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By Julie Hunt

Rimfire Minerals Corporation: early stage precious metal exploration specialists with discovery opportunities in partnership with major and mid-tier gold producers or prominent junior exploration firms. Mike Roberts, Senior Geologist

May 1, 2006

By D. M. Maijer, S. L. Cockcroft, A. B. Phillion, P. Fan, C. Reilly

"A numerical model has been developed to study macrosegregation associated with liquid feeding in the Low Pressure Die Casting of A356 aluminum alloy wheels. The model of the wheel casting process has been implemented within the commercial CFD software package, FLUENT, using a User Defined Function (subroutine) to account for Si rejection based on the Scheil approximation. The model has been validated against temperature and microstructural data taken from a commercially cast wheel. The amount of segregation in the wheel has been shown to be significant in a couple of key areas. The implications of accounting for segregation include an improved ability to predict shrinkage porosity, fatigue performance and potentially also hydrogen porosity.INTRODUCTION The aluminum alloy A356 is widely used in the automotive and aerospace industries for various components. Examples include automotive wheels, automotive suspension components and airframe castings. Focusing on automotive wheels, Low-Pressure Die Cast (LPDC) A356 wheels offer significant design freedom and are far more aesthetically appealing to consumers than conventional stamped steel wheels. A356 wheels now dominate the market, appearing in all but the entry level offerings of the OEM manufacturers. However, they are typically over-designed to allow for the various casting related defects that degrade their mechanical performance. Thus, their potential to save weight has not been fully realized. Wheel manufacturers are under constant pressure to ensure their products meet strict mechanical requirements (ductility, fatigue, vibration), tight geometric tolerances and high aesthetic quality. The mechanical properties of the final product are determined by the microstructure – e.g. SDAS – and the defect population (porosity and oxides). Depending on their size and location, both porosity and oxides, can act as crack initiation sites reducing fatigue life (Caton, 2001; Jordan, 2010; Wu, 2015). There are a number of examples appearing in the literature (Atwood, 2000; Carlson, 2007; Lee, 2001; Yao, 2011) of numerical models that have focused on hydrogen-based pore formation that have demonstrated an ability to predict porosity formation and pore size distributions in geometrically simple castings. These models assume that the local gas species diffusion through the liquid metal to the pores is the rate-controlling factor of pore growth. Another common source of porosity is liquid encapsulation (Dantzig, 2009). As the pressure within the isolated liquid drops, pores form first due to the pressure dropping below the equilibrium partial pressure of hydrogen in solution and then second grow substantially as the pressure continues to drop falling below the vapour pressure of Al. One factor that can affect both mechanisms of pore formation is species macrosegregation, which has received comparatively little attention in die-casting."

Jan 1, 2017

By B. R. Conard

Occupational epidemiology of the nickel-producing industry has found that inhalation exposures to certain nickel-containing substances are linked to respiratory cancers and to nonmalignant respiratory endpoints. Establishing such a linkage, however, is complicated by the fact that some diseases occur long after exposure to a causal agent (i.e., some diseases have long latencies). Furthermore, most chemical agents (especially nickel substances) vary significantly in their toxicological properties and their concentrations in workplace air have varied over processing history. Because of these complications, it is critical to understand historical exposures to specific nickel substances. To assist in this effort, the author focuses on the history of smelting and its related processes at Vale Canada’s (Inco’s) Ontario operations in the first half of the 20th century.

Jan 1, 2012

By Fathi Habashi

"Hydrochloric acid (HCl), although more expensive than sulfuric, find uses as a leaching agent in reactions involving iron oxide. The reason for this substitution was the discovery that oxyhydrolysis of ferrous chloride by which HCl can be recycled economically. This avoided the pollution of the environment by ferrous sulfate. It was found further that the rate of leaching of sulfides is faster when HCl is used as compared with sulfuric apparently due to the formation of aqueous chlorine. In case of refractory gold ores, HCl leaching under pressure avoids the use of cyanide solution since gold chloride is produced which can be recovered by standard methods. Hydrochloric acid find also uses in the leaching of scheelite and apatite but its use in leaching clay and anorthosite is questionable.INTRODUCTION Sulfuric acid is the cheapest acid and is used as a leaching agent in many hydrometallurgical processes. However, hydrochloric acid (HCl), although more expensive since it is prepared by reaction of sulfuric with sodium chloride, has replaced sulfuric acid in many reactions involving iron oxide. It replaced sulfuric acid for the first time in 1960s in pickling of steel because of pollution problems (Habashi, 2000). Ferrous chloride produced in pickling can be economically decomposed to ferric oxide and HCl according to:2FeCl2 + 2H2O + 1/2O2 ? Fe2O3 + 4HCl (1)which also shows that the acid can be regenerated but ferrous sulfate cannot be economically decomposed to recover sulfuric acid for recycle. Since then, HCl has been used in many leaching processes. Hydrochloric acid is a corrosive acid and is usually handled in rubber-lined equipment. REGENERATION OF HYDROCHLORIC ACID Regeneration of HCl is conducted in fluidized bed or in spray roaster Fluidized bed oxyhydrolysis In a fluidized bed, ferrous chloride solution is introduced onto a bed of hot ferric oxide where heating is provided by the hot fluidizing combustion gases (Figure 1). The solution is fed on top of the bed of oxides. The liquid feed wets the outer layer of the hot oxide particles and is quickly evaporated to form a layer of new solid oxide on top of the existing oxide, thereby producing dense homogeneous particles."

Jan 1, 2017

By T. T. Wang, T. H. Huang, S. S. Zhan

"Fractures with diverse features dominate the hydraulic behavior of fractured rocks and are one of the major subjects for hydrogeological characterization of a site. This study investigates curve patterns obtained by packed tests, and as well the influence of fracture features based on 59 sets of in situ packer tests with different fracture combinations and fracture features. The result shows that, in the example of Heshe site, neat and tidy fractures usually provide stable channel for water flow during testing, and the hydraulic properties of fractures infilled with breccia and mud may change during testing because of leaching and/or washed out of infilling breccia and mud. Different combinations of fractures with diverse features in packed test sections lead to different curve patterns for in situ hydrogeological tests. For groundwater flowing predominately through neat and tidy fractures, the pressure-discharge curve of modified Lugeon tests are usually linear curve pattern, and the pressure decrease while the discharge increase in pressure-discharge-time curves of single-hole double packer tests, which benefit statistically determining the transmissivity of dominant fracture sets. INTRODUCTIONFractures interlaced in rock masses are major channels for groundwater flow and generally account for the anisotropic and heterogeneous characteristics of permeability for fracture rocks. To describe reasonably the permeability of a fracture rock, the Discrete Fracture Network (DFN) approach and others with similar ideals have been developed. Many methodologies and associate equipment, for instance, the televiewer and the in situ hydrogeological test, have been proposed to investigate the spatial distribution and the transmissivity for different fracture sets, which are two main parameters necessary for the DFN or similar model simulation (Pearson & Money, 1977; Barker & Black, 1983; Hsieh et al., 1985; Bernard et al., 2006; Quinn et al., 2012). However, diverse outlooks for the pressure-discharge curves and the temporal pressure and associate temporal discharge curves often confuse the investigation results by significant deviations on derived permeability (Houlsby, 1976; Zlotnik, 1994; Royle, 2009; Camilo, 2010).Aiming on technical development for in situ hydrogeological tests and fracture investigation, an experimental well site with 10 wells has been established in Heshe in central Taiwan since 2011 (Wang et al., 2011; Song, 2012; Zhan et al., 2013). Extensive geological survey and well-hole scanning by a televiewer provide spatial distributions and outlooks of fractures in detail. Additionally, a series of Lugeon tests, double packer injection tests and pumping tests have been performed to investigate the permeability of fracture rocks, and dominate fracture sets as well. Based on the results obtained from the Heshe site, this study classifies the curve patterns of hydraulic packer tests. The features of fractures involved in packed sections for packer tests are then inspected in detail. Relationship between the curve patterns of hydraulic packer tests and associated features of corresponding fractures in rock are discussed and addressed accordingly."

Jan 1, 2015

By Steve Scott

Green Economy Toyota Prius Hybrid contains about 50 kg of copper. All-electric cars have about 100 kg of copper. From where will all the copper come? Wind turbines have 1 metric ton of copper China is building 221 cities of 1 million people by 2025 (13 cities per year from 2008) = 10 New Yorks. The Greater Toronto Area has 5.6 million people, so a new GTA every 22 weeks!

May 1, 2013

By J. W. Rogers, S. K. Schwartz

"The Cape Breton Development Corporation (CBDC) is a federal Crown corporation which operates two coal mines (Phalen and Prince Collieries), a coal preparation plant, a railway, a central workshop and a deep water shipping facility.The Sydney coal field consists of 11 major seams, which range from 0.8 m to over 3.7 m in thickness. Of the 2.4 billion tonnes of known coal resources in the field, approximately 550 million tonnes can be mined with present mining technology. These parameters define reserves which extend more than 8 km beneath the ocean to a depth of 1200 m. With today’s design and present high production faces, the colliery life is projected at approximately 20 years."

Jan 1, 1996

By Q. F. Wang, M. H. Lai, T. Q. Liu, G. G. Dong

Compared with the traditional pre-treatment process, biological oxidation process has many advantages including higher gold recovery, less cost, easier operation. The bio-oxidation reactor is the most important equipment for biological oxidation process. In this paper, the characteristics of biological oxidation are investigated, and the design principles are proposed based on laboratory tests. Both increasing the tank height and taking new inflation system can enhance higher dissolved oxygen. The new type of large-scale industrial bio-oxidation reactor is designed, which is 9.5 m in diameter and 10 m in height. The bio-oxidation reactor metallurgical performance has been tested by industrial-scale experiment. The slurry of flotation concentrate is divided into two parts to feed two bio-oxidation reactors. The feeding rates of two reactors are adjusted on the basis of getting the same content of S, Fe, As in overflow. The result shows that the feeding rate of the new type of 700 m3 bio-oxidation reactor is 3.72 m3 per hour, and the feed rate of the conventional 700 m3 bio-oxidation reactor was 3.23 m3 per hour. The processing capacity of the former is 15.2% higher than that of the later, which demonstrates the new type of bio-oxidation reactor has higher oxidation rate.

Jan 1, 2015

By G. S. Hume

THE discovery of natural gas with naphtha in 1924 in the Upper Palaeozoic limestone of Turner Valley, 35 miles southwest of Calgary, has led to continuous developments in this field. Drilling undertaken soon after this discovery demonstrated that the anticlinal structure was in reality a major drag-fold cut off on the east side by a westerly inclined fault of large displacement. The faulted edge of the .limestone at depth determines the eastern limits of the field, which between 1924 and 1936 was shown to have a gas area 14 miles long by about 1 mile wide. Since the strata dip westerly, away from the axis of the fold, drilling becomes progressively deeper to the west and, with the advent of deeper drilling, crude oil was discovered in 1936 on the west flank of the structure but in the same porous reservoir rocks as the gas on the crest and upper parts of the fold. Since 1936, drilling has been undertaken wholly for the production of crude-oil and at present two producing areas have been found within the Turner Valley structure. The larger of these, at the south end of the field, in the vicinity of Highwood river, has a length of about 4 3/4 miles and a proved width of one mile, whereas the smaller, in the north end of the field, south of the north fork of Sheep river, has only a few producing wells.

Jan 1, 1939

By B. W. Steele

"Dofasco began operations in 1912 as a steel foundry located in Hamilton, Ontario. Today, Dofasco is a fully integrated mill that manufactures hot rolled, cold rolled, galvanized and tinplate steels. Customers include the automotive, construction, tubular, manufacturing, appliance, packaging and steel ser-vice centre industries. Raw steel production and purchased semi-finished steel processed in1994 was 3.5 million net tonnes. Dofasco employs 7300 people at its Hamilton facility.Environmental management at Dofasco is guided by its environment policy and associated commitments. This paper discusses Dofasco’s responsibility for its products as it relates to these commitments. Dofasco is com-mitted to:n the principles of sustainable development that require that activities be conducted in a manner that provides for the present without compromising the ability of future generations to meet their needs. These principles will be integrated into product design, manufacturing and business planning;n managing renewable and non-renewable resources through the responsible application of reduce, reuse, and recycle principles;n minimizing any potential impact of its operations and products on the environment, employees, customers and the community;n continuous improvement of the effectiveness and integrity of our environmental management systems;n developing understanding among all employees about their responsibilities, and assigning the necessary authority; andn meeting the standards set by relevant legislation and international agreements through participation with governments and the diligent application of economically feasible and scientifically sound methods and technologies."

Jan 1, 1996

By Zihe Ren, Edouard Asselin, Marcus Tomlinson, Tianbi Zhang, Jing Liu

"Raman spectroscopy is used to quantify the extent of disorder in the carbonaceous matter associated with preg-robbing ores. Previous studies of Goldstrike ores showed that the height and width of the peaks for the “D” (disordered) and “G” (graphite) bands, the so-called “Raman ratio” had a strong correlation to the preg-robbing value (PRV) measured for various ore samples. A brief literature review on Raman spectroscopy as it applies to preg-robbing ores is presented. Further, recent studies, presented here, have shown no correlation between the Raman ratio and the PRV for a wide variety of ores. This suggests that the extent of organic carbon crystal disorder is not the main factor in determining preg-robbing characteristics.INTRODUCTION Valuable base metals, such as nickel, cobalt, molybdenum, vanadium and tungsten, are used in a wide range of important technological applications. The demand for many of these metals has increased significantly over the last few decades, driven especially by economic expansion in Asia generally and China in particular. This has led in turn to a large growth in the output of mines in order to satisfy this increasing demand, as shown by the data in Table 1 (USGS, 1994, 2014). These data reflect an even longer trend of growth of these metals, with nickel, for example, showing an average rate of 5.3% per year from 1980 until 2015 (International Nickel Study Group, 2017). This rapid and sustained rate of growth means that annual mine outputs for nickel, tungsten, molybdenum and vanadium have had to double roughly every 11 to 14 years, whilst cobalt mine output has had to double roughly every 7 years, over the period from 1994 until 2014. With the average working life of a nickel mine being between 17 and 22 years (Statista, 2017), this means that from the time a nickel mine opens until it closes, the industry needs to find the equivalent of another three or four mines of a similar output to satisfy this relentless growth in demand for the metal."

Jan 1, 2017

By Ahmad Ghahreman, James McNeice

"Cerium is the most abundant rare earth metal and is often found in deposits along with small amounts of more valuable metals such as neodymium and gadolinium1. As a result, the production of cerium oxide often exceeds market demands, thus in some cases it would make more sense to remove the cerium from the process solutions before further purification. A common method of cerium removal is to precipitate CeO2 from the acidic leach liquors by raising the pH to oxidize cerium(III) to cerium(IV). This study investigates the oxidation kinetics using three oxidants; hydrogen peroxide, sodium hypochlorite, and potassium permanganate. The effect of oxidant, pH, cerium concentration and temperature on the oxidation kinetics will be discussed. Cerium oxidation in solutions with pH ranging from 1.0 to 4.0 was investigated at cerium concentrations ranging from 2.0 g/L to 16.0 g/L. A cerium recovery of 40% can be achieved at different conditions with each oxidant at room temperature, with higher recovery at 60°C.INTRODUCTION Over the last 70 years, the rare earth elements (REE) have become crucial components of modern technology. These metals are categorized as light rare earths (LREE) or heavy rare earths (HREE) by governments and miners based on weight, abundance, and therefore value. The minerals bastnaesite, monazite, and xenotime compose the majority of the world?s exploitable sources of these metals (Binnemans, 2013; Parker and Baroch, 1971). Geologists classify the LREE ores as „cerium group? minerals, approximately 50% cerium oxide by weight. The cerium group minerals monazite and bastnaesite compose the majority of world production, leading to an overproduction of cerium relative to world demand. This ratio of light to heavy REE in deposits has led to a phenomenon referred to as the balance problem (Binnemans et al., 2013). As an example, to produce 1 tonne of europium oxide from a bastnaesite deposit 450 tonnes of cerium oxide must be processed. This means that any push to increase production and access the value of the HREE metals will drive down the value of the LREE metals leading to diminishing returns (Zepf, 2016). These ores also contain measurable levels of thorium, subjecting them to complex radioactive waste regulations. During the 20th century, the USA was the largest producer of rare earth metals (REMs), primarily sourced from the Mountain Pass mine in California. However, due to a combination of market dynamics and regulations, China has dominated the market for the last two decades. The largest Chinese REE mine, Bayan Obo, produces rare earth (RE) concentrate as a byproduct of iron mining, decreasing their relative production costs (Gupta and Krishnamurthy, 2005). This mine alone represents about half of world bastnaesite production (Zhi and Yang, 2014). Rising demand for high-tech products has forced Chinese producers to commission other large mines, climbing to 90% of world production in the early years of the new millennium (Mancheri, 2016). This presents the west with a looming supply risk of these critical metals in the future."

Jan 1, 2017

By Ralph H. Cleland

Introduction The mines of northern Ontario have entered the class of deep mines. It has often been asked: How deep can operations be carried on? What will the temperature be? This paper is a résumé of a brief survey of rock temperatures made by the Ontario Department of Mines during the year 1932. Present temperatures were recorded and the geothermal gradients that now exist were determined. No alarming situations were found, but many interesting ones have been noted. Northern Ontario mines are fortunately situated as compared with most deep-level mines of the world. The mean yearly temperature, as determined from meteorological records of the Federal Department of Marine, is from 33 to 38 degrees Fahrenheit. The tables on the next page show the temperature range in and about our mining camps ( l ). As no exact figures were obtainable for Kirkland Lake, the data for Iroquois Falls, which is about 50 miles northwest, were taken as applicable there. The figures for Timmins were checked against those of Cochrane and Iroquois Falls and found to be very similar, so that the Cochrane data may be used for the Porcupine camp. The yearly mean temperature is considered to be 33.5 F.

Jan 1, 1933

By Michael T. G. Brown

Syncrude Canada Ltd. has recently completed construction of its ambitious tar-sand mining and processing facilities at Mildred Lake, Alberta. The Syncrude site is approximately 48 km (30 miles) north of Fort McMurray near the west shore of the Athabasca River. The Syncrude operation involves the open-pit mining of approximately 270,000 tonnes (300,000 tons) of tar sand daily using draglines and a conveyor system. Bitumen is extracted from the tar sand, upgraded to oil-gas and transported to refineries in Edmonton and other locations for final processing . The Beaver Creek Dam forms part of the mining facilities for the Syncrude tar-sand mining operation. Water from Beaver Creek is diverted from the open-pit mine site south to the Athabasca River via Ruth Lake and the Poplar Creek Dam. General site layout is shown on Figure I . Design of the dam was completed by R. M. Hardy and Associates Ltd. of Edmonton, Alberta (now Hardy Associates (1978) Ltd) . Construction was undertaken during the summers of 1974 and 1975 under the direction of Canadian Bechtel Limited, managing contractors for Syncrude Canada Ltd. Total length of the dam is approximately 2.8 km (1.7 miles), with a maximum height in the order of 16 m (50 ft) The Beaver Creek Dam is located in a broad, flat, poorly drained valley. About 50 per cent of the site is covered with treeless peat deposits, which ranged in thickness from in excess of 5 m (15 ft) at the east end of the dam to less than 1 m (3 ft) at the central portion. The peat deposits overlie Pleistocene meltwater sediments on top of clay/clay shales of the Clearwater Formation and the tar sands of the McMurray Formation. The peat deposits and high groundwater levels at the site combine to make the excavation and construction of a conventional rolled clay cutoff impractical. For these reasons, the slurry cutoff trench technique was utilized to produce an efficient and effective seepage cutoff under various sections of the Beaver Creek Dam .

Jan 1, 1979

By Z. Z. Öztürk, N. Sarica, A. H. Üçisik, C. Bindal

"Titanium oxide films were fabricated on commercially pure titanium surfaces via anodization procedure. Anodization parameters, anodization time and voltage were altered, whereas temperature and chemical composition of anodization bath were kept constant. The main idea in this study is to obtain rough titanium-oxide surfaces. The type and feature of titanium oxide formed were observed via SEM and EDX analyses. What was revealed from SEM and EDX analyses were combined with Ti-O phase diagram in order to make judgment on the type of phases obtained, e.g. solid solution and/or compounds. Studies on the different regions of each sample showed that surfaces consist of different titanium oxide compounds with various O/Ti ratios in nano level and solid solutions varying in terms of chemistry on the same sample. Thus together rough surfaces and inhomogeneous distribution of "titanium oxides" were obtained. It was also found that when anodization time and voltage were increased, more granular surface with higher O/Ti atomic ratio was obtained."

Jan 1, 2015

By F. E. Lathe

RECENT events have emphasized with renewed force the well known fact that war greatly intensifies the demand for certain metals, particularly for iron, copper, and zinc. Any increase in the use of iron and steel, whether in war or peace, is also accompanied by increased consumption of those metals which find their chief application as ferro-alloys, such as nickel, chromium, manganese, molybdenum, tungsten, and vanadium. Further, since high temperatures are essential for the production of all these metals, activity in the metal industry is inevitably accompanied by an insistent demand for refractories. For example, in North American practice the consumption of magnesitic hearth refractories is frequently expressed in pounds per ton of steel. This quantity (not including straight dolomite) ranges on individual plants from about 7 to 12 pounds. When the industry is operating at approximately full capacity, the ratio of refractory to steel tends to increase, since the tonnage of steel produced is recognized as of paramount importance, and this leads to the harder driving of furnaces and less regard for the effect on refractories. It should also be observed that the cost of refractories per ton of metal produced is always so low, in comparison with other items, that it may even increase while the cost of metal per ton is being reduced through more continuous operation and the use of higher temperatures. As one prominent Canadian copper metallurgist has tersely expressed it, he is "not in business to save refractories but to smelt ore". The effect of war demands and of general industrial activity upon the production of basic and neutral refractories is clearly shown in Figure 1, which gives the value of chrome ore and magnesitic-dolomite produced in Canada during the period 1907 to 1937. Tonnages have not been shown, as these are not available for the full period; such figures as have been published from time to time are not strictly comparable, since both raw rock and finished products have on occasion been included. The preliminary figures for 1938, which are now available, have been prepared by the Dominion Bureau of Statistics on a different basis from those immediately preceding, and have therefore not been shown.

Jan 1, 1940

By Mingxia Liu, Hao Li, Qi Liu

"Laboratory batch flotation tests were carried out on fine (-20 µm) hematite to investigate the non-polar oil’s influences when sodium oleate, octyl hydroxamic acid, or oleyl hydroxamic acid were used as a collector. Batch flotation tests were performed with artificial mixed minerals (hematite:quartz = 1:1) under natural pH condition and kerosene was utilized as the model oil. The experimental results showed that kerosene emulsion behaved differently when used in conjunction with the three collectors. Kerosene helped improve the flotation when sodium oleate or oleyl hydroxamic acid was used as a collector. Nevertheless, it reduced concentrate weight yield, grade and recovery to a noticeable extent when octyl hydroxamic acid was used as a collector, especially at low dosages. In addition, single hematite batch flotation kinetics tests coupled with water recovery measurement were carried out to study the role of kerosene at different collector dosages. It was observed that water drainage and the resulting froth destabilization by kerosene was dominant at low collector dosages, especially in the flotation using octyl hydroxamic acid. At higher collector dosages, the water drainage and froth destabilization effect by kerosene was possibly counter-balanced by the higher hematite hydrophobicity and bubble surface tension gradient, which led to more stable froth layer.INTRODUCTION The minerals industry is facing a steady decline in ore grade, compounded by increasing complexity of mineral dissemination. As a result, the ore has to be ground sufficiently fine to have a suitable degree of mineral liberation, which produces large percentages of fine and ultrafine particles outside of optimal size range for ore dressing. Due to the unique characteristics of fine particles, i.e., small mass, high specific surface area, and problems such as increased solubility of complex minerals (Finkelstein, 1997; Finkelstein & Allison, 1976; Fornasiero & Ralston, 2005), high reagent consumption, fast surface oxidation in the case of sulfides (Collins & Read, 1971; Klassen & Mokrousov, 1963), severe particle entrainment (Subrahmanyam & Forssberg, 1988; Warren, 1984), low flotation rates (Glembotsky, 1953; Philippoff, 1952; Ye & Miller, 1988), slime coating (T. K. Mitchell et al., 2005; Parsonage, 1984), etc., flotation performance of these finely ground ores is very poor in terms of low concentrate grade and recovery."

Jan 1, 2017

By A. Blackmore, A. Lamoureux, J. Woloshyn

This paper provides an overview of recent applications of Computational Fluid Dynamics (CFD) to combustion related fugitive emissions problems. The aim is to illustrate the capabilities and discuss the present limitations in this field. Examples include design of retrofitted NOx reduction technology in a kiln and in a boiler, and the prediction of pollutants such as SO2 and metallurgical dust emanating from a copper flash smelting furnace. It is demonstrated that CFD is an effective tool for reducing technical risk in design, for identifying the root-cause problems and testing solutions, and for concurrently assessing emissions reduction and process impact. In addition, the value of CFD for demonstrating due diligence for regulatory compliance is discussed.

Jan 1, 2015

By M. G. Mena, M. S. Mena-Junio

Silver (Ag) filler is the most attractive choice among all the conductive fillers of die attach materials for the attachment of silicon devices because of its balanced properties and relatively low cost. However, a major problem of silver is that it electrochemically migrates in the presence of moisture and applied bias. In microelectronic devices, silver migration can occur between adjacent conductors/electrodes, which leads to the formation of dendrites and eventually results in short-circuit failure. In order to assess the reliability of these conductive fillers, an investigation for two types of Agfilled die attach materials was done using the water drop test at room temperature and using a 1000 hour temperature-humidity-bias (THB) test under 85 ºC and 85% RH conditions. Four different bias/voltages and six different electrode distance spacing were used. Both dendrite and cloud/lace-like growths were observed as a result of the electrochemical migration of silver, Water drop test results revealed that increasing the applied bias/voltage and decreasing electrode spacing causes migration to occur faster, thus resulting into shorter time to fail (TTF). It was also observed that the growth rate of the dendrites from the cathode increased linearly as the dendrite approached the anode, probably due to a combination of increased ion availability and electric field. A minimum applied bias of 3 volts was required for migration to occur in Epoxy A as compared to 2 volts for Epoxy C. The higher migration voltage requirement for Epoxy A was attributed to the higher volume resistivity of the said epoxy. In addition to the minimum voltage requirement, it was observed that a minimum electric field of about 1 volt/mm is required for migration to occur. The 1000 hour THB testing did not result into any failures. It is surmised that the presence of condensed moisture is another requirement for migration. Such condition is not present during the THB testing.

Jan 1, 2012

By X. S. Fan, T. R. Feng, D. Chen

To meet the flotation process requirements, the large-scale flotation cell must be designed for sufficient pulp mixing, reasonable air dispersion and solid suspension, which is very difficult to design for super large-scale flotation cell. Hence, the flotation cell scale-up and optimization for a short period is a challenge for super large-scale flotation cell design. Computational fluid dynamics simulation has been applied in flotation cell study, which is effective, timesaving and low cost in the study of the flow field distribution for super large-scale flotation cell. This paper demonstrates the flow field characteristics in the 600m3 flotation cell by CFD. The flotation cell model is meshed with hexahedral grid and the high mesh quality assures the computational precision. MRF model, namely a steady-state approximation, ensures that individual cell zones can be assigned different rotational speed. Euler-Euler approach is chosen for multiphase flow simulation to treat different phases as interpenetrating continua. Numerical simulation of single phase, two-phase and three-phase are investigated respectively. Results suggested that the flotation cell has the apparent upper and lower flow circulation. In condition of the impeller rotation, the air is dispersed reasonably. In addition, the solid phase volume concentration distribution in the cell has a little difference.

Jan 1, 2015