JPH05105600A - Method for producing alpha-sic whisker - Google Patents

Abstract

PURPOSE:To industrially produce alpha-SiC whiskers by using ash residue of gramineous plant as a silicon source raw material. CONSTITUTION:Ash residue of rice hulls is mixed with 110-400wt.% carbon material of carbon black to give a raw material system, which is blended with 1-30wt.%, based on the raw material system, of Na2CO3 as a third component. The blended raw material is reacted under heating at 1,300-1,800 deg.C in an N2 atmosphere to form SiC whiskers consisting essentially of a crystal system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing α-type crystalline SiC whiskers using the ash residue of rice plants as a silicon source material.

[0002]

2. Description of the Related Art Various methods are known in the art of producing SiC whiskers, which are useful as composite reinforcing materials for metals, plastics, ceramics and the like. When the conventional manufacturing techniques are classified according to the raw material system, SiC is used as the silicon source.
_{l 4, SiHCl 3, (CH} 3) 4 decomposable silicon compound such as Si, and the vapor process for gas phase reaction by using a _{CH 4, C 3 H 8,} CCl 4 as the carbonaceous material, the SiO ₂ It can be roughly classified into a solid-state raw material method in which a solid-state silicon source containing it is mixed with a carbonaceous material such as carbon powder, or a substance containing these components in a complex manner is heated and reacted. Among them, the method using a gas phase raw material has a drawback that it is not suitable for industrial production in terms of process and equipment, because a gaseous substance such as halogen and hydrogen which is extremely difficult to handle is used. On the other hand, the solid phase raw material method is industrially advantageous because it uses a stable powder raw material, and is currently regarded as a practical manufacturing technique.

The silicon source materials that have been used as solid phase materials so far include rice husk ash, silica sand, silica gel, shirasu, cullet (waste glass powder) and the like. Of these, synthetic materials such as silica gel are used. In the case, usually, Fe, C
The addition of a transition metal-based compound containing o, Ni, etc. as a catalyst component is an important requirement for increasing the yield of SiC whiskers (for example, Japanese Patent Publication No. 60-4428).
No. 0 bulletin). However, when a natural material such as rice husk ash is used as a raw material, since a small amount of Fe and the like is mixed in itself, the generation of SiC whiskers can be smoothly performed without adding a transition metal compound as the third component. proceed.

[0004] By the way, there are β cubic type and α type crystalline whiskers as crystal types, but when the silicon source raw material containing the component of the transition metal is used as described above, β type SiC whiskers are mainly produced. To generate. The same applies to the case of using rice husk ash, and β-type SiC whiskers are also produced by the method described in JP-A-56-93086 and JP-A-56-109811 using this as a raw material.

[0005]

It has been demonstrated that β-SiC whiskers have excellent composite performance as a strengthening substance for metals and alloys, but recent research has shown that composite strengthening of ceramic materials is possible. For α rather than β
It has been clarified that the performance improvement is remarkable in the crystal system.

In view of the above technical background, the present invention has hitherto been difficult to industrially manufacture with a solid-phase raw material system.
-SiC whiskers result generation technique was repeated research about, the specific amount in the raw material systems based on rice husk ash Na ₂ CO
_The development was made by confirming the fact that α-type SiC whiskers are efficiently formed when ₃ is added and heated and reacted.

Therefore, it is an object of the present invention to provide a method for industrially producing α-SiC whiskers by using the ash residue of rice plants as a silicon source material. The α-SiC whiskers targeted by the present invention are the generated Si.
It refers to the property of mainly α crystal system in which the mixture ratio of α-SiC in C whiskers is 70% or more.

[0008]

A method of manufacturing an α-SiC whisker according to the present invention for achieving the above object comprises:
1 to 30% by weight of Na ₂ CO ₃ as a third component in a raw material system in which carbon black carbonaceous material is blended with an ash residue obtained by incinerating fruit shells or stems of rice plants
The composition is characterized in that the mixture is added and mixed in a ratio of 1) and heat-treated in a temperature range of 1300 to 1800 ° C in a non-oxidizing atmosphere.

As the silicon source material of the present invention, powders obtained by incineration and ashing the fruit shells or stems of rice, cereals such as wheat and millet, as well as various rice plants such as reeds and kaya are used. For the ashing treatment, the rice plants are dried and crushed if necessary.
After cutting, it is heated and incinerated by a heating device such as an electric furnace in a temperature range of 600 ° C or higher, and then continued to be heated until a constant weight is reached. By this incineration treatment, rice plants are converted into an ash with a composition of about 10 to 20% by weight and 90% or more of which is composed of amorphous SiO ₂ .

As the carbonaceous material, carbon black obtained by thermally decomposing petroleum-based or coal-based heavy hydrocarbons is used. As the properties of carbon black, particularly those having a fine particle / high structure structure having a nitrogen adsorption specific surface area of 40 m ² / g or more and a DBP adsorption amount of 90 ml / 100 g or more are effectively used.

A silicon source material consisting of ash residue and carbon black carbonaceous material are blended at an appropriate ratio to form a raw material system. It is necessary to set the blending ratio of both components to at least 110% by weight of carbon black carbonaceous material with respect to the ash residue, and if the carbonaceous material blending ratio is less than this, shot generation increases and SiC whisker This results in a decrease in yield. However, blending of carbon black carbonaceous material in excess of 400% by weight is no longer involved in the formation reaction, and is rather undesirable because it complicates the post-treatment associated with the increase in residual carbonaceous material. Therefore, it is desirable to set the blending range of the carbon black carbonaceous material to the ash residue to be in the range of 110 to 400% by weight.

In the above raw material system, Na _{2 as a} third component is used.
CO ₃ is added. Na ₂ CO ₃ is a component that functions to convert the produced SiC whiskers into the α crystal system, and is mixed with the raw material system in the form of powder or an aqueous solution. The amount of addition needs to be set within the range of 1 to 30% by weight as Na ₂ CO _{3 with} respect to the raw material system. If the amount added is less than 1% by weight, the crystal system of the SiC whiskers is not mainly α-type, and if the amount added exceeds 30% by weight, a large amount of glass products adhere to the reaction furnace and the operability deteriorates.

The raw material system and the third component, Na ₂ CO _3, are mixed in a sufficiently uniformly dispersed state, and then lightly charged into a reaction vessel made of a graphite material and subjected to a heating reaction. Then, the reaction vessel is transferred to a heating furnace maintained in a non-oxidizing atmosphere such as N ₂ or Ar, and heat-treated in the reaction temperature range. As the heating furnace, a normal resistance heating furnace, an Acheson furnace, a pusher type tubular furnace, or the like is applied. The reaction temperature is 1300-1800
℃, preferably set in the range of 1500 ~ 1700 ℃.

After the reaction, the unreacted carbon black carbonaceous material remaining in the product in the reaction vessel is separated and removed by means such as incineration or liquid phase separation. The SiC whiskers produced in this way are mainly α-type SiC without lattice defects.
It is a needle-shaped single crystal with a small shot content and excellent extensibility.

[0015]

According to the process of the present invention, by combining a raw material system using a silicon source raw material composed of ash residue of rice plants and Na ₂ CO ₃ added as a third component, an α-SiC whisker can be efficiently produced. Can be generated. Therefore, when a silicon source material such as silica gel or silica sand is used, the α-crystal-based SiC whiskers targeted by the present invention cannot be produced.

Although the mechanism of formation has not yet been elucidated in detail above, SiO ₂ and Na ₂ CO _{3, which} have special characteristics obtained by ashing rice plants, are treated with water glass at a relatively low temperature during the reaction process. It is presumed that this is due to the effect that α-type growth nuclei dominate during the crystal growth from this liquid phase.

[0017]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 3 The dried rice husks were heated in an electric furnace at a temperature of 600 ° C. to be incinerated and ashed to a constant weight. The obtained ashing residue was a fine powder showing a light gray color, and the residual rate was 20.5% by weight and the SiO ₂ content rate was 91.9% by weight. This ash residue is used as a silicon source material, and carbonaceous material has a nitrogen adsorption specific surface area of 99 m ² / g and DBP oil absorption
129ml / 100g of furnace carbon black 143wt%
Was mixed at a ratio of to obtain a raw material system.

Na ₂ CO ₃ powder was added to the above raw material system in various amounts, and the mixture was stirred and mixed until sufficiently dispersed.
The mixed raw material was lightly filled in a graphite reaction vessel, covered with a graphite lid and sealed, and then in an electric heating furnace in an N ₂ gas atmosphere.
The temperature of 1700 ° C was maintained for 2 hours. After the heating reaction, the contents are recovered from the reaction vessel and heat-treated in the atmosphere at a temperature of 800 ° C for 1 hour to incinerate and remove the residual carbonaceous material components, and then 5% HF
It was washed with an aqueous solution to remove impurities such as SiO ₂ .

The properties of each of the SiC whiskers thus obtained were measured, and the results are shown in Table 1 in comparison with the addition amount of Na ₂ CO ₃ used as the third component. The α-SiC mixed ratio in the SiC whiskers is shown as α degrees in the following formula. α degree = (H ₁ × 2 / H ₂ ) × 100 where H ₁ is 2θ when CuKα is used as a radiation source in X-ray diffraction.
The diffraction line intensity of 34.2 deg (single peak of α-SiC, specific intensity 50), and H ₂ are the diffraction line intensity of 35.6 deg (mixed peak of β-SiC and α-SiC, both specific intensities are 100).

Comparative Example 4 A SiC whisker was manufactured under the same conditions as in Example 1 except that the silicon source material of Example 1 was changed to silica gel powder containing 7.0% by weight of CoCl ₂ .6H ₂ O as a catalyst. The properties of the obtained SiC whiskers were measured, and the results are also shown in Table 1.

[0022]

[Table 1]

From the results shown in Table 1, in the examples satisfying the conditions of the present invention, SiC whiskers having a crystal system in which the degree of α-SiC inclusion exceeds 70% and having other good properties are produced. It is recognized that

[0024]

As described above, according to the present invention, a high quality α-SiC whisker can be industrially manufactured. Therefore, it is useful as a manufacturing technology of a composite reinforcing material for ceramic materials.

Claims (1)

[Claims] 1. A raw material system in which carbon black carbonaceous material is mixed with an ash residue obtained by incinerating the fruit shells or stems of rice plants, and Na ₂ CO ₃ as a third component is added to the raw material system in an amount of 1 to ₃ times. Add and mix at a ratio of 30% by weight in a non-oxidizing atmosphere
A method for producing an α-SiC whisker, which comprises performing heat treatment in a temperature range of 1300 to 1800 ° C.