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By D. W. McGlashan

[Becaune ad ;the extennive nwrgace anea od u.X chopRex2 in emmiom, emuhion dRokdtiun oddeh poaaibWa don ;the necove/ry ul; BinQey divided minmcd pa~LL&a, Swr~aC;tavu% mu2 akab&ze ;the emu-bion and poan an an ad~i&y don ;the dahed mina&. OZhm hpohtant acto oh me ;the naAwre od ;the em&iun inghedied, ;the nQRaLLve volwna 06 the colz;tinuoun and dincon;tinuoun phaa, ;the change aign bonne by the dnuplm ad the o.X phae, ;the z&a pu;tenticd od ;the dahed minmd, the ~olubRe am curdent 06 khe wcr;ten-pulped and gnuund onu. AX on nem ;the AoQRec;trtic point on ZPC, ;the doubRe Raym about ;the minW-&den oil dnopR& i~ neduced in ;tkichnaa and the dn_opR& wU codace and continue to aggnegate into agglommaka . Invetmion dnom O/U ko W/O can UCCWL depending upon a nwnbm a 6 in;tmQeaked daotuh~. EReothokin&Lc inn&wnenta;t/iun to meanwre ;the ZPC, QReckProphonQkic mobilXty z&a pokeW and hakerning cuttrtent me invcduabte in ;the appficatiun ud emu-bion dRo;tat;iun ;to m&~c and nonm&~c minu.&. ] INTRODUCTION Recent interest in emulsion flotation can be ascribed to the necessity of selective separation and concentration of extremely fine minerals. That which follows is an elucidation of the many factors-in emulsion technology in application. In applied surface chemistry for solid-particulate separation and concentration, emulsion flotation is one of the intermediate processes between froth flotation, in which the continuous phase is water (99.5 to 99.999% by volume), and particulate extraction, in which the continuous phase is almost entirely an organic-fluid. Another intermediate process is particulate exchange (or partition) in which immiscible or very limitedly miscible phases are in controll¬ed but appreciable volumes. Surfactants are common to all of these

Jan 1, 1968

By David R. Maneval, W. E. Foreman, J. Richard Lucas

INTRODUCTION The objective of this chapter is to inform the industry, as well as the public, of the challenges in dealing with the problems associated with the contamination of air and water from coal preparation plants. The need for an informed industry is most important. It is hoped that some contribution may be given to a more efficient and economical approach to the problems of plant waste contaminants at individual plants. The problem has many facets, and consideration to specific area should begin early before any significant problems develop at a given plant. It is then possible to have a reasoned approach before the pressures of an emergency environment force hasty and incomplete solutions. It will be necessary to anticipate these problems in the design of new preparation plants and advance consideration should be given to all the problems concerned with contaminants. The first part of the chapter will concern itself mainly with the contamination aspects of fine-coal cleaning and "black-water" disposal. Also attention will be given to the nature and formation of water from coal-mine drainage systems and the treatment of these waters for industrial use. Some attention will be devoted to the cost of installing and operating the various beneficiation systems for the removal of suspended solids. The second part of the chapter will analyze the problems of air contaminants from coal preparation plants. The nature and the effects of these contaminants and their potential for air pollution will be examined. One of the most critical is the measurement and analysis of these contaminants. As a result of identifying and determining the extent of the problem, better control can be planned. One of the most serious contaminants in air involves the element sulfur, and its elimination as a source of air pollution is one of the most challenging areas in coal preparation today. The last part of the chapter will emphasize the long-range problem of refuse disposal and control. Minimum operating and maintenance costs are functions of the proper selection and geometry of refuse disposal areas. Disposal procedures are varied but must be rigidly pursued or difficulties will result. Maintenance of refuse areas, including monitoring of burning refuse, is critical. It should be recognized that fine-solid refuse disposal systems must be carefully designed to minimize contamination. WATER CONTAMINANTS FROM PREPARATION PLANTS Pollution Aspects of Fine-Coal Cleaning and "Black-Water" Disposal The effluents from coal washeries and waters draining from plant-site surfaces inevitably contain fine coal and coal refuse materials in suspen-

Jan 1, 1968

By Paul Rhedey

Various commercial pelroleum cokes were heat-1,reated at temperatures between 500° and 1500°C, in a nitrogen atmosphere, in laboratovy induction furnaces. The rate of tenlperature rise was varied betzveen 10" and 300°C per min, or the green cokes were flash-calcined, orv a combination of heating rates was used. Changes in the rate of heating had only negligible effects on the degree of' calcination as characterized by mean crystallite thickness and the chemical properties of the calcined coke. The physical structure of the cake was however significantly affected when rate of heating during calcination exceeded 50°C per min over the temperature range of 600° to 900°C. Surface-accessible porosily increased with the .rate of temperature rise, and this was accompanied by a change in pore size distribution. Source and properties of the green coke also had an influence on the structure of the calcined coke. The evidence presented suggests a similar mechanism of porosity development in petroleuiiz coke during calcination in industvial equiplnenl, such as rotary kilns. An increase in surface accessible povosity incveased the pitch binder requirement when the coke was used as aggregate in Soderberg paste. A correlation was established between calcined coke porosity and paste binder requiremenl. ManY results have been published on the changes of properties of petroleum coke during calcination, such as chemical composition, real density, electrical resistivity, crystallite and pore structure. The correlation of these properties with temperature of calcination and time at maximum temperature has been rather well established in both laboratory and pilot plant experiments. Surprisingly little attention has been given however to the effect of calcination conditions, such as rate of temperature rise or furnace atmosphere, on the chemical and structural properties of the calcined coke. It has been observed that petroleum coke, when calcined in industrial equipment, acquires higher porosity and lower real density than those attainable in laboratory furnaces at apparently identical calcina- tion temperature and soaking time. This paper describes a study of the effect of rate of heating during calcination on calcined coke properties using green petroleum cokes of different volatile matter, hydrogen, and sulfur content. An attempt was made to correlate the changes in coke structure with the flowability of anode paste of the type normally used in aluminum reduction cells. EXPERIMENTAL Petroleum Cokes Used. In the study of release of volatile matter and sulfur during calcination and the effect of rate of heating on calcined coke properties two delayed cokes of different sulfur contents were used. The results of analysis of the green cokes are given in Table I. In the study of the effect of flash calcination thirty-six commercial petroleum cokes from twelve different refineries were used with a range of properties shown in Table 11. Calcination Conditions. Calcination experiments were carried out in a laboratory induction furnace. In each run a 200-g sample of dry green coke sized to 10 by 65 Tyler mesh was calcined in a graphite crucible. The crucible containing the sample was placed in the middle of a stack of eight others filled with metallurgical coke to reduce temperature gradients within the sample. Temperature was measured by two Pt, Pt-10 pct Rh thermocouples and controlled by a Celectray instrument. The two couples generally agreed within 5°C. In the study of volatile matter and sulfur release the samples were heated to temperatures in the range of 500" to 1500°C at a rate of 10°C per min in a nitrogen atmosphere and held at the final temperatures for 30 min. In the study of the effect of heating rate on calcined coke properties the desired rates between 10' and 300°C per min were obtained by manually adjusting the power input. Flash calcination was carried out by dropping 100 g of the green coke into the graphite dish preheated to the calcination temperature. Because of the small heat capacity of the furnace the coke was introduced in 20-g portions at a time. For this purpose a 2-in.-long nipple between two 1-in. gate valves installed on the top flange of the furnace served to provide a gas seal while feeding coke to the furnace. It was estimated that the temperature of the coke reached that of the furnace at a rate of approximately 1000°C per min. Holding time at final temperature was also 30 min. Calcined Coke Proper- Determined. Porosity was determined on 20 by 35 Tyler mesh samples using an Aminco-Winslow mercury pressure porosimeter with an operating range of 1.8 to 3000 psi absolute pressure (100 to 0.05 p pore diameter range).' Apparent density was obtained by the mercury poro-simeter. It represents a particle density of the 20 by

Jan 1, 1968

By C. Graeme-Barber, R. L. Bell, T. G. Langdon

An analysis is made of the formulas and ,methods used to estimate the contribution of grain boundary sliding to the overall strain of a polycrystal. The errors involved in the approximations and/or ,mistakes in earlier work are assessed quantitatively so as to make possible the critical use of previously published data. SINCE it has been found that, under conditions of very slow creep, the strain due to grain boundary sliding (?gb) may contribute as much as 80 pct of the total creep strain,1,2 it is obviously important to have reliable methods for estimating this grain boundary strain. In two recent papers Stevens3,4 has drawn attention to the pitfalls encountered in assessing ?gb. He criticizes 1) the assumptions made in the derivation of some of the formulas for ?gb, and 2) the indiscriminate averaging procedures used for obtaining the quantities substituted in these formulas. These and further criticisms of earlier work are mostly valid. Unfortunately the only formulas and procedures recommended are either impossible or very difficult to apply in practice. Furthermore no attempt is made to assess the errors involved by the earlier approximations or mistakes, and so it is not possible to make critical use of any of these early dab. The present article attempts to improve on these shortcomings by reference to empirical verification of easily applied formulas whose theoretical derivations involve some otherwise unjustifiable assumptions, and by a quantitative assessment of the errors in previous work. DEFINITIONS First it is necessary to define the terms and symbols to be used. The choice of symbols preferred here is a logical combination and extension of the v introduced by McLean5 and the u by Brunner and rant.' In Fig. 1 the two grains X and Y are displaced by the sliding vector AC. u is the component of sliding resolved along the stress axis, v is that measured perpendicular both to the stress axis and to the specimen surface, and w is that measured perpendicular to the stress axis but in the plane of the surface. Two angles define the orientation of the grain boundary: 8, between the stress axis and the surface trace of the boundary, and +, the internal angle on a longitudinal section cut perpendicular to the surface. In computing the strain resulting from the boundary displacement at all the in- dividual boundaries in a polycrystal the components u, v, or w are sometimes averaged along a longitudinal line (i.e., parallel to the stress axis), sometimes along a transverse line, and sometimes at randomly chosen boundaries. Averages obtained in these three ways are given subscripts 1, t, and r, respectively. Stevens rightly calls attention to the possibility of non-equiaxed grain shapes either at the start or at the end of deformation. In this article all values of numbers of grains per unit length will refer to measurements made before deformation. The subscripts 1 and t will be used for the number of grains per unit length obtained along longitudinal and transverse lines, r for that obtained by averaging along a number of randomly directed lines. FORMULAS FOR ?gb ?gt, as a Function of u. An obvious truth is that cgb can, in principle, be obtained by summation of all the v components at the boundaries intersected by a longitudinal line of known length I, viz.: where nl is the number of grains per unit length, parallel to the stress axis, in the unstrained specimen. There are assumptions in the analytic derivation of Eq. [I] due to Brunner and rant' but ~achinger' arrived at Eq. [la] by a rigorous method. Unfortunately the experimental procedure required by Eq. [ la] proves very difficult as boundary migration tends to obscure the points at which the longitudinal line meets the grain boundary and the errors on such measurements tend to be large, see Fig. 2. For example, on a specimen of Magnox AL 80 at a creep strain of 9.7 pct, 300 measurements of u obtained from the points of intersection of a longitudinal line with the grain boundaries gave ul = 8.95 ± 3.58 pm, or an error of ±40 pct, at the 95 pct confidence limit. These large errors due to migration may be avoided by measuring u from the separation of the segments

Jan 1, 1968

By C. C. Shale

Electrical resistivities for various coal ashes in air and in a nitrogen atmosphere are given over the range 100° to 1,500° F. Resistivity of low-carbon ash in air is very high at low temperature, rises to a maximum at about 250° F, decreases very rapidly with increasing temperature to about 800° F, then decreases gradually to approach an asymptote at 1,500° F. Resistivity of high-carbon ash in air follows this same general trend at values which are much lower and are proportional to the carbon content. After the carbon has been burned off, resistivity of the remaining ash approaches the high values corresponding to low-carbon ash of similar chemistry. Two factorial experiments show the effects of temperature, particle size, chemical content, and compressibility on the resistivities of four fly ashes of widely different chemical composition in the temperature range proposed for coal-fired turbines. Resistivities of all low-carbon ashes tested fall in the range 106 to 107 ohm cm at 1,500° F and should be removable by electrostatic precipitators. Ashes containing carbon in excess of about 8 percent, however, have low resistivity (as determined in nitrogen), especially at high temperatures. Therefore, high-carbon materials may not be collectable in precipitators because the resistivity is below the minimum value necessary for precipitation. Consequently, high carbon residues from partial combustion of coal probably could not be removed effectively at high temperatures.

Jan 1, 1968

By Culver, Richard S.

In spite of the widespread interest in rock bolt research, relatively little is known about the critical region surrounding the bolt anchor. In analyzing the stress distribution around an opening resulting from rock bolt support, it is commonly assumed that the bolt is fixed at a point far enough from the surface so that the anchor does not influence the performance of the bolt. Furthermore, a bolt anchor is assumed to per- form satisfactorily if it will hold the design load with a minimum amount of load relaxation, commonly called bleedoff. From the standpoint of the design engineer both of these assumptions are reasonable, but they ignore the fact that the extremely high stresses in the region of the anchor are capable of generating fractures in the rock. Lang estimated the bearing stresses for a slot and wedge anchor on a one-inch-diameter bolt to be as high as 125,000 psi. This paper describes a more thorough analysis of the magnitude of the stresses around the anchor and the nature of the potential fractures that might result.

Jan 1, 1968

By G. A. Brady

Seven samples of Pennsylvania anthracite from the Bottom Ross bed were analyzed and tested to obtain data on cleaning characteristics, proximate and ultimate analyses, specific gravity, grindability, heating value, and ash softening temperature. Ash content of the samples varied irregularly from 9.0 to 34.4 percent, the range being narrowed to an upper limit of 14.8 percent ash by removing impurities dense enough to sink in a medium with a specific gravity of 1.90. Ash content of the sink material with specific gravity greater than 1.90 ranged from 56.4 to 80.4 percent; corresponding specific gravities were 2.095 to 2.534. Volatile matter contents were indicated to be higher for the ash-forming minerals than for the pure coal substance in the various specific gravity fractions of a given sample. Specific gravities of anthracites with compa¬rable ash contents but from different locations in the bed varied as much as 0.06. The grindability index increased significantly with increasing ash con¬tent of specific gravity fractions from all the samples.

Jan 1, 1968

By A. J. Strauss

The solubilily of lead in PbS as a funclion of lemperature has been investigated by means of Hall coej'icient (RH) measurentents OIL samples prepared by annealing and quenching Bridgman-grourz single crystals, which contain excess lead incorporated during /heir growth from the mell. For sufficiently long annealing times and sufficiently rapid quench rules, the samples obtained consist of n-lybe PbS snturated with In the semiconducting compounds PbS, PbSe, and PbTe, the point defects associated with the presence of lead in excess of the stoichio metric composition are shallow donors. The defects associated with the presence of excess nonmetal are shallow acceptors. lead at the annealing teuiperatiire, together luilh a dispersed second phase of lead microprecipitates. Due to the retrograde solubility of lead, the measured free carrier concentration (n = l/eR77) decreases with decreasing annealing tewperature (T) from- 2.4 X 10 em-3 for 1l85OK to 1.3 X 1018 cm-3 for 623°K. The dala are well-represented by the equation n =(1.08 x 102) exp[ - (0.37 ev.)/kT] cm-3 For most undoped samples of these compounds, the carrier concentration at room temperature and below is determined primarily by the stoichiometry, since the concentration of either excess lead or excess non-metal is large compared to the concentrations of intrinsic carriers and electrically active impurities. Therefore the dependence of composition in temperature and partial pressure can be investigated by means of Hall coefficient measurements, even though the deviations from stoichiometry do not exceed 0.03 at. Pct

Jan 1, 1968

By F. E. Rizzo, L. R. Bidwell, D. F. Frank

THE poor high-temperature oxidation resistance of the refractory metals becomes an important problem as higher operating temperatures are sought. A meaningful analysis of their oxidation behavior requires a knowledge of the phases that can appear during oxidation as well as their relative stability. Although several extensive investigations have been carried out to obtain this information for the W-0 system,1-10 serious inconsistencies still remain. First, the standard free energies of formation (AG°) determined in recent studies which used the solid electrolyte galvanic cell technique6,7,9 differ significantly from those obtained primarily from gas equilibration measurements.1,3,4,10 The disagreement is especially large for the highest oxides. These data have been used to predict the decomposition temperatures of WO2. 72 and WO2.90.1 A considerable extrapolation is required, resulting in a large uncertainty in the decomposition temperatures. Second, Bousquet and perachon3 have presented convincing evidence, ob- tained by gas equilibration measurements, in support of the long-contested existence of W30. Phillips and chang,ll on the other hand, were not able to observe this phase under similar experimental conditions. The purposes of this work, which is part of a continuing investigation of the W-Mo system, were to resolve the discrepancies between the AGO measured by gas equilibration and solid electrolyte galvanic cell techniques, to extend the latter measurements to lower temperatures, to redetermine the WO2.72 and WO2.90 decomposition temperatures, and to apply the more sensitive electromotive-force method to the question of the existence of W3O. I) EXPERIMENTAL PROCEDURE The measurement of ?G° of reaction by the use of calcia-stabilized zirconia solid electrolyte galvanic cells has been described previously.12 The method is based on the measurement of the difference in chemical potential of oxygen between an electrode containing the two oxides of interest and a reference electrode of known oxygen activity. Two different types of cell holders were used in this study. The first type of apparatus has been described earlier." It consisted of two solid electrodes separated by a disc of electrolyte. Both electrodes were exposed to the same stream of purified helium. With this design a gaseous transport of oxygen between the two electrodes is possible. The second type of apparatus, which has also been described earlier,14 effectively separated the two electrode atmospheres. It utilized a closed-end impervious, calcia-stabilized zirconia tube that was open to the atmosphere. The tube served as an electrolyte for the cell and provided a means for separating the anode compartment, which was held under a static vacuum, from an air reference cathode. The cells and reactions of interest are described in Table I. High-purity tungsten metal was obtained from the Fansteel Metallurgical Corp. and the Allied Chemical Corp. Table II contains an analysis of each material. WO3 was prepared by oxidizing the metal in air at approximately 600°C in high-purity recrystallized alumina boats and by the dehydration of reagent-grade tungstic acid in alundum boats. The two methods of preparing WO3 resulted in slightly different purities.

Jan 1, 1968

By Robert A. Bradburn

The Bureau of Mines has developed a miniature, portable two-level oxygen-deficiency alarm and produced three prototype models. Each operates from a 4.2-v dc power source, and the highest current drain of any model is 80 ma. An electrochemical cell, which produces an electrical output in proportion to the partial pressure of oxygen to which it is exposed, is used as an oxygen detector. The output of the cell is applied to an electronic circuit that detects two different levels of oxygen percentage below that of normal air, and produces distinct audible signals at these levels. The hazard alarm mode is activated when the oxygen percentage first drops below normal and produces a 500-cps "beep" tone with an intermittency of 1 cps. The danger mode produces a continuous 500-cps audible signal when the oxygen percentage drops still lower.

Jan 1, 1968

By David Kramer, Cecil G. Rhodes

Critical transport currents were measured as a function of perpendicular external magnetic field in Ti-22 at. pct Nb wire samples. These samples were heat-treated to yield w Phase precipitates at denslties ranging from 10 to 10 17cm-3. The Precipitates are ellipsoids of revolution with major axes of 50 to 1300A. Flux-Pinning by w precipitates is responsible for the high critical transport currents that were ob- ThE ability of a type II superconductor to sustain a zero-resistance transport current (Jc) in an external magnetic field (H) is due to the presence of micro-structural features which can impede the motion of magnetic flux penetrating the superconductor under the influence of a Lorentz force. Such features are referred to as pinning sites. The pinning strength is tained. A sample cooled from 800°C and annealed 1 hr at 450°C carried a critical tramport current of 10 amp per sq cm at 30 kG. Variations in the current-carrying ability of this alloy are due to changes in its pinning strength which is a function of precipitate density and composition and of the composition of the matrix. the reaction of the bulk superconductor to the Lorentz force and depends on the efficiency of the individual pinning sites and on their volume density. The super -current density increases with pinning strength, other things being equal. The above concepts are discussed in detail in a comprehensive review by Livingston and Schadler.' In Ti-Nb alloys, as in other binary titanium alloys, the metastable hexagonal w phase usually forms below the p/a + p phase boundary near the titanium side of the phase diagram. Stiegler et a1.' have summarized much of what is known about w phase in titanium and zirconium binary alloys. The present work deals with

Jan 1, 1968

By Sam Friedman

The Bureau of Mines conducted experiments using bench-scale apparatus to explore the effect of large changes in process variables on the yield and composition of the gases produced by passing 800° C steam through a fixed bed of Pittsburgh seam (hvab) coal. The total yield of combustible gases increased throughout the given range for the following variables: Superficial steam velocity increasing from 0.02 to 0.12 fps, pressure increasing from 1,000 to 6,000 psig, residence time increasing from 0 to 60 minutes, and temperature increasing from 800° to 900° C; however, a greater increase in the yield of hydrogen in comparison with the increase in yield of methane reduced the gross heating value of the gas to around 470 Btu per scf at conditions giving the maximum yield. Pressures of 1,000, 3,000, and 6,000 psig at 0.09 fps steam velocity, 800° C, and 60 minutes residence time, respectively, produced methane yields of 20, 24, and 22 percent, based on maf coal, with the gross heating value of the CO2-free gas decreasing from 552 to 520 and to 470 Btu per scf. Methane concentrations in the CO2-free gas were 26, 22, and 14 percent, respectively. Based on the gross heating value of the coal, the percentage of the heating value recovered in the gas was 60, 71, and 87 percent, respectively. The use of tungsten sulfide as a catalyst for converting carbon oxides and hydrogen into methane was explored briefly using both a sulfur-free gas rich in methane and a sulfur-bearing synthesis gas (3H2:1CO).

Jan 1, 1968

By P. R. Schmidt, N. J. Themelis

A study zvas made of the deoxidation of copper at 1170°C by injecting a jet of carbon monoxide vertically upwards into the melt. The effects of submersion depth (2 to 20 cm), orifice diameter (& to 5 in.), and gas velocity (100 to 3650 ft per sec) were examined. In the oxygen range 0.1 to 1.0 pct 0, the overall rate was conlrolled by gaseoLcs mass Lransfer. The results were interpreted in terms of a rate coefficient per unit depth which was found to be constant with distance along the jet axis and nearly proportional to the orifice Reynolds number in the range 1000 < NReo < 9100. AS the gas flow rate through an orifice submerged in a liquid is progressively increased, at least three regions of bubble formation may be distinguished. At very low rates, the formation of bubbles is practically a static phenomenon, depending on the orifice diameter, the liquid surface tension, and the densities of the two phases. In this region, the bubble size is constant while the frequency of bubble formation increases with gas flow rate.&apos;-3 At higher flows (500 < NR~, < 2100), the frequency of bubble formation reaches a steady value and the bubble size increases with gas flow rate; when the bubbles issuing from the orifice become so large that they start coalescing to form larger bubbles, the turbulence induced in the liquid by the passage of previous bubbles shatters them into small bubbles of varying size. Finally, for gas velocities in the intermediate and turbulent regions of flow (NR,, > 2100) a tangential separation surface is created around the jet and momentum transfer takes place between it and the surrounding liquid medium. The entrainment of liquid and the resulting deceleration of the gas-liquid dispersion causes the jet to expand forming a characteristic jet cone. The large velocity and density differences between the jet and the liquid result in a high degree of instability and the jet envelope fluctuates rapidly.The characteristic jet cone can be observed by means of time exposure photographs such as those shown in Fig. 1 for an air jet introduced vertically upwards in a water bath. High-speed photography has showns that the gas-liquid dispersion within the cone consists of small bubbles the size of which depends mainly on the jet orifice diameter and Reynolds number. In the laminar region of flow, the following correlation was obtained by Leibson: The results of Liebson et a1.&apos; are plotted in Fig. 2. It can be seen that the region 2000 < NReo c 10,000 is not well-defined experimentally. In the entrance to the fully turbulent region of flow (NR,, = 10,000), the mean bubble diameter decreased to about 0.4 cm and varied only slightly from there on according to the correlation:

Jan 1, 1968

By D. W. Fuerstenau, L. M. Berlioz

In 1957, Charles1 first presented an analysis of a relationship between the energy expended in comminution and the extent of size reduction achieved. Subsequently, Schuhmann extended and interpreted Charles&apos; approach to comminution. According to their analysis, the energy, E, expended in comminuting unit mass of fairly uniformly-sized material is related to the size modulus of the product, k, by where a is the distribution modulus (slope of the log-log cumulative size distribution plot) and C is a constant, which is primarily determined by properties of the solid. If there is any fundamental basis for the E vs k relationship, E must necessarily be concerned with the useful work for the size reduction process and not necessarily the work input, as discussed in detail by Harris.3 Charles and numerous other investigators tested this equation only by relating k to the grinding time, assuming expended energy to be directly proportional to time, but never directly measuring power. In our laboratories, we recently constructed a special batch ball mill with which the power could be accurately determined with torque measuring apparatus.4 With this device, a direct test of the Charles relationship could then be made for ball milling. 5 EXPERIMENTAL A stainless steel mill, 11.5 in. long and 10 in. in inside diam, lined with eight low-silhouette lifter bars, was used for these experiments. The grinding media consisted of 30 kg of single sized, 1-in. diam, stainless steel balls, which occupied about 50% of the total mill volume under static conditions. The void fraction of the static ball load was approximately 0.4, and for the dry grinding conditions used, the corresponding interstitial volume was filled when about 3300 g of the dolomite feed material was present. The 7x9 mesh dolomite used as feed was obtained as a natural, uncrushed product thus as- suring a random distribution of feed particle shapes. Charge weights of 660, 1320, 1980, 2480, 3300, 3960 and 5280 g, which correspond to 20%, 40%, 60%, 80%, l00%, 120%, and 160% of the interstitial load, respectively, were used. Grinding times of 20, 40, 60, 80, 100, 150, 200 and 300 revolutions were considered, with the mill operating at 54 rpm (approximately 60% of critical speed). The tests were made sequentially, in that the size distribution obtained after a certain grinding interval was utilized as the feed for the subsequent period of grinding. Agreement with control experiments where the mill ran continuously for the entire interval was excellent. Torque measurements were made utilizing a Baldwin-Lima-Hamilton SR-4 torque pickup in the manner that has been described previously.3 Standard wet (to obtain the -400 mesh material) and dry sieving procedures were followed using the Tyler full screen series. RESULTS The Gaudin-Schuhmann size distributions obtained in all of these experiments are characterized by distribution moduli (slopes), a, of about 0.66 and are representative of normal dry batch ball milling of a material like dolomite. As an illustration of typical

Jan 1, 1968

By I. R. Kramer

The stress associated with the surface layer was deter-minedfor iron and molybdcnum. These measurements show that the surface layer plays a very important role in the plastic deformation of bcc metals. From the relationship between strain arui the surface layer stress and the back stress imposed by the internal obstacles, it is Proposed that the term of of the Hall-Petch equation is related only THE large number of studies on plastic flow of bcc metals have failed to delineate clearly the nature of the obstacles influencing dislocation movement. Since there have been numerous articles which have reviewed the mechanisms proposed to explain various aspects of plastic flow of bcc metals (for example, conrad1 and Keh and weissmann2), no attempt will be made here to discuss their conclusions. However, it should be to the surface stress while the term Kfd is the stress required to move dislocations through internal obstacles. Further, it was possible to derive the well-known empirical equation C = , and it is shown that the terprz a is comprised of two terms: a term Cs associated with the surface layer stress and Ci related to internal dislocation obstacles. pointed out that in all of these publications it has been tacitly assumed that plastic flow occurred uniformly throughout the cross section of the specimen (except, of course, for the Luders band region), It has generally been further assumed that the nature and distribution of the obstacles opposing the motion of dislocations are of the same type throughout. The role of the surface layer in bcc metals has not, as yet, been considered even though its role in fcc metals has been shown clearly to be of primary importance.3-5 Investigations on fcc metals have shown that at the onset of plastic deformation a surface layer acts to

Jan 1, 1968

By F G. Cooke

"This paper describes a medium-sized copper mine's results in making innovations and changing operational practices to combat increasing expenditures due to higher labour and supply costs, extended workings, scarcity of experienced manpower and problems created by deteriorating ground conditions.OPEMISKA COPPER MINES (QUEBEC) LIMITED is located at Chapais in the Chibougamau area, in central eastern Quebec, approximately 300 miles north of Montreal and 150 miles north west of Lake St. John. The latter area, developed by lumbering and farming, has supplied the majority of the employees, who, with training and experience and a desire to work and improve themselves, have become the backbone of the Company's 600 personnel.Opemiska began production in 1954 at a rate of 400 tons per day, using diesel power and road transportation. The rate was progressively increased and, by 1959, with hydro-electric power and rail transportation, the mine had reached its present production rate of 2,000 tons per day. It has produced concentrates containing over 430 million lbs of copper."

Jan 1, 1968

By G. S. Crawford

Forecasts prepared by the B.C. Research Council for the National Harbours Board suggest that mineral shipments through B.C. Lower Mainland port facilities will increase more than four-fold, from 6 to about 25 million tons, during the decade 1965 to 1975. The longer term outlook is for a six-fold increase to about 35 million tons by 1985. In 1967, minerais accounted for more than one-third of the total deep-sea traffic tonnage, nearly as much as grain. By 1975, the minerals' share will be about half the total. The principal items are exports of potash from Saskatchewan, and of coal and sulphur from Alberta and British Columbia. Additional exports include copper and other mineral concentrates and propane. Imports are chiefly salt and phosphate rock. Coastal traffic in such items as cement, sand and grave!, and limestone totalled 3.3 mil-lion tons in 1967. They will continue to be of major importance, but do not have the spectacular growth potential of the deep-sea traffic.

Jan 1, 1968

By A. W. Henderson

Methods for converting WOCl4 to WCle were investigated in small-scale, laboratory apparatus to devise a method for preparing pure WCls suitable for conversion to tungsten metal. Chlorine, COCI2, and CCI4, alone and in combination with various forms of carbon, were tested as chlorinating agents at various temperatures. More than 95 percent conversion of WOCl4 to WCls was achieved with all reagents at 8000 C in the presence of activated carbon. Only CCl4 maintained its effectiveness in the absence of carbon at 800° C. The effectiveness of carbon was found to be related directly to its surface area.

Jan 1, 1968

By Herbert K. Kutter

This paper is concerned with the physical phenomena in the fracture process of presplitting and only indirectly with the establishment of the optimum presplitting parameters. Its nature is therefore qualitative, rather than quantitative. Before examining the problem of presplitting, it is first necessary to study the phenomena which occur when an explosive charge is detonated in a borehole. To do this it is desirable to consider the action of the explosion wave separately from that of the expanding gases.l In the theoretical analysis such a separation poses no problems. Experimentally this was accomplished by use of an underwater-spark discharge to generate the stress wave and by pressurized oil to simulate the pressure of the explosion products. The main role of the wave is to generate a densely radially fractured zone around the borehole. The subsequent gas pressure, exerted against the walls of a highly (radially) fractured cavity, generates a quasi-static stress field (henceforth referred to as static stress field). This stress field was found to be the same as that of a pressurized cylindrical "equivalent cavity" with a radius equal to that of the crack tips. Under these conditions the quasi-static stresses become appreciable and cause further extension of the radial cracks. It was further found that, under gas pressure, the longest of the radial cracks would extend first, and extension of two diametrically opposed radial cracks requires the least pressure. From these observations concerning the single shot the transition to a whole series of more or less simultaneous shots, as in presplitting, can readily be made. In the case of multiple shots, as in presplitting, exactly the same effects occur, but at numerous locations and sufficiently close in time that they interfere with

Jan 1, 1968

By R. B. Gavert, David J. Mack

ROOM- and elevated-temperature compression tests were made on the binary 3/2 electron compounds AuZn, CuAu, AgZn, AgMg, AuCd, and NiA1. These compounds possess either the B2 CsC1-type ordered structure or the A2 bee disordered structure represented commonly as ß and ß on equilibrium phase diagrams. In testing at room temperature, cylindrical specimens 0.508 cm by 0.330 cm diam were seated directly on an instron compression load cell (CF 0 to 10,000 lb). At elevated temperatures, testing included a special apparatus with a furnace heat source and a protective atmosphere.&apos; The specimens were strained at a rate of 1 pet per min. The compounds were prepared from 99.99 pet or better high-purity elements. Vacuum and/or argon cover gas was used throughout the mixing, melting, and specimen drawing processes. The generally equi-axed specimen grains varied in size from 0.5 to 1.5 mm for the five different compounds. The stress-strain curves in compression showed

Jan 1, 1968