General Electric Company

Mary Sue Kaliszewski

Curtis E Scott

Lionel M Levinson

Paul G Mathews

Randolph E Maxwell

Marshall Gordon Jones

Charles D Greskovich

Timothy D Russell

Carl Edward Erikson

Ranajit K Datta

Harry M Laska

Charles N Stewart

William E Ishler

H Michael Laska

Csaba F Rappensberger

A high transmittance polycrystalline alumina arc tube for a metal halide discharge lamp is formed by treating an alumina arc tube material having a few percent of closed porosity in a two step process, which provides a high-transmittance arc tube. An initially porous arc tube is formed by extruding or die pressing individual components of the tube from a mixture which includes powdered alumina, assembling the components into an arc tube body, and then partially sintering the components to seal them together. The two step process includes hot isostatic pressing of the partially sintered arc tube and then chemically polishing the surface of the tube. The first, pressing step involves heating the alumina arc tube in an inert atmosphere, such as argon, at a temperature of 1600 to 1900&deg; C. and a pressure of about 700 to 2100 kg/sq.cm. for from about one to three hours. This reduces porosity in the crystalline structure. In the second step, the surface of the tube is immersed in a flux comprising a molten alkali metal borate at moderately elevated temperatures, or coated with a flux material which is heated to form the flux, to remove surface imperfections. The finished arc tube has transmittance values which approach those of single crystal sapphire arc tubes.

High transmittance alumina for ceramic metal halide lamps

An arc discharge lamp, such as a metal halide arc discharge lamp, has an extended life by reducing loss of the metallic portion of the fill. At least one component of the fill reacts with fused silica in the arc tube or diffuses through the arc tube walls. The fill will generally comprise a sodium halide, at least one additional metal halide, and an inert starting gas. A borosilicate glaze which is vitreous and light-transmissive is provided on the wall of the arc tube. The borosilicate glaze is comprised of a borosilicate glass containing at least one metal oxide selected from aluminum, scandium, yttrium, and the rare earth elements. The borosilicate glaze may further contain additional rare earth elements or transition metals to alter the light or energy emission of the lamp by absorbing select wave lengths. For instance, titanium, ceria, cobalt, chromium, iron or neodymium, or combinations of the foregoing, may be added.

High temperature glaze for metal halide arctubes

A ceramic arc tube for a metal halide discharge lamp is soaked in a dopant solution. The dopant solution includes a salt of a UV-absorbing additive, such as europium, cerium, or titanium. The salt is converted to the oxide form of the UV-absorbing additive during sintering of the arc tube. Lamps fabricated using the doped arc tubes filter UV from light emitted from the discharge without appreciably absorbing light in the visible range. The UV retained in the lamp causes the lamp to run at a hotter temperature, improving light output.

Ultraviolet and visible filter for ceramic arc tube body

A method of producing a ceramic-metal-halide (CMH) discharge lamp having a monolithic seal between a sapphire (single crystal alumina) arc tube and a polycrystalline alumina end cap. The method includes the steps of providing an arc tube of fully dense sapphire and providing an end cap made of unsintered compressed polycrystalline alumina powder. The end cap is heated until it is presintered to remove organic binder material at a low temperature relative to the sintering temperature. The presintered end cap is placed on an end portion of the arc tube to form an interface therebetween. The assembled presintered end cap and arc tube are then heated to the sintering temperature wherein the end cap is fully sintered onto the arc tube and the sapphire tube grows into the end cap. A monolithic seal is formed at the previous interface between the end cap and the arc tube as the sapphire tube grows into the polycrystalline alumina end cap.

Monolithic seal for sapphire CMH lamp

845 A method of producing a ceramic-metal-halide (CMH) discharge lamp having a monolithic seal between a sapphire (single crystal alumina) arc tube and a polycrystalline alumina end cap. The method includes the steps of providing an arc tube of fully dense sapphire and providing an end cap made of unsintered compressed polycrystalline alumina powder. The end cap is heated until it is presintered to remove organic binder material at a low temperature relative to the sintering temperature. The presintered end cap is placed on an end portion of the arc tube to form an interface therebetween. The assembled presintered end cap and arc tube are then heated to the sintering temperature wherein the end cap is fully sintered onto the arc tube and the sapphire tube grows into the end cap. A monolithic seal is formed at the previous interface between the end cap and the arc tube as the sapphire tube grows into the polycrystalline alumina end cap.

Process of preparing monolithic seal for sapphire CMH lamp

A solid state method of converting a polycrystalline ceramic body to a single crystal body includes the steps of doping the polycrystalline ceramic material with a conversion-enhancing dopant and then heating the polycrystalline body at a selected temperature for a selected time sufficient to convert the polycrystalline body to a single crystal. The selected temperature is less than the melting temperature of the polycrystalline material and greater than about one-half the melting temperature of the material. In the conversion of polycrystalline alumina to single crystal alumina (sapphire), examples of conversion-enhancing dopants include cations having a +3 valence, such as chromium, gallium, and titanium. The polycrystalline body further can be inhomogeneously doped to form a first portion of the polycrystalline body that is doped to the selected level of the conversion-enhancing dopant and a second portion that is not doped such that heating the doped polycrystalline body causes conversion of first portion to a single crystal structure and the second portion retains a polycrystalline structure.

Conversion of doped polycrystalline material to single crystal material

A protective layer or precoat of a metal oxide for an internal conductive layer in a rapid-start fluorescent lamp is formed of yttria, ceria or silica to suppress the occurrence of localized appearance defects referred to as measles. The protective layer may be used in combination with conductive layers having a uniformly flat profile or a U-shaped bathtub profile to further enhance the suppression of measle defects. The lamp retains the desirable qualities of good startability and energy efficiency while at the same time avoiding the undesirable measle appearance defects.

Precoated fluorescent lamp for defect elimination

Conversion of doped polycrystalline material to single crystal

A solid state process for the bulk conversion of a dense polycrystalline ceramic body to a single crystal body has been accomplished by heating the polycrystalline material to a temperature above one-half of the melting temperature of the material but below the melting point of the material. As the process is a solid state process, no melting of the ceramic body is necessary to convert it to a single crystal. The process has been used to convert a dense polycrystalline alumina body (PCA) containing less than 100 wppm of magnesia to sapphire (single crystal alumina) by heating the PCA to temperatures above 1100.degree. C. but below 2050.degree. C., the melting point of alumina.

Solid state thermal conversion of polycrystalline alumina to sapphire

Polycrystalline alumina bodies have been converted to sapphire by a solid state conversion process in which a localized energy source is used to heat only a portion of the body to a temperature above 1800.degree. C. Using a laser as the energy source resulted in conversion to sapphire in less than an hour. The polycrystalline alumina bodies had a magnesia content below 50 wppm, an average grain size below 100 microns, and a density greater than 3.97 g/cc.

Solid state formation of sapphire using a localized energy source

An arc tube of fused silica for a metal halide arc discharge lamp including a fill for the arc tube comprised of a sodium halide, at least one additional metal halide, and an inert starting gas, the arc tube including a tube of fused silica having an inner wall defining an arc chamber, the inner wall of the tube having provided thereon a metal silicate coating which is vitreous and light-transmissive, and which is comprised of a silicate of at least one metal selected from the group consisting essentially of scandium, yttrium, and a rare earth element, and preferably which is the same metal as that of the at least one additional metal halide. Protection of the fused silica arc tube with the metal silicate coating reduces loss of the metallic portion of the fill by diffusion or reaction and corresponding buildup of free halogen in the arc tube.

Growing community of inventors

Cleveland Heights, OH, United States of America

Mary Sue Kaliszewski