Showing papers on "Thermal decomposition published in 2021"

Ionic liquid facilitated melting of the metal-organic framework ZIF-8.

Abstract: Hybrid glasses from melt-quenched metal-organic frameworks (MOFs) have been emerging as a new class of materials, which combine the functional properties of crystalline MOFs with the processability of glasses. However, only a handful of the crystalline MOFs are meltable. Porosity and metal-linker interaction strength have both been identified as crucial parameters in the trade-off between thermal decomposition of the organic linker and, more desirably, melting. For example, the inability of the prototypical zeolitic imidazolate framework (ZIF) ZIF-8 to melt, is ascribed to the instability of the organic linker upon dissociation from the metal center. Here, we demonstrate that the incorporation of an ionic liquid (IL) into the porous interior of ZIF-8 provides a means to reduce its melting temperature to below its thermal decomposition temperature. Our structural studies show that the prevention of decomposition, and successful melting, is due to the IL interactions stabilizing the rapidly dissociating ZIF-8 linkers upon heating. This understanding may act as a general guide for extending the range of meltable MOF materials and, hence, the chemical and structural variety of MOF-derived glasses. The variety of hybrid glasses from metal-organic frameworks (MOFs) has remained strongly limited to only a handful of compounds. Here, the authors introduce a route to melt highly porous and non-meltable MOFs using ionic liquids in order to extend the range of MOF glasses.

Thermal Stability of Ionic Liquids: Current Status and Prospects for Future Development

Abstract: Ionic liquids (ILs) are the safest solvent in various high-temperature applications due to their non-flammable properties. In order to obtain their thermal stability properties, thermogravimetric analysis (TGA) is extensively used to analyze the kinetics of the thermal decomposition process. This review summarizes the different kinetics analysis methods and finds the isoconversional methods are superior to the Arrhenius methods in calculating the activation energy, and two tools—the compensation effect and master plots—are suggested for the calculation of the pre-exponential factor. With both parameters, the maximum operating temperature (MOT) can be calculated to predict the thermal stability in long-term runnings. The collection of thermal stability data of ILs with divergent cations and anions shows the structure of cations such as alkyl side chains, functional groups, and alkyl substituents will affect the thermal stability, but their influence is less than that of anions. To develop ILs with superior thermal stability, dicationic ILs (DILs) are recommended, and typically, [C4(MIM)2][NTf2]2 has a decomposition temperature as high as 468.1 °C. For the convenience of application, thermal stability on the decomposition temperature and thermal decomposition activation energy of 130 ILs are summarized at the end of this manuscript.

Effect of stabilizers and nitrogen content on thermal properties of nitrocellulose granules

Abstract: The granules containing nitrogen of various content (12.2–13.3%) and stabilizers (centralite I, centralite II, akardite II, triphenylamine) were obtained in laboratory scale, and the study of their physicochemical and thermal properties was conducted. It has been observed that the helium density of granules depends on the degree of gelling of nitrocellulose by the stabilizer as well as the lack of effect of the stabilizer type on the heat of combustion value. In turn, the heat of combustion depends on the content of nitrogen in nitrocellulose. Granules of 13.3% N nitrocellulose were characterized by a more rapidly developing thermal decomposition than the granules containing 12.2 and 12.9% N nitrocellulose. The maximum temperature of decomposition shifts toward higher temperatures (from 207.6 to 209.8 °C) with decreasing nitrogen content in nitrocellulose for granules containing triphenylamine as a stabilizer. All values of heat generation rate obtained for granules with triphenylamine were lower than the respective rates for granules with centralite I. Thermal properties and chemical stability of granules containing triphenylamine have better properties, when compared to other examined stabilizers. On the basis of differential scanning calorimetry and thermogravimetry, kinetic parameters were calculated by means of Ozawa–Flynn–Wall analysis. The effect of stabilizers and nitrogen content on kinetic parameters was determined. The kinetic model of thermal decomposition of granules was adjusted—the best fit was nth-order reaction with autocatalysis. The activation energy of thermal decomposition process according to the adopted chemical reaction model increases from 190 to 239 kJ mol−1 with increasing nitrogen content in the granulate.

Enhanced Thermal Conductivity of Epoxy Composites Filled with Al 2 O 3 /Boron Nitride Hybrids for Underfill Encapsulation Materials.

Abstract: In this study, a thermal conductivity of 0.22 W·m−1·K−1 was obtained for pristine epoxy (EP), and the impact of a hybrid filler composed of two-dimensional (2D) flake-like boron nitride (BN) and zero-dimensional (0D) spherical micro-sized aluminum oxide (Al2O3) on the thermal conductivity of epoxy resin was investigated. With 80 wt.% hybrid Al2O3–BN filler contents, the thermal conductivity of the EP composite reached 1.72 W·m−1·K−1, increasing approximately 7.8-fold with respect to the pure epoxy matrix. Furthermore, different important properties for the application were analyzed, such as Fourier-transform infrared (FTIR) spectra, viscosity, morphology, coefficient of thermal expansion (CTE), glass transition temperature (Tg), decomposition temperature (Td), dielectric properties, and thermal infrared images. The obtained thermal performance is suitable for specific electronic applications such as flip-chip underfill packaging.

Green synthesis of CuO nanoparticles using Malva sylvestris leaf extract with different copper precursors and their effect on nitrocellulose thermal behavior

Abstract: In this work, we have synthesized copper oxide nanoparticles (CuO NPs) by a precipitation method using leaf extract of Malva sylvestris as a stabilizing agent and three different copper precursors. The obtained CuO NPs have been characterized in detail by X-ray diffraction, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The as-prepared CuO NPs present the same pure chemical composition and belong to a monoclinic crystalline phase, with a spherical shape and crystallite diameter in the range of 19–26 nm, according to their precursors. Based on the differential scanning calorimetry (DSC) analyses performed at different heating rates, the thermal behavior of pure nitrocellulose (NC) and NC-CuO NPs composites has been investigated using four integral isoconversional kinetic methods. The obtained results show that, whatever the precursor, CuO NPs could be safely used as a catalyst for NC. Moreover, the added nanocatalysts could reduce the activation energy and slightly decrease the peak temperature. Finally, the thermal decomposition process of both NC and NC-CuO composites determined with Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa) models, respectively, is classified as R2, contracting cylinder $$g \, \left( \alpha \right) \, = 1 - (1 - \alpha )^{\frac{1}{2}}$$ , whereas that of Trache–Abdelaziz–Siwani integral model is ascribed to F1/3 and F3/4 chemical reaction $$g \, \left( \alpha \right) \, = 1 - (1 - \alpha )^{\frac{2}{3}}$$ .

Morphology-dependent catalytic activity of Fe2O3 and its graphene-based nanocomposites on the thermal decomposition of AP

Abstract: The spherical, hollow and tubular Fe2O3 (s, h and t) and their graphene-based nanocomposites rGO-Fe2O3 (s, h and t) were fabricated using the facile solvothermal methods. The morphologies and compositions of the as-synthesized Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites were systematically characterized by SEM, TEM, XRD, FTIR and XPS methods. Then, the effect of the catalytic performance of Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites on the thermal decomposition of ammonium perchlorate (AP) were studied by DSC method. The DSC results showed that all of the Fe2O3 (s, h and t) and rGO-Fe2O3 (s, h and t) nanocomposites can effectively promote the thermal decomposition of AP. Besides, rGO-Fe2O3(s) nanocomposite has the best catalytic performance, and the high-temperature decomposition exothermic peak of AP was significantly reduced after its mixing with rGO-Fe2O3 (s) nanocomposite. It can be seen that the effects of Fe2O3 on AP decomposition is mainly reflected in the high temperature process, while the effects of rGO-Fe2O3 (s) on AP decomposition is reflected in both high and low temperature stages, and the effect on the high temperature stage is more significant. The excellent catalytic performance of rGO-Fe2O3 (s) nanocomposite can be attributed to the in-situ growth of Fe2O3 on the surface of rGO, which contributes to the low temperature decomposition process of AP.

Thermal Decomposition of Anionic, Zwitterionic, and Cationic Polyfluoroalkyl Substances in Aqueous Film-Forming Foams.

Abstract: In this study, we investigated thermal decomposition mechanisms of cationic, zwitterionic, and anionic polyfluoroalkyl substances, including those present in aqueous film-forming foam (AFFF) samples. We present novel evidence that polyfluoroalkyl substances gave quantitative yields of perfluoroalkyl substances of different chain lengths during thermal treatment. The results support a radical-mediated transformation mechanism involving random-chain scission and end-chain scission, leading to the formation of perfluoroalkyl carboxylic acids such as perfluorooctanoic acid (PFOA) from certain polyfluoroalkyl amides and sulfonamides. Our results also support a direct thermal decomposition mechanism (chain stripping) on the nonfluorinated moiety of polyfluoroalkyl sulfonamides, resulting in the formation of perfluorooctanesulfonic acid (PFOS) and other structurally related polyfluoroalkyl compounds. Thermal decomposition of 8:2 fluorotelomer sulfonate occurred through end-chain scission and recombination reactions, successively yielding PFOS. All of the studied polyfluoroalkyl substances began to degrade at 200-300 °C, exhibiting near-complete decomposition at ≥400 °C. Using a high-resolution parent ion search method, we demonstrated for the first time that low-temperature thermal treatments of AFFF samples led to the generation of anionic fluoroalkyl substances, including perfluoroheptanesulfonamide, 8:2 fluorotelomer sulfonic acid, N-methyl perfluorooctane sulfonamide, and a previously unreported compound N-2-propenyl-perfluorohexylsulfonamide. This study provides key insights into the fate of polyfluoroalkyl substances in thermal processes.

Thermal decomposition and combustion characteristics of Al/AP/HTPB propellant

Abstract: Aluminum(Al)/ammonium perchlorate(AP)/hydroxyl-terminated polybutadiene (HTPB) propellant is the most widely used propulsion system currently. Its ignition and combustion processes are fairly complex and need to be better understood. In this study, the thermal decomposition, ignition, and combustion properties of an Al/AP/HTPB propellant were investigated using a thermogravimetry–differential scanning calorimetry and a laser ignition testing system. The morphology and size distribution of the condensed combustion products (CCPs) were analyzed using a laser particle size analyzer and scanning electron microscopy. Results showed that the thermal decomposition process of the propellant consisted of three stages. The first stage (100–430 °C) was a major mass loss stage and exhibited typical features of AP decomposition. The second stage (430–630 °C) was mainly accompanied by the decomposition of remaining HTPB as well as slight oxidation of Al particles. In the third stage, further oxidation of Al particles resulted in a small mass increase. Due to the continuous emission problem, only a few combustion intermediates were identified in the combustion emission spectrum curves. The propellant combustion process could be roughly divided into three stages, and the flame development stage lasted longer than the flame decline stage. As the pressure increased, the propellant ignition delay time decreased and the burning rate increased significantly. The effect of pressure on ignition delay was more pronounced at low pressures. The CCPs consisted of three types. The oxidation of Al particles in the propellant followed the diffusion reaction mechanism. Agglomerates appeared in several different morphologies and had relatively low combustion efficiency under experimental conditions. A 2-D pocket-like structure was observed on the propellant surface.

Enhanced thermal decomposition, laser ignition and combustion properties of NC/Al/RDX composite fibers fabricated by electrospinning

Abstract: Nano aluminum (Al) has always been the research hotspot in the field of energetic materials because of its high energy density and combustion temperature, and has been considered to be a promising fuel to enhance the energy release of various propulsive systems. In this work, nanocomposite fibers were fabricated by electrospinning technology, in which nano Al and recrystallized cyclotrimethylene trinitramine (RDX) particle were integrated with nitrocellulose (NC) fibers. The agglomeration of nano Al particles in fibers is significantly inhibited. The morphology and chemical components of NC/Al, NC/RDX, and NC/Al/RDX composite fibers were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET). The thermal analysis shows that nano NC fibers have lower thermal decomposition temperature (202.1 °C) and apparent activation energy (149.3 kJ mol−1) than raw NC (208.2 °C and 218.5 kJ mol−1), and NC/Al/RDX exhibits improved thermal decomposition properties compared with NC/RDX and NC/Al. The laser ignition experiments suggest that the uniformly dispersed nano Al particles could obviously promote the combustion and shorten ignition delay time. RDX may delay ignition due to its high decomposition temperature, but can significantly enhance the combustion properties of NC/Al/RDX fibers. The combustion propagation velocity of composite fibers is obvious higher than that of its physical mixture. The condensed combustion product is mainly spherical aluminum oxide (Al2O3) with a median diameter of about 180 nm. The reason can be attributed to the intimacy between fuel and oxidizer in composite fibers, which enhances heat and mass transfer. Aluminum with high enthalpy and high combustion temperature is an essential ingredient for improving combustion performance of propellants. In this work, NC based composite fibers containing nano Al were fabricated by electrospinning, which significantly improved laser ignition and combustion performance. The electrospinning technique would also be extended to other composite preparation for broader application beyond the energy materials.

Graphene Oxide/Fe 2 O 3 Nanocomposite as an Efficient Catalyst for Thermal Decomposition of Ammonium Perchlorate via the Vacuum-Freeze-Drying Method.

Abstract: The combination of graphene oxide (GO) and iron oxide (Fe2O3) may induce property enforcement and application extension. Herein, GO/Fe2O3 nanocomposites were synthesized via the vacuum-freeze-drying method and used for the thermal decomposition of ammonium perchlorate (AP). A series of characterization techniques were applied to elucidate the as-obtained nanomaterial's physicochemical properties. These results show that the treated GO is consistent with the pristine GO after the freeze-drying treatment. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses show that iron oxide nanoparticles are anchored on and between the GO sheets. The catalytical effect investigation on AP with different Fe2O3: GO ratios indicates that the high-temperature decomposition temperature of AP could be decreased by a temperature as high as 77 °C compared to pure AP accompanied by 3 wt % GO/Fe2O3 nanocomposite which proves the high catalytic performance of the nanocomposites. The first-principles calculation was employed to elaborate the synergistic effect, and the findings demonstrate that the presence of graphene in the catalyst can enhance the catalytic effect via reducing the activation energy barrier by ∼17% in the reaction of AP thermal decomposition.

Co-pyrolysis of microalgae and municipal solid waste: A thermogravimetric study to discern synergy during co-pyrolysis process

Abstract: Synergism during the co-pyrolysis of microalgae (CC), municipal solid waste (MSW), and their blends (CC/MSW) (w/w %), 25/75 (CM-1), 50/50 (CM-2), and 75/25 (CM-3), was evaluated based on thermal decomposition pattern, evolved gases, rate and extent of thermal decomposition, and kinetic parameters. Three stages of devolatilization attributed to dehydration, devolatilization of major structural compounds of biomass and decomposition of solid residues were noticed during the co-pyrolysis of biomass samples. The main pyrolysis stages for CC, MSW, CM-1, CM-2 and CM-3 were 175–520, 151-523, 164-504,168-510, 160–501 °C, respectively. Microalgae, CC, appeared to be thermally resistant, while MSW is noticed to be thermally sensitive. The kinetics analysis was studied by deconvoluting the DTG profile into independent stages, followed by application of isoconversional methods to evaluate the activation energy and the pre-exponential factor. Furthermore, the reaction mechanism of each stage was determined by using the master plot method. The semi-quantitative method was used to evaluate the evolved gases and CO, CO2 and H2 were noticed to be the dominant gas species. The obtained thermal and kinetic data for co-pyrolysis of microalgae and MSW can serve are basis for scale-up and reactor design of pyrolysis process for similar kind of waste streams.

Dielectric barrier discharge and radio-frequency plasma effect on structural properties of starches with different amylose content

Abstract: The effect of the dielectric barrier discharge atmospheric (DBD) and radio-frequency (RF) cold plasma treatment on the morphology, helical order, and structural stability of starches with different amylose content (30, 50, & 70%) was investigated. The cavities formed after RF plasma treatment allowed the active species to modify the internal structure of the granule, probably reaching its center and expanding to the periphery, where the amorphous regions were damaged and gradually removed by the treatment, increasing the amylose helix order and thermal stability of starch molecule as suggested by the SEM, FTIR, DSC, and TGA analysis. In contrast, DBD treatment promoted a thicker coating deposition and HMDSO functional groups inclusion, which increased both the granular interaction and the decomposition temperature. Overall, active species of HMDSO plasma generated in RF and DBD reactors modified mainly the amylose chains in a distinctive way, favoring the ordering or stability of starch molecules, respectively. These findings could be useful when looking for potential applications in the food industry or in other fields like semiconductors. Industrial relevance Atmospheric pressure dielectric barrier discharge (DBD) and radio-frequency (RF) plasma are sustainable and quick methods to modify the structural properties of corn starch. After short-time treatments (10 min) both reactors change the granule surface (HMDSO coating and holes), which resulted in structural changes at different extent, such as increase of helical order and high thermal stability. These results showed that the DBD and RF treatments are suitable methods to obtain starches with high resistance to gelatinization (≈91 °C), especially those with high amylose content; however, due to their distinctive properties, they could have different end uses. DBD treated starch with HMDSO chemical group incorporation could be used in the paper, packaging, and electronic industry. Although HMDSO plasma is not yet approved for food industry, the results of FTIR confirmed that RF plasma treatment does not incorporate new elements in the starch molecules but only promoted interactions between them. Therefore, HDMSO plasma treatment could be considered as a safe and chemical-residue free technique useful to modify starches, which can be explored in food matrices development. Furthermore, they could be employed in an industrial food process that involves the use of high temperature.

A synergistic strategy for fabricating an ultralight and thermal insulating aramid nanofiber/polyimide aerogel

Abstract: Shortcomings of the otherwise very desirable ultralight nanocomposite aerogels urgently need to be solved, such as the poor compatibility of different components, low thermal decomposition temperature, and low production. Herein, a synergistic strategy using ultrahigh-speed homogenizing, freeze drying, and high-temperature imidization methods was proposed to fabricate an ultralight aramid nanofiber/polyimide (ANF/PI) composite aerogel from aramid nanofibers and water-soluble polyamide acid salt, which possess similar chemical structures. The polyamide acid salt greatly inhibited the aggregation of aramid nanofibers without any additional dispersant due to hydrogen bond interactions. The uniform aramid nanofiber skeleton decreased the shrinkage of the low concentration of polyamide acid salt during imidization. This synergistic effect contributed to the porous structure and ultralow density (5.18 mg cm−3) of the ANF/PI nanocomposite aerogel. The aerogel showed excellent elasticity, fatigue resistance (1000 compressive cycles), high thermal decomposition temperature (470 °C), and ultralow thermal conductivity (28.6 ± 0.53 mW (m K)−1). Therefore, it has excellent application prospects in various fields, including heat management, thermal insulation, lightweight construction, water treatment, and vibration or shock energy damping, especially in harsh environments.