Initial Stages Of Decomposition Research Articles

The Dynamics of Allelochemicals and Phytotoxicity in Eisenia fetida during the Decomposition of Eucalyptus grandis Litter.

Allelopathy is an underlying and controversial mechanism for detrimental environmental effects in the management of Eucalyptus plantations. However, little attention has been paid to the dynamics of allelochemicals and phytotoxicity in soil fauna during litter decomposition. To explore the relationship between the dynamics of phytotoxicity and allelochemicals, a decomposition experiment was conducted using 4-year-old and 8-year-old Eucalyptus grandis litter (0, 10, 20, 30, and 45 days). The acute toxicity of Eisenia fetida was assessed, and a chemical analysis of the eucalyptus leaves was performed. Biochemical markers, including total protein, acetylcholinesterase (AChE) activity, and oxidative stress levels (SOD and MDA) were measured. A comet assay was used to determine DNA damage in E. fetida cells. The results showed that after 20-30 days of decomposition, E. grandis litter exhibited stronger phytotoxic effects on E. fetida in terms of growth and biochemical levels. After 20 days of decomposition, the weight and total protein content of E. fetida first decreased and then increased over time. SOD activity increased after 20 days but decreased after 30 days of decomposition before increasing again. MDA content increased after 20 days, then decreased or was stable. AChE activity was inhibited after 30 days of decomposition and then increased or stabilized with further decomposition. Soluble allelochemicals, such as betaine, chlorogenic acid, and isoquercitrin, significantly decreased or disappeared during the initial decomposition stage, but pipecolic acid significantly increased, along with newly emerging phenolic fractions that were present. More allelochemicals were released from 8-year-old litter than from 4-year-old E. grandis litter, resulting in consistently more severe phytotoxic responses and DNA damage in E. fetida. Scientific management measures, such as the appropriate removal of leaf litter in the early stages of decomposition, might help support greater biodiversity in E. grandis plantations.

Thermal decomposition mechanism of HMX/HTPB hybrid explosives studied by reactive molecular dynamics.

The thermal decomposition process of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine/hydroxyl-terminated polybutadiene (HMX/HTPB) hybrid explosives and pure HMX explosives at different temperatures (2000 ~ 3500 K) was investigated using the reactive molecular dynamics method. This study aimed to analyze the effect of binders on the thermal decomposition of HMX at the atomic scale and reveal the thermal decomposition mechanism of HMX/HTPB. The results showed that the thermal decomposition process of the HMX molecule in the HMX/HTPB hybrid system involves a continuous denitration followed by the disintegration of the main ring. The HTPB chain will experience dehydrogenation, dehydroxylation, and chain fragmentation. Including HTPB in the hybrid system significantly increased the presence of H and OH radicals. These radicals then interacted with HMX and its decomposition products and produced more of the final products H2O and H2 in the HMX/HTPB hybrid system compared to pure HMX. Additionally, it was observed that the HTPB chain fragments attached to the HMX decomposition products prevented the formation of N2 and CO2. Furthermore, the activation energies (Ea) of the initial and intermediate decomposition stages of the HMX/HTPB hybrid system were 98.45 kJmol-1 and 90.69 kJmol-1, respectively. The results showed that the activation energies of the HMX/HTPB hybrid system are lower than the pure HMX system in these two stages. Consequently, HTPB will enhance HMX's thermal decomposition and decreased the system's insensitivity to heat stimuli. The molecular dynamics simulation of the HMX/HTPB hybrid system was performed using the ReaxFF module in the LAMMPS software, and the ReaxFF/lg force field was used to describe the interatomic interactions as well as the chemical reactions.

Microscopic experimental study on the effects of NaCl concentration on the self-preservation effect of methane hydrates under 268.15 K

It is known that salt ions are abundant in the natural environment where natural gas hydrates are located; thus, it is essential to investigate the self-preservation effect of salt ions on methane hydrates. The dissociation behaviors of gas hydrates formed from various NaCl concentration solutions in a quartz sand system at 268.15 K were investigated to reveal the microscopic mechanism of the self-preservation effect under different salt concentrations. Results showed that as the salt concentration rises, the initial rate of hydrate decomposition quickens. Methane hydrate hardly shows self-preservation ability in the 3.35% (mass) NaCl and seawater systems at 268.15 K. Combined the morphology of hydrate observed by the confocal microscope with results obtained from in situ Raman spectroscopy, it was found that during the initial decomposition stage of gas hydrate below the ice point, gas hydrate firstly converts into liquid water and gas molecules, then turns from water to solid ice rather than directly transforming into solid ice and gas molecules. The presence of salt ions interferes with the ability of liquid water to condense into solid ice. The results of this study provide an important guide for the mechanism and application of the self-preservation effect on the storage and transport of gas and the exploitation of natural gas hydrates.

Changes and driving factors of microbial community composition and functional groups during the decomposition of Pinus massoniana deadwood.

Clarifying changes in the microbial community in deadwood at different stages of decomposition is crucial for comprehending the role of deadwood in the biogeochemical processes and the sustainability of forest development. However, there have been no reports on the dynamics of microbial community during the decomposition of Pinus massoniana. We used the "space-for-time" substitution to analyze the characteristics of microbial community changes and the key influencing factors in the P. massoniana deadwood during different decomposition stages by 16S and ITS rRNA gene sequencing. The results suggest that the microbial community structure of the early decomposition (decay class I) was significantly different from the other decay classes, while the diversity and richness of the microbial community were the highest in the late decomposition (decay class V). The Linear Discriminant Analysis Effect Size analysis revealed that most bacterial and fungal taxa were significantly enriched in decay classes I and V deadwood. During the initial stages of decomposition, the relative abundance of the bacterial functional group responsible for carbohydrate metabolism was greater than the later stages. As decomposition progressed, the relative abundance of saprophytic fungi gradually decreased, and there was a shift in the comparative abundance of mixed saprophytic-symbiotic fungi from low to high before eventually decreasing. Total organic carbon, total nitrogen, carbon-to-nitrogen ratio, total potassium, total phenol, condensed tannin, lignin, and cellulose were significantly correlated with microbial community structure, with the carbon-to-nitrogen ratio having the greatest effect. Our results indicate that the physicochemical properties of deadwood, microbial community structural composition and functional group changes were related to the decay class, among which the carbon-to-nitrogen ratio may be an important factor affecting the composition and diversity of microbial communities.

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

СРАВНИТЕЛЬНАЯ ОЦЕНКА СКОРОСТИ РАЗЛОЖЕНИЯ РАСТИТЕЛЬНОГО ОПАДА В ЕЛОВЫХ И СОСНОВЫХ ЛЕСАХ НА СЕВЕРНОМ ПРЕДЕЛЕ РАСПРОСТРАНЕНИЯ

A comparative assessment of the processes of the initial stages of decomposition of plant residues (pine needles, spruce needles, leaves of boreal shrubs, moss thalli) in lichen-shrub pine forests and shrub-green-moss spruce forests formed under natural conditions at the northern limit of distribution was carried out. The characteristics of the litterfall initial composition, the rate of decomposition, and changes in the chemical composition of plant residues in the process of destruction caused by the forest type were studied. The higher initial content of Corg in the plant tissues of pine forests is associated with favourable lighting conditions under the forest canopy, while the high content of Mn in the tissues of ground cover plants in spruce forests is due to the direct influence of spruce needle litterfall rich in this nutrient. The results of the study clearly demonstrated that the forest type has a significant impact both on the initial quality of the litterfall of the same plant species and on the rate of decomposition: in the spruce forest, spruce needles and lingonberry leaves with a higher content of nutrients (Mg, Mn, P) and narrow ratios of elements (C:N, C:P) were characterised by more active decomposition processes. However, green moss litter, despite its high quality in spruce forests, decomposed more actively in pine forests, which may be due to a large amount of precipitation in pine forests. Thus, differences in the rate of decomposition of plant residues are influenced by a combination of the plant material quality, temperature conditions, and precipitation amount associated with the forest type.

Degradation of peat-forming plants at the first stages of decomposition in natural and post-pyrogenic peatlands of West Siberia

The aim of the study. Assessment of the phytomass stocks and decomposition rate of peat-forming plants’ residues in peat deposits of natural and post-pyrogenic peatlands at the initial stages of decomposition. Location and time of the study. The study was carried out in 2022 (May-September) at two oligotrophic bog sites: “Bakcharskoye” (field station “Vasyuganye”, IMCES SB RAS) and “Iksinskoye”, which are located in the north eastern spurs of the Great Vasyugan mire in the Bakcharsky and Shegarsky districts of the Tomsk region, Russia. Methods. The phytomass stocks were determined by the cutting method. The following fractions were separated: living phytomass (annual and perennial photosynthetic phytomass, i.e. green parts of grasses, shrubs leaves, mosses); perennial non-photosynthetic phytomass, i.e. shrubs stems, roots of grasses and shrubs; and dead phytomass (mortmass), i.e. litter, moss litter, standing dead phytomass. The decomposition rate of plant residues was determined by the method of litter bags placement in peat (Chamaedaphne calyculata, Sphagnum fuscum, Mixed sample consisting of 60% S. fuscum and 40% Ch. calyculata). In the initial and decomposed samples, the ash content was determined by the dry combustion method. The total carbon and nitrogen content, as well as the carbon and nitrogen isotopic composition, were determined using a DELTA V Advantage isotope ratio mass spectrometer. Results. This short-term study conducted during the growing season in conditions of undisturbed (Natural Ryam) and post-pyrogenic (Gar) phytocenoses showed that due to a significant amount of mortmass (2402 g/m2) Natural Ryam had organic matter stock exceeding that in the Gar by 1.7 times. On average, 59% of organic matter loss from the total losses during the growing season occurred in the first month. In both Gar and Natural Ryam conditions, minimal losses of organic matter were characteristic for Sphagnum fuscum (3.1 and 3.5% respectively). For the remaining samples the Gar conditions were more favorable for the degradation at the initial stages of decomposition. The Mixed sample occupied an intermediate position between its individual components in terms of mass losses. Carbon losses correlated well with mass losses both over 1 month of degradation (r=0.87) and over 4 months (r=0.96). In contrast to carbon, nitrogen accumulated in the Mixed sample at the initial stages of degradation, both after 1 month and 4 months. Conclusions. With smaller phytomass stocks in areas of post-pyrogenic succession, more active decay at the initial stages of organic matter decomposition occurs exactly under these conditions. The impact of post-pyrogenic succession on the rate of organic matter decomposition of Chamaedaphne calyculata plant residues and the Mixed sample was demonstrated. The most intensive decomposition of litter occured during the first month of degradation. Additionally, in the conditions of a burnt bog, a more intense release of nitrogen from all plant residues and accumulation of ash elements in Sphagnum fuscum samples were observed. The mixing of litter components influenced both the rate and dynamics of decomposition. The carbon and nitrogen isotopic composition began to change during the initial stages of decomposition, leading to enrichment with heavier isotopes 15N and 13C. This research emphasizes the importance of studying the processes of plant litter decomposition at the initial stages and considering the plant residue composition when studying the processes of organic matter transformation.

Structural and decomposition analysis of TKX-50 with vacancy defects: insights from DFT and AIMD simulations.

Vacancy defects are commonly present in crystals of energetic materials, and significantly influence the structural stability and decomposition mechanisms. However, there is a lack of profound understanding regarding the introduction of vacancy defects in energetic ionic salt, dihydroxylammonium 5,5'-bitetrazole-1,1'-dioxide (TKX-50). Due to the 1 : 2 ratio of anions to cations, TKX-50 possesses a more complex distribution of vacancy defects compared to traditional energetic materials. Based on the density functional theory method, the relatively favorable thermodynamic formation of vacancy defect distributions was revealed. The noncovalent interactions within the system, as well as the planarity of the anions, were investigated to understand the structural stability of TKX-50. Through ab initio molecular dynamics simulations, we discovered that vacancy defects can expedite the proton transfer during the initial decomposition stage of TKX-50 and affect the pathways of proton transfer. In the subsequent decomposition process, introduction of vacancy defects in the TKX-50 crystal leads to an earlier onset of ring-opening reactions and accelerates the appearance of decomposition products. The findings have the potential to provide insights into modeling vacancy defects in energetic ionic salts and reveal the impact of such defects on the structural stability and decomposition mechanisms of these materials.

Impact of Temperature and Moisture on the Decomposition of Peat-Forming Plants: Results of a Two-Year Incubation Experiment

The decomposition rate of plant residues is determined by both abiotic (temperature, moisture) and biotic factors (biochemical composition). To separate the contribution of each factor to the decomposition process, long-term incubation experiments under controlled conditions are required. Two-year incubation experiments were conducted with various types of peat-forming plants (Sphagnum fuscum, Chamaedaphne calyculata, Eriophorum vaginatum, and a mixed sample consisting of 60% Sphagnum fuscum and 40% Chamaedaphne calyculata). The experiments were carried out at temperatures of 2, 12, and 22 °C, with varying moisture levels (W = 30, 60, and 90% of their water-holding capacity). In all plant samples, the highest rates of C(CO2) emission (DecR) were observed in the initial stages of decomposition. The cumulative carbon loss (Ccum) during the experiment ranged from 45 to 196 mgC/g of plant material at 22 °C and 23 to 156 mgC/g of plant material at 2 °C. The decay constant (k) for all plant samples increased with rising temperature. The results of the three-way ANOVA showed that the influence of the examined factors on the cumulative losses of C(CO2) decreased in the following order: the type of plant > temperature > moisture. Throughout the experiment, the influence of the type of plant and moisture on DecR increased, while the effect of temperature decreased. The highest temperature sensitivity (Q10 = 0.71–6.19) was observed in the low-temperature range (2–12 °C) during months 4 to 6 of incubation. These results are relevant for modeling and predicting the rate of transformation of peat organic matter under changing climatic conditions.

Characterization of intrapuparial development of Musca domestica (Diptera: Muscidae), under different temperatures in laboratory conditions.

Musca domestica (Linnaeus, 1758) (Diptera: Muscidae), popularly known as "housefly", is a highly synanthropic species, with economic, medical-sanitary, veterinary, and forensic importance. It is able to cause damage to health, transmit pathogenic agents, cause infection in domestic animals, and, in its immature stage, cause secondary myiasis. The scavenging habit of its immature stages makes these flies pioneers in colonizing both human and animal carcasses, from the initial stages of corpse decomposition to the final stages. Intrapuparial development studies of all stages of the biological cycle of these insects help estimate pupal age, being useful to forensic entomology to aid in determining the minimum postmortem interval (minPMI). This study describes, morphologically, the external structures of the pupae, under temperatures of 23, 27, and 30 ± 1 °C aiming to identify the characteristics that define their developmental stages and estimation of the pupae age of M. domestica. The whole experiment was carried out under laboratory conditions, with relative humidity 60 ± 10% and 12 hours of photoperiod. The process of pupariation and pupation including pre-pupae phases were observed; larvae pupae apolysis; early cryptocephalic pupae; late cryptocephalic pupae; phanerocephalic pupae; pharate adult, discriminated by eye color (transparent eyes, pink eyes, and red eyes); and the emergency of adults, which occurred in the intervals of 162-180; 138-144, and 96-102 hr, respectively, being described throughout the metamorphosis of the external morphological characteristics of the pupal stage of M. domestica.

Assessment of thermal stability of two N-ethoxyethyl-N-methylpiperidinium borate ionic liquids by non-Arrhenian incremental kinetic method

Thermal stability of two borate-based ionic liquids (ILs) recently proposed as effective additive for high voltage batteries, N-ethoxyethyl-N-methylpiperidinium bis(oxalato)borate (BOB) and N-ethoxyethyl-N-methylpiperidinium difluoro(oxalato)borate (DFOB), was investigated. Thermogravimetry–differential thermal analysis measurements performed under nitrogen at 1, 2, 4, and 7 °C min−1 show gradual mass loss above 220 °C for both compounds. The TG curves were processed by isoconversional kinetic analysis under the assumption of non-Arrhenian behavior. The outcome of the analysis suggests that even the initial decomposition stages occur by a complex mechanism, probably via competing evaporation–decomposition paths with relative contributions varying with the heating rate. The service lifetimes estimated by the kinetic analysis result in a stability of DFOB up to 10-times higher than that of BOB in the 25–125 °C range. Further experiments were carried out by the Knudsen effusion mass spectrometry (KEMS) in order to get information on the composition of the vapor phase produced upon heating under effusion conditions. The mass spectra of the vapor phase showed a rapid onset of decomposition at 110 °C and 130 °C for BOB and DFOB, respectively, with a large release of the ion species with m/q = 98. This decomposition path dominates the simple evaporation to neutral ion pairs, which was nonetheless observed at m/q = 172 (integer cation). All the results seem to point toward a higher stability of DFOB compared to BOB, most probably due to the charge-stabilizing inductive effect of fluorine atoms.

Pore-Scale Investigation of Decomposition-Methods-Dependent Fluid Flow Properties in Hydrate-Bearing Sediments

Summary Depressurization (PD) and thermal stimulation (TS) are the primary methods for producing gas from natural gas hydrate (NGH) sediments. Fluid flow properties of the hydrate sediment, such as permeability, are fundamental parameters for simulating both processes. Most of the existing formulated permeability models are based on the numerical or experimental investigation of hydrate morphology evolution without considering the decomposition methods. In this study, we investigate the hydrate-decomposition-methods (PD and TS processes)-dependent fluid flow properties of hydrate sediments, which is achieved by microcomputed tomography (micro-CT) scanning of hydrate morphology evolution during PD- and TS-induced decomposition, as well as pore-scale modeling of fluid flow in the extracted 3D fluid-rock-hydrate images. We find that the decomposition behavior during TS is much more complicated than that during PD. The retardation zone in the PD sample increases the heterogeneity of the pore structure, while the secondary hydrates generated during TS cause even more heterogeneity in the pore space. The better facilitation of the TS method on hydrate split is favorable for the continuity of the gas phase. The pore-scale fluid flow simulation shows that the modified Kozeny-Carman (K-C) model is the best to describe the evolution of the normalized permeability with hydrate saturation during PD. However, a single model is not sufficient to describe the normalized permeability during TS decomposition due to the stronger heterogeneous porous structure reformed by the local accumulation of secondary hydrates. The two-phase flow capability is best at the initial stage of PD decomposition, while the two-phase flow region becomes wider as TS decomposition progresses. These results provide significant references for the simulation of the natural hydrate extraction process using different decomposition methods.

Reactive molecular dynamics insight into the thermal decomposition mechanism of 2,6-Bis(picrylamino)-3,5-dinitropyridine

2,6-bis(picrylamino)-3,5-dinitropyridine (PYX) has excellent thermostability, which makes its thermal decomposition mechanism receive much attention. In this paper, the mechanism of PYX thermal decomposition was investigated thoroughly by the ReaxFF-lg force field combined with DFT-B3LYP(6–311++G) method. The detailed decomposition mechanism, small-molecule product evolution, and cluster evolution of PYX were mainly analyzed. In the initial stage of decomposition, the intramolecular hydrogen transfer reaction and the formation of dimerized clusters are earlier than the denitration reaction. With the progress of the reaction, one side of the bitter amino group is removed from the pyridine ring, and then the pyridine ring is cleaved. The final products produced in the thermal decomposition process are CO2, H2O, N2, and H2. Among them, H2O has the earliest generation time, and the reaction rate constant (k3) is the largest. Many clusters are formed during the decomposition of PYX, and the formation, aggregation, and decomposition of these clusters are strongly affected by temperature. At low temperatures (2500 K–2750 K), many clusters are formed. At high temperatures (2750 K–3250 K), the clusters aggregate to form larger clusters. At 3500 K, the large clusters decompose and become small. In the late stage of the reaction, H and N in the clusters escaped almost entirely, but more O was trapped in the clusters, which affected the auto-oxidation process of PYX. PYX’s initial decomposition activation energy (Ea) was calculated to be 126.58 kJ/mol. This work contributes to a theoretical understanding of PYX’s entire thermal decomposition process.

Preparation of lignin-based epoxy resins with tunable properties through constructing a partially ordered crosslinking network

In this work, lignin-based epoxy resins with tunable thermomechanical properties were prepared through constructing a partially ordered crosslinking network, which is designed on the curing behavior of phenyl glycidyl ether (PGE) and phenolated lignin-based epoxy resin (PLBER) with methyl nadic anhydride. Curing kinetics analysis illustrated that the introduction of PLBER could substantially reduce the activation energy (Ea) of curing reaction, indicating that PLBER have higher reactivity than PGE. Epoxy resins exhibited improved flexural strength, impact toughness, storage modulus, and glass transition temperature with the increase in lignin content. Based on the atomic force microscopic images of the thermosets, the highly crosslinked lignin-based epoxy resin was embedded in the epoxy matrix to form a heterogeneous network structure, which confirms that PGE reacted with PLBER as an active monomer to form a partially ordered crosslinked network, where PLBER represents the high-density region in the epoxy network. Moreover, the incorporation of lignin decreased the initial degradation temperature (Td5%) of epoxy resins, whereas Td50% (the temperature at 50% weight loss), Tmax (the temperature at the maximum rate of weight loss), and char yield (Char800) were improved with the increase in lignin content. This result may be attributed to the abundant β–O–4 bonds in lignin, which are degraded rapidly to form a protective carbon layer at the initial stage of decomposition, thereby slowing down the decomposition rate of epoxy resins.

Manganese indicates root decomposition rates across soil layer, root order, and tree species: Evidence from a subtropical forest

Different spatial locations provide different external conditions for root decomposition, while species and root order cause obvious differences in root substrate quality. Both differences in internal and external conditions may determine root decomposition rate. We explored the effects of decomposition position, root order, and species differences on root decomposition, and determined the role of manganese (Mn) in root decomposition. We conducted a fine root decomposition experiment using roots from Schima superba, Cleyera japonica, and Eurya loquaiana (separated into orders 1−3, 4−5, and 6) in the litter layer, and at 0−10 cm, 20−30 cm, and 40−50 cm soil depth in a subtropical forest. Root mass and concentration of C, N, P, Mn, condensed tannins and total phenolics were measured during two years of decomposition. Root decomposition rates decreased with increasing soil depth for all root samples. Compared to decomposition at 0−10 cm soil depth, remaining mass (% of initial) declined by 7%–34% in the litter layer and increased by 17%–37% at 40−50 cm soil depth. Lower-order roots had a higher decomposition rate than higher-order roots in the litter layer, but at 40−50 cm soil depth, we observed the opposite. Root litter Mn concentration and remaining mass were negatively correlated during the whole decomposition period including the early, middle, and late stages. Initial root Mn content was negatively correlated with remaining mass after two years of decomposition in the litter layer, and at 20−30 cm, 40−50 cm soil depth. However, no significant relationship between mass remaining and initial root N, P, condensed tannins and total phenolics were observed in the subsoil. Variance partitioning showed that the soil layer contributes significantly to the variance in remaining root mass, C, and Mn, whereas root order group contributed more than the soil layer to remaining root N and P. Our results indicate that soil depth is more important than root order for fine root decomposition rate at a site scale. Relative root decomposition rate between lower- and higher-order roots depends on the decomposition environment. Overall, this study strongly suggests that root Mn concentration (whether in initial or other decomposition stages) was much more consistently correlated with mass remaining than traditional predictors of N, P, condensed tannins, or total phenolics. Root Mn concentration greatly indicates root decomposition rates across soil layers, root orders, and species. Initial root Mn concentration and Mn supply capacity of the decomposition environment jointly control root decomposition rates throughout the decomposition process.

Thermal Behaviors and Interaction Mechanism of Ammonium Dinitramide with Nitrocellulose.

The initial interaction mechanism is very important for the design and safety of nano-scale composite energetic materials composed of ammonium dinitramide (ADN) and nitrocellulose (NC). The thermal behaviors of ADN, NC and an NC/ADN mixture under different conditions were studied by using differential scanning calorimetry (DSC) with sealed crucibles, an accelerating rate calorimeter (ARC), a self-developed gas pressure measurement instrument and a DSC-thermogravimetry (TG)-quadrupole mass spectroscopy (MS)-Fourier transform infrared spectroscopy (FTIR) combined technique. The results show that the exothermic peak temperature of the NC/ADN mixture shifted forward greatly in both open and closed circumstances compared to those of NC or ADN. After 585.5 min under quasi-adiabatic conditions, the NC/ADN mixture stepped into the self-heating stage at 106.4 °C, which was much less than the initial temperatures of NC or ADN. The significant reduction in net pressure increment of NC, ADN and the NC/ADN mixture under vacuum indicates that ADN initiated the interaction of NC with ADN. Compared to gas products of NC or ADN, two new kinds of oxidative gases O2 and HNO2 appeared for the NC/ADN mixture, while NH3 and aldehyde disappeared. The mixing of NC with ADN did not change the initial decomposition pathway of either, but NC made ADN more inclined to decompose into N2O, which resulted in the formation of oxidative gases O2 and HNO2. The thermal decomposition of ADN dominated the initial thermal decomposition stage of the NC/ADN mixture, followed by the oxidation of NC and the cation of ADN.

Thermal decomposition, flame propagation, and combustion reactions behaviours of stearic acid by experiments and molecular dynamic simulation

To better look into the thermal decomposition and combustion progress of stearic acid (C18H36O2), the experimental tests and Reaction Force Field (ReaxFF) molecular dynamics simulation were conducted. Also, an investigation into the flame propagation characteristics and the reaction mechanisms of stearic acid was explored under different conditions. The thermal decomposition activation energy of stearic acid obtained by the TG tests was 105.01 kJ/mol. This is consistent with the initial decomposition stage reaction activation energy calculated to be 94.273 kJ/mol in the simulation. The flame propagation process of stearic acid combustion was explored and involved three stages: the flame growth stage, the stable flame stage, and the flame decay stage. The flame growth stage was subdivided into the flame growth inside the tube, upper the tube, and mushroom-shaped cloud. Besides, the flame growth stage could correspond to three flame propagation velocity peaks. Furthermore, the simplified reaction mechanism scheme for stearic acid radicals could explain the macro flame propagation behaviours. The main reaction pathway through which the C18H36O2 molecules were decomposed into C2H4 and C2H3, C2H5, and other free radicals was found to correspond to the initial flame growth stage, and the flame decay stage was dominated by the generation of final reaction products (H2O, CO2, and CO2, etc.). Concerning the overall reaction mechanism, the unburned stearic acid was continuously ignited, and the combustion products were continuously generated at the same time, thereby corresponding to the stable flame propagation stage. According to the flame propagation process and the simulation results, combustion reaction mechanisms of stearic acid were constructed.

Effects of Different Guests on Pyrolysis Mechanism of α-CL-20/Guest at High Temperatures by Reactive Molecular Dynamics Simulations at High Temperatures.

The host-guest inclusion strategy has the potential to surpass the limitations of energy density and suboptimal performances of single explosives. The guest molecules can not only enhance the detonation performance of host explosives but also can enhance their stability. Therefore, a deep analysis of the role of guest influence on the pyrolysis decomposition of the host-guest explosive is necessary. The whole decomposition reaction stage of CL-20/H2O, CL-20/CO2, CL-20/N2O, CL-20/NH2OH was calculated by ReaxFF-MD. The incorporation of CO2, N2O and NH2OH significantly increase the energy levels of CL-20. However, different guests have little influence on the initial decomposition paths of CL-20. The Ea1 and Ea2 values of CL-20/CO2, CL-20/N2O, CL-20/NH2OH systems are higher than the CL-20/H2O system. Clearly, incorporation of CO2, N2O, NH2OH can inhibit the initial decomposition and intermediate decomposition stage of CL-20/H2O. Guest molecules become heavily involved in the reaction and influence on the reaction rates. k1 of CL-20/N2O and CL-20/NH2OH systems are significantly larger than that of CL-20/H2O at high temperatures. k1 of CL-20/CO2 system is very complex, which can be affected deeply by temperatures. k2 of the CL-20/CO2, CL-20/N2O systems is significantly smaller than that of CL-20/H2O at high temperatures. k2 of CL-20/NH2OH system shows little difference at high temperatures. For the CL-20/CO2 system, the k3 value of CO2 is slightly higher than that for CL-20/H2O, CL-20/N2O, CL-20/NH2OH systems, while the k3 values of N2 and H2O are slightly smaller than that for the CL-20/H2O, CL-20/N2O, CL-20/NH2OH systems. For the CL-20/N2O system, the k3 value of CO2 is slightly smaller than that for CL-20/H2O, CL-20/CO2, CL-20/NH2OH systems. For the CL-20/NH2OH system, the k3 value of H2O is slightly larger than that for CL-20/H2O, CL-20/CO2, CL-20/N2O systems. These mechanisms revealed that CO2, N2O and NH2OH molecules inhibit the early stages of the initial decomposition of CL-20 and play an important role for the decomposition subsequently.

Полуэмпирический анализ начальной стадии роста очага разложения за фронтом ударной волны

The paper presents analysis results of the initial stage of decomposition of phlegmatized RDX behind the front of a shock wave with pressure at the front approximately equal to 2 GPa, presumably during the time preceding the merging of the initially isolated decomposition centers. In this case, the time dependences of the mass fraction of explosive decomposition products behind the shock wave front and their specific volume obtained by processing the results of experiments carried out by the method of quasi-thin layers (layers tenths of millimeters thick placed between blocks of an inert reference material) are used. Based on the dynamics of changes in the parameters of the state of the reacting charge revealed from the results of the experiment, the time dependences of the characteristics of the matrix explosive movement around the decomposition site were established within the framework of an elementary spherical charge cell model. It is taken in the form of a sphere containing a central pore filled initially with air. Time dependences (within tenths of a microsecond) of the radius of the decomposition site, represented as a spherical cavity filled with explosive combustion products and compressible initial pore gas, are obtained; tangential deformation and its velocity on control spherical surfaces located at different distances from the surface of the decomposition site; strains and strain rates on the spherical combustion surface are revealed. The influence on the estimates of these characteristics of the concentration of decomposition sites in the range of variation 1012....1013 m–3 and the residual air pressure in the pores remaining after the pressing of charges (0,1 MPa and 1 MPa). Deformations and strain rates on the surface of the decomposition site, considered as a combustion surface, can reach values equal to 25% and 106 1/s, respectively. The surface area of the decomposition site can be an order of magnitude greater than the combustion surface area, which would be if the specific volume of decomposition products was not significantly less than that of the explosive. The speed of displacement of the surface of the decomposition site can exceed the linear combustion rate by an order of magnitude.

Emission of odor pollutants and variation in microbial community during the initial decomposition stage of municipal biowaste

Odor pollution often occurs in the initial decomposition stage of municipal biowaste, including throwing/collection and transportation. However, this aspect of odor impact from municipal biowaste has not been well studied. In this study, a practical dustbin (120 L) equipped with flux chamber and filled with three types of municipal biowaste was used to simulate garbage storage conditions. The result indicated that the emission rate of odor pollutants for uncooked food waste (UFW) represented a nearly linear growth trend, reaching the maximum (3963 ± 149 μg kg−1 DM h−1) at 72 h. Cooked food waste (CFW) increased rapidly from 8 h to 24 h, and then remain fluctuated, reached the maximum (2026 ± 77 μg kg−1 DM h−1) at 72 h. Comparatively, household kitchen waste (HKW) reached the maximum emission rate (10,396 ± 363 μg kg−1 DM h−1) at 16 h. Sulfide and aldehydes ketones were identified as dominant odor contributor to UFW and CFW, respectively. While aldehydes ketones and sulfides were both dominant odor contributor to HKW. Moreover, the microbial diversity analysis suggests that Acinetobacter was the dominant genus in UFW, and Lactobacillus was the dominant genus in CFW and HKW. In addition, it was evident that each odorous pollutant was significantly associated with two or more bacterial genera, and most bacterial genera such as Acinetobacter, were also significantly associated with multiple odorous pollutants. The variation of odorants composition kept consistent with microbial composition. The present study could provide essential evidence for a comprehensive understanding of odorant generation in the initial decomposition stage of municipal biowaste. It could contribute to setting out strategies for odor control and abatement in municipal biowaste management systems.