Morphology Of Glass-ceramics Research Articles

Investigation on phase evolution of the ZnO-B2O3-SiO2 glass ceramics

ZnO-B2O3-SiO2-Al2O3-Na2O glass doped with nucleating agent TiO2 was prepared with melting-quenching method and the effect of nucleating agent on the crystallization behavior and phase evolution of this glass was investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results show that the glass transition temperature and the first crystallization temperature decrease from 630 °C and 765 °C to 595 °C and 740 °C, respectively, with introduction of TiO2 into glass. There is no diffraction peaks in the XRD pattern but it is no longer transparent for the base glass without nucleating agent after heat treatment, which suggests the serious phase separation occurred, and the observation by SEM indicates that the phase separation is developed by nucleation and growth mechanism. However, there are two different crystals ZnAl2O4 and NaAlSiO4 present in the glass containing TiO2 after heat treating at 575 °C for 2 h and 740 °C for 6 h, respectively. What is interesting is that NaAlSiO4 disappears as the crystallization time at 740 °C increases from 6 h to 12 h, and more ZnAl2O4 crystal is formed, namely, the further formation of ZnAl2O4 is at cost of NaAlSiO4 with increasing crystallization time. And observation of the morphology of glass ceramics shows great difference with increasing crystallization time. Moreover, the ability of ZnO-B2O3-SiO2-Al2O3-Na2O glass ceramics against attacking of 1M HCl solution is increased by the crystals precipitated in heat treatment process.

Effect of zinc substitution for calcium on the crystallisation of calcium fluoro-alumino-silicate glasses

A series of 25, 60, 75 and 100mol% zinc substituted for calcium ionomer glasses of the composition 4.5SiO2–3Al2O3–1.5P2O5–3CaO–2CaF2 were produced following a well-established melt quench route. Similar glass compositions have been widely used in dentistry as the glass component in glass ionomer cements. The glasses crystallise to an apatite and mullite phase after appropriate heat treatments and are interesting materials for bone repair. Zinc is a bactericidal agent and has shown ability to stimulate osteogenesis. The new zinc containing glass compositions were characterised by Helium Pycnometer, DSC, TGA, SEM and EDX. The density of the zinc substituted glasses and glass–ceramics increased with increasing the zinc content as expected. The glass transition temperature decreased with zinc substitution, whereas the crystallisation temperature increased with zinc substitution. Zinc substituted glasses lead to the formation of gahnite in expense of mullite. Fluorapatite formation was not favoured in high zinc content glass ceramics, whereas loss of fluorine in the form of SiF4 was suggested. SEM and EDX analysis showed significant changes in the morphology of glass ceramics with zinc substitution. The formation of gahnite during glass crystallisation may open new application avenues for these materials in the field of semiconducting materials.

Crystallization of spodumene-diopside in the las glass ceramics with CaO and MgO addition

Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (Tp) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.

Growth behavior, morphology and properties of lithium aluminosilicate glass ceramics with different amount of CaO, MgO and TiO 2 additive

Li 2O–Al 2O 3–SiO 2 glass with CaO, MgO and TiO 2 additive were investigated. With more CaO + MgO addition, the crystallization temperature ( T p) and the value of Avrami constant ( n) decreased, the activation energy ( E) increased. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. With more TiO 2 addition, the crystallization temperature decreased, E and n had a little change. The crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization. Plate-like, high mechanical properties spodumene-diopside glass ceramics were obtained. The mechanical properties related with crystallization and morphology of glass ceramics.

Crystallization and Mechanical Properties of Spodumene-Diopside Glass Ceramics

The mechanical properties of spodumene-diopside glasses ceramics with 4-12% TiO2 were investigated. The main crystalline phases precipitated were eucryptite, β-spodumene and diopside. As TiO2 content increasing, the morphology of glass ceramics transformed from coarse to fine microstructure, then to reverse. The flexural strength, elastic moduli, Vickers hardness and fracture toughness of the glass-ceramics were measured. The flexural strength of glass–ceramics containing 9%TiO2 was 198MPa, the Young’s modulus and fracture toughness were 91.3GPa and 2.3 MPa·m1/2 respectively. It was indicated that the mechanical properties were correlated with crystallization and morphology of glass ceramics

Crystallization and properties of a spodumene-willemite glass ceramic

Spodumene-willemite glass ceramics were produced by replacement of Al 2O 3 in lithium aluminium silicate by ZnO. With replacement of Al 2O 3 by ZnO, the batch melting temperature, glass transition temperature ( T g) and crystallization temperature ( T p) all decreased. The main crystalline phases precipitated were eucriptite, β-spodumene and willemite (Zn 2SiO 4). All compositions of glass ceramics showed bulk crystallization. As ZnO content increased, the grain sizes and thermal expansion coefficients increased, while the flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.