Thermal decomposition behavior, kinetics, and thermal hazard evaluation of CMDB propellant containing CL-20 by microcalorimetry

The thermal decomposition behavior of composite modified double-base propellant containing hexanitrohexaazaisowurtzitane (CL-20/CMDB propellant) was studied by microcalorimetry. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The effect of different proportion of CL-20 to the thermal decomposition behavior, kinetics, and thermal hazard was investigated at the same time. The critical temperature of thermal explosion (T _b), the self acceleration decomposition temperature (T _SADT), and the adiabatic decomposition temperature rise (??T _ad) were calculated to evaluate the thermal hazard of the CL-20/CMDB propellant. It shows that the CMDB propellant with 38% CL-20 has relative lower values of E and lgA, and with 18% CL-20 has the highest potential hazard.     

Thermal study of HNIW(CL-20) and mixtures containing aluminum powder

The thermal behavior of the energetic material 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-tetracyclo-[5.5.0.0^5,9.0^3,11]-dodecane (HNIW or CL-20) and its mixtures with aluminum under linear temperature control condition and adiabatic condition were investigated by DSC-TG-MS-FT-IR and ARC. Two different particle sizes of aluminum powder (10 μm and 50 nm) were added into CL-20. The influence of particle size on the thermal behavior of CL-20 was studied by using of these apparatuses. The enthalpies of reaction and onset temperatures were determined for various heating rates. The kinetic parameters were found according to Kissinger method, Ozawa method, and Friedman method based on DSC data. The gaseous products from the decomposition of CL-20 and its mixtures were determined by simultaneous MS-FT-IR experiments. ARC measurements were performed to investigate the thermal stability of the samples. The onset temperature, adiabatic temperature rise, self-heat rate, time to maximum rate, and pressure–temperature profile were found from the data measured by ARC. Based on these results, the catalytic effect of aluminum powder was studied.     

A facile way to synthesis insoluble sulfur with high thermal stability by low temperature melting method

In order to prepare insoluble sulfur (IS) with high thermal stability by a low temperature melting method, the factors affecting the IS performance were systematically studied. Stabilizers and curing approaches were also employed to improve the thermal stability for the synthesized IS. The synthesized IS was further treated with a distinctive curing method, and the thermal stability can reach up to more than 54%. Furthermore, the synthesized IS of HD was also compared with commercial product of OT20 from FlexSys Inc. The comparative results showed that the synthesized IS of HD reached the performances of commercial product of OT20 from FlexSys Inc.     

Thermal behavior of cardanol resin reinforced 20 mm long untreated bagasse fiber composites

Recently the attention in composite materials reinforced with natural fibers has significantly increased due to the new environmental legislation as well as consumer pressure that forced manufacturing industries to search substitutes for the conventional materials, e.g., glass fibers. In this way, the objective of the paper was to evaluate the thermal properties of sugarcane bagasse fiber-cardanol resin composites. Fibers were cut down to 20?mm length in diagonally. These fibers were mixed with the cardanol and epoxy resin, and fabricate in a biocomposites with different compositions, such as 0, 5, 10, 15, and 20?wt%. The thermal properties were evaluated by thermal gravimetric analysis and differential thermogravimetry analysis and also chemical formulation studied in Fourier transform infrared spectroscopy. The results showed the improved thermal strength of the composites in comparison to the neat polymer (0?wt%).     

Thermal degradation kinetics of polystyrene/cadmium sulfide composites

The thermal degradation kinetics of polystyrene/CdS composites were studied by thermogravimetry. The samples were heated in nitrogen, with three different heating rates: 5, 20 and 40 °C min⁻¹. We calculated kinetic parameters using KAS isoconversion method. The results showed that the maximum activation energy of thermal degradation is achieved for PS/CdS composite with about 10% of the CdS filler. Higher concentration of CdS in the composite (20%) induced acceleration of the thermal degradation, approaching the rate of degradation of the pure polystyrene matrix.     

CHARACTERIZATION OF POLY(VINYL ALCOHOL)-KONJAC GLUCOMANNAN BLEND FILMS

This article deals with the characterization of blend films obtained by mixing poly(vinyl alcohol) (PVA) and konjac glucomannan (KGM) in aqueous solution. The DTA curves of PVA/KGM blend films showed overlapping of the main thermal transitions characteristic of the individual polymers. The exothermic peak at 312°C, which resulted from the thermal degradation of the KGM, shifted slightly to a higher temperature at low PVA content (≤20 wt%). The weight-retention properties of the blend films indicated that thermal stability of the blend films were better than pure KGM film at PVA content below 20 wt%. The crystallinities, tensile strength, and elongation at break of the films increased with the PVA content, and reached the maximum values at 20 wt% PVA, then decreased. Changes in the carbonyl stretching band of KGM and hydroxyl stretching regions of KGM and PVA were detected by FTIR analysis. Those are attributable to the existence of a certain degree of inteaction between KGM and PVA, and resulted from intermolecular hydrogen bonds. Phase separation phenomena were observed by examining the surface of the blend films by SEM.     

三维氧化铁/石墨烯的构建及其对CL-20的热分解性能的影响

High-performance solid propellants are very important for the development of modern weapons. Aside from their high energy and high burning rate, safety performance is regarded as the most important factor that should be considered whenever a new solid propellant recipe is formulated. Therefore, exploring a new type of combustion catalyst that can improve both catalytic activity and reduce the sensitivity of the energetic component is significant. Traditionally, transition metals or metal oxides are used as a combustion catalyst for accelerating the thermal decomposition of energetic components. However, the existing problem of these catalysts is the aggregation of particles accompanied by poor surface area. Coupling metal oxides with graphene is a promising approach to obtain a binary composite with stable structure and large specific surface area. In this work, rod-like and granular Fe₂O₃ nanoparticles were synthesized using a hydrothermal method. Then, the two as-prepared Fe₂O₃ nanoparticles were coupled with graphene sheets using an interfacial self-assembly method, which can effectively prevent the aggregation of Fe₂O₃ particles and simultaneously increase the active sites that participate in the reaction. X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the phase states and chemical compositions of the prepared samples. The morphology and internal structures were further demonstrated through scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption tests. Both phase analysis and structure identification indicate that the prepared Fe₂O₃/G has high purity and high surface area. The catalytic performance of the prepared Fe₂O₃ and Fe₂O₃/G in the thermal decomposition of hexanitrohexaazaisowurtzitane (CL-20) was evaluated based on thermal gravimetric analysis-infrared spectroscopy (TGA-IR) and differential scanning calorimetry (DSC) tests. The non-isothermal decomposition kinetics of CL-20, Fe₂O₃/CL-20, and Fe₂O₃/G/CL-20 were further studied by DSC. The results reveal the excellent catalytic activity of Fe₂O₃/G in the thermal decomposition of CL-20, which is attributed to the presence of abundant pore structure and large surface area. The reaction mechanisms of the exothermic decomposition process of CL-20, Fe₂O₃/CL-20, and Fe₂O₃/G/CL-20 were obtained by the logical choice method, and the composites all followed same mechanism function model as CL-20. Through comparison, the rod-like Fe₂O₃ coupled with graphene was found to have the best catalytic activity in the thermal decomposition of CL-20. Thus, the rod-like Fe₂O₃ and its Fe₂O₃/G composite were used to investigate their influence on the impact sensitivity of CL-20 by fall hammer apparatus. The results show that rFe₂O₃/G can effectively decrease the impact sensitivity of CL-20 compared with pure CL-20 and rFe₂O₃/CL-20. Therefore, rFe₂O₃ coupled with graphene not only promotes the thermal decomposition but also improves the safety performance of CL-20.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.     

Thermal Properties of Copolymers of Sodium 2-Acrylamido-2-methylpropanesulfonate with N-Vinylpyrrolidone

Thermal transformations of sodium 2-acrylamido-2-methylpropanesulfonate-N-vinylpyrrolidone copolymers of various chemical compositions were studied by thermogravimetric, differential thermal, and thermomechanical analyses within 20-600°C in air. The thermal degradation parameters in various temperature ranges were estimated, as well as the heat resistance of the copolymers.     

The effect of crystal structure on the thermal reactivity of CL-20 and its C4-bonded explosives

The critical temperature and mechanism functions for thermal decomposition of ε-CL-20, RS-ε-CL-20, α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 were evaluated based on non-isothermal TG data. A two-step mechanism has been found for thermal decomposition of α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4, where the initial step is partly controlled by crystal structure of CL-20. The more reasonable mean activation energies could be obtained after peak separation for each individual steps. In fact, the activation energy for the post integrated process is almost equivalent with that of the second step, indicating that the total activation energy at the main decomposition process is dominated by thermolysis of CL-20 molecular. Besides, it has been found that the decomposition of C4 matrix does not affect the decomposition of normal ε-CL-20, resulting in identical activation energy and reaction model. However, the interaction between the C4 matrix and RS-ε-CL-20 is significant especially at the initial stage, where the activation energy of RS-ε-CL-20/C4 was overestimated before peak separation, while the activation energy for the second step due to thermolysis of CL-20 molecular is underestimated. The first decomposition step for α-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4 could be considered as autocatalytic process (AC model), whereas the second as JMA model, which is also applicable to that of pure ε-CL-20 and RS-ε-CL-20. Moreover, The critical temperatures of thermal explosion (T _b) are obtained as 205.6, 205.5, 209.4, 214.4, and 227.5 °C for α-CL-20, ε-CL-20, RS-ε-CL-20, ε-CL-20/C4, and RS-ε-CL-20/C4, respectively. It proves that the C4 matrix could stabilize ε-CL-20 while the crystal form of CL-20 has little effect on its thermal stability.     

UV-cured hyperbranched polyester polythiol(H20-SH)-epoxy acrylate networks: Preparation,thermal and mechanical properties

A hyperbranched polyester polythiol(H20-SH) was synthesized and characterized by FTIR spectral analysis, ¹H-NMR spectral analysis and GPC analysis. H20-SH was added into the formulation of UV-curable epoxy acrylate networks based on thiol-acrylate chemistry. The effects of H20-SH on polymerization kinetics, thermal and mechanical properties of thiol-epoxy acrylate networks were investigated by Real-time infrared spectroscopy, dynamic mechanical analysis (DMA), thermogravimetric (TGA), tensile test and water absorption characterization. Results show that epoxy acrylate resin with the addition of H20-SH massively reduces oxygen inhibition, improves the uniformity of cured films and enhances the tensile strength of the films. However, the thermal stability and glass transition temperature (T_g) decreases with the increasing amount of H20-SH.     

Synthesizing of silver nanoparticles by thermal implantation of its ions in ED-20 epoxy oligomer

Stable silver particles of 39 nm in diameter were synthesized by the thermal implantation of its ions in ED-20 epoxy oligomer.     

Thermo-optical properties of silver and gold nanofluids

This work focuses on the study of thermal diffusivity and physical properties of nanofluids with very low concentrations of silver or gold nanoparticles. Thermal measurements were performed by means of thermal lens spectroscopy in the dual beam configuration. Improvements of 20 and 16 % in the thermal diffusivity were observed for silver and gold nanofluids, respectively, in comparison with pure water. The estimation of the size distribution of the metallic nanoparticles was obtained through the fitting of the extinction spectra via Mie theory and images of field emission gun scanning electron microscopy.     

Thermal studies on polycaprolactam

Initial granules and thin folia of polycaprolactam formed by pressing under various conditions were studied. Using an apparatus for simultaneous thermal analyses STA 449 F3 Jupiter (NETZSCH—Germany), the thermal behavior of the objects were studied in the temperature interval from 20 to 600 °C. From the DSC curves obtained, a number of thermal and thermo physical properties were determined, including the heats of melting and degrees of crystallinity of the crystalline phases formed. For comparison, the effective kinetic parameters and the most probable rate-determining mechanisms of thermal degradation of certain samples in air and inert media were determined from the TG data curves. The crystalline structure perfectness was proved to exert stabilizing effect while the moisture contained had negative effect on polymer thermal stability, especially in oxidative medium.     

Defect mode and crystal-electric-field effects on the thermal expansion and heat capacity of RB<Subscript>50</Subscript> boride

This study aimed to evaluate the suitability of using unfired and fired pumice as cement replacement materials as well as their effect on the thermal resistance of hardened ordinary Portland cement (OPC) pastes. Different OPC–pumice (unfired and fired) blends were prepared by partial replacement of OPC by 0, 10 and 20 of pumice (mass%). The effect of the addition of 1 and 5 % of active alumina on the mechanical properties and thermal resistance of different OPC–pumice (unfired) blends was investigated. The fire resistance test was done by exposing the hardened blended cement cubes to elevated temperatures of 200, 400, 600 and 800 °C for 3 h and allowed them to cool down to room temperature before testing for their mechanical properties. The phase composition and thermal analysis of some selected specimens were investigated by XRD, DSC and DTA/TG techniques. The obtained results indicated that replacing OPC by 10 and 20 % by pumice (unfired and fired) improved its thermal stability at different firing temperatures. The cement blend prepared by replacement of OPC with 10 % pumice showed the highest fire resistance. The addition of 1 and 5 % of alumina (A) to OPC–pumice blends causes a notable improve in their mechanical properties and thermal resistance.     

Thermal Stability of Robust Unsymmetrical Copperporphyrins with Multiple Diphenylamino and Nitro Substituents

The syntheses and thermal stability properties of a series of amino and nitro substituted copperporphyrins are described. The thermal decomposition temperatures of the porphyrins were determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The on-set thermal decomposition temperatures of the unsymmetrical porphyrins were found to be high in the range of 350 – 405 °C (DSC), 374 – 441 (TGA in air), 395 – 411 °C (TGA under nitrogen atmosphere), and 410 – 424 °C (DTA in air). Substituent dependent thermal stability trends were also studied. The trend is variable depending on the thermal analysis technique utilized. Possible reasons for such variation are discussed. These porphyrins are thermally robust even in the melamine-based sol-gel matrix. Containing 20% by weight of the substituted unsymmetrical copperporphyrin, melamine-based sol-gel showed no indication of decomposition until ?400 °C.     

Degree of crystallinity and lattice thermal conductivity of polyethylene at low temperatures

The lattice thermal conductivity of a semicrystalline polymer was studied at low temperatures by calculating the total lattice thermal conductivities of four samples of polyethylene with different degrees of crystallinity between 0.43 and 0.81 and temperatures between 0.4 and 20 K. The contributions of the crystalline and noncrystalline natures and their percentage contributions were taken into account. The predicted lattice thermal conductivity of polyethylene was in fairly good quantitative agreement with the experimental value, and showed a strong crystallinity dependence, with a distinctive cross-over point at about 2 K.     

Thermochemical Reactions of Polyacrylonitrile with Fullerene C6 0

Reactions occuring in mixtures of polyacrylonitrile with fullerene C_{6 0} at 20-1000°C were studied by thermal analysis. The greatest thermal effects were observed in diffusion-controlled reactions of anionic polyacrylonitrile with fullerene. Carbonizate is formed with the yield of about 60%, which is of practical interest.     

Preparation of reflective and electrically conductive surface-silvered polyimide films from silver(I) complex and PMDA/ODA via an in situ single-stage technique

Optically reflective and/or electrically conductive surface-silvered polyimide films have been prepared by thermal curing of the (1,1,1-trifluoro-2,4-pentadionato) silver(I) (AgTFA)-containing poly(amic acid) derived from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (4,4′-ODA) in dimethylacetamide. Films with specular reflectivity of 20-40% and surface electrical resistivity less than 7 Ω/sq were obtained. Two different thermal curing cycles were applied for the imidization and silver reduction process, and film conductivity were only obtained under rapid thermal treatment. The metallized films exhibit mechanical properties close to that of the parent polyimide films. Films were characterized by dynamic mechanical thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and mechanical measurements.     

Self-immobilization and/or thermal treatment for preparing silica-poly(methyloctylsiloxane) stationary phases

Batches of poly(methyloctylsiloxane) (PMOS)-loaded silica were prepared by the deposition of PMOS, into the pores of HPLC silica. Portions of PMOS-loaded silica were allowed to remain at ambient temperature, without further treatment for 2, 9, 20, 31, 51, 105 and 184 days after preparation to undergo self-immobilization (irreversible adsorption of a layer of polymer on silica at ambient temperature in the absence of initiators). Other portions were subjected to a thermal treatment (100 degrees C for 4h) after 1, 2, 5, 7, 9, 15, 20, 25, 70, 111 and 184 days. Self-immobilized and thermally treated samples were characterized by % C, 29Si cross-polarization magic angle spinning (CP/MAS) NMR spectroscopy and reversed-phase column performance. The results show that thermal immobilization accelerates the distribution and rearrangement of the polymer on the silica surface. However, from the time that a monolayer has been formed by self-immobilization (approximately 100 days for PMOS on Kromasil silica), the thermal treatment does not alter this configuration and, thus, does not change the resulting chromatographic parameters.