Method for the production of extraction grids for ion generation and grids produced according to said method

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For the production of an extraction grid, a lattice structure is first produced, and is formed by two sets of metal, in particular molybdenum or tungsten, wires or filaments, disposed as illustrated in FIGS.
2 and 3.
More particularly, a first set of wires 3 parallel to each other is provided, together with a second set of wires 5 disposed with an orientation of 90.
degree.
with respect to the wires 3, and parallel to each other.
The wires 3 and 5 are spaced apart by an amount d, and are connected to form the grid by means of the boron which will be deposited on their surfaces according to the technique described below.
This disposition of wires is introduced into a high-vacuum chamber 7 of an installation of the type schematically shown in FIG.
6.
The wires prepared in this way are connected to electrical contacts, in such a way that it is possible to make an electrical current flow through the wires to heat them by the Joule effect, in order to perform the deposition by a pyrolytic method of the boron on the surfaces of the wires.
The installation in FIG.
6 comprises, in addition to the high-vacuum chamber 7, a vacuum pump 9, an inert gas container 11, a hydrogen container 13, and a container 15 for the boron trichloride.
The three containers 11, 13 and 15 are connected by flow passages to the chamber 7 with the interposition of flowmeters 17, 19 and 21 and a mixing chamber 23.
A means 25 for the removal of oxygen and a means 27 for the elimination of moisture are also provided in the hydrogen supply line from the reservoir 13.
The process for the deposition of the boron on the structure formed by the wires 3 and 5 is as follows.
The chamber 7 is initially evacuated by means of the high-vacuum pump 9, and is then flushed with the inert gas, for example argon, contained in the reservoir 11.
After the flushing, hydrogen is introduced into the chamber 7, and the wires are heated by the Joule effect, by making a suitable electrical current pass through them, to a temperature of 930