Novel aqueous inorganic particle slurries, wherein some of the particles have had their charge potential altered to a sufficient extent to prevent segregation or settling of the particles, are described, along with a method for their preparation. The method of forming slurries of negatively charged particles comprises treating some of the particles with a cationic agent to reduce their charge and mixing these treated particles with the remainder of the particles to form a thick, cream-like flowable composition of a thixotropic nature. When slurries of positively charged particles are to be formed, an anionic agent is used instead of a cationic agent.
A method of preparing dense ceramic product is described, wherein a coagulated network of ceramic powder particles in water is formed and then treated to increase the volume fraction of particles, thereby forming a water-saturated powder compact. The compact is formed into a desired shape and fired to provide the dense ceramic product. A coagulated network may advantageously be formed by mixing a ceramic powder with water at a pH that produces a net surface charge, to form a dispersed slurry and adding a sufficient amount of salt to the dispersed slurry to cause particles within the slurry to form the coagulated network. In view of the unique rheological properties of the powder compacts prepared from coagulated networks of ceramic powder particles, the compact may be processed into complex, near-net-shaped forms by introducing the compact into a mold and subjecting the mold to vibration, whereby the compact adopts the shape of the mold; once removed from the mold, the compact retains its shape without distortion.
Process for the production of refractory shapes of ceramic fiber-containing mateial, wherein a slurry of refractory fibers and particulate refractory materials is produced in water, the particulate refractory materials are flocculated on the fibers by use of a flocculant, and the desired shape is produced by dewatering the slurry in a suitable mold that enables the water to be removed, and the shape is dried. At least 90% of the fibers have a maximum length of not more than 500 .mu.m; flocculant is added as an aqueous solution to the dispersion of the fibers and particulate refractory material; and pressure is applied to the shape being formed during the dewatering of the slurry to form the desired shape in order to compress the shape.
Method for the production of light-weight molded articles wherein, in a first embodiment, a dispersion of ceramic fibers is flocculated with a cationic flocculating agent, a dispersion of finely divided refractory material and inorganic bonding agent is flocculated with an anionic flocculating agent, the flocculated dispersions are mixed together, and following settling of the mixture and optional removal of excess liquid, the mixture is filled into molds, converted by dewatering into molded articles, and dried. According to a second embodiment, a dispersion of ceramic fibers is flocculated with a cationic flocculating agent, finely divided refractory material and inorganic bonding agent which may be stirred in with water are added to this flocculated dispersion, an aqueous solution of an anionic flocculating agent is mixed into this mixture, and following settling of the mixture and optional removal of excess liquid, the mixture is filled into molds, converted by dewatering into molded articles, and dried.
A method for preparing a suspension for coating a substrate with particles which includes determining a pH range in which the heterostability ratio of the substrate and the particles: ##EQU1## is less than 10.sup.10, the homostability ratio of the substrate: ##EQU2## is greater than 10.sup.10, and the homostability ratio of the particles: ##EQU3## is greater than 10.sup.10, wherein a.sub.1 is the radius of the substrate, a.sub.2 is the radius of the particles, V.sub.T is the total potential energy of the interaction between component i and component j, wherein i and j are the consecutive subscripts of the stability ratio being considered, T is temperature, k is Boltzmann's constant, and r is distance which varies from (a.sub.i +a.sub.j) to infinity. The suspension is useful for coating the substrate with the suspended particles by exposing the substrate to the suspension.
There is disclosed a process for treating a clay mineral thereby to change its rheological properties when in aqueous suspension such that the fluidity of the aqueous suspension at a given temperature and percentage by weight of completely deflocculated clay mineral solids in the suspension is increased, which process comprises the steps of mixing with the clay mineral in a plastic state a minor proportion by weight of a water-soluble organic compound having a plurality of basic groups and a number average molecular weight not greater than 1000, and subsequently or simultaneously subjecting the mixture to mechanical working under conditions such that from 25 to 1000 KJ of energy per Kg of dry clay mineral are dissipated in the mixture.
