Tubular microstructures by Hf-, Zr- and Ti-butoxide gel sheet rolling
Date
2011-06-04
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Abstract
Õhukeste kilede rullumine mikro- ja nanotorudeks on kümne aasta vanune aktuaalne valdkond materjaliteaduses. Selle materjali vormimise ideoloogia ellurakendamiseks on seni kasutatud kõrgvaakumis läbiviidavaid materjali sadestamise ja vormimise meetodeid. Valmistatud struktuurid on potentsiaalselt kasutatavad mikrokanalite, optiliste resonaatorite, mikrosensorite või biomaterjalidena.
Käesolev väitekiri käsitleb uudset ja originaalset sool-geel meetodit metalloksiidsete mikrorullide valmistamiseks metalli alkoksiididest saadavate geel-kilede rullumise teel. Meetod põhineb geelkile iseeneslikul jagunemisel segmentideks selle pragunemise tulemusena ja moodustunud materjali mehaanilistest pingetest tingitud spontaansel rullumisel. Tavapäraselt peetakse selliseid protsesse sool-geel meetodite puhul soovimatuteks.
Käesolevas töös uuriti geelkile pragunemise protsesse, mis määravad rulluva kilesegmendi mõõtmed ning hinnati lähteine koostise ning geelistumisreaktsioonide kestvuse mõju rullumise teel saadavate struktuuride mõõtmetele.
Meetod kohandati ka titaan- ja hafnium(IV)butoksiidist torujate mikrostruktuuride valmistamiseks, ühtlasi näidati et geelstruktuure on võimalik kuumutada oksiidmaterjali saamiseks ilma, et mikrostruktuurid laguneks. Tsirkooniumoksiidi puhul täheldati struktuuride lagunemist tetragonaalse ja monokliinse faasi vahelise siirde tõttu kuumutamisel 700 ºC kraadini. Ühtlasi näidati, et materjali lagunemist kuumutamisel on võimalik vältida üttriumi lisamise teel materjali koostisesse.
Geelkile pragunemiskatsete tulemuste põhjal konstrueeriti plokk-vedru mudel, mis võimaldab eksperimendis nähtavate pragunemismustrite suhteliselt hea kokkulangevusega simuleerimist.
Uudse kujuga metalloksiidse materjali võimalike rakendustena nähakse muu-hulgas optilisi resonaatoreid, elongeeritult vabastavaid materjale, mikrokonteinereid, katalüsaatoreid ja biomaterjale.
Micro- and nanotubes by self-rolling of films is an exciting emerging field in materials science. This ideology of material forming was introduced a decade ago and has been since adapted to the preparation of nano- and microrolls from different materials by vacuum deposition and lithography methods with potential applications as microfluidic channels, optical resonators, microsensors or biomaterials. Present thesis is an overview of our studies on the formation of metal oxide microtubes by original metal alkoxide gel nanofilm rolling that opposes to previously reported approaches mainly by being simpler in its nature as no sophisticated material processing methods are required. The method is based on spontaneous gel cracking and rolling due to mechanical stress, phenomena that are conventionally considered as unwanted in sol-gel processes. Phenomenologic studies were conducted on gel film cracking that defines the dimensions of rolled film segments. Influence of precursor composition and precursor reacting time with humid air on the diameter of obtained roll structures and thickness of gel film was also estimated. The preparation method was also adapted to titanium(IV)butoxide and hafnium(IV)butoxide as starting compounds and the gel structures were successfully heat treated to achieve metal oxide composition. Roll shape was preserved despite shrinkage that is typical to sol-gel materials. Although the roll shape of structures prepared from zirconium(IV)butoxide did not withstand annealing at 700 ºC causing a transition from tetragonal to monoclinic phase they were found to be excellent hosts to Sm3+ ions in photoluminescence studies. As a successful solution to the problem of material fracture during heat treatment, yttria-doped zirconia microrolls were also prepared. Based on crack formation observation results, a discrete element method model was developed for cracking simulations. Relatively good concurrency with experimental data was achieved. Proposed applications of microtubular metal oxide structures include optical resonators, controlled release, microcontainers, catalysis and biomaterials.
Micro- and nanotubes by self-rolling of films is an exciting emerging field in materials science. This ideology of material forming was introduced a decade ago and has been since adapted to the preparation of nano- and microrolls from different materials by vacuum deposition and lithography methods with potential applications as microfluidic channels, optical resonators, microsensors or biomaterials. Present thesis is an overview of our studies on the formation of metal oxide microtubes by original metal alkoxide gel nanofilm rolling that opposes to previously reported approaches mainly by being simpler in its nature as no sophisticated material processing methods are required. The method is based on spontaneous gel cracking and rolling due to mechanical stress, phenomena that are conventionally considered as unwanted in sol-gel processes. Phenomenologic studies were conducted on gel film cracking that defines the dimensions of rolled film segments. Influence of precursor composition and precursor reacting time with humid air on the diameter of obtained roll structures and thickness of gel film was also estimated. The preparation method was also adapted to titanium(IV)butoxide and hafnium(IV)butoxide as starting compounds and the gel structures were successfully heat treated to achieve metal oxide composition. Roll shape was preserved despite shrinkage that is typical to sol-gel materials. Although the roll shape of structures prepared from zirconium(IV)butoxide did not withstand annealing at 700 ºC causing a transition from tetragonal to monoclinic phase they were found to be excellent hosts to Sm3+ ions in photoluminescence studies. As a successful solution to the problem of material fracture during heat treatment, yttria-doped zirconia microrolls were also prepared. Based on crack formation observation results, a discrete element method model was developed for cracking simulations. Relatively good concurrency with experimental data was achieved. Proposed applications of microtubular metal oxide structures include optical resonators, controlled release, microcontainers, catalysis and biomaterials.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
materjaliteadus, dissertatsioonid, õhukesed kiled, metalloksiidid, mikrostruktuur, sool-geel protsessid, materials science, thin films, metal oxides, microstructure, sol-gel processes