Effect Of Initial Structure Research Articles

Experimental investigation on the effect of initial structure on the water retention behavior of Mile clay

Soil structure has strong effect on hydro-mechanical properties of soils, particularly in the case of expansive clays. Along the wetting–drying path, expansive clays undergo significant volume changes that can pose serious challenges for infrastructures built on them. Moreover, the hydro-mechanical behaviour of intact, compacted, and reconstituted expansive clay exhibits notable differences. In this study, the effect of natural soil structure of intact Mile expansive clay on water retention behaviour was studied by comparing two states of Mile clay, intact and compacted states. The corresponding water retention behavior along the main wetting and drying paths were analysed and compared. Utilizing scanning electron microscope and mercury intrusion porosimetry tests, the different water retention behaviours observed between intact and compacted Mile clay were further elucidated from a microstructural aspect. It shows that bonding between and within soil aggregates in intact Mile clay constrained volume changes in specimens along the drying and wetting paths. Along these paths, the volume of micropores in intact specimens was consistently larger than that of compacted specimens, resulting in a good water retention behavior, particularly along the main wetting path. Volume changes of intact and compacted specimens were primarily driven by changes in macropore volume. Only when specimens become unsaturated, the changes in micropore volume became significant. At very high suction, the effect of bonding between and within soil aggregates diminished, which was possibly due to the destruction of bonding, resulting in similar water retention properties for intact and compacted specimens.

Effect of Initial Structure on Performance of High-Entropy Oxide Anodes for Li-Ion Batteries

Two different high-entropy oxide materials were synthesized and studied as Li-ion battery anodes. The two materials have the same active metal constituents but different inactive elements which result in different initial crystalline structures: rock salt for (MgFeCoNiZn)O and spinel for (TiFeCoNiZn)3O4. Local structural studies of the metal elements in these two materials over extended electrochemical cycling reveal that the redox processes responsible for the electrode capacity are independent of the initial crystallographic structure and that the capacity is solely dependent on the initial random distribution of the metal atoms and the amount of active metals in the starting material.

Effect of Initiator Structure on Thiol‐Ene Polymerization: A DFT Study

AbstractThe performance of commercial initiators on thiol‐ene polymerization has been investigated by utilizing the M062X/6‐31++G(d,p) level of theory. The reactivity of initiators has been explained by the rate coefficients of addition (ki), which is considered side reaction and hydrogen abstraction (kHA) reactions. In this respect, radicals generated from azobisisobutyronitrile (AIBN) and 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA) have been modeled. In the case of AIBN and the propene‐methyl thiol couple as reactants, it has been illustrated that side reaction is highly possible because the calculated rate coefficients ki and kHA are close to each other 1.02E+00 and 1.50E+02 l mol–1 s–1, respectively. In styrene, methyl methacrylate, and maleimide applications, the discrepancy between these reaction rates is relatively less. The high reactivity of DMPA has been explained by possessing high kHA values of formed radicals. The hydrogen abstraction reaction is significantly faster than the addition reactions for generated radicals methyl (CH3•) and benzoyl (C6H5CO•). For methyl methacrylate, side reaction is probable even in the application of DMPA since relatively fast addition reactions (the ki for CH3• and C6H5CO• radicals are 4.71E+04 and 3.42E+04 l mol–1 s–1 respectively.). Styrene and maleimide show a similar reactivity tendency with methyl methacrylate.

Noncovalent Protection for Direct Synthesis of α-Amino-ω-hydroxyl Poly(ethylene oxide)

The synthesis of poly(ethylene oxide) (PEO) with amino end group, a key functionality for PEGylation, is a long-standing challenge. Multistep routes based on postmodification or covalent protection have been adopted to circumvent ethoxylation of the amino group by ethylene oxide (EO). Here, we report a noncovalent protection strategy for one-step synthesis of PEO amine. An amino (di)alcohol is mixed with a small amount of mild phosphazene base and excess triethylborane (Et3B) before addition of EO. The complexation of the amino group with Et3B guarantees that polymerization of EO occurs selectively from the hydroxyl group through the bicomponent metal-free catalysis. Simply by precipitation in diethyl ether, the protective Et3B as well as the catalyst can be removed to afford α-amino-ω-hydroxyl PEO with controlled molar mass, low dispersity, and complete end functionality. The effect of initiator structure and retention of Et3B on the storage (oxidative) stability of PEO amine is also revealed.

Effect of Initial Structure on the Characteristics of Austenite Formed Under Heat Treatment of Spring Steels

Effect of Initial Structure on the Characteristics of Austenite Formed Under Heat Treatment of Spring Steels

Effects of Initial Structure and Reversion Temperature on Austenite Nucleation Site in Pearlite and Ferrite–Pearlite

Austenite nucleation sites were investigated in near-eutectoid 0.8 mass pct C steel and hypoeutectoid 0.4 mass pct C steel samples with full pearlite and ferrite–pearlite initial structures, respectively. In particular, the prior austenite grain size had been coarsened to compare grain boundaries in the hierarchical pearlite structure, i.e., the low-angle pearlite colony and high-angle block boundaries with ferrite/pearlite interfaces in the austenite nucleation ability. When the full pearlite in 0.8 mass pct C steel underwent reversion at a relatively low temperature, austenite grains preferentially formed at pearlite block boundaries. Consequently, when the full pearlite with the coarse block structure underwent reversion just above the eutectoid temperature, the reversion took a long time due to the low nucleation density. However, austenite grains densely formed at the pearlite colony boundaries as well, as the reversion temperature became sufficiently high. On the other hand, when ferrite–pearlite in the 0.4 mass pct C steel underwent reversion to austenite, the ferrite/pearlite interface acted as a more preferential austenite nucleation site than the pearlite block boundary even in the case of low-temperature reversion. From these results, it can be concluded that the preferential austenite nucleation site in carbon steels is in the following order: ferrite/pearlite interface > pearlite block > colony boundaries. In addition, orientation analysis results revealed that ferrite restricts the austenite nucleation more strongly than pearlitic ferrite does, which contributes to the preferential nucleation at ferrite/pearlite interfaces. This suggests that austenite grains formed at a ferrite/pearlite interface tend to have an identical orientation even under high-temperature reversion. Therefore, it is thought that the activation of austenite nucleation within pearlite by increasing the reversion temperature may be effective for rapid austenitization and the grain refinement of austenite structure after the completion of reversion in carbon steels.

Simulation of agglomerate breakage and restructuring in shear flows: Coupled effects of shear gradient, surface energy and initial structure

Nano- and submicron particles typically exist in the form of agglomerates. The shear flow, a common local flow, plays an important role in the breakage and restructuring of agglomerates. In this work, the discrete element method (DEM) with a cohesive contact model is used to simulate the dynamic evolution of agglomerates under shear flow. The results show that the size and structure of agglomerates at a steady state are the results of competition among the shear gradient of the flow field, the surface energy and the initial structure of the agglomerates. Based on the variation of the radius of gyration (Rg) and fractal dimension (Df) of agglomerates with time, the following three stages can be distinguished: (a) a stage dominated by stretch and breakage, (b) a stage dominated by agglomeration and densification, and (c) a stage characterized by the steady size and structure of agglomerates. With increasing shear gradient, the agglomerate fragments at the steady stage become smaller, more compact and more uniform. When the shear gradient is high, increasing the surface energy can result in larger fragments with a more compact structure. However, when the shear gradient is low, increasing the surface energy does not lead to larger fragments. The effect of initial structure on the stable size and structure of fragments disappears gradually with the increase in shear gradient. The detailed simulation results can improve the understanding and control of the size and structure of agglomerates in practical devices.

Titanium Alloys 2017

n/a

The Effect of Initial Structure on Phase Transformation in Continuous Heating of a TA15 Titanium Alloy

The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed α, III-trimodal structure with 18% equiaxed α and 25% lamellar α. Differential scanning calorimetry (DSC), dilatometry and quantitative metallography were carried out on specimens with the three initial structures at heating rates from 5 to 40 °C/min. The transformation kinetics was modeled with the Johnson–Mehl–Avrami (JMA) approach under non-isothermal condition. It was found that there exists a four-stage transformation for microstructures I and III. The secondary and third stages overlap for microstructure II. The four stages of phase transformation overlap with increasing heating rate. In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α. Phase transformation is controlled by the growth of existing large β phase.

Group 4 complexes bearing bis(salphen) ligands: Synthesis, characterization, and polymerization studies

ABSTRACTSix different complexes containing bis(salphen) [salphen = N,N'‐phenylenebis(salicylideneimine)] ligands were synthesized and characterized by various spectroscopic techniques and elemental analysis. In the presence of benzyl alcohol as an initiator, all the complexes catalyze the ring‐opening polymerization of lactide and ε‐caprolactone, generating high molecular weight (Mn) polymers in a controlled fashion. The linear relationship between the % conversion and Mn proved the control over the polymerization process. The presence of OBn group as an end group was confirmed by MALDI‐TOF and 1H NMR spectral analysis of low Mn oligomers. The polymerization followed first‐order kinetics as revealed by kinetic experiments. All the complexes were good precatalysts for the polymerization of ethylene. The effect of temperature and time on the yield and activity toward the polymerization of ethylene were widely investigated. In addition, in the presence of tetrabutylammonium bromide as cocatalyst, the formation of degradable polycarbonate with moderate Mn value and narrow molecular weight distributions was observed by the copolymerization of cyclohexene oxide with CO2. The effect of initiator structure, temperature, CO2 pressure, catalyst/cocatalyst loading on the activity, and selectivity toward copolymerization were systematically examined. The thermal properties of the copolymer synthesized were explored using differential scanning calorimetric and thermogravimetric analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 809–824

Optimisation of Diffusion Bonding Parameters of Ti Alloys through the Structure and Surface Conditions

Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state was performed. The effect of initial structure and surface condition, as well as temperature and time, on the quality of joints was established. It is shown that, due to low-temperature superplasticity and high diffusion rate, samples with ultrafine grained structure demonstrate better bondability than coarse grained samples

The effect of initial structures of Mg/Cu super-laminates on hydrogen absorption/desorption properties

Abstract The effect of initial structures of Mg/Cu super-laminates on hydrogen absorption/desorption properties was investigated experimentally. Mg/Cu super-laminates were prepared by a repetitive fold and roll method using a conventional two-high roll mill. Three types of specimens were prepared by changing rolling reduction in cold rolling. Each of them had a fine, medium, coarse microstructure, respectively. Hydrogen absorption/desorption properties were measured with HP-DSC and a Sieverts’ type instrument. Microstructures were observed with SEM. Two types of MgCu 2 forms, 3D-network and layered forms, were observed after hydrogenation under the conditions of 573 K, 86.4 ks and 3.3 MPa of H 2 , respectively. This implies that Mg/Cu super-laminates can be hydrogenated by two kinds of processes. The dominant process depends on the initial structures of Mg/Cu super-laminates. Repetitive hydrogenation/dehydrogenation tests using HP-DSC indicate that, even after 20 cycles, the initial microstructures of Mg/Cu super-laminates can affect their hydrogen absorption/desorption properties.

Controlled radical polymerization of tert-butyl acrylate at ambient temperature: Effect of initiator structure and synthesis of amphiphilic block copolymers

Controlled and very rapid ambient temperature polymerization of tert-butyl acrylate (tBA) via atom transfer radical polymerization (ATRP) and single electron transfer living radical polymerization (SET-LRP) conditions is reported. Two initiators, one that would generate a secondary radical and another that would generate a primary radical, upon activation, are used. A very active catalyst CuBr/Me6TREN was found to initiate rapid polymerization whether it was the primary or the secondary initiator. The polymerization was well controlled and very rapid. The initiator that produces secondary initiating site is found to result in more rapid polymerization than the one that produces primary initiating site. To explore the possibility of rapid ambient temperature polymerization through the SET-LRP mechanism, the polymerization was also carried out in the presence of DMSO. It was found that the polymerization was much faster compared to the bulk ATRP, without loss of control. Styrene was block copolymerized from PtBA macroinitiators and vice versa. In both the cases, block copolymers with controlled molecular weights were obtained. The tBA block of the polymer was selectively hydrolyzed to get amphiphilic block copolymers. This amphiphilic block copolymer was found to be useful in preparing stable cadmium sulfide (CdS) nanoparticulate dispersion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Analysis of structure-property relationships in isolated cells during OD treatments. Effect of initial structure on the cell behaviour

Isolated apple cells were osmotically dehydrated in sucrose solutions (25%, 35% and 45% (w/w)) inside a heating/cooling stage with temperature control (30 °C), and examined by video-microscopy. The purpose of this work was to analyse the progress of cell microstructural changes by direct observation and further study of the digital images captured during the treatments. Cell features were identified and measured. Protoplast shrinkage increased as did sucrose concentration; however, the cell wall underwent more deformation at the lowest concentration assayed. High sucrose concentration led to an almost instantaneous protoplast separation since the membrane-to-wall linkers did not resist the stretching of the contracting protoplast; this response frequently resulted in membrane lysis and loss of cellular compartmentation. Cells structure was characterized and was proved to be related to the phenomenon undergone by the cell (shrinkage, complete plasmolysis, or membrane lysis). The response of the cell was found to be a function not only of the osmotic solution concentration but also of initial cell microstructural features. Results also suggested that a better preservation of membrane integrity and membrane-to-wall connections might be achieved if cells are dehydrated in increasingly concentrated OS solutions.

Efficient ring-opening polymerization of ɛ-caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

A number of new anilido-imine–Al complexes ortho-C6H4(CHNAr1)(NAr2)AlMe2 [Ar1=C6H5, Ar2=C6H5 (2a); Ar1=2,6-Me2C6H3, Ar2=2,6-Me2C6H3 (2b); Ar1=2,6-Et2C6H3, Ar2=2,6-Et2C6H3 (2c); Ar1=2,6-iPr2C6H3, Ar2=2,6-Me2C6H3 (2d); Ar1=2,6-iPr2C6H3, Ar2=2,6-Et2C6H3 (2e)] were synthesized, characterized and used as initiators for the ring-opening polymerization of ɛ-caprolactone in the presence of benzyl alcohol. The effect of initiator structure and reaction conditions, such as benzyl alcohol/Al molar ratio and reaction temperature on the reactivity, and polymer molecular weight were investigated. The polymerization of ɛ-caprolactone initiated by these complexes was found to take place in an immortal fashion.

Effects of initial structure on the shape memory properties of Ti 50Ni 25Cu 25 ribbons

The effect of annealing temperature and initial structure (amorphous and fully crystallized) on shape memory properties of Ti 50Ni 25Cu 25 melt-spun ribbons was studied by using DSC and thermomechanical analyzer (TMA). M s of the annealed ribbons increased with the annealing temperature below 550 °C. It decreased with annealing temperature above 550 °C. The fully crystallized as-spun ribbon showed the highest shape recovery strain under 45 MPa. With the increase of annealing temperature the recovery strain of the two ribbons decreased significantly.

Effect of initial structure on the mechanical properties of specimens of titanium alloy VT6 joined in the superplastic state

The mechanical properties in tensile tests of specimens of double-phase titanium alloy VT6 differing in grain size and in temperature of solid-phase joining by pressure welding in the state of superplasticity are studied.

Effect of Initial Structure on Recrystallized Austenite Grain Size of Fe-32%Ni Alloy

Recrystallization behaviors have been investigated with respect to two different kinds of the initial structures, original austenite and martensite, in an Fe-32%Ni alloy. The recrystallized austenite grain size from the martensite is much smaller than that from the original austenite, and decreases linearly with increasing the initial hardness, independent of the initial structure. The recrystallization sequences are different between the two structures: only one step due to recrystallization appears in hardness-temperature curve of the original austenite, whereas two steps corresponding to reverse transformation of α’ to r’ and recrystallization are shown in that of the martensite.

Effect of Initial Structure on the Deformability and Properties of Steel Subjected to Cold Rolling During Preliminary Thermomechanical Treatment

Results of a study of the effect of the initial structure (granular and lamellar pearlite) of medium-carbon alloy steel 45KhN2MFA-Sh used for the production of torsion shafts on its deformability and hardenability in the process of preliminary thermomechanical treatment (PTMT) involving cold longitudinal rolling in dead rollers are presented. The metal with an initial structure of lamellar pearlite is shown to be more advantageous with respect to the hardening intensity during the rolling and the combination of mechanical properties after the PTMT.

Effects of initial structure on the deformation behavior of PP hollow fiber in continuous drawing

Effects of initial structure on the deformation behavior of PP hollow fiber in continuous drawing