U.S. patent application number 11/946417 was filed with the patent office on 2008-06-05 for discharge cell for ozonizer.
This patent application is currently assigned to SUMITOMO PRECISION PRODUCTS CO., LTD.. Invention is credited to Takashi MATSUNO.
Application Number | 20080128269 11/946417 |
Document ID | / |
Family ID | 39474450 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080128269 |
Kind Code |
A1 |
MATSUNO; Takashi |
June 5, 2008 |
DISCHARGE CELL FOR OZONIZER
Abstract
Decrease in the ozone concentration that becomes a problem when
high purity oxygen is used as a raw material gas is prevented. A
high purity alumina substrate having a high screen degree is used
as a dielectric. A catalytic substance to hinder the decrease of
the ozone concentration is fixed on the surface of the alumina
substrate as the dielectric by a baking fixing agent. The baking
fixing agent is a glass that becomes a paste form that is capable
of powder kneading the catalytic substance and attaching to the
surface of the dielectric, fixes the catalytic substance on the
surface of the dielectric by hardening by baking, and shows ozone
resistance and sputtering resistance under the production of ozone
in the discharge gap, and forms a functional film containing a
large amount of the catalytic substance and is stable on the
surface of the dielectric.
Inventors: |
MATSUNO; Takashi;
(Amagasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SUMITOMO PRECISION PRODUCTS CO.,
LTD.
Amagasaki-shi
JP
|
Family ID: |
39474450 |
Appl. No.: |
11/946417 |
Filed: |
November 28, 2007 |
Current U.S.
Class: |
204/242 |
Current CPC
Class: |
C01B 2201/34 20130101;
C01B 13/11 20130101; C01B 2201/12 20130101 |
Class at
Publication: |
204/242 |
International
Class: |
C25B 9/00 20060101
C25B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2006 |
JP |
2006-324109 |
Claims
1. A discharge cell for an ozonizer in which a dielectric is
arranged contacting at least one electrode in order to form a
discharge gap for generating ozone between a pair of electrodes,
wherein a functional substance to hinder a decrease of the ozone
concentration is fixed on the surface of the dielectric by a baking
fixing agent showing ozone resistance and sputtering resistance
under the production of ozone in the discharge gap.
2. The discharge cell for an ozonizer according to claim 1, wherein
the functional substance is Ti, W, Sb, Mn, Fe, Co, Ni, V or Zn, or
an oxide of these metals (MxOy).
3. The discharge cell for an ozonizer according to claim 1, wherein
the baking fixing agent is a glass that becomes a paste form that
is capable of powder kneading the functional substance and
attaching to the surface of the dielectric, fixes the functional
substance on the surface of the dielectric by hardening by baking,
and shows ozone resistance and sputtering resistance under the
production of ozone in the discharge gap.
4. The discharge cell for an ozonizer according to claim 3, wherein
the glass is SiO.sub.2--Al.sub.2O.sub.3--B.sub.2O.sub.3 based and
satisfies SiO.sub.2: 60 to 70% by weight, Al.sub.2O.sub.3: 1 to 10%
by weight, and B.sub.2O.sub.3: 10 to 20% by weight.
5. The discharge cell for an ozonizer according to claim 1, wherein
the dielectric is an alumina sintered plate with a purity of 80% or
more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a discharge cell used in a
discharge type ozonizer, and in more detail, relates to a discharge
cell for an ozonizer that is capable of bringing out the maximum
ability of the ozonizer even in the case where nitrogen is not
added or a small amount of nitrogen is added into the raw material
gas.
[0003] 2. Description of the Related Art
[0004] Discharge cells used in a discharge type ozonizer, called as
an ozonizer, are roughly divided into a plate type and a tube type.
Each of the discharge cells have a pair of electrodes arranged with
a gap therebetween, and have a configuration in which a dielectric
is arranged between the electrodes so as to contact at least one of
the electrode surfaces of the pair of electrodes to form a
discharge gap between the electrodes. Ozone gas is produced by
circulating a raw material gas such as oxygen in the discharge gap
with a condition in which a silent discharge is generated by
applying a prescribed high frequency high voltage in the discharge
gap.
[0005] Recently, a configuration has emerged in which a pair of
dielectrics is arranged inside each pair of electrodes and the
discharge gap is formed between the pair of dielectrics in order
not to expose the electrodes consisting of metal to the discharge
gap. Furthermore, by considering this as one unit, a multi-layer
structure is often used in which a plurality of the units is
layered in the thickness direction.
[0006] The dielectrics in the discharge cell are roughly divided
into a substrate type having rigidity in shape and a coated type in
which the surface of the gap side of the electrode having rigidity
is coated. In the case of the coated type, there is a problem such
that non-uniformity of the thickness distribution cannot be avoided
and this leads to non-uniformity of the gap amount of the discharge
gap, and the substrate type such as a ceramic plate that is hard
and has chemical resistance has recently becoming the
mainstream.
[0007] Incidentally, the ozonizer has begun to be used broadly in
semiconductor manufacturing equipment while being used in various
chemical processing equipment. In the case of an ozonizer for
semiconductor manufacturing used in formation of an oxide film,
ashing of a resist, cleaning of a silicon wafer, and the like,
there is a necessity of generating pure ozone gas with extremely
low contamination (metal impurities and particles, abbreviated as
contami below) because high cleanliness is demanded, and because of
this, oxygen gas with high purity is used as the raw material
gas.
[0008] Further, the configuration in which a pair of dielectrics
are arranged inside each pair of electrodes and the discharge gap
is formed between the pair of dielectrics as described above is
adopted as a structure of the discharge cell in order not to expose
the electrodes consisting of metal to the discharge gap. A high
purity alumina substrate having high mechanical strength and
superior in ozone resistance and sputtering resistance is
recommended as the dielectric here, especially a dielectric of the
substrate type from the viewpoints of maintaining cleanliness, and
the like.
[0009] Furthermore, from the necessity of producing high
concentrated ozone gas, decreasing the gap amount in the discharge
gap and making it uniform are attempted together with making high
purity oxygen gas, and a gap amount decreased to 0.2 mm or less can
be found at present.
[0010] In the case of using high purity oxygen gas as the raw
material gas, a problem has been known widely in which ozone
concentration of ozone gas rapidly decreases right after the
operation is started and the prescribed performance is not
exhibited. In order to solve this problem, adding a catalyst gas to
the high purity oxygen gas is considered to be effective, and high
purity nitrogen gas that is easily obtained in a semiconductor
manufacturing process is often used as the catalyst gas.
[0011] The case where the dielectric is the above-described high
purity alumina substrate is also not an exception, and performance
as an ozonizer is hardly exhibited in the case where the raw
material gas is high purity oxygen gas. On the contrary, in the
case of a high purity alumina substrate, it has been found that the
ozone concentration does not increase sufficiently even when
nitrogen gas is mixed into the oxygen gas. In more detail, in the
case of arranging a high purity alumina substrate on both surface
sides of the discharge gap, especially the effect of adding
catalyst gas can not be obtained sufficiently. This is considered
to be because impurities are extremely removed from the surface of
the dielectric contacting with the discharge gap.
[0012] From such circumstances, attempts of increasing the ozone
concentration without using a catalyst gas have proceeded in every
direction, one of the attempts is to use a functional substance in
the dielectric, and using titanium oxide as the functional
substance is described in Japanese Patent Application Laid-Open
(JP-A) No. 11-21110 and JP-A No. 2005-350336. Further,
effectiveness of a tungsten substance as the functional substance
is described in U.S. Pat. No. 5,932,180 and JP-A No.
2005-320223.
[0013] When the countermeasures described in JP-A Nos. 11-21110 and
2005-350336, U.S. Pat. No. 5,932,180 and JP-A No. 2005-320223 are
roughly divided from a viewpoint of a fixing method of the
functional substance to the dielectric, there are two methods
including a method of mixing into the dielectric and a method of
coating onto the surface of the dielectric, that is, formation of a
functional film on the surface of the dielectric. For example, in
the case where the functional substance is titanium oxide, in order
to achieve a high effect by mixing, mixing of 10% by weight or
more, desirably about 50% by weight becomes necessary. In the case
where the dielectric is an alumina substrate, when such large
amount of additive is added, sintering becomes difficult, strength
of the substrate remarkably decreases, and manufacturing itself may
become impossible depending on the case. Because of this, an added
amount of the functional substance is limited, and an effect toward
the ozone concentration becomes insufficient.
[0014] Stating further, an alumina substrate having a purity of
99.5% has been widely on the market for example as an alumina
substrate with less impurities. When the functional substance is
mixed into the dielectric, such alumina substrate on the market
cannot be used, and a separately made substrate becomes necessary.
Because of this, there is a practical problem that the cost of the
dielectric raises remarkably. The reason that the content becomes
large in the case of mixing the functional substance into the
dielectric is that the exposure amount of the functional substance
on the surface of the dielectric has to be secured at a certain
amount or more, and because of this, its content cannot help being
large naturally.
[0015] On the other hand, coating of the functional substance onto
the surface of the dielectric substrate has an advantage that a
large amount of the functional substance on the surface of the
dielectric can be secured, and a functional film with 100% of the
functional substance can be formed on the entire surface of the
dielectric with flame spraying or vapor deposition. However, in the
flame spraying or the vapor deposition of the functional substance,
surface roughness of the functional film formed on the surface of
the dielectric becomes large and management of the film thickness
is difficult, and unevenness of the distribution of the gap amount
in the discharge gap becomes large. This becomes a cause of
decrease of the ozone concentration. Further, a high cost required
in the coating becomes a problem. Furthermore, the functional film
formed with flame spraying or vapor deposition is easily peeled
because it is in the state of simply being placed on the surface of
the dielectric. When the functional film is peeled, not only the
contami is generated, but also the primary effect by the functional
substance decreases, and unevenness is generated on the surface of
the dielectric and it becomes a cause of decreasing the ozone
concentration.
[0016] Further, in order to give a small and uniform gap amount in
the discharge gap, a rib may be formed on the surface of the
dielectric with a glass substance, or the like (refer to JP-A No.
2005-68003). In the case of forming a film of the functional
substance on the surface of the dielectric with flame spraying or
vapor deposition, a film of the functional substance is formed on
the entire surface of the dielectric, and then a rib is formed on
top of the film. Because the functional film consisting of the
functional substance is easily peeled, there are problems that the
formation of the rib is difficult and that the formed rib is peeled
when the rib is formed on top of the film. That is, a rib to secure
the gap amount is required to be formed directly on the high purity
alumina substrate that is the main body of the dielectric.
[0017] Moreover, in the case where the functional substance is a
tungsten substance, in U.S. Pat. No. 5,932,180, metal tungsten is
applied on the surface of the dielectric. However, this metal
tungsten is changed to a tungsten oxide (WO.sub.3) due to a strong
oxidation power of ozone produced in the discharge gap, and this
WO.sub.3 is considered to actually cover the surface of the
dielectric. Incidentally, WO.sub.3 is an insulator.
[0018] Further, in JP-A No. 2005-320223, a conductive tungsten
oxide having a prescribed resistivity is applied on the surface of
dielectric contacting the discharge gap and the surface of the
electrodes. Among tungsten oxides, WO.sub.3 is an electric
insulator. However, WO.sub.2 has good conductivity, and the
resistivity of the tungsten oxide can be actually changed by
changing the oxygen amount. However, because this conductive
tungsten oxide also contacts with the discharge gap and directly
contacts to ozone, WO.sub.x (x<3) is also considered to change
to WO.sub.3 that is an insulator when it is used.
[0019] That is, although expression of the technique described in
Reference Document 3 and the technique described in Reference
Document 4 differs from each other, WO.sub.3 is considered to be
applied as a catalytic substance on the surface contacting the
discharge gap in the discharge cell that is used actually.
SUMMARY OF THE INVENTION
[0020] An objective of the present invention is to provide a
discharge cell for an ozonizer that can effectively prevent a
decrease of ozone concentration in the case where nitrogen is not
added or a small amount of nitrogen is added while avoiding peeling
of a functional substance from the surface of a dielectric and a
harmful influence to a rib for forming a gap without mixing the
functional substance into the dielectric.
[0021] In order to achieve the above-described objective, the
present inventors devotedly investigated a method of effectively
fixing the functional substance on the surface of the dielectric by
giving up mixing of the functional substance into the dielectric
and focusing on the application of the functional substance onto
the surface of the dielectric. That is, using a less expensive
product on the market such as a high purity alumina substrate as
the dielectric, a new method replacing flame spraying and vapor
deposition as a means of attaching and fixing the functional
substance on the surface was investigated from various angles. As a
result, the following facts were discovered.
[0022] In the application technique of the functional substance up
until now, the technique has been developed by attaching the
functional substance itself on the surface of the dielectric.
Typical examples are flame spraying and vapor deposition. However,
most of the functional substances are primarily a fine powder as
seen in titanium oxide. In the flame spraying and the vapor
deposition, film formation is performed using a target obtained by
sintering a fine powder of the functional substance. However, it is
as described above that the functional film formed in such a manner
has many problems.
[0023] Accordingly, the present inventors concentrated their power
into development of a fixing means by converting a concept into a
direction of fixing a fine powder of the functional substance as it
is onto the surface of the dielectric. As a result, it was
discovered that a large amount of the functional substance can be
fixed stably onto the surface of the dielectric by mixing the fine
powder of the functional substance into a glass paste, attaching it
onto the surface of the dielectric, and baking. Further, at the
same time, it became clear that changes in quality due to ozone and
sputtering, and generation of contami due to the sputtering can be
suppressed by selecting a composition of the paste, that adjustment
of the film thickness is easy by using screen printing or the like,
and formation of a thin film such as those having a thickness of a
few .mu.m is possible, that a film formation avoiding a part of a
rib for forming a gap is possible and a harmful influence is not
given to the rib, and the like.
[0024] The discharge cell for an ozonizer in the present invention
is developed with such knowledge as a basis and in which an
ozonizer contains a dielectric arranged to contact at least one of
the electrodes in order to form a discharge gap for generating
ozone between a pair of the electrodes, and a functional substance
to hinder a decrease of the ozone concentration is fixed on the
surface of the dielectric by a baking fixing agent showing ozone
resistance and sputtering resistance under ozone production in the
discharge gap.
[0025] In the discharge cell for an ozonizer in the present
invention, a functional substance such as titanium oxide or
tungsten oxide is fixed on the surface of the dielectric in a film
form in a powder state by a baking fixing agent. By this, a
functional film containing a large amount of the functional
substance exceeding 50% by weight is stably formed on the surface
of the dielectric, and an effect of preventing decrease of the
ozone concentration by a functional substance can be exhibit to the
full. On top of that, for example, an alumina substrate on the
market of 99.5% purity can be used as it is as the dielectric.
Furthermore, because the baking fixing agent shows ozone resistance
and sputtering resistance, there is almost no fear that the fixing
agent itself becomes a source of contami.
[0026] The functional substance is a metal or its oxide
M.sub.xO.sub.y (M is a metal element), specifically it is a metal
such as Ti, W, Sb, Mn, Fe, Co, Ni, V or Zn, or an oxide of these
metals (for example, TiO.sub.2, WO.sub.2, WO.sub.3,
Sb.sub.2O.sub.3, Mn.sub.3O.sub.4, Fe.sub.2O.sub.3, CO.sub.3O.sub.4,
NiO, V.sub.2O.sub.5, and ZnO), and these powders can be used alone
or in a mixed state. The particle size of the powder is preferably
0.1 to 10 .mu.m on average. This is because the film thickness of
the functional film is about 10 .mu.m as described later, its
powder is required to be finer than this, and on the other hand,
handling of an extremely fine particle becomes difficult.
[0027] The baking fixing agent is preferably a substance that is in
a form of a paste that is capable of powder kneading the functional
substance and attaching to the surface of the dielectric, and that
shows ozone resistance and sputtering resistance under the
production of ozone in the above-described discharge gap in
addition to fixing the functional substance onto the surface of the
dielectric by hardening with baking. Typical baking fixing agent is
a glass, specifically a SiO.sub.2--Al.sub.2O.sub.3--B.sub.2O.sub.3
glass is preferable, and among these, a glass is especially
preferable in which the amount of SiO.sub.2 is 60 to 70% by weight,
the amount of Al.sub.2O.sub.3 is 1 to 10% by weight, and the amount
of B.sub.2O.sub.3 is 10 to 20% by weight. When the glass is used,
it is in a fine powder state, it becomes in a paste state by mixing
with a binder called a vehicle in which a resin is dissolved by a
solvent, and the film formation and control of the film thickness
are made easy by making this into a paste by mixing with a fine
powder of the functional substance and making screen printing and
the like onto the surface of the dielectric possible. By baking, a
glass powder in the paste becomes amorphous and the binder
disappears, and as a result, a solid thin functional film in which
a fine powder of the functional substance is dispersed and mixed
into the glass is formed on the surface of the dielectric.
[0028] The particle size of the glass powder is preferably 0.1 to
10 .mu.m on average. This is because mixing becomes easy when the
powder of the functional substance and a glass powder having the
particle size in this range are mixed. Further, the viscosity in
the paste state is preferably 200 to 300 Pas. This is because the
viscosity of this range is suitable for application in screen
printing and the like.
[0029] The content of the functional substance is preferably 0.5 to
70% by weight in a hardened state after baking, and more preferably
40 to 60% by weight. This is because in the case where the content
of the functional substance is too small, the effect of preventing
a decrease of the ozone concentration becomes insufficient although
fixing strength of the functional substance onto the surface of the
dielectric is sufficient, and in the case where it is too large on
the contrary, the fixing strength of the functional substance onto
the surface of the dielectric decreases although there is no
problem in the effect of preventing a decrease of the ozone
concentration.
[0030] The film thickness of the functional film consisting of a
mixture of the functional substance and the fixing agent is
preferably 0.1 to 20 .mu.m in a hardened state. In the case where
the film thickness is too thin, there is a risk that the effect of
preventing a decrease of the ozone concentration is insufficient,
and on the contrary, in the case it is too thick, uniformity of the
film thickness distribution decreases, and it becomes difficult to
make the gap amount in the discharge gap uniform.
[0031] The dielectric is preferably a high purity ceramic, and
especially preferably an alumina sintered plate with a purity of
80% or more, 90% or more, particularly 95% or more, and more
particularly an alumina sintered plate of 99% or more is
preferable. A purpose of using the alumina sintered plate is to
secure cleanliness due to ozone resistance and sputtering
resistance.
[0032] The thickness of the dielectric is preferably 0.05 to 1 mm.
When it is too thin, the voltage resistance value becomes low, and
securing of the necessary mechanical strength becomes difficult. In
the case where it is too thick, the distance between the electrodes
becomes large, and the discharge voltage becomes high.
[0033] Use of a conductive plate as the electrode structure is
common. However, a film in which the electrode is formed on the
surface of the anti-discharge gap side of the dielectric as a thin
film is also preferable from the viewpoing of preventing abnormal
discharge. The material of the electrode film includes Cu, Ag, Al,
and Au. The thickness of the electrode film is preferably 5 to 70
.mu.m. When it is too thin, heat is generated at a narrow part of
the pattern width, and there is a fear that breaking of a wire
occurs. In the case where it is too thick, there are many technical
problems, and the formation of a uniform film thickness is
difficult. Metal foil adhesion, sputtering, vapor deposition, flame
spraying, screen printing, or the like is preferable as the forming
method of the electrode film from the viewpoint of making the film
thickness uniform.
[0034] Because a functional substance for preventing a decrease of
the ozone concentration is fixed on the surface of the dielectric
using a baking fixing agent in the discharge cell for an ozonizer
in the present invention, a highly concentrated functional
substance that is difficult to be contained in the dielectric can
be made to exist on the surface of the dielectric, and the cell is
superior in the effect of preventing a decrease of the ozone
concentration by the functional substance. Because of this, the
ability of the ozonizer can be brought to full without adding
nitrogen into oxygen gas or with adding a small amount of nitrogen.
On top of that, because the dielectric is not processed, a less
expensive product on the market and a general-purpose material can
be used as the dielectric, and a cell cost can be kept low.
Furthermore, being different from the formation of the functional
film with flame spraying and welding, because film fixing strength
is high, peeling and falling-out can be prevented during a cell
operation. Further, a film forming coat is less expensive, and from
this respect, a cell cost can be kept low. Furthermore, film
thickness control is easy, formation of a very thin film with a
thickness of a few .mu.m is possible, and there is no risk of
having a harmful influence on a rib for forming a discharge
gap.
BRIEF DESCRIPTION OF THE DRAWING
[0035] FIG. 1 is a schematic cross-sectional view of the discharge
cell for an ozonizer showing one embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] In the following, an embodiment of the present invention is
explained based on the drawing. FIG. 1 is a schematic
cross-sectional view of the discharge cell for an ozonizer showing
one embodiment of the present invention.
[0037] The discharge cell for an ozonizer in this embodiment is
equipped with plate-shaped dielectrics 10, 10 which are arranged in
parallel at a prescribed space therebetween. The dielectrics 10
consist of a high purity alumina sintered substrate available from
the market.
[0038] A seal part 11 and a rib 12 are provided on opposing
surfaces of the dielectrics 10, 10 in order to form a discharge gap
20 with a prescribed gap between the opposing surfaces. These
consist of a glass sintered material, the seal part 11 is located
at a peripheral part between the counter surfaces, a plurality of
the ribs 12 are provided inside of the seal part 11, the
dielectrics 10, 10 are bonded and unified with a prescribed space
between them by bonding the ribs that are corresponding to each
other with a glass sealing agent 13, and the discharge gap 20 of
which the circumference is sealed is formed between the opposing
surfaces.
[0039] The seal part 11 and the rib 12 are provided on both
opposing surfaces of the dielectrics 10, 10 here. However, they may
be provided on one of the surfaces.
[0040] The discharge gap 20 is connected to a raw material gas flow
path and an ozone gas flow path formed in the perpendicular
direction to the peripheral part of the dielectrics 10, 10. A
smaller gap amount of the discharge gap 20 is better in order to
make the purity of ozone gas high, specifically 200 .mu.m or less
is preferable, more preferably 100 .mu.m or less, and especially
preferably 50 .mu.m or less.
[0041] A functional film 14 is provided farther inside than the
seal parts 11, 11 of the opposing surfaces of the dielectrics 10,
10 together with the rib 12. The functional film 14 is a thin film
formed by fixing a fine powder of the catalytic substance like
TiO.sub.2 that hinders a decrease of the ozone concentration on the
counter surface in a film form by a baking fixing agent consisting
of glass, and formed on a part excluding the rib 12 that is farther
inside from the seal part 11. A step of forming the functional film
14 is normally before bonding the dielectrics 10, 10 and after
forming the seal part 11 and the rib 12. However, the seal part 11
and the rib 12 can be formed at the same time. The film thickness
of the functional film 14 is sufficiently smaller than the height
of the seal part 11 and the rib 12, and is a few .mu.m.
[0042] On the surface of the anti-discharge gap side (back side) of
the dielectrics 10, 10, film-formed electrodes 30, 30 are formed
individually with metal foil adhesion remaining on the peripheral
part in a frame form, a high frequency high voltage power supply 40
is connected to this. The one terminal of the power supply 40 is
grounded, the electrode 30 connected to this terminal is a low
voltage electrode, and the other electrode 30 is a high voltage
electrode.
[0043] On farther back side of the dielectrics 10, 10, a
plate-shaped cooling body or the like is provided through an
insulating plate, and with this, a discharge cell unit is
configured. The plate-shaped cooling body may be a ceramic plate
the same as the dielectric 10, or it may be a metal plate. Any
cooling body has a configuration in which a coolant circulates
inside in the direction parallel to the plate surface. Then, a
discharge cell for an ozonizer is formed by layering such a
discharge cell unit in the thickness direction.
[0044] In the operation of the ozonizer, high purity oxygen gas is
supplied to the discharge gap 20 of the discharge cell as a raw
material gas. The purity of the oxygen gas is preferably 99.9% or
more from the viewpoint of cleanliness or the like, and especially
preferably 99.99% or more. Further, a prescribed high frequency
high voltage is applied between the electrodes 30, 30 to generate
silent discharge in the discharge gap 20. Furthermore, cooled water
as the coolant is supplied in the cooling body arranged on back
side of the electrodes 30, 30.
[0045] The high purity oxygen gas circulating in the discharge gap
20 is exposed to the silent discharge, ozonized, and ozone gas is
produced. Because a high purity alumina sintered substrate is used
in the dielectrics 10, 10 and high purity oxygen gas is used as a
raw material, normally the original performance of the ozonizer is
not exhibited, and the ozone concentration of the ozone gas is low.
However, because the functional film 12 containing a large amount
of the catalytic substance such as TiO.sub.2 is formed on the
opposing surfaces of the dielectrics 10, 10 and a large amount of
the catalytic substance is exposed to the discharge gap 20, high
purity ozone gas is produced.
EXAMPLES
[0046] Next, an advantage of forming the functional films 14, 14 on
the opposing surfaces of the dielectrics 10, 10 is explained using
a case where the catalytic substance in the functional films 14, 14
is TiO.sub.2 and NiO.
[0047] In the above-described discharge cell for an ozonizer, a
high purity alumina powder sintered substrate with a purity of
99.5% available from the market was used as the dielectric. The
thickness is 0.5 mm. The area of the discharge gap is 100 cm.sup.2,
and the gap amount is 0.1 mm (100 .mu.m). Oxygen gas with a purity
of 99.99% or more was supplied as a raw material gas with a flow
rate of 1 L/min and a pressure of 0.2 MPa. Power supply was set to
be the maximum power of the ozonizer. The ozone concentration of
the produced ozone gas was 10 g/m.sup.3 (N) and was extremely low
compared with the objective ozone concentration 200 g/m.sup.3
(N).
[0048] 0.5 vol % of nitrogen gas was added to the above-described
high purity oxygen gas. However, the ozone concentration was still
10 g/m.sup.3 (N). That is, the effect of adding nitrogen gas was
not realized.
[0049] A functional film was formed on a part excluding the rib
inside of the seal part on the dielectric counter surface with the
following method. Three types of metal oxide powders of TiO.sub.2,
NiO and WO.sub.3 and three types of metal powders of Ti, Ni and W
were used as the functional substance. The maximum particle size of
the oxide powder is 5 .mu.m. Although some of the metal powders
have a particle size larger than 5 .mu.m, there is no adverse
effect on formation of the functional film because the large
particle size is reduced during the mixing process. The baking
fixing agent is SiO.sub.2--Al.sub.2O.sub.3--B.sub.2O.sub.3 glass,
it satisfies SiO.sub.2: 60 to 70% by weight, Al.sub.2O.sub.3: 1 to
10% by weight, and B.sub.2O.sub.3: 10 to 20% by weight, and the
particle size is about 3 .mu.m in average.
[0050] A mixture of a functional substance powder and a glass
powder was made to be a solid, and it was made to be a paste by
adding a vehicle. The compounded ratio and paste viscosity are
shown in Table 1. That is, the compounded ratio of the solid to
vehicle was 60:40 in % by weight, and there were three types of
compounded ratios of the functional substance powder to the glass
powder in the solid that were 18:42 (3:7), 24:36 (2:3), and 30:30
(1:1). That is, an amount of the functional substance in the solid
was very large and being 30% by weight, 40% by weight, and 50% by
weight, and it was a level that cannot be contained in an alumina
sintered substrate.
TABLE-US-00001 TABLE 1 CONDI- TION 1 CONDITION 2 CONDITION 3
FUNCTIONAL 18 24 30 SUBSTANCE POWDER (wt %) GLASS POWDER (wt %) 42
36 30 VEHICLE (wt %) 40 40 40 PASTE TiO.sub.2 260 275 300 VISCOSITY
NiO 230 240 245 (Pa s) WO.sub.3 205 220 260 Ti 206 221 240 Ni 224
243 255 W 218 239 250 OZONE TiO.sub.2 198 253 320 CONCENTRA- NiO
172 215 288 TION WO.sub.3 173 201 226 (g/m.sup.3 N) Ti 230 244 263
Ni 120 173 198 W 174 202 208
[0051] After forming the seal part and the rib, the paste prepared
in such a manner was screen-printed in a thickness of about 15
.mu.m on a part excluding the seal part and the rib on the surface
of the above-described alumina substrate, and it was baked with a
condition of 850.degree. C. for 10 minutes. The vehicle in the
paste was removed by baking, and a functional film in which the
functional substance powder was fixed by the glass was formed on a
part excluding the seal part and the rib on the surface of the
alumina substrate. The thickness of the functional film was about 9
.mu.m. Each height of the seal part and the rib was made a little
larger so that 0.1 mm (100 .mu.m) as the gap amount of the
discharge gap was secured. The formed functional film attached
firmly on the substrate surface and the film itself fixed the oxide
powder firmly in spite that it contained a large amount of the
catalytic substance.
[0052] Moreover, the seal part and the rib were formed by mixing a
glass powder (SiO.sub.2: 60 to 70% by weight, Al.sub.2O.sub.3: 1 to
10% by weight, and B.sub.2O.sub.3: 10 to 20% by weight) and an
alumina powder, applying the mixed powder that had been made into a
paste by mixing a binder, and baking with a condition of
850.degree. C. for 10 minutes. The height of the film formed with
one time application and baking was about 25 .mu.m, and the
application and baking were repeated until the prescribed height is
secured. The re-melt temperature after baking as a characteristic
of a baked glass was considerably higher than the baking
temperature. Because of this, there was no risk of softening and
melting of the seal part and the rib part that had been formed in
advance in the formation of the seal part and the rib and
furthermore the formation of the functional film.
[0053] A discharge cell for an ozonizer was assembled using the
produced dielectric, and the ozonizer was operated with the same
condition as described above. The ozone concentration is written
down in Table 1. In the case of any dielectrics, either the
objective ozone concentration [200 g/m.sup.3 (N)] was secured or an
ozone concentration closer to the objective was secured although
the objective was not secured, and an ozone concentration exceeding
300 g/m.sup.3 (N) at the highest was observed. Further, the contami
was not observed in the produced ozone gas.
* * * * *