A structured device placed in an aerated crucible to pack ceramics molding substance that is to be processed was designed. The structure is wrapped by sealing material made of pyrex glass and graphite foil or sheet with a weight attached on top of it. The crucible is made of carbon; the ceramics material to be treated through heat intervenient press process is molding substance consisting mainly of silicon nitride

Fujikawa, T.

Miyanaga, J.

Moritoki, M.

English

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NASA TECHNICAL MEMORANDUM
SEALING CERAMIC MATERIAL IN LOW MELTING POINT GLASS
Masahito Moritoki, Takao Fn;ikawa, Junichi Miyanaga
Translation of Japanese Kokai Patent No. 58-88180;
Published, May 26, 1983; `.pplication No. , 56-186567; Filing
Date, November 19, 1981; Inventors, Masahito Moritoki et al.;
Assignee, Kobe Seikosho Co., Ltd., Kobe-shi, Japan
(NASA-TH-77599) SEALING CIBAMIC MATERIAL IN
LOW MELTING POINT GLASS (National
Aeronautics and Space Administration) 10
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D. C. 20546
	 AUGUST	 1984
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STANDARD TITLE PAGE
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1.	 Report No.
NASA TM-77.599
2.	 Coesrnrs ent Acceuion No.	 ( L
	
Rociplent's'Cateloo Me.
Title end SQ ► talo
SEALING CERAMIC MATERIAL IN LOW MELTING
S. Repoee Data
AUGUST 1984
POINT GLASS /. Peefenalno Otponiretien Cod.
7.	 Awdier(e) f1. Peefensino Oiooniaetion Report Me.
Masahito Moritoki, Takao Fujikawa,
10. work unit He.Junichi Miyanaga
9 ,
	Po,form:no Q r ;on reet.on Nar,:e and Address
Leo Kanner Associates
Redwood City,	 CA 94063
11.	 Contrast of G#ont No_
-NASW-3541
it	 Type of Report cnd Period CoosreA	 1
Translation
17.	 koneo r rn; Agency Ne.n• and Address
National Aeronautics and Space Admin-
istration,	 Washington,	 D.	 C.	 20546
14.	 SponserinpA;enc,Code
1
IS. 5r;;ler1n t c r y Note,
l Translation of Japanese Kokai Patent %. 58-88180;
Published, May 26, 1983; Application No., 56-186567; Filing 	 -
Date, November 19, 1981; Inventors, Masahito Moritoki et al.;
!Assignee, Kobe Seikosho Co., Ltd., Kobe-shi, Japan
This is an invention of a structured device placed in an aera-
ted crucible to pack ceramics moldinc substance that is to be
processed. The structure is wrapped by sealing material made
of pyrex glass and Fraphite foil or sheet that has a weight
attached on top of it. The crucible is made of carbon; the
ceramics material to be treated through heat intervenient press
Vrocess is molding substance consisting mainly of silicon nitride.
1, Key Words (Selected by Autnor(t))	 1!!. Ole,rlbuoon $totem"?
•UNLIMITED
1
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1. Name of the invention	 #/415
Sealing ceramic material in low melting point glass.
2. Scope of the patent application
(1) The structured device placed in an aerated crucible
to pack ceramic molding substance which is to be processed by the
heat intervenient press. The entire device is covered by sealing
material made of glass and graphite foil or sheet that has a weight
attached on top of it.
(2) The packing device for molding substance to be
treated described in para 2 (1) of which the aerated crucible is
made of carbon.
(3) The pack;.ng device for molding substance to be
treated described in para 2 (1) and (2) of which the c.^ramics
substance to be treated is molding substance consisting mainly of
silicon nitride.
(4) The packing device for molding substance to be
treated describe: in para 2 (1), (2) and (3) of which surface is
surrounded by the top and the bottom glass plate and glass granules
in betweet:.
(5) The packing device for molding substance to be
treated described in para 2 (1) and (4) of which the glass is pyrex
glass.
3. Detailed description of the invention
This invention is in regard to the structured packing
*Nu:nbers in the margin indicate pagination in the foreign text.
device for molding substance to be treated by the heat intervenient
press. To be precise, it is the device that uses a glass seal made
of liquefied glass as the sealing material for ceramic molding
substance in the process of the heat intervenient press.
The heat intervenient press (hereinafter referred to as
HIP) method that uses glass as the sealing material has several
advantages - molding of a variety of forms and shapes is possible;
high temperature HIP is possible, in con i.ist with copper, which is
commonly used as capsule material. Its application in high density
ceramics of which development is being pushed forward these days is
being attempted. For example, the glass capsule method (Ref. to
Kokai Patent No. 46-2731). and the method to imbed moldine
substance in glass granules (Ref. to Kokai Patent No.
55-89405) are some of the examples.
These methods all use crucibles made of carbon such as
graphite, and it surrounds the molding substance by melting glass
within the crucible. Because ceramics powder has a high sintering
temperature requiring high HIP temperature compared to metal powder
molding of the past, glass is used to process ceramics such as
silicon nitride and silicon carbide. At this time, ceramics
molding substance, regardless of the method - glass sealing method
as mentioned earlier or glass powder imbedding method - used,
become imbedded in the mass of glass. However, because the
specific gravity of ceramics molding substance until it becomes
high density substance is lower (1.8 - 2.1 g/m 3 ) ' han that of glass
(2.2 - 2.3 g/m3 ), molding substance tends to surface from its
original position and contact the surface of the carbon crucible
/416
3
when the glass dissolves.
In this instance, gas used as pressuring medium enters
the crucible from the contact point during the process of HIP
resulting in imperfect sealing, which causes incomplete HIP. In
addition, a very small amount of oxygen contained in gas used as a
medium causes chemical reactions with ceramics. Also, even if BN
powder is used to promote smooth separation of the carbon crucible
and molding substance, solidified glass is difficult to remove from
the carbon crucible.
In spite of the shortcomings of glass as mentioned above,
its use is industrially advantageous due to its low cost and ease
in handling. Therefore, improvement of the shortcomings is hoped
for.
This invention, meeting the needs of the time, aims to
provide an improved packing device with an improved sealing
structure that can effectively provide sealing by glass with a low
melting temperature.
The characteristics of this invention, which is capable
of attaining the above mentioned aims, are : (1) the device pack,;
glass sealing material by surrounding the molding substance placed
in the molding substance packing crucible inserted in the HIP
device, (2) the device surrounds the molding substance and glass
sealing material with an airproof graphite sheet,, while a free
moving weight is placed on top.
The following are more detailed explanation of this
invention w_th figures:
The figure is one example of the structure by this
4
*V
V
invention. Molding substance (2) is packed surrounded by the top
and the bottom glass plates (3) (3') and glass granule (4) in
between. Next to the molding substance (2) and glass (3)(3')(4) is
an a'_rproof sheet of graphite (5), a main part of this invention.
On top of the graphite sheet (5) is a free moving weight which
prevents the molding substance (2) from surfacing at the time of
HIP.
The crucible (1) is air-permeable, usually made of
carbon, so that Ar, N2 and other pressure media gases may go
through.
On the other hand, the molding substance (2) includes all
material that are processed by HIP, eg. metallic or ceramics
powder. Among molding substance, ceramic substance, with glass as
sealing material, is the most suitable for the high temperature
process of HIP. Among them, the most favorable ones are ceramics
substance composed mainly of silicon nitride, silicon carbide and
boron carbide. Also, the molding substance (2) is not just an
ordinary powder - it sometimes contains sintering promoting agent,
and it is sometimes in the form of preparatory sintering substance.
As for glass to be used for sealing, any glass commonly
used for HIP process, eg. silica glass, pyrex glass ... etc., can be
used. Among those commonly used, pyrex glass is the most favorable
because of its characteristics during and after HIP process - no
reaction with ceramics and easily removable after HIP. According
to the fig.ire, the structure for the sealing glass consists of the
top, bottom plates and in-between glass granules, but the formation
does not have to be followed strictly. The structure can be
s
1
/417
5
V
moa'ified to suit the need. Glass granule alone may be used
sometimes, and molding substance may be placed in a glass capsule.
Also, in addition to plate and granule forms of glass, other forms
can be used effectively.
The air-proof graphite sheet prevents gases through the
crucible (1) from entering during HIP process as well as conveying
even compression force to molding substance (2). It is required to
be air -proof as well as dissolution-proof at the high temperature
of HIP processing.
Among possible materials that can satisfy the above
requirement are graphite, molybdenum and other metals of high
dissolution points. All except graphite are unacceptable due
mainly to their costs. The most suitable one is graphite prrduct
named grafoil (a trade name) which possesses all the necessary
qualities mentioned earlier.
On top of the glass sheet (S) is a weight (6) which
prevents the molding substance (2) from surfacing when the glass is
dissolved. It is made of material suitable for usage in high
temperature, and has enough weight to prevent the molding substance
which has less specific gravity than glass from surfacing. The
suitable material for the weight are silicon nitride, tungsten,
molybdenum and others. The weight (6) needs to be movable in order
than changes of shapes and forms of material below during the
process do not affect the up and down movement of the weight along
the inner wall of the crucible.
in the figure, (7) indicates a layer of BN powder applied
on the inner surface of the crucible. Although it is not
t
6
indispensable for an easy removal of molding substance from the
crucible, it is effective in the same manner as the graphitc sheet
after the process.
The packing structure for molding substance thus far,
used in HIP process with Ar and N2 used as pressure media gas, and
inserted in the crucible in its original form. In case pyrex glass
is used, the glass starts to dissolve at 1200 degrees C; molding
substance not yet in high density form starts to surface due to its
low specific gravity and pushes up the graphite sheet placed above
it; u portion of molding substance within glass sealing begins to
surface.
However, because of the weight (6) placed on top, the
surfacing of the substance as well as the entry of pressure media
gases are kept off, thus, complete sealing is maintained. Gases
released from molding substance during the early stage of HIP flow
between the glass because the glass seal is not completed.
After the glass has dissolved, the eases are dissolved in
glass (a characteristic of pyrex glass); molding substance can
attain the desired high density under the designated HIP
temperature and pressure level. The gases dissolved in the glass
are re-vaporized making the glass foam, which is ideal for removal
of glass after the process.
As described thus far, the packing structure for molding
substance by this invention surrounds molding substance with an
air-proof graphite sheet, and prevents pressure media gases from
entering the area of molding substance by a weight placed on top of
the molding substance. In addition, the long standing problem
7
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associated with HIP - surfacing of molding substance during HIP -
can be effectI:•ely solved by the weight which pushes down molding
substance and provides a complete sealing.
Moreover, the graphite sheet by this invention does not
prevent molding substance from changing itself to high density
substance; solidified glass after HIP can be removed from the
crucible easily because of the effect of the graphite sheet. Above
all, most importantly, the graphite sheet prevents pressure media
gases from mixing with molding substance - the basic principle of
HIP. The following is an example of a practical application:
Powder form of Si3 N4 , purity 99X,4 ele;nent 70%, average
diameter 1 micron, was placed in a tube made of silicon rubber;
5000 Kg/cm pressure was evenly applied to form a preparatory
molding substance ( 18 mm / x 30 mm 1).
The preparatory molding substance was placed in a
graphite crucible of which the inner surface was coated with 8N.
r
The preparatory molding substance was placed between two sheets of
pyrex glasses, one at the top and one at the bottom. Pyrex glass
granules were filled in the space between the two glass plates.
The preparatory molding substance and glasses were wrapped by
graphite foil; a weight was placed on top of the substance. After
these preparations, the preparatory molding substance was placed in
a HIP device where HIP process was started at 300 degrees C
temperature at the beginning. After decompression down to 10 Torr,
two exhaustion operations by injecting N. gas, 15 tag/cm". The
temperature was raised to 1200 degrees C until the glass was
dissolved.; Nz gas was re-supplied and the temperature was raised
I
8
yagain, and HIP process was continued for two hours at 1750 degrees
C temperature and 2000 Kg f/cm 2 .
The molding substance taken out of the HIP device,
covered with dark glass substance, was completely free of media
gases on the surface of Si 3 IN 41 and its relative density was 98.5
4. Brief _xplanation of the figure
The figure indicates one example of the packing structure
of the molding substance by this invention.
Assignee: Kobe Seikosho Co., Ltd.
Agent:	 Yasukazu Miyamoto
KEY LIST
(1) crucible	 (2) molding substance
(3)(3') glass plate	 (4) glass granules
(5) graphite foil or sheet (6) weight
(7) a layer. of BN agent
6	 f
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ORIGINAL E
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Sealing ceramic material in low melting point glass

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