Aluminum exists in nature mainly in the form of compounds, such as bauxite and cryolite. The process of extracting aluminum requires high-temperature electrolysis, which consumes a lot of energy. Nevertheless, aluminum occupies an important position in the global economy due to its excellent properties and wide application.
How does high-temperature electrolysis, the process of extracting aluminum, work, and why does it consume so much energy?
The high-temperature electrolysis process of aluminum extraction, the Hall-Héroult process, is currently the main method for industrial production of aluminum. This process is carried out at a high temperature of about 970°C, using a molten sodium-fluoride-based electrolyte (such as sodium aluminum fluoride NaF-AlF3) as a solvent for aluminum oxide (Al2O3). In the electrolytic cell, an electric current is passed through the cell between the carbon anode and cathode, causing the aluminum oxide to dissolve and electrolyze to extract metallic aluminum.
There are several reasons why this process consumes a lot of energy:
1.High temperature operation: The electrolysis process needs to be maintained at a high temperature (about 950-970°C), which requires a lot of energy to maintain the temperature. High temperature operation not only increases energy consumption, but also causes excessive corrosion of battery materials, further reducing energy efficiency.
2.Consumption of carbon anodes: The traditional Hall-Heroult process uses carbon anodes, which are continuously oxidized during the electrolysis process to form carbon dioxide (CO2) gas, which not only increases greenhouse gas emissions but also leads to energy inefficiency. For every ton of aluminum produced, the consumption of carbon anodes can produce more than 1.3 tons of CO2.
3.Cell voltage and current density: To sustain the electrolysis process, a relatively high voltage (typically 3-5 V DC) and a high current density (e.g. close to 5000 A/m²) need to be applied, which further increases energy consumption. For example, in some advanced cells, the current density can reach over 500 kiloamperes.
4.Energy requirements of thermodynamic and electrochemical reactions: It takes about 20 MJ of thermodynamic energy to generate one kilogram of aluminum, while the electrical energy consumed by actual batteries is much higher, close to 40 MJ per kilogram. This shows that although the thermodynamic reaction itself requires a certain amount of energy, the electrical energy required in actual operation is much higher than the theoretical value.
5.Joule effect: During electrolysis, the heat generated by the large amount of current helps maintain the temperature of the electrolytic cell, but this also means that some of the electrical energy is converted into heat and lost. According to some data, about 83% of the heat is lost due to the Joule effect.
How is aluminum's corrosion resistance formed, and in what specific ways does this dense aluminum oxide film protect aluminum?
Aluminum's corrosion resistance comes primarily from the protective aluminum oxide film that forms spontaneously on its surface. When aluminum is exposed to air, it quickly reacts with oxygen to form a dense and stable aluminum oxide (Al2O3) film that is about 20-100 microns thick. This oxide film has excellent dielectric properties and can prevent electrical ion exchange, thus acting as a corrosion protection barrier.
The protective effect of this dense aluminum oxide film on aluminum is specifically manifested in the following aspects:
1.Prevent direct corrosion: Aluminum oxide film can effectively prevent direct corrosion of aluminum. Even in extreme or special environments, the corrosion rate of aluminum will gradually decrease over time.
2.Self-repairing ability: If the oxide film is mechanically damaged, it can almost instantly repair itself and re-form a protective layer.
3.Resistance to pitting and crevice corrosion: In nearly neutral solutions of most non-halogenated salts, the oxide film is particularly stable, resulting in excellent resistance to pitting corrosion. However, in solutions containing halide ions such as chloride ions, aluminum is susceptible to pitting corrosion.
4.Environmental adaptability: Aluminum exhibits the best corrosion resistance under neutral or slightly acidic conditions, when the protective oxide film is most stable. Strong alkalis and strong non-oxidizing acids will destroy the oxide film and accelerate corrosion.
5.Effect of alloying elements: Alloying elements such as magnesium and copper can positively or negatively affect corrosion sensitivity by changing the properties of the aluminum oxide film.
6.Effect of pH: Aluminum oxide films are unstable above pH 4 or below pH 9, a chemical phenomenon known as the control of "amphoteric" substances.
Aluminum extraction process
The extraction process of aluminum mainly includes two steps: first, pure aluminum oxide is extracted from bauxite, and then aluminum is produced by electrolyzing the melted aluminum oxide. During the electrolysis process, cryolite is often added to lower the melting point of aluminum oxide. The specific steps are as follows:
1.Bayer process: Bauxite is heated together with limestone and soda ash and dissolved in a caustic solution, the insoluble phase is separated by filtration, and then aluminum hydroxide is precipitated and calcined into alumina.
2.Hall-Herard process: Alumina is dissolved in molten cryolite to form an electrolyte. The electrolytic cell is lined with graphite as the cathode, and the anode is made of a carbon rod immersed in the electrolyte. Through the electrolytic reaction, aluminum molecules and oxygen molecules are separated to produce pure aluminum metal.
What is the global market demand for aluminum and how important is it in the economy?
The global aluminum market demand is growing. According to 2023 data, global aluminum consumption reached 70.2 million tons, an increase of 1.7% year-on-year. This growth was mainly driven by increased consumption in China, which increased by 4.9%. In addition, CRU predicts that by 2027, global demand for primary aluminum will increase by an average of 2.0% per year to 76.2 million tons.
Aluminium is important in the economy in many ways:
1.Transportation: Aluminum is increasingly used in vehicles such as cars and airplanes because its lightweight and durable properties help improve energy efficiency and safety.
2.Construction industry: Aluminum is widely used in building construction, including frames, exterior walls, roof structures, etc., especially in the field of sustainable construction.
3.New energy field: With the development of new energy vehicles, photovoltaics and wind power, the demand for aluminum is also increasing. It is expected that by 2025, these fields will significantly boost the demand for aluminum.
4.Packaging Industry: Aluminum’s use in packaging is also growing, especially in food and beverage packaging.
5.Power industry: Aluminum is also very important in the application of power transmission and distribution systems.
aluminum alloy is widely used in doors and windows, and its advantages are mainly reflected in the following aspects:
1.Lightweight and high strength: Aluminum alloy is lightweight and high strength, which enables it to reduce the load-bearing burden of buildings in door and window design while maintaining the stability of the structure.
2.Corrosion resistance: After anodizing treatment, the aluminum alloy surface has good corrosion resistance, is not easy to rust, and has a long service life.
3.Heat insulation and sound insulation: Aluminum alloy doors and windows usually adopt a thermal insulation aluminum alloy design. By adding insulation materials (such as PA66 nylon) in the middle of the aluminum profile, heat transfer can be effectively prevented, thereby improving the thermal insulation and sound insulation effects of doors and windows.
4.Diversified design: Aluminum alloy windows can undergo a variety of surface treatments, such as powder coating, anodizing, electrophoretic coating, etc., providing a rich selection of colors and wood grains to meet different architectural styles and decoration needs.
5.Environmental protection and energy saving: Aluminum alloy materials can be recycled, which is in line with the energy-saving and environmental protection trend of modern buildings. In addition, the high-efficiency heat insulation and energy-saving effect of thermal insulation
Aluminum Alloy Sliding Windows is also popular in the market.
6.Easy installation and maintenance: The processing, manufacturing and installation of aluminum alloy
Casement Door can be carried out in the factory, which is conducive to the standardization and serialization of product design. At the same time, it is simple to maintain and has a long service life.
7.Wide application: Aluminum alloy windows are not only suitable for residential buildings, but also widely used in commercial buildings, public facilities and other fields. They are favored for their excellent performance and beautiful design.
8.High safety: Aluminum alloy windows have good fire resistance and anti-theft performance, which can effectively prevent the spread of fire and external intrusion.
Aluminum alloy windows have been widely used in modern buildings due to their advantages such as light weight and high strength, corrosion resistance, heat insulation and sound insulation, diversified design, environmental protection and energy saving, and easy installation and maintenance. They have become an ideal choice for replacing doors and windows and renovating old windows.
