Neither graphite nor stainless steel are suitable as a crucible material for melting aluminum at 800°C. Steel dissolves in molten aluminum, and graphite oxidizes at 800°C in air.

For melting aluminum in large furnaces, refractory linings based on Al2O3 are used, and a small crucible is best made of aluminum titanate (Al2TiO5).

Vadim Verlotski

Thanks for your informative reply but we have noticed that Al is not as best compatible as cast iron and stainless steel for induction heating. That is why we want to use a crucible which is best compatible with induction heating and can withstand upto 800 degrees. So that the metal placed inside it, could be melted i.e indirect heating. The crucibles like Al2O3 are used when we want to melt a metal which is usually ferromagnetic in nature i.e. direct heating.

So could you suggest any other material?

Dear Muhammad Talha Khalil

For melting aluminum, graphite crucible is a better option than stainless steel. The main reason for this is that graphite is resistant to high heat. While graphite can generally withstand temperatures exceeding 3000°C, stainless steel melts at around 1500°C and carries the risk of oxidation or deterioration at high temperatures. In addition, graphite does not chemically react with aluminum, which allows the melted metal to maintain its purity. Stainless steel, on the other hand, can react with aluminum at high temperatures and negatively affect the quality of the metal. Graphite has better thermal conductivity than stainless steel, which also speeds up the melting process. For these reasons, graphite crucible is a more suitable choice for aluminum melting.

To melt aluminum up to 800°C, graphite is a better crucible material compared to stainless steel for the following reasons:

1. Thermal Stability:

• Graphite: It can withstand much higher temperatures than 800°C, with a melting point above 3,000°C. It remains stable and doesn’t deform at the temperatures needed to melt aluminum.
• Stainless Steel: Stainless steel has a melting point in the range of 1,400–1,530°C. While it can handle the temperature required to melt aluminum, prolonged exposure to molten aluminum at high temperatures can degrade the stainless steel due to potential chemical reactions and thermal stresses.

2. Chemical Reactivity:

• Graphite: Aluminum does not react significantly with graphite under normal melting conditions. Graphite crucibles are chemically inert in the aluminum melting process, which helps maintain the purity of the molten aluminum.
• Stainless Steel: Aluminum can react with stainless steel at high temperatures, particularly because aluminum is highly reactive in its molten state. This can lead to contamination of the molten aluminum, damage to the crucible, and shorter crucible life due to corrosion or erosion.

3. Thermal Conductivity:

• Graphite: Graphite has excellent thermal conductivity, which allows for even heating of the crucible and the aluminum inside. This can lead to more efficient melting and uniform temperature distribution.
• Stainless Steel: Stainless steel has lower thermal conductivity compared to graphite, which may result in less efficient heat transfer.

4. Durability:

• Graphite: Graphite crucibles are highly durable under the conditions required for melting aluminum. However, graphite can oxidize at high temperatures if used in an open environment, so it’s important to protect it or use it in a controlled atmosphere.
• Stainless Steel: While durable, stainless steel can suffer from oxidation, chemical reactivity with aluminum, and thermal stresses, which can shorten its lifespan when used repeatedly at high temperatures.