The title porous ceramics, having a controlled microstructure consisting of pores of predetd. size, shape, and spatial distribution, are prepd. by (a) forming a colloidal suspension of ceramic material and uniform and identical polymeric microspheres, (b) stabilizing the interaction between the microspheres and the ceramic particles, (c) consolidating the colloidal suspension by removing the liq. and forming a compact body, and (d) heating the body to decomp. the microspheres and sintering the body to obtain a porous ceramic body having multiple, evenly distributed, noncontiguous pores. These porous ceramics are useful for a variety of applications, including multilayer tape casting. A 54-vol.% aq. α-Al2O3 suspension was prepd. using 0.5 wt.% NH4 salt of polyacrylic acid as anion surfactant and 0.08 wt.% (based on dry Al2O3) citric acid as a stabilizer. The suspension was treated with ultrasound to break up agglomerates with a polystyrene suspension (30-40 vol.%), and the colloidal suspension was then slip-cast, dried, and sintered to form a single porous layer, that was slowly dried, heated to 1000° at 22.5°/h, and sintered at 1550° to obtain a ceramic body with controlled microstructure. [on SciFinder(R)]

The low-d. composite consists of B carbide porous compact and infiltrated Al, or Al alloy (e.g., Al-Cu, Al-Mg, Al-Si, Al-Mn-Mg, and/or Al-Cu-Mg-Cr-Zn). To reduce the reaction rate between B carbide and Al during infiltration, the B carbide is heated to 1800-2250° in the presence of free C (e.g., graphite). Prepn. of the composite comprising (1) dispersing a B carbide having particle size <10 μ in water or an inorg. medium; (2) consolidating B carbide into a porous compact by slip casting, pressure casting, injection molding, or isostatic pressing; (3) infiltrating the compact with Al by submerging in molten Al bath at 1150-1250°; (4) heat treatment at <1800°. Optionally, the porous compact is sintered at ∼1800-2250° prior to Al infiltration. The composite has high fracture toughness, strength, hardness, and stiffness. Thus, B carbide powder was dispersed in water at pH = 8, and the suspension was consolidated by slip casting. The porous compact was removed from the mold, dried 12 h at 45°, and 24 h at 110°, and heat treated 30 min at 2150°. The resulting compact was infiltrated with molten Al in a graphite furnace under vacuum at 1190° for 30 min. Final microstructure of the composite included B carbide 64, and Al 31%. The composite had fracture toughness of 9.7 MPa m1/2, fracture strength 621 MPa, and Young's modulus of 290 GPa. [on SciFinder(R)]

Cermets based on a ternary system with B, C, and a reactive metal are manufd. with controlled structures having ≥1 ceramic phases distributed in an alloy matrix. A starting compn. as well as reaction temp., time, and atm. are selected for controlling the manufg. process and final structures, with emphasis on initial powder consolidation, early melt wetting, and final sintering. Surfactant selection is considered for obtaining a uniform blend of initial feed powders having particle size of ≤5 μ. Thus, powd. B4C (av. size 5 μ) 80 and Al 20 vol.% were mixed in EtOH by using an ultrasonic probe, and slip cast in a mold from plaster of Paris for dewatering. The powder mixt. removed from the mold was pressed at 10,000 psi and room temp. Pellet preforms were heated in 10 min to 1050° in a furnace, and then sintered at 800° for 24 h. The final composite contained an unknown Al-rich phase 34, B4C 32, AlB2 23, Al 5, α-AlB12 3, Al4C3 2, and AlB12C2 1 vol.%. The unknown phase showed crystallog. structure intermediate between hexagonal and rhombohedral. Cermet products of this type showed bend strength >110 kpsi and fracture toughness 12 kpsi-in.0.5, with the latter exceeding the value of ∼4 for conventional Al2O3-B4C composites. [on SciFinder(R)]