Microstructure, toughness and flexural strength of self-reinforced silicon nitride ceramics doped with yttrium oxide and ytterbium oxide

Silicon nitride ceramics were prepared by gas pressure sintering (GPS) with different sintering additives, including La2O3, Sm2O3 and Al2O3. Effect of sintering additives on the phase-transformation, microstructure and mechanical properties of porous silicon nitride ceramics was investigated. The results show that the reaction of sintering additives each other and with SiO2 had key effects on the phase-transformation, grain growing and grain boundaries. With 9MPa N2 atmosphere pressure, holding 1h at 1850°C, adding 10wt% one of the La2O3, Sm2O3, Al2O3, porous silicon nitride was prepared and the relative density was 78%, 72%, 85% respectively. The flexural strength was less than 500MPa, and the fracture toughness was less than 4.8MPam1/2. Dropping compounds sintering additives, such as La2O3+Al2O3, Sm2O3+Al2O3 effectively improves the sintering and mechanical properties. The relative density was 99.2% and 98.7% with 10wt% compounds sintering additives. The grain ratio of length to diameter was up to 1:8. The flexural strength was more than 900MPa, and the fracture toughness was more than 8.9MPam1/2.

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Microstructural Evolution and Mechanical Properties in Yb2O3–Fluxed Silicon Nitride Ceramics

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.336-338.1172 ◽

2007 ◽

Vol 336-338 ◽

pp. 1172-1174

Author(s):

Gang Feng Guo ◽

Xiao Zhan Yang ◽

Jian Bao Li ◽

Hong Lin ◽

Long Liang ◽

...

Keyword(s):

Mechanical Properties ◽

Fracture Toughness ◽

Silicon Nitride ◽

Flexural Strength ◽

Microstructural Evolution ◽

Intergranular Fracture ◽

Fracture Mode ◽

Transgranular Fracture ◽

Sintering Additive ◽

Nitride Ceramics

Silicon nitride ceramics were fabricated with Yb2O3 as the sintering additive. The effects of the amount of Yb2O3 on the microstructure and the mechanical properties such as the flexural strength and the fracture toughness were investigated. Almost fully densified Si3N4 was obtained when only 4 wt% Yb2O3 was added. Both the flexural strength and the fracture toughness increased steadily with the Yb2O3 content. The transgranular fracture mode was observed in the specimen containing 4 wt% Yb2O3, however, the intergranular fracture mode was observed in the specimen containing 10 wt% Yb2O3.

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Preparation of Low Dielectric Constant Porous Silicon Nitride Ceramics for Radome Application

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.281.610 ◽

2018 ◽

Vol 281 ◽

pp. 610-615

Author(s):

Ling Li ◽

Bao Xin Zhu ◽

Hong Sheng Wang ◽

Jie Zhang

Keyword(s):

Dielectric Constant ◽

Silicon Nitride ◽

Porous Silicon ◽

Flexural Strength ◽

Dielectric Material ◽

Core Layer ◽

Low Dielectric Constant ◽

Low Dielectric ◽

Dielectric Constant And Loss ◽

Nitride Ceramics

The porous silicon nitride ceramics with low dielectric constant and high flexural strength were obtained by adding pore-forming agent through partial sintering technique. The effects of pore-forming agent amount on the properties of porous silicon nitride ceramics were investigated. Microstructure was analyzed by means of scanning electron microscopy. The results show that the porous structure is formed by the overlap of pillar β-Si3N4 with high length diameter ratio. The porosity of samples rises with the increase of pore-forming agent content, which leads to the decrease of the dielectric constant and loss, but the decrease of flexural strength. When the pore-forming agent of PMMA with mass fraction of 20% was added, the volume density, porosity, dielectric constant and loss of porous silicon nitride ceramics were 1.17g/cm3, 66.5%, 2.33 and 0.8×10-3 respectively, with higher flexural strength of 75MPa which is satisfactory as low dielectric material for core layer of broadband radome.

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Microstructure and Strength of Oxidation-Bonded Porous Silicon Nitride Ceramics

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.353-358.503 ◽

2007 ◽

Vol 353-358 ◽

pp. 503-506

Author(s):

Shu Qiang Ding ◽

Yu Ping Zeng ◽

Dong Liang Jiang

Keyword(s):

Silicon Nitride ◽

Porous Silicon ◽

Flexural Strength ◽

Amorphous Silica ◽

Fracture Mechanism ◽

Bonding Process ◽

Nitride Ceramics ◽

Porous Si3n4 ◽

Si3n4 Ceramics ◽

Porous Si3n4 Ceramics

An oxidation bonding process was developed to fabricate oxidation-bonded porous silicon nitride (Si3N4) ceramics from α-Si3N4 powder in air at 1100-1400oC. Si3N4 particles are bonded by the oxidation-derived silica (SiO2) and the pores derive from the stack of Si3N4 particles and the release of N2 and SiO gas during the sintering. The microstructure of oxidation-bonded porous Si3N4 ceramics was observed. Moreover, the fracture mechanism was analyzed. Effects of the bonding phases and pores on the flexural strength were investigated. Oxidation-bonded porous Si3N4 ceramics with high flexural strength was obtained by restraining the crystallization of amorphous silica and forming the well-developed necks between Si3N4 particles.

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