A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

When ethyne (C2H2) is used for welding, it is often mixed with oxygen for combustion in the welding torch. The primary reason for using a mixture of ethyne and oxygen instead of ethyne and air is related to the combustion characteristics and temperature control required for welding processes.

1. Higher Flame Temperature: Oxygen supports combustion more efficiently than air because it is a more concentrated source of oxygen molecules. When ethyne reacts with oxygen, the combustion reaction releases a significant amount of heat, leading to a high flame temperature. This high temperature is crucial for welding processes, as it allows for the melting and joining of metals.

2. Precise Temperature Control: In welding, it is essential to have precise control over the flame temperature to melt and weld specific metals effectively. The use of pure oxygen ensures better control and a higher flame temperature compared to a mixture with air, which contains nitrogen. Nitrogen does not participate in the combustion process and can act as a heat sink, reducing the overall flame temperature.

3. Reduced Impurities: Air is a mixture of gases, and it contains nitrogen, which is inert and does not participate in combustion. When nitrogen is present in the flame, it can lead to the formation of oxides of nitrogen (NOx), which are undesirable and can affect the quality of the welding process. Using pure oxygen helps minimize the presence of nitrogen in the flame.

4. Efficiency: Combusting ethyne with oxygen is a more efficient process than using air because it provides the necessary oxygen for combustion without the dilution effects of inert gases like nitrogen. This efficiency is crucial for achieving the high temperatures required for welding.

In summary, using a mixture of ethyne and oxygen instead of ethyne and air in welding processes allows for higher flame temperatures, better temperature control, and a more efficient combustion process, ultimately contributing to the success of welding applications.