The application of “superacidic” metal oxides and their platinum doped counterparts to methane combustion

A range of metal oxides have been compared as methane combustion catalysts. The effect of modification to generate “superacidic” behaviour on the activities of ZrO₂ and Fe₂O₃ systems has been studied. It has been shown that whilst sulphation lowers the activity of Fe₂O₃, sulphation and, particularly, molybdation enhance the performance of ZrO₂. Despite enhancing the activity of the unmodified base oxides, the addition of low levels of Pt has been demonstrated to poison the activity of “superacidic” zirconias.     

Theory of “Cohesive” vs “Adhesive” Separation in an Adhering System

It is shown that there is limited validitity to the doctrine that true interfacial separation, in an adhering system, is highly improbable. An analysis employing the Griffith-Irwin crack theory yields these results: The important parameters are, difference in elastic moduli, ΔE; differences in g, the energy dissipation per unit crack extension; thickness, Δ₁ or δ₂, of the region where dissipation occurs; and the presence or absence of strong interfacial bonds. If the forces across the interface are appreciably weaker than the cohesive forces in either phase, there is a strong minimum in g at the interface. For flaws of equal size, an interfacial flaw will be the site of initiation of failure. If strong interfacial bonds are present, then if Δg and ΔE have the same sign, failure is most probable, deep within one phase. If Δg and ΔE have opposite signs, failure may be initiated, and may propagate, at a distance δ from the interface, in the phase with lower g. This may be mistaken for weak-boundary layer failure.     

From “Strong” to “Much Stronger”: Utilization of Green Tea Extract Dispersant for SWCNT‐Reinforced Polymer Composites

PVA is reinforced with SWCNTs using green tea extract as a dispersant to achieve good dispersion of the SWCNTs in an organic solvent and finally high‐performance composite fibers. A combination of green tea extract/DMSO/SWCNT/PVA is found to disperse larger aggregates of SWCNTs to individual or thin bundles of a few nanotubes. Incorporation of 0.5 wt% SWCNTs into PVA fibers yields a tensile strength of 2.42 GPa, a Young's modulus of 46 GPa, toughness of 105 J · g^?1 at a failure strain of 11%, and a loop strength of 245 MPa, much higher than the values of commercial PVA fibers. The incorporation of highly dispersed SWCNTs suppresses the fibrillation tendency of the PVA fibers. The applied load is effectively transferred from the matrix to the SWCNTs.

     

Inhibitor properties of “green” pigments for paints

Zinc chromate is one of the anticorrosive pigments most frequently used in the formulation of primers. However, its environmental aggressiveness and toxicity severely restrict its use, and different green alternatives have been proposed in order to replace zinc chromate. In the last decade, the behaviour of zinc phosphate as anticorrosive pigment has been intensively researched. During this time, various modifications have been made to this family of pigments to improve its properties, and a “second generation” of phosphate pigments, incorporating elements such as molybdenum, aluminium, or iron, has been produced. In this paper, the inhibitive properties of zinc phosphate and three second-generation phosphates have been investigated, using zinc chromate pigment as a reference. Pigment extract solutions, at different values of pH, have been used as corrosive media. Carbon steel samples were immersed in such solutions and their corrosion rates were measured using electrochemical techniques. The data obtained suggest that zinc chromate provides the highest percentage of inhibition in neutral and basic solutions, but phosphate-based pigments showed better results in acid solutions. Given this performance advantage, together with their less harmful environmental impact, these phosphate-based pigments can be proposed as realistic alternatives to chromates in the formulation of protective paints for use in acidic conditions.     

The role of pore structure in the catalytic behavior of “unaged” and “aged” silica-alumina catalysts

This is a review of research concerning the role played by the porous structure of silica-alumina catalysts on the evolution of organic catalytic processes. A strong effect of the geometrical shape of the pores on catalytic activity and selectivity has been evidenced. The experimental results have also been interpreted by means of a simplified mathematical model, able to relate selectivity for a reaction of the type A → B → C to the geometrical features of macro-microporous catalyst pellets, or granules. The theoretical results are in qualitatively satisfactory agreement with the experimental data.     

The “alexandrite effect” in gemstones

The term “alexandrite effect” is used in gemology to describe a distinct change of color appearance when a gemstone is switched from daylight to incandescent light. Gemstones that exhibit the alexandrite effect can actually be divided into four categories based upon the value of the calculated absolute hue-angle change of the material under different pairs of illuminants. the alexandrite effect is a non-color-constancy phenomenon. It can be explained by a combination of both chromaticity adaptations to the different light sources, and vision system responses to the spectral distribution of the light emitted by alexandrite effect gemstones when they are illuminated alternatively by the different light sources.