US1782909A - Apparatus for the electrodeposition of iron - Google Patents

Description

NOV. R. D. PIKE I APPARATUS FOR THE ELECTRODEPOSITION 9F IRON Filed July 20, 1926 3` Smets-Sheet 1 23\ H Il f', aga uw, n, mw H HI lan, m .n n l 28 -wg I .1. A, l. INVENTOR.

A TTORNEYS.

Nov. 2.5, 1930. R. D. PIKE 1,782,909

APPARA'IIUS I'OR THE ELECTRODEPOSITION OF IRON Filed July 2o, 192e. :s sheets-snare; 2

ATTORNEYS.

Patented Nov. 25, `1930 i l UNITED s'ri-srrr-:s PATENr OFFICE Application liled July 20, .1926. Serial No. 123,626. I

This invention relates to an improved tallic deposit,"free from trees or snags, can be method of electro-.deposition of iron. It has continued for much longer periods of time particular reference 'to an improvement in and with higher current densities, resulting deposition of iron from solutions in electroin greater thicknesses of the deposit, than is lytic cells with insoluble anodes, but certain, possible by present known methods. It is 55 features of my invention are also applicable also likely that the rubber brush, or wiper, has to deposition 'of iron in cells with soluble the further benefcialeli'ect of smoothing out iron anodes.` inequalities of hydrogenion concentration in Up to the present time no commercially .the thin layer of catholyte solution which adsuccessful method has been devised for depheres to the deposit as it emerges from the e0 osition of iron in electrolytic cells with insolution in the cell, and that this, in turn, prosoluble anodes; nor have means hitherto been motes the smoothnessof deposits by eliminatknown for making thick deposits of 1A: inch ing dierences of hydrogen concentration in or more of substantially homogeneous elecadjoining areas of the metal. The wiperI l5 trolytic iron with a relatively smooth surface also serves to remove minute bubbles of hy- 65 at current densities much Vin excess of drogen. I have discovered that if thev suramperes per square foot, whether in cells with vface of the rotating deposit be rubbed with insoluble or soluble anodes. soft iron strips applied under gentle pressure',

In prior known methods for'making plates an even better resultqis attained than with l0 of electrolytic iron from solutions in cells rubber, because the latter tends to contami- 70 with insoluble anodes, hydrogen -dep'osition nate the deposit to some extent with Gand S, on the cathode causes the growth of trees or whileno contamination results from the use snags of iron which pierce the diaphragms, of soft pure iron strips. In,using the pure causing their destruction when the cathode iron strips I find the best position for placing is lifted from theV cell. This renders the meth- Athem is on the down-moving side of the de- 75 od impractical because of the high cost of the posit, just before it rev-enteros the catholyte. I diaphragms and the interruption to operahave also found'that if, for example, the total tion. l A period of deposition is from tWo to` three I have discovered that, if iron be deposited weeks, it is not necessary to apply the strips upon a slowly moving cathode surface part for more than the Afirst two or three days. 80

of which surface is continually exposed to the This is probably explained by the fact that atmosphere, an eect is produced which is the strips promote the formation of uniformbeneficial to the deposit, and is apparently the ly sized grains in the young deposit, and u niresult of a depolarizing reaction whereby the formly sized grains, once having been formed,

- oxygen of the atmosphere combines with a tend to continue to grow as more or less uni- 85 portion of the 'cathodically deposited hydroformly sized grains, during the entire period gen, or with the hydrogen ions in the layer of of deposition. This is in accordance with a solution which adheres to the surface of. the 'well-recognized' ,law of grain growth in deposit, thereby inhibiting theotherwise bad metals, which is to the effect that if the grains K .effect of hydrogen upon thephysical nature are of uniform size to start with, they tend S0 of the deposit. p to remain uniform in size during growth; but The action of the atmospheric oxygen also .if the mass is made up of large and small tends to produce basic salts which, in time, grains, the former tend to grow even larger at tend' to give the deposit an oxidized appearthe expense of the latter. ance, 4but I have discovered that by'employ- I consider the rubbing of the deposit with ing a rubber brush or wiper, which continsoft strips of pure iron, as-just described, tobe ually rubs on the exposed depositvwith a genthe preferable method for applying my inventle pressure, the basic particles are removed tion', and by its use I have-produced iron plates and the deposition of iron in the form of a about il/ inch thick and composed entirely 5 substantially smooth, homogeneous, fully meof homogeneous, non-porous iron. Samples f'f of such iron after annealing, when prepared with polished and etched surfaces and examined in the metallograph at 1,000 diameters, show a pure structure of ferrite grains with no inclusions of oxide and no porosity. Furthermore, these plates can, after one annealing for a few minutes at 1,000 degreescentigrade, be cold-rolled into thin sheets without any work hardening. It has not been possible by hitherto known commercial methods to produce directly flat cathode plates of electrolytic iron having the above properties. It is well known that thin cylinders of electrolytic iron of good physical properties have been produced on fully-submerged, rapidly rotating cylinders by the so-called Grenoble process of Societ Le Fer; but it is entirely impractical to construct such cells for cheap production o f iron from solutions with insoluble anodes, because of mechanical dificulties, but principally because of the high investment cost per unit output in unit time. My present invention isthe first known method for producing large quantities of the highest grade of electrolytic iron by a cheap process comparable in costs to well known electro-metalf lurgical processes for producing zinc and copper; and it is the only successful method worked out, up to the present time, for producing electrolytic iron from solutions in diaphragm cells with insoluble mnodes. When this process is carried out in connection with the process covered by my pending application for metallurgical process, lSerial Number 87,509, I am able to produce iron which is more pure than is possible by any soluble anode process, including the above-mentioned Grenoble process. This follows because prac? f tice has demonstrated that certain impurities,

such as sulphur and phosphorus, tend to pass from the anode to the cathode, yand if Vthe former is insoluble and the solution properly purified, this source of contamination is removed.

My method eliminates the growth of trees or snags on the deposit and prevents injury to the diaphragms in cells with insoluble anodes.

This latter feature is of essential importance because of the high cost of pure asbestos diaphragms, which latter material alone will resist the attack .of ferrie chloride.

Tf deposition is made at 35 to 50 amperes per square .foot of submerged cat-hode area, the same can be continued for as long as three weeks, and deposits can be made 1% inch or Y more in thickness, having relatively smooth surfaces of deposition and a structure consisting entirely, after one annealing at 900 to 10000 centigrade, of pure ferrite grains free from nonmetallic inclusions, a result not attainable by any other known process. The,

thick electrolytic iron produced by this process is so non-porous and free from inclusions of? oxide and electrolyte as to be on this account a. novel and valuable product, particularly as a new material for the manufacture of high-grade magnetic materials. n

` When the period of deposition is finished 1t is usual to strip the deposited iron from the cathode basis metal, which is preferably that of the cathode disc, or it may be a cylinder; but the disc method is the preferable way for carrying out my process. One way to do this is to electrolytically deposit upon the discs in a suitable cell for that purpose, and before they are inserted in the iron cells, about .001 inch of electrolytic lead. The iron is then deposited upon the lead surface. When the deposition has been completed, the discs are heated to a temperature a little above the melting point of lead. This of course melts the lead and effects an easy separation of the electrolytic iron from the basis metal. The discs are then cleaned, usually with a sand blast, coated again with lead, and put back in the iron cell.

A preferable method for stripping is to cover the starting disc with a coating of blue oxide. This is done by mounting the discs on a mandrel and slowly rotating in a furnace which is brought up to a temperature of about 1000 degrees centigrade. The discs are then cooled in a current of air and passed through flattening rolls to make substantially flat. They are then pickled for a few minutes as anode in an electrolytic bath of dilute hydrochloric acid, care being taken not to entirely remove the coating of oXide. A surface thus prepared is in condition to take and securely hold a deposit of iron while the same is being electro-deposited, but the entire deposit can be easily removed by a few well directed blows of a hammer.

Having stated the general nature of my invention, I will now set forth, for descriptive purposes but not for limitation, an eX ample of the carrying out of the method in practice. The nature of my discovery is of broad application, and applies to any type of apparatus in which the necessary conditions-( 1) of continual exposure of a portion of the moving deposit to the atmosphere; and (2) the rubbing or wiping of the deposit with a device of suitable nature,

preferably soft ironare met. It will be understood that an improvement in deposition is effected by condition (l) alone, and that by further applying condition (2), deposition can be made thicker and the physical nature of the deposit is further improved.

Inthe drawings:

Figure 1 is a part longitudinal section, part elevation, of a 12-cathode (S0-inch cell.

Figure 2 is a plan view of same with cover removed. f

Fig. 3 is a section through an anode com partment showing the anode.

Figure 4 is-a section through the anode compartment showing the diaphragm.

lll.

, discs.

The cell illustrated is a commercial unit having twelve (S-inch cathode discs and producing33l pounds of iron. daily at a cathodic current density of 35 amperes per square foot and a cathodic current efficiency of 95%. The cell voltage is 3.48 and the D. C. power required is 1.65 kilowatt hours perv pound of Fe. The cell assembly comprises the following principal parts: The reinforced concrete tank 1', which is preferably made of reinforced Portland cement concrete which has been dipped in moltensulphur to render the concrete immune to attack by ferrous and ferrie chloride; the graphite anodes 2 (I .have found that the life of these anodes is greatl 'increased b dipping them in molten su phur, and at t e same the electrical resistance is increased but little); the asbestos cloth diaphragms 3, which are described inmy co-pending application, Serial Number 58,010; t .e cathode disc assembly 4; the cover 5; the rubber'. assembly 6.

Incoming electrolyte, consisting principally ofa water solution of ferrous chloride containin about 12% IkFexx and .05% or less Fexxx wit pH about 2.5 and at a temperature of 80 centigrade to 90 centigrade, en-

vtersthe cell at 8, and flowing` through the distributing channel 9, enters into each cathode compartment through `side branches 9a. About twice as much 4electrolyte is introduced as is actually required, the surplus passing through branches 10 into channel 11 and thence out of the cell over wier 12, which is employed to keep the level constant in the cathode compartments. Gatholyte f lows through the porous diaphragms v3 into the anode compartments, and thence through thel channels 13, of which` there are two in the bottom f each anode compartment, into the longitudinal passages 14, which connect with A.the upcoming channels 15. In these latter are placed steam ejectors a which cause an upward flow of anolyte in the channels 15 'and discharge same over dams 16 into channels 17, which connect by branches shown with longitudinal channels 18, which in turn connect by side branches with each anode compartment. Thisarrangement provides an active circulation of anolyte downwardly in the anode compartments, which -is the proper direction o f circulation, because I have found that Athe t fferric chloride as formed'at. the anode, tends 51, means of which the draw-olf of anolyte from cellf is regulated. As the porous diavto flow downwardly. A single side channel connects-.with a regulatable wier 21, by

I''.phr'agms become blinded it is desirable to A by-pass freslelectrolyte through a suitable valve (Fifg. 2)ag'directly from 8 into 17 so as to control the percentage of Feom in the anolyte. Ordinarily the anolyte will contain 10% total Fe, of which 4.5% to 5% is Fexx", and the Fexxx content ofthe catholyte willl not be above .05%. The rate of circu? lation of anolyte through the anode compartments is many times the rate of withdrawal of anolyte over wier 21. The exact amountA of circulation willbe decided by the amount of steam required .in the steam ejectors to maintain a temperature of 90 degrees centigrade to 95 degrees centigrade in the anolyte.

The anodes, 2, consist. of anode plates 22 secured to anode cross-bars 23, which in turn engage copper lingers 24` which are in elec trical contact with the positive bus bars 25. The anodes are supported at their lower extremities b piers 26.

The diap ragms 3 are set into grooves (not shown) provided in 'the cell body,and are cemented into place with suitable mortar.

The cathode disc assembly 4 is described in my copending application, Serial Number 58,010, andis comprised of discs 27, journal and bearings 28, pulley 29, negative commutator 30, protective rubber` sleeves 31, the shaft 32, and keeper nut 33. The shaft assembly is rotated at from one to two R. l?. M. by suitable driving means (not shown).

I have found that satisfactory deposition of iron cannot be carried out if the rotating discs are completely exposed'to the chilling effect of the, atmosphere. If so exposed the deposit cracks and peels away from the basis metal. On this account -the hood 5 is provided. This is made of. a suitable rubber- 'covered steel supporting frame (not shown). The hood proper is preferably made of asbestos lumber, and is thermally insulated by a layer of cork-board on the outside.. Suitable sight holes (not shown) are provided,

and a vent (not shown) is provided for removing steam from beneath the hood and conducting the same away from thecell room. The entire hood is removable by lifting, and is of course taken olf the cell when the disc assembly is being placed or the deposits removed.

Rubber assembly 6 comprises supporting ber 34. A spring 39 is employed to draw together the arms 36 of the two rods34 situated on opposite sides o f each cathode, thus causing the rubbers 35 to ress with a gentle pressure uponthe faces o the de osit.

In operation, after a fresh cat ode assem' bly has been placed, the cover is put on the cell and the rubber assembly inserted. The current is gradually brought up to full strength of 35 amperes per square foot of submerged cathode area in eight hours. About two hours after starting the current the pressure is applied to the brushes. After twoto three day-s the rubber assemblies are removed, and deposition is continued for from ten to'twelve days more. After a run the assembly will hold about 5,000 pounds of new electrolytic iron. The discs are removed from the assembly and the new iron recovered as complete discs by a few Well directed blows of a hammer.

As is well known to electro-metallurgists, each metal has certain characteristic peculiarities involving difficulties which have to be overcome in electro-deposition. Iron is' a very diicult metal to successfully deposit, and the merit of my process resides in over-` coming certain specific obstacles in the way of large scale deposition of pure homogeneous deposits of iron, which obstacles have not been hitherto overcome. y i p Having thus described -my invention, what I claim as new and desire to secure by Letters Patent is:

1. A cell for electrolytic deposition of iron comprising a plurality of alternating anode and cathode compartments separated from each other by porous diaphragms, insoluble anodes suspended in the anode compartments, rotating disc cathodes mounted on a shaft and dipping into the'electrolyte in the cathode compartments, the upper part of said disc being above the level of the electrolyte, means for introducing fresh electrolyte into the cathodecompartment, and an overflow wier for keeping a substantially constant ylevel of catholyte, means for cause` ing a downward circulation of anolyte in the anode compartment, means for heating the anolyte during such circulation, and means for withdrawing the net flow of anolyte from the cell and maintaining its level slightly below that of the catholyte. e

2. A cell for electrolytic deposition of iron comprising a plurality of alternating anode and cathode comparements separated from each other by porous diaphragms, insoluble anodes suspended in the anode compartments, rotating disc cathodes mounted on a shaft and dipping into the electrolyte in the cathode compartments, the upper part of said1 disc being above the level of the electrolyte, means for introducing fresh electrolyte, into the cathode compartment, andan overiiow wier for keeping a substantially constant level of catholyte, means for causing a downward circulation of anolyte in the anode compartment, means for heating the anolyte during such circulation, means for withdrawing the net flow of anolyte from the cell and maintainingits level slightly below that of the catholyte, and a thermally insulated hood for covering the exposed part of the assembly of cathode discs to prevent cooling by the outside atmosphere. t

3. In a cell for electrolytic deposition of iron in combination with partially submerged rotating cathode discs, rotatably mounted rods on each side of the separate discs, spring strips attached to and depending from the rods facing the downwardly rotating faces of the discs, soft iron strips attached to the lower end of the spring strips and adapted to engage with their inner edges substantially the entire downwardly rotating faces of the discs, arms attached to one end of each rod and a spring engaging each pair of arms associated with each disc and adapted to cause a pressure of the said iron strips against the faces of the discs.

4. A cell for electrolytic deposition of iron, comprising a plurality of alternating anode and cathode compartments separated from each other by porous diaphragms,insoluble anodes in the anode compartments, rotating disc cathodes mounted on a shaft and dipping into the electrolyte in the cathode compartments, the upper part of said discs being above the level of the electrolyte, means for introducing fresh electrolyte into the cathode compartment, and for maintaining its level substantially constant, means for causing a circulation of anolyte in the anode compartment, means for heating the anolyte during such circulation, and means in communication with the anode compartments for withdrawing the net flow of anolyte from the cell.

5. Al "cell for the electro-deposition of metals comprising a plurality of alternating anode and cathode compartments separated from each other by porous diaphragms, insoliible anodes in the anode compartments, cathodes in the cathode compartments, means for introducing fresh electrolyte to the cathode compartments and for maintaining its level substantially constant, means for clrculating electrolyte and for controlling its temperature during circulation, means for maintaining the level of the anolyte substantially constant, and slightly below the level of the catholyte, and means for withdrawing the net flow of anolyte from the cell.

' ROBERT D. PIKE.

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