The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Seung Taik Lim - One of the best experts on this subject based on the ideXlab platform.
-
Effects of Physical Aging on Thermal and Mechanical Properties of Glassy Normal Corn Starch
Starch - Stärke, 2005Co-Authors: Hyunjung Chung, Byoungseung Yoo, Seung Taik LimAbstract:Physical aging of glassy corn starch and its effect on the physical properties of compressed starch bars were investigated by using differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA), and Instron texturometer. Amorphous corn starch samples were prepared by drying a starch paste, followed by compressing the dried powders to bar-type specimens under heat (1007C, 1.38610 7 Pa). These bars were then aged at 257C for up to 22 days, after which thermal and mechanical characteristics were determined. There were progressive increases in glass transition temperature and Relaxation Enthalpy during the aging, which reached limiting values as structural equilibrium of the amorphous matrix was approached. The peak temperature of the Relaxation endotherm (DSC thermogram) changed with time in a trend similar to the Relaxation Enthalpy. The storage modulus (DMTA) increased with aging time, but the peak intensity of tan d decreased. The breaking strength (Instron texturometer) increased gradually with time of aging and reached a maximum. It has been demonstrated the Relaxation kinetics for glassy amorphous corn starch can be characterized by both thermal and mechanical properties, such as Relaxation Enthalpy, storage modulus, and breaking strength.
-
Physical aging of glassy normal and waxy rice starches: Thermal and mechanical characterization
Carbohydrate Polymers, 2004Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Physical aging of glassy amorphous rice (normal and waxy) starches (14.5% moisture) was characterized in terms of thermal and mechanical properties, using a differential scanning calorimeter (DSC), dynamic thermal analyzer (DMTA), and Instron texturometer. The starch samples were prepared by compressing under heat (100 8C, 2000 psi), and subsequently aged at 25 8C for up to 29 days. Relaxation Enthalpy, as measured by DSC, increased gradually with aging time, reaching a structural equilibrium. The peak temperature of the Relaxation endotherm in DSC thermogram linearly increased with the logarithm of aging time. Relaxation kinetics revealed that Relaxation rate was much slower for normal rice starch than for waxy rice starch. DMTA showed that storage modulus increased by aging, but the tan d peak height reduced, indicating that the chain mobility of glassy starch was reduced by aging. Dual glass transitions were observed in both DSC and DMTA thermograms for normal rice starch samples, whereas a single transition was observed for waxy rice starch samples. It suggests that the amorphous regions in normal starch samples are heterogeneous. Breaking strength, measured using an Instron texturometer, increased gradually with aging time, in accordance with the change in Relaxation Enthalpy. The Relaxation kinetics of glassy starch aging could be explained by thermal transition Enthalpy and by mechanical properties such as storage modulus and breaking strength. q 2004 Elsevier Ltd. All rights reserved.
-
physical aging of glassy normal and waxy rice starches effect of aging time on glass transition and Enthalpy Relaxation
Food Hydrocolloids, 2003Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Abstract Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher T g than waxy rice starch. The T g and Δ C p at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The Relaxation Enthalpy and Relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter ( β ) of both starches was in a range of 0.3 β t c ), normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition.
-
physical aging of glassy normal and waxy rice starches effect of aging temperature on glass transition and Enthalpy Relaxation
Carbohydrate Polymers, 2003Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher Tg than waxy rice starch. The Tg and DCp at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The Relaxation Enthalpy and Relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter ðbÞ of both starches was in a range of 0:3 , b , 0:7; but higher at a lower moisture content, and for normal starch than for waxy starch. Maximum Relaxation Enthalpy for normal starch (1.10 and 2.69 J/g, respectively, at 11 and 15% moistures) was higher than those of waxy starch (0.77 and 2.48 J/g). Based on the characteristic time ðtcÞ; normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition. q 2003 Elsevier Ltd. All rights reserved.
Hyunjung Chung - One of the best experts on this subject based on the ideXlab platform.
-
Effects of Physical Aging on Thermal and Mechanical Properties of Glassy Normal Corn Starch
Starch - Stärke, 2005Co-Authors: Hyunjung Chung, Byoungseung Yoo, Seung Taik LimAbstract:Physical aging of glassy corn starch and its effect on the physical properties of compressed starch bars were investigated by using differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA), and Instron texturometer. Amorphous corn starch samples were prepared by drying a starch paste, followed by compressing the dried powders to bar-type specimens under heat (1007C, 1.38610 7 Pa). These bars were then aged at 257C for up to 22 days, after which thermal and mechanical characteristics were determined. There were progressive increases in glass transition temperature and Relaxation Enthalpy during the aging, which reached limiting values as structural equilibrium of the amorphous matrix was approached. The peak temperature of the Relaxation endotherm (DSC thermogram) changed with time in a trend similar to the Relaxation Enthalpy. The storage modulus (DMTA) increased with aging time, but the peak intensity of tan d decreased. The breaking strength (Instron texturometer) increased gradually with time of aging and reached a maximum. It has been demonstrated the Relaxation kinetics for glassy amorphous corn starch can be characterized by both thermal and mechanical properties, such as Relaxation Enthalpy, storage modulus, and breaking strength.
-
glass transition and Enthalpy Relaxation of cross linked corn starches
Carbohydrate Polymers, 2004Co-Authors: Hyunjung ChungAbstract:Thermal transition of cross-linked corn starches was characterized by using a differential scanning calorimeter (DSC) in the presence of excess (67%, based on total weight) or limited (15%) water. Normal corn starch (∼24% amylose) was cross-linked by reacting with a mixture (99:1) of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) in an aqueous alkaline slurry containing sodium sulfate. The amount of the cross-linking agent (STMP/STPP mixture) in the starch slurry (100 g starch, 140 ml water, and 10 g sodium sulfate) was varied (4–12 g), and the level of cross-linking was monitored by the level of incorporated phosphorus, swelling volume, and α-amylase resistance. When analyzed with excess water, the glass transition temperature (Tg′, −5.6 and −5.7 °C) of the cross-linked starches was higher than those of native and control starches (−6.6 and −6.5 °C, respectively), and the ice melting Enthalpy was also increased by the cross-linking, indicating the increased amount of freezable water. However, in the DSC analysis with limited water, Tg and heat capacity increment (ΔCp) at Tg decreased by cross-linking. It indicates that the free volume for starch chains was increased by the bulky and ionic phosphate groups. The Relaxation Enthalpy increased, but the peak temperature of Relaxation endotherm decreased as the cross-linking level increased. Retrogradation Enthalpy after a week storage at 4 °C was decreased by cross-linking.
-
Physical aging of glassy normal and waxy rice starches: Thermal and mechanical characterization
Carbohydrate Polymers, 2004Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Physical aging of glassy amorphous rice (normal and waxy) starches (14.5% moisture) was characterized in terms of thermal and mechanical properties, using a differential scanning calorimeter (DSC), dynamic thermal analyzer (DMTA), and Instron texturometer. The starch samples were prepared by compressing under heat (100 8C, 2000 psi), and subsequently aged at 25 8C for up to 29 days. Relaxation Enthalpy, as measured by DSC, increased gradually with aging time, reaching a structural equilibrium. The peak temperature of the Relaxation endotherm in DSC thermogram linearly increased with the logarithm of aging time. Relaxation kinetics revealed that Relaxation rate was much slower for normal rice starch than for waxy rice starch. DMTA showed that storage modulus increased by aging, but the tan d peak height reduced, indicating that the chain mobility of glassy starch was reduced by aging. Dual glass transitions were observed in both DSC and DMTA thermograms for normal rice starch samples, whereas a single transition was observed for waxy rice starch samples. It suggests that the amorphous regions in normal starch samples are heterogeneous. Breaking strength, measured using an Instron texturometer, increased gradually with aging time, in accordance with the change in Relaxation Enthalpy. The Relaxation kinetics of glassy starch aging could be explained by thermal transition Enthalpy and by mechanical properties such as storage modulus and breaking strength. q 2004 Elsevier Ltd. All rights reserved.
-
physical aging of glassy normal and waxy rice starches effect of aging time on glass transition and Enthalpy Relaxation
Food Hydrocolloids, 2003Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Abstract Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher T g than waxy rice starch. The T g and Δ C p at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The Relaxation Enthalpy and Relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter ( β ) of both starches was in a range of 0.3 β t c ), normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition.
-
physical aging of glassy normal and waxy rice starches effect of aging temperature on glass transition and Enthalpy Relaxation
Carbohydrate Polymers, 2003Co-Authors: Hyunjung Chung, Seung Taik LimAbstract:Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher Tg than waxy rice starch. The Tg and DCp at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The Relaxation Enthalpy and Relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter ðbÞ of both starches was in a range of 0:3 , b , 0:7; but higher at a lower moisture content, and for normal starch than for waxy starch. Maximum Relaxation Enthalpy for normal starch (1.10 and 2.69 J/g, respectively, at 11 and 15% moistures) was higher than those of waxy starch (0.77 and 2.48 J/g). Based on the characteristic time ðtcÞ; normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition. q 2003 Elsevier Ltd. All rights reserved.
Jamie J. Kruzic - One of the best experts on this subject based on the ideXlab platform.
-
Role of pre-existing shear band morphology in controlling the fracture behavior of a Zr–Ti–Cu–Ni–Al bulk metallic glass
Materials Science and Engineering: A, 2020Co-Authors: Sergio Scudino, Bernd Gludovatz, Jamie J. KruzicAbstract:Abstract Shear bands were introduced into a Zr–Ti–Cu–Ni–Al bulk metallic glass (BMG) by one-directional cold rolling and the effect on fracture toughness anisotropy was examined. Two different rolling and shear band orientations relative to the crack plane were used, with the rolling force oriented along either the width (CR-W) or thickness (CR-T) direction of single edge notched bend specimens. The results showed the CR-W samples demonstrated a 50% reduction in KQ relative to the as-cast material while the CR-T samples demonstrated the highest fracture toughness. The low fracture toughness of the CR-W samples was attributed to easy crack propagation paths formed by the shear bands. In contrast, the higher fracture toughness of the CR-T samples was attributed to the difficulty of crack twisting out of the mode I precrack plane onto the shear band planes and the high energy absorption of mode III tearing between the parallel crack planes. Overall, when cold rolling BMGs for structural applications, care must be taken to design the shear band morphologies to achieve the desired fracture toughness properties rather than solely focusing on increasing the average Relaxation Enthalpy/free volume.
-
Toughness enhancement and heterogeneous softening of a cryogenically cycled Zr–Cu–Ni–Al–Nb bulk metallic glass
Acta Materialia, 2019Co-Authors: Shenghui Xie, Jamie J. KruzicAbstract:Abstract In this study, as-cast and cold-rolled Zr63.78Cu14.72Ni10Al10Nb1.5 bulk metallic glass (BMG) samples were subjected to 20, 70, 120, and 170 cryogenic thermal cycles prior to fracture toughness testing. Thermal cycling raised the fracture toughness by promoting plastic deformation and stable crack growth, with the most significant increase occurring after the first 20 thermal cycles. Thermally cycled samples showed more tortuous crack paths and stable crack propagation left periodic blunting marks spaced at ∼57.5 μm on the fracture surface corresponding to each increment of crack advance. Microhardness mapping revealed a microstructure of hard and soft domains (∼63 μm × 105 μm), and thermal cycling heterogeneously softened the hard domains while the soft domains remained apparently unchanged. In addition to the observed softening, large increases in the Relaxation Enthalpy, and thus the average free volume, were found over the first ∼70 thermal cycles. While cold rolling the samples prior to the thermal cycling did not raise the mean fracture toughness values, the scatter was reduced compared to as-cast thermal cycled samples. This was attributed to the introduction of shear bands giving a more repeatable initial microstructure than casting.
Akihisa Inoue - One of the best experts on this subject based on the ideXlab platform.
-
pd40ni40si5p15 bulk metallic glass properties variation as a function of sample thickness
Intermetallics, 2013Co-Authors: D V Louzguineluzgin, Na Chen, Yu V Zadorozhnyy, Ichiro Seki, Akihisa InoueAbstract:Abstract This work presents a comparative study of different properties variation of Pd 40 Ni 40 Si 5 P 15 bulk metallic glass (BMG), namely: density, hardness, Relaxation Enthalpy and mechanical properties as a function of the sample thickness. The samples were produced in the form of a long pyramid by conventional Cu-mold casting in an Ar atmosphere. The results illustrate significantly different sensitivity of these properties of the glassy phase to the cooling rate. The difference in crystallization behavior is also discussed.
-
Plastic deformation by glassy structure control in Zr–Al–Ni–Cu-based BMGs
Journal of Alloys and Compounds, 2010Co-Authors: J. Saida, A. D. Setyawan, H. Kato, Mitsuhide Matsushita, Akihisa InoueAbstract:Abstract Zr 65 Al 7.5 Ni 10 Cu 17.5− x Pd x ( x = 0–17.5) bulk metallic glasses (BMGs) were produced in various chamber atmospheres in Cu mold casting. The glassy structure with a larger amount of Relaxation Enthalpy can be obtained casting under the ambient Ar and He atmospheres, which originates from enhanced cooling effect. These unrelaxed BMGs exhibit an improvement of ductility in the compressive deformation. Especially, Pd-containing BMGs have a significant plasticity of approximately 6%, in which deformation-induced inhomogeneous nanocrystallization also occurs. The synergistic effect of unrelaxed glassy structure and deformation-induced nanostructure change is regarded as a new technique for the improvement of ductility in the BMGs.
-
phase transformation behaviour in continuously cooled zr65al7 5ni10cu17 5 xpdx x 0 17 5 glass forming alloys and consequences for structure and property control
Philosophical Magazine, 2008Co-Authors: A. D. Setyawan, J. Saida, H. Kato, Akihisa InoueAbstract:Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5− x Pd x (x = 0 − 17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x = 5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x = 17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural Relaxation during continuous heating, could be fabricated for the low-Pd alloy (x = 5). Plasticity was found to increase proportionally with the Relaxation Enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7...
-
Phase transformation behaviour in continuously cooled Zr65Al7.5Ni10Cu17.5-xPdx (x = 0 - 17.5) glass-forming alloys and consequences for structure and property control
Philosophical Magazine, 2008Co-Authors: A. D. Setyawan, J. Saida, H. Kato, Akihisa InoueAbstract:Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5− x Pd x (x = 0 − 17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x = 5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x = 17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural Relaxation during continuous heating, could be fabricated for the low-Pd alloy (x = 5). Plasticity was found to increase proportionally with the Relaxation Enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7...
-
The relation between the bulk and ribbon Zr55Ni25Al20 metallic glasses
Materials Science and Engineering: A, 1997Co-Authors: Emília Illeková, Matej Jergel, Pavol Duhaj, Akihisa InoueAbstract:Abstract The planar-flow-casting technique and quenching in flowing water were used to produce the glassy Zr 55 Ni 25 Al 20 ribbon and bulk samples. The thermodynamic states of these two types of samples were compared using differential scanning calorimetry and analysis of the structural Relaxation kinetics. The Relaxation Enthalpy is 3 times larger and the glass transition temperature is higher by 67.5 K in the case of the ribbon sample. These differences were theoretically confirmed by a kinetic model and were caused by the different quenching rates for the ribbon and bulk samples, namely 10 5 and 10 2 K s −1 , respectively. X-ray analysis has shown, that the main difference between the studied glassy structures consists in the different degree of the short-range order in the samples.
Kefu Yao - One of the best experts on this subject based on the ideXlab platform.
-
Unique energy-storage behavior related to structural heterogeneity in high-entropy metallic glass
Materials Science and Engineering: A, 2020Co-Authors: Hengwei Luan, Shao-fan Zhao, Yang Shao, Kefu YaoAbstract:Abstract Structural heterogeneity dominates energy-storage behavior of metallic glasses. Ti20Zr20Hf20Be20Cu7.5Ni12.5 high-entropy bulk metallic glass (HE-BMG) shows extraordinary energy-storage behavior under cryothermal cycling: the Relaxation Enthalpy monotonically increased with cryothermal cycling cycles, even after 240 cycles of treatment. By comparison, the Relaxation Enthalpy of Ti41Zr25Be22Ni12 BMGs reached a maximum only at 30 cycles and then dramatically decreased as prototypical BMGs reported. The as-cast HE-BMG demonstrates an extremely low fraction of loose-packing regions (~7.8%, fractions for Ti- and Zr-based BMGs are above 15.6%), indicating degraded structural heterogeneity that would induce smaller local internal stress during cryothermal cycling and eventually lead to the sluggish energy-storage behavior. In addition, the increase in the fraction of loose-packing regions accompanied by the energy storage also lead to significant improvement in ductility of the HE-BMG, the plastic strain increased from 0.6% (the as-cast sample) to 5.2% (the sample treated 240 cycles).
-
The effect of simulated thermal cycling on thermal and mechanical stability of a Ti-based bulk metallic glass
Journal of Alloys and Compounds, 2013Co-Authors: Xiaodong Wang, Yang Shao, Pan Gong, Kefu YaoAbstract:Abstract The effects of simulated thermal cycling in vacuum in a temperature range of −196 °C to 150 °C on the thermal and mechanical stability of a lightweight Ti 41 Zr 25 Be 29 Al 5 bulk metallic glass (BMG) has been studied. It has been found that the thermal cycling treatment has not induced obvious changes of thermal and mechanical properties of the BMG even after 400 cycles. No embrittlement evidence has been observed despite of that the structural Relaxation Enthalpy of the BMG has been decreased with the increment of cycling number. It indicates that the reduction of structural Relaxation Enthalpy which is related to the reduction of free volume within the glassy alloy, does not imperatively result in embrittlement. It shows the effect of thermal cycling of 400 cycles on the property and structural Relaxation of the BMG is similar to but weaker than that of sub- T g annealing at 150 °C for 30 days. The good stability of thermal and mechanical properties indicates that the lightweight BMG has the potential of applying in the experimental temperature range such as the low Earth orbit environment.