The effect of microsilica and refractory cement content on the properties of andalusite based Low Cement Castables used in aluminum casthouse

Abstract

The bonding system in low cement castables is achieved by the use of calcium aluminate cement, microsilica and reactive alumina. The lime/silica ratio critically impacts the liquid phase formation at high temperatures and subsequently the corrosion resistance and the mechanical and physical properties of the refractory. In the current study, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated. Alcoa Cup test was used to evaluate the corrosion resistance of the castables at 850 ºC and 1160 ºC. The study showed that an increase in the microsilica/cement ratio improves the physical and mechanical properties of the castable, but at the expense of the corrosion resistance. When a fixed amount of BaSO4 was added to the base refractory material, barium celsian along with glassy phase formation was observed to increase with the increase in the microsilica/cement ratio in the refractory. The presence of the glassy phases was noted to lower the positive effect of Ba-celsian formation on improving the corrosion resistance of the refractory. The observed results were validated using thermodynamic calculations which indicated that Ba-celsian phase was more resistant than Ca-anorthite for applications involving contact with molten aluminum.

Effects of Different Barium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

“…In all samples, the cement and microsilica contents were kept constant at 7 and 3 wt pct, respectively. These proportions were determined in a previous study [43] and are based on the resultant mechanical, physical, and corrosion properties of the andalusite LCC refractory. Tripolyphosphate sodium (STTP) has been used as a dispersant to increase the flow properties of the castable.…”

Interfacial Reactions Between Anorthite (CaAl2Si2O8) and Al 7075 Alloy at 850°C and 1150°C

“…These reactions result in the formation of a corroded region, which may be composed of alumina (corundum) with interpenetrating Al alloy channels . Owing to the differences in true densities between the solid product (Al 2 O 3 : 3,970 kg/m 3 ) and the reactants (SiO 2 and 3Al 2 O 3 .2SiO 2 : 2,620 kg/m 3 and 3,050 kg/m 3 , respectively), substantial changes in specific volume occur during reaction (35.30%) or reaction (24.69%), which cause extensive cracking . These cracks become filled with reactive Al alloy at high temperatures, leading to further interactions between the components .…”

Šamotinio ugniai atsparaus betono šarminio atsparumo tyrimai

“…Tai siejama su SiO2 mikrodulkių ir reaktyvaus ar kalcinuoto aliuminio oksido panaudojimu šios serijos betono sudėtyje (2.3 lentelė). Sistemoje su CaO (kai naudojamas sumažintas kalcio aliuminatinio cemento kiekis betone) pastarieji priedai 800-1100 °C temperatūroje reaguoja, susidarant CA, CA2, anortitui ir gelenitui (Martinovic et al 2009;Firoozjaei et al 2010).…”