Thermal Decomposition Process Research Articles

Effects of oxidizing molecules on the thermal decomposition of TTDO by ab initio molecular dynamics simulations

Oxidizing molecules play a very important role in improving the comprehensive properties of energetic materials. Recently, a series of energetic cocrystals containing 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) and oxidizing molecule have been successfully prepared. Therefore, ab initio molecular dynamics were used to simulate the thermal decomposition process of TTDO, TTDO:H2O2, TTDO:HNO3, and TTDO:HClO4 crystals at 3000 K to study the role of oxidizing molecules during the thermal decomposition of TTDO. The initial decomposition paths of the TTDO crystal include N–H bond breaking, C–N bond breaking, and intramolecular and intermolecular H transfers. The formation mechanisms of H2O, N2, and CO2 in the four crystals are completely different. The key formation mechanism of H2O is the combination of O with OH, that of N2 is the formation of the -N-N- structure, and that of CO2 is to form the intermediate CO-R with carbonyl structure that form the fragment with the -O-C-O- structure. All the oxidizers H2O2, HNO3, and HClO4 involve in the formation of H2O, N2, and CO2. The formation mechanisms of urea during the decomposition process of the four crystals are completely different, but the key step is to produce the structure of -N–CO–N-. An analysis of Nx shows that H2O2, HNO3 and HClO4 affect not only the types of Nx, but also its formation mechanisms. Among them, HNO3 has the greatest influence on Nx.

Thermal Decomposition Behavior of Polyimide Containing Flame Retardant SiO2 and Mg(OH)2.

The effects of flame retardant silica (SiO2) and magnesium hydroxide (Mg(OH)2) on the thermal decomposition process of polyimide (PI) are discussed in this paper. Firstly, the decomposition process of PI in a nitrogen and oxygen atmosphere was studied by thermogravimetric analysis and differential scanning calorimetry methods, and the kinetic parameters were calculated by the nonlinear fitting method. In an inert atmosphere, PI decomposition consists of a three-step endothermic reaction, whereas in an oxygen atmosphere, PI decomposition consists of two steps, in which the first step does not change, and the second step changes to a violent exothermic peak. The effects of 3 wt % SiO2 (SPI) and 3 wt % Mg(OH)2 (MPI) on the degradation kinetics of PI are discussed. The results show that under an oxygen atmosphere, SiO2 and Mg(OH)2 hydroxide mainly delayed the second-step oxidation exothermic peak temperature of PI by 5 °C. In summary, the first step of the PI degradation is not affected by oxygen, and the flame retardant mainly acts in the second step, which can delay the oxidation heat release. In addition, the addition of SiO2 could prevent PI from aging whereas Mg(OH)2 has barely effect on the aging of PI.

Revisiting the Decomposition Process of Tetrahydrate Co(II) Acetate: A Sample’s Journey through Temperature

Cobalt oxides, CoO and Co3O4, were obtained from Co (II) acetate tetrahydrate. The thermal decomposition pathway of the starting product was followed by combining thermogravimetric analysis and in situ X-ray thermodiffraction. Under a nitrogen atmosphere, cobalt monoxide with Zn-blende and rocksalt polymorphs could be obtained almost as single phases at 330 and 400 °C, respectively. In addition to these oxides, a Co (II) oxyacetate, Co3O(CH3COO)4, was stabilized as an intermediate phase. Under an air atmosphere, Co3O4 (spinel structure type) was obtained as the only final product. The involved phases in this thermal decomposition process were characterized with scanning and transmission electron microscopy (SEM and TEM, respectively).

Influence of dolomite particle size on the kinetics of its thermal decomposition process

The results of an experimental study of the thermal decomposition of natural dolomite, carried out on laboratory equipment at constant temperatures of 650 °C, 700, 750, 800 and 850 °C, are discussed. Particles of Belarusian dolomite weighing 0.58 g, 0.88, 2.3, 2.7, 7.6 and 16.3 g were used as the test samples. An integral equation describing the kinetics of thermal decomposition of natural dolomites of Belarus is presented. It is shown that the reaction rate of thermal decomposition of dolomite depends not only on the temperature regime in the reaction zone, but is also largely determined by the mass of the samples under study. It has been established that the rate constant of thermal decomposition of dolomite in the studied range of sample masses can be determined by the empirical expression identified in the course of this study. The rate constants of thermal decomposition of dolomite particles of various masses have been determined. The values of the rate constants obtained empirically and those calculated taking into account the mass of the samples are compared. It is noted that the developed model is physically justified, and the dependence proposed in the work can be incorporated into existing engineering methods for calculating generator gas purification systems using dolomite as a catalyst and sorbent.

Sol-gel synthesis of nano block-like ZnMn2O4 using citric acid complexing agent and electrochemical performance as anode for lithium-ion batteries

Spinel ZnMn 2 O 4 anode material has high research value as a potential alternative anode material for lithium-ion batteries due to the limited theoretical capacity of commercial graphite. This study prepared a block structured lithium-ion battery anode material ZnMn 2 O 4 using the citric acid sol-gel combustion method. The thermal decomposition process of the xerogel precursors was investigated using thermogravimetric differential thermal analysis. When the ratio of citric acid to metal cations is 4:1, the prepared ZnMn 2 O 4 material had an uneven block structure (ca. 0.3–1.3 µm). The material shows high electrochemical performance: the initial capacity is as high as 1100.2 mAh·g −1 at 0.1 C, and the capacity remains at 277.6 mAh·g −1 after 40 cycles. Finally, the first discharge and the second charge–discharge processes of ZnMn 2 O 4 were thoroughly investigated, and the electrochemical behavior in the electrochemical process was analyzed. • ZnMn 2 O 4 block-like structure are synthesized by sol-gel combined combustion method. • Smaller particle size can effectively increase the reactive sites between electrolyte and material. • The optimized sample shows good lithium storage properties.

Suppression mechanisms of ammonium polyphosphate on methane/coal dust explosion: Based on flame characteristics, thermal pyrolysis and explosion residues

To explore the suppression mechanisms of ammonium polyphosphate (APP) on methane/coal dust explosion flame, the experiment tests of methane/coal dust explosion flame propagation under different mass fraction of APP were conducted in a vertical pipe. Using Simultaneous Thermal Analysis and Py-GC/MS to analyze the effects of APP on the thermal decomposition process and thermal pyrolysis products of coal dust. The chemical characterization of explosion residues was carried out by confocal Raman and Fourier transform infrared spectroscopy (FTIR). Based on the apparent suppression ways of APP such as absorption of heat, reduction concentration of combustibles and adsorbent of free radicals, APP also limited the thermal decomposition process of coal dust and leaded to the reduction or even disappearance of some organic matters at coal dust pyrolysis. Noticeably, the investigation of explosion residues found that the carbonization effect of APP pyrolysis products and the activity reduction of functional groups (–CH3/–CH2 and –OH) which contribute to ignition of coal dust, these coupling effects made it difficult for coal dust to ignite, and thus the methane/coal dust compound explosion were suppressed significantly.

Thermal decomposition kinetics of FAPbI3 thin films

In the realm of organic-inorganic-hybrid metal-halide perovskites, ${\mathrm{FAPbI}}_{3}$ is seeing increasing attention as a potentially more stable alternative to ${\mathrm{MAPbI}}_{3}$. To add to our previous paper, where we studied the reaction kinetics of the thermal decomposition of ${\mathrm{MAPbI}}_{3}$, here we analyze the compositional change and crystal phase evolution during the thermal decomposition of ${\mathrm{FAPbI}}_{3}$ thin films. To this end, we prepare the perovskite using thermal coevaporation and monitor the growth and thermal decomposition in vacuum with an in situ x-ray diffraction setup. The experimental procedure has been carried out via three approaches: producing a partially decomposed sample with the help of a graded temperature profile, using a temperature ramp and a set of isothermal decomposition experiments. From this data we analyze and calculate the stoichiometry and phase changes, the activation energy $E$ and the frequency factor $A$ of the thermal decomposition process, in addition to the thermal expansion coefficient during heating. We compare our results to the ones obtained for ${\mathrm{MAPbI}}_{3}$ thin films by the same experimental method, confirming the enhanced thermal stability of ${\mathrm{FAPbI}}_{3}$.

RANCANG BANGUN ALAT KONVERSI PLASTIK MENJADI BAHAN BAKAR MINYAK DENGAN METODE PIROLISIS UNTUK PENANGANAN SAMPAH PLASTIK

The volume of plastic waste is increasing day by day, due to the lack of management technology and plastic is a non-biodegradable material. Plastic waste causes pollution to the environment and living things if left alone. Various efforts have been made to deal with plastic waste, but only cause other problems such as blockage of water flow. This research introduces the technology of converting plastic waste into fuel oil called pyrolysis. Pyrolysis is a method of converting plastic into fuel oil through a thermal decomposition process in the absence of oxygen. The purpose of this study was to determine the weight of oil produced in the pyrolysis process with variations in condenser temperature. The type of plastic used is LDPE, the reactor temperature is constant at 200° C. The pyrolysis process was carried out for 1 hour for each condenser temperature variation at 28° C, 14° C, and 4° C. Based on the research results, the condenser temperature variation at 28° C gets the lowest oil weight, which is 17 grf, while the condenser temperature variation at 14° C produces 32 grf of oil weight, and the highest oil weight is obtained at 4° C condenser temperature variation of 62 grf.

Exploration of the Crystal Structure and Thermal and Spectroscopic Properties of Monoclinic Praseodymium Sulfate Pr2(SO4)3.

Praseodymium sulfate was obtained by the precipitation method and the crystal structure was determined by Rietveld analysis. Pr2(SO4)3 is crystallized in the monoclinic structure, space group C2/c, with cell parameters a = 21.6052 (4), b = 6.7237 (1) and c = 6.9777 (1) Å, β = 107.9148 (7)°, Z = 4, V = 964.48 (3) Å3 (T = 150 °C). The thermal expansion of Pr2(SO4)3 is strongly anisotropic. As was obtained by XRD measurements, all cell parameters are increased on heating. However, due to a strong increase of the monoclinic angle β, there is a direction of negative thermal expansion. In the argon atmosphere, Pr2(SO4)3 is stable in the temperature range of T = 30–870 °C. The kinetics of the thermal decomposition process of praseodymium sulfate octahydrate Pr2(SO4)3·8H2O was studied as well. The vibrational properties of Pr2(SO4)3 were examined by Raman and Fourier-transform infrared absorption spectroscopy methods. The band gap structure of Pr2(SO4)3 was evaluated by ab initio calculations, and it was found that the valence band top is dominated by the p electrons of oxygen ions, while the conduction band bottom is formed by the d electrons of Pr3+ ions. The exact position of ZPL is determined via PL and PLE spectra at 77 K to be at 481 nm, and that enabled a correct assignment of luminescent bands. The maximum luminescent band in Pr2(SO4)3 belongs to the 3P0 → 3F2 transition at 640 nm.

Kinetic parameters of thermal destruction of the copolymer of polyethylene glycol fumarate with acrylic acid in inert medium

Thermal decomposition of the copolymer of polyethylene glycol fumarate with acrylic acid (p-EGF:AA) of two different compositions synthesized earlier was studied in the present work. TG and DTG curves prove that decomposition takes place in several stages. According to thermogravimetric curves it has been found out that for the copolymer with higher content of acrylic acid the decomposition of the copolymer’s sample is started at higher temperatures. It has been shown the shift of the temperature of decomposition’s start to the higher area with the increase of heating rate which is necessary for the detorsion of macromolecular coil. Experimental data processed using graphical methods of Kissinger–Akahira–Sunose and Friedman allowed us to calculate the activation energy of the thermal decomposition process. It has been established that the copolymer with the composition of 21.03:78.97 mass.% has lower meaning of activation energy than the one with the composition of 68.96:31.04 mass.%. As a result of calculation one can see that the meanings found out using these methods depend slightly on conversion. Using Achar-Brindley-Sharp method and the method of invariant kinetic parameters the kinetic triplet of the decomposition process has been found which was used to build the calculated curve. The dependences of g(α) on α using these parameters showed a satisfactory agreement of calculated curves with the experimental ones. One can conclude that the decomposition process of the copolymer of polyethylene glycol fumarate with acrylic acid is well described with of D3 (three-dimensional diffusion) model.

Reversible and Irreversible Laser Interference Patterning of MOF Thin Films

Laser interference patterning on top of a thin film and inside a crystal is a powerful tool today to create the desired patterns for optical data processing. Here, we demonstrate reversible and irreversible laser interference patterning on a metal-organic framework (MOF) thin film through the water desorption and thermal decomposition processes, respectively. The irreversible interference pattern with a period of the strips of up to 5 µm has been realized, and its morphology has been characterized using confocal Raman and reflection spectroscopy as well as atomic force microscopy. We revealed that reducing the distance between the interference maxima from 10.5 to a record of 5 µm for MOFs yields a 10-fold increase in the surface roughness of the irreversible pattern; on the other hand, the reversible laser pattern provides a completely non-destructive effect of variable optical contrast. The experimental results obtained open up prospects for the use of MOF crystals as photosensitive materials in the template drawing of the desired patterns for different application scopes.

Flame retardant polyacrylonitrile fiber modified with hydrazine hydrate and copper ions

The limiting oxygen index (LOI) of polyacrylonitrile (PAN) fiber is only around 18%, making it urgently needed to enhance flame retardancy. Treatment with hydrazine hydrate as cross-linking agents followed by adsorption of metal ions endows PAN fibers with excellent flame retardancy. The Fourier-transform infrared spectroscopy (FT-IR) was employed to investigate the evolution of the chemical structure of the fibers. The atomic adsorption spectrometer (AAS) was carried out to study the adsorption capacity for copper ions. The wide-angle X-ray diffraction (WAXD) and scanning electron microscope (SEM) were used to study the aggregate structure and morphology of the fibers. In addition, LOI, thermogravimetric analysis/infrared spectrometry (TG-FTIR), and thermogravimetric analysis (TGA) were employed to clarify the flame-retardancy and the mechanisms. The mechanical property was studied via a single fiber tensile tester. The results showed that more chelating groups arose in macromolecular chains of PAN fibers after the reaction with hydrazine hydrate, with increased adsorption capacity for Cu2+. The LOI reached 24.0% after the treatment of hydrazine hydrate and the fiber was still flammable in the air. After the treatment with metal ions, the LOI of the fibers dramatically rose to 45.2%. The thermal decomposition process differed after the treatment of hydrazine hydrate, resulting in a more violent release of ammonia and a sharp reduction of flammable gases. The introduction of copper ions made fibers form dense carbon residue during thermal decomposition, which was beneficial for the improvement of flame retardancy.

Thermal decomposition paths of calcium nitrate tetrahydrate and calcium nitrite

Thermal decomposition processes of calcium nitrate tetrahydrate and calcium nitrite were studied by TG/DSC-FTIR, TG-MS and in-situ DRIFTS. Calcium nitrate tetrahydrate melts at ca. 50 °C and then 1/4, 1/2 and 1/4 of water molecules are released in the range of 50–150 °C, 160–180 °C and 190–220 °C respectively. Calcium nitrate melts at ca. 550 °C and is consecutively decomposed into CaO, O2, NO and NO2, where the ratio of NO to NO2 changes from 2:1 to 1:1 after decomposition maximum point at ca. 580 °C. After melting at ca. 380 °C, calcium nitrite is decomposed into calcium nitrate, CaO and NO first in the range of 470–550 °C, overlapped with the decomposition of calcium nitrate in the range of 550–600 °C. Both decomposition paths are not changed by excess oxygen which only oxidizes part of NO to NO2 in the gas phase.

Temperature and Pressure Effects on HMX/Graphene via ReaxFF Molecular Dynamics Simulations

Studying the thermal decomposition of energetic materials at high temperatures can provide detailed reaction and mechanistic information, which is critical for understanding the reactivity of energetic materials, designing mixed explosives, and achieving improved safety. In this work, the effects of temperature and pressure on graphene (Gr)-based HMX crystals were investigated using ReaxFF molecular dynamics simulations. The thermal decomposition processes of perfect HMX crystals, HMX crystals with (001), (010), or (100) crystal planes, and HMX/Gr mixed systems were studied at high temperatures and pressures. In the mixed systems, different configurations of HMX molecules adsorbed on the Gr surface were confirmed by theoretical calculation methods. With the pressure ranging from atmospheric pressure to 31 GPa, 3, 5, and 3 configurations of HMX adsorbed on the Gr surface were identified for the (001)/Gr, (010)/Gr, and (100)/Gr systems, respectively. The time-dependent curves for the evolution of fragments, intermediates, and pyrolysis products were analyzed. The rate constant for the thermal decomposition of HMX was found to be significantly affected by the addition of Gr. In particular, the thermal decomposition reaction was strongly inhibited in the (010)/Gr system. This result indicates that Gr promotes an anisotropic thermal effect, resulting from the steric hindrance of the NO2 functional groups and the interaction between Gr and HMX molecules. Gr also affected the initial reaction pathway of homolytic N–NO2 bond cleavage, with C=O, C–OH, and C–OC bonds on the Gr surface participating in the formation of nitro radicals and HONO.

Atmospheric entry of sub-millimetre-sized grains into Mars atmosphere: white soft mineral micrometeoroids

AbstractIn this work, we study the passage through the Martian atmosphere of micrometeorites with a white soft mineral (WSM) composition, which have been proposed as transporters of organic molecules in the solar system. The atmospheric entry model includes the dynamics of the atmospheric entry and the physico-chemical aspects of the thermal decomposition process. The results show that, due to the reduced entry speed, Mars may have been a promising collector of matter in this form. In particular, the chemical decomposition process is much more effective than in the case of the Earth's atmosphere in maintaining a moderate temperature of the micrometeorite during most of the entry process.

A sustainable process for tungsten extraction from wolframite concentrate

Aiming to explore a sustainable process for tungsten extraction from wolframite concentrate, the digestion behavior and mechanism of wolframite in HCl solution at atmospheric pressure were firstly investigated in this work. The results showed that the digestion efficiency of wolframite reached 99.3% at the optimum condition: particle size of D(95) = 20 μm, stirring intensity of 250 r/min, reaction temperature of 90 °C, HCl stoichiometric ratio of 3.0, liquid to solid ratio of 3:1, and duration of 4 h. In the initial stage of digestion, tungsten was mainly dissolved into HCl solution, when the tungsten dissolution reached balance, solid H2WO4 layers were formed on the particle surface. The accumulation of Fe2+ and Mn2+ in HCl solution reduced the digestion efficiency of wolframite. The process of atomization-oxidative thermal decomposition is feasible for the recovery of Fe and Mn and recycling of HCl from the mother solution of digestion. Additionally, it was showed that the digested product had an excellent leachability of tungsten in NH3·H2O solution with WO3 leaching efficiency above 99.5%, and the (NH4)2WO4 solution was qualified for ammonium paratungstate (APT) production. The wrapping of wolframite by quartz, as well as the solid H2WO4 layers covering on wolframite particles, is a crucial factor for the incomplete digestion. This work has the potential to develop a novel technique for tungsten extraction from wolframite concentrate bypassing the alkali leaching process.

Comparison of the thermal decomposition of (NH4)3ZrF7 in air and N2 gas

To understand the effect of gas on the thermal decomposition process of (NH4)3ZrF7, the comparison of the thermal decomposition progress of (NH4)3ZrF7 in air and N2 gas at 340°C was investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The results showed that (NH4)3ZrF7 decomposed sequentially in air at 340°C through a several-step: (NH4)3ZrF7→ (NH4)2ZrF6 → NH4ZrF5→ NH4Zr2F9. After that, the hydrolysis of NH4Zr2F9 to form zirconium oxyfluorides occurred slowly. However, pure ZrF4 quickly formed at 340°C in a short time under N2 gas. The result indicates that the using of N2 gas not only accelerates the decomposition rate of (NH4)3ZrF7 and but also decreases the formation temperature of ZrF4.

Theoretical calculation and experimental verification of the vacuum thermal decomposition process of lunar silicon oxide

Thermal decomposition of oxides can be achieved at a lower temperature under vacuum condition. For In Situ Resource Utilization (ISRU), using the thermal decomposition method to obtain resources can avoid complex processing. This study, through thermodynamic equilibrium calculation found that oxides such as iron(II) oxide (FeO), and magnesium oxide (MgO), are easy to decompose. While oxides, such as silicon monoxide (SiO), titanium(II) oxide (TiO), etc., are difficult to decompose. Silicon dioxide (SiO2) is selected as the sample for the nanosecond laser experiment under a vacuum. Temperature simulation showed that a laser can give the sample high-temperature energy above 4700 K. Dynamic analysis showed that the sample undergoing complete plasma decomposition was the most thorough. The results of thermal decomposition of silicon monoxide is the most difficult to achieve. Under the conditions of 75 mJ laser pulse energy, 10−4 Pa initial vacuum, etc., the oxygen-silicon atom ratio of the products ranged from 1.74 to 0.12 and decreased with decreasing particle radius. Understanding the decomposition behavior of lunar surface oxides is crucial for the clean utilization of lunar surface resources. Moreover, it also provides a theoretical basis for high-temperature processing and element migration of airless objects.

Impact of structure and magnetic parameters of nanocrystalline cores on surface properties of molecularly imprinted nanoconjugates for analysis of biomolecules – A case of tyramine

In this paper, the investigations were carried out to reveal the complex nature of the nanocrystalline magnetic cores and to validate the hypothesis that magnetic molecularly imprinted polymer (MMIP) could be used as an effective sorbent during analysis of biomolecules but the adsorbate-sorbent process is independent from the amount of siloxane functionalized magnetite core (Fe3O4@SiO2-MPS). For that purpose, molecularly imprinted shell layer composed from poly(methacrylic acid-co-ethylene glycol dimethacrylate) was conjugated to various amounts of Fe3O4@SiO2-MPS. Magnetic measurements showed single-domain-type magnetic behavior for all materials. Thermal decomposition process revealed different enthalpies (110 to 279 J g−1) with the highest value for MMIP prepared from the lowest amount of Fe3O4@SiO2-MPS. The morphological and structural analyses proved a presence of single magnetite crystallite and elemental mapping confirmed core–shell structure. The binding capacities for MMIPs revealed similar values (0.897 ± 0.114 to 1.019 ± 0.129 µg g−1) and specificity (IF: 3.36 to 3.99). The MMIP sorbent was used to determine model biomolecule of tyramine in wine in the validated analytical method, proving the stability of sorbent. The lower tyramine levels were found in Chilean and Australian wines (0.42 ± 0.03 and 0.15 ± 0.01 mg L-1, respectively) and higher in French one (7.58 ± 0.15 mg L-1).

Dependence of the structure of Bi-2212 superconducting thin film prepared by sol-gel method on different complexing agents

The complexed sol-gel method has unique advantages in the preparation of multi-component functional thin films. In this paper, Bi2212 superconducting thin films were prepared by sol-gel method on SrTiO3(100) single crystal substrates. Glycine and glycolic acid were used as complexing agents. The thermal decomposition processes of the two sols were analyzed by contrasting thermal-thermogravimetric curves. The heat treatment processes of the different complexing agent systems were optimized to obtain films with flatter surface morphology. The phase composition of the intermediate products during the precursor heat treatment was changed by adjusting the conditions of the complexing agent and the acidity of the sol, which expanded the pure phase temperature interval of the final product. The pure phase temperature interval, morphology, surface roughness, and electrical transport properties of Bi2212 superconducting films prepared with different complexing agent sol-gel systems were investigated. When glycolic acid was used as the complexing agent, the Bi-2212 superconducting films showed the widest phase formation temperature zones of 25 K. They also had a smaller surface roughness of 10–15 nm. Other than that, all samples had good epitaxial properties, and electrical transport properties. This work provides a new idea for expanding the phase-forming temperature region of multicomponent functional ceramics. It also shows the promising potential of sol-gel method for preparing multicomponent functional films with high quality surfaces.