Abstract: A process for drip casting silicon nitride slurries.

Abstract: A method of making shaped, gelled bodies, comprising: (1) producing a mixture comprising a first liquid, a granular substance or precursor thereof, and a gelation compound which quickly gels at a gelation temperature, and (2) introducing portions of the mixture into a first fluid in which the first liquid is immiscible, said first fluid having a temperature of about the gelation temperature, thereby causing the portions to take on a shape and then gel to form shaped, gelled bodies.

Abstract: Aqueous suspensions of ceramic particles in which the particle are coated by a metal oxide sintering aid or metal hydroxide precursor thereto and which have a sufficiently high solids content to produce casting slips which can yield net shape castings are provided. The suspensions are produced by concentrating lower solids content suspensions by crossflow filtration which disrupts hydroxide gels which inherently form by interaction of the coating with water. The resultant highly loaded aqueous suspensions may be used in net shape casting to produce cast bodies of high dimensional stability, high green strength, and with a low incidence of cracking.

Abstract: Ceramic molding or casting powders, particularly nitride, oxide and carbide powders, that have substantial internal surface and volume produce improved dispersions after being coated with a cover material, such as polyethylene glycol, that reduces the specific surface area of the powder by at least about 10% and reduces the amount of penentration of the binder used for dispersion into the internal volume of the powder. The viscosity of dispersions of such coated powders, or of conventional uncoated ceramic powders, can be further reduced by treatment of the powders with organotitanate, organozirconate, or organosilane coupling agents that are chosen to interact favorably with the specific powders and binders used.

Abstract: Fibers for use in forming fiber reinforced ceramic composites may be effectively deagglomerated and/or dispersed in the precursor from which the continuous phase of the composite is to be derived by passing the fibers through a screen with openings that are from two to ten times as wide as the fiber diameter. By using this technique, composites of alumina fibers in a partially stabilized zirconia matrix have been prepared with better fiber orientation and fiber aspect ratio than previously achieved.

Abstract: A vacuum fluidized powder feed apparatus for filling an evacuated mold. The fluidized powder feed apparatus has a feed cup defining a cylindrical cavity for holding a quantity of powdered material and a powder exit aperture provided through the bottom of the feed cup mating with the fill aperture of the mold. A porous annulus disposed at the bottom of the cylindrical cavity has a conically shaped internal surface sloping toward and mating with the exit aperture of the feed cup. Vent holes provided in the side walls of the feed cup cause a fluid flow through the porous annulus into the interior of the cylindrical cavity which is connected to the evacuated mold cavity through the exit aperture. A pneumatic piston received in the cylindrical cavity engages the top of the powdered material and produces a force cavity urging the powdered material towards the exit aperture.

Abstract: An apparatus for molding complex powder articles having a two part dilatant mold resiliently coupled. The two halves of the mold are resiliently pressed into physical contact with each other by external means. A vacuum pump connected to the mold produces a fluidized powder material flow from a powder feed mechanism into the mold cavity. A vibrator vibrates the mold during the filling of the mold cavity with powdered material with a force sufficient to slightly separate the two halves of the mold cyclically dilating the volume of the mold cavity. The dilation of the mold cavity in combination with the fluidized powder feed permits the mold cavity to be uniformly filled with powder material. Dilation of the mold cavity also compacts the powder material received in the mold.

Abstract: The resistance of a honeycombed structure to damage from asymmetric thermal shock occurring across its surface during use and formed with cells having anisotropic Young's moduli in the planes perpendicular the central longitudinal axis of each cell can be improved by varying the orientation of the anisotropic cells with respect to one another so as to minimize the number of such cells being oriented with an axis of maximum Young's moduli aligned with the direction of either the maximum temperature difference or maximum localized temperature gradient occurring across the cell.

Abstract: A method of improving the thermal shock resistance of a honeycombed structure through which fluids flow and formed by joining a plurality of cellular segments to one another along their peripheral walls, by providing discontinuities through the joints formed between the adjoining segments in the direction of the fluid flow through the structure so as to lessen temperature differences occurring in the joint area, to provide the structure with greater flexibility and to act as crack arrestors lessening the transmission of stresses between adjoining segments and through the joints. In two preferred embodiments, the invention is practiced in forming a heat recovery wheel by joining a plurality of cellular segments to one another with cement which is striped to the segments so as to form a plurality of hollow, straight walled, channels extending essentially axially through some or all of the joint areas of the resulting wheel.

Abstract: The thermal shock resistance of a honeycombed structure or a structure having a honeycombed surface formed by bonding together a plurality of cellular segments each having a honeycombed face forming a portion of the structure or surface of the structure, respectively, is improved by recessing the bond joints between the joined cellular segments from the surface. The thermal shock resistance of a heat recovery wheel operated in a counterflow heat exchanger system and formed from joined cellular segments is improved by recessing the bond joints joining the cellular segments, preferably approximately one-half inch (12.7 mm), from the face of the wheel exposed to the gases at their highest temperatures.

Abstract: An improved seal column design for use in counterflow heat exchanger systems having a centrally supported rotary heat exchanger or heat recovery wheel having an integral strengthened central hub. According to the invention, the edges formed between the end wall of each seal column juxtaposed an annular face of the wheel and the side walls of the column exposed to and separating the fluid flows are straight and parallel to one another and evenly spaced, at their point of closest approach, between one-half inch (1.27 cm) and one and one-half inches (3.81 cm) and preferably one inch (2.54 cm) beyond the outer circumference of the hub. Also, the side walls of the columns are straight and parallel to one another in the vicinity of the end wall.