Evaporation Of Material Research Articles

Numerical simulation on nanosecond laser ablation of titanium considering plasma shield and evaporation-affected surface thermocapillary convection

Nanosecond laser ablation of metal is a complicated process, which consists of many strongly coupled physical phenomena, including material heating, melting, evaporation, vapour dynamics, and plasma shield. In this work, the nanosecond laser ablation process of titanium is investigated at 1064 nm wavelength. A multi-physics axisymmetric two-dimensional (2D) model is presented. The evolution and the distribution of titanium target’s temperature were solved using governing equations and the vapour dynamics was determined using the Knudsen relations. The maximum temperature of titanium grown slower with the increase in laser fluence and the maximum flow velocity of liquid materials reached 121 m/s with the laser fluence of 12 J/cm2. In addition, the plasma shield effect was taken into account to correct the energy distribution of the incident laser. As the laser fluence increases, the energy efficiency decreases. At the laser fluence of 12 J/cm only 55.9% of the energy was absorbed at the centre of titanium. Furthermore, the surface morphology profiles were analysed after the laser ablation on different laser fluences lying within the range of 2 - 12 J/cm2. The results showed that the surface morphology after ablation has a crater-like form and the increment of laser fluence leads to a slower non-linear increment in ablation depth and diameter of melt zone. The calculated results are in good agreement with the experimental results. The study provides useful information for nanosecond laser precision fabrication.

Investigation on the Cooling and Evaporation Behavior of Semi-Flexible Water Retaining Pavement based on Laboratory Test and Thermal-Mass Coupling Analysis.

The Semi-Flexible Water Retaining Pavement (SFWRP) has the capability to cool down the temperature of the road surface through its evaporation behavior, including absorbing and evaporating water; this is an efficient approach to relieve the heat island effect in a big city. The temperature feedback from different material surface were investigated in this paper in the same test condition, it has been proved that the SFWRP material can remarkably cool down the temperature of the road surface. The mechanism of the material evaporation behavior, including flux calculation formula of the water vapor inside the air void, were studied by inter-phase continuous function, in which the structural properties of the SFWRP material was taken into account. Furthermore, the function calculating the evaporation of the water vapor was then developed in this research through heat and mass transfer analogy. Besides, the calculating results can be captured by the self-coding program in Finite Element Modeling (FEM) for water evaporation simulation. Also, the results of laboratory tests were adopted to validate the calculating model. Finally, it has been proved that the mortar was recommended to be used in semi-flexible water retaining pavement to serve as material with permeable and water retaining property, and the semi-flexible water retaining pavement material is recommended to applied in the surface layer of the permeable pavement.

Film deposition by thermal laser evaporation

We study the thermal evaporation of materials by irradiation with laser light to deposit layers with atomically precise thickness. Under ultrahigh to moderate vacuum pressures, a focused laser beam is directed to the front surface of a source target to heat it to temperatures suitable for thermal evaporation. The local heating, combined with efficient radiative heat dissipation at high temperatures, allows the evaporation of solid elements from self-supported targets, eliminating the need for crucibles. The temperature is controlled by a sensor on the back of the target with feedback to the laser power. Evaporating representative metals, we achieve ultrahigh evaporation temperatures exceeding 2000 °C as well as temperature stabilities of better than ±0.1 °C. Combined with laser substrate heating, this enables a thermal laser epitaxy process that is capable in principle of accurately co-depositing any combination of chemical elements at any substrate temperature under a vacuum pressure only to provide a mean free path exceeding the target–sample distance.

No Particle Mass Enhancement from Induced Atmospheric Ageing at a Rural Site in Northern Europe

A large portion of atmospheric aerosol particles consists of secondary material produced by oxidation reactions. The relative importance of secondary organic aerosol (SOA) can increase with improved emission regulations. A relatively simple way to study potential particle formation in the atmosphere is by using oxidation flow reactors (OFRs) which simulate atmospheric ageing. Here we report on the first ambient OFR ageing experiment in Europe, coupled with scanning mobility particle sizer (SMPS), aerosol mass spectrometer (AMS) and proton transfer reaction (PTR)-MS measurements. We found that the simulated ageing did not produce any measurable increases in particle mass or number concentrations during the two months of the campaign due to low concentrations of precursors. Losses in the reactor increased with hydroxyl radical (OH) exposure and with increasing difference between ambient and reactor temperatures, indicating fragmentation and evaporation of semivolatile material.

Numerical Analysis of Molten Pool Behavior and Spatter Formation with Evaporation During Selective Laser Melting of 316L Stainless Steel

During the selective laser-melting process, material evaporation and resultant spatter are common phenomena that bring about many defects. However, the underlying physical phenomena such as molten pool behavior and spatter formation, as evaporation occurred, are sparsely understood and difficult to observe during the process. Thus, a three–dimensional powder-scale model was established to investigate the thermal and flow behavior of the molten pool, the morphology evolution of the molten pool and keyhole, and the spatter formation with evaporation in the selective laser-melting processing of 316L stainless steel. Phase transitions and variations in interfacial force were taken into account in this model. The modified phase-field method was applied to trace the melt–gas interface. The results showed that keyhole formed in molten pool under recoil pressure, and that there were some differences in the temperature distribution and flow behavior inside and outside the keyhole. In addition, the dimension and surface morphology of the molten pool and keyhole depth altered and gradually stabilized during the process. Moreover, droplet spatter formation at rear of molten pool proceeded roughly as follows: the backward ejection of melt vapor would induce a depression in molten pool and a bump on the molten pool surface, the bump moved backward and subsequently a liquid column formed, then the liquid column formed a neck and gradually pinched off, resulting in the droplet spatter. Furthermore, the characteristic morphology of the scan track and dimension of the molten pool were obtained through experiments, which showed good agreement with the simulation results.

Investigation of Short-Arc High-Pressure Xenon Discharge: Effect of Electrode Material Evaporation on Discharge Properties and Pulse Operation

This paper presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources.

Field electron emission induced glow discharge in a nanodiamond vacuum diode

The present paper extends the prior findings on self-induced heating of solid state field emission devices. It was found that a vacuum diode (base pressure ∼10−9 Torr), that makes use of graphite-rich polycrystalline diamond as cathode material, can switch from a diode regime to a resistor regime to a glow discharge plasma regime without any external perturbation, i.e. all transitions are self-induced. Combined results of in situ field emission microscopy, ex situ electron microscopy and Raman spectroscopy suggest that it is the nanodiamond cathode of the diode heated to about 3000 K which causes self-induced material evaporation, ionization and eventually micro-plasma formation. Our results confirm that field emission, commonly called cold emission, is a very complex phenomenon that can cause severe thermal load. Thermal load and material runaway could be the major factors causing vacuum diode deterioration, i.e. progressive increase in turn-on field, decrease in field enhancement factor, and eventual failure.

Iron Mineralogy and Magnetic Susceptibility of Soils Developed on Various Rocks in Western Iran

AbstractThe characterization of magnetic minerals and the relationship of these minerals to the magnetic susceptibility of soils that have developed on various parent materials can provide valuable information to various disciplines, such as soil evolution and environmental science. The aim of the study reported here was to investigate variations in the magnetic susceptibility (χ) of soils in western Iran due to differences in lithology and to examine the relationship of χ to ferrimagnetic minerals. Eighty samples were collected from eight parent materials taken from both intact rocks and associated soils. The soil parent materials included a range of igneous and sedimentary rocks, such as ultrabasic rocks (Eocene), basalt (Eocene), andesite (Eocene), limestone (Permian), shale (Cretaceous), marl (Cretaceous), and the Qom formation (partially consolidated fine evaporative materials, early Miocene). The 80 samples were analyzed for χ using a dual-frequency magnetic sensor and for mineralogy using X-ray diffraction (XRD). The highest χ values were found in the ultrabasic rocks and associated soils, while the lowest χ values were observed in the limestone rocks and associated soils. The pedogenic processes significantly enhanced the χ values of soils developed on the sedimentary rocks due to the formation of ferrimagnetic minerals. In contrast, χ values decreased as a result of pedogenic processes in soils developed on igneous rocks due to the dilution effects of diamagnetic materials, such as halite, calcite, phyllosilicates, and organic matter. The significant positive correlation between the XRD peak intensity of the maghemite/magnetite particles and χ values confirmed that χ values in soils are largely controlled by the distribution and content of ferrimagnetic minerals. These results show that χ measurements can be used to quantify low concentrations of ferrimagnetic minerals in the soils of semiarid regions.

Resonance excitation of surface capillary waves to enhance material removal for laser material processing

The results of detailed experiments and high fidelity modeling of melt pool dynamics, droplet ejections and hole drilling produced by periodic modulation of laser intensity are presented. Ultra-high speed imaging revealed that melt pool oscillations can drive large removal of material when excited at the natural oscillation frequency. The physics of capillary surface wave excitation is discussed and simulation is provided to elucidate the experimental results. The removal rates and drill through times as a function of driving frequency is investigated. The resonant removal mechanism is driven by both recoil momentum and thermocapillary force but the key observation is the latter effect does not require evaporation of material, which can significantly enhance the efficiency for laser drilling process. We compared the drilling of holes through a 2 mm-thick Al plate at modulation frequencies up to 20 kHz. At the optimal frequency of 8 kHz, near the resonant response of the melt pool, the drilling efficiency is greater than 10x with aspect ratio of 12:1, and without the collateral damage that is observed in unmodulated CW drilling.

Effect of KF Addition to (Cu,Ag)2SnS3 Thin Films Prepared by Sulfurization Process

(Cu,Ag)2SnS3 thin films and solar cells are prepared by sulfurization of KF/Sn/(Cu + Ag) stacked precursors in a sulfur and tin mixing atmosphere. Their properties are investigated. Stacked KF/Sn/(Cu + Ag) precursors are deposited on Mo/soda lime glass substrate by sequential evaporation of Cu + Ag, Sn elements, and KF. The molar ratios of the evaporation materials are held constant at (Cu + Ag):Sn = 1.0:0.6 and Ag/(Cu + Ag) = 0.05, and the KF/Cu molar ratio is changed from 0 to 0.05. The precursors are crystallized by annealing for 30 min at 570 °C in a sulfur and tin mixing atmosphere. The compositions are approximately constant, and the dependence of the composition ratio on the KF addition quantity is not observed. For all samples, the X‐ray diffraction patterns and the Raman spectra corresponding to CATS are obtained. The values of Voc increased with increasing KF/Cu molar ratio until KF/Cu = 0.03. The best solar cell in this study showed a Voc of 248 mV.

Material evaporation with ultrashort laser exposure

The task is to analyse the temperature distribution in the material under ultrashort laser irradiation. The mathematical model is built on the basis of a two-temperature model describing transition phenomena in a nonequilibrium electron gas and lattice with an ultrashort laser effect on the material. The vaporized body is considered as a thin plate and the problem is formulated as a system of one-dimensional boundary-value problems of the heat equation written for the electron and lattice components. The initial problem is reduced to solving a system of singularly perturbed boundary problems of the heat equation with nonlinear boundary conditions on moving boundaries, an approximate solution of which is obtained in the form of an asymptotic expansion of the solution in the Poincaré sense in powers of small parameters.

Effect of the Conditions of Formation of W–C Nanopowders in a Plasma Jet on the Synthesis of Hexagonal Tungsten Carbide

The effects of the conditions of a raw material introduction as well as mixing of it with a high-temperature gas flow under the plasma chemical synthesis of superdispersed powder of W–C have been studied. In the case of incomplete raw material evaporation and its fast quenching, preferred cubic tungsten carbide β-WC formation is found to occur, as well as nano- and microparticles with a complicated phase composition. In the case of complete raw material evaporation, the products of reducing synthesis are nanopowder of tungsten or semicarbide W2C depending on the amount of hydrocarbon introduced. There is a second stage of the process of low-temperature synthesis which leads to a single-phase of tungsten carbide α-WC formation. Complete evaporation of raw material must be ensured in the plasma chemical process for obtaining of α-WC powder with a maximum specific surface area.

Numerical investigation of the thermal transformation of composition powder particles in the technology of selective laser melting

The results of mathematical model development for evaluation of thermal state of spherical particles of powder composition equally treated in the technology of selective laser melting are presented. This model considers: features of laser irradiation energy transfer to the particles having smaller size but comparable with the size of radiation spot diameter; energy transfer through the sphere upper half; material melting in the solidus and liquidus range; possibility of surface material evaporation and dependence of material thermophysical parameters on temperature. This model is adapted to be used in standard finite-element software ANSYS Transient Thermal that has been applied for numerical simulation using powder of heat-resistant nickel-chromium alloy. Process regularities have been discovered, and it was shown that the range value of particles size scatter of powder composition fraction used determines principle possibility of choosing laser treatment mode to provide high quality material after melting.

Enhancement of Heat Transfer Performance Using Ultrasonic Evaporation

Abstract The ultrasonic evaporator is a new type of evaporation equipment which uses ultrasonic technology to assist evaporation of liquid materials. Due to the lack of mechanism of ultrasonic technology to enhance the heat transfer in evaporation process, there are few reports on the use of ultrasonic evaporator in industrial production. The tap water was selected as experimental material and the heat transfer performance of ultrasonic evaporator was studied. It could be obtained from the single factor analysis that the heat transfer coefficient increased first and then decreased with the increase of ultrasonic power density. The increase of heat transfer due to the increase of temperature difference is basically stable at 20 %. When the ultrasonic wave acts on evaporator, the heat transfer coefficient would increase about 17.06 %–29.85 %. According to the orthogonal test and analysis of variance, it can be obtained that the influence of temperature difference on heat transfer coefficient is the largest, the second is feed flow rate, and evaporation time has the least influence.

Sample cartridge with built-in miniature molecule evaporator for in-situ measurement with a photoemission electron microscope

We present a new sample holder that is compatible with Photoemission Electron Microscopes (PEEMs) and contains a molecule evaporator. With the integrated low cost evaporator, a local and controlled material deposition in clean ultra-high vacuum conditions can be achieved minimizing the contamination of the analysis chamber. Different molecule systems can easily be studied by exchanging the sample holder. This opens up new possibilities for in-situ investigation of thin film growth by means of spectromicroscopy and element-selective imaging at the nanometer scale. As an example of the performances of the setup, we present a study of the hybrid inorganic/organic system (HIOS) consisting of the organic acceptor molecule 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6TCNNQ) and ZnO, which is of great interest for novel HIOS-based optoelectronic devices. Here, the ZnO surface work function modification by F6TCNNQ adsorption is investigated in-situ in a spatially resolved manner. In addition, we employ PEEM to selectively probe the chemical state of F6TCNNQ molecules in contact with ZnO (in the first monolayer) and those molecules located in multilayers (in 3D islands).

Numerical simulation and validation of material loadings during electrical discharge machining

The material removal mechanism of electrical discharge machining of steel bases on melting and evaporation of material by a spark discharge between two electrodes. Consequently, the electrode materials are stressed by an intensive thermal load that leads to changes of microstructure in the rim zones. For modelling these loads, a combined simulation approach of modeling heat transfer and fluid dynamics was implemented. Aim of this research is to develop a heat transfer model, which can reproduce the material removal and predict the local thermal load in the electrodes for correlation with the modifications in electrodes rim zones.

A model of femtosecond laser ablation of metal based on dual-phase-lag model

Femtosecond laser ablation possesses a variety of applications due to its better control, high power density, smaller heat-affected zone, minimal collateral material damage, lower ablation thresholds, and excellent mechanical properties. The non-Fourier effect in heat conduction becomes significant when the heating time becomes extremely small. In order to analyze the femtosecond laser ablation process, a hyperbolic heat conduction model is established based on the dual-phase-lag model. Taken into account in the model are the effect of heat source, laser heating of the target, the evaporation and phase explosion of the target material, the formation and expansion of the plasma plume, and interaction of the plasma plume with the incoming laser. Temperature-dependent optical and thermophysical properties are also considered in the model due to the fact that the properties of the target will change over a wide range in the femtosecond laser ablation process. The effects of the plasma shielding, the ratio of the two delay times, and laser fluence are discussed and the effectiveness of the model is verified by comparing the simulation results with the experimental results. The results show that the plasma shielding has a great influence on the femtosecond laser ablation process, especially when the laser fluence is high. The ratio between the two delay times (the ratio <i>B</i>) has a great influence on the temperature characteristic and ablation characteristic in the femtosecond laser ablation process. The augment of the ratio <i>B</i> will increase the degree of thermal diffusion, which will lower down the surface temperature and accelerate the ablation rate after the ablation has begun. The ablation mechanism of femtosecond laser ablation is dominated by phase explosion. The heat affected zone of femtosecond laser ablation is small, and the heat affected zone is less affected by laser fluence. The comparison between the simulation results and the experimental results in the literature shows that the model based on the dual-phase-lag model can effectively simulate the femtosecond laser ablation process.

Forevacuum electron beam plasma synthesis of multilayer metal–ceramic coatings

The paper describes a method of synthesizing multilayer metal–ceramic coatings through the evaporation of solid materials and their condensation on substrates with a forevacuum plasma electron source. Research data are presented on the thermal barrier properties of such coatings and on their in-depth elemental composition.

Self-assembly of three-dimensional 1-octadecanol/graphene thermal storage materials

A self-assembly method is introduced to prepare composite phase change materials (PCMs) consisting of 1-octadecanol (OD) and graphene. The shape stability and thermal properties of 1-octadecanol/graphene composite PCMs with three-dimensional network structure are investigated. Graphene is dispersed evenly in OD matrix and the three-dimensional network structure is getting tighter with increasing ratio of graphene. OD is completely encapsulated at relatively low amount of graphene about 1.5 wt%. XRD and Raman results show that the combination between OD and graphene is physical adsorption. The 1-octadecanol/graphene (OG) composite phase change materials possess excellent shape stability, which can prevent the leakage of molten OD during phase transition. In addition, around 99.3% phase change enthalpy of pure OD is maintained by connected network structure of graphene while the melting and solidifying temperature merely have small fluctuations. The thermal conductivity of composite phase change material with 1.5 wt% graphene increases to 0.358 W/(m K), which is 1.5 times higher than that of pure OD. Furthermore, the porous network of graphene can delay the evaporation and thermal decomposition point of the composite phase change materials, thus extending the operating temperature of OD efficiently. This work provides a promising way to encapsulate low-temperature organic phase change materials with little carbon additives, and enhance the thermophysical properties of base materials simultaneously.

Effect of perspired moisture and material properties on evaporative cooling and thermal protection of the clothed human body exposed to radiant heat

Perspired moisture plays a crucial role in the thermal physiology and protection of the human body wearing thermal protective clothing. Until now, the role of continuous sweating on heat transfer, when simultaneously considering internal and external heat sources, has not been well-investigated. To bridge this gap, a sweating torso manikin with 12 thermal protective fabric systems and a radiant heat panel were applied to mimic firefighting. The results demonstrated how the effect of radiant heat on heat dissipation interacted with amount of perspired moisture and material properties. A dual effect of perspired moisture was demonstrated. For hydrophilic materials, sweating induced evaporative cooling but also increased radiant heat gain. For hydrophilic station uniforms, the increment of radiant heat gain due to perspired moisture was about 11% of the increase of heat dissipation. On the other hand, perspired moisture can increase evaporative cooling and decrease radiant heat gain for hydrophobic materials. In addition to fabric thermal resistance ( Rct) and evaporative resistance ( Ret), material hydrophilicity and hydrophobicity, emissivity and thickness are important when assessing metabolic heat dissipation and radiant heat gain with profuse sweating under radiant heat. The results provide experimental evidence that Rct and Ret, the general indicators of the clothing thermo-physiological effect, have limitations in characterizing thermal comfort and heat strain during active liquid sweating in radiant heat. This paper offers a more complete insight into clothing thermal characteristics and human thermal behaviors under radiant heat, contributing to the accurate evaluation of thermal stress for occupational and general individuals.