JPS6047203B2 - Method for manufacturing α-type silicon nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides α-type silicon nitride (S1) which directly nitrides metal silicon (Si).

This relates to a manufacturing method of No. Conventionally, the direct nitriding method of 51 is known.

For example, there is a method of heating at a temperature of 1200 to 12500C for a long time, but if you try to shorten the reaction time,
Although it is necessary to raise the temperature to a high temperature of ℃ or higher, the generated α-Si3
N. has the disadvantage that it changes to β-Si,N. Furthermore, JP-A-50-128698 discloses a method of adding compounds of Na) and Li as nitriding reaction promoters to Si powder, but these nitriding reaction promoters and 51 powder partially react with each other. Therefore, there is a drawback that these nitriding reaction promoters cannot be uniformly mixed unless they are mixed for a long time of one hour or more. In the present invention, first, a Si powder having a particle size of 100 mesh or less or a nitriding reaction promoter is added to a Si powder having a particle size of 100 mesh or less.
A composition powder containing 0.01 to 3% by weight of acetic acid or more is molded, and the molded product is loaded into a nitriding furnace and heated and nitrided at a temperature of 1100 to 1250 ° C. in a nitrogen or ammonia gas atmosphere. Si in the molded product.

N. The content of α-Sj3N characterized in that the material is loaded into a nitriding furnace and re-nitrided at a temperature of 1250 to 14000C in a nitrogen or ammonia gas atmosphere. This is a manufacturing method. The present invention will be further explained in detail below.

The present invention is characterized in that 51 powder as a raw material is molded in the presence or absence of a nitriding reaction promoter, nitrided, then pulverized and molded, and re-nitrided.

In general, 51 powder has poor thermal conductivity, and its nitriding is an exothermic reaction, and its melting point is around 1400°C, so heat dissipation during the nitriding reaction is not sufficient, and it may sinter.
Since the metal may melt, a sufficient nitriding reaction cannot be carried out. In the present invention, SI powder is nitrided and α-Si3N4
In producing Si3N4, whose main component is After molding, secondary nitriding is performed to generate Si3N4 with a high content of α-Si3N4.

The Si used in the present invention is commercially available Si with a purity of 95%.
Above, the powder must have a particle size of 100 mesh or less.

If the Si particles exceed 100 mesh, the nitriding reaction will be delayed, which is not preferable.

Si with particles of 100 mesh or less, polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose,
Water-soluble binders such as molasses, valve waste liquid, and gum arabic are added and mixed, and after being molded, this is nitrided in a nitriding furnace.

In addition, one or more halides of alkali metals and alkaline earth metals may be added to Si as a nitridation reaction accelerator.
If 01 to 3% by weight is added, the content of α-Si3N4 will further increase.

Although any of the halides of alkali metals and alkaline earth metals can be used, the fluorides NaF and CaF2 are particularly effective in the present invention, and their effects are remarkable.

If the amount of the nitriding reaction promoter added is less than 0.01% by weight, the promoting effect will be small, and if it exceeds 3% by weight, the effect will be slow. Next, these mixed raw materials are rotary granulated using a drum or compression molded at a pressure of 10 to 10,000 k91 cIt to form blocks, granules, and prickets.
A molded article is obtained.

The molded product is loaded into a nitriding furnace and nitrided at a temperature of 1100 to 1250°C.

As the nitriding gas, a gas such as nitrogen or ammonia is used. The nitriding furnace is a fixed bed type, and the heating method is to insert an electrode into the center of the furnace! Nitriding is carried out by a method using electrical heating, but the method is not limited thereto. Through this primary nitriding reaction, more than 55% by weight of Si3N4 (among which α-Si,
(containing N44 vol.%) is obtained.

In the present invention, the end point of the primary nitriding reaction is Si3N45
The reason why the amount is set at 5% by weight or more is that even if the nitriding reaction is continued beyond this point, it takes time for nitriding. Next, the obtained nitride is ground to 100 mesh or less using a grinder.

A ball mill type crusher is usually used. To this pulverized material, one or more selected from alkali metal and alkaline earth metal halides are added as a nitriding reaction accelerator in a range of 0.01 to 0.0%. After adding a water-soluble binder and kneading, the mixture is formed into blocks, prickets, and granules. Note that the above-mentioned NaFlCaF2 is preferably used as the reaction accelerator. Note that when a nitriding reaction accelerator is added in the primary nitriding, the same nitriding reaction accelerator and additive amount are used in the secondary nitriding as in the primary nitriding. This is because the effect as a nitriding reaction accelerator decreases due to oxidation or volatilization.

Furthermore, in addition to this, iron compounds such as metallic iron are added to Si7.
．． Addition of 01 to 5% by weight further improves the production rate of α-Si3N4. The molding method is the same as described above. This molded product is loaded into a fixed bed type nitriding furnace, and nitrogen gas or ammonia gas is blown into the molded product and nitrided by heating with electricity.

The secondary nitriding temperature is 1250-1400°C which is 100-150°C higher than the primary nitriding temperature 1100-1250°C.

The reason for this limitation is that Sl3 is contained in the molded product due to primary nitriding.
This is because the presence of N4 controls the reaction heat and promotes the reaction. The nitride thus obtained is
Si3N4 is 95% by weight or more, and α-Si3N4 is 8% or more by weight.

As explained above, in the method of the present invention, raw material powder is molded in the presence or absence of a nitriding reaction promoter, and a temperature of 1100 to 1
At 250°C, 55% by weight or more of Sl3N4 is generated, preventing abnormal heat generation due to powder nitriding, and further improving the α-
In order to increase the amount of Sl3N4 and at the same time reduce unnitrides as much as possible, there is a method of re-pulverizing, adding a nitriding reaction accelerator and molding, and re-nitriding unnitrided metallic silicon. The obtained nitride is crushed to a specified particle size and used for refractories.
Can be used for ceramics. Further, if necessary, the nitriding reaction accelerator and the like can be removed by removal means such as acid treatment. The present invention will be specifically described below with reference to Examples and Comparative Examples.

The descriptions in Tables 1 to 5 of Examples and Comparative Examples were made as follows.

(1) The blending ratio of the reaction accelerator is expressed as an internal weight ratio (%).

(2) The amounts of silicon nitride and α-silicon nitride were determined using an X-ray diffraction apparatus manufactured by Rigaku Corporation under the trade name "Ziegler Flex 2013".

Example 1 1 rut volume % of a 3% concentration polyvinyl alcohol aqueous solution was added to Si powder of 100 mesh or less, and thoroughly kneaded for 15 minutes.
It was molded into a block of 30×30×30 Tf$L under a pressure of 0k9 nod, and nitrided at a temperature of 1200° C. for 5 hours in a nitrogen gas atmosphere.

The molded product was pulverized to 100 mesh or less, and as a result of analysis by X-ray diffraction, I3N4 in the molded product was 55% by weight, and α-Si3N4 was 5% by weight. This nitride was crushed to 100 mesh or less using a ball mill, and the reaction accelerator shown in Table 1 was added, followed by addition of 15 mL of a 3% by weight polyvinyl alcohol aqueous solution and kneading. It was molded into a $& book.

This block was loaded into a nitriding furnace and heated for 13 minutes under nitrogen gas atmosphere.
The composition of the nitrided proboscis obtained by nitriding at a temperature of 50° C. for 4 hours is shown in Table 1.

Example 2 After adding the reaction accelerator shown in Table 2 to Si powder of 100 mesh or less, adding and kneading 1.5% by weight of a 3% by weight polyvinyl alcohol aqueous solution, a 30 x 30 x 30 wn powder under a pressure of 150k91d Molded into blocks.

This block was loaded into a nitriding furnace and heated under nitrogen gas atmosphere for 12 hours.
Nitriding was carried out at a temperature of 00° C. for 5 hours to obtain nitrides as shown in Table 2. This nitride was ground to 100 mesh or less using a ball mill, each of the reaction accelerators shown in Table 3 was added thereto, and a 15% by weight polyvinyl alcohol aqueous solution with a concentration of 3% by weight was added and kneaded. It was molded into a 30 x (to) long block.

This molded product was loaded into a nitriding furnace and heated for 135 minutes under a nitrogen gas atmosphere.
The composition of the nitride obtained by nitriding for 4 hours at a temperature of 0'C is shown in Table 3. Example 3 A reaction accelerator shown in Table 4 was added to Si powder of 325 mesh or less, and 15% by weight of an aqueous solution of carboxymethyl cellulose having a concentration of 2% by weight was added and kneaded.

The granules of 10 to 50 T$t obtained by rotary granulation were
The mixture was placed on an iC plate stand, loaded into a nitriding furnace, and nitrided at a temperature of 1150° C. for 3 hours in an ammonia gas atmosphere to obtain the nitrides shown in Table 4. This nitride was ground to 325 mesh or less using a vibration mill, and the reaction accelerator shown in Table 5 was added thereto, followed by a 5% by weight aqueous polyvinyl alcohol solution.
Add 2% of the amount and granulate it with a granulator to 10-50Tf0! L
granules were obtained.

Claims (1)

[Claims] 1 Metal silicon powder of 100 mesh or less or 1 selected from halides of alkali metals and alkaline earth metals as a nitriding reaction promoter for the metal silicon powder.
A composition powder containing 0.01 to 3% by weight of silicon nitride or more is molded, and the molded product is heated and nitrided at a temperature of 1100 to 1250°C in a nitrogen or ammonia gas atmosphere to remove silicon nitride in the molded product. After making the content of at least 55% by weight or more, the molded product is pulverized to 100 mesh or less, 0.01 to 3% by weight of the nitriding reaction accelerator is added and mixed therein, and then this is molded, The molded product was heated in a nitriding furnace to 1250 to 14
A method for producing α-type silicon nitride, the method comprising re-nitriding at a temperature of 0.0°C.