A gas surrounding a burning hot piece of metal in a sealed glass container, why dont they explode immediately?
In: Chemistry
There are two main ways a badly designed light bulb could explode.
1. The gas catches fire. To prevent this, they fill them with a highly non-reactive gas such as argon.
2. Thermal expansion shatters the glass. This requires making the glass strong enough to withstand the in-use pressure.
They do!
Or, they used to.
But, home voltages are much more controlled than they used to be, manufacturing defects happen much less often than they used to, and most bulbs sold today do not have a strip of tungsten heated to hundreds of degrees in a sealed vacuum.
The “sealed vacuum” bit above is why they didn’t just explode randomly all the time before. Explosions require fuel, like oxygen, and there isn’t any in a properly sealed bulb.
Not all gases are flammable, ie want to oxidize (combine or remix with oxygen) and release energy.
Something like hydrogen is flammable. Helium is not. There are plenty in either category.
In addition to that, you’d need an oxidizer to complete the reaction, often just oxygen, which would presumably be absent from inside the bulb although it may leak in over time.
In a typical incandescent bulb, the gas inside the bulb is argon, which doesn’t burn, meaning there isn’t a risk of explosion. It also is non-reactive, which prevents the tungsten filament from simply burning away in the presence of oxygen.
IIRC icandescent bulbs were often partially vacuum-ized, so there was less gas inside than outside.
The filament would heat up any gas inside, yes, but that doesn’t mean it creates enough pressure to break glass. This is especially true if the regular pressure of the gas is less than the air outside, but could easily be true without that.
The gases present inside a light bulb consist of a small amount of argon. The pressure is low enough that heating up with the filament doesn’t cause the glass to become stressed, while argon’s non-reactive property doesn’t let the filament actually burn.
Usually it’s because of the lack of oxygen inside the bulb. You can’t have combustion or fire without oxygen.
Oxygen is removed from incandescent light bulbs either by vacuum or by replacing it with an inert gas like argon.
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