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1.
Anna Semykina Jinichiro Nakano Seetharaman Sridhar Volodymyr Shatokha Seshadri Seetharaman 《Metallurgical and Materials Transactions B》2011,42(3):471-476
The oxidation of FeO in 30 wt pct FeO-35 wt pct CaO-35 wt pct SiO2 slag was investigated as part of a wider study on the recovery of Fe units through magnetic separation. A confocal scanning laser microscopy (CSLM) technique was used to visualize the oxidation of FeO in the liquid slag. The formation event was observed in situ under the CSLM and the onset of precipitation on a surface of the slag liquid was recorded at various temperatures in an oxidizing atmosphere. A Time-Temperature-Transformation (TTT) diagram was constructed based on the CSLM results. Samples obtained from the CSLM heating chamber were analyzed by a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS). 相似文献
2.
Kinetics of Oxidation of Divalent Iron to Trivalent State in Liquid FeO-CaO-SiO<Subscript>2</Subscript> Slags 总被引:1,自引:0,他引:1
Anna Semykina Volodymyr Shatokha Masanori Iwase Seshadri Seetharaman 《Metallurgical and Materials Transactions B》2010,41(6):1230-1239
This work was devoted to the kinetics studies of the oxidation of divalent iron in liquid FeO-CaO-SiO2 slags to the trivalent state. The experiments were carried out using a thermogravimetric technique (TGA) in the temperature range of 1623 K to 1773 K (1350 °C to 1500 °C) in an oxidizing atmosphere. The reaction products after oxidation were analyzed by X-ray diffraction and optical and scanning electron microscopy. The results obtained show that during the first 10 to 15 minutes of oxidation, 70 to 90 pct of the Fe2+ in the slag was oxidized. Kinetic analysis of the TGA results indicates that the oxidation process may consist of three distinct steps, viz an initial incubation period, followed by a chemical-reaction-controlled stage, and later, a diffusion-control stage. Appropriate mathematical relationships were set up for the first two consecutive steps. After combining these equations suitably as the mechanism of oxidation shifts from one form to another, the experimental results for the first two parts could be reproduced. A linear correlation was found between the thermodynamic activity of FeO in the slag and the degree of oxidation. 相似文献
3.
To understand the desulfurization process during the refining of Cr-containing steel grades, this work was initiated to study
the reactions between Cr-sulfur and chromium-containing slags. The sulfide capacities of CaO-SiO2-CrOx pseudo-ternary slags were measured using the traditional gas-slag equilibration technique between 1823 K and 1923 K. Sixteen
different slag compositions were examined, and two different equilibrium oxygen partial pressures were used to understand
the impact of the varying valence of Cr on the sulfide capacities. The results showed that log10 Cs varied linearly with the reciprocal T, and the slope was higher than the corresponding value reported for the binary CaO-SiO2 of corresponding composition. It was difficult to isolate the relative effects of the bi- and trivalent Cr in the slags because
the Cr2+/Cr3+ ratio was influenced by the basicity of the slag. By using the equation developed by these authors earlier that related Cr2+/Cr3+ with basicity, oxygen partial pressure, and temperature, it was possible to obtain an approximate trend of the CrO effect
on the sulfide capacities; viz. the sulfide shows a decreasing trend as Cr2+ replaces Ca2+ in the slag. With a continued increase of Cr2+ content, indications of the occurrence of a minimum point were observed; beyond which the sulfide capacities showed a slight
increasing trend. The latter was attributed, based on slag-structure analysis by Gaskell et al., to the increasing extent of the polymerization reaction releasing oxygen ions for sulfide reactions. 相似文献
4.
5.
Density measurements of a low-silica CaO-SiO2-Al2O3 system were carried out using the Archimedes principle. A Pt 30 pct Rh bob and wire arrangement was used for this purpose.
The results obtained were in good agreement with those obtained from the model developed in the current group as well as with
other results reported earlier. The density for the CaO-SiO2 and the CaO-Al2O3 binary slag systems also was estimated from the ternary values. The extrapolation of density values for high-silica systems
also showed good agreement with previous works. An estimation for the density value of CaO was made from the current experimental
data. The density decrease at high temperatures was interpreted based on the silicate structure. As the mole percent of SiO2 was below the 33 pct required for the orthosilicate composition, discrete
\textSiO44 - {\text{SiO}}_{4}^{4 - } tetrahedral units in the silicate melt would exist along with O2– ions. The change in melt expansivity may be attributed to the ionic expansions in the order of
\textAl 3+ - \textO 2- < \textCa 2+ - \textO 2- < \textCa 2+ - \textO - {\text{Al}}^{ 3+ } - {\text{O}}^{ 2- } < {\text{Ca}}^{ 2+ } - {\text{O}}^{ 2- } < {\text{Ca}}^{ 2+ } - {\text{O}}^{ - } 相似文献
6.
The distribution of arsenic between calcium ferrite slag and liquid silver (wt pct As in slag/ wt pct As in liquid silver)
with 22 wt pct CaO and between iron silicate slag with 24 wt pct SiO2 and calcium iron silicate slags was measured at 1573 K (1300 °C) under a controlled CO-CO2-Ar atmosphere. For the calcium ferrite slags, a broad range of oxygen partial pressure (10–11 to 0.21 atm) was covered, whereas for the silicate slags, the oxygen partial pressure was varied from 10–9 to 3.1 × 10–7 atm. The measured relations between the distribution ratio of As and the oxygen partial pressure indicates that the oxidation
state of arsenic in these slags is predominantly As3+ or AsO1.5. The measured distribution ratio of arsenic between the calcium ferrite slag and the liquid silver was about an order of
magnitude higher than that of the iron silicate slag. In addition, an increasing concentration of SiO2 in the calcium-ferrite-based melts resulted in decreases in the distribution of arsenic into the slag. Through the use of
measured equilibrium data on the arsenic content of the metal and slag in conjunction with the composition dependent on the
activity of arsenic in the metal, the activity of AsO1.5 in the slags was deduced. These activity data on AsO1.5 show a negative deviation from the ideal behavior in these slags. 相似文献
7.
Lars Klemet Jakobsson Merete Tangstad 《Metallurgical and Materials Transactions B》2018,49(4):1699-1708
Slag refining is one of few metallurgical methods for removal of boron from silicon. It is important to know the thermodynamic properties of boron in slags to understand the refining process. The relation of the distribution coefficient of boron to the activity of silica, partial pressure of oxygen, and capacity of slags for boron oxide was investigated. The link between these parameters explains why the distribution coefficient of boron does not change much with changing slag composition. In addition, the thermodynamic properties of dilute boron oxide in CaO-MgO-Al2O3-SiO2 slags was determined. The ratio of the activity coefficient of boron oxide and silica was found to be the most important parameter for understanding changes in the distribution coefficient of boron for different slags. Finally, the relation between the activity coefficient of boron oxide and slag structure was investigated. It was found that the structure can explain how the distribution coefficient of boron changes depending on slag composition. 相似文献
8.
Jie Qi Chengjun Liu Chi Zhang Maofa Jiang 《Metallurgical and Materials Transactions B》2017,48(1):11-16
Aiming at devising new mold flux for Ce-bearing stainless steel, a fundamental investigation on the effect of Ce2O3 on properties of the CaO-Al2O3-Li2O-Ce2O3 slag was provided by the present work. The results show that adding Ce2O3 could decrease the viscosity of the slag due to its effects on decreasing the polymerization of the slag. The crystalline process was restrained by increasing the content of Ce2O3, and the crystalline phases also can be influenced by the slag structure. The crystalline phases were transferred from LiAlO2 and CaO to LiAlO2 and CaCeAlO4 with the addition of Ce2O3 to the slag, which could be well confirmed by the structure of the unit cell of the crystals. 相似文献
9.
The crystallization kinetics of CaO-SiO2-Al2O3-MgO (CSAM) slags was studied with the aid of single hot thermocouple technique (SHTT). Kinetic parameters such as the Avrami exponent (n), rate coefficient (K), and effective activation energy of crystallization (E A ) were obtained by kinetic analysis of data obtained from in situ observation of glassy to crystalline transformation and image analysis. Also, the dependence of nucleation and growth rates of crystalline phases were quantified as a function of time, temperature, and slag basicity. Together with the observations of crystallization front, they facilitated establishing the dominant mechanisms of crystallization. In an attempt to predict crystallization rate under non-isothermal conditions, a mathematical model was developed that employs the rate data of isothermal transformation. The model was validated by reproducing an experimental continuous cooling transformation diagram purely from isothermal data. 相似文献
10.
Fengshan Li Xianpeng Li Shufeng Yang Yanling Zhang 《Metallurgical and Materials Transactions B》2017,48(5):2367-2378
In order to effectively enhance the efficiency of dephosphorization, the distribution ratios of phosphorus between CaO-FeO-SiO2-Al2O3/Na2O/TiO2 slags and carbon-saturated iron (\( L_{\text{P}}^{\text{Fe-C}} \)) were examined through laboratory experiments in this study, along with the effects of different influencing factors such as the temperature and concentrations of the various slag components. Thermodynamic simulations showed that, with the addition of Na2O and Al2O3, the liquid areas of the CaO-FeO-SiO2 slag are enlarged significantly, with Al2O3 and Na2O acting as fluxes when added to the slag in the appropriate concentrations. The experimental data suggested that \( L_{\text{P}}^{\text{Fe-C}} \) increases with an increase in the binary basicity of the slag, with the basicity having a greater effect than the temperature and FeO content; \( L_{\text{P}}^{\text{Fe-C}} \) increases with an increase in the Na2O content and decrease in the Al2O3 content. In contrast to the case for the dephosphorization of molten steel, for the hot-metal dephosphorization process investigated in this study, the FeO content of the slag had a smaller effect on \( L_{\text{P}}^{\text{Fe-C}} \) than did the other factors such as the temperature and slag basicity. Based on the experimental data, by using regression analysis, \( \log L_{\text{P}}^{\text{Fe-C}} \) could be expressed as a function of the temperature and the slag component concentrations as follows: 相似文献
$$ \begin{aligned} \log L_{\text{P}}^{\text{Fe-C}} & = 0.059({\text{pct}}\;{\text{CaO}}) + 1.583\log ({\text{TFe}}) - 0.052\left( {{\text{pct}}\;{\text{SiO}}_{2} } \right) - 0.014\left( {{\text{pct}}\;{\text{Al}}_{2} {\text{O}}_{3} } \right) \\ \, & \quad + 0.142\left( {{\text{pct}}\;{\text{Na}}_{2} {\text{O}}} \right) - 0.003\left( {{\text{pct}}\;{\text{TiO}}_{2} } \right) + 0.049\left( {{\text{pct}}\;{\text{P}}_{2} {\text{O}}_{5} } \right) + \frac{13{,}527}{T} - 9.87. \\ \end{aligned} $$ 11.
Understanding the viscous behavior of copper smelting slags is essential in increasing the process efficiency and obtaining
the discrete separation between the matte and the slag. The viscosity of the FeOt-SiO2-Al2O3 copper smelting slags was measured in the current study using the rotating spindle method. The viscosity at a fixed Al2O3 concentration decreased with increasing Fe/SiO2 ratio because of the depolymerization of the molten slag by the network-modifying free oxygen ions (O2−) supplied by FeO. The Fourier transform infrared (FTIR) analyses of the slag samples with increasing Fe/SiO2 ratio revealed that the amount of large silicate sheets decreased, whereas the amount of simpler silicate structures increased.
Al2O3 additions to the ternary FeOt-SiO2-Al2O3 slag system at a fixed Fe/SiO2 ratio showed a characteristic V-shaped pattern, where initial additions decreased the viscosity, reached a minimum, and increased
subsequently with higher Al2O3 content. The effect of Al2O3 was considered to be related to the amphoteric behavior of Al2O3, where Al2O3 initially behaves as a basic oxide and changes to an acidic oxide with variation in slag composition. Furthermore, Al2O3 additions also resulted in the high temperature phase change between fayalite/hercynite and the modification of the liquidus
temperature with Al2O3 additions affecting the viscosity of the copper smelting slag. 相似文献
12.
In the present work, the relationship between the microscopic structure and macroscopic thermophysical properties in a basic CaO-SiO2-MgO-Al2O3 quaternary system was identified using Fourier transformation infrared, Raman and 27Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The Raman spectra quantitatively proved that with increasing Al2O3 content, the concentrations of the symmetric units of Q0(Si) and Q2(Si) decreased, while those of the asymmetric units of Q1(Si) and Q3(Si) increased; consequently, the degree of polymerization of the networks increased, which resulted in an increase in slag viscosity. The 27Al MAS-NMR spectra demonstrated that three structural units of Al atoms, namely, AlO4, AlO5, and AlO6, mainly existed in the networks. With increasing Al2O3 content, the concentration of AlO4 slightly decreased, while those of AlO5 and AlO6 increased; overall, Al2O3 acted as a network former in the present system. The increasing Al2O3 content led to additional AlO6 and Si-NBO-Ca-NBO-Al frameworks, which replaced Si-NBO-Ca-NBO-Si in the networks (NBO: non-bridging oxygen) and induced a change in the primarily precipitated crystalline phase from Ca2MgSi2O7 and Ca2Al2SiO7 to MgAlO4. 相似文献
13.
The effects of reducing agent, CaF2 content, and reaction temperature upon the silicothermic reduction of MnO in the BaO-MnO-MgO-CaF2 (-SiO2) slags were investigated. Mn recovery was proportional to Si activity in the molten alloy. Moreover, 90 pct yield of Mn recovery was obtained under 5 mass pct CaF2 content and 1873 K (1600 °C) reaction temperature. Increasing CaF2 content above 5 pct yielded little or no further increase in Mn recovery, because it was accompanied by increased slag viscosity owing to the precipitation of high melting point compounds such as Ba2SiO4. 相似文献
14.
Haijuan Wang Lidong Teng Jiayun Zhang Seshadri Seetharaman 《Metallurgical and Materials Transactions B》2010,41(5):1042-1051
The oxidation mechanism of liquid Fe-V alloys with V content from 5 to 20 mass pct under different oxygen partial pressures
using CO2-O2 mixtures with CO2 varying from 80 pct to 100 pct was investigated by thermogravimetric analysis between 1823 K and 1923 K (1550 °C and 1650 °C).
The products after oxidation were identified by scanning electron microscopy energy-dispersive spectrograph and X-ray diffraction.
The results indicate that the oxidation process can be divided into the following steps: an apparent incubation period, followed
by a chemical reaction step with a transition step before the reaction, and diffusion as the last stage. At the initial stage,
a period of slow mass increase was observed that could be attributed to possible oxygen dissolution in the liquid iron-vanadium
coupled with the vaporization of V2O. The length of this period increased with increasing temperature as well as vanadium content in the melt and decreased with
increasing oxygen partial pressure of the oxidant gas. This analysis was followed by a region of chemical oxidation. The oxidation
rate increased with the increase of the O2 ratio in the CO2-O2 gas mixtures. During the final stage, the oxidation seemed to proceed with the diffusion of oxygen through the product layer
to the reaction front. The Arrhenius activation energies for chemical reaction and diffusion were calculated, and kinetic
equations for various steps were setup to describe the experimental results. The transition from one reaction mechanism to
the next was described mathematically as mixed-control equations. Thus, uniform kinetic equations have been setup that could
simulate the experimental results with good precision. 相似文献
15.
Kinetics of the reaction of lead slags (PbO-CaO-SiO2-FeO x -MgO) with CO-CO2 gas mixtures was studied by monitoring the changes in the slag composition when a stream of CO-CO2 gas mixture was blown on the surface of thin layers of slags (3 to 10 mm) at temperatures in the range of 1453 K to 1593 K (1180 °C to 1320 °C). These measurements were carried out under conditions where mass transfer in the gas phase was not the rate-limiting step and the reduction rates were insensitive to factors affecting mass transfer in the slag phase. The results show simultaneous reduction of PbO and Fe2O3 in the slag. The measured specific rate of oxygen removal from the melts varied from about 1 × 10?6 to 4 × 10?5 mol O cm?2 s?1 and was strongly dependent on the slag chemistry and its oxidation state, partial pressure of CO in the reaction gas mixture, and temperature. The deduced apparent first-order rate constant increased with increasing iron oxide content, oxidation state of the slag, and temperature. The results indicate that under the employed experimental conditions, the rate of formation of CO2 at the gas-slag interface is likely to be the rate-limiting step. 相似文献
16.
To derive a correlation between sulfide and chloride capacities through our own systematic experimental studies by using a
gas equilibrium technique involving Ar-H2-H2O-HCl gas mixtures, the solubilities of chlorine were determined for CaO-SiO2-MgO-Al2O3 slags at temperatures between 1673 K and 1823 K (1400 °C and 1550 °C). As a formula to correlate sulfide and chloride capacities,
the following equation that is the function of temperature only was obtainable;
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