Stevan P. Dimitrijević

Anti-tarnish silver alloys in system Ag-Cu-Zn-Si with the addition of aluminum

This paper presents investigations of aluminum addition influence on the corrosion characteristics of the sterling silver Ag-Cu-Zn-Si alloys. The procedure for obtaining Ag-Cu-Zn-Al-Si alloys in small ranges of predefined composition was also presented. Open circuit potential measurements, linear polarization resistance method and potentiodynamic polarization tests were employed to determine corrosion characteristics of the alloys. The materials were tested in a 0.01M sodium sulfide solution. It was shown that the addition of aluminum improves sulfidization resistance and corrosion characteristics. Best results are achieved for the alloy with the following composition 92.5% Ag, 1.9% Cu, 3.7% Zn, 1.6% Al and 0.3% Si.

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.

Modelling, simulation and optimisation of pulse-reverse regime of copper, silver and gold electrodeposition

Abstract Pulse-reverse power modes are used in galvanotechniques in order to obtain coatings with better characteristics in terms of gloss, adhesion, tracking sharp edges and uniform distribution of deposits on complex shape objects, compared with the coatings produced by constant current modes. Pulse-reverse modes also allow the use of a higher current density, and thus the production speed of electroplating cells increases. Systems for standard electroplating of copper, silver and gold are optimised by the suitable choice of duration and intensity of the pulses. It is shown that coatings with satisfactory quality can be deposited using higher current density, different modes of pulsed current in a very short period of time, without expensive and often dangerous additives in the electrolyte. Parameters of the model for certain electrochemical systems were determined by modelling and computer simulation, so the system behaviour under different circumstances becomes predictive.

Design of anti-tarnish sterling silver Ag-Cu-Zn alloy and investigation of silicon addition influence on mechanical and corrosion characteristics

This paper presents investigations of the influence of silicon addition on the mechanical and corrosion characteristics of the sterling silver Ag-Cu-Zn alloys. The procedure for obtaining Ag-Cu-Zn-Si alloys in small ranges of composition was also presented. Vickers hardness tests and three electrochemical tests were performed on the samples in this study. Open circuit potential measurements, linear polarization resistance method, and potentiodynamic polarization tests were employed to determine corrosion characteristics of the alloys. The materials were tested in 0.9% NaCl solution, artificial sweat, 0.1 and 0.01 M sodium sulfide solutions. It was shown that addition of silicone increases hardness and generally improves sulfidation resistance and corrosion characteristics in near-neutral chloride solutions of the Ag-Cu-Zn alloys.

Characterization of the Ag43Cu37Zn20 alloy surface after potentiostatic polarization using LDI-TOF mass spectrometry

Abstract This work is the first to demonstrate the possibilities of direct analysis of the corrosion film formed on Ag43Cu37Zn20 alloy using laser desorption/ionization (LDI) on a commercial matrix-assisted LDI time of flight mass spectrometry (MS) instrument. In the LDI mass spectra measured from the water solution of the corrosion film, the ion species Zn+, Zn(H2O)+, AgH+, Cu2H+, Cu2O(OH)+, Cu3O(OH)+ (high intensity), and Cu(OH)(H2O)+, ZnCl(OH)(H2O)+, AgCl+, CuCl+ (low intensity) were identified. The LDI mass spectra of the propan-2-ol solution of the corrosion film contains the ions Zn5Cl(OH)3(H2O)11+, Zn5Cl2(OH)8(H2O)6+, and Zn5Cl2(OH)(H2O)14+. Mass spectra were observed at laser energies in the range of 1340–1860 arbitrary units in positive ion mode. Previously, Raman spectra and X-ray diffraction (XRD) analysis of the same anodic film have shown similar results as LDI MS – that the anodic film contains the mixture of Ag, Cu2O, CuCl, Zn5Cl2(OH)8·H2O, and β-Zn(OH)Cl. LDI MS could be a complementary method for XRD and Raman, as demonstrated in this investigation. The LDI MS method greatly reduces the analysis time and amount of the sample compared to traditional methods. For this reason, the LDI MS method can be a useful tool for the fast qualitative screening of corrosion films.

Microhardness of decorative gold coatings obtained from gold complex based on mercaptotriazole: Comparison with cyanide

Abstract The aim of this work was to investigate the effects of current density, temperature, pH and concentration of ethylhexilsulfonate additive on the microhardness of electrochemically deposited gold decorative coatings obtained from a conventional cyanide electrolyte and gold complex based on mercaptotriazole. Mechanically and chemically prepared brass samples were first nickeled from acidic electrolyte. Nickel was a substrate deposit, and then decorative gold coatings were deposited from two types of electrolytes at different current densities and temperatures. Decorative gold coatings were deposited from auri-mercaptotrizole at different pH values and from electrolyte with and without the ethylhexilsulfonate additive. The microhardness of the gold coating was measured using the Knoop method. The highest values of microhardness were obtained at a current density of 1 A dm−2 at room temperature for both electrolytes. The microhardness of the gold coatings from cyanide electrolytes was HK = 740 MPa, and the coatings obtained from auri-mercaptotriazole HK = 660 MPa. This difference is not relevant for decorative purposes. The highest values of microhardness, HK = 660 MPa, were obtained at pH = 9 from the gold complex based on mercaptotriazole without the additive.

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.

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.