Electrochemical and surface characterization of ternary alloys of the system Ag-Cu-Zn in near neutral chloride solutions.

Abstract

Alloys of the Ag-Cu-Zn system with wide range of silver content, selected to have similar phase compositions, were the subject of the research. Metals for all examined alloys are obtained by recycling of electronic waste. After obtaining alloys by double melting and homogenization annealing for 24 h under nitrogen, surface and electrochemical characterization of these alloys were performed. For comparative analysis, binary alloys of Ag-Zn and Cu-Zn systems were used. They had similar composition as the phases of the examined alloys. For the same purposes the Ag40Cu30Zn30 alloy with different phase composition than three other alloys of the same system was used. Thermodynamic analysis of the Ag-Cu-Zn system was performed using phase diagrams and Pandat software. Surface characterization of the homogenizated alloys was performed by Scanning Electron Microscopy with X-ray microanalysis (SEM/EDS) and X-diffraction (XRD). Electrochemical behavior of the alloys of the Ag-Cu-Zn system in deaerated and naturally aerated neutral 3.5 wt.% NaCl solution, synthetic seawater, natural filtered seawaters and borate buffer (pH=8.1) with 3,5% NaCl has been investigated using the potentiodynamic measurements, linear polarization, cyclic voltammetry and potentiostatic measurements. The anodic layer formed on examined alloys by chronoamperometry at 0.0 and +0.25 V (vs. SCE) has been characterized by X-ray diffraction, FE SEM/EDS, Raman spectroscopy and MALDI mass spectrometry. The same mechanism of corrosion under anodic polarization was found for all alloys in all chloride solutions except buffered 3.5% NaCl solution. The behavior of alloys Ag43Cu37Zn20 and Ag25Cu52.5Zn22.5 is particularly similar. The alloy with 25 wt. % content of silver has similar corrosion resistance in 3.5% NaCl solution as the alloy with 40 wt. % silver, which is clearly the consequence of phase composition. For a similar phase composition of alloy, corrosion resistance increases with higher content of silver (Ag-rich phase). All investigated alloys of the Ag-Cu-Zn system have no passive area in all solutions, except in buffered solution, where a pseudo-passive area appears on polarization curves. Copper rich phase (Cu) is critical for corrosion resistance of alloys. Preferentially dissolution of this phase is determined by polarization curves analysis, chemical...

Predmet istraživanja disertacije bile su legure sistema Ag-Cu-Zn sličnog sastava faza u širokom opsegu sadržaja srebra. Metali za sve ispitivane legure dobijeni su reciklažom elektronskog otpada. Nakon dobijanja dvostrukim topljenjem i homogenizacionog žarenja u trajanju od 24h u atmosferi azota izvršena je površinska i elektrohemijska karakterizacija ovih legura. Kao legure za uporednu analizu korišene su legure sistema Ag-Zn i Cu-Zn, sastava sličnog fazama ispitivanih legura i legura Ag40Cu30Zn30 čiji se fazni sastav značajno razlikuje od preostale tri trokomponentne legure istog sistema. Termodinamička analiza Ag-Cu-Zn sistema izvršena je korišćenjem faznih dijagrama i Pandat softvera. Za površinsku karakterizaciju homogenizovanih legura korišćena je skenirajuća elektronska mikroskopija sa rentgenskom analizom (SEM/EDS) i rentgenskom difrakcijom (XRD). Elektrohemijsko ponašanje legura sistema Ag-Cu-Zn ispitivano je u deaerisanim i prirodno aerisanim neutralnim rastvorima NaCl koncentracije 3,5% (masenih), sintetičkoj morskoj vodi, prirodnim filtriranim morskim vodama i boratnom puferu (pH=8.1) sa (masenih) 3,5% NaCl, korišćenjem potenciodinamičkih merenja, linearne polarizacije, ciklične voltametrije i potenciostatskih merenja. Anodni film formiran na ispitivanim legurama hronoampermetrijski na 0,0 V i +0,25 V (vs. ZKE) je ispitivan: rentgenskom difrakcijom, FE SEM/EDS metodom, Raman spektroskopijom i MALDI masenom spektrometrijom. Utvrđen je isti mehanizam korozije prilikom anodne polarizacije za sve legure u svim hloridnim rastvorima, osim u puferisanom rastvoru NaCl. Naročito je slično ponašanje legura Ag43Cu37Zn20 i Ag25Cu52,5Zn22,5. Legura sa 25% (mas.) srebra ima sličnu otpornost na koroziju u 3,5% rastvoru NaCl kao legura sa 40% (mas.) srebra, što je nedvosmisleno uticaj faznog sastava. Pri sličnom faznom sastavu legura koroziona otpornost raste sa većim udelom srebra (faze bogate srebrom). Sve ispitivane legure sistema Ag-Cu-Zn nemaju pasivnu oblast u svim rastvorima osim puferskog, gde se javlja pseudo-pasivna oblast na polarizacionim krivama...