As a project engineer at SHJ CARBON, I have encountered numerous projects over the past 18 years, and one thing has become clear: whenever a furnace operates at temperatures above 1500°C, carbon-based materials are indispensable. This is not a coincidence, but rather a result of the inherent properties of the materials themselves.

Carbon materials are primarily used in the high-temperature sections of industrial furnaces, such as vacuum heat treatment furnaces, high-purity processing furnaces, single-crystal silicon pulling furnaces, and graphitization furnaces, which operate at temperatures above 1500°C. These materials are classified based on their application, including heating elements, thermal insulation materials, furnace body structural components, and transport fixture materials. To make this clearer, here's a simple analogy:

• Heating Element: The heart that generates heat
• Insulating Material: The outer layer that retains heat
• Structural Material: The skeleton that supports the entire system
• Transport Fixture: The tools used to move materials at high temperatures

Under the protection of inert gases, carbon materials can be used stably at temperatures above 1500°C. They are not only cost-effective and readily available but also the only superior material for such applications. Depending on their intended use, carbon materials are flexibly employed while considering their machinability, high-temperature characteristics, and shaping techniques, all while maintaining a controlled furnace atmosphere.

In heating elements, the main materials used are graphite particles or processed graphite products. In structural materials or transport fixtures, graphite products or C/C composite materials are used. Artificial graphite or C/C composites serve as heating elements, furnace structures, or transport fixtures, and the properties of these materials often dictate the performance of the components.

The key properties of these materials are typically related to electrical resistivity, strength, and sometimes even bulk density, thermal conductivity, and thermal expansion coefficient. In semiconductor fields, such as single-crystal silicon pulling furnaces and optical fiber production furnaces, high-purity products with low impurity concentrations are required to prevent contamination.

High-temperature industrial furnaces use heating elements that can be categorized into two main types: metallic and non-metallic. Metal heating elements include Fe-Cr-Al alloys, Ni-Cr alloys, tungsten, molybdenum, etc., while non-metallic heating elements include silicon carbide, molybdenum carbide, nickel-chromium, and carbon-based materials. Among these, graphite heating elements, when protected by inert gases, can reach a maximum operating temperature of approximately 3000°C, and are widely used in both vacuum and non-vacuum furnaces. Carbon-based heating elements are divided into graphite and carbon materials, with graphite being the primary choice in most cases.

Carbon materials that have been roasted at around 1000°C have 3-4 times higher resistivity than graphite, so they are only used when high-resistance materials are needed. However, if the operating temperature exceeds the heat treatment temperature, the size of carbon-based materials will change, and their resistivity will decrease, leading to material degradation. Therefore, careful attention must be paid to usage conditions.

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