This study provides the newest information regarding the synthesis of gold nanoparticles via the ultrasonic spray pyrolysis method and reduction in aqueous solution. Ultrasonic spray pyrolysis (USP) is the mostly used method for the synthesis of particles with controlled and uniform particle size because of easy powder morphology control and the availability of cheap precursor solutions. In the USP process a metal-containing solution is cold atomized forming an aerosol. Special attention is given in this paper to the formation of Gold nanoparticles from gold auric acid solution using sodium citrate as the reducing agent in an aqueous solution under atmospheric and high pressure.
B.04 Guest lecture
COBISS.SI-ID: 16906774LENS technology represents a modern additive technology for the application of metallic materials. In this dissertation, the conceptual design of the use of high-tech materials is presented in tools for injection moulding as well as tools for die casting of light metals fabricated with this technology. In practice, deviations of dimensional and design tolerances of the product frequently occur during the solidification due to uneven temperature distribution in the tool and consequently, in the product during cooling. At the same time, thermal conductivity of tool steels limits the cooling time and consequently, the productivity of tools. The presented problem of synthesizing a H13 tool steel and copper alloy using functionally graded materials with specific microstructure and a combination of properties represents new possibilities for optimization in this field. The dissertation shows the influence of the layered deposition and thermal conditions of the LENS technology on the development of microstructure and consequently, mechanical properties. For easier understanding, we characterized reference samples of different chemical compositions using the traditional casting technology. Using various analyses, such as microstructural, chemical, thermal and phase, we determined phase compositions as well as the impact of technology on the formation of cracks and the development of microstructure, depending on the chemical composition and solidification conditions. In the field of chemical compositions which are susceptible to cracking, we examined the crack-filling mechanism, which is a result of complete wetting of copper and temperature conditions during the deposition of new layers. To examine the effects of phase compositions on mechanical properties of the alloys, tensile tests and microhardness measurements were carried out. Results show the possibility of a successful fabrication of samples of functionally graded materials H13-Cu using the LENS technology. Finally, the influence of solidification conditions on microstructure development as well as the model of microstructure development and stability are explained.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 18007830This work deals with the influence of plastic deformation on microstructural evolution of dispersion strengthened copper with the aim of uniting the mechanism of dispersion and deformation strengthening to produce nanostructured composite with improved properties. Within the work the possibility of achieving greater depths of internal oxidation zone was studied. With the modified Rhines package a sufficient depth of internal oxidation zone was reached to study the behaviour of dispersion strengthened alloy during ECAP (Equal channel angular pressing) process. Material flow in a partly internally oxidized billet and in a homogenous reference sample made of modelling mass was also studied to analyse on the macro scale the influence of the internal oxidation zone on material flow behaviour during the ECAP process. The analysis was performed with the aim of revealing the uniformity of strain distribution and to get the information about deformation strengthening across the volume of the billet. It was found out, that on the macro scale the oxide particles do not affect the material flow, therefore there is no difference in flow of internal oxidation zone and solid solution. The influence of oxide particles on the mechanism of plastic deformation was evaluated by comparing the microstructural evolution during ECAP process of dispersion hardened material and solid solution. It was discovered, that the oxide particles increase the fragmentation of the grains during severe plastic deformation, which leads to the formation of nano-sized equiaxed grains with amorphous grain boundaries. Based on the results, the model of plastic flow for nanostructural composite was developed, in which it is assumed, that the plastic flow is carried out with sliding along amorphous grain boundaries.
D.09 Tutoring for postgraduate students
COBISS.SI-ID: 272702208Within the current literature there exists a vast amount of data, derived from numerous observations confirming a sluggish bainite formation at low temperatures. This feature is so predominant it is considered an inherent property of the bainite transformation, and has been known as far back as the very first mention of bainite, where the steel was transformed at 200°C in excess of 10 days. The new methodology and alloy design concept of KAB (Kinetically activated bainite) steels enables the formation of carbide free nanostructured bainite in a matter of seconds. The bainite formed within the new grade is very fine and exhibits a hardness between 660 HV1 upon air cooling, which corresponds to tensile strengths of up to 2800 MPa, with predominantly uniform elongations due a pronounced TRIP effect. This contribution focuses on the physical metallurgy of this new steel grade, the formation of the micro structure and the mechanical properties obtained during continuous cooling.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 19091990This paper discusses the application of rapid solidification by the centrifugal atomization method for preparation of thin NdFeB flakes. Metallographic characterization is an important way to evaluate material properties, therefore the effect of alloy composition and different conditions of centrifugal atomization on the microstructure of rapidly solidified NdFeB alloy were investigated. The microstructures and different phases were examined by optical and scanning electron microscopy. Additionally the influence of the processing methods on microstructures of flakes will be discussed.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 18951702