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By Frank C. Appleyard

Gypsum, the dihydrate form of calcium sulfate, has a history of usefulness to man dating back several thousand years, and a worldwide industry has been built on the mining and processing of this versatile industrial mineral. However, anhydrite, the other principal calcium sulfate mineral has very limited use, so much so that separate statistics for it are not always kept, but are usually included with those for gypsum. Although often found in close association, the two minerals have important chemical differences in that anhydrite is the anhydrous form of calcium sulfate (CaSO,) whereas gypsum is the dihydrate (CAS0;2H20). These two molecules of combined water result in significant differences in hardness, density, and solubility of the two minerals. However, of most importance is the difference in thermal properties wherein gypsum, upon the application of a modest amount of heat, can be converted to the hemihydrate of calcium sulfate (CaS0;Vi H,O) or plaster of paris, an intermediate product upon which is based over 90% of the value of all calcium sulfate end products. Anhydrite, on the other hand, is inert at these temperatures and its uses have been limited to only those few cases where calcium sulfate in the anhydrous form may have an advantage. The earliest known use of gypsum plaster dates back some 5000 years to the time of the Pharaohs of Egypt who had discovered that gypsum rock, when exposed to fire, broke down into a powder which when mixed with water would form a putty that could be "plastered" on a rough mud brick or stone wall to make a smooth finish. It was used down through the centuries in a limited way for ornamental purposes, but did not achieve wide acceptance because of its quick (25 to 30 min) setting or hardening time which made it difficult to use. The first real understanding of gypsum chemistry was developed in France about 1755, and the gradual growth of its present utilization dates from that time. In the United States, the first utilization of gypsum was to grind it to a fine material for use as a soil conditioner at about the time of the Revolutionary War, and the term "land plaster" for ground gypsum has remained in use. Another cementituous material-lime or calcium oxide-had become the usual plastering material, but by about 1870 a method for retarding the set of gypsum plaster was discovered and it has today almost completely replaced lime as a plastering material. In recent years, gypsum products sold in the United States have reached a total valuation of approximately $500 million per year as illustrated in [Table 1].

Jan 1, 1975

By E. F. Miller

The subject " Safe Timbering of Working Places in Mobile Loading" is one that requires an analytical study of the strata both above and below the coal seam as well as the characteristics of the coal seam itself. The projection or mining plan must be based on economic roof control in which the application of timber can be minimized without incurring cost increases in other phases of production. The several types of loading machines in common use today are not adaptable to the same projections or timbering systems. Consequently the type of equipment to be used must also be considered. For these reasons the writer does not believe that the problems of timbering in working places can be discussed without simultaneously considering economic production as well as the safety of men and the conservation of equipment. Prior to the introduction of loading machines as a substitute for the pick and shovel system of loading coal, the care and maintenance of the individual working places were generally the responsibility of the coal loaders who worked in them. Up to that time very few coal companies had developed and applied fixed and definite standards for timbering the working places in the mines they operated. It is common knowledge that mechanical loading of coal has had several false starts in the last twenty-five years and it is only in the last decade that it has developed to the stage at which we now find it. During this twenty-five year period the management of the more responsible companies have come to realize the tremendous importance of roof control in coal mining. From a safety viewpoint, the lack of roof control has been and still is responsible for more than a third of the industry's annual fatality experience. In recent years workmen's compensation and insurance rates have steadily increased while the profit margin has decreased almost to the point of elimination. From an economic operating viewpoint, the failure to properly control roof is quite often the most costly single phase of coal mining. Since the manufacturers of loading machine equipment have so improved their machines that normal care and maintenance can reduce to a minimum the time lost because of mechanical failure the production delays from other causes have assumed a far greater importance. Roof control in the broad sense and in the light of concentrated mining plans or projections that are adapted to mobile loading should be regarded as one of the major problems in the inseparable phases of production and safety of the workman and equipment at the working face. The subject of this paper cannot be treated properly unless what is said here is based upon the broad and fundamental problem of genera' roof control. The suc-cessful solution of a problem arising in any industry must have its origin in a complete analysis of the known facts or factors that pertain to it. The several illustrations

Jan 1, 1949

By A. H. Bromly

THE small agricultural village of Santa Barbara, in the State of Guanajuato, has been the center of spasmodic tin-mining operations during recent years. The deposits, so far as I know, are unique, and a few brief notes may be of interest. Santa Barbara, about 12 miles west of San Felipe station on the Mexican National Railway, and at an elevation of 2,400 m. above sea-level, is situated in a flat valley extending east and west, and bounded north and south by broken rugged bills rising about 330 m. above the general level of the valley. Tin-mining operations have been conducted-at the Queensland mine, near this village. A small concentrating-mill was erected and attempts were made to smelt the ore in reverberatory furnaces. The country-rock of the district for many miles is rhyolite of great thickness. There are some local variations due to differences in cooling, or subsequent alteration or impregnation; but throughout the whole district the principal constituents of the rocks remain the same, viz., free silica, orthoclase-feldspar and sanidine. The latter is especially marled. The crevice and joints of the rock are frequently filled with calcedonic and opalescent quartz. The ore-formation at the Queensland mine is of an unusual nature, consisting of cracks in the rhyolite which have been filled with clay. This phenomenon is largely developed over a width of from 80 to 100 m., in which the principal fissuring follows an approximate direction of north and south. The av¬erage clip ranges between 70 to 80 degrees. Some of the fissures bold sufficiently true for a time to afford the impression that they are clue to dynamic causes, or earth-movement. This may be true of some of the north by south fissures; but considering

Jul 1, 1905

By G. Abowitz, R. B. Gordon

The velocity of sound, mass density, and thermal expansion coefficient were measured in dilute lead, tin, zinc, bismuth, cadmium, indium, and potassium amalgams as a function of composition. Measurements in the Hg-TI system extended ovev the wider range of composition, 0 to 40 at. pct TI. The sonic velocity was measured as a function of temperature. The calculuted adiabatic compressibility in all cases was found to decrease much more rapidly than would be expected on the basis of a linear variation with composition. An interpretation of the results is given in terms of changes in the Debye characteris -tic temperature of mercury on alloying and a possible change in the bonding of mercury itself. If a liquid is considered as an isotropic elastic medium, the phase velocity of a longitudinal elastic wave traveling in the liquid is given by where K is the bulk modulus, G the shear modulus, and d the mass density. G can be neglected for liquids of ordinary viscosity, i.e., approximately 1CT2 poise, because the shear stress component is relaxed essentially at once. That is, for liquids of ordinary viscosity and at frequencies of the applied stress up to several hundred megacycles, the relaxation time of the shearing process is much shorter than the period of the applied stress. Eq. [I] then reduces to The adiabatic rather than the isothermal compressibility is measured at the megacycle frequencies used in ordinary ultrasonic velocity measurements. The sonic velocity and compressibility have been determined for many organic liquids and aqueous eletroltes,' and the results have been interpreted in terms of existing theories for these fluids. The velocity of sound and compressibility are important parameters in theories of the liquid state. For example, equations of state have been proposed relating the free volume of liquids to the acoustic velocity.3 Comparatively very little work has been done on the acoustic properties of liquid metals and alloys. leppa,' orddon, and several other investigators

Jan 1, 1963

By William Rawles

THIS report is the first of a series planned by The Mineral Inquiry, organized by the American Institute of Mining and Metallurgical Engineers to make factual studies of the world's mineral resources in their political and international relations. The efforts of The Inquiry are directed toward filling certain notable gaps in available information, without duplication of many other investigations touching this field which are being conducted by other organizations, public and private. Much of its work is indirect-suggesting topics for study by other individuals and organizations and aiding in their planning and correlation. The present report is designed to show the nationality of the commercial control of mineral resources, in addition to the geographic distribution of production by nation-in other words, the overlapping of political and commercial control. Detailed accuracy cannot be claimed for the figures presented. For some companies division of ownership by nationality has been very difficult to ascertain, as many companies are reluctant to dis-close the extent of their holdings in other corporations, and the impossi-bility of tracing all stock ownership is obvious. Also there are frequent changes in the distribution of stock control. The percentages given rep¬resent only the participation that has been identified definitely, even though it is known in some cases with fair certainty that larger interests exist, as, for instance, American participation in foreign chromite companies. In bringing together these figures we have had the cordial co-operation of the United States Bureau of Mines, the United States Geological Survey, the Mineral Division of the Bureau of Foreign and Domestic Commerce, the Brookings Institution, and of many specialists connected with the mineral industries covered. The report does not cover the entire list of minerals. Coal, although it is, one of the most important minerals, was omitted because not more than one or two per cent of the world's production comes from mines that are owned by companies foreign to the countries where the coal is produced. Others, such as gold, are omitted because sufficient data have not yet been accumulated. It is hoped that some of these may be covered in subsequent reports. It is not our purpose here to discuss the significance of the figures sub-mitted, but only to point out the general nature of the problems on which they have a bearing.

Jan 1, 1933

By J. L. Walter

Extra-low carbon iron sheet, when deformed and annealed, undergoes exaggerated or abnormal grain growth in the critically deformed regions of the sheet. This exaggerated pmth occurs, for low strains (3 to 6 pct), only in sheet which has a fine dispersion of precipitates in the subsurface region of the sheet and fewer and coarser precipitates in the sheet interior. These particles have been identified as manganese sulfides. Wing the anneal, grains near the surface are gvowth-inhibited by the fine particles but the grains in the interior are free to grow normally. With the additional driving force provided by the strain energy, the interior grains first grow into the small subsurface pains. Eventually, these growing grains grow completely through the sheet. Calculations of limiting grain sizes at various values of strain indicate that a volume fraction of precipitates in excess of 10-' would be required to eliminate exaggerated growth in material strained to 10 pct. OPEN-COIL annealing has made decarburization of sheet steel both efficient and economically practical. Use of such material for porcelain-enameling stock is one of many possible applications of low-carbon iron since carbon in steel is deleterious to porcelain-enameling properties.' However, the extra-low carbon iron presently available presents another problem, that of exaggerated grain growth in regions where the sheet has been deformed as by bending or stretching. In exaggerated grain growth a few grains start to absorb their neighbors and these may become very much larger than the average grains of the sheet. Other names for exaggerated grain growth are coarsening, critical grain growth, secondary recrystallization, abnormal grain growth, or discontinuous grain growth. While this grain growth does not affect the enameling qualities of the low-carbon iron sheet, their presence results in a marked reduction of tensile-yield strength in the region of the sheet containing the large grains. The loss of tensile yield strength may render the material unsuitable for many applications . This report describes the results of a study undertaken to determine the cause of the exaggerated grab growth in extra-1ow carbon iron and, if possi- ble, to prescribe practical procedures for its prevention. GENERAL THEORY The driving force for exaggerated grain growth is the grain boundary free energy. This driving force is proportional to (l/rl + l/r2) where rl and r2 are the mutually perpendicular radii of curvature of the boundary between the growing grain and the grain being consumed. Thus, the greater the difference in size between the growing grain and the matrix grains, the higher the driving force for grain growth. If, however, the matrix grains are free to grow simultaneously, the driving force for exaggerated growth will be diminished. Stability toward growth of the matrix grains may be caused by a) a strong single orientation texture (texture inhibition),' b) a dispersed second phase,3"5 c) the thickness effect,' or d) intergranular segregation.7"9 As exaggerated growth occurs when growth of the matrix grains has been slowed by the stabilizing processes mentioned above, there must be an additional factor acting to promote growth of a few of the grains to the point where they are enough larger than the matrix grains that boundary energy driving forces are sufficient to cause continued growth. For instance, at the annealing temperature, growth-inhibiting inclusions may slowly dissolve and coalesce. Eventually, a grain boundary becomes unlocked and migration occurs at the expense of neighboring grains. Or, an additional driving force may be supplied to some of the grains if the material is strained. Then, since some grains will be strained less than others, the difference in strain energy between adjacent grains may be sufficient to overcome boundary locking and allow growth of the grains with lower strain energies. In the present study, therefore, such factors as the presence or absence of dispersed phases, the nature of the exaggerated growth, and the effect of strain have been considered. EXPERIMENTAL PROCEDURE I) Material and Processing. Three types of low-carbon iron were used in this study; types A and B were commercial grades, each from a different supplier.* The precise details of the processing of

Jan 1, 1963

By Robert L. Dean, Michael Hoch, Samuel M. Wolosin, Chung K. Hwu

The general shape of the 1450°C isotherm of the Ti-TiO-ZrO2-Zr region was evaluated from the surrounding binary phase diagrams and from thermo-dynamic data on the metal-oxygen binaries. The phase boundaries were accurately determined using X-ray and metallographic techniques. At 1450°C the system shows a large bcc ß field, which extends from the two metal-oxygen binary systems as a Gaussian error function, and is stable up to 30 at. pct 0 when Ti and Zr are present in equal amounts. At higher O Concentrations, the ß field is in equilibrium with t-ZrO . The following four regions, with three solid phases, are present: two a ß t-ZrO,, a TW t-ZrO,, and TiO t-ZrO2 c-ZrO2. On cooling the ß phase transforms into the a phase, going through the w transition phase. The isotherm at 1500°C for the region TiO-TiO,-ZrO, was obtained by using X-ray diffraction. At 1500°C a large c-ZrOz region is present as well as a large two-phase field, Ti0 c-ZrO,. The following regions, with three solid phases in equilibrium, were found These regions are relatively small. The solidus and liquidus relationships were determined by observing samples suspended in a tungsten crucible by means of a fine tungsten wire and heated in vacuum. Eleven univariant points were found. C-ZrO, decomposes through a peritectic reaction into liquid t-ZrO2. The activities of Ti and TiO in the TiO t-ZrOz and in the two a ß t-ZrO regions were measured using the Knudsen effusion method. In the a TiO t-ZrO, region the activities of Ti and Ti are the same, as in the a — Ti TiO binary. In the two a t-ZrO, regions, the Ti activity is high and the Ti0 activity very low, although all phases present contain at least 30 at. pct 0. This indicates a short-range order in the solid phases, Zr atoms being preferentially surrounded by 0. 1 HE system Ti-Zr-0 is of interest because of the wide ranges of solid solubility exhibited by the boundary systems; as titanium and zirconium both belong to the same group of the periodic table, large single-phase regions should occur within the system, with a great variation of properties (as the composition changes within the single-phase region). Furthermore, the possibility of modifying ZrO, to make it a more usable refractory by the addition of other metals makes this system also of interest. Because of the high affinity of titanium and zirconium for oxygen, the oxygen partial pressure is very low at all compositions; thus, there exists a ternary metal-metal-oxygen system in which the oxygen pressure is not an important variable, so long as it is low enough. When a sample is heated in vacuum to a temperature high enough for vaporization to occur, the vapor phase will consist of metal and metal-oxide gas, the oxygen concentration being very low. The phase relationships in the surrounding binary systems have already been reported in the literature; therefore, the study of the ternary diagram

Jan 1, 1962

By H. W. Reinhardt, J. W. Dally

A dynamic photoelastic analysis of stress waves interacting with a free surface is described. The free surface is that of a bench with a fixed bottom so common in quarry applications. The stress waves are generated by line charges of lead azide (Pb N,). Four models of identical geometry are investigated with the direction of detonation of the line charge varied between the four models. Dynamic photoelastic patterns are recorded and analyzed to indicate which method of detonating the line charge produced the largest magnitude of tension at the free surface. The mechanics of rock breakage by means of explosives has received considerable treatment by many investigators including Duvall, Obert, Broberg, Rinehart, and Langefors1-11 over the past two decades. Indeed in more recent years several texts12-15 have been written on the topic, treating a wide variety of subjects which are logically related to the modern technique of rock blasting. In rock blasting the chemical energy of a concentrated explosive contained in a relatively small diameter borehole is utilized to fragment the rock. The explosive is transformed into a gas with enormous pressures which exceed 10-5 bars18 This high pressure shatters the rock in the area adjacent to the borehole and produces dilatational and distortional stress waves which propagate radially away from the borehole. The state of stress associated with these outgoing waves produces a system of cracks which extend for a few feet from the borehole. The breakage produced in this manner is limited as the dynamic stress in the pulse attenuates markedly with distance. In the absence of a free surface, the stress wave propagates away from the source without further fracture. With a free face of rock near the drill hole, another mode of breakage occurs which is due to scabbing failure of the layer of rock adjacent to the free face. These scabbing failures are produced by the reflection of the incident waves and the conversion of compressive stresses into tensile stresses sufficiently large to fracture the rock. The detailed nature of the interaction of the stress waves with the free surface is complex and difficult to treat analytically. However, dynamic photoelasticity offers an experimental approach which gives a fullfield visual display of propagating stress waves and the reflection process. Applications of static photoelasticity to solution of problems related to mining technology have become relatively common (see, for instance, Refs. 17 and 18) with a plastic model loaded to produce a state of stress representative of that occurring in the workings of a mine. The application of dynamic photoelasticity is ex tremely limited. Tandanand and Hartman19 have used a multiple spark camera to study fracture in glass and plastic plates impacted by a chisel-shaped tool. This paper describes a dynamic photoelastic analysis of stress waves interacting with a free surface. The free surface is that of a bench with a fixed bottom so common in quarry applications. The stress waves are generated by line charges of lead azide (Pb-N6). Four models of identical geometry are investigated with the direction of detonation of the line charge varied between the four models. Dynamic photoelastic patterns are recorded and analyzed to indicate which method of detonating the line charge produced the largest magnitude of tension at the free surface. Experimental Procedure The model illustrated in [Fig. 1] was fabricated from a sheet of Columbia Resin CR-39 to represent a bench with a fixed bottom. Properties of the CR-39 pertaining to these dynamic experiments are listed in [Table 1]. Scribe lines on 1-in. centers are used to identify locations along the bench face. The bench height was 8 in., the burden was 3 in., and the overall dimensions of the sheet, 16 and 18 in., were large enough to eliminate reflections from nonessential boundaries during the period of observation of the dynamic event. To simulate a charge in a borehole, a groove 0.062 in. wide and 0.080 in. deep groove was cut into the sheet from one side. The lower end of the groove was 1 in. or 1/3 the burden distance below the bottom of the bench. The upper end of the groove was 3 in. or one times the burden distance below the upper level of the bench. The groove was packed with 60 mg of Pb No per in. of length, and ignited with a bridge wire detonator. Four different ignition procedures were used to examine the effects of detonation direction on the stress wave interaction with the free face of the bench. In Test 1 the line charge was ignited at the top and the line charge detonated downward. In Test 2 the line charge was ignited at the bottom and the charge burned upward. In Test 3 the charge was ignited in the center with the top half burning upward and the bottom half burning downward. Finally in Test 4 the line charge was ignited at both ends simultaneously. Sixteen high-speed photographs of the photoelastic fringe patterns representing the stress wave propagation were recorded for each of the tests. A Cranz-Schardin multiple spark gap camera 20,21 was operated at framing rates which were systematically varied from 110,000 to 250,000 frames per sec during each test.

Jan 1, 1972

By H. J. Tschirner, L. P. Davidson, R. K. Carpenter

HE electrolytic zinc plant of the American Zinc Co. of Illinois, at Monsanto, was expanded in 1943 to a capacity of 100 tons of slab zinc daily. This capacity was not attained because of inability of the leaching plant to deliver an adequate amount of solution for electrolysis. Changing the leaching method so that the acid was added to the roasted zinc material reversed the usual procedure and made it possible to attain the desired capacity. The conditions which prevented satisfactory work before this change and the difficulties which arose in reversing the usual leaching procedure are described. The "reverse" leach operation as now practiced is carried out as follows: All the calcine to be leached is fed continuously to a slurry mixing tank. About one third of the acid to be used is fed to the tank with the calcine. The slurry is discharged continuously to a Dorr duplex classifier in closed circuit with a Hardinge mill. The classifier overflow is pumped to any of six leaching tanks where the leach is completed. A finished leach is discharged through Allen-Sherman-Hoff pumps to Dorr thickeners, from which the overflow goes to the zinc dust purification and the underflow to vacuum filters. This change in leaching procedure from the usual one of adding calcine to a large amount of acid made it possible to provide an adequate amount of purified solution to the electrolyzing division and at the same time filter and dry all the residue produced. Operating savings in reagents and better metallurgical recoveries were also important benefits. The original flowsheet of the leaching plant provided leaching, sedimentation of the insoluble residue, and purification of the neutral zinc sulphate solution with zinc dust. The thickened residue was filtered and washed. The purification cake of excess zinc dust, precipitated copper and cadmium, and any insoluble residue was filtered off on plate-and-frame duplex classifier. Settlement in the thickeners was inadequate and the suspended solids in the thickener overflow gave rise to filtration difficulties after the zinc dust purification. Further, the filtration and washing of the leach residue was poor, and it became necessary to pump a large amount of unwashed or poorly washed residue to storage ponds outside the plant building. Two causes of the poor settling and filtration were determined: Soluble silica and ferrous iron in the calcine treated. The latter was a result of poor roasting and with more experience ceased to be a major problem. The silica was a normal constituent of the feed and the working out of the problem became a matter of controlling its solubility. The obvious method to render the silica insoluble was by intensive roasting. This, however, met with total failure as such roasting resulted in silicates, probably zinc, soluble in the 13 pct acid used for leaching. Attempts were made to coagulate the fine gelatinous slime with addition agents. Glue, lime, starch, beef-blood serum and others were tried without success. All the suggested tried-and-tested means of operating the thickeners gave no consistently good results. Variations in leaching time, in addition of calcine to the leaching tanks, "conditioning" of the pulp by prolonged agitation, immediate discharge of the leach upon completion to avoid breaking up flocs were all tried and given up as ineffective. Byron Marquis, of Singmaster and Breyer, worked with the plant staff on a beaker scale until a leaching procedure was developed which gave consistent results and a promise of overcoming the difficulties which had plagued the plant operation. It was suggested that the difference in solubility of silicates and zinc oxide in sulphuric acid could be made use of in a leaching method where the acidity was controlled carefully. Such control is possible when acid is added to a slurry of calcine. This process reverses the normal procedure of adding calcine to a vessel of acid, hence the term "reverse leach" was applied. In this way, the overall acid concentration can be kept very low. In the tests made, it did not exceed 0.05 g per liter free sulphuric acid. Numerous advantages were realized when no silicates were taken into solution and later precipitated as a bulky gel. The gel had made reasonable thickening and filtration of the leach pulp and practical drying of the residue impossible. When the gel was eliminated, thickening rates were increased as much as five times. The volume of residue after thickening represented about 10 pct of the total leach pulp and had been as high as 95 pct when the gel was present. The thickened pulp was filterable and the filtered cake was dried readily after washing. The zinc extraction from the calcine was slightly lower. This was more than compensated for by the increase in zinc recovered in solution from zinc which had been trapped in the gelatinous residue. The amount of copper recovered was lower. However, the amounts of other impurities, such as arsenic, antimony, and germanium, taken into solution were lower. This was particularly true of antimony. Since the inception of reverse leaching, no concentrates have failed to yield solutions free of antimony even when present in the calcine to the extent of 0.2 to 0.3 pct. Oxidation of ferrous iron is a problem of reverse leaching. Ferrous hydrate does not precipitate at pH 5.3 to 5.4 where a leach is finished. The usual oxida-

Jan 1, 1952

By C. W. Nicolson

THE Tri-State zinc and lead-mining district is in the northeast corner of Oklahoma, the southeast corner of Kansas and the southwest corner of Missouri. The area throughout which active mining has been conducted is about 45 miles long and about 5 miles wide, extending northeasterly from Commerce, Okla., to Alba, Missouri. Although the lead ores were mined on a very small scale in the vicinity of Joplin, Mo., as early as 1848, nothing of any importance was done in the district until 1870, since when both mining and smelting have been prosecuted with considerable vigor. In the beginning the lead ores only were exploited, but within a few years extensive deposits of zinc ores were found and since that time the production of zinc ore has far exceeded that of lead. Both the surface and mineral rights in Missouri and Kansas were under individual ownership by the time ore was discovered. Although some of these rights were purchased by mining companies, most of the mining has been done under leases covering small areas, usually 40 acres, although in the past many leases were given on much smaller tracts. In Oklahoma most of the mineral land had been alloted by the Government to various Indian tribes and although the title to some of these lands had been acquired by various white men before the discovery of the rich Picher field, the title to most of the land has remained with the Indian tribes and the leasing of the mineral rights has been done by the Federal Government for the benefit of the Indians. The Indian allotments were of 200 acres each and some of the mining leases covered entire allotments, although many leases were granted for only 40 acres or even less.

Jan 1, 1938

By A. Spilners, M. Simnad

The rates of formation of the different oxides on molybdenum in pure oxygen at 1 atm pressure have been determined in the temperature range 500° to 770°C. The rate of vaporization of MOO, is linear with time, and the energy of activation for its vaporization is 53,000 cal per mol below 650°C and 89,600 cal per mol at temperatures above 650°C. The ratio Mo03(vapor.lzing)/MoOS3(suriace) increases in a complicated manner with time and temperature. There is a maximum in the total rate of oxidation at 6W°C. At temperatures below 600°C, an activation energy of 48,900 cal per mol for the formation of total MOO, on molybdenum has been evaluated. The suboxide Moo2 does not increase beyond a very small critical thickness. At temperatures above 725°C, catastrophic oxidation of an autocatalytic nature was encountered. Pronounced pitting of the metal was found to occur in the temperature range 550° to 650°C. Marker movement experiments indicate that the oxides on molybdenum grow almost entirely by diffusion of oxygen anions. USEFUL life of molybdenum in air at elevated temperatures is limited by the unprotective nature of its oxide which begins to volatilize at moderate temperatures. Although the oxide/metal volume ratio is greater than one, the protective nature of the oxide film is very limited. Gulbransen and Hickman' have shown, by means of electron diffraction studies, that the oxides formed during the oxidation of molybdenum are MOO, and MOO,. The dioxide is the one present next to the metal surface and the trioxide is formed by the oxidation of the dioxide. Molybdenum dioxide is a brownish-black oxide which can be reduced by hydrogen at about 500°C. Molybdenum trioxide has a colorless transparent rhombic crystal structure when sublimed, but on the metal surface it has a yellowish-white fibrous structure. It is reported to be volatile at temperatures above 500" and melts at 795°C. It is soluble in ammonia, which does not affect the dioxide or the metal. In his extensive and classic investigations of the oxidation of metals, Gulbransen2 has studied the formation of thin oxide films on molybdenum in the temperature range 250" to 523°C. These experiments were carried out in a vacuum microbalance, and the effect of pressure (in the range 10-6 yo 76 mm Hg), surface preparation, concentration of inert gas in the lattice, cycling procedures in temperature, and vacuum effect were studied. The oxidation was found to follow the parabolic law from 250" to 450°C and deviations started to occur at 450 °C. The rates of evaporation of a thick oxide film were also studied at temperatures of 474" to 523°C. In vacua of the order of 10- km Hg and at elevated temperatures, an oxidation process was observed, since the oxide that formed at these low pressures consisted of MOO, which has a protective action to further reaction in vacua at temperatures up to 1000°C. Electron diffraction studies showed that, as the film thickened in the low temperature range, MOO8 became predominant on the surface. Above 400°C MOO, was no longer observed, MOO, being the only oxide detected. The failure to detect MOO, on the surface of the film formed at the higher temperatures does not militate against the formation of this oxide, since according to free energy data MOO3, is stable up to much higher temperatures. At the low pressures employed, this oxide would volatilize off as soon as it was formed. Its vapor pressure is relatively high and is given by the equations" log p(mm iig) = -16,140 T-1 -5.53 log T + 30.69 (25°C—melting point) log p(mm He) = -14,560 T-1 -7.04 log T+1 + 34.07 (melting-boiling point). Lustman4 has reported some results on the scaling of molybdenum in air which indicate a discontinuity at the melting point of MOO, (795°C). Above the melting point of MOO,, oxidation is accompanied by loss of weight, since the oxide formed flows off the surface as soon as it is formed.5,6 Qathenau and Meijering7 point out that the eutectic MOO2-MOO3 melts at 778C, and they ascribe the catastrophic oxidation of alloys of high molybdenum content to the formation of low melting point eutectics of MOO3 with the oxides of the melts present. Fontana and Leslie -explain the same phenomenon in terms of the volatility of MOO,, which leads to the formation of a porous scale. Recent unpublished work by Speiser9 n the oxidation of molybdenum in air at temperatures between 480" and 960°C shows that the rate of weight change of molybdenum is controlled by the relationship between the rates of formation and evaporation of MOO,. They have measured the rates of evaporation of Moo3 in air at different temperatures and estimated an activation energy of 46,900 cal. This compares with the value of 50,800 cal per mol obtained by Gulbransen for the rate of sublimation of MOO, into a vacuum.

Jan 1, 1956

By C. A. Bruch, W. E. McHugh, R. W. Hockenbury

EXPERIMENTAL results of the last decade have shown that both accelerator particles and reactor radiations produce significant changes in the properties of metals. These changes, called radiation damage, are important from both academic and engineering viewpoints. An understanding of the radiation damage produced by reactor radiations is difficult, because many kinds of particles having varying energies are present. Therefore, many fundamental studies are being conducted using accelerators in order to obtain nearly mono-energetic beams of various charged particles. Furthermore, many of these experiments are conducted at low temperatures in order to freeze in the radiation-produced lattice defects, after which the specimens are annealed to study the movement of the defects. It is found that although much of the low temperature radiation damage disappears by annealing at room temperature, a significant amount remains. Because there is no assurance that irradiation followed by annealing at a higher temperature will produce the same effect as irradiation at the higher temperature, and because there is an immediate interest in reactor radiation effects during exposures at and above room temperature, a major program is in progress at this laboratory to investigate some of these effects. This paper, representing a part of the program, compares the radiation damage to a group of metals which were exposed under nearly identical irradiation conditions. The metals, representing the three major crystal systems, include copper, nickel, titanium, zirconium, iron, molybdenum, and type 347 stainless steel. The effects of reactor radiations have been treated from a theoretical viewpoint by Seitz' and Ozeroff.' The problem considered by them has been the atomic displacements produced in an infinite medium by mono-energetic beams of both neutrons and charged particles. For reactor experiments, this treatment is not wide enough in scope, because specimens and reactor components are finite, and there are continuous energy spectra of the various particles. Therefore, the theoretical considerations will be extended in this paper to cover reactor conditions and the findings will be compared with the observed radiation damage. Experimental Materials—The six basic metals for this investigation were of commercial or higher purity, and the type 347 stainless steel was of commercial quality. These materials were supplied in various forms ranging from ingots to finished rods, and were fabricated to rods approximately % in. in diam and annealed for specimen stock. A summary of data pertinent to these materials is shown in Table I. The values for chemical compositions include both actual analytical values and typical values supplied by the manufacturer. More information concerning typical

Jan 1, 1957

By Frank J. Tolonen, Nicholas H. Manderfield, Paul Jasberg

EARLY in the study of the low grade iron formations of Michigan, wide variations in their structure and texture became evident. Because of these variations no simple method of concentration is possible, and those portions of the formations that can be exploited profitably under a given stage of metallurgical progress and existing economic conditions must be searched for carefully. Both structure and texture of the formations have an important bearing on their amenability to bene-ficiation. By structure is meant the banding planes of easy fracture, the porosity, and the degree of leaching. Texture, which includes grain sizes, shapes, and degree of interlocking, determines the amount of grinding necessary to liberate the mineral grains. Structure determines the liberation of portions richer in one mineral. Structure and texture may be termed the gross features of the formation. Earliest surveys of the formations were conducted to outline the parts that could be concentrated at % in. (3 mesh). Operators agreed on this size because anything finer required sintering or other agglomeration processes. At 3 mesh only the structural features, as defined above, would be liberated. With suitable ores concentration was easy, as any of the gravity methods could be used. Sink-and-float gave good results, but with this method only limited portions of the iron formations yielded a desilrable product.1,2 n general, the iroa content could be raised to shipping grade, but the silica content remained too high—sometimes 20 pct—instead of 9 or 10 pct. Grinding did not greatly increase the liberation ofsilica until 2010 mesh or finer was reached. To find the reason fpr this T. M. Broderick began micros~opic examin'ations of the formations in 1933.3 Procedure: The purpose of this discussion is to correlate the appearance of typical portions of the iron formations with their amenability to concentration. As liberation is essential before separation becomes possible, much of the work is based on measuring the liberation achieved by crushing and grinding. Both heavy media and magnetic tube tests were used in this work. On the basis of general structural features such as banding, degree of alteration, and leaching, a specimen was selected from each part of the iron formations studied. The specimen represents the gross features of the formation and not necessarily the particular formation quantitatively. One half of the specimen was polished for macro-study, and the remainder was used for analyses to obtain the grades represented by variations appearing in the macrosection. Specimens for microscopic examination were also prepared for each variation in gross appearance. For correlation of microstructure with liberation, the previous work by sink-and-float methods was supplemented by magnetizing roasting followed by magnetic separation. The results show the liberation of silica to be very important at the sizes used, because any silica particle with iron minerals occluded would be held in the concentrate. A magnetizing roast changes the crushing and grinding character of the sample. For partly leached soft samples the change is slight, but with harder types and those in which there is a considerable change in crystal structure of the minerals, the increase in liberation of the iron minerals may be 30 pct more than that of unroasted samples at the same crusheH size. Gogebic Range Iron Formations: The Gogebic Iron Range is located in the extreme western and southern parts of Michigan's Upper Peninsula, extending westward into Wisconsin. Samples for this study were obtained from the Ironwood formation, comprising three chief members—the Plymouth, Norrie, and Ahvil—with several intermediate slates and thick overlying slates. (The slates are not considered in this discussion because grinding finer than present practice is usually required to liberate the iron minerals.) The predominant iron mineral is hematite, about half of which is hydrated to goe-thite. Limonite occurs in some of the partly leached areas, and siderite in parts of the formation.

Jan 1, 1958

By James H. Courtright, Kenyon Richard

SILVER Bell is situated 35 airline miles northwest of Tucson, Ariz., in a small, rugged range rising above the extensive alluvial plains of this desert region. Its geographical relation to other porphyry copper deposits of the Southwest is shown on the inset map in the lower left corner of Fig. 1. The climate is semi-arid. Altitudes range within 2000 and 4000 ft. Opening of the Boot mine, later known as the Mammoth, in 1865 was the first event of note in the district's history. Oxidized copper ores containing minor silver-lead values were mined from replacement deposits in garnetized limestone and treated in local smelters. Copper production had approached 45 million pounds by 1909 when the disseminated copper possibilities in igneous rocks were recognized. Extensive churn drill exploration carried out during the next three years resulted in partial delineation of two copper sulphide deposits, the Oxide and El Tiro. Although the then submarginal tenor discouraged exploitation of these disseminated deposits, selective mining of orebodies in the sedimentary rocks continued intermittently until 1930, providing a production total of about 100 million pounds of copper. The American Smelting & Refining Co. began exploratory and check drilling in 1948 and subsequently made plans for mining and milling the Oxide and El Tiro orebodies at the rate of 7500 tons per day. Production began in 1954 at a rate of about 18,000 tons of copper annually. Formations ranging in age from Pre-Cambrian to Recent are exposed in the Silver Bell vicinity. The more erosion-resistant of these, Paleozoic limestone and Tertiary volcanics, predominate in the scattered peaks and ridges comprising the Silver Bell mountains. The porphyry copper deposits are located along the southwest flank of these mountains in hydrothermally altered igneous rocks. These are principally intrusives which cut Cretaceous and older sediments and are considered to be components of the Laramide Revolution. For three-fourths of its length the zone of alteration strikes west-northwest, Fig. 1. There now is no single structure that accounts for this alignment. However, indirect evidence suggests that a fault representing a line of profound structural weakness existed in this position prior to the advent of Laramide intrusive activity. This line will be referred to as the major structure. It was obliterated by the Laramide intrusive bodies but exerted a degree of control on their emplacement, as evidenced by their shapes and positions. The influence of fault structures on the shapes of intrusives in other porphyry copper districts has been noted by Butler and Wilson' and by others. As shown on the inset map on Fig. 2, a fault of parallel trend and considerable displacement lies to the north. This fault is now marked by a line of small Laramide intrusive bodies. To the south is a third fault of large displacement. Evidence of its age in relation to the Laramide intrusions and mineralization is not recognized, but its conformance in strike with the other two major faults is significant. These three breaks establish a pronounced trend of regional faulting. They are high-angle, and the southerly one may be reverse, Stratigraphic separations on these faults are of the order of several thousand feet. The local Paleozoic section is about 4000 ft thick. It is composed predominantly of limestone with a basal quartzite member. The Cretaceous section appears to exceed 5000 ft. Conglomerates, red shales, and arkosic sandstones (the youngest) characterize the three principal members. Intrusion of alaskite marked the beginning of Laramide igneous activity. It was emplaced as an elongate stock with one side closely conforming to the major structure line throughout a distance of nearly 4 miles. The alaskite was at one time regarded as a thrust block of pre-Cambrian rock'; however, its intrusive relationship and consequent post-Paleozoic age has been established by inclusions of limestone found in outcrops north of El Tiro. The next event was the intrusion of a large stock of dacite porphyry into Paleozoic sediments and alaskite. The stock was some 3 miles wide and at least 6 miles long in a northwesterly direction. It was sharply confined along its southwest side by the major structure line. A number of large pendants of moderately folded Paleozoic sediments occur within and along its southwest edge. Thus the inferred, original major fault between Paleozoic and Cretaceous sediments became a contact between alaskite and Paleozoic sediments and then a contact between dacite porphyry and alaskite. Andesite porphyry may have been intruded later than the dacite porphyry, but relationships are not clear; it may be simply a facies of the latter. The intrusive activity was at this stage interrupted by an interval of erosion. The erosion surface probably was rugged, as there were local accumulations of coarse, angular conglomerate. Subsequently a series of volcanic flows and pyroclastics several thousand feet thick was deposited. A similar unconformity has been recognized elsewhere in the Southwest, particularly in the Patagonia Mountains near the Flux mine some 75 miles southeasterly. Here, as at Silver Bell, volcanics were deposited on an erosion surface cut in Cretaceous and older sediments which had been intruded by alaskite. Though no evidence is offered that closely defines the age of this unconformity, and proper analysis of the problem is beyond the scope of this paper, it is

Jan 1, 1955

By James Ferguson

THE fact that little if anything has appeared in the technical press or in the Transactions of the Institute on the subject of roll shells proper, used in various grinding appliances such as Cornish rolls or Chilean mills, may be taken as an incentive, if not an excuse, for the present article. No attempt is made to enter into a. discussion as to the theory or mathematics of crushing as performed by rolls, the subject being treated in a general way with respect to the manufacture of roll shells 'and some salient points touching on their adaptability and wear in service. While it stands to reason that skill coupled with judgment in the mechanical design of rolls, Chilean mills or other types of grinding machinery, with special reference to strength of parts, nicety of adjustment and other mechanical features, stand for efficiency in their operation .and satisfaction in service, the exceedingly important item. of roll shells or other wearing parts entering into their construction should not be lost sight of. In other words, a well-designed piece of grinding machinery is just as inefficient in service, when equipped with poor roll shells or shells made of the wrong or an inferior grade of metal, as good roll shells made according to the best practice the steel maker knows, working on an old or antiquated set of rolls. Unfortunately there is a tendency occasionally for the machinery builder to blame the steel maker or vice versa if roll shells do not wear well or evenly, or if they break before being worn down to their ultimate thin point. There is no occasion for this attitude, as the product, of each must stand on its own merits. But it is essential that the two work in harmony since the machinery builder usually does not furnish the shells for his rolls or grinding mills, but depends on the steel maker, who makes a specialty of this rolled product, to give the particular needed element of efficiency to his machine.

Jan 9, 1914

By G. K. Manning, C. H. Lorig

Two metallurgical tools have acquired wide use within the past several years as a means of studying the transformation characteristics of steel. One is a technique used first by Bain and Davenport for determining the transformation characteristics of a steel at constant temperature; the second is the end-quench hardenability test. Constant-temperature transformation curves like those of Bain and Davenport have done much to rationalize the metal¬lography of steel; however, in commercial practices, constant-temperature transformation is seldom encountered, therefore only rarely can such curves be directly applied. The real reason for the determination of such curves lies, in the fact that they provide a way of thinking about transformation that is both convenient and productive. The end-quench hardenability test is a more practical means of studying transformation, for, by correlating positions on the hardenability bar with shapes of different masses, an almost direct application of the results can be made. Unfortunately, the end-quench test, though practical, can do very little toward improving the metallurgists' way of thinking about transformation. These two metallurgical tools, dealing with precisely the same phenomenon, should be very closely associated in metallurgists' minds. Actually, they are frequently pushed into separate mental corners and considered as being more or less distinct and unrelated. The reason for this is that no strong connecting link between them has been developed. An attempt is sometimes made to relate these two tools by projecting the critical cooling rate on the isothermal transformation plot as illustrated in Fig. I. The critical cooling rate is considered as a constant rate-though in practical applications, cooling rates are never constant-and this constant cooling rate is given uniform significance from the Ae temperature down to the temperature of initial transformation. A little thought indicates the errors of such a procedure. Certainly the time interval spent just below point A of Fig. I cannot be as effective in promoting nucleation as is the time interval spent just above point B. Yet the procedure represented in Fig. I considers all the time spent between temperatures A and B to be just as effective in promoting nucleation as though all the time were spent at temperature B. Furthermore, change the shape of the isothermal curve between points B and C in any way desired, and the required critical cooling rate is not changed one iota. This cannot possibly be true. Such a way of thinking about critical cooling rates not only is incapable of giving any results that are quantitatively satisfactory but is likely to give very misleading qualitative results.

Jan 1, 1946

By Alexander R. Troiano, Eugene P. Klier

SINCE the very early work on quenched structures, where the products of the martensite transformation had been recognized, this transformation has provoked much interest and study. Theoretically it was desirable to account for the extreme changes in physical properties resulting from the formation of martensite, as that information might lead to results of practical importance. Desirable information, therefore, was on the kinetics of transformation from austenite to martensite as well as on the physical constitution of the martensite. It has been known for years that certain steels quenched to room temperature will contain persistent austenite as well as martensite. Other important and now well- established features of the martensite reaction are the progress of the reaction on cooling only and the independence of Ar" with cooling velocities exceeding the critical velocity. These facts have been experimentally determined by various methods and investigators. Notable among the early investigators were Tammann and Scheill and Wever and Engel.2 Unfortunately, all investigators did not fully interpret their results, which, coupled with several investigations that yielded conficting results, caused a state of confusion that was not clarified until quite recently. X-ray investigations of martensite in steels3-6 indicate it to be a supersaturated solid solution of carbon in alpha iron. This supersaturation is evident from the appearance of a body-centered tetragonal structure with the addition of sufficient carbon. The dimensions of this tetragonal structure are alinear function of the carbon content within the limits of accuracy of the determinations. Slight tempering of tetragonal martensite leads to the destruction of the tetragonal structure, which is converted to a body-centered cubic structure. This phenomenon has precipitated a controversy concerning the nature and mechanism of the tempering of martensite. The facts in the case have been outlined by Epstein7 and more recently by Antia, Fletcher, and Cohen.8 The significance of Ar" on theoretical grounds is not clear, however, although considerable study has been devoted to its determination. The precise position of Ar" as a function of carbon content was first stated by Greninger and Troianos for steels covering a range of approximately 0.7 to 1.8 per cent carbon. The effect of alloying elements on Ar" has recently been the subject matter of investigation by various methods.

Jan 1, 1945

By W. A. Oates, J. A. Lambert, P. T. GaIIagher

Monte Carlo methods have been used to compute the arrangements of interstitial atoms dissolved in tetrahedral sites in bcc lattices. It is assumed that the presence of an interstitial atom "blocks " a certain number of neighboring sites and prevents their occupancy. Sites "blocked" by more than one filled site are allowed for. The computed values of. the mean occupation number (defined as the ratio of the total number of sites blocked to the number of solute atoms are used to calculate the configurational entropies of the solutions. These entropies are compared with those resulting from previous theoretical studies of this problem and also with available experin~ental data for the p Zr-H, Nb-H, V-H, and Ta-H systems. Evidence is also given that the "blocking" explanation of low limiting compositions in these systems, rather than this being due to initial limitations on the number of sites available, is probably correct. THE ideal partial configurational entropy of mixing of an interstitial solute in a metal is given by: where p is the number of interstitial sites per metal atom and Xi is the atomic fraction of the interstitial. For the bcc lattice. which we shall be concerned with in this paper, the interstitial positions are shown in Fig. 1. It can be seen that for the tetrahedral sites, p=6. whereas for the octahedral sites, p = 3. Different emphasis has been placed on the relative importance of energy and entropy effects in determining deviations from ideality in interstitial solid solutions. In some cases the same system, e.g., Fe-C, has been described by the contradictory regular and athermal solution models indicating that the enthalpy and entropy functions, derived from equilibrium data, are frequently not accu.rate enough to differentiate between these treatments. However, for certain metal-hydrogen solutions the equilibrium data is available over sufficiently wide ranges of temperature and composition to permit a reasonably accurate determination of the compositional variation of the heats and entropies. Hoch&apos; has attempted to interpret the results of interstitial solid solutions in terms of a regular solution model. In the case of the Ta-H system where 13 = 6, this model entails fitting the experimental relative partial entropies of solution, asH, to the equation: where ASgs is the relative partial excess entropy of solution of hydrogen. Hoch found that the results of Mallett and Koeh1 could be fitted to this equation with an approximately constant value of AF up to XH = 0.25. However, it is apparent from the solubility isotherms in this system which become asymptotic to the composition TaH that, since (Xh /6 - ~Xh ) becomes infinite only at TaH6, it is necessary that AS<&apos; tends to infinity at TaH. In other words, the low saturation composition of TaH, instead of the anticipated TaH,, eliminates the possibility of applying regular solution theory to such systems. Rather large negative excess configurational entropies must exist at higher hydrogen concentrations in order to explain the lower saturation values. To account for these low limiting compositions and excess entropies two distinctly different approaches have been followed. Rees and many others1-l2 have assumed that not all interstitial sites are crystallographically equivalent with respect to the interstitial addition; that is, in Eq. [I] p is less than the value anticipated from geometrical considerations. To describe, say, a bcc metal-hydrogen system with a limiting composition of MH by this approach one would consider that p = 1 in the first instance instead of p = 6.&apos;j3 In some cases, nonintegral values of B have been taken in order to improve the fit with the experimental data over limited ranges of composition. The other approach which has been used to explain the low saturation compositions is to assume that, although all sites are available for occupancy, strong repulsive interactions exist between the neighboring interstitial atoms, and hence occupancy of any site excludes or blocks a certain number of neighboring sites from being occupied. Earliest treatments of this concept considered the exclusion of an integral number, of nearest-neighbor sites from being occupied at all concentrations. In this case, the partial configurational entropy is given by: These early treatments failed to allow for the overlap of the blocked sites which will arise at all but the very lowest concentrations. More recently attempts have been made to calculate the effect of this decrease in the number of blocked sites on the configurational entropy. Using the quasichemical treatment of interstitial solid solutions as given by Lacher and assuming that an infinite repulsive interaction energy existed between the solute atoms. atom obtained an approximate configurational entropy applicable to the blocking with overlap case:

Jan 1, 1970

ALTHOUGH the refining period of the heat is generally defined as A starting after the charge has been completely melted, it may more properly be considered as beginning with the first efforts to facilitate the shaping up of the slag and the making of corrective additions for the control of slag or metal composition. Such actions may be initiated during the latter half of the lime boil. The early part of the refining period may, then, in essence overlap the latter part of the melting period. The primary aims of the refining period are to reduce phosphorus and sulphur from the steel bath to levels safely below the maximum contents specified, to eliminate carbon as rapidly as possible and still allow time for proper conditioning of the slag and attainment of the necessary bath temperature, and to deliver the heat ready for tapping or furnace deoxidation, with slag in the proper physical and chemical condition, and with carbon and oxygen contents and the temperature of the steer bath at the proper levels for the composition and grade of steel being produced. The particular conditions that fulfil these aims are distinctly different, depending upon whether the steel is to be finished according to fully-killed, semikilled, or rimming practice and also depending upon the carbon range specified. Regard- less of the type of charging practice employed, the object of the refining period is to produce repeatedly the desired finishing and tapping conditions for the grade of steel being produced. The variations and proportions of raw materials used in the charge may cause some variations in the degree of control required during refining, but not in the method of control. The refining period can therefore be discussed from a viewpoint largely independent of charging and melting practice. SHAPING UP THE SLAG In the first helper&apos;s vocabulary, refining practice consists in "shaping up" his heat. This includes elimination of sulphur, phosphorus, and carbon, putting the slag in proper condition, and adjusting bath temperature. Shaping up the slag is a major consideration because

Jan 1, 1944

By L. L. Swift

AT the present time there are four base metals being used for automotive bearing alloys. Of course there are numerous variations in the amounts of alloying elements added to each base metal and nearly all of these alloys have the conventional, if not classical, duplex structure; that is, they are composed of a hard constituent embedded in a soft matrix. The well-known theory is that the former will wear well, while the latter will be plastic enough to allow the bearing to be broken in and conform to the contours of the shaft. The requirements of the modern bearing have been most aptly described by W. M. Corse: In order to meet the engineering demands of today a good bearing metal must be able to carry the weight of the shaft and stand up under steady or suddenly applied loads, or even blows in some types of service. A certain amount of plasticity is desired to compensate for minute irregularities in the shaft or bearing surface, and to permit yielding, thereby avoiding dangerous stresses in bearing and shaft and preventing overheating and rapid wear of parts. Less plasticity is required in a bearing metal if the surfaces of bearings and journals are machined accurately, aligned, and kept in alignment. It is desirable, of course, that a bearing metal have a low coefficient of friction. Under most operating conditions the friction depends on the unit pressure of the bearing, the speed, the temperature, and the properties of the lubricant. A good bearing metal must have a low rate of wear to reduce the necessity for frequent replacements, and adjustment of the bearings. It must wear more rapidly, however, than the journal or shaft running on it, because replacement of the journal or shaft is more difficult and costly than replacement of the hearing., The hardness of, the bearing alloy is a property closely related to several of the foregoing. With a duplex microstructure, the measurement of hardness with any of the usual commercial devices means little. The Bierbaum method of measuring the hardness of the individual constituents was developed to, fill this need. MICROCHARACTER The Bierbaum microcharacter2.3 measures the scratch-hardness of a solid by pulling a weighted diamond point over the surface. The diamond point is ground. so that it is the corner of a cube, and mounted

Jan 1, 1938