US2374454A - Production of iron oxide - Google Patents

Description

Patented Apr. 24, 1945 PRODUCTION OF IRON OXIDE Thomas C. Oliver, Jackson Heights, N. Y., Ralph D. Long, Charlotte, N. C., and Leo H. Crosson, Arlington, Va., assignors to Charlotte Chemical Laboratories, Inc., a corporation of North Carolina No Drawing. Application October 23, 1942, Serial No. 463,074

2 Claims.

' In times of emergency such as now characterize the second WorldWar, the demands on high quality iron ore and eventually metallic iron for manufacture of precision products assume critical proportions. Also, the usual importation from produce gear teeth and other forms is a time consuming, precision job, requiring skilled machinists.

One solution, heretofore suggested, for the problems of casting and machining these parts, is powder metallurgy, that is, preparing the iron in such finely divided state that when molded it will bond autogenously to form an article of the desired shape. This molding procedure is far more rapid than castingand machining but is dependent upon the use of a pure, iron powder of very fine particle size. Such powder has been obtained from Sweden and has also been manufactured in this country fby the carbonyl process,

, which involves forming iron carbonyl by treatment of iron ore with carbon monoxide, followed by distillationand heat treatment of the carbony] to deposit out the fine iron powder. The

carbonyl process is not simple to carry out and the iron powder so produced is expensive. Accordingly, it has serious limitations for large commercial use, and cannot satisfy the need of an inexpensive, locally available, moldalble iron. Now, we have discovered a solution to this pressing problem by supplying a satisfactory, fine iron powder that is easily and inexpensively manufactured and is imminently. suited for rapid molding of various precision parts. We have found that a precipitated iron oxide prepared by ammoniation of inexpensive waste ferrous sulfate solution, when dried and reduced, will give an extremely finely divided iron powder that possesses all of the necessary and desirable properties for molding.

property of the precipitated iron oxide and certainly there is no established commercial use of such a procedure today. The process offers the tremendous advantage, especially in these critical times, of utilizing a widely available cheap raw material, ferrous sulfate, which is commonly produced in the manufacture of titanium oxide pigment and in steel pickling operations. It is now disposed of in immensequantities as a waste material.

We are aware of previous proposals for treating ferrous sulfate with ammonium hydroxide or carbonate, and oxidizing agents to obtain ammonium sulfate and iron oxide as a mixture or in crudely isolated form for general use. For example, such iron oxide in mass form has been proposed for use in a blast furnace infplace of or in addition to iron ore. However, there has beenlno prior perception 0r realization of our commercially important utilization of the precipitated iron oxide as an intermediate product to be reduced and prepared as a finely divided metallic iron powder for molding. Also, the prior processes require use of very large amounts of the ammonium compound.

As far as we are advised there has b'een no' In accordance with our invention, we react ferrous sulfate, advantageously at normal temperatures and pressures, with an excess of gaseous ammonia suflicient to precipitate the iron. This precipitated iron may be in the form of iron hydroxides or oxides or mixtures but for sake of simplicity we refer to such su bstances herein after as oxides, with the understanding that this is an inclusive term for identifying any and all of the products in question.

If a large excess of ammonia, e. g.-about 12% to 20% or. more, is used, the ammonium sulfate formed is precipitated out of solution (salted out) along with the iron oxide and may be separated from the iron oxide according to the procedure disclosed, in our copending application Serial No. 396,154 filed May 31, 1941. As disclosed in that application a co-precipltate of ammonium sulfate and iron oxide is produced, and when this co-precipitate is, heated to a temperature not in excess of about C. the unstable iron oxide is converted to a stable form of iron oxide. As will be clearly understood by those skilled in the art, this heating effects removal of amammonium sulfate and leave the iron oxide as a residue. i l

This iron oxide product, after separation from the ammonium sulfate as described above, and dried, is in the form of a pure, light, and extremely finely divided, powder. We have found that this powder may be reduced with hydrogen or carbon monoxide or coke to produce a pure, metallic iron powder which is especially suitable for molding into various shapes or small articles such as the gears, cams, etc., mentioned above.

In the above described process for producing the finely divided iron oxide powder, no treatment other than the reaction of the ferrous sulfate with ammonia and the subsequent heat treatment, is necessary for obtaining the useful iron oxide powder. The large excess of ammonia serves in some manner to cause the formation primarily of magnetic iron oxide.

In the case in which a smaller excess of ammonia, such as for example 6% to 12%, is used for reacting with the ferrous sulfate, the amammonium sulfate stays in solution the reaction is reversible to the extent that the precipitated ferrous oxide will go back into solution and be admixed with the ammonium sulfate.

This condition can be remedied by use of additional amounts of ammonia, but in lieu of this the iron oxide may be oxidized by blowing air into the reaction mixture. If the air blowing is con-- tinued over a long period of time the iron oxide is converted to a stable form and may then be reduced and molded as described above t form essential war time as well as peace time products.

A third procedure for forming the iron oxide, which may be used in accordance with our invention, involves the use of a relatively small amount of ammonia as compared with the excess amounts of 6% to 20% used in the two processes described above. In this third procedure very slight excess, if any excess, of ammonia is used and the amount is Just about sufficient to carry out the reaction. In other words a stoichiometric amount of ammonia may be used. We have not found this procedure as desirable commercially as the above two methods in view of the fact that it forms an iron oxide which is extremely dflicult to wash and filter. It is more or less gelatinous in character and requires repeated washings with large amountsof water to separate the iron oxide from the other product of the reaction, namely, ammonium sulfate. It would have the advantage of requiring lesser amounts of ammonia and therefore less expense for chemicals but it is subject to the processing disadvantage-just mentioned. The resulting iron oxide product is not magnetic and analysis indicates that it is predominantly, if not entirely, red, ferric, iron oxide.

When the iron oxide obtained by one of the processes discussed above (preferably the first or second process), is reduced with hydrogen, for example, at a temperature of about 1000 F. and at atmospheric'pressure, a metallic iron powder of light weight and extremely fine particle size is obtained. This metallic iron powder has an apparent specific weight of about 0.9, when determined by the technique commonly used in the powder metallurgy art. The powder passes substantially through a 325 mesh screen. In fact, the particle size of these powders is probably considerably finer than 325 mesh but the presently available methods for determining the actual size are both tedious and inaccurate.

The fine particle size characteristic of the iron powder makes the product especially suita le for molding and in fact of such nature that no bonding agent is required, the fine particles of the powder itself tightly cohering during the molding process to form a rigid, hard, molded product. The molding procedure may be carried out either at normal temperatures or at elevated temperatures, as desired, and the molded products formed in a conventional molding press in which the fine powder is poured into the molding press hopper.

The products molded from this powder may be produced at a high production rate such as for example 40 to 500 an hour. In addition to the advantage of speed, the molded products are also extremely accurate in dimensions and are uniformly within tolerances of Mamie of an inch.

The following are illustrative laboratory examples of formulae and procedures that will serve as a guide for commercial operations on a larger scale.

Example I Grams Ferrous sulfate, e. g. FeSO4 192 Water 250 Ammonia (NHa) 92 and iron oxide is then heat treated at a temperature not exceeding C., the ammonium sulfate leached out, and the remaining iron oxide reduced for molding as described above.

Example II Grams Ferrous sulfate, e. g. FeSO4 192 Water 250 Ammonia (NI-Ia) In this case the gaseous ammonia is introduced into the ferrous sulfate in the same manner as in Exampl I and is in sufficient amount to form all of the iron oxide and ammonium sulfate possible but is insuificient to salt out the ammonium sulfate. The latter stays in solution and the reaction mixture is then blown with air over a period of time, such as 5 to 6 hours, to convert the ferrous iron, which is probably present in the form of ferrous hydroxide, to the ferric state. The resulting iron oxide is predominantly, if not entirely, the magnetic iron oxide, of characteristic black color. It is filtered, washed, dried, and reduced to a fine metallic iron powder suitable for molding.

Example III Grams Ferrous sulfate, e. g. FeSOu 192 Water 250 Ammonia (NI-1a). 43

The procedure in this case is the process referred to generally hereinbefore as the third process, and in which the amount of ammonia used is not in excess but is the amount theoretically required for reacting with the ferrous sulfate to produce ammonium sulfate and ferrous hydroxide according to the following reaction:

When the ferrous hydroxide shown in the above reaction is blown with air a gelatinous iron oxide is produced which is very difiicult to wash and free of the ammonium sulfate, but when obtained in dry powdery form may be reduced to form metallic iron powder suitable for molding.

The ironoxides used in our invention distinguish from the oxides of iron ore both from the standpoint of purity and particle size. The precipitated iron oxides described above, after thorough washing to remove the ammonium sulfate, are substantially free of any and all impurities. For example, the oxide produced according to our first procedure described hereinabove has a purity of approximately 99.9%. In addition to this advantage of extremely high purity, the iron oxides of our invention, because of their chemical method of manufacture, have a much finer particle size than is possibly obtainable by grinding of ores or by other mechanical procedures.

In the chemical formation of the iron oxide of our invention, we believe that the precipitated material is in substantially colloidal state which means that it is extremely finely divided and of a uniform particle size that could not be reproduced mechanically by grinding or otherwise. Furthermore, the precipitated oxides have the desirable character of not agglomerating or forming undesired hard cohesive masses of the material. n the contrary they remain dispersed in an extremely fine particle state that is characteristic of true powders. They form a cake when filtered but this cake is very easily disintegrated into the fine powder. The metallic iron powder, which results from the ensuing reduction process, also has the finely divided characteristic and is especially suitable for molding purposes.

Various modifications and changes may be made in the above described materials and procedures without departing from the scope of our invention, some of the novel features of which are defined in the appended claims.

We claim:

l. A method of producing from ferrous sulfate a pure, extremely finely divided, precipitated, iron oxide suitable for reduction and use in powder metallurgy, comprising treating a solution of said ferrous sulfate with gaseous ammonia .in an excess of about 6% to 12% to precipitate the iron oxide, then blowing the iron oxide and the reaction solution with air to convert the iron oxide into a stable water insoluble, easily filtrable, form V and prevent it from going back into solution in the presence of the ammonium sulfate, separating the stable iron oxide from the ammonium sulfate and thereby obtaining the pure finely divided iron oxide.

2. A method of producing from ferrous sulfate a pure, extremely finely divided, precipitated, iron oxide suitable for reduction and use in powder metallurgy, comprising treating a solution of said ferrous sulfate with gaseous ammonia in an excess to precipitate the iron oxide, then blowing the iron oxide and the reaction solution with air to convert the iron oxide into a stable water insoluble, easily filtrable, form and prevent it from going back into solution in the presence of the ammonium sulfate, separating the stable iron oxide from the ammonium sulfate and thereby obtaining the pure finely divided iron oxide.

THOMAS C. OLIVER.

RALPH D. LONG.

LEO H. CROSSON.