Oxidation Onset Temperature Research Articles

The thermal stability of carbon materials in the air: Quantitative structural investigation of thermal stability of carbon materials in air

The variability of the nanostructure of carbon materials results in a uniquely wide range of physical and chemical properties. This work analyses how the nanostructure affects the thermal stability of 2D and 3D graphene-based materials (graphene, fullerenes, nanotubes, zeolite-templated carbon), disordered and 3D ordered mesoporous carbon materials (activated carbons, CMK-3, 3DOMM), and layered carbon materials (few-layer graphene, graphene nanoplatelets, graphite) in the air. Combination of structural, thermogravimetric and calorimetric analyses under identical conditions for all the carbon nanomaterials showed that the most decisive factor increasing the stability is the stacking of graphene layers with long-range order parallel to each other, increasing the onset oxidation temperature (Ton) with the number of graphene layers from 530 °C for graphene up to 800 °C for graphite. The unsaturated carbon atoms at the defects and edges and the bending stress in the 3D graphene layers cause that graphene, the 3D non-defective monolayer in fullerenes and the defective monolayer in zeolite-templated carbon exhibit similar stability to disordered amorphous materials, as well as 3D organised mesoporous materials. All these materials are oxidized in a narrow Ton interval from 485 to 530 °C. The most significant factor for reducing the stability is the presence of specific oxygen-containing functional groups, which decrease Ton for materials with oxidized edges and with predominant hydroxyl groups by up to 150 °C. The relationships between the carbon structure and its stability in the air facilitate targeting the nanostructure of carbon materials in relation to their stability.

Enzyme-catalyzed synthesis of 4-methylcatechol oligomer and preliminary evaluations as stabilizing agent in polypropylene

Abstract In the present work, 4-methylcatechol oligomer has been prepared by using enzyme-catalyzed polymerization in water and preliminary evaluations as stabilizing agent in polypropylene (PP) was performed. In comparison with intrinsic PP, the oxidation onset temperature of the 4-methylcatechol oligomer/PP composite increased by 66°C, and the oxidation induction time increased by 40 min. In addition, the mixing of a 4-methylcatechol oligomer with PP (i.e., in the formation of a 4-methylcatechol oligomer/PP composite) did significantly enhance the long-term stability of PP in a thermal oxidative environment. Moreover, the tensile strength of this composite did not significantly decrease after aging for 800 h in an air atmosphere at 120°C. These results show that the addition of a 4-methylcatechol oligomer will markedly delay the aging and degradation of PP materials, even under extreme conditions. Thus, an enzyme-catalyzed polymerization of phenol compounds may provide a new avenue toward the preparation of novel antioxidants.

Modification of cottonseed oil with lipases and ionic liquid catalysts to prepare highly branched lubricant with low pour point and high viscosity

In response to the problems of non-renewable and difficult degradation of current lubricants, a cottonseed oil (CSO) is modified into a highly nonyl-branched isodecyl esters (NIEs) bio-based lubricant in the work. The lubricant synthesized process undergoes hydrolysis-esterification-epoxidation-ring opening and branching steps, just in the presence of green, non-polluting lipases, and insoluble ionic liquid catalysts. The pour point (−47 °C) of NIEs is much lower than that of CSO (−3 °C), the kinematic viscosity at 40 °C (200.3 mm2/s) is much higher than CSO (32.55 mm2/s), and the viscosity index reaches 141, which exhibits excellent low-temperature fluidity and viscous-temperature performance. Moreover, its oxidation onset temperature is 307.21 °C and its oxidative induction time is 21 min, which far exceeds CSO (300.1 °C, 13 min), indicating its excellent thermal oxidation stability. In addition, in the high-frequency reciprocation test, the coefficient of friction (COF) is 0.07, the average wear scar diameter (AWSD) is 132 µm, and the oil film coverage rate (OFCR) is 100%, which is much superior to CSO (COF: 0.09, AWSD: 219 µm, OFCR: 92%) and commercially SN lubricants (COF: 0.11, AWSD: 196 µm, OFCR: 98%), indicating it is superior in reducing friction as a lubricant. In conclusion, the bio-based lubricant has the potential to replace mineral lubricants and the synthesis method provides a reference for the synthesis of such lubricants.

Packaging Materials Based on Styrene-Isoprene-Styrene Triblock Copolymer Modified with Graphene.

This study presents the improved stabilization effects of graphene on a polymer substrate, namely a styrene-isoprene-styrene triblock copolymer (SIS) which creates opportunities for long-term applications and radiation processing. The added graphene has a remarkable activity on the protection of polymer against their oxidation due to the penetration of free macroradical fragments into the free interlayer space. The chemiluminescence procedure used for the evaluation of the progress of oxidation reveals the delaying effect of oxidative degradation by the doubling extension of oxidation induction time, when the material formulation containing graphene is oxidized at 130 °C. The pristine polymer that is thermally aged requires an activation energy of 142 kJ mol-1, while the modified material needs 148, 158 and 169 kJ mol-1, for the oxidative degradation in the presence of 1, 2 and, respectively, 3 wt% of graphene. The contribution of graphene content (1 wt%) on the stability improvement of SIS is demonstrated by the increase of onset oxidation temperature from 190 °C for neat polymer to 196 °C in the presence of graphene and to 205 °C for the polymer stabilized with graphene and rosemary extract. The addition of graphene into the polymer formulations is a successful method for enlarging durability instead of the modification of receipt with synthesis antioxidants. The presumable applications of these studied materials cover the areas of medical wear, food packaging, commodities, sealing gaskets and others that may also be included through the products for nuclear power plants.

Investigation on Some Algal Extracts as Appropriate Stabilizers for Radiation-Processed Polymers.

This study presents the appropriate solution, algal extracts, for the improvement of polymer durability when the material is subjected to acute oxidation damage. The investigated support, styrene-isoprene-styrene (SIS), is modified by three algal extracts: Chlorella vulgaris, Spirulina platensis, and Ascophyllum nodosum (Kelp) with a low concentration (1 wt%). The presence of polyhedral oligomeric silsesquioxane (POSS) ensures the growth of stability with respect to the pristine polymer. The thermal performances of the host polymer, indicated by chemiluminescence, reveal the essential contribution of an additive to the improvement in oxidation strength. The stability of the polymer adjusted by algal extracts is proved by the activation energy values, which increase from 49 kJ mol-1 to 89 kJ mol-1 for the same polymer modified with Ascophyllum nodosum. This main important characteristic is the consequence of the highly efficient activity of the polyphenol components of algal extracts and the effect of the three natural additives on the favorably changed kinetic parameters (oxidation induction time and onset oxidation temperature). The exposure of the polymer matrix to the damaging action of γ-rays does not affect the proper contributions to the fast delay in material ageing. The irradiation of 100 kGy, a usual technological dose, may be successfully applied in the radiation processing of a polymer stabilized with algal extracts due to the efficient protection of the additive as the chain-breaking agents.

Influence of oxygen addition on the oxidation resistance of TiAlN

Here, we explore the effect of O-addition on the oxidation resistance of TiAlN coatings by experimental and theoretical methods. Due to the retarded transformation of anatase to rutile TiO2, Ti0.41Al0.59(O0.08N0.92)1.02 with the raised oxidation onset temperature and slow oxidation process reveals improved oxidation resistance than Ti0.42Al0.58N0.95. Further ab initio calculations attribute the optimization to the preferential adsorption of oxygen to form the protective Al2O3 phase and suppressed formation of metastable a-TiO2 phase in the initial stage of oxidation. However, both experimental and calculated results reveal that further increasing oxygen content to Ti0.41Al0.59(O0.12N0.88)1.06 shows the rapid transformation of TiO2 accompanied with the cracking of the protective Al-oxide rich top-layer, which tremendously deteriorates the oxidation resistance. After oxidation at 800 °C for 30 h, Ti0.42Al0.58N0.95, Ti0.41Al0.59(O0.08N0.92)1.02 and Ti0.41Al0.59(O0.12N0.88)1.06 coatings present oxide layers of ∼953, ∼640 and ∼971 nm, respectively.

Nickel improving the combustion of boron powder

Boron (B) powder has a very high energy density and is often used as an additive to solid propellants. However, its high melting point and the presence of oxide film on its surface make it more difficult to ignition and incomplete combustion. This problem can be effectively improved by the addition of other metal particles. Therefore, nickel-modified boron-based complexes (B/Ni) were prepared by adding nickel (Ni) nanoparticles to the B powder. The effect of different Ni contents on the ignition and combustion of B powder was investigated. The appropriate addition amount of Ni nanoparticles to B powder can significantly decrease the onset oxidation temperature, and effectively increase the exothermic heat, but it has little effect on the maximum combustion intensity of B powder. The addition of Ni nanoparticles changes the reaction path of B and promotes its oxidation. These results may provide a reference for the application of Ni nanoparticles in boron-based solid propellants.

On the influence of the Cr/(Cr + Ta) ratio on the microstructure, mechanical properties and thermal stability of magnetron sputtered CrxTa1-xN coatings

CrxTa1-xN coatings were deposited by magnetron sputtering and the influence of the Cr/(Cr + Ta) ratio on microstructure, mechanical properties, thermal stability and oxidation resistance was investigated. X-ray diffraction revealed that all coatings exhibit an fcc-CrxTa1-xN crystal structure with an increasing size of coherently diffracting domains as the Cr/(Cr + Ta) ratio increases. A balanced Cr/(Cr + Ta) ratio of 0.46 results in the highest hardness of 27.4 ± 1.0 GPa, whereas binary fcc-TaN was determined to have the highest Young's modulus of 417 ± 20 GPa. All Ta-containing coatings exhibit a KIC value of 2.40 ± 0.10 MPa × m1/2 and thus exceed the fracture toughness of CrN (1.53 ± 0.21 MPa × m1/2). While vacuum annealing at 1000 °C already provokes a decomposition of the binaries, N-deficient compounds only form in the ternaries at temperatures ≥1200 °C. The oxidation onset and end temperature as well as the phase composition of the oxides were found to depend significantly on the Cr/(Cr + Ta) ratio. Among the investigated coatings, Cr0.75Ta0.25N exhibits the most promising thermal stability, both in inert and oxidizing atmosphere.

Methanol oxidation up to 100 atm in a supercritical pressure jet-stirred reactor

Methanol (CH3OH) has attracted considerable attention as a renewable fuel or fuel additive with low greenhouse gas emissions. Methanol oxidation was studied using a recently developed supercritical pressure jet-stirred reactor (SP-JSR) at pressures of 10 and 100 atm, at temperatures from 550 to 950 K, and at equivalence ratios of 0.1, 1.0, and 9.0 in experiments and simulations. The experimental results show that the onset temperature of CH3OH oxidation at 100 atm is around 700 K, which is more than 100 K lower than the onset at 10 atm and this trend cannot be predicted by the existing kinetics models. Furthermore, a negative temperature coefficient (NTC) behavior was clearly observed at 100 atm at fuel rich conditions for methanol for the first time. To understand the observed temperature shift in the reactivity and the NTC effect, we updated some key elementary reaction rates of relevance to high pressure CH3OH oxidation from the literature and added some new low-temperature reaction pathways such as CH2O + HO2 = HOCH2O2 (RO2), RO2 + RO2 = HOCH2O (RO) + HOCH2O (RO) + O2, and CH3OH + RO2 = CH2OH + HOCH2O2H (ROOH). Although the model with these updates improves the prediction somewhat for the experimental data at 100 atm and reproduces well high-temperature ignition delay times and laminar flame speed data in the literature, discrepancies still exist for some aspects of the 100 atm low-temperature oxidation data. In addition, it was found that the pressure-dependent HO2 chemistry shifts to lower temperature as the pressure increases such that the NTC effect at fuel-lean conditions is suppressed. Therefore, as shown in the experiments, the NTC phenomenon was only observed at the fuel-rich condition where fuel radicals are abundant and the HO2 chemistry at high pressure is weakened by the lack of oxygen resulting in comparatively little HO2 formation.

Enhanced performance of bio-lubricant properties with nano-additives for sustainable lubrication

PurposeThe purpose of this study is to evaluate the potentials of nano-additives in enhancement of oxidation and thermal stability of biolubricants thereby, improving the resistance of dispersed nanolubricants to thermal degradation under elevated temperature.Design/methodology/approachThis study evaluates the oxidation stability and tribological performance of nano-enhanced biolubricants. Graphene and maghemite nanoparticles at 0.1% volume concentration were dispersed into coconut oil. Oxidation stability was analysed using a thermal analyser to understand the effect of nano-additives on thermal degradation of lubricants under increasing temperature. In addition, tribological performance and viscosity of the tested lubricants were evaluated using a four-ball friction tester and viscometer according to American Society for Testing and Materials standards.FindingsThe results reveal that the oxidation stability of biolubricants dispersed with nano-additives improves due to delayed thermal degradation. The nano-enhanced biolubricants’ oxidation onset temperature was delayed by 18.75 °C and 37.5 °C, respectively, for maghemite (MGCO) and graphene (XGCO) nanolubricants. This improvement imparts the performance viscosity and tribological performance positively. For graphene-enhanced nanolubricant, 10.4% and 5.6% were reduced, respectively, in coefficient of friction (COF)and wear scar diameter (WSD), whereas 3.43% and 4.3% reduction in COF and WSD, respectively, for maghemite-enhanced nanolubricant compared with coconut oil. The viscosity index of nanolubricants was augmented by 7.36% and 13.85%, respectively, for maghemite and graphene nanolubricants.Research limitations/implicationsThe excellent performance of nanolubricants makes them suitable candidate as sustainable lubricants for machining with regard to environmental benefits and energy saving.Originality/valueThe effect of graphene and maghemite nanoparticles on the oxidation stability and tribological performance of biolubricants has been investigated. It is an original work and yet to be published elsewhere.

Friction and wear improvement by using Curcumin as a natural additive in green lubricants

Lubrication is an essential mechanism to make machines and engines more efficient by lowering friction and wear. Despite this, to mitigate environmental damage, lubricants must come from renewable sources and be biodegradables. Therefore, this study analyzed the use of Curcumin as a natural additive in two green oils to improve their tribological and oxidative performance. The density and viscosity of lubricants with and without curcumin additive, as well as the lubrication regime, were determined. The operational performance was analyzed by tribological tests under a ball-on-disk configuration at 100°C based on the ASTM G99. The oxidative behavior of lubricants was examined by studying the IR bands for primary and secondary oxidative products, as well as by DSC-TGA techniques for evaluating the Oxidation Onset Temperature and the thermogravimetric behavior. At the studied conditions, the incorporation of Curcumin into the oils increased the viscosity of the lubricants up to 46%, the friction coefficient decreased up to 70%, and wear was diminished up to 96%, despite working in boundary lubrication. Moreover, the addition of curcumin noticeably enhanced the oxidation behavior of lubricants. The results of this research suggest that Curcumin is an excellent option to improve the physical properties, operational performance, and oxidative stability of green oils to create effective and environmentally friendly lubricants.

Effect of V-type crystallinity and starch particle structure on the oil loading capacity and anti-oxidation

Starch-based carriers have a great potential in functional oil encapsulation because of their mild preparation conditions, but the oil loading capacity and underlying anti-oxidation mechanism remain unclear. Here V-type starches were applied to fabricate flaxseed oil powder. Particle size analysis and scanning electron microscopy showed a loose aggregation microstructure of normal maize starch (NMS) prepared using the anti-solvent (AS) precipitation method, with an average size of 24.9 μm. Differential scanning calorimetry displayed a good thermo-oxidation resistance of NMS-derived V-type starch prepared via AS precipitation. Principal component analysis revealed that the oil loading capacity, related closely to V-type crystallinity and D50, has a significant positive correlation with the onset oxidation temperature and a negative correlation with the peroxide, thiobarbituric acid, and ρ-anisidine values. Our original study reveals the effects of V-type crystallinity and aggregation microstructure on the oil loading capacity and anti-oxidation, providing theoretical guidance for developing novel, starch-based carriers.

Availability of PLA/SIS blends for packaging and medical applications.Part II: Contribution of stabilizer agents

The extending material durability of poly(lactic acid) (PLA)/styrene-isoprene-styrene copolymer (SIS) blend with 30% of SIS by the presence of acrylic acid (AA) and two stabilizers, caffeic acid or vanillic acid, is evaluated by γ-irradiation at technological doses (25 or 50 kGy) applied for sterilization or for the manufacturing of several commodities, medical, and packaging items, respectively, where an advanced exposure would affect the post-irradiation oxidation stability. The chemiluminescence investigations provide the onset oxidation temperature values from which the activation energies of degradation were calculated. Differential scanning calorimetry and infrared spectroscopy complete the evaluation of improvement efficiencies that characterize the thermal behavior of these materials. The effects of γ-exposure on the material properties are discussed relative to the radiolysis modifications occurred during radiation processing. The relevance of oxidation protectors is analyzed based on the efficient delay of ageing. The results are the qualification information for the packaging and medical products subjected to the radiation processing and radiation sterilization.

Accelerated Photo‐Oxidation of Polyamide 11 Nanocomposites under Various Clays Nanofillers

AbstractThe effect of various clays nanofillers on the photo‐oxidation of polyamide 11 (PA11) has been investigated by accelerated ultraviolet (UV) test up to 780 h. Organo‐modified montmorillonite, halloysite nanotubes, and sepiolite were selected and incorporated separately to PA11 at 5 wt.%. The samples were prepared by melt compounding. Fourier transform infrared (FTIR) data showed a linear increase of carbonyl index (CI) in the first 360 h of exposure indicating a rapid oxidation of all samples without any induction period. Further, the nanocomposite samples exhibit faster oxidation kinetics than PA11, being however less pronounced for PA11/sepiolite. This is consistent with both the yellowing index (YI) evolution determined by UV–Vis spectroscopy and also the onset oxidation temperature (OOT) determined by differential scanning calorimetry (DSC).

Structure characterization and steam oxidation performance of U3Si2 with Zr alloying additions

Research and development of high uranium density fuels supports the on-going effort to enhance reactor technology, safety, performance, and economics. Among high uranium density fuels, U3Si2 is a favored fuel candidate due to its higher uranium density and improved thermal conductivity when compared to traditional UO2. While U3Si2 demonstrates an improved fuel economy, it suffers from rapid degradation when exposed to water at T > 300°C. In order for U3Si2 to be implemented in water cooled reactors, the water reaction must be understood and mitigated. Reported here is the performance of Zr alloying additions to U3Si2 exposed to high temperature steam oxidation environments. The investigation shows that homogenization heat treatment contributes to a delayed onset of oxidation and an improved homogeneity throughout the arc-melt fabricated alloyed compositions. Of the pre- and post-annealed samples, the post-annealed 7 vol% Zr addition exhibited the highest onset temperature of oxidation. A preliminary computational investigation to complement the experimental analysis assesses the solubility of Zr in U3Si2 and its incorporation in the crystal lattice.

A rapid method for approximative evaluation of thermooxidative stability of organic materials.

In this work, a novel procedure for fast assessment of the material residual stability is proposed. The method resides in integral isoconversional kinetic analysis of the thermal oxidation of unaged material employing the Berthelot–Hood temperature function. Subsequently, the obtained conversion-independent kinetic parameter D is also employed for samples aged in various regimes. The value of conversion-dependent parameter A for aged samples is calculated from the oxidation onset temperature measured at 5 °C min−1. The residual stabilities are then calculated as a simple ratio of the parameter A of aged material to that of the unaged one. The method has been applied and verified for the samples of low-density polyethylene aged by thermal, radiation and combined ageing. The method can also be employed for high-throughput screening of the effect of various stabilizers and antioxidants in a given organic matrix.

Essential oil composition of Polylophium Involucratum and evaluation of antioxidant capacity of seeds ethanolic extracts by DSC

Recently natural antioxidants have obtained greater attention due to the fact natural food components are safer than synthetic ones. Antioxidant activities of Polylophium Involucratum seeds extract were analyzed. In this research, radical scavenging capacity was utilized to measure the antioxidant efficacy of ethanolic extraction. The half-maximal inhibitory concentration (IC50) for diphenylpicrylhydrazyl (DPPH) radical scavenging activity was 423 µg/ml for ethanolic extract and 10 mg/ml for essential oil. Furthermore, total phenolic and flavonoid contents in the ethanolic extract were 89.22 (mg gallic acid equivalent (GAE)/g dry weight (DW)), and 48.24 (mg rutin equivalent/g DW), respectively. The antioxidant effect of P. Involucratum and a synthetic antioxidant on oxidative stability of tallow was assessed by differential scanning calorimetry (DSC). DSC revealed showed the addition of P. Involucratum extract at 400 ppm to tallow increased its oxidation onset temperature in comparison to 200 ppm of butylated hydroxytoluene (BHT) and a control (no antioxidant added), thereby making P. Involucratum a source of natural antioxidants.

The Effect of Potassium Inclusion in a Silver Catalyst for N2O-Mediated Oxidation of Soot in Oxidising Exhaust Gases

It has previously been shown that an Ag/CZA catalyst can simultaneously remove NOx and soot from an oxygen-rich exhaust gas at low temperatures, by utilising the N2O generated preferentially during incomplete NOx reduction. Here, we examine the effect of reformulating the catalyst to include potassium, which is a known promoter of soot combustion. On including 2 wt% K, NOx-reduction occurs both in the absence and presence of soot, but the N2O formed does not play a part in the oxidation of soot. At higher K loadings (5, 10 and 15 wt%), NOx reduction is almost completely disabled, and only contributes to the activity of the catalyst containing 5 wt% K when tested in the presence of soot. At a loading of 20 wt% K, the potassium phase segregates, leaving NO and NH3 adsorption sites exposed. In the absence of soot, this catalyst can remove NOx by reduction on the Ag/CZA component and through nitration of the potassium phase. Although the presence of potassium lowers the onset temperature for soot oxidation to within the range of NOx reduction over Ag/CZA, the mobile K species prevents the desirable C+N2O reaction.

Oxidation of U3Si2: The role of exothermic energy

Uranium silicide (U3Si2) is one of the candidate accident tolerant fuel materials under consideration for adoption in power producing nuclear reactors. The development of this fuel material including the bulk scale manufacturing route, and factors which may affect this route, are still under investigation. One such factor is the influence of oxygen on the material and the consequent release of exothermic energy. This work uses combined thermogravimetric and differential scanning calorimetry (DSC) methods to study oxidation of arc melted U3Si2 material, including ramp tests, isothermal experiments and varying particle sizes. It is found that there is a difference in mass gain profile between fragments and small powder samples, with fragments delivering the same heat load (∼4.6 ± 0.5 kJ.g−1) over a significantly shorter period of time. The measured exothermic heat output is in agreement with thermodynamic modelling once corrections have been made for the presence of elemental silicon in the reaction product. The onset temperature of rapid oxidation also reduces with particle size. Initial reactivities of freshly prepared powder samples during isothermal experiments give appropriate reaction constants, which are used to construct an Arrhenius plot. Supporting DSC data indicate that one of the higher temperature data points (275 °C in this instance) had exhibited exothermic energy-induced self-heating and an accelerated rate of reaction. The resultant calculated activation energy from oxidation of freshly prepared U3Si2 powder is approximately 36 kJ.mol−1.

Mechanisms responsible for enhancing low‐temperature oxidation resistance of nonstoichiometric (Zr,Ti)C

AbstractA series of (Zr,Ti)Cx (x = 0.7–1.0) samples were fabricated by a modified spark plasma sintering apparatus to investigate the effects of carbon concentration and Ti substitutions on the oxidation behavior. Crushed powders of (Zr,Ti)Cx were oxidized in lab air (N2–20‐vol.% O2) from room temperature to 900°C. The results indicated that Zr0.8Ti0.2C0.8, with a nominal carbon concentration x = 0.8, displayed good oxidation resistance, which was attributed to the formation of dense t‐(Zr,Ti)O2 oxide solid solution. During the oxidation of (Zr,Ti)Cx, Ti substitutions for Zr enhanced the outward diffusion of carbon, enabling a uniform carbon layer and a Zr–Ti–C–O layer on the surface of carbides. The formed carbon layer improved the oxidation resistance of (Zr,Ti)Cx below 550°C, where carbon is relatively oxidation resistant. Increasing the Ti concentration was found to enhance the oxidation resistance of (Zr,Ti)Cx with an increased oxidation onset temperature (672 ± 2°C for Zr0.8Ti0.2C0.8).