Early Stage Of Aging Research Articles

Effect of combined addition of Ag and Cu on the precipitation behavior for an Al-Mg-Si alloy

The effect of combined addition of Ag and Cu on the precipitation behavior for an Al-Mg-Si alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and three-dimensional atom probe (3DAP) analysis. At the early aging stage, Ag and Cu atoms participate in the clustering process and accelerate the transformation of clusters to GP zones and β″ phases. In the peak aging stage, Ag atoms preferentially segregate at the β″/α-Al interfaces, while Cu atoms enter into the interior of the β″ phase and form a symmetry substructure, Cu sub-unit clusters. With prolonged aging, Ag atoms gradually incorporate in the β″ phase and form Ag sub-unit clusters. The incorporated Ag and Cu atoms can promote the formation of β′Ag, disordered QP1 and QP2 phases during the over aging stage. Almost all of these precipitates have a composite structure with various unit cells (β′, β′Ag, Q′ and C) or substructures (LDC, Cu sub-unit clusters, Ag sub-unit clusters), and Ag segregation is found in the interfaces of these precipitates. For the lath-like QP2 phase, Cu and Ag atoms segregate at the coherent and semi-coherent QP2/α-Al interfaces, respectively, which can reduce their strain energy and interfacial energy. These findings provide new insights in understanding the precipitate evolution of the Al-Mg-Si-Ag-Cu alloy, which is a potential alloy for automobile applications.

Evolution of the structure of precipitation-hardening steel during heat treatment

In order to identify the mechanism of the processes responsible for the formation of the properties of deposited steels of type 15N4M2D2G2AYuF and 20N4M2D2G2YuF, we studied the patterns of formation of their structure and phase composition as a result of heat treatment. The analysis of the results made it possible to recommend tempering at the temperature of 550 °C for two hours as the main mode of heat treatment of these steels. The development of the properties and structure of the deposited steel of the presented type is the result of multi-step interaction of several hardening mechanisms. The main role in the formation of the structure and properties is played by martensitic transformations, as well as solid-solution hardening by interstitial and substitutive atoms. At the first stage, the hardening is caused by the deposition of dispersed intermetallic compounds and carbides. In addition, dispersed particles of intermetallic phases are released at the early stages of aging and slow down the annihilation of dislocations in the matrix. With longer aging, carbides deposited at fixed dislocations contribute to hardening.

Performance changes of hot recycled asphalt mixture in different layers under coupling of multiple aging factors

A climate simulation test system (CSTS) was developed to couple the aging factors including light, heat, oxygen and moisture. In the paper, 16 kinds of hot recycled asphalt mixtures modified by 3.5 wt‰ granular polymer reinforcing agent (GPR) were obtained and the pavement performances (high temperature performance, low temperature performance, water stability and fatigue resistance) of them were tested. The results indicated that the aging had a negative impact on the low temperature performance and fatigue resistance of the hot recycled asphalt mixture, especially after 30 days of long-term aging, the low temperature performance of the hot recycled asphalt mixture decreased obviously. However, the water stability of hot recycled asphalt mixture had a peak value with aging time. Besides, in the early and middle stage of long-term aging, GPR could significantly improve the pavement performances of hot recycled asphalt mixture.

Accelerated weathering simulation on rheological properties and chemical structure of high viscosity modified asphalt: A temperature acceleration effect analysis

High viscosity modified asphalt (HVMA) is widely used as the binder for permeable asphalt pavement. The service life of permeable asphalt pavement strongly depends on the weathering aging resistance of HVMA due to the large porosity of permeable asphalt pavement. In order to investigate the accelerated deterioration effect of temperature on the weathering aging process, a laboratory accelerated weathering aging tester was used to simulate the long-term weathering aging of HVMA at different aging temperatures (30 °C, 50 °C, and 70 °C) and different weathering aging days (0 ~ 12d). A series of rheological tests were conducted to study the influence of weathering aging temperature on the rheological properties of HVMA. Then, FTIR test was applied to characterize the changes in chemical composition of HVMA at different weathering aging temperatures. Furthermore, an aging kinetics model was put forward to further understand the effect of aging temperature on the weathering aging rate of HVMA. The results indicate that the weathering aging rate of HVMA is fast in the early aging stage (0 ~ 2d) and slows down in the later aging stage (2 ~ 12d). The increase of aging temperature has a significant accelerated deterioration effect on the chemo-rheological properties of HVMA during weathering aging process. At 30 °C aging temperature, the deteriorated rheological properties of HVMA are mainly due to the aging of solar radiation. As the aging temperature increases to 50 °C, the thermal aging effect of HVMA begins to appear under the stimulation of solar radiation. When the aging temperature rises to 70 °C, HVMA has suffered from a severe coupled aging of high temperature, solar radiation and humidity. This coupled aging effect leads to a significant asphalt oxidation and polymer degradation, which is the main reason for the severely deteriorated rheological properties of HVMA. The proposed aging kinetics model results also confirm the accelerated deterioration effect of temperature during weathering aging process.

The modifying role of physical activity in the cross-sectional and longitudinal association of health-related quality of life with physiological functioning-based latent classes and metabolic syndrome

BackgroundSingle cardio-metabolic risk factors are each known modifiable risk factors for adverse health and quality of life outcomes. Yet, evidence on the clustered effect of these parameters and the metabolic syndrome (MetS) on health-related quality of life (HRQoL) is still limited and mostly cross-sectional. The objectives of this study were to identify clusters of cardio-metabolic physiological functioning, to assess their associations with HRQoL in comparison with the MetS, to elucidate the modifying role of physical activity, and to assess differences in health service utilization.MethodsThis study is based on longitudinal data from two time points (2010/11 & 2017/18) of the Swiss Study on Air Pollution and Lung and Heart Diseases (SAPALDIA). Latent class analysis (LCA) grouped participants based on a priori selected cardio-metabolic and MetS related physiological functioning variables (Body mass index, body fat, glycated hemoglobin, blood triglycerides, blood pressure). The 36-item Short-Form Health Survey (SF-36) was used to assess HRQoL. Quantile regressions were performed with and without adjustment for physical activity, to detect independent associations of the latent classes, MetS and physical activity with HRQoL. To assess the modifying role of physical activity, we additionally grouped participants based on the combination of physical activity and latent classes or MetS, respectively. Logistic regressions were used to investigate health service utilization as outcome.ResultsThe LCA resulted in three classes labeled “Healthy” (30% of participants in 2017/18), “At risk” and “Unhealthy” (29%). The Unhealthy class scored lowest in all physical component scores of HRQoL. Compared to healthy and active participants, inactive participants in the “Unhealthy” class showed lower scores in the physical functioning domain both cross-sectionally (− 9.10 (− 12.02; − 6.18)) and longitudinally. This group had an odds ratio of 2.69 (1.52; 4.74) for being hospitalized in the previous 12 months.ConclusionsThese results point to subjects with adverse cardio-metabolic physiological functioning and low activity levels as an important target group for health promotion and maintenance of well-being. The promotion of physical activity at the early stages of aging seems pivotal to mitigate the impact of the MetS on HRQoL at higher age.

Effect of Electrolyzed Alkaline-Reduced Water on the Early Strength Development of Cement Mortar Using Blast Furnace Slag.

This study evaluated the use of electrolyzed alkaline-reduced water instead of an alkaline activator for the production of a strong cement matrix with a large blast furnace slag replacement ratio. The flexural and compressive strength measurements, X-ray diffraction analysis, and scanning electron microscopy images of the cement matrices produced using electrolyzed alkaline-reduced water and regular tap water, and with blast furnace slag replacement ratios of 30 and 50% were compared to a normal cement matrix. The cement matrix produced using electrolyzed alkaline-reduced water and blast furnace slag exhibited an improved early age strength, where hydrate formation increased on the particle surface. The cement matrix produced using electrolyzed alkaline-reduced water exhibited a high strength development rate of over 90% of ordinary Portland cement (OPC) in BFS30. Therefore, the use of electrolyzed alkaline-reduced water in the place of an alkaline activator allowed for the formation of a very strong cement matrix in the early stages of aging when a large blast furnace slag replacement ratio was used.

Nanocluster formation and two-step aging behavior in Al–Mg–Si(-xCu: X = 0–4 mass%) alloys

The effects of Cu addition on the clustering and two-step aging behavior in Al–Mg–Si(-Cu) alloys were analyzed by differential scanning calorimetry (DSC), the Vickers hardness and tensile tests, the three dimension atom probe (3DAP) and the transmission electron microscope (TEM). A high amount of Cu up to 4 mass % was added to the Al–Mg–Si alloys. Several types of clusters, namely, Cu–Mg, Cu–Si, Cu–Cu and Mg–Si–Cu, after natural aging for 2419.2 ks were formed in the Al–Mg–Si–Cu alloys. The size distribution and chemical composition of the clusters were characterized using 3DAP based on the maximum separation method. The cluster formation was promoted by 1Cu addition, but it was suppressed by 2Cu and 4Cu additions based on the analyses of cluster formation temperature and activation energy. Thermally unstable clusters were confirmed at the early stage of two-step aging at 170 °C after natural aging for 2419.2 ks. The amount of thermally unstable clusters was increased based on the hardness results. The peak hardness during single aging at 170 °C increased with an increasing Cu content. The negative and positive effect of two-step aging at 170 °C after natural aging for 2419.2 ks was clarified in Al–Mg–Si and Al–Mg–Si–Cu alloys, respectively. The formation temperature, activation energy, cluster size, and hardness changes with the cluster formation during natural aging and dissolution of cluster and precipitate formation during two-step aging at 170 °C are quantitatively described and those behaviors are discussed based on the age-hardening phenomena.

Climatic Aging of Aviation Polymer Composite Materials: II. Development of Methods for Studying the Early Stages of Aging

The review systematizes the results of studying the early stages of climatic aging of polymer composite materials by the methods that are sensitive to destruction in the surface layer of samples. The surface relief height, the diffusion coefficient of moisture, and the glass transition temperature of epoxy binders are shown to be sensitive to the action of temperature, humidity, solar radiation and other environmental factors.

Nanoscale short-range ordering induced cellular structure and microchemistry evolution in Sm2Co17-type magnets

Sm2Co17-type permanent magnets have important application value due to their advanced magnetic properties, which can be ascribed to their unique cellular structure and element segregation in various phases developed after isothermal aging treatment. In this study, the evolution of the microstructure combined with the microchemistry of Sm2Co17-type magnets from solid solution precursor to the cellular structure is investigated, and a new insight into the formation of the cellular structure is provided. We report for the first time that a large number of strip-like nanoscale short-range ordered micro-domains are distributed in the disordered matrix of the solution precursor, which serve as the nucleation centers in the formation of the embryos of the cellular structure. Based on atomic scale structural analyses, a new mechanism concerning the ordering transformation from short-range 2:17R microtwins to long-range 2:17R phase is proposed, involving collective glide of three partial dislocations on successive basal planes with the net Burgers vector to be zero. Furthermore, microchemistry analysis reveals that the segregation of Cu and Fe in the early stage of isothermal aging is accelerated substantially during the ordering transformation, indicating that the ordering transformation can act as a new driving force for element segregation in Sm2Co17-type magnets. These findings provide new considerations for the development of high performance Sm2Co17-type magnets.

Co-precipitation of T′ and η′ phase in Al-Zn-Mg-Cu alloys

The ageing precipitates and strengthening effects of Al-Zn-Mg-Cu alloys with different Zn contents were investigated. The results showed that increasing Zn contents can significantly improve the age-hardening response and influence the type of precipitates as well. The low Zn-containing alloy (1.70 at.%) is strengthened by nano-scale T′ phases in the peak aged condition. However, the microstructure of the high Zn content (2.34 at.%) alloy in the peak aged condition consists of a higher density of globular T′ phases and a small proportion of plate-like η′ phases. The results of atom probe tomography revealed that clusters formed at the early stage of ageing with a Zn/Mg atomic ratio higher than 1.3 transform into η′ phases and these clusters with a lower Zn/Mg ratio transform into T′ phases. The composition of a T′ phase varies with its size, where the concentrations of Zn and Mg increase with its increasing radius, while the concentration of Al presents an opposite trend.

Short-term enhancement of motor neuron synaptic exocytosis during early aging extends lifespan in Caenorhabditis elegans.

The functional decline of motor activity is a common feature in almost all aging animals that leads to frailty, loss of independence, injury, and even death in the elderly population. Thus, understanding the molecular mechanism that drives the initial stage of this functional decline and developing strategies to increase human healthspan and even lifespan by targeting this process would be of great interests to the field. In this study, we found that by precisely targeting the motor neurons to potentiate its synaptic releases either genetically or pharmacologically, we can not only delay the functional aging at NMJs but also slow the rate of aging at the organismal level. Most importantly, we have demonstrated that a critical window of time, that is the early stage of NMJs functional decline, is required for the beneficial effects. A short-term treatment within this time period is sufficient to extend the animals' lifespan.

Enhanced age-hardening by synergistic strengthening from Mg[sbnd]Si and Mg[sbnd]Zn precipitates in Al-Mg-Si alloy with Zn addition

The accelerated age-hardening response and the enhanced peak-hardness in Al-Mg-Si with Zn addition were investigated by three-dimensional atom probe and transmission electron microscopy. The results showed that Zn addition significantly increased the number density of solute aggregates by stimulating the formation of more MgSi precipitates and resulted in a higher Mg/Si ratio because of the formation of MgZn precipitates. Furthermore, a synergistic strengthening from MgSi and MgZn solute aggregates was quantitatively estimated in accelerating the age-hardening response at the early aging stage, and a coexistence of β″ phases for Mg2Si system and GPI zones/η′ phases for MgZn2 system was confirmed to enhance the peak-hardness of Al-Mg-Si alloy with Zn addition.

Factors Related to Diabetes Mellitus in the Middle-Aged and Over in Taiwan

Study Objective: to investigate the factors related to diabetes mellitus in the middle-aged and over in Taiwan. Method: data from seven surveys (in 1989–2011) from the “Taiwan Longitudinal Study on Aging” (TLSA), among cohort B (above the age 60 in 1989), cohort A (aged 50–66 in 1996), and cohort C (aged 50–66 in 2003), were analyzed by the interval-censored Cox model. Results: in the early aging stage (aged 60–64), diabetes mellitus prevalence among the same age appeared the lowest in cohort B, followed by cohort A; cohort C reveals the highest than the young generation. Moreover, suffering from hypertension and kidney diseases are closely related to diabetes mellitus, with the diabetes mellitus suffering hazard ratio of 2.53 (95%: 2.35, 2.73) and 1.26 (95%: 1.11, 1.44) times, respectively. For people with fair and poor self-rated health, the risk of suffering from diabetes mellitus is 1.16 (95%: 1.07, 1.27) and 1.50 (95%: 1.35, 1.67) times compared to people with good self-rated health, respectively. Conclusions: in this study, it is considered that an advanced interval censoring model analysis could more accurately grasp the characteristics of factors in people who are middle-aged and over suffering from diabetes mellitus in Taiwan.

Growth behavior and strengthening mechanism of Cu-rich particles in sanicro 25 austenitic heat-resistant steel after aging at 973 K

Precipitation and growth behaviors of Cu-rich particles in Sanicro 25 austenitic heat-resistant steel after aging at 973 K were systematically investigated by using transmission electron microscope (TEM) and three-dimensional atom probe (3DAP), and the strengthening mechanism of Cu-rich particles was discussed. The results show that many fine and well-dispersed Cu-rich particles precipitate at the early stage of aging at 973 K. This is because Cu atoms are supersaturated in the matrix after solid solution treatment and Cu-rich particles are coherent with austenitic matrix. The growth of Cu-rich particles during aging at 973 K follows diffusion-controlling LSW theory. The reduction of interfacial energy due to the segregation of Mn is estimated to be 8.1, 8.4, 14.7 and 16.7 mJ/m2 after aging for 10, 50, 100 and 1000 h, respectively. The segregation of Mn at interfaces of Cu-rich particle/matrix retards the growth of Cu-rich particles by reducing the interfacial energy, and the retarding effect increases with increasing aging time. The strengthening mechanism of Cu-rich particles in Sanicro 25 transforms from the combination of coherency strain and stacking-fault strengthening to Orowan strengthening when the average radius is about 13 nm. Cu-rich particles play an important role in affecting the strength and hardness of Sanicro 25 during aging. Increasing the content of Cu properly is beneficial to improve the strength of Sanicro 25 from the viewpoint of increasing the volume fraction of Cu-rich particles. Also, the addition of Mn is useful to improve the strength of Sanicro 25 since it can reduce the interfacial energy of Cu-rich particle/matrix.

Charge transport dynamics and the effects on electrical tree degradation under DC voltages in thermally aged silicone rubber

Electrical tree is one of the major issues for insulation failure in high voltage power cables. In this paper, we investigate electrical tree degradation under DC voltages in thermally aged silicone rubber (SIR). Charge transport dynamics are revealed by means of space charge measurement and simulation to give a better insight into the electrical tree initiation and evolution. The results show that a thermal oxygen reaction enhances the SIR cross-linked networking and thus gives rise to a higher tree initiation voltage in the early stage of aging. Subsequently intensified thermal degradation and cracking reaction accelerate SIR cross-linked network breakdown and generate micro-cracks. The increased deep traps and significantly decreased charge carrier mobility after thermal aging result in greater homo charge accumulating near the needle tip. The mechanism of DC electrical tree initiation in SIR is clarified based on the trap theory. It is argued that more trapped charges in the low-density region near the tip in the late thermally aged stage would decrease the tree initiation voltage, while the resultant homo charges would in turn reduce the electric field around the tip. Therefore, after thermal aging, the reduction of tree initiation voltage under DC voltage is less than that under AC voltage.

First-Principles Study on the Cu/Fe Interface Properties of Ternary Cu-Fe-X Alloys.

The supersaturated Fe in Cu is known to reduce the electrical conductivity of Cu severely. However, the precipitation kinetics of Fe from Cu are sluggish. Alloying is one of the effective ways to accelerate the aging precipitation of Cu-Fe alloys. Nucleation plays an important role in the early stage of aging. The interface property of Cu/γ–Fe is a key parameter in understanding the nucleation mechanism of γ-Fe, which can be obviously affected with the addition of alloying elements. In this paper, first principles calculations were carried out to investigate the influence of alloying elements on the interface properties, including the geometric optimizations, interfacial energy, work of adhesion and electronic structure. Based on the previous research, 14 elements including B, Si, P, Al, Ge, S, Mg, Ag, Cd, Sn, In, Sb, Zr and Bi were selected for investigation. Results showed that all these alloying elements tend to concentrate in the Cu matrix with the specific substitution position of the atoms determined by the binding energy between Fe and alloy element (X). The bonding strength of the Cu/γ-Fe interface will decrease obviously after adding Ag, Mg and Cd, while a drop in interfacial energy of Cu/γ–Fe will happen when alloyed with Al, B, S, P, Si, Ge, Sn, Zr, Bi, Sb and In. Further study of the electronic structure found that Al and Zr were not effective alloying elements.

Enhanced nucleation and precipitation hardening in Al–Mg–Si(–Cu) alloys with minor Cd additions

This work reports a novel effect of impurity element Cd on enhancing the precipitation kinetics and increasing the peak hardness of Al–Mg–Si(–Cu) alloys during artificial ageing. It is found that the number density of age hardening Mg–Si(–Cu) precipitates is greatly increased by Cd addition (~0.06 at.%) at both the under-aged and peak-aged stages. A systematic study on the precipitation behaviour by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) shows that most Mg–Si(–Cu) precipitates in the Cd-containing Al–Mg–Si alloys are associated with Cd-rich precipitates and have highly disordered structures. It is also found that the formation of Q'/C-like sub-units in Mg–Si(–Cu) precipitates is significantly promoted by Cd additions. To explore the nucleation mechanism under the influence of Cd addition, atom probe tomography (APT) is applied to study the solute clustering behaviour in the early stages of artificial ageing, and density functional theory (DFT) calculations are used to evaluate the binding energies of different solute-vacancy complexes and therefore the formation kinetics of Mg–Si–Cd clusters.

Synthesis, characterization, and thermodynamic study of selected Na-based zeolites

Zeolites are crystalline aluminosilicates with three-dimensional framework structures that can form in alkali-activated cements, Roman cements, and the interaction zone of cements and clays. However, their stability domains are uncertain due to their high structural variability and the lack of experimental solubility data. Thermodynamic data were here determined for selected Na-based zeolites built from six different secondary building units that could possibly form in the interaction zones of cement/clay. The zeolites were synthesized by hydrothermal methods and full-scale characterized with respect to framework structures, extra-framework cations, Si/Al ratios, and water contents. Their thermodynamic properties were determined based on the experimental solubility products at different temperatures using GEMS. Predominance diagrams of zeolite-clay/mica-SiO2/Al(OH)3 minerals in the chemical sub-systems of Na2O-SiO2-Al2O3-H2O were successfully established using PHREEQC-PhreePlot code. The experimentally derived thermodynamic data provide insights on the early stage of the zeolite ageing and predicting zeolite stability domains during cementitious material hydration.

The influence of Sc–Si clusters on aging hardening behavior of dilute Al-Sc-(Zr)-(Si) alloy

The aging hardening behaviors of Al-0.12Sc and Al-0.12Sc-0.2Zr (wt.%) alloys with the addition of Si range from 0.05 wt% to 0.3 wt% were investigated by microhardness and transmission electron microscopy. The results indicate that content of ∼0.15% Si is optimal and Sc–Si clusters forming at the early ageing stage hinder the evolution process of Al3Sc. Upon aging isochronally, Al-Sc-(Zr)–Si alloy shows two stages hardening. The first strengthen stage occurs because of the formation of Sc–Si clusters, and peak hardness of the second stage owes to (Al,Si)3Sc evolving from the clusters. During aging isothermally at 275 °C, Al-Sc-Si and Al-Sc-Zr-Si show similar hardening characteristics. But ageing at 225 °C, the Sc–Si clusters are relatively stable, the second stage increase in the Al-Sc-(0.15, 0.3%)Si alloys have no appearance. Clustering behavior of Sc and Si does not be changed by the addition of Zr. The Al-Sc-Zr-Si alloy exhibits better thermal stability. Because partition of Zr to the preceding formed (Al,Si)3Sc reduces the coarsening rate of the precipitates.

Salt contents and aging period effects on the physicochemical properties and sensory quality of Korean traditional fermented soybean paste (doenjang)

The aging of Korean traditional fermented soybean paste (doenjang) is an important step in obtaining flavorful and tasty products. The objective of this study was to investigate the effect of the salt contents (8, 12, 16, and 20%) on doenjang production during the early stage of the aging (zero to two months) on sensory profiles and consumer acceptability. Generally, the salt content and aging of doenjang significantly influenced the physicochemical and sensory qualities of the samples. The moisture, amino nitrogen, titratable acidity and browning index were lower and the salt, Na, and Mg were higher as salt increased in doenjang production. The amino nitrogen, titratable acidity and browning index were increased as aging progressed. The 8% salt samples showed a different change pattern in sensory characteristics during the early stage of aging. Since the 8% salt samples had different sensory profiles, they were less acceptable to consumers during the aging period unlike the 12 and 16% salt samples. These different sensory characteristics and lower consumer acceptance ratings may be a hurdle in bringing low salt doenjang to market.