Sintered bodies containing 1-32.5 Si oxide and  1.5 wt.% SiC (Si oxide/SiC wt. ratio  3/2) are prepared and kept in a 10-3000 kg/2 sq. cm. N (g) atmosphere at 1500-2300 degrees, while simultaneously maintaining the CO (g) partial pressure around the body lower than the nitrogenation equil. pressure to give a dense sintered body. The prepared dense sintered body has high strength at high temperatures. Thus, SiC 40, oxide 30 and Si3N4 30 wt% were fired to a body which was kept in 1500 kg/sq. cm. N (g) for 20 h at 2000 degrees to give a dense sintered body having high bending strength at high temperatures

Hasegawa, Y.

Hirota, K.

Ogura, K.

Yashima, Y.

English

NASA Technical Reports Server

  
 
 
N O T I C E 
 
THIS DOCUMENT HAS BEEN REPRODUCED FROM 
MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT 
CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED 
IN THE INTEREST OF MAKING AVAILABLE AS MUCH 
INFORMATION AS POSSIBLE 
https://ntrs.nasa.gov/search.jsp?R=19860005926 2020-03-20T16:40:20+00:00Z
iI
NASA TECHNICAL MEMORANDUM 	 I	 NASA TM-77929
MANUFACTURE OF DENSE SINTERED BODIES CONTAINING SILICON NITRIDE
K. Hirota, Y. Hasegawa, K. Ogura, Y. Yashiaa
Translation of "Chikka keiso o fukusu chiaitsu na shoketsutai no
seizoho," National Institute for Research in Inorganic Materials,
Jpn. Kokai Tokkyu Koho, Japan Patent 59-111,981, June 28, 1984,
nn. 1 -4.
(NASA-TM-77929) MANU FACTURE Of 
DENSESINTERED BODIES CCNTAINING SIIICCa 
NITfiiJE(National Aeronautics and 
S	
N86-15356
Adaiaistration )	 Face10 P UC A 02/CF !!O1 CSC% 11G
uaclas
G3/27 05067
•	 • t
WIT
^1(Jw r.ti
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546	 DECEMBER 1985
s n
n tt®
_r; a
2
NASA-NO
1	 ,
STANDARD TITLE PAGE
1.	 Report Me. 2. Governeent Accession Me. 3.	 Recipient's Catalog No.
NASA TM-77929
I.	 Title and Subtitle S.	 Revert Date
MANUFACTURE OF DENSE SINTERED BODIES ^')8
CONTAINING SILICON NITRIDE 6.	 Performing Or	 ,lien Cede
•.	 Performing Oruonisotion Report No.7.	 Author(O
K. Hirota,	 Y. Hasegawa, K. Ogura, Y. Yashima 	 10. work Unit No.
Contract or Grant No.1).
9. Performing Organisation None and Address NASW-4006
The Corporate Word 13-	 Tyr of Report end Period Covered
1102 Arrott Building ^Translation
Pittsburgh,PA	 15222
1s.	 Sponsoring Agency Nome and Address
National Aeronautics and Space Administration 11.	 Sponsoring Agency Cede
Washington, D.C.	 20546
13. Supplementary Notes
Translation of "Chikka keiso o fukumu chimitsu na shoketsutai no
seizoho," National Institute for Research in Inorganic Materials,
Jpn. Kokai Tokkyo Koho, Japan Patent 59-111,981, June 28, 	 1984,
PP .	1-4.
16.	 Abstract
Sintered bodies containing 1-32.5 Si oxide and >1.5 wt.% SiC	 (Si
oxide/SiC wt. ratio <3/2) are prepared and kept in a 10-3000 kg/cm2
N (g) atmosphere at 1500-2300 degrees, while simultaneously maintain-
ing the CO (g) partial pressure around the body lower than the
nitrogenation equil. pressure to give a dense sintered body. 	 The
prepared dense sintered body has high strength at high temperatures.
Thus, SiC 40, Si oxide 30 and Si 3N4 30 wt% were fired to a body which
was kept in 1500 kg/cm2 N (g) for 20 h at 2000 degrees to give a
dense sintered body having high bending strength at high temperatures.
17. Key words I"OcteA by Author(s)) 11.	 Distribution Statement
Unlimited
19.	 Security Claasif. (of this report) 20.	 Security Clossil. (of IN$ page) 21• No. of Pages 22.	 Prlcsi'
Unclassified Unclassified 11
t
.^..•HIi1,13a...
s
i
a
i
ORIGINAL PAGE IS
OF POOR QUALITY
(19) JAPAN NATIONAL PATENT OFFICE (JP)
	 (11) Patent
Application
Publication
(12) PUBLIC PATENT REPORT (A)
	 59-111981
(51) Int.C1. 3
 Identification Internal Control (43) Published
No.	 No.
C 04 B 35/58	 102
	 7158-4G
No. of Patents:
	 1
Investigation
applied for?	 yes
Total pages: 4
(54) Method for Manufacture of Dense Sintered Bodies Containing
Silicon Nitride
(21) Patent Application:	 57-221276
(22) Date of Application: December 17, 1982
(72) Inventor:
	 K. Hirot;.
11-4, 2-chome, Takesono
Sakuramura, Shinji-kun
Ibaraki-ken
(72) Inventor:
	 Y. Hasegawa
3-8, Roku, 3-chome, Nakamura,
Nerima-ku, Tokyo
(72) Inventor:
	 K. Ogura
110-103, 3-chome, Takesono, Sakuramura
Shinju-kun, Ibaraki-ken
(72) Inventor:	 Y. Yashima
104-202, 3-chome, Takesono,
Sakuramura, Shinji-kun, Ibaraki-ken
(71) Applicant: Head, Inorganic Materials Research Institute
Office of Science and Technology
Kagaku Kijutsu-cho
-3-
MANUFACTURE OF DENSE SINTERED BODIES CONTAINING SILICON NITRIDE
K. Hirota, Y. Hasegawa, K. Ogura, Y. Yashima
10
Deidiled Specifications	 /427*
1. Name of Invention:
Method for Manufacture of Dense Sintered Bodies Containing
Silicon Nitride
2. Scope of Patent Claims
Manufacture with a method characterized by use of sintered
bodies from a compound which contains 1-32.5 wt% silicon carbide,
and which also has a ratio of three parts silicon oxide to two or
more parts silicon carbide; and by keeping the body in nitrogen
gas at 10-3000 kg/cm 2 and 1500-2300mC while simultaneously
maintaining the carbon monoxide partial pressure around the body
lower than the nitrogenation equilibrium pressure.
3. Detailed Explanation of the Invention
This inventions concerns a method of manufacturing dense
sintered bogies which contain silicon nitride and which, more
specifically, exhibit a high degree of strength at temperatures
above 1200xC.
Sintered bodies of silicon nitride, or with silicon nitride
as one ingredient and silicon carbide, etc., as the others, are
superior in hardness and chemical stability, do not lose their
*Numbers in the margin indicate pagination in the foreign text.
-4-
M!I
rigidity at high temperatures, show a high degree of strength,
and almost never break because of thermal shock. This has lead
to the expectation that they might be used as heat- resistant
materials.
They have not, however, exhibited properties commensurate
with the abovementioned expectations. This is due to the fact
that, when the powdered material is being sintered into a molded
form, the agent added to aid the sintering process acts to
decrease the strength of the sintered body at high temperatures.
This occurs when the silicon oxide contained as an auxiliary
agent in the material undergoing sintering combines with such
substances as MgO, Y203, or CaO, thereby forming solid-phase
oxides with a low melting point and, consequently, lowering the
high-temperature strength of the sintered body. In addition,
even though there exists a method for making a comparatively pure
silicon nitride sintered body by means of nitrogenating elemental
silicon powder, the body obtained with this method does not
attain a full degree of strength because of vacancies left within
it.
This invention eliminates these problems by providing a
manufacturing method which does not allow material which vitiates
high-temperature strength to remain in the body and which, by
attaining a full degree of density, produces a body with a high
degree of high-temperature strength.
The inventors took experimental results which would lead to
attaining the aforementioned goals and put the invention into
final form by using a certain quantity of silicon oxide as an
auxiliary agent for sintering, then making a sintered
	 [428
body containing a certain
	
g	 percentage of silicon carbide, giving
the body high-heat treatment in nitrogen gas at high pressure,
and expelling the carbon monoxide produced. Once this was
accomplished, the resulting sintered body was highly dense and
contained no
41
,M
-5-
-6-
rf,►
silicon oxide and, therefore, had superior high-temperature
strength.
The distinguishing features of the invention are:
Making a high-density sintered body with a silicon oxide
content of 1-32.5 wt% and a silicon carbide content of 1.5 wt% or
above, with a ratio of three parts (by weight) silicon oxide to
two or more parts silicon carbide, and keeping the sintered body
in nitrogen gas at 10-3000 kg/cm 2 and 1500-2300 • C while
simultaneously keeping the carbon monoxide partial pressure
around the body below the nitrogenation equilibrium pressure.
Acid salts of silicon may be used instead of the silicon
oxide powder as an ingredient in this invention.
It is desirable for the silicon oxide powder to be spread
evenly over the surface of the silicon carbide particles. For
example, it is desirable for the surfaces of the silicon carbide
powder particles to be covered with a film of silicon oxide while
oxidation takes place. This minimizes the occurence of the
miniscule sintering faults which are caused by structural
irregularities. It is desirable for the silicon oxide content to
be within 1-32.5 wt% and the silicon carbide content to be above
1.5 wt%. Less than 1% silicon oxide would create problems with
density, while more than 32.5% is not necessary to attain the
desired density, and could have negative effects during the
latter stages of the prolonged nitrogenation treatment. Since
less than 1.5% silicon carbide would cause the presence of
unreacted S102, a ratio of 3 parts silicon oxide to at least
two parts silicon carbide must be maintained. This is so that
when the reaction between SiOa, SiC and Nz is complete, some
SiC, but no Si02, will remain in the sintered body.
The powdered ingredients which are subjected to sintering
may, in addition to silicon oxide and silicon carbide, have
silicon nitride and such metallic oxides as alueina, zirconia,
etc., mixed into them as needed.	 4
No special conditions are required for sintering, but a moist
hydrogen atmosphere, which facilitates the process, is
desirable. Under such conditions there are up to 1000 ppm of
water present in the silicon oxide, which reduces the viscosity
of the silicon oxide and facilitates sintering. Densification
should reach the extent at which vacancies take the form of
independent bubblef forming within the sintered body. When such
bubbles fora, they shrink and disappear during the
high-temperature, high-pressure nitrogenation treatment.
When the sintered body thus obtained is kept in nitrogen gas
at 10 -3000 kg/cm2 and 1500- 2300°C, the temperature and pressure
cause the silicon oxide and silicon carbide contained in the body
to react with the nitrogen. This chemical reaction takes place
as shown below.
Si02 + 2SiC + 2N2 4 Si3N4 + 2C0............(1)
2Si02 + 2SiC + 2N2 - ► 2Si2N20 - 2C0......... (2)
Si2N20 + SiC + N2 i Si3N4 + C0........... (3)
In these formulas the silicon oxide is represented by
Si02. Though variation in composition of ingredients for
sintering may occasion the use of a silicon acid salt or metallic
acid salts instead of silicon dioxide, use of these other
substances is also represented by Si02. The phases of silicon
dioxide nitrogenation include not only silicon nitride
(Si3N4), but, since complex compounds frequently form, also
include both Si3N4 and Si2N20. Furthermore, in this
-7-
invention, when silicon nitride is mentioned, both S13N4 and
S12N20 are included.
As shown in the formulas, the oxygen in the silicon oxide
contained in the sintered body combines with the carbon in the 	 *i
silicon carbide particles to produce carbon monoxide gas. The
nitrogen, on the other hand, combines with the available silicon
to form silicon nitride.
The use of HIP treatment, that is, the use of gas at high
temperature and high pressure to force gas bubbles out of
sintered bodies, has already been discovered. The material
usually used for this method is argon gas, though nitrogen gas
has also been used.
The nitrogenizing method used in this invention is 	 L429
different from the HIP treatment ir. the following ways:
(1) First, in this invention more than 1 wt% of silicon
oxide is included in the body which undergoes sintering. Since
the silicon oxide has a low degree of high-temperature strength,
and sintered bodies which contain a large amount of it are not
suitable for use as heat-resistant materials, inclusion of this
substance is restricted. In this inventiion, it is necessary to
include more than 1 wt% because the silicon oxide is used
together with silicon carbide and transformed into silicon
nitride, which has a high degree of high-temperature strength.
(2) The second point concerns expulsion of the carbon
monoxide produced during nitrogenation and the maintenance of the
carbon monoxide partial pressure around the sintered body at a
level below that of the equilibrium pressure for the reaction.
If this were not done, the reactions described in the formulas
above would not continue until nitrogenation was complete. The
-8-
i.
'Ir
S
carbon monoxide equilibrium pressure is expressed as a function
of the nitrogenation temperature in Figure 1. When using a
nitrogen pressure of 1000 kg/cm2 , the carbon monoxide partial
pressure at 1500 0 C is 200 kg/cm2 , and at 2000 • C it would be 410
kg/cm2 , showing the tendency for carbon monoxide partial
pressure to increase as temperature increases. Beeping carbon
monoxide partial pressure low causes the gases around the body
undergoing sintering to flow, and makes the nitrogen flow in
where carbon monoxide partial pressure is low. The process
whereby silicon oxide and silicon carbide interact, allowing
nitrogenation to take place, proceeds in two stages, as shown in
formulas (2) and (3). That is to say, in addition to the
reaction shown in Formula (1), a sequence is followed whereby the
reaction in Formula (2) produces a compound containing both
oxygen and nitrogen, and then the reaction in formula (3)
produces a nitride. In the latter case, if reaction (2) proceeds
rapidly and reaction (3) is delayed because carbon monoxide
partial pressure has not been fully lowered, it is easy for a
situation to arise in which the carbon monoxide is not promptly
expelled. It is, however, permissible to stop with reaction (2)
and have a sintered body composed mainly of Si2N20. For
reaction (3) - complete nitrogenation - to take place, if
nitrogen partial pressure is 1000 kg/cm 2 , carbon monoxide
partial pressure should be kept at 0.5 kg/cm 2 , or, even better,
below 0.1 kg/cm2
 in order for the reaction to proceed very
rapidly. The nitrogenation temperature must be within the
1500-2300°C range. Since silicon oxide softens at about 1500•C
and melts above 1740°C, nitrogenation would be difficult at
temperatures below 1500°C, and the best range is above 1700°C.
Since silicon nitride decomposes at temperatures above 2300 • C, it
is necessary to stay below this point.
Required time for nitrogenation at 1750°C is more than 10
hr. Higher temperatues decrease the time required. If, however,
the temperature is too high, the body undergoing treatment may
form coarse crystals.
f
-9-
In order to prevent coarse crystallization, the silicon
carbide content should exceed 2/3 that of silicon oxide, and it
is preferable to leave some excess of silicon carbide in the
sintered body. Generally, a processing time not exceeding thirty
minutes and a low processing temperature yield a good-quality
sintered body.
Experiment
A sintered body with a vacancy ratio of less then 1% was made
by taking a powdered mixture with particle diameter of 1 u,
composed of 40 wt% silicon carbide, 30 wt% silicon oxide and 30
wt% silicon nitride. This mixture was treated for 10 min. at
1700 • C under 30 kg/cm2 pressure. A sample in the form of a
square column measuring 4* by 40* was cut out and kept in
circulating nitrogen at 1500 kg/cm 2 and 2000 • C for 20 hr. A
28-H -type sintered body composed entirely of silicon nitride was
obtained. The three-point bending strength of this sample at
1300 1 C was 52 kg/mm2.
As shown above, this invention makes it possible to
manufacture a sintered body with a high degree of high-
temperature strength and high density.
4. Explanation of Illustration
The illustration shows carbon monoxide partial pressure (the
result of the reaction in which silicon carbide, silicon oxide
and nitrogen produce silicon nitride and carbon monoxide) as a
function of temperature.
[*Translator's note: Illegible word, perahps mm.]
-10-
^l
ORIGINAL PAGE IS
OF POOR QUALITY
f 00u
fw,	
X000 
4A01
0
o ,^0 st
M
1500	 2000
	
2300 M)
R
10
i
a
1
11


Manufacture of dense sintered bodies containing silicon nitride

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server