Mechanism Of Thermal Oxidation Research Articles

Deconvoluting the Mechanisms of Thermal Degradation and Oxidation during the Aging Simulation of Elastomeric Modified Asphalt Binders

Deconvoluting the Mechanisms of Thermal Degradation and Oxidation during the Aging Simulation of Elastomeric Modified Asphalt Binders

Thermal oxidation mechanism of palmitic aicd

The oxidation and degradation of fats lead to a decrease in the nutritional value of food and pose safety concerns. Saturated fatty acids also hold a significant position in the field of lipid oxidation. In this study, the oxidation products of methyl palmitate were investigated by using gas chromatography mass spectrometry (GC–MS). Seven monohydroperoxides and 72 secondary oxidation products were detected. Combined with density functional theory (DFT) calculations, the formation mechanisms of oxidation products can be summarized into four stages. The initial stage involved the formation of monohydroperoxides and alkanes, followed by the subsequent stage involving methyl x-oxo(hydroxy)hexadecanoates. The third stage involved the formation of methyl ketones, carboxylic acids, and aldehydes, while the final stage involved lactones. Meanwhile, methyl ketones were the most abundant oxidation product, approximately 25 times more abundant than aldehydes; the calculated results agreed well with the experimental results. The establishment of a comprehensive thermal oxidation mechanism for palmitic acid provided a new foundation for future lipid oxidation analyses.

Effect of Hyperthermal Hybrid Gas Composition on the Interfacial Oxidation and Nitridation Mechanisms of Graphene Sheet.

Graphene is one of the most promising thermal protection materials for high-speed aircraft due to its lightweight and excellent thermophysical properties. At high Mach numbers, the extremely high postshock temperature would dissociate the surrounding air into a mixture of atomic and molecular components in a highly thermochemical nonequilibrium state, which greatly affects the subsequent thermal chemical reactions of the graphene interface. Through establishing a reactive gas-solid interface model, the reactive molecular dynamics method is employed in this study to reveal the influences of the thermochemical nonequilibrium gas mixture on the thermal oxidation and nitridation mechanisms of graphene sheet. The results show that three distinctive stages can be recognized during bombardment of various nonequilibrium gas components toward the graphene sheet: (i) collision and surface adsorption stage, (ii) gas-solid heterogeneous reaction stage, and (iii) gas phase homogeneous reaction stage. The surface catalysis effect is found to be dominant during the first two stages, which can influence the following ablation behavior of graphene significantly at high-temperature conditions. Moreover, surface catalysis, oxidation, nitridation, and ablation mechanisms between nonequilibrium gas and graphene interface are revealed, which is of high relevance for future interfacial design and application of graphene as a thermal protection material.

In situ EPR spin-trapping tracking of macroradical formation and the role of a hindered phenol anti-oxidant in reducing thermo-oxidative phenomena of poly(ethylene terephthalate)

One of the major issues concerning poly(ethylene terephthalate) (PET) produced with titanium-based catalysts is its sensitivity to high-temperature oxidation, which results in performance loss and discoloration. Here, the thermo-oxidative phenomena of titanium-catalyst-produced PET during its synthesis and post-processing in the presence of hindered phenol anti-oxidant Irganox 1425 has been investigated by a spin-trapping technique. Three types of spin adducts have been determined and quantified; –O−•CH− is the dominant radical intermediate, while •CH2− and –O−•CH− are mainly produced by the decomposition of diethylene glycol (DEG) units. An excessively high DEG content leads to instability of PET chains at high temperatures and so is not conducive to suppressing oxidation. An anti-oxidant can effectively eliminate radicals induced by thermo-oxidative reactions and improve the thermal stability of PET, especially in the post-processing stage. A comprehensive thermal oxidation mechanism is proposed, in which PET thermolysis starts with hydrogen abstraction to produce –O−•CH−, and then auto-oxidation ensues by radical intermediates attacking other PET chains. The cyclic reaction is reasonably terminated by the anti-oxidant serving as a hydrogen donor to quench radical intermediates.

Mechanism of thermal oxidation into volatile compounds from (E)-4-decenal: A density functional theory study

Unsaturated aliphatic aldehyde oxidation plays a significant role in the deep oxidation of fatty acids to produce volatile chemicals. Exposing the oxidation process of unsaturated aliphatic aldehydes is crucial to completely comprehend how food flavor forms. In this study, thermal desorption cryo-trapping in conjunction with gas chromatography-mass spectrometry was used to examine the volatile profile of (E)-4-decenal during heating, and 32 volatile compounds in all were detected and identified. Meanwhile, density functional theory (DFT) calculations were used, and 43 reactions were obtained in the 24 pathways, which were summarized into the peroxide reaction mechanism (ROOH), the peroxyl radical reaction mechanism (ROO·) and the alkoxy radical reaction mechanism (RO·). Moreover, the priority of these three oxidative mechanisms was the RO· mechanism > ROOH mechanism > ROO· mechanism. Furthermore, the DFT results and experimental results agreed well, and the oxidative mechanism of (E)-4-decenal was finally illuminated.

Unveiling the mechanism of thermal catalytic oxidation of HCHO from the kiln exhaust gas using Sc-decorated Cr2CO2-MXenes

Sc/Cr2CO2 is a novel efficient thermal catalyst for HCHO oxidation.

Promotion effects of thermal oxidation on zeolitic imidazolate framework-8 (ZIF-8) for efficient broad-spectrum photocatalysis

The development of photocatalysts with broad-spectrum response and efficient electron transfer yet remains a great challenge. Herein, we report a systematic research on the thermal oxidation mechanism of ZIF-8 and its promotion effects on photocatalytic performance. The activation energy E of organic ligands decomposition during ZIF-8 thermal oxidation was calculated to be 103.7 kJ/mol by Kissinger-Akahira-Sunose (KAS) model. The wurtzite ZnO crystal and oxidizing functional groups (HNCO, CO, etc.) formed in oxidized ZIF-8 were crucial to the superior photocatalytic performance. In particular, O350/ZIF-8 had the broadest optical absorption band (∼750 nm) and largest photocurrent density, which exhibited the highest photocatalytic activity of methylene blue (MB) with rate constant k of 0.0374 min−1. The photogenerated ·O2− and ·OH radicals were found to react as main oxygen species in photocatalytic reaction. Taken together, this study not only offered a simple method to prepare ZIF-8 based photocatalyst with high activity and stability, but also provided guidance for the efficient photocatalytic degradation of organic compounds in wastewater.

Volatile metabolite profiling of linolenic acid oxidation in the heating process

Linolenic acid is an important fatty acid, and volatiles generated by its oxidation are the major components of food flavor. In this study, volatile components generated from linolenic acid during heating were detected and analyzed by using thermal desorption cryo-trapping system coupled with gas chromatography-mass spectrometry. A total of 52 volatile compounds were identified, including aldehydes (18), ketones (12), alcohols (6), furans (4), acids (6) and aromatic compounds (6). The forming temperature of each volatile compound was also determined. It was found that most volatile compounds with shorter carbon chains were mainly generated at lower temperatures, while volatile compounds with longer carbon chains were mainly produced at higher temperatures. Results of principal component analysis show that most of the identified volatiles were considered as the characteristic ones of the high temperature points. Potential thermal oxidation mechanism of linolenic acid was also given at the same time.

Thermal oxidative aging mechanism of lignin modified bitumen

Lignin is the most abundant renewable resource in nature, which can be applied to not only improve resource utilization but also improve bitumen road performance. In this study, the evolution of lignin during thermal-oxidative aging of bitumen was investigated by dynamic shear rheology test (DSR), thermogravimetric test (TG) and Fourier transform infrared spectroscopy (FTIR). The thermo-oxidative aging mechanism of lignin modified bitumen was analyzed. The results show that lignin-modified bitumen had better aging resistance than the virgin bitumen. Meanwhile, the changes of functional group indices at 1460 cm−1, 1512 cm−1, and 1600 cm−1 in the infrared spectra proved that the thermal-oxidative aging mechanism was the decomposition of lignin itself under the action of thermal oxygen, which inhibited the aging process of bitumen.

Solution-Processed Two-Dimensional Metal Oxide Anticorrosion Nanocoating.

Molecularly thin two-dimensional (2D) nanomaterials are attractive building blocks for constructing anticorrosion nanocoatings as an ultimate pursuit in the metal-related industry. However, the nanocoating of prefocused graphene is far from industrial demands due to its high cost, low scalability, and insufficient quality. We propose all requirements to realize rational anticorrosion nanocoating of metal oxide nanosheets. The proof-of-concept study with Ti0.87O2 and Ca2Nb3O10 nanosheets demonstrates that the 10 and 20 nm thick coatings fabricated by a facile layer-by-layer (LbL) self-assembly on stainless steel (SUS) give perfect inhibition efficiency (IE) values of 99.92% and 99.89%, respectively. A driving test with a nanosheet-coated car-baffle demonstrated suitable corrosion resistance and mechanical and thermal robustness for industrial applications. The revealed and controlled thermal oxidation mechanisms are critical toward high-temperature application of the 2D oxide anticorrosion nanocoating. The advantages of nanosheet coating and extensible materials design will open a solid but exciting route to anticorrosion nanotechnology.

New Advances in the Kinetic Modeling of Thermal Oxidation of Epoxy-Diamine Networks

This article deals with the thermal oxidation mechanisms and kinetics of epoxy-diamine (EPO-DA) networks used as composite matrices reinforced with carbon fibers in the aeronautical field. The first part of this article is devoted to a detailed presentation of the new analytical kinetic model. The so-called “closed-loop” mechanistic scheme, developed in the last 3 decades in our laboratory in order to accurately describe the thermal oxidation kinetics of saturated hydrocarbon polymers, is recalled. Its main characteristics are also briefly recalled. Then, the system of differential equations derived from this oxidation mechanism is analytically solved without resorting to the usual simplifying assumptions that seriously degrade the reliability of all kinetic models. On the contrary, the generalization of the proportionalities observed between the steady concentrations of the different reactive species (i.e., hydroperoxides and alkyl and peroxy radicals) to the entire course of thermal oxidation gives a series of much sounder equations. From this basis, the kinetic model is completed by considering new structure/property relationships in order to predict the consequences of thermal oxidation on the thermomechanical properties, in particular on the glass transition temperature (Tg). To reach this second objective, the two main mechanisms responsible for the alteration of the macromolecular network structure are recalled: chain scissions and crosslinking. Like any other chemical species, their kinetics are directly expressed from the oxidation mechanistic scheme using the classical concepts of chemical kinetics. The second part of this article is devoted to the checking of the kinetic model reliability. It is shown that this latter accurately simulates the experimental curves of carbonyl build-up and Tg decrease versus time of exposure determined in our laboratory for three EPO-DA networks under study, exposed in a wide variety of thermal oxidative environments. The values determined by inverse solving method for the different model parameters are discussed and their temperature dependence are elucidated. Finally, an end-of-life criterion is proposed for predicting the lifetime of EPO-DA networks involving a predominant chain scission process.

Non-microbial methane emissions from tropical rainforest soils under different conditions.

Non-microbial methane (NM-CH4), emissions from soil might play a significant role in carbon cycling and global climate change. However, the production mechanisms and emission potential of soil NM-CH4 from tropical rainforest remain highly uncertain. In order to explore the laws and characteristics of NM-CH4 emission from tropical rainforest soils. Incubation experiments at different environmental conditions (temperatures, soil water contents, hydrogen peroxide) and for soils with different soil organic carbon (SOC) contents were conducted to investigate the NM-CH4 emission characteristics and its influence factors of soils (0-10cm) that collected from a tropical rainforest in Hainan, China. Incubation results illustrated that soil NM-CH4 release showed a linear increase with the incubation time in the first 24 hours at 70 °C, whereas the logarithmic curve increase was found in 192 h incubation. Soil NM-CH4 emission rates under aerobic condition were significantly higher than that of under anaerobic condition at first 24 h incubation. The increasing of temperature, suitable soil water contents (0-100%), and hydrogen peroxide significantly promoted soil NM-CH4 emission rates at the first 24 h incubation. However, excessive soil water contents (200%) inhibited soil NM-CH4 emissions. According to the curve simulated from the NM-CH4 emission rates and incubation time at 70 °C of aerobic condition, soil would no longer release NM-CH4 after 229 h incubation. The NM-CH4 emissions were positively corelated with SOC contents, and the average soil NM-CH4 emission potential was about 6.91 ug per gram organic carbon in the tropical mountain rainforest. This study revealed that soils in the tropical rainforest could produce NM-CH4 under certain environment conditions and it supported production mechanisms of thermal degradation and reactive oxygen species oxidation. Those results could provide a basic data for understanding the soil NM-CH4 production mechanisms and its potential in the tropical rainforest.

Pit Formation Mechanism of Monolayer MoS2 By Thermal Oxidation

Generating pits and thereby active edge sites of molybdenum disulfide (MoS2) monolayers is desirable for many electrochemical catalytic reactions including hydrogen evolution reaction (HER). Thermal oxidation is one of the potentially scalable and facile methods to effectively create the pits on MoS2 monolayers. Therefore understanding the thermal oxidation mechanism is very important to precisely control the generation of active edge sites of MoS2-based electrocatalysts. To date, pits are assumed to be favorably formed on MoS2 at undercoordinated sites such as sulfur (S) vacancies at high temperatures. However, the thermal oxidation studies have not considered the existence of adventitious carbon (C) that exists almost everywhere and interact with oxygen at elevated temperatures. Herein, we investigated the influence of adventitious C on the thermal oxidation of MoS2 monolayers. We employed in situ environmental transmission electron microscopy (ETEM) to demonstrate the pit formation mechanism with the presence of adventitious C at the oxidation temperature of 300 °C. The in situ ETEM results show that the adventitious C is agglomerated at high temperatures. Then, the interfaces between monolayer MoS2 and C nanoparticle provide preferred sites for thermal oxidation of MoS2 and thus pit formation while the individual S vacancies exist intact. Density functional theory (DFT) calculations show the interfaces between MoS2 and C nanoparticle make the sequential adsorption of oxygen atoms thermodynamically favorable, unlike only S vacancy sites. We also tested the electrochemical performance of MoS2 with pits for HER and it reduced the overpotential by ~ 130 mV. These results demonstrate the combination between ETEM experiment and DFT calculation can be effectively used to study the chemical reaction mechanism between 2-dimensional materials such as MoS2 and gaseous species. Furthermore, we provide the potential to control the active edge site of MoS2-based electrocatalyst by understanding the fundamental pit formation mechanism by thermal oxidation.

Microwave plasma oxidation kinetics of SiC based on fast oxygen exchange

Gate oxide process is one of the most important issues for making high performance SiC power MOSFETs. Previously, it has been demonstrated that plasma oxidation provides a promising way for making advanced SiC power MOSFETs. To further boost the performance of SiC MOSFETs, understanding the plasma oxidation kinetics becomes inevitable. In this contribution, microwave plasma oxidation kinetics of SiC are investigated by labelling the SiO2 with 18O isotopes. Growth of SiO2 chemically comparable to that from 1300 °C thermal oxidation with flat interface is confirmed by XPS and TEM. Moreover, SiO2 with thickness over 50 nm is demonstrated to be obtainable with rapid growth rate (>2 nm/min) at relatively low temperatures (<1000 °C) by properly adjusting the power and pressure. During the plasma oxidation, fast oxygen exchange is proved by experiments, which is significantly different from the oxidation mechanism of thermal oxidation. Furthermore, several possible reasons, such as thermal effect, water vapor oxidation and atomic oxygen diffusion for the fast oxygen exchange are discussed and eliminated, while the presence of defects in SiO2 or SiO2 structural changes are left as possible reasons for the fast oxygen exchange.

The thermal oxidation mechanism of TMPTO with antioxidants investigated by ReaxFF MD

PurposeThis paper aims to study the thermal oxidation performance of antioxidant additives in ester base oils deeply.Design/methodology/approachReaxFF molecular dynamics was used to simulate the thermal oxidation process of butyl octyl diphenylamine and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate as two antioxidant additives act on the Trimethylolpropane trioleate (TMPTO) base oil. Meanwhile, combining with the infrared spectroscopy characterization results of the thermal oxidation test, this paper provides theoretical support for the development of high-performance synthetic lubricants and their antioxidant additives.FindingsThe results show that butyl octyldiphenylamine easily removes the hydrogen atom on the secondary amine, which promotes the formation of more long carbon chain diene radicals or polyene hydroperoxides from TMPTO. Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate could easily decompose into octadecyl hydroperoxide and 2,6-di-tert-butyl 4-propionylphenol, which could convert into 2-tert-butyl-4-peroxyethyl-6-hydroperoxy-tert-butylphenol in the middle of the thermal oxidation reaction, prompting TMPTO to form more short-chain alkenyl and olefin hydroperoxide or other oxide.Originality/valueThe main change characteristics of base oil molecules are the first thermal decomposition to form oleic acid groups and ethane cyclopropane methyl oleate. Under the action of butyl octyldiphenylamine and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate, the deep oxidation and decomposition reaction are slowed down.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0037/

Thermal Oxidation Mechanism and Test Method of Lubricating Oil

Thermal Oxidation Process Mechanism of lubricating oil is described, at the same time, the thermal oxidation test methods of lubricating oil-infrared spectrum, rotating oxygen bomb, Cyclic voltammetry and sludge content are introduced and compared. The correlation and difference between them were compared by experiments.

Exploration on the influence mechanism of heteroatom doped graphene on thermal oxidative stability and decomposition of polypropylene

The inferior thermal oxidative stability of polypropylene (PP) is a limitation for its practical applications. In this study, PP composites filled with heteroatom doped graphene are prepared. Heteroatoms with different electronegativity values, including nitrogen, phosphorus and boron, are successfully doped into the structure of reduced graphene oxide (RGO) through high temperature annealing. Doped RGO is characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. PP/doped graphene composites are acquired by solution blending. The effects of heteroatom doped RGO on thermal oxidative stability and decomposition behavior of PP are investigated by thermogravimetric analysis and thermogravimetric-infrared spectrometry, respectively. The results indicate that doped RGO can significantly improve thermal oxidative stability of PP. Compared with neat PP, the temperature at maximum weight loss rate of PP/N-RGO-2.0, PP/B-RGO-2.0 and PP/P-RGO-2.0 are increased by 112 °C, 141 °C and 122 °C, respectively. Thermal oxidative decomposition mechanism of PP/doped RGO composites is discussed based on the analyses of pyrolysis gaseous products and chemical structures of doped RGO. This work provides a novel exploration for enhancing thermal stability of polymer. This work provides an investigation strategy for in-depth study of enhancement mechanisms of graphene on thermal stability of polymers.

Воздействие некоторых сложных хемостимуляторов и модификаторов на термооксидирование InP

Воздействие некоторых сложных хемостимуляторов и модификаторов на термооксидирование InP

Oxidative stabilities of olive and camellia oils: Possible mechanism of aldehydes formation in oleic acid triglyceride at high temperature

Olive and camellia oils were monitored and compared during heating at 120 °C, 150 °C and 180 °C for 24 h to determine the possible thermal oxidation mechanism of oleic acid triglyceride. The results demonstrated that octanal, nonanal, decanal, 2-decenal and 2-undecenal were the characteristic carbonyls for oleic acid-rich oils. The oxidation rule of oil was easily determined at 120 °C, at which point changes in the acid value, peroxide value, anisidine value and carbonyl compounds corresponded to changes in fatty acids and tocopherols. However, the oxidation rule of oil was different at higher temperatures. According to the evolution of five characteristic aldehydes, four types of oxidation pathways of oleic acid triglyceride were obtained: Decanal and 2-undecenal came from the homolysis of 8- hydroperoxide. Nonanal was from the homolysis of 10- hydroperoxide and 9- hydroperoxide. Octanal was from the homolysis of 11- hydroperoxide. 2-Decenal was from the homolysis of 9- hydroperoxide. Homolysis B-scission of 10-hydroperoxide (nonanal), 11-hydroperoxide (octanal) and 8- hydroperoxide (decanal) was predominant at 120 °C, but was weakened as the temperature increased to 180 °C. Hence, the temperature had a significant effect on the formation and decomposition of hydroperoxide positional isomers.

Research results of makeup influence on semi-synthetic motor oils thermal oxidation stability

During the running motor oil quality determination oil makeup has a big influence on thermal oxidation mechanism, however there is a problem of insufficient examination of makeup influence on motor oil conditions. Main goal of these researches is to determine how makeup effects on motor oil’s thermal oxidation stability. For the research Lube oil Lukoil Super 10W - 40 SG/CD has been chosen. Thermal oxidation stability results assessment was conducted basing on obtained values of: light stream absorption criteria, volatility and thermal oxidation stability criteria in cases of research with makeup and without it. There was offered a criteria of makeup influence on thermal oxidation stability values, which identified as change of light stream absorption rate proportion and thermal oxidation stability criteria in case of research with and without makeup. Research methodology involved motor oil test on thermostating device consequently under temperatures 180, 170 and 160 °C with makeup and without it in condition when quantity of makeup oil corresponded to vaporized oil quantity. Research results demonstrated that oil makeup decrease thermal oxidation intensity on the whole temperature test rate.