Ceramics Process Systems Corporation

Bruce E Novich

Richard L Pober

Mark A Occhionero

John W Halloran

Cathryn A Sundback

Richard W Adams

Richard Waack

Wen-Cheng J Wei

Krishna Venkataswamy

Angelica E Karas

Removal of classified particles from the classifier apparatus is simplified by the addition of a polymeric dispersant in the slurry, added in an amount substantially in excess of that needed to disperse the particles.

Process for facilitating removal of classified powders

A process for forming articles from inorganic sinterable particulates includes providing a well-dispersed, low pressure injectable slurry, freeze-forming the slurry into a desired geometry, and drying the piece so formed by a predominantly sublimative process, to produce a green article that can be conventionally sintered. The vehicle has a volume change on freezing of not more than .+-.10% by volume; to further control the volume change on freezing, an emulsion derived from different vehicles can be tailored. The slurries preferably have a solids content of at least about 35 v/o, a viscosity of preferably not more than about 1000 cP at 100 s.sup.-1, and are preferably injectable at not more than about 1000 psi, usually at less than 100 psi.

Complex ceramic and metallic shaped by low pressure forming and

Dense, flaw free, complex, 3-dimensional, metal or refractory shapes are formed by preparing a low viscosity, pourable aqueous-based suspension. The aqueous suspension preferably contains ceramic or metal particulates, water, and a compatible mixture of additives for performing dispersant, cryoprotectant, and strength enhancing functions. The low viscosity slip is cast or injection molded at low pressure into a complex mold, frozen, demolded, and freeze dried without the formation of a continuous liquid phase. The green part is subsequently sintered by conventional techniques to achieve a dense part.

Forming of complex high performance ceramic and metallic shapes

An improved method and system are provided for centrifugally separating a suspended colloidal phase. The method in accordance with a preferred embodiment of the invention involves filling a spinning centrifuge bowl with a fluid medium distinct from the suspension, so that a static zone of liquid forms in the bowl, and then introducing the suspension into the bowl in a feed location concentrically inside of the static zone.

Centrifugation system using static layer

A solution containing polymerizable monomers and volatile solvents can be used to disperse ceramic particles along with ceramic whiskers and remain pourable even with high solids. Using this dispersion, a high solids ceramic article can be molded, polymerized in situ and fired with a good binder burnout.

Forming whisker reinforced sintered ceramics with polymerizable binder

Whisker reinforced composites having improved strength and toughness are prepared by a process including densification by essentially pressureless sintering. There is no need to hot press or hot isostatic press to achieve a density of 99+% of theoretical for 10 vol. % whiskers and 93+% for 20 vol. % whiskers. The composites are derived from the desired volume fraction of whiskers, a sintering aid preferably submicron in average size range, and a major portion of a pressureless sinterable matrix material having an average particle size of not more than about 0.5 micron. Yttria-alumina composites are sintered at less than about 1800.degree. C. and for less than about two hours to avoid surface degradation.

Method for preparing dense, pressureless sintered SiC whisker reinforced

Slurries or suspensions for forming sintered ceramic or metallic articles are described as having a high volume fraction of sinterable particles, at least 55% by volume. while the slurries maintain a pourable viscosity, such as not more that 2000 cPs at 100 s.sup.-1 ; the slurries can be dilatant and/or pseudoplastic. The slurries are prepared by using specific families of dispersants; namely acrylic acid-based polymeric polyelectrolytes, polyethylene imine-based polyelectrolytes, and coupling agents from the subfamilies of oxy-silane esters and phosphate esters. Fabrication of the compositions includes milling under high energy and the addition of at least a portion of the particles in a step-wise manner.

Highly loaded, pourable suspensions of particulate materials

A highly loaded, uniform ceramic composite can be made by first preparing a highly loaded suspension. Due to the particle-particle interactions of a highly concentrated system, virtually any dopant can be added, including other suspensions, fibers, and whiskers. The process is particularly useful for making composites of materials which coagulate when mixed at low concentration.

Liquification of highly loaded composite systems

Slurry for centrifugal classification of colloidal particles

Suspensions of ceramic or metallic colloidal particles having a high volume fraction (greater than about 55 vol. %) solid particles are provided in a pourable form. The pourable suspension includes at least about 55 vol. % ceramic or metallic colloidal particles, an aqueous vehicle, and an acrylic acid-based polymeric polyelectrolytic dispersant. Such suspensions can be prepared by mixing the colloidal particles in a staged order of addition and under a high shear rate with the other components. The suspensions are suitable for making ceramic or metallic articles, and can exhibit a low viscosity.

Liquefaction of highly loaded particulate suspensions

Commercial wide size distribution powders are size classified into precise size fractions by means of a controlled, semi-continuous, multi-stage centrifugal classification system. The system has utility for a wide range of colloidal materials. The throughput of the semi-continuous process is higher than that of batch processes, and the semi-continuous process produces narrow size ranges and optimum yields.

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Lexington, MA, United States of America

Bruce E Novich