This article is based on corundum-based casting materials, primarily researching and analyzing the impact rules of ultra-fine powder, particle composition, and non-oxide materials (graphite, Sialon) on the fluidity and high-temperature mechanical properties of corundum refractory casting materials.

The seminar focused on four main aspects:
(1) The NXS-11A viscometer was used to investigate the effects of fine powder, cement, flake graphite, and Sialon on the rheological properties of the matrix.
(2) Investigated the effects of micronized powder, particle composition, magnesium sand fines, flake graphite, granulated graphite, and β-Sialon on the rheological properties of the casting material using a rheometer.
(3) Discussed the effects of micron powder, cement, magnesia sand, graphite, and Sialon on the conventional physical properties of castable materials after heat treatment.
(4) The study investigated the effects of micro-filler content, granular graphite, and Sialon on the high-temperature flexural strength and thermal shock resistance of casting materials, using three-point bending tests and treatment at different temperatures after water-cooling cycles.
Research findings indicate:
1) The rheological behavior of the matrix exhibits Bingham fluid characteristics; the micro-filler content, cement, magnesia, flake graphite, and Sialon all influence the rheology of the matrix. Among them, the SiO2 micro-silica powder is the primary factor improving the rheology of the matrix, reducing its viscosity, shear stress, and yield stress. This is primarily due to the small specific gravity, spherical particles, and high surface activity of the SiO2 micro-powder, which can effectively fill the particle voids and displace the water present; the addition of alumina micro-powder slightly improves the rheology of the matrix; the inclusion of magnesia and Sialon is detrimental to the rheology of the matrix; and flake graphite significantly worsens the rheology of the matrix.
2) The particle composition, proportion of Al2O3 micro-powder/SiO2 micro-powder, and flake graphite significantly affect the rheology of the casting material; the fine powder of magnesia and Al2O3 micro-powder have a lesser impact on the rheology; granulated graphite and β-Sialon have a negative effect on the rheology. The rheological behavior of the casting material exhibits Bingham fluid characteristics. Adjustments to the Al2O3 micro-powder/SiO2 micro-powder proportion, with the addition of SiO2 micro-powder, significantly reduce the required water volume, leading to a substantial improvement in the self-flow value and enhanced rheology—decreased shear stress, shear viscosity, and flow resistance. As the particle composition changes (q-value from 0.29, 0.26 to 0.23), the increase in fine powder proportion leads to a larger total surface area of the particles, requiring more water to moisten the surface, resulting in a slight increase in water volume and a slight decrease in the self-flow value, worsening the rheology—increased shear stress, shear viscosity, and flow resistance. With the addition of flake graphite, due to its non-wettability and poor dispersibility, the required water volume significantly increases (an increase of 100% when adding 5% flake graphite), leading to a significant deterioration in rheology. With the addition of granulated graphite and β-Sialon, there is a slight increase in water volume (from 5% to 6.2%) and a slight reduction in the activity value, having a minor negative impact on the rheology. Due to the improved surface characteristics and density of granulated graphite, and the weaker polarity of the β-Sialon covalent bonds, which are much better wetted than flake graphite, their negative impact on rheology is far less than that of flake graphite.
3) Upon adjusting the micro-powder share, when the Al2O3 micro-powder/SiO2 micro-powder ratio is 100/0 to 50/50, an increase in SiO2 micro-powder content results in a higher sample bulk density post-heat treatment, reduced porosity, improved compressive strength at room temperature, and increased flexural strength. For a 25/75 to 0/100 Al2O3 micro-powder/SiO2 micro-powder ratio, the conventional physical properties slightly decrease. As the amount of cement, magnesia fine powder, and Sialon fine powder increases, the sample porosity increases, bulk density decreases, and compressive strength and flexural strength at room temperature decrease. With the addition of Flake graphite and granulated graphite, due to the poor interaction between graphite and refractory oxides, the sample porosity increases, bulk density decreases, and compressive strength and flexural strength at room temperature significantly decrease.