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  • Author or Editor: P. Mošner x
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Abstract  

DTA was used to study thermal properties and thermal stability of (50-x)Li2O-xTiO2-50P2O5 (x=0–10 mol%) and 45Li2Ot-yTiO2-(55-y)P2O5 (y=5–20 mol%) glasses. The addition of TiO2 to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO3, Li4 P2O7, TiP2O7 and NASICON-type LiTi2(PO4)3. DTA results also indicated that the maximum of nucleation rate for 45Li2O-5TiO2-50P2O5 glass is close to the glass transition temperature.

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Abstract  

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na2O-xTiO2-50P2O5 and 45Na2O-yTiO2-(55-y)P2O5 glasses. The addition of TiO2 to the starting glasses (x=0 and y=5 mol% TiO2) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO2 content. With increasing TiO2 content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were NaPO3, TiP2O7 and NaTi2(PO4)3. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na2O or P2O5 by TiO2, it increases sharply.

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Abstract  

Thermal behaviour of the glass series (100–y)[0.5ZnO0.1B2O30.4P2O5]yTiO2 (with y=0–39 mol% TiO2) was investigated by DSC and TMA. The addition of TiO2 results in a non-linear increase of glass transition temperature. The compositional dependences of thermal stability, evaluated by two criteria exhibit two maxima for the glasses doped with 10.7 and 35.9 mol% TiO2. All the glasses crystallize on heating in the temperature range of 576–670C. The crystallization mechanism was studied at the glasses with 19.4 and 35.9 mol% TiO2 and the results showed that surface nucleation mechanism prevails in these glasses over the internal one.

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Abstract  

Thermal behaviour of the glass series (100-x)[50ZnO-10B2O3-40P2O5xSb2O3 (x=0-42 mol%) and (100-y)[60ZnO-10B2O3-30P2O5ySb2O3 (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb2O3 results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously increases with increasing Sb2O3 content in both series and varies within the range of 6.6–11.7 ppm °C−1. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb2O3 content the ‘fragility’ of the studied glasses increases.

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Abstract  

The kinetics of ZnFe2 O4 and ZnCr2 O4 formation under non-isothermal conditions using DTA is discussed. It was determined activation energy and kinetic model for studied reactions in the case of used various sources of starting materials (ferric pigments, chromic oxides). The activation energies for ZnFe2 O4 are positioned in a range of 200–475 kJ mol−1 (in dependence of used ferric pigments) and in case of ZnCr2 O4 in a range of 130–160 kJ mol−1 . The autocatalytic kinetic model (Šestk-Berggren) was found to be the most convenient description of the studied processes.

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Abstract  

The paper deals with the possible application of various methods to follow the course of reaction between zinc oxide and Fe(III) oxide with respect to various kinds of Fe(III) oxides used (Fe(III) pigments - red, yellow and black). Differential thermal analysis and chemical analysis can be recommended as the most suitable methods for following reactions leading to spinel formation. The possibilities of determining the activation energy of the studied processes are discussed. When Fe(III) red pigment is used as a reactant and therefore no reaction occurs except spinel formation, conductometric thermal analysis was found to be suitable and more sensitive for the evaluation of differences in reactivities. It has also been observed that the kind of Fe(III) pigment, due to its individual reactivity significantly affects the colouring properties of the final product (e.g., of the ceramic stain).

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Abstract

The effect of TeO2 additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B2O3–0.4P2O5]–xTeO2 by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO2 to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO2 content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn2P2O7, BPO4 and α-TeO2. Annealing of the powdered 50ZnO–10B2O3–40P2O5 glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn2P2O7 and BPO4 during subsequent heating.

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Summary The forms of vibrations and displacements of particles in amorphous structures have been investigated. The particles, moving on highly non-linear amplitude, are responsible for the creation of disordered structures of amorphous bodies. The non-linear oscillators, even if 'few' in concentration, are characterized by unpredictable trajectories in phase space. The non-linear oscillators are fully developed in the liquid state above the crossover temperature T cr and between T cr and T g their number decreases. Under T g they completely disappear. The interconnection between the linear oscillators in blocks plays the most important role in the characteristic time spectra in liquid state. Using the additive properties of elements polarizibilities, the number of acoustical units in individual blocks at T cr is estimated to be about 600 units. The diameter of blocks at T cr was estimated to be about 1.8 nm. Even if the non-linear high amplitude motions disappear at solidification, the remnants of structural irregularity remain and the disordered structure of glass is formed.

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