Active Standard ASTM D748 | Developed by Subcommittee: D09.19
Book of Standards Volume: 10.01
Historical (view previous versions of standard)
This specification covers the electrical, visual, and physical properties of natural blocks and films made from mica that are suitable for use in fixed mica-dielectric capacitors. The materials under this specification are of three forms and four classes. Samples should be taken and tested according to the test methods prescribed here. All samples should adhere to the specified values of conducting path, Q value, dielectric constant, weight loss on heating, thickness uniformity, temperature coefficient of capacitance and retrace, and amount of air inclusions, waves, cracks, tears, pin holes, stones, buckles, and ridges.
This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.
Significance and Use
The properties included in this specification are those required to identify the types of natural block mica and mica films (cut and uncut) suitable for use in the manufacture of fixed mica-dielectric capacitors. There may be other requirements necessary to identify particular characteristics. These will be added to the specification as their inclusion becomes generally desirable, and the necessary test data and methods become available. Natural block mica and mica films that do not conform to the requirements of this specification for capacitor use may well be capable of meeting the requirements for other critical electrical insulation purposes.
The system of classifying electrical quality of natural block and mica films (cut and uncut) covered by this specification is based on a combination of electrical and physical properties, and visual qualities specified herein, which the mica must possess. This system differs radically from past practices and previous concepts of mica quality for capacitor use. The electrical classification system does not discriminate against the presence of spots and stains in even first quality electrically selected mica, provided the mica conforms to specific and physical requirements. Appreciable amounts of air inclusions and waviness also are permitted in all electrical quality classes, provided the mica meets specific electrical and physical requirements. Mica meeting these requirements is acceptable without regard to color or origin. However, mica meeting these electrical and physical requirements but having lower visual quality than that meeting the requirements for the visual quality classification is not considered generally as desirable.
In capacitor fabrication, one or more pieces of cut film or block mica having lower than required electrical and physical properties may prevent meeting the end requirements of the capacitor. It is therefore required that each piece of block (cut) or film (cut or uncut), or both, be tested for the electrical requirements and inspected for the visual requirements listed in this specification.
1.1 This specification covers natural block mica and mica films (cut and uncut) suitable for use in the manufacture of fixed mica-dielectric capacitors, based on electrical, visual, and physical properties as determined by tests specified herein.
1.2 The values stated in inch-pound units are to be regarded as the standard.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D149 Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies
D351 Classification for Natural Muscovite Block Mica and Thins Based on Visual Quality
D1082 Test Method for Dissipation Factor and Permittivity (Dielectric Constant) of Mica
ICS Number Code 29.035.50 (Mica based insulating materials)