Thermal Reaction Process Research Articles

Detailed Microscopic Reaction Mechanism during the Combustion Process of HAN-Based Propellant.

Hydroxylamine nitrate (HAN)-based propellants, renowned for their high energy efficiency and nontoxic properties, are considered candidates for next-generation green propellants. The ab initio molecular dynamics (AIMD) method was used to theoretically study the thermal decomposition reaction process of the HAN aqueous solution and the system mixed by HAN and fuel methanol/ethylammonium nitrate. The principal reaction pathways of HAN-based propellants are delineated by scrutinizing AIMD trajectory results. HAN-based propellants transition from an ionic state to a neutral state during combustion, and the thermal decomposition of HAN begins with the breakdown of HNO3 itself into ·NO2 radicals and ·OH radicals. Although the thermal decomposition reaction of HAN is complex and a large number of intermediates are produced, only a few key free radicals and small molecules drive the subsequent reaction forward. The thermal decomposition of the fuel lags behind that of HAN in the combustion process of HAN-based propellants. The oxidants such as ·NO2 produced by HAN decomposition react with fuel molecules, and the free radicals produced by the decomposition of oxidative products such as HONO further act as oxidants to react with fuel molecules again.

Metal-organic framework confined preparation of hydrophobic nickel/carbon nanofibers for lightweight and enhanced microwave absorption

The use of a metal-organic framework (MOF) confinement strategy to achieve controllable growth and even allocation of magnetic metal nanoparticles (NPs) in carbon nanofibers (CNFs) can significantly improve the microwave absorption performance of absorbers. Herein, we constructed Ni-MOF in the spinning solution and prepared Ni/CNFs with confined structures using electrospinning combined with carbon thermal reduction. The microstructure of Ni/CNFs was regulated by adjusting the amount of organic ligands added. Ni NPs with single domain size and uniform allocation could optimize impedance matching and enhance electromagnetic synergistic effects, which was beneficial for enhancing microwave absorption performance. When the additional amount of organic ligands was 4 wt%, the absorber reached the optimal microwave absorption performance as the filling ratio was only 3 wt%, the minimum reflection loss (RL) reached –24.9 dB at 13.6 GHz when the thickness was 2.0 mm, and the effective bandwidth (EBW) attained 5.22 GHz. In addition, the excellent hydrophobic performance of nanofibers (NFs) endowed them with potential self-cleaning functions. In addition, to verify the practical application value of the prepared samples in radar stealth technology, we used computer simulation technology (CST) to simulate the samples. Therefore, this work provides a new approach for the controllable preparation of novel magnetic metal/carbon fiber-based absorbers, and also provides a model reference for the controllable growth of magnetic metal particles in the carbon thermal reduction reaction process.

The influence of Nano-composite metal oxides on the thermal decomposition performance of RDX

Abstract In order to investigate the effect of nano-composite metal oxides on the thermal decomposition performance of hexogen (RDX), this study prepared nano nickel-iron (NFO), nickel-cobalt (NCO), and nickel-iron-cobalt (NFCO) composite oxides by liquid-phase co-precipitation method. The precursor of Prussian blue analogs was synthesized and then calcined in air at 600°C. The addition of nano nickel-iron (NFO), nickel-cobalt (NCO), and nickel-iron-cobalt (NFCO) composite oxides to RDX has a significant impact on its thermal decomposition process. The peak exothermic temperatures were delayed by 8.4°C, 8.5°C, and 8.3°C, respectively, after adding the nano-composite metal oxides, and the heat release also increased to a certain extent. Among them, the addition of NCO nano-composite metal oxides had the greatest impact on the exothermic peak temperature of RDX, while the addition of NFCO nano-composite metal oxides resulted in the largest increase in heat release. This indicates that the addition of NFO, NCO, and NFCO to RDX altered the thermal decomposition reaction process to some extent.

Insight into the formation mechanism of higher-molecular-weight gases during the spontaneous combustion of coal

Higher-molecular-weight gases (HMWGs), which have not received much attention, also contain invaluable information about the coal spontaneous combustion (CSC) development process. In order to investigate the formation mechanism of HMWG, the emission behaviors of HMWG from coal oxidation and pyrolysis experiments were compared, and FTIR and ESR were used to analyze the microstructural evolution of the coal sample. The results show that the volume fractions of most HMWGs increased regularly with increasing temperature. The contribution of the pyrolysis process to the yield of most hydrocarbon HMWGs was close to 100 %, while it was below 89 % for C4 ∼ C6 n-alkanes and benzene and less than 10 % for acetaldehyde and acetone. The decomposition of active structures could produce free radicals, the concentration of which increases with increasing temperature. The formation mechanism of HMWGs was proposed based on the experimental results: HMWGs came from both the thermal reaction and the coal-oxygen reaction process. The thermal reaction process would release the majority of hydrocarbon HMWGs from room temperature. Some active structures began participating in the coal-oxygen reactions to produce oxygen-containing HMWGs at 90 ℃. After reaching 170 ℃, the coal-oxygen reactions were further intensified to release minority n-alkanes, benzene, and small amounts of C4 olefins.

Catalytic role of various clay minerals during the thermal reaction process with oxidized and pyrolyzed oils

Catalytic role of various clay minerals during the thermal reaction process with oxidized and pyrolyzed oils

In‐Situ Growth of MgO@rGO Core‐Shell Structure via CO2 Thermal Reaction for Enhanced Photocatalytic Performance

AbstractDegradation of organic pollutants in wastewater is crucial for global environmental health. Semiconductor‐based photocatalytic technologies have received widespread attention due to their ability to directly utilize solar energy, produce no secondary pollution, and offer long‐lasting functionality. However, current photocatalyst preparation technologies face issues such as complex manufacturing processes, low efficiency, and the need for various additives. Therefore, this work proposes a simple and eco‐friendly method to in‐situ growth of reduced graphene oxide (rGO) onto magnesium oxide (MgO), forming a MgO@rGO core‐shell structured photocatalyst through CO2 thermal reaction process. After systematic study, the incorporation of rGO onto MgO core greatly extends the light absorption range from ultraviolet (UV) to visible wavelength, enabling substantially enhanced light capture and photoexcited carriers. Additionally, the core‐shell heterojunction with a built‐in electric field at the interface between MgO and rGO facilitates distinctly the separation and migration of the photogenerated charges. This structure‐induced synergistic effect boosts the photocatalytic performance of MgO@rGO by a factor of 1.7, 4.1, 41.8, and 6.4, compared with MgO (stripped), MgO (pure), rGO, and commercially used TiO2, respectively. This work provides a simple and effective strategy for designing advanced functional nanocomposites to address environmental problems.

Complete Prevention of Bubbles in a PDMS-Based Digital PCR Chip with a Multifunction Cavity.

In a chamber-based digital PCR (dPCR) chip fabricated with polydimethylsiloxane (PDMS), bubble generation in the chambers at high temperatures is a critical issue. Here, we found that the main reason for bubble formation in PDMS chips is the too-high saturated vapor pressure of water at an elevated temperature. The bubbles should be completely prevented by reducing the initial pressure of the system to under 13.6 kPa to eliminate the effects of increased-pressure water vapor. Then, a cavity was designed and fabricated above the PCR reaction layer, and Parylene C was used as a shell covering the chip. The cavity was used for the negative generator in sample loading, PDMS degassing, PCR solution degassing in the digitization process and water storage in the thermal reaction process. The analysis was confirmed and finally achieved a desirable bubble-free, fast-digitization, valve-free and no-tubing connection dPCR.

Transformation simulation of N-containing functional groups in coal pyrolysis and combustion processes by using ReaxFF

In order to explore the formation mechanism of NOx precursors and NOx during coal pyrolysis and combustion, four typical N-containing functional groups in coal, including pyridine-N (N-6), pyrrole-N (N-5), protonation-N (N-Q) and oxidized pyridine-N (N-X), were taken for study. Firstly, the thermal reaction processes of N-containing functional groups under different conditions were simulated via ReaxFF, then the transformation processes of N-containing functional groups to NOx precursors were obtained via Ovito, finally the reaction networks of NOx precursors and NOx were built via ReacNetGenerator. According to the study results, we speculated that the transformation process of N-containing functional groups to NOx precursors involved 4 steps, including the ring opening of N-6 and N-5, the shift of N atom to the edge, the shortening of carbon chain and the formation of NOx precursors. Besides, we found that the increasing of temperature greatly promoted the transformation processes of NO to HNO and HO2N.

A real-time early warning method for electric vehicle fast charging safety based on multiple time scales

Abstract This paper puts forward the support technology of fast charging supply and demand matching in charging stations and analyzes the common large-capacity electrochemical energy storage technical parameters in charging stations. For the safety of electric vehicle charging, the thermal reaction and thermal runaway processes of power batteries are introduced. Design the electric vehicle charging state monitoring and safety warning methods, and select the multi-timescale ARIMA algorithm to build the electric vehicle charging safety warning model. The sliding window method is used to process the residual mean and residual standard deviation of electric vehicle charging data to improve prediction data and decrease the chance of misjudging pre- and alarms. Combined with the evaluation standard of the safety early warning model, set reasonable pre- and alarm thresholds using the residual analysis method. The safety warning model designed in this paper is verified by different charging fault warnings. Different charging fault warning examples show that the ARIMA-based charging safety early warning model proposed in this paper can be good for the charging facility’s output voltage, output current, and charging module temperature faults for early warning to ensure that the warning is carried out before the alarm of the actual fault information, to protect the charging safety of electric vehicles.

Identifying Thermal Decomposition Mechanisms of the Solid Electrolyte Interphase with in-Situ Gas Analysis of Lithium-Ion Batteries

The global shift away from fossil fuels has generated an unprecedented demand for electric vehicles and a steady increase in the prevalence of lithium-ion batteries. Additionally, increases in the energy density of storage technologies has led to a corresponding increase in safety concerns regarding thermal runaway reactions. The components of a lithium-ion battery can self-react when exposed to an external heat source, which can cause a thermal runaway reaction process and large-scale fires of the cell. The initial reactions in this process involve the decomposition of the Solid Electrolyte Interphase (SEI) breakdown and conductive salt. The underlaying mechanisms behind these reactions are unclear; in-depth investigations are needed in order to develop a detailed understanding of the thermal runaway process and guide the development of strategies to mitigate the safety hazards posed by these battery systems. In the past, differential/online electrochemical mass spectrometry (DEMS/OEMS) was utilized to analyze the buildup of the SEI as well as decomposition due to overcharge. Our new methodology of high temperature (HT-)OEMS, with a maximum temperature of 132 °C, can simulate heating events with thermal ramps on an in-situ test cell battery. These measurements reveal information regarding reaction product gases and cell voltage drop during first formation and thermal stress tests, and provide novel insight into the electrochemical and thermodynamic phenomena during thermal abuse of lithium-ion batteries.In this study, we use (HT-)OEMS to investigate the behavior of lithium-ion cells with varied additive concentrations and formation currents. This new methodology allowed us to clearly determine that both of the testing parameters impact the formation gas evolution and thus influence the SEI-composition. Systems with high formation rates, as well as with lower concentrations of additives, exhibited an increase in the fraction of CO product gases, which can be explained with a higher presence of lithium alkoxides in the SEI. Additionally, the evolution of H2, CO2 and POF3 gases were observed at temperatures around 80 °C for cells during the thermal stress test after formation. These results allow us to establish a correlation between the thermal conductive salt decomposition and the formation of the SEI-components Li2CO3 and (CH2OLi)2.The identification of the underlying degradation mechanisms and process correlations via (HT-)OEMS provides a novel and important understanding of the phenomena that give rise to thermal runaway in lithium-ion batteries. This cell chemistry-based insight can be used to guide future prevention-focused safety assessments. Figure 1

Electrochemical CaC2‐Mediated Conversion of Biochar to C2H2: High Carbon Efficiency and Low Contamination

AbstractThe carbon to CaC2 route is promising to provide a sustainable elementary unit, C2H2, for the organic synthesis industry, but the traditional thermal reaction process suffers from low carbon efficiency, harmful gas contamination, high temperature operation, and risky CO management. We herein report a high carbon efficiency (ca. 100 %) conversion of biochar to C2H2 through an electrolytic synthesis of solid CaC2 in molten CaCl2/KCl/CaO at 973 K. The main reactions are carbon reduction to CaC2 at the solid carbon cathode and oxygen evolution at an inert anode. Meanwhile, the electrolysis removes S and P from the solid cathode, avoiding the formation of CaS and Ca3P2 in CaC2 and consequently eliminating H2S and PH3 contamination in the finally produced C2H2.

Electrochemical CaC2 -Mediated Conversion of Biochar to C2 H2 : High Carbon Efficiency and Low Contamination.

The carbon to CaC2 route is promising to provide a sustainable elementary unit, C2 H2 , for the organic synthesis industry, but the traditional thermal reaction process suffers from low carbon efficiency, harmful gas contamination, high temperature operation, and risky CO management. We herein report a high carbon efficiency (ca. 100 %) conversion of biochar to C2 H2 through an electrolytic synthesis of solid CaC2 in molten CaCl2 /KCl/CaO at 973 K. The main reactions are carbon reduction to CaC2 at the solid carbon cathode and oxygen evolution at an inert anode. Meanwhile, the electrolysis removes S and P from the solid cathode, avoiding the formation of CaS and Ca3 P2 in CaC2 and consequently eliminating H2 S and PH3 contamination in the finally produced C2 H2 .

Advances in thermal‐related analysis techniques for solid‐state lithium batteries

AbstractSolid‐state lithium batteries (SSLBs) have been broadly accepted as a promising candidate for the next generation lithium‐ion batteries (LIBs) with high energy density, long duration, and high safety. The intrinsic non‐flammable nature and electrochemical/thermal/mechanical stability of solid electrolytes are expected to fundamentally solve the safety problems of conventional LIBs. However, thermal degradation and thermal runaway could also happen in SSLBs. For example, the large interfacial resistance between solid electrolytes and electrodes could aggravate the joule heat generation; the anisotropic thermal diffusion could trigger the uneven temperature distribution and formation of hotspots further leading to lithium dendrite growth. Considerable research efforts have been devoted to exploring solid electrolytes with outstanding performance and harmonizing interfacial incompatibility in the past decades. There have been fewer comprehensive reports investigating the thermal reaction process, thermal degradation, and thermal runaway of SSLBs. This review seeks to highlight advanced thermal‐related analysis techniques for SSLBs, by focusing particularly on multiscale and multidimensional thermal‐related characterization, thermal monitoring techniques such as sensors, thermal experimental techniques imitating the abuse operating condition, and thermal‐related advanced simulations. Insightful perspectives are proposed to bridge fundamental studies to technological relevance for better understanding and performance optimization of SSLBs.image

Study on the Mechanism of Antioxidants Affecting the Spontaneous Combustion Oxidation of Coal.

In this paper, in order to further reveal the mechanism of oxidation inhibitors inhibiting coal spontaneous combustion, the mechanism of typical antioxidants butylated hydroxytoluene (BHT) and vitamin C (VC) inhibiting coal low-temperature oxidation was studied by thermogravimetry (TG), Fourier transform infrared spectroscopy, and quantum chemical simulation. This paper studies the thermal reaction process of coal by TG. The experimental results showed that the characteristic temperature of coal samples increased significantly after adding an antioxidant, and the maximum exothermic peak temperature of coal samples with BHT was 36 °C higher than that of raw coal, and the dehydration activation energy was 1.22 times higher than that of raw coal. Then, through the Fourier transform infrared spectroscopy experiment, it is concluded that antioxidants have a great influence on the content of active groups in the process of oxidative heating of coal, and the hydroxyl structure changes in coal are the most obvious. After BHT and VC were added to the coal, the hydroxyl content in the coal was reduced by 5.90 and 4.20%, respectively. Finally, the molecular models of antioxidants and oxygen-containing functional groups (RCOOH, R-CHO, and R-CH2-CH2-OH) in coal are constructed using quantum chemical theory, and their frontier orbitals and thermodynamic data are calculated according to density functional theory. The reaction mechanisms of antioxidants reacting with hydroxyl groups and with hydroxyl groups and oxygen-containing functional groups were comparatively analyzed. The results of orbital gap analysis indicated that antioxidants react more easily with hydroxyl groups than with oxygen-containing functional groups, and the order of their reaction activity is BHT > VC > R-CH2-CH2-OH > R-CHO > RCOOH. Compared to reactions containing oxygen-containing functional groups and hydroxyl groups, the thermodynamic reaction of hydroxyl groups and antioxidants is more active. Because antioxidants preferentially react with hydroxyl radicals and inhibit part of the chain cycle reaction during spontaneous combustion of coal, antioxidants play a good inhibitory role in spontaneous combustion of coal.

Study on the thermal decomposition reaction process and kinetics of SF6 and tungsten

The thermal reaction of SF6 with tungsten powder was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), combined with the characterization of solid decomposition products of SF6 and tungsten by SEM, EDS, XPS and Raman. Based on above experiments, a two-stage decomposition process of SF6 with tungsten was proposed: the first stage is the surface vulcanization reaction W+SF6→S2, mainly taken place at 600 °C, with the activation energy valued at 152.8 kJ·mol-1, according to Avrami-Erofeev equation; the second stage is the endothermic fluorination reaction WS2+SF6 →WF6, mainly taken place at 750 °C,, with the activation energy valued at 126.0 kJ·mol-1 according to the Avrami-Erofeev equation.

Theoretical study on thermal decomposition mechanism of 1-nitroso-2-naphthol

1-nitroso-2-naphthol has thermal instability of thermal decomposition, spontaneous combustion and even explosion. Its thermal decomposition characteristics were tested by synchronous thermal analyzer (TGA/DSC); The activation energy of the thermal decomposition process was calculated by Kissinger method; The infrared absorption characteristic spectra of the gas products produced in the thermal decomposition process were measured by TGA/DSC-FTIR, and the thermal decomposition reaction process was speculated. The results show that the initial temperature (Tonset) of TGA exothermic decomposition of 1-nitroso-2 naphthol is between 129.01 and 155.69 °C, and the faster the heating rate(β), the higher the Tonset, but the faster the thermal decomposition rate, the greater the heat release and the worse the thermal stability. The activation energy (E) of the thermal decomposition process is 83.323 kJ/mol calculated by Kissinger method. The dynamic test results of TGA/DSC-FTIR show that the main reaction of 1-nitroso-2 naphthol during heating is intermolecular dehydration to form ether, and the secondary reaction is decomposition into aliphatic nitro compounds, carbonyl compounds and amines. Sodium hydroxide will reduce the thermal stability of 1-nitroso-2 naphthol. After adding sodium hydroxide, the thermal decomposition process of 1-nitroso-2 naphthol has changed. The main reaction is that 1-nitroso-2-naphthol reacts with sodium hydroxide to produce sodium nitrophenol, which is further decomposed into aliphatic nitro compounds. The research results have guiding significance for finding the reasonable conditions and temperature of 1-nitroso-2 naphthol during storage and transportation.

High-Temperature Reaction Mechanism of Molybdenum Metal in Direct Coal Liquefaction Residue

In this paper, the extraction residue of direct coal liquefaction residue-DCLR(ER) was used as raw material. The high-temperature reaction mechanism of Mo compound in DCLR(ER) was investigated using a synchronous thermal analyzer and the Factsage database. The high temperature reaction of DCLR(ER)-MoO3 in an oxygen atmosphere consists of pyrolysis of organic components at 400–600 °C, molybdenum trioxide sublimation at 747–1200 °C, and a stable stage at 600–747 °C. The thermal reaction process of the DCLR(ER)-MoS2 system in the oxygen atmosphere involves the pyrolysis of unreacted coal and asphaltene, the oxidation of molybdenum sulfide at 349–606/666 °C, the diffusion of MoO3 at 606/666–85 °C, and the sublimation reaction process of MoO3 at 854–1200 °C. The results show that the lower heating rate can promote the oxidation of the Mo compound and the sublimation of molybdenum trioxide. On the other hand, the oxides of aluminum, calcium, and iron in DCLR(ER) can inhibit the oxidative pyrolysis efficiency of the DCLR(ER)-MoS2 system.

Evaluation of oxygen concentration on low-temperature oxidation kinetics of long-flame coal

Oxygen concentration is the vital environmental factor affecting the evolution of coal spontaneous combustion. Long-flame coal was heated from 30 to 800 °C at different oxygen concentrations (3, 5, 9, 13, 17, and 21 mass%) and heating rates (2.0, 5.0, 10.0, and 15.0 °C/min). The thermal reaction process was explored and analyzed. The effects of oxygen concentration on characteristic temperature and related parameters were assessed. The effects of heating rate and oxygen concentration on characteristic temperature and related parameters were evaluated. Under the condition of oxygen deficiency, the oxidation rate of coal was low, it took more time to consume the active groups in a given quality coal, and the increase of oxygen concentration had a strong positive effect on early and late combustion. The apparent activation energy (Ea) increased and decreased the conversion degree of oxygen absorption (mass gain) and high-temperature combustion stage, respectively. With the decrease of oxygen concentration, Ea in each stage decreased. These results contribute to the understanding of the evolution of coal fires in oxygen-lean environments.

Oxidative torrefaction of microalga Nannochloropsis Oceanica activated by potassium carbonate for solid biofuel production

Oxidative torrefaction is a promising way for biomass upgrading and solid biofuel production. Alkali metals are considered to be efficient activators for enhancing biofuel upgrading during the thermal reaction process. Herein, the microalga Nannochloropsis Oceanica is selected as the feedstock for assessing potassium carbonate activated effect on solid biofuel production through oxidative torrefaction. The potential of potassium carbonate on microalgal biofuel properties upgrading is deeply explored. SEM observation and BET analysis show that torrefied microalgae can be transformed from a spherical structure with wrinkles to smaller particles with larger surface areas and higher total pore volumes, implying that potassium carbonate is a promising porogen. Moreover, potassium carbonate can significantly change the DTG curve at the temperatures of 250 °C and 300 °C from one peak to two peaks, inferring that the activated effect of potassium carbonate occurs on the torrefied microalgae. 13C NMR analysis reveals that the microalgal components significantly change as the torrefaction severity increases, with the decomposition of carbohydrate and protein components. When the potassium carbonate ratio increases from 0:1 to 1:1, the graphitization degree increase from 3.065 to 1.262, along with the increase in the HHV of solid biofuel from 25.024 MJ kg−1 to 31.890 MJ kg−1. In total, this study has comprehensively revealed the activated effect of potassium carbonate on improving the properties of microalgal solid biofuel.

Synthesis, characterization, and catalytic behaviour of nano‐bimetallic nickel oxide on the thermal decomposition of dihydroxylammonium‐5,5′‐bistetrazole‐1,1′‐diolate

Abstract(Synthesis, characterization, and catalytic behaviour of nano‐bimetallic nickel oxide on the thermal decomposition of dihydroxylammonium‐5,5′‐bistetrazole‐1,1′‐diolate)Bimetal combustion catalyst has become an emerging field in recent years, which is still in its infancy. When the combustion catalyst is used in double‐base propellants, it can produce effects that conventional catalysts cannot achieve. In this study, nano‐bimetallic nickel oxides (nanospheres of NiFe2O4 and the sub‐nanometre flower NiCo2O4) were prepared by hydrothermal method and characterized using X‐ray powder diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and N2 adsorption–desorption test (BET). Moreover, its thermal catalytic action on dihydroxylammonium 5,5'‐bistetrazole‐1,1'‐diolate (TKX‐50) was studied. The thermal analysis of composite TKX‐50/NiFe2O4 and TKX‐50/NiCo2O4 was carried out by thermogravimetric differential scanning calorimetry (TG‐DSC). The results show that when the addition amount of NiFe2O4 is 10%, the heating rate is 5.0 K min−1, the NiFe2O4 has the best catalytic activity for TKX‐50 thermal decomposition, and the high thermal decomposition peak temperature (Tpeak1) is decreased by 29 °C. More interestingly, the apparent activation energies of the two composites were calculated by Kissinger, Ozawa, and Starink methods. The advanced thermal analysis kinetics software (AKTS) was used to perform kinetic calculations on the DSC experimental curves of the above‐mentioned composite energetic materials, and reaction rate curves obtained by the simulation are in good agreement with the experimental curves of the thermal decomposition reaction process, further proving that the accuracy of the experiment is high. Therefore, the addition of NiFe2O4 shows high catalytic efficiency on the thermal decomposition of TKX‐50 components, and this would be beneficial to promote the burning rate of propellants containing TKX‐50 components. © 2022 Society of Chemical Industry (SCI).