Influence of pre-synthesized Al2O3–SiC composite powder from clay on properties of low-carbon MgO–C refractories

Silicon nitride (Si 3 N 4 ) ceramics doped with two different sintering additive systems (Al 2 O 3 -Y 2 O 3 and Al 2 O 3 -Yb 2 O 3 ) were prepared by hot-pressing sintering at 1800°C for 2 h and 30 MPa. The microstructures, nano-indentation test, and mechanical properties of the as-prepared Si 3 N 4 ceramics were systematically investigated. The X-ray diffraction analyses of the as-prepared Si 3 N 4 ceramics doped with the two sintering additives showed a large number of phase transformations of α-Si 3 N 4 to β-Si 3 N 4 . Grain size distributions and aspect ratios as well as their effects on mechanical properties are presented in this study. The specimen doped with the Al 2 O 3 -Yb 2 O 3 sintering additive has a larger aspect ratio and higher fracture toughness, while the Vickers hardness is relatively lower. It can be seen from the nano-indentation tests that the stronger the elastic deformation ability of the specimens, the higher the fracture toughness. At the same time, the mechanical properties are greatly enhanced by specific interlocking microstructures formed by the high aspect ratio β-Si 3 N 4 grains. In addition, the density, relative density, and flexural strength of the as-prepared Si 3 N 4 ceramics doped with Al 2 O 3 -Y 2 O 3 were 3.25 g/cm 3 , 99.9%, and 1053 ± 53 MPa, respectively.When Al 2 O 3 -Yb 2 O 3 additives were introduced, the above properties reached 3.33 g/cm 3 , 99.9%, and 1150 ± 106 MPa, respectively. It reveals that microstructure control and mechanical property optimization for Si 3 N 4 ceramics are feasible by tailoring sintering additives.

Section: Methodsmentioning

confidence: 99%

Section: Microstructure Characterization and Measurement Of Mechanica...mentioning

confidence: 99%

Effects of Al ₂ O ₃ –Y ₂ O ₃ /Yb ₂ O ₃ additives on microstructures and mechanical properties of silicon nitride ceramics prepared by hot‐pressing sintering

Tang

Deng

2022

“…The addition of SiC improves the strength, 19 toughness, 20 slag corrosion resistance, 21 and thermal shock resistance 22 of multiphase materials. Ma et al [23][24][25] found that the addition of the synthesized Al 2 O 3 -SiC could improve the slag permeability and slag resistance of low-carbon MgO-C refractories due to the formation of spinel dense layer and high-viscosity isolation layer. Therefore, the addition of SiC to MgO-C refractories has essential research significance.…”

Section: Introductionmentioning

confidence: 99%

In situ synthesis and interfacial bonding mechanism of SiC in MgO–SiC–C refractories

Luo

Zhang

et al. 2022

Adding SiC directly to MgO–C refractories possesses the disadvantages of low dispersion and interfacial bonding strength. Herein, the in situ synthesized SiC was introduced into the MgO–SiC–C refractories to maintain the original excellent performance of MgO–C refractories and reduce the carbon dissolution in molten steel. With the increase of Si and C content in raw materials, the morphology of SiC changed from whisker to network, whose growth mechanism was vapor–solid and vapor–liquid–solid. The network structure and uniform distribution of SiC improved the thermal shock resistance of MgO–SiC–C refractories. According to the analysis of molecular dynamics simulation by Materials Studio software, SiC strengthened the relationship between periclase and graphite to enhance the structure of the compound.

“…[12][13][14][15][16][17] Recent researches demonstrated that the ceramic reinforcement phases of carbon containing refractories play a major role in the enhancement of mechanical properties. [18][19][20][21][22] One of the best-known methods to increase the strength of the matrix of Al 2 O 3 -C refractories is the in situ formation of SiC whiskers by adding metallic Si powder. [23][24][25][26][27] For example, Al 2 O 3 -C refractories containing ultrafine microcrystalline graphite fostered the formation of intertwined SiC whiskers, which caused a significantly higher strength.…”

Section: Introductionmentioning

confidence: 99%

“…Recent researches demonstrated that the ceramic reinforcement phases of carbon containing refractories play a major role in the enhancement of mechanical properties 18–22 . One of the best‐known methods to increase the strength of the matrix of Al 2 O 3 ‐C refractories is the in situ formation of SiC whiskers by adding metallic Si powder 23–27 .…”

Section: Introductionmentioning

confidence: 99%

Enhanced mechanical properties of lightweight Al₂O₃‐C refractories reinforced by combined one‐dimensional ceramic phases

Chen

Yan

Schafföner

et al. 2021

We prepared a new lightweight Al2O3‐C refractory material with a higher strength by using microporous corundum aggregates instead of dense tabular corundum aggregates, which was reinforced by in situ formed SiC whiskers, multi‐walled carbon nanotubes (MWCNTs), and mullite rods. A comparative study of the microstructure, mechanical properties, and fracture behavior was carried out for dense and lightweight Al2O3‐C refractories coked at 1200°C and 1400°C, respectively. By using the microporous corundum aggregates, a better aggregate/matrix interface bonding and an optimized distribution of SiC whiskers were obtained. The SiC whiskers formed inside the microporous corundum aggregates and simultaneously in the matrix by a vapor‐solid reaction mechanism, resulting in an enhancement at the microporous aggregate/matrix interface. Furthermore, the in situ formed MWCNTs and well‐developed mullite rods at 1200°C in the matrix also contributed to the better interface structure. Thus, due to the improved microporous aggregate/matrix interface, the crack propagation along the aggregate/matrix interface was suppressed, resulting in an increased crack propagation within the aggregates. Consequently, the synergy between microporous corundum aggregates and combined one‐dimensional ceramic phases caused a lower bulk density but a markedly higher strength, a higher fracture energy, and a higher toughness of lightweight Al2O3‐C refractories compared to the dense ones. Overall, our study allows to overcome the traditional concept that a higher strength of refractories is reached by a higher density.