Relationship between Microstructure and Mechanical Performance of a 70% Silicon Nitride–30% Barium Aluminum Silicate Self‐Reinforced Ceramic Composite

Abstract

The abnormal grain growth of ␤-Si 3 N 4 was observed in a 70% Si 3 N 4 -30% barium aluminum silicate (70%-Si 3 N 4 -30%-BAS) self-reinforced composite that was pressureless-sintered at 1930°C; Si 3 N 4 starting powders with a wide particle-size distribution were used. The addition of coarse Si 3 N 4 powder encouraged the abnormal growth of ␤-Si 3 N 4 grains, which allowed microstructural modification through control of the content and size distribution of ␤-Si 3 N 4 nuclei. The mechanical response of different microstructures was characterized in terms of flexural strength, as well as indentation fracture resistance, at room temperature. The presence of even a small amount of abnormally grown ␤-Si 3 N 4 grains improved the fracture toughness and minimized the variability in flexural strength.

Experimental Investigation on a Novel Electrolyte Configuration for Cylindrical Molten Carbonate Fuel Cells

“…For constant differential pressures, better performances are obtained by increasing H 2 flow rate and reducing O 2 flow rate: 1.94 mW and 8.28 mW are respectively the average and the maximum difference between the produced power at 620 C in (7)(8)(9)(10)(11)(12) tests and in (1-6) tests; 3.36 mW and 15.92 mW are, respectively, the average and the maximum difference between the produced power at 640 C in (7)(8)(9)(10)(11)(12) tests and in (1)(2)(3)(4)(5)(6) tests.…”

“…The cylindrical geometry of the cell components (electrodes, matrix) helps to reduce the traditional problems of square and rectangular geometry MCFCs. In fact, traditional MCFC elements are produced by the tape casting technique [7]; cylindrical cell elements may be easily obtained by injection moulding, a technique which may be conveniently used for large scale productions of small size cells, with high benefits in terms of fabrication times and costs. Furthermore, traditional MCFCs are characterized by high thermal outward dispersions.…”

In situ Reinforced Silicon Nitride — Barium Aluminosilicate Composite

“…An example of a seeded microstructure is shown in Figure 16. Feng and White reported 64 that bimodal microstructure could be obtained by introducing various fractions of two different Si 3 N 4 powders (UBE Industries, E10 and ESP), where the size distribution and initial ␤ phase content of the starting powders is controlled. The characteristic pronounced abnormal grain growth (Table 4) suggests the role of the ESP powders in improved fracture toughness, although no significant changes in strength seem evident.…”

“…The flexural strength remains unchanged with the initial growth of those larger whiskers at 50E10 and 70E10 samples. Further increase in large whisker amount causes a dramatic strength drop to around 800 MPa 64 . The result indicates that the achievement of both high fracture toughness and high strength in this composite is made possible by encouraging the abnormal grain growth, where the size and content of large grains is controlled as mentioned above.…”

“…Therefore, the key factor in optimizing both the fracture toughness and strength in Si 3 N 4 materials is to generation of a distinct bimodal microstructure with the large elongated grains well dispersed in a fine matrix 63 . In the Si 3 N 4 -BAS composite, bimodal microstructure is introduced by either seeding 38 or tailoring ␣-rich Si 3 N 4 starting powders 64 . An example of a seeded microstructure is shown in Figure 16.…”