Graphite furnace fixtures are typically used in a vacuum furnace for several reasons:

High-Temperature Capability: Graphite can withstand very high temperatures, which makes it suitable for use in furnaces that operate at temperatures that would melt or degrade other materials.

Thermal Stability: Graphite remains stable under high-temperature conditions, which is crucial for processes that require precise temperature control.

Low Reactivity: In a vacuum or inert atmosphere, graphite does not easily react with other materials, which is essential to prevent contamination of the products being heat-treated.

Good Thermal Conductivity: Graphite has excellent thermal conductivity, which helps in uniform heating and cooling cycles within the furnace.

Strength at High Temperature: Graphite retains its strength at high temperatures, ensuring the structural integrity of furnace fixtures.

Graphite fixtures are commonly used in processes such as heat treatment of metals, sintering of ceramics, melting, and refining of precious metals, and in the production of high-purity materials where contamination needs to be minimized. They are also used in industries that produce semiconductors and in laboratories for analytical applications where high-temperature processes are required under controlled atmospheres.