Crystal growth of K2TiGe3O9 in the glass

The kinetics and mechanism of isothermal crystal growth of K2TiGe3O9 from a glass of the same stoichiometric composition were studied. The crystal growth rate U = 1 x 10-11-1.27 x 10-10 m s-1 was experimentally determined in the temperature interval of t = 540-600°C. In the range of high undercooling, Δt=435-375°C, spherical crystals growing at (374 ± 19) kJ mol-1 was observed

A study of the primary crystallization of a mixed anion silicate glass

This paper presents the results of a study of the primary crystallization of a multicomponent mixed anion silicate glass. The primary phase, leucite, and the secondary phase, diopside, were formed by surface crystallization, while the secondary phase, phlogopite, was formed by volume crystallization. The influence of the particle size of glass powder samples in the range 0-1 mm on the temperature of the DTA crystallization peak, T-p, the height of the peak, (delta T)(p), and the parameter T-p(2)/(Delta T)(p) was studied. The behaviors of the parameters (delta T)(p) and T-p(2)/(Delta T)(p). depend only on the change in the surface-to-volume nuclei ratio, as is the P case with polymorphic crystallization. However, the particle size ranges in which the surface, volume and mixed crystallization mechanism dominate are considerably narrower for this glass. The influence of the duration of a pre-DTA heat treatment on the parameters T-p, (delta T)(p), and Delta T-p for fixed temperatures in the range T = 550-750 degrees C was investigated. The T-p of the samples thermally treated for different times, at fixed temperatures, decreased up to t = 5 h and then increased to a value close to that of an as-quenched sample, after which the value remained constant. The curves of (delta T)(p), and Delta T-p as a function of time for fixed temperatures show a maximum. The influence of the temperature of the pre-DTA heat treatment on the parameters T-p (delta T)(p), and Delta T-p, for fixed times of t = 1-5 h was also investigated. On increasing the pre-DTA heat treatment time, the curves changed significantly. The curves for 3 and 5 h in the temperature range 580-660 degrees C were similar to the nucleation curve, which indicated that the volume nucleation process proceeded in this temperature range. The behavior of these parameters, as a result of the simultaneous action of different nucleation mechanisms and crystal growth differ from those previously reported for the case of polymorphic crystallization

The nucleation behavior of k2o center dot tio2 center dot 3geo(2) undercooled melt

The nucleation of K2TiGe3O9 crystals in an undercooled melt of stoichiometric composition was studied. Volume nucleation with spherical morphology of the growing crystals was determined. The nucleation range is in the temperature interval 540-630 degrees C. A maximum of the steady state nucleation rate of I-max = 1.4 x 10(15) m(-3).s(-1) was determined at the temperature T-n(max) = 582 degrees C. The temperature and time dependence of the nucleation rate was analyzed and it was shown that such a nucleation behavior was the result of a low thermodynamic and kinetic barrier. The results showed that the temperature intervals of nucleation and crystal growth of this undercooled melt partly overlapped

The crystallisation of calcium phosphate glass containing vanadium oxide

The crystallisation behaviour of calcium phosphate glass containing vanadium oxide was studied. Glass with a molar ratio of [CaO]/[P2O5] = 1.13 and a V2O5 content of 8 mol.% was prepared for the experiments. The crystallisation of bulk glass samples was performed tinder isothermal conditions at T = 650-820 degrees C. The surface crystallisation mechanism of studied glass with dendritic growth of the primary alpha-Ca2P2O7 phase was observed. In all crystallised samples, beta-Ca2P2O7 and VP2O7 appeared as the secondary phases. In the investigated temperature range, crystal growth rates 9 x 10(-9) - 2.14 x 10(-6) m/s were determined. The temperature dependence of the crystal growth rate makes possible to calculate activation energy E-a = 407 +/- 30 kJ/mol of crystallization. The experimental data were compared with those estimated by using a theoretical model of the crystal growth rate and good agreement between the results was found

Non-isothermal crystallization of k2o center dot tio2 center dot 3geo(2) glass

The crystallization of K2O center dot TiO2 center dot 3GeO(2) glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization was dominant and an activation energy of crystal growth of E-a,E-s = 327 +/- 50 kJ mol(-1) was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes gt 0.45 mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E-a,E-v = 359 +/- 64 kJ mol(-1) was calculated

Rast kristala K2TiGe3O9 u staklu

The kinetics and mechanism of isothermal crystal growth of K2TiGe3O9 from a glass of the same stoichiometric composition were studied. The crystal growth rate, U, in the range 1x10-11-1.27x10-10 m s-1 was experimentally determined in the temperature interval 540-600°C. In the range of high under-cooling, Δt, 435-375°C, spherical crystals growing at (374±19) kJ mol-1 was observed.Pod izotermskim uslovima proučavana je kinetika i mehanizam rasta K2TiGe3O9 kristala iz stakla istog stehiometrijskog sastava. U intervalu temperature 540-600°C eksperimentalno su određene brzine rasta kristala, U, 1x10-11-1.27x10-10 m s-1. Pokazano je da se u oblasti visokih pothlađenja, Δt, 435-375°C, rast sfernih kristala ove faze odvija po mehanizmu zavojne dislokacije. Dobijena je energija aktivacije rasta kristala GD=(374±19) kJ mol-1

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)

Preparation of glass-ceramic in Li2O-Al2O3-GeO2-P2O5 system

The results of preparation and structural characterization of glass-ceramics from the system Li2O-Al2O3-GeO2-P2O5 are shown in this paper. The crystallization behaviour of the selected glass was examined under non-isothermal and isothermal crystallization conditions. DTA, XRD and SEM methods were employed for analyses. It was confirmed that this glass crystallizes by the volume crystallization mechanism. The results also showed that the glass crystallize by primary crystallization. As a primary phase the LiGe2(PO4)3 is formed and the traces of GeO2 as a secondary one is present. The crystallization process occurred at a high homogeneous nucleation rate and the spherical morphology of crystal growth. By applying the Kissinger relation the activation energy of crystal growth Ea = 462 kJ/mol was determined

Sekundarni postupci smanjenja emisije oksida azota u procesu topljenja stakla

In this paper the new methods for reduction of NOx emission from glass melting furnaces were presented. The secondary measures are focused on development of different methods for elimination of nitrogen oxide from the smoke gasses. The main characteristics of the selective catalytic reduction process (SCR), selective non catalytic reduction process (SNCR) and 3R process were presented and some advantages and limitations of these processes were analyzed.U ovom radu su prikazani novi postupci smanjenja emisije NOx iz peći za topljenje stakla. Zbog visokih temperatura do kojih se zagreva vazduh neophodan za sagorevanje dolazi do visoke emisije oksida NOx iz staklarskih peći. Sekundarne mere usmerene su na razvoj postupaka za uklanjanje azotnih oksida iz dimnih gasova. Dat je prikaz selektivno nekatalitičkog, selektivno katalitičkog redukcionog i 3R postupka kao i njihove prednosti i nedostaci