Production of highly porous carbon sorbents for methane storage from coal, coke, and individual organic compounds

Highly porous carbon sorbents for methane storage are produced from coal, coke, and individual organic compounds. A static high-pressure volumetric system is used to establish the dependence of the methane and hydrogen adsorption on the micropore volume in the sorbents. The mean specific adsorption of CH₄ and H₂ at 60 atm (6 MPa) and 300 K is ～150 and ～6.5 mg/cm³, respectively. The results confirm physical adsorption of the gases (CH₄ and H₂).     

Joining of C<Subscript>f</Subscript>/SiC Ceramics to Nimonic Alloys

C_f/SiC ceramic composites have been brazed to Nimonic alloys using TiCuAg filler metal. In order to improve wettability and to provide compatibility between ceramic and metal, the C_f/SiC surface was metallized through the deposition of a chromium layer. Subsequent heat treatments were carried out to develop intermediate layers of chromium carbides. Excellent wetting of both the composite ceramic and the metal from the filler metal is observed in the fabricated joints. Shear tests show that failure occurs always within the ceramic material and not at the joint. In the filler region depletion of Ti and formation of Ag and Cu rich regions are observed. At the C_f/SiC-filler interface a layered structure of the filler metallic elements is observed. Titanium interacts with the SiC matrix to form carbides and silicides.     

Investigations on synthesis of HfB2 and development of a new composite with TiSi2

This paper presents the results of investigation carried out on synthesis and densification of monolithic HfB₂ and the effect of TiSi₂ as sinter additive. Pure phase HfB₂ was prepared by boron carbide reduction of HfO₂ and hot pressed to full density with the addition of TiSi₂. Isothermal oxidation study of this composite was carried out at 850 °C up to 64 h. Formation of HfB₂ was seen at 1200 °C but pure HfB₂ was formed at a much higher temperature of 1875 °C in vacuum. Hot pressing of HfB₂ at 1850 °C and 35 MPa pressure gave a compact of 80% TD. Addition of TiSi₂ helped in achieving a much higher density at a lower temperature of 1600 °C and a pressure of 20 MPa. A fully dense composite of HfB₂ and TiSi₂ was obtained with 15% TiSi₂. Hardness and fracture toughness of this composite were 27.4 ± 1.9 GPa and 6.6 ± 0.2 MPa m^1/2, respectively. Considerable deflection was observed in the crack propagation in composites. Oxidation studies indicated the formation of HfO₂, SiO₂, TiO₂ and HfSiO₄ with some glassy phase and the composite with 15% TiSi₂ was seen to be completely covered with a protective glassy layer.     

Effect of Substrate Grain Size on the Growth, Texture and Internal Stresses of Iron Oxide Scales Forming at 450 °C

The oxidation behavior of iron polycrystals and single crystals with (110) surface orientation was studied at 450 °C. Energy-dispersive diffraction with synchrotron radiation provided in situ information regarding the evolution of stress gradients and fiber texture in the oxide scales. Within this low-temperature regime, grain boundaries caused the oxidation kinetics of polycrystalline iron to be more rapid than iron single crystals only during the first minutes of oxidation. Epitaxial growth of iron oxides occurred only on single crystal substrates during the initial oxidation. In situ stress analyses suggested that stress relief occurred invariably in the magnetite layer due to the formation of a fine-grained seam near the iron substrates. Above the magnetite and in the hematite layer, the growth stresses depend initially on volumetric strains and later on inner oxide formation and creep of the hematite.     

Elastic anisotropy of polycrystalline Au films: Modeling and respective contributions of X-ray diffraction,nanoindentation and Brillouin light scattering

Elastic properties of non-textured and {1 1 1}-fiber-textured gold thin films were investigated experimentally by several complementary techniques, namely in situ tensile testing under X-ray diffraction (XRD), nanoindentation and Brillouin light scattering (BLS). Specimens were probed along different directions to reveal the strong effects of elastic anisotropy at the (local) grain and (global) film scales. XRD allows the investigation of both local and global anisotropies, while BLS and nanoindentation are limited to global analyses. A micromechanical model, based on the self-consistent scheme, and accounting for the actual microstructure of the films, is applied to interpret experimental data. Although different types of elastic constants can be determined with the used experimental techniques (static/dynamic, local/global), a good agreement is obtained, showing that comparison of these techniques is feasible when carried out carefully. In particular, the use of a micromechanical model to estimate the effects of the local elastic anisotropy at the film scale is unavoidable. The presented results show that XRD, BLS and nanoindentation should capture anisotropic texture effects on elastic constants measurements for materials with a Zener anisotropy index larger than 2. Conversely, the actual texture of a given specimen should be taken into account for a proper analysis of elastic constants measurements using those three experimental techniques.     

Ammoxidation activity of in situ synthesized ammonium salt of molybdophosphoric acid on VOPO4 catalysts

Two isomorphous VOPO₄ samples were synthesized by means of well-known aqueous and organic preparation methods. These materials are further used for the in situ generation of ammonium salt of 12-molybdophosphoric acid (AMPA) from their solid phase phosphate components. Formation of AMPA was confirmed by XRD, FTIR, Raman and XPS analyses. The activity of the catalysts was tested in a fixed bed tubular glass reactor at atmospheric pressure for the selective ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP). The reaction was carried out in the temperature range of 360–420 °C. Between the two mono-phosphates tested, the α-VOPO₄ is observed to show somewhat better activity compared to β-VOPO₄. Interestingly, in situ synthesized AMPA catalysts displayed significantly better performance compared to their corresponding parent VOPO₄ solids. Among all catalysts tested, AMPA-α-VOPO₄ exhibited the best performance (conversion (MP) = ca. 90%, selectivity (CP) = 65% at T = 420 °C). The differences in catalytic performance of the tested catalysts are ascribed to the structural differences of the used VOPO₄ solids.     

Single‐walled carbon nanotube/poly(methyl methacrylate) composites for electromagnetic interference shielding

Single‐walled carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) composites were prepared using coagulation method. The electrical conductivity and the electromagnetic interference (EMI) shielding of SWNT/PMMA composites over the X‐band (8–12 GHz) and the microwave (200–2000 MHz) frequency range have been investigated. The electrical conductivity of composites increases with SWNT loading by 13 orders of magnitude, from 10^?15 to 10^?2 Ω^?1 cm^?1 with a percolation threshold of about 3 wt% SWNTs. The effect of the sample thickness on the shielding effectiveness has been studied, and correlated to the electrical conductivity of composites. The data suggest that SWNT/PMMA composites containing higher SWNT loading (above 10 wt%) be useful for EMI shielding and those with lower SWNT loading be useful for electrostatic charge dissipation. The dominant shielding mechanism of SWNT/PMMA composites was also discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Experimental investigation on explosion characteristics of nano-aluminum powder—air mixtures

Explosion characteristics of nano-aluminum powders with particle sizes of 35, 75, and 100 nm are investigated in a 20-liters spherical explosion chamber. Results show that the maximum explosion pressure and the maximum rate of pressure rise mainly depend on the dust concentration. For dust concentrations below 1000 g/m³, the maximum explosion pressure increases gradually to a maximum value with increasing dust concentration. After the dust concentration increases above 1250 g/m³, the maximum explosion pressure starts to decrease. The trends of the maximum rate of pressure rise follow the same pattern with increasing dust concentration. The lower explosion concentration limits of nano-aluminum powders with sizes of 35, 75, and 100 nm are found to be 5, 10, and 10 g/m³, respectively, while the lower explosion concentration limit of ordinary aluminum powders is about 50 g/m³.     

Coating the inner walls of metal tubes with carbon films by physical vapor deposition at low temperature

Tubes are often required to exhibit better performance in corrosion and wear behavior than the material the tube is made of can offer. The situation can be improved when the tube is coated with a protective film. This can be achieved by sputter coating with an ion beam. A sputter target is located inside the tube. Energetic ions are accelerated into the tube and impinge onto the target. Thus, material is sputtered from the target onto the inner walls of the tube. Two apparatus for coating tubes of different lengths and diameters are described. Aluminum and stainless steel tubes were coated with amorphous carbon films. Results on adhesion, corrosion performance in aqueous media and thickness uniformity are shown.