Magnetna i električna svojstva keramičkih kompozitnih materijala na bazi nikl-cink-ferita i barijum-titanata dobijenih postupkom auto-sagorevanja

Abstract

U ovoj doktorskoj disertaciji ispitivana su magneto-električna svojstva kompozitnih materijala koji se sastoje od magnetne faze, nikl-cink ferita, i feroelektrične faze, barijum titanata u razlicitim masenim odnosima. Maseni odnosi ovih faza su menjani u cilju dobijanja kompozitnog materijala dobrih magnetnih i električnih svojstava. Prahovi čistih polaznih materijala, nikl ferita i barijum titanata sintetisani su hemijskom metodom auto–sagorevanja. Ova metoda predstavlja važnu tehniku za sintezu kompozita, legura, katalizatora, itd. Danas metoda auto-sagorevanja čini veoma popularan pristup za pripremu nanomaterijala koji su našli industrijsku primenu u mnogim zemljama. Prahovi nikl ferita i nikl cink ferita su dobijeni kalcinacijom prekursora na temperaturi od 1000 °C tokom 1h dok je kalcinacija barijum titanata vršena na od 900 °C tokom 2h. Prahovi kompozita dobijeni su homogenizacijom prahova nikl ferita, nikl cink ferita sa prahom barijum titanata u izopropanolu kao medijumu za mlevenje i u planetarnom mlinu u trajanju od 24 h. Dobijeni prahovi su presovani i sinterovani na različitim temperaturama. Izvršena je optimizacija procesa sinterovanja kojom su određene temperature sinterovanja svakog kompozita pojedinačno u intervalu od 1120-1200 °C u cilju dobijanja najveće gustine keramičkih uzoraka. Karakterizacija dobijenih keramičkih kompozita vršena je različitim fizičko hemijskim metodama analize. Metodom rendgenske difrakcije praćen je fazni sastav dobijenih prahova i keramike i na osnovu XRD dijagrama određene su optimalne temperature sinterovanja. Morfologije čestica praha čistog nikl cink ferita i barijum titanata određene su na osnovu analize mikrofotografija dobijenih skenirajućom elektronskom mikroskopijom. Analizom je utvrđeno da se prah nikl cink ferita sastoji od individualnih čestica sfernog oblika, koje su malih veličina (< 200 nm). Čestice praha barijum titanata su veličine oko 100 nm, a njihov oblik čestica je takođe sferan. Analizom SEM mikrografija keramike čistog nikl cink ferita utvrđeno je da gustina uzoraka raste sa povećanjem koncentracije cinka što dovodi do rasta zrna i povećavanja stepena zgušnjavanja materijala Prosečne veličine zrna se kreću između 0.8 i 1 μm gde sa povećanjem udela cinka dolazi do povećanja srednje veličine zrna. Iz SEM slika za dobijene kompozite može se uočiti da postoje dva tipa zrna u ovom kompozitu, poligonalna nikl cink ferita i sferna barijum titanata, dok BSE mikrografije pokazuju homogenu faznu raspodelu u dobijenim kompozitima...

In this doctoral dissertation magneto-electric properties of composite materials consisting of magnetic nickel zinc ferrite phase and ferroelectric barium titanate phase in different mass ratios were investigated. Mass ratios of these phases were differed in order to obtain composite materials with optimal magnetic and electrical properties. Powders of pure starting materials, nickel zinc ferrite and barium titanate were synthesized by the chemical auto-combustion method. This is important technique for the synthesis of composites, alloys, catalyst, etc. In the present time the auto-combustion method is becoming rather popular method for the preparation of nano materials with industrial application in many countries. Powders of nickel ferrite and nickel zinc ferrite were obtained by the calcination of precursors at the temperatures of 1000 °C with duration of 1h, while the calcination of barium titanate was conducted at 900 °C for 24h. Powders of composites were obtained by homogenization of nickel ferrite and nickel zinc ferrite powders with the powder of barium titanate in isopropanol as the milling medium and in the planetary ball mill for 24h. The obtained powders were then pressed and sintered at different temperatures. The sintering process was optimized and the particular sintering temperatures of each composite within the temperature interval of 1120-1200 °C were determined in order to obtain ceramic samples with high density. The characterization of the obtained ceramic composites was performed by different physical-chemical analytical methods. The X-ray diffraction method was used for monitoring the phase composition of obtained powders and ceramics and based on XRD patterns the optimal sintering temperatures were determined. The morphologie of the powders of pure nickel zinc ferrite and barium titanate powders were analyzed based on the analyses of the images obtained by scanning electron microscopy. It was determined that the powder of nickel zinc ferrite is consisted of the individual spherical particles, small in size (<200 nm). The size of the particles of barium titanate powders was approximately 100 nm in size and with spherical shape. The analysis of SEM images of pure nickel zinc ferrite ceramics showed that the sample densities increases with the increase of the zinc concentration, leading to the grain growth and good densification of materials...