Electrochemical processes and systems: application for tutors

The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та технології"

Electrochemical processes and systems: application for tutors

The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та технології"

Inhibition of metal dusting corrosion on Fe-based alloy by combined near surface severe plastic deformation (NS-SPD) and thermochemical treatment

Combined NS-SPD and thermochemical treatment has been used to improve the metal dusting corrosion resistance of Incoloy 800. After testing under infinite carbon activity for 20−100 h, carbon was not found in the NS-SPD region while corrosion products formed in the non-NS-SPD region. The improved resistance is a result of the NS-SPD yielding a high density of defects in the deformation zone that developed into an ultra-fine-grained structure near the surface during the subsequent thermochemical treatment. These microstructural changes increase the effective diffusion coefficient for Cr in the alloy, hence promoting the formation of a highly protective oxide scale.publishedVersio

Inhibiting carbon growth at the initial stage of metal dusting corrosion of high temperature alloys

Metal dusting corrosion is a high temperature degradation phenomenon affecting Fe-, Ni- and Co- based alloys when exposed to strongly carburizing gases (carbon activity ac > 1) at elevated temperatures (> 400˚C). The alloy disintegrates into a powdery mixture of metallic, carbidic, and carbonaceous dusts. In order to capture the initial carbon formation on the Ni-based high temperature alloy samples (Inconel 601), systematically pretreated alloy coupons were subjected to metal dusting conditions as a function of time, composition, and pressure at 750˚C. The carbon deposition on the alloy coupon is clearly a function of the gas composition during exposure, less carbon is formed under 10% CO in Ar with infinite carbon activity than under synthesis gas with finite low carbon activity, which points to the impact of the reaction mechanism and kinetics. The characterization indicates that the metal dusting corrosion rate is lowered when Cr2O3 rather than (Ni, Fe, Cr)3O4 spinel is the major phase of the oxide scale formed on the alloy coupons. Fine-grain structure on the alloy surface is also found beneficial to resistance the metal dusting corrosion. Formation of carbon on the Incoloy 800 alloy surface of pre-oxidized samples was investigated by exposure to reducing, highly carburizing atmosphere (CO in Ar) at 20 bar and varying temperature (550-750 ˚C). The amount and the type of carbon materials are found to vary strongly with the exposure temperature and the interaction with the metallic matrix. At the highest temperature i.e. 750 ˚C, also the alloy coupons undergo considerable change in the elemental distribution as a function of depth. Finally, efforts have been devoted to inhibiting of metal dusting corrosion on Incoloy 800. Results show that Incoloy 800 samples treated by combined near surface severe plastic deformation (NS-SPD) and thermochemical treatment at elevated temperature exhibit no carbon formation, compared with the region not treated by NS-SPD on the sample. The good corrosion resistance performance is a result of the mechanical process produced an ultrafine-grained structure with a higher fraction of grain boundaries together with other microstructure defects near the surface. These microstructure defects increase the effective diffusion coefficient for Cr in the alloy, promoting the formation of a thin, protective Cr-rich oxide scale during the thermal treatment, which prevents contact between the carburizing atmosphere and the Ni and Fe contained in the bulk of alloy. The results imply that the metal dusting resistance performance of Incoloy 800 in industrial applications can be improved significantly by NS-SPD followed by thermochemical oxidative treatment

Energy Technology Division research summary 2004.

The Energy Technology (ET) Division provides materials and engineering technology support to a wide range of programs important to the US Department of Energy (DOE). The Division's capabilities are generally applied to technical issues associated with energy systems, biomedical engineering, transportation, and homeland security. Research related to the operational safety of commercial light water nuclear reactors (LWRs) for the US Nuclear Regulatory Commission (NRC) remains another significant area of interest for the Division. The pie chart below summarizes the ET sources of funding for FY 2004

Performance of chromia- and alumina-forming Fe- and Ni-base alloys exposed to metal dusting environments: The effect of water vapor and temperature

Fe- and Ni-base alloys including an alumina-forming austenitic alloy were exposed for 500h under metal dusting environments with varying temperature, gas composition and total pressure. For one H2–CO–CO2–H2O environment, the increase in temperature from 550 to 750°C generally decreased metal dusting. When H2O was added to a H2–CO–CO2 environment at 650°C, the metal dusting attack was reduced. Even after 5000h at a total pressure of 9.1atm with 20%H2O, the higher alloyed specimens retained a thin protective oxide. For gas mixtures containing little or no H2O, the Fe-base alloys were less resistant to metal dusting than Ni-base alloys