Evaporation-condensation Technique Research Articles

Production of highly dispersed powders of metal-oxides by evaporation-condensation technique when heated by focused radiation of terahertz-range gyrotron setup

Abstract The paper describes the experimental setup and some results of experiments on the production of highly dispersed metal oxides powders using the example of tungsten trioxide WO3 by the evaporation-condensation method when the initial material is heated by focused radiation of 0.53 THz / 240 W gyrotron. By focusing the gyrotron radiation, it was possible to achieve an intensity of several kW/cm2 on the surface of the evaporated initial sample. The use of a system with a rotating crucible made it possible to increase the evaporation rate of the substance by 3–4 times, which is very important in conditions of a lack of power.

Insight into the thermal kinetics and thermodynamics of sulfuric acid plant sludge for efficient recovery of sulfur

The disposal and management of sulfur-rich sludges (SRS) are challenging issues for the industries due to their adverse environmental impact. The present study reports the detailed characterizations and assessment of the thermo-kinetics of sludge generated from the sulfuric acid plant. In addition, the sulfur was retrieved with the help of the evaporation–condensation method. In the active devitalization zone (200–400 °C), a substantial mass loss (91 ± 3%) was observed, primarily due to the vaporization of sulfur. The isoconversional model-free methods were used to appraise kinetic parameters for the pyrolytic process. The average activation energy (64.5 kJ mol−1) estimated by the Starink method admired the less energy-intensive process and validated the occurrence of thermochemical reactions at low temperatures. The thermodynamic parameters and frequency factor calculated at 10 °C min−1 were ΔG* = 149.1 kJ mol−1, ΔH* = 59.8 kJ mol−1, ΔS* = −0.157 kJ mol−1K−1, and A = 2.1 × 105 s−1. Criado's Z-master plot revealed the dominance of the diffusion mechanism on the process. The efficient recovery of sulfur (≈96% with purity 99 ± 0.5%) was achieved at 440 °C by evaporation–condensation technique, and the findings closely complemented the kinetic and thermodynamic parameters. This study provides a background for a better understanding SRS and efficient sulfur recovery.

Hazardous maize processing industrial sludge: Thermo-kinetic assessment and sulfur recovery by evaporation-condensation technique

In the present work, a detailed thermo-kinetics of hazardous sulfur-rich sludge generated from the corn processing industry was performed for acquiring the optimum parameters for the efficient recovery of sulfur using the evaporation-condensation technique. Sulfur in the sludge was found to be 79 ± 3% (wt%) as estimated by the Bureau of Indian Standards method. A weight loss of 77 ± 3% was found in the active devolatilization zone from ≈ 200–400 °C. The online FTIR confirmed the evolution of mainly sulfur vapors (S8) along with some sulfur dioxide (SO2) and disulfur (S2). The thermogravimetric data (TG) was used to evaluate the kinetic parameters with the help of model-free methods, and Z-master plots determined additional insight into the reaction mechanism. Furthermore, the calculated activation energy (Ea) was used to determine the thermodynamic feasibility. The average Ea values appraised by FM, FWO, sDAEM, and ST models were 55.43, 72.04, 62.33, and 62.67 kJ mol−1, respectively. Overall, 91.2% of sulfur was successfully recovered at 400 °C, having 99 ± 0.5% purity. The approximate cost analysis of the sulfur recovery process was also estimated to check the economic viability. Recovered sulfur could be directly used for industrial and agricultural applications without any further purification.

Application of the 263 GHz/1 kW gyrotron setup to produce a metal oxide nanopowder by the evaporation-condensation technique

The use of a subterahertz gyrotron setup with output frequency of 263 GHz and a nominal power of 1 kW as a radiation source to obtain nanoscale particles of metal oxides by the evaporation-condensation technique is demonstrated. Zinc oxide ZnO and tungsten trioxide WO3 were the test substances. The substance evaporation was provided by a focused beam of electromagnetic radiation with an estimated microwave-energy flux density of about 20 kW/cm2 and was followed by deposition of the particles on the water-cooled surface. The sizes of the obtained particles ranged from 20 to 500 nm. A threefold increase in the substance evaporation rate compared with the previous experiments, in which a technological gyrotron setup with a frequency of 24 GHz and a nominal power of 7 kW was used, has been shown.

Direct Deposition of Gas Phase Generated Aerosol Gold Nanoparticles into Biological Fluids - Corona Formation and Particle Size Shifts

An ongoing discussion whether traditional toxicological methods are sufficient to evaluate the risks associated with nanoparticle inhalation has led to the emergence of Air-Liquid interface toxicology. As a step in this process, this study explores the evolution of particle characteristics as they move from the airborne state into physiological solution. Airborne gold nanoparticles (AuNP) are generated using an evaporation-condensation technique. Spherical and agglomerate AuNPs are deposited into physiological solutions of increasing biological complexity. The AuNP size is characterized in air as mobility diameter and in liquid as hydrodynamic diameter. AuNP:Protein aggregation in physiological solutions is determined using dynamic light scattering, particle tracking analysis, and UV absorption spectroscopy. AuNPs deposited into homocysteine buffer form large gold-aggregates. Spherical AuNPs deposited in solutions of albumin were trapped at the Air-Liquid interface but was readily suspended in the solutions with a size close to that of the airborne particles, indicating that AuNP:Protein complex formation is promoted. Deposition into serum and lung fluid resulted in larger complexes, reflecting the formation of a more complex protein corona. UV absorption spectroscopy indicated no further aggregation of the AuNPs after deposition in solution. The corona of the deposited AuNPs shows differences compared to AuNPs generated in suspension. Deposition of AuNPs from the aerosol phase into biological fluids offers a method to study the protein corona formed, upon inhalation and deposition in the lungs in a more realistic way compared to particle liquid suspensions. This is important since the protein corona together with key particle properties (e.g. size, shape and surface reactivity) to a large extent may determine the nanoparticle effects and possible translocation to other organs.

Effect of Different Parameters on Synthesis of MoO3 Nanopowder by the Evaporation–Condensation Technique

In the present study, MoO3 nanopowder was produced by evaporation of molybdenum oxide powder at high temperature (around 1,000°C) and its subsequent cooling in inert gas. The effect of different parameters such as pressure, temperature, and type of inert gas on the morphology and particle size were examined. The samples were characterized in terms of structure, morphology, particle size, and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer–Emmett–Teller (BET) method. Particles of the synthesized nanopowder had spherical shape with specific surface area of 18.64 m2g−1 and the average diameter of about 31 nm in optimum conditions.

Size-controlled aerosol synthesis of silver nanoparticles for plasmonic materials

Aerosol techniques were used to synthesize spherical and monodisperse silver nanoparticles for plasmonic materials. The particles were generated with an evaporation–condensation technique followed by size selection and sintering with a differential mobility analyzer and a tube furnace, respectively. Finally, the nanoparticles were collected on a glass substrate with an electrostatic precipitator. The particle size distributions were measured with a scanning mobility particle sizer and verified with a transmission electron microscope. A spectrophotometer was used to measure the optical extinction spectra of the prepared samples, which contained particles with diameters of approximately 50, 90 and 130 nm. By controlling the particle size, the dipolar peak of the localized surface plasmon resonance was tuned between wavelengths of 398 and 448 nm. In addition, quadrupolar resonances were observed at shorter wavelengths as predicted by the simplified theoretical model used to characterize the measured spectra.

Direct Synthesis of Aqueous Quantum Dots through 4,4′-Bipyridine-Based Twin Ligand Strategy

We report a new class of derivatized 4,4'-bipyridinium ligands for use in synthesizing highly fluorescent, extremely stable, water-soluble CdSe and CdTe quantum dots (QDs) for bioconjugation. We employed an evaporation-condensation technique, also known as solvated metal atom dispersion (SMAD), followed by a digestive ripening procedure. This method has been used to synthesize both metal nanoparticles and semiconductors in the gram scale with several stabilizing ligands in various solvents. The SMAD technique comprised evaporation condensation and stabilization of CdSe or CdTe in tetrahydrofuran. The as-prepared product was then digestively ripened in both water and dimethyl formamide, leading to narrowing of the particle size distributions. The ligands were synthesized by nucleophilic substitution (S(N)2) reactions using 4,4'-bipyridine as a nucleophile. Confocal microscopy images revealed the orange color of the nanocrystalline QDs with diameters of ~5 nm. The size has been confirmed by using transmission electron microscopy. As a part of our strategy, 85% of the 4,4'-bipyridinium salt was synthesized as propionic acid derivative and used to both stabilize the QDs in water and label basic amino acids and different biomarkers utilizing the carboxylic acid functional group. Fifteen percent of the 4,4'-bipyridinium salt was synthesized as N-propyl maleimide and used as a second ligand to label any protein containing the amino acid cysteine by means of a 1,4-Michael addition.

Influence of paraffin wax characteristics on the formulation of wax-based binders and their debinding from green molded parts using two comparative techniques

The influence of paraffin wax characteristics on the formulation of wax-based binders has been examined. Four paraffin waxes (PW 1, PW 2, PW 3 and PW 4) were physically and molecularly evaluated and four binder systems 1–4 were formulated by mixing the major binder consisting of the paraffin wax with stearic acid (SA) and the minor binder; poly (ethylene-co-vinyl acetate) (EVA). Differential scanning calorimetric (DSC) and thermo gravimetric analysis (TGA) were used to evaluate the thermal characteristics of the pure binder components and the formulated binder systems. Also, the rheological properties of the formulated binder systems and feedstock were studied to measure their viscosities. Data indicated that the binder system no. 4 consisted of 35 wt.% EVA (containing vinyl acetate content of 9 wt.%), 62 wt.% of PW 4 and 3 wt.% of SA is the preferable binder for powder compression or injection molding. Also, in order to compare between the two debinding techniques (solvent evaporation–condensation and solvent immersion techniques) to extract the soluble binder components (paraffin wax and SA) completely from the green molded parts, powder compression molded parts were prepared and subjected to both techniques. It can be concluded that solvent immersion is a preferable technique as it saves the amount of solvent used as compared with the evaporation–condensation technique. Consequently, the solvent immersion technique using cyclohexane solvent at extraction temperature of 40 °C and after extraction time of 5 h are the most suitable conditions for extracting the major binder and SA constituents completely from the binder mixture in the green molded part.

Luminescence response of ZnO nanowires to gas adsorption

Zinc oxide nanowires were synthesized by means of evaporation–condensation technique and their green photoluminescence emission at room temperature was studied during exposure to nitrogen dioxide, ethanol and humidity. A reversible modification of static photoluminescence efficiency was obtained upon exposure to low concentrations of nitrogen dioxide. The optical sensor was able to detect NO 2 values as low as 0.1 ppm in dry air, that is the attention level for outdoor detection. Time-resolved photoluminescence measurements in presence of NO 2 showed small modification of recombination rates and lifetimes due to introduction of quencher gas. The results support a surface static quenching model, according to which the gas molecules suppress a fraction of radiative transitions instead of merely reducing their probabilities.

Size effects on melting and wetting in the Ga–Pb nano-alloy

Ga–Pb alloys with 15 at% Pb mean concentration have been prepared at the nanoscale by means of evaporation-condensation technique in ultra high vacuum conditions. Transmission electron microscope images indicate that at room temperature, the system is a two-components breath figure composed of liquid Ga nanodrops containing Pb nanocrystals. Some thermodynamic properties of this nano-alloy are investigated for different temperatures and particle sizes. The results obtained put in evidence a large modification of the Ga–Pb bulk phase diagram: a decrease of the melting temperatures of the two components as well as the ones of the miscibility gap. Changes in the microscopic structure of the system as a function of temperature have been investigated and a full wetting transition from a dry to a completely wet state has been put in evidence.

Silica coated nanoparticles: Synthesis, magnetic properties and spin structure

In therecent years, magnetic nanoparticles have been extensively studied for their superparamagnetic properties providing useful labels in biology or for fundamental aspects including the size dependence of magnetic atomic moment and the effect of surface anisotropy. In most cases, the particles were smaller than 10 nm and interestingly, the sizes ranging between 10 and 100 nm have been poorly investigated until now. This is mainly due to the fact that usual chemical routes produce 5–10 nm oxide or metallic particles or eventually 20 nm at most. On the over side, atomization techniques yield particles in the micrometer range. Metallic particles are particularly interesting for better magnetic properties compared to oxides, but they have two big drawbacks: they are not biocompatible and they are conducting electricity. Consequently, it’s necessary to produce core–shell particles, for which the shell is biocompatible and insulating and with a perfect control of thickness and uniformity of that shell. In this work, we are studying metallic particles synthesized by an original evaporation–condensation technique that produces particles of several tens of nanometers. We prepared hard magnetic cobalt particles and soft FeNi ones coated with a silica shell using a modified sol–gel method. Morphological and magnetic properties are presented, showing the efficiency of ultrasonic sol–gel process for that purpose.

Optical properties of silicon micro and nanocrystals

Silicon nanocrystal aggregates have been produced in an inert argon gas by a pulsed laser vaporization-condensation technique using the second harmonic of a Nd: YAG laser. In our previous work, it has been shown that materials generated by evaporation-condensation technique present a variety of structures depending on the conditions of production. A theoretical model has been elaborated from a multitude of metallic samples, taking into consideration the effect of the main physical factors on the resulting morphology. This model has been applied to silicon in order to produce silicon nanocrystals with specific structural characteristics. We carried out an investigation of the influence of the structure on the optical properties of silicon nanocrystals. In this report, we present the first results from this investigation. We have explored the inert gas pressure variation effect on the resulting nanocrystallite structures. Investigation under scanning electron microscopy (SEM) has revealed a weblike arrangement whose density gradually increases with the value of pressure. The deposits have been exposed to ambient air for eight months before photoluminescence (PL) measurements. The oxidized nanocrystals exhibited PL and the broad bands seem composed of multiple narrower bands. Silicon nanocrystals are the best candidates for the understanding of the extended red emission (ERE) visible in spectroscopic observations of many astronomical objects.

Three-body collisions as a particle formation mechanism in silver nanoparticle synthesis

Silver nanoparticles were prepared in a tubular flow reactor using an evaporation–condensation technique. The size distribution of the particles was measured using standard aerosol instruments and electron microscopy. A comparison with results obtained by a discrete population balance model with molecule-by-molecule resolution suggest that the particles probably nucleate kinetically through a dimerization process instead of a thermodynamic pathway over a free energy barrier, as is typically described by classical nucleation theory. Furthermore, the kinetic rate of dimerization seems to be accompanied by a correction term, associated with the requirement of energy and momentum conservation in molecule–molecule collisions. This energy conservation requires the presence of three-body collisions at the very initial step of particle formation.

Ellipsometric study of optical properties of liquid Ga nanoparticles

The investigation of the optical properties of liquid Ga nanoparticles embedded in a dielectric matrix by means of spectroscopic ellipsometry is reported. The particles, which have the shape of truncated spheres and a radius which is varied in a controlled way between 5 and 16 nm, are grown by the evaporation-condensation technique. The results are discussed in terms of the current effective medium models and give new information on the distribution of the particles in the matrix as well as on their optical properties. A resonance peak due to the plasmon-polariton electron excitations in the particles is observed in the imaginary part of the effective dielectric function of the layer. Its position shifts to higher photon energies and the half width of the resonance increases with the decrease of the particle size. The dielectric function of the particles is parametrized using the Drude dispersion equation. The obtained electron damping parameter increases with the decrease of the particle size in accordance with the predictions of the size theories of the optical properties of small particles.

Raman versus interband absorption in Ge quantum dots

In this work, we present evidence of quantum confinement effects on Ge nanocrystals, grown by an evaporation–condensation technique, through the inspection of the above the gap spectral structures and the Raman peak. In particular, when the nanoparticles size is reduced, the E 2 absorption peak shows a relevant blueshift, whereas the Γ 5 + phonon peak has a contemporary broadening and redshift. This different behavior is related to the different curvature of the electronic and phononic bands which originate the structures.

Beryllium armour produced by evaporation–condensation technique

Beryllium, as armour material for ITER plasma facing components, has a limited erosion lifetime. In order to repair the surface of eroded tiles in-situ, Be-deposition technologies are under consideration. One of them uses the physical vapour deposition of beryllium on copper or beryllium substrate produced by a hot Be-target placed in the vicinity of this substrate. Three different options for using this technology for ITER Be-armour application are considered. The first option is the repair in-situ of eroded Be-tiles. The second option suggests the use of this technology to provide the joining of Be to Cu-substrate. The third option assumes the use of evaporated–condensed beryllium as a bulk tile material bonded to copper substrate by conventional joining (Brazing et al.) techniques. The first results and prospects of these approaches are presented below.

In situ determination of the activation energy for restructuring of nanometer aerosol agglomerates

A new approach to the kinetics of the rearrangement of aerosol agglomerates is presented. This analysis is based on the change in free energy per primary particle during restructuring. The excess free energy compared with the final state drives the agglomerate to become more compact which results in an increase in the coordination number, as estimated from the changing fractal dimension of the aerosol agglomerates The analysis was tested on agglomerates of nanometer silver and copper particles produced by an evaporation-condensation technique and by laser ablation. The assumption that the rearrangement is an activated process was supported by the results. It was concluded that the interaction between the primary particles occurs over a short range. The activation energies were one order of magnitude lower than the bond energies expected from the bulk Hamaker constants for silver and copper. Within the measured size range no significant difference in the activation energies of silver and copper agglomerates was found. A maximum in the activation energy was found for particles about 18 nm in diameter. Larger particles showed decreasing activation energy with increasing diameter. The addition of oxygen (50%) before the agglomeration of the primary particles increased the activation energy by a factor of two and shifted the maximum in the activation energy to 15 nm. The prefactor in the rate coefficient for restructuring increased by four orders of magnitude when oxygen was added

Self Organized Growth and Ultrafast Electron Dynamics in Metallic Nanoparticles

ABSTRACTWe present ultrafast transient reflectivity measurements performed on metallic tin nanoparticles with an average radius between 20 and 60 Å in amorphous matrix. The samples, grown using an evaporation-condensation technique, were characterized by a relatively low nanocrystals size dispersion and a negligible clusters-matrix interaction. The excitation decays exhibited a size-dependent behaviour, which is interpreted in terms of the important role played by the electron-surface interactions.

Properties of ferromagnetic micropowders

Very small particles of iron, cobalt, and iron-cobalt alloys have been prepared by an evaporation-condensation technique. The crystal structure and shape of these particles have been investigated by X-ray diffraction and electron microscopy. The iron and alloy particles were all found to be bcc and the cobalt particles fcc. No hcp cobalt was observed. The shape of all particles was predominantly spherical. The electron microscope showed that the particles possessed a distribution of sizes and were linked together to form chains. Magnetic measurements have been carried out at 290 K on assemblies of these particles. Coercivity, saturation and remanence curves obtained using a Faraday balance magnetometer and pulsed field magnetometer are presented. These show the particles to have fairly high coercivities (typically 1 kOe) but fairly low remanence to saturation ratios (typically 0.25).