DSC Curves Research Articles

Boron/Difluoroamino (B/NF2) Composites Prepared Through an Energetic Fluorinated-Centerd Surface Modification Strategy to Enhance Their Ignition and Combustion Characteristics

To enhance the ignition and combustion characteristics of boron (B), in this study, a suitable, energetic fluorinated group (NF2) that can improve energy and promote combustion efficiency was utilized and B/NF2 composites (B/PDB) with three different particle sizes (10–20 μm, <5 μm, and 0.5–2 μm) were prepared through energetic fluorinated surface modifications with a PDB layer, a copolymer of difluoroaminomethyl-3-methylethoxybutane and 3,3′-bis(azidomethyl)oxetane, coated on the surface of B. The morphology and structure of B/PDB were characterized via the FTIR, SEM, TEM, and XPS techniques. The results indicate that all B/PDB particle sizes were successfully coated by NF2 on the surfaces of B particles through the PDB layer. The TG curves in the thermal analyses were used to determine the amount of the PDB layer of B/PDB with different particle sizes. Based on the DSC curves, NF2 of composites with better catalysis during ammonium perchlorate (AP) decomposition. Additionally, the effects of NF2 on both B/PDB and B/PDB with AP were investigated through PY-GC/MS, ignition, and combustion. Compared with pure B, NF2 significantly improved the thermal conductivity, thereby decreasing the ignition delay of B/PDB, and the ignition delay of B/PDB with AP. The combustion of B/PDB and AP was more intense, extending the combustion duration, forming volatile fluorine compounds, and increasing combustion reaction efficiency. In general, this energetic fluorinated-centred surface modification has potential applications to enhance the ignition and combustion characteristics in B.

Thermal analysis, flexural mechanical properties and FTIR analysis of an HDPE matrix composite reinforced with alumina and silicon carbide

This research developed an HDPE composite reinforced with Al2O3 and 1% SiC in the proportions of pure HDPE, 40 %, 50 % and 60 % of ceramic load. The mechanical flexural test showed results of sMAX 19.09 ± 2.89 MPa and E 1806 ± 400 MPa for the A60 group and concluded that with ceramic loadings above 60 % contribute to crystallization in the regions around the particles. TGA analysis showed initial degradation at 409 °C and final degradation between 499 and 504 °C, with a residue in pure HDPE of 0.46%. The DSC curves showed an endothermic peak at 132 °C and crystallization around 119 °C, and the crystallinity of the HDPE was 95.29 %, and the analyses showed a decrease in the enthalpy of fusion and crystallization with increasing ceramic loading due to the decrease in the polymer fraction in the composite. DMA analysis showed that temperatures above the Tg of the crystalline phases were the mechanism that contributed most to the storage modulus. FTIR analysis showed several interactions in different bands between the 3 compounds in the composite.

Synthesis and properties of superhydrophobic monomer stearyl methacrylate-modified polyacrylate latex pressure sensitive adhesives

Hybrid surfactants of long carbon chain hydrophobic nonionic emulsifier N-390 and conventional anionic emulsifier CO-436 were utilized in this study to enable successful emulsion polymerization of super-hydrophobic monomer stearyl methacrylate (SMA) together with butyl acrylate (BA), acrylic acid (AA), and 2-hydroxyethyl acrylate (HEA). The influences of SMA on the resulting latex and film properties were thoroughly investigated. Both FTIR and 1H NMR were used to confirm the successful participation of SMA in the emulsion polymerization. The results indicated that with introduction of SMA, the roughness of the latex film increases, while the light transmission decreases. It was also found that with the addition of SMA, contact angle of the latex PSA film increased from 115.1° to 127.2°, while water absorption decreased from 5.76 to 2.89 wt%. DSC curves demonstrated that SMA has participated more in the homopolymerization reaction than in the copolymerization reaction. TGA results showed that the initial decomposition temperature (T5%) of the latex film was increased from 302.8 to 332.7 °C with the increase of SMA dosage from 0 to 20 wt%. Finally, adhesion properties results indicated that loop tack and 180° peel force of the PSA films were decreased from 11.51 to 1.88 N/25 mm and 6.36 to 3.44 N/25 mm, respectively, while shear strength was increased from 732 to 2865 min.

Thermal Behavior and Infrared Absorbance Bands of Citric Acid

Citric acid is widely used in the Food and Pharmaceutical Industry. Various issues regarding its thermal behavior and infrared spectrum require clarification. Here, we studied citric acid monohydrate (raw, heated, freeze-dried and recrystallized from D2O) via Differential Scanning Calorimetry, Thermogravimetric Analysis, Infrared Spectroscopy, and antioxidant capacity assay. Also, we used ab initio Density Functional Theory calculations for further supporting the interpretations of the experimental results. Citric acid monohydrate exhibits desolvation inability and upon heating does not dehydrate but esterifies. Nor by freeze drying can it be dehydrated. The heated sample is not anhydrous, it exhibits melting inability, and any fluidization occurs simultaneously with decomposition. In other words, the interpretations regarding the two endothermic peaks in the DSC curve of citric acid that have been attributed to water evaporation and melting are not correct. The increase in the molecular weight due to esterification is most likely responsible for the increased antioxidant/chelation capacity of the heated sample. We concluded that what we call citric acid monohydrate and anhydrous do not exist in a pure form (in the solid state) and actually are mixtures of different compositions of citric acid, water and a citric acid oligomer that is produced through esterification. The esterification reaction seems to be able to proceed easily under mild heating or even at room temperature. The presence of the ester oligomer and water affect the infrared spectrum of citric acid monohydrate and anhydrous and is responsible for the existence of multiple peaks in the C=O stretching region, which partially overlaps with the water H-O-H bending vibration. The insights presented in this work could be useful for optimizing the design, performance and quality of food and drug products in which citric acid is used.

Living anionic copolymerization of 1,3-pentadiene isomers with alpha-methylstyrene in the presence of 2,2-di(2-tetrahydrofuryl)propane

The synthesis of statistical copolymers of alpha-methylstyrene (AMS) and 1,3-pentadiene (PD) isomers in the presence of 2,2-di(2-tetrahydrofuryl)propane (DTHFP) by living carbanionic polymerization was investigated in this paper. To the best of our knowledge, either AMS or PD monomer was rather difficult to homopolymerize in non-polar solvents without the help of polar additives even at high temperature due to its low ceiling temperature or relatively high electron cloud density of the conjugated CC double bond. However, the combination of RLi initiator and DTHFP regulator (0.1<DTHFP/Li < 0.5) allowed the rapid synthesis of the well-defined poly(AMS-stat-PD) with controlled molar masses (up to 32.5 kDa) and relatively narrow molecular weight distributions (1.10 < ĐMs < 1.52). Calculation of reactivity ratios by the Kelen–Tüdos method suggested that AMS copolymerized much more readily to with (Z)-1,3-pentadiene (ZP) than with (E)-1,3-pentadiene (EP) under the same conditions, whereas the EP/AMS copolymer exhibited much lower dispersity. 1H NMR results indicated that the polymer chain was found to be a mixture of 1,2-addition and 1,4-addition units, in the absence of 3,4-units. Kinetic experiments also showed that the apparent activation energy of EP/AMS copolymerization was slightly higher than that of the ZP/AMS case. To ensure complete conversion of the monomer, the feed ratio of AMS (fAMS) must be controlled to be within 0.3. In addition, the incorporation rate of AMS into the polymer chain increased with the increase in the feed ratio of AMS monomer. DSC curves showed that the Tg of the resulting copolymers increased gradually and could reach up to 25 °C (FAMS = 47). Based on the observation of the anionic statistical copolymerization behavior, an interpretation of the formation mechanism is presented here.

Reorientation of interfacial water molecules during melting of brain sphingomyelin is associated with the phase transition of its C24:1 sphingomyelin lipids

Melting of brain sphingomyelin (bSM) manifests as a broad feature in the DSC curve that encompasses the temperature range of 25 – 45 °C, with two distinguished maxima originating from the phase transitions of two the most abundant components: C24:1 (Tm,1) and C18:0 (Tm,2). While C24:1/C18:0 sphingomyelin transforms from the gel/ripple phase to the fluid/fluid phase, the dynamics of water molecules in the interfacial layer remain completely unknown. Therefore, we carried out a calorimetric (DSC), spectroscopic (temperature-dependent UV-Vis and fluorescence) and MD simulation study of bSM in the absence/presence of Laurdan® (bSM ± L) suspended in Britton-Robinson buffer with three different pH values, 4 (BRB4), 7 (BRB7) and 9 (BRB9), and of comparable ionic strength (I = 100 mM). According to DSC, T̅m, 1 (≈ 34.5 °C/≈ 32.1 °C) and T̅m, 2 (≈ 38.0 °C/≈ 37.2 °C) of bSM suspended in BRB4, BRB7, and BRB9 in the absence/presence of Laurdan® are found to be practically pH-independent. Turbidity-based data (UV-Vis) detected both qualitative and quantitative differences in the response of bSM suspended in BRB4/BRB7/BRB9 (T̅m: ∼ 35 °C/32.0 ± 0.2 °C/36.4 ± 0.4), suggesting an intricate interplay of weakening of van der Waals forces between their hydrocarbon chains and of increased hydration in the polar headgroups region during melting. The temperature-dependent response of Laurdan® reported a discontinuous, pH-dependent change in the reorientation of interfacial water molecules that coincides with the melting of C24:1 lipids (on average, T̅m (LTC/HTC): ≈ 31.8 °C/30.6 °C/30.5 °C). MD simulations elucidated the impact of Laurdan® on a change in the physicochemical properties of bSM lipids and characterized the hydrogen bond network at the interface at 20 °C and 50 °C.

Ti/CuO Nanothermite-Study of the Combustion Process.

A study of the combustion processes of Ti/CuO and Ti/CuO/NC nanothermites prepared via electrospraying was conducted in this work. For this purpose, the compositions were thermally conditioned at 350, 550 and 750 °C, as selected based on our initial differential scanning calorimetry-thermogravimetry (DSC/TG) investigations. The tested compositions were analysed for chemical composition and morphology using SEM-EDS, Raman spectroscopy and XRD measurements. Additionally, the thermal behaviour and decomposition kinetics of compositions were explored by means of DSC/TG. The Kissinger and Ozawa methods were applied to the DSC curves to calculate the reaction activation energy. SEM-EDS analyses indicated that sintering accelerated with increasing equivalence ratio and there was a strong effect on the sintering process due to cellulose nitrate (NC) addition. The main combustion reaction was found to start at 420-450 °C, as confirmed by XRD and Raman study of samples annealed at 350 °C and 550 °C. Moreover, increasing the fuel content in the composition led to lower Ea, higher reaction heats and a more violent combustion process. Conversely, the addition of NC had an ambiguous effect on Ea. Finally, a multi-step combustion mechanism was proposed and is to some extent in line with the more general reactive sintering (RS) mechanism. However, unusual mass transfer was observed, i.e., to the fuel core, rather than the opposite, which is typically observed for Al-based nanothermites.

Preparation of low‐temperature curing single‐component epoxy adhesives with sedimentation coated accelerators

AbstractSingle‐component epoxy adhesives are widely used in various fields due to their simple operation process and excellent bonding properties. However, the excessively high curing temperature of the traditional single‐component epoxy adhesives may easily damage the electronic devices, limiting their further application. Hence, it is of great significance to develop the low‐temperature‐curing single‐component epoxy adhesives. However, the room temperature storage stability of low‐temperature curing system is generally poor. This work selected epoxy resin (EPON‐828), pentaerythritol tetra (3‐mercaptopropionate) (PETMP), 1‐benzylimidazole (1‐BMZ), and stabilizer (salicylic acid) as materials to prepare low‐temperature curing single‐component epoxy adhesives. In order to improve the storage stability of the system, polycarbonate (PCM‐A‐37) with low molecular weight was employed to coat the accelerator 1‐BMZ by physical sedimentation. The results showed that the room temperature storage period of the system reached 140 h, which was 2.18 times longer than before coating, and the curing temperature of 75°C was determined through DSC curves fitting. The epoxy adhesives have been completely cured at 75°C for 5 h, and shear strength reached 10.20 ± 0.51 MPa, which was not significantly different from that of the system with uncoated accelerators. We believe our paradigm can provide a feasible approach for preparing low‐temperature curing single‐component epoxy adhesives, and has reference significance for the preparation of single‐component adhesives in other systems, too.

Kinetic investigation of aschalcha heavy oil oxidation in the presence of cobalt biocatalysts during in-situ combustion

The catalytic effect of cobalt tall oil and cobalt sunflower oil catalysts on the oxidation kinetics of heavy crude oil was investigated in this study. Comprehensive kinetic analyses, employing differential scanning calorimetry, thermogravimetric analysis, and kinetic modeling techniques, revealed that the presence of these catalysts significantly influenced the oxidation behavior of heavy oil. The catalysts exhibited pronounced shifts in the DSC and TG curves towards lower temperatures, indicating facilitated initiation of oxidation reactions at lower onset temperatures. Quantitative kinetic parameters, including activation energies and frequency factors, were determined using the Friedman and Kissinger-Akahira-Sunose analyses. The cobalt tall oil catalyst demonstrated superior performance, effectively lowering the activation energy barrier and increasing oxidation rates, particularly at higher conversion degrees. Catalyst characterization techniques, including X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy, revealed the formation of highly crystalline cobalt oxide nanoparticles with optimal dispersion and size distribution, as well as the presence of favorable functional groups for surface interactions. The results elucidated the role of these catalysts in facilitating the oxidation process through the provision of active sites, altered reaction pathways, favorable steric environments, and efficient oxygen activation capabilities. These findings contribute to the development of efficient catalytic systems for heavy oil upgrading processes and offer insights for further optimization of catalyst properties to achieve desired oxidation kinetics behavior.

Annealing improves the mechanical properties in poly(butylene succinate) films with oriented lamellar structure: The effect of metastable lamellae

AbstractThe application range of biodegradable Poly(butylene succinate) (PBS) is highly dependent on its mechanical properties, which can be improved by the annealing process. In this study, the mechanical properties and microstructure of PBS films with oriented lamellar structures annealed at different temperatures were characterized. It was found that the annealing process effectively improves the elastic modulus and yield strength of the oriented PBS film with the increase of annealing temperature, which is completely different from the previous results of other oriented semicrystalline polymers such as PP, PMP, PE, and PVDF. The long periods, lateral dimensions and orientation of the lamellae of the oriented PBS film increase with the increasing annealing temperature. Meanwhile, the low‐temperature endothermic plateau in the DSC curve and the g1,r/Q in the SAXS experiment decrease with annealing temperature, indicating that increasing annealing temperature would reduce the thin and metastable lamellae in the PBS films. Compared the annealing results of oriented PBS films and that of other‐oriented semicrystalline polymers, we suggested the annealing process for the oriented PBS films would reduce the thin lamellae and form thicker lamellae, resulting in an increase in the elastic modulus and yield strength of the annealed PBS films. This study clarifies how the annealing temperature affects the microstructure and mechanical properties of the oriented semicrystalline films.

Extension of a phase-field KKS model to predict the microstructure evolution in LPBF AlSi10Mg alloy submitted to non isothermal processes

The out-of-equilibrium heterogeneous microstructure typical of AlSi10Mg processed by Laser Powder Bed Fusion (LPBF) is often modified by further heat treatment to improve its ductility. According to literature, extensive experimental investigations are generally required in order to optimize these heat treatments. In the present work, a phase-field approach is developed based on an extended Kim–Kim–Suzuki (KKS) model to guide and accelerate the post-treatment optimization. Combined with CALculation of PHAse Diagrams (CALPHAD) data, this extended KKS model predicts microstructural changes under anisothermal conditions. To ensure a more physical approach, it takes into account the enhanced diffusion by quenched-in excess vacancies as well as the elastic energy due to matrix/precipitate lattice mismatch. As the developed model includes the computation of the evolution of the thermo-physical properties, its results are validated through comparison with experimental DSC curves measured during the non-isothermal loading of as-built LPBF AlSi10Mg. The computed microstructure evolution reproduces the microstructural observation and successfully explains the peaks in the DSC heat flow curve. It thus elucidates the detailed microstructural evolution inside the eutectic silicon phase by considering the growth and coalescence of silicon precipitates and the matrix desaturation.

Antimicrobial ion-imprinted chitosan-derived hydrogel with quaternary ammonium and thermoresponsive components for UO22+ adsorption

Uranium recovery from wastewater or seawater is important for both pollution control and uranium supply. Due to the complexity of the water body, it requires that the adsorbent should not only be highly efficient for selective adsorption but also have good antimicrobial properties. In this study, an antimicrobial thermosensitive hydrogel (UITAC) for uranium adsorption was prepared by one-step ion-imprinted polymerization using chitosan as a substrate and allyl trimethylammonium chloride as the antimicrobial modifier. UITAC showed excellent antibacterial rate against Escherichia coli and Staphylococcus aureus, being 98.8 % and 89.1 %, respectively. Endothermic and exothermic peaks respectively showed up at 36.3–38.5 °C and 30.5–34.1 °C in the DSC curves. UITAC quickly achieved its adsorption equilibrium in 30.0 min at 50 °C, pH 5.0 in the 0.8 mg/mL UO22+ solution, with an adsorption capacity of 81.2 mg/g. The adsorption capacity could remain at 80 % after 5 cycles of repeated use. UITAC showed better adsorption selectivity to UO22+ than vanadium and other metal ions, with selectivity coefficients α(UO22+/Mn+) being 1.4–10.3. The pseudo-second-order kinetics and Langmuir adsorption model had a better fit for UO22+ adsorption by UITAC. The adsorption was a spontaneous process. The Gibbs Free Energy change, enthalpy change, and entropy change at 323.2 K were − 16.0 kJ/mol, 64.3 kJ/mol, and 248.4 J/mol·K, respectively. UITAC showed high potential in practical application environment.

Synthesis of HHTPB by partial hydrogenation of HTPB using copper chromite as a catalyst

AbstractHTPB (hydroxyl‐terminated polybutadiene) is a well‐established binder in the composite solid propellant owing to its excellent compatibility with ammonium perchlorate (AP) and aluminium (Al) particles in giving rise to optimal ballistic and mechanical properties. Efforts are being made to improve the ballistic properties further, such as specific impulse. One way of increasing the specific impulse is to hydrogenate HTPB, which decreases the molecular mass of the combustion product gases. This paper is a summary of efforts in synthesizing hydrogenated HTPB (HHTPB) using copper chromite (CC) as a catalyst. A novel synthesis methodology is developed for HHTPB using a temperature‐programmed batch reactor with a variable speed stirrer and an instrumentation system to maintain the desired liquid reactant temperature. A process cycle is developed that includes addition sequence and reaction time. The product is analyzed using 1H‐NMR and FTIR to estimate the degree of hydrogenation and the geometrical isomers respectively. The estimated apparent equilibrium rate constants from the degree of hydrogenation values are respectively 74 and 2034 L/(mol MPa) for non‐catalyzed and catalyzed systems, indicating the effectiveness of the catalyst. This is also substantiated by the reduction in Gibbs free energy (ΔG), to an extent of 4.48 kJ/mol. Thermogravimetry examination indicates that the decomposition temperature of HHTPB produced by the catalytic method is marginally higher compared to HTPB. DSC curves indicate that the decomposition enthalpy of HHTPB is higher than that of HTPB. In summary, this paper proposed and validated a novel method in the preparation of HHTPB using copper chromite.

S+E+O-band luminescence and enhancement in Nd3+/Tm3+/Ce3+ doped tellurite glass

A new, to our knowledge, doped combination of Nd3+, Tm3+, and Ce3+ ions was developed in tellurite glass with a fundamental composition of TeO2-ZnO-WO3-Bi2O3, and the structural, thermal, and especially near-infrared (NIR) luminescent properties in O-, E-, and S-bands were explored. The XRD pattern confirmed the amorphous nature of synthesized tellurite glass, the Raman spectrum disclosed different structural units that make up the glass network, the DSC curve confirmed good host thermal stability, while XPS measurement revealed that cerium mainly exists in the trivalent form in a glass network. Upon being pumped with an 808 nm laser, a 1.34 µm band fluorescence from Nd3+:4F3/2level→4I13/2 level transition and a 1.46 µm band fluorescence from Tm3+:3H4level→3F4 level transition were observed, which in turn formed a wide luminescence band from 1260 to 1560 nm in the tellurite glass containing both Nd3+ and Tm3+ ions owing to their spectral overlapping. The measured full width at half maximum (FWHM) for the aforementioned wideband luminescence was about 203 nm with Nd2O3 and Tm2O3 concentrations of 0.015 mol. % and 0.5 mol. %, respectively, and exhibited a further ∼60% increase in peak intensity after the incorporation of 0.4 mol. % amount of CeO2, which arises from the phenomena of cross relaxation and energy transfer among the three trivalent rare earth ions. The experimental evidence presented in this work shows that tellurite glass containing Nd3+, Tm3+, and Ce3+ has potential as an active material for S-, E-, and O-band wideband luminescence.

Engineering interfacial interactions for hydrogen separation enhancement in Torlon®/mixed-linker ZIF-8 mixed matrix membranes

Polymer membranes traditionally used for gas separation can be easily fabricated via a solution process; however, they have limitations in gas separation performance. Mixed matrix membrane (MMM) with dispersed high-performance filler within a polymer matrix achieves both excellent separation efficiency and productivity. In this study, we employed Torlon® (polyamide-imide), a chemically stable and commercially available polymer, as the matrix of the membranes. To enhance the separation performance through the fabrication of MMM, we utilized 2abIm-mixed-linker ZIF-8 (ML-ZIF-8) as the filler particles to improve the interfacial interaction with the Torlon® matrix. FT-IR and XPS analyses on the Torlon®/ML-ZIF-8 MMM confirmed the occurrence of interactions between the Torlon® and ML-ZIF-8. As a result, the analysis of both the DSC and stress-strain curves confirmed the effectiveness of incorporating ML-ZIF-8 into the Torlon® for improving the stability of the polymer-filler interface. This enhancement resulted in an approximately 2.7 times higher H2 permeability for the Torlon®/ML-ZIF-8 MMM compared to the pure Torlon® membrane. Furthermore, the selectivity of H2/N2 and H2/CH4 separation increased by around 11 times and 9.6 times, respectively, leading to a significant overall improvement in separation performance.

Assessment of perlite by-product as pozzolanic material in cement pastes

This research investigates the suitability of perlite by-product as a potential pozzolanic material in cement-based pastes and compares its performance with natural pozzolan. The study evaluates both the fresh and hardened properties of the pastes. The investigation involves analysis of hydration heat records, hydration formed products, water demand, and setting times, that preseted small deviations. The findings reveal that the perlite by-product exhibits promising characteristics, suggesting its viability as a pozzolanic material in cement pastes. Perlite specimens presented greater mass loss due to calcium-aluminum species, according to TG at early age, as well at later age as depicted in DSC curves. Diffraction patterns and IR assignments showed that waste-perlite systems formed carbonated species with different crystallinity at 180 days. Nevertheless, compressive strength and open porosity of those pastes exhibited behavior similar to the ones incorporating natural pozzolan, apart from 10 % to 20 % systems, where perlite seems to offer slightly greater strength at later age. This study sheds light on the potential benefits of utilizing perlite by-product as an alternative pozzolanic material, rather than depositing it and cause environmetanl problems. Based on its later age properties, perlite could enhance the performance and sustainability of cement-based products in various applications.

Magnetic, dielectric and thermal study of CoNiFe2O4 nanoparticles

CoxNi1-xFe2O4 (x = 0.2–0.8) (CNFO) nanoparticles have been prepared using a low temperature hydrothermal technique. X-ray diffraction confirmed the cubic spinel structure of the nanoparticles, offering an increasing trend of lattice parameters from 8330 to 0.8345 nm as a function of Co-content. The microstructures were analysed using FESEM and TEM. The average grain size determined using FESEM images for x = 0.2–0.8 was found in the range from 110 to 183.7 nm. The TEM images show asymmetrical sphere-like particles, with the particle size changing from 69.4 to 82.1 nm as a function of ‘x’. The hysteresis curves were recorded for x = 0.2–0.8 to understand the ferrimagnetic behavior. The saturation magnetization (Ms) varies unsystematically between 35.3 and 43.3 emu/g with ‘x’, while a high magnetic moment of 1.819 μB/f.u. is found at a high Co-content. The paramagnetic term (χ x 10−5) goes on increasing from 125 to 148 emu/g.Oe with ‘x’. The zero-field cooled (ZFC) and field cooled (FC) curves provide the decreasing trend of variation blocking temperature (TB) from 270 to 260 for x = 0.2–0.6, whilst for x = 0.8, it is increased to 280 K. The high real part of the permittivity of ∼ 12.42 and low imaginary part of the permittivity of ∼0.638 are recorded at 8 MHz for x = 0.2, indicting energy storage applications. The power law fit was applied to log σac-log ω plots and the dc-electrical conductivity was evaluated. The TG-DTG and DSC curves revealed mass loss and transition temperatures for x = 0.2–0.8 as a function of temperature.

Multi-step scheme and thermal effects of coal smouldering under various oxygen-limited conditions

Coal smouldering fires are global disasters and notoriously challenging to characterize. To better understand combustion and chemistry within these coal fires, TG-DSC experiments were carried out in two different coal samples in nitrogen and oxygen-limited (including ambient air) atmospheres. A mechanism with 8-step reactions simulating coal combustion was proposed, including one drying, two pyrolysis, two oxygen adsorption, and three high-temperature oxidations. The kinetic parameters were optimized via a Genetic Algorithm (GA). It was found that this 8-step mechanism created unnecessary overfitting to the TGA data. Therefore, two alternative schemes were developed with 5- and 4-step, which included and neglected oxygen adsorption, respectively. To compare the two schemes, GA and Gaussian multi-modal fitting were used to quantify the mass change rates in each step and their thermal effects as functions of oxygen concentrations. Moreover, the heat flow rates of coal samples were calculated and compared with measured DSC curves. The results indicated that oxygen adsorption could play a critical role in the transition from water evaporation to high-temperature combustion, and the 5-step scheme could reflect coal's intrinsic oxygen-limited combustion characteristics more accurately. Altogether, this study provides novel insight into coal smouldering under oxygen-limited conditions.

Study on combustion characteristics and pyrotechnic cutting effects of bimetal thermite Ni/Al/Fe2O3 system

AbstractNano‐thermite has become a subject of significant interest in the composite energetic materials field due to its high energy release rate. To cater to diverse engineering needs, thermite formulations are often customized to fulfill specific criteria. This study investigates the potential of metal nickel (Ni) as an additive to modify nano‐thermite formulations, selected for its optimal calorific values and chemical reactivity. The base materials, nano‐aluminum (Al) and iron oxide (Fe2O3), are blended with varying mass ratios of Ni (1 %, 3 %, 5 %, 7 %, 9 %) using the wet ball milling method. Pre‐reaction and post‐reaction morphological and compositional alterations in the resultant thermite samples are scrutinized through SEM and XRD characterization tests. Moreover, DSC analysis and combustion experiments were conducted to examine the pyrolysis and combustion behaviors of the evaluated samples. The results reveal a reduced exothermic peak on the DSC curves with the introduction of Ni, making the liquid‐solid (L‐S) phase reaction more challenging compared to the Al/Fe2O3 thermite. Intriguingly, Ni addition progressively decreases the combustion temperature of thermites as the Ni's mass ratio increases, with a peak efficiency at 7 % in the perforation tests on stainless‐steel plates. This research further reveals that the thermite reaction mechanism is a combined consequence of the “pre‐ignition‐fusion” and “fusion‐diffusion” mechanisms. These insights can provide valuable guidance for designing thermite formulations for potential applications in storage, management, and pyrotechnic cutting areas.

Determination of Wax Deposition Rate Model of Blended Oils with Different Blending Ratios

Blending with light oil is a commonly used and reliable method of crude oil transportation, and the blending ratio is a crucial operating parameter in determining the safe and efficient operation of the pipeline. In this paper, in-house flow and deposition experiments are used to evaluate the flow and deposition characteristics of crude oils with varying blending ratios. The results show that (1) blending with light oil basically does not affect the shape of the DSC curve of crude oil; (2) blending with light oil will not eliminate the thermal treatment effect, and the mixed oil flowability still remains highly dependent on the thermal treatment temperature; (3) blending with light oil can greatly decrease the abnormal point and oil viscosity, in which the low-temperature viscosity decreases more significantly; and (4) a wax deposition model of mixed oil is obtained through the fitting of Huang’s model, where the blending ratio is a crucial factor in the determination of the model parameters k, m, and n.