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Abstract  

The crystallization mechanism of the glass-ceramics obtained from Romanian (Şanoviţa) basalt in the presence of 3 and 5% CaF2 as nucleation agent has been investigated under non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using the Kissinger-Akahira-Sunose, Ozawa-Flynn-Wall, Starink and Tang isoconversional methods. The monotonous decreases in the activation energy (E a) with the crystallized fraction (α) confirms the complex mechanism of the glass-ceramics crystallization process. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process.

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Abstract  

The paper presents the kinetic study of the crystallization processes which take place in basalt glasses containing variable amount of nucleation agent (CaF2, 310%). The activation energies have been calculated using Kissinger's equation and verified with the Ozawa-Flynn-Wall equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20 degrees/min. A correlation equation between the activation energy and the amount of nucleation agent (% of CaF2) was established. By X-ray diffraction it was proved that the crystalline phase formed in the crystallization process represents a pyroxenic solid solution, Ca(Mg,Fe)SiO3.

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Abstract  

A study is reported of the crystallization behaviour of some glass compositions which belong in the system MgO-Al2O3-SiO2 and which lead to vitreous ceramics with α-cordierite as a main phase. DTA, X-ray diffraction and dilatometric analysis were used to investigate the influence of the type and concentration of the nucleation agents. The activation energies of crystallization were calculated and the crystalline phases were identified.

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Abstract  

In previous works, the effects on the devitrification mechanism of a certain composition calcium phosphate with additives of TiO2, SiO2, Al2O3, CeO2 have been studied. It was found that some metal oxide additives played a key role as the nucleation agent in calcium phosphate glass-ceramics, and the devitrification mechanism of calcium phosphate glass system was changed drastically by addition such as metal oxide. Hydroxyapatite (HAp), tricalcium phosphate (TCP) and β-calcium phosphate (β-CaP2O6) whisker are the three most biologically compatible materials to human bone in bio-ceramics field. In this work, the effect on devitrification mechanism and the physical properties of certain composition calcium phosphate glass with three above additives were investigated, and the result shown that although no fine crystalline was induced in the certain composition of calcium phosphate glass when a large amount of additive was added, but such additives play a catalyst role by lowering the activation energies of devitrification. It would supplement the mechanical properties and the biocompatibility for the calcium phosphate glasses.

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Abstract  

Characteristic temperatures, such as T g (glass transition), T x (crystallization temperature) and T l (liquidus temperature) of glasses from the V2O5-MoO3-Bi2O3 system were determined by means of differential thermal analysis (DTA). The higher content of MoO3 improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was investigated and following energies of the crystal growth were obtained: glass #1 (80V2O520Bi2O3) E G=280 kJ mol-1, glass #2 (40V2O530MoO330Bi2O3) E G=422 kJ mol-1 and glass #3 (80MoO310V2O510Bi2O3) E G=305 kJ mol-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide acts as a nucleation agent and facilitates bulk crystallization.

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was large enough to destroy the filler network and align the clay layers along the flow direction, then oriented crystals including cylindrites and strings of spherulites were formed. These aligned clay layers acted as heterogeneous nucleation agents

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of filler which is expected to act as nucleation agent in the filled PP would increase the crystallization rate. The scientific and technological interest for tailoring and modifying the PP properties has been driving a very vivid research on the base

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composites. The results obtained indicated that the presence of WF enhanced both the melt and crystallization of the PP by acting as a heterogeneous nucleation agent. The more the contents of WF, the more influence on the crystallization of PP. The PP showed

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. Pǎcurariu , C , Lazǎu , RI , Lazǎu , I , Ianos , R , Tita , B . Non-isothermal crystallization kinetics of some basaltic glass-ceramics containing CaF 2 as nucleation agent . J Therm Anal Calorim 2009 97 : 507 – 13 10.1007/s10973

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[ 21 ]. Joseph et al. [ 24 ] used polypropylene modified with a specific nucleation agent which promotes crystallization in the β-phase. Until this time, no investigations were carried out on the impact of filler in the form of lignified tissue

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