Abstract: An ultra-high-tenacity multifilament fiber of polyvinyl alcohol having a degree of polymerization of at least 1500, said filament having a tensile strength of at least 12 g/d and an initial modulus greater than 280 g/d, which is produced by a process for producing an ultra-high-tenacity polyvinyl alcohol fiber which comprises the steps of dissolving polyvinyl alcohol having a degree of polymerization of at least 1500 in a solvent, dry-spinning the resulting polymer solution through a spinneret into an environment of air or inert gas, introducing the dry-spun filaments into a coagulating bath, and drawing the coagulated filaments at a total effective draw ratio of at least 20 times.

Abstract: In order to produce mineralic bodies of high porosity, usable inter alia as adsorbers, purifiers and catalyst carriers, a predominantly mineralic mass with organic admixtures--both preferably obtained from industrial waste products--are subjected to a three-phase treatment. In a first phase, the mass is heated in an inert or reducing atmosphere to a sintering temperature between about 1000.degree. C. and 1350.degree. C. whereby the organic constituents are carbonized and partly penetrate the consolidating mineralic structure. In a second phase, still under the same nonoxidizing atmosphere and at the sintering temperature referred to, the mineralic structure is sintered into a coherent matrix. In a third phase, with reduction of the temperature to a lower level between about 600.degree. and 1000.degree. C. and exposure to the atmosphere, the carbonaceous substances occluded in the mineralic skeleton are burned off to increase its porosity.

Abstract: A molten resin to be injected into a mold cavity in use of an injection molding machine has a temperature, i.e. viscosity difference between at the injection starting point and the injection completing point. In order to eliminate or make small this difference, a high temperature and highly pressurized gas, preferably an inert gas, is preliminarily supplied to and sealed in the mold cavity and the pressure of the supplied gas is continuously controlled in accordance with the position of the screw during the injection molding operation thereby to maintain the temperature of the supplied gas in the mold cavity to be higher than the softening temperature of the molten resin to be injected.

Abstract: High density composites consisting of graphite and metal borides by pressing blended powders of pitch-free coke and boride powder. The pressing may be hot pressing at temperatures of about 2200.degree. C. and pressure of about 1500 psi or cold pressing at about room temperature followed by high temperature sintering. Some of the boron from the boride diffuses substitutionally into the structure at the processing temperatures promoting graphitization; whereby densification and bonding the resulting degree of graphitization of the shapes is comparable to that of conventional graphite articles processed at temperatures in excess of 2800.degree. C. The mechanical strength of these composites is equivalent to and often exceeds the strength of conventional graphites and the oxidation resistance in dry air is much superior at temperatures as high as 800.degree. C. Overall processing time is reduced from months to days thus improving the economics of the process.

Abstract: In a melt spinning operation, a heated wash gas such as nitrogen or nitrogen and air is blown across the melt spinning nozzles to remove volatiles thereby preventing wetting of the nozzle discharge. The wash gas is maintained at a temperature substantially equal to the melt spinning temperature. The preferred melt spinning material is petroleum pitch.

Abstract: Juxtaposed nozzle openings apply the same or different melts to the surface of a moving cooler surface for producing thin metal strips or foils with a considerable width. The nozzle openings can be staggered in the direction of movement of the cooler surface and apply different materials to produce a metal strip with juxtaposed and sharply defined regions with different characteristics. Amorphous or mixed amorphous/-crystalline, or solely crystalline material structures can also be produced. Alternatively, different cooling capacities on different cooler surface areas and different structuring of different cooler surface areas permit the melt to solidify on the cooler surface such that the strips or foils obtained have adjacent regions with different metallic and/or geometrical structures. By geometrical configuration of the cooler surface, foils with a structured surface or with shape-limited individual regions can be used for mass production of small parts from sheet or strip material.

Abstract: A process for the production of a multi-layer pipe to be used for formation of a bottle by drawblow-forming, comprising forming by co-extrusion a pipe having inner and outer layers of a polyester composed mainly of ethylene terephthalate units and an intermediate layer of an oxygen-barrier resin interposed between the inner and outer layers. An adhesive resin layer is preferable interposed between every two adjacent layers. The co-extruded multi-layer pipe is sized in the molten state so that the diameter of the pipe is uniform. The process continues by cooling the outer portion of the molten multi-layer pipe by contact with water and simultaneously introducing an inert gas or an inert gas containing a water mist into the interior of the pipe to thereby cool the inner portion of the pipe and prevent oxidation in the pipe. A multi-layer pipe prepared according to this process is excellent in the transparency and the draw-formability into a multi-layer drawn bottle.

Abstract: Dry polycaprolactam granules containing from 8 to 13% by weight of caprolactam and its oligomers are prepared by a method in which a caprolactam melt is extruded, the extrudates are cooled to 100.degree.-150.degree. C., left at this temperature until the polycaprolactam has substantially crystallized, and then immediately granulated, and the granules are left in a stream of inert gas, in the absence of molecular oxygen, for from 1 to 4 hours at from 100.degree. to 150.degree. C., and are then cooled.

Abstract: The lens is molded in a rotating concave lens mold. Liquid lens monomer is placed in the concave mold and a controlled stream of gas from a narrow opening extending across the lens and positioned over the lens center shapes the concave surface to a toric. The lens mold and the gas nozzle rotate in synchronization until the lens monomer is polymerized.

Abstract: A nonflammable layer is made by drying an aqueous alkali metal silicate composition on a substrate in the presence of a drying atmosphere containing at least 30% free oxygen by volume so that the resulting layer remains bubble-free on aging even under intense ultraviolet radiation.

Abstract: The invention pertains to a method for casting polymeric gels from volatile mixtures of monomers in open molds and to apparatus for performing this method.The principle of the invention resides in the fact that the same concentrations of volatile components present in the polymerization mixture are also present in the gaseous state within a protective gas maintained above the free surface of the polymerization mixture, said gaseous volatile components being in the equilibrium state with those in the polymerization mixture at polymerization temperature.The apparatus for performing said method comprises a main pipe branch which introduces a pure protective gas into a polymerization apparatus and at least one auxiliary pipe branch for saturating the protective gas with a volatile component.

Abstract: A tire manufacturing process of the type which employs a reusable rubber or the like curing bag or bladder. The process includes deflating, between curing cycles of the tire manufacturing process, the curing bag or bladder; preventing oxygen bearing medium entering the curing bag or bladder; and supplying a non-reactive medium upstream of the curing bag or bladder to maintain the bag or bladder in its unstretched state until the bag or bladder is next inflated.

Abstract: The invention relates to a method for the manufacture of implantable electrodes of vitreous carbon with an electrode head and an electrode stem, by pyrolysis of cross-linked synthetic resins. Electrodes manufactured in accordance with such a method exhibit high surface quality. In accordance with embodiments of the disclosure, the electrode stem is manufactured in the form of a blank by hardening a resin precondensate, then the electrode head is cast onto the blank in a casting mold, using a resin precondensate, and is cross-linked. Subsequently hardening takes place and then the synthetic resin is converted into vitreous carbon by pyrolysis, and the electrode obtained in this manner may, if desired, be activated to provide the electrode with a microporous surface structure.

Abstract: Shaped articles are prepared from rigid rod heterocyclic liquid crystalline polymers. The articles are prepared by polymerizing the polymer in a reaction medium whereby a solution of the polymer is formed and by forming the articles directly from the polymer solution.

Abstract: A method for spinning filament yarns of high strength, high modulus carbon fibers is provided by way of a melt-spinning process in which a heated inert gas or a non-oxidative gas such as hydrocarbons of small C-numbers is injected steadily onto the surfaces of spinning nozzles to stabilize and ease the melt-spinning.

Abstract: Polyolefin fibers, which are suited for at least partially substituting the cellulose fibers in the manufacture of paper, are produced by a process which consists in preparing in a pressure vessel a solution of a polyolefin at a temperature higher than the boiling temperature of the solvent under normal conditions, and under autogenous pressure or a pressure greater than the autogenous pressure, in ejecting said solution under the above stated conditions into a zone of lower pressure, in allowing the ejected solution to expand at least partially in said zone, and in then hitting the at least partially expanded solution with a jet of a high-speed fluid, which is at a temperature lower than that of the solution, and has an angled direction with respect to the direction of ejection of the solution.

Abstract: In order to prepare thermoplastic polyurethane elastomers(a) organic diisocyanate,(b) polyhydroxyl compounds with molecular weights of 500 to 8,000, and(c) chain extenders with molecular weights of 60 to 400 in the presence of(d) catalysts, and optionally(e) auxiliaries, and/or(f) additivesare reacted in two reaction stages at temperatures from 60.degree. C. to 250.degree. C. In the first reaction stage the components are continuously mixed, the reaction mixture is applied to a carrier, preferably a conveyor band of thermoplastic material, and is allowed to react at the reaction temperature until solidified. Subsequently, the solidified reaction mixture is melted in an extruder and the reaction is completed in the second reaction stage.

Abstract: The present invention relates to a method for producing a thermoplastic polymeric sheet, wherein a molten thermoplastic polymer is extruded from an extrusion die in the form of a sheet onto a moving quenching member, with an electric potential difference being established between the surface of the moving quenching member and the extrusion die, whereby the polymer is caused to electrostatically solidify and adhered to the surface of the quenching member. The contact area of the polymeric sheet with the moving quenching member is held in an atmosphere of a gas which posesses better insulating properties than standard air. Thus the present invention provides a useful method that can produce, at higher speeds than conventional method, polymer sheets of high surface quality which avoid the operational problems encountered in the conventional methods.

Abstract: A hot isostatic pressing system including a hot isostatic pressing station having a high pressure container constituted by a vertical pressure-resistant cylinder closed at the top end thereof and a lower lid detachably fitted to the bottom of the pressure resistant cylinder and a treating chamber internally provided with a heater and enclosed by a heat insulating wall, and a mechanism for adjusting an atmospheric gas pressure and temperature of the pressing station into a condition suitable for the hot isostatic pressing of a work item accommodated in the treating chamber; a plurality of auxiliary stations each provided with an opening for receiving from beneath thereof the heat insulating wall of the treating chamber accommodating the internal heater and a work item, a support structure for supporting the heat insulating wall, and a mechanism for cooling the work item and internal heater in an inert gas atmosphere; a carriage for transferring the lower lid and work item or the lower lid, work item, heat insu

Abstract: Melt extruded poly(6-oxy-2-naphthoate-4-oxybenzoate) shaped articles of relatively high strength and modulus are produced in a lesser period of time than commonly heretofore required in the prior art. The required polymer is capable of exhibiting an anisotropic melt phase and is formed through the reaction of 6-acetoxy-2-naphthoic acid and 4-acetoxybenzoic acid under a combination of melt polymerization conditions which surprisingly has been found to yield a shaped article following melt extrusion which may be heat strengthened in an unusually brief period of time (i.e. two hours or less). The polymerization is catalyzed by a potassium salt (e.g. potassium acetate), and the polymerization conditions require a relatively highly elevated final polymerization temperature. Substantially all of the acetic acid by-product is removed from the polymerization zone prior to concluding the polymerization under reduced pressure conditions.

Abstract: Sintering and gas hot isostatic pressing are used to prepare polycrystalline yttria-gadolinia ceramic scintillator bodies. Multicomponent powder compacts, formed by cold pressing and cold isostatic pressing, are sintered to the closed porosity stage. The density of the sintered compacts is then increased by gas hot isostatic pressing. The finished scintillator includes Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, and one or more of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Pr.sub.2 O.sub.3, and Tb.sub.2 O.sub.3 rare-earth activator oxides. At least one of the oxides of elements Zr, Th, and Ta is included as a transparency promoting densifying agent. At least one of CaO and SrO may be included as a light output restorer.

Abstract: A process for enhancing the adhesion of the surface of a polyolefin shaped product which comprises applying corona discharge the said surface under the continuous movement between an electrode for discharge and another electrode opposite thereto while jetting a gaseous material other than the air itself onto the part of the said surface to which corona discharge is applied so as to achieve the following relationships among the carbon atoms, the nitrogen atoms and the oxygen atoms present within 100 .ANG. from the said surface:(a) -3.5.ltoreq.([O]/[C]-[O']/[C'])/([N]/[C]-[N']/[C']).ltoreq.1.8(b) 3.0.ltoreq.[N']/[C']wherein [C], [N] and [O] are respectively the numbers of the carbon atoms, the nitrogen atoms and the oxygen atoms within 100 .ANG. from the said surface before the application and [C'], [N'] and [O'] are respectively the numbers of the carbon atoms, the nitrogen atoms and the oxygen atoms within 100 .ANG.

Abstract: The properties of shaped articles of poly {[benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl]-1,4-phenylene}, its cis isomer and mixtures thereof are improved by a process of heat treatment under tension. The articles may be prepared from a dope obtained by dissolving the formed polymer in an appropriate solvent or by forming the polymer under conditions which enable the article to be prepared directly from the reaction medium.

Abstract: A process and apparatus as provided for substantially eliminating surface melt fracture during extrusion of a thermoplastic polymer such as a molten narrow molecular weight distribution, linear, ethylene copolymer, by using a die having a die land region defining opposing surfaces at least one of which is fabricated from an alloy containing 5 to 95 parts by weight zinc and 95 to 5 parts by weight of copper.

Abstract: Melt fracture of films made from LLDPE resins is reduced by using a die having a die land region fabricated from stainless steel and wherein the length of the die land to the width of the die gap is about 35:1 to about 60:1.

Abstract: A process for producing a blow molding resin comprises pelletizing a high density polyethylene prepared by means of a highly active Ziegler catalyst, at a temperature of at least 230.degree. C. in the presence of air or oxygen so as not to change the average molecular weight and the molecular weight distribution.

Abstract: Sintering and gas hot isostatic pressing are used to prepare polycrystalline yttria-gadolinia ceramic scintillator bodies. Multi-component powder compacts, formed by cold pressing cold isostatic pressing, are sintered to the closed porosity stage. The density of the sintered compacts is then increased by gas hot isostatic pressing. The finished scintillator includes Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, and one or more of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Pr.sub.2 O.sub.3, and Tb.sub.2 O.sub.3 rare earth activator oxides. The finished scintillator may also include at least one of SrO and CaO as afterglow reducers.

Abstract: A rotational moldable polyamide composition, a method of preparing the composition, and a method of rotational molding. The composition contains from about 0.001 percent to about 0.5 percent by weight of a copper compound, preferably cuprous iodide. Preferably, the composition contains from about 0.001 percent to about 0.3 percent by weight of potassium iodide.

Abstract: A film of poly{[benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl]-1,4-phenylene}, its cis isomer or mixtures thereof is formed by extruding a solution of the polymer on a casting roll which is rotating to yield a surface speed slightly greater than the rate of extrusion. The solution of the polymer may be prepared by dissolving the polymer in an appropriate solvent or by reacting the monomers in a selected reaction medium. The cast film is washed, subjected to an elevated temperature, preferably heat treated under tension, and recovered.

Abstract: An improved gas feed means adapted to accommodate and secure the lower end of a polymerization column for synchronous rotation therewith and adapted to supply a controlled amount of a gaseous medium, such as nitrogen, into and through the rotating polymerization column so as to purge any undesirable gas within the polymerization column that could adversely affect the quality of the objects being centrifugally casted.

Abstract: The invention relates to dense shaped articles of polycrystalline .alpha.-silicon carbide containing from 0.1 to 0.4%, by weight, of aluminum and optionally, a small amount of nitrogen and/or phosphorus, having a homogeneous virtually single-phase microstructure. The additional constituents are substantially in the form of a solid solution in the .alpha.-SiC lattice. The shaped articles are distinguished by flexural strength of at least 600 N/mm.sup.2 up to 1450.degree. C. and low subcritical crack propagation under mechanical stress. The fracture mechanism is trans granular up to at least 1450.degree. C. The shaped articles are manufactured by simultaneously shaping and hot pressing pulverulent .alpha.-silicon carbide containing a small amount of an aluminum-containing additive, such as aluminum powder, aluminum nitride and/or aluminum phosphide, at temperatures between 1850.degree. C. and 2300.degree. C. under a pressure of at least 100 bar (10 MPa).

Abstract: In order to manufacture molded bodies by pressing finely divided material with a binder while the binder sets, such as to avoid problems caused because of contact of the binder or vapors therefrom with oxygen, the pressing and setting is carried out in a gas atmosphere different from air.

Abstract: The lens is molded in a concave lens mold, the liquid lens monomer is placed in the concave mold and a controlled stream of gas is directed at the center of the liquid surface and shapes the concave lens surface upon polymerization of the monomer.

Abstract: A process of making a hollow article from polymeric material is taught. The article is molded in two parts. The two parts are caused to remain in their respective exterior molds. If the hollow article is to be filled with a desired material, a measured amount of filler material is added to one of the formed parts. The exterior molds are brought into opposed position and sealing relationship. The space between the exterior molds is purged with a purging gas and subjected to a partial vacuum. The exterior molds are then closed and subjected to a clamping pressure to join the part halves together and remove flash from the joint. Portions at least of the exterior molds are heated and then cooled. The exterior molds are then opened, and the finished filled article is removed therefrom.

Abstract: A method of moulding a shaped article from a curable composition in which the composition is cured in a mould comprising at least two mould parts defining a cavity characterized in that prior to introducing the curable composition into the mould cavity, the pressure inside the cavity is increased above atmospheric pressure, preferably to at least 0.3 bar above atmospheric pressure, the dispersion is injected into the mould against this pressure and is subsequently cured. The method is useful for overcoming problems of color banding on the surface of the moulding which originate in the filling process and are particularly evident when high mould temperatures are used.

Abstract: A method and apparatus for the continuous melting of silicon for use in semiconductor devices, the method tending to reduce the time and expense associated with conventional melting and forming. The method for melting silicon comprises charging silicon into a melting vessel having a drain therein, heating the silicon in the vessel to a temperature above the melting point of silicon, and allowing the molten silicon to pass through the drain out of the vessel.

Abstract: A hose construction and method of making same are provided wherein such hose construction comprises a polyolefin tube which has a tubular fluorocarbon barrier layer defining the inner portion of the tube and such barrier layer renders the tube substantially impermeable to the passage of nonpolar hydrocarbons present in the fluid being conveyed through the hose.

Abstract: An improved modified silicon aluminum oxynitride based composite cutting tool is made by forming a homogeneous matrix of a modified silicon aluminum oxynitride prior to uniformly dispersing a hard refractory material throughout the homogeneous matrix, then densifying the combined materials to form a composite cutting tool having a density greater than 98 percent of the theoretical density of the combined materials.

Abstract: A method for restoration and re-utilization of discharged gas for use in a vulcanization employing inert gas in part of the vulcanization of elastomer products, which includes the steps of restoring a mixture of used inert gas discharged from a vulcanizing unit and vulcanizing medium for steam separation thereof, subjecting the elastomer product mounted in a metal mold to a preshaping by supplying the inert gas obtained by the steam separation to the vulcanizing unit prior to starting of the vulcanization, and subjecting the inert gas obtained by the steam separation to supplementary pressurization by inert gas obtained from an inert gas generating unit when the inert gas is to be supplied to the vulcanizing unit, and also an arrangement for carrying out the above method in an efficient manner.

Abstract: Iron-containing refractory balls, in a retorting process for oil shale, permit effective magnetic separation of the balls from the spent shale. These ceramic balls can be made by a process such as admixing powdered alumina and water to form an extrudable mixture, extruding to form cylinders, reshaping cylinders into balls, overcoating with iron particles, further overcoating with alumina, and firing.

Abstract: Iron-containing refractory balls, in a retorting process for oil shale, permit effective magnetic separation of the balls from the spent shale. These ceramic balls can be made by a process such as admixing powdered alumina and water to form an extrudable mixture, extruding to form cylinders, reshaping cylinders into balls, overcoating with iron particles, further overcoating with alumina, and firing.

Abstract: A cable for cryogenic use includes an inner conductor and a solid polymeric insulator loosely positioned about said inner conductor above 0.degree. C. A collapsible spacer can be positioned between the inner conductor and the polymeric insulator to further space the insulator away from the conductor and thereby accommodate greater shrinkage of the insulator. In fabricating the cable, the cable is sealed and pressure is applied to the cable to expand the insulation. The cable is placed inside a rigid cylinder having an inside diameter larger than the outside diameter of the cable. The cylinder is heated to facilitate expansion of the insulation, and the cylinder is subsequently cooled while maintaining pressure to the cable.

Abstract: An improved electrolytic cell is provided for production of a metal such as aluminum by electrolysis of a compound of the metal in a solvent or bath such as molten salt. Electrolysis is carried out by passing a current from an anode to a cathode between which the solvent bath is situated. The cathode comprises a base cathode and cathode extension surfaces comprising graphite and at least 90% refractory hard metal such as titanium diboride. The cathode extension surfaces are produced from a mixture comprising at least 90% refractory hard metal and a carbonaceous binder with little or substantially no particulate carbonaceous material and graphitizing said mixture above 2350.degree. C. to graphitize the carbonaceous material therein to exhibit the graphitic structure.

Abstract: An improved process for vulcanization of elastomer products which includes the steps of heating under pressure, the elastomer product mounted in a metal mold by supplying vulcanizing medium, suspending the supply of the vulcanizing medium when the elastomer product has reached a predetermined temperature or passed through a predetermined time period, and subsequently supplying insert gas preliminarily extracted from atmospheric air and maintained at least under approximately the same pressure as that of the vulcanizing medium, up to the termination of the heating step so as to maintain the elastomer product at the predetermined temperature.

Abstract: Dense silicon nitride bodies are fabricated using conventional hot-pressing techniques using cerium oxide as a densification aid. The bodies are then further treated in a flowing inert atmosphere at a temperature of from 1400.degree.-1600.degree. C. for from several hours to 48 hours to remove all or substantially all of the densification aid from grain boundaries. Silicon nitride bodies so treated exhibit superior elevated temperature slow crack growth resistance and strength properties and are suitable for use as structural components in high temperature environments such as jet and internal combustion engines, rockets, atomic power generation, and the like.

Abstract: Iron-containing refractory balls, in a retorting process for oil shale, permit effective magnetic separation of the balls from the spent shale. These ceramic balls can be made by a process such as admixing powdered alumina and water to form an extrudable mixture, extruding to form cylinders, reshaping cylinders into balls, overcoating with iron particles, further overcoating with alumina, and firing.

Abstract: An improved process for vulcanization of elastomer products which includes the steps of heating under pressure, the elastomer product mounted in a metal mold by supplying vulcanizing medium, suspending the supply of the vulcanizing medium when the elastomer product has reached a predetermined temperature or passed through a predetermined time period, subsequently supplying inert gas preliminarily extracted from atmospheric air and maintained at least under approximately the same pressure as that of the vulcanizing medium, up to the termination of the heating step so as to maintain the elastomer product at the predetermined temperature, and, upon termination of said heating step, restoring a mixture of the inert gas and the vulcanizing medium so as to derive the inert gas through steam separation for re-utilization of the inert gas for a preshaping of the elastomer product prior to the vulcanization of the elastomer product and the like.

Abstract: A method for manufacturing a thin and flexible ribbon wafer of semiconductor material such as germanium, silicon, selenium, tellurium, PbS, InSb, ZnTe, PbSe, InAs, InP, GaSb, PbTe, ZnS, Bi.sub.2 Te.sub.3, and mixtures thereof comprises melting the semiconductor material at a temperature within the range from a melting point thereof to 300.degree. C. above the melting point to form a uniform melt; ejecting under a pressure the melt through a nozzle against a cooling surface of a moving substrate to cool very rapidly a jet flow of the melt at a cooling rate of 1,000.degree. C. to 1,000,000.degree. C./sec to form the ribbon type thin and flexible wafer of fine and compact microscopic structure having a large mechanical strength and an excellent electrical property. It is possible to add to the melt various additives as fluxes or impurities such as B, P, BP, Sb Sn, As, B, P, Sb, In, Al and alloys intermetallic compounds, and conjugates thereof.

Abstract: An apparatus and process is provided for electromagnetically casting molten material into a desired shape. A containment zone is established. The containment zone has a first section for electromagnetically containing the molten material and a second section downstream and communicating with the first section for forming the molten material into the desired shape. The improvement comprises a heat extraction device for directing a cooling medium into the containment zone whereby the cooling medium passes the molten material in the second section to rapidly solidify the molten material prior to passing the molten material in the first section to lower the temperature in the contained molten material to minimize superheating. A second embodiment of the invention includes a secondary cooling device associated with the heat extraction device for directing a cooling medium against the solidified material.

Abstract: A method of densifying an article formed of reaction bonded silicon nitride is disclosed. The reaction bonded silicon nitride article is packed in a packing mixture consisting of silicon nitride powder and a densification aid. The reaction bonded silicon nitride article and packing powder are sujected to a positive, low pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause any open porosity originally found in the reaction bonded silicon nitride article to be substantially closed. Thereafter, the reaction bonded silicon nitride article and packing powder are subjected to a positive high pressure nitrogen gas treatment while being heated to a treatment temperature and for a treatment time to cause a sintering of the reaction bonded silicon nitride article whereby the strength of the reaction bonded silicon nitride article is increased.