CA6-based macroporous refractory thermal insulators containing mineralizing agents

Abstract

Aiming at reducing the temperature of CaO.6Al2O3 (CA6) formation, SiO2, ZnO, and TiO2 were evaluated as mineralizing agents in an Al2O3-CaCO3 based macroporous thermal insulator. For the concentrations tested (0.6mol% to 2.8mol%), SiO2 presented a small effect in the temperature of CA6 formation. However, ZnO and TiO2 favoured full CA6 generation at 1400ºC, 200ºC below the reference composition. All analysed systems, besides 2.8Si, showed high porosity (>80%), suitable mechanical strength and expansion after firing at 1600ºC for 5h. Softening temperature evaluation highlighted that ZnO-and TiO2-containing compositions could be used at higher temperatures than the SiO2 ones. Thus, compositions containing 2.8mol% of ZnO or TiO2 were evaluated according to their thermal conductivity (keff), showing lower keff than the reference composition. Therefore, using these mineralizing agents, which are easily available, may provide reductions in the energy input to produce CA6-containing thermal insulators and benefits to all other required properties.

Binder effect on ZnAl2O4-containing high-alumina refractory castables

“…Additionally, zinc oxide has the ability to speed up the formation of calcium aluminate phases (i.e., CaAl 4 O 7 , CaAl 12 O 19 , etc.) and MgAl 2 O 4 (MA) in Al 2 O 3 -CaO-MgO containing compositions [22,23]. Wang et al [22] pointed out that ZnO accelerated the formation of MA phase at high temperatures in Al 2 O 3 -MgO-CaCO 3 ceramics by replacing Mg 2+ by Zn 2+ in the spinel grains to give rise to a uniform (Mg 1-x Zn x )Al 2 O 4 solid solution.…”

Development and Testing of Castables with Low Content of Calcium Oxide

“…The advantage of alumina sol is its purity. The use of mullite sol as a binder for refractory castables is mentioned as well, for example, in combination with CA cement, A cement or micro silica [ 21 , 27 , 28 , 29 ]. Use of spinel sol as a binder has also been reported by some authors in ultra-low cement compositions [ 21 , 27 ].…”