Search Documents

By Lijuan Li, Zheng Lu, Xin Xia, Qijie Zhai, Qingchun Li

"Pulsed current and pulsed magnetic field have been applied to the bainite transformation of Cr5 steel. Three groups of experiments were conducted. In the first group, ordinary resistance furnace was used for heat treatment. The Cr5 specimens were rapidly heated up to austenitization temperature 940 °C, held for 20 min, air cooled to bainite transformation temperature 350 °C, held for 10, 20, or 40 min and then air cooled to room temperature. The second and the third group shared the same temperature-time curve with that of the first group, but their heat resources came from the Joule heat produced by pulsed current. 1.5 T pulsed magnetic field was exerted on the third group specimens when they were held at 350 °C, but the second group specimens did not undergo the treatment of magnetic field. It was found that both pulsed current and pulsed magnetic field obviously retarded the bainite transformation. The phenomena were discussed in terms ofliterature results.IntroductionApplying pulsed current and pulsed magnetic field technology are very pronnsmg ways to change the microstructure of materials by affecting the phase transformation process. People had found that pulsed current dramatically influences the behaviors of materials, for example, electromigration effect [l], the solidification of metals and alloys [2, 3], electroplasticity [4, 5], crystallization of amorphous alloys [6], healing of metal materials [7] and so on. As to pulsed magnetic field technology, a lot of effort had been spent on grain refinement in solidification of metals [8, 9], recrystallization of cold-worked metals and alloys [10] and Fe-based alloys solid-state phase transformation [11, 12]. Though application of pulsed current and pulsed magnetic field technology have proliferated in recent years, investigation on their effects on solid/solid phase transformation, especially bainite transformation, is lacking. The aim of this paper is to show the effects of pulsed current treatment (C-T) and the combined treatment of pulsed current and pulsed magnetic field (CM-T) on bainite transformation of commercial Cr5 steel"

Jan 1, 2014

By Wantae Kim, Furnia Saito, Qiwu Zhang

"A novel mechanochemical processing technique for the preparation of zeolites from kaolinite in NaOH solution was investigated. Dry and wet mechanochemical treatments combined by subsequent moderate heat treatment could accelerate the synthetic reaction for zeolites from kaolinite. This stimulating process produced zeolite-A and zeolite-X from activated kaolinite at extremely lower reaction temperature than conventionally applied for zeolites production. Conversion to zeolite-A and zeolite-X was strongly dependent on the activated state of kaolinite. Wet mechanochemical treatment modified the chemical composition of activated solids. Rapid dissolution of AIO species rather than SiO ones in the reactant solution was accelerated by wet milling together with NaOH that promoted the formation of zeolite-X of high specific surface area.IntroductionZeolites are a family of hydrated alumina-silicate minerals contains alkali and alkaline earth metals. They have a framework structure that encloses inter-connected cavities occupied by large metal cations and water molecules. Zeolites are characterized for their ability toward ion exchange and reversible dehydration. Properties of them are exploited through commercial productions of particular structural and chemical features. Zeolites are used as commercial uses for catalysis for FCC (fluidized catalytic cracking) of petroleum refining, drying reagents of gases and liquids, and selective adsorbent for pollution control [1-3]. In such purposes, artificially synthesized zeolites are employed, although natural ones are associated with hydrothermal and hot spring alteration of volcanic materials. Commercially, a hydrothermal process has been used for the preparation of zeolite synthesis. This preparation method gives zeolites of high chemical homogeneity and purity, however, this wet-chemistry-based processing is significantly influenced by reaction temperature, pH, concentration, and composition of starting substances [4]."

Jan 1, 2000

By R. Padilla

In most of the Chilean copper and gold concentrates, arsenic is present mainly as enargite, Cu3AsS4, which at the conventional roasting or smelting temperatures decomposes liberating arsenic as gaseous compounds. The objective of this investigation was to study the decomposition reaction of enargite in an inert atmosphere in the range of 500 °C - 750°C. The results obtained indicated that the decomposition begins at about 525 °C. Two distinct regions in the temperature dependence of the decomposition rate were observed: a low temperature region between 525 °C to 650°C and a high temperature region between 650 °C to 725 °C. The X-ray diffraction analysis suggests that the decomposition of enargite occurs through the formation of intermediate tenantite, according to the following sequential reactions: 4Cu3AsS4(s) ? Cu12 As4S13(s)+ 3/2S2(g) Cu12 AS4S13(s) ? 6Cu2S(s) + 2As2S3(g) + 1/2S2(g) The decomposition kinetics was analyzed by using the model for a topochemical reaction of spherical particles: 1-(1-X) 1/3 = kt, which represented well the data. Apparent activation energies of 113 kJ/mol and 60.5 kJ/mol were found for the low and high temperature regions, respectively.

Jan 1, 1999

By C. L. Lin

Transformation of linear grade distribution to volumetric grade distribution has been used to estimate the actual mineral liberation during wet, batch, ball mill grinding of a copper ore. The degree of liberation based on the multicomponent-multisize grinding liberation model using volumetric grade is lower than the apparent degree of liberation estimated from using King's linear intercept model.

Jan 1, 1987

By Takashi Miyamoto, Hideo Nakae, Hideki Yamaura, Takeshi Yanagihara

"For the production of partially composed metal matrix composites, namely discontinuous MMCs, using a casting· process, the interpenetrated phase composites with SiC particles were fabricated by pressureless iDfiltration using molten Al-Si alloys. This process is based on a wetting phenomenon, therefore, we discussed the technique based on the reactive wetting. The SiC particles coated by diluted water glass were sintered in a mullite Tammann tube and simultaneously infiltrated with molten Al-Si alloys in air at 1173~1573K. As for the improvement of the wettability between the SiC and the liquid aluminum alloy, Fe3O 4 powder was mixed with the water glass due to the thermit reaction between Fe3O4 and molten aluminum alloy. In some experiments, pure aluminum powder was placed on the sintered SiC to increase the interfacial area and the chemical reaction between the sintered Sic. and the melt. By combining these conditions, we succeeded in the complete infiltration without pressure at 1173K.IntroductionAs is well known, the mechanical properties of metal matrix composites (abbreviated MMCs) are superior than that of ordinary metals. However, their use has not been widely accepted because the production cost is very high due to their poor machinability. Therefore, the production of partially composed, namely discontinuous MMCs, by as the Lanxide process [l,2] has been investigated for many years. The Lanxide process, it takes a long time, sometimes up to 10h, in a nitrogen atmosphere for the infiltration. Therefore, the cost will be higher for common use. On the other hand, a high 'pressure process has been adopted for the production of discontinuous MMCs by the Toyota Motor Corp.[3]."

Jan 1, 2000

By Kazusuke Sato, Takahiro Uno, Koji Hoshino

"A novel Ni coating technique of Ni(OH)2 powders was developed to improve the positive-electrode performance· of the Ni-MH batteries. It was found out that Ni(OH)2 powder was reduced by N2H4 without any catalysts in an alkaline - solution at high temperatures. In result of observation of pH and potential changes in the solution during the reaction, it was found that the reduced species was HNio2- ion dissociated from Ni(OH)2 in the alkaline solution. The molar fraction of reduced Ni of the Ni(OH)2 was increased in proportion to the amount of added N2H4. At the small Ni fraction, a porous Ni layer was formed on the surface of Ni(OH)2 powder. Open cell tests were carried out with the paste type electrodes made of either the Ni coated Ni(OH)2 powder or non-coat powder, and cell performances were compared. In result, it was found that the Ni coating technique is effective on improvement in the utilization of Ni(OH); as a positive-electrode active material under high current densities.IntroductionNi-MH rechargeable battery is generally used for the power source of portable machines and electric vehicles because of its good performance at high energy density and. long term cyclical life as well as cleanness and good safety. Cell component materials have been improved respectively, and as concerns ·the positive-electrode reducing 'the internal resistance is a principal problem to improve the discharging performance at higher current densities.In recent years, improved Ni(OH)2 powders coated with conductive materials as NI. or CoOOH have been developed for the· positive-electrode active materials in order to· reduce the internal resistance of the electrode1)· 2) The Ni coated Ni(OH)2, however, is costly because it is fabricated by .the -non-electrode plate technique which needs a expensive precious ·metal catalyst as PdC12We found that Ni(OH)2 powder was reduced by N2H4 without any cryatalysts in an alkaline solution at high temperatures. After the treatment, Ni(OH)2 powder become gray color like Ni powder from light-green color; and. turned into a magnetic. In this study, the mechanism of the -reducing reaction was investigated to apply the reactions .to a novel Ni coating technique of Ni(OH)2 powders, · and the performance of the Ni coated Ni(OH)2 powder obtained by the reducing process was evaluated as an -positive-electrode active material of Ni-MH batteries."

Jan 1, 2000

By Sang Han Son

The vapor pressures of FeCL2 and ZnCL2 in the FeCL2?ZnCL2 system were measured by the transpiration method at 873K and 9I7K, The vapor pressure data were interpreted to indicate the formation of complex ions in the FeCL2?ZnCL2 melts, It is presumed that the complex molecule FeZnCl4 as well as FeCL2 and ZnCL2 exists in the vapors in equilibrium with molten FeCL2-ZnCL2 mixtures, The activities in the FeCL2-ZnCL2 system are shown a negative deviation from Raoult's law. These results suggest the formation of complex ions such as ZnCL14 in molten FeCI2?ZnCL2 mixtures.

Jan 1, 2003

By Robert D. Pehlke

"The evolution of oxygen steelmaking is reviewed and new operating processes are described. The developments which could impact this technology are summarized. Staged and continuous steelmaking are considered in the light of new technologies. The future opportunities for oxygen steelmaking processes are overviewed. IntroductionThe use of oxygen in steelmaking was originally brought on the scene by the development of pneumatic steelmaking. Sir Henry Bessemer in England originally conceptualized the use of gaseous oxygen in steelmaking, and then he and William Kelly in Eddyville, Kentucky independently developed the original pneumatic process which involved blowing air through a bath of molten pig iron to oxidize the carbon and silicon and produce steel. This process and many following processes, including those which would use pure oxygen gas, have been proposed.Beginning with the first commercial oxygen steelmaking vessels at Linz, Austria in 1952, the world steelmaking industry has adopted this style of processing. In general, the process has involved the use of steel scrap in amounts from 20 to 35% of the metallic charge with molten pig iron produced in blast furnaces making up the remainder. The impurities in the charge are oxidized through the use of oxygen gas injected into the steelmaking vessel.However, currently being adopted into commerical practice and on the horizon are a number of advances in this process which include the use of iron ores as a source of iron and oxygen, the use of an all scrap charge, incorporation of pre-reduced iron, the use of auxillary fuels to change the balance of cold and liquid iron-base charge materials and numerous refining techniques."

Jan 1, 1988

By M. M. Coleman

An investigation of the behaviour of sphalerite, chalcopyrite, galena and pyrite during flotation was conducted on selected circuits in the Brunswick Mining and Smelting Corporation Ltd. concentrator in Bathurst, NB. Samples were collected from 59 locations and analyzed for Zn, Pb, Cu, Ag, Fe, As, Sb, Sn, Bi and S. Metal balances were computed using the CAMP Material Balance Program (MATBAL 5) and the metal recoveries for each cell and circuit were calculated. An automated image analyzer interfaced with an electron microprobe was programmed to measure the size of sphalerite, chalcopyrite, galena and pyrite grains in each sample. The percentage of each mineral occurring as free grains and the relative amount of each mineral present in binary and ternary particles was calculated. The recoveries and losses of Pb, Zn and Cu are compared with the amount of liberated and unliberated galena, sphalerite and chalcopyrite present in the concentrates and tailings.

Jan 1, 1989

By R. G. Reddy

The effect of solid particles on viscosity behavior of Na2O-O-B2O3-SiO2 melts of composition XSio2/XNa2o =0.5 and in the temperature range of 900- 1150 K was studied. Samples were analyzed by X-ray diffraction and optical microscopy. The results showed that a crystalline phase (NaBO2) was formed and its amount increases with decrease in X,, from 0.50 to 0.25. The experimental viscosity values were compared with the predicted values using our viscosity model developed earlier. At low temperatures, for low content of B2O3 , the experimental values exhibits a large deviation from the predicted values. It was concluded that the deviation was due to the formation of solid particles in the molten slags. The existence of these solid particles increased the viscosity values significantly. A new viscosity model was developed to include the effect of solid particles.

Jan 1, 1993

By Sadi Medina

As it is characteristic from Custom Smelters, ENAMl Las Ventanas Smelter has to deal with different qualities and quantities of mining products from about 70 suppliers, that contain a variety of impurities that would be harmful for copper production. In order to increase the smelting capacity, an oxygen plant has been running since September of 1990. Moreover, to improve the environmental conditions, a new sulphuric acid plant started up to neutralize the metallurgycal off-gases from the Teniente Converter and partially from the Peirce-Smith converters. Based on the on-line operation among the reverberatory furnace and the Teniente Converter using oxygen enriched air to produce high grade matte, most of the volatilizing impurities, mainly arsenic, are collected as discarding compounds in the gas cleaning system of the acid plant. This paper describes the continuous performance of the Teniente Converter with acid plant, the results attained, the operation problems and how they were solved. The impurities distribution achieved in this process is also included.

Jan 1, 1993

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 Yue Tian, Shengqian Wang, Lifeng Zhang

This paper is to discuss the removal of non-metallic inclusions from molten steel using a high frequency magnetic field. In experiments, a certain amount of aluminum was added to the molten steel in a crucible to generate aluminum inclusions. A layer of aluminum clusters were observed close to the wall of the crucible after the electromagnetic (EM) field was imposed. Three dimensional EM field and fluid flow simulation were performed and showed that over 91% inclusions transported to the skin depth (2.31 mm) of the molten steel. The calculation of inclusion removal agreed well with the experimental observation. The separation mechanisms of inclusions from the molten steel by the high frequency EM field were discussed.

Jan 1, 2014

By Lei Zhang, Shining Chen, Lina Wang, Pu Liu, Benquan Fu, Jiannyang Hwang

A three-dimensional (3D) electrode reactor combined with Fenton reagent was used for advanced treatment of coking wastewater from secondary biological treatment. Effects of some key factors on total organic carbon (TOC) removal rate were investigated, and the results were compared with those of the common three-dimensional electrode reactor. Experimental results showed that TOC removal rate could reach 51.7%, when optimal operating conditions were as follows: initial pH value 3.5, H2O2 dosage 17.6mmol/L, reaction time 90min and FeSO4·7H2O dosage 3.5mmol/L. Analytical results from UV absorption spectra indicated that the organic substances in the coking wastewater were well degraded by this system, which provided good experimental basis for the practical application of this process in the treatment of coking wastewater. This can be meaningful for the treatment of other kinds of wastewater.

Jan 1, 2015

By Thomas Brynjulfsen, Merete Tangstad, Eli Ringdalen

Manganese ore fines cannot be added to the submerged arc furnace directly as they will prevent even gas flow through the burden. Low gas permeability in the burden will lower the degree of pre-reduction of ore subsequently increase the carbon and energy consumption of the process. In order to utilize manganese ore fines in the furnace, they are typically agglomerated into sinter. In this work, the melting and reduction properties of Gabonese sinter and Gabonese ore have been investigated in pilot scale experiments. Two experiments were conducted, one with 100% sinter as manganese source and one with 50/50 sinter and ore. Lime was used to achieve a charge basicity of 0.72 in both experiments. The composition of slag samples from the excavation of the furnace was established using EPMA(WDS), and the composition of the tapped slag and metal was found using XRF. It was found that while the coke-bed size would determine the tapped slag composition, the melting behavior of the Mn source would determine the mixing with lime.

Jan 1, 2014

By Nobuaki Sato, Tetsuo Fukasawa, Akira Kirishima

To apply the fluoride volatility process for the treatment of fuel debris formed in the damaged nuclear reactors, study on the fluorination behavior of main constituents, such as fuel and cladding is essential. The mixture of uranium and zirconium oxides is formed under severe conditions such as high temperature and oxidizing atmospheres. In this paper, fluorination and volatilization behavior of uranium and zirconium oxides have been studied by TG-DTA method in the presence of fluorine. From the TG-DTA result of UO2 in F2 atmosphere, the weight gradually increased up to 7% at 350 oC followed by rapid weight decrease with exothermic peak showing the vaporization of uranium as UF6. ZrO2 showed similar fluorination behavior to that of UO2. However, fluorination of UO2-ZrO2 seemed to be suppressed with increasing ZrO2 amount. This may be caused by the formation of solid solution.

Jan 1, 2016

By Cong Wang, Kexin Jiao, Yongan Zhao, Haibin Zuo, Jianliang Zhang

The carbon composite brick is a new refractory used in blast furnace hearth and bottom. It caused wide attention due to its high thermal conductivity and low erosion by molten iron. In this paper, chemical constituents, SEM-EDS and X-ray diffraction were carried out in order to understand reaction mechanisms. A series of experiments of oxidation resistance characteristics were made. The oxidation mechanisms of carbon composite bricks in the presence of air were analyzed. According to the analysis on many experimental results, the oxidation process of carbon composite bricks under different temperatures were controlled by different mechanisms. In the condition of high temperature, SiO2 as oxidation product hindered the diffusion of O2, and reduced the oxidation loss of graphite in the internal.

Jan 1, 2015

By Chikabumi Yamauchi, Mitsuru Tanahashi, Tsuyoshi Taniguchi, Nobuo Furuta, Toshiharu Fujisawa

"It is essential to clarify the equilibrium relations among nonmetallic inclusions of the Mn0-SiO2-CrOx system and molten stainless steel in order to control non-metallic inclusions formed by the deoxidation of stainless steel with silicon. In the present study, the phase equilibria of the MnO-SiO2-CrOx system were measured by conducting the following experiments under controlled oxygen partial pressure, Po2, at 1873 K:1) Phase equilibria of the MnO-Cr20 3 binary system were measured for Po2 = 2 x 10-6 ~2 x 102 Pa.2) Phase equilibria of the MnO-SiO2-CrOx ternary system were measured for Po2 = 2 X 10-6 Pa.Based on the results, the phase diagram of this ternary system was established under the condition of the Si-deoxidation process of stainless steel (Po2 = 2 x 10-6 Pa and T = 1873 K).IntroductionAt the deoxidation stage in steelmaking process, generally multiple deoxidizers participate in deoxidation reactions, and the composition of deoxidation products ""non-metallic inclusions"" greatly varies depending on deoxidizing efoments and their contents. In order to control non-metallic inclusions formed by the refining process of steel, it is essential to clarify the equilibrium relations among non-metallic inclusions and molten steel.Especially, during the refining process of stainless steel, nonmetallic inclusions in molten steel seem to- change as follows. After the oxidation refining, Mn-chromite is formed in molten steel as non-metallic inclusion. By the deoxidation with silicon addition (mainly less than 1 mass%), Mn-chromite inclusions are changed their compositions to Mn-silicate. Segawa et al.[l] have reported the effect of amount of silicon addition on composition and mass ratio· of non-metallic inclusions during the Sideoxidation process of 18Cr-8Ni stainless steel at 1873 K, as shown in Figuri; L At higher silicon content than 0.5 mass%, only Mn-silicate was identified as non-metallic inclusion. On the other hand, at lower silicon content, both of Mn-chromite (MnO Cr2O 3) and Mn-silicate were identified. However, the thermodynamic and the kinetic analyses of the above-mentioned Sicdeoxidation process have not been made due to lack in the thermodynamic data for the non-metallic inclusions· of the MnO-SiO2-CrOx system, such as the phase diagrams, the activities of the components, and the free energy of intermediate compounds. In relation to the phase diagram of this system, those of the MnO-SiO2 [2] and the SiO2-Cr2O 3 [3] binary systems have been only reported"

Jan 1, 2000

By H. J. Thevik, A. K. Dahle

"A mathematical model that calculates the stress development in a coherent and stationary dendritic network due to interdendritic flow is proposed. The fluid flow is assumed to be related to the solidification shrinkage, and under the assumption of no porosity formation and unidirectional solidification, the shrinkage-induced flow within the mushy zone is calculated analytically. The interdendritic melt flow exerts a force on the solid network and an analytical expression for the stress build-up in the network is developed. Parameter studies illustrating the influence of cooling conditions, mushy zone length, dendrite coherency, fraction solid, volume fraction of eutectic, and solidification shrinkage upon the stress development within the solid network are presented. Comparing the magnitude of the calculated stresses to measurements of the strength in equiaxed mushy zones shows that it is possible for the stresses to exceed the strength, thereby resulting in reorientation or collapse of the dendritic network.IntroductionInterdendritic fluid flow is at present regarded as a very important mechanism for feeding of shrinkage during solidification of metal alloys. Solidification of many alloys is often characterised by heterogeneous nucleation of the primary phase on substrates in the melt with subsequent evolution of equiaxed dendrites. These equiaxed dendrites can initially grow freely, but impinge on each other and form a continuous dendritic network, ie. dendrite coherency, quite early in the solidification process. Measurements of the dendrite coherency point have shown that the dendritic network is established at solid fractions ranging between 0.1 and 0.5, and most often around about 0.2 [l]. Depending on the alloy composition this means that as much as 70 to 80% of the volumetric shrinkage has to be compensated by flow of liquid through the interdendritic network. Interdendritic flow occurs with a much larger resistance compared to free flow of the liquid and flow of a liquid with dispersed crystals. The pressure drop associated with the interdendritic flow increases rapidly with decreasing fraction ofliquid."

Jan 1, 1999

By Micheal McCarter, Biswadeep Saha, Meenakshisundaram Ramanathan, Chai Ren, Sivaraman Guruswamy

"Three-point bend test was used to study the effect of electrochemically charged hydrogen and magnetic field on the embrittlement behavior of AISI 4340 steel in this work. Acoustic emission signals were collected during the test and analyzed to gain an understanding of the crack growth process. Cathodic hydrogen charging in AISI 4340 steel resulted in drastic reduction of ductility and strength. Hydrogen embrittlement was characterized by a change in fracture surface from dimpled ductile surface to quasi cleavage type fracture. No significant effect was observed in the presence of magnetic field. The acoustic emission signals collected during the test provided an indication of the extent of energy released during the crack growth process.*Support of this work by NSF through the award DMR-0854166 is gratefully acknowledgedIntroductionGrowing interest in hydrogen as a clean fuel and use of steel and other iron based alloys for storage and transport of hydrogen has led to extensive study of the influence of hydrogen on the mechanical properties of these alloys. Hydrogen interaction with materials may result in degradation of mechanical properties. Embrittlement, either ductile or brittle, can be described as a condition which decreases the toughness of the material or increases the ease of crack growth. Hydrogen present even in few parts per million is sufficient to embrittle steels at room temperature [1]. In most cases, hydrogen exposure is through an electrochemical process in aqueous corroding environments. In such cases, they are prone to be exposed simultaneously to electrically induced magnetic fields, which are also believed to affect the hydrogen embrittlement susceptibility of these alloys. So it is also important to study the effect of magnetic field on the hydrogen embrittlement susceptibility. Hydrogen solubility by electrochemical process in aqueous solution is proportional to square root of current density for iron. [2,3]"

Jan 1, 2012