DE889807C - Electrical capacitor, the dielectric of which consists of conversion products of the occupancy - Google Patents

Description

Electrical capacitor, the dielectric of which is made up of reaction products the Belecruncr consists in the construction of temperature-resistant electrical capacitors, whose dielectric consists of non-conductive metal compounds, one creates the desired: metal compounds by converting the surface of the capacitor coating, because as a result: the dielectric is simply more uniform in layer form Strength and sufficient homogeneity can be produced. Plus you have it in .the hand, by forming thinner or thicker layers, any wishes with regard to the breakdown voltage, the capacity yield and the like. more to meet. It was already discussed elsewhere that it is appropriate to use the .dielectric To produce layers in the manner of corrosion-resistant coatings: d. H. the implementation the covering surface within an electrolytic process and to bring such baths into use, the so-called current-dependent layers generate, in which the product electricity times time is decisive for, .the generated Layer thickness is.

This production method is particularly important because Layers produced by other methods are usually thinner and thereby make one require large rejects in production. The explanation for this is presumably the following.

Metals are used for the covering that are not roo ° / o pure, but small foreign components contain. These foreign components are distributed in the occupancy and can also be on the surface of the occupancy be embedded. If you now turn the surface of the covering into a non-conductive one Product around, then arise in the places where foreign components are stored are, no dielectric conversion layers, because the baths used are natural are matched to the covering metal and not to the foreign components. the stored foreign components thus form a conductive bridge between the parent metal of the assignment and the opposite assignment of the capacitor, which is thus is short-circuited. Since practically always, even with very pure covering metals, must be expected with foreign inclusions, these imperfections can only be then effectively avoid if the dielectric layer is formed so strong that that their strength is at least as great as the diameter of the largest embedded Foreign constituents. These are then, as it were, from the non-conductive layer undergrowth and isolated from the parent metal of the occupancy. Because depending on the Purity content of the starting metal used for the occupancy a certain Conclusion about the largest grain size of the trapped foreign matter can, this inevitably results in a minimum thickness for the dielectric layer.

It was now, in particular on the basis of so-called aluminum oxide capacitors, d. H. Capacitors, their allocation from aluminum and their dielectric from This coating consists of grown aluminum oxide, found that the breakdown voltage such capacitors is relatively small and at times fluctuates strongly. There were to improve the penetration values and thereby the scope To enlarge these capacitors, investigations made the following result had.

Since aluminum oxide as a dielectric or insulating body has a relatively good breakdown voltage, the low breakdown values found on the finished capacitors must be attributed to the pores in the oxide layer, which are normally filled with air. According to the investigations by P as ch en, the breakdown voltage between flat electrodes decreases to a minimum with the falling product of the flashover width and the pressure of the gas filling, and surprisingly increases to an unusual extent at very low values of the product. With air as the gas filling, at a pressure of 76o mm of mercury column there is a minimum flashover voltage of a little over 300 V with a throw of 7.2 u. This means, however, that the insulating, the conversion layers are used in this order of magnitude that even the smallest changes in the layer thickness can have a considerable influence on the breakdown voltage, which means that both the low breakdown voltage of such capacitors and their large ones Scatter can be explained. At the same time, this superposition also means that it is beneficial to improve the breakdown behavior if one chooses the pitch, ie the pore length or the layer thickness of the dielectric, as far as possible below the critical value from the product pressure of the gas filling and pitch.

This and the condition described at the beginning with regard to the layer thickness result now united, the rule to dielectric capacitors with inorganic Produce dielectric. According to the invention, the dielectric conversion layers must then at least as strong as the largest foreign matter trapped on the surface, however, at most be so strong that the product from the possibly by additional Measures shortened pore length of this layer and the pressure of its filling gas below , the critical value for this filling gas remains. So while on the one hand The aim is to make the layer as strong as possible in order to avoid stored On the other hand, there is a need to clearly isolate foreign components to make the layer as thin as possible, because this increases the breakdown voltage. The rule according to the characteristic of the invention places between these two extremes represents a compromise and gives a lower and an upper limit for the layer thickness on,: which, however, are often very close to each other.

It can now happen that when determining the minimum layer thickness a thickness is found which is greater than the thickness of the layer after the second Part of the flagged rule is required. In this case there is in itself a Capacitor cannot be produced or its breakdown voltage is in proportion very inconvenient for the effort. The rule according to the invention also gives one for this Solution by then shortening the pore length through additional measures. On the assumption that the pressure of the filling gas is constant, the shortening calls the pore length results in a reduction in the product pressure times throw distance, whereby a better breakdown voltage is established. The shortening of the pore length can, for example, be caused by the fact that they are at least partially with fillers of an organic or inorganic nature by impregnation or deposition solid body fills. The type of application of the counter occupancy can also have an influence be. If this z. B. formed by condensing metal vapor, then you can it achieve that the pores are partially steamed on the inner wall, whereby the true pore length also changes. So although .the dielectric layer one corresponding to the normal pressure of a certain filling gas, for example air If the stench is too large, changing the pore length can make it too strong Layer nevertheless the breakdown voltage of the layer can be improved. One can also in proceed the way "that you kept several appropriately thin dielectric layers superimposed so that long pores are not continuous but in the different parts of the dielectric with different pore parts correspondingly smaller length are available. To clearly identify the individual layers separate with regard to their pores and avoid the formation of continuous pores, it can be useful to assign a blind occupancy to each layer produced provided, which only acts as an equipotential surface.

Furthermore, in such a case, you can also use a different gas filling, z. B. nitrogen, carbonic acid, oxygen, because the different gases have their minima at different points on the diagram. This is not enough either off, then you can operate the condenser at a more or less high vacuum, because this also makes the product pressure times the pore length smaller.

In the case of aluminum oxide capacitors, in those of an aluminum with 99.81 / o purity is assumed, inclusions of foreign constituents may under certain circumstances with a diameter of 5, u be included. According to the characteristic of the invention The dielectric layer must therefore have a minimum thickness of 5 u. if the condenser is still not operated in a protective gas atmosphere, in the pores .there is air in the oxide layer, then the lowest breakdown voltage is obtained at atmospheric pressure of the enclosed air with a layer thickness of 7.2, u. So with such a capacitor you become. the layer expediently as possible near 5, u, maybe at 5.5 to 6, u, train to both a flawless Isolation as well as to get the most favorable breakdown value with this isolation.

In another example, it would be made of less pure aluminum assumed a diameter of included components of, for example, straight 7, u result, then one would have to avoid the capacitor straight .at the minimum To have to operate breakdown voltage, install it vacuum-tight and for example operate at a pressure of 50 mm of mercury, which increases the breakdown voltage around i oo 1 / o.

Claims (3)

PATENT CLAIMS: i. Electrical capacitor, its dielectric from non-conductive reaction products formed on the surface of a coating consists, in particular capacitor with aluminum coating and aluminum oxide as a dielectric, characterized in that the dielectric conversion layer is at least as thick like the largest foreign matter enclosed on the surface, however at most so strong that the product can be removed by additional measures shortened pore length .this layer and the pressure of its filling gas below the remains critical for this gas. 2. Electrical capacitor according to claims, , characterized in that in arrangements where .denen the minimum layer thickness is greater than the maximum layer thickness, the pore length by additional measures, for example by partially filling with fillers such as impregnating agents, embedded or separated solid bodies and the like, or by superimposing them different, correspondingly thin insulating layers with or without intervening Blind assignments is shortened. 3. Electrical capacitor according to claim i, .due to this characterized in that in arrangements in which the minimum layer thickness is greater than the maximum layer thickness is when a gas with a higher critical value is used or that the condenser is operated at negative pressure.