A great deal of this variety of mica is used for other insulating purposes. There are a vast variety of uses, such as for sheets, washers and disks in dynamos, electric-light sockets, guards in rheostats, fuse boxes, telephones, etc.
Sheet or block phlogopite is used for general electrical insulation—particularly where mica softer than muscovite is required.
Mica splittings of both muscovite and phlogopite are employed for the manufacture of “built-up mica,” which is used widely for electric insulation in many different forms, such as sheets, tubes, cups, etc. Mica board built up from phlogopite splittings is used extensively for insulation between the copper segments of commutators.
Among the less essential uses of sheet or block mica (mainly muscovite) are in windows for stove fronts and ovens; chimneys and shades for lamps and lanterns; and for many other purposes where a transparent non-inflammable, non-shattering material is required. It is also used for heat insulation, in various electric heating devices.
Ground mica is also used for heat insulation, as in pipe and boiler covering, etc.; and as a patent roofing, both as a coating to prevent sticking when rolled, and as a filler in the roofing itself. It is also used in annealing steel, and as a lubricant for wooden bearings.
Among the non-essential uses of mica, those for which a satisfactory substitute is known, are the uses of sheet or block mica for phonograph diaphragms, and for decorative purposes, chiefly in India. On a similar basis are the uses of ground mica (mixed with oil) as a lubricant for metal bearings; as a filler for rubber goods, etc.; and for decorative purposes—in wall paper, decorative paints, ornamental stone, etc.
Substitutes.
—No other substance possesses the combination of elasticity, toughness, flexibility, transparency, ability to withstand excessive heat and sudden changes in temperature, high dielectric strength, flatness and amenability to splitting into thin films, which belongs to mica.
For the vast variety of electrical equipment in which mica is used, no satisfactory substitute has been found. In the manufacture of certain low-tension condensers sheets of oiled paper have been used instead of mica films, but attempts to substitute this material more widely have met with little success. According to one report a compressed paper product called “Pertinax” was developed in Germany during the war which is claimed to be “most satisfactory” for all electrical purposes, even for the manufacture of high-tension condensers. The fact, however, that Germany was paying $75 a pound for mica from Norway, and continued to use mica in the manufacture of condensers for airplane magnetos, indicates that complete substitution was not possible.
For a great many glazing purposes it is possible to substitute heat-withstanding or non-shattering varieties of glass.