ASTM D748-00(2011)
(Specification)Standard Specification for Natural Block Mica and Mica Films Suitable for Use in Fixed Mica-Dielectric Capacitors
Standard Specification for Natural Block Mica and Mica Films Suitable for Use in Fixed Mica-Dielectric Capacitors
ABSTRACT
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.
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 fo...
SCOPE
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.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D748 −00(Reapproved 2011)
Standard Specification for
Natural Block Mica and Mica Films Suitable for Use in Fixed
Mica-Dielectric Capacitors
This standard is issued under the fixed designation D748; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope films (cut and uncut) suitable for use in the manufacture of
2 fixed mica-dielectric capacitors. There may be other require-
1.1 This specification covers natural block mica and mica
ments necessary to identify particular characteristics. These
films (cut and uncut) suitable for use in the manufacture of
will be added to the specification as their inclusion becomes
fixedmica-dielectriccapacitors,basedonelectrical,visual,and
generally desirable, and the necessary test data and methods
physical properties as determined by tests specified herein.
become available. Natural block mica and mica films that do
1.2 The values stated in inch-pound units are to be regarded
not conform to the requirements of this specification for
as the standard.
capacitor use may well be capable of meeting the requirements
for other critical electrical insulation purposes.
2. Referenced Documents
3 4.2 The system of classifying electrical quality of natural
2.1 ASTM Standards:
block and mica films (cut and uncut) covered by this specifi-
D149 Test Method for Dielectric Breakdown Voltage and
cation is based on a combination of electrical and physical
Dielectric Strength of Solid Electrical Insulating Materials
properties,andvisualqualitiesspecifiedherein,whichthemica
at Commercial Power Frequencies
must possess. This system differs radically from past practices
D351 Classification for Natural Muscovite Block Mica and
and previous concepts of mica quality for capacitor use. The
Thins Based on Visual Quality
electrical classification system does not discriminate against
D1082 Test Method for Dissipation Factor and Permittivity
the presence of spots and stains in even first quality electrically
(Dielectric Constant) of Mica
selected mica, provided the mica conforms to specific and
2.2 ASTM Adjuncts:
4 physical requirements. Appreciable amounts of air inclusions
Test electrodes
and waviness also are permitted in all electrical quality classes,
Grid test electrodes
provided the mica meets specific electrical and physical
3. Terminology requirements. Mica meeting these requirements is acceptable
without regard to color or origin. However, mica meeting these
3.1 For definitions pertaining to this specification see Clas-
electrical and physical requirements but having lower visual
sification D351.
qualitythanthatmeetingtherequirementsforthevisualquality
4. Significance and Use classification is not considered generally as desirable.
4.1 The properties included in this specification are those 4.3 In capacitor fabrication, one or more pieces of cut film
required to identify the types of natural block mica and mica
or block mica having lower than required electrical and
physical properties may prevent meeting the end requirements
ofthecapacitor.Itisthereforerequiredthateachpieceofblock
This specification is under the jurisdiction of ASTM Committee D09 on
(cut) or film (cut or uncut), or both, be tested for the electrical
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.19 on Dielectric Sheet and Roll Products.
requirementsandinspectedforthevisualrequirementslistedin
Current edition approved April 1, 2011. Published April 2011. Originally
this specification.
{1
approved in 1943. Last previous edition approved in 2005 as D748 – 00 (2005)
. DOI: 10.1520/D0748-00R11.
Coutlee, K. G., “Electrical Quality Classification of Raw Mica by a Rapid, 5. Forms
Direct-Reading Test Method,” Proceedings, ASTM, Vol 46, 1946, p. 1486.
5.1 This specification covers the following three forms of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
natural mica, suitable for use in the manufacture of mica-
Standards volume information, refer to the standard’s Document Summary page on
dielectric capacitors:
the ASTM website.
4 5.1.1 Form 1—Full-knife trimmed natural block mica 0.007
Available from ASTM International Headquarters. Order Adjunct No.
ADJD074801. Original adjunct produced in 1953.
to 0.035 in. (0.18 to 0.89 mm) in thickness.
Available from ASTM International Headquarters. Order Adjunct No.
ADJD074802. Original adjucnt produced in 1965. NOTE 1—Acertain percentage of block mica thinner than 0.007 in. may
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D748−00 (2011)
be accepted under this specification, upon agreement between the pur-
suitable for use in foil electrode molded and clamped type
chaser and the manufacturer.
capacitors (Note 3) used in less critical circuits for blocking
5.1.2 Form2—Half-knifetrimmednaturalblockmica0.007 and coupling purposes where high Q value, high stability, and
to 0.035 in. in thickness. low temperature coefficient are not required.
5.1.3 Form 3—Films (cut or uncut) split or manufactured
NOTE 3—Experience has shown that silver electrode molded capacitors
from natural block mica in any range from 0.0008 up to and
made with Class C-3 mica which contained slightly conducting spots and
including 0.006 in. (0.020 to 0.15 mm).
stains but contained “very slight” air inclusions and “nearly flat” waves,
had temperature coefficient and capacitance stability characteristics just as
6. Grades (Sizes) good as that obtained with capacitors made with the best Class C-1 mica.
6.1 For grades see Classification D351.
8. Electrical and Physical Properties, and Visual
Qualities
7. Classes
8.1 Natural block mica and mica films shall conform to the
7.1 This specification covers the following four classes and
requirements as to electrical and physical properties and visual
subdivisions of natural block mica or mica films. The class of
qualities as prescribed in Table 1. Visual qualities not covered
mica desired shall be specified by the purchaser. Block mica or
in this specification are permitted provided mica meets the
mica films shall conform to all of the requirements of its
electrical and physical requirements.
respective class, unless otherwise specified by the purchaser.
7.1.1 Class C-1 Special—Class C-1 special mica films, in
9. Test Methods
addition to having the highest Q obtainable for mica in the
megacycle range also have the highest Q generally obtainable
9.1 The properties enumerated in this specification shall be
for mica in the audio frequency range (1000 min at 1 kHz).
determined in accordance with the following:
Such mica therefore is particularly suitable for capacitors
9.2 Grading According to Size—Classification D351.
which must meet highest Q requirements at both high and low
9.3 Electrical Conductivity—See Annex A1.
frequencies.
7.1.2 Class C-1—Class C-1 block mica or mica films have
NOTE 4—For the purpose of this specification, electrical conductivity in
the highestQ value obtainable for mica (2500 min at 1 MHz in spotted and stained areas of block mica is revealed when visible sparking
or glowing takes place inside or on the surface of the mica in the vicinity
capacitors)andissuitableforuseinallsizesandtypesofsilver
of the test probe and not by actual puncture of the mica by the
and foil electrode, molded and clamped unit capacitors, includ-
high-potential current. If actual puncture of the test specimen does take
ing the most critical types, for use in high stability tuned
place this indicates the presence of mechanical faults, such as pinholes,
circuits,aswellashighcurrentradiofrequencycapacitorsused
tears, or cracks which extend completely through the mica.While this test
method had been found suitable for controlling conductivity in spots and
in radio transmitter circuits.
stains and dielectric weakness due to mechanical faults in block mica, an
NOTE 2—Based on commerical experience Class C-1 block mica or
even greater factor of safety will be realized if this flash test is applied
micafilmsaresatisfactoryforthemanufactureofallofthesetypesofmica
directly to capacitor films. In this instance the purpose of the test is to
capacitors.However,ithasbeenfoundthat“mediumtoheavy”air-stained
detect dielectric weakness due to any cause.
mica may produce a slightly lower yield of highest stability and high
9.4 Q Value or Dissipation Factor— Test Method D1082 at
current radio frequency types of capacitors as well as a somewhat lower
yieldofsatisfactorysilverelectrodemicalaminations.Likewise,“medium 1 MHz, or by the rapid, direct-reading method described in
to heavy” wavy mica may also adversely influence the application of
Appendix X1.
silver electrodes. In addition, there is some possibility that excessive
NOTE 5—In cases of dispute arising from borderline cases ofQ value or
waviness may cause cracked laminations in molded capacitors due to the
high molding pressures employed and it may be less suitable from a dissipationfactoranddielectricstrength,thetestspecimensshallbebaked
foraminimumperiodof2hatatemperatureof121°C(250°F),andtested
stacking standpoint. Similarly, some reduction in unit volume capacitance
immediately upon cooling to room temperature.
offoilelectrodecapacitorsmayresultfromexcessiveamountsofeitherair
inclusions or waviness.
9.5 Dielectric Strength—Test Method D149,usingthe
7.1.3 ClassC-2—Class C-2 block mica and mica films have
short-time test with ⁄4-in. (6.4-mm) diameter electrodes in oil.
a high order of Q value (1500 min at 1 MHz in capacitors) and
9.6 Weight Loss on Heating—Preheat the test specimens in
are suitable for use in all sizes and types of silver and foil
an oven at 121°C (250°F) for a minimum time of 2 h and then
electrode molded and clamped unit capacitors similar to those
weigh. Then heat the specimens in the oven at 600°C (1110°F)
specified for Class C-1 mica. However, a certain percentage of
for 5 min and reweigh. Calculate the percentage loss in weight
capacitors made with Class C-2 block mica and films may
after heating based on the weight of the specimen at the end of
show a somewhat higher temperature rise in transmitter types
the 2-h preheating period.
than capacitors made with Class C-1 block mica or mica films.
9.7 Thickness [Uniformity (Films)]—Judge splitting quality
7.1.4 ClassC-3—Class C-3 block mica and mica films have
by the uniformity of thickness of films split from mica by
the lowest Q value (200 min at 1 MHz in capacitors) of the
viewing between crossed polaroids.
three classes covered by this specification. Such Q value,
however, is sufficiently high to permit this mica to be classed
9.8 Visual Qualities—See Classification D351.
as a low-loss insulating material. This mica is particularly
9.8.1 Air Inclusions—Reflected daylight or equivalent.
9.8.2 Waves,Buckles,Ridges,etc.—Reflected daylight or its
equivalent where distortion of parallel and vertical lines of
Coutlee, K. G., “Judging Mica Quality Electrically,” Transactions, Am. Inst.
Electrical Engrs., Vol 64, 1945. reflected image, such as a window frame, can be judged.
D748−00 (2011)
TABLE 1 Electrical, Physical, and Visual Quality Requirements of Natural Block Mica and Mica Films for Use in Capacitors
Class C-1 Class C-2 Class C-3
Electrical Properties:
A
Conducting paths none none none
B B B
Q value or dissipation factor at 1 MHz E-1 E-2 E-3
average
Dielectric strength, min 1000 1000 1000
H
V/mil at 60 Hz single 850 850 850
CCC
Dielectric constant
Physical Properties:
Weight loss on heating (5 min at 600 °C), max % 0.2 0.2 0.2
D
Thickness uniformity (mica films) best best intermediate
EE
Temperature coefficient of capacitance and retrace
F
Visual Qualities:
H H H
Air A very slight very slight very slight
I F I
G
slight slight slight
inclusions
B
J J J
H medium medium medium
C
A nearly nearly nearly
flatslight flatslight flatslight
B
medium medium medium
C
K
Waves heavy heavy heavy
D
Cracks none none none
Tears none none none
Pin holes none none none
Stones none none none
Buckles none none none
Ridges none none none
A
This applies to the conductivity of visible spots and stains only and excludes air stains or air inclusions.
B
The Q values or dissipation factor Q5 of block mica or mica films suitable for use in capacitors shall fall within specified electrical quality groups,
S D
dissipation factor
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 2
or the corresponding scale readings of the vacuum-tube voltmeter when tested by the rapid, direct-reading method described in Appendix X1.
C
As the dielectric 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 coefficient of capacitance and retrace of capacitors made with Classes C-1, C-2, and C-3 mica are more dependent on such factors
as 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 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.
H
Few and tiny in one fourth of usable area (must not contain air chains, etc.).
I
In one half of usable area (must not contain air chains, etc.).
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 A, B, C or D, as the case
may 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 A
Best electrical quality slight air inclusion in one half usuable area nearly flat waves
9.8.3 Cracks, Tears, Pinholes, and Stones—Determine the a statement of precision or bias. No activity has been planned
presence of such mechanical defects as cracks, tears, pinholes, to develop such information.
and stones by the spark coil test as prescribed in AnnexA1,or
by visual inspection as judged by transmitted daylight or its
11. Keywords
equivalent.
11.1 block mica; capacitor; classes; dielectric stren
...
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