ارزيابي رفتار خوردگي داغ آلياژهاي زير كونيوم در نمك هاي نيترات مذاب

چكيده انگليسي :

Evaluation of hot corrosion behaviour of zirconium alloys in molten nitrate salts Iman Momeni i momeni@ma iut ac ir September 22 2013 Department of Materials Engineering Isfahan University of Technology 84156 83111 Isfahan Iran Degree M Sc Language Persian Dr Keyvan Raeissi Assoc Prof Supervisor E mail k raeissi@cc iut ac ir Dr Mohamad Ali Golozar Prof Supervisor E mail golozar@cc iut ac ir Abstract The most important application of zirconium and its alloys is in nuclear reactors thus the corrosion behavior of zirconium at high temperature in the vicinity of reactors coolant is of particular importance One of the reactors coolant are molten nitrate salt that in a wide range of temperatures in the high temperature are used in liquid form In this study the corrosion behavior of the high temperature of Zircaloy II alloy investigated by electrochemical polarization test electrochemical impedance spectroscopy test and Mott Schottky test in molten eutectic sodium nitrate potassium nitrate For this purpose an electrochemical cell was equipped with a heating system Sodium nitrate and potassium nitrate salts eutectic ratio of 50 50 eutectic conditions was used as the electrolyte Polarization tests to evaluate the corrosion behavior of Zircaloy II alloy were performed in the electrolyte at four temperatures 250 300 350 and 400 C and Inhibitory effect of K2CrO4 and NaNO2 were studied at 350 C also the corrosion behavior of zirconium alloy was compared with the corrosion behavior of 304 stainless steel at 350 C In order to identify potential properties of the passive layer and the their differences electrochemical impedance spectroscopy tests were performed and in two potential 0 2 and 0 2V at 350 C Mott Schottky tests were performed in three ranges of potential in the passive area at 250 and 350 C by polarization curves for Zircaloy II alloy was concluded passive conditions at four temperatures reach above it and it was found that corrosion potential corrosion current density and passive current density increases with increasing temperature Corrosion behavior of zirconium alloy in molten salt eutectic of sodium nitrite potassium nitrate was better than 304 stainless steel because the passive current density of the zirconium sample was lower K2 CrO4 inhibitor Indicated most effective in reducing the corrosion rate and passive current density in lower concentration but inhibition efficiency of NaNO2 was higher By Mott Schottky curves determined that passive layer is changing near the zero potential than reference electrode silver silver nitrate and the type p semiconductor is converted to n type semiconductor therefore the slope of the polarization curves changes in the vicinity of this potential the slope of Mott Schottky diagrams in temperature 250 C was higher than the temperature 350 C due to the lower number of anionic and cationic vacancies The difference of anionic and cationic vacancies causes changing passive layer properties and samples color after polarization tests at different temperatures Electrochemical impedance spectroscopy curves showed that the increasing potential 0 2 to 0 2V increase thickness of passive layer By anodic branches of the polarization curves was observed the anodic dissolution mechanism change by changing the oxidation state of zirconium from Zr2 to Zr4 Keywords Zirconium alloys Hot corrosion Nitrate salts PDF created with pdfFactory trial version www pdffactory com

مومني، ايمان

ارزيابي رفتار خوردگي داغ آلياژهاي زير كونيوم در نمك هاي نيترات مذاب