Abstract: The present invention relates to methods of producing synthetic crystals (typically minerals) or comparable inorganic compounds by reactions of metal salts and metal oxyhydroxides under near-critical, critical or supercritical solvent conditions, avoiding thereby many of the difficulties associated with conventional solid state or wet chemistry synthesis. The metal oxyhydroxides are typically divalent or trivalent metals and the preferred solvent is typically (but not exclusively) water under near-critical, critical or supercritical conditions. The crystals so produced have a controlled particle size distribution. The crystals produced by the present invention also have morphologies with favorable properties for compaction into green bodies for subsequent sintering into near-net-shapes, approaching maximum theoretical densities. Avoidance of noxious by-products is another advantage of the present synthetic methods.

Abstract: The present invention relates to the separation and recycling of polymer materials containing inorganic additives by means of processing with a solvent under near-critical, critical or supercritical solvent conditions, achieving thereby a segregation of such inorganic additives from the polymeric material. In particular, the yellow colorant cadmium sulfide (CdS) is separated from polyethylene using a water solvent in the critical domain.

Abstract: A reaction product is formed and transferred from an autoclave to a receiving vessel at a laminar flow rate, using a self-adjusting transfer mechanism. A specific amount of water in the receiving vessel is heated and vaporized prior to the reaction product transfer to raise the pressure in the receiving vessel to saturation pressure. A flow passage between the autoclave and the receiving vessel is now opened, and a resulting pressure differential between the autoclave and the receiving vessel initiates the transfer process. A heat exchanger cools the reaction product flowing from the autoclave to the receiving vessel, where the amount of cooling is dependent upon the transfer rate of the reaction product. An increased transfer rate will cause the hotter reaction product entering the receiving vessel to increase the pressure inside the receiving vessel, thereby reducing, or self-adjusting, the transfer rate.

Abstract: A reaction product is formed by a process which involves the transfer of the reaction product from the autoclave to a receiving vessel at a substantially constant flow rate. Just prior to this transfer, the pressure in the receiving vessel is brought up to the pressure in the autoclave by passing gas from the autoclave to the receiving vessel. The flow of gas from the autoclave to the receiving vessel is then stopped, and the pressure in the receiving vessel is allowed to drop due to transfer of heat from the gas to the walls of the receiving vessel. The resulting pressure difference between the autoclave and the receiving vessel is used to initiate the transfer of the reaction products from the autoclave to the receiving vessel. A pressure release valve on the receiving vessel is then controlled by means a signal derived from a flow meter which measures the flow rate of the reaction products flowing from the autoclave to the receiving vessel to maintain constant this flow rate.

Abstract: Composite powders for spinels, MgO.nAl.sub.2 O.sub.3 (n=1 and 2), are synthesized hydrothermally using commercially available hydroxide reactants. The synthesis is carried out in an aqueous suspension within an autoclave under a pressure of 4 Mega-Pascals (MPa) and at a corresponding saturated steam temperature of 523.degree. K. Powder characterization has shown that the particle size ranges from 2 to 10 .mu.m. Sintering of preformed green bodies comprising compressed powder, without the use of additives, is then carried out at 1873.degree. K. in one atmosphere, resulting in a spinel having a density 94% of theorietical. Structure and microstructure have been studied by X-ray diffraction and scanning electron microscopy, and compressive strength of the resulting spinels has been determined.

Abstract: A reaction product is formed by a process which involves the transfer of the reaction product from an autoclave to a receiving vessel at a substantially constant flow rate. Just prior to this transfer, the pressure in the receiving vessel is brought up to the pressure in the autoclave by passing gas from the autoclave to the receiving vessel. The flow of gas from the autoclave to the receiving vessel is then stopped, and the pressure in the receiving vessel is allowed to drop due to transfer of heat from the gas to the walls of the receiving vessel. The resulting pressure difference between the autoclave and the receiving vessel is used to initiate the transfer of the reaction products from the autoclave to the receiving vessel. A pressure release valve on the receiving vessel is then controlled by means a signal derived from a flow meter which measures the flow rate of the reaction products flowing from the autoclave to the receiving vessel to maintain constant this flow rate.

Abstract: Calcium silicate is formed by a process wherein the viscosity of the calcium silicate produced in an autoclave is lowered by adding an acetate to the reaction constituents prior to the reaction of these constituents to form the calcium silicate crystals. In one embodiment, manganese acetate is added to comprise between approximately 1% and 3% by weight of the solids contents of the reaction constituents. The result is to lower the viscosity of the reaction product and thus to allow a higher solids content in the autoclave than heretofore commonly used. In one embodiment, water is added in-line to the reaction products as they are transferred from the autoclave to a holding vessel or from a holding vessel to a storage tank. In a further embodiment, fibrous material is added to the holding vessel prior to the transfer of the reaction product into the holding vessel, thus to reduce the amount of energy required to bring the pressure in the holding vessel up to a selected pressure beneath that of the autoclave.

Abstract: A system for forming a reaction product such as calcium silicate comprises an autoclave for receiving the reaction constituents and for reacting these constituents to form a reaction product, a holding vessel for receiving the reaction product and a flow passage connecting the autoclave to the holding vessel and for allowing the passage of the reaction product from the autoclave to the holding vessel. The flow passage includes a heat exchanger for transferring heat from the reaction product during its passage through the flow passage to another medium. The system includes an electronic control system for maintaining the pressure in the holding vessel a controlled amount beneath the pressure in the autoclave during the transfer of the reaction product from the autoclave to the holding vessel. This minimizes the structural damage to the reaction product during its transfer to the holding vessel. The holding vessel can, if desired, be used to mix additional material into the reaction product.

Abstract: The annular space between inner and outer coaxially-mounted pipes is sealed by a bellows diaphragm with a cylindrical surface corrugated in the longitudinal direction formed in and at one end of said annular space, wherein one end of said bellows is circumferentially attached to a circumferential portion of the outer surface of the inner pipe and the other end of said bellows is circumferentially attached to a circumferential portion of the inner surface of said outer pipe. The other end of said annular space is sealed by a ring attached to a circumferential portion of the outer surface of the inner pipe and to a circumferential portion of the inner surface of the outer pipe. In one version of the invention this ring includes a pressure release valve to allow any high pressure fluids in the annular space to escape.

Abstract: Calcium silicate insulation is formed by a process which involves the transfer of the calcium silicate crystals from an autoclave to a holding vessel at a flow rate selected to minimize or prevent damage to the reaction product and through a flow passage such that heat can be removed from the reaction product to stabilize the reaction product prior to its arrival at the holding tank. The calcium silicate material produced by this process is particularly suitable for use as high temperature insulation and has a porosity of in excess of 84% and a permeability to gas of about 0.01% or less. The thermal conductivity of the reaction product is substantially lower than prior art calcium silicate insulations at high temperature.