Ispitivanje procesa korozije mesinga u rastvoru natrijum sulfata

Abstract

Bakar ubrajamo u grupu najvažnijih obojenih metala, koji ima veoma široku komercijalnu (tehničku) primenu. Poznat je od davnina, jedan od prvih elemenata koje je upoznao čovek. Značaj koji su imali bakar i njegove legure, ogleda se u nazivima čitavih epoha u razvoju čovečanstva. Arheološki nalazi bakarnih predmeta u borskoj okolini potiču iz bakarnog doba i ukazuju na korišćenje samorodnog bakra od koga su se izrađivale bakarne alatke, nakit, oružje, a kao poseban raritet tog doba (eneolitsko doba) pominje se bakarna sekira. Zahvaljujući svojim vrlo dobrim konstrukcionim osobinama, a pre svega fizičkim, a zatim i srazmerno znatnoj rasprostranjenosti u prirodi (iako količina bakra u zemljinoj kori iznosi svega 0.01%), bakar je jedan od metala koji je našao najširu primenu, odmah posle železa. Glavno područje primene bakra je elektroindustrija, nešto manje bakra se upotrebljava u obliku proizvoda dobijenih preradom u plastičnom, i to kako u tehnički čistom obliku, tako i u obliku legura. Bakar i njegove legure, pre svih mesing, nalaze široku primenu zbog svojih fizičkih i hemijskih osobina. Korozija predstavlja specifičan proces koji uključuje gubitak ili degradaciju metalnih komponenti i obično je elektrohemijske prirode, sa velikom primenom kod galvanskih ćelija. Korozija je dezintegracija metala pomoću nenamernih hemijskih ili elektrohemijskih reakcija, koja počinje sa površine. Svi metali imaju tendenciju oksidacije, neki lakše od drugih. Sklonost ka oksidaciji formira galvanski niz. Poznavanje mesta metala u galvanskom nizu važna je informacija za razumevanje i njegovu moguću upotrebu u konstruisanju i prilikom kontakata različitih metala. Kvalitetan inženjering zahteva razumevanje kompatibilnosti materijala. Često postoje zahtevi da različiti metali budu u kontaktu i tada galvanska kompatibilnost dovodi do patiniranja površine jednog od metala i njegove zaštite od dalje korozije. U legurama mesinga količina cinka kreće se od 5-45%. Uopšteno, koroziona otpornost mesinga opada sa povećanjem količine cinka. To je uobičajena različitost između onih legura koje sadrže manje od 15% cinka (bolja koroziona otpornost) i onih sa većom količinom cinka. Glavni problemi kod legura sa visokom koncentracijom cinka su procesi decinkacije i naponske korozije (Stress Corrosion Cracking-SCC). U ovom radu dato je tumačenje korozionog ponašanja dve vrste mesinga (CuZn-28 i CuZn-42), sa pet stepeni deformacija (0, 20, 40, 60 i 80%), u različitim korozionim sredinama. Ispitivanja su vršena elektrohemijskim postupkom, potenciostatskom metodom. Određene su zavisnosti potencijala od vremena i korozioni potencijali, kao i zavisnosti gustina korozionih struja od potencijala. Izmerene vrednosti korozionih potencijala i gustina korozionih struja posmatrani su kao karakteristike procesa decinkacije i korozione otpornosti ispitivanih uzoraka hladno-deformisanih uzoraka mesinga CuZn-42 i CuZn-28. Kao radni elektrolit korišćen je 0.1M rastvor Na2SO4, u koji su dodavani hloridni joni, u koncentracijama: 5·10-4M, 5·10-3M, 5·10-2M, 1·10-1M, 5·10-1M i 1.0M i bakar(II)-joni, u koncentracijama: 1·10-3M, 5·10-3M, 1·10-2M i 5·10-2M. Takođe, ispitan je i uticaj različitih inhibitora korozije, sa različitim koncentracijama, na povećanje korozione otpornosti mesinga. Inhibitori korozije, čiji je uticaj na koroziono ponašanje mesinga ispitivan, bili su: benzotriazol (BTA), tiourea (TU), etilen-diamin-tetra-sirćetna kiselina (EDTA), 2-butin-1,4-diol (DS-3) i hidrazin-sulfat (HS), u koncentracijama 1·10-2% i 1·10-1% (zapreminski)...

Copper is included to a group of the most important non-ferrous metals, which has a wide commercial (technical) use. It has been known since ancient times, one of the first elements that the man met. The importance of copper and its alloys is reflected in the names of whole epochs in development of mankind. Archaeological findings of copper objects in the Bor vicinity, originated from the Bronze Age, and indicate the use of native copper in making the copper tools, jewelry, weapons, and as a special rarity of that age (the Eneolithic period) the copper ax is mentioned. Thanks to its very good constructional characteristics, especially physical, and then also to the significant proportion of distribution in nature (although the amount of copper in the earth's crust is only 0.01%), copper is one of the metals that has found the widest use, immediately after iron. The main area of copper use is the electrical industry; less copper is used in the form of products obtained by the processing in plastic, both in technically pure form and in the form of alloys. Copper and its alloys, first of all brass, are widely used due to their physical and chemical properties. Corrosion presents a specific process that involves the loss or degradation of metal components and it is usually of electrochemical nature, with extensive use for galvanic cells. Corrosion is a disintegration of metals by unintentional chemical or electrochemical reactions, starting from the surface. All metals have a tendency to oxidation, some more easily than the others. A tendency to oxidation forms a galvanic series. Knowledge of metals in a galvanic series is an important information for understanding and its possible use in the construction and contacts of different metals. Quality engineering requires the understanding of material compatibility. There are often requirements that different metals are in contact, and then the galvanic compatibility leads to a surface patination of metal and protecting it from further corrosion. The zinc amount ranges from 5-45% in the brass alloys. Generally, corrosion resistance of brass decreases with increasing amount of zinc. It is a common difference between those alloys containing less than 15% zinc (better corrosion resistance) and those with higher amount of zinc. The main problem in the alloys with high concentration of zinc is the processes of dezincification and stress corrosion cracking - SCC. This work presents the interpretation of corrosion behavior of two types of brass (CuZn-28 and CuZn-42), with five deformation degree (0, 20, 40, 60 and 80%), in a variety of corrosive environments. Tests were carried out using the electrochemical procedure, the potentiostatic method. The potential dependences on time and corrosion potentials were determined, as well as the dependence of corrosion current densities on potential. The measured values of corrosion potentials and corrosion current densities were observed as the characteristics of dezincification process and corrosion resistance of tested samples of cold-deformed samples of brass CuZn-42 and CuZn-28. As the working electrolyte, 0.1M solution of Na2SO4 was used, in which chloride ions were added in concentrations of: 5·10-4M, 5·10-3M, 5·10-2M, 1·10-1M, 5·10-1M and 1.0M and copper(II)-ions in concentrations of: 1·10-3M, 5·10-3M, 1·10-2M and 5·10-2M. Also, the effect of different corrosion inhibitors was tested, with different concentrations, on increase in corrosion resistance of brass. Corrosion inhibitors, whose effect on corrosion behavior of brass was tested, were the followings: benzotriazole (BTA), thiourea (TU), ethylene-diamine-tetra-acetic acid (EDTA), 2-butin-1.4-diol (DS-3) and hydrazine-sulfate (HS), in concentrations of 1·10-2% and 1·10-1% (by volume)...