Gold anion catalysis of methane to methanol

The oxidation of CH₄ has been investigated in the presence and absence of the atomic Au⁻ ion catalyst. We have employed the first principles density functional theory (DFT) and dispersion-corrected DFT calculations for the transition state on the Au⁻ ion and analyzed the thermodynamics properties of the reactions as well. Our results demonstrate that atomic gold anions could be used to catalyze CH₄ into valuable industrial products without the emission of CO₂, thereby making gold extremely valuable. The fundamental mechanism involves breaking the C–H bond through the formation of the anionic Au⁻(CH₄) molecular complex permitting the oxidation of CH₄ to methanol at the temperature of 325 K which is below that of CO₂ emission. Potentially, this could significantly impact the quality of our environment.     

A spectroscopic and electrochemical investigation of the oxidation pathway of glycyl-d,l-methionine and its N-acetyl derivative induced by gold(III)

The ¹H nuclear magnetic resonance spectroscopy was applied to study the reaction of the dipeptide glycyl-d,l-methionine (H-Gly-d,l-Met-OH) and its N-acetylated derivative (Ac-Gly-d,l-Met-OH) with hydrogen tetrachloridoaurate(III) (H[AuCl₄]). The corresponding peptide and [AuCl₄]^– were reacted in 1:1, 2:1, and 3:1 molar ratios, and all reactions were performed at pD 2.45 in 0.01 M DCl as solvent and at 25°C. It was found that the first step of these reactions is coordination of Au(III) to the thioether sulfur atom with formation of the gold(III)-peptide complex [AuCl₃(R-Gly-Met-OH-S)] (R=H or Ac). This intermediate gold(III) complex further reacts with an additional methionine residue to generate the R-Gly-Met-OH chlorosulfonium cation as the second intermediate product, which readily undergoes hydrolysis to give the corresponding sulfoxide. The oxidation of the methionine residue in the reaction between H-Gly-d,l-Met-OH and [AuCl₄]^– was five times faster (k ₂ = 0.363 ± 0.074 M^-1s^-1) in comparison to the same process with N-acetylated derivative of this peptide (k ₂ = 0.074 ± 0.007 M^-1s^-1). The difference in the oxidation rates between these two peptides can be attributed to the free terminal amino group of H-Gly-d,l-Met-OH dipeptide. The mechanism of this redox process is discussed and, for its clarification, the reaction of the H-Gly-d,l-Met-OH dipeptide with [AuCl₄]^– was additionally investigated by UV-Vis and cyclic voltammetry techniques. From these measurements, it was shown that the [AuCl₂]^– complex under these experimental conditions has a strong tendency to disproportionate, forming [AuCl₄]^– and metallic gold. This study contributes to a better understanding of the mechanism of the Au(III)-induced oxidation of methionine and methionine-containing peptides in relation to the severe toxicity of anti-arthritic and anticancer gold-based drugs.     

Oxidation Behavior of Nickel-Base Single-Crystal Superalloy with Rhenium-Base Diffusion Barrier Coating System at 1,423 K in Air

The oxidation behavior of the nickel-base single-crystal superalloy TMS-82+ coated with a duplex Re(W)–Cr–Ni/Ni(Cr)–Al layer was investigated in air at 1,150 °C for up to 100 h. The coating layer was formed by electroplating Re(Ni) and Ni(W) films on the alloy, followed by Cr-pack cementation at 1,300 °C, and as a result, forming a continuous Re(W)–Cr–Ni diffusion-barrier layer. A Ni film containing fine Zr particles was then electroplated on the duplex layer, followed by Al pack cementation at 1,000 °C for 1 and 5 h to form an Al reservoir layer with a duplex Ni₂Al₃/γ-Ni layer, which changed quickly to γ-Ni phase containing (10∼13)at.% Al for the 1 h Al-pack coat and a mixture of γ′-Ni₃Al and β-NiAl phases for the 5 h Al-pack coat during high-temperature oxidation. A protective α-Al₂O₃ scale formed during oxidation at 1,150 °C in air, and parabolic rate constants of 7.4 × 10⁻¹¹ and 6.6 × 10⁻¹⁰ kg² m⁻⁴ s⁻¹ were obtained for the 1 h- and 5 h-Al pack-coatings, respectively. There was little change in the structures of the superalloy substrate after oxidation at 1,150 °C in air for up to 100 h. It was found that the Re(W)–Cr–Ni layer remained stable, acting as a diffusion barrier between the alloy substrate and Al reservoir layers.     

Restoration of the microstructure of Ba2YCu3O7 ? δ at T > 900°C after low-temperature decomposition

Transmission electron microscopy and optical microscopy have been used to study the structure of the nonstoichiometric YBa₂Cu₃O_{7 − δ} compound subjected to low-temperature annealing (200–300°C) and subsequent restoration annealing at 930–950°C. It was shown that the retention of part of structural defects, which were formed during decomposition and interaction with water vapor, after restoration annealing determines structural state of the compound that is typical of materials exhibiting improved electrophysical characteristics.     

Di-(2-ethylhexyl) dithiophosphoric acid surface protected gold nanoparticles: micellar synthesis, stabilization, isolation, and properties

Gold nanoparticles (AuNPs) were synthesized in the organic solution by means of the reduction of HAuCl₄ by hydrazine in reverse micelles of oxyethylated surfactant Triton N-42, with decane as the dispersion medium. To isolate the powder of particles, the micelles were destroyed with chloroform in the presence of di-(2-ethylhexyl) dithiophosphoric acid as a surface protecting agent. According to the results of several experiments, the yield is within the limits of 90–98%, calculated for gold. The obtained preparations are dark blue hydrophobic powders containing aggregated but not agglomerated gold nanoparticles, as well as microcrystals (∼0.08–0.2 μm) of NaCl. The powders get re-dispersed in weakly polar organic solvents with the formation of colloidal solutions. The shape of the nanoparticles is spherical. Their nuclei are gold single crystals with a narrow size distribution; their diameter (d _Au) is about two times as large as the diameter of the aqueous nucleus (d _c) of initial micelles: d _Au = 7.7 ± 1.4 nm (d _c = 3.6 nm) and 8.8 ± 1.5 nm (4.6 nm). The preparations were studied by means of dynamic light scattering, atomic force microscopy, transmission electron microscopy, UV–vis spectroscopy, IR spectroscopy, X-ray powder diffraction, and thermogravimetric and elemental analyses. In the case of the particles with d _Au = 8.8 nm, the product is a mixture of AuNPs and the salt with the molar ratio Au/NaCl ≈ 1:4.54, while the gross composition of AuNPs per one gold atom is estimated as Au(C₁₆H₃₄O₂PS₂Na∙2N₂H₄)_0.16 with the number of gold atoms in one particle ∼21,000.     

Surface Plasmon Resonance Tunability in Au?VO2 Thermochromic Nano-composites

A new type of photo-active nano-composite material appropriate for Ultra-fast Nonlinear Optical χ⁽³⁾ (ω) applications has been synthesized and optically characterized. Compared to standard noble metal particles- oxide nano-composites exhibiting a superior effective χ⁽³⁾ (ω) due to the enhancement of the local electric field, these Au−VO₂ nano-composites display an additional reversibly tunable surface plasmon frequency under external temperature stimuli. Such a smart plasmon tunability is correlated to the Mott’s type semiconducting/metallic 1st order transition of the host VO₂ matrix. The nano-gold surface plasmon wavelength shifts reversibly from 645 nm to 598nm when the Au−VO₂ nano-composites temperature varies from 25°C to 120°C.     

High-temperature deformation behavior and processing map of 7050 aluminum alloy re]20101008

The high-temperature deformation behavior and processing map of 7050 aluminum alloy were investigated by tensile tests conducted at various temperatures (340, 380, 420, and 460 °C) with various strain rates of 10⁻⁴, 10⁻³, 10⁻², and 0.1 s⁻¹. The results show that the instability region with a peak power dissipation efficiency of 100 % occurs at the low deformation temperature region of 340 °C to 380 °C and high strain rates (>10⁻³ s⁻¹). The 7050 aluminum alloy exhibited a continuous dynamic recrystallization domain with power dissipation efficiency of 35% to 60 % in the deformation temperature range of 410 °C to 460 °C and the strain rate range of 10⁻⁴–10⁻³ s⁻¹. The domain with a power dissipation efficiency of 35 % to 50 % occurring at high deformation temperatures and strain rates was interpreted to represent dynamic recovery. Dynamic recovery and continuous dynamic recrystallization provide chosen domains for excellent hot workability.     

Density of liquid gold measured by a non-contact technique

Electrostatic levitation together with multi-beam laser heating and ultraviolet imaging made possible to handle a sample of liquid gold, without any contamination, and to determine its density over a large temperature range. Over the 1337–1800 K interval, the density of Au was measured as ρ(T)=1.74× 10⁴−1.44 (T−T_m) kg·m⁻³, where Tm, the melting temperature, was 1337 K. These data yield a calculated volume expansion coefficient of 8.3×10⁻⁵ K⁻¹. The values agree well with the literature values.     

Mechanical properties of high-temperature alloy ZhS32 at 1150–1250°C

The mechanical properties of single crystals of alloy ZhS32 at a temperature of 1150–1250°C and deformation rates of 3 × 10⁻⁵, 10⁻⁴, and 10⁻³ sec⁻¹ are studied. The characteristics of true ductility in tests for long-term strength in a temperature range of 1150–1250°C are determined. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 38–40, January, 2006.     

Oxidation Behavior of TiAl<Subscript>3</Subscript>/Al Composite Coating on Orthorhombic-Ti<Subscript>2</Subscript>AlNb Based Alloy at Different Temperatures

This paper reports the oxidation behavior of TiAl₃/Al composite coating deposited by cold spray. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The oxidation kinetics of the coating was tested at 650, 800, and 950 °C, respectively. The parabolic rate constant for the coating oxidized at 650 °C was k _p = 7.2 × 10⁻² mg·cm⁻²·h^−1/2 for the tested 1200 h. For the coating oxidized at 800 °C, the oxidation kinetics could be separated into two stages with k _p value of 39.8 × 10⁻² mg·cm⁻²·h^−1/2 for the initial 910 h and 17.7 × 10⁻² mg·cm⁻²·h^−1/2 for the stage thereafter. For the coating oxidized at 950 °C, the oxidation kinetics can be separated into three stages with k _p of 136.9 × 10⁻² mg·cm⁻²·h^−1/2 in the first 100 h, followed by 26.9 × 10⁻² mg·cm⁻²·h^−1/2 from 100 to 310 h, and 11.8 × 10⁻² mg·cm⁻²·h^−1/2 from 310 to 1098 h. XRD, SEM, and EPMA were used to study the microstructure of the coating. The results indicated that the oxidation took place throughout the entire coating instead of only at the surface. The aluminum phase in the composite coating was soon oxidized to Al₂O₃ in all tested cases. The aluminum in TiAl₃ phase was depleted gradually and oxidized to Al₂O₃ along with the degradation of TiAl₃ to TiAl₂ and TiAl as the temperature increased and time proceeded. AlTi₂N was also a typical oxidation product at temperature higher than 800 °C. The experimental results also indicated that the protection of the coating was attributed greatly to the interlayer formed between the coating and the substrate.     

Electrical properties of dense and nanocrystalline Sm3+-doped Ce1?xSmxO2?δ (0.05 ≤ x ≤ 0.3) electrolytes for IT-SOFCs

Sm³⁺-doped Ce_1−xSm_xO_2−δ (0.05 ≤ x ≤ 0.3) nano-sized powders for solid electrolytes were synthesized by a solution combustion method, using aspartic acid as a combustion fuel. The calcined Ce_1−xSm_xO_2−δ powders were a ceria-based single phase with a cubic fluorite structure. The nano-sized Ce_1−xSmxO_2−δ powders provided a high density, ultra-fine grain size, and high electrical conductivity even at a low sintering temperature of 1400 °C. The grain size and relative density of the Ce_1−xSm_xO_2−δ pellets ranged from 329 nm to 496 nm and from 91.9 % to 99.2 %, respectively. The grain size and density of the Ce_1−xSm_xO_2−δ pellets decreased with an increase of Sm³⁺ content. The electrical conductivity of the Ce_1−xSmxO_2−δ increased with an increase of Sm³⁺ content up to x = 0.25 and then decreased with higher Sm³⁺ content. The maximal electrical conductivity (0.105 Scm⁻¹) was obtained with Ce_0.75Sm_0.25O_2−δ at 800 °C.     

Surface characterization of (111) and (100) textured diamond coatings deposited to silicon

The use of diamond for infrared (IR) transmitting applications is of paramount importance to the defense industries. Diamond-coated IR transmitting materials are used on smart weapons and aircraft that use substrate materials such as silicon and germanium. In this investigation, diamond sheets were deposited using chemical vapor deposition. The as-grown diamond sheets were characterized for hydrogen content using detailed IR analysis. The deconvolution of the spectra in a three-phonon region (2700–3150 cm⁻¹) showed a number of vibration modes corresponding to the sp ^m CH _n phase of carbon. The spectra representing (100) and (111) textured diamond sheets, grown under different conditions, were compared. The (100) textured sheets contained two dominant peaks centered at 2860 and 2930 cm⁻¹, which correspond to the symmetric and asymmetric stretch bands of the CH₂ group. However, the sheet with (111) texture displayed multiple CH, CH₂, and CH₃ peaks on the spectrum. Using a standard sample called polymethyl methacrylate with known concentration, the hydrogen content associated with various modes was evaluated in the diamond sheets. IR active hydrogen in the chemical vapor deposited diamond sheets was also calculated by evaluating the area of the IR band. A discrepancy of one order of magnitude was found in the calculated and measured value. Using these measurements we suggest that the oscillator strength of the different IR modes varies depending upon the structure and H content of CVD diamond sheets.     

Physicochemical study of the nanodiamond surface

Suspensions of five types of ultrafine diamond of a detonation synthesis in distilled water and 0.9 mol/l NaCl solution were found to have pHs in the range of 3–6, which results from the intrinsic acidity of their surfaces. The possibility of quantitatively determining the protogenic groups of a surface is found using the pH-potentiometric method. The data on the kinetics of the varying pH of suspensions in water and 0.9 mol/l NaCl solution and the data on the curves of the alkali titration of the suspensions of nanodiamond in the indicated systems make it possible to infer the presence of one or two types of acid groups on the surface of a diamond. The constants of dissociation (pK ₁) of these groups on the assumption of their single-base nature are estimated. From 1 × 10⁻³−5 × 10⁻² mol/l chloride solutions of H[AuCl₄] and RhCl₃ on the surface of diamond, gold(III) and rhodium(III) are found to be adsorbed; the adsorption of methylene blue from its 2.5 × 10⁻⁴−5 × 10⁻⁴ mol/l solutions reaches more than 90% (upon adsorption from 5 ml of the initial solution by a 0.05-g nanodiamond).     

Thermal properties and microstructure of a plasma sprayed wollastonite coating

Wollastonite coatings were deposited using an atmospheric plasma spraying technique. The microstructure and phase compositions of the coating before and after heat treatment were investigated using scanning electron microscopy (SEM), x-ray diffraction (XRD), and differential thermal analysis (DTA) technologies, respectively. In addition, the coefficient of thermal expansion and thermal diffusivity of the coating were also investigated. Crystalline wollastonite, glassy phase, and tridymite (SiO₂) were observed in the coating. Tridymite (SiO₂) likely reacted with other composites such as CaO and glassy phase to form crystalline wollastonite when the coating was heated at about 882 °C. During the first thermal cycle, the coefficient of thermal expansion of the coating decreased dramatically between 700 and 850 °C and the thermal diffusivity of the coating was 2.7–3.1 × 10⁻³cm²/s between 20 and 1000 °C. During the second thermal cycle, the coefficient of thermal expansion of the coating increased slightly between room temperature and 1000 °C and the thermal diffusivity of the coating increased by about 20% compared with that of the first thermal cycle. The atmospheric plasma sprayed Wollastonite coating may be used as thermal barrier coating.     

Accelerated Corrosion of Fe–xCr–10Al Alloys Containing 0–20 at.% Cr Induced by Sulfur and Chlorine in a Reducing Atmosphere at 600 °C

The corrosion behavior of five Fe–xCr–Al alloys with a constant Al content of 10 at.% and Cr contents ranging from 0 at.% to 20 at.% was examined at 600 °C in a H₂–HCl–H₂S–CO₂ gas mixture providing 3.7 × 10⁻²² atm O₂, 2.4 × 10⁻¹⁴ atm Cl₂ and 3.9 × 10⁻⁹ atm S₂. All the alloys formed duplex scales containing an outermost layer of iron oxide plus an inner layer composed of mixtures of the oxides of all the alloy components. Besides, a region of internal attack of Al or Al + Cr, whose depth decreased with increasing Cr content, formed in all the alloys. The simultaneous presence of chlorine and sulfur in the gas mixture significantly accelerated the corrosion of all the alloys with respect to their oxidation in a simpler H₂–CO₂ mixture providing the same oxygen pressure, by forming thick and cracked scales. The effect was particularly large for the high-Cr alloys due to their inability to form external protective alumina scales in the present gas mixture.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.     

Dependence of the surface charge and the fluorine adsorption by γ-aluminum oxide on the solution temperature

The dependence of the surface charge of the γ-aluminum oxide and the fluorine adsorption on the solution temperature (20, 30, and 40°C), the pH (3.5–10), and the equilibrium concentration of fluorine in the solution (from 1.0 × 10⁻³ to 1.5 × 10⁻¹ M/l) is studied by the method of potentiometric titration and adsorption variations with the view to elucidate the nature of the processes that take place upon the removal of fluorine with the use of ECDM sludge of an aluminum alloy that was calcined at a temperature of 800 °C. The adsorption isotherms were processed using the Freundlich, Langmuir, and BET equations. The best coincidence with the experimental data is obtained with the use of the Langmuir equation. It is shown that both the solution temperature increase and the amount of fluorine adsorbed by the sample surface shift the pH_PZC to a more acid range. The fluoride adsorption occurs due to the exchange of the OH⁻-groups of the hydrated oxide surface for fluorine ions due to the interaction of the charged AlOH₂⁺ centers of the surface with F⁻ ions and due to the formation of hydrogen bonds of F⁻ and uncharged AlOH centers.     

Continuous dynamic recrystallization of AISI 430 ferritic stainless steel

The high-temperature deformation behavior of AISI 430 ferritic stainless steel was studied by torsion tests. The deformation tests were performed in the temperature range of 900–1100°C and strain rate range of 5.0×10⁻² −5.0/sec. The evolutions of flow stress and microstructure show the characteristics of continuous dynamic recrystallization (CDRX). The flow stress gradually decreased with strain over the peak stress without steady state. Below the 100% effective strain, grains appeared in small angle grain boundaries with a misorientation of 3–9°. In addition, when heavy deformation (>300%) was applied, higher misorientation (∼15°) was achieved. The tendency of CDRX increased with increasing strain rate and decreasing temperature. The dependence of CDRX grain size on the strain rate and temperature was discussed.     

A study of the corrosion properties of plasma nitrocarburized and oxidized AISI 1020 steels

Plasma nitrocarburized AISI 1020 steels were oxidized for 15, 30 and 60 min to evaluate their corrosion and microstructural properties. After plasma nitrocarburizing for 3 h at 570°C in a gas mixture comprising 85 vol.% N₂, 12vol.% H₂ and 3 vol.% CH₄, the compound layer composed of ɛ-Fe_2–3(N,C) and γ’-Fe₄(N,C) phases and the diffusion layer above the matrix were observed. The top oxide layer, consisting mainly of magnetite (Fe₂O₄) and hematite (Fe₂O₃) phases, forms after post-oxidation treatment at 500°C. However, the oxide layer was severely degraded by spallation as a result of increases in post-oxidizing time. The difference in corrosion resistance should be attributed to the thickness of the top oxide layer, which was governed by post-oxidizing time.     

Infrared brazing of Fe3Al intermetallic compound using gold-based braze alloy

Infrared-brazing Fe₃Al with Au–44Cu as filler metal has been investigated. The brazed joint consists mainly of a β-phase, Au_8 − x Cu_4 + x Al₄, caused by the dissolution of Al from Fe₃Al substrate into the braze alloy. The depletion of Al from Fe₃Al substrate results in the formation of a layer of β-phase particles dispersed in the Fe-rich phase. The highest shear strength for AuCu filler is 327 MPa for specimens infrared brazed at 880°C for 180 s. The brazed joint is mainly fractured along the central β-phase in which the fractograph exhibits quasi-cleavage with dimples. Increasing the brazing time or temperature will deteriorate the bonding strength of the joint, and the fracture mode is prone to cleavage of brittle fracture. Au–44Cu filler demonstrates a great potential for bonding Fe₃Al intermetallic compound.