Abstract: Polycrystalline alumina and methods for manufacturing polycrystalline alumina exhibiting improved transmission in the infrared region. In one embodiment, polycrystalline alumina articles are formed by providing a powder of substantially alpha phase alumina having a grain size of up to about 1 ?m, dispersing the powder in a liquid to form a slurry comprising powdered solids and liquid, removing excess of the liquid from the slurry to form a body, heating the body to provide a densified body, hot isostatically pressing the densified body under conditions to provide an article having a density of at least about 99.9% of theoretical density, and optionally annealing the article, wherein one or more of the annealing or heating are performed in an inert, dry gas.

Abstract: Polycrystalline alumina and methods for manufacturing polycrystalline alumina exhibiting improved transmission in the infrared region. In one embodiment, polycrystalline alumina articles are formed by providing a powder of substantially alpha phase alumina having a grain size of up to about 1 ?m, dispersing the powder in a liquid to form a slurry comprising powdered solids and liquid, removing excess of the liquid from the slurry to form a body, heating the body to provide a densified body, hot isostatically pressing the densified body under conditions to provide an article having a density of at least about 99.9% of theoretical density, and optionally annealing the article, wherein one or more of the annealing or heating are performed in an inert, dry gas.

Abstract: A composition is provided that includes a plurality of calcined particles of terbium aluminum oxide having a mean particle domain size of between 30 and 600 nanometers. A translucent article having a surface includes polycrystalline terbium aluminum garnet having a mean grain size from 1 to 10 microns and light scattering inclusions of aluminum-rich oxide and/or terbium-rich oxide that are present at less than 2 surface area percent of the surface. A process for forming such an article involves sintering the above provided composition at a temperature between 1500° C. and 1700° C. to yield a sintered article. The article has improved translucency and even transparency as sintering is performed under vacuum at a temperature between 1610° C. and 1680° C. Hot isostatic pressing alone or in combination with article polishing also improves article translucency.

Abstract: A composition is provided that includes a plurality of calcined particles of terbium aluminum oxide having a mean particle domain size of between 30 and 600 nanometers. A translucent article having a surface includes polycrystalline terbium aluminum garnet having a mean grain size from 1 to 10 microns and light scattering inclusions of aluminum-rich oxide and/or terbium-rich oxide that are present at less than 2 surface area percent of the surface. A process for forming such an article involves sintering the above provided composition at a temperature between 1500° C. and 1700° C. to yield a sintered article. The article has improved translucency and even transparency as sintering is performed under vacuum at a temperature between 1610° C. and 1680° C. Hot isostatic pressing alone or in combination with article polishing also improves article translucency.

Abstract: Polycrystalline alumina and methods for manufacturing polycrystalline alumina exhibiting improved transmission in the infrared region. In one embodiment, the percent real in-line transmittance is within about 2% of sapphire at selected wavelengths. In one or more embodiments, polycrystalline articles exhibit improved mechanical properties such as thermal shock resistance and hardness, which may find use in armor applications.

Abstract: A composition is provided that includes a plurality of calcined particles of terbium aluminum oxide having a mean particle domain size of between 30 and 600 nanometers. A translucent article having a surface includes polycrystalline terbium aluminum garnet having a mean grain size from 1 to 10 microns and light scattering inclusions of aluminum-rich oxide and/or terbium-rich oxide that are present at less than 2 surface area percent of the surface. A process for forming such an article involves sintering the above provided composition at a temperature between 1500° C. and 1700° C. to yield a sintered article. The article has improved translucency and even transparency as sintering is performed under vacuum at a temperature between 1610° C. and 1680° C. Hot isostatic pressing alone or in combination with article polishing also improves article translucency.

Abstract: Alumina arc tube sealing members including a highly pure, fine alumina doped with yttrium oxide, and magnesium oxide. The sealing members are used in the formation of sintered hermetic seals to a green, prefired, or fully sintered translucent alumina arc tube and niobium electrical feedthrough assemblies with or without the use of sealing frits or brazing alloys.

Abstract: Alumina arc tube sealing members including a highly pure, fine alumina doped with yttrium oxide, and magnesium oxide. The sealing members are used in the formation of sintered hermetic seals to a green, prefired, or fully sintered translucent alumina arc tube and niobium electrical feedthrough assemblies with or without the use of sealing frits or brazing alloys.

Abstract: A process for sealing of niobium-ceramic through-wall assemblies for ceramic or metal vessels for high temperature and high pressure or vacuum applications, for example an electrical feedthrough and sealable fill opening in an alumina arc tube for a high intensity discharge (HID) lamp. The process produces a fritless hermetic seal while maintaining the ductility of the niobium components. The niobium-ceramic through-wall assembly includes an axially bored alumina or yttria sealing means having a ductile niobium throughpiece close fitted to and extending through the bore. The throughpiece is preferably essentially pure niobium, but may contain up to about 2% zirconium. The assembly is fired at about 1400.degree.-2000.degree. C. in a pure oxygen- and hydrogen-free (<5 ppm each) inert, preferably flowing, atmosphere or vacuum for a time sufficient to form a hermetic seal between the throughpiece and the sealing means. The fired assembly is then cooled to below 250.degree. C.

Abstract: A process for sealing of niobium-ceramic through-wall assemblies for ceramic or metal vessels for high temperature and high pressure or vacuum applications, for example an electrical feedthrough and sealable fill opening in an alumina arc tube for a high intensity discharge (HID) lamp. The process produces a fritless hermetic seal while maintaining the ductility of the niobium components. The niobium-ceramic through-wall assembly includes an axially bored alumina or yttria sealing means having a ductile niobium throughpiece close fitted to and extending through the bore. The throughpiece is preferably essentially pure niobium, but may contain up to about 2% zirconium. The assembly is fired at about 1400.degree.-2000.degree. C. in a pure oxygen- and hydrogen-free (<5 ppm each) inert, preferably flowing, atmosphere or vacuum for a time sufficient to form a hermetic seal between the throughpiece and the sealing means. The fired assembly is then cooled to below 250.degree. C.

Abstract: A method of making a translucent alumina article is described. The method comprises the following steps:Step 1 - An alumina powder and a sintering aid are mixed in a liquid for a period sufficient to form a homogeneous slurry.Step 2 - The homogeneous slurry from Step 1 is dried remove the liquid to form a dried powder.Step 3 - The dried powder is shaped to form a compacted green body.Step 4 - The compacted green body from Step 3 is heated at a temperature equal to or less than 500.degree. C. and for a period sufficient to form a compacted green body having a density of at least 30% of theoretical density.Step 5 - The compacted green body having a density of at least 30% of theoretical density from Step 4 is heated at a temperature from about 800.degree. C. to about 1300.degree. C. in an oxygen containing atmosphere for a period sufficient to impart green strength to said compacted green body to form a prefired compacted green body.

Abstract: An improved process for producing a translucent polycrystalline alumina body comprising rapid-sintering a prefired compacted green body of alumina of predetermined shape is disclosed. The green body of alumina includes alumina doped with one or more sintering aids. Rapid sintering in accordance with the method of the present invention comprises the steps of raising the temperature of the prefired compacted green body of predetermined shape up to maximum sintering temperature at a heating rate greater than or equal to about 0.1.degree. C./second and less than the rate at which the green body experiences thermal shock; and heating the green body at the maximum sintering temperature for a period of time sufficient to produce a translucent polycrystalline alumina body. The rapid sintering is carried out under a flowing gas mixture of nitrogen and at least about 2.5 volume percent hydrogen.

Abstract: An improved process for producing a translucent polycrystalline alumina body comprising sintering a prefired compacted green body of alumina of predetermined shape is disclosed. The green body of alumina includes alumina doped with one or more sintering aids. The method of the present invention comprises sintering the prefired compacted green body of predetermined shape at a maximum sintering temperature in an atmosphere containing nitrogen and an amount of hydrogen greater than or equal to about 2.5 volume percent and less than 75 volume percent for a period of time sufficient to produce a translucent polycrystalline alumina body.

Abstract: A high pressure arc lamp has a ceramic arc tube envelope. A niobium feedthrough positions electrodes within the tube. A ceramic insert at each end of the tube forms a direct high temperature hermetic seal with the niobium feedthrough and the ceramic tube without the use of frits or brazing.

Abstract: The invention is directed to a transparent alumina material and a method of preparing this material.The material is characterized as a dense primary recrystallized polycrystalline structure having a degree of preferred crystal orientation. The material is transparent to visible and infrared light and quantitative values are given.The transparent alumina covered by this invention is made by means of hot forging and an annealing process for powders or dense compacts of high-purity alumina.

Abstract: An electric gas ignitor is disclosed having a gas igniting fiber comprising a core of conductive refractory material and an outer, high strength, oxidation resistant coating. One aspect of the invention concerns a primary current path defined by at least a portion of the fiber core and comprising a material having a highly uniform resistance per unit length. A substantially uniform temperature distribution is thereby promoted on the fiber surface and the formation of localized "hot spots" is inhibited. The primary current path is preferably an anisotropic material having a preferred crystal orientation which uniformly conducts electricity along the fiber length.A second aspect of the invention is directed to the inclusion of a diffusion-barrier material between the fiber core and the oxidation-resistant coating to prevent diffusion of the core and coating, which changes the fiber operating temperature and decreases its operating life.

Abstract: An article of manufacture comprising a substantially transparent high density polycrystalline yttria-based body consisting essentially of yttria and from 0.1 to 5 wt. % MgO or from 0.1 to 5 wt. % MgAl.sub.2 O.sub.4.Transparent yttria-based bodies according to this invention are particularly useful as envelopes for high pressure sodium vapor lamps.

Abstract: An article of manufacture is provided comprising a substantially transparent high density polycrystalline yttria-base body consisting essentially of yttria and from about 0.01 to 5 wt. % alumina.A method for preparing the transparent yttria doped with alumina is also provided comprising admixing alumina or a precursor thereof with yttria or a precursor thereof, drying the admixed powders, calcining the admixed powders and pressing the calcined powders into a desired shape and thereafter sintering the shaped powder for about 1/4 to six hours at a temperature above the eutectic temperature at a sufficiently low oxygen atmosphere to prevent oxidative contaminants.

Abstract: An article of manufacture is provided comprising a substantially transparent high density polycrystalline yttria-base body consisting essentially of yttria and from about 6 to 14 mole percent lanthana.A method for preparing the transparent yttria doped with lanthana is also provided comprising admixing or co-precipitating lanthana or a precursor thereof with yttria or a precursor thereof, washing, drying and screening the mixture, calcining the admixed or co-precipitated powders, pressing the calcined powders into a desired shape and thereafter sintering the shaped powder for from about 1/6 to 6 hours at a temperature above the H-phase transition and for from about 1/2 to 6 hours at a temperature below the H to C phase transition, said sintering being effected at a sufficiently low oxygen atmosphere to prevent oxidative contaminants.

Abstract: An article of manufacture is provided comprising a substantially transparent high density polycrystalline yttriabase body consisting essentially of yttria and from about 6 to 14 mole percent lanthana.A method for preparing the transparent yttria doped with lanthana is also provided comprising admixing or co-precipitating lanthana or a precursor thereof with yttria or a precursor thereof, washing, drying and screening the mixture, calcining the admixed or co-precipitated powders, pressing the calcined powders into a desired shape and thereafter sintering the shaped powder for from about 1/6 to 6 hours at a temperature above the H-phase transition and for from about 1/2 to 6 hours at a temperature below the H to C phase transition, said sintering being effected at a sufficiently low oxygen atmosphere to prevent oxidative contaminants.