The growth of silicon crystal need the graphite crucible,graphite parts etc.graphite material,and the isostatic graphite material is one of the most important material in the world now. The isostatic graphite material is made in a high pressure container,and use the liquid media with an un-pressed property and the uniform delivery pressure property. As it will press the material from all the directions,so the pressure will be the same from all the directions.
The isostatic graphite material from Japan meet the world advanced level,no matter the quality,items,specification etc, the most representative company is TOYO Carbon. And the U.S is the first country to do the business and research on the isostatic graphite material. Another one is SGL from Germany,and except for the isostatic graphite material ,SGL also do well in the extruded graphite material,molded graphite material,the products are widely used in the photovoltaic industry.
The characteristic of the isostatic graphite material is : the properties is same from different directions,and the structure of the material is compact,the strength of the surface is strong,the resistance to shock is well,and the property of thermal resistance is better than other materials.
As the graphite parts have many good performance such as thermal resistance,pressure resistance,corrosion resistance and good electrical conductivity,stable property etc. So it’s widely used for the polysilicon production. But the selection criteria of graphite is very strictly,the graphite material need to purify to reduce the metal particle and other impurities. Currently,the way to purify is accessing the chlorine gas.
The technology to purify the graphite material is taking advantage of the high stable of the carbon,through the high temperature, vacuum and oxidizing gas to purify the graphite material.
the pressure should be the 5% of the atmospheric pressure,and the temperature should be above 2000centigrade,during this processing,it should be access the oxidizing gas such as the chlorine gas.