As an expert sommelier and brewer, I can confidently say that CO2 cartridges cannot be melted under normal circumstances. CO2 cartridges are typically made of steel or aluminum and are designed to withstand high pressures. The purpose of these cartridges is to store and release carbon dioxide gas for various applications, such as carbonating beverages or inflating bike tires.
The metal used in CO2 cartridges has a melting point that is much higher than the temperatures typically encountered in everyday situations. Steel, for example, has a melting point of around 1370 degrees Celsius (2500 degrees Fahrenheit), while aluminum melts at around 660 degrees Celsius (1220 degrees Fahrenheit). These temperatures are significantly higher than what most people would encounter in their daily lives.
That being said, it is important to note that extreme heat can cause the soft metal seal in the neck of the cartridge to melt, allowing the stored CO2 to escape forcefully. This can be dangerous and should not be attempted. Heating a CO2 cartridge to such high temperatures would require specialized equipment and precautions, and it is not something that should be done without proper knowledge and experience.
In my personal experience as a brewer, I have never come across a situation where melting a CO2 cartridge was necessary or even possible. These cartridges are designed to be used as a sealed unit, and they are not intended to be melted down or manipulated in any way.
CO2 cartridges cannot be melted under normal circumstances. While extreme heat can cause the soft metal seal to melt and release the stored CO2, this is not something that should be attempted without proper knowledge and equipment. It is always important to handle and use CO2 cartridges safely and according to manufacturer guidelines.