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By A. De, J. S. Zuback, T. Mukherjee, T. DebRoy

For successful commercial applications of additive manufacturing, metallic parts need to be defect free, structurally sound and reliable. However, additively manufactured metallic parts are susceptible to distortion, lack of fusion defects and compositional changes. Methods to measure susceptibilities of various alloys to these defects are needed but not currently available. Here we show that the necessary theories can be developed based on a well-tested numerical heat transfer and fluid flow model and decades of research in the field of welding. The proposed theories are validated with experimental results reported in the literature.

Jan 1, 2016

By Fuqiang Zheng, Feng Chen, Wenting Duan, Yufeng Guo, Tao Jiang

High-quality titanium-rich material is of significance in the development of titanium industry as it is the main raw material to produce sponge titanium and titanium white using chloride process. Activation roasting of titanium slag with high Ca and Mg contents as adding H3PO4 followed by acid leaching was investigated to prepare titanium-rich material. The effects of H3PO4 dosage, roasting temperature and time, hydrochloric acid quantity, acid leaching temperature and time on TiO2 grade and removal of impurities were studied. The results show that after the finely ground titanium slag roasted with 8% H3PO4 at 1000 for 2h, most Mg impurities in anosovite solid solution structure were converted into simple acid–soluble compounds. The impurities such as Ca and Mg obviously decreased when the hydrochloric acid concentration was 20%, leaching at 100 °C for 2h, from which a titanium-rich material containing 82.56% TiO2 and 1.15% (CaO+MgO) was obtained.

Jan 1, 2016

By Peng ZANG, Qihang Liu

Experimental work was conducted to determine the relationships of coal char conversion with temperature and heat absorption. The results show that at an earlier stage of the coke forming process, lump coal would absorb large amounts of heat but the increase of high temperature strength of lump coal was not significant. Contrarily, the lump coal’s high temperature strength was greatly improved at later stage of coke forming process. A number of residual coal was found in most tuyere coke samples illustrating that the lump coals added in the melter gasifier were not completely transformed into coke when they arrived at the tuyere region. The results indicate that the improvement of lump coal’s high temperature performance is limited in the melting gasifier by the low coke forming rate which could become the core factor of fines generation of lump coal in the melting gasifier.

Jan 1, 2016

By P. M. Tait, N. A. Warner

"The refining of thermally produced zinc is currently performed using a highly energy intensive and arguably outmoded process, distilling zinc under atmospheric pressure at temperatures of 900°C to 1000°C. In order to produce refined zinc more profitably and with less environmental impact a new process has been proposed. This process is generic to all thermal zinc smelters and aims to match the purity of zinc from current technology (99.99%-99.999%). The objective is to perform all separation processes using only the heat contained in the smelter product stream. Vacuum conditions are extensively used lowering operating temperatures and enhancing separations. As part of this process zinc is distilled under vacuum from high concentration obtaining a refined product with respect to lead content. A mathematical model has been developed from fundamental principles to describe this stage, the distillation of zinc across a temperature difference between two circulating zinc streams in open channels under vacuum. Heat for the distillation is supplied by the liquid phase, necessitating a large recycle to maintain high operating temperatures, and keep zinc concentrations high. In determining this model and the operating conditions required, relationships between temperature, pressure and composition are considered.IntroductionCurrent technology (the Refluxer) used to refine thermally produced zinc is both expensive and highly inefficient. At present 80% of the worlds zinc is produced via the electrolytic process reflecting the poorer performance of the thermal route, the zinc-lead blast furnace and Refluxer. A new process is proposed to overcome the drawbacks of current processes. These drawbacks are both economic and environmental. The Refluxer requires 6.6 GJ of energy to refine one tonne of SHG zinc 1, other disadvantages of the Refluxer stem from high operating temperature, around 900°C, and liquid zinc being highly corrosive towards ferrous metals. The Refluxer is constructed from silicon carbide sections which join together by means of flat machined faces making liquid metal leaks inevitable. The Refluxer columns are very sensitive to thermal cycling, thermal shock and mechanical vibration, which easily lead to structural failure. To avoid thermal stress on the columns the feed rate and feed temperature need to be kept constant which means the feed baths to the columns must be able to accept solid and liquid feed as the Refluxer has to operate when the smelter is shut down."

Jan 1, 1998

By Hani Henein, J. Barry Wiskel

"The easy accessibility and power of the PC, as well as the education of our engineering students in the use of these tools, are compelling reasons for developing computer aided instructional (CAI) tools. There are a wide range of areas in the engineering curriculum where students must learn the steps and the process of applying judgement in problem solving. In the typical course instruction, · an instructor introduces theory to students; the application of the theory to solving problems is often demonstrated in the abstract. Students therefore spend a significant amount of time learning how to apply the theory to problem solving. Additional time and effort must then be spent to get students to the point of learning concepts and integrating this knowledge. A number of computer aided packages have therefore been developed for use in several courses in the materials science and engineering curriculum that encompass both calculational and instructional capabilities. This paper presents an overview of some of these packages which include the solution of a non-linear equation, the instruction of binary diffusion couples, an introduction of crystallography, an introduction to heat transfer and the solution of thermodynamic stability diagrams. The context in which these CAI Tutorials were developed and are being used will be discussed. The pitfalls in the development of these packages will also be discussed. The use of the tutorials has important implications on the expectations from an engineering education of both instructor and student.IntroductionTraditionally, it is quite routine to teach engineering students how to use a computer (the PC today for undergraduates) as a tool in performing engineering calculations or in simulating a process or a unit operation. This often takes the form of one course in computer programming, whether it is Fortran, Visual basic or a spreadsheet, and another course in numerical computation. However, the materials and electronic revolution have brought about considerable advances in computer power and speed, and accessibility. Today, the manipulation of digital images, movies, and speech are commonplace on a desktop PC.' Many mathematical models that were executed only on workstations can now be readily handled on a PC. Concurrently, more of our students own a PC even if their curriculum does not require them to purchase one. Today, virtually every university student has been introduced to the PC in either their elementary or high school education. Hence, the increased capabilities and accessibility of the PC and the familiarity of students with this tool make it compelling to explore its use as an educational tool for our engineering students. This is not a traditional role of a computer in our engineering curriculum."

Jan 1, 2000

By Don Ibana

The use of solvent extraction (SX) in process metallurgy is particularly attractive as it is applicable to a wide range of solute concentration and pH, and it allows complete separation of chemically similar metals such as nickel and cobalt and the rare earths among others. It is therefore applicable to the processing of low grade and complex ores, which is increasing and expanding owing to the diminishing reserves of quality ores, and this has driven the increasing and expanding use of SX.The current SX technology, however, has inherent limitations owing to the use of mechanical agitation as it induces high shear mixing. Excessive shear produces very fine droplets, and while this favours mass transfer, it also leads to sluggish phase separation. High shear mixing is also known to favour crud formation. All these factors as well as high power and reagents consumptions contribute to poor process efficiency. Electrostatic solvent extraction (ESX) is similar to conventional SX except that mechanical agitation is replaced with electrostatic agitation. In direct contrast to mechanical agitation, it allows the production of very small droplets that can be made to maintain intense motion, which favours mass transfer, without affecting the phase separation. In addition, as it uses an electrostatic field, the power consumption is minimal. Hence, it promises to be a superior alternative to conventional SX mixing although an application of the technique is yet to be achieved.Our work to develop an application of the technique in process metallurgy has now established that electrostatic field has no effect on either the stability of the reagents or the chemistry of the process. A volumetric flowrate that is comparable to that of a conventional sieve plate pulse column is achievable. We have also established that electrostatic fields can be made to yield much narrower droplet size distributions than those of mechanically agitated contactors, and they allow better control of droplet motions, which include oscillation and linear motion and hence, mass transfer. These are significant advancements toward our goal and shall be discussed in this presentation.

By Kouji Mimura, Tamas Kekesi, Yongfu Zhu, Masahito Uchikoshi, Minoru Isshiki

"The formation and anion exchange sorption of chloro complex ions can offer a great potential to be utilized for the separation and purification of metals in aqueous solutions. Available stability data were primarily used to estimate the predominance of chloro complex species, indicating the feasibility of such separations. Anion-exchange sorption functions, describing the equilibrium distribution of a number of important elements have been determined by the batch equilibrating method in the practical HC1 concentration range. Various oxidation states were stabilized by the addition of appropriate agents. Tendencies in oxidation, complex formation and anion exchange sorption were confirmed by spectrophotometric investigations. Based on the fundamental results, anion exchange processes have been developed for the purification of iron, cobalt, copper and zinc. The efficiency of separation was assessed and the procedure optimized by the analysis of experimental elution curves. Results have demonstrated that by properly controlling the oxidation states and HC1 concentrations, practically all the impurities can be eliminated. Computer programs have been developed to estimate complex formation and redox equilibria, to screen and correct analytical data, to determine distribution coefficients and to evaluate efficiencies of separation.IntroductionBase transition metals have long been used as the staple materials in various fields of industry. In general, there has been an increasing tendency in purity requirements but recent advances have created a rapidly increasing demand for ultra-high purity metals. To give a few examples, ultra high purity copper can be used as bonding wire and interconnection in integrated circuits, or as material for superconductor stabilizing, high-field magnets, beside its use in cryogenics and ultra high vacuum technology [1]. Iron holds promises as a constituent element in the ß-FeSi2 material to be applied in new opto-electronic devices [2] and it is currently used, together with chromium and manganese, in the production of special magneto-optical materials for digital recording. The use of ultra high purity manganese and chromium in semiconductor technology is evolving. Although not considered a transition metal, zinc is also treated here because of the major significance in compound ZnSe semiconductors [3], and the possibility to purify it by the anion exchange method."

Jan 1, 2000

By Xin Zhang, Mengqi Li, Hongxu Li, Xinrong Zhang, Hao Bai, Ning Li

"Organic Rankin Cycle (ORC) is an effective technology to transform low-grade energy resource into electricity. In this paper, based on thermodynamic principle, considering the waste heat resource lower than 120°C, thermodynamic properties of ORC with working fluids ofR245fa, mixed R21/R245fa and mixed Rl52a/R245fa were assessed. The results show that high evaporation temperature contributes to improved system performance. The Rankine Cycle that uses R21/R245fa can increase net cycle output, thermal efficiency and exergy efficiency by 3.02%, 2.35%, and 4.44%,respectively, as compared to that with pure R245fa. When using Rl52a/R245fa as working fluid, the net cycle output can increase by 3.83% at most, while the thermal efficiency decreases by 8.7%. These results indicate that R21/R245fa has a good advantage in improving the cycle thermodynamic performance.IntroductionOrganic Rankine cycle is usually used for low temperature power generation, and is applied to the conversion of geothermal energy, low-temperature solar energy, ocean thermal energy and industrial low-temperature waste heat etc. Traditional Rankine cycle is quite mature already, however, organic working fluids would affect significantly the general efficiency of the entire thermodynamic system. Thus, selection of proper working fluids and development of new highperformance cycle is becoming important."

Jan 1, 2013

By Julien Favre, Akihiko Chiba, Damien Fabregue, Yuichiro Koizumi, Eric Maire

"The mechanical behavior of Co-20Cr-15W-10Ni alloy is studied by compression tests at high temperature. Microstructures after deformation are evaluated using SEM-EBSD. Significant grain refinement occurs by dynamic recrystallization for high temperature and low strain rate (T>1100°C, <0.1s-1), and at high strain rate (~10s-1). Dynamic recrystallization is discontinuous and occurs by grain boundaries nucleation, leading to a necklace structure. The nucleation mechanism is most likely to be bulging of grain boundaries. However, recrystallization occurs also by rotation of annealing twins which can bulge as well. The modeling of mechanical behavior gives a fair quantification of flow softening due to dynamic recrystallization, indicating the progress of dynamic recrystallization with deformation.IntroductionCobalt-chromium alloys are used in biomedical applications for the elaboration of implants due to their outstanding mechanical properties and their high resistance to corrosion. For stent application a large ductile behavior is required in addition to the high mechanical strength. Indeed stents have to undergo a deformation until e˜40% during their expansion [1]. Conventional Co-Cr-Mo (CCM) alloys exhibit limited ductility (maximal deformation about e˜30%) [2]. Co-Cr-W-Ni (L-605) alloy is a better candidate for stent elaboration since its fracture strain can exceed 40% (comparable to nickel superalloys (Figure 1), while it keeps high mechanical strength. In spite of the presence of nickel element in this alloy, biocompatibility is sufficient for vascular implants, therefore L-605 alloy is extensively used for heart valves and stent elaboration [3]."

Jan 1, 2012

By K. Morsi

Titanium-titanium boride whisker (TiBw) composites are emerging as strong candidate materials for advanced applications within the automotive, aerospace and defense industries. Although increasing TiBw volume fraction improves the specific stiffness and wear resistance of titanium, it is usually on the expense of fracture toughness and ductility especially at increased volume fractions of reinforcements where whiskers interlock. This research addresses strategies for microstructural design that may overcome these shortcomings, by generating titanium composites that are locally reinforced with TiBw through in-situ reaction in segregated regions of the microstructure and separated by ductile Ti matrix. The effect of varying composite reinforcement particle sizes (i.e. size of the reinforced regions) on the pressure-less sintering of these dual matrix composites is discussed. Electric current activation was also used to generate high density dual matrix composites and a new simultaneous imaging and modulus mapping technique was used to characterize these unique microstructures.

Jan 1, 2008

By Guo Chen, Jin Chen, Jinhui Peng

In this study, the influences of the green evaluation variables on the characterization of microwave shaft furnaces were systematically investigated. These variables include: resource consumption, environment impact, production cost, processing time and quality of microwave shaft furnaces. A greenness evaluation index, evaluation system and evaluation model of microwave shaft furnaces were established. The analytic hierarchy process and fuzzy comprehensive evaluation were applied to the evaluation process. Resource consumption and environment impact had a statistically significant effect on the green evaluation of microwave shaft furnaces. The results indicated that green evaluation techniques can be applied effectively and efficiently to the process manufacturing of microwave shaft furnaces.

Jan 1, 2015

By Bing Song, Fei Xi, Xuewei Lv, Kai Zhang

The electric arc furnace process is a common method to produce high TiO2 slag from ilmenite. The pre-reduction process was proposed in recent years in order to reduce electricity consumption. In order to enhance the pre-reduction degree, high energy ball milling was proposed to improve the specific surface area of the ilmenite prior to reduction. In this study, the carbothermic reduction behavior of milled ilmenite concentrate was investigated. It was found that the ball milling method can result in a higher reduction rate and improved metallization of iron. The metallization of iron increased with increasing the time of ball milling. The metallization of iron with milling reached 89.49% when the time of ball milling was 70 min., while the FeO content decreased with 70 min. of milling from 11.84% to 4.76%.

Jan 1, 2014

Laboratory trials were performed in an induction furnace to study droplet formation during lance blowing. Compressed air was blown on a molten iron bath consisting of iron alloyed with carbon and silicon. Steel droplets were collected using a specially designed sampler. The average steel droplet composition and the oxide layer thickness were determined using scanning electron microscopy combined with energy dispersed spectroscopy. In addition, the concentration gradient of elements was determined using a microprobe. It should be noted that a special technique had to be developed in order to prepare the droplet sample. The size distribution and composition of the droplets was also determined using the microprobe. It was found that the carbon content in the droplets was lower than the carbon content in the bulk.

Jan 1, 2006

By Guo-Sen Zhu

Research on the formation mechanism and control of corner transverse cracks was carried out. The optical microscope and SEM were applied to analyze the characteristics of cracks. It is found that the cracks occur at the relatively lower temperature due to unbending strain and have almost nothing to do with the mold cooling and powder. The keys to prevent corner transverse cracks are to optimize the corner temperature of slab and maintain the good state of casting machine. Increasing casting speed and decreasing the cooling water flux at the corner in the unbending segments, resulting in mild cooling, were applied during investigation to control corner temperature above the upper limit temperature of the No.3 brittle zone of Nb-contained steel tested by Gleeble-1500 system. As a result, corner transverse cracks were minimized, but centerline segregation got worse. And then increasing the cooling water flux at the corner (intensive cooling) was applied to make corner temperature below the lower limit temperature of the No.3 brittle zone. Great diminution of both corner transverse cracks and centerline segregation was achieved finally.

Jan 1, 2006

By Jae-Chun Lee

One of the main advantages of the supported liquid membrane(SLM) would be that different kinds of ions can be extracted selectively or simultaneously from multi-component solutions by parallel treatments with multi-SLM units. This distinctive feature of the SLM extraction is originated from its non-dispersive contacting operation between organic and aqueous phases. In this study, simultaneous and selective extractions of zinc and copper ions from their mixed solutions have been demonstrated using two parallel modules of SLMs. PC88A and LIX84 were used as the extractants for zinc and copper, respectively, and the Hoechst Celanese hollow fiber modules(Liqui-Cel Lab Module) as the supporters. The performance of the simultaneous system was compared with those of the system in which the extraction of each component was achieved by individual runs

Jan 1, 1998

By M. Cowling, S. Kumarl, A. W. Piper, R. A. Forsdick, C. Bailei, M. Patell

"The lead-refining process takes place in hemispherical vessels called kettles. In these kettles, lead-bullion is mixed at a certain temperature to remove impurities from the melt. This paper presents steps in a novel method for calculating vortex shape and flow field in the refining kettle using Computational Fluid Dynamics (CFD). First of all a two-dimensional axisymmetric model is used to calculate the vortex shape at the liquid-air interface. Here action of impellers and baffles are accounted for by adding source and sink terms to the appropriate momentum equations. The model includes Yolume of Fluid (YOF) method to predict the shape of interface deformation, i.e. vortex. This strategy reduces the computationally intensive three-dimensional transient simulations to a more efficient two-dimensional model. The calculated vortex shape is then used to regenerate a full three-dimensional grid. This grid is used to carry out steady-state simulation using the standard multiple-reference-frame method of impeller-fluid-baffle interaction within the commercial code Fluent. Simulation results for both stages of the development are compared with experimental data.IntroductionOne of the most important steps in Lead Refining process is impeller stirred mixing of Lead Bullion in hemispherical vessels. During this process, the melt is treated with one or more reagents in order to remove impurity elements such as copper, antimony, silver and bismuth. These impurities react selectively with the reagents and float to the melt surface in the form of a powdery layer, which is then skimmed for further processing. Figure-! shows (a) the lead refining kettle and (b) the schematic representation of involved flow pattern. Stirring of the lead bath using specific impeller designs, which creates a central vortex, provides a mechanism for draw-down and dispersion of the buoyant reactants. Clearly, effective control of the impeller generated vortex and flow pattern is crucial to achieving efficient operating conditions."

Jan 1, 2001

By J. L. Hill, M. A. R. Sharif, J. Lin

"A numerical algorithm has been developed to simulate the movement, breakup, and entrapment of the oxide film inclusions encountered during the mold-filling processes of aluminum castings. The flowfield is solved using the well-known Marker and Cell (MAC) method by a time marching process. The Volume of Fluid (VOF) method is used to track the free surface boundaries. A kinematic approach is employed to track the movement and breakup of the oxide films on the free surface or in the bulk liquid metal. The computer program based on the proposed algorithm is able to model the flow behavior and oxide film movement, breakup, and entrapment in mold cavities for aluminum castings.IntroductionMetallographic and fractographic studies of the aluminum castings show tangled networks of oxide films in the castings. These oxide films can form in the furnaces or during the mold filling processes. Green and Campbell [I] concluded that the oxide film defects dominate the strength of aluminum castings. The main cause of oxide film entrapment into the bulk molten metal during the casting processes is the surface turbulence. In film-forming alloys, if the surface breaks, due to a drop, a fountain, or a breaking wave, then the surface film is folded over and incorporated into the bulk liquid. The incorporation of surface films leads to cracks in the casting and other defects that are nucleated by the presence of the folded films, such as porosity and hot tears. Campbell [2] estimated that up to 80% of scrap in light-alloy casting is the result of surface turbulence."

Jan 1, 1999

By M. J. Collins

Pressure leaching of zinc sulphide concentrates has been practiced commercially for nearly two decades. The process, which includes direct leaching of concentrate with spent electrolyte in an autoclave, has been commercialized at four separate locations to date. In pilot studies carried out in the Dynatec lab in Fort Saskatchewan, dozens of additional zinc concentrates have been shown to be amenable to pressure leaching. This paper highlights recent improvements in zinc pressure leaching that have been identified through process development studies, and how the experience gained in these studies has been utilized in the development of a new copper pressure leach process.

Jan 1, 2000

By J. Chen Kuriyama

One method to store hydrogen effectively involves the use of metal complexes such as the alkali-element aluminum hydrides. The hydriding/dehydriding properties of these materials depend on how to prepare them with different structures and microstructures. The present work focused on a high-energy ball milling technique to produce Ti-doped lithium tetrahydridoaluminate (LiA1H4) and lithium hexahydroalanate (Li3AIH6) powders with nanocrystallites. The phase structures and dehydriding/rehydriding characteristics were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller measurement, thermogravimetry, and differential scanning calorimetry. The mechanism of dehydrogenation and rehydrogenation was also examined by means of X-ray photoelectron spectroscopy (XPS). The results on the relation between the reversible hydrogen storage and catalysis function of the Ti-doped complex hydride indicate that both the homogenous distribution of Ti+AI nanoclusters and the Ti¬catalyst with Ti e> Ti3+ (Ti0/Ti2+/Ti3+) defect sites play important roles in optimizing the reversible hydrogen storage.

Jan 1, 2002

By Shufeng Yang, Anping Dong, Yongfeng Chen, Jingshe Li, Lifeng Zhang, Liyuan Sun

"Instead of nickel-based stainless steel, a nitrogen-bearing stainless steel was produced to reduce the production cost stemming from the shortage of nickel recourses. Thermodynamic model to calculate the saturation nitrogen content in the stainless steel were developed and the model was validated by experimental measurement. The experiments were performed with a high temperature induction furnace. Nitrogen gas under constant pressure was injected into the crucible with a top lance by which the nitrogen was transferred to the molten stainless steel. The effects of chemical composition, temperature, superficial active elements and nitrogen-flow rate on transferring nitrogen to the steel were investigated and discussed.IntroductionWith the rapid production growth of stainless steels, nitrogen-bearing stainless steel has recently attracted more and more attention for their high strength and excellent corrosion resistance imparted by interstitial nitrogen without decreasing its toughness and ductility. Moreover, the addition of nitrogen to the stainless steel as a substitute for nickel leads a lower consumption of nickel, so significantly lowers the high production cost stemming from the shortage of nickel recourses. However, production of the nitrogen-bearing steel is difficult since nitrogen is a gas element and has a low solubility in the steel. So efficiently increasing the amount of nitrogen in steel continues to be one of the main concerns for the production of nitrogen-bearing steels.Currently there are some special processes to produce austenitic stainless steels with a very high N content, including pressurized electroslag remelting, counter-pressure casting, special induction melting and powder metallurgy, etc [1]. Special expensive vacuum system was required for these processes. Alloying nitrogen at a normal pressure can be performed by alloy addition or gas injection. Blowing nitrogen gas is a more economic and advisable method since the nitrogen-bearing alloy is quite expensive and contains high content of impurities. A number of investigations have been reported on the solubility of nitrogen gas in pure iron [2] but few in iron-based multi-component alloys such as stainless steel.In the current study, the effects of steel chemical composition, temperature, superficial active elements and nitrogen-flow rate on transferring nitrogen to the steel were experimentally investigated with a high temperature induction furnace."

Jan 1, 2011