Dynamic Aging Research Articles

Study on Thermal Oxygen Aging Characteristics and Degradation Kinetics of PMR350 Resin.

The thermal stability and aging kinetics of polyimides have garnered significant research attention. As a newly developed class of high thermal stability polyimide, the thermal aging characteristics and degradation kinetics of phenylene-capped polyimide prepolymer (PMR350) have not yet been reported. In this article, the thermo-oxidative stability of PMR350 was investigated systematically. The thermal degradation kinetics of PMR350 resin under different atmospheres were also analyzed using the Flynn-Wall-Ozawa method, the Kissinger-Akahira-Sunose method, and the Friedman method. Thermogravimetric analysis (TGA) results revealed that the 5% thermal decomposition temperature (Td5%) of PMR350 in a nitrogen atmosphere was 29 °C higher than that in air, and the maximum thermal degradation rate was 0.0025%/°C, which is only one-seventh of that observed in air. Isothermal oxidative aging results indicated that the weight loss rate of PMR350 and the time-dependence relationship follow a first-order exponential growth function. PMR350 resin thermal decomposition reaction under air atmosphere includes one stage, with a degradation activation energy of approximately 57 kJ/mol. The reaction model g(α) fits the F2 model, and the integral form is given by g(α) = 1/(1 - α). In contrast, the thermal decomposition reaction under a nitrogen atmosphere consists of two stages, with degradation activation energies of 240 kJ/mol and 200 kJ/mol, respectively. The reaction models g(α) correspond to the A2 and D3 models, with the integral forms represented as g(α) = [-ln(1 - α)]2 and g(α) = [1 - (1 - α)1/3]2 due to the oxygen accelerating thermal degradation from multiple perspectives. Moreover, PMR350 resin maintained high hardness and modulus even after thermal aging at 350 °C for 300 h. The results indicate that the resin exhibits excellent resistance to thermal and oxygen aging. This study represents the first systematic analysis of the thermal stability characteristics of PMR350 resin, offering essential theoretical insights and data support for understanding the mechanisms of thermal stability modification in PMR350 and its engineering applications.

Analysis of the Thermal Aging Kinetics of Tallow, Chicken Oil, Lard, and Sheep Oil.

Understanding the thermal aging kinetics of animal oils is of vital importance in the storage and applications of animal oils. In this work, we use four different techniques, including UV-Vis spectrometry, viscometry, impedance spectroscopy, and acid-base titration, to study the thermal aging kinetics of tallow, chicken oil, lard, and sheep oil in the temperature range from 120 °C to 180 °C. The evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration are discussed with the defect kinetics. The evolutions of the color centers, defects for dynamic viscosity, and electric dipoles follow second-order, first-order, and zero-order kinetics, respectively. The temperature dependence of rate constants for the evolutions of the UV-Vis absorbance, dynamic viscosity, electric impedance, and acid titration satisfies the Arrhenius equation with the same activation energy for individual animal oils. The activation energies are ~43.1, ~23.8, ~39.1, and ~37.5 kJ/mol for tallow, chicken oil, lard, and sheep oil, respectively. The thermal aging kinetics of the animal oils are attributed to the oxidation of triglycerides.

Kinetics of Aging and Changes in the Mechanical Properties of Mg – Y – Nd – Gd – Zn – Zr Cast Magnesium Alloy During Overburning

Kinetics of Aging and Changes in the Mechanical Properties of Mg – Y – Nd – Gd – Zn – Zr Cast Magnesium Alloy During Overburning

Toward a rational approach for polyphenol usage in the shelf-life extension of oenological products

The durability of food items, i.e. their shelf life, plays a crucial role in optimizing their quality and exploitation with the aim of limiting food and beverage waste. The primary factor contributing to prolonged deterioration is the oxidation of food products, leading to the generation of by-products that compromise their sensory qualities, such as off-flavors and organoleptic features in general. Concerning beverages, and wine in particular, polyphenols from wood and grapes extracts have gained significant popularity as natural agents able to preserve the quality and desired features due to their recognized antioxidant and anti-radical properties. Although the ability of oak to release polyphenols able to enhance the long-term stability of wines is widely acknowledged, effective methods for monitoring both their kinetics of oxidation and browning are still lacking. A spectrophotometric approach was exploited to develop a novel method for monitoring wine oxidation in the attempt of filling the gap. Such approach was successfully applied to track qualitatively the aging kinetics in oxidative conditions using a wine simulant with the addition of 16 natural extracts. Chestnut and oak extracts resulted the most performing in both hue conservation and oxidized species limitation. Principal component analysis demonstrated that polyphenol of different class can be recognized even after 30 days of oxidation, thus suggesting potential applications of the method in quality and conformity control of polyphenol extracts. The results allow a rational choice of the best polyphenol extract for each specific application in wines, with potential application to other beverages and foods.

Aging mechanisms and kinetics of bis(2,2 dinitropropyl) formal facilitated by transition state bifurcation and HONO catalysis

Serving as energetic plasticizer, revealing the aging mechanisms and kinetics of bis(2,2-dinitropropyl) formal is helpful to remove the safety hazards. Here, based on the DFT barrier of methylene-H abstraction by nitro group (HONO elimination) and the continuous reaction model, an experimentally comparable half-life of BDNPF is reported by transition state theory simulation. Rather than the HONO elimination-addition reactions, HONO bimolecular decompositions are preferred, where the energetically preferred pathway involves formation of N2O3, and generation of N2O4 and HNO catalyzed by HONO. Interestingly, newly reported transition state bifurcations lower the barriers and accelerate HONO decomposition, which also leads to the rate constant of generating HNO consistent with experiments. Moreover, HNO undertakes hydrogen transferred bimolecular pathway and HONO-catalyzed pathway to decompose into N2O and H2O. This work clarifies the degradation pathways and species, and is helpful to the deep understanding of the aging procedures of energetic materials.

Study on the Aging Precipitation Behavior and Kinetics of Al-10.0Zn-3.0Mg-2.8Cu Alloy by Pre-Deformation Treatment.

In this paper, the effect of thermomechanical treatment process on the hardening behavior, grain microstructure, precipitated phase, and tensile mechanical properties of the new high-strength and high-ductility Al-10.0Zn-3.0Mg-2.8Cu alloy was studied, and the optimal thermomechanical treatment process was established. The strengthening and toughening mechanisms were revealed, which provided technical and theoretical guidance for the engineering application of this kind of high strength-ductility aluminum alloy. Al-10.0Zn-3.0Mg-2.8Cu alloy cylindrical parts with external longitudinal reinforcement were prepared by a composite extrusion deformation process (reciprocal upsetting + counter-extrusion) with a true strain up to 2.56, and the organizational evolution of the alloys during the extrusion deformation process and the influence of pre-stretching treatments on the subsequent aging precipitation behaviors and mechanical properties were investigated. The results show that firstly, the large plastic deformation promotes the fragmentation of coarse insoluble phases and the occurrence of dynamic recrystallization, which results in the elongation of the grains along the extrusion direction, and the volume fraction of recrystallization reaches 42.4%. Secondly, the kinetic study showed that the decrease in the activation energy of precipitation increased the nucleation sites, which further promoted the diffuse distribution of the second phase in the alloy and a higher number of nucleation sites, while limiting the coarsening of the precipitated phase. When the amount of pre-deformation was increased from 0% to 2%, the size of the matrix precipitated phase decreased from 5.11 μm to 4.1 μm, and when the amount of pre-deformation was increased from 2% to 7%, the coarsening of the matrix precipitated phase took place, and the size of the phase increased from 4.1 μm to 7.24 μm. The finalized heat treatment process for the deformation of the aluminum alloy tailframe was as follows: solution (475 °C/3 h) + 2% pre-stretching + aging (120 °C/24 h), at which the comprehensive performance of the alloy was optimized, with a tensile strength of 634.2 MPa, a yield strength of 571.0 MPa, and an elongation of 15.2%. The alloy was strengthened by both precipitation strengthening and dislocation strengthening. After 2% pre-stretching, the fracture surface starts to be dominated by dense tough nest structure, and most of them are small tough nests, and small and dense tough nests are the main reason for the increase in alloy toughness after 2% pre-stretching deformation.

Twofold Facet of Kinetics of Glass Aging.

We employ fast scanning calorimetry to monitor the isothermal aging kinetics in glassy polymers, complemented with measurements on other glasses. Apart from following the time evolution of the glass enthalpic state, we monitor the aging kinetics of the devitrification width on heating, ΔT_{dev}. We find that significantly below the glass transition temperature, T_{g}, the glass enthalpy attains equilibrium earlier than ΔT_{dev}, which evolves at long aging times toward enhanced heterogeneity. Hence, our results indicate that the description of time dependent evolution in glassy materials requires information beyond the mere description of its enthalpic state.

Kinetics of Radiation-Oxidative Aging of Polyamide Fibers and Composites Based on Them

Kinetics of Radiation-Oxidative Aging of Polyamide Fibers and Composites Based on Them

Two-stage aging treatment to accelerate aging kinetics without impairing strength in B4C/7A04Al composite

Two-stage aging treatment to accelerate aging kinetics without impairing strength in B4C/7A04Al composite

Kinetics of radiation-oxidative aging of HDPE fibers with simultaneous destruction and macromolecules crosslinking

Kinetics of radiation-oxidative aging of HDPE fibers with simultaneous destruction and macromolecules crosslinking

Artificial aging behavior of SiCP/AA2009 composite by electric heating: Mechanisms and modelling

SiCP/Al composite is regarded as a superior alternative material in the aerospace industry due to its excellent properties. Meanwhile, electrically-assisted aging (EAA) heat treatment has emerged as a promising method for artificial aging to obtain better aging performances. This study explores the potential of EAA heat treatment to enhance the aging kinetics of SiCP/Al composite. The impact of EAA on the aging behavior of SiCP/AA2009 composites is investigated and compared with conventional furnace aging treatment, ranging from microstructure to macroscopic properties. The electric current has few effects on the evolution trend of aging strength, but can enhance the aging process of SiCP/AA2009 with higher yield strength (about 13.7 MPa improvement) and ultimate tensile strength (about 9.7 MPa improvement). Analysis of microstructures demonstrates that EAA can generate more nucleation sites and reduce consumption of Cu atoms by Cu–Mg co-clusters near SiCP interface, resulting in more θ’ phases compared to conventional aging (CA). Additionally, more fine precipitates and dislocations contribute to higher strength under EAA condition. Subsequently, a precipitation kinetic model based on the Lagrange-like approach is employed to predict the particular electric current effects on the particle size distribution and evolution during aging, and to calculate yield strength by establishing a relationship between microstructural characteristics and macroscopic performance, providing a model basis for the design of potential EAA processes.

On the Dynamic Mechanical Behavior of Wrought and AM 17-4 Precipitation-Hardenable Stainless Steels Under Rapid Heating

Dynamic large-strain plasticity problems in metals can produce temperatures high enough to alter the microstructure, but the limited time-at-temperature prevents complete transformation, thereby making the material strength time-dependent. Precipitation reactions (age-hardening) are an important class of transformations that can create time-dependent dynamic plasticity under rapid heating and loading. This work explores the dynamic behavior of a precipitation-hardenable stainless steel (17-4) produced by wrought and Additive Manufacturing (AM) methods with a rapidly-heated Kolsky bar technique. Wrought 17-4, a martensitic stainless steel, is examined in three common heat treatments (solution-treated, peak-aged and over-aged) at temperatures up to 1000 °C and heating times limited to about three seconds. Solution-treated wrought 17-4 is observed to thermally-harden at aging temperatures (> 400 °C) due to rapid precipitate growth. Peak-aged precipitation strengthening becomes ineffective above 550 °C, as peak-aged material becomes indistinguishable from the solution treated-condition. Over-aged wrought 17-4 does not behave like either of the other conditions, owing to the effect of the extended heat treatment on the precipitates and on the martensite matrix. Stress-relieved AM 17-4 exhibits high dynamic strength and strain hardening at room-temperature due to its meta-stable austenite content and partial age-hardening during the build or stress-relief treatment. A plasticity model is developed for solution-treated wrought 17-4 that captures time-dependent aging effects that are derived from separate aging kinetics experiments. A separate model is developed for over-aged wrought 17-4 that contains no time-dependence as the precipitate population in this material appears to be more stable under rapid heating.

The reactivation kinetic analysis, molecular docking, and dynamics of oximes against three V-type nerve agents inhibited four human cholinesterases

Nerve agents pose significant threats to civilian and military populations. The reactivation of acetylcholinesterase (AChE) is critical in treating acute poisoning, but there is still lacking broad-spectrum reactivators, which presents a big challenge. Therefore, insights gained from the reactivation kinetic analysis and molecular docking are essential for understanding the behavior of reactivators towards intoxicated AChE. In this research, we present a systematic determination of the reactivation kinetics of three V agents-inhibited four human ChEs [(AChE and butyrylcholinesterase (BChE)) from either native or recombinant resources, namely, red blood cell (RBC) AChE, rhAChE, hBChE, rhBChE) reactivated by five standard oximes. We unveiled the effect of native and recombinant ChEs on the reactivation kinetics of V agents ex vitro, where the reactivation kinetics characteristic of Vs-inhibited BChE was reported for the first time.In terms of the inhibition type, all of the five oxime reactivators exhibited noncompetitive inhibition. The inhibition potency of these reactivators would not lead to the difference in the reactivation kinetics between native and recombinant ChE. Despite the significant differences between the native and recombinant ChEs observed in the inhibition, aging, and spontaneous reactivation kinetics, the reactivation kinetics of V agent-inhibited ChEs by oximes were less differentiated, which were supported by the ligand docking results. We also found differences in the reactivation efficiency between five reactivators and the phosphorylated enzyme, and molecular dynamic simulations can further explain from the perspectives of conformational stability, hydrogen bonding, binding free energies, and amino acid contributions. By Poisson-Boltzmann surface area (MM-PBSA) calculations, the total binding free energy trends aligned well with the experimental kr2 values.

Prediction of storage lifetime of rubber materials for flexible joint elastomers

To investigate the aging performance and storage lifetime of rubber materials used in flexible joint elastomers for solid rocket engines, a compression permanent deformation was used as the performance evaluation index to conduct aging tests on the elastic specimens of joint rubber materials at different temperatures. The results showed that the compression permanent deformation increased with the aging time and temperature, and the value of compression permanent deformation was greater in the initial stage of aging than in the later stage. Based on the regularity of material aging performance, the storage lifetime of rubber materials at room temperature of 25°C is extrapolated to be approximately 17.35 years through the linear equation of aging kinetics. Given that the aging mechanism remains unchanged, the calculation based on the principle of time-temperature equivalence reveals that as the aging temperature of the rubber material increases, the accelerated aging time to reach the regular storage lifetime becomes faster. Aging for 11.25 days at 140°C is equivalent to storing for this rubber material 15 years at 25°C. This research provides references for the future design, manufacturing, maintenance, and storage reliability of flexible joints.

Effect of equal-channel angular pressing on microstructure, aging kinetics and impact behavior in a 7075 aluminum alloy

Among the precipitation hardenable 7xxx series aluminum alloys, AA7075 alloys (one of the most important engineering alloys) due to their low density (lightweight), high toughness and strength, and enhanced fatigue behavior have been used over the years in aerospace, aircraft, automotive, construction and marine applications. In the present study, the influence of the artificial aging through conventional heat treatment (i.e., precipitation hardening) and the thermomechanical treatment (equal-channel angular pressing (ECAP) + post-ECAP aging) on the quasi-static tensile, impact toughness and precipitation behavior as well as on the microstructure of an AA7075 alloy is investigated systematically. The results indicate that the ECAP process as well as post-ECAP aging result in considerably increased strength and hardness of the AA7075 alloys because of the superimposed effects of grain boundary strengthening (Hall-Petch relation), strain hardening (by means of the increased dislocation density) and precipitation hardening (due to the fine precipitates formed in Al matrix). Multi-pass ECAP processing has been found to result in a considerable decrease of the impact toughness (from 15.3 J·cm−2 to 7.6 J·cm−2) associated with the failure mode (i.e., ductile-to-brittle transition) of the AA7075 alloys, whereas the artificial peak aging leads to a marked improvement (∼67 %) in the impact toughness in ECAPed conditions. Moreover, the ECAP process noticeably accelerates the precipitation kinetics of AA7075 alloys: The peak aging time in the ECAPed alloy is reduced significantly – from 30 h to 4 h. The results of the present study provide a deeper understanding of the combination of ECAP and heat treatment, and their effect on the fracture mode and toughness under impact loading, the aging kinetics and the microstructural evolution of an AA7075 alloy.

Structural insights into T1 precipitation and age hardening by Zn alloying for T6 treated Al–Cu–Li based alloys with a high Cu/Li ratio

T1 (Al2CuLi) nano-phase precipitation has been a major focus in developing new multi-microalloyed Al–Cu–Li alloys. Nevertheless, more understanding is required. This work investigated the effect of Zn alloying on the microstructure and mechanical properties of multi-element Al–Cu–Li alloys with a high Cu/Li ratio using a combination of advanced electron microscopy and first-principles calculations. Zn alloying (i) induced a higher density of geometrically-necessary dislocations after solid-solution treatment, which increased the T1 nucleation rate during the early aging stage; (ii) promoted T1 growth by substituting Al or Cu atoms in the T1 structure; and (iii) profoundly increased the aging kinetics, the age hardening response, and the strength. In addition, the co-segregation of Zn, Mg and Cu at the T1/Al interface helped to stabilize the fine T1 nano-platelets. These structural insights into T1 precipitation and age hardening by Zn alloying can help to guide the optimal design of high-performance Zn micro-alloyed multi-element Al–Cu–Li alloys.

Effects of storage temperature on the solubility of cross-linked micellar casein powders

Micellar casein powders (MCP) are added to food products to enhance their protein content and functional qualities. Enzymatic cross-linking (CL) with microbial transglutaminase (mTGase) is a promising method for improving the functional properties of MCP. Non-cross-linked (N-MCP) and enzymatically cross-linked (C-MCP) at different CL degrees (0, 36, 48, and 58 %), were evaluated to assess the changes in MCP powder solubility after storage at two temperatures (25 and 40 °C) for up to 180 days. The MCP were examined periodically to determine the browning index (BI), the loss of solubility, the variations in the wetting time, and the morphological surface composition evolution with aging. The solubility of both N-MCP and C-MCP decreased similarly with storage, and this phenomenon was enhanced by increasing the severity of the storage (temperature and time). Based on changes in the BI and solubility loss, N-MCP and C-MCP have similar aging kinetics. According to relaxation time analysis, the CL degree reduced the interaction between the powder particles and the solvent, which further diminishes with storage. The results suggest that CL would trigger changes in the MC powder surface, but the evolution of the functional properties is not related to the storage-induced CL formation.

Mass-composite activation energies for recycled binder blends

Using reclaimed asphalt pavement (RAP) has become an appealing development for economic and environmental benefits. One of the key issues when incorporating RAP materials is to ensure the performance of recycled binder blends. Despite extensive researches dealing with physical and chemical aspects, concerns about recycled materials combinations remain. This paper focuses on the kinetics of aging, cracking and healing process for blended binders with a novel hypothesis of mass-composite activation energies. Firstly, four blends were prepared with different ratios of virgin bitumen and laboratory-produced RAP binders. Then, Fourier-transform infrared spectroscopy was utilized to track the carbonyl formation in all samples initially and with aging, and aging activation energy (Eacr) was computed in terms of Arrhenius equation. Thirdly, strain-controlled oscillatory measurements were conducted; moreover, representative energy change rates of dissipated pseudo strain energy and recoverable strain energy were obtained to determine the activation energy for cracking (Eac) and healing (EaH), respectively. Finally, hypotheses of mass-composite activation energies were validated with the test results. It shows that Eacr of recycled binder blends are smaller than that of RAP binders, indicating a lower kinetic barrier to oxidation reaction for blended bituminous system. With the increase of RAP binder content, the blends exhibit a decrease in Eac and an increase in EaH, which reveals the adverse effect introduced by oxidation in cracking resistance and healing capability. Excitingly, the measured activation energies of recycled binder blends are consistent with the calculated mass-composite activation energies, which will hopefully provide support for performance estimation.

Effect of conformation of interfacial adsorbed chains on physical aging of polymer nanocomposites.

The dynamics of polymer nanocomposites varies depending on the physics and chemistry at the polymer-nanoparticle interface. The physical aging of the nanocomposites is accelerated or retarded based on interfacial interactions and the state of polymer adsorption at the interfaces. In this study, we investigated the aging kinetics of silica-polystyrene nanocomposites using differential scanning calorimetry, focusing on the effect of local conformations of chains adsorbed on the nanofiller surface. The results show that the temperature dependence of the aging rate follows a Vogel-Fulcher-Tammann relationship at high temperatures, whereas it exhibits an Arrhenius-like behavior below a characteristic temperature (Tc). Notably, at T < Tc, the aging rate decreases with increasing loop height of the chains adsorbed on the filler surface, but the activation energy remains unchanged. We proposed that the suppression of the aging rate at T < Tc is likely related to an increase in the length scale over which the slow interfacial dynamics can propagate due to the increased topological interactions between the chain loops of a larger size and the free chains in the matrix. The increased packing frustration occurring at the filler surface occupied by the larger loops might also contribute to the decreased aging rate.

Mesoscopic irreversible thermodynamics of aging kinetics of alpha polypeptides [DNA] under various constraints: Special reference to the simple spring mechanics

The mesoscopic irreversible thermodynamic treatment of α-polypeptides and the helical polynucleotides (DNA) furnishes two sets of analytical expressions, which allow us not only to analyze the reversible force–extension experiments performed by atomic force microscopy (AFM) but also to predict the irreversible “aging” kinetics of the single-stranded and double-stranded polynucleotides (ssDNA and dsDNA) helical conformations exposed to aqueous solutions and applied static stress systems under the various constraints. The present physicochemical cage model emphasizes the fact that the global Helmholtz free energy of the helical conformation acts not only under the stored “intrinsic” unusual torsional and bending elastic energies inherited by the unfolded helical structure of the amino-acid (peptides) or the nucleic-acid (nucleotide) backbone but also reveals the importance of the interfacial Helmholtz free energy density associated with the interaction of the side-wall branches within the surrounding aqueous solutions. The analytical expression obtained for the unfolding force vs extension (FE) shows a strong non-linear elasticity behavior under the twist angle constraint when the interfacial Helmholtz energy term is incorporating into the scenario. This behavior is in excellent quantitative agreement with the AFM test results obtained by Idiris et al. (2000) on the poly-L-glutamic acid [Glu(n)-Cys] exposed to aqueous solutions, which show that acidity increases the degrees of helicity.