Atomic Hydrogen

Atomic hydrogen welding

When pieces of metal are joined together by welding, they are heated strongly, so that their edges melt and mix together. Usually some extra metal is added by melting a welding rod. When the melted metal sets again, there is one piece. All forms of welding require a source of heat.

The heat from an oxy-acetylene burner comes from the heat of combustion of ethyne (–1299 kJ mol^–1 or 50 kJ g^–1). It can reach a temperature of 3315 °C, which is hot enough to melt most metals — but not all.

In 1926 American chemist Irving Langmuir wanted to melt tungsten, which melts at 3407 °C, so he invented a completely different kind of welding torch, the atomic hydrogen torch.

What Langmuir did was use electricity to break hydrogen molecules into separate atoms (an endothermic process), and then allow these atoms to recombine, releasing their bond energy in a concentrated spot.

H(g) + H(g) H₂ (g) ΔH = –422 kJ mol^–1

This method releases an incredible 218 kJ g^–1 of hydrogen. Langmuir could have got more energy per mole of gas used by breaking apart oxygen or nitrogen molecules, but these elements are much heavier than hydrogen. On an energy per gram basis, nothing beats hydrogen. Using his torch he was able to reach temperatures of over 3700 °C.

Atomic hydrogen welding (AHW) was used extensively in the 1930s and 1940s. Not only is the flame hotter than other systems, but the hydrogen gas shields the weld from the air, so the metals don’t oxidise.

In 1948 a new form of welding was invented — gas metal arc welding (GMAW), followed by the similar gas tungsten arc welding (GTAW). In both systems the heat comes from an electric arc while the weld is shielded from the air with some sort of unreactive gas — mixtures of helium, argon, nitrogen or sometimes carbon dioxide. In GMAW one electrode is the consumable weld rod, while the other electrode is the metal being welded. In GTAW two tungsten electrodes are used, with the weld rod being added separately (as it is in AHW). These welding systems are much cheaper than AHW, and produce temperatures sufficient to weld steel, aluminium and the other metals commonly in use today.

Click here to download a 4Mb video clip showing atomic hydrogen welding.

Irving Langmuir 1881–1957

Irving Langmuir was an American chemist employed by General Electricity. His first assignment was to extend the life of the electric light bulb. In 1909, when Langmuir began his investigation, GE had begun to use tungsten filaments. They already knew that if the bulbs contained any oxygen, that the tungsten would rapidly oxidise, so they tried to make bulbs with a good vacuum. Unfortunately, the tungsten filaments still had a short life. It was suggested that what was needed was a better vacuum, but Langmuir was able to show that in the vacuum, tungsten atoms slowly evaporated off the thin filament. The wire became thinner and thinner until it eventually broke.

The solution was obvious: replace air in the bulbs with an unreactive gas. Langmuir used nitrogen, and later bulbs were filled with the even more unreactive argon. Not only did the gas-filled bulbs last longer, but they also used less electricity (the thinner the filament, the greater its resistance). General Electric were very pleased with their young researcher, and gave him the freedom to pursue other interests, whether there was an obvious profit for their company or not.

Langmuir contributed to the work on chemical bonding initiated by Gilbert Lewis. He also investigated the reactions on the surfaces of metals, worked out how to cut down glare on glass surfaces, and was first to try rain making by the method of ‘cloud seeding’. He won the Nobel prize in 1932 for his work on surface chemistry.

Find out more about Langmuir.

	Atomic hydrogen welding
Back to Notes Next Story Previous Story	When pieces of metal are joined together by welding, they are heated strongly, so that their edges melt and mix together. Usually some extra metal is added by melting a welding rod. When the melted metal sets again, there is one piece. All forms of welding require a source of heat. The heat from an oxy-acetylene burner comes from the heat of combustion of ethyne (–1299 kJ mol^–1 or 50 kJ g^–1). It can reach a temperature of 3315 °C, which is hot enough to melt most metals — but not all. In 1926 American chemist Irving Langmuir wanted to melt tungsten, which melts at 3407 °C, so he invented a completely different kind of welding torch, the atomic hydrogen torch. What Langmuir did was use electricity to break hydrogen molecules into separate atoms (an endothermic process), and then allow these atoms to recombine, releasing their bond energy in a concentrated spot. H(g) + H(g) H₂ (g) ΔH = –422 kJ mol^–1 This method releases an incredible 218 kJ g^–1 of hydrogen. Langmuir could have got more energy per mole of gas used by breaking apart oxygen or nitrogen molecules, but these elements are much heavier than hydrogen. On an energy per gram basis, nothing beats hydrogen. Using his torch he was able to reach temperatures of over 3700 °C.
	Atomic hydrogen welding (AHW) was used extensively in the 1930s and 1940s. Not only is the flame hotter than other systems, but the hydrogen gas shields the weld from the air, so the metals don’t oxidise. In 1948 a new form of welding was invented — gas metal arc welding (GMAW), followed by the similar gas tungsten arc welding (GTAW). In both systems the heat comes from an electric arc while the weld is shielded from the air with some sort of unreactive gas — mixtures of helium, argon, nitrogen or sometimes carbon dioxide. In GMAW one electrode is the consumable weld rod, while the other electrode is the metal being welded. In GTAW two tungsten electrodes are used, with the weld rod being added separately (as it is in AHW). These welding systems are much cheaper than AHW, and produce temperatures sufficient to weld steel, aluminium and the other metals commonly in use today. Click here to download a 4Mb video clip showing atomic hydrogen welding.	Atomic hydrogen welding still occurs in a few research laboratories around the world when very high temperatures are required.
	Irving Langmuir 1881–1957 Irving Langmuir was an American chemist employed by General Electricity. His first assignment was to extend the life of the electric light bulb. In 1909, when Langmuir began his investigation, GE had begun to use tungsten filaments. They already knew that if the bulbs contained any oxygen, that the tungsten would rapidly oxidise, so they tried to make bulbs with a good vacuum. Unfortunately, the tungsten filaments still had a short life. It was suggested that what was needed was a better vacuum, but Langmuir was able to show that in the vacuum, tungsten atoms slowly evaporated off the thin filament. The wire became thinner and thinner until it eventually broke. The solution was obvious: replace air in the bulbs with an unreactive gas. Langmuir used nitrogen, and later bulbs were filled with the even more unreactive argon. Not only did the gas-filled bulbs last longer, but they also used less electricity (the thinner the filament, the greater its resistance). General Electric were very pleased with their young researcher, and gave him the freedom to pursue other interests, whether there was an obvious profit for their company or not. Langmuir contributed to the work on chemical bonding initiated by Gilbert Lewis. He also investigated the reactions on the surfaces of metals, worked out how to cut down glare on glass surfaces, and was first to try rain making by the method of ‘cloud seeding’. He won the Nobel prize in 1932 for his work on surface chemistry. Find out more about Langmuir.

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