Carbon corrosion analysis

Following from the previous work of Kinoshita and Bett,49 50 a detailed analysis of carbon corrosion in hot phosphoric acid was carried out by Stonehart and MacDonald.68... 

Linse, N., Scherer, G.G., Wokaun, A., and Gubler, L. (2012) Quantitative analysis of carbon corrosion during fuel cell start-up and shut-down by anode purging. J. Power Sources, 219, 240-248. 

Carbon corrosion through evolution especially of carbon dioxide and a corresponding reduction in catalyst support surface area can be detected with exhaust gas analysis. The increase in the cathode resistance can be observed with impedance spectroscopy. 

Acknowledgments The authors would like to thank Susan Yan and Chunxin Ji for providing MEA samples. Furthermore, we would hke to acknowledge Mike Budinsld, Brian Brady, and Brian Litteer for their analysis of carbon corrosion induced electrode thinning, as well as Robert Moses and Kaiman Subramanian for their experiments on the effect of potential cycling on carbon corrosion. 

One should keep in mind that carbon corrosion, especially in a later stage of the tests performed here, also may change the porous structure of the cathode catalyst layer concomitant with a void volume loss (Patterson and Darling 2006 Yu et al. 2006) and also with complete deterioration of the catalyst layer, which was confirmed by scanning electron microscopy postmortem analysis of the start-stop-cycled MEA. 

Other online techniques can be used to examine the change in electrode or electrolyte materials. If parts of the electrode or electrolyte are lost due to reaction, finite vapor pressure, or other reasons, analysis of the effluent product can often be correlated to the particular loss mechanism. For example, in PEFCs, one mode of physicochemical electrolyte degradation is accompanied by loss of the fluorine ion, which can be detected by measurement of the effluent condensed water fluorine content. Also, if carbon corrosion is occurring, carbon monoxide or carbon dioxide gas is produced, and this can be measured with a sufficiently sensitive device. In general, if there is a chemical reaction causing the degradation, the product species from this can be detected in the effluent and correlated with the measured loss. 

Specifications, Shipping, and Analysis. Hydrogen fluoride is shipped in bulk in tank cars (specification 112S400W) and tank tmcks (specification MC312). A small volume of overseas business is shipped in ISO tanks. Bulk shipments are made of anhydrous HF as well as 70% aqueous solutions. A small amount of aqueous solution may be shipped as 50%. Cars and tmcks used for anhydrous HF transport are of carbon steel constmction. It is possible to ship 70% aqueous in steel from a corrosion standpoint however, mbber lining is commonly used to eliminate iron pickup, which is detrimental to product quaUty in a number of appHcations. Hydrogen fluoride of less than 60% strength must always be shipped in lined containers. 

A typical microbiological analysis in a troubled carbon-steel service water system is given in Table 6.2. Table 6.3 shows a similar analysis for a cupronickel utility main condenser that showed no significant corrosion associated with sulfate reducers. When biological counts of sulfate reducers in solid materials scraped from corroded surfaces are more than about 10, significant attack is possible. Counts above 10 are common only in severely attacked systems. 

Recommended practice for applying statistics to analysis of corrosion data Practice for operating light- and water-exposure apparatus (carbon-arc Type) for exposure of nonmetallic materials Method for detecting susceptibility to intergranular attack in wrought nickel-rich, chromium-bearing alloys... 

Corrosion under insulation is a major problem with carbon steels and must be taken into consideration in the RBI analysis of any plant to avoid serious failures. Several techniques are available to minimize this attack including painting, spraying with aluminum, and/or wrapping with aluminum foil. 

Partial what-if analyses for the two example processes described in Section 4.0 are shown in Tables 4.9 and 4.10. Although for actual, more complex analyses, the what-if tables for each line or vessel would be separate, for these examples, a single table was developed. A preliminary hazard analysis (PHA) would identify that the intrinsic hazards associated with HF are its reactivity (including reactivity with water, by solution), corrosivity (including carbon steel, if wet), toxicity via inhalation and skin contact, and environmental toxicity. The N2 supply system pressure is not considered in this example. The specific effects of loss of containment could be explicitly stated in the "loss of HF containment" scenarios identified. Similarly, the effects of loss of chlorine containment, including the reactivity and toxicity of chlorine, could be specified for the second example. 

SACHEM Inc., located in Cleburne, Texas, is a producer of high-purity bulk chemicals for companies that have high-purity requirements in their chemical processing. As stated in Workplace Scene 1.2, one of their products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. The analysis of TMAH for trace anions such as chloride, nitrate, nitrite, and carbonate is critical for SACHEM s quality control laboratory. If these ions are present on the integrated circuit boards manufactured by one of their semiconductor customers, they may cause corrosion severe enough to affect the functionality and performance of the electronic devices in which the circuit boards are used. In SACHEM s quality control laboratory, ion chromatography procedures have been developed to measure the anion concentrations in TMAH. Because the concentration levels are trace levels, a clean room environment, like that described in Workplace Scene 1.2, is used. A special procedure for carbonate analysis is required so that the absorption of carbon dioxide from the atmosphere can be minimized. 

Surface Carbon Analysis. This method is based on the observation that the presence of carbon on automotive body sheet steel, for instance, can be linked to poor corrosion performance. The carbon content on the surface can be determined by subjecting the body sheet to about 500°C in an oxygen environment and determining the CO2 thus formed. 

Occasionally a species of whito lead is produced by tho Dutch method, which yields on analysis numbers corresponding to the formula 3 (Pb 0, COa) Pb 0, IIO that is, three equivalents of carbonate to one of oxide of lead. It has a loose friable texture when drawn from the heights, quite distinct from the hard cratos of whito lead obtained when the metal is almost wholly converted and is invariably the result of defective corrosion of tho motal. This kind of white lead does not cover so well as the hard lead. 

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

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