Search Documents

By L. L. Handy

The most common method of identifying hydrocarbon-bearing strata in a well that penetrates many different formations involves measurement and interpretation of the electrical properties of the formations as determined by electrical logs. Even though this method is used extensively, and even though in a great many instances it is capable of indicating presence of oil or gas, situations arise for which it is extremely difficult, if not impossible, to deduce the presence of hydrocarbons. These situations may involve the following. 1. A thin formation, bounded by highly resistive formations, in which it is impossible to obtain the actual resistivity of the uninvaded zone with existing logging devices. 2. A formation in which invasion has been so extensive that a value for the uninvaded zone resistivity cannot be obtained. 3. A very shaly formation in which the resistivity index, I, is lower than that usually associated with productive formations. 4. Laminated formations comprised of thin productive sands separated by thin shale streaks in which the individual sand and shale streaks are too thin to permit measurement of uninvaded-zone resistivity with existing logging devices. 5. Productive formations in which the water saturation is high. To extend the utility of electric log interpretation to identification of hydrocarbons in all types of formations, there is strong incentive to find a method not subject to these limitations. Some time ago, in connection with research on the wettability of reservoir rock, an investigation was conducted in which the resistivities of cores were measured shortly after they were removed from a core barrel, and again after they had been extracted and restored to their original oil and brine saturation.' The resistivities after extraction were generally lower. Other tests made on the cores indicated that they were more nearly water wet after they were extracted; thus, it was assumed that the observed changes in resistivities were due to a change in wettability of the cores. Other experiments'," have shown that resistivities of rock samples are sharply dependent on wettability. These experiments have shown that oil-wet samples are more resistive than water-wet samples. To obtain an understanding of how the wetting properties of the surfaces of core material affect electrical resistivity, a series of experiments was conducted. Two groups of core samples were prepared for testing. One group contained brine, but no residual oil. The other group was saturated with brine, flooded with oil to a low water saturation, then flooded with brine to a final residual oil saturation. Resistivity measurements were made on each group. Both groups were then flooded with the original brine to which a chemical had been added that renders sand and clay surfaces preferentially oil wet, a so-called reverse-wetting agent. very little change in resistivity was observed in cores containing only water. The group containing residual oil, however, showed resistivity increases of 100 to 200 per cent. These experiments showed that the resistivity of a core containing oil could be altered by changing wet-tability of the core. Moreover, the possibility was introduced that reverse-wetting agents might be employed as the basis for a logging method for identification of oil-bearing strata. Since behavior of a porous rock containing gas and water might be expected to be similar to that of a rock containing oil and water, such a method should also be applicable to identification of gas-bearing zones. In principle the wettability of the invaded zone could be reversed without altering conductivity of the interstitial water or the hydrocarbon saturation therein. Those strata showing significantly increased invaded-zone resistivities would, therefore, contain hydrocarbons; those with no significant change would be filled only with water. Addition of a reverse-wetting agent to a hydro carbon -bearing zone which is, by nature, already preferentially oil wet would not result in an enhancement of its resistivity. It is generally believed, however, that most hydrocarbon-bearing strata are preferentially water wet.

By F. H. Vitovec, D. W. Hoeppner

Pusk-pull fatigue tests were conducted on copper tricrystals of 99.988 pct purity to ascertain the role of grain boundaries in the initiation and propagation of fatigue cracks. Significant differences in behavior were found for specimens which possessed different transverse-boundary misorientation. In speciwens with low boundary angles cracks initiated within the transverse boundary, while higher angles led to transcrystalline fatigue failure. It is suggested that at low angular misorientation moving dislocations may interact with dislocations of the boundary or dislocations present in adjacent pains on favorably oriented glide planes, thus initiating a fatigue crack. MANY fatigue studies have been concerned with fatigue-crack initiation within grains and the mechanism causing initiation and propagation1-3 Although the initiation of fatigue cracks in or near grain boundaries of pure metals has been observed and reported in the literature, the mechanism of this phenomenon has received little attention.4"11 EXPERIMENTAL PROGRAM Testing Procedure. To investigate the role of grain boundaries regarding initiation and propagation of fatigue cracks, copper tricrystals were tested in push-pull. Axial-stress tests were used to avoid the stress gradients introduced by stressing of some other nature. Copper was selected as the most suitable test material since extensive work has been done on the formation of fatigue-induced slip in copper. Tricrystal specimens were used to provide a grain boundary geometry with one boundary transverse to the principal stress axis and one or more boundaries nearly coincident with the direction of maximum resolved shear stress. The boundary energy and the slip characteristics in the vicinity of the transverse boundary depend on the relative orientations of grains across the boundary. Testing was done at room temperature, at a frequency of 700 cpm, in an atmosphere of either air or argon. It is known that the incidence of grain boundary cracking increases with increasing temperature and decreasing frequency.4 The fatigue machine applied a uniaxial tension-compression load to the specimen by a flat spring which was actuated by an adjustable eccentric. Use was made of an adjustable head and a load cell which had strain gages mounted at 120-deg intervals around its periphery, thus providing a means for eliminating any detectable superimposed bending moment. A clip gage was mounted between the gripping heads to record the cyclic strain amplitude applied to the specimen. Each specimen's hysteresis characteristics were recorded by supplying the load and strain signals to an oscilloscope. Microstructural changes were observed and recorded with an optical microscope which was mounted on the fatigue machine. Immediately prior to insertion in the machine, each specimen was chemically polished. Extreme care was exercised while inserting the specimen in the test machine to avoid either bending the specimen or introducing a mean load. Each specimen was stressed in the tensile direction first and subsequently the load was reversed. Specimen Preparation. Tricrystal fatigue specimens of 99.988 pct Cu were grown from the melt using a modified Bridgman technique. Ingots about 1 in. high were grown to the configuration shown in Fig. 1. Upon sectioning the resultant ingot, several specimens were provided with an identical shape and grain boundary orientation. Except for plane sectioning and final polishing, this method eliminated machining the specimens. The apparatus used for growing the tricrystals is shown in Fig. 2. A spectrographically pure graphite mold, Fig. 3, was inserted in a vycor tube which was mounted on a vertical zone-refining table. Prior to insertion in the tube the mold was assembled as follows. The insert and graphite rods were fixed in position in the mold. The copper was then placed in the mold and the entire mold assembly was positioned in the vycor tube, Fig. 2. At this point the tube was sealed, evacuated, purged with helium gas, and finally placed under a slightly positive helium pressure. The heating coil was then adjusted to melt the copper charge, after which it was raised at a speed of 4 in. per hr. It is also possible to use

Jan 1, 1964

By S. J. Burns, W. W. Webb

The dislocation arrangements formed during unsteady propagation of cleavage fractures on (010) planes in LiF have been investigated by high-resolution etch-pit techniques and by X-ray diffraction topogvaphy. In impurity-hardened crystals, cracks propagating in any direction on (010) planes at velocities of about 103 cm per sec are usually accompanied by light plastic deformation which is enhanced wherever the crack is allowed to hesitate. Dislocations with [011] type Burger's vectors are often formed looped around the crack tip. They are dragged along with the crack tips leaving edge dislocations lying nearly parallel with the clearage surface about 5µ from it. These dislocations are easily overlooked since they may initially intersect with the cleavage surface infrequently and later may disappear from the crystals due to image forces during aging at room temperature. Although the plastic work associated with these dislocations is only comparable with the reversible (010) surface energy, an instability in crack propagation appears due to a limit of the velocity with which dislocations can be dragged along with the crack. Transition to a fully brittle nonplastic fracture mode occurs when the crack velocity exceeds the velocity with which dislocations can be moved by the stress field of the crack. TRANSITIONS between brittle and ductile modes of fracture appear to be common processes in the behavior of materials in which the flow stress is close to the stress at which brittle cracks can propagate. High-strength engineering alloys fit into this category and the transition from ductile to brittle modes of crack propagation may be associated with catastrophic failures in these important materials. The methods of theoretical mechanics indicate the geometrical conditions in which these processes may occur but the detailed mechanisms controlling the generation of dislocations in the initiation of the plastic mode and the process by which the loss of plasticity occurs on transition to the brittle mode are not yet clear. Since these mechanisms are not amenable to direct observation in engineering alloys we have chosen a semi-ductile alkali halide LiF as a model system in which to observe transition mechanisms between plastic and brittle modes of crack propagation. Cleavage cracks in this system are known to undergo a plastic-elastic transition at velocities between 103 to 104 cm per secl and dislocation configurations in LiF are amenable to study by optical-microscopic observation of dislocation etch pits2 and by X-ray diffraction topography.3 We have been able to identify a dislocation mechanism responsible for the transition from brittle to slightly plastic modes of crack propagation in LiF. A model based on this mechanism permits calculation of the critical crack-propagation velocity for this transition and indicates the importance of the stress dependence of dislocation velocity in determining the critical crack velocity. Of course, this model cannot be carried directly over to more complex materials but it is quite possible that its qualitative features are generally applicable. Dislocations intersecting fresh cleavage surfaces in LiF were reported by Gilman,4 by Forty,5 and by Wash-burn et a1.6 Such dislocations were construed to have been nucleated where the cleavage crack hesitated or stopped, near stress concentrators, such as cleavage steps, on the crystal face. The loci of such dislocations deposited On the cleavage plane in bands were called "stop lines" or "deformation zones". Gilman, Knudsen, and walshl measured the velocity of cleavage cracks in lithium fluoride by evaporating thin resistive strips on the crystal side and recording

Jan 1, 1967

By Gerald Edmunds

Castings of pure metals and many alloys usually have a coarse-grained structure characterized by long columnar grains throughout the main body of the casting. Frequently, the surface exhibits finer, sometimes nearly equiaxed grains, and such grains may also compose other parts of the casting. This paper deals .primarily with determinations of the grain-orientation textures of the columnar and surface grains of polycrystalline zinc castings. It includes some results upon a cadmium casting and a magnesium casting. A hypothesis is developed to account for the observations on columnar grains and to use as a basis for predicting orientations in other cast metals. A general description of the position of the columnar grains in castings is that their long axes are approximately parallel to the direction of the thermal gradient during crystallization. Thus, in cylindrical castings the columnar grain axes tend to be radial, and in large flat castings where most of the cooling is through one or both of the large mold surfaces they tend to be perpendicular to the mold surfaces. At the edges and corners the direction of heat flow and therefore the position of the grains is more cornplex. Actually observation shows that even in castings made in flat molds the cooling seems to be somewhat irregular, since columnar grains tend to emanate from certain areas of the cooling surface, indicating that thermal contact was better there than in neighboring areas. The nucleus from which a columnar grain grows may be so oriented that its direction of maximum growth rate does not coincide with the direction of the thermal gradient. In this case the long axis of the grain probably assumes an intermediate position. Notwithstanding these minor irregularities, the situation does exist that the long axes of the columnar grains are generally disposed approximately perpendicular to the mold surface. Schmid and Wassermanl and Nix and Schmid2 have determined the orientation texture of columnar grains in castings of several cubic, tetragonal, hexagonal close-packed and rhombohedra1 metals. For zinc and cadmium, they report the basal plane to be parallel to the columnar grain axes, with no preference for any particular direction in this plane to coincide with the grain axes. This texture, termed a ring fiber texture,3 is uncommon in metals; zinc and cadmium are the only ones reported to exhibit it. Generally, it is stated, a simpler texture exists in which a principal, though not necessarily the most closely packed, crystallographic direction is parallel to the direction of heat flow. In cast magnesium (also hexagonal close packed) they report a digonal axis I, [100] direction, parallel to the direction of heat flow. The writer is not aware of any other orientation-texture determinations on cast polycrystalline hexagonal metals. In view of the observations reported in the present paper it is of interest also to note that Nix and Schmid stated that a

Jan 1, 1941

By J. C. Yannopoulos, N. J. Themelis

Ah electronic thermogravirnetric balance was used to measure the veductioiz rule o single cirpric oxide particles suspended in a stream of hydrogen. Very jzne thermocouples embedded in lie center and at the surface of the sphere recorded the variation of terw perature during reduction. In contrast to iron oxide reduction, where in most instances the rate of interface reactiokl is controlling, the heat- and mass-transfer phenotnena play a predolrinant role in the reduction of cupric oxide. The correlation of experitnental data or tnass lransfev lhrough the boundary layer at Reynolds nunlber 0-4 50 was as jollocs: ThE reduction of cupric oxide by hydrogen is represented by the equation: It is a highly exothermic reaction and the amount of heat released varies only slightly with temperature (-21,430 cal per g-mole at 400°C). Most of the published studies on this system have been conducted at temperatures in the range of 34 to 280c.l-&apos; The concensus of opinion has been that at temperatures below 200°C the reaction is preceded by an induction period during which there is very little or no reduction. The length of this period diminishes as the temperature of the reaction is increased1l5 and aseawa found that at 280°C reduction starts practically immediately when the oxide is exposed to hydrogen gas. The existence of an induction, or incubation, period has led experimenters to believe that the reduction of CuO by hydrogen is catalyzed by metallic copper.&apos; Boldurev and rmolaev found that mechanical additions of powdered copper to oxide did not affect its reduction, although metallic copper produced during the reduction seemed to have a catalytic effect. At least three other authors2&apos;5&apos;7 have reported that addition of copper had no effect on the rate of reduction. Pease and alor&apos; observed that water vapor had a strong inhibiting effect on the reduction at 1503C, but its effect was greatly diminished at 200 C. Pavlychenko and Rubinchik5 studied this reaction at 159 to 235 C and found that, once the reaction had been initiated, there was no inhibiting effect due to the introduction of water in the hydrogen stream; at temperatures above 183°C there was no inhibiting effect due to water vapor, either before or during reaction. The same authors noted that the rate of reduction was independent of pressure in the range of 200 to 700 mm Hg. aseawa investigated the kinetics of the CuO-Hz system at 160 to 280°C and estimated the apparent activation energy at 14,000 cal per g-mole. A similar value (13,500 1200 cal per g-mole) was reported by ond&apos; in the temperature range 148 to 216°C. Bond also reported that there was no incubation period and that water vapor had no inhibiting effect on reduction at temperatures above 190 C. The above studies have been conducted at temperatures below 280°C and the physical configuration of the system under investigation has not been defined adequately. However, it is well-known that the mechanism of gas-solid reactions depends on a number of in series physical and chemical rate prcesses.&apos;&apos; It is, therefore, essential to include among the experimental factors the geometry of the solid system and the mass-transport characteristics of the reducing gas. Scott studied the reduction of packed beds of cupric oxide cylinders by Hz-He streams of very low hydrogen concentrations at temperatures 400 to 600 C, pressure of 10 to 30 atm, and gas velocity from 0.18 to 5.8 ft per sec (3 < Rep < 30). The reduction rate was found to be mainly controlled by diffusion through the boundary layer and through the pores of the reduced copper phase. The following correlation was proposed: Scott in an earlier work studied the reduction of fixed beds of cupric oxide wire and found that the rate of flow of the gas stream through the bed had a controlling effect on the rate of reduction. The same mass-transfer phenomenon was observed by Bond and clark13 on a similar reduction system. The analogy between mass and heat transfer through the boundary layer which exists between a solid surface and the bulk stream stems from the similarity of the differential equations representing these phenomena

Jan 1, 1967

By J. B. Clark, A. J. McEvily, R. L. Snyder

The nonuniform distribution of precipitate particles has been recognized as a leading factor contributing to the relatively low fatigue resistance of aluminum alloys. The structure of many of these alloys is characterized by narrow precipitate-free zones adjacent to the grain boundaries. Alloys with such zones exhibit a tendency for brittle inter crystalline fracture. The interrelation between this type of structure and mechanical properties was investigated in an Al-10 wt pct Mg alloy. It was found that deformation during fatigue occurs preferentially along these zones and cracks initiate there. In Al-10wt pct Mg, the zones were found to be supersaturated even after extensive general precipitation and are due to the absence of proper precipitate nuclei in the region near the grain boundaries. Cold working the alloy prior to aging improves the mechanical properties by inducing precipitation within the zones and also by jogging of grain boundaries. The mode of fracture is changed from brittle inter crystalline to more ductile trans granular fracture. THE process of fatigue is highly structure sensitive, with the strength of the whole often dependent upon some localized discontinuity, either geometrical or metallurgical in nature. Much has been learned about the role of geometrical discontinuities, e.g., notches, in fatigue, but with the exception of the effects of inclusions or the shapes of carbides, relatively little is known about the specific effects of discontinuities in metallurgical structure such as nonuniform precipitation. In most age-hardening aluminum alloys, metallo-graphic studies have shown that the extent of precipitation adjacent to grain boundaries is much less than that which occurs in the interior of the grains. The width of these almost precipitate-free regions, which are sometimes called denuded zones, and the extent of solute depletion within them, are dependent upon the particular alloy and its aging treatment. It has been observed1 that these zones are relatively soft with the result that plastic deformation takes place preferentially within them. It has also been shown 2-4 that there exists a tendency for intercrys- talline cracking in fatigue when such zones are present. It is of interest to note that Broom et al.2,3 were able to reduce the incidence of this type of failure in an A1-4 wt pct Cu alloy by stretching the material 10 pct prior to aging. In the present study, the effects of precipitate-free regions on the fatigue properties of an A1-10 wt pct Mg alloy were studied in detail, and the effects of deformation prior to aging on the nature of the precipitation process as well as on fatigue properties were also investigated. MATERIAL AND PROCESSING An A1-10 wt pct Mg alloy was selected for this study, because it was known that well-defined precipitate-free regions along the grain boundaries are readily obtained in this alloy after aging at 200oC.5 The starting materials were 99.998 pct A1 and singly sublimed magnesium of about 99.9 pct purity. The aluminum was induction melted in a graphite crucible, and then the magnesium addition was immersed until dissolved. Chlorine gas was then bubbled through the molten alloy for 4 min to degas the melt, after which the melt was cast at a pouring temperature of 730" to 760°C into a cold, graphite-coated, tapered steel mold. Since A1-Mg alloys are difficult to homogenize,5 special care was taken to obtain a uniform composition. Two-in. cubes were cut from the ingot and heated at 446°C for 30 min. These cubes were then hot forged approximately 35 pct in each of the three cube directions and homogenized for 16 hr at 446°C. Sheet specimens were then obtained by pressing 40 pct and rolling 35 pct per pass with reheating between reduction steps to a final thickness of approximately 0.10 in. The sheet was then solution treated for 16 hr at 446°C and water quenched. The age hardening behavior of this material at 200°C was then determined, and the results are shown in Fig. 1. The age hardening of this alloy when subjected to cold work prior to aging is also shown in this figure. Preliminary work indicated that extensive deformation after quenching was required to affect drastically the precipitate-free regions in this alloy, and a rolling reduction of 50 pct was chosen. For purposes of comparison the following three conditions were studied: a) Solution treated, quenched, and aged 20 hr at 200°C

Jan 1, 1963

By R. V. Sara

Determination of the Hf-C phase diagram was conducted primarily by metallographic and X-ray diffraction studies on appropriate alloys. The only intermediate phase observed in this binary system was HfC. This phase was found to be homogeneous between 34.0 and 48.0 at. pct C at 2200°c and between 36.0 and 49.3 at. pct C at 3150°C. The lattice-parameter variation was also determined for HfCI-, compositions prepared at 2200° and 3150°C. The most most refractory composition, with a melting point of 3830°c, was established at 47.5 at. pct C from melting-point data. Solidus temperatures of 2240&apos; and 3150°C occur on the high-kafnium and high-carbon sides of the monocarbide, respectively. The invariant point between HfC and carbon is located at 66.0 at. pct C, whereas the 2240°C solidus corresponds to the peritectic temperature at which hafnium is formed from HfC and hafnium-rick liquid. Hafnium has a melting temperature of 2208°C and is capable of taking carbon into solution to the extent of 10.5 at. pct at this temperature. ALTHOUGH the Hf-C phase diagram has not been previously evaluated experimentally in its entirety, the belief has been that the general configuration would resemble the chemically similar Group rV carbide systems, Ti-C and Zr-c.&apos; These binaries are characterized by a single carbide phase with a simple NaC1-type structure which is maintained over wide compositional ranges. This family of carbides has high thermal stability that increases substantially as the atomic number of the metal component increases. This trend characterizes HfC as one of the highest melting materials. According to Agte and Alterthum,2 the melting point for this monocarbide is 3890°C, a value that has been quoted quite extensively for the past several decades. Recently, in repeating the work of Agte and Alter-thum, Adams and Beall3 determined the melting point of HfC to be 3895°C. A significant departure from the commonly accepted version of the Hf-C system was reported by Avarbe and his coworkers,4 who proposed that there is an extreme stabilization of a hafnium in a narrow field to 2820°C, above which it melts peritectically to form HfC and liquid. Their study was also concerned with the melting temperature of various HfCI-, compositions, but the peak melting point was taken from the work of Agte and Alterthum. Avarbe and his associates were not concerned with the high-carbon region of the system. However, three widely varying temperatures have been reported for the HfC-C solidus by other investigators. Cotter and Kohn5 observed approximately 2800°C; Portnoy et al.&apos; reported 3260°C; and, more recently, Krikorian7 indicated 2915°C. Equally as uncertain is the solidus between hafnium and HfC. As noted above, Avarbe et al. report a peritectic temperature of 2820°C, Krikorian7 measured 2150°C, and Benesovsky and Rudy&apos; estimated 2000°C on their diagram. I) EXPERIMENTAL PROCEDURE The starting materials for this study consisted of reactor-grade hafnium hydride obtained from Fair-mount Chemical Co., Newark, N.J., hafnium carbide supplied by Wah Chang Corp., Albany, Ore., and Union Carbide spectroscopic-grade graphite, SP-1. The graphite analysis indicated impurities at levels of only 0.5 ppm or less. According to the suppliers, the hydride and carbide contained the typical impurities listed in Table I. The samples required for these studies were prepared by dry blending either graphite and hafnium hydride or hafnium hydride and hafnium carbide powders for approximately 5 min in a "Spex Mixer Mill". The latter combination was used only for preparing several samples in the HfC1-, melting-point studies. Small pellets, varying between 3/16

Jan 1, 1965

By S. K. Mitra

A refinement of the Seeger model for intersection process is investigated which is in better agreement with experimental observations than the original. It is shown that, in single crystals, the strain hardening in Stage II is mainly due to the short-mnge interactions when intersection is the rate-controlling process. It is also demonstrated that the creep curves, as predicted by this theory, are in good agreement with the experimental observations. MOTT: Cottrell? and Seeger have developed an approximate theory for plastic deformation of single crystals over the range of variables where the strain rate is controlled by the rate of intersection of dislocations. Although it is now generally agreed that the low temperature deformation of many pure metals is controlled by the intersection mechanism, various dictates of the over-simplified Seeger model are not in good agreement with all the experimental facts. It is the purpose of this paper to reveal that by appropriate extensions of the Seeger model, particularly those suggested by Basinski: a much more reliable theory results. The refined model to be presented here will be shown to account, in a satisfactory way, for the effect of stress, temperature, and strain on the creep rate under constant stress and for the effect of temperature and strain on the flow stress in constant strain-rate tests. EXPERIMENTAL METHOD To Check the theoretical deductions, both creep and tension tests were conducted on single crystals of high-purity Al (99.994 pct Al) so oriented that both the active slip plane and the Burger&apos;s vector of the operative dislocations on that plane made angles of about 45 deg to the tension axis. Single crystals of aluminum (5/8 in. by 1/10 in. by 8 in.) were grown in a graphite mold under an inert atmosphere using the Bridgman method. The chemical composition of the aluminum is given in Table I. A common seed was used for all crystals and their orientation is shown in Fig 3. The extensometry consisted of two differential transformers with matched outputs mounted so as to measure the extension in a 2 in. gage length. The amplified difference in output of the two transformers was recorded by a potentiometer. The amplification was calibrated before each run so that one chart division of the recording potentiometer indicated a 105 shear strain on the specimen. Stresses were measured to the nearest 1 x l04 dynes per sq cm. ACTIVATION VOLUME The concept of Basinski that the activation volume is not constant but is a function of the force that aids thermal fluctuation in effecting the cutting of dislocations will be adopted in this section. The force acting due to an applied shear stress on the dislocation being intersected is where L is the mean spacing between the forest dislocations, is the Burger&apos;s vector and T is the back stress. A detailed discussion about the origin of back stress will be taken up later in this report. As shown by Basinski, the activation energy, U, that must be supplied by a thermal fluctuation in order to effect intersection, is equal to where x is the distance through which the dislocation must be translated for complete intersection, and Fm is the maximum force encountered in intersection. When the applied stress is decreased abrupt ly F also decreases and the activation energy increases correspondingly as documented in Eqs. [ 1 ] and [2]. The Seeger equation for the strain rate when the deformation is controlled by rate of intersection of where the shear strain rate (per sec) N = the number of points per unit vol at which intersection can take place

Jan 1, 1962

By B. M. Larsen

ATTEMPTING to review the fundamental aspects of segregation in steel ingots of all types in a paper of reasonable length, we encounter two difficulties: (I) the fact that a large number of different physical and chemical effects are involved, and (2) rather incomplete and confusing evidence on certain aspects of detail and mechanism in the freezing process in which the segregation effect is involved. The best solution seemed to be to link together most of the underlying factors into a simplified theoretical picture that appears to the writer to explain most of the observed data, in the hope that this will serve as a reasonably good target for discussion and criticism. Segregation effects, especially in steel ingots or castings, are often divided into " microscopic " and " macroscopic," depending on whether the variations in concentration of solutes? or dissolved elements in the iron occur as: (I) a periodic variation over the small distances between the nuclei and the surfaces of the primary grains, or (2) as a larger scale effect involving concentration gradients over distances of the order of several inches, more or less. The reason for this somewhat artificial division is, of course, that it is only the macroscopic scale effect that has much practical importance. About the only effect of practical importance that results from microscopic segregation is the banded structure often left in rolled sections, and even this is relatively harmless in most cases. However, the causes of microscopic segregation also underly the larger scale effect, so we must first consider matters such as the formation and growth of crystal nuclei, selective freezing and diffusion, and others that are fundamental to all segregation effects. UNDERCOOLING AND NUCLEI FORMATION It is probable that although the degree of undercooling is small in iron, as in metals in general, a certain amount of it takes place, and also that the number of crystal nuclei increases very rapidly with increased undercooling below the liquidus tempera¬ture. In practical terms this means that the nuclei number increases very rapidly with increased cooling or freezing rate, thus being dependent on the rate of heat flow out from the zone of crystallization. TEMPERATURE GRADIENTS AND HEAT DISSIPATION DURING FREEZING Each pound of steel evolves about 100 B.t.u. when freezing. In addition to this, the temperature gradient in the solidified portion (required to dissipate the heat as freezing progresses into the axis) necessitates a loss of heat required to cool the solid metal below its freezing range, which is equivalent to an amount of not so much less in magnitude. In a 5-ton ingot, the total would include about one million B.t.u. for freezing alone and about 0.4 to 0.5 million B.t.u. for the gradient, up to the end of the freezing period: Thus the rate of freezing depends primarily on the rate of heat dissipation. In the ordinary ingot shapes, the axial rate of growth of the solid

Jan 1, 1944

By G. V. Jere, V. Krishnan, C. C. Patel

Standard free energy and standard enthalpy changes as a function of temperature have been calculated for the chlorination reactions of different oxides constituting columbite and tantalite. The tallies of standard lee-energy change (F) indicate the possibility of pvefeential chlorination of different oxides but the ease 0.f chlorination of columbium pentoxide at about 250°C and the chlorinating tendency of columbium pentachloride in promoting the chlorination of tantalum and other metal oxides, p7-evetzt the separation of columbiu?n and tantalum from other oxides and pom each othel.. It is likely that low temperatuves of chlorination and continuous 1err2oval of columbium pentachloride from the ..eaction zone may help partial separation of columbium from tantalum as well as from titanium. The standavd enthaply change (AH?) values shotr that 1ou.-temperature chlorination around 300" to 500°C is likely to sustain the chlorination , without external heating. COLUMBIUM (niobium) and tantalum metals, their alloys and interstitial compounds are finding extensive uses in nuclear reactors and high-temperature equipment.la-3 These metals also find uses in chemical process plants, electrical rectifiers and capacitors and as "getters" in electronic tubes.la With the development of Kroll process of reduction of volatilized titanium tetrachloride by magnesium for the production of titanium metal, chlorine metallurgy is receiving greater attention. Chlorine metallurgy has several advantages, the foremost amongst them are: the ease of chloride formation, separation of the different constituents of minerals by selective chlorination, and the reduction of the chlorides in vapor phase to the respective metals. Recently, Si-bert, Kolk, and Steinberg4 have considered a number of methods for the preparation of columbium metal and the most promising is found to be the halide reduction. Since the minerals columbite and tantalite are comparatively abundant in nature, the future of the metallurgical processes depends on the utilization of these minerals for the production of columbium and tantalum chlorides by chlorination. In this paper, an attempt has been made to interpret thermodynamically the chlorination of individual oxides constituting columbite and tantalite, with the help of the recent thermodynamic data.5-8 For this purpose, standard free energy and standard enthalpy changes of the chlorination reactions of the oxides with chlorine, both in absence and presence of carbon as the reductant, have been calculated as a function of temperature and represented graphically. Similar calculations for the reactions employing carbon tetrachloride and carbonyl chloride as chlorinating agents have also been incorporated in this paper. REPORTED WORK ON CHLORINATION Cuvelliezg has patented a process for the separation of columbium and tantalum from their concentrate, wherein 75 pct Cb05 is claimed to be chlorinated at 1050°C in the course of 7 hr using chlorine or chlorine containing nonreducing gases, the products of reaction being CbC1, or CbOC1,. At this temperature, Ta,05 is claimed to remain unaffected. It is further claimed1° that at higher temperatures, the proportion of Ta205 chlorinated increases while that of Cb205 diminishes. During the studies on the action of chlorine on individual metal oxides, Kangro and Jahn" have observed that Ta,05 is not chlorinated even at 1200" in the stream of chlorine, while 75 pct of Cb,05 is converted into CbOC1, around 900 to 1100°C. The chlorination of Cb205 by chlorine in the presence of carbon, investigated by Lind and Ingle,&apos; and

Jan 1, 1962

By J. E. Neal, C. T. Naber, O&apos

Silicon thin films were deposited by electron beam evaporation in an ultrahigh vacuum onto (0001) and (1102) sapphire substrates. Attempts were made to correlate the structural properties of the deposited silicon films with the following: 1) substrate orientation, 2) substrate surface condition, 3) substrate temperature, and 4) deposition rate. The substrate temperatures were varied between 500° and 1000°C and the deposition rates were varied between approximately 50 and 700A per min. The following sapphire surface treatments were investigated: 1) annealing in the ultrahigh vacuum at 1200° C; 2) heating in a hydrogen atmosphere at about 1350°C; and 3) etching with silicon by evaporating silicon onto sapphire substrates heated to 1200° or 1300°C. Twinned silicon films were occasionally formed at substrate temperatures between the 800° and 1000°C on unprocessed mechanically polished substrates; however, the reproducibility and crystallinity of these films were generally poor. Single-crystal and twinned silicon films were formed at substrate temperatures between 700° and 1000°C on substrates which were silicon-etched at 1300°C prior to deposition. Fiber texture films were formed at substrate temperatures between 500° and 700°C. The (111) lattice plane of the silicon single-crystal films was parallel to the (0001) sapphire plane and the (100) silicon plane was parallel to the (1102) sapphire plane. TECHNIQUES are well-established for growing single-crystal silicon thin films on sapphire by chemical methods.&apos;-* Vacuum epitaxial techniques have a number of advantages over chemical epitaxial techniques in the fabrication of thin film microcircuits.5 One of the most significant is that vacuum techniques are compatible with well-established procedures for forming vacuum-deposited thin-film resistors, capacitors, and interconnections. Salatna, Tucker, and young6 recently reported the formation of relatively poor crystalline-quality silicon films on sapphire by electron beam evaporation in a vacuum of about 7 x 10-7 Torr. The purpose of the investigation described here is to determine the relationships between the structural properties of silicon thin films deposited on sapphire substrates by electron beam evaporation in an ultra-high vacuum and the following: 1) substrate orientation; 2) substrate surface condition; 3) substrate temperature; and 4) deposition rate. The substrate temperatures were varied between 500° and 1000° C and the deposition rates were varied between approximately 50 and 700A per min. Two orientations of sapphire were used: (0001) and (1102). The thick-nesses of the films were between 8000 and 16,000A. The morphology and crystallinity of the deposited films and substrate surfaces were investigated by optical microscopy, electron microscopy, and electron diffraction. APPARATUS AND PROCEDURE A cross section of the ultrahigh-vacuum thin-film evaporator is shown in Fig. 1. The bell jar is stainless steel and copper gaskets are utilized at all seals. High vacuum is attained by a 6001iter per sec ion pump and a titanium sublimation pump. Sorption pumps are used to rough the system to a pressure of about 10 µ prior to starting the ion pump. Vacuums in the 10- 10 Torr range were attained after baking the system at about 250°C for 8 hr. Vacuums in the 10-8 to 10-9 Torr range were maintained during silicon evaporation. The silicon charges, which were cut from p-type single-crystal boules which had resistivities between 2000 and 4500 ohm-cm, were placed in the water-cooled copper crucible of a 180 deg bent-beam 5-kw electron beam evaporator. During evaporation, a molten zone was formed in the top center of the silicon charge, and the portion of the silicon charge in contact with the water-cooled crucible remained solid. The substrate heater, which has been described

Jan 1, 1969

By R. H. McLean

Velocity, kinetic energy and shear in crossflow beneath three-cone jet bits may influence cleaning of the bottom of the borehole and the teeth of the bit. Laboratory investigation shows that each of these parameters is a function of the diameter of the borehole and the product of the volume rate of flow and velocity through the nozzles (QVn). Increasing QV, or decreasing the diameter of the borehole increases each parameter. These functions provide means of predicting the magnitude of each parameter and of scaling the cleaning forces. INTRODUCTION In drilling operations using conventional jet-type rock bits, the impinging jels create an important flow mechanism. Called crossflow, this flow mechanism originates in the impact area of the jets, spreads across the bottom of the hole and supplies the principal source of energy to clean the teeth of the bit and most of the bottom.&apos; Besides providing the means of cleaning cuttings from the bit and the hole bottom, crossflow may also have other, less direct, effects on the rate of penetration. The shear stress generated on the bottom by crossflow will inIluence the thickness and permeability of any filter cake of mud solids or crushed material which forms on the bottom.&apos; These factors may affect the rate of penetration. A previous pulblication introduced some fundamental concepts of crossflow.&apos; Crossllow was shown to occur in a thin layer adjacent to the bottom, and to cover the bottom completely. The maximum velocity in the crossflow above any position on the bottom was found to be directly proporlional to the square root of the product of the volume rate of flow and velocity through the nozzles—the jct QV,,—and inversely proportional to the diameter of the borehole. This information indicated that the effectiveness of crossllow in scavenging the bottom can be improved by maximizing the jet QV. The investigation reported herein amplifies the definition of crossflow. Complete velocity profile data above a representative position on the bottom are analyzed. These data better illustrate control of the capacity of crossflow to scavenge the bottom, and also relate shear stress on the bottom to known, controllable parameters. The conclusion reached in the previous publication that maximization of the jet QV. produces the maximunl cleaning beneath current jet bits is unchanged by these new data; rather, it is strcngthened. Data presented here show that the kinetic energy flux above a representative position on the bottom is maximized by maximizing the jet QV. The shear stress on the bottom will also be shown to be maximized in the same manner. Since the functions relating the jet QV. to velocity, shear stress and kinetic energy also involve the diameter of the borehole, means of equating, or scaling, these quantities in different sizes of boreholes will be illustrated. EXPERIMENTAL EQUIPMENT AND TECHNIQUE JET BIT MODEL Data were recorded from the same laboratory model as used in the aforementioned investigation of the flow around a jet bit.&apos; The model consisted of a 43/4-in. three-cone, jet-type rock bit in a smooth, flat-bottomed borehole constructed of lucite. The bit had a shape and nozzle placement closely resembling larger three-cone jet bits commonly used in field operations. Fig. 1 illustrates the impact area on the bottom of a jet from this bit. Details of the orientation of the jets may be found in the previous publication. TECHNIOU&apos;E OF MEASUREMENT Measurements of the crossflow were made by inserting a very small Pitot tube through the bottom of the simulatetl boreholc. Extreme thinness of the layer of crossflow necessitated accurate measurements of the height of the Pitot tube above the bottom to achieve close definition of the velocity profile. A cathetometer, which could be read to the nearest 0.005 cm, was used to make this measurement.

Jan 1, 1966

By C. E. Taylor, L. V. Fegan

With on-stream electrical-resistance measurement as a basis, Bethlehem Steel developed a system for the completely automatic control of moisture in the feed to pelletizing. This system was later successfully adapted to the sintering process, with automatic control of moisture serving to maintain the air permeability required for effective burnthrough. Control of moisture content is an important factor in the agglomeration processes by which iron ores are converted into either pellets or sinter for use in blast furnace burdens. In both pelletizing and sintering the iron ore feed must be mixed with the proper amount of water so that capillary attraction and surface tension forces can be utilized to cause the ore particles to coalesce and form larger agglomerates. The success or failure of the entire pelletizing or sintering process depends on maintaining the proper moisture. Therefore, continuous automatic control of moisture is one of the conditions for the automation and optimum use of both pelletizing and sintering processes. In pelletizing, variation in moisture can cause ball size to change and is a common cause of cycling which results in a fluctuating feed to induration. Excessive moisture can cause lumps to form at the cutter bar and contributes to the formation of buildup on the green pellet screens. Green pellets with excess moisture deform and reduce bed permeability. In sintering, accurate control of moisture is also important because moisture must be within the limits that give the bed the required permeability for good burnthrough. In response to these problems, a moisture meter, based on the principle of electrical resistance measurement, was developed. This moisture meter has been a key factor in the development of systems for providing uniform feed of concentrates in most of Bethlehem&apos;s pelletizing and sintering plants. The automatic moisture control system for pelletizing was successfully plant-tested and resulted in the following: (1) Control of moisture in the green pellets to +0.2%. (2) Up to 50% reduction of bentonite consumption. (3) Control of unscreened green pellets so that 85% of the furnace product at Cornwall was within the size range of -5/8 +3/8 in. (4) Improved quality of product with a tumble test of 94 and a "Q" index of 90 as the result of feeding a consistently uniform feed to a shaft furnace. In sintering, where sinter-mix temperature change and variable feed could cause errors in moisture measurement, the system was designed to maintain the correct moisture under virtually all plant operating conditions. It was successfully plant-tested and is now in use in most of Bethlehem&apos;s sintering plants. The system achieves: (1) Control of moisture within the desired limits for optimum production. (2) Continuous measurement and control of moisture even with intermittent feeding of mix, so that attention by the operator is seldom required. The two automatic control systems provide smoother startup, minimize upsets and contribute to the consistent control of process variables in pelletizing and sintering. MOISTURE-CONTROL SYSTEM FOR PELLETIZING Fig. 1 shows the general arrangement of the system for automatic control of moisture in pelletizing.1 In this system a bin level controller, using a single probe which regulates filter speed, maintains a uniform low concentrate level in the bin.&apos; The moisture meter, comprised of an analyzer and control components, continuously measures the moisture in the bed and adds water to adjust to the desired level. The meter is placed in an open-loop (feed-forward) control, i.e., water addition occurs downstream from the probes. Filter vacuum must be set so as to produce a filtercake moisture which is below the optimum for pelletizing. Bentonite is added after the

Jan 1, 1969

By Ogden B. Malin

In conducting the manufacture of extruded brass rods and brass forgings it has been noticed that there is considerable variation in the physical properties, particularly the machinability of different rods and forgings, even though the composition, working temperatures and method of manufacture remain the same. It is the purpose of this paper to attempt to establish the cause and extent of this variation, and also to determine whether variations in composition within certain defined limits influence hardness and machinability to any marked degree. The writer believes that this variation probably is due to the variation in grain size of the metal, therefore the microstructures of several compositions under various conditions of working were examined in an effort to establish this as a fact. Survey of Previous Work in Studying Extrusion Defects Very little has been published concerning defects in extruded and forged brass. In 1921, R. Genders1 $ delivered a paper before the British Institute of Metals, relative to a defect inherent in the extrusion process. This defect, commonly found in extruded brass rod, shows up in the form of a circle in a transverse section consisting of oxides and impurities, and is generally present in the last 25 to 30 per cent of the rod. Genders concluded that the defect is caused by the turning inward of the skin of the billet at the edge of the plunger because the inside of the billet is more plastic than the outside, which is in contact with the cooler container; the outside skin will lag behind to form the rear end of the rod. Genders suggested a movable die as a remedy, and while this met with fair success, it is not used in present practice. About the same time as Genders&apos; experiments, Tucker2 and Rosen-hain3 conducted experiments using colored plasticene in the form of a billet, and found much the same defect as Genders. Dr. Rosenhain State College, Pa.

Jan 1, 1932

By R. S. French

THE purpose of this paper is to present data that have been obtained during the past two years concerning the effects of prior cold-work and temperature and time of anneal upon the recrystallization and grain growth of 70-30 cartridge brass. It was desirable to study certain of these phases so that an accurate picture of the principles of the subject could be shown. The work is not intended to provide explicit annealing data, but to provide material examples that may help to clarify analogous problems concerning this alloy. Specifications often set limitations upon the grain size of annealed materials because of the importance of grain size upon subsequent manufacturing operations. It was, therefore, worth while to study the variables that affect the recrystallized grain size of this material. C. H. Mathewson and A. Phillips,1 W. R. Webster,2 and others have presented annealing characteristic curves of this alloy. A recent typical curve presented by R. S. Pratt3 is shown in Fig. I. The tensile properties and grain sizes are shown as functions of the annealing temperature. Such curves serve as a useful guide in determining the physical properties of annealed material, but as they are made generally under carefully controlled laboratory conditions they do not indicate the performance of metal annealed in a mill muffle, where conditions are different and the amounts of metal require necessarily longer heating times and temperatures. Study of the effect of time and temperature upon grain growth and subsequent recrystallization was made with a coil of metal having the following analysis: 70.04 per cent copper; 0.007 lead; 0.007 iron; 0.00 tin; 0.00 silicon; 0.001 nickel; 0.000 phosphorus; balance zinc. The sample coil was obtained from metal that had been rerolled from hot-rolled mill stock, and was received at 0.228-in. gauge, soft, with a grain size of 0.125 mm. This material was then rolled 43.5 per cent to 0.125-in. gauge and annealed to a 0.053-mm. grain size. In this condition, samples were cut and used in all of the experimental work reported in this paper. TIME The first study was of crystal growth at a constant temperature over a moderate length of time. Material was cut from the stock coil at 0.129-in. size and rolled 75 per cent hard to 0.032-in. gauge. From this piece small samples were cut ½ by 2 in., suitable for grain-size determinations. Twelve samples were placed in an electric furnace uniformly across the width, approximately an inch from the floor, A thermocouple was wired to the center sample, so that the approximate metal temperature could be followed. At various

Jan 1, 1944

By W. B. Price

AT the New York meeting of the American Institute of Mining-and Metallurgical Engineers held in February, 1926, W. H. Bassett and J. C. Bradley presented a paper entitled "Exudations on Copper Castings."§ The purpose of the present paper, as the title suggests, is to call attention to somewhat similar phenomena which the authors have encountered in brass and bronze. From a study of the examples given, a more-or-less speculative theory of "inverse segregation" is advanced. PROTUBERANCES ON ADMIRALTY BRASS In the rolling mill of the Scovill Manufacturing Co., there have been found quite commonly bars of certain alloys which had a sort of shaggy roughness on the surface due to slight metallic protuberances. No special attention was paid to these until some bars were found on which these protuberances were heavy enough at the bottom of the bars to produce a blistered appearance. A sample of the protuberances was milled off the surface of the bar illustrated (Fig.. 1a) and upon analysis was found to contain 66.66 percent. copper, 4.02 per cent. tin and .03 . per cent. lead, whereas the average composition of the bar was 70.21 per cent. copper, 1.21 per cent. tin, and .01 per cent. lead. A sample of the shaggy-rough protuberances at the -very top of a bar was also analyzed and was found to contain 2.45 per cent. tin, indicating that it was probably of the same origin as the blistered areas. These results were not entirely unexpected for previous analyses of this alloy had -revealed that the surface was richer in tin than the rest of the bar. This, of course, is contrary to what we would expect from a consideration of the equilibrium diagram and has been called "inverse segregation."

Jan 10, 1926

By V. J. Kniazeff, S. A. Naville

The problem of unsteady-state condensate-gas flow through porous media leads to a set of second-order non-linear partial differential equations. Such a set of equations is numerically solved in the case of radial two-phase flow around a well, taking into consideration both the thermodynamical properties of the fluid and the mechanical properties of the reservoir. The fluid properties, reflecting the PVT relationship of the gaseous and liquid phases, are expressed by using the partial specific masses of the two main separator products in these phases. The flow properties of the reservoir rock are expressed by the generalized Darcy&apos;s law for the liquid phase and by a quadratic relationship between the rate of flow and the pressure gradient for the gaseous phase. The numerical solution of the equations for pressure and saturation US radius and time is worked out through programs written for a computer. The evolution of bottom-hole pressures, well productivities or- deliverabilities and effluent compositions with the depletion of the reservoir is easily derived. The application to the Saharian gas-condensate field Hassi R&apos;Mel led to a better understanding of the drainage mechanism. A zone of fairly high liquid saturation develops around the wells, reducing the effective permeability, and represents a loss of condensible products in addition to the PVT-like retrograde condensation. lnside this zone, near the well, the deviation from Darcy&apos;s law for the flow of the gaseous phase governs the well deliver-ability. A back-pressure test has been computed and correlates with the field results. INTRODUCTION Two-phase flow of volatile hydrocarbons, like condensate gas or light crude oil, may be treated as the flow of a binary mixture by an arbitrary division of the chemical components into two groups. This is translated into two equations of mass continuity, which constitute a set of relation- ships for the pressure and the saturations vs the space coordinates and the time. The equations contain the laws governing the composition and the motion of the phases. The problem so defined is solved with the assumption that the compositions of the phases at any pressure are respectively the same as those observed in a PVT measuring cell under differential liberation. In a first series of computations, it was assumed that the flow obeys the generalized Darcy&apos;s law. A satisfactory representation of the retrograde condensation around the well was thus obtained. In addition, the trend toward decreasing effective permeabilities was obtained, and the computed composition of the effluent checked the laboratory values. However, it has not been possible within this basic assumption to represent the non-linear relationship between the production rate and the bottom-hole pressure drawdown as observed for gas wells in the field. Following the advice of A. Houpeurt it was decided to consider the relative permeability to gas as a function of the velocity of the gas Phase.1 The necessary physical determinations were made by E. COstaséque using a method devised by A. Houpeurt and R. Iffly. As numerical processing of the equations progressed, several difficulties were encountered which were overcome through collaboration with the computer manufacturer. This mathematical model of two-phase flow in porous media had been primarily intended for and extensively applied to the case of the Hassi R&apos;Mel gas-condensate field, operated by SN Repal for SEHR, a joint subsidiary of SN Repal and CFP (A). The programs have also found their applications to forecast the behavior of several fields in the Sahara area containing light and volatile hydrocarbons. BASIC EQUATIONS We will consider a zone in the porous reservoir where the flow properties and the in situ composition of the fluids can be assumed to be uniform. A part of the equations of transient flow can be written with the specific gravity of the fluids being taken equal to the sum of the contributions due to the

Jan 1, 1966

By H. F. Silliman, Daniel R. Hull, John R. Freeman

IN the normal operation of a brass-rolling mill, sheet and strip has, for the most part, been finished in comparatively thin gauges, involving a substantial amount of coldwork and a considerable number of anneals. This condition has been disturbed by the prep0nderance of cartridge brass, which is not rolled to thin gauges, and particularly by brass for artillery cartridge cases, on which the mill may finish its work at a thickness between 0.400 and 0.900 in. Obviously, the amount of rolling and the number of anneals to which such a product can be subjected are small compared with strip that is carried to a thickness of a few hundredths of an inch. As a result, critical examination into the internal condition of metal has been made on an extensive scale at a stage of manufacture that would not, in normal times, have been chosen for complete inspection. Under these conditions, a type of defect has been recognized that is not seen at thinner gauges. It might be more accurate to call it the appearance of a defect, since it refers to an apparently laminated, discontinuous structure, which, in fact, does not exist as such, and disappears after suitable treatment. For this reason it has been called a phantom lamination, which the authors consider an appropriate term. It is the purpose of this paper to describe the phenomenon and the conditions of its occurrence and, at least tentatively, to discuss its nature and cause. Great numbers of phantoms may be found in 2: 1 brass, either hot-rolled or cold-rolled. They are also found in 70-30 brass, sometimes when hot-rolled and generally when cold-rolled. It is not believed that phantoms are confined to these alloys but this paper is limited to them for the purpose of description. HOT-ROLLED 2:I BRASS For illustration, therefore, a typical cake of hot-rolled 2: 1 brass has been chosen. This was rolled to a slab 7/8 in. thick, from a casting 5 in. thick by 24 in. wide by 18 in. high, which was believed to have been sound. After hot-rolling and cooling, the slab was sheared and a portion of such a shear cut is shown in Fig. 1. It would be difficult to convince anyone viewing this specimen that the metal was not unsound. The impression would be confirmed by the appearance of a tensile break, as shown in Fig. 2. This is an ordinary tensile-test piece from metal just described. Although there was nothing in its tensile strength or elongation that suggested unsoundness, it appeared run through with pipes and laminations. To question the reality of such a condition would imply questioning the obvious. But, considering the history of the metal, it w0uld be difficult to believe that it could be so bad as it appeared. It seemed reasonable, though, that if the defects were what they appeared to be, they could be traced back from the sheared or broken face.

Jan 1, 1945

By R. H. Oliver

The purposes, types, preparation, and testing of flocculants are discussed. A flocculation compendium is included, indicating choice of flocculant for a given set of conditions. An economic evaluation of the process is presented. Solid-liquid separation is a major expense in most mineral processing flowsheets today. Proper use of flocculation can often lower the overall cost of a solid-liquid separation by reducing the size of sedimentation or filtration equipment. PURPOSE OF FLOCCULATION When is use of a flocculant justified in terms of overall process economy? 1) when it results in process improvement, such as producing a clear liquor for electrolysis, precipitation, ion exchange, or solvent extraction; 2) when it results in satisfying requirements of pollution abatement ordinances; 3) when it results in increased recovery of values that would otherwise be lost; or 4) when it results in considerable savings in capital expenditure due to use of smaller equipment. When can the use of a flocculant adversely effect overall process economy? 1) when it results in increased filter cake moisture, 2) when it results in decreased filtration rates, 3) when it results in considerable bulking of sedimentation underflow, 4) when it contaminates either the supernatant or sludge, or 5) when the cost of using the flocculant is greater than the savings due to its use. First step in consideration of flocculants for a given application is establishment of desired goals in terms of increased clarity of effluent, increased recovery of solids, or decreased size of equipment. The most economical solution to a solid-liquid separation problem is that combination of equipment and flocculant costs which meets the established goals at the lowest total annual expenditure. This economic decision can be made only after technical data has been obtained as outlined in next four sections. TYPES OF FLOCCULATION Flocculation is a process wherein individual particles are united into more or less tightly bound agglomerates or flocs, thereby increasing effective particle size of solids suspended in a liquid. Degree of flocculation of a suspension of finely divided solids in a liquid is controlled by a combination of probability of collision between particles and probability of adhesion after the collision has occurred.&apos; Probability of collision can be increased commercially through use of a paddle-type flocculator, combination flocculator, and clarifier or flocculating-type feedwell. Probability of adhesion usually can be increased by addition of a reagent known as a flocculant. Reagents act as flocculants through one or a combination of three possible mechanisms. The first is electrolytic neutralization of inter molecular repulsive force due to Zeta potential. This neutralization enables Van der Waal&apos;s cohesive force to hold the particles together after they collide.&apos; The second is the precipitation, within a definite pH range, of voluminous metallic hydroxide flocs which entrap fine particles. This process is known as coagulation.14 Third is the bridging of two or more particles by either natural or synthetic long-chain, high-molecular-weight organic polymers. This bridging is accomplished by adsorption of two particles at different sites on the same molecule or by bonding of two molecules, each adsorbed to a different particle. Considerable effort has been expended in explaining the action of these polyelec-trolytes and detailed accounts are available in the literature. CHOICE OF FLOCCULANTS It is impossible, at the present time, to specify the optimum type or amount of flocculant for a given application from a knowledge of the material to be treated. The standard procedure is to choose reagents or combination of reagents most likely to be effective on the slurry; then test them.&apos; The accompanying Flocculation Compendium (Table I) contains details of all currently available reagents sold as flocculants and it should be used when selecting the group of reagents for tests. This selection can be based on information listed in columns 4 and 5. Column 4 presents industries in which each floc-

Jan 1, 1961

By D. B. Robinson, C. A. Macrygeorgos, G. W. Govier

Experimental data have been obtained on the volurrletric behavior of ternary mixtures of methane, hydrogen sulfide and carbon dioxide at temperalures of 40°, 100" and 160°F up to pressures of 3,000 psia. The results indicate that the compressibility factors for this system do not agree with compressibility factors for sweet natural gases at the same pseudo-reduced conditions. The deviation increases as the temperature and methane content decrease. Discrepancies of up to 35 per cent were observed. A careful analysis has been made of the existing pUrblished data on compressibility factors for binary systems containing light hydrocnrbons and hydrogen sulfide or carbon dioxide. It has been found that the deviation of actual from predicted compressibility factors for methane-acid gas mixtures is a function of the methane content and the pseudo-critical properties,.v of the mixture. The ratio between actual compressibility factors for methane-acid gas mixtures and compressibility factors for sweet natrlral gases at the same pseudo-reduced conditions has been currelated over a range of pP,, from 0 to at least 7 arid a range of pT, from about 1.15 to at 1east 2 0 with an error not exceeding 3 per cent and over most of the range within I per cent. The validity of the correlation for mixtures containing appreciable hearvier hydrocorbons has not been fully established, but it is shown to be preferable than the use of a corretation based only on hydrocarbons. INTRODUCTION Although a relatively accurate method for predicting compressibility factors of pure materials is provided by charts based on reduced properties and the assumption that the compressibility factor is a unique function of T P and z the determination of the correct values of compressibility factors for gas mixtures is somewhat difficult. Two general methods of dealing with gaseous mixtures have been proposed. The first assumes a direct or modified additivity of certain properties of the mixture in terms of the properties of the individual components. Examples of this method are based on the familiar laws of Dalton and Amagat. The second method averages the constants of an equation of state applicable to the pure components. Both of these methods are of limited value in engineering calculations because the first usually provides reliable answers only over narrow ranges of pressure and temperature and the second is cumbersome to handle. In petroleum engineering practice accurate estimations of the volumetric behavior of natural gases arc frequently required. To fulfill this need, several generalized compressibility charts have been developed.&apos; &apos; Of these, the one prepared by Standing, el al is widely used at present. In the construction of charts of this type a third method for dealing with mixtures has been followed. It is based on correlation of pseudo-critical properties as outlined by Kay and calculated from the critical properties of the individual components in a mixture. Although these charts provide relatively accurate information on the compressibility of dry or wet sweet natural gases, they are less reliable when used for gases containing high concentrations of hydrogen sulfide or carbon dioxide or both. Thus, an experimental program, although time consuming, is the best means now available for the determination of the volumetric behavior of sour or acid gas mixtures. An increased interest in the behavior of these gas mixtures, particularly in connection with some of the fields in Western Canada where the acid gas concentration of the reservoirs may be as high as 55 per cent and where hydrogen sulfide alone may be as high as 36 per cent, provided the incentive for this study. It was the purpose of the investigation to determine the volumetric behavior of selected mixtures of methane, hydrogen sulfide and carbon dioxide over a range of temperature from 40" to 160°F and at pressures up to 3,000 psi. EXPERIMENTAL METHOD The apparatus used in this investigation was basically the same as that described by Lorenzo.&apos;" The amount of each pure component used in preparing the gas mixtures was measured over mercury in a glass-windowed pressure vessel. The pure components were then transferred individually in the desired amounts to a second glass-windowed pressure vessel where the volumetric behavior of the mixture was determined. Volume was varied by mercury injection or withdrawal. The capacity of the cell was about 125 cc. Temperatures in the cells were measured with copper-constantan thermocouples and a Leeds Northrup semi-