Showing papers on "Thermal stability published in 2013"
TL;DR: The kinetics and thermodynamics of thermal degradation are revealed piece by piece, assisted with computational methods, and the better understanding of the behaviour of ionic liquids at high temperature allows selective and application driven design, as well as mathematical prediction for engineering purposes.
Abstract: The increasing amount of papers published on ionic liquids generates an extensive quantity of data. The thermal stability data of divergent ionic liquids are collected in this paper with attention to the experimental set-up. The influence and importance of the latter parameters are broadly addressed. Both ramped temperature and isothermal thermogravimetric analysis are discussed, along with state-of-the-art methods, such as TGA-MS and pyrolysis-GC. The strengths and weaknesses of the different methodologies known to date demonstrate that analysis methods should be in line with the application. The combination of data from advanced analysis methods allows us to obtain in-depth information on the degradation processes. Aided with computational methods, the kinetics and thermodynamics of thermal degradation are revealed piece by piece. The better understanding of the behaviour of ionic liquids at high temperature allows selective and application driven design, as well as mathematical prediction for engineering purposes.
679 citations
TL;DR: In this article, a detailed review is reported for thermal stability of different groups of phase change materials (PCMs) used in the latent heat energy storage system, including organic (paraffins and non-paraffin), inorganic (salt hydrates and metallics) and eutectics (organic eutectorics and inorganic eUTectics).
Abstract: Successful utilization of the latent heat energy storage system depends considerably on the thermal reliability and stability of the phase change materials (PCMs) used. Thermal stability of phase change material can be established by measuring the thermo-physical properties of the PCM after a number of repeated thermal cycles. A comprehensive knowledge of thermal stability of the PCMs as functions of number of repeated thermal cycles is essential to ensure the long-term performance and economic feasibility of the latent heat storage systems. In this paper, a detailed review is reported for thermal stability of different groups of PCMs. The PCMs are categorized as organic (paraffins and non-paraffins), inorganic (salt hydrates and metallics) and eutectics (organic eutectics and inorganic eutectics). Further, a broad database of different PCMs is developed for which thermal cycling tests were carried out by different researchers and reported in the literature. Some conclusions are derived after critical evaluation of thermal stability of different groups of PCMs. This review will assist to identify the most reliable PCM to be used for a particular application of latent heat energy storage system.
550 citations
TL;DR: In this paper, the authors show that there are significant changes in chemical and thermal stability of Zr6O4(OH)4 MOFs with the incorporation of different organic linkers.
Abstract: Metal–organic frameworks (MOFs) with the Zr6O4(OH)4 secondary building unit (SBU) have been of particular interest for potential commercial and industrial uses because they can be easily tailored and are reported to be chemically and thermally stable. However, we show that there are significant changes in chemical and thermal stability of Zr6O4(OH)4 MOFs with the incorporation of different organic linkers. As the number of aromatic rings is increased from one to two in 1,4-benzene dicarboxylate (UiO-66, ZrMOF–BDC) and 4,4′-biphenyl dicarboxylate (UiO-67, ZrMOF–BPDC), the Zr6O4(OH)4 SBU becomes more susceptible to chemical degradation by water and hydrochloric acid. Furthermore, as the linker is replaced with 2,2′-bipyridine-5,5′-dicarboxylate (ZrMOF–BIPY) the chemical stability decreases further as the MOF is susceptible to chemical breakdown by protic chemicals such as methanol and isopropanol. The results reported here bring into question the superior structural stability of the UiO-67 analogs as reported by others. Furthermore, the degradation mechanisms proposed here may be applied to other classes of MOFs containing aromatic dicarboxylate organic linkers, in order to predict their structural stability upon exposure to solvents.
535 citations
TL;DR: Thermogravimetric analyses reveal that P-CNCs exhibit a much higher thermal stability than partially sulfated CNCs (S-C NCs), which are frequently employed, but suffer from limited thermal stability.
517 citations
TL;DR: In this article, a polyimide (PI) nanofiber-based nonwovens have been fabricated via electrospinning for the separators of lithium-ion batteries (LIBs).
343 citations
TL;DR: The results revealed that hydrogen bonding and high interfacial adhesion between GO filler and Al matrix significantly changed thermal stability and mechanical properties of the nanocomposite films.
311 citations
TL;DR: In this article, a form-stable composite phase change materials (PCM) was proposed by vacuum impregnation of paraffin within graphene oxide (GO) sheets for thermal energy storage applications.
307 citations
TL;DR: This discovery proves that interfaces can be designed within bulk nanostructured composites to radically outperform previously prepared bulk nanocrystalline materials, with respect to both mechanical and thermal stability.
Abstract: Nanostructured metals are known to exhibit poor thermal stability, reducing their high strength at elevated temperatures. Here, Zheng et al. fabricate a bulk two-phase bimetal composite that retains its high strength after annealing at 500 °C for 1 h.
300 citations
TL;DR: In this article, a facile surfactant-assisted process was used to improve the dispersion and exfoliation level of highly dispersed graphene in epoxy composites, resulting in increased tensile properties compared with those without surface modification.
297 citations
TL;DR: In this paper, a two-stage crosslinking reaction process was correlated to differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA).
Abstract: Melamine formaldehyde (MF) resin was synthesized by the reaction between melamine and formaldehyde under alkaline condition in tetrohydrofuran medium with 1:3 melamine to formaldehyde molar ratio. The synthesized resins were characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Curing and reaction mechanism was studied by thermal and spectroscopic analysis. Two exothermic peaks were observed in the DSC analysis indicating a two-step crosslinking reaction process was correlated to TGA analysis. FTIR studies at different temperatures explained the two-stage curing mechanism which is concurring with the DSC data. At a temperature range of 140–160 °C, reversible demethylolation is dominating to the crosslinking reaction. At temperature >160 °C, the crosslinking reaction dominates. On the basis of DSC and FTIR data, a possible crosslinking reaction route was derived and explained. The first stage of curing is the conversion of methylol groups to primary amine and the second stage is the crosslinking of methylol groups to the final product, methylene bridges. The thermal stability of the methylol groups, methylene bridges and the triazine ring, as well as the evaporation of effluents at different stages of curing, are also discussed based on combined TGA and DSC results. Curing studies and reaction mechanism of MF resin was studied by thermal and spectroscopic tools comparing DSC and FTIR studies explains the two-stage thermal curing mechanism. The first step of thermal curing at temperature range of 140–160 °C is the reverse reaction of methylol groups to melamine and second step occurring at temperature >160 °C is the crosslinking of methylol groups to the final product, methylene bridge. Hence, by the mutual agreement of DSC and FTIR studies, a possible reaction route was derived for the thermal curing process. The DSC–TGA thermogram supports the two-step process of the cure reaction by exhibiting two peaks in the same temperature region.
277 citations
TL;DR: In this article, high-temperature analyses of the desodiated state NaFeP2O7 showed an irreversible phase transition from triclinic (P1) to the ground state monoclinic polymorph above 560 °C.
Abstract: Vying for newer sodium-ion chemistry for rechargeable batteries, Na2FeP2O7 pyrophosphate has been recently unveiled as a 3 V high-rate cathode. In addition to its low cost and promising electrochemical performance, here we demonstrate Na2FeP2O7 as a safe cathode with high thermal stability. Chemical/electrochemical desodiation of this insertion compound has led to the discovery of a new polymorph of NaFeP2O7. High-temperature analyses of the desodiated state NaFeP2O7 show an irreversible phase transition from triclinic (P1) to the ground state monoclinic (P21/c) polymorph above 560 °C. It demonstrates high thermal stability, with no thermal decomposition and/or oxygen evolution until 600 °C, the upper limit of the present investigation. This high operational stability is rooted in the stable pyrophosphate (P2O7)4– anion, which offers better safety than other phosphate-based cathodes. It establishes Na2FeP2O7 as a safe cathode candidate for large-scale economic sodium-ion battery applications.
TL;DR: Sterically demanding Ni(II) α-diimine precatalysts were synthesized utilizing 2,6-bis(diphenylmethyl)-4-methyl aniline and demonstrated remarkable thermal stability at temperatures appropriate for industrially used gas-phase polymerizations.
Abstract: Sterically demanding NiII α-diimine precatalysts were synthesized utilizing 2,6-bis(diphenylmethyl)-4-methyl aniline. When activated with methylaluminoxane, the catalyst NiBr2(ArN═C(Me)–C(Me)═NAr) (Ar = 2,6 bis(diphenylmethyl)-4-methylbenzene) was highly active, produced well-defined polyethylene at temperatures up to 100 °C (Mw/Mn = 1.09–1.46), and demonstrated remarkable thermal stability at temperatures appropriate for industrially used gas-phase polymerizations (80–100 °C).
TL;DR: In this paper, the authors present the synthesis and characterization of seven triazine-based porous polyimide (TPI) polymer networks and evaluate their applicability as CO2 sorbent materials.
Abstract: Porous organic polymers with polar surfaces are promising materials for capture and storage applications for carbon dioxide. Here, we present the synthesis and characterization of seven triazine-based porous polyimide (TPI) polymer networks and evaluate their applicability as CO2 sorbent materials. The TPIs were synthesized in good yields by a condensation reaction of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and the respective dianhydride building blocks in m-cresol. The resulting TPI polymer networks exhibited high chemical and thermal stability under air (up to 450 °C). Argon sorption isotherms demonstrated that specific BET equivalent surface areas up to 809 m2 g–1 (TPI-1) were reached. The characterization of the pore structure revealed mainly micropores with pore diameters ranging from 0.4 to 3 nm. The highest uptake values for CO2 (2.45 mmol g–1) were observed for TPI-1 and TPI-2 at 273 K and 1 bar. The highest binding selectivity (56) for CO2 over N2 at 298 K was observed for TPI-7. The high...
TL;DR: In this paper, the thermal behavior of the fully lithiated nano-silicon electrode in contact with an 1-M LiPF6 in EC/DEC electrolyte is investigated by differential scanning calorimetry (DSC) in the absence and presence of fluoroethylene carbonate (FEC) and vinylene carbonates (VC) electrolyte additives.
TL;DR: In this paper, the shape stability and thermal conductivity of composite phase change material (PCM) with GPNs were investigated for thermal energy storage applications, where the maximum mass percentage of PA absorbed by GNPs was 91.94% without leakage of PA in molten state as proven by dropping point test.
TL;DR: The anisotropic thermal diffusion property observed in hBN/PI films exhibited strong correlation with the orientation of hBN particles estimated using scanning electron micrographs and wide-angle X-ray diffraction, reflecting the effect of the rigid and densely packed PI chains preferentially orienting parallel to the film plane.
Abstract: A series of inorganic/organic composite films exhibiting high thermal stability and high thermal diffusivity was prepared from five different grades of flake-shaped hexagonal boron nitride (hBN) and aromatic polyimides (PIs). Thermal diffusivities along the out-of-plane (D⊥) and in-plane (D//) directions of hBN/PI films were separately measured and analyzed in terms of particle size, shape, concentration, and orientation, as well as molecular structures of rigid and flexible PI matrices. hBN/PI films filled with large flake-shaped particles exhibited a large anisotropy in D⊥ and D// due to the strong in-plane orientation of heat-conducting basal plane of hBN, while smaller anisotropy was observed in composites with small flakes and aggregates which tend to orient less in the in-plane direction during film processing. The anisotropic thermal diffusion property observed in hBN/PI films exhibited strong correlation with the orientation of hBN particles estimated using scanning electron micrographs (SEM) and ...
TL;DR: The low thermal stability of 1-ethyl-3-methylimidazolium acetate has important implications for biomass experiments employing this ionic liquid, and the activation barriers for the S(N)2 nucleophilic substitution mechanisms are in good agreement with the experimentally determined values.
Abstract: The thermal stability of a series of dialkylimidazolium carboxylate ionic liquids has been investigated using a broad range of experimental and computational techniques. Ionic liquids incorporating fluoroalkyl carboxylate anions were found to have profoundly differing thermal stabilities and decomposition mechanisms compared with their non-fluorinated analogues. 1-Ethyl-3-methylimidazolium acetate was observed to largely decompose via an SN2 nucleophilic substitution reaction when under inert gas conditions, predominantly at the imidazolium methyl substituent. The Arrhenius equations for thermal decomposition of 1-ethyl-3-methylimidazolium acetate, and the C2-methylated analogue 1-ethyl-2,3-dimethylimidazolium acetate, were determined from isothermal Thermogravimetric Analysis experiments. The low thermal stability of 1-ethyl-3-methylimidazolium acetate has important implications for biomass experiments employing this ionic liquid. For these two ionic liquids, ion pair and transition state structures were optimised using Density Functional Theory. The activation barriers for the SN2 nucleophilic substitution mechanisms are in good agreement with the experimentally determined values.
TL;DR: In this paper, the authors studied the thermal stability of single layer graphene synthesized by either chemical vapor deposition or mechanical cleavage and found that the defects are initially sp3 type and become vacancy like at higher temperature.
Abstract: The thermal stability in air of graphene synthesized by either chemical vapor deposition or mechanical cleavage is studied. It is found that single layer graphene prepared by both methods starts to show defects at ~500 °C, indicated by the appearance of a disorder-induced Raman D peak. The defects are initially sp3 type and become vacancy like at higher temperature. On the other hand, bilayer graphene shows better thermal stability, and the D peak appears at ~600 °C. These results are quite different from those annealing in vacuum and controlled atmosphere. Raman images show that the defects in chemical vapor deposition graphene are not homogeneous, whereas those in mechanical cleavage graphene are uniformly distributed across the whole sample. The factors that affect the thermal stability of graphene are discussed. Our results could be important for guiding the future electronics process and chemical decoration of graphene. Copyright © 2013 John Wiley & Sons, Ltd.
TL;DR: The grafted cellulosic polymers were subsequently subjected to the evaluation of different physico-chemical properties in order to access their application in everyday life, in a direction toward green environment.
TL;DR: In this article, the authors introduced boron species by impregnation into silica-supported copper catalysts prepared by an ammonia evaporation hydrothermal method and investigated their catalytic activity and thermal stability for hydrogenation of dimethyl oxalate.
TL;DR: In this paper, the preparation of polyethylene terephthalate (PET) based on fibrous membranes and their use as separator in lithium ion battery was performed by an electrospinning method.
TL;DR: Li et al. as mentioned in this paper investigated the structural and thermal stability of sub-micro Li 4 Ti 5 O 12 particles by the density functional theory (DFT) plane-wave pseudopotential technique and experimental method.
TL;DR: In this article, it has been proved that surface adsorption of polymers on cellulose nanocrystal (CN) as compatibilizer, such as hydrophilic polyoxyethylene (PEO), can improve its thermal stability due to the shielding and wrapping of PEO.
Abstract: Impressive mechanical properties and reinforcing capability make cellulose nanocrystal (CN) a promising candidate as biomass nanofiller for the development of polymer-based nanocomposites. With the recent announcement of large-scale CN production, the use of industrial processing techniques for the preparation of CN-reinforced nanocomposites, such as extrusion, is highly required. However, low thermal stability of sulfuric acid-prepared CN limits the processing since most polymeric matrices are processed at temperatures close to 200 °C or above. It has been proved that surface adsorption of polymers on CN as compatibilizer, such as hydrophilic polyoxyethylene (PEO), can improve its thermal stability due to the shielding and wrapping of PEO. However, the weak combination between CN and PEO allows the free movement of surface polymer, which can induce the self-aggregation of CN and microphase separation in composites especially during melt processing. Using carboxylation–amidation reaction, short chains pol...
TL;DR: In this paper, a reduced graphene oxide paper was fabricated by incorporating polydopamine, which showed increased tensile strength and elongation, and higher thermal stability compared to conventional graphene oxide.
TL;DR: In this paper, three microporous polyimides with uniform pore sizes were synthesized via one-pot polycondensation from tetrakis(4-aminophenyl)methane, tris-4-amphenyl)amine and 1,3,5-tris-tricornyl-benzene with pyromellitic dianhydride.
Abstract: Three microporous polyimides, MPI-1, MPI-2, and MPI-3, with uniform pores were synthesized via one-pot polycondensation from tetrakis(4-aminophenyl)methane, tris(4-aminophenyl)amine and 1,3,5-tris(4-aminophenyl)benzene with pyromellitic dianhydride, respectively. The amorphous networks exhibit excellent thermal stability, large BET surface areas up to 1454 m2 g–1, and narrow pore size distribution in the range from 5 to 6 A. Their adsorption–desorption isotherms of CO2 are reversible, and the CO2 uptakes at 273 K and 1 bar are up to 16.8 wt %. Moreover, based on the ratios of initial slopes of isotherms, the CO2/N2 and CO2/CH4 separation factors are as high as 102 and 12, respectively. The above CO2 adsorption and separation properties are attributed to the presence of abundant electron-rich heteroatoms in the polyimide networks and the unifrom ultralmicroporous structures. In addition, for MPI-1, the adsorption capacity of benzene vapor is 119.8 wt %, while the separation factors of benzene over nitrogen...
TL;DR: It is shown by FTIR, TGA that IL partly complexes with the polymer PVdF-HFP and partly remains dispersed in the matrix, and the variation of ionic conductivity with temperature of these gel polymeric membranes follows Arrhenius type thermally activated behavior.
Abstract: PVdF-HFP + IL(1-butyl-3-methylimidazolium tetrafluoroborate; [BMIM][BF4]) polymeric gel membranes containing different amounts of ionic liquid have been synthesized and characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR), differential scanning calorimetry, thermogravimetric analysis (TGA), and complex impedance spectroscopic techniques. Incorporation of IL in PVdF-HFP polymer changes different physicochemical properties such as melting temperature (Tm), thermal stability, structural morphology, amorphicity, and ionic transport. It is shown by FTIR, TGA (also first derivative of TGA, “DTGA”) that IL partly complexes with the polymer PVdF-HFP and partly remains dispersed in the matrix. The ionic conductivity of polymeric gel membranes has been found to increase with increasing concentration of IL and attains a maximum value of 1.6 × 10–2 S·cm–1 for polymer gel membrane containing 90 wt % IL at room temperature. Interestingly, the values of conductivity of memb...
TL;DR: The electrospun nanofibers encapsulating CD-IC of active compounds such as eugenol may be quite useful in the food industry due to the extremely large surface area of nan ofibers along with specific functionality, enhanced thermal stability, and slow release of the active compounds by CD inclusion complexation.
Abstract: Polyvinyl alcohol (PVA) nanofibers encapsulating eugenol (EG)/cyclodextrin (CD) inclusion complexes (IC) (EG/CD-IC) were produced via electrospinning technique in order to achieve high thermal stability and slow release of EG In order to find out the most favorable CD type for the stabilization of EG, three types of native cyclodextrins (α-CD, β-CD, and γ-CD) were used for the formation of EG/CD-IC In the case of PVA/EG/α-CD nanofibers, uncomplexed EG was detected indicating that α-CD is not a proper host for EG/CD-IC formation However, for PVA/EG/β-CD-IC and PVA/EG/γ-CD-IC nanofibers, enhanced durability and high thermal stability for EG were achieved due to the inclusion complexation The electrospun nanofibers encapsulating CD-IC of active compounds such as eugenol may be quite useful in the food industry due to the extremely large surface area of nanofibers along with specific functionality, enhanced thermal stability, and slow release of the active compounds by CD inclusion complexation
TL;DR: These environmentally friendly, biobased hybrid organic aerogels exhibited a series of desirable properties including a high specific compressive strength and compressive failure strain, ultralow density and thermal conductivity, good thermal stability, and moisture resistance, making them potentially useful for a broad range of applications including thermal insulation.
Abstract: Hybrid organic aerogels consisting of polyvinyl alcohol (PVA), cellulose nanofibrils (CNFs), and graphene oxide nanosheets (GONSs) were prepared using an environmentally friendly freeze-drying process. The material properties of these fabricated aerogels were measured and analyzed using various characterization techniques including compression testing, scanning electron microscopy, thermogravimetric (TGA) analysis, Brunauer–Emmet–Teller (BET) surface area analysis, and contact angle measurements. These environmentally friendly, biobased hybrid organic aerogels exhibited a series of desirable properties including a high specific compressive strength and compressive failure strain, ultralow density and thermal conductivity, good thermal stability, and moisture resistance, making them potentially useful for a broad range of applications including thermal insulation.
TL;DR: The thermal stability of the nanostructured emitters and their optical properties before and after annealing are tested, observing no degradation even after 144 h (6 days) at 900 °C, which demonstrates the suitability of these selective emitters for high-temperature applications.
Abstract: We present the results of extensive characterization of selective emitters at high temperatures, including thermal emission measurements and thermal stability testing at 1000°C for 1h and 900°C for up to 144h. The selective emitters were fabricated as 2D photonic crystals (PhCs) on polycrystalline tantalum (Ta), targeting large-area applications in solid-state heat-to-electricity conversion. We characterized spectral emission as a function of temperature, observing very good selectivity of the emission as compared to flat Ta, with the emission of the PhC approaching the blackbody limit below the target cut-off wavelength of 2 μm, and a steep cut-off to low emission at longer wavelengths. In addition, we study the use of a thin, conformal layer (20 nm) of HfO2 deposited by atomic layer deposition (ALD) as a surface protective coating, and confirm experimentally that it acts as a diffusion inhibitor and thermal barrier coating, and prevents the formation of Ta carbide on the surface. Furthermore, we tested the thermal stability of the nanostructured emitters and their optical properties before and after annealing, observing no degradation even after 144h (6 days) at 900°C, which demonstrates the suitability of these selective emitters for high-temperature applications.
TL;DR: In this article, a facile microwave synthesis through polymerization reaction between cyanuric chloride(C 3 N 3 Cl 3 ) and sodium azide (NaN 3 ) using acetonitrile (ACN) as solvent, and the prepared samples were investigated by XRD, FTIR, XPS, SEM, TEM, UV-Vis, PL, TGA and BET.