Platinization, effect

Anson and King [47] noticed the accelerating effect of surface oxides on both steps in the reduction of oxygen and explained it by the fact that reduction of oxides leads to a slight platinizing effect on the electrode. The authors were inaccurate in that the first stage is not accelerated but retarded under the influence of oxides [48]. 

In such cases basket anodes are frequently used. These have a relatively large surface and work at a low driving voltage due to their special construction. A cylinder of platinized titanium-expanded metal serves as the basket to which a titanium rod is welded. This serves as the current lead and carrier, and ends in a plastic foot that contains the cable lead and at the same time serves as the mounting plate. The expanded metal anode exhibits a very uniform anode current density distribution, even at large dimensions, in contrast to the plate anode. The reason is the many comers and edges of the metal that make the point effect only evident at the outer edges of the anode. 

Similar size effects have been observed in some other electrochemical systems, but by far not in all of them. At platinized platinum, the rate of hydrogen ionization and evolution is approximately an order of magnitude lower than at smooth platinum. Yet in the literature, examples can be found where such a size effect is absent or where it is in the opposite direction. In cathodic oxygen reduction at platinum and at silver, there is little difference in the reaction rates between smooth and disperse electrodes. In methanol oxidation at nickel electrodes in alkaline solution, the reaction rate increases markedly with increasing degree of dispersion of the nickel powders. Such size effects have been reported in many papers and were the subject of reviews (Kinoshita, 1982 Mukerjee, 1990). 

Smirnova NW, Petrii OA, Grzejdziak A. 1988. Effect of ad-atoms on the electro-oxidation of ethylene glycol and oxalic acid on platinized platinum. J Electroanal Chem 251 73-87. 

In the case of complexes such as (21) and (23) which have an extended planar ligand, a significantly higher proportion of interstrand cross-links in DNA is formed in comparison to either cis- or trans-platin.172 The steric effects of these planar ligands result in the formation of structurally unique 1,2-interstrand cross-links like those formed by cisplatin, a unique example of how steric effects may alter a nonactive lesion into an active one (Figure 13).173,174 Model studies predicted this outcome by preparation of the monofunctional models trans-[PtCl(9-ethylguanine) (NH3)(quinoline)] and comparison of substitution rates of the Pt—Cl bond by G or C mononucleotides.175 176 Interestingly, the iminoether compound (25) appears to form predominantly monofunctional adducts with DNA.177... 

Bioassays of a considerable number of drugs embodying a combination of porphyrin and cis-platin moieties in the same molecule have led to compound (43) in vitro and in vivo studies on this compound showed a phototoxicity which was additive to the cytotoxic effect of the platinum moiety.190-193... 

Harbour, J.R., Wolkow, R., and Hair, M.L, Effect of platinization on the photoproperties of CdS pigments in dispersion. Determination by H2 evolution, 02 uptake, and electron spin resonance spectroscopy, /. Phys. Chem., 85, 4026, 1981. 

The first explicit information appeared in 1953 in two U.S. patents (9) which showed that platinum black as well as platinized asbestos or silica were effective for addition of trichlorosilane to olefins. Platinum on charcoal was unusually active with trichlorosilane and acetylene, ethylene, butadiene, vinyl chloride, or vinylidene fluoride. Temperatures as low as 130°C were sometimes employed. 

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

The largest uncertainty with using this method to measure densities arises from the surface tension effect between the liquid surface and the wire or string. To circumvent this problem many workers (4) have platinized the wire in the region at which it contacts the liquid surface. Another problem with this method is that it is difficult to control evaporation from the solution being studied. For precise work it is necessary to analyze an alloquot of solution after the density is determined. 

The porosity of an electrode surface will significantly influence its electrochemical behavior, especially because of a considerable decrease of the effective current density in case of materials with a high microporosity and consequently a large effective surface area. A well-known example is platinized platinum that can enable... 

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