JPS62138312A - Preparation of powdery silicon nitride - Google Patents

Abstract

PURPOSE:To obtain superfine particles of alpha-Si3N4 powder having high purity at high yield by heating powder mixture of SiO2 and C with reducing atmosphere at >=specified temp. to form SiO and then nitriding generated SiO. CONSTITUTION:SiO is formed by heating a powder mixture of SiO2 and C in reducing atmosphere at >=1,700 deg.C, and formed SiO is nitrided. Generation of the above described SiO is performed by replacing the atmosphere with CO after replacing the atmosphere with gaseous Ar.

Description

Detailed Description of the Invention (1) Industrial Application Field The present invention relates to a method for producing ultrafine silicon nitride particles, and in particular, to obtain α-8i 6N4 ultrafine particles with high yield and high quality. That is.

(2) Prior Art S i 3N4 is a compound with extremely strong covalent bonding properties.

It maintains high bonding strength even at high temperatures, has a small coefficient of thermal expansion, and has excellent corrosion resistance, making it a promising material for high-temperature structural members such as engine parts. In order to use this S i 3N4 powder in ceramic engines, it is necessary to mass-produce raw materials with high purity at low cost.

The following four methods are known for the synthesis of 513N4.

ω Silicon direct nitriding method 3 S l +2N2→5i3N4 (2) Silica reduction method 3810 +6C+2N2 →S i 3N4+ 6CO ■Gas phase reaction method 3SxC1+4N'H3→S 13N4 + 12HC
L(4) Pyrolysis method 3S i (h old) 2→S 13N4 +2S.

(3) Problems that the invention attempts to solve Among these methods, method (1) introduces impurities during pulverization.

The reaction time is long, and the resulting powder is coarse and β-813N4 is easily mixed. Since method (2) is an exothermic reaction, the reaction operation is simple, but SiC and Si2ON2 are likely to be mixed in.

Method (3) can yield products with high purity, but is expensive. Method (4) causes non-uniform reaction and requires low temperature treatment, resulting in high cost.

As mentioned above, each method has problems, and it has been difficult to obtain Si and N4 fine powders of high purity and high alpha ratio in high yield.

The present invention aims to solve these problems by using α-813N4 of high purity and ultrafine particles (particle size of several tens of times to hundreds of years).
The aim is to stably obtain powder with high yield.

(4) Means for Solving the Problems The present invention uses +8102 powder and C powder as raw materials and generates SiO gas by heating reductively to 1700°C or higher in a high-frequency induction heating furnace, and then converts the SiO
It is something that nitrides. The generation of SiO is caused by changing the atmosphere to A.
This is done by replacing with r gas and then with CO.

(5) Function In the present invention, it is necessary to include N2 gas in order to carry out the nitriding reaction.

That is, the nitriding reaction of SiO□ is as follows.

5in2+C-) SiO+ Co
(1) S+02+CO-+SlO+CO□
(2) C+C02→2 Co
(3)'2S io + 3C+ 2N2→S i
3N4+ 3CO(4) where the reaction (1), i.e. S
In order to promote the production of iO, the presence of COO20 and the setting of the heating temperature are important. It is necessary to consider SiC as well as SiO as a product under high temperature and low oxygen partial pressure. The generation of SiO is expressed by equation (1), and the equilibrium conditions are a8. O2...5IO2 activity Ps.・
・・Partial pressure PCO of SjO ・Partial pressure T of CO ・・Absolute temperature, while the SiC production reaction from S t O2
O2+3C-+SiC+2CO (7).

Under conditions where equation (1) and equation (7) conflict, SiO
The following relationship holds between and SiC.

SiC+ Co = SiO+ 2C (9) This relationship is calculated for 1650°C, 1700°C, and 1750°C in Figure 1. In the figure, the straight line is (9)
Under the conditions of Eq. Therefore, in the region above this straight line, where b Pco is high, the generated SiC is generated as SiO, and in this way, the CO partial pressure above the straight line in the figure is selected in the present invention. be.

Next, the generation rate equation for SiO is a first-order reaction equation.

S+02+C-+5lO (gas) + Co
...(1)' However, Jsi□ -SiO generation rate (
mol/5ec) k・-SiC generation rate constant (mol/
crn-see) A...Contact area between powder and crucible (
crn2), and it can be seen that the amount of SiO generated can be compared by the value of k. ' As a result of numerous experiments conducted by the present inventors, the relationship between the 1sIO generation rate constant and the holding temperature Tem, p (° C.) or I/T was obtained as shown in FIG. In the figure, Temp=1700
Below ℃, iogk=-5. Below 5, it tilts gently to the upper left, but above 1700℃, iogk=-5.
, 5, the slope becomes steeper. This means 1700℃
, that is, by exceeding 1700°C
This means that the generation of O is rapid. As a result,
In the present invention, the heating temperature is set to 1700° C. or higher in order to form a uniform SiO generation layer.

(5) As Example Sample 1, a powder containing 5i02:C=1:3 was passed through a 100 mesh sieve, and 0.25 gr was inserted into a graphite crucible.

Furthermore, S was added to the powder of Sample 1 at a weight ratio of 0.
Sample 2 containing 4% was also prepared in a different crucible.

This crucible is set in a high frequency induction heating furnace, and A
After sufficiently replacing with r gas (400 cc/min), further replacing with CO gas (400 cc/min), heating to 1400°C, and introducing N2 gas (2500 cc/min) together with co gas. , the temperature was raised to 1750°C.

White smoke due to SiO generation was generated in about 2 to 4 minutes after the temperature was raised to 1750°C.

(6) The powder that captures the effects of the invention is α-8i3N4 containing no SiC or Si2ON2, with a purity of 98% or more and tens to hundreds of times.
Ultrafine particles with a particle size of .

Incidentally, FIG. 2 shows the relationship between the amount of 515N4 produced and the heating time at this time, and it can be seen that the 515N4 is produced in an extremely short time.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the partial pressure of SiO and the activity of SiO2. FIG. 2 is a diagram showing the heating time at 1750° C. (during heating) and the amount of Si3N4 generated in the example. Figure 3 shows SiO
The relationship between the generation rate constant and the holding temperature is shown. P510 (atm) Figure 1 Time (min)

Claims (1)

[Claims] (1) A method for producing silicon nitride fine powder, characterized by heating a mixed powder of SiO_2 and C in a reducing atmosphere at 1700° C. or higher to generate SiO, and nitriding the SiO.