Marija Korać

Sintered Materials Based on Copper and Alumina Powders Synthesized by a Novel Method

The intensification in research of nanostructure materials that occurred in recent years was mainly due to their striking potential, i.e. mechanical and physical properties significantly improved compared to the conventional grain materials (Moriarty, 2001; Ristić, 2003). Nano-structured materials rank in the group of ultra fine, metastable structures containing a high concentration of defects (point defects, dislocations) and boundaries (grain boundaries, interphase boundaries, etc.). These materials are structurally different from crystals and amorphous forms because of the fact that grain boundaries and interphases represent a specific state of the solid matter, since the atoms on boundaries are subjected to a periodical potential field of the crystal from both sides of the boundary (Koch, 1999). The synthesis of powders represents the starting and crucial stage in the production of sintered metal materials with required properties. Considering that the starting structure undergoes certain changes during further processing, but remains essentially preserved in the structure of the final product (Ristić, 2003; Motta et al. 2004), there is an increased necessity for a great number of methods for producing powders. Copper is widely exploited in industry because of its high electrical and thermal conductivity, even though it possesses low strength especially at elevated temperatures. In order to overcome this problem it can be strengthened by using finely dispersed particles of stable oxides like alumina, titania, yttria etc. Copper-based composite materials are widely applied in the field of electronics and electrical engineering as highly conductive materials for operation at elevated temperatures, as electrodes for resistance spot and seam welding, different contact materials, various switches, thermal and electric conductors, microwave tubes, etc (Lee & Kim, 2004). Introduction of fine dispersed particles into matrix of base-metal has considerable strengthening effect and nano particles of oxides are especially suitable. Due to their hardness, stability at elevated temperatures and insolubility in copper they represent obstacles for dislocation, grain and sub-grain boundary movement increasing mechanical properties of these materials with insignificant effect on thermal and electrical conductivity (Naser et al., 1997; Trojanova et al., 1999, Tian et al. 2006). Significant reinforcing effects can

Hydrometallurgical process for extraction of metals from electronic waste-part I: material characterization and process option selection

Used electronic equipment became one of the fastest growing waste streams in the world. In the past two decades recycling of printed circuit boards (PCBs) has been based on pyrometallurgy, highly polluting recycling technology which causes a variety of environmental problems. The most of the contemporary research activities on recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled. In this paper mechanically pretrated PCBs are leached with nitric acid. Pouring density, percentage of magnetic fraction, particle size distribution, metal content and leachability are determined using optical microscopy, atomic absorption spectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis. Three hydrometallurgical process options for recycling of copper and precious metals from waste PCBs are proposed and optimized: the use of selective leachants for recovery of high purity metals (fluoroboric acid, ammonia-ammonium salt solution), conventional leachants (sulphuric acid, chloride, cyanide) and eco-friendly leachants (formic acid, potassium persulphate). Results presented in this paper showed that size reduction process should include cutting instead of hammer shredding for obtaining suitable shape & granulation and that for further testing usage of particle size -3 +0.1mm is recommended. Also, Fe magnetic phase content could be reduced before hydro treatment.

Influences of synthesis methods and modifier addition on the properties of Ni-based catalysts supported on reticulated ceramic foams

A method of synthesizing Ni-based catalysts supported on α-Al2O3-based foams was developed. The foams were impregnated with aqueous solutions of metal chlorides under an air atmosphere using an aerosol route. Separate procedures involved calcination to form oxides and drying to obtain chlorides on the foam surface. The synthesized samples were subsequently reduced with hydrogen. With respect to the Ni/Al2O3 catalysts, the chloride reduction route enabled the formation of a Ni coating without agglomerates or cracks. Further research included catalyst modification by the addition of Pd, Cu, and Fe. The influences of the additives on the degree of reduction and on the low-temperature reduction effectiveness (533 and 633 K) were examined and compared for the catalysts obtained from oxides and chlorides. Greater degrees of reduction were achieved with chlorides, whereas Pd was the most effective modifier among those investigated. The reduction process was nearly complete at 533 K in the sample that contained 0.1wt% Pd. A lower reduction temperature was utilized, and the calcination step was avoided, which may enhance the economical and technological aspects of the developed catalyst production method.

Combustion of Metallurgical Wastes Using Secondary Aluminum Foils

ABSTRACT Simulating the reactions in a complex system can lead to self-sustaining and energy efficient treatment of wastes in recycling promoting manner. In this contribution, the synergic combination of electric arc furnace dust (EAFD), mill scale, and secondary aluminum, in a form of waste foil, was researched aiming to use exothermal energy of reactions and to obtain environmentally favorable products. The secondary aluminum in the form of foil was prepared in different ways in order to develop aluminum surface and to be suitable for aluminothermic reactions. The commercial aluminum powder was used to determine optimal conditions using full factorial experiment design. After that, research was performed on aluminothermic reactions with the aluminum powder obtained from secondary aluminum foils. Results show that the secondary aluminum can be successfully used for a treatment of oxides bearing hazardous wastes in an energy efficient and environmentally friendly manner. The comparative life-cycle assessment revealed several advantages of using the secondary aluminum foil as a reduction agent compared to the conventional recycling of the secondary aluminum foil.

The effect vanadium content and heat treatment on wear resistance and fracture toughness of Fe-Cr-C-V alloy

Experimental results indicate that the volume fraction of the carbide phase, carbide size and distribution had an important influence on the wear resistance of Fe-Cr- C-V alloys under low-stress abrasion conditions. Besides, the martensitic or martensiteaustenitic matrix microstructure more adequately reinforced the M7C3 eutectic carbides, minimizing cracking and removal during wear, than did the austenitic matrix. The secondary carbides which precipitate in the matrix regions of high chromium iron also influence the abrasion behaviour. The results of fracture toughness tests show that the dynamic fracture toughness in Fe-Cr-C-V white cast irons is determined mainly by the properties of the matrix. The high chromium iron containing 1.19 wt.% V in the as-cast condition, showed the greater dynamic fracture toughness when compared to other experimental alloys. The higher fracture toughness was attributed to strengthening during fracture, since very fine secondary carbide particles were present mainly in an austenitic matrix. In heat treated Fe-Cr-C-V alloys with varying contents of vanadium, lower Kid values were obtained, compared with as-cast alloys.

Photographs of Cu-As-Sn binary and ternary metal pellets as supporting material for the article: "Experimental design of the Cu-As-Sn ternary colour diagram"

The dataset supports the article: Radivojevic, M., Pendic, J., Srejic, A., Korac, M., Davey, C., Benzonelli, A., Martinon-Torres, M., Jovanovic, N., and Kamberovic, Ž. (2017). Experimental design of the Cu-As-Sn ternary colour diagram. Journal of Archaeological Science, https://doi.org/10.1016/j.jas.2017.12.001. Abstract: The aesthetic appearance of metals has long been recognised in archaeometric studies as an important factor driving inventions and innovations in the evolution of metal production. Nevertheless, while the studies of ancient gold metallurgy are well supported by the modern research in colour characteristics of gold alloys, the colour properties of major prehistoric copper alloys, like arsenical copper and tin bronzes, remain either largely understudied or not easily accessible to the western scholarship. A few published studies have already indicated that alloying and heat treatment change the colours of copper alloys, although they are mainly based on the examples of prehistoric tin bronze objects and experimental casts. Here we present the procedure for building the Cu-As-Sn ternary colour diagram, starting with experimental casting of 64 binary and ternary alloys in this system. We used two types of information to produce two different ternary colour diagrams: one, based on photographs of the samples, and the other, established on the colorimetric measurements. Furthermore, we developed the procedure for creating a graphic representation of colours in the Cu-As-Sn ternary diagram using QGIS. As an initial case study, we plotted the composition of the world’s earliest tin bronze artefacts; the graphic representation further supports claims about the importance of golden hue for their invention and demand, c. 6,500 years ago. We argue that the presented colour diagrams will find wide use in future investigations of aesthetics of prehistoric copper alloys.

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.

Pyro-Refining of Mechanically Treated Waste Printed Circuit Boards in a DC Arc-Furnace

This paper presents the results of theoretical assessment and a preliminary experimental investigation of the modified pyrometallurgical processing of metallic granulate obtained after mechanical treatment of waste printed circuit boards (WPCBs). The studied two-step process included oxidation of metallic granulate followed by pyrometallurgical refining in a DC arc-furnace. In the investigated process, the oxygen bounded in metal oxides, obtained during the oxidation annealing of granulate, was used as a “solid” oxidizer for subsequent pyrometallurgical refining in a DC arc-furnace. According to the obtained results, the Cu content in the produced metallic phase (anodic copper) was 98.4% and is suitable for further electro-refining process. In addition, over 94% of Au was concentrated in metallic phase, suggesting that a high Au yield could be attained. However, owing to the distribution between slag phase and filter product, only 60% of Ag was collected in the metal phase. In-between metal and slag is the metal-oxide phase, containing Cu with metals impurities, such as Sn and Pb, which was obtained as well, and could be further treated using conventional processes for additional metal valorization. The investigated concept would allow substitution of the long-lasting oxygen blowing process and application of complicated pyrometallurgical reactors and create a feasible alternative for lower operating capacities.

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.

Integrated procedure for recycling and valorization of useful components from secondary raw materials based on hard metals

Wide application of hard metals requires increased consumption of their constituents. Their high cost and scarcity impose the need for finding new, both ecologically and economically justified ways for their production. In presented research, on the basis of previous research, a review of an integrated technological procedure of recycling and valorization of useful components from hard metals secondary raw materials is given.Integrated procedure for processing of hard metals waste enables the preparation of a wide range of powders with required properties, a high efficiency and reducing the duration of individual stages of procedures for their processing. Therefore, besides conservation of natural resources there are also significant economic and energetic benefits. The developed technological procedure is in service of sustainable development.