Glass/ceramic engineering and design is the science and technology of creating objects, such as windshields and back and sidelites, from inorganic, non-metallic materials for transportation purposes. This is done either by the action of time or temperature. Glass ceramics may have an amorphous or glassy structure, with limited or short-range atomic order. They are either formed from a molten mass that solidifies on cooling, formed and matured by the action of heat, or chemically synthesized at low temperatures using, for example, hydrothermal or sol-gel synthesis.
The special character of ceramic materials gives rise to many applications in materials engineering, electrical engineering, chemical engineering, and mechanical engineering. As ceramics are heat resistant, they can be used for many tasks for which materials such as metals and polymers are unsuited. Ceramic materials are used in a wide range of industries, including mining, aerospace, ground transportation, medicine, refinery, food and chemical industries, packaging science, electronics, industrial and transmission electricity, and guided light-wave transmission. Throughout the book, the two terms, glass-ceramics and glass, will be used interchangeably.
Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous (glassy-like) phase and one or more crystalline phases, being produced by a so-called “controlled crystallization,” which is typically avoided in glass manufacturing.
In the processing of glass-ceramics, molten glass is cooled down gradually before reheating and annealing. In this heat treatment, the glass partly crystallizes. In many cases, so-called “nucleation agents” are added to regulate and control the crystallization process Because there is usually no pressing and sintering, glass-ceramics do not contain the volume fraction of porosity typically present in sintered ceramics.
The term mainly refers to a mix of lithium and aluminosilicates, which yields an array of materials with useful thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. The negative thermal expansion coefficient (TEC) of the crystalline ceramic phase can be balanced with the positive TEC of the glassy phase. At a certain point (~70% crystalline), the glass-ceramic has a net TEC near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000°C. A near- zero balance is the manufacturer’s desired outcome.