Low Temperature Domain Research Articles

Unveiling the Microstructural Features during Compression of a High-Modulus Mg-15Gd-8Y-6Al-0.3Mn Alloy Reinforced by a Large Volume of Al2RE Phases

Magnesium alloys with a high volume fraction of secondary phases exhibit inferior formability. Therefore, investigating their thermal deformation characteristics is critical for optimizing thermal processing techniques. In this work, isothermal compression experiments were performed on a Mg-15Gd-8Y-6Al-0.3Mn alloy with an elastic modulus of 51.3 GPa with a substantial volume of aluminum-rare earth (Al2RE) phases. The rheological behavior and microstructural evolution of the material were systematically investigated at varying temperatures (350–500 °C) and strain rates (0.001–1.000 s−1). The calculated thermal processing diagram indicates that the unstable region gradually enlarges with increased strain, and all unstable regions appear within the high-strain-rate, low-temperature domain. The ideal thermal processing range of the alloy is 350–500 °C at strain rates ranging from 0.001 to 0.016 s−1. Particle-stimulated nucleation and discontinuous dynamic recrystallization are both verified to be responsible for the recrystallized microstructure of the alloy. The recrystallized grains exhibit a relatively random crystallographic orientation. As recrystallization proceeds, the texture gradually transitions from a typical [0001] texture in the compression direction to a random texture accompanied by decreased texture intensity. This work sheds new light on the thermo-mechanical processing of high-modulus Mg alloys, which could help design suitable processing techniques for related materials.

Development of eco-friendly and high-content rubberized asphalt modified by waste cooking oil desulfurized crumb rubber and waste crumb rubber

To conserve non-renewable petroleum-based asphalt resources and address the limitations of incorporating high-content waste crumb rubber (CR) in conventional crumb rubber modified asphalt (CRMA), this study examines the feasibility of utilizing waste cooking oil desulfurized crumb rubber (ODR) in conjunction with CR to prepare high-content rubberized asphalt (HCRA). The basic, chemical, rheological, and asphalt-aggregate adhesion properties of HCRA, both with and without a small quantity of styrene-butadiene-styrene (SBS) copolymer modifier, were evaluated using infrared spectroscopy (FTIR), dynamic shear rheometer (DSR), bending beam rheometer (BBR), asphalt-aggregate pull-off test, contact angle test, and atomic force microscopy (AFM). The results showed that the modification involving ODR and CR primarily constitutes a physical process, rather than a chemical reaction, as evidenced by the lack of new functional groups. Similarly, the addition of an SBS modifier predominantly results in physical modifications accompanied by minor chemical interactions. The improved desulfurization degree of ODR diminishes the elastic stiffening effect of CR on the matrix asphalt at the high-temperature (low-frequency) domain and reduces adhesion properties between HCRA and aggregates, while enhancing the flexibility of HCRA at the low-temperature (high-frequency) domain. The inclusion of a small quantity of SBS modifier allows HCRA to demonstrate high-temperature performance and adhesion properties on par with CRMA, alongside superior low-temperature stress relaxation, phase stability, storage stability, and water damage resistance. These attributes indicate that the HCRA with a small quantity of SBS modifier has a broader service temperature range compared to CRMA. This study achieves approximately 33.3 % replacement of asphalt materials while preserving the performance of rubberized asphalt.

Hierarchical structure growth across different length scales in the two-phase coexistence region of myristic acid Langmuir monolayers: correlation of static and dynamic heterogeneities.

We investigated the hierarchical structure growth of myristic acid monolayers at the air-water interface across different length scales in the two-phase coexistence region of the first order liquid expanded (LE)-liquid condensed (LC) phase transition. A combined study of surface pressure-area (π-A) isotherm measurements with Brewster angle microscopy (BAM) observations was done at different temperatures. At the nanometer scale, the analysis of the π-A isotherm by application of a thermodynamic cluster equation allowed us to obtain the π dependence of cluster size (cluster distribution) in the LE-LC coexistence region. The cluster distributions showed a peak at the midpoint pressure of the transition. At higher temperature the larger nanocluster size was obtained at the transition midpoint. At the micrometer scale, BAM showed that LC domains have characteristic textures depending on the temperature. At low temperature domain density was lower and the average size of circular domains was larger. A large number of circular domains revealed a virtual boojum texture from the initial to the late stage of the transition. At the final stage some circular domains coalesced to form larger circular stripe domains and others coalesced to each other without the formation of stripe domains, finally resulting in a uniform texture over the entire water surface. At high temperature the domain texture was predominantly uniform, and a small number of domains only included straight line defects from the intermediate to the late stage of the transition. All domains coalesced to each other without the development of any texture including the stripe, different from the case at low temperature. The phase boundary line tension is highly likely to play a key role for understanding the hierarchical growth and coarsening (coalescence) process in the LE-LC transition between the different length scales from the nanometer to the micrometer scale consistently together.

Reactive Extrusion of Waste Plastics with Compatibilizer and Lightly Pyrolyzed Crumb Rubber for Asphalt Modification

Modifying asphalt is a potentially high-value application for reusing waste plastics because of the high-volume usage of asphalt in highway construction. However, simply blending hot plastics and asphalt encounters difficulties related to the poor solubility of polymers, which limits the formation of a swollen network with asphalt molecules. The polymer phases also tend to coalesce and separate from asphalt during high-temperature storage in static conditions. The present study developed an innovative process to stabilize waste plastics in asphalt and improve binder storage stability by using lightly pyrolyzed crumb rubber together with a chemical compatibilizer. Both polymers were extruded to produce a thermoplastic elastomer (TPE) for asphalt modification. The mechanical performance and chemical reactions of TPEs were characterized via tension test and Fourier transform infrared spectroscopy. The storage stability and rheological properties of modified binder blends were evaluated through laboratory asphalt stability test and dynamic shear rheometer test. Polymer phases and network structures were characterized through optical microscopy. It was found that the pyrolyzed and reactive extrusion process improved the rubber solubility and polymer interaction, and therefore the storage stability of modified binder blends. The co-existence of rigid plastic and soft rubbery regimes in an entangled network provided a promising pathway to improve the mechanical performance of asphalt binders in both high- and low-temperature domains.

A Model Study on the Effects of n-Mesons on Thermodynamics of Strongly Interacting Systems

Properties of strongly interacting matter are quite well-described by the Polyakov loop enhanced Nambu-Jona—Lasinio (PNJL) model as it incorporates two important symmetries. However, discrepancies in low temperature domain remain unless hadronic effects are entwined. Here we have tried to observe the effect of lowest lying hadrons i.e. ?-mesons (pions) considering their medium-dependent masses for zero chemical potential. The thermodynamic quantities now show satisfactory matches with existing lattice QCD and HRG results over the finite temperature window of interest.

Transparent, thermoplastic, aliphatic polyesters through crystallization under molecular confinement

•We report segmented polyesters with nanoscale crystalline poly(L-lactic acid) domains •Polymers possess high modulus and elongation at break and can be melt processed •Solution processing yields transparent films that are degradable and cytocompatible •Films can be bonded by plasma activation and undergo infrared-activated shape change In semi-crystalline biodegradable polymers, uncontrolled evolution of crystallinity impacts processing and bulk properties, limiting their application. Through molecular confinement of low-molecular-weight poly(L-lactic acid) (PLLA) segments by polysiloxane blocks and processing at far-from-equilibrium conditions, PLLA crystallization into lamellae of a few nm in thickness with coherence lengths below 100 nm was achieved, thus giving access to films that are optically transparent for over 5 years, possess high Young’s modulus and elongation at break, undergo controlled degradation, and support functional endothelialization. The films possess a nanophase segregated bulk morphology with a hydrophobic siloxane-dominated surface that can be pressure bonded following cold oxygen plasma activation and low-temperature glassy PLLA domains interspersed by nanoscale crystalline physical crosslinks that enable glass transition temperature-triggered shape change. The segmented thermoplastic polyesters (STEPs) can additionally be processed using melt-extrusion printing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart textiles, and packaging. In semi-crystalline biodegradable polymers, uncontrolled evolution of crystallinity impacts processing and bulk properties, limiting their application. Through molecular confinement of low-molecular-weight poly(L-lactic acid) (PLLA) segments by polysiloxane blocks and processing at far-from-equilibrium conditions, PLLA crystallization into lamellae of a few nm in thickness with coherence lengths below 100 nm was achieved, thus giving access to films that are optically transparent for over 5 years, possess high Young’s modulus and elongation at break, undergo controlled degradation, and support functional endothelialization. The films possess a nanophase segregated bulk morphology with a hydrophobic siloxane-dominated surface that can be pressure bonded following cold oxygen plasma activation and low-temperature glassy PLLA domains interspersed by nanoscale crystalline physical crosslinks that enable glass transition temperature-triggered shape change. The segmented thermoplastic polyesters (STEPs) can additionally be processed using melt-extrusion printing into 3D objects, thus opening potential application opportunities in the fabrication of implantable/degradable electronics, smart textiles, and packaging.

Effects of Zr/(Sc+Zr) microalloying on dynamic recrystallization, dislocation density and hot workability of Al−Mg alloys during hot compression deformation

AbstractThe deformation behavior and microstructure characteristics of Al−6.00Mg, Al−6.00Mg−0.10Zr and Al−6.00Mg−0.25Sc−0.10Zr (wt.%) alloys were investigated by hot compression tests and electron microscopy methods. The results show that after deforming under the maximum processing efficiency condition (673 K, 0.01 s−1), dislocation densities of Al−6.00Mg, Al−6.00Mg−0.10Zr and Al−6.00Mg−0.25Sc−0.10Zr alloys are 2.68×1016, 8.93×1016 and 6.1×1017 m−2 respectively. Their dynamic recrystallization fractions are 19.8%, 15.0% and 12.7%, respectively. Kernel average misorientation (KAM) analyses indicate that dislocation accumulation near grain boundaries is enhanced by adding Zr or Sc+Zr. Besides, the established hot processing maps, based on the dynamic material model (DMM), reveal that the addition of Zr or Sc+Zr can reduce the range of low-temperature unstable domain but expand the unstable domain at high temperatures and high strains. The experimental results further verify that under the testing deformation condition, only the Al−6.00Mg−0.25Sc−0.10Zr alloy cracks at 773 K and 1s−1.

Measuring and Regression Modeling of Gas–Particle Partitioning of Atmospheric Oxidized Mercury at a Coastal Site in Shanghai

Gas–particle partitioning between reactive gaseous mercury (RGM) and particle bound mercury (PBM) controls the fates of atmospheric oxidized mercury (namely reactive mercury, RM). We conducted a long-term observations of gaseous elemental mercury (GEM), RGM, PBM, and auxiliary parameters in Chongming Island, Shanghai, China, to understand the characteristics of speciated mercury and their gas–particle partitioning behaviors. The entire average abundances of GEM, RGM and PBM were 2.12 ± 0.94 ng/m3, 14.75 ± 9.94 pg/m3 and 21.81 ± 30.46 pg/m3, respectively. An observation data dependent empirical gas–particle partitioning relationship of partitioning coefficient and temperature log(1/KP) = −2692.20/T + 10.57 was obtained, and it varied in different season being by the temperature. To further evaluate the influences of temperature, particulate matter (PM), relative humidity on RGM and PBM partitioning process, the particulate fraction (φ = PBM/(PBM + RGM)) was used in this study. High φ values (φ > 0.8) mainly occurred at low temperature domain (<281 K), and high PM concentration enhanced this influence. In addition, high relative humidity shifts RGM from atmosphere partitioning to PBM in response to the diurnal valley φ values at 13:00–16:00 in the summer. Photochemical reactions were proposed to play important roles on partitioning processes between RGM and PBM. This study will benefit for the understanding of oxidized mercury fate and influencing factors in the complex atmospheric pollutants.

Thermal and electrical transport in partly-reduced graphene oxide films: The effect of low temperature and structure domain size

Understanding the effect of grain size on the overall electrical and thermal transport properties of PRGO films on a large scale is not only fundamental but also technologically important in order to tune their properties for wide applications. In this work, by adjusting the annealing temperature, we control the density of the oxygen containing functional groups and thus the structural domain size of PRGO film. The annealing effect on the temperature dependency of thermal and electrical transport is studied. In addition, the linear relationship between thermal diffusivity and electrical conductivity is confirmed from 320 K to 10 K. The temperature dependent thermal diffusivity of the amorphous region in PRGO is reported. In the last, based on the residual thermal reffusivity at 0 K limit, the structure defects induced phonon mean free path against the annealing temperature is obtained, and compared with the cluster size calculated from XRD, TEM and Raman. A linear relationship among the structure domain size, thermal diffusivity, and electrical conductivity is further revealed, which demonstrates the strong effect of structure domain size on the thermal and electrical transport of PRGO.

Multifunctionality of Li2 SrNb2 O7 : Memristivity, Tunable Rectification, Ferroelasticity, and Ferroelectricity.

Layered Li2 SrNb2 O7 , an inorganic oxide in its bulk single-crystalline form, is experimentally demonstrated to exhibit multiple structural facets such as ferroelasticity, ferroelectricity, and antiferroelectricity. The transition from a room temperature (RT) centrosymmetric structure to a low-temperature out-of-plane ferroelectric and in-plane antiferroelectric structure and the low-temperature (LT) ferroelectric domain configuration are unveiled in TEM, piezoresponse force microscopy, and polarization loop studies. Li2 SrNb2 O7 also exhibits highly tunable ferroelasticity and excellent Li+ in-plane conduction, which leads to a giant in-plane memristor behavior and an in-plane electronic conductivity increase by three orders of magnitude by electric poling at room RT). The accumulation of Li+ vacancies at the crystal-electrode interface is visualized using insitu optical microscopy. The Li-ionic biased state shows a clear in-plane rectification effect combined with a significant relaxation upon time at RT. Relaxation can be fully suppressed at LTs such as 200K, and utilizing an electric field cooling, a stable rectification can be achieved at 200K. The results shed light on the selective control of multifunctionalities such as ferroelasticity, ferroelectricity, and ionic-migration-mediated effects (a memristor effect and rectification) in a single-phase bulk material utilizing, for example, different directions, temperatures, frequencies, and magnitudes of electric field.

Pronounced interplay between intrinsic phase-coexistence and octahedral tilt magnitude in hole-doped lanthanum cuprates

Definitive understanding of superconductivity and its interplay with structural symmetry in the hole-doped lanthanum cuprates remains elusive. The suppression of superconductivity around 1/8th doping maintains particular focus, often attributed to charge-density waves (CDWs) ordering in the low-temperature tetragonal (LTT) phase. Central to many investigations into this interplay is the thesis that La1.875Ba0.125CuO4 and particularly La1.675Eu0.2Sr0.125CuO4 present model systems of purely LTT structure at low temperature. However, combining single-crystal and high-resolution powder X-ray diffraction, we find these to exhibit significant, intrinsic coexistence of LTT and low-temperature orthorhombic domains, typically associated with superconductivity, even at 10 K. Our two-phase models reveal substantially greater tilting of CuO6 octahedra in the LTT phase, markedly buckling the CuO2 planes. This would couple significantly to band narrowing, potentially indicating a picture of electronically driven phase segregation, reminiscent of optimally doped manganites. These results call for reassessment of many experiments seeking to elucidate structural and electronic interplay at 1/8 doping.

Quantum Brownian motion of a charged oscillator in a magnetic field coupled to a heat bath through momentum variables

We study the Quantum Brownian motion of a charged particle moving in a harmonic potential in the presence of an uniform external magnetic field and linearly coupled to an Ohmic bath through momentum variables. We analyse the growth of the mean square displacement of the particle in the classical high temperature domain and in the quantum low temperature domain dominated by zero point fluctuations. We also analyse the Position Response Function and the long time tails of various correlation functions. We notice some distinctive features, different from the usual case of a charged quantum Brownian particle in a magnetic field and linearly coupled to an Ohmic bath via position variables.

Influence of alternative rice husk ash filler on bitumen emulsion-based recycled asphalt

The influence of rice husk ash (RHA) as an alternative active filler on the mechanical properties of bitumen emulsion-based recycled asphalt specimens in high- and low-temperature domains was investigated. The experimental methodology was comprised of static indirect tensile and wheel-tracking testing, as well as scanning electron microscopy using secondary electrons and energy dispersive X-ray spectroscopy. The results showed that the increase in the mass fraction of RHA gradually improved the water sensitivity and the high-temperature performance of specimens, but also negatively affected their low-temperature performance. The mass fraction of RHA above 1.5%, resulted in a tensile strength ratio after freeze–thaw and immersion of more than 80%, and in the dynamic stability in rutting test above 4500 mm−1, but also the low-temperature indirect tensile strength below 2.0 MPa. Considering the relevant regulations, the mass fraction of RHA should be in the range of 1–1.5%.

Simulation of Electrical Resistance of ZnO nanostructures using BG and SPC Models

We theoretically interpreted the anomalous temperature-dependence of electrical resistivity (T) of zinc oxide (ZnO) nanostructures. Resistivity in the metallic phase is investigated using the Bloch- Gruneisen [BG] model of resistivity, whereas the resistivity (T) in the semiconducting phase of ZnO nanostructures is investigated using the small polaron conduction (SPC) model. In the low temperature domain, T indicates the presence of the semiconducting phase; it reaches an absolute minimum at 180 K and grows linearly with temperature in the high temperature region. The Bloch-Gruneisen [BG] model of resistivity was used to determine the contributions to resistivity made by intrinsic acoustic phonons (ac) and optical phonons (op) characterized by high frequency. The theoretically calculated resistivity by taking into account both phonons i.e. ac and op, as well as the temperature independent resistivity is summed along with the electron-electron interaction e-e to get the overall resistivity of the material. The small polaron conduction (SPC) approach is used to study resistivity in the semiconducting phase at low temperatures below 180 degrees Celsius.

Thermal and Electrical Transport in Partly-Reduced Graphene Oxide Films: The Effect of Low Temperature and Structure Domain Size

Thermal and Electrical Transport in Partly-Reduced Graphene Oxide Films: The Effect of Low Temperature and Structure Domain Size

Hot deformation behavior and processing map of AZ61/SiC composites

The hot deformation behavior of as-cast AZ61/SiC composites during uniaxial compression test at temperatures ranging from 280 to 440 ℃ and a strain rate of 0.001–1 s−1 was investigated. There was an increase in the flow stress of the composites with a decrease int the temperature and increase in the strain rate. Processing maps were developed based on the dynamic material model (DMM) at a maximum strain of 1.2. The effects of the incorporation of silicon carbide (SiC) particles into the base alloy are discussed. The findings show that the incorporation of SiC particles into the base alloy effectively enhanced its workability in the low temperature domain. The SiC particles promoted the generation and reduced the mobility of dislocations, effectively meeting the energy requirements for dynamic recrystallization (DRX) needed to improve low temperature workability. The optimal processing workability conditions for a AZ61/SiC composite with a higher dissipation efficiency of (PDE) of 39.5% were determined to be 440⁰C/0.001 s−1. The instability domain did not exist in the composite because the material could be deformed without micro cracks or flow visualization. The activation energy was calculated to be 131.5 kJ/mol using a constructive model of the composite.

Kinetics of the two-dimensional long-range Ising model at low temperatures.

We study the low-temperature domain growth kinetics of the two-dimensional Ising model with long-range coupling J(r)∼r^{-(d+σ)}, where d=2 is the dimensionality. According to the Bray-Rutenberg predictions, the exponent σ controls the algebraic growth in time of the characteristic domain size L(t),L(t)∼t^{1/z}, with growth exponent z=1+σ for σ<1 and z=2 for σ>1. These results hold for quenches to a nonzero temperature T>0 below the critical temperature T_{c}. We show that, in the case of quenches to T=0, due to the long-range interactions, the interfaces experience a drift which makes the dynamics of the system peculiar. More precisely, we find that in this case the growth exponent takes the value z=4/3, independently of σ, showing that it is a universal quantity. We support our claim by means of extended Monte Carlo simulations and analytical arguments for single domains.

An enhanced midstream design method for cryogenic turbomachinery

An enhanced midstream design method for cryogenic turbomachines is presented in this article by reformulating that given by Hasselgruber and Balje. The enhanced formulation incorporates non-idealities such as turbomachinery inefficiency and flow angle deviation. Moreover, certain other issues faced by high speed cryogenic turbomachinery operating in low temperature domains, such as those arising due to gas property variations and impeller length shortening from rotordynamic considerations, have also been addressed. In the enhanced design method proposed in this article, to start with, graphical schedules of various flow and profile parameters are used to rectify the defects arising in the turbomachine profiles, followed by design accomplishment through blade loading specifications. The average blade loading is arrived at by incorporating effects of splitter blades and spanwise blade geometry. The effects of blockage due to blade thickness and splitter blades are also incorporated in the formulation. The proposed design method proceeds through a parametric study of the graphical schedules on the impeller profile followed by subsequent enhancement of the impeller geometry through a framed algorithmic procedure.

Primary study of germanium isotope composition in sphalerite from the Fule Pb–Zn deposit, Yunnan province

The Sichuan–Yunnan–Guizhou metallogenic province in southwest China is one of the most important low-temperature metallogenic domains in the country, and more than 400 Pb–Zn deposits and/or mineralization points are located in this area. The Fule deposit is better known that the other Pb–Zn deposits in the region because it is extremely highly enriched with dispersed elements, including Ge, Ga, and Cd. Based on information obtained from our previous studies, the contents of Ge and its isotopic compositions in sphalerite are investigated herein. Results show that the Ge content ranges from 60 ppm to 141.5 ppm, and δ74/70Ge values vary from −6.57‰ to 0.97‰. In this respect, −6.57‰ is the most negative Ge isotope composition value reported in any sphalerite or seafloor sulfides to date. The Cd and Ge contents in sphalerite have a good negative relationship, and it is suggested that the mechanisms of Cd and Zn substitution are responsible for the low incorporation of Ge and relate to the high Cd content (up to 3%) of the sphalerite. In addition, there is a good positive correlation between the Ge contents and δ34S values, which was likely triggered by variations of fluid temperature. In the same hand specimen, light Ge isotope is more likely to be enriched in dark sphalerite rather than light sphalerite, similarly to Cd isotope distribution in dark and light-colored sphalerite. In addition, Cd and Ge isotope compositions, measured in an ore profile from SBFL22 to SBFL26, show a good positive relationship, suggesting that the fractionation mechanisms between Cd and Ge isotopes may be similar and they were controlled by kinetic fractionation during sphalerite precipitation. Based upon previous limited studies, we conclude that Ge in the Fule deposit is derived from mixing sources and sediment is likely the dominant one.

Influence of h-BN as additive on microstructure and oxidation mechanism of C/C-SiC composite

Due to the favorable self-healing performance, hexagonal boron nitride (h-BN) as additive in the matrix can significantly influence the oxidation behavior and the kinetic characteristics of C/C-SiC composites. In this work, C/C-SiC composites modified by h-BN (C/C-BN-SiC) were prepared by low-temperature compression molding (LTCM), pyrolysis and liquid silicon infiltration (LSI). Microstructure, oxidation behavior and kinetic characteristics of the C/C-BN-SiC composites were investigated compared with the C/C-SiC composite. Because h-BN is non-wetted by liquid silicon, the h-BN flakes in the matrix can obstruct and prolong the flow path of silicon, and protect the carbon fibers from corrosion to a certain extent. The oxidation kinetics of composites occur in low and high temperature domains, with different oxidation-controlling mechanisms, and the addition of h-BN can hinder the inward diffusion and lead to the decline of carbon recession and apparent activation energy.