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By Real Daigneault, François Robert, J. Paul Golightly, Jean-Yves Cloutier, Jayanta Guha, Pierre Pilote

"The Casa-Berardi East, Center and West deposits, located in the Archean Abitibi, Sub province, are hosted by volcanic and sedimentary units of varying compositions, less than300 m from the Casa-Berardi fault (CBF). The CBF, a brittle structure, represents an increment in the structural evolution of a regional-scale deformation zone showing ductile-brittle behavior known as the Casa-Berardi deformation zone (CBDZ). The CBDZ is characterized by a mylonitic Sc1 foliation which is folded a.n4 deformed by a later sczfoliation in high strain zones.Four generations of quartz vein and fracture systems have been recognized within the Casa-Berardi deposits. Most economic gold mineralization, occurring in the second generation system, is found within high strain zones. This system hosts three types of mineralized structures: (1) banded quartz veins; (2) swarms of veins and mineralized host rocks; and (3) disseminated sulphides along fractures. An early carbonate hydrothermal alteration zone (pre- to syntectonic) surrounds the deposits. Alteration associated with gold mineralization is contemporaneous to late ( syn- to post-tectonic) relative to the development of progressive deformation in the CBDZ. The geological characteristics and paragenesis of the four quartz vein and fracture systems developed as an integral part of the geodynamic evolution of the Casa-Berardi deformation zone."

Jan 1, 1990

By P. S. Daly

"The purpose of this paper is to describe the types of instrumentation used at Sherritt Gordon's Ruttan Mine to monitor the"" effects of mining. The aim of the monitoring program is to establish parameters to achieve a maximum ore recovery with minimum dilut ion in a safe environment.The copper-zinc Ruttan Mine is in northwestern Manitoba, approximately 760 km from Winnipeg (Fig . I) . Production commenced in 1973 from the open pit at the rate of 10,000 tons per day. Pit bottom lies 58 metres above the first mine level. Underground development has overlapped with open-pit mining throughout. The open pit was phased out in the latter part of 1980.Underground production began in early 1979. The mining method employed in the first lift is sub-level blasthole open stoping with delayed hydraulic filling. Large-diameter (6.5-in.) holes are being drilled in the crop stope area and are also planned for some other areas for vertical retreat mining into a slot. GeologyThe orebody consists of numerous sulphide lenses of variable size, geometry and geology . The lenses occur within volcanoclastic host rocks which exhibit a strong variability in intensity and type of alteration and structural characteristics. Stope design and sequencing were based on these complex geological factors."

Jan 1, 1981

By A. J. Jacobs, J. W. Spretnak, R. Speiser

The activities of nickel in liquid iron-nickel solutions containing from 10 to 90 at. pct Ni were measured over the temperature range .1510° to 1600°C. A special function was devised whereby activities can be computed by a graphical integration using the results of chemical analyses on the vapor phase alone. The liquid solutions studied exhibit negative deviation from Raoult's law, but they approach ideality as the temperature is raised from 1510° to 1600°C. The maximum heat of solution is less than -8.0 kcal per mole. The entropy of solution is less than —2.5 kcal per mole deg at 1510°C, and changes negligibly as the temperature is raised. The liquid iron-nickel solutions do not follow regular solution behavior. THE activities of the components of a liquid alloy system can be determined in favorable cases from the partial pressure of the vapor in equilibrium with the liquid alloy.' Assuming that the vapor over the alloy behaves as an ideal gas, the activity of component i is given by the expression, Where the superscripts 1, v, and o signify the liquid, the vapor, and the pure component, respectively; the f's are the fugacities, and the P's, the pressures. The quantities Pi and Pi can be determined by the

Jan 1, 1960

By G. H. Martindill

Complex chemical and physical changes occurring during carbonization result in a heterogeneous system composed of gaseous, liquid, and solid phases, whose relative proportions and chemical compositions change constantly as temperature increases. Studies in which the participating variables are isolated and controlled should be useful in formulating the mechanism of coal carbonization. The most characteristic property of a coking coal is its ability to form a plastic mass at a certain stage of the carbonization process. During this period it is believed that fluidity of the coal influences the properties of the resultant coke. This report gives results of an investigation by the Federal Bureau of Mines of the influence of the maximum fluidity attained by the charge on the physical quality of the coke or char produced. As a first approach to the problem, researchers investigated high-melting-point pitches, which are relatively simple carbonaceous materials. The plastic properties of these pitches, prepared specially for this work, varied greatly; their fluidities, as measured by the Gieseler plastometer, covered most of the fluidity range characteristic of coking coals. Blending these pitches with increasing pro-portions of fine coke progressively reduced their fluidities. Coal-pitch and coal-coke blends also were treated; their fluidities were varied by changing their blending ratios. The various blends were carbonized in a small-scale carbonizer and the resistance of the carbonized residue (char) to abrasion was determined in a small-scale tumbler test, using the Roga drum.

Jan 1, 1960

By Louis D. Huntoon

The Hammond Mining and Metallurgical Laboratory is the gift of Prof. John Hays Hammond to the Sheffield Scientific School of Yale University. Professor Hammond was graduated from this school in the class of 1876, and has always shown great Merest in its welfare and progress. In 1903, he offered to build and equip for it a mining and metallurgical laboratory. This offer was gratefully accepted by the trustees; and in October of the same year the architect, W. Gedney Beatty, and I were employed to draw up plans for the building, which is the largest of its kind in this country. The Treasurer's report shows the total gift of Professor Hammond, including land, building, and equipment, to have been $128,741.53. This does not include $5,000 given by Professor Hammond to defray incidental expenses. The detailed cost of the machinery and installation, included in the above sum, is as follows: Macbinery,.......$9,846.00 Pipe and fittings,......925.05 Hangers, shafting, pulleys, belts, etc.,.. Steel-work, tanks, launders, etc.,...272.19 Screens for sizing ore,.....411.37 Lumber,.......1,896.36 General Supplies : Hardware,......$135.96 Tools,.......263.66 Paints,.......204.63 Electric and incidental,.... 439.57 ----------1,043.82 Machine-shop material, . 259.44 Labor,.. 722.29 ----------981.73

Jan 1, 1910

By Anna Paula Littig Berger

O objetivo do presente trabalho foi estudar a influência da adição de argônio à atmosfera de redução a plasma sobre a redução de pós de hematita. Os experimentos de redução foram realizados em reator a plasma pulsado DC, sob pressão de 533 Pa, temperatura de 380ºC, tempo de 60 min, fluxo total de hidrogênio e de argônio de 400 cm3/min e variando os teores de argônio e hidrogênio. Os resultados mostram que os aglomerados de partículas após redução possuem um aspecto esponjoso. Verificou-se que o uso de uma mistura gasosa contendo 2% de Ar e 98% de H2 permite um aumento de aproximadamente 7,76% na fração de redução.

Aug 8, 2018

Since the beginning of the computing age, technical software packages have not been developed to address only programming specialists but have been dedicated to process engineers. For process analysis, BRGM is developing and commercializing three packages: ? sampling software: ECHANT 2.0 for Windows ? material balance calculation: BILCO 2.0 for Windows ? steady-state simulator for plant design, adaptation and optimization: USIM PAC 2.1 for Windows This paper deals in a first part with the main features of these three packages. In a second part, advanced models are presented for SAG/ AG mills and flotation columns. An industrial case of application is shown for each of them.

Jan 1, 1997

By S. G. Kumar

The performance of nickel based high temperature materials is directly related to their microstructure, which is controlled by the various processing steps. Nickel base alloys are melted and refined by a variety of processes that include Vacuum Induction Melting (VIM), Vacuum Arc Remelting (VAR) and Electroslag Remelting (ESR). The limitation of VIM is that the metallrefractory reactions lead to the disintegration of the crucible and hence contamination of the product due to macrosegregation. This macrosegregation is alleviated to some extent by controlling the solidification in VAR. The main attraction of ESR is its ability to produce a clean product by controlling the deleterious inclusions. In recent years Electron Beam Melting (EBM) is emerging as an alternative to the VIM, VAR and ESR. This paper reviews the current status of these processes and outlines the scope for further improvements in the processing technology.

Jan 1, 1993

By Robert Snow, Shibo Zheng, Wenyi Song, Xiaoqing Ma, Patrick Zhang

Numerous phosphate mineral depressants have been reported in the literature for use during anionic flotation of dolomite from carbonate fluorapatite in slightly acid circuits. In one part of this research, laboratory flotation experiments were conducted to compare the effectiveness of phosphate depressants to process ground, deslimed high-MgO Florida phosphate pebbles. Ten potential phosphate depressants were evaluated during laboratory anionic flotation of dolomite from phosphate in a slightly acid circuit using a sulfonated oleic acid soap plus oil as the dolomite collector. Eight of the depressants have been used by various investigators with foreign and domestic carbonate-phosphate ores. Four of the depressants were found to be reasonably effective during the current flotation study, namely: sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP), tetrasodium pyrophosphate (TSPP) and diphosphonic acid (DPA). Without depressants, the sulfonate collector required to produce cell underflow phosphate products containing <0.80% MgO and MgO/ P2O5 ratio <.033 was 1.13 kg/ton of flotation feed at a flotation pH range = 5.5-6.0. Using this collector level with 0.91 - 1.36 kg/ton of feed of STPP, SHMP or TSPP yielded phosphate products analyzing 0.73-0.92% MgO and MgO/ P2O5 ratios = .027-.034 at 90.0-96.8% P2O5 recovery. Similar grade phosphate products were obtained using DPA as the phosphate depressant at 84.1-87.5% P2O5 recovery. When no depressant was used, a similar grade phosphate product was obtained at only 65.9% P2O5 recovery. Another part of the research aimed at reducing MgO content in the final concentrate from Florida phosphate plants by conducting dolomite flotation on the final concentrate. Numerous phosphate depressants were tested for this purpose, including acidic, neutral and alkaline reagents. The most effective phosphate depressant was found to be phosphoric acid, giving both high grade and recovery.

Jan 1, 2014

By Antonio Segatori, Bjørn Holmedal, Kai Zhang, Trond Aukrust, Knut Marthinsen

"The visual appearance and mechanical properties of aluminium alloy extrusions are strongly dependent on the microstructure and texture of the extruded profiles, where the desired microstructure and texture may depend on the specific applications. In the present work, the evolution of deformation, as well as recrystallization textures during extrusion of AA6xxx aluminium alloys, have been experimentally and numerically investigated. Extrusion trials were performed in a laboratory extrusion set-up, which enabled immediate water-quenching of the profiles at the exit of the die, and thus the possibility to capture the deformation texture prior to post-extrusion recrystallization. The textures and their through-thickness variations were experimentally measured by the electron back-scatter diffraction technique (EBSD, and the deformation textures numerically modelled by coupling FEM flow simulations and crystal plasticity (CP) simulations. Different CP models as well as different choices of model parameters were employed and evaluated for texture predictions. With an appropriate choice of crystal plasticity model and model parameters, the deformation texture can mainly be predicted, although the accurate intensities are hard to reproduce. The corresponding recrystallization textures, either generated through spontaneous recrystallization of the extruded profiles or through post-extrusion annealing, are far more challenging to reproduce with available recrystallization models.INTRODUCTION Extrusion is a widely applied thermal-mechanical process to produce aluminium profiles. The properties of the profiles, for example mechanical, fatigue, fracture, corrosion as well surface appearance, are strongly dependent on the underlying microstructure and texture, and the requirements with respect to these aspects may vary with applications (Ralston et al., 2010; Dumoulin et al., 2012; Donati et al., 2013). Moreover, it is often a challenge to produce extrusions with a consistent and homogenous grain structure and texture along as well as through the cross section of the profiles. It is thus vital to understand and be able to predict (model) how different microstructures and textures are formed and how they evolve during and after extrusion, as basis for controlling the final appearance and properties of extruded profiles."

Jan 1, 2018

By C. K. Leith

OTHERS here are far better qualified than I to discuss some of the specific proposals for government regulation of the oil industry. I shall make no attempt to carry oil to Oklahoma. The question of public control, however, is inherent in other branches of the mineral industry in varying degrees, and my comments will be directed mainly toward some of the trends affecting the mineral industry as a whole, as a background for your more specific consideration of oil legislation. A proud American tradition has been the insistence on freedom of competition, on equality of economic opportunity, on a policy of laissez faire. Nowhere has this principle been given wider application than in the mineral industry. The mineral field has been open to all comers, and the job of mineral exploitation has naturally attracted daring and independent spirits. The laws governing conditions of discovery and development, as well as the anti- trust laws, have been devised to foster the spirit of private initiative. The result has been the building of a mineral industry on a scale never before approximated anywhere in the world. The impetus thus gained, the methods, the technique, the financial resources, have been projected be- yond our boundaries and have made the American mineral industry the purveyor to the world for many essential commodities and first in the exploitation of the world&apos;s minerals. Our habits of individual self-reliance and success are deeply ingrained, and there is hardly an individual in the entire mineral field who does not instinctively recoil fro111 the extension of collective control, whether public or private.

Jan 1, 1932

By G. E. Rowan

"DURING the dark ages, the cherished dream of chemists was to find a process for converting base metal into gold. Many a wealthy-but-gullible patron lost a fortune in the search. Men who work with metals today are a bit more realistic. I haven't heard of a metallurgist who expects to develop any one alloy that will resist all corrosive media. In the field of stain-less steels, there are about forty different types of alloys that are used where corrosion is a •problem.A stainless product is ordinarily selected because it offers one or more of the following qualities:(1) Resistance to corrosion (2) Resistance to oxidation at high temperatures (3) Good mechanical properties at room temperature (4) Good mechanical properties at high or low temperature (5) Attractive appearance (6) Ease of maintenanceToday we are interested in discussing the stainless steel family of alloys because of their .ability to resist corrosion. We• will not try to explain the Theory of Corrosion. Let us assume that, when surface potential and oxide formations are properly controlled, iron will resist attack in various chemi.cal solutions. The addition of alloying elements to iron does this for stainless steels. The principal stainless alloys used by various Canadian industries are listed in the accompanying Table."

Jan 1, 1959

By William E. Horst

Ore grindability data based on various techniques to measure comminution characteristics are used to evaluate the crushing and grinding efficiency in mineral processing operations. The importance of achieving improved comminution efficiency, in terms of energy consumption, has been emphasized by recent increases in the cost of electricity. From a theoretical standpoint, the objective of a grinding operation might be expressed as maximizing the production rate at a given grind size while minimizing the energy consumption per ton of material ground. To achieve this objective in an industrial operation presents a challenge especially in view of changes in the raw material which are normally encountered. Various procedures1-5 used to determine energy-size parameters and grindability measurements have been reported. The proposed relationships between particle size and energy consumed have much in common between many of the techniques for measuring grindability. Probably the most widely used parameter to measure ore grindability in recent years is the Bond work index6, Wi, which is defined as the kw-hr per ton required to break from infinite size to a product size of 80 percent passing 100 microns. If the breakage characteristics of a material remain constant over all size ranges, then the calculated work index would be expected to remain-constant since it expresses the resistance of material to breakage. However for most naturally occurring raw materials differences exist in the breakage characteristics depending on particle size, which can result in variations in the work index depending on grind size. Consequently work index values are generally obtained for some specified grind size which typifies the comminution operation being designed or evaluated.

Jan 1, 1975

By Richard H. Johnson

White Pine Copper Company, a subsidiary of Copper Range Company located in Michigan&apos;s Upper Peninsula, mines a Precambrian sedimentary deposit containing finely disseminated chalcocite, native cop- per and native silver. Silver occurs predominately in certain strata and presently provides a mill head averaging 0.25 ounces per ton. This technical publication traces the development of silver recovery at White Fine beginning in early 1961. White Pine refined copper contains an excess of silver over and above that required to impart Lake Copper properties. The copper does not require electrolytic refining to meet industry purity requirements, nor is there sufficient silver to justify electrolysis.

Jan 1, 1970

By Elmer Pabel Huayna Peraltilla

El proceso de lixiviación es un método para el tratamiento de minerales sulfuros y sulfuros mixtos que consiste en la utilización de un consorcio microbiano acidófilo y una solución rica en cloruro de sodio. En ese sentido, el presente texto destaca el método de la biolixiviación como la alternativa adecuada -en tanto solución ácida (cobre) que contiene el metal en su forma soluble. Dicho proceso se desarrolla en dos etapas: En la primera se usa una solución de cloruro de sodio, el compuesto protector, más un inóculo del consorcio microbiano. La mezcla permite obtener una recuperación de cobre de hasta un 80% basados en pruebas preeliminares. En la segunda etapa, se le agrega un agente oxidante, que no daña a las bacterias, con el fin de disminuir la pasivación del mineral y un inóculo fresco del consorcio y así prolongar la recuperación.

Sep 1, 2013

By Harry F. Weaver

WHEN 1 was assigned by the Director of the United States Bureau of Mines to present a paper at this annual meeting of the Mining Society of Nova Scotia, 1 was grateful, honoured, and elated to realize finally a life-long desire to see your beautiful land and visit with you who have the good fortune to live and work here. Naturally, in preparing for this important event, 1 wanted to give you something of special interest within the limits of the subject so I chose an area dose to my heart -the operation of our Federal coal mine inspection service, which has, as its fundamental purpose, the prevention of accidents in and around ?Coal mines. In 1957 the United States had 10,879 active coal mines scattered throughout 28 States and the Territory of Alaska. The production of coal for the year was about 515,472,000 tons, including 2.5,472,000 tons of anthracite and 490,000,000 tons of bituminous coal and Hgnite. Anthracite is mined principally in a comparatively small area of one State. AU the 28 States and the Territory produce bituminons coal and/or lignite. The beds mined range from 18 inches to more than 100 feet in thickness and from the horizontal to the perpendicular.

Jan 1, 1958

By Jerry Gagnon, Matt Burr, Timothy Ellis, Abbas Mirza, Larry Webb

"The mechanical properties of RSR anode alloys (lead-calcium-tin, 009+ and lead-strontium-tin) were investigated as a function of time with an objective of developing lead anodes for use in high temperature electrolytic processes such as in copper liberator cells and in cobalt and nickel electrowinning. At a temperature of 70 oC, the mechanical properties of rolled RSR lead-calcium-tin (PbCaSn) alloy currently used in copper electrowinning decreased gradually while the mechanical properties of rolled RSR lead-strontium-tin (PbSrSn) decreased relatively quickly and stabilized at low strength levels. Cast PbSrSn started off as the weakest alloy but its properties remained stable with time. Rolled RSR 009+ anode alloy showed improvement in ageing properties over the other alloys tested. However, its mechanical properties did not stabilize in the study timeframe of 284 days. Further investigations are planned to study the effect of alloying elements on mechanical properties of RSR 009+ anode alloy over several years as a function of time at 70 oC. The mechanical properties will be evaluated to determine the time at which they stabilize. Comparative plant trials with rolled RSR PbCaSn and RSR 009+ will also be performed in copper liberator cells and in cobalt and nickel electrowinning tankhouses to determine their mechanical and electrochemical performance at temperatures of 65-75 oC.INTRODUCTIONLead-based alloys are the primary anodes used in the electrowinning of copper, zinc, nickel, cobalt and manganese from sulfate-based aqueous systems. Lead anode technology has evolved over the years migrating from pure lead and lead-antimonial alloys to the present day PbCaSn alloys for copper and PbAg and PbCaAg alloys for zinc electrowinning (Prengaman, Ellis and Mirza, 2010). It has also migrated from cast to rolled microstructures in search of improved mechanical properties and higher corrosion resistance. Although great strides have been made in the development of new lead anode alloys and production processes for lead anodes to be used in copper electrowinning, the industry still has some unresolved issues. These relate to the necessity of having higher mechanical properties especially for the lead anodes in liberator cells in copper electrorefining and for cobalt and nickel electrowinning as these tankhouses operate at temperatures of 65-75 oC compared to 40-45 oC in case of copper electrowinning."

Jan 1, 2016

By Jinxing Ji

Several fundamental aspects related to the nickel electrowinning from chloride electrolytes have been addressed in this paper. The thermodynamic study includes the activity coefficient of the hydrogen ion and the speciation diagram of NiCI2 solutions. The activity coefficient of the hydrogen ion (YH+) was calculated and estimated experimentally using a combination glass pH electrode. It was found that YH+ was greater than one in concentrated NiCl2 solutions and increased significantly with increasing NiCl2 concentration. The speciation diagram for NiCl2 solutions was plotted with YH+ and the effect of the ionic strength on the equilibrium constants being taken into account. It was discovered that the predominant nickel species in the acidic region were Ni2+ and NiCI+ in 0.937 M NiCl2 solution at 25°C. Electrodeposition tests demonstrated that higher Nit&apos; concentration in the electrolyte improved the current efficiency of nickel electrodeposition (CENi). The additions of H3BO3, and NH4Cl increased very little the current efficiency of nickel electrodeposition at pH 1.5 and temperature 60°C. However, the addition of sulfate decreased the current efficiency of nickel electrodeposition. Nickel electrodeposition was also found to be a steady-state process since the amount of acid added to the electrolyte at a constant pH increased linearly with time during galvanostatic electrodeposition. The cathode surface pH during nickel electrodeposition was measured using a flat-bottom combination glass pH electrode and a 500-mesh gold gauze as cathode. The cathode surface pH was found always to be higher than the pH in the bulk electrolyte, and if the current density was sufficiently large, it would eventually reach a level causing precipitation of insoluble Ni(OH)2(s) on the cathode surface. Rotating disc electrode studies revealed that the rate of nickel electrodeposition was first order with respect to the activity of nickel ion and zero order with respect to the activities of chloride and hydrogen ions. The rate of hydrogen evolution was found to be first order with respect to the activity of hydrogen ion and to be zero order with respect to the activities of nickel and chloride ions. These findings indicate that nickel deposition and hydrogen evolution proceed independently.

Jan 1, 1995

By Lang Tao, Jun Wang, Wei Xiao, Wenqing Qin, Pan Cao, Guanzhou Qiu, Key Lab of Biohydrometallurgy of Ministry of Education, Central South University

"The effect of metal cations on the rutile flotation using styryl phosphoric acid (SPA) as the collector was investigated by micro-flotation test, bench scale flotation test, zeta-potential measurements and adsorption measurements. The micro-flotation results indicated that Fe (?) and Al (?) ions in low concentrations had obvious activation on the rutile flotation, and Pb (?) ions in low concentrations had smaller activation of rutile, but Fe (?), Al (?), Pb (?), Ca (?) and Mg (?) have strong inhibition of rutile flotation in high concentrations. The bench scale flotation results indicated ethylene diamine tetraacetic acid (EDTA), boracic acid, and sodium hexametaphospate can decrease the metal ions concentrations, and increase the recovery of rutile flotation. Adsorption measurements and zeta-potential measurements revealed that Fe (?), Al (?) and Pb (?) ions were adsorbed on the rutile surface, and had interaction with SPA. But when these ions concentration were over the largest adsorption capacity, residual metal ions could occur chemical reaction with SPA.INTRODUCTIONRutile is one of the favored minerals for production of titanium dioxide white pigment, primarily through the chloride manufacturing process (Stanaway 1994; Hou et al., 2013) However, the majority of rutile ores belong to refractory ores, while flotation is one of the most efficient methods to separate fine rutile from gangue (Dolbear et al., 1937). With the flotation development, many effective collectors were successfully applied in the oxide ore. Many reviews have indicated that organic phosphonic acid collectors showed good selectivity on oxide ores such as ilmenite and rutile (Bulatovic & Wyslouzil 1999; Liu & Peng 1999).It is inevitable that many types of metal cations are present in ore pulp. These metal cations significantly influence the flotation of minerals. Liu et al. (2015) showed that Ca2+ and Mg2+ could improve the floatability of spodumene at pH 12.5 and 10.0, respectively. The authors proposed that Ca2+ and Mg2+ ions readily form hydroxy complexes (CaOH(l) and MgOH(l)) and precipitates as (Ca(OH)2 and Mg(OH)2) in strongly alkaline solutions. Fan and Rowson (2000) investigated the effect of Pb(NO3)2 addition as an activator on ilmenite flotation and showed that it could improve ilmenite floatability. The addition of Pb(NO3)2 resulted in an increase of ilmenite zeta potential in both weakly alkaline and acidic aqueous solutions. Mehdilo, Irannajad, and Rezai (2015) studied three kinds of ilmenite of different origins and discovered that both Mg and V had a negative correlation with ilmenite flotation, while the Mn content seemed to correlate positively with flotation efficiency. A number of studies have also showed that Fe3+ can improve the floatability of ilmenite (Fan et al., 2009; Nuri, Mehdilo, & Irannajad, 2014)."

Jan 1, 2016

By F. Garofalo

It has been shown by various investigators that during constant stress creep the dependence of minimum creep rate, 6,, on stress, o, is given by em = A onat low stress levels, md by 6, = A&apos; exp [ß s] at high stress levels. In these relations A, n, A&apos;, and ß are constant at constant temperature. A single relation has been found which satisfies conditions for both high and low stresses and agrees well with experimental results. This relation is 2, = AN (sinh a s)n, where A" is a constant at constunt temperature and a = p/n. This relation also satisfies the linear relation, 6, = k s, found at temperatures near the melting point at low stresses. EXPERIMENTAL creep results have led to a number of empirical relationships between minimum creep rate, 6,, and the applied stress, s. Under conditions of constant stress it is generally found that at low-stress levels,&apos;-&apos; the dependence of minimum creep rate is given by 6, = Asn. At high-stress levels&apos;74 the experimental results fit the relation, 6, = A&apos; exp [po l. In these relations A, n, A&apos; and ß are constant at constant temperature. A model based on climb-of-edge dislocations from a pile-up array leads to a relation similar to that found experimentally at low stresses.&apos; On the other hand. theories based on chemical-reaction rate,5 nonconservatively moving dislocation jogs, and jog migration and climb-of-edge dislocations4 lead to a relation similar to that found experimentally at high stresses. No difference in mechanism between low and high stress levels has been clearly defined; it is questionable whether such a difference really exists. In any event, the major argument usually given in substantiation of a change in mechanism from low to high stresses is that no single relation exists for defining the stress dependence of the creep rate over wide ranges in stress. However, such a relation has been found and is of the form, dm = A" (sinh a s)n, where A" is a constant at con- stant temperature and a = ß/n. This relation agrees well with experimental results over wide ranges in stress and temperature for copper, aluminum, an A1-3.1 pct Mg alloy, and an austenitic stainless steel. STRESS DEPENDENCE OF MINIMUM CREEP RATE At low stress levels the minimum creep rate, gm, depends on the stress, 0, under conditions of constant stress creep through the relation em=Aon [1] The quantities A and n have been defined previously. In the range in which this relation applies, a linear dependence is found in a log em,-log o plot. Above the stress range of application of relation [I], the minimum creep rate increases much mar; rapidly than predicted by relation [I]. This behavior is shown in Fig. 1 for a series of creep tests on copper4 at various temperatures ranging from 673 o to 973°K. Relation [I] is satisfied at the lower stresses, although the results at 973°K are quite limited. In all cases the transition beyond the applicable range of relation [I] is a gradual one indicating no abrupt change in mechanism. For all test temperatures, values of n have been determined from the results in Fig. 1. These are reported in Table I under Alog tm/hlog o. At high stress levels the stress dependence of minimum creep rate under conditions of constant stress is given by im = A&apos; exp [ß a] 2] All factors have been defined previously. In a log em-0 plot, relation [2] predicts a linear function. Experimentally, a pronounced deviation from the prediction of relation [2] is found at lower stresses. As the stress is lowered, the minimum creep rate decreases more rapidly than predicted by relation [2]. This shown for copper in Fig. 2. Again it is found that the transition from high to low stresses is gradual and no really sharp change is found. Values of p determined from the high stress results are given in Table I. The dependence of minimum creep rate on stress at constant temperature for all ranges in stress

Jan 1, 1963