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Magnetne tekočine sodijo v kategorijo nanomaterialov zaradi velikostnega razreda suspendiranih magnetnih nanodelcev v nosilni tekočini. Njihova uporabnost se kaže na različnih področjih inženiringa, znanosti in medicine. Ena izmed pomembnejših lastnosti magnetne tekočine je viskoznost, ki je bila predmet opazovanja v magistrski nalogi. Vpliv viskoznosti smo preverili teoretično kot tudi eksperimentalno. V teoretičnem delu smo uporabili in prilagodili matematični model izračuna izgub magnetne tekočine v visokofrekvenčnem magnetnem polju ter raziskali vpliv različnih modelov viskoznosti suspenzije in različnih nosilnih tekočin. Za validacijo matematičnega modela izgub smo na izbranem vzorcu opravili serijo meritev izgub po kalorimetrični metodi, pri kateri se glede na temperaturni odziv merjenca ugotovi specifična stopnja absorpcije (SAR). V eksperimentalnem delu naloge smo opravili meritve viskoznosti možnih nosilnih tekočin po dveh različnih metodah, in sicer najprej s Hoepplerjevim in nato z rotacijskim viskozimetrom. V sklopu meritev z rotacijskim viskozimetrom smo sistematično skušali ugotoviti temperaturno odvisnost in dokazati pojav magnetoreologije. Magnetic fluids fall into a category of nanomaterials due to the size of magnetic nanoparticles suspended in the carrier fluid. They are used in various areas of engineering, science, and medicine. One of the most important properties of a magnetic fluid is its viscosity which was observed in this master thesis. Effects of viscosity on magnetic losses were tested both theoretically and experimentally. In the theoretical part, we used and adjusted a mathematical model for the calculation of magnetic fluid losses in a high-frequency magnetic field and studied the influence of different models of suspension viscosity and different carrier fluids. In order to validate the mathematical model, a series of measurements was performed on the sample, using the calorimetric method, which, based on the temperature response of the sample, determines the specific absorption rate (SAR). In the experimental part, we carried out viscosity measurements of different carrier fluids by two methods, first using a Hoeppler and then a rotational viscometer. As a part of the rotational viscometer measurements, we systematically tried to determine the temperature dependence and prove the phenomenon known as magnetoreology.

Namen magistrskega dela je raziskati odziv segrevanja magnetnih tekočin v spremenljivem magnetnem polju ter ugotoviti njegovo odvisnost od količine magnetnih delcev v magnetni tekočini. Meritve so izvedene s pomočjo kalorimetrične metode, ki bazira na merjenju temperaturnega odziva vzorca magnetne tekočine glede na jakost ter frekvenco magnetnega polja. V delu je okvirno predstavljeno teoretično ozadje magnetizma ter magnetnih materialov, izdelava magnetnih tekočin, načini karakteriziranja magnetnih izgub, ki se kažejo kot segrevanje materiala ter opis principov magnetne in kalorimetrične metode. V nadaljevanju je opisan eksperimentalni del ter oprema, s katero izvajamo meritve, delo pa se zaključi s prikazom in komentarjem rezultatov segrevanja pri različnih jakostih in frekvencah magnetnega polja, koncentracijah magnetnih delcev ter medsebojnih primerjav specifičnih absorpcijskih stopenj posameznih meritev v grafični ter tabelarni obliki. Amplitude in frekvence magnetnega polja so pri izvajanju eksperimentov izbrane tako, da delno omogočajo medsebojno primerjavo rezultatov različnih vzorcev magnetne tekočine. The purpose of the master’s thesis is to research a heating response of magnetic fluids in an alternating magnetic field and to determine its dependence on the amount of magnetic particles in the magnetic fluid. Measurements are performed by using calorimetric method, which is based on measuring the temperature response of the sample magnetic fluid according to the amplitude and frequency of magnetic field. The thesis presents an outline of the theoretical background of magnetism and magnetic materials, production of magnetic fluids, characterization of magnetic losses that are evident as heating of material and a description of the principles of magnetic and calorimetric methods. The following describes the experimental work and the equipment with which the measurements are performed. The thesis concludes with presentation and commentary of results of heating with different amplitudes and frequencies of magnetic field, concentrations of magnetic particles and the comparison of specific absorption rates of individual measurements in graphical and tabular form. The amplitudes and frequencies of magnetic field used in experiments are selected to partially allow the comparison of results from different samples of magnetic fluid.

Magnetne tekočine so tekočine, v katerih so enakomerno porazdeljeni zelo majhni nanodelci magnetnega materiala, ki so trajno suspendirani v nosilni tekočini. Zaradi svojih posebnih lastnosti jih danes uporabljamo na različnih področjih strojništva in biomedicine. V magistrskem delu je opisan postopek merjenja magnetnih izgub pri vzorcu magnetne tekočine. Meritve smo izvedli v laboratoriju po metodi magnetnega merjenja pri konstnatni ferkvenci in različnih temparaturah vzorca. Pri tej metodi s pomočjo dveh merilnih tuljavic izmerimo magnetno poljsko jakost, gostoto magnetnega pretoka in magnetno polarizacijo. S pomočjo teh signalov tvorimo histerezno zanko, katere površina določa izgube. Na podlagi dobljenih rezultatov so določene specifične moči izgub SPL (specific power loss). Rezultati so podani v grafični obliki in prikazujejo, da se z višanjem temparature vzorca izgube magnetne tekočine manjšajo. Magnetic fluids are fluids containing evenly distributed small nano-particles of the magnetic material, which are permanently suspended in the carrier fluid. Nowadays, we use them in fields of mechanical engineering and biomedical sciences, due to their special features. The thesis describes the proces of measuring the magnetic losses in a sample of the magnetic fluid. The measurements were performed in the laboratory using the magnetic measurement method at a constant frequency and different temparature of the sample. In this method, we measure magnetic field strenght, magnetic flux density and magnetic polarization with the help of two pickup coils. With the help of these signals, we form a hysteresis loop, the surface of which provides losses. Based on the results, we determine specific power losses SPL. The results are presented in a graphical form and show that by increasing temparature of the sample, losses of the magnetic fluid are decreasing.

V doktorskem delu smo obravnavali sintezo in karakterizacijo nanodelcev zlitin NiCu in NiCr za uporabo v samoregulativni magnetni hipertermiji. V prvem delu smo pripravili zlitine NiCu in NiCr s tremi različnimi sinteznimi postopki: mehansko mletje, sinteza s pomočjo mikroemulzij in sol-gel metoda, pri čemer smo preučevali reakcijske pogoje posamezne sinteze. Sledila je karakterizacija pridobljenih zlitin s pomočjo rentgenske praškovne difrakcije, transmisijske elektronske mikroskopije, magnetnih meritev, meritev Curiejeve temperature in kalorimetričnih meritev. S pomočjo mehanskega mletja smo uspeli sintetizirati zlitine NiCu in NiCr, z različnimi sestavami, v inertni atmosferi dušika. Kot rezultat smo dobili superparamagnetne nanodelce, njihova ocenjena velikost je okrog 14 nm za NiCu in 11 nm za NiCr. Pomerjene vrednosti Curiejevih temperatur rastejo z naraščanjem vsebnosti niklja. Vzorca sestave Ni72Cr28 in Ni72.5Cu27.5 imata Curiejevo temperaturo, ki je v območju od 42 °C do 46 °C, kar ustreza uporabi v magnetni hipertermiji. Pod vplivom zunanjega izmeničnega magnetnega polja se delci zelo dobro odzivajo. Dosežene stacionarne temperature so prav tako v območju uporabe v magnetni hipertermiji. S pomočjo transmisijske elektronske mikroskopije smo ugotovili, da je porazdelitev velikosti delcev široka, da so sintetizirani nanodelci sestavljeni iz večjih agregatov, da so nehomogeni, kar pripisujemo posledicam mehanskega mletja. S pomočjo mikroemulzijske metode smo sintetizirali nanodelce zlitin NiCr in NiCu, ti imajo ožjo porazdelitev velikosti, vendar pa so nehomogeni, saj so oksidacijski potenciali kovin različni in dobimo tako imenovano "core-shell" strukturo. Homogenizacija pri zlitinah NiCr ni bila uspešna, medtem ko smo zlitine NiCu uspeli ustrezno prevleči z 10 nm plastjo silike oziroma smo jih vgradili v matrici NaCl, da smo preprečili aglomeracijo med samo homogenizacijo. Homogenizacija pri zlitinah NiCu je bila uspešna, kar kaže Curiejeva temperatura. Specifična magnetizacija za oblečene delce je veliko manjša kot za neoblečene, kar je posledica diamagnetne prevleke SiO2, vendar pa lahko to prevleko poljubno tanjšamo oziroma odstranimo s pomočjo raztopine NaOH, prav tako lahko odstranimo tudi matrico NaCl. Vzorcem smo določili še specifično absorpcijsko hitrost (SAR), ki narašča z naraščajočim magnetnim poljem. Sol-gel metoda se je izkazala kot najuspešnejša za sintezo zlitin NiCu z različnimi sestavami, saj smo kot rezultat dobili okrogle monodisperzne nanodelce. Pripravili smo homogene zmesi kovinskih oksidov v SiO2 matrici s kalcinacijo prekurzorjev v gelu in naknadno homogenizacijo in redukcijo produkta v cevni peči v inertni atmosferi Ar/H2. Velikost delcev, ocenili smo jo s pomočjo Sherrerjeve formule, magnetnih meritev in s pomočjo transmisijske elektronske mikroskopije, je znašala okrog 16 nm. S pomočjo raztopine NaOH in hidrazina smo SiO2 uspešno izlužili. Curiejeve temperature vzorcev naraščajo z naraščajočo vsebnostjo niklja in so v okviru predvidenih temperatur za uporabo v magnetni hipertermiji. Tudi vrednosti magnetizacije in temperaturni odziv v kalorimetru rasteta z naraščajočo vsebnostjo niklja. The doctoral thesis considers the synthesis and characterization of NiCu and NiCr nanoparticles for the magnetic hyperthermia applications. The synthesis of nanoparticles of NiCu and NiCr alloys using three different methods: mechanical milling, microemulsion method and sol-gel method, were studied with respect to the reaction conditions. We characterized the alloys nanoparticles by XRD measurements, transmission electron microscopy, magnetic measurements, Curie temperature determination and calorimetric measurements. The NiCu and NiCr particles with the desired composition were synthesized by mechanical milling under an inert atmosphere of N2. We prepared superparamagnetic NiCu nanoparticles with an average size of around 14 nm and around 11 nm for NiCr. The measurements of the Curie temperature of various compositions showed that the Curie temperature increased with the increasing of the Ni content. The nanoparticles of Ni72.5Cu27.5 and Ni72Cr28 exhibit a Curie temperature in the range between 42 °C to 46 °C, what corresponds to the application demand in the magnetic hyperthermia. The magnetic particles also showed a significant heating effect and might be the good candidates for hyperthermia applications. Transmission electron microscopy of mechano-chemically synthesized particles showed a broad size distribution with the presence of some larger grains in the shape of platelets at some locations. NiCu and NiCr nanoalloys with a narrow size distribution were synthesized by microemulsion method. The Curie temperatures of samples were high, indicating a compositional heterogeneity and probably a “core-shell” structure. To prevent the agglomeration during the homogenization of the NiCu alloys, we coated particles with a 10 nm thick layer of silica or we performed thermally homogenization in a NaCl matrix. The relatively low magnetization of the silica coated NiCu particles was a result of the diamagnetic envelope of SiO2, which can be thinned and/or remowed with sodium hydroxide. In parallel the NaCl matrix can be removed with dissolution in water. The calculated specific absorption rate (SAR) increases with the increasing of the magnetic field. Nickel-copper (NiCu) alloy magnetic nanoparticles with a narrow size distribution were prepared by a sol-gel method. We used the temperature resistant silica matrix as a nanoparticles holder during high-temperature treatment of metal oxides and a specially developed etching procedure that subsequently removes silica matrix, leaving the alloy nanoparticles intact. We estimated the size of the particles around 16 nm, using the Sherrer equation, magnetic measurements and transmission electron microscopy. The Curie temperature, the magnetization and the temperature response in the calorimeter increase as well with the increase of the Ni content.

Magnetne tekočine sodijo v kategorijo nano-materialov in so po definiciji stabilne koloidne disperzije magnetnih nanodelcev, trajno suspendiranih v nosilni tekočini. Kot takšne imajo določene specifične lastnosti, ki jih s pridom izkoriščajo na različnih področjih, kot na primer v mehaniki za rotacijsko tesnjenje, mehansko blaženje, odvajanje toplote in tudi v biomedicini za ciljno doziranje zdravilnih učinkovin, kontrastni agenti pri slikanju z magnetno resonanco, hipertermiji, itd. Ne glede na aplikacijo pa je za varno in učinkovito rabo potrebno dobro poznavanje fizikalnih lastnosti materiala. V doktorski disertaciji smo obravnavali nekatere lastnosti magnetnih tekočin s poudarkom na obnašanju v izmeničnem magnetnem polju. V tem primeru se magnetni delci oziroma vektor magnetizacije delcev poravnajo s smerjo magnetnega polja, kar opisujeta pojava Brownove in Néelove relaksacije. Obračanje magnetnih domen znotraj materiala opisujemo kot magnetne izgube, katerih posledica je povišanje temperature tekočine. Z višanjem amplitude in frekvence magnetnega polja so izgube intenzivnejše. Ravno ta pojav, ki ga imenujemo hipertermija, se izkorišča v medicini in predstavlja alternativno metodo zdravljenja rakavih tkiv, kjer z vbrizganjem magnetne tekočine v tkivo in njeni izpostavitvi visokofrekvenčnemu magnetnemu polju dosežemo njihovo termično uničenje. Za uspešno izvajanje takšnega zdravljenja pa je bistvenega pomena karakterizacija magnetnih izgub magnetne tekočine. Glavni namen doktorske disertacije je izgradnja merilnega sistema, ki omogoča merjenje parametrov za določitev magnetnih izgub magnetih tekočin. Merilni sistem je zasnovan tako, da z uporabo kalorimetrične metode na osnovi povišane temperature tekočine določi parameter izgub SAR (specific absorption rate). V tem primeru gre za izboljšanje uveljavljene metode, kjer je poudarek na homogenosti magnetnega polja ter na boljši toplotni izolaciji vzorca in okolice. Druga metoda za določitev magnetnih izgub pa je metoda magnetnega merjenja, kjer lahko na osnovi površine histerezne zanke določimo specifične moči izgub SPL (specific power loss). Bistvo metode sta dve merilni tuljavici okoli merjenega vzorca, ki sta bili predhodno umerjeni v magnetni normali in merita inducirani napetosti, na osnovi katerih lahko izračunamo magnetno poljsko jakost v sistemu ter gostoto magnetnega pretoka vzorca. Ta dva signala definirata histerezno zanko, katere površina je proporcionalna magnetnim izgubam. Za komercialno dostopen vzorec magnetne tekočine je izvedena karakterizacija izgub po obeh metodah, kjer so izgube podane v odvisnosti od amplitude in frekvence magnetne poljske jakosti, določena pa je tudi njihova temperaturna odvisnost. V disertaciji je predstavljena tudi analiza magnetnega polja merilnega sistema s pomočjo metode končnih elementov (MKE), v istem sistemu pa je izvedena še termična analiza, kjer temperaturno odvisne izgube povzročijo časovno spremembo temperature vzorca, rezultati obeh analiz pa so skladni z meritvami. fluids fall into the category of nano-materials and are, by definition, a stable colloidal dispersion of magnetic nanoparticles permanently suspended in a carrier liquid. As such, they are distinguished by certain specific characteristics which are effectively utilized in various fields such as mechanics as rotary seals, mechanical dampers, heat conductors and in biomedicine to target the dosage of medicinal substances, contrast agents for magnetic resonance imaging, magnetic fluid hyperthermia, etc. For safe and effective use of the material a good knowledge of its physical properties is required, regardless of the applications. In this thesis, some properties of magnetic fluids with an emphasis on its behavior in the alternating magnetic field are discussed. In this case, the magnetic particles or its magnetization vector align with the direction of magnetic field, which describes the Brownian and Neel’s relaxation. Rotating magnetic domains, within the material, are recognized as magnetic losses that among others result in an increase of fluids’ temperature that intensify with increasing amplitude and frequency of magnetic field. This exact property is used in the application of medical hyperthermia, which represents an alternative method for cancer treatment, where the magnetic fluid is injected into the tumor tissue and heated by means of magnetic field to achieve thermal destruction of tumor. For successful implementation of such treatment the characterization of magnetic losses of magnetic fluids represents the essential role. The main purpose of this dissertation is to build a measurement system that enables the measurement of crucial parameters for determining the losses of magnetic fluid. The measurement system is designed in a way that allows the determination of loss parameter SAR (Specific Absorption Rate) using a calorimetric method. In this case, we deal with the improvement of established method, where the emphasis is on the homogeneity of the magnetic field and a better thermal insulation of the sample and its surroundings. Second method for determining the magnetic losses that is tackled in this dissertation is method of magnetic measurement. It is based on determination of the hysteresis loops area for determination of the parameter of SPL (specific power loss). The essential parts of this method are two pickup coils wound around the measured sample. They are calibrated in the magnetic normal and therefore enable the calculation of magnetic field strength in the system and the magnetic flux density of the measured sample out of measured induced voltages. These two variables define the hysteresis loop whose area is proportional to magnetic losses. Characterization of magnetic losses is carried out by both methods for commercially available sample of magnetic fluid, where the results are given as a function of amplitude and frequency magnetic field. This thesis also presents a magnetic field analysis of the measurement system using the finite element method (FEM) and thermal field analysis results of both analyses are consistent with measurements.