Silica container and method for producing the same

Abstract

The present invention is a method for producing a silica container having a substrate containing gaseous bubbles in its outer peripheral part and an inner layer comprised of a transparent silica glass formed on an inner surface of the substrate, wherein a powdered raw material for forming a substrate containing Li, Na, and K with the total concentration of 50 or less ppm by weight and a powdered raw material for forming an inner layer containing Ca, Sr, and Ba with the total concentration of 50 to 2000 ppm by weight are prepared; a preliminarily molded substrate is formed in a frame; a preliminarily molded inner layer is formed on an inner surface of the preliminarily molded substrate; and the preliminarily molded substrate and molded inner layer are heated from inside thereof by a discharge-heat melting method under a gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof with the ratio of more than 10% by volume thereby making an outer peripheral part of the preliminarily molded substrate to a sintered body and an inner peripheral part of the preliminarily molded substrate and the preliminarily molded inner layer to a fused glass body. With this, a method for producing a silica container, producible with a low cost and having a high durability and dimensional precision, and a container of this sort can be provided.

1 - 9 . (canceled) 
     
     
         10 . A method for producing a silica container arranged with a substrate, having a rotational symmetry, comprised of mainly a silica, and containing gaseous bubbles at least in its peripheral part, and an inner layer, formed on an inner surface of the substrate and comprised of a transparent silica glass; wherein the process comprises at least:
 a step of preparing a powdered silica having particle diameter of 10 to 1000 μm and containing Li, Na, and K with the total concentration of 50 or less ppm by weight as a powdered raw material for forming the substrate,   a step of preparing a powdered silica having particle diameter of 10 to 1000 μm and containing at least one of Ca, Sr, and Ba with the total concentration of 50 to 2000 ppm by weight as a powdered raw material for forming the inner layer,   a step of forming a preliminarily molded substrate, wherein the powdered raw material for forming the substrate is fed into a frame and then preliminarily molded to an intended shape with rotating the frame,   a step of forming a preliminarily molded inner layer, wherein the powdered raw material for forming the inner layer is fed onto an inner surface of the preliminarily molded substrate and then preliminarily molded to an intended shape in accordance with an inner surface of the preliminarily molded substrate, and   a step of forming the substrate and the inner layer, wherein the preliminarily molded substrate and the preliminarily molded inner layer are heated from inside of the preliminarily molded substrate and inner layer by a discharge-heat melting method under a gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof with the ratio of more than 10% by volume thereby making an outer peripheral part of the preliminarily molded substrate to a sintered body while an inner peripheral part of the preliminarily molded substrate and the preliminarily molded inner layer to a fused glass body.   
     
     
         11 . A method for producing a silica container arranged with a substrate, having a rotational symmetry, comprised of mainly a silica, and containing gaseous bubbles at least in its peripheral part, and an inner layer, formed on an inner surface of the substrate and comprised of a transparent silica glass; wherein the process comprises at least:
 a step of preparing a powdered silica having particle diameter of 10 to 1000 μm and containing Li, Na, and K with the total concentration of 50 or less ppm by weight as a powdered raw material for forming the substrate,   a step of preparing a powdered silica having particle diameter of 10 to 1000 μm and containing at least one of Ca, Sr, and Ba with the total concentration of 50 to 2000 ppm by weight as a powdered raw material for forming the inner layer,   a step of forming a preliminarily molded substrate, wherein the powdered raw material for forming the substrate is fed into a frame and then preliminarily molded to an intended shape with rotating the frame,   a step of forming the substrate, wherein the preliminarily molded substrate is heated from inside of the preliminarily molded substrate by a discharge-heat melting method thereby making an outer peripheral part of the preliminarily molded substrate to a sintered body while an inner peripheral part of the preliminarily molded substrate to a fused glass body, and   a step of forming the inner layer on an inner surface of the substrate, wherein the powdered raw material for forming the inner layer is spread from inside of the substrate with heating at high temperature from its inside by a discharge-heat melting method under a gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof with the ratio of more than 10% by volume.   
     
     
         12 . The method for producing a silica container according to  claim 10 , wherein the discharge-heat melting step is conducted with aspirating from outside of the preliminarily molded substrate through the frame. 
     
     
         13 . The method for producing a silica container according to  claim 11 , wherein at least one of the discharge-heat melting steps is conducted with aspirating from outside of the substrate or the preliminarily molded substrate through the frame. 
     
     
         14 . The method for producing a silica container according to  claim 10 , wherein the powdered raw material for forming the inner layer is made to contain Ba with the concentration of 100 to 1000 ppm by weight and Al with the concentration of 10 to 100 ppm by weight. 
     
     
         15 . The method for producing a silica container according to  claim 11 , wherein the powdered raw material for forming the inner layer is made to contain Ba with the concentration of 100 to 1000 ppm by weight and Al with the concentration of 10 to 100 ppm by weight. 
     
     
         16 . The method for producing a silica container according to  claim 12 , wherein the powdered raw material for forming the inner layer is made to contain Ba with the concentration of 100 to 1000 ppm by weight and Al with the concentration of 10 to 100 ppm by weight. 
     
     
         17 . The method for producing a silica container according to  claim 13 , wherein the powdered raw material for forming the inner layer is made to contain Ba with the concentration of 100 to 1000 ppm by weight and Al with the concentration of 10 to 100 ppm by weight. 
     
     
         18 . The method for producing a silica container according to  claim 10 , wherein a dew-point temperature of the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof be set between 15° C. and −15° C. and controlled within ±2° C. of the set dew-point temperature. 
     
     
         19 . The method for producing a silica container according to  claim 11 , wherein a dew-point temperature of the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof be set between 15° C. and −15° C. and controlled within ±2° C. of the set dew-point temperature. 
     
     
         20 . The method for producing a silica container according to  claim 12 , wherein a dew-point temperature of the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof be set between 15° C. and −15° C. and controlled within ±2° C. of the set dew-point temperature. 
     
     
         21 . The method for producing a silica container according to  claim 13 , wherein a dew-point temperature of the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof be set between 15° C. and −15° C. and controlled within ±2° C. of the set dew-point temperature. 
     
     
         22 . The method for producing a silica container according to  claim 10 , wherein, in the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof, the ratio of a hydrogen gas or a helium gas or a gas mixture thereof is made to 100% by volume. 
     
     
         23 . The method for producing a silica container according to  claim 11 , wherein, in the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof, the ratio of a hydrogen gas or a helium gas or a gas mixture thereof is made to 100% by volume. 
     
     
         24 . The method for producing a silica container according to  claim 12 , wherein, in the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof, the ratio of a hydrogen gas or a helium gas or a gas mixture thereof is made to 100% by volume. 
     
     
         25 . The method for producing a silica container according to  claim 13 , wherein, in the gas atmosphere containing a hydrogen gas or a helium gas or a gas mixture thereof, the ratio of a hydrogen gas or a helium gas or a gas mixture thereof is made to 100% by volume. 
     
     
         26 . A silica container arranged with a substrate, having a rotational symmetry, comprised of mainly a silica, containing gaseous bubbles in its peripheral part, and having a transparent silica glass in its inner peripheral part, and an inner layer, formed on an inner surface of the substrate and comprised of a transparent silica glass; wherein
 the substrate contains Li, Na, and K with the total concentration of 50 or less ppm by weight and shows a linear light transmittance of 91.8 to 93.2% at a light wavelength of 600 nm for a sample having 10 mm thickness cut-out from the inner peripheral part and finished with both surfaces being parallel and optically polished, and   the inner layer contains Li, Na, and K with the total concentration of 100 or less ppb by weight and at least one of Ca, Sr, and Ba with the total concentration of 50 to 2000 ppm by weight and shows a linear light transmittance of 91.8 to 93.2% at a light wavelength of 600 nm for a sample having 10 mm thickness cut-out from the inner layer and finished with both surfaces being parallel and optically polished, and amount of water molecules released from a sample cut-out from the inner layer upon heating under vacuum at 1000° C. is less than 2×10 17  molecules/g.   
     
     
         27 . The silica container according to  claim 26 , wherein the inner layer is made to contain Ba with the concentration of 100 to 1000 ppm by weight and Al with the concentration of 10 to 100 ppm by weight. 
     
     
         28 . The silica container according to  claim 26 , wherein the inner layer is made to contain OH groups with the concentration of 1 to 50 ppm by weight, Li, Na, and K with each concentration of 20 or less ppb by weight, and Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Mo, and W with each concentration of 10 or less ppb by weight. 
     
     
         29 . The silica container according to  claim 27 , wherein the inner layer is made to contain OH groups with the concentration of 1 to 50 ppm by weight, Li, Na, and K with each concentration of 20 or less ppb by weight, and Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Mo, and W with each concentration of 10 or less ppb by weight.