FLAMES OF ATOMIC HYDROGEN 123 



The rate at which energy may be dehvered to a surface by atomic 

 hydrogen can be calculated readily by equation (13). Let us consider that 

 a flame or stream of atomic hydrogen is directed against a plane metallic 

 surface which is at a temperature of less than 2000 deg. and which catalyzes 

 the combination of atoms. Thus at the surface the concentration of atoms is 

 practically zero. At a distance of 5 mm. from the surface let us assume that 

 the degree of dissociation is 0.50 and the temperature is 4000 deg. The 

 shape factor 6" in equation (13) is the area of the surface divided by the 

 thickness through which diffusion occurs. Thus we find that the energy 

 is delivered to the surface at the rate of 450 watts per cm-, which is 25 

 per cent greater than that radiated from a tungsten surface at its melting 

 point (3660 deg. K.). The rate of diffusion of atomic hydrogen is there- 

 fore so great that it is not necessary, for the rapid melting of metals, that 

 the blast of gas from the flame should carry the atomic hydrogen closer 

 than about 5 mm. from the surface. 



A stream of molecular hydrogen of 100 cc. per second (about 12 cubic 

 feet per hour) measured at room temperature, if converted to atomic 

 hydrogen at 5000 deg. (x = 0.95) would be capable of supplying energy at 

 the rate of about 1.6 kw. These figures may help to give more concrete 

 ideas as to the manner in which atomic hydrogen can be used for the melt- 

 ing or welding of metals. 



It may be of interest to compare some features of the atomic hydrogen 

 arc process with the process described by Mr. Alexander. In the latter 

 process conducting vapor is ordinarily produced at the electrodes and enters 

 the arc. The heat delivered to the weld is in large part due to anode and 

 cathode potential drops where the arc leaves the electrode and enters the 

 metal. Atomic hydrogen produced in the arc and at its surface carries heat 

 from the arc (and thereby raises the voltage) to the surface of the metal 

 and contributes greatly to the speed of welding. The atomic hydrogen is 

 also of great value in reducing oxides and thus makes possible the arc weld- 

 ing of alloys containing chromium, manganese, silicon, etc. The function 

 of the hydrogen in neutralizing the action of small admixtures of air is not 

 necessarily dependent on the presence of atomic hydrogen. 



By adjusting the position of the flame with respect to the surface the 

 rate of melting is under accurate control in the atomic hydrogen flame 

 process, and this feature makes it possible to weld very thin sheet metals or 

 other objects of small size. 



It may seem at first sight peculiar that the addition of nitrogen to the 

 hydrogen decreases the arc drop in the process described by Mr. Alexander 

 whereas it increases it when the atomic hydrogen torch is used. In the first 

 case, however, the arc is carried largely through conducting vapor, the arc 

 IS short and its length is not modified by the composition of the surround- 



