ABSTRACT
Synchrotron-radiation-based techniques are a powerful tool for the investigation of materials. In particular, the availability of highly brilliant sources has opened the possibility to develop techniques sensitive to dynamics at the atomic scale such as X-ray photon correlation spectroscopy (XPCS). XPCS is particularly relevant in the study of glasses, which have been often investigated at the macroscopic scale by, for example, differential scanning calorimetry. Here, we show how to adapt a Flash calorimeter to combine XPCS and calorimetric scans. This setup paves the way to novel experiments requiring dynamical and thermodynamic information, ranging from the study of the crystallization kinetics to the study of the glass transition in systems that can be vitrified thanks to the high cooling rates reachable with an ultrafast calorimeter.
ABSTRACT
Studying complex relaxation behaviors is of critical importance for understanding the nature of glasses. Here we report a Kovacs-like memory effect in glasses, manifested by non-monotonic stress relaxation during two-step high-to-low strains stimulations. During the stress relaxation process, if the strain jumps from a higher state to a lower state, the stress does not continue to decrease, but increases first and then decreases. The memory effect becomes stronger when the atomic motions become highly collective with a large activation energy, e.g. the strain in the first stage is larger, the temperature is higher, and the stimulation is longer. The physical origin of the stress memory effect is studied based on the relaxation kinetics and the in-situ synchrotron X-ray experiments. The stress memory effect is probably a universal phenomenon in different types of glasses.
ABSTRACT
The removal of dyes from textile effluents utilizing advanced wastewater treatment methods with high efficiency and low cost has received substantial attention due to the rise in pollutants in water. The purpose of this work is to give a comprehensive analysis of the different treatments for removing chemical dyes from textile effluents. The capability and potential of conventional treatments for the degradation of dyeing compounds in aqueous media, as well as the influence of multiple parameters, such as the pH solution, initial dye concentration, and adsorbent dose, are presented in this study. This study is an overview of the scientific research literature on this topic, including nanoreductive and nanophotocatalyst processes, as well as nanoadsorbents and nanomembranes. For the purpose of treating sewage, the special properties of nanoparticles are currently being carefully researched. The ability of nanomaterials to remove organic matter, fungus, and viruses from wastewater is another benefit. Nanomaterials are employed in advanced oxidation techniques to clean wastewater. Additionally, because of their small dimensions, nanoparticles have a wide effective area of contact. Due to this, nanoparticles' adsorption and reactivity are powerful. The improvement of nanomaterial technology will be beneficial for the treatment of wastewater. This report also offers a thorough review of the distinctive properties of nanomaterials used in wastewater treatment, as well as their appropriate application and future possibilities. Since only a few types of nanomaterials have been produced, it is also important to focus on their technological feasibility in addition to their economic feasibility. According to this study, nanoparticles (NPs) have a significant adsorption area, efficient chemical reactions, and electrical conductivity that help treat wastewater effectively.
ABSTRACT
The ability to produce high-entropy alloys with an amorphous structure, so-called high-entropy metallic glasses (HEMGs), offers the possibility to produce new compositions with good mechanical properties and resistance to corrosion. In this study, corrosion behavior was studied in two HEMGs, FeCoNiCrB and FeCoNiCr(BSi). In both cases, the total amount of metalloid atoms was kept constant at 20 at.%. The electrochemical behavior of these alloys was studied by means of linear polarization resistance (LPR) measurements and electrochemical impedance spectroscopy in a 3 wt.% NaCl solution. The effect of corrosion was characterized by using X-ray photoelectron spectroscopy (XPS) and the surface morphology was checked using a scanning electron microscope (SEM). The results show that samples with B but without Si exhibit better corrosion resistance due to its chemical homogeneity and lack of structural heterogeneity.
ABSTRACT
Elastomers have been used in a variety of biomedical fields, including tissue engineering, soft robotics, prostheses, and cosmetics. Elastomers used for skin grafting scaffolds tend to be biodegradable, but other applications require perdurable elastomers. Advances in perdurable elastomers would allow for the development of a range of substrates useful in the creation of joint prostheses, chronic neural electrodes, implantables, and wearables. Still, for these, tailored mechanical properties and biocompatibility are required. In this work, several perdurable alkene-styrene elastomers and novel polymer blends are investigated for their stress-strain curves; with quantification of Young's moduli, fatigue behavior and standard biocompatibility. In particular, this study attempts to study polymers with mechanical properties similar to the complex characteristics of skin, through comparison with porcine skin samples. Poly (vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), a flexible polymer previously used as a wearable sensor and second skin component, was here used for comparison studies. Interestingly, this study points out that elastomer mechanical properties can be modulated to better replicate the elastic modulus of skin, in particular for KratonTM D1152, a Styrene-Butadiene-Styrene block copolymer. Namely, this is the case when such an elastomer is prepared as an electrospun matrix or as a flat dense film under low temperatures. Moreover, a specific method was optimized to obtain electrospun fibers of this alkene-styrene copolymer.
Subject(s)
Biocompatible Materials , Polystyrenes , Animals , Elastomers , Polymers , SwineABSTRACT
The stress relaxation dynamics of metallic glass Pd40Ni40P20was studied in both supercooled liquid and glassy states. Time-temperature superposition was found in the metastable liquid, implying an invariant shape of the distribution of times involved in the relaxation. Once in the glass state, the distribution of relaxation times broadens as temperature and fictive temperature decrease, eventually leading to a decoupling of the relaxation in two processes. While the slow one keeps a viscous behavior, the fast one shows an anelastic nature and a time scale similar to that of the collective atomic motion measured by x-ray photon correlation spectroscopy (XPCS). These results suggest that the atomic dynamics of metallic glasses, as determined by XPCS at low temperatures in the glass state, can be related to the rearrangements of particles responsible of the macroscopically reversible anelastic behavior.
ABSTRACT
Manganese-Aluminum powders were recently reported to show high efficiency and fast reaction rates as decolorization materials for azo-dye aqueous solutions. This work presents a detailed study of different aspects of this material. Firstly, the influence of the crystalline phase and the microstructure was studied by comparing the efficiency of powders obtained by different production protocols. Secondly, the decolorization efficiency was investigated on various types of dyes, including real textile wastewater samples. The analysis of the treated water and the particles showed that the main reaction mechanism was the breaking of the azo-dye molecules, although important adsorption on the metallic surface was observed for some colorants. Finally, the reusability of the particles and the reduction of toxicity achieved during the treatments were assessed. The simple production and application methods, the high efficiency and the use of environmentally friendly metallic elements are the main advantages of Manganese-Aluminum powders compared to other high-efficient decolorizing metallic materials.
Subject(s)
Water Pollutants, Chemical , Azo Compounds , Coloring Agents , Powders , WastewaterABSTRACT
As ultrastable metallic glasses (UMGs) are promising candidates to solve the stability issues of conventional metallic glasses, their study is of exceptional interest. By means of x-ray photon correlation spectroscopy, we have investigated the stability of UMGs at the atomic level. We find a clear signature of ultrastability at the atomic level that results in slower relaxation dynamics of UMGs with respect to conventional (rapidly quenched) metallic glasses, and in a peculiar acceleration of the dynamics by near T_{g} annealing. This surprising phenomenon, called here anti-aging, can be understood in the framework of the potential energy landscape. For all samples, the structural relaxation process can be described with a highly compressed shape of the density fluctuations, unaffected by thermal treatments and regardless of the ultrastability of the glass.
ABSTRACT
We study the mechanical relaxation spectrum of Pd42.5Ni7.5Cu30P20 metallic glass. The effect of aging on the relaxation behavior is analyzed by measuring the internal friction during consecutive heating runs. The mechanical relaxation of the well-annealed glass state is modeled by fitting susceptibility functions to the primary and secondary relaxations of the system. The model is able to reproduce the mechanical relaxation spectrum below the glass transition temperature (sub-Tg region) in the frequency-temperature ranges relevant for the high temperature physical properties and forming ability of metallic glasses. The model reveals a relaxation spectrum composed by the overlapping of primary and secondary processes covering a wide domain of times but with a relatively narrow range of activation energies.
ABSTRACT
We use coherent x rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. The rich diversity of this behavior reflects a complex energy landscape, giving rise to a unique type of glassy-state dynamics.
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The distribution of spatial domain structures originated during one- and three-dimensional Poisson-Voronoi transformations are computed analytically extending the recently obtained results for the two-dimensional case. The presented method gives a full description of the developed microstructure and is valid for tessellations of any dimensionality. The temporal and spatial dependences of the domain structure are completely discriminated and separated, showing the existence of geometric configurations independent of time. A single computation of the probability distribution of these geometric configurations allows us to calculate the total free-boundary and size probability distributions at any desired time. The obtained results show full agreement with stochastic simulations and reproduce completely the previously existing partial results. A discussion about the potential applications of the method to the calculation of other geometrical properties and the characteristics of the final static structure leading to a Gamma distribution of sizes is also presented.
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We present an analytical result for the evolution of the domain-size distribution during the growth of simultaneously nucleated domains. The final stage of this transformation is the well-known Poisson-Voronoi tessellation. The method can be easily extended to the calculation of the probability distribution of any other geometric characteristic. As far as we know, it is the first time that an exact result is given for this classic system.
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Random subdivisions in a D-dimensional Euclidean space are commonly observed in many scientific fields, such as metallurgy, geology, biology, and even, in the case of large D, in subjects related to information codification. This paper presents an analytical approximation of the size probability distribution in space subdivisions generated by random point processes, which include the well-known cases of the Poisson-Voronoi and the Johnson-Mehl cellular structures. Based on the calculations of Ann. Math. Stat. 33, 958 (1962)] and an assumption for the distribution shape, the cell size distributions are obtained in a general way for a very wide range of random space subdivisions.
