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By D. R. Uhlmann, T. P. Seward, O. Chalmers

A magnetic field has been used to damp out liquid convection during the solidification of castings. Ingots of Al-2 pct Cu were poured from various sperheats (10" to 65°C) into a room-temperature graphite mold located between the poles of an electromagnet. The effect on ingot structure of varying the strength and time of application of the magnetic field was investigated, and the results are interpreted in light 01- current theories of ingot structure. In the solidification of alloy systems, thermal gradients in the melt and differences in density of the constituents are expected to produce convective motion in the liquid. The thermal convection caused by temperature gradients should be present during the freezing of both alloys and pure materials, while the solute convection caused by density differences should be of concern only for alloys. The possible influence of this natural convection on the structure of castings has been discussed by Ruddle,' Chalmers, and Tiller. More recently, an experimental investigation of such effects was carried out by Cole and Bolling. These workers took stationary molds containing lead- and tin-based alloys and. using a brine solution. quenched them from various superheats above their respective liquidus temperatures. When grids were placed across the mold diameter to suppress convection, the grid region was later observed to contain a larger percentage of columnar grains than other parts of the casting or than similar castings poured without the grids present. From thermocouple measurements, they found the temperature in the grid region to be higher than that in the region outside the grids throughout the freezing process, and concluded that convection should be an important mode of heat transfer in normal castings. In addition to such convection arising from thermal gradients or differences in density of the constituents, a further source of convective motion, which we shall call "momentum convection", may be particularly important in small (laboratory-size) castings. By this term we refer to the convective motion produced in the initial pouring process, a motion which is damped out as the linear momentum and angular momentum of the liquid are dissipated. Besides these sources of convection, which are present to some extent in all castings. external influences may also be effective in producing convective motion. Examples of such "forced" convection which have been discussed in the literature include stirring the melt, shaking the mold, rotating the mold, and so forth The purpose of the present study was to examine the effect of convection on the structure of castings poured into a cold mold. In this work, a magnetic field was employed to damp out the convective motions within the liquid, and hence control the extent of con- The effect of a magnetic field on convective currents in a conducting liquid is to induce eddy currents which oppose and damp out the convective motion. vection. The technique of magnetic damping was previously used by Utech and F1emings" in their study of convective effects on impurity banding and other substructure in alloy crystals grown unidirectionally from the melt. In their investigation, fields as small as 200 gauss were found to be effective in damping the convection currents which influence the banding. I) EXPERIMENTAL TECHNIQUE In the present study, alloys of A1-2 wt pct Cu were poured into a room-temperature graphite mold. The mold, in the shape of a circular cylinder, 2 in. ID, 2-3/4 in. OD, 5 in. inside height, and 5-1/2 in. outside

Jan 1, 1967

By E. O. Wagner, V. F. Parry, J. B. Goodman

The low-rank coals containing 10 to 50 pct natural bed moisture represent over half of the tonnage reserve of the available solid fuels of the United States, but only about 2 pct of United States coal production is derived from these fuels. Increased utilization of these large reserves will result if the bed moisture can be removed at the mine in high-speed low-cost processes. This paper presents a theoretical and experimental study of the factors affecting high-speed drying of coal dusts. The time required to heat particles of coal is proportional to the square of their diameter, and it is calculated that the probable time in minutes is equal to 6D2. In other words, a 1/16 in. coal particle should be heated to drying temperature in 1.5 to 2.0 sec. Likewise, 1/8 in. particles should be heated in about 6 sec. The net heat required to dry subbituminous coal and lignite varies from 240 to 375 Btu per pound, depending upon the moisture removed, and this heat can be obtained from 42 to 61 cu ft of hot gases at 600°F. The necessary heat also can be obtained from 7.5 to 11 cu ft of gas at 2000°F. A description of the design and operation of a pilot plant for flash drying coal dusts is presented. This plant dries 1/16 in. by 0 coal dust in suspension in 1.5 to 2 sec with 600°F gas at a rate of 1300 lb per hour per square foot of column area and operates continuously at an efficiency of about 85 pct. The design and operation of another pilot plant for drying 1/8 in. by 0 coal dusts Is also described. This unit dries coal in the fluidized state using the sensible heat of gases introduced at 2000°F and processes coal at a rate of about 1500 Ib per hour per square foot of grate area at 85 to 90 pct efficiency. Over 90 pct of the bed moisture of low-rank coal dusts can be removed by the methods described. The heating value of lignite can be increased 45 pet and that if subbituminous coal 25 pct in a few seconds. The physical and chemical properties of coal dusts before and after drying are presented in the report, and it is shown that the bulk density of the dried coal is equal to that of the raw coal. This phenomenon makes it possible to ship 25 to 45 pct more heat in a railroad car with consequent savings in freight costs. Introduction For several years the Subbituminous Coal and Lignite Section of the Coal Branch of the Bureau of Mines at Golden, Colo., has been concerned with upgrading low-rank coals by removal of natural bed moisture. These fuels contain 10 to 50 pct total moisture, which reduces their industrial value considerably. In 1938, investigations were initiated in cooperation with the University of North Dakota to study drying of lignite by the Fleissner process with heat derived from high-pressure saturated steam. Two pilot plants were built, and two reports were published giving the results of this work.l,2 It was demonstrated that lump lignite and subbituminous coal

Jan 1, 1950

By C. G. Dunn, F. W. Daniels

IN recent publications1-5 the existence and behavior of subgrain boundaries in high-purity metals has been clearly brought to light. Lacombe and Beaujardl by means of special etching methods disclosed in polycrystalline sheets of aluminum the existence of substructures differing in orientation by small amounts (about 1/4"). Boundaries of these structures at relatively high temperatures had the remarkable property' of moving about while the ordinary boundaries remained stationary. Cahn2 also observed substructures in bent and annealed single crystals of aluminum, zinc, magnesium, and rock salt. The position of subboundaries could be explained in terms of a dislocation mechanism of polygonization in which dislocations move into lines at right angles to the bent glide planes thereby relieving elastic stresses in these planes. Guinier and Tennevin8,6 disclosed the further interesting feature that polygonized structures coarsened significantly upon prolonged annealing. Somewhat similar subgrain phenomena have been observed in silicon iron of commercial purity. Although some evidence for the development of macro-mosaic structures in silicon iron already has been reported by one of the authors6,7 under the phenom-enological term "crystal recovery," much better evidence recently has been obtained due to improved etching techniques. In addition, phenomena regarding structural changes have been uncovered. The present investigation is divided into three parts: (1) The phenomenon of Laue spot sharpening on annealing cold-rolled crystals, (2) the phenomena of polygonization and subgrain coarsening The material used in the present investigation was high-grade commercial silicon iron sheet of nominal composition, 3.3 pct Si, 0.004 C, 0.011 P, 0.010 S, 0.04 Mn, 0.01 Al, 0.04 Cu, 0.01 Sn. Large single crystals of this material Were prepared for cold-rolling or bending as scheduled. Cold-rolling of 12 pct was carried out on a laboratory 8-in, diam rolling mill. The bending deformations were performed by pressing the crystals between a solid Fig. 2—lllustrative foue patterns to show Laue spot sharpening. a (Left)—Specimen as cold rolled, b (right)—After 48 hr at 1400°C. round bar and a mating half cylinder, both heavily greased. Individual specimens were cut from the deformed crystals, and the cut edges were deeply etched prior to annealing. Laue photographs were made using 40-kv tungsten radiation. The technique used to disclose the various subboundaries was an electropolish and electroetch in a bath of chrome-acetic acid.' The anodic polishing done at 22 v was immediately followed by etching at a reduced voltage, which was dependent upon the nature of the subboundaries. Phenomenon of Laue Spot Sharpening on Annealing Cold-Rolled Crystals Fig. 1 gives the initial and final orientations of the specimens cold-rolled 12 pct. Each specimen was annealed at a temperature and for a time which caused significant structural changes as evidenced by alterations in Laue patterns. Representative Laue patterns and micrographs showing the essential changes are given in Figs. 2, 3, and 4. The essential points to be derived from these illustrations follow: 1. Annealing at 950°C clearly develops a substructure with the orientation of the cold-rolled specimen. 2. The subboundaries formed obviously separate regions of nearly the same orientation. Some of the subboundaries appear as a sequence of dots similar to those observed in aluminum by Lacombe and Beaujard,' but whether this is due to extremely small differences in orientation is not known at present. 3. The substructure coarsens upon prolonged annealing. 4. Prolonged annealing also causes a decrease in orientation spread according to Laue spot sharpening'

Jan 1, 1952

By P. P. Gregory

The rate of drilling operations in the West Texas district during 1940 was approximately equal to that of 1939. The total number of wells dillled in the area during the year was 1834, of which 1716 were completed as oil producers, 12 were gas wells and 106 were dry holes. The number of wildcat wells drilled during the year was comparatively small. The drilling of inside locations in proven areas and the drilling of wells for the purpose of extending the productive limits in producing fields constituted the bulk of development during 1940. Gaines County led all other counties in the district in the total number of oil-well completions. The oil production totaled 83,345,381 bbl., the highest figure for any year since proration was begun. The 1940 oil production exceeded the 1939 production by approximately four million barrels. Discoveries While comparatively few new oil-producing areas were discovered during 1940, it appears that the oil production found in simpson lime in the Abell field, pecos County, was an outstanding discovery for the year. This was the second Ordovician discovery in Pecos County. Taubert, McKee & Siemoneit located its discovery well, V. W. Crockett No. 1, set. 4 1/2 H. & T. C. R.R, co, survey in the Imperial area of northwestern Pecos County. The top of pay was encountered at 5270 ft., and the well was bottomed at 5357 ft. in simpson lime, on act. 17, I940. The initial production was 928 bbl. of 43" gravity sweet oil in 11 hr. 23 min., flowing naturally through 2-in. tubing with gas-oil ratio of 783 cu. ft. per barrel. Following the completion of the discovery well, large blocks of land were leased in the area, and several locations were made toward the close of the year. There is every indication that the Abell field will become a major producing field in the West Texas district. There was no pipe-line outlet for the field at the end of the year. Shipley-Silurian field, discovered by the Gulf Oil Corporation, appears to be another major addition to the oil reserves in 1940. The discovery well, Wristen Brothers No. 5, is in sec. 18, block 5, H. & T. C. R.R. Co. survey in Ward County. The well was drilled to a total depth of 9187 ft. and was plugged back to 7075 ft. The Silurian lime section was acidized with 3000 gal., from 6993 to 7075 ft., and on Dec. 5, 1940, the well was completed for initial production of 3040 bbl- of 32.2" gravity oil in 24 hr., flowing through tubing. Todd Deep field, Crockett County, was discovered by the Continental Oil Co. et al. The discovery well, J. S. Todd No. 2, set. 29, block WX1 G.C. & S.F. R.R. Co. survey, was completed on April 3, 1940. The top of pay was encountered at 5623 ft., and the well was bottomed at 5691 ft. for initial production of 1613 bbl. of 40.6' gravity oil flowing naturally through 2-in. tubing. The pay section was found in Strawn lime of Pennsylvanian age. There were six producing wells in the field at the end of the year. This appears to be another major discovery in 1940. There was no pipe-line outlet in the field at the end of the

Jan 1, 1941

By P. P. Gregory

The rate of drilling operations in the West Texas district during 1940 was approximately equal to that of 1939. The total number of wells dillled in the area during the year was 1834, of which 1716 were completed as oil producers, 12 were gas wells and 106 were dry holes. The number of wildcat wells drilled during the year was comparatively small. The drilling of inside locations in proven areas and the drilling of wells for the purpose of extending the productive limits in producing fields constituted the bulk of development during 1940. Gaines County led all other counties in the district in the total number of oil-well completions. The oil production totaled 83,345,381 bbl., the highest figure for any year since proration was begun. The 1940 oil production exceeded the 1939 production by approximately four million barrels. Discoveries While comparatively few new oil-producing areas were discovered during 1940, it appears that the oil production found in simpson lime in the Abell field, pecos County, was an outstanding discovery for the year. This was the second Ordovician discovery in Pecos County. Taubert, McKee & Siemoneit located its discovery well, V. W. Crockett No. 1, set. 4 1/2 H. & T. C. R.R, co, survey in the Imperial area of northwestern Pecos County. The top of pay was encountered at 5270 ft., and the well was bottomed at 5357 ft. in simpson lime, on act. 17, I940. The initial production was 928 bbl. of 43" gravity sweet oil in 11 hr. 23 min., flowing naturally through 2-in. tubing with gas-oil ratio of 783 cu. ft. per barrel. Following the completion of the discovery well, large blocks of land were leased in the area, and several locations were made toward the close of the year. There is every indication that the Abell field will become a major producing field in the West Texas district. There was no pipe-line outlet for the field at the end of the year. Shipley-Silurian field, discovered by the Gulf Oil Corporation, appears to be another major addition to the oil reserves in 1940. The discovery well, Wristen Brothers No. 5, is in sec. 18, block 5, H. & T. C. R.R. Co. survey in Ward County. The well was drilled to a total depth of 9187 ft. and was plugged back to 7075 ft. The Silurian lime section was acidized with 3000 gal., from 6993 to 7075 ft., and on Dec. 5, 1940, the well was completed for initial production of 3040 bbl- of 32.2" gravity oil in 24 hr., flowing through tubing. Todd Deep field, Crockett County, was discovered by the Continental Oil Co. et al. The discovery well, J. S. Todd No. 2, set. 29, block WX1 G.C. & S.F. R.R. Co. survey, was completed on April 3, 1940. The top of pay was encountered at 5623 ft., and the well was bottomed at 5691 ft. for initial production of 1613 bbl. of 40.6' gravity oil flowing naturally through 2-in. tubing. The pay section was found in Strawn lime of Pennsylvanian age. There were six producing wells in the field at the end of the year. This appears to be another major discovery in 1940. There was no pipe-line outlet in the field at the end of the

Jan 1, 1941

By R. L. Hadley, G. Derge

The amounts of oxygen in liquid iron-titanium alloys up to 50 pct Ti were measured and the oxide phases in equilibrium with these alloys were determined by using TiO² crucibles. A minimum of about 0.003 pct 0 occurs at less than 1 pct Ti. The various liquid and solid oxide phases can be arranged on a ternary isotherm. THREE characteristics of titanium contribute to the interesting aspects of its reaction with oxygen in liquid iron: 1—It forms a number of stable oxides. 2—All oxides have large negative free energies of formation. 3—The pure metal exhibits high solubility for oxygen. In addition, the use of titanium as a stabilizing and strengthening element in alloys suggests a need for investigation of its reactions in amounts greater than those normally required for deoxidation. These higher compositions are also of interest because they occur during the addition of ferroalloys and produce deoxidation products before dilution is achieved. Titanium Deoxidation in the Literature While the use of titanium as an alloying element and deoxidizer has been common for several decades, the first detailed study of its deoxidizing characteristics was carried out by Wentrup and Hieber' in 1939. These authors determined the extent of deoxidation possible with titanium and identified, by microscopic examination, the products formed. They found that titanium in excess of 0.2 pct did not reduce the oxygen content of iron below 0.004 pct at 1600°C. They identified the spinel FeO-TiO² at low titanium concentrations and Ti2O³ in melts containing more than 0.2 pct Ti. A portion of the area surveyed by Wentrup and Hieber has been investigated recently by Evans and Sloman² using X-ray diffraction for inclusion identification. They concurred in general with the findings of Wentrup and Hieber, but reported the existence of Ti³O5 as a deoxidation product in the range near 0.1 pct Ti. Comstock, Urban, and Cohen³ discussed the deoxidation of iron with titanium, correlating the data of Wentrup and Hieber with free-energy data for the titanium oxides. Scatter at high titanium values was considered attributable either to the formation of an oxide exhibiting high solubility in liquid iron or to the entrainment of solid oxide particles leading to high apparent solubility. Chipman' has calculated the deoxidation curves for titanium based on free-energy data for titanium oxides. These calculations (Fig. 1) and those of Comstock, Urban, and Cohen involve assumptions as to the activity coefficients of oxygen and titanium in liquid iron, since such data have not been determined. Investigation of the deoxidizing characteristics of chromium" and vanadium0 have shown that these elements decrease the activity coefficient of oxygen in liquid iron, leading to a tendency toward relatively high oxygen values and experimental scatter in highly alloyed melts. Experimental This investigation involved two major objectives: 1—determination of the composition of the oxide phases in equilibrium with liquid Fe-Ti alloys, and 2—establishing the pattern of oxygen solubility in liquid Fe-Ti alloys at titanium concentrations in excess of that required for attainment of minimum oxygen content. Raw Materials Ingot iron was used having the following composition: 0.02 pct C, 0.017 pct Mn, 0.01 pct Si, 0.02 pct S, 0.006 pct P, and 0.03 pct 0. The titanium used

Jan 1, 1956

By A. D. Schwope, L. R. Jackson, A. M. Hall

IN the course of an extensive investigation of the comparative properties of several types of copper, data were obtained on the cold working and subsequent recovery and recrystallization of the copper. In this paper, relations between the degree of cold work and the course of recrystallization are developed. In particular, it is shown that the course of recrystallization over long periods of time and at low temperatures can be predicted with reasonable accuracy from short-time high-temperature recrystallization data. MATERIALS USED IN THE INVESTIGATION Three types of copper were used in this investigation; these were tough pitch, OFHC, and OFHC copper with 15 oz per ton of silver added identified herein as Lots C, D, and F, respectively. The material was supplied by the American Metal Co. Ltd., and processed by the Rome Cable Co. The analyses of the three types of copper are given in Table 1. Originally, it started as wire bars 4 X 4 X 54 in. These bars were heated to 871°C in air and hot rolled to 3/8 in. rod. This rod was cold drawn to 0.204 in. rod (70 pct reduction) in three passes and annealed at 427°C for 4 hrs. A portion of the 3/8 in. rod was saved for more detailed cold-drawing experiments. Starting with the annealed 0.204 in. rod, hard-drawn wires were produced by cold drawing to 0.081 in. wire in 7 passes (84.4 pct reduction in area). Half-hard wires were made by cold drawing the 0.204 in. rod to 0.102 in. wire, (75 pct reduction) in 6 passes and annealing at 427°C for 4 hrs. This annealed wire was then drawn to 0.081 in. wire, (37.1 pct reduction) in 2 passes. Square rod was made by hot rolling wire bars to 9/16 in, rod in 8 passes. This rod was then cold drawn to 0.445 in.-diam rod and annealed for 3 1/2 hrs at 538°C. It was then cold drawn to 0.325 in. rod and again annealed at 538°C for 3 1/2 hrs. Hard square rods were then made by cold rolling this material to 0.257 X 0.257 in. rod, a reduction in area of 20.5 pct. Half-hard square rods were made by cold rolling to 0.268 X 0.268 in. square, annealing for 332 hrs at 538°C and cold rolling to 0.257 X 0.257 in., a reduction of 8.5 pct. Soft wire or rod was made from all types of copper by annealing the hard-drawn material at 343°C for 3 hrs in steam. The grain size of the annealed 0.081 in. wire varied slightly among the three lots: from 0.015-0.025 mm in the silver-bearing OFHC to 0.035-0.045 mm in the OFHC copper. The annealed 0.257 in. wires were more uniform in grain size, averaging about 0.035-0.045 mm. Representative structures are shown in Fig I. EFFECT OF COLD DRAWING AND TENSILE STRAIN ON STRENGTH OF COPPER Conventional tensile tests were performed on the three types of copper in the various degrees of hardness described above. Results of these tests are tabulated in Table 2. The results in Table 2 are

Jan 1, 1947

By W. A. Backofen, B. B. Hundy

THE pole figure interpretation in a recent paper' on the torsion texture of copper was questioned in discussion,2 nd a simpler alternative interpretation was proposed. In the hope of reaching a positive decision in favor of one or the other, further studies were undertaken with 70-30 brass and Armco iron. This additional work has not answered all the questions about torsion textures, but the new pole figures do offer support for the original interpretation and show that the texture is more complicated than the alternative suggests. From the previous paper,' the appropriate method of describing the texture in a twisted bar is known to be a pole figure plotted on a plane tangent to the surface of the bar. The axes of the pole figure are chosen to coincide with directions in the tangent plane which are parallel and at right angles to the bar axis (the longitudinal direction, L.D., and the transverse direction, T.D.), for these directions define symmetry axes of the texture. Therefore any ideal orientation that might be selected to represent the texture gives the crystallographic plane parallel to the tangent plane and the crystallographic direction parallel to the axis of the torsion specimen. A unique texture was assumed in the original interpretation, and the four ideal orientations, (112) [111], (111) [112], (110) [001], and (112) [131], were used in its description. Of the four orientations, the first three provide possible slip directions along the direction labeled T.D. in the pole figure, which is one of maximum shear stress in a specimen being twisted. The alternative, however, simply considered the texture to be made up of two components, one a [Ill] alignment along the specimen axis with a random orientation about the axis as in the wire texture, and the other a superimposed orientation (110) [0011. Experimental evidence for this simpler interpretation was derived from two observations: 1—twisting did not alter the orientation of a single-crystal torsion specimen of a brass in which an octahedral plane was perpendicular (and a [Ill] direction parallel) to the axis, and 2—deformation bands with approximately the (110) [001] orientation were seen to develop in the crystal during the test. The new pole figures were obtained with a brass and an iron torsion specimen of 3/4 and 1 in. gage length diameter, respectively. After annealing, polishing, and twisting, seven rods, about 0.030 in. in diameter and with different orientations, were prepared from material near the surface of each specimen; these were required for the method of constructing pole figures by using a Geiger counter as developed by Norton.5 Since the shear strain gradient in plastic torsion is linear, it was readily computed that the material supplying the brass rods had been subjected to a shear strain of about 3.2, and that supplying the iron rods had received a shear strain of about 2. All details concerning specimen design, testing procedure, rod preparation, and use of the Norton technique can be found in ref. 1. Only this procedure was followed in working out the (111) and (100) pole figures for brass, Figs. 1 and 2. However, X-ray photograms were also involved in the construction of the (110) pole figure for Armco iron, Fig. 3. The photograms were made according to the conventional transmission diffraction technique using a small sheet taken parallel to the specimen surface and etched to a thickness of about 0.0025 in. They were especially important in locating the boundaries

Jan 1, 1954

By David Cornell, Yusuf K. Sukkar

The fundamental differential equation for fluid flow has been rearranged, integrated numerically for natural gases, and the results presented in tabular and graphical form suitable for the direct calculation of vertical gas flow problems. The integration is rigorous except for the use of a constant average temperature. Both static and flowing bottom-hole pressures may be calculated by (his method without resort to trial and error procedures. INTRODUCTION Bottom-hole pressures can be determined either by direct measurement with a bottom-hole pressure gauge or by calculation. Since measurement with a bottom-hole pressure gauge is costly, calculation of bottom-hole pressures is to be preferred when possible. Calculation involves knowledge of the wellhead pressure, the properties of the gas, the depth of the well, the flow rate, the temperature of the gas, and the size of the flow line. These quantities must be combined in a suitable equation for vertical flow. Several equations have been developed for the purpose of calculating gas flow through both horizontal and vertical pipes1,2,4,5,6,7,8,9 These equations all have the basic differential equation for flow as their starting point. They differ only in the assumptions which are made in order to simplify the integration step. The bottom-hole pressures calculated using any of the better known equations are in good agreement with bottom-hole pressures calculated by a more rigorous but considerably more tedious stepwise integration method. All of these methods, however. require a trial and error solution for the calculation of flowing bottom-hole pressures. The purpose of this paper is to present a method which provides a direct solution of static and flowing bottom-hole pressures without use of a trial and error solution. At the same time the method involves fewer simplifying assumptions than any of the previous methods used, except lor the lengthy stepwise method. The derivation of any practical flow equation begins with the basic differential equation which is rigorous for almost all flow problems. The five terms in Equation 1 represent the potential energy, the potential energy of position, the kinetic energy, the shaft work done, and the energy losses due to motion of the fluid respectively. Equation 1 reduces to Bernoulli's theorem for the case of horizontal flow of an incompressible fluid, no work done, and no energy losses due to friction. In the present case, the term (v) (dv)/(g,.) can be shown to be quite negligible compared to the other terms, and is therefore neglected in the derivation. The term — dws includes work done by a pump or turbine in the system and is zero in this case. The frictional losses in the pipe are included in the term — d(lw) which is expressed in terms of the Moody friction factor as in Equation 2. (f) (v2) (dL) d(lW) = (f)(V2) (dl)/(2) (g) (d) The specific volume of a gas can be expressed in terms of the temperature, pressure, molecular weight, and compressibility factor. The velocity of the gas can be expressed in terms of the weight rate of flow, the specific volume, and the dimensions of the pipe.The reduced pressure Pr is to be used because z can be expressed as a function of Pr and Tr alone for most natural gases:

Jan 1, 1956

By M. C. Fuerstenau, A. M. Gaudin

A homogeneous suspension is viewed by X-rays. The radiation density seen, affords a measure of the extra absorption due to the solids contained. This radiation density, at a predetermined depth, varies with time. The chart of this relationship gives the desired determination. s it is frequently necessary to know the distribu-rt tion of particle sizes in various products used in industrial applications, a number of means have been devised for these determinations. Some of them include direct microscopic measurement, screening of product, extraction of samples from a settling slurry, air and liquid elutriation, adsorption of gases and liquids, and light absorption. The absorption of light as a means for particle size analysis has been known and employed for some time. X-ray absorption has not received the attention that light has enjoyed primarily because of the complex and costly instrumentation involved with X-rays. In 1954, Brown and Skrebowskil suggested the use of X-rays for this type of determination but did not supplement their suggestion with experiment. In 1958, the authors conducted size analysis experiments on suspensions of quartz with the Trans-viewer: an X-ray unit specifically adapted for sedimentation research, and Rossa conducted experiments in a similar manner in 1959 with a stable gamma emitter, AmZ4l, on suspensions of uranium oxide. To illustrate the applicability of X-ray absorption for analyzing particle size distributions, an essentially mono-energetic and well collimated X-ray beam was used as a source. The beam was made mono-energetic by placing a zirconium filter before the counting window together with feeding the pulses from the proportional counter into a reverter, a device capable of discriminating against pulses of various heights. The sketch in Fig. 1 shows the collimation arrangement in more detail. As shown, the X-ray beam was collimated by inserting a 3/8-in. ID pipe into one of the ports of the X-ray tube and further by two small steel plates with slits 3/32-in. wide and 1/2-in. long placed in front of the window of the Geiger-Mueller (G-M) tube. One of the plates was located 1/2 in. and the other 2 1/2 in. from the window of the counter; both plates were contained in an aluminum holder mounted on the box containing the G-M tube. This type and degree of collimation should eliminate any intensity due to scattered radiation; the transmitted intensity would then be solely a functior. of the absorption by the suspension at that level. Experimentally, homogeneous suspensions of finely ground quartz were prepared, Daxad (a sulfo-nated compound made from wood) was added as dis-persant, and the transmitted X-ray intensity measured as a function of time at a fixed depth in the suspension. In more detail, the experimental procedure involved the following: 1) measuring the transmitted X-ray intensity through the Daxad solution at a predetermined position or settling depth in the absence of solids, 2) placing a known amount of dry solids into the vessel and agitating thoroughly, 3) measuring the transmitted X-ray intensity at time zero (i.e., immediately upon cessation of stirring), and 4) measuring the transmitted X-ray intensity as a function of time (a 10-sec counting interval being chosen and counting being started 5 sec before the desired time). Since a linear relationship exists between percentage solid in a slurry and the logarithm of transmitted intensity for a homogeneous material, the cumu-

Jan 1, 1961

By P. R. Sperry, P. A. Beck, Hsun Hu

As described by means of quantitative pole figures, the inside texture of highly rolled aluminum and copper strips may be approximately described by four equivalent ideal orientations near (123) [121]. If rolled in reversed passes, the surface texture of copper is also near (123) [121], that of aluminum is (100) [011]. The inside texture of highly rolled brass is (110) [112]. The surface texture is the same, if rolled in reversed passes. The surface texture of all three metals is related to the inside texture, but asymmetrical, if rolled without reversal between passes. MANY previous investigations dealing with the subject of the present work were reviewed by Wassermann.1 Barrett,2 Brick,3 and Richards.' The recent introduction of quantitative methods for pole figure determination by Decker, Asp, and Harker,5 Schulz5 and others made it possible to reinvestigate some of the finer points which the earlier more qualitative photographic methods left undecided. The rolling textures of silver and of 70-30 cartridge brass have been quite consistently characterized by the ideal orientation of (110) parallel to the plane of rolling and [112] parallel to the rolling direction. On the other hand, it has been recognized by several investigators that certain other face-centered cubic metals, such as copper and aluminum, developed rolling textures rather different from that of brass. These textures have been variously described by the following ideal orientations, singly or in combinations with each other: (110 [112]: (112) [111]; (135) [335]; (135) [211], etc. The discrepancies usually have been attributed to the lack of sharpness in the textures and to the attendant difficulty of associating "ideal orientations" with pole figures showing great scatter of orientations. It seemed desirable to investigate by the new quantitative methods to what extent the apparent lack of sharpness may have been brought about by the qualitative methods used previously, rather than by the textures themselves, and to decide, if possible. between the various ideal orientations which have been proposed. Another problem, not satisfactorily settled by earlier investigations. concerns surface textures in rolled metals. For instance, in rolled aluminum the surface texture in some cases appeared to be similar to the texture inside the sheet, whereas in other cases it was reported to be entirely different.' The conditions under which such differences may have arisen, and the possibility of the occurrence of different surface textures in other face-centered cubic metals do not appear to have been examined in detail. The present work was undertaken to investigate the above questions. Some of the results obtained have been described- riefly. Experimental Procedure Specimen Preparation: In the present investigation 2s aluminum, electrolytic tough-pitch copper, and commercial 70-30 brass were used. These materials were available in the form of cold-drawn rods. 1 in. diam for tough-pitch copper and commercial 70-30 brass and 11/2 in. diam for 2s aluminum. The cold-drawn bars were alternately annealed and rolled 30 pct lengthwise in several cycles until a penultimate thickness of 0.500 in. was reached. The intermediate and the penultimate anneals were carried out for 30 min at 380°C with 2s aluminum, and for 30 min at 550°C with 70-30 brass. For tough-pitch copper, the intermediate anneals were 30 min

Jan 1, 1953

By d&apos, K. Mukherjee, C. R. Antonio, R. J. Maciag, G. J. Fischer

Tensile data indicate that over the range of strain rates 10-5 to 10-1 sec-1 and in the temperature range 298° to 743°K the flow stress at a given temperature may be expressed as: C0 = Cem where m changes abruptly at a critical strain rate of 10-2 sec-1. The Zener-Hollomon parameter was tested and found to be invalid except at temperatures exceeding 700° K. Values of AH calculated for temperatures above 700°K ranged from 30 to 47.5 kcal per g-mole. ThE flow characteristics of aluminum and aluminum alloys as a function of temperature and strain rate have been of interest to various experimenters for many years. Trozera et al.1 determined tensile flow curves for pure aluminum and concluded that the combined effect of temperature and strain rate on the flow stress could be related using the Zener-Hollomon parameter. More recently, Hockett2 proposed a relationship between compressive flow stress, temperature, and true strain rate which could be represented by a surface. Holt et al.3 studied strain rate effects on flow stress in a number of aluminum alloys at room temperature. It was determined that there is a critical strain rate above which a strain rate effect is observed. It was also reported that the strain rate sensitivity was significant in aluminum alloys in the "0" condition only. In a recent review paper McQueen4 has considered a number of mathematical expressions which have been used to describe the relationship between stress, strain rate, and temperature. These expressions have been applied to the flow characteristics of a number of different metals and alloys including aluminum. In the present work the strain rate sensitivity of 7075-0 aluminum was determined in the temperature range of 298° to 743°K. The tensile flow stress at 0.2 pct offset was obtained over a nominal strain rate range of 10-5 to 10-1 sec-1. EXPERIMENTAL Threaded tensile specimens were cut from a single heat of 7075-T6 aluminum. The composition of this heat is given in Table I. The test bars had a gage section 1.5 in. long by 0.250 in. diam and conformed to ASTM specification E-8-57T. After machining, the bars were annealed at 413° ± 10°C for 2 hr. They were then cooled to 260°C in 3 hr, and finally air cooled to room temperature. This treatment is commonly used to produce the "0" condition. Load-time curves at constant crosshead speeds were obtained at various temperatures using an Instron testing machine. Crosshead speeds ranged from 0.002 to 40 in. per min. A three-zone resistance tube furnace was used for the elevated-temperature tests. Temperatures were measured at three points along the gage length by means of suitably placed thermocouples. Each tensile bar was held at temperature for 30 min prior to testing and the maximum temperature variation along the gage length was kept below 1°C. In all, 275 samples were tested and each data point plotted is an average of at least two tests. In many cases the point represents up to six tests. RESULTS AND DISCUSSION Values of the flow stress at 0.2 pct offset at six different temperatures are plotted vs strain rate on log-log coordinates in Fig. 1. Over discrete ranges of strain rate, the data for each temperature fit the expression:

Jan 1, 1969

By R. H. Cox, A. S. Allen, James Paone

The southwestern Illinois communities of Belleville and Maryville lie within the greater metropolitan area surrounding St. Louis. Missouri. They also lie within that part of the Illinois coal basin where the Number 6 coalbed has been mined for more than a century. About half the coal was left as pillars to support the ground surface. Years later, however, damaging movements are affecting buildings, streets, and public utilities in some areas. They are generally believed to be related to abandoned mine workings. The threat of continued or increasing incidence of damage raises the need to explore other subsidence-control measures for protecting affected areas with high population density. Because of experience gained in a subsidence-control program of backfilling abandoned coal mines in the Applachian region and in Rock Springs, Wyoming, the Bureau of Mines was called upon to investigate the subsidence occurrences at Belleville and Maryville, and recommend protective measures. Funds ware appropriated for the Bureau to initiate subsidence-control projects at two residential sites in Belleville and one in Maryville. Subsurface investigation of the sites by diamond core drilling revealed two conditions that differ from those encountered at most sites of previous subsidence-control projects. The mine workings were found to be dry and the mine floor consisted of soft underclay which characteristically loses strength with increase of moisture. It had been anticipated that water would have percolated into the mine workings at one .or more of the sites through cracks resulting from subsidence. Under such conditions Bureau engineers believed that injection of mine waste by the pumped; slurry technique3 would provide support and stabilize any movements initiated by the softening of the clay. With discovery that the underclay deposits at the three sites have apparently not been exposed to water since the mines were operating, hydraulic backfilling of any type was considered inadvisable on the basis of present knowledge. To avoid introducing water, a portable pneumatic system is being devised for injecting minus 0.01 27 m (1/2 in.) mine waste into the mine workings. Machines for pneumatic backfilling have been used in Europe not only for subsidence protection but also for strata control, for reducing spontaneous combustion and methane accumulation, and as a means of waste disposal. The Bureau experimented with a pneumatic machine in the Northern anthracite field of Pennsylvania in the 1950's. Previously pneumatic machines have been installed in active mine workings discharging from horizontal pipelines which conveyed air- borne material into rooms to be filled. In the present adaptation to abandoned mines, the machine and air compressor will be operating at the surface, to impel material vertically down injection boreholes with sufficient air pressure to disperse fill material laterally in mine workings at the base of injection holes. Large diameter access and ventilation boreholes will be provided at one site for entry into mine workings to observe backfilling progress. The Belleville and Maryville projects are part of the Mined Land Demonstration Program of the Bureau of Mines. The Illinois State Geological Survey and Department of Mines and Minerals are furnishing technical support.

Jan 1, 1979

By Walter L. Crow

MUCH has been published on highly technical phases of grinding. Very little has been written on how a mill man can improve his operations by determining the optimum size assortment of grinding balls that should be added as a makeup charge. This ball rationing is not to be confused with the ball ration used as an initial charge when the mill is started up. Ball rationing is considered for one or more of the following purposes: 1) to increase throughput of the mill, 2) to reduce the power required per ton of ore ground to the desired size, 3) to reduce steel consumption per ton of ore ground, 4) to improve product size, and 5) to lower retention time of ore in the mill.

Jan 7, 1957

Jan 1, 1930

By N. S. Stoloff, R. G. Davies

The annealing behavior of a heavily cold-worked FeCo-V alloy has been studied at temperatures both above and below Tc, the critical temperature for ordering. It was found that re crystallization and grain growth can take place below Tc in the ordered state and that, in agreement with results for fcc alloys, order retards grain growth. The activation energy for pain growth is -55 kcal per mole in the disordered condition; it was not possible to assign a value to the activation energy for grain growth below Tc because the degree of order is changing rapidly over the temperature interval investigated. Precipitation of an fcc y phase was observed upon annealing the cold-worked alloy at temperatures of 675°C and below. SINCE it is known that diffusion constants are greatly affected by long-range order,' it is not unreasonable to anticipate that order will influence the diffusion-controlled phenomena of recrystallization and grain growth. In the course of a study of strain aging of ordering alloys around the composition Ni3Fe Vidoz, Lazarevic, and cahn2 noted that a disordered cold-worked alloy annealed at a temperature T1 just below Tc will order but not recrystallize; Tc is the critical temperature for order. The same alloy annealed at a temperature T2 just above Tc, or an alloy of different (nonordering) composition annealed at either T1 or T2, will recrystallize after equivalent amounts of cold work. Initially Selisskii and coworkers,3,4 who examined a series of cold-worked and annealed bcc Fe- Co alloys, reported that alloys forming the B2 FeCo super lattice could not be recrystallized below Tc. However in a later paper5 it was shown that FeCo ordered alloys could be recrystallized below Tc. Thus the first question to be answered by the present investigation was whether or not a heavily cold-worked Fe-Co-V alloy could be recrystallized below Tc. When it was found that the alloy would indeed re-crystallize below Tc, the influence of long-range order upon subsequent grain growth was studied. EXPERIMENTAL PROCEDURE The grain-growth measurements were made upon FeCo-2 pct V wire of 0.031 in. diam; the alloy was the same as that used in an earlier study of the mechanical properties of FeCO-v.6 The wire was produced by cold swageing and drawing a rod 0.125 in. diam that had been quenched into iced brine from 850°C to disorder the alloy; the initial grain size was 0.05 mm. Rates of grain browth were measured after isother-mally annealing the wire in the temperature range 675° to 825°C; T, is -720°C. Grain diameters were measured on the transverse cross section of the wires. The line-intercept method of determining the grain diameter was used; conventional light photomicrographs were taken when the grain size was greater than 10 . Carbon replicas were produced and examined in the electron microscope if the grain size was less than Dislocation configurations after recrystallization anneals were studied by electron transmission microscopy of foils produced by cold rolling a 0.125-in.-thick strip of the quenched material to 0.012 in. The foils, after heat treatments similar to the wire samples, were thinned by electropolishing in a chromic-

Jan 1, 1967

By D. N. Seidman

In the course of a study of the electronic and thermodynamic properties of Pb-Se alloys it was found necessary to have an accurate knowledge of the phase diagram. However, the literature is in disagreement as to whether or not a monotectic reaction occurs in the lead rich portion of the phase diagram. Pelabonl reported only a two-phase region consisting of lead-rich liquid and solid PbSe extending from almost pure lead to the compound PbSe, and gave the melting point of PbSe as 1065°C. The data of Friedrich and Leroux2 are in general agreement with this type of diagram, with the melting point of the compound being 1088°C. However, Nozato and Igaki by inverse rate thermal analysis observed a monotectic reaction isotherm exlacing at 860°C with a monotectic composition of 20.5 at. pct Se. The miscibility gap in the liquid state extends from 7.5 to 20.5 at. pct Se. Hansen and Anderko4 accepted Nozato and Igaki's phase diagram in the region of the lead-rich monotectic. To reinvestigate this portion of the phase diagram, both thermal analysis and metallographic examination of various compositions were performed. The thermal analysis apparatus was constructed according to the specifications of the National Bureau of Standards. A t/t-l pct Rh thermocouple was calibrated against the melting point of copper (NBS), zinc (NBS), and antimony (A. D. Mackay), the emf being measured with a Rubicon Type B potentiometer sensitive to lpv. The absolute accuracy of the thermal analysis obtainable with this system is ± 0.5oC. Starting materials were semiconductor grade lead and selenium purchased from the American Smelting and Refining Co. Both elements were 99.999 pct pure with only trace impurities detected upon spectroscopic examination. One hundred galloys were sealed in quartz crucibles with a central thermocouple well under a vacuum of less than 1 p. This procedure prevented any composition change due to vaporization during the run. Cooling curves were obtained on the alloys listed in Table I. Data was taken by the direct method at cooling rates ranging between 1/2 to 2°C per min. The alloys were heated well above the liquidus and shaken vigorously to insure homogeneity. No evidence of an arrest indicative of the monotectic reaction was observed, and the two-phase region reported by Pelabonl and Friedrich and Leroux? was confirmed in general, although our data give higher liquidus temperatures than Friedrich and Leroux. The melting point of stoichiomet-ric PbSe determined for two different samples was 1080.7 0.5oC. The results of this investigation are compared with Nozato and Igaki's data in Fig. 1. To Complement the thermal analysis data, an 86 at. pct Pb specimen was examined microscopically. This composition was in the center of the miscibility gap reported by Nozato and Igaki.3 The alloy was heated to 1000°C, held for 1/2 hr, and water quenched. The specimen was polished using standard metallographic techniques for lead. The alloy was etched with an acetic-nitric acid etchant for 10 min at 45°C. Microscopic examination did not indicate the existence of two separate layers or solidified droplets imbedded in a matrix, as would be expected if a miscibility gap were present. The mi-crostructure shown in Fig. 2 consists of uniformly dispersed, dendritic PbSe in a lead-rich matrix.

Jan 1, 1962

By A. J. Opinsky

ThE superior performance of nonsag tungsten wire in lamps has been ascribed to the large-grained micro-structure that can be developed in it. The orientations of these large grains have been studied several times; most published data1-' appear to be similar to those plotted in Fig. 1. These new data were obtained by X-ray back-reflection Laue technique from all of the large grains occurring in thirteen different wires that had been heated at the lowest possible temperature for the formation of large grains. Here the wire axis is plotted in terms of the principal directions of the cube. Rosi decided that the preferred orientation of the large crystals could be described by a single ideal orientation, (531), being parallel to the wire axis.' Rieck2,3 and Mannerkoski' have essentially confirmed this finding. Opinsky, Orehotsky, and Seigle argued that the data suggest that (211) is parallel to the wire axis instead of a single ideal orientation.5 This {211} contains the (531) ideal orientation and would appear to be a more general case. Ahlborn and Wassermann report that their orientation data stretch from ( 110) through (531) to (311) 8 This is part of the locus of (211). All these investigators have determined the orientations of the large grains by back-reflection Laue techniques. They have all obtained essentially similar results. On the other hand, Swalin and Geisler, who obtained their data by neutron diffraction, indicated that the preferred orientation of the large grains in doped wire is (110) .7 These findings cannot presently be reconciled with the pole density data described in the previous paragraph. Rosi1 and Rieck2 have advanced arguments about how their orientations could occur. Nevertheless, the crystallographic link between the (110) (cold-worked) fiber texture and the preferred orientation of the large grains has remained missing. This link can be provided through the concept of coincidence-type boundaries. Such boundaries separate two grains that have a certain number of common lattice sites. Coincidence relationships that result from rotations about low index directions are given by Brandon et a1 .' What is desired is a calculation of those orientations that bear a coincidence relationship with the (110) fibers of the cold-worked matrix. This situation arises in the following fashion. Heating the tungsten wire for a combination of time and temperature falling short of the formation of the nonsag structure yields a structure that is still fibrous in nature and the preferred orientation remains (110). During grain growth, the growing grain is in contact with these fibers. It is hence possible that the entire process may begin by the passage of a coincidence boundary into a (110) fiber. The calculations were carried out analytically and checked graphically. Following Brandon et a1.,8 coincidence relationships from 1 in 5 to 1 in 19 have been considered. The results of the calculations are given in Fig. 2. Of the coincidences examined, some of those occurring upon rotation about ( 110) come closest to the experimental points in Fig. 1. Nineteen of the twenty-three data points in Fig. 1 can be attributed to the ideal orientations A, B, C, and D in Fig. 2. As determined analytically, three crystals lie within 4 deg of point A, four lie within 21/2 deg of point B, eleven lie within 5 deg of point C, and one lies within 1 deg of point D-a total of nineteen. The off-lying points are near the |110| point of the triangle.

Jan 1, 1968

By Philip R. Strand, O. F. Stewart

Vermiculite is the name generally applied to the group of hydrated ferromagnesian aluminum silicates that are characterized by the ability to expand when heated. This process, called exfoliation, results in a lightweight product of commercial value. Most uses of vermiculite are for the expanded material. The chief markets are in construction, agriculture, and horticulture, with lesser uses in general industry. Composition and Properties Vermiculite, in its natural state, has the characteristic micaceous habit, a perfect basal cleavage which causes splitting into thin laminae that are soft, pliable, and inelastic. The structure of vermiculite is basically that of a talc. The prominent monoclinic crystal faces are often marked by lines at 60° and 120°. Hardness varies from 1.5 to 2 or more; specific gravities are between 2.1 and 2.8; color varies from almost clear to amber, bronze, brown, green, or black. Vermiculite feels like talc, especially when wet. Although much research has been performed on the chemical and structural composition, there is not yet complete agreement on the exact formula. This is to be expected when different workers have examined the many different varieties. Vermiculite is not considered to be a single mineral species but a family of related minerals. The structural formula for a trioctahedral vermiculite may be written: (H20)-(Mg,Ca,K)-(A12,Fe,Mg)-(Si,A1,Fe)4O10 (OH) 2 Hydrobiotite also occurs with vermiculite and is usually considered a vermiculite for commercial uses. When heated quickly to elevated temperatures, vermiculite expands by exfoliating at right angles to the cleavage into wormlike particles. The name vermiculite is derived from the Latin vermiculare, to breed worms. This characteristic of expansion is the result of the mechanical separation of the layers by the rapid conversion of contained water to steam. The decrease in bulk density of commercial grades is usually approximately 10 times, from 50 to 5 lb/ft3, but varies depending on the quality, size, and furnace efficiency. Individual flakes may expand up to 30 times. Vermiculite may also be expanded by soaking in chemicals such as hydrogen peroxide, weak acids, and other electrolytes. Color change during expansion is dependent upon the type of vermiculite and furnace conditions. Heating in an oxidizing atmosphere produces a dull gray or tan color, whereas a reducing atmosphere can produce a bronze or gold color. The expansion of the vermiculite crystal results in large pores being formed between the platelets. Thus, exfoliation makes available a large increase in void volume which is important in the application of vermiculite as a chemical carrier. Mathieson and Walker (1954) state vermiculite must be regarded as a true clay mineral. The characteristic properties of the mineral, such as high cation exchange capacity, organic complexing ability, and variable interlamellar distance are very similar to those of montmorillonite. The cation exchange capacity of vermiculite is one of the highest of all the clay minerals. The interplatelet space is accessible to penetration by some electrostatically neutral molecules. Water and glycerine are two common substances whose molecules may be so imbibed. In the natural state and under normal atmospheric conditions, water occupies the spaces between the silicate layers. The crystal d-spacing is near 14.2A. By differential thermal analysis, it has been determined that the water

Jan 1, 1983

By D. G. Westlake

NUMEROUS hydride habit planes in zirconium, Zircaloy-2, and Zircaloy-4 have been observed by various researchers and have been compiled by Louthan and Angerman.1 While only partial agreement exists on the identification of these habit planes, there is a growing consensus that a tensile stress applied on a polycrystalline rod during slow cooling will cause the hydride platelets to lie perpendicular to the tensile axis. walters2 agrees with Louthan and Angerman who reason that "The particular plane on which precipitation will occur is the plane that will result in the maximum relief of stress by precipitation of the low-density hydride." The experiment described below was initiated to test this hypothesis on a single crystal of zirconium. A single-crystalline tensile specimen of zone-refined zirconium, designated number 13 in a previous study,3 had a square cross section with one pair of parallel faces only 4 deg from the basal plane of the hcp structure. The tensile axis was about 86 deg from the (0001) pole, 14 deg from the (1010) pole, and 16 deg from the (1150) pole. The specimen was charged to 50 ppm H by allowing reaction with the correct amount of hydrogen at 1073°K, homogenizing at this temperature for 2 hr, and cooling in the furnace. Two- surface analysis revealed that hydride platelets had precipitated parallel to the three {1010} prism planes. The specimen was heated to 673°K, in air, for 16 hr to bring the hydrogen back into solid solution, and furnace-cooled to 573°K.* It was then stressed in ten- sion at 1.2 kg per sq mm. (This produced a resolved shear stress of 0.6 kg per sq mm for glide on the prism plane with the highest Schmid factor. A higher stress would have produced significant strain at this temperature because the critical resolved shear stress for prism-plane glide in this crystal was only 1.0 kg per sq mm at ambient temperature.) The poles of the three prism planes were at angles of 14, 46, and 74 deg to the tensile axis so that an applied stress would exert normal stresses on the three planes in the approximate ratios 10:5:1, respectively. As soon as the stress was applied, the sample was furnace-cooled to room temperature. It was ground on wet Sic paper and chemically polished in 50 parts HNO3, 50 parts water, and 7 parts HF before examination. The result of the experiment was negative; i.e., the three (1010) planes were of equal importance as hydride habit planes.* It must be admitted that the ex- periment is not entirely comparable to those performed by walters,2 Louthan,5 and Louthan and Marshall6 on polycrystalline materials. They have found that some critical stress (below the macroscopic yield stress) is required for stress-orienting the hydrides. The applied stress in the present experiment was, by necessity, smaller by an order of magnitude than the critical stresses they report for the various materials. If the critical stress was related to the microstructure, one might postulate that it should be decreased by increasing the degree of perfection of the metal lattice and by increasing the grain size. But the experiment above suggests that, for the extreme case of a zone-refined single crystal of zirconium, the critical stress lies above that which one can apply without introducing gross plastic strain as another variable.

Jan 1, 1967