Industrial silicon, also known as metallic silicon or crystalline silicon, is a pure silicon product produced by smelting silica (primarily composed of silicon dioxide) with a carbon-based reducing agent at high temperatures in an electric arc furnace. It appears silver-gray or dark gray in color, has a metallic luster, is hard and brittle, and has a melting point as high as 1,410°C. Different downstream industries have varying purity requirements for industrial silicon; therefore, industrial silicon is classified into different grades based on impurity content.
Naming Conventions for Industrial Silicon Grades
The naming convention is actually quite simple: the four-digit number in an industrial silicon grade designation represents, in order, the maximum allowable content of the three impurity elements-iron, aluminum, and calcium. Specifically, the first two digits indicate the iron and aluminum content to one decimal place (i.e., in parts per thousand), while the last two digits indicate the calcium content to two decimal places (i.e., in percent).
For example:
- 553: Indicates iron content ≤ 0.5%, aluminum content ≤ 0.5%, and calcium content ≤ 0.3%
- 441: Indicates iron content ≤ 0.4%, aluminum content ≤ 0.4%, and calcium content ≤ 0.1%
- 3303: Indicates iron content ≤ 0.3%, aluminum content ≤ 0.3%, and calcium content ≤ 0.03%
Additionally, it should be noted that the silicon content of industrial silicon is generally 98.5% or higher. As the grade increases, the silicon content also increases accordingly. High-purity industrial silicon can even reach 99.99% or higher and is widely used in the semiconductor and photovoltaic industries.
Differences in the Applications of the Three Grades
| Applications | 553 | 441 | 3303 |
| Cast aluminum alloys (e.g., ADC12) | ✓ Primary use | ✗ | ✗ |
| General steel smelting | ✓ Primary use | ✗ | ✗ |
| Aerospace/automotive aluminum alloys | ✗ | ✓ Primary use | ✗ |
| General-purpose silicones | ✗ | ✓ Common | ✗ |
| High-performance silicones | ✗ | ✗ | ✓ Primary use |
| Polysilicon (photovoltaic) | ✓ Available | ✓ Common | ✓ Optional |
| Polysilicon (semiconductor-grade) | ✗ | ✗ | ✓ Preferred |
Common By-products of Industrial Silicon
In addition to various grades of industrial silicon ingots, the processing of industrial silicon also yields several important by-products:
- Silicon fume (also known as microsilica or silica fume): This is dust collected during the industrial silicon smelting process. It is widely used in the refractory and concrete industries and can significantly improve the strength and durability of concrete.
- Edge-skin silicon, black-skin silicon, and silicon slag: These are by-products generated during industrial silicon production. Depending on their impurity content, they can be recycled for other industrial applications.
Summary
Grade 553 is renowned for its cost-effectiveness and serves as the primary choice in the basic metallurgy sector; Grade 441 represents a quality upgrade over Grade 553 and is suitable for mid-to-high-end aluminum alloys and silicone applications; Grade 3303, with its high purity, sets the quality standard in the silicone and semiconductor industries.
The choice of grade depends primarily on your specific application and quality requirements. If you have any questions regarding industrial silicon products, please feel free to consult our professional team at any time. We will provide you with the most suitable product recommendations and technical support.
