JPS5836909A - Continuous manufacture of si3n4 type substance - Google Patents

Abstract

PURPOSE:To prevent the clogging of pellets of a mixture of a powdered starting material contg. SiO2 with carbon powder due to SiO and to enhance the productivity when the pellets and gaseous nitrogen are introduced into a reaction furnace to manufacture an Si3N4 type substance, by allowing generated gaseous SiO to be absorbed in a granular carbon material among the pellets. CONSTITUTION:To powder of an SiO2-contg. starting material such as silica sand or silica is added powder of a carbonaceous material such as coke or coal by 2mol as C per 1mol SiO2. They are molded into pellets having 2-10mm. size with a binder such as starch or dextrin. The pellets are blended with granules of activated carbon or charcoal having 6-15mm. size as carbon to be externally charged, and the blend is charged into a reactor. While introducing gaseous nitrogen into the reactor, the pellts are reacted at 1,400-1,450 deg.C for about 240min to manufacture Si3N4. Since gaseous SiO generated from the starting material is absorbed in the externally charged carbon and converted into SiO, it does not stick the pellets together and does not clog them. Accordingly, Si3N4 is stably manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention continuously processes 5in2 containing raw materials such as silica stone, silica sand, zirconite, mullite, etc. It relates to a manufacturing method.

It is known to produce Si3.N4 by mixing 5102-containing raw materials, such as silica powder, with coal powder, making pellets, and heating the pellets while blowing nitrogen gas. in this case,
A continuous method is used to increase productivity. The reactor used in the continuous method is generally vertical and uses a cylindrical container made of graphite or the like, and is equipped with a heating element on the outside.The raw materials are supplied from the top of the cylinder, heated and reacted in the center, and the product is removed from the bottom. This is a method to extract the . N2 gas is blown into the cylinder from the top or bottom, flows inside the cylinder, and is subjected to a reaction. Since the charge normally falls down due to its own weight, the reaction time etc. are controlled by the rate at which the product is taken out.

As a result of research on this continuous method, the present inventor found that the most problematic point was that the pellets and gaseous silicon oxide (
SiO gas (hereinafter referred to as SiO gas) escapes as a side, and this condenses in the form of various compounds such as 5i3N, 5io2, etc. on the surface of the pellets or between the pellets, causing the pellets to stick together. It was also discovered that clogging occurred between the pellets, preventing the passage of gas and preventing the smooth flow of raw materials within the furnace. The generation of this SiO gas cannot be avoided, and it has been found that this is the biggest obstacle in continuous manufacturing. This is a common problem in the reaction between 8i0*-containing raw materials and C, and SiO□ has ZrO,..., M,
The same applies to raw materials in which , 03, etc. coexist.

The present invention is a method developed under these circumstances, and its characteristics are that the SiO gas generated outside the pellets is fixed by absorption and reaction with the granular carbon material placed between the pellets, and the SiO gas is fixed at a low temperature. This is because it prevents precipitation around the pellets.

The present invention will be explained in detail below.

The raw material can be used without particular restriction as long as it contains 5in2. This raw material is powdered, mixed with carbon powder (hereinafter referred to as internal coal), and granulated into pellets for use. S
The iO2-containing raw material and inner coal are crushed to about 44 microns or less in order to improve the reactivity and increase the strength of the pellets. Various types of internal coal can be used, including coal, coke, petroleum coke, and carbon black. The amount of internal charcoal is S10. It is determined by considering the composition of the raw materials contained and the composition of the reaction product. 8i, N, production reaction is based on the following equation.

Therefore, when silica stone is used as a raw material, 2 moles of C are blended for 1 mole of 5I02. Also, zircon sand (
If you want to obtain a composition of 5isN and ZrO2 mainly from Zr3i04), 02
Blend the moles. Although this amount of C is a stoichiometric amount, the amount of C may be increased or decreased to some extent based on this amount as necessary. If the amount of C is increased, the amount of 8i0 gas released outside the pellet will be reduced, but it cannot be completely eliminated.

The pellet size is 2fl due to gas permeability, reactivity, etc.
~10m is suitable. For granulation, starch, dextrin,
An aqueous solution of CMC or the like may be added as a primary binder.

Granular carbon material placed between pellets (hereinafter referred to as carbonization)
is the basis of the present invention, and it is necessary to use as much SiO as possible.
It is desirable to have a material that absorbs gas and has high reactivity, and in terms of surface area, it is 100 m'/g or more. Specifically, activated carbon, charcoal, carbon black, etc. are desirable. It is used by granulating the powder. The size of the outer charcoal is set to 6 to efficiently absorb SiO gas and to avoid any operational problems.
~15s+m is appropriate. In this case, it is desirable to select the size in relation to the raw material pellets. That is, since both the raw material pellets and the outer charcoal usually maintain the same shape after the reaction, if the particle sizes of the two are made different, the products can be easily separated.

If the amount of outer charcoal is too small, the effect will not be sufficient, and if it is too large, the productivity of the target product will decrease. Therefore, the desirable range is carbon per mole of SiO in the raw material.
(fixed carbon) is 0.1 to 15 mol. It is preferable to disperse the outer charcoal and raw material pellets as uniformly as possible.

In order to carry out the heating reaction of these raw materials continuously, a vertical furnace as described above is used.

Pellets and outer charcoal are supplied from the top of the reaction vessel, heated and reacted in the vessel, and after a predetermined residence time, the product is taken out from the bottom of the vessel.After drying, the pellets can be supplied to the vessel. Desirably, when using a raw material containing water of crystallization, it is preferable to heat it to remove the water of crystallization before use.The heating temperature should be selected within an appropriate range depending on the desired product, but for example, 1350 to 1 to obtain Si, N, and single components
A range of 450°C is suitable.

The residence time in the reaction zone is suitably 60 to 300 minutes within the above temperature range.

In the reaction of the present invention, since 8i02 and C are present in the pellet, heating causes an intermediate or side reaction of S.
iO gas is generated. Most of this becomes nitride due to C in the pellet and N2 gas permeating from the outside, but a portion escapes to the outside of the pellet. In the conventional method, this escaped Si
O gas precipitates as 5i02.5ilN4 on the pellet surface or between the pellets in the low-temperature part 9 of the raw material in the container, and causes the pellets to stick to each other or clogs the pellet layer and obstructs the gas flow, thereby impeding the operation. This was the cause of the above problem. In the present invention, this SiO gas is absorbed into the outer charcoal surrounding the pellets, where it is precipitated and solidified by a reaction or the like. The precipitate is a reaction product of SiO, CO gas, N2 gas, etc., and its composition varies depending on the partial pressure of these components, but it is thought that SiC, Si, N4, etc. are the main components.

Since the reaction proceeds as the SiO gas is absorbed into the outer charcoal, the size of the outer charcoal having the SiO coating after the reaction is approximately the same as the initial size of the outer charcoal, including the coated portion.

The reaction starts from the surface layer of the outer charcoal and gradually progresses to the inside, but normally the center of the outer charcoal is made of carbon! ! I will remain, so
After the reaction, the outer charcoal has carbon in the center and SiC around it.

By fixing the SiO gas generated outside the pellets in this way, the flow of raw materials within the reaction vessel became extremely smooth, which had a great effect on continuous operation.

Example 1 Silica stone powder (5i02>99cm, below 44μ) and coal coke powder (fixed carbon 99%, below 44μ) were mixed into 5 inches.
The molar ratio of 2 and C was 1:2, and a small amount of starch aqueous solution was added to form pellets with a diameter of 4u. After drying this,
Approximately 6 to 10 mg of activated carbon (fixed carbon 95%) is added to Sin
, were uniformly mixed at a ratio of 0.5 mol as C per 1 mol. These blended raw materials were charged into a vertical furnace and heated while blowing N2 gas from the bottom of the furnace to continuously produce Si3N4.

The vertical furnace was a graphite cylinder with an inner diameter of 12 crn and a reaction zone length of 30 cvt, with a raw material supply port with a seal at the top and a tapered cylinder tapered toward the tip at the bottom. A rotary feeder was attached to the tip so that the product could be extracted while being sealed with gas. The tapered cylinder was equipped with four N2 gas injection nozzles around its periphery.Heating of the reaction vessel was carried out by energizing eight rod-shaped heating elements vertically installed outside the vessel.

The temperature of the reaction zone was 1400 to 1450°C, and the residence time in this reaction zone was 240 minutes. The amount of N2 gas blown was 0.
The amount was 12 Nmy (5 times the theoretical amount).

The products could be easily separated by particle size, and the pellets were mostly β-8i and N4. Moreover, SiO was mainly generated on the surface of the granular carbonaceous material.

Continuous operation was possible in these reactions without any problems.

Patent applicant: Showa Denko Co., Ltd. Agent Sei Kikuchi

Claims (1)

[Claims] Carbon powder is mixed with 5in2-containing raw material powder and formed into pellets, granular carbonaceous material is blended with the pellets, and the pellets are fed to the top of a vertical reactor, and heated while feeding N2 gas into the reactor. 1. A method for continuous production of Si3N4-based materials, characterized in that 8isN4 is produced in a vertical reactor, and the product is taken out from the lower part of a vertical reactor.