Search Documents

By John Gross

THE deductions drawn in crushing and grinding operations have heretofore been based on a separation of the products into various sizes. A crushed product may be sized by sieving, by elutriation, and by aid of the microscope. To estimate the surface of each size the relation of the surface to the estimated average diameter must be assumed. Such a relation, owing to the irregularity of the particles, may involve two assumptions: First, a factor to convert average diameter to surface for one particular size; and second, a variation in the factor as the diameter of the particle changes. Obviously a surface measurement in which such assumptions and estimates are involved is questionable. In the first paper of this series1 a method has been given by which an accurate measure of surface of quartz can be obtained from its dissolution rate. By the use of this method, surface measurements have been made on a series of sieve sizes of crushed quartz, the results of which are given and discussed in this paper.

Jan 1, 1928

By Henry F. Hebley

This paper brings within the compass of one comparatively brief article a general description of the situation concerning the nation's water resources. It touches upon the phenomenal growth in the demand for water supply and emphasizes the problems facing the coal industry both with regard to acid mine water drainage discharged from active and abandoned mines and the suspended solids discharged to the stream system from wet coal preparation plants.

Jan 4, 1953

By Philip B. Bucky

[ ] FOREWORD THIS symposium brings together points of view, experiences and ideas on rock bursts from a goodly portion of the globe. Some conceptions, particularly those regarding the necessity of depth, have been fairly well shattered, as we find that they are present in the water tunnels of New York, on the surface at marble quarries in Vermont, and in the coal mines of the United States, as well as in the deep mines of the South African and Kolar gold fields, and in the nickel, copper and gold mines of Canada. Their occurrence under such a variety of conditions is, therefore, a challenge,

Jan 1, 1942

By F. M. Lewis, J. F. Meyers

This second progress report of grinding presents comments regarding ball consumption and data pertaining to the hydroscillator, which is closed circuited with the tricone mill. A study and postulate of how balls function is presented. The paper summarizes cost reduction obtained by the method of "grinding for the tail race" rather than for "mesh tons." AT the Regional meeting in Columbus, Ohio, in September 1949, the authors presented a progress report of the first year's operation with a Hardinge tricone mill in closed circuit with a Dorr hydroscillator. The present report covers our findings on this grinding circuit to January, 1950. In order to clarify our position, the authors wish to state that no invention or discovery is claimed. The Tennessee grinding circuit is simply an engineered arrangement of known equipment arranged to incorporate all of the recognized efficiency factors of comminution as they are known today. As we concluded our first report, it was not clear how effective the Tennessee mode of operation would be on harder ores. The only information we had at that time was that the Bond grindability test at 48-mesh gave 6.04 g of undersize per revolution. A later test on the same sample at 100-mesh reduced this to 2.04 g, which is definitely in the harder ore class, and which makes the reported 8.80 kw-hr per ton of —200-mesh produced a very creditable figure. Hydroscillator Operation The machine as now developed has proved dependable and easy to operate. It starts easily under full load and responds quickly to operating adjustments. The hydraulic holes in the oscillating plate do not plug when shut down under full load. Absolutely clean hydraulic water is essential. An Elliott water screen or similar device should be an essential part of the machine to keep all scale and trash of all kinds from the hydraulic compartment. The shift operators have expressed approval of the machine. In table I we show a typical screen analysis of the hydroscillator rake sand as compared to conventional classifier rake sand on our ore. We have previously reported that of the 28.7 pct reduction in power, the hydroscillator contributed 6 pct, on a —200-mesh basis. This is a conservative figure. Some of our test runs indicated that the saving was as high as 10 pct. Laboratory studies by the Dorr Co. engineers indicate that still greater efficiency is possible. Nevertheless, the 10-ft plate is overflowing 2100 tons per day at 3 to 4 pct + 65-mesh, which is a very creditable performance by

Jan 1, 1951

By F. M. Lewis, J. F. Meyers

This second progress report of grinding presents comments regarding ball consumption and data pertaining to the hydroscillator, which is closed circuited with the tricone mill. A study and postulate of how balls function is presented. The paper summarizes cost reduction obtained by the method of "grinding for the tail race" rather than for "mesh tons." AT the Regional meeting in Columbus, Ohio, in September 1949, the authors presented a progress report of the first year's operation with a Hardinge tricone mill in closed circuit with a Dorr hydroscillator. The present report covers our findings on this grinding circuit to January, 1950. In order to clarify our position, the authors wish to state that no invention or discovery is claimed. The Tennessee grinding circuit is simply an engineered arrangement of known equipment arranged to incorporate all of the recognized efficiency factors of comminution as they are known today. As we concluded our first report, it was not clear how effective the Tennessee mode of operation would be on harder ores. The only information we had at that time was that the Bond grindability test at 48-mesh gave 6.04 g of undersize per revolution. A later test on the same sample at 100-mesh reduced this to 2.04 g, which is definitely in the harder ore class, and which makes the reported 8.80 kw-hr per ton of —200-mesh produced a very creditable figure. Hydroscillator Operation The machine as now developed has proved dependable and easy to operate. It starts easily under full load and responds quickly to operating adjustments. The hydraulic holes in the oscillating plate do not plug when shut down under full load. Absolutely clean hydraulic water is essential. An Elliott water screen or similar device should be an essential part of the machine to keep all scale and trash of all kinds from the hydraulic compartment. The shift operators have expressed approval of the machine. In table I we show a typical screen analysis of the hydroscillator rake sand as compared to conventional classifier rake sand on our ore. We have previously reported that of the 28.7 pct reduction in power, the hydroscillator contributed 6 pct, on a —200-mesh basis. This is a conservative figure. Some of our test runs indicated that the saving was as high as 10 pct. Laboratory studies by the Dorr Co. engineers indicate that still greater efficiency is possible. Nevertheless, the 10-ft plate is overflowing 2100 tons per day at 3 to 4 pct + 65-mesh, which is a very creditable performance by

Jan 1, 1951

By Reuel A. Cochrane, Harry H. Angst

The successful exploitation by opencut methods of the low-grade porphyry copper deposits is due to the economical handling of large tonnages. Large tonnages are possible only if the rock material is broken so that the large power shovels can operate with minimum delays. This is particularly true at the New Cornelia mine, where the dense, hard, tough rock material creates problems not encountered in most of the porphyry copper mines. The introduction of churn drills at the New Cornelia for primary drilling, in 1936, necessitated a complete change in the methods of breaking ground as formerly air drills had been used. The blasting operations are of particular interest because of the handling of great quantities of high explosives in safely and efficiently fragmenting the hard rock material. Rock Formations At the New Cornelia mine the rocks are quartz monzonite with a diorite border facies intruding a rhyolitic series. Overlying these formations is a fanglomerate formation composed of boulders of monzonite, diorite, rhyolite, and other types of rock of unknown derivation. (The word "fanglomerate" is used in this paper in referring to the local conglomerate type of rock formations.) The ore body is approximately 4800 ft. long and 2800 ft. wide, and is of the disseminated type. Mineralization occurs principally in the quartz monzonite and to some extent in the adjacent diorite and rhyolite. The principal ore minerals are chalcopyrite, bornite, and a small amount of chalcocite. Over a considerable area the quartz monzonite is extremely hard and siliceous in character, owing to pegmatitic zones of alteration. The hardness of the ground depends on the intensity of the silicification. In a small area in the pit, the monzonite contains an abundance of pyrite accompanied by sericitization and is soft and easily fragmented. This is true also in the remaining oxidized portion of the ore body. The diorite and rhyolite formations, like the monzonite, vary from extremely hard to very soft material, but on the whole are easier to fragment than the monzonite. Jointing is prevalent in all the rock formations and plays an important role in the blasting efficiencies. In the fanglomerate formation, numerous well-defined joints, widely spaced, tend to make the ground blocky when blasted. This is a deterrent to good fragmentation. In the other rocks the joints are more numerous and are closely spaced, except in localized areas where the formations are extremely hard. These descriptions indicate that the lowest blasting efficiency will be obtained in the harder formations, from which the major portion of the mine production is obtained; namely, the monzonite and rhyolite. All rock formations mined at the New Cornelia pit are so hard that excavation

Jan 1, 1943

By Harry H. Angst, Reuel A. Cochrane

The successful exploitation by opencut methods of the low-grade porphyry copper deposits is due to the economical handling of large tonnages. Large tonnages are possible only if the rock material is broken so that the large power shovels can operate with minimum delays. This is particularly true at the New Cornelia mine, where the dense, hard, tough rock material creates problems not encountered in most of the porphyry copper mines. The introduction of churn drills at the New Cornelia for primary drilling, in 1936, necessitated a complete change in the methods of breaking ground as formerly air drills had been used. The blasting operations are of particular interest because of the handling of great quantities of high explosives in safely and efficiently fragmenting the hard rock material. Rock Formations At the New Cornelia mine the rocks are quartz monzonite with a diorite border facies intruding a rhyolitic series. Overlying these formations is a fanglomerate formation composed of boulders of monzonite, diorite, rhyolite, and other types of rock of unknown derivation. (The word "fanglomerate" is used in this paper in referring to the local conglomerate type of rock formations.) The ore body is approximately 4800 ft. long and 2800 ft. wide, and is of the disseminated type. Mineralization occurs principally in the quartz monzonite and to some extent in the adjacent diorite and rhyolite. The principal ore minerals are chalcopyrite, bornite, and a small amount of chalcocite. Over a considerable area the quartz monzonite is extremely hard and siliceous in character, owing to pegmatitic zones of alteration. The hardness of the ground depends on the intensity of the silicification. In a small area in the pit, the monzonite contains an abundance of pyrite accompanied by sericitization and is soft and easily fragmented. This is true also in the remaining oxidized portion of the ore body. The diorite and rhyolite formations, like the monzonite, vary from extremely hard to very soft material, but on the whole are easier to fragment than the monzonite. Jointing is prevalent in all the rock formations and plays an important role in the blasting efficiencies. In the fanglomerate formation, numerous well-defined joints, widely spaced, tend to make the ground blocky when blasted. This is a deterrent to good fragmentation. In the other rocks the joints are more numerous and are closely spaced, except in localized areas where the formations are extremely hard. These descriptions indicate that the lowest blasting efficiency will be obtained in the harder formations, from which the major portion of the mine production is obtained; namely, the monzonite and rhyolite. All rock formations mined at the New Cornelia pit are so hard that excavation

Jan 1, 1943

By J. D. Forrester

Many have been prone to credit the decline of professional interest in some branches of mineral industry education to the industrialists and other agencies who use our graduates. We hear the cry that industrial salaries are too low, opportunities for advancement do not exist, and the mineral industry specifically and generally is not interested in the engineer's efforts. Perhaps the time now has come when we should "dress-ranks," examine our practices, and publicize and encourage advanced technical training instead of laying all our troubles elsewhere. There can be no doubt but that industry is interested and stands ready and willing to co-operate. This is demonstrated by the numerous grants-in-aid and co-operative industrial projects which have been made available to those relatively few schools which have been encouraging graduate study and research. There is no dearth of research problems in any of the mineral industry fields and the sooner we realize the great opportunities for constructive, technical research in all areas of our profession the sooner we will reap the benefits of our engineering enterprises by closer liaison and broader understanding with industry. An analysis is offered here of the status of graduate work and research in various phases of mineral industry education in the United States. It is

Jan 1, 1949

E. O?C. Acker Jinzoc Adachi Truman H. Aldrich Walter H. Aldridge Anson W. Allen John H. Allen William R. Appleby W. Lawrence Austin W. S. Ayres David Baker John Henry Banks Henry C. Banon Alonzo F. Bardwell Walter A. Barrows H.C. Bellinger Wm de L. Benedict Robert Bentley John F. Berry Andrew A Blair George D. Blood Charles A. Bohn Walter M. Brodie Elwin F. Brown Fredrick Burbidge H.H. Burden Charles Butters

Jan 1, 1943

By H. G. Doll

THIS paper discusses a method and apparatus for determining the dip of formations traversed by a drill hole, by means of electrical measurements in the hole. The process consists in recording the Spontaneous Potentials present along three oriented generatrices in the hole. By comparison of the three curves thus obtained, after application of a correction factor to compensate for any deviations of the hole, the dip angle and the dip direction are determined. Excellent accuracy is obtained for dip angles over 10°. Because the method is simple and the apparatus rugged, the measurements are rapid and reliable; consequently, they can be made at all the levels that are of interest at any time after the well has been drilled. Mechanical cores are not needed to evaluate the dips. A convenient, timesaving procedure is to perform the dipmeter survey at the time the electrical log is taken, using for both operations the same cable and truck. Actual examples of results obtained in wells of the Gulf Coast area are given.

Jan 1, 1944

NEW MEMBERS The following list comprises the names of those persons who became members during the period Sept. 10, 1916, to Oct. 10, 1916. BLOOMFIELD, EDWIN CHARLES, Min. Engr., 1012 Standard Bank Bldg., Vancouver, B. C., Canada. BRINGS, HENRY, Min. and Met. Engr., Chief Engr., and Geol., Mollet-Mesrine, 1212 Mills Bldg., El Paso, Texas. CHASE, MARCH F., Vice-Pres., Commercial Acid Co., 1906 Boatmens Bank Bldg., St. Louis, Mo. CUMMINGS, ALVIN M., Asst. Mine Supt., Witherbee, Sherman & Co., Inc., Mineville, Essex Co., N. Y. DOUGLASS, GEORGE M., Genl. Safety Inspector, Amer. Smelt. & Ref. Co. 120 Broadway, New Fork, N. Y. EMRICH, CLARENCE T., Chief Chemist, Old Dominion Copper Min. & Smelt. Co., Box 1163, Globe, Ariz. GARDANIER, SUTTER ALBERT, Assayer, Mgr., Douglas Assay Co., Douglas, Cochise Co., Ariz.

Jan 10, 1916

By R. E. Lund

Josephtown Smelter employs the St. Joe-developed electrothermic process for producing zinc metal and zinc oxide. The process uses resistance-type electric furnaces. Flow of current through the sintered ore and coke charge develops the energy required for smelting at the reaction sites. To produce zinc metal, the furnace off-Gases bubble through a large "U"-tube filled with molten zinc which condenses the zinc to liquid; the metal is then mechanically cast into slabs. To produce zinc oxide, the furnace vapors burn in air and the resultant powders are collected. The smelter comprises three distinct circuits. One circuit produces American Process zinc oxide and high grade metal; another circuit produces tailor-made alloys of controlled lead and cadmium content; the third circuit produces prime western zinc metal and feedstock which is refined into special High grade metal and French Process zinc oxide. The roasting circuit utilizes multiple-hearth furnaces for deleading the zinc concentrates; fluid bed and suspension roasters are employed for desulfurization. Sintering produces a hard, porous furnace feed. The flexible smelting process is adaptable to consuming various kinds of secondary material. Extensive residue treatment accomplishes high overall zinc recovery. Smelter by-products include sulfuric acid, cadmium, and mercury.

Jan 1, 1970

By W. C. Maurer

Although millions of feet of rock are drilled annually, the basic drilling mechanisms involved are not well understood. The primary reason for this lack of knowledge is because the basic principles of rock failure are not well understood and rock failure is the primary mechanism in drilling. A better understanding of the drilling mechanisms would enable a more scientific approach to the design and use of drills and bits. The paper reviews several models which have been proposed to explain various aspects of the different drilling methods. These models are described and their limitations and areas of application are discussed. Drilling rate relationships are developed and related to the basic rock failure mechanisms. TYPES OF MECHANICAL DRILLS There are three basic methods of mechanically attacking rock: 1) percussive action, 2) rotary action, and 3) combined rotary-percussive action. A percussion drill applies a force perpendicular to the rock surface and the bit moves into the rock perpendicular to the surface, forming a crater beneath it (Fig. 1). A rotary drill applies a constant thrust to the bit while a torsional force moves the bit parallel to the rock surface, breaking the rock ahead of it. A rotary-percussive drill applies both a rotary force and a percussive force to the bit which moves into the rock at an angle to the surface. The commonly used drills can be classified as: rotary-drag, diamond; percussive-hammer, piston, churn; and combination-rotary-percussive, roller.

Jan 1, 1967

By Alfred W. Gauger, George A. Burrell

The senior author of this paper, while in Colorado on other official business, made a trip to the Cripple Creek gold-mining district to get more data than are at present available regarding the composition of the gas that issues from the rock into the mines of the district. This was done at the suggestion of George S. Rice, Chief Mining Engineer of the Bureau of Mines. There are -many questions of interest and importance in connection with the ventilation of the mines in the Cripple Creek district, such as the menace to life and mining of a suffocating gas entering the mines from the rock, the danger due to powder smoke (from blasting operations), and danger of continued inhalation of rock dust by the miners. This report confines itself to the first problem, the gas from the rock, and principally to one phase of this question, the composition of the gas and its effects on men and lights. A more thorough study of this and other ventilation problems is planned. That the rock gas is a real menace is shown by the fact that miners (variously estimated from 25 to 50 by different persons interviewed) have been killed by it in the 25 years that mining has been vigorously carried on at Cripple Creek. Many men have had narrow escapes from death, some of them having been incapacitated for days. In addition, much loss of time results because at certain periods of the year or on certain days it is impossible to enter some workings. At a few mines, fans force air into the workings, thus supplementing the natural ventilation and much improving conditions, but the improvement is not entirely adequate at all times. Origin of the Gas Lindgren and Ransome1 think that the gas found in the rocks of the Cripple Creek mining district represents the last exhalations of the ex-

Jan 1, 1917

By C. A. Herbert, C. M. Young

WithIn the past few years, considerable development has been made in the coal-mining industry in Illinois and Indiana and it is the purpose of the authors to record its most important phases. Perhaps the two most striking features are the entry into the producing fields of certain large consumers of coal and the magnitude of some of the new operations. Mines are now being equipped by the Chicago & Northwestern R. R., the Chicago, Burlington & Quincy R. R., the Standard Oil Co., of Indiana, and the Union Electric Light & Power Co. of St. Louis. Besides, the U. S. Steel Corpn. has increased its coal-mining activities by commencing operations on its large holdings northeast of Benton, Franklin CO., Ill. Until recent years, the supply of coal has commonly been adequate and prices have generally been favorable, especially to large consumers, as the magnitude of their purchases enabled them to obtain satisfactory quotations from producers. In fact, most consumers of coal have believed that they could buy their fuel more satisfactorily in the open market than they could produce it themselves. The entry of the United States into the war was accompanied by various disarrangements of industrial conditions, and a demand for coal in excess of the supply seemed likely to be experienced for an indefinite period. Under these circumstances it seemed that the greatest assurance of a supply of fuel was its production by the operation of mines. In the case of the Chicago & Northwestern R. R. and the U. S. Steel Corpn. the production of coal has been carried on for many years with satisfactory results, but the C. B. & Q. R. R., the Union Electric Light & Power Co. and the Standard Oil Co. of Indiana had not been producers of coal, at least in this district. Apparently the most impressive feature of the newest mines is their capacity, for in some cases it is planned that production shall be in the neighborhood of 1000 tons per hr. There are mines now in this field having nearly that output, but these were not planned for such output; in fact, when the shafts were sunk and the machinery installed it was generally supposed that the daily outputs would be only in the neighborhood of 4000 to 5000 tons. Incidentally, there has risen

Jan 1, 1920

By W. A. Backofen, B. C. Wonsiewicz

The Plasticity transition in magnesium was studied by plane-strain compression of single crystals and polycrystalline material at temperatures from about 20" to 307°C. Reduction of single crystals along the c axis was accommodated by twinning on {1011) and retwinning on (10 12}, followed by basal shear in the doubly twinned volume. Deformation in that mode can result in sufficient independent shears for arbitrary shape change. Fracture in c axis compression, below about 100°C, has been related to excessive shear caused by unloading from the stress for {1011} twinning (-50 ksi at 20°C) to that for slip within the twin (-3 ksi); ductility follows from heating because the stress difference is lowered and the twin volume, in which elastic strain energy is dissipated on unloading, is increased. The stress for (1011) twinning is strongly temperature-dependent but not given by a critical resolved shear stress law. The latter is attributed to the influence of stress concentration from prior intersecting shear on nonbasal planes, the former to the temperature dependence of the preliminary slip. THE basic symmetry of hcp crystals has the effect of limiting the number of independent slip systems and making twinning an important deformation mechanism. The general result in wrought polycrystalline aggregates is a more or less sharply developed texture (or preferred orientation) which underlies a strong anisotropy in mechanical behavior. Knowing how the one influences the other is essential background for the use of such materials. Magnesium was of interest in this work because of the unexplained plasticity transition that it undergoes somewhere in the neighborhood of 200°c.''~ At lower temperatures plastic deformation before fracture in polycrystalline material is limited, while at higher temperatures extensive deformation is possible. The transition temperature commonly determines the lower limit of the range in which magnesium is worked. The limited ductility can be traced to a lack of independent crystallographic shears. A minimum of five are required for arbitrary shape change.' Around room temperature, however, slip on all known systems provides only four.' In each case, the slip direction is in the (0001) basal plane so that slip does not allow strain along the c axis. With increasing temperature, more slip occurs on the ( 1011) pyramidal plane and the ( 1010) prism plane but without change in direction.'?' Thus, that development alone cannot explain the transition temperature.

Jan 1, 1968

By J. WILLIAM WETTER

WHEN the privilege was extended to me to address this meeting I could not help but make a mental review of my own activities and experiences in connection with association work. After having spent about 16 years in the mining engineering field, I entered into the operating branch of coal mining which afforded, about 12 years ago, my first opportunity of attending a meeting of our local Association and sitting in with the "big boys" of the industry. This was quite a thrilling experience because I had heard a great deal about the various operators who belonged to the Association and knew, or at least thought I knew, that a certain group dominated its affairs and that a "clique" was in control of a sizable "roller" which could be "steamed up" at will to flatten out any opposition which might appear upon the horizon or under it, too, for that matter. Now, I was to have the privilege of observing this "clique" at first hand, of seeing a small group making the policies and shaping the destinies of a great industry and planning the activities of an important Association while a large majority of the members would sit by either complacently or otherwise with the full knowledge that the "roller" was in waiting to reduce them to ribbons at the first sign of resistance.

Jan 1, 1930

By Warren Howes, C. O. Anderson, Robert E. Illidge, M. D. Harbaugh, S. J. Burris

The Tri-State zinc-lead mining district embraces an extensive area, including the northeastern part of Ottawa County, Oklahoma, the southeastern part of Cherokee County, Kansas, and adjacent portions of Missouri, mainly in Jasper County. The Oklahoma-Kansas portion of the district, in the vicinity of Picher, Okla., has been the principal producing area since 1917, and the present milling practice in that section is the subject of this paper. This district is the largest zinc-producing field in the United States. In 1926 it produced 55 per cent of the nation's zinc and 15 per cent of its lead, and in 1933 it produced 35 per cent of the zinc and 10 per cent of the lead. From 1842 to 1933, inclusive, the total output of the district was 18 1/2 million tons of zinc and lead concentrates valued at 818 million dollars. Of this production, the Oklahoma-Kansas, or Picher, field yielded over 9 million tons valued at over 400 million dollars. Mining operations in the Oklahoma-Kansas field near Picher and Baxter Springs began in 1915. The mills built it that time consisted merely of gravity concentration plants employing jigs and tables and the same flow sheets as had proved satisfactory with the free-milling ores such as were mined in the Joplin-Webb City fields in Missouri. The Kansas-Oklahoma ores proved to be much richer but also more refractory to treatment than those in the Joplin area, and contained a considerable percentage of zinc mineral not freed by the amount of crushing usually practiced in preparing the ores for jigging. Thus the old Joplin type of mill, with its usual two or four jigs and a few tables, proved inadequate and resulted in excessive tailings losses sometimes as high as 50 per cent

Jan 1, 1935

By R. L. Fleischer, B. Chalmers

In order to observe size effects associated with a grain boundary, aluminum single crystals and bicrystals of various cross-sectional dimensions were deformed in tension. Typical stress-strain curves are presented in conjunction with measurements of the effects of changes in crystal dimensions. Some effects of the growth rate used in preparation of crystals are also described. It is indicated that the macroscopic constraints at a grain boundary are responsible for the most prominent grain-boundary effect, the production of multiple slip. Two measurements of the width of the region of double slip are in agreement. It is concluded that the yield stress of aluminum is affected markedly by the inherent oxide coating. THE general problem to be examined is that of dimensional effects in the plastic deformation of metal crystals. These effects will be termed "size effects" and are here defined as follows: A size effect occurs in a series of crystals if their plastic-deformation properties are a function of crystal dimensions. Clearly then size effects depend on the nature of the boundary conditions imposed on the crystal. Crystal boundaries can be of three types: interphase, inter-crystalline, and free surface. Such deformation effects as are caused by distribution of phases, grain size, lineage structure, and single crystal external geometry are specific types of size effects. This discussion will be confined primarily to grain-boundary and single-crystal size effects, though in practice most "single crystals" not only have a number of small angle boundaries but also have one or more surface phases, so that the boundary conditions appropriate to a free surface do not necessarily apply. Hence, to this extent interphase size effects will be considered. The question of size effects associated with grain boundaries (called here intercrystalline size effects)

Jan 1, 1959

By J. Wright, R. J. Tyler

Changes in the pore structure of hematite pellets during reduction to iron were investigated under a variety of experimental conditions. Pore structures were determined by a mercury penetration technique. The reduction temperature was found to be the major influence on structure, the pore system being bimodal below 7.50°C and unimodal above 900°C. Pore sizes ranging front 0.04 to 20 m were observed in complete metabolized pellets produced over the temperature range 650 - 1050°C. Gas composition and reduction rates also influenced the pore structure of the metabolized pellets, although to a lesser extent than the reduction temperature. An apparent activation energy of 24 kcal/mole was derived for the pore formation process.

Jan 1, 1979