JPS5812694B2 - Grid electrode for discharge vessel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a grid electrode comprising wires forming molybdenum or tungsten and an intermediate layer consisting of intermetallic bonds coated with white metal.

In order to reduce electron emission due to heat, it is known to coat the grid electrode with a noble metal from group 1 of the periodic table, such as platinum in particular.

In order to reduce the diffusion of platinum into the grid wire (wire base metal) and increase the radiation capacity, it has already been proposed to provide an intermediate layer between the base metal and the coating.

Carbon, boron or silicon compounds of refractory metals have been proposed as materials or substances suitable for the production of the intermediate layer.

Such known methods have the following drawbacks.

That is, the discontinuity between the coating material and the base metal is a disadvantage in that a more or less rapid reaction occurs between a number of coating components, and the reaction products are activated by the evaporation products of the Th-W cathode. .

All methods of using carbide as an intermediate layer include
An additional drawback is that over time, the base metal and carbide make the lattice brittle.

In view of the above, an object of the present invention is to provide a grid electrode with high withstand voltage and slight reproducibility that does not cause high electron emission due to heat even when the thermal load on the grid is quite large, and at the same time has secondary electron emission. It is about providing.

According to the present invention, the above-mentioned grid electrode is characterized in that the grid electrode includes wires forming molybdenum or tungsten and an intermediate layer consisting of intermetallic bonds coated with a platinum layer, in which the intermetallic bonds are Zr and Pt. It consists of the following.

The above-mentioned grid electrode can be obtained, for example, by applying an intermetallic compound as a powder to the electrode and then sintering it.

In this case, by selecting the particle size of the powder it is possible to precisely determine the surface roughness and therefore the two
Secondary electron emission can be controlled as desired.

EXAMPLE Stoichiometric amounts of zirconium and platinum are melted together in vacuum to form the intermetallic compound ZrPt3.

A cured sample of this compound was
The hard material, e.g. tungsten carbide, is then ground to the desired particle size, e.g. 3μ, in a coated grinder.

Traditional transmitter tube grids made of molybdenum or tungsten wire are
It is fired in hydrogen at a temperature of 1000 to 1100°C.

The grid is then coated with ZrPt3, produced in powder form as described above, preferably in a layer thickness of 5 to 10 .mu.m.

The grid with this deposited intermediate layer is then fired at 1500-1600 DEG C. under vacuum or under protective gas for 20 minutes, so that the deposited intermediate layer is sintered while maintaining its roughness.

Subsequently, the grid with the sintered intermediate layer is electrolytically deposited with a platinum layer and then further calcined under vacuum at a temperature of 1500-1600 DEG C. in order to effect degassing.

After degassing, the grid is ready for use.

In grids made in this way, the adhesion between the intermediate layer and the base metal as well as between the intermediate layer and the platinum coating is greatly increased and, as a result, the high voltage resistance is also increased.

Furthermore, as mentioned above, the high adhesion properties also increase the mechanical robustness of the grid, so that it is possible to make very thin grids, for example mesh grid electrodes.

By selecting the grain size of the zrPt3 deposited on the grating, the grain size of the grating surface, and therefore also the secondary electron emission, can be varied reproducibly.

Furthermore, high specific radiation values are measured in such grids, high thermal loads are possible, and therefore high electrical loads can be tolerated.

Depending on the selected roughness of the grating surface, specific radiation values of 20 W/cm 2 to 29 W/cm 2 at 1525°K can be achieved.

This corresponds to 65% to 95% of the blackbody radiation.

At the same temperature, the specific primary electron emission will be about 1 μA/cm 2 .

This approximately corresponds to the driving conditions in an electric discharge vessel.

This primary electron emission does not increase even after prolonged thermal overload up to 1800°K.

Furthermore, in the grid electrode of the present invention, the intermediate layer ZrPt3
No reaction takes place between the platinum and the platinum of the coating layer (see Figure 1).

This is because ZrPt3 in the Zr-Pt system is a bond with the highest enthalpy of formation.

Platinum diffusion within the intermediate layer (ZrPt3) or core material (
Similarly, diffusion into tungsten (tungsten) or molybdenum does not occur.

This is because, on the one hand, the concentration difference between the covering layer (100Pt) and the intermediate layer (87% Pt) is slight, and on the other hand, the concentration difference between Pt and Z
This is because the bond enthalpy between r is several times larger than the bond enthalpy between platinum and tungsten or molybdenum.

Tantalum carbide is 1200 like other carbides.
It is impossible to sinter or hardly sinters at temperatures of .degree.

That is, sufficiently homogeneous and firm bonds between individual carbide particles cannot be achieved at this temperature.

ZrPr3, on the other hand, is sinterable. The tight bonding between the individual particles results in proper adhesion of the intermediate layer at the lattice core.

As can be seen from FIG. 2, none of the known grid electrodes yields good specific radiation values during their entire lifetime.

For this reason, the lattice electrode according to the invention has advantages over known ones in terms of lattice electron emission.

As can be seen from FIG. 3, the primary electron emission of the grid electrode according to the invention is 1 μA/cm 2 after about 7500 working hours.

In contrast, grid electrodes with a tantalum carbide interlayer exhibit a primary electron emission that is at least 100 times greater.

For this reason, the electrical discharge vessel with the electrodes of the invention guarantees a working life of up to 4000 working hours.

This is because before this time elapses, it is certain that 1μA/
This is because the primary electron emission of cm2 is not exceeded.

This is something that cannot be achieved with known grid electrodes under the same conditions.

Experiments have shown that with a known grid electrode of this type, a lattice primary electron emission of 125 times greater than in the grid electrode according to the invention was obtained after the course of the TaC+Pt=TaPt+C reaction at half the heat load.

BRIEF DESCRIPTION OF THE DRAWINGS: FIG. 1 shows the combination of compositions of a grid electrode according to the invention;
FIG. 2 is a diagram showing a comparison over time of the specific radiation values of a grid electrode according to the present invention and a known grid electrode, and FIG. 3 is a diagram showing the progress of lattice primary electron emission over time.

Claims (1)

[Claims] 1. A grid electrode comprising wires forming molybdenum or tungsten and an intermediate layer of intermetallic bonds coated with a layer of platinum, characterized in that the intermetallic bonds consist of Zr and pt.