Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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,¦ TITLE OF THE INVENTION
~igh-power radiator
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a high-power radiator,
in particular for ultraviolet light, having a discharge
space which is filled with a filling gas emitting radia-
tion under discharge conditions and whose wall~ are
formed by a first and a second dielectric provided with
metallic latticed or reticular first and second electro-
des on its surfaces remote from the discharge space, and
having an alternating-current source connected to the
first and second electrodes for supplying the discharge.
In this connection, the invention proceeds from
the prior art which emerges, for instance, from
EP-A O 254 111.
Discus~ion o~ Backaround
The industrial use of photochemical processes is
heavily dependent on the availability of suitable W
sources. The conventional W radiators provide low to
medium UV intensities at a few discrete wavelengths such
as, for examplé, the low-pressure mercury lamps at 185 nm
and, in particular at 254 nm. Really high UV powers are
obtained only from high-pressure lamps (Xe, Hg) but these
then distribute their radiation over a larger wavelength
range. The new excimer lasers have made a few new wave-
lengths available for fundamental photochemical experi-
ments and are at present suitable for an industrial
process probably only in exceptional cases for cost
reasons.
The EP patent application mentioned in the
introduction or, alternatively, the conference reprint
entitled ~Neue W - und YUV- Excimerstrahler" ("New W and
V W excimer radiators~) by U. Kogelschatz and B. Eliasson
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distributed at the Tenth Seminar of the Society of German
Chemists, Specialist Group on Photochemistry, in Wurzburg
~FRG) on 18-20 November 1987, describe a new excimer
radiator. This new type of radiator is based on the
principle that excimer radiation can also be generated in
dark electrical discharges, a type of discharge which is
used on a large industrial scale in the generation of
ozone. In the current filaments of this discharge, which
are only present for a short time (< 1 microsecond),
electron impact excite~ noble-gas atoms, which r~act
further to form excited molecular complexes (excimers).
Said excimers live only for a few hundred nanoseconds and
give off their bonding energy in the form of W radiati-
on when they decompose.
The construction of such an excimer radiator
largely corresponds to that of a conventional ozone
generator including the power supply, with the essential
difference that at least one of the electrodes and/or
dielectric layers bounding the discharge space is trans-
parent to the radiation generated. In addition to the
high W transmission, said electrodes must also have,
inter alia, the following properties: good electric
current conductivity, low cost, good flexibility in order
to produce as intimate as possible a contact with the
dielectric, and long service life. The long service life
reguires, in particular, a low chemical reactivity with
the environment of the radiator. If it is desired to use
the radiator as a light source in chemical reactors, even
chemi~al inertness towards some substances is absolutely
necessary for many applications.
SUMMARY OF THE INVENTION
Proceeding from the prior art, the o~ject of the
invention is to provide a high-power radiator, in par-
ticular for W or V W radiation, whose electrodes are
ideally protected against environmental effects in
addition to high W transmission.
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To achieve this object, provision is made,
according to the invention, that at least the first
electrodes are provided with a protective layer or
embedded in such a layer.
A radiator having such a structure fulfills all
the practical requirements:
- The electrodes exposed to the environment are
protected against chemical attacks ~prolonging of
the service life);
10 - The electrodes are also protected, in addition,
against physical attacks: discharges cause erosion;
erosion removes electrode material which deposits on
the transparent areas of the dielectric and reduces
the transparency at those points;
15 _ If the environment itself is a gas or liquid to be
treated with W radiation, a metallic contact with
this substance is avoided in order not to initiate
any additional chemical reactions in which metals
are involved (chemical inertness);
20 - Any discharges (for example, Korona) in the environ-
ment of the electrodes onto the dielectric or to
voltage-carrying parts situated in the vicinity, or
surface discharges over the dielectric are avoided
by better contact with the dielectric; the better
electrical insulation of the electrodes prevents, in
addition, undesirable energy-consuming discharges.
The invention can be implemented practically in
various ways. In addition to the mere coating of the
metallic wires, for example, by immersing the electrodes
in a suitable bath, the immersion of the completely
assembled radiator in a bath is advantageously possible.
Coatings with so-called thick-film casting compounds
which result in the advantage of an easy-to-clean outer
surface of the radiator are also possible.
3~ Suitable as coating or embedding material are,
in particular, dielectric substances which make a good
contact to the dielectric of the radiator and are at the
same time easy to apply. If materials are also used in
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this process which are W-curing, they can be extremely
rapidly cured by the radiator itself.
~ Particular developments of the invention and the
further advantages achieved therewith are explained in
S greater detail below by reference to the drawings.
BRIEF DESCRIPTION OF TH~ DRAWINGS
A more complete sppreciation of the invention and
many of the attendant advantages thereof will be readily
obtained as the same becomes better understood by refer-
ence to the following detailed description when con-
sidered in connection with the accompanying drawings,
wherein embodiments of h.igh-power radiators are shown in
extremely simplified form; in the drawing
Figure 1 shows a cylindrical W radiator of known
construction;
Figure 2 shows a portion of the outer dielectric tube of
a W radiator with outer electrode which is
disposed thereon and composed of round wire
coated with dielectric material;
Figure 3 show~ a portion of the outer dielectric tube of
a W radiator with outer electrode which is
disposed thereon and composed of round wire,
the entire outer surface being provided with a
coating material;
Figure ~ shows a portion of the outer dielectric tub~ of
a UV radiator with outer electrode which is
disposed thereon and composed of round wire
situated in the depressions in the outer
dielectric tube which are filled in their turn
with coating material;
Figure 5 shows a portion of the outer dielectric tube of
a UV radiator with outer electrode which is
disposed thereon and is composed of round wire,
with a smooth outer dielectric tube and a
thick-film casting compound in which the
electrodes are embedded;
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Figure 6 shows a portion of a UV radîator which emits
radiation both outwards and inwards.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like
reference numerals designate identical or corresponding
parts throughout the several views, the W high-power
radiator shown diagrammatically in Figure 1 comprises an
outer dielectric tube 1, for example made of quartz
glass, and an inner dielectric tube 2 which is disposed
concentrically therewith and whose inner wall is provided
with an inner electrode 3. The annular space between the
two tubes 1 and 2 forms the discharge space 4 of the
radiator. The inner tube 2 is inserted in a gastight
manner into the outer tube 1, which has previously been
filled with a gas or gas mixture which emits W or VUV
radiation under the influence of dark electric
discharges.
The outer electrode 5 used is a metal net or
metal lattice which extends over the entire circumference
of the outer tub~ 1. Both the outer electrode 5 and the
outer dielectric tube 1 are transparent to the W ra-
diation generated.
The electrodes 3 and 5 are routed to the two
poles of an alternating-current source 6. The alternat-
ing-current source basically corresponds to those such as
are used to feed ozone generators. Typically it delivers
an adjustable alternating voltage in the order or mag-
nitude of several 100 volts to 20,000 volts at frequen-
cies in the range of industrial alternating current up to
- 30 and including a few 1000 k~z, depending on the electrode
geometry, pressuxe in the discharge space 4 and composi-
tion of the illing gas.
The filling gas is, for example, mercury, noble
gas, noble gas/metal vapor mixture, noble gas/halogen
mixture, optionally with the use of an additional further
noble gas, preferably Ar, He, Ne, as buffer gas.
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Depending on the desired spectral composition of
the radiation, a substance/substance mixture in
accordance with the table below may be used in this
connection:
5 Fillinq qas Radiation
Helium 60 - 100 nm
Neon 80 - 90 mn
Argon 107 - 165 nm
Argon + fluorine 180 - 200 nm
Argon + chlorine 165 - 190 nm
Argon + krypton + chlorine 165 - 190, 200-240 nm
Xenon. 160 - 190 nm
Nitrogen 337 - 415 nm
Xrypton 124, 140 - 160 nm
Krypton + fluorine 240 - 255 nm
Krypton + chlorine 200 - 240 nm
Mercury 185, 254, 320-370, 390-420 nm
Selenium 196, 204, 206 nm
Deuterium 150 - 250 nm
Xenon + fluorine 340 - 360 nm, 400-550 nm
Xenon + chlorine 300 - 320 nm
In addition, a whole of number of further filling
gases are possible:
- a noble gas (~r, He, Kr, Ne, Xe) or Hg with a gas or
vapor composed of F2, I2, Br2, C12 or a compound which
releases one or more F, I, Br or Cl atoms in the
discharge;
- a noble gas (Ar, He, Kr, Ne, Xe) or Hg with 2 or a
compound which releases one or more O atoms in the
discharge;
- a noble gas (Ar, He, Kr, Ne, Xe) with Hg.
In the dark electric discharge (silent discharge)
which forms, the electron energy distribution can be
ideally adjusted by the thickness of the dielectrics and
their properties and the pressure andJor temperature in
the discharge space.
When an alternating voltage is applied between
the electxodes 3, 5, a multiplicity of discharge channels
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(partial discharges) forms in the discharge space 4.
These interact with the atoms/molecules of the filling
- gas, and this ultimately results in W or VUV radiation.
In the portion shown in Figure 2, the individual
wires 7 of the outer electrode are provided with a
coating 8. In the simplest case, this may be composed of
wire enamel. Such insulated wires with baked enamel are
standard in transformer construction. Depending on the
enamel thickness and the type of enamel, the additional
voltage advantage due to the enamel can be optimized with
respect to the voltage of the discharge.
In the portion shown in Figure 3, not only the
wire but the entire radiator surfa~e is provided with a
coating 8a of clear enamel. Although this arrangement
reduces the W radiator output of some wavelengths, it
can be produced particularly easily by immersing the
completely assembled radiator in a bath of enamel, or by
spraying on an enamel or, alternatively, by brushing it
on and then curing it. For a 308 nm radiation and a
typical layer thickness of 1 to 2 ~m, the transmission is
in this case more than 80%. Preferably, UV-curiny clear
enamels are used in this process which can be cured
extremely rapidly by the radiator itself and for which
the transmission improves after the curing because of the
chemical transformation.
In the arrangement shown in Figure 4, the in-
dividual wires 7 of the outer electrode 5 are situated in
depressions in the outer dielectric tube 1 and are
completely embedded in the coating 8b, for example a
clear enamel. The enamel layer ~b then has alternately
varying thickness along the radiator surface. Since thin
enamel layers transmit the UV radiation generated better
than thick ones, a corresponding intensity pattern is
produced. This is of advantage for applications in which
an object which is to be W-irradiated is moved along the
surface and well-defined exposure intervals are to occur.
Finally, Figure 5 illustrates the arrangement of
wires compl~tely embedded in a W-transparent thick-film
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casting compound ~c on a smooth outer dielectric tube l.
The modern development of W-curing products has made it;
possible to produce such casting compounds from clear
enamel and even pigmented systems. Examples of UV-curing
epoxy resins and UV-curing acrylates are described, for
example, in the lecture manuscript of the Panacol-Elosol
GmbH company entitled " W-E~OXIES - Neue Moglichkeiten
mit strahlungshartenden Klebstoffen und Vergussmassen"
("UV-EXPOXIES - New possibilities using radiation-curing
adhe~ives and casting compounds"), Hau~ der Technik e.V.,
Essen dated 20.11.1990. In such an arrangement, the
"base" of the casting compound 8c, the outer dielectric
tube 1, can be of thinner construction and in the limit
case can even be omitted if the dielectric properties of
the casting compound are matched to the discharge
process.
The rearrangement, according to the invention, of
the electrodes can be used successfully not only in
cylindrical radiators but also in two-dimensional radia-
tors. The outer electrodes themselves may also be of
different design, for example not reticular or latticed,
but con isting only of parallel strips, and this suggests
itself, in particular, in an arrangement as shown in
Figure 3.
Instead of separate or discrete electrode
arrangements, those which are deposited by strip-type or
lattice/reticular metallizations on the outer surface of
the dielectric tube 1 and are then provided with a
coating using the process described in connection with
Figure 3 can also be used.
The invention was explained a~ove by reference to
exemplary embodiments which relate to so-called outward
radiators. The measureg of protecting the electrodes
disclosed in this connection also apply, of course, to a
so-called inward radiator. Apart from the position of the
transparent electrodes 5, such an inward radiator
corresponds to the outward radiator shown in Figure l.
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Furthermore, radiator configurations are also
possible in which the UV radiation is radiated both
~ outwards and inwards. Figure 6 illustrates a portion of
such a radiator. In such arrangements, both dielectric
tubes 1, 2 and also the respective electrodes 3, 5 have
to be transparent to the radiation generated. In this
cas~, both the first electrodes 5 and the second elec-
trodes 3 can be ideally protected against chemical and
physical attacks in the way described above.
Outward and inward radiators are norm~lly cooled
with a liquid coolant. In outward radiators, this is
passed through the inner dielectric tube 2 and in inward
radiators the coolant flows round the outer dielectric
tube 1. Here, again, protective layers composed of the
materials described contribute to preventing the erosive
attack by the coolant or at least to reducing it. Insofar
as electrodes are involved in this connection which must
not transmit any W radiation, other protective layers
may also be used, for example those applied by anodizing,
enameling etc. In the case of aluminum electrodes vapor-
deposited or sputtered onto the dielectric, anodization
of the free surface suggests itself. In the case of
reticular or latticed electrodes which must not transmit
any UV xadiation, care must be taken that no (external)
discharges occur between electrode and dielectric sur-
face, which may take place as a result of filling the gap
with an enamel or other fillers such as adhesive or
nonconducting or conducting pastes, for ex~mple fluid
s Llver .
Obviously, numerous modifications and variations
- of the present invention are possible in light of the
above teachings. It is therefore to be understood that
wi~hin the scope of the appended claims, the invention
may be practiced otherwise than as specifically described
herein.
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