Why Is Molybdenum Sheet Chosen as Reflective Screens in Sapphire Crystal Growth Furnaces?

As a critical component of sapphire crystal growth furnaces, the reflective screen plays a key role in thermal management: it concentrates radiant heat from high-temperature sources through high infrared reflectivity, optimizing the temperature field distribution within the furnace and ensuring a stable temperature gradient at the crystal growth interface, while reducing heat loss to enhance thermal efficiency. This demands excellent high-temperature resistance, thermal shock resistance, and chemical stability from the reflective screen to ensure the uniformity and yield of sapphire crystal growth. Molybdenum sheet, with its high melting point, high infrared reflectivity, low thermal expansion coefficient, and superior chemical stability, is the ideal material for reflective screens.

The main reasons molybdenum sheet is used as reflective screens in sapphire crystal growth furnaces are as follows:

Sapphire crystal growth requires a high-temperature environment, and molybdenum’s melting point of 2,620°C allows it to maintain a stable solid structure without melting or deforming, enduring prolonged high-temperature conditions.

Molybdenum sheet has high infrared reflectivity, effectively reflecting radiant heat from the furnace’s high-temperature source to concentrate heat in the crystal growth area, reduce heat loss, and improve thermal efficiency. The mechanism involves redistributing heat via the reflective screen to optimize the furnace’s temperature field, ensuring a stable temperature gradient at the sapphire crystal growth interface and preventing defects like cracks or impurity precipitation due to temperature fluctuations.

Despite being a metal, molybdenum has a low thermal expansion coefficient, closely matching that of sapphire crystals to prevent stress cracking from thermal expansion and contraction in environments with rapid temperature changes. During crystal growth, frequent temperature adjustments are necessary, and the thermal shock resistance of molybdenum sheet ensures the reflective screen’s structural stability, avoiding equipment failure or growth interruptions due to thermal shock.

In the inert or reducing atmosphere of sapphire crystal growth, molybdenum sheet exhibits good chemical stability, resisting reactions with furnace gases or molten sapphire raw materials to prevent crystal contamination or material corrosion.

Molybdenum sheet can be processed into complex shapes like cylindrical or curved reflective screens through rolling, cutting, and welding, adapting to various growth furnace designs.

• < Prev
• Next >