JPS61227993A - Production of sic whisker - Google Patents

Abstract

PURPOSE:To produce an SiC whisker long in a fiber length in the high yield by heating a mixture contg. an SiO2 source, a C source and a prescribed NaF source in the nonoxidizing atmosphere. CONSTITUTION:A mixture 2 which is mixed in the proportion of 1mol part SiO2 source (e.g. sedimentary silicic acid anhydride), 1.5-5mol part C source (e.g. activated carbon) and 1/24-1/2mol part NaF source is incorporated up to a position A of a base part of a crucible 1 and a space 3 for producing a long fiber whisker is formed up to the range of the height B in an upper part of the crucible 1. Then 200-1,000cm<3>/min inert gas such as Ar is introduced into the spaces 12, 3 through the introduction pipes 11, 17 and an inflow port 18 and the mixture 2 in the crucible 1 is heated with a heater 6 at the pre scribed temp. T1 within the range of 1,400-1,700 deg.C in the nonoxidizing atmo sphere and also heated while keeping the temp. T2 of the space 3 and the temp. gradient DELTAT2/DELTAZ (the upper a position is, the lower the temp. becomes) in a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing silicon carbide (S i C) whiskers.

[Prior Art] There is no known method for producing SiC whiskers by heating a mixture containing silicon dioxide (Si02) and carbon (C) with sodium fluoride (NaF) in a non-oxidizing atmosphere. (For example, Special Publick
Publication No. 57).

[Problems to be Solved by the Invention] However, as disclosed in, for example, Japanese Patent Publication No. 15557/1983, when NaF is added at a molar ratio of about 1 or more to SiO2, SiC whiskers with a long Ilt length are The yield was found to be low.

The present invention was made based on the above-mentioned new findings,
The purpose is to provide a method for producing SiC whiskers that can produce SiC whiskers with a long fiber length in high yield.

In this specification, with respect to SiC whiskers, “II
``long fibers'' or ``long fibers'' have a length of 500 JIR.
Refers to the above SiC whiskers. When this long fiber whisker is used as a composite reinforcing fiber composited with, for example, Aj) metal, its composite effect is far superior to that of SiC whiskers having a length of 100 Jll or less.

In addition, high yield refers to the amount of Si forming the long fiber SiC whiskers being 20% or more of the amount of 3i in 5i02 in the mixed raw material powder, in terms of the amount of 3i used. (Incidentally, in the conventional synthesis method using the 5i02=C-NaF system, the maximum yield of long 11118 i C whiskers was about 10%).

[Means for Solving the Problems J According to the present invention, the above-mentioned object is achieved by
02) source, carbon (C) source, and sodium fluoride (NaF) in a molar ratio of 1/24 to 1/2 with respect to SiO2
Si
This is achieved by a method of manufacturing C whiskers.

[Operations and Effects] According to the present invention, in a mixture containing sto, c and NaF, the molar ratio of NaF to 51o2 is 172
4 to 1/2, long fiber SiC whiskers can be produced in high yield.

NaF added to the mixed raw material forms a silicate melt with 5i02 when heated in a non-oxidizing atmosphere,
The reaction between 5102 and C is promoted, and as a result, the generation of SiO and CO gas from the mixed raw materials is promoted, and the synthesis reaction of SiC is promoted.

The proportion of NaF is determined by the yield of long fiber SiC whiskers (S
2 or less) with respect to the amount of i), and NaF
When the molar ratio is less than 1724 to 5102, and when it is more than 1/2, the yield of long fiber SiC whiskers will be 5% or less.

If the proportion of NaF contained in the mixture is too large, the amount of silicate melt formed when the mixed raw material is heated in a non-oxidizing atmosphere becomes too large, and SiO and CO are rapidly generated. , it is thought that more 3i components are discharged unreacted to the outside of the system, that is, to the outside of the whisker generation region. It is also believed that the partial pressure of fluoride becomes too high, which prevents the generation of SiC whiskers.

On the other hand, if the proportion of NaF is too small, a sufficient amount of silicate melt will not be formed and a long time will be required for the reaction between SiO2 and C, which will actually reduce the yield of SiC whiskers. It is thought that then.

Further, powdered SiC is easily synthesized in the mixed raw material.

In addition, NaF is N a 3 Aj' F 6 or A11
Compared to other fluorides such as F3, it is preferable because it has a high vapor pressure and is less likely to be mixed into the product, but other fluorides such as Na5AjF6 may be used depending on the case.

As the SiO□ source, for example, precipitated silicic anhydride is preferable from the viewpoint of high reactivity and high purity. SiO□ raw material may be used, and in some cases, Kira (fine powder waste generated in the refining process of clay minerals, mainly composed of quartz, feldspar, kaolinite, and mica, usually about 5 in2 70 weight 1
%, Al2O3 about 20 iJ (amount %, K 20 'fr
(containing about 5'a I%), rice husks, etc. may also be used.

The C source may be a highly reactive source such as activated carbon or a graphite source such as carbon black.

The proportion of carbon C in the mixture is determined so that it reacts with 5io2 in just the right amount, and if the molar ratio of C to 5i02 is less than 1.5, the carbon content is insufficient and the carbon content is insufficient. There is a risk of a large amount of 5to2 remaining in the reaction, while C is
If the molar ratio to i O2 is more than 5, there is a risk that a large amount of unreacted carbon will remain.

Therefore, from the viewpoint of raw material utilization efficiency, it is preferable that the molar ratio of C in the carbon source to S i O2 in the silicon dioxide source in the mixed raw material is 1.5 to 5. Note that before heating, 5f02. It is preferable that C and NaF are mixed uniformly, and in some cases, they may be granulated.

The non-oxidizing atmosphere during heating of the mixed raw materials is preferably made of Ar, but in place of Ar, other rare gases such as Le or N2 may be used.

Note that A is applied to the area containing the mixture and the whisker generation area.
A non-oxidizing atmospheric gas such as r may be simply introduced, or a non-oxidizing gas such as Ar may be allowed to flow through these regions at a desired flow rate.

Heating of the mixture under a non-oxidizing atmosphere is preferably carried out at a temperature in the range from 1,400 to 1,100°C.

If the heating humidity is less than 1400°C, there is a risk that the reaction rate will decrease and the yield of SiC whiskers will decrease. If the heating temperature is higher than 1700°C, the reaction rate will be too high and the SiC whiskers will be reduced. There is a possibility that more SiC powder will be generated.

According to the invention, preferably 1 molar part of SiO2, C
A mixed raw material containing i, s to 5-E parts and 1/24 to 112 mol parts of NaF was heated to 1400 to 17 mol parts in a non-oxidizing atmosphere.
Heating to 00°C produces SiC whiskers.

In this case, according to the present invention, long fiber SiC whiskers of approximately several layers can be produced in a high yield in the whisker generation space on the surface of the mixed raw material, and the length of 1001
Around m SiC whiskers can be generated.

Next, a preferred example of an apparatus for carrying out the method of the present invention will be explained based on the drawings.

In Fig. 1, 1 is a graphite crucible;
For example, at the bottom of crucible 1 with an inner diameter of 150 mm,
(For example, t [about 30+n)
A mixed powder 2 of a predetermined ratio of F is accommodated. At this time, the upper part of the crucible 1 has a height B (preferably B>5A,
For example, the space 3 for producing long fiber whiskers is formed to a range of about 150,111). The crucible 1 may be made of SiC or the like having high chemical stability instead of graphite.

The crucible 1 has a reduced diameter at the upper part 4, and is connected to a graphite tube 5 (for example, inner diameter 651-1 length 1300 mm) that serves as an exhaust pipe.

Reference numeral 6 denotes a carbon heater arranged so as to surround the crucible 1, and the crucible 1 and the heater 6 are further surrounded by an inner wall portion T made of a heat insulating material block. As long as the mixed raw material 2 in the crucible 1 can be heated to about 1400 to 1700°C for a long period of time, the heater 6 shape 0 position 9 heat generation method can be other shapes! ! (For example, a high frequency induction heating method) may be used.

Reference numeral 8 denotes an outer wall portion made of a heat insulating material block, and the outer wall portion 8 constituting the outer frame of the whisker generation device i9 is similar to the wall portion 7.
and surrounds the tube 5.

Note that another tube 10 is connected to the tip of the graphite tube 5 and protrudes through the outer wall portion 8.

Note that the connection between the upper end 4 of the crucible 1 and the tube 5.10 is usually not completely sealed, but may be completely sealed if desired.

11 is a pipe for introducing an inert gas such as Ar, and when producing whiskers, a predetermined amount of 1ffiC (for example, 200
~1,0OOd/min; In this specification, regarding the gas flow rate (flow rate), d in cdZ minute indicates the amount at normal temperature and normal pressure). After passing through the cylindrical space 12 between the outer wall 8 and the tube 5, it flows through the cylindrical space 13 between the outer wall 8 and the tube 5, and flows out from the outlet 14.

The non-oxidizing gas flowing in from the inlet 11 and flowing out from the outlet 14 is heated to about 1400 to 1100°C by the heater 6.
The space 15 between the outside of the graphite crucible 1 and the carbon heater 6 and the space 16 around the carbon heater 6 are kept non-oxidizing.
(approximately 0 ciZ minute) enters the chi 1-75 from the connection between the upper part 4 of the crucible 1 and the tube 5, and flows out through the tube 5.

Reference numeral 17 denotes a gas introduction pipe that penetrates from the outside to the whisker generation space 3 so that Ar gas can be introduced into the whisker generation space 3 in the crucible 1. After putting the raw material mixed powder 2 for whisker generation into the crucible 1 and before heating the crucible 1, Ar gas is introduced from the inlet 18 and the crucible 1 is heated.
The interior and tube 5 are completely filled with Ar gas, and then,
Close the inlet 18.

If desired, this inlet 18 can also be used to introduce other gases such as CO or HF into the crucible 1 for a desired period of time.

In addition, 9a is a 1m thermocouple, 9b is a current-carrying terminal of the heater 6,
9C is a fixture.

When generating whiskers, the heater 6 is energized and the mixed powder 2 is heated through the crucible 1 to 1400~
While heating to a predetermined temperature T1 within the range of 1700°C,
The temperature T2 and temperature gradient ΔT2/ΔZ (lower temperature toward the top) of the space 3 where whiskers are to be generated are maintained at predetermined values.

The temperature of the mixed powder 2 and the temperature of a desired part of the whisker-forming space IJli3 are detected by a temperature detection means such as a thermocouple (not shown), and based on the temperature detected by this detection means,
Adjust the current flowing through the heater 6 to adjust the heating.

In the figure, there is only one heater 6, but if desired, a plurality of independently controllable heaters may be used so as to adjust the temperature of each part of the crucible 1.

The temperature gradient ΔT2/ΔZ can be adjusted by, for example, changing the position, thickness, quality, etc. of the heat insulating block 7, but if desired, it can be adjusted by forcibly cooling the outer surface of the crucible 1, etc. You may also do so.

Next, examples of the present invention will be described.

Friend 1 ■ YuS i 02 (precipitated silicic anhydride) is 1 mole part, C
138 g of a powder mixture consisting of 3 mole parts of activated carbon and 173 mole parts of NaF was added to the raw material filling area at the bottom of the graphite crucible 1! 2a was filled. The air in the crucible 1 and tube 5 was completely replaced with Ar gas from the inlet 18, and the inlet 18 was closed.

The lower part 2 in the crucible 1 is heated by the carbon heater 6.
The temperature T1 of the mixed raw material 2 of a was maintained at 1500°C for 12 hours (ΔT2 /ΔZ:; 1 (roll/IGOam)
.

In addition, from the tube 11 to the outside of the crucible 1, C-500cIi
Ar was flowed at /min.

As a result, about 100 long Ni1S iC whiskers with a thickness of about 0.1 to 1p and a length of several μm are obtained on the surface of the whisker generation space 3 in the upper part of the crucible 1 and the residue 2b of the raw material 2. It was done. When looking at Si, this corresponds to a yield of 20%.

On the other hand, when residue 2b of raw material 2 was taken out and unreacted C was removed by heat treatment at 100°C in air, approximately 3
A residue of 013 was obtained, but scanning electron microscopy! It (
When observed with SEM), most of this residue had a thickness of 0.
．． 1~Its, length around 100u11 (7) SiC whiskers.

In the low J112 raw material powder 2, the molar ratio of NaF to 5i02 was 1/12, and the at! ! 1 is 12
SiC was prepared in the same manner as in Example 1 except that the amount was 3 g.
Generated whiskers.

As a result, about 20 g of long-line Is i C whiskers with a thickness of 0.1 to 1 p1 and a length of several 1 were obtained in the whisker generation space 3 on the surface of the raw material residue. When looking at SiC, this corresponds to a yield of 40%.

On the other hand, the residue 2b of the raw material 2 was taken out and heated to 100°C in the air.
When unreacted C was removed by heat treatment at
517 residues were obtained, but when observed with SEM,
It contained SiC whiskers with a thickness of 0.1 to 1 μm and a length of about 100 mm, as well as a considerable amount of SiC in the form of powder or agglomerated lumps thereof.

SiC whiskers were produced in the same manner as in Examples 1 and 2 by changing only the ratio of NaF to Si02 (while keeping the molar ratio of C to 5i02 (precipitated silicic anhydride) at 3). , long fiber SiC whiskers are 3
ik: was obtained in the yield shown in Table 1 (multiple values are average values observed for 3 to 5 samples).

In Table 1, N a F / S i 02-1/3 C corresponds to Example 1, N a F / S +,
02 = 1/12 corresponds to the second embodiment. Second
The solid line indicated by reference numeral 19a in the figure is a graphical representation of Table 1.

As is clear from Table 1 and Figure 2, NaF/S
If iO is too small or too large, the yield of long fiber SiC whiskers will decrease.

When the ratio of C to 5tO2 is changed, that is, C
/5i02 (molar ratio)=1.2, 4, and 5.6, the yields are as shown in Table 2.

In FIG. 2, reference numeral 19b corresponds to the case where C/S i O2=2.

Table 2: NaF/SiO with different proportions of C
Relationship between □ and yield In addition, in the above, NaF is used as fluoride.
An example using N'a3 was shown as a fluoride.
Aj! When F6 was used, the same results as in the case of NaF were obtained, except that the appropriate molar ratio to SiO2 was slightly different and All was more likely to be mixed into the SiC whiskers.

138g of adjusted powder 2 consisting of 1 mole part of Si O2 (precipitated silicic anhydride), 3 mole part of C (activated carbon), and 1/3 mole part of NaF. The raw material filling area 2a at the bottom of the fitter crucible 1 was filled with the raw material. At this time, a space 3 for whisker production was formed at the upper part of the crucible 1 at a height B~682 801, that is, about six times the raw material filling volume.

Air in the crucible 1 and tube 5 is inflowed from A
Fully replaced with r gas and inlet 018 was closed.

The temperature T1 of the mixed raw material 2 in the lower part of the crucible 1 was maintained at 1311500° C. at 12:00 by heating with the carbon heater 6. The darkness of this heating, ΔT2 in the whisker generation sky 1113
A temperature gradient of /ΔZ-50 degrees/100 mm was given.

Incidentally, on the outside of the crucible 1, there is a c-so from a pipe 11.

Ar gas was passed for 17 minutes.

As a result, the whisker generation space 1i13 at the top of crucible 1
contains long Si fibers with a thickness of 0.1 to 1-1 and a length of about 1
Approximately 5 g of C whiskers were produced. This corresponds to a yield of 10% for SiC.

On the other hand, when the residue 2b of the raw material 2 was taken out and unreacted C was removed (decarburized) by heat treatment at an air width of about 700°C, about 30 g of residue was obtained.
When observed with SEM), most of this residue had a thickness of 0.
．． It was a SiC whisker with a length of 1 to 7 m and a length of about 100/1 m.

Tomo tti ΔT2 /4Z210011! /100111'a8j
I! A whisker synthesis experiment was conducted under the same conditions as in Example 4 (this is the same example as in Example 1).

As a result, the whisker generation space 5113 at the top of crucible 1
A long wire with a thickness of 0.1 to 1-1 and a length of several ■ SiC
Approximately 109 whiskers were generated. This corresponds to a yield of 20% for SiC.

On the other hand, when decarburization was carried out in the same manner as in Example 4, a residue of approximately 300 mm was obtained, but when observed by SEM, most of this residue was SiC with a thickness of 0.1 to 1 JI11 and a length of approximately 100 mm. It was a whisker.

1 亙■1 Improve the insulation around crucible 1, ΔT2/Δ2yuo degrees/
A whisker synthesis experiment was conducted under the same conditions as in Example 4, except that the length was 100 mm.

As a result, the amount of long fiber SiC whiskers with a thickness of 0.1 to IJm and a length of several tens of meters generated in the whisker generation space 3 in the upper part of the crucible 1 was about 0.3 g, which was very small. On the other hand, when decarburized in the same manner as in Example 4, approximately 30Q
A residue of
It was the front and rear SiC whiskers.

Based on the above Examples 4, 5, 6, etc., (1) A whisker generation space 3 of at least 5 times the raw material filling volume is provided above the filled raw material 2 (B>5
A), ■ Whisker generation sky [ΔT2/ΔZ≧25 degrees/
It can be seen that long IMS i C whiskers can be generated in high yield in the whisker generation space 3 by providing a temperature gradient of 1100a or more.

It should be noted that the weighing rate increases as △-“2/ΔZ increases.

Kira as a SiO2 source (composition after heat treatment at 700°C, S i 0273.33% by weight Al2O3 20.03% by weight Fe2O3G, 59111% 20 5.15% by weight N820 0.171% by weight M Q OO ,08% T i 02 0.341%Ca OO,0
6% by weight) of 1 mole part of S + 02, 2 mole parts of C (activated carbon), and 1/3 mole part of NaF were mixed in a ball mill, and 100 g of mixed powder 2 was placed in graphite crucible 1. The raw material filling area 2a at the bottom of the was filled with the raw material filling area 2a. The air in the crucible 1 and tube 5 was completely replaced with Ar gas from the inlet 18, and the inlet 18 was closed.

The lower part 2 in the crucible 1 is heated by the carbon heater 6.
The temperature of the mixed raw material in a was kept at 1570°C for 12 hours (ΔT2/ΔZ2100°/1GG11).

In addition, on the outside of the crucible 1, from the pipe 11 to the Q-500d/
Ar gas was flowed for 1 minute.

As a result, 14Q of long-fiber SiC whiskers with a thickness of 0.5 to 1.0 and a length of 5 oons or more were obtained in the whisker generation space 3 in the upper part of the crucible 1.

This corresponds to a yield of 40% in terms of Si.

On the other hand, when the 34Q residue 2b remaining in the lower part 2a of the crucible 1 was investigated by SEMII observation and X-ray diffraction, it was found that the remaining 1
12b contained a considerable proportion of SiC whiskers with a length of about 100 voices.

1151 Precipitated silicic anhydride was used instead of Kira as the SiO2 source, and 5i02 (precipitated silicic anhydride) was 1 mol part, C (activated carbon) was 2 mol parts, and NaF was 1/3 mol part. A SiC whisker synthesis experiment was carried out in the same manner as in Example 7, except that 130 g of mixed powder 2 consisting of the following was filled into the raw material filling area at the bottom of the crucible 1.

As a result, 7113 whiskers are being generated at the top of crucible 1.
Long fiber S with a thickness of around 081 to 1-1 and a length of about 1
5 g of iC whiskers were obtained. This corresponds to a yield of 10% for Si.

On the other hand, when we investigated the 30g of residue 2b remaining in the lower part 2a of the crucible 1, we found that most of it had 100% of its length.
It was iC whisker.

As is clear from the results of Examples 7 and 8 above, the long 1f! As far as the production of SiC whiskers is concerned, it can be seen that cheap chira can be used in place of the highly pure and highly reactive precipitated silicic anhydride.

When synthesizing this SiC whisker, AR2 in Kira
o3. 20th grade is 5in2. Silicic acid that reacts with NaF etc. and has a lower melting point! ! It is thought that it forms caries and promotes the whisker synthesis reaction.

Even during heating by the heater 6, the pipe 11,
SiC whiskers were synthesized in the same manner as in Example 1, except that Ar gas was flowed through crucible 1 at a rate of E-100 ai/min.

As a result, whiskers are being generated at the top of crucible 1! 13
For example, long 88 i C whiskers with a thickness of 0.1 to 1.0 tones and a length of approximately one number were obtained with a yield of 6% relative to 3i.

The conditions were the same as in Example 1, except that the tube 5 was removed from the synthesis apparatus 9 shown in FIG. In SiC
We synthesized whiskers.

As a result, only white lumps were produced in 1ffi3 during whisker generation, and most of the lumps were SiO2.

From the results of Example 1, Example 9 and Example 10 above,
If a region such as the inside of the crucible 1 where a reaction related to whisker production takes place can be maintained under an inert gas atmosphere such as Ar, the regions 2a and 3 where a reaction related to whisker production takes place are kept in the furnace atmosphere outside the crucible 1. 12.13, etc., and the yield of SiC whiskers will be higher if the gas in the SiC whisker generation space 3 does not flow out, and if there is a flow, the flow rate is lower. I understand.

111 138 g of mixed powder 2 obtained by mixing powder containing 1 mol part of SiO2 (precipitated silicic anhydride), 3 mol parts of C (activated carbon), and 173 mol parts of NaF in a ball mill, The raw material filling area 2a at the bottom of the graphite crucible 1 was filled with the raw material.

Ar gas is supplied to the outside of the crucible 1 from the pipe 11 at a flow rate of C-1, Gooti/min, and inside the graphite crucible 1 is supplied from the inflow 018 to the pipe 17. Crucible 1. tube 5
．． A mixed gas containing 90 mol % of Ar and 10 mol % of CO was flowed at RflE-50 cIi/min so as to pass through the tube.

While maintaining the above gas flow, the temperature of the mixed raw material in the lower part 2a of the crucible 1 is increased by heating by the carbon heater 6.
1 was kept at 1500°C for 12 hours (ΔT2/ΔZ2100°/10100l.

As a result, the whisker-generated air FrA3 at the top of crucible 1
In this method, long fiber SiC whiskers having a thickness of 0.1 to 1p and a length of about several III were obtained at a yield of 15% with respect to 3i. Note that the whiskers generated in this generation space 3 are 5
% HF solution showed a 111 reduction of 3.6%. This weight reduction is considered to be due to SiO2 contained in the SiC whiskers.

On the other hand, the residue 2b in the lower part 2a of the crucible 1 has a length of 11
A considerable proportion of SiC whiskers around 00J was included.

"Disaster 1" (■ From the inlet 18, A instead of the mixed gas of Ar and CO
SiC whiskers were synthesized under the same conditions as in Example 11, except that a gas consisting only of r was flowed in at a rate of E-50c+j/min.

As a result, the whisker generation space 3 has a thickness of 0.1 to
Long fibrous SiC whiskers with a length of about 1.0/Jfi and length + im were obtained with a yield of 13% with respect to Si. When the SiC whiskers generated in the generation space 3 were subjected to IF treatment in the same manner as in Example 11, they showed a weight reduction of about 22.3%. (It is believed that the whiskers synthesized in Examples 1 and 2 also contain about 20% Sin.) As is clear from the results of Examples 11 and 12 above, the whiskers synthesized in Examples 1 and 2, etc. When CO is included in the non-oxidizing atmospheric gas in the generation space 3, the amount of Sio2 mixed on the surface, gaps, etc. of the long fiber SiC whiskers generated in the whisker generation space 3 can be suppressed to a low level.

The reason for this is thought to be as follows. That is, the synthesis reaction of SiC whiskers is as follows: 3SiO+GO-→3iC+2Si02 or SiO+3Go-)SiC-1-2Co
2 It may seem like a secondary equation, but when Co gas is added to the atmosphere, S i O + 3 CO → S + C + 2 G
It is promoted by the reaction of O2, and as a result, the production of Sio2 is suppressed.

Example 13 138 g of mixed powder 2 obtained by mixing a powder mixture consisting of 1 mole part of SiO2 (precipitated silicic anhydride), 3 mole parts of C (activated carbon), and 173 mole parts of NaF in a ball mill was mixed. The raw material filling area 28 at the bottom of the graphite crucible 1 was filled. The air in the crucible 1 and tube 5 was completely replaced with Ar gas from the inlet 18, and the inlet 18 was closed.

Outside the crucible 1, from the tube 11, C = 1000ai/
The Ar gas was continued to flow at a flow rate of 100 min to maintain the furnace spaces 15, 16 and 12, 13 outside the crucible 1 in an inert atmosphere.

The lower part 2 in the crucible 1 is heated by the carbon heater 6.
The temperature of mixed raw material 2 in a was kept at 1500°C for 12 hours (ΔT2/ΔZ2100°/100ml).

In addition, during the 12-hour heating period m, from the time when 9 hours have passed from the start of heating until the end of heating, the flow from the inlet 18 to the pipe 17
．． Crucible 1. Ar is applied at 90°C so as to pass through the tubes 5 and 10.
IE-50 flows a mixed gas containing 10 mol% of HF.
It was run at cIi/min. , As a result, during whisker generation r! In 13, long fiber SiC whiskers with a thickness of 0.1 to 1.07 m and a length of several ■ are s+&:m and 15
% yield.

In addition, the long fiber SiC whiskers generated in the generation space 3 are
% HF solution showed a weight loss of 1.2%. This weight reduction is due to the S contained in the SiC whiskers.
It seems to be caused by iO2.

On the other hand, the residue 2b remaining in the lower part 2a of the crucible 1 contained a considerable proportion of SiC whiskers with a length of about 1007ff1.

SiC whiskers were synthesized under the same conditions as in Example 13, except that no gas was introduced from the inlet 18 during the heating period of 12 hours in November.

(This example is the same as Example 1 except that the Ar gas flow rate from the pipe 11 is different.) As a result, the whisker generation space 3 has a thickness of 0.1 to
At 1.0 J, long fiber SiC whiskers with a length of several meters or more can be obtained with a yield of 22% for 81, but the yield of SiC whiskers in production space 3 is 21.5% by treatment with a 5% HF solution. showed a weight loss.

As is clear from the results of Examples 13 and 14 above, during the last few hours of SiC whisker generation at a predetermined heating temperature, gas HF (reaction formula S i 02 +4HF→ S i F 4 +2H2
0) or CH4 (reaction formula CH4+5102→SiC+2
H20) etc. during whisker generation 1
SiO2 between the whiskers generated in 53 or on the surface etc.
can reduce the proportion of mixed materials.

Song 1 Sin2 138 g of mixed powder 2'' obtained by mixing in a ball mill a powder mixture consisting of 1 mole part of Sin2 (precipitated silicic anhydride), 3 mole part of C (activated carbon), and 1/3 mole part of NaF.
was filled to a height A into the lower raw material filling region 28 of the graphite crucible 1C having a cross-sectional shape as shown in FIG.

At this time, a whisker generation space 3 having a volume approximately five times the filling volume of the mixed raw material 2 was formed in the upper part of the crucible 1C.

In a device 9 in which a crucible 1c is arranged instead of the graphite crucible 1, the inside of the crucible 1C and the upper end 1 of the crucible 1C
After replacing the inside of the tubes 5 and 10 connected to d with Ar gas, the tube 11 is placed outside the crucible 1C around the crucible 1C.
While flowing Ar gas at a rate of C-200 to 1,000 cd/min, the crucible 1c is heated by carbon heater 6.
The temperature T1 of the mixed raw materials in the lower part of the chamber was kept at 1,500℃ for 12 hours.
I kept it. (ΔT2/ΔZ~100 degrees/10011m
).

As a result, long fiber SiC whiskers with a thickness of 0.1 to 1.0 μs and a length of several mm are formed in the whisker generation space 3 above the crucible 1c, as shown in FIG.
It was obtained in the form of an aggregate 20 having the same shape as .

This SiC whisker aggregate 20 has a bulk density of about 0.
01~0.02Q/d, porosity 98.5~99.0
It had a microstructure with extremely uniform void distribution of %.

On the other hand, take out the residue 2b of raw material 2 and heat it to an air width of about 700°C.
After removing unreacted C by heat treatment (1g2 charcoal), most of the remaining bacteria were SiC whiskers with a diameter of 0.1 to 1.0 J and a length of about 1004.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram of a preferred example of a production apparatus for carrying out the method for producing SiC whiskers of the present invention, and FIG. 2 is a diagram showing the length of 11tS i with respect to N a F / S i O2 (molar ratio) in the mixed raw material. A graph showing the dependence of the yield of C whiskers, FIG. 3 is a cross-sectional explanatory diagram of a modified example of the crucible of the apparatus shown in FIG. 1, and FIG. 4 is a graph showing the dependence of the yield of C whiskers.
FIG. 2 is an explanatory diagram of an iC whisker aggregate. 1.1C...crucible, 2...mixture,
6... Heater. Figure 2 NaF/5Kh (9 Le Y Otsu) Figure 3 Figure 4

Claims (3)

[Claims] (1) A mixture containing a silicon dioxide source, a carbon source, and a sodium fluoride source at a molar ratio of 1/24 to 1/2 to silicon dioxide is heated in a non-oxidizing atmosphere to form SiC whiskers. How to do manufacturing. (2) The mixture contains 1 mol part of SiO_2 and 1.5 to 1.5 molar parts of C.
5 mol parts, and 1/24 to 1/2 mol part of NaF. (3) The method according to claim 1 or 2, wherein the heating temperature is between 1,400°C and 1,100°C.