Thermal Equilibrium Process Research Articles

Microstructure evolution in semi-solid A356 aluminium alloy treated by ICTE process

ABSTRACT The effects of parameters of a novel internal cooling thermal equilibrium (ICTE) process on microstructure evolution in semi-solid A356 aluminium alloys were investigated. The results indicated that a low predetermined temperature (T P), a higher mechanical stirring intensity for the thermal equilibrium body (TEB) and a reduced melt mass contributed to obtaining fine grained semi-solid structures. The cooling effect of TEB combined with dendritic remelting fractures of solidified shells formed on surface of TEB at room temperature promoted massive nucleation in alloy melt and contributed to obtaining numerous fine primary solid phases. The ICTE process, which regulated stirring time of TEB, obtained numerous spherical grains and simplified the operational process.

Forward osmosis, reverse osmosis, and distillation membranes evaluation for ethanol extraction in osmotic and thermic equilibrium

One of the significant challenges of the industry is the economic extraction of ethanol from aqueous solutions of interest to the food industry. Specifically, in the alcoholic beverages industry, the non-alcoholic beverage market has gained importance, demanding more non-alcoholic drinks with higher organoleptic quality. In this context, the technology related to the use of membranes has shown great potential. Our research aims to determine the performance of forward osmosis using FO, RO, and MD membranes as an option in the extraction of alcohol in an osmotic (Δπ = 0) and thermal (ΔT° = 0) equilibrium process. The results showed that all the membranes have the potential to dealcoholize a 12% v.v. synthetic ethanol solution. The results showed that Membrane Distillation is a viable strategy as a complement in a hybrid FO-MD approach, achieving ethanol flux values close to those offered by FO membranes and much higher than those shown by RO membranes. We also proposed other technical criteria for membrane performance evaluation, such as maintaining a low reverse salt flux and a low or no water flux to keep the organoleptic properties of a hypothetical alcoholic beverage subjected to the FO-MD hybrid process. For a high Ethanol/Salt flux ratio, the RO-82V and FO-CTA membranes presented the best performance. Furthermore, in an Ethanol/Water flux ratio, RO membranes perform best when working in an osmotic equilibrium process with a water flux equal to zero. Regarding the FO membranes, in an Ethanol/Water flux ratio, the FO-TFC membrane presented the best performance.

Volatile and Nonvolatile Switching of Phase Change Material Ge2Sb2Te5 Revealed by Time-Resolved Terahertz Spectroscopy.

Phase change materials exhibit unique advantages in reconfigurable photonic devices due to drastic tunability of photoelectric properties. Here, we systematically investigate the thermal equilibrium process and the ultrafast dynamics of Ge2Sb2Te5 (GST) driven by femtosecond (fs) pulses, using time-resolved terahertz spectroscopy. Both fs-pulse-driven crystallization and amorphization are demonstrated, and the threshold of photoinduced crystallization (amorphization) is determined to be 8.4 mJ/cm2 (10.1 mJ/cm2). The ultrafast carrier dynamics reveal that the cumulative photothermal effect plays a crucial role in the ultrafast crystallization, and modulation depth of volatile (nonvolatile) THz has switching limits up to 30% (15%). A distinctive phonon absorption at 1.1 THz is observed, providing fingerprint spectrum evidence of crystalline lattice formation driven by intense fs pulses. Finally, multistate volatile (nonvolatile) THz switching is implemented by tuning optical pump fluence. These results provide insight into the photoinduced phase change of GST and offer benefits for all optical THz functional devices.

Thermal and non-thermal equilibrium processes of charge extraction in accumulated charge measurement (ACM)

Accumulated charge measurement (ACM) is an experimental technique for studying the charge-injection and extraction processes in a condenser comprising the following: metal electrode 1, insulator (INS), organic semiconductor (OS), and metal electrode 2 (M2). In this method, the change in the accumulated charge (Qacc) is estimated by integrating the displacement current when the applied voltage changes from Voff to Voff + Va. Voff is the constant offset voltage and Va is the alternating voltage that is changed step-by-step; Qacc is expressed as a function Va. From the observed dataset of Qacc and Va, ΔQ and VOS are derived, where ΔQ is the degree of charge injection and VOS is the voltage drop within the OS layer caused by Va. The injection barrier at the OS/M2 interface can be evaluated from the plot of ΔQ as a function of VOS. In this study, two theoretical models for analyzing ACM data are developed using the Poisson–Boltzmann equation. On the one hand, the thermal equilibrium (TE) model reflects the TE process, in which charge evacuation simultaneously occurs at the INS/OS and OS/M2 boundaries. On the other hand, the non-thermal equilibrium (NTE) model assumes a two-step charge evacuation process at the interfaces: charge evacuation at the OS/M2 boundary occurs in the first step, followed by charge evacuation at the INS/OS boundary in the second step. The ACM data for condensers constituting pentacene and H2Pc are well reproduced by the TE and NTE models, respectively. The different behaviors of the two condensers can be attributed to the difference in their diffusion constants.

Enhanced thermionic emission of mayenite electride composites in an Ar glow discharge plasma

Mayenite electride has attracted increasing research interests because of its unique electronic properties. The thermionic emission behavior of the mayenite electride is relatively unknown. Previous studies revealed that mayenite electride exhibited a bare work function ranged from 2.1–2.6 eV when the thermionic emission was tested in vacuum, and enhanced emission currents could be achieved by applying a super-high external electric field. In this paper, the thermionic emission behavior and the corresponding effective work function of two types of mayenite electride based composites, mayenite electride-titanium and mayenite electride-carbon, were investigated in an Ar glow discharge plasma at elevated temperatures (400–1000 K) without applying a high external electric field, which is critical for the application in electric propulsion and other aerospace apparatus, yet never had been done before. During the testing, the thermal equilibrium process and plasma sheath expansion were observed. The effective work function of the two mayenite electride composites were determined as a function of temperature. The Rasor-Warner model was applied to determine the bare work function and adsorption-site density of the mayenite electride based composites. Results suggested that the adsorption of Ar ions led to the enhanced thermionic emission (~30 A/m2 at 985 K) and low effective work functions (0.9–2.2 eV) of mayenite electride based composites, without the need of applying high electric fields. Our findings will pave the ways for the application of mayenite electride and its composites as the thrust cathode materials for electric propulsion where plasma is present.

Reversible Valence Photoisomerization between Closed-Shell Quinoidal and Open-Shell Biradical Forms.

We report here a kinetic study on the thermal equilibrium process between the biradical form and the quinoidal form starting from the singlet biradical form alone. A photochromic phenoxyl-imidazolyl radical complex repeatedly generates biradical species upon UV light irradiation, and the following thermal equilibrium process responsible for valence isomerization from the open-shell singlet biradical to the closed-shell quinoidal form is observed in the microsecond time region. The thermodynamic parameters for the equilibrium process were determined for the first time by nanosecond laser flash photolysis. We also found that visible-light excitation to the equilibrium state causes valence photoisomerization from the quinoidal to the biradical form, which returns thermally to the quinoidal form.

Determination of neutral temperature using fiber Bragg grating sensor in capacitively coupled argon plasmas

Neutral temperature Tg in capacitively coupled argon plasmas was measured by using a fiber Bragg grating sensor. The measurement of Tg is based on the thermal equilibrium process between the sensor and neutral gases, which is found to become fast upon increasing pressure, due to enhanced heat conduction. Additionally, Tg was found to increase with increasing high frequency power due to enhancive collisions with charged particles. It is also observed that Tg exhibits a significant gradient in space, ranging from 10 to 120 °C higher than room temperature for the conditions investigated. In addition, the spatial profiles of Tg at different pressures generally resemble those of the Ar+ density ni, measured with a floating double probe. The neutral gas is mainly heated via elastic collisions with ions in the sheath region followed by heat conduction among neutrals.

A numerical study of EGS heat extraction process based on a thermal non-equilibrium model for heat transfer in subsurface porous heat reservoir

With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process.

A Study of Fundamental Law of Thermal Radiation and Thermal Equilibrium Process

The fundamental law of thermal equilibrium radiation includes two elements: the law of energy distribution of matter vibrators in the radiation field and the law of energy exchange between vibrators and the radiation field. This paper discovers the law of how vibrators stimulate and absorb radiation, by a study of the black-body radiation law and the characteristics of vibrators’ absorption of radiation. As for the fundamental law of thermal equilibrium radiation, its complete expression should be: the energy distribution of vibrators in the thermal equilibrium radiation field follows the energy distribution law by L. Boltzmann; the probability of vibrators’ stimulating radiation is directly proportional to their state of energy levels and that of their absorbing radiation is directly proportional to their energy distribution probability. The author, on the basis of the fundamental law of thermal radiation, proposes conditions for thermal equilibrium radiation and analyses the micro momentum theory and characteristics in the process of thermal equilibrium.

Thermal Analysis on Machine Tools and Research on Time Parameters of Machine Thermal Equilibrium

Machine thermal equilibrium seriously influences the machining accuracy,a significant amount of research has been dedicated to the task of achieving and reasonablely controlling the thermal equilibrium time.In this paper,based on the analysis of the trait of thermal equilibrium process of machine tool ,the affection of room temperature and spindle speed on this process and the temperature when each point reaches to the heat balance is investigated.A new method of estimating thermal equilibrium time of each measured points based on spindle thermal model theory and multivariate optimization is presented,the results are analysed,further research about the control of machine thermal equilibrium process can be made based on this paper.

The unified first law in “cosmic triad” vector field scenario

In this Letter, we try to apply the unified first law to the “cosmic triad” vector field scenario both in the minimal coupling case and in the non-minimal coupling case. After transferring the non-minimally coupling action in the Jordan frame to the Einstein frame, the correct dynamical equation (Friedmann equation) is gotten in a thermal equilibrium process by using the already existing entropy while the entropy in the non-minimal coupled “cosmic triad” scenario has not been derived. And after transferring the variables back to the Jordan frame, the corresponding Friedmann equation is demonstrated to be correct. For complete arguments, we also calculate the related Misner–Sharp energy in the Jordan and Einstein frames.

Microscopic expression of entransy

Boltzmann found that a proportional relation exists between the entropy and the logarithm of the microstate number in an approximate non-interaction particle system. The relation was expressed as the Boltzmanns entropic equation by Planck later. Boltzmanns work gives a microphysical interpretation of entropy. In this paper, a microscopic expression of entransy is introduced for an ideal gas system of monatomic molecules. The changes of the microstate number, the entropy and the entransy of the system are analyzed and discussed for an isolated ideal gas system of monatomic molecules going through the initial stage of unequilibriun thermal state to the thermal equilibrium state. It is found that the microstate number and the entropy always increase in the process, while the entransy decreases. The microstate number is a basic physical quantity which could measure the disorder degree of the system. The irreversibility of a thermal equilibrium process is attributed to the increase in microstate number. Entropy and entransy both are single value functions of the microstate number and they both could reflect the change of the state for the system. Therefore, both entropy and entransy could describe the irreversibility of thermal processes.

Kinetics of Oxygen Adsorption and Initial Oxidation on Cu(110) by Hyperthermal Oxygen Molecular Beams

Oxygen adsorption and subsequent oxide formation on Cu(110) using a hyperthermal oxygen molecular beam (HOMB) were investigated using X-ray photoelectron spectrometry. The O-uptake curves, which were determined from the evolution of the O-1s peaks, indicate that simple Langmuir type kinetics can describe dissociative adsorption of O(2) with an incident energy (E(i)) below 0.5 eV under Theta < or = 0.5 ML. The reaction order dependence on E(i) implies two competing dissociation mechanisms, trapping-mediated and directly activated adsorption. Oxidation at Theta > or = 0.5 ML proceeds rather effectively using highly energetic HOMB at E(i) > or = 1.0 eV. The azimuthal dependence of the sticking probability during the effective oxidation using HOMB incidence suggests that the added rows, which consist of the Cu-O structure, shade the reactive hollow sites in the trough where oxygen penetrates into the subsurface. The surface Cu(2)O formed with highly energetic HOMB incidence decomposes with desorbing subsurface oxygen even at room temperature, demonstrating that HOMB can induce a metastable surface structure that cannot be produced in the thermal equilibrium process.

Stability of p-type conductivity in nitrogen-doped ZnO thin film

The behavior of p-type conductivity in nitrogen-doped ZnO prepared by thermal oxidation of zinc oxynitride thin film was investigated. The sample exhibited a stable p-type characteristic in the darkness over a 1yr period after deposition. However, when the p-type sample was irradiated by 2.72eV photons, it underwent a classic-mixed conductivity transition from p type to n type. An anomalously thermal equilibrium process was observed. It took 24h for the persisted n type photoconductivity to fade away in the dark and transit back to original p type. A local potential fluctuation model was used to explain the transient electrical behavior.

Critical phenomena in microgravity: Past, present, and future

This review provides an overview of the progress in using the low-gravity environment of space to explore critical phenomena and test modern theoretical predictions. Gravity-induced variations in the hydrostatic pressure and the resulting density gradients adversely affect ground-based measurements near fluid critical points. Performing measurements in a low-gravity environment can significantly reduce these difficulties. A number of significant experiments have been performed in low-Earth orbit. Experiments near the lambda transition in liquid helium explored the regime of large correlation lengths and tested the theoretical predictions to a level of precision that could not be obtained on Earth. Other studies have validated theoretical predictions for the divergence in the viscosity as well as the unexpected critical speeding up of the thermal equilibrium process in pure fluids near the liquid-gas critical point. We describe the scientific content of previously flown low-gravity investigations of critical phenomena as well as those in the development stage, and associated ground-based work.

A Stem Study of P and Ge Segregation to Grain Boundaries in Si1-xGex Thin Films

AbstractThe segregation of phosphorus to grain boundaries in phosphorus implanted Si0.87Ge0.13 films, deposited by chemical vapor deposition (CVD), was directly observed by scanning transmission electron microscopy (STEM) with energy dispersive x-ray (EDX) microanalysis. The segregation was determined to be a thermal equilibrium process by measuring and comparing the average phosphorus concentrations at the grain boundaries in Si0.87Ge0.13 films subjected to 700, 750 or 800°C annealing, following the implantation and 1000°C annealing processes. The measured segregation energy was 0.28 eV/atom. No Ge segregation was found at grain boundaries in phosphorus implanted Si0.87Ge0.13 films by STEM x-ray microanalysis. Neither was evidence shown by STEM microanalysis that Ge segregated to grain boundaries in intrinsic Si1-xGex films with x = 0.02, 0.13 and 0.31. Secondary ion mass spectrometry (SIMS) analysis showed that these intrinsic Si1-xGex films contained 1019 to 4 × 1019/cm-3H, depending on the deposition temperature.

Thermal equilibrium process in hydrogenated amorphous silicon npnp doping-modulated superlattices

Thermal equilibrium process in hydrogenated amorphous silicon(a-Si:H) npnp doping-modulated superlattices has been studied. Thermal quenching from above 130°C, equilibrium temperature of n-type a-Si:H, gives rise to the increase of defect density of p-layers and raises the Fermi-level of n-layers in a-Si:H npnp superlattices. The resultsv suggest that both dangling bonds and dopants are involved in thermal equilibration of doped a-Si:H and the dangling bonds of a p-type a-Si:H increase upon thermal quenching.

Thermal equilibrium process in undoped hydrogenated amorphous silicon and silicon-carbon alloy films

We find the thermally induced defects in undoped hydrogenated amorphous silicon carbon (a-Si1−xCx:H) by electron spin resonance and conductivity measurements. The equilibrium temperature (Te) determined from the annealing temperature-dependent density of dangling bonds after fast cooling decreases with increasing C content, from 190 °C for hydrogenated amorphous silicon to 150 °C for a-Si0.82C0.18:H. Possible microscopic mechanisms for the observed thermally induced defects in a-Si1−xCx:H alloys are discussed.

Effects of 4He impurities on 3He nuclear spin-lattice relaxation in hcp solid 3He

Nuclear spin-lattice relaxation properties of hcp solid 3He with 4He impurities have been studied. At temperatures below the exchange plateau region, three kinds of relaxation time were observed. To analyze the data, a phenomenological four-bath model was developed, the four baths being the Zeeman bath, the phonon bath, an “X-bath,” and a “Y-bath.” The X-bath consists of the exchange bath and a part of the 4He-4He elastic interaction bath. The Y-bath is the main part of the elastic interaction bath. We measured the concentration dependence of the energy constants of all the baths, as well as the temperature and concentration dependences of the three kinds of relaxation time. The relaxation behavior corresponding to the process between the X-bath and the Y-bath could not be expressed by a single exponential function of time and the relaxation rate was strongly dependent on the concentration. This process may be related to the internal thermal equilibrium process within the elastic interaction bath. The impurity-dependent relaxation time between the X-bath and the phonon bath had a temperature dependence of T −n with n = 7.4±0.3.

Negative surface ionisation of hyperthermal halogen atoms

Negative surface ionisation of hyperthermal halogen atoms was studied as a function of their kinetic energy on thoriated tungsten and on niobium wires. The transition from a thermal equilibrium process to direct reflection causes the ionisation to increase drastically above thermal energies: efficiencies up to 40% were found for 30 eV Cl atoms impinging on thoriated tungsten.