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Патент USA US3022189

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United States Patent ()
3,922,17 9
Patented Feb. 20, mm
1.
2
3,022,179
ly formed, which requires only a small amount of energy,
supplied by the thermal treatment, to be converted from
CERAMIC MATERIAL AND METHOD OF
MAKlNG THE SAME
an amorphous, vitreous phase to a crystalline ceramic
phase by a process of auto-crystallization.
The invention is further signi?cant in that the composi
tion employed does not, after being cast, tend to rapidly‘
crystallize or devitrify under ordinary cooling procedures
as is characteristic of known types of ceramic-forming
William J. Morrissey, Pitts?eld, Mass., assignor to Gen
eral Electric Company, a corporation of New York
No Drawing. Filed Sept. 23, 1959, Ser. No. 841,678
4 Claims. (Cl. 106—39)
The present invention relates to the preparation of
ceramic products, and more particularly to an improved
process for making crystalline ceramic products of high
mechanical strength and good electrical properties.
compositions, and elaborate procedures to avoid uncon
trolled devitri?cation are therefore unnecessary.
The composition of the barium ceramic material pro
duced in accordance with the invention is as follows, the
Ceramic materials such as porcelain, alumina, and the
approximate ranges of the'constituent amounts being in
like have been found advantageous for use as electrical
percent by weight:
insulating material where high strength coupled with good
"
Percent
15
electricalinsulating properties are desirable. A di?iculty
in the use of the known materials of this type, however, has
been the relatively complicated and expensive processes
MgO
__
SiOg
__
BaO
_
__
_
’
__
_
'
3-35
__
'
'
25-50‘
3-35
necessary to fabricate such materials in the desired prod
FluXing agent __________ _'_Q _________ __'______. l0—35
uct con?guration. Such processes normally entail the use 20
of elevated ?ring temperatures and extremely high mold
As used herein, “?uxing agents” is intended to mean
ing pressure to properly compact and harden the material
glass modi?ers which can improve the glass properties or
and mold it in the desired shape. While glass-forming
the properties of the ?nal product, or which can improve
mixtures have been readily formed into insulating prod
the melting characteristics of the glass compositions, as
ucts of desired shape by simple casting techniques, such a 25 well understood in the art.
procedure is not effective or practical with porcelain or
Fluxmg agents which may be suitably used in the above
other known ceramic type compositions. For one thing,
composition include, but are not limited to, MgF2, B203,
the ceramic compositions would require. extremely high
A1203, LiZO, NagO, K20, K2SlF6 and Al2(SiF6)3, and coin
temperatures, e.g., of the order of‘ 1800° C., to make
them suiiiciently ?uid for casting purposes. A further dif—
?culty is that such compositions, even if'made su?iciently '
binations thereof.
The following are examples of compositions which
have produced satisfactory results in accordance with the
molten for casting, would tend to crystallize immediately
invention, it being understood that the following speci?c
upon being poured into a mold, giving rise to a process of
compositions are given for illustration only and are not
devitri?cation which is di?icult to control. The usual
intended to limit the scope of the invention.
e?ect of such rapid crystallization or devitri?cation is the 35
formation of crystals which are relatively large and non
Example I
uniform in size, and consequently the mechanical and elec
trical qualities of the ?nal ceramic product are much less
Batch Material
favorable than those obtained in products composed of
small, uniformly sized, compactly arranged crystals.
Batch,
‘
Percent
Product Product,
Material
Percent
v40
It is an object of the present invention to provide hard,
dense, ceramic products having high mechanical strength
and good electrical properties by ‘a simpli?ed process
which avoids the above disadvantages of the known meth
ods for making ceramic products.
45
Magnesium Oxide ____________________ __
22. 2
MgO
25. 0
Barium Carbonate_ _ _-_
_
11. 4
BaO
10. 0
Magnesium Flu0ride___
_
6. 2
MgFg
_
6. 5
LizO
3.0
_
19. 5
sic:
40. 0
Kaolin ________________________________ __
34. 2
A1303
15. 0
Lithium Carbonate_____
Flint_____________ __
7. 0
It is another object of the invention to provide a method
of making ceramic products of the above type which is
simple and economical, and is readily carried out to pro~
The above composition produced a pale brown, hard,
duce ceramic products of any desired con?guration.
dense ceramic body and had a melting temperature of
It is still another object of the invention to provide a 50 about 1375” C. The initial crystallization temperature
composition of material which is adapted to produce
was about 800° C. and the optimum crystal growth tem
ceramic products by simple casting techniques.
perature was 1050” C. In the above composition 18%
It is a further object of the invention to provide a bari
SiOZ was derived from the kaolin.
um ceramic body which is adapted to be made by the
above-described process.
Example 11'
55
The above objects and others which will be apparent
from the following description and appended claims, are
attained in accordance with the invention by forming a
melt of a composition comprising MgO, SiOZ, B210, and
a ?uXing agent, in proper proportions as hereinafter more 60
fully described, cooling the melt to arrest the formation
of crystals therein and forming thereby an amorphous,
vitreous material, and thereafter heating the thus formed
vitreous material for converting it to a micro-crystalline
barium ceramic ‘body composed predominantly of a 65
homogeneous mass of minute, randomly oriented crystals.
Batch Material
Magnesium Oxide ____________________ __
Batch,
Product Product,
Percent
Material Percent
3. 5
MgO
4. 1
Barium Carbonate.“
Magnesium Fluoride
Lithium Carbonate
34.1
16. 1
6. 4
BaO
MgFz
L120
30.8
18. 8
3. 0
KiiOlill __________ __
Fhnt ___________ __
l9. 2
20. 7
Also:
SiO:
8. 8
34. 5
The above composition, which had a melting point of
In accordance with the present invention, it is unnec
about 1350° 0, yielded a white, hard, dense barium
essaryto incorporate a nucleating agent in the molten
ceramic body. The initial crystallization temperature was
composition to induce the nucleation or growth of crystals
during the subsequent thermal treatment of the vitreous 70 about 850° C. and the optimum crystal growth tempera
material. The composition ingredients and proportions
there‘of‘are‘such that a metastable glass material is initial
, ture was about 1050° C. In ‘the above composition 10.2%’
SiOz was derived from the kaolin.
3,022,179
,
3
4
Example 111
Batch Material
1400“ C. andan oft-white ceramic body was produced.
Batch,
The initial crystal growth temperature was 850° C. and
the optimum growth temperature was about 1050° C.
Product Product,
Percent Mammal Percent .
‘ .
'
22.4
“SI-g0
BaO
2:2
32.9
Miangnesmm Oxide -------------------- ___________________ __
.
Barium_Garbonate _____ -_
1£§?1%§§$u<g§,{§f;;§f_;;; ____________ __
‘Kaolin
'
‘It will be understood that the oxides contained in the
5
products of the above examples may be introduced as pure
. 15- 0
20.0
40.0
compounds or as minerals containing two or more of the
oxides. For example, as already indicated, the kaohn
151%’
5:8
shown above may be used for introducing both A1203
A120;
15.0
102
V
.
_
e
,
and part of the S102.
I.
.
Talc may be used to yield both
l0 MgO and SiO-;, and mullitemay be used to yield both
The above composition had a melting point of about
1375° C. and yielded a pale ‘brown, hard ceramic body.
The initial crystallization temperature was 850° C., and
an optimum crystal growth temperature of 1050° C. In '
A1203 and SiO%. Many other types of minerals could
‘be used to provide the necessary oxide components.
made on typical products obtained by the com
posltlons and process of the invention showed that then‘
this composition 17.7 % SiOz was derived from the kaolin. 15 mechanical strength and electrical properties were, in gen
Exam ,2 IV
eral, at least equivalent, and in some cases superior to that
p
.
of high grade electrical porcelain. Of particular signi?
,
'
Batch Matenal
'
cance is the excellent electrical properties of the described
113612313 {fgi‘rlfé Igé’gg?' '
'
Magnesium Oxide ____________________ _-
21.7'
iiii‘i?r??ii?ééiiijjj
Kia<1111iiI1---6--,-----t-~-L
--
um among 9 """""""""" "
_
_ _
-
.MgO
24.0
590° C-
181g Mir,
1210
Ohms, under high and low voltages at different temper
33-2
14-8
$0.1
rnuunan?mt. ........ -
product and the marked thermal stability as shown by the
20 electrical resistance properties at temperatures up'to even
go;
.338
‘$119;
'
12
_
‘
.
_
_
'
re ared from the com osition of Exam le I:
p p
p
'
o
' The
samecrystal
as thosegrowth
of the preceding
temperatures
example.
were substantially
In this composi~
the 30
p
R
Temperature
_
V
45x10‘.
.
.
2x102.
Batch, Product Product,
Percent Material Percent
Magnesium Queen-..“ .-__-_.--_--
27.i
Mgo
glgllgflg'c'gr'ggga'gen
2::
£1281},
1532(2)“
Magnesium Flu0ride-.__
..... --
5.4
MgFz
hither'er;1;a;1a:.::::::-.---._-:::::::
32:2 ‘35%
-
'
'
1'3‘
0-33
20.0
X-ray diffraction analysis made of the products of the
33:8
present invention indicates that the ceramic material is
6.0
composed of a micro-crystalline mass containing barlum
1313 4° 38 a component of the crystal structure; However, the
'
The melting temperature of the above composition was
>1425 ‘' C. and a brown, hard ceramic product was ob
tained. The initial crystallization temperature was about
950° C. and the optimum growth temperature was about
105 0° C. The kaolin in this composition yielded 16.7%
SiO2.
I
50° ‘T- 13-0
1b
15x 0.
20x10“.
.
Batch Material
I
85 "- D-C-
tion, the kaolin contributed 16.7 % SiO,;.
‘
Example V
,
“Kg
atures obtained from a typical recrystallized barium ce
C. and a brown, dense ceramic product was obtained.
'
'
'25 ramic product of the present invention, this product being
This composition had a melting temperature of 1400"
~
_
The fOl‘IOWm-g illustrates the resistance values, in meg- ‘
pattern ‘for these crystals was not mdenta?able m terms of
known crystalline material and its exact crystal structure
is not known. The crystals appear, in an examination by
a re?ected light microscopy, to be platy, but somewhat
needlelike radiating from common centers forming clusters
in a. ‘very ?ne matrix.
The following is a typical process for making the ce
ramic material of the invention and is applicable in par
ticular to the composition of Example I, it being under
50 stood that variations may be made in the speci?c pro
Batch, Product Product,
cedure and values set forth herein without departing from
Percent Material Percent
the inventive. concept.
The raw materials of the batch composition, ?nely di
23 0
MgO
26.0
Example VI '
Batch Material
Magnesium Oxide ____________________ __
Flin _____________ __
-_.-
__-
19 3
Slot
41.0
Barman Carbonate".
5 5
13210
5.0
Magnesium Fluoride
7 1
MgFg
8.0
Lithium Carbonate.
Kaolin
8 8
36 3
M10
A1203
4. 0
16.0
The above composition had a melting temperature of
vided by a ball
or the like, are mixed in the proper
55 proportions and melted in an electric furnace at a temper
ature in the vicinity of 1300“ C. A centrifugal steel mold
is prepared for producing a bushing con?guration of the
melt, and the necessary metal hardware is placed in the
mold ‘for embedding in the ?nal product. With the mold
about 1400“ C. and’ a brown ceramic product was ob 60 pro-heated to a temperature of about ZOO-300° C. the
tained. The initial crystallization growth temperature
was about 850° C. and the optimum growth temperature
was about 1050° C. In this composition, 19.2% Si02
was obtained from the kaolin.
Batch,
Magnesium Oxide.-
24. 0
The mold con
65 so that the molten contents take on the con?guration of
Example VII . ', .
Percent
terial at this stage was about 1375° C.
taining the molten material therein is spun about its axis
'
Batch Material, .
molten batch composition is poured therein to a predeter
mined level. The casting temperature of the molten ma
the mold. The material is allowed to cool in the mold
Product Product,
Material Percent
MgO
25. 4
to below'the annealing temperature, e.-g., about 700° C.,
that is to say, to a temperature at which the molten ma
terial becomes sufficiently solidi?ed to prevent its slumping
70 in the mold and to ensure su?icient rigidity to provide a
self-supporting cast product.
Of particular signi?cance in accordance with the inven
Boric Acid ____________________________ __
2.0
B103
_ 1.1
tion is the arresting of crystallization of the molten ma
terial by such cooling to a temperature at which the amor
The melting temperature of-the above composition was 75 phous material becomes extremely viscous or almost solidi
Flint ___________ __
44. 0
Barium Carbonat
Magnesium Fluoride-
_
SiO;
46. 5
20. 0
BaO
16. 4
10.0
MgF;
10. 6
,
3,022,179
5
5
?ed. This prevents the formation of large crystals of non
What I claim as new and desire to secure by Letters
Patent of the United States is:
uniform size which would otherwise occur to produce what
is known as devitri?cation, a cnystallizing action which is
not readily controlled and which yields crystals of a type
1. A hard, dense, mechanically strong electrically in
sulating ceramic material formed of a substantially homo
geneous microcrystalline mass composed essentially of
and arrangement which are not desired for the purposes
of the present invention.
synthetic barium-containing crystals, said material having
With the cast material thus cooled, the melted amor
the following approximate composition in percent by
phous article is removed from the mold, placed in an
weight:
annealing furnace at 700° C., and retained therein for a
Percent
su?icient period of time for the entire structure to attain 10 MgO
3-35
the furnace temperature. At this stage the molded prod
SiO2
25-50
uct is an amorphous, vitreous-material having no crystals
BaO
3-35
therein. The article is then heated up to about 850° C.
F-luxing agent
10-35
and held at this temperature for the purpose of initiating
the auto-crystallization process. The article is maintained 15 said ?uxing ‘agent being selected from the group consist
ing of MgF2, B203, A1203, Li20, N320, K20, KzSiFe, and
at this temperature for a sut?cient period, e.g., 15 minutes
Al2(SiF6)3 and combinations thereof.
to 21/2 hours, with 1/2 to 1 hour being optimum, in order
2. The method of making a hard, dense, mechanically
to produce a support skeleton of crystals in the product
strong, electrically insulating ceramic material which
to ensure that it is self-supporting before the temperature
comprises forming a melt of a material having the follow
is raised to the optimum crystallization level. As soon
ing
approximate composition in percent by weight:
as this result is obtained, the temperature is raised to about
Percent
1050° C. and held for about 1 to 8 hours, with 4 hours
MgO
3-35
being the optimum time. These conditions are optimum
BaO
3-35
for inducing the growth of crystals of the desired form
and orientation. Thereafter the product is gradually 25 SiOz
25-50
Fluxing agent
cooled to room temperature.
If desired, during the initial cooling step, the product
_ 10-35
said ?uxing agent being selected from the group consist
may be cooled to room temperature for the purpose of
ing of MgF2, B203, A1203, Li20, N320, K20, K2SiF5, and
inspection to determine whether the amorphous glassy
Al2(SiF6)3, and combinations thereof, cooling said melt
phase of the molded article has any defects. After this 30 to a temperature not higher than about the annealing
procedure, the article may be subjected to the heating
temperature thereof to arrest the formation of crystals
temperatures described above to initiate and complete
therein and forming thereby an amorphous, vitreous
the auto-crystallization process.
material heating the thus formed vitreous material to a
As will be understood, the particular temperatures and
temperature of about 800-950” C. for a period sufficient
other values set forth may be different from those stated 35 to initiate crystallization of said material, and thereafter
depending on the particular composition employed, since
heating the material to about 1050“ C. for converting the
different compositions may be characterized by different
same to a micro-crystalline ceramic body composed es
annealing, melting, and initial and optimum crystalliza
tion temperatures.
As a result of the described process there is obtained 40
a hard, dense, crystalline ceramic-like body of excellent
electrical and mechanical properties wherein the metal
sentially of randomly oriented synthetic barium-contain
ing crystals.
3. The method of making a hard, dense, mechanically
strong, electrically insulating ceramic material which oom
prises forming a melt of a material having the following
hardware and ceramic material are joined in a strong,
approximate composition in percent by weight:
?uid-tight ceramic to metal seal.
The invention thus provides a novel ceramic product 45 MgO
and method of making the same which affords numerous
BaO
advantages over the prior known ceramic materials and
Si02
processes. For example, as compared to porcelain, more
Fluxing agent
precise dimensional tolerances are obtainable in the ?nal
Percent
3-35
3-35
20-50
10-35
product due to less shrinkage during the processing, the 50 said ?uxing agent ‘being selected from the group consist
material is easier to Work, shorter ‘and more e?icient manu
facturing cycles are made possible, better hermetic seals
Al2(SiF6)3,
ing Of MgF2,and
B203,
combinations
A1203, Lil-20,thereof,
NaZO, K20,
castingKzslFs,
said melt
into a mold of predetermined con?guration, cooling the
with metal parts are achieved, the ceramic product can be
melt in said mold to a temperature not higher than about
reused even if broken, and, in general, lower cost com
ponents are employed.
55 the annealing temperature of the melt to arrest the forma
Although the described material is particularly adapted
for simple casting procedures, it may, after being poured
tion of crystals therein and forming thereby an amorphous,
vitreous material having said predetermined con?guration,
removing said material from the mold, heating the thus
in molten form into a mold, be subjected to pressing
formed vitreous material to about 800-950" C. for a
operations to achieve more sharply de?ned con?gurations.
It is not, however, necessary to employ high pressures to 60 period sufficient to initiate crystallization of said material,
and thereafter heating the material to about 1050° C. for
achieve coherence or high density of the mass, as in the
converting the same to a microcrystalline ceramic body
case of porcelain and other ceramics.
The described material has also been found useful as
a bonding agent, as for example for such materials as
composed essentially of synthetic barium-containing
crystals.
alumina, magnesia, silicon carbide, mica isomorphs, and 65 4. The method of making a hard, dense, mechanically
the like, and affords thereby improved electrical properties
strong, electrically insulating ceramic material which com
for such bodies as compared to glass-bonded or porcelain
prises forming a melt of a material having the following
bonded materials.
approximate composition in percent by weight:
While the present invention has been described with ref
Percent
erence to particular embodiments thereof, it will be under 70
MgO
___ 3-35
stood that numerous modi?cations may be made by those
BaO
3-35
skilled in the art without actually departing from the
SiOz
25-50
scope of the invention. Therefore, the appended claims
are intended to cover all such equivalent variations as
come within the true spirit and scope of the invention.
Fluxing agent
1()_35
75 said ?uxing agent being selected from the group consist
3,022,179
7
ing Of MgF2, B203, A1203, Llzo, Nazo, K20, KZSiFB, and
Al2(SiF6)3, and combinations thereof, casting said‘y-melt
into a mold having metal parts an'anged therein for em
' bedding in the cast product, cooling the melt inv said mold
,to a temperature not higher than about the annealing,
temperature of the melt to arrest the formation of crystals
therein and forming thereby ‘an amorphous, vitreous ma
terial having ‘a con?guration imparted thereto by the mold
and having embedded therein said metal parts, removing
said material from the mold, heating the thus-formed 10
vitreous material to about 800-950.” C. for a period su?i
cient to initiate crystallization of said material, and there
after heating the material to about 1050° C. for convert
8
ing the same to a mierocrystalline ceramic body composed
essentially of synthetic ban'um-containing crystals.
References Cited in the ?le of this patent
UNITED STATES PATENTS
_
1,333,400
Fisk ________________ __ Mar. 9, 1920
1,955,821
1,973,408
McDougal ..»_ ______ __,_-_ Apr. 24, 1934
Curtis ______________ ___. Sept. 11, 1934
Fenity et a1 ___________ __ June 17, 1958
2,839,414
2,876,120
Machlanv __.._-_..__,___.'___ Mar. 3, 1959
2,878,130
2,920,971
Harman et a1 _________ __ Mar. 17, 1959
Stookey _____________ _.. Jan. 12, 1960
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