Search Documents

By C. Beckermann

"A diffuse interface model is derived for the direct simulation of two-phase flows with surface tension, density differences between the phases, and phase change. The derivation starts from the balance equations for a sharp interface and uses a formal averaging procedure on an atomic scale to obtain diffuse interface versions of the equations. Two approaches are considered: (i) the two phases have different velocities inside the interface and separate conservation equations are solved for each phase, and (ii) the two phases have the same velocity inside the diffuse interfuce and mixture conservation equations are solved. Based on a superposition of microscopic (atomic-scale) and macroscopic interface morphologies, an expression for the interfacial momentum source term is introduced that models surface tension effects and accounts for immiscibility between the phases.IntroductionDiffuse interface methods have been a popular tool in the direct simulation of two-phase flows [I]. In diffuse interface approaches, the interface between the two phases is characterized by a rapid but smooth transition in the properties, such as density and viscosity. Usually, a phase function ? is introduced to represent this transition, and the evolution of ? in the domain is computed from a separate equation or recipe. A unique set of conservation equations (e.g., mass and momentum) is solved on the entire domain, irrespective of the phase present, by accounting for the transition in the properties and introducing terms that account for interfacial sources. The continuum surface force (CSF) model of Brackbill et al. [2], which accounts for surface tension, is an example of the latter. The volume-of-fluid (VOF), level set, and phase-field methods are all examples of diffuse interface approaches. The major advantage of diffuse interface methods is that explicit tracking of the interface and the application of traditional sharp interface conditions are avoided. A disadvantage can arise from the artificial smearing of what is in reality an interface of atomic-scale width; however, techniques have been developed to overcome this problem."

Jan 1, 2004

By Ivo André

Sorption of copper ions from aqueous solutions by dried biomass of the aquatic plant Potamogeton luscens was studied at laboratory scale. The aquatic plant was collected in water resources in Brazil, washed, dried at 60°C and ground in a bladed mixer. Sorption experiments were conducted in agitated flasks and in a packed bed column. Maximum copper removal was obtained between pH 5.0 and 6.6 when copper was present in the ionic form Cu'. Sorption followed the Langmuir isotherm with saturation attained at 35 mg/g. Free energy of sorption was found, to be of the order of -25 kJ/mol. Sorption kinetics data were better described by a second order reaction and rate constants were calculated in 0.030 1/(min.mg) for - 4.0 mm particles and 0.081 1/(min.mg) for - 0.59 mm particles. Removal of metal ions in a packed bed column showed that Potamogeton luscens biomass can be used in several sorption/dessorption cycles. After sorbent saturation, copper ions can be recovered from the loaded biomass by elution-with H2SO4, solution. Main mechanism responsible for heavy metal uptake was found to be ion exchange. Results are discussed in terms of the surface properties of the biomaterial, solution chemistry of copper ions and thermodynamics parameters.

Jan 1, 1995

By Tengfei Qi, Liqiang Fan, Huiqing Tang

A new method to process the oolitic high phosphorus iron ore for phosphorus removal has been proposed in this research. It is an integration of direct reduction and melting separation with carbon-containing pellets prepared using biomass char. Experiments of direct reduction were preceded using a tubular furnace and three parameters were investigated and they were reduction temperature, biomass char adding ratio(molar ratio of carbon to oxygen） and atmosphere. Results show that the optimum condition is of reduction temperature is 1373 K, biomass adding ratio 0.9, PCO2/PCO 1.0 and reduction time 15~25 min. Under this condition, the reduced briquettes with a metallization of 75.0~80.0 % and a residual carbon content of 0.69~0.11 wt% could be obtained. Subsequent melting separation experiments were conducted using a Si-Mo high temperature furnace. Results show metal with phosphorus content of about 0.4 mass% could be obtained from the reduced sample.

Jan 1, 2015

By Qingchun Yu, Bin Yang, Yong Deng, Heng Xiong, Fei Wang, Minxiu Chen

"Metal aluminum produced by non-electrolysis process received much attention due to its lower energy consumption. In this paper, carbothermic reduction and carbothermic-chlorination of alumina in normal pressure and vacuum were studied. The products were examined by means of XRD, EDS and SEM. During the carbothermic reduction process using carbon reductant in normal pressure, no metal aluminum was found. However, when coal was used as reductant, a mixture containing metallic aluminum, A14C3, and silicon was obtained, but metallic aluminum couldn't be separated from the mixture. During the carbothermic-chlorination process in vacuum, Al404C and Al4C3 were produced by the reaction between alumina and carbon, and Al Ch gas reacted with Al404C and Al4C3 to produce Al Cl gas. Metallic aluminum was produced due to the disproportionation of A!Cl gas and condensed on the collecting plate. Meanwhile, the initial temperature of carbothermic reduction of alumina reduced in vacuum compared with that in normal pressure.IntroductionIndustrial production of primary aluminum is carried out in alumina cell by the so-called Hall- Heroult process, necessitating the use of very high currents of low voltage. The alumina from which metallic aluminum is gained must be chemically pure, otherwise impure metal results. The main drawbacks of the electrolytic production are its very high energy consumption, the release ofperfluorocarbons, and the high specific C02 emissions [1]. During the past years, there were a lot of attempts to produce metallic aluminum by carbothermic reduction of A1203 [2, 3]. Cox [4] determined the vapor pressure over the A1203-C system and performed X-ray diffraction analysis of condensed products. It was demonstrated that an increase in the carbon content in the system leaded to the sequence of transitions: A1203~Al404C~A1zoc~A14C3 ~AI [5]. In any carbothermic reduction process for aluminum, extremely high temperatures (2000 °C ) were required [6]. In spite of considerable effort, the carbothermic reduction of alumina to aluminum remains a formidable technical challenge, due to the high temperatures required, and to the formation of aluminum carbide and oxycarbide byproducts [7]."

Jan 1, 2013

By Harry Littleton, Jr. Scarber, Wanliang Sun

"The Lost Foam Casting (LFC) process is relatively immature when compared to other casting processes. To make the process more robust, computer modeling is needed to reduce lead times and casting defects. In this study, metal filling of lost foam aluminum castings was visualized using state-of-art real time X-Ray technology. Metal filling of the lost foam casting was simulated using a commercial software package. The result of the computer simulation was compared with the results of the real time X-Ray visualization. Some of the computer simulation results agreed with the real time X-Ray visualization, but some did not. Based on other studies using real time X-Ray technology, new input variables, such as foam density variations, were developed for the computer modeling. With the new variables, modeling of the lost foam casting process becomes more realistic. IntroductionMold filling of the Lost Foam Casting (LFC) process is an important step toward making a quality part. In the LFC process, molten metal is poured against a refractory coated foam pattern surrounded by dry sand. At the pouring temperature of aluminum, the foam pattern is decomposed into 30% (wt) gaseous and 70% (wt) liquid foam pyrolysis products. Existence of the gaseous foam decomposition products significantly increases the back pressure on the metal stream compared with the conventional open cavity sand mold. Entrapment of the liquid pyrolysis products during the metal filling generates many casting defects, such as internal pores, fold and blisters. Existence of these casting defects sometimes seriously degrades the quality of the components manufactured by the LFC process. Understanding and controlling the metal filling of the LFC process will certainly make this process more robust."

Jan 1, 2004

By B. Ozturk, K. Ito, R. J. Fruehan

"A simulation model for bath smelting processes for the production of iron was developed which predicts the coal, flux, ore, and oxygen consumptions and the off gas volume, temperature and composition. The model is comprehensive in that it takes into account all of the important variables including coal composition, metal composition, ore composition, slag basicity, post combustion ratio, (PCR), prereduction degree (PRO), heat transfer coefficient (HTC) , flux, scrap charge, and heat losses. Four basic cases were considered: I. 30% PRO-50% PCR; II. 90% PRO-O% PCR; III. 60% PRO-30% PCR; and IV. 0% PRO-50% PCR. Several different coals were considered and a sensitivity analysis of the critical variables was performed. The model also estimates the sulfur content of the metal. The major conclusions included:1. Post combustion significantly reduces coal consumption but above 20% PCR little reduction of FeO to Fe can be performed with the off gas.2. Prereducing to FeO (Case I) and having as much post combustion as consistent with good heat transfer is an attractive process. This process only requires a simple pre reducer, uses less coal, and is relatively insensitive to the type of coal used.3. High off gas temperatures may pose a potential problem. The off gas temperature can be reduced by using an 02-Air mixture for post combustion, limiting post combustion or adding water to the gas.4. The use of CaC03 in place of CaO or of supplemental electricity does not appear attractive.5. The melting unit is theoretically an energy efficient scrap melter. For Case I using 200 kg of scrap as part of the charge the coal consumption decreases by about 80 kg.6. With PCR > 30% the FeO content of the slag is expected to be 2-5%, and the metal will not be saturated with carbon. These factors and the increased sulfur load since coal is the fuel indicate the sulfur content of the metal may exceed 0.25%"

Jan 1, 1988

By Yun Li

In 1999 Yunnan Copper Corporation (YCC) decided to modernise their copper smelter and change the existing sinter plant I electric furnace process to a combination of ISASMEL T and electric slag cleaning furnace. The main aim of the project was to improve the environmental performance and decrease the energy consumption. Generally the project has been successful, partly attributable to the selection of a reliable and fully demonstrated technology. The design capacity for the ISASMEL T furnace is 600,000 tonnes of dry copper concentrate per year. The furnace has been running smoothly since heat up in May 2002. YCC expended considerable effort in the preparation for plant operation. An extensive training program for key YCC personnel at the Mount Isa Copper Smelter improved their understanding of the process significantly and ensured successful hand-over of the technology. This paper describes the project history and summarizes initial operating results.

Jan 1, 2003

By Shanlu Yang

In this study, laser-GTAW hybrid welding was used to the lap joint of galvanized dual-phase (DP) 980 steel in a gap-free configuration. The effects of welding parameters such as the laser power, the distance between the laser beam and the electrode torch, the arc current on the quality of hybrid welds were fully studied. The reason for the formation of different weld defects arises from the development of the highly-pressurized zinc vapor at the interface of two metal sheets. Experimental results demonstrated that the elongated molten pool introduced by the GTAW can suppress the formation of spatters to some extent. However, the hybrid laser-arc welding process still suffers from a large amount of spatters that degrade the weld quality. Furthermore, it was found that the weld quality was enhanced with the increase in the laser beam-arc distance and welding current.

Jan 1, 2009

By A. F. Saavedra, N. E. Richards, C. J. McMinn

"The aluminum industry in general and Reynolds Metals Company in particular have continued to support development work for improvement of the Hall cell design and for alternative processes for the reduction of alumina. The evolution of the Hall cell design will continue into the next century as a result of further development of mathematical models, sophisticated control systems and new materials for cell components. This paper discusses the areas in which the new generation cell advances will differ from the present day design. Additionally, Reynolds Metal s has supported work for the development of a carbo thermic process to reduce alumina. Theoretical work has indicated that this process could possibly have economic advantage over the Hall process. Several complicated furnace configurations have been proposed to provide the conditions for successfully reducing alumina. The results of small pilot scale operation and most promising furnace design are discussed. For comparison, projected capital investment costs and operation costs are discussed. IntroductionThe evolution of the Hall-Heroult process will continue into the next century. This evolution will be influenced by economics, more .restrictive environment and worker protection requirements, and technological development. These factors will also cause changes in the competitive position of alternate processes for aluminum production.Several aluminum producers have made major investments in alternate processes for aluminum production in the past three decades and there is continued support in some companies for improvements in the Hall-Heroult process and for alternate processes. The more visible development work in reduction technology, not aimed at significant process changes, is in the areas of higher amperage cells with bus bar designs to reduce harmful magnetic effects, more advanced and automated feed, voltage and electrolyte composition control, improved energy efficiency and sol id waste disposal . Efforts to bring significant change to the reduction process are being made in development of materials that can function as inert anodes and cathodes. These materials could lead to the development of reduction cells with multiple bipolar electrodes operating on oxide feed and fluoride electrolytes. Development work on new processes was reduced in the last decade by several companies because of economic and technological realities. Reynolds Metals supported work on a carbothermic process to reduce alumina and produce commercial pure aluminum. This work progressed through small pilot plant operation, and resulted in development of furnace designs and operation regimes. This paper reviews how this and other technologies could influence the reduction of alumina beyond the year 2000."

Jan 1, 1988

By Berger. P.

The accepted definition of the function of an edge protector fails to specify adequately the several tasks which it must perform to be functionally effective: detailed analysis of these tasks leads to the reasoned conclusion that they cannot satisfactorily be fulfilled by the conventional types of "edge-strips". The true cost of edge protector failure is cumulative: renewal costs are dwarfed by the increased operating expenses and production losses which result from but partial or incipient failure of the edge-strip; yet, the several supposedly improved types, for use with starter-blanks, generally were "built down to a price", prolonging the agony, as it were. Clearly, a fresh appraisal of the problem was overdue, and more especially so with the advent of "permanent" cathodes. As a result, new methods of edge .protection have been developed, including the so-called "EDGEWISE" system in which the present author as patentee *) has a vested interest-which he hereby declares. Due mention is made of recent progress in protecting the edges of aluminium "Jumbo" cathodes in zinc electrowinning operations, although the present Paper is more concerned with edge protection of starter-blanks and permanent cathodes in copper ER/EW processes, where most of the "old" problems now may justifiably be claimed to have been overcome, Mention is also made - albeit at this time necessarily only briefly, and confined to edge protection - of "rigidized" metal blanks and permanent cathodes: a most recent development**) which may prove to represent a "breakthrough": time will tell.

Jan 1, 1987

By G. C. Gullo, H. Wabusseg, P. J. Uggowitzer, H. Kaufmann

"The basic concept of New Rheocasting (NRC) is described and the application of wrought alloys with this process is discussed. Practical experiments with the aluminium alloy AIMgSi I are explained. For this alloy the proper NRC - casting temperature was determined by using Thermo Cale - computer software and DT A and the essential processing conditions are shown. In the experiments the melt was taken from an aluminium holding furnace and cast into NRC steel cups. After controlled cooling the resulting slurries were cast into a 4-step die on an UBE HVSC 350 Squeeze Casting machine. The characteristic microstructural values such as grain size and shape factor were measured and compared with classical casting alloys. The influence of the wall thickness of the step part (6 mm, 10 mm and 14 mm) on the microstructure is described. Tensile properties in different heat treatment states are compared with characteristic prope1ties of the same alloys in forged condition. The ew Rheocasting - process CNRC)The NRC process is a recently developed new semi-solid processing method which allows the production of pore-free, pressure tight components.In the NRC process a fu lly liquid, but only slightly superheated melt is taken from a holding furnace and poured into specially designed steel crucibles, which are placed on a carousel next to the Vertical Squeeze Casting machine. In this ,NULL,slurry maker'· globul ar a-Al grains grow, following forced homogeneous nucleation at the cup wall [ 1, 2]. In the few minutes during which the melt is cooled to sem i-so lid processing temperature, a stable ske leton of a-Al phase forms. The resulting slug keeps a cylindrical shape during its slide into the sleeve of the Vertical Squeeze Casting machine, where it is cast into shape."

Jan 1, 2000

By Isabella Lancellotti, Fabrizio Passarini, Luisa Barbieri, Fernanda Andreola, Ivano Vassura, Luciano Morselli

"The techniques able to incorporate wastes by means of a heat treatment present the advantage to fix the residue with chemical bonds. Among these techniques there are vitrification and sintering which are characterised by different operating temperatures in the range of 950-1500°C and the involved raw materials develop silicatic crystalline phases and glassy matrices capable to immobilize heavy metal contents in the waste matrix. In this work incinerator bottom ash, polishing and glazing ceramic sludges have undergone to thermal treatments in order to valorise the waste as secondary raw material for the obtainment of re-products. The chemical efficiency of the process adopted has been evaluated by comparing the results of release tests applied to the as-received wastes and to the thermally treated materials in order to verify the effectiveness of the different matrices to fix the waste components.IntroductionVitrification is one of the most promising technological options for the treatment of some kinds of waste. The high temperature involved in the process (1200-1500°C) leads to the complete destruction of organic pollutants, such as dioxins, and glassy network formed can incorporate heavy metals. Some vitrification processes naturally occur: glasses produced by volcanic eruptions, such as obsidians (Na2O-K2O-Al2O3-SiO2) and basaltic (CaO-MgO-Al2O3-SiO2) rocks, are basically inert materials even when they contain toxic elements, because these are embedded in an extremely stable glassy matrix. The disadvantage of vitrification is that it is an energy-intensive process involving relatively high costs, therefore its use is better justified if a high-quality product with optimised properties can be fabricated. The most effective way to improve the properties of the vitrified material is the transformation into glass ceramic. This is a fine-grained polycrystalline material (typically from 50% to 98% of the volume may be crystalline) formed when a glass of suitable composition is heat treated and hence undergone to controlled crystallisation (phenomenon named devitrification). The three key variables in the design of a glass-ceramic are: glass composition which controls glass viscosity related to the effectiveness of nucleation and rapidity of crystallisation; glass-ceramic phase assemblage (that is, the types of crystals and the proportion of crystals to glass) which is responsible for many of the physical and chemical properties; nature of the crystalline microstructure (crystal size and morphology and the textural relationship among the crystals and glass) which is the key to many mechanical and optical properties. In particular, a partly crystalline material can be obtained by powder sintering."

Jan 1, 2008

By Zhang Hengzhong

Based on thermodynamics of surfaces and a proposed two-dimensional state equation for surfaces, the relationship between the surface tension (Y) of a solution and the activity (a1) of its component (i) was derived: (1/Y)r2-.¬E (ai/Yl) The derived equation was verified with reported experimental data of water-alcohol systems and water-acetone system, the calculated results showed astonishing coincidence with experimental. Applications of the equation to the five matte systems Cu2S-FeS, Ni3S2-FeS, FeS-PbS, Cu2S-PbS and FeS-Cu22S-PbS also demonstrated that at given matte compositions the calculated surface tensions agreed with experimental fairy well.

Jan 1, 1993

By Yoshiyuki Matsui

As one of the factors of frequent troubles on iron-making blast in recent years, increased size of the blast furnace and high-productivity operation are pointed out. Consequently, great importance is attached to deadman shape and solid flow at the lower part of furnace. In the present study, firstly, the blast furnace raceway formation under the intensive coal injection by measurement of micro wave reflection gunned through a tuyere is discussed. As the flow rate of coke as the momentum of coke into raceway decreases by combustion of coal injected into tuyeres, the depth of raceway defined as the maximum position of micro wave reflection is easy to contract. It is expected that this new technology could detect the raceway collapse phenomena in short time and that the stability of raceway in coal injection is different from that in all coke operation. Secondly, the reduced stockline surface profile was measured by the reflection intensity of microwave struck from the furnace top after blow-off with stockline reduced, and investigation was made on the countermeasures for changes in the raceway depth and furnace body profile during operation. As a result, it has been clarified that flow-down of coke into the lower part of blast furnace and inflow into the raceway are greatly subject to the existence of deadman which is the packed structure of the lower part of furnace, and further, they are closely related to dynamic behavior of the raceway, and affect changes of the furnace body profile.

Jan 1, 2006

By Judy Che, Steven Ceccio, Gretar Tryggvason

"A detailed understanding of drop deformation and solidification is essential for quantitative predictions of geometry and properties of parts made by ballistic particle manufacturing processes. Axisymmetric results of towers built by the deposition of multiple drops are presented. In these computations, fluid flow, heat transfer, and phase change are fully coupled throughout the drop deformation and solidification process. The solution method is based on a single set of conservation equations written for all phases simultaneously. The phase boundaries are treated as imbedded interfaces by adding the appropriate source terms to the conservation equations. A parameter study demonstrates the effect of Weber number, Peclet number, and drop deposition frequency on the final shape of the structure. Numerical results show that most successful method of building uniform towers is when two conditions are met. First, each drop solidifies at the same time in the deformation cycle. Second, the cooling rate is slow enough to allow for good adhesion between drops. The ability to predict the final shape of deposited drops will greatly reduce the amount of experimentation necessary to select the desired set parameters for any artifact.IntroductionMaterial deposition techniques based on layering small molten metal drops holds the promise to build small, coherent three-dimensional structures. In this process, numerous 20-100 µm diameter drops are deposited onto a substrate with a low impact velocity (on the order of 5 mis). Both the momentum and trajectory of each drop are controlled precisely to build up complex parts. This material layering technique differs from processes such as spray forming and splat quenching which involve high impact velocities (on the order of 100 mis) and high frequency deposition with little control over individual drop placement. This process of layering small drops can produce parts with near net shape accuracy, while spray forming produces slabs of material which must then be worked to make a usable part. The ability to computationally predict final drop shape and cooling rate has the advantage of allowing the user to select parameters to produce parts with desired shape and mechanical properties. However, the development of such predictive methods requires a thorough understanding of both drop deformation and solidification"

Jan 1, 1999

By Xie Zhang, Chongyang Zhao, Qingyun Huang, Bing Xie, Xiaopeng Zhen

"Extracting vanadium from vanadium containing hot metal into vanadium slag by BOF is the main vanadium production process in China. In this paper, the influence of Si content in hot metal on the quality of vanadium slag is analyzed. Synthetic vanadium slag with different SiO2 content were melted at 1673 K and then cooled to 303K at the cooling rate of 3?/min. Optical microscopy, SEM, EDS and XRD were used to analyze the mineralogical phases and crystallization behavior of vanadium slag. The results show that vanadium slag mainly contains spinel phase and silicate phase; V is enriched in the spinel phases while Si is concentrated in Fe2SiO4 CaFeSi2O6 and (Fe,Mn)2SiO4 as silicate phase. The melting point of slag increases gradually with the addition of SiO2; whereas viscosity decreases with an addition of 15~19% SiO2 and increases with an addition of 19~27% SiO2.IntroductionVanadium is an important element which is used almost exclusively in ferrous and non-ferrous alloys. The major vanadium products include FeV, V2O5, V2O3, VN and Al-V-Ti alloy. Furthermore, vanadium slags are mostly produced by oxidizing the elements in V-containing hot metal during a duplex refining process. Therefore, the process of removing vanadium from hot metal has its significance on the subsequent process[1].The extraction of vanadium is greatly affected by the mineralogical composition of vanadium slag[2], the distribution of the elements between the spinel and silicate phases and its physic-chemical properties. These characteristics of vanadium slag have been studied in some details. It has been reported that Si mainly exists mainly in the form of silicate which wraps the spinel crystals while small amount of Si stands as phosphorus quartz or diopside[2]. Chen et al.[3, 4] points out, when SiO2 content in vanadium slag increased every 1%, V2O5 decreased 1.48%. Moreover, silicate phases would embarrass the oxidation of V-containing spinels through decreasing the exposing probability[5]. Meanwhile, melting point and viscosity of vanadium slag has been greatly influenced by the SiO2 content. Therefore, this work attempts to analyze the above-mentioned questions systematically."

Jan 1, 2012

By John Pilling

The concept of microstructure, its evolution through materials processing and its effect on the properties of the material is, perhaps, the foundation upon which the science of materials is built. PHAUST, a computer aided learning program, attempts to provide instruction in establishing the relationships between phase diagrams, thermal processing and microstructure. Using phase diagrams derived from a database or created by the user, the evolution of microstructure during processing is quantified using the lever rule and/or the Scheil equation and tracked through a doubly linked list (a form of binary tree). Microstructures, in the form of full colour cartoons are then drawn using the quantitative and logical information contained within the linked list using bitmapped templates and logigal operators such as NOT. AND, OR and XOR, giving the student a view of the structure as it would be seen under the optical microscope. The software provides complete diagnostics of student answers, locates errors and misconceptions as well as providing tutoring towards the correct solution method and answer.

Jan 1, 1991

By N. A. Warner

To filly secure the environmental and social acceptability benefits of making a sulphide smelting facility and its ancillary sulphuric acid plant or other means for fixing sulphur, a virtually zero gas emission operation, it will be necessary to utilise exclusively technically pure oxygen. The strategy proposed for preventing the smelter from overheating involves highly efficient energy transfer by promoting sulphur trioxide formation at a relatively higher temperature than normal. A closed-loop gas circuit uses an eductor system actuated by the process oxygen to recirculate sulphur trioxide and unconverted sulphur dioxide back to the smelter, the endothermic dissociation of sulphur trioxide becoming a major contributor to the removal of excess heat. The only gases leaving the system relate to the bleed of nitrogen impurity introduced in the tonnage oxygen.

Jan 1, 1998

By Animesh Jha, Catherine Davey

"Carbothermic reduction and nitridation reactions using synthetic kaolinite mineral were investigated for the formation of silicon based nitrogen ceramics. The temperature dependence of the reaction rate and its effect on phases formed are reported. The effect of the reactivity of carbon on the kinetics of formation of AIN and ShN4 is discussed. Using the standard Gibbs free energy values for the formation of nitrides and oxides of aluminium and silicon, a log po2 verses I/T diagram is constructed. The experimental data results are discussed and compared with the predicted phase equilibria. We also report the influence of sub-oxide gaseous species on the microstructure of the ceramic phases produced.IntroductionSynthetic kaolinite is a clay containing alumina, silica and water of crystallisation, and has a chemical formula 3(Al2O 3.2SiO2.2H2O). This mineral is relatively inexpensive and, is therefore an ideal candidate for use in the production of ceramic powder mixtures for example silicon nitride and aluminium nitride for composite material formation, When the mineral is heated, the water of crystallisation from the crystal lattice is lost via the 3(Al2O 3.2SiO2.2H2O) = 3(Al2O3.2SiO2) + 6H2O reaction. It has been shown [1·2j that on further heating to 1673K, the anhydrous kaolinite decomposes to a mixture of mulllte and silica, 3(Al2O3.2SiO2) = 3Al2O 3.2SiO2 + 4SiO2 which is consistent with the alumina-silica phase diagram, shown in figure 1.The binary alumina-silica phase diagram has a well-defined sub-eutectic immiscibility dome and this characteristic dernixing behaviour is reflected in the thermal decomposition of anhydrous kaolinite consequently the microstructural features resemble the spinodal decomposition process. It is well established that the spinodal decomposition process raises the nucleation frequency due to their low free energy barrier, (?G). The small magnitude of this barrier consequently promotes the evolution of a very fine microstructure. The process of spinodal decomposition is therefore expected to be influential during the reduction-nitridation of kaolinite minerals."

Jan 1, 1996

By A. Iván, Patiño C. Francisco, Flores B. Javier, Peréz L. Miguel, Hernandez A. Juan, Trapála P. Norma, Salinas R. Eleazar, Rivera L. Isauro, G. Flores, U. Mizraim

"Tills work is related with the production of tiles using wastes from mining and metallurgical industry of Hidalgo State, as raw material. These wastes present a majority particle size (60 %), minor than 53 m (mesh 270, in Tyler Series) with the following composition; 70.01 % wt. of Si02, 12.82 % wt. of Ah03, 3.80 % wt. of Fe, 0.70 % wt. of Mn, 3.98 % wt. ofK20, 3.34 % wt. of CaO, 2.50 % wt. ofNa20, 0.04 % wt. of Zn, 0.026 % wt. of Pb, 56 grams per ton of Ag and 0.6 grams per ton of Au. In this work, the partial results and experimental conditions for the preparation of some composites to produce tiles are shown. The composite that offers the best results in productions of tiles was that with 66.67 % wt. of mining waste, 26.67 % wt. of red mud and 6.67 % wt. of black mud.IntroductionTo now, mining activities carried out during more than 457 years in Hidalgo State, Mexico; has lead a great volume of wastes; which can be classified into different types, having among the more common; Acid mining water, solid transport water, elements in radical form, abandoned minerals without processing and processing minerals wastes known as burrows, being these the most abundant in the region counting with an approximated volume of 110 million of tons, presenting a fine particle size that can affect population health during windy epochs [1 -4].Form metallurgical point of view, is well known that a fundamental characterization study it is necessary to know the viability of reusing or recycling of these wastes. According this, these residues can also be considered as raw materials in other economical activities, due its Si, Fe, AI, Ca, Na and P oxides contents, its mineralogy and the distribution of chemical elements in the primary and secondary phases [1,2,5,6]."

Jan 1, 2012