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By G. A. Vissac

The drying of fine coal involves special techniques, which are discussed and analyzed. Types of dryers employing these techniques are described. Calculations are presented for new methods of dealing with the entrained dust that is always present in fine coal drying operations. NEW conditions, new requirements, and new methods have increased the demand for more efficient and more economical methods of drying fine coal. Dewatering of larger sizes may reduce the surface moisture to 8 or 9 pct. It is more difficult, however, to dewater sizes below 1/4 in., and some filter cakes still contain as much as 20 or 25 pct moisture. Increased freight rates and stricter consumer specifications have resulted in a demand for further reductions in moisture content. This can be obtained only by heat drying. Most modern methods of heat drying disperse or spread the mass of coal to be dried, in an atmosphere of dry hot gases. The more intimate the contact between coal particles and hot gases, the quicker and more efficient the drying operation will be. Two different techniques are generally employed, using either a fluidized condition or an entrained condition of the coal to be dried. Fluidized Condition Fluidization of a body of sand was defined and explained by Fraser and Yancey in a paper published in 1926.' This condition was artificially obtained and maintained by proper regulation of the rate of air flowing through the sand body. "The sand bath 'boils' uniformly on the surface," they write, "and feels like a fluid." The fluidization technique was also described and analyzed by Steinmetzer2 in connection with the operation of an air cleaning table. His main conclusions are as follows: "Fluidity is, for the particles involved, the possibility of motion with minimum friction. . . . Then fluidity requires the introduction of various forms of energy capable of neutralising frictions. Two solutions can be used— air and/or mechanical motions (such as the shaking motion of the carrying deck of the air table). The combination of mechanical and air energy will give the widest margins of size ratios and of bed thickness, translated in capacity per unit area of the carrying table." Richardson and Langston3 have indicated results obtained with a dryer working with a fluidized bed. They used a vertical tube type of dryer, however, without the assistance of any mechanical energy, and without any lateral motion of the fluidized bed. The capacity of such a dryer is too limited for practical applications, since the speed of the acceptable air currents is held to the speed of fall of the particles involved. Capacities as low as 182 Ib of coal per hr per sq ft of dryer area are indicated. As stated by Richardson: "A basic limitation to a fluidised bed dryer is that the velocities of the gas must be held within a definite range; with velocities of 10 ft per second, all coal minus 6 mesh in size will be entrained, and the operation is then similar to that of a Flash dryer." A fluidized bed must be virtually static. The coal particles simply kept in suspension offer a minimum resistance to the flow of gases, insuring the most favorable conditions for rapid evaporation of surface moisture. However, very wet fine coal, i.e., over 12 pct of surface moisture, will be delivered in the forms of mud balls, or as a soggy, sticky mass, almost impossible to disperse, sticking and acting as a wet blanket on the deck. Strong currents of gases and wide deck perforations will be required to punch holes in the wet mass and gradually loosen and fluidize it. The mechanics of fluidizing a bed of coal in a gas medium for the purpose of obtaining the most efficient drying condition are entirely similar when the fluid used is water and the purpose is to break up and distend a bed of coal to be cleaned so that perfect stratification according to densities will be insured. Purely mechanical energy is used in the basket-type jig, water pulsations in the piston and in the Baum-type jigs. A combination of mechanical motion and of air pulsation offers the most efficient and favorable conditions. Entrained Condition The most critical factor to be considered in the design of a dryer employing the entrained condition technique is the speed of the hot gases to be circulated in the drying column. With insufficient gas velocity, excessive amounts of the largest sizes will drop to the bottom of the dryer column without being thoroughly dried. On the other hand, high gas velocity will cause degradation, dust losses, and high power consumption. Figs. 1 and 2, reproduced from Hanot,4 show the relative importance of speed and temperature for various sizes of particles. It can be seen, for instance, that to maintain in unstable equilibrium particles of 1/4-in. size in a gas current at 500°C, a speed of 30 meters per sec, or 6000 fpm, will be required. For % -in. particles an almost prohibitive speed of 45 meters per sec, or 9000 fpm, will be necessary. In practice, maximum gas velocities of 3000 fpm are recommended; since power increases as the cube of the velocity, it can be seen that beyond certain limits such dryers would not be economical. If the particles were moving at the same speed as the hot gases they would remain in the same

Jan 1, 1954

By H. L. Riley, B. W. Gandrud

AS far as the present writers know, this system of flotation has not been used elsewhere in this country, but in the last couple of years it has been introduced, with minor variations, at one plant in England and one in Wales.' The system has been described and discussed in a number of publications.2-5 The following is quoted from an abstract of the latest of these,5 a paper presented at an International Conference on Industrial Combustion in 1952. On the basis of experience to date with the commercial plants, it is believed that the kerosene-flotation process incorporates all the necessary elements to make it greatly superior to anything else now available for treating of fines in wet processes of coal preparation. Additional study and investigation are still needed, however, to determine if certain phases of the process can be improved to such an extent as to make it generally satisfactory and acceptable to the industry. Further improvements will be needed with respect to the capacities of the flotation cells and the reagent consumption. The situation referred to above explains why an investigation is being made of the possibilities of achieving better cell capacities. Results obtained from this investigation, which is still in progress, are believed significant with regard to both cell capacity in general and the relation of cell design to cell capacity in particular. Commercial equipment now being used in a laboratory-type investigation should have performance characteristics similar to those of the larger machines. Equipment and Procedures: All flotation tests have been made in a standard Denver sub-A 24x24-in. unit cell of 12-cu ft volume. Cell modifications to make it more suitable for the tests were an adjustable front-wall section for varying cell depth and a perforated scraper-drag assembly for removal of the float product. There is also an apron dry-coal feeder, a gravity-feed water supply, reagent feeders, and a centrifugal pump that feeds the mixture of coal, water, and reagents into the flotation cell. A wattmeter connected into the drive-motor circuit records the power requirements of the impeller throughout each run. Dry coal, water, and reagents are all fed through a pan-type intake to the feed pump. A Sturtevant blower was set up to furnish air for supercharging. A centrifugal pump with a garbage-can intake provides for disposal of refuse flow to an outside settling tank. Figs. 1 and 2 show the flotation cell; Fig. 2 also illustrates the blower for supercharging. For purposes of this investigation, the percentage by weight of the feed coal recovered in the float product under a standard set of conditions has been considered as the criterion of cell capacity. The authors realize that such a criterion may be somewhat unorthodox, as the term cell capacity is usually understood to refer to feed input and ordinarily takes into account the ash analyses of the float product and refuse. However, the word capacity is flexible enough so that Webster gives one definition as maximum output, a definition which seems to justify, at least partly, acceptance of the above criterion. It has been the authors' experience in the Birmingham district that the ash-reduction efficiency of the coal-flotation process is generally satisfactory and that the only real problem is to increase the rate of float recovery so that the feed rate to any given bank of cells can be increased without undue loss of coal in the refuse. Originally it was planned to operate the flotation cell to simulate continuous operation during sampling periods. It was assumed that operating for reasonable time with feed coal, water, and reagents turned on would stabilize conditions so that the weight of float coal discharged during a fixed time interval would be an accurate measure of the rate at which the coal was being floated. It developed, however, that this supposition was erroneous. The float coal, caught for fixed time intervals and weighed, gave widely varying results in duplicate runs. Efforts to correct this trouble failed, and it was decided to try to operate on a batch-test basis, whereby all the float coal produced during a run on a known weight of feed coal would be caught in tubs, dewatered, and weighed. This method gives consistent and reproducible results, with total float product weight rarely varying by more than 3 or 4 pct on duplicate runs. The standard test procedure is as follows: A 132-lb sample of dry feed coal is weighed and placed in the feed hopper. The feeder is adjusted for a rate of 800 lb per hr. Feed water and reagents are turned on, and the feed and refuse pumps are started. One minute later the impeller is started. Six minutes are allowed for the cell to fill up with the water-reagent mixture. The feed of dry coal is started at the end of this 6-min period. One minute later the float-coal removal drag is started. The float coal is caught in one tub for the first 6 min after the flow of feed coal starts. Tubs are then changed, and the float coal is caught in a second tub until the feed coal runs out, when the tubs are again interchanged to catch the float coal for the remainder of the run in the first tub. The cell is kept running for 3 min with the water and reagents on after the feed stops to allow residual float coal to be removed. At the end of a test the wet float coal in both tubs is weighed and the total weight recorded. The product in the second tub is used for moisture determination and screen-size analyses. When the

Jan 1, 1956

By Hobart M. Kraner

THE mineralogy of blast furnace sinter is of interest because its mineral content is one of the important factors contributing to its character. There are so many other factors affecting the properties of the sinter, however, that it is well to mention them here. The proportion and character of the raw materials, that is, raw ores, concentrates, returns, and fuel, as well as the mixing and the water content, all have a marked effect on the physical properties of the product and the degree to which sintering action can be carried on. The process of sintering is a relatively fast operation. In as much as appreciable time is required to carry on processes of fusion in such masses of low thermal conductivity, large lumps of hematite ore frequently remain unfused and partly unchanged in state of oxidation in the sintering process. The kind, the grain size, and the amount of fuel used affect both the completeness of the fluxing reaction and the prevailing atmosphere. The rate of reduction in laboratory tests is not only dependent upon the state of oxidation of the sinter but also upon the sizing and porosity. Atmosphere and temperature affect the state of oxidation of the iron oxide, and the atmosphere alone may determine the ferrous minerals that finally develop. The rate and extent of cooling, the type of coolant, the subsequent handling, and screening all have serious effects upon the type of sinter that eventually enters blast furnace bins. The degree to which actual fusion or fluxing takes place in the sintering operation has a marked effect upon density. A sinter which has been extensively fused by high content of fuel in the batch will no doubt have a higher weight on the bulk basis than one which had a lower fuel content. As high temperatures are required to do this job, the iron oxide under these conditions will be largely magnetite. Sintering at low temperatures to produce larger proportions of hematite means a decrease in the amount of liquid formed and a much more sensitive bonding process. In this case the liquid must be distributed more uniformly and thereby used more efficiently than would be the case where higher temperatures were permitted to prevail more or less indiscriminately. Where coarse ore particles are used in a sinter mix it is not expected that any particles coarser than 1/4-in. can be fused and incorporated in the system to such an extent that the gangue contained within these lumps will have been converted or fused by the sintering process. It is for this reason that coarse ore, returns, or both, in a sinter usually result in a sinter which breaks easily and at the same time may contain some of the original minerals of the lump, such as quartz and hematite. In examination of sinters at Bethlehem Steel Co. minerals such as quartz and corundum have been found, none of which are considered normal associ- ates of wustite or magnetite. Some degree of heterogeneity or lack of equilibrium is not unusual in the sintering process. The differences in specific gravity between hematite and magnetite might be ample reason for poor strength in a not very well sintered mass containing coarse particles of. ore or returns. The shrinkage taking place in a lump of hematite in its conversion to magnetite by temperature and/or atmosphere is appreciable. Sintering of ores as it is carried out is crude chemistry, for the grain size is relatively coarse, the application of heat is certainly not uniform, and the time factor is inadequate for other than partial completion of reactions. Coarse lumps of coke or coal cause local heating around these centers, and fuel which is too fine may result in such slow burning that sufficiently high temperatures are not always obtained. High temperatures are essential to the work required. The Swedish practice of sintering is established on the basis of producing an easily reducible product high in hematite. This is achieved through uniformity of grain size in the sinter mix and close control of the temperature through careful regulation of fuel and sintering rates. This produces a sinter which is very tough in character and which has a high degree of porosity. Although the hematite content is not produced upon cooling by drawing air through the mass, there would be greater possibility of accomplishing this reaction with this type of sinter than is the case in American practice. In the latter, the temperatures are so high that temperature alone converts most of the mass to magnetite. The grains are so coarse in the final product that together with the fluxed condition it would be difficult to reoxidize them to hematite upon cooling. An examination of the iron-oxygen diagram' shows that hematite does not exist above 2651°F. It also shows that there is no liquid in the pure magnetite-hematite system until 2881°F is reached. On the other hand, in the system magnetite-wustite liquids exist at considerably lower temperatures than this. It will be seen, therefore, considering only the iron oxides, that the bonding action obtained in America in sinters comes about through considerable temperature and/or reducing conditions that produce compositions containing even less oxygen than is contained in magnetite or than results from the fusion of silicates. The bonding obtained from the iron oxides is encouraged by the reducing conditions that prevail in the vicinity of the fuel particles in a mass of this sort, where temperatures are above 2600°F. As magnetite and wustite are opaque, they do not lend themselves to petrographic study by transmitted polarized light. The silicates found in sinter and the glass that has not crystallized transmit light and can be studied by these methods in which indices of refraction and other optical properties of anisotropic crystals lead to their definite identification. The index of refraction is the only property that can be measured in glass under the microscope, and this is a clue to its probable approximate composition.

Jan 1, 1954

By J. Walter Snavely

PRESENT-DAY processing in many industries, calcining, sintering, briquetting, beneficiation and nodulizing, increasingly calls for the handling of large volumes of hot bulk materials. Various types of conveyors have been employed. This discussion will cover the factors governing their selection. For temperature ranges up to 400°F, or approximately 200 °C, a wide range of conveyors is available. Special constructions of rubber conveyor belts, steel conveyor belts, vibrating and shaker conveyors, apron conveyors, and drag chain conveyors, all are used successfully. As temperatures go well above 400 2F, however, choice of conveyors is narrowly limited. This paper will consider the problem of handling bulk materials only where the temperatures exceed 400°F. The arbitrary selection of 400 °F as a dividing point undoubtedly can be challenged, as special conveyor belting constructions are available which are suitable for temperatures in excess of 400°F. However, when the relatively short life of such belts and the cost of their replacement, with the attendant down time, are balanced against the reliability and long service life of the properly designed steel constructed units to be discussed, there is little question in any operator's mind that the special belts are more expensive to use. Because the conveyors under study are for the handling of bulk materials, inevitably including a high proportion of fines, obviously wire mesh belts cannot be included for consideration. Even though this type of conveyor is widely used at high temperatures, i.e., for carrying glassware through a lehr, it is unsuited for the conveying of bulk materials, and therefore will be excluded from further discussion in this paper. Preliminary to the study of the conveyor itself is the determination as to whether the material is to be cooled while it is being handled, or whether the processing requires retention of all heat and the maintenance of a given temperature range. In the majority of cases cooling is incidental to or part of the handling process, when the handling, for example, follows completion of sintering, roasting, calcining, refining, or some other process. To meet such operating conditions successfully, the conveying medium used must have: 1—a construction capable of withstanding maximum initial temperatures of the material being handled. 2—a construction providing efficient heat transfer for cooling. 3—a construction providing dependable operation and long life with minimum service requirements, and 4—a construction providing controlled and efficient conveying. Under the usual conditions of cooling during the handling, the construction selected to withstand the initial maximum temperatures does not necessarily involve using alloys, as excellent results can be achieved with normal carbon steels and cast irons, when they are properly applied and proportioned. The earliest and simplest type of conveyor for handling very hot materials is the cast steel drag chain conveyor, still widely used for handling hot cement clinker, as illustrated by Figs. I and 2. Because of the rugged and generous proportions of the chain link design, low carbon steels are entirely suitable for the links. The pins, however, must be alloy steel. The simple, rugged construction of this type of conveyor makes it readily capable of withstanding high initial temperatures, even though the chain is operating buried in the material. The drag-chain type of conveyor has advantages and limitations. Although the efficiency of the heat transfer is relatively poor, the life of the conveyor is reasonably long, and because of its crude simplicity it does not require much servicing. However, as a conveyor, it is limited in capacity, and largely limited to horizontal runs. Furthermore, because of the crude design, heavy weight, and the chain operating at the temperature of the material, greatly reducing permissible operating chain pulls, this type of conveyor is limited to relatively short centers. Another type of conveyor that has been used for very hot materials is the cast pan conveyor. Because of its very generous proportions the cast pan, which is made of either cast iron or malleable iron, can withstand initial maximum temperatures. It also provides efficient heat transfer for cooling. Further, it is on efficient conveyor construction, which can be used for inclines. Because the chain employs rolling friction instead of sliding friction, and is not in the maximum temperature zone, much longer centers are possible. It is this type of conveyor that is frequently used in the casting of various metal pigs, pig iron, and aluminum; it is obvious, therefore, that very high initial temperatures are being handled. With this kind of conveyor the return run is frequently sprayed with water to accelerate heat transfer. The build-up of residual heat in the very heavy cast pans is thus overcome. The outboard roller steel pan conveyor is an improved pan conveyor' which provides high rates of heat transfer and substitutes formed steel pans for the heavy cast pans. It is a very efficient conveying medium. The details of this particular construction are clearly shown in Fig. 3. An early application of this type of conveyor is shown in Fig. 4. In this case the conveyor units are handling roasted phosphate rock at average temperatures of 1000" to 1500°F, and frequent maximum temperatures as high as 1900°F. Several widths are used. The capacity of the unit at a speed of 50 fpm is approximately 30 tph per inch of width at peak loadings, average capacity being about 1/3 of peak loading. The assembled conveyor is shown in Fig. 5, with views of both the top and the underside to show all the construction details. In particular, the following general design principles were carried out in this construction:

Jan 1, 1954

By E. T. Turkdogan

The activity of sulfur was determined as a function of composition of ferrous sulfide by equilibrating with hydrogen sulfide-hydrogen gas mixtures at 670° , 800°, and 900". The present results supplement the available data over the composition range from 36.6 to 39.5 pct S. The X-ray lattice spacing measurements made are in accord with the available data and indicate that the limiting composition FeSl.008 may be taken for the iron-iron sulfide equilibrium. The growth rate of ferrous sulfide on iron was measured by reacting iron strips or blocks in hydrogen sulfide-hydrogen gas mixtures. Owing to the slow approach to equilibrium between the gas phase and the surface of the sulfide layer, The sulfidation experiments were carried out for several days. It is shown that the growth rate ullimately proceeds in accordance wilh the parabolic rate law. From the parabolic rate constants and the thermodynamic data on iron sulfide the self-difiusivity and chemical diffusivity of iron in ferrous bisulfide are evalualed. The self-diffusivity of iron thus derived zs found to increase with increasing sulfur content. THE ferrous sulfide known as "pyrrhotite" is a non-stoichiometric phase having a wide composition range from about 50 to about 58 or 60 at. pct, depending on the sulfur activity. RosenQvistl studied the thermodynamics of this phase over wide ranges of temperature and composition. Hauffe and Rahmel' and Meussner and ~irchenall~ studied the parabolic rate of sulfidation of iron in sulfur vapor. By using markers, these investigators showed that the iron cations were the predominant diffusing species in iron sulfide. This is confirmed decisively by the self-diffusivity measurements of condit4 who showed that the self-diffusivity of sulfur in ferrous sulfide is several orders of magnitude lower than the self-diffusivity of iron. Although much has been learned from these studies about the Fe-S system, further research on this subject was considered desirable for better understanding of the physical chemistry of iron sulfide. This work was confined to the study of the kinetics of sulfidation of iron in hydrogen sulfide-hydrogen gas mixtures. The results of this study are given in two consecutive parts. Part I, the present paper, is on the parabolic rate of sulfidation of iron and the diffusivity of iron in ferrous sulfide. The second paper, Part 11, is on the kinetics of the surface reaction between hydrogen sulfide and ferrous sulfide. EXPERIMENTAL Three types of experiments were carried out: i) equilibration of ferrous sulfide with gas of known E. T. TURKDOGAN, member AIME, is Manager,Chemical Metallurgy Division, Edgar C. Bain Laboratory for Fundamental Research, U. S. Steel Corp., Research Center, Monroeville, Pa. Manuscript submitted March 6. 1968. ISD sulfur potential; ii) X-ray studies of ferrous sulfide; and iii) measurements of the parabolic rate of sulfidation of iron. Equilibrium Studies. About 1 g of iron powder or foil. contained in a small recrystallized alumina crucible ind suspended from a calibrated silica spring, was reacted with a hydrogen sulfide-hydrogen mixture of known ratio until no further change in weight was observed. %hen the gas composition was changed and the new state of equilibrium was established after several hours of reaction time. The composition of the sulfide was obtained from the initial weight of the sample and the weight after equilibration. X-Ray Studies. The lattice parameters of some of the equilibrated samples were determined using the General Electric XRD-5 diffractometer with a cobalt tube (no filter) set at 40 kv apd 10 ma; the CoK, radiation was taken as 1.79020A. Observed 220 and 311 diffraction peaks of silicon served as an internal comparison standard to correct for possible misalignment of the goniometer. The lattice parameters of the sulfide phase were calculated from the corrected Bragg angles of the 110 and 102 peaks. Rate Studies. In the initial experiments attempts were made to measure the parabolic rate of sulfidation by measuring the gain in weight of a thin iron strip, -0.05 cm thick, suspended from a silica spring in the reacting atmosphere. The preliminary experiments showed that this technique was not reliable for the measurement of the parabolic growth rate of the iron sulfide layer. In the subsequent experiments the data on growth rate were obtained by measuring, on a microscope stage, change in the thickness of the sample after reaction for a specified time in a hydrogen sulfide-hydrogen mixture of known sulfur activity. For each reaction time a new sample was used. Precision-machined iron blocks, 0.5 by 2 by 5 cu cm, were de-greased and annealed in hydrogen for several hours prior to the sulfidation rate measurements. The experiments were carried out at 670°, 800°, and 900°C in gas mixtures having the ratios, and 1.0 for periods of times from a few hours up to 8 days. Apparatus and Materials. A vertical globar tube furnace with a 3-in.-long uniform temperature zone was used. The glass tube fittings were fused on the zircon reaction tube, 1.5 in. diam. The temperature was measured with a Pt-10 pct Rh/Pt thermocouple placed in the hot zone of the furnace inside the reaction tube (an alumina thermocouple sheath was used). A separate thermocouple was used for the temperature controller which maintained the furnace temperature constant within about 2°C. Anhydrous liquid hydrogen sulfide and oxygen-free dry hydrogen from gas tanks were used in preparing the gas mixtures by the constant head capillary flow-meters. In all cases volume flow rate was 1000 cu cm per min at stp, corresponding to a linear velocity of about 6 cm per sec at 800°C; under these conditions

Jan 1, 1969

By Milton R. Pickus, Earl R. Parker

THE modern theories of creep¹-4 in general have been based upon the concept of generation and migration of dislocations, with the generation process normally assumed to be rate controlling. The theories are generally deficient in that they fail to take into account many factors that are known to influence creep. The influence of the state of the surface of the test specimen has been almost completely overlooked; yet the present report shows that the nature of the surface may, in certain cases, govern the creep characteristics of a specimen. In the period since Taylor" applied the concept of dislocations to a study of metals, a school of thought has developed that closely relates the plastic deformation of metals to the generation and migration of dislocations through the crystal lattice. It might be expected that the thermal energy required for the generation of a dislocation would be different from that for migration of the dislocation through the lattice. Furthermore, the activation energy for generation would be expected to vary for different parts of the solid metal. It has been predicted that dislocations would be generated most easily at external surfaces, but could also be activated at certain internal surfaces such as grain or phase boundaries. Within the body of the metal a range of values for the activation energy might be expected because of different degrees of disorder at such regions as grain boundaries, impurities, and second-phase particles. The particular value of the activation energy that was rate determining could then depend on the specific conditions of a test. If, for example, the surface atoms were by some means constrained, the generation of dislocations in the body of the metal might become the important factor. On the other hand, other conditions may favor generation at the surface. It is possible then that the creep behavior may not be completely determined by the inherent properties of the metal. Even the environment in which a test is carried out could have a significant effect. In fact it is conceivable that in order to obtain the maximum creep resistance from a given alloy, the surface atoms must be so constrained that the activation energy for generating dislocations on the surface is at least equal to that required for generation in the body of the metal. On the basis of such considerations, and in view of the limited number of publications discussing this subject, it seemed that an investigation of the influence of the state of the surface on creep might yield information of both theoretical and engineering interest. Experiments on single crystals, demonstrating a variation in the mechanical properties due to alterations in the surface layer, have been reported by several investigators.6-13 he results of these experiments have been briefly summarized;14 consequently, the earlier work will not be reviewed here. As an example of these findings the observations of Cottrell and Gibbons may be cited. They reported the critical shear stress of a lightly oxidized cadmium single crystal is greater by a factor of 2½ than a specimen with a clean surface. Materials and Methods Single crystals M in. in diam and 8 in. long were prepared from Horse Head Special zinc, melted under an atmosphere of helium in a large pyrex test tube, and drawn up into a long ½ in. diam pyrex tube by means of a vacuum pump. The cast zinc rods thus produced were cut into convenient lengths and sealed in evacuated pyrex tubes. Single crystals were grown by gradual solidification of the remelted rods. Cleaving the ends of the single crystal specimens chilled by liquid nitrogen proved a simple method for determining orientations from the exposed basal plane from the markings left on the cleaved surface that gave the slip directions with sufficient accuracy for the experimental work. The specimens chosen for the experiments were those having the angle between the basal plane and the specimen axis within the range of 15" to 65". Since zinc single crystals are quite delicate, it was necessary to devise an appropriate method of gripping the specimens in order to suspend them in the furnace and apply the load. Stainless steel collars were prepared having an inside taper, the smaller end of the taper being of such a size that the specimen could just pass through freely. The tapered hole did not extend the full length of the collar; a sufficient thickness of metal remained so that a hook could be attached to provide a means of applying the load and suspending the specimen. One of the collars was slipped over the upper end of a specimen which was supported vertically in a steel jig. The collar was then heated electrically until the end of the crystal melted and filled the collar with molten zinc. At this point the application of heat was discontinued, whereupon the molten zinc quickly solidified, due to the chilling effect of the jig. The specimen was then inverted and the second collar applied in a similar manner. The jig served several purposes: limiting the length of specimen that was melted, providing excellent alignment of the collars with respect to the specimen axis, and protecting the specimen from mechanical damage. Once the specimen was suspended in the furnace and loaded, it was desired to accomplish the surface treatment with a minimum of disturbance of the specimen. Around the specimen was a long pyrex tube, the upper portion of which was approximately 1 in. in diam, and in it was a copper coil of such a diameter to fit snugly against the tube. A specimen, approximately ½ in. in diam and 4 in. long, was suspended by means of a stainless steel rod so that it hung within the copper coil. The lower portion of the glass tube was approximately ¼ in. in diarn, and passing through it was a 5/32 in. diam stainless steel rod which hung from the lower specimen collar. This portion of the glass tube and the stainless steel rod extended through the bottom of the furnace. A T-connector, with suitable packing, was attached to the lower end of the stainless rod to provide a water-

Jan 1, 1952

By W. Bonfield

A study has been made of the dislocation substructures produced in hot-pressed beryllium specimens strained to various levels in the range from 800 x 10-6 In. pev in. to fracture. A number of distinctive dislocation configurations were observed in this region which had not been noted at lower levels of strain. These included dislocation-dislocation interactions to form networks, dislocation "walls", subgrain boundaries and complex arrays, interactions between dislocations and large beryllium oxide particles, and the generation of dislocations from certain particles. The nature of these differences in substructure and their relation to the stress-strain characteristics of polycrystalline beryllium are discussed. In a previous study1 of the plasticity of commercial-purity, hot-pressed beryllium a transition was found in the deformation characteristics in the mi-crostrain region. The initial plastic deformation could be represented by a parabolic stress-strain equation, but above a critical stress there was a complete departure from this relation and a reduction in the strain-hardening rate. The dislocation configurations produced by various levels of micro-strain in this region were examined by transmission electron microscopy and a general correlation was established between the observed transition in deformation characteristics and the dislocation structure of the material. The two stages in the micro-strain region distinguished in these experiments were designated as Stage A' and Stage B'. Stage A' type deformation generally was noted up to a plastic strain of -80 x 10"6 in. per in. and Stage B' type from -80 x 10-6 to -800 x 10'6 in. per in. The discovery of two stages in the microstrain region naturally posed pertinent questions as to the existence of any further distinct stages in the subsequent plastic deformation. The purpose of this paper is to present a study of the dislocation configurations produced in similar beryllium specimens strained to various levels in the range from -800 x 10 in. per in. to fracture and to discuss the relation between substructure and the stress-strain characteristics. It is concluded that this region of strain can be considered as a distinct stage in the plastic deformation of polycrystalline beryllium. Tensile specimens of gage length 1 in. and cross section 0.18 by 0.06 in. were prepared from commercial-purity, hot-pressed QMV beryllium and then annealed at 1100°C for 2 hr. 2 followed by a careful chemical polishing procedure.3 The specimens were strained at a constant rate to various levels of strain in the range from -800 x 10-6 in. per in. to fracture (at 0.5 to 2 pct elongation), using the Tuckerman strain-gage technique1 to measure plastic and total strain. Thin foils were obtained from the strained and fractured specimens by chemical polishing3 and were examined using an RCA-EMU 3 electron microscope. Considerable care waS taken to avoid both accidental deformation during the preparation of the thin foils and excessive heating during their examination. Selected-area diffraction patterns were determined for each micrograph. Tilting experiments were also performed whenever appropriate to establish the dislocation zero-contrast position and hence determine the Burgers vector. This operation was sometimes not possible due to the rapid contamination of the foils which occurred in the electron microscope. RESULTS AND DISCUSSION To enable the distinctions between the dislocation arrays at high and low strain levels to be adequately made, the main characteristics of Stage A' and Stage B' deformation are briefly reviewed. 1) Stage A'. In the annealed starting condition there was a variable density (5 x 107 to 3 x 10' cm per cu cm) of isolated dislocations within a grain. The initial deformation in a tensile specimen was heterogeneous, with the dislocation density increasing in a few grains to 5 x 10g to 1.5 x 101° cm per cu cm. The deformation occurred exclusively on the basal plane by the movement of one or more 1/3 (1130) type dislocation systems. The dislocations were long and regular in form and nearly all the intersections exhibited a simple four-point node configuration. No interactions between glide dislocations and beryllium oxide particles were observed. 2) Stage B. In Stage B' there was a large increase in the number of grains exhibiting dislocation movement and also a change in the nature of the deformation, in which jogged dislocations and elongated loops became the characteristic feature. The splitting up of the elongated loops into smaller loops and the possibility of source action from the re-

Jan 1, 1965

By Fred C. Bond

MOST investigators are aware of the present unsatisfactory investigatorsstate of information concerning the fundamentals of crushing and grinding. Considerable scattered empirical data exist, which andare useful for predicting machine performance and give acceptable accuracy when the installations and materials compared are quite similar. However, there is no widely accepted unifying principle or theory that can explain satisfactorily the actual energy input necessary canexplain commercial installations, or can greatly extend the range of empirical comparisons. Two mutually contradictory theories have long existed in the literature, the Rittinger and Kick. They were derived from different viewpoints and logically lead to different results. The Rittinger theory is the older and more widely accepted.'TheRittinger In its first form, as stated by P. R. Ritted.'tinger, it postulates that the useful work done in crushing and grinding is directly proportional to the new surface area produced and hence inversely proportional to the product diameter. In its second form it has been amplified and enlarged to include the concept of surface energy; in this form it was precisely stated by A. M. Gaudin' as follows: "The efficiency of a comminution operation is the ratio of the surface energy produced to the kinetic energy expended." According to the theory in its second form, measurements of the surface areas of the feed and product and determinations of the surface energy per unit of new surface area produced give the useful work accomplished. Computations using the best values of surface energy obtainable indicate that perhaps 99 pct of the work input in crushing and grinding is wasted. However, no method of comminution has yet been devised which results in a reasonably high mechanical efficiency under this definition. Laboratory tests have been reported- hat support the theory in its first form by indicating that the new surface produced in different grinds is proportional to the work input. However, most of these tests employ an unnatural feed consisting either of screened particles of one sieve size or a scalped feed which has had the fines removed. In these cases the proportion of work done on the finer product particles is greatly increased and distorted beyond that to be expected with a normal feed containing the natural fines. Tests on pure crystallized quartz are likely to be misleading, since it does not follow the regular breakage pattern of most materials but is regularrelativelybreakage harder to grind patternat the finer sizes, as will be shown later. This theory appears to be indefensible mathematically, since work is the product of force multiplied by distance, and the distance factor (particle deformation before breakage) is ignored. The Kick theory4 is based primarily upon the stress-strain diagram of cubes under compression, or the deformation factor. It states that the work required is proportional to the reduction in volume of the particles concerned. Where F represents the diameter of the feed particles and P is the diameter of the product particles, the reduction ratio Rr is F/P, and according to Kick the work input required for reduction to different sizes is proportional to log Rr /log 2." The Kick theory is mathematically more tenable than the Rittinger when cubes under compression are considered, but it obviously fails to assign a sufficient proportion of the total work in reduction to the production of fine particles. According to the Rittinger theory as demonstrated by the theoretical breakage of cubes the new surface produced, and consequently the useful work input, is proportional to Rr-l.V f a given reduction takes place in two or more stages, the overall reduction ratio is the product of the Rr values for each stage, and the sum of the work accomplished in all stages is proportional to the sum of each Rr-1 value multiplied by the relative surface area before each reduction stage. It appears that neither the Rittinger theory, which is concerned only with surface, nor the Kick theory, which is concerned only with volume, can be completely correct. Crushing and grinding are concerned both with surface and volume; the absorption of evenly applied stresses is proportional to the volume concerned, but breakage starts with a crack tip, usually on the surface, and the concentration of stresses on the surface motivates the formation of the crack tips. The evaluation of grinding results in terms of surface tons per kw-hr, based upon screen analysis, involves an assumption of the surface area of the subsieve product, which may cause important errors. The evaluation in terms of kw-hr per net ton of —200 mesh produced often leads to erroneous results when grinds of appreciably different fineness are compared, since the amount of —200 mesh material produced varies with the size distribution characteristics of the feed. This paper is concerned primarily with the development, proof, and application of a new Third Theory, which should eliminate the objections to the two old theories and serve as a practical unifying principle for comminution in all size ranges. Both of the old theories have been remarkably barren of practical results when applied to actual crushing and grinding installations. The need for a new satisfactory theory is more acute than those not directly concerned with crushing and grinding calculations can realize. In developing a new theory it is first necessary to re-examine critically the assumptions underlying

Jan 1, 1953

By Maurice Rey, Victor Formanek, Paul Chataignon

IT is found when floating oxidized lead ores by sulphidization, that the presence of calcium salts in the water is usually detrimental and lowers the recovery. This effect is particularly marked in dry countries such as North Africa, where the waters often carry large amounts of calcium sulphate and where the ore may even contain gypsum. This effect is particularly marked in dry countries such as North Africa, where the waters often carry large amounts of calcium sulphate and where the ore may even contain gypsum. The effect of calcium salts is readily visible. Whereas in their absence cerussite is quickly stained brown and then .black by sodium sulphide, in their presence the mineral remains very light in color. A similar- effect is produced when barium sulphide is used as a sulphidizing agent instead of sodium- sulphide. Magnesium salts have little or no effect and even tend to reduce the detrimental effect of calcium salts. A study of this phenomenon indicates that it is due to the precipitation of calcium or barium carbonate in contact ,with the mineral simultaneously with the formation of lead sulphide.

Jan 1, 1950

By Anthony G. Reid

INTRODUCTION At the time of the death of Mao Tse-tung in 1976, China was a major oil producing country with a daily oil flow in the order of 1.735 million barrels. This position had been achieved with minimal assistance from the outside world. Further, only some fifteen years had elapsed since the country's daily oil production capacity had hovered at the barely significant level of one hundred thousand barrels. Why then did the new leaders of China, after this very creditable record of success, suddenly change the direction of the country's drive for future hydrocarbon production? First, by switching much of the emphasis of exploration from onshore to the offshore continental shelf basins, and further by apparently abandoning the philosophy of self reliance calling upon the world's oil industry to share in the task of locating and developing these potential offshore energy reserves. The answer is probably only partly understood by those of us outside China, However, a number of factors exerting an important influence on this decision can be identified. THE MOVE OFFSHORE The new leadership was anxious to rapidly move China into her rightful place amongst the powerful and technologically advanced nations of the world. Modernization became the slogan, specifically modernization on four fronts, agriculture, industry, technology and military with the goal to "catch the west by the year 2000". But how to generate the capital to finance this massive modernization program? The rapid escalation of the price of crude oil following the 1973 Oil Embargo and the continuing apparently insatiable world demand for this now extremely precious primary resource was very clear to all. China, as a major producer, could export crude to help finance the ambitious development programs of the government. To do this, however, would require a very significant in¬crease in present production capacity, as the domestic demand even for China with her relatively low per capita energy consumption, is essentially equal to the current production. Trying to rapidly move the new regime's programs into actions, one can only assume that the planners looked at the success of the petroleum industry over the preceding fifteen years and quickly concluded that this well established curve could be maintained and indeed steepened with an increase in effort. The rapid discovery of a few more Daqing's (China's premier oil field, producing one million barrels a day) would have the country's ambitious modernization goals within reach. Petroleum would At the time of the death of Mao Tse-tung in 1976, China was a major oil producing country with a daily oil flow in the order of 1.735 million barrels. This position had been achieved with minimal assistance from the outside world. Further, only some fifteen years had elapsed since the country's daily oil production capacity had hovered at the barely significant level of one hundred thousand barrels. Why then did the new leaders of China, after this very creditable record of success, suddenly change the direction of the country's drive for future hydrocarbon production? First, by switching much of the emphasis of exploration from onshore to the offshore continental shelf basins, and further by apparently abandoning the philosophy of self reliance calling upon the world's oil industry to share in the task of locating and developing these potential offshore energy reserves. The answer is probably only partly understood by those of us outside China, However, a number of factors exerting an important influence on this decision can be identified. THE MOVE OFFSHORE The new leadership was anxious to rapidly move China into her rightful place amongst the powerful and technologically advanced nations of the world. Modernization became the slogan, specifically modernization on four fronts, agriculture, industry, technology and military with the goal to "catch the west by the year 2000", But how to generate the capital to finance this massive modernization program? The rapid escalation of the price of crude oil following the 1973 Oil Embargo and the continuing apparently insatiable world demand for this now extremely precious primary resource was very clear to all. China, as a major producer, could export crude to help finance the ambitious development programs of the government. To do this, however, would require a very significant increase in present production capacity, as the domestic demand even for China with her relatively low per capita energy consumption, is essentially equal to the current production. Trying to rapidly move the new regime's programs into actions, one can only assume that the planners looked at the success of the petroleum industry over the preceding fifteen years and quickly concluded that this well established curve could be maintained and indeed steepened with an increase in effort. The rapid discovery of a few more Daqing's (China's premier oil field, producing one million barrels a day) would have the country's ambitious modernization goals within reach. Petroleum would be the principal bridge to the bright future. The next decision involved the question of where to look for these vast new reserves. Chinese exploration teams had already looked at most of the onshore sedimentary basins and, while they were the first to admit that there was much yet to do, it was fairly clear to them that the potential for large new accumulations was confined to two areas: the little explored, remote, inhospitable regions of western China, principally Xinkiang Province and the equally unexplored offshore basins of the continental shelf and slope. In both cases China faced a very serious problem. The inhospitable environments were severely straining her petroleum industry's current technological ability to cope, particularly as the government needed rapid results. Thus the pragmatic and, to the foreign oil industry, unexpected decision to invite cooperation with the outside world. The reasons for the initial emphasis on the exploration of the offshore basins with the cooperation of foreign oil companies are again supposition on my part, but probably involved considerations of technical merit, ease of development and delivery to markets together with more sensitive issues such as controling the influence of foreign philosophies and values on the Chinese population by containing most foreign activity to the offshore. So within three years of the death of the great helmsman, China had developed a plan to involve foreign oil companies, both state and private, in a grand plan to rapidly increase the nations oil production. In fact, by this time, the first round of talks had been concluded and the first phase begun, and what a beginning. Some forty eight companies from thirteen countries had signed documents to participate formally in this world scale event. It was far easier to list those companies which did not participate than to list those which did. FOREIGN COMPANY INTEREST Why the rush by the world's oil industry to be involved in China? What was China offering which made everyone so anxious to join in? Again the answer is complex in detail, but principally involved a combination of factors which together caused this virtual stampede. Timing was a major element. Oil Companies, despite an ever increasing take by governments, were beginning to benefit. from the' rapid escalation of crude prices induced by OPEC and were looking for suitable areas to reinvest these funds. Producers

Jan 1, 1982

F. L. Clerc, Chicago, Ill. (communication to the Secretary): On page 681 in Mr. Winslow's paper, he refers to me as having "advocated the view that the ores were derived from the patches of Coal-

Jan 1, 1895

By R. J. Woody

Design of the most economic continuous counter-current decantation (CCD) circuit is based on selection of the number of stages and the wash volume that will give the minimum summation of the following items: 1) Capital and operating costs of the CCD circuit. 2) Capital and operating costs of the precipitation circuit. 3) Value of the dissolved product lost.

Jan 1, 1959

By Orson Cutler, Shepard

THE OBJECT of this paper is twofold: (1) To analyze the forces that cause air bubbles to spread on mineral surfaces in the flotation process; and (2) To develop a rational expression that will serve as a criterion of the floatability of minerals, to the end that the efficiencies of various flotation reagents can be accurately compared. Heretofore, the subject of the spreading of air bubbles has been dismissed with the statement that the surfaces of minerals on which bubbles spread are water-repellent. Imperfect understanding of the forces involved has led to the use, hitherto, of various erroneous formulas for the calculation of the comparative effectiveness of flotation reagents.

Jan 1, 1932

Edward K. Landis, Philadelphia, Pa.: In studying Mr. Thackray's paper it seemed that a critical comparison of the results from different methods therein reported would he of interest. For this purpose Table I. was constructed by grouping all determinations made by the same method, and the probable errors were calculated. In this table all chemists titrating with permanganate (A1, E, F, G and 0 of Mr. Thackray's paper) are classed under "Emmerton;" those titrating with nitric acid (C, J, S and Y) under " Handy; " those re Probable error of result: a, ±0.0008996; b, ±0.000694; c, ±0.00107; d, ±0.00115; e, ±0.000674; f, ±0.000473; g, ±0.003675; h, ±20.0007959; i,0.000.5098; k, ±0.0008303. Probable error of single determination: a, ±0.001989; b, ±0.001547; c, ±0.00214; d, ±0.0023;e, ±0.00116;f, ±0.000818;g, ±0.0019;h, ±0.00224; i, 40.00143; k, ±0.00234. The formula for calculating the probable error is 0.6745, where N (N— 1)' S is the sum of the squares of the differences from the mean and N is the number of determinations.

Jan 1, 1897

By G. J. Ballmer

Drilling and blasting 12-in. blastholes started about the middle of 1946 and has worked out so well that about one half of the blasting, formerly done with 9-in. holes, is now done with 12-in. holes. In most of this work the harder benches were chosen for the 12-in. size because these were the areas where the greatest difficulty was encountered in thorough fragmentation. At the start of this experimental work a 42-T Bucyrus- Erie churn drill was available whereas all other blasthole drilling was being done with 29-T rigs. The large drill was first equipped with a standard 9-in. string of tools but it could not drill quite as fast as the 29-T drills. How- ever, when the weight of the string was increased about 700 lb, or to a total weight of about 3500 lb, it was found that the 42-T exceeded the drilling speed of the 29-T by about 25 per cent. When a 12-in. bit was substituted for the 9-in. bit the 42-T rig again dropped behind the drill- ing rate of the 29-T rigs. At this stage of the experiment the 42-T was using a 12-in. bit with detachable points and the total weight of the string of tools was about 3800 lb. It took longer to change the drill points than it did the regulation bit and this accounted for some of the slower drilling rate. When a heavier stem and standard construction 12-in. bits were used it was found that the 42-T could drill a 12-in. hole slightly faster than a 29-T could drill a 9-in. hole even in the hardest rock in the pit.

Jan 1, 1949

William P. Blake, TUCSON, Ariz. (communication to the Secretary): As one who in youth, now nearly half a century ago, had the privilege of participating in the initial explorations which have alreacly resulted, within a single lifetime, in the establishment and Development of a vast continental empire, so well described by Dr. Douglas, I may be permitted to supplement with some additional details the comprehensive sketch given in his paper. Before the War Department, in 1853, sent out the Pacific railroad exploring parties, Fremont had already made his memorable expeditions, exploring the Great Basin and the passes into California; Sitgreaves had traversed, from east to west, the Zuni and Moqui country; and, still later, Emory had examined the region along the boundary-line between the United States and Mexico. The services of these pioneers deserve to be mentioned in even an outline of the history of continental development. Concerning the five practicable railroad-routes, suggested in the Reports of Explorations aid Surveys," etc., as published

Jan 1, 1900

By Daniel T. O’Brian

Mineral exploration activities are benefiting from new interpretive techniques which have become economically practical with computers. Government agencies, educational institutions, and industry have each contributed research and development efforts for improving the mathematical analysis and graphical display of exploration data, resulting in operational aids not foreseeable a decade ago. Progress has been worldwide and is expanding rapidly. Books 1-10 are supplementing the periodic literature, at least one abstracting service is now active, 11 and an association has recently been formed to encourage and publicize advances in this field. 12 With the diversity of applications, only partial coverage of the subject can be made at any single symposium. Four of the six papers in this section report on the current state-of-the-art in selected areas of interest: graphics, time-sharing, mathematics, and economic analysis. The remaining two papers are descriptions of advanced statistical techniques for gaining additional information during exploration, and illustrate methods which will become more commonly applied in the future. "Computer Graphics: A New Tool for Exploration and Mining" describes the use of a computer and accessory equipment as an information retrieval device, graphically merging and displaying pertinent information for visual inspection and interpretation. This is a rapid means of studying information which has been pre-stored in a form accessible to the computer. Time-sharing is a means of achieving a comparable rapid response when calculations are being performed. The paper, "Some Applications of Time-Sharing in Mining Geophysics," describes the experience of one company using a time-sharing facility for geophysical computations. Another paper on this subject, stressing mining applications, has recently been published. 13

Jan 1, 1969

By L. W. Blau

THE entrance of geophysics and geochemistry into petroleum engineering may be viewed with apprehension by some engineers. They may not remember the time when "practical oil men" opposed the invasion of engineers into the field of petroleum production. By their excellent contributions they established themselves. In the popular mind, engis veers are practical men whereas physicists and chemists are suspected of being theoretical. It will be best to annihilate this misconception right now at the beginning of a closer relationship between petroleum engineers. geophysicists, and geochemists.

Jan 1, 1943

By William Victor Vietti

A METHOD of determining the average density of the fluid column in a flowing oil well is presented. Actual field data from several wells are used to illustrate the application of the method in the Yates Field, Pecos County, Texas. The depth of the wells in the Yates Field varies from 900 to 1700 ft. depending on surface elevation and the location of the wells on structure. Production rates over 8000 bbl. hourly have been determined and many

Jan 1, 1930

By Fleming, R. C.

ONE OF THE NEWEST developments of industry rising from the commercial application of scientific knowledge is in the making of solid carbon dioxide from the gas about 1925 the first efforts were made to manufacture "dry ice" on a large scale and at a price to permit widespread use. From that beginning the industry has grown to a consumption of 40,000 tons in 1930. Carbon-dioxide ice, as the name implies, is merely the gas compressed and cooled to a solid. The ice has a temperature of 109° F. below zero and is in many ways superior to water ice. It evaporates to a gaseous form so it is not wet and leaves no trace; in fact, one suggested minor use is as coasters under water glasses on the dining table. The gas is harmless except in large concentrations and. when the ice is used as a refrigerant, the resulting gas actually becomes a preservative, keeping oxygen away from perishable products. Not only does the ice have a greater amount of cold in a small volume than water ice but cooling is effected by direct contact of the resulting gas with the materials to be refrigerated rather than by convection air currents.

Jan 1, 1932