Minutes In Vacuum Research Articles

Fabrication and investigation of zinc telluride thin films

Zinc Telluride ZnTe alloys and thin film have been fabricated and deposited on glass substrates by thermal evaporation method which may be a suitable window layer of zinc telluride with different annealing temperatures (373 and473) K for 60 minutes in vacuum. Deposited thin films with thickness 100 nm was characteristic by using X-ray diffraction XRD to know structures, Atomic Force Microscopy (AFM) to evaluate surface topology, morphology. It was found out that the vacuum annealing improves on thin ZnTe films structure and surface morphology. Structural analysis reveals that ZnTe films have zinc blende structure of cubic phase with (111) preferred reflection and grain size is enhanced from 8.6 to 16.7 nm with annealing. Optical properties where optical bandgap energy values slightly decreased (2.3-2.2) eV as the annealing temperatures.

The Investigation of Oven and Vacuum Oven Drying Kinetics and Mathematical Modelling of Golden Berries

Golden berry (Physalis peruviana) is a fruit that is natively cultivated in the Andean region. Due to its significant nutritional and functional properties, golden berry has been gradually attracting worldwide attention. In this study, oven and vacuum oven drying of golden berries were performed at 60, 70 and 80 °C. Throughout the experiments, the drying kinetic parameters of effective moisture diffusivity (Deff) and activation energy (Ea) were investigated. Moreover, mathematical modeling of drying data was established with the most known modeling equations presented in literature. Experiments revealed that the drying times decreased with increasing temperature and with vacuum addition. The highest and lowest drying times were encountered as 480 minutes in oven drying at 60 °C, and 195 minutes in vacuum oven drying at 80 °C, respectively. Deff values were calculated between 1.95×10-10-3.80×10-10 m2/s and 2.20×10-10-5.45×10-10 m2/s for oven and vacuum oven drying, respectively. Ea values, on the other hand, were found as 32.81 kJ/mol for oven drying and 44.30 kJ/mol for vacuum oven drying. Among the fourteen mathematical models applied to drying curve data, Midilli & Kucuk model provided the best fit for both oven and vacuum oven drying.

Свойства магнитотвердого порошкового сплава Fe – 30 Cr – 20 Co – Mo с повышенной пористостью

The purpose of this work is an experimental study of the influence of the sintering environment (vacuum and argon) on the structural and magnetic characteristics of the Fe – 30 Cr – 20 Co – Mo magnetically hard alloy with increased porosity. The material was synthesized by powder metallurgy. In the present work, studies were carried out on materials with a porosity of about 4 %. All porosity of the material was closed. Powders of pure elements were used to synthesize the alloy. The samples were sintered at a temperature of 1140 °C for 150 minutes in vacuum and argon. The experiments were carried out on materials in three states — after sintering, quenching material and material after heat treatment to obtain magnetic properties. Sintering in argon increases the density of samples by approximately 0.3 % compared to samples sintered in vacuum. Vacuum sintered material has slightly higher magnetic properties compared to argon sintered material, despite the lower density. Hardened samples have significantly higher plasticity compared to materials after sintering and after heat treatment. Such samples are deformed without fracture at a deformation of more than 60 %. Hardening simultaneously reduces the yield strength. Samples after sintering have the lowest plasticity (about 10 %), approximately three times less than after heat treatment. There is a good correlation between yield strength values and hardness data. For specimens with higher yield strengths, there are also higher hardness values. The grain size of the material sintered in vacuum is almost the same as the size of the material sintered in argon. Their size is about 30 µm. Irregularity is not observed, which indicates that the process of secondary recrystallization did not occur. Anisotropy is also not observed. Thus, it was experimentally established that the Fe – 30 Cr – 20 Co – Mo alloy can be sintered both in vacuum and in argon. In this case, the mechanical and magnetic properties are approximately at the same level acceptable for technical applications.

Bonding pressure effects on characteristics of microstructure, mechanical properties, and mass diffusivity of Ti-6Al-4V and TiAlNb diffusion-bonded joints

This research highlights the influence of bonding pressure on the features of diffusion-bonded joints (DBJs) between Ti6Al4V alloy and TiAlNb alloy investigated at 900 °C for 120 minutes in vacuum with variable pressures of 0.5, 1, 2, 3, and 4 MPa. Characterization of the bonded interfaces was conducted using optical microscopy and scanning electron microscopy in backscattered mode. A molecular dynamics (MD) model was developed with the commercial Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package utilizing second nearest neighbor modified embedded atom method (2NN MEAM) potentials to predict the diffusion mechanism with variable compressive pressures along the TiAlNb|Ti6Al4V joint interface. Microstructural characterization with light microscopy and scanning electron microscopy in back-scattered mode (SEM-BSE) along the TiAlNb|Ti6Al4V DBJs revealed no interfacial intermetallic phase nucleation. Energy dispersive spectroscopy (EDS) maps and line profiles helped to understand composition variation across the interface. The maximum joint tensile strength of ~ 875 MPa, ~ 13.1% elongation, and mass diffusivity on both sides were obtained at 4 MPa processing pressures with a significant tendency of diffusivity improvement in the TiAlNb side.

Microstructural Analysis of Ti/Ni Bilayer Ohmic Contacts on 4H-SiC Layers

The micro-structural analysis of Ti/Ni bilayer as Ohmic contacts to n-type 4H-SiC is reported. There was no carbon segregation at the interface between the NiSi layer and the 4H-SiC layer for Ti/Ni contacts, unlike pure Ni contacts. The diffraction pattern image shows the presence of the cubic NiSi film which grows on the SiC surface. The film interface with the SiC was uniform and more planar. An optimized contact in terms of contact morphology was achieved using a bilayer contact Ti/Ni (20/100nm) annealed at 1100 °C for 5 minutes in vacuum.

Vacuum brazing of 316L stainless steel based on additively manufactured and conventional material grades

Many industrial applications require components with an increasing geometric complexity and specific material properties. Furthermore, the production costs and the affordable production time have to be minimized in order to ensure competitiveness. These divergent objectives are difficult to achieve with a single manufacturing technology. Therefore, joining of selective laser melted (SLM) complex shaped parts to conventionally produced high-volume components provides a high potential. The current investigation focuses on vacuum brazing conventionally manufactured to non-hipped SLM generated AISI 316L stainless steel. Cylindrical samples (Ø 14 mm) were brazed using a B-Ni2 foil (50 µm) at 1050 °C for 30 minutes in vacuum (< 4.5·10-5 mbar) and directly cooled down to room temperature with 4 bar overpressure to prevent the formation of chromium carbides within the base material. It could be proven that the brazing quality is extremely sensitive to even marginal porosities (< 0.2 %) and/or oxide inclusions of the SLM microstructure. Therefore, the fracture mirror in SLM/conventional steel brazements was at the joint braze/SLM steel interface, leading to a joint strength of 317.4 MPa. This corresponds to only 67.4 % of the joint strength obtained with conventional steel, where the fracture propagated through the diffusion area.

Fabrication of Miniaturized Capacitive Pressure Sensor Using Thin Film Metallic Glass

In this paper, we proposed the process of the diaphragm for miniaturizing MEMS capacitive pressure sensor and controlling its sensitivity. We fabricated micro diaphragm using a Ru 65 Zr 30 Al 5 (at.%) thin film metallic glass (TFMG). The as-sputtered TFMG on Si substrate were annealed at 315-440°C for 5 minutes in vacuum. After annealing, micro diaphragms were fabricated by an etching Si substrate using a reactive ion etching system. Although the diaphragm without annealing had dome structure, the diaphragm annealed above 340°C formed a flat structure. The deflection of the diaphragm against applied pressure depended on the annealing temperature and decreased at higher temperatures. The pressure sensor was modeled using this diaphragms. The pressure measurement range and sensitivity were 250 Pa and 6.4×10-3 pF/Pa, respectively, for annealed at 340°C, and 1800 Pa, and 8.1 × 10-4 pF/Pa, respectively for annealed at 440°C.

Enhanced Dissolution of Platinum Group Metals Using Electroless Iron Deposition Pretreatment

In order to develop a new method for efficiently recovering platinum group metals (PGMs) from catalyst scraps, the authors investigated an efficient dissolution process where the material was pretreated by electroless Fe deposition. When Rh-loaded alumina powder was kept in aqua regia at 313 K (40 °C) for 30 to 60 minutes, the Rh hardly dissolved. Meanwhile, after electroless Fe plating using a bath containing sodium borohydride and potassium sodium tartrate as the reducing and complexing agents, respectively, approximately 60 pct of Rh was extracted by aqua regia at 313 K (40 °C) after 30 minutes. Furthermore, when heat treatment was performed at 1200 K (927 °C) for 60 minutes in vacuum after electroless plating, the extraction of Rh approached 100 pct for the same leaching conditions. The authors also confirmed that the Fe deposition pretreatment enhanced the dissolution of Pt and Pd. These results indicate that an effective and environmentally friendly process for the separation and extraction of PGMs from catalyst scraps can be developed utilizing this Fe deposition pretreatment.

Differing Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in Vacuum.

Azobenzenealkanethiols in self-assembled monolayers (SAMs) on Au(111) exhibit reversible trans-cis photoisomerization when diluted with alkanethiol spacers. Using these mixed SAMs, we show switching of the linear optical and second-harmonic response. The effective switching of these surface optical properties relies on a reasonably large cross section and a high photoisomerization yield as well as a long lifetime of the metastable cis isomer. We quantified the switching process by X-ray absorption spectroscopy. The cross sections for the trans-cis and cis-trans photoisomerization with 365 and 455 nm light, respectively, are 1 order of magnitude smaller than in solution. In vacuum, the 365 nm photostationary state comprises 50-74% of the molecules in the cis form, limited by their rapid thermal isomerization back to the trans state. In contrast, the 455 nm photostationary state contains nearly 100% trans-azobenzene. We determined time constants for the thermal cis-trans isomerization of only a few minutes in vacuum and in a dry nitrogen atmosphere but of more than 1 day in ambient air. Our results suggest that adventitious water adsorbed on the surface of the SAM stabilizes the polar cis configuration of azobenzene under ambient conditions. The back reaction rate constants differing by 2 orders of magnitude underline the huge influence of the environment and, accordingly, its importance when comparing various experiments.

Electrochemical Synthesis and Characterization of Cu2ZnSnS4 Thin Films

Cu2ZnSnS4 (CZTS) thin films have been electrochemically deposited from aqueous electrolyte containing CuCl2, ZnCl2, SnCl4 and Na2S2O3 onto fluorine doped tin oxide (FTO) coated glass substrates. A conventional three-electrode geometry consisting working, counter and reference electrodes was used to perform the electrochemical experiments. The films were deposited at - 1.1 V with respect to Ag/AgCl reference, which was optimized by cyclic voltammetry. CZTS layers were annealed in tubular furnace at 400°C for 15 minutes in vacuum. As-deposited and annealed CZTS films were characterized using range of characterization techniques to study the structural, optical, morphological, and compositional and optoelectronic properties. Annealed sample revealed (112), (220) and (312) planes corresponds to tetragonal kesterite CZTS structure and secondary peaks of CuZn alloy. The optical study shows that the band gap of the as-deposited CZTS film was found to be 1.68 eV. Upon annealing the optical band gap ~ 1.49 eV corresponds to CZTS were estimated from UV-Visible Spectroscopy and photoluminescence. Densely packed, void free and relatively uniform thin films were deposited by electrodeposition technique. The grain size has been increased upon the heat treatment. Copper and zinc rich off-stoichiometric films were deposited at -1.1 V. Current density-Voltage (J-V) measurements showed Schottkey behavior. The flat band potential and carrier concentration estimated by C-V measurement for annealed CZTS sample was 0.30 V and ~ 2.4 x 1016 cm-3 respectively.

The Effects of Processing Time on the Microstructure and Composition of Plasma Pack-Aluminized and -Oxidized Surface Layers on Low Carbon Steel

Low carbon steel was plasma pack aluminized at 973 K (700 °C) for 5, 10, and 15 minutes in vacuum of 15 mbar. A paste of aluminum was packed around the samples, and the process was carried out in glow discharge of argon gas in one step without further diffusion processes. The aluminized samples were oxidized at 973 K (700 °C) and 15 mbar for 60 minutes in synthetic air. The aluminized and oxidized layers were characterized for iron-aluminum intermetallic phases, local composition, morphology, and hardness of the phases. At 973 K (700 °C) after 5-, 10-, and 15-minute treatments, FeAl3 and Fe2Al5 intermetallic compounds were observed in the surface layers. After 60-minute oxidation, Fe3Al and FeAl compounds appeared at the interface between the compound layers and the oxide scale. Oxidation products were mainly Al2O3 and a few amounts of Fe3O4 and Fe2O3. The thicknesses of the compound layers on the samples were up to 350 μm. The maximum hardness of the aluminized layers was 980 HV0.5.

Electronic, Optical and Electrical Properties of Nickel Oxide Thin Films Grown by RF Magnetron Sputtering

Nickel oxide (NiO) thin films were grown on soda-lime glass substrates by RF magnetron sputtering method at room temperature (RT), and they were post-annealed at the temperatures of 100℃, 200℃, 300℃ and 400℃ for 30 minutes in vacuum. The electronic structure, optical and electrical properties of NiO thin films were investigated using X-ray photoelectron spectroscopy (XPS), reflection electron energy spectroscopy (REELS), UV-spectrometer and Hall Effect measurements, respectively. XPS results showed that the NiO thin films grown at RT and post annealed at temperatures below 300℃ had the NiO phase, but, at 400℃, the nickel metal phase became dominant. The band gaps of NiO thin films post annealed at temperatures below 300℃ were about 3.7 eV, but that at 400oC should not be measured clearly because of the dominance of Ni metal phase. The NiO thin films post-annealed at temperatures below 300℃ showed p-type conductivity with low electrical resistivity and high optical transmittance of 80% in the visible light region, but that post-annealed at 400℃ showed n-type semiconductor properties, and the average transmittance in the visible light region was less than 42%. Our results demonstrate that the post-annealing plays a crucial role in enhancing the electrical and optical properties of NiO thin films.

Effect of the annealing temperature on dynamic and structural properties of Co2FeAl thin films

10 nm and 50 nm thick Co 2 FeAl (CFA) thin films have been deposited on thermally oxidized Si(001) substrates by magnetron sputtering using a Tantalum cap layer and were then ex-situ annealed at 415°C, 515°C and 615°C during 15 minutes in vacuum. X-rays diffraction indicates that films CFA are polycrystalline and exhibit an in-plane isotropy growth. Ferromagnetic resonance measurements, using a microstrip line (MS-FMR), reveal a huge interfacial perpendicular magnetic anisotropy and small in-plane uniaxial anisotropy both annealing temperature-dependent. The MS-FMR data also allow concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with annealing temperature. Finally, the FMR linewidth decreases with increasing annealing temperature due to the enhancement of the chemical order, and allow deriving a very low intrinsic damping parameter (1.3×10 −3 at 615°C).

Annealing-induced magnetic moments detected by spin precession measurements in epitaxial graphene on SiC

We present results of non-local and three terminal (3T) spin precession measurements on spin injection devices fabricated on epitaxial graphene on SiC. The measurements were performed before and after an annealing step at 150 degrees Celsius for 15 minutes in vacuum. The values of spin relaxation length L_s and spin relaxation time tau_s obtained after annealing are reduced by a factor 2 and 4, respectively, compared to those before annealing. An apparent discrepancy between spin diffusion constant D_s and charge diffusion constant D_c can be resolved by investigating the temperature dependence of the g-factor, which is consistent with a model for paramagnetic magnetic moments.

Diffusion Bonding of 17-4 Precipitation Hardening Stainless Steel to Ti Alloy With and Without Ni Alloy Interlayer: Interface Microstructure and Mechanical Properties

In the present study, the diffusion bonding of 17-4 precipitation hardening stainless steel to Ti alloy with and without nickel alloy as intermediate material was carried out in the temperature range of 1073 K to 1223 K (800 °C to 950 °C) in steps of 298 K (25 °C) for 60 minutes in vacuum. The effects of bonding temperature on interfaces microstructures of bonded joint were analyzed by light optical and scanning electron microscopy. In the case of directly bonded stainless steel and titanium alloy, the layerwise α-Fe + χ, χ, FeTi + λ, FeTi + β-Ti phase, and phase mixture were observed at the bond interface. However, when nickel alloy was used as an interlayer, the interfaces indicate that Ni3Ti, NiTi, and NiTi2 are formed at the nickel alloy-titanium alloy interface and the PHSS-nickel alloy interface is free from intermetallics up to 1148 K (875 °C) and above this temperature, intermetallics were formed. The irregular-shaped particles of Fe5Cr35Ni40Ti15 have been observed within the Ni3Ti intermetallic layer. The joint tensile and shear strength were measured; a maximum tensile strength of ~477 MPa and shear strength of ~356.9 MPa along with ~4.2 pct elongation were obtained for the direct bonded joint when processed at 1173 K (900 °C). However, when nickel base alloy was used as an interlayer in the same materials at the bonding temperature of 1148 K (875 °C), the bond tensile and shear strengths increase to ~523.6 and ~389.6 MPa, respectively, along with 6.2 pct elongation.

Studies and Researches on the Obtaining of Sintered Gradual Porous Structures by Irregular Nickel Powders Sedimentation

The aim of this work is to obtain sintered porous membranes with graded structure for microfiltration by sedimentation and sintering of metallic powders. Our previous studies have demonstrated the possibility of obtaining sintered porous materials with graded structure by sedimentation. In this paper, irregular nickel particles were used having a grain size in the 2-90 µm range evaluated using scanning electron microscopy and laser scattering particle size analyzer. The powders were sedimented into a sintering die in a sedimentation medium consisting of water and dispersant agent. After drying, the samples were sintered at 1000°C for 10 minutes in vacuum (~1•10-3 Pa). The structures obtained were characterized by scanning electron microscopy and mercury porosimetry. The pore size distribution was between 5-72 µm. The flow rate - pressure drop curves were experimentally determined and the viscous permeability coefficient was calculated using Darcy’s law (Ψv=0.14•10-12 m2). The absolute filtration fineness measured was 20 µm and the relative filtration fineness (95%) obtained for our membranes was 11 µm respectively. The possible applications for the studied membrane are: water microfiltration, environmental technologies, filtering lubricants and cleaning agents

Structural Analysis of PM Biocomposites Based on Hydroxyapatite Nanopowders Elaborated by Spark Plasma Sintering Route

The objective of this research is the development of a detailed structural analysis of biocomposites with ceramic matrix of hydroxyapatite (Hap) reinforced by titanium (Ti), elaborated by powder metallurgy technology. Nanometric Hap powders (&lt;200nm) 75% wt and micrometric Ti powders (&lt;150μm) are homogenized in a high energy ball mill Pulverisette 6. Spark plasma sintering (SPS) is the sintering route able to lead to nanostructured sintered samples when nanopowders are used as raw material. The SPS parameters are: the sintering temperature, T=(1000-1100)°C and the maintaining time, t=(10-20) minutes in vacuum. The influence of the sintering parameters on the composites structures is monitored using the optical microscopy (OM), electronic microscopy (SEM) and the X-Ray diffraction (XRD).

The Influence of Processing Parameters on the Magnetic Properties of the Nanocrystalline Soft Magnetic Composites Based on Ni&lt;sub&gt;3&lt;/sub&gt;Fe

The nanocrystalline Ni3Fe powders were obtained via wet mechanical alloying route in argon atmosphere. As process control agent (PCA) the benzene (C6H6) was used. In order to release the internal stresses an annealing at 350 °C for 4 hours was performed. Alternatively, the nanocrystalline Ni3Fe powder was subjected to a process of incipient recrystallization at 600 °C for 30 minutes in vacuum. The recrystallised powders have a crystallite size of 30 nm. The magnetic properties (the frequencies dependence of permeability and magnetic losses) were investigated in AC field of 0.05, 0.1 and 0.2 T. It was found that the polymerization process has a strong influence over the magnetic properties of compacts. If the polymerization was performed by heating the powders into a mould, generally we observed a positive influence over the permeability but a negative influence over the magnetic losses.

Metallic Foams Obtained from Nickel Based Superalloy Hollow Spheres

In this work, hollow spherical nickel based superalloy powders obtained by liquid phase atomization were used. The obtained powder was divided into six size particle ranges between 200 µm and 630 µm using a shatter box. Samples from all six ranges were obtained by spreading the powder into the sintering die and consolidating them by sintering at 900°C and 1000°C for 30 minutes in vacuum (10-4 Torr). The metallic foams obtained by sintering hollow particles presents high porosity, and can be used as thermal barriers, catalyst support, shock absorbers or lightweight structural elements.

The Migration Behavior of Atomic Clusters in Early Nanocrystalline Process of Soft Magnetic Finemet Alloy

The Finemet alloys are commonly used as cores in transformers and generators, stress and field sensors in technological application for their excellent soft magnetic characteristics. To clarify the nanocrystallization mechanism of Finemet especially about the atomic migration in early stage is very essential for developing their distinctive characteristics. In this study, we investigate the migration behavior of atoms in order to clarify the mechanism of the early-stage nanocrystallization in amorphous Finemet alloys. The Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous ribbons were prepared by single-roller melt-spinning process in argon atmosphere, and then annealed at 350 degrees C-400 degrees C for 10 minutes in vacuum. The atom force microscope (AFM) and the coincidence Doppler broadening spectra (CDB) were used to characterize the migration behavior of different atoms in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloy during the early-stage nanocrystallization. The X-ray diffraction (XRD) patterns show that all annealed samples are in the amorphous state. But the AFM observation shows clearly that there are many small atomic clusters (nuclei) which distribute in the amorphous matrix of the annealed samples. With increasing annealing temperature, there is a significant increase in the amount of atomic clusters and a dramatic drop in the average size of clusters with very limited Cu contention in the samples, which reflect the structural evolution into more homogeneity. The CDB spectrum indicates that the peaks of positron annihilation spectrum are gradually reduced, which means the number of grain boundary and the defects in samples are gradually increased. It can be concluded that more defects are introduced by the formation of atomic clusters through atomic migration during the early-stage nanocrystallization in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloys.