1、Designation: D748 00 (Reapproved 2011)D748 14Standard Specification forNatural Block Mica and Mica Films Suitable for Use in FixedMica-Dielectric Capacitors1This standard is issued under the fixed designation D748; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This specification covers natural block mica2 and mica films (cut a
3、nd uncut) suitable for use in the manufacture of fixedmica-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 Documents2.1 ASTM Standards:3D149
4、Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials atCommercial Power FrequenciesD351 Classification for Natural Muscovite Block Mica and Thins Based on Visual QualityD1082 Test Method for Dissipation Factor and Permittivity (Dielectric Cons
5、tant) of Mica2.2 ASTM Adjuncts:Test electrodesGrid test electrodes3. Terminology3.1 For definitions pertaining to this specification see Classification D351.4. Significance and Use4.1 The properties included in this specification are those required to identify the types of natural block mica and mic
6、a films(cut and uncut) suitable for use in the manufacture of fixed mica-dielectric capacitors. There may be It is possible that otherrequirements will be necessary to identify particular characteristics. These will be added to the specification as their inclusionbecomes generally desirable, and the
7、 necessary test data and methods become available. Natural It is possible that natural blockmica and mica films that do not conform to the requirements of this specification for capacitor use may well be are capable ofmeeting the requirements for other critical electrical insulation purposes.4.2 The
8、 system of classifying electrical quality of natural block and mica films (cut and uncut) covered by this specification isbased 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
9、 and previous concepts of mica quality for capacitor use. The electricalclassification 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 i
10、nclusions and waviness also arepermitted in all electrical quality classes, provided the mica meets specific electrical and physical requirements. Mica meeting theserequirements is acceptable without regard to color or origin. However, mica meeting these electrical and physical requirements buthavin
11、g lower visual quality than that meeting the requirements for the visual quality classification is not considered generally asdesirable.1 This specification is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommit
12、teeD09.19 on Dielectric Sheet and Roll Products.Current edition approved April 1, 2011Nov. 1, 2014. Published April 2011December 2014. Originally approved in 1943. Last previous edition approved in 20052011 asD748 00 (2011). (2005) 1 . DOI: 10.1520/D0748-00R11.10.1520/D0748-14.2 Coutlee, K. G., “Ele
13、ctrical Quality Classification of Raw Mica by a Rapid, Direct-Reading Test Method,” Proceedings,ASTM, Vol 46, 1946, p. 1486.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, re
14、fer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all c
15、hanges accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100
16、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.3 In capacitor fabrication, one or more pieces of cut film or block mica having lower than required electrical and physicalproperties may will possibly prevent meeting the end requirements of the capacitor. It is there
17、fore 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 thisspecification.5. Forms5.1 This specification covers the following three forms of natural mica, suitable for use in the manufa
18、cture of mica-dielectriccapacitors:5.1.1 Form 1Full-knife trimmed natural block mica 0.007 to 0.035 in. (0.18 to 0.89 mm) in thickness.NOTE 1A certain percentage of block mica thinner than 0.007 in. may be accepted under this specification, upon agreement between the purchaserand the manufacturer.5.
19、1.1.1 It is acceptable for a certain percentage of block mica thinner than 0.007 in. to be accepted under this specification, uponagreement between the purchaser and the manufacturer.5.1.2 Form 2Half-knife trimmed natural block mica 0.007 to 0.035 in. in thickness.5.1.3 Form 3Films (cut or uncut) sp
20、lit or manufactured from natural block mica in any range from 0.0008 up to and including0.006 in. 0.006 in. (0.020 to 0.15 mm).0.15 mm).6. Grades (Sizes)6.1 For grades see Classification D351.7. Classes7.1 This specification covers the following four classes and subdivisions of natural block mica or
21、 mica films. The class of micadesired shall be specified by the purchaser. Block mica or mica films shall conform to all of the requirements of its respective class,unless otherwise specified by the purchaser.7.1.1 Class C-1 SpecialClass C-1 special mica films, in addition to having the highest Q ob
22、tainable for mica in the megacyclerange, also have the highest Q generally obtainable for mica in the audio frequency range (1000 min at 1 kHz). Such mica thereforeis particularly suitable for capacitors which must meet highest Q requirements at both high and low frequencies.7.1.2 Class C-1Class C-1
23、 block mica or mica films have the highest Q value obtainable for mica (2500 min at 1 MHz incapacitors) and isare suitable for use in all sizes and types of silver and foil electrode, molded and clamped unit capacitors,including the most critical types, for use in high stability tuned circuits, as w
24、ell as high current radio frequency capacitors usedin radio transmitter circuits.NOTE 1Based4 on commericalcommercial experience Class C-1 block mica or mica films are satisfactory for the manufacture of all of these typesof mica capacitors. However, it has been found that some “medium to heavy” air
25、-stained mica maywill produce a slightly lower yield of highest stabilityand high current radio frequency types of capacitors, as well as a somewhat lower yield of satisfactory silver electrode mica laminations. Likewise, itis also possible that some “medium to heavy” wavy mica maywill also adversel
26、y influence the application of silver electrodes. In addition, there is somepossibility that excessive waviness maywill cause cracked laminations in molded capacitors due to the high molding pressures employed and it may beemployed, thus making it less suitable from a stacking standpoint. Similarly,
27、 excessive amounts of either air inclusions or waviness could cause somereduction in unit volume capacitance of foil electrode capacitors may result from excessive amounts of either air inclusions or waviness.capacitors.7.1.3 Class C-2Class C-2 block mica and mica films have a high order of Q value
28、(1500 min at 1 MHz in capacitors) andare suitable for use in all sizes and types of silver and foil electrode molded and clamped unit capacitors similar to those specifiedfor Class C-1 mica. However, a certain percentage of capacitors made with Class C-2 block mica and films may show a somewhathighe
29、r temperature rise in transmitter types than capacitors made with Class C-1 block mica or mica films.7.1.4 Class C-3Class C-3 block mica and mica films have the lowest Q value (200 min at 1 MHz in capacitors) of the threeclasses covered by this specification. Such Q value, however, is sufficiently h
30、igh to permit this mica to be classed as a low-lossinsulating material. This mica is particularly suitable for use in foil electrode molded and clamped type capacitors (Note 32) usedin less critical circuits for blocking and coupling purposes where high Q value, high stability, and low temperature c
31、oefficient arenot required.NOTE 2Experience has shown that silver electrode molded capacitors made with Class C-3 mica, which contained slightly conducting spots and stainsbut contained “very slight” air inclusions and “nearly flat” waves, had temperature coefficient and capacitance stability charac
32、teristics just as good as thatobtained with capacitors made with the best Class C-1 mica.8. Electrical and Physical Properties, and Visual Qualities8.1 Natural block mica and mica films shall conform to the requirements as to electrical and physical properties and visualqualities as prescribed in Ta
33、ble 1. Visual qualities not covered in this specification are permitted provided mica meets the electricaland physical requirements.4 Coutlee, K. G., “Judging Mica Quality Electrically,” Transactions, Am. Inst. Electrical Engrs., Vol 64, 1945.D748 1429. Test Methods9.1 The properties enumerated in t
34、his specification shall be determined in accordance with the following:9.2 Grading According to SizeClassification D351.9.3 Electrical ConductivitySee Annex A1.NOTE 3For the purpose of this specification, electrical conductivity in spotted and stained areas of block mica is revealed when visible spa
35、rking orglowing takes place inside or on the surface of the mica in the vicinity of the test probe, and not by actual puncture of the mica by the high-potentialcurrent. If actual puncture of the test specimen does take place this indicates the presence of mechanical faults, such as pinholes, tears,
36、or cracks whichextend completely through the mica. While this test method had been found suitable for controlling conductivity in spots and stains and dielectricweakness due to mechanical faults in block mica, an even greater factor of safety will be realized if this flash test is applied directly t
37、o capacitor films.In this instance the purpose of the test is to detect dielectric weakness due to any cause.9.4 Q Value or Dissipation FactorTest Method D1082 at 1 MHz, or by the rapid, direct-reading method described inAppendix X1.NOTE 4In cases of dispute arising from borderline cases of Q value
38、or dissipation factor and dielectric strength, the test specimens shall be bakedfor a minimum period of 2 h at a temperature of 121C (250F), and tested immediately upon cooling to room temperature.9.5 Dielectric StrengthTest Method D149, using the short-time test with 14-in. (6.4-mm) diameter electr
39、odes in oil.TABLE 1 Electrical, Physical, and Visual Quality Requirements of Natural Block Mica and Mica Films for Use in CapacitorsClass C-1 Class C-2 Class C-3Electrical Properties:Conducting pathsA none none noneQ value or dissipation factor at 1 MHz E-1B E-2B E-3BDielectric strength, minV/mil at
40、 60 Hz Haveragesingle100085010008501000850Dielectric constant C C CPhysical Properties:Weight loss on heating (5 min at 600 C), max % 0.2 0.2 0.2Thickness uniformity (mica films)D best best intermediateTemperature coefficient of capacitance and retrace E EVisual Qualities:FAirinclusionsG HABCvery sl
41、ightHslightImediumJvery slightHslightFmediumJvery slightHslightImediumJWavesK 5ABCDnearlyflatslightmediumheavynearlyflatslightmediumheavynearlyflatslightmediumheavyCracks none none noneTears none none nonePin holes none none noneStones none none noneBuckles none none noneRidges none none noneA This
42、applies to the conductivity of visible spots and stains only and excludes air stains or air inclusions.B The Q values or dissipation factor Q5S 1dissipation factorD of block mica or mica films suitable for use in capacitors shall fall within specified electrical quality groups,based on end-use requi
43、rements, designated E-1 Special, E-1, E-2, or E-3. These quality groups shall conform to the Q or dissipation factor values prescribed in Table 2or the corresponding scale readings of the vacuum-tube voltmeter when tested by the rapid, direct-reading method described in Appendix X1.C As the dielectr
44、ic constant of natural block mica suitable for use in capacitors is fairly uniform, no value is specified.D Until definite values can be specified, the permissible amounts of such defects shall be agreed upon between the purchaser and the manufacturer.E It has been found that the temperature coeffic
45、ient of capacitance and retrace of capacitors made with Classes C-1, C-2, and C-3 mica are more dependent on such factorsas electrical and mechanical design and manufacturing technique than on any differences in the mica itself.F See Classification D351.G The amount of air inclusions shall not excee
46、d the specified limits for each subclass. The permissible amount of air inclusions shall be stated by suffixing the letterappropriate letter (in other words, either A, B, C, or D as the case may be, D) to the required electrical quality class.H Few and tiny in one fourth of usable area (must not con
47、tain air chains, etc.).and so forth).I In one half of usable area (must not contain air chains, etc.).and so forth).J In two thirds of usable areas.K The waviness shall not exceed the specified limits for each subclass. The permissible amount of waves shall be stated by suffixing the letter appropri
48、ate letter (in otherwords, either A, B, C or D, as the case may be, D) to the letter denoting the amount of permissible air inclusions. For example, Class C-1 B A block mica or mica filmsdenotes:C-1 B ABest electrical quality slight air inclusion in one half usuable area nearly flat wavesD748 1439.6
49、 Weight Loss on HeatingPreheat the test specimens in an oven at 121C (250F) for a minimum time of 2 h and then weigh.Then heat the specimens in the oven at 600C (1110F) for 5 min and reweigh. Calculate the percentage loss in weight after heatingbased on the weight of the specimen at the end of the 2-h preheating period.9.7 Thickness Uniformity (Films)Judge splitting quality by the uniformity of thickness of films split from mica by viewingbetween crossed polaroids.9.8 Visual QualitiesSee Classification D351.9.8.1 Air InclusionsReflected daylight or
