What are the applications of tantalum crucibles for smelting sapphire?

Tantalum has the characteristics of high melting point and good chemical stability. In the smelting process of sapphire (the main component is alumina), it can withstand high temperature environment and has a low possibility of contaminating sapphire raw materials, which can ensure a relatively pure environment for the growth process of sapphire. However, the process conditions need to be strictly controlled during use to ensure that the performance of the crucible is fully utilized to successfully melt high-quality sapphire.

The advantages of tantalum crucible are as follows:

1. High melting point and high temperature resistance: The melting point of tantalum is as high as 2996℃, ranking fifth among single substances. This enables tantalum crucibles to remain stable in high temperature environments and withstand the temperature requirements of most high-temperature treatment processes such as smelting and sintering of materials. It is suitable for rare earth smelting, high-temperature sintering and other working scenarios.

2. Excellent chemical stability: Tantalum does not react to hydrochloric acid, concentrated nitric acid and "aqua regia" under both cold and hot conditions, and will only be corroded in a few cases such as hydrofluoric acid, hot concentrated sulfuric acid, and phosphoric acid at high temperature. This property makes it less susceptible to corrosion when handling various chemical substances, and can be used for the treatment of corrosive substances in a variety of chemical experiments and industrial production, such as in the equipment for the preparation of various inorganic acids.

3. Good deformation resistance: Tantalum has a very small thermal expansion coefficient, expanding only 6.6 parts per million for every degree Celsius increase, and its toughness is very strong, which makes the tantalum crucible less likely to deform when the temperature changes, and can maintain good dimensional stability, which helps to ensure the accuracy and repeatability of the experiment or production process.

4. Good processing performance: Tantalum has moderate hardness and rich ductility, and can be drawn into filaments or made into thin foils, which makes tantalum crucibles easy to process into various shapes and sizes to meet the needs of different application scenarios.

5. Reusability: If used and maintained properly, tantalum crucibles can be reused many times, reducing the cost of use.

6. High purity: High-purity tantalum materials can be used to make crucibles, which can avoid the contamination of the crucible materials on the processed substances and ensure the purity requirements of experiments or production. It is widely used in the fields with high purity requirements such as the electronics and semiconductor industries and precision chemical synthesis.

The main disadvantages of tantalum crucibles include:

1. Expensive: Tantalum is a rare metal with relatively scarce resources, which leads to high manufacturing costs and high prices for tantalum crucibles, which to a certain extent limits its wide application.

2. Easily corroded by some substances at high temperatures: Although tantalum has excellent chemical stability at room temperature, the oxide film on its surface may be destroyed at high temperatures, so that it can react with a variety of substances. For example, in a high temperature environment above 2000℃, the aluminum vapor decomposed from aluminum nitride powder can react with tantalum, shortening the service life of the tantalum crucible.

3. Welding is difficult: Tantalum has a high affinity for atmospheric gases when heated and molten, which can easily lead to pores and weld joint embrittlement. Therefore, the welding of tantalum crucibles requires high technical requirements and special welding processes, which increases the difficulty of manufacturing and repair.

4. High mass: Tantalum has a relatively high density, which makes the mass of tantalum crucibles large, which may cause inconvenience during transportation and use, and the use of tantalum crucibles may be restricted in some occasions with strict requirements on equipment weight.