The properties of glass-ceramic are dependent on such microstructural parameters such as the amount and properties of crystalline phase, the size, shape and orientation of crystal, and the amount, composition, and distribution of the glassy phase.
Thermal Properties
Low expansion materials are being employed with thermal shock resistance. Thermal expansion coefficient at 25-300° C is 13 ´ 10-7/°C.
Thermal Stability
The low expansion lithis aluminosilicate composition can survive >1000 hr at 1000-1100°C without any appreciable change in properties.
Thermal Conductivity
The thermal conductivity at 25° C is 2.008 W/(m.K)
Optical Properties
The degree of transparency is a function of the optical properties of the crystalline species, the grain size, and the difference in the refractive indexes of the glass and the crystals. Visionsâ and Pyrex â are made with great optical clarity materials, ie. b -quartz solid solutions as the crystal phase with compositions ranging widely in the system SiO2.LiAlO2.-Mg(AlO2)2.Zn(AlO2)2.
Chemical properties
The chemical durability of the common lithia aluminosilicate glass-ceramics is generally on a par with borosilicate glasses. The Chemical corrosion rate is reported as 0.12 mg/cm2 after 24 hour in 5% HCl at 95°C.
Mechanical properties
Glass-ceramics are tough and brittle. The abraded modulus of rupture is 83 Mpa at 20 °C. High strength glass-ceramics can go up to 1300 MPa. The high strength attributes to the formation of a surface-compressive layer either through differential crystallization of low expansive crystal phase, or by an external chemical ion exchange. The glass-ceramics are generally more abrasion resistant than the common glasses, and require more energy for fracture due to the fine-grained structure. The Knoop hardness number with a 100g loading is reported as 593kgf/mm2. Young's modulus at 20°C is 86.2 GPa. The density is 2.50g/cm3 at 20°C.
Electrical Properties
Glass-ceramics are good insulators. The conduction mechanism is primarily ionic, and is more complicated than in a glass of the same composition because of the complex microstructure. The dielectric constant at 1 MHz at 20°C is 6.9. The dissipation factor at the same magnitude is reported at 0.023 at the same testing temperature.
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