The sintering aids play an important role in affecting the properties of porous Si3N4 ceramics. However, there are few researches on the properties of porous Si3N4 ceramics fabricated by digital light processing (DLP) with different ratios of sintering aids. In this paper, porous Si3N4 ceramics with different ratios of sintering aids (Y2O3-Al2O3) were formed by DLP technology. The influence of Y2O3-Al2O3 ratios on the properties of Si3N4 slurry and porous ceramic was studied systematically. The ratio of Y2O3-Al2O3 had little effect on the rheology and cure depth of Si3N4 slurry due to the low addition of sintering aids. The increase of Y2O3-Al2O3 ratio promoted the anisotropic growth of β-Si3N4. When the ratio of Y2O3-Al2O3 was 9:1, the aspect ratio of β grains reached the maximum. As the ratio of Y2O3-Al2O3 powders increased, the linear shrinkage of porous Si3N4 ceramics showed an increasing and then decreasing trend in three directions. When the Y2O3-Al2O3 ratio was 3:7, the shrinkage rate in the length, width and height direction reached the maximum (27.03%, 30.27% and 40.02%, respectively). The bulk density and flexural strength exhibited an initial increase followed by a subsequent decrease, while the porosity showed the opposite trend. When the Y2O3-Al2O3 ratio was 9:1, the porosity reached a maximum of 28.1%. And the bulk density and flexural strength were 2.42 g/cm3 and 421.58 MPa, respectively. This study is of great significance as it lays the experimental foundation in the performance control of porous Si3N4 ceramics fabricated by DLP. 

Influence of the ratio of sintering aids on the properties of porous Si3N4 ceramics fabricated by digital light processing

In this study, the fused silica slurries with an ultra-high solid loading of 85 vol%, low viscosity of 0.34 Pa s at 99.4 s−1, and good suspension stability were successfully prepared using two-gradation fused silica raw powders by optimizing the preparation processes. Owing to the inherent characteristics of gelcasting and good dispersion stability of resulting fused silica slurries, all the fused silica ceramics prepared with various solid loadings exhibited a homogeneous bimodal size distribution microstructure after pressureless sintering at 1250 °C for 4 h. Furthermore, a small amount of nanoscale cristobalite was precipitated from fused silica, and solid loading had no significant effect on the crystallization kinetics of cristobalite. A significant increase in solid loading effectively facilitated the densification of fused silica ceramics, enhanced bulk density, decreased sintering shrinkage, and strengthened mechanical properties. However, the increase in solid loading deteriorated dielectric properties within the range of 2–18 GHz. When the solid loading was 85 vol%, the bulk density, linear shrinkage, flexural strength, dielectric constant, and dielectric loss tangent were 2.12 g/cm3, 1.1 %, 72.3 MPa, 3.91–4.36, 0.0081–0.0171, respectively. These properties were favorable making the materials potential applications in the field of microwave transmission. 

Effect of solid loading on phase composition, microstructure, mechanical and dielectric properties of fused silica ceramics by gecasting

High-strength and low-dielectric ZrO2 reinforced fused silica ceramics by gelcasting

Mechanical properties and microstructure of quartz fiber-reinforced silica matrix composite with a single layer pyrocarbon interphase

To address critical limitations of ultra-low viscosity supercritical CO2 fracturing fluids, including excessive fluid loss and inadequate proppant transport capacity, a series of thickeners designed to significantly enhance CO2 viscosity were synthesized. Initially, FT-IR and 1H NMR characterization confirmed successful chemical reactions and incorporation of both solvation-enhancing and -thickening functional groups. Subsequently, dissolution and thickening performance were evaluated using a custom-designed high-pressure vessel featuring visual observation capability, in-line viscosity monitoring, and high-temperature operation. All thickener systems exhibited excellent solubility, with 5 wt% loading elevating CO2 viscosity to 3.68 mPa·s. Ultimately, molecular simulations performed in Materials Studio elucidated the mechanistic basis, electrostatic potential (ESP) mapping, cohesive energy density analysis, intermolecular interaction energy, and radial distribution function comparisons. These computational approaches revealed dissolution and thickening mechanisms of polymeric thickeners in CO2. 

Synthesis of Linear Modified Siloxane-Based Thickeners and Study of Their Phase Behavior and Thickening Mechanism in Supercritical Carbon Dioxide

Fused silica ceramics are widely applied for radome materials, crucibles, and vanes, but the mechanical properties were deteriorated due to the cristobalite crystallization. The fused silica ceramics added with by β-Si3N4 whiskers were prepared by a slip-casting method to retard the cristobalite crystallization. The influences of the sintering environments and the β-Si3N4 whiskers on the microstructure and phase structure were investigated. The silanol (Si-(OH)n) and oxygen vacancies (VO) in the fused silica in formed in different conditions were studied by Fourier Transform Infra-Red (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the results indicated that the ball-milled produced a large amount of the silanol groups onto the surface of the fused silica particles. The fused silica heated in the vacuum created the maximum oxygen vacancies (24.2%) on the surfaces. Silanol groups reacted with the β-Si3N4 whiskers, and the O atoms in the silanol groups were fixed into the bulk materials. And the crystallization kinetics and the activation energy of Si3N4w/SiO2 ceramics at the temperature ranging from 1200 to 1400°C were calculated based on the JMA(Johnson-Mehl-Avrami) model. The activation energy of the fused silica ceramics with the addition of the β-Si3N4 is 506.2 kJ/mol, increased by 23.6% than that of the pure fused silica ceramic. 

Influence of β‐Si
 3
 N
 4
 whiskers on sintering and crystallization of fused silica ceramics

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Influence of β‐Si 3 N 4 whiskers on sintering and crystallization of fused silica ceramics