CN1387499A - Pure fused silica, furnace and method - Google Patents

Abstract

Provides a relatively pure silica product, a kiln (50) for manufacturing such a product, and a method thereof. The product is manufactured by collecting molten silica particles in a refractory kiln (50), in which at least a portion of the refractory material (32) has been treated with a halogen-containing gas that reacts with contaminating metal ions in the refractory material (32).

Description

Pure fused silica, furnace and method

This application claims the benefit of U.S. Patent Application 60/153,422, filed September 10, 1999, entitled "Furnace Top Refractories for Fabrication of Fused Silica" (Lawrence H. Kotacska and Robert S. Pavilik, Jr.) priority. This application is also related to U.S. Patent Application 09, filed August 13, 1998, entitled "Pure Fused Silica, Kiln, and Process" (Robert S. Pavilik, Jr., Daniel R. Sempolinski and Michael H. Wasilewski) /125,208, which patent applications are hereby incorporated by reference.

field of invention

This invention relates to articles of relatively pure fused silica, a furnace and a method for making such articles.

Background of the invention

Purer fused silica is produced by thermal decomposition of its precursors and deposition of the resulting oxides. The precursor may be in vapor form or supported by vapor. Decomposition takes place by flame hydrolysis or pyrolysis.

One such method is the hydrolysis or pyrolysis of silicon tetrachloride to produce fused silica. Early patents disclosing this method of preparing silica are: US Patents 2,239,551 (Nordberg) and 2,273,342 (Hyde). An industrial application of flame hydrolysis is the formation and deposition of silica to form larger objects (boules). Such glass bodies can be used directly, or processed or assembled into large optical bodies such as lenses for telescopes. In this method, _SiCl4 is hydrolyzed, and the vapor formed by the hydrolysis is passed through a flame to form fused particles of silica. These particles are successively deposited in a bait or in a crucible called a cup, forming a glass body.

This approach suffers from the serious drawback of the need to dispose of the by-product HCl in an environmentally safe manner. Thus, in US Pat. No. 5,403,002 (Dobbins et al.), a halide-free silicon-containing compound is used instead of _SiCl4 . This patent specifically proposes the use of polymethylsiloxanes such as octamethylcyclotetrasiloxane to provide vaporous reactants for hydrolysis or pyrolysis processes.

To introduce a substituted precursor, of course, a significant change in the properties of the fused silica product must strictly be avoided. Unfortunately, the precursor substitution proposed by Dobbins et al. leads to a noticeable change in performance. Another disadvantage is the occurrence of fluorescence in the resulting glass, which fluorescence increases when the glass is irradiated with short-wave radiation.

These studies revealed that one factor in the transmission loss is the sodium content of the glass. US Patents 5,332,702 and 5,395,413 (Sempolinski et al.) describe remedies used to reduce sodium levels. These measures primarily consist of the use of zirconia refractories in the construction of furnaces for fused silica deposition to form glass bodies. Specifically, dispersants, binders and water containing as little sodium ions as possible must be used in the manufacture of zirconia refractory components for such kilns.

Improved products were obtained using the method described in the Sempolinski et al. patent. However, some fused silica applications clearly require further improvements to meet the stringent requirements of these applications. One such use is in lenses for the transmission of very short wavelength ultraviolet light emitted by excimer type lasers. Such lasers emit radiation at a wavelength of approximately 193-248 nm.

It was found that lenses made from commercially available fused silica did not provide acceptable transmission of short wavelength radiation and showed poor fluorescence. Both conditions get worse with time. Transmission loss or darkening of glass is generally referred to as UV absorption damage.

The main object of the present invention is to provide a fused silica material which solves these problems. A second object is to provide improved fused silica glasses for laser lenses, especially for fine lithographic processes. A third object is to provide an improved furnace for collecting fused silica in the form of vitreous bodies. A fourth object is to provide a method of making the improved collection furnace and of making glass in the furnace.

Summary of the invention

The present invention includes a method of making fused silica glass. The method comprises the steps of providing a silica feedstock, providing a roof and cup consisting essentially of aluminum oxide, the roof being positioned above a consolidated non-porous fused silica glass body. The method also includes conveying the silica feedstock to a burner mounted at a reaction site within the alumina furnace roof where the silica feedstock is converted into fused silica particles that are redeposited and solidified. The junction is fused silica glass.

The present invention also includes a fused silica glass furnace for converting a silica precursor feedstock liquid other than silica into fused silica glass, the furnace having a contained furnace interior within which is Maximum furnace operating temperature MFOT. Inside the kiln there is a transformation deposition consolidation site where the precursor material is transformed into silica soot which is then deposited and consolidated into fused silica glass. The interior of the kiln is located in alumina refractory bricks and is insulated by them. The sintering temperature of alumina refractory bricks is FT>1650°C, mainly composed of Al and O.

One embodiment of the present invention relates to an improved method of making a body of fused silica by passing a silicon-containing compound into a flame to form fused silica particles and collecting the particles in a refractory constructed kiln. At least a portion of the refractory material comprising the construction of the furnace has been purified from contaminating metals by exposure to a reactive halogen-containing gas capable of reacting therewith.

Yet another aspect of the invention relates to relatively pure fused silica material having a transmittance of at least 99.5% to 248 nm radiation and at least 98% to 193 nm radiation, the body of which at least a substantial portion is exposed to such It has a qualified amount of fluorescence when irradiated, and the content of contaminating metal ions in the fused silica material is less than 100ppb.

Another aspect of the invention relates to a refractory furnace for collecting fused silica particles in solid form, the furnace being constructed at least in part from a refractory material containing less than 300 ppb mobile metal contaminants.

Brief description of the drawings

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of the apparatus and method for making fused silica glass according to the present invention.

Fig. 2 is a plan view of a domed roof of a fused silica glass furnace refractory according to the present invention.

Fig. 3 is a cross-sectional view of the domed roof of the present invention.

Fig. 4 is a cross-sectional view of a fused silica glass furnace cup of the present invention.

Fig. 5 is a schematic diagram of the carbon-chlorination purification furnace treatment method of the present invention.

Description of the invention

The conventional glass body fabrication method employed in the manufacture of fused silica is a one-step process. In this method, a carrier gas is bubbled through a _SiCl4 feedstock kept at a certain low temperature. The SiCl ₄ vapor is transported to the reaction site in the carrier gas. The reaction site includes several burners that burn at a temperature higher than 1600°C and oxidize SiCl ₄ vapor to deposit silicon dioxide.

The main requirements of this conventional method are: the equipment and delivery system should be able to gasify the raw material and transport the gasified raw material to the burner in a vapor state. As described in the Dobbins et al. patent, the apparatus and process are essentially the same as conventional except for one major difference, which is the substitution of polymethylsiloxane for the _SiCl4 feedstock. Using this alternative material would require some minor adjustments, such as a slightly higher delivery temperature (eg, 100-150°C). This is because the vapor pressure of siloxane is slightly lower than that of SiCl ₄ .

Figure 1 is a schematic diagram of an apparatus and method for making and depositing fused silica particles to form large fused silica glass bodies. The apparatus is shown generally at 10 and includes a source 12 of raw material. Use nitrogen or a nitrogen/oxygen mixture as the carrier gas. A bypass stream 14 of nitrogen is introduced to prevent saturation of the vapor stream. The vaporous reactants pass through a distribution means to the reaction site, where there are burners 18 near the roof 20 of the furnace. The reactants are mixed with a fuel/oxygen mixture in these burners, combusted and oxidized at temperatures above 1600°C, depositing silica. High purity metal oxide soot and heat are conveyed downward through the refractory roof 20 . Silica is immediately deposited in the hot cup 26 and consolidates into the non-porous body 24 .

As disclosed in the Sempolinski et al. patent, improvements in zirconia refractories can mitigate the effects of sodium ion contamination in fused silica products. However, other contaminants besides sodium were found to be present in the refractories of the furnace. These contaminants include alkaline earth and transition metals such as iron, lead, phosphorus, sulfur, other alkali metals, and aluminum, especially free metal contaminants that reduce the UV light transmission of the glass.

These metal contaminants have varying degrees of volatility at temperatures above 1650°C (the temperature at which silica is deposited). Therefore, they will be present in the furnace environment where they will be entrained in the silica as it is deposited. The presence of these contaminants in fused silica lenses can result in reduced transmission of the glass and can also cause undesirable fluorescence in the glass. These disadvantages are even more serious when the lens is exposed to short-wavelength UV radiation during use.

Refractory materials inherently have varying amounts of metallic impurities as well as varying volatilities of these metals. This makes it difficult to control glass quality in fused silica collection furnaces, and often even to obtain acceptable glass. This problem becomes particularly acute when polysiloxanes are used as precursor materials for fused silica. As demonstrated in the Sempolinski et al _. patent, the self-purifying effect of the HCl by-product of SiCl decomposition is lost when using a siloxane precursor.

Contaminating metals can be present in the raw materials used to manufacture furnace refractories. Metal can also be entrained during sintering of the refractory or during subsequent operations such as sawing or grinding.

We have found that metal contamination in collection kilns can be suppressed by constructing furnaces that contaminate refractories with less than 300ppm metal content. In particular, it has been found that this can be done when using zirconia refractories to construct collection furnaces for fused silica deposition. This is achieved according to the invention by sintering the kiln refractories in a halogen-containing atmosphere. Reaction of the halogen with the contaminating metal on at least the exposed surfaces of the refractory material enables removal of the contaminating metal from these surfaces.

We have found that chlorine or fluorine are particularly suitable as such or in the form of their acid gases. Substantially pure purification gases may be used. However, it has been found to be effective and convenient to use purifying gases as low as 5% in concentrations of as little as 5% in an inert gas such as helium or argon, although longer processing times are required. The purification process can use a continuous flow of halogen gas. Alternatively, a pulse type process can be used, in which the gas is passed into the purification chamber for a period of time and then discharged, and then repeated many times.

Purification can occur at temperatures as low as 700°C. However, it is generally preferred to use higher temperatures in the range of 1100-1500°C.

The invention will now be described with reference to the various parts of a refractory furnace.

Preferably, the refractory body is purified first, and then assembled into a furnace. This treatment is carried out during the manufacture of refractory materials before the furnace is built into the furnace.

The use of chemically purified refractory materials according to the present invention provides several advantages. Purified deposition furnaces provide high purity fused silica products and also fused silica glass with qualified high transmission of short wavelength UV radiation and low fluorescence at consistently high yields. This glass will not increase UV absorption damage and fluorescence in use. These requirements can be met without requiring changes to the kiln structure or the silica formation and deposition process. These advantages are significant because these features are critical to achieving uniformity of the refractive index of the glass.

The effectiveness of the purification process was demonstrated by comparing two sets of fused silica coupons made in a zirconia refractory kiln. One set was obtained from glass bodies deposited in a collection kiln built with untreated zirconia refractories. Another set was taken from glass bodies deposited in a collection furnace built of treated zirconia refractory. The two kilns use sintered zirconia refractory materials to build the furnace roof and cup lining, which are basically the same. The purification treatment of zirconia refractories is to keep the temperature in a purification furnace at 1300°C for 8 hours, and maintain a flowing atmosphere of 5.7% Cl ₂ and 94.3% helium throughout the time.

The relevant properties were determined on test pieces taken from comparable parts of fused SiO ₂ glass bodies produced in two furnaces (refractory treated and unrefined). Table I lists the internal transmittance (%) measured by radiation at 248nm and 193nm wavelengths.

Table I unprocessed deal with 248nm 99.08 99.82 193nm 95.28 99.18

The above fused silica vitreous was also analyzed to determine the percentage of depth of the vitreous showing acceptable low fluorescence as a percentage of its depth in the collection cup. Fluorescence was determined by integrating the intensity measured in the range 400-700 nm. To be acceptable, the glass coupon must have a value of less than 4.2 x ^10-9 W/ ^cm2 when exposed to laser light emitted by a 15 mJ/ ^cm2 and 200 Hz laser.

The glass from the untreated kiln was totally off-spec. There are no parts of the vitreous with acceptable low fluorescence values. Glass from the furnace was acceptable up to a depth of 3.53 inches. This depth is 59.3% of the total depth.

The present invention includes a method of making a body of fused silica by passing a silicon-containing compound through a flame to form fused silica particles which are collected in a furnace constructed of alumina refractory lining to fused silica Silicon form. The improvement includes configuring at least a portion of the refractory material of the kiln collecting the silica particles to have been treated with a reactive halogen-containing gas capable of reacting therewith to purify it from contaminating metals.

The present invention includes a method of making fused silica glass. The method includes providing a silica feedstock, providing a roof consisting essentially of alumina over a consolidated non-porous fused silica glass body. The process involves conveying the silica precursor feedstock to multiple reaction site burners mounted on the alumina furnace roof where the silica precursor feedstock is converted into silica particles, deposited and consolidated into a molten Congealed silica vitreous.

Figures 1-5 illustrate the method of the present invention for making high purity silica glass. As shown in FIG. 1 , a silica feedstock is provided from a feedstock source 12 . The silica feedstock is preferably delivered to burner 18 in a vapor state. Preferably, a feed evaporator is used to generate the silica feed vapor, and the feed vapor is conveyed through piping by means of a carrier gas such as nitrogen and oxygen. The method includes providing a furnace roof 20 consisting essentially of alumina. An alumina roof 20 is provided above a consolidated non-porous body 24 of hot fused silica. The silica feedstock vapor is delivered to burners 18 installed at various reaction sites in the alumina furnace roof 20 . By the reactive flame/heat of the burner, the incoming feedstock is converted into fine silica soot particles 30 which deposit and consolidate into a fused silica glass body 24 . This method preferably has a cup 26 for containing and contacting the silica glass 24 within the furnace. The cup 26 of the kiln is preferably composed primarily of alumina. The silicon dioxide raw material provided is preferably a high-purity silicon dioxide raw material with a contaminating metal ion content of less than 100 ppb, so that the contaminating metal ion content of the consolidated fused silica glass body is less than 100 ppb. The silica raw material is preferably a halide-free silica raw material, most preferably a siloxane. In another embodiment, the silica feedstock is a halide-containing feedstock, preferably _SiCl4 . In a preferred embodiment, providing the silica feedstock further includes providing a source of titanium dopant such that the fused silica glass body is titanium doped fused silica.

Providing the alumina furnace roof 20 preferably includes providing Cl-untreated alumina refractory bricks 32 which are then exposed to a reactive halogen-containing gas 33 . As shown in FIG. 5 , the refractory brick 32 is purified with a reactive halogen-containing gas to produce a halogen purified refractory brick 34 . The method preferably includes laying halogen-purified alumina refractory bricks 34 to obtain a furnace roof 20 consisting essentially of alumina. Likewise, providing the alumina cup 26 includes providing a Cl-untreated alumina refractory component 32, which is then exposed to a reactive halogen-containing gas 33 to produce a halogen-purified alumina refractory component 34, and then They are assembled to form a cup body as shown in Figure 4, which is mainly made of alumina. In this preferred embodiment of the method, an alumina refractory preform 32 is formed/machined. The preforms are preferably formed into predetermined shapes and dimensions so that they can be assembled into the roof 20 and cup 26 . The preform is preferably machined with a saw and drill into the refractory component 32. In one embodiment, the alumina refractory is wet machined. The machining/forming of the refractory component 32 is preferably carried out first, followed by the purification process of the reactive halogen gas. This purification process preferably consists of building the purified brick component 34 into the kiln cup body 26 and furnace roof 20 Before the last step of the manufacturing process. The preferred purification process of the reactive halogen-containing gases of the present invention involves carbochlorination of the refractory brick components. As shown in Figure 5, the refractory brick components are processed in a carbo-chlorination furnace 36. The carbo-chlorination furnace 36 is preferably a graphite vessel 38 with at least one vacuum/process gas inlet/outlet 40 for evacuating and allowing process gases such as chlorine, helium, hydrogen and mixtures thereof to be evacuated in a controlled manner within the sealed vessel 38. input and output. The preferred graphite treating furnace vessel has a bed 42 of granular/powdered carbon, such as graphite carbon black powder, to provide an appropriate amount of carbon in the furnace for carbon-chlorination of refractory components. The treatment furnace 36 includes a suitable heating source such as an induction heating element or a resistance heating element, so that the interior of the vessel 38 and its contents can be heated to a reaction temperature of 1000-1500° C., preferably at least 1200° C. to carbonize the contents. - Chlorination. In addition to removing impurities from refractory parts by reacting with halogen chlorine reagents, it is also possible to react impurities with carbon in the furnace (carbon reduces metal contaminants in refractories) to reduce metal contaminants in refractories. A preferred carbo-chlorination purification treatment operation involves loading the refractory component with the carbon bed into a treatment furnace. The temperature of the furnace is raised to a preferred reaction temperature range of 1000-1500°C (preferably at least 1200°C), while vacuuming and maintaining for a certain period of time, so that the carbon and the oxides present are properly reacted, and then the chlorine gas is treated The container is repeatedly fed, preferably the chlorine gas treatment lasts about 30-60 minutes between each injection of chlorine gas, and the treatment is carried out for 30-60 minutes at an elevated reaction temperature, preferably 2-5 times. The preferred chlorine gas treatment atmosphere contains 2.5-20% Cl ₂ , preferably 3-10% Cl ₂ , more preferably 4-8% Cl ₂ , most preferably 6±1% Cl ₂ , and the balance is helium . After such chlorine feed sparging, the vacuum was drawn again while maintaining the temperature. It is good practice to repeat this vacuum-chlorine-vacuum form of carbo-chlorination at least once more to ensure proper carbo-chlorination of refractory components. After final evacuation, the process vessel and its contents are preferably purged with a process purge gas such as helium or hydrogen. After carbon-chlorination purification, before building into kiln, furnace roof and cup body, the processing and contact of refractory parts should be minimized. It is best to carry out at least two carbo-chlorination treatments on refractory brick parts. The refractory brick parts adopting the carbon-chlorination treatment of the present invention can provide high-purity fused silica with a UV transmittance of at least 99.9%/cm at KrF 248nm, at least 99.3%/cm at ArF 193nm, and even 99.7%+/cm.

As shown in Figures 1 and 4, the present invention includes providing a furnace cup 26 consisting essentially of alumina for containing a consolidated non-porous fused silica glass body 24 .

The alumina roof and cup refractory components 34 are preferably uncoated alumina.

The alumina roof and cup refractory components 34 are preferably alumina substantially free of Si and _SiO2 . The SiO ₂ content in the alumina is preferably less than 2000 ppm (by weight).

Providing the refractory component 34 of the alumina furnace roof and cup preferably includes providing an unsintered alumina refractory precursor, then sintering the alumina refractory precursor at a temperature of at least 1660° C., and building the sintered alumina refractory The material part 34 forms and provides the roof and cup. The alumina refractory precursor is preferably sintered at a temperature of at least 1665°C, more preferably at least 1670°C, most preferably at least 1675°C.

As shown in Figure 2-3, the provision of alumina furnace roof preferably includes providing many porous alumina refractory bricks and building these refractory bricks into the furnace roof. The porosity of the refractory bricks is preferably in the range of 25-70%. As best shown in Figures 2-3, alumina roof 20 includes a plurality of alumina refractory bricks 34 provided and assembled to form a self-supporting vaulted roof. The alumina furnace top 20 is preferably made of alumina refractory parts 34 with a bulk density of less than 3.9 g/ ^cm3 , preferably ≤3 g/ ^cm3 , more preferably ≤2.5 g/ ^cm3 , and most preferably ≤2 g/ ^cm3 and ≤1.4 g/ ^cm3 . The bulk density of the alumina refractory is preferably ≥ 1.2 g/ ^cm3 , in the range of about 1.2-3.8. Providing the alumina roof 20 preferably includes providing an alumina refractory material having a Young's modulus at 20-1200°C of at least 2 x 106 psi. Providing alumina roof 20 preferably includes providing alumina refractory material 34 having a percent creep < 5%, preferably ≤ 2%, more preferably ≤ 1.2% creep at 1600°C and 25 psi load for 150 hours. The preferred alumina roof 20 has an emissivity of <0.35 at 1100°C.

The present invention preferably includes avoiding the deposition of silica particles 30 on the furnace roof 20 . This is done by controlling the focus of the burner 18 soot streams downwards and ensuring that they are fixed downwards in the roof, thus avoiding and inhibiting the deposition of silica particles over the alumina roof.

The present invention also includes terminating the input of the silica raw material into the burner 18, cooling the fused silica glass body 24, dismantling the alumina furnace roof 20, and disposing of the dismantled alumina furnace roof brick 34 with a service temperature higher than 1300°C .

The present invention also includes a fused silica glass furnace for converting a liquid silica precursor feedstock other than silica into fused silica glass. The fused silica glass furnace 50 has a contained furnace interior 52 having the highest furnace operating temperature MFOT, the furnace interior 52 including the deposition consolidation site where the precursor feedstock is converted to the secondary The silica soot is then deposited and consolidated into fused silica glass. The interior 52 of the kiln is surrounded and insulated by many alumina refractory bricks 34. The sintering temperature FT of the alumina refractory bricks 34 is >1650° C., and the alumina refractory bricks are mainly composed of Al and O.

The sintering temperature FT of the alumina refractory brick 34 is preferably FT>MFOT+20°C. The SiO ₂ content of the alumina refractory brick 34 is preferably less than 2000 ppm (by weight). The contaminating metal ion concentration of the alumina refractory brick 34 is preferably less than 300 ppm, and the alumina refractory brick 34 is preferably a carbon-chlorinated alumina refractory brick purified by Cl treatment. Alumina refractory bricks preferably have Na concentration ≤ 100ppm (weight), K concentration ≤ 20ppm (weight), and Fe concentration ≤ 250ppm (weight) (preferably Fe ≤ 150ppm). The alumina refractory brick 34 is preferably a refractory brick without microcracks. The alumina refractory bricks 34 should be assembled together to form a self-supporting domed roof above the kiln interior 52 . Alumina refractory bricks 34 are also built together to form a cup-shaped container, which is filled with deposited and consolidated fused silica glass, and the glass should flow in the rotating cup.

The present invention includes a fused silica glass furnace 50 . Furnace 50 includes a self-supporting domed roof 20 (shown in FIG. 2 and shown in cross-section in FIG. 3 ). The arched furnace roof 20 is preferably formed by stacking 34 dislocations of alumina refractory bricks. The refractory brick 34 is preferably composed mainly of Al and O. The bulk density of the refractory brick 34 is preferably in the range of 1.2-3 g/ ^cm3 . As shown in Figures 2-3, the furnace roof 20 has a plurality of burner holes 18 and a support ring 120 of steel metal ring structure, which is used to surround the furnace roof 20 and hold the bricks 34 in the round arch during masonry/construction of the furnace. position within the shaped roof structure, while the roof rests on the base side walls of the furnace during operation of the kiln. The sintering temperature of alumina refractory bricks is preferably higher than 1650°C. The silica content of the alumina refractory brick 34 is preferably less than 2000ppm (weight), the Fe content is preferably less than 250ppm (weight), and the Na content is preferably less than 100ppm (weight). The Young's modulus of the furnace top alumina refractory brick 34 is Preferably at least 2 x ¹⁰⁶ psi with a percent creep of less than 5% after 150 hours at 1600°C under a 25 psi load. Furnace roof bricks 34 should be built together in a herringbone pattern.

Those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention. Accordingly, the present invention includes the modifications and variations provided within the scope of the claims and their equivalents.

Claims (50)

1. An improved method of producing a fused silica body, the method comprising: passing a silicon-containing compound into a flame to form fused silica particles in a kiln constructed of alumina refractory material, and collecting the fused silica particles Silica bulk particles, the improvement comprising at least a portion of the kiln in which the silica particles are collected has been previously reacted with a reactive halogen-containing gas to purify the refractory material from contaminating metals. 2. A method of making fused silica glass, the method comprising: Provide silica raw material, providing a furnace roof consisting essentially of alumina overlying a consolidated non-porous fused silica glass body, The silica feedstock is conveyed to multiple reaction site burners installed in the alumina furnace roof where the silica feedstock is converted into a multitude of silica particles that are deposited and consolidated into the fused silica glass. 3. The method of claim 2, wherein the method includes providing a cup consisting essentially of alumina containing the consolidated non-porous fused silica glass body. 4. The method according to claim 2, characterized in that the silica raw material provided is a high-purity silica raw material, and the contaminating metal ion content of the fused silica glass body is less than 100 ppb. 5. The method of claim 2, wherein said silica feedstock provided comprises a titanium dopant source material and said fused silica glass body is fused silica doped with titanium. 6. The method according to claim 2, characterized in that the step of providing said alumina furnace roof comprises providing a plurality of alumina refractory bricks without Cl treatment; subjecting the alumina refractory bricks without Cl treatment to a reaction containing Purification treatment of neutral halogen gas, providing a plurality of halogen-purified alumina refractory bricks; and installing said halogen-treated purified alumina refractory bricks to form and provide said substantially alumina furnace roof. 7. The method of claim 3, wherein the step of providing the alumina cup comprises providing a plurality of non-Cl treated alumina refractory parts; performing the non-Cl treated alumina refractory parts Purification of reactive halogen-containing gases, providing a plurality of halogen-purified alumina refractory parts, and building up said halogen-treated purified alumina refractory parts, forming and providing said substantially alumina cup . 8. The method of claim 2, wherein the step of providing the alumina roof comprises providing an uncoated alumina roof. 9. The method of claim 2, wherein the step of providing the alumina roof comprises providing a silica-free alumina roof substantially free of Si. 10. The method of claim 2, wherein the step of providing said alumina roof comprises providing an unsintered alumina refractory precursor, sintering said alumina refractory precursor at at least 1600°C, Provide sintered alumina refractory material, and build the sintered alumina refractory material to form and provide the furnace roof. 11. The method of claim 10, wherein the alumina refractory precursor is sintered at at least 1665°C. 12. The method of claim 10, wherein the alumina refractory precursor is sintered at at least 1670°C. 13. The method of claim 10, wherein the alumina refractory precursor is sintered at at least 1675°C. 14. The method of claim 2, wherein the step of providing said alumina furnace roof comprises providing a plurality of porous alumina refractory bricks, said refractory bricks being built into said furnace roof, said porous refractory The porosity of the bricks is in the range of 25-70%. 15. The method of claim 2, wherein the step of providing said alumina roof comprises providing a plurality of alumina refractory bricks, said refractory bricks being assembled to form a domed roof. 16. The method of claim 2, wherein the step of providing said alumina roof includes providing alumina refractory having a bulk density of <3.9 g/ ^cm3 . 17. The method of claim 16, wherein the alumina glass material has a bulk density ≥ 1.2 g/ ^cm3 . 18. The method of claim 16, wherein the step of providing said alumina roof comprises providing an alumina refractory having a bulk density < ³ g/cm3. 19. The method of claim 16, wherein the step of providing said alumina roof comprises providing an alumina refractory having a bulk density < 2.5 g/ ^cm3 . 20. The method of claim 16, wherein the step of providing said alumina roof comprises providing an alumina refractory having a bulk density < 2 g/ ^cm3 . 21. The method of claim 16, wherein the step of providing said alumina roof comprises providing an alumina refractory having a bulk density < 1.4 g/ ^cm3 . 22. The method of claim 2, wherein the step of providing said alumina roof includes providing an alumina refractory having a Young's modulus of at least 2 x ¹⁰⁶ psi. 23. The method of claim 2 wherein the step of providing said alumina roof includes providing alumina refractory having a percent creep < 5% at 1600°C and 25 psi load for 150 hours. 24. The method of claim 2 wherein the step of providing said alumina roof includes providing alumina refractory having a percent creep < 2% at 1600°C and 25 psi load for 150 hours. 25. The method of claim 2, wherein the step of providing said alumina roof includes providing alumina refractory having a post-creep percentage < 1.2% at 1600°C and 25 psi load for 150 hours. 26. The method of claim 2, wherein the alumina roof has an emissivity of <0.35 at 1100°C. 27. The method of claim 2, further comprising preventing deposition of silica particles on the furnace roof. 28. The method of claim 6, further comprising terminating input of silica feedstock to said burner, cooling said fused silica glass body, and dismantling and removing said alumina furnace roof bricks, many of which had operating temperatures above 1300°C were disposed of. 29. The method of claim 2, wherein the step of providing a silica feedstock comprises providing a halide-free silica feedstock. 30. A fused silica glass furnace for converting silica precursor feedstock into fused silica glass, The fused silica glass furnace has a contained furnace interior having a maximum furnace operating temperature MFOT, and a transformation deposition consolidation site within the furnace interior where the precursor material into silica fume, which then deposits and consolidates into fused silica glass, The inside of the kiln is surrounded and insulated by many alumina refractory bricks, the sintering temperature FT of the alumina refractory bricks is >1650° C., and the alumina refractory bricks are mainly composed of Al and O. 31. The fused silica glass furnace as claimed in claim 30, characterized in that the alumina refractory brick has a FT of FT>MFOT+20°C. 32. The fused silica glass furnace of claim 30, wherein the alumina refractory brick has a _SiO2 content of less than 2000 ppm by weight. 33. The fused silica glass furnace of claim 30, wherein the alumina refractory brick has a _SiO2 content of less than 300 ppm by weight. 34. The fused silica glass furnace according to claim 30, characterized in that the alumina refractory bricks are alumina refractory bricks purified by Cl treatment. 35. The fused silica glass furnace according to claim 30, characterized in that the Na concentration of the alumina refractory bricks is ≤ 100 ppm. 36. The fused silica glass furnace according to claim 30, characterized in that the K concentration of the alumina refractory brick is ≤ 20 ppm. 37. The fused silica glass furnace according to claim 30, characterized in that the Fe concentration of the alumina refractory brick is ≤ 250 ppm. 38. The fused silica glass furnace according to claim 30, characterized in that the Fe concentration of the alumina refractory brick is ≤ 150 ppm. 39. The fused silica glass furnace of claim 30, wherein said alumina refractory brick is a single oxide component non-microcracked refractory brick. 40. The fused silica glass furnace of claim 30 wherein said alumina refractory bricks comprise alumina furnace bricks assembled together to form a domed roof over said furnace interior top brick. 41. The fused silica glass furnace of claim 30, wherein said alumina refractory bricks comprise alumina cup-shaped bricks assembled together to form a cup-shaped vessel, said cup-shaped vessel containing and Contacting the deposited and consolidated fused silica glass. 42. The fused silica glass furnace of claim 30, wherein the bulk density of the alumina refractory bricks is in the range of 1.2-3 g/ ^cm3 . 43. A fused silica glass furnace, said furnace comprising a self-supporting dome-shaped furnace roof formed by stacking a number of alumina refractory bricks interlaced, said alumina refractory bricks Refractory bricks are mainly composed of Al and O, and their bulk density is in the range of 1.2-3 g/ ^cm3 . 44. The fused silica glass furnace of claim 43, wherein the temperature at which the alumina refractory bricks are fired is greater than 1650°C. 45. The fused silica glass furnace of claim 43, wherein said alumina refractory bricks have a silica content of less than 2000 ppm by weight. 46. The fused silica glass furnace of claim 43, wherein said alumina refractory brick has an Fe content of less than 250 ppm by weight. 47. The fused silica glass furnace of claim 43, wherein said alumina refractory bricks have a Na content of less than 100 ppm by weight. 48. The fused silica glass furnace of claim 43, wherein the alumina refractory brick has a Young's modulus of at least 2 x ¹⁰⁶ psi. 49. The fused silica glass furnace of claim 43, wherein said alumina refractory brick has a percent creep of <5% at 1600°C and 25 psi load for 150 hours. 50. The fused silica glass furnace of claim 43, wherein said alumina refractory bricks are assembled together in a herringbone pattern.

Images