Trends in the Electrochemical Polarization Potentiodynamic Reactivation Method – EPR

This method designed to examine the susceptibility to nonuniform corrosion, ranks among the more successful technique developments. One of its numerous advantages is that it allows nondestructive, on-site examination. EPR measurements are used to establish the resistance of stainless steels and alloys to intergranular corrosion and stress corrosion cracking e.g. in nuclear engineering applications as well as to study grain boundary precipitation and other minute local changes in alloy composition and structure. By the EPR test, the specimen and/or the field object (working electrode) is tested in acid solutions, most often in solutions of sulfuric acid (c = 0.01–5 mol dm–3 H2SO4) and potassium thiocyanate (c = 0.001 to 0.1 mol dm–3 KSCN). The principle of the measurements is to reactivate the sample from the incomplete passivity region. This indicates local changes in chemical composition in relation to phase transformations

Critical Pitting Temperature Measurements for Evaluating Superaustenitic Stainless Steels Resistance to Solutions Modeling Wastewater Treatment of Flue Gas Desulfurization Plants

Critical pitting temperature (CPT) determination by potenciostatic procedure is often used as a method of screening stainless steels in solutions with activity range 0.067 – 4.3. Values of activity of chloride ions as well as pH values for those solutions are quite different from the values of the same parameters in solutions modeling wastewater treatment of flue gas desulfurization plants. In those waters the soluble components, mainly calcium chloride (which must be treated by evaporation and crystallization) can give solutions with pH values below 4and activities of chloride ions much more higher. Thus, even small changes of CaCl2 concentration can give an increase in chloride ions activity. In the work reported here the effect of two different activities of chloride ions was investigated using potenciostatic CPT measurements on superaustenitic stainless steels in c = 5.685 and 5.88 mol L–1 CaCl2 solutions with pH values below 4. The results demonstrated that an increase in the activity of chloride ions causes a decrease in the potentialat which, for given a temperature, the growth of stable pits is possible

Gender differences in coerced patients with schizophrenia

European Commission (Quality of life and Management of Living Resources Programme, contract number QLG4-CT- 2002-01036), Czech Ministry of Education research grant MSM002160849, and research grants PRVOUK–P26/LF1/4 and PRVOUK–P03/LF1/

The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel

The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures

A thermodynamic and kinetic basis for understanding chromium depletion in Ni-Cr-Fe alloys

Thermodynamic and kinetic models are constructed to describe the development of the chromium depleted zone in Ni-Cr-Fe alloys heated in the range 773-1173 K. The models are interactive and constitute a computer program called DEPLETE. The thermodynamic model is constructed using the Kohler method for the description of the free energy of a multi-component system. It provides the chromium concentration at the carbide-matrix interface as a function of alloy composition and temperature. The kinetic model tracks the shape of the chromium profile as a function of time at temperature and grain size. Model results show that the interfacial chromium concentration decreases for increasing carbon concentration and decreasing heat treatment temperature. Experimental verification of the model is made using high resolution energy despersive X-ray analysis via STEM. Measured results agree well with model results for the dependence of chromium depletion on various input parameters as well as the magnitude and shape of the chromium depleted zone. Experimental measurements also show that the grain boundary carbides are of the form M7C3 where M is about 96% chromium. Results confirm that carbide precipitation at the grain boundary is controlled by volume diffusion of chromium in the matrix and that in the temperature range 873 to 1073 K the chromium concentration in the grain boundary accurately approximates the carbide-matrix interfacial concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25692/1/0000246.pd