Platinum foils, etching

Fig. 17. The character of etching of platinum foils in ethylene/oxygen mixtures is a function of gas phase composition. Under excess fuel conditions between 500 and 700°C, carbon films containing platinum particles form on top of the foil. TEM micrograph of a carbon film formed after 40 h of treatment at 587°C in a fuel excess O2/C2H4 mixture (region IV). (Reprinted with permission from (55). Copyright 1985 American Chemical Society.)...

Dean, V. W., Frenklach, M. and PhiUips, J. (1988), Catalytic etching of platinum foils and thin films in hydrogen-oxygen mixtures. Journal of Physical Chemistry, 92, 5731-8. 

A three-electrode electrochemical cell was used for electropolymerisation connected to a Solartron 1470 MultiStat potentiostat. An Al-2024 panel, previously cleaned by etching in NaOH and desmuting in HN03, was the working electrode and a platinum foil served as the auxiliary electrode. All potentials were recorded versus a saturated calomel electrode (SCE) serving as the reference electrode. A 0.2 M electrolytic solution was used in the case of CSA, pTSA, PPA and OA, with a 0.1 M solution of Ce(N03)3 and 0.1 M pyrrole monomer for all solutions. Deposition took place under a potentiodynamic regime by sweeping the potential from 1 to +3 V vs SCE for five cycles at a scan rate of 30 mV s h... 

Figure C.7 illustrates the steps required to electrochemically etch Si. A Teflon cell fitted with a Viton o-ring is shown in (a). A silicon wafer is placed polished side down onto the top of the o-ring, (b). A piece of aluminum foil is placed on top of the wafer backside and the plastic backplate is screwed into place, (c). The polished side of the wafer is shown from the top of the Teflon cell in photograph (d). The wafer surface is treated with 10% HF(aq) for 10 min. to remove any native oxide layer, followed by rinsing with water and ethanol. The cell is then filled with an electrolyte consisting of 12.5% HF (HF H20 Et0H of 1 4 3), and a platinum electrode is immersed into the solution, (e). Electrical connections to the platinum and aluminum electrode surfaces are made (note current flows from the bottom to top) and appropriate current started. Photograph (g) shows the presence of tiny bubbles that indicate the electrochemical anodization of the silicon substrate. The final etched wafer is shown in (h), which is rinsed with water and ethanol and dried under a flow of nitrogen. Using a current of 54 mA.cm for 20 min. for a p-type Si(lOO) substrate with a resistivity of 20-50 fl.cm results in a macroporosity (70%) with pores 2-3 pm in diameter and 40-50 pm depth (e.g.. Figure C.8).

Nowadays, while reaction conditions are more or less the same, seven to ten layers of gauze are rrsed to ensitre that the gauze is imiformly heated, and to avoid carbon deposition. The process operates at about 70% conversion and reqitires rapid cooling. As in ammonia oxidation, the siuface of the platinum alloy is etched as it is activated. Metal foil catalysts have often been formed from expanded sheets... 

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