US2538992A - Electrolytically deposited iron products - Google Patents

Description

Patented Jan. 23, 1951 ELEGTROLYTIGALLY DEPOSITED IRON PRODUCTS Harold V.-Trask, Cooley, Minn, 'assignor'to Buel' Metals company. Paul; Minn, a corporation of Ohio NoDraWin'g. Application-January 15,, 1947, Serial No. 722,283

This invention relates 'to electrolytically deposited brittle iron plate and the powdersand colddie pressed hodi'e's formed from such plate.

The presentapplication is a continuation in part of my application for letters Patent of the United States-Serial No. 611,947, filed August 22, I945, which is a continuation-impart of my ap plication Serial No. 560,783, file'd- October 28, 1 944, now abandoned;

The principal objects of my invention are:

1. To provide a low 'costiron deposit which is characterized by the presence of a sufficient quantity of oxide and 'hydroxideof iron to render the product readily "grindable to particles-of. sizes suitable for use in iron powder metallurgy and from which the hardening constituents may be readily removed bysimpleannealing. treatment.

2. To provide-ya. brittle iron plate which may be ground economically to minus 325 mesh :sizes and of such equiaxial-particleshapes-as to form in the subsequent annealing treatment porous clusters of particles which remain as porous clusters after the final crushing and screening operations.

3. To provide an electrolytically deposited, porous, brittle iron= plate whichadheres well to the cathodes during deposition.

4. To provide-aniron powder \vhiclrin structure and composition is superior to the products of this kind heretofore produced Tonnes in cold die pressing operations.-

5. To provide an iron. powder which-is char acterized by its good flow rate, uniform screen size distribution, uniform apparent density and 'high green strength when-compacted preparatory to sintering, combined with a high degree of purity, 'i. e.,;abovev 99.5

6. To provide an ironrpowder which is particularly adapted to receive conventional cold die pressing and. sinteri-ng treatment to. form bodies having high tensile strength andv good elongation, dueto theuniformity of composition and improved grain. structure, substantially devoid of planes ofweakness.

7 To provide iron powders. having apparent densities which are controllable within narrow limits not exceeding 0.1 gram .per. cc. thereby affording uniformity in the compression ratio and greatly facilitating. standardized compacting operations.

8.. To provide iron powders .in. thefform of particles of controlled mesh sizes and off such purity, softness and structure that the compacted' articles formed therefrom do. not expand appreciably or substantially when the pressure is removed preparatory'to sintering and also of 2 such composition that the compacts do not shrink substantially-as a result of the sinteringtreatment.

Other objects wilillappe'ar' and be more fully pointed out. in the following specification and claims.

My improved iron products may be electrodepos'ited' as described and claimed in my applica'tion Serial No. 660,039, filed April 6,1946, or in accordance with my application SerialNo. 611,947, filed August 22, I945, 'he'reinbefore' referred to. In accordance with either process it is essential that the conditions present in the deposition cells with respect to (1) solution composition, (2) current density of the deposition and (3') temperature of deposition, shall be controlled and maintained within the limits presently to be described. The range of permissible valuesfrom a technical standpoint" must be further limited; to minimize the'c'ost ofproduction and facilitate control in commercial operations;

Solution composition An electrolyte comprising a ferrous chloride solution has been found best suited for my purposes. The limits of the solution concentration are: interrelated with those of the temperature and current density of deposition. For example, the upper limit of iron concentration, as ferrous chloride, in the solution is somewhat dependent on the lowest temperature which can be economi'cally maintained in the cell. If, as in most installations, it is not economical to keep the deposition temperature below 15 degrees C. the maximum concentration of. iron is approximately grams per liter for dull ironplate deposition.

It is, however, much more economical to keep 7 the iron concentration below this figure and I have found for most economical operation that the iron in solution should be maintained at between 50 and '75 grams perliter. With more dilute solutions it is necessary to increase the voltage inorder .to obtain a givencurrent density of deposition and this progressively increases the power consumed per pound ofiron depsited. .It is feasible, however, to obtain dTullfiron plate with maximum solution. concentrations ranging from about '67 to 86 grams of iron per liter where the currentdensities range from about 10 to 40' amperes per square foot, and temperatures at or below 25 degrees C. are maintained in the cells.

A further necessary control involves hydrogen ion concentration or the solution. Its ,pl-I should 'be'ma'intainedbetween 3.0 "and 5.5. A pH lower than '3' indicates "the presence of excessive acid 3 or ferric chloride and results in a bright iron cathode deposit which is unsuited for my purposes and is otherwise not satisfactory because of its poor adherence to the cathode plates. In practice the pH of my solution naturally adjusts itself between 5 and 5.5. With pI-Is above 5.5 the solution tends to hydrolyze and a deficiency of iron in solution develops under conditions indicated by substantially higher pH values. solution is neither desirable nor necessary for the functioning of my process. Other additions to the electrolyte, such as ammonium chloride and calcium chloride which have been used heretofore, are also detrimental.

The electrolyte for use in my process may be obtained by dissolving scrap iron, preferably of low carbon content, in hydrochloric acid. This concentrated solution of ferrous chloride is diluted so that it contains iron within the limits hereinbefore described and preferably about 60 grams of iron, as ferrous chloride, per liter of solution.

Current density In order to produce my dull iron plate economically, the current density between electrodes of the deposition cells must be maintained between certain values which are interdependent upon the concentration of iron in solution and temperature of deposition. In general, the higher the solution concentration the greater must be the current density at any given temperature within the feasible range. As hereinbefore indicated, practical limits of the current density are from about to 40 amperes per square foot where the solution concentration ranges from a maximum of about 67 to 87 grams of iron per liter of solution and where a temperature at or below 25 degrees C. is maintained in the cell. The power consumed per pound of iron deposited increases in direct proportion to the current density and in inverse proportion to the temperature of deposition.

Temperature of deposition In order to produce dull iron plate most economically the temperature of deposition should be maintained between degrees and 35 degrees C. and preferably at approximately degrees C. where the economical ranges of current densities andsolution concentrations hereinbefore described are maintained. An unsatisfactory, bright, malleable deposit results when a temperature substantially above 40 degrees C. is reached in a cell of the character described.

Cells and electrodes My process may be carried out in inexpensive open cells without diaphragms between the anodes and cathodes. In accordance with my application Serial No. 650,039, ingot iron plates of suitable thickness, preferably about one-half inch thick, may be used as the electrodes in the cells. These plates may contain up to 2% of carbon and substantial amounts of other impurities. For example, they may contain .03% carbon together with manganese, silicon and sulphur totaling approximately .10 and copper approximately .15 Such electrodes are placed in spaced, parallel, electrical series arrangement in the cells and for maximum anode recovery are completely submerged in the electrolyte. They are preferably spaced from two to three inches, center to center, and furnished preferably in sizes that can be The presence of ferric chloride in the 1 4 handled without the aid of power driven hoists,

cranes or conveyors.

To control the temperature of deposition, inexpensive heat exchangers may be placed in the cells or built into the walls of the same, or the electrolyte may be circulated through a heat exchanger located exteriorly of the cells.

Direct current conductors are connected respectively to the end electrodes of each cell and current is passed at the required voltage through the electrodes in series each of them constituting a soluble anode at one face and receiving a cathode deposit on its opposite face. t the start of the electrolysis, all electrodes are alike and they may comprise ingot iron plates or other inexpensive iron plates containing impurities as hereinbefore described. Either of the end electrodes may act as a soluble anode and the other as a cathode depending on the direction of flow of current.

During the electrolysis, the concentration of the electrolyte is maintained as described and its pH tends to remain at its required value of from 3 to 5.5. Periodically, if necessary, a small amount of hydrochloric acid may be added. A cell temperature below 40 degrees C. maintained and current at the density required, preferably from 16 to 18 amperes per square foot, is passed between electrodes in the series arrangement so that the metal from the positive face of each electrode goes into solution and is re-deposited on the negative face of the electrode adjacent to it. The electrolysis may be continued until all i the electrodes have been converted into electro-deposited iron of the desired dull gray and porous character. This product is subsequently subjected to the successive grinding, annealing, regrinding and screening to produce my improved powders.

Further details of my series deposition process for forming dull iron plate are herein included by reference to my application Serial No. 660,039.

As an alternative, the electrically parallel arrangement of electrodes in the cells, more fully described in my application Serial No. 611,947, may be employed. Accordingly, the electrodes may be provided individually with leads extending to bus bars along opposite sides of the cell and the anodes may comprise ingot iron plates of suitable thickness, preferably from one-half to one inch thick and may contain up to 2% carbon and substantial amounts of other impurities. As the cathodes from which the dull iron plate may be removed periodically and with ease, flexible cathode starting sheets comprising stainless steel, for example, that contains 18% chromium and 8% nickel may be used. Sheets of inch to inch thickness have been found to be adequately stifi to remain straight in the cells while affording the flexibility necessary for removal of the brittle iron deposit. The electrolyte for use in the parallel arrangement of anode and stainless steel cathode starting sheets may be obtained by dissolving scrap iron as hereinbefore described and may be diluted so that it contains iron within the limits specified and preferably between 50 and '75 grams of iron per liter. The cells are cooled to maintain a temperature of electrolyte therein below 40 degrees C. Where anode plates of approximately one inch thickness are used they may be spaced about two inches, center to center, relative to the adjacent stainless steel cathode sheets. The current is supplied at a voltage such that there is a voltage drop between adjoining electrodes within the range 1.5 to 2 volts. Direct coatingis allowed to accumulate toai-thickness of from%=to inch. The flexing-'of-theiron coatedsheets may be performed I manually by" bending thesheets oven a roller or bar, orotherwise in a" machine designed-for'the purpose; It maybe necessary to' clean the cathodesheets periodically and this "may be accomplished" by dipping: them in dilute hydrochloricacidfor a period" of "from one-tonve minutes: Cathode sheets of the character described are so'durable thatthey maybe used almost indefinitely. The anode plates are merely replaced :by'new. ones periodically as they are'dissolvedinzthe' electrolyte. Other details of I the operation are well knowntinthis art and require no furtherrexplanation.

By maintaining: the-preferred conditions hereinbefore described in the cells, I obtain a porous, brittle, coherent; .dulliron deposit with current efil'ciencies" above. 100 The reasons for this amazingly highefliciencyare notientirely clear. but'it is thought that itis; at least in part due to the porosity and.- coherentnatureof my cathodedeposit.- The outer layer of iron as it is formed: may-.act-asan intermediate electrode between the anode plate and cathode sheet and electrolysismaycause. decomposition of water in the pores between this outerlayer and the cathode sheet' whereby hydrogen and oxygen are liberated inthese pores; Since the outer layer is iron in a: very pure. form itmay combinerwith .therliberated gases'to form iron .oxide. and hydroxide under theconditions existing in the cell. Accordingly, cur rent efficiencies above. 100% may indicate that the iron is first deposited and later partially altered to the oxideand hydroxide state without affecting the carrying power of the current pass ing between the anode and cathode. Further substantiation of this theory may be found in the fact that analyses of" the dull iron plate show that iron constitutes only from 95% to 97.5% of theproductand that thehardening. contaminants areoxide and'hydroxidev compounds which can be easily removed-by annealing in. a hydrogen atmosphere.

My improved'iron is suffi'ciently brittle as deposited at the cathode electrodes to permit economical crushing or grinding and contains iron oxides and iron hydroxides together with a small amount-of chlorine, totaling approximately 3% to 5% of the deposit. This product has a dark gray color and is herein called dull iron plate. Otherphysical. characteristics of my dull iron plate are itsrhardness; diamond scale. ranging: from-. about; 400yto. 520; and its porositywhich gives it: a specific: gravityranging; from apnroxi's' mately 6.3 to 7.25. By crushing or grinding-it: may be reduced to particles of the desired size (usually minus 100 mesh) and of equiaxial structure well adapted for use in iron powder metallurgy. Economical grinding to minus 325 mesh size is feasible and advantageous for many uses. The dull iron plate may be ground in a ball mill with air separation, or in any other suitable assays-92 grinder orpulverizer at low cost. It maybepul verizedto minus 100' mesh sizes and with 50% or more of the particles of minus 325 mesh sizes in a ball mill at the rate of 20 to" 25'poundsper 100 pounds of balls per hour. Ordinary electrodeposited iron of comparable purity pulverizes at a rate of from 0.25 to 1.0 pound per 100 poundsof balls per hour and cannot be pulverized to 'minus3251nesh sizes except at prohibitive cost. The hardening impurities, oxides and hydroxides, of my dull iron plate may be reduced and the resulting gaseous elements together with any chlorine carried over from the electrolyte may be driven oh by simple annealing treatment leaving a product which is more than 99.5% pure iron. Theannealing treatment preferably comprises heating the ground product in a hydrogen atmosphere at approximately 800' degrees'C. for from one to three hours, depending on the fineness of the product. Such annealing treatment causes substantial fritting which, in the case of particlesin the smaller ranges of sizes forms clustersadapted to withstand'the subsequentpulverizing and screening. After the second pulverizing and screening a controlled percentage as high as:%: of the final pure iron powder may compriseqpar ticlesbetween 325 and 100 mesh sizes; ailarge pro:." portion of particles thereof *being'porous clusters? of smaller particles of substantially equiaxial; as distinguished from flat, shapes.

Analyses of a number of specimens: of' my dull 1 iron plate showthe following ranges of composi tion in percentages by weight:

. Per cent.

Total cathode iron -975- Cathode chlorine .3-.6: Weight loss after heating: in nitrogen at 950 degrees C. for one'hour- 1.004155: Weight loss after heating in hydrogenat 950 degrees C. for one-hour 2.00-3.55

Total iron after reduction 99.5-99.9

By the annealing treatment in a hydrogen atmosphere, without previous heating in a nitrogen atmosphere, the weight loss amounts to from 3 to 5% by weight.

Typical exampes of the physical'structure of" powders produced from such dull iron plate are as follows:

Example 1 The dull iron plate was ground in a ball mill withair separation to produce a powder all of which passed through a screen having openings per lineal inch and 75% of which, by-weight, passed through a screen or 325 mesh size. This powder-was then annea ed in a hydrogen atmosphere and maintained at a temperature" of ap-- proximately 000 degrees C. for one and one-half hour; The resulting fritted mass, after cooling, was-pulverized in a hammer mill in closed circuit with a screen of 100 mesh size. Numerous testsof the final powder showed the following physical properties:

Flow rate, 50 grams through Hall flow meter, 30

to 33' seconds Screen analyses:

All minus 100 mesh 70% plus 325 mesh 30% minus 325 mesh Apparent density: 2.40 to 2.45 grams per cc. Apparent density variation: .05 gram per cc.

Example 2 Initial ball mill powder screen sizes, same as Example 1 Annealing treatment: Same as Example 1 Screen analysis of final powder (after second grinding) All minus 80 mesh 80% plus 325 mesh 20% minus 325 mesh Flow rate: 34 to 36' seconds Apparent density:2.l5 to 2.20 grams per cc. Apparent density variation: .05 gram per cc.

Example 3 Initial ball mill powder screen sizes:

All minus 100 mesh 50% minus 325 mesh 50% plus 325 mesh Annealing treatment: Same as Examples 1 and 2 Screen analyses of final powder:

All minus 80 mesh 80% plus 325 mesh 20% minus 325 mesh Flow rate: 30 to 32 seconds Apparent density: 2.65 to 2.70 grams per cc. Apparent density variation: .05 gram per cc.

All tests show that the finished product fiows readily and has remarkably uniform apparent density, since the apparent density variation for each example amounted to only .05 gram per cc. Moreover, the finished powders have unusually uniform screen size distribution. Microscopic examination shows further that the marked increase in grain sizes above 325 mesh in the final product as compared with the product of the first grinding treatment is due to the fritting of the finer particles in clusters under the annealing temperature so that clusters of highly porous and substantially equiaxial structure form a major fraction of the finished powder. Uniformity of apparent density is of great importance since it is a major factor in imparting a uniform compression ratio to the powder thereby greatly facilitating the cold compacting operations. Since the second grinding does not reduce a large proportion of the original particles to original size and form, the particles are not reworked and hardened as in the case of ordinary iron powders formed from bright iron plate. Consequentlymy final powder is softer and more amenable to compact pressures. Its good fiow property further facilitates the filling of intricate die cavities and promotes uniformly reliable results.

According to the present commercial practice in cold die pressing operations, pressures within the range 30 to 100 tons per square inch are employed and my improved powder shows substantially no tendency to increase in volume when such pressures are released from the compacted articles. The green or unsintered strength of the compacted articles or bodies formed from my powder are sufiiciently high so that the articles may be handled and transferred from the cold dies to the sintering ovens readily and without danger of breakage. Further, according to present commercial practice, green compacts are subjected to sintering temperatures of the order of magnitude of 1000 to 1100 degrees C. for periods of from one to three hours, depending on the size of the compact. Articles so sintered and comprising my improved powders show less than 8 0.5% shrinkage due to the sintering treatment and my tests indicate that the shrinkage usually ranges from .05 to 40%. The several advantageous properties described result in finished articles which are so accurately formed to dimension that machining is seldom required even for precision products.

Test bars comprising the powders of Examples 1, 2 and 3, hereinbefore described, formed under 30 tons per square inch pressure and sinte'red for one and one-half hours at 850 degrees C. have tensile strength ranging from 23,000 to 26,000 pounds per square inch and show elongation under test equal to from 7% to 10% in one inch. Improved compaction as well as unusually equiaxial grain structure and lack of planes of weakness are evident from microscopic examination of polished: surfaces of the compacts. The pure iron powder may be mixed with other substances to modify the properties of the end product.

Having described my invention, what I claim.

as new and desire to protect by Letters Patent is:

1. An electrolytically deposited, porous iron characterized by its dull gray color, hardness, diamond scale, 400 to 520; specific gravity between 6.3 and 7.25; weight loss after heating in nitrogen at 950 degrees C. for one hour, 1.00 to 1.55%; weight loss after heating in hydrogen at 950 degrees C. for one hour, 2.00 to 3.55% and total iron after reduction, above 99.5%.

2. An iron powder characterized by its dull gray color, specific gravity between 6.3 and 7.25; weight loss after heating in hydrogen at 950 degrees C. for one hour, 3.0 to 5.0%, all particles being of mesh and smaller sizes and a major fraction of the particles by weight being of minus 325 mesh sizes and of substantially equiaxed shape.

3. An electrolytically deposited iron characterized by its specific gravity between 6.3 and 7.25; hardness, diamond scale, 400 to 520; the hardening impurities comprising oxide and hydroxide compounds which are readily removable by annealing, and the purity after reduction being above 99.5%.

HAROLD V. TRASK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Hardy et a1 May 9, 1939 Whitfield et a1 Dec. 3, 194:0 Bauer June 23, 1942 Young Sept. 22, 1942 Talmadge June 29, 1943.

FOREIGN PATENTS Country Date Germany Dec. 5', 1949 OTHER REFERENCES Num er Number

Claims (1)

1. AN ELECTROLYTICALLY DEPOSITED, POROUS IRON CHARACTERIZED BY ITS DULL GRAY COLOR, HARDNESS, DIAMOND SCALE, 400 TO 520; SPECIFIC GRAVITY BETWEEN 6.3 AND 7.25; WEIGHT LOSS AFTER HEATING IN NITROGEN AT 950 DEGREES C. FOR ONE HOUR, 1.00 TO 1.55,; WEIGHT LOSS AFTER HEATING IN HYDROGEN AT 950 IRON AFTER REDUCTION, ABOVE 99.5%.