INDUSTRIAL AND ENGINEERING CHEMISTRY
1734
Vol. 45, No. 8
LITERATURE CITED
ing of the dyed fabric for light fastness ( 1 ) and gas fastness ( a ) was conducted by the standard procedures of the American Association of Textile Chemists and Colorists. Determination of Absorption Spectra. The absorption spectra were determined using a General Electric recording spectrophotometer. The dyes were dissolved in methanol. The concentration used was 1 part in 20,000 by weight.
(1) American rissociation of Textile Chemists and Colorists, “Technical Manual and Year Book,” Vol. 27, p. 101, New York, Howes Publishing Co., 1951. (2) Ibid., p. 91. (3) Daudt, H. W., and Woodward, H. E. (to E. I. du Pont de Nemours & C o . ) , U. S. Patent 2,194,925 (1940). (4) Ibid., 2,194,926 (1940). (5) I b i d . , 2,194,927 (1940). (6) Dickey, J. B. (to Eastman Kodak Co.), U. S.Patent 2,436,100 SUMMARY (1948). (7) Ibid., 2,491,481 (1949). N-Fluoroalkyl groups in the coupler cause the color t o shift Ibid., 2,492,972 (1950). from violet toward yellow in the following order: CH~CFZCHZ- (8) (9) Ibid.. 2,516,106, 2,616,107, 2,516,302, 2,516,303 (1950); 2,590,CH*CH*--, CHzFCHz-, CH3CFzCHZCHa-, CHFzCH2CHz-, 092, 2,594,297, 2,615,013, 2,615,014, 2,618,630 (1952). C F I C H ~ C H ,CHaCFzCHz-, CHFzCHg-, CFzCHz-, CFa(10) Ibid., 2,618,631 (1952). CFzCFzCHz--. Thus, the degree of color shift is dependent (11) Dickey, J. B., and McXally, J. G. (to Eastman Kodak C o . ) , upon the number and position of the fluorine atoms. When a t U. S. Patent 2,432,393 (1947). least two fluorine atoms are present on the second or third carbon (12) Ibid., 2,442,345 (1948). atom from the nitrogen atom in the N-fluoroalkyl group, the dyes (13) Dickey, J. B., et al., to be presented before the Division of Inhave enhanced light fastness and excellent gas fastness. dustrialand EnpineerinRChemistrv at the 124th Meeting A4.C.S., A 2-trifluoromethyl or 2-fluor0 group in a 4-nitrodiazonium Chicago, Ill., 1953. constituent shifts the colorof the dye slightly toward blue and (14) Fischer. Paul, Ber., 2 4 , 3196 (1891). gives enhanced light fastness. When a 6-nitro group is also (15) Friedrich, 31. E., and Schniepp, L. E. (to E. I. du Pont de present in the diazonium constituent, the dyes are much bluer Nemours & Co.), U. S. Patent 2,257,093 (1941). but have poor light fastness. (16) Gesellschaft fur Chemische Industrie in Basel, Swiss Patent The diazonium compounds, 178,224 (1935). (17) Henne, A. L., in “Organic Chemistry-An Advanced Treatise,” 2nd ed., Vol. I, p. 963, Xew York, John Wiley & Sons, 1943. NG, - D - N z (18) Heyna, H., and Huber, H. (to General Aniline Works, Inc.), U. S. Patent 2,016,495 (1935). \ \ (19) I. G. Farbenindustrie, French Patent 745,293 (1932). SOdX CF3 (20) Krishna, Sri, J . Chem. Soc., 1923, p. 156. (21) McKally, J. G., and Byers, J. R., Jr. (to Eastman Kodak Co.), Br / U. S. Patent 2,391,179 (1945). (22) XcNally, J. G., and Dickey, J. B., I b i d . 2,342,678 (1944). N02--C>-N2X (23) I b i d . , 2,358,465 (1944). (24) I b i d . , 2,375,804 (1945). \ CF3 CF3 (25) Scherer, P., Angew. Chem., 5 2 , 457 (1939). (26) Swarts, F., Bull. classe sci., h a d . roy. Belg., Ser. 4 , 383-414 react with couplers containing a CF~CHZ-, CHFZCHZ-, (1901). CH3CF&Hz--, or CF3CH2CH2- group to give a series of superior (27) Towne, E. B., and Dickey, J. B. (to Eastman Kodak Co.), orange-to-red, gas- and light-fast dyes for cellulose acetate. U. S. Patent 2,500,218 (1950).
/”’
NO,--N,X
ACKNOWLEDGMENT
The authors are indebted to Sherman Hubbard, of the acetate yarn laboratory, for the absorption spectra.
RECEIVED for review November 17, 1952. ACCEPTED May 14, 1953. Presented as part of the Symposium on Fluorine before the Division of Industrial and Engineering Chemistry a t the 122nd Meeting of the AMERICAN CHEMICAL SOCIETY,Atlantic City, N. .J.
Oxide Film on Nickel-Chromium Allovs J
CRYSTAL STRUCTURE STUDIES EARL A. GULBRANSEN AND WILLIAM R . MCMILLAY Westinghouse Research Laboratories, East Pittsburgh, Pa.
B
ECAUSE of theirhighresistance to oxidation, the80%nickel20% chromium alloys are one of the most useful alloy systerns. Over the past 30 years the performance of alloys of this nominal composition in cyclic oxidation tests has been improved by over 600%, by reducing the manganese content, increasing the silicon content, and adding minor amounts of calcium, aluminum, zirconium, cerium, etc. Because of the complexity of the problem, comparatively little scientific work has been directed toward understanding the oxidation resistance properties of these alloys. The essential problem is: What factors
in the composition and crystal structure of the oxide film and alloy can be related to the improved protective properties? The resistance to oxidation a t constant temperatures of metals such a s nickel and probably chromium (8, 9) can be correlated with the formation of cation vacancies and positive holes by solution of oxygen in the oxide and the diffusion of the severalmetal ions through these vacancies and electrons through the positive holes. Figure 1 shows two possible schemes of oxidation for a metal such asnickel. A shows the mechanism of diffusion of metal ions through the oxide to the oxide-gas interface where reaction
August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
occurs, while B shows the alternative mechanism of oxygen diffusion. Method A is a t present the accepted mechanism. In order to understand the mechanism of oxidation of a given metal or alloy it is essential to determine the structure of the oxide film a s well as the mechanism of electrical and ionic conductivity of the oxide.
3 2e-
o=+ 0,+ 2 e
Me+Me2++2e-
O2(g)+
Me +o*-+ Me0 tee-
3 02(g) + 2 e f o 2 '
G3
ELECTRON
HOLE Me3+
0, Me2+ VACANCY Figure 1.
Oxidation Scheme
For the metals nickel and chromium the structure of the oxide film during normal oxidation has been determined. Nickelous oxide (NiO) is the only oxide found on nickel (IO),while chromic oxide ((3208) is the only oxide found for chromium (10). Nickel oxide is a p type of semiconductor and the effect of minor alloying elements such as chromium, manganese, and lithium on the electrical conductivity and concentration of vacancies has been studied ( I C , 29). Unfortunately, no similar work exists for chromic oxide or for the oxides NiO.CrzO3 and Mn0.Cr203. If, on the other hand, the metal or alloy is subjected to periodic temperature cycles during oxidation, the oxide is placed under stress because of the different expansion coefficients of the alloy and oxide. For these conditions the over-all lifetime may no longer be governed by diffusion processes. Instead, the physical properties of the oxide, alloy, and oxide-alloy interface may determine the useful life. Two previous papers from this laboratory (16, 81) have presented electron diffraction and x-ray diffraction studies of the composition and crystal structure of the oxide films formed on three alloys representing the. historical development of alloys of this nominal composition. A third paper (18) has dealt with the decarburization reaction of the surface oxides. This paper presents crystal structure studies on five new alloys of the same nominal composition in which the weight percentages of manganese and silicon are varied. LITERATURE
The crystal structure of the oxide film formed on a heated surface of a n 80% nickel-20% chromium alloy was studied by Iitaka and Miyake (18) using electron diffraction. They reported the oxide NiO.CrzO3 and interpreted the nonoxidizing property of this alloy as due to the formation of this oxide. Hickman and Gulbransen (16) studied three alloys of this composition with a sixfold variation in the ASTM useful life. A highsilicon, low-manganese alloy with added minor components when oxidized gave a n oxide film essentially of chromic oxide. This alloy had the highest useful life of the group. A low-silicon, highmanganese alloy with no added minor components, when oxidized, gave an oxide film made up of either a spinel XO.Y~OS or a mixture of spinel and chromic oxide. Here X and Y refer t o the cations making up the spinel structure. This alloy had the short-
1735
est useful life. It was concluded that chromic oxide was the more protective oxide film. The results of this study were essentially confirmed by Lustman ( % I ) ,using x-ray diffraction methods on the same alloys but carrying out the oxidation in a cyclic manner at 1175' C. Under these conditions nickel oxide was found in all the oxides from the alloys in addition to chromic oxide and spinel. Scheil and Kiwit (84) in a study of the scaling of iron-chromium-nickel alloys showed that satisfactory alloys from a protection point of view were characterized by the presence in the oxide of chromic oxide only. Unsatisfactory alloys were characterized by the presence of iron oxides. The effect of small quantities of minor components such as calcium, zirconium, and cerium on the lifetime tests of the nickelchromium alloys has been the subject of much work because of its commercial significance. This has been discussed by Hessenbruch (15) and reviewed by Hickman and Gulbransen (16). The addition of minor amounts of certain elements such a s cesium and thorium is shown to have a very marked effect on the lifetime tests of the alloys of the 80% nicke1-20% chromium composition. The effect of oxidation on the composition of the alloy itself has been studied by Holler (17) and by Sully (86). Holler has reported that the 80% nickel-2OR chromium alloy undergoes failure because of the loss of chromium, which forms chromic oxide in the scale. This loss of chromium results in a marked increase in the temperature coefficient of resistance and thus leads to failure a t certain points in the wire. OXIDE
METAL
A b
Figure 2. 1. 2.
3. 4.
5.
Effect of M i n o r E l e m e n t s on Oxide Film
Effect Method of Study Forms own oxide i n outer layer A E.D. reflection Forms mixed oxides or spinels i n A E.D. reflection and E.D. or B transmission Forms new oxide i n inner layer, C E.D. transmission Substitutes i n lattices of oxides of Conductivity measurements major elements, changing vaeancy concentration, B Acts by concentrating i n surface Electron and light micrographs of surface and cross layer of alloy, D , in oxide, C , or section through oxide forms silica or silicate films, C, and thus changes physical properties of oxide or oxide-alloy interface
The specifications of the life tests on metallic resistor materials for electrical heating have been reported by Bash and Harsch (1). The American Society for Testing Materials useful life is defined as the time for a 10% change in resistance of the alloy when subjected t o cyclic heating in a certain manner at the given temperature. ROLE OF MINOR ELEMENTS IN OXIDATION
It is of interest to consider the possible effects of these minor components in the alloy on the composition and crystal structure of the oxide, the oxide-alloy interface, and the alloy. Figure 2 shows a schematic summary of some of these effects. 1. Formation of New Oxide of Minor Components in Outer Layer at A . For the minor components of high mobility, these may form a new oxide in the form of a segregated layer a t A . If diffusion through this layer were rate-controlling, the over-all rate of reaction could conceivably be lowered. However, these segregated layers of oxides in the film may have different expan-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1'136
ON NICKELCHROMIUM ALLOYS TABLEI. SURFACEREACTIOKS
A.
Direct oxidation 1. Nifs
C. Formation of spinels 1. 2.
3.
4. 5.
++ ++
NiOi,, (3) . CrzOds) NiO. CrzOs(s) hfnO(s) CrzOi(s)'f h t n O , CrzOds) FeO(s) CrzOds) ,FeO.CreOa(s) CaO(s) CrzOa(s) $ CaO. CrzOs(s) Plus similar reactions with Fez08
leads to powdering of the oxide, will occur when a brittle oxide is formed t h a t has poor adhesion to the alloy. This may be true where there is a segregation of oxide crystallites. Figure 3 shows schematically the first two conditions. Thus an oxide which is embrittled for one reason or another, but possesses good bonding between the oxide and the alloy, may be more protective than a more flexible oxide with poor adhesion between the oxide and the alloy. In addition t o physical considerations, the concentration of minor components a s oxides or a s elements a t the oxide-alloy interface may alter the reactivity of the grain boundary between the alloy crystals. This has been discussed in a micrographic study by Lustman (21). THERMODYNAMIC PREDICTIONS
D.
of oxides and similar
E.
F.
Vol. 45, No. 8
Decarburization reactions C (in solid solution in alloy) $ CO(g) 4-N i ( s ) 1. NiO(s) 3CO(g) 2Cr(s) 2. CrzOa(s), C (in solid solution in alloy) 3. Plus similar reactions with oxides of minor components
++
+
+
Vaporization reactions 1. Ni(s) $ Ni(g) 2. C r ( s ) s C r k ) 3. S i b ) Si(g) 4. Plus similar reactions f o r other elements
-
sion coefficients. This condition may be detrimental t o performance based on cyclic tests such as the ASTM useful life tests. I n general, the appearance of a minor component in the outer layer of the oxide film signifies a high rate of attack of this component by oxygen, irrespective of its thermodynamic stability. 2. Formation of Mixed Oxides or Spinels. The formation of randomly distributed crystallites of t x o or more oxides may be unfavorable for good performance in cyclic temperature testing, as the individual crystallites would have different expansion coefficients and local stresses may develop between crystals. Quarrel1 (23) has suggested that the oxidation resistance of heat-resisting steels is due to the formation of a stable spinel. As many minerals and oxides possess this structure, the spinel structure allows the substitution of many metal ions without a great change in the lattice parameter. It would seem that the spinel structure is both flexible and stable. 3. Formation of New Oxide in Inner Layer at C. If one or more of the minor components diffuse with great difficulty through the oxide for reasons of size or charge, segregation of the oxides of these elements may occur in contact with the alloy interface. This may happen for silicon, calcium, etc. As silica films are amorphous and silicate films may also be amorphous except after long periods of heating, the presence of these films would be difficult to detect by diffraction techniques. If sufficiently impervious, this film could control the rate of the reaction. 4. Change in Conductivity and Cation Vacancy Concentration. The effect of substituting ions of valency different from the cations in the oxide is to change the cation vacancy and positive hole concentrations and thus the rate of reaction (14, 29) and electrical conductivity. 5. Change in Physical Properties and Adhesive Properties of Oxide and Oxide-Alloy Interface. The minor components may concentrate in the surface layer of the alloy, as oxide in the oxidealloy interface, or may form silica or silicate films and thus change the physical properties of the oxide-alloy interface or the bonding between the oxide and alloy. Thus, if minor components tend to embrittle the oxide, stresses set up between the oxide and metal may cause cracks within the oxide rather than between the oxide and the alloy. If the concentration of the minor components or their oxides tends to weaken the bonding between the oxide and metal, the oxide may scale in large sections. A third case, which
Table I shows a list of the main reactions which may occur in the oxidation of nickel-chromium alloys. The thermodynamic evidence presented below is given for the standard state (unity activity) of the metal in the alloy. This is not strictly correct, in view of the fact that several of the elements considered are present in a concentration of the order of 0.1%. However, activity coefficients are not known and it is therefore impossible to make a precise calculation. For many of the calculations the correction due to the activity of the metal in the alloy will be small compared t o the free energy change of the reaction considered. Wagner (38) has shown the importance of the activity corrections for binary alloy s y s t e m in which stabilities of the two oxides are similar. However, in the reaction of nickel oxide with chromium and the minor components the free energy changes for the reaction are large. Therefore, the activity corrections are small in comparison.
A.
BRITTLE CRACKING OF ADHERENT OXIDE
B.
PEELING OF NON-ADHERENT OXIDE
Figure 3. Physical Failures of Oxide Films Table I1 shows the thermodynamic evidence for reactions A1 1. The logarithm of the decomposition pressure is tabulated for temperatures from 26" to 1200" C. The literature references used in the calculation are shown in the headings. All the oxides are stable to decomposition at temperatures as high as the temperatures used in testing the performance of the alloys. However, in a relative sense nickel oxide is the least stable oxide and calcium oxide the most stable. Table I11 shows the solid phase reactions of chromium, silicon, manganese, and calcium with nickel oxide (reactions B1 to Bi of Table I). All the reactions are possible thermodynamically. It is readily seen that although nickel oxide may form, the other components should react with it and form their own oxides. One may conclude that the most stable oxides of the several metals present should form if the reaction with oxygen were carried out i n h i t e l y slowly. Under practical oxidation conditions the reltn A5 in Table
August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1737
the inner layer of the oxide. I n this sense calcium and silicon
PRESSURES OF NICKEL,CHROMIC, may have a major influence on the oxide and interface between TABLE 11. DECOMPOSITION SILICON,AND MANGANOUS OXIDES - log %,' Atmospheres
the oxide and the alloy. The formation of silicates, shown in reactions D1 to D4, Table Temp., NiO CrzOa Si02 MnO CaO I, may be expected from considerations of the phase diagrams of c. (27) (4,67) (4,97) (97) (4,80) the oxides (IS). 140,O 130.2 209,4 125.0 79.2 25 79.8 128.6 74.6 84.9 46.0 200 The decarburization reactions shown in E l and E 2 have been 54.4 87.4 49.6 57.1 29.4 400 discussed (12). If a carbon content of the metal of 0.0570 is 40.4 65.6 42.1 34.8 20.4 600 31.8 51 .O 27.4 32.6 14.8 800 assumed, calculations show for the reaction between carbon and 25.8 40.8 21.6 26.1 11.0 1000 21.4 21.4 33.8 17.3 8.3 1200 nickel oxide a n equilibrium pressure of 1 atmosphere of carbon monoxide at 790" C. Similar calculations for chromic oxide, TABLE 111. SOLIDPHASE REACTIONS OF NiO WITH CHROMIUM, manganous oxide, and silicon dioxide show the decarburization SILICON,MANGANESE, AND CALCIUM reaction t o occur only under vacuum conditions at high temperEquation Reference atures. The importance of this reaction in the oxidation of 1. 2/3Cr(s) + N i O ( s ) z 1/3CrzOa(s) + N i b ) (4, $7) nickel-chromium alloys a t high temperatures containing carbon 2. 1/2Si(s) + NiO(sL- 1/2S102(s) + N i b ) appears to have been overlooked, as a t the ASTM test tempera3. Mn(s) + NiOWX MnO(s) + Nl(s) 4. C a b ) + NiO(s) CaO(s) + Nib) ture of 1175 'C. the equilibrium pressure of carbon monoxide over log K nickel oxide for a carbon content of 0.05% is over 60 atmospheres. Temp., C. Reaction 1 Reaction 2 Reaction 3 Reaction 4 The curves of vapor pressure us. temperature have been determined with good precision for nickel (19) and for chromium (8, 25). Data on the other elements haye been compiled b y Dushman ( 5 ) . The vaporization reactions become of special importance at high temperature when the alloy is operated in neutral or reducing atmospheres or under vacuum conditions. One other type of reaction is of interest.
-
ative rate of attack of the several metals must be considered as well as interdiffusion in the alloy itself. This has recently been discussed by Wagner ( M ) . Thermodynamic data for the spinels other than FeaOl are not available. I n order t o predict the stability of the several spinels i t is of interest to tabulate some of their structural information. Table IV shows the lattice parameters of the known ferrites and chromites as a function of the ionic radii of the bivalent ions. BBnard ( 2 ) has suggested from a consideration of a similar table that the ferrites of nickel(II), magnesium, cobalt(II), andiron (11) form readily, while the ferrites of copper(I1) and manganese(11) form incompletely and the ferrites of calcium and barium do not form because of the size of the biva!ent ion
PARAMETERS OF CHROMITES AND FERRITES OF A
TABLE IV.
NUMBEROF METALS(SO)
Divalent Metal
Atomic Number
Nickel Magnesium Cobalt Iron Zinc Copper Manganese Cadmium Calcium Strontium Barium a
50 atom
28 12 27 26 30 29 25 48 20 38 56
Radius of Ion,
A.
0.74 0.75 0.78 0.80 0.83 0:83 0.99 1.05 1.18 1.38
Parameter of Oxide MO, A. 4.1684 4.203 4.24 4.332a
....
....
4.4345 4.689 4.797 5.144 5.523
Parameter Parameter
of
of
Chromite,
Ferrite,
8.289 8.305 8.319 8.344 8.296
8.340 8.366 8.35 8.374 8.423 8.445 8.457 8.684
A.
8:436 8.667
... ...
...
A.
. .. ... ...
70Fe.
Although less information is available on the chromites, it suggests t h a t chromites do not form readily with ions of atomic radii larger than that of cadmium(I1) and a series of chromites is formed similar to the ferrites. Several interesting conclusions can be drawn from this comparison. Nickel, chromium, manganese, and iron should form spinels and mixed spinels. Even though manganese and iron are present in minor amounts in the alloy, they can substitute in the spinel structure and thus appear in the oxide film. Calcium and silicon, npt being able to form spinels with chromic oxide and ferric oxide, may form their own oxides or silicates in
Fez08(s)
+ FeO.CrzO8(s)F= FeO.FezOs(s) + CrzOs(s)
According to BBnard ( 2 ) , this type of reaction is not possible in oxides because the trivalent ion diffuses with difficulty. EXPERIMENTAL
The experimental part of this paper is concerned with reflection and transmission electron diffraction studies of the oxide films formed on a series of eight alloys. Table V shows the classification of the alloys, their composition, and the results of the ASTM useful life tests. These alloys are grouped for convenience as follows: 1. Thirty-year improvement in 80 Ni-20 Cr series 2. Effect of silicon 3. Effect of manganese
These samples were prepared and analyzed, and the useful life was tested and made available by the Driver-Harris Co. and the Hoskins Co. The life tests were made by the standard ASTM life test machine at 1175 O C. The apparatus used for most of the electron diffraction experiments has been described ( 6 , 7 ) . The chief feature of interest is the high temperature furnace adapter for reflection studies which makes it possible to study the oxide in situ and at the given temperature after removing the gas atmosphere. For the transmission electron diffraction patterns and for the reflection studies made on the sheet alloys, the electron diffraction attachment of the R.C.A. model EMB-4 electron microscope was used (82). Two sets of experiments are described. The first group is reflection studies on cylinders of the alloy in which the reaction is carried out in the camera a t temperature ( 6 , 7 ) . T h e second group is transmission and reflection studies made on strip specimens previously oxidized in the vacuum microbalance. Preparation and Oxidation Procedures. DIRECT REFLECTION STUDIES. The specimens 3/9 inch in diameter were surface ground and given an abrasion treatment in a precision abrader starting with No. 2/0 polishing paper and finishing with 4/0 paper under purified kerosene. The specimens were cleaned in soap and water, distilled water, and absolute alcohol and stored i n a desiccator. Experiments were made b y heating in vacuo of the order of 10-6 mm. of mercury t o temperature and adding oxygen t o a pressure of 1 mm. of mercury for various lengths of time. Photographs of the electron diffraction patterns were taken in vacuo before reaction and after oxidizing for 1, 10, 30, and 60
INDUSTRIAL AND ENGINEERING CHEMISTRY
1738
Vol. 45, No. 8
mTR' x
x
X
X
x
x @
@TR
X
OXIDE STRUCTURES
OXIDE STRUCTURES
0
=MnOC.r2
x:Cr203
O3
, I
( 8
0
10
20
30
TYPE OF PATTERN
0
= ORIENTED SHARP hl 'MEDIUM D 'DIFFUSE TR. = TRACE S.A. SMALL AMOUNT
= Cr203
0
0 = ORIENTED S = SHARP M = MEDIUM D = DIFFUSE TR.: TRACE SA.=SMALL AMOUNT, 40 50 60
0 : N i O
-+:MnO, L
TYPE OF PATTERN
S
= NiD.Cr2D3
1I u = NiO
0
TIME (MIN.)
I
I
I
!
IO
20
30 TIME I M I N . )
40
Figure 5 .
Figure 4. Oxide Films on Nichrome 13246
I 50
1
60
Oxide Films on Nichrome AI-493 Low- Mn, low, Si
minutes. Further pictures were taken after holding in vacuo a t temperature for 30 minutes and after cooling to 25" C. REFLECTION AND TRANSMISSIOK STUDIES. I n another paper (9) kinetic studies on the oxidation of three alloys of this series will be described. These specimens are sheets 1 cm. wide, 5 em. long, and 5 mils thick, which were given the surface abrasion treatment and cleaned as described for the other specimens. The oxidation experiments were made in the laboratory vacuum microbalance a t a series of temperatures and for different times. Therefore, specimens were available having a known thickness of oxide. For these specimens the oxidation pressure was 7.6 em. of mercury of oxygen. For reflection electron diffraction studies a small disk was punched from the sheet after oxidation. A 1 X 1.5 em. section was coated with Parlodion and the oxide film removed by electrochemical attack (11) using the alloy as the anode in a n electrochemical cell with a deaerated saturated solution of potassium chloride. The small squares of oxide film were washed several times in distilled water and mounted on the conventional electron microscope specimen screens. RESULTS AND DISCUSSION
Reflection Technique. HISTORICAL GROUP. The 13246, 12246, and 12046 series of alloys represent progressive stages in the development of heater alloys over a 30-year period, with the useful life being increased BOOYO. I n a previous work Hicknian and Gulbransen ( 1 6 ) presented existence diagrams in temperature and time of the oxides formed on these alloys over the temperature range of 400" to 950" C. and for oxidation times up to 1 hour for an oxygen pressure of 1 mm. of mercury.
TABLE
NO. 49 1 492 493 494
49 5
12046 12246 13246
h-iokel-C hroniium 4lloys Low M n . intermediate Si High >In, interpediate Si Low hIn, low SI Low M n , intermediate Si Low M n , high Si S e w Ni-Cr alloy V Old Ni-Cr alloy V Old Ni-Cr alloy I V
v. C
cOl\IPOSITION AND
Mn 0.05 2.30 0.04
0.02 0.02 0.01 0.01 1.70
Si
Further studies on these and other alloys have confirmed t,he results for alloys 12046 and 12246. However, several changes are now suggested in the interpretation for the oxides found on alloy 13246. The crystal structures plotted on a temperaturetime chart are shown in Figure 1. Each oxide is represented by a particular symbol as described in the figure. A st'udy of the influence of mangmrse on the crystal structures of the oxides has shown that the spinels on high-manganese alloys gave a unit cell size of 8.40 to 8.43 A., while spinels formed on low-manganese alloys gave a parameter characteristic of Ni0.Cr203 (16) of 8.32 A. This and other evidence suggests that the spinels formed on alloy 13246 are MnO.Cr208. A careful analysis of the patterns formed a t 600" and 700" C. suggests that a mixture of chromic oxide and the spinel hIn0.Cr& was formed instead of chromic oxide or KiO.CrzOi as previously described ( 1 6 ) . This was checked by a t,ransmission electron diffraction study. At 950" C., chromic oxide formed first, Tyith lines of the spinel MnO.Cr2Os appearing as the oxidation progressed. Previous interpretations gave only the spinel structure a t 950" C. With alloy 13246 where three or more oxides may exist in the film it is extremely difficult to make a proper identification. Many of the lines are common to one another or overlap. For this work i t has been found necemary not only t o plot and compare the observed diffraction patterns with all of the possible
LIFE TESTS O F NICKEL-CHROMIUhI A L L O Y > Cr 20.0
Composition, Per Cent Ni Fe Zr 0.25 0.25 0.25 0.25 0.26 0 34 o:io 0.05 0.32
.. ..
.. ..
0.20
Ca 0.020 0.035 0.028 0.040 0.039 0.024 0.029 . I .
hlg
...
... ... ... ... I
.
.
0.'006
-11 0.13 0.15 0.20
0.17 0.15 0.07 0.08
Useful Life, Hours 105 106 63
124 178 157 86 25
Temp., O
C.
1177 1177 1177 1177 1177 1175 1175 1175
August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1000
l
I
0
4001
I
OXIDE STRUCTURES
0
900-
x x x
xx
7001
I
I
10
20
El El
x x
800-
P
3n 6ooI-
5oo
TYPE
I
I
30
40
10
60
Figure 7.
0 S M
El
= ORIENTED = SHARP
a MEDIUM E DIFFUSE TR. = TRACE SA. E SMALL AMOUNT
20
30 TIME ( M I N . )
I
I
I
40
50
60
Oxide Films on Nichrome M-495 Low Mn, high Si
Si
(400' t o 950" C.
Group 1. Historical) Lifetime a t Oxide Film Analyses 1177' C., Tzmp., Hours C. Crystal structure 157 400 NiO 500 NiO (1 rnin.), CrzOa (5-00 min.) 600 CrzO8 700 CrzOs 800 CriOs 900 CmOa XO.YZO~ * 950 CraO8 86 400 NiO 500 NiO 600 CrzOa 700 CrzOa 800 CrzOa 900 CrzOa XO.YzOa 950 CrzOs 1-5 min.) CrzOa XO.dz08 (30-60 min.) 26 400 NiO 500 NiO 600 CrzOa MnO.CraOa 700 CrzOs MnO.CrzOa 800 MnO. CrzOa 900 MnO MnO.CrzO8 (1 MnO.CmO8 (5-60 min (1-5 min.). Cr?Oa CrnOa (30-80 min.)
+
+
13246 High Mn, low Si, no minor components Zr, Ca, and AI
TYPE OF PATTERN
I 0
I
TABLE VI. OXIDESFOUND ON 80 NICKEL-20 CHROMIUM ALLOYS
+
@A.
D
patterns but also to compare in a similar way enlarged positive prints of the diffraction patterns from the unknown oxide and the pure componenta The latter procedure shows up the intensity factor more clearly and is illustrated in Figure 12. . Table VI shows a summary of the oxides found on the three alloys. Nickel oxide was formed on all these alloys a t 400' and 500 C. for short oxidation periods, b u t i t was not formed a t higher temperatures except under the most vigorous oxidizing conditions. Chromic oxide formed a t temperatures of 600" C. and higher for all the alloys except 13246. Lines of a spinel X0.Y20a were formed at 900" and 950" C. together with chromic oxide. For high-manganese alloy 13246 the spinel MnO.CrzOs formed at 600 O C. and existed alone at 800' and 900 O C.
12240 Low, -&In, low Si minor components Zr, Ca, and AI
, A w . A .
x
-- N i O - CreQ3
= SHARP = MEDIUM = DIFFUSE = TRACE = SMALL AMOUNT
50
x
OX ID€ STRUCTURES
Figure 6. Oxide Films on Nichrome M-494
+
-@
= ORIENTED
I
(gp O J R WTR' mTR
xx
OF PATTERN
TIME ( M I N . )
Heat No. 12046 Low Mn, high Si minor components Zr, Ca, and AI
x
700-
X
0 S M D TR. SA.
Low Mn, i n t e r m e d i a t e
1739
++ +
+
+
TABLEVII.
OXIDE SCALESFORMED O N NICKEL-CHROMIUM SCALES(LUSTMAN)
Sample
Oxidea
CrzOa NiO
NiO, b i n e l , CrzOa NiO, spinel, Crz08 fi
Relative amounts of several components decrease toward right.
The spinel identified as XO.Yg03 was probably Ni0.Cr20+for alloys 12046 and 12246. However, the number of lines was too few for a good identification of the particular spinel. Since the electron diffraction results were determined by reflection studies of the outer few Angstroms of an oxide film of several thousand Angstroms, i t was of interest to compare these results with those obtained under the most vigorous oxidizing conditions, where the oxide was of the order of 100 to 1000 times as thick. Table VI1 shows the results of an x-ray study by Lustman ( 2 1 ) on oxide scales formed at 1175" C. in a special cvrlic oxidation test. These results are in agreement with the oxides found on these alloys a t 950" C. using the electron diffraction method, except that nickel oxide is found in all the x-ray patterns. This suggests that nickel oxide is formed under vigorous oxidizing conditions at 1175" C. An electron diffraction (16) study of the oxide found on alloy 12046 after 72 hours of oxidation in air a t 1050" C. showed that only chromic oxide was formed. It is concluded that the nickel oxide forms a major constituent in the oxide for two conditions: ( 1 ) a t temperatures of 500" C. and lower for short oxidation times and (2) a t temperatures of the order of 1175' C. for long oxidation times and cyclic heating. An analysis of these results tends to confirm the conclusions reached by Hickman and Gulbransen (16) and by Scheil and Kiwit (24)that the better heater alloys are characterized by the
INDUSTRIAL AND ENGINEERING CHEMISTRY
1140
Vol. 45, No. 8
loo(
I 90(
700
1
8OC
@R
800
@ @
x
x E El
$
70c
-@ @ '
60(
xo
a:
3
8
50(
SA#
s.l
400t
OXIDE STRUCTURES
TYPE OF PATTERN
Le]
40(
TYPE OF PATTERN
0 = ORIENTED S = SHARP M = MEDIUM D =DIFFUSE TR. =TRACE S.A.' SMALL AMOUNT 0
Figure 8.
I
I
I
I
I
IO
20
30
40
50
TIME (MIN.!
0 = S = M D = TR = S A. =
60
ORIENTED SHARP MEDIUM DIFFUSE TRACE SMALL AMOUNT
II
I
I
I
I
I
I
0
IO
20
30
40
50
60
TIME (MIN.)
Oxide Films on Nichrome 31-491
Figure 9.
Oxide Films on Nichrome M-492
Low Mn. intermediate Si
High Mn, intermediate Si
appearance of chromic oxide in the scale and the poorer heater alloys by the appearance of a spinel structure. To teat this conclusion i t is necessary to study the individual effects of silicon, manganese, calcium, etc. EFFECTOF SILICOX'.Three compositions are studied in which the silicon content was varied from 0.23 to Z,09yo while the manganese and calcium were maintained essentially constant. The ASTV useful life increases with the silicon content and varies from 63 to 178 hours a t 1177" C. Figures 5 , 6, and 7 show the existence diagrams of the oxides formed on these alloys, while Table VI11 shows a summary of the results. Nickel or oxide was formed a t 400' C. for all three alloys, while a t 500 a C. it formed only on the alloy of intermediate silicon content. Chromic oxide formed on all three alloys between 500" and 900" C. The spinel Ni0.Cr20s was found in addition to chromic oxide a t 900' C. These results showed that changing the silicon content of a series of low-manganese alloys with calcium present had only a small effect on the coniposition and crystal structure of the oxide films. However, the useful life was changed by a factor of 300%. A comparison of theee results with those for alloy 13246 suggested that the manganese content was important in detrrmining the composition of the oxide film. Two alloys were studied in which EFFECT OF AIANGANESE. the manganese content was changed from 0.05 to 2.30y0 while the silicon and calcium contents were maintained constant. The ASTM useful life tests were essentially the same a t 105 hours. Figures 8 and 9 show the existence diagrams of the oxides formed on these alloys while Table I X summarizes the results. Both alloys showed the oxide nickel oxide a t 400" C. and nickel oxide plus chromic oxide a t 500" C. The low-manganese alloy formed chromic oxide and spinel a t 600" C. and higher, while the high-manganese alloy a t these temperatures formed either the RIn0.Cr203spinel or the spinel mixed with manganous oxide. These results showed that manganese was the most important
element in modifying the composition and crystal structure of the oxide film. Although manganese may have an influence on the useful life of the alloys for low-silicon alloys or for alloys Kithout the calcium, i t had little influence on the composition tested here. Manganese concentrated in the surface layer and in the bulk of the oxide film, as shown in Figure 2. Since the composition of the oxide for these alloys had no effect on the useful life, it must be concluded that the useful life was not determined by thc normal oxidation process. The identification of the spinel on the high-manganese-content alloy is shovin in Figure 10. Pattern F shows the experimental data plotted on a reciprocal scale. B, C, and G are calculated
TABLEF'III.
OXIDES
FOCND OK 80 ALLOYS
(400' t o 950' C.
Heat KO.
M 493 Low Si, low M n
Group 2.
Lifetime a t 1177' C., Tzmp., Hours C.
+
63
minor component, Ca
JZ 494
Intermediate Si, low Mn minor component, Ca
124
+
M 495
High Si, low M n 4minor component, CR
tr. = trace. s a . = small amount.
178
NICKEL-20
CHROMIUM
Effect of silicon) Oxide Film Analyses
-
C rys t a1 s t ruct 11 re
NiO Crno8 t r . XO.Yroa CrrOa CrnOa CrzOa CrzOs s a . Xo.Y108 (1 min.) CrzOs t r . XO.Yz08 (10-60 nun.) 400 X i 0 .500 X i 0 CrzOa 600 CrnOa 700 CrzOa 800 C1'203 900 CrzOa XO.Yz0a 400 Si0 500 CrpOs S . R . X0.YzOs 600 CrzOa 700 Cr203 t r . XO.Yz0a 800 C r 8 a (1 min.); CrzOa tr. X0.Y203 (10-60 min.) 9 0 0 CrzOa sa. XO.YaO3
400 500 600 700 800 900
+
++
+
+ + + +
+
August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1741
patterns of the spinels NiO.CrzOa, MnO.CrzOs, and Fed&. The fit is best for Mn0.Crz03. As the MnO.FezOs has a high parameter and the possibility of solid solutions does exist, an(400' t o 900" C. Group 3, Effect of Mn) other interpretation based on MnO. Fez03 would also fit the data. Lifetime a t Oxide Film Analyses Spectrographic analyses of oxides stripped from the oxidized 1177' C., Temp., Heat No. Hours ' C. C ryst a1 s truc t use metal ribbon showed that manganese was one of the important M 491 105 400 NiO components in the oxide for the high-manganese alloy, while it Low hfn, inter500 NiO + tr. CrzOa (1-10 min.) was present only in small amounts for the low-manganese alloy. mediate Si + NiO + s.a. CrzOa (30-60 rnin.) minor compo600 CrzOa This confirms the composition as derived from the structural idennent, Ca 700 CrzOa tification. 800 CrsOa 900 CrzOa + s.&. NiO.CrzOa For the case of manganese additions t o the nominal compoM 492 106 400 NiO sition, the thermodynamic predictions that manganous oxide and High M n inter500 NiO (1-30 min.), NiO s.a. CrzOa MnO.CrzOs would form with chromic oxide are verified experim?diate' Si + (60 rnin.) minor compo600 CrzOa (1 rnin.), AfnO.CrzOa (10.rnin.) mentally. T h e fact that manganese is present t o a large extent nent, C a 7oo no(^^^ in the film suggests that manganese in the alloy is readily attacked CrzO;o,+ tr. MnO + t r . NiO.CrzOs by oxygen. (60 rnin.) 800 MnO + MnO.CrzOa Transmission and Reflection Studies. The 13246, 12246, and 900 MnO + MnO.CrrOa 12046 series of alloys were oxidized a t 7.6 em. of mercury of oxygen a t 500' C. for 2 and 30 hours, a t 600" C. for 6 hours, and tr. = trace. s. a. = small amount. at 850" C. for 6 hours. The thickness of the oxide was determined by microgravimetric procedures (9) and the color of the oxide noted. This information is tabuTABLEX. CRYSTAL STRUCTURE OF OXIDESFORMED O N SHEETSPECIMENS lated in Table X, together with crystal structures of the oxide (Oxidation a t 7.6 cm. mercury of oxygen) films as determined by transmisTime of ThickOxidaness, Crystal Structure sion electron diffraction on the (All Patterns Sharp, N o Orientation) Temp., tion, y/Sq. stripped oxides and by reflection Alloy C. Hours Cm. Color Reflection Transmission electron diffraction directly from 12046 500 2 2.26 Lt. straw NiO, 8.a.a CrzOs NiO, tr. CrzOa 500 30 4.75 Pink CraOs, tr. NiO Crzoa the oxidized surface. 600 6 10.12 Blue CrzOa tr. sp prob. FeaOa crzo3 For alloys 12046 and 12246, 6 a50 45.4 Gray CraOa: tr. sp:: prob. Be804 CrzOa nickel oxide was the predomi12246 500 2 2.82 Lt. purple NiO, tr. CrzOa NiO, tr. CrzOa nant oxide for a 2-hour oxida500 30 4.5 Pink CrzOa 8.8.. NiO CrzOs 600 6 6.89 Blue CnOa: ti-. sp prob. FeaOa CraOa 850 6 28.0 Green CrzOa, tr. sp.:'prob. NiO.CrzOa CrzOa, tr. MnO (2.24A.line) tion at 500" c* chromic oxide was the predominant oxide 13246 500 2 4 . 5 5 StrawNiO, tr. CrzOs htnO.CrzOa, NiO, s a . CrrOs purple after 30 hours. A somewhat 500 30 3 . 6 4 Pink Crz03, Mn0.Cr~Oa CrzOa, MnO.CrzOa, tr. NiO similar phenomenon was ob600 6 6.75 Pink MnO.CraOa CnOa, MnO.CrzOs 850 6 58.2 Gray MnO.CrzOa Cr20a Or Fea04, tr. Crzoa served for alloy 13246, while the tr. = trace, s. a. = small amount, sp. = spinel. nickel oxide disappeared as the oxidation proceeded.
TABLE IX. OXIDESFOUND ON 80 NICKEL-20 CHROMIUM ALLOYS
+
$3
i*
::;;' "$io
O
d hkl
- ANGSTROMS
IRECIPROCAL SCALE )
Figure 10. Comparison of Diffraction Data of Several Oxides with Data for Oxide Formed in Nickel-Chromium Alloy
M-492 High Mn, intermediate Si
INDUSTRIAL AND ENGINEERING CHEMISTRY
1742
P
HOURS ALLOY 12046
I
I
I
I
I
I
5s In
Vol. 45, No. 8
chromic oxide struct,we on heating to 700 O C. while alloy 13246 changed to the spinel Mn0.Cr203. Nickel oxide was not formed again on cooling. This indicated that the reactions were irreversible. The loss of nickel oxide may occur by one of the following reactions: 3KiO(s)
+ 2Cr(s) --+ 3Ni(s) + CrzOB(s) (1)
Zm
1.-
2KiO(s)
nu: $0
KiO(s) f Mn(s) --+ blnO(s)
xi
6 HOURS ALLOY 12246
+ Si(s) --+ SiOp(s)+ 2Si(s)
d go
(2)
+ Si(s)
I--
(3)
v u
00
I
U%
SiO(sj
+ Ca(s) --+
CaO(s)
+ Ni(s) (4)
KiO(s)
a@
t
C (in solid solution) e Ws) CO(gj (5)
+
-I
Reactions 1 to 4 arc' favorable a t 500" C. Reaction 5 i ~ o u l d occur only in vacuo or in inert atmospheres a t 500" C. Studies dJ by Gulbransen, IT)-song, and Andrew (12) : * I I n c . . on the decarburization of these alloys b y .. ., I 3: the surface oxide indicated that the rate of Figure 11. Crystal Structure Observed i n Oxidation of Nickel-Chromium Reaction 5 was very slow below 800" C. Alloys At present it is impossible to say which of Reactions I t o 4 is responsible. The rcappearance of nickel oxide a t 1175" C. may be accounted Figures 11 and 12 illustrate this reaction. Figure 11 shows enlarged photographs of the diffraction patterns of nickel oxide, for by depletion of the silicon, chromium, manganese, or calcium chromic oxide, and MnO.CreOs, while Figure 12 shows the actual to a point where the kinetic factors again favored the formation oxide patterns found for the 2- and 30-hour oxidation periods of nickel oxide. for alloys 12046 and 13246. The loss of nickel oxide was shown Discussion. The thermodynamic and structural predictions that chromic oxide, manganous oxide, hInO.Ci-203, and KiO.CrzOo nicely in alloy 12046. I n alloy 13246 the nickel oxide lines should form in the oxide film of t.liese alloys were essentially veri(shown by the arrows) were greatly diminished in intensity. These experiments showed that the nickel oxide structure was fied. The fact that nickel oxide is formed for the initial stages of formed during the initial period of the reaction for temperatures thr low temperature reaction can be explained by t,he high rate of 400 and 500 C. However, for long periods of oxidation the of at,tttck of t'he nickel in the alloy. From a thermodynamic point of view silicon and calcium should nickel oxide structure disappeared and the chromic oxide strucform their own oxides within the film. The fact that t'hey were ture appeared. The formation of nickel oxide could not be explained thermodynamically or by a consideration of the characnot observed suggests that' these eIenients form oxide8 or other compounds a t the oxide-alloy interface, and ~vouldnot be norteristic rate of oxidation of nickel and chromium following mally observed by reflection electron diffraction. Another exKagner's (28) analysis. The explanation probably lap in the perimental difficulty is that silicon dioxide is usually of a very fact that the instantaneous rate of attack of oxygen on the alloy small crystallite size and may not be observed readily by transwas much faster than one would normally assume in a theoretical mission electron diffraction or by x-ray diffraction. analysis. Vacuum microbalance experiments (9) showed a rate Although silicon dioxide, calcium oxide, or silicat,es were not of oxidation of several hundred times that calculated from the observed in the oxide, these materials are probably present in the later stages of the reaction. Chromic oxide would be expected film or a t the oxide-alloy interface. A recent, paper by Caplan to form after the initial rate of attack had slowed down. and Cohen ( 3 ) in a study of the scaling of iron-chromium alloys One of the interesting questions was how to account for the showed that silica is present in the oxide film and that a concendisappearance of the nickel oxide. Several theories may be trat,ion occurs a t the oxide-alloy interface. proposed: (1) The excess nickel(I1) diffused back to the alloy, A s silica does not appear to concentrate in the outer layer of the (2) the nickel(I1) dissolved in the chromic oxide lattice, and (3) oxide or within the body of the film, its effect on the performance the nickel(I1) formed small crystallites of the metal which may of these alloys must be attributed to one or more of mechanisms or may not react with oxygen a t a later time. 3, 4, or 5 of Figure 2. This question is difficult to answer experimentally because of Preliminary studies of rate of oxidation (9)a t constant temthe problem of chemically analyzing a filni weighing a few microperature showed relatively small differences for the alloys of varygrams. ing silica content. This suggested that a silicon or silicate film, Effect of Heating and Cooling on Crystal Structures of Oxide Films. It was of interest t o study the effect of heating and even though present, was not controlling the normal oxidation process by mechanism 3 of Figure 2. It was also apparent that cooling on the composition and crystal structures of the oxide the concentration of vacancies was not effect'ively changed by the under vacuum conditions. Figure 13 shows the results for three addition of silicon, since the rate of reaction a t constant temperaalloys (16) with the oxide being formed a t 500' C. For alloys tures was not appreciably changed. 12016 and 12246 the nickel oxide structure transformed to the 6 HOURS ALLOY 13246
.
t
O
.
.
-
August 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1743
As silicon does have a strong effect on the useful life of the alloy, its effect must be ascribed to a change in the physical prop& a erties of the oxide and oxide-alloy interface E which will determine the way the oxide t cracks. If silicon distributes itself through0 out the film as oxide, even though in small f amount, i t may embrittle the oxide and cause brittle cracking due to temperature cycling procedures as shown in Figure 3,A. On the other hand, a concentration of silicon l5 dioxide or silicon in the alloy a t the oxideJ alloy interface may increase the binding of the oxide to the alloy and thus decrease the tendency of the oxide to crack from the alloy as shown in Figure 3, B. This would tend to lead to a mechanism of cracking of the oxide as shown in A . The exact manner in which silicon and the minor elements affect the physical properties of the oxide, alloy, and interface cannot be studied effectively by crystal structure methods and is beyond the scope of this work. The effect of manganese on the useful life is small. This is expected if i t concenI t I ! I ill 11i I 1 i 1 I I I trates in the oxide film rather than at the I oxide-alloy interface. It is concluded there3 fore that oxides made up of the spinel ON& Mn0.Cr208are as protective as chromic ox3a ide or the spinel NiO.CrzO8 for alloys having gF5 L at least 1% silicon and calcium present. In the choice of addition elements i t is thought that metals which will readily substiEffect of Time of Oxidation at 500' C., 7.6 Cm. of Mercury of Oxygen, on Composition of Oxide Film tute in a form of spinel structure with chromic oxide or ferric oxide will have rather small effects on the useful life. On the other hand, metals which cannot substitute in the spinel lattice, and which 12046 12246 &g& will form silicates, may modify the useful life greatly.
6
s"
P HOURS]
ALLOY 1PO46
1 1 II
I
30 HOURS
I I I II
1 . 1
R
.
13146
6 so
30 HOURS1
Figure 12.
-
-
Af
SUMMARY
I A
IA
V
x
H
400-
25
V
x
OXIDE STRUCTURE
A
x
I
MnO-CraOj
= Cr203
c]= N i D
L 'TYPE OF PATTERN 0
= ORIENTED
S = SHARP M =MEDIUM D =DIFFUSE
Figure 13. Heating and Cooling Oxide Films in Vacuo
Crystal structure studies were made on eight alloys of the nominal 80% nicke1-20% chromium composition using electron diffraction methods. The silicon and manganese compositions of these alloys were varied in a systematic way. The alloys were oxidized over a temperature range of 400" to 950" C. and over a time range of 1 hour for an oxygen pressure of 1 mm. of mercury. Electron diffraction patterns were used t o study the effect of time and temperature on the crystal structure as the oxide formed on the alloy. The crystal structure information was correlated with the composition of the alloy and with its useful life in high temperature cyclic oxidation tests. Although the SO% nicke1-20% chromium alloys of low manganese composition showed a 300% improvement as a result of increasing silicon alone, the crystal structures and compositions of the oxides showed no appreciable differences. Nickel oxide was formed a t temperatures of 400" and 500" C., chromic oxide was formed a t higher temperature, and a little spinel was formed with the chromic oxide a t the highest temperatures. I n contrast, a larger change in the manganese content changed the crystal structure of the oxide greatly. However, for a 1% silicon alloy the useful life was independent of the manganese content. It is concluded that there is no unique oxide composition for good protection to cyclic tests. Instead, i t is suggested t h a t the useful life can be correlated not with normal oxidation processes but rather with changes in the physical properties of the alloyoxide interface.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1744
LITERATURE C I T E D
(1) Bash, F. E., and Harsch, J. W., A m . Soc. 7 ’ & i n ~ Materinls Proc., 29, Part 11, 506-19 (1929). (2) BBnard, J., BulE. SOC. chim. Fmnce, 13, 511-21 (1946). (3) Caplan, D., and Cohen, &I., J . Metals, 4, 1057-65 (1952). (4) Chipman, J., Trans. Am. Soc. Metals, 22, 385-435 (1934). (5) Dushman, S., “Scientific Foundations of Vacuum Technique,” New York, John Wiley & Sons, 1949. (6) Gulbransen, E. A., J . A p p l . Phys., 16, 718-24 (1945). (7) Gulbransen, E. A,, Rev. Sci. Instr., 18, 546-50 (1947). (8) Gulbransen, E. A , and Andrew, K. F., J . Electrochem. Soc., 99, 402-6 (1952). (9) Gulbransen, E. A . , and Andrew, K. F., I b i d . , to be published. (10) Gulbransen, E. A , , and Hickman, J. W., Trans. Am. Inst. Mining Met. Engrs., 171, 306-31 (1947); T.P. 2068. (11) Gulbransen, E. A., Phelps, R. T., and Langer, A , IND.EKC. CHEM.,ANAL.ED., 17, 646-52 (1945). (12) Gulbransen, E. A., Wysong, W. S., and Andrew, K. F., Trans. A m . Inst. Mining M e t . Engrs., 180, 565-78 (1949); T.P. 2438.
(13) Hall, F. P., and Insley, H., “Phase Diagrams for Ceramists,” Columbus, Ohio, Am. Ceram. SOC.,1947. (14) Hauffe, K., and Pfeiffer, H., quoted by K. Hauffe, Wiss. 2 . Universitiit Greifswald, Jahrgang I, Mathematisch-naturwissenschaftliche Reihe, Nr. 1 (1951/52). (15) Hessenbruch, W., “Metalle und Legierungen fur hohe Temperaturen,” Berlin, Julius Springer, 1940.
Vol. 45, No. 8
(16) Hickman, J. W., and Gulbransen, E. A , , Trans. Am. Pmt. Mini n g Met. E n g ~ s .180, , 519-33 (1949); T.P. 2372. (17) Holler, H. D., Trans. Electrochem. Soc., 92, 91-7 (1947). (18) Iitaka, I., and Miyake, S., Xature, 137,457 (1935). (19) Johnston, H. L., and Marshall, A. L., J . A m . Chem. Soc., 62, 1382-90 (1940). (20) Kelley, K. K., U. S.Bur. Mines, Bull. 383 (1935). (21) Lustman, B., Trans. A m . Inst. Mining Met. Engrs., 188,995-6 (1950). (22) Picard, R. G., J . A p p l . Phys., 15,678-84 (1944). (23) Quarrell, A. G., Nature, 145,821-2 (1940). (24) Scheil, E., and Kiwit, K., Arch. Eisenhiittenw., 9, 405-16 (1935-6). (25) Spciser, R., Johnston, H. L., and Blackburn, P., J . A m . Chem. SOC.,72, 4142-3 (1950). (26) Sully, 9.H., J . S C ~Inst?., . 22, 244-5 (1945). (27) Thompson, M. de Kay, “Total and Free Energies of Formation of the Oxides of Thirty-Two Metals,” New York, Electrochemical Society, 1942. (28) Wagner, C., J . Electrochem. Soc.. 99, 369-80 (1952). (29) Wagner, C.: and Zimens, K., Acta Chem. Scand., 1, 547-65 (1947). (30) Wyckoff, R. W. G., “Crystal Structures,” Kew York, Interscience Publishers, 1951. RECEIVED for review March 6, 1953. ACCEPTED X a y 7, 1933. Presented before the Division of Physical and Inorganic Chemistry at t h e 123rd Meeting of the AMERICAN CHEMICAL SOCIETY,Lo8 Angeles, Calif. Scientific Paper 1719, Westinghouse Research Laboratories.
Tetraethvl Radiolead Studies of J Combustion Chamber Deposit Formation H . P. LANDERL AND B. YI. STURGIS Jackson Laboratory and Petroleum Laboratory, Organic Chemicals Department, E. Z, d u Pont de Nemours & Co., Inc., Wilmington, Del.
D
EPOSITS which form in the combustion chambers of automotive and aircraft engines have been shown to cause certain undesirable effects. The elimination of these deposits, which are a combination of residues from the fuel and oil, may be possible if the mechanism of their formation and scavenging is understood more completely. Some of the physical aspects of deposit formation have been studied by Dumont ( I ) , who found t h a t lead salt deposits accumulate at a nearly constant rate under fixed engine operating conditions until a certain thickness is reached, at which time flaking sets in and maintains the total deposits a t a fairly constant weight. Flaking is believed to be the result of thermal stresses developed within the deposits as they grow thicker. More recently, Newby and Dumont ( 2 ) have discussed the chemistry of deposit formation from leaded fuels and have demonstrated t h a t reactions between solid deposits and reactive compounds in the hot combustion gases are of great importance in controlling deposit formation and composition. I n spite of the new knowledge made available by theee studies, many details of the mechanism of deposit formation and scavenging are still unknown. The study of combustion chamber deposit formation is very difficult since no direct method is known for following the formation a t the time it is occurring. The appearance of the deposits at any time during their formation only suggests the processes which have occurred. The use of tetraethyl radiolead in tracer amounts in the fuel provides a new procedure for such a study. The exact location and distributioii of the radioactive
lead salts which this additive deposits within the combustion chamber can be detected by means of x-ray film. It has been possible by this technique to observe the formation and removal of deposits resulting from tetraethyllead during a relatively short time a t any stage of the deposit growth. The importance of the temperature and physical state of a surface in influencing deposit laydown has been indicated. The efficiency of halogen scavenging also has been demonstrated and a previously unrecognized type of scavenging mechanism observed. RADIEMD AS RADIOLEAD TRACER. The radioactive lead used in this investigation was radium D, one of the decomposition products of the uranium series. The sequential decomposition of radium D occurs predominantly by the following path. RaD
p (0.026 m.e.v.)
-
22 years half life Pb;:O
-
RaE
p (1.17 m.e.v.) 5.0 days half life Biz10 83
RaF
(5.3 m.e.v.) 140 days half life-
RaG
01
p0;:o
Pbg;“ inactive
The medium energy beta particles from radium E are the only radiations in this series which can be detected easily either with a Geiger counter or with photographic film. Radium E, very
