Karakterizacija metamiktnih minerala kompleksnih kristalokemijskih svojstava primjer allanita

doctoral thesis

• Title (english): Characterization of metamict minerals with complex crystal-chemical properties - allanite example
• Author: Andrea Čobić; MBZ: 318345
• Mentor: Vladimir Bermanec (mentor)
• Committee member: Nenad Tomašić (predsjednik povjerenstva)
• Committee member: Goran Kniewald (član povjerenstva)
• Committee member: Andreja Gajović (član povjerenstva)
• Committee member: Darko Tibljaš (član povjerenstva)
• Committee member: Stanko Popović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Geology); Zagreb
• Defense date and country: 2015-05-22, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Geology; Mineralogy and Petrology
• Universal decimal classification (UDC): 55 - Geology. Meteorology. Hydrology ; 54 - Chemistry. Crystallography. Mineralogy

Abstract

Rekristalizacija uzoraka allanita različitog stupnja metamiktnosti je inducirana žarenjem uzoraka na zraku, te u uvjetima inertne i reduktivne atmosfere na odabranim temperaturama. Do 800C metamiktni uzorci allanita djelomično rekristaliziraju u kristalnu strukturu allanita, no kod jače metamiktnih uzoraka već na ovoj temperaturi dolazi do pojavljivanja novih faza, cerijanita i hematita. Zbog oksidacije Fe2+ i Ce3+, te posljedično otpuštanja OHaniona, u danim uvjetima, nemoguće je ostvariti potpunu rekristalizaciju, a na višim temperaturama (> 900C) kristalna struktura allanita se u potpunosti raspada na jednostavnije okside (cerijanit, hematit), fosfate (britholit) i silikate (anortit). Iz tog razloga su odabrani uzorci hidrotermalno tretirani na nižim (150 -250C), te višim (400-800C) temperaturama na kojima dolazi do potpune rekristalizacije metamiknih uzoraka allanita, neovisno o stupnju metamiktnosti, bez pojave dodatnih faza. Jedan uzorak allanita je podvrgnut bombardiranju neutronima radi rušenja kristalne strukture, što je djelomično uspješno izvršeno. Svi procesi su praćeni difrakcijom rentgenskih zraka na prahu, visokorazlučujućom transimisijskom elektronskom mikroskopijom, te elektronskom difrakcijom, IR, Raman i Mössbauer spektroskopijom te termičkim metodama.

Abstract (english)

Recrystallization of allanite with different degrees of metamictization is induced by annealing of samples in air, inert and reductive atmosphere at chosen temperatures. Up to 800C metamict samples of allanite partially recrystallize to allanite crystal structure, but with heavily metamictized samples, already at these temperatures, new phases such as cerianite and hematite, occur. It is impossible to accomplish complete recrystallization in these conditions due to oxidation of Fe2+ and Ce3+, and escape of OHanion from the structure, and at higher temperatures (> 900C), allanite crystal structure breaks down to a mixture of simple oxides (cerianite an hematite), phosphate (britholite) and silicate (anorthite). Thus, chosen samples were hydrothermally treated at lower (150 -250C), and higher (400-800C) temperatures when complete recrystallization, without additional phases and regardless of the degree of metamictization, occurs. One allanite sample was bombarded with neutron flux, in order to destroy its crystal structure, what was partially accomplished. All processes were monitored by X-ray powder diffraction, high-resolution transmission electron microscopy coupled with electron diffraction, IR, Raman and Mössbauer spectroscopy, and thermal methods.

• Keywords: allanit; kompleksna kristalokemijska svojstva; metamiktizacija; rekristalizacija
• Keywords (english): allanite; complex crystal-chemical properties; metamictization; recrystallization
• Language: croatian
• URN:NBN: urn:nbn:hr:217:876230
• Study programme: Title: Doctoral study of Geology; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje geologija (doktor/doktorica znanosti, područje prirodnih znanosti, polje geologija)
• Type of resource: Text
• Extent: 193 (+XLVII) str. ; 35 cm
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-02-16 12:34:43