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By Randal J. Barnes

A system, such as a mine production system or a mine ventilation system which includes the movement of commodities or some material between decision points may, in many instances, be effectively modelled as a network. Mining has often been characterized as primarily a materials handling function. To a great extent this is true, even though it is an over simplification of all the activities involved in a mining operation. Accepting the materials handling characterization of a mining operation permits the extension of the characterization to a flow process. That is, the ore flows from the mining face through the mining phase (excavation & loading, hauling, dumping) through the milling phase (crushing, grinding, recovery) through the smelter phase and finally to marketing. With this concept it is possible to depict a mining operation as a simple network. For example consider an operation consisting of two mines (A and B) with mills at each mine (MA and MB) with the possibility open to treat ore from mine b at mill NB, but it is not feasible to treat mine B ore at MA. The product of both mills is sold.

Jan 1, 1983

By B. C. Allen

Grain boundary grooving has been studied in chromium, molybdenum, and tungsten under a variety of conditions using high vacuum techniques and tantalum -gettered argon. The average surface free energy of solid chromium, and the chromium-liquid silver interface free energy were respectively found to be 2200 ± 250 and 500 i 130 ergs per sq cm from groove formation kinetics and estimates of pertinent volume difffusion coefficients. The results for chromium were unffected by variations in interstitial content ranging from 0.003 to 0.09 pct C, or 0.003 to 0.03 pct O. Surface diffusion is the primary mechanism of groove formation in chromium under 1 atm argon at 1200" to 140O°C, and is essentially unaffected by 0.003 to 0.09 pct C, 0.003 to 0.03 pct O , metastable nitrogen contents up to -0.01 pct, and up to 2 torr Ag vapor. At higher temperatures, the major mechanism is volume diffusion in argon or evaporation-condensation in stutic vacuum. Surface diffusion occurs in molybdenum at 0.5 to 0.96 and in tungsten at 0.5 to 0.9 of the absolute melting tempera -ture by a single mechanism, possibly by the migration of single adatoms or vacancies. Results were slightly affected by up to 23 tory Sn vapor, and in molybdenum were essentially unaffected by 0.5 Ti or carbon in the range 0.002 to 0.02 pct. Volume difffusion through the liquid is the mechanism of groove formation in chromium-liquid silver at 1200" to 1400°C and in molybdenum-, Mo-0.5Ti-, and tungsten-liquid tin at 1200" to 2000°C. The solid-liquid interface free energies involved were estimated from grooving kanetics. WHEN a grain boundary intersects a solid surface, a groove tends to form along the line of intersection at temperatures above about half the absolute melting point (0.5 TM). The groove progressively grows by preferential atomic migration either by diffusion or evaporation. Establishment of a groove angle occurs in accordance with the grain boundary and surface free energies involved. The motivation for groove formation is a reduction in the total surface free energy of the system. This study is a continuation of previous work on thermal grooving of chromium, molybdenum, and tungsten.&apos; The temperature ranges were extended, and the effect of metallic and interstitial impurities was evaluated. The results were such that certain interface free energies and surface self-diffusion coefficients were deduced from the grooving kinetics. EXPERIMENTAL WORK Materials and Preparation. As indicated in Table I, the 0.05-0.08-cm-thick chromium, molybdenum, and tungsten sheet used was nominally 99.99 pct after recrystallization. Two lots of molybdenum with about the same analysis, Mo-0.5Ti,* and tungsten were ob- *Alloy compsitions are expressed in weight percent . tained commercially. Extruded chromium rod,&apos; prepared from iodide process crystals, was warm rolled to sheet at 700°C. Sheet of three Cr-0 impurity alloys containing up to 0.03 pct 0 was prepared by warm rolling arc melted, extruded, and swaged rod. Two Cr-C impurity alloys containing up to 0.09 pct C were made by equilibrating unalloyed chromium with a known amount of CH4 for 24 hr at 1150°C in previously evacuated quartz capsules. Chromium containing nominally 0.015 and 0.06 pct N was similarly prepared by equilibration with NH3. The sheet was recrystallized to give a stable grain size about equal to the sheet thickness. Molybdenum and Mo-O.5Ti were recrystallized in a tantalum resistance furnace 1 hr at 1 x lo-5 torr at 2300" and 220O°C, respectively. Tungsten was similarly annealed for 1 hr at 2500°C. Chromium and its impurity alloys were outgassed at 1100°C and recrystallized 1 hr at 1700°C under 1 atm Ar. Except for nitrogen, the impurity content stayed roughly constant. Nitrogen in both alloys was reduced to <0.001 pct. In fact, over 80 pct of the added nitrogen was lost after outgassing at llOO°C and annealing sheet 1 hr at 1300°C in argon in the presence of tantalum. Such a rapid loss can be rationalized since -2 torr N are required for equilibrium with 0.04 pct N in solution,3 while the equilibrium pressure is ~10-5 torr over tantalum at 1300°C.4 The recrystallized sheet was cut into small coupons which were metallographically ground and polished on one side with a minimum of grain boundary relief. The surface roughness was on the order of 0.01 µ. The tin and silver used were nominally 99.999 spec-trographically pure. After being outgassed at 1100°C and equilibrated in a molybdenum crucible for 0.5 hr at 1800°C in argon, the tin contained 3 ppm 0, <0.3 ppm N, and 0.1 ppm H. Following outgassing at 900°C and equilibration in a chromium crucible 1 hr at 1400°C in argon, the gas content of the silver was 1 ppm O, <0.5 ppm N, and 0.3 ppm H. Grooving Under Argon or Vacuum. All specimens were placed in unsealed containers made from rod or sheet of the same alloy, thereby enabling the polished surface to achieve gas-solid equilibrium. The annealing fixtures are shown in Fig. 1. The specimen was placed in a resistance furnace with a tantalum or Ta-10W heating element plus tantalum fixtures or radiation shields. Chromium was outgassed at 1100°C, and molybdenum and tungsten were outgassed at 1900°C to 1 x l0-5 torr or at the grooving temperature, whichever was lower. In vacuum anneals, the specimen was then heated directly to the intended grooving temperature. In argon anneals, 99.996 Ar was admitted

Jan 1, 1970

By E. Petrakis, K. Komnitsas

The main objective of batch grinding modeling is the estimation of the product particle size distribution over time or specific energy input to the mill. So far, the developed analytical methods require often complicated calculations which are timeconsuming. Thus, more simple approaches that allow the reliable prediction of the complete product size distribution need to be developed. In the present paper, an approach, based on the population balance model (PBM), that reliably predicts the product size distribution is proposed. In order to enable this, the simplified form of the fundamental batch grinding equation was transformed into the well-known Rosin–Rammler (R-R) distribution, thus allowing the determination of the breakage rate for each grinding period. A time-dependent breakage rate framework was developed where the traditional linear theory of the PBM is considered a partial case. This approach allows the deviations from the linear theory to be categorized and the degree of the acceleration-deceleration of the breakage rate to be predicted. Modeling results were validated by laboratory grinding studies using two homogeneous materials, quartz and marble, and one heterogeneous, a limonitic laterite. The experimental data revealed that grinding exhibits non-first-order behavior and the degree of deviation from the linear theory depends on the tested material. The reliability of the proposed model was validated with the use of the distribution modulus n, the a value of the breakage rate parameter, and the optimum n values that minimize the sum of the differences between the experimental and estimated particle size distributions.

Feb 8, 2021

By Robert B. Parsons

"Finance Minister Paul Martin&apos;s second budget might be good for Canada&apos;s mining industry in the long run, but the budget raises a number of concerns for the industry in the near term. The budget papers suggest that the 25% resource allowance is not working as intended, and report that the Department of Finance will be reviewing this valuable allowance. The so-called ""large corporations tax"" rate will be increased. This annual tax, which is imposed on a corporation&apos;s capital even when the corporation is not in production, is particularly harmful to the mining sector.IntroductionThe Honourable Paul Martin, in his second federal budget, emphasized spending cuts and made only modest tax changes. However, two of these tax changes could have a serious impact on the Canadian mining industry: the proposed review of the 25% resource allowance; and, the increase in the large corporations tax rate.Personal Tax Measures Personal Tax Rates UnchangedThe government has been under political pressure not to increase personal tax rates. Mr. Martin&apos;s announcement that rates would not change will be popular."

Jan 1, 1995

By C. E. Tsoutrelis

A new method for determining rock drillability in diamond drilling is discussed; the method takes into consideration both penetration rate and bit wear. The method is based on drilling a rock specimen under controlled laboratory conditions using a model bit. The technique used for determining the experimental variables is extremely simple, quick, and reliable. Drillability is then determined by the mathematics of drilling. In considering the different factors that affect diamond drilling performance, the nature of the rock to be drilled is of outmost importance since it affects significantly the drilling costs and such other variables as bit type and design, drilling thrust, and bit rotary speed. Many attempts have been made to study this effect by correlating actual drilling performances either to certain physical properties of the rock being drilled1-? or to test drilling data obtained under laboratory conditions.7-13 These attempts were aimed at providing a reliable method of predicting by simple means the expected rock behavior in actual drilling, thus giving the engineer a tool to use in estimating drilling performances and costs in different types of rock. The purpose of this paper is to describe such a method by which rock drillability (a term used in the technical literature to describe rock behavior in drilling) could be determined in diamond drilling. It is believed that the proposed simple and reliable method will cover the need of the mining industry for a workable method of measuring the drillability of rocks. It should be emphasized, however, that since drill-ability depends on the physical properties of rock and each drilling process (diamond, percussive, rotary) is affected by different or partly different rock properties,14-l6 the proposed method of determining rock drillability cannot be extended to the other drilling processes. The results presented in this paper form part of an extensive three-year research program carried out by the author in the laboratories of the Greek Institute of Geology and Subsurface Research. During this period the effects of the physical properties of rocks and of such operational variables as drilling thrust and bit rotary speed in diamond drilling were investigated in detail. DRILLABILITY CONCEPT The literature is not devoid of drillability studies. While there are a number of investigators1,3,5-7,9-0,12-13,17 who have attempted to establish by direct methods (i.e., drilling tests under laboratory conditions) or indirect (i.e., through a physical property of rock) an index from which the drilling performance in a given rock may be estimated, very few6-7,9,12, of the proposed methods seem to be of much practical value to the diamond drilling engineer and none to date has been universally accepted. Commenting on the proposed methods for assessing rock drillability, Fish14 remarks that "for a measure of drillability to be accepted it is essential that penetration rate at a given thrust and bit life are elucidated as otherwise the method is of little value." This statement should be examined in more detail by making use of the penetration rate-drilling time diagram obtained in drilling a rock under constant operational conditions. Furthermore, the merits of using this diagram to describe rock drillability will be pointed out. At the same time reference will be made to this diagram when discussing some previously proposed methods. Fig. 1 illustrates such a diagram for three rocks,A, B, and C, which have been diamond drilled under identical conditions. It is assumed here that rocks A and B have the same initial penetration rate, i.e., VOA = Vog, but since rock B is more abrasive than A, rapid bit wear occurs and as a result the fall of its penetration rate with respect to time is more vigorous than in rock A. This is shown graphically by a steeper V = f(t) (0 curve in this rock than in rock A. Rock C has a lower initial penetration rate, due to higher strength properties16 but since it is not very abrasive, only a slight fall of its penetration rate occurs during drilling (in this category are some limestone and marbles with compressive strength above 1000 kg per sq cm). It follows from the foregoing considerations that the characteristic for each rock curve (I) is a function of (i), the penetration rate of the rock Vo recorded at the instant of commencing drilling, which determines the starting point of the curve (1) on the y-axis and (ii), the abrasive rock properties which determine the rate of fall of Vo with respect to time. Thus, curve (I) provides an actual picture of the rock behavior in drilling for given operational conditions, and it can be used with complete satisfaction to assess rock drillability. It can be seen clearly from Fig. I that proposed methods for assessing rock drillability by measuring the

Jan 1, 1970

By W. T. Isbell

Although the pressure to meet the heavy demand for lead still took precedence over new metallurgical developments in the field of roasting, smelting, and refining of lead in 1948 there nevertheless has been considerable activity in the experimental development of new processes and improvements as well as plans for the modernization of many plants both here and abroad. Increasing labor and material costs have stimulated the trend to greater mechanization, revamping of flow sheets, and construction of larger units wherever possible. Although there have been many serious labor stoppages in the United States, Mexico, and Europe, labor supply has improved in most plants even if it has fallen off in efficiency.

Jan 1, 1949

NEW MEMBERS The following list comprises the, names of those persons who became members during the period June 10 to July 10, 1914: Members ALDRICH, HAROLD W., Supt. of Leaching Plant, Washoe Red. Wks., Anaconda Copper Co., Anaconda, Mont. AYER, FRANK ASHTON, Mine Foreman.. ..Detroit Copper Co., Morenci, Ariz. BELL, ARTHUR F. L., Chief Engr., Associated Oil Co.., 817 Sharon Bldg., San Francisco, Cal. BERGMAN, JULIUS GUSTAF, Mech. Engr., Chief Draftsman, Arizona Copper Co. Morenci, Ariz. BURT, CURTIS F., Min. Engr., Pittsburg-Dolores Mining Co., Rockland, via Yerington, Nev. CALLAWAY SCOTT DAVID, Chem La Harpe Smelter Co., La Harpe, Kan. CAMPBELL, W. C., Min. Engr 4 Princess St., Roodeport, Transvaal, So. Af. CARROLL, GEORGE A., Genl. Mgr Kildare Min. Co., Manson, B. C., Canada. CARUTHERS, JOHN LYTLE, Min. Engr., Asst. Engr., St. Louis, Rocky Mountain & Pacific Co.. Raton. N. M.

Jan 8, 1914

By J C. Furness, F S. Cannon

Metal casting operations are a significant source of hazardous air pollutants. In particular, high production iron foundries emit significant quantities of volatile organic compounds (VOCs) during pouring, cooling and shakeout of iron castings made in green sand molds. End-of-the-pipeline capture and destruction methods to reduce VOC emissions add crippling costs to foundries. Alternately, the incorporation of advanced oxidants (AO) into metal casting green sand systems has been shown to reduce emissions from high production iron foundries in the US, and at the same time reduce operating costs. Cost savings are driven by the benefits of AO in clay recovery systems. Emissions reductions are the direct result of cascading AO-based reactions taking place in green sand molds. This sustainable greening of the metal casting process is a prototype for the development of other AO and non-AO process-based solutions for sustainable high temperature processing of materials. Fundamentals of AO technologies will be discussed along with the performance characteristics of AO processing systems in the metal casting industry and the breadth of other processing and remediation applications for which AO technologies have the potential to be successfully employed.

Jan 1, 2002

By Stokes WPC

The capital requirements to develop a new mining venture are becoming very large; amounts of the order of US$1,000 million are not now unusual among estimates to bring new mining complexes into production. At the same time prevailing political and economic conditions are making it increasingly difficult to determine whether or not a project is likely to be viable. These factors emphasise the need to carry out thorough evaluation studies of all mineral prospects before making major investment. Additionally with the rapidly changing economic climate existing at the present time, it is becoming more and more necessary to carry out reappraisals of existing mines. An important function of both initial evaluations and reappraisals is to provide the operators of the mine with effective mining plans to ensure that the operation will meet its required economic targets. P, p M. tl p b, c v, s c 1 n 1 f r d c e c e u w Modern computers are well equipped to store and manipulate large amounts of data with speed and reliability. Their use in the mining field r is increasing and this trend serves to free f technical staff from much of the time consuming m and error prone hand calculations which were o formerly required in determining reserves and w carrying out all forms of mine planning. r Nevertheless, computers are not a universal

Jan 1, 1980

By Qian Li, Honggui Han, Jun Wang, Shichao Yu, Chunxiao Zhao, Maoxing Hong, Rui Liao, Xingxing Wang

In this study, bioleaching experiments, synchrotron X-ray Diffraction (SR-XRD), X-ray absorption near edge structure (XANES) and X-ray Photoelectron Spectroscopy (XPS) were conducted to investigate the intermediates and surface species of bornite leached by mesophilic mixed bacteria of Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. CuS, Cu9Fe9S16 and S8 were the main intermediate species during bornite bioleaching by mesophilic mixed bacteria, and CuFeS2 was also detected. The surface species of S2− and S2 2− would be polymerized to Sn 2− during bioleaching. The formation of element sulfur and the increase of its content were confirmed by the fitted results of XPS spectra. The presence of polysulfide and element sulfur did not inhibit the bornite bioleaching. The formations of CuS and CuFeS2 were confirmed by the results of Cu K-edge XANES spectra.

Mar 1, 2018

By V. T. Taniguchi

A process for large scale chromatographic separations using a continuous chromatography technique is described. The process combines the advantages of large scale batch fixed column displacement chromatography with conventional analytical or elution continuous annular chromatography (CAC) to enable large scale displacement chromatography to be performed on a continuous basis (CDC). Such large scale, continuous displacement chromatography separations have not been reported in the literature. The process is demonstrated with the ion exchange separation of a binary lanthanide (Nd/Pr) mixture. The process is, however, applicable to any displacement chromatography separation that can be performed using conventional batch, fixed column chromatography.

Jan 1, 1989

By Ann M. Hagni

"Ceramic matrix composites are inorganic materials that are particularly resistant to heat and abrasion. A magnesia (MgO) and aluminum nitride (AlN) based composite is formed by exposing a magnesia preform to a metallic alloy block in a nitrogen atmosphere at 950°C. The metallic alloy, which is composed primarily of aluminum, is wicked into the preform. Aluminum nitride matrix is grown between MgO particles as the wicked metallic aluminum reacts with nitrogen. Unused metallic alloy, remnant metallic alloy (carcass), and composite produced after 8 hours, 50 hours, and 225 hours of processing are characterized mineralogically. Reflected light microscopy, transmitted light microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques reveal that in addition to anhedral to euhedral AhNi, AbSbSr, and Al crystallizing in the metallic alloy carcass, AIN and (Al,Si)N have formed as well. Nitride rings and nodules in the carcass may hinder AIN growth in the composite. Fine-grained residual AhNi and AhShSr are dispersed throughout the composite matrix. The nitride matrix is composed of AIN and (Al,Si)N. Rim replacement of MgO by spine! occurs in the composite. Aluminum nitrides in the metallic carcass cathodoluminesce deep violet-blue, unlike non-luminescent AIN in the composite matrix. This distinction in cathodoluminescence suggests a different mode of formation for composite AIN than for carcass AIN. Phase interpretations and textural characterizations deduced from the implementation of sophisticated mineralogical techniques have contributed to the understanding, and will aid in the improvement, of MgO/ AlN-based ceramic matrix compositeprocessing."

Jan 1, 1999

By R Razanatsimba, A Galli

A mining company has entered into contractual commitments to supply certain quantities of its product to clients in each time period. Failure to fulfil its obligations would damage its reputation as a reliable supplier. The planned production would normally be sufficient unless major problems such as highwall failures, roof falls, natural disaster, or strikes that interrupt production or delays in obtaining environmental permits, occur. To overcome these difficulties, the company may be able to obtain more of the commodity: from its strategic stockpile (if there is sufficient there); by buying it on the spot market; or for some commodities such as gold and uranium, by leasing it. Two sources of uncertainty, the spot price of the commodity and the occurrence of serious incidents that interrupt production, are considered. For simplicity it is assumed that the commodity price follows a geometric Brownian motion, that productions incidents have a binomial distribution, that they are independent from one time period to another and that they do not affect prices. A branching tree structure is used to model the joint evolution of prices and production incidents. The aim of this research project was to evaluate the companyÆs options for fulfilling its contractual commitments. When evaluating these options, multi-stage stochastic programming with recourse was used to solve this problem because in addition to providing the dollar value of the project, it gives decision-makers the æroadmapÆ to reach the optimal value. That is, how much material should be bought/sold on the spot market, how much to add to/subtract from the stockpile, how much to lease and in the worst case what the shortfall would be, for each time period as a function of the current spot price and breakdown status. A case-study over a five-year period is used to illustrate the proposed procedure. In this study the production would be sufficient to cover the companyÆs contractual commitments unless production incidents occur. Focus is on evaluating the impact of the quantity initially in the stockpile on the value of the project when the commodity market is tight, that is, when only small quantities can be bought on the spot market or by leasing.

Sep 26, 2011

By Carlos Gualdron, Elizabeth Gomez, Rafael Bolivar

The productivity index of the Coopracarcegua Ltda., a mid-size coal mining company of Norte de Santander, Colombia, was related absenteeism using accident, productivity and profit data four years. The analysis was based on type, severity and frequency of accidents, number of absentee days; price per metric ton, and other relevant parameters. The enterprise is formed by 5 different mines of thermic coal, each one with different exploitation technologies and different productivity. Each mine was analysed separately and the loss of profit due to absenteeism was calculate for each one. The study showed that the foregone earnings due to absenteeism in terms of the whole productivity of the enterprise was about of 6.6% of the total profit average the 4 years, with calculated values of 14.7%, 3.5%, 8.4% and 4% per year in the evaluated period. The study identified that the most important cause of absenteeism was "General Disease". The foregone earnings in 2009, the highest loss for the analysed period, was about US$ 0.937 million and during the whole evaluated period was US$ 2.46 million.

Jan 1, 2014

By Patrick J. Hannigan, Frank Rausche, Rozbeh B. Moghaddam

Large diameter open-end pipe piles are increasingly used as deep foundations to support heavy onshore and offshore structures. During the driving process, several factors such as subsurface conditions, hammer type, hammer efficiency, pile type, plug conditions, temporarily increased base resistance, and loss of shaft resistance have direct impact on the driveability of large diameter open-end pipe piles. In a uniform subsurface condition, the unit shaft resistance increases with depth. Consequently, more resistance is accumulated as piles penetrate to greater depths which results in higher driving resistance. However, according to the friction fatigue analysis, the greater the number of shearing cycles occurring on a soil segment along the pile shaft, the greater the reduction of its shear resistance. As a consequence, since upper soil layers are subjected to a greater number of blows than those at greater depths, they have a relatively lower resistance compared to what would be calculated with standard geotechnical analysis methods. As a result of this progressive and nonuniform loss of shaft resistance with driving, blowcounts tend to increase at a lower rate than expected from traditional analyses. This paper discusses one of the approaches to the driveability analysis with the geotechnical friction fatigue consideration. It also shows comparisons between predicted driveability obtained from wave equation analysis and field driving records. All analyses were performed for a 2.134 m (7.0 ft) diameter open-end pipe pile installed at a total depth of 192.90 m (554 ft). Two separate static resistance and wave equation analyses were completed for the case study presented in this paper: 1) Friction Fatigue analysis based on the recommendations of Alm and Hamre (2001), subsequently referred to as the FF model, and 2) Standard Driveability analysis based on soil set- up factors, hereafter referred to as the SD model in this paper. Results from analyses included the shaft resistance distributions compared to the result of the signal matching analyses determined from the pile dynamic measurement. Furthermore, predicted blowcounts were compared to observed blowcounts during the pile driving. The comparison analyses indicated a 54.4 percent resistance loss of the Static Resistance during Driving (SRD) due to the geotechnical friction fatigue corresponding to a 46 percent reduction in total resistance. The analyses also showed that average predicted blowcounts using the friction fatigue were 6.4 percent lower than measured blowcounts, whereas, the standard driveability approach showed 42.1 percent higher blowcounts compared to the blowcounts shown in the driving log values.

Jan 1, 2019

By R. A. Oriani

The partial molal volume of hydrogen is one of the parameters that describe the elastic interaction between the solute and the stress fields about inclusions, dislocations, and cracks. As such the partial molal volume is probably of importance in the elucidation of phenomena such as hydrogen embrittlement and hydrogen yield point. A knowledge of this quantity would also be helpful in thinking about the state of dissolved hydrogen in iron. However, because of the very low lattice solubility of hydrogen in iron the usual ways of determining the lattice expansion are not practicable. It is therefore of interest to apply the thermodynamics of stressed bodies to two sets of measurements of the effect of elastic stress upon the permeability of hydrogen in order to deduce a value of the partial molal volume, VH, of hydrogen dissolved in a iron. Beck ..&apos; and previously de Kazinczy, observed that a uniaxial tensile stress increases the permeability of hydrogen in iron and in various steels. Beck et 01. employed Armco iron and A.I.S.I. 4340 steel, whereas de Kazinczy used a steel the composition of which was 0.13 C, 0.23 Si, 0.46 Mn, 0.006 P, and 0.038 S. Upon releasing the stress the permeability increment disappeared if the stress was below the elastic limit. Both investigators employed cathodic charging to introduce the hydrogen. de Kazinczy measured the permeation through a thin-walled tube by collecting the gas, whereas Beck et al. measured the permeation through sheets of various thicknesses by a very sensitive electrochemical technique. Both investigators measured the steady-state permeation at constant rate of hydrogen ion discharge, and Beck measured in addition the hydrogen diffusivity by a time-lag technique which is independent of the boundary conditions. Beck et al. and de Kazinczy found a linear relationship between log (J,/Jo) and the stress, where Ju/Jo is the ratio of the flux of hydrogen when the metal is under uniaxial tensile stress, a, to the flux under zero stress, for the same temperature and charging current. Beck et al. found in addition that the diffusivity of hydrogen is not changed by stress. Both investigators concluded that the observed change in permeability is due to an increase in hydrogen concentration, and furthermore that the increase in concentration is due directly to the thermodynamic effect of stress upon concentration. Accepting this assessment of the situation for reasons given below, one may use the equation3j4 in order to evaluate I/H, the partial molal volume of hydrogen. This equation is valid for the domain of a/E «¦ 1 (where E is the Young&apos;s modulus) and under the assumption that hydrogen expands the lattice isotrop-ically. From the data of Beck el al, one calculates V7H - 2.0 cu cm per g-atom, and from those of de Kazinczy one obtains 1.8 cu cm per g-atom. That the increase of concentration with stress is indeed of thermodynamic origin is attested to by the facts that the experimental results conform to the thermodynamic relation, Eq. [I], and that the results are the same whether a pure iron1 or each of two different steels172 is used. Neither of these facts wou1.d necessarily be expected if the effect of stress were, rather, to increase the ratio kn/k, of the kinetic factors of the following competing reactions: H(ads) — H (dissolved) Such a change of kinetics at the surface could be an alternative explanation of the effect of stress on the permeability. Although this writer does not deem this explanation to be the correct one for the reasons given above, it must be admitted that unambiguous proof that the phenomenon has a thermodynamic origin does not yet exist. Two kinds of experiments may be suggested. One is to plate a variety of metals on the input surface of the steel and repeat the stress experiment at a variety of hydrogen charging currents. The other is to employ somewhat thicker specimens in order to be able to apply uniaxial compressive stress. Eq. [I] shows that ln(c,/c,) depends on the sign of the stress, but it is difficult to see a physical basis for which k2/kl would depend on the sign of a. The present value of V^ in a iron agrees with phragmen&apos;s5 estimate, which he based on comparisons with the lattice expansion by hydrogen of titanium, zir-

Jan 1, 1967

By Michael Cullen

The Quinsam Coal Mine is in the process of extracting a panel beneath the mine access road. To prevent damage to the road, and adjacent powerline, it was necessary to establish a ?protection zone? within which the extent of mining would be limited. The protection zone is analogous to the setback limit. For economic reasons it was desirable to make the protective zone as small as possible, and with the greatest extraction ratio possible. The size of the protective zone was established by determining the angle of critical deformation using the numerical model FLAC, coupled with field data on subsidence from the Mine. The angle of critical deformation (defined as the angle, measured from the vertical, at which intolerable damage is sustained by a structure) was determined to be between 0 and 5 degrees. The allowable extraction ratio in the protection zone was established using the ARMPS method of pillar design coupled with field data on pillar stability from the Mine. Excavations spans to prevent caving were determined by historical experience and field data on span stability from the Mine, coupled with numerical modeling. The minimum pillar size was determined to be 7.5m. The maximum pillar height was established at 2.5m. The maximum allowable excavation span was determined to be 8.5m. With these criteria, extraction ratios between 54 and 73% (measured in plan view) were determined to be appropriate for the protection zone.

May 1, 2001

By V. K. Gupta

A detailed experimental study of the variations in grinding rate with particle size, particle load, ball diameter, ball load, mill diameter, and mill speed was carried out for a soft cement clinker and a hard cement clinker. The effects of the ball diameter, ball load, and particle load were observed to be material (hardness) independent, and those of the particle size, mill diameter, and mill speed to be material dependent. A sharp change in grinding behavior was observed for both the clinkers at about 150 µm size. Below this critical size: (1) the hardness difference between the two clinkers became insignificant, (2) variation in the grinding rate with particle size became markedly more pronounced, and (3) mill speed had little or no effect on grinding rate. The importance of these results in the context of process optimization and control is discussed.

Jan 1, 1988

By J. E. Rowland

NIOCALITE is a new mineral species which has been identified in rock from the Oka district, Quebec. It occurs as prismatic crystals up to l 0 mm. in length and I mm. in width, in coarse, white, crystalline calcite with associated apatite, diopside, biotite, pyrochlore, and niobian perovskite. The crystals of niocalite are light yellow in col-our and have a vitreous lustre. The optical properties of niocalite (I) are as follows: Biaxial negative -2V = 56° a = 1.700, [ ] = 1.730 Birefringence y -a = 0.030 Optic orientation: X = b, Z/\c 12°, Y , /\a = 32° The specific gravity is 3.32 and the hardness is approximately 6 (Mohs scale). A detailed analysis performed on 2.4 gm. of hand-picked material reveals that niocalite is essentially a calcium niobium silicate. Table I gives the result of the analysis. Crystals of niocalite, apparently suitable for X-ray diffraction work, were selected, and single crystal photographs were obtained using both Weissenberg and Precession cameras. Initial difficulties were encountered in interpreting these films, and in correlating the crystal data with the optical data. The in-consistencies were explained by the fact that every grain examined was twinned to some extent.

Jan 1, 1957

By J. M. Pachter

Property sales and acquisition are prominent features of today&apos;s coal industry. Before selling or buying a site, a company must know the property&apos;s economic net worth. Any evaluation of economic net worth would be inadequate if determinations of a property&apos;s environmental liabilities and costs were omitted. Short-term and long-term costs can result from liabilities related to reclamation, water treatment, subsidence, and hazardous waste disposal. A structured, interdisciplinary approach can aid in the delineation, summation, and scheduling of these costs and liabilities.

Jan 1, 1986