Crystallization and sinterability of lanthanum-strontium-borate-glass powders

Abstract

The subject of this doctoral thesis is the study of the crystallization behavior and the sinterability of the borate glasses system La2O3-B2O3-SrO. In literature there are limited data from the crystallization characteristics and sinterability of these glasses. Preliminary goal of this study was to investigate 4 different composition of the system, in which the content lanthanum of was increased at the expense of the strontium, while the boron content remained unchanged: 5,7La2O3·22,9SrO·71,4B2O3; 9,5La2O3·19,1SrO·71,4B2O3; 14,3La2O3·14,3SrO·71,4B2O3 and 19,1La2O3·9,5SrO·71,4B2O3. Physical and the structural properties as well as the crystallization characteristics and sinterability of glasses were investigated. Crystallization behavior was studied by the differentially thermal analysis (DTA), X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM), while the sinterability by the hot stage microscopy (HSM) and DTA. For the identification of the crystalline phases after thermal treatment (after the crystallization) XRD was used. Mechanism of the crystallization and the resulting phase microstructure were observed by SEM. The results of the preliminary investigations revealed that the glass 14,3La2O3·14,3SrO·71,4B2O3 shows the specific crystallization and sinterabilty characteristics. Based on XRD, TEM and SEM results the surface crystallization mechanisam was detected, where the obtained crystalline phase was of the same composition as the initial glass (polymorphic crystallization). In the literature there are no data for this crystalline phase, so XRD and TEM were used for the determination of the unit cell parameters. In order to obtain the best possible sintering results, the glass powder of extremely small particles (nanoparticles) was prepared. The sintering process was followed by the DTA, HSM and the contactless optical dilatometer. The effects of the sintering temperature, as well as the heating rate up to sintering temperatures, on the sintering efficiency were investigated. The quality of sintering, densification of the samples, was evaluated by the measuring the porosity of samples after the thermal treatment. XRD was used to determine the composition of the phase resulting from sintering. The sintered samples were analysed by SEM, equipped with secondary electron (SE) and backscattered electron detectors (BSE), to gain insight in the porosity and the microstructure of the obtained glass-ceramic...

Predmet ove doktorske disertacije je ispitvanje kristalizacionog ponašanja i sinterabilnosti boratnih stakala iz sistema La2O3-SrO-B2O3, o čemu postoji ograničen broj podataka u literaturi. Preliminarna ispitivanja su obuhvatala dobijanje 4 različita sastava ovog sistema, tako što se sadržaj lantana povećavao na račun stroncijuma, dok je sadržaj bora bio konstantan: 5,7La2O3·22,9SrO·71,4B2O3; 9,5La2O3·19,1SrO·71,4B2O3; 14,3La2O3·14,3SrO·71,4B2O3 i 19,1La2O3·9,5SrO·71,4B2O3. Isptivana su fizička i strukturna svojstva kao i kristalizacione karakteristike i sinterabilnost. Kristalizaciono ponašanje stakala praćeno je diferencijalnom termijskom analizom (DTA), rendgenskom difrakcijom praha (XRD), transmisionim i skenirajućim elektronskim mikroskopima (TEM i SEM), dok je sinterabilnost prahova praćena primenom termomikroskopa (TM) i DTA. Rendgenskom difrakcijom praha identifikovane su faze nastale tokom toplotne obrade, odnosno nakon kristalizacije, dok je mehanizam kristalizacije, kao i mikrostruktura stakla nakon toplotne obrade ispitivana SEM-om. Rezultati početnih ispitivanja ukazali su da staklo 14,3La2O3·14,3SrO·71,4B2O3 pokazuje niz specifičnosti u pogledu kristalizacionih karakteristika, kao i sinterabilnosti. Na osnovu rezultata XRD, TEM i SEM analize utvrđen je površinski mehanizam rasta kristalne faze koja je istog sastava kao i staklo (polimorfna kristalizacija). Za ovu fazu u literaturi ne postoje podaci, tako da su na osnovu TEM i XRD analize dobijeni podaci za jediničnu ćeliju. U cilju dobijanja što boljih rezultata sinterovanja pripremljen je prah stakla izuzetno malih veličina čestica. Proces sinterovanja, odnosno, sinter-kristalizacije praćen je korišćenjem DTA, TM i optičkog dilatometra. Ispitivan je uticaj temperature sinterovanja, kao i brzine zagrevanja do izabrane temperature sinterovanja na efikasnost sinterovanja. Stepen denzifikacije, uzoraka je određen merenjem poroznosti nakon toplotne obrade. Za identifikaciju faza koje su nastale u sinterovanim uzorcima korišćena je XRD tehnika. Sinterovani uzorci su analizirani skenirajućim elektronskim mikroskopom, primenom detektora sekundarnih elektrona, SE, i povratno rasejanih elektrona, BSE, da bi se stekao uvid u poroznost i u mikrostrukturu nastale staklo-keramike...