Liquid-phase stereoselective thymol hydrogenation over supported nickel catalysts

The stereoselective hydrogenation of thymol was studied in liquid phase over several nickel catalysts, modified by coimpregnation of inorganic compounds containing chlorine. The total activity of all catalysts studied was decreased and was on the same order of magnitude, indicating that chlorine even after reduction remains on the surface and is responsible for the poisoning effects. Such blocking of accessible sites results in similar reaction rates for the catalysts studied. Selectivity and stereoselectivity to menthols and menthones changed significantly. The modifiers could influence the rate of keto-enol transformations, which is thought to be the key selectivity and stereoselectivity governing step.     

Potentiostatic step experiments on pasted Pb-Sb and Pb-Sn-Ca electrodes

A range of cyclic electrochemical experiments have been carried out on electrodes of porous PbO₂ supported on a number of Pb-Sb and Pb-Sn-Ca alloys using micro-computer controlled potentiostatic stepping techniques. The results show that, in certain cases, the differences in electrochemical behaviour of the PbO₂ can be interpreted as being due to the effect of the support alloy.     

The anodic behaviour of zinc in KOH solution. V: Galvanostatic polarization with an interruption

Galvanostatic polarization experiments, in which the current flow is interrupted and re-established, show that the process of passivation is controlled by the transport of mass in the solution phase.Part IV: M. J. Brook and N. A. Hampson,Electrochim Acta 15 (1970) 1749.     

The differential capacitance of solid tantalum in some aqueous solutions

The differential capacitance of tantalum has been measured in a number of aqueous electrolyte solutions. The metal is generally covered with an oxide layer in solutions of simple inorganic anions and the electrode capacitance is 5–10 F cm^–2. In solutions of oxalate anions the electrode capacitance is much higher and corresponds to that expected for a clean metal in contact with an aqueous solution.     

Interactive image processing in research

The objective of the work described here was to build an interactive and multi-purpose image processing system and to use that system to solve practical problems. The system was built and it was demonstrated that it could be used to measure the size of gas bubbles in a gas---liquid reaction system. Photographs of gas bubbles were available from high-speed schlieren motion picture studies and image processing is a feasible way to make large numbers of measurements of bubble size quickly and accurately.     

Nonlinear Optic Nanocomposites Based on Oxide Glasses

The first nonlinear optic nanocomposite based on a low-melting vitreous matrix and a ferrielectric crystal has been obtained. The matrix consists of lead-borate glass and the filler is single-phase powder of ferrielectric KNbSi₂O₇. The quadratic optical nonlinearity of composites was studied depending on temperature and time of dissolution of crystals in the glass matrix. Conditions for producing transparent nanocomposites that generate the second optic harmonic are identified.     

Product composition of the dynamic conversion of brown coal in supercritical water

The product composition of the dynamic conversion of brown coal, which was continuously supplied as a water-coal slurry to a flow reactor at 30 MPa, was studied. The temperature of water and coal particles was increased from room temperature to 400°C (top part of the reactor). The conversion of the organic matter of coal was ～48%, and the products collected at the reactor outlet consisted of solid tar components, substances dissolved and emulsified in water, and volatile substances, whose major constituent was CO₂. The composition of solid tar components and oils was determined.     

Acid- and alkali-catalyzed tannin-based rigid foams

Acid- and alkali-catalyzed polyflavonoid tannin-based rigid foams were prepared. These foams have comparable physical and mechanical properties to the synthetic phenolic rigid foam used as a comparative standard. The fluid polymer phase was based on a mimosa tannin-formaldehyde resin with a minor addition of a fortifier resin. Expansion of the fluid phase was brought about by a physical blowing agent, whereas dimensional stabilization was achieved through cross-linking at the desired density. In the case of the acid-catalyzed foam, a heat-generating agent in the form of furfuryl alcohol was employed. The polymer composition of tannin–formaldehyde/urea–formaldehyde systems as a function of pH was predicted from the respective gel times and rate constants, i.e., above pH 7, the copolymer proportion will tend to 100% and, that at pH 3.4, the polymer blend proportion will tend to a maximum. © 1994 John Wiley & Sons, Inc.     

Unfired dolomite refractories with increased hydration resistance

Conclusions The use of dolomite burnt in grain form for the manufacture of unfired goods with a tar bond makes it possible to obtain refractories with a high hydration resistance and with high physicomechanicai properties. Coal tar with a 65–70% pitch content should be used as a bonding agent.Sintered grain dolomite should be added to the batch without being ground, preferably in combination with finely ground metallurgical magnesite or magnesite-dolomite clinker.