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By Robert E. Barieau

In the design of plants to separate helium from natural gas , it is necessary to estimate the enthalpies of the various streams at various positions in the process . This Bureau of Mines report surveys the various methods that have been used to determine enthalpies and gives information on the organizations with such capabilities . The minimum information required for developing an enthalpy diagram is presented , and the relative merits of the various methods are discussed . It is concluded that methods that require no mass flow rate or energy measurements are to be preferred .

Jan 1, 1965

By R. A. Govender, A. Mudau

"Rockbursts continue to be a major contributor to mine accidents and cause of damage to mine excavations, particularly at great depth. The problem of rockbursts has also escalated in civil engineering tunnels driven at depth, due to high levels of in situ stress at such depths. Attempts have been made in the past to mitigate the impact of rockbursts, with rock support remaining the ultimate method for providing stability in rockbursting environments. However, records show that, on many occasions, conventional support elements such as rockbolts, wire mesh, shotcrete, and lacing fail to withstand severe rockburst events.Recently, a support method termed ‘sacrificial’ support was proposed as a potential additional method to prevent rockburst damage, based on observations made after rockburst events in a mine. The philosophy behind a sacrificial support system is that, under dynamic loading conditions, support in the form of a liner must fail; leaving behind, undamaged, what was previously supported rock mass. The sacrificial support concept reported herein is applicable in situations where the source (i.e. seismic event) of the rockburst is located remote from where rockburst damage is likely to occur.Spalling tests based on the split Hopkinson pressure bar (SHPB) technique were conducted to study some aspects of dynamic rock fracturing in tension at high strain rates and the role a sacrificial layer plays in combating dynamic rock failure. A single Hopkinson pressure bar, with a long cylindrical intact rock specimen attached at the bar free end, was impacted by a striker on the opposite free end in order to generate a dynamic stress pulse responsible for spall failure upon reflection from the specimen free end. Different liners and liner combinations were then introduced at the specimen free end as support. Such a simple, yet robust, experimental set-up allowed the potential benefits and failure mechanisms associated with sacrificial support under dynamic loading to be demonstrated and compared with ‘sacrificial support’ behaviour observed in real rockburst events in a mine. Analysis of the results revealed that varying liner thickness and mechanical impedance between rock and support liner play a significant role in limiting rockburst damage."

Jan 1, 2016

By Prasad S. Mulukutla

INTRODUCTION The use of specialty chemicals In mining Is an Important consideration In determining the economic efficiency of a floatation plant. The plant metallurgist would like to maximize the recovery of valuable minerals while maintaining an acceptable grade product. The direct cost of the reagents, while significant, Is only a part of their economic effect. Reagents determine the flotation rates and the selectivity of the mineral separation. In flotation practice, mineral selectivity can be achieved through the addition of various reagents that can control the wettablllty of a particular mineral In the flotation pulp. The reagents which will generally optimize the flotation process are commonly classified Into three distinctive categories: collectors frothers and modifiers. Large tonnages of metal sulphide concentrates which are the source of most of the common base metals are produced economically by fairly standard flotation techniques. The advent of modern technology coupled with the necessity of processing finely disseminated and complex ores of low grade has Increased the need for utilization of non traditional and high selective chemicals reagents for the economic recovery of metals and raw materials. Mining operations in developing countries continue to progress at a rapid growth as many countries mine and process both metallic and nonmetallic ores. The total mine production of base metals, precious metals, Iron ores and coal In developing countries In Africa, Asia and South America has been much higher as compared to the western world production In terms of tonnage and dollar value. Global capital Investments In mining during 1991-95 Is $ 55.1 billion and It Is anticipated that the development of new and specialty reagents may be concentrated In the processing of aluminum , copper, precious metals and Industrial minerals with special reference to potash, phosphates, kaolin and silica sands.(1) The challenge for the design and development of new specialty chemicals Is dependent on Its cost performance and environmental acceptability. Information on the theory and application on the development of mining chemicals has been reviewed In several conference proceedlngs,(2-4) publications(5) and also discussed by several Individual authors.(1,6-10) These publications serve as a comprehensive reference source on the reagents used In several flotation processes. This paper discusses the present trend in the use of specialty mining chemicals In diversified mining operations on several mineral systems with particular reference to sulfide ore systems. The necessity to expose these specialty chemicals through aggressive marketing techniques In mining operations In many developing countries Is also presented. SPECIALTY CHEMICALS Specialty mining chemicals, like other specialty chemicals, share common business characteristics that transcend geographic boundaries. They are manufactured 1n a few selected areas, generally expensive relative to commodity chemicals, shipped and compete globally and usually require specialized knowledge for proper use. Specialty mining chemicals are relative newcomers to chemical markets. The vast majority of mining chemicals are derived from products that are less than two decades old. Traditional collectors and frothers have been available for a considerably longer time. The emphasis on adding value to existing products and byproducts Is responsible for several characteristic features of the mining chemicals business. Most raw materials for these chemicals are related to oil and gas byproducts, chemical refineries, pulp and paper mills and all chemical manufacturers. Until the last several years these operations were located In Industrialized countries, while a significant number of mining chemical users were In developing countries. Therefore International trade In mining chemicals developed through agencies or agents in each particular country.

Jan 1, 1993

By J. W. Downey, J. B. Darby, L. J. Norton

THE only previous investigation of the phase equilibria in the Ta-Pd system was reported by Greenfield and Beck.1 Their work (actually a portion of a much broader survey) was limited to the composition range 50 to 75 at. pct Ta and to a single temperature, 1000°C. The results indicated that no intermediate phases were present at this temperature. They pointed out that this was an unexpected result in view of the fact that niobium, which belongs to the same group in the periodic table as tantalum and has essentially the same atomic size, forms a o phase with palladium.' Also, tantalum in combination with rhodium,' iridium,' or platinum' stabilizes the s phase. By analogy, the Ta-Pd system would also be expected to contain a s phase. The present investigation was therefore undertaken to explore more fully the phase relationships in this system. Alloys were prepared by arc melting on a water-cooled copper hearth in an argon-helium atmosphere. The purity of the starting materials was greater than 99.9 pct. The weight losses on melting were less than 1 pct and therefore the alloys were not analyzed chemically. Specimens were wrapped in molybdenum foil, encapsulated in quartz capsules under a vacuum of at least 1 x 10-5 mm of Hg, annealed as indicated in Table I, and water quenched. Optical and X-ray metallography were used for identifying the phases present in the annealed and quenched alloys. The alloys were resistant to attack by several acids; however, a sodium cyanide electroetch and an immersion etch containing 1 part HF, 1 part HNO3, 2 parts H2SO4, and 5 parts H2O by volume were found satisfactory. The X-ray diffraction patterns were taken with a Straumanis-type Debye-Scherrer camera and filtered copper or chromium radiation. A summary of the phases found in this investigation is presented in Table I. No attempt was made to determine the composition limits of the various phases. The present results indicate that this system consists of two terminal solid solutions separated by at least four intermediate phases at the approximate compositions Ta3Pd, -TaPd, TaPd,, and TaPd3. The Ta-rich solid solution, containing less than 10 at. pct Pd at 1150°C, is in equilibrium with a o phase which is stable in the vicinity of 25 at. pct Pd. The latter phase is also in equilibrium with a bct phase at the equiatomic composition. At high temperatures it appears that the Pd-rich solid solution extends to at least 66.6 at. pct Pd and is in equilibrium with the bct phase. When annealed at 900°C, a sample containing 66.6 at. pct Pd transformed to an unidentified phase designated as X. An X-ray diffraction pattern of this phase contained sharp low-angle lines while the high-angle lines were characteristically diffuse. The observed d-spacings and relative intensities for lines in the low-angle region are presented in Table 11. In the vicinity of 70 at. pct Pd an intermediate phase having the TiA13-type structure is formed. It is stable to at least 1100°C, and presumably dissolves congruently into the ter-

Jan 1, 1963

By M. B. Bever, A. B. Michael

THE structure of cast A1-Si alloys is altered profoundly by modifying agents. Sodium, in particular, reduces the size of the silicon particles in the eutectic and tends to change their shapes from plates to nearly rounded grains. This refinement is accompanied by a shift of the eutectic to higher silicon concentrations and lower temperatures. Similar effects can be attained by rapid solidification. Hypotheses advanced to explain modification have involved the formation of a ternary eutectic,1 the removal of oxides by fluxing,' and even a presumed allotropic transformation of silicon. Other hypotheses assume that the modifying agent causes an envelopment of the silicon particles by the aluminum-rich solid solution, but attribute this envelopment to different mechanisms. According to various explanations, the growth of the silicon particles is obstructed by an immiscible sodium-rich liquid," an adsorbed layer of sodium,' or a ternary compound;5 his obstruction has been conceived as purely mechanical or as a colloidal action.' It has also been proposed that sodium reduces the surface tension on the Al-Si interface, thus permitting the aluminum-rich solid to grow faster and to envelop the silicon particles.? Still other hypotheses stress undercooling and the attendant change in the rate of nucleation of silicon, but fail to ascribe any definite function to the sodium addition." '" Procedure High-purity alloys of aluminum and 3 or 7 pct Si were treated with modifying agents containing radioactive sodium tracers. The experiments were intended to investigate the partition of sodium between the primary aluminum-rich solution and the eutectic, and, if possible, to determine whether sodium is concentrated in or around the silicon particles in the eutectic. Radioactive sodium fluoride, alone or mixed with stable sodium chloride, was allowed to react with the alloy for 5 min immediately before solidification in the crucible. Modification could not be attained with additions of less than the equivalent of approximately 0.1 pct Na. Some alloys were not completely modified, but comparison of the structures of treated and untreated specimens indicated a very considerable reduction in particle size of the silicon in all of the former. A treated alloy is shown in Fig. 1. Radioactive sodium fluoride was prepared by bombardment with deuterons having an energy of 14 mev. This bombardment (totaling, for example, 6 microampere-hours in one run) produced radioactive Na24 (half-life 14.8 hr) by the reaction 11Na23 (d,p) 11Na24. The radioisotopes of fluorine also produced have short half-lives and were not detected. A half-life determination by counting confirmed that the measured activity was due to Na24. The distribution of the sodium in the solidified alloys was determined by an autoradiographic technique by which a suitable stripping film is attached to a very thin metallographic specimen. After exposure and development, this emulsion remains superimposed on the specimen and may be examined microscopically or photographed by reflected light. The emulsion of the autoradiograph can be correlated directly with the underlying surface by simple adjustment in focus. The details of this technique have been described elsewhere." Results Fig. 2 is a micrograph of the autoradiographic emulsion ("autoradiograph") lying directly above the area of eutectic in Fig. 1. Fig. 3 shows a similar autoradiograph of a region consisting of primary solid solution. The small black dots (tracks) in these autoradiographs are developed grains in the emul-

Jan 1, 1954

By Robert Klug, Nils Engelke

"In order to extract proportionately small quantities of valuable minerals, mining companies move large amounts of earth. A resulting waste product of this process has traditionally been stored in a semi-liquid phase known as tailings, typically stored in a large pond created by an earthen dam at the low end of a drainage basin. It is generally expected that these dams are stable enough to withstand the pressure of the stored material. Unfortunately, history shows us that this is not always the case. The Baia Mare dam in Romania failed in 2000, causing tragic and prolonged environmental damage to several major European rivers. The Bento Rodrigues dam in Brazil failed on Nov. 5, 2015, and that event resulted in the loss of 16 lives.In hard rock mining, many minerals are imbedded within the ore. As part of the mining process, valuable minerals are extracted from the ore; often, the mineral content is only a fraction of the total ore volume processed. To extract the minerals, the ore is typically crushed and pulverized into very fine particles, then wetted to form slurries. The minerals are extracted from the slurries through a series of flotation and/or sedimentation steps with the aid of water-soluble separation chemicals typically known as reagents. Following the mineral extraction, the resulting residual wetted ore cuttings are labeled as tailings. At the end of the extraction process, the tailings are in a thick semi-fluid sludge state, often with trace elements of the extraction reagents.Historically, these tailings are deposited in giant basins or sludge ponds, where they pose a great threat to the environment while binding large volumes of waste process water.Process water recovery and achievingdry tailingsCurrent generation engineering studies, trials and successful field implementation have shown that an alternate process known as dry stacking is practical. The dry stacking process deposits dewatered tailings into containment areas that are smaller in overall footprint and significantly safer by reducing the transfer of reagents into the tailings storage area. In addition to achieving the dry tailing benefits mentioned, it is possible to recover valuable process water while dewatering the tailings sludge utilizing modern separation technology."

Jan 4, 2018

By Michael Brittan

For several years, Independence Mining Co. (IMC) has routinely used oxygen fluid-bed roasting to pre-oxidize refractory gold ores ahead of conventional carbon-in-leach (CIL) processing. Oxygen serves jointly as the fluidizing medium and the combustion gas. This technology has proven to be reliable, environmentally sound and cost-effective. IMC is a subsidiary of the Minorco group. The company operates the Jerritt Canyon (a joint venture with FMC Gold) and Big Springs gold mines in the Independence mountain range north of Elko, NV. Ore bodies in the range contain characteristic refractory ore. It requires pre-oxidation ahead of conventional CIL processing. This article describes the technology developed specifically to treat these difficult ores.

Jan 1, 1995

By J. A. C. Diering

The simulation of mining in faulted ground was recently described by Crouch. His method is extended here to enable a wide range of non-homogeneous mining problems to be modelled. Essentially, the boundary conditions at geological interfaces are incorporated into the overall iterative solution, which is necessary if faults and joints are to be modelled realistically. Two examples are given to demonstrate the method: the mining of coal a seam below a thick dolerite sill, and the mining of a flat reef in close proximity to a vertical fault where hangingwall and footwall rocks have different properties.

Jan 1, 1980

By Dale Verran, Jared Orynik, Chad Sorba, David Bronkhorst

Denison Mines Corp. (“Denison”) has a 90% interest in the Wheeler River Uranium Project (“Wheeler River”) located along the eastern edge of the Athabasca Basin in northern Saskatchewan between the Key Lake mill and the McArthur River uranium mine. The project is host to the high-grade Phoenix and Gryphon uranium deposits, discovered by Denison in 2008 and 2014 respectively, which include combined Indicated Mineral Resources of 132.1 million pounds U3O8 (1,809,000 tonnes at an average grade of 3.3% U3O8). The Pre-Feasibility Study (“PFS”), completed in accordance with NI 43-101 in September 2018, is highlighted by the selection of the In-Situ Recovery (“ISR”) mining method for the development of the Phoenix deposit, with an estimated average operating cost of $4.33 (US$3.33) per pound U3O8. Phoenix is the highest-grade undeveloped uranium deposit known globally, including Indicated Mineral Resources of 166,000 tonnes at 19.1% U3O8 for 70.2 million pounds U3O8. The paper aims to provide a summary of Wheeler River and an overview of the proposed development of the Phoenix and Gryphon deposits according to the PFS completed for the Project. Further details regarding the PFS, including additional scientific and technical information are described in greater detail in the NI 43-101 Technical Report titled "Pre-Feasibility Study for the Wheeler River Uranium Project, Saskatchewan, Canada" dated October 30, 2018 with an effective date of September 24, 2018. A copy of this report is available on Denison's website and under its profile on SEDAR at www.sedar.com and on EDGAR at www.sec.gov/edgar.shtml.

Jan 1, 2020

By R. D. Caudle, Yoginder P. Chugh, V. K. Agarwala

Longwall coal mining is a growing mining technique in the United States. However, very little premining exploration data are collected presently by coal companies to 1) select coal winning equipment, 2) select and design face supports and supports in gate and tail entries, or 3) optimize operational parameters such as length, width, and orientation of face. The authors are of the opinion that much of the data needed for mine planning and design for longwall mining can be obtained during exploration. In this paper, the authors identify the data requirements, discuss how these data can be obtained during exploration, propose an exploration program and estimate the cost to obtain the necessary data.

Jan 1, 1982

By Dimitris Pachakis

In this paper, the authors give a brief overview of the current practice guidelines and tools for the seismic design of sheet pile quay walls, emphasizing how the design guidelines are lacking when the existing structure performance evaluation is required to meet performance-based criteria. Relying on recent experience they explain how the existing practices can be amended to focus more on performance evaluation as opposed to design. An example is given of an old sheet pile quay wall analyzed and evaluated for its performance according the recent performance criteria devised for Californian Marine Oil Terminals.

Jan 1, 2011

By U. S. Geological Survey

In 2025, the estimated total value of nonfuel mineral production in the United States was $112 billion compared with $106 billion in 2024. The estimated value of metal production in 2025 increased by 13 percent to $38.1 billion from a revised total of $33.6 billion in 2024. The total estimated value of industrial minerals production was $73.7 billion, 2 percent more than the revised total of $72.2 billion in 2024 (Table 1). Increases in production of certain nonfuel mineral commodities, along with increases in prices of some industrial minerals contributed to the overall increase in the total value of domestic nonfuel mineral production in 2025. For the industrial minerals sector, the production value of natural aggregates, which comprised approximately 60 percent of the total production value of all industrial minerals, increased by 4 percent even though production volumes decreased by 1 percent in 2025 compared with production in 2024. The largest percentage increases in production value in 2025, in descending order, were for dimension stone, wollastonite, potash, mica and portland cement. The largest percentage decreases, in ascending order, were for high-purity quartz, industrial sand and gravel, lithium carbonate, bromine and boron. For the metal sector, production decreased for several mineral commodities and prices decreased for several metals due to oversupply. Lithium, manganese and nickel had some of the largest percentage decreases in production value.

May 1, 2026

By Liam Bussey, Graham Speirs

Si bien la automatización de plantas de proceso es quizás la norma actual en la minería, la adopción de esta en la minería subterránea se ha retrasado. En este artículo se compartirán algunas ideas de cómo implementar los sistemas de automatización en la mina subterránea y se explicará cómo la tecnología puede mejorar la operación, de manera que las minas sean más seguras y sus operaciones más competitivas. Se discutirán diversos aspectos tales como los sistemas de comunicación, los sistemas de seguridad, los equipos de producción, los servicios mineros y la gestión de operaciones.

Sep 20, 2019

By Antonio Fernández, Javier Cáceres, Enrique Ramírez, Camila Yepez

El sector minero es una de las pocas industrias que depende de los precios de mercado para producir. Por lo cual, mantener ventaja competitiva y garantizar la eficacia del proceso para alcanzar las metas propuestas por la empresa minera representan un desafío constante. Esta investigación tecnológica tiene como objetivo maximizar la eficacia en los procesos de transporte y perforación manteniendo los costos más bajos en su proceso productivo. La investigación presentó dos desafíos durante la etapa de prueba que fueron la especialización del personal y modificación progresiva de los equipos para cada actividad específica.

Sep 30, 2022

By Edwin M. Chance

EDWIN M. CHANCE, Wilkes-Barre, Pa. (communication to the Secretary*).-I have read with great interest Mr.. Liebermann's paper reporting dynamometer tests of mine cars and wish to express my appreciation of this investigation. The coal-mining industry needs just such precise study of the problems with which it is confronted.

Jan 10, 1916

By F. O., Garrabrant

ELECTRIC power requirements for Climax are similar to those of most metal mines, except that large blocks of power are used underground and there are a number of other unusual applications. Power is furnished to the Company by the Public Service Co. of Colorado over two 100,000-volt lines to a bank of three 3333-kva. transformers 100/13.8 kv. These transformers are designed so that with the addition of forced cooling their capacity may be increased a third at 12,000-ft. altitude. On the secondary side of this bank is a 15-kv., 1200-amp. oil circuit breaker provided with automatic reclosing relays allowing three successive short circuits before lockout. From this breaker 13.8-kv. power is transmitted to a central switching station where all circuits radiate to the different operations of the property. Each circuit is protected by a 23-kv., 600-amp. oil circuit breaker with by-pass and isolating disconnecting switches. (A more complete description of the electrical distribution system at Climax, with detailed drawings, is contained in T.P. 1734, A.I.M.E., Mining Technology, July, 1944.)

Jan 1, 1946

By Patricia Negrini Siqueira

Abstract. Polymers are susceptible to changes in their chemical structures that affect their mechanical properties under weather condition. Exposure of plastics to UV radiation causes a loss in their mechanical properties and/or change in appearance, including reduced ductility, color changes, yellowing and cracking. Today, there are several additive systems (light stabilizers) developed to work according to resin, final application, type of cultivation, and other characteristics. This study evaluates the different additive systems (Hindered Amine Light Stabilizer - HALS, nano calcium carbonate - NPCC, nZnO and nTiO2), applied 0.75% (in weight) in linear low density polyethylene (LLDPE). The samples were mixed by high rotation homogenizer and extrusion. Later, the samples were molded by injection and aged in QUV-B simulating 6 months of exposure to weather. Tests of FT-IR and tensile strength comparing to the non-aged samples were carried out in order to evaluate the performance of several additive systems.

Jan 1, 2015

By Che, C. W. Spencer, C. A. Steidel, Yu Li

Grain boundary grooving as it occurs in a 5.5-deg simple-tilt nickel bicrystal immersed in a saturated Ni-S liquid has been studied. A 1/3 (t= time) dependence for the depth of the groove indicates that the rate -controlling meckanism for groove developvnent is volume diffusion in the liquid. The activation energy for the diffusive process is estimated at 15 kcal per mole. Using an extended form of W. W. Mullins&apos; analysis for grooving reactions, a computer is employed to fit the appropriate diffusion equation by a numerical method. From the analysis a possible method of measuring L.S. the solid-liquid interfacial tension is demonstrated. WHEN a polycrystalline solid is heated in equilibrium with a saturated fluid phase, grooves will form at the intersections of the grain boundaries and surface. The equilibrium root angle of these grooves is determined by the balance between the grain boundary and solid-fluid interfacial tensions. The grooves deepen and widen with time due to a difference in chemical potential between the flat interface and the curved interface of the groove. In this investigation solid-liquid interaction at a grain boundary is studied, with the object to determine the mechanism of grain boundary grooving in the presence of a saturated liquid. Extension of Mullin analysis then permits the estimation of the solid-liquid interfacial tension. Herring has demonstrated by dimensional analysis that the quasi-steady state change of the dimensions of a small particle during sintering is proportional flow, evaporation-condensation, volume-diffusion, and surface-diffusion mechanisms, respectively, if geometric similarity of consecutive configurations of the particles holds. Mullins has extended this analysis to grain boundary grooving. In the case of shallow grooves he solves the diffusion equations for evaporation-condensation, volume-diffusion, and surface-diffusion mechanisms, and obtains the same time dependence for any linear dimension of a groove as Herring found for the change in dimension of small particles. In Mullins&apos; analysis2&apos;3 grain boundary grooving of a bicrystal by volume diffusion in the presence of a saturated fluid phase was considered. Several assumptions were made prior to the analysis: 1) the solid-fluid interfacial tension is independent of crystallographic orientation; 2) the Gibbs-Thompson equation relating curvature and chemical potential is applicable at the solid-fluid interface; 3) the relaxation time of the diffusion field is small compared with the time for appreciable changes in the curvature of the groove, so that the diffusion is divergence-less; and 4) the groove has a small slope relative to the initial flat interface. Usually this last condition is fulfilled only for solid-gas systems. The solution of the diffusion equation under the above conditions produces a t1/3 dependence for any linear dimension of the groove in the case where volume diffusion is rate-controlling. The t1/3 dependence is valid because geometric similarity of the grooves exists for all time. EXPERIMENT In the experiment a 5.5-deg nickel bicrystal of <100> simple-tilt orientation was used.4 Grooving was studied in the presence of a saturated Ni-S liquid alloy as a function of time at 750°, 800°, 850°, and 900°C. A low-angle bicrystal was chosen for study to insure that 2L.S. > .b., where l.s.

Jan 1, 1964

By O. A. Bascur

The lack of integration of mining and metallurgical information with sufficient detail for analysis causes inefficient operation and hence sub-optimal energy and water use. It is difficult to analyze the performance of mining and metallurgical processes without an integrated view of mine transactions, stockpile inventories, process flows and assays. To take action requires real time information from manufacturing assets, corrected for gross errors from trucks, shovels, conveyors, faulty sensors, bad instrument calibration. This paper presents an infrastructure with advanced tools that sift through available data, identify and eliminate gross errors, and transform the data into business information for continuous improvement and optimization. Collaboration is a key component of improving efficiency of energy and water use, and the evolution of Web technology enables collaboration and troubleshooting of plant information to more quickly act on issues to reduce wasteful operation. Keywords: Mine Concentrator Optimization, Real Time Performance Management, Data Unification, Integration of Operational and Business systems, Mass and Energy Balances, Real Time Web Services, Equipment Availability, Efficiency.

Jan 1, 2009

By D. T. Peters, C. R. Cupp

Aging of commercial 18 pct Ni maraging steel and of related binary, ternary, and quaternary alloys has been studied by electrical resistivity, X-ray diffrac-tion, and hardness measurements. The aging process is in three stages: 1) recovery of martensite; 2) two precipitation reactions; 3) formation of nickel- rich austenite. The main objective of this work was to discover the nature of the Co-Mu interaction. Addition of cobalt to the Fe-18 pct Ni-5pct Mo alloy results in acceleration of the pvecipitation reaction by increasing the super-sat~lration 0f molybdenum. The cobalt-containing al- loys show no incubation period for the precipitation reaction, but the alloy without cobalt shows an initial slow reaction. These results are interpreted in terms of precipitation on dislocations. At low aging temperatures, the presence of cobalt leads to the appearance of a second type of precipitate which is a particularly effective hardener. Cobalt was found to retard the formation of austenite. Overaging is a combination of classical overaging and the formation of austenite in the structure. he- activation energy for the precipitation reaction determined from resistivity ,measurements is 42.8 kcal per mole and the growth of the precipitate is found to obey at law at high tenzperatures and a tU3 law at low temperatures. HE mechanism of strengthening of the 18 pct Ni maraging steels has been studied extensively since 1962.&apos;-? The strengthening is due to precipitation hardening of the martensitic matrix. The main precipitate is an inter metallic compound involving molybdenum, but there is disagreement about its identity.

Jan 1, 1967