JPS5888113A - Purification of metallic silicon - Google Patents

Abstract

PURPOSE:To obtain high purity metallic Si for the raw material of Si3N4, by heating a rod-shaped ingot of metallic Si at a specific temperature from the bottom upward using a vertically movable heating device. CONSTITUTION:Metallic Si 1 having a purity of 97-98% is roughly crushed to about 10-1mm.phi, put into a graphite die 2 placed in a high frequency induction furnace, completely molten by heating at >=1,420 deg.C, and cooled to obtain a rod- shaped ingot of 2-10cmphi. A vertically movable heating device 8 is lowered to the bottom of the ingot. After heating the ingot at 1,500-1,600 deg.C for 5-30min, the heating device 8 is shifted upward by 0.5-10cm at a rate of 0.5mm./min, and the heating is continued for 5-30min. The procedure is repeated until the heating device reaches the top of the ingot, when the ingot is cooled. Since the impurities in the metallic Si are shifted upward to the top of the layer, the crude metallic Si can be purified easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining metallic silicon, in particular, by completely melting metallic silicon, forming it into a rod-shaped inject, and heating it from the surface to unidirectionally solidify impurities in metallic silicon. The present invention relates to a method for refining metallic silicon for use as an α-type silicon nitride raw material in which impurities are moved to the upper part of the ingot.

Generally commercially available JIB No. 1 products contain I as an impurity.
Fe is 0.74, Mg O,0! l 9j, At is 0.
28%.

Oao, about 1m is contained. When producing high-purity silicon nitride from these metal silicones, if these impurities are mixed into the product, a large amount of glass phase may be produced in the final silicon nitride molded product, or defects (a phase different from Si3N4) may occur. It is desired to remove these metals or voids, which reduce the strength of the molded product.

The present invention aims to remove these impurities and to provide a method for refining metallic silicon for highly purified silicon nitride raw material by moving the impurities to the upper part.

In the present invention, when refining a rod-shaped ingot of metallic silicon, the surface of the ingot is heated at a temperature of 15% from the bottom to the top.
It is characterized by heating to 00 to 1600°C and then cooling.

The present invention will be further explained in detail below. A high-frequency induction furnace will be described below as a melting furnace, but the present invention is not limited to this as long as it is a heating device that can be moved up and down.

First, the rod-shaped input of metal silicon is 10 pieces of commercially available metal silicon.
III+ or less, for example, coarsely crushed to about 10 to 111 m1,
This is placed in a vertical graphite crucible and heated in a high frequency induction furnace until its melting temperature is higher than the melting point (1420°G).
Preferably, the temperature is about 1650°C to completely dissolve. This is then cooled to form a rod-shaped input. Note that the volume of coarsely crushed metallic silicon decreases when it is melted, so if a long rod-shaped body is desired, additional melting is required. The temperature is 1500 to 160 from the bottom to the top of this rod-shaped inuit surface.
Heat to 0°C. In this case, the heating means that the diameter,
Although it depends on the length etc., it is preferable to make the width as narrow as possible so that the molten zone moves in order.

The reason for this is the power of unidirectional coagulation and purification. The width of the molten zone is the diameter of the rod-shaped ingot, or 4 to 10 cI.
If it is about L, it should be 0.5 to 10 cm, preferably 1 to 10 cm.
The length should be approximately 5 cm, and the moving speed should be at least 0.5 m/min.
The object of the present invention can be achieved if the heating time is about 5 to 30 minutes.

The metal silicon used in the present invention is Sl with a purity of 97
'98q6, TIS No. 1-2 is preferred, but not limited thereto.

The rod-shaped ingot used should have a diameter of about 2 to 1 degrees; if the diameter is too large, it will be difficult to heat it evenly in a direction perpendicular to the axial direction, so it is preferably 2 to 5 C1.
It should be about 1.

In this way, by heating the bar-shaped ingot from the surface in a uniaxial direction from the bottom to the top, the impurities move upward, making it easy to purify the impurities in metallic silicon.

By repeating this method 2 to 5 times, most of the impurities are removed.

A more detailed explanation will be given below with reference to Examples.

Graphite die 2 was manufactured using the Fuji Denpa high frequency induction furnace shown in the example drawings.
Metallic silicon No. 5181 with a purity of 98 sl crushed to 10 to 111 m was placed in the molten metal and melted to create a rod-shaped input. The graphite die used had an outer diameter of 12o4, an inner diameter of 404, and a height of 500 W (depth 25 Q m/m). The heating temperature was 1,650°C, and the mixture was completely melted after being held for about 30 minutes. This melt was cooled to a temperature below its melting point to form a rod-shaped ingot. Next, the furnace was lowered to the bottom of the 9 rod-shaped ink rods and heated at 1550°C for 10 minutes, then moved to the upper part of the furnace and heated again at 1550°C for 10 minutes.
Heated for a minute. After repeating this operation and moving the high frequency coil to the top of the ingot, turn off the power, cool it down, take out 9 ink tubes of 150u length from the graphite crucible, and cut them with a diamond cutter at the bottom 10 Jul / 7 FL. Then, the inside was sliced to a thickness of 5M to prepare a sample for analysis.

Next, using this sample, Fe was irradiated with fluorescent X-rays.

Perform quantitative analysis of Mg, At, and Oa and display the results in a table.

[Brief explanation of the drawing]

The drawing is a sectional view of a high frequency induction furnace used in an example of the present invention. Code 1...Metal silicon, 2...Graphite die, 3...Graphite die lid, 4...Temperature tube, 5... Quartz tube, 6...Graphite stand, 7.
...Criditor grain, 8...High frequency coil.

Claims (1)

[Claims] In the final method of purifying a rod-shaped ingot of metallic silicon by moving the impurities in the ingot to the upper part using a vertically movable heating device, the heating device heats the ingot to a temperature of 1500 to 1600°C from the bottom to the top. A method for purifying metallic silicon for use as a raw material for α-type silicon nitride, which is characterized by cooling after cooling.