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Since the comprehensive review of the Persian fields presented by Sir John Cadman last year, operations have proceeded normally. No developments of especial importance fall to be recorded and it remains only to bring up to date the full information given at the beginning of 1933. Controlled production from the Masjid-i-Sulaiman and Haft Kel fields has been maintained at slightly higher rates than during 1932. The figures for the past five years are as follows: These represent crude oil and products piped to the coast but exclude products reinjected into the reservoir, a process that has been in continuous operation at Masjid-i-Sulaiman during the period under review. The systematic delimitation of the Haft Kel field has been continued during the past year and results have been sufficiently encouraging to justify the inception of a wider scheme for distribution of production. Drilling has been resumed recently in the Persian sector of the Naft Khaneh field, and preliminary survey work is in progress for the selection of a site for a refinery at Kermanshah arid the construction of a connecting pipe line. Investigations in connection with the scientific control of reservoir were dealt with in considerable detail in last year's review. This work has been steadily pursued during 1933 and certain of the investigations have been the subject of papers presented to the World Petroleum Congress held in London in July of last year.

Jan 1, 1934

By Charles B. Manula

Judging from the rapid pace of increased demands for mineral products, technological forecasting will become an increasingly necessary tool in mining. Even though the mining industry in 1966 produced more are than ever before, current extraction rates are only a fraction of what is expected in the later years of the twentieth century. If metal and mineral commodities continue to hold their respective and present share of markets, the prospect of coping with demands from a population that will double in the next thirty years can become an impossible task when viewed outside the limits of technological advance and change. Those mining companies that are doing little to develop new and expanding horizons for their operations cannot expect to survive. Nearly 90% of all metals and mineral products consumed last year was recovered by open-pit mining. This has placed great pressure on this segment of the industry which, consequently, has resulted in some spectacular developments. Already production rates at many places are dwarfing those of the Panama Canal and other well-known earth moving projects which are frequently identified as massive undertakings. With projects of this scale, the need for increased sophistication of engineering, planning, management and administration of modern mining installations has never become more apparent. The design of complete systems for the mine and plant that fit the mould of today's business and social environments is undergoing an evolutionary process.

Jan 1, 1968

By R. Scott

This article describes and evaluates the establishment of Kuyasa Mining including the search for a suitable deposit, the ongoing lack of finance, and market constraints. Despite the dramatic initial growth and success of their Ikhwezi Colliery near Delmas, Mpumalanga, Kuyasa?s experiences offer some sobering arguments for significant changes to mineral rights ownership, the attitude of financial institutions and government policy if South Africa is to have a dynamic and successful junior and small-scale mining sector.

Jan 1, 1998

By William Stewart

Recitations were taking place in the red schoolhouse at Orneville, Maine. It was winter and the snow lay deep on the ground, but some of the scholars were in bare feet, and only half as many hats hung on the pegs as there were potential wearers in the seats. That was forty years ago; and the pioneers of northern New England were more noted for their industry than for their possession of the fruits of it.

Jan 1, 2007

"The most widely used method for predicting the onset of continuous caving is Laubscher’s caving chart. A detailed examination of this method was undertaken which concluded that it had limitations which may impact on results, particularly when dealing with stronger rock masses that are outside current experience. These limitations relate to inadequate guidelines for adjustment factors to rock mass rating (RMR), concerns about the position on the chart of critical case history data, undocumented changes to the method and an inadequate number of data points to be confident of stability boundaries.A review was undertaken on the application and reliability of a numerical method of assessing cavability. The review highlighted a number of issues, which at this stage, make numerical continuum methods problematic for predicting cavability. This is in particular reference to sensitivity to input parameters that are difficult to determine accurately and mesh dependency.An extended version of the Mathews method for open stope design was developed as an alternative method of predicting the onset of continuous caving. A number of caving case histories were collected and analyzed and a caving boundary delineated statistically on the Mathews stability graph. The definition of the caving boundary was aided by the existence of a large and wide-ranging stability database from non-caving mines. A caving rate model was extrapolated from the extended Mathews stability graph but could only be partially validated due to a lack of reliable data."

Jan 1, 2003

By James Dunn

“The strongest argument of the detractor (of mining)is that the fields are devastated by mining operations ...They argue that the woods and groves are cut down, for there is need of an endless amount of wood for timbers, machines and the smelting of metals. And when the woods and groves are felled, then are exterminated the beasts and birds, very many of which furnish a pleasant and agreeable food for man. Further, when the ores are washed, the water which has been used poisons the brooks and streams, and either destroys the fish or drives them away.” Georgius Agricola, 1556, De Re Metallica, translated by Hoover, 1950. Technical problems associated with the cleanup of historic mines are not new. Nor are they unique to the mining industry or the governmental agencies addressing them. Both face the same issues and challenges of defining the problems, evaluating remediation options and finding the most economic and effective solutions.

Jan 1, 1999

By C. Overton, R. W. Nice

"With todays economic trials and tribulations we have all become deeply engaged in costs and cost cutting in our field of mineral processing. Grinding is one of the most expensive unit operations. The cost of grinding media is the most expensive item in grinding costs. Therefore, it is only reasonable to attack the cost-cutting area by trying to reduce the consumption of media. This introduces the field of autogenous or rock-on-rock grinding.Rock-on-rock grinding is not new to us. It has been known for many decades;The South Africans used pebble grinding in the '20's for gold.Mr. B. Crocker was prompted for the same reasons to introduce pebble grinding at Lakeshore Mines in Kirkland Lake during the last war.The Buffalo Anchorite used beach pebbles in grinding prior to the war.Autogenous and semi-autogenous grinding is used quite successfully in the iron ore field. Base metals have their examples in Australia at Caba, in Africa at Komato and in Sweden at Aitik.Recently three mills in British Columbia and one in Arizona started with autogenous mills in their circuits. One was originally conceived to utilize a modified autogenous grind with a crusher in the circuit. All except the same mill had contingency plans for converting to semi-autogenous. All four mills have since converted to the semi-autogenous mode. These are Island Copper, Lornex, and Similkameen in B.C. and Pima Mining in Arizona."

Jan 1, 1975

By Dean McDonald

The Committee Bay Greenstone Belt extends over 300km and is one of the largest unexplored greenstone belts in North America with excellent gold and diamond potential. Committee Bay Resources Limited holds over 550,000 acres of land with prospective geology in the Committee Bay area southwest of Melville Peninsula, Nunavut. Committee Bay is a typical Archean greenstone belt comparable to the Yellowknife, Red Lake, Kirkland Lake and other prolific gold belts. Drilling during 2003 at Committee Bay resulted in: 1) the discovery of high-grade gold-bearing quartz veins with silicification and sulphidation at Three Bluffs, and 2) the continuation of high-grade gold mineralization in the hinge area of the iron formation at Inuk. Gold mineralization at Three Bluffs is identified in iron formation and adjacent sediments and has been traced by drilling for over 700m. The Three Bluffs iron formation is open to depth and along strike where is has been traced on surface for over 6km. In January 2004 Committee Bay and joint venture partner Gold Field?s announced a $7.1 million exploration program for the Committee Bay project in 2004. A total of 8,000m in exploration drilling has been approved for the expansion of the Three Bluffs to the resource stage and drilling of at least five new target areas. Additional mapping, sampling and geophysics will be used to identify new gold targets along the very prospective Committee Bay belt.

May 1, 2004

By Teale E. O

The purpose of the present communication is to put on record the discovery, in October, 1916, in the Howqua district, of a new locality for the occurrence of phosphatic rocks in Victoria, and to give a preliminary description of its characters and geological occurrence. Owing to the great use of superphosphates for agricultural purposes in recent years in Australia, search has been stimulated for the discovery of local and workable supplies of phosphatic rocks. Phosphorus is an element very widely distributed in igneous rocks, usually in the form of the mineral apatite, and also occurs in sedimentary rocks and in soils as a detrital constituent. Under these conditions of occurrence, however, the amount of P 205 present in a rock or soil seldom approaches, and very rarely exceeds, 1 %. Very occasionally it occurs in such a concentrated form as to constitute workable deposits. In such cases they are usually of organic origin. Sometimes they occur as geologically recent deposits of guano or rock...

Jan 1, 1918

By S. Felderhof, W. S. Vaughan

"Over the years, it has been increasingly difficult for the minerals industry to raise the necessary capital for its activities. To alleviate this phenomenon, complete transparency and capital market efficiency is needed. Since a company’s mineral resources and mineral reserves base is an essential component to obtaining capital, reporting these assets must also be transparent and efficient. This must occur, however, at an international level given that mineral industry operations, and its financing, are international. To achieve this, an international committee (i.e. Australia, Canada, South Africa, the United Kingdom and Europe, and the United States) was formed and has been developing standards for the reporting of mineral resources and mineral reserves.The effectiveness of these standards, however, depends on adoption by the required regulators. Unfortunately, these standards have not been recognized by the U.S. Securities and Exchange Commission (SEC). Instead, the SEC adheres to its old standard (Industry Guide 7), making it increasingly expensive and difficult for international mining companies to obtain capital in the United States. Compounding the problem is the SEC’s influence over the current work of the International Accounting Standards Board and the International Organization Organization of Securities Commissions. These organizations are in the process of standardizing international accounting practices and international securities rules and regulations. Their current position may prevent adoption of the industry-developed mineral resources and mineral reserves standards which are internationally recognized."

Jan 1, 2005

By I. Loomis, D. Rachmad, I. Duckworth

During the past two years the Underground Mine Ventilation Group at PT Freeport Indonesia has undertaken to upgrade their Hygiene Laboratory. This process has included upgrading equipment for dust sampling and gas monitoring, as well as procurement of an OCEC analyzer for Diesel Particulate Matter analysis. While the laboratory equipment represents one factor, these changes have also required re-evaluation of the sampling protocols and the burden of ventilation monitoring personnel. This paper provides a review of these experiences.

Jan 1, 2006

By Kenneth A. Grace

Introduction The 1980s have not been kind to the mining industry, especially in the United States. As mineral commodities prices plunged, marginal producers were squeezed out and then major players were forced to cut back or close down operations. Base metal miners suffered the most. Gold was all that glittered. As had been the case throughout min¬ing's history, exploration activity was an early victim of these depressed conditions. Mining companies had to economize drasti¬cally and exploration was deemed a nones¬sential activity. Funding for new explora¬tion ventures dried up as mining was seen as a poor investment. A national magazine even proclaimed the death of the industry. Indeed, ignoring matters of independ¬ence of supply and the relationship of min¬eral production to national security, it was argued that mining was but a small cog in the overall scheme of things in the United States. The industry made a relatively small contri¬bution to the gross national output. We were becoming a service industry economy, re¬member? But what of those countries where mining plays a major role in the economic well-being? In some, mining is the national economy. In a few specific cases, special conditions actually brought prosperity. Copper production in Chile is one example. There, high grade copper, low production costs, and a technically advanced industry reaped the benefits of mine closures else¬where. In most other cases, however, par¬ticularly in the lesser developed countries, whole economies were devastated. This article will show what one major mineral producer, Canada, did to ensure the survival and even growth of its minerals exploration activity during these lean years. Background While Canada is among the world's mining leaders, mining is not its dominant industry. Still, it plays a far more important role than in the United States. It is a major earner of foreign exchange, currently accounting for about 25% of the total value of exports. Through spinoffs and a multiplying effect, it is a significant employer. In the far north, particularly, mining is the major nongovernment industry and a leading factor in the opening up of frontier territory. The industry cannot be allowed to die because it is often the main economic underpinning for vast, remote areas. Thus, exploration for new deposits cannot be cur¬tailed significantly without it having a long¬term negative impact on the very fabric that melds such a large, sparsely-populated ex¬panse of country into a nation. Over the years, Canadian governments have employed various means to encourage the development of new mines. Often, these incentives were tax-oriented, such as the three-year income tax holiday that applied to new mines in the 1950s and 1960s. The advantage of the tax connection is that any such incentive policy can be applied across the board to the 10 provinces and two territories that make up the federation of Canada. This is important because mining, except for the two federally-administered northern territories, comes under provincial government jurisdiction. Mining taxation is a complex give-and-take between the central and provincial authorities. In Canada, expenditure on mineral exploration is an allowable cost against reve¬nue for tax purposes. This works well pro¬vided there is some revenue from which to deduct. New exploration companies, those with no income from mining activities, de¬rive little benefit from this type of tax provi¬sion. Similarly, in times of depressed prices and reduced or nonexistent profits, the tax deductibility of exploration spending loses its value even for the major mining compa¬nies. To encourage exploration in Canada during the lean years, a different sort of incentive was required. The instrument used during the 1980s was again tax connected. It became known as flow-through financing or, simply, flow-through shares. When it assumed its final shape, it worked dramati¬cally. Flow-through shares Flow-through shares are so-named because they permit tax benefits earned by a corporation to 'flow-through' to the share¬holder. Basically, when an investor buys a flow-through share and the proceeds de¬rived by the company from this transaction are used for Canadian exploration, the in¬vestor can claim a deduction for tax pur¬poses as if the exploration expenditure was made by him personally. Flow-through shares go back to the early 1970s when Canada revamped its mineral income tax law. At that time, it permitted full deduction of exploration and development expenditures and provided for an automatic depletion allowance of one¬ third of operating profits from mining. There was also the three-year income tax holiday for new mines. New legislation replaced the depletion allowance with an earned depletion arrange¬ment whereby one dollar of depletion was earned for every three dollars spent on ex¬ploration and development. This earned depletion was `banked' during a transitional period (to 1974). After that it could be deducted from resource profits up to a maximum of 25% of such profits in any one year, with the excess carried forward. To promote exploration and mine de¬velopment in Canada, the earned depletion allowance plus the continued deductibility of exploration and development expendi¬tures permitted the recovery of risk capital before taxation. The three-year tax holiday, however, disappeared. Also, mining com¬panies that did not reinvest in exploration lost the depletion allowance benefit.

Jan 1, 1989

By A. Totani, S. Nakajima, H. Okazaki

The phase diagram for the SnTe-SnSe system has been studied in the temperature range from 300° to 900°C by differential thermal and quenching techniques. The X-ray measurements were made on quenched specimens. High-temperature diffraction was also made to study the phase transition in SnSe. The system is proved to be of a eutectic type in which no intermetallic compound exists. The eutectic point is at the composition SnTeo.55 Seo.45. the eutectic temperature being 755°C. Solid solubility limits are SnTeo.6Seo.r and SnT eo. 3s Seo.6s at the eutectic temperature, and change almost linearly to SnTeo.aaSeo.lz and SnTeo.18 Seo.az as temperature decreases to 300°C. It was shown that the SnSe phase has a phase transition of the second order at about 540°C and that the transition temperature decreases with increase of the SnTe content. THERMOELECTRIC properties of tin telluride (SnTe) and tin selenide (SnSe) have been studied extensively in recent years. The variation of physical properties with composition could be of interest if these compounds form an appreciable crystalline solution. The purpose of present investigation is to confirm the formation of crystalline solution or intermetallic compound, if any, and to establish the phase diagram for this system. The crystal structure of SnTe is NaCl type with a cubic unit cell1 (a = 6.313A). The crystal of SnSe having an orthorh2mbic unit cellz (a = 11.496, b = 4.1510, and c = 4.4437A) is isomorphous with tin sulfide (SnS) which has a distorted sodium chloride structure. It has been known that SnSe has a phase at at 540°C; the transition has been assumed to be of the second order. As far as we know, only two studies on the SnTe-SnSe pseudobinary system have been reported. The conclusion obtained in these papers is that, in the composition regions near SnTe and SnSe, the system forms a crystalline solution of the SnTe structure and the SnSe structure, respectively, and that, in the intermediate region, both phases coexist. However, neither the variation of the solid solubility vs the temperature nor the liquidus and solidus were investigated. Hence present writers have attempted to determine the phase diagram of the system by differential thermal analysis (D.T.A.) and X-ray diffraction. EXPERIMENTAL Sample Preparation. Starting materials, SnTe and SnSe, were prepared by the direct fusion of commercially available high-purity (99.999 pct) elements. Stoichiometric amounts of each couple Sn-Te or Sn-Se were weighed into a clear fused silica ampule. After evacuation to a pressure below 10-3 mm Hg, the am- pule was sealed, and annealed at 900°C for 5 hr. The melt was quenched in water. X-ray analysis confirmed the formation of a single phase of SnTe or SnSe. The other samples, SnTel-,Sex were synthesized from these SnTe and SnSe by mixing them in the required ratio, followed by annealing at 900°C and quenching. These samples were used directly for D.T.A. For X-ray measurements, samples were annealed at 700°, 600°, or 500°C for 100 hr or at 300°C for 150 hr, and then quenched in water. It was found that the lattice constants of the SnTe phase annealed for 150 hr at temperatures above 500°C did not differ from those annealed for 100 hr at the same temperatures. However the X-ray phase analysis showed that at 300°C the annealing for 150 hr was necessary to attain a true equilibrium state. D.T.A. The solid-liquid equilibrium temperature was determined from D.T.A. measurements. The sample was sealed in an evacuated silica tube and molybdenum powders sealed in an another tube were used as a reference material. The sample and the reference tube were placed in a nickel block and were heated from room temperature to 900°C at a rate of 3°C per min and then cooled down at the same rate to 600°C. Thermocouples for these measurements were Pt-Pt. Rh (10 pct) and the error of temperature measurements was within + l0C. D.T.A. curves were obtained on a two-pen recorder and an automatic controller (PID type) was used for the program of heating and cooling. When temperature reaches the solidus from the low-temperature side, there appears an endothermic peak. The solidus temperature was determined by extrapolation of the straight portion of the starting flank of this peak to the base line. In a similar way, the liquidus temperature was determined from an exothermic peak on D.T.A. cooling curve. In the case of supercooling, if any, its degree can be estimated from the magnitude of the abrupt temperature rise. X-Ray . X-ray powder patterns were taken by a diffractometer using CuK, radiation. Since the SnSe crystal is cleaved easily, the powders become flaky when SnSe-rich samples are ground in an agate

Jan 1, 1969

By Strathmore R. B. Cooke, Iwao Iwasaki, C. S. Chang

The effects of aeration on an aqueous suspension of pyrrhotite were studied and their results correlated with flotation tests using xanthates as collectors. The effects of copper activation and of pH variation were determined and possible mechanisms postulated. PYRRHOTITE has long been considered a gangue mineral to be eliminated as tailing in the treatment of various sulphide ores. However, in recent years the world-wide lack of sulphur resources has called attention to this mineral as a potential source of both sulphur and iron. Its importance as an economic mineral, however, has not been particularly emphasized. For this reason very little is known about its response to flotation, except that it can be depressed easily in alkaline circuit, by long aeration,1,2 addition of oxidizing agents,3 or by starch.' The object of this work was to study the floatabil-ity of pyrrhotite. This includes the effect of oxidation by aeration, of copper activation, and of change in pH. Preparation of the Pyrrhotite Sample: It was desirable that the highest grade of pyrrhotite obtainable be used for this experiment, since the presence of other minerals could affect the surface properties.5 However, no pyrrhotite was available as crystals, and massive deposits of hydrothermal origin commonly contain considerable amounts of chalcopyrite. Pyrrhotite concentrate was, therefore, prepared from a sulphide deposit occurring near Aitkin, Minn. The deposit is of pyrometamorphic nature consistirlg mainly of pyrrhotite and pyrite with graphite, silicates, and carbonates as gangue. The ore, already crushed through 3 mesh when received, was screened at 65 mesh and the undersize discarded. The oversize was crushed through rolls, and then stage-ground dry in an Abbe porcelain mill, the —65 mesh portion being screened out after every 15 min of grinding until all the material passed through this size. The ground product was then concentrated with a drum-type dry magnetic separator. The rougher concentrate was cleaned twice and then demagnetized. The final product was split in a Jones splitter and stored in air-tight bottles. Microscopic examination of the concentrate showed that it was relatively clean and free of pyrite, locked particles, and gangue. By means of the krypton gas adsorption method," the specific surface was determined to be 3000 cm2 per g. The chemical and screen analyses of the final concentrate are given in Tables I and II respectively. It is a well-recognized fact that the oxidation of some sulphide ores during stockpiling, grinding, and conditioning affects their flotation behavior. The problem of oxidation may become serious in the case of pyrrhotite, since this is known to be more easily oxidized than many other sulphides. To ascertain the extent of oxidation, an experiment was carried out by aerating an aqueous suspension of pyrrhotite with air, oxygen, and nitrogen as follows. A 300-g sample of pyrrhotite in 2700 ml of water was agitated and simultaneously aerated in a Fager-gren-type laboratory flotation machine. A Precision wet test meter was connected to the air inlet valve, the flow rate of the gas being kept constant at 0.3 cu ft per min throughout the experiment. Samples of approximately 30 ml each were taken from the cell at 0, 4, 10, 20, 35, 60, and 90 min. After the pH was taken, each sample was filtered and the filtrate was analyzed for total iron and sulphur. The iron was determined colorimetrically by the thioglycolate method using a green filter.' The filtrate was oxidized with bromine to convert all of the soluble sulphur compounds into sulphate and this was determined with a Parr turbidimeter." When aeration tests were made in alkaline circuit, calcium hydroxide or sodium hydroxide was added at regular intervals to maintain a constant pH. A similar procedure was followed in an experiment to determine the abstraction of copper. ion by pyrrhotite. In this case various quantities of cupric chloride were added. The filtrate from each sample taken was analyzed for copper, total iron, and sulphur. The carbamate method with a green filter was used for the copper analysis,' since this method could tolerate a considerable amount of iron in the solution. A pneumatic cell, made from a 350-ml fritted glass Buechner funnel, was used for this experiment. The detail of the assemblage has been described elsewhere." In the present work a stainless steel baffle was inserted in the cell. This baffle overcame the tendency for the coarse pyrrhotite particles to be swirled around the wall of the cell and thus fail to collect in the froth. A 50-g sample of pyrrhotite was added to the cell which contained 260 ml of water. When pretreat-ment of the sample was desired, reagents, such as activator and pH regulator, were then added and the pulp was conditioned for a specified conditioning time. Prior to the addition of the collector approximately 15 ml of the solution were removed for pH measurement and for iron and sulphur analyses. Copper when used as activator was also determined. Collector and frother were then added and the pulp was conditioned for an additional 2 min. Air was admitted to the cell and the froth removed. The separation required from 4 to 6 min, depending on the characteristics of the froth. The float and non-float products were filtered, dried, weighed, and assayed for iron.

Jan 1, 1955

By L. Leibowitz, M. G. Chasanov, L. W. Mishler

A drop calorimeter system is described for use in measuring enthalpies to 3600°K. Data are presented for tungsten between 2800" and 3600°K. The enthalpy of tungsten in cal per mole between 2000° and 3600°K can be represented by the equation HºT- Hº298 = - 1.7622 X 103 + 5.7772T + 8.9861 where T is in degrees Kelvin. A tabulation of com -puted values is presented for heat capacity, entropy, and free energy function. A drop calorimeter has been constructed to carry out enthalpy measurements at temperatures to 3600°K. Samples are heated by induction1 and dropped into a commercial adiabatic calorimeter, modified for this purpose. The experimental temperature is limited by the melting point of container materials and compatibility of the container and its contents. Several high-temperature drop calorimeters have been described in the literature1-5 but none has been used at temperatures as high as those in the present work; our measurements of the enthalpy of tungsten range from 2800" to 3600°K. DESCRIPTION OF EQUIPMENT An overall schematic view of the equipment is shown in Fig. 1. Power for the induction coil is supplied by a 25-kw 250 kHz Ther-Monic generator coupled to an iron core RF transformer. The Sample capsule is suspended in the work coil by 10-mil diam tungsten wires which are wrapped around a horizontal 5-mil diam tungsten wire. The horizontal suspension wire is clamped between two massive copper electrodes which are fixed in an x-y motion device that allows adjustment of the position of the heated capsule from outside the vacuum chamber. The copper electrodes are connected by flexible copper straps to a 1250-joule (5 kv, 100 pfarad) condenser bank. When it is desired to release the capsule, the condensers are discharged through the horizontal suspension wire causing it to vaporize rapidly. Very reliable and precise release of the capsule is achieved in this manner. Experiments have shown that no heat correction is required for this discharge energy. As part of the temperature measuring system, two prism holders have been incorporated in the apparatus. The upper prism holder is in the main vacuum chamber itself, whereas the lower one is in a side arm attached to the drop tube below the gate valve. The upper prism is mounted on a rotary vacuum feed-through, and may be moved under a protective shield when not in use. This prevents deposition of vapors on the prism surfaces when temperature measurements are not being made. Similarly, the lower prism is mounted on a push-pull vacuum feed-through, and when not in use may be pulled into its side tube. The prism mountings are fitted with guides and stops so that they may be moved precisely into the desired position. The aim throughout is to minimize the time the prisms are exposed to vapors from the hot samples. At the high temperatures reported in this paper, only the lower prism was used. The upper prism holder in these cases was fitted with an additional radiation shield. By using a prism and viewport, the lower surface of the samples can be observed by an optical pyrometer. The measurements discussed in this paper were obtained with a Leeds and Northrup 8622-C-S series manual pyrometer which is estimated to be accurate to 0.5 pct. Pyrometer calibrations and prism and window corrections were carried out in the conventional manner6 using tungsten strip lamps calibrated by the National Physical Laboratory, Teddington, England. Prism corrections were rechecked after each use. All work to date has been done in vacuum, and no measurable change has been observed in the prism correction below -2300°K for the upper prism and below -2800°K for the lower one. The total time of exposure of the prisms is about 50 sec per run. At high temperature, the final temperature reading is corrected by using the final A value for the prism; see Ref. 6 for details of this procedure. The calorimeter is a modified Parr Instrument Co. (Moline, lll.), Series 1230 adiabatic calorimeter with automatic jacket control. Other authors5 have used a similar calorimeter with good results. The calorimeter jacket cover and calorimeter cover are attached to the drop tube which contains a radiation shield. This shield is a gold-plated copper disc which can be operated manually from outside the calorimeter. The receiver is attached below the radiation shield and is lined with tungsten. In a typical experiment, the calorimeter and its jacket water temperatures were adjusted to 0.000°K temperature difference. The sample was allowed to equilibrate in the furnace at the desired temperature for about 20 min. The initial calorimeter temperature was then recorded, the sample dropped, and appropriate shutters closed. After about 3 min, the drop tube and receiver were filled with helium to 60 torr. The final calorimeter temperature was recorded after it had remained constant over a 5-min period. The equilibration time in the calorimeter was about 25 min. Thermistor probes are used to operate a hot and cold water supply system to maintain the jacket temperature equal to the calorimeter temperature. For actual measurements of the calorimeter temperatures, a quartz thermometer was used (Hewlett Packard Dymec Thermometer, Model #2801A). This thermome-

Jan 1, 1970

By E. S. Fisher, L. C. R. Alfred

The elastic anisotropy factors, c4,/c6,, c3,/cll, and c12/cl,, for hcp metal crystals vary significantly among the dgferent unalloyed metals. Significant variations with temperature are also found. The effects of elastic anisotropy on the dislocation in an elastic continuum with hexagonal symmetry have been investigated by computing the elasticity factors for the self-energies of dislocations in fourteen different metals at various temperatures where the elastic moduli have been reported. For most of the metals the effects of the orientation of the Burgers vector, dislocation line, and glide plane are small and isotropic conditions can be assumed without significant error. Significant effects of anisotropy are, however, found in Cd, Zn, Co, Tl, Ti, and Zr. The elasticity factors have been applied in the calculations of dislocation line tensions, the repulsive forces between partial dislocations, and the Peierls-Nabarro dislocation widths. It is predicted that the increase in elastic anisotropy with temperature in titanium and zirconium makes edge dislocations with (a), (a + c), and (c) Burgers vectors unstable in basal, pyramidal, and prism planes, respectively. The probability of stacking faults forming by dissociation of Shockley partials in basal planes also decreases with increasing c4,/c6, ratio, when the stacking fault energy is greater than 50 ergs per sq cm. The widths of screw dislocations with b = (a) in titanium and zirconium increase very significantly in prism planes and decrease in basal planes as c4,/c6, increases. The effects of elastic anisotropy on various dislocation properties in cubic crystals have received considerable attention during the past few years. In the case of cubic symmetry the departure from isotropic elasticity depends entirely on the shear modulus ratio, A = 2c4,/(cl, —c12); i.e., the medium is elastically isotropic when A = 1. Foreman1 showed that an increase in the ratio A produces a systematic lowering of the dislocation self-energy for a given orientation and Poisson's ratio. ~eutonico~, has shown that large anisotropy can have a marked effect on the formation of stacking faults by the splitting of glissile dislocations in (111) planes of fcc and (112) planes of bcc crystals. ~iteK' made similar calculations for (110) planes of bcc metals. Both studies of bcc metals showed that the large A values encountered in the alkali metals tend to reduce the repulsive forces between Shockley partial dislocations. In fcc metals, however, A does not vary over the large range encountered in bcc metals; consequently, the effect of A on the forces between Shockley partials is masked somewhat by the differences in Poisson's ratio between metals. The effect of A on the line tension of a bowed out pinned dislocation has also been investigated for cubic crystals, first by dewit and Koehler5 and more recent- ly by Head.6 In both cases the line energy model is applied and the core energy is not taken into account, thus making the conclusions somewhat tenuous with regard to the physical interpretation. Nevertheless, the fact that a large A decreases the effective line tension is clearly evident and the tendency for large A to produce conditions that make a straight dislocation unstable (negative line tensions) also seem evident. Head, in fact, shows visual microscopic evidence that stable V-shaped dislocations occur in 0 brasse6 For hcp metals the definition of elastic anisotropy is more complex and, furthermore, significant deviations from an isotropic continuum are found among a number of real hcp metals, especially at higher temperatures. The present work was carried out to survey the effects of elastic anisotropy on the elasticity factors, K, that enter into the calculations of the stress fields around a dislocation core. Some isolated analytical calculations have previously been carried out for several hcp metals but they are restricted in the dislocation orientations and temperature.8'9 The present computations are based on single-crystal elastic moduli that have appeared in the literature and consider various orientations requiring numerical computations. The results are then applied to survey the effects of temperature on the dislocation line tension and dislocation splitting in hcp metals. PROCEDURE Anisotropy Factors. The degree of elastic anisotropy in hcp crystals cannot be described by a single parameter, such as the A ratio in cubic crystals. The following three ratios must be simultaneously equal to unity in order to have an elastically isotropic hexagonal crystal: The magnitudes of these ratios at several temperatures, as computed from the existing data for the elastic moduli of unalloyed hcp metals, are given in Table I. There are no cases of complete elastic isotropy, but the large anisotropy ratios encountered in the cubic alkali metals are also missing. There are, however, several significant differences among the hcp metals, the most notable being the relatively small A and B ratios in zinc and cadmium and the differences in the magnitudes and temperature dependences of A. It has been noted that the temperature dependence of A has a consistent relationship to the occurrence of the hcp — bcc tran~formation. For cadmium, zinc, magnesium, rhenium, and ruthenium, A is less than unity at 4'~ and, with exception for rhenium, decreases with increasing temperature. In the case of rhenium, A has essentially no temperature dependence between 923' and 1123"~, so that it is clear that A does not approach unity at higher temperatures. Cobalt is similar to the above-mentioned group of metals in that it also does

Jan 1, 1969

By James M. Barker, George S. Austin

Stone, one of the oldest building materials, today remains a well-established material throughout the construction industry. The use of natural stone is much less prevalent now than in the past. It is still widely considered to be the most aesthetically pleasing, prestigious, and durable building material. New and re-opened quarries are coming onstream to meet increased demand related to new building technology and increased residential use of stone. CLASSIFICATION No classification can completely eliminate overlap between dimension stone, aggregate, and decorative stone because most stone is multi-purpose. Many used for decorative purposes are not produced specifically for that end use. Rock otherwise considered waste in dimension stone or aggregate quarries can be decorative stone coproducts (Fig. 1). Many uses require a compromise between decorative and structural qualities (Bowles, 1992, written commu¬nication). Shipley (1945) used decorative stone interchangeably with or¬namental stone. Gary et al. (1972) defined decorative stone as that used for architectural decoration, such as mantels, columns, and store fronts, but added that it is sometimes set with silver or gold in jewelry as curio stones. Bates and Jackson (1987) also restricted decorative stone to that used for architectural decoration. Meanings of otherwise identical terms used in the stone industry differ be¬tween geologists, engineers, and quarriers. They often carry a much broader meaning for quarriers and engineers compared to their very specific use by geologists (Makens et al., 1972). Decorative stone, including ornamental stone, is more broadly defined by geologists as any stone used primarily for its color, texture, and general appearance. It is not used primarily for its strength or durability, such as construction stone, or in specific sizes, such as dimension stone. The decorative stone industry uses a much wider range of stone types compared to stone that is dimensioned. Decorative stone usually serves some structural pur¬pose, but is not load-bearing to any great extent. Weak or costly stones serve in decorative, not structural, applications. STATISTICS AND END USES Decorative and dimension stone data are difficult to separate because the US Bureau of Mines keeps statistics only on dimension stone and crushed stone. The value of domestic dimension stone production in 1990, which includes some decorative stone, was about $210 million compared to imports of about $524 million and exports of about $35 million. Production was 1 080 t of which at least one-third was for decorative uses (Taylor, 1992). The principal uses are rough blocks in building construction (23%) and monu¬ments (18%); the remainder is used as ashlar (18%), curbing (12%), and miscellaneous (29%). Major rock types are granite (50%), limestone (30%), sandstone (10%), slate (3%), marble (2%), and other (5%) (Harben, 1990). Crushed stone valued at $5.6 billion was produced in the United States in 1990 by 1700 companies operating 3400 active quarries in 48 states (Tepordei, 1991). About 52% is used in con¬struction, 9% in cement and lime manufacturing, 2% in agricul¬ture, 2% in industrial uses, and 35% for unspecified uses including decorative aggregate. Limestone and dolomite comprise about 71%, granite 14%, and traprock 8% of the stone crushed in the United States. The remaining 7% are, in descending quantity, sandstone, quartzite, miscellaneous rock, marble, shell, calcareous marl, volcanic cinder and scoria, and slate. The basic types of decorative stone are: rough stone, aggregate, cut or dressed stone, and manmade stone [(Table 1)]. Rough Stone Rough stone is used as it is found in nature with very limited processing such as minor hand shaping, edge fitting, and size or quality sorting (Perath, 1992, written communication). This stone type is often marketed locally in relatively small tonnages and includes fieldstone and flagstone. The primary end uses of rough stone are landscaping, edging, paving, or large individual stone landscape or interior accents [(Fig. 2)]. Fieldstone: Fieldstone is picked up or pried out of the ground (gleaned) without extensive quarrying and includes garden or large landscaping boulders (Austin et al., 1990, Hansen, 1969). Boulders and cobbles may be split or roughly trimmed for use in rubble walls and veneers, both interior and exterior. Popular fieldstone rock types include sandstone, basalt, limestone, gneiss, schist, quartzite, and granite, but many others are suitable. Much fieldstone is col¬lected by individuals or small companies because the industry is labor intensive and markets are small. The stone may be sold locally in small quantities from the back of vehicles (Austin et al., 1990). Fieldstone includes many rock types, sizes, and shapes with the only common denominator that it must be set by hand and be durable (Power, 1992, written communication). Moss Rock. Moss rock is fieldstone partially covered by algae, mosses, lichens, and fungi that give the rock an aged and variegated patina (Austin et al., 1990). The plants are supported by moisture and nutrients in the stone. Moss rock is used for landscaping, walls, and fireplaces. Although almost any durable rock can be a moss rock, most are slabby or rounded sandstone and limestone (Fig. 3). Flagstone: Flagstone or flagging consist of thin irregular slabs used for paving, walkways, and wall veneers. Random-shaped flagging is produced widely in the United States. Suitable stone

Jan 1, 1994

By R. Newman

An inexpensive slow-speed data acquisition system has been adapted to digitally record multiple parameters simultaneously at intervals of 15 seconds. The system was built for use with standard soils testing equipment to automatically record load and displacement parameters at predetermined instants in time. Simultaneous readout is achieved by the use of special signal conditioner and sample-and-hold circuits which read the multiple signals simultaneously and hold them until the slow acting system can print out. Three channels of a 10-channel system have been converted and found to operate successfully during a series of direct shear tests. A unique feature of the system, which significantly reduced its cost, is the power supply units. Dummy circuits are used to maintain a constant power demand during sampling) thus eliminating the need for a costly power supply with rapid response characteristics. The entire system, having an overall accuracy of 0.25 percent, was put in operation for a cost under $2,500.

Jan 1, 1970

By P. L. Hendricks, J. W. Spretnak

The interstitial atom principally responsible for the yield point and strain aging in electron-beam-melted tantalum is identified by analysis of the kinetics of the return of the yield point after an increment of plastic deformation. Two sets of specimens contained two levels of oxygen with very low hydrogen contents and the third set had comparable oxygen and hydrogen contents. The activation energy for the return of the yield point agrees well with that for diffusion of oxygen for the first two sets of specimens. For the third set of specimens, the activation-energy value lies between those for diffusion of hydrogen and for diffusion of oxygen. The advent of the dislocation model of plastic deformation in metals has revitalized interest in the yield point and strain aging in bcc metals containing a certain minimum content of interstitial solute elements. Much theoretical and experimental work has been performed in recent years to elucidate the detailed mechanism of these phenomena. The purpose of this investigation is to attempt to identify the principal interstitial element responsible for the yield-point phenomenon in electron-beam-melted tantalum by analysis of the kinetics of the return of the yield point after an increment of plastic deformation. Some of the earlier theories of the yield-point phenomenon proposed a grain boundary film of iron carbide. Such models could not satisfactorily explain all features of strain aging and the yield-point phenomena. The most widely accepted explanation is that of Cottrell,1 later extended by Cottrell and Bilby.2 Strain aging is ascribed to "locking" of dislocations by interstitial solute "atmospheres". The yield-point phenomenon results when the dislocations are torn away from their atmospheres. The strain-aged condition is re-established after sufficient time to allow the interstitial atoms to diffuse to the dislocation lines and re-establish the locking atmospheres. Clearly, the Cottrell-Bilby model is concerned with the bulk of the grain and does not specifically involve the grain boundary. The recent modification of the Cottrell-Bilby model is a redirection of attention to the role of the grain boundary and the possibility of multiplication of a limited number of free dislocations rather than unlocking all of the dislocations. Theories have been advanced by Hahn3 and conrad4 which are modifications of the Cottrell-Bilby theory. The model proposed by Hahn indicates that, although the possibility of un- locking anchored dislocations is not excluded, it implies that unlocking is not necessarily required to explain yield drop. Locking of dislocations during the aging treatment is a necessary part of the theory; however, it assumes that dislocations once locked remain locked. It is suggested that the yield drop observed is a result of the following factors: 1) the presence of a small number of mobile dislocations initially, 2) rapid dislocation multiplication, 3) the stress dependence of dislocation velocity. In the case of bcc metals, locking is considered to be the means by which dislocations are immobilized. Cold working of the metal results in the generation of larger numbers of new dislocations and the stress dependence of the dislocation velocity accounts for yield drop observed. Conrad' has proposed a model similar to the one just described which applies to strain aging of iron and steel and which logically could be extended to other bcc metals. This model also does not require large-scale unlocking of dislocations. It is proposed that, during initial loading of a specimen below the upper yield stress, a few dislocations are torn free of their Cottrell atmospheres at regions of stress concentrations. With an increasing stress, some multiplication of dislocations occurs by a double cross slip mechanism, thus giving a preyield microstrain. At some critical stress represented by the upper yield stress, sudden profuse multiplication of dislocations occurs, enabling plastic flow to proceed at a lower stress. In this model, microstrain, preyielding, and flow represent the movement of free dislocations. It should be noted that this model also requires the locking of dislocations by interstitial solute atoms for the occurrence of a yield point; however, unlocking of large numbers of dislocations is not required. If it is assumed that the yield point will return when some fraction of free dislocations produced during pre-straining are pinned, the number of solute atoms required to pin unit length of a dislocation line can be calculated when prestrain and reloading are done at the same temperature and strain rate. Since the migration of solute atoms back to the stress fields of dislocation lines is controlled by the diffusion rate of interstitial solute atoms, it is to be expected that the activation energy for strain aging would be identical to the activation energy for diffusion. It would also be expected that the strain aging observed will be controlled by the fastest diffusing species capable of producing locking over the temperature range investigated. The rate of yield-point return has been found to be adequately expressed by an empirical rate equation of the form: rate=Ae-Q/RT [1] where A = constant, Q = activation energy, R = gas constant, and T = absolute temperature. Cottrell and Bilby2 have expressed the number of atoms per unit length of dislocation line which arrive

Jan 1, 1967

By H. P. Willard, R. W. Gates

Basic Inc., has been mining magnesite and brucite for 27 years at Gabbs, Nev. This is a medium sized open-pit mine. The magnesite deposits are in north-western Nye County about 30 miles east of Luning, Nev., on the west slope of the Paradise Range, at an elevation between 5000 and 6000 ft. The magnesite and associated brucite is used to make magnesia refractories employed principally in the steel industry and magnesium oxide for various chemical uses.

Jan 10, 1963