Uticaj inkluzija na fazne transformacije mrežnih alumosilikata
The influence of inclusions on phase transformations of framework aluminosilucates
Doktorand
Radulović, Aleksandra M.Mentor
Dondur, VeraČlanovi komisije
Damjanović, LjiljanaĆirić-Marjanović, Gordana
Vulić, Predrag
Metapodaci
Prikaz svih podataka o disertacijiSažetak
Iako termalno indukovane transformacije mrežnih alumosilikata daju jedinstven metod
za formiranje novih faza sa poboljšanim osobinama, zbog kompleksnosti samog procesa,
mehanizam konverzije još uvek nije u potpunosti razjašnjen. Usled male jedinične ćelije
(Na12Si12Al12O4827H2O) i dobro proučene mrežne strukture i raspodele van-mrežnih
katjona, zeolit Na-LTA predstavlja model supstancu za ispitivanje promena u uređenju na
kratkom, srednjem i dugom dometu u procesu termalnih transformacija zeolita u popunjene
derivate SiO2 polimorfa. Iako su još prva istraživanja pokazala da svaki sintetisan Na-LTA
zeolit nije čist u kristalografskom smislu i u zavisnosti od uslova sinteze sadrži različite
količine Na, Al i Si inkluzija unutar i kaveza, u literaturi ne postoje podaci o
katalitičkom uticaju ovih vrsta na mehanizam termalne konverzije Na-LTA zeolita.
Prezentovana teza sumira rezultate istraživanja uticaja Na, Al i Si inkluzija na mehanizam
termalno indukovanih transformacij...a Na-LTA zeolita u karnegitske i nefelinske polimorfe.
U prvom delu teze opisan je potupak sinteze Na-LTA zeolita sa različitim sadržajem
Na, Al i Si inkluzija. Ispitan je uticaj variranja Na2O : Al2O3 : SiO2 odnosa u polaznoj
reakcionoj smeši na stehiometriju sintetisanih Na-LTA zeolita i morfologiju kristalnih zrna.
Kao postupak uklanjanja inkluzija zaostalih u Na-LTA zeolitima nakon sinteze, predložen
je tretman refluksovanja Na-LTA zeolita na 100 ºC, koji ne izaziva amorfizaciju i dodatne
strukturne promene u Na-LTA zeolitima.
Drugi deo teze fokusiran je na ispitivanje uticaja Na, Al i Si inkluzija na termalnu
stabilnost Na-LTA zeolita i njegovu konverziju u karnegitske i nefelinske polimorfe.
Posebna pažnja je posvećena ispitivanju mehanizma fazne transformacije Na-LTA zeolita u
nisko-temperaturni karnegit koji je u literaturi prezentovan dvema različitim šemama: kao
direktna topotaktička transformacija Na-LTA → nisko-temperaturni karnegit i kao
dvostepeni mehanizam Na-LTA → Amorfna faza → nisko-temperaturni karnegit.
Metodama XRPD, DTA i IR spektroskopije je utvrđeno da Na i Al inkluzije podstiču fazni
prelaz Na-LTA zeolita u nisko-temperaturni karnegit uz nemogućnost detekcije kolapsa
LTA mreže u amorfnu strukturu, izazivajući brzo raskidanje i formiranje novih veza, pri
čemu brzina termalne transformacije raste sa povećanjem sadržaja Al. Sa druge strane, u
slučaju faznog prelaza refluksom tretiranih Na-LTA zeolita idealne stehiometrije u niskotemperaturni
karnegit, utvrđen je kolaps LTA mreže u stabilnu amorfnu strukturu iz koje je
zatim kristalisala faza nisko-temperaturnog karnegita. Karakterizacijom amorfne NaAlSiO4
faze infracrvenom i ramanskom spektroskopijom, utvrđeno je prisustvo četvoročlanih i
šestočlanih tetraedarskih prstenova čime je zaključeno da su kolapsom zeolita u amorfnu
fazu zadržani fragmenti LTA mreže, što može biti polazna osnova u sintezi „perfektnih“
stakala.
Na višim temperaturama, ispitani su uslovi formiranja nefelinskih struktura,
rekonstruktivnom faznom transformacijom nisko-temperaturnog karnegita, što je usled
velikog broja nefelinskih polimorfa različite simetrije, veoma aktuelna problematika.
Rezultati ispitivanja su pokazali da Na, Al i Si inkluzije u Na-LTA zeolitu uslovljavaju
transformaciju nisko-temperaturnog karnegita u smešu monokliničnog trinefelina i
osnovnog heksagonalnog nefelina, dok se u procesu termalno indukovanih transformacija
refluksom tretiranih zeolita idealne LTA stehiometrije, formira faza čistog osnovnog
heksagonalnog nefelina. Takođe, ispitani su uslovi termalne konverzije monokliničnog
trinefelina u osnovni heksagonalni nefelin.
U prisustvu Na i Si inkluzija sintetisana je intermedijerna faza nefelinskog
(„ABABAB...“) strukturnog tipa koja nije mogla biti identifikovana na osnovu poznatih
nefelinskih struktura. Razlike u uređenju na kratkom i srednjem dometu visokotemperaturnih
NaAlSiO4 polimorfa dobijenih termalnom konverzijom Na-LTA zeolita
različite stehiometrije, pripisane su uticaju Na, Al i Si inkluzija u kavezima zeolita.
Ovim istraživanjem predloženo je da Na-LTA zeolit predstavlja primer mnogo šireg
problema uticaja nestehiometrije na tok i mehanizam termalno indukovanih transformacija
zeolita, kao i da se isti zaključci mogu primeniti i na druge tipove zeolita koji sadrže
različite van-mrežne katjone.
Although thermally induced transformations of framework aluminosilicates provide
unique method for synthesis of materials with advanced properties, conversion mechanism
is not explained yet because of the complexity of the process. Because of the small unit cell
(Na12Si12Al12O4827H2O) and well known framework structure and extra-framework cation
distribution, zeolite Na-LTA represents ideal model for investigation of changes in the
short, middle and long range order, in the processes of zeolite thermal transformation into
stuffed derivatives of SiO2 polymorphs. Even though investigations showed that Na-LTA
zeolite is not pure from crystallographic point of view and, depending on synthesis
procedure, contains different amounts of Na, Al and Si inclusions inside α and β cages,
there are no data regarding catalytic influence of these species on the mechanism of thermal
conversions. Presented thesis surmises results of investigations of the influence of Na, Al
and Si inclusion s...pecies on the mechanism of Na-LTA thermally induced transformations
into carnegieite and nepheline polymorphs.
The first chapter of thesis deals with Na-LTA synthesis procedure with different
amounts of Na, Al and Si inclusions. The influence of small variations of Na2O:Al2O3:SiO2
ratio in initial reaction mixture on stoichiometry of synthesized Na-LTA zeolites and
crystal grain morphology is described. Refluxing treatment at 100 ºC is suggested as
method for removing extra-framework species remained after synthesis process, which
does not induce amorphization or other structural changes of zeolite.
The second chapter of the thesis is focused on the investigation of the influence of Na,
Al and Si inclusions on zeolite Na-LTA thermal stability and conversion into carnegieite
and nepheline polymorphs. Special attention is dedicated to the investigation of the
mechanism of zeolite Na-LTA transformation into low-temperature carnegieite, which is
presented with different conversion routes in the literature. In one aspect Na-LTA zeolite
transforms directly into low-temperature carnegieite: Na-LTA → low-temperature
carnegieite, while in the other, unfolds through amorphous phase: Na-
LTA →Amorphous phase → low-temperature carnegieite.
XRPD, DTA and IR investigations showed that Na, Al and Si inclusions catalyze
zeolite Na-LTA transformation into low-temperature carnegieite, without the possibility of
detection of amorphous phase, inducing rapid breaking and formations of bonds, whereby
the rate of transformation increases with increasing Al content. On the other hand, in the
case of reflux treated Na-LTA zeolite with ideal stoichiometry, thermal transformation into
low-temperature carnegieite is preceded by collapse of LTA framework and formation of
stable amorphous phase, which subsequently crystallized into low-temperature carnegieite.
Characterization of amorphous NaAlSiO4 phase by IR and Raman spectroscopy showed the
presence of four- and six-membered tetrahedral rings, which lead to conclusion that by the
collapse of zeolite into amorphous phase, relicts of LTA frameworka are retained. This can
can be used as a starting point in synthesis of perfect glasses.
On higher temperatures, formation conditions of nepheline structures by reconstructive
phase transformations of low-temperature carnegieite were investigated. Because of the
various nepheline polymorphs with diverse symmetry, formation conditions of different
nepheline structures are current problem in mineralogy. Investigation showed that Na, Al
and Si inclusion species in Na-LTA zeolite, induce transformation of low-temperature
carnegieite into mixture of monoclinic trinepheline and basic hexagonal nepheline, while in
the process of thermally induced transformation of reflux treated samples with ideal
stoichiometry, pure basic hexagonal nepheline was formed. Also, conditions of thermal
conversion of monoclinic trinepheline into basic hexagonal nepheline were investigated.
Intermediate phase of nepheline (“ABABAB…”) structure type, which could not be
identified according to known nepheline phases, was synthesized in the presence of Na and
Si inclusion species. Differences in the short and middle range order between hightemperature
NaAlSiO4 polymorphs, formed by thermal conversion of Na-LTA with
different stoichiometry, were ascribed to the influence of Na, Al and Si inclusions in zeolite
cages.By this investigation we propose that Na-LTA is the example of much wider problem
of non-stoichiometry influencing the course of zeolite thermal transformation route and can
be extended to other zeolite types containing various extra-framework cations.
Fakultet:
Универзитет у Београду, Факултет за физичку хемијуDatum odbrane:
24-06-2013Projekti:
- Porozni materijali na bazi oksida u zaštiti životne sredine od genotoksičnih supstanci (RS-MESTD-Basic Research (BR or ON)-172018)