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Corrosion investigation of rapidly solidified Cu- Al-Ni alloy in NaCl solution
Get PDFThe corrosion behavior of the Cu-Al-Ni alloy ribbons obtained by rapid solidification was investigated in 0.9% NaCl solution (pH 7.4) at temperatures of 24, 37 and 50 ºC. Measurements have been performed by electrochemical methods such as monitoring the open circuit potential, linear and potentiodynamic polarization methods. The influence of chloride ions concentration on corrosion of Cu-Al-Ni ribbons has also been investigated in 0.1% and 1.5% NaCl solution. Results of the investigations have shown that an increase in chloride concentration and electrolyte temperature leads to increase the corrosion current density and decrease the polarization resistance values which mean higher corrosion attack on Cu-Al-Ni alloy. Microscopic images have shown significant pitting corrosion damages on the Cu-Al-Ni alloy surface. Increasing the electrolyte temperature increases the surface damages of the electrode due to more intense corrosion. SEM surface images of Cu-Al- Ni electrodes have confirmed that with the elevation of chloride concentration a more intense corrosion attack occurs. EDS surface analysis indicated dominant percentage of copper, chlorine and oxygen on the surface, indicating the formation of copper oxide and chloride as the major corrosion products on the surface. The presence of a small percentage of aluminum indicates its distribution in the form of aluminum oxide and chloride in the surface layer
Resistance testing of multiphase structural steels to local corrosion
Get PDFU ovom radu ispitana je otpornost modernih višefaznih konstrukcijskih čelika na lokalnu
koroziju u 3,5%-tnoj otopini NaCl. Ispitivanja su provedena na 3 uzorka TRIP -čelika oznake
VA, J i K koji se međusobno razlikuju prema kemijskom sastavu i mehaničkim svojstvima.
Metodom cikličke anodne polarizacije dobiveni su parametri lokalne korozije te je otpornost
ispitanih čelika određena prema kriteriju piting potencijala.
Elektrokemijska mjerenja su pokazala da ispitani TRIP čelici pokazuju slabiju otpornost na
lokalnu koroziju od konvencionalnog konstrukcijskog čelika, o čemu svjedoče niži iznosi piting
potencijala. Pošto su registrirani piting potencijali ispitanih TRIP-čelika približno istih
vrijednosti, ne može se ustanoviti njihov poredak otpornosti prema lokalnoj koroziji.
Metalografska ispitivanja su pokazala da se radi o modernim TRIP-čelicima koji se sastoje iz
tri mikrostrukturne faze: ferit, bainit i zaostali austenit. Zbog izrazito sitnozrnate mikrostrukture
otpornost TRIP-čelika prema piting koroziji je uvelike smanjena, zbog mnoštva granica zrna
koje predstavljaju idealna korozijska mjesta za nastanak i razvoj pitinga.In this paper, the resistance to local corrosion of modern multiphase structural steels in 3.5%
NaCl solution was investigated. The tests were performed on the three samples of TRIP steels
marked as VA, J and K which differ by the chemical composition and mechanical properties.
By the method of cyclic anode polarization, the local corrosion parameters were obtained and
the resistance of the tested steels was determined according to the pit ting potential criterion.
Electrochemical measurements have shown that tested TRIP steels exhibit less resistance to
local corrosion than conventional structural steel, as evidenced by lower pit ting potential. Since
the registered pitting potentials of the tested TRIP-steels are approximately the same, their order
of resistance to local corrosion can not be established.
Metalographic analysis has shown that this modern TRIP steels consist of three microstructural
phases: ferrite, bainite and residual austenite.
Because of the extremely fine-grained microstructure, the resistance to pitting corrosion is
greatly reduced due to the multitude of grain boundaries that represent the ideal corrosion sites
for the occurrence and development of the pittings
Effect of spherical blockage configurations on film cooling
Get PDFWith increasing inlet temperature of gas turbines, turbine blades need to be effectively protected by using cooling technologies. However, the deposition from the fuel impurities and dust particles in the air is often found inside film holes, which results in partial hole blockage. In this paper, the deposition geometry is simplified as a rectangular channel, and the effect of three blockage ratios is investigated by using the computational fluid dynamics. In addition, water droplets are also released from the coolant inlet to provide a comparison of the results with and without mist injection. It is found that the lateral film cooling effectiveness is reduced with increasing blockage ratio. For all the cases with the blowing ratio 0.6, 1% mist injection provides an improvement of the cooling performance by approximately 10%
Review of the latest research on coal, environment, and clean technologies
Get PDFFossil fuels, coal in particular, are indispensable sources of energy necessary for today's technological and economical progress throughout the world. Their burning releases numerous environmental contaminants, like CO2, SO2, and a range of organic and inorganic compounds. Arguably, however, and despite the fact that these emissions have resulted in air pollution and regional acid rain problems, there is no evidence yet of their usage completely replaced by a low-CO2–producing energy source. Coal, due to its unique composition and characteristics, has been actively investigated by scientists and technologists from various disciplines in a search for economically valuable metals and medically active substances. Also, coal is used universally for the fabrication of new nanomaterials in laboratories, and utilized in waste-treatment and clean-coal technologies. The aim of the paper was to focus on the latest advancements in coal research of leading international scientists from India, China, and USA. Also, the paper is briefly presenting selected papers of several Indian and Croatian research groups addressing environmental issues and emerging waste-treatment technologies. Although the two countries are different from the geographical, historical, economical, and industrial point of view, the both have been linked with the coal extraction and its usage in power generation and associated heavy industries
Numerical investigation of the transient spray cooling process for quenching applications
Get PDFWater spray quenching distinguished itself as a promising method for industry production, especially for the parts which require good mechanical strength while simultaneously retaining the initial toughness. Studies have shown that the heat transfer process during the spray quenching is mostly influenced by the spray impingement density, particle velocities and sizes. The application of advanced numerical methods still plays insufficient role in the development of the production process, in spite of the fact that industry today is facing major challenges that can be met only by development of new and more efficient systems using advanced tools for product development, one of which is computational fluid dynamics. Taking the above stated, the object of this research is numerical simulation of spray quenching process in order to determine validity of mathematical models implemented within the commercial computational fluid dynamics code Fire, especially droplet evaporation/condensation and droplet-wall heat transfer model. After review of the relevant literature suitable benchmark case was selected and simulated by employing discrete droplet method for the spray treatment and Eulerian approach for the gas phase description. Simulation results indicated that existing droplet/wall heat transfer model is not able to reproduce heat transfer of dense water spray. Thus, Lagrangian spray model was improved by implementing experimental correlation for heat transfer coefficient during spray quenching. Finally, verification of the implemented model was assessed based on the conducted simulations and recommendations for further improvements were given
Properties, production and application of gray iron
No full textSivi lijev pripada skupini željeznih ljevova koji sadrže grafitne čestice u mikrostrukturi. Grafitne čestice u sivom lijevu imaju listićav oblik i međusobno su povezane, što negativno utječe na njegova vlačna svojstva. Međutim, zbog takvog oblika grafitnih čestica sivi lijev ima visoku sposobnost prigušenja vibracija, visoku toplinsku vodljivost, jako dobra tribološka svojstva i vrlo dobru strojnu obradivost. Specifična kombinacija svojstava sivog lijeva, koja udovoljava za mnoge aplikacije, te jednostavna i jeftina proizvodnja glavni su razlozi njegove vrlo široke primjene. Već dugi niz godina sivi lijev je najviše korišteni materijal za izradu metalnih odljevaka. Gotovo 45 % svjetske proizvodnje odljevaka u 2015. godini čine odljevci od sivog lijeva.
Ovaj pregledni rad prikazuje klasifikaciju, skrućivanje, utjecaj kemijskog sastava na mikrostrukturu i svojstva, proizvodnju taline, svojstva i primjenu sivog lijeva.Gray iron belongs to the group of cast irons containing graphite particles in the microstructure. Flake shaped graphite particles in gray iron are interconnected, which negatively affects its tensile properties. However, because of this form of graphite particles gray iron has high damping capacity, high thermal conductivity, very good tribological properties and very good machinability. A specific combination of properties of gray iron, which is suitable for many applications, and simple and inexpensive production are the main reasons for its widespread use. For many years, gray iron is the most widely used material for the production of metal castings. Grey iron castings cover almost 45 % of world casting production in 2015.
This review paper shows the classification, solidification, the influence of chemical composition on the microstructure and properties, production of melt, properties and application of gray iron
The influence of microalloying element niobium on stress distribution in cold deformation
Get PDFIspitivanje ponašanja niskougljičnih čelika predstavlja veliki interes u znanstvenom svijetu obzirom na njihovo različito ponašanje tijekom procesa deformacije. U ovom završnom radu provedena je termografska analiza niskougljičnih čelika sa i bez dodatka mikrolegirajućeg elementa niobija. Statičko vlačno ispitivanje provedeno je na kidalici uz istovremeno korištenje metode termografije. Ispitivani niskougljični čelici sa 0.035% i bez dodatka elementa niobija pokazali su da mikrolegirajući element niobij i brzina razvlačenja imaju utjecaj na raspodjelu naprezanja kod hladne deformacije.Testing the behavior of low carbon steels presents a major interest in the scientific world due to their different behavior during the deformation process. In this bachelor thesis a thermographic analysis of low carbon steels was performed with and without the addition of microalloying element niobium. The static tensile test was performed on the testing machine simultaneously using the thermographic method. Examined low carbon steels with 0.035% and low carbon steels without niobium showed that microalloying element niobium and stretching speed have an effect on stress distribution in cold deformation
The effect of waste dental metallic materials on environment
Get PDFDental medicine is a profession dedicated to promoting and enhancing oral health and well- being and therefore plays a significant role in human health. Dental practices produce many types of dental wastes, such as: heavy metals and biomedical waste, which could cause harm to the environment if it is disposed improperly. Among them, mercury, silver and lead are the most harmful for humans and the environment as well. In order to reduce the impact on the environment dentists should take all possible activities to completely avoid the production of any waste or at least try to reduce the amount of waste to a minimum. In that context, eco- friendly dentistry as a new approach to dental practice is developed. It is based on use of non-toxic products, waste reduction, energy conservation and pollution prevention. Finally, education regarding the proper management and disposal of waste from dental offices needs more attention
Hidrometalurška proizvodnja iz perspektive holističkog environmentalizma
Get PDFAnaliza hidrometalurške proizvodnje iz perspektive holističkog environmentalizma zahtjeva interdisciplinarni pristup jer je nužno sagledavanje ne samo tehnoloških mogućnosti provedbe određenog hidrometalurškog procesa, već i preispitivanje društvene opravdanosti gradnje ili održavanja tehnološkog postrojenja koje onečišćuje materijalni okoliš. Hidrometalurška proizvodnja iz perspektive holističkog environmentalizma promatra se dvojako: s jedne strane kao mogućnost, a s druge strane kao prijetnja. Hidrometalurška proizvodnja suvremenom čovječanstvu omogućava korištenje niza proizvoda bez kojih bi bilo nemoguće zamisliti našu tehničku civilizaciju, no ona može postati ozbiljna prijetnja ukoliko se tijekom proizvodnog procesa zanemaruje važnost očuvanja čistoće vode, zraka i tla. Za opravdanost funkcioniranja hidrometalurških postrojenja, iz pozicije holističkog environmentalizma, potrebna je socijalna odgovornost hidrometalurških poduzeća
Kinetic study of adsorption of heavy metals on blast furnace slag
No full textIn this paper, blast furnace slag was investigated as a potential adsorbent for the removal of zinc and copper ions from the aqueous solution. The adsorption was performed by a static, so - called "batch" process. Adsorption properties were studied by monitoring the influence of contact time adsorbent with adsorbate. Performed studies have shown that the equilibrium in the tested system is achieve in 30 minutes. Intraparticle diffusion model, heterogeneous diffusion model and film diffusion model were used to test the zinc and copper ion diffusion in a competitive adsorption. The obtained results showed that intraparticle diffusion contr olled the adsorption process