SILICONES

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03642A000700100011-1
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 20
• Document Creation Date: December 22, 2016
• Document Release Date: August 10, 2011
• Sequence Number: 11
• Publication Date: February 1, 1955
• Content Type: MISC

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CONFIDENTIAL
September 4, 1958
I C-' Y
In our recent conversations, you requested an explanation
of the comments contained in the patent and royalty report dated
April 18, 1958, on the patentability of the device conceived under
Task Order No. A, Work Order No. IX.
I have talked with Our Patent Section on this matter and
they indicated that the constant-temperature-environment device
conceived was the type of device that could be the subject of a
patent. We have no knowledge of an existing device, publication,
or patent that would bar the issuance of a patent on such a
device. As was indicated in the letter of April 18, no effort
has been made from a patent standpoint to uncover such information.
Our Patent Section has indicated that it is common practice to
survey the patent literature before filing an application, in
an effort to determine the novelty of the discovery in question.
You may want to have your patent people do this.
If you have any questions with regard to the above,
please let us know.
IDE
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coNFiDENTIAL
CONFIDENTIAL
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MATERIALS & METHODS
MANUAL No. 113
This is another in a series of
comprehensive articles on engineering
materials and their, processing. Each
is complete in itself. These special
sections provide the reader with use
ful data on characteristics of mate
rials or fabricated parts and on their
processing and applications.
by Kenneth Rose, Midwestern Editor, Materials & Methods
In the last'decade, a new group of materials has emerged
from the laboratories to become part of our everyday lives.
They are the silicon-base polymers, and they may be found
in a multitude of industrial and consumer products rang-
ing from aircraft gaskets to auto polishes. This manual
describes the significant properties and the most important
current applications of the "silicones", including-
Silicone Fluids E Silicone Resins
and Compounds ? Silicone Rubbers
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The element carbon has al-
ways been unique in chemistry
in that it has been possible to
build from it an infinite num-
ber of compounds by substitu-
tion and joining reactions. The
chemistry of the complex car-
bon compounds is called or-
ganic chemistry. Recent de-
velopments now make it possi-
ble to duplicate this chemistry
to some extent with the ele-
ment silicon which, like carbon,
is tetravalent. Polymerized
compounds of some complexity,
based upon a silicon-oxygen
linkage, have been developed,
and these organosilicon com-
^ THE TERM "SILICONES" is a
convenient designation for a di-
verse group of chemical com-
pounds having a silicon-oxygen
linkage somewhat analogous to
pounds are known as silicones.
Although the chemistry of
organosilicon compounds is
more than a hundred years
old, the production of commer-
cial silicones only began dur-
ing World War II with the for-
mation of the Dow Corning
Corp. as a jointly owned op-
eration of Dow Chemical Co.
and Corning Glass Works in
1943. All production at that
time was channeled into mili-
tary uses, but at the end of
the war fluid silicones became
generally available to industry.
By 1945, both Dow Corning
and General Electric Co. an-
nounced the development of
silicone rubbers, and in the fol-
lowing year General Electric
opened-its own silicone-produc-
ing plant. In 1949, Plaskon,
then a division of Libby-
Owens-Ford Glass Co., started
to use silicone-alkyd resins in
paints. About that same time,
Linde Air Products Co., a di-
vision of Union Carbide and
Carbon Corp., began pilot plant
production of silicones. Dow.
Corning, General Electric and
Linde Air Products are the
three producers of primary
silicones in the United States
today.
the carbon linkage in organic
compounds. Addition of organic
side-chains often produces a ma-
terial that is actually more or-
ganic than inorganic. Also, many
Significant
Major Current
Type
Forms
Properties
Applications
FLUIDS
Pure liquid or water
Wide range of viscosities,
Dampingfluids, hydraulic
("oils")
emulsion.
good heat stability, high
fluids, dielectric fluids,
flash points, low volatil-
water-repellents, mold
ity, low freezing points,
release agents, lubricants,
good dielectric proper-
antifoam agents, polishes
ties, wide useful temper-
or cleaners, immersion
ature ranges, good water
baths.
repellency, chemical in-
ertness.
COMPOUNDS
Fluid thickened with
Same as above. Do not
Lubricants, sealants,
("greases")
filler.
soften and flow readily at
packing impregnations,
elevated temperatures.
vibration dampers, mold
release agents, antifoam
agents, rust preventives.
RESINS
Solid in solvent solution
Good heat stability, good
Molded parts, electrical
or sometimes in water
dielectric properties, good
insulation impregnations,
emulsion. Formulated
water repellency, chemi-
electrical insulating lami-
(often with fillers and/or
cal inertness, good re-
nates, water-repellents,
organic materials) for
sistance to weathering
heat- and chemical-re-
molding, laminating, coat-
and ozone.
sistant coatings, mold
ing or foaming.
release agents, foamed
core structures.
RUBBERS
Solid gums, or com-
Retention of useful
Gaskets, electrical insula-
pounds containing fillers,
strength and flexibility
tion. Fabric coatings and
vulcanizing agents and
over long period at high
impregnations for both
additives. Rubber com-
and low temperature ex-
electrical and mechanical
pounds may be (1) solid
tremes, chemical inert-
applications, including
and formulated for mold-
ness, relatively good oil
gaskets, mats, belting,
ing, extruding, calender-
resistance, good dielec-
hose, sleeving, dia-
ing or sponging, (2)
tric properties, good re-
phragms. Sealing, calk-
in form of paste, or (3) in
sistance to weathering
ing and potting com-
solvent dispersion. Also
and ozone.
pounds.
plain or reinforced sheet,
tubing and extruded
shapes.
of the commercial silicones are
formulated by mixing them with
silica, soaps and other fillers.
Thus, the properties of materials
called "silicones" may vary over
a wide range. In general, how-
ever, silicones are chosen for
their:
1. Resistance to deterioration
at elevated temperatures. Many
types can withstand tempera-
tures of 500 F or higher for pro-
longed periods with little loss of
important properties.
2. Maintenance of properties
at low temperatures. Silicone
resins and rubbers retain flexi-
bility at low temperatures that
cause other resins and rubbers
to become brittle and useless.
Silicone fluids show little change
in viscosity in going from ordi-
nary temperatures to low tem-
peratures.
3. Long life. Silicones not
only stand up better than organic
materials under extreme tem-
peratures, but also last longer
than organic materials at inter-
mediate temperatures.
4. Chemical inertness. Incom-
patibility with many chemicals
is important in mold release
applications, defoaming, etc.
5. Excellent resistance to de-
terioration during prolonged out-
door exposure. Resistance to the
effects of sunlight and oxidation
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U
is important in paints, insula-
tion on electric wire, etc.
6. Good water repellency. Sili-
cone fluids and resins are used
on both organic and inorganic
materials where water repellency
is desired. Water repellency is
also important in connection
with other properties such as
dielectric strength.
Of even greater importance
than any single property is the
unique combination of proper-
ties. No other fluids have the
combination of good oxidation
resistance, low vapor pressure,
low freezing point, good heat
stability and flat.viscosity curve
that makes silicone fluids out-
standing for aircraft instru-
ments. No other resins or rub-
bers have the combination of
good dielectric strength, good
arc resistance, good heat stabil-
ity, outstanding resistance to
ozone and weathering, and good
low temperature properties that
make silicone resins and rubbers
excellent insulation for electrical
conductors.
Principal disadvantages of the
silicones are high cost, incom-
patibility with many other sub-
stances, some processing difficul-
ties and, in the rubbers, rela-
tively poor strength and extensi
bility. Also, silicones will burn,
and they are adversely affected
Silicone Fluids and Compounds
The silicone fluids or "oils"
are clear liquids having excellent
stability at elevated tempera-
tures, low freezing or "pour"
points, a wide range of viscosi-
ties from about 0.65 to higher
than 1,000,000 centistokes, and
only small change in viscosity
through a wide temperature
range. They have an oily feel,
but conventional types have little
lubricating ability and must be
used as lubricants only with
caution. They are nontoxic and
have little chemical reactivity,
yet they are effective as addi-
tives even in very small amounts.
They are colorless, or nearly so.
Silicone fluids may be classi-
fied in two composition groups :
the dimethyl silicones, and sili-
cones other than dimethyl. The
first group has two methyl
groups for each silicon atom. In
the second group some of the
methyl radicals are replaced by
another organic radical-some-
times ethyl but usually phenyl.
The phenyl types are stable at
higher temperatures and have
slightly better lubricity than the
dimethyl silicone fluids.
Silicone fluids are used as bulk
fluids, as films, and as additives
to other materials. Although
high in price;" the .. amount -re-
quired in many applications is
so small that overall cost is often
lower than that of less expen-
sive materials. In addition, of
course, silicone fluids often make
possible economical designs that
would otherwise be impossible.
Dimethyl silicones
The dimethyl silicone fluids
are known commercially as Dow
mum
Hot immersion bath for accelerated aging tests on magnesium at Dow
Chemical Co. utilizes high-phenyl silicone fluid. The silicone bath has oper-
ated continuously for three years and has provided a net saving, since the
previous inexpensive hydrocarbon oil bath had to be replaced each month.
(Dow Corning Corp.)
0
by many petroleum compounds,
particularly the aromatic hydro-
carbons used in aviation fuel.
Resistance to straight-chain hy-
drocarbon oils is good, however.
Chemical classification of the
silicones is difficult. In this arti-
cle chemical nomenclature has
been largely omitted, and the
silicones have been somewhat
arbitrarily classified according to
their physical state. Hence, five
groups are distinguished: fluids,
greases and other compounds,
resins, rubbers, and specialties.
Such a classification is common
in the industry and provides a
fairly convenient basis for con-
sidering specific applications.
Corning "200 Fluids", General
Electric SF-96 and Viscasil ser-
ies, and Linde L-series. These
materials can be specified by
means of the commercial desig-
nation, together with the desired
viscosity. Significant properties
are summarized below :
Heat stability-Stable for long
periods at 300 F if in contact
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with air, and at 400 F if pro-
tected from air. At 475 F in air,
viscosity shows considerable in-
crease within 12 hr, and fluid is
converted into, or coated with,
tough rubbery gel within 48 hr
(addition of antioxidant retards
gel formation). Heat in the
absence of oxygen breaks down
fluid into polymers of lower
molecular weight (slowly at 475
F, and rapidly above 650 F).
Boiling point-Lowest viscos-
ity fluids boil in the 275 to 350 F
range. Fluids with viscosity
above 50 cs. are practically un-
boilable even at reduced pres-
sures. Heated strongly long
enough they decompose without
boiling, but the lower-viscosity
decomposition products may boil.
Freezing ("pour") point-Most
dimethyl silicone fluids retain
useful fluidity at temperatures
no lower than -40 F, but some
low-viscosity fluids are useful at
temperatures of -100 F and lower.
Viscosity-temperature-Change
in viscosity over wide tempera-
ture range is much less than for
petroleum oils. For example,
over the temperature range from
-50 to 300 F, the viscosity of a
100-cs. fluid varies from 1000 to
25 cs. The change is small
enough so that the normal vis-
cosity index is not applicable and
a new viscosity-temperature co-
efficient has been established.
Viscosity breakdown-Good re-
sistance to viscosity breakdown
during prolonged exposure to
elevated temperatures. No meas-
urable shear breakdown in fluids
having viscosity less than about
1000 cs. Higher-viscosity fluids
show small drop in viscosity un-
der shear, but original viscosity
is reestablished when shear
ceases. Maximum of 10% drop
in viscosity reported for 16-hr
exposure.
Water resistance-Insoluble in
water but not impermeable to
water vapor.
Solvent resistance-Insoluble
in vegetable oils. Low viscosity
fluids are somewhat more soluble
in other organic solvents than
higher viscosity fluids. See ac-
companying list.
DAMPING FLUID. High-vis-
cosity fluid, together with fly-
wheel mechanism, absorbs tor-
sional vibration energy of
crank in diesel and automotive
engines. Drop of high-viscosity
fluid on pivot or spindle bear-
ings minimizes flutter of indi-
cating needle in automotive
and aircraft instruments.
HYDRAULIC FLUID subject
to considerable temperature
fluctuations, as in aircraft in-
struments and controls. Such
applications have been limited
because of certain lubrication
difficulties encountered in con-
ventional designs and because
of incompatibility of the fluid
with rubber seals. However,
special rubber compounds have
been developed for gaskets in
prolonged contact with silicone
fluids.
DIELECTRIC FLUID for
transformers. Relatively non-
inflammable fluid with low
vapor pressure makes it un-
necessary to keep transformers
outdoors for safety.
WATER-REPELLENT FILM
for wood, rubber, glass, ce-
ramics, and other solid sur-
faces. One familiar method
of application: impregnated
paper or "lens tissue" for
cleaning spectacles. However,
a much higher degree of water
repellency is provided by sili-
cone resins. Fluids also blended
or compounded with organic
resin in water-repellent film
for fabrics or leather. Silicone-
modified organic resin, when
cured, imparts smooth, resilient
"hand" to fabrics and increases
their tear and abrasion resist-
ance.
MOLD RELEASE AGENT
applied by wiping or spraying.
Widely used for long-lasting
release film on automotive tire
molds. Also used for glass
molding, plastics molding, shell
molding and die casting, es-
pecially of zinc parts that are
not to be painted. Often applied
most economically as water
emulsion. Silicone fluids elimi-
nate smoke and fumes result-
ing from carbonization of older
petroleum-type parting agents.
LUBRICANT for plastics and
sometimes rubber parts. Lubri-
cant for metals where rolling
friction is involved. Lubricant
for certain metallic combina-
tions where sliding friction is
involved. Light to moderate
loads only. Example: parking
meters. Also used for impreg-
nation of porous bronze bear-
ings. Cutting fluid for machin-
ing plastics.
ANTIFOAM AGENT in proc-
essing of petroleum oils, tars,
hydraulic fluids, syrups, latex
coatings, paper pulp slurries
and adhesives. Often used in
automotive crankcase oil to
reduce foaming caused by other
common additives. Not applic-
able to solvents for silicones.
Some silicone antifoam agents
contain a few percent of a
specially purified fine silica.
LUBRICATING FILM ON
GLASS. Reduces self-abrasion
of woven or unwoven fibers so
cloth or mat can withstand
repeated flattening without de-
struction. On glass bottles,
inside coating reduces cracking
due to impacts during filling
and allows contents to be re-
leased more readily. Outside
coating reduces scratching
caused by contact with other
bottles. Glass bottle coatings
applied simultaneously by va-
porizing fluid in oven.
ADDITIVE FOR RUBBER.
Incorporated by special tech-
niques into rubber, especially
butadiene-styrene and chloro-
prene synthetics, silicone fluid
improves abrasion resistance,
weather resistance and stabil-
ity at slightly elevated tem-
peratures.
POLISH OR CLEANER for
automobiles, furniture, win-
dows. Often combined with
waxes.
ADDITIVE FOR PAINT in
amounts of about 0.2%. Re-
duces pigment-floating tenden-
cy, aids gloss retention, acts as
antiflooding agent, and reduces
orange peel.
SPRINGS that utilize the com-
pressibility o si icon uids.
112 MATERIALS & METHODS
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SOME SOLVENTS FOR
(SILICONE FLUIDS
Amyl acetate Kerosene
Benzene Methylene chloride
Carbon tetrachloride Mineral spirits
Chloroform Naphtha
Cyclohexane Toluene
Ethylene dichloride Trichloroethylene
Gasoline Turpentine
Hexyl ether Xylene
PARTIAL SOLVENTS*
Acetone Ethyl alcohol
Butyl alcohol Isopropyl alcohol
Dioxane Orthodichlorobenzene
* Partial solvents only for silicone oils having
viscosity in 10-50 centipoises range.
Chemical resistance-General-
ly inert to dilute aqueous solu-
tions of acids and alkalies, par-
affin hydrocarbons. Strong re-
agents such as solid ferric or
aluminum chloride cause increase
in viscosity and finally gel for-
mation. Slowly destroyed by
concentrated sulfuric or phos-
phoric acid. Slowly oxidized by
concentrated nitric acid at ele-
vated temperatures. Decomposed
by gaseous hydrochloric acid or
chlorine.
Effect on materials-Do not
/ react with plastics, lacquers and
/ other organic coatings
Fluids
.
of low viscosity and low molecu-
lar weight are reported to cause
slight leaching of plasticizer and
some shrinkage in rubber sub-
jected to prolonged immersion.
Noncorrosive to metals. Pro-
longed contact with steel, alu-
minum, tin zinc, cadmium or
silver has no a ec on fluids.
Prolonged contact with lead or
tellurium at 400 F seems to in-
crease viscosity, and prolonged
contact with copper or selenium
seems to decrease viscosity
slightly.
Flammability-Can be ignited,
but will not support combustion
alone.
Dielectric properties - Vary
with viscosity. Dielectric con-
stant varies from about 2.2 to
2.8, and is little affected by
change in temperature or fre-
quency. Power factor, also little
affected by temperature, remains
low for frequencies up to 100
mc., then rises sharply. Volume
resistivity is approximately 1014
ohm-cm, and is nearly constant
up to about 400 F. Dielectric
strength at 10 mils has been re-
ported as 250 to 300 v per mil,
and at 100 mils on the order of
500 v per mil. However, values
as high as 35 to 40 kv have also
been reported for thoroughly-
dried fluids at a 100-mil gap.
Lubricating properties-Good
for rolling friction. For sliding
friction, lubricating ability of
dimethyl fluids varies widely wth
materials involved. Generally not
suitable for steel on steel, though
some light-load applications have
been successful. Not suitable for
steel shaft in graphite bearing.
Apparently satisfactory for zinc-
plated, chromium-plated, bronze
or cadmium-plated (at light
loads) shaft in steel bearing and
for steel shaft in babbitt, silver
or nylon bearing. Also suitable
for plastics and rubber bearing
combinations.
Compressibility-Low-viscosity
fluids more compressible than
mineral oils, glycerin and similar
fluids. Compressibility decreases
with increase in viscosity.
Other silicone fluids
The most important advantages
of phenyl-containing or diethyl
silicone fluids, compared to the
more common dimethyl fluids,
are greater heat stability and a
broader useful temperature
range. Some of these fluids have
a freezing or "pour" point as low
as -95 F combined with a flash
point of 550 F. As the accom-
COMPRESSIBILITY OF SILICONE FLUIDS
Compressibility
Type of Fluid
(Kinematic Viscosity, cs.)
Under
7100 psi
Under
35,000 psi
Under
284,000 psi
Under
568,000 psi
0.65
6.3
16.3
Freezes
-
2.0
4.9
14.3
31.5
36.9
100
4.5
12.7
28.6
34.0
1000
4.6
12.7
28.2
33.5
USES OF OTHER SILICONE FLUIDS
HOT IMMERSION BATH.
Examples : sterilizing fluid for
dental instruments that does
not cause rusting and does not
smoke when hot; laboratory
constant temperature bath;
calibration bath. A similar use:
heat exchange fluid.
LUBRICANT FOR METALS
over wider temperature range
than possible with dimethtyl
silicone fluids. Suitable for roll-
ing friction and, for certain
metallic combinations, sliding
friction. Light loads only. Ex-
amples: permanent lubrication
of electric clocks, electric
razors, scientific equipment.
One new fluid appears suitable
for steel-on-steel sliding fric-
tion applications, heretofore
not possible with silicones.
WATER-REPELLENT FILM
FOR FABRICS. Fluid and
resin combined in coating ma-
terial that must be set with
heat-a few minutes at 300 F
or less than a minute at higher
temperatures. Used for fab-
rics; also for paper used for
protection or interleaving of
asphalt packaging, pressure-
sensitive tapes, partially cured
rubber, etc.
DIFFUSION PUMP FLUID.
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Methyl silicone oil
Low-phenyl silicone oil
Medium-phenyl silicone oil
High-phenyl silicone oil
100 200 300 400 500
Temperature, F
Useful temperature ranges for silicone fluids.
KAMM
Relay made by Heinemann Elec-
tric Co. utilizes silicone fluid as
damping medium. (General Electric Co.)
Car polish is one of many prod-
ucts that have been improved by
silicone fluids. (Linde Air Products Co.)
panying chart indicates, many
are suitable for continuous use
at temperatures up to 500 F.
Some can be used at higher tem-
peratures for short periods or
where a brief service life is
acceptable. For example, high-
phenyl fluids have been used at
700 F where relubrication of
bearings was possible. Addition
of an antioxidant increases serv-
ice life, although the antioxidant
itself is eventually destroyed at
high temperatures.
Variation of viscosity with
temperature is generally greater
in phenyl-containing fluids, par-
ticularly in the high-phenyl
fluids, than in the dimethyl
fluids, but this variation is never
as large as in petroleum oils.
Phenyl-containing fluids are also
much more compatible with or-
ganic materials than are dime-
thyl fluids and, consequently, are
not nearly so suitable as mold
release agents or as lubricants
for plastics. They are also less
useful as polishes.
Because of the greater heat
stability and broader useful tem-
perature range, phenyl-contain-
ing fluids are sometimes pre-
ferred to dimethyl fluids as lub-
ricants despite a steeper temper-
ature-viscosity curve. In addi-
tion, a phenyl-containing fluid
recently announced appears to be
suitable for the common lubrica-
tion problem of steel-on-steel
sliding friction, a type of appli-
cation for which neither dime-
thyl nor phenyl-containing sili-
cone fluids have previously been
satisfactory. The new fluid is
reported to have a useful tem-
perature range from -100 to 500
F and a flatter viscosity curve
than most phenyl-containing
fluids. It can also be compounded
as a grease.
Silicone compounds
Silicone compounds or
"greases" are made by thicken-
ing silicone fluids by means of
small filler additions. Common
fillers are specially purified fine
synthetic silica, natural silicates
in the form of diatomaceous
earth, lithium soap and carbon
black. Both dimethyl and phenyl-
containing fluids are used in
compounds.
Useful temperature ranges for
silicone compounds. are similar
to those for the corresponding
silicone fluids. Compounds differ
from the fluids in that they can
be made so that they do not flow
readily at temperatures up to
375-400 F. Like the fluids, they
have good dielectric strength,
low volatility, chemical inertness,
and surface properties useful in
lubrication and defoaming.
Springs utilizing silicone fluids were developed by the Hydra Spring Div.
of Wales-Strippit Corp. for use in heavy-duty punches and machine tools.
They have almost 10% compressibility at 20,000 psi, and about the same
capacity as a conventional spring 12 times as large and five times as heavy.
(Dow Corning Corp.)
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USES OF SILICONE COMPOUNDS (Greases)
LUBRICANT. Dimethyl types
used especially for intermittent
motion in high-temperature
steam or corrosive environ-
ments. Examples: pipe line
valves, stopcocks.
LUBRICANT FOR METALS.
Low-phenyl and some dimethyl
types used especially in low
temperature environments, also
over broad temperature ranges
and at high temperatures. Ex-
amples: motor bearings, ball
bearings carrying light to mod-
erate loads, time clocks, radar
tuning devices, electricity me-
ters and microphone switches.
LUBRICANT FOR METALS.
Medium-phenyl types suitable
for especially wide variety of
uses, including high tempera-
ture-high speed applications,
contact with corrosive liquids
or atmospheres.
LUBRICANT FOR METALS.
High-phenyl types, compound-
Silicone Resins
Silicone resins make the
unique combination of proper-
ties characteristic of the silicone
family available to the broad
field known as "plastics." What
is more important thus far, sili-
cone resins, along with the com-
mercial development of glass
fibers and fabrics, have made
possible the advent of Class H
electrical insulation, capable of
long life at continuous operating
temperatures much higher than
are possible with Class A or B
insulation.
The most important proper-
ties of silicone resins are good
heat stability, good dielectric
properties, good water repel-
lancy, chemical inertness and
good resistance to weathering
and ozone. Since the resins are
often filled, reinforced, blended or
combined with other materials,
the properties of structures made
from silicone resins may depend a
great deal on the properties of the
other materials and on their
FEBRUARY, 1955
ed with carbon black, particu-
larly suitable for high tem-
perature-low speed applica-
tions. Can withstand 500 F
continuously, up to 1000 F for
short periods. Examples: bear-
ings in furnace cars, oven
doors and oven conveyors.
SEALANT for spark plugs,
switches, terminals and other
electrical connections in high-
flying military aircraft, X-ray
equipment, etc. Prevents mois-
ture absorption, corrosion, co-
rona discharge. Also sealant
for vacuum and distillation
equipment.
PACKING IMPREGNATION
to lengthen life of packing in
pumps handling corrosive chem-
icals.
VIBRATION DAMPER. Ex-
ample: phonograph pick-up.
MOLD RELEASE AGENT
Even though more costly, com-
pound sometimes preferred to
compatibility with the silicone
resins.
Generally, silicone resins can
be classified as molding resins,
laminating resins, coating res-
ins and foaming resins. The
resins themselves are ordinarily
supplied as solvent solutions or
water emulsions. Like the sili-
cone fluids and compounds, they
are high in cost and are used
only for special applications not
otherwise feasible or where im-
provement in performance is
sufficient to justify the addi-
tional materials cost.
Molding resins
Most thermosetting organic
moldings, such as the phenolics,
are not suitable for continuous
exposure to temperatures much
above 300 F. Silicone moldings,
therefore, are used primarily
in the 300-500 F temperature
range that is out of reach for
the organics.
A silicone molding compound
fluid. Similar uses: prevents
glue and resin from sticking to
press platens in manufacture
of plywood; prevents plastics
packaging film from sticking
to heating irons or heat-sealing
equipment.
ANTIFOAM AGENT used in
bottling soft drinks and chem-
icals, cooking varnishes, con-
centrating sugar, loading tank
cars with latex or tar, etc.
RUST PREVENTIVE. New
compound designed for protec-
tion of ferrous artillery com-
ponents during long storage is
expected to be useful for deli-
cate instruments that might be
adversely affected by ordinary
rust preventives.
LUBRICANT FOR RUBBER.
New compound has been devel-
oped for automotive door
weatherstrips, hood bumpers
and other parts made of
rubber.
212 300 400 500
Hottest Spot Temoeroture,F
Life expectancy of Class A, B and
H (silicones) insulation for various
"hottest spot" temperatures.
(Dow Corning Corp.)
is usually made by mixing filler
with a toluene or xylene solution
of the silicone resin, flashing
off the solvent under a par-
tial vacuum, drying the mixture
(about 10 min at 225 F) and
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breaking it up. Fillers are always
used. Because most applications
involve high temperatures, fillers
are limited to heat-stable mate-
rials such as silica, glass, asbes-
tos and mica. Of these, glass is
most common.
At present, the cost of a sili-
cone molding may vary consider-
ably depending on the source of
materials. Some compounds re-
quire extremely long post-cures
for optimum properties. A post-
cure cycle for such compounds is
given in the accompanying box
which outlines a typical molding
cycle. Other new compounds,
however, require only a 2-hr post-
cure at 300-400 F for optimum
properties and are usually not
post-cured at all unless a high
TYPICAL MOLDING
CYCLE FOR GLASS-
FILLED SILICONE RESIN
Molding temp
300-350 F
Molding pressure
1000-15,000
Curing time in mold
10-30 min
Mold shrinkage
0.1-0.8%
Postcure (oven)
16 hr at 200 F
2hrat260F
2 hr at 300 F
2 hr at 350 F
2 hr at 400 F
0.1%
TYPICAL PROPERTIES
OF GLASS-FILLED
SILICONE MOLDINGS
Specific Gravity
1.7-2.0
Tensile Strength
2000-6000 psi
Water Absorp, 24 hr
0.2-0.9%
Max Temp for Contin-
uous Exposure
450-570
Heat Distortion Temp 500-930 F
Dielectric Strength
at 60 cycles/sec
Dielectric Constant:
100-300 volts/mil
60 cycles/sec
3.2-5.0
1 megacycle/sec
3.2-5.0
Power Factor:
60 cycles/sec
0.002-0.007
1 megacycle/sec
0.002-0.007
Volume Resistivity 1013 ohm-cm
heat distortion temperature is
needed. Such compounds, with
molding cycles approaching those
for phenolics, seem likely to
broaden the industrial appli-
cations for silicone moldings.
Typical properties of a glass-
filled silicone molding are shown
in the accompanying table.
Laminating resins
Silicone laminates cost more
than organic thermosetting lam-
inates, and they are not as
strong as the organic laminates
at ordinary temperatures. How-
ever, the strength of most or-
ganic laminates drops off rapidly
above 300 F, whereas silicone
laminates retain most of their
strength at temperatures up to
500 F and above.
Like silicone moldings, there-
fore, silicone laminates are con-
fined primarily to applications
involving continuous exposure to
temperatures in the 300-500 F
range or brief exposures to
higher temperatures. They are
widely used for Class H electri-
cal insulation. Glass cloth is the
most common reinforcement, al-
though asbestos and mica are
also used.
Silicone laminates and molded
laminates are made by proced-
ures similar to those used for
organic laminates. Typical lam-
inating procedures and some prop-
erties of a typical laminate are
given in accompanying boxes.
One peculiar advantage of sil-
icone laminates as electrical in-
sulation in certain applications
is the electrically insulating ash
that remains even when the in-
sulation has been completely
burned. For example, the Navy
found that armored cable might
continue to function after a se-
vere local fire, thus allowing a
TYPICAL PROPERTIES
OF CURED SILICONE-
GLASS LAMINATES
Tensile strength 35-45,000 psi
Water absorp, 24 hr 0.05-0.7%
Dielectric str, % in. 360-420 v/mil
Power factor, 100 me 0.003
ship to return to base for re-
pairs under its own power.
Coating resins
Silicone and modified silicone
resins are widely used in paints,
as nonadhesive films, and as
water-repellent films.
Silicone coatings alone are
serviceable at temperatures up
to about 500 F. Aluminum-pig-
mented modified-silicone coatings
can be used at 1000 F and for
short periods as high as 1500 F.
At such temperatures, the sili-
cone film no longer exists as such
but the pigmented paint continues
to provide protection against oxi-
dation.
In "modified" paints, silicone
resins are combined with organic
resins, primarily alkyd resins.
The resins may be combined
merely by blending or by copoly-
merization. Silicone additions,
generally of 25% or more, im-
prove the heat stability, gloss re-
tention, non-yellowing properties
and water repellency of conven-
tional alkyd paints. Even a 5-10%
addition improves weather resist-
ance. Silicone-alkyd paints have
top service temperatures about
TYPICAL LAMINATING
PROCEDURE FOR
SILICONE-GLASS CLOTH
1. Remove any organic sizing
from glass cloth by heat-clean-
ing. 4
2. Immerse cloth in solvent solu-
tion of silicone laminating resin.
3. Air-dry impregnated cloth about
30 min.
4. Further dry impregnated cloth
5-10 min at about 225 F.
5. Lay up (or wind) impregnated
sheets to form sheet, rod, tube,
moldings, etc.
HIGH-PRESSURE:
6. Cure laminate 14 hr at 350
F under 900 psi, and cool 30
min under pressure.
7. Heat 15 hr at 200 F.
8. Raise temperature to 375 F
through 8 hr, and heat 16 hr
at 375 F.
9. Heat 4 hr at 480 F, and cool.
LOW-PRESSURE :
6. Cure laminate at 350 F under
contact pressure for 15-60 min,
depending on section thickness,
and cool.
7. Heat 16 hr at 200 F.
8. Raise temperature to 480 F
through 4 hr, and heat 80-150
hr at 480 F.
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0
Net contact heater made by
Pre-Fab Co. for melting 5-gal
drums of plastisol has nylon-re-
inforced glass cord insulation
impregnated with silicone resin
varnish. Device was originally de-
veloped to keep high altitude aerial
cameras and control mechanisms
operative in sub-zero environments.
(Dow Corning Corp.)
Electric motor emerges from dip
tank en route to baking oven where
silicone resin varnish will be cured.
Overall silicone coating is final step
in rewinding motor with Class H
insulation. (Linde Air Products Co.)
100 F lower than those for sili-
cone films alone. However, the
modified silicone films are more
easily applied and quicker drying
than the straight silicones.
Silicone and modified silicone
paints are applied preferably by
spraying. Roller coating and
especially brushing are not gen-
erally recommended. Optimum
properties are obtained by an
elevated temperature cure.
Straight silicone coatings may
d ES OF SILICONE RES N&
f l
? iNAtTE. nrimari1y .for. useeiin`,>:
th'e 300 500 F~ range. special!-3
MA spacers and bar er
sheets+m ry transor--mere, and
ftg
electric
mechanical supports VIP
Y 4 .. .ms st+...~,:~s
glass, asbestosi'or a mica glass
cloth ,sandwich increasI~per-
missible 3operating tempera-'
tares and therebymake possi-
ble smaller, lighter transform-
e s anmotorsffor given out
put It hasp ben !estimated
that although '-a',.,1:
motor costs about 75%
more than a~Class A or B mo-
'A 0
tor~ofthe same 'size, fits +cost
based *,on dollars ,pert horse 11
powerloutput aboutt the same
orj, ometimes less.
, :
SILICONE P NAT OR lVA~R'
on electric motors, circuit chas-
sis. Aluminum-pigmented mod-
ified-silicone paints especially
suitable for use in the 300-500
F range and for brief ex-
,,posures to temperatures as
iaa igiw as 1500;=F..' Examples:
andn furna#ces, steam ,pipes, ex-
hausr Wines .~ ands steriliziing
n yellowny
Beaters no
hide:
aament : 'Modified-silicone enamel
also use,'d aspwire` insulio
, eResults+ of oneiaeries,~of, tssrw
indicated thatiriduction m t rs.
wound with silicone-coated wire
had
and operating at 325-366P
the "same life` expectancy as
similar motors, wound' with
Class A insulation andoperat-
ing at about 190 F.
HEAT-RESISTANT. 'MOIkD
ING utilizing,+glass, asbestos or"
1 cw t`t'; l "fit ~' xy '
diatomaceous earth filler Ex-
amples : switch 'parts, "brush'
ring holders in ele'ctr'i'c}motors,
coil forms.
tr sheen
Expected annlications: cores'n
of "high-?temp,erature.w_struAc"-z,
cures.
MOLDER+E{LEASEAGENgT
solution Es `eci3 11"'~
4 p~ y - effectiveG
with metal patterns ; m. shell
moldings process ' ht? iei ,+ x-.
on bake y pans Vlasts for weeks,
ehminatingfost fiof mater
and labor rcquir d to grease"
pan}before, each'bake and pro
vidin net sa~tn~ng despite nn
? I P1 11 goods from' pan' much easier.
WxATER=RREPE
fCOANG for mnry and?
that ? is` permeae tto ter'
vapor and thus' reduces' con-
densation of moisture inside
walls.
WETTING AGENT. Exam-
pies., Coatuig'for alumma'gr`its
yep. I ' 4t i.
to improvebonding in resm-
bon~p grindngwheels ''Sizing'
for "glasscloth+~to~impioveadP' ~`
hesiontopolyesterresms in
low pr(ess~ure~la mates
S+PE;C AL ,A?PPLICIWTrI(O
chemical-resistant lectncam-
su anon for glass radiant heat
Se sulat one
ipata e
ng jpli~mrj-
,Unrdt~ctedi ;aluminum etched
away+ by caustic soda leav-
ing silicone insulated aluminum
A+D~DI~TdIV~EF~ORPIGMENT
'Ij
s,
Ito impro a dispersion paint
'STABLE MOLD N ,110.0 VI=
ganic
PU15Dt+base dwon1fo1
resin.': Now under.'development. '
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ffiffillill
Electric motor-How silicone fluids, greases, resins and rubbers increase
its efficiency. (General Electric Co.)
be cured in about 1 hr at 480 F
or 4 hr at 400 F. Lower tem-
peratures can be. used for the
modified silicones. Silicone and
modified silicone paints are often
cured automatically in service.
Silicone resin release films may
be applied from either solvent
solution or water emulsion and
cured by baking. They are used
for semi-permanent release appli-
cations, as on bakery pans.
Resin solutions or emulsions
for water repellency applications
contain about 5% or less solids as
applied and are used on non-flex-
ible surfaces. Films for masonry
and concrete generally cure at
ordinary temperatures.
Foaming resins
Foamable silicone resins, anal-
ogous to the foamable organic
resins, are available for the pro-
duction of low-density parts.
Silicone Rubbers
Like the other silicones, sili-
cone rubbers have an exception-
ally broad useful temperature
range compared with organic ma-
terials. Silicone rubbers not only
supplemented the resins in cre-
ating Class H electrical insula-
tion for use at high operating
temperatures but, at the other
extreme, provided the first prac-
tical answer to gasketing prob-
lems in high-altitude military
aircraft subject to prolonged sub-
zero temperatures. Whereas other
heat-resistant synthetic rubbers
have poor low temperature prop-
erties, silicone rubbers make it
possible to obtain good properties
at both ends of the temperature
scale in a single material.
Some of these silicone resins can
be foamed in place and can
therefore be used to form low-
density cores in relatively inac-
cessible cavities. Other resins
cannot be foamed in place but
can be used to make prefoamed
blocks and sheets which can be
formed with woodworking tools.
Both types of silicone foams are
produced by application of heat
at temperatures in the 260-360
Fil range.
Foamed silicone structures
can be produced in densities
ranging from 6 to 24 lb per cu
ft. They are reported to show
virtually no dimensional change
after 20 hr exposure at 700 F,
and less than 2% weight loss
after 220 hr at 570 F. Pre-
fo a in e d structures generally
have somewhat better strength
than foamed-in-place structures
at elevated temperatures. How-
ever, foamed-in-place structures
made from one resin retain good
compressive strength at temper-
atures as high as 500-600 F.
Moisture absorption of foamed
structures after exposure in air
at 96% relative humidity for 7
days has been reported as less
than 0.05%. Foamed silicones
are nonflammable.
For some time, silicone resin
formulations for foaming in
place were available only as two
separate components that had to
be mixed properly at time of
use. Recently, however, a pre-
mixed powder has been made
available. Shapes made from one
of these resins can be post-
formed considerably when heat-
ed to about 200 F.
Properties
The range of properties offered
by silicone rubbers is indicated by
the accompanying tables adapted
from AMS and ASTM specifica-
tions. These and other signifi-
cant properties are summarized
briefly below :
Heat stability-Maintain prop-
erties indefinitely at about 300 F.
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Type
Propertyb
3301B
(General
purpose)
3302B
(General
' purpose)
3303C
(General
purpose)
3304B
(Low com-
pression set)
3305C
(Low com-
pression set)
Hardness, durometer "A"
Tensile Strength (min)
psi
40 f 5
50 t 5
60 f 5
70 f 5
00
80 f 5
500
,
Elongation (min),%
500
250
500
200
400
100
5
60
60
Tear Resistance (min), lb/in.
55
35
35
25
25
Oil Resistance: after 70 hr in Change in Durometer "A" Hardness No.
ASTM Oil No. I at 350 F Reduction in Tensile Stren
th (max)
-15 to +5
50
-15 to +5
40
-10 to +5
20
-10 to +5
20
-10 to +5
10
g
, %
(ASTM D471-51T)? Reduction in Elongation (max), %
50
20
20
20
10
Change in Volume, %
0 to +15
0 to +15
0 to +10
0 to +10
0 to +10
Dry Heat Resistance: after 24 hr Change in Durometer "A" Hardness No.
0 to +10
0 to +10
0 to +10
0 to +10
0 to +10
at 450 F (ASTM D573-48)d Reduction in Tensile Strength (max), %
15
10
10
10
10
Reduction in Elongation (max), %
25
25
25
25
25
Compression Set: compressed Percent of Original Deflection (max)
22hr at 350 F (ASTM D395 49T
72?
72t
60t
30'
36'
,
Method B) Percent of Original Thickness (max)
Method
29?
22t
18t
86
9'
Temperature Brittleness
(ASTM D736-46T)
Pass 5 hr at
Pass 5 hr at
Pass 5 hr at
Pass 5 hr at
Pass 5 hr at
-85 F
-85 F
-70 F
-70 F
-70 F
? Adapted from Aeronautical Materials Specifications copyrighted 195 by Society of Automotive Engineers, Inc.
b Other requirements: satisfactory resistance to weathering, corrosion.
? Other requirements: no decomposition, no tackiness.
s Other requirements: no surface hardening, no cracking or checking when bent flat (90? on 8t radius for 8806C).
??t. ?. Compressed to 60%, 70% and 75% of original thickness, respectively.
At 400 F, hardness increases
gradually and elongation de-
creases. Tensile strength may
drop or increase slightly, depend-
ing on the particular material.
Changes are rather sharp dur-
ing first 20 days at temperature,
then level off, indicating reten-
tion of useful residual proper-
ties. At 480 F the same changes
occur, but the initial changes are
greater. Subjected to excessive
heat in air, silicone rubbers be-
come hard and dry and eventu-
ally decompose as brittle mate-
rials. Heated in the absence of
air, however, they become soft.
Low temperature flexibility-
Ordinarily retain flexibility down
to -70 F, and materials formu-
lated especially for low tempera-
ture service can be used at -130 F
or slightly below. Since low tem-
perature flexibility is obtained by
slight change in basic compo-
sition, not by addition of a
plasticizer, low-temperature rub-
bers retain good elevated tem-
perature properties. In ordinary
silicone rubbers, hardness starts
ASTM STANDARDS FOR SILICONE RUBBERS?
Grade
Specification
TA 505
TA 604
TA 704
TA 805
BASIC REQUIREMENTS
Durometer Hardness No.
Tensile Strength (min), psi
50 f 5
500
60 f 5
400
70 f 5
400
80 f 5
500
Ultimate Elongation (min), %
200
100
75
50
Change in Durometer Hardness No. (max)
+20
+20
+15
+15
Heat aged 70 hr at 450 F JChange in Tensile Strength (max), %
-30
-30
-25
-25
Change in Ultimate Elongation (max), %
-40
-50
-40
-40
SPECIAL REQUIREMENTS
Suffix B Compression set after 70 hr at 300 F (max), %
50b
40b
40b
40b
Change in Tensile Strength (max), %
Suffix E, (70 hr at 300 F Change in Ultimate Elongation (max), %
-20
-20
-20
-20
-20
-20
-20
-20
in ASTM Oil No. 1) Change in Durometer Hardness No. (max)
-15
-15
-15
-15
Change in Volume, %
Suffix Es (70 hr at 300 F Change in Durometer Hardness No. (max)
0 to +20
-30
0 to +20
-35
0 to +20
-40
0 to +20
-45
in ASTM Oil No. 3) Change in Volume, %
+60
+60
+60
+60
Suffix F2 (5 hr at -65 F)
Suffix L (168 hr in water R
in Durometer Hardness No. (max)
Pass
-10?
Pass
-10
Pass
-10
Pass
-10
at 158 F) JChange in Volume, %
ange
+100
+10
+10
+10
? Adapted from table on "Physical Requirements of Synthetic Rubber Compounds, Type T, Class TA, Temperature Resistant" in ASTM D786-6$aT (Rubber and
Synthetic Rubber Compounds for Automotive and Aeronautical Applications).
b Lower values can be obtained with sacrifice of tensile strength and elongation.
? These values can be met with sacrifice of tensile strength and elongation.
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Type
Property
Low Compres-
sion Set
(Class 300)
General
Purpose
(Class 400)
Extreme
Low Temp
(Class 500)
Hardness, Shore A durometer
50-80
50-90
40480b
Tear strength, lb/in.
30-50
50-75
50-75b
Tensile strength, psi
570-750
570-800'
700-840b
Elongation, %
175-100
370-70'
350-906
Compression set after 22 hr at 300 F, %
20-7
50-60
50-80
Brittle temp, (ASTM D 736, 5-hr soak), F
-80 to -65
-90 to -80
below -130 to -120
Stiffness temp, (ASTM D 797, 24-hr soak,
modulus = 10,000 psi), F
-50 to -45
-60 to -45
below -120 to -110
Increase in durometer hardness no. after
70 hr at 450 F (heat stability)
6-5
6-3
5-3
Increase in volume after 70 hr in ASTM
Oil No. I at 300 F (oil resistance), %
8-5
9-6
9-7
Increase in volume after 70 hr in water
at 212 F (water absorption), %
high to