Macor machinable glass ceramic is thermally robust enough as a substrate and reflector in high-intensity lamps
Glass ceramics are ideal materials in heat-resistant lamps and as reflectors in high-pressure discharge lamps.
Such lamps are used to project images using discharges of high-pressure electric arcs with the aim of producing a light beam of a very high intensity. This is used for a digital data projection in any type of electronic device, from a hand-held sensor or smart device to a large television screen.
The crucial requirement in such a set-up is that the reflectors remain stable at the very high temperatures needed to produce an image of high brightness and balanced colour on a receiving screen.
Such reflectors and their substrates have to operate at temperatures usually above 550 degrees Celsius. This is well above the melting temperature of borosilicate glass – the usual glass product used in electrical device screens.
The reflector and its substrate also have to have a low thermal expansion coefficient, as the process of switching a device on and off creates high thermal gradients. These in turn lead to a deformation and eventual fracture of a conventional reflector and substrate as it expands and contracts in the generated heat The reflectors and substrates also have to act as heat sinks. This means they have to transfer the heat generated from the infra-red part of the light spectrum away from the light source.
Glass ceramics such as Macor have all of these physical attributes. In addition, it is produced with a smooth surface that does not require any polishing after crystallisation.
The composition of Macor is essentially fluorphlogopite mica that is contained in a matrix of borosilicate glass. It is highly machinable and can be fabricated into many complex shapes and designs. It has a surface finish of 0.5 microns, which with further polishing can be reduced to 0.013 microns. It can be machined with standard tools for metalworking and does not require users to invest in expensive diamond-tipped tools.
This glass ceramic is capable of remaining stable continuously up to temperatures of 800 degrees Celsius, peaking at a maximum temperatures of 1,000 degrees C if there is no load on it.
Although it is chemically resistant, especially to strong alkalis such as caustic soda, Macor’s one shortcoming is that it is attacked by halogens at high temperatures.