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

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...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..

Influence of reducing agents and surfactants on size and shape of silver fine powder particles

Silver fine powder with different shapes and sizes were prepared by chemical reduction and characterized by scanning electron microscope. In this paper was presented the method for the preparation of the fine Ag powder with particles size smaller than 2.5 µm with suitability for the mass-production scale. Reduction was performed from nitrate solution directly by vigorous stirring at room temperature by three different reduction agents, with and without presence of two dispersants. Scanning electron microscopy revealed the preferred size of the particles obtained in all experiments with aim of the protecting agent. Larger particles and wider size distribution were obtained without surfactants although with average size of about 1 µm and small quantity of larger clusters of primary particles that is out of the fine powder classification. High purity, 99.999%, of silver was obtained in every experiment.  http://dx.doi.org/10.5937/metmateng1402073

CHANGES IN Pt-Rh CATALYSTS IN THE WORKING ENVIRONMENT

Abstract The surface reconstruction on rhodium-platinum catalyst gauzes has been examined using the scanning electron microscope techniques

The influence of novel organic gold complex on photoresist layers of printed circuit boards

The goal of this paper was to study the influence of organic gold complex based on mercaptotriazole on photoresist layers used in manufacturing of printed circuit boards (PCBs). Investigations were performed by immersion the previously prepared boards in electrolytes with different pH values (pH=2, 4, 7, 9 and 12) at gold concentration of 2.5 g/dm3 and in gold complexes with different gold concentrations (1.5; 2.0; 2.5; 3.0 and 3.5 g/dm3) at pH value of pH=9. Investigations showed that photoresist layers on boards are the most resistant at optimal operating conditions, pH=9 and concentration of gold of 2.5 g/dm3

Silver micro-sized powder obtained by the chemical reduction

This paper presents the method for preparation the fine Ag powder with a particles size smaller than 2 μm. Reduction was performed from the nitrate solution directly by the vigorous stirring at the room temperature by the use of ascorbic acid as the reducing agent and polyvinylpyridine as the protecting agent. Silver powder with nearly spherical particles and size of micrometers were prepared by the chemical reduction and characterized by the scanning electron microscope (SEM). The SEM analysis has shown that preferred size, less than 2 μm was obtained. Silver with purity of 99.9% or more was obtained

Application of mineral processing methods in recycling the waste printed circuit board

Recycling of the waste printed circuit boards (PCBs) is necessary from both an economic and an environmental point of view. Large amounts of waste contain significant amounts of valuable metals used as the secondary source. The PCBs can be viewed as a complicated mineral raw material on which mineral processing procedures can be applied. This work presents the mineral processing procedures used in the certain stages of recycling waste printed circuit boards

Stability of the gold mercaptotriazole complex at pH=4

The objective of this work was to investigate the stability of the gold complex based on mercaptotriazole in slightly acid media, at pH=4. The gold complex complex was studied by the visual monitoring and electrochemical characterization of electrolytes in the period of three months. Electrochemical characterization was performed by the open circuit potential measurement, cycling voltammetry method and recording the polarization curves, with pH of the electrolyte measurement before and after each electrochemical experiment. These tests, performed at pH=4 and optimal concentration of gold in the electrolyte of 2.5 g/dm3, for a period three months, did not show any visual or other essential changes of investigated electrolyte characteristics

Energetski efikasni pulsno-reverzni režimi galvanizacije

Pulse reverse power modes are used in order to obtain metal coatings with similar or better characteristics, compared with the coatings produced by constant current. Pulse reverse modes increase production and energy efficiency of electroplating cells with the use of higher density currents. In this paper, we investigate optimisation of systems for standard electrodeposition by choosing the suitable duration and intensity of the pulses. It was shown that energy efficiency of the process can be achieved with satisfactory quality of coatings and without expensive and often dangerous additives in the electrolyte

THE INFLUENCE OF RHODIUM CONTENT ON THE MECHANICAL PROPERTIES OF PLATINUM

The paper presents the results of investigation the influence of rhodium as an alloying element on the mechanical properties of platinum. A short-term and tensile strength were tested, at room and high temperatures, and also sliding rate and time to the destruction of the Pt-Rh system alloys at high temperatures. The results showed that alloying with rhodium strengthens the platinum while reducing its plasticity. Time to destruction is much longer in Pt-Rh alloys compared to pure platinum

Changes in Pt-Rh catalysts in the working environment

The surface reconstruction on rhodium-platinum catalyst gauzes has been examined using the scanning electron microscope techniques. The nucleation and growth of large cage-like features, developed on the gauze surfaces during operation in the ammonia oxidation process, were studied in detail. It is concluded that a vapor phase mechanism involving transport of platinum oxide is responsible for the observed reaction, and the reason why this process operates only over a limited range of temperature and pressure is explained. Some comments are also made on the related reconstruction observed on gauzes, used during the production of hydrogen cyanide by the Andrussow process