FUNDAMENTALS REVIEW Granet, I., and Kass, P., Petroleum Refiner, 32, KO.3, 149-50 (1953). Gutmann, F., and Simmons, L. M., J . Appl. Phys., 24, 1067-8 (1953). Haycock, E. W., Alder, B. J., and Hildebrand, J. H., J . Chem. Phys., 21, 1601-4 (1953). Heath, H. R., Proc. Phys. SOC. (London),66B, 362-7 (1953). Held, van der, E. F. M., Hardebol, J., and Kalshoven, J., Physica, 19, 208-16 (1953). Hilsenrath, J., and Touloukian, Y. S., paper 53-A-186 presented a t Annual Meeting, Am. Soc. Mech. Engrs., New York (December 1953). Holleran, E. &I., J . Chek. Phys., 21, 2184-7 (1953). Hugel, G., Kolloid-Z., 131,4-10 (1953). Ishikawa, T., Bull. Chem. SOC.Japan, 25,3840 (1952). Jeffries, Q. R., and Drickamer, H. G., J . Chem. Phys., 21, 1308 (1953). Johnson, J. F., and LeTourneau, R. L., J . Am. Chem. Soc., 75, 1743-4 f 1953). Junk, W.'A., and Comings, E. W., Chem. Eng. Progr., 49, 263-6 (1953). Kestin, J., and Pilarczyk, K., paper 53-A-67 presented a t Annual Meeting, Am. Soc. Mech. Engrs., New York (December 1953). Keyes, F. G., Ibid., paper 53-A-58. Kiyama, R., and Makita, T., Rev. Phys. Chem. Japan, 12, 49-58 (1952). Knappwost, A., Z . physilc. Chern., 200,81-9 (1952). Koeller, R. C., and Drickamer, H. G., J . Chem. Phys., 21, 267-73 (1953). Ibid.,575-88. LeFevre, E. J., paper 53-.4-192 presented a t Annual Meeting, Am. SOC.Mech. Engrs., New York (December 1953). Lenoir, J. M., Junk, W. A., and Comings, E. W., Chem. Eng. Progr., 49, 539-42 (1953). Lewis. H. W.. Anal. Chem.. 25. 507-8 (1953). Lyons, P. A , and Sandquist,' C. L.,'J. A m . Chpm. SOC.,75, 38969- (1963). Maikenzie, H. A. E., and Raw, C. J. G., J . S. African Chem. Inst., 6,8-13 (1953). Maeda, K., J . Chem. Soc. Japan, Pure Chem. Sect., 74, 136-8 (1953). Mason, H. L., paper 53-A-40 presented at Annual Meeting, Am. Soc. Mech. Engrs., New York (December 1953). Meixner, J., 2.Naturjorsch., 8a, 69-73 (1953). Michels, A., and Botren, A., Physica, 18, 605-12 (1952). Moore, R. J., Gibbs, P., and Eyring, H., J . Phys. Chem., 57, 172-8 (1953). \ - - - - ,
\ - - - - ,
Morgan, C. R., and Olds, W. F., IND.ENG.CHEM.,45, 2592-4 (1953). Moyle, M. P., and Tyner, M., Ibid., 45, 1794-8 (1953). Mukherjee, A. K., J . Indian Chem. Soc., 29, 56-60 (1952). Mysels, K. J., and Stigter, D., J . Phys. Chem., 57, 104-6 (1953). Nadi, M., El, J . Phys. Chem., 57,589-91 (1953). Naiki, T., Hanai, T., Shimizu, S., Bull. Inst. Chem. Research, Kyoto Univ ,31, No. 1,56.8 (1953). Othmer, D. F., and Thakar, M. S.,IXD. ENG. CHEM.,45, 589-92 (1953). Parthasarathy, S., and Bakhshi, - . - _,d o n ) , 66B, 368-70 (1953). Prager, S.,J . Chem. Phys., 21, 1344-7 (1953). Prigogine, I., Brouckbre, L. de, and Buess, R., Physica, 18, 915-20 (1952). Richter, G. N., Reamer, H. H., and Sage, B. H., IND.ENa. CHEM..45, 2117-19 (1953). Roth, W., and Rich, S.R., J. A p p l . Phys., 24,940-50 (1953). Rowlinson, J. S.,and Townley, J. R., Trans. Faraday Soc., 49, 20-7 (1953). Sakiadis, B. C., and Coates, J., Louisiana State Univ. Eng. Erpt. Station, Bull 34 (1952) Ibid., Bull. 35 (1953). Saxton, R. L., and Drickamer, H. G., J . Chem. Phys., 21, 1362 (1953). Schmidt, A. F., and Spurlock. B. H., paper 53-A-184 presented a t Annual Meeting, Am. SOC.Mech. Engrs., New York (December 1953). Semenchenko, V. K., and Zorina, E. L., Zhur. Fiz. Khim., 26, 520-9 (1952). Senftleben, H., 2. angew. Phys., 5,33-9 (1953). Shrivastava, B. N., and Madan, M. P., Current Sci. (India), 22.71-2 (1953). Silawat, H.- G., and Bhagwat, TV. V., J . Indian Chem. Sac., 29, 706-8 (1952). Strehlow, R. A., J. Chem. Phys., 21, 2101-6 (1953). Tamura, M., Kurata, M., and Sata, S., Bull. Chem. Soc. Japan, 25, 124-6 (1952). Umstatter, H., Makromol. Chem., 10, 30-4 (1953). Vines, R. G . , Australian J . Chem., 6,1-26 (1953). Webber, H. A . , Goldstein, D., and Fellinger, R. C., paper 53A-79 presented a t Annual Meeting, Am. SOC.Mech. Engrs., New York (December 1953). Zwanzig, R. W., Kirkwood, J. G., Stripp, K. F., and Oppenheim, I., J . Chem. Phys., 21,2050-5 (1953).
CHEMICAL RATE PROCESSES
Diffusion and Oxidation of Solid Metals C. E. BIRCHENALL Princeton University, Princeton, N. J.
T
HE foremost questions in dealing with diffusion in metals are :
1. How t o adapt theories which appl simply to crystals in which diffusion defects are nearly in locaf thermodynamic equilibrium concentration t o real systems which, when appreciable chemical concentration gradients are present, seem t o develop excess diffusing defects 2. How t o explain the generation of the defects in required numbers (to date no evidence has been presented t o indicate that diffusion is retarded in any instance due t o a deficit of generators) and the annihilation or aggregation of defects where required in the diffusing couple 3. How to relate the measured diffusion coefficients to fundamental roperties of the crystal, and 4. 8 o w to obtain reliable and useful experimental data in the face of the many difficulties that have not been resolved. Reviews. Several review articles dealt with the progress that has been made in recent years along these lines. Le Claire has
May 1954
undertaken a brief general review ($80)in which he recommended that more diffusion experiments be carried out in the absence of appreciable concentration gradients to avoid some of the more obvious pitfalls. H e has also given a more extensive review (84D) devoted mainly t o the period 1949-52. Seith ( S 4 D ) has discussed effects arising from the inequality of partial diffusion coefficients in binary systems and suggests that many of the discrepancies in the experimental data have been due t o cross-sectional area changes and the development of porosity. This suggestion has been advanced frequently in the past few years and is generally accepted as a part of the trouble. Mathematical and Theoretical. Making use of the fact that the extremes of the penetration curve usually become linear on a probability plot Hall ( l 8 D ) has proposed an analytical method for calculating the diffusion coefficient as a function of concentration at the extremes for a given couple which should be
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT much more accurate than the graphical method. This procedure did not predict a simple exponential relationship between diffusivity and concentration. Cohen, Wagner, and Reynolds ( 6 0 ) have used distance parameters introduced by Hartley and Crank t o transform Fick's Law into a form suitable for calculating diffusivities when volume changes occur due to nonlinear dependence of the specific volume on the weight fraction for the alloy system. They also pointed out the advantages that attend the use of small concentration increments in diffusion couples. Beginning with kinetic theory Prager ( 3 1 0 ) has derived equations of the Onsager-Fuoss and Darken type. This has been extended to include cases in which volume changes accompany diffusion and to steady state permeation. Prager and Eyring ( 3 2 0 ) have concluded that mass flow accompanying thermal diffusion may be analyzed to permit separation of the heat of formation and heat of motion in diffusion. An equation which takes into account the stresses arising due t o variations in lattice parameters accompanying diffusion initially developed by Konabeevskii has been derived phenomenologically by Lynbov and Fastov (R5D). For carbon in austenite a t eutectoid temperature they predicted that the effective diffusion coefficient Jvould be equal to (1 20C)D where C is the carbon content in TT eight per cent, and D is the dilute solution diffusivity. Heumann ( 1 6 0 ) has presented a treatment of single and multiphaee diffusion (growth of alloy layers) based upon Fick's first law which is independent of volume changes of the system and interface control of the reactions. The case of silver-zinc has been examined. He ( 1 6 0 )has derived phenomenological equations for couples of any concentration increment which reduce to the equations of Darken when the extreme concentrations are pure metals. Whereas Darken's equations yield a physically meaningless partial diffusivity for copper for Landergren and Mehl's data on beta brass, Heumann's equation gives reasonable values. One of the unsatisfactory features of statistical mechanical theories of diffusion has been the use of the Debye frequency for the number of attempts an atom makes per unit time to surmount the energy barrier about its equilibrium site when it is known that the only frequencies that matter are those for a n atom adjacent to a vacancy or €or an interstitial atom. Similarly, the assumption that the change in vibration frequencies for the atoms surrounding the diffusing atom a t the saddle point, as well as for the diffusing atom itself, may be represented entirely by the analogy with strains produced by macroscopic external stresses has not met with universal acceptance. The controversy relating t o Zener's theory of the entropy of activation for diffusion and the frequency coefficient D Oin the Arrhenius equation has become centered on the relative importance t o be attached to the altered vibrational frequencies in the formation of a defect and when the defect is in has estimated that the entropy the act of diffusing. Dienes (8D) change resulting from the change in vibrational frequencies in the activated configuration might overbalance the entropy change due t o thermal lattice expansion and t o the lowered vibration frequency of an atom adjacent t o a vacancy. Especially Iyhen the activation energy is low, this effect might lead t o a negative activation entropy. I n a similar study Huntington, Shirn, and Wajda (200)concluded that the entropy change may be negative for some defects. On the basis of their particular model fitted to the elastic data for copper an interstitial gave a negative activation entropy and a vacancy a positive entropy. Because of its importance in radiation damage studies Huntington (19D)calculated the activation energy for motion of an interstitial in copper and arrived a t a value of about 0.25 electron-volts. Le Claire (620),by developing Zener's hypothesis that all of the activation energy in the unit act of diffusion goes into local straining of the lattice, found that the insertion of experimental values into his equations yielded reasonable values for the unknown parameters if it was assumed that face-centered cubic lead, silver, gold, copper, cobalt, and gamma iron utilized a vacancy mechanism while body-centered cubic wolfram and alpha iron required a ring mech-
+
894
anism. Other possibilities yielded unreasonable parameters. Based on this analyeis equations for the self-diffusion of aluminum and molybdenum have been proposed. Other questions of mechanism have been examined also. Bartlett and Dienes ( 2 0 ) have considered the probability that appreciable concentrations of vacancies exist and diffuse as associated pairs. For a model based on copper they concluded that the concentration of pairs was probably small, but that these pairs were much more mobile than single vacancies. Overhauser ( 3 0 0 ) has considered the effect of lattice distortions due to impurit,ies differing in size from solvent atoms on the distribution of heights of potential barriers for diffusion. Hoffman, Anders, and Crittenden ( 1 8 0 ) have cited experimental results which may be due t o the collapse of sheetlike aggregates of vacancies to form dislocation rings. Seitz ( 3 5 0 ) has extended his kinetic theory to permit, a diecussion of experimental evidence relevant t o the question of whether the porosity observed concurrent with the Kirkendall effect nucleates in good lattice a t high supersaturation of vacancies or on inhomogeneities a t ION supersaturation. The effectivencss of dislocation for removing vacancies and the probable mean free paths of vacancies in diffusing systems have been estimated. The latter appeared to lie in the range of 109 to 1013 jumps, where values less than log would be required to maintain equilibrium concentrations. Recognizing that the Kirkendall effect does not distinguish explicitly between vacancy and interst,itial mechanisms, Shockley ( 3 8 0 )has proposed three experiments n-hich appear to be capable of making the distinction. Volume Diffusion: Self-Diffusion. Shirn, Rajda, and Huntington ( 3 7 D )have re-examined the self-diffusion in zinc with carefully prepared single crystals of favorable orientation. Their results parallel t o the c axis agreed with the earlier work of Miller and Banks, but the diffusivities perpendicular to the c axis showed an appreciably lower activation energy. The authors concluded that two mechanisms must be active, a nonbasal vacancy mechanism and a basal vacancy or three-ring mechanism. I n an appendix they discussed experimental errors due t o the finite thickness of lathe cuts and possible misalignment in sectioning. Guzin ( 1 2 0 ) has reported self-diffusion data on cobalt which lie appreciably higher than both earlier studies. MacDonald (RCSD) has attributed the anomalous rise in resistivity of the alkali metals about 270' C. and their melting points to vacancy diffusion. Activation energies have been given for lithium, sodium, and potassium. The sodium value is roughly 10% below that given by Kachtrieb, Catalano, and TT7eil from tracer studies in a lower temperature range. Volume Diffusion: Chemical Diffusion. Th.e impetus of transistor development has led t o strong interest in the diffusion of dissolved elements in germanium and silicon. Fuller and Ditzenberger (110)and Severiens and Fuller ( 3 6 0 )have reported equat,ions for the diffusion of lithium in germanium and silicon. Like copper, lithium displayed an unexpectedly high mobility. Continuing their study of the diffusion of dilute solutions in silver Sonder, Slifkin, and Lazarus (400)have determined diffusivities for antimony, while Tomizuka, Slifliin, and Lazarus ( 4 1 0 ) gave only an approximat,e activation energy for cadmium. Diffusion of silicon in ferrite has been the subject of two investigations. Bradshaw, Hoyle, and Speight ( 3 0 ) used welded couples with a concentration range of 3 to 4% silicon at 1436" C., while Fitzer (10D)used multiphase couples which yielded values for the concentration dependence of the diffusion coefficient at 1150" C. Smith (890)has completed an extensive study of carbon diffusion in austenite by the steady state method. Diffusivities mere obtained as a function of concentration a t 802", %lo, and 1000" C. found that the Erdmann-Jesnitzer, Schumann, and Beckert (9D) decarburization of iron-carbon alloys in hydrogen- or oxygencontaining gases produced what they called diffusion or pin grain.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 5
FUNDAMENTALS REVIEW The grain boundaries were vertical to the sheet surface, and the size of the pins decreased with increasing initial carbon content. Busby, Warga, and V(Tells ( 6 0 )have decarburized and deboronized steels in wet hydrogen. From spectragraphic analyses of the depleted zone they have been able to determine both diffusivities (9500 to 13000 c.) and solubilities (800" to l l O O o C.) for boron in the steels. has obtained difBy the internal friction method, Ang fusivitiesand activation energies for both oxygen and nitrogen in niobium and tantalum. Mallett, Baroody, Nelson, and Papp ( 2 7 D ) determined the solubility of nitrogen at one atmosphere pressure in beta-zbconium and the rate of diffusion in the solid. This material contained approximatelv 2% hafnium, 8o Belle, and Cleland (380) the diffusivities when higher purity beta-zirconium (o.015% hafnium) became available, They also measured the rate of reaction that obeyed a parabolic law. Schumann and Erdmann- Jesnitzer ( 3 8 0 ) have found that in nonalloSed steel the permeability to hydrogen is increased by that hydrogen plastic deformation, Norton ( w 9 ~has ) enters steel and diffuses through it at temperature when corroded by moisture in the air. Deuterium and mass spectrametric analysis R,ere employed to show that it took only minutes at 90" C. for detectable amounts to pass through 200 sq. em. of 0.16 mm. thick steel wall. Kirkendall Several papers tvere mainly concerned
,
Oxidation
Increasing amounts of attention are being given t o the relations between the defect structure of oxides, sulfides, and and to the rates at which these phases groxl' When oxygen, sulfur, or halogen-containing gases react with solid metals. Isolated study of the properties of the reaction products are often as informative as direct study of the reaction itself. In a recent review article Hauffe U7-W has presented an admirable summary of achievements Of this Of primary importance $0 the oxidation field is the new monograph by Kubaschewslii and Hopkin8 W E )which gives a comprehensive survey of the general kinetic problem, theories of oxidation rates and mechanisms, special features that often accompany these reactions like cracking and blistering, and includes a survey of experimental methods and experimental results; the results are classified according t o the nature of the metal or alloy. References as recent as 1952 have been Kubaschewski and von Goldbeck ( % E ) have contributed a shorter review on scale formation in alloys. Evans (13E)has taken a more general look at oxidation under both ideal and real conditions. The importance of scale plasticity, the effect of cracking and porosity on the rate laws, boundary control, and accelerated oxidation due to nondissipation of the heat of reaction are among the topics considered. Hauffe (16E) has discussed the theory of the scaling process as applied to iron, coppsr, nickel, silver, titanium, zinc, and their alloys. Cubiciotti ( 6 E ) has reviewed the scaling characteristics of high temperature a paper which marker movements and porosity. metals. The transition from low temperature parabolic growth bined earlier work and new results Heumann and Kottmann (17D) have discussed porosity effects and cross-sectional area rates t o high temperature linear rates has been emphasized. changes which accompany the movement of markers in binary Rhodin (S@) and Gulbransen (14E) have reported on the contributions made b y the vacuum microbalance to surface studies diffusing systems, They have pointed out that the defect con~ lhigh temperature ranges, respectively. Details of centration should be abnormally low on the side of the ~ l dif- ~ in ~the 1 ~0 and ~ fusing atom and abnormally high on the side of the rapidly difinstrumentation have been Diffusion in Oxides. Direct measurements of diffusivities of fusing atom. They have proposed that the maximum defect is the favored site for porosityformation and deions in oxides and similar materials undoubtedly will play an imcrease in cross-sectional area while the minimum defect coneenPortant part in the development of an adequate theory of alloy tration is the site of the groM,th of new planes and lateral expanoxidation as they are now doing in the interpretation of the oxidation of pure metals. I n this regard the diffusion measuresion. Experimental evidence to supportthese contentionshas ments which Lindner and his coworkers have been carrying out been included. They found that different diffusion coefficients 011a variety of substances are of special interest. Diffusivities may be measured in a given binary system when different initial have been reported on the following materials: calcium and iron in conditions are used. Multilayer phase growth has been treated to monocalCium ferrite (30E), iron in hematite (aFe203),and the permit calculation of diffusion coefficients. In a discussion ofthe aeumann and Kottmann paper Bdckle ( 4 0 ) criticized their refzinc-iron spinel (ZnO.FenOd ($YE), zinc in the zinc-iron spinel and zinc oxide (SOE),lead in lead oxide (g88E), calcium in calcium erences to his earlier work. He presented curves for the growth oxide ( 2 9 E ) J and barium in barium metatitanate (43E). I t is not of phases in the copper-zinc system that indicated that the phase were not those appearing in the phase certain to what extent the large internal surface area due to the boundary extensive use of pressed and sintered powder tablets contributed diagram. to the results obtained. There has been some evidence within givena preliminary reporton Landergren and n f e h l ( g 1 ~ have ) diffusion studies in beta brass which displayed large markcr disthese studies that simple volume diffusivities are not being reported in all cases. placements and copious porosity. cou1ing and smoluHimmel, Mehl, and Birchenall (d1E) have determined selfBoundary and Surface chowski ( 7 ~referring ) ~ tothe diffusion of silver and zinc in copper diffusion coefficients for iron in wustite (ferrous oxide) including the dependence upon variation in composition and temperature. grain boundaries, proposed a model for the structureof grain boundaries, F~~~ 150 to 350 difference in orientationof the Under conditions of less rigorous composition control diffusivities grains there are rods of distorted lattice caused by clustering of in magnetite (FeaOa) and hematite ( aFe20s) were also obtained. Utilizing Wagner's theoretical treatment and the diffusion and dislocations and vacancies, leading to anisotropy of diffusion in thermodynamic data from these experiments the growth rates and different directions in the boundary. At larger angles a mechanisms for the three Oxides were random boundary region exists which yields little or no anisoDravnieks (10E)has examined various ways to correlate paratropy of diffusion. Haynes and Smoluchowski ( 1 4 0 ) have pre< 110 > bolic oxidation rate constants with properties of the oxides which pared bicrystals of irOn-3% silicon alloy with should affect diffusion rates of metal ions in MelO and Me0 and directions. With angles between { 110) planes lying between 50 and 86" and in the temperature range 804" t o 8 2 i " C., they found oxide ions in MezOa and MeOz. Oxidation of Pure Metals. Moore ( 3 4 E ) has attempted a preferential boundary diffusion between 20" and 85" with a possynthesis of the rates of oxidation of pure metals at temperatures sible cusp near 45". in the range of 300" to 1000" C. with the theory of lattice defects Winegard ( 4 3 0 )has observed preferential surface migration in silver in the < 110 > directions on (110) planes, although migraon the statistical mechanical basis provided by Eyring's rate theory. Heats and entropies of formation and activation of detion was isotropic on { 100) and { 111) planes. An atomic surface roughness mechanism described by Ahearn and Becker on the fects have been estimated for possible mechanisms and compared with observed values. A single diffusion measurement a t 400" C. basis of field emission microscope studies has been recalled. May 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
895
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT for zinc in zinc oxide has been reported and used in discussing possible oxidation mechanisms for zinc. An amendment ( S S E ) has been published which modifies some of the earlier proposals. -1 number of st,udies have been devoted specifically to the oxides and oxidation of copper. Tylecote (41E) has st'udied the oxidation process in the temperature range 200' t o 800" C. in oxygen, dry air, wet air, and nitrogen and the effects of specimen shape, preformed films, and recrystallizat'ion in cold worked copper. A continuously recording semimicrobalance was employed. A crack-heal type of sequence was observed for nonduct)ile films formed below 500" C. At higher temperatures an initially cubic rate law followed by an abrupt weight increase and transition to parabolic growth often was observed. Moore @$E) has sought density changes in a copper sphere oxidized a t 1000" C. and found none. Oxidation of the outside of a copper tube a t 1000" C. while pure argon flowed over the inside produced a small decrease in inside diameter. Moore concluded that the vacancy current in the oxide cannot continue through the metal and that the oxide must deform plastically to remain adherent. Few attempts have been made t o study oxidation at high pressures. However, McKewan and Fassell ( S I E ) have measured oxidation rates on copper in t'hc temperature range 600" t o 900" C. at oxygen pressures up t o 400 pounds per square inch. Parabolic growth rate curves were obt,ained with the rate practically independent of pressure since cupric oxide overlay cuprous oxide in all cases. The oxidation or iron has been attacked from several points of view in addition to the diffusion experiments mentioned above. Caule and Cohen ( S E ) , investigating the electropolishing mechanism, have found an oxide film about 100 A. thick formed during polishing or drying. Vernon, Calnan, Clews, and Nurse (44E) have confined their attention to the change in activation energy observed around 200' C. for the oxidation of iron. They compared the weight increase of the specimen lvith the iron content (as ferrous and ferric ions) in the stripped film, finding good agreement a t 225' C., but poor agreement at 180" C. Thelattertemperature gave logarithmic and inconsistent growth rates; the former gave consistent parabolic rates. Elect,ron diffraction showed that the films were a mixture of aiFezOBand a cubic oxide which a t short times seemed more like rFezOI and a t long times more like FesOa in composition. At 225' C. the cubic oxide approached FeiOd parameters much more rapidly than a t 180' C. Explanations of many of the effects have been proposed. Bardolle ( I E ) has developed a method for revealing the grain structure of gamma iron by the formation of a thin oxide film at low air pressure above the allotropic transformation temperature. Collongues, Sifferlen, and Chaudron ( 5 E )have oxidized very pure iron in mixtures of hydrogen and water vapor and have studied the microstructure of the scale produced. They observed a compact outer layer and a very thin fine-grained inner layer about a micron thick-although the presence of small amounts of alloying elements cause it to grow thicker. Lattice parameter measurements indicated that the major concentration change in the wustite layer occurred in the thin inner layer in these specimens. They also studied the isothermal eutectoid decomposition of wtistites of several compositions and the anisothermal formation of a martensitic constituent. Hauffe and Pfeiffer (19E) have studied the kinetics of wustite formation, 850" to 1000" C., in mixtures of carbon monoxide and carbon dioxide. At 1000' C. they found slow linear rates in this mixture compared with faster parabolic rates in air or oxygen at reasonable pressures. They proposed that the rate controlling step occurred a t the gas-oxide interface. At 850' C. where diffusion n-as much slower the linear rate law was no longer valid. Davies, Simnad, and Birchenall ( 8 E ) have revised the interpretation of their marker movement studies during the growth of magnetite on wustite. The1 have coneluded that these results favored an iron ion diffusion mechanism as the predominant
896
factor in magnetite grovith rather than oxide ion diffusion as prcviously suggested. Wrazej (48E) has published some micrographic observations on scale growth on iron, and Paidassi ( S 7 E ) has presented an extensive discussion to that paper in which he described the care necessary t o achieve optimum results. Paidassi also reviewed in this discussion the phenomenon of growth of hematite whiskers or needles on detached scales between 450" and 600' C. n-hich was the subject of another paper ( N E ) . Ehlers and Raether (11 E ) looked for pseudomorphic structures in very thin oxide films on zinc cleavage faces. Finding only the normal zinc oxide lattice they questioned the generality of the Frank-van der Merive theory of overgrowths. Williams and Wallace (47E) formed chloride films on silver with triphenyl met>hylchloride dissolved in t'oluene or acet,onitrile. iit 44.9" C. they observed a logarithmic rate that later became linear rather than parabolic as Cabrera and Mott's theory would predict. rl mechanism for this behavior has been proposed. Anodic oxidat,ion of aluminum has been studied by Charlesby (@), while similar studies have been made on tantalum by Vermilyea (4%'). Both concluded that the Cabrera and Mott equations would not explain their current (gro~vth)-voltagerelations Fithout considerable modification. Hoar and Tucker (2bE)have found t,hat,the sulfidation oC copper by sulfur in benzene or dilute aqueous solutions of ammonium polysulfide was controlled by diffusion in the liquid in the early st'ages, with solid st,ate diffusion assuming control after the sulfide layer had thickened. Photoacceleration v a s observed. The sulfidation of silver by hydrogen sulfide has been investigated from room temperature to 800" C. by Tereni ( @ E )who vaiicd the air and humidity content of the gas phase. Preferential mobility of ions at grain boundaries in cast silver bromide has been demonstrated by clect,rolyzing the solid crystal betxeen solutions of silver nitrate and pot,assium bromide. Goddard and Urbach ( I S E ) found that ridges appeared along t'he grain boundaries of the slab which was several millimeters thick. Electrochemical studies on silver sulfides by Wagner ( @ E ) has yielded thermodynamic potentials for CY and B A g S . The relation between the chemical diffusion coefficient and the mobility of silver ion in the sulfide, the diffusion potential when in contact with silver on one side, and sulfur on the other, deviations from stoichiometric composition, and the alpha-beta phase transformation have been considered. Alloy Oxidation. Application of the law of mass action to ionic crystals containing small concentrations of cationic impurities has been made by Wagner (46E)in terms of the theory of lattice defects. ilttention has been drawn to solubility problems rather than to the more frequently discussed electrical conduct'ivity aspects. Hauffe, Grunewald, and Tranckler-Greese (188) have employed electrical conductivity methods to investigate the behavior of chromium in the rutile (TiOs) lattice. They concluded that an equilibrium exists between Ghromium ions in the trivalent st,ate and chromium ions in the five- or six-valent stat(:. The former was favored at low temperature, the latter a t high temperature. By means of x-ray diffraction and microscopy Moreau (S5E) has examined the structure of the scales formed a t 1250" C. on a series of iron-chromium alloys containing, respectively, 2.6, 7.5, 18, 23, and 30% chromium. The external layer w m aFe203, under which a single phase layer of cubic spinel, nearly pure Fed34 at the outside but with increasing chromium content inside, was found. The innermost layer in contact with the alloy was a two-phase aggregate of granules of FeCr204 in wustite. An explanation was proposed in t,erms of the relative diffusion rates of the ions in the variom oxides. ilfter reducing the surface of an 18% chromium 8% nickel stainless steel Levina and Burshiern (86E)measured oxygen sorption isotherms from 20" to 500" C. which they compared with their earlier results on pure iron. Dankov ( 7 E )has discussed the oxidation of an 80% Ni-209/0 Cr
INDUSTRIAL A N D ENGINEERING CHEMISTRY
VoL 46. No. 5
FUNDAMENTALS REVIEW alloy from the standpoint of Smirnov’s theory. On the basis of the mass action law and the difference in diffusion coefficients of the cations he proposed that the process should occur in three successive steps: (1) NiO overlying a mixture of NiO . Crz03 plus N O ; (2) later r\’iO*CrnO~ plus CrzO3 forms; (3) then the outer layer becomes CrgO8 over the mixture of NiO.Cr?03 plus Crz03. For this alloy a t 1 mm. mercury oxygen pressure in the range 400’ to 900” C. Gulbransen and hlchlillan ( I 6 E )found that small alloying additions had a very strong effect on the rate of oxidation. I n some cases this was due t o an important modification of the oxides appearing &a products, but in the case of silicon, one of the most effective additions, it appeared t o be due largely to an improvement in the bond at the metal-oxide interface, thus reducing cracking and spalling. Spooner, Thomas, and Thomassen ( S 9 E ) have investigated the rapid deterioration of nickel-chromium and nickel-chromium-iron alloys in weakly oxidizing atmospheres and have concluded that the so-called green rot is the result of depletion of chromium due to internal oxidation in atmospheres too weakly oxidizing to attack nickel. Honjo (,BE) has utilized electron diffraction analyses of oxide films on a series of copper alloys-O.30jo beryllium, 0.5% aluminum, 0.1% magnesium, 7% manganese, and 7% nickel-and 13% aluminum in iron to determine the oxygen pressure and temperature combinations which permitted the selective formation of external oxides rich in the alloying element. Dennison and Preece (QE) have determined the microstructure and composition of scales on a series of copper alloys. They found that the oxidation rates were little affected by variations in the oxidizing atmosphere. The effects of 2 to 10% aluminum, 1 and 2% beryllium, 0.5 and 1.2%chromium, 0.9% magnesium, and 2 and3.6~osilicon have been described. Brasunas ( 2 E ) has ascertained that chromium rich alloys, incone1 and 80-20 nickel-chromium, developed subsurface porosity when leached in alkali fluorides, evacuated or oxidized at high temperatures. This is similar t o the observation that Rhines and Nelson made earlier on the oxidation of brass. Thus, while it appears difficult t o force vacancies from an oxide growing by diffusion of cation vacancies t o continue into the metal phase, porosity may be developed by selective removal of one of the components of a n alloy in a manner analogous t o the Kirkendall effect.
Literature Cited
Oxidation
(1E) (2E) (3E) (4E) (5E) (BE)
(7E) (8E) (9E) (10E)
Diffusion
(11E)
Ang, C. Y., Acta. Met., 1, 123 (1953). Bartlett, J. H., and Dienes, G. J., Phys. Rev., 89, 848 (1953). Bradshaw, F. J., Hoyle, G., and Speight, K., Nature, 171, 488 (1953). Buckle, H., Z . Metallkunde, 44, 393 (1953). Busby, P. E., Warga, M. E., and Wells, C., J . Metals, 5 , Trans., 197, 1463 (1953). Cohen, M., Wagner, C., and Reynolds, J. E., Ibid., 5, Trans., 197, 1534 (1953). Couling, L., and Smoluchowski, R., Phys. Rev., 91, 2458 (1953). Dienes, G. J., Ibid., 89, 185 (1953). Erdmann-Jesnitaer, F., Schumann, H., and Beckert, M., Arch. Eisenhiittenw., 24, 215 (1953). Fitser, E., 2. Metallkunde, 44,462 (1953). Fuller, C. S., and Ditaenberger, J. A,, Phys. Rev., 91, 193 (1953). Guain, P. L., Doklady Akad. Nauk S.S.S.R., 86,289 (1952). Hall, L. D., J . Chem. Phys., 21,87 (1953). Haynes, C. W., and Smoluchowski, R., Phys. Rev., 91, 2458 (1953). Heumann, T., Naturwissenshaften, 40, 164 (1953). Heumann, T., 2. physik. Chem., 201, 168 (1952). Heumann, T., and Kottmann, A., 2. Metallkunde, 44, 139 (1953). Hoffman, R. W., Anders, F. J., and Crittenden, E. C., Jr,, J. Appl. Phys., 24,231 (1953). May 1954
(19D) Huntington, H. B., Phys. Rev., 91, 1092 (1953). (20D) Huntington, H. B., Shirn, G. A,, and Wajda, E. S., Ibid., 91, 2468 (1953). (21D) Landergren, U. S., and Mehl, R. F., J . Metals, 5 , 153 (1953). (22D) Le Claire, A. D., Acta Met., 1,438 (1953). (23D) Le Claire, A. D., J . Iron SteelInst. (London), 174, 229 (1953). (24D) Le Claire, A. D., “Progress in Metal Physics,” Vol. 4, p. 265, New York, Interscience Publishing Co., 1953. (25D) Lynbov, B. Ya., and Fastov, N. S., Doklady Akad. Nauk S.S.S.R., 84,1939 (1952). (26D) MacDonald, D. K. C., J. Chem. Phys., 21,177 (1953). (27D) Mallett, M.W., Baroody, E. M., Nelson, H. R., and Papp, C. d.,J . Electrochem. Soc., 100, 103 (1953). (28D) Mallett, MI.W., Belle, J., and Cleland, B. B., Ihid., 101, 1 (1954). (23D) Norton, F. J., J . Appl. Phys., 24, 499 (L) (1953). (30D) Overhauser, A. W., Phys. Rev., 91,246A (1953). (31D) Prager, S., J . Chem. Phys., 21, 1344 (1953). (32D) Prager, S., and Eyring, H., Ihid., 21,1347 (1953). (33D) Schumann, H., and Erdmann-Jesnitzer, F., Arch. Eisenhattenw., 24, 353 (1953). (34D) Seith, W., Plansee Pioc., 1952,65 (1953). (35D) Seita, F., Acta Met., 1, 355 (1953). (36D) Severiens, J. C., and Fuller, C. S., Phys. Rev., 92, 1322 (1953). (37D) Shirn, G. A., Wajda, E. S.,and Huntington, H. B., Acta Met., 1, 513 (1953). (38D) Shockley, W., Phys. Rev., 91, 1563 (1953). (39D) Smith, R. P., Acta Met., 1, 578 (1953). (40D) Sonder, E., Slifkin, L., and Lazarus, D., Phgs. Rev, 91, 2459 (1953). (41D) Tomiauka, T,,Slifkin, L., and Laaarus, D., Ibid., 91, 245A (1953). (42D) R‘inegard, W. C., Acta Met., 1, 230 (1953).
(12E) (13E) (14E) (15E) (16E) (17E) (ME) (19E) (20E) (21E) (22E) (23E) (24E) (25E) (26E) (27E) (28E)
Bardolle, J., Compt. rend., 236, 1790 (May4, 1953). Brasunas, A, de S., Metal Progr., 62, No. 6,88 (1952). Caule, E. J., and Cohen, M., Can. J . Chem., 31, 237 (1953). Charlesby, A., Proc. Phys. Soc. (London), 66B,317 (1953). Collongues, R., Sifferlen, R., and Chaudron, G., Rev. mbt., 50, 727 (October 1953). Cubiciotti, D. D., Iron Age, 171, No. 21, 144 (1953). Dankov, P. D., Zhur. Fiz. Khim., 26,753 (1952). Davies, M. H., Simnad, M. T., and Birchenall, C. E., J. Metals, 5 , Trans., 197, 1250 (1953). Dennison, J. P., and Preece, A., J . Inst. Metals, 81, 229 (1953). Dravnieks, A., J . Electrochem. SOC.,100,95 (1953). Ehlers, H., and Raether, H., Naturwissenschaften, 39, 487 (1952). Evans, U. R., Research (London). 6 , 130 (1953). Goddard, P. E., and Urbach, F., J . Chem. Phys., 20, 1975 (1952). Gulbransen, E. A., Advances in Catalysis, 5,119 (1953). Gulbransen, E. A., and McMillan, W. R,, IND.ENG.CHEM, 45, 1734 (1953). Hauffe, K., Arch. Eisenhiittenw., 24, 161 (1953). Hauffe, K., “Progress in Metal Physics,” Vol. 4, p. 71, New York, Interscience Publishing Co., 1953. Hauffe, K., Grunewald, H., and Tranckler-Greese, R., 2. Elektrochem., 56, 937 (1952). Hauffe, K., and Pfeiffer, H., Z. Metallkunde, 44, 27 (1953). Hedvall, J. A., Brisi, C., and Lindner, R., Arliiv. Kemi, 4, 377 (1952). Himmel, L., Mehl, R. F., and Birchenall, C. E., J . Metals, 5 , Trans., 197, 827 (1953). Hoar, T. P., and Tucker, 9.J., J . Inst. Met., 81, 665 (1953). Honjo, G., J. Phys. Soc. Japan, 8 , 113 (1953). Kubaschewski, O., and Goldbeck, 0. von, Metalloberfltiche, 7A, 113 (1953). Kubaschewski, O., and Hopkins, B. E., “Oxidation of Metals and Alloys,” New York, Academic Press, 1953. Levina, S. D., and Burshtein, R. Kh., Zhur. Fie. Rhim., 26, 555 (1952). Lindner, R., Arkiv. Kemi., 4, 381 (1952). Ibid., p. 385.
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT (29E) Lindner, R., Austrumdal, S.,and Kkerstrom, A,, Acta Chem. Scend., 6 , 468 (1952). (30E) Lindner, R., Campbell, D., and fikerstrom, A , , Ibid., 6, 457 (1952). (31E) ICIcKewan, W.,and Fassell, W.11 , Jr., J . Metals, 5 , Trans., 197, 1127 (1953). (32E) Moore, W. J., J . Chem. Phys.. 21, 1117 (1953). (33E) Moore, W.J., J . Electrochem. Soc., 130, 2S4C (1953). (34E) Ibid., p. 302. (35E) Moreau, J., Compt. rend., 235, 85 (1953). (36E) Paidassi, J., BoZ. soc. C'hilena quinz., 4 , 61 (1952). (37E) Paidassi, J., J . Metals, 5 , 1570 (1953). (38E) Rhodin, T. X',, J r . , Adaancea in Ca'al:ysis, 5 , 43 (1953)
(39E) Spooner, N., Thomas, J. RI., and Thomassen, L., J . Metals, 5 , Trans., 197, 844 (1953). (40E) Terem, H. N., Rew..fac.sci. unia. Istanbul, 18A, 81 (1953). (41E) Tyleoote, R. F., J.Inst. M e t , , 81, 681 (1953). (42E) Verduch, A., and Lindner, R., Arkiu. Kemi, 5 , 313 (1953). (43E) Vermilyea, D. A., Acta Met., 1, 282 (1953). (44E) Vernon, W. H. J., Calnan, E. A., Clews, J. B., and X'ursc, T. J., Proc. R o y . SOC.(London),216A,375 (1953). (453) Wagner, C., J . Chem. Phys., 21, 1819 (1953). (46E) Wagner, C., J . Phys. Chem., 57, 738 (1953). (47E) Williams, R. C., and Wallace, P. R., J . Chem. Phys., 21, 1234 (1953). (49E) Wrazej, W. J., 9.X e t a l s , 5 , Trans,, 197, 265 (1953).
GEOFFREY B ROUG HTON University of Rochester, Rochester, N. Y.
The year has seen much activity i n this field, with increasing recognition of its practical importance. T h e introduction of modified cottons, new textile polymers, advances in dyeing and aerosol technology and still further innovations in the plastics field can all be ascribed to progress in, and a better understanding of, colloid chemistry.
I N last year's review, the topics of ion exchange (4)and adsorption ( 3 )will not he covered because they are included in the annual "Chemical Engineering Unit Operations Review." The latter topic was also reviewed a t considerable length in another periodical (1). Among general publications a general text on the preparation and properties of colloidal solutions and gels by Duclaux (2) and a review of colloid science and its industrial applications by Matalon (6) should receive mention.
Experimental Methods Some useful notes on the use of the microscope have appeared (6.4). The television scanning system has been applied t o the compound microscope in the so-called flying-spot microscope ( f d 7 A ) . This should permit automatic counting of particles such as powders, blood cells, and photographic grains. A new commercial infrared microscope attachment for a n infrared spectrometer, which should find wide application in crystal and fiber study, has been described ( I d O A ) as has a n easily used ultraviolet microscope objective ( l 7 6 A ) . Ultraviolet microspectrophotometry ( f O A )and phase microscopy ( @ A ) were discussed. Much useful information on natural and synthetic textile fibers ( 4 f A ,7'34, 83A j and on soaps (129-4 j can be obtained by optical microscopy. The field of electron microscopy has seen the publication of an authoritative book b y one of the leading workers in the field (65A). I t s increasing importance as an aid in the study of colloids, surfaces, and fibers is well illustrated in articles by Drummond (41Aj and Mering (f074), although Hauser (6811)has pointed out that conventional microscopic methods may offer advantages over the electron microscope for the study of certain organic materials such as rubber. As usual, a number of new techniques have been introduced in replica preparation (149A, f 8 f A ) ;
898
in the preparation of nietal ( % A ) , mineral (84A), crystal (S&l), and biologica'l specimens (14A); in the exposure of the internal fine structure of fibers ( 2 8 A ) ; the use of carbon coverings - .( 5 Q A ) :and electrostatic precipitation of bhe macromolecule under study on the standard grid while dispersed as an aerosol (36'8). Several of these are described in the report by Drummond ( 4 fA ) . Among recent electron microscope studies should be mentioned those on organic pigments (f6QA), aluminum black (156A!, iron oxide (18OA), port,land cement, (160A), collagen and leather (18A, 77A), Hevea latex (29A, 163.4), elastomer latices ( 1 6 6 8 ) ,deter-. gents in oil (119A), aluminum hydroxide (1409),vanadium pentoxide sols (led),paper sizing (85A),rubber fillers (16'7A), sodium deoxyribonucleate ( 7 9 A ) and fibrillar proteins (654). The electron microscope has been applied also to problems of geI' and gel structure (la), surface finish (109-4 j, particle growth, (164A j, and the hiding power of pigments (101A ) ; t,o precipitation processes (474, l@d, 168A); to fiber structure and breakdown both of woo1 (lO5A, 106A), cellulose (42A, 51~1,1364, 1544) and synthetics (824); and to the determination of the, part,icle size of diat'omit'e (l6$.4), carbon black (95A ), and ferromagnetic powders (50A). Donnet (%A, 5 9 4 ) has compared results oht'ained by means of the electron microscope with those. obtained hydrodynamically. Internal standards for the calibration of electron microscopes are discussed by Rouze and Watson (f3224). Particle Size Determination. An unusual book b y Herdan and Smith (71A) demonstrates the power of statistics when applied in the field of part,icle physics and collects in easily accessible form much of the important work on particle size determination. Rose (128A)also covers in a useful book the measurement of part,icle size. Sedimentation continues to be the most readily available. method for particle size determinabion and has again been reviewed by Mueller (111.4). Wilson ( f 79A), with suspensions of microspheres, has continued his work directed to the elucidation
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, NO. 5-
