US3540877A - Method for making mixed metal compositions - Google Patents

Description

3,540,877 METHOD FOR MAKING MIXED METAL COMPOSITIONS Tyson Rigg, Henry Ross Huttman, and Conrad Percival Gravenor, Edmonton, Alberta, Canada, assignors to Peace River Mining & smelting Ltd., Edmonton, Alberta, Canada, a corporation of Canada No Drawing. Filed July 7, 1967, Ser. No. 651,665 Int. Cl. C22b 5/12 US. Cl. 75-5 9 Claims ABSTRACT OF THE DISCLOSURE Providing an intimate mixture of at least two metals selected from iron, nickel, cobalt and chromium by a recrystallization mechanism. A mixture of metal-containing components, at least one metal being in the chloride form, is reduced with hot hydrogen to the metal state. Recrystallization occurs during reduction. A spongy mass is produced formed of interconnected particles, each particle being comprised of an aggregate of metallic crystals chemically constituted of a mixture of the metals used. The pulverized product is suitable for making alloy wrought products by powder metallurgy techniques.

BACKGROUND OF THE INVENTION This invention relates to a method for producing compositions comprising an intimate mixture of at least two metals. The metals are selected from the group consisting of nickel, cobalt, iron and chromium. The invention further relates to the mixed metal compositions so produced.

It is known to produce metal powders for fabrication into finished articles such as strip and other shapes. Such powders are used to produce alloys. Generally, such use involves blending powders of different composition and compacting the blend into articles which are then sintered to interdifiuse the metal constituents to produce a homogenized alloy.

Care must be exercised in producing well homogenized alloys using such techniques. The powders must be Very well blended so as to prevent segregation. In addition, the powder particles must be of a very small size to provide an intimate enough mix so that homogenization will be complete in a reasonably short sintering period. When such powder mixtures are subjected to vibration during storage and handling they tend to segregate, thereby making it difiicult to maintain a suitable stock on hand. The cost of producing alloys using such techniques is high. There is a need for intimately mixed metal products, produced by a relatively low cost process, which may be used to provide feed material in the making of alloys. It will be appreciated that the more intimate the mix, the shorter will be the period of sintering required for complete homogenization.

SUMMARY OF THE INVENTION This invention provides an economic process for producing powder compositions wherein the particles are comprised of an intimate mixture of selected metals. In the key step of the process, a mixture of two or more selected metals, at least one of them being present in chloride form, is more intimately mixed by a vapor phase transport mechanism. The mechanism takes place during hot hydrogen reduction of the mixture of metal-containing constituents to metal form.

In the first step of the invention, a starting mixture comprised of two metal-containing components is provided. There are two cases to be considered, depending on whether or not chromium metal is to form one of the constituents of the final product.

-- States Patent In the case where chromium is not to form a constituent of the final product, the first component comprises a nickel, cobalt or iron chloride (that is, an iron group chloride) in either the anhydrous or hydrated state. The second component in the mixture comprises at least one metal chloride, or at least one metal powder which is different in metal composition from the metal in the first component, or mixtures of metal chloride and metal powder. The metal chloride in the second component may be either in the anhydrous or hydrated state and the metal in the metal chloride is selected from the iron group. The metal powder is also selected from the iron group.

In the case where chromium is to form a constituent of the final product, the first component comprises anhy drous chromic chloride and the second component comprises at least one iron group metal powder.

vIn the second step, the mixture of components, preferably having been compacted into pellet or briquette form, is reacted with hot hydrogen for a period of time sufficient to reduce the metal chlorides to the metallic state. During hot hydrogen reduction of the mixture of components, an intimate mixing of the metal constituents takes place by virtue of the vapor phase transport mechanism involved in the chloride reduction.

The resultant reduction product is a porous, spongy, microcrystalline mass of interconnected metal particles, each of such particles physically comprised of an aggregate of metallic crystals and has been chemically constituted of a mixture of the metals used. In this form, the metals are in a very intimately mixed condition suitable for making alloys using powder metallurgical techniques.

In a preferred embodiment of the invention, when applied to nickel, cobalt, and iron, a mixture of metal chlorides in the hydrated state may be provided by subjecting an aqueous solution of the specified metal chlorides to crystallization and drying to adjust the water of crystallization content of the metal chlorides whereby they will not melt in their own water of crystallization in the reduction furnace. In this condition the metal chlorides are already well mixed and are suitable for reduction with hot hydrogen. If desired, they may be blended with metal powders prior to reduction.

PROVIDING THE STARTING MIXTURE The invention is first described with regard to the general case wherein a composition comprised of a mixture of two or more difierent metals selected from the group consisting of nickel, cobalt and iron is produced.

The starting mixture comprises two metal containing components as defined hereinabove.

The source of the metal chlorides and the metal powders used is immaterial for the purposes of the invention. Various known techniques are available whereby metal chlorides may be produced in a form suitable for hot hydrogen reduction. These metal chlorides, whether anhydrous or in a hydrated state, such that they will not melt in their own water of crystallization on heating, may be pulverized and mixed with conventional metal powders prior to reduction.

There is no restriction on the proportions of metal constituents provided in the starting mixture.

A particularly advantageous technique for mixing two or more of the nickel, cobalt and iron chlorides is described hereinbelow.

In accordance with this technique, two or more metal chlorides are provided in aqueous solution. The metal chlorides may be present in any proportion. The solution may be obtained by any suitable technique such as leaching nickel, cobalt or iron bearing ore or concentrate with hydrochloric acid or simply dissolving metal chlorides in water.

The solution is evaporated to crystallize out the metal chloride. The metal chlorides are usually crystallized in a high hydrate state: for example, as FeCl -4H O, NiCl -6H O or CoCl -6H O. By crystallizing the metal chlorides together, mixture of the metal values is achieved.

It is preferable to partially dehydrate the metal chlorides to a lower hydrated state prior to hot hydrogen reduction whereby they will not melt in their own water of crystallization when heated. For example, hydrated metal chlorides having the formulas FeCl -2H O,

and CCl -2H O have been found to be particularly suitable for hot hydrogen reduction. Partial dehydration of the crystallized metal chlorides may conveniently be carried out in conventional equipment, such as 8. Raymond drier.

It is possible to employ metal chlorides in the high hydrate state as the feed material during reduction by providing a rapid enough hydrogen flow in the reduction vessel whereby the crystals are dried before reduction commences. However, metal chloride mixtures in the high hydrate state are difficult to handle and store.

One or more metal powders, selected from the group consisting of nickel, cobalt and iron, may be admixed with the crystals of metal chloride or metal chlorides prior to hot hydrogen reduction. To promote intimate mixing, the powders should preferably be fine, such as will pass through a screen having 100 meshes to the inch. The metal chlorides or mixture of metal chlorides may be pulverized and well blended with the said metal powder using any conventional blending device such as a twin cone shell blender.

PELLETIZING OR BRIQUE'ITING The mixture of components is compacted by conventional techniques to produce a pellet or briquette suitable for hot hydrogen reduction. It is preferable that the mixture being reduced is in a form which will ensure proper contact with the metal chlorides by the hot hydrogen. The provision of the mixture in powder form for reduction is somewhat unsuitable as the hot hydrogen tends to channel through the powder leaving zones of incomplete reduction. By using pellets or briquettes, void spaces are provided through which the hydrogen and reaction product gases can readily flow. As a result, complete reduction of the mixture is promoted. Pellets or briquettes weighing less than 20 grams are preferred. It has been found that the residence time required for complete reduction increases with the size of the pellets or briquettes.

HOT HYDROGEN REDUCTION The pellets or briquettes are placed within a reactor capable of withstanding the reduction temperatures discussed hereinbelo'w, and the corrosive gases produced during the reaction. Hot hydrogen is passed through the reactor containing a bed of the metal containing components and reduces the metal chlorides in the pellets to the metallic state.

The hydrogen used for reduction of chlorides of nickel cobalt, or iron need not be completely pure and can be quite moist-as it would be for example on leaving a conventional hydrochloric acid absorption tower. As much as of non-condensable impurities such as nitrogen or methane has very little elfect on the rate of the reduction process.

The rate of flow of hydrogen gas over the pellets is controlled to ensure that the partial pressure of hydrogen chloride produced during reduction should not exceed more than about 70% of the equilibrium value.

The hydrogen gas which is flowed through the reaction vessel is preheated. Since reduction is more rapid as the temperature is increased, the temperature to which the gas is heated is only limited by the temperatures which the process equipment used can withstand. At the present time, it is impractical to heat the gas beyond about 850 C. as the cost of the reaction vessel and other equipment becomes excessive. However, the hydrogen must be hot enough to ensure that the pellets will be raised to a temperature sufficiently high to permit reduction of the metal chlorides to take place. For example, it has been shown that useful rates of reduction of nickel chloride commence at about 300 C., cobalt chloride at about 400 C. and iron chloride at about 500 C. The metal chlorides should, of course, be maintained at high temperature until reduction is complete.

It is not fully understood how the process of this invention accomplishes the intimate mixing which takes place during hot hydrogen reduction of the metal values present in the pellets and it is not intended that this invention be bound by the explanation given.

However, during reduction with hot hydrogen, it is believed that metal chloride vapourizes on heating, initially at the surface face of the individual metal chloride crystals. The metal chloride vapour appears to react with the hot hydrogen in accordance with the following general equation:

H +MeCl (vapor) ZMe-l-ZHCl As a result of the reaction, nuclei of the reduced metal are formed. As additional metal chloride vapourizes, it is believed that the metal is deposited on the nuclei and these nuclei gradually grow into well defined crystals.

In the case where the mixture subjected to reduction consists of two or more metal chlorides from the selected group, the metal values react in the following order: nickel, cobalt and finally iron. As a result, for example, in pellets containing iron and nickel the iron is believed to deposit on at least some nickel nuclei.

In any case, particles are formed during reduction which are comprised of aggregates of minute crystals, ranging in size from about 2 to 30 microns. The particles vary in size and are interconnected to form a porous, spongy, microcrystalline mass and are chemically constituted of a mixture of the metals used.

In the case where one or more pulverized metal chlorides are mixed with a metal powder, it is believed that some of the hydrogen chloride, which is released as the metal chloride is reduced, reacts with the metal powder to form metal chloride vapour. The newly made metal chloride vapour is believed to nucleate and deposit metal, thus contributing to the growth of existing crystals or creating new crystals. The product comprises particles composed of aggregates of minute crystals, ranging in size from 2 to 30 microns. The particles vary in size and are interconnected to form a porous, spongy, microcrystalline mass and are chemically constituted of a mixture of the metals used.

In the case where chromium is to be included as one of the metal constituents used in the invention, certain limitations must be observed. The affinity of chromium toward forming oxides which are not reduceable by hot hydrogen is well known. For this reason, chromium chloride or chromium metal should not be included in a mixture prior to reduction which contains hydrated metal chlorides.

It has been found that anhydrous chromic chloride may be mixed in any proportion with at least one nickel, cobalt or iron metal powder. This mixture is suitable for reduction with pure hot hydrogen. Alternatively, chromous chloride, could be used; however, its aflinity for water is much greater than that of anhydrous chromic chloride and it is very difficult to prevent contamination with water. For this reason, anhydrous chromic chloride is considered the only compound of practical value.

The hot hydrogen provided during reduction must be of high purity and the level of oxygen bearing impurities, including moisture, should be kept below about 50 parts per million if high quality chromium is desired. One known method of ensuring such purity involves passing the hydrogen through beds of activated charcoal maintained at 80 C. prior to use in the high temperature reduction system. The hydrogen must be hot enough to ensure the pellets will be raised to a temperature of about 600 C., the reduction temperature of anhydrous chromic chloride. During reduction with pure, hot hydrogen, it is believed that anhydrous chromic chloride is reduced to the chromous state, vapourized and chromium is subsequently deposited in crystalline metallic form. The chromium, after reduction, is found to be intimately mixed with the other metal constituents which formed the remainder of the starting mixture.

The mass of mixed metals obtained from the reduction step may be easily pulverized. The resultant powder is particularly suitable for working by powder metallurgical techniques due to the crystalline nature of its particles. Upon compacting, the angular faces of the powder particles are conducive to inter-particle locking to provide strong green compacts. Additionally, the material sinters well due to the nature of the particle surfaces. The most desirable characteristic of the material is its very intimate mixing of the metal values so that on subsequent sintering a well homogenized alloy may be obtained without prolonged heating to cause the desired degree of interdifiusion of the metals.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given.

EXAMPLE I Commercial grade, pure ferrous chloride and nickelous chloride salts were dissolved in 1% hydrochloric acid to give a solution containing the metals in the ratio of 1:1. The solution was heated in the open atmosphere to evaporate it and crystallize out the metal chlorides. The metal chlorides were recovered in the form of discrete crystals. It was not possible, upon visual examination to distinguish individual crystals of ferrous or nickelous chloride. The discrete crystals were then partially dehydrated by heating them in air at 110 C. for 24 hours. During this period of dehydration, the crystals broke down and the product metal chloride crystals were found to contain about 2 molecules of water of hydration per metal atom. The dehydrated crystals were pulverized using a pestle and mortar and the pulverized material was pressed, without binder, into cylindrical pellets having a diameter of one inch and a height of one-half inch using a pressure of l-ton per square inch. The resultant pellets were placed in a closed stainless steel tube having a diameter of 4 inches. Hot hydrogen was admitted to the tube at an inlet temperature of 750 C. and flowed at 40 standard cubic feet per hour over the pellets for a period of one hour. After cooling to room temperature in hydrogen, the pellets were examined and were found to have been reduced to the metallic state.

Each pellet comprised a porous, spongy, microcrystalline mass of interconnected particles. Individual metals could not be distinguished within the particles upon microscopic examination. Each of the said particles was comprised of an aggregation of minute crystals varying in size from about 2 to 30 microns.

The pellets were pulverized using a hammer mill to 100 mesh per inch size. The resultant powder particles each comprised an aggregate of minute crystals varying in size from about 2 to 30 microns.

The powder was then compressed into 1.25" x 0.5" x 0.1 compacts using a closed die at 40 tons per square inch. The briquettes were sintered at 1100" C. for minutes in flowing hydrogen.

Metallographic examination of the sintered compact using polishing and etching technique showed a complete solid solution alloy of iron and nickel had been formed.

The very short sintering time required to achieve complete homogenization of the metal constituents is indicative of the degree of intimate mixing of the metals prior to sintering which results from the use of the inventive process.

EXAMPLE II Pure iron powder, sized to pass through a 100 mesh per inch screen, was mixed with commercial grade, pulverized, hydrated nickel chloride (NiCl -6H O) by grinding the powders using a pestle and mortar. The metal constituents were provided in equal amounts in the said mixture. The mixture was then pressed into cylindrical pellets having a length of one-half inch and a diameter of one inch using a pressure of 2 tons per square inch. The pellets were reduced in accordance with the conditions of Example I for a period of 4 hours, by which time the metal values were in the metallic state.

Each pellet comprised a porous, spongy, microcrystalline mass made of interconnected particles. Individual metals could not be distinguished within the particles upon microscopic examination. Each particle was comprised of an aggregate of minute crystals varying in size from about 2 to 30 microns.

The reduced pellets were then pulverized and compacted into briquettes as was done in Example I and sintered in flowing hydrogen at 1100 C. for a period of 5 minutes.

Metallographic examination of the sintered compact showed the product to be comprised of a complete solid solution alloy of iron and nickel.

This example shows that metal powder may be mixed with metal chlorides to provide a material, prior to sintering, in which the metal constituents are intimately mixed.

EXAMPLE III Commercial grade, pure chromic chloride powder, sized to pass through a 20 mesh per inch screen, was mixed with iron powder, sized to pass through a 100 mesh per inch screen, by grinding together, using a pestle and mortar. The metal ratio of iron to chromium in the said mixture was 8:1. The powder mixture was pressed into cylindrical pellets /2 inch long having a diameter of 1 inch using a compacting pressure of 1 ton per square inch. The pellets were placed in a 4 inch stainless steel tube and pure hot hydrogen heated to 825 C. was passed through the tube at a rate of 40 standard cubic feet per hour for a period of minutes. Upon cooling in pure hydrogen, examination of the reduced pellet showed the metal constituents were in the metallic state. Each pellet comprised of porous, spongy, microcrystalline mass of interconnected particles. Individual metals could be distinguished within the crystals upon metallographic examination. The crystals appeared to consist of iron nuclei surrounded by a layer of chromium. Each particle was comprised of an aggregate of minute crystals varying in size from 2 to 30 microns. The pellets were ground to mesh per inch size powder. The resultant powder particles each comprised an aggregate of minute crystals. The powder was then compacted in a closed die at 40 tons per square inch to form compacts 1.25" x 0.5" x 0.1". The compacts were sintered at 1180 C. for 2%. hours in pure, flowing hydrogen and examined metallographically. Metallographic examination of the sintered compact showed a complete solid solution of chromium and iron. The grain structure of the alloy was oxide free.

We claim:

1. The method of producing compositions comprised of an intimate mixture of two or more metals which comprises:

providing a mixture of two metal-containing components, the first component comprising a metal chloride selected from the group consisting of nickel chloride, cobalt chloride, iron chlorides and anhydrous chromic chloride, and, where said first component is a nickel, cobalt or iron chloride, the second component comprising at least one other nickel, cobalt or iron chloride, or at least one nickel, cobalt or iron metal power which is different in metal -2. The method of claim 1 wherein:

the first component comprises a hydrated metal chloride which will not melt in its own water of crystallization, said hydrated metal chloride being selected from the group of hydrated nickel, cobalt and iron chlorides; and the second component comprises at least one other hydrated metal chloride from the said group, or at least one nickel, cobalt or iron metal powder which is different in metal composition from the metal in the first component. 3. The method of claim 2 wherein: providing the mixture of hydrated metal chlorides to be reduced comprises the following steps:

providing a solution containing at least two of the said hydrated metal chlorides; crystallizing the said chlorides from solution to provide an intimate mixture thereof; and separating the said chlorides from the mother liquor. 4. The method of claim 3 wherein: the crystallized, hydrated metal chlorides are partially dehydrated prior to reduction to lower hydrated states which will not melt in their own water of crystallization. 5. The method of claim 1 wherein: the spongy mass is pulverized to produce a plurality of discrete particles.

6. The method of claim 4 wherein:

the spongy mass is pulverized to produce a plurality of discrete particles.

7. The method of producing compositions comprised of an intimate mixture of metals which comprises:

providing a mixture of two metal-containing components, the first component comprising anhydrous chromic chloride and the second component comprising nickel, cobalt or iron metal powder, or mixtures thereof, and

reducing the mixture with pure hot hydrogen to the metallic state to produce a porous, microcrystalline, spongy mass comprised of interconnected particles. 8. The method of claim 7 wherein: reduction is carried out using pure hot hydrogen containing less than about parts per million of oxygen-bearing impurities. 9. The method of claim 8 wherein: the spongy mass is pulverized to produce a plurality of discrete particles.

References Cited UNITED STATES PATENTS 1,878,589 9/1932 Marris -.5 2,279,013 4/1942 Roseby 75.5 2,642,356 1/1953 Beidler 75-.5 2,642,357 1/1953 Beidler 75-.5

L. DEWAYNE RUTLEDGE, Primary Examiner T. R. FRYE, Assistant Examiner US. Cl. X.R.