Kristina Božinović

This study investigates white willow bark extract (WWBE) as a potential corrosion inhibitor for Cu-DHP in a 0.5 M NaCl solution, using a non-destructive electrochemical methods, namely electrochemical frequency modulation (EFM), and electrochemical impedance spectroscopy (EIS). Electrolytes consisted of 0.5 M NaCl solutions both with and without the addition of WWBE (0.1–0.5 g l−1). The 0.5 M NaCl solution containing 0.5 g l−1 WWBE, both in the presence and absence of a copper plate, was analysed by ultraviolet-visible spectroscopy (UV-Vis). The experiments were conducted at room temperature. The EFM results indicated that WWBE functioned as a cathodic copper corrosion inhibitor, with the highest inhibition efficiency observed for the 0.5 M NaCl solution containing 0.5 g l−1 WWBE. The EIS results suggested the formation of a protective WWBE inhibitor film. The corrosion process was diffusion-controlled, both with and without the addition of WWBE. Both electrochemical methods demonstrated that WWBE adsorbed onto the copper surface in 0.5 M NaCl solution via physisorption, following the Langmuir adsorption isotherm. The Gibbs free energy values of adsorption were similar for EFM and EIS. The UV-Vis results showed that immersion of copper in an electrolyte containing 0.5 g l−1 WWBE for 24 h led to a change in the absorbance maximum, indicating the formation of a copper–WWBE complex. Overall, the results indicate that WWBE is an effective inhibitor of copper corrosion in chloride conditions. Further research will focus on the identification of compounds and organometallic complexes in WWBE and their individual effects on the corrosion process.

In the present study, the Sn78Bi22 alloy was investigated as a potential solder material. The study focused on the evaluation of thermal diffusivity and thermal conductivity over a defined temperature range, differential scanning calorimetry (DSC) analysis, and an assessment of soldering behavior through measurements of contact angle, spreading area, spreading ratio, and intermetallic compound (IMC) layer thickness. The investigated alloy exhibited reduced thermal diffusivity and thermal conductivity compared with literature data for pure Sn. DSC analysis indicated a decrease in melting temperature compared with pure Sn reported in the literature, resulting from the addition of Bi. Soldering behavior was evaluated as favorable, characterized by a thin IMC layer, a low contact angle on a Cu substrate, and high spreading ratio and spreading area. Based on these results, the Sn78Bi22 alloy shows potential for lead-free soldering applications.

This paper presents the results of SEM-EDS and DTA-TGA analysis of corn stalks before and after the biosorption of Cu2+ ions. Certain differences in the adsorbent structure and in the elemental analysis of the sample surface were observed. In micrographs of raw corn stalks, pores and cavities can be seen, which facilitate the penetration of the aqueous phase into the adsorbent structure, where copper ions are adsorbed at the internal active sites. After the biosorption of Cu2+ ions, a distinctly different surface morphology of corn stalks can be observed. The absence of cavities and channels is evident, with a compact and uniformly ordered lamellar structure. The EDS spectra of corn stalks, before and after copper ion biosorption, indicate the possible exchange of potassium, calcium, and magnesium with copper during the biosorption process. Based on the DTA-TGA analysis, the degradation of the corn stalk sample occurs in several stages.

The present work investigates the effect of Ni and Si additions on functional properties of Cu-30Zn brass. One base alloy without Ni and Si additions and one alloy with Ni and Si additions were prepared by conventional casting from high-purity Cu, Zn, Ni and Si, followed by solution annealing at 900 °C for 2 h and water quenching, cold pressing, and subsequent ageing at 300 °C for 8 h. Building on earlier studies of Ni₂Si-strengthened Cu-Zn and Cu-Ni-Si alloys, this processing route was selected to promote the formation of fine Ni-Si-rich precipitates within an α-brass matrix and to combine solid-solution and precipitation strengthening with acceptable electrical and thermal conductivities. The heat-treated alloys were characterized by measurements of electrical conductivity, Vickers microhardness (HV0.15), Leeb hardness (HLD) and thermal conductivity. Increasing Ni and Si contents is expected to raise hardness through solid-solution and Ni₂Si-type precipitation strengthening, while moderately reducing conductivity due to enhanced electron scattering by solute atoms and nanoscale particles. The results of this study provide composition-property guidelines for designing lead-free, precipitation-strengthened brasses based on the Cu-30Zn system.

The development of reliable lead-free solder alloys remains essential for applications in the electronics industry. This paper investigates the mechanical, electrical, and microstructural properties of a Sn78Bi22 solder alloy. The alloy was prepared by melting and casting, followed by a homogenization heat treatment. Tensile testing, Vickers microhardness measurements, electrical conductivity testing, and SEM/EDS microstructural analysis were performed at room temperature. The investigated alloy exhibited enhanced ultimate tensile strength (~93 MPa) and microhardness (45.5 HV0.05) compared with pure Sn, while electrical conductivity decreased to 5.4 MS/m. These changes were attributed to solid-solution strengthening, grain refinement, and the formation of a Bi-rich secondary phase, which also promoted brittle fracture during tensile testing. Microstructural observations revealed a Sn matrix with finely distributed Bi-rich phases, particularly along grain boundaries. The results contribute additional experimental data on the mechanical, electrical, and microstructural characteristics of non-eutectic Sn-Bi solder alloys.

Copper ion biosorption using raw and calcined chicken eggshells as biosorbents was conducted. The change in metal removal degree over time was monitored. Biosorption experiments were carried out in batch conditions for 90 minutes, as this duration is considered sufficient to reach equilibrium between phases. The experiments were conducted at three temperatures: 25 °C, 30 °C, and 35 °C. The results showed that the Cu2+ removal degree increased with time for both raw and calcined chicken eggshells. The results also indicated that system temperature significantly affects the efficiency of the biosorption process. Copper ion biosorption onto raw eggshells was considerably faster and more efficient, with a higher copper removal degree at higher temperatures. Biosorption onto calcined eggshells was less dependent on temperature, with Cu2+ removal being slightly faster at 35 °C, but the overall efficiency remained the same at all temperatures.

This paper focuses on the investigation of thermal and electrical properties of copper alloys produced at Copper Mill Sevojno. The investigated copper alloys include high-purity copper (Cu-DHP) and a series of brass alloys with different zinc content (CuZn15, CuZn28, CuZn30, CuZn37). The samples were subjected to different thermomechanical treatments, including annealing at different temperatures and plastic deformation to different degrees, resulting in soft, semi-hard, or hard material states. Measurements of thermal diffusivity, specific heat capacity, and thermal conductivity were carried out in the temperature range from 25 to 400 °C using the light flash method (Discovery Xenon Flash, DXF-500). Differential scanning calorimetry (DSC) was applied to determine thermal characteristics, while electrical conductivity was measured using the “Institut Dr. Förster Sigmatest 2.063” device. The results showed significant differences between the samples, depending on their chemical composition and thermomechanical treatment. For instance, Cu-DHP demonstrated the highest thermal and electrical conductivity, while conductivity for a series of brass alloys decreased with increasing zinc content. The collected data provide a clearer picture of the behavior of these alloys, especially in terms of heat and electrical transport.

As an important source for nickel extraction, millerite (NiS) has been investigated in the past, however there is still a notable deficiency in literature data regarding its behaviour and phase transformations at elevated temperatures. In order to better understand millerite oxidation process, the characterization of the initial sample and its oxidation products was investigated. Thermal and kinetic analysis were performed in order to identify phase transformations, propose a possible reaction mechanism and to determine the kinetic parameters of the process when heating the sample in the temperature range from 25 oC to 1000 oC. Experimental results showed that thermal decomposition end-products consist of nickel oxide and spinel phase trevorite as well as hematite and maghemite at elevated temperatures. Kinetic analysis results indicate that oxidative roasting occurs in kinetic field, with temperature-dependant reactions.