US2244771A - Composite conductor and contact between conductors - Google Patents

Description

June 10, 1941.

H. FIGOUR COMPOSITE CONDUCTOR AND CONTACT BETWEEN CONDUCTORS Fi led Aug. '2, 19:59

Fig. 4.

/n ventor H'gaur fltt'ornez/ Patented June 10, 1941 COMPOSITE CONDUCTOR AND CONTACT BETWEEN CONDUCTORS Henri Figour, Paris, France, assignor to International Standard Electric Corporation, New

York, N. Y.

Application August 2, 1939, Serial No. 287,888 In France August It, 1938 6 Claims.

The present invention relates to composite conductors and more particularly to means for ensuring contact between successive elements comprising these conductors, or between two conductor elements with temporary contact.

In particular, the object oi the invention is to provide composite conductors in which a satisfactory electrical contact is ensured in a simple manner and having no appreciable danger of deterioration of the component conducting materials. w

In order to ensure contact between the conductor and/or semi-conductor elements, for example, between a conductor conveying the current and the surface of the substance forming an arrester layer in a dry rectifier, precautions must be taken not to have an excessive contact resistance. Such contact is normally ensured by pressure on the arrester layer, or by volatilisation in vacuo of any metal which is deposited on the arrester layer, or by pulverisa'tion of a metal or an alloy. These methods, however, have considerable drawbacks. For example, in the case in which the contact is ensured by pressure, the pressure necessary in order to obtain a satisfactory contact usually involves dangerous mechanical tensions. In the case in which the contact is ensured by metallic deposit on a semi-conducting layer of an additional metallic layer by 'volatilisation in vacuo this layer must be as thin as Possible so as to prevent mechanical tensions which might involve separation at the time of the pressing on this layer of the second conductor. If this layer is very thin and forms a resistive film, its ohmic resistance in the direction parallel to the surface of the first element is relatively high and it is necessary that the contact ensuring the junction to the external circuit may be made on the largest possible surface, which involves relatively high pressures which are also capable of ageing or deteriorating the resultant composite conductor.

The main object of the invention is to Provide means "for avoiding. these excessive pressures.

In accordance with certain characteristics of the invention, a composite conductor comprising at least two layers of conducting or semi-conducting elements, is characterised in this, that one of-the two elements is of a spongy structure or has a rough surface, the particles of which are microscopic and irregularly arranged, the surface portion composed of these particles having the crushing characteristics of a spongy structure when pressed against a hard surface.

Two layers, one of which has the above-mentioned characteristics, may then be assembled so as to ensure a satisfactory contact by means of reduced pressure which crushes the spongy struc.- tures but does not risk causing deterioration or premature ageing of the resultant product.

The invention in particular provides, in accordance with certain characteristics. devices conducting the electrical current uni-directiom ally in which a metallic conducting layer, covered with a semi-conducting layer forming a current arrester layer, is pressed against a conducting layer made spongy either superficially or deeply, as mentioned above.

In accordance with other characteristics, the invention provides a method of manufacturing uni-directional current-conducting elements, comprising the normal operations for forming on a base conducting member a semi-conducting layer serving as arrester layer, the preparation of a conducting plate or element for rendering the latter of spongy structure on the surface or in the mass, and the application of this spongy element against the semi-conducting layer by means of a low pressure. In order to render the conducting element spongy, this element may be chemically or electro-chemically treated, and this chemical or electro-chemical attack may or may not be preceded by a suitable mechanical or thermic treatment.

The invention will be described in more detail in relation to the attached drawing in which:

Figure 1 shows in cross-section a uni-directional device such as a dry rectifier, and

Figures 2, 3 and 4 show in section spongy structures which may be employed in the device of Figure 1.

Figure 1 to which I will now refer represents, by way of embodiment of a device employing characteristics of the invention, a d y rectifier element comprising a metallic layer I, for example, of copper; covered with a semiconducting arrester layer 2, for; example, a layer of copper oxide, covered in turn with a film of vapourised metal 3, and a conducting layer 6. The layer 4 consists, in accordance with certain characteristics of the invention, of a metal sheet or member having such a structure as those shown in Figures 2, 3 or 4. By the use of this sheet, good contact may be obtained between the film of vapourised metal and the sheet 4 with a very low pressure, Without involving the ohmic resistance in the direction parallel to the layer of oxide.

The various spongy structures considered in the invention are indicated schematically in cross-section in Figures 2, 3 and 4. Figure 2 shows a structure which has already been made superficially spongy; the treatment of the sheet has been such that a chemical or electrochemical or other attack has caused the appearance on this sheet of an irregular superficial layer of microscopic structure, the particles of which are distributed at random and which offers such crushing facility that a slight pressure against any conducting surface flattens the uneven portions, so as to form a conducting layer modelled on this conducting surface with which it makes contact at all points.

In Figure 3, this superficial layer has been obtained for a substance of natural crystalline structure, but the crystals of the substance have no particular desired orientation.

In Figure 4, the attack has been accomplished in the whole mass of the substance and thus it is an actual spongy structure. The crushing properties of the two latter layers are the same as those of the layer of Figure 2.

The means for manufacturing such structures may consist of a chemical or electro-chemical treatment which may or may not be preceded by a mechanical or thermic treatment of the substance.

Nearly all the usual metals such as aluminium, silver, nickel, lead and others are capable of giving such structures.

The baths employed, whether acid or alkaline, may be of various compositions according to the nature of the metal, its degree of purity, and in accordance with the nature of the desired spongy structure.

By way of example, a spongy surface may be obtained by chemically attacking a sheet of aluminium in the following bath:

Water cubic centimeters 555 Sulphuric acid do 65 Nitric acid do 65 Ammonium chloride do 35 The sheet of aluminium will be plunged in the bath at the temperature of 70 C. for about five minutes in order to obtain a suitable spongy structure.

By increasing the proportions of nitric acid and decreasing that of ammonium chloride the structure becomes coarser and the attack is deep for the greater part.

A spongy structure can be obtained on a sheet of silver by attacking it electro-chemically, in a bath of the following composition:

Water grams 960 Nitric acid cubic centimeters 30 Sulphuric acid -do The sheet of silver constituting the anode of the cell, the cathode being constituted of any metal, or a plate of gas carbon.

This treatment may be preceded by annealing at 600 for one hour, so as to start with-a metal which is always in the same physical condition. This heat treatment may be followed by a carding of the surface by means of metallic cards so as to create a differential cold hammering of the surface which, with preferential points of attack favours the depth of etching,

It is clear that the two treatments have only been given by way of example, and that various the invention is not limited to these and that any composite conductor comprising layers of conducting or semi-conducting substances of which the contact must be ensured in a satisfactory manner may employ,-for one at least of the layers, a layer of which the treatment or superficial structure has been rendered spongy or rough in the manner described so as to ensure the desired contact.

It is also clear that the invention is not limited to the permanent examples of conducting'and/or semi-conducting layers, one of which has been made spongy before assembly, but that such layers may be employed to ensure better temporary contacts such as contacts of electric relays, or the like.

The invention is also capable of numerous modifications and adaptations which will be clear to one skilled in the art without departing from the scope of the invention.

What is claimed is:

1. A conducting element comprising at least two conducting layers, one of said layers having an easily crushed spongy coating thereon, said coating and the surface of said other layer being in contact with each other, and means for pressing said two layers together at a pressure sufficient to crush the spongy surface.

2. A uni-directional current conducting element comprising a metallic base member, a semiconductive coating thereon, a conducting mem her having a spongy irregular surface, said surface and coating being in contact with each other, and means for pressing said conducting member against said coating at a pressure sufficient to crush the spongy surface.

3. The method of manufacturing a unidirectional current conducting element which comprises applying a semi-conductive coating to a base member, toughening the surface of a conductive member, said surface being spongy after roughening, and pressing said surface against said coating at a pressure sufficient to crush the spongy surface.

4. The method according to claim 3 wherein said surface is roughened by etching.

5. The method of manufacturing a unidirectional current conducting element which comprises applying a semi-conductive coating to a base member, annealing a sheet of aluminum, carding a surface of said sheet, roughening the surface thereof by immersing said sheet in a solution comprising by volume 555 partswater, parts sulphuric acid, 65 parts nitric acid, and 35 parts ammonium chloride at 0., and pressing said surface against said coating.

6. The method of manufacturing a unidirectional current conducting element which comprises applying -a semi-conductive coating

Images