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A new lightweight magnesia refractory for working linings of high-temperature furnaces was prepared by using microporous magnesia aggregates instead of conventional dense magnesia aggregates. The median pore size of the microporous magnesia aggregates was 2.97 μm, while the apparent porosities of the microporous and dense aggregates were 33.3% and 5.5%, respectively. The phase composition, microstructures, fracture behaviors and strengths at room and high temperature of the lightweight magnesia refractory in comparison with those of the dense one were measured by means of XRD, SEM and three-point bending instrument. After the dense aggregates were replaced by the microporous ones, a better aggregate/matrix interface bonding was observed and the fracture mode changed from intergranular to transgranular fracture, which significantly improved the mechanical properties. Thus, the lightweight magnesia refractories had a lower bulk density of 11.8%, a higher apparent porosity of 56.2% as well as a higher flexural strength at room and high temperature of 48.4% and 160.0% comparing with the dense one, respectively.

Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and micro-pore-foaming agent (MPFA, the main composition was sodium dodecyl benzene sulfonate) as foaming agent. Effect of the MPFA addition on the phase compositions, microstructures and physical properties of the foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that the specimens fired at 1500 °C mainly consisted of needle-like mullite, corundum, and a small amount of glass phase. The MPFA decreased the viscosities and then increased the volume expansion of foamed slurries. Meanwhile, the adding of the MPFA caused the increases of apparent porosities and average pore sizes, and the decrease of strengths of the fired specimens. The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C which had a high porosity of 73.7%, a proper compressive strength of 3.05 MPa, a low thermal conductivity of 0.287 W/(mK) (1000 °C) and a positive reheating linear change. Based on the experimental dates, an emendatory GE model was presented, which could predict accurately the effective thermal conductivity at 1000 °C of the mullite-corundum foamed ceramics with different pore characteristics.

This study investigates five lightweight corundum-magnesium aluminate spinel castables (LCSC) which consisted of porous corundum-spinel aggregates and matrices with 0–2.8 wt% silicon carbide (SiC). The effect of the SiC powder content (SPC) in the matrix on the microstructure, strength, thermal conductivity and slag resistance was analyzed by XRD, SEM and EDS as well as by the thermochemical software FactSage. The addition of SiC powder resulted in a significantly improved interface bonding between the porous aggregates and the matrix enhancing the strength and slag resistance. Whereas the thermal conductivity at 300 °C and 500 °C remained unchanged, it increased significantly at 800 °C and 1000 °C. The optimized LCSC contained 1.9 wt% SiC powder which combined a suitable apparent porosity (32.5%), a low bulk density (2.41 g/cm3), a high flexural strength (17.62 MPa), a high compressive strength (100.76 MPa), a low thermal conductivity (0.978 W/m·K, 1000 °C) and a high slag resistance.

The present study investigated five lightweight periclase-magnesium aluminate spinel refractories containing porous spinel aggregates with a varying spinel content. The cement clinker resistance and adherence properties of the lightweight refractories were analyzed by a static crucible test and a sandwich test, respectively. The effect of the spinel content of the aggregates (SCA) on the cement clinker resistance and adherence properties was investigated with SEM, EDS and with the thermochemical software FactSage®. The reaction between the spinel in the refractories with the cement clinker caused the formation of a liquid phase. This liquid phase determined the adherence properties of the refractories and also affected their cement clinker resistance. When the SCA was 0–25 wt%, the refractories had a high corrosion resistance and the cement clinker successfully adhered to the refractories. Yet, when the spinel content was between 50 wt% and 100 wt%, excessive liquid phase formation seriously impaired the refractories. Consequently, the optimized periclase-spinel refractories contained porous aggregates with 25 wt% spinel, which resulted in a high corrosion resistance together with an excellent adherence ability regarding the cement clinker.

This study presents a new lightweight periclase-magnesium alumina spinel castable (LPSC) for the working lining of steel ladles using porous periclase-spinel aggregates to replace conventional dense magnesia aggregates. The porous periclase-spinel aggregates were produced by an in-situ decomposition technique resulting in an apparent porosity of 23.3% and a median pore size of 5.66 μm. Scanning electron microscopy revealed a better porous aggregate/matrix interface bonding in the LPSC, which significantly improved its strength and thermal shock resistance. Additionally, the higher amount of micropores of the porous aggregates in the LPSC absorbed more penetrated slag from the matrix, which enhanced the slag resistance. Thus, compared with conventional castables, the LPSC had a lower bulk density of 9.2–10.8% and a lower thermal conductivity of 18.8% (1000 °C) while at the same time a higher strength, thermal shock resistance and slag resistance was achieved.

The effect of the amount of magnesium aluminate spinel powder (MASP) in lightweight periclase-spinel refractories on the cement clinker corrosion and adherence properties was investigated by the static crucible test and sandwich test. The results showed that MASP addition significantly affected the cement clinker corrosion resistance and adherence properties although it had little effect on the apparent porosity and pore size of refractories. The spinel in the refractories reacted with the cement clinker rather than periclase to generate the glass phase. Its amount and viscosity increased from 0 to 13 wt% MASP addition in refractories, which brought the benefit to the adherence strength. However, the excessive glass phase deteriorated the corrosion and penetration resistances of refractories as MASP was added up to 19 wt%. So, the addition amount from 9 to 13 wt% MASP into periclase-spinel refractories balanced the cement clinker resistance and adherence strength.

The corrosion and adherence properties of cement clinker on porous periclase-spinel refractory aggregates with varying spinel content were examined using a static crucible test and a sandwich test, respectively. The reaction characteristics of porous periclase-spinel aggregates and cement clinker and the effects of spinel content on the adherence property were investigated through scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and FactSage ® thermo-chemical software. It was observed that the spinel content and pore characteristics strongly affected the corrosion results and thus affected the adherence ability of cement clinker on porous periclase-spinel aggregates. With an increase in the spinel content, the amount of glass phase formed from the reaction of the refractory and cement clinker increases because the rate of the spinel dissolution into the cement clinker is higher than that of periclase. The glass phase acts as a bridge between the cement clinker and the aggregate to enhance the adherence property, which depends on the amount, area distribution and viscosity of the glass phase and its penetration in aggregates. When the spinel content is 15–40 wt%, the refractory aggregate not only has a high cement clinker resistance but also a high adherence property. Once the spinel content exceeds 50 wt%, the skeletal structure of the aggregate will be destroyed, which will lead to a substantial decline in the cement clinker resistance.

In this study, the degradation mechanisms of dense periclase-magnesium aluminate spinel refractory bricks used in the upper transition zone of cement rotary kilns were investigated by XRD, SEM and EDS. And the results indicated that the damage of the used brick was main due to the structural spalling as well as the formation and extension of cracks, caused by the corrosion of cement clinker, the deposition of alkali salts and thermal stress resulted from changing temperature field. The bricks reacted with the cement clinker forming a liquid phase at the reacting interface, and then the penetration of this liquid phase by reaction sintering altered the microstructure and compositions of bricks. Additionally, the constantly changing temperature field and the precipitation of alkali salts with the high thermal expansion coefficient in colder zones led to tremendous thermomechanical stress. Thus, joint effects of these factors caused the structural spalling and deterioration of refractory linings.