US2340867A - High resistance element and method of producing the same - Google Patents

Description

Patented Feb. 8, 1944 HIGH RESISTANCE ELEMENT AND METHOD OF PRODUCING THE SAME Reginald S. Dean, Salt Lake City, Utah, assignor to Chicago Development Company, Chicago, 111., a corporation of Illinois Ni Drawing. Application March 8, 1940, Serial No. 322,929

4 Claims.

This invention relates to electrical resistances, especially to resistances of very high order, together with processes for producing such resistances.

The object of the invention is to make available to the electrical industry, in practical commercial form, very much higher resistances than have been heretofore available.

I have foundthat electrolytic manganese in thin deposits possesses an electrical resistance of 600 to 2000 michroms/cm. depending on the conditions of deposition and subsequent treatment. I have further found that the high resistance is due to the fact that thin deposits of manganese are in the alpha form, and are very fine crystal size.

While strips or shapes fashioned from cathode sheets of electrolytic manganese may be used and are suitable for many purposes, I have found that the desired form can be more easily obtained by depositing the manganese in a thin film on a preformed cathode. The manganese and cathode may be separated mechanically, or the cathode may be made either of low melting metal which can be removed by melting or of a metal such as aluminum which can be removed with a solvent such as caustic which does not attack the manganese deposit.

As an example of my invention, I deposit electrolytic manganese from a solution of manganese and ammonium sulphate in a diaphragm cell using a lead anode and a cathode in the form of a helix of a eutectic alloy of lead and tin, viz., about 37% lead and 63% tin. A cathode strip of such alloy is formed .02 inch wide and .02 inch thick. The strip may be extruded, or formed in any other suitable way. The strip is then wound on a core of non-conductor, such as synthetic resin. The wound core is placed in the cathode compartment of the cell and manganese is deposited at 20 amperes per square foot to a thickness of .01 inch. The core and plated cathode are now removed, and after washing and drying the whole is placed in an oven at 200 degrees C. or above the melting point of the eutectic mixture of lead and tin. When the lead-tin mixture has become molten, the core is forced out and replaced with another slightly larger core which just supports the manganese coil which is in the form of a filamentary body.

In another example of my invention, I deposit manganese as before on a helix cut from aluminum foil. After depositing .01 inch of manganese, I dry the plated cathode and cement it with the manganese side down on an alkali resistant plastic. I then treat the whole with dilute caustic so as to dissolve the aluminum foil and leave a helix of manganese cemented to the plastic block.

Resistances produced in accordance with the above examples may be employed without further treatment, but preferably they are allowed to stand an appreciable length of time, or may be heated for several hours at a suitable temperature, to bring them into a stable condition. As deposited, the manganese appears to contain an appreciable proportion of manganese other than alpha manganese. This is apparently beta manganese, and the relative proportion seems to be greater as the thickness of the deposit increases. On standing for several days at ordinary room temperature, most, if not all, of the manganese changes to the alpha form. Heating for several hours at about degrees C. will also result in stabilization. A higher or lower temperature may also be used, but the degree and length of heating may have an effect upon crystal growth with the effect of modifying the resistance somewhat. Properly controlled, it may at times be desirable to carry out the heat treatment for the purpose of modifying the resistance, since once it has been stabilized, there will be very little if any further change during ordinary use. Thus suitably treated resistances are constant and highly satisfactory.

A number of variations may be followed in the method of producing the resistances, and also in the form which the final resistance material assumes. The cathode may be of various types, so long as its removal is made possible. In one form which the invention may take, the cathode may be left in position.

As examples, thin layers of separating substances, such as graphite and the like, may be provided between the cathode and electrolytic deposit to facilitate mechanical separation. I have found, also, that graphite may beplaced upon a non-conducting surface and electrically coupled to form a cathode. The manganese may be deposited in a very thin film directly upon the graphite carbon, and the product so produced may be used as a resistance without further treatment. This product has a resistance value of the order of that found in the so-called lead pencil mark resistance, but is much more stable and resistant to change due to atmospheric conditions.

Resistances of my invention may have various forms. So-called slide wire resistances of high resistivity may be produced. Alpha manganese may be provided in accordance with my invention in various cross sections and various shapes, depending upon the resistance desired per unit length, and the form of device of which it forms.

a part.

The resistance per unit length depends upon the character of the manganese and the cross section thereof. The specific resistance of alpha manganese will in general vary between about 600 and 2000 microsxns/cm with the average at about 750 to 1000 microhms/cmfi. The specific resistance depends at least in part upon the thinness of the film, the speed of deposit, and the time and temperature of stabilization. All of these factors are readily controllable. The examples given above produce resistances having several ohms per linear foot, which is much higher than usually available in commercial resistance elements. Resistances as high as 1000 ohms per linear foot, with suitable precautions, may, however, be produced. Thus it will be seen that I may produce electrical resistances having extreme ranges of resistances, running from a fraction of an ohm per linear foot to as much as 1000 ohms per linear foot, or even higher.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. An electrical resistance having high resistivity per linear dimension, said resistance com 5 prising a resistance element in the form of a filal0 deposited filamentary body of pure manganese and supporting means therefor.

3. An electrical resistance comprising a nonconducting support member, a very thin layer of graphite on said non-conducting support, and

15 a thin layer of alpha manganese on said graphite, said manganese being electrolytically deposited on said graphite as a cathode.

4. The method of producing an electrical resistance element which comprises providing a 20 cathode having a shape adapted for use as a resistance element, introducing said cathode into an electrolytic cell containing a solution of a manganese salt dispersed in an electrolyte, plating a thin deposit of manganese on said pre- 25 formed cathode, mounting the manganese deposit upon a support, and removing the cathode.

REGINALD S. DEAN.