<p><strong>Apstrakt je obrađen tehnologijama za optičko prepoznavanje teksta (OCR).</strong></p><p>Mehanizam nastanka mulita zavisi od načina doziranja polaznih oblika reaktanata kao što su alumina i silika. Dobijanje mulita sol-gel postupkom je u velikoj meri poboljšano u odnosu na klasično procesiranje zbog mogućnosti homogenog mešanja AI<sub>2</sub>O<sub>3</sub> i SiO<sub>2</sub> komponenti i kontrole dodataka. Sol-gel metod omogućuje pripremu vrlo homogenih i reaktivnih gelova koji mogu da sinteruju na nižim temperaturama pri čemu se može postići vrlo fina mikrostruktura. U ovom radu koji se odnosio na procesiranje mulita sol-gel postupkom, hipoteza je bila da se na samom početku procesiranja aluminijumovi joni iz alkoholnog rastvora Al-soli uključuju u polimernu gel strukturu koju formira silika. Svrha ovog rada, je proučavanje uticaja procesnih promenjivih, dodatka fluornog jona i “seedinga” na temperaturu nastanka sol-gel mulita pri čemu se očekuje što je moguće niža tempertura nastanka mulita (niža od 980<sup>0</sup>C). Polimerni sol je dobijen u prvom slučaju mešanjem TEOS-a i aluminijum nitrata nanohidrata koji je prethodno rastvoren u etil alkoholu. U drugom slučaju, u polimerni sol je dodavan fluorni jon u koncentraciji 2 do 5 % mas. u odnosu na očekivani prinos mulita i u trećem slučaju je dodavana različita količina mulitnih klica (2-4 % mas.). Eksperimantalno je potvrđeno da procesne promenljive; pH, temperatura geliranja i R odnos imaju, veliki uticaj na brzinu geliranja i na nastanak mulita. U slučaju dodavanja fluornog jona, potvrdena je hipoteza da fluorni jona na različite načine utiče na mehanizam nastanka mulita, pri čemu u prvom slučaju prisustvo fluornog jona obezbeduje mesta u oblastima razdvajanja granica faza nakon geliranja koja utiču na proces nukleacije. Ova mesta slično procesu kristalizacije stakla, omogućuju lakšu nukleaciju mulita prilikom njegove transformacije iz gela. Mesta na granici razdvanja faza postaju mesta na kojima se uspostavlja proces heterogene nukleacije što je jedan od mogućih načina za snižavanje temperature nastanka mulita. Pored ovoga, dodavanje fluornog jona je doprinelo promeni mulitnih gel struktura, pri čemu je promena brzine hidrolize silike imala za posledicu promenu sadržaja vezane vode u toku geliranja što se takođe značajno odražavalo na temperaturu nastanka mulita. Eksperimentalni rezultati termički obradenih gelova su pokazali, da dodavanje lluornog jona u polimerni mulitni sol stvara uslove za snižavanje temperature obrazovanja mulita sve do 890<sup>0</sup>C. U ovom radu je takođe pokazano da mulitne čestice, kao nukleanti pri “seeding" procesiranju, doprinose nastanku mulitnog gela koji nakon termičke obrade na 1000<sup>0</sup>C pokazuje veoma finu mikrostrukturu.</p> / <p><strong>Abstract was processed by technology for Optical character recognition (OCR).</strong></p><p>The mechanism of mullite formation depends upon the method of combining the alumina and silica containing reactants. Mullite can be obtained through the sol-gel process and can be greatly improved by the control of some reaction conditions particulaiiy by homogeneous mixing of Al2O3 and SiO2, and controlling of the additions. Sol-gel method allow preparation of very homogenous and reactive gels which can be sintering at low temperature and consequently submicronic microstructure can be reached. In this study of the mullite formation by sol-gel method, the hypothesis was that aluminium ions from alcoholic solulion of its salts incorporate to polymeric silica gel structure. The aim of this work was the investigation of the effect processing variables, fluorine addition and “seeding”on the temperature of sol-gel mullite formation and to obtain as lower temperature of mullite formation as possible (smaller than 980°C). Polymeric sols, were prepared by the mixing of TEOS and aluminum nitrate nanohydrate dissolved in absolute ethyl alcohol and by adding fluorine ions in the second case from 2 wt.% to 5 wt.% and by different content of mullite seeded (2- 4 wt. %). Experimentally is determined that the processing variables as pH, gelling temperature and R ratio have high influence on the gelling rate and mullite formation. The hypothesis in the case of fluorine addition was that addition of fluorine ions could have different effects on the mechanism of mullite formation; the first it makes the sites at boundary of phase separation regions after gelling which influence at the process of the nucleation. These sites will act as a place for easy mullite nucleation, similar to process of the glass crystallization. The boundaries of the phase separation are the sites for heterogeneous nucleation which is one of the condition for lowering the temperature of mullite formation. Besides, fluorine addition could change the mullite gel structure (by changing the rate of hydrolyses of silica and it could change the content of bonded water during gelling), which should be very important for the temperature of mullite formation, too. The experimental results of heat treated gels showed that the addition of fluorine ion does decrease the temperature of mullite formation (in respect to classical sol-gel mullite processing) up to 8900C. As a nucleant in this study the mullite powder by “seeding” process contribute to muillite gel formation that after heat treatment up to 10000C showed very fine microstructure.</p>
| Identifer | oai:union.ndltd.org:uns.ac.rs/oai:CRISUNS:(BISIS)71471 |
| Date | 12 September 2003 |
| Creators | Simendić Borislav |
| Contributors | Radonjić Ljiljana, Ranogajec Jonjaua, Gal Ferenc |
| Publisher | Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, University of Novi Sad, Faculty of Technology at Novi Sad |
| Source Sets | University of Novi Sad |
| Language | Serbian |
| Detected Language | English |
| Type | PhD thesis |
Page generated in 0.0159 seconds