates the thermal stability of composites composed of polyvinyl alcohol (PVA) reinforced with biodegradable fillers: cellulose nanocrystals (CNC) or cellulose nanofibrils (CNF). Combinations of PVA with CNC and PVA with CNF at 2, 4, 6, and 8 % cellulose by weight underwent several different thermogravimetric analysis (TG) heating programs—constant heating rate, isothermal, and high resolution with a dynamic heating rate. The starting materials (PVA pellets, PVA film, aqueous CNC at 11.8 % solids, and aqueous CNF at 3 % solids) were also tested in the TG after drying. Temperatures at the onset of degradation and at maximum degradation for the principal pyrolysis stage were quantified. Kinetic parameters (activation energy, pre-exponential factor) were calculated using the Flynn–Wall–Ozawa (FWO) method. CNC or CNF incorporation in the PVA matrix did not markedly shift temperatures at the onset of degradation or at maximum degradation for the major stage of pyrolysis, compared to neat PVA. However, the inclusion of nanocellulose lowered the maximum rate of degradation, with larger reductions at higher filler contents. A larger portion of the composites’ original mass remained intact following the major degradation peak. Incorporation of CNF in composites with PVA produced films with activation energies higher than the activation energy of neat PVA film.

Kinetic studies of thermal decomposition of sugarcane bagasse and cassava bagasse

Abstract: The thermal decomposition of sugarcane bagasse and cassava bagasse was investigated by the use of the non-isothermal thermogravimetric technique. The experiments were performed with the following heating rates: 5, 10, 15, 20 and 30 °C min−1. The kinetic parameters of thermal decomposition were estimated by the Flynn–Wall–Ozawa and the Kissinger methods. The results obtained for activation energy by the Flynn–Wall–Ozawa method were in the range of 126.62–148.80 kJ mol−1 for the sugarcane bagasse and 157.64–227.74 kJ mol−1 for the cassava bagasse, whereas the Kissinger method resulted in 124.54 kJ mol−1 for the sugarcane bagasse and 144.31 kJ mol−1 for the cassava bagasse. The pyrolysis of sugarcane bagasse occurred in the temperature range 270–480 °C with average efficiency of 85.23 %, whereas the pyrolysis of cassava bagasse occurred in the range 270–540 °C with average efficiency of 98.85 %. The experimental result for the high heating value was 16.103 MJ kg−1 for sugarcane bagasse and 15.274 MJ kg−1 for cassava bagasse, which means that these materials are suitable for use as alternative fuels.

The influence of carbon fillers on the thermal properties of polyurethane foam

Abstract: The aim of this work was to investigate the influence of different types of carbon filler on the thermal stability and flammability of rigid polyurethane foams. As a filler, multi-walled carbon nanotubes and graphite fakes were used. Scanning electron microscopy was used to observe the structure of foam and dispersion of nanofiller in polymer matrix. Thermal stability of these composites was determined by thermogravimetry analysis. Test was carried out under both nitrogen and air atmosphere. The degradation products were evaluated by thermogravimetry (TG) combined with infrared spectroscopy (TG–IR) measurements. The activation energy was measured by the Flynn–Wall–Ozawa method from the TG curves. Flammability tests like limiting oxygen index and smoke density were also measured. No significant changes in the thermal stability of the composites were observed. The activation energy of sample containing carbon filler increased. Based on TG–IR, one can notice that there were no differences in the emitted volatile products during thermal degradation. Carbon filler enhanced fire retardancy of polyurethane foam; however, graphite gives better results.

Influence of graphene nanoplatelets on curing and mechanical properties of graphene/epoxy nanocomposites

Abstract: The influence of graphene nanoplatelets (GNPs) on the curing of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) and cross-linked with 4,4′-diaminodiphenylmethane (DDM) was studied. Dynamic mechanical properties and tensile properties of the corresponding graphene/epoxy nanocomposites were obtained. Two compositions 1 and 5 mass% of GNPs were studied. The cross-linking reaction of the epoxy resin is accelerated in dispersions with 5 mass% GNPs. In the presence of GNPs, the curing reaction becomes less exothermic, obtaining less perfect epoxy networks compared to neat epoxy (DGEBA–DDM) thermoset. Accordingly, the glass transition temperatures (T g) of the nanocomposites are lower than that of the neat epoxy thermoset. This effect is not detected for low content of graphene (1 mass%). Protocol of curing having two isothermal steps leads to more perfect networks than the dynamic curing in the DSC. The T g reduction is minimized in the samples cured through two isothermal steps. The storage moduli of the nanocomposite containing 5 mass% graphene, both in the glassy (T < T g) and the rubbery (T > T g) states, are higher than the ones of neat epoxy thermoset, being most pronounced this effect at T > T g. Tensile tests confirmed the higher elastic moduli of the nanocomposites; however, a decrease in strain at break and tensile strength was observed for the nanocomposite containing 5 mass% of GNPs. This brittle behavior is consistent with the morphology of the samples studied by scanning electron microscopy.