DOI: 10.3724/SP.J.1077.2014.13531

Journal of Inorganic Materials (无机材料学报) 2014/29:7 PP.701-705

Effects of Nitrogen Pressure on Microstructure and Mechanical Performance of Porous Silicon Nitride Ceramics

Porous silicon nitride ceramic was fabricated by using α-Si3N4 as raw material and Y2O3 as a sintering additive, with nitrogen pressure of 0.12 MPa, 0.32 MPa and 0.52 MPa. Effects of the nitrogen pressure on grain morphology and mechanical properties of the resultant porous Si3N4 ceramics were characterized by SEM, XRD and flexural strength. With the increasing of nitrogen pressure, sintering shrinkage decreased, with a corresponding increased porosity. Due to the increase of nitrogen pressure, the viscosity of liquid phase increased due to increased N solubility, leading to the low densification in the sintering. Fibrous β-Si3N4 grains were developed in the porous microstructure and the grain morphology and aspect ratio were greatly affected by the nitrogen pressures. The high viscosity of the liquid phase in nitrogen at high pressure led to restraining of the β-Si3N4 nucleation, and preferential growth of β-Si3N4. Due to the formation of elongated β-Si3N4, flexural strength of the porous Si3N4 ceramic was improved by the increase of nitrogen pressure, while decreased with the increase of porosity. The porous Si3N4 ceramics with porosity of 58% and flexural strength of 140 MPa were obtained at the nitrogen pressure of 0.52 MPa.

Key words:Si3N4 nitrogen pressure,aspect ratio

ReleaseDate:2016-07-11 11:25:01

[1] MEN W W, MA N, XUAN L X, et al. Research progress of wave-transmitting porous silicon nitride ceramic materials. J. Ceram., 2012, 33(2): 241-244.

[2] LU Y, YANG J F, LI J L. Fabrication of porous silicon nitride with high porosity by carbothermal reduction-reaction bonding. Journal of Inorganic Materials, 2013, 28(5): 469-473.

[3] XU J, ZHOU W C, WANG J B, et al. The preparation of porous Si3N4 ceramic material for radome application. Funct. Mater., 2011, 42(Suppl 3): 411-415.

[4] ZHANG Y W, YU J B, XIA Y F, et al. Microstructure and mechanical performance of silicon nitride ceramics with seeds addition. Journal of Inorganic Materials, 2013, 27(8): 807-812.

[5] YANG J F, ZHANG G J, OHJI T, et al. Effect of MgAl2O4-ZrO2 addition on sintering behaviors and mechanical properties of silicon nitride ceramics. J. Ceram. Soc. Jpn., 2000, 108(8): 697-700.

[6] KITAYAMA M, HIRAO K, KANZAKI S. Effect of rare earth oxide additives on the phase transformation rates of Si3N4. J. Am. Ceram. Soc., 2006, 89(8): 2612-2618.

[7] PAINTER G S, BECHER P F, SHELTON W A, et al. First-principles study of rare-earth effects on grain growth and microstructure in β-Si3N4 ceramics. Phys. Rev. B, 2004, 70(14): 144108-1-4.

[8] SHIBATA N, PENNYCOOK S J, GOSNELL T R, et al. Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions. Nature, 2004, 428(15): 730-733.

[9] YANG J, YANG J F, SHAN S Y, et al. Effect of sintering additives on microstructure and mechanical properties of porous silicon nitride ceramics. J. Am. Ceram. Soc., 2006, 89(12): 3843-3845.

[10] HAMPSHIRE S, JACK K H. In Progress in Nitrogen Ceramics, ed. Martinus Nijhoff Publishers, Boston/The Hague/Dordrecht/ Lanc-aster 1983: 225-230.

[11] HAMPSHIRE S. The role of additions in pressureless sintering of nitrogen ceramics for engine applications. Metals Forum, 1984, 7(3): 162-168.

[12] PULLUM O J, LEWIS M H. The effect of process atmosphere on the intergranular phase in silicon nitride ceramics. J. Eur. Ceram. Soc., 1996,16(11): 1271-1275.

[13] HAMPSHIRE S, POMEROY M J. Grain boundary glasses in silicon nitride: a review of chemistry, properties and crystallisation. J. Eur. Ceram. Soc., 2012, 32(9): 1925-1932.

[14] SHARAFAT A. Preparation, Characterization and Properties of Nitrogen rich Glasses in Alkaline Earth-Si-O-N Systems. Stockholm: Stockholm University, 2009.