Longer Aging Times Research Articles

Mechanical strength, surface abrasion resistance and microstructure of fly ash-metakaolin-sepiolite geopolymer composites

Compressive strength, flexural strength, surface abrasion resistance, Vickers-hardness of surface and microstructure evolution of fly ash-metakaolin geopolymer blended with 0–20% sepiolite by mass with an interval of 5% were investigated. The experimental results reveal that the compressive strength increases dramatically before 7 days of curing but it slows down with increasing curing ages. A pronounced increase in compressive strength can be found at longer ageing times after 7 days when sepiolite is added. Sepiolite exhibits improving effect on compressive strength especially at longer curing times of 14 days with optimal 10% addition level. Similarly, up to 10% sepiolite addition exhibits optimal improving effect on flexural strength regardless of days of curing. Sepiolite enhances the resistance to abrasion. The most pronounced decrease in weight loss was observed in 10% sepiolite added geopolymer. Vickers-hardness increases with increasing replacement levels of sepiolite, and 10% sepiolite added specimen has the highest values due to the highest strength. With the increasing addition levels of sepiolite from 5% up to 10%, compact surface can be observed. The microstructure changes of geopolymer matrix are similar to that of geopolymer surface. The mechanical properties of the geopolymer specimens are closely related to the microcrack development and the bonding between sepiolite and geopolymer matrix.

Effect of Grit Type, Aging Temperature, and Aging Time on Particle Size of Ground Natural Rubber/Zeolite Composite Powder

This study reports the results of investigation on the main and interaction effects of grit type, aging temperature, and aging time on particle size of ground natural rubber/zeolite (GNR/Z) composite powder using general factorial design of experiment. GNR/Z composite powder produced by mechanical grinding is porous, like an aggregated chain structure. These aggregates exist in clusters of irregular shape. Analysis of variance (ANOVA) shows that the effects of aging temperature and aging time depend on the particle size range. GNR/Z composite powder with large particle size is produced when aging is done at low temperature and short time due to high resistance of rubber to oxidation. On the other hand, GNR/Z composite powder with small particle size is produced when aging is done at low or high temperature and longer aging time. Low temperature condition offers high O2 concentration available to oxidize rubber while high temperature condition leads to more chain scissions due to higher oxidation rate.

Prediction Models for Textural Properties of Puffed Rice Starch Product by Relative Crystallinity

AbstractThis research aimed to determine the textural attributes of fried puffed rice starch products by the relative crystallinity (RC) of pellets (RCp). Three factors, amylose content (AC), aging time and cooling rate were varied to obtain various levels of RCp. The different textural characteristics of the puffed rice products were evaluated by instrumental and descriptive sensory analysis. The higher AC and longer aging time resulted in higher RCp. Pellets with higher RCp had smaller and denser air cell structures and lower expansion, resulting in higher crispness, hardness and fracturability. High correlation between the RCp and the instrumental and the sensory texture characteristics were determined and regression models (with R2 > 0.80) were established. These models can be used to predict some properties of puffed products, such as crispness, hardness, and brittleness. Panelists rated samples with an AC of 9% (in a range of 2.8–3.7% RCp) highest in appearance and texture scores.Practical ApplicationsThe RCp and textural properties of puffed products can be affected by many factors including ingredients and process parameters. This study provides a better understanding of both the textural characteristics of puffed rice starch products using sensory and instrumental approaches, but also their correlations. The relationship between the RCp and sensory evaluation data can be applied for the prediction of puffing quality.

Determination of rheological property and its effect on key aroma release of Shanxi aged vinegar.

The rheological property of Shanxi aged vinegar (SAV) was determined by rheometer, and its effects on release in eight key aroma components of SAV was investigated by SPME-GC-MS. In order to simulate the change of rheological property of SAV, a modified SAV system was developed from a finished SAV using carboxymethylcellulose, pectin, glucose, fructose, sodium chloride and tannic acid at indicate levels. The consistency coefficients (K) of SAV ranged from 1.09e-5 to 0.0137, which was correlated to glucose, polyphenol, acids and oBx. SAV changed from shear-thickening to Newtonian fluid during long-time ageing. In the modified SAV system, the K values increased significantly, and two modified vinegar became quasi-Newtonian fluids too. Furthermore, release of the eight key aroma compounds decreased significantly and decreased was pronounced, for acetic acid, furfural and tetramethylpyrazine. The results demonstrated rheological property correlated to the concentrate of sugar, salt, polyphenol, acids and macromolecule, which significantly affected the release of major aroma compounds.

Spectroscopic probe to contribution of physicochemical transformations in the toxicity of aged ZnO NPs to Chlorella vulgaris: new insight into the variation of toxicity of ZnO NPs under aging process

Zinc oxide nanoparticles (ZnO NPs) are one of the most abundantly applied nanomaterials in nanotechnology-based industries and they may cause unexpected environmental and health risks with their physicochemical transformations in the environment. Currently, there is still a lack of the in-depth understanding of the toxicity of aged ZnO NPs to aquatic organisms, particularly demanding quantitative analysis of the physicochemical transformations to distinguish their contributions in the toxicity assessment. For this purpose, therefore, we initiated the study of the toxicity of aged ZnO NPs to the model aquatic microalga, i.e. Chlorella vulgaris, and with the aid of spectroscopic tools for characterization and quantification of the physicochemical transformations, we scrutinized the toxicity variations for ZnO NPs with different aging times. As a result, we found that the toxicity altered in an abnormal manner with the aging time, i.e. the toxicity of aged ZnO NPs for 30 days showed the higher toxicity to the green alga than the fresh ZnO NPs or the ZnO NPs aged for longer time (e.g. 120 and 210 days). Through spectroscopic tools such as XRD, FTIR and Raman spectroscopy, we made both the qualitative and quantitative assessments of the physicochemical changes of the ZnO NPs, and confirmed that in the early stage, the toxicity mainly stemmed from the release of zinc ions, but with longer aging time, the neoformation of the nanoparticles played the critical role, leading to the overall reduced toxicity due to the less toxic hydrozincite and zinc hydroxide in the transformed compounds.

Microstructure Changes in Polyester Polyurethane upon Thermal and Humid Aging.

The microstructure of compression molded Estane 5703 films exposed to 11%, 45%, and 80% relative humidity and 70 °C for 1 and 2 months has been studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Scattering data indicated increase of the interdomain distance and domain size with a higher humidity and longer aging time. GPC data showed a progressive shortening of polyurethane chains with increasing humidity and aging time. The shortening of the polyurethane chains caused a drop of the glass transition temperature of soft segments, and promoted crystallization of the soft segments during long-time storage of the aged samples at room temperature. FTIR showed a substantial increase in the number of inter-urethane H-bonds in the aged samples. This correlates with the increase of the hard domain size and the degree of phase separation as measured by SANS. The data collected reveals that the reduced steric hindrance caused by hydrolysis of ester links in polybutylene adipate residues promotes the organization of hard segments into domains, leading to the increase of domain size and distance, as well as phase segregation in aged Estane. These findings provide insight into the effects of humidity and thermal aging on the microstructure of aged polyester urethane from molecular to nanoscale level.

Carbides in Co–Re–Cr-based high-temperature alloys

Co–Re-base alloys with very high melting point are being developed to supplement Ni-superalloys in future gas turbines in which much higher gas entry temperatures are expected. The microstructure of Co–17Re–23Cr–2.6C and Co–17Re–23Cr–1.2Ta–2.6C alloys has been investigated by scanning and transmission electron microscopy. These alloys are mainly strengthened by carbides of Cr and/or Ta, but it is not trivial to accurately quantify the composition of the carbides. The compositions of the various carbides in Co–Re–base alloys were quantified with near-atomic resolution using atom probe tomography. The Cr as well as Ta carbides exists in the alloys with different morphologies, ranging from extremely fine (nm scale) to large (μm scale) sizes. The composition and the crystal structure of the investigated phases were measured and reported. It is shown that both types of carbides are stable up to 1000 °C but the Ta carbides are more stable than the Cr carbides at 1200 °C after long-time ageing. They are also effective as strengthening precipitates.

The thermo-mechanical degradation of ethylene vinyl acetate used as a solar panel adhesive and encapsulant

The thermal ageing of an ethylene-vinyl acetate (EVA) polymer used as an adhesive and encapsulant in a photovoltaic module has been investigated. The EVA is used to bond the silicon solar cells to the front glass and backing sheet and to protect the photovoltaic materials from the environment and mechanical damage. Using a range of experimental techniques, including Dynamic Mechanical Analysis, Differential Scanning Calorimetry and Thermo-gravimetric Analysis, it was possible to show a link between changes in mechanical properties with both the transient temperature and the degree of long-time thermal ageing. Importantly, it was possible to show that the ageing related property changes were likely due to long term structural changes rather than any modification of the chemistry of the material.

Precipitation of the ordered α2 phase in a near-α titanium alloy

Precipitate evolution in a near-α alloy was studied using transmission electron microscopy (TEM) and correlative atom probe tomography (APT) after ageing at 550–700 for times up to 28days. It is found that precipitation occurs much faster and is more prolific in samples heat treated at higher temperatures. Particles were spherical after ageing at 550°C, while after ageing at 700°C they become ellipsoids with the major axis lying close to the [0001] direction. At longer ageing times, the α2 precipitates were found to contain greater amounts of Sn+Si, indicating that Sn and Si are stronger Ti3(Al,Sn,Si) formers than Al.

On nano-oxide coarsening kinetics in the nanostructured ferritic alloy MA957: A mechanism based predictive model

Nanostructured ferritic alloys are dispersion strengthened and imbued with remarkable neutron irradiation damage tolerance by an ultrahigh density of nano-oxide precipitates that must remain stable under prolonged high-temperature service. Here, previously reported long-time and high-temperature thermal aging data is used to derive a simple, but physically based and quantitatively predictive nano-oxide coarsening model using least square fits to equations representing different underlying mechanisms. A dislocation pipe diffusion model adequately fit the data with a dislocation-detachment climb mechanism providing the best fit. This model is consistent with microstructural observations and recently reported thermo-kinetic nano-oxide nucleation, growth and coarsening simulations that rationalize the underlying physics of coarsening. It is predicted that the nano-oxides will remain fully stable up to 900°C. This remarkable coarsening resistance is due to the extremely low matrix solubility and diffusion rate of Y in equilibrium with Y2Ti2O7 that activates lower resistant paths along dislocations.

B22-O-09Analysis of stable precipitates in beta-titanium alloys aged at medium temperature for long-time periods

Figure 1 shows diffraction patterns of Ti-20 Mo alloys aged at 823 K for 3.6 ks (a) and 18.0 ks (b) after aging at 623 K for 12.6 ks under a tensile stress [ 1 ]. Incident beam directions were parallel to [110] of the matrix beta-phase (bcc). In Fig. 1 (a), small well-known extra-spots of omega-phase precipitates are visible. The two extra-spots can be seen on a line from 020 and 101 spots of the matrix. In Fig. 1 (b), the similar extra-spots are visible, but those spots are not on the line from 020 to 101 spots, which means that the precipitates causing these spots are not omega-phase precipitates. It is considered that the precipitates are alpha-phase ones because of long-time aging at temperatures under the beta-transus. It has been also reported that the extra-spots appear due to double-diffraction [ 2 ]. The similar extra-spots have been observed in several beta-titanium alloys such as Ti-15Mo, Ti-15-3, Ti-4.5Al-3V-2Mo-2Fe and Ti-5553 alloys. It seems that the understanding of the extra-spots is not necessarily satisfied.

Influence of Gemini Surfactant with Modified TiO2 Nanoparticles on the Interfacial Tension of Oil/Water

The research on the impacts of modified TiO2 nanoparticles (NPs) on interfacial tension (IFT) is in its infancy. Our work focuses on the IFT of the modified TiO2 and Gemini surfactant N,N,N′,N′-tetramethyl-N,N′-dimyristyl-1,2-ethane diammonium dichlone (YND1233) complex solutions for reservoir stimulation purposes. The factors of YND1233, modified TiO2 NPs, temperature, aging stability, adsorption loss, and mineralized degree were explored with the comparison of unmodified TiO2 NPs and YND1233 as contrast samples. The results indicate that the dynamic IFTs decrease and then increase with the concentrations of YND1233 and modified TiO2 NPs, and the minimum IFT appears at 0.200 and 0.010 wt%, respectively. YND1233/modified TiO2 complex solutions show lower and more stable IFTs, better temperature resistance, longer aging time, and lower adsorption on the surface of quartz sand. The modified TiO2 NPs and YND1233 in the YND1233/modified TiO2 complex solution can be adsorbed to the interface and decrease the IFTs through synergistic effect. A mixed diffusion-kinetic mechanism is provided for the adsorption and interactions with Ca2+/Mg2+ involved in YND1233/modified TiO2 complex solution.

Micro-structural evolution and biomineralization behavior of carbon nanofiber/bioactive glass composites induced by precursor aging time

Bioactive glass (BG)—containing carbon nanofibers (CNFs) are promising orthopaedic biomaterials. Herein, CNF composites were produced from electrospinning of polyacrylonitrile (PAN)/BG sol–gel precursor solution, followed by carbonization. Choosing 58S-type BG (mol%: 58.0% SiO2-26.3% CaO-15.7% P2O5) as the model, micro-structural evolution of CNF/BG composites was systematically evaluated in relating to aging times of BG precursor solution. With aging time prolonging, BG precursors underwent morphological changes from small sol clusters with loosely and randomly branched structure to highly crosslinked Si-network structure, showing continuous increase in solution viscosity. BG precursor solution with low viscosity could mix well with PAN solution, resulting in CNF composite with homogeneously distributed BG component. Whereas, BG precursor gel with densely crosslinked Si-network structure led to uneven distribution of BG component along final CNFs due to its significant phase separation from PAN component. Meanwhile, BG nanoparticles in CNFs demonstrated micro-structural evolution that they transited from weak to strong crystal state along with longer aging time. Biomineralization in simulated body fluid and in vitro osteoblasts proliferation were then applied to determine the bioactivity of CNF/BG composites. CNF/BG composites prepared from shorter aging time could induce both faster apatite deposition and cell proliferation rate. It was suggested weakly crystallized BG nanoparticles along CNFs dissolved fast and was able to provide numerous nucleation sites for apatite deposition, which also favored the proliferation of osteoblasts cells. Aging time could thus be a useful tool to regulate the biological features of CNF/BG composites.

Effects of thermal aging on creepage discharge in oil- impregnated pressboard under combined AC-DC voltage

In this study, we investigate the characteristics of creepage discharge on oil-impregnated pressboard under combined AC-DC voltage conditions using a sphere-plane electrode configuration. In our experiments, we use four oil-impregnated pressboard samples subjected to different thermal aging time. Experimental results show that the creepage discharge inception voltage (CDIV) and creepage discharge flashover voltage (CDFV) are lowest under pure AC voltage and gradually increase with higher DC voltage components. Longer aging time may contribute to higher CDIV with low DC voltage components; however, with higher DC voltage components, the effect of aging time is less pronounced. The CDFV is not significantly influenced by aging time. The length of carbonized tracks and the development velocity of the creepage discharge increase and the endurance time decreases with longer aging time and higher DC voltage components. We divide the development of creepage discharge in aged pressboard into four stages according to changes in the discharge characteristic parameters. With longer aging time, characteristic parameters exhibit less fluctuation and development velocity exhibits greater sensitivity to the DC voltage component. Our experimental results demonstrate that the characteristics of creepage discharge are significantly influenced by the age of the pressboard and by DC voltage components.

Effect of repeated pulsed electric field treatment on the quality of hot-boned beef loins and topsides

The effects of repeated (1×, 2×, 3×) pulsed electric field (PEF) treatment (10kV, 90Hz, 20μs) on the quality of beef loins and topsides were evaluated, including the tenderness, purge loss, cooking loss, myofibrillar protein profile and post-mortem proteolysis. Both muscle types were obtained from each of 12 steers and were processed within 6h. After PEF treatment samples of both muscle types were subjected to 3, 7, 14 and 21days ageing. The 1× and 2× PEF treatments had no effect on the tenderisation of hot-boned beef Musculus longissimus lumborum muscle for all ageing treatment times, while the 3× treatment reduced the tenderness. The opposite effect was observed in hot-boned beef Musculus semimembranosus muscles where the 3× treatment produced meat with lowest shear force at 3days post-treatment time, but this beneficial effect disappeared with longer ageing times. An increase in proteolysis of troponin T was seen to the largest extent with 1× PEF treatment and decreased with every extra application of treatment.

The effect of precipitates on the superelastic response of [1 0 0] oriented FeMnAlNi single crystals under compression

FeMnAlNi shape memory alloys were recently discovered to have a small temperature dependence of the superelastic critical stress in a large superelastic temperature window from −196°C to 240°C. In this work, we investigated the effect of B2 nanoprecipitates on the superelastic characteristics of [100] oriented Fe43.5Mn34Al15Ni7.5 single crystals under compression, and found that the size, volume fraction and composition of precipitates strongly influence the transformation temperature, superelastic strain, critical stress for stress-induced martensitic transformation and stress hysteresis of the single crystals. The single crystals aged at 200°C for 3h show 7.2% superelastic strain with the precipitate size of about 6–10nm. Longer aging times or higher aging temperature reduces superelastic recovery due to the coarsening of the precipitates.

Effects of Isothermal Aging on Microstructure Evolution of Biomedical Co-Cr-Mo Alloy

Cobalt based alloys have been widely used in orthopedic implants. These alloys are an allotropic metal, which commonly exhibits two crystal structures, namely, FCC and HCP lattice. In this work, developed microstructure and hardness of a Co-Cr-Mo alloy after isothermal aging treatment were investigated. The applied aging procedure included soaking at the temperature of 850°C for five different holding times of 1, 3, 6, 9 and 12 h with subsequent water quenching. Microstructure examination, X-ray diffraction analysis and micro-hardness test were carried out for both as-received and heat-treated cobalt based alloys. The results showed that the FCC to HCP phase transformation occurred during the isothermal aging. It was observed that phase fraction of the identified HCP phase increased with longer aging time. Microstructure of the samples aged for 12 h showed very fine lamellae morphologies similar to a pearlitic structure with different orientations within each FCC grain. Apparently, these occurred lamellae structures could be well correlated with the formation of the HCP martensite. Additionally, it was found that in the Co-Cr-Mo alloy sigma phase precipitated early at the grain boundaries and further grew along these boundaries by increasing aging time. The hardness value of the examined alloy slightly increased with larger HCP phase fraction. The increased aging time certainly led to higher amount of the HCP martensite and consequently increased hardness and possible wear resistance properties.

Coarsening and Hardening Behaviors of Cu-Rich Precipitates in Super304H Austenitic Steel

The coarsening and hardening behaviors of Cu-rich precipitates in Super304H austenitic steel aged at 923 K, 973 K, and 1023 K (650 °C, 700 °C, and 750 °C), respectively, have been investigated through measuring the particle size by transmission electron microscopy and microhardness. The results showed the Cu-rich precipitates have a cubic-to-cubic crystallographic relationship and coherent interface with the austenitic matrix during long-time aging, and that the coarsening behavior of the Cu-rich particles can be predicted with the help of the Lifshitz–Slyozov–Wagner theory. The activation energy for coarsening of the Cu-rich precipitates was evaluated to be 212 ± 3 kJ/mol. The coarsening of Cu-rich precipitates is controlled mainly by the volume diffusion of copper atoms in the austenitic matrix. The contributions to the maximum microhardness occurring at different aging temperatures from precipitation strengthening range from about 17 to 25 pct. The strengthening of the Cu-rich precipitates arises mainly from the coherency strain and partially from stacking-fault strengthening.

Geometry effect on mechanical performance and fracture behavior of micro-scale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints

Solder joint integrity has long been recognized as a key issue affecting the reliability of integrated circuit packages. In this study, both experimental and finite element simulation methods were used to characterize the mechanical performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with different standoff heights (h, varying from 500 to 100μm) and constant pad diameter (d, d=480μm) and contact angle under shear loading. With decreasing h (or the ratio of h/d), results show that the stiffness of BGA solder joints clearly increases with decreasing coefficient of stress state and torque. The stress triaxiality reflects the mechanical constraint effect on the mechanical strength of the solder joints and it is dependent on the loading mode and increases dramatically with decreasing h under tensile loading, while the change of h has very limited influence on the stress triaxiality under shear loading. Moreover, when h is decreased, the concentration of stress and plastic strain energy along the interface of solder and pad decreases, and the fracture location of BGA solder joints changes from near the interface to the middle of the solder. Both geometry and microstructure greatly affect the shear behavior of joints, the average shear strength shows a parabolic trend with decreasing standoff height. Furthermore, the brittle fracture of BGA solder joints after long-time isothermal aging was investigated. Results obtained show that, under the same shear force, the stress intensity factors, KI and KII, and the strain energy release rate, GI, at the Sn–3.0Ag–0.5Cu/Cu6Sn5 interface and in the Cu6Sn5 layer obviously decrease with decreasing h, hence brittle fracture is more prone to occur in the joint with a large standoff height.

Effects of Different Heat Treatment on Microstructure, Mechanical and Conductive Properties of Continuous Rheo-Extruded Al-0.9Si-0.6Mg (wt%) Alloy

Al-0.9Si-0.6Mg (wt%) alloy conductive wires were designed and produced by continuous rheo-extrusion process. The effects of different heat treatment on microstructure, mechanical and conductive properties of the wires were studied. Results show that, after T6 heat treatment, conductive property of the alloy increased while elongation decreased with the higher aging temperature and longer aging time. After T8 and T9 heat treatment, acicular strengthening phase β''-Mg2Si homogeneously precipitated, which effectively improved mechanical and conductive property of the alloy. The tensile strength, elongation and resistivity of T8 heat treated alloy reached 336 MPa, 13.7% and 29.3 nΩm respectively. After T9 heat treatment, the alloy’s tensile strength, elongation and resistivity was 338 MPa, 6.0% and 30.2 nΩ·m respectively.