1、Designation: D 748 00 (Reapproved 2005)e1An American National StandardStandard Specification forNatural Block Mica and Mica Films Suitable for Use in FixedMica-Dielectric Capacitors1This standard is issued under the fixed designation D 748; the number immediately following the designation indicates
2、the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEAdjunct references were corrected editorially in Apri
3、l 2006.1. Scope1.1 This specification covers natural block mica2and micafilms (cut and uncut) suitable for use in the 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
4、are to be regardedas the standard.2. Referenced Documents2.1 ASTM Standards:3D 149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD 351 Classification for Natural Muscovite Block Mica andThins Based on Visual
5、 QualityD 1082 Test Method for Dissipation Factor and Permittivity(Dielectric Constant) of Mica2.2 ASTM Adjuncts:Test electrodes4Grid test electrodes53. Terminology3.1 For definitions pertaining to this specification see Clas-sification D 351.4. Significance and Use4.1 The properties included in thi
6、s specification are thoserequired to identify the types of natural block mica and micafilms (cut and uncut) suitable for use in the manufacture offixed mica-dielectric capacitors. There may be other require-ments necessary to identify particular characteristics. Thesewill be added to the specificati
7、on as their inclusion becomesgenerally desirable, and the necessary test data and methodsbecome available. Natural block mica and mica films that donot conform to the requirements of this specification forcapacitor use may well be capable of meeting the requirementsfor other critical electrical insu
8、lation purposes.4.2 The system of classifying electrical quality of naturalblock and mica films (cut 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 radica
9、lly from past practicesand previous concepts of mica quality for capacitor use. Theelectrical classification system does not discriminate againstthe presence of spots and stains in even first quality electricallyselected mica, provided the mica conforms to specific andphysical requirements. Apprecia
10、ble amounts of air inclusionsand waviness also are permitted in all electrical quality classes,provided the mica meets specific electrical and physicalrequirements. Mica meeting these requirements is acceptablewithout regard to color or origin. However, mica meeting theseelectrical and physical requ
11、irements but having lower visualquality than that meeting the requirements for the visual qualityclassification 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 may prevent
12、meeting the end requirementsof the capacitor. It is therefore required that each piece of block(cut) or film (cut or uncut), or both, be tested for the electricalrequirements and inspected for the visual requirements listed inthis specification.1This specification is under the jurisdiction of ASTM C
13、ommittee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.19 on Dielectric Sheet and Roll Products.Current edition approved Sept. 10, 2000. Published November 2000. Originallyapproved in 1943. Last previous edition approved in 1994 as D 748 71
14、(1994)1.2Coutlee, 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 Customer Service at serviceastm.org. For Annual Book of ASTMSt
15、andards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from ASTM International Headquarters. Order Adjunct No.ADJD074801. Original adjunct produced in 1953.5Available from ASTM International Headquarters. Order Adjunct No.ADJD074802. Original adjucnt p
16、roduced in 1965.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Forms5.1 This specification covers the following three forms ofnatural mica, suitable for use in the manufacture of mica-dielectric capacitors:5.1.1 Form 1Full-knife
17、trimmed natural block mica 0.007to 0.035 in. (0.18 to 0.89 mm) in thickness.NOTE 1Acertain percentage of block mica thinner than 0.007 in. maybe accepted under this specification, upon agreement between the pur-chaser and the manufacturer.5.1.2 Form 2Half-knife trimmed natural block mica0.007 to 0.0
18、35 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 grades see Classification D 351.7. Classes7.1 This specification covers the following four classes andsu
19、bdivisions 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 class, unless otherwise specified by the purchaser.7.1.1 Class C-1 SpecialClass C-1 special mica films, inad
20、dition 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 is particularly suitable for capacitorswhich must meet highest Q requirements at both high and lowfrequen
21、cies.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 is suitable for use in all sizes and types of silverand foil electrode, molded and clamped unit capacitors, includ-ing the most critical types, for use in high stab
22、ility tunedcircuits, as well as high current radio frequency capacitors usedin radio transmitter circuits.NOTE 2Based6on commerical experience Class C-1 block mica ormica films are satisfactory for the manufacture of all of these types of micacapacitors. However, it has been found that “medium to he
23、avy” air-stainedmica may produce a slightly lower yield of highest stability and highcurrent radio frequency types of capacitors as well as a somewhat loweryield of satisfactory silver electrode mica laminations. Likewise, “mediumto heavy” wavy mica may also adversely influence the application ofsil
24、ver electrodes. In addition, there is some possibility that excessivewaviness may cause cracked laminations in molded capacitors due to thehigh molding pressures employed and it may be less suitable from astacking standpoint. Similarly, some reduction in unit volume capacitanceof foil electrode capa
25、citors may result from excessive amounts of either airinclusions or waviness.7.1.3 Class C-2Class C-2 block mica and mica films havea high order of Q value (1500 min at 1 MHz in capacitors) andare suitable for use in all sizes and types of silver and foilelectrode molded and clamped unit capacitors
26、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 temperature 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 f
27、ilms 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 permit this mica to be classedas a low-loss insulating material. This mica is particularlysuitable for use in foil electrode molded and clampe
28、d typecapacitors (Note 3) used in less critical circuits for blockingand coupling purposes where high Q value, high stability, andlow temperature coefficient are not required.NOTE 3Experience has shown that silver electrode molded capacitorsmade with Class C-3 mica which contained slightly conductin
29、g spots andstains but contained“ very slight” air inclusions and “nearly flat” waves,had temperature coefficient and capacitance stability characteristics just asgood as that obtained with capacitors made with the best Class C-1 mica.8. Electrical and Physical Properties, and VisualQualities8.1 Natu
30、ral block mica and mica films shall conform to therequirements as to electrical and physical properties and visualqualities as prescribed in Table 1. Visual qualities not coveredin this specification are permitted provided mica meets theelectrical and physical requirements.9. Test Methods9.1 The pro
31、perties enumerated in this specification shall bedetermined in accordance with the following:9.2 Grading According to SizeClassification D 351.9.3 Electrical ConductivitySee Annex A1.NOTE 4For the purpose of this specification, electrical conductivity inspotted and stained areas of block mica is rev
32、ealed 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 by thehigh-potential current. If actual puncture of the test specimen does takeplace this indicates the presence of mechanical faults, such a
33、s pinholes,tears, or cracks which extend completely through the mica. While this testmethod had been found suitable for controlling conductivity in spots andstains and dielectric weakness due to mechanical faults in block mica, aneven greater factor of safety will be realized if this flash test is a
34、pplieddirectly 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 Test Method D 1082 at1 MHz, or by the rapid, direct-reading method described inAppendix X1.NOTE 5In cases of dispute arising from borderline
35、cases of Q value ordissipation factor and dielectric strength, the test specimens shall be bakedfor a minimum period of2hatatemperature of 121 C (250 F), andtested immediately upon cooling to room temperature.9.5 Dielectric StrengthTest Method D 149, using theshort-time test with14-in. (6.4-mm) diam
36、eter electrodes in oil.9.6 Weight Loss on HeatingPreheat the test specimens inan oven at 121 C (250 F) for a minimum time of 2 h and thenweigh. Then heat the specimens in the oven at 600 C (1110 F)for 5 min and reweigh. Calculate the percentage loss in weightafter heating based on the weight of the
37、specimen at the end ofthe 2-h preheating period.6Coutlee, K. G., “Judging Mica Quality Electrically,” Transactions, Am. Inst.Electrical Engrs., Vol 64, 1945.D 748 00 (2005)e129.7 Thickness Uniformity (Films)Judge splitting qualityby the uniformity of thickness of films split from mica byviewing betw
38、een crossed polaroids.9.8 Visual QualitiesSee Classification D 351.9.8.1 Air InclusionsReflected daylight or equivalent.9.8.2 Waves, Buckles, Ridges, etc.Reflected daylight or itsequivalent where distortion of parallel and vertical lines ofreflected image, such as a window frame, can be judged.9.8.3
39、 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,orby visual inspection as judged by transmitted daylight or itsequivalent.10. Precision and Bias10.1 This test method has been i
40、n 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 information.11. Keywords11.1 block mica; capacitor; classes; dielectric strength; elec-trical conductivity; form; grades; mica; mica film
41、s; 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 Class C-2 Class C-3Electrical Properties:Conducting pathsAnone none noneQ value or dissipation factor at 1 MHz E-1BE-2BE-3BDielectri
42、c strength, minV/mil at 60 HzHaveragesingle100085010008501000850Dielectric constantCCCPhysical Properties:Weight loss on heating (5 min at 600 C), max % 0.2 0.2 0.2Thickness uniformity (mica films)Dbest best intermediateTemperature coefficient of capacitance and retraceEEVisual Qualities:FAirinclusi
43、onsGHABCvery slightHslightImediumJvery slightHslightFmediumJvery slightHslightImediumJWavesK5ABCDnearlyflatslightmediumheavynearlyflatslightmediumheavynearlyflatslightmediumheavyCracks none none noneTears none none nonePin holes none none noneStones none none noneBuckles none none noneRidges none no
44、ne noneAThis applies to the conductivity of visible spots and stains only and excludes air stains or air inclusions.BThe Q values or dissipation factor Q =S1dissipation factorDof block mica or mica films suitable for use in capacitors shall fall within specified electrical quality groups,based on en
45、d-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 corresponding scale readings of the vacuum-tube voltmeter when tested by the rapid, direct-reading method described in Appendix X1.CAs th
46、e 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 amounts of such defects shall be agreed upon between the purchaser and the manufacturer.EIt has been found that the temperature
47、 coefficient of capacitance and retrace of capacitors made with Classes C-1, C-2, and C-3 mica are more dependent on suchfactors as electrical and mechanical design and manufacturing technique than on any differences in the mica itself.FSee Classification D 351.GThe amount of air inclusions shall no
48、t exceed the specified limits for each subclass. The permissible amount of air inclusions shall be stated by suffixing the letter A,B, C, or D as the case may be, to the required electrical quality class.HFew and tiny in one fourth of usable area (must not contain air chains, etc.).IIn one half of u
49、sable area (must not contain air chains, etc.).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 letter A, B, C or D, as the casemay be, 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 B ABest electrical quality slight air inclusion in one half usuable area nearly flat wavesD 748 00 (2005)e13ANNEX(Mandatory Information)A1. METHOD OF TEST FOR CONDUCTING P
