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1.
A thermodynamic equilibrium between the Fe-16Cr melts and the CaO-Al2O3-MgO slags at 1823 K as well as the morphology of inclusions was investigated to understand the formation behavior of the
MgO-Al2O3 spinel-type inclusions in ferritic stainless steel. The calculated and observed activities of magnesium in Fe-16Cr melts
are qualitatively in good agreement with each other, while those of aluminum in steel melts exhibit some discrepancies with
scatters. In the composition of molten steel investigated in this study, the log (X
MgO/X
Al
2O3) of the inclusions linearly increases by increasing the log [a
Mg/a
Al
2
·a
O
2
] with the slope close to unity. In addition, the relationship between the log (X
MgO/X
Al
2O3) of the inclusions and the log (a
MgO/a
Al
2O3) of the slags exhibits the linear correlation with the slope close to unity. The compositions of the inclusions are relatively
close to those of the slags, viz. the MgO-rich magnesia-spinel solid solutions were formed in the steel melts equilibrated with the highly basic slags saturated
by CaO or MgO. The spinel inclusions nearly saturated by MgO were observed in the steel melts equilibrated with the slags
doubly saturated by MgO and MgAl2O4. The spinel and the Al2O3-rich alumina-spinel solid solutions were formed in the steel melts equilibrated with the slags saturated by MgAl2O4 and MgAl2O4-CaAl2O4 phases, respectively. The apparent modification reaction of MgO to the magnesium aluminate inclusions in steel melts equilibrated
with the highly basic slags would be constituted by the following reaction steps: (1) diffusion of aluminum from bulk to the
metal/MgO interface, (2) oxidation of the aluminum to the Al3+ ions at the metal/intermediate layer interface, (3) diffusion of Al3+ ions and electrons through the intermediate layer, and (4) magnesium aluminate (MgAl2O4 spinel, for example) formation by the ionic reaction. 相似文献
2.
Joo Hyun Park Dong Joon Min Hyo Seok Song 《Metallurgical and Materials Transactions B》2004,35(2):269-275
The viscosity of CaO-SiO2 (-MgO)-Al2O3 slags was measured to clarify the effects of Al2O3 and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the
quenched slags were analyzed to understand the structural role of Al2O3 in the polymerization or depolymerization of silicate network. The Al2O3 behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about
10 mass pct Al2O3, while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al2O3. This amphoteric role of Al2O3 in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of
Al2O3 on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation
of the [AlO4]-tetrahedra into the [SiO4]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on
the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of
the [AlO6]-octahedral units. The relative intensity of the IR bands for the [SiO4]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO4]-tetrahedra with high NBO/Si increased with increasing Al2O3 content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition
indirectly supported those of viscosity and structure of the aluminosilicate melts. 相似文献
3.
Refractive indexes for the Al2O3-Na2O-SiO2 system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800
K). Two kinds of sample were used: xAl2O3-(40-x)Na2O-60SiO2 and yAl2O3-yNa2O-(100-2y)SiO2, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative
to positive on increasing the concentration of Al2O3. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO2, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes
in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization
of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing
temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases.
The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance
between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration
of Al2O3 has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts.
This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties
& Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002. 相似文献
4.
Ramaraghavulu Rajavaram Hyelim Kim Chi-Hoon Lee Won-Seung Cho Chi-Hwan Lee Joonho Lee 《Metallurgical and Materials Transactions B》2017,48(3):1595-1601
The effect of Al2O3 concentration on the density and structure of CaO-SiO2-Al2O3 slag was investigated at multiple Al2O3 mole percentages and at a fixed CaO/SiO2 ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al2O3 content was less than 15 mole pct, density decreased with increasing Al2O3 content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al3+ ion as a network modifier. 相似文献
5.
The Cu solubility was measured in the CaO-B2O3 and BaO-B2O3 slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with
oxygen partial pressure in the CaO-B2O3 slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag
basicity, which value of slope was close to –0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism
established as follows:
\textCu + \frac14\textO2 = \textCu + + \frac12\textO2 - {\text{Cu}} + \frac{1}{4}{\text{O}}_{2} = {\text{Cu}}^{ + } + \frac{1}{2}{\text{O}}^{2 - } 相似文献
6.
Yunshu Zhang Xiaoxia Wu Robert A. Rapp 《Metallurgical and Materials Transactions B》2004,35(1):133-141
Experiments to measure the solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 were performed, and the results confirmed existing literature values. The solubilities of NiAl2O4 and FeAl2O4 in Al2O3-saturated cryolite melts at 1300 K were modeled thermodynamically in terms of the Ni-containing complexes Na2NiF4 and Na4NiF6, and the Fe-containing solutes FeF2, Na2FeF4, and Na4FeF6. The experimental solubility data were fitted to multiple simultaneous equilibria. Equilibrium constants and ΔG
f
0
values for the formation reactions of the these solutes were thereby estimated. The solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 and solute distributions in Al2O3-undersaturated cryolite melts were calculated for a number of melt compositions from the present model. The existence of
several competitive solute species is inherent to highly buffered ionic cryolite solutions where the traditional log-log methodology
had previously failed to identify dominant single solutes. In such solutions, individual solutes of oxides are not likely
to dominate over a wide composition range so that a more global modeling is required. The principal solute species identified
in the present study exhibit reasonable three-dimensional (3-D) anion geometries. 相似文献
7.
In an attempt to systematize the knowledge of the heat conduction of liquid silicates, the effective thermal diffusivities
of some synthetic slags containing CaO, Al2O3, and SiO2 have been measured, using the three-layer laser-flash method on a differential scheme in the temperature range of 1625 to
1825 K. The effective thermal diffusivities measured, which are a combination of the phononic and photonic heat-transfer mechanisms,
were found to increase with increasing temperature for all the presently investigated slags. The slag compositions were chosen
in such a way that the changes in the effective thermal diffusivities would reflect the changes in the structure of the slags.
It was observed that, at a CaO/Al2O3 molar ratio of 4.42, an increase of the SiO2 content had very little effect on the effective thermal diffusivity values. On the other hand, addition of SiO2 to a slag with the CaO/Al2O3 molar ratio of 2.59 resulted in a significant increase in the effective thermal diffusivity. The addition of Al2O3 to slags with a constant CaO/SiO2 molar ratio resulted in a marked increase in the effective thermal diffusivity. Both these trends indicate that there might
be an influence of the network formation in silicate melts on the effective thermal diffusivity. 相似文献
8.
The glass series with general formula 15 Li2O–(85 − x) B2O3–x La2O3 was prepared. Electrical and optical properties of these glasses were studied. It is observed that the conductivity of these
glasses decreases while density, glass transition temperature and refractive index increases with the addition of La2O3. Ion concentration of La3+ in glasses, polaron radius, field strength, molar refractivity and molar electronic polarizability were calculated. The absorption
coefficient and direct optical band gaps are evaluated using the absorption edge calculations. The different factors that
play a role for controlling the refractive indices such as electronic polarizability, field strength of cations and rigidity
of glass structure are discussed in accordance with the obtained index data. 相似文献
9.
Pavel S. Pershin A. A. Kataev A. A. Filatov A. V. Suzdaltsev Yu. P. Zaikov 《Metallurgical and Materials Transactions B》2017,48(4):1962-1969
Physical–chemical investigations of KF-AlF3 melts were carried out in order to develop the scientific basis of the technology for Al-Zr alloy synthesis. The possibility of Al-Zr alloy synthesis via the aluminum-thermal method was shown. The liquidus temperatures of KF-AlF3 and KF-NaF-AlF3 melts with additions of Al2O3 and ZrO2 were determined using the thermal analysis method in the temperature range from 873 K to 1173 K (600 °C to 900 °C). The dependency of the solubility of ZrO2 in KF-AlF3 and KF-NaF-AlF3 melts on Al2O3 concentration was measured. 相似文献
10.
Joo Hyun Park Sang-Beom Lee Henri R. Gaye 《Metallurgical and Materials Transactions B》2008,39(6):853-861
11.
Cu-10Cr-3Ag (wt pct) alloy with nanocrystalline Al2O3 dispersion was prepared by mechanical alloying and consolidated by high pressure sintering at different temperatures. Characterization
by X-ray diffraction and scanning electron microscopy or transmission electron microscopy shows the formation of nanocrystalline
matrix grains of about 40 nm after 25 hours of milling with nanometric (<20 nm) Al2O3 particles dispersed in it. After consolidation by high pressure sintering (8 GPa at 400 °C to 800 °C), the dispersoids retain
their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. The hardness and
wear resistance of the pellets increase significantly with the addition of nano-Al2O3 particles. The electrical conductivity of the pellets without and with nano-Al2O3 dispersion is about 30 pct IACS (international annealing copper standard) and 25 pct IACS, respectively. Thus, mechanical
alloying followed by high pressure sintering seems a potential route for developing nano-Al2O3 dispersed Cu-Cr-Ag alloy for heavy duty electrical contact. 相似文献
12.
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
13.
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
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