Dow Corning Corporation

Other

James A Rabe

Chi-long Lee

Jonathan Lipowitz

Therese M Bauman

Myron T Maxson

Duane R Bujalski

Paul P Lu

Richard E Jones

Gary E LeGrow

Eric Jude Joffre

Kimmai Thi Nguyen

Thomas Duncan Barnard

William H Atwell

David C DeLeeuw

Neal Roger Langley

David Charles Deleeuw

Chi-Tang Li

Patrick Weyburne

Chi-Long Lee

Sefa Yilmaz

Harvey A Freeman

A siloxane composition, comprising from 70 to 99 parts by weight of a solid particulate having a median particle size of from 0.1 to 3000 &#x3bc;m and from 1 to 30 parts by weight of a binder having a median particle size of from 5 to 250 &#x3bc;m, wherein the composition is a powder and the binder comprises a siloxane resin having the formula: (RSiO)(RSiO)(RSiO)(SiO), wherein each Ris independently selected from hydrogen, hydrocarbyl, substituted hydrocarbyl, &#x2014;O&#x2550;NRR, &#x2014;OR, &#x2014;O&#x2014;R&#x2014;OR, and an epoxy-substituted organic group, wherein Ris Cto Chydrocarbyl, Ris Ror &#x2014;H, Ris hydrocarbylene, w+x+y+z=1, y/(w+x+y+z) is at least 0.67, and the siloxane resin has a softening point of from 30 to 115&#xb0; C.; an agglomerate, and a method preparing the agglomerate.

Siloxane composition, agglomerate, and method of preparing

This invention pertains to a method for production of polycrystalline ceramic fibers from silicon oxycarbide (SiCO) ceramic fibers wherein the method comprises heating an amorphous ceramic fiber containing silicon and carbon in an inert environment comprising a boron oxide and carbon monoxide at a temperature sufficient to convert the amorphous ceramic fiber to a polycrystalline ceramic fiber. By having carbon monoxide present during the heating of the ceramic fiber, it is possible to achieve higher production rates on a continuous process.

Continuous method of producing silicon carbide fibers

A process for the preparation of substantially polycrystalline silicon carbide fibers is provided. The fibers may be fabricated to have a small diameter and are thermally stable at high temperatures. The process is carried out by initially forming fibers from a preceramic polymeric precursor comprising methylpolysilane resins. The fibers are then infusibilized to render them nonmelting followed by a pyrolysis step in which the fibers are heated to a temperature in excess of 1600.degree. C. in a nonoxidizing atmosphere to form substantially polycrystalline silicon carbide fibers. The substantially polycrystalline silicon carbide fibers which are formed by the process of the present invention have at least 75% crystallinity and have a density of at least about 2.9 gm/cm.sup.3. The polymeric precursor or the fibers contain, or have incorporated therein, at least about 0.2% by weight boron. This incorporation of boron may be accomplished either prior to or during formation of the fibers or during at least one of the infusibilizing or pyrolyzing steps of the process.

Preparation of substantially polycrystalline silicon carbide fibers from

This invention relates to the preparation of polycrystalline silicon carbide fibers from ceramic fiber. The process involves heating the ceramic fiber in an environment containing a volatile sintering aid to a temperature sufficient to convert the ceramic fiber to the polycrystalline silicon carbide fiber.

Polycrystalline silicon carbide fibers

Ceramic SiCO fibers are formed by spinning a mixture of a substantially linear polysiloxane fluid having unsaturated hydrocarbon substituents and a photoinitiator into a fiber, exposing the fiber to radiation, and heating the fiber in an inert environment to a temperature above about 800.degree. C.

Process for preparing ceramic fibers from polysiloxanes

This invention relates to the preparation of polycrystalline silicon carbide fibers from ceramic fibers. The process involves heating the ceramic fiber in an environment containing a volatile sintering aid to a temperature sufficient to convert the ceramic fiber to the polycrystalline silicon carbide fiber.

Preparation of polycrystalline ceramic fibers

A process for the preparation of substantially polycrystalline silicon carbide fibers is provided. The fibers may be fabricated to have a small diameter and are thermally stable at high temperatures. The process is carried out by initially forming fibers from a preceramic polymeric precursor comprising methylpolydisilylazane resins. The fibers are then infusibilized to render them nonmelting followed by a pyrolysis step in which the fibers are heated to a temperature in excess of 1600.degree. C. in a nonoxidizing atmosphere to form substantially polycrystalline silicon carbide fibers. The substantially polycrystalline silicon carbide fibers which are formed by the process of the present invention have at least 75% crystallinity and have a density of at least about 2.9 gm/cc. The polymeric precursor or the fibers contain, or have incorporated therein, at least about 0.2% by weight boron. This incorporation of boron may be accomplished either prior to or during formation of the fibers or during at least one of the infusibilizing or pyrolyzing steps of the process.

The present invention relates to ceramic fibers of the Si-C-N-O series with a diameter less than about 20 micrometers. It has been unexpectedly found that the thermal stability of these fibers can be increased by minimizing the impurity content, primarily the content of metals or metallic compounds. Such fibers with low levels of contaminants retain greater than about 60 percent of their initial tensile strength when subjected to temperatures of 1300.degree.-1400.degree. C. for at least 30 minutes in a non-oxidative environment.

Polymer derived ceramic fibers having improved thermal stability

A process for the preparation of substantially polycrystalline silicon carbide fibers are provided. The fibers may be fabricated to have a small diameter and are thermally stable at high temperature. The process is carried out by initially forming fibers from a preceramic polymeric precursor comprising phenyl-containing polyorganosiloxane resins. The fibers are then infusibilized to render them nonmelting followed by a pyrolysis step in which the fibers are heated to a temperature in excess of 1600.degree. C. in a nonoxidizing atmosphere to form substantially polycrystalline silicon carbide fibers. The substantially polycrystalline silicon carbide fibers which are formed have at least 75% crystallinity and have a density of at least about 2.9 gm/cm.sup.3. The polymeric precursor or the fibers contain, or have incorporated therein, at least about 0.2 % by weight boron. This incorporation of boron may be accomplished either prior to or during formation of the fibers or during at least one of the infusibilizing or pyrolyzing steps of the process.

The elastic modulus and density of an amorphous, ceramic article derived from a resinous organosilicon polymer and having a composition consisting essentially of silicon, nitrogen and/or carbon are increased while substantially maintaining or improving tensile strength by heat treating the ceramic article at an elevated temperature under superatmospheric nitrogen pressure to increase its density while avoiding crystallization. During heat treatment, at least some of the conditions of time, temperature, heating rate, cooling rate, pressure and atmosphere are controlled to minimize erosion of the article which could otherwise occur due to the loss to the surrounding atmosphere, as a gas or gaseous component, of at least one of nitrogen, silicon and carbon. The heat treated, ceramic article is amorphous and non-crystalline and has a density substantially greater than 2.5 g/cc together with desirable values of tensile strength and elastic modulus.

Method for densification of amorphous ceramic material

A rapid method of infusibilizing (curing) preceramic polymers comprising treatment said polymers with gaseous nitrogen dioxide. The infusibilized polymers may be pyrolyzed to temperatures in excess of about 800.degree. C. to yield ceramic materials with low oxygen content and, thus, good thermal stability. The methods are especially useful for the production of ceramic fibers and, more specifically, to the on-line production of ceramic fibers.

Curing preceramic polymers by exposure to nitrogen dioxide

A process for preparing ceramic materials with reduced carbon levels is described. The process involves treating a silicon-containing preceramic polymer with ammonia at a temperature of 550.degree.-800.degree. C. for a time sufficient to reduce the carbon content prior to pyrolysis at 900.degree.-1500.degree. C. Another process also involves the pyrolysis of a silicon-containing preceramic polymer in an ammonia atmosphere. The carbon level of ceramic materials produced by this invention can be controlled to a given, desired level by varying the process conditions. Suitable silicon-containing preceramic polymers include polycarbosilanes, polysilazanes, polysilanes, organosilsesquioxane-containing sol-gels, and organopolysiloxanes which are capable of being converted to ceramic materials when fired to elevated temperatures. Ceramic fibers can be prepared by the processes disclosed which contain less than 0.25 weight percent carbon.

Process for preparing ceramic materials with reduced carbon levels

A method of producing elastomeric silicone foams from a two-part system is disclosed. The method mixes the ingredients then allows a froth to form and cure at ambient temperature to an elastomeric silicone foam. The method mixes a vinyl-containing polydiorganosiloxane (1), a hydroxylated polydiorganosiloxane (2), a platinum catalyst (3), an organohydrogensiloxane (4) and a profoamer (5). The profoamer is a resinous, benzene-soluble organosiloxane copolymer consisting essentially of SiO.sub.4/2 units, silicone bonded hydroxyl groups, (CH.sub.3).sub.3 SiO.sub.1/2 units, and fluorine-containing units. An embodiment of the method includes a liquified blowing agent and stores the mixture under superatmospheric pressure, forming a foam by releasing the mixture to atmospheric pressure. Another embodiment includes an alcohol in the mixture to provide a foam of lower density. when lauryl alcohol is used and the alcohol is mixed with (1), (3), and (5) before (2) is admixed, the foam has a Bashore resiliency of less than 20.

Method of producing elastomeric silicone foam

A method of producing elastomeric silicone foams from a two-part system is disclosed. The method mixes the ingredients then allows a froth to form and cure at ambient temperature to an elastomeric silicone foam. The method mixes a vinyl-containing polydiorganosiloxane (1), a hydroxylated polydiorganosiloxane (2), a platinum catalyst (3), an organohydrogensiloxane (4) and a profoamer (5). The profoamer is a resinous, benzene-soluble organosiloxane copolymer consisting essentially of SiO.sub.4/2 units, silicone bonded hydroxyl groups, (CH.sub.3).sub.3 SiO.sub.1/2 units, and fluorine-containing units. An embodiment of the method includes a liquified blowing agent and stores the mixture under superatmospheric pressure, forming a foam by releasing the mixture to atmospheric pressure. Another embodiment includes an alcohol in the mixture to provide a foam of lower density. When lauryl alcohol is used and the alcohol is mixed with (1), (3), and (5) before (2) is admixed, the foam has a Bashore resiliency of less than 20.

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Midland, MI, United States of America

James A Rabe