Hydrogen reduction etching

Measurements of channel roughness by Atomic Force Microscopy for two Philips Photonics MCPs, etched-only and etched and weak-acid-polished , found rms surface roughness of 50A and 22A respectively [5]. There is also some evidence [5] that the hydrogen reduction process used in MCP manufacture also reduces the surface irregularities. It therefore does not seem unreasonable that manufacturers will be able to produce MCPs with surface roughnesses of lOA as required for efficient hard X-ray focusing. 

We reported in a recent paper (18) that a "fresh" n-Ti02 electrode (i.e., the electrode just prepared by the procedures of polishing, etching, annealing and hydrogen reduction at an elevated temperature as described in the experimental section) showed only a weak photocurrent and no PL in the first potential scan, but both the photocurrent and the PL intensity increased very much with time nearly in parallel to each other and finally reached maxima while the the potential scans were repeated under illumination in 0.05M H2SO4. Such initial changes were in most cases accompanied by the formation of a lot of micropores at the electrode surface. 

Crevice corrosion on titanium typically generates irregularly shaped pits. Microstructural examination of hand-polished and etched sections of crevices often reveals a surrounding layer of predpi-tated titanium hydride in a alloys. These are a by-product of hydrogen reduction at cathodic sites surrotmding the crevice. 

Here we describe some of the results. In each of these studies, the compound semiconductor was first etched in either acid or base to remove the oxide. The specific surface groups following the etch are not well understood. However, Pluchery et al. have followed the acid etching of InP by in situ infrared spectroscopy [175] and observed the removal of the oxide. Unlike Si, for which an acid (HF) etch leaves the surface hydrogen-terminated and temporarily passivated, acid etching of InP does not produce a chemically passivated surface. Presumably, the surface is left unprotected, and quickly oxidizes if not passivated by another process. Similar results showing reduction or removal of the oxide are seen for GaAs [174,176,177]. 

Tonkovich et al. [123] claimed a 90% size reduction due to the introduction of micro channel systems into their device, which made use of the hydrogen off-gas of the fuel cell anode burnt in monoliths at palladium catalyst to deliver the energy for the fuel evaporation. A metallic nickel foam 0.63 cm high was etched and impregnated with palladium to act as a reactor for the anode effluent It was attached to a micro structured device consisting of liquid feed supply channels and outlet channels for the vapor, the latter flowing counter-flow to the anode effluent... 

The shortened electron life model is mainly based on the observation that the decrease of etch rate with boron concentration exhibits an inverse fourth power dependence on the boron concentration. Raley et postnlated that etching in KOH is a corrosion process and that the etch rate reduction at high boron doping levels is due to the decreased electron concentration required for the reduction of hydrogen in the etching process described by the following reactions ... 

In this reactor, the feed solution enters via a central channel between the anode and cathode beds and then flows in the upward and downward vertical directions (where the majority of the solution passes through the porous cathode). When the cathode bed is filled to capacity with deposited metal, the polarity of the electrode beds is reversed and the metal is electrochemically etched into a small liquid volume to create a concentrated solution. The longer the contact time of the metal-laden solution in the porous cathode, the greater the extent of metal removal (where the contact time is inversely proportional to the catholyte flow rate and directly proportional to the cathode bed thickness). To maximize the energy efficiency for metal removal, the entire bed should operate at or near the metal reduction limiting current density, but this is difficult to achieve because of unwanted hydrogen gas evolution. The relevant differential equations are solved to obtain the metal ion concentration, electric potential, and current density distributions in the cathode bed are [125]... 

Decoking of catalyst pellets Ion exchange reactions Hydrogen storage in metal lattice Semiconductor doping Combustion of coal Reduction of ore Production of acetylene from CaC2 Semiconductor etching... 

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