The effect of aluminium on the electrical and mechanical properties of BaTiO3 ceramics as a function of sintering temperature
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The effect of aluminium additions on the mechanical behaviour of BaTiO3 positive temperature coefficient of resistance ceramics sintered in air at temperatures ranging between 1220 and 1400° C has been investigated. Tensile strength has been measured indirectly by the diametral compression of lapped discs using concave loading anvils. Values of ∼ 85 and ∼ 110 MPa for samples fired near their optimum sintering temperature were determined for two batches of material, the latter of which contained additions of Al2O3 (0.55 mol%). Strength did not vary systematically with grain size and appeared to be controlled by near surface defects. The size of these cavities, which were generally crescent shaped, was consistent with the material having a bulk fracture toughness of ∼1.3 MPam1/2. The higher mechanical strength of samples which contained Al2O3 additions was attributed to the enhanced “healing up” of these cavities by the liquid phase giving a smaller inherent critical defect size rather than by increasing the bulk toughness of the ceramic.
KeywordsAl2O3 Tensile Strength Fracture Toughness BaTiO3 High Mechanical Strength
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- 2.A. G. EVANS, in “Fracture Mechanics of Ceramics”, Vol. 3, edited by R. C. Bradt, D. P. H. Hasselman and F. F. Lange (Plenum, New York, 1978) p. 31.Google Scholar
- 3.F. L. L. B. CARNIERO and A. BARCELLOS, Union of Testing and Research Laboratories for Materials and Structures, no. 13 (1953).Google Scholar
- 5.M. S. STUCKE and A. S. WRONSKI,Proc. Brit. Ceram. Soc. 25 (1975) 109.Google Scholar
- 6.R. M. SPRIGGS, L. A. BRISSETTE and T. VASILOS,Mater. Res. Stand. 4 (1964) 218.Google Scholar
- 7.O. VRDAR and I. FINNIE,Int. J. Fracture 11 (1975) 495.Google Scholar
- 8.M. C. SHAW, P. M. BRAIDEN and G. J. DeSALVO,Trans ASME, J. Engng Ind. 97 (1975) 77.Google Scholar
- 9.H. AWAJI and S. SATO,Trans ASME, J. Engng Mater. Technol. 101 (1979) 139.Google Scholar
- 10.H. AWAJI, —ibid.102 (1980) 257.Google Scholar
- 11.J. W. FLEMING, H. M. O'BRYAN and J. THOMSON, US Pat. 4175060 (1979).Google Scholar
- 12.G. DE WITH and H. PARREN, in “Science of Ceramics”, Proceedings of the 12th International Conference, Saint-Vincent, Italy (1984) p. 537.Google Scholar
- 13.R. C. POHANKA, S. W. FREIMAN and B. A. BENDER,J. Amer. Ceram. Soc. 61 (1978) 72.Google Scholar