Crystallization behaviour of multicomponent germanate glasses

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)..

The analysis of the crystal growth process of the lithium germanium phosphate glass : [invited presentation]

The crystal growth rate of lithium germanium-phosphate glass was studied. The glasses have been homogenized using the previously established temperature-time conditions, which make it possible to remove a volatile substances from the glass melt. The AAS was used to determine the chemical content of obtained glass, the differential thermal analysis (DTA), and scanning electron microscope (SEM) were used to reveal the isothermal process of crystal growth, respectively. It has been found that the experimental determined crystal growth rate has a tendency toward of exponentially increase with an increase the temperature

The crystal growth of NASICON phase from the lithium germanium phosphate glass

The crystal growth rate of LiGe2(PO4)3 phase from lithium germanium-phosphate glass was studied. The glass have been homogenized using the previously established temperature-time conditions, which make it possible to remove volatile substances from the glass melt. The atomic absorption spectrophotometry (AAS) was used to determine the chemical content of the obtained glass and scanning electron microscope (SEM) were used to reveal the isothermal process of crystal growth. The crystal growth rates were determined experimentally and theoretically

The nucleation of K2O center dot TiO2 center dot 3GeO(2) glass under non-isothermal conditions

The nucleation of germanate K2O center dot TiO2 center dot 3GeO(2) glass under non-isothermal conditions was studied by the DTA method. The temperature ranges of nucleation and crystal growth of this glass partly overlap. The influence of the mass of the glass sample as well as, the time and temperature of the pre-DTA heat treatment on the DTA parameters T-p, (delta T)(p), and Delta T-p was investigated. A complex behavior of these parameters was evidenced. It was shown that for fixed temperatures, increasing the annealing time of the pre-DTA heat treatment resulted in a decrease in the temperature of the DTA peak (T-p). The curve of the dependence of DTA peak heights (delta T)(p) on time showed a maximum and the parameter Delta T-p continually increased with increasing time. The influence of the temperature of the pre-DTA heat treatment on the DTA parameters showed that for annealing times t gt t(ind), the dependences of T-p(-1) and Delta T-p vs. T corresponded to the dependence of Ion Tin the case when the regions of I and U partly overlapped. As shown, in this case. the change of (delta T)(p) vs. T is not convenient for an analysis of the nucleation behavior of the glass

The effect of K2O on the crystallization of niobium germanate glasses

The effect of K2O content on the crystallization of niobium germanate glasses with 22.7- 24.27 wt% of GeO2 and 54.59-57.48 wt% of Nb2O5 was examined. The glasses crystallize by primary crystallization and the formed crystalline phases were K6Nb6Ge4O26, K3.8Nb5Ge3O20.4 and KNbO3. Increasing the K2O content caused a decrease in the GeO2 content of the primary phases. The effect of the K2O content on the kinetics of primary crystallization was analyzed. It was demonstrated that an increase of the K2O content decreased the activation energy of crystal growth at first of the crystallization peaks (Ec1). At second crystallization peaks the activation energies of crystal growth increased (Ec2).Ispitan je uticaj sadržaja K2O na kristalizaciju niobijum germanatnih stakala sa 22,7-24,27 mas % GeO2 i 54,59-57,48 mas % Nb2O5. Ova stakla kristališu primarnom kristalizacijom i stvaraju se kristalne faze K6Nb6Ge4O26, K3.8Nb5Ge3O20.4 i KNbO3. Povećanje sadržaja K2O prouzrokuje smanjenje sadržaja GeO2 u primarnim fazama. Analiziran je uticaj sadržaja K2O na kinetiku primarne kristalizacije. Pokazano je da povećanje sadržaja K2O smanjuje energiju aktivacije rasta kristala na prvom kristalizacionom piku (Ec1). Na drugom kristalizacionom piku energije aktivacije rasta kristala se povećavaju (Ec2)

Structure and Microstructure Characterization of the La2SrB10O19 Glass-ceramics

The crystal structure of new lanthanum strontium borate glass-ceramics was refined by the Rietveld method. The results showed that La2SrB10O19 has the monoclinic crystal structure, space group C2 (No. 5) with a = 11.1170(6), b = 6.5667(3), c = 9.2363(3) angstrom,beta = 91.481 degrees, V = 674.04(7) angstrom(3), two formula units per unit-cell, and density 3.830 g cm(-3). The main building units of the crystal structure are BO4 tetrahedra and BO3 triangles. Clusters composed of [B5O12] form an infinite double layer running perpendicular to the c-axis. Lanthanum atoms, situated in [B5O12](n) layers, are coordinated with 10 oxygen atom in a form of LaO10 polyhedra, while Sr atoms, located between [B5O12](n) layers, are coordinated with 8 oxygen atoms in a form of SrO8 polyhedra. Microstructural measurements contain both crystallite domain sizes and microstrain calculations obtained by the Warren Averbach and the simplified integral-breadth methods

Sintering, crystallization and foaming of La2O3 center dot SrO center dot 5B(2)O(3) glass powders - effect of the holding temperature and the heating rate

The peculiarities of sinter-crystallization of La2O3 center dot SrO center dot 5B(2)O(3) fine glass powder (below 1 mu m) are investigated and discussed. The sintering was studied by contactless optical dilatometry and porosity measurements. The crystallization process was evaluated by differential scanning calorimetry (DSC) and the crystalline phase formation was analyzed by X-ray diffraction (XRD). Finally the microstructures of the samples sintered at different temperatures were observed by field emission scanning electron microscope (FESEM). The specific aim of this study was to highlight the influence of sintering temperature and heating rate on the densification process and the final structure of glass-ceramic samples. It was shown that zero water adsorption and minimum closed porosity of similar to 3% were obtained at heating rate of 2 degrees C/min and at about 1 h holding at 690 degrees C. The temperature increase accelerated intense foaming process that resulted in formation of total porosity of 35-45%. It was also demonstrated that the foaming depended on the heating rate: the higher the heating rate - the more intensive was the bloating. The observed foaming process was related to intensive crystallization and re-crystallization of La2O3 center dot SrO center dot 5B(2)O(3) crystal phase. The phase formation processes entirely completed after 30-60 min at 730-740 degrees C with the formation of intriguing and unusual crystal structures

Sintering, crystallization and foaming of La2O3 center dot SrO center dot 5B(2)O(3) glass powders: effect of the holding time

Sintering, crystallization and foaming of nano glass powders with composition La2O3 center dot SrO center dot 5B(2)O(3) were studied by hot stage microscopy (HSM) and simultaneous thermal analysis (DTA-TG) under non-isothermal regime at 10 degrees C/min and by optical contactless dilatometer under isothermal conditions at 700 degrees C up to 10 hours for different times. After the thermal treatments, specimens were characterized by gas pycnometry, X-ray Powder Diffraction (XRD) and Field Emission Scanning Electron Microscopes (FE-SEM). The results demonstrate that the densification completed before the crystallization process, thus forming well sintered samples. Then, during the phase formation gas is released, which leads to foaming process. After holding of 160 minutes at 700 degrees C the degree of crystallization reached about 0.8 and the foaming stopped. The obtained sample had high closed porosity and quite intriguing structure composed of two fairly different crystal arrangements. The first was "sponge-like", while the second was denser and consisted of "sheets", 10-30 nm thick. The subsequent holding led to re-crystallization, formation of larger denser zones that reached even 10-15 mu m and an increase in open porosity. These results highlight that in the case of sinter crystallization of nano powders, some intriguing features can be expected

Crystallization and sinterability of glass-ceramics in the system La2O3-SrO-B2O3

Glasses with a constant B2O3 and an increasing La2O3 content in the system La2O3-SrO-B2O3 were obtained by the usual melt quenching procedure. The crystallization and sinterability of the glasses were investigated by hot stage microscopy (HSM), differential thermal analysis (DTA), X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD analysis of the bulk samples evidenced the formation of the crystalline phases: La2SrB10O19, SrB6O10 and SrLaBO4. XRD and TEM/SAED analyses showed a polymorphic crystallization of the glass sample containing 14.3 mol% La2O3 with precipitation of the La2SrB10O19 phase. SEM analysis confirmed the surface crystallization mechanism of this sample. The kinetics of crystallization of the same sample was examined by DTA and the activation energy of crystal growth was calculated by the Kissinger model to be E-a=458 +/- 63 kJ mol(-1)

DTA study of the crystallization of Li2O-Nb2O5-SiO2-TiO2 glass

In this study, the crystallization of 30Li(2)O center dot 15Nb(2)O(5)center dot 50SiO(2)center dot 5TiO(2) (mol%) glass was examined. The parent glass was prepared by the standard melt quenching method, and the investigations were performed under non-isothermal and isothermal conditions using the DTA, XRD, SEM and EDS methods. The results revealed primary crystallization of this glass and the dendritic morphology of crystal growth. Three crystalline phases were formed in the glass matrix during crystallization, whereby LiNbO3 was formed as the primary phase, followed by Li2Si2O5 and SiO2 as the secondary. The surface and volume mechanisms of crystallization occur. The condition that both the mechanisms were dominant was determined. In the case of volume crystallization, the characteristics of the nucleation process were examined. The kinetic parameters of crystallization under different mechanisms of crystallization were determined