Characterization of Melting of Some Slags in the Al2O3–CaO–MgO–SiO2 Quaternary System

Abstract

Ladle treatment plays increasingly important role in making clean steels nowadays. In many industrial practices, synthetic ladle slags are based on the Al 2 O 3 -CaO-MgOSiO 2 quaternary system. Usually, the compositions of the slags are targeted on the single liquid region of the phase diagram. On the other hand, the phase diagram information of the Al 2 O 3 -CaO-MgO-SiO 2 quaternary involves considerable uncertainties. The available sections of the phase diagrams in this system in Slag Atlas 1) are after Osborn et al., 2,3) Gutt and Russel 4) as well as Cavalier and SandreoDendon.5) Unfortunately, many liquidus temperatures are given as dotted lines. Disagreements between the phase diagram and the reality have been found by both the present research laboratory and the steel industry.6) Since ladle refining is very often operated at temperatures between 1 823 K and 1 923 K, the present communication aims at a study of a number of slag compositions to examine whether these slags are single liquids or multiphase mixtures at 1 858 K.While the differential thermal analysis (DTA) is well established to determine the temperature of phase transformation, the measurements of the liquidus temperatures of slags using this technique are difficult because of the invariable supercooling of the slags. The exothermic peak associated with the solid separation at the liquidus temperature occurs at much lower temperatures. During the heating mode, the compositional inhomogenities would result in considerable uncertainties. Hence, a quenching technique was employed in the present studyThe Al 2 O 3 , CaO, MgO and SiO 2 oxide powders were calicined at 1 073 K for 24 h before being thoroughly mixed in an agate mortar. The oxide mixtures were pressed into small pellets of about 1.3 g and sealed in a glass bottle. The bottle was kept in a desiccator before the experiment.A horizontal furnace was employed for most of the experiments. The experimental setup is schematically shown in Fig. 1. The furnace had KANTHAL SUPER 1800 (molybdenum silicide) heating elements with a maximum working temperature of 1 973 K. The furnace having an even temperature zone of 40 mm was controlled with an accuracy of Ϯ3 K by a programmable EORUTHERM 2408 P4 regulator using a Pt-30%Rh/Pt-6%Rh thermocouple. The alumina reaction tube had the dimensions of 60 mm o.d. and 50 mm i.d. Platinum crucibles were used to hold the samples. The crucibles were carefully shaped to avoid creeping-out of the slag during the experiments. An alumina holder was used to support two crucibles along with the samples. In a typical run, the samples on the alumina holder were carefully introduced into the reaction chamber and placed in the even temperature zone. Argon gas was passed through the reaction tube at low flow rate. A constant argon flow was maintained through out the experiment. The samples were heated up to 1 858 K and kept there for more than 5 h. After equilibration of the samples, the sample holder was rapidly pulled out of the furnace. After a quick visual examination, ...

Phase Equilibria in the CaO–SiO₂–Al₂O₃–MgO System with CaO/SiO₂ Ratio of 1.3 Relevant to Iron Blast Furnace Slags

“…In addition, the pseudoternary sections reported as CaO-MgO-SiO 2 at fixed Al 2 O 3 or Al 2 O 3 -CaO-SiO 2 at fixed MgO cannot accurately predict the effect of MgO/Al 2 O 3 on liquidus temperature which is important for the current BF operations. It has also been demonstrated in recent studies that significant differences are observed for the phase diagrams in the Al 2 O 3 -CaOMgO-SiO 2 system between the new results [8][9][10][11][12] and those reported in the early research. [5][6][7] On the other hand, solid solutions presented in the system Al 2 O 3 -CaO-MgO-SiO 2 , in particular melilite phase in which industrial slags are operated, are important for optimisation of the thermodynamic database.…”

Experimental Determination of the Liquidus in the High-Basicity Region in the Al2O3(25 mass pct)-CaO-MgO-SiO2 and Al2O3(35 mass pct)-CaO-MgO-SiO2 Systems

“…Some disagreements between experimental results and the phase diagram from Osborn et al [1] have been reported. [5] In a recent work by some of the current authors, [6] liquidus lines for 1773 K and 1873 K (1500°C and 1600°C) were determined experimentally in the 30 mass pct Al 2 O 3 section in the CaO-rich corner of the Al 2 O 3 -CaO-MgO-SiO 2 system. The results generally agreed well with the work by Osborn et al [1] with a few exceptions.…”

“…[5] was evaluated to 188 in an previous work [6] at 1773 K (1500°C) under similar circumstances. This term is denoted by f 1773 K AlO 1:5 .…”

ANÁLISE DE FASES DE AMOSTRAS DE ESCÓRIAS SIDERÚRGICAS DO SISTEMA CaO-MgO-Al2O3-SiO2

“…Esse sistema é adotado com frequência devido à sua alta compatibilidade com os refratários utilizados no refino secundário do aço na panela [4,5]. Geralmente, a composição das escórias do sistema CMAS (CaO-MgO-Al₂O₃-SiO₂) fica numa região líquida do diagrama de fase, mas esses diagramas encontrados na literatura apresentam muitas regiões incertas, que podem ser uma região de fase líquida ou múltiplas fases [4]. O que ocasiona divergências entre os resultados encontrados experimentalmente em comparação com a literatura.…”