Low-temperature synthesis of nanocrystalline α-Si3N4 powders by the reaction of Mg2Si with NH4Cl

Article abstract of DOI:10.1111/j.1551-2916.2004.01810.x

Nanocrystalline α-Si₃N₄ powders have been prepared with a yield of 93% by the reaction of Mg₂Si with NH₄Cl in the temperature range of 450° to 600°C in an autoclave. X-ray diffraction patterns of the products can be indexed as the α-Si₃N₄ with the lattice constants a = 7.770 and c = 5.627 A. X-ray photoelectron spectroscopy analysis indicates that the composition of the α-Si₃N₄ samples has a Si:N ratio of 0.756. Transmission electron microscopy images show that the α-Si₃N₄ crystallites prepared at 450°, 500°, and 550°C are particles of about 20, 40, and 70 nm in average, respectively.

Full text of DOI:10.1111/j.1551-2916.2004.01810.x

J. Am. Ceram. Soc., 87 [9] 1810–1813 (2004)
journal
Low-Temperature Synthesis of Nanocrystalline ␣-Si N Powders by the
3
4
Reaction of Mg Si with NH Cl
2
4
†
Yunle Gu, Luyang Chen, and Yitai Qian
Structure Research Laboratory, Department of Chemistry, University of Science and Technology of China,
Hefei, Anhui 230026, Peoples Republic of China
Nanocrystalline ␣-Si N powders have been prepared with a
3
4
yield of 93% by the reaction of Mg Si with NH Cl in the
2
4
temperature range of 450° to 600°C in an autoclave. X-ray
diffraction patterns of the products can be indexed as the
␣
-Si N with the lattice constants a ؍ 7.770 and c ؍ 5.627 Å.
3 4
X-ray photoelectron spectroscopy analysis indicates that the
composition of the ␣-Si N samples has a Si:N ratio of 0.756.
3
4
Transmission electron microscopy images show that the
-Si N crystallites prepared at 450°, 500°, and 550°C are
␣
3
4
particles of about 20, 40, and 70 nm in average, respectively.
I. Introduction
ILICON nitride (Si N ) is a very important material for high-
3
4
S
temperature applications due to its attractive properties. Such
properties include thermal and chemical stability, high strength,
1
stiffness, and good wear, creep and corrosion resistance.
Traditionally, Si N powders were prepared by carbothermal
3
4
2
reduction of silica in the temperature range of 1500° to 1550°C,
Fig. 1. XRD patterns of the products prepared by reacting Mg Si with
2
or by nitridation of silicon powders in nitrogen in temperatures
ranging from 1200° to 1400°C. Some other reactions also
NH Cl for 10 h in an autoclave at (a) 450°, (b) 500°, (c) 550°, and (d)
4
3
600°C.
developed to prepare Si N include: the reaction of SiCl with
3
4
4
4
NH to form ultrafine Si N powders; the gas-phase ammonolysis
3
3 4
of SiH4 in 500°–1100°C to produce amorphous silicon nitride
powders of 50–200 nm; and the pyrolysis of an organic precursor,
Table I. The X-ray Diffraction Spectrum of the
5
As-prepared ␣-Si
N Compared with that of
3 4
which was prepared by hydrolyzing a mixture of phenyltrimethox-
ysilane and tetraethoxysilane in 500°–600°C under nitrogen fol-
lowed by annealing in 1450°–1550°C to form crystalline Si N
JCPDS# 83-0700
Experimental
JCPDS# 83-0700
3
4
No.
2␪
d (Å)
hkl
d (Å)
6
powders. F. Hofer et al. prepared mixtures of oxynitride and
7
nitride of silicon by the reaction of CaSi with NH Cl. ␣-Si N
2
4
3
4
1
2
13.200
20.611
22.920
26.472
31.005
31.840
34.572
35.32
38.872
39.556
40.194
41.881
43.428
46.914
48.182
48.911
50.538
51.586
56.091
57.641
61.539
62.239
64.716
65.642
66.430
69.419
6.7013
4.3056
3.8768
3.3641
2.8818
2.8081
2.5923
2.5392
2.3148
2.2763
2.2416
2.1552
2.0819
1.9350
1.8870
1.8606
1.8044
1.7702
1.6382
1.5978
1.5056
1.4904
1.4392
1.4211
1.4061
1.3527
100
101
110
200
201
002
102
210
6.7246
4.3157
3.8825
3.3626
2.8863
2.8137
2.5956
2.5416
2.3163
2.2783
2.2415
2.1578
2.0824
1.9412
1.8861
1.8650
1.8068
1.7703
1.6381
1.5978
1.5093
1.4878
1.4385
1.4199
1.4068
1.3527
8
fibers were prepared by ammonolysis of FeSi at 1370°C, and
Si N mixtures of both ␣ and ␤ phases were produced by the
3
3
4
nitridation of high-silicon ferrosilicon in nitrogen at temperatures
4
9
5
ranging from 1300°–1500°C. In earlier research, we prepared
6
nanocrystalline Si N through a novel reaction of excessive SiCl
3
4
4
1
0
7
with NaN heated at 670°C for 30 min in an autoclave. As the
3
8
o
reaction is strongly exothermic (calculated ⌬H ϭ Ϫ920
៮
៮
9
211
Ϫ1
kcal⅐mol ), the product, a mixture of ␣- and ␤-Si N , may
៮ ៮
3
4
10
11
12
13
112
actually be formed due to instantaneously high local temperature.
In this paper, we report a reaction of Mg Si with NH Cl in the
300
202
301
220
2
4
temperature range of 450°–600°C in an autoclave under a pressure
1
1
1
1
1
1
2
2
2
2
2
4
5
6
7
8
9
0
1
2
3
4
៮
៮
212
310
103
៮
៮
311
203
L. Klein—contributing editor
៮
៮ ៮
៮
៮
222
៮
213
៮
321
303
Manuscript No. 10226. Received May 18, 2003; approved August 12, 2003.
This work was supported by the Key Project of National Fundamental Research
and the National Science Research Foundation of China.
៮
៮
411
004
*
Member, American Ceramic Society.
25
6
†
Author to whom correspondence should be addressed: e-mail: ytqian@ustc.
edu.cn.
2
322
៮ ៮
1
810

September 2004
Communications of the American Ceramic Society
1811
Fig. 2. TEM images and selected area electron diffraction (SAED) patterns of the ␣-Si N samples prepared at (a and b) 450°, (c) 500° and (d) 550°C.
3
4
of about 30–40 MPa. Preparation of nanocrystalline ␣-Si N
II. Experimental Procedure
3
4
powders are based on the reaction as follows:
In a typical process, 26.08 mmol of Mg Si (99.5%, stock #
2
4
50–600 °C
¡ alpha-Si N ϩ 6 MgCl
12837 Alfa Aesar, Ward Hill, MA, USA) and 0.1047 to 0.1122
3
Mg Si ϩ 12 NH Cl
2 4
3
4
2
mol of NH Cl (99.5%, analytical pure grade, Shanghai Chem-
4
ical Reagent Corp., Shanghai, P. R. China) were mixed and
placed in an autoclave with a glass-tube liner. The autoclave of
ϩ 8 NH ϩ 12 H (1)
3
2

1
812
Communications of the American Ceramic Society
Vol. 87, No. 9
Fig. 3. XPS spectra of the as-prepared ␣-Si N powders.
3
4
about 75 mL in capacity was sealed under an argon atmosphere
and maintained at 450°, 500°, 550°, and 600°C (Ϯ 5°C) for
the wide-scan XPS spectrum except a small amount of carbon
(reference mark) and oxygen, with binding energies of C1s and
O1s at 284.26 and 531.95 eV, respectively, in which oxygen is
1
0 h. The autoclave was cooled to room temperature naturally.
1
6
The products were collected and washed with distilled water
several times to remove MgCl and remaining NH Cl. The final
from surface adsorption.
According to the free energy calculations, the reaction between
2
4
products were dried in vacuum at 70°C for 12 h and white
powder products were obtained.
Mg Si and NH Cl to form ␣-Si N , MgCl , NH , and hydrogen
2
4
3
4
2
3
o
gases is thermodynamically spontaneous (calculated ⌬G ϭ Ϫ400
Ϫ1 o
kcal⅐mol ) and mildly exothermic (calculated ⌬H ϭ Ϫ227
Ϫ1
kcal⅐mol ). A gust of gases with an ammonia smell were noticed
III. Results and Discussion
when the autoclave was unsealed. An approximately stoichiomet-
ric amount of Mg(OH) according to the amounts of Mg Si was
2
2
The X-ray diffraction (XRD) patterns were recorded on an
X-ray diffractometer (XRD)(D/MAX-␥A, Rigaku, Japan) with Cu
K␣ radiation (wavelength ␭ ϭ 1.54178 ⌭). Figure 1 shows the
XRD patterns of the as-prepared products at 350°–600°C. As
shown in Table I, all the 26 peaks can be indexed as the hexagonal
cell of ␣-Si N , with lattice constants of a ϭ 7.770 and c ϭ 5.627
obtained by treating the water used to wash products with NaOH.
The maximal pressure is about 30 to 40 MPa in the temperature
range of 450° to 600°C, which is estimated according to the
amount of NH and hydrogen treated as ideal gases. Varying the
3
reaction temperature in the range of 450°–600°C did not signifi-
3
4
cantly affect the crystallinity or the yields of Si N (about 93%
Ϫ4
3 4
Å (The rms error is 3.153 ϫ 10 , calculated by the least squares
fitting method), in good agreement with a ϭ 7.765 and c ϭ 5.627
Å (JCPDS card# 83–0700). No evidence of ␤-Si N , cubic-Si N ,
according to the amount of Mg Si). In comparison, polycrystalline
2
silicon powders were found unreacted and Si N was not produced
3
4
3
4
3 4
when excessive NH Cl and mixed powders of magnesium and
4
and impurities were observed. As reaction temperatures decrease
from 600° to 450°C, the diffraction peaks broaden, indicating the
crystalline particles of the products become smaller.
silicon were heated at 600°C for 10 h in an autoclave. A mixture
of amorphous Si N and polycrystalline silicon was produced
3
4
when CaSi (Alfa Aesar, stock #14676) was heated with excessive
2
The morphology of the ␣-Si N powders was investigated by
3
4
NH Cl at 600°C for 10 h in an autoclave. When FeSi powders
4
transmission electron microscopy (TEM) (H-800, Hitachi, Japan),
which was taken with a Hitachi H-800 transmission electron
microscope. Figure 3 shows the typical TEM images and selected
area electron diffraction (SAED) patterns of the samples prepared
at 450°, 500°, and 550°C for 10 h. The products have particle
morphology. The ␣-Si N crystallites prepared in 450° (Fig. 3(a)
(
primitive cubic phase, a ϭ 4.415 Å, prepared by the reaction of
17
FeCl and Mg Si at 600°C for 12 h ) were used instead of Mg Si,
3
2
2
Si N was not produced and the FeSi remained unreacted, indi-
3
4
cating that Mg Si is the key factor for preparing nanocrystalline
2
␣
-Si N at the low temperature range of 450° to 600°C.
3 4
3
4
and (b)), 500° (Fig. 3(c)), 550° (Fig. 3(d)), and 600°C (not
published) are about 20, 40, 70, and 90 nm in average, respec-
tively. As shown in Fig. 3(b), the diffraction rings from inner to
outer, at d-spacings of 6.70, 4.29, 2.90, 2.60, 2.54, and 2.30 Å,
match ␣-Si N (100), (101), (201), (102), (210) and (Ϫ2–11)
IV. Conclusions
In summary, about 20- to 90-nm ␣-Si N powders have been
3
4
prepared by the reaction of Mg Si with NH Cl in the temperature
2
4
3
4
range of 450° to 600°C in an autoclave. XRD patterns of the
products can be indexed as ␣-Si N with the lattice constants of
planes, in good agreement with the XRD results.
3
4
The composition of the as-prepared ␣-Si N powders was
3
4
a ϭ 7.770 and c ϭ 5.627 Å. XPS analysis indicates that the
composition of the ␣-Si N samples has a Si:N ratio of 0.756.
studied by X-ray photoelectron spectroscopy (XPS) (ESCALAB
MKII, VG Scientific, U.K.), which was recorded on a VGES-
CALAB MKII X-ray photoelectron spectrometer with a non-
monochromatized Mg K␣ X-rays (h␥ ϭ 1253.6 eV) as the
excitation source. As shown in Fig. 2, the binding energy of Si2p
and N1s are 101.70 and 397.75 eV, respectively, which are in good
agreement with those of Si N (101.7–102.34 eV and 397.4–397.9
3
4
Such nanocrystalline ␣-Si N powders hold great potential for
3
4
improving properties of ceramic structural materials. This study
demonstrates an important route to nanocrystalline ␣-Si N that
3
4
can be applied for industrial use in the future.
3
4
1
1,12,13,14,15
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