Abstract
In refractory castables during heat treatment, there is a dynamic change from a hydraulic bond to a ceramic bond. During heating, the emission of water takes place; this changes the conditions inside the material to something similar to the hydrothermal ones. This influences the processes that occur during the heating of the castables, and in consequence, the properties of the final material. The aim of the work was to evaluate the influence of the chelate compounds like citric and tartaric acids, often used in castables as dispersing agents, on the properties of the MgO–Al2O3 phase system during hydrothermal treatment. The performed tests included an XRD analysis, a thermal analysis (TG–DSC–EGA), infrared spectroscopy (FTIR), and an SEM–EDS analysis. Based on the obtained results, it was found that even small amounts of chelate compounds have a strong impact on the processes under hydrothermal conditions which results in changes in the phase composition of the materials.
Highlights
It can be stated that magnesium oxide, in the experimental conditions, completely reacted with water for sample 1 while some traces of it remained in the sample with the addition of citric and tartaric acids
This suggests that when increasing the temperature to the maximum assumed value (240 ◦ C) in the experiment, the hydration process proceeds with gibbsite synthesis as an intermediate stage
The current work based on the obtained results shows a strong influence of even small amounts of citric and tartaric acids on the hydration of the MgO–Al2 O3 system under hydrothermal conditions
Summary
The so-called insitu synthesis of spinel is used In this kind of process, the spinel is generated from the substrates directly in the refractory castables, during high-temperature heat treatment. In this method, the presence of water modifies the course of the synthesis reaction. The starting substrates are oxides and hydroxides of magnesium, and aluminum, and the conditions in the material during the increase in temperature become similar to the hydrothermal ones This is the difference between the classical solid state synthesis of the spinel and the insitu synthesis of this phase in castables. Spinel solid state synthesis from oxides is well characterized [1,2,3,4,5,6,7,8], there is still a lack of knowledge about the insitu synthesis of the spinel in refractory castables, especially at the early stage of such a reaction at the temperature level where water vapor can be present
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