Activation Energy Spectrum Research Articles

Photocunductivity spectra of thin solid solution films CdSexS1-x

This paper presents the results of a study on the energy spectra of activation of intrinsic defects in photosensitive films of solid solution CdSexS1-x depending on the conditions of their preparation and thermal treatment in different environments. This study investigates the photoconductivity spectra of thin films composed of the solid solution CdSexS1-x, focusing on the impact of preparation and thermal treatment conditions on the activation energy spectra of intrinsic defects. The films were synthesized using thermal evaporation in a vacuum and subjected to various thermal processes. The results indicate that the photoconductive properties are highly influenced by structural defects and point defects within the crystalline lattice, which create deep levels in the forbidden zone of the semiconductor. These findings advance the understanding of the physical processes in polycrystalline films and highlight the potential of CdSexS1-x films for developing light-emitting diodes and lasers in the infrared and visible spectra.

Investigation on the rheological behavior of PA6 film during biaxial stretching

In this work, the rheological behavior of polyamide 6 (PA6) film during biaxial stretching was investigated. Firstly, the cast film was subjected to different ratios of biaxial stretching, and the stress calculation expression of biaxial stretching was derived. Then the generalized Maxwell model was employed to fit the stress-time curves in the heat setting stage. It was found that the elastic-plastic deformation during biaxial stretching influenced the stress rebound or relaxation in the heat setting. Finally, the relaxation spectrum and activation energy spectrum were calculated according to the fitting curves. It was found that the stress relaxation process of PA6 film was divided into multiple stages, but the stress rebound process was relatively simple. According to the activation energy spectrum, we speculated that stress relaxation was a process of releasing energy, and stress rebound was a process of absorbing energy. With the increased stretching ratio, the peaks on the activation energy spectrum became sharper and the intensity increased. Indicating that more energy was released or absorbed under the larger stretching ratio. The obtained results would provide theoretical guidance for further understanding the biaxial stretching deformation mechanism of polymer films.

Relaxation behavior of biaxially stretched PLA film during the heat setting stage

In this paper, the relaxation behavior of polylactic acid (PLA) film in the heat-setting stage of biaxial stretching was studied. Firstly, the polylactic acid casting films were stretched synchronously in different ratios. We found that the Machine direction (MD) and Transverse direction (TD) stress relaxation curves exhibited a separation trend with the increase in the stretching ratio, and the relaxation amplitude increased gradually. Then, the stress relaxation curves were fitted by the expansion exponential equation (KWW equation). The results showed that the coefficient used to characterize the homogeneity of stress relaxation increased with the increase in the stretching ratio, and the homogeneity in Machine direction was better than that in Transverse direction. Finally, we analyzed the evolution of rheological units and the activation energy spectrum during stress relaxation. We found that the volume of rheological units gradually decreased with the increase in the stretching ratio. The activation energy spectrum exhibited a Gaussian distribution, and the symmetry axis of distribution curves shifted to the high energy. The above results would be of great significance in further understanding the deformation mechanism of polylactic acid film during biaxial stretching and providing theoretical guidance for the preparation of high-performance BOPLA films.

Dynamical relaxation and stress relaxation of Zr-based metallic glass

The relationship among dynamic relaxation, deformation and microstructural heterogeneity of amorphous alloy is one of the important research contents in the field of amorphous physics. In this paper, we utilize Zr<sub>48</sub>(Cu<sub>5/6</sub>Ag<sub>1/6</sub>)<sub>44</sub>Al<sub>8</sub> bulk amorphous alloy with excellent glass forming capability and good thermal stability as a research carrier, and investigate the effects of temperature and structural relaxation on dynamic relaxation and deformation behavior through dynamic mechanical analysis and stress relaxation experiments. The results show that the dynamic relaxation spectrum of the model alloy is sensitive to temperature, showing four stages as the temperature increases, namely, iso configuration, aging, glass transition and crystallization. Based on the isothermal measurement of dynamic mechanical parameters under the glass transition temperature, the structural relaxation causes the amorphous alloy to migrate from the non-equilibrium high energy state to the low energy state, and the evolution of internal friction with aging time can be described by Kohlrausch-Williams-Watts (KWW) stretched exponential function. In addition, based on the KWW equation and activation energy spectrum, the activation of heterogeneous structure in the stress relaxation process of model alloy is analyzed, which involves the transformation from elastic deformation to nonelastic deformation. Owing to the microstructural heterogeneity and energy fluctuations in amorphous alloys, the activation of deformation units is not a single characteristic time, but follows a certain distribution. By considering that the characteristic time distribution of activation of deformation units is symmetric Gauss distribution or asymmetric Gumbel distribution on a logarithmic time scale, the heterogeneous activation process in stress relaxation response can be reconstructed.

Kinetic Salt Effect on Base-Catalyzed Isomerization of d-Glucose into d-Fructose.

Isomerization of d-glucose (Glc) into d-fructose (Fru) is of great importance for food sector as well as for valorization of lignocellulosic biomass. Soluble and solid bases exhibit high catalytic activity for the isomerization. Here, we report a salt effect on the base-catalyzed aqueous-phase Glc-Fru isomerization. Addition of soluble salts (Na2 SO4 , NaNO3 , K2 SO4 , and NaCl) results in an increased apparent reaction rate (factors of 1.5 to 6). The salt effect was observed both in the presence of soluble base NaOH at constant pH value and solid bases MgO, Li3 PO4 , and Mg-Al hydrotalcite. Apparent activation energy and UV absorption spectra were not significantly influenced by addition of salts. Potentiometric titration showed that the acidity constants of the saccharides increase in the presence of electrolytes. Since the rate of the isomerization depends on the thermodynamic acidity constant of Glc, the isomerization is accelerated by the presence of electrolytes.

Vanadium trapped by oblique nano-sheets to preserve the anisotropy in Co–V thin films at high temperature

In this study, oriented nano-sheets generated during the growth of cobalt-rich Co–V and Co–Zn thin films induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted 52–54 deg. with respect to the substrate plane, ≈ 3.0–4.0 nm thick, ≈ 30–100 nm wide, and ≈ 200–300 nm long, with an inter-sheet distance of ≈ 0.9–1.2 nm. In spite of the different microstructures of the two kinds of samples where the Co–V films were amorphous, whereas the Co–Zn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens. This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology caused by thermal treatments, and hence in their anisotropic properties, were studied. While the Co–V samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished for the annealed Co–Zn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed to establish the nature and the activation energy spectra of the atomic relaxation processes during heating. These processes displayed a single peak at 1.63 eV for the Co–V and two peaks at 1.67 and 2.0 eV for the Co–Zn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The Co–V films retained their nano-sheet morphology almost up to 500 ºC; the Co–Zn films lost their nano-sheets at 290 ºC. The thermal stability exhibited by the Co–V films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magneto-electric devices.

Comprehensive insights into the thermal and mechanical effects of metallic glasses via creep

• Evolution of deformation and relaxation behavior of a Zr-based MG was explored by extensive creep tests under physical aging and cyclic loading. • Relaxation-time spectra were further utilized to quantitatively describe the time scales involve in the creep of MGs. • An annihilation of local deformation units during physical aging and cyclic loading was detected through the diminution of amplitude in both activation energy and relaxation-time spectra. Evolution of deformation and relaxation behaviors of a prototypical Cu 46 Zr 46 Al 8 metallic glass was explored by extensive creep tests under both physical aging and cyclic loading. Deep insights into the microstructure-induced dynamic heterogeneity which accommodates creep deformation were successively revealed via experimental measurements and spectral analyses. An annihilation of local defects within metallic glass with increasing annealing time and cyclic numbers was observed through the reduction of amplitude in both activation energy spectra and relaxation-time spectra, which were also accompanied by an ascending value of β K W W . It is further found that the corresponding deformation units within the metallic glass do not disappear permanently, but are recoverable over the course of cyclic loading. The apparent suppressed relaxation process can be gradually alleviated with increasing resuming time between two consecutive cycles, behaving differently from physical aging, which indicates a notable discrepancy between thermal treatment and mechanical treatment.

Tailoring Magnetic and Transport Anisotropies in Co100−x–Cux Thin Films through Obliquely Grown Nano-Sheets

The magnetic and transport properties of pulsed laser-deposited Co100−x–Cux thin films were tailored through their nano-morphology and composition by controlling for the deposition geometry, namely normal or oblique deposition, and their Cu content. All films were composed of an amorphous Co matrix and a textured growth of Cu nanocrystals, whose presence and size d increased as x increased. For x = 50, all films were superparamagnetic, regardless of deposition geometry. The normally deposited films showed no in-plane magnetic anisotropy. On the contrary, controllable in-plane uniaxial magnetic anisotropy in both direction and magnitude was generated in the obliquely deposited films. The magnetic anisotropy field Hk remained constant for x = 0, 5 and 10, Hk ≈ 35 kAm−1, and decreased to 28 and 26 kAm−1 for x = 20 and 30, respectively. This anisotropy had a magnetostatic origin due to a tilted nano-sheet morphology. In the normally deposited films, the coercive field Hc increased when x increased, from 200 (x = 0) to 1100 Am−1 (x = 30). In contrast, in obliquely deposited films, Hc decreased from 1500 (x = 0) to 100 Am−1 (x = 30) as x increased. Activation energy spectra corresponding to structural relaxation phenomena in obliquely deposited films were obtained from transport property measurements. They revealed two peaks, which also depended on their nano-morphology and composition.

Relaxation behavior of high-entropy bulk metallic glass: Influences of physical aging and cyclic loading

<p indent="0mm">In this study, the correlation among the relaxation behavior, deformation mechanism, and structural heterogeneity of metallic glasses is examined using La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass as the model glass. Dynamic mechanical analysis (DMA) was used to investigate the influences of physical aging and cyclic loading on the dynamic relaxation and deformation mechanism of the model glass. The correlation between the deformation units and the structural heterogeneity was analyzed on the basis of the activation energy spectrum (AES). The results demonstrated that La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass displays an apparent β relaxation. A more stable state can be achieved during physical aging below the glass transition temperature and in cyclic loading because the atomic rearrangements are suppressed during these processes. This structural relaxation during the physical aging process enables the transition from liquid-like regions to an elastic matrix. Further, more time is required to activate the deformation units that are frozen during the transition. The applied stress results in a decrease in the number of liquid-like regions, which suppresses the activation of the deformation units during the cyclic loading process. As a result, the intensity of the β relaxation in the metallic glass decreases. Therefore, the origin of the β relaxation in La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass is ascribed to the liquid-like regions.

Stress relaxation in high-entropy Pd20Pt20Cu20Ni20P20 metallic glass: Experiments, modeling and theory

The viscoelastic properties of Pd20Pt20Cu20Ni20P20 high-entropy metallic glass were probed by dynamic mechanical spectroscopy and stress relaxation. The experimental evolution of stress can be characterized by the empirical Kohlrausch-Williams-Watts function during the tensile stress relaxation measurement. We develop a linear relaxation model able to describe the whole process of stress relaxation in a wide range of temperatures. The linear relaxation model takes into account the microstructural heterogeneity of the glass, and thus its dynamical heterogeneity, so that the thermal effect and stress-driven process are physically decoupled. The activation energy spectra at various temperatures reveal the changes of the deformation units during stress relaxation, which is the result of the interplay between stress and temperature. This study decomposes the widespread hierarchical dynamics due to structural heterogeneity which accommodates the viscoelastic deformation of the high-entropy metallic glasses.

Internal friction and dynamic shear modulus of a metallic glass in a seven-orders-of-magnitude frequency range

Abstract We report measurements of the internal friction and shear modulus of glassy Cu49Hf42Al9 at sub-hertz frequencies (0.03–1 Hz) and at a high frequency of 560 kHz at temperatures from the room one up to well above the glass transition temperature Tg. It is found that an increase of the frequency in this range results in a drastic decrease of the internal friction and shear modulus relaxation both below and above Tg. The relaxation kinetics is analyzed within the framework of a classical phenomenological approach in terms of the real and imaginary parts of the dynamic shear compliance both for the initial and relaxed states of the glass under investigation. A law describing the frequency dependence of the imaginary compliance component in the whole frequency range investigated is determined. A new method for the determination of the Gibbs activation energy of relaxation is derived. The underlying activation energy spectrum determined on this basis is found to smoothly increase with the activation energies accessible in the experiment. A change of the activation energy with temperature below and above Tg is determined. The phenomenological analysis is combined with a physical interpretation of the relaxation, which is assumed taking place due to the activation of interstitial-type defects (essentially elastic dipoles) frozen-in from the melt upon glass production. It is argued that there exist at least three mechanisms of energy losses, which are related to changes of the dipoles’ orientation in the same energy states and transitions between their low- and high-energy states.

Energy Activation Spectrum of Low-Temperature Acoustic Relaxation in High-Purity Iron Single Crystal. Solution of the Inverse Problem of Mechanical Spectroscopy by the Tikhonov Regularization Method

When studying the temperature dependences of the acoustic absorption and the modulus of elasticity, absorption peaks are often observed, which correspond to the characteristic step on the temperature dependence of the modulus of elasticity. Such features are called relaxation resonances. It is believed that the occurrence of such relaxation resonances is due to the presence in the structure of the material of elementary microscopic relaxors that interact with the studied vibrational mode of mechanical vibrations of the sample. In a sufficiently perfect material, such a process is characterized by a relaxation time τ, and in a real defective material by a relaxation time spectrum P(τ). Most often such relaxation processes have a thermally activated character and the relaxation time τ(T) is determined by the Arrhenius ratio τ(T)=τ0exp(U0/kT), and the characteristics of the process will be U0 - activation energy, τ0 - period of attempts, Δ0 - characteristic elementary contribution of a single relaxator to the dynamic response of the material and their spectra. In the low temperatures region the statistical distribution of parameters τ0 and Δ0 can be neglected with exponential accuracy, and the relaxation contribution to the temperature dependences of absorption and the dynamic elasticity modulus of the material will be determined only by the activation energy spectrum P(U) of microscopic relaxors. The main task of mechanical spectroscopy in the analysis of such relaxation resonances is to determine U0, τ0, Δ0 and P(U). It is shown, that the problem of recovering of spectral function P(U) of acoustic relaxation of a real crystal can be reduced to the solving of the Fredholm integral equation of the first kind with an approximately known right part and concerns to a class of ill-posed problems. The method based on Tikhonov regularizing algorithm for recovering P(U) from experimental temperature dependences of absorption or elasticity module is offered. It is established, that acoustic relaxation in high-purity iron single crystal in the temperature range 5-100 K is characterized by two-modes spectral function P(U) with maxima at 0.037 eV and 0.015 eV, which correspond to the a-peak and its a' satellite.

Evolution of defect concentration in Zr&lt;sub&gt;50–&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cu&lt;sub&gt;34&lt;/sub&gt;Ag&lt;sub&gt;8&lt;/sub&gt;Al&lt;sub&gt;8&lt;/sub&gt;Pd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; (&lt;i&gt;x&lt;/i&gt; = 0, 2) amorphous alloys derived using shear modulus and calorimetric data

Amorphous alloys exhibit unique physical and mechanical properties, which are closely connected with their microstructural heterogeneity. The correlation between structural heterogeneity and mechanical properties is one of the important issues of amorphous alloys. Micro-alloying is an effective way to tune the mechanical and physical properties of amorphous alloys. In the present study, Zr&lt;sub&gt;50–&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cu&lt;sub&gt;34&lt;/sub&gt;Ag&lt;sub&gt;8&lt;/sub&gt;Al&lt;sub&gt;8&lt;/sub&gt;Pd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; (&lt;i&gt;x&lt;/i&gt; = 0 and 2) amorphous alloys with ability to form excellent glass are chosen as model alloys. The evolutions of heat flow and shear modulus in different states (as-cast, relaxed and crystalline) with temperature of Zr&lt;sub&gt;50–&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cu&lt;sub&gt;34&lt;/sub&gt;Ag&lt;sub&gt;8&lt;/sub&gt;Al&lt;sub&gt;8&lt;/sub&gt;Pd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; (&lt;i&gt;x&lt;/i&gt; = 0 and 2) glass system are studied by differential scanning calorimetry (DSC) and electromagnetic-acoustic transformation (EMAT) technique, respectively. The experiment demonstrates that a decrease of the shear modulus is accompanied by the endothermic heat flow and vice versa. The correlation between the heat flow and shear modulus is investigated according to the interstitialcy theory. The calculations of the interstitialcy defect concentration and activation energy spectra suggest that the microstructure remains stable at relatively low temperatures. When temperature increases, the interstitialcy defect structure is activated. Compared with that in the as-cast state, the interstitialcy defect concentration in the relaxed state is reduced by structural relaxation, indicating that temperature-dependent shear modulus softening is inhibited. At temperatures above glass transition temperature, a rapid growth of interstitialcy defect concentration results in the accelerated shear softening, which is accompanied by significant endothermic heat flow. It is noted that the minor addition of palladium reduces the interstitialcy defect concentration in the Zr&lt;sub&gt;50–&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cu&lt;sub&gt;34&lt;/sub&gt;Ag&lt;sub&gt;8&lt;/sub&gt;Al&lt;sub&gt;8&lt;/sub&gt;Pd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; (&lt;i&gt;x&lt;/i&gt; = 0 and 2) metallic glass systems. It is suggested that the introduction of Pd reduces the atomic mobility and increases the characteristic relaxation time. In parallel, the change of shear modulus as a function of the aging time (below the glass transition temperature) is studied by using EMAT equipment. The results indicate that the interstitialcy defect concentration decreases in the physical aging process, which is accompanied by an increase of shear modulus. The interstitialcy defect concentration and shear modulus change towards the quasi-equilibrium state with aging time increasing. A reduction of the interstitialcy defect concentration leads to a decrease of the shear modulus change upon microalloying by Pd into Zr&lt;sub&gt;50–&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; Cu&lt;sub&gt;34&lt;/sub&gt;Ag&lt;sub&gt;8&lt;/sub&gt;Al&lt;sub&gt;8&lt;/sub&gt;Pd&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; (&lt;i&gt;x&lt;/i&gt; = 0 and 2) metallic glass system.

Thermodynamic Properties, Viscosity, and Structure of CaO-SiO2-MgO-Al2O3-TiO2-Based Slag.

The effect of TiO2 and the MgO/Al2O3 ratio on the viscosity, heat capacity, and enthalpy change of CaO–SiO2–Al2O3–MgO–TiO2 slag at constant heat input was studied. The variation of slag structure was analyzed by the calculation of activation energy and FTIR spectrum measurements. The results showed that the heat capacity and enthalpy change of the slag decreased with the increase of TiO2 content. Under constant heat supply, the fluctuations in slag temperature were relatively apparent, and the temperature of slag increased as the TiO2 content increased. The viscosity of slag decreased due to the increase in slag temperature. Increasing the MgO/Al2O3 ratio could decrease the temperature and viscosity of slag. The effect of increasing the MgO/Al2O3 ratio on the viscosity was more pronounced than the decreasing temperature caused by increasing the MgO/Al2O3 ratio. The apparent activation energy decreased with increasing TiO2 content and MgO/Al2O3 ratio. The Ti–O bonds formed with TiO2 addition, and the Ti–O bonds were weaker than Si–O bonds, which resulted in the decrease in heat capacity and viscosity of slag.

ORIGIN OF HEAT EFFECTS AND SHEAR MODULUS CHANGES OF A Cu-BASED AMORPHOUS ALLOY

Shear modulus is one of important parameters to control the viscous flow, diffusion and structural relaxation of amorphous alloy. Macroscopic shear elasticity determines the change of heat flow. The correlation between the mechanical properties and the heat flow during the structural relaxation and glass transition is one of the important issues to understand the origin of mechanical properties of amorphous alloy. In the framework of the interstitialcy theory, the shear modulus, heat flow and viscosity of Cu$_{49}$Hf$_{42}$Al$_{9}$ amorphous alloy were used to probe the correlation between shear modulus and heat flow. In parallel, evolution of interstitialcy defects concentration was determined by shear modulus in initial and relaxed states. From the perspective of energy, the influence of interstitialcy defects concentration on the thermodynamic properties of amorphous alloy was investigated by activation energy spectrum (AES). Dynamic mechanical analysis (DMA) was used to investigate the dynamic mechanical process of the Cu$_{49}$Hf$_{42}$Al$_{9 }$ amorphous alloy. Structural relaxation induced by physical aging and the evolution of internal friction in-situ annealing was discussed. The results demonstrated that interstitialcy theory could accurately describe the relaxation kinetics, shear softening and other phenomena induced by structural relaxation of amorphous alloy. Temperature dependence of the shear modulus in initial and relaxed states can be well predicted by the data of differential scanning calorimetry (DSC). Activation energy spectrum directly reflects the interstitialcy defects concentration, which can be activated per unit activation energy. Structural relaxation leads to a reduction of the defect concentration, which indicates the structure transforms to a more stable state. During the glass transition process, defect concentration rapidly increases, which corresponds to the shear softening accompanied by heat absorption. Structural relaxation induces decrease of both internal friction and atomic mobility of amorphous alloy. However, the atomic mobility is high enough to eliminate the influence of structural relaxation on defect concentration in the supercooled liquid region.

The structural and dynamic heterogeneities of Ni-P nanoglass characterized by stress-relaxation

The method of stress-relaxation is applied to study the structural and dynamic heterogeneities of Ni-P nanoglass (NG) prepared by pulse electro-deposition. We provide direct evidence that the Ni-P NG has more flow units with better plasticity than conventional Ni-P metallic glass (MG) prepared by rapid quenching. Moreover, an anomalous peak is observed in the activation energy spectra of NG at 435 K, which may relate to a hidden polyamorphous phase transition in Ni-P NG. Our study provides insights on the understanding of the discrepancy in structural heterogeneity and dynamic and thermodynamic properties between the NG and MG. • Ni-P NG has the stronger structural heterogeneity and more flow units than MG by stress-relaxation. • An anomalous thermal expansion was found in NG at 435 K. • A phase transition happend in NG at 435 K which is related to polyamorphous phase transition.

Soft-Mode Parameter as an Indicator for the Activation Energy Spectra in Metallic Glass.

The activation energy (EA) spectra of the potential energy landscape (PEL) provide a convenient perspective for interpreting complex phenomena in amorphous materials; however, the link between the EA spectra and other physical properties in metallic glasses is still mysterious. By systematically probing the EA spectra for numerous metallic glass samples with distinct local geometric ordering, which correspond to broad processing histories, we found that the shear moduli of the samples are strongly correlated with the arithmetic mean of the EA spectra rather than with the local geometrical ordering. Furthermore, we studied the correlation of the obtained EA spectra and various well-established physical parameters. The outcome of our research clearly demonstrates that the soft-mode parameter Ψ and the EA spectrum are correlated; therefore, this could be a good indicator of metallic glass properties and sheds important light on the structure-property relationship in metallic glass through the medium of the PEL.

Transformation of m-aminophenol by birnessite (δ-MnO2) mediated oxidative processes: Reaction kinetics, pathways and toxicity assessment

The m-aminophenol (m-AP) is a widely used industrial chemical, which enters water, soils, and sediments with waste emissions. A common soil metal oxide, birnessite (δ-MnO2), was found to mediate the transformation of m-AP with fast rates under acidic conditions. Because of the highly complexity of the m-AP transformation, mechanism-based models were taken to fit the transformation kinetic process of m-AP. The results indicated that the transformation of m-AP with δ-MnO2 could be described by precursor complex formation rate-limiting model. The oxidative transformation of m-AP on the surface of δ-MnO2 was highly dependent on reactant concentrations, pH, temperature, and other co-solutes. The UV-VIS absorbance and mass spectra analysis indicated that the pathway leading to m-AP transformation may be the polymerization through the coupling reaction. The m-AP radicals were likely to be coupled by the covalent bonding between unsubstituted C2, C4 or C6 atoms in the m-AP aromatic rings to form oligomers as revealed by the results of activation energy and mass spectra. Furthermore, the toxicity assessment of the transformation productions indicated that the toxicity of m-AP to the E. coli K-12 could be reduced by MnO2 mediated transformation. The results are helpful for understanding the environmental behavior and potential risk of m-AP in natural environment.

The Structural and Dynamic Heterogeneities of Ni-P Nanoglass Characterized by Stress-Relaxation

The method of stress-relaxation is applied to study the structural and dynamic heterogeneities of Ni-P nanoglass (NG) prepared by pulse electro-deposition. We provide direct evidence that the Ni-P NG has more flow units with better plasticity than conventional Ni-P metallic glass (MG) prepared by rapid quenching. Moreover, an anomalous peak is observed in the activation energy spectra of NG at 435 K, which may relate to a hidden polyamorphous phase transition in Ni-P NG. Our study provides insights on the understanding of the discrepancy in structural heterogeneity and dynamic and thermodynamic properties between the NG and MG.

Rheological and thermorheological assessment of polyethylene in multiple extrusion process

The relationship between rheological properties and structural changes in polyethylene chains due to the recycling of two linear low-density polyethylenes (LL-A and LL-B) has been investigated. These samples were subjected to multiple extrusion processes (9 extrusion steps). According to the results of gel content experiments, crosslinking did not occur. The results of the gel permeation chromatography indicated that the chain scission was slightly predominant during the re-extrusion, while the rheometry results clearly show the effects of long-chain branching during degradation. Therefore, the degradation proceeded through both paths. Based on the rheological results and the Cole-Cole method, LL-B exhibited a higher degradation rate during the extrusion process (because of the low antioxidant content), compared to LL-A. The results of thermorheological methods including van-Gurp-Palmen and activation energy spectra indicated that the extent of thermorheological complexity was intensified with increasing the number of extrusion cycles and consequently increasing the number of long-chain branches.