Kristalizaciono ponašanje višekomponentnih germanatnih stakala

Abstract

Predmet ove doktorske disertacije je ispitivanje kristalizacionog ponašanja germanatnih i germanatnofosfatnih stakala iz sistema K2O-Nb2O5-GeO2 i Li2O-Al2O3- GeO2-P2O5. Na osnovu preliminarnih ispitivanja za proučavanje su izabrana stakla sastava: 30K2O·34Nb2O5·36GeO2 (mol%) i 22,5Li2O·10Al2O3·30GeO2·37,5P2O5 (mol%). Kristalizacione osobine ispitane su pri izotermskim i neizotermskim uslovima kristalizacije. Dobijeni rezultati pokazuju da trokomponentno germanatno staklo kristališe primarnom kristalizacijom, pri čemu fazni sastav kristalisanog uzorka kao i nastajanje pojedinih kristalnih faza zavise od temperature kristalizacije. Na temperaturama kristalizacije < 800 °C kao primarna faza javlja se K3.8Nb5Ge3O20.4, a kao sekundarne faze javljaju se K4Nb6O17 i K6Nb6Ge4O26. Na temperaturama kristalizacije > 800 °C kao primarna faza javlja se K6Nb6Ge4O26, a kao sekundarne faze javljaju se: K3.8Nb5Ge3O20.4, K10Nb22Ge4O68 i KNbO3 faza. Dimenzije kristalita su 20-100 nm. U slučaju četvorokomponentnog germanatnofosfatnog stakla utvrñena je primarna kristalizacija LiGe2[PO4]3 faze sa dimenzijama kristalita 30-500 nm. Odreñen je uticaj granulacije praha stakla na mehanizam kristalizacije i fazni sastav kristalisanih uzoraka. U slučaju kompaktnih uzoraka stakla konstatovan je zapremiski mehanizam kristalizacije sa sferulitskom morfologijom rasta kristala kod oba sastava. Ispitan je proces nukleacije i odreñena je temperaturna i vremenska zavisnost brzine nukleacije. Brzine nukleacije ovih stakala su u oblasti 1,77·1014 - 7,34·1016 m-3s-1 . Odreñena je temperaturna zavisnost brzina rasta kristala i energije aktivacije koje iznose od 294 kJ/mol do 1150 kJ/mol u zavisnosti od faze koja se formira. Odreñene su oblasti nukleacije i rasta kristala, temperature maksimalne brzine nukleacije i procenjene temperature maksimalne brzine rasta kristala. Konstatovano je preklapanje oblasti nukleacije i rasta kristala kod oba sastava. U ispitivanjima su korišćene metode atomske apsorpcione (emisione) spektrometrije (AAS), spektrofotometrije, dilatometrije, diferencijalno-termijske analize (DTA), diferencijalno-skenirajuće kalorimetrije (DSC), infracrvene spektroskopije (FT-IC), rendgenske difrakcione (XRD) i skenirajuće elektronsko mikroskopske (SEM) analize...

The subject of this thesis is the study of the crystallization behavior of germanate and germano-phosphate glasses from the systems K2O-Nb2O5-GeO2 and Li2O-Al2O3-GeO2- P2O5. Based on preliminary experiments the glasses of composition 30K2O·34Nb2O5·36GeO2 (mol%) and 22,5Li2O·10Al2O3·30GeO2·37,5P2O5 (mol%) were selected for examination. The crystallization properties were examined under isothermal and non-isothermal crystallization conditions. Three-component germanate glass crystallize by primary crystallization while the phase composition of crystallized sample and formation of the crystalline phases depends on temperature of crystallization. At crystallization temperatures < 800°C as the primary phase K3.8Nb5Ge3O20.4, appeared and as seconday ones are K4Nb6O17 and K6Nb6Ge4O26. For T > 800 °C, the K6Nb6Ge4O26 appeared as primary phase and as secondary ones are K3.8Nb5Ge3O20.4, K10Nb22Ge4O68 and KNbO3. In the case of four-component germano-phosphate glass the primary crystallization of LiGe2[PO4]3 phase with crystallites dimension of 30-500 nm was detected. The effect of the grain size of glass powders on crystallization mechanism and phase composition of the crystallized samples was determined. For both glass compositions the volume crystallization mechanism with a spherulitic growth morphology of crystals was determined on compact glass samples. The nucleation process was studied and the temperature and time dependencies of nucleation rate were defined. The nucleation rate of these glasses are in the range 1,77·1014 - 7,34×1016 m-3s-1 . Also, the temperature dependence of crystal growth rate was determined and the activation energies calculated are 294 - 1150 kJ/mol depending on the phase formed. The temperature ranges of nucleation and crystal growth and the temperature of maximal nucleation rate and the temperatures of maximal crystal growth rates were determined. For both glass compositions, an overlapping of nucleation and crystal growth range was noted. The methods employed for investigation are: atomic absorption spectroscopy (AAS), spectrophotometry, dilatometry, differential thermal analysis (DTA), differential scanning calorimetry (DSC), infra reed spectroscopy (FTIR), X- ray diffraction (XRD) and scanning electron microscopy (SEM)...