740
INDUSTRIAL AND ENG INEERING CHEMISTRY
under the conditions described. Steam supplies (moles per hour) below the recorded values in Table I11 were found to give such a slow rate of gas generation as to be impracticable, while values above those given changed the gas composition very little. The rate of gas generation in the later case was increased somewhat, but little change, either in gas composition or in decomposition of steam, was noted. A tabulated summary showing the general influence of various factors in the production of water gas from steam and younger coal cokes is shown in Table IV. The plus signs indicate an increased and the minus signs a decreased yield of the several gases. A question mark indicates some variation, but the general trend is as given.
TABLEIv. GENERALEFFECT OF CERTAIN FACTORS COMPOSITION COz
++ +-
Decrease in contact time Decreased % of steam decompn. Increased steam supply Increased temp. Increased pressureo +? Incomplete carbonization prior to water-gas run" + O See synopsis at beginning of this paper.
CO
+ -
+
-
-1
GAS
Hz0 VAPOR CHd I N G A S
Hz
++ + -
-
UPON
- ? -1 - ?
-
+?
+++ -
-?
?
+
?
The work here presented is being continued with added selective catalysts for the lower temperatures, and applications of the investigations are being extended to semiplantscale practice. The mechanism of the formation of water gas
Vol. 26, No. 7
rich in hydrogen covering the present and extended investigations now in progress will be reserved for a future publication. ACKNOWLEDGMENT The authors wish to express their sincere thanks for the splendid services of their assistants, Robert M. Miller and William J. Mitchell, for aid in the experimental work. Grateful acknowledgment is made also to W. M. Lauer and Frank H. Stodola for the ultimate analyses of carbon and hydrogen in the sample of lignite char. LITERATURE CITED Clement, J. K., Adams, L. H., and Haskins, C. N., Bur. Mines, Bull. 7 (1911). Dolch, P., Gas- u. Wasserfach, 75,807-11 (1932). Haslam, R. T., Entwistle, F. E., and Gladding, W. E., TND. ENO.CHEY., 17,586-8 (1925). Horne, J. W.,and Bauer, A. D., Bur. Mines, Repts. Investigations 2832 (1927). Kassler, R., Mitt. Kohlenforschungsinst. Prag, No. 5, 305-32 (1933); Chimie & industrie, 29, Special No., 315-26 (June, 1933). Logan, L., Am. Gus Assoc. Proc., 14, 976-1015 (1932). Neumann, B., and van m e n , A., Brennstoff-Chem., 15, 5-10 (1934). Neurnann, B., Kroger, C., and Fingas, E., Z. unorg. allgem. C h m . , 197, 321-38 (1931). Rideal, Erick, J. Soc. Chem. Ind., 40, 10-14T (1921).
RECEIVED August 22, 1933. Presented before the Division of Gaa and Fuei Chemistry at the 86th Meeting of the American Chemical Society, Chicago, Ill., September 10 to 15, 1933. Part of the work reported waa rnsde poasible through a grant from the Graduate School, University of Minnesota.
Mechanism of Dezincification Corrosion of €-Brass CHARLESW. STILLWELL' AND EDWARD S. TURNIPSEED, University of Illinois, Urbana, Ill.
D
EZINCIFICATION, the removal of zinc from brass the probable effect of corrosion agents of various strengths by corrosion, is a common cause of failure in Admiralty upon the corrosion of an alloy, such as brass, in which condenser tubes, brass pipe, and other brass fittings. several intermetallic compounds exist. One advantage of' Most investigators agree that this phenomenon is the result studying this system lies in the fact that a decrease in of the solution of both comer and zinc and the redeposition zinc content is accompanied by a change in phase and crystal s t r u c t u r e and therefore a of copper (I, 6,7, 9, IO). bnly marked change in x-ray diffraca small m i n o r i t y believes I n an attempt to establish the mechanism of tion pattern. During the rethat the d e z i n c i f i e d brass is dezincijication, the corrosion of €-brass has been moval of one metal from a solid residual copper (2). A recent studied by means of x-ray difraction data. s o l u t i o n , o n t h e other hand, x-ray diffraction s t u d y of t h e The corrosion of e-brass m a y occur in at least only minute changes in diffraccorrosion of gold-copper alloys, tion pattern occur. h o w e v e r , suggests that zinc three digerent ways: (1) I n strong oxidizing may be removed from b r a s s If €-brass2 is corroded, there agents (nitric acid) both copper and zinc are w i t h o u t dissolving the copper are at least four possible courses dissolved; a trace of copper is redeposited f r o m the action may take: (6). It was found that strong very dilute nitric acid. (2) I n acid of intermedioxidizing a g e n t s dissolve both 1. The e-brass may dissolve ate strength (normal sulfuric, concentrated hydrogold and c o p p e r a n d the gold completely as such, since an interis then r e d e p o s i t e d . Weak chloric) both copper and zinc are dissolved and metallic compound has a definite oxidizing agents, on the other electrode potential. copper is redeposited. (3) I n very weak acids hand, are unable to ionize the 2. The e-brass may dissolve (dilute hydrochloric, acetic) only zinc is removed g o l d , a n d o n l y p a r t of t h e a n d copper may b e redeposited f r o m the alloy, resulting in the successive formaby displacement. copper is dissolved, leaving a 3. Only zinc may dissolve, the tion of y-brass, @-brass, and copper or a-brass. surface of solid solution which rem aini ng surface layer being is richer in gold than the origiDezinciJication m a y occur in two ways: ( I ) y-brass, the compound richer in nal. by the solution of copper and zinc and the recopper than cbrass. It is of interest t o consider 4. Only zinc may dissolve, deposition of copper in strong corroding agents; 1 Present address, Denniaon Manufacturing Company, F r a m i n g h a m ,
Mass.
(2) by the solution of zinc only, in weak corroding agents.
2 In order of decressing zinc content the phases of brass are 7 , e, y, 8, a.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1934
741
OF CORROSION OF €-BRASS TARLEI. PRODUCTS ACID
16 N HNOI 4 N HNOa 2 N HNOr 1 N HzSOd; x-ray beam reflected from outer surface ~
~~
TIMEOF ETCHINQ Minutes 0.25-1 5 30-120
Striisturea 6
el 6:
(Cull cu cu (trace)
Slight surface tarnish; not particularly copper colored
e
4-8 12 30 60
6
Definite copper color on surface; surface is metallio in appearance; scrapes off easily; powder beneath
cu
ku, 8 , Y, 6 Cu, 8, Y , Cu, 8
-
CORROBION LAYBR -4ppearance
7
(trace)
]
Black powder beneath copper colored powder
1 N HzSO4; x-ray beam reflected from inner surface after removal of most of the powder
30-60 8, Y , e. (Cu) 180 Cu, 8, Y , ZnO, 6 e, 7 , u? see text) Tarnish hardly visible 1 hr. 12 hr. y. $7, ku7, see text) Very metallic shell drops away from uncorroded metal; is not powdery but may be powdered 24 hr. Cu.'znO. Y 2 Copper colored surface 12 N HCI 20 No copper color on surface 45 0.5 N HCI 5 T h e several phases in each surface layer are listed in t h e order of their relative concentrations in the layer as estimated roughly from diffraction intensities; the predominant phase is a t the left.
leaving a surface layer of pure copper in contact with tbrsss, but this is very improbable.
EXPERIMENTAL PROCEDURE €-Brass, annealed until homogeneous, was corroded in nitric, sulfuric, hydrochloric, and acetic acids. The duration of corrosion and the strength of the acids are recorded in Table I. The structure and composition of the corroded surfaces were determined from x-ray diffraction data. The x-ray beam, MoK, radiation from a Coolidge tube, was reflected from the corroded surface of brass. The details of the method used have been discussed elsewhere (8). Typical data and their analyses are shown in Table 11.
RESULTS OF CORROSION TESTS The significant points bearing upon the mechanism of corrosion and brought out by the data are: The first corrosion layer formed by etching with sulfuric acid (for 4 minutes) is copper.s 1.
DATAFOR TABLE11. DIFFRACTION 2 '1 ETCHED I N H?SOr 12 min. 4 min. 2.54 vwb 2.37 w 2:37 a 2.14a 2.13 8 2.08 vs 2.08vs 1.885 w 1:805 w 1.800 s 1.735 vw 1 595 vs 1.589 m 1.476 m 1.372 w I : ~ S Om 1.308 vw 1 ; 275 vw 1.274 s 1.250 vw 1:i26 VI 1.225s 1.208m i:i93 w 1.162 vs 1:iia m 1.152 m 1.147 w
:
1:OSs m 1.073 m 1.043 m 0.978 m
1:O88 8 1.073 w 1.042m 0.977 m
3 ETCHED IN HC;HaOy 1 HR. 2 55vw 2.38 w 2.13 vs 2.08 s 1.885 vw 1.805 vw 1.740vw 1.595 m 1.477 w 1.375 m 1.302 vw 1.276 w 1.250 w 1.224 I 1.204 w 1.199 w 1.158 m 1.147 w 1.121 w 1.OS7 w 1.070 w 1.042 m 0.975 m 0.936 w 0.913 m
4 +BRASS (hkl)
...
100 002 101
THE
6
Zhz 12 14
... ...
ioi
...
2. After 12 minutes in sulfuric acid, p- and ?-brasses are also formed, lying between the outer layer of copper and the unattacked e-brass. 3. The first corrosion layer formed by etching with acetic acid (for one hour) is y-brass, not copper. The data do not disprove the presence of a trace of copper, since several of the stronger interplanar spacings for copper coincide with those for 7-brass. A consideration of the relative intensities of the lines, however, suggests that no copper is present.
The presence of y-brass as the first detectable result of corrosion with acetic acid indicates that zinc is dissolved from the +brass lattice until a composition range is reached in which not +brass, but y-brass is the stable phase. The zinc and copper atoms will then become readjusted into the lattice of the stable phase. The corrosion layer retains the properties of massive metal and is not particularly powdery in appearance, although it can be scraped from the surface of the uncorroded metal. Microscopic examination does not reveal the sharp line of demarcation which is usually evident
* This product may be a-brass containing a small amount of zinc in solid solution, but this possibility has no bearing on t h e discussion and the product will be referred to as copper. CORRODED SURFACE LAYEROF €-BRASS 6 7 Y-BRASS do Intensity 8.83 W 8.87 w w 8.84
..
m ,.
36
5
8
(4)
9
10
(MI
Zh¶
#-BRASS
Zhz *.
*. .. .. 4
....
a0
.. ..
..
3
3 .'SO
4
.. .... ..
3161
......
S
.. ..
3:61
.. .. ,.
..
..
2:95
110
... ...
... ...
103
200 112 201
... ...
004 202 104
...
..
..
..
54
.. *. ..
62 66
68 72 82 90
8:86
.. ..
8:83 8.85 8.84 8.84 8.82 8.87
..
..
8
..
.. .. ..
W S W I
.. .. ..
6
2:95
..
.. .. ..
,.
.. .. .. 8 ..
11 COPPER
..
.. ..
.. ..
..
..
11
3:6l
2:95
12
3:61
10
2:96
..
..
..
..
.. ..
.. ..
o.'Qi5m 203 .. .. .. .. 0.901 w 210 .. .. .. .. .. 16 3:60 0.881 w 0:sSl w 211 .. .. .. .. ,. 0.846 m 0.844 m 114 . . .. 12 2:93 .. 0.828 w ... ... 19 3:61 .. 0.807m ... 105 20 3.61 .. .. .. ,. 0.736 vw 24 3.61 .. .. .. 16 2:94 01694 vw 0.693vw 27 3.60 .. .. .. 18 2.94 Columns 1 2 and 3 show complete diffraction data for three different specimens treated a3 indicated Column 4 identifies those lines which belong t o the attern of i-bkass indicating only t h e Miller indices. Columns 5 , 8 a n d 7 identif ' the linea which belong to y-brass; the intensities of column 7 are those recor&d by Bradley and Thewlis (4). Columns 8-11 identif lines which belong to &ass and to copper. b Intensity of lines: VB, very atrong; I, strong; m, m e b u m ; w, weak; vw, very weak 0:9i7 s 0.902w 0.883s 0.847m 0.828rn 0.808 a
.. ..
... ...
..
742
I N D U S T R I A I, A K D E N G I K E E R I N G C H E & I‘ SIT R 1
when a layer of metal has been electrodeposited. This evidence eliminates the fourth proposed course of corrosion : The removal of zinc only does not leave an initial layer of residual copper. On the other hand, as shown in Table I, a layer of copper is formed in time by etching in acetic acid, but it is formed by the removal of zinc from E-, y-, and 8brass successively, not from e-brass directly. Etching with normal sulfuric acid produces first a layer of copper. Here is proof that the copper surface is redeposited, not residual. It has been demonstrated that, if only zinc is dissolved, the first corrosion layer is y-brass. In a relatively strong acid (normal sulfuric) both zinc and copper are dissolved; in a weaker acid only zinc goes into solution. (If acetic acid dissolved both zinc and copper, . but dissolved zinc at a faster rate, it could be argued that a y-brass surface would be formed; but in this case some copper should also be redeposited, and it is not.) The P- and y-brasses in the corrosion layer after 12 minutes of etching with sulfuric acid may also have been redeposited, or they may have resulted from the solution of zinc only from the original brass. With the deposition of a layer of copper, the diffusion of acid into the brass will be impeded and the concentration of hydrogen ions may be decreased to the point where sulfuric acid will act like acetic acid, dissolving only zinc. On the other hand, the deposition of Pand y-brass can also be justified. It has been shown that the structure of an electrodeposited alloy is essentially the same as that of a thermal alloy of the same composition (8) and it is known that the composition of an alloy deposited from solution depends, among other things, upon the relative concentrations of the two metallic ions in solution.4 As copper and zinc are dissolved by the acid, a t first only copper is redeposited, since the concentration of zinc ion is too low. The accumulation of spongy copper hinders the diffusion of the dissolved ions and the concentration of zinc ions is thus built up until the relative concentration of copper and zinc ions reaches the point a t 15-hich P-brass may be deposited. The decrease in acidity which is also brought about by the inhibition of diffusion xi11 favor the deposition of zinc. With increasing thickness of the spongy surface, the concentration of zinc ions may increase until y-brass is precipitated. SF7elldefined layers of P- and y-brass were not detected. Some experimental evidence of this distribution may be found in Table I. Reflection of x-rays from the surface of brass etched 60 minutes with sulfuric acid indicated the presence of copper and P-brass. If the x-ray beam is reflected from this same specimen after most of the surface powder has been removed, y-brass is also detected. Apparently the y-brass lies farther beneath the surface than the P-brass. Table I shows that, as would be expected, strongly oxidizing nitric acid dissolves both zinc and copper, and there is only a slight tendency, in the case of dilute acid, for the copper to reprecipitate. The behavior of hydrochloric acid depends upon its Concentration. Etching with concentrated acid produces a redeposited layer of copper, while very dilute acid acts similarly t o acetic acid, producing an initial layer of y-brass. To summarize, the mechanism of corrosion depends upon the acidity and oxidizing power of the corroding agent. Strong acids dissolve both zinc and copper, and copper may be redeposited. A weak acid solution dissolves only zinc. Crystalline zinc oxide is usually found in the corrosion layer of specimens which have stood for some time in solutions. It may be due to the reprecipitation of zinc ions which have been occluded in the corrosion layer from which Cf numerous papere by Colin G Flnk and collaborators, and by L. E. Stout a n d collaboratore
Vol. 26, SO.i
the acid has been exhausted, as a result of the limited possibilities of diffusion.
~ I E C H A NOF I SDEZINCIFICATIOK U In X-ieTv of the foregoing results, both theories of dezincification mag be correct, depending upon the conditions of corrosion. The trouble with most investigations of the problem has been that, specimens were studied only after they had corroded for some time, and in all cases copper (or better than 90 per cent copper) was present on the surface. I t has been shown, hoir-ever, that two pieces of c-bra;: may yield the same end products of corrosion in the same relative positions on the surface of the original alloy, and yet the mechanism of corrosioii for the two may be quite different. To understand this mechanism, the first product of corrosion must be identified. When, with sulfuric acid, the first product is copper, it follows that the corrosion layer has been formed by the solution of copper and zinc and the redeposit’ionof copper, followed by the formation of either redeposited or residual layers of P- and y-brass. When the first product of corrosion is y-brass, it is evident that this, and therefore the succeeding products, are formed by the solution of zinc only: first from €-brass to form y-brass, then from y-brass t o form &brass, and finally from P-brass to form a-brass and copper. Apparently if the corroding agent causes rapid corrosion the dezinced surface is redeposited copper. If, under the influence of a weaker corroding agent, corrosion proceeds slowly, the dezinced surface is residual copper. Bassett points out ( 2 ) that in tubes which give long service in sea water the corrosion deposit is very hard; in condenser tubes which fail quickly, the deposit is soft and has not the continuous enamel-like appearance of the hard layer. The physical characteristics of redeposited copper and of residual copper as they have been observed in these experiments resemble those attributed by Bassett to “rapid-corrosion” and “slow-corrosion” deposits, respectively. Some of the results reported herewith have a distinct bearing upon findings of previous investigators, as enumerated below :
--
1. Abrams ( 1 ) has reported that in sulfate solutions the brass dissolves completely and there is no copper deposited, apparently because no membrane can be formed to prevent the escape of copper ions. But sulfuric acid causes dezincification by the redeposition of copper. This has been stated by Reutel and Kutzlnigg ( 3 ) and has been confirmed in the present work. The importance of a “membrane” in causing the redeposition of copper seems t o have been overestimated, because, given a sufficient concentration of copper ions in solution, deposition occurs without any membrane. 2 . ilbrams states that concentrated hydrochloric acid dissolves brass completely in 10 days. It has been shown above that after 2 minutes in this acid a redeposited corrosion layer of copper appears. 3. Nixon (6) notes that no dezincification occurs when brass is corroded wit,h 0.5 N hydrochloric acid, and Abrams ( 1 ) states that, in zinc sulfate no dezincification occurs. Both these investigators were working with a-brass, and it is quite possible that no corrosion will take place. It has been found, however, that, in the case of e-brass, dezincification does occur with both these reagents, but the corrosion layer is not pure copper. It is a residual layer (y-brass) containing less zinc than the original. The investigators cited did not use a method which would detect this type of dezincification.
It must be emphasized that all previous investigations to which reference has been made were conducted with abrass. +brass is more susceptible to dezincification than is a-brass and has been deliberately chosen so that the process could be followed by the identificat’ion of intermetallic compounds (although, because of the different distribution of zinc and copper atoms in the several phases, the corrosion
Jul), 1931
1 1 - D U S T R I A I, A N D
E N G I N E E I 1 I N G C €I E M I S T R Y
of e-braw and of a-brav may not be analogous in all details). It ii reaqonable to assume, however, that in regard to the two general mechanisms of corrosion leading to either a residual or a redeposited corrosion product, the €-brass and a-brash are analogous.
LITERATURE CITED (1) Abrams, Trans. Electlochem. Soc , 42,39 (19221 (2) Bassett, M e t & Chem Eng , 27,340 (1922). (3) Beutel and Kutalnigg. Z l1etaZZhnde 21, 412 (1929).
743
(4) Bradley and Thewlis, Proc. Roy. Sac. (London), -4112, 678 (1928). (5) Graf, .IletalZrcirtschaft,11, 77 (1932)). (6) Nixon, Trans. Electrochem. Soc., 45, 297 (1924). (7) Rhodes and Carty, IND.ENG.CHEW, 17, 909 (1925). ( 8 ) Stillwell and Stout, J . Snz. C'hcm. Soc., 54, 2593 (193'2). (9) Storey, M e t . R. Chem. Eng.. 17, 653 (1917). (10) Thum, Ihid., 26, 301 (1922). RFEEIVEDhlarch 19, 1934. Presented before the Division of Physical and Inorganic Chemistry a t the 86th hieeting of the .imerican Chemical Society, Chicago, Ill., September 10 to 15, 1933
Effect, of Aging upon Oils in Chrome Leather' EDWINR. THEIS. ~ N DJ. 31. GRAHAM,Lehigh University, Bethlehem, Pa. 30 per cent. This a m o u n t of effect of hydrogenAging of chrome-tanned leather affects the oil insoluble in petroleum ether concentration upon ratio of free and combined oils in the leather. d o e s n o t c h e c k w i t h the inadsorption and the As leafher ages, some of the absorbed oils, effect of various oils upon oil creased amount of oil removed especially the sulfonated or polar groups, comadqorption a n d resulting by s u c h s o l v e n t s as alcohol, bine with the leather and cannot be extracted. acetone, and chloroform. When strength of the finished leather the oils are of a low sulfonation, have already been shown ( 4 ) . Comparisons of these effects are made f o r mixI n the previous wcirk the shaved the petroleum ether appears to tures of sulfonated neat's-foot, castor, and cod c h r o m e - t a n n e d leather was r e m o v e a l m o s t a l l of t h e oils. A s leather ages, the free oil hydrolyzes soluble or free oil. The writers treated with a particular type and becomes rancid, and this effect progresses of fat liquor a t a given temperabelieve, in view of all the conthroughout a n aging period. W i t h most oils flicting evidence, that the values ture, and the leather was washed, of free oil obtained by petrodried, and analyzed for oil by aging reaches a n equilibrium within 2 weeks the official American L e a t h e r leum ether extraction are more af ter f a t-liquor ing. C h e m i s t s ;Issociation method nearly the c o r r e c t values. In Such e#ects as noted here hat!e a practical which uses petroleum ether as view of t h e fact that the fatbearing upon leather which needs to be degreased; solvent. M a n y years ago liquored leather is dried before if the leather is degreased shortly after fatWilson (S)criticized this method e x t r a c t i o n , they believe that of e x t r a c t i n g leather and admost of the s u l f o n a t e d o i l liquoriny, more free oil will be remoted by the v i s e d the use of chloroform as fraction is removed from the naphtha than after aging 2 weeks, and such the solvent removing the greatl e a t h e r . On the other hand, effects will necessarily hare their effect upon the est quantity of oil. He pointed they think that acetone, alcohol, Jinished leather. Data show that degreasing out that petroleum ether as used or chloroform tends to dissolve remoues only the free oil in the leather, and the would n o t r e m o v e from the some of the oil actually bound leather such oils as m o e l l o n s in the skin and with the chrofeel and temper of the resulting leather must and sulfonated oils, and showed mium compounds. In the case be due to the oil actually combined with the that chloroform would extract of c o m p o u n d s s u c h a s t h e leather. these oils. Stiasny and Riess moellons, continuous extraction (2) have pointed o u t t h a t in a liqui'd-liquid extractor a fraction bf the sulfonated oils is insoluble in petroleum extracts them more or less completeiy.' For- these reasons ether but soluble in, acetone and alcohol. Stather and the writers believe that petroleum ether extraction represents Lauffmann (1) in their work on the fat-liquoring of chromed more nearly the free oil content of the leather. However, hide powder used petroleum ether and alcohol. They if chrome-tanned leather is fat-liquored with a mixture found that even the drastic extraction with alcohol did of raw and sulfonated oil and another sample fat-liquored not remore all of the adsorbed oil and termed this residue with the same total concentration of raw oil and sufficient ('bound'' fat. soap for emulsification purposes, the petroleum ether will Although it is true that petroleum ether will not extract all extract more oil from the leather fat-liquored with raw of the sulfonated oil from the leather, it extracts a great por- oil than from the sample fat-liquored with sulfonated oil. tion of it. In the analysis of many sulfonated oils by the This result may possibly be explained by the fact that the Schindler method modified by Theis and Graham (S), it was sulfonated or polar fraction of the sulfonated oil actually found that the petroleum ether extracted from alcohol solu- combines with the leather. This combination may be of tions of various sulfonated oils varying quantities of the three distinct types: (a) combination with the skin itself, treated oil. The amounts of oil remaining behind after ( b ) entrance of the sulfonated or polar fraction of the sulcontinuouq extraction with petroleum ether varied from 9.1 to fonated oil into the chromium complex, and (c) formation of 50.5 per cent. Table I shows results as obtained by the actual chromium soap. modified Schindler method for various sulfonated oils. This investigation mas undertaken in order to determine However, for many of the sulfonated oils actually used in the the changes in the fat content of chrome-tanned leather fat-liquoring of chrome-tanned leather, the polar or sulfonated during aging. It had been noticed in some previous work fraction (insoluble in petroleum ether) varies between 10 and that, as leather aged, the petroleum ether extractive became less as time of aging increased, and the writers wished to find 1 This paper IS the third of a series on "Fat-Llquorlng of Chrome Leather" out if combination with the leather took place a t the time of (4)
