Thermal Reaction Properties Research Articles

Study on the Size Dependence of the Shell-Breaking Response of Micro/Nano Al Particles at High Temperature

The reactivity of Al nanoparticles is significantly higher than that of micron Al particles, and the thermal reaction properties exhibit notable distinctions. Following the previous studies on micron Al particles, the shell-breaking response of Al nanoparticles under vacuum conditions was analyzed using COMSOL simulation. Relationships between thermal stabilization time, shell-breaking cause, shell-breaking response time, and particle size were obtained, and a systematic analysis of the differences between micrometer and nanometer-sized particles was conducted. The results indicate that the thermal stabilization time of both micrometer and nanometer particles increases with the enlargement of particle size. The stress generated by heating Al nanoparticles with sizes ranging from 25–100 nm is insufficient to rupture the outer shell. For particles within the size range of 200 nm to 70 μm, the primary cause of shell-breaking is compressive stress overload, while particles in the range of 80–100 μm experience shell rupture primarily due to tensile stress overload. These results provide an important basis for understanding the shell-breaking mechanism of microns and nanoparticles of Al and studying the oxidation mechanism.

Transformation and migration of key elements during the thermal reaction of coal spontaneous combustion

As deep coal mining continues to expand, the problem of coal spontaneous combustion (CSC) becomes increasingly severe, posing a significant threat to the safe extraction of energy resources. For preventing CSC, it is of great significance to determine the relationship between the content changes of major elements in the constituent coals and CSC, and it is a necessary study to reveal the mechanism of CSC. By utilizing elemental analyzers, it was found the coal experienced dominant changes in O/C ratios up to 120 °C, H/C ratios between 120 and 270 °C, and O/C ratios beyond 270 °C; By employing a correlation approach, it was determined that the key elements influencing heat release during CSC, i.e., C, H, and O. Additionally, with the key elements as monomers, the migration and transformation process of its mutual composition and structure was investigated, and mastered the influence of elemental migration on the thermal reaction properties in the CSC, as well as uncovering migration and transformation pathways in the CSC. Meanwhile, both the critical groups and temperatures that promote CSC generation were obtained, i.e., –CH2, –CO, and 150 °C, It is expected that the study results may provide theoretical support for the development of fire extinguishing materials.

Insight into the precise catalytic mechanism of CuO on the decomposition and combustion of core–shell Al@AP particles

Burning rate modulation is a crucial but challenging technology for designing solid propellants. The core–shell structured Al@AP and Al@AP/CuO were prepared and their thermal reaction properties were investigated at different pressures. The precise catalytic mechanism of doped CuO in oxidizer and the key reason for its burning rate modulating effect on solid propellants were elucidated by combining DFT calculations. The *NH4ClO4 on the CuO (111) surface is more likely to undergo a dehydrogenation reaction first. The large difference in activation energy between *NH4ClO4→*NH3+*ClO4+*H and *NH4ClO4 → NH3 + HClO4 explains the reasons that CuO can reduce the ignition delay of the Al@AP. CuO promotes the decomposition of the AP@Al at the low- and high-temperature decomposition (LTD and HTD) stage. For the Al@AP-CuO, the temperature of the high-temperature decomposition peak (THTD) does not shift to the lower temperature range with increasing pressure. These results are responsible for a reduction of pressure exponent in the presence of minor CuO as reported in the literature. CuO can facilitate the transformation process *NH3→*NH2 on the CuO (111) surface at low-temperature and low-pressure conditions. However, at high-temperature and high-pressure conditions, it can inhibit the reaction *NH2→*NH→*N, so the burning rate of solid propellants can be controlled.

Preparation and Energy Release Properties of nB@F2603@CL-20 Microspheres by Electrospray

Nano-boron, as a potential high-energy additive due to its high calorific value, is widely studied in propellants, explosives, and thermites. However, the unexpected agglomeration of surface oxidation hinders its further application, especially in the casting of energetic materials. The fluorine-modified nano-boron nB@F2603 and nB@F2603@CL-20 preagglomerated microspheres were prepared by electrospray to improve the ignition and combustion reactions and the rheological properties of boron-containing casting systems. Sphericity microspheres could be obtained by controlling the voltage and propulsion rate. The morphology and elemental distribution of the microspheres were characterized by the scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). Results showed that the particle size of the microspheres ranged from 4 to 14 µm. Boron, fluorine and nitrogen were uniformly distributed on the surface of the microspheres. XRD results showed that CL-20 in nB@F2603@CL-20 microspheres was β-crystal. The thermal reaction properties were studied by differential scanning calorimetry, thermogravimetry and mass spectrometry (TG-DSC-MS), oxygen bomb calorimeter, laser ignition, and volume combustion cell test. Results showed that F2603 could significantly promote the ignition and combustion of nano-boron, causing higher energy release and pressurization rates, and lower ignition temperature. Adding CL-20 to the microspheres could also greatly promote the reaction rates and energy release. The hydrophobicity and corrosion resistance of the structures were also studied, and results showed that the preagglomerated microspheres had good stabilities. Therefore, fluorine-containing nB@F2603 and nB@F2603@CL-20 microspheres might be used in composite energetic materials, replacing nano-boron.

A Study of Thermal Degradation and Fire Behaviour of Polymer Composites and Their Gaseous Emission Assessment

The use of polymer composite materials in the aeronautics and automotive sectors has increased dramatically, and their fire behaviour has become a critical parameter in terms of fire safety. On this premise, it is critical to demonstrate that these composite materials constitute elements whose safety justifies a high level of confidence. This is based on their combustibility and the rate at which flammable and toxic gaseous species are emitted. Thus, strict fire safety regulations are enforced by the relevant authorities concerned because of their potential fire risk. This study analysed papers published between 1970 and 2021 that described the devices used to characterise the thermal behaviour of composite materials at various scales. The objective was to highlight the thermophysical phenomena, making it possible to accurately assess the flammability and thermal stability of polymer composite materials. The results of this research reveal that the small-scale facilities provide detailed understanding and mastery of the thermal reaction properties of the composites. While with the medium scale, the extended fire reaction parameters, which are the key indicators of the fire safety performance, can be determined. On a large scale, the tests were carried out using devices such as the NexGen burner recommended by the FAA. Therefore, with such assays, it is possible to assess the rates of thermal degradation as well as quantified pyrolysis gases. However, compared to other scales, there were very few works on a large scale. In addition, by focusing on the polluting nature of synthetic composite materials, there is also few research studies aimed at designing new polymer composite materials from biological sources.

Synthesis of3,13‐diglycidyloxypropyloctaphenyldouble‐decker polyhedral oligomeric silsesquioxane and the thermal reaction properties with thermosetting phenol‐formaldehyde resin

Abstract3,13‐Diglycidyloxypropyloctaphenyl double‐decker silsesquioxane (EP‐DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction of methyldichlorosilane, followed by hydrosilylation with allyl glycidyl ether, and the resultant structure was confirmed by fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance (NMR), respectively. The thermosetting phenol‐formaldehyde (PF) resin was then modified by EP‐DDSQ, and the reactivity of PF resin with EP‐DDSQ and thermal pyrolysis of modified cured resin were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The surface morphologies of modified resins at high temperature were characterized with field emission scanning electron microscope (FESEM), and chemical structure of modified resins was analyzed through X‐ray photoelectron spectrometer (XPS). The results showed that the appropriate addition of EP‐DDSQ did not affect the curing temperature of the PF resin itself, but could improve the heat resistance of the system. When the amount of EP‐DDSQ added was 10%, the initial degradation temperature of PF resin was increased by 49.31°C, and when the amount of EP‐DDSQ added was 16%, the char yield of which was reached up to 61.39%, compared with that of pure PF resin (TGA1,000°Cof 57.62%) at Ar atmosphere. More importantly, the modified resin formed a regular and dense layer of SiC and SiOxceramic on the surface after ablation in the muffle furnace at 800°C air atmosphere, which is very important for ablative resistant materials.

Thermal reactions of nitrocellulose-encapsulated Al/CuO nanoenergetic materials fabricated in the gas and liquid phases

We examined the effect of polymer encapsulation on the insensitivity and thermal reactions of Al and CuO-based nanoenergetic materials (nEMs). The nEMs were encapsulated by nitrocellulose (NC) polymer using aerosol and solution drying processes for comparison. Severe aggregation and precipitation of Al/CuO reactants in the NC matrix were made in the liquid phase during the drying process so that the thermal reactions of the resulting Al/CuO/NC composites was unstable. However, the rapid aerosol drying process in the gas phase resulted in the formation of uniformly mixed NC-encapsulated Al/CuO composites. The NC content in the Al/CuO composites fabricated in the gas phase strongly affected the thermal reactions by perturbing thermochemical interactions between the Al and CuO reactants. Meanwhile, the insensitivity of Al/CuO composites gradually increased with increasing NC content. Therefore, the aerosol drying process in the gas phase is suggested as a viable and effective method to generate polymer-encapsulated homogeneously mixed nEMs with enhanced insensitivity and thermal reaction properties.

In-situ investigation of the thermal reaction properties of multilayered aluminum–nickel nanofoils

The reduction of the overall mass is a well-established strategy to improve the resource efficiency of vehicles. In terms of lightweight construction, the trend is to produce components consisting of dissimilar materials. Consequently, joining techniques are required that best fulfill the associated requirements. Joining based on reactive nanofoils represents an innovative approach to produce components in a multi-material design. However, nanofoils are not yet used in the industry due to the limited knowledge concerning the effective reaction characteristics during joining. Therefore, this study addresses the characterization of the thermal reaction properties of commercially available aluminum–nickel nanofoils. An experimental setup based on high-speed two-color infrared pyrometry was developed to ascertain the reaction temperature profile during the reaction time of ignited nanofoils. The layer composition of the samples and the ignition strategy were varied within the study. As a result, the effective reaction temperature profile and the duration of the reaction were determined in-situ with high temporal and spatial resolution for the first time. Furthermore, an analytic model was developed to accurately predict the reaction period with respect to the layer structures of the nanofoils. Finally, the sequence of developed intermediate aluminum-nickel phases during the reaction process was ascertained.

Thermal reaction properties of aluminum/copper (II) oxide/poly(vinylidene fluoride) nanocomposite

The thermal reaction properties of the aluminum nanoparticles/copper (II) oxide nanoparticles/poly(vinylidene fluoride) (Al-NPs/CuO-NPs/PVDF) nanocomposite (mass ratio of Al-NPs/CuO-NPs/PVDF = 20/60/20) were investigated by means of thermogravimetry–differential scanning calorimetry–mass spectrometry (TG/DSC-MS) and X-ray diffraction (XRD) analysis. Al-NPs/PVDF (mass ratio of Al-NPs/PVDF = 50/50) and CuO-NPs/PVDF (mass ratio of CuO-NPs/PVDF = 75/25) nanocomposites were also prepared as a comparison. It is observed that PVDF in the Al-NPs/PVDF nanocomposite acts as an oxidizer. The fluorine ions/fluorinated gases formed at elevated temperatures react with the Al2O3 shell leading to the formation of aluminum fluoride (AlF3). The oxide shell is degraded from the reaction between fluoride ions and Al2O3, leaving the core Al available for reaction with fluorine ions/fluorinated gases. H 2 + (m/z = 2), OH+ (m/z = 17), H2O+ (m/z = 18), HF+ (m/z = 20), CF+ (m/z = 31) and CH2F+ (m/z = 33) fragments were detected in the gaseous products. For CuO-NPs/PVDF nanocomposite, oxygen was released due to the decomposition of CuO to Cu2O and then Cu metal, oxidizing hydrocarbon groups in PVDF. Species of OH+ (m/z = 17), H2O+ (m/z = 18), CO 2 + (m/z = 44), C2H2F+ (m/z = 45) and HF+ (m/z = 20) were detected in the gaseous products. The final reduction product of CuO is Cu metal. It is observed that PVDF in the Al-NPs/CuO-NPs/PVDF nanocomposite acts as both oxidizer and reducer in the thermal decomposition. Below 550 °C, PVDF is oxidized by CuO-NPs and oxidizing Al-NPs at the same time, resulting mass reduction. After 550 °C, the remaining Al-NPs and copper (I)/copper (II) oxide will proceed the exothermic solid-state thermite reaction. OH+ (m/z = 17), H2O+ (m/z = 18), CO 2 + (m/z = 44), C2H2F+ (m/z = 45) and HF+ (m/z = 20) were the main products of the decomposition of Al-NPs/CuO-NPs/PVDF nanocomposite.

Characterization of thermal reaction of aluminum/copper (II) oxide/poly(tetrafluoroethene) nanocomposite by thermogravimetric analysis, differential scanning calorimetry, mass spectrometry and X-ray diffraction

The application of fluoropolymers as reactive agent in energetic materials have attracted significant interest recently. In this study, the thermal reaction properties of the aluminum nanoparticles/copper (II) oxide nanoparticles/poly(tetrafluoroethene) (Al-NPs/CuO-NPs/PTFE) nanocomposite (mass ratio of Al-NPs/CuO-NPs/PTFE=20/60/20) were investigated by means of thermogravimetry/differential scanning calorimetry–mass spectrometry (TG/DSC–MS) and X-ray diffraction (XRD) analyses. The Al-NPs/PTFE (mass ratio of Al-NPs/PTFE=50/50) and CuO-NPs/PTFE (mass ratio of CuO-NPs/PTFE=75/25) nanocomposites were also prepared and tested for comparison. It is observed that PTFE is acting as both oxidizer and reducer during the thermal decomposition process of Al-NPs/CuO-NPs/PTFE nanocomposites. Before 615°C, PTFE is oxidized by CuO-NPs and oxidizing Al-NPs, resulting mass reduction. After 615°C, the excessive aluminum and copper (I)/copper (II) oxide will proceed the exothermic condensed phase reaction.

Electro-optical properties of fluorene derivative with acetylenic functionalities

An aromatic compound with acetylenic functionalities, dipropargylfluorene (DPF), was synthesized and characterized. DPF itself was thermally crosslinkable and showed wide processing window. DPF showed characteristic UV-visible absorption band at 337 and 354 nm and blue PL spectrum at 432 nm corresponding to the photon energy of 2.87 eV. DPF-based EL device showed a typical rectifying diode characteristics, blue EL and turn-on voltage of 12 V. The thermal reaction properties of DPF were studied by differential scanning calorimeter. DPF exhibited to melt and react at 117 and at 247 °C, respectively.