Needle-like nanocrystalline mullite powders were prepared through the molten salt process at the temperature of 900 • C using coal gangue as raw material. Then, mullite-based composite ceramics were prepared by a conventional solid-state reaction between in situ synthesized mullite and Al 2 O 3 powders. Effects of Al 2 O 3 content and sintering temperatures on phase compositions, microstructure, and mechanical properties of the mullite-based composite ceramics were also studied. The results show that mullite content productivity increase from 72% to 95%, as the sintering temperature increased from 1480 • C to 1580 • C, which led to the improvement in the bulk density and flexural strength of the samples. The three-dimensional interlocking structure for mullite-based composite ceramics was obtained by the in situ solid-state reaction process. The maximum bulk density, flexural strength, and fracture toughness for the sample with 15 wt% Al 2 O 3 content are 2.48 g/cm 3 , 139.79 MPa, and 5.62 MPa⋅⋅m 1/2 , respectively, as it was sintered at the temperature of 1560 • C for 3 h. The improved mechanical properties of mullite-based composite ceramics maybe ascribed to good densification and increased mullite phase content, as well as to the in situ three-dimensional network structure. Therefore, the results would provide new ideas for high-value utilization of coal gangue.

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This study examines the effects of zirconium basic carbonate (ZBC) added to alumina powders on the mechanical behavior of binder jetting porous alumina ceramic. ZBC powder is easily decomposed to form zirconia particles and then is deposited in the interparticle void spaces. Green alumina samples were obtained with different ZBC contents of 0~8 wt%. The density, linear shrinkage, bending strength, and microstructural evolution of ceramic parts were analyzed and categorized in different ZBC contents. Results showed that the formation of zirconia particles was dominant and improved the performance of sintered samples. Sintering at 1450°C resulted in a denser Al2O3 part with a comparable bending strength of 75.2 MPa and an accessible linear shrinkage of 10% for the ZBC content range of 0 to 6 wt%. At ZBC content of 8 wt%, the gas generated by ZBC decomposition reduced the sintering density. Therefore, adding 6 wt % ZBC content is the optimal choice for binder jetted porous alumina ceramic.

This study presents new lightweight periclase-magnesium alumina spinel refractories for the working lining of cement rotary kilns in which magnesium alumina spinel hollow spheres are used to replace conventional dense fused magnesiaaluminate spinel aggregates. The effects of adding spinel hollow spheres on the physical properties, mechanical strength, thermal conductivity, and slag resistance of the samples were explored. The results showed that compared with the sample prepared with dense aggregates, the sample prepared with hollow spheres had a 10.3% higher cold compressive strength, 44.1% higher modulus of rupture (MOR), and lower bulk density. Additionally, with increasing hollow spheres content, the thermal conductivity decreased from 3.79 W/(m⋅K) to 2.53 W/(m⋅K), and the high-temperature MOR increased from 2.82 to 4.09 MPa. The highest residual strength ratio was 90.73% (15 wt.% hollow spheres), which is 1.17 times that of the sample prepared without hollow spheres. Moreover, microstructure and energy dispersive spectroscopy of crucible specimens after corrosion by cement clinker showed that specimens with 15 wt.% hollow sphere additions had a better slag resistance. Introducing hollow spheres reduced the thermal conductivity of the refractories, providing a new strategy for improving the heat insulation performance of kiln linings.

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