Slip Degassing to Improve the Properties of Slip Cast and Reaction Bonded Si3N4


Article Preview

The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si3N4 was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si3N4. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm3, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si2N2O, and SiC likely resulted from the reactions between O2 and C impurities with Si3N4.



Edited by:

Peerapong Pinwanich and Akrapol Soisungval




K. Somton et al., "Slip Degassing to Improve the Properties of Slip Cast and Reaction Bonded Si3N4", Key Engineering Materials, Vol. 751, pp. 358-362, 2017

Online since:

August 2017




* - Corresponding Author

[1] J.S. Lee, B.D. Mun, H.D. Kim, B.C. Shin, I.S. Kim, Effect of raw-Si particle size on the properties of sintered reaction-bonded silicon nitride, Ceram. Int. 30 (2004) 965-976.


[2] B.T. Lee, J.H. Yoo, H.D. Kim, Size effect of raw Si powder on microstructures and mechanical properties of RBSN and GPSed-RBSN bodies, Mater. Sci. Eng. A333 (2002) 306-313.


[3] B.S. Bail, M.N. Rahaman, Orthopedic applications of silicon nitride ceramics, Acta. Biomater. 8 (2002) 889-2898.

[4] A.M. Nymark, Oxidation of silicon powder in humid air, Master Thesis, Norwegian University of Science and Technology, Norway, (2012).

[5] W. Volland, Online introductory chemistry, information on: http: /www. 800mainstreet. com/9/0009-006-henry. html. Accessed 15 November (2016).

[6] K. Somton, K. Dateraksa, P. Laoratanakul, M. Rodchom, R. McCuiston, A study of slip solids content and wall thickness on thermal shock behavior of a slip cast reaction bonded silicon nitride ladle, Ceram. Int. 41 (2015) 3324-3329.


[7] P.C. Silva, J.L. Figueiredo, Production of SiC and Si3N4 whiskers in C + SiO2 solid mixtures, Mater. Chem. Phys. 72 (2001) 326-331.


[8] L. Gavoret, Processing of SiC whisker reinforced reaction bonded silicon nitride composites, Master Thesis, McGill University, Canada, (1992).

[9] D. Yao, Y. Xia, Y.P. Zeng, K.H. Zou, D. Jiang, Porous Si3N4 ceramics prepared via slip casting of Si and reaction bonded silicon nitride, Ceram. Int. 37 (2001) 3071-3076.


[10] F. Wang, G.Q. Jin, X.Y. Guo, Sol-gel synthesis of Si3N4 nanowires and nanotubes, Mater. Lett. 50 (2006) 330-333.

[11] S. Chen, Y. Zhou, F. Xia, Stability of phases in SiC and Si3N4 Whisker formation, Chin. J. Met. Sci. Technol. 8(1992) 103-106.