Difference Between Aluminum and Stainless Steel

Main Difference – Aluminum vs Stainless Steel

Aluminum is a metal having a light weight. Aluminum has many applications in different industries including automobile industry. Aluminum occurs in nature as aluminum oxide in aluminum ores. These ores are known as bauxite. Stainless steel is a man-made metal alloy. It is a very important form of steel which has the useful property of corrosion resistance. The addition of chromium in the production of stainless steel is done to prevent the metal from rusting. The main difference between aluminum and stainless steel is that aluminum can be extracted from naturally occurring aluminum ores whereas stainless steel cannot be extracted from any ore as it should be made by man.

Key Areas Covered

1. What is Aluminum
      – Definition, Extraction, Use
2. What is Stainless Steel
      – Definition, Different Types
3. What is the Difference Between Aluminum and Stainless Steel
      – Comparison of Key Differences

Key Terms: Aluminum, Chromium, Cryolite, Electrolysis, Rusting, Stainless Steel, Steel

What is Aluminum

Aluminum (Al) is a soft metal with a silvery-gray color. It has a shiny appearance. Aluminum has a light weight compared to other metals. It is malleable, i.e., it can be deformed under pressure. Due to these properties, aluminum is used in aircraft manufacturing.

Aluminum is highly resistant to corrosion since it can form a protective layer on its surface by oxidation into aluminum oxide. In addition, it is a good conductor of heat and electricity. The degree of ductility is high for aluminum; this means, aluminum can be easily molten and drawn into wire-like structures. Aluminum foils are impermeable even when they are very thin.

Aluminum Extraction

Aluminum ore is known as bauxite. Bauxite is purified into a white powder which is aluminum oxide. From aluminum oxide, aluminum metal can be extracted. The extraction uses an electrolytic technique. First, the aluminum oxide is made molten so that electricity can be passed through it. Since the melting point of aluminum oxide is very high, a high temperature is required for this. Therefore, the techniques are expensive. But instead of melting aluminum oxide, we can mix it with cryolite which will help to melt aluminum oxide at a lower temperature.

Figure 1: Aluminum Extraction Using Cryolite

Graphite is used for both electrodes. When electrolysis is done, aluminum metal is formed at the negative electrode. This formed aluminum will sink to the bottom of the container. Therefore, it can be easily separated from molten aluminum oxide.

What is Stainless Steel

Stainless steel is an iron alloy composed of around 10% of chromium. Chromium is added to this metal alloy in order to protect it from corrosion when exposed to oxygen and moisture. Chromium forms a thin layer of oxide on the surface of the metal. This metal oxide can protect the surface from rusting.

There are four main types of stainless steel categorized based on the microstructure of the alloy.

• Ferritic stainless steel
• Austenitic stainless steel
• Duplex stainless steel
• Martensitic stainless steel

Figure 2: Microstructure of Stainless Steel (Grade: Type 304 Stainless Steel)

The microstructure of ferritic stainless steel is body-centered cubic structure. The microstructure of austenitic stainless steel is face-centered cubic structure. The duplex stainless steel has a combination of these two microstructures (of ferritic and austenitic). Martensitic stainless steel contains a higher carbon content than other three grades of stainless steel.

Difference Between Aluminum and Stainless Steel

Definition

Aluminum: Aluminum (Al) is a soft metal with a silvery-gray color.

Stainless Steel: Stainless steel is an iron alloy composed of around 10% of chromium.

Category

Aluminum: Aluminum is a metal.

Stainless Steel: Stainless steel is a metal alloy.

Occurrence

Aluminum: Aluminum naturally occurs in aluminum ores called bauxite.

Stainless Steel: Stainless steel does not naturally occur, it is a man-made metal alloy.

Rusting

Aluminum: Aluminum does not rust.

Stainless Steel: Rustin is prevented in stainless steel.

Conclusion

Aluminum and stainless steel are very important in different industries. Although they have a similar appearance, these substances have different chemical and physical properties. The main difference between aluminum and stainless steel is that aluminum can be extracted from naturally occurring aluminum ores whereas stainless steel cannot be extracted from any ore since it is man-made.

References:

1. “GCSE Bitesize: Extraction of aluminium.” BBC, Available here.
2. “Stainless steel types.” Outokumpu, Available here.

Image Courtesy:

1. “Cryolite extraction of aluminium (labeled-en)” By Schmelzflusselektrolyse_von_Aluminium.svg: *1993: Andreas SchmidtSVG-Umsetzung/Modifikation: Cepheiden.The original uploader was Cepheiden at German Wikipediaderivative work: NikNaks talk – gallery – wikipedia – Schmelzflusselektrolyse_von_Aluminium.svg (CC BY-SA 3.0) via Commons Wikimedia
2. “Unsensitised structure of type 304 stainless steel” By Webcorr – Own work (CC BY-SA 3.0) via Commons Wikimedia