Evaporation Of Powder Research Articles

Sublimation rate of solid NaCl powders and evaporation rate of liquid NaCl upon heating in vacuum and air

The volatilization of sodium chloride (NaCl) is important for multiple applications, such as energy storage, manufacturing porous parts, and purification and recycling of composites. Until now, only limited information on this feature has been published. To expand the knowledge in this field, we investigated the sublimation and evaporation of two NaCl powders by thermal gravimetry in vacuum and air. The study has shown that the volatilization kinetics of powders with different shapes and sizes are identical. The volatilization of NaCl powders in vacuum occurs mainly by sublimation before melting. In contrast, the volatilization of NaCl in the air is preferentially caused by the evaporation of the melt. In a vacuum, the evaporation of NaCl powder after melting is significantly slower than the sublimation before melting, because of a drastic decrease in the volatilization area. The Hertz-Knudsen relation with an appropriate fitting coefficient satisfactorily describes the mass loss by volatilization in vacuum and air.

In-situ synthesis of SiC/SiO2 nanowires by catalyst-free thermal evaporation of silicon powder and their photoluminescence properties

Core-shell structured SiC/SiO2 nanowires (SiC/SiO2 NWs) were synthesized by a simple thermal evaporation method without a catalyst. The influence of the growth temperature and holding time on the microstructure and composition of the nanowires were investigated. The results indicate that within the temperature range of 1150 to 1550 °C, the color of SiC/SiO2 nanowires gradually transitions from pure white to off-white with increasing temperature. During this process, the average diameter of SiC/SiO2 increases from ∼74 nm to ∼291 nm, while the surface SiO2 layer thickness decreases from ∼17 nm to ∼5 nm, with nanowires can reach lengths of hundreds of micrometres. Variations in supersaturation of SiO and CO at different temperatures lead to discrepancies in nanowire diameter and SiO2 shell thickness. At 1350 °C, prolonged holding time enhances silicon powder reaction, resulting in increased structural disorder of the obtained SiC/SiO2 nanowires. The nanowire growth follows a vapor-solid (VS) mechanism. Additionally, the study demonstrates that the photoluminescence (PL) characteristics of the nanowires exhibit a blue shift attributable to their nanoscale dimensions, while variations in emission spectra correlate with stacking faults, SiC diameter, and SiO2 thickness. This work may be provide a theoretical basis for preparing SiC/SiO2 nanowires with different diameters and SiO2 shell thicknesses, which is crucial for advancing the development and application of SiC/SiO2 nanoceramics.

Synthesis of binder-free nanostructured MoS2 films for optoelectronic applications

The binder-free polycrystalline nanostructured molybdenum disulfide (MoS2) films are synthesized on glass substrates placed at 15, 16 and 17 cm with respect to source material by powder vapor transport technique. The X-rays diffraction analysis confirms the development of different diffraction planes related to MoS2 and Mo2S3 phases. The formation of surface morphologies (nano-boxes and nano-fibers) of MoS2 films is associated with increasing substrate distances. The changes in reflectance (0.18–0.09), refractive index (2.52–1.91), energy band gap (1.62–2 eV), Urbach energy (0.61–1.11 eV), dielectric constant (7-5.6), dissipation factor (0.04–0.06), surface/volume energy loss functions (0.0017–0.005/0.002–0.005), optical & electrical conductivities (1.23–2.04 × 1014 s−1 and 9.86–6.70 × 1019 S m−1), single oscillator energy (5.70–3.36 eV), dispersion energy (26.45–5.80 eV), nonlinear and static refractive index (0.041–1.58 × 10−5, 5.64–2.72), linear & nonlinear optical susceptibilities (0.37–0.14 and 0.011–6.16 × 10−6) are strongly associated with increasing substrate distances. Results indicate that the synthesized MoS2 films can be used in optoelectronic and solar cell devices.

Synthesis of flower like microstructured CdZnS films for optoelectronic applications by powder vapor transport technique

Cadmium zinc sulfide (CdZnS) is a remarkable semiconducting material used as window layer in solar cells. Herein, the flower’s like microstructured CdZnS film is synthesized by powder vapor transport (PVT) technique. The structural parameters like lattice constant, various diffraction planes, crystallinity, preferential orientation factor and standard deviation of CdZnS film of good quality growing preferentially along (110) orientations. The growth of longitudinal optical phonons modes at 303 and 599 cm−1 confirms the synthesis of CdZnS film. The values of transmittance and refractive index are ranged from 89.9%–95.2% and 1.53–2.67 whereas the values of energy band gap, oscillator energy and dispersion energy are found to be 2.79, 0.73 and 1.73 eV respectively. The values of dielectric constant are increased with increasing photon energy. The smaller values of dissipation factor and volume/surface energy loss functions of CdZnS film is suitable to make it a good quality capacitor. The electrical conductivity (1.68×103 S cm −1 ) of CdZnS film is increased nonlinearly with increasing temperature and the activation energy is found to be 0.31 eV. It is determined that the synthesized CdZnS film may be used as window layer in solar cells and to make good quality capacitor, hence it may be used in optoelectronic applications.

Synthesis and Physical Characteristics of Undoped and Potassium-Doped Cubic Tungsten Trioxide Nanowires through Thermal Evaporation.

We report an efficient method to synthesize undoped and K-doped rare cubic tungsten trioxide nanowires through the thermal evaporation of WO3 powder without a catalyst. The WO3 nanowires are reproducible and stable with a low-cost growth process. The thermal evaporation processing was conducted in a three-zone horizontal tube furnace over a temperature range of 550-850 °C, where multiple substrates were placed at different temperature zones. The processing parameters, including pressure, temperature, type of gas, and flow rate, were varied and studied in terms of their influence on the morphology, aspect ratio and density of the nanowires. The morphologies of the products were observed with scanning electron microscopy. High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanostructures. Additionally, the growth mechanism has been proposed. Furthermore, we investigated the potassium doping effect on the physical properties of the nanostructures. Photoluminescence measurements show that there were shorter emission bands at 360 nm and 410 nm. Field emission measurements show that the doping effect significantly reduced the turn-on electric field and increased the enhancement factor. Furthermore, as compared with related previous research, the K-doped WO3 nanowires synthesized in this study exhibited excellent field emission properties, including a superior field enhancement factor and turn-on electric field. The study reveals the potential of WO3 nanowires in promising applications for sensors, field emitters and light-emitting diodes.

Effect of laser power on the forming quality of Al6061 alloy manufactured via selective laser melting

A systematic work was studied to illustrate the influence of laser power on the forming quality of Al6061 alloy by selective laser melting (SLM). The relationship between laser power and molten pool was simulated by finite element analysis (FEA). Phase composition, defects, and microhardness were also measured and analyzed. The results show that, with the increase of laser power, the molten pool gradually changes from rectangular shape to droplet shape. And the cooling rate gradually increases from 3.282 × 104°C/s to 5.189 × 104°C/s. Higher laser power (400 W) is accompanied by higher molten pool maximum temperature (2012.73°C). This may lead to larger temperature gradient inside the sample causing evaporation and spatter of powder. On the contrary, lower laser power leads to unmelt of some powders, which increases the number of pore defects and influences the forming quality of samples. X-ray diffractogram (XRD) displays the Al6061 alloy characterized by the obvious preferred orientation under different laser powers and the grain size increased from 32.57 nm to 35.38 nm. With the increase of laser power, the number of defects, especially holes and microcracks, was first decreased and then increased. However, the microhardness of the sample decreased almost linearly from 98.6 HV0.05 to 88.86 HV0.05. All changes are the result of the comprehensive action of laser power and molten pool state. Besides, the action mechanism of laser power on the forming quality was also clarified in this work.

Structural and optical properties of broccoli-based nanostructured ZnS films synthesized by powder vapor transport technique

Structural and optical properties of broccoli-based nanostructured ZnS films synthesized by powder vapor transport technique

Effect of the metallization method on properties of hybrid zirconia/Ti–6Al–4V joints

The addition of titanium powder and physical vapor deposition of titanium were applied for metallization of zirconia surface. The hybrid members of stabilized ZrO2/Ti–6Al–4V were fabricated using the Ag–28Cu filler metal. Different phases including TiCu3, Ti3Cu3O, Ti2Cu, and Ti6O were observed in the microstructure of joints. The sound joints were obtained when physical vapor deposition method was used for metallization; while various defects were observed after addition of the metallic powder to the joint. The increased thickness of filler metal or the metallized layer of zirconia promoted formation of the interaction layer between ceramic and filler metal. The formation of Ti3Cu3O along the joint interface encouraged the brittle fracture and decreased strength of the dissimilar joint. The maximum shear strength of the joint was obtained for the specimen which was metallized for 6 min by the physical vapor deposition method and was joined using the 50 μm thick filler metal.

Role of annealing temperature on structural and optical properties of zinc oxy-nitride films synthesized by powder vapor transport technique

Zinc oxy-nitride (ZnON) is an emerging semiconductor having tunable energy bandgap (Eg) and refractive index (n). Herein, the effect of annealing temperature on ZnON films synthesized on glass substrates at different (50, 100 and 150 sccm) nitrogen gas flow rates (NGFR) by simple powder vapor transport (PVT) technique is studied. All the synthesized ZnON films are annealed at 300 °C for 60 min. The unannealed and annealed ZnON (Un-&-An-ZnON) films are characterized by XRD, SEM, Raman and UV spectroscopies. XRD analysis confirms the formation of polycrystalline ZnN films and no diffraction plane related to oxide phase. The crystallinity of Un-ZnN films is increased after annealing, however, it is maximum for 100 sccm NGFR. Raman analysis indicates the presence of vibrational modes related to ZnN and ZnO phases, thereby confirming the formation of ZnON films. After annealing, the surface morphologies of Un-ZnON films is transformed from nano-sheets/nano-blocks to rounded nanoparticles. The change in structural and morphological features of ZnON films, associated with annealing temperature causes to create stresses and defects and hence Eg and n. The values of n (1.85–1.87) and Eg (2.6–2.7 eV) of Un-ZnON films are increased to (1.98–2.62) and (3.16–3.25 eV), after annealing, respectively. These inexpensive but high quality ZnON films can be used for semiconducting and optoelectronic devices.

Synthesis, structural and optical properties of ZnS/ZnO heterostructure-alloy hexagonal micropyramids

Heterostructure alloys with controlled structure and composition are essential for future electronics and optoelectronics. While heterostructure formation creates sharp electronic junction, alloying allows bandgap tunability. Herein, ZnS/ZnO heterostructure-alloy hexagonal micropyramids are grown on Si/SiO2 wafers for the first time by facile thermal evaporation of ZnS powder. It is found that the pyramids with a based size of few micrometers are grown along different crystallographic directions and neighbored by ZnS microrods. XRD and XPS spectra showed that ZnS, ZnO, and ZnSO wurtzite phases coexist in the as-received samples. FESEM images, in situ point, and EDS elemental mapping spectra reveal that the micropyramids are composed of Zn, S, O, but each element's ratio changes with substrate temperature and is different at different faces of a single micropyramid. Using a high-spatial CL-FESEM, the profile of CL spectra along the substrate and at different faces in a single micropyramid were in-situ measured and disclosed red-shifted of ZnS band-edge emission with increasing substrate temperature, and the formation of new emission bands in the range from ∼345 to 352 nm. This new emission band is attributed to the formation of the ZnSO alloy phase. Our results demonstrated that the optical properties of the obtained ZnS/ZnO heterostructure-alloy hexagonal micropyramids could be tunned by controlling the substrate temperature and indicates potential applications of the ZnS/ZnO heterostructure alloy in optoelectronic and photonic applications.

Analysis of the ZnO/Cu2O and CdSe/Cu2O Thin Film Hetero-structure Electrode for Photo Electro chemical Solar Cell Applications

This paper proposes an economical route to the production of CdSe/Cu2O and ZnO/Cu2Obased on commercial ZnO, CdSe corpuscle. The deposition of CdSe thin films was prepared by partial thermal oxidation method, Powder Vaporization method, and microwave oven method on the cleaned Cu2O substrate at room temperature. The solar cell fabrication process is greatly simplified by this method and opens a door in the direction of inexpensive techniques based on saleable available materials. The results show that the solar cell based on the mixture of CdSe/Cu2O has electron transportability, better light absorption, and high power conversion efficiency (PCE) of 0.7 was obtained. These materials have been characterized using FTIR, at which numerous peaks are present in the sample, and were assessed in detail. Multiple current-voltage characteristic curves were plotted, an open-circuit voltage VOC, a short circuit current Isc, and the maximum power points Pmax were also noted. This work throws off more light in enhancing the photo response of the electrode in both solar H2generation and photo electro chemical solar cell

Influences of Powder Source Porosity on Mass Transport during AlN Crystal Growth Using Physical Vapor Transport Method

We developed a two-dimensional (2D) transport model to investigate mass transport during bulk AlN crystal growth via the physical vapor transport (PVT) process using the finite element method (FEM), taking the powder source porosity, buoyancy, and vapor diffusion into account. The porosity effects of the powder source on mass transport under various growth conditions were investigated in detail. The simulation results show that the porosity of the powder source significantly affects the mass transport process during AlN sublimation growth. When the porosity of the powder source decreases, the growth rate becomes more uniform along the seed deposition surface, although the sublimation rate and crystal growth rate decrease, which can be attributed to the reduced specific surface area of the powder source and the reduced flow rate of Al vapor in the powder source. A flat growth interface can be achieved at a porosity of 0.2 under our specific growth conditions, which in turn facilitate the growth of high-quality AlN crystals and better yield. The decomposition of the powder source and the transport of Al vapor in the growth chamber can be suppressed by increasing the pressure. In addition, the AlN growth rate variation along the deposition surface can be attributed to the Al vapor pressure gradient caused by the temperature difference in the growth chamber.

Preparation of nano-crystalline tungsten powders from gaseous WO2(OH)2

The industrial production of tungsten powder is carried out by the reduction of tungsten oxide powder via hydrogen. In this process, the size of the W particles is limited to particle sizes larger than 100 nm. To get below this limit, alternative processes are needed. In the current work, the possibility of preparing W powder below 100 nm via a vapour phase reduction of volatile WO2(OH)2 by hydrogen was investigated. The process consists of two stages. In the first stag,e WO2(OH)2 is formed by reacting WO3 with water vapour at temperatures of 1000–1100 °C. In the second stage, WO2(OH)2 is reduced by hydrogen at about 1000 °C to form metallic tungsten. The influence of process parameters such as furnace temperature, humidity and gas flow on the WO2(OH)2 evaporation and formation of tungsten powder was investigated. The characterization of the resulting powders was performed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). By optimization of the reaction conditions, powder with a metallic tungsten content of about 70 at% besides tungsten oxides was produced with metal particle sizes down to 5 nm. Further optimization should lead to a high tungsten content and a high product yield. Due to the small particle size, applications in catalysis might be possible, although an industrial realization of the process seems unrealistic at moment.

Numerical Analysis of the Interactions between Plasma Jet and Powder Particles in PS-PVD Conditions

Plasma spray-physical vapor deposition (PS-PVD) refers to a very low-pressure (~100 Pa) deposition process in which a powder is injected in a high-enthalpy plasma jet, and mostly vaporized and recondensed onto a substrate to form a coating with a specific microstructure (e.g., columnar). A key issue is the selection of the powder particle size that could be evaporated under specific spray conditions. Powder evaporation takes place, first, in the plasma torch between the injection location and nozzle exit and, then, in the deposition chamber from the nozzle exit to the substrate location. This work aims to calculate the size of the particles that can be evaporated in both stages of the process. It deals with an yttria-stabilized zirconia powder and two commercial plasma torches operated at different arc powers with gas mixtures of argon and helium or argon and hydrogen. First, it used computational fluid dynamics simulations to calculate the velocity and temperature fields of the plasma jets under very low-pressure plasma conditions. Then, it estimated the evaporation of the particles injected in both plasma jets assuming an isothermal evaporation process coupled with momentum and heat transfer plasma-particle models in a rarefied plasma. The calculations showed that, for different powers of the Ar–H2 and the Ar–He operating conditions of this study, the heat flux from the plasma jet to particles inside the torch is much higher than that transferred in the deposition chamber while the specific enthalpy transferred to particles is comparable. The argon-helium mixture is more efficient than the argon-hydrogen mixture to evaporate the particles. Particles less than 2 μm in diameter could be fully evaporated in the Ar–He plasma jet while they should be less than 1 µm in diameter in the Ar–H2 plasma jet.

Improving the thermoelectric properties of zinc tin oxide thin films by varying post growth annealing duration

In this research work, we have successfully improved the thermoelectric properties of Zinc tin oxide thin films by controlling the post annealing duration. Initially, zinc tin oxide thin films were grown by direct evaporation of zinc and tin metal powder using the thermal evaporation method. After deposition, post growth annealing of the grown thin films was performed at 500 °C for different annealing durations (0.5, 1, 1.5 & 2 h). XRD data show the structural transformation from amorphous to mixed phases of Zn2SnO4, ZnSnO3, ZnO, and SnO2 with the increase in post-growth annealing duration. While the sample annealed for 2 h represent only two phases of ZnO and ZnSnO3. UV–vis data shows the decrease in band gap value from 3.8 to 3.61 eV with the increase in annealing duration. Seebeck data suggested the improvement in the Seebeck coefficient value from 24 to 104 μV/°C with the increase in annealing time duration while the electrical conductivity value was also improved from 34 to 63 S/cm. This increase in Seebeck coefficient and electrical conductivity was associated with the phase transformation into ZnSnO3 by suppression of un-wanted secondary phases leads to a high power factor up to 3.1 × 10−4 Wm−1K−2. In addition, we have also performed Raman and SEM as supplementary measurements to support our purposed argument.

A new approach for the growth of copper nitrides thin films by thermal evaporation using nitrogen as source gas

Thin films of copper nitride (Cu3N) were successfully synthesized by thermal evaporation method. The Cu powder was evaporated on glass substrate ina horizontal glass tube furnace having central temperature 1000 °C under a vacuum of 10−2 m Torr for 25 mints. After evaporation of Cu powder, the temperature of tube furnace was set as 300 °C and nitrogen gas was flown into a tube furnace at a rate of 100 sccm for different time durations of 2–8 h respectively. XRD data demonstrated that only one XRD peak (53.916°) of Cu3N phase was observed for sample prepared using nitrogen gas flow time duration 2 h. But as we increased the time duration for nitrogen flow, three diffraction peaks at 2theta 23.005°, 32.9° and 38.228° were observed, which are related due to the (100), (111) and (200) planes of Copper Nitride. The intensity of Cu3N related diffraction peaks was found to be increased with increasing the time duration which suggested that good crystal quality was observed in the sample having the time duration of 8 h. We argued that for large time durations of nitrogen gas flow, the surface diffusion of the adatom is increased causes the nitrogen atoms react with free Cu atoms to form Cu3N thin films. Raman spectroscopy data demonstrated peaks of Cu3N structure at 487 and 608 cm−1 for samples prepared using 6 and 8 h time duration. SEM data further confirmed our XRD and Raman data that sample prepared using 8 h time duration has best crystal quality. The XPS and FTIR measurements were also performed on 8 h annealed sample to further justified the presence of Cu3N structure.

Hybrid perovskite films deposited by thermal evaporation from a single source

Hybrid perovskites, such as MAPbI3, are very promising materials to fabricate highly efficient and low-cost solar cells and photodetectors. In this work, we propose a new method of deposition of hybrid perovskite thin films through thermal evaporation of MAPbI3 powder from a single source for which was evaluated the effect of evaporation parameters (distance, time, substrate temperature, chamber pressure, and crucible heating rate) on the structural, optical, and morphological properties. It was found that it is necessary to control adequately the chamber partial pressure, substrate temperature, and the crucible heating rate in order to obtain single-phase MAPbI3 perovskite films. Also, it was studied the solvent annealing treatment as a method to increase the grain size of evaporated films. Finally, a study of transient and steady-state photoconductivity allowed verifying that the evaporated MAPbI3 films present fast band to band photogeneration and bimolecular recombination, and also that the grain size growth leads to an increase of the photoconductivity intensity due to the improvement of the diffusion length.

Elucidation of Molybdenum Trioxide Sulfurization: Mechanistic Insights into Two-Dimensional Molybdenum Disulfide Growth.

Powder vaporization is a common method for the generation of large-area, single-crystal, two-dimensional molybdenum disulfide. While commonly employed as a growth method, the fundamental molecular mechanisms are not well understood. Recent ab initio analyses have shown that molybdenum oxysulfide rings play a key role in the sulfurization of molybdenum trioxide from elemental sulfur. In this study, we utilize molecular dynamics simulations with a reactive force field and ab initio calculations to elucidate the reaction pathway of sulfur with molybdenum trioxide. The molecular dynamics simulations demonstrated that for all sulfur allotropes the reaction pathway could be reduced to that of disulfur, trisulfur, or a combination of the two and that molybdenum trioxide can catalyze the decomposition of larger sulfur allotropes. Ab initio calculations were used to illuminate the intermediates and transition states in the reaction pathways for disulfur and trisulfur. Analysis of the temperature dependence of the transition state energies shows that the maximum reaction rates occur between 1000 and 1100 K, which corresponds with commonly reported experimental growth temperatures for molybdenum disulfide.

TiO x /Pt3Ti(111) surface-directed formation of electronically responsive supramolecular assemblies of tungsten oxide clusters.

Highly ordered titanium oxide films grown on a Pt3Ti(111) alloy surface were utilized for the controlled immobilization and tip-induced electric field-triggered electronic manipulation of nanoscopic W3O9 clusters. Depending on the operating conditions, two different stable oxide phases, z’-TiOx and w’-TiOx, were produced. These phases show a strong effect on the adsorption characteristics and reactivity of W3O9 clusters, which are formed as a result of thermal evaporation of WO3 powder on the complex TiOx/Pt3Ti(111) surfaces under ultra-high vacuum conditions. The physisorbed tritungsten nano-oxides were found as isolated single units located on the metallic attraction points or as supramolecular self-assemblies with a W3O9-capped hexagonal scaffold of W3O9 units. By applying scanning tunneling microscopy to the W3O9–(W3O9)6 structures, individual units underwent a tip-induced reduction to W3O8. At elevated temperatures, agglomeration and growth of large WO3 islands, which thickness is strongly limited to a maximum of two unit cells, were observed. The findings boost progress toward template-directed nucleation, growth, networking, and charge state manipulation of functional molecular nanostructures on surfaces using operando techniques.

Synthesis of nanograined ZnO nanorods functionalized with NiO nanoparticles and their enhanced hydrogen sensing properties

NiO nanoparticle (NP)-functionalized nanograined ZnO nanorods (NRs) were grown by using the thermal evaporation of ZnSe powders; this was followed by the thermal oxidation of the ZnSe NRs to synthesize ZnO NRs and a solvothermal process for NiO functionalization. The diameters of the grains in the synthesized nanograined ZnO NRs are in the range of 50–150 nm. The ZnO grains were not spherical, but they were shaped like rice grains. The diameters and the lengths of the ZnO NRs were in the range of 40–50 nm and 1–6 µm, respectively. The diameters of the NiO NPs were in the range of 40–80 nm. A multiple-networked chemiresistive sensor was fabricated by pouring the IPA solution containing NiO NP-decorated nanograined ZnO NRs onto SiO2/Si substrates with a patterned electrode. A pristine nanograined ZnO NR sensor was also prepared in a similar manner. The NiO NP-functionalized nanograined ZnO NR sensor exhibited a greater and faster response to H2, as compared to its pristine nanograined ZnO counterpart; it also showed higher selectivity toward H2 against other reducing gases, as compared to the pristine nanograined ZnO counterpart. Herein, the origin of the enhanced sensing performance of the NiO NP-functionalized nanograined ZnO sensor is discussed in detail.