INDUSTRIAL AND ENGINEERING CHEMISTRY
686
Vol. 18. No. 7
Some Sand-cast Alloys of Aluminum Containing Cobalt‘ By Samuel Daniels WAR DEPARTMENT, AIR SERVICE, MCCOOK FIELD,DAYTON, OHIO
OBALT-bearing alloys of aluminum have received but scant mention in the literature. Brunck2 in 1901, investigating metallic compounds in aluminum, found the bluish Co3A113; and later Guillet3 published a liquidus curve for the binary system. Gwyer4 in 1908 presented the equilibrium diagram shown in Figure 1. At the aluminumrich end occurs the compound Co&lI3, which forms the eutectic with less than 1 per cent of cobalt a t 644’ C. (1191’ F.) and is practically insoluble in aluminum in the solid state. Schirmeister gave his attention to the properties of both the
C
1700,
,
,
,
,
,
,
I n order more carefully to determine the properties of sandcast aluminum alloys to which cobalt has been added, using the current types of raw materials, foundry practice, test specimens, heat treatment, and methods of testing, the Material Section, Engineering Division, Air Service, U. S. A., conducted the present investigation. The work concerns primarily the binary series bearing cobalt in contents up to 10 per cent; but Borne reconnaissance was effected in ternary and more complex alloys carrying-besides cobalt-copper, nickel, and silicon. Methods of Alloying
Fourteen melts of various compositions were prepared. Nine melts of binary aluminum-cobalt alloys were cast in the form of test specimens to the calculated cobalt contents of 0.5, 1.0, 2.0, 3.0, 5.0, and 10 per cent. After this group had been studied, five other alloys were m a d e 9 6 aluminum4 copper, 95 aluminum-4 copper-1 cobalt, 94 aluminum4 copper-2 cobalt, 93.75 aluminum-4.75 copper-1 silicon0.5 cobalt, and 95 aluminum-3 nickel-2 cobalt. Table I gives the analysis of the aluminum ingot and of the hardeners. The aluminum was of “Special” grade under Air Service Specification 11,010-B, having an aluminum content, by difference, of 99.56 per cent. The aluminum-cobalt hardener was alloyed from commercial cobalt metal and the aluminum previously described. No analysis was made of this cobalt, but it was evidently of 99f per cent purity. The copper, nickel, and silicon were introduced as binary hardeners. Per cent Cobalt F i g u r e 1-Equilibrium D i a g r a m f o r A l u m i n u m Cobalt Alloys (Gwyer)
sand-cast5 and the rolled6 alloys. The strength of alloys containing up to 20 per cent of cobalt, cast in dry-sand molds as test specimens which were machined from 16 mm. (0.630 inch) to 12 mm. (0.472 inch) in diameter over a length of 120 mm. (4.72 inches), for no percentage of cobalt exceeded the strength of the pure aluminum, but it was considered that the alloys with from 9 to 12 per cent of cobalt might be useful because of their density and their resistance to atmospheric corrosion and despite the coarse crystallinity imparted by the cobalt. He improved upon this objectionable structure by adding about 1 per cent of tungsten or of molybdenum. As to the mechanical working of the aluminum-cobalt alloys, his results showed that rolling was possible with cobalt contents up to 11 per cent and that 4 per cent of cobalt was the most advantageous composition. During the war the British experimented unsuccessfully with complex itluminum-base alloys containing cobalt for piston materials.’ Cobalt is rarely, if at all, a constituent in the present commercial alloys. 1 Received February 17, 1926. Published by permission of the Chief of Air Service, War Department. * Ber., 34, 2733 (1901). a GLnie ctoil, 1901. 4 2. anorg. Chem., 67, 140 (1908). 8 Metallurgic, 8, 650 (1911). 0 Stahl u. Eisen, 96, 648,873, 996 (1916);Rev. mdfal.,19, 464 (1915). 7 Institute Mechanical Engineers, 11th Rept. to Alloys Research Comm., 1991, p. 25.
FIGORE 2 TENS11E BHRCDNfSS PROPfQTIL3 OF
SAND- CAST ALUM/NUM-CiBALT ALLOYS
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1926
687
The aluminum-cobalt alloys were poured from the various temperatures indicated in Table IV. When, with a given Melt MATERIAL Copper Iron composition, several pouring temperatures were tried, the 3538 A1 ingot 0.04 0.26 ... . ... practice was first to take the alloy to the highest temperature, .. 4297 AI-Cu hardener 5 0 . 0 1 0 . 1 8 4901 AI-Ni hardener 0.07 .. . . ::: pour the test specimen molds, and then to pig the remaining 4903 AI-Co hardener 0.10 . metal in chill molds. When the pigs were cold enough to 4960 AI-Si hardener 0 . 1 6 0 : IS . . .. .. handle with tongs, they were returned to the crucible and I n the manufacture of the 90 aluminum-10 cobalt hardener' heated to the next highest pouring temperature, etc. These the aluminum was carried to 816" C. (1500" F.) in a plum- temperatures were ascertained by using a bare chromelbago crucible and the cobalt was added gradually. There alumel thermocouple and a potentiometer. The copper and was some ebullition (and no rise in temperature such as oc- nickel-bearing alloys containing cobalt were all poured from curs in the preparation of aluminum-nickel hardener), but about 704" C. (1300" F.). the cobalt seemed to melt very slowly. After 15 minutes of The tension test specimens were cast to size (1.28 cm., or desultory soaking, the temperature of the bath was increased 0.505 inch in diameter), three to the mold, with individual to 999" C. (1830' F.), a t which point solution occurred. A risers and a common pouring sprue, in green Albany-Sandusky sand. A vhotouaDh of the rather heavy layer of dross Air Servick Staida-rd TB-1 was removed from the alloy, t e s t b a r mold has been which was then poured into HERE is no useful casting alloy in the binary series shown in a previous article.* s h a l l o w i n g o t s to avoid containing up to 10 per cent of cobalt. The addisegregation. tion of more than 0.5 per cent of this element increases Methods of Testing The foundry practice emthe solidification shrinkage greatly, and more than 1 ployed in alloying the binary per cent imparts a crystalline fracture, whose coarseC H E M I C AANALYSISL series is outlined in Table 11. ness is the more pronounced as the pouring temperaWhen copper and iron were The proper a m o u n t s of tures become necessarily high. The tensile properties to be determinedaccurately, aluminum and of aluminumare inferior, even at the optimum composition of from the samples were dissolved cobalt hardener were melted 0.5 to 1.0 per cent of cobalt, and they are not improved in the acid mixture. The t o g e t h e r in a plumbago by heat treatment. Corrosion testing indicated that silicio a c i d was then recrucible, with gas or oil as the alloys are superior to those in the aluminum-copmoved, +d subsequently the fuel. Essentially the per series. Metallographically, the A1-Co3Alla(I) eutecthe copper was plated from same general procedure was tic point occurs probably in the neighborhood of 0.6 per the sulfuric acid solution. used in the case of those cent of cobalt; and it is doubtful whether the transThe iron was found, if the alloys which were to contain formation line established at 550' C. by Gwyer has cobalt content was less than copper and nickel. proper basis. about 1per cent, by passing Cobalt carries over its peculiarities into the ternary Pouring T e m p e r a t u r e s t h e f i l t r a t e through the and more complex alloys. The 95 aluminum-4 copperand Casting of Test Jones reductor and titrating Specimens 1 cobalt alloy has fairly good tensile properties but with permanganate. J&th shrinks heavily. The addition of 1 per cent of silicon higher cobalt content, its 'tV h e r e a s t h e m e l t i n g neutralizes the shrinkage caused by small amounts of pink color interferes and the point of the binary alloys cobalt. It seems that heat treatment can effect no standard method for iron poor in cobalt content is not great improvement in the tensile properties of polynary is probably necessary, unless far above that of the eutectic alloys bearing cobalt unless a ternary cobaltiferous come l e c t r o m e t ri c titration is (644" C . or 1191" F.), that pound may be formed. possible. When the copper of the alloys c o n t a i n i n g content could be estimated, over about 2 per cent incaustic separation was emc r e a s e s rapidly with increase in cobalt" (Figure 1). It was decided to examine the ployed. The copper and cobalt were simultaneously plated effect upon shrinkage, soundness, and mechanical properties out of an ammoniacal solution and the cobalt was deterof pouring from within the solidification range and from about mined by difference. The results of these analyses are given in Tables I and 111. 60" C. (140" F.) above the liquidus. T a b l e I-Percentage
Composition of Raw Materials
AlumiMannum Silicon ganese Cobalt Nickel (Diff.) 0 . 1 4 None 99.56 0.08 0.15 20123 0.15 . 9:90 . . . ... 11.66 . ...
T
T a b l e 11-Foundry co calcd. Per cent 10.0 10.0
Melt 4903 5090-1 -2 -3
5091-1 -2 -3 5092-1 -2 -3 5093-1 -2 5094-1 -2 5101 5111-1 -2 5115 5116 ,5117-1 -2 a
5.0
3.0 1.0 0.5 None 2.0 2.0
0.5 10.0
T a b l e 111-Analyses of M e l t s Investigated -Cobalt-(Per cent)
Practicea
(Furnace, Monarch) Wt. of Time in charge furnace FUEL Lbs. Minutes OBSERVATIONS h-ew melt Gas 40 140 Remelt 4903 Oil 35 10 Remelt 5090-1 20 7.5 Remelt 5090-2 25 5.0 New melt Oil 8.0 20 Remelt 5091-1 5.5 15 Remelt 5091-2 3.0 10 h'ew melt Oil 8.0 30 Remelt 5092-1 20 5.5 Remelt 5092-2 15 3.0 h'ew melt Gas 20 5.0 2.5 Remelt 5093-1 15 New melt 5.0 I5 Gas Remelt 5094-1 2.5 15 Remelt 3538 3.0 Gas 30 Gas S e w melt 20.0 40 Remelt 5111-1 17.5 25 Remelt 5111-1 9.5 Gas 30 Remelt 5094-2 plus new melt Gas 85 7.7 Gas Remelt 4093 4.5 8.5 Remelt 5117-1 30 6.0
See Table IV for pouring temperatures.
Melt 4903 5092-2 5093-2 5094-2
Calcd. 10.0 3.0 1.0 0.5
Actual 9.90 2.82 0.94 0.40
Copper 0.10
.. ..
..
Iron
..
0:48 0.50
Silicon 0.15
.. .. ..
MECHANICAL TEsTrxc-Tensile, Brinell hardness (500-kg. load, 10-mm. ball), and specific gravity tests were made according to standard methods and with the results embodied in Table IV and in Figure 2. Each value is the average from three bars in the mold and in similar condition of treatment, with the exception that only one specific gravity test was made to represent each mold of specimens. The bars were tested within 2 days after having been cast. CORROSION TESTING-The unmachined grip-ends of broken specimens were subjected in the cast condition to corrosion tests in salt spray and in distilled water. I n the set of sam8
Daniels, THIS J O U R N A L , 16, 1243 (1924)
uere then aged at room temperature for 1 day before the tensile test. copper and nickel were suhlected to a 24hour s o a k i n g a t 510" C., q u e n c h e d i n t o cold water, and aged at 100'' C. (212' P.) for 1 hour or a t 149' C. (300" F.) for 2 hours. Preparation and Examination of Metal-
ples were pure aluminum from inelt 3538 (5101), poured from
707" C . (1305' F.); 8 per cent copper alloy from melt 5018, poured from 707" C.; 1 per cent cobalt alloy 5093, poured from 702' C. (1295' F.); and halt alloy from melt 5090, poured froin 838" C . (1540" P.). The salt spray test was conducted in an inclosure permeated with the indirect spray of a 20 per cent salt solution and practically 100 per ceiit humidity for 100 hours. The condition of the specimens was iioted several times during tlie first 24 hours, and thereafter a t the end of 48, 72, and 100 hours. In the distilled water t,est the specimens u'ere immersed half way in order to observe both the aqueous and water-line corrosion. The rpecimens were tested over a period of 30 days. Method of Heat Treatment
As it was realized that the cobalt-hearing of inferior solubility in aluminum, not m placed on the heat treatment of the binary tempt WRS made, however, to investigate tlie which Gwyerh found at 550" C . and attributed to the formation of a compound containing less cobalt than is present in
was cut from the riser each inold i ~ scast and in the Id3 contain~iig0 5 arid 2.0 per cent of cohak. T h ie of polishtng these spociinens has aley were examined, unetvhed and ermediate, and a t high (1 9 mm. ohjective under oil iinmersion) graphs are of unetched structu the various aluSeveral constituents were d minum-cobalt alloys. Chief amo bearing compound, presumably C in color, and took tlic form skeletons, and needlcil wlien P large elliptical pa s when pnmary. The purple coinpound FeAL wa4 iit as needlei;, oftrn difficult to dirtinguish fiom CoAl,, Minute slatc-eolored paitlclei of cutcetic silicon were found sparsely xri the ( a t but not In the heat-treated specimens, which latter fact was to he expected. Occasionally some wateiy-blue skeleton5 or frarments mingled with siliron were to he seen, and theie uere thought to he the X constituent No rim reaction products aere noticod.
nd with the nitric arid quench. The consisted in heating the alloys for 24 hour
and aged a,t 100' C. (212" F.) for 1 hour. accomplished in an aut,oinat,icallFeontrnllet and the artificial aging in boiling water. The specimens
C \STAmous-There is little question hut that the addition of inore than ahout 1 per cent of cobalt to aliiininum 1s detri-
July, 1926
I N D U S T R I A L A N D EAVGINEERINGC H E M I S T R Y
mental from every standpoint; and the same statement probably applies to ternary and more complex alloys in which a ternary compound containing cobalt is not formed. As may be seen in Figure 3. the presence of only 0.5 per cent of cobalt materially increases the solidification shrinkage; and increasing amounts of cobalt serve only to enhance this condition, regardless of pouring temperature. Furthermore, with the current price of cobalt a t 82.50 per pound the addition of a material percentage of this element entails a considerable item of expense.
689
4.0-44 to 23,390-6.0-47 (ultimate strength, pounds per square
inch elongation in 2 inches. per cent-Brinell hardness), and the fracture %-asfibrous and free from crystallinity. With 2 per cent of cobalt, the sand-cast ternary alloy had inferior properties of 20,760-3.3-50, accompanied by very heavy shrinkage and coarsely crystalline fracture. The addition of 1 per cent of silicon to the 4.75 per cent copper alloy was sufficient, hoivever, to counteract the shrinkage caused by 0.5 per cent of the cobalt, and the material gave 20,750-3.550. The ternary melt with 3 per cent of nickel and 2 per
P r o p e r t i e s of S a n d - c a s t A l u m i n u m - C o b a l t Alloys Elongation in Cobalt Pouring temperatures Ultimate strength 2 inches Brinell Specific CHARACTER OF FRACTURE F. Lb./sq. in. Percent hardness gravity Melt Per cent C. Fibrous 2 4 . 3 2 3 . 2 2.689 1305 13,070 5101" Xone 707 Fibrous 24.7 28.5 14,450 1305 5094-Za 0.40 707 Fibrous 26.2 23.7 14,100 707 1305 5116 Fibrous 25.1 29.0 14,410 1400 760 5094-1 2.692 Fibrous 16.2 2i.1 1295 15,410 702 0.94 5093-Za 27.4 Fibrous 19.5 1400 15,540 760 5093-1 Fine crystalline 2 7 . 7 1 0 . 7 14,740 7 04 1300 ?ll5 2.05 Medium-coarse crystalline 28.0 11.3 14,980 707 1305 5111-2a Coarse crystalline 4.3 31.3 14iO 13,850 5111-1 799 29.5 Heterogeneous, medium crystalline 5,s 1265 13,040 2.82 685 5092-3 Coarse crystalline 28.2 3.3 774 1428 11,920 5092-Z5 Very coarse crystalline 27.3 3.5 1615 11,190 880 5092-1 27.1 Drossy, medium crystalline 1.0 ll,i40 1400 5091-3 LO'] 760 29.9 2.709 Coarse crystalline 2.0 1515 11,720 824 5091-2" Very coarse crystalline, misran 30.6 2.0 92i 1700 10,060 5091-1 1500 9.90 816 5117-2 Drossy, fine crystalline 1.0 31.7 11,800 1540 83s 5090-3 7,798 Medium crystalline 1.5 32.9 12,630 1665 907 5090-2a 1.5 Medium-coarse crystalline 31.8 11,970 982 1800 5117-1 Very coarse crystalline 1.3 40.0 12,430 1865 1019 5090-1 Values used in plotting Figure 2. b Calculated.
Table IV-Mechanical
The best combination of foundry qualities, tensile proper- cent of cobalt proved mechanically to be worthless (Table ties, and fracture was obtained when the alloys were poured VI). HEAT-TREATED Amow-Table V shows that the quenchas cold as possible. When the cobalt content did not exceed about 2 per cent, they could be properly cast from 701" C. 'ing and aging of the binary alloys containing nominally 0.5 (1300" F.). The melts richer in cobalt had to be poured and 2.0 per cent of cobalt was without beneficial outcome. from much higher temperatures and within the solidification There was no difference in properties whether the soaking and quenching temperature was 510' C. (950" F.) or 610" C. range, wherein the gas absorption was undoubtedly high. Figure 2 is a graph of the tensile and hardness properties (1130OF.). of the aluminum-cobalt series and is based on the values s of H e a t - T r e a t e d A l u m i n u m - C o b a l t (Table IV) from molds considered to have been poured from T a b l e V-Mechanical P r o p e r t i e Alloy8 Cobalt Ultimate Elongation the most advisable temperature. It indicates that the calcd. COKDITION OF strength in 2 inches Brinell strength of the aluminum-rich alloys reaches a low maximum Melt Per cent SPECIMENS Lb./sq. in. Per cent hardness 5116 0.5 As sand-cast 14,100 25.2 23.7 of about 15,000 pounds per square inch a t 1 per cent of co510-24CW-212-1" 14,060 27.3 23.8 balt. Inasmuch as the percentage of elongation suffered a 610-24CW-212-1 14,010 28.0 22.3 5115 2 . 0 As sand-cast 14,740 1 0 . 7 27.7 serious decline for this composition, i t seems that the best 510-24CW-212--1 15,090 10.3 29.8 610-24CU'-212-1 14,760 25.6 9.8 tensile properties occur with 0.4 per cent of cobalt, which a Heated a t 510' C. (950' F.) for 24 hours, quenched into cold water, alloy has a strength of about 14,500 pounds per square inch a n d then aged in boiling water for 1 hour. and an elongation of 28 per cent, close to that of the aluminum ingot. Although the ultimate strength of the melts con- T a b l e VI--IMechanical P r o p e r t i e s of P o l y n a r y A l u m i n u m - C o b a l t - X Alloys taining from approximately 3 to 10 per cent of cobalt was conUltimate E1,onstant a t 12,000 pounds per square inch, the Brinell hardness, strength gation in Brinell CALCD.,PER cEh-T., CONDITION OF Lb:/ 2 inches hardroughly, increased continuously, with cobalt content, from Melt Cu Co N i bi SPECIMENS sq. in. Per cent ness 23 to 33. The specific gravity followed a similar trend. 5151 4 . . , , As sand-cast 18,780 4.0 44 As heat-treateda 25,970 6.5 44 As Schirmei~ter~ has reported, cobalt imparts a decided 5150 4 1 . . . As sand-cast 23,390 6.0 47 crystallinity to the fractures of the binary alloys; but it was As heat-treateda 27,260 6.0 52 5147 4 2 . , . As sand-cast 20,760 3.3 50 found that this effect (Table IV) did not arise until the coAs heat-treateda 22,370 2.3 56 5167 4 . 7 5 0 . 5 . 1 . 0 Assand-cast 20,750 3 . 5 50 balt content exceeded 1 per cent. The structural arrangeheat-treated" 25,930 4.2 58 ment of the primary CoAl13 is conducive to well-defined 4907 . . 2 3 . . As As sand-cast 10,450 1.0 .. As heat-treatedb 10,500 1 . 0 cleavage planes (Figures 8 and 9). a 510-24cw-212-1. No corroboration of Schirmeister's attribution of density b 510-24CW-300-2. to the cobalt-rich alloys was manifest. I n fact, they were The heat treatment of the polynary alloys was only modinclined to be unsound, probably because of their avid absorption of gas during the melting operation and at the high erately effective, if at all, and such improvement in strength as resulted (Table VI) was attributable to the solution and temperatures necessary for casting. It was established in several alloys that cobalt rarried over reprecipitation of the cupriferous compound, CuA12. When its peculiarities to ternary and quaternary alloys. Though to the 4 per cent copper alloy 1 per cent of cobalt was added, the binary 4 per cent copper-aluminum alloy piped but slightly, the effect of quenching and aging was to increase the strength when 1 per cent of cobalt was added its volume of pipe in- slightly to about 27,000 pounds per square inch and the creased tremendously. At the same time, however, the hardness 8 Brinell numbers to 52, while the elongation retensile and hardness properties were improved from 18,780- mained unchanged at about 6 per cent. Two per cent of .
I
Fieure . 4-Aluminum Innot. X 100 Siind-cast. 13.07rb24.3-23.2. . N e e d 1 , e r end rkeletons. mostly iormer, or iron-beanng constitumts, and little AI-Si, except in segiepited e r a
FiOure 5-0.40 Co. X 100 Sailrt-cast. 14,430-25.8-24.7. hi -CoaAln eufecfic. Iron-bcsring FonititUentY not abundant. Somc AI-Si present
Figure G 5 . 0 Co.(Cnlcd.) Send-cast.
x
FiBure 6-0.40 Co. X 100 Sand-cast. Praeticnily entirely eutectic area "ea* pipe. F'eAi. 0)needie :it center
100
11.720-2.0-20.9. Primary and eutectic CorAiir
in this specimen
cobalt., h o w e v e r , a.ct e d disastrously upon both strengt,h and percentage of e l o n g a t i o n , The aluminum-nickel cobalt alloy was wholly un r esponsive. Corrosion
X 100 Sand-l-BFt 23 380-6 0-47 CuAI,, *ranhearing compounds. and elongated A I - C a A h
Figure 10-4
eufecllc
Cu, I Co. (Csbd.)
In the salt spray test the 0.94 and 9.9 per cent cobalt all o "~ v s nerformed equally well (Table V I I ) . A f t e r 100 hours' exposure they were only s l i g h t l y more corroded than the pure aluminum
aud were {roe from pitt.ing. They w ' x perior to the 8 per cent c.opper alloy, iron rust and pitting in addition to the usual product. The tnvo cobalt-hearing alloys mai in the distilled water test. They were not quite so resistant as the pure aluminum, and the 9.9 per cent cobalt alloy was somewhat better than the 0.94 per cent alloy. Both showed, in addition to the white product, a bluish green (basic) cobalt salt. They were very much less corroded than the 8 per cent copper alloy, which was heavily coated from the water line down with a flaky substance, which chipped off and disclosed brown tarnish beneath. At the water line thcre was some bluish green corrosion product. The iron stain did not appear on this specimen. Metallography
compound assumed a number of forms, dependThe ing upon the amount of cobalt added. The structure of the alurninnm ingot is shown in Figure 4. Both FeAL and X were present, chiefly the former, as was some A M . The
July, 1926
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Al-Co3;1113 eutectic was quite abundant in the 0.40 per cent cobalt alloy. The compound is blue-gray in color and in this composition was spherulitic in character, with a fan-shaped arrangement (Figure 5 ) . I n the same specimen, in a segregated area, the structure became entirely eutectic, the pattern being frostlike (Figure 6) and with a n acicular tendency a t the outer edges. The 0.94 per cent cobalt alloy contained both acicular and vermicular eutectic Co&113 (Figure 7) and primary, roughly rhombic, Co&ll3. With further increase of cobalt content the primary C o a l l 3 passed through the disjointed columnar forms illustrated in Figures 8 and 9. Figure 10 is of the 4 copper-1 cobalt alloy. I n the alloys containing 1 per cent and more of cobalt the iron-bearing constituents were not readily identified, because the general structure is acicular. Heat treatment of the 0.5 and 2.0 per cent cobalt alloys was accomplished without much metallographic change. I n both the 0.5 and 2.0 per cent alloys the 24-hour treatment a t 510" C. (950" F.) did nothing except cause the silicon to go into solution. The treatment a t 610" C. (1130' F.), below the eutectic temperature, was no more effective for the 0.5 per cent alloy. but in the 2.0 per cent alloy there was some suggestion of rounding of the eutectic Coal13 particles, indicat,ing possibly minor solubility. This same circumstance may have obtained in the alloy less rich in cobalt, but the alteration would naturally be difficult to distinguish, because the CO3-4113 T'i'as originally spherulitic.
Table VII-Corrosion
of
691 Sand-cast Aluminum-Cobalt
Alloys
CHEMICAL COMPOSITION SALTSPRAY EXPOSURE A1 ingot No appreciable corrosion u p t o 48 hours. After 100 hours very slight white corrosion. h-o pitting 0 . 9 4 Co-A1
9 . 9 Co-AI
DISTILLEDWATGRTEST Up t o 48 hours 0. K. a f t e r 10 d a y s slight water-line corrosion. After 30 days same a n d slight white corrosion and 3 / i brown tarnish below water line 0. K. a t 8 hours. Slight Water-line corrosion in 48 hours. After 10 d a y s white white surface corrosion a t corrosion below water line. 24 a n d 48 hours. After 100 hours light white corrosion. After 30 d a y s slightly more general corrosion than 9.9 No pitting per cent Co a n d less of blue-green product Same as 0.94 per cent C o a t all Water-line corrosion in 45 hours. After 10 days mixintervals, except bubbles a t ture of white and blue8 hours green corrosion product below water line. Same plus slight brown tarnish after 30 davs ~. Slight white corrosion in 8 Slight corrosion a t a n d below hours. General surface corwater line in 48 hours. Afrosion in 24 a n d 48 hours. ter 10 d a y s heavy waterAfter 100 hours iron rust line corrosion and general a n d general pitting in addibluish white surface cortion to white corrosion m o d rosion below water line. After 30 days badly coruct roded from water line down. Corrosion product bluewhite a n d flaky, with brown tarnish beneath. At water line, product is blue-green ~~
8 Cu-AI
Acknowledgment
Grateful acknowledgment is herewith made to E. R. Irwin, M. R. Whitmore, J. L. Hester, and to Clifford McMahon for their assistance in this experimentation.
Inhibiting Agents in the Oxidation of Unsaturated Organic Compounds' By Otto M. Smith and Robert Eri Wood OKLAHOMA AGRICULTURAL A N D MECHASICAL COLLEGE, STILLWATER, OKLA.
A study has been made of those substances which or more ethenoid -C=CPOILAGE, d e t e r i o r a retard the rate of atmospheric oxidation of organic l i n k a g e s . These unstable tion, and rotJting are substances, especially oils, fats, fatty acids, and soaps. carbon atoms easily become frequently due to atOver one hundred chemicals have been tried. Resaturated in the presence of mospheric oxidation. Sometarding agents behave like negative catalysts. Very oxygen, forming a t first pertimes the rate of oxidation is small amounts are required and so far as has been obe x c e e d i n g l y slow and the o x i d e ~ . ~I n the first stage, served do not enter into the reaction, only in a very the induction period, oxygen products are stable, a t other loosely bound form. is absorbed very slowly; as times it is so rapid as to cause Retarding agents may be classed, somewhat in the oroxidation proceeds the rate beinstantaneous combustion. der of their effectiveness, in the following groups: comes exceedingly rapid. By During the last four years phenyl substituted alcohols, organic and inorganic plotting the oxygen absorbed Moureau, Dufraisse, and coreducing agents, amines, and alkalies. against time a characteristic authors have published many logarithmic curve is obtained. papers on the oxidation of When an inhibitor or antioxidant is added the rate of acrolein. Those substances which inhibit oxidation are called antioxygen or antioxidizers, antioxidants, anti- or oxidation is retarded, even stopped for a period. If the negative catalysts, stabilizers, inhibitors, and preservatives. mechanism of oxidation is the same for similarily situated Oxidation is accelerated by light. moisture, increase in ethenoid linkage, then it is logical to assume that those suboxygen concentration and temperature, catalysts and auto- stances which inhibit in one case should do likewise in another. catalysts, acids and electrolytes. I n the case of oils the ab- This fact is well established by experiments on oil, fats, fatty sorption of oxygen is accelerated by the products of their acids, soaps, acrolein, rubber, and petroleum. oxidation and by the presence of unsaturated oils.2 It is Experimental usually indicated by a darkening in color, change in odor or taste, appearance of waxes, or a precipitate, stiffening or I n the case of oils and fatty acids the usual quantitative hardening, and changes in the mechanical and chemical tests of unsaturation are not sufficiently sensitive to measure properties of the substances. I n unsaturated oils, fats, and the small amounts of oxygen absorbed while those used to acids, rubber, and many other organic substances are one detect rancidity seem too sensitive. The amount of oxygen 1 Presented b y Mr. Smith before the joint session of the Divisions of combined was obtained by placing the substance in an at-
S
Organic Chemistry a n d Medicinal Products Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9 , 1926. 2 Greenbank a n d Holm, THISJOURNAL, 16, 595 (1924).
8 Gardner, paper on "Paint a n d Varnish," 1920, p. 121. Publisher.
P. N . Butler,
