Si3 N4 powder (amorphous, alpha-, and beta-Si3 N4) was mixed with MeOH containing 8.87 mol. % H2O and ground. The NH3 generation rapidly increased after a grinding time of 100 hours. Silicon nitride sintered material was chosen as one of the high temperature, high strength structural materials and studies of the control of the raw material powder, preparation of the sintered body (finding the right assistant, hot press, high pressure sintering, fracture toughness and oxidation at high temperature were performed

Kanno, Y.

Kuwahara, Y.

Suzuki, K.

English

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fNASA TM-77746NASA TECHNICAL MEMORANDUM
AMMONIA FORMATION CAUSED BY THE PRESFNCE OF WATER IN TF_E
WET GRINDING OF SILICON NITRIDE POWrER
Kanno, Yoshinori; Suzuki, Kazuo; and
K.uw Ahara, Yoshitaka
Translation of "Si 3N 4 no shisshiki Funsai ni okesu
Suikuanc- Kango to NH3 Seisei", Yogyo K.yokaishi, Vol. 91,
No. 8, :983, pp. 386-388.
(NASA - Td - 77746)
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'Translation of11 Si N	 no sh: sshiki Funsai ni Okesu Suikuano Kango to NH3
Seisei",	 YogyoKy&alishi , Vol. 91, No. 8, 1983, pages 386-388.
14. Abe~'
Si	 Id4 natvier (amorph,-)us, a-, and ^-Si 3 N*) was mixed with McOH containing
8A7 mol. % H 2O and ground. The 14H 3 generation rapidly increased after
a grinding time of 100 hours.
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Silicon ",itride
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mechanochemical reaction
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AMMONIA FORMATION CAUSED BY THE PRESENCE OF WATER IN THE WET
GRINDING OF SILICON NITRIDE POWDER**
Kanno, Yoshinori; Suzuki, Kazuo; and Kuwahara, Yoshitaka
(Government Industrial Research Institute, Nagoya 1, Hirate-
cho, Kita-ku, Nagoya-shi 462 [Received May 30, 19831)
/48*
Silicon Nitride (Si 3N 4 ) sintered material was chosen as
one of the high-temperature,high-strength structural materials,
and studies of the control of the raw material powder [1), prepara-
tion of the sintered body (finding tine proper assistant [2],
hot press [3], high pressure sintering [4], fracture toughness
and oxidation at high temperature knave been performed. In order
to obtain highly efficient ceramics as a structural material,
it is generally necessary to use a raw material powder which is
highly purified and controlled. Among the ceramic manufacturing
processes, a method of grinding or pulverizingraw material powder
and improving its powder characteristics and improving the
characteristics of the sintered body is often used. The writers
-are going to report here that a mechanochemical reaction of Si3N4
raw material powder from a grinding process was investigated and
some n,2w information was obtained.
a-Si,N,
	 and ^$ ► sN ,•	 , and amorphous (Am) -Si 3N4 , which have three
crystal structures, were used for the Si 3N 4
 raw material powder.
The concentrations of metallic impurities (Al,B, Ca, Cr, C li, Fe, K,
Mg, Mn, Mo, Na, Ni, Ti, V, Zn) by ICP (inductive coupling plasma)
emission analysis and atomic absorption analysis were almost all
less than 10 ppm, except for 100 ppm of Fe. Furthermore, the a
molecular ratio of asi^N, sample was measured as 86% by using a r- B
molecular ratio assay curve [6) from the integral strength ratio
of powder X-ray analysis.
Numbers in margin indicate foreign pagination.
**Presented May 30, 1983.
1
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A glass container was filled with Si 3N 4 powder for preprocess-
ing under an atmosphere of nitrogen in a glove box (P.A.C.E.
chamber) manufactured by Lab-Line Company) and the air was removed
by vacuum for an entire day and night at 400°C. After that 15 g
of the powder, which was vacuum processed, was weighed in a
glove box and combined with methanol of various moisture contents
(212 g) in the chamber of a vibrating ball mill under an atmos-
phere of nitrogen, and wet grinding was performed. The materials
for the chamber and ball which were used was Si 3N 4 .	 5 Ol solvent
was withdrawn with a microsyringe from the small hole (sealed by
silicon rubber) which was made in the chamber before every scheduled
grinding time (20 hours, 100 hours and 200 hours) and analyzed
by gas chromatography. The gas chromatographic analysis was per-
formed with He carrier gas by using a chromosorb 103 and PEG 1000
column at 110°C. Furthermore, the measurement of the specific
surface area of Si 3N4 was performed by the BET method with nitro-
gen gas adsorption and the sample before grinding (original) and
200 hours after grinding ;aas measured. The results of this are
shown in Table 1.
2!0 Iron r
...!r ph—Si IN, 319.4 IR:,n
•
- Si 3M6 13.9 99.0
p-Si 3 N4 2.35 79.3
According to Table 1, it is assumed that the specific
surface area of Am-Si 3N 4 is very large, :end active. Furthermore,
the specific surface area after 200 hours of grinding decreases
for Air-Si 3N 41 but a remarkable increase was recognized for 
osi,N,, and
Figure 1 exhibits the relationship between the degree of
ammonia formation and grinding time in the case of various
amounts of included moisture.
2
04cIG#NAL Ffa E 'it
OF POOR QUALITY
,III' 1
i
so
•
40
V ^
s 70
O
. O
c 20
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0
0	 too	 200
C—d(. 0
 tt.. ( h.");
Crl.4-2 tt..	 ( liour)
s
N
O ti
i ^
• Y
O ^
C
o"
It is understood that there .;'.s a tendency for the degree
of ammonia formation to increase nearly proportional to the
moisture content. Therefore, it is assumed that the ammonia
formation reaction in Si 3N 4
 has a close relation with the water
concentration. Furthermore, ammonia was not detected during
grinding by purified methanol, and this shows that ammonia forma-
tion is not from a reaction which is related to methanol but
from the small amount of water which is included.
Figure 2 exhibits the relationship between ammonia formation
amount per unit mass of Si 3 N 4
 and grinding time for three kinds
of Si 3N 4
 in the case when methanol of a moisture content of
8.86 mol % (H 2 0/ (H 2 0 + Ch 3 OH) x 100 (mol/mol) was made as a
solvent.
According to Figure 2, there is a tendency for the amount of
ammonia formation to increase from a grinding time of 100 hours
and it is considered that a delay phenomenon exists in a surface
reaction. And also it is considered that the surface reaction
proceeds when a sufficient amount of water has been adsorbed by
the active sites on the new surfaces which have appeared from
grinding and which have a high specific area, and ammonia was
formed. If the ammonia formation amount per Si 3N 4
 unit surface
area is found with Table 1 and Figure 2, Am->Q->fiSi.N.	 This shows
that as Si 3N 4
 has a higher anJ steadier temperature, activity
toward ammonia formation reaction is lower.
3
4U+
Processing powder by sintering gives a large influence
toward the characteristics of the final products and es pecially in
the case when an amorphous powder is processed, great attention
is required. Ammonia formation suggests that the surface of the
Si 3N 4 powder is being changed to heterogeneous material. Because
of that, sufficient attention must be paid toward water in the
ceramic manufacturing process. Furthermore, also in the high
temperature stable type A6'-N, if it is considered that ammonia is
formed by grinding, service condition of Si 3 N 4 as a structural
material must be chosen carefully, especially for heat resistance
and corrosion resistance.
We deeply thank Dr. N'rio Ishizuka of Department 3 of the
Nagoya Industrial TFchnical Laboratory for the analysis of the
metallic impurities in this study.
REFERENCES
[1] M. Mitomo, H. Tanaka and J. Tanaka.	 Yogyo-Kyokai-Shi,
Vol. 82, pp. 144-45 (1974).
[2] J. A. inan gels and G.J. Tennenhouse. Am. Ceram. Soc. Bull.,
Vol. 80 1 i306-10 (1981) .
[3] J. A. Palm, C.D. Greskovich, Am. Ceram. Soc. Bull.,
Vol. 59, pp. 447-52 (1980).
[4] T. Yamada, M. Shimada and M. Ko i 7umi. Am. Ceram. Soc.
Bull., Vol. 80, pp. 1225-28 (1981).
[5] G. Grathwohl, S.B. Hanna and F. Thummler. Trans. J. Brit.
Ceram. Soc. Vol. 81, pp. 193-96 (1982).
[6] Suzuki, Kazuo; Sugano, Yoshinori: Presented to "Ceramics".
J
im


Ammonia formation caused by the presence of water in the wet grinding of silicon nitride powder

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