JPS61227995A - Production of sic whisker - Google Patents

Abstract

PURPOSE:To produce an SiC whisker inexpensively and securely by heating a mixture contg. the scum, a C source and an NaF source in the nonoxidizing atmosphere. CONSTITUTION:The scum being the fine powder waste such as quartz contg. about 70wt% SiO2, about 20wt% Al2O3 and about 5 wt% K2O is used and a mixture 2 contg. 1mol part SiO2 caused to the scum, 1.5-5mol part C and 1/24-1/2mol part NaF is packed up to the height A of a base part of a crucible 1 and a space 3 producing a long fiber whisker is formed in the range of B>=5A up to the height B of the upper part thereof. After an inert gas such as Ar is introduced through the introduction pipes 11, 17 and an inflow port 18 and the insides of the crucible 1 and a tube 5 are completely filled with gaseous Ar, the mixture 2 is heated at the prescribed temp. T1 in the range within 1,400-1,700 deg.C with a heater 6 and also while keeping the temp. T2 of the space 3 and the temp. gradient DELTAT2/DELTAZ (the upper a position is, the lower the temp. is) in >=25 deg.C/100mm prescribed value, an SiC whisker having the long fiber of about >=500mum length is produced in the space 3.

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 v#] The method itself for producing SiC whiskers by heating a mixture containing a silicon source and a carbon source in a non-oxidizing atmosphere is known. It has also been proposed to use inexpensive rice husk, whitebait, etc. as a silicon source (see, for example, Japanese Patent Publication No. 59-9516 and Japanese Patent Application Laid-open No. 58-20799).

[Problems to be Solved by the Invention] However, when attempting to use rice husks as a silicon source, it is necessary to ash the rice husks prior to whisker synthesis, which is undesirable because the operation becomes complicated. , □ On the other hand, whitebait is not preferable because it has a large compositional fluctuation (compared to Kira).

The present invention has been made based on the above-mentioned points, and its object is to inexpensively and reliably use a silicon source that is inexpensive, has a relatively stable composition, and has good reactivity. An object of the present invention is to provide a method for manufacturing SiC whiskers by WA.

[Means for Solving the Problems] According to the present invention, the above object is a method for producing SiC whiskers by heating a mixture containing Kira, a carbon source, and a sodium fluoride source in a non-oxidizing atmosphere. achieved by.

In this specification, Kira is a general term for fine powder waste generated during the production process of clay minerals, mainly quartz, feldspar,
Composed of kaolinite and mica, usually containing about 70% SiO□
It contains about 20!1% by weight of Al2O3 and about 5% by weight of K2O.

[Operations and Effects] According to the present invention, since Chira, which is inexpensive and has a relatively stable composition, is used as a silicon source, SiC whiskers can not only be manufactured relatively cheaply and easily, but also be easily synthesized. At the time, Kira Junior High School (7) Aj! 203, K
20 and the like can react with S i O 2 , IN a F, etc. to form silicate melts and promote whisker synthesis reactions.

Furthermore, since Kira is usually obtained in the form of a fine powder with a stable composition, operations such as crushing and dividing are not necessary, and drying alone is sufficient as a pretreatment.

When NaF added to the mixed raw material is heated in a non-oxidizing atmosphere, it forms a silicon salt melt with S i 02,
It promotes the reaction between 5102 and C, thereby promoting the generation of 810 and Co gas from the mixed raw materials, and promoting the SIC synthesis reaction.

The proportion of NaF is determined by the yield of long 111NtSiC whiskers (
Regarding the amount of Si (less than 2), the amount of Na
When the molar ratio of F to 8102 is less than 1124 or more than 1/2, the yield of long fiber SiC whiskers becomes 5% or less.

If the proportion of NaF contained in the mixed raw material is too high, 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.

Note that NaF is preferable compared to other fluorides such as Na5Aj'F6 or AjF3 because it has a high vapor pressure and is less likely to be mixed into the product.
Other fluorides such as j'F6 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 5i02 in just the right amount, and if the molar ratio of C to 5in2 is less than 1.5, the carbon content is insufficient and unused. There is a risk that a large amount of SiO2 from the reaction will remain, while C is
If the molar ratio to iO2 is more than 5, there is a risk that unreacted carbon will remain in each company. Therefore, from the viewpoint of utilization efficiency of the fL material, the molar ratio of C as a carbon source in the mixed raw material to silicon dioxide and 5i02 as an elementary source is 1.5 to 5.
It is preferable that

It is preferable that S+O2, C and NaF are uniformly mixed before heating, and may be granulated depending on the case.

The non-oxidizing atmosphere during heating of the mixture is preferably made of Ar, but other rare gases such as Ha or N2 may be used instead of Ar.

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 1,400 to 1,700°C.

If the heating temperature of 81 degrees is lower than 1400 degrees Celsius, 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 1700° C., the reaction rate becomes too high and there is a possibility that SiC powder is generated rather than SiC whiskers.

According to the present invention, preferably 1 mol part of 8102, 1.5 to 5 mol parts of C, and 1/24 to 17 mol of NaF in Kira.
A mixed raw material containing 2 mole parts was heated to 1400 molar parts in a non-oxidizing atmosphere.
Heating to ~1100°C produces SiC whiskers.

In this case, according to the present invention, long fiber 3iC whiskers with a length of about 1 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 3iC whiskers with a length of about 1
Front and back SiC whiskers can be generated.

In this specification, regarding S i C whiskers, "long fiber length" or "1° long fiber" refers to a fiber length of 50
Refers to 0% or more SIC whiskers. This long fiber SiC
When a whisker is used as a composite reinforcing fiber composite with, for example, A1'* group, the composite effect is considered to be far superior to that of a SIC whisker having a length of 100 tones or less.

In addition, in Specification 1, the yield for SiC whiskers refers to the amount of Si used;
It refers to the ratio of Si1 forming whiskers to the 3i amount of SiO2 in the filler in the mixed raw material powder.

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, reference numeral 1 is a graphite crucible. For example, in the lower part of the crucible 1 with an inner diameter of 150-1, Kira as a SiO2 source, activated carbon as a C source, and NaF A predetermined ratio of mixed powder 2 is accommodated. At this time, a space 3 for producing whiskers having a length II up to a height B (preferably B≧5A, for example about 1501) is formed in the upper part of the crucible 1. The crucible 1 may be made of SiC or the like, which has high chemical stability, instead of the graphite group.

The diameter of the crucible 1 is reduced at the upper part 4, and a graphite tube 5 (for example, inner diameter 65 mm, length 1
．． 30011).

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 7 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 time and can be heated continuously, the heater 6 may have another form (for example, high-frequency induction heating).

8 is the outer wall made of insulation block and has a whisker generation device! The outer wall portion 8 constituting the outer frame of the wall portion 7
and surrounds the tube 5.

Note that another tube 71 is attached to the tip of the graphite tube 5.
0 is connected 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 as desired □
If it is, it may be completely sealed.

Reference numeral 11 denotes a pipe for introducing an inert gas such as 711r, and when producing whiskers, a predetermined flow 1i1G (for example, 2
00-1,000 ffl/min; in this specification,
Regarding the gas flow rate (flow rate), the Ar gas introduced at ai1 minute (d indicates the amount at normal temperature and normal pressure) fills the cylindrical air 1i112 between the inner wall part 1 and the outer wall part 8. After passing through, it flows through the cylindrical space 13 between the outer wall 8 and the tube 5 and exits through 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 1700°C by the heater 6.
The space 1115 between the outside of the graphite crucible 1 and the carbon heater 6, which is heated to It enters the tube 5 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 inside of the tube 5 is completely filled with Ar gas, and then the inlet 18 is opened.

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 thermocouple for temperature measurement, 9b is a current-carrying terminal of the heater 6,
9C is a fixture, and 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 within the range of 1700°C, the temperature T2 of the space 3 where whiskers are to be generated and the temperature gradient ΔT2/Δ2 (from 8 to 25 degrees/100 degrees from upper to lower)
Maintain a predetermined value of m- or more.

Note that ΔT2/ΔZ may differ depending on the location. For example, even if Δ゛r2/Δ2 is larger in the lower part, ΔT2 in the upper part is larger.
/Δ2 may be large.

Within the range of ΔT2/ΔZ of 200 degrees/100gu+ or less, the larger ΔT2/Δ2 is, the better.
Higher whisker yield.

Note that the temperature of the whisker generation space 3 is preferably at least 1200°C or higher.

The temperature of the mixed powder 2 and the temperature of a desired part of the whisker generation space 3 are detected by temperature detection means such as a thermocouple (not shown), and the heater 6 is controlled based on the temperature detected by this detection means. Adjust the current to flow and 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, for example, by changing the position, thickness, length 2, 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.

Example 1 Kira as S102 source (composition after heat treatment at 700°C, S + 02 73.333 Juumaru A1203
20.03 wt% Fe OO, 59 wt% to 20 s, 1 s wt% Na2O0, 177 weights MgO0 108 weight% T i 02 0.34 weights 11% Ca OG,
06% by weight), 1 mole part of 5i02, 2 mole parts of C (activated carbon), and N
A powder containing 1/3 mole part of aF was mixed in a ball mill, and 100 (l) of the mixed powder 2 was filled into the raw material filling area 2a at the bottom of the graphite crucible 1.The air in the crucible 1 and the tube 5 was The atmosphere 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 91570°C at 12 hours (ΔT2/Δz2100 degrees/1001 m2).

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

Ar gas was flowed at d/min.

As a result, the whisker generation space 3 at the top of the crucible 1 has a thickness of 0.5 to 1.0iI11 and a length of 500JI.
14Q long fiber SiC whiskers of II or higher were obtained.

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 SEM observation and X-ray diffraction, it was found that
A considerable proportion of SiC whiskers with a length of about 10 G (cm) was contained in b.

5i02 (precipitated anhydrous silica II is 1 mol part, C (activated carbon) is 2 mol parts, NaF is 1/3 mol). A SiC whisker synthesis experiment was carried out in the same manner as in Example 1, except that 130 g of mixed powder 2 consisting of

As a result, in the whisker generation space 3 at the top of the crucible 1, long fibers of SiC with a thickness of 0.1 to 1 ring and a length of several square meters are formed.
5 g of whiskers were obtained. This is about SiC.
This corresponds to a yield of 10%.

On the other hand, when the 42Q residue 2b remaining in the lower part 2a of the crucible 1 was examined, most of it was found to be SiC whiskers with a length of about 100 voices.

As is clear from the results of Example 1 and Comparative Example 1 above, as far as the production of long-fiber SiC whiskers is concerned, it can be seen that inexpensive Kira can be used in place of precipitated silicic anhydride, which has high purity and high reactivity. .

When synthesizing this SiC whisker, io in Kira,
Ko et al. 5h02. It is thought that it reacts with NaF and the like to form a silicate melt and promote the whisker synthesis reaction.

[Brief explanation of the drawing]

The figure is a cross-sectional explanatory view of a preferable example of a manufacturing apparatus for carrying out the method for manufacturing SiC whiskers of the present invention. 1...crucible, 2...mixture, 3...
... Whisker generation space, 6 ... Heater,
A: Height of the filling region, B: Height of the production region. Ex-J member Hajime Sai Sou

Claims (3)

[Claims] (1) A method for producing SiC whiskers by heating a mixture containing Kira, a carbon source, and a sodium fluoride source in a non-oxidizing atmosphere. (2) The method according to claim 1, wherein the mixture contains 1 mole part of SiO_2 caused by Kira, 1.5 to 5 mole parts of C, and 1/24 to 1/2 mole part of NaF. . (3) The method according to claim 1 or 2, wherein the heating temperature is between 1,400 and 1,700°C.