J. Shirokoff

Use of X-ray diffraction in assessing the aging pattern of asphalt fractions

The X-ray diffraction (XRD) method was employed to investigate and compare some of the crystallite parameters and aromaticity of asphaltenes obtained from fresh and aged Arabian asphalts, procured from Ras Tanura (RT) and Kuwait (KW) refineries. A few crystallite parameters in the polar aromatics, naphthene aromatics and saturate fractions of these Arabian asphalts were also determined. The results obtained by XRD method for both the types of asphaltenes and other fractions were evaluated and compared. Significant differences were observed between the structure and the aging patterns of fresh and aged asphaltenes of RT and KW asphalt. The results indicate that the source and chemistry of asphalt are responsible for the aging behavior of its components. The rolling thin-film oven and the pressurized aging vessel tests were used to simulate asphalt aging in this research.

Electrodeposition and characterization of tin-zinc alloy coatings

Abstract This paper reports the electrodeposition of tin-zinc alloy coatings from a non-cyanide alkaline stannate/zincate bath formulation containing a complexing/stabilizing agent. The bath also comprises addition agents which considerably improve the coating properties and give a semi-bright finish. The effects of variables of the process on deposit composition were studied. The 25 ± 5% zinc (balance tin) alloy coatings offer excellent corrosion protection with no obvious white corrosion product. The deposit offers protection which is better than cadmium, zinc and zinc-nickel alloy coatings for equal thicknesses. The tin-zinc deposit obtained from the stannate/zincate bath is fine grained, semi-bright, and shows considerable improvements over the tin-zinc deposit from the previously used cyanide plating process. Electron microscopy and X-ray methods reveal microstructural information and structure-corrosion properties of these alloy coatings.

On the usefulness of epitaxy experiments in evaluating interface models

Abstract New results on low energy interfaces for the system gold on sodium chloride are presented together with a short review of the various versions of the sphere-plate technique which are used to study interface systems. The observed low energy orientation relationships as well as those recently found for the systems silver on sodium chloride and silver on silicon are compared with preferred orientations observed in epitaxy experiments. It is concluded that results for epitaxy are extremely useful when evaluating interface models for their predictive power.

Production of methyl tert-butyl ether (MTBE) over MFI-type zeolites synthesized by the rapid crystallization method and modified by varying Si/Ai ratio and steaming

Abstract The reaction of isobutene and methanol to produce methyl tert-butyl ether (MTBE) has been studied over MFI-type zeolites (ZSM-5) with varying Si/Al ratios. All the zeolites were synthesized by the rapid crystallization method. The number of Bronsted acid sites on the zeolite surface have been shown to increase proportionally with the aluminum contents of the zeolites. Under kinetically limited reaction conditions, the activity of the catalysts increased with number of acid sites. However near reaction equilibrium, the rate of increase of catalyst activity slowed down. The maximum activity was achieved at 80°C which was an optimum temperature condidering the catalyst activity and equilibrium conversion. Mild steaming caused a modest increase in isobutene conversion which was close to equilibrium conditions. On the other hand, severe steaming resulted in a decrease in activity. The effect of steaming was best attributed to new adsorption sites and/or enhanced Bronsted acidity. The zeolite gave a stable performance in an extended test up to at least 30 h on stream. All the catalysts tested displayed 100% selectivity for the production of MTBE at all the reaction conditions studied.

Long-range ordering effects in metal-non-metal interfaces revisited

The effect of long-range ordering across metal-non-metal interfaces is revisited. For this purpose, measurements of preferred orientations of low interfacial energy were made for Au and Ag on NaCl ...

Measurement of preferred orientations in the silver-silica interface

Abstract The crystal orientation of thin silver films evaporated onto amorphous silica substrates was studied by X-ray pole figure measurements before and after annealing. Orientation relationships resulting in interfaces of low energy were measured by observing the rotation of single-crystal silver spheres on silica. The orientation distribution of these spheres revealed two cusps in the interfacial energy vs. misorientation curve. The cusps correspond to orientations for which close-packed planes in silver lie parallel to the substrate surface.

The Effect of Fluorine on the Phase Formation and Properties of Tl-Based Superconductors

Fluorine was found to affect the phase formation and superconducting properties of Tl-based superconductors. By varying x in (Tl0.5Pb0.5)Sr1.6Ba0.4Ca2Cu3OyFx synthesized superconductors, an increase was found in the transition temperature and critical current density. These improvements in the superconducting properties are discussed in terms of partial substitution of fluorine into the oxygen sites which in turn affects the hole doping in this material. Structure, microstructure and elemental analysis by XRD, SEM and EDX techniques are reported; the latter of which shows the fluorine distribution.

The role of interfacial energy in the development of preferred orientations of silver on silicon

Abstract The existence of cusps in the interfacial energy against misorientation curve has been studied for Ag/Si(l00) and Ag/Si(111) interfaces using the modified sphere-plate technique. The following preferred orientations were obtained: Ag(100)//Si(100) with Ag[011]//Si[011], and Ag(111)//Si(111) with Ag[110]//Si[114]. These are the same preferred orientation relationships previously found in studies of thin-film growth and appear to be due to low interfacial energies. In addition, preferred orientations Ag(100)//Si(100), Ag(111)//Si(100) and Ag(111)//Si(111) without any preferred directional alignment were observed. These latter orientations are believed to be the result of the native silicon oxide layer present between silver and the silicon single crystals.

Anisotropic stress of a (Bi,Pb)2Sr2Ca2Cu3O10 high-Tc superconductor

The residual stresses in a (Bi,Pb)2Sr2Ca2Cu3O10 high-Tc superconductor have been determined using X-ray and sin2 psi analysis. The results indicate high anisotropy in the stress of this material for planes along the c-axis, compared with stress along the mixed-index planes. The calculated anisotropic ratios of the stress in this material are in agreement with ratios obtained from thermal expansion data for the same material.

The Slip Transfer Process Through Grain Boundaries in HCP Ti

Information on the mechanisms of slip transfer across grain boundaries in an HCP α-Ti alloy has been obtained from deformation experiments performed In situ in the transmission electron microscope. Initially, lattice dislocations are accommodated within the grain boundary until a critical local dislocation density is reached. The boundary then responds by activating slip in the adjoining grain on the slip system experiencing the highest local resolved shear stress and producing the residual grain-boundary dislocation with the smallest Burgers vector. Slip on secondary slip systems may be initiated provided they reduce the magnitude of the Burgers vector of, or eliminate, the residual grainboundary dislocation. The selection rules used to predict the slip system activated by the grain boundary are the same as apply in ordered and disordered FCC materials.