Effects of microsilica content on microstructure and strength of lightweight castable refractories containing porous corundum-spinel aggregate

Abstract

High-strength, lightweight castable refractories based on spinel were prepared by introducing porous corundum-spinel aggregate and appropriate microsilica. The effects of microsilica content on microstructure and properties of lightweight castable refractories were investigated using SEM, XRD, mercury porosimetry measurements and FactSage thermochemical software. It's found that microsilica was almost dissolved into a liquid phase at high temperature, which promoted liquid sintering. With increasing microsilica content, the matrices became denser and average pore size of matrices increased, then apparent porosity decreased, crushing strength increased and content of liquid phase in castables at 1600°C increased. The appropriate microsilica content is 0.65 to 1.95 wt%, which reaches to a compromise among apparent porosity (33-38%), crushing strength (82-125MPa) and liquid content (1.80~4.97 wt%)

Effect of particle size on microstructure and strength of porous spinel ceramics prepared by pore-forming in situ technique

“…The high thermal conductivities of traditionally dense refractories as metallurgical furnace lining result in a large energy waste (Wen et al 2005). Recently, with increased demand for saving energy, more attention has been paid to lightweight refractories (Wen et al 2005;Yan and Li 2006, 2009, 2010. Traditionally lightweight refractories mainly consisted of Al 2 O 3 -SiO 2 materials, which are acidic and have low strength, and cannot be used as working line in many furnaces (Dunaeva 2006).…”

“…Smaller pore size and homogenous pore distribution are thought to be helpful to improve the strength of aggregates (Wen et al 2005). The lightweight Al 2 O 3 -MgO refractories with high strength and high slag resistance were prepared, using the porous spinel ceramics with small pore size and homogenous pore distribution as aggregates (Yan et al 2008(Yan et al , 2009.…”

A low bulk density, low thermal conductivity permanent lining castable for tundish obtained by adding pearlescent sand

“…In order to improve the thermal insulation performance of castables and reduce their heat storage loss, lightweight porous aggregates are often used instead of traditional dense aggregates. [4][5][6][7][8] At present, the representative high-strength lightweight aggregates include hollow corundum spherical aggregates, 9,10 lightweight microporous mullite aggregates, 11 and lightweight microporous bauxite aggregates. 12 The bulk density and thermal conductivity of the castables prepared with these lightweight aggregates are extremely low, but their key properties such as strength and thermal shock are still insufficient to meet the requirements of tundish permanent linings, and the prices of high-strength lightweight aggregates are much higher than that of traditional aggregates.…”

Microstructures and strengths of microporous MgO‐Al2O3 refractory aggregates using two types of magnesite

“…To address this issue, recent studies have shown that the thermal conductivities of refractories can be reduced by using microporous aggregates instead of dense aggregates. [12][13][14][15][16][17][18][19][20][21] For example, a new lightweight periclase-spinel refractory was prepared by using microporous aggregates instead of dense aggregates, and the thermal conductivity was reduced by 18.8% at 1000°C. 13 Therefore, it is of great significance to develop microporous MgO-Al 2 O 3 refractory…”

“…The high thermal conductivities often cause immense heat losses through the linings of high‐temperature furnaces, which is not conducive to energy‐saving and emission‐reduction. To address this issue, recent studies have shown that the thermal conductivities of refractories can be reduced by using microporous aggregates instead of dense aggregates 12‐21 . For example, a new lightweight periclase‐spinel refractory was prepared by using microporous aggregates instead of dense aggregates, and the thermal conductivity was reduced by 18.8% at 1000°C 13 .…”