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

Positive effects of naringenin on near-surface membrane fluidity in human erythrocytes

Purpose: Deformability/rheologic behavior of erythrocytes are related to near-surface membrane fluidity. Specific agents can increase erythrocyte membrane fluidity in order to adjust hemodynamics in cardiovascular diseases. Grapefruit flavanone naringenin has been proposed for potential use in an alternative therapy of cardiovascular conditions. In respect to this, we assessed here effects of two nutritionally relevant concentrations of naringenin (0.1 and 1 μg/ml) on near-surface membrane fluidity in human erythrocytes. Methods: We used electron paramagnetic resonance spectroscopy and fatty acid spin probes (5-DS and 7-DS), the spectra of which are dependent on membrane fluidity. Results: The results showed a significant (p = 0.029) increase of membrane fluidity near the hydrophilic surface in erythrocytes treated with higher concentration of naringenin. In the deeper layer, just below the erythrocyte membrane phospholipid heads, both lower and higher concentration of naringenin significantly increased membrane fluidity (p = 0.036 and p = 0.028, respectively). Conclusions: These data document the positive and dose dependent effect of naringenin on near-surface membrane fluidity in human erythrocytes, recommending its use in the cardiovascular conditions characterized by disturbed hemodynamics

Numerical optimisation of processes in the furnace considering NOx emission and efficiency of utility boiler

Razvijen je matematički model, namenjen za predviđanje procesa u energetskim parnim kotlovima TE Kostolac B tangencijalno loženim sprašenim lignitom. Model je primenjen za numeričku analizu rada kotla radi smanjenja emisije NOx, uz istovremeno održavanje visokog stepena korisnosti kotla. Kompleksni dvofazni tok gas-čestice modeliran je Ojler-Lagranževim pristupom. Povezivanje faza je ostvareno kuplovanjem pomoću PSI-Cell koncepta. Radi ostvarivanja željenih analiza, ugrađen je pod-model formiranja/destrukcije NO, unutar složenog koda za sagorevanje, koji se koristi za predviđanje emisije na izlazu iz ložišta. Modelirani su termički i gorivi NO, kao najuticajniji oksidi azota pri sagorevanju ugljenog praha. Proračunski program je razvijen radi lakše upotrebe od strane inženjerskog osoblja prilikom analiza procesa u kotlovskim postrojenjima. Numeričke simulacije su izvršene za različite radne uslove kotla, prilikom loženja lignitom sa kopa Drmno. Suprotstavljeni zahtevi a smanjenjem emisije i efikasnim sagorevanjem, sa osvrtom na bezbedan rad pregrejača pare često zahtevaju rad kotla u uskim granicama radnih parametara, koji su utvrđeni pomoću termičkog proračuna kotla.Mathematical model, aimed for prediction of processes in TE Kostolac B power plant utility boiler furnace tangentially fired by pulverized lignite, was developed in-house. The model was applied in numerical analysis of boiler operation, in order to reduce NOx emission by combustion modifications in the furnace, while maintaining high efficiency of the boiler unit. Complex two-phase gas-particle flow was modelled using Euler-Lagrange approach. Coupling between phases was done by using PSI-Cell concept. In order to perform necessary analysis, NO formation/destruction sub-model was implemented, within comprehensive combustion code, used to predict emission from the furnace. Thermal and fuel NO were modelled, as the most influential nitrogen oxides during pulverized coal combustion process. The computational code was developed to be easily used by engineering staff dealing with the process analysis in boiler units. Numerical simulations were performed for the boiler fired by the lignite Drmno, under different operating conditions. Contradictory requirements with respect to emission reduction and efficient combustion with safe operation of super-heaters often require boiler to operate within narrow limits of operation parameters, which is determined by means of the boiler thermal calculation

Mere i metode za smanjenja emisije oksida azota iz peći za topljenje stakla

The nitrogen oxides emitted to atmosphere effect significantly on formation of photochemical smog, acidic rains and destroying of ozone shell of the earth. Therefore, the regulations for limited emission of nitrogen oxides to atmosphere become very strict. Glass manufacturing is a high-temperature, energy-intensive activity, because of the high temperature NOx emissions are extremely high. NOx emissions could be reduced by primary process modifications measures end secondary post-combustion measures. Primary process modifications are usually based on the following techniques: stoichiometric combustion and advanced burners systems, staged combustion (air- or fuelstaged), recircylation of flue gasses.Razvojem tehnike i tehnologije javlja se potreba za većom proizvodnjom energije. Iako se danas uvode u upotrebu i drugi izvori energije, još uvek je najzastupljenije dobijanje energije u procesu sagorevanja goriva. Zbog visokih temperatura koje nastaju pri sagorevanje dolazi do velike emisije NOx oksida. U ovom radu opisane su mere i metode kojima je moguće smanjiti emisiju NOx u procesima dobijanja stakla

Crystallization and sintering behaviors of the polyphosphate glass doped with Zn and Mn

The crystallization and sintering behaviors of polyphosphate glass doped with trace elements Zn and Mn were examined. The heating experiments on bulk and powder glass samples were performed. The parent glass revealed low crystallization ability and the glass crystallization carried out under simultaneous acting of the surface and volume mechanisms. The bulk glass sample isothermally heated at

Bioactive glass-ceramics prepared by powder sintering and crystallization of polyphosphate glass containing strontium

Melt-quenching method was employed for obtaining a glass-ceramic with the following composition 42P(2)O(5). 40CaO.5SrO.10Na(2)O.3TiO(2) (mol%) glass. The crystallization and sintering behavior of glass have been studied by using DTA, HSM, XRD, FTIR and SEM methods. It was determined that the surface and volume crystallization mechanisms act simultaneously in bulk glass samples. The comparison of DTA and HSM data revealed that the sintering and crystallization processes are independent. The sintered calcium phosphate glass ceramic which contained bioactive beta-Ca-3(PO4)(2) and beta-Ca2P2O7 phases was successfully prepared. It was determined that during crystallization the primary phase in the precipitate was beta-Ca(PO3)(2). Other phases appearing in the resulting glass-ceramic were: alpha-Ca2P2O7, gamma-Ca2PO7, Ca4P6O19 and CaHPO4(H2O)(2). Crystalline phases containing Sr and Ti were not detected. SEM analysis of the glass-ceramic microstructure revealed surface crystallization of glass particles and plate-like morphology of crystal growth. The result of the in vitro bioactivity showed that no apatite layer was formed on the surface of the as-prepared glass-ceramic samples after immersion in the simulated body fluid (SBF)

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

Effect of la2o3 on the structure and the properties of strontium borate glasses

The selected lanthanum-strontium borate glasses were prepared by a conventional melt-quenching technique. The compositions of the investigated glasses were chosen to be: 5.7, 9.5, 14.3, 19.1 mol% for La2O3, 22.9, 19.1, 14.3, 9.5 mol% for SrO and 71.4 mol% for B2O3. The density, molar volume, oxygen molar volume, oxygen packing density, oxygen/boron ratios and structural transformations in the glass network were investigated according to the substitution of SrO by La2O3. The density and the molar volume increased in parallel with La2O3 content increase. Simultaneously, oxygen molar volume values increased while the oxygen packing density values decreased. A hot stage microscope (HSM) and a differential thermal analysis (DTA) were used to determine the characteristic temperatures. By increasing the content of lanthanum, the glass transition temperatures, changed with the same trend as the molar volume. Glass stability parameters were calculated from the temperatures obtained by DTA and HSM. The HSM results were used to obtain the viscosity curves by applying the Vogel-Fulcher-Tamman (VFT) equation

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

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