Effect of TiO2 Addition on Crystallization Behaviour of Potassium Mica-Cordierite Based Glass Ceramics

Glass-ceramics in the CaO-MgO-Al2O3-SiO2 quaternary base glass system was produced via melting technique using feldspar, limestone and magnesite as sources of starting materials. Glass-ceramics production involves making a base glass, annealing and cooling to room temperature and then reheating the base glass to nucleation and crystal growth temperatures. Characterization of the produced glass-ceramics was carried out using a scanning electron microscope (SEM). The effects of the crystallization process on some properties such as hardness, chemical durability in acid and alkali media of samples were determined. The results portrayed that glass-ceramic samples to which various amounts of TiO2 (2,4,6,8 and 10 wt.%) were incorporated showed the formation of crystalline phases dispersed in the matrix of their respective residual glassy phases. Significant improvement in hardness, as well as minimum weight loss, were recorded for all the glass-ceramic samples. On the contrary, the glass samples did not crystallize despite subjecting them to heat treatment, their hardness values were low and they were not resistant to acid (1M HCl) and alkali (1M NaOH) attacks. The inability of TiO2 addition to fully transform them into glass-ceramics remains a shortcoming. However, the glass-ceramic samples obtained from this study can be used for tiling works.

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The Influence of Metal Diffusion and Interfacial Reactions on the Crystallization Behaviour of Glasses Employed in the Manufacture of Glass-Ceramic-to-Metal Seals

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.39-40.369 ◽

2008 ◽

Vol 39-40 ◽

pp. 369-374

Author(s):

Ian W. Donald ◽

Brian L. Metcalfe ◽

Lee A. Gerrard

Keyword(s):

Glass Composition ◽

Glass Ceramics ◽

Crystallization Behaviour ◽

Metal Species ◽

Effective Control ◽

Interfacial Region ◽

Bulk Glass ◽

Factors Affecting ◽

Metal Diffusion ◽

Lifetime Behaviour

One of the major attributes of glass-ceramics is an ability to tailor their thermal expansion characteristics and this makes them ideal candidates for sealing to a wide variety of metals and alloys; however, during the sealing process, reaction of diffusing metal species with glass constituents may occur, and this can lead to the formation of undesirable phases within the interfacial region. In addition, diffusion of metal species into the bulk glass away from the interface may affect the overall crystallization kinetics and can result in the formation of unwanted crystalline phases which may be detrimental to the lifetime behaviour of a seal component. This contribution outlines and discusses the factors affecting the crystallization behaviour of glasses employed in seal manufacture and describe methods by which undesirable reactions can be alleviated or minimized through effective control of the process parameters and starting glass composition.

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