DE1021482B - Process for the production of an oxide cathode for low-pressure discharge lamps and other gas-filled electrical discharge tubes - Google Patents

Description

Process for the production of an oxide cathode for low-pressure discharge lamps and other gas-filled electric discharge tubes. The invention relates to a. Process for the production of an oxide cathade for low-pressure discharge lamps and other gas-filled electrical discharge tubes whose activating substance consists of a. Mixture of barium oxide, strontium oxide and calcium oxide exists, which in the formation the cathode by decomposition of the corresponding used as the starting substance Erda: lkalika.rbonate arise as a result of heating.

The aforementioned known oxide cathodes are generally thereby manufactured by applying the carbonate of the alkaline earth metals to the cathode core, the oxide is generated by heating and then the cathode is activated.

To decompose the alkaline earth metal: 'oil carbon: ate becomes a considerable Amount of heat required. The decomposition temperature is above 1000 ° C, e.g. B. at 1100 ° C. Glowing at such high temperatures has a harmful effect on the remaining electrodes of the tube. If, on the other hand, which is often the case, that Not glowing, and decomposing sufficiently during one; carried out for a long time will so. carbonates remain, especially in the cathodes of fluorescent lamps which then only decompose in the course of operation :. This will not only the operation, the cathode has a detrimental effect, but it arises in the tube, z. B. in the fluorescent lamp, circulating carbon dioxide, which the luminosity of the Adversely affected tube.

The above disadvantages are achieved according to the invention. a manufacturing process verm4-eden, in the case of the alkaline earth carbonate mixture for the cathode type mentioned at the beginning an inactive additive consisting of at least one oxide of the following Elements: titanium, germanium, aluminum and other elements of group III of the periodic Systems, especially the rare ones: earth metals; too is set in such a Amount because: ß the total amount of additional oxides in the finished cathode at most equal to the amount of the least. Amount of Erda used: lkalim-etalloxyds and the cathode by heating to a temperature below 1000 ° C, preferably to 800 to 900 ° C, is formed.

The invention is based on the knowledge that it is advantageous if: the cathode mass is mixed with oxides, which reduce the emission to a minimum Adversely affect the size, but allow. To reduce the formation temperature, without any harmful carbonic acid being released afterwards.

It has been found that such additives are the oxides of the elements of group III of the periodic system and / or oxides of the a, mphoteric elements of Group IV of the Periodic Table with an atomic weight; greater than 30, however at most with an atomic weight of 90 are suitable. It turned out to be particularly suitable the Ti 02, the Ge 02 and the aluminum oxide. These oxides lower the decomposition temperature der- alkaline earth metal carbonates. The cause of this phenomenon is likely to be that connections arise between the cathode mass and between these substances and the formation temperature of these compounds depends on the amount of heat in. which is to be fed to the reaction from the outside in order to bring about the decomposition.

As a result, the temperature necessary to decompose the carbonates is significantly below 1000 ° C. Depending on the quantity and nature of the Additives will decompose! advantageous z. B. between 800 and 900 ° C before yourself: go.

The total amount of additives should be used to ensure a good one Em @ issioni the amount of the oxide of the alkaline earth metal oxide used in the smallest amount not exceed.

This can be done to reduce the decomposition temperature of the carbonates Add oxides used individually or at the same time to several. the The best results of the process have been achieved with cathodes in which the Mo @ oil ratio between Ba0, SrO, Ca0 was 2: 1: 2.

The oxide cathode according to the invention is particularly advantageous for gas discharge tubes, z. B. fluorescent lamps, but can also be used in vacuum tubes. The special one The advantage is that, as I said, the carbonates applied to the cathode are rapidly and completely decomposed at low temperature and in operation, the tubes, no carbonic acid is released, so this gas is particularly common in fluorescent lamps no longer occurs.

Claims (2)

PATENT CLAIMS: 1. Process for the manufacture of an oxide cathode for Low pressure discharge, unigslampen and other gas-filled electric discharge tubes, its activating substance from a mixture of barium oxide, strontium oxide and calcium oxide which occurs during the formation of the cathode by decomposition as the starting substance The corresponding alkaline earth carbonates used arise as a result of heating, thereby characterized in that the alkaline earth carbonate dust is a non-active additive, consisting of at least one oxide of the following elements: titanium, germanium, aluminum and other elements of group III of the periodic table, especially the rare ones Earth metals, is added in such an amount that the total amount of the additional oxides in the fully formed cathode is at most equal to the amount in the smallest Amount used alkaline earth metal oxide and the cathode by heating to one Temperature below 1000 ° C, preferably to 800 to 90d ° C, is formed. 2. The method according to claim 1, characterized in that the barium, strontium and calcium oxides used have a molar ratio of 2: 1: 2. Considered publications: German Patent Nos. 540 618, 597 580, 696 506; French Patent No. 966 907; British Patent No. 182,817; U.S. Patent No. 2,547,869; Technical-scientific treatises of the Osram Gesellschaft, Vol. 5, 1943, pp. 311 to 332. Older rights cited: German Patent No. 860 384.