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By R. S. Wagner, R. G. Treuting, W. C. Ellis

Use of the Weisseizbevg goniometer for the study of the morphology of whisker crystals and transfer of the results to a stereograplzic projection are described. While in almost all instances a complete and rapid solution is obtained with a purely gaphical treatment, an absolute analytical treatment applicable to difficult cases is given. Examples are given for determination of growth direction and external features of a crystal, for detection of 'twintzittg, and for establislting the orientation relntionships in a kinked whisker crystal. We give here a method for the use of the Weissen-berg goniometerl" in the study of orientation relationships in "whisker" (micro) crystals3-8 and direct transference of the data to the stereographic projection. The operations are straightforward and require no involved calculations: in almost all cases solely graphical treatment is adequate. In a few complex instances, a more exact analytic method may be required. In the method, not only are equatorial reflections of an oscillation photograph used, but also those on higher layer lines, or those not occurring on a recognized layer line. Such reflections off the zero level are often essentialy to detect the presence of twinning. The method is particularly suitable for examination of whisker crystals since the axial or growth direction is almost always one of high symmetry, permitting a more restricted oscillation range to obtain the necessary reflections and an accordingly shorter exposure time. The method is also applicable when there is no lattice-related external symmetry, and is as well able to identify external crystal surfaces, when such exist, with the aid of an optical beam. Thus growth direction, identification of lateral faces, twinning, and orientation relationships in a kinked crystal can be established. A test for the Eshelby twist6-8 can readily be made. The method can be used for orientation, for structure analysis, and as an aid in the identification of an unknown crystal. Moving-film techniques have previously been employed variously for crystal-orientation studies.1,2,9-13 In particular, use of the Weissenberg method for orientation determination has been reported by Wooster and wooster.14 While their method derives the same data as here described, it differs in depending on the tracing of constant p streaks, a less than dependable phenomenon with small specimens, a few microns or less in cross section. The Laue method can and has been used for orientation studies of microcrystals,15 e.g., 2 p in cross section, but requires the extreme intensity and concentration from a microfocus tube to obtain reasonable exposure time. PRINCIPLES OF THE PRESENT METHOD Consider a crystal of random orientation with respect to the oscillation axis in a Weissenberg goniometer. Its diffraction pattern need not necessarily result in recognizable layer lines. In Fig. 1, a stereo-graphic projection of the reference sphere is given with the equatorial plane XZ normal to the oscillation axis Y, and the X-ray beam directed from X towards 2. The great circle ZZ is then normal to the beam, and the axes are right-handed. Thus the reflected X-ray beam lies at the intersection R of small circle ARB of radius 28 from 2, and of small circle RE of radius a from the rotation axis Y. a is the conventional semiapex angle of a cone of diffracted rays from the atoms aligned in the direction

Jan 1, 1967

By S. Leber, R. F. Hehemann

Diffusion coefficients for the Cb-W system were measured using couples prepared from poly crystalline, commercially pure metals. The diffusion coefficients, measured in the temperature range between 1700° and 2300°C, decreased exponentially as the tungsten concentration was increased from 0 to 50 at. pct, then decreased abruptly at higher concentrations. A decrease of two orders of magnitude was observed over the entin? compositional range. The diffusion coefficients were in the range defined by the self-difiusion coefficients of the individual elements, indicating their general validity. An activation energy of 60,500 cal per mole was measured for the 20 pct W composition. Such low values, when compared with energies over 100,000 cal per mole for the pure constituent elements, indicated that transport mechanisnzs more rapid than volume diffusion were contributing substantially to inter dijfusion. Difference should, therefore, be expected between these data and the intrinsic diffusion coefficients. These differences should be significant in the kinetics of 'transport phenomena in practical systems. CONSIDERABLE attention has been devoted in recent years to the mechanical behavior and other properties of the refractory metals and their alloys. The Cb-W system has been of special interest as a base for the development of more complex compositions of commercial interest. In spite of the importance of mass transport to all aspects of elevated-temperature behavior, and especially to the production of alloys by powder-metallurgy techniques, little attention has been paid to diffusion in the Cb-W system. Results from a previous study of this system1 appeared to be anomalously high. The present investigation is, therefore, an attempt to obtain more accurate diffusion coefficients in this system. Intrinsic diffusion coefficients, of primary importance from the theoretical viewpoint, can only be obtained accurately from studies utilizing compositional gradients approaching zero. However, many practical problems involve diffusion under significant concentration gradients. The diffusion coefficients determined in this investigation were, therefore, obtained from couples prepared from elemental metals. The data obtained should be of value in the analysis of problems such as homogenization during powder-metallurgy alloying or reactions between base and clad in coated structures. In this vein, the investigation was conducted on poly crystalline materials of commercial purity. PROCEDURE Diffusion couples were prepared by sandwiching a columbium sheet between two sheets of tungsten. The composite was welded around all edges, the tungsten forming a protective can for the columbium. The composite was soaked for 4 min at 1600°C in a hydrogen-atmosphere furnace, quickly forged to 40 pct reduction in thickness, and then rapidly cooled to room tempera-

Jan 1, 1967

By G. Y. Chin, M. T. Dolan, W. L. Mammel

In the case of plastic deformation by slip, von Mises&apos; showed that an arbitrary shape change of a crystal generally requires the activation of five independent slip systems. The selection of the five active systems was worked out by Taylor ,&apos; who hypothesized that, among all combinations of equivalent slip systems which are capable of accommodating a given imposed strain, the active combination is that one for which the sum of the absolute values of the glide shears is a minimum. Taylor analyzed the case of {lll}( 110) slip for fcc metals and applied the analysis to crystals undergoing axisymmetric flow, which approximates the shape change of an embedded grain in a polycrystalline aggregate deformed in tension (or compression). For the twelve equivalent (111) (110) slip systems, there are 384 independent combinations of five slip systems that satisfy the imposed strain.&apos; Taylor laboriously calculated the value of M = ZjIyj /E for each combination (although some were missed) and obtained the minimum M, hence the active combination, for a number of axial orientations distributed throughout the stereographic triangle. (yj is shear from slip on the th system and e is the tensile strain). Detailed contours of constant minimum M were recently obtained by Hosford and Backofen using a simplified but equivalent Bishop and ill&apos; analysis. Due to the numerous combinations of slip systems involved in the calculations, however, the full potential of the powerful Taylor analysis has not been exploited. For this reason, we have recently utilized techniques of linear programming to obtain solutions of the Taylor analysis for axisymmetric flow, for slip on {110)(< 111), {112)(111), and {123)(111) systems as well as mixed slip composed of these three systems. These slip modes are of obvious importance in the deformation of bcc crystals. Some of the salient results are summarized below. 1) Stress-Strain Data for Polycrystal. The value of M averaged over all axial orientations is the ratio of the tensile flow strength of a randomly oriented aggregate to the critical resolved shear stress for slip. This value enters importantly in theoretical deductions of the polycrystalline stress-strain curve from single-crystal data.2&apos;3&apos;5 Table I lists the values of Ma,, for the several cases of slip, as obtained by the present computer work. 2) Texture Hardening. Since the value of M depends on the axial orientation, the (tensile) flow strength of a specimen may be increased through texture control.&apos; An example of the computer results is shown in Fig. 1, where contours of minimum M have been computer-plotted for the case of mixed slip on {110}(111), {112)(111),and {123}(11 1) systems. It may be seen that, under axisymmetric flow, wires of (111) and (110) axial orientations are 50 pct stronger than those oriented at (100) .

Jan 1, 1968

By K. G. Davis, P. Fryzuk

VALUES for the equilibrium distribution coefficient, ko, are required for solidification studies. The procedure generally adopted1-3 is to progressively solidify alloy rods over a range of growth rates, under conditions where a high degree of convective mixing is present in the melt. The measured effective distribution coefficients are plotted as a function of growth rate, and the extrapolated value at zero growth rate is taken to be the equilibrium ko. The method is limited by the experimental difficulty in obtaining steady growth rates less than approximately 10-4 cm per sec. Extrapolation from rates greater than this can lead to inaccuracy. In the present investigation, an alternative method for determining ko, previously used by the authors for the Ag-Sn system,&apos; was applied to alloy of thallium in tin. Specimens were grown under conditions where convective mixing was absent, and experimental concentration-distance curves in the region of the initial transient were compared with curves calculated for trial values of ko. The ko which gave the best fit was taken as the correct value. To obtain the calculated curves, a value for the diffusion constant in the liquid near to the melting point was needed. This was determined by the capillary-reservoir method. Diffusion Constants. Details of the experimental procedure used by the authors in the capillary-reservoir technique have been described in previous papers,5&apos;6 the only variation being in the use of Tl204, a ß emitter, as tracer, in contrast to previous work where ? emitters were used. The activity of a ß-emitting sample, as measured in a Geiger counter, is proportional to the surface area. To measure the concentration of thallium along the capillary after diffusion had taken place, the solidified capillary (1 mm diam) was cut into 2.5-mm lengths and each length compressed between parallel steel plates to form a disc approximately 5 mm in diam. The discs were placed in a flat-bottomed dish, covered by a thin lead shield with a central aperture, and counted in a 0 counter with fixed geometry. Each disc was etched lightly in a dilute solution of nitric and hydrochloric acids a short time before counting, to eliminate sur-

Jan 1, 1968

By D. G. Westlake

Levine has concluded that prismatic slip in titanium is controlled by two distinct thermally activated processes in the temperature ranges O° to 220°K and 220" to 300°K. We feel that his evidence is not convincing. He has drawn a curve through the plot of activation volume u* vs temperature T with a break at 22WK, Fig. 2. We believe that considering the possible experimental error apd the fact that there are only four points between 4° and 196°K, one could be justified to represent these points by the smooth curve we show as a solid line in Fig. 12. Levine believes that (8rf/aT)+ is discontinuous at 220°K, but he hints that he recognizes the possible doubt. We doubt seriously that the results shown in Fig. 1 indicate a discontinuity at 220°K. Certainly if he were justified in drawing a straight line through only four points on Fig. 2, we are even more justified in drawing straight lines through the seven points between 77" and 297°K on Figs. 1 and 3, because a straight line touches all seven of his circles. If his measurements of t were so precise that his decision to draw two curves in Fig. 3 is valid, then the experimental technique is deserving of further mention. We have drawn a smooth curve through the results in Fig. 3 and used this and the curve in Fig. 12 to obtain the values of shown in Fig. 13. Finding continuous is a contradiction of Fig. 4, which deserves comment itself. Levine obtained the solid circles in Fig. 4 using Fig. 2 and a smooth curve through the points shown in Fig. 3. We have replotted these solid circles in Fig. 14. We submit that there is no basis for his two straight lines (dashed in Fig. 14), and therefore have superimposed the curve that we believe is indicated. Certainly, there is reasonable doubt that a discontinuity in dH/dT exists at 220°K, even when one accepts Fig, 2. Furthermore, if one draws the straight lines indicated by least-squares treatments of the results presented as open circles in Fig. 4, their intersection is at about 196°K, not at 220°K as shown. Thus the alleged agreement between Figs. 3 and 4 with respect to "break" temperatures is not apparent. In Fig. 9, Levine has drawn a straight line very much different from the one indicated by a least-squares treatment. Obviously, he has done this because he recognized that H = 0 when T = 0. He is consistent in drawing the low-temperature curves in

Jan 1, 1968

By Norikazu Hashimoto

SILICIDE coatings on refractory metals are often applied by transporting a silicon halide vapor to a hot metal surface . The coatings are usually grown by solid-state diffusion reaction. The diffusion is often slower than the vapor transport and hence may become rate-controlling.

Jan 1, 1968

By D. G. Westlake

THE structure observed in thin foils by transmission electron microscopy is not necessarily representative of the initial bulk material. We have shown that hydrogen, originally present in a specimen of vanadium, niobium, or tantalum, can be concentrated by the thinning operation used to prepare foils from the bulk materials.&apos; These foils exhibited domain walls indicative of a tetragonal distortion of the bcc unit cells, probably caused by ordering of the hydrogen in preferred interstitial sites. We believe this ordering does not occur at room temperature in the bulk material which contains less than 1 at. pct H. In a continued effort to prepare metal foils whose hydrogen concentrations remain constant during preparation, we have developed some new chemical and electrothinning techniques for vanadium. Each of the procedures presented in Table I produced foils that were thin enough for transmission electron microscopy. The experiments described below were performed to test the effect of each thinning procedure on hydro-

Jan 1, 1968

By B. B. Rath, Hsun Hu, R. S. Cline

FOLLOWING the techniques used by Beck and co-worker~ "~ the characteristics of selective growth in the recrystallization of a zone-refined aluminum single crystal, rolled 80 pct at -78°C in the (110)[112] orientation, have been studied. The material was 99.999+ pct pure. The as-grown crystal had a resistance ratio, R(298°K) /R(4,2°K), of approximately 5000. The method of preparation of the single crystals and the necessary precautions in handling them during rolling in order to avoid recrystallization in locally distorted regions were described in an earlier paper.3 The rolling texture of this zone-refined aluminum crystal is practically identical with that of less pure aluminum crystals rolle! in the same orientation, i.e., a very sharp (110)[112]. Random nuclei were provided by artificial nuclea-tion by abrading one face of the rolled crystal on 600-grit emery paper in a random fashion. The thin layer of disturbed metal recrystallized at room temperature into fine grains almost immediately. An X-ray diffraction pattern was taken from the abraded surface of the crystal, and the relative intensities of the various reflection peaks were compared with those obtained from a powder specimen. As shown in Fig. 1, the relative intensities of the various peaks from the recrystallized layer varied somewhat from experiment to experiment, depending presumably on the abrading technique. However, the texture of the recrystallized layer produced by this method is nearly as random as that of a powder specimen. Fig. 2 shows the texture determined from the "growth side" (face opposite the abraded surface) of the crystal after it was kept at room temperature for 100 hr. The specimen was only partially recrystallized, as shown by the remaining deformation texture. The new orientations are derived from the recrystallized grains grown through the thickness of the crystal from the "nucleation side" (the abraded surface). Fig. 3 shows the texture after complete recrystallization produced by annealing at 60°C for 1 hr. The arrows indicate 40-deg rotation around the (111) axes of the deformation texture. The microstructure of a completely recrystallized specimen is shown in Fig. 4. As shown in Figs. 2 and 3, the texture of the re-crystallized grains grown from the nucleation side to the growth side is essentially the same as that observed in less pure aluminum&apos; (99.994 pct) and dilute alloyz crystals rolled in the same orientation. How-

Jan 1, 1968

By D. G. Westlake, U. F. Kocks

WHILE single crystals of most materials with cph lattice structure show essentially unlimited ductility, polycrystalline specimens of the same materials exhibit the entire range of ductilities. A difference between the ductility of single crystals and polycrystals may be associated with the special stress concentrations to be expected, for example, at the intersections of slip bands or twin lamellae with grain boundaries. Whether such stress concentrations prove catastrophic depends on the cleavage strength of the material, the size of the stress concentrations, and the speed with which they are formed. Thus, the ductility may vary in degree from material to material. Another possible reason for differences in ductility between single crystals and polycrystals is that a sufficient number of independent deformation modes must be available to insure compatibility between the macroscopic strains in neighboring grains.&apos;&apos;2 This criterion is often taken to be a necessary condition for any polycrystal ductility whatsoever, not as one that determines different degrees of ductility; thus, a material with an insufficient number of independent deformation modes would have to be brittle as a polycrystal. The "sufficient number" is five if every grain is to accommodate arbitrary shape changes ("von Mises criterion "). We should like to argue that fewer than five independent modes may be sufficient to satisfy compatibility conditions; and that the internal stresses set up when the plastic strains are not compatible reach the theoretical fracture stress only after a significant amount of macroscopic strain has taken place which may vary in magnitude from case to case, allowing an influence on the degree of ductility. Experimental evidence for these statements is taken from the following review of the number of independent deformation modes observed in the various cph

Jan 1, 1968

By Yoichi Ishida, Ching-Yao Cheng, John E. Dorn

Tile creep behavior of a iron was investigated over the range of temperatures from 375° to 1150°K. Apparent activation energies for creep, obtained by the effect of sudden changes in temperature on the creep rate, revealed the presence of- four distinguishable regions. The creep behavior of a iron in Regions II (480° to 774°K) and 111 (775° to 1045°K) was found to correlate well with a model where the creep rate is controlled by the nonconsevualive motion. of jogged screw dislocations. An anomalous increase in the apparent activation energy fur creep in Region III was found to be in harmony with the known decrease in the free activation energy for self-diffusion over the Curie transformation range. Furthermore, the creep rates in Regions II and III were found to increase with stress due not only to the effect of stress on the activation energy but also to an increase in density of mobile dislocations. The evidence suggests that pipe diffusion along moving dislocations could be a significant factor over the lower temperatures of Region II. ALTHOUGH the creep properties of iron and steel have been of interest to metallurgists for some time and an extensive literature is now available, most of the published information has not produced much toward understanding the fundamental dislocation processes controlling the creep behavior of these materials. Whereas the activation energy for high-temperature creep of metals usually agrees well with that for self-diffusion, Sherby, Orr, and Dorn1 deduced from the data of Tapsell -and c1enshaw2 that the activation energy for creep of Armco iron is about 78,000 cal per mole and more recently Lytton and sherby3 reviewed the data of Jenkins and Mellor4 and found an activation energy for creep of a iron of 80,000 cal per mole. Both values are substantially greater than the activation energy for self-diffusion in a iron. Because of the limited data suitable for purposes of identifying the controlling dislocation mechanisms of creep and the unusually high activation energies for creep quoted above, it was considered desirable to reinvestigate in detail the creep of a iron by more reliable techniques which would provide sufficient data for determination of the creep mechanisms. EXPERIMENTAL TECHNIQUE Creep specimens were prepared from 3/8 by 4 in. iron bar stock of the following composition by weight percent: 0.001 C, 0.0120 0, 0.001 N, 0.004 S, and 0.003 P. The as-received bars were cold-rolled to a thickness of 0.100 in., annealed under argon for 30 min at 1113°K, cold-rolled to a final thickness of 0.063 in., and machined into tensile specimens having gage section 0.250 in. wide and 1.70 in. long. Finally they were recrystallized under argon at 1113°K. Specimens to be crept above 1060°K were recrystallized at 1173°K. Both recrystallization treatments gave the same reproducible equiaxed ASTM No. 4 grain size. Creep testing was conducted in machines fitted with Andrade-Chalmers arms that maintained a constant stress to within ±0.2 pct of the reported values. Deformation over the specimen gage section was sensed with a linear differential transformer and recorded auto-graphically as a function of time. The strains deduced from these measurements were sensitive to ±5 x 10-5. During creep the specimens were contained in an argon-filled chamber which was immersed in a temperature-controlled molten tin bath. Creep temperatures, as measured by thermocouples attached to the specimen, were maintained to within ±10.25°K of the reported values. For activation-energy determinations rapid changes in temperature of about 12°K were obtained within 30 sec by direct resistance heating of the creep specimen, and maintained to ±1°K of the reported values. Observations of structural details of specimens before and after creep tests were made by electrolytic polishing and etching in acqueous ammonium persulfate. EXPERIMENTAL RESULTS A typical example of the determination of apparent activation energies, Q, by the effect of small changes in temperature is illustrated in Fig. 1. Q is defined by

Jan 1, 1967

By Thomas C. Wilder

The concentration and activity of oxygen in liquid copper has been measured by the reversible galvanic cell: at 1100°and 1200°C for the concentration range of oxygen of 3 to 5600 ppm Measurements for approximately thirly alloys at each temperature indicate that the activity of oxygen roughly follows Henry&apos;s law, the activity coefficients of oxygen being 0.12 and 0.205 at 1100° and 1200°C, respectively. These results compare javorably with the results of seven other electrochemical and gaseous equilibrium studies on this system, the free energy of the solution reaction 1/2 O2 = O (7 at. pct in Cu, liq) being -18.10 * 0.30 kcal per gfw at 1200°C. Estimates of the standard molar free energy of formation of CupO(S) are also made. Praclicul consideration of this cell as an oxygen sensor for liquid metals is discussed briefly. SOLID mixed-oxide electrolytes which have a defect structure in the anion sublattice have recently become a very popular means by which the chemical potential of oxygen is measured at high temperatures. Since the pioneering work of Kiukkola and Wagner1 such electrolytes have been used in numerous cell studies for determining the thermodynamic properties of metallic oxides and oxy compounds, the partial pressure of oxygen in vacuum systems and other atmospheres, and the properties of oxygen dissolved in metals and alloys. The use of a solid electrolyte in a cell for a fast reliable method of oxygen determination in liquid metals would be a very important tool to the process metallurgist. In copper, for example, the oxygen content of the molten metal in the cathode furnace is a prime factor in determining the "set" or solidification profile of cast wire bars. In this investigation the activity of oxygen in liquid copper was measured by an electrochemical cell employing the electrolyte ZrO2 + 7 1/2 wt pct CaO. The cell used at 1100° and 1200°C was

Jan 1, 1967

By N. L. Svensson

The model developed by Tuylor for the calculation of Polycrystalline yield strength has been applied to the case of an aggregate hawing a preferred orientation. In general this procedure requires the specification of texture by means of weighting factors applied to specific orientations. The problem to which the model has been applied is that of the yield-strength aniso-tropy of cold-rolled aluminum whose rolling texture was described as a combination of (110)[112] and (311) [112] In this case yield-strength anisotropy is defined by the rutio of yield strength measured at an angle 8 to the rolling direction to that measured along the rolling direction. The method of calculation of yield-strength ratio as a function of ? is described and the results show good agreement with experimental values. The orthotropic yield criterion suggested by Hill has been applied to the results and the strain ratio R also calculated as a function of ?. This has been compared with calculations using the method suggested by Elias, Heyer, and Smith which does not exhibit suck good agreement with observation. one deficietlcy of the method presented is that the strain ratios used by are those applying to iso-Irobic materials. The method should therefore be reg-clrded only as a first abbroximation to the prediction of anisotropy. THE problem of calculating the stress-strain characteristics of polycrystalline aggregates from the properties of single crystals has attracted attention for a number of years. The most important contributions to this study have been those due to: Sachs,&apos; Cox and sopwith,2 Taylor,3 Kochendorfer,4 Batdorf and Budiansky,5 Calnan and Clews,6 Bishop and Hill,7,8 Kocks,9 Budiansky, Hashin, and sanders, 10 Kroner,11 Cyzak, Bow, and payne, 12 Budiansky and Wu,13 and Lin.14 While the earlier work has been largely superseded, recent developments tend to support Taylor&apos;s solution" within the restriction imposed by his assumptions. The essential features of Taylor&apos;s approach were: 1) the material is rigid-plastic; 2) each grain experiences the same strain components as the aggregate as a whole (the problem was that of uniaxial deformation with principal strain components in the ratio 3) all regions of each grain deform uniformly; 4) work hardening occurs equally on all slip systems. While Bishop and Hill7 have generally validated this approach, there has been some criticism offered. Kocks? as pointed out that since multiple slip must occur the single-crystal data must be determined from orientations arranged such that polyslip takes place. Boas and Hargreaves,15 and others, have shown experimentally that the strain distribution within grains is not uniform, the strains in the vicinity of grain boundaries being less than those in the center of the grains. Both of these criticisms can be largely offset by the suitable choice of single-crystal critical shear stress. However, for the problem analyzed below, the critical shear stress is not directly used and, consequently, these criticisms lose their importance. The more recent contributions have attempted to obtain a more complete analysis by considering an elas-toplastic material and considering interactions between grains of differing orientations. Lin14 has considered the early stages of yielding for a polycrystalline aggregate having specific regions of defined slip plane orientations. On the other hand, Budiansky and Wu13 have allowed for these interactions for randomly disposed grain orientations and have calculated the polycrystalline stress-strain curves for crystals exhibiting either elastic-ideally plastic or kinematic hardening characteristics. This work has shown that yielding commences when the macroscopic stress is 2.2 times the critical shear stress for slip in a single crystal (7,). The yield stress-strain curve then rises becoming asymptotic to a value of 3.072 7,. This is close to the value obtained by Bishop and Hill (3.06) in their confirmation of Taylor&apos;s method. This, of course, is to be expected since, at large strain values, the elastic strains are negligible and the rigid-plastic model is satisfactory. The results of Budiansky and Wu indicate that the result obtained by Taylor is 7.7 pct high at a plastic strain which is two times the elastic strain at the initiation of yield. By defining the anisotropy in terms of relative values, the ratio of yield strength at orientation ?, to that measured in the rolling direction, the effect of the discrepancy in Taylor&apos;s solution is considered to be of lesser consequence. Therefore, it is anticipated that an analysis based on Taylor&apos;s solution, which can be quite straightforward, should provide a reasonable estimation of the anisotropy of materials having a preferred orientation texture. OUTLINE OF TAYLOR&apos;S METHOD In fee metals there are four possible slip planes (the octahedral planes) and in each there are three possible slip directions (the edges of the octahedron), that is a total of twelve possible slip systems. von Mises16 has shown that at least five independent slip systems must become operative in each grain of the polycrystalline aggregate in order to preserve continuity of strain. With this geometrical requirement as basis and the assumptions previously listed, Taylor determined the operative slip systems for a number of orientations of the tensile stress axis specified in the unit stereographic triangle. For the ith slip system, the critical shear stress

Jan 1, 1967

By S. H. Gelles

Samples of poly crystalline zinc of 99.999+ pct purity were observed metallographically after having been exposed to hydrostatic pressures of up to 27 kbars. The deforrnation produced by this treatment was analyzed using X-ray and metallogaphic techniques. Basal-plane slip occurred universally in all grains exumined at the lowest pressure used (8 kbars). At pressures of >23 kbars, {1012} twin nucleation and growth were noted as well as slip. Formation of bend planes, complex kink bands, and recrystallization at the gain boundaries were also observed in this pressure range. These observations are discussed in reference to the expected deformation behavior of zinc under high hydrostatic pressure. It has been shown over the past few years1&apos;3 that anisotropic, poly crystalline metals can be made to deform plastically by the application of a hydrostatic pressure. The effect is greater 1) the larger the anisotropy of linear compressibility and 2) the smaller the stress level needed to produce plastic deformation. Zinc having both very anisotropic linear compressibilities and a very low critical resolved shear stress (CRSS) for basal-plane slip has been shown to exhibit large amounts of plastic deformation when subjected to a hydrostatic pressure.2,3 At pressures up to 15 kbars, grain boundary migration and slip on one set of glide planes have been reported.&apos; After exposing samples to 20 kbars pressure, grain boundary migration, single slip, multiple slip, and twinning have been noted.&apos; The identification of the deformation modes operative under these conditions has not been reported. It was the purpose of this research to identify the deformation modes induced in poly crystal line zinc by the action of a hydrostatic stress and to study the strain accommodation at grain boundaries. Hydrostatic pressure could affect the operational modes of deformation by altering the Peierls-Nabarro stress. This may be roughly approximated by the relationship4

Jan 1, 1967

By P. Marier, T. R. Ingraham

When cylindrical powder compacts of nickelous oxide (NiO) are heated in an equilibrated stream of SO3, SO,, and 02, in the temperature range 500°to 800°c, tlickelous suljate (NiSO4) is formed as an adherent layer on the oxide. The reaction is diffusion-controlled, with an activation energy of 13 ± 3 kcal per mole. When cylindrical powder compacts of NiSO4 are heated in a stream of dry nitrogen in the temperature range 1000 0to 11500C, NiO is formed at a well-defined interface between the sulfate and oxide. The interjhce migrates into the sulfate at a constant rate at a constant temperature and gas flow. The reaction rate increases with increasing gas flow and decreases with increasing partial pressure of SO3 in the gas stream. Resolution of the partial-pressure data with a Lang-itzliir Adsorption Isothern suggests that about 80 pct of the NiO interface is covered with SO3. The heat of adsovption is about 68 kcal per mole. The activation energy of the decomposition process is 61 ± 3 kcal per mole. MOST of the work reported on the formation and decomposition of nickel sulfate is related to thermodynamics.1-3 No quantitative work has been reported on the decomposition process. The only kinetic work reported on the formation is that by Fletcher and shelef.4-6 whose main purpose was to study the effects of alkali metal sulfate additions on increasing the rate of nickel sulfate formation. They found that, in the absence of an additive, only small amounts of sulfate were formed and the kinetic data were difficult to interpret. However, they suggested that the sulfa-tion of nickel oxide is a diffusion-controlled process for which the activation energy is approximately 17 kcal per mole.6 In this paper, both the formation and decomposition reactions will be examined; and based on the effects of temperature, flow rate, interfacial area, and partial-pressure of sulfur trioxide, mechanisms and activation energies will be suggested for both processes. EXPERIMENTAL Material. The nickel source material used in all experiments was Baker and Adamson Reagent Grade NiSO4. 6H2O, for which the following analysis was supplied by the manufacturer: C1, 0.001 pct; NO3, 0.005 pct; Co, 0.02 pct; Cu, 0.005 pct; Pb, 0.002 pct; Fe, 0.001 pct: insol, 0.005 pct. The anhydrous sulfate was prepared by heating the hydrate at 420°C in a muffle furnace for 5 hr. Nickel oxide was prepared by decomposing the sulfate at 950°C over a period of 10 hr. Method. The technique used for measuring the rates of formation and decomposition was developed earlier in these laboratories.7-8 The method is based on the observation that the kinetic parameters of a reaction can be established in a flow system, with specimens prepared by compacting powder to a uniform pellet shape. The results are identical with those established with solid polycrystalline specimens or single

Jan 1, 1967

By J. M. Tobin, L. H. Cadoff, L. M. Adelsberg

The reaction between liquid zirconium and graphite at temperatures above 2000 °C has been investigated. The reaction products were found to be carbon-saturated zirconium metal and ZrC which formed between the graphite and the metal. Parabolic growth behavior was observed for the ZrC Phase at all temperatures of this investigation. The parabolic growth constant at temperatures between 2000° and 2860°C was measured to be 1.83 exp 84,300/RT) sq cm per sec. The reaclion mechanism was proposed to be the rapid carbon saturation of the liquid metal and the formation of ZrC at the metal-carbide interface with diffusion of carbon through the ZrC, the "rate - determining step" of the reaction. The concentration-independent diffusion coefficient of carbon in ZrC, (DZrC), was expressed as 0.95 exp? 78,700/RT) sq cm per sec. This value mas calculated using the temperature-invariant ZrC phase fields proposed in the literature. The [ZrQiq)] — [ZYQiq) + ZrC] phase boundary over the temperature range 2000° to 2800°C was determined and the ZrC + C eutectic temperature was found to be 2890° ± 50°C. ThE Group IV and VB transition-metal refractory carbides are of interest because of their high melting points, high temperature strength properties, and relative inertness in certain corrosive environments. The present-day understanding of these materials, however, is limited by the general unavailability of accurate and reliable physical and chemical property data. This is due primarily to the difficulties associated with the preparation of suitable, high-density, high-purity carbide samples, and the achievement and control of uniform high-temperature environments. Accurate measurement of temperature is also an important factor limiting the reliability of reported data. The Zr-C reaction was selected for investigation because of the high melting point (>34000C) and favorable nuclear properties of the reaction product, ZrC. The direct reaction method afforded an opportunity to obtain kinetic data on the fully dense carbide. In this paper, layer-growth techniques were used to estimate the diffusivity of carbon in ZrC and to investigate the phase equilibria in the Zr-C system at temperatures above 2000°C. EXPERIMENTAL PROCEDURES AND DATA Crystal bar zirconium (99.9 pct Zr), purchased from the Nuclear Materials and Engineering Corp., and ZTA graphite (99.9+ pct) were used in this study. The analyses of the materials are listed in Table I. A schematic of the high-temperature carburization apparatus is shown in Fig. 1. The sample was a zirconium metal charge in a 1/2 -in.-ID graphite crucible which was capped with a tightly fitting graphite stern. The crucible and stem were designed to closely approximate black-body conditions. The graphite crucible was packed in lampblack (outgassed 1 hr at 2100°C) which provided insulation and thermal stability to the system. The inert atmosphere was maintained by a constant flow of high-purity argon or helium gas. The nozzle-diffuser section on the top flange was sufficient to prevent back-diffusion of air into the system. Chemical analysis of the carburized samples revealed oxygen and nitrogen concentrations of less than 44 and 20 ppm, respectively. The sample was heated by induction with a Westing-house 5 kw-450 kc power source. Temperature was measured with a Milletron two-color pyrometer which was sighted into the crucible by reflection from an overhead front surface mirror. Optical losses due to glass absorption and light reflection at air-glass interfaces were minimized by the employment of the dynamic-gas seal. It was found that no correction was required for the front surface reflector. The pyrometer was calibrated periodically against a U.S. Bureau of Standards tungsten ribbon secondary standard. Temperatures inside the crucible were also calibrated against the Zr-ZrC eutectic (1850°C)1 and the Nb-Nb2C eutectic (2335°C)2,3 temperatures and agreed to within ±10°C of these values. The temperature was controlled by manually adjusting the power input; variations of

Jan 1, 1967

By Charles L. Mantell, James E. Hoffmann

Mechanical inclusion, electrophoretic deposition, and adsorption were studied as mechanisms for code-position of aluminas present in copper-plating electrolytes as an insoluble disperse phase. Mechanical inclusion was not a significant factor. That codeposi-tzon of aluminas by an electrophoretic mechanism was unlikely was substantiated by measurements of the potential of the aluminas. The alumina content of the deposits was studied as a function of the pH of the bath. These tests in conjunction with sedimentation studies demonstrated the absence of an isoelectric point for the alutninas over the pH range examined. Thiourea in the electrolyte (a substance known to be adsorbed on a copper cathode during electrodeposition) affected the amount of alumina in the electrodeposit. However, no adsorption of thiourea on aluminas in aqueous dispersions was detected. If it were possible to produce a dispersion-hardened alloy of copper and alumina by electrodeposition, an alloy possessing both strength and high conductivity at elevated temperatures might be anticipated. Investigation of the mechanism of codeposition of aluminas with copper was undertaken with the hope that knowledge of the mechanism would aid in the development of such an alloy. The word "codeposit" here does not necessarily imply an electrolytic phenomenon but rather that the materials codepositing, the various aluminas, are transported to and embedded in the electrodeposited copper by some means. Mechanical inclusion in electrodeposition implies a mechanism of codeposition which is wholly mechanical in nature; the only forces acting on a particle are gravity and contact forces. Such a particle is presumed to be electrically inert and incapable of any electrical interaction with electrodes in an electrolytic plating bath. Processes for matrices containing a codeposited phase by electrodeposition from a bath containing a disperse insoluble phase frequently state that code-position is caused by mechanical inclusion.10,2,12 If settling, i.e., gravity, be the controlling mechanism for codeposition of aluminas, then assumptions may be made that 1) the content of alumina in the electrodeposit should be enhanced by increasing the particle size, 2) the geometry of the system, that is, the disposition of the cathode surfaces relative to the di- rection of the falling particles, should affect the alumina content of the electrodeposit, 3) in geometrically identical systems the chemical composition of the electrolyte employed should exercise no effect on the alumina content of the deposit, that is, the alumina content should be the same in all cathode deposits irrespective of bath composition. A bent cathode19 evaluates the clarity of filter effluent in electroplating baths by comparing the roughness of the deposit on the vertical surface with that on the horizontal surface. Two difficulties are inherent in this technique: 1) the current density on the horizontal portion of the cathode would be substantially greater than that on the vertical surface; 2) should the deposit obtained be rough, projections on the vertical face could act as horizontal planes and vitiate the relationship between the vertical and horizontal surfaces. Bath composition should have no substantial effect on the alumina content of the deposit. Two different electrolytic baths were employed. They possessed variant specific conductances and substantially different pH ranges. The experimental tanks were rectangular Pyrex battery jars 6 in. wide by 3 1/4 in. long by 9 3/4 in. deep. The cathodes were stainless steel 316 sheet of 0.030 in. thickness, cut to 7.5 by 1.75 in. and bent at right angles to form an L-shaped cathode whose horizontal surfaces measured 1.75 by 3.0 in. All edges and vertical surfaces were masked with Scotch Elec-troplaters Tape No. 470. The anodes were electrolytic cathode copper 9 in. high by 2.25 in. wide by 0.5 in. thick. To eliminate inordinately high current densities on the projecting edge of the cathode, the anode was masked 1 in. above and below the projected line of intersection of the cathode with the anode. The exposed area of the anode was equal to that of the cathode, providing both with equal average current densities. The agitator in the cell was of Pyrex glass and positioned so its center line was equidistant from cathode and anode, and a plane passed horizontally through the center of the blade would be located equidistant from the bottom of the cathode and the bottom of the deposition tank. The assembled apparatus is depicted in Fig. 1. Hatched areas on anode and cathode represent the area of the electrodes wrapped with electroplaters tape. MATERIALS The chemicals were copper sulfate—CuSO4 • 5H2O— technical powder (Fisher Scientific Co.). Spectro-graphic analysis showed substantial freedom from antimony, arsenic, and iron. Traces of nickel were present.

Jan 1, 1967

By B. W. Roberts, V. A. Phillips

A copper alloy containing- 25.5 at, pct Zn and 19.0 at. pct Ni, which was previously found to show an anoma1old.s hardening effect on quenching- from 600 "C and aging- at 400oc, has now been examined by neutron diffraction. No evidence of long-range order was found. The aged sample showed diffuse scattering- consistent with clustering. The anomalous hardening effect is now attributed to lattice strains caused by clustering rather than (long-range) order hardening. SOLID-solution Cu-Ni-Zn alloys (the commercial &apos;nickel silvers") have been reported to show anomalies in: change of resistivity on cold working,1-6 temperature coefficient of resistance,2-12 resistivity at low temperatures,13,14 parameter (vs temperature),2"4 calorimetric data,2,4 specific heat,15,16 dilation,2-4 and elastic modulus.17 The structure responsible for the anomalies is produced by annealing typically near 400°C and is rather loosely referred to as the (&apos;K-Zustands" (K state), a term coined by Thomas1&apos; who apparently meant simply that the arrangement of atoms on the sites deviated from that expected statistically. Thomas proposed that the K state occurred in a variety of (solid-solution) alloys such as Cu-Ni-Zn, Ni-Cr, Ni-A1, Ni-Cu, Fe-A1, and Fe-Si and is recognized because its formation is strongly temperature-dependent and results in an increase in electrical resistance which can then be decreased by cold working. Later workers on (&apos;nickel silver" have interpreted the K state variously as short-range order, long-range order. or a combination. The present work was prompted by the discovery by Phillips and Jones19 of a substantial hardening effect when an 18 pct "nickel silver" alloy which is fairly close to the Cu2NiZn composition, was reheated in the range 150" to 450 C after previously quenching from 600°C or, alternatively. was slow-cooled from 600°C or above. The phenomenon was attributed to (long-range) order hardening. Due to the similarity in the atomic scattering factors of copper. nickel, and zinc atoms, the &apos;&apos;nickel silvers" are unfavorable for X-ray diffraction studies aimed at detecting ordering. Nevertheless Bialas et a1.,20 using a powder sample containing 47.96 wt pct Cu, 24.03 wt pct Ni, and 27.98 wt pct Zn, slow-cooled from 400" to 200°C taking 500 hr, observed weak super lattice lines. Further unpublished work" using an anomalous dispersion X-ray technique indicates that zinc atoms are regularly ordered at the corner points of the lattice cell, while the nickel and copper atoms are statistically distributed on the remaining sites. Köster 17 also observed X-ray superlattice lines, for example, in an alloy containing 43.5 wt pct Cu, 28.6 wt pct Ni, and 27.9 wt pct Zn superimposed on the basic fcc cell with a = 3.62 kX. He proposed a Cu3Au-type superlattice with the Ll2 structure in which the A sites were statistically occupied by copper and nickel atoms and the B sites by zinc. He adds that substitution must be possible so that zinc atoms partly occupy A sites. Below about 35 pct Cu, Koster had some evidence for a CuAu-type superlattice with the Llo tetragonal fcc structure with a = 3.82 kX, c/a = 0.88 which could be preserved by quenching. This is suggested17722 to correspond to CuNiZn. While the present work was in progress Hirabaya-shi et a1.23 made an independent comprehensive neutron-diffraction study of a single crystal containing 50.05 at. pct Cu, 26.57 at. pct Ni, 0.25 at. pct Mn, 0.13 at. pct Fe, balance zinc. The presence of manganese and iron is surprising since the crystal was supposedly grown from high-purity metals. The homogenized crystal showed evidence of long-range ordering after an anneal of 5 months at about 300°C. Three possible crystal models were proposed. A curious feature of their results23 is that they could not find any neutron-diffraction evidence of ordering in a powdered polycrystalline near-stoichiometric Cu2NiZn alloy. There appears to be some essential difference between a near-stoichiometric Cu2NiZn alloy and one somewhat further off stoichiometry as used by the present authors. Thus Sato14 was able to reproduce the low-temperature resistivity anomaly reported by one of the authors13 on the present alloy if he used a similar composition, but found the normal behavior of the residual resistivity in a near-stoichiometric alloy. satol2 found that the resistivity of a cold-drawn slightly off-stoichiometric alloy increased to a maximum on isothermally annealing at 300°C and then decreased ("over-aged"). Since he could not explain this on the basis of ordering phenomenon, he proposed that zinc atoms were segregating to stacking faults (Suzuki effect) and found etching bands on the surface by replication which were attributed to the widening of faults. Sato suggested14 that the hardening effect observed by Phillips and Jones19 is partly due to the Suzuki effect. EXPERIMENTAL The starting material was 1/4-in.-diam hard-drawn rod of a commercial 18 pct "nickel silver" alloy identical with that used in a previous study by Phillips

Jan 1, 1967

By Paul A. Farrar, Sanford Adler

The Tz-Zr system was reinvestigated using both metallographic and X-ray diffraction techniques. It mas found that titanium and zirconium are soluble in all proportions in both the a and 0 phases. The minimum in the transformation was found at 50 at. pct and 535°C. THE Ti-Zr system has previously been the subject of several investigations.1-6 A study by Hayes et al.5 using magnesium-reduced titanium and zirconium melted in graphite crucibles indicated that the system was a continuous series of solid solutions in both a and 0 phases with a minimum at approximately 545°C and 65 pct* Zr. These conclusions were substantiated by the work of Duwez4 as well as by the limited data of Craighead et al.,3 Fast,2 and deBoer.1 However, a more recent investigation of the titanium-rich region by Ence and Margolin6 indicated that the solubility of zirconium in a, titanium at 500°C is approximately 22 pct with the a + 0 field extending to approximately 47 pct Zr. Therefore in order to resolve this discrepancy the following investigation was initiated. EXPERIMENTAL PROCEDURES The alloys used in this investigation were prepared as 20- to 30-g buttons by nonconsumable electrode melting in a helium atmosphere. The starting materials were Bureau of Mines titanium BHN 71 and Foot Mineral iodide crystal bar zirconium. The titanium was premelted before the alloys were prepared to avoid excessive weight losses in the final melting. The compositions of the alloys prepared were as follows: Ti-12.0, 22.2, 29.0, 39.6, 50.0, 58.0, 72.4, 83.5. and 90.8 pct Zr. Prior to heat treatment the alloys were cold-worked 10 to 20 pct, stopping at the first signs of cracking. Specimens for heat treatment were wrapped in molybdenum sheet and annealed in argon-filled quartz capsules for the following times and temperatures: 750°C-40 days, 675°C-61 days, 600°C—109 days, 575°C-112 days, 550°C-112 days, 525°C—127 days, and 450°C —153 days. Quenching was accomplished by breaking the capsules in an iced-brine solution. The standard techniques used for polishing the specimens involved belt grinding, grinding on emery paper, polishing electrolytically, and etching with Remington "A" etch7 or "R" etch 8 Debye-Scherrer X-ray powder photograms were obtained for a number of samples using a 114.6-mm camera and CuK, radiation. Exposure times were from 19 to 23 hr. The powder samples were obtained by filing to 270 mesh size. After filing the samples were wrapped in molybdenum foil capsuled in quartz and reannealed at the temperature of original heat treatments; following the heat treatment the samples were quenched into iced brine without breaking the capsules. RESULTS AND CONCLUSIONS On the basis of the microstructural examinations of the heat-treated samples and of the X-ray diffraction data, the Ti-Zr system shown in Fig. 1 was constructed. The data indicate that a, and 0 titanium form a complete series of solid solutions with a, and ß zirconium. The minimum was found to occur at 65 pct (50 at. pct) Zr and 535°C, in excellent agreement with the earlier investigations,1-5 see Fig. 2. Typical microstructures are shown in Figs. 3 to 7. Figs. 3, 4, and 5 show the 22.2, 39.6, and 50.0 pct Zr alloys after heat treatment at 675°C for 61 days with the 22.2 pct Zr showing equiaxed a, and the 39.6 pct Zr alloy a + transformed ß, while the 50 pct Zr alloy shows only transformed B. Figs. 6 and 7 show the 29.0 and 39.6 pct Zr alloys after heat treatment for 109 days at 600°C. The 29 pct Zr alloy has an equiaxed a structure while the 39.6 pct alloy has a partially recrystallized a+ß structure. X-ray diffraction data obtained from the 50 pct Zr alloys after heat treatment at 525° and 450°C as well as from the as-cold-rolled material showed only those lineos which couid be indexed a: a titanium, good agreement with the previously published values. 2,4,5,9 Chemical analysis* of the 50 pct Zr alloy

Jan 1, 1967

By B. H. Kear, S. M. Copley

A dynamic theory of precipitation hardening in alloys containing cohevenl, stvess-.free, ordered particles is developed. The yield stvess is predicted from the stress dependence of the plastic strain vale, which is related to a derived dislocation velocity-stress function. The theory is shown to predict the magnilude and temperature dependence of the yield stress of a commercial nickel-base superalloy as well as many details of its slip structure. GLEITER and Hornbogen have developed a theory of the yield stress in alloys hardened by coherent, stress-free ordered ptrticles based on the observation that dislocations (b = a/2 (110)) glide in pairs.&apos; When a dislocation pair shears through an ordered particle, the glide motion of the leading dislocation is impeded since it must create antiphase boundary (APB), whereas the motion of the trailing dislocation is assisted because it annihilates APB produced by the first one. Taking into account the APB energy, the size, and spacing of the particles, G-H predict the observed yielding behavior in Ni/18.8 Cr/6.2 A1 alloys composed of a matrix phase y &apos;(nickel-solid solution) and particles of y&apos; (basically Ni3A1). The G-H theory, as well as all previous theories of hardening by coherent ordered particles, do not include the details of dislocation motion; the present dynamic theory is an attempt to overcome this limitation. In the dynamic theory, the yield stress is predicted from the stress dependence of the plastic strain rate, which is related to a derived dislocation velocity-stress function. This function can be evaluated if the structure of the alloy, the APB energy of the ordered phase, and the characteristic drag or frictional stresses of the matrix and precipitate phases are known. The theory is shown to account for the observed temperature dependence of the yield stress in a commercial nickel-base superalloy. 1) NICKEL-BASE SUPERALLOYS Although their compositions are complex, the nickel-base superalloys have remarkably simple structures. A detailed examination of the commercial superalloy

Jan 1, 1968

By Ravindra M. Nadkarni, Milton E. Wadsworth

The kinetics of cetnentation of copper with iron were observed to follow first-order kinetics and increase with speed of agitation to a limiting value. Maximum rates agree closely with theoretical values based upon a model of aqueous solution diffusion through a litniting boundary film. Back reaction kinetics are shown both theoretically and experimentally to be independent of ferrous iron concentration in solution. The inlportance of attnospheres of air, oxygen, nitrogen, and hydrogen was studied and the results have been correlated with several impovtant oxidation processes involving metallic iron and copper. The kinetics of the reaction of ferric ion with metallic iron were found to be slow in the absence of metallic copper and essentially proportional to the surface area of metallic copper present in the system. THE precipitation of copper on iron is classic as an example of a relatively ancient art applied successfully for centuries with little fundamental understanding of the important parameters involved. There is some indication that the process has been a commercial means to produce copper since the sixteenth century.&apos; The amount of fundamental work on the cementation of copper with iron is not great. Wartman and Roberson2 carried out a series of detailed copper cementation experiments using natural and synthetic mine water. The following were presented as the three principal reactions: Reaction [I] is the desired cementation reaction and accordingly 0.88 lb of iron would produce 1 lb of copper. In actual practice iron consumption would more normally fall in the range of 1.5 to 2.5 lb per lb of copper. Wartman and Roberson attributed the excess consumption of iron to Reactions [2] and [3]. They found that Reactions [I] and [2] proceeded at approximately the same velocity while Reaction [3] was much slower and would be diminished by controlling the contact time. It was also pointed out that increased agitation is beneficial in removing hydrogen bubbles and barren layers of solution at the iron surface as well as removing contaminants resulting from the hydrolysis of iron. Episkoposyan3 and Episkoposyan and Kakovskii4 studied copper and silver cementation on rotating iron disks in chloride solutions. The kinetics based upon a diffusion model were first order and varied linearly with surface area and with angular velocity raised to the one-half power according to the Levich equation. The experimental activation energy for both copper and silver was approximately 3 kcal per per mole. Excess iron consumption was found to increase with temperature. The rate of cementation first increased with increasing acidity and then diminished at high acid concentrations. sutolov5 has presented an excellent review of the Leach-Precipitation-Flotation (LPF) process including a discussion of copper cementation from an electrochemical point of view although few experimental results were presented. From voltage considerations he predicted that cementation should not be influenced by the concentration of ferrous iron in solution. He considered several secondary reactions including Reactions [2] and [3] and pointed out the importance of oxidation of ferrous iron to ferric with oxygen. In addition it was suggested that Reaction [2] was enhanced by the dissolution of metallic copper by ferric iron which in turn consumed excess iron by the cementation reaction, Eq.[1]. Cementation of copper on metals other than iron has been studied by several investigators but, as in the case of iron, the amount of fundamental work is not extensive. Bashkova and kovalenko6 and Bashkova7 studied the cementation of copper on indium from copper and indium sulfate solutions. The rate was found to be first order and to increase with acidity. This was associated with a decrease in potential (EIn — ECu) and the simultaneous reduction of hydrogen ions at low pH. The rate of cementation also decreased with increasing indium concentrations which was postulated to be due to the decrease in the rate of diffusion of the ions in solution. Below 97°C the experimental activation energy was found to have the unusually low value of 2 kcal per mole and was attributed to diffusional control. Above 97°C the rate increased suddenly and was explained as a change in the rate-controlling step to a chemical reaction. In Part I of this study Nadkarni et a1 .1 have reported on preliminary results obtained in a laboratory study of the kinetics of the cementation process. The rate was found to be first order, proportional to the surface area of the iron, and to increase with speed of stirring until a maximum rate was observed. At low stirring speeds the deposit was spongy and adherent. At medium speeds the copper peeled off in bright strips and at high speeds finely divided copper was produced and continually removed from the surface. The amount of excess iron consumed increased with speed of stirring and with temperature. The average experimental activation energy combining results from several types of iron was 5.8 + 1.6 kcal per mole suggesting diffusional control through a limiting boundary film. Traditionally copper cementation has been carried out over the centuries in gravity-fed launders of various design containing scrap iron. More recently rotating drum precipitators and activated launders8&apos;10 have been used. In the latter, copper-bearing solutions are

Jan 1, 1968