Atomic hydrogen welding

Atomic hydrogen welding (AHW or Athydo) is an arc welding process that uses an arc between two tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen. The electric arc efficiently breaks up the hydrogen molecules, which later recombine with tremendous release of heat, reaching temperatures from 3,400 to 4,000 °C (6,150 to 7,230 °F). Without the arc, an oxyhydrogen torch can only reach 2,800 °C (5,070 °F). This is the third-hottest flame after dicyanoacetylene at 4,987 °C (9,009 °F) and cyanogen at 4,525 °C (8,177 °F). An acetylene torch merely reaches 3,300 °C (5,970 °F). This device may be called an atomic hydrogen torch, nascent hydrogen torch or Langmuir torch. The process was also known as arc-atom welding. The heat produced by this torch is sufficient to weld tungsten (3,422 °C (6,192 °F)), the most refractory metal. The presence of hydrogen also acts as a shielding gas, preventing oxidation and contamination by carbon, nitrogen or oxygen, which can severely damage the properties of many metals. It eliminates the need of flux for this purpose. The arc is maintained independently of the workpiece or parts being welded. The hydrogen gas is normally diatomic (H2), but where the temperatures are over 6,000 °C (10,830 °F) near the arc, the hydrogen breaks down into its atomic form, absorbing a large amount of heat from the arc. When the hydrogen strikes a relatively cold surface (i.e. the weld zone), it recombines into its diatomic form, releasing the energy associated with the formation of that bond. The energy in AHW can be varied easily by changing the distance between the arc stream and the workpiece surface. In atomic hydrogen welding, filler metal may or may not be used. In this...