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By H. R. Shakeri, R. Mayer, M. J. Worswick, A. Rahem

The current focus of research and development in transportation industry is to use lightweight materials such as aluminium alloys for more structural components. In this regard, maintaining safety of the passenger and vehicle is the most important; therefore crashworthiness of components made of lightweight materials must be evaluated prior to sizable application of these materials. The focus of the present study is to understand failure and damage mechanisms during the axial crushing of aluminium tubes made of A1Mg3.5Mn alloy of 2 and 3.5 mm thickness. Due mainly to complexity of the crushed tubes, a microstructural approach is considered. In this study optical, stereo as well as scanning electron microscopy techniques have been used to study damage and failure mechanisms in these types of tubes, which are essential energy absorbing components in passenger vehicles.

Jan 1, 2006

By A. Demers, M. Chapman, N. Reynier, R. Lastra, M. Courchesne, C. Laviolette

Historic medical isotope production at Canadian Nuclear Laboratories (CNL) in Chalk River involved the dissolution of irradiated isotope targets prior to extraction of Mo-99. This process generated liquid waste that was cemented in 5-gallon containers and transferred to an outdoor waste-management facility for intermediate storage. Research was undertaken to develop an innovative method for uranium, mercury and cesium recovery from the radioactive cemented waste (RCW). Regulations prohibit the removal of active radioactive waste from the Chalk River facility. Thus, CanmetMINING produced surrogate material following the same procedures and conditions to those used at CNL. The selective recovery of the uranium from the surrogate radioactive cemented waste (SRCW) could offer CNL more disposition options for the resulting wastes. Leaching tests were performed using four different SRCW at 1 kg scale. Different conditions, operating parameters, and the presence of plastic and corrosion products were evaluated on solubilization. The research investigated the use of potassium iodide with the sulphuric acid leach to increase metals recovery. Iodine improves the solubilisation of metals and the U dissolution reached 99%. The increase of leaching time reduces the U solubilization due to silica gel formation. Therefore, it will be important to control leaching time to avoid the loss of U during the pilot scale experiments. For Hg, the solubilization ranged from 60 to 80% due to the presence of metallic mercury and mercury sulphide found in SRCW cured at 60°C and/or aged for 30 months. Ion exchange (IX) was found the best method to separate the uranium from the impurities and produce a purified and concentrated uranium solution suitable for yielding a uranium product (yellow cake).

Jan 1, 2020

By I. M. R. Duarte, J. A. Rodrigues-Carvalho, F. R. S. Rosa, A. B. Pinho

"This paper aims to contribute to the knowledge of the mechanical properties of the shales and greywackes which constitute the flysch-type deposits of the Baixo Alentejo Flysch Group, in the south of Portugal. These formations are flysch-type deposits constituted by sequences of usually thick greywacke beds alternating with thin shale beds, which include sometimes intercalations of conglomerate beds. All the sedimentation of these flysch formations was controlled by tectonics. At the same time, should have occurred along with the first Hercynian deformation phase, a low-grade metamorphic event (chlorite zone), that affected these flysch deposits. This study highlights the influence of anisotropy and heterogeneity of these flysch rocks on their physical and mechanical characteristics. The anisotropy verified in some physical properties and on mechanical properties, due to the foliation makes difficult the sample preparation for the laboratory tests. Besides, it induces a scattering of the properties values measured, as for example, the strength and the deformability. The heterogeneity is related to the main features of these geological formations, which are constituted mostly by thinly stratified greywackes and shale beds, which sometimes may affect the results of the laboratory tests making them less representative. The study is made by using both shales and greywackes that constitute these flysch-type deposits in order to evaluate their geotechnical properties, mainly of the shales. Samples of these two rock materials, are tested accordingly a laboratory testing programme, which includes which included mineralogical analysis (X-ray diffraction), physical tests (bulk density, porosity, and void index) and mechanical tests (uniaxial compression, and deformability tests). INTRODUCTIONOne of the factors that most influence the geomechanical behavior of rocks, as well as rock masses is the anisotropy. The word anisotropy comes from two Greek words ""anisos"" (meaning uneven) and ""tropos"" (meaning direction). A body or material is considered to be anisotropic, where the same property has different values depending in which direction it is measured, therefore, an anisotropic material is one whose magnitude of the properties depends on the direction in which these are studied or measured. Otherwise, it is about an isotropic material. However, the fully isotropic materials are quite rare in nature."

Jan 1, 2015

By H. J. lgner

Hydraulic fills are widely used in the tabular, steeply dipping stopes of the South African gold and platinum mines as an integrated process within a daily cycle of drill and blast. There is therefore only a small time window in which to fill the geotextile bags used as primary fill containment, without the risk of loosing production. Consequently, mines tend to increase the flow rate to the stopes, although this compromises adequate drainage, consolidation and strength development during filling. Recent underground measurements inside the geotextile bag have revealed that at high rates of rise and at 25 degrees dip, the backfill can remobilise within a limited area inside the geotextile bag during filling. This sudden downward surge of backfill exerts, for only a few seconds, additional loading on the geotextile, its supporting mesh and the props. This unstable behaviour poses a serious threat as it can push props out of place, thereby damaging the geotextile bag and causing a mud slide in the stope. To reduce the risk of accidents, the phenomenon of sudden slumping was further investigated for various filling conditions in the laboratory. The results confirmed that the maximum pressures associated with the sudden slumping can be more than five times those experienced during steady-state consolidation. Based on this new insight, the current best practice for hydraulic backfilling was critically reviewed. A practical approach to implementing meaningful standards is presented to ensure safe operations in relation to the consistency of the backfill quality and the appropriate matching of geotextile characteristics with backfill properties.

May 1, 2007

By P. E. Weidmark

Allard, M., Hucka, V.J., Das, B., and Borchtch-Komponietz, V.I., "Investigation of seismic vibration due to large blasts in Gaspe Copper Mines"; (in Russ); The Industry of Chemical Raw Materials; Referativnyi sbornik; 5:18-20: 1978. Askew, J., McCarthy, P.L. , and Fitzgerald, D.J ., "Backfill research for pillar extraction at ZC/NBHC"; Mining with Backfill; Proc 12th Cdn Rock Mech Symp; May 23-25, 1978; Sudbury; CIM Spec Vol 19:100-lJO; 1978. Barrett, J.R., Coulthard, M.A., and Dight, P.M., "Determination of fill stability" ; Mining with Backfill; Proc 12th Cdn Rock Symp; May 23-25, 1978; Sudbury; CIM Spec Vol 19:85-91; 1978.

Jan 1, 1979

By R. E. Baylis, M. R. Tolley, S. Singh, A. J. Murray, R. Boden, L. E. Macaskie, T. P. Hathway, D. Vavlekas

We report rare earth element (REE) recovery using immobilized Serratia biofilm depositing metal phosphate via a robust enzymatic mechanism. Activity was approximately halved at pH 3.5 and restored at pH 5.5. REE(III) was recovered selectively against Th(IV) but the method was non-selective between different REEs (La, Y, Eu, Nd). Biofilms were active for a year (half life of ~ 3 months). The activity of aged biofilm was enhanced by pre-nucleation (‘priming’) with NdPO4 prior to onset of flow-through conditions. The use of different ‘priming’ metals and bacteria via a combinatorial approach revealed some REE selectivity through the selective exclusion of specific REEs.

Jan 1, 2014

By Shuo Zhang, Wenying Liu

"In dump leaching, the efficiency of metal extraction from ores is strongly influenced by the mechanisms of fluid flow. Particle size distribution acts as a fundamental parameter in the determination of fluid flow properties in packed ore beds. In this study, we investigated the particle size distribution in dump leaching by using image analysis technique. The results showed that the particles in the dump varied from smaller than 2 cm to larger than 200 cm in diameter. P80 was calculated to be 200 cm, which was significantly higher than the historical data used by the operation. P25, P50 and P80 were found to increase non-linearly with increasing depth towards the toe of the dump, suggesting the segregation of fine and coarse particles. The image analysis results were verified by applying the rock fragmentation models. The model with the Swebrec function was found to be in better agreement with the image analysis results. Future research will investigate the effect of particle size distribution on the behaviour of fluid flow.INTRODUCTION Fluid flow plays an essential role in the extraction of valuable metals using heap/dump leaching (Amos et al., 2009). The rates of the chemical leaching reactions and microbial activities determine metal concentrations in the leachates and therefore the efficiency of the metal extraction. The reaction rates are influenced by two fundamental processes: transport phenomenon and reaction kinetics (Bouffard & Dixon, 2001). The transport phenomenon refers to the percolation of fluids through channels and pores in a packed ore bed, which carries lixiviants and reaction products to/from ore surfaces by convection and diffusion. The percolation rate of the leaching solution is determined by the hydraulic conductivity of the packed ore bed, which is a function of the permeability and the degree of saturation (Guzman et al., 2008). Permeability, an intrinsic property of a packed ore bed, is strongly influenced by the particle size distribution of the ore grains (Bouffard & Dixon, 2001). Hence, the objective of this study was to investigate the particle size distribution in dump leaching."

Jan 1, 2017

By R. A. L. Drew, G. Mendoza-Suarez, J. Filipi, R. Vintila, J. A. Kozinski

Economics and environmental considerations along with the increasing demand of hydrogen encourage development of novel technologies such as plasma processing of hydrocarbons and thermal cracking of natural gas. Plasma discharges, either in thermal or non-thermal regimes are expected to allow low temperature and fuel flexible on-site hydrogen generation. The main drawback of thermal plasma reformers is the high-energy consumption resulting from high-temperature operation. On the other hand, non-thermal plasma, generated by dielectric barrier discharge (DBD), is able to simulate the chemical reactions employing much lower energies than those required by thermal treatment processes. The non-thermal plasma process allows for instance, a direct conversion of methane into hydrogen and carbon black with no CO2 release. The focus of this research was on the GHG-free method of H2 generation in compact non-thermal plasma reactors using low, medium and high permittivity dielectric ceramics. A stable, non-thermal plasma was generated by placing a dielectric ceramic between two electrodes with a 25 thou gap and applying an alternating current of 1-5kHz and voltages of 4-8kV. In order to ensure energetic efficient plasmas, experiments were conducted to analyze the behaviour of different permittivity ceramics. It was found that the dielectric properties of a ceramic, when used in a DBD reactor, have a strong influence on the discharge characteristics, which in turn influence the power consumption. Higher dielectric constant resulted in higher conversion rates of methane (higher yield of hydrogen and carbon). At the same time, the mechanical properties of the dielectric material, which are closely associated with its processability, influenced its resistance to electron bombardment, as well as thermal and mechanical damage. Therefore a reliable ceramic should have good dielectric properties, in addition to good thermo-mechanical stability.

Jan 1, 2004

By E. M. De Souza, J. F. Archibald

This paper examines aspects of Canadian mine backfilling operations that may be implemented to assist in reducing solid waste production, lowering energy costs, and restricting Greenhouse Gas emissions. Many Canadian underground mines use backfill to mitigate environmental effects associated with tailings disposal. Backfill production and disposal are energy intensive processes that require an average energy cost of 37.7 MJ/tonne of backfill to complete. Mine backfills, in engineering applications, also commonly make use of cement as a stabilizing agent. Cement requires an additional energy cost ranging between 4,637 and 6,600 MJ/tonne to produce. The large energy needs associated with mine backfilling and cement production operations create significant CO2 and Greenhouse Gas emissions. Approximately 1 tonne of CO2 and Greenhouse Gas is emitted for each tonne of Normal Portland Cement produced. For single mines producing 3,000 tonnes of backfill per day, considering both backfill and cement emission source terms, total emissions of CO2 ranging between 120.36 tonnes and 169.44 tonnes/day are anticipated. In Ontario, mining operations contribute 700,000 - 840,000 tonnes/year of CO2 and Greenhouse Gas emissions to satisfy backfill cement consumption needs alone. Potential reductions of cement in backfill would significantly reduce emission of these gases and lower their adverse environmental impacts. This paper identifies alternate, equally effective and lower cost binder agent strategies for cement in backfill that may lead to cement consumption reductions. Post-consumer glass represents one such potential alternative backfill binder. Over 950,000 tonnes of glass are disposed of annually in Canada, two-thirds of which exists in the form of easily recoverable glass packaging that is not currently recycled or reused. The partial replacement of cement by waste glass may address goals for reducing non-recyclable glass waste disposal; enhancing mine back filling operations; reducing total backfill energy costs; and ultimately reducing Greenhouse Gas emissions levels currently generated by the Canadian mining industry.

Jan 1, 2004

By X. Xu, J. K. -W. Wong, J. -Y. Delenne, K. Soga

Hydraulic fracturing (HF) is a mulit-scale and multi-physics process which makes numerical modelling challenging. Conventional numerical models focus on multi-physics nature of HF but the multiscale nature is compromised by idealization of reservoir to be continuous, homogeneous and isotropic. However, natural fractures take a significant role in the success of HF for exploration of unconventional resources like Shale gas. Advancement in microseismic monitoring provides useful data for simulation in a much greater details. There is an urgent need to develop a suitable numerical tool for multi-scale threedimensional simulation to better understand the roles of discontinuities and heterogeneity in reservoir and its interaction with HF, especially to address the environmental concerns such as induced seismicity. In this paper, a simple discontinuum numerical method – Lattice Element Method (LEM) is proposed to model HF in a large scale three-dimensional model. A reservoir is modelled as a lattice network composed of 1D Hookean’s spring. Fracturing is modelled simply by removing lattices that meet a specified threshold as determined by the critical energy release rate of the rock. By introducing disorder in the model, mesh dependency in modelling fracture growth is minimized. Fluid flow is simplified as flow in pipe network and the permeability of pipe is related to fracture aperture by cubic flow law. Therefore, fracture flow and rock deformation are fully coupled. In this paper, four simulations of the same configuration except with different degrees of reservoir heterogeneity are presented. Fractures formed are diffusive and two groups of fracture are identified – connected fractures and isolated fracture without clear spatial correlation. The former forms a ‘fracture cloud’ and contributes to fluid flow and modeled by pipe network. The flow of fluid is highly tortuous and pipe network is sparely connected. The degree of reservoir heterogeneity controls the growth of ‘fracture cloud’ and pipe network. Microseismic monitoring often shows diffusive fracturing during HF on site and hence the outcome of the proposed model can be compared to such monitoring results.

Jan 1, 2015

By K. Szczesny

This paper considers the integration of uncertain real-time logistics data for reactive construction scheduling. In order to manage a construction project efficiently, an accurate schedule representing the current project progress is inevitable. The quality and up-to-dateness of such a schedule depends on the availability of real-time data. Typically, real-time logistics data contain information about the availability of material, equipment and personnel as well as delivery dates and site conditions. The accuracy and inherent uncertainty depends on the location where the real-time data was acquired. Currently, the integration of such data into a construction schedule is a very time-consuming, manual and, thus, errorprone process. Therefore, this paper proposes a methodology that enables an automatic integration of such uncertain data into construction schedules. By integrating uncertainties into the existing schedule their impacts on the construction work can be evaluated. For this, discrete event simulation is applied. In order to model uncertain input parameters for simulation models this methodology applies the fuzzy sets theory. In combination with alpha-cut sampling technique, discrete model input parameters are obtained. By applying reactive scheduling with several discrete event simulation experiments, the results can be used to modify construction schedules according to agreed timeframes and costs. In order to demonstrate and validate the presented approach an example is conducted.

Aug 1, 2013

By T. J. Langan, M. Ramajayam, T. Dorin

"6xxx-series Al alloys are the most commonly used alloys in the automotive industry as they have an appropriate balance of strength, corrosion resistance and formability. The main strengthening phase in these alloys is the ß’-Mg2Si precipitates. One opportunity to achieve stronger 6xxx-series Al alloys, without affecting corrosion and formability, is the use of Sc. The main challenge of using Sc in 6xxx-series lies in the heat treatment, which must be designed to allow for a fine precipitation of both Al3Sc and ß’-Mg2Si. In this work, two model alloys are used, an Al-Sc-Zr and an Al-Mg-Si-Cu-Sc-Zr, to explore the impact of the 6xxx-series key elements (Mg, Si and Cu) on the Al3Sc precipitates. Transmission electron microscopy and atom probe tomography are used to investigate the precipitates present in the microstructure after casting. We find that higher Si content results in the formation of dispersoids upon casting. The average composition of these dispersoids is (Al0.8,Si0.2)3 (Sc0.888,Zr0.024,Mg0.08,Cu0.008). A closer look at the solid solution reveals that most of the Sc and Zr is supersaturated after casting even in the presence of Mg, Si and Cu. We discuss the impact of these results on the design of a suitable heat treatment for 6xxx-series alloys with Sc.INTRODUCTION The most common strategy to strengthen aluminum (Al) alloys is by micro-alloying to form a fine distribution of precipitates (Gladman, 1999). Whilst precipitates enhance the strength, this is often done to the detriment of ductility and corrosion performance (Davis, 1999). The 6xxx-series Al alloys are heavily used in the automotive industry as they offer an appropriate balance of strength, ductility and corrosion resistance (W. S. Miller et al., 2000). The strength increment in these alloys comes from the formation of the ß’–Mg2Si and the quaternary Q’ phase (Chakrabarti & Laughlin, 2004; Polmear, St. John, Nie, & Qian, 2017). One opportunity to achieve stronger 6xxx-series alloys, whilst keeping good balance of corrosion resistance and formability, is the use of small additions of scandium (Sc). Sc is one of the most potent strengtheners in Al alloys (Dorin, Ramajayam, Vahid, & Langan, 2018; Røyset & Ryum, 2005). Most of the strengthening benefits from Sc come from the formation of fine Al3Sc dispersoids. The following strengthening mechanisms apply to Sc: 1) Solid solution strengthening, 2) precipitation hardening, 3) inhibiting recrystallization, 4) assisting nucleation of other strengthening phases (Dorin, Ramajayam, Lamb, & Langan, 2017). As compared to other dispersoid phases, Al3Sc dispersoids have good electrochemical compatibility with Al alloys and hence do not affect their corrosion resistance (Cavanaugh, Birbilis, Buchheit, & Bovard, 2007). The coarsening resistance of Al3Sc is often improved by adding zirconium (Zr), as it forms a Zr rich shell around Al3Sc which prevents Sc from moving across the interface."

Jan 1, 2018

By S. Hunt, S. Jayasekera, J. Kyle, N. Perera, K. Stone

A preliminary investigation has been conducted to determine the conditions for the precipitation of phosphate from the liquor produced after a hydrochloric acid pre-leach and rare-earth recovery from a rare earth containing fluorapatite concentrate from the Nolans rare earth deposit in the Northern Territory of Australia. The results show that at 50oC the phosphate can be precipitated in two stages using limestone to produce a Stage 1 precipitate containing most of the impurities including iron (94%), aluminium (92%), fluoride (98%), uranium (84%) and thorium (94%), followed by a relatively pure Stage 2 dicalcium phosphate precipitate (DCP) containing only 0.05% Fe, 0.05% Al, 0.1% F, 0.01% U, and <0.01% Th. The initial Stage 1 precipitate contained about 25% of the phosphate while the remaining 75% reported to the Stage 2 phosphate precipitate. Depending on the required radioactivity specifications, the amount of phosphate in the Stage 1 precipitate could be reduced. Reagent requirements were 11.4 kg limestone (as pure CaCO3) per cubic metre of solution for the Stage 1 precipitate and 39.7 kg limestone (as pure CaCO3) per cubic metre for Stage 2. The analysis of radionuclide balance indicated that radionuclides deported mainly to the final filtrate (86.4%) compared to Stage 1 precipitate (5.4%) and Stage 2 precipitate (8.2%). Settling and pressure filtration tests indicated the precipitates were both readily settled and filtered. The final moisture contents of the Stage 1 and Stage 2 precipitates were 62.5% and 49.3%, respectively.

Jan 1, 2014

By Ashu Garg, Anirban Bhattacharya

"Friction stir spot welding of aluminum alloy AA6061-T6 sheets was performed with circular (plunge depths 0.4 and 0.6 mm), square and triangular tool pin (plunge depth 0.4 mm) with constant 0.2 mm shoulder penetration to characterize various zones of weld nugget. It was observed that the depth of the stir zone formed below the tool pin is comparatively similar for different tool pins but wider for circular tool pin. The size of another stir zone formed at the interface of tool pin and a tool shoulder is observed to be larger for triangular and square tool pin due to the higher swept rate. Predicted strain from finite element analysis, calculated strain rate using Zener-Hollomon relationship and experimentally measured grain size distribution indicates severe amount of plastic deformation in-and-around the nugget/spot region. Finer grains in various stir zones were observed than thermo-mechanically and heat affected zones. Grain size (at distribution peaks) in stir zones varied around 2.54 µm to 3.69 µm for different tool pin profiles as compared to base metal grain size of 20 µm. Microhardness results indicate that the welded region is quite softened than base metal and maximum hardness is mostly observed around the thermo-mechanically affected zone.INTRODUCTION Friction stir spot welding (FSSW) is widely used for joining the sheets of materials like aluminum, copper, magnesium, etc. The process begins by plunging a rotating tool (generally having a pin and a shoulder) into the sheets to be welded. Continuous stirring of the tool and downward plunging force generates localized heat due to friction at the tool-sheet interface and plastic deformation of the sheet metal. The material gets softened and the plasticized material adjacent to the tool pin starts flowing due to the action of tool rotation and tool plunge thereby causing intermixing and bonding between the overlapped sheets. The tool stirring also promotes grain refinement in the weld nugget associated with high strain, strain rate and thermal cycle. The formation of new microstructure also affects the mechanical properties and efficiency of FSSW joints. Studies also showed that the tool pin design and tool shoulder feature exerts a noteworthy influence on the material flow and intermixing during the FSSW process (Reilly et al., 2015; Hirasawa et al., 2010). Sarkar et al. (2016) studied the material flow and intermixing during FSSW using tracer material method and reported that the size and width of flow zone increases with tool penetration depth. The influence of tool rotational speed on microstructure and stir zone temperature was investigated during FSSW of dissimilar AA6061-AA5754 alloys (Gerlich et al., 2007). They reported that the average grain size in stir zone of AA6061 weld increases with increase in tool rotational speed. In another work, Gerlich et al. (2008) studied the local melting and tool slippage during FSSW of Al alloys. Tool slippage was investigated by calculating the strain rate using Zener-Hollomon relation. Garg and Bhattacharya (2017a) studied the effect of dwell time, tool pin profiles and tool rotational speed on shear strength, microstructure, temperature and strain distribution during FSSW of AA6061. In another work, Garg and Bhattacharya (2017b) analyzed the effect of different tool pins and pinless tools on the shear strength and microstructure during similar and dissimilar FSSW of AA6061-T6 and pure Cu. Chang et al. (2004) proposed mathematical relationship between the average grain size and Zener-Hollomon parameter during friction stir processing of Mg alloy. Solhjoo (2010) presented a mathematical approach to determine the critical strain as a function of peak strain required for initiation of dynamic recrystallization in austenitic stainless steel. Fratini and Buffa (2005) also proposed the numerical model to determine the grain size during continuous dynamic recrystallization phenomenon."

Jan 1, 2018

By M. A. Clayton, D. Kinakin

The Mitchell Creek Landslide is a large, structurally controlled, complex bedrock instability located in northwestern British Columbia. Characterization of the landslide using aerial photograph, exploration geology, and geotechnical investigation data has been completed allowing the development of a three dimensional conceptual model of the landslide domains and slope behaviour. Three domains have been identified in the landslide, from top to bottom: the Sliding domain, a relatively intact slab slowly sliding into the valley; the Transition domain, located in the mid slope of the landslide and showing evidence of significant extension and continuing to subside and displace into the valley; and a Toppling domain, at the toe of the landslide in an area of overturned foliation. Movement is greatest in the Toppling domain, with long term estimated rates of movement up to 4 times that of the Sliding domain; the Transition domain exhibits the greatest range of displacement rates, with average long term values approximately double the slower Sliding domain. This paper documents the results of numerical modelling of the Mitchell Creek Landslide with variation in geomechanical properties, basal rupture surface configuration, structural fabric, and pore water pressure conditions. The locations of internal shear surfaces within the landslide have been estimated from surface scarps, structural fabric orientation, and borehole monitoring data. The performance of each numerical model was evaluated against observed behaviour of the landslide. The configuration and properties of the basal rupture surface were identified as critical to model behaviour, as was spacing and location of internal structures.

Jan 1, 2015

By R. Darlington, S. Ji

"High pressure die casting is a promising process to make thin-wall components with high dimensional accuracy and excellent surface quality. However, the non-uniformity is one of the important features in castings. The inhomogeneity in tensile properties and microstructural characteristics were studied for the castings with different thicknesses made by high pressure die-cast Al-Mg-Si alloys. For the local mechanical properties in the die-castings, the casting skin provided the highest, whereas the casting centre provided the lowest yield strength, UTS and elongation. The yield strength, UTS and elongation were significantly decreased towards the casting centre. The microstructural inhomogeneity is characterised by the segregation of coarse fragmented dendrites, the reduction of solute concentrations of Mg and Si, and the increase of porosity level from the surface to the centre of castings. The growth velocities of eutectic a-Al phase estimated using the Jackson-Hunt model confirm that the growth variation is larger in the thin castings than that in thick castings.INTRODUCTION Inhomogeneity is an inherent characteristic in as-cast microstructures of a variety of alloys because of their non-uniform chemistry, microstructure, defects, topology and the resultant mechanical properties in the different ranges of localization (Campbell, 2003). Generally, three types of inhomogeneities characterise casting microstructures, which include (a) the casting defects of shrinkage and gas porosity, misruns, cold shuts, inclusions, hot tears and hot spots; (b) the non-uniform microstructure from the surface to the centre of castings; and (c) the non-uniform microstructure from the dendrites grown from primary solidification and the structure formed during the subsequent eutectic solidification in inter-dendritic regions. The chemical composition and the morphology between the primary dendrites and the inter-dendritic eutectics also differ in the as-cast microstructure. Obviously, the inhomogeneity is different in the castings obtained from different casting processes."

Jan 1, 2018

By D. B. Dreisinger, M. Mokmeli, B. Wassink

Dissemination of selenium and tellurium in sulphide minerals results in the contamination of pregnant leach solutions and electrolytes in the hydrometallurgical treatment of sulphide ores and residues. The selenium and tellurium content of the copper sulphate-sulfuric acid solution may be reduced into insoluble precipitates of copper selenides and tellurides using cuprous ion. This study presents the use of the thermodynamics and kinetics for the removal process of selenium and tellurium in real life application. Dominant species of selenium and tellurium in acidic copper sulfate solutions were identified and the reduction rates of species were compared. The findings were applied to industrial conditions by modeling the Vale’s CRED (Sudbury, Canada) plant’s selenium and tellurium purification circuit. Rate reducing factors on selenium and tellurium removal were identified and discussed.

Jan 1, 2014

By Takayuki Takasugi, Naoya Masahashi, Yasuyuki Kaneno, Satoshi Semboshi, Yusuke Kadoi

Cu–Ti alloy wires doped with and without a small amount of Ni were fabricated by over-aging and using intense drawing procedures. For both the Cu–Ti alloys with and without Ni doping, the over- aged microstructure was occupied fully with a coarse lamella of Cu solid solution and β-Cu4Ti plates precipitated discontinuously by grain boundary reactions. The full-lamellar microstructure was developed much more rapidly by aging in multi steps at 873 K to 723 K rather than by isothermal aging at 723 K. Ni doping in Cu-Ti alloy was also effective to accelerate the formation of the lamellar microstructure. When drawing the over-aged alloy with inferior hardness but superior electrical conductivity, the strength increased steadily and eventually exceeded that for the wires drawn from the peak-aged alloy. In addition, the electrical conductivity of the wires drawn from the over-aged alloy was always much greater than that from the peak-aged alloy. Eventually, the procedure of over-aging, followed by intense drawing, could enhance both the strength and electrical conductivity of Cu-Ti alloys, whichever they contain a small amount of Ni or not, rather than the conventional peak-aging and drawing process. INTRODUCTION Cu-based alloy wires, which have an excellent combination of strength and electrical conductivity, have attracted extensive attention for highly mechanically stressed electrical devices, such as conductive lead wires and wires in suspension springs. Cu-Be alloys are widely used for such electrical components owing to their combination of strength and electrical conductivity among industrial Cu-based alloys. However, since beryllium is potentially toxic and also a rare element, substitute materials for Cu-Be alloys have been searched for several decades. Age-hardenable Cu–Ti based alloys have been proposed as candidates because their mechanical and physical properties are comparable to those of Cu-Be alloys; however, their electrical conductivity is inferior (Datta & Soffa, 1976; Soffa & Laughlin, 2004). In order to satisfy the requirement of downsizing and streamlining electrical devices, further improvement of the mechanical and electrical properties of Cu–Ti alloy wires is needed. Age-hardenable Cu–Ti alloys, which contain approximately 3 to 6 at.% Ti, are typically prepared using a solid solution treatment above 1100 K and then aging at a moderate temperature of 700 K to 800 K. It has been revealed that the microstructural events during aging progress as follows (Soffa & Laughlin, 2004): (1) compositional modulation of the parent supersaturated Cu solid solution in an initial aging stage (Laughlin & Cahn, 1975), (2) continuous nucleation and growth of fine needle-shaped precipitates of metastable β’-Cu4Ti with a tetragonal structure in a peak-aged stage, and (3) discontinuous precipitation of cellular components laminating the plates of a terminal Cu solid solution and stable β-Cu4Ti with an orthorhombic structure at the grain boundaries in an over-aging stage. It has been also accepted that the highest number density of dispersed fine β’-Cu4Ti needles should contribute to maximal strengthening. On the other hand, decease of the strength in the over-aging stage occurs due to the replacement of the fine β’- Cu4Ti needles with cellular components containing coarse β-Cu4Ti plates, while the electrical conductivity is significantly enhanced due to the depletion of solute Ti in the Cu matrix. This suggests that a combination of strength and electrical conductivity for age-hardenable Cu-Ti alloys is in a trade-off relationship, and that innovative improvement of both properties might be limited to tuning the aging conditions.

Jan 1, 2019

When selecting a method for monitoring crack growth in pipeline steel, the sensitivity or crack-size resolution plays a dominant role. Even though there are several visual and non-visual methods, the direct current potential drop (DCPD) method is very effective for monitoring crack growth because of its resolution. This method has been used for the past few decades and has gained increasingly wide acceptance in fracture research as one of the most accurate and efficient methods for monitoring the propagation of cracks. Furthermore, most R&D experience has proven that the electrical potential method can be used in most "aggressive" environments. For these reasons, the DCPD method was selected to design a testing machine to monitor corrosion fatigue crack growth. The use of finite-element modelling is shown to facilitate the application of the DCPD method for monitoring crack growth in steels. The 2D model calibration provided a good description of the test data and proved more accurate than the analytic Johnson&apos;s formula.

Jan 1, 2005

By V. F. Kozyrev, L. B. Tsymbulov, L. Sh. Tsemekhman, A. N. Golov

Gipronickel Institute, JS has developed a new process and equipment for melting copper raw material in a two-zone Vaniukov furnace resulting in the production of white matte and low-grade slag in terms of copper content. Tests on processing copper nickelcontaining ore from Norilsk (Cu - 17 %), Ni - 3 %) were conducted in Vaniukov pilot furnace (total area 11.4m2) of Severonickel Combine. The amount of the processed material was about 11 thousand tons. Principal results of pilot testing are presented.

Jan 1, 2007