Gases in molten aluminum and how to remove them

What gases are contained in molten aluminum?

The main gas contained in molten aluminum is hydrogen. In the smelting process of aluminum and aluminum alloys, hydrogen is the main component of the gas content in the aluminum melt, accounting for 70% to 90% of the total gas in the aluminum melt. Hydrogen mainly comes from the humidity in the surrounding air, the exhaust gas generated by the fuel in the furnace (such as oil or gas), the moisture or organic compounds carried by the raw materials, and the hydrogen in the alloy additives.

In addition, the anode products in the aluminum electrolysis process mainly include carbon dioxide and carbon monoxide gases, which contain a certain amount of harmful gases such as hydrogen fluoride and solid dust. These gases and dust must be purified before discharge to protect the environment and human health.

What gases can the degassing box remove from molten aluminum?

The main gases the degassing box can remove from molten aluminum include hydrogen, oxygen, and nitrogen. Hydrogen is the most important impurity gas in aluminum melt. It is mainly generated by the reaction of water vapor in the atmosphere with aluminum. Therefore, the hydrogen content in aluminum melt is closely related to air humidity. Oxygen and nitrogen react with aluminum and its alloys at high temperatures to form oxides (such as Al?O?) and nitrides (such as AlN), affecting aluminum's physical and chemical properties in liquid and solid aluminum.

Degassing boxes remove gases from molten aluminum in the following ways:

Hydrogen removal: Hydrogen is adsorbed into bubbles and removed. As bubbles rise, hydrogen diffuses from the aluminum liquid into the bubbles, floats to the liquid surface with the bubbles, and is removed.

Alkali metal removal: Alkali metals are removed by chemical reaction with chlorine (forming chlorides).

Inclusion removal: Non-metallic inclusions are captured by bubbles and then rise to the surface of the melt to form slag.

Types and application scenarios of degassing boxes:

There are many types of degassing boxes, including single-rotor, double-rotor degassing boxes， and three-rotor boxes. Three-rotor?degassing units?are particularly suitable for launders with large aluminum liquid flow, high gas content, and many inclusions and have higher degassing efficiency and stability. The equipment is usually connected to a flow trough, which can achieve 24-hour online uninterrupted degassing, greatly reducing the degassing time and improving production efficiency.