Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-05-17
2003-02-11
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S435000, C204S421000, C204S291000, C029S746000
Reexamination Certificate
active
06517694
ABSTRACT:
BACKGROUND
High temperature and high pressure aqueous solutions have an enormous number of applications in sciences and industries, including geosciences, synthesis and deposition of ceramics, supercritical water oxidation, fossil, nuclear, and geothermal power generation, pulp and paper production, and chemical productions. Potentiometric and pH measurements provide important information for studying thermodynamics and electrochemistry in high temperature aqueous solutions and in-situ monitoring and control of physical and chemical processes, e.g. speciation and corrosion, in industrial systems. More and more electrochemical sensors are used in industries. However, there are only a few devices having pH sensing electrodes for use during measurement in high temperature environments. Currently, the only primary and reliable pH sensing electrode available for use at high subcritical and supercritical temperatures (>374° C.) is the Yttria-Stabilized Zirconia (YSZ) membrane electrode.
Two typical designs of YSZ electrodes used in the laboratory are shown in
FIGS. 1 and 2
. The electrode
10
of
FIG. 1
is a YSZ tube
12
with a closed tip
14
and an open top
22
. The closed tip
14
of the tube
12
is filled with a small amount of Hg|HgO paste
16
. A Platinum (Pt) wire
18
that is partially covered with a shrinkable PTFE tube is placed in the tube
12
, whereby the uncovered portion of the PT wire
18
is inserted into the Hg|HgO paste
16
. The tube
12
is then filled with zirconia sand
20
. The Pt wire
18
is used to provide electrical contact. The open top
22
of the tube
12
is typically sealed with epoxy
24
over the sand
20
. The whole tube
12
is fitted into a CONAX fitting
26
at the top
22
of the tube
12
whereby the CONAX fitting
26
is a tube fitting used for gripping and sealing a tube. The wall of the tube
12
is the boundary separating the high pressure fluid (typically 300 bars) and the low pressure outside of the system. Under high pressures, the tube
12
will break, especially at the point where the CONAX fitting
26
grips t he YSZ tube
12
. The electrode
27
of
FIG. 2
is designed to eliminate breaking at the gripping location of the CONAX fitting
26
. The electrode
27
utilizes complex techniques of joining ceramics to metals, such as brazing, to produce a tube
12
having an upper portion
28
of metal and a lower portion
30
of ceramic. Thus, allowing the CONAX fitting
26
to grip the metal upper portion
28
part of the tube
12
. The problem with the metal-ceramic electrode
27
of
FIG. 2
is that the metal-ceramic joint is normally not strong enough to sustain high temperatures and high pressures for a long period of time. Other methods of joining metals to ceramics have been tried or proposed. However, these methods are either not reliable or extremely costly.
The object of the present invention is to provide a more reliable YSZ membrane electrode.
SUMMARY OF THE INVENTION
The present invention is an improved yttria-stabilized zirconia electrode having a ceramic tube. The electrode is improved by replacing the method of sealing the electrode with an epoxy seal and filling the tube with a ceramic glue without completely filling the tube. The ceramic glue is added in a small amount and the ceramic glue is heated in the tube before the next small amount of ceramic glue is added, until the final amount of ceramic glue is added and heated. Also, an area of cover on a wire in an area between a top of the ceramic glue and a top of the tube is partially removed. A sealing glue above the top of the ceramic glue that adheres to the wire at the removed area of the cover, adheres to the tube and seals the top of the tube. Finally, an outside portion of the wire which extends beyond the top of the tube is gripped with a CONAX fitting, instead of the fitting gripping the tube.
REFERENCES:
patent: 4264424 (1981-04-01), Niedrach
patent: 4576667 (1986-03-01), Taylor et al.
patent: 5238553 (1993-08-01), Hettiarachchi et al.
patent: 5556534 (1996-09-01), Alcock et al.
patent: 6357284 (2002-03-01), Kim et al.
Lvov Serguei
Ulyanov Sergey M.
Zhou Xiangyang
Bell Bruce F.
Elnitski, Jr. John J.
Penn State Research Foundation
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