JPS61275122A - Production of reducing agent for producing silicon suitable to solar cell - Google Patents

Abstract

PURPOSE:To obtain a reducing agent for producing a silicon which is suitable to producing a solar cell, and improves the productivity by making carbonaceous powders controlled the ratio of a specific surface area and a mean particle size to coagulate into lumps with an aqueous solution of a sugar, thereby improving reactivity and stability against a crack. CONSTITUTION:The carbonaceous powders contolled a contour having the ratio of the specific surface area (m<2>/g)/the mean particle size (mum) of 1X10<3>-6X10<3>(m/g) to the prescribed value are prepared. The obtd. particles are formed into the lumps with the aqueous solution of a sort of sugars (such as a saccharose), followed by drying the obtd. massive carbon particles.

Description

[Detailed Description of the Invention] Industrial Application Fields The present invention relates to a method for producing a carbonaceous reducing agent used in the production of solar cell-grade silicon, and in particular a method for agglomerating high-purity carbonaceous powder with an aqueous solution of sugars. The present invention relates to a method of manufacturing the same.

<Prior art and its problems> Solar grade silicon (Solar Grade-!Ji)
, 5OG-Si) is currently produced by chlorinating metallic silicon obtained by reducing silica stone to form a gas, and then reducing this gas to a refining process, but the energy required for production is extremely large. It is said that there are limits to cost reduction.

On the other hand, a technology has recently been established for refining domestically produced low-grade silica sand to a purity that can be used as a raw material for 5OG-5i. In this way, when directly producing silicon from Si02, highly purified carbon powder such as activated carbon or carbon black is used as a reducing agent by mixing it with a binder such as saccharide or carbohydrate.

In the specification of West German Patent No. 3013319, 5OG-9i
A process is disclosed in which carbon activated in a high temperature melt process for the reduction step of Sin 2 for production is used in the form of tablets bound with quartz sand with a binder such as sugar or cellulose, and also in JP-A-58 190809, a method is disclosed in which carbon powder is granulated, preferably with a phenolic resin, and reduced together with previously granulated high-purity SiO2 at high temperature.

Furthermore, JP-A No. 52-88895 describes a method of granulating carbon black by mixing an aqueous saccharide solution.
No. 8118 discloses a method of pelletizing activated carbon or carbon black with a binder such as sugar, starch, or cellulose.

However, as a result of examining various reducing agents for producing 5OG-5i that agglomerates carbonaceous powder, we found that the surface shape of the carbonaceous powder is particularly important in terms of the reactivity of the reducing agent and the strength of the agglomerated product. I found out.

If the surface shape is too smooth, the reactivity will be poor and SiO → Si
C The reaction becomes slower. The 5rC-+S+ reaction slows down due to the stagnation of the penetration rate of SiC into the pores of the agglomerate, resulting in 5OG
-5i production rate decreases.

Furthermore, if the surface shape is too rough, the amount of binder consumed during agglomeration of the carbonaceous powder increases, and the amount of thermal decomposition under heating increases significantly. As a result, the occurrence of thermal cracking becomes noticeable, which may cause operational difficulties due to increased generation of fine powder during operation and shelf hanging.

<Object of the Invention> Therefore, the object of the present invention is to produce solar cells stably and with high productivity by controlling the surface shape of carbonaceous powder to an appropriate level and giving the agglomerated product appropriate reactivity and thermal cracking stability. The present invention aims to provide a method for producing a reducing agent for producing grade silicon.

<Structure of the Invention> The present invention provides a method for producing a reducing agent for producing solar cell-grade silicon by agglomerating carbonaceous powder. ) is the ratio of I
1G3~6 X103 (m/g) A reducing agent for producing solar cell-grade silicon, which is characterized by agglomerating TEAL carbonaceous powder with an aqueous solution of at least one type of saccharide and drying the agglomerated carbon grains. A manufacturing method is provided.

The present invention will be explained in more detail below.

In the 5OG-9i manufacturing process, carbon grains are charged into a shaft furnace and SiO2 is introduced from the bottom for reduction.
~20■, porosity of 45 to 55, crushing strength of 3 kgf or more, higher reactivity, and a rough surface so that the generated SiC can penetrate into the pores in the carbon grains are required. .

As raw materials for such carbon grains, creosote oil obtained by tar distillation, ethylene bottoms, etc.
It can be said that carbon black produced by spraying into a high-temperature flame of 00 to 1900°C is excellent in terms of reactivity, productivity, and cost.

Carbon black usually has an average particle size of 20 to 100-1
Those having a specific surface area of 20 to 300 rn'/g are commercially available.

Compared to pitch coke and metallurgical coke, it is characterized by a smaller particle size and a 10 to 100 times higher specific surface area.

However, because the particle size of the cloth is narrow and the surface activity is low, it is difficult to agglomerate. Even when agglomerated, the strength is low.

However, carbon black has a good affinity with aqueous solutions of sugars, and for example, in the case of an aqueous solution containing 10 to 30% sucrose, it is possible to agglomerate the solution to 10 to 20 mm using a dish-type granulator.

However, according to the findings of the present inventors, if the surface shape of the carbonaceous powder is too rough, the strength of the agglomerated product decreases.

On the other hand, if the surface shape is too smooth, although the strength of the agglomerated product is improved, the reactivity tends to decrease, the rate of silicon production slows down, and the productivity tends to decrease.

Therefore, the present inventors conducted extensive studies on the surface properties, agglomerated product strength, and silicon production rate of carbonaceous powder, and found that the specific surface area (m''/
It is suitable to express it as the ratio (s/g) between g) and the average particle diameter (-), and further, that value and L[I
03, preferably 2X1G3 to 3X103, has been found to be favorable in terms of both strength and reactivity of the agglomerated product.

Agglomerate strength and S vs. ratio of specific surface area to average particle size
The relationship between i generation speed is shown in FIG. 1, which is based on an example described later. In the figure, the ratio of specific surface area to average particle diameter (hereinafter referred to as A value) is I x 103 (m/
If it is less than g), the surface shape becomes too smooth and SiO→
(SiC and SiCq) Si productivity is poor because penetration into carbon grains is reduced. When the A value exceeds 8X103 (■/g), the amount of binder used during agglomeration increases, and crack formation due to thermal decomposition of the binder during heating becomes noticeable.
Strength is significantly reduced. A showing the surface characteristics of carbonaceous powder
When the value is in the range of 1X103 to 6X103 to 6X103 (m/g), the strength of the agglomerated product is 3 kgf or more and the Si production rate is 20 g/H or more, which shows good results.

Carbon black is preferable as the carbonaceous powder, but
Activated carbon and other carbonaceous powders that exhibit the above-mentioned surface properties are suitable for the purpose of the present invention.

Carbonaceous powder exhibiting this characteristic is used as a raw material and agglomerated with an aqueous solution of sugars. In addition to blood sugar, which has good compatibility with carbon black, suitable sugars include sugars that exhibit thermal decomposition properties similar to blood sugar.For example, monosaccharides such as glucose, disaccharides such as maltose and lactose, cellulose, It can also be applied to polysaccharides such as sognin, and these saccharides may be used alone or in combination of two or more.

When agglomerated with an aqueous solution of these saccharides, the amount of saccharides is also important in order to define the strength of the agglomerated carbon particles. A suitable amount for the above-mentioned surface properties is lO~3
It is 0wt$. If it is less than 10 wtX, cracks will occur during the drying process and the strength will decrease.

It is not economical to exceed 30wt$.

Next, the target reducing agent is produced by drying the agglomerated carbon particles. This drying condition is preferably 12
Blow drying is performed at 0 to 130°C to reduce the moisture content of the carbon particles to 8 wH or less. If it exceeds 8 wt%, the strength of the carbon grains will be low and cracks will occur. By agglomerating carbonaceous powder with controlled surface properties as a raw material in an aqueous solution of sugars and drying it, carbon particles with high crushing strength and a good rate of Si production can be obtained.

Furthermore, after drying, the
By heat-treating at a temperature of 0 to 320°C, preferably around 300°C, the strength of the carbon grains becomes higher, no cracks occur, and carbon grains are obtained that are most suitable as a reducing agent in the 5OG-Si manufacturing process. .

<Example> The ratio A value of specific surface area to average particle size is 0. lX103~10
Carbon black having a range of
(Carbon grains of 1 to 20 ■■ were produced. The moisture content of the carbon grains at this time was 35 to 4'0%. After drying with air at 125°C for 70 minutes to bring the moisture content to 8%, The product was maintained at 300° C. for 80 minutes in a N2 atmosphere in a Matsufuru furnace and then cooled to obtain a finished product.

The product was placed in a Tammann furnace maintained at 1500° C., and Si02 was blown into it from the bottom at a rate of Ig#+in to conduct an Si production experiment.

These results are shown in Table 1, and the A value is lX103 (m/g
), the crushing strength is as high as 5 kgF or more, but S
The production rate of i is as low as 15 g/H or less, but the A value of the present invention is 1X103 to 8X103 (turbidity/1), the crushing strength is 3 kgf or more, and the Si production rate is 20 to 22 g.
/)I, good results were obtained with a yield of 70-80%.

On the other hand, when the A value exceeds 8 x 103 (W/g), the crushing strength decreases to less than lltgf, and during the experiment,
Agglomerated products frequently hung on shelves, making it difficult to conduct experiments smoothly.

Table 1

[Brief explanation of the drawing]

Figure 1 shows the surface characteristics of carbonaceous powder (ratio of specific surface area to average particle size), strength of carbon particles, and reactivity of reducing agent.
It is a graph showing the relationship between i generation speed. Note that curve (a) shows the relationship between the A value and the Si production rate, and curve (b) shows the relationship between the A value and the compaction strength of carbon grains.

Claims (1)

[Claims] In a method for producing a reducing agent for producing solar cell-grade silicon by agglomerating carbonaceous powder, the specific surface area (
m^2/g) and the average particle diameter (μm) is 1 x 10^3
A method for producing solar cell-grade silicon characterized by agglomerating carbonaceous powder with a particle size of ~6×10^3 (m/g) in an aqueous solution of at least one type of saccharide and drying the agglomerated carbon grains. Method for producing reducing agent.