Glass-ceramics, 70 Years Since the Discovery

Ove će se godine navršiti 70 godina od otkrića staklokeramike. Tim povodom u ovom je članku dan sveobuhvatan opis ovog materijala i njegovog napretka od otkrića do danas. Objašnjeno je što je staklokeramika te ukazano na rast interesa i komercijalni uspjeh ovog materijala. Opisan je proces priprave staklokeramike, a posebna pozornost posvećena je ulozi nukleatora te procesu nukleacije i rasta. Navedeni su čimbenici koji presudno utječu na svojstva staklokeramike poput kristalne faze, njenog udjela, sastava preostale staklene faze i mikrostrukture. Zahvaljujući utjecaju navedenih čimbenika moguće je pripraviti različite vrste staklokeramike, s različitim kristalnim fazama i morfologijama te posljedično različitim svojstvima, prikladne za različite namjene. Predstavljeni su najvažniji sustavi i vrste staklokeramike, opisana su i objašnjena njihova svojstva i navedene namjene, a spomenuti su i nazivi najvažnijih robnih marki komercijalne staklokeramike. U zaključku je dano viđenje perspektive ovog materijala te vrste staklokeramike i područja primjene u kojima je napredak najizvjesniji.This year will be the 70th anniversary of the discovery of glass-ceramics. On this occasion, a review paper presenting this material and its progress from discovery to the present day is given. It is explained what glass-ceramic is and pointed out to the growth of interest in this material and its commercial success. The process of preparing glass-ceramics is described, while special attention is paid to the role of nucleating agents and the process of nucleation and growth. Factors that decisively affect the properties of glass-ceramics, such as the crystalline phase, its proportion, the composition of the remaining glass phase and the microstructure, are listed. Owing to the influence of the mentioned factors, it is possible to prepare different types of glass-ceramics, with different crystal phases and morphologies and consequently different properties, suitable for different purposes. The most important systems and types of glass-ceramics are presented, their properties and uses are described and explained. The names of the most important brands of commercial glass-ceramics are also mentioned. In the conclusion, a view of the perspective of this material, glass-ceramic types and areas of application in which the progress is most certain is given

On the Temperature Corresponding to a = 0.632 in Non-isothermal JMA Kinetics

The expression for rate, da/dT, of the nucleation and growth (NG) process under non-isothermal conditions, as described by the Johnson-Mehl-Avrami (JMA) kinetic model, served as the basis for a detailed study of a class of functions F(m) = (da/dT)Tm, where m ÎÂ. Studies of the fractional conversion, a, of the NG process at the temperature of the maximum of function F(m), T = T(m), have shown that when reduced activation energy, x = E/RT, approaches infinity (x®¥), fractional conversion, a, at the temperature corresponding to the maximum of function F(m), a(m), converges to a = 0.632, for any value of m. It has been further shown that fractional conversion, a, for the NG process is equal to a = 0.632 at the temperature corresponding to the maximum of function F(m) = (da/dT)Tm for the particular value of parameter m from the interval: 1 £ m £ 2

Thermal evolution process, properties and photocatalytic activity of sol-gel derived nanocrystalline anatase in dye degradation process

Nanocrystalline anatase aimed to be used as a photocatalyst for dye degradation processes in industrial effluents and has been prepared and investigated. Amorphous titania gel has been prepared using sol–gel process by slow hydrolysis of titanium n–butoxide. The prepared gel has been investigated using Fourier–Transformed Infra–Red Spectroscopy (FTIR), Powder X–ray Diffraction (PXRD), Differential Thermal Analysis (DTA), Thermo–Gravimetric Analysis (TGA), N2 gas adsorption–desorption isotherms and Diffuse Reflectance UV–Vis Spectroscopy (DRS). It was determined that the amorphous gel was comprised of non-hydrolyzed butoxy groups as well as hydroxyl groups bonded to titanium. The thermal evolution of gel is consisted of five steps: elimination of adsorbed water and butanol in temperature range between room temperature and 200 °C, decomposition and elimination of butoxy groups between 200 and 300°C. The crystallization of anatase centered at 404°C, transformation to rutile starting from 540 °C and oxidation of char and tar above 600°C. Thermal treatment of gel at 350 °C for 2 h yields with pure nanocrystalline anatase with average crystallite size of 13.2±0.2 nm, specific surface area of 65.48 m2 g–1 and bandgap, of 3.24 eV. The preliminary assessment of prepared catalyst photocatalytic activity was obtained through degradation process of methylene blue dye under UV light and the 99 % degradation of dye took place within 150 min

Application of a Numerical Method for the Analysis of Metglas 2826 MB Crystallization Kinetics

Crystallization kinetics of y-FeNiMo solid solution in Metglas 2826 MB was studied by isothermal differential scanning calorimetry (DSC). The Johnson-Mehl-Avrami (JMA) equation was used to describe the crystallization process. In order to calculate the kinetic parameters, a new model of the numerical analysis of isothermally obtained DSC data was successfully applied. For the purposes of method evaluation, the classical analytical method of data analysis was also performed. The apparent activation energies obtained were (280 ± 22) kJ mol-1 and (296 ± 23) kJ mol-1 for the analytical and numerical methods, respectively. The Avrami exponents obtained by both methods lie between 1.75 and 1.95

Electrochemical and catalytic applications of cerium(IV) oxide

Cerium(IV) oxide is one of the most important rare earth metal oxides owing to its high oxygen storage and release capacity, as well as thermal and mechanical stability. Its various applications range from sensors, solid oxide fuel cells and supercapacitors to the most important catalytic application in three-way catalytic converters, oxidation of volatile organic molecules, water-gas shift reaction, etc. This short review article gives a brief introduction to rare earth metals, then describes in detail the properties of cerium(IV) oxide and ways to improve them, as well as presents an overview of the most important and current applications of cerium(IV) oxide. Finally, it gives an overview of the results obtained by our group regarding pure and doped cerium(IV) oxide for various applications