US3449115A - Methods of making alloy powders and the corresponding powders - Google Patents

Description

United States Patent I 3,449,115 7 METHODS OF MAKING ALLOY POWDERS AND THE CORRESPONDING POWDERS Philippe Marie Galmiche, Paris, and Andr Hivert, Pontoise, France, assignors to Ofiice National dEtudes et de Recherches Aerospatiales 0.N.E.R.A., Chatillon-sous-Bagneux, France, a body corporate of France a No Drawing. Filed Apr. 5, 1966, Ser. No. 540,216 Claims priority, application France, Apr. 8, 1965,

12 Int. Cl. B22f 9700,- C22c 27/00 US. Cl. 75-5 9 Claims ABSTRACT OF THE DISCLOSURE This invention is directed to a method of preparing an ultra-fine alloy powder by preparing a mixture of a powder of a reducible metal compound and of an inert diluting powder, then reducing the metal compound in the presence of the inert diluting powder, after which a powder of a difierent metal is mixed into the reduced mixture and the resultant mixture is heated in a hydrogenated and halogenated atmosphere to cause diffusion of one of the metals into the other to form the desired alloy powder.

the present time and, in particular, a powder of finer grain size and which does not ignite spontaneously in air, while'being of a cost acceptable from the industrial point of view.

The present invention consists chiefly in heating, in a hydrogenated and'halogenated containing atmosphere, a mixture of at least two powders of two different metals, respectively, and of an inert diluting powder, at least one of said two metal powders having been obtained by the action of a reducing agent upon at least one metal compound (oxide, oxalate, formiate and carbonate, in particular) which is reducible and which can be obtained, in particular by chemical precipitation or by crushing, in the state of an ultra-fine powder (of sub-micron grain size and preferably of a grain size lower than about 0.1 micron), said compound being intimately mixed, in the state of powder (in particular of ultra-fine powder), with a diluting powder of a grain size at most equal to that of the compound powder, which permits, provided there is a suflicient percentage of inert diluting powder to avoid risk of coalescence of the metallic grains thus kept out of contact with one another by the grains of said inert diluting substance, of performing complete reduction, advantageously by means of hydrogen, of said metal compound, at a temperature ranging advantageously from 900 to 1100 C., the inert diluting substance which has served to the production of the alloy powderwhich diluting substance may be the same as that having served to the reduction treatment) being subsequently eliminated through any suitable physical or chemical .means, in particular by being attacked by means of a suitable acid under dilution and temperature conditions avoiding a substantial attack of the metallic grains obtained by reduction.

- geously consist of magnesia or calcium oxide,

3,449,l l5 Patented June 10, 1969 Among the alloys which may be obtained in the form of ultra-fine powders by such a method may be cited in particular the alloys containing at least two metals of the group consisting of iron, nickel, cobalt, molybdenum and tungsten.

As for the inert diluting substance it may advantapossibly barium oxide, the inert diluting powder being as above stated, of a grain size at most equal and preferably lower than that. of the metallic powder compound.

The proportion of inert diluting powder must, as above stated, he suflicient to keep away from one another the grains of the metallic compound, thus preventing coalescence of the metallic grains formed by reduction, which generally leads to adopting a proportion of inert diluting substance .such that, after reduction, the proportion in volume of the inert diluting substance is at least 25% of the total volume.

Every grain of the alloy to be obtained may then contain.

Either, according to a first embodiment of the invention, at least one metal obtained by reduction and at least one other metal obtained in the form of a powder, either alone or mixed with a diluting substance.

Or, according to a second embodiment of the invention, only at least two metals both obtained by reduction, either simultaneously from a single mixture as the result of a single reduction operation or separately from two distinct mixtures.

In both cases, it will be of interest to use the powdered metal or metals obtained by reduction when it is, or they are, still mixed with the inert diluting substance used in their formation, the subsequent effect of this inert diluting substance being hereinafter explained.

The first embodiment will first be examined. A distinction will be made between the case where the second mentioned metal is considerably more electropositive than the metal obtained by reduction, and the case where said second mentioned metal is of an electropositivity little different from that of the metal obtained H by reduction.

In the first case, the grains of the second mentioned metal will disappear, as grains, during the formation by thermal diffusion of the alloyed grains and, consequently, the grain size of the second metal must be sufficiently small to prevent the operation from lasting too much, without it being necessary to use, for this second metal, a grain size as small as that of the metal obtained by re duction.

For the sake of clarity, in this first case the metal obtained by reduction will be called acceptor and the other metal, the grains of which are to disappear, giver.

In order to obtain such alloyed powders, advantageously a halogenated and hydrogenated atmosphere vapor is made to act in the hot state upon an intimate mixture of a powder of an acceptor metal (obtained as above indicated), a powder of at least one giver metal and an inert diluting powder.

Of course, it is possible to use for this purpose a wholly elaborated acceptor metal powder, that is to say a powder made of grains free from any inert diluting substance but I it seems advantageous in view of the fact that the giver Subsequently to proceed to the action of the halogenated and hydrogenated gaseous medium advantageously performed in partly gastight boxes placed in a hydrogen atmosphere inside a furnace and containing, preferably mixed together, the chemical bodies necessary for creating in said boxes the desired hydrogenated and halogenated atmosphere, hydrogen either coming from the atmosphere in the furnace or being generated in the boxes, and

Finally to eliminate the inert diluting substance which has permitted of avoiding coalescence of the metallic grains in two successive circumstances (first during the reduction of the acceptor metal compound, and then during the addition of giver metal), this elimination being advantageously obtained by attacking the mixture by means of an acid (for instance nitric acid) in the case where the metallic grains are protected against such an attack by the presence, on the surface thereof, of a superficial diffusion alloy containing a protective giver metal (for instance chromium).

If the alloy grains are not so protected, elimination of the diluting substance is obtained in another suitable way, for instance magnettic separation, difference of density, action of a suitable acid in suitable dilution and temperature conditions.

As metals capable of acting as a giver metal in such a method of production of ultra-fine powders of alloys, in particular stainless or refractory alloys, may be cited, in particular, chromium, aluminum, silicon, titanium, tantalum, thorium, manganese and vanadium. It should be pointed out that the reducible metallic compounds subjected to the reduction operation may be either compound of commercial origin directly incorporated in the mixture at the beginning of the operation or compounds precipitated or co-precipitated in situ by chemical reaction before incorporation of the inert diluting substance.

Likewise, concerning the inert diluting substance, it is possible to use either a commercial product or a product elaborated in situ by precipitation or co-precipitation, for instance at the same time as the reducible metallic compound or compounds when the latter is or are elaborated in situ at the beginning of the operation.

On the other hand, it will be of interest to make use I of one of the following steps:

To incorporte a suitable liquid, such for instance as an alcohol, and in particular isopropyl alcohol, or a hydrocarbon, when it is desired to perform by the moist way the mixing and/ or the crushing of the metallic compounds and of the inert diluting substance,

To calcine the mixture, before reduction by a hydrogen stream, of the starting metallic compounds, such a calcination having for its effect to reduce the consumption of hydrogen and being, if necessary, performed in a decarburazing atmosphere, and

More especially for the preparation of ultrafine powders, to incorporate magnesium filings to the mixture to be subjected to the addition reaction in hydrogenated and halogenated atmosphere, said filings being intended to catch the traces of oxygen that might remain in said mixture.

In order to illustrate the preceding description some examples will now be given relating to the first case (that is to say that where one or several of the metals is, or are, strongly electro-positive) of the first embodiment, it being well understood that in each of these examples it would be possible, if it were desired merely to obtain an ultrafine metallic powder containing only the acceptor metal or metals to proceed to the elimination of the inert diluting substance once the operation of reduction of the starting metallic compound is achieved.

In all the following examples, the amounts that are indicated correspond to the production of one kilogram of ultra-fine metallic powder.

Example 1.-Metallic powder of an alloy of nickel and chromium (20%) 2.5 kgs. of commercial nickel oxalate and 0.65 kg. of calcined magnesia are mixed in 7.5 liters of isopropyl alcohol, the mixture being mixed for five hours in a ball crusher in such manner as finally to obtain the desired grain size even if said grain size were initially greater after which the liquid is driven out from this mixture.

The product thus obtained, preliminarily spread into a thin layer, is calcined during six hours at 750 C.

It is then reduced by hydrogen for five hours at 950 C.

To the product thus obtained we add 220 g. of fine magnesothermic chromium (grain size from 1 to 10 microns), 21 g. of ammonium chloride, 11 g. of iodine and 25 g. of magnesium filings and these constituents are intimately mixed in a helical screw mixing machine.

The mixture that is obtained is placed in a partly gastight nickel box and heated to 950 C. in a hydrogen atmosphere, for three hours.

The diluting substance is eliminated by washing with diluted nitric acid (for instance nitric acid at 40 Baum added with an equal volume of water), after which the product is Washed in distilled water and centrifugated, and the powder that is obtained is dried at C.

An alloy powder is thus obtained, having practically the desired composition and the grain size of which is below one micron.

Example 2.Metallic powder of an alloy of iron (74% chromium (18%) and nickel (8%) In order to obtain a more perfect mixture there is performed in this case a co-precipitation of iron and nickel oxalates, by dissolving, in 6 liters of water at 20 C., 2.65 kgs. of hydrated iron chloride, (FeCl 4H O) and 0.32 kg. of hydrated nickel chloride (NiCl 6H O'). 1.8 kgs. of oxalic acid are dissolved in 12 liters of water at 28 C. The two solutions are suddenly mixed together. The whole is allowed to rest, then is washed and the precipitate is separated.

To the whole of the co-precipitate thus obtained we add 0.7 kg. of calcined magnesia and 7.5 liters of isopropyl alcohol and the mixture thus formed is passed to a ball crusher where it remains for five hours, after which it is centrifugated.

The product obtained is then calcined in a slightly moist argon atmosphere for one hour at 650 C., then reduced by moist hydrogen for five hours at 1000 C.

To the product resulting from this reduction there is added 198 g. of fine chromium, 22 g. of ammonium chloride, 11 g. of iodine and 25 g. of magnesium in the form of filings the mixture being stirred in a screw mixer.

The product is then placed in a partly gastight iron box and heated for four hours at 850 C. in a hydrogenated atmosphere, after which it is washed in diluted nitric acid, then in pure water centrifugated and dried at 110 C.

We thus obtain an alloy powder containing no oxide having approximately the desired composition and the grain size of which is lower than 1 micron.

Example 21:

This example differs from the preceding one in that use is made of 22 g. of ammonium bromide instead of 22 g. of ammonium chloride and 11 g. of bromine instead of 11 g. of iodine.

Example 3.'-Metallic powder of an alloy of iron (55% chromium (25%) and nickel (20%) For the same reasons as in Example 2 we form in situ oxalates of iron and nickel, and also oxalate of calcium and for this purpose we dissolve, in 8 liters of water at 20 C., 1.97 kg. of hydrated iron chloride, 0.8 kg. of hydrated nickel chloride and 1.3 kg of calcium chloride. We dissolve 3.2 kgs. of oxalic acid in 20 liters of water at 28 C. We suddenly mix the two solutions. Then they are allowed to rest, after which the whole is washed and the precipitate is separated by centrifugation.

' This precipitate is calcined in a slightly moist argon atmosphere during two hours at 650 C., which has for its effect in particular, to transform the iron and nickel oxalate into oxides reducible by hydrogen, and the calcium oxalate into calcium oxide, which is not reducible by hydrogen and will constitute the inert diluting substance.

We perform the reduction operation in a moist hydrogenated atmosphere for five hours at 1000 C.

To the product thus obtained we add 275 g. of fine chromium, 25 g. of ammonium chloride, 12 g. of iodine and 30 g. of magnesium in the state of filings.

The product is placed in a partly gastight iron box and the whole is heated for four hours at 850 C. in a hydrogenated atmosphere of cracked ammonia. The product obtained is finally Washed, first With diluted nitric acid, then with pure water and centrifu-gated, after which it is heated at 110 C.

We thus obtain a non-oxidized alloy powder the composition of which is very approximately the desired one and of sub-micron grain size, which may be below 1 tenth of a micron for some portions of the product obtained.

. The percentage of nitrogen in the powder reaches 02 approximately (in the form of very fine chromium nitrides).

' Example 4.-Metallic powder of iron 67% nickel (12% chromium (18%) and molybdenum (3% We mix, in 7.5 liters of isopropyl alcohol, 1.14 kgs. of commercial ferrous oxalate. 0.37 of commercial nickel oxalate, 0.045 kg. of 'molybdic anhydride and 0.7 kg. of calcined magnesia. This mixture is treated for six hours in a ball crusher. The product finally obtained is then centrifugated and calcined in an atmosphere of moist argon for two hours at 700 C.

Then we proceed to the reduction treatment by means of hydrogen for six hours at 980 C., after which we add to the product thus obtained 198 g. of fine chromium, 22 g. of ammonium chloride, 11 g. of iodine and 25 g. of magnesia in the form of filings, the whole being intimately mixed in a screw mixer.

The product obtained is then placed in a partly gastight iron box which is heated for five hours in a hydrogen atmosphere at 950 C.

The operation is concluded by washing first in diluted nitric acid, then in pure water and by centrifugating followed by drying at 110 C.

. We thus obtain a non-oxidized alloy powder having very approximately the desired composition and the grain size of which is below 1 micron. The percentage of nitrogen in the powder reaches approximately 0.15 (in the form of chromium nitrides).

Example 5.--Metallic powder of an alloy of cobalt (65%) chromium (30% and molybdenum (5%) We mix for six hours, in a ball crusher, 1.5. kgs. of commercial cobalt formimate, 0.075 kg. of molybdic anhydride, 0.5 kg. of calcined magnesia and 6.5 liters of isopropyl alcohol. 1

We centrifugate. The product thus obtained is calcined, having been preliminarily spread into a thin layer, for six hours in air at 800 C. We proceed to a reduction by means of hydrogen for five hours at 1000 C.

We add, to the whole of the product thus obtained, 350 g. of fine chromium, 35 g. of ammonium chloride, 15 g. of iodine and 30 g. of magnesium in the form of filings, the whole being passed through a screw mixer.

The mixture thus formed is then placed in a partly gastight cobalt or nickel box and heated for six hours at We thus obtain a non-oxidized alloy powder of a composition very close to the desired one and the grain size of which is lower than 1 micron.

Example 6.--Metallic powder of an alloy of nickel (75%), chromium (21%), titanium (2%) and aluminum (2%) We mix for five hours, in a crusher, 2.42 kgs. of commercial nickel oxalate, 0.65 kg. of calcined magnesia, 7.5 liters of isopropyl alcohol after which we proceed to centrifugation then to calcination in air for six hours at 950 C.

Then the reduction treatment by means of hydrogen is performed for five hours at 1000 C.

We add, to the product thus obtained, 240 g. of fine chromium, 30' g. of titanium hydride, 22 g. of aluminum in the powder state, 20 g. of bromine, 12 g. of iodine and 22 g. of magnesium in the state of filings.

We place this mixture in a partly gastight nickel box, which is heated for five hours at 950 C. in an argon and hydrogen atmosphere. After this we proceed as in the preceding cases, to a washing in diluted nitric acid, to a. washing in pure water, to centrifugation and to drying at C.

We thus obtain a non-oxidized alloy powder the composition of which is very close to the desired composition and the grain size of which is below one micron. The alloy powder that is formed is free from any trace of nitrogen.

Example 7.Metallic powder of an alloy of nickel (97% and thorium (3%) We mix for five hours, in a ball crusher, 3.02 kgs. of commercial nickel oxalate, 0.775 kg. of calcined magnesia and 8.5 liters of isopropyl alcohol. Then the product is dried and calcined in air in the form of a thin layer for six hours at 750 C.

The treatment of reduction by hydrogen is then performed for six hours at 1000 C. Then we add to the resulting product 45 g. of thorium in the form of a fine powder, 20 g. of bromine, 12 g. of iodine and 20 g. of magnesia in the form of filings.

This mixture is placed in a partly gastight nickel box which is heated for four hours at 900 C. in an argon and hydrogen atmosphere.

Then we proceed to washing in acetic acid while cooling to washing in pure water, to centrifugation and to drying at 110 C.

We thus obtain a non-oxidized alloy powder, the composition of which is very close to the desired composition and the grain size of which is below 1 micron. This powder is free from any trace of nitrogen.

Example 8.Metallic powderof an alloy of molybdenum (63%) and silicon (37%) We mix for six hours, in a ball crusher, 0.945 kg. of commercial molybdic anhydride, 0.5 kg. of calcined magnesia and 4.5 liters of isopropyl alcohol, after which we proceed to a centrifugation.

The reduction operation is then performed by means of hydrogen directly on the centrifugated product, for six hours at 1000 C. and we add to the product thus obtained 402 g. of silicon in the state of a fine powder, 25 g. of ammonium chloride and 5 g. of iodine.

This mixture is placed in a partly gastight box and heated for four hours at 850 C.

We then proceed to washing in diluted nitric acid followed by washing in pure water, centrifugation and drying at 110 C.

We thus obtain an alloy powder the composiation of which is very close to the desired composition and the grain size of which is below 1 micron.

Example .9.-Powder of an alloy of chromium (85%) and aluminum (15% In a mixer we heat for twenty minutes a mixture of:

Magnesothermic chromium powder of a grain size of about 1 micron 850 Aluminum in fine powder of the quality used as pigment for paint 155 Calcined magnesia 900 Ammonium chloride 25 Magnesium in the form of filings 20 This preparation is introduced into a partly gastight chromized iron box which is heated for four hours at 1000" C. in a hydrogen atmosphere. During this heating, aluminum, which is substantially more electro-positive than chromium, is conveyed onto the particles of chromium into which it diffuses.

After cooling, the product is washed with diluted nitric acid, then with distilled water and dried at 110 C.

We thus obtain a powder of the desired composition, all the grains of which are homogeneous and of a size equal to or lower than 1 micron.

In a modification, we might utilize magnesothermic chromium which is not separated from the magnesia mixed therewith for its preparation, the proportion being substantially those corresponding to 2Cr+3MgO. 1760 g. of this mixture contain approximately 850 g. of chromium and 910 g. of magnesia.

Example 10.-Powder of an alloy of chromium (85%) and aluminum (15%) dispersed in alumina In a screw mixer We mix for twenty minutes:

G. Magnesothermic chromium powder of a grain size equal to or lower than 1 micron 850 Aluminum in fine powder of the quality used as pigment for paint 155 Calcined alumina in the form of fine powder 850 Ammonium chloride 25 This preparation is placed in a partly gastight chromized iron box heated for four hours at 1000 C. in a hydrogen atmosphere. After cooling, the product is in the form of a grey powder which is a dispersion in alumina of particles of a chromium aluminum alloy in the proportions of 85-15%, these particles being homogeneous and of a diameter lower 1 micron.

We will now examine, still within the scope of the first embodiment of the invention (application to alloys every grain of which contains at least one metal obtained by reduction and at least one other metal obtained in the form of a powder either alone or mixed with an inert diluting substance), the case where this other metal has an electro-positivity little different from that of the meta] obtained by reduction.

In this case, there will be produced only, between the metallic elements placed in the presence of each other, a co-diffusion due to the action of hydrogenated and halogenated vapors which serve to convey each of the metals on all the others.

Metals capable of such a co-diffusion may According to a first solution, be obtained individually, as above indicated, in distinct mixtures with an inert diluting substance, or

According to a second solution, be obtained simultaneously, still as above indicated, in the same mixture with an inert diluting substance, or again according to a third solution be obtained in the form of an ultra-fine powder by other suitable methods.

We then utilize, in this second case of the first embodiment of the invention, to form the grains of alloy, at least one first metal obtained by the first of the second solution and at least one second metal obtained by the third solution.

The first metal, including its inert diluting substance is mixed with the second metal and to the mixture are added chemical bodies intended to create the hydrogenated and halogenated atmosphere necessary to co-diffusion.

We will now give an example of alloy grains corresponding to the second case above referred to.

Example 11.Metallic powder of an alloy of nickel (60%), iron (20%) and molybdenum (20%) We mix, in 7.5 liters of isopropyl alcohol, 1.9 kg. of commercial nickel oxalate and 0.62 kg. of ferrous oxalate with 0.8 kg. of calcined magnesia and the mixture is treated for six hours in a ball crusher, after which it is centrifugated and the product obtained is calcined in the presence of slightly moist argon for two hours at 700 C. Then we proceed to reduction by hydrogen for six hours at 980 C.

We add to the total product thus obtained 200 g. of commercial molybdenum powder of a grain size below 1 micron and we proceed to an intimate mixing in a screw mixer for about one hour.

The product thus obtained is placed in a partly gastight nickel box after adding thereto 22 g. of ammonium chloride, 11 g. of iodine and 10 g. of magnesium in the form of filings. The diffusion treatment is performed in a hydrogenated atmosphere for six hours at 1100 C. We wash with cooled acetic acid then with pure water. We centrifugate and dry the product at 110 C. We thus obtain an alloy powder of a composition very close to the desired composition and the grain size of which is below 1 micron.

We will now examine the second embodiment of the invention, according to which the metals which constitute every alloy grain are all obtained by a reduction.

In this case, it is necessary to make use of metals the electro-positivities of which are of the same order of magnitude and the formation of the alloyed grains results, as in the preceding case, from a co-diffusion due to the action of the hydrogenated and halogenated vapors.

The metals which constitute the alloy may then be obtained individually either in distinct mixtures with an inert diluting substance or together in the same mixture with an inert diluting substance.

We will now give an example of this second embodiment.

Example 12.Metallic powder of an alloy of iron and nickel (25%) We mix, in 7.5 liters of isopropyl alcohol, 2.83 kgs. of iron oxalate and 0.79 kg. of nickel oxalate (both of commercial origin) with 0.95 of calcined magnesia, the mixture being treated for eight hours in a ball crusher, then centrifugated.

We then proceed to calcination under argon for two hours at 700 C. and then to reduction by hydrogen for six hours at 1000 C.

We then add 22 g. of ammonium chloride, 11 g. of iodine and 12 g. of magnesium in the form of filings, the whole being passed through a screw mixer.

The mixture that is obtained is placed in a partly gastight iron box and heated for five hours at 950 C. in a hydrogenated atmosphere.

The diluting substance is eliminated by washing in diluted acetic acid and cooled, then it is washed in pure water, centrifugated and dried in an oven at C.

We thus obtain an alloy powder the composition of which is very close to the desired one and the grain size of which is below 1 micron.

It should be pointed out that whatever he the application of this invention it is always possible to incorporate at least a metalloid, such as carbon or nitrogen.

This incorporation of a metalloid may be performed either after the formation of the ultra-fine powder or during the diffusion treatment in the hydrogenated and halo genated atmosphere.

This is an example of this last case.

Example 13.Metallic powder of an alloy of iron (74.5%), nickel (25%) and carbon (0.5%)

This example differs from Example 12 merely by the presence of 0.5% of carbon instead of the corresponding amount of iron, the operation being conducted in the same manner as stated in this Example 12, with the only dilferonce that when ammonium chloride, iodine and magnesium are added, we add also 6 g. of acetylene black.

Finally, it should be pointed out that the term hydrogenated atmosphere relative to the atmosphere surrounding the partly gastight treatment boxes includes pure hydrogen, mixtures of hydrogen with gases inert with respect to the powders to be treated and mixtures of hydrogen with gases having an action upon the powders to be treated (nitrogen for instance).

What we claim is:

1. The method of producing an ultra-fine alloy powder having a grain size not greater than about 1 micron which comprises, preparing a mixture of at least one powder of a reducible metal compound and of an inert diluting powder, reducing said reducible metal compound in the presence of said inert diluting powder, then adding to the reduced mixture at least one powder of a: different metal, then diffusing one of said metals into the other thereof by heating the resultant mixture in a hydrogenated and halogenated atmosphere, and removing said inert diluting powder from the resultant alloy powder.

2. The method according to claim 1 wherein said reducible compound 'is a body of the group consisting of oxides, oxalates, formiates and carbonates.

3. The method according to claim 1 wherein said reducible compound is reduced by hydrogen.

4. The method according to claim 1 wherein said re- 10 ducing step is performed at a temperature ranging from 900 to 1100 C.

5. A method according to claim 1 wherein the metal obtained by reduction is at least one metal of the group consisting of iron, nickel, cobalt, chromium, molybdenum, tungsten and alloys of at least two of said last mentioned metals.

6 A method according to claim 1 wherein the other metal of the mixture is obtained by a process other than reduction of a reducible compound and is more electropositive than the metal obtained by reduction.

7. A method according to claim 8 wherein the other metal of the mixture is a metal of the group consisting of chromium, aluminum, silicon, titanium, tantalum, therium, manganese and vanadium.

8. The method of claim 1 wherein at least two powders of said reducible metals are present and are obtained by coprecipitation from a common solution of compounds of said metals.

9. The method of claim 8 wherein said inert diluting powder is also obtained by precipitation from the common solution containing the compounds of said reducible metals.

References Cited UNITED STATES PATENTS 2,816,048 12/1957 Galmiche l48-126 3,157,532 11/1964 Galmiche 117-100 L. DEWAYNE RUTLEDGE, Primary Examiner. W. W. STALLARD, Assistant Examiner.

U.S. Cl. X.R. 117-107; 148126