Wear resistance improvement of thermal plant fan mill impact plates based on numerical flow simulation

Numerical simulation of 3D multiphase flow is performed to determine the velocity field in the fan mill. The mixture model of the Euler-Euler approach is used. Recirculating gas is a primary phase that carries granular phases including the coal powder and sand. The latter causes heavy wear of mill impact plates. The optimal form of hardfacing geometry and technology has an impact both on velocity magnitude and direction of flow in such a way as to reduce plate wear. This paper presents results of surface modification (based on numerical simulation), implemented on impact plates of the fan mill in the Kostolac B power plant in Serbia. Fishbone hardfacing is made in order to increase the lifetime of impact plates and extend the period between overhauls of fan mills. The experimental tests of fishbone surfacing plates, in exploitation conditions, show that the applied modification, hardfacing technologies and coating materials, give expected results. The application of this hardfacing in the form of a fishbone is simpler, faster and more economical compared to complete overlaying and honeycomb impact plate surfacing. The relative weight loss of base plate after an 1440-hour period of exploitation is 8%, while the weight losses for the hard-faced plate is below 7%

Wear resistance improvement of thermal plant fan mill impact plates based on numerical flow simulation

Numerical simulation of 3D multiphase flow is performed to determine the velocity field in the fan mill. The mixture model of the Euler-Euler approach is used. Recirculating gas is a primary phase that carries granular phases including the coal powder and sand. The latter causes heavy wear of mill impact plates. The optimal form of hardfacing geometry and technology has an impact both on velocity magnitude and direction of flow in such a way as to reduce plate wear. This paper presents results of surface modification (based on numerical simulation), implemented on impact plates of the fan mill in the Kostolac B power plant in Serbia. Fishbone hardfacing is made in order to increase the lifetime of impact plates and extend the period between overhauls of fan mills. The experimental tests of fishbone surfacing plates, in exploitation conditions, show that the applied modification, hardfacing technologies and coating materials, give expected results. The application of this hardfacing in the form of a fishbone is simpler, faster and more economical compared to complete overlaying and honeycomb impact plate surfacing. The relative weight loss of base plate after an 1440-hour period of exploitation is 8%, while the weight losses for the hard-faced plate is below 7%

Zeleni inhibitori korozije sa cisteinom i kompleksom cerijum-cisteina na 7000 seriji aluminijumske legure

The aim of this study was to investigate environmentally-friendly corrosion inhibitors based on the cerium-cysteine and their effect on 7xxx series aluminum alloy. The cysteine and cerium-cysteine complex structures were analyzed by Fourier-Transform Infrared spectroscopy (FTIR). The structure of cerium-cysteine was additionally determined using Nuclear Magnetic Resonance (NMR) and Elemental Analysis. Inhibitors efficiency was analyzed with Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic polarization techniques in 0.1M NaCl at room temperature, while Scanning Electron Microscopy analyzed the surface appearance and microstructure of the tested aluminum alloy with Energy Dispersive Spectroscopy (SEM / EDS) and Optical Microscope (OM). Different amounts of cysteine were examined in order to find an optimal concentration of inhibitor. The adsorption of the inhibitors followed the Langmuir isotherm, and based on the EIS results and calculated thermodynamic potential (Gibbs free energy), cysteine and cerium-cysteine proved to be good inhibitors for tested aluminum alloy. The optimal cysteine concentration of 0.06 mM as a corrosion inhibitor of 7xxx series aluminum alloy was determined. EIS diagrams confirmed that cysteine showed better inhibition than Ce-Cys complex

The disbonding of powder polyester coating on steel pretreated by zinc-phosphate and iron-phosphate coatings

The influence of different types of conversion phosphate coatings on the corrosion stability of top powder polyester coating on steel was investigated. The morphology of phosphate coatings was investigated using scanning electron microscopy (SEM), composition by energy dispersive X-ray spectroscopy (EDS) and surface coverage by voltametric anodic dissolution (VAD) technique. The corrosion stability of polyester coating on steel pretreated by phosphate coatings was investigated by electrochemical impedance spectroscopy (EIS). It was shown that small crystal nuclei of iron-phosphate coating have sporadically emerged on the steel substrate while zinc-phosphate coating had more compact structure with better surface coverage. After prolonged exposure, there was a significant decrease in Rp values for polyester/zinc-phosphate protective system, as a result of the disbondment of polyester coating, while Rp values for polyester coating on steel pretreated with iron-phosphate coating remained almost unchanged, pointing to a greater stability of this protective system

Surface coverage determination of iron-phosphate coatings on steel using voltammetric anodic dissolution technique

In this study, the effect of deposition time and concentration of NaNO2 in the phosphate bath on the surface morphology of iron-phosphate coatings on low carbon steel was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition of iron-phosphate coatings was determined using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), while surface coverage was evaluated by the voltammetric anodic dissolution (VAD) technique in the borate solution. The addition of NaNO2 in the phosphate bath significantly increased the surface coverage since better packed crystals of smaller size, which favour the phosphate nucleation, were obtained. It was also shown that prolonged deposition time increased the surface coverage, coating roughness and crystal size in lateral direction, altering also the crystal shape from big platelets nonuniformly distributed on steel surface during initial time, to better packed laminated and needle-like structures during prolonged exposure. [Acknowledgement. This research was financed by the Ministry of Education, Science and Technological Development, Republic of Serbia, Grant III 45019

Corrosion and conservation of weapons and military equipment

This paper analyzed the conditions for the occurrence of corrosion processes on historically important weapons and military equipment made of steel during the period in outdoor environment. A considerable attention has been given to the characteristics of the most important corrosion products formed on the steel surface. The formation of akaganite, β-FeOOH is a sign of active corrosion under a layer of corrosion products. The conditions that cause the formation and regeneration of hydrochloric and sulphuric acid during the exposure to the elements were analyzed. The most often applied methods of diagnostics and procedures of removing active corrosion anions (desalination) were described as well. The NaOH solution of certain pH values still has the most important application for the desalination process. The procedures for cleaning the surface before the application of protective coatings and the application of chemicals that transform rust into stable compounds were discussed. As protective coatings, different types of organic coatings plated on well-prepared steel surfaces were used and sometimes special types of waxes as well. This paper presents the results of the tests of corrosion products taken from the exhibits of weapons and military equipment from the Military Museum in Belgrade

Cerium lactate as green corrosion inhibitor of AA2024 alloy

This paper evaluated the inhibitory effect of Ce-chloride and Na-lactate mixture on the AA2024 aluminum alloy in 0.1 M NaCl solution. Electrochemical impedance spectroscopy (EIS) was applied for testing the general corrosion resistance, while potentiodynamic polarization measurement was applied for determining the alloy pitting corrosion resistance in NaCl and inhibitive solutions. The presence of cerium on the cathodic intermetallic particles was confirmed by scanning electron microscope/energy-dispersive X-ray spectroscopy analysis. The mixture of Ce-chloride and Na-lactate was a more effective corrosion inhibitor than Ce-chloride alone. The inhibitors mixture is a mixed-type corrosion inhibitor with a higher influence on slowing down the cathodic reaction of oxygen reduction. The adsorption of the inhibitor, the presence of cerium in different oxidation states (Ce3+ and Ce4+), and lactate anion (C–C/C–H, C–OH, C═O, and O–C═O group) were confirmed by X-ray photoelectron spectroscopy analysis. A mechanism of inhibitor adsorption on the surface of AA2024 alloy in NaCl solution was proposed