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By W. C. Leslie, R. M. Fisher, K. G. Carroll

A nitride, believed to be Si3N, has been separated from three nitrided silicon steels. Germanium nitride, Ge3N4, has been prepared from pure germanium. Comparison of the diffraction patterns indicates that the two nitrides are isomorphous; on orthorhombic structure is suggested in place of the rhombohedral structure previously reported for Ge3N4. THE possibility that a nitride of silicon may, under appropriate conditions, precipitate in silicon steels or in steels killed with silicon makes it desirable to have some positive means of identifying such a compound. One such means is the X-ray or electron diffraction pattern of the nitride. A review of the meager data in the literature indicates that the nitride most likely to form is Si3N4, a conclusion supported by the results of a study of nitrided silicon steels to be published shortly by L. S. Darken and R. P. Smith, of this Laboratory. Unfortunately, there is available no diffraction pattern for this nitride. Data have been reported, however, for Ge3N4 which, judging from the similarity between germanium and silicon, might be expected to be isomorphous with Si3N4. An effort was made, therefore, to form such a silicon nitride, to determine its composition and diffraction pattern and, if possible, its structure. To this end a series of three silicon steels was nitrided under controlled conditions with the resultant formation of nitride particles which yielded an electron diffraction pattern in situ. The particles were then extracted from the steel and an attempt was made to determine their chemical composition. X-ray and electron diffraction patterns were also obtained from the extracted particles, which indicate that the nitride is isomorphous with Ge3N4, although a complete determination of the structure has not been possible. These results show that a silicon nitride with a well-defined diffraction pattern can form in silicon steels, and they suggest that this nitride is Si3N4. Materials and Procedures The sillicon steels investigated were In the form of thin sheet or strip and had the composition shown in Table I. The 0.58 and 1.21 pct Si steels were nitrided by holding them at 1110°F in an H2-NH3 atmosphere containing 3 pct ammonia for 48 hr. The nitride particle size was increased by subsequent heating at 1500°F for 13 1/2 hr in helium. The resulting microstructure is shown in Fig. 1. The steel containing 3.20 pct Si was nitrided at 1200°F for 16 1/2 hr after which it was held in helium at 1500°F for 4 hr. Its structure as seen under the electron microscope is illustrated by Fig. 2. As would be expected from the higher silicon content and the shorter holding time at 1500 °F, the nitride particles are smaller and more numerous than those in the 1.21 pct Si steel. The ammonia-hydrogen treatment reduced the carbon content of the steels to a very low level, so no interference was encountered from carbon or carbides. In the case of the 3.2 pct Si steel, the carbon was reduced to 0.003 pct before nitriding by heating in dry hydrogen. Attempts to obtain an X-ray diffraction pattern from polished and etched surfaces of the 1.21 and the 3.20 pct Si steels were unsuccessful. However, an electron diffraction pattern was obtained from the surface of the steels. The interplanar spacings obtained from these patterns arc shown in Table 11, col. 5. The nitride particles were then extracted from all three steels by dissolving the ferrite matrix in bromine-methyl acetate, the solution used in the Beeghly method for the extraction of aluminum nitride from steel. X-ray diffraction patterns of these residues, obtained by means of a spectrometer and by a 57 mm Debye-Scherrer powder camera using filtered cobalt or chromium radiation, are given in Table II along with the pattern obtained by

Jan 1, 1953

By Jack Washburn, E. R. Parker

Kinking in zinc single-crystal tension specimens was observed under conditions of low stress and high temperature. Kinking is discussed in relation to other plastic bending phenomena on the basis of dislocation theory. Experiments on the stress-induced motion of small angle boundaries are reported. KINKING was first reported by Orowan1 as a new deformation mechanism. He observed the phenomenon in cadmium single crystals loaded in compression. Glide lamellae in a local region of the rod were observed to snap over suddenly to a tilted position, resulting in a sudden shortening of the specimen. Between the tilted portion and the rest of the crystal there were fairly sharp boundaries, with the slip plane assuming approximately mirror image positions on opposite sides of these boundaries. Orowan considered the boundaries to be regions where dislocations had concentrated. Hess and Barrett' observed the formation of kinks in critically oriented zinc compression specimens. It was found that the sudden snapping over of the tilted region was not an essential part of the kinking phenomenon but rather was associated with the method of loading. Kinking was explained on the basis of the accepted mechanisms of slip and flexural glide. It was also suggested that a kink can be considered as a special type of deformation band. During a recent investigation of the effect of surface condition on creep of zinc single crystals," a similar phenomenon was observed in crystals which were loaded in tension. The specimens were 0.4 in. diam cylindrical rods with a free length of 4 in. between end connections. All of the crystals were tested at a constant load. adjusted to give an extension rate of approximately 0.05 pct per hr. Kinking, as shown in Fig. 1, occurred in some of the tests performed at temperatures above 200°C. Kinking was observed in specimens varying widely in initial orientation, scattering about a 45" angle between the slip plane and the specimen axis. The condition leading to kinking in tension appeared to be non-uniform distribution of flow along the gage length combined with the restraint imposed by the tensile load. At low temperatures and fast strain rates, the distribution of strain throughout the midsection of tension specimens was generally quite uniform; therefore, bend planes developed only near the ends as described by Miller.4 However, at high temperatures under creep conditions it was difficult to obtain specimens in which the distribution of flow was uniform. Some of the factors which may have caused differences in flow stress along the length of the crystals are: Nonuniform distribution of impurities, accidents of growth (lineage structure), slight bending or other damage during handling, surface conditions, and strain-aging characteristics due to dissolved nitrogen." Plastic flow, once started in a local region, often continued to a relatively large strain before other parts of the gage length became active. Under these conditions a series of kinks, such as those in Fig. 1, were produced. Fig. 2 illustrates how a nonuniform distribution of slip produces bending moments which- are responsible for kink formation. If no plastic bending were to occur while the rod extended by pure slip in two separate sections of the rod, it would assume a shape such as that in Fig. 2a. A specimen having this shape and being subjected to a tension load would have concentrations of stress at the concave surfaces C and lower than average stress would exist at the convex surfaces D. Therefore a bending moment is superimposed on the average stress in the regions between C and D. The positions of potential bend planes under these conditions are shown as dotted lines. Actually no such shape as Fig. 2a develops because plastic bending in the region C-D occurs simultaneously with pure slip in the intervening regions. The observed structure of a tension kink is indicated by Fig. 2b. Perhaps the best approach to an understanding of kinking as well as other related plastic bending phenomena, such as the bend planes discussed by Miller,' cell formation studied by Wood et al.,6 and polygonization,7 is consideration of the dislocation model of a bent lattice. Current theories of the slip process postulate generation or multiplication of dislocations at certain lattice imperfections. The mechanism proposed by Frank and Read8 results in continuous generation of concentric dislocation loops which spread out

Jan 1, 1953

By M. Bevis, E. O. Fearon, P. C. Rowlands

Fe-Ni and Fe-Ni-C martensite specimens have been deformed in compression at room temperature and the habit planes of operative deformation twins determined by two-surface optical trace analysis. The full orientations of the martensite crystals were determined from divergent X-ray beam diffraction patterns. The experimental results are in excelled agreement with predicted twinning modes. In particular, the habit planes of some deformation twins in bcc martensites are consistent with a "Type XI compound'' twinning mode with Kl, Kz, 71, 77~ elements given by {5, 8, 11) {ioi}, (33) (ill) Tetragonal derivatives of this mode are operative in bct martensites. UnUSUAL deformation twinning modes have been reported by Richman' to occur in Fe-Ni-C martensites with bcc and bct structures. The twin habit planes were determined by single-surface trace analysis (pole locus method) and the remaining twinning elements were determined from the geometry of twin-twin intersections. The indices assigned to the observed habit planes are (3 101, "(089)" and "{0, 1,13)" or "{1,2,7} ", and only in the first case do the twinning elements correspond to a predicted twinning mode. This is mode 1.4 in the paper by Bevis et al. The results presented in Ref. 2 indicate that previously unpublished bcc and bct modes should be operative in preference to the (130) mode and anomalous modes reported by Richman. In view of these results and the uncertainties involved in determining habit planes from single-surface trace analysis and twinning elements from twin-twin intersections5 a two-surface trace analysis of deformation twins in Fe-Ni and Fe-Ni-C martensites has been carried out. EXPERIMENTAL PROCEDURES Two alloys with compositions Fe-23 pct Ni-0.6 pct C and Fe-30.4 pct Ni were prepared from 4N pure materials by induction melting under a vacuum of 10"5 mm Hg. The alloys were homogenized at 1350'~ for 5 days. Both of these alloys are austenitic at room temperature with M, temperature - — 50"C. The aus-tenite grain size of the Fe-Ni-C alloy was approximately 300 to 400 p. The Fe-Ni alloy was remelted in a vertical tube furnace and the melt lowered slowly from the hot zone of the furnace to produce s ingle -crystal austenite specimens. Specimens approximately 10 by 5 by 5 mm were cut from the ingots and quenched to various temperatures below the Ms temperature. The specimens were elec-tropolished in a 10 pct perchloric acetic electrolyte before being deformed in compression at room temperature. Martensite plates which exhibited profuse deformation twinning were selected for analysis and the specimen polished on a second surface such that the two surfaces which contained the martensite plate enclosed an obtuse angle of approximately 145 deg. The specimens were then electropolished to reveal the traces of the deformation twins on both surfaces. The full orientations of the martensite crystals were determined using a divergent X-ray beam technique (Kossel line technique) employing an AEI SEM2 electron probe microanalyzer. Details of this technique which include a detailed description of the Kossel camera attachment to the microanalyzer used in the present experiments have been discussed elsewhere.3 Only additional details relevant to this investigation are discussed here. The specimens were mounted with one surface normal to the incident electron beam as illustrated schematically in Fig. 1. The martensite plates to be analyzed were located using the normal scanning equipment of the microanalyzer. The position of the electron beam and hence the position of the source of divergent X-rays generated within the crystal could be located to within 1 p. Exposure times of approximately 8 to 10 min were required for back-reflection Kossel patterns and it was found that useful diffraction patterns could be obtained consistently from heavily deformed martensite plates. A reference line (carbon contamination mark) produced on the two surfaces of the specimen by scanning the electron beam in a direction having a known relationship with the reference !ine in the X-ray camera enabled the full orientation of the crystals to be determined. Martensite plates with widths as small as 8 p could be oriented using this procedure. The Kossel line patterns were interpreted using the charts developed by Rowlands and ~evis~ as generally

Jan 1, 1969

By A. V. Bradshaw, R. I. L. Guthrie

The behavior of large bubbles in the size range 4 to 25 cm3, rising through molten silver, has been studied. It was found that rising velocities were equivalent to those in aqueous systems of low viscosity. Mass transfer coefficients for oxygen bubbles dissolving in silver were found to be 0.036 ± 0.007 cm sec-1, being close to those predicted for transfer through the front surface of the spherical cap bubble only. It is suggested that the surface active nature of oxygen in silver could account for the relatively low coefficients obtained. MANY metallurgical processes involve interactions between gas bubbles and liquids. Examples include the removal of carbon monoxide in Open Hearth Steelmak-ing, the removal of sulfur by blowing air through copper matte during converting, and the removal of hydrogen from steel during vacuum degassing or inert gas flushing. The steps involved in such refining processes include; transport of the dissolved species to the bubble interface, adsorption and chemical reaction of the species at the interface, desorption of product molecules from the interface, and transport of product gas into the bulk gas phase of the bubble. It has been concluded1 that all the interfacial steps involved proceed so rapidly at steelmaking temperatures that transport of the solutes, present in the metal, become the important rate controlling factors provided nucleation phenomena are not restrictive. The O-Ag system was chosen for the investigation into gas bubble-molten metal interactions due to the relatively high solubility of oxygen that enables rates of oxygen transfer to be measured from changes in bubble volume. Other advantages of this system include the absence of a stable oxide phase at an oxygen pressure of 1 atm and the relatively low melting point of the metal which permits the use of a metallic container, providing that it is resistant to oxidation. In those metallurgical processes where bubbles have an important influence, bubble volumes are usually greater than 5 cm3. For this reason the present study relates specifically to single large bubbles of oxygen rising in silver. These bubbles adopt the characteristic spherical cap shape similar to that shown in Fig. 1 for a 30 cc bubble rising in water. After an initial investigation to determine the velocities of inert (nitrogen) bubbles rising in molten silver, experiments were carried out with oxygen and the rates of mass transfer between the oxygen bubbles and the silver were measured. EXPERIMENTAL Apparatus. The apparatus, Fig. 2, for containing molten silver, was constructed from "Nimonic 75" Alloy (75 pet Ni, 20 pet Cr, 5 pet Fe, Mn) and provided for the release of single bubbles from an hemispherical cup, situated at the bottom of the column. The cup was turned by translating the rotation of the drive shaft through 90 deg. This was accomplished by the use of a bevelled gear system, and a smooth drive was provided by the lubricating action of the silver on the gears. Since reliable high temperature seals at 1000°C were found to be impracticable, the filling and drive shaft tubes were extended outside the 3.5 kw resistance wire tube furnace, where connections were made using easily accessible O-ring seals. The apparatus remained gas tight to the atmosphere at pressure differentials far in excess of those used. The filling tube was connected via a small bore tube to the differential pressure transducer. Gas could be bubbled into the inverted cup from two i-in. tubes which passed down the inside of the column to preheat the gas. The temperature of the silver was maintained at 1020°C during all experiments. Measurement of Bubble Volume. In order to calculate mass transfer rates, it was necessary to obtain a continuous record of the bubble's volume during its passage through the column of molten silver. The method adopted for measuring the bubble volume involved closing off the top gas space to the atmosphere prior to each experiment, and recording the variation in gage pressure of this space during the formation and rise of the bubble. Since any change in bubble volume results in an equal change in top space volume, Boyles Gas Law may be applied (for isothermal con-

Jan 1, 1970

By D. R. Bomberger, M. Deul

An automatic microscope has been developed to measure the size and populations of macerals and minerals in fine coal particles. Differentiations are made on the basis of reflectance. This study is concerned with the size distribution of pyrite inclusions. Most fine coal cleaning processes do not remove pyrite as completely as a straight density separation. Consideration of the pyrite size distribution is suggested as a more accurate method of predicting sulfur reduction by a cleaning process. Analyses of float-sink results and Deister Table operation in terms of pyrite particle sizes are made. Other potential applications of automatic microscopy are also discussed. In the study of coal cleaning by pseudo-gravity methods (tables, cyclones, hydrotators, etc.), it is customary to express the deficiency of the process relative to float-sink measurements in some form of "percent efficiency". These have been calculated in many different ways in order to provide a means of extrapolation of test data to untested coal feeds. This works quite well with coarse coal (here defined as larger than one-eighth in.). Large, heavy pieces of refuse are rejected rather thoroughly by many cleaning processes, and the efficiencies relative to float-sink results approach 100%. In coarse coals, the difference in the sizes of fine pyrite is masked by the averaging effect of the large coal envelopes. The existence and fate of fine pyrite is often hidden in the larger numbers representing coarse (and easily removed) pyrite. There are cases where it is desirable to subject fine coal (here defined as smaller than one-eighth in.) to cleaning processes. This is true of naturally occurring fie coal streams and in cases where comminution followed by cleaning is necessary to provide the quality desired. It is in this area that the use of process efficiency relative to float sink fails. Percent efficiencies decline to very low figures, and equivalent separation densities become a matter for conjecture. The net result is that an attempt to estimate product quality from float-sink data and a process efficiency figure often results in large errors. This work represents a new approach to the problem by observing the fate of pyrite particles, grouped by sizes, in a cleaning process. Examples are given which relate pyrite size measurements to float-sink washability and to a Deister Table operation. EXPERIMENTAL WORK The automatic microscope used here has been previously described.' Briefly, it is an instrument which measures the diam of particles (as defined by a range of reflectance) exposed on a polished specimen. The instrument scans a sample briquet, measures diam of exposed pyrite inclusions and records the data by size intervals. Preparation of the briquet is critical, due to the automatic nature of the process. The principal requirement is for an optically flat surface, so that focus will be maintained as the motorized stage moves the specimen under the lens. The various substances present must be polished to the same level in spite of the wide difference in hardness between coal substance and minerals. The polishing method must not pluck out small grains, which might be rather loosely held by surrounding coal. The procedure below was successful in producing all of these results. The coal sample (8 mesh or finer) was riffled (a micro vibrating riffle is essential) to obtain 15 g. One volume of Lucite powder (thermosetting plastic mounting medium) was mixed with three volumes of coal and mixed thoroughly. A briquet was formed using a cylindrical die (1 1/4 in. diam) at 3000 lb per in.* pressure and 150°C. Preparation of the optical surface was accomplished on automatic polishing equipment, according to the following schedule: 1) Grinding: 3 stages, using successively fine Carborundum grits of 180, 320 and 600 mesh. 2) Rough polishing: 2 stages, using 3µ alumina on cast iron, followed by 1µ alumina on lead. 3) Fine polishing: 2 stages, using 0.5µ alumina on napless broadcloth over bronze, followed by 0.1µ alumina on silk filament cloth over bronze. Raw data were corrected for the fact that the chords

Jan 1, 1964

By D. C. Seidel, E. F. Fitzhugh

The cementation of nickel from acidic solutions by metallic iron is discussed. The cementation is carried out in pressure vessels at temperatures above 100°C. The results from bench scale studies on variables such as retention time, temperature, and solution pH are presented. A continuous processing flowsheet is proposed. Cementation is one of the oldest known hydrometal-lurgical reactions. The cementation of copper on iron was recorded by 'Paracelsus the Great' in about 1500,1 and by 1600 the technique was being used to recover copper at the Rio Tinto operations in Spain.2 At least one early author felt that cementation may have been one of the primary reasons for the alchemists' belief in the transmutation of metals.' The early writings state that when iron was placed in the clear waters from some mountain springs, the iron disappears and copper is found in its place. To the alchemists this may well have been one of the most convincing proofs that transmutation could and did occur. Since these early times the recovery of copper from acidic solutions by cementation has been practiced in plants throughout the world. Probably the cementation technique in some form has been common to more copper mining and milling operations than any other single recovery process. During current hydrometallurgical extraction studies, which were sponsored by the Republic Steel Corp. at the Colorado School of Mines Research Foundation, Inc., it was found that under the proper conditions, metallic nickel could be cemented from acidic solutions by powdered iron. The reactions are apparently similar to those that occur during the cementation of copper, but the nickel cementation had not been anticipated because iron and nickel are nearly adjacent in the electromotive series. The potential difference between iron and copper is approximately 0.78 v, while the potential difference between iron and nickel is less than 0.21 v. The cementation of nickel with iron at room temperature is almost negligible, but when the reaction is carried out in a closed vessel at temperatures in excess of 100°C, the nickel can be cemented almost quantitatively. The part played by this discovery in a practical method of nickel recovery is set forth in a separate paper.3 The following paragraphs are a discussion of experimental studies that were made to investigate this cementation reaction. The technique has been designated the HTC or High Temperature Cementation procedure. The cementation work was part of a study on hydrometallurgical techniques for the extraction of nickel from the garnierite or silicate type nickel ores. A hydrothermal extraction procedure had been developed, and this technique produced an acidic pulp or solution that contained both nickel and appreciable amounts of magnesium.3 Small quantities of ferric and ferrous iron were also present along with cobalt, manganese, and chromium. The potential for recovering the nickel from these acidic solutions by ion exchange or solvent extraction did not appear to be promising because of the relatively high magnesium content. The Ni ++ and Mg++ have nearly identical ionic dimensions and tend to be co-absorbed or extracted during ion exchange or solvent extraction treatments. Preliminary tests indicated that the nickel could be precipitated as a sulfide when using the high pressure H2S precipitation technique developed for the Moa Bay operations of the Freeport Nickel CO.4 This technique gave good recoveries, but the nickel sulfide product requires considerable additional processing before a marketable form of nickel is realized. The process also requires clarified feed solutions, and the solids-liquid separations on the garnierite residues are difficult. A program was initiated to investigate alternate procedures that might shorten the route to a marketable nickel product, and hopefully also permit bypassing the difficult solids-liquid separation steps required for the H2S precipitation technique. It was during these studies that the nickel cementation reaction with iron was encountered. EXPERIMENTAL EQUIPMENT AND PROCEDURES The bench scale precipitation tests which were conducted during this experimental program were made in 2-liter stirred autoclaves.* A photograph showing the form and arrangement of the autoclave

Jan 1, 1968

By T&apos Ke, ing-sui

NUMEROUS investigators have observed that internal friction accompanies cold-working of metals and the effect of annealing is to reduce this internal friction.1,2 However, - most of the experiments were made at high stress amplitudes and the principal purpose was to study the increase of internal friction as a result of the applied cyclic stress during measurement. In order to study the internal friction introduced by cold-working applied prior to the measurement, the stress level applied during the measurement of internal friction must be sufficiently small. The results of measurement are significant and can be used for a base of comparison only when the applied cyclic stress is so small that the internal friction is independent of stress amplitude. Internal friction of cold-worked metals under small stress level has been studied by a number of workers8 -" he internal friction was measured around room temperature with a frequency of vibration of the order of kilocycles per second. The purpose of this paper is to report a study of the change of internal friction when severely cold-worked aluminum was annealed at successively higher temperatures until it was completely recrys-tallized. The measurements of internal friction were made over a range of temperature extending from room temperature up to the temperature of prior anneal. The frequency of vibrations used was about one cycle per second. The apparatus used for the internal friction measurements to be reported in this paper was a torsion pendulum with the specimen in wire form as the suspension fiber. The description of this apparatus and the method of measurement have been previously given.7,8 The applied stress was sufficiently small SO that the magnitude of internal friction is independent of stress level at each temperature range concerned. Corresponding to this stress the maximum shearing strain on the surface of the specimen is of the order of l0-5 and lower. The in- ternal friction (Q-1) is reported as 1/p times the logarithmic decrement. Internal Friction Versus Temperature of Anneal: Fig. 1 shows the internal friction measurements performed upon 99.991 pct aluminum subjected to 95 pct reduction in area. The final diameter of the wire is 0.033 in. This figure gives a general survey of the effect of temperature of anneal and of temperature of measurement. The internal friction of the cold-worked specimen was first measured at room temperature. It was then annealed at 50°C for one hour and the internal friction measured at 50°C and at room temperature. The same wire was successively annealed at higher temperatures for one hour and measurements were taken at the annealing temperatures and lower temperatures as before. Such a procedure was followed in order to stabilize the internal friction at the temperature of measurement so that during the measurement which generally takes about half a minute, there is no detectable change in internal friction. This series of measurements .was made up to 450°C. After each annealing a short test piece of the specimen, which had received the same past thermal and mechanical treatments, was taken out for metallographic examination. It is seen from fig. 1 that up to the annealing temperature of 250°C we have the following observations: for any given temperature of measurement, the internal friction is lower the higher the temperature of prior anneal. When the annealing temperature is 290°C or higher, the internal friction at the annealing temperature drops abruptly to a value which is much smaller than that for the previous curve. Metallographic examinations showed that the recrystallization of the specimen was completed after the annealing at 290°C. Fig. 1 shows that, as far as internal friction is concerned, there is no abrupt transition between the processes of recovery and recrystallization. Averbach has also reached the conclusion that recovery may be a process analogous to recrystallization on the basis of X ray extinction measurements in brass." The effect of annealing temperature upon the internal friction at room temperature is shown by curve I of fig. 2. In this figure the internal friction at room temperature was plotted as a function of annealing temperature. It is seen that the internal friction decreases rapidly at first with an increase

Jan 1, 1951

By T. Yamasaki, S. Usu

Adsorption of potassium dodecyl xanthate from aqueous solutions on artificial and natural zinc sul-fides was studied by means of infrared absorption spectroscopy. The adsorption species and their stabilities varied depending upon the conditions of the surfaces of the zinc sulfides. Adsorption products were analyzed after they had been removed from the surface with pyridine. Zinc dodecyl xanthate was confirmed for surfaces covered with oxidized products while dodecyl alcohol and carbon disulfide were detected on purified or weakly oxidized surfaces. It is of great significance to study the adsorbed species of collectors on the surface of sulfide minerals with a view of increasing our understanding of the mechanism of flotation. Compared with other methods, infrared spectroscopy promises to be of particular value in determining the nature of the species adsorbed at the mineral/solution interface since it gives direct identification of the adsorption products; and, furthermore, it has an advantage over the electron diffraction technique which has been employed in similar problems in that infrared spectroscopy utilizes radiation of very low energy so that the probability of changing the unstable surface films during examination should be correspondingly decreased. Infrared spectroscopic studies concerned with sulfide mineral flotation have already been reported by several investigators on zinc sulfide-hexanthi01' and lead sulfide-xanthate2,3 systems. The purpose of the present study was to investigate the adsorption of potassium dodecyl xanthate (KDX) at the zinc sulfide-aqueous solution interface by means of infrared spectroscopy. Rarely is the pure zinc sulfide-xanthate system encountered in practical flotation since zinc sulfide is usually activated with small amounts of certain metallic ions, such as copper ion. However, investigation of the pure zinc sulfide-xanthate system appeared promising for studying the fundamental mechanism of the adsorption of xanthate on the sulfide minerals. Although there are few cases where xanthates having an alkyl radical higher than hexyl are employed in practical operations, KDX was used in this study since it was reported that the adsorbability of xanthate on zinc sulfide was increased with an increasing number of carbon atoms of the alkyl radicals.4 EXPERIMENTAL Samples: Experiments were made on artificial zinc sulfide and natural sphalerite. The artificial zinc sulfide was obtained commercially from Dainihon Toryo Co. as a fluorescent pigment of the purest grade A. Considering the fact that there are often cases where the surface of sulfide minerals are apt to be oxidized so that the adsorption of xanthate at sulfide mineral/solution interfaces may be substantially affected, two different procedures were employed in preparing the samples of the artificial zinc sulfide. 1) The zinc sulfide was washed with hot concentrated ammonium chloride solution (300 g per liter) to remove surface oxidation products and followed by washing with deoxygenated hot distilled water by centrifugation until the constant electric conductivity of the solution was reached (Sample I) (specific conductivity of the solution = 8.6 x l0-5 ohm-' cm-'). 2) Sample I in a suspension of 5% by weight was oxidized with a 1.5% aqueous hydrogen peroxide solution for about one hour, and then was washed with distilled water as mentioned in the preparation of Sample I (Sample 11) (specific conductivity of the solution = 1.0 x 10"4 ohm-' cm-'). Both Samples I and II were dried under vacuum and stored in a vacuum desiccator. The specific surface areas of the samples determined by the BET method using carbon dioxide gas were 19 x l04 cm2 per g for Sample I and 35 x l04 cm2 per g for Sample 11. In addition, a sample which was derived from Sample I was also prepared. In 40 ml of 3 x 10-2 M zinc sulfate solution was placed 2 g of Sample I for 2 hours, washed with distilled water by successive centrifugation until no sulfate ion could be detected and dried under vacuum (Sample 111). The purpose of this treatment will be described later. Natural sphalerite was carefully selected by hand, ground in a mechanical agate mortar for about 40

Jan 1, 1965

By J. W. Sandelin, L. S. Birks

The group five metals, vanadium, niobium, and tantalum all show cold-rolled textures of {100)(011) and {112)(0ll) with a preference for the (100) in vanadium and niobium and for the {112) in tantalum. Recrys-tallization texture of (100) and (111) was reported1 for vanadium after annealing (no temperature stated). For tantal~m ,~ annealing below 1200°C strengthened the (112) texture but the (111) texture increased and was predominant as the annealing temperature was raised to 2500°C. Annealing niobium up to 1100°C strengthened the ( 100) texture and developed a weak (111) texture.' In the present work niobium has been annealed up to 2000°C. Nearly 70 pct of the grains showed {111) texture with only a weak (112) component and an insignificant (100) component remaining. In addition, double-crystal rocking curves were used to follow the increase in crystal perfection of the grains with increased annealing time. Material and Treatment. Samples i by 4 in. were sawed from & -in.-thick cold-rolled niobium sheet obtained from Wah Chang. Chemical analysis of the material showed it to be 99.4 pct pure with tantalum as the major impurity. Individual pieces were annealed for 2, 15, 30, and 60 rnin in a vacuum of 10'* Torr using an rf generator. They were etched until the grain boundaries were well-defined, Fig. 1. Average grain size varied from 1 mm for 2 min annealing to 2 mm for 60 rnin annealing. Experimental Results. Preferred Orientation. The orientations of 97 of the 117 grains in the specimens of Fig. 1 were determined by back-reflect ion Laue patterns. A General Electric 10-cm-diam cylindrical camera was used rather than the conventional flat camera in order to record more of the low-index spots. The method proposed by Forest, Barton, and schieltz4 was used to transform the cylindrical film patterns to standard stereographic projections. Table I gives the compilation of data. Even 2 rnin anneal at 2000°C is sufficient to yield a strong (111) preferred orientation, and the percentage of grains with this orientation increases steadily with annealing time at the expense of all other orientations. Crystal Perfection. X-ray topographs were taken of each specimen in both the (111) and (112) orientation using the method described by Birks and Grant.' As the anneal time increases, the grains become larger and the individual reflections become slightly more uniform in intensity, indicating an increase in crystal perfection. For a more quantitative measure of crystal perfection, it was necessary to measure the double-crystal rocking curve. The spectrometer employed was a Gaertner instrument of Compton design. LiF was chosen for the first crystal because the (400) reflection with d spacing of 1.05 AU is a good match to the (222) niobium reflection with d spacing of 0.95 AU. CuKp radiation was used in order to further reduce the d spacing mixmatch correction.' A variable aperture was placed between the LiF and the niobium specimen so that a single grain or even a small portion of a grain could be examined. Fig. 2 shows typical rocking curves for the four annealing times. For the 2-min specimen, a single peak is observed with 10' of arc full-breadth at half maximum. As the annealing time is increased to 15 or 30 min, several sharper peaks of 40 to 80" breadth can be seen within a single grain. After 60 rnin anneal only a single peak of about 30" is observed. Table I1 shows the corrected rocking curve breadths and the dislocation densities, ND. The latter were calculated from the equation7 where W is the corrected rocking curve breadth at half maximum in radians and b is the effective Burger's vector. For (110)(111) slip in niobium, b is 2.86 AU. Discussion. The annealing of cold-rolled niobium at 2000°C causes rapid preferential growth of grains with {ill} orientation. After only 2 rnin annealing time, 35 pct of the grains have the (111) orientation, and after

Jan 1, 1968

By L. B. Harris

Continuous cyclic unloading during tensile work hardening of polycrystalline zinc at room temperature enables specimens to sustain greatly increased extension. Such enhanced ductility is associated with creep-type extension, during which the cyclic component appears to promote relaxation of internal strains. It is possible to trace the transitions from tension, through enhanced cyclic extension, to fatigue and relate the observed behavior to simpler types of deformation. DISTINCTIVE deformation behavior has been shown to occur when loading includes both cyclic and unidirectional components. For aluminum and copper extended by a sequence of progressively biased strain reversals, coffin1 observed greater fracture ductility and lower flow stresses than during monotonic tension. This may be compared with the reduction in hardness obtained from conventional fatigue softening. But fatigue softening is accompanied by enhanced fatigue life,' whereas Benham3 found that fatigue life was reduced when copper continuously extended during axial load cycling. The corresponding specimen elongation, for large cyclic load amplitudes, was greater than during normal tension. Under different conditions, Bendler and wood4 found that torsional fatigue initiated extension in copper under low tensile loads previously in equilibrium with the specimen; fatigue life was again reduced. Thus there is a type of cyclic softening which is associated with reduced fatigue life and which occurs when the cyclic loading is accompanied by a unidirectional strain component. Further, the fracture ductility or extension obtained from the unidirectional component can exceed that obtained in the absence of cyclic load. Specimen extension was not initiated by axial fatigue at small load amplitudes;3 hence Benham's work distinguishes between fatigue at large and small amplitudes, the former often being linked with unidirectional deformation because of similarities in strain Structure. The initiation of tensile extension during torsional fatigue,4 however, occurred with small amplitudes. Comparable changes in behavior have been ob- served during creep. kennedy' found that combined cyclic and creep stresses on lead at 32°C increased the rate of elongation over that for simple creep, the consequence being a reduction in creep life. It was also demonstrated that small cyclic stresses applied after creep deformation initially increased recovery, but that prolonged application produced only normal fatigue hardening. It is clear that physical properties can be changed by interaction between the cyclic and unidirectional deformations, but owing to the number of different ways in which the deformations can be combined and the large number of possible variables for each combination, trends of behavior become easily obscured. One definite conclusion is that enhanced ductility or increased extension can be obtained by cyclic action, and it is this process that has been investigated for the tensile test by measurements of the extra tensile strain produced by the addition of a cyclic tensile component. EXPERIMENTAL PROCEDURE Material. Specimens were 99.99 pct Zn wire of 1.6 and 2.0 mm diam. Mean grain diameter was 0.02 mm, sufficiently small to give a ductile necked-down fracture under all loading conditions. All experiments were conducted at an average temperature of 20°C. Normal Tension. Unidirectional tensile curves at different strain rates were obtained from an In-stron testing machine, on which load-time curves were recorded autographically, using gage lengths of 5 and 10 cm. Straining was at constant cross-head velocity, and quoted strain rates are with reference to initial specimen length. Measurements of total elongation under simple tension were also made on the tensile machine that had been modified to incorporate an added fluctuating load. Combined Tension and Rapid Cyclic Load. An electromagnetic vibrator was coupled to the elastic beam of a Hounsfield ensometer- and driven sinus-oidally from a power amplifier at frequencies from 20 to 360 cps, the flexible connecting links on the tensometer being replaced by rigid fixtures to eliminate lateral vibration in the specimen. One end of the specimen was pulled by the normal extension drive of the tensometer while the other end, fixed to the elastic beam and vibrator, was subjected to rapid oscillations of load. It was thus possible to apply cyclic load to a tensile test without altering the rate of extension of the specimen

Jan 1, 1964

By J. W. Snavely

A practical mathematical treatment is presented for the determination and control of conveyor belt acceleration, particularly for conditions of starting where vertical curves are involved. A typical sample problem is analyzed, with required calculations, to clarify the procedure. THE part that acceleration plays in starting a belt conveyor and its effect on belt conveyor design are well understood in a general way. Its practical importance is easily overlooked, however, and under some conditions, it is absolutely necessary to give the problem of acceleration detailed study. Most handbooks on conveyor belting design adequately present basic data for the determination of acceleration values. This paper will only attempt to present practical thinking and a convenient method of treatment of acceleration in belt conveyor design. Mathematical Analysis In working out the various problems of conveyor belt acceleration, the starting point, as presented by the handbooks, is the familiar formula of "force of acceleration is equal to the mass times acceleration." By expressing these fundamental quantities in terms of belt conveyor design, it is possible to arrive at the unsuspected conclusion that the acceleration time for horizontal belt conveyors is independent of the load, and instead, dependent upon the belt speed, the type of drive arrangement and drive pulley, and the idler coefficient of friction. The mathematics leading to this conclusion are shown in Table I, which has been prepared to show this derivation. While at first the conclusion just given may not seem to be reasonable, further reflection indicates that obviously the type of drive pulley and the type of drive do affect materially the tension in the conveyor belt, and thus, as clearly shown, the time of acceleration is dependent upon the factors mentioned. Inasmuch as all of the factors except time are predetermined by the belt conveyor design, it becomes relatively easy to establish the accelerating time and to reduce further this time determination to a simple graph from which the time in seconds can be read directly. Such a graph is given in Fig. 1. The table appearing on Fig. 1 should be explained further. For a given belt speed, the time of acceleration can be expressed as a percentage of the belt speed. The time of acceleration is also dependent on the drive arrangement, and changes in the drive arrangement consequently change the time of acceleration. It further follows that for a given belt speed, the time expressed as a percentage of that belt speed also changes with the type of drive. Obviously then, it becomes possible to graph the percentage of speed for .each type of drive against the belt speed and accelerating time, after which, for a given belt speed and type of drive, the time can be read directly in seconds. Two constants were established for Fig. 1, the first one being the limiting of the maximum acceleration tension to 35 pct of the full load operating tension in the belt. The purpose of this is to limit the total tension imposed upon the belt during the acceleration period to 135 pct of the full load operating tension, 'which is the amount required to start or breakaway the fully loaded belt conveyor from rest. The other constant is the friction factor used for the idler equipment, which has been established as 0.022. For installations where it is necessary to establish the values of acceleration, invariably high grade idler equipment is used, and it has been established from field experience that 0.022 for the idler friction factor is amply conservative. The use of this friction factor for idlers must be tempered with judgment, of course, for occasions will arise where more power than indicated is required to start, even with the very best of equipment, such as low temperature operations that tend to congeal the grease in the bearings and thus produce additional friction drag. An inspection of the table in Fig. 1 affords a convenient rule of thumb method for determining the acceleration time, which conveniently can be 5 pct of the belt speed in seconds. The 5 pct of belt speed figure is close to the average for most types of drives. In using Fig. 1 it must be emphasized that it applies accurately to horizontal belt conveyors only.

Jan 1, 1953

By J. F. Smith, J. E. Davison

A value for the enthalpy of formation of z2 of -3.14 i 0.21 kcal per g-atom has been measured by the technique of acid solution calorimetry. This result is in quite good agreement with two earlier determinations by tin solution calorimetry and by direct reaction caloriinetry, and averaging of values determined from the three independent calorimetric techniques gives enhanced precision and accuracy with AHh8 (CaMgZ) = - 3.15 i 0.05 kcal per g-atom. For comparison with experimental data, values for the enthalpies of formation of CaMgz, SrMgz, and BaMgz of -9.8, -7.9, and -2.8 kcal per g-atom were estimated from a calculation based on the LVigizer-Seitz approximation as modified by Raimes for polyvalent elements. While complete quantitative accord between these calculated talues and available experimental data is lacking, nonetheless numerical accord is better than might be expected and, more importantly, parallel numerical trends are observed between experimental and calculated vnlues. WITHIN the past decade the enthalpy of formation of CaMg, has been determined a) from measurement of magnesium vapor pressures over binary Ca-Mg alloys,' b) by solution calorimetry with liquid tin as the solvent,' c) from measurement of hydrogen vapor pressures over ternary alloys of calcium, magnesium, and hydrogen,3 and d) by direct reaction alorimetr. The value from tin solution calorimetry is the most precise and is probably the most reliable, and this value is within the quoted uncertainties of the other three experimental results. The overall agreement among the four independent investigations is quite good, particularly so when the diversity of techniques is noted. On the basis of this agreement, CaMgz was chosen as a test material to evaluate the operation of a newly constructed apparatus for the determination of enthalpies of formation of intermetallic phases by acid solution calorimetry. This was believed to be a severe test because of the high chemical reactivity of both calcium and magnesium which reactivity presumably accounts for the fact that an early determination5 of the enthalpies of formation of Ca-Mg alloys by acid solution calorimetry yielded values significantly more negative than the four recent determinations. EXPERIMENTAL APPARATUS AND MATERIALS Experimental Apparatus. The enthalpy of formation of CaMg, was determined by measuring the difference between the heat evolved when dissolving the metallic compound and the heat evolved when dissolving equivalent amounts of unreacted metallic elements in hydro- chloric acid. This was done differentially with an apparatus consisting of twin calorimeters which were constructed to be as nearly identical as possible. The advantage of differential calorimetry is that systematic errors arising from the individual calorimeter design tend to cancel. A schematic representation of the apparatus is shown in Fig. 1. A dead air space around both calorimeters was provided by a large, thermally insulated jacket. Each calorimeter consisted of a 2-liter Dewar flask which was completely enclosed in a copper container. Each Dewar contained 1600 g of 2.5hr HCl to act as the solvent, and thermal effects resulting from solvent evaporation were minimized by covering the acid with 50 g of mineral oil. There was no detectable reaction between the acid and the mineral oil. Equivalent amounts of mechanical energy were added to the calorimeters through twin stirring rods which were driven at the same rpm by a single motor with the intent of the stirring being to maintain thermal equilibrium throughout the solvent. To calibrate the heat capacities of the calorimeters, known amounts of electrical energy could be added by passing measured voltages and currents for known times through submerged heaters, approximately 20 ohms, which were wound noninductively from Manganin wire. A 6-v storage battery was used as a power source, and a dummy heater was used as an exercise circuit to allow the battery to stabilize at a constant electromotive force before energizing one or the other of the calorimetric heaters. A type K-2 potentiometer was used to measure the potential drop across an energized heater while the current was determined from the potential drop across an external standard resistor. Times of energization were measured with an electric timer, and the electrical energy supplied to a heater

Jan 1, 1969

By J. W. Snavely

A practical mathematical treatment is presented for the determination and control of conveyor belt acceleration, particularly for conditions of starting where vertical curves are involved. A typical sample problem is analyzed, with required calculations, to clarify the procedure. THE part that acceleration plays in starting a belt conveyor and its effect on belt conveyor design are well understood in a general way. Its practical importance is easily overlooked, however, and under some conditions, it is absolutely necessary to give the problem of acceleration detailed study. Most handbooks on conveyor belting design adequately present basic data for the determination of acceleration values. This paper will only attempt to present practical thinking and a convenient method of treatment of acceleration in belt conveyor design. Mathematical Analysis In working out the various problems of conveyor belt acceleration, the starting point, as presented by the handbooks, is the familiar formula of "force of acceleration is equal to the mass times acceleration." By expressing these fundamental quantities in terms of belt conveyor design, it is possible to arrive at the unsuspected conclusion that the acceleration time for horizontal belt conveyors is independent of the load, and instead, dependent upon the belt speed, the type of drive arrangement and drive pulley, and the idler coefficient of friction. The mathematics leading to this conclusion are shown in Table I, which has been prepared to show this derivation. While at first the conclusion just given may not seem to be reasonable, further reflection indicates that obviously the type of drive pulley and the type of drive do affect materially the tension in the conveyor belt, and thus, as clearly shown, the time of acceleration is dependent upon the factors mentioned. Inasmuch as all of the factors except time are predetermined by the belt conveyor design, it becomes relatively easy to establish the accelerating time and to reduce further this time determination to a simple graph from which the time in seconds can be read directly. Such a graph is given in Fig. 1. The table appearing on Fig. 1 should be explained further. For a given belt speed, the time of acceleration can be expressed as a percentage of the belt speed. The time of acceleration is also dependent on the drive arrangement, and changes in the drive arrangement consequently change the time of acceleration. It further follows that for a given belt speed, the time expressed as a percentage of that belt speed also changes with the type of drive. Obviously then, it becomes possible to graph the percentage of speed for .each type of drive against the belt speed and accelerating time, after which, for a given belt speed and type of drive, the time can be read directly in seconds. Two constants were established for Fig. 1, the first one being the limiting of the maximum acceleration tension to 35 pct of the full load operating tension in the belt. The purpose of this is to limit the total tension imposed upon the belt during the acceleration period to 135 pct of the full load operating tension, 'which is the amount required to start or breakaway the fully loaded belt conveyor from rest. The other constant is the friction factor used for the idler equipment, which has been established as 0.022. For installations where it is necessary to establish the values of acceleration, invariably high grade idler equipment is used, and it has been established from field experience that 0.022 for the idler friction factor is amply conservative. The use of this friction factor for idlers must be tempered with judgment, of course, for occasions will arise where more power than indicated is required to start, even with the very best of equipment, such as low temperature operations that tend to congeal the grease in the bearings and thus produce additional friction drag. An inspection of the table in Fig. 1 affords a convenient rule of thumb method for determining the acceleration time, which conveniently can be 5 pct of the belt speed in seconds. The 5 pct of belt speed figure is close to the average for most types of drives. In using Fig. 1 it must be emphasized that it applies accurately to horizontal belt conveyors only.

Jan 1, 1953

By W. C. Thurber, C. J. McHargue

THE deformation textures of metals have been extensively studied because of both the practical implications in metal fabrication and the fundamental insight into the behavior of the metal during deformation. Most studies have been concerned with pure metals or solid-solution alloys and relatively little attention has been directed toward more complex alloy systems. Barrett' and Brick2 have summarized work on multiphase systems in terms of the relative ease of deformation of the phases. Thus, if the phases are deformed about equally, each develops its usual texture for the particular fabrication process. This behavior has been reported for Ag-Cu and Cd-Zn alloys3 and 62-38 brass.4 A dispersion of hard particles in a softer matrix interferes with the normal reorientation of the matrix lattice during deformation, thus distorting the texture or in some cases preventing its development. Increasing the amount of carbon in steel has been observed to increase the randomness of the ferrite5 and almost random textures have been reported for A1-12 pct Si eutectic alloy wires.6 It has also been noted that if the second phase is platelike, deformation causes the platelets to line up in a common direction. The present work concerns a quantitative study of the deformation textures in aluminum-uranium alloys containing 5 or 13 wt pct U. Alloys in this composition range are characterized by a pure aluminum matrix in which the intermetallic compound UA14, is dispersed. From a fundamental standpoint, this system affords the opportunity for studying the effects of a dispersed phase on texture development in an essentially pure metal matrix. Further, these alloys are commonly used as fuels for nuclear research and testing reactors, and a knowledge of the preferred orientation may be useful in evaluating physical and mechanical properties as well as response to fabrication. The deformation textures in sheets of aluminum (99.996 pct), Al-5 pct U alloy, and Al-13 pct U alloy were determined for reductions in thickness of 90 pct by cold rolling. The texture in an alloy rod of the latter composition which had been extruded at 455°C was also determined. It can be readily ascertained from the aluminum-uranium phase diagram that the 5 pct U alloy is hypoeutectic and contains 7.3 wt pct (3.4 vol. pct) UAl4. The 13 pct U alloy has the eutectic composition and contains 18.9 wt pct (9.4 vol. pct) UAl,; however, because of nonequilibrium solidification conditions, the typical eutectic microstructure was not developed. The alloys were prepared by open-air melting in graphite crucibles. The slab castings were cropped and cold reduced 90 pct in thickness on a two-high mill. The slabs were reversed after each pass. Although the uranium-bearing alloys exhibited edge cracking, they could be cold rolled to the desired thickness. Small coupons 1.5 by 0.75 by 0.1 in. thick were sheared from the center of the rolled plate with a major axis parallel to the rolling direction. To obtain a specimen of sufficient thickness for machining of the X-ray diffraction specimen, three coupons were laminated into a single three-ply sandwich with a suitable adhesive. Adhesives which could be cured at room temperatures were selected in order to prevent recrystallization during bonding. Bondmaster M-648 (Rubber and Asbestos Corp.) was used for the pure aluminum laminate and Armstrong A-6 (Armstrong Products Co.) was used for the alloys. The alloy for extrusion was cast in a cylindrical graphite mold! cropped and machined into a 3-in. diam by 4-in. long billet. This billet was preheated to 455°C, upset to 3.125 in. diam, and extruded on a 700-ton hydraulic press at a speed of 6 fpm through a flat-face, 1-in. diam die. The rod was quenched with a water spray as it emerged from the die. Pole-distribution data were obtained using the diffractometric method described by Jetter and Borie.7 A spherical X-ray diffraction specimen of

Jan 1, 1961

By R. F. Stewart, A. W. Hall

A method has been developed for continuously measuring the moisture content of coal. The method is based on the thermalization of fast neutrons by hydrogen in the coal. Neutrons from a small radio-isotope source penetrate the coal, are scattered by hydrogen, and measured by a thermal neutron detector. The number of thermal neutrons counted can be directly correlated with the moisture content of coal. In a pilot-scale system, moisture was measured continuously within 0.2% in coal moving at rates up to 20 tph. The method is adaptable in industry for continuously measuring the moisture content of coal at high tonnage flow rates. Such an application would permit continuous recording of moisture in coal without sampling and facilitate quality control. An automatic and continuous method of measuring the moisture content of coal is needed by the coal industry. Automatic control of the coal quality would reduce the cost of coal preparation, improve the product, and thus indirectly increase the use of coal. Moisture in coal can be determined by several methods, but the time required to obtain samples and analyze them by existing methods makes it difficult, if not impossible, to control the quality of the product. Both producers and consumers need a method for continuous and instantaneous measurement of moisture content without sampling in order to regulate process equipment and keep the moisture content of coal within specifications. At the Morgantown, W. Va., Coal Research Center we are developing a nuclear method for continuous measurement of moisture in coal. This method is based on the thermalization of fast neutrons by hydrogen in the water and organic matter of coal. Neutrons from a small radioisotope source penetrate the coal, are scattered by hydrogen, and are measured by a thermal neutron detector. The number of thermal neutrons counted can be directly correlated with the moisture content of coal. Design of a moisture meter based on neutron thermalization depends on many variables, any or all of which can affect the sensitivity of the meter. These factors include those related to the nuclear aspect; type and size of neutron flux and source, type of detecting device, and background count; and those related to the coal being tested: rank, particle size, and ash content. A survey was initiated to eliminate the relatively insignificant factors and to ascertain the magnitude of the major effects. Such information was necessary to fully evaluate the technique and to establish design criteria. Coal contains a relatively large amount of hydrogen in the organic coal substance and the water of hy-dration of the shaly material as well as in the moisture. To apply this concept of moisture measurement to coal requires that the organic substance in coal from any one seam of a particular mine be uniform in hydrogen content. The difference in total hydrogen content of wet and dry coal is relatively small, so that a moisture measurement based on this concept requires a measurement between two large numbers to a high degree of precision. Thus, it was necessary to develop a highly precise instrumentation system for continuous measurement and to obtain a physical arrangement permitting measurement of moving coal with a minimum effect from density variation. EXPERIMENT WITH TRAYS OF COAL Tests were conducted with metal trays containing SO to 100 lbs of coal to develop an instrument system of high precision. A scaling system with a maximum instrument error of 0.2% was used to test different types of thermal neutron detectors. The most suitable type of detector was a boron-10-lined proportional counter tube. While this type of detector showed satisfactory stability, extensive testing disclosed a long-term count reduction probably due to some type of deterioration in the detector. However, development of an electronic system using dual detectors eliminated this deterioration as a serious problem. (The second detector would be used to measure a reference drum of dry coal — the difference in count rate between the wet coal and dry reference coal being a direct measure of moisture content.) Table I, column 1, shows typical results with a 1-curie plutonium-beryllium neutron source and a thermal neutron detector beneath a tray of coal and illustrates the precision of measurement. Consecutive measurements (indicated in Table 1, columns 2-5) of thermal neutrons at various times and positions be-

Jan 1, 1968

By E. J. Ripling

A NY mechanism proposed to explain hydrogen embrittlement in titanium and its alloys must, of course, be consistent with the experimental data that characterize this embrittlement. Unfortunately, however, the mechanical behavior of hydrogen-bearing titanium, at least a-ß titanium, has not been unequivocally defined. Lenning, Craighead, and Jaffee have clearly shown that hydrogen cmbrittles a-titanium by elevating its transition temperature, probably as the result of the formation of titanium hydrides. Therefore, in these alloys, hydrogen acts like at least one other interstitial contaminant, namely, nitrogen.&apos; On the other hand, ß-titanium has been shown by these same investigators to tolerate very large amounts of hydrogen without suffering severe mechanical damage.2 Mixing these two phases, however, to form the most important class of commercial alloys, the a-ß alloys, again results in severe hydrogen embrittlement, although the mechanism by which the embrittlement is produced is not of the same type as that which causes brittleness in a alloys. Ductility damage due to hydrogen increases as the strain rate is reduced in a-ß alloys, while embrittlement in a alloys increases as the strain rate is increased, since the latter is a transition temperature behavior. Steel, like the a-ß alloys, becomes more hydrogen sensitive at slow strain rates, suggesting that the mechanism producing the embrittlement in these two metals is similar. Brown and Baldwin&apos; described the hydrogen-produced ductility depression in steel as a function of testing temperature and strain rate by defining the slope of the two surfaces that produced the depression in a three dimensional chart, Fig. 1. One of these surfaces was given by the equations (de/de)4 > 0 (de/dT) < 0 [1] while the other was defined by the pair of equations Surfaces of the type given by Eq. 1 are suggested in two ways. One is an embrittlement mechanism wherein the diffusion rate of hydrogen is competitive with the rate at which the material is being deformed, as suggested by the planar pressure theory of Zapffe and his co-workers.&apos; The other is the diffusion controlled extension of Orowan&apos;s theory on delayed fracture in glass by Petch and Stables.&apos;&apos; Surfaces of the type given by Eq. 2 are also compatible with a mechanism of pressure build up in voids, according to de Kazinczy,&apos; since the solubility of hydrogen in the metal increases with testing temperature so that as the temperature is raised, the pressure in the voids is reduced. Kotfila and Erbin recently presented some data on the dependence of ductility on testing temperature and strain rate for the a-ß 3 pet Mn complex alloy at four different hydrogen levels.H Although data were presented for only three testing temperatures at three different strain rates, their results indicated that surfaces of the types defined in Eqs. 1 and 2 are produced in the alloy when the hydrogen level is sufficiently high—200 and 300 ppm—Fig. 2. Jaffee and his co-workers presented data on a number of different a-ß alloys which indicated the existence of surfaces of the type described by Eq. 2, but the ductility recovery at low temperatures as given by Eq. 1 was not found." In an attempt to aid in crystallizing this description of the ductility dependence of hydrogen-bearing a-ß alloys, tests were conducted by the author on a-ß titanium 140A with three different hydrogen contents. The tensile properties of two as-received rods and one vacuum annealed rod* were obtained over a range of testing temperatures and strain rates as shown in Figs. 3 and 4. Hydrogen analyses were made by the Battelle Memorial Institute on four pieces of the rod whose properties are shown as solid circles in Fig. 4. The hydrogen content of these pieces, taken at widely spaced intervals within the rod, were 280, 270, 289, and 270 ppm, indicating that the hydrogen content within a single as-received rod was quite uniform. One of the broken test pieces whose properties are shown in Fig. 3 as solid circles was also analyzed, and found to have a hydrogen content of 310 ppm. The analyses obtained on two of the vacuum annealed specimens were 92 and 170 ppm.

Jan 1, 1957

By W. W. Stephens, W. J. Kroll, H. P. Holmes

THE only two methods for producing commercial quantities of malleable zirconium, up to now, have been using magnesium reduction of the anhydrous chloride under a neutral gas, and using purification of raw zirconium by the iodide dissociation method on a hot filament. The purity of the metal obtained by the latter process is about the same as that resulting from the chloride reduction, with the exception of the oxygen content, which may be about 0.05 pct lower in the iodide metal. Even traces of oxygen have a strong hardening effect on zirconium. Since, in the iodide process, the impurities, Si, Al, Fe, Ni, and Mg in the raw zirconium used, are carried over, it would appear uneconomical to use this method of refining solely to eliminate the traces of oxygen, unless very soft metal is desired. One important step to improve the iodide method, namely, dissociating pure iodide made from carbide and recycling the iodine, which would change this refining process into a method for extracting zirconium from the ore, has not yet been made. The Bureau of Mines, by using the chloride reduction, wanted to produce quantities of a reasonably pure and malleable metal at low cost for large-scale industrial use. This aim has been achieved, and a pilot plant permitting production of 600 lb of malleable zirconium per week will be described (fig. 1). Briefly, the Bureau of Mines process consists of reducing purified gaseous anhydrous zirconium chloride with fused magnesium under a noble-gas atmosphere. The reaction product, magnesium chloride, and any excess magnesium metal present are removed from the sponge zirconium in the next step by fusion and evaporation in a good vacuum at about 925°C. In this process, care is taken to keep air out of contact with the hot metal, which otherwise would contaminate the product with oxygen and nitrogen. Both these impurities embrittle zirconium even when present in an amount as low as 0.1 pct. A number of previous reports1-3 describe the method and the various improvements that finally led to a workable process. The major steps made were the production of large quantities of carbide, which is the raw material for producing the chloride, its chlorination with reasonable efficiencies, and the elimination of iron trichloride contained in the raw chloride, as well as that of the zirconium oxide which is always present in this product. The physical nature of the anhydrous chloride, which sublimes at 331°C at atmospheric pressure and melts at 420°C under a pressure of 25 atm, made it necessary to provide a special safety device on the purification and reduction vessels in the form of a lead-alloy seal, permitting escape of excess gases if pressure tended to build up. The main difficulties encountered in the reduction and in the following step, salt separation in a vacuum at elevated temperature, were caused by the material from which the reaction pot was constructed—iron. This metal reacts with zirconium at about 940°C with formation of a eutectic. The last step, salt separation by evaporation of the magnesium and magnesium chloride in a vacuum, is quite unconventional and has not been used before on such a scale. It is only due to the improved construction of high-vacuum pumps, especially oil-diffusion pumps, that such a method could be used. The various steps of the Bureau of Mines process, as described in the general outline above, may be summarized as follows: (1) production of the carbide, (2) chlorination of the carbide, (3) purification of the raw chloride, (4) reduction of the pure chloride with fused magnesium, (5) separation of excess magnesium and magnesium chloride in vacuum at elevated temperature, and (6) melting of the sponge obtained. Production of Carbide The arc furnace, described in a previous report,&apos; was improved both to reduce the graphite consumption caused by the burning of the bottom plates and to concentrate the heat in order to obtain better power efficiency. This was achieved by providing the bottom with graphite plates entirely embedded in refractory bricks, the contact with the current being made with three water-cooled copper plugs. Figs. 2 and 3 show the arrangement. The crucible, made

Jan 1, 1951

By F. Garofalo

It has been shown by various investigators that during constant stress creep the dependence of minimum creep rate, 6,, on stress, o, is given by em = A onat low stress levels, md by 6, = A&apos; exp [ß s] at high stress levels. In these relations A, n, A&apos;, and ß are constant at constant temperature. A single relation has been found which satisfies conditions for both high and low stresses and agrees well with experimental results. This relation is 2, = AN (sinh a s)n, where A" is a constant at constunt temperature and a = p/n. This relation also satisfies the linear relation, 6, = k s, found at temperatures near the melting point at low stresses. EXPERIMENTAL creep results have led to a number of empirical relationships between minimum creep rate, 6,, and the applied stress, s. Under conditions of constant stress it is generally found that at low-stress levels,&apos;-&apos; the dependence of minimum creep rate is given by 6, = Asn. At high-stress levels&apos;74 the experimental results fit the relation, 6, = A&apos; exp [po l. In these relations A, n, A&apos; and ß are constant at constant temperature. A model based on climb-of-edge dislocations from a pile-up array leads to a relation similar to that found experimentally at low stresses.&apos; On the other hand. theories based on chemical-reaction rate,5 nonconservatively moving dislocation jogs, and jog migration and climb-of-edge dislocations4 lead to a relation similar to that found experimentally at high stresses. No difference in mechanism between low and high stress levels has been clearly defined; it is questionable whether such a difference really exists. In any event, the major argument usually given in substantiation of a change in mechanism from low to high stresses is that no single relation exists for defining the stress dependence of the creep rate over wide ranges in stress. However, such a relation has been found and is of the form, dm = A" (sinh a s)n, where A" is a constant at con- stant temperature and a = ß/n. This relation agrees well with experimental results over wide ranges in stress and temperature for copper, aluminum, an A1-3.1 pct Mg alloy, and an austenitic stainless steel. STRESS DEPENDENCE OF MINIMUM CREEP RATE At low stress levels the minimum creep rate, gm, depends on the stress, 0, under conditions of constant stress creep through the relation em=Aon [1] The quantities A and n have been defined previously. In the range in which this relation applies, a linear dependence is found in a log em,-log o plot. Above the stress range of application of relation [I], the minimum creep rate increases much mar; rapidly than predicted by relation [I]. This behavior is shown in Fig. 1 for a series of creep tests on copper4 at various temperatures ranging from 673 o to 973°K. Relation [I] is satisfied at the lower stresses, although the results at 973°K are quite limited. In all cases the transition beyond the applicable range of relation [I] is a gradual one indicating no abrupt change in mechanism. For all test temperatures, values of n have been determined from the results in Fig. 1. These are reported in Table I under Alog tm/hlog o. At high stress levels the stress dependence of minimum creep rate under conditions of constant stress is given by im = A&apos; exp [ß a] 2] All factors have been defined previously. In a log em-0 plot, relation [2] predicts a linear function. Experimentally, a pronounced deviation from the prediction of relation [2] is found at lower stresses. As the stress is lowered, the minimum creep rate decreases more rapidly than predicted by relation [2]. This shown for copper in Fig. 2. Again it is found that the transition from high to low stresses is gradual and no really sharp change is found. Values of p determined from the high stress results are given in Table I. The dependence of minimum creep rate on stress at constant temperature for all ranges in stress

Jan 1, 1963

By M. E. Wadsworth, A. S. Peck

Infrared spectra disclose that oleic acid will not adsorb on the surface of pure beryl unless the mineral is first activated with HF. The adsorption of oleic acid on HF activated beryl is attributed to the hydrogen bonding of oleic acid monomers to F-surface bridging sites. These sites are formed as a result of the reaction of HF with chemisorbed water or surface hydroxyl. Characteristic infrared spectra of physically adsorbed oleic acid are correlated with flotation at different pH at temperatures of 25°C and 75°C for colloidal and -60-mesh particles. The usual mode of occurrence of the beryllium mineral beryl, Be3A12Si6O18, is in granite pegmatites as pale green, white, or yellow crystals. A dark green gem variety, emerald, may be found in the wall rock of pegmatite veins or in mica schist. The most important beryl deposits in the United States are in the Black Hills District of South Dakota, and several mountain ranges of central and west-central Utah contain potential commercial sources of this mineral. Several papers have been published concerning the flotation of beryl with different conditioning reagents. Kennedy and O&apos;Meara1 reported on the essential use of HF in the flotation of beryl from different ores. The use of calcium hypochlorite to separate HF activated beryl from feldspar after flotation with an amine collector was made by Runke.2 A report on the activation of beryl with different cations using sodium oleate collector was presented by Viswa-nathan and co-workers.3 Flotation of beryl with sulfonate collector and different activating salts was employed by Fuerstenau and Bhappu.4 The role of the surface charge or zeta potential in the flotation of beryl with different collectors and salts was also extensively investigated.5"7 Previous infrared investigations by the authors8 disclosed that the orthosilicate beryllium mineral, phenacite, reacts with oleic acid to form a chemisorbed oleate monolayer on the mineral surface. Thus, chemisorption is the effective mode of adsorption in the phenacite-oleate acid flotation system. In contrast, neither chemisorption or physical adsorption of oleic acid occur on the surface of pure beryl as evidenced in this study. Efforts were subsequently made to determine the mechanism of activation and collector adsorption for HF pretreated beryl. EXPERIMENTAL PROCEDURES Large, white, terminated crystals of beryl were obtained from Madagascar through Ward&apos;s Co., Monterey, Calif. The crystals were broken into -60-mesh fragments in a porcelain mortar. Part of this prepared material was ground to a powder with a Fisher Grinder using an agate mortar and pestle. The powder was transferred to a graduated cylinder and mixed with 500 ml of distilled water. After 5 min, the colloidal suspension was separated from the settled particles by decantation and used as a stock for infrared test determinations. Adsorption tests were performed by first transferring 20 ml of colloidal suspension to 50 ml glass centrifuge tubes. The solids were then centrifuged out and the liquid was discarded. Then, the solids were pretreated with one molar HC1 or one molar HF. After 15 min, the solids were again centrifuged out. The mineral solids were washed free of residual acid by repeated centrifuging and water washing operations. Then, 20 ml of distilled water was added to the solids, and the resultant suspension was used for test purposes. In the preparation of mineral for flotation tests, 1.5 g of -60-mesh beryl was deslimed by removing the colloidal fraction by three successive water washes and decantations. Then, the coarse particles were pretreated with either one molar HCl or one molar HF for 15 min. The mineral was next washed free of acid with distilled water, and 20 ml of distilled water was added to the beryl prior to collector conditioning. The conditioning of mineral with collector was performed in 50 ml centrifuge tubes to which either NaOH or HC1 was added for pH modification. One drop (6.0 mg) of U.S.P. reagent grade oleic acid or 2 ml of 0.01 molar sodium oleate was added to the pulp and stirred at about 1500 rpm for 3 min at a

Jan 1, 1968

By J. T. Norton, A. L. Mowry

The monocarbides of the A subgroup elements in the fourth and fifth group of the periodic table in addition to being hard and refractory are of special interest in that they are isomorphous in crystalline structure. They are cubic with a sodium chloride type structure in which the metal atoms are essentially close packed in a face-centered cubic arrangement with the carbon atoms placed in the interstices between. Interstitial structures of this close packed type were first investigated systematically by Egg1 and he gave the rule for their formation, stating that the radius ratio of the nonmetal to the metal atom should not exceed the value of 0.59. The carbides of interest are those of titanium and zirconium of the fourth group and vanadium, columbium and tantalum of the fifth group. Table 1 shows the radius ratio using the Goldschmidt radii for 12 coordination for the metal atoms and the diamond radius for the carbon atom. It will be noted that while there is considerable variation in the size of the metal atom, in all cases the ratio is smaller than the limit of 0.59 placed by Hägg. It has been known for some time that these cubic carbides are soluble in one another, at least to some extent or, in other words, the metal atoms can be replaced, one by another without destroying the stability of the structure. Since the stability of these close packed interstitial substances appears to depend more upon geometry than upon the exact chemical nature of the atoms involved, it is of interest to examine the possibilities of replacement in these carbides in some detail. Hume-Rothery2 has pointed out the importance of the difference in size of solute and solvent atom as a factor in limiting the solubility in simple binary solid solutions. Largely on an empirical basis, he states that if the difference in size between solvent and solute atom is more than 14-15 pct of the solvent atom, the range of solubility is very restricted. The atom size was based on the distance of closest approach in the elements involved. While there is some question as to how one should calculate the size of the metal atom in the carbide structures, reference to Table 1 will show that zirconium is the largest and vanadium the smallest of the group and that the difference is about 15 pct. The Ti-Zr difference is about 9 pct and the others are smaller. Thus one would predict that if the size factor controls the solubility, all of the pairs except VC-ZrC would have wide or complete solubility whereas this latter pair is on the border line and might have restricted solubility. The purpose of the present investi- gation was to examine the solubility of the several pairs of carbides by heating them together until equilibrium was established and then examining the product by X rays. Previous Work Agte3 and his associates prepared various transition metal carbides and determined the melting points of binary mixtures. He concluded from the shapes of the melting point curves that there was extensive solubility in the case of the cubic carbides. Umanskii and his colleagues made an investigation of a number of pairs of the cubic carbides, using X rays and plotted lattice parameter vs. composition curves for the systems TaC-Tic, CbC-Tic, TaC-ZrC and CbC-ZrC. All pairs showed a continuous series of solid solutions. The first two pairs gave a linear relation while the latter two showed a negative deviation from Vegard&apos;s law. Kiefer and Nowotny, in a paper which became available after the present work was well advanced, investigated the binary pairs of the five cubic carbides by means of X rays. Relatively few points were obtained and results indicated that in some cases, at least, equilibrium was not reached at the temperatures used. The results indicated that solubility in the VC-ZrC system was not complete. All of the results of previous investigations indicated the desirability of a more detailed study. Materials The raw materials used were mono-carbides of titanium, zirconium, vanadium, columbium and tantalum and were the purest which could readily be obtained commercially. Spectrographic qualitative analysis showed that the CbC and TaC contained less than 1 pct

Jan 1, 1950