DE2303587C3 - Reed switch and process for its manufacture - Google Patents

Description

The invention relates to a reed or reed switch with an encapsulated piston, two in the Piston wall sealed supply lines and two interacting rhodium contacts. $ 3

Conventional reed switches (Fig. 1) have one encapsulated glass bulb 1, two usually made of Fe-Ni-Permalloy supply lines 2 and on whose inner ends have arranged contacts 3, which are normally plated by electroplating or plating of a precious metal.

Generally rhodium is used as this noble metal because it is suitable for use as a contact material well suited for reed switches. However, rhodium has the disadvantage that the contact resistance very strong between the contacts after a comparatively small number of actuations increases. Although there are several possible reasons for this, it is primarily due to rhodium its own surface adsorption and its catalytic effect. When contacts are made Rhodium, the surfaces of which have adsorbed various organic substances and other impurities, opening and closing several times are due to the impact energy and the catalytic effect of Rhodium polymers formed, which cause an increase in contact resistance.

As a result, it is desirable to have a novel method for surface treatment of the contacts develop by which the catalytic effect of rhodium can be eliminated, so that reliable Contacts are formed which are free from any abnormal increase in contact resistance.

The invention is therefore based on the object of a reed switch or reed switch with rhodium contacts and to develop a process for its production that is also comparatively high Closing or opening number no increased contact

45

50

55

65

has resistance

According to the invention, this object is achieved by a new surface treatment solved which is characterized by the fact that the rhodium contacts a The reed switch can be oxidized to form extremely thin films of rhodium oxide. To this end the contacts coated with thin rhodium coatings are kept in an oxygen-containing system for 3 to 15 minutes Atmosphere heated to a temperature of 480 ° C ± 100 ° C. Surprisingly, it has been shown that the resulting thin rhodium oxide films largely prevent the adsorption of impurities and reduce the catalytic effect of the metallic rhodium. The following are preferred Embodiments of the invention in comparison to the prior art with reference to the drawing explained. It shows

F i g. 1 is a schematic representation of a conventional reed switch,

F i g. 2 is a graphical representation for the purpose of illustration the change in the contact resistance of a known reed switch with rhodium contacts,

F i g. 3 is a graph showing the change in contact resistance in accordance with the invention Rhodium contacts produced by a process,

4 shows a schematic representation of a used to illustrate the advantages of the invention Experimental device and

F i g. Fig. 5 is a graph showing the relationship between the deterioration the contact resistance and the firing temperature.

As mentioned, the contacts of reed switches are produced according to the invention by plating or electroplating rhodium onto the leads of the reed switch and then oxidizing the applied rhodium under the above-mentioned conditions in an oxygen-containing atmosphere. To compare the change in contact resistance in known rhodium contacts and rhodium contacts which, according to the invention, have been provided with thin coatings of rhodium oxide, the following experiment is carried out: According to FIG. 4, a bowl-shaped container or a shell 9 with leads 7 for reed switches, the contacts of which were produced by the method according to the invention, and another bowl-shaped container or a shell 9 'with leads 7', which have conventional rhodium-plated contacts, is placed on a perforated one The bottom 6 of an encapsulated vessel 4 is placed on top. A certain amount of benzene 5 is poured into the lower part of the vessel 4 and is sucked off by means of a vacuum pump (not shown) connected to a suction line 8. After 24 hours, the supply lines 7 and 7 'are removed from the vessel 4 and each used to produce reed switches, on which service life tests are then carried out. According to FIG. 2, the contact resistance of the conventional contacts increases already after a comparatively small number of actuations, while the contact resistance of the contacts treated according to the invention according to FIG. 3 changed only very slightly for a significantly larger number of actuations (namely 10 ^{6 actuations).}

Examination under the microscope shows that polymers form at the known contacts, as they absorb the benzene, which is then due to the impact energy of the contacts and the catalytic Effect of rhodium converted to polymers

will. On the contacts produced according to the invention on the other hand, no polymer formation whatsoever can be observed.

F i g. 5 illustrates a preferred range of the oxidation temperature, the ordinate indicating the percentage of ^{contacts rejected due to excessive increase in contact resistance after 10 7} actuations, i.e. a typical number of actuation cycles in a life test, while the abscissa indicates the burning or oxidation temperature for the plated ones Rhodium contacts are applied as shown in FIG. 5, the percentage of contacts rejected is practically zero at a firing temperature of about 380 ° C to about 580 ° C, while it increases rapidly at temperatures below 380 ° C and above 580 ° C. This is due to the fact that the reaction at Temperatures below 380 ° C is insufficient, while at temperatures above 580 ° C the surface layer of the rhodium is subject to recrystallization under the influence of heat or the diffusion of the plated or electroplated metal occurs

In summary, the invention thus creates an improved reed switch, its contacts consist of rhodium oxide. These contacts are made by placing rhodium on the The leads of the reed switch are plated or galvanized and then the surface layers the plated rhodium contacts by heating for 3 to 15 minutes at 380 to 580 ° C in one oxygenated atmosphere.

For this purpose 3 sheets of drawings

Claims (5)

Patent claims: 1. Reed switch with an encapsulated piston, two feed lines sealed into the piston wall and two interacting rhodium contacts, characterized in that that the contacts (3) are provided with a thin layer of rhodium oxide. Z reed switch according to claim 1, characterized in that the contacts (3) have a plated or have galvanized rhodium layer and a thin rhodium oxide layer applied over it. 3. A method for producing a reed switch, characterized in that on lead pieces Rhodium contacts are formed that the rhodium contacts are oxidized and that the Leads with the oxidized rhodium contacts are sealed in an encapsulated flask. 4. The method according to claim 3, characterized in that that each contact with rhodium to oxidize in an oxygen-containing atmosphere 3 to 15 min is heated to a temperature of 380 to 580 ° C for a long time. 5. The method according to claim 3, characterized in that the rhodium contacts by plating or electroplating of rhodium can be formed on the leads.