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Si 2 N 2 O composites were achieved via direct ink writing technique and pressureless sintering. The design and optimization of inks and the effect of mass ratio of Si 3 N 4 and SiO 2 on the phase composition, microstructure, mechanical properties and dielectric properties of composites were systematically investigated. The inks exhibit superior stability and printability. Increasing SiO 2 content facilitated densification and enhancement of mechanical property. The generation of β-Si 3 N 4 and Si 2 N 2 O and the nucleation of cristobalite were restrained by high content SiO 2. The ceramic composites with the flexural strengths from 74.1MPa to 104.9MPa and low dielectric constant (≤4.68) were fabricated. This strategy provides a systematic reference for synthesis of high-performance porous Si 2 N 2 O composites based on the DIW. [ABSTRACT FROM AUTHOR]

Porous Si 2 N 2 O ceramics strengthened by directional β-Si 3 N 4 are fabricated by direct ink writing technique and seeding method. Slurries prepared with different contents of β-Si 3 N 4 grains exhibited superior printing behavior. The degree of orientation of β-Si 3 N 4 grains increased with the increase of grains content. The mechanical properties of the porous Si 2 N 2 O ceramic are effectively improved by interspersed β-Si 3 N 4 grains and present anisotropy. This novel strategy provides a reference for fabricating high-performance anisotropic complex structure ceramics. [ABSTRACT FROM AUTHOR]

Si2N2O ceramic foam is developed by the combination of biological foaming (BF) technique and direct ink writing (DIW). The effect of yeast content on the rheological properties of inks and phase composition, microstructure, and mechanical properties of ceramic foam are systematically investigated. The inks consist of different proportions of yeast suspension and ceramic start powder suspension that exhibit superior printing behavior and proper fermentation capacity. Yeast cells and additives derived from commercial active yeast are fully utilized as BF agent, nutrient, and emulsifier. The variation of yeast contents bring about the evolution of phases, pores density, and mechanical properties of ceramic parts. The Si2N2O foams with porosities from 61.5 ± 4.3% to 71.0 ± 4.5% are successfully fabricated. The corresponding compressive strength decreases from 33.1 ± 2.6 to 8.3 ± 1.5 MPa. As a result, a promising reference for the design and preparation of BF ceramic ink and hierarchical ceramic foam based on DIW is provided. [ABSTRACT FROM AUTHOR]

A novel, efficient, versatile strategy was carried out to fabricate highly porous ceramic parts based on the combination of strong colloidal gel ink fabricated with high boiling point organic solvents and DIW technique. The preparation and optimization of inks and the effect of heating temperature on the phase composition, microstructure, mechanical properties and dielectric properties of ceramic parts were systematically investigated. The strong colloidal ink exhibits excellent ambient stability and printability. The sintering temperatures bring about the evolution of phases, structural mechanical properties and dielectric properties of ceramic parts. Ultimately, Si 2 N 2 O single wall ceramic parts with a frame density of 1.07˜1.14 g/cm3 and an apparent porosity of 53.13 ± 1.29% were successful fabricated. The dielectric constant and dielectric loss of Si 2 N 2 O sample (1650℃) are only 4.24 and 0.0049, respectively. This strategy provides a reference for in-situ synthesis of high-performance porous ceramic components based on the DIW. [ABSTRACT FROM AUTHOR]

An embedded dense coating was fabricated on the direct ink writing Si 2 N 2 O porous ceramic by impregnating the SiO 2 -sol and in-situ sintering. The influence of different heat-treatment atmosphere and temperature on the microstructure, phase composition, mechanical properties and water resistance was studied systematically. A relatively flat and dense seal layer was obtained in the air atmosphere. The crystallization of SiO 2 was inhibited by nitrogen atmosphere. The resulting embedded coatings effectively improved the mechanical properties and water resistance of Si 2 N 2 O porous ceramic, and the specimens treated in air exhibited better comprehensive performance due to the higher densification. This strategy provides a reference for in-situ surface reinforced components with complex structures. Unlabelled Image • A strategy for fabricating embedded dense coating on complex structure ceramic was provided. • The samples heat-treated in air exhibits better sealing effect than that in nitrogen. • The crystallization of SiO 2 was inhibited by nitrogen atmosphere. • Mechanical properties and water resistance are improved due to the good sealing effect. [ABSTRACT FROM AUTHOR]

A convenient direct ink writing porous ceramic preparation strategy incorporating green body strengthening measure was provided. Different hydrogen bond interactions between particles in polar and nonpolar solvents have been successfully applied to regulate the rheological properties of 3D printing ink. Inks with different (NH 4)H 2 PO 4 content were systematically optimized, which exhibited acceptable ambient stability and superior printing behavior. The phosphoric acid generated by decomposition of (NH 4)H 2 PO 4 reacts with silica or oxide layer of silicon nitride to form Si–O–P binder by a pretreatment at low temperature to strengthen the green body. The compressive strength of green body fabricated by ink with 0.2 g/mL (NH 4)H 2 PO 4 was increased by 415%. The Si 2 N 2 O single wall frame structure parts with a compressive strength of 3.33 ± 0.14 MPa under a frame density of 1.14 ± 0.05 g/cm3 were fabricated. The dielectric constants of the developed ceramic parts range from 3.57 to 4.21. A systematic study of design and preparation of ink and quantization of molding parameters provide a reference for in-situ reinforced the ceramic green body of silica, silicon nitride and their composites, as well as fabrication of their corresponding highly porous ceramic components based on the direct ink writing. Image 1 • A strategy for direct ink writing of high-strength Si 2 N 2 O green bodies as well as their ceramic components was provided. • The rheological properties of inks were regulated by the different hydrogen bond interactions between particles in C 10 H 22 O 5 and H 2 O. • The phosphorus elements introduced by (NH 4)H 2 PO 4 aqueous solution were evenly distributed in green body and ceramic part. • The compressive strength of Si 2 N 2 O green body was increased up to 415% due to the strengthening of Si–O–P binder. [ABSTRACT FROM AUTHOR]