Min In Argon Research Articles

Sintering High Green Density Direct Powder Rolled Titanium Strips, in Argon Atmosphere

Presently, the majority of titanium powder metallurgy components produced are sintered under high vacuum due to the associated benefits of the vacuum atmosphere. However, high-vacuum sintering is a batch process, which limits daily production. A higher daily part production is achievable via a continuous sintering process, which uses argon gas to shield the part from air contamination. To date, there has been limited work published on argon gas sintering of titanium in short durations. This study investigated the properties of thin high green density titanium strips, which were sintered at the temperatures of 1100 °C, 1200 °C and 1300 °C for a duration of 30 min, 60 min and 90 min in argon. The strips were produced by rolling of −45 µm near ASTM (American Society for Testing and Materials) grade 3 hydride–dehydride commercially pure titanium powder. The density, hardness, tensile properties and microstructure of the sintered strips were assessed. It was found that near-full densities, between 96 and 99%, are attainable after 30–90 min of sintering. The optimum sintering temperature range was found to be 1100–1200 °C, as this produced the highest elongation of 4–5.5%. Sintering at 1300 °C resulted in lower elongation due to higher contaminant pick-up.

Efficient destruction of sodium cyanide by thermal decomposition with addition of ferric oxide

Abstract Efficient destruction of cyanide by thermal decomposition with ferric oxide addition was proposed. The mechanism of destruction of sodium cyanide with or without ferric oxide addition under various conditions was examined by XRD, DSC−TG, and chemical analysis technologies. In the absence of ferric oxide, sodium cyanide decomposes at 587.4 °C in air and 879.2 °C in argon atmosphere. In the presence of ferric oxide, about 60% of sodium cyanide decomposes at 350 °C for 30 min in argon, while almost all sodium cyanide decomposes within 30 min in air or O2 with mass ratio of ferric oxide to sodium cyanide of 1:1. The increase of ferric oxide addition, temperature, and heating time facilitates the destruction of sodium cyanide. It is believed that with ferric oxide addition, NaCN reacts with Fe2O3 to form Na4Fe(CN)6, Na2CO3, NaNO2 and Fe3O4 in argon. NaCN decomposes into NaCNO, Na4Fe(CN)6, minor NaNO2, and the formed NaCNO and Na4Fe(CN)6 further decompose into Na2CO3, CO2, N2, FeOx, and minor NOx in air or O2.

Investigation of the interactions between titanium and calcium zirconium oxide (CaZrO3) ceramics modified with alumina

Powdered mixtures of CaO, ZrO2 and Al2O3 in various ratios were hot pressed. The mixtures reacted with titanium at 1600?C for 30min in argon to evaluate the suitable ceramic crucibles for casting of titanium. The interfacial microstructures between titanium and ceramic composites were characterized using X-ray diffractometer, scanning and transmission electron microscope. The produced hot pressed mixtures that were chemically bonded together, contained calcium aluminate (CaAl2O4), calcium dialuminate (CaAl4O7), cubic zirconia (c-ZrO2), and calcium zirconium oxide (CaZrO3). The increase in Al2O3 amount led to the decrease in CaZrO3 amount and an increase in the amount of CaAl2O4, CaAl4O7 and c-ZrO2 due to the reaction of CaO and Al2O3. At the end of the reaction of the ceramic mixtures with Ti at 1600?C for 30min, the acicular ?-Ti and ??-Ti were formed at the interface of Ti and the composites containing up to 10 vol.% Al2O3. In composites containing more than 20 vol.% Al2O3, Ti3Al5 was found at the interface instead of ?-Ti and ??-Ti. Furthermore, CaZrO3, ZrO2 and Ca3Al2O6 existed on the sides of the ceramic far away from the interface. CaZrO3/Al2O3 composites with less than 20 vol.% Al2O3 could be a potential crucible or mould material for productive applications in titanium casting.

Microstructure and mechanical properties of Mo-ZrC-Cu composites synthesized by reactive melt infiltration of Zr-Cu melt into porous Mo2C preforms at 1300 °C

Mo-ZrC-Cu composites have been synthesized by reactive melt infiltration of Zr-Cu binary alloys into porous Mo2C preforms at 1300 °C for 10 min in argon. The influence of Zr content in the Zr-Cu infiltrator on microstructure and mechanical properties of Mo-ZrC-Cu composites are investigated. The as-synthesized composites consist of three major phases of Mo, ZrC and Cu, after a complete reaction of Mo2C(s) + Zr-Cu(l) → Mo(s) + ZrC(s) + Cu(l). Mo2Zr phase is formed when Zr content exceeds 50 at% in the Zr-Cu infiltrator. The formed ZrC grains have sizes less than 1 μm with Mo solid solute inside. Meanwhile, nanoscale zones enriched in Cu and C are also detected in ZrC grains. The angular ZrC particles and rounded Mo grains become larger with increasing Zr content in the Zr-Cu infiltrator. With decreasing Cu content from 43.5 to 31 vol% in Mo-ZrC-Cu composites, the elastic modulus and flexure strength increase from 146 to 156 GPa and from 542 to 569 MPa, respectively.

Epitaxially-Grown Europium-Doped Barium Titanate Films on Various Substrates for Red Emission.

Intense red photoluminescence under ultraviolet excitation was observed in epitaxially-grown europium-doped perovskite BaTiO3 thin films deposited on the SrTiO3 (100), MgO (100) and sapphire (0001) substrates using metal carboxylate complexes. Precursor films prepared by spin coating were pyrolyzed at 250 °C for 120 min in argon, followed by final annealing at 850 °C for 60 min in argon. Crystallinity and epitaxy of the films were analyzed by X-ray diffraction θ-2θ scan and pole-figure analysis. Photoluminescence of the thin films at room temperature under 254 nm was confirmed by a fluorescent spectrophotometer. The obtained epitaxial BaTiO3 thin films on the SrTiO3 (100) and MgO (100) substrates show an intense red-emission lines at 615 nm corresponding to the (5)D0 --> (7)F2 transitions on Eu(3+) with broad bands at 595 and 650 nm.

In-vitro calcium phosphate formation on electrostatic sprayed – perovskite BaTiO3 layer on Ti implant after poling treatment

Ferroelectric BaTiO3 thin films were coated on titanium implants using an electrostatic spraying deposition method to combine the biocompatibility of a ceramic with the high mechanical strength of a metal. As-deposited films were annealed at 850°C for 30min in argon. Crystallinity, chemical structure, and surface morphology of the films were analyzed. Perovskite-type tetragonal BaTiO3 films were obtained after post-annealing. Their ability to form calcium phosphate after poling treatments at above the Curie temperature was investigated with an in-vitro test in a simulated body fluid. Un-poled BaTiO3 layer on titanium implant was partially covered with Na, Cl, and relatively small amounts of P and O ions, while the poled BaTiO3 layer was wholly covered with calcium phosphate.

Characterisation of thermally degraded polycrystalline diamond

Polycrystalline diamond (PCD) is extensively used in the abrasives industry for cutting, drilling and milling due to its outstanding mechanical properties. However, this material suffers from thermal instability when exposed to temperatures above 750°C. This paper investigated the mechanisms of thermal degradation that operate at elevated temperatures in PCD drill bit inserts. Two tests of thermal stability were performed. In the first part of the study thermo-mechanical milling tests were performed on PCD tools. The second part of the study involved a controlled investigation of the chemical changes in the PCD as a function of temperature with the aid of electron microscopy and X-ray diffraction. The experimental results indicated that graphitisation induced cracking occurred in the samples heated to temperatures of 500°C and above during the granite milling test. The formation of η-phase (Co,W)6C in the residual cobalt pools preceded graphite formation in the thermally soaked PCD samples. The formation of the (Co,W)6C was controlled by the diffusion of solid solution tungsten in the cobalt. Graphitic carbon nucleated in the cobalt pools after exposure at 800°C for 30min in argon. This indicated that the temperature at the contact surface of the tool and granite block must have exceeded 800°C during the milling test.

Study of molar ratio on the characteristics of metal–organic decomposed LaxCe1−xOz film as a metal reactive oxide on Si substrate

A metal–organic decomposition technique was employed in this study for the preparation of a solution precursor using different molar ratios of lanthanum (La) to cerium (Ce), which was spin-coated on an n-type Si substrate. Post-deposition annealing was subsequently performed at 1000°C for 15min in argon on the samples to transform the precursor into lanthanum cerium oxide (LaxCe1−xOz) film. This work correlated the influence of decreasing content of La3+ in the LaxCe1−xOz film with formation of oxygen vacancies. Generation of higher amounts of oxygen vacancies in LaxCe1−xOz has evoked an interest in the study of LaxCe1−xOz as a metal reactive oxide on Si substrate for oxygen gas sensing. These oxygen vacancies would serve as active sites for capturing oxygen ions, which were formed as a result of chemisorption of oxygen atoms originating from oxygen gas. The response of oxygen gas sensing for the fabricated Al/LaxCe1−xOz/Si metal–oxide–semiconductor structures was characterized and discussed.

Schottky nature of InSe/Cu thin film diode prepared by sequential thermal evaporation

Highly oriented indium selenide (InSe) thin films were prepared by sequential thermal evaporation on tungsten (W) substrate and subsequently annealed at 300°C for 30 min in argon (Ar) atmosphere. The films were characterized by Glancing Incidence x-ray diffraction (GI-XRD), scanning electron microscopy (SEM), Energy dispersive x-ray analysis (EDX), Diffused reflectance spectroscopy (DRS) and current-voltage (I–V) measurements. Highly crystalline InSe thin film was obtained after annealing and confirmed by XRD analysis. Band gap energy of the InSe system is deduced from the DRS measurements and found to be 1.3 eV. SEM analysis revealed that selenium (Se) content plays an important role in determining the surface morphology of the film. InSe thin film diode structure was fabricated as W/InSe/Cu system. The estimated values of barrier height for the film of thickness 3000 A and 7000 A are 0.65 eV and 0.61 eV respectively. Thickness dependent schottky nature of the InSe/Cu thin film diode is discussed in detail.

Analyzing the quality of grinding and mixing of copper and chromium powders in a new-type mill

The potential use of a new-type mill developed at the Frantsevich Institute for Problems of Materials Science to produce copper and chromium powder mixtures intended for the manufacture of electrical-grade materials is studied. The mill ensures mechanical grinding of loose materials by mechanisms similar to those acting in vortex and jet mills. The greater powder refinement in this mill is due to the sliding interaction of particles with abrasive surfaces of the mill chamber. It is shown that common grinding of electrolytic copper and reduced or aluminothermic chromium for 10–30 min in argon promotes variation in the shape of particles, facilitates their mixing, and provides uniform distribution of components in the mixture.

Effect of oxide shell growth on nano-aluminum thermite propagation rates

Flame propagation rates for nanometric particle composites of aluminum (Al) and molybdenum trioxide (MoO3) were examined. The Al particles were prepared by thermally treating the particles at 480°C for time increments up to 180min in oxygen and 90min in argon. This treatment caused the aluminum passivation shell to grow and there is also evidence of shell damage due to treatment. Results reveal several interesting behaviors: flame speeds initially on the order of several hundred meters per second were reduced with damage to the oxide shell, and there is a weak dependence of the flame speed on the ratio of particle radius to shell thickness (M) in the range 6.1<M<13.4. The sharp drop in flame rate at further reduction in M down to 5.0 is consistent with a similar drop observed for adding alumina to the reactive mixture. All observations are consistent with the melt dispersion mechanism associated with Al nanoparticle oxidation.

Fabrication and properties of Ti(C,N) based cermets reinforced by nano-CBN particles

Titanium carbontride (Ti(C,N)) based cermets with and without nano-cubic boron nitride (CBN) particles were prepared by microwave sintering in argon and nitrogen environment, respectively. Two kinds of core–rim microstructure, black core–grey rim and white core–grey rim, are shown in the cermets by scanning electron microscopy (SEM) in combination with energy dispersive X-ray analysis (EDX). It is found that, for the cermet with 1.5% nano-CBN particles sintered at 1500°C for 30min in argon, its transverse rupture strength (TRS) and hardness are improved to about 25.9% and 1.4%, respectively. The SEM analysis shows that the inhibition effect of nano-CBN particles on the dissolution of Ti(C,N) is weakened with the increase of content of nano-CBN particles. Moreover, for the cermet sintered in argon reinforced by 1.5% nano-CBN particles, more fine black core–grey rims are found in the microstructure compared to the others. For the material sintered in nitrogen, its microstructure accompanied with many white core–grey rims in number and big black core and thin outer rim in size, results in high hardness and low TRS.

Amorphous vanadium pentoxide thin films prepared by electrostatic spraying-pyrolysis deposition

Vanadium pentoxide thin films were prepared on Pt/TiO 2/SiO 2/Si (1 1 1) substrates by electrostatic spraying deposition at 200 °C for 10 min. As-deposited thin films were finally annealed at 200 °C for 60 min in argon. Crystallinity and surface morphological properties were examined by X-ray diffraction θ–2 θ scanning, field emission scanning electron microscope and scanning probe microscope. Electrochemical tests were performed using cycler in a 1 mol LiPF 6, EC:DMC = 1:1 liquid electrolyte. Cycling tests were carried out for up 250 cycles in the range of 1.5–3.8 V at constant current density was 20 μA/cm 2. The relationship between the electrochemical and structural properties are described and discussed.

Effect of Yttria on Interfacial Reactions Between Titanium Melt and Hot‐Pressed Yttria/Zirconia Composites at 1700°C

Various Y2O3/ZrO2 samples were fabricated by hot pressing, whereby Y2O3 was mutually dissolved or reacted with ZrO2 as a solid solution or Zr3Y4O12. Hot‐pressed samples were allowed to react with Ti melt at 1700°C for 10 min in argon. Microstructural characterization was conducted using X‐ray diffraction and analytical electron microscopy. The Y2O3/ZrO2 samples became more stable with increasing Y2O3 because Y2O3 was hardly reacted and dissolved with Ti melt. The incorporation of more than 30 vol% Y2O3 could effectively suppress the reactions in the Ti side, where only a very small amount of α‐Ti and β′‐Ti was found. When ZrO2 was dissolved into Ti on the zirconia side near the original interfaces, Y2O3 reprecipitated in the samples containing 30%–70 vol% Y2O3, because the solubility of Y2O3 in Ti was very low. In the region far from the original interface, α‐Zr, Y2O3, and/or residual Zr3Y4O12 were found in the samples containing more than 50 vol% Y2O3 and the amount of α‐Zr decreased with increasing Y2O3.

Synthesis of Ti 3Si 0.8Al 0.4C 1.8 solid solution from Ti–Si–Al–C powder mixture

In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti 3Si 0.8Al 0.4C 1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti 3Si 0.8Al 0.4C 1.8 solid solution. XRD results showed that predominantly single phase samples of Ti 3Si 0.8Al 0.4C 1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti 3Si 0.8Al 0.4C 1.8 lay between those of Ti 3SiC 2 and Ti 3AlC 2. SEM observation showed that the grains of Ti 3Si 0.8Al 0.4C 1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti 3SiC 2 and Ti 3AlC 2.

Thermal stability of silver selenide thin films on silicon formed from the solid state reaction of Ag and Se films

Thermal stability of silver selenide thin films grown on silicon substrates by the solid state reaction of Se and Ag films is studied. The as-deposited as well as films annealed at different temperatures for 60 min in argon were investigated using X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM) measurements. Analysis of the XRD and RBS data of as-deposited films indicated the formation of single phase orthorhombic silver selenide from the reaction of Ag and Se films at room temperature. RBS spectra of films annealed at 473 K and above showed features characteristic of agglomerated morphology. SEM images showed the smooth morphology of the as-deposited films to evolve into a discontinuous island state with annealing temperature. The results suggest that above ∼473 K, the films are thermally unstable and agglomerate through holes generated at grain boundaries.

Optical properties in the Cu-fused silica system irradiated with swift heavy ions

Swift heavy ions are used to study the effects of electronic energy loss on Cu cluster formation in fused silica after post-irradiation annealing. Fused silica substrates covered with 10nm thin Cu-films were irradiated using beams of either 120MeV Ag9+ ions or 350MeV Au26+ ions at fluences ranging from 2×1013 to 1×1014cm−2. After irradiation, the samples were annealed for 30min in argon, at temperatures of 773–1200K and characterized by UV–VIS absorption spectroscopy. The swift ion irradiations created E′ and B2 defects in silica, which were partially eliminated during annealing. In addition, Cu cluster formation in silica was observed after annealing. Irradiation fluences exceeding 4×1013cm−2 and annealing temperatures above 1100K are more effective in forming larger nanoclusters.

Characterization of Ground and Low-Lying Excited States of CoO4: A Combined Matrix Isolation and DFT Study

The nature of the reaction products between CoO(2) and molecular O(2), isolated in rare gas matrices, have been investigated using IR absorption spectroscopy. In this paper, we report on the vibrational spectrum of the CoO(4) molecule in its ground and first low-lying excited states. Isotopic substitutions using (16)O(2) and (18)O(2) precursors, as well as (16)O(2) + (18)O(2) and (16)O(2) +( 16)O(18)O + (18)O(2) mixtures in either excess argon or neon, enable demonstration of C(2)(v)() and C(s)() structures for the respective states. CoO(4) is formed following molecular diffusion by complexation of ground-state CoO(2) by an O(2) molecule. The molecule is first formed in the excited state and then spontaneously relaxes to the ground state after remaining in the dark. The kinetics of relaxation can be fitted to a first-order exponential decay with an excited-state lifetime estimated around 23 +/- 2 min in argon and 15 +/- 2 min in neon, indicative of a slow, spin-forbidden process. Population of the excited state is induced by photons around 4250 +/- 250 cm(-1). Experimental results are compared to density functional theory (DFT) calculations at the BPW91/6-311G(3df) level. Electronic and geometrical optimizations were carried out starting from the ground-state precursors (i.e., (3)Sigma(g)(-) for O(2) and (2)Sigma(g)(+) for CoO(2)). Calculations predict a (2)A(2) (C(2)(v)()) ground state and a (4)A' (C(s)()) first excited state 0.37 eV above, close to the 4250 +/- 250 cm(-1) experimental excitation energy. The transition pathway is found to involve two supplementary states with crossed potential energy surfaces (PESs): a (2)B(1) excited state, 0.48 eV above the ground state, reached first through an adiabatic transition with a photon around 4800 cm(-1), and a (4)B(1) transition state into which the system relaxes before finally attaining the (4)A' (C(s)()) excited state. Harmonic frequencies and absolute intensities are also calculated and compared with the experimental data, indicating however that the DFT underestimates the internuclear distances for both configurations. Force and interaction constants were obtained with a semiempirical harmonic force-field potential calculation. They were then used in an empirical rule of plot linking force constants and internuclear distances in order to obtain an estimate of the Co-O bond lengths for each state and are compared to the DFT predictions.

Transport and exchange of hydrogen isotopes in silicon-device-related stacks

Thermally driven transport and exchange of hydrogen and deuterium in silicon-based metal-oxide-semiconductor (MOS) device-related structures were experimentally investigated using elastic recoil detection analysis. The samples were planar stacks of different materials on crystalline silicon. The materials studied included silicon oxide prepared by thermal growth, polycrystalline silicon silicon nitride, silicon oxynitride, and borophosphosilicate glass (BPSG) prepared by chemical vapor deposition (CVD). CVD was performed using either standard (hydrogen-containing) or deuterated precursors. Thermal annealing was carried out at 350–800 °C for 10–300 min in argon or in forming gas, either standard (90 vol. % N2,10 vol. % H2) or deuterated. All materials except silicon nitride were permeable to hydrogen and deuterium in the temperature range studied. Isotope exchange in the polycrystalline Si/SiO2 structure was observed above 450 °C. BPSG showed very little relative isotope exchange. Implications to MOS device processing are discussed.

Photoluminescence in Er-implanted AlGaN/GaN superlattices and GaN epilayers

Photoluminescence (PL), structural and electrophysical properties of Al0.26Ga0.74N/GaN superlattices grown by metal-organic chemical vapor deposition, implanted by erbium (Er) ions with 1MeV energy and 1×1015cm−2 dose as well as annealed at 700–1100°C for 4min in argon have been investigated. A comparison of the properties of the superlattices with that of the GaN epilayers grown, implanted and annealed at the same conditions is also given. The Er-related peak with a maximum at λ∼1.54μm dominated and the defect-related emission band at λ∼1–1.4μm was observed in the PL spectra of both types of samples. When the measurement temperature was increased from 80 to 300K, practically the same temperature quenching of the Er-related intensity was observed in the superlattices and GaN epilayers implanted and annealed at the same conditions. The Er-related intensity at 300K increased monotonically as the annealing temperature was raised from 700 to 1000°C, but the intensity in the superlattices was higher by several times than that in the epilayers. A decrease of the Er-related PL intensity in the superlattice after annealing at 1100°C is associated with the formation of non-radiative recombination centers.