The maximum substitution of monovalent, divalent, and trivalent metal ions for b-tricalcium phosphate (b-TCP) was investigated, and a substitution model of these metal ions for b-TCP was proposed. Monovalent metal ions (M I ) could replace Ca(4) site and vacancy (V Ca (4) ) in b-TCP as 2M I 5 Ca 21 1V Ca(4) and the maximum substitution was about 9.1 mol%. In the case of divalent metal ions (M II ), Ca(4) and Ca(5) sites were replaced by divalent metal ions as M II 5 Ca 21 , and the maximum substitution was about 13.6 mol%. Trivalent metal ions (M III ) could be substituted for Ca(4) site and vacancy as 3M III 5 2Ca 21 1V Ca(4) , and the maximum substitution was about 9.1 mol%.

The thermal shock behavior of isotropic and anisotropic porous Si3N4 was evaluated using the water‐quenching technique. The critical temperature difference for crack initiation was found to be strongly dependent on the ratio of fracture strength to elastic modulus. Because of a very high strain‐to‐failure, anisotropic porous Si3N4 showed no macroscopic cracks and was able to retain its strength even at a quenching‐temperature difference of ∼1400°C.

Porous CaZrO3/MgAl2O4 composites were synthesized in air by pressureless reactive sintering of an equimolar mixture of dolomite (CaMg(CO3)2), monoclinic zirconia (m‐ZrO2), and α‐alumina powders, with a 0.5 wt% lithium fluoride additive. The reaction behavior of the mixed powders (with/without LiF additive) was studied using high‐temperature X‐ray diffraction. A bulk porous composite resulted from sintering at 1300°C for 2 h (in a nearly closed container, so as to increase the LiF‐doping effect), which consisted of fine grains (CaZrO3 and MgAl2O4, ∼0.5–1 μm) and well‐grown idiomorphic ones (MgAl2O4 octahedra ∼ 2–4 μm). The idiomorphic spinel grains were located around the inner walls of relatively large pores. The composite showed appreciably high bending strength (σf= 110 ± 8 MPa for a porosity of 31%). The porous CaZrO3/MgAl2O4 composites can be applied as high‐temperature filters and lightweight structural components.

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