Manufacturing
As a rare metal, indium has almost the same manufacturing processes as other metals. However, not all metals have the same properties, the processes of indium selected due to its unique properties can be divided into several categories.
The classification scheme of metal fabrication techniques is shown in Figure 1. Not all fabrication methods in the figure can be applied to indium. All of these methods can be classified into cold working and hot working. Hot working can cause large deformation with less deformation energy than cold working. But it can also result in material loss and poor surface finish.
Products produced by cold working have higher-quality surface finish, more preferable mechanical properties and closer dimensional control. However, it is more expensive than hot working.
As for indium, it can be applied to fields requiring high precision such as semiconductors, and fields not requiring high precision such as solders. Therefore, both hot and cold working are suitable for indium with different application areas.
Figure 1 Classification scheme of metal fabrication techniques [24]
- Forming
(i) Rolling
Rolling is the most common fabrication techniques for indium. (see Fig. 2) In used as ITO target materials is manufactured by rolling. The indium ingot is forced to pass through rollers. The rollers can reduce the thickness of indium and make the thickness uniform.
Rolling has three basic steps which are primary rolling, hot rolling and cold rolling. [25]
- Primary rolling
This step converts the primary indium ingot into simple stock. This refines the structure of indium and removes the defects.
- Hot rolling
During hot rolling, the stock is changed into sheets or plates for next step.
- Cold rolling
Cold rolling gives last shape for the products. This enhances the overall performance of the final sheet or plate.
Figure 2 The process of rolling [26]
(ii) Extrusion
Extrusion (see Fig. 3) is mainly used to produce indium wires which can be utilized to sealing and soldering.
During extrusion, indium ingot is forced through several dies to create continuous wires. In the extruder shown in Fig. 3, indium billet is forced by a ram with a pressure pad continuously to pass through a die held by a die holder. For indium, the final products are usually wires.[27]
Figure 3 The process of extrusion [28]
- Casting
Casting is a technique that used to fabricate indium alloys. The alloy melt was poured into the mold which contains a hollow cavity inside to create parts and prototypes. The liquid was then solidified and broken out of the mold. The molds have various shape and materials. Indium and its alloys both have low melting point so they can be cast in molds made of glass, quartz, mica, and ceramic. [29]
The classification of casting shown in Fig. 1 is related to the complexity of the final parts. For instance, sand casting and continuous casting is to create large and simple parts and investment casting is to form small and complex shape. Die casting is specifically suitable for alloys having low melting temperatures such as indium.
- Powder Metallurgy
Powder Metallurgy is a manufacture method to make objects from powder rather than molten materials. It hardly produces little smoke or chemical pollution. Because the raw materials powder is usually recycled from waste and the final objects have no cutting, it produces less waste loss and has higher materials utilization. Furthermore, the entire process does not need melting, the energy efficiency is also higher. ITO target materials can be processed by powder metallurgy. [30]
References:
[24] 2014. Materials Sience And Engineering: An Intruduction. 9th ed. p.434.
[25] Your Article Library. 2020. Rolling Of Metals: Process And Principles (With Diagram). [online] Available at: <https://www.yourarticlelibrary.com/metallurgy/rolling-of-metals-process-and-principles-with-diagram/95556> [Accessed 29 May 2020].
[26] Themetalcasting.com. 2020. Cold Rolling. [online] Available at: <http://www.themetalcasting.com/cold-rolling.html> [Accessed 29 May 2020].
[27] Encyclopedia Britannica. 2020. Extrusion | Industrial Process. [online] Available at: <https://www.britannica.com/technology/extrusion-industrial-process> [Accessed 29 May 2020].
[28] OpenLearn. 2020. Hot Extrusion. [online] Available at: <https://www.open.edu/openlearn/science-maths-technology/engineering-technology/manupedia/hot-extrusion> [Accessed 29 May 2020].
[29] Mcmaster.com. 2020. Mcmaster-Carr. [online] Available at: <https://www.mcmaster.com/indium-alloys/> [Accessed 29 May 2020].
[30] Encyclopedia Britannica. 2020. Powder Metallurgy. [online] Available at: <https://www.britannica.com/technology/powder-metallurgy> [Accessed 29 May 2020].