Resistive anode

A dimensionally stable anode consisting of an electrically conducting ceramic substrate coated with a noble metal oxide has been developed (55). Iridium oxide, for example, resists anode wear experienced ia the Downs and similar electrolytic cells (see Metal anodes). 

Rise in anode resistance, anode exhausted Raise rectifier voltage or install extra anodes, test anode cormection... 

Resistive Anode Encoder (RAE). This detector has the advantage that the single-ion events are detected digitally. It therefore it delivers quantitative results, irrespective of local differences in the amplification of the channel plate. One disadvantage is that the count rate is limited to 200000. 

For detection of secondary ions a laterally resolving detector is necessary. In the first step a channel plate for amplification is used secondary electrons from the output of this device are accelerated either to a fluorescent screen or to a resistive anode. If a fluorescent screen is used the image is picked up by a CCD camera and summed frame by frame by use of a computer. The principal advantage of this system is unlimited secondary ion intensities, but compared with the digital detection of the resistive anode encoder the lateral and intensity linearity is not as well-defined. 

In solvents that strongly resist anodic oxidation as MeCN, CH2CI2/CF3CO2H, or T SOjH CH-bonds in the alkyl chain can be oxidized. In acetonitrile a preferential acetamidation in the (co-2)- and ((B-l)-position occurs (Eq. 43) [352]. 

Many substances are oxidized only at rather high anodic potentials, which narrows the available selection of corrosion-resistant anode materials. An alternative to platinnm metals are certain metals with an oxide coating (Pb02, Mn02, Sn02) which... 

Cheng, Z, Zha, S, and Liu, M. Stability of materials as candidates for sulfur-resistant anode of solid oxide fuel cells, J Electrochem Soc, 2006 153 A1302-A1309. 

S. Charbonneau, L. B. Allard, J. F. Young, G. Dyck, and B. J. Kyle, Two-dimensional time resolved imaging with 100-ps resolution using a resistive anode photomultiplier tube, Rev. Sci. Instrum. 63(11), 5315-5319 (1992). 

Ceramic Materials An example of a sufficiently conductive metal oxide is magnetite Fe304, which has been used, for example, in the past as corrosion resistant anode material for industrial chlorine evolution (it can be smelted and casted at 1500 °C, but it is a very brittle material). 

Even though the above work is providing a stable, non-sintering, creep-resistant anode, electrodes made with Ni are relatively high in cost. Work is in progress to determine whether a cheaper material, particularly Cu, can be substituted for Ni to lower the cost while retaining stability. A complete substitution of Cu for Ni is not feasible because Cu would exhibit more creep than Ni. It has been found that anodes made of a Cu - 50% Ni - 5% A1 alloy will provide long-term creep resistance (36). Another approach tested at IGT showed that an "IGT" stabilized Cu anode had a lower percent creep than a 10% Cr - Ni anode. Its performance was about 40 to 50 mV lower than the standard cell at 160 mA/cm. An analysis hypothesized that the polarization difference could be reduced to 32 mV at most by pore structure optimization (37). 

For an electrolyser, instead of an isentropic coefficient, we take into account the overvoltage necessary for driving the electrolysis (ohmic resistance, anodic-cathodic overvoltage) here the exergy loss is simply connected to this overvoltage by Faraday s law ... 

In general Cu is added to lead in amounts of up to 0.08% Alloys with addition of Ba, Ca, Co, Au, Li, Mg, Ni, Pt, Na, Ti and Zn have been tested for corrosion resistance anodes made of Ni and Ti give good performance in sulfuric acid solutions Ni in lead improves the weldability of steel during lead coating... 

Figure 3.16. Schematic representation of the correlation between polarization resistances (anode, cathode, and cell) and polarization curves [23], (With kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Characterization of membrane electrode assembhes in polymer electrolyte fuel cells using a.c. impedance spectroscopy, 32(8), 2002, 859-63, Wagner N. Figure 6.)...

In addition to yields, current density and anode life are also important in evaluating an electrochemical synthesis. Although the current density should drop as water (a strong electrolyte in HF) is consumed, it does not always do so. Instead, for the first 15-30 minutes of electrolysis it increases in both continuous and interrupted electrolysis. This may be caused by a breakdown in a resistive anode coating. Once a maximum current is reached, the current density remains constant however, it drops as the last few tenths percent of water are consumed. Also, high water levels (>3%) cause low current densities. The current density maximum was at 0.5-1.0 mole % water. 

Ionic path impedance through the ceramic phase and electronic path impedance through the metallic phase have been found to be dominant factors in determining the electrode characteristics.In order to provide a low sheet resistance anode, it is imperative that the metallic and ceramic phases have maximized continuous paths that allow ionic and electronic migration from the electrolyte/anode interface throughout the entire anode. 

Many start-up/shutdown procedures have aimed to reduce the corrosion current through practices such as anode purging and shunting. Others have attempted to nse more stable carbon materials such as graphitized carbon and carbon nanotnbes (CNTs). - To delay the onset of the COR during fuel starvation, WOR catalysts have been incorporated into the anode electrodes. Increasing anode ionomer content has also been recommended for a fnel starvation-resistant anode because it increases the amount of water available for the WOR. - In general, the materials approaches are applicable to all kinds of carbon corrosion. 

The anodic oxidation of chemisorbed Q also appears to follow the above reaction pathway. Evidence is provided by HREELS spectra (Fig. 22) obtained when the potentials are made progressively more positive. It can be seen that the spectral features for unimpaired Q persist, but with diminished intensities, at anodic-oxidation potentials. The new peaks above 3000 cm are due to the formation of hydrated surface oxides. Evidently, a small fraction of chemisorbed Q is also able to resist anodic oxidation Unfortunately, no acceptable EC-STM images could be obtained due... 

The resistive chain, shown in Fig. 8, can be a resistive anode wire itself, for instance in a linear position sensitive detector, or it can consist of resistors connecting the cathode read-out pads. 

As compared to the previous method, this technique uses the resistive chain as a component of a diffuse transmission line The resistive elements are replaced by a highly resistive anode wire which, together with its capacitance per unit length, forms a distributed RC-transmission line. The anode wire can be made as a quartz fiber coated with carbon. 

In fact, in this method there is no necessity of any other read-out electrode, as for instance in the case of the delay-line technique. This can be certainly an advantage. But unluckily, the highly resistive anode wire shows to be very sensitive to mechanical damage. An occasional high voltage breakdown either destroys the coating or, at least, changes its properties locally and thus the detector response. 

In the case of an ac discharge, the thermal nature of the sample volatilization may decrease in favor of sputtering, as the thermal energy released is lower. Therefore, ablation of the anode begins to occur, which may be kept low by taking very hard and high-temperature resistant anode materials such as tungsten. This approach may be useful for the ablation of very weak and easily volatile metals such as lead alloys. 

The anode is stabilized by using mixed powders of Ni-Cr, Ni-Al, or refractory oxides and sintered at 900-1100°C under a reducing atmosphere to provide a creep resistant anode structure. The function of the additives is to reduce the loss of porosity during sintering and develop creep resistant materials. The creep is referred to as the shrinkage in thickness and change in shape. The sintering resistance is increased by the additives, which are usually metals or oxides of metals. 

Resistive anode position readout systems have been used extensively in applications with MCP s and gas proportional counters (78-91). The anode consists of a resistive coating (several 100 kft) applied to an insulating substrate, ensuring that the coating resistivity is uniform. A simple one dimensional readout can take the form of a rectangular sheet with contacts at opposite ends, and a simple two dimensional readout can be a square sheet with contacts at the corners. A particular advantage of resistive anode readouts is the small number of amplifiers required only four amplifiers are required for full 2 dimensional imaging. These anodes are usually mounted close (< 1 mm) behind the MCP output face. 

The above discussion is presented merely to give an idea of the types of EUV detectors and their applications in use on present fusion plasma experiments. It is by no means an exhaustive list of possibilities. Indeed, several different detectors are in use or being planned in future experiments. Resistive anode encoders will probably see more use in fusion experiments as they become commercially available. However, the low count rates available ( 10 to 10 sec-1) will result in these detectors being used mostly for line profile studies (e.g., ion temperature measurements via Doppler broadening measurements). Intensified CCD arrays (back-illuminated or otherwise), vidicon or CID systems, lens-coupled intensifiers, and anode detectors have all seen some use on tokamak experiments or are planned for the near future, but have not been widely used as yet. However, in terms of availability, pixel format, dynamic range, insensitivity to magnetic fields, compact package, and moderate cost, the IPDA remains the most versatile multichannel EUV detector for plasma spectroscopy. 

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