U.S. patent application number 15/274468 was filed with the patent office on 2017-05-04 for purified quartz powder modified for cladding optic fiber cable.
This patent application is currently assigned to Unimin Corporation. The applicant listed for this patent is Unimin Corporation. Invention is credited to Paul Calderone, Chris Capobianco, Brian Mosher.
Application Number | 20170121217 15/274468 |
Document ID | / |
Family ID | 58638263 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170121217 |
Kind Code |
A1 |
Calderone; Paul ; et
al. |
May 4, 2017 |
PURIFIED QUARTZ POWDER MODIFIED FOR CLADDING OPTIC FIBER CABLE
Abstract
A highly purified quartz powder having a low level of naturally
occurring lithium modified for cladding a fiber optic cable, said
modified quartz powder having an increased total amount of lithium
in solid solution in said powder, said increased total amount being
in the range of more than 0.50 ppm and less than 1.00 ppm and a
method of modifying an highly purified quartz powder to make the
same.
Inventors: |
Calderone; Paul; (Mars Hill,
NC) ; Mosher; Brian; (Asheville, NC) ;
Capobianco; Chris; (Asheville, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Unimin Corporation |
New Canaan |
CT |
US |
|
|
Assignee: |
Unimin Corporation
|
Family ID: |
58638263 |
Appl. No.: |
15/274468 |
Filed: |
September 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62250579 |
Nov 4, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 2235/3217 20130101;
C03C 25/1068 20180101; C04B 35/62805 20130101; C03C 13/045
20130101; C04B 35/62813 20130101; C03C 2213/00 20130101; C04B
2235/443 20130101; C04B 2235/3418 20130101; C04B 35/14 20130101;
C04B 2235/442 20130101; C04B 2235/72 20130101; C03C 25/007
20130101; C04B 2235/96 20130101; C03C 23/0095 20130101; C04B
2235/3203 20130101 |
International
Class: |
C03C 13/04 20060101
C03C013/04; C03C 23/00 20060101 C03C023/00 |
Claims
1. An highly purified quartz powder having a low level of naturally
occurring lithium modified for cladding a fiber optic cable, said
modified quartz powder having an increased total amount of lithium
in solid solution in said powder, said increased total amount being
in the range of more than 0.50 ppm and less than 1.00 ppm.
2. The modified high purity quartz powder as defined in claim 1
wherein said increased total amount of lithium in said modified
powder is in the range of 0.6 to 0.8 ppm.
3. The modified highly purity quartz powder as defined in claim 1
wherein said increased total amount of lithium in said modified
powder is in the range of 0.60 to 0.85 ppm.
4. The modified highly purified quartz powder as defined in claim 1
wherein said increased total amount of lithium in said modified
powder is about 0.6 ppm.
5. The modified highly purified quartz powder as defined in claim 1
has a maximum particle size D99 in the range of 200-400 microns and
a minimum particle size D5 in the range of 50-70 microns.
6. The modified highly purified quartz powder as defined in claim 1
wherein said low level of naturally occurring lithium of said
modified powder is less than 0.3 ppm lithium.
7. The modified highly purified quartz powder as defined in claim 1
wherein said low level of naturally occurring lithium of said
modified powder is about 0.2 ppm.
8. The modified highly purified quartz powder as defined in claim
1, which modified highly purified quartz powder results in an
attenuation less than 0.187 dB/km when used for cladding of a fiber
optic cable.
9. The modified highly purified quartz powder as defined in claim
1, which modified highly purified quartz powder results in an
attenuation less than 0.184 dB/km when used for cladding of a fiber
optic cable.
10. A method of modifying an highly purified quartz powder having a
low level of naturally occurring lithium for use in cladding a
fiber optic cable, said method comprising: a) forming a solution of
a lithium doping agent; b) blending said highly purified quartz
powder with said doping solution to provide a blended mass with a
given level of lithium comprising lithium of said doping solution
coated onto said highly purified quartz powder and the low level of
naturally occurring lithium of said highly purified quartz powder;
c) gassing said blended mass with a gas heated to a temperature of
at least 1000.degree. C. for a time to dope said highly purified
powder with lithium in said doping solution; and, d) controlling
the amount of lithium from said doping solution that is doped into
said highly purified quartz powder so the total lithium in solid
solution in said modified highly purified quartz powder is at a
final level of 0.50-1.00 ppm.
11. The method as defined in claim 10 wherein said lithium amount
controlling operation includes adjusting said given level of
lithium in said blended mass.
12. The method as defined in claim 10 wherein said lithium amount
controlling operation includes the temperature of said gassing
operation.
13. The method as defined claim 10 wherein said lithium amount
controlling operation includes the time of said gassing
operation.
14. The method as defined in claim 10 wherein said final level is
in the range of more than 0.50 ppm and less than 1.00 ppm.
15. The method as defined in claim 10 wherein said final level is
in the range of 0.6 to 0.8 ppm.
16. The method as defined in claim 10 wherein said final level is
in the range of 0.60 to 0.85 ppm.
17. The method defined in claim 10 wherein said final level is
about 0.60 ppm.
18. The method as defined in claim 10 wherein said given level of
lithium in said blended mass is in the range of 0.80 to 2.0
ppm.
19. The method as defined in claim 10 wherein said given level of
lithium in said blended mass is in the range of 0.80 to 1.0
ppm.
20. The method as defined in claim 10 wherein said gassing
temperature is in the range of 1200-1300.degree. C.
21. The method as defined in claim 10 including drying said blended
mass at a temperature of 80-100.degree. C. before gassing of said
blended mass.
22. The method as defined in claim 10 wherein said blended mass has
a moisture content of 2-5 percent.
23. The method as defined in claim 10 wherein said lithium doping
agent is a lithium salt.
24. The method as defined in claim 23 wherein said lithium doping
agent is LiNO.sub.3.
25. The method as defined in claim 10 wherein the lithium doping
agent includes aluminum to increase the portion of lithium from
said blended mass converted to solid solution doped into said
highly purified powder during said gassing operation.
26. The method as defined in claim 25 wherein said lithium doping
agent is LiAlO.sub.2.
27. The method as defined in claim 25 wherein said lithium doping
agent is a lithium salt combined with an aluminum salt.
28. The method as defined in claim 27 wherein said aluminum salt is
Al(NO.sub.3).sub.3.
Description
[0001] This application claims priority to provisional patent
application Ser. No. 62/250,579 filed on Nov. 4, 2015 which is
incorporated by reference herein.
[0002] The present invention relates to the highly purified natural
quartz powder industry and more specifically to a modification of
commercially available purified quartz powder that is specifically
modified for improving the cladding of optic fiber cable and the
method of making this new modified highly purified quartz
powder.
BACKGROUND OF THE INVENTION
[0003] In making optic fiber cable, a cladding is used around the
central core for protecting and improving the operation of the
optic signal passing through the cable. Significant efforts have
been made to optimize the physical and operating characteristics of
the cladding beyond its general purpose of protecting the core of
the cable. In the past, the cladding has been made by various
materials, such as quartz powder which are highly purified to
drastically reduce impurities occurring in natural quartz powder.
Quartz powder was employed because it was relatively inexpensive
and provided great physical properties when it had an even particle
size distribution and was highly purified, such as IOTA 4 powder
sold by Unimin Corporation of New Cannan, Conn. Such commercially
available, highly purified, naturally occurring quartz powder was
physically excellent for cladding, but did not result in the best
attenuation of the cladded cable. Indeed, the attenuation was
greater than 0.190 dB/km, a level not generally wanted in the
industry. The present invention relates to a modification of the
commercially available, highly purified, quartz powder, which
modification results in a quartz powder that causes vastly improved
attenuation and, indeed, has a reduced attenuation at a level of
less than 0.187 dB/km and preferably at a level below the targeted
attenuation value of 0.184 dB/km. Consequently, by the modification
of the highly purified quartz powder in accordance with the present
invention, this modified powder is now not only well designed to be
used in the optic fiber cable industry, but also causes cladding
using the new quartz powder to have improved attenuation
properties.
[0004] As background to the present invention, the highly purified
quartz powder, which is the starting point of the present
invention, is a powder of the type marketed by Unimin Corporation
under the trademark IOTA, preferable IOTA 4 or alternatively IOTA
6, which often is made from IOTA 4. To create this background
powder, the naturally occurring quartz is ground and sized into a
powder typically at having about a 100 screen size and has a low
level of naturally occurring lithium in solid solution, which
lithium remains after the high purification process. The quartz
particles of the natural silica are purified so the particles have
only a minute level of natural occurring impurities. Indeed, the
processing reduces the impurities combined with the SIO.sub.2
particles to the lowest level commercially practical, such as less
than 0.3 ppm lithium and generally about 0.2 ppm lithium. This is
the background material of the present invention. This material is
modified to render a "new" powder with an increased amount of
lithium in solid solution, which new powder is used for the
cladding of optic fiber cables. It creates an attenuation value not
heretofore obtained by the commercially available highly purified
quartz powder.
SUMMARY OF THE INVENTION
[0005] In accordance with the invention, commercially available,
highly purified quartz powder having a low level of naturally
occurring lithium is modified for cladding in the fiber optic cable
art. This existing powder is pre-processed by being leached and has
a particle size distribution with a maximum particle size D99 in
the range of 200-400 microns and a minimal particle size D5 in the
range of 50-70 microns. The highly purified quartz powder is then
modified by adding a specific amount of lithium by a SOP doping
process, so the powder which normally has about 0.20 ppm of solid
solution lithium is modified to have a higher solid solution
lithium value, which level is broadly in the range of more than
0.50 ppm and less than 1.00 ppm. In the preferred embodiment, the
increased solid solution lithium level by doping is in the range of
0.6 to 0.8 ppm. Indeed, it is preferred to define the increased
solid solution lithium as being about 0.60 ppm, which is defined as
0.60 ppm to less than 0.70 ppm. This preferred level of solid
solution lithium in the modified, highly purified commercial quartz
powder results in an attenuation of less than 0.184 dB/km, which is
the targeted attenuation sought in the optic fiber cable industry.
The invention reduces the attenuation of the cladding to less than
about 0.187 kB/km and preferably less than 0.184 dB/km. The
invention is performed by using a lithium doping solution to
increase the ultimate solid solution level of lithium in the new
powder.
[0006] This preferred modification of the existing commercial
quartz powder has been tested and it was determined that a small
increase in aluminum in the lithium doping agent increased the
level of lithium in the solid solution added to the commercial
quartz powder by doping. Lesser amounts of lithium were lost while
doping the new powder when aluminum was in the doping solution.
Thus, in a secondary aspect of the invention, the new quartz powder
uses a lithium doping solution with aluminum.
[0007] In accordance with another aspect of the present invention,
there is provide a method of modifying highly purified quartz
powder constituting the basic aspect of the present invention
defined above. In accordance with this method, commercially
available highly purified quartz powder with a small particle size
and a low level of naturally occurring lithium is provided as the
starting particle mass. A solution of lithium doping agent is
formulated. The particle mass of commercial powder is then blended
with the lithium doping solution for a time and by a vigorous
mixing action to produce a homogeneous distribution of the doping
agent in the quartz powder. Blending creates a mass of particles
with a moisture content in the range of 2 to 5 percent. The blended
powder is thereafter dried at a high temperature to provide a
"given amount" of lithium in the quartz powder, which given amount
is the original solid solution natural lithium and the lithium
doping solution coated on the quartz powder. In the broadest
aspect, the total given amount of lithium associated with the
blended powder is in the range of 0.80 to 2.00 ppm, but preferably
it is in the range 0.80 to 1.0 ppm. This given amount of lithium in
the blended powder is a combination of the original lithium,
usually about 0.20 ppm, and the lithium added by the doping
solution. In summary, the first aspect of the novel method is to
coat the commercial quartz powder with a small amount of lithium
from a lithium doping solution to bring the lithium content to a
higher level, which higher level is less than 2.0 ppm and
preferably 1.0 ppm or less.
[0008] As so far described, the novel method involves coating, by a
blending action, commercial quartz particles with a defined
additional amount of lithium. This lithium increase is accomplished
by subjecting the powders to a solution of a lithium doping agent
and blending the powder and solution into the homogeneous mass.
Thereafter, the blended particles and lithium solution are gassed
with a gas heated to a temperature of at least 1,000.degree. C. for
a time to dope the commercial powder with the added lithium
introduced at the blending operation. The hot gassing operation is
controlled by temperature and time so a portion of the lithium
coated on the particles, after the powder is mixed with the lithium
doping solution, is converted by doping to solid solution lithium
in the quartz powder Only a part of the lithium in the blended
powder is doped into the original powder to create the new modified
powder. This action created a solid solution level of lithium in
the final powder having the range of more than 0.50 ppm, but less
than 1.0 ppm. Broadly, attenuation is less than 0.187 dB/km for the
modified powder, the preferred embodiment causes attenuation of
less than the targeted amount in the industry, which is 0.184
dB/km. In other words, broadly stated, the invention is used to
produce a drastically reduced attenuation value, which reduced
value in the preferred embodiment, is less than the targeted amount
of attenuation desired in the optic fiber cable industry.
Consequently, the inventive modification of the quartz powder makes
the new powder substantially better than the prior art for
cladding.
[0009] The method of the present invention is defined above;
however, certain further limitations have been created such as the
concept of passing the mass of particles through a gassing chamber
for a distance, such as 10 feet, to control the gassing time. In
practice, the gassing chamber is horizontal; however, it can be
vertical. Furthermore, the hot gas is preferably AHCI, but can be
AqHCI.
[0010] In accordance with the invention, the amount of lithium
coated onto the provided quartz powder brings the total lithium of
the powder blend into the range of 0.80 to 2.0 ppm and preferably
into the range of 0.80 to 1.0 ppm. Even though the broadest aspect
of the invention has a solid solution level of lithium in the final
product of between 0.50 ppm and 1.00 ppm, in the preferred
embodiment, the range of solid solution lithium in the final
modified powder is preferably in the range of 0.6 to 0.8 ppm. As a
tested, preferred powder, the solid solution level of lithium in
the final powder is about 0.60 ppm. This preferred level of solid
solution lithium in the final product produces the desired reduced
level of attenuation when the powder is used for cladding of optic
fiber cable.
[0011] In accordance with the preferred embodiment, the gassing
temperature in the final gassing operation is in the range of
1200.degree.-1300.degree. C. and in practice has been about
1,250.degree. C. In practice, the doping agent is normally lithium
nitrate. However, lithium carbonate and lithium chloride have also
been used successfully in practicing the present invention. In an
embodiment using a doping agent including aluminum, the doping
agent was lithium aluminate with or without being in combination
with aluminum nitrate. When a combination of lithium and aluminum
is used in the doping agent, the liquid or moisture percentage of
the solution is selected to give a stoichiometric resolution of the
components. Aluminum has been shown to increase the lithium doping
action.
[0012] In accordance with another aspect of the method to produce
the novel modified powder, the hot gassing operation is created by
passing the blended mass of powders through a gassing chamber with
a distance to control the gassing time. Thus, the lithium coated
onto the particles and the low amount of lithium in the natural
particles of the blended mass is converted to a total level of
lithium in solid solution in the final powder, as defined
above.
[0013] The gas temperature used for the final heating operation and
the time the particles are subjected to the hot gas are controlled
to produce a final doping action to obtain a final solid solution
level of lithium in the range of at least 0.50 ppm, but less than
1.00 ppm. An adjusted level of lithium coated on the blended powder
is also used to control the amount of lithium doped into the final
modified powder. Not all the coated lithium is doped into the final
powder so the starting level is a control factor. The highly
purified quartz powder is modified to reduce the attenuation in
general of fiber optic cable cladded by the new powder. In
accordance with the broadest aspect of the invention relating to
adding lithium, the attenuation is less than 0.187 dB/km and
preferably less than 0.184 dB/km, the target level in the
industry.
[0014] In summary, there is provided a previously "purified" quartz
powder, which powder is modified so it has more than 0.5 ppm, but
less than 1.0 ppm lithium in solid solution and preferably 0.6 to
0.8 ppm lithium in solid solution. It has been proven by tests that
this increase level of lithium improves the attenuation of the
optic fibers in a cable to a level below 0.184 dB/km, the sought
after target level of the optic fiber industry. As is known,
attenuation in a fiber optic cable is a measure of the loss of
signal strength or light power that occurs as the light pulses
propagate through a run of fiber. Measurements typically are
defined in the terms of decibels or dB/km. By using a lithium
doping solution with aluminum, it has been determined that aluminum
reduces the amount of lithium lost by the hot gassing operation.
More of the lithium coated on the powder is actually doped into the
powder.
[0015] These and other objects, aspects, features and advantages of
the invention will become apparent to those skilled in the art upon
a reading of the Detailed Description of the invention set forth
below taken together with the drawing which will be described in
the next section.
BRIEF DESCRIPTION OF THE DRAWING
[0016] The invention may take physical form in certain parts and
arrangement of parts, a preferred embodiment of which will be
described in detail and illustrated in the accompanying drawing
which forms a part hereof and wherein:
[0017] FIG. 1 is a schematic representation of the new method for
making the modified quartz powder constituting the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] In accordance with the invention, there is provided method
10 used to modify a highly purified quartz powder. This method is
schematically shown in the figure. Processed, purified quartz
powder, with the general properties of IOTA 4, preferably having a
maximum particle size D99 of 200-400 microns and a minimum particle
size D5 of 50-70 microns is provided at operation 12. IOTA 6 could
also be the starting powder at operation 12, but it is not
preferred. The purified quartz powder is a leached quartz powder
which has been aggressively cleaned so only a minute amount of
impurities remain in the powder. In these highly purified quartz
powders, the inherent lithium content of the starting powder is
low, i.e. generally about 0.20 ppm. Though it is known that the
powder is used for cladding, the invention improves the powder by
drastically reducing the attenuation of the cladding. This
previously purified quartz powder is directed to station 14 where
it is mixed with a doping solution from station 20. At this
solution station, a compound of a lithium doping agent from station
30 is combined with water or other liquid solvent from supply 22 to
form a doping solution. This solution is mixed with the purified
quartz powder at station 14. This is a blending operation where the
quartz powder with the doping solution is aggressively blended for
a time sufficient to produce a homogeneous distribution of the
doping agent into the purified quartz powder to coat the powder
evenly with the doping solution. Consequently, the purified quartz
is coated with a selected amount of lithium doping solution to give
a total lithium content of the powder in the general range of 0.80
to 2.0 ppm and preferably in the range of 0.80 to 1.0 ppm. This
range has an effect on the final level of doped lithium in the
modified powder.
[0019] In practice this selected doping agent or compound for
station 30 is preferably a lithium agent from station 40, such as
LiCl provided by supply 42, LiNO.sub.3 provided by supply 44 or
Li.sub.2CO.sub.3 provided by supply 46. Tests indicate that lithium
nitrate from supply 44 is preferred. In an alternative, quartz
powder 12 is not only coated with a lithium doping agent, but also
a lithium agent combined with an aluminum doping agent or compound
from station 50. To accomplish this alternative, a doping compound
with aluminum is provided from station 20 to station 14. If
aluminum doping agent is selected for method 10, either LiAlO.sub.2
provided by the doping agent is supply 52 or Al(NO.sub.3).sub.3 and
the preferred LiNO.sub.3 provided by supply 54. One of these
aluminum doping agents is provided to station 20 from station 30 to
make a solution for dual doping of lithium and aluminum at station
20 for reasons previously described.
[0020] The doping solution, preferably lithium or, alternatively,
lithium and aluminum is mixed at station 14 with the commercially
purified quartz powder to obtain a mass of coated particles which
mass has a moisture content of 2-5 percent. Other appropriate
moisture contents can be used. When the aluminum doping agent at
station 50 from either supply 52 or supply 54 is employed, the
solution at station 20 must include more liquid so that the
solution is a stoichiometric resolution of aluminum and
lithium.
[0021] Station 14 mixes the doping solution from station 20 to give
a blended mass. In practice, the blending action is by dripping the
solution into a tumbling cone blender operated at a batch mode for
a time to create a homogeneous mass of moist particles as
previously described. This operation generally requires at least
1.0 hour. The time may be effected by the percentage of doping
solution. It is necessary for the thorough blending at station 14
to produce a specific blended mass with a level of lithium on the
surface of the quartz particles, which particles, after prior
purification, already had a standard low level of naturally
occurring lithium, i.e. less than 0.3 ppm and normally about 0.2
ppm. The amount of lithium coated onto the powder brings the total
level of lithium in the blended mass to a level in the range of
0.80 to 2.0 ppm and preferably to a level in the range of 0.80 to
1.0 ppm. The selected level is used to control the final level of
lithium in the final powder. Now the commercially available
purified quartz powder having a particle size distribution PSD of
50 to 400 microns is evenly coated with the desired amount, or
controlled amount, of lithium. The blended mass has a total lithium
level, with about 0.2 ppm in solid solution and the rest coated
onto the particles.
[0022] The moist, homogeneously mixed quartz powdered particles or
blended mass from station 14 is mixed and dried in a vacuum dryer
60 operated at a high temperature of at least about
80.degree.-100.degree. C. for a time of at least about 1.0 hour. In
this manner, the quartz particles of the blended mass are dried and
the doping compound is structurally associated with the surface of
the quartz powder. Now the coated powder or blended mass is passed
through a continuous hot gassing operation 70 (doping operation),
which operation is performed in a rotary tube reactor surrounded by
a furnace having a temperature preferably
1,200.degree.-1,300.degree. C. controlled by heating step 72. The
rotatory reactor has an effective length of about 10 feet, which
gives a heating time of about 45 minutes. Gassing or doping station
70 directs the heated gas over the moving particles. In practice,
the speed of the moving particles is about 1 pound/minute. The hot
gassing operation is performed preferably by AHCI heated to a high
temperature. Doping of the lithium, with or without aluminum, is
caused by the gassing operation 70, with or without providing air
from supply 74. The air is optional and helps retain the level of
doping content, especially when aluminum is employed as one of the
doping compounds. As an alternative, an AqHCI liquid gassing
operation is performed by reactor 70. This option is employed
especially when aluminum addition is being used. Thus, the quartz
particles are doped by the high temperature gassing. Consequently,
the doped quartz powder, after hot gassing has an increased amount
of lithium in solid solution in the quartz particles forming the
original powder of the blended mass. The increased lithium in solid
solution is by the portion of lithium doped into the particles from
the solution coated on the particles. The doped level is controlled
at gassing operation 70 and is affected by temperature, time and
amount of lithium coated on the particles. The doped quartz is a
new powder collected and then shipped from the site of method 10 as
indicated by station or operation 100.
[0023] As indicated in the drawing and discussed in the following
section regarding examples, several doping agents have been
identified and tested for "adding" lithium to highly purified
quartz powder having a naturally existing lithium level of about
0.2 ppm or less. Lithium nitrate (supply 44) was found to be the
preferred doping agent due to its high solubility in water at
station 20 and its superior results when used in method 10.
Furthermore, it was discovered that when lithium nitrate is the
selected doping agent, standard doping protocol was successfully
employed to add the desired amount of lithium to the highly
purified quartz powder.
EXAMPLES
[0024] Extensive testing was conducted by producing a blend of
highly purified quartz powder, such as IOTA 4, with lithium of
about 0.2 ppm in solid solution in the quartz powder and a solution
of a lithium doping agent to obtain a given, increased amount of
lithium in the known powder. Lithium nitrate is preferred and used
in the first two examples. The targeted increased level of solid
solution lithium from the doping action at station 70 was 0.60 ppm.
This laboratory testing suggested that increased lithium level
carried by the existing quartz powder by way of the doping solution
coating should be 1.0 ppm. The powder with this coated lithium
level was blended at operation 14 and then gassed with AHCI at
operation 70. As indicated, this action was designed to yield a
desired 0.6 ppm lithium level in solid solution for the final
powder. This targeted level is near the lower level of the
invention. However, the lithium in solid solution in this process
was actually about 0.80 ppm, instead of 0.60. The initial tests
indicated that using air did not have an effect on the lithium
doped into the original powder. This testing was with gassing by
AHCI at 1250.degree. C. for 45 minutes. This first example with a
solid solution content of about 0.80 ppm was found to be successful
in improving attenuation of quartz powder. The attenuation was
below 0.187 dB/km. This attenuation was not obtained by
commercially available purified quartz powder of the type modified
in the invention. Attenuation of the prior powder was over 0.190
dB/km. However, this first example exceeded the originally targeted
level of 0.60 ppm in solid solution. It was about 0.823 ppm.
Consequently, this first test example was used to define the
general upper limit for lithium doping in accordance with the
objective of invention. Example 2 was then produced in an effort to
obtain a better powder with a solid solution of lithium closer to
the targeted level of added lithium, i.e. 0.60 ppm. The first
example seeking the targeted 0.60 ppm level had merely reduced the
lithium level in the blended powder by 0.2 ppm when the powder was
doped at operation 70. Using this fact to produce the powder of
Example 2, with a solid solution level nearer the targeted value of
the invention, the initial level of the total lithium in the
blended powder from operation 14 was adjusted to a lower starting
value of 0.85 ppm lithium. The coated level of lithium was reduced
to a level less than 0.10 ppm. With gassing by AHCI at the
1250.degree. C. temperature for 45 minutes, as used in Example 1,
Example 2 is a new powder with the solid solution lithium level of
about 0.65 ppm (actually 0.665 ppm). This is close to the targeted
level of 0.60 ppm. So both Examples 1 and 2 created a quartz powder
for use in cladding optic fiber cable, which new quartz powder is
acceptable to the fiber optics industry and had a reduced
attenuation, the objective of this invention. Example 1 is near the
highest final level of lithium in solid solution and Example 2 is
near the lower, but preferred level of lithium in solid solution in
the final powder. Both examples reduced attenuation when used as
cladding of an optic fiber cable.
[0025] Since the two powders with increased lithium doped into the
powder were both acceptable as an improved quartz powder for use as
cladding of an optic fiber cable, they defined the final solid
solution lithium level limitations of the invention. Example 1 was
a little over 0.80 ppm and Example 2 was about 0.60 ppm. From these
successful examples of improved quartz powders using the invention,
the invention is broadly defined as adding solid solution lithium
to high purity quartz powder to obtain a final level of lithium in
solid solution at a value of more than 0.50 ppm and less than 0.10
ppm, but preferable the tested levels of doped lithium is 0.6 to
0.8 ppm. More preferably a solid solution lithium level is about
0.60 ppm.
Example 1
[0026] The blended mass of powder had 1 ppm lithium and was gassed
by AHCI at 1250.degree. C. to give a solid solution lithium level
in the final product of 0.823 ppm. The attenuation was reduced to a
level below 0.187 dB/km.
Example 2
[0027] The blended mass of powder had 0.83 ppm lithium and was
gassed by AHCI at 1250.degree. C. to give a solid solution lithium
level in the final product of 0.665, which conforms to the desired
targeted level. Example 2 was tested and found the attenuation was
0.183 dB/km. This constitutes the primary object of the invention
to decrease the attenuation by using high lithium and preferably an
attenuation level less than 0.184 dB/km.
[0028] Broadly the added lithium of the invention is an improvement
because it reduces the attenuation obtained when purified quartz is
used as cladding of optic fiber cable over prior art purified
quartz powder. Example 1 was acceptable for improving commercial
purified quartz powder for cladding. However, Example 1 was
determined to be near the upper limit of the solid solution level
to accomplish the inventive improvement of purified quartz powder
for the fiber optic industry. Example 2 was preferred because it
reduced the lower attenuation of the invention to a much desired
level.
[0029] From Example 1 and Example 2 and other tests, it was found
the lithium nitrate from supply 44 was the preferred doping agent
for forming the solution at station 20 to obtain the objective of
the invention, i.e. increased solid solution lithium in commercial
high purified quartz powder. Further examples were generated using
method 10 to determine the merits of various doping agents.
Example 3
[0030] This example was formulated by suing Li.sub.2CO.sub.3 from
supply 46. It was determined that if the preferred maximum amount
of total lithium in the blended mass of powder from station 14,
i.e. 1.0 ppm, doping by gassing 70 of method 10 resulted in the
final solid solution of lithium to about 0.4 ppm which, is less
than the lithium level of the present invention. Consequently, more
lithium carbonate doping agent is needed to practice the invention.
It is less efficient in its doping action. It was found that LiCl
from supply 42 performed as Example 3. Consequently, testing to
obtain the lithium level of the invention established that lithium
nitrate from supply 44 is preferred, the other similar doping
agents from supplies 42 and 46 required higher levels of lithium at
station 14.
Example 4
[0031] After it was determined that the invention could be
performed using lithium doping agents from supplies 42, 44 and 46,
further alternative laboratory work was conducted to determine if
aluminum could help retain the lithium level after hot gassing at
station 70. In the first example LiNO.sub.3 and Al(NO.sub.3).sub.3
from supply 54 was used to make Example 4. It was found that by
making a stoichiometric solution a desired 1.0 ppm lithium level
for the blended mass of powder resulted in 0.4 ppm aluminum. After
the blended mass of powder was gassed at 1250.degree. C., the
resulting final solid solution lithium level was "about" 0.60, i.e.
it was 0.619. Consequently, Example 4 establishes that the
invention could be performed with an aluminum containing doping
agent, such as from supply 54. This additional of aluminum appears
to increase the amount of lithium from the level in the blended
powder at station 12 that was actually doped into the new, modified
powder at station 70. Alternative use of aluminum is not preferred
due to complexity and cost; however, it can be used to control the
resulting lithium doping levels.
Example 5
[0032] Since it was determined by Example 4 that aluminum can
affect lithium levels when using method 10, a test was then
conducted with an aluminum doping agent, not including the
preferred lithium nitrate. Lithium aluminate by itself from supply
52 was used in method 10. It has been was established that aluminum
could increase the lithium from the level at station 14 doped into
the powder. Consequently, next Example 5 started with a reduced
original level of lithium at station 14. In this test, lithium was
reduced from 0.10 ppm to a level of 0.6 ppm, i.e. the desired final
doped solid solution level after hot gassing. The test was to
determine the ability of aluminum in the doping solution to
increase the solid solution level of lithium after the hot gassing.
A first version of Example 5 merely heated the described blend from
station 14. It was found that heating did not substantially change
the lithium level, but the lithium was still merely at the level
coated on the original powder. Then the doping process of method 10
was fully performed to make the second version of Example 5. In
this version, the level of lithium in the blended mass of powder
from station 14 after the hot gassing or doping operation was
generally reduced from the undoped level 0.60 ppm to the doped
solid solution level 0.40 ppm. The small decrease in total lithium
from 0.60 to 0.40 in the final product does establish the fact that
aluminum helps retain the lithium level during the doping process,
but it is only an alternative to the preferred embodiments made
preferably from doping agent from supply 44. Examples 4 and 5 using
supplies 54 and 52 respectively confirms same benefit to using
aluminum in the doping solution 20. However, this concept is an
alternative in practicing the invention because of various factors
explained above.
[0033] In summary, samples with added lithium obtained solid
solution lithium levels in the range about 0.50 to 1.00 ppm. Such
modified powder has been shown to reduce attenuation caused by
cladding. This attenuation reduction is the objective of the
invention. It was determined that the lower level of added lithium
in solid solution, i.e. more than 0.50 ppm, is needed to obtain the
desired reduced attenuation. The upper level of added lithium in
solid solution, i.e. less than 1.00 ppm, was the value selected by
research and development team to prevent a higher level of lithium
that adversely affects other properties when using the new powder
for cladding.
SUMMARY
[0034] A new quartz powder with a particle size distribution PSD of
70-400 microns, which powder has been previously "purified", as
this term is used in the industry, is modified. This new "purified"
powder has broadly more than 0.50 ppm, but less than 1.00 ppm of
lithium (0.50 to 1.00 ppm) in solid solution. Preferably, the solid
solution lithium level is 0.60-0.80 ppm or more preferably the
level is about 0.60 ppm.
[0035] This new modified powder involves doping a previously
purified quartz power with a limited controlled level of lithium.
Such new method 10 is shown in the Figure. This new method is
preferably performed by adding a solution of lithium doping agent
to the previously purified quartz powder. The soaked powder is
aggressively agitated into a homogeneous mass and then this blended
mass is dried. The dry mass of particles coated with lithium are
gassed by a counter-current, high temperature (1,200-1,300.degree.
C.) procedure with a gas, such as AHCI. Additional lithium is doped
into the purified quartz powder to make a "new" quartz powder for
use in cladding to reduce attenuation. The total amount of lithium
in the final modified powder is determined by the amount of lithium
in the solution coated onto the powder that is actually "doped"
into the particles. This doped amount is always less than the
lithium originally coated onto the blended mass at station 14. The
desired results are to employ standard doping at station 70 to give
an increase in the lithium in solid solution in the quartz
powder.
[0036] Unimin has developed (invented) an available small grain
quartz powder to reduce attenuation when the quartz powder is used
for cladding of fiber optics. The new powder is uniquely modifying
previously purified quartz powder. In summary, the invention is a
new powder modified to reduce attenuation obtained by prior use of
purified quartz powder. The appended claims are also a part of the
disclosure of the invention herein described.
[0037] While considerable emphasis has been placed on the preferred
embodiments of the invention illustrated and described herein, it
will be appreciated that other embodiments, and equivalences
thereof, can be made and that many changes can be made in the
preferred embodiments without departing from the principles of the
invention. Furthermore, the embodiments described above can be
combined to form yet other embodiments of the invention of this
application. Accordingly, it is to be distinctly understood that
the foregoing descriptive matter is to be interpreted merely as
illustrative of the invention and not as a limitation.
* * * * *