1、Designation: 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 adoption or, in the case of rev
2、ision, 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*1.1 This specification covers natural block mica2and micafilms (cut and uncut) suitable for use in the
3、 manufacture offixed mica-dielectric capacitors, based on electrical, visual, andphysical properties as determined by tests specified herein.1.2 The values stated in inch-pound units are to be regardedas standard.2. Referenced Documents2.1 ASTM Standards:3D149 Test Method for Dielectric Breakdown Vo
4、ltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD351 Classification for Natural Muscovite Block Mica andThins Based on Visual QualityD1082 Test Method for Dissipation Factor and Permittivity(Dielectric Constant) of Mica2.2 ASTM Adjuncts:Test electr
5、odesGrid test electrodes3. Terminology3.1 For definitions pertaining to this specification see Clas-sification D351.4. Significance and Use4.1 The properties included in this specification are thoserequired to identify the types of natural block mica and micafilms (cut and uncut) suitable for use in
6、 the manufacture offixed mica-dielectric capacitors. It is possible that other re-quirements will be necessary to identify particular character-istics. These will be added to the specification as their inclusionbecomes generally desirable, and the necessary test data andmethods become available. It
7、is possible that natural blockmica and mica films that do not conform to the requirements ofthis specification for capacitor use are capable of meeting therequirements for other critical electrical insulation purposes.4.2 The system of classifying electrical quality of naturalblock and mica films (c
8、ut and uncut) covered by this specifi-cation is based on a combination of electrical and physicalproperties, and visual qualities specified herein, which the micamust possess. This system differs radically from past practicesand previous concepts of mica quality for capacitor use. Theelectrical clas
9、sification system does not discriminate againstthe presence of spots and stains in even first quality electricallyselected mica, provided the mica conforms to specific andphysical requirements. Appreciable amounts of air inclusionsand waviness also are permitted in all electrical quality classes,pro
10、vided the mica meets specific electrical and physicalrequirements. Mica meeting these requirements is acceptablewithout regard to color or origin. However, mica meeting theseelectrical and physical requirements but having lower visualquality than that meeting the requirements for the visual qualityc
11、lassification is not considered generally as desirable.4.3 In capacitor fabrication, one or more pieces of cut filmor block mica having lower than required electrical andphysical properties will possibly prevent meeting the endrequirements of the capacitor. It is therefore required that eachpiece of
12、 block (cut) or film (cut or uncut), or both, be tested forthe electrical requirements and inspected for the visual require-ments listed in this specification.5. Forms5.1 This specification covers the following three forms ofnatural mica, suitable for use in the manufacture of mica-dielectric capaci
13、tors:5.1.1 Form 1Full-knife trimmed natural block mica 0.007to 0.035 in. (0.18 to 0.89 mm) in thickness.5.1.1.1 It is acceptable for a certain percentage of blockmica thinner than 0.007 in. to be accepted under thisspecification, upon agreement between the purchaser and themanufacturer.1This specifi
14、cation is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Products.Current edition approved Nov. 1, 2014. Published December 2014. Originallyapproved in 1943. Last previous e
15、dition approved in 2011 as D748 00 (2011).DOI: 10.1520/D0748-14.2Coutlee, K. G., “Electrical Quality Classification of Raw Mica by a Rapid,Direct-Reading Test Method,” Proceedings, ASTM, Vol 46, 1946, p. 1486.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custom
16、er Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
17、 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization T
18、echnical Barriers to Trade (TBT) Committee.15.1.2 Form 2Half-knife trimmed natural block mica 0.007to 0.035 in. in thickness.5.1.3 Form 3Films (cut or uncut) split or manufacturedfrom natural block mica in any range from 0.0008 up to andincluding 0.006 in. (0.020 to 0.15 mm).6. Grades (Sizes)6.1 For
19、 grades see Classification D351.7. Classes7.1 This specification covers the following four classes andsubdivisions of natural block mica or mica films. The class ofmica desired shall be specified by the purchaser. Block mica ormica films shall conform to all of the requirements of itsrespective clas
20、s, unless otherwise specified by the purchaser.7.1.1 Class C-1 SpecialClass C-1 special mica films, inaddition to having the highest Q obtainable for mica in themegacycle range, also have the highest Q generally obtainablefor mica in the audio frequency range (1000 min at 1 kHz).Such mica therefore
21、is particularly suitable for capacitorswhich must meet highest Q requirements at both high and lowfrequencies.7.1.2 Class C-1Class C-1 block mica or mica films havethe highest Q value obtainable for mica (2500 min at 1 MHz incapacitors) and are suitable for use in all sizes and types ofsilver and fo
22、il electrode, molded and clamped unit capacitors,including the most critical types, for use in high stability tunedcircuits, as well as high current radio frequency capacitors usedin radio transmitter circuits.NOTE 1Based4on commercial experience Class C-1 block mica ormica films are satisfactory fo
23、r the manufacture of all of these types of micacapacitors. However, it has been found that some “medium to heavy”air-stained mica will produce a slightly lower yield of highest stability andhigh current radio frequency types of capacitors, as well as a somewhatlower yield of satisfactory silver elec
24、trode mica laminations. Likewise, itis also possible that some “medium to heavy” wavy mica will alsoadversely influence the application of silver electrodes. In addition, thereis some possibility that excessive waviness will cause cracked laminationsin molded capacitors due to the high molding press
25、ures employed, thusmaking it less suitable from a stacking standpoint. Similarly, excessiveamounts of either air inclusions or waviness could cause some reductionin unit volume capacitance of foil electrode capacitors.7.1.3 Class C-2Class C-2 block mica and mica films havea high order of Q value (15
26、00 min at 1 MHz in capacitors) andare suitable for use in all sizes and types of silver and foilelectrode molded and clamped unit capacitors similar to thosespecified for Class C-1 mica. However, a certain percentage ofcapacitors made with Class C-2 block mica and films mayshow a somewhat higher tem
27、perature rise in transmitter typesthan capacitors made with Class C-1 block mica or mica films.7.1.4 Class C-3Class C-3 block mica and mica films havethe lowest Q value (200 min at 1 MHz in capacitors) of thethree classes covered by this specification. Such Q value,however, is sufficiently high to p
28、ermit this mica to be classedas a low-loss insulating material. This mica is particularlysuitable for use in foil electrode molded and clamped typecapacitors (Note 2) used in less critical circuits for blockingand coupling purposes where high Q value, high stability, andlow temperature coefficient a
29、re not required.NOTE 2Experience has shown that silver electrode molded capacitorsmade with Class C-3 mica, which contained slightly conducting spots andstains but contained “very slight” air inclusions and “nearly flat” waves,had temperature coefficient and capacitance stability characteristics jus
30、t asgood as that obtained with capacitors made with the best Class C-1 mica.8. Electrical and Physical Properties, and VisualQualities8.1 Natural block mica and mica films shall conform to therequirements as to electrical and physical properties and visualqualities as prescribed in Table 1. Visual q
31、ualities not coveredin this specification are permitted provided mica meets theelectrical and physical requirements.9. Test Methods9.1 The properties enumerated in this specification shall bedetermined in accordance with the following:9.2 Grading According to SizeClassification D351.9.3 Electrical C
32、onductivitySee Annex A1.NOTE 3For the purpose of this specification, electrical conductivity inspotted and stained areas of block mica is revealed when visible sparkingor glowing takes place inside or on the surface of the mica in the vicinityof the test probe, and not by actual puncture of the mica
33、 by thehigh-potential current. If actual puncture of the test specimen does takeplace this indicates the presence of mechanical faults, such as pinholes,tears, or cracks which extend completely through the mica. While this testmethod had been found suitable for controlling conductivity in spots ands
34、tains and dielectric weakness due to mechanical faults in block mica, aneven greater factor of safety will be realized if this flash test is applieddirectly to capacitor films. In this instance the purpose of the test is todetect dielectric weakness due to any cause.9.4 Q Value or Dissipation Factor
35、Test Method D1082 at1 MHz, or by the rapid, direct-reading method described inAppendix X1.NOTE 4In cases of dispute arising from borderline cases of Q value ordissipation factor and dielectric strength, the test specimens shall be bakedfor a minimum period of2hatatemperature of 121C (250F), and test
36、edimmediately upon cooling to room temperature.9.5 Dielectric StrengthTest Method D149,usingtheshort-time test with14-in. (6.4-mm) diameter electrodes in oil.9.6 Weight Loss on HeatingPreheat the test specimens inan oven at 121C (250F) for a minimum time of 2 h and thenweigh. Then heat the specimens
37、 in the oven at 600C (1110F)for 5 min and reweigh. Calculate the percentage loss in weightafter heating based on the weight of the specimen at the end ofthe 2-h preheating period.9.7 Thickness Uniformity (Films)Judge splitting qualityby the uniformity of thickness of films split from mica byviewing
38、between crossed polaroids.9.8 Visual QualitiesSee Classification D351.9.8.1 Air InclusionsReflected daylight or equivalent.9.8.2 Waves, Buckles, Ridges, and so forthReflected day-light or its equivalent where distortion of parallel and verticallines of reflected image, such as a window frame, can be
39、judged.4Coutlee, K. G., “Judging Mica Quality Electrically,” Transactions, Am. Inst.Electrical Engrs., Vol 64, 1945.D748 1429.8.3 Cracks, Tears, Pinholes, and StonesDetermine thepresence of such mechanical defects as cracks, tears, pinholes,and stones by the spark coil test as prescribed in Annex A1
40、,orby visual inspection as judged by transmitted daylight or itsequivalent.10. Precision and Bias10.1 This test method has been in use for many years, but noinformation has been presented to ASTM upon which to basea statement of precision or bias. No activity has been plannedto develop such informat
41、ion.11. Keywords11.1 block mica; capacitor; classes; dielectric strength; elec-trical conductivity; form; grades; mica; mica films; Q value;visual quality; weight lossTABLE 1 Electrical, Physical, and Visual Quality Requirements of Natural Block Mica and Mica Films for Use in CapacitorsClass C-1 Cla
42、ss C-2 Class C-3Electrical Properties:Conducting pathsAnone none noneQ value or dissipation factor at 1 MHz E-1BE-2BE-3BDielectric strength, minV/mil at 60 HzHaveragesingle100085010008501000850Dielectric constantCCCPhysical Properties:Weight loss on heating (5 min at 600 C), max % 0.2 0.2 0.2Thickne
43、ss uniformity (mica films)Dbest best intermediateTemperature coefficient of capacitance and retraceEEVisual Qualities:FAirinclusionsGHABCvery slightHslightImediumJvery slightHslightFmediumJvery slightHslightImediumJWavesK5ABCDnearlyflatslightmediumheavynearlyflatslightmediumheavynearlyflatslightmedi
44、umheavyCracks none none noneTears none none nonePin holes none none noneStones none none noneBuckles none none noneRidges none none noneAThis applies to the conductivity of visible spots and stains only and excludes air stains or air inclusions.BThe Q values or dissipation factor Q5S1dissipation fac
45、torDof block mica or mica films suitable for use in capacitors shall fall within specified electrical quality groups,based on end-use requirements, 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 correspon
46、ding scale readings of the vacuum-tube voltmeter when tested by the rapid, direct-reading method described in Appendix X1.CAs the dielectric constant of natural block mica suitable for use in capacitors is fairly uniform, no value is specified.DUntil definite values can be specified, the permissible
47、 amounts of such defects shall be agreed upon between the purchaser and the manufacturer.EIt has been found that the temperature coefficient 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 man
48、ufacturing technique than on any differences in the mica itself.FSee Classification D351.GThe amount of air inclusions shall not exceed the specified limits for each subclass. The permissible amount of air inclusions shall be stated by suffixing the appropriateletter (in other words, either A, B, C,
49、 or D) to the required electrical quality class.HFew and tiny in one fourth of usable area (must not contain air chains, and so forth).IIn one half of usable area (must not contain air chains, and so forth).JIn two thirds of usable areas.KThe waviness shall not exceed the specified limits for each subclass. The permissible amount of waves shall be stated by suffixing the appropriate letter (in other words,either A, B, C or D) to the letter denoting the amount of permissible air inclusions. For example, Class C-1 B A block mica or mica films denotes:C-1
