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Alloys used in electric light sources

In electric light sources, the properties of a pure metal often do not fully meet the requirements for application. For example, pure tungsten wire is easy to deform when used as a filament, and pure copper has excellent conductivity, but has low hardness and poor mechanical strength. Alloys can provide metal raw materials with special properties for the production of electric light sources.

As the name suggests, the so-called alloy is a uniform substance formed by the fusion of a metal with one or more other metals or non-metals. Most metals, such as tin and lead, copper and zinc, can completely dissolve each other in a molten state and become a uniform solid after cooling. However, some metals, such as lead and zinc, cannot be fused in any proportion and can only be mixed with each other within a certain limit to form a uniform whole.

There are also some high-melting-point metals that use the method of making alloys in a solid state, such as sintering and solid-state diffusion of tungsten and thorium powders. This alloy is a component that cannot dissolve in each other and does not react chemically. After mechanical mixing, it diffuses in a molten state and then condenses into a uniform whole.

In addition, some non-metals, such as carbon, silicon, phosphorus, sulfur, etc., can sometimes be dissolved in molten metal to form a uniform whole, and should also be called alloys from the overall point of view. For example, "non-falling" tungsten wire with silicon oxide, pig iron, carbon steel, etc. are such alloys.

Of course, alloys are not just a simple, solution-like mixture, and their internal composition and structure are very complex. Some may form compounds with a certain composition; some may also be single crystals combined in a certain way to form a specific crystal structure. Therefore, the physical properties of an alloy (except density) are not the sum of the properties of its components. Generally speaking, the melting point of most alloys is lower than the melting point of any of the metal components that make it up. Sometimes the melting point can drop to an unexpectedly low level. For example, the melting points of tin, bismuth, cadmium, and lead are all above 200 to 300 degrees. The alloy can be made into a power fuse according to the weight ratio of 1:4:1:2, and its melting point is only 67°C.

On the contrary, the hardness of an alloy is generally greater than the hardness of the metal components that make it up. However, the electrical conductivity and thermal conductivity of the alloy are generally reduced, and the plasticity increases and decreases.

Some alloys also have great changes in chemical properties, and are acid-resistant, alkali-resistant, and corrosion-resistant.

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