Used in coating filaments of light bulbs
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When incandescent light bulbs are manufactured, they are filled with an inert gas to insulate the filament and prevent its sublimation. The pressure inside a freshly manufactured light bulb is something like 80% of the normal atmospheric pressure. The gases normally used are argon and a little bit of nitrogen.
The coating on the filaments of light bulbs is typically made from a material called tungsten, which helps to improve the bulb's performance and efficiency. Tungsten is chosen for this purpose because of its high melting point, which enables it to withstand the high temperatures generated when the filament is heated.
To understand why tungsten is used for coating filaments, it's helpful to know a bit about how incandescent light bulbs work. Inside the bulb, there is a filament made of tungsten wire. When an electric current passes through the filament, it heats up and emits light. However, the high temperatures also cause the filament to slowly evaporate over time, leading to a decrease in its lifespan.
To mitigate this issue, manufacturers coat the tungsten filament with a layer of another material, such as alumina or a mixture of silica and alumina. This coating acts as a barrier, preventing the tungsten from evaporating too quickly. It also helps to maintain the filament's shape and improve its durability.
The process of coating the filament involves various techniques, such as chemical vapor deposition or sputtering. These methods allow for precise control over the thickness and composition of the coating, ensuring optimal performance and longevity of the light bulb. Overall, the coating plays a critical role in increasing the efficiency and lifespan of incandescent light bulbs.