# Patent

## Title
Boride having chemical composition Na—Si—B, and polycrystalline reaction sintered product of boride and process for production thereof

## Abstract

Provided are: a novel bonds useful as a highly-functional material; and a novel production method for a polycrystalline sintered product of a bonds, of which the energy cost is low, which does not require a sintering promoter, which enables the product to be worked into complicated forms and which enables a development to a polynary boride.
Provided are a boride having a composition Na—Si—B, and a polycrystalline reaction-sintered product thereof. A mixed compact of boron and an element, M (M means Si and/or C) is heated along with metal sodium to give a polycrystalline reaction-sintered product.

## Background
TECHNICAL FIELD
The present invention relates to a novel boride having a composition Na—Si—B, and to a polycrystalline reaction-sintered product of a boride and a method for producing it.
BACKGROUND ART
A boride, in which, in general, the boron atoms bond firmly to each other, has a high hardness, and its melting point or decomposition temperature is high. Accordingly, heretofore, a boride has been used for a heat-resistant material or an abrasion-resistant material. There are known many borides having electrically-specific characteristics such as semiconductor characteristics, thermal electron emission characteristics, superconductivity characteristics, etc. Lanthanum hexaboride (LaB6) has been put into practical use for a hot-cathode material, and magnesium dibromide (MgB2) is specifically noted as a superconductive material.
The electric characteristics of a boride strongly depend on the crystal structure thereof; and a boride having a small boron content exhibits electroconductivity, while a crystal that contains a structure of a boron icosahedron (B12 icosahedral cluster) has semiconductive electric characteristics.
Heretofore, as borides, there are known binary borides composed of two component elements such as the above-mentioned LaB6 and MgB2, and also B4C, BN, etc.; and polynary borides with three component elements. As the borides comprising a B12 icosahedral cluster, many substances have been discovered, for example, M-Al—B (where M means an alkali metal or an alkaline earth element) (for example, see PTL 1), RE1-xB12Si4-y (RE means one or more rare earth elements selected from Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; x and y are each fall within a range of 0≦x≦7 and 0≦y≦2) (for example, see PTL 2), etc.
In addition to application development of such already-existing borides, research and development of a further wide variety of borides to thereby develop highly-functional materials having any other novel function heretofore unknown and capable of being used for various applications has become an important theme.
On the other hand, a boride or a boron-containing carbide is a substance that is difficult to sinter since, in general, the covalent character thereof is strong. At present, as a method for producing a sintered product of a boride such as typically B4C, there is employed a hot isostatic press sintering method (HIP method) or a spark plasma sintering method (SPS method). In any case, the method requires high-temperature and high-pressure conditions, and the polycrystalline products capable of being produced by the sintering method are limited to those having a simple form. In addition, a boride that is a superhard material is difficult to work after production of the polycrystalline products thereof, and the limitation on the form thereof is a significant bar to industrial application of the material.
Apart from the above-mentioned pressure sintering method, a pressureless sintering method using a sintering promoter such as alumina, tungsten carbide or the like has been developed (for example, see NPL 1, 2). However, precipitation of the second phase to be caused by the sintering promoter used in such a sintering method may have some negative influence on the mechanical behavior of borides. In addition, as being carried out at a high temperature around 2000° C., the pressureless sintering method has another problem in that the energy cost thereof is high.
PRIOR ART DOCUMENTS
Patent Documents
Patent Documents 1: JP-A 2006-104037
Patent Documents 2: JP-A 2003-137535
Non-Patent Documents
Non-Patent Documents 1: J. Mater. Sci. Letter, 7 (1988) 695-696
Non-Patent Documents 2: J. Mater. Sci., 27 (1992) 6335-6340
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
The present invention has been made in consideration of the current situation as mentioned above, and the first object thereof is to provide a novel boride useful as a highly-functional material. The second object is to provide a novel production method for a polycrystalline sintered product of a boride, of which the energy cost is low as compared with that of any other conventional sintering method, which does not require a sintering promoter, which enables the product to be worked into complicated forms and which enables a development to a polynary boride.
Means for Solving the Problems
The boride of the invention is characterized by the following:

    (1) A ternary boride having a composition Na—Si—B,
    (2) The boride having a composition Na—Si—B of (1), wherein the boride is a compound represented by a general formula NaxSiyBz, (0<x, x<y<4x, 8x<z<20x).
    (3) The boride having a composition Na—Si—B of (1) or (2), wherein the crystal structure of the boride is a hexagonal system or a rhombohedral system.


The polycrystalline reaction-sintered product of a boride and the production method for the product of the invention are characterized by the following:

    (4) A polycrystalline reaction-sintered product of a ternary boride having a composition Na-M-B (where M means Si and/or C).
    (5) The polycrystalline reaction-sintered product of a boride of (4), wherein the ternary boride is a compound represented by a general formula NaxSiyBz (0<x, x<y<4x, 8x<z<20x).
    (6) A method for producing a polycrystalline reaction-sintered product of a boride of (4) or (5), which comprises heating a mixed compact of boron and an element, M (where M means Si and/or C) along with a metal sodium.
    (7) A method for producing a polycrystalline reaction-sintered product of a boride of (4) or (5), which comprises heating a boron compact along with a metal sodium and an element, M (where M means Si and/or C).
    (8) The method for producing a polycrystalline reaction-sintered product of a boride of (6) or (7), wherein the heating temperature is 800° C. or higher.
    (9) The method for producing a polycrystalline reaction-sintered product of a boride of any of (6) to (8), wherein the heating is in an inert gas atmosphere.


Effect of the Invention
The boride and the polycrystalline reaction-sintered product of a boride of the invention are unknown and new, and these are industrially-useful materials that are expected to be applicable to heat-resistant materials, abrasion-resistant materials, lightweight structural materials, thermoelectric conversion materials, etc.
The production method for a polycrystalline reaction-sintered product of the invention is a simple production method that comprises mere reaction sintering of a previously-molded, boron (B)-containing compact with any other substance than boron (B), in which it is easy to produce a polycrystalline reaction-sintered product of a boride having a complicated form without adding any foreign element thereto. According to the production method of the invention, various types of novel polynary boride sintered products containing Na and B can be produced in a simplified manner, and therefore the invention provides a direction that is extremely advantageous for research and development of polynary boride sintered products



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1(a) is a schematic view of a reactor for producing an Na—Si—B boride to be applied to Example 1 and Example 2. (b) is a schematic view of a reactor for producing a polycrystalline reaction-sintered product of an Na—Si—B boride to be applied to Example 3. (c) is a schematic view of a reactor for producing a polycrystalline reaction-sintered product of an Na—Si—B boride to be applied to Example 4. (d) is a schematic view of a reactor for producing a polycrystalline reaction-sintered product of an Na—C—B boride to be applied to Example 5.
FIG. 2 This is a scanning electron-microscopic (SEM) picture of a crystal sample of the Na—Si—B boride obtained in Example 1.
FIG. 3 This is an X-ray diffraction pattern of a crystal sample of the Na—Si—B boride obtained in Example 1.
FIG. 4 This is an X-ray diffraction pattern of a crystal sample of the Na—Si—B boride obtained in Example 2.
FIG. 5 This shows pictures of the outward appearance of the B compact (a) in Example 3 and a sample of the polycrystalline reaction-sintered product (b) obtained therein.
FIG. 6 This is an X-ray diffraction pattern of a sample of the polycrystalline reaction-sintered product obtained in Example 3.
FIG. 7 This shows pictures of the outward appearance of the B/Si mixed compact (a) in Example 4 and a sample of the polycrystalline reaction-sintered product (b) obtained therein.
FIG. 8 This shows pictures of the outward appearance of the B/C mixed compact (a) in: Example 5 and a sample of the polycrystalline reaction-sintered product (b) obtained therein.
FIG. 9 This is an X-ray diffraction pattern of a sample of the polycrystalline reaction-sintered product obtained in Example 5.



BEST MODE FOR CARRYING OUT THE INVENTION
The ternary boride having a composition Na—Si—B {ternary horde containing metal sodium (Na), silicon (Si) and boron (B)} (hereinafter this may be referred to as Na—Si—B boride) of the invention is described concretely. Needless-to-say, the following description is for easy understanding of the concept of the invention and is not for restricting the invention.
<Na—Si—B Boride>
The Na—Si—B boride of the invention is obtained by mixing Na, Si and B followed by heating at a high temperature of generally 800° C. or higher. Needless-to-say, the Na—Si—boride of the invention may be contaminated with minor impurities that are derived from the starting materials and the reactor used not interfering with the production of the boride having a composition Na—Si—B.
Na to be used in the invention may be any known Na and is not specifically defined. Si to be used in the invention may be any known Si and, not specifically defined, any massive or powdery Si can be used here. B to be used in the invention may be any known B, and not specifically defined, any crystalline or amorphous one is usable here.
The stable existence region of the Na—Si—B boride of the invention may be represented by a general formula, NaxSiyBz. The value of x is 0<x, preferably 0<x<10; the value of y is x<y<4x; and the value of z is 8x<z<20x. The crystal structure of the boride belongs to a hexagonal system or a rhombohedral system, including a structure of a boron icosahedron (B12 icosahedral cluster). The compound having a typical composition is Na8Si17.5B74.5 with x=8, of which the lattice constants of the hexagonal system are a=1.024±0.008 nm and c=1.092±0.008 nm.
The Na—Si—B boride of the invention is superior to conventional known borides in that the former can provide a crystal having a strength and a hardness on the same level as that of the crystals of the latter at a low temperature.
<Production of Na—Si—B Boride>
The Na—Si—B boride of the invention can be obtained, in general, by putting the components of the above-mentioned Na, Si and B in a specific blend ratio as rough standards, into a reactor, then sealing up the reactor along with an inert gas also put thereinto, and heating them therein.
The blend ratio of the components of Na, Si and B is generally in a range of (1 to 10)/(0.1 to 5)/(0.1 to 10) as the ratio by mol of Na/Si/B, and for example, the blend ratio may be 5/1/6 by mol. The inert gas to be put into the reactor may be any gas with low chemical reactivity and, not specifically defined, includes rare gases, nitrogen gas, etc. In the invention, argon gas is especially preferably used.
The method for supplying Na is not specifically defined, for which is employable a supply method of vapor supply, melt supply, etc.
Regarding the heating condition, the heating temperature may be 800° C. or higher, preferably from 800° C. to 1200° C., and the heating time may be from 1 to 48 hours, preferably 24 hours. The heating condition enables sufficient reaction of the components in the reactor.
The condition of the heating time mentioned above is one based on the crystal size and the blend amount of B used in Examples given below, and in case where the crystal size and the blend amount of B are smaller than those in Examples, the heating time could be shorter than the above-mentioned condition for sufficient reaction.
In the reactor after the reaction, there may exist some residues such as NaSi compounds and others in addition to the Na—Si—B boride compound of the invention; and by removing the other substances than the Na—Si—B boride compound through washing with ethanol and distilled water, the Na—Si—B boride compound of the invention can be obtained.
The crystal structure of the Na—Si—B boride of the invention mentioned above may be a hexagonal system when an amorphous powder B is used and reacted at a temperature lower than 1000° C. or when a crystalline B is used, or may be a rhombohedral system when an amorphous powder B is used and reacted at 1000° C. or higher.
<Polycrystalline Reaction-Sintered Product of Na-M-B Boride (where M is Si and/or C)>
The polycrystalline reaction-sintered product of an Na-M-B boride (where M means Si and/or C) of the invention (hereinafter this may be referred to as a boride polycrystalline product or a polycrystalline product) can be obtained by sintering the Na—Si—B boride or the like of the invention mentioned above, and has the same composition as that of the starting boride. In producing the reaction-sintered product of the Na-M-B boride (where M means Si and/or C) of the invention, the same as the above-mentioned Na—Si—B boride may be used as the precursor thereof,
Various types of borides are usable here, but preferably, compounds represented by a general formula NaxSiyBz are used (0<x, x<y<4x, 8x<z<20x).
Any known Na is usable in the production method for the above-mentioned boride polycrystalline product of the invention. The Na supply method for the compact is not specifically defined, for which suitably employable is a method of vapor supply, melt supply, etc. B to be used here may be any ordinary known crystalline or amorphous one. As the element M to constitute the polynary boride along with Na and B, usable here is Si and/or C.
The production method for the boride polycrystalline product of the invention enables production of polynary borides that cover ternary borides composed of three components of Na-M-B and any others combined with multiple elements M. More concretely, the production method may be any of a method for producing a boride polycrystalline product by heating a mixed compact of B and M along with Na, or a method for producing a boride polycrystalline product by heating a B compact along with Na and M.
In the production method for the boride polycrystalline product of the invention, preferably, the compact and the other constituent material are put into a reactor along with an inert gas, and then the reactor is sealed up and heated. Not specifically defined, the inert gas may be any one having low chemical reactivity, and includes rare gases, nitrogen gas, etc. In the invention, argon gas is especially preferably used.
As the indication thereof to be taken into consideration here, the heating temperature may be 800° C. or higher, preferably from 800 to 1200° C., and the heating time may be from 1 to 48 hours, preferably from 20 to 30 hours. The heating condition makes it possible to fully compound and sinter the constitutive components for the boride polycrystalline product in the reactor, thereby giving the boride polycrystalline product of high quality.
The condition of the heating time mentioned above is one for the case where the dimension of the compact to be used is about 2.0 m×3.0 mm×14.0 mm, but in the other case where the dimension of the compact to be used is smaller than in that case, the heating time could be shorter than the above-mentioned condition for sufficient compounding and sintering.
In the reactor after the reaction, there may exist some residues such as other compounds than the boride polycrystalline product of the invention; and by removing the other substances than the boride through washing with ethanol and distilled water, the boride polycrystalline product of the invention can be obtained.
In the production method for the boride polycrystalline product of the invention, used are Si and/or C as the above-mentioned M. C is any ordinary known one, including powdery substances of carbon black, fullerene, etc. Si may also be any ordinary known one, including massive or powdery Si.
Preferred embodiments of the production method for the boride polycrystalline product of the invention are mentioned below, in which Si is used as M to give a boride sintered product, or C is used to give a boride sintered product.
<Production of Na—Si—B Boride Polycrystalline Product (1)>
In the production method using a B compact, first, amorphous B is powdered and compressed to give a B compact. Next, in an inert gas atmosphere, Na and Si are weighed so that the ratio by mol of Na/Si/B could fall, as a rough standard thereof, within a range of (1 to 10)/(0.1 to 5)/(0.1 to 10), more preferably the ratio could be 3/1/1, put into a reactor and sealed up therein, and heated under the condition of the invention mentioned above, and thereafter cooled to give an Na—Si—B boride polycrystalline product.
<Production of Na—Si—B Boride Polycrystalline Product (2)>
In the production method using a B—Si mixed compact, amorphous B and Si are so weighed that the ratio by mol of the two could be, as a rough standard thereof, 4/x (where x is from 1 to 4), and mixed, and then powdered and compressed to give a B—Si mixed compact. Next, in an inert gas atmosphere, the B—Si mixed compact and Na are put in different crucibles, the two crucibles are put into a reactor and sealed up therein, and heated under the condition of the invention mentioned above, and thereafter cooled. In this method, Na is supplied as a vapor phase and compounded with the B—Si mixed compact to give an Na—Si—B boride polycrystalline product.
<Production of Na—C—B Boride Polycrystalline Product>
In the production method using a B—C mixed compact, B and C are so weighed that the ratio by mol of B/C could be, as a rough standard thereof, from 2 to 8, and mixed, and then powdered and compressed to give a B—C mixed compact. Next, in an inert gas atmosphere, the B—C mixed compact and Na are put into a reactor and sealed up therein, and heated under the condition of the invention mentioned above, and thereafter cooled to give an Na—C—B boride polycrystalline product. In the method where the molar ratio B/C is 5, an NaCB5 boride polycrystalline product can be produced.
In the boride polycrystalline product production method of the invention, the compact to be prepared through powdering followed by compression may be made to have any desired form, and therefore in the method, it is easy to produce a polycrystalline reaction-sintered product of a boride having a complicated form that has theretofore been extremely difficult to produce according to sintering methods. In addition, the method does not require any high-temperature high-pressure condition such as that in a hot isostatic press sintering method (HIP method) or a spark plasma sintering method (SPS method) heretofore employed for production of sintered products, and does not require any sintering promoter used in pressureless sintering methods, and therefore in the method, a high-quality boride polycrystalline product can be produced at low energy cost.
EXAMPLES
Next, the Na—Si—B boride and the polycrystalline reaction-sintered product of an Na-M-B boride (where M means Si and/or C) of the invention are described concretely with reference to Examples; however, the invention is not whatsoever restricted by the following Examples.
Example 1
In a glove box having therein a high-purity argon gas atmosphere (in which the concentration of O2 and H2O was less than 1 ppm each), 0.09 g of Na (by Nippon Soda, having a purity of 99.95%), 0.02 g of powdery Si (by Kojundo Chemical Laboratory, having a purity of 99.999% and a particle size of less than 75 μm), and 0.05 g of crystalline B (by Wako Pure Chemicals, having a purity of 99.5%) were so weighed that the ratio by mol of Na/Si/B could be 5/1/6.
Next, as shown in FIG. 1(a), the weighed Na1, Si2 and B3 were put into a BN crucible 6. The BN crucible 6 used here is a sintering BN crucible (by Showa Denko).
The BN sintering crucible 6 was set inside a reactor 7 (made of stainless SUS316), and the reactor 7 was sealed up with a cap 8 made of stainless in a high-purity argon atmosphere. The reactor 7 used here has an inner diameter of 10 mm and an outer diameter of 80 mm. Subsequently, the reactor 7 was set in an electric furnace, and heated up to 800 to 1200° C. taking 2 hours, then left as such for 24 hours, and thereafter cooled to room temperature, and the reactor 7 was taken out.
The reactor 7 was cut in the globe box, and the BN crucible 6 was taken out. Inside the crucible, there existed a mixture of black powdery substance and a silver substance. The formed silver substance was analyzed through X-ray diffractiometry (using Rigaku's “Rint” (trade name) with a radiation source of CuKα), by which the substance was identified as one mainly comprising an intermetallic compound of NaSi (compositional ratio 1/1) and Na.
The mixture obtained in the above was washed with ethanol and distilled water to thereby remove the NaSi compound and Na. After the washing, the remaining black crystal substance was recovered.
Next, a scanning electron-microscopic (SEM) picture of a crystal sample obtained by heating Na, Si and crystalline B at 1000° C. is shown in FIG. 2. The observed crystals are hexagonal columns and have a size of from about tens to 200 μm.
Of the above sample, a single crystal having a size of about 100 μm was cut out, and the single crystal was analyzed through X-ray diffractiometry using a single-crystal X-ray diffractometry apparatus (Rigaku's “RAPID” (trade name) with a radiation source of MoKα) equipped with an imaging plate. The X-ray diffraction spots confirmed that the obtained crystal sample was a hexagonal system crystal having a space group of P63/mmc and lattice constants of a=1.024±0.008 nm and c=1.092±0.008 nm.
In the crystal, the boron icosahedrons (B12 icosahedral cluster) formed a three-dimensional network.
Tables 1 to 4 show the results obtained from the single-crystal X-ray diffractiometry data of the Na—Si—B boride of Example 1.







TABLE 1







X-Ray Diffraction Data of Example 1














h
k
l
2θ
d
Iobs

















1
0
0
9.963
8.8710
20



1
0
1
12.862
6.8772
1



0
0
2
16.269
5.4439
2



1
1
0
17.300
5.1217
3



1
0
2
19.113
4.6399
15



2
0
0
20.002
4.4355
6



2
0
1
21.617
4.1077
18



1
1
2
23.835
3.7303
0



2
0
2
25.890
3.4386
46



1
0
3
26.514
3.3590
14



2
1
0
26.564
3.3529
1



2
1
1
27.819
3.2044
34



3
0
0
30.200
2.8570
2



2
1
2
31.307
2.8549
30



3
0
1
31.321
2.8536
51



2
0
3
31.834
2.8088
48



0
0
4
32.878
2.7219
28



1
0
4
34.437
2.6022
31



3
0
2
34.469
2.5984
5



2
2
0
35.011
2.5608
70



2
1
3
36.453
2.4628
35



3
1
0
36.490
2.4604
16



1
1
4
37.384
2.4036
2



3
1
1
37.444
2.3999
13



2
0
4
38.785
2.3199
11



2
2
2
38.831
2.3172
100



3
0
3
39.269
2.2924
23



3
1
2
40.189
2.2420
5



4
0
0
40.649
2.2177
9



4
0
1
41.521
2.1731
2



1
0
5
42.723
2.1148
23



2
1
4
42.755
2.1132
2



4
0
2
44.055
2.0539
1



3
1
3
44.450
2.0365
8



3
2
0
44.481
2.0351
64



3
0
4
45.243
2.0027
0



3
2
1
46.294
2.0005
9



2
0
5
46.417
1.9547
29



4
1
0
46.897
1.9358
7



3
2
2
47.667
1.9063
1



4
1
1
47.677
1.9059
2



4
0
3
48.039
1.8924
4



2
2
4
48.787
1.8651
3



2
1
5
49.897
1.8262
36



3
1
4
49.925
1.8252
9



4
1
2
49.964
1.8239
0



0
0
6
50.237
1.8146
2



1
0
6
51.352
1.7778
0



3
2
3
51.437
1.7751
1



5
0
0
51.465
1.7742
1



3
0
5
52.120
1.7534
11



5
0
1
52.194
1.7511
7



4
0
4
53.234
1.7183
1



1
1
6
53.532
1.7104
0



4
1
3
53.614
1.7080
0



3
3
0
53.641
1.7072
26



5
0
2
54.341
1.6869
2



2
0
6
54.600
1.6795
1



4
2
0
54.707
1.6765
2



4
2
1
55.407
1.6569
3



3
1
5
56.380
1.6306
0



3
2
4
56.406
1.6299
39



3
3
2
56.441
1.6290
0



4
2
2
57.472
1.6022
2



2
1
6
57.721
1.5959
12



5
0
3
57.798
1.5939
1



5
1
0
57.824
1.5933
1



4
1
4
58.457
1.5775
2



5
1
1
58.500
1.5765
11



4
0
5
59.440
1.5539
2



3
0
6
59.742
1.5466
9



1
0
7
60.371
1.5320
0



5
1
2
60.497
1.5291
1



4
2
3
60.813
1.5219
3



3
2
5
62.406
1.4869
1



5
0
4
62.431
1.4663
0



2
2
6
62.700
1.4806
1



6
0
0
62.799
1.4785
17



2
0
7
63.311
1.4678
0



6
0
1
63.442
1.4651
2



3
1
6
63.668
1.4604
4



5
1
3
63.742
1.4589
4



4
3
0
63.766
1.4584
1



4
1
5
64.339
1.4468
3



3
3
4
64.363
1.4483
21



4
3
1
64.404
1.4455
9



4
2
4
65.318
1.4274
13



6
0
2
65.350
1.4268
0



5
2
0
65.677
1.4205
0



2
1
7
66.177
1.4110
10



4
3
2
66.297
1.4087
1



5
2
1
66.305
1.4066
2



4
0
6
66.526
1.4044
1



3
0
7
66.053
1.3766
1



5
0
5
66.116
1.3755
34



5
1
4
68.140
1.3750
0



5
2
2
68.171
1.3745
0



6
0
3
68.468
1.3692
1



0
0
8
68.943
1.3610
0



3
2
6
69.324
1.3544
0



4
3
3
69.394
1.3532
20



6
1
0
69.418
1.3528
0



1
0
8
69.866
1.3452
6



6
1
1
70.029
1.3425
3



4
2
5
70.884
1.3284
1



4
1
6
71.160
1.3239
0



5
2
3
71.230
1.3228
1



1
1
8
71.696
1.3153
1



3
1
7
71.734
1.3147
3



6
1
2
71.850
1.3129
0



2
0
6
72.603
1.3011
2



6
0
4
72.726
1.2992
1



5
1
5
73.606
1.2858
3



4
3
4
73.629
1.2855
0



4
4
0
73.969
1.2804
3



4
0
7
74.444
1.2734
0



5
0
6
74.775
1.2686
7



6
1
3
74.843
1.2676
0



7
0
0
74.866
1.2673
2



5
3
0
74.866
1.2673
0



2
1
8
75.301
1.2610
0



5
2
4
75.422
1.2593
0



5
3
1
75.460
1.2588
7



7
0
1
75.460
1.2588
0



4
4
2
76.343
1.2464
3



3
3
6
76.559
1.2434
0



3
0
8
77.080
1.2363
1



3
2
7
77.118
1.2358
2



7
0
2
77.230
1.2343
0



5
3
2
77.230
1.2343
1



4
2
6
77.446
1.2314
1



6
2
0
77.536
1.2302
0



6
0
5
78.063
1.2232
2



6
2
1
78.122
1.2224
8



4
1
7
78.885
1.2125
0



4
3
5
78.944
1.2117
3



6
1
4
78.967
1.2114
0



2
2
8
79.727
1.2018
9



6
2
2
79.875
1.1999
3



1
0
9
79.977
1.1987
2



5
1
6
80.089
1.1973
4
















TABLE 2





Crystal data and structure refinement for Na6Si17.5B74.5.
















Empirical formula
Na6Si17.5B74.5


Temperature
293(2) K


Wavelength
0.71075 Å


Crystal system, space group
hexagonal, P63/mmc









Unit cell dimensions
a = 10.2392(3) Å
alpha = 90 deg.



b = 10.2392(3) Å
beta = 90 deg.



c = 10.9215(4) Å
gamma = 120 deg.








Absorption coefficient
0.690 mm−1


Limiting indices
−13 <= h <= 13, −13 <= k <= 13,



−14 <= l <= 13


Refinement method
Full-matrix least-squares on F2


Data/restraints/parameters
467/1/52


Goodness-of-fit-on F2
1.139


Final R indices [I > 2sigma(I)]
R1 = 0.0389, wR2 = 0.0938


R indices (all data)
R1 = 0.0439, wR2 = 0.0965


Largest diff. peak and hole
0.919 and −0.455 e · A−3
















TABLE 3







Atomic coordinates (×104) and equivalent isotropic displacement


parameters (A2 × 103) for Na6Si17.5B74.5. U(eq) is defined as one


third of the trace of the orthogonalized U§ tensor.












x
y
z
U(eq)
















Na(1)
1665(1)
3331(2)
2500
16(1)



Na(2)
3333
6667
2500
15(1)



B(1)
3763(3)
 340(3)
 762(2)
11(1)



B(2)
1575(3)
4893(3)
 504(2)
11(1)



B(3)
5187(2)
 373(4)
6654(3)
7(1)



B(4)
5748(2)
1497(5)
 942(3)
13(1)



B(5)
3333
6667
6500(20)
16(2)



Si(1)
3333
6667
6844(6)
16(2)



Si(2)
1300(1)
2600(1)
6421(1)
9(1)



Si(3)
  0
  0
1053(2)
11(1)
















TABLE 4-1







Observed and calculated structure factors for Na8Si175B74.5














h
k
l
10Fa
10Fc
10s

















−1
2
0
127
113
1



0
2
0
230
187
1



−1
3
0
92
69
1



0
3
0
170
153
2



−2
4
0
1337
1361
9



−1
4
0
482
472
2



0
4
0
531
537
3



−2
5
0
1145
1171
5



−1
5
0
349
376
1



0
5
0
272
284
2



−3
6
0
1303
1323
10



−2
6
0
279
277
2



−1
6
0
181
172
2



0
6
0
1279
1305
10



−3
7
0
169
160
3



−2
7
0
37
29
5



−1
7
0
27
42
9



0
7
0
577
600
4



−4
8
0
654
632
5



−3
8
0
34
28
7



−2
8
0
36
22
6



−1
8
0
684
692
3



0
8
0
773
772
6



−4
9
0
256
263
3



−3
9
0
54
53
5



−2
9
0
29
18
10



−1
9
0
531
528
5



0
9
0
242
235
8



−5
10
0
1105
1089
11



−4
10
0
323
321
4



−3
10
0
152
157
5



−2
10
0
85
91
5



−1
10
0
34
22
22



0
10
0
441
430
8



−5
11
0
374
365
4



−4
11
0
273
262
6



−3
11
0
94
104
9



−2
11
0
65
66
14



−1
11
0
455
443
7



0
11
0
347
319
13



−6
12
0
604
595
9



−5
12
0
49
55
21



−4
12
0
144
145
7



−3
12
0
292
293
7



−2
12
0
309
300
7



−6
13
0
163
192
16



−5
13
0
104
138
13



0
3
2
250
239
2



−2
4
2
1315
1275
6



−1
4
2
224
225
1



0
4
2
204
219
2



−2
5
2
123
105
1



−1
5
2
59
40
2



0
5
2
237
237
3



−3
6
2
75
85
3



−2
6
2
205
231
1



−1
6
2
119
110
2



0
6
2
113
100
4



−3
7
2
114
117
2



−2
7
2
106
91
1



−1
7
2
39
25
5



0
7
2
57
63
6



−4
8
2
418
432
3



−3
8
2
248
259
2



−2
8
2
375
366
2



−1
8
2
164
164
3



0
8
2
99
110
6



−4
9
2
80
78
3



−3
9
2
23
18
8



−2
9
2
215
213
3



−1
9
2
164
163
3



0
9
2
45
42
9



−5
10
2
109
110
4



−4
10
2
100
105
3



−3
10
2
41
38
8



−2
10
2
354
343
3



−1
10
2
73
73
5



0
10
2
80
95
8



−5
11
2
43
45
6



−4
11
2
129
145
4



−3
11
2
230
220
4



−2
11
2
133
152
5



−1
11
2
162
169
7



0
11
2
40
11
25



−6
12
2
56
40
13



−5
12
2
10
6
9



−4
12
2
160
184
6



−3
12
2
192
212
7



−2
12
2
63
56
19



−6
13
2
57
62
9



−5
13
2
15
10
15



0
1
3
315
330
1



0
2
3
689
689
3



−1
3
3
455
468
1



−2
5
4
855
884
3



−1
5
4
142
140
2



0
5
4
67
44
5



−3
6
4
990
999
5



−2
6
4
629
643
2



−1
6
4
41
30
5



0
6
4
314
299
3



−3
7
4
61
64
3



−2
7
4
61
65
4



−1
7
4
160
153
2



0
7
4
693
688
5



−4
8
4
82
77
4



−3
8
4
93
84
2



−2
8
4
246
235
3



−1
8
4
550
540
3



0
8
4
871
858
5



−4
9
4
253
249
2



−3
9
4
74
77
4



−2
9
4
0
9
1



−1
9
4
356
346
3



0
9
4
268
258
5



−5
10
4
655
678
12



−4
10
4
576
563
3



−3
10
4
85
90
5



−2
10
4
242
233
4



−1
10
4
0
3
1



0
10
4
46
46
14



−5
11
4
462
459
4



−4
11
4
53
58
7



−3
11
4
37
24
12



−2
11
4
34
37
14



−1
11
4
107
119
6



0
11
4
58
82
18



−6
12
4
122
103
8



−5
12
4
107
116
6



−4
12
4
32
35
17



−3
12
4
315
304
4



0
1
5
695
693
3



0
2
5
821
832
4



−1
3
5
724
729
2



0
3
5
532
562
3



−1
4
5
127
121
1



0
4
5
302
316
2



−2
5
5
139
134
2



−1
5
5
286
286
1



0
5
5
1366
1386
8



−2
6
5
157
159
1



0
7
6
45
37
10



−4
8
6
479
469
4



−3
8
6
400
404
2



−2
8
6
216
215
3



−1
8
6
240
222
3



0
8
6
308
310
5



−4
9
6
92
102
3



−3
9
6
175
174
5



−2
9
6
336
329
3



−1
9
6
185
183
5



0
9
6
49
56
14



−5
10
6
392
372
6



−4
10
6
105
104
4



−3
10
6
58
70
8



−2
10
6
260
249
4



−1
10
6
140
146
6



0
10
6
41
30
19



−5
11
6
0
13
1



−4
11
6
209
212
9



−3
11
6
402
391
5



−2
11
6
258
256
5



−6
12
6
194
209
17



0
1
7
50
18
3



0
2
7
77
85
2



−1
3
7
472
480
2



0
3
7
211
209
2



−1
4
7
291
295
2



0
4
7
37
28
3



−2
5
7
257
250
2



−1
5
7
23
4
9



0
5
7
158
143
3



−2
6
7
118
118
2



−1
6
7
128
124
3



0
6
7
61
73
4



−3
7
7
221
217
2



−2
7
7
106
89
3



−1
7
7
67
76
4



0
7
7
58
56
8



−3
8
7
178
188
4



−2
8
7
0
5
1



−1
8
7
104
109
4



0
8
7
69
58
9



−4
9
7
76
90
5



−3
9
7
16
4
16



−2
9
7
380
373
4



−1
9
7
294
280
4



0
9
7
65
80
12



−1
4
9
361
368
2



0
4
9
79
68
5



−2
5
9
60
66
3



−1
5
9
309
308
2



0
5
9
400
403
4



−2
6
9
18
6
17



−1
6
9
303
292
2



0
6
9
284
288
4



−3
7
9
87
84
4



−2
7
9
370
366
3



−1
7
9
208
208
4



0
7
9
389
364
8



−3
8
9
521
514
4



−2
8
9
445
432
4



−1
8
9
102
117
8



0
8
9
104
118
15



−4
9
9
68
87
9



−3
9
9
38
45
14



−2
9
9
110
149
10



−1
9
9
40
45
13



−4
10
9
37
16
25



−3
10
9
441
442
11



0
8
10
940
899
25



0
1
10
27
9
27



−1
2
10
335
345
4



0
2
10
512
518
4



−1
3
10
312
311
2



0
3
10
565
551
4



−2
4
10
294
286
4



−1
4
10
229
225
3



0
4
10
374
370
4



−2
5
10
294
290
3



−1
5
10
109
110
4



0
5
10
640
642
5



−3
6
10
51
35
9



−2
6
10
108
115
4



−1
6
10
453
440
3



0
6
10
272
270
4



−3
7
10
152
156
4



−2
7
10
413
407
3



−1
7
10
158
164
4



0
7
10
16
18
16



−4
8
10
276
276
5



−3
8
10
252
250
5



−2
8
10
349
339
5



−1
8
10
84
106
8



0
8
10
218
222
18






















TABLE 4-2






h
k
l
10Fa
10Fc
10s






















0
2
1
226
235
1



−1
3
1
414
388
1



0
3
1
730
726
3



−1
4
1
245
257
1



0
4
1
243
246
2



−2
5
1
310
286
1



−1
5
1
139
163
1



0
5
1
502
511
2



−2
6
1
268
267
1



−1
6
1
451
455
1



0
6
1
339
368
2



−3
7
1
528
536
2



−2
7
1
263
258
1



−1
7
1
290
286
1



0
7
1
176
148
3



−3
8
1
502
492
2



−2
8
1
579
582
2



−1
8
1
29
9
8



0
8
1
142
143
3



−4
9
1
61
60
4



−3
9
1
231
230
2



−2
9
1
224
215
3



−1
9
1
106
106
3



0
9
1
44
42
10



−4
10
1
292
280
2



−3
10
1
277
275
2



−2
10
1
304
299
3



−1
10
1
91
98
4



0
10
1
705
667
7



−5
11
1
32
28
9



−4
11
1
103
121
3



−3
11
1
234
234
5



−2
11
1
287
289
5



−1
11
1
191
209
5



0
11
1
104
88
11



−5
12
1
339
340
4



−4
12
1
205
201
6



−3
12
1
9
16
9



−2
12
1
17
21
17



−6
13
1
154
151
8



−5
13
1
341
339
5



0
0
2
188
185
1



0
1
2
218
222
1



−1
2
2
56
42
1



0
2
2
565
586
2



−1
3
2
421
400
1



0
1
14
79
92
14



0
3
3
609
600
2



−1
4
3
351
331
1



0
4
3
321
336
2



−2
5
3
153
148
1



−1
5
3
56
62
3



0
5
3
164
185
3



−2
6
3
232
237
1



−1
6
3
295
316
2



0
6
3
234
234
3



−3
7
3
753
775
2



−2
7
3
176
176
2



−1
7
3
48
45
4



0
7
3
263
278
4



−3
8
3
29
16
6



−2
8
3
23
11
13



−1
8
3
104
98
3



0
8
3
184
172
5



−4
9
3
114
121
2



−3
9
3
127
132
3



−2
9
3
186
192
3



−1
9
3
7
2
7



0
9
3
124
123
6



−4
10
3
0
4
1



−3
10
3
79
82
5



−2
10
3
180
179
4



−1
10
3
97
96
5



0
10
3
320
311
5



−5
11
3
150
154
5



−4
11
3
34
42
10



−3
11
3
326
317
3



−2
11
3
53
55
8



−1
11
3
71
71
8



0
11
3
26
31
25



−5
12
3
261
253
6



−4
12
3
161
170
7



−3
12
3
47
64
12



−2
12
3
148
159
6



0
0
4
1335
1267
17



0
1
4
639
652
2



−1
2
4
87
94
2



0
2
4
477
470
2



−1
3
4
118
104
1



0
3
4
18
5
10



−2
4
4
287
270
2



−1
4
4
354
371
1



0
4
4
203
191
1



−1
2
14
366
325
9



−1
6
5
304
296
2



0
6
5
396
389
3



−3
7
5
345
344
2



−2
7
5
356
359
2



−1
7
5
174
165
2



0
7
5
36
35
12



−3
8
5
426
434
2



−2
8
5
348
346
3



−1
8
5
102
105
4



0
8
5
158
146
5



−4
9
5
233
249
3



−3
9
5
176
178
3



−2
9
5
385
387
3



−1
9
5
78
81
5



0
9
5
29
4
20



−4
10
5
24
9
23



−3
10
5
415
403
3



−2
10
5
346
334
4



−1
10
5
32
20
14



0
10
5
367
360
5



−5
11
5
479
478
4



−4
11
5
163
175
6



−3
11
5
293
291
5



−2
11
5
93
104
7



−1
11
5
272
266
4



−5
12
5
26
6
25



−4
12
5
185
195
6



0
0
6
652
623
16



0
1
6
76
66
2



−1
2
6
117
117
3



0
2
6
141
156
2



−1
3
6
497
507
2



0
3
6
606
612
4



−2
4
6
179
161
2



−1
4
6
324
322
1



0
4
6
181
166
2



−2
5
6
32
31
5



−1
5
6
38
41
3



0
5
6
689
678
4



−3
6
6
23
15
10



−2
6
6
202
196
2



−1
6
6
394
396
2



0
6
6
534
540
4



−3
7
6
163
168
2



−2
7
6
287
286
2



−1
7
6
85
71
4



−4
10
7
102
118
7



−3
10
7
226
234
9



−2
10
7
17
16
16



−1
10
7
73
83
8



0
10
7
134
153
14



−5
11
7
59
86
11



−4
11
7
123
152
11



−3
11
7
78
91
8



0
0
8
387
334
12



0
1
8
561
565
3



−1
2
8
107
99
2



0
2
8
325
330
2



−1
3
8
37
21
4



0
3
8
259
269
3



−2
4
8
809
806
4



−1
4
8
241
235
2



0
4
8
119
122
3



−2
5
8
469
471
2



−1
5
8
51
51
5



0
5
8
29
5
12



−3
6
8
316
316
3



−2
6
8
65
55
4



−1
6
8
42
54
4



0
6
8
142
133
3



−3
7
8
126
130
3



−2
7
8
30
35
8



−1
7
8
241
237
3



0
7
8
560
566
6



−4
8
8
215
226
9



−3
8
8
154
162
4



−2
8
8
197
198
6



−1
8
8
241
256
9



0
8
8
254
253
6



−4
9
8
199
207
8



−3
9
8
28
13
17



−2
9
8
35
39
15



−1
9
8
80
101
7



0
9
8
151
178
15



−5
10
8
278
277
7



−4
10
8
166
192
15



−3
10
8
0
16
1



−2
10
8
160
174
10



0
1
9
233
242
3



0
2
9
370
374
4



−1
3
9
284
279
2



0
3
9
413
408
3



−4
9
10
0
8
1



−3
9
10
331
315
5



0
1
11
122
123
9



0
2
11
84
93
6



−1
3
11
73
69
4



0
3
11
81
91
7



−1
4
11
68
78
5



0
4
11
190
192
5



−2
5
11
193
194
3



−1
5
11
45
51
7



0
5
11
82
83
7



−2
6
11
32
18
11



−1
6
11
243
230
3



0
6
11
55
50
15



−3
7
11
192
206
6



−2
7
11
34
26
18



−1
7
11
110
116
7



0
7
11
40
37
23



−3
8
11
209
223
8



−2
8
11
124
130
6



0
0
12
377
317
20



0
1
12
112
130
20



−1
2
12
92
113
15



0
2
12
95
113
15



−1
3
12
50
61
9



0
3
12
226
227
12



−2
4
12
222
221
9



−1
4
12
47
58
9



0
4
12
56
64
12



−2
5
12
138
164
8



−1
5
12
140
153
8



0
5
12
165
175
14



−3
6
12
117
130
9



−2
6
12
53
65
9



−1
6
12
100
117
6



0
6
12
112
132
10



−3
7
12
156
172
7



0
1
13
24
35
24



0
2
13
421
389
7



−1
3
13
325
313
7



0
3
13
252
247
22



−1
4
13
7
23
7



0
4
13
62
73
17



−2
5
13
116
139
10



−1
5
13
214
229
15



0
0
14
114
177
102









FIG. 3 shows the X-ray diffraction pattern of the above-mentioned crystal sample. The X-ray diffraction pattern can be explained by the above-mentioned lattice constants.
As a result of the compositional analysis according to a wavelength dispersion X-ray analysis method (WDX), the obtained crystal sample was confirmed to comprise Na, Si and B. In the crystal, no other element than Na, Si and B was detected. These results confirm that the obtained crystal sample is an Na—Si—B boride of the invention having a composition of Na6Si17.5B74.5.
The c-plane of the obtained single crystal was analyzed in a micro-Vickers hardness test and, as a result, the hardness of the crystal was 20.4±0.6 GPa.
Example 2
A crystal sample was obtained under the same condition and according to the same method as in Example 1 except that the crystalline B in Example 1 was changed to amorphous powdery B (by Wako Pure Chemicals, having a purity of 95%).
The crystal sample obtained by heating Na, Si and amorphous Bat 1000° C. had a crystal structure of a rhombohedral system, and the lattice constants thereof were a=1.020±0.00 nm and c=1.661±0.008 nm.
Table 5 shows the X-ray diffraction data of the Na—Si—B boride of Example 2.







TABLE 5







X-Ray Diffraction Data of Example 2














h
k
l
2θ
d
Iobs

















1
0
1
11.352
7.7881
2



0
1
2
14.700
6.0211
2



0
0
3
16.159
5.4808
6



1
1
0
17.355
5.1055
1



0
2
1
20.767
4.2698
31



2
0
2
22.818
3.8940
15



1
1
−3
23.799
3.7358
2



1
1
3
23.799
3.7358
2



1
0
4
23.852
3.7276
30



1
2
−1
27.205
3.2753
0



2
1
1
27.205
3.2753
0



2
1
−2
28.611
3.0962
0



1
2
2
28.811
3.0962
0



0
1
5
28.945
3.0623
37



0
2
4
29.650
3.0105
100



3
0
0
30.297
2.9477
5



0
0
6
32.650
2.7404
68



2
0
5
33.946
2.6387
7



3
0
3
34.522
2.5960
26



0
3
3
34.522
2.5960
27



1
2
−4
34.559
2.5933
1



2
1
4
34.559
2.5933
1



2
2
0
35.126
2.5527
24



3
1
−1
37.090
2.4258
1



1
3
1
37.030
2.4258
1



1
1
−6
37.207
2.4146
0



1
1
6
37.208
2.4146
0



1
3
−2
38.265
2.3502
0



3
1
2
38.265
2.3502
0



1
2
5
38.369
2.3441
1



2
1
−5
38.369
2.3441
1



2
2
−3
38.887
2.3141
0



2
2
3
38.887
2.3141
76



1
0
7
39.670
2.2702
2



4
0
1
41.167
2.1910
2



0
4
2
42.300
2.1349
16



1
3
4
42.905
2.1062
1



3
1
−4
42.905
2.1062
1



0
2
7
43.597
2.0744
38



3
2
1
44.967
2.0135
5



2
3
−1
44.987
2.0135
5



3
0
6
45.138
2.0070
5



0
3
6
45.138
2.0070
0



0
1
8
45.260
2.0019
26



2
3
2
46.044
1.9696
1



3
2
−2
46.044
1.9696
1



1
3
−5
46.134
1.9660
1



3
1
5
46.134
1.9660
1



4
0
4
46.610
1.9470
2



4
1
0
47.054
1.9297
1



1
4
0
47.054
1.9297
1



1
2
−7
47.259
1.9216
1



2
1
7
47.259
1.9218
1



2
2
−6
48.710
1.6679
0



2
2
6
48.710
1.8679
0



2
0
8
48.824
1.8638
4



0
4
5
49.650
1.8347
0



0
0
9
49.875
1.8269
0



1
4
−3
50.074
1.8202
0



4
1
−3
50.074
1.8202
2



4
1
3
50.074
1.8202
0



1
4
3
50.074
1.8202
2



2
3
−4
50.102
1.8192
5



3
2
4
50.102
1.8192
2



0
5
1
51.960
1.7565
1



1
2
8
52.206
1.7508
8



2
1
−8
52.205
1.7506
8



5
0
2
52.912
1.7290
3



3
2
−5
52.992
1.7266
2



2
3
5
52.992
1.7266
2



1
1
−9
53.207
1.7201
0



1
1
9
53.207
1.7201
0



3
3
0
53.825
1.7018
6



3
1
−7
54.011
1.6964
0



1
3
7
54.011
1.6964
0



4
2
−1
55.202
1.6626
1



2
4
1
55.202
1.6628
1



4
2
2
56.116
1.6377
3



2
4
−2
56.116
1.6377
3



3
3
−3
56.582
1.6253
0



3
3
3
56.582
1.6253
0



0
5
4
56.607
1.6246
0



1
0
10
56.916
1.6165
0



4
0
7
57.173
1.6099
2



1
5
−1
58.321
1.5809
0



5
1
1
58.321
1.5809
0



4
1
−6
58.447
1.5778
2



1
4
−6
58.447
1.5778
0



1
4
6
58.447
1.5778
2



4
1
6
58.447
1.5778
0



1
3
−6
58.548
1.5753
0



3
1
8
58.548
1.5753
0



1
5
2
59.203
1.5594
1



5
1
−2
59.203
1.5594
1



5
0
5
59.278
1.5576
1



0
3
9
59.478
1.5529
16



3
0
9
59.478
1.5529
6



4
2
−4
59.679
1.5481
2



2
4
4
59.679
1.5481
2



0
2
10
59.977
1.5411
5



3
2
7
60.226
1.6353
4



2
3
−7
60.225
1.5353
4



0
4
8
61.559
1.5053
3



2
4
−5
62.268
1.4898
2



4
2
5
62.268
1.4898
2



2
2
9
62.462
1.4857
7



2
2
−9
62.462
1.4857
7



5
1
4
62.657
1.4815
1



1
5
−4
62.657
1.4815
1



2
1
10
62.947
1.4754
0



1
2
−10
62.947
1.4754
0



0
1
11
63.019
1.4739
7



6
0
0
63.020
1.4738
1



3
4
−1
64.272
1.4461
0



4
3
1
64.272
1.4481
0



3
3
−6
64.391
1.4457
4



3
3
6
64.391
1.4457
4



3
2
−8
64.486
1.4438
0



2
3
8
64.486
1.4438
0



3
4
2
65.106
1.4316
0



4
3
−2
65.106
1.4316
0



5
1
−5
65.177
1.4302
0



1
5
5
65.177
1.4302
0



6
0
3
65.533
1.4233
1



0
6
3
65.533
1.4233
1



2
0
11
65.910
1.4160
0



2
5
0
65.912
1.4160
0



5
2
0
65.912
1.4160
19



0
5
7
66.076
1.4129
5



5
2
−3
68.368
1.3710
0



2
5
−3
68.368
1.3710
0



5
2
3
68.368
1.3710
1



2
5
3
68.368
1.3710
0



4
3
4
68.391
1.3706
0



3
4
−4
68.391
1.3706
0



0
0
12
68.413
1.3702
2



3
1
−10
68.668
1.3657
2



1
3
10
68.668
1.3657
6



1
2
11
68.738
1.3645
0



2
1
−11
68.738
1.3645
0



4
2
−7
68.900
1.3617
4



2
4
7
68.900
1.3617
4



1
6
1
69.937
1.3440
0



6
1
−1
69.937
1.3440
0



5
0
8
70.143
1.3406
7









FIG. 4 shows the X-ray diffraction pattern of the above-mentioned crystal sample. The X-ray diffraction pattern can be explained by the above-mentioned lattice constants,
As a result of the compositional analysis according to a wavelength dispersion X-ray analysis method (WDX), the crystal sample obtained here was confirmed to comprise Na, Si and B like in Example 1. In the crystal, no other element than Na, Si and B was detected. These results confirm that the obtained crystal sample is an Na—Si—B boride of the invention.
Next, the Na—Si—B boride reaction-sintered product of the invention is described concretely. The high-purity argon gas, the BN crucible and the reactor used in the following Examples 3 and 4 are the same as those used in Examples 1 and 2.
Example 3
0.1 g of amorphous powdery B (by Wake Pure Chemicals, having a purity of 95%) was diced, powdered and compressed to give a B compact (1.9 mm×3.0 mm×14.0 mm). In a glove box having therein a high-purity argon gas atmosphere, Na (by Nippon Soda, having a purity of 99.95%) and powdery Si (by Kojundo Chemical Laboratory, having a purity of 99.999%) were so weighed that the ratio by mol of Na/Si/B could be 3/1/1.
As shown in FIG. 1(b), Na1 and Si2 were put into a BN crucible 6 along with the formed B compact 4 put therein. Next, the BN crucible 6 was set inside a reactor 7, and the reactor 7 was sealed up with a cap 8 in a high-purity argon atmosphere. Subsequently, the reactor 7 was set in an electric furnace, and heated up to 800 to 1000° C. taking 2 hours, then left as such for 24 hours, and thereafter cooled to room temperature, and the reactor 7 was taken out.
The reactor 7 was cut in the globe box, and the BN crucible 6 was taken out. Na and NaSi surrounded the compact. This was washed with ethanol and distilled water to remove Na and NaSi, and a polycrystalline sample was thus collected.
FIG. 5 shows optical micrographs of the B compact (a) used as the starting material and the obtained polycrystalline sample (b). The dimension of the polycrystalline product (b) was 1.99 mm×3.1 mm×14.40 mm, and the volume thereof expanded by about 11% as compared with that of the B compact (a) before heating.
The polycrystalline sample was analyzed through X-ray diffractiometry using an X-ray diffractometry apparatus (Rigaku's “RINT” (trade name) with a radiation source of CuKα). The X-ray diffraction pattern of the polycrystalline sample is shown in FIG. 6. The X-ray diffraction pattern confirms that the obtained polycrystalline sample is Na8Si17.5B74.5 (P63/mmc with lattice constants of a=1.024±0.008 nm and c=1.092±0.008 nm), and is an Na—Si—B boride polycrystalline product of the invention.
The density of the polycrystalline reaction product sample was 1.88 Mg/m3, and was about 76% of the theoretical density of Na8Si17.5B74.5, 2.47 Mg/m3.
The obtained polycrystalline reaction-sintered product sample was tested according to a room temperature bending test, and the bending strength of the sample was 104 MPa,
Example 4
Amorphous powdery B (by Wako Pure Chemicals, having a purity of 95%) and powdery Si (by Kojundo Chemical Laboratory, having a purity of 99.999%) were weighed in a ratio by mel of 4/x (where X is 1, 2 or 3), thereby preparing three different types of mixtures, and the mixtures were separately ground, using an agate mortar for each. About 0.16 g of each mixed powder was diced, further powdered and compressed, thereby giving three different types of B/Si mixed compacts (2.4 b 2.5 mm×3.0 mm×14.0 mm). In a glove box having therein a high-purity argon gas atmosphere, about 0.5 g of Na (by Nippon Soda, having a purity of 99.95%) and the compact prepared above were put in different BN crucibles 6.
Next, as in FIG. 1(c), the BN crucible 6 containing the B/Si mixed compact 5 therein and the BN crucible 6 containing Na1 therein were separately set in a reactor 7, and the reactor 7 was sealed up with a cap 8 in a high-purity argon atmosphere. Subsequently, the reactor 7 was set in an electric furnace, and heated up to 900° C. taking 2 hours, then left as such for 24 hours, and thereafter cooled to room temperature, and the reactor 7 was taken out.
The reactor 7 was cut in the globe box, and the BN crucible 6 was taken out. Na and NaSi surrounded the compact 5. This was washed with ethanol and distilled water to remove Na and NaSi, and a reaction-sintered product sample was collected. The above three different types of starting mixtures with the Si ratio x of 1, 2 or 3 gave the respective polycrystalline samples,
FIG. 7 shows optical micrographs of the Na/Si mixed compact (a) under the condition of Si ratio x=1 and the polycrystalline sample (b) obtained under that condition. The dimension of the Na/Si mixed compact before heating was 2.5 mm×3.0 mm×14.0 mm, while the dimension of the obtained polycrystalline sample was 2.7 mm×3.1 mm×14.3 mm. All the polycrystalline samples produced under the condition of Si ratio, x=1, 2 or 3 maintained the Na/Si mixed compact before heating.
The polycrystalline samples were analyzed through X-ray diffractiometry using an X-ray diffractometry apparatus (Rigaku's “RINT” (trade name) with a radiation source of Cukα). The X-ray diffraction patterns confirm that all the polycrystalline reaction-sintered product samples are Na8Si17.5B74.5 (P63/mmc with lattice constants of a=1.024±0.008 nm and c=1.092±0.008 nm), and are Na—Si—B boride polycrystalline products of the invention.
The density of the polycrystalline samples obtained under the condition of Si ratio x=1, 2 or 3 was 1.45, 1.24 or 0.92 Mg/m3, respectively, and was about 59, 50 or 37%, respectively, of the theoretical density of Na8Si17.5B74.5, 2.47 Mg/m3.
Example 5
Amorphous powdery B (by Wako Pure Chemicals, having a purity of 65%) and, as C, carbon black powder (by Mitsubishi Chemical) were weighed in a ratio by mol of 5/1, and mixed using an agate mortar. 0.12 g of the mixed powder was diced, further powdered and compressed to give a B/C mixed compact 9 (2.0 mm×3.0 mm×14.0 mm).
Next, as shown in FIG. 1(d), the compact 9 was put into a BN crucible 6 along with about 0.2 g of metal sodium 1 (by Nippon Soda, having a purity of 99.95%) as Na, in a glove box having therein a high-purity argon gas atmosphere (in which the concentration of O2 and H2O was less than 1 ppm each). The BN crucible 6 used here is a sintering BN crucible (by Showa Denko).
Next, the BN crucible 6 was set inside a reactor 7 (made of stainless SUS316), and the reactor 7 was sealed up with a cap 8 made of stainless in a high-purity argon atmosphere. The reactor 7 used here has an inner diameter of 10 mm and a length of from 80 to 100 mm. Subsequently, the reactor 7 was set in an electric furnace, and heated up to 800 to 1000° C. taking 2 hours, then left as such for 24 hours, and thereafter cooled to room temperature, and the reactor 7 was taken out.
The reactor 7 was cut in the globe box, and the BN crucible 6 was taken out. The surface of the sample in the BN crucible was covered with Na.
The sample obtained in the above was washed with ethanol and distilled water to remove Na, thereby giving a polycrystalline product sample.
FIG. 8 shows optical micrographs of the B/C mixed compact (a) and the obtained polycrystalline sample (b). The dimension of the polycrystalline reaction product sample was 2.16 mm×3.12 mm×14.58 mm, and the volume thereof expanded by about 17% as compared with that of the B/C mixed compact before heating.
The polycrystalline reaction product sample was analyzed through X-ray diffractometry using an X-ray diffractometry apparatus (Rigaku's “RINT” (trade name) with a radiation source of CuKα). The X-ray diffraction pattern of the sample is shown in FIG. 9. The X-ray diffraction pattern confirms that the obtained polycrystalline product sample is NaCB6 (Pm-3 m with a lattice constant a=0.409±0.008 nm), and is a boride polycrystalline product of the invention.
The density of the polycrystalline product sample was 1.61 Mg/m3, and was about 75% of the theoretical density of NaCB5, 2.16 Mg/m3.
The obtained polycrystalline product sample was tested according to a room temperature bending test, and the bending strength of the sample was 92 MPa.
DESCRIPTION OF REFERENCE NUMERALS


    1 Metal Sodium
    2 Silicon
    3 Boron
    4 Boride Compact
    5 Boron/Silicon Compact
    6 BN Crucible
    7 Reactor
    8 Cap
    9 Boron/Carbon Compact

## Claims

1. A ternary boride represented by formula NaxSiyBz, wherein 0<x, x<y<4x, and 8x<z<20x.

2. A ternary boride having a composition Na—Si—B, wherein a crystal structure of the boride is a hexagonal system or a rhombohedral system.