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By P. W. Bennett, E. M. Elkin

A new technique for the recovery of palladium and platinum and sludge from go12 electrolyte eliminates many of the drawbacks of the zinc-dust cementation process. In the electrolytic refining of gold by the Wohwill method, the electrolyte contains about 100 gpl gold as AuCl, and 100 gpl free hydrochloric acid. Any palladium and platinum contained in impure gold dissolve and accumulate in the electrolyte. When their concentration approaches that of gold, it becomes desirable to discard the electrolyte and to recover the gold and the palladium and platinum. As practiced at Canadian Copper Refiners until recently, discarded electrolyte was treated with sulfur dioxide to precipitate the gold. 2AuCl3 + 6H2O + 3SO2 —2Au + 6HC1 + 3H2SO4 The gold precipitate was filtered off, washed with water, and melted with scrap anodes. The wash water was added to the gold-free filtrate and treated with zinc dust to cement the palladium and platinum. PdCl2 + Zn — Pd + ZnCl2 PtCl4 + 2Zn—Pt + 2ZnCl2 The precipitate was separated and sold as Pd-Pt concentrate, and the barren filtrate and wash water were discarded. The receipts of palladium and platinum at this company were too small to warrant their refining. The process suffered from a number of disadvantages. Handling the gold-free solution was disagreeable, as it was laden with sulfur dioxide even after blowing with air overnight. Subsequent treatment with zinc dust was also troublesome. A large excess of zinc dust was required. Spray, acid mist, and vigorous evolution of hydrogen accompanied the reaction. The Pd-Pt precipitate was grossly contaminated with occluded unreacted zinc and with yellow granules of sulfur, thought to be formed by the reduction of sulfur dioxide and its derivatives. Repeated boiling of the precipitate with hydrochloric acid and washing with water decreased somewhat, but did not eliminate, the zinc. After drying overnight, the precipitate hardened to a clinkerlike mass that was difficult to grind. Grinding, handling, and packing created heavy dusting. Even weighing in an analytical balance generated dust, indicating that the powder was easily charged with static electricity. The total palladium and platinum content of the powder varied from 56 to 72 pct, with an average of 65 pct. The powder dissolved in aqua regia with difficulty, leaving a small amount of insoluble residue. However, the main drawback of the process was the strongly hygroscopic Pd-Pt product. The powder showed a marked though erratic increase in weight and a corresponding decrease in assay on exposure to air, even during the course of laboratory analysis. Such changes were the source of disagreement between Canadian Copper Refiners and the buyers of concentrate. The cause of the change in weight is believed to be hydrogen, liberated by the action of zinc dust on hydrochloric acid. Some of this hydrogen was adsorbed so strongly by the precipitate that it could not be driven off during the drying. On exposure to air it oxidized catalytically, forming water. Experiments soon showed that the entire process of treatment of discarded electrolyte then in use would have to be changed. A small quantity of apparatus was moved into the gold room, and experimentation was held to a minimum compatible with the development of a new process. PALLADIUM AND PLATINUM PRECIPITATION It was thought that zinc could be replaced with a reagent other than a hydrogen-evolving metal. Semiquantitative experiments showed that platinum and palladium could be precipitated completely from the gold-free solutions with such well-known reagents as sodium formate, formic acid, formaldehyde, and paraformaldehyde. Sodium formate was the preferred reagent, since the other three are volatile and somewhat toxic. The gold-free solutions used were those saturated with sulfur dioxide, partly freed of sulfur dioxide by aerating overnight, completely freed by boiling, as well as strongly and weakly acidic, neutral, and alkaline solutions. The reactions are complex and can be represented by these over-all equations: PdC1, + HCOONa — Pd + NaCl + HC1 + Co2 PtCl4 + 2HCOONa — Pt + 2NaCl + 2HC1 + 2CCX, Strongly acidic solutions required as much as five times the theoretical amount of sodium formate as did solutions neutralized to pH 4.5. Increasing the pH decreased the consumption of

Jan 1, 1965

By Bryson D. Trexler

Man's activity in developing, operating, and abandoning a mine often affects the quality of the ground water and surface water. Acid water drainage from mines is an example of an impact from mining that results in degradation of ground and surface water. New flow systems are created by the mining activity. The mining made possible complex chemical reactions that, with water movement, create a discharge of low pH, poor quality water. Remedies for these problems fall into two general solutions: 1) treatment of the end product and 2) reversal of some aspect of man's disturbance of the natural system. The relative reversibility of various aspects of man's impact from mining activities ranges from relatively easy to very difficult, from economically feasible to economically infeasible, and from technically possible to essentially impossible with present knowledge. The relative reversibility of a mine-related problem cannot be assessed without first understanding the detailed physical interactions that combine to form the problem. Acid water drainage is a combination of the availability of several chemical factors with the availability of water for a transport mechanism.

Jan 1, 1982

By A. B. Hooker, L. C. IlsLey

"Field inspections and data relative to the use of rubber-sheathed trailing cables in mines show that much cable is ruined or its probable life shortened by being overheated in service.The length of cable required to make connection from a source of supply to a machine at the face workings may be 100 to 500 feet. As a rule, the cable is carried on a reel and unreeled as required; and thus in most cases soma of the cable is not removed from the reel. The overheating generally occurs in that part of the cable which is left on the reel.Factors that determine the heating of trailing cables are:1. The size of the conductors in the cable.2. The maximum energy to be supplied through the cable, based upon the horsepower of the motor and the degree to which the motor is loaded.3. The voltage of the supply and the variation of the voltage at the receiving end.4. The time length of current flow and whether continuous or intermittent.5. The kind of current (direct or alternating).6. The amount of ca· le left or the reel.7. The type of cable used.8. The kind of reel used.In connecti0n with an investigation of the general performance of rubber-sheathed trailing callas, the Bureau of Mines has made a limited study of some of these factors, including the following points:"

Jul 1, 1931

By H. Chaouki

The aim of this work is to simulate the forming process of a green anode. For this purpose, a nonlinear compressible viscoelastic constitutive law is presented. The concept of natural reference configuration is considered. Within an isothermal thermodynamic framework, a Helmholtz free energy is proposed to take into account the nonlinear compressible deformation process occurring between natural reference configuration and current configuration. A dissipation potential is introduced in order to characterize the irreversible aspect of compaction process. Thus, the constitutive law is formulated through two equations: 1) an expression of Cauchy stress tensor and 2) a differential equation characterizing the evolution of the natural reference configuration. Material parameters are assumed to be a function of the bulk density. This allows capturing the micro-mechanical phenomena within the chosen macroscopic approach. An experimental study based on compaction tests is carried out in order to characterize the mechanical behaviour of the anode paste. A user's material VUMAT subroutine for finite element dynamic explicit analysis has been developed and implemented in the ABAQUS commercial software. To evaluate the model predictive capability, numerical simulations of the compaction forming process of anode paste were performed. Simulation results show that the constitutive law predicts the experimental trends and gives interesting physical responses. This constitutes a first step toward making a benchmark with experimental results on the forming process of anode paste.

Jan 1, 2011

By Totterdell JM

The Permian-Triassic Bowen Basin and the Jurassic-Cretaceous Surat Basin evolved in a backarc tectonic setting behind an active convergent plate margin in eastern Gondwana. Several extensional (Early Permian; Eocene) and contractional (mid- Permian; Early Triassic; Middle-Late Triassic; early Late Cretaceous) intraplate deformational events are recognised in the basins. These can be correlated with similar events in the New England Orogen that was being deformed in the Late Permian- Late Triassic as a foreland thrust belt. The intraplate deformations were probably the consequence of plate interactions, including the accretion of terranes, at the ancient active plate margin, remnants of which now occur in New Zealand.

Jan 1, 1995

By H. T. Byck

The plastering properties of six representative California drilling muds were studied over a temperature range of 70 to 175 F. at several mud weights, using a high-pressure circulating filter press with full size consolidated cores. In all tests, with untreated as well as with chemically treated muds, the filtration rates at elevated temperature were higher than at low temperatures and in nearly every case this increased filtration rate was notably larger than could be attributed alone to the decreased viscosity of water—the flowing medium—at elevated temperatures. It is concluded that no existing method will permit even an approximate determination of the filtration rate at high temperature from data at room temperature. It is necessary to measure filtration at the temperature actually anticipated in the well, or to make a sufficient number of tests at various lower temperatures so that a small extrapolation of these data to the anticipated well temperature may be applied. Such tests should be carried out on the mud as actually used in the well. The viscosity of each of the muds was determined over the same temperature range. While no relationship was observed between mud viscosity and plastering properties, it was found that chemical treatment of the muds for viscosity reduction shifted the temperature of minimum viscosity to appreciably higher values than for untreated muds. Importance of Plastering Properties A survey of the literature on rotary drilling muds clearly shows the growing realization of the importance of plastering properties,'-5 not only from the point of view of the successful completion of the mechanical operation of drilling the well but also from the point of view of minimum impairment of the natural flow possibilities of a given well. Poor plastering properties with attendant high filtration rate (large water loss to the formation) and thick mud sheath, lead to stuck drill

Jan 1, 1940

By H. T. Byck

The plastering properties of six representative California drilling muds were studied over a temperature range of 70 to 175 F. at several mud weights, using a high-pressure circulating filter press with full size consolidated cores. In all tests, with untreated as well as with chemically treated muds, the filtration rates at elevated temperature were higher than at low temperatures and in nearly every case this increased filtration rate was notably larger than could be attributed alone to the decreased viscosity of water—the flowing medium—at elevated temperatures. It is concluded that no existing method will permit even an approximate determination of the filtration rate at high temperature from data at room temperature. It is necessary to measure filtration at the temperature actually anticipated in the well, or to make a sufficient number of tests at various lower temperatures so that a small extrapolation of these data to the anticipated well temperature may be applied. Such tests should be carried out on the mud as actually used in the well. The viscosity of each of the muds was determined over the same temperature range. While no relationship was observed between mud viscosity and plastering properties, it was found that chemical treatment of the muds for viscosity reduction shifted the temperature of minimum viscosity to appreciably higher values than for untreated muds. Importance of Plastering Properties A survey of the literature on rotary drilling muds clearly shows the growing realization of the importance of plastering properties,'-5 not only from the point of view of the successful completion of the mechanical operation of drilling the well but also from the point of view of minimum impairment of the natural flow possibilities of a given well. Poor plastering properties with attendant high filtration rate (large water loss to the formation) and thick mud sheath, lead to stuck drill

Jan 1, 1940

By R. H. Rubisov

Sulphuric acid pressure leaching of nickeliferous laterites has attracted considerable attention from the nickel industry during the past five years. The process is especially advantageous for limonitic laterites that mostly contain goethite, because iron precipitates releasing acid and thus rendering low acid consumption. It is also applicable to mixtures of limonites and saprolites, although at higher acid consumption due to magnesium. Effective process design requires the solubility of metals that precipitate during the process to be known. In the present work, determination of metal solubilities is based on a simple speciation program that assumes the presence of only one dominant complex for each metal. The thermodynamic data for the precipitation reactions are extracted from high-temperature experiments with monometallic systems published previously. The validity of the approach is then tested against mixed bimetallic systems, and finally applied to calculate the solubility of aluminium, iron and magnesium in laterite leaching effluents "at temperature". In both cases of limonitic feed and limoniticfsaprolitic blends, the prediction closely follows metal solubilities measured experimentally at temperatures from 230 to 270°C and at terminal he acidities ranging from 10 to 75 g/L.

Jan 1, 1999

By Cemal Can Maslak, Vijaya Bhushan Rao, Vidyaranya Bandi, Karsten Beckhaus

A Large Earth Cum Rock Fill, ECRF Dam is under construction at Polavaram in the state of Andhra Pradesh in India as part of an irrigation project. The Embankment crest width of the dam is 12.5m and base width is of approximately 136.75m with a stepped sloping height of 27m on both upstream/downstream sides. Once the 1.2m Thick Plastic concrete cut-off wall is constructed below the dam along the longitudinal central axis to avoid seepage, this magnificent structure will be supported on a series of Deep Mixing Columns and Stone Columns that are evenly arranged under the footprint of ECRF Dam forming a smooth transition of gradually reducing stiffness moduli of treated ground from the center of the embankment, where the foundation stresses are high, towards the edges in order to be able to progressively limit the settlements under the dam to a specified allowable limit. As such the required post treatment stiffness in case of stone columns is 2 times of the in-situ stiffness of foundation soil, whereas it is expected to be 5 times improvement for Deep Mixing as per project specifications. Laboratory testing and Field Trials undertaken successfully to verify the design.

Sep 1, 2022

By D. B. McWhorter, J. D. Nelson

Conventional analyses of seepage through saturated media do not apply when tailings impoundments are located above a partially saturated zone. Three stages of seepage are identified and methods for estimating the seepage rates and duration of each stage, based upon flow in partially saturated and saturated porous media, are demonstrated. The effectiveness of earthen liners is discussed and procedures for estimating the required properties of the porous media are provided.

Jan 1, 1981

By J. E. Hoffman, Corby G. Anderson, T. J. Keefe, O&apos, Suzzann M. Nordwick

Antimony removal has become necessary as it is commonly found in precious metal refractory ore bodies. The Sunshine Mine in Kellogg, Idaho has recovered metallic electrowon antimony from its argentiferous tetrahedrite (Cu2S'Sb2S3) deposits for over fifty years. Recently, Sunshine conducted an intense research effort to improve and modernize its antimony facility. This paper presents information which was learned about the antimony electrowinning processes and the development of a single¬-electrolyte antimony electrowinning technology. The relevant effects of process variables were investigated. The research results and the relevant chemistries involved in metallic antimony electrowinning will be discussed.

Jan 1, 1993

By Bearman R. A, Parkin R. M

Traditional quality control procedures for aggregates production within the quarry industry rely on off-line laboratory analysis, resulting in poor performance and inconsistent product quality. A high speed on-line aggregate classification system is described here. A product sampling system directs aggregate through an inspection chamber where a novel imaging system digitises the particle geometry. Data processing algorithms extract dimensional data and image features, while a neural network classifier assigns a qualitative shape descriptor to each rock particle. This system provides each sampled batch with a complete analysis of size and shape distributions, complementing a new generation of cone crusher technology to maximise product quality and plant efficiency.

Jan 1, 1995

By R. J. Lutton

Empirical data from 91 rock excavations have been used to construct a family of slope curves on a chart relating excavation height and inclination. The highest and steepest slopes from each excavation are plotted and connected by a line. The 31 1ines appear to establish one or two geometrical slope fields through which the curves are projected. The curves apparently represent a lumped eflect of many factors too complex to be considered individually. Important factors such as geological structure or ground-water conditions can dominate the picture, but where these factors do not overshadow others, the slope chart should be useful for estimating or checking optimum inclination. The U.S. Army Corps of Engineers (USAE) has been engaged since 1962 with the U.S. Atomic Energy Commission in a joint research program to develop nuclear excavation technology. The Corps is responsible for collecting the requisite data on engineering and construction problems associated with nuclear excavation. The ultimate objective is to develop a capability to use nuclear explosives as a construction tool on public works projects such as harbors and canals. The present study on empirical inclination-height curves for conventionally excavated slopes is an outgrowth of an investigation' sponsored by the USAE Nuclear Cratering Group on applicability of data from existing excavations in establishing guides for engineering judgment in crater excavation. Data were generously contributed by over 50 mining companies among other organizations. Inasmuch as several companies preferred that their contribution be anonymous, all data are treated so here. Some Factors Affecting Stability Many factors affect or are suspected of affecting the stability of excavated slopes, e.g., adverse structural orientation, degree of structural ordering, ground water, climatic conditions, mechanics of excavation, and plan-profile configuration. Such factors are lumped together in developing a slope chart. Obviously geological structure and ground water can overshadow all other factors. Where such is the case, the simplification of slope charts may give an erroneous picture (not conservative enough). A further complication results from the fact that the concept of stability may vary according to the use of the excavations. For example, slope adjustments that would be regarded as failure in a powerhouse excavation, might be tolerable in a mining operation. Mine slopes are continually being modified by further excavation, and instability that would develop in a similar permanent excavation slope over a period of years might not have time to develop in a mine. Inclination vs. Height Charts Charts of inclination vs. height for particular formations or conditions have been used in the past as an aid for designing excavation slopes. Some of these have been based upon empirical analyses of collections of data and experience. MacDonald" and Lane have presented slope tables and charts for excavated and natural slopes in relatively weak sandstone and shale. Coates' has shown an inclination-height chart for slopes in incompetent rock. Most organizations have developed slope design criteria which relate bench widths, heights, and inclinations to use in various rocks. Slope data collected in present studies can be similarly used to develop inclination-height charts; however, a plot of all slopes on such a chart shows very little because of the wide spread of the data. Reasons for the dispersion of points are: (1) many slopes are not carried at optimum inclination, particularly in mines where maintaining roadways and following irregularities of ore bodies are more important than achieving steep inclinations; (2) many engineers and geologists with varied backgrounds and viewpoints have been involved in designing these slopes; and (3) each slope is characterized by a unique combination of factors affecting stability and in turn optimum inclination. Significant curves can sometimes be constructed where the points can be grouped into related clusters from the same excavation. The essence of this approach appears when only two slopes from each excavation are considered—the highest slope and the steepest slope, connected by a line segment (Fig. 1). This reduces considerably the usable data because in many cases only one of these two slopes is available. Nevertheless, the concession seems justified. Construction of Slope Curves Ninety-one pairs of points and connecting line segments were assembled in this study. The line segments were assumed to approximate a geometrical slope field (Fig. 2), and a family of curves has been visually projected through to represent the slope field. It should be

Jan 1, 1971

By R. Le Houillier, M. Nagamori, A. J. Plumpton

"Asbestos tailings are a typical serpentine, hydrated magnesium silicate, consisting primarily of antigorite and a few per cent of unrecovered fibrous chrysotile. Serpentine has unique thermal properties in that dehydroxylating calcination at 600 to 700°C can yield an amorphous structure in which most of the magnesia is liberated from the original bond with silica and thereby rendered chemically active. The amount of activated magnesia can be quantified by selective leaching with a weak acid such as acetic acid. Many wet processes have been proposed to extract magnesium values from calcined or natural serpentine by means of various acids and their ammonium salts. However, the only commercial utilization of serpentine today is found in dry processes such as the production of fused magnesium phosphate fertilizer .The present paper reviews the physical chemistry of the dehydroxylation of serpentine and also various wet and dry processes in order to provide a general view regarding the chemical transformation of asbestos tailings.IntroductionAsbestos fibers occur as chrysotile, a serpentine polymorph. More than nine tenths of mined asbestos ores consist of massive non-fibrous serpentine, primarily the polymorph antigorite, which is discarded as tailings after fiber extraction. For many decades, Quebec has been a world leader in the production of asbestos fibers. As a result, colossal tonnages of serpentine have accumulated in the Eastern Townships'!'. Serpentine minerals are found in large deposit s throughout the world, and significant research efforts have been made, particularly in Japan and the USSR, mostly in attempts to extract magnesia or silica values therefrom.The chemical composition of serpentine (chrysotile and antigorite) may be ideally expressed as Mg3Si2Os(OH). which corresponds to 43.7% MgO and 43.3% SiO2. Natural serpentines often contain a few per cent of Ni-bearing magnetite and other impurities, and therefore the contents of MgO and Si02are both about 40% or lower.Serpentine (hydrated magnesium silicate) is virtually insoluble in weak acids. However, when dehydroxylated under controlled conditions, ' it decomposes to an amorphous state in which magnesia and silica are isolated and chemically active. The magnesia so activated is readily soluble in weak acids. This unique characteristic of calcined serpentine, first discovered in 1942,, has since attracted the attention of innumerable researchers, whence many processes have been proposed."

Jan 1, 1980

By Laas JJ, Spearing AJS

Considering the capital outlay, running costs and inherent difficulties of backfilling operations at depth the benefits need to be clearly established, quantified and then exploited. Expansion of Vaal Reefs Exploration and Mining Company towards even deeper, highly faulted ground, and the process of establishing codes of practice for the management of rockfalls and rockbursts, required that a sound support strategy be formulated. This paper describes the derivation of an overall backfilling strategy on Vaal Reefs. Use was made of experience gained over some 12 years with backfilling. Numerical modelling was used to estimate potential benefits of backfilling the deepest mining areas still to be extracted. In exploiting a probably unique opportunity, two contiguous mining areas bounded by the same major geological structures, were compared. One was extensively backfilled and the other not at all. Shaft sinking through a backfilled stope added another dimension to the database. Backfilling was introduced in 1985 and several potential spin-offs were expected. These included improved local strata control for fall of ground and rockburst conditions, regional benefits in rock mass stability and mine ventilation optimisation.

Jan 1, 1998

A form of wet pelletization is described where the bridging of the individual particles is achieved by a second liquid phase that pref- erentially wets the suspended solid particles. The phenomenon can be used to obtain efficient separation of solids from carrier liquids, to form spheres from finely divided solid materials, and to separate selected constituents from a body of mixed solids. Typical examples of each of these applications are presented.

Jan 1, 1974

By G. A. Hayes

The range of gold ores tested at AMMTEC LTD over several years has resulted in the requirement to analyse for the mode of occurrence of gold in order to assist selection of ore processing options. The aim of this paper is to describe the laboratory testwork and analytical procedures which have been of benefit in detail­ing the mode of occurrence and mineral associations of gold and hence being of value in developing an optimised ore processing route. The range of ore and mineral assemblages described include relatively simple pyrite and free milling ores, more complex pyrite plus arsenopyrite gold ores and the quite com­plex associations of gold in copper bearing ores or with car­bonaceous mixed sulphide ore assemblages. The aim of this paper is to describe the laboratory testwork and analytical procedures which have been of benefit in detail­ing the mode of occurrence and mineral associations of gold and hence being of value in developing an optimised ore processing route. The range of ore and mineral assemblages described include relatively simple pyrite and free milling ores, more complex pyrite plus arsenopyrite gold ores and the quite com­plex associations of gold in copper bearing ores or with car­bonaceous mixed sulphide ore assemblages.

Jan 1, 1996

By R. L. Loofbourow

Reasons for reexamining underground mining include: 1. The assurance that more deep deposits of useful minerals will be found. 2. The existence of deeply covered deposits of industrial minerals near large markets where quarries are becoming depleted or are lacking. 3. Surface property values, zoning and other limitations on open pit mining. 4. Expectation that underground space will be increasingly used for transportation, power plants, storage and similar purposes. 5. The improvements which have been made in underground mining. During the last three or four decades many changes and improvements have been made underground. All underground construction and mining has benefitted to some extent but the effect on the productivity of labor employed with some methods- has changed little and the use of these methods has declined. Productivity of labor in other methods has increased substantially. The relative usefulness of mining methods has changed and a vital industry, bituminous coal, has been returned to health. In this paper, consideration is limited to nine methods used with high productivity during the period under review. These methods are not necessarily better than others but they may be considered the prime methods in the sense that, in our economy, many, low grade ores, coal and the principal industrial minerals could hardly be produced by less productive means.2 Although most of the examples cited are from mining as such., the first four methods discussed can be used for the construction of stable excavations of various' shapes in sound rock.

Jan 1, 1967

By Adriana de Aquino Soeiro da Silva, Joao Alves Sampaioa, Luiz Carlos Bertolino, Francisco Manoel Garrido, Marta Eloisa Medeiros

"Brazil has a large agricultural potential and its production success is related to the chemicaland physical soil characteristics. Therefore, the demand in the use of a great quantity offertilizers to compensate the low amount of nutrients in the soil includes about 40% of foodproduction costs. In order to develop economical alternatives to traditional fertilizers, rockswith potential use in agriculture will be studied. In this work the potassium rock, a greensandslate, will be chemically and structurally characterized for the development of a potassiumthermophosphate. This alternative fertilizer will be obtained based on a fusion of a ponderedmixture of potassium, magnesium and phosphate rocks to be applied in the Brazilianagriculture. Preliminary characterization results indicate that the greensand slate presents ahigh percentage of glauconite, quartz and micas.Keywords: Potassium thermophosphate, alternative fertilizers, greensand slate.IntroductionBrazil has a great agricultural potential and its production success is closely related to thesoil's chemical and physical characteristics. However, the country's soils present lownutrients content and high acidity due to weather conditions. Thus, the use of a high amountof fertilizers makes up for the soils' lack of nutrients and accounts for 40% of food productioncosts. Therefore, research on obtaining new alternative fertilizers is a constant worry due tothe increase on food demand [ 1].The lack of raw material for the preparation of NPK fertilizers in Brazil is a concern and theissue of potassium fertilizers a priority. Such a fact is because in 2008 only 608.000 tons ofKCl were produced, corresponding to just 10% of the Brazilian necessity. Thus, the use ofrocks as agricultural nutrients can contribute to reduce the need for industrial fertilizers.This way, the development of a new agricultural raw material originated from a rock thatalready exists in the country's soil is of great importance for the mineral and agriculturalsectors."

Jan 1, 2011

By L. S. Castleman, H. A. Froot

A study was made of the growth kinetics of B-brass layers in a-brass us y-brass diffusion couples in which both phases were saturated in the 6 phase. It was found that useful estimates can be made of the difhsion coefficients at the ß-phase interfaces from interface displacement data, which are relatively easy to measure experimentally; also, a useful estimate can be made of the mean heat of activation for diffusion from layer growth data. The effects of pressure on layer growth kinetics were explored and found to be consistent with a vacancy model for diffusion in 6 brass in both the disordered and ordered temperature range. 1 HE study of multiphase diffusion receives relatively little attention in comparison with that devoted to diffusion in homogeneous materials. Of the hundred or so papers on diffusion written each year,' only a few are devoted to the subject, and it is the rare review article2,3 that devotes any space to multiphase diffusional phenomena. This is unfortunate, since the metallurgist frequently encounters practical situations involving cementation processes such as cladding, protective coating of metals, and so forth in which he needs guidance of a fundamental nature. The investigation of multiphase diffusion phenomena is complicated by the fact that one must consider reactions at phase interfaces as well as the migration of atoms within the individual phases; these reactions cause the interfaces to be displaced within the diffusion zone. The relative displacement of two adjacent interfaces corresponds to the growth of an intermetallic layer, and it is not difficult to determine experimentally the kinetics of layer growth. In the past few years it has been pointed out4,5 that valuable fundamental information may be gained about diffusion coefficients and the concentrations at interfaces through a study of their motion. Accordingly, it is the purpose of this paper to report the results of an investigation of interface motion in a simple multiphase binary system. In the work reported herein, attention was focussed on the growth of a 6 -brass layer in a diffusion couple prepared from a- and y-brass compositions saturated with respect to the 6 phase. This particular system was chosen for a number of reasons. First, the bcc ß-brass phase is disordered for all compositions at temperatures above 468°C and becomes increasingly long-range ordered for all compositions at temperatures below 454° C;6,7 thus, the effects of a variation in order on interface displacement could be determined. Second, diffusion coefficients have already been obtained as a function of temperature in the ß phase both in the ordered and disordered Re- and a theoretical picture of the mechanism of diffusion in this and other ordered solutions is emerging.11'12 Third, some thermodynamic data are available for the a-, ß-, and ?-brass phases,13,4 and these data could be used to gain insight into questions of phase equilibria and concentrations at phase interfaces.

Jan 1, 1963