JPS61227998A - Production of sic whisker - Google Patents

Abstract

PURPOSE:To obtain an SiC whisker wherein the included amount of SiO2 is suppressed in a low level by heating a mixed raw material such as SiO2 in the nonoxidizing atmosphere and also flowing a specified gas in the region. CONSTITUTION:A mixed raw material 2 contg. 1mol part SiO2, 1.5-5mol part C and 1/24-1/2mol part NaF is packed in a base part of the inside of a crucible 1 set in an apparatus 9 and an inert gas such as Ar is introduced through an introduction pipe 11 to keep the spaces 12, 13, 15, 16 in a nonoxidizing state and flowed out through an outflow port 14. After the above-mentioned mixed raw material 2 is heated at the temp. in the range within 1,400-1,700 deg.C for the prescribed period with a heater 6, it is heated while a comparatively small amount of at least one kind of gas selected from among an inert gas (e.g. Ar, N2, He) and gaseous HF is flowed in a space 3 through an inflow port 18 for at least one part of the period in the latter half of the whole period of the heating and the suppression of the inclusion of SiO2 contained in the produced SiO whisker and the removal of SiO2 are performed.

Description

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

[Prior Art] A method of producing SiC whiskers by heating a mixture containing silicon dioxide and a carbon source in a non-oxidizing atmosphere is known (for example, Japanese Patent Laid-Open No. 58-20799
@Refer to Japanese Patent Publication No. 54-17720).

[Problems to be solved by the invention] JP-A-58-20799, JP-A-54-1772
When SiC whiskers were synthesized according to the conventionally known method such as in Publication No. (Usually about 20% based on the total product) as 100).

Therefore, in order to remove the mixed 5in2 from the product, it was necessary to treat the product with an HF solution.

The present invention has been made in view of the above-mentioned points, and an object thereof is to provide a method for manufacturing SiC whiskers that can suppress the amount of 5102 mixed in at a low level.

In this specification, the mixed amount of S t O2 refers to the ratio of the weight of SiO□ in a product to the total weight of the product in a predetermined whisker generation region, expressed in percent.

[Means for Solving the Problems] According to the present invention, the above-mentioned object is achieved by heating a mixed raw material containing a silicon dioxide source and a carbon source in a non-oxidizing atmosphere.
When generating iC whiskers, this is achieved by a method for producing SiC whiskers, which comprises flowing at least one of an inert gas and hydrogen fluoride gas into a SiC whisker generation region.

[Operations and Effects] When at least one of an inert gas and hydrogen fluoride gas is flowed into the SiC whisker production region according to the method of the present invention, it is in an equilibrium relationship with the solid phase of 5102 in the SiC whisker production region. Partial removal of some gas phase content from the production region may accelerate the SiO2 evaporation reaction and reduce the amount of SiO2 solid phase.

When the flowing gas contains hydrogen fluoride gas, in the generation region, for example, 5in2+48F-) SiF4+2)-120
5102 can be removed according to the following reaction.

The flowing gas may consist of only an inert gas, a mixed gas of HF gas and an inert gas, or only HF gas, but preferably a mixed gas is used.

Note that the inert gas may be a rare gas such as Ar gas or He gas, or a noble gas such as N2.

Note that when only an inert gas, for example only Ar gas, is flowed, it is preferable to raise the temperature of the whisker generation space by about 50 diameter degrees compared to when HF gas is flowed.

It is preferable that the time point 2 when the gas starts flowing is after the time point when the heating starts, and the period during which the gas is flowing is preferably at least a part of the latter half of the heating period. .

For example, after substantially or substantially reacting a mixed raw material effective for producing SiC whiskers to produce SiC whiskers, the gas is flowed into the SiC whisker producing region while keeping the temperature constant. Generated S i 02
may be removed.

According to the method of the present invention, simultaneously with the synthesis of SiC whiskers or subsequent to the synthesis of SiC whiskers, it is possible to suppress the presence of Zsiio2 in the SiC whiskers or remove SiO2 by a series of operations. It is efficient compared to the conventional processing methods used.

The flow rate of the gas to be flowed depends on the type of gas, the timing of flowing the gas, the mutual position, shape, and size of the mixed raw material filling region and the whisker generation region, the amount of one patch, the type of Sio2 source and C/source, and Although it varies depending on the amount of fluoride etc., it is usually preferable to use a relatively small amount, for example, 5i
02:C:NaF=1:3:1/3 (-E ratio)
When one batch is 1389°C and the holding temperature is 1500°C, it is about 50 cd/min.

The mixed raw material used in the method of the present invention is preferably 5i
02, contains NaF in addition to C.

When NaF added to the mixed raw material is heated in a non-oxidizing atmosphere, it forms a silicate melt with SiO2 etc. as a silicon source, promotes the reaction between SiO2 and C, and as a result It promotes the generation of 810 and CO gas from the mixed raw materials and promotes the synthesis reaction of SiC.

The proportion of NaF sensitively affects the yield of long-fiber SiC whiskers (with respect to the amount of Si: a, same below);
i If the molar ratio to O2 is less than 1/24 or more than 1/2, the yield of long fiber SiC whiskers will be 5% or less (in this specification, SiC whiskers are referred to as "long fibers"). refers to whiskers with a length of 500 or more).

If the proportion of NaF contained in the mixed raw material is too large, the amount of silicate melt formed when the mixed raw material is heated in a non-oxidizing atmosphere becomes too large, resulting in S i O? It is considered that GO is rapidly generated and a large amount of Si 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 5i02 and C, which will actually reduce the yield of SiC whiskers. It will be done.

In addition, powdered SiC is easily synthesized in the mixed raw materials.

Note that NaF is preferable compared to other fluorides such as Na3AlF6 or Al1F3 because it has a high vapor pressure and is less likely to be mixed into the product, but in some cases NaF
Other financial instruments such as IF6 may also be used.

As a source of 5102, for example, precipitated silicic anhydride is preferable from the viewpoint of high reactivity and high purity. A SiO2 source may be used, and in some cases, Kira (fine powder waste produced during the fi-making process of clay minerals, consisting primarily of quartz, feldspar, kaolinite, and mica, usually containing about 5i02 70% by weight, approximately 20% by weight of Al1203, 5% by weight of K2O
), rice husks, etc. may also be used.

The C source may be a highly reactive material such as activated carbon, or a graphitic material such as carbon black.

The proportion of carbon C in the mixture is determined so that it reacts with S i O2 almost in excess and deficiency, and when C is 5tO2
If the molar ratio of C to S i O2 is less than 1.5, there is a risk that the carbon content will be insufficient and a large amount of unreacted S i O2 will remain; If the amount is too large, there is a risk that a large amount of unreacted carbon may remain. Therefore, from the viewpoint of raw material utilization efficiency, in the mixed raw material, the molar ratio of C as a carbon source to 5102 as a silicon dioxide source is 1.5.
-5 is preferable.

Note that 5i02, C, and NaF are preferably mixed uniformly before heating, and may be granulated depending on the case.

When heating the mixed raw materials, the air in the crucible and the exhaust pipe is replaced with an inert gas such as Ar before heating so that the gas atmosphere in the crucible is initially non-oxidizing. As this inert gas, N2, He, etc. may be used instead of Ar.

Heating of the mixture under a non-oxidizing atmosphere is preferably carried out at a temperature in the range from 1,400 to 1,700°C.

If the heating temperature is less than 1,400°C, there is a risk that the reaction rate will decrease and the yield of SiC whiskers will decrease.
When the heating temperature is higher than 1,700° C., the reaction rate becomes too high and there is a possibility that SiC powder is produced rather than SiC whiskers.

According to the present invention, preferably 1 molar part of SiO2, 1.5 to 5'f:) It part of C, and 1/24 to 1/24 of NaF
A mixed raw material containing 1/2 mole part was added to 1 part in a non-oxidizing atmosphere.
, to produce SiC whiskers by heating to 400 to 1,700°C.

In this case, according to the present invention, long fiber SiC whiskers with a length of several layers can be produced in a high yield in the whisker generation space on the surface of the mixed raw material, and at the same time, long fiber SiC whiskers with a length of 100-
Front and back 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 the figure, 1 is a crucible made of graphite, and at the bottom of the crucible 1 with an inner diameter of 15 G, for example, up to a height A (for example, about 30 G), precipitated silicic anhydride is used as a source of SiO2, and precipitated silicic acid is used as a C source. A mixed powder 2 of activated carbon and NaF in a predetermined ratio is accommodated. At this time, the upper part of the crucible 1 has a height B (preferably B>5A, for example, about 150 feet).
A space 3 for producing long fiber whiskers is formed up to a range of .

The crucible 1 may be made of SiC or the like, which has high chemical stability, instead of being made of graphite. The diameter of the crucible 1 is reduced at the upper part 4, and a graphite tube 5 (for example, inner diameter 65mm, length 1mm, 300mm) serves as an exhaust pipe.
It is connected to the.

Reference numeral 6 denotes a carbon heater arranged so as to almost surround the crucible 1, and the crucible 1 and the heater 6 are further surrounded by an inner wall portion 7 made of a heat insulating block. Mixed raw material 2 in crucible 1 is 1,400~1,70
The shape of the heater 6, as long as it can be heated to about 0℃ for a long time,
Position, heat generation method is other form (e.g. high frequency induction heating)
But that's fine.

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 19 is similar to the wall portion 7.
and surrounds the tube 5.

In addition, another tube 1 is attached to the tip of the graphite tube 5.
0 is connected, and the upper end 10a of the tube 10, which cooperates with the tube 5 to constitute an exhaust pipe, penetrates the outer wall portion 8 and protrudes. In addition, top #i14 of crucible 1, tube 5
, 10 connections are usually not completely sealed, but
It may be completely sealed if desired.

Reference numeral 11 denotes a pipe for introducing an inert gas such as Ar, and when producing whiskers, a predetermined flow fltc (for example, 200
~1. Good d/min: In this specification, the Ar gas introduced at 17 minutes with respect to the gas flow rate (flow rate) indicates the amount at normal temperature and normal pressure) After passing through the cylindrical cavity 1!112 between the outer wall 8 and the tube 5, it flows through the cylindrical cavity 11113 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 flows through the circle between the carbon heater 6 and the outside of the graphite crucible 1, which is heated to approximately 1,400 to 1,700°C by the heater 6. The space 15 around the carbon heater 6 and the space 16 around the carbon heater 6 are kept non-oxidizing, and a part of the space (about 50d1 minute) enters the tube 5 from the connection between the upper part 4 of the crucible 1 and the tube 5, It flows out through tube 5.

Reference numeral 11 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 inside 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 to completely fill the inside of the crucible 1 and the tube 5 with Ar gas. .

In addition, 9a is a thermocouple for temperature measurement, 9b is a current-carrying terminal of the heater 6, and 9
C is a fixture.

When generating whiskers, the heater 6 is energized and the mixed powder 2 is passed through the crucible by the heater 6 at a rate of 1,400
The hot water is heated to a predetermined temperature T1 within the range of ~1,700°C, and the temperature T2 of the space 3 where whiskers are to be generated and the temperature gradient Δ'[21ΔZ (lower at the top) are 25 degrees/10.
Maintain a predetermined value of 0 or more. Note that Δ° "2/Δ2 may differ depending on the location. For example, ΔT2/ΔZ may be larger as the area moves downward, and ΔT2/ΔZ may be larger as it moves upwards.

When ΔT2/Δ2 is within a range of approximately 200 degrees/1100a or less, the yield of long culm fiber SiC whiskers with a large ΔT2/ΔZ is high.

Note that the temperature of the whisker generation space I13 is preferably at least 1200°C or higher.

In addition, yA price of mixed powder 2 and whisker generation space 1ffi3
The temperature of the desired part of the heater 6 is detected by a temperature detection means such as a thermocouple (not shown), and the current flowing through the heater 6 is adjusted based on the hot water temperature detected by this detection means 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, length, etc. of the heat insulating block T, but if desired, the outer surface of the crucible 1, etc. can be forcedly cooled.
The adjustment may be made by doing this.

The mixed powder 2 is heated to a temperature of 1 by the heater 6 to fill it at a predetermined time (for example, most of the effective amount of the mixed powder 2 is SiC).
After the elapse of time (time required for whisker synthesis), a mixed gas (for example, HF gas and Ar gas) is supplied from the inlet 18 through the pipe 17 to the whisker generation space 3 above the raw material filling area 2a. For example, HF/A r-0,05~1
(molar ratio)) at a rate of about 20 to 100aj/min.

In this device i9, when the mixed raw material 2 in the crucible 1 is heated by the heater 6, fluoride generated in the crucible 1 is
Since it can be discharged to the outside through the tube 5.10, there is less risk that the insulation walls 7, 8, etc. will be corroded or deteriorated by the fluoride.

In addition, in this device 9, after a predetermined period of time has elapsed after starting the heating of the mixed raw material 2, gas containing, for example, HF gas is introduced into the whisker generation space 3 from the pipe 17, so that SiC whiskers are generated in the SiC whisker generation space 3. The amount of Sin mixed in SiC whiskers can be reduced.

Back 1”.

138 g of mixed powder 2 obtained by mixing powders containing 1 mole part of Si0,2 (sedimented anhydrous silica), 3 mole parts of C (activated carbon), and 1/3 mole part of NaF in a ball mill, was filled into the raw material filling region 2a at the bottom of the graphite crucible 1.

A
It was completely replaced with r gas and the inlet 18 was closed.

On the outside of the crucible 1, from the tube 11, C-1,000ai/
The Ar gas was continued to flow at a flow rate of 100 min to maintain the furnace space 15, 16, 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 T1 of the mixed raw material 2 in a was maintained at 1,500°C for 12 hours (ΔT2/Δz2100 degrees/10G, ).

In addition, during the 12-hour heating period, from the time when 9 hours have passed from the start of heating until the end of heating, the pipe 11 is
, crucible 1, and Ar 90 to pass through tube 5.10.
Flowing a mixed gas containing 10 mol% of HF ME-50
CI! Flowing in / minute.

As a result, the whisker generation space 113 has a thickness of 0.
Long fiber SiC whiskers having a length of 1 to 160 −1 layers or more were obtained with a yield of 15% for 3i. When the long m1lls i C whiskers generated in the generation space 3 were treated with a 5% HF solution, they showed a weight 1 decrease of 1.2%. This weight loss is believed to be due to 5i02 contained in the SiC whiskers. .

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 1 ooJIR.

Except for the point that only Ar gas was flowed for E-50d1 minute instead of the mixed gas of Ar gas and HF gas, and the holding temperature when flowing the Ar gas was raised to 1,570℃. SiC whiskers were synthesized under the same conditions as in Example 1.

As a result, the whisker generation space 3 has a thickness of 0.1 to
1.0 *, the length is about several layers long! [18i C whiskers were obtained in a yield of 17% with respect to Si.

The long fiber whiskers generated in this generation space 3 are heated to 5% H.
Treatment with F solution showed a 5.4% lfi decrease.

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 100 mm.

1 Next day 1 S was heated under the same conditions as in Example 1, except that no gas was introduced from the inlet 18 during the 12-hour heating period.
iC whiskers were synthesized.

As a result, the whisker generated space rrA3 has a thickness of 0.
Although long fiber SiC whiskers of several layers in length were obtained with a yield of 22% with respect to Si, the SiC whiskers in production space 3 had a yield of 21.0% by treatment with a 5% HF solution. It showed a weight loss of 5%.

As is clear from the results of Example 1.2 and Comparative Example above, during the latter half of the generation of SiC whiskers at a predetermined heating temperature, the whisker removal gas is caused to flow for 5i02 minutes into the whisker generation space 3. It is possible to reduce the proportion of 5 in 2 mixed between whiskers generated in the generation space 3 or on the surface.

[Brief explanation of drawings]

The figure is a cross-sectional explanatory view of a preferred example of a manufacturing apparatus for carrying out the SiC whisker manufacturing method of the present invention. 1...crucible, 2...self-mixture, 3...
...Whisker generation space, 5.10...Tube, 6...Heater, 17...Tube, 1
8... Inlet. *vtt) #6 q

Claims (5)

[Claims] (1) When heating a mixed raw material containing a silicon dioxide source and a carbon source in a non-oxidizing atmosphere to generate SiC whiskers, at least one of an inert gas and hydrogen fluoride gas is applied to the SiC whisker generation region. A method for producing SiC whiskers comprising flowing a gas. (2) The method according to claim 1, wherein the time when the gas starts flowing is after the time when the heating starts. (3) The method according to claim 2, wherein the period during which the gas is flowed is at least a part of the latter half of the period during which the heating is performed. (4) The mixed raw material is 1 mole part of SiO_2, 1.5~
4. A method according to any one of claims 1 to 3, comprising 5 molar parts of C and 1/24 to 1/2 molar parts of NaF. (5) The method according to any one of claims 1 to 4, wherein the heating is performed at a temperature within the range of 1,400°C to 1,700°C.