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Patented Dec. 31, 1946
‘Harold R. Feiehter, Canton, Ohio, assignor to
United States Quarry Tile Company, Canton,
Ohio, a corporation of Delaware
No Drawing. Application August 27, 1942,
Serial No. 456,414
1 Claim. (Cl. 106-66)
to attack by the lead compounds present in the
combustion‘ gases of high octane tetra ethyl lead
The discovery and invention relate in general
to compositions of matter for vitreous Products
and the like, and for vitri?able bodies and the
Mullite porcelains, composed chie?y of clay and
like, and methods of making the same.
The discovery and invention particularly re
silica minerals, such as sillimanite, ?red together
at a temperature of approximately 2700” F., de-v
velop into strong crystalline structures having im
late to substances requiring high temperatures ,
for vitri?cation, and more parti?ularly t0 compo
proved mechanical strength and improved hot di
electric strength as compared to ordinary porce
lains, but still lacking su?icient thermal conduc
tivity and chemical stability necessary for use as
spark plug insulators in high compression aircraft
sitions of‘ matter including aluminum oxide.
Products made by vitrifying or ?ring at high
temperatures body compositions having as their
principal constituent aluminum oxide are used as
spark plug insulators, particularly for aircraft
engines, wear resistant and similar parts having
It has been determined to be desirable for use
extreme hardness, and for other purposes.
Spark plug insulators adapted for use in a high 15 as spark plug insulators in high compression air
-craft motors to provide a ?red composition of
compression internal combustion engine such as
matter having the greatest attainable combina
an aircraft engine or motor become increasingly
tion of the following properties:
di?icult to produce, the higher the compression
1. vitreousness to a high degree and extremely
of the engine, and the tendency is always to in
crease the compression of an aircraft engine 20 low porosity;
whenever possible.
ohms at 1000° F.;
Mica has been'used for the insulators of air
3. Resistance to thermal shock so as not to be
craft engine spark plugs, but most mica having
subject to ‘fracture when quenched in water at
the required special mineral and physical prop
room temperature from a temperature of 400° F.;
erties must be imported into the United States,
4. Mechanical strength greater ‘than 100,000
the forming and machining of mica insulators is
relatively costly, and the quality of mica insular _ lbs. per sq. in. in compression;
5. Thermal expansion of 7.00x10-“;
tors is not always satisfactory.
Mica being a natural mineral and contain
ing a varying amount of chemically combined wa
ter of crystallization in its composition, tends to
decompose when heated giving up its water of
crystallization and deteriorating in crystalline
6. High thermal conductivity;
7. Hardness and resistance to wear such that
the hardness is 9 or over On Mohs’ scale;
8. Inert with common acids at normal temper
atures, that is notsubj'ect to appreciable loss in
form to that of an anhydrous powder, and thus . hot or cold HCl, H2SO4,‘HNO3, or ,HaPOr; '
deteriorates rapidly from its initial characteris 35 9. Resistant to corrosion in molten lead oxide;
10. Absorptive Of radiant energy.
tics when used as a spark plug insulator in a. high
compression engine.
Pure aluminum oxide has been found to attain
a combination of the above properties satisfactory
for use in the vitri?ed state as insulators for air
tory as an insulator for the spark plugs for the 40 craft engine spark plugs.
The commercial production ofvitri?ed articles
motors, and other substanceshave been used in
With the development of higher compression
motors, mica becomes increasingly unsatisfac
cluding ordinary porcelain and mullite porcelain.
Ordinary porcelain, such as a composition of
feldspar, pure clay, and ?int ?red to a tempera
ture of 2300" to 2500° F., constitutes a superior
form of burned clay product, but for spark plug
I from pure aluminum oxide, or alumina, has not
been found practicable because of'the extremely "
high temperatures required to bring about the
condensationof a purealumina body to the point
of complete vitreousness freev from porosity, and
because the lack of plasticity of pure alumina ren
insulator use has relatively poor resistance to the
ders its formation as a body into any particular
thermal shock imposed upon the spark plug insu
shape such as that of an insulator very di?icult.
lators of a high compression motor.
By the present discovery and invention, it has
Furthermore ordinary porcelain has a low di 50
been found that the presence of a very small
electric strength, particularly when hot, and is
in fact an electrical conductor when hot. " Ordi
amount of substantially any other'inorganic sub
nary porcelain also has insu?icient thermal con
ductivity for use as a satisfactory aircraft engine
stance in a body otherwise including substantially
all alumina will produce a pronounced depression
spark plug insulator, and furthermore is subject
in the temperature necessary fcrthe vitri?cation
of the body composition, and will improve the
It is preferable that the total number of added
forming adaptability.
substances be more than three.
All the added substances are selected from the
following metals in their oxide or other compound
It has further been discovered that a combina
tion of a relatively great variety of other sub
stances to a total of a very small amount in a
body, the remainder of which is substantially all
only one or two other substances with alumina
10 Barium
are used for the body.
It has further been discovered that by using a
combination of four or more other substances
alumina, has a more pronounced e?ect in de
pressing the vitri?cation temperature than when _
with alumina in the body; that the total amount
of the added substances can be kept very low in
proportion to the alumina and that in this way 15 Caesium
the properties of the body and the ?red product
are predominately those of alumina, and stability
is attained in the production of the ?red prod
ucts without the sacri?ce of any substantial
amount of the desired properties of the major in 20 Columbium
gredient alumina.
Plotting the eil'ects of the various added sub
stances on a phase rule diagram reveals a level
ling of! of the effects through the combination of
the various added ingredients, so that instead of 25 Gold
sharp changes affecting the combination, the
changes are more gradual and the firing range of
the combination is greatly extended and sta
Furthermore, the addition of a relatively great 30 Lead
Zinc '
variety of substances to the predominant alumina
provides a factor of safety against the variations
that normally exist in the commercial forms of
the substances, so that a more stable and de
The above metals are included in groups 1, 2, 3,
pendable body is obtained through the use in the 35 4, 5, 6, '1, 8 of the periodic table of elements of
body composition of a wide variety of substances
added to the alumina.
While it has been found that the presence of
Also it has been discovered that regardless of
the alkalis of group 1 of the periodic table of
the speci?ed substance added to the alumina, if
40 elements, particularly sodium and potassium, are
added in minute amount, the effect on the alu
mina will be about in the same degree. The
alumina in the resultant mixture or body is over
whelmingly the predominant material, and the
resultant body has substantially the properties of
that of pure alumina.
In attaining a combination of the highest de
gree of the above enumerated properties for a
deleterious to the ?red composition in causing a
reduction in hot dielectric strength, it is a prac
tical impossibility to avoid traces to measurable
amounts of these substances in the body.
Furthermore, it has been found that a pro
portion of these alkalis not in excess of 95% does
not sufficiently deteriorate the body dielectrically
to cause any seriously harmful results, and that
their presence in combination with other sub
engine spark plug insulators, it has been found
stances, particularly the alkaline earths of group
preferable to use body combination of aluminum
2 of the periodic table of elements and boron,
oxide with the addition of chromium oxide in a
develops low fusion combinations and intensi?es
minor quantity plus the addition of small quan
the ?uxing action of the mass. Therefore allow
titles of other inorganic substances preferably the
ance for the presence of these alkaline substances
oxides of the other metals. '
is made in the particular body compositions of
In particular the chromium oxide produces in 55 the present discovery and invention.
the ?red article a strong pink or rose color at
The alumina in the body composition or mix
room temperature. Without the chromium oxide
ture should be in excessof 92% and preferably
the ?red articles are white in color. The strong
in excess of 95%. It has been found impractical
from a ?ring standpoint to vitrify mixtures much
pink or rose color produced in the ?red article
in excess of 95% alumina. However the proper
by the chromium oxide changes when hot, as
ties of the product are much improved as the
when the article is in use as an insulator in an
alumina is increased, and laboratory products
aircraft engine spark plug, to black which im
have been made at temperatures of 3400' I". in
parts to the insulator the property of greater heat
which compositions as high as 98% of alumina
absorption by the absorption of radiant heat from
were vitri?ed, yielding an excellent product, but
the gases of combustion in the engine cylinder,
impractical to produce in commercial practice
the radiant heat being otherwise reflected by
present because of the exceedingly high tem
white or coated bodies.
perature required.
To the predominant alumina, the chromium
The alumina is preferably in excess of 99%
oxide is added and small quantities of other sub 70 A120: and as stated free from alkalis in excess
stances selected from a wide variety of metallic
¢Bf5ég5% and also free from silica in excess of
oxides and compounds.
The total amount of the added substances
The silica content of the body is minimisedby
should preferably not exceed 8% of the total
avoiding silica contamination in the processing,
?red composition of matter for use as aircraft
composition, the remaining 92% being alumina, 76 andbyusingsilicatesaslittleaspossibleinthe
various eutectics are active, whereas with a lesser
body composition. Where calcium, magnesium,
number, the range is correspondingly shorter.
The above described Body Composition I after
chromium, beryllium, and barium are used in the
body composition, the forms of these substances
may be in the compounds including fluorides,’
the second ?ring to a temperature of over 3000°
F., produces a ?red product consisting of alumi
num in excess of 92 %, and the oxides of the added
carbonates, oxides, phosphates, sulphates, etc., to
avoid the silicates. All the added substances
should be preferably in the dehydrated form, and
free from the alkalis, lithium, sodium, and potas
metals, silicon, calcium, chromium, and magnesi
um, the ?red product having desired properties
as set forth herein for use as an aircraft spark
However, by the introduction of fluorides into 10 plug insulator, and other purposes.
Examples of other body compositions, made
the body composition, silicates of the metals, such
according to the present discovery and invention,
as magnesium in the form of talc may be used to
and processed as set forth herein to produce the
ya limited extent without harmful results from
improved ?red product including alumina and
subsequent silica contamination, because the flu
orine set free by the reaction resulting from the 15 other metallic oxides, are as follows:
?ring of the body composition combines with the
Body Composition II
silica to form gaseous silicon tetra?uoride which
escapes and constitutes a volatilization of the
Describing one particular composition of mat
ter or Body Composition I of the discovery and
invention and the method of making the same,
the principal ingredient of the body composition
Per cent
Alumina, aluminum oxide _____________ __ 92.25
Talc, magnesium silicate _______________ __ 1.25
20 Fluorspar, calcium fluoride _____________ .. 2.00
Clay, aluminum silicate ________________ __ 3.50
Chromium oxide ______________________ __ 1.00
is calcined aluminum oxide, which before use in
the compounding of the body is highly re?ned
and freed of soluble impurities by lixiviation after
being ground to a sub-microscopic grain size.
To 92 parts by weight of this puri?ed and
?nely ground alumina A1203 is added and thor
oughly mixed 11/2 parts of calcium ?uoride CaFz
and 1 1/2 parts magnesium phosphate
Mg: (P04) 2.4H2O
4 parts of plastic ball clay ahoazsioaznzoand
1 part of chromic oxide CraOa.
In the grinding of the alumina to sub-micro
Body Composition III
Per cent
Alumina, aluminum oxide ______________ __ 91.68
Talc, magnesium silicate _______________ _. 1.25
30 Whiting, calcium carbonate ____________ __ 2.57
Clay, aluminum silicate ________________ __ 3.50
Chromium oxide
scopic grain size quartz stones are generally used
as grinding media, and in the grinding the abra
siveness of the calcined alumina on the quartz
grinding stones causes about 11/2 to 2% of silica
to be ground into the alumina so that the alumina 40
after grinding has a composition of 98 to 981/2%
A120: and 11/2 to 2% SiOz.
In the preferred manner of grinding the alumi
na for the bodies of the present invention, a
Body Composition IV
Per cent
Alumina, aluminum oxide ______________ __ 92.04
Talc, magnesium silicate _______________ __ 1.25
vBarium carbonate _____________________ __
Whiting, calcium carbonate ____________ __
Clay, aluminum silicate ________________ __
Chromium oxide _____________________ __
Beryllium silicate _____________________ __
are formed of ?red alumina, thereby avoiding the
The embodiments of the compositions of matter
pick-up of silica in the ground alumina.
and the method steps of making the same de
It has further been discovered that the initial
scribed herein are by'way of example, and the
calcination of the ?uxing ingredients alone or in
scope of the present discovery and invention is
combination with Part or all of the alumina is
not limited to the same or to the particular de
desirable before the ?nal body is formed and the
tails thereof, but is commensurate with any, and
?nal ?ring effected.
all novel subject matter contained herein which
rubber‘ lined mill is used, and the grinding balls
Eutectics are formed between alumina and a
may at any time properly under the United States
combination of various other substances. How
patent laws be set forth in the claims hereof or
ever the formation of these eutectics requires ini
originating herein, and the elements of any such
tially a very high temperature, at which point the
claims are intended to include their reasonable
?ring range of the mixture is very short due to
the sudden depression of the melting point at the
I claim:
temperature of the formation of the eutectics.
A body composition. of matter, for a ?red
When however the mixture is fused or calcined 60 vitreous product, including the following com
and then ground and re-f‘ormed, as the ?nal body
pounds in parts by weight:
composition, upon the second heating, the sinter
ing point is reached at a much lower temperature
' because of the previously formed eutectics.
A combination of many ingredients yields a
Calcium ?uoride, CaF: ___________________ __ 1.5
Magnesium phosphate, Mga(PO4)2.4HzO_____ 1.5
superior result than when only few are used, since
Plastic ball clay, A1203.2S102.2H2O ________ __
the eutectics formed between alumina and a
wide variety of substances in combination pro
vides a wide range of temperature over which the
Chromic oxide, CraO: ____________________ ....
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