Aluminum capacitor plate for electrolytic capacitor and process for making the same

DETAILED DESCRIPTION The present invention aims at solving the problems pointed out with respect to the known capacitor plates and the known process of producing the same, and has for its object to provide an aluminum capacitor plate having an enhanced capacitance, and a process for producing such capacitor plates.
Other objects and advantages of the present invention will become more apparent from the following detailed description, when taken in conjunction with the accompanying drawings which show, for the purpose of illustration only, one embodiment in accordance with the present invenion.
According to the present invention there is provided an aluminum capacitor plate for use in an electrolytic capacitor, which plate comprises: a layer of a sponge-like structure having a predetermined thickness, the layer including a plurality of projections extending inward and outward with respect thereto, the projections individually having heights of not higher than 1 .
mu.
m on average; and a titanium film having accumulated titanium particles each including projections having heights of not higher than 1 .
mu.
m, wherein the titanium particles are unevenly distributed in the film with a number of pores interposed therebetween.
The layer of sponge-like structure can be produced by controlling the etching conditions, in which a mixture of HCl and one or more solutions selected from HNO.
sub.
3, H.
sub.
3 PO.
sub.
4 and H.
sub.
2 SO.
sub.
4 is used as an electrolyte.
The titanium film is preferably produced by more than two steps of vapor-plating; if the film having 1 .
mu.
m or more is produced by a single step the temperature of the aluminum plate is likely to rise by the influences of the latent heat generated when the titanium condenses into particles and of the radiation from the source of heat for evaporating titanium.
While the vapor-plating is in process the aluminum plate is cooled in a cooling vessel but nevertheless its temperature normally reaches 300.
degree.
C.
or more.
Because of the high temperature of the aluminum plate the titanium particles tend to become fluid, and make a flat film