Chemistry: analytical and immunological testing – Carbon containing
Reexamination Certificate
1999-01-14
2001-10-02
Soderquist, Arlen (Department: 1743)
Chemistry: analytical and immunological testing
Carbon containing
C430S133000, C430S144000, C430S155000, C430S173000, C430S181000, C250S282000
Reexamination Certificate
active
06297058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to fabrication of glass optical fiber, including fabrication of preforms for forming such fiber.
2. Discussion of the Related Art
As the use of glass optical fiber has increased, the demand for stronger, more durable fibers with improved optical properties has similarly grown. Loss mechanisms and structural faults in optical fiber, e.g., bubbles, typically result from imperfections and impurities existing in the glass preform from which the fiber is drawn, and much effort has gone into finding useful ways to detect, monitor, and reduce, remove, or eliminate these imperfections and impurities. Problems encountered in the detection and monitoring of impurities include the time required to obtain an accurate measurement, and the difficulty with which that measurement is made. For example, hydrogen impurities in silica articles for preform manufacture, e.g., tubes or core rods, are typically measured by forming a preform from the article or articles, drawing fiber from the preform, and measuring the OH absorption of light transmitted through the fiber. Thus, it is not possible to determine whether the material contains undesired amount of hydrogen without going through the entire fiber fabrication process. Similarly, carbon content of silica materials is generally measured by placing a relatively large sample, e.g., tens to hundreds of grams, into a furnace, baking and decomposing the silica, and measuring the evolved carbon dioxide at high temperatures (greater than 2000° C.). This method, however, takes a relatively long time, does not offer as high a precision as desired, demands a relatively large sample, and requires expensive apparatus.
Improved techniques for determining impurity content of glass preforms and/or the resultant fiber are therefore desired.
SUMMARY OF THE INVENTION
The invention provides a process for forming a refractory article, in which carbon and/or hydrogen impurities in a refractory material, particularly silica, are measured by an improved technique. According to the invention, a small sample of a refractory material, e.g., about 0.1 g to about 10 g, is heated to at least 1000° C. Evolved hydrogen-containing gases and/or carbon-containing gases are monitored, e.g., by mass spectrometry at a pressure of less than about 10
−5
Torr, and, based on the amount of the evolved gases, the concentration of hydrogen and/or carbon in the sample is calculated. The process makes it possible to accurately determine the hydrogen and carbon concentration from a small sample of a material, by a process much less burdensome than conventional techniques. For example, it is possible to take a small sample from a preform, or from a tube or rod from which a preform will be formed, and determine from that sample if the carbon and hydrogen concentration are acceptable for optical fiber fabrication. This is in sharp contrast to the conventional need to draw fiber from a finished preform (for hydrogen determination) and/or obtain a large sample and particular equipment (for carbon determination).
In one embodiment, a small silica sample is cleaned, placed in a vacuum chamber, and heated to at least 1000° C., optionally at least 1400° C., and the evolved carbon-containing and hydrogen-containing gases are monitored by a mass spectrometer. Upon such heating, the evolved gases include hydrogen, carbon dioxide, and formaldehyde, from which the hydrogen and carbon concentration are calculated. Significantly, it has been found that after carbon evolution substantially ceases during the initial heating step, the addition of more hydrogen to the sample makes it possible, upon reheating, to evolve additional carbon-containing gases. This hydrogen addition/reheating technique therefore provides a more accurate determination of carbon concentration.
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Agere Systems Optoelectronics Guardian Corp.
Rittman Scott J.
Soderquist Arlen
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