US1296938A - Composition of matter for platinum substitute. - Google Patents

Description

F. A. FAIIRENWALD.

COMPOSITION 0F MATTER FOR PLATINUM SUBSTITUTE.

APPLICATION FILED IuLv I3, 191e.

l ,296,938. Patented Mar. 11, 1.919.

w 1100 gj/00 man 10 Au a a 71 ma 11a/m6 @i Ugg l da laolfalaa'af {m} mo Io 20 sa 4050607012055 W7.'

UNITED STATES PATENT oEEIoE.

FRANK A. FAHRENWALD, 0F CLEVELAND, OHIO, ASSIGNOR TO THE RHOTANIUM COMPANY, 0F CLEVELAND, OHIO, A. CORPORATION OF OHIO. v

COMPOSITION OF MATTER FOR PLATINUM SUBSTITUTE.

specification of Letters Patent. Patented Mar, 11, 1919 Application mea July 13.1916. serial No. 108.991.

To cZZ'wwmfz't/may cancer/nf: f. i.

Be it known that I, FRANK A. FAHREN- WAL, a/citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Compositions of Matter for Platinum Substitute, of which the following is a full, clear, and exact description, reference being had to the accmpanying drawings. in a loys, and has for its object to provide a com osition of metal which may be employe in many cases asa metallic substitute for platinum and expensive platinum alloys in various typesI of electrical construction, spark devices, resistance elements, thermo-couple elements, etc.) and in articles of jewelry, chemical containers, and the like, thus effectively conserving this scarce and valuable metal for those scientific purposes in Iwhich its use is at present imperative.

The physical and chemical properties that I have developed in my alloy are the result of scientific investigations covering a period of years, and they selection of the components of my alloy, and the adjustment of the proportions of these components, are based upon a study of the relations of each metal to the other, and to the alloy body as a whole.

In view of thisfact, I consider it advisable to describe in some detail the methods and principles that I have discovered and used in working out my invention. Before undertaking the development of a new material that would serve instead of platinum in its various applications, it was necessary to adopt certain criteria which should serve as specifications for physical and chemical properties of any material that would be satisfactory.

- high temperatures are the prime requisites,

invention relates to an improvement y These requirements inV a platinum substl'tute may be detailed as follows:

1. Its melting point should be higher than pure gold. (This would not be necessary in artlcles of jewelry and the like but for general chemical ware and units of electrical construction high melting-point is imperative.)

2. It must not be affected by chemicals or gases encountered in its application.

3. It must not oxidize at any temperature up to and including that necessary to melt it. (This is very necessary in chemical applications and of great importance in the case of spark devices. I have observed that the arcing produced in many Vbreaker designs is sufficient to melt the surface of even pure platinum. A` careful microscopical examination of the surface' of a used point Y duced on the contact surface of the points themselves by this conditionA of local high temperature, the circuit would be broken, or at least it would be most diilicult to start the device after it had once been stopped, duev to thel insulating effect of .this oXid film. This is the chief objection to the use of tungsten contacts.) i

4. It must possess sufiicient strength and hardness to withstand stresses tending to change its form while in place. (Even pure platinum is deficient in this property, but this is'often overcome by adding upto 30% of iridium, which, however, greatly increases the cost. In my experiments with contact devices it was observed that soft metals suchA as gold, were battered out of shape by the continued hammering'efect. Strength is very valuable in chemical and other electrical construction also.) y

5. The electrical resistance should preferably be greaterthan that for platinum. (A material of this nature often finds applica- `tion in electrical heating units. I have found that low electrical conductivity is not amount of current carried is very small for the large cross section employed, while the thermal and electrical resistance across surfaces of contact formed in fastening are very greaJ vhen compared with that of the metal itsel 6. It must Abe suliciently malleable and ductile to permit of rolling, drawing, stampin or otherwise working, to a desired shape.

g. Its cost of production must be low as compared with that of platinum.

It will be seen at once that the above requirements of physical and chemical stability at high temperatures form a set of specifications of a very exacting nature, and at once exclude from consideration all metals of a readily fusible or oxidizable nature.

A consideration of all materials at present available, using the above specifications as criteria, proved that no single metal was suitable., It was evident, therefore, that any Search forv the rdesired material must be in the field 'bf alloys, since experience has shown that the physical and chemical prop erties of a metal may be radically changed by the addition of varying amounts of another elem'ent, or of several elements.

Vhen two or more metals are brought together in the liquid state, they behave exactly like two ordinary liquids. When the temperature is lowered the solidified mass may contain any one of the four following-constituents: pure components; solid solutions; compounds; and eutectics-or some combination of these. While a theoretical contemplation of the properties of diil'erent metals will to some extent suggest the probable properties of an alloy thereof, still it is only by experiment and .test that its mechanical and physical properties can be absolutely settled. However, if a certain application is desired as in the problem under consideration, a definite limit may be placed upon the number and amount of constituents permissible.

Fortunately, the number of fundamentaly conditions is limited to four, as given above. Pure metals impart their own characteristics; solid solutions are, in general, of a ductile and malleable nature (if formed of ductile metals, or of a preponderance of one ductlle metal) compounds and usually, eutectlcs, are hard and brittle; while the latter, even when plresent in very small amounts, tend to soli ify between the grains of the alloy, thus producing segregation and destroying its ductility.

Alloys of the solid-solution type would therefore produce the most satisfactory platinum substitute, for compounds are too brittle to permit of being worked, while the segregation produced by eutectics would produce selective erosion and corrosion. The alloying of metals serves to increase hardness, to produce resista/RCC t0 QOI'IOSOLI,

etc., but my experiments have shown it will not prevent oxidation at or near the melting temperature. For instance more than a trace of base metal, as copper, nickel, iron,

etc., in any of the precious metals will cause present in appreciable quantities, wherefore the substance sought must be a solid solution alloy of two or more of the noble metals silver, gold, palladium, platinum, rhodium, iridiu'm, ruthenium and osmium.`

In view of the fact that a substitute for platinum was the object of my researches, this metal was not to be included to more than very small amounts, in the desired alloy. Likewise the metals rhodium, ruthenium, osmium, and iridium are too rare and costly to be used at least in large amounts, in an inexpensive platinum substitute.

Thus after my researches had included the entire list of elements separately, it` was found that only gold, silver, and palladium fulfilled to the greatest degree, the preliminary set of governing specications. Not one of these, however, was suitable, when used alone. Silver is too soft and of too low melting point, and is not suliiciently chemically inert. Gold, also, is not sufliciently hard or refractory, while palladium alone is too costly.

These three metals form solid solution binary and ternary alloys in all proportions, although it is found that differences in composition"V have very great eil'ects upon the hardness, meltin chemical resistivity of the resulting alloy. Some of these effects are illustrated graphically in the drawing accompanyin and forming a part of this application werein Figure 1 represents the hardness curve and melting point curve for gold-silver alloys; 7Fig. 2 the similar curves for the silver palladium alloys; Fig. 3 the similar curves for the gold palladium alloys; Fig. 4 represents a photomicrograph section of the gold palladium alloy, Fig. 5 a photomicrograph section ofthe sllver palladium alloy; Fig.

pomt and electrical and 6 a diagram showing the melting points of.

other increases the hardness to a remarkable extent. This is shown in the curves given for the three binary series .of old-silver, silver-palladium, and gold-pa.l adium, fFigs. 1, 2 and 3, respectively. These metallic solid solutions are truly crystalline, and in the crystalline arrangement (or space lattice `The space volumes occupied by atoms of different elements are not the same, so that, if the metals, whose atomic volumes are not equal and whichl possess other intrinsic differences, form symmetrical, solid-solution-space lattices, there must result a contraction of the larger atom and-an expansion of the smaller, and other energy adjustments,thus producing an internal strain which increases the hardness, lowers the electrical and thermal conductivity, and variously affects other properties of the components.

It is evident also that this internal strain and the corresponding .resulting properties will be a function of the number of atoms dissolved. This is shown in the case of the hardness curve, which shows a maximum at the point where equal atomic proportions prevail, z. e., at 50 atomic per cent. of each component in a binary series. The curves for electrical and thermal conductivity likewise show a minimum at this composition. Experiment proves that those metals, like gold and silver, which possess the most nearly equal atomic volumes will replace each other and form solid solutions most readily and with the least amount ofsegregation.V Their atomic volumes are: gold, 10.20; silver, 10.23. Palladium, however, with an atomic volume of 8.9 tends to segregate upon solidiication of thebinary allo with either, as shown in Figs. 4 and 5 w ich are photo-micrographs, showing the.

internal structure of silver-palladium -and gold-palladium alloys respectively, this tendency being partiularly marked in the case of palladium silver alloys. I-have discovered, however, that the addition of a quantity of gold to this palladium-silver alloy markedly decreases the segregating tendency arid signally improves the character of the alloy in other respects. Y"

I have, therefore, discovered that a ternary alloy containing gold, silver, and palladium fulils the requirements of a platinum substitute in a remarkable degree. The pro-y portions ofvthese ingredientsmay be varied through a considerable range depending upon the price limitations and the rigidity of the requirements.l The addition of silver to an alloy of gold and palladium even up to 50 atomic per cent. has comparatively small effect upon the melting point of the composition but decreases the cost per unit volume in great degree, and in case of alloys containing a relatively low per cent. of palladium is of material service in increasing the hardness.

The addition of palladium even in small quantities to alloys of gold and silver greatly increases the melting point and hardness and chemical resistivity. The addition of gold to alloys of silver and palladium markedlydecreases the segregating tendency and increases its chemical resistivity.

The portion of Fig. 6 included withinthe heavy line thereon indicates the area of most valuable commercial percentages, those alloys corresponding to the lower right hand portions of this area being the least expensive though ysuiciently conformin to the above expressed basic requirements or many electrical purposes. Alloys corresponding to portions above and toward the left will conform to more rigid requirements. For example any alloy fallin within the left hand half of this area exhi its the most perfect physical 'and chemical stability at high temperatures, fully comparable in most of its applications to that of platinum. n Investigation of these ternary proves the following: (l) That the addition of over one per cent. of silver to any alloy containing gold and palladium increases the hardness up to a certain limit, lowers the melting point very little, and at the same time decreases the cost.

The increased hardness is. very valuable, in many cases where increased silver is not objectionable and the decreased cost is of importance. By adding varying amounts of silver therefore, I obtain the same necessary hardness as would be obtained by using higher percentages of palladium, as shown on Fig. 3. For certain chemicalapplications `of rigid requirements, however, I use the pure binary alloy of gold and palladium.

(2) -The addition of more than 10 atomic of palladium to the gold-silver series raises the melting point to a degree where ltheV alloys can withstand high temperatures without fusing. The approximate melting point of any alloy within the diagram may be judged from its position with reference to the series of dotted lines which areJ drawn through points representing alloys of equal melting point. These lines are marked 11000' C.,l150 C.,1200 C.,etc. The alloys decrease in degree ofnobility from thegold end of the series, but to a very slight extent for small amounts of silver but the increased hardness. increased electrical resistance and decreased cost in many cases more than balance this.

3) The addition of more than 5 atomic of gold to the silver-palladium alloys reduces segregation, reduces volatilization and alloys increases resistance to erosion and corros1on.

(4) I ernary'alloys of these vthreemetals` are more satisfactor than a silver-palladlum or gold-silver blnary alloy of any com;

position.

Limits ofA palladium.

4 Because of the results of my experiments as outlined above, and their evident lrelation to theatomic proportions of these elements,

y I have based my descriptions and claims upon the relative number of atoms or atomic percentages of each element present.. My experiments have shown that a melting point of at least 1150o C. is necessary in a platinum substitute to be used under most avorable conditions.

lixed the lower limit for palladium content I, therefore, have to aline coinciding with that dotted line representing a melting temperature of 1150 Because of high cost andl other undesirable features, as tendency to segregate, etc., I ix the upper limit of palladium at 40 atomic Limits of gold.

I have found'that at least 5 atomic of gold is required Ato produce homogeneous la1- loys, and to reduce excessive spark erosion and 80 atomic of that element.

Alili Lim/its of silver.

My experiments have shown that, for certain purposes where increased hardness or electrical resistivity is required, itis advisable to add over 1 Iatomic of silver. I have found that rhodium, iridium, etc., are better than silver but too costly;

If conditions of application are not too r1g1d, even up to 75 atomic of silver may be used. The limits of total variation in composition are therefore contained within the area bounded by the lines AB-BC- CD-DE-EF-FA.

By the term palladium asused herein I mean the commercial material which contains on the average about one-half of one` per cent. of platinum as an impurity and frequently other noble metals as gold, iridium, or rhodium; it is very? rarely free Afrom these substances, especially platinum,

and in exceptional instances has run as high as ve per cent. of that substance. I have always ignored this lnoble metal impurityas not injuring the product, which from the nature of the commercial substances used 'will frequently contain small percentages of these substances, in addition to which small amounts of the same may be added as heretofore suggested.

The alloys near the gold end of this area are more noble in character, are more insoluble in acids, and less afected by gases than those higher in silver. None, however, are in the least oxidized at any temperature by arcing across terminals composed of them.

Below 5 atomic of silver these alloys are practically insoluble in boiling concentrated acids, as hydrochloric, nitric or in alkalis. Above 5 atomic 'of become slightly soluble in nitric or sulfuric acids, though practically insoluble in aqua regia.

It is advisable, but not necessary, to cool highpalladium alloys very slowly to allow diffusion to take-place.

Having thus described my invention, what I claim is l 1. A platinum substitute containing palladium together with silver and one at least of the other noble metals immediately surrounding palladium in the periodic table, all of the 'constituent metals having atomic weights, between one hundred and two hundred times that .of hydrogen, the palladium constituting not less than ten atomic per cent. of the whole.

2. A platinum substitute containing palladium alloyed with silver and one or more of the metals in the gold series of the periodic table,I all the constituent metals having atomic weights between one hundred an two hundred -times that of hydrogen, silver being preponderant, and the palladium constituting not less than about ten atomic per cent. of the whole.

3. A composition of matter for platinum substitute in electrical and chemical apparatus containing between ten and forty atomic per cent. of palladium, the remainder being gold and silver.

,4. A composition of matter containing palladium from 10 at. to `40 at. gold 5 at. to 80` at. and silver 1 at. to

5. A-compositionfof matter containing at least '10 atomic per cent. and not over 40 atomic per cent. of palladium, at least 10 atomic per cent, and not over eighty atomic per cent'. of silver, the remainder being a metal or metals of the gold series in the periodic table having an atomic weight between one hundred and two hundred times that of hydrogen. y

6. An alloy for the distributionof electric current by contact composed of gold and silver in approximately equal proportions and approximately ten per cent. of,- palladium.

7 A11 alloy for the distribution of electricsilver, they 1,2ee,sas

current by contact composed of gold and silver with the addition of ten `per cent. of palladium.

8. An electric sparking terminal made 0f gold and silver in a preponderating degree with the addition of at least ten per cent. of palladium.

9. A11 electric current communicating element formed of an alloy consistingy of approximately forty-five per cent. of gold, forty-*five er cent. of silver, and ten 'per cent. of pa ladium.

1,0. An electrlc current communicating element formed of an alloy containing palladium and silver together with one or more of the other noble metals immediately sur? rounding palladium in the periodic tablekall of the constituent metals having atomic weights between one hundred and two hun dred times that of hydrogen and the palladium consti-tutin not less. than about ten atomic per cent. o the whole.

In testimony whereof, hereunto aix my signature,

FRANK A. FAHRENWALD;

Images