Istraživanje procesa relaksacije ranih metastabilnih stanja sistema Fe40Ni40Si14B6

An investigation of the low-temperature relaxation process has been performed in which the structure of the frozen liquid metal is transformed into the structure which the sample acquires at the room temperature. The samples were obtained by quenching on a Cu single roll and then conserved at low temperature as soon as formed. It was noted that the activation of the relaxation process occurs in a temperature interval of 10-125 K. That is somewhat unexpected, because of the nature of the usual relaxation process in amorphous systems. The activation energy of the so-called early metastable states in Fe40Ni40Si14B6 amorphous system was found to be 1.5 kJ/moleU radu je opisano istraživanje niskotemperaturnog relaksacijskog procesa kojim se struktura zamrznutog tekućeg metala, dobijenog kaljenjem na jednom valjku, transformira u strukturu koju traka ima kada dostigne sobnu temperaturu. Uočeno je da se proces relaksacije počinje aktivirati pri određenoj energiji, što nije bilo za očekivati s obzirom da se radi o relaksacijskom procesu u amorfnom sistemu. Za aktivacijsku energiju kojom se relaksiraju rana metastabilna stanja u sistemu Fe40Ni40Si14B6 dobivena je vrijednost 1.5 kJ/mol

Scale-up of the solid polymer electrolyte reactor for electro-organic synthesis

PhD ThesisElectro-organic reactions are often complicated by the need to add supporting electrolytes and co-solvents. In many cases these additives take part in side reactions causing low yields and hinder the purification stages. The solid polymer electrolyte (SPE) reactor uses an ion exchange membrane to transfer charged species between the electrodes and so eliminates the need for any additives. In this way improvements in electrochemical processing can be achieved. The SPE reactor has only been studied for model organic and aqueous based electrochemical reactions. The aims of this project were to develop the reactor for use as a suitable means of synthesising alcohols and acids based on substituted toluenes. This involved selection of suitable electrode material, polymer electrolyte pre-treatment and reactor modelling. According to published reports the direct electro-oxidation of toluene takes place with maximum yields of 19% with an acetic acid co-solvent and a nitric acid supporting electrolyte. Higher yields are possible with inorganic mediators such as Mn³⁺ and Cr⁶⁺. 30% yields of methoxylated products are possible from electrolysis in methanol although many non volatile by-products are formed. Initial research was spent investigating the oxidation of toluene in sulphuric acid at a lead dioxide rotating disk electrode. It was found that the reaction is mass transfer limited in the potential region below gas evolution. The order of reaction with respect to toluene was 0.5. Electrolysis of toluene on platinum mesh in nitric acid with and without acetic acid was found to produce benzyl alcohol and benzaldehyde with low current efficiencies. Without co-solvent the maximum current efficiency was 10% at 2S0Alm². An SPE reactor fabricated from glass with an active electrode area of Scm2 was used to perform electrode tests. Highest yields of benzaldehyde were obtained using nickel foam, graphite felt and palladium coated mesh electrodes. The current efficiencies were 52.4%, 20.3% and 10.7% respectively. This work highlighted the need for a good membrane-electrode contact. The oxidation of benzyl alcohol in the same reactor using nickel foam Abstract was accomplished with a current efficiency of 85.4% showing that the difficult step in the oxidation of toluene was the first one to benzyl alcohol. Pre-treatment of the membrane by swelling in solvents was considered to be an important factor in the performance of the SPE reactor. Several ion exchange membranes were pre-treated in a variety of aqueous and organic solvents including methanol, toluene, DMF, water and sulphuric acid. Nafion® 117 was found to increase in size more than the other tested membranes in all solvents except water and sulphuric acid. Many of the pre-treated membranes were tested in an SPE reactor made from steel with an active electrode area of 2lcm2 for the oxidation of toluene in methanol. The anode-membrane potential was measured as a function of time and current density with Nafion® 117 having the lowest values of potential. Selection of the pre-treatment method for future use was determined by assessing the performance in the reactor, contamination of products and chemical hazards. Swelling in aqueous solvents was the chosen procedure. The steel SPE reactor was operated in continuous mode with recycle for the oxidation of toluene in methanol. Galvanostatic electrolysis took place at several current densities, temperatures and feed concentrations. Two products were identified as ⍺-methoxytoluene and ⍺,⍺-dimethoxytoluene and these were formed at low current efficiencies between 1.4% and 9%. The main product was thought to be an oligomer of toluene. The gas generated was found to be mainly hydrogen with a small amount of oxygen thought to come from residual water in the pre-treated membrane. A computer simulation of the SPE reactor for toluene oxidation in methanol was based on two series and one parallel reaction. These were first order in reactant species and followed Tafel type kinetics. Mass transfer of dilute reactants was based on Fickian diffusion. Parameters not available in the literature such as membrane potential and electro-osmotic flow were correlated to applied variables using experimental data and multiple linear regression. The importance of electro-osmotic flow in the SPE reactor was demonstrated by considering its effect on product distribution. The model showed that the oligomerisation of toluene was the dominant reaction making the SPE reactor unsuitable for the oxidation of toluene.The Engineering and Physical Sciences Research Council: The British Council: The CASE Award Sponsorship

Peltier element based tankless heater/cooler

Bakalářská práce se zabývá možnostmi návrhu průtokového chlazení a ohřevu s využitím Peltierových článků. V teoretické části jsou rozebrány konvenční možnosti chlazení, princip a možnosti nasazení Peltierových článků a zvážení problematiky konstrukce zařízení pro použití v potravinářském průmyslu. V praktické části se autor zaměřuje na návrh a konstrukci mechanické části, návrhu a konstrukci procesorem řízeného zdroje. Hotové zařízení je porovnáno s alternativním komerčním řešením a jsou zhodnoceny možnosti jeho reálného nasazení.Barchelor thesis focuses on the design of tankless heating and cooling using Peltier elements. The theoretical part deals with conventional cooling capabilities, principles and options of using Peltier elements and considerate issues of design for use in the food industry. In the practical part, author focuses on the design and construction of mechanical parts, design and construction of processor controled power source. Final device is compared to the alternative commercial product and possibilities of real usage are considered.

Tunable Magnetization and Damping of Sputter-Deposited, Exchange Coupled Py|Fe Bilayers

We report on magnetic damping of exchange coupled, polycrystalline Py(Ni80Fe20)|Fe and Fe|Py bilayers, prepared by sputter-deposition on an amorphous 3nm Ta seed layer. FMR measurements are performed on varying thicknesses of the individual Py and Fe layers while keeping the total bilayer structure thickness fixed. When Fe is grown directly on Ta, there is large magnetic inhomogeneity and damping. However, when a Py layer is deposited between Fe and Ta, both the magnetic inhomogeneity and damping significantly decrease even if Fe is covered by Ta. The intrinsic damping of the Ta|Py|Fe film can be further lowered by increasing the Fe to Py ratio. SQUID measurements show a linear increase in saturation magnetization with increasing ratio of Fe to Py. A combination of in-plane and out-of-plane X-ray diffraction measurements show that Py is textured along the ⟨111⟩ directions and Fe is textured along the ⟨110⟩, with Fe texture significantly improving if it is deposited on Ta|Py instead of Ta. By improving the texture of Fe by introducing a thin Py layer between Fe and Ta, one can grow Fe thin films with zero in-plane anisotropy, tunable magnetic moment, and low magnetic damping, approaching that of the best single crystal Fe

Proizvodnja amorfnih traka gotovo stalnog stupnja amorfnosti

This paper describes a modified melt spinning method that provides for production of amorphous ribbons with a nearly constant short-range order. The ribbon structure can be controlled by relevant parameters, and if these parameters are constant, the ribbons produced have approximately the same degree of amorphousness. A detailed investigation proved that it was necessary to control accurately the melting temperature and the surface velocity of the drum on which the quenching is made. The system is computer controlled using specially adapted software. The particular phases during the process of amorphous ribbon production are turned on in accordance with the temperature of the melt. We made a comparative measurement of produced ribbons proving that ribbons produced with the same parameters have approximately the same degree of amorphousness.Opisujemo usavršenu metodu taljevine na rotirajućem valjku kojom se proizvode amorfne trake gotovo stalnog kratko-dosežnog uređenja. Struktura traka može se upravljati putem parametara, a ako su ti parametri stalni, proizvedene trake imaju jednake stupnjeve amorfnosti. Pažljiva ispitivanja su pokazala da je potrebno točno podesiti temperaturu taljevine i obodnu brzinu hlađenog valjka kojim se postiže brzo hlađenje. Uređajem upravlja računalo koje rabi posebno preuređen program. Pojedine faze proizvodnje se uključuju ovisno o temperaturi taljevine. Načinili smo usporedbena mjerenja s proizvedenim trakama uz jednake parametre koja pokazuju da postižemo stalne stupnjeve amorfnosti

On the origin of noncollinear magnetization coupling across RuX layers

We present a simple atomistic model for the description of noncollinear coupling in magnetic multilayers with hybrid spacer layers made of Ru alloyed to ferromagnetic atoms such as Fe. In contrast to previous analytical and micromagnetic models that explain the noncollinear coupling by means of lateral fluctuations in the coupling constant, the presented model accounts for atom-atom coupling in all three spatial dimensions within the spacer layer. The new model is able to accurately predict the dependence of the macroscopic bilinear and biquadratic coupling constants on the spacer-layer composition and thickness, showing much better quantitative agreement than lateral-fluctuation models. Moreover, it predicts noncollinear coupling even for infinitely stiff ferromagnetic layers which goes beyond the predictions of previous models