Search Documents

By A. R. Laplante

Recent developments in gold metallurgy are used to illustrate how the interface between gravity recovery and hydrometallurgy has evolved in recent years. Of particular interest is the use of gravity recovery to produce high-grade concentrates that can be subjected to intensive cyanidation. It is expected that a growing proportion of gold production, possibly close to 50% in certain countries, will follow this route. Other examples of the interaction between gravity recovery and cyanidation are also provided. Implications for new and renewed research directions are discussed.

Jan 1, 2003

By Chen Dong, Yuanling Gao, Jilai Xue, Jun Zhu, Luxing Feng

"Porous Ni-Ti alloy has many applications in a wide range of engineering areas. The porous NiTi alloys were prepared from Ti and Ni powders in sintering process under argon atmosphere. The major chemical compositions of the sintered Ni-Ti body were Ni Ti, Nh Ti4O and Nh Ti, respectively, the internal pore structures were characterized by image analysis technique, which were dependent on various processing parameters such as sintering temperature, amount of poreforming agent, forming pressure, etc. The results show that the porous alloy samples had the characteristics of uniform pore and high open porosity; pore-forming agent and sintering temperature are important factors in porous; pressure affected the sintered products' pore, by affecting the combination of alloy powder with pore-forming agent.IntroductionPorous Ni-Ti alloy materials exhibit not only excellent shape-memory and superelasticity, high yield strength and ductility, good corrosion resistance and biocompatibility, but also have low density, low stiffness, and high energy absorption rate due to their porous structures [1]. In recent years, these porous Ni-Ti alloys have found applications in a wide range of engineering areas, such as bone implants [2-4], impedance-matching connectors [5], energy-absorbing structures [6,7], separators [8] and actuators [9], etc.Pore characteristics can play very important role in determining of the performance of porous NiTi alloys. For example, when the alloys are used to repair or replace hard tissue implant material, the pore shape and size not only determine their mechanical properties, but also have great effect on the fluid transmission of human body. The pore characteristics can also influence the stressstrain behavior of the porous Ni-Ti alloy and, thus, strongly affect their mechanical properties, superelasticity, and fracture mechanisms [10].In this study, the Ni-Ti alloys with high porosity were prepared in a powder sintering process under argon gas. The pore characteristics were investigated using SEM, XRD and image analysis techniques, especially in association with the content of pore-forming agent, sintering temperature and compacting pressure."

Jan 1, 2011

By Scott Samson, Weidong Wang, Shekhar Bhansali, Vandana Upadhyay

"We present an improved design for the two-arm polysilicon thermal actuator. The classic thermal actuator design produces a localized hot spot at approximately the center of the thin actuator arm. This phenomenon limits the actuator efficiency, lifetime, and reliability. Since the actuator deflection is based on thermal expansion of the material, advantage may be gained by making the temperature profile more uniform along the hot-arm length. In our design, the geometry of the thin arm is modified by forming a nonlinear structure near the approximate location of the original hot spot. Electromechanical simulations of this design show an increase in deflection, due to a flattening of the temperature profile along the hot arm. The solid model generation, finite element analysis and simulations are carried out using PEA software. Experimental devices are in the process of being fabricated by using a polysilicon rnicromachining process.1. IntroductionMost active MEMS devices employ some kind of actuating mechanism to increase functionality. Various actuating mechanisms like magnetic, electrostatic, thermal, magnetostatic and piezoelectric have been investigated and incorporated for actuating microstructures. The primary features required from many on-chip actuating mechanisms are large deflection (>10 µm), low actuation voltage, low power.consumption, reliability, fast response, ease of design and fabrication, and small size. Thermal actuation is an attractive mechanism for rnicromechanical devices requiring high actuation forces, large deflections, good linearity and low actuation voltage. Thermal actuators, also known as ""electrothermal actuators"", ""heatuators"" or ""U-shaped thermal actuators"", have been largely used in MEMS based devices to provide both in-plane and out-of-plane actuation [l] .Thermal actuators are also easily compatible with standard CMOS circuitry due to their low driving voltage. However, high power consumption remains a major drawback of the thermal actuation mechanism."

Jan 1, 2004

By H. -P. Behrendt

Muldenhiütten Recycling und Umwelttechnik GmbH is a lead smelter with a very long tradition. The first reference to the existence of smelters on this site is given by a document of inheritance dated 1318. Originally run as a primary lead smelter, which was supplied with ores from the Freiberg mining district and from overseas, it was required to change it over to secondary raw materials due the abandonment of mining in the Freiberg area in 1968. Today, Muldenhüitten Recycling und Umwelttechnik GmbH has two production lines; lead production from secondary lead and waste incineration, which are closely connected and gain advantage from each other. Installations, improved technologies, and the highly skilled personnel have contributed to satisfy all demands for a production concerning quality and environment.

Jan 1, 2000

By Ashish D. Patel, Ramesh S. Minisandram

"Vacuum Arc Remelting (VAR) is the final and, hence, critical melting step for the production of a sound, segregation-free ingot for the manufacture of alloys used in rotating components in aircraft engines. A mathematical model for this process has been developed by the Specialty Metal Processing Consortium (SMPC). The model predicts temperature distribution in the solidifying ingot, flow in the molten metal pool, and the electromagnetic field in the ingot. These predictions may be used to estimate the effect of melting parameters on the pool profile in the ingot. In this paper, typical pool shapes and flow fields during VAR of Alloy 718 and Ti-6Al-4V are presented. The differences in the pool profile are primarily due to vastly different melting conditions. The model predictions are compared to the observed pool shapes from industrial-size VAR ingots.1. IntroductionVacuum Arc Remelting (VAR) is a process in which an electrode is melted in vacuum by the heat from a DC electric arc. Metal droplets from the electrode fall into the molten metal pool, which solidifies in a water-cooled copper crucible to form the ingot, as shown in Figure I. The ingot obtained from VAR is sound, and has superior cleanliness and chemical homogeneity. Hence, the process is the final melting process for most nickel-base superalloys and titanium alloys used in the manufacture of critical rotating components (discs & blades) of aircraft engines. Modeling of this process provides an insight into the effect of melting parameters on the molten metal pool in the solidifying ingot, which is a key first step in process optimization and defect prevention. In this paper, typical pool shapes, both measured and predicted, for VAR of Alloy 718 and Ti-6Al-4Vare presented. Alloy 718 is the most common VAR-processed nickel-base superalloy; whereas Ti-6Al-4V is the ''workhorse"" alloy for titanium-based alloys."

Jan 1, 2004

By D. A. Milligan

Ammonia leaching of copper sulfide concentrates, matte, scrap or other sources of copper yields copper amnine sulfate solutions which are converted to metal in a two-stage process involving precipitation of inter- mediate sulfites and their thermal decomposition to copper powder of high purity. Processing details and results are given. Considerable simplification in circuitry and cost savings are indicated. Energy requirements are reduced by substitution of copper powder precipitation and ammonium sulfate crystallization for solvent extraction, electrowinning and lime boil.

Jan 1, 1976

By Shenghui Guo, Jian Chen, Hongbo Zhu, Jinhui Peng, Linqing Dai, Qianxu Ye

"Response surface method (RSM) based on mono-factor experiment was applied for the process optimization of sintering of chromite fines by microwave. In RSM analysis, effects of binder addition amount, sintering temperature and holding time on the compression strength and shatter strength of the sinter were examined. Results showed that the optimal values of the above parameters were determined as follows: binder addition amount of 1.90% (in mass), sintering temperature of 1153? and holding time of 16 min. Under the optimized conditions, the compression strength was 11155.8? and shatter strength was 95.6849%. The results show that the process was optimized by response surface methodology is stable and feasible, and provide a new way for sintering of chromite fines.IntroductionChromite ore is the main feedstock for ferrochrome, and ferrochrome can be used as steelmaking additive to produce a variety of great strength, corrosion resistant and oxidation resistant special steel, which can be widely used in the aerospace, automotive, shipbuilding, military departments[1], and it has important strategic significance. At present, among the annual world's mined chromite the number of lump ore continues to diminish with its price rising sharply, while the proportion of ore fines been always increased, and the difference in prices between ore fines and lump ore is growing[2]. Despite the low price of chromite fines, and its rich in resources, it can be only used for ferrochrome smelting after agglomeration. Thus manufacturing blocks by using cheap chromite fines is an effective measure to reduce the cost of ferrochrome production and use the chromite resources[3]."

Jan 1, 2013

By JiaPeng Xu, Brian Lo, Uday B. Pal, Yihong Jiang, Soumendra N. Basu

"The Solid-Oxide Oxygen-Ion-Conducting Membrane (SOM) electrolysis process has been successfully tested on a laboratory scale, producing silicon directly from silica in a cost-effective and environmentally friendly way. A yttria-stabilized zirconia (YSZ) tube, closed at one end was employed to separate the molten salt containing dissolved silica from a liquid metal anode placed inside the YSZ tube. When the applied electric potential between the liquid tin cathode in the molten salt and the anode exceeds the dissociation potential of silica, oxygen ions are pumped out of the molten salt through the YSZ membrane and oxidized at the anode while the silicon cations in the flux are reduced to silicon at the liquid tin cathode. The presence of high-purity silicon crystals on the surface of liquid tin cathode was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Silicon crystals were extracted from tin cathode by chemical etching.IntroductionPhotovoltaics (PV) generate electrical power by using solar cells, and dramatically reduce the emissions of greenhouse gases (GHG). Through 2006 to 2011, it grew the fastest of all renewable technologies with operating capacity increasing an average of 58% annually [l]. However, the cost of manufacturing solar-grade silicon (SoG-Si) for high-efficiency solar energy production represents a major barrier to achieving the industrial goal for solar power of $1/Wp (watt at peak exposure) which would enable widespread grid parity. The current contract price of silicon to PV manufacturers is $50-$60/kg, with the spot market in 2007-2008 showing prices as high as $300/kg [2]. This makes the development of low cost and environmentally friendly manufacturing of high purity silicon very important."

Jan 1, 2013

"Hematite pellets were electro-deoxidized to iron in molten sodium hydroxide to produce iron containing about 10-wt % oxygen. The anodic reaction was the evolution of oxygen on an inert nickel anode. Before the electrochemical reaction, there is a reaction between sodium hydroxide and ferric oxide to form sodium ferrite and, in order to compensate for the reduction in sodium oxide content, 1 wt % sodium oxide is added to the melt. In a laboratory cell, the cell voltage was 1.7 V with a current density of 5000 A m-2, a current efficiency of 90% and an energy consumption of 2.8 kWh kg-1.Introduction The iron and steel industry contributes about 2.3 bn tonnes/annum of the carbon dioxide to the atmosphere, which is about 10% of the total, and some believe that, in order to prevent a catastrophic rise in the earth’s temperature, carbon dioxide emissions must be reduced by 50% come 2050. However, by 2050, it is likely that the iron and steel industry would have grown significantly so that the production may have risen to 2 or 3 bn tonnes/year so in order to meet the 50 % reduction on today’s figure, the carbon dioxide may have to be reduced to 25% or less, which is a very demanding requirement. There are probably three ways of reducing the carbon dioxide output:1. By capture and sequestration, but this may be technically very demanding.2. Reduction using hydrogen in place of carbon."

Jan 1, 2009

By Makiko Takahashi

A tool is being developed to predict and visualize the microstructural evolution of steels during quenching. This tool utilizes experimental data and reference data that are stored in a database to predict the microstructural development. The visualization tool animates qualitative representation of two- dimensional microstructure drawings as well as the quantitative volume fractions of phases present as a function of time. This is achieved by superimposing the Jominy End-Quench test results over the Continuous Cooling Transformation diagram of the alloy. The predicted microstructure is presented through the web browser to maximize the ease of use. In addition, a parallel coordinate system is used to aid in identifying similarities within the data set by presenting the large number of data at a glance. The results for 4140 steel that was quenched in a wide variety of quenchants will be presented to illustrate the prediction and visualization tools. Keywords: Quenching, Microstructure Prediction, Simulation, Data Visualization, Database, Applet, Animation

Jan 1, 2003

By Sylvain Gouttebroze, Mohammed M'Hamdi

In a previous work, a small scale Bridgman furnace has been used to study silicon bi-grain crystallization at different cooling rate. This work expands the analysis by studying the mechanical interaction between the crucible and ingot during the solidification and cooling. The thermal model is based on a 2D-axisymetric heat-transfer model. The flux histories are then transferred to the ingot-crucible 3D-model. Anisotropic Elastic and Crystal Plasticity model are used to model the silicon deformation. Four different assumptions are applied to model the mechanical contact crucible-ingot and three grain misorientations are considered. The results show the strong impact of the alumina crucible contraction on the stresses and deformations in the silicon ingot.

Jan 1, 2015

By Sadegh Safarzadeh, Anne-Marie Suriano, Stanley Howard

The electrodeposition of metal ions from aqueous electrolyte solutions has been a well-known process for the last half century. With numerous industrial applications such as electroplating, electrowinning and electrorefining, the kinetics of electrochemical reactions involved in the process has been extensively researched. Arrhenius-type rate equations, the Butler-Volmer equation, and the empirical Tafel equation are among the most important models to explain the rate of electrochemical reactions. The study of the kinetics of metal deposition is critical to understanding the underlying mechanisms through which a certain morphology of metal deposit is formed on the cathode. The purpose of this paper is to elucidate the influence of experimental parameters such as pH and additives on the rate and the reaction mechanism determining the rate limiting step of the electrodeposition reactions.

Jan 1, 2015

By W. Zhao

Several years ago, Reddy and Blander presented upriori model for calculating the sulfide capacity of binary silicate melts. It is modified now to apply to CaO-AlO 1.5 melts at different temperatures and compositions. Our predictions are in very good agreement with the available experimental data. From a comparison of binary calcium aluminate and calcium silicate systems, higher sulfide capacities are obtained in aluminate systems. The sulfur can be removed from hot metal more effectively by adding aluminate melts.

Jan 1, 1995

By R. J. Mitchell

Results from investigations into impurity distributions over cathodes are presented with implications for various sampling methods, Selection of an optimum treatment procedure for the test sample is outlined. The impact of both these studies on the development of an in-house method for sampling Isa Process cathode is discussed. The economic compromise actually undertaken, satifying wants and needs to sustain confidence in high grade cathode purity is detailed.

Jan 1, 1987

By Jie Li, Shu Yang, Zhongliang Tian, Xun Hu, Yanqing Lai, Shaolong Ye

The electrolyte with high solubility for Sc2O3 is very important to realize the preparation of Al-Sc master alloy by the molten salt electrolysis. The solubility of Sc2O3 in K3AlF6- Na3AlF6-AlF3 melts is determined with an isothermal saturation method. The effects of KR (ratio of K3AlF6 to K3AlF6+Na3AlF6), the concentration of Al2O3 and the temperature on the solubility of Sc2O3 are also investigated. The results indicate that the solubility of Sc2O3 in K3AlF6-Na3AlF6-AlF3 melts increases and then decreases with KR increasing. The solubility of Sc2O3 is 8.698 wt.% in (K3AlF6-Na3AlF6)(KR25%)-18 wt.%AlF3 melts at 940℃. The effect of temperature on the solubility is little, and the values are 8.575 wt.% and 8.762 wt.% respectively when the temperatures are 930℃ and 960℃. The solubility decreases from 8.809 wt.% to 7.058 wt.% as the concentration of Al2O3 increases from 1.5 wt.% to 5.0 wt.% at 950℃.

Jan 1, 2015

By Mark Cross, Andrew P. Campbell, Koulis A. Pericleous

"Computational Fluid Dynamics (CFD) modelling is being used to simulate the freeze layers formed within direct smelting processes. There has been some concern whether water-cooled elements can withstand the p~ocess conditions and in particular abnormal cases where they may be splashed in molten metal.To validate the models being developed, two cases from literature have been modelled for solidification and stress analysis. The solidification case is presented in detail and is for hot molten metal flowing through a cylindrical pipe. The walls are at a temperature below the melting point for the metal. The resulting solid (or freeze) layer is within 3% of the value calculated by Sampson & Gibson9 •Preliminary modelling of the refractory-slag interactions is presented. Although three basic mechanisms: Penetration; Corrosion; and Erosion will eventually be modelled, only the penetration is considered here. The corrosion mechanism is to be modelled by tracking the time that the penetrated refractory is at the required temperature.Future work, after adding all the required physics, will focus on the modelling of a water-cooled element placed lower in the smelter. Process perturbations will be simulated to examine what these elements will withstand."

Jan 1, 2001

By H. L. Ludtke

Microlaminate composites were fabricated by electron-beam physical vapor deposition. The microlaminates consisted of five layers, each 2 to 4 pm thick, and were composed of either pure metal layers (Cu-Ag), or alternated between metal and intermetallic layers (Nb(Al)- Nb3Al). The microlaminates were heat treated in an Ar atmosphere for 2 to 12 hours, at temperatures of 600°C for the Cu-Ag and 1000°C to 1200°C for the Nb(Al)-NbsAl. Microlaminates were examined after deposition and after heat treatment by scanning electron microscopy and energy dispersive x-ray spectrometry. The effects of heat treatment on the morphological stability of these composites will be described.

Jan 1, 1999

By Kenneth G. Thomas

This paper reviews the alkaline and acid gold autoclaving experiences gained at Barrick Gold Corporation. Alkaline autoclaving was operational at Barrick Mercur, Utah, U.S.A., on carbonaceous/sulphide refractory ore for eight years commencing in 1988. Acid autoclaves have been operational at Barrick Goldstrike, Nevada, U.S.A., on sulphide refractory ore since 1990 and now process 17,500 stpd of ore through six large autoclaves. Information is presented on operating costs, materials of construction, reagent requirements and flow sheet developments that reduced capital and operating costs.

Jan 1, 2000

By C. E. Dodson

Conventionally hydrometallurgical recovery processes from sulphide concentrates include roasting, leaching, precipitation, impurity removal and zinc electrowinning. The use of the novel (yet commercially proven in other mineral and metallurgical industries) TORBED process reactor for the flash roasting of sulphides will be proposed. The potential advantages in its application will be discussed including very fine particle processing capability, lower cost smaller roasters, waste minimization, improved leaching efficiency and overall process simplification.

Jan 1, 1999

By Seshadri Seetharuman

The present paper summarises a series of measurements of the interaction parameter of oxygen in liquid copper with respect to a third element, e(M)o, where M is Mn, Zn, As, Se or Te which are common impurities in the liquid metal. The technique employed was the solid electrolyte galvanic cell method. The cell used may be represented as Pt, W or cermet / Cu-O-M // ZrO2 - CaO // AO, A /PT where AO/A represents a suitable oxide/metal reference. The measurements indicate that Mn and Zn interact very strongly with oxygen in liquid copper while, in the case of arsenic the interaction parameter is nearly zero. The behaviour of the elements Se and Te is unique with respect to oxygen interactions in copper bath. At oxygen levels, xo= 10-4 ? 10-5, the apparent interaction parameters are negative, comparable to that for sulphur. On the other hand, at lower oxygen levels, the results indicate that the interaction parameter values are positive. The results are discussed in the light of some of the theoretical models for solute interactions in liquid metals.

Jan 1, 1993