Abstract
To investigate the action mechanism of titanium, the effects of different Ti-bearing compounds, including CaTiO3, MgTiO3, and nano-TiO2, on the properties of alumina–magnesia castables were studied. By analyzing the phase compositions, microstructures, and physical and mechanical properties of the castables, it was demonstrated that an intermediate product, CaTiO3, was first generated. This was then consumed by solid-solution reactions, and titanium was involved in the liquid formation as the temperature increased. The solid-solution reaction of CA6 (CaAl12O19) was more prominent due to the incorporation of more titanium in the crystal lattice of CA6 instead of spinel (MgAl2O4). Moreover, the liquid formation was strongly promoted when more titanium accompanied the calcium, which finally accelerated the densification and improved the strengths of alumina–magnesia castables. On the whole, castables with CaTiO3 addition presented higher bulk density and excellent strength after the heat treatment. Besides, the castables with 2 wt.% CaTiO3 contents were estimated to possess greater thermal shock resistance.
Highlights
Alumina-magnesia castables served at high temperatures mainly comprise alumina, spinel, and CA6
As reported in a previous study, the formation temperature of CA6 was up to 1400 ◦ C in alumina-magnesia castables without mineralizer addition [12]. This demonstrated that the formation of CA6 was accelerated to a great extent by the introduction of Ti-bearing compounds
Calcium existed in the form of CA2, CaTiO3, and anorthite at a relatively low temperature (1150 ◦ C) and gradually transformed to CA6 as the temperature increased
Summary
Alumina-magnesia castables served at high temperatures mainly comprise alumina, spinel, and CA6. The formation of CA6 and spinel leads to volume expansions of 3.01 and 8%, respectively, which would result in the spalling of castables at elevated temperatures [8] Mineralizers, such as TiO2 , B2 O3 , ZrO2 , and rare earth oxides, have been introduced into this system to accelerate the densification of castables [9,10]. Among these additives, TiO2 is regarded as one of the most effective multifunctional mineralizers, which can control the expansion behavior of alumina-magnesia castables and speed up the formation of CA6 and spinel [11]. It was found that the apparent activation energy of spinel formation varied with the content of TiO2 in the same system [13]
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