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Selective Leaching as a Method of Metallic Nanoparticles Preparation
Michalcová, A.; Vojtěch, D.; Kubatík, Tomáš František; Marek, I.; Svobodová, P.; Novák, P.
2014 - English
Selective leaching is process used mainly in analytical praxis–alloy matrix is dissolved and the residuum can be study by different methods. In this article, modification of selective leaching determined for production of metallic nanoparticles is described.Selective leaching technique lays in preparation of supersaturated solid solution of desired element in matrix metal –by convenient heat treatment or by rapid solidification of the binary alloy. Consequently, the matrix metal is selectively dissolved and metal nanoparticles from other metal are formed. The size, shape and agglomeration of forming metallic nanoparticles are dependent on many factors such as reaction temperature, concentration of leaching solution, additives present in leaching solution. The metal mainly used as matrix component is aluminium due to is amphoteric behaviour. It enables aluminium dissolution in sodium hydroxide without affecting the minor metal. Nobel metals like silver or copper forms
Keywords:
Nanocrystaline materials; selective leaching
Available at various institutes of the ASCR
Selective Leaching as a Method of Metallic Nanoparticles Preparation
Selective leaching is process used mainly in analytical praxis–alloy matrix is dissolved and the residuum can be study by different methods. In this article, modification of selective leaching ...
Global Power Balance in Non-Stationary Discharge Phases in the COMPASS Tokamak
Havlíček, Josef; Imríšek, Martin; Kovařík, Karel; Weinzettl, Vladimír
2014 - English
The global power balance between different input power and sink/loss channels is important for understanding of tokamak physics, particularly for various scaling laws. The power balance is measured easily during stationary discharge phases because the terms for both magnetic field energy and plasma thermal energy build-up can be neglected. However, many important events in tokamak plasmas occur during non-stationary phases of the discharge. This article describes, quantifies and discusses the terms of the global power balance, including time dependent parts, and exemplifies them on the typical ohmic discharge of the COMPASS tokamak.
Keywords:
tokamak; global power balance; power through separatrix; COMPASS
Available at various institutes of the ASCR
Global Power Balance in Non-Stationary Discharge Phases in the COMPASS Tokamak
The global power balance between different input power and sink/loss channels is important for understanding of tokamak physics, particularly for various scaling laws. The power balance is measured ...
Silicon carbide for chemical application prepared by SPS method
Brožek, Vlastimil; Kubatík, Tomáš František; Vilémová, Monika; Mušálek, Radek; Mastný, L.
2014 - English
Silicon carbide discovered more than 121 years ago has a wide usage in the mechanical engineering industry as well as in electrical engineering.It is an excellent abrasive medium as well as a construction material with high resistance to mechanical and chemical deterioration.Under standard condition, silicon carbide has no melting point (decomposes at 2700 °C – principle used for industrial production of silicon),thus the bulk form must be prepared in a composite form with a metallic, ceramic or polymer binder. This method is suitable for tailoring of mechanical properties; nevertheless,it does not produce SiC form applicable for laboratory purposes.Binder-free sintering of SiC is practically impossible, despite decreased chemical resistivity of the produced material. Pure SiC is insoluble in all acids except hydrofluoric acid.Reaction of SiC with HF is enabled only due to residual SiO2 created during the industrial production.However, SiO2 located between the planes of growth of SiC
Keywords:
silicon carbide; spark plasma sintering; silicon carbide corrosion; impurities in silicon carbide
Available at various institutes of the ASCR
Silicon carbide for chemical application prepared by SPS method
Silicon carbide discovered more than 121 years ago has a wide usage in the mechanical engineering industry as well as in electrical engineering.It is an excellent abrasive medium as well as a ...
Planar acoustic metamaterials with the active control of acoustic impedance using a piezoelectric composite actuator
Nováková, Kateřina; Mokrý, P.; Václavík, J.; Marton, P.; Cernik, M.; Psota, Pavel; Doleček, Roman; Lédl, Vít
2013 - English
In the Paper, there are presented methods for a precise active control of the acoustic impedance of large planar structures, e.g glass plates or shells, by means of distributed flexible piezoelectric composite actuators which are connected to passive or active electronic shunt circuits. Design of tunable acoustic metamaterials is realized using Finite Element Method simulations and their acoustic properties are evaluated using acoustic transmission loss measurements. Static and dynamic displacements of the metamaterials produced by electric voltage are measured using Digital Holographic Interferometry. We believe that deep understanding of presented systems should result in future applications that improve the quality of everyday life.
Keywords:
Planar acoustic metamaterials; Active control of acoustic impedance; Piezoelectric composite actuator
Available at various institutes of the ASCR
Planar acoustic metamaterials with the active control of acoustic impedance using a piezoelectric composite actuator
In the Paper, there are presented methods for a precise active control of the acoustic impedance of large planar structures, e.g glass plates or shells, by means of distributed flexible piezoelectric ...
Possibilities of welding observation with regard of sielding gas
Rohan, P.; Vojtíšek, Petr
2013 - English
MAG welding is characterized by very rapid processes in extreme condition of electric arc. To describe welding is necessary to use sufficiently quick equipment. Especially in the transition region between dip and spray transfer the processes develop quickly. Characterization of transition area in active three component shielding gas was carried out visually by hi speed camera equipment and electrically by quick response electronic measurement system.
Keywords:
Welding; direct observation; welding gas
Available at various institutes of the ASCR
Possibilities of welding observation with regard of sielding gas
MAG welding is characterized by very rapid processes in extreme condition of electric arc. To describe welding is necessary to use sufficiently quick equipment. Especially in the transition region ...
Tungsten coatings and free standing parts
Brožek, Vlastimil; Ctibor, Pavel; Matějíček, Jiří; Mušálek, Radek; Weiss, Z.
2013 - English
Tungsten powders, 20 – 100 µm in size, were melted in the jet of thermal plasma generated by a water-stabilized spray system WSP®. The molten tungsten was deposited on steel and graphite or boron nitride substrates, whereas the spray-ability itself was tested as well as cohesion with other substrates. One of the goals of this experimentation was to gain skills for covering variously shaped walls of nuclear fusion devices (Tokamaks). Also spraying of free-standing tungsten bodies was realized, by means of substrates easily machainable-out after deposition, as graphite and BN. Other option consists of covering a tungsten mesh or plates armored with tungsten wires. Protection of tungsten against oxidation in the plasma jet was a problem to be solved – the best results were gained with shroud gas, Ar with 7% hydrogen, and simultaneous placement of the substrates into graphite cells. The whole spray process was maintained to avoid temperatures over 700°C at which the oxidation is
Keywords:
tungsten coatings; tungsten filters; plasma spraying; shrouding; tungsten plasma spraying; protection against oxidation
Available at various institutes of the ASCR
Tungsten coatings and free standing parts
Tungsten powders, 20 – 100 µm in size, were melted in the jet of thermal plasma generated by a water-stabilized spray system WSP®. The molten tungsten was deposited on steel and graphite or boron ...
Preparation of gold, silver and platinum colloid solutions by precursors decomposition in low temperature plasma
Brožek, Vlastimil; Kutílek, Zdeněk; Mastný, L.; Sýkora, V.; Benešová, L.; Sofer, Z.
2013 - English
Liquid precursor decomposition in the low temperature plasma generated by WSP® was used for synthesis of precious metals nanoparticles. The gold in the form of H[AuCl4], silver in the form of AgNO3 and platinum in the form of H2[PtCl6] were used to generate colloid solutions with concentration of 5 mg.l-1 – 70 mg.l-1 and particle size of 20 nm – 120 nm. The solution contained elevated concentration of nitrite and nitrate ions due to the reaction of plasma with nitrogen form air. In order to reduce the concentration of nitrite and nitrate ions the plasma generated nanoparticles was projected by plasma torch to the ammonium chloride solution. Other way used for reduction of NO3- and NO2- concentration was optimization of geometry of plasma system. The other way was also by application of shrouding effect by nitrogen and ammonia gas. The size of nanoparticles and their concentration can be influenced by geometry of plasma torch, composition of carrier gas and by geometry of
Keywords:
colloidal suspension; gold nanoparticles; silver nanoparticles; platinum nanoparticles; plasma generator; low temperature plasma
Available at various institutes of the ASCR
Preparation of gold, silver and platinum colloid solutions by precursors decomposition in low temperature plasma
Liquid precursor decomposition in the low temperature plasma generated by WSP® was used for synthesis of precious metals nanoparticles. The gold in the form of H[AuCl4], silver in the form of AgNO3 ...
Thermal plasma gasification of organic waste and biomass
Hrabovský, Milan
2013 - English
The paper presents description of thermal plasma gasification processes. Analysis of energy balances of plasma gasification is presented, kinetics of the gasification process is discussed and relations between particle size, reaction temperature and gasification rate are analyzed. Examples of results of gasification of biomass and pyrolysis oil from used tires are given. Syngas with high heating value, high hydrogen content and low tar contamination is produced by plasma gasification.
Keywords:
Thermal plasma; plasma gasification; syngas
Available at various institutes of the ASCR
Thermal plasma gasification of organic waste and biomass
The paper presents description of thermal plasma gasification processes. Analysis of energy balances of plasma gasification is presented, kinetics of the gasification process is discussed and ...
Comparison of holographic setups used in heat and mass transfer measurement
Doleček, Roman; Psota, Pavel; Lédl, Vít; Vít, Tomáš; Kopecký, V.
2013 - English
The authors of the paper deal with measurement of heat and mass transfer for several years and they have frequently used few techniqes for measurement of refractive index distribution based on holographic interferometry. Some of the well known techniques have been modified some and some new ones developped. Every technique could be applied with success in different type of meassurement and obviously every one has set of properties making them unique. We decided to digest few different basic techniques and describe its properties in this paper with the aim to help the reader select the proper one for their measurement. The list of techniques and its properties is not comprehensive but schould serve as a basic orientation in the field.
Keywords:
Digital holography; Holographic setup; Heat and mass transfer measurement
Available at various institutes of the ASCR
Comparison of holographic setups used in heat and mass transfer measurement
The authors of the paper deal with measurement of heat and mass transfer for several years and they have frequently used few techniqes for measurement of refractive index distribution based on ...
Measurement of Vibration Mode Structure for Adaptive Vibration Suppression System by Digital Holography
Psota, Pavel; Lédl, Vít; Doleček, Roman; Mokrý, P.; Kopecký, V.
2013 - English
Previously the frequency-shifted digital holographic interferometry (FSDHI) for measurement of vibration amplitudes in range of nanometers was introduced and verified by authors [1,2]. The method FSDHI addressed some of the drawbacks of the conventional methods and was used mainly for piezoelectric transformer vibration amplitudes and mode structures measurement [3]. The limiting factor for application of this method is the maximal measured value of the vibration amplitude without the risk of ambiguity. The value is approximately 80nm for the frequency doubled Nd: YAG line. Since FSDHI enables us to precisely measure vibration amplitudes over the whole inspected area with very high lateral resolution, it could also be a very useful tool for measurement of vibration amplitudes and mode structures for research in the field of adaptive suppression systems. Such a measurement would provide a necessary feedback about the system behavior.This was the reason why we put an effort
Keywords:
digital holography; vibration measurement; vibration suppression
Available at various institutes of the ASCR
Measurement of Vibration Mode Structure for Adaptive Vibration Suppression System by Digital Holography
Previously the frequency-shifted digital holographic interferometry (FSDHI) for measurement of vibration amplitudes in range of nanometers was introduced and verified by authors [1,2]. The method ...
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