Method of making titania-doped fused silica

Details Method of making titania-doped fused silica Method of making titania-doped fused silica

1999-12-13

2002-12-03

Derrington, James (Department: 1731)

Glass manufacturing

Processes of manufacturing fibers, filaments, or preforms

Process of manufacturing optical fibers, waveguides, or...

C065S413000, C065S421000, C065S423000, C065S435000, C065S060520

Reexamination Certificate

active

06487879

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the manufacture of high purity metal oxide glass, and specifically to a method of doping high purity fused silica using organotitanium materials.
BACKGROUND OF THE INVENTION
Titania-doped silica glasses have found numerous use in the industry due to its low expansion properties as well as for its excellent resistance to fatigue. In addition, optical fiber having one or more outer layers doped with titania has been shown to exhibit superior strength, as compared to homogeneous silica clad fibers. Superior strength is desirable in optical fiber as it reduces the potential for rupture and consequential replacement.
Various methods and apparatus for the production of high purity metal oxides, and particularly fused silica, from a chloride-based feedstock have been well documented. Such equipment generally include a number of burner arrangements and feedstock delivery systems, all based on the oxidation of a metal chloride through flame hydrolysis or pyrolysis. Illustrative examples are, U.S. Pat. No. 4,491,604 (Lesk et al.) wherein trichlorosilane, dichlorosilane, and silicon tetrachloride are flame hydrolyzed to form soot, and U.S. Pat. No. 3,666,414 (Bayer) wherein silicon halides, such as silicon chloroform, are flame hydrolyzed. In similar processes, U.S. Pat. No. 3,486,913 (Zirngibl) and U.S. Pat. No. 2,269,059 (McLachlan) teach of oxidation of halides: inorganic halide components in vapor form such as TiCl
4
, CrCl
3
, CrO
2
Cl
2
, SiCl
4
, AlCl
3
, ZrCl
4
, FeCl
2
, FeCl
3
, ZnCl
2
, or SnCl
4
oxidized with air, steam, or oxygen are employed in '913; while silicon halides and AlCl
3
, TiCl
4
, and ZrCl
4
are employed in '059.
U.S. Pat. No. 2,326,059 (Nordberg) details a technique for making silica-rich, ultra-low expansion glass by vaporizing tetrachlorides of Si and Ti into the gas stream of an oxy-gas burner, depositing the resultant mixture to make a preform, vitrifying the preform at 1500° C. to make an opal glass, and firing the opal preform at a higher temperature to cause it to become transparent. Unlike the instant invention, the stated reference does not employ the use of halide-free, titanium-containing source compounds.
U.S. Pat. No. 4,501,602 (Miller et al.) describes the production of glass and glass/ceramic articles via a vapor phase oxidation process wherein &bgr;-diketonate complexes of metals selected from Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, and the rare earth series of the Periodic Table are vaporized, the vapor is transported to an oxidation site, such as a burner or a hot plasma zone which is adjacent to a deposition substrate or within a deposition tube, and oxidized in the vapor phase to form particulate metal oxide soot.
&bgr;-diketonate complexes are also available of metals in Group VA of the Periodic Table, notably tantalum and vanadium. Miller et al. did not refer to the halide-free, titanium-containing source compounds employed in the present invention.
Japanese Patent Application No. 90838-1985, entitled MANUFACTURING METHOD OF QUARTZ GLASS PREFORM FOR OPTICAL TRANSMISSION, (Okamoto et al.) discloses a method of doping quartz glass by utilizing an ester silane expressed by the general formula R
1
nSi(OR
2
)
4-n
and one or more dopants defined by the formulas Ge(OR
3
)
3
, B(OR
3
)
3
and PH
3
, where R
1
is a hydrogen atom, methyl or ethyl group; R
2
is a methyl or ethyl group; R
3
is an univalent hydrocarbon group; and n is an integer ranging between 0 and 4. A plethora or organometallic compounds are disclosed including methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, tetramethoxysilane, methyltriethoxysilane, and tetraethoxysilane, though none of the halide-free titania-containing source compounds of the instant invention are mentioned.
Recently, various methods have been suggested for the manufacture of titania-doped silica. For example, co-assigned, U.S. Pat. No. 5,067,975, disclosed a method of doping silica with titania using SiCl
4
and TiCl
4
for optical fiber applications. The resulting optical fiber includes a core, an inner cladding, and two outer claddings, one nominally about 8% by weight TiO
2
and a bump layer, with the bump layer having a TiO
2
concentration greater than 10.5 % by weight. The sole purpose of the bump layer being to control the loss of titania during consolidation.
More recently, co-assigned U.S. Pat. No. 5,154,744, disclosed a method of doping silica with titania which method eliminates the need for the bump layer without compromising the strength of the fiber. This patent discloses a method of making titania-doped silica glass having excellent fatigue resistance as well as excellent retention of titania after consolidation, by extracting titania from organometallic compounds selected from titanium tetra isopropoxide, titanium tetra ethoxide, titanium tetra 2-ethylhexyloxide, titanium tetra cyclopentyloxide, and titanium amides.
While the methods disclosed in the above patents have been found adequate for the production of titania-doped fused silica, there continues to be a need for more efficient methods of producing such products. In particular, there is an ongoing need for methods which can be used to produce titania-doped fused silica of improved physical properties.
SUMMARY OF THE INVENTION
Briefly, the invention relates to a method of making titania-doped fused silica using a group of organotitanium materials which are less sensitive to air and moisture, and which tend to decompose less than previously disclosed organotitanium materials.
In one aspect, the invention relates to a method of making a non-porous body of high purity fused silica glass doped with titania comprising the steps of:
(a) forming amorphous particles of high purity fused silica;
(b) doping said particles with titania in vapor form;
(c) depositing said titania-doped amorphous particles onto a support; and
(d) either essentially simultaneously with said deposition or subsequent thereto consolidating said deposit of titania-doped amorphous particles into a non-porous body;
the improvement being that the titania is produced using titanium chelates as the titanium-containing compound. Preferred chelates include titanium acetylacetonate, titanium ethyl acetoacetate, and combinations of these.
It is a further object of the instant invention to provide a method of making titania-doped optical fiber having superior strength using as the titania source, the inventive group of organotitanium materials.


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