US1339505A - Composition of matter for platinum surstitute in electrical terminals and other uses - Google Patents

Description

F. A. FAHRENWALD.

COMPOSITION 0F MATTER FOR PLATINUM SUBSTITUTE IN ELECTRICAL TERMINALS AND OTHER USES.

APPLICATION FILED FEB. I8, 1918.

1,339,505. Patented May 11, 1920.

fly-5 winrar UNITED sTATEs PATENT oEEIcE.

TRANI: A. EAHEENWALD, 0E CLEVELAND, omo, AssI'GNoE To TIIE EIIOTANIUM CCIEPANY, or CLEVELAND, omo, A CoEPoEATIoN oF oIIIo. y

AND OTHER UsEs.

d www of Letters ment. Patented May 11, 1920. Original applications No. 108,991, lcd' July 13, 1916, and No. 129,911, filed November 6,1918. Divided and this application illed February 18,1919 vSerial No. 217,885. i .i

To all whom it may concern.'

Be it known that I, FnANx A. FAIIEEN- WAL'D, 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 Composition of Matter for latinum Substitute in Electrical Terminals and other Uses, of which the followin is a full, clear, and ex` act description, re erence being had to the accompanying drawings.

This invention relates to an improvement in alloys and has for its object to provide a composition of metal which may be employed in many cases as a substitute formetallic platinum and expensive platinum alloys in various types of electrical construction, as spark devices, resistance elements, thermo-couple elements, etc., and in articles of jewelry, chemical containers, and the like, as well as in dentistry philosophical instruments and surgery. 'lhe qualities of platinum which render it of such great use in these fields have been Iits hardness (especially when alloyed with iridium), its high melting point (which is also heightened y alloying with iridium or the like), and its resistance to oxidation and chemical action, which prevents it from erosion by electrical influences or from corrosion by acids or oxidizing influences.

The objects of my invention are the provision of an alloy material which shall be substantially'equal to platinum in respect of hardness, melting point, and electrical and chemical resistivlty so as to be usable for spark points, electrical terminals, resistance elements, electro chemical apparatus, chemical containers, and other uses where it is exposed t0 severe corrosive conditions. Another obj ect is the provision of an alloy havin the above characteristics and also sufficiently malleable, ductile, and homogeneous to permit ofl rolling, drawing, stamping or otherwise working to the desired shape; the provision of an alloy of such homogeneous character as not to be hot short or subject to selective corrosion; the provision of an alloy which shall not only conserve the worlds supply of platinum but shall be less expensive than platinum; while other objects and advantages will appear as the descrip tion proceeds; this application being a vision of my two earlier applications Nos.

vIn view of the 108,991 and 129,911 sled July 13, 191e and November 6, 1916, respectively.

The exacting Inature of the uses in view immediately exclude from consideration all metals of a readily fusible or oxidizable nature; and `alloys of the solid solution type are always preferable to other alloys as bemg more ductible, malleable, homogeneous alld chemically resistant than other types of a oys.

I have discovered that the alloys of gold and palladium, if made of the proper percentage composition, and of the proper degree of purity, (or if certain improper impurities are avoided), will make a complete series of solid solutions of remarkable malleability, ductility and homogeneity; of a hardness fully comparable with that of platinum, a melting point sufliciently high for all practical purposes for which platinum is generally used, an electrical resistivity fully equal `to that of platinum, and a chemical resistivity even more pronounced than that of platinum. fact that a substitute for platinum is the object of this invention platinum itself should not be included to more than a small percentage, although in small quantities it is not injurious. Likewise the metals rhodium, ruthenium and iridium are too rare and costly to be used in large amounts, although they are not deleterious. In fact commercial palladium contains on the average about one half of one per cent. of platinum as' an impurity and, requently other noble metals as iridium or rhodium also; itis very rarely free from these substances, especially platinum, and I have known commercial palladium to contain as much as ive per cent. of platinum. The cost of refining being greater than the value of the noble metal impurities, I have never taken the precaution of purifying the palladium, and consequently my invention is t0 be considered as independent of the presence or absence of these substances tol a small percentage, whether intentionally or inadvertently present. against the presence of base metals, such as iron, cobalt, nickel, copper, lead and other oxidizable substances.

In the drawings accompanying and forming a part of this application, Figure 1 rep- It is necessary, however, to guard coMrosITIoN CE MATTER Eon. PLATINUM suns'rITUTE` vIN ELECTRICAL TEEMINALS resents the melting point and hardness curves of the gold-palladium series; Fig. 2 illustrates the melting points and hardness value of pure gold, silver, platinum and alladium upon the same scale; Fig. 3 il ustrates the conductivity (both thermal and electrical) of the gold-palladium series;-Fi 4 illustrates the conductivities of pure gol silver, platinum and palladium upon the same scale; Fig. 5 represents a photomicrograph section showing .the se egation of palladium from achilled solutlon in gold;

ig. 6 represents a photomicrograph section of the same alloy magnified much more strongly; Fig. 7 represents the condition of the same alloy upon slow cooling; Fig. 8 illustrates a pair of spark points constructed from my im roved gold-palladium alloy; and Fi 9 i ustratesa chemical utensil of the sai improved material.

The range of temperature through which partial fusion occurs in an alloy of gold and palladium is very small both ascending and descending, and the melting point increases rapidly with the first increment of palladium, so that a decided advantage is afforded by the addition of small proportions of this substance, out of all ratio to its cost. It will also be seen from Fig. 1 that the hardness of the alloy is greater in each case than the hardness-of either constituent, being at a maximum substantially at the time that the two metals are present in equal atomic proportions, which is equivalent approximately to palladium 40, gold 60 by wei ht. A hardness equal to that of platinum 1s obtained with only twenty per cent. of palladium, while the maximum hardness is about twenty per cent. greater than that of pure platinum. Reference to Fig. 3 shows that the conductivity of the alloy is much less than the conductivity of either of the component metals, the curve showin a very decided slope at each end, indicatlng a sudden increase of resistance caused by the admixvture of a small amount of the other metal, the conductivity also, as will be expected, reaching a minimum under the condition of equal atomic proportions. In fact an alloy of gold eighty-five per cent. palladium fifteen per cent. (atomic) has the same resistance as pure platinum, while an increase in the palladium content lowers the conductivity only to one third that of platinum; this, coupled with the chemical resistivity of the alloy and its resistance to fusion or oxidation at high temperatures, indicates clearly its value as an electrical resistance wire, for spark points it can be made wide and low to offset this as shownl in Fig. 8. In fact the 20 per cent. alloy which is the one most frequently used, is not appreciably inferior to platinum in this regard.

gation upon cooling is very small, but -experience proves that if a molten solution of .the two substances containing more than about ten atomic per cent. of palladium is l suddenly chilled, a sli htly segregated condition 1s secured suc as represented in exa gerated fashion in Fi.` 5 and in a more hig ly magnified way in ig. 6, the' center of each metallic crystal being peculiarly rich in palladium and the margins of the crystals grading off to a lower composition. An artic e so constituted possesses a resistivity to heat, electrical abrasion and chemical action equivalent only to the lowest alloy which it contains; but by cooling the same alloy slowly or by maintaining the alloy fora considerable eriod at a temperature near but not above its melting point, a re-arrangement of each crystal can be secured and perfect homogeneity obtained as shown in Fig. 7.

For many uses in s ark points, electrical contact terminals, philoso hical ap aratus and dentistry, an alloy ofp old andp palladium in the proportions o palladium 10 per cent. gold 90 per cent. (atomic) will be suflicient, (equivalent to Pd. 5.6, Au. 94.4 by weight) since such an alloy will have a melting point 100 C. higher than that of pure gold and a hardness substantially midway between that of gold and platinum. f

Such an alloy, however, is hardly sufiiciently resistant physically for use in crucibles and like chemical apparatus, owing to its softness and the dan er of accidental melting, although it is o great value in dental foil, its hardness being suiiciently small to permit manipulation, and its melting point being sufliciently high to permit the melting of gold thereon if performed with reasonable care.

For the majority of uses, both electrical and chemical, I recommend an alloy containing approximately gold 80 per cent. atomic),palladium 20 per cent. (atomic) equivalent approximately to Au. 88, Pd.

2, by weight), since such an alloy will have a melting point approximatel 1250o C. which is sufficiently high to avoi an danger of being melted accidentally un er ordinary conditions of use. Such an alloy has a hardness substantiall equal to that of platinum,l and is o such resistance to chemical, electrical and atmospheric corrosion as to be satisfactory in all cases excepting where the 4requirements are excessively rigid. For the last named uses I recommend an alloy of gold 60 per cent. (atomic) palladium 40 per cent. (atomic equivalent to Au. 73.6 Pd. 26.4, by weight since such an allo has a hardness substantially equal to t at of possesses a melting point of approximately 1350 C.

w'hich is 300O more than that of gold, and will resist practically all the corroding influences which pure platinum will withstand, and many to which pure platinum will succumb.

As heretofore explained I do not limit myself against the use in the above named alloys of small quantities of other noble metals, particularly such as are ordinarily found in association `with palladium, so long as the same are used only in small amounts compared with the primary substances herein mentioned. It is necessary, however, that base metals be excluded.

Having thus described my invention, what I claim is l. A spark point consisting largely of gold and palladium whose melting point is above 1150o C. and. whose hardness is at least twice that of gold.

2. An electric current communicating terminal made of an alloy comprising gold and to 40 atomic per cent. of palladium.

3. Electrical apparatus made of an alloy containing gold and ten to 40 weight per cent. of palladium.

4. Apparatus of the character specified having a Working surface consisting vof an alloy containing palladium and one or vmore noble metals surrounding palladium in the periodic table, gold constituting at least At. per cent., and palladium at least 10 At. per cent. of such alloy.

In testimony whereof I hereunto aix my signature.

FRANK A. FAHRENWALD.

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