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By H. I. Aaronson, H. A. Domian, A. D. Brailsford

A current study of the growth kinetics of k (hcp) plates in a Cu-Si (fcc)' has generated a requirement for data 02 the chemical interdiffusion coefficient in a (termed D,) as a function of temperature at the composition of the a/a + k pJase boundary. Rhines and Mehl 2 have determined D, as a function of composition at lower silicon contents by making Matano analyses of concentration-penetration curves. However, the accelerating increase in B, which they demonstrated as the phase boundary composition is approached at constant temperature and the rapidly diminishing accuracy of this analysis as the limiting compositions of a diffusion couple are approached (the silicon-rich component of their couples contained appreciably less silicon than is permitted by the solubility limit) indicate that the required information cannot be safely obtained by extrapolation of their data. Although the quite different method employed in this study is not exact, it will be shown that the approximations made are not serious ones, particularly from the viewpoint of the prgcipal application anticipated for these data. D, was determined from the migration kinetics of the a :k boundaries formed in sandwich-type diffusion couples produced by welding a block of high-purity copper to opposite sides of a cube (* in. on edge) of homogenized high-purity Cu-5.82 wt pct Si alloy. The alloy is pure k in the temperature range employed. The surfaces of the couple components which were normal to the diffusion direction were machined accurately flat and parallel, lightly polished, and carefully cleaned. Welding was then accomplished by means of the vacuum-encapsulated pressure jig technique previously employed.3 Welding was always conducted at the intended diffusion temperature; thus the welding anneal also served as the first diffusion anneal. Subsequent diffusion anneals were performed in evacuated Vycor capsules. Following the welding anneal, one of the surfaces parallel to the diffusion direction was machined, ground, and polished flat; additional material was removed from this surface after each diffusion anneal in order to avoid any effects of composition changes. After etching,4 the average distance between a : k boundaries was measured by means of a traveling microscope with an accuracy (per measurement) of better than 1 p. Satisfactory results were obtained at four temperatures in the range 775° to 655°C; attempts to obtain data at two lower temperatures were unsuccessful, evidently as the result of the interference of surface contamination during the welding process.

Jan 1, 1969

By Norman P. Goss

What would appear to be a very simple process on paper has proved to be overrun with a multitude of unseen difficulties. For more than 70 years attempts have been made to cast metals in a continuous manner, but it has been only within the last Io years that some degree of success has been achieved.1 Historical Development Bessemer's Experiments—Method I Bessemer was the first to try to cast molten metal in a continuous manner. His method is fully described in U. S. Patent No. 49053, issued in 1865. The patent drawing is shown in Fig. I. In this method the molten metal was poured between a pair of rolls of large diameter, which were cooled by water sprays. Means were provided to prevent moisture from coming into direct coptact with the molten metal. The width of the strip was controlled by the flanges. On paper this should work to perfection, but it is beset with many difficulties still awaiting solution. Bessemer failed to reduce his invention to commercial practice. About 1890 Bessemer's method was revived by Norton and associates (U. S. Patent No. 441375). They formed the Fluid Metal Rolling Co. at Maywood, Ill., and spent $250,000 in endeavoring to develop the technique for this simple method. Finally they had to abandon it. Naturally, they did carry the technical development far beyond anything Bessemer had done, but even so it was far from being a useful commercial success. In recent years it has undergone further development by C. W. Hazelett (U. S. Patent No. 2058447), who has succeeded in obtaining long lengths of copper, brass, aluminum, and even stainless steel. He introduced many' ingenious devices but the greatest obstacle still remained—the disintegration of the roll surface when the surface is heated and chilled in rapid succession. Difficulty is also experienced in maintaining a uniform supply of molten metal to the rolls. The patents pertaining to this method would indicate these to be the major obstacles. Experimental work by Mellen—Method 2 A departure from the method introduced by Bessemer, was tried by Grenville Mellen, of East Orange, K. J., sometime between 1914 and 1920, who obtained a number of patents.2 His method is illustrated in Fig. 2. This method failed to make an impression upon the art; however, it is of value in pointing out the difficulties the inventor ran into and the way in which he tried to meet them. The split mold sections form two endless chains. When going through the center of the apparatus, these sections engage each other to form a complete mold. As the engaged mold section moves downward at a constant speed, molten metal is teemed into it. As this is going on, another set of cooperating mold sections move into position on top of the one being filled. The molten metal is teemed into the mold through a silica tube. According to the teachings of this patent, the level of molten

Jan 1, 1945

By William J. Davis, R. Blair Hrabi, Sally Pehrsson, Amelia V. Logan, Ross Sherlock

"Abstract - The Meadowbank gold deposits are hosted by a series of polydeformed and metamorphosed auriferous iron formations located in the Neoarchean Woodburn Lake group, western Churchill province, Nunavut. The supracrustal rocks in the Meadowbank area consist of a thick sequence of intermediate-composition volcanic rocks with intercalated iron formation, ultramafic volcanic rocks, and quartzite to quartz arenite. U-Pb geochronology gives an interpreted age of 2711 ± 3 Ma for the host strata at Meadowbank.The intermediate volcanic rocks are predominately volcaniclastic and have a geochemical composition that is consistent with an active continental margin setting. Iron formation deposition was coeval with the intermediate volcanism, as indicated by incorporation of volcanic detritus in the chemical precipitate. The geochemistry of the iron formation indicates that it precipitated from a fluid that at one time was at high temperature (>250°C), reducing, and likely acidic. Intercalated ultramafic rocks rarely show spinifex textures and have trace element ratios that are consistent with mantle plume-related undepleted mantle asthenosphere, likely recording episodic mantle upwelling associated with rifting in an active continental margin. The contact between the ultramafic volcanic rocks and the overlying quartz arenite is a disconformity marked by a quartz pebble conglomerate. However, similar geology on the structural hanging wall and footwall of the contact suggests that the conglomerate does not represent a significant hiatus in deposition, and is more likely a prograding terriginous siliciclastic unit.Three metamorphic events are recognized. The first, M1, is a cryptic greenschist facies event that is pre-D2. The second event, M2, is a mid-greenschist to amphibolite facies, syn-D2 event. M3 is the last event recognized, and is a post-tectonic greenschist facies event that is regional but inhomogeneous in extent, possibly reflecting thermal aureoles around post-tectonic 1.7 to 1.8 Ga Nueltin granites. The structural geology of the area is complex with four phases of deformation recognized, two of which had a significant effect on the geometry of the deposit. All of these regional events are interpreted as Paleoproterozoic in age. Relationships between deformation fabrics and mineralization, as well as the overall geometry of the mineralized envelopes, suggest that the deposit formed during syn- to late-D2. Superimposed on the mineralization are D4 structural elements that postdate gold mineralization.The main control on gold mineralization is replacement of magnetite by pyrrhotite and pyrite in high-strain corridors. The composition of amphiboles and chlorites associated with gold mineralization is remarkably consistent and shows no spatial or temporal variation, suggesting that it was buffered by the iron-rich nature of the host rocks. The bulk metasomatic effect on the intermediate volcanic rocks is characterized by the addition of K2O and the loss of CaO, Na2O, and MgO, with little variation in the total iron content. The elemental losses are likely the result of destruction of feldspars, stilpnomelane, and ferroactinolite, which are relatively common in the unmineralized rocks, and the formation of sericite, chlorite, and grunerite."

Jan 1, 2004

By R. C. A. Minnitt, A. Akpabio

This study presents a rigorous comparison between ordinary kriging and commonly used machine learning algorithms, those being, linear regression, support vector regression, decision trees, random forests (RF), and k-nearest neighbours for spatial interpolation of platinum grade estimates in a complex ore body within the Bushveld Igneous Complex. Using only X and Y coordinates as predictors, both ordinary kriging and machine learning models were evaluated at point and block supports under traditional and spatial block cross validation frameworks. While naive validation results suggested superior performance for k-nearest neighbour and random forest (R² = 0.92 and 0.86, respectively), these were revealed to be overly optimistic under spatial dependence. Spatial block cross validation results demonstrated substantial declines in model performance, with R² often falling below zero, particularly for decision trees and k-nearest neighbour, indicating strong overfitting and limited generalisability. Ordinary kriging exhibited more stable, albeit modest, performance under spatial validation, reflecting its strength in geostatistical interpolation when contextual geological variables are unavailable. The study underscores the critical importance of spatially aware validation in resource estimation and highlights that machine learning models constrained to spatial coordinates behave as interpolators rather than true learners of geological variability. Recommendations are provided for future work incorporating geological information to enhance predictive robustness.

Mar 30, 2026

By E. G. King

THIRD-LAW entropy data for zirconium-containing compounds are sparse. Kelley a lists entropies at 298° K. for the oxide, tetrachloride, nitride, and silicate, as well as for the metal. The present paper presents heat capacities between 51° and 298° K. and entropies at 298.15° K. for the zirconates of the alkaline-earth metals-calcium, strontium, and barium. The authors believe magnesium zirconate does not exist as a stable compound at room temperature. Entropies of formation from the constituent oxides also are given. MATERIALS The materials used in this investigation were synthesized and analyzed in the Berkeley Laboratory of the Bureau of Mines. Calcium zirconate was prepared by heating an intimate mixture of reagent-grade calcium carbonate and pure zirconia for 30 hours between 1,200° and 1,300° C. and for 32 hours between 1,400° and 1,500° C. As part of the heating schedule, the sample was ground and mixed seven times. Periodic analyses and minor adjustments of composition were made. Analysis of the final product gave 31.19 percent calcium oxide (theoretically 31.28 percent) and 68.67 percent zirconia (theoretically 68.72 percent). The X-ray diffraction pattern agreed with that in the ASTM catalog.

Jan 1, 1960

By Elger. G. W.

The Bureau of Mines investigated preheating of continuously fed, fragmented ferrous scrap charges by furnace offgases and utilizing substitutes for imported fluorspar to condition electric steelmaking slags. Three types of continuous scrap charging procedures were investigated to determine electrical energy consumption in a I-st (short ton) electric arc furnace. Cold and preheated scrap charges were continuously fed at rates averaging 37.5 and 43.7lb/min, respectively. The feed rate varied appreciably from test to test owing to hangup of the scrap in the charge bin. Approximately 7 pct less electrical energy was consumed in melting scrap preheated to 8400 to 1,1100 F by furnace off-gases than in melting cold scrap. Overall energy consumptions were 888 kW'h/st for cold scrap, 829 kW'h/st for preheated scrap" and 637 kW'h/st for conventional backcharged scrap. Stack gases from scrap preheating averaged 1200 F and a flow rate of 1,615 scfm compared with 2200 F and 1,302 sefm for cold-charged scrap. Slag conditioners tested included synthetic fluorspar, boric acid, hydroboracite, used aluminum potlining wastes and aluminum anode tailing wastes, and Sorelflux B. The boron-containing conditioners fluidized the slags the best, followed in order by the conditioners containing fluorine and titanium.

Jan 1, 1987

By William A. Fuchs

A study of carbonaceous ore at the Santa Fe mine (Corona Gold Inc.) shows that there is no quantitative relationship between organic carbon content and preg rob, although much of this material preg robs. However, there is a relation between K20 and preg rob. Preg rob generally occurs only in those samples with greater than 2% K20. X-ray diffraction and chemical . studies show that the critical factor is the illite content of mixed (possibly interstratified) illite-smectite. Apparently illite, at a certain threshold, "geo-activates" the carbon. The potential for easily monitoring preg rob using a gamma ray spectrometer is discussed.

Jan 1, 1990

By Kimio Itagaki

The distribution ratios of Ag, Pb, As, Sb and Bi for the Cu2S-FeS or Ni3S2-FeS matte / FeOx SiO2, FeOx-SiO2-CaO or FeOx-CaO slag equilibration in a MgO crucible were determined experimentally at 1523~1573K under controlled partial pressures of S2 and O2 at given PSO2 of 10.1, 50.7 and 101.3 kPa (0.1, 0.5 and 1 atm) and be observed dependency of distribution ratio on the matte grade, SO2 pressure and slag basicity were analyzed on the basis of thermodynamics,

Jan 1, 2003

By Kimio Ilagaki

The distribution ratios of Ag, Pb, As, Sb and Bi for the Cu2S-FeS or Ni3S2-FeS matte I FeOx-SiOl, FeOx-Si02-CaO or FeOx-CaO slag equilibration in a MgO crucible were determined experimentally at 1523 ~1573K under controlled partial pressures of S2 and 02 at given PS02 of 10.1,50.7 and 101.3 kPa(O.I, 0.5 and I atm), and the observed dependency of distribution ratio on the matte grade, S02 pressure and slag basicity were analyzed on the basis of thermodynamics.

Jan 1, 2003

By W. Dresler

Design details of a 100 kVA DC electric-arc reduction furnace are described. The furnace is equipped with a 610 mm (24 inch) diameter graphite crucible hearth. A 76 mm (3 inch) diameter top graphite electrode is used as a cathode. The current passes through the bottom of the crucible and is carried to a bottom plate (the anode) by conductive magnesia carbon bricks. The furnace can be operated up to a maximum of 120 V, 1800 A, and presently 100 kW. The start-up operating experiences and metallurgical results of one reduction test with a Montana chromite containing 38% Cr2O3 are discussed.

Jan 1, 1994

By Jinsheng Wang, Wei Lv, Xuewei Lv, Pingsheng Lai, Jie Dang

The isothermal reduction kinetics of vanadium titanium magnetite sintering ore was investigated by thermo-gravimetric analysis at a temperature range of 1123–1223 K under 30% CO + 70% N2 gas mixtures. The apparent activation energy of reduction was calculated by iso-conversional method and its value is 36.7 kJ/mol. The model function describing the reduction mechanism was discussed by Sharp analysis and the results revealed that the reduction process is controlled first by random nucleation and nucleus growth mechanism (RNNGM) as reduction degree is lower than 0.5, followed by the mixed influence of RNNGM and phase boundary reaction when reduction degree is higher than 0.5.

Mar 1, 2017

By H. C. Ko

Heats of solution of calcium carbon-ate (calcite) and calcium oxide in hydrochloric acid were determined by solution calorimetry. Combination of these two heats yields a value of 42.643±0.024 kcal/mole for the enthalpy of calcination of calcite at 298.15 K. Literature data on ?H°298.15 of calcination of calcite were reviewed and compared. Thermodynamic properties for the calcination process were calculated from 298.15 to 1,500 K using Gibbs energy functions. This research was undertaken by the Bureau of Mines as an effort to provide thermodynamic data for the advancement of minerals technology, energy conservation, and environmental preservation.

Jan 1, 1982

By D. F. Malan, T. E. Oates

A recent experimental pillar extraction project at a UG2 bord-and-pillar mine presented a unique opportunity to compile a new pillar database. Currently, the South African hard rock bordand- pillar mines are designed using the Hedley and Grant formula with a modified K-value. This empirically derived formula was developed for uranium mines in the Elliot Lake district of Canada. The use of this formula for the design of pillars in South Africa is questionable. Very few pillar failures have nevertheless been observed and its current calibrations for the various reef types are possibly too conservative. A new UG2 pillar database of 66 pillars, of which seven are classified as failed, was compiled by the authors. This enabled a revised ‘first-order’ calibration of the K-value for the Hedley and Grant formula. The new estimated value for the UG2 is K = 75 MPa. This gives a pillar strength that is more conservative than the PlatMine formula. This work should nevertheless be considered as only a preliminary calibration as the database was small. Further work is also required to determine whether the exponents in the formula for the width and height parameters are appropriate for UG2 pillars.

May 3, 2023

By A. J. Lewis, P. J. Hutcheson, M. E. Robertson, P. A. Moir, K. M. Barfoot

With the content of gold and platinum in the vast majority of ore deposits typically averaging 6 parts per million and less, the accurate and precise measurement of these metals in samples of ore and mining process streams has proven very difficult to achieve by modem spectroscopic analytical techniques. Largely because no other technique has proven suitable, the basic fire assay process has become the accepted international standard for these metals. Fire assay, however, suffers a number of disadvan­tages in the modem, competitive, high technology, and increas­ingly environmentally aware world. It is a labour intensive technique that is difficult to automate, and requires high levels of skill to ensure accuracy and consistency of results. Potentially hazardous chemical reagents are employed, of which, lead, in particular, can be a serious source of contamination to both personnel and the environment if not effectively controlled. Other dangerous elements, such as mercury and arsenic, liberated in high energy furnace operations, are further sources of possible health and pollution hazards. n contrast, the energy dispersive K X-ray fluorescence (K­XRF) technique devised by K X Technology Ltd overcomes many of the technical constraints of conventional low energy X­ray analysis, and has the potential to revolutionise assay opera­tions in precious metal mining. The technology is simply automated, requires basic operator skills, uses no chemicals, consumes less than 20kW, and is capable of detecting gold and platinum to an accuracy of O .1 parts per million by mass. The new third generation design of AZTEC laboratory instrument, released in 1994, is the result of significant technical development. Capable of analysing over 1200 samples per day, and developed primarily for grade control sampling, its applica­tions have spread to gold ore accounting from on-line conveyor belt sampling; screening of exploration samples; measurement of gold in carbon granules for Carbon-in-Pulp process control; and for conducting rapid checks to support key managemen decisions. The economic, rapid, and non destructive analysis ofup to 80g of ore for large numbers of samples, reduces sampling and sub-sampling errors, and provides improved grade estimates for ore bodies. When interfaced to a LIMS, laboratory automation and cost-savings can be further enhanced. The AZTEC design is also being modified for the analysis of platinum. The GOLDSTREAM on-line analysis system is an important new application of K-XRF to the continuous monitoring of process streams in gold ( or platinum) plants and mills. Integrat­ing the technologies of K-XRF to measure total gold, and dissolved gold spectroscopy to measure gold in solution, the insoluble fraction of gold can be deduced, and the effectiveness of the extraction process determined. Slurries are sampled automatically from selected points of the plant and pumped to the system for analysis. The information produced forms the basis for plant control and optimisation.

Jan 1, 1995

By E. Bane Kroeger

In underground coal mining, there is often a need for supplemental support for mine openings. In the past, one of the most common types of supplemental support was wooden posts that were installed against the roof using opposing wooden wedges. Underground, wood has the tendency to shrink from moisture loss and dislodge if not under load. Another drawback to using wood is the variability in strength between posts. Defects in the wood such as knots can cause weaknesses that often lead to premature failure of supplemental support. Many mines that install large amounts of supplemental support in certain areas of the mine such as bleeder entries in longwall mining have switched to using steel props rather than wood posts or cribbing. The reactions of steel props under loading are well- defined and there is little variability in strength between props. Steel props and can be fabricated so they can be used in a variety of roof heights without modification. Wooden posts often have to be cut to a usable length underground before installation. This adds to the installation time of the wooden posts. Steel props are more compact and can be lighter than their wooden counterparts, depending on the length and carrying capacity. Often times it is desirable to prestress the supplemental support to improve roof stability. This is often problematic and time consuming with some types if supplemental support. With these factors in mind, research was undertaken at Southern Illinois University Carbondale (SIUC) to design a new steel roof prop. Several new clamping designs were developed and prototypes were fabricated and tested in the labs at SIUC in the spring of 2003. The designs were modified and refined and the first full-size prototype roof prop was tested in January 2004. With the success of the full-size prototypes, a cooperative research program was established between SIUC and Excel Mining Systems, Inc. to further develop the new prop. Development went smoothly and the prop has performed as expected. In February 2005, SIUC and Excel entered into an exclusive licensing agreement. The prop design under license, the K-Prop, will be installed using a lightweight portable hydraulic jacking system under design that can be used to prestress the props, applying load to the roof and floor during installation. By varying the installation load, the prestress load can be varied from about 1,000 to 10,000 pounds (4.448 to 44.48 kN) and at the same time, the carrying capacity of the K-Prop can be varied from 10,000 to 100,000 pounds (44.48 to 444.8 kN). The K- Prop is composed of only 3 pieces and laboratory testing has suggested that it can be installed by a pair of workers in less than two minutes. The speed of installation of the K-Prop should significantly reduce the total installed cost for supplemental support and should provide a safer working environment by prestressing the prop, which will add support load to the roof and floor during installation.

Jan 1, 2005

By J. A. Procarione

Introduction Ventilation engineers have always felt somewhat uneasy when, in the normal course of their work, they are forced to consider the flow in any mine entry as "wholly rough." Under such conditions in pipes, friction factor is no longer a function of Reynolds' number. This assumption serves to simplify the problem and overcome an evident lack of information concerning the variability of K-factors. During the summer of 1985, a unique opportunity to investigate the reaction of friction factor to changing flow rates presented itself. A Utah coal mine was temporarily directing a substantial airflow through a single entry. By regulating the quantity, it would be possible to obtain a wide range of Reynolds' numbers in an entry composed of two distinct coal thicknesses. This paper describes the conducted study. The theory covering basic fluid flows in pipes that led to the questioning of constant K-factor is presented first. Experimental procedures are then described, including the use of a view camera in determining entry area and perimeter. Finally, a discussion of the observed variations in friction factor versus Reynolds' number is given. Changes of 34% and 45% in K-factor were seen in this study for the two entry heights. The implications of ignoring the relationship in this case and a call for an expanded research effort are also presented. Theory Since a gas is a fluid, the general principles of fluid mechanics are equally applicable to airflow in a mine entry as they are to the flow of water in a pipe. The Darcy equation is, therefore, equally applicable to pressure drop calculations in both situations. This famous formula was originally derived for use in circular cross sections and may be modified for any other shape by the use of hydraulic radius (defined as the area divided by the "wetted" perimeter). The Darcy equation relates the physical parameters of the pipe (diameter, length, and resistance to flow) and fluid velocity to the energy needed to create the flow. A study by Nikuradse (1933) brought to light the suspected dependency of the friction factor term in the Darcy equation upon Reynolds' number. By performing a large number of laboratory experiments, he established some basic concepts upon which other researchers built. Chief among these contributors was Colebrook (1939). Using commercial-grade pipe, he established an empirical relationship between Darcy's friction factor and Reynolds' number that is still in use today. If Colebrook's system of equations is plotted on log-log paper (as was done by Moody, 1944), the curves have some very distinct features. Of importance to the subject at hand is the relative response of friction factor to Reynolds' number at a given relative roughness. Simply stated, a pipe can appear to be either smooth or rough, depending on the flow conditions. As the Reynolds' number increases, the friction factor decreases at a decreasing rate until it becomes nearly a constant value. At this point, the flow is said to be "wholly rough." It is upon this condition that many traditional ventilation solution methods depend. For calculating pressure drops in a mine entry, Atkinson's equation is much more popular than the Darcy equation. Both of these formulas describe the same phenomenon and so have similar forms and functions. The K-factor in the Atkinson equation is equivalent to the Darcy friction factor and can be related by simply changing units, equating the pressure drops, and canceling like terms. A generalized form of this relationship is presented below as equation 1. K = yf/28,800g = [q]f/28,800 (1) where K is Atkinson's friction factor in kg/m3 (lb - min2/ft4), Y is the specific volume in Nt/m3 (lb per cu ft), p is the fluid density in kg/m3 (slugs per cu ft), g is the acceleration due to gravity (9.8 m/s2 or 32.2 fpsz), and f is Darcy's friction factor, which is unitless. The objective behind Eq. 1 is to show the strong correlation between K and f. Since these two quantities differ only by a constant (q]/28,000), the assumed independence of K-factor and Reynolds' number is suspect in light of the known response of f. Unfortunately, the formulation does not provide information concerning the actual relationship, as entry geometry likely plays a major role in the response curve. Only an indirect indication that such a relationship might exist is provided. Previous work on this subject was performed by Thomas Falkie (1958). The study involved a laboratory model composed of sections of straight, steel duct and a range of Reynolds' numbers from 15,610 to 137,200. Results from this work show a variation in friction factor with Reynolds' number in much the same way as it was found to vary in pipes. Over the range of velocities examined, a decrease of approximately 38% in K-factor was observed. This previous experience provides additional incentives to investigate the phenomenon under field conditions. Past model studies done at the University of Utah by Ozukurt (1945), Biron (1944), and Greenhalgh (1942) present similar evidence of this variability. More recently, Kharkar's (1974) study of coal mine friction factors contains similar indications that K-factor is not constant in all situations. Taken together, the data

Jan 1, 1988

By A. R. Taylor

In recent years, thermodynamic data have been used to a greater degree than ever by the chemical and metallurgical engineer as a means of predicting and controlling chemical reactions. To satisfy the spiraling demand for basic physical data needed for the calculations, the Bureau of Mines is studying the heat capacities of a variety of chemical compounds at high and low temperatures. This paper is one of a series presenting such data. The heat capacities of two alkaline earth compounds, strontium bromide and strontium nitrate, were measured in a temperature range of 60° to 300° K. in an adiabatic calorimeter and at temperatures of 300° to about 1,200° K. in a Bunsen ice calorimeter. The construction and operation of the calorimeters are discussed in other reports.3 4 The heat-capacity data presented in this report were extrapolated to 0° K., and smooth values of heat capacity, entropy, enthalpy function, and free-energy function were calculated and tabulated at even 10-degree intervals. The enthalpy data were fitted with algebraic equations by applying the method of least squares; calculations a£ heat-capacity values, entropy, enthalpy function, and free-energy function were made at even 50-degree intervals. The heat and entropy of fusion of strontium bromide were calculated from the enthalpy measurements.

Jan 1, 1962

By E. G. Davis

As a result of interest by the U.S. Department of Energy, the Bureau of Mines conducted studies on comminution of bituminous coal to the 2-um particle size range using the Bureau-developed turbomill. Both "plant grind" size (80 pct minus 75 um) and microsize (minus 10 um) coal can be produced in a single step with the Bureau's turbomill. In 15 min, minus 2.4-mm coal milled in water with steel shot was reduced tc 65 pct minus 75 m and 26 pct minus 2 m, with an energy requirement of 139 kW^h/mt coal. Plant-grind size coal milled in water, with Ottawa sand as the milling medium, was reduced to more than 45 pct minus 2 m in 15 min, at 175 kW?h/mt. Plant-grind coal milled with steel shot was reduced to 57 pct minus 2 um in 15 min, at 138 kW?h/mt. When diesel fuel was substituted for water, the milling of the coal was less effective and less energy efficient. Keeping the pulp dispersed was critical. Without an effective dispersant, the slurry became very viscous with increased milling time, resulting in higher energy requirements, low heat dissipation, and poor grinding efficiency.

Jan 1, 1987

By M. Hertzberg

Results of a comprehensive study of the absolute spectral radiance of the infrared emissions from methane-air explosions are reported. The spectral growth of these expanding flames were recorded with a time resolution of 1 msec in the spectral range of 1.7 to 5.0 µm. Time-resolved spectra were obtained for methane-air mixtures as a function of stoichiometry, nitrogen dilution, and Halon dilution, in a 9-liter vessel under different venting conditions. Data are also presented for coal dust-air explosions. Temperatures, obtained from the absolute radiances and from a band ratio technique for methane-air, are internally consistent and are generally 50° to 200°K below adiabatic flame temperatures. All near limit mixtures gave essentially the same flame temperatures (1,500° to 1,600° K) regardless of whether the limit was obtained by dilution with excess air, excess methane, excess nitrogen, or Halon. The coal dust explosion spectrum is essentially a blackbody continuum at 1,500° K with some selective emission at 4.4 µm from hotter CO2. The data are analyzed in terms of the radiative dynamics of a sperically expanding flame zone. The importance of radiative transport is assessed. An equation is derived which relates the instantaneous fraction of combustion power radiated to adiabatic variables.

Jan 1, 1973

By Pradeep K. Rohatgi, David N. French, Surendar M. Jain, Clyde M. Adams

The effect of solute concentration and diffussivity on dendritic solidification of dilute binary aqueous solutions has been investigated; chlorides of sodium, potassium, lithiurn, and hydrogen were used as solutes. Dendrite spacings were measured in spherical droplets and in unidirectionally solidified specimens. In the droplets, the freezing rate is uniform over the entire specimen and remains constant from the beginning to the end of solidification. In the unidirec-tionally frozen specimens the freezing rate varies within a given volume of liquid during the solidification cycle; in addition, it varies with location uithin the specimen. Mass transport analysis has been used to calculate the supersaturation, AC, supercooling, AT, and transcerse growth velocity, V , of ice dendrites during solidijication from the dendrite spacings measured in the droplels. The ice dendrite spacing in a given solute increases lineary with the solule concentralion at a fixed freezing rate. The ualues of AC, AT, and V increase with an increase in solule concentration. The value of AT in the aqueous solution is of the same order of magnitude as in Al-Cu alloys of the same concentration; the dendrite spacings in Al-Cu alloys also increase with an increase in solute concentralion. For the jamily of aqueozrs solulions incestigaled, the dendrite spacing increases linearly with solute diffusivity at fixed values of concertralion and freezing ,rate. The values of ?C and ?T decrease, whereas the value of V increases with an increase in solule diffusicity. The measured dendrite spacings , L, can be expressed by the relatiun: L = K;(dfa/db) 4 K2C +K3D - K4 where dfs/d? is-change in fraction solid with time (freezing rate), C is solute concentration, D is solute diffusivit K1 = (14 * 4)pmin1'2, K2 = (70 ± 10) pl (moles)- K3 = (24 r 3) . l05 psec (cm)-~. K. = -132 ± 10) 1. FREEZING of solutions is almost always an ehunmix-ing" process because the composition of crystallizing solid generally differs from that of the parent liquid. " Solute concentration and transport are therefore in]portant considerations in solidification of solutions. The influence of these factors on the dendritic solutions produced from metallic solutions is of practical significance since the properties of the solid aggre-gate are often strongly influenced by dendrite spacing.''' Alexander and Fthines3 found that dendrite spac- ings generally increase with solute concentration in several metallic systems. Michael and Bever1 have observed an increase in a aluminum dendrite spacings in dilute A1-Cu alloys. Rohatgi and AdamsJ have reported a linear increase in a aluminum dendrite spacings with increasing copper contents up to 28 pct in A1-Cu alloys. Bolling and Tiller"' have theoretically examined the effects of solute concentration and diffusivity on the growth of cells and dendrites. Their analysis of dendritic growth assumes a steady-state growth and the maximum possible velocity for dendrite propagation. In addition, the quantitative analysis is restricted to dendrites of rotational symmetry and is therefore not directly applicable to the plate-shaped dendrites of ice obtained in the present study. There are practically no experimental observations of the effect of solute diffusivity on dendrite spacings in metallic systems. The reason appears to be the lack of experimental data on solute diffusion coefficients in liquid metallic solutions. The present work is concerned with the effect of solute concentration and diffusivity on dendritic solidification of dilute aqueous solutions: the solutes examined are potassium chloride. sodium chloride, lithium chloride. and hydrogen chloride. There were several reasons for selecting these solutes. The variation of dendrite spacing with freezing rate in these solutiolls is similar to that observed in A1-Cu alloys.8 These aqueous solutions have almost identical phase diagrams at dilute concentrations. Fig. 1. and the diffusion coefficients show very little variation with solute Concentration.9,10 Dendrite spacings were measured as a function of freezing rate. solute concentration. and solute diffusivity. Dendrite spacings were measured in two different types of freezing systems. droplet and unidirectional, respectively. In the droplet freezing system

Jan 1, 1970