Institute Standard and Research Industrial of Iran

Karaj, Iran

Institute Standard and Research Industrial of Iran

Karaj, Iran

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Mirhadi B.,Imam Khomeini International University | Mehdikhani B.,Institute Standard and Research Industrial of Iran
Journal of Non-Crystalline Solids | Year: 2011

The effects of chromium oxide on the crystallization behavior of glass compositions in the calcium, zirconium and silicon oxides system were investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopic. Results indicate that crystallization is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 1.0 mol% of doping oxide. The effect of heating rate on differential thermal analysis curves was studied in order to investigate nucleation mechanisms and to extract the corresponding crystal growth activation energies E c for the different crystalline phases. Activation energy (E c) was found to be 490 ± 5 kJ/mol for 5.0 mol% chromium oxide in glasses. The most suitable nucleation temperature was determined as 810 °C for the above mentioned glass. The results of this study have highlighted that a small percentage of chromium oxide strongly affects the crystal formation thereby reducing the time and temperature of the thermal treatment and enhancing the degree of crystallization of calcium, zirconium and silicon oxides glasses. © 2011 Elsevier B.V. All rights reserved.


Mirhadi B.,Imam Khomeini International University | Mehdikhani B.,Institute Standard and Research Industrial of Iran | Askari N.,Imam Khomeini International University
Solid State Sciences | Year: 2012

Glass-ceramic in the MgO-Al 2O 3-SiO 2 system with crystallization ability of gahnite (ZnO·Al 2O 3) and mullite were synthesized. It was found that the glass-ceramic containing gahnite phase had desirable mechanical behavior and reached to an acceptable hardness and density. The compositions were designed based on magnesium oxide replacement (from MgO-Al 2O 3-SiO 2 glass-ceramic system) with zinc oxide. Glass-ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. Heat treatment at 1100 °C cause form gahnite crystals in glass-ceramic. Microhardness increased with increasing gahnite crystals. To achieve good mechanical properties, the initially formed high gahnite phase must transform. © 2012 Elsevier Masson SAS. All rights reserved.

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