Method of treating electrodes intended for operation in argon as cathodes of an electric arc

A method of treating electrodes intended for operation in argon as electric arc cathodes. Each of the electrodes being treated consists of a holder with an active insert. The active insert comprises elements selected from the series of rare-earth elements, yttrium, alkali-earth elements, elements of Group IV A of the periodic system and compounds thereof, taken separately or in combination. The electrodes are treated in an electric arc burning in an atmosphere of argon and an active gas, such as nitrogen or oxygen. During the course of treatment the electrode functions as a cathode. A mixture of argon and oxygen or argon and nitrogen is fed to the cathode area of the arc. The duration of the electrode treatment cycle is at least 100 times less than that of the electrode operation time in an argon arc. Treatment is conducted by currents that do not exceed the maximum operating current values of the treated electrode. The volume concentration of the active gas in the mixture varies from 0.1 to 100%.

The present invention relates mainly to the field of arc and plasma 
treatment of metals, and more particularly, to a method of treating 
electrodes intended for operation in argon as electric arc cathodes. The 
invention can be used in plasma and electric-arc metallurgy, and employed 
in the cathodes of electron-beam devices. 
Known in the prior art are electrodes for arc processes made of a tungsten 
rod with uniformly distributed alloying admixtures which reduce the work 
function of the electrodes. The alloying admixtures are for example 
lanthanum oxide, thorium oxide, yttrium oxide, and other compounds in 
various combinations. By varying the geometry of such electrodes (i.e., 
the diameter or the angle of backing-off) the upper limit can be increased 
or the lower limit reduced for the control of the current. However, the 
range of current control at which stabilization of the arc occurs remains 
comparatively narrow for all types of electrodes. The ratio between the 
lower limit of controlling the current and the upper limit within the 
entire range of control is at best 1 to 5 for said electrodes. 
Also known in the prior art are electrodes for arc and plasma processes 
comprising a holder made from a high-melting material, wherein the working 
surface of the holder that is in contact with the arc, contains active 
substances such as barium oxide, zirconium nitride, yttrium oxide. For 
example, there is known an electrode consisting of a zirconium rod with a 
tip made from a mixture of zirconium and zirconium nitride (cf. U.S. Pat. 
No. 2,892,924, Cl. 219-118), or an electrode consisting of a tungsten 
holder with an active insert made from thorium oxide, cesium oxide, and 
zirconium oxide (cf. U.S. Pat. No. 2,922,028 to T. E. Butler, Cl. 219-145, 
Jan. 19, 1960). 
These electrodes make it possible to lower the minimum value of the working 
current and improve stabilization of the arc within the range of the 
current control but the range of the working current control remains 
unchanged, and the ratio between the lower and the upper limits of the 
current control is on the order of 1 to 5. 
All the above-mentioned electrodes suffer from one more substantial 
disadvantage. 
When the current at which the arc is initiated is low, for example, 20 A, 
the arc is stable and located in space. When the current intensity 
increase, the stabilization of the arc and its spatial location with such 
electrodes is retained even at the maximum permissible values of the 
current. But at any lowering of the current the stabilization of the arc 
and its spatial location are disturbed. 
This disturbance appears when the current is smoothly reduced from any 
great value to a lower one, as well as during the repeated striking of the 
arc at a lower value of the current. 
In this case stabilization of the arc and its spatial location are 
disturbed. 
For example, when a tungsten electrode with an active insert made from 
zirconium oxide is used (cf. U.S. Pat. No. 2,922,028, to T. E. Butler, Cl. 
219-145, of Jan. 19, 1960) the maximum permissible value of the current is 
500 A, whereas the stabilization of the arc and its spatial location are 
reached in the range of 20 to 100 A during both the increase and decrease 
of the working current. 
One further disadvantage inherent in all the above-mentioned electrodes is 
a high cathode voltage drop. 
It is an object of the present invention to eliminate the above 
disadvantages. The present invention relates to a method of treating 
electrodes. The object of the present invention is to develop a method of 
electrode treatment providing for a widening of the electrode operating 
current range, improvement in the arc stability in all spatial positions 
within the entire current control range, reduction in heat losses and a 
decrease in the cathode voltage drop. 
While working to attain said objects the inventors discovered an unexpected 
effect which is graphically illustrated by the following examples. 
1. An electrode known in the prior art was taken, consisting of a tungsten 
holder with an active insert of yttrium oxide, the diameter of the 
electrode being 4 mm. This electrode working as a cathode in an argon arc 
ensured a stabilization of the arc in space, with the working current 
lowered to a minimum value of 20 A. 
This electrode was further treated for a short period in oxygen under the 
conditions of arcing of the electric arc. The unexpected effect discovered 
by the inventors was that after the above treatment the lower limit of the 
range of working current during operation as a cathode in argon dropped a 
hundred-fold to 0.2 A, and the cathode voltage drop substantially 
decreased in the entire range of current. 
2. An electrode known in the prior art which consisted of a 4 mm diameter 
zirconium holder with an active insert of zirconium nitride, was tested as 
the cathode of an argon arc. 
The tests showed that this electrode operated in a range of current not 
exceeding 300 A and did not ensure the stabilization of arc in all the 
positions in space within the entire range of current control. 
The electrode was further treated in an arc containing nitrogen. 
The unexpected effect was that after treatment in an arc in the atmosphere 
of nitrogen, the cathode with an active insert of zirconium nitride began 
operating in argon in the range of working current from 50 to 500 A. The 
stabilization of the arc was preserved during multiple variations in the 
working current in both directions--from 50 to 500 A and from 500 to 50 A. 
3. After arc treatment in nitrogen of a cathode, consisting of a 4 mm 
diameter hafnium holder with an active insert of cerium oxide, the upper 
limit of the range of working current increased to 700 A, heat losses in 
the electrode considerably decreased and stabilization of the arc 
improved. 
At the same time the maximum permissible magnitude of the current at the 
hafnium cathode with an active insert of cerium oxide without treatment in 
nitrogen was 5 times lower. 
The unexpected effect was that the treatment of the hafnium cathode with an 
active insert of cerium oxide in a nitrogen arc imparted new properties to 
the electrode. 
It was established that arc treatment in oxygen of cathodes, containing 
oxides of different elements on the working surface, and treatment in 
nitrogen of cathodes, containing nitrides on the working surface, as well 
as arc treatment both in nitrogen and oxygen of cathodes, containing 
oxides or nitrides on the active surfaces, result in a considerable 
increase in the emission activity, decrease in the work function of 
electrons and localization of the cathode spot. This makes it possible to 
considerably expand the range of working current, reduce the heat losses 
in the electrode and the cathode voltage drop. 
The unexpected effect discovered by the inventors served as a basis for 
developing a method of treating electrodes which ensured the attainment of 
these objects. 
This is attained by the proposed method of treating electrodes intended for 
operation in argon as the cathodes of an electric arc, wherein the active 
working surface of the electrodes that contacts the arc, incorporates 
elements selected from a series of rare-earth metals, yttrium, 
alkali-earth elements, elements of Group IV A of the periodic system and 
compounds thereof, taken both separately and in combination. According to 
the invention, the treatment of the electrodes is carried out under 
conditions of arcing of the electric arc so that the electrode being 
treated functions as a cathode. A mixture of argon with an active gas is 
fed to the cathode area of the arc which, together with at least one of 
said elements, namely, rare-earth metals, yttrium, alkali-earth elements, 
elements of Group IV A and compounds thereof, taken both separately and in 
combination, forms compounds whose work function is not more than three 
electronvolts, and the electrode is treated for a period which is at least 
100 times less than the period of operation of the electrode in argon, 
with the current not exceeding the upper limit of the range of working 
current, the volumetric concentration of the active gas in the mixture 
being from 0.1 to 100%. 
It is advisable to use oxygen as an active gas. 
Alternatively, nitrogen can be used as an active gas. 
It is also advisable to add periodically to the cathode area of the arc an 
active gas for continuous operation of the electrode in argon, and the 
repeated addition of active gas to argon should be carried out for a 
period which is at least 100 times less than the period of operation of 
the electrode in argon. 
The treatment of cathodes whose active working surfaces contain the 
elements from a series of rare-earth metals, yttrium, alkali-earth 
elements and elements of Group IV A of the periodic system, in active gas 
ensures an increase in the emission activity, a decrease in the work 
function of the electrons and the localization of the cathode spot, which 
results in an expansion of the range of working current and a reduction of 
heat flow to the electrode. At the same time a considerable reduction of 
the cathode voltage drop is ensured. 
A great advantage of cathodes which have been treated in an active gas is 
an improvement in the stabilization of the arc and its spatial location in 
the entire range of the working current control. 
In addition, the cathodes treated according to said method have a longer 
service life in an argon arc as compared with untreated cathodes.

The treatment of electrodes intended for operation in argon as the cathodes 
of an electric arc is carried out in an active gas. The cathodes active 
working surfaces that contact the arc, contain elements selected from a 
series of rare-earth metals, yttrium, alkali-earth elements, elements of 
Group IV A of the periodic system and compounds thereof, taken both 
separately and in combination. The treatment is carried out under 
conditions of arcing of the electric arc so that the electrode being 
treated functions as a cathode. A mixture of argon is fed to the cathode 
area of the arc with an active gas which, together with one of the 
rare-earth metals, yttrium, alkali-earth elements, elements of Group IV A 
of the periodic system and compounds thereof, taken both separately and in 
combination, forms a compound having a work function of not more than 
three electronvolts. The period of treatment of the electrode should be at 
least 100 times less than the period of operation of the electrode as the 
cathode of an arc in argon. The electrodes are treated with currents not 
exceeding the upper limit of the range of working currents, with the 
volumetric concentration of the active gas in the mixture being from 0.1 
to 100%. 
The method of treating electrodes resides in the following. 
An electric arc 1 (FIG. 1) is excited in argon between an electrode 2 being 
treated, connected to the negative pole of a supply source 3 and an anode 
4 connected to the positive pole. The current of the arc is established to 
be not higher than the maximum working current. 
A controlled amount of argon is supplied from a cylinder 5 via a flowmeter 
6 and enters the arc 1 through a nozzle 7. Then a valve 8 opens and an 
active gas which together with argon is supplied to the near-the-cathode 
area of the arc 1 also through the nozzle 7 is fed from a cylinder 9 
through a flowmeter 10. The volumetric concentration of the active gas in 
the mixture with argon is established to range from 0.1 to 100%. The 
active gas entering the near-the-cathode area of the arc forms, together 
with one of the elements located on the active working surface of the 
cathode in the place of contact with the arc, a compound with a work 
function of not more than three electron-volts. After a period which is at 
least 100 times less than the period of operation of the electrode in 
argon, the valve 8 closes. Thereafter, the supply source 3 is cut off, the 
arc 1 is extinguished and the supply of argon is stopped. The electrode 2 
has thus passed the treatment and is ready for use as a cathode of arc and 
plasma devices. 
It is preferable to use nitrogen as an active gas during treatment of 
electrodes intended for operation as cathodes in argon at high currents 
(over 500 A). 
It is advisable to use oxygen as an active gas in treatment of electrodes 
intended for operation in argon at low currents (from 0.1 A). 
The periodic treatment of electrodes in the process of continuous operation 
in an argon arc is carried out in the following manner. An electrode 
treated in an active gas and ready for operation is taken, an arc is 
excited in argon and the technological process is conducted in argon for a 
required period. Then, without interrupting the process, fed to the 
near-the-cathode area of the arc is a small amount of an active gas (not 
less than 0.1%) together with argon, for a short period (at least 100 
times less than the period of the technological process). Then the supply 
of the active gas is stopped and the process goes on in argon. The 
repeated supply of the active gas is carried out in a similar manner. 
To illustrate the method of treating electrodes in an active gas, several 
examples are given. 
EXAMPLE 1 
An electrode was taken, consisting of a tungsten rod 11 (FIG. 2) having a 
diameter of 4 mm and a length of 45 mm, and an active insert 12 which was 
a blind cylindrical hole in the tungsten rod having a depth of 4 mm and a 
diameter of 1.5 mm and filled with cerium oxide. 
The preliminary treatment of the electrode in the arc containing oxygen was 
carried out in the following manner. The treatment was conducted under the 
conditions arcing of the electric arc, according to FIG. 1, so that the 
electrode being treated was functioning as a cathode. The arc 1 was 
excited from the supply source 3 with a current of 50 A in argon whose 
consumption was 0.3 g/sec. In 10 seconds when the active insert 12 (FIG. 
2) was sufficiently hot, oxygen was fed (a 10% addition of oxygen to 
argon) for one second. In one second the supply of oxygen was stopped. 
After treatment with oxygen this electrode underwent tests in an arc in 
argon for 8 hours. The tests showed that this electrode ensured the 
stabilization of the arc and its spatial location during operation in 
argon in the range of from 5 to 200 A; the working current could be varied 
in both directions. 
Multiple striking and extinguishing of the arc at currents of from 5 to 200 
A also showed that the electrode operated in argon under conditions of 
steady stabilization of the arc. 
EXAMPLE 2 
A cylindrical rod electrode from titanium with a diameter of 4 mm and an 
active insert from semarium oxide was made. Samarium oxide was pressed 
into a blind hole in the end face of the electrode with a depth of the 
hole being 4 mm and a diameter of 1.5 mm. 
The electrode was treated in an arc containing nitrogen. For this purpose 
the electrode 2 (FIG. 1) was connected to the negative pole of the supply 
source 3. The arc 1 was excited for 5 seconds on the electrode with a 
current of 20 A in a mixture of argon and nitrogen. The argon consumption 
was 0.3 g/sec, and the volumetric concentration of nitrogen in the mixture 
was 20%. 
Thereafter, the nitrogen supply was stopped. The electrode was tested in 
argon. The maximum permissible current magnitude at the electrode was 300 
A. The test of the electrode in argon was carried out under the following 
conditions; first the arc was excited with a current of 20 A, then the 
current intensity was smoothly increased to a certain magnitude and the 
arc was extinguished. The next excitation was also done at 20 amps. The 
current was adjusted from 20 to 300 A in 20 A increments with the 
subsequent extinguishing of the arc, i.e., the arc was extinguished at 
currents of 20, 40, 60, . . . 300 A. The two-hour test showed that the 
electrode was working in argon under conditions of steady stabilization of 
the arc in the range of the current control in both directions from 40 to 
300 A. 
EXAMPLE 3 
The electrode consisted of a tungsten holder with a diameter of 4 mm and a 
length of 30 mm with an active insert which was a blind hole in the end 
face of the tungsten rod with a depth of 4 mm and a diameter of 1.5 mm 
filled with an yttrium oxide. The electrode 2 (FIG. 1) was connected to 
the negative pole of the supply source 3, and an arc was excited on the 
electrode in argon with a current intensity of 5 A for 10 seconds. In 10 
seconds oxygen was supplied and the volumetric concentration of oxygen in 
the mixture was 0.1%. The treatment in the mixture of argon with oxygen 
was conducted in an arc for 30 seconds, then the oxygen supply was cut 
off. The tests carried out in argon showed that the electrode ensured the 
stabilization of the arc when the current was reduced to 0.2 A. The 
maximum exciting current of the arc was 0.3 A. The cathode voltage drop in 
the entire range of currents was considerably reduced. 
The tests of the cathode which had been treated in an arc, containing 
oxygen were carried out together with the initial cathode which had not 
been pre-treated. At the same time tests were conducted of cathodes from 
thoriated tungsten for microplasma Secheron burners and cathodes from 
yttriated and lanthanated tungsten. The rod cathodes from thoriated, 
lanthanated and yttriated tungsten with a diameter of 2.5 mm were 
taper-turned at an angle of 20.degree. to 30.degree.. 
In the process of testing the range of working currents, the minimum 
exciting current of the arc and voltage-current characteristics were 
determined. 
The tests showed the following: the minimum exciting current of the arc on 
a tungsten electrode with an insert from yttrium oxide was 5 amps, on 
thoriated tungsten (Secheron) 3 A, and on lanthanated and yttriated 
tungsten 3 A. 
But the minimum exciting current of the arc on a tungsten electrode with an 
insert from yttrium oxide which had been treated in oxygen was 0.3 A. 
The stabilization of the arc and its spatial location on electrodes from 
thoriated (Secheron), lanthanated and yttriated tungsten were disturbed 
when the current was reduced to 1.8 A, whereas there was no disturbance of 
the stabilization of the arc on the electrode treated by said method when 
the current was reduced to 0.2 A. 
The comparative voltage-current characteristics of all the electrodes which 
had undergone testing are shown in FIG. 3, wherein on the Y-axis there are 
shown the values of voltage drops in the arc in volts, and on the X-axis 
there are shown intensity of the current in amperes. The voltage-current 
characteristics 13 of the electrode which had been treated in oxygen was 
considerably lower than those of electrodes from thoriated tungsten 14 
(Secheron), lanthanated tungsten 15 and yttriated tungsten 16. The voltage 
drop on the arc for a cathode treated in an oxygen arc with low current 
was twice as low as for the cathodes known in the art, a feature of 
substantial importance in designing supply sources. 
EXAMPLE 4 
The present example illustrates a method of periodic treatment of an 
electrode during its continuous operation in an arc in argon in the 
process of welding copper with a normal polarity. The electrode was a 
tungsten rod with a diameter of 4 mm and a length of 45 mm. In the end 
face of the tungsten rod there was drilled a blind hole into which an 
insert from hafnium was pressed with a diameter of 1.5 mm and a length of 
5 mm. 
The arc was excited in argon on an extendable strip. During the burning of 
the arc on the extendable strip with a current of 200 A a mixture of argon 
with nitrogen (20% of nitrogen) was fed to the cathode area for 5 to 8 
seconds. When the arc approached the beginning of the working section of 
the weld, the supply of nitrogen was stopped, the current was increased to 
1,000 A and the welding was conducted in argon. After passing the weld and 
the exit of the arc onto the extendable strip, the current was again 
reduced to 200 A and 20% of nitrogen was again fed for 5 to 8 seconds. The 
addition of 20% of nitrogen when the arc was on the extendable strip and 
the cathode was moving from one welded joint to another (5 to 8 seconds) 
ensured a reliable operation of the electrode in argon and a strict 
localization of the arc during passing the weld. 
The method of periodic treatment ensured a 20 fold reserve of the time of 
fitness of the electrode for operation in argon. After 10 hours of 
operation the electrode had no noticeable destruction and ensured a 
reliable operation with currents from 1,000 to ,1200 A.