Note: Descriptions are shown in the official language in which they were submitted.
96
PHN 10,009 1 1-12~1981
"Method of producing a low-pressure mercury vapour di~s-
charge lamp ~nd lo~-pressure mercury vapour discharge
lamp produced by means of said method".
The invention relates to a method o~ produoing
a low-pressure mercury vapour discharge lamp having a
discharge vessel, a-t least a metal or an alloy which forms
an amalgam with mercury being disposed in -the discharge
vessel before the desired gas atmosphere is established in
the discharge vessel and the discharge vessel is closed
in a vacuum-tight manner. Such a method is disclosed in
USP 4,157,4~5 (PHN 8O57). The in~ention further relates
to lamps produced by means of such a method.
In ~he prior art method an alloy of indium and
bismuth (the amalgam-forming component) are pressed to
form a ductile wire the end of which is thereafter heated
to a temperature just above the melting point of said alloy
and is sprayed onto a portion of the lamp wall According
to the said Patent Specification this portion is preferably
the foot o~ the stem. Such a stem carries, for example,
an electrode, an au~iliary electrode, leading-in wires and
similar elementsO The use of the said stems (which are o~te~
provided with an ex~aust tube) is customary in the product~
ion of low-pressu~e mercury vapour discharge lamps. The
stems and accesories (such as leading-in wires, electrodes
etc.) are first produced separately ~rom the other lamp
components. ~he indium and bismu-th alloy is applied onto
the ~oot o~ the stem before the stem is sealed in a vacuum-
tight manner to the discharge vessel. Thereafter the lamp ispumped (that is to say the walls and the othe~ lamp com-
ponents are outgassed, the electrodes are annealed and
outgassed, the discharge vesse] is filled with the re~uired
gas atmosphere etc~)~ Thereafter the discharge vessel is
closed in a vacuum-tight manner by sealing the e~haust tube.
Thereafter the discharge vessel is filled with mercury, for
example by heating a glass container which comprises the
; mercury and is present in the discharge vessel (see
g~
PHN 1~.009 -2- 1-12-1981
G~-PS 1,267,175~. Then at least a portion of the mercury
iIl combination with the amalgam-forming component ~orms an
amalgam for the control o~ the mercury vapour pressure in
the discharge vessel during operation of the lamp.
One o~the problems encountered in said method
is that the consecutive operations during the production
o:~ the lamp, during whi-ch the temperature rises to a com-
paratively high value (~or e~amplc during sealing of the
stem to the wall of the discharge vessel.or during the
indispensable heating of components, for example out-
gassing of the electrodes, activation o~ the electrodes
e-t~) oxidizing of the amalgam-~orming alloy or the amalgam-
~orming metal .easily occurs, a thin oxide layer -then being
formed on the metal or the alloy, which during operation
Of the lamp greatly impedes the absorption and release
of mercury (which is necessary for a proper operation of
an amalgam). In addi-tion, with the known method i-t is
di~ficult to dose the quantity of tha amalgam-~orming
component accurately.
The invention has for its object to.provide a
me-thod o~ producing a low-pressure mercury ~apour discharge
lamp which mitigates these drawbacks, wherein attack of
tha amalgam-~orming alloy and the amalgam-forming metal,
respectively, by oxidation is prevented ~rom occurring.
According to the invention, the method o~ pr~-
ducing a low pressure mercury vapour discharge lamp is
characterized in that at leas-t the amalgam-forming alloy
or the amalgam-~orming metal is present in a closed con-
tainer which is provided near a portion o~ the in-terior
wall of the discharge vessel, which container is opened
after the discharge vessel has been closed in a vacuum~
tight manner, at least a portion o~ the alloy or the
metal then leaving the container ~nd moving ~o -the interior
wall portion located near the container.
In the method in accordance with the invention
the amalgam-~orming metal and the amalgam-~orming alloy 9
respectively are not exposed to a hot~ oxygen-containing
- atmosphere, so that no o~ide layer is formed on the alloy
~9~
PHN IO.OO9 -3- 1-12-1981
and metal, respectively. Namely, during the entire pro-
cedure the metal or the alloy are located in a closed con-
tainer which is not opened until the discharge ~essel has
been closed in a vacuum-tight manner.
An additional advantage o~ the method in acordance
with the invention is -tha-t the amalgam-forming ~etal or the
alloy can be applied in very accurate doses in the discharge
~essel. The ratio o~ the quanit~ of metal and alloy,
respec-tively~ to the quantity of mercury in the lamp is
accura-tely determined. The temperature range in which the
mercury vapour ~ressure is substantially stable during
operation o~ the lamp is then as wide as possible.
In this method it is not necessary that the entire
content of the container moves to the wall portion located
near the container. An adequate control o~ the mercury
vapour pressure is obtained even if a portion o~ the
content, ~or example hal~ the content, remains in the
container. During operation of the lamp, the absorption
and releasa o~ mercury ~rom the portion of the amalgam
located in the con-tainer proceeds _ia the opening in the
container wall.
Pre~erably the container is provided in a compa-
ratively cool spot in the discharge vessel1 for example in
a position behind the elec-trode near an end o~ the dischar-
ge vessel. In one embodiment the opening is pro~idedinsuch a place in the container that a portion o~ the con-
tent moves *o a posi-tion near the electrode ~or e~ample
the pinch or a ring or band around the electrode). During
operation of the lamp an amalgam ~hich has almost exclusi-
vely a ~apour pressure-controlling function forms in the
container with the mercury present in the discharge vessel,
the material present in a place near the electrode being
*ree ~rom mercury during operation. Only during extinguish-
ing of the lamp said material absorbs some mercury whichS
however, when the lamp is switched on, is released from the
amalgam in response to the rapid increase o:~ -the tempera~
ture there 7 as a result o~ which the lamp readily igni*es.
` J The `container iS 0~ such a shape and is so
a~
P~IN 10.009 l~ 12-1981
positioned in the discharge vessel that the material which
is released on the opening of the container moves as rapidly
as possible to a discharge vessel wall portion near the
container. The container consis-ts 9 for example, of glass
or me-tal. In a practical embodiment the container is formed
by two metal parts which are welded toge-ther, one part
being provided with a recess in which the amalgam-forming
ma-terial is present. The container is connec-ted to the stem
or to a supply wire of an electrode by means of, for
e~ample, a wire.
A container of this type metal is opsned by,
for e~Yample, inductive heating~ The container then bursts
open in a weak spot in the wall specially provided for that
purpose. The weak spot faces, for example~ and is located
at a s~all distance from the wall portion of the discharge
vessel on ~hich at least the amalgam-forming component is
provided. In a practical embodiment of the method the con-
tainer is opened by means of a laser beam which is focused
onto the wall of the container~
The mercury required for the operation of the lamp
may be dosed in the discharga vessel separately from
the amalgam-~orming alloy and the amalgam-forming mstal,
respectively, for example by means of a glass mercury
container described in the United Kingdom Patsnt Speci~
25 cation 1,267,175 mentioned already in the foregoing.
Preferably, in the method in accordance with -the invention,
the mercury required for the operation of the lamp is
placed together with the said amalgam-forming component
in the container and provided on the wall of the discharge
3~ vessel. No additional step for the separa-te dosing of the
mercury is then required. A fur-ther advantage in this em-
bodiment is -that the container holding the amagam opens
rapidly when being heated as a res~lt of the mercury vapour
pressure which rapidly increases as a function o~ -tem-
perature. The mutual ratio of the elements which are partof the arnalgam may moreover be determined very accurately,
so that a proper opera-tion of the amalgam during operation
of -the lamp is obtained.
PHN 10.009 -5- 1-12-1981
The amalgam may be composed o~ mercury and a
metal, such as indium, tin, or lead or alternatively o~
mercury and an alloy 9 such as an alloy o~ indium and
bismuthO In a practical embodiment of the method in accord-
ance with the invention a mi~ture o~ an alloy o~ indiumand mercury is ~irst placed together with bismuth in a
closed metal container, a spherical bismuth member being
positioned on a ductile tablet o~ the indium and mercury
alloy. The spherical members and the tablets can be mass-
produced in a simple way. 1~hen the spherical bismu-th member
is positioned in the holder it is enveloped substan-tially
wholly by the ductile mass o~ the indium and mercury alloy~
The spherical member and the ductile mass are therea~-ter
heated ~or some time~ which results in a proper mi~ing
~ the said elements. The holder is o~ such a shape that
the amalgam is tightly enclosed and unwanted trapping o~
gas is avoidedO It has ~een found that the said elements
can be eas-ly positioned in the container in a mechanized
process.
In low-pres-sure mercury vapour discharge lamps
produced by means o~ the method the mercury vapour pres-
sure remains reasonably stable over a wide temperature
range around 6 x ~0 3 Torr ~o.8 Pascal). Lamps o~ this
t~pe, having an amalgam, are, ~or e~ample, suitable ~or
use in places where the ambient te.nperature is high.
In addition, the me-thod can be used with great
. advantage in small discharge lamps~ for e~ample in lamps
having a shape as described in DE-OS 2,940,563-(P~IN 92l~2).
In this type o~ lamp -the temperature in -the discharge
vessel is rather high during operation~ T'n3 pre~ence
a~ outer envelope reduces the heat discharge ~rom the
discharge vessel.
An opening o~ the container is per~ormed, as
mentioned in the ~oregoing, wholly separately ~rom the
~urther operations on the lamp, it is optionally possible
to market discharge vessels which are closed in a vacuum-
tight manner, but which still include a closed container.
This container may then be opened later at a suitable
P~IN IO.OO9 -6~ 12-1981
moment~ *or example by the buyer of these "lamps". This
operation is namely so simple (particularly if high-*re-
quency inductive hea-ting or a converging laser beam is
used) that a buyer can per~orm these operations without
elaborate equipment. ~ll -this has the advan-tage that during
trans-portation of the "lamps" the amalgam-*orming metal or
the amalgam-forming alloy cannot become detached from the
lamp wall; should these "lamps" containing amalgams break
during transportation no mercury vapour can be released into
the environment. The invention -there*ore also relates to
discharge vessels o* -this type.
The invention will now be further described by-
way o* e~ample with reference to a drawing in which
Fig. 1 shows an embodiment o* a low-pressure mer-
cury vapour discharge lamp produced by means o* a method
in accordance with the invention and
Fig. 2 shows one end, partly in cross-sectional
view, o* a discharge vessel containing a container still
to be opened.
In ~i-g. 1 reference numeral I denotes the wall
o~ a tubular discharge vessel o* a low-pressure mercury
vapour discharge lamp, stems 2 and 3 with electrodes ~ and
5~ respectively being provided one at each end. The
interior wall of the discharge vessel is coated with a
25 luminescent layer 6 consisting, *or example 9 of a mixture
o* trivalent europium-activated yttrium-oxide and tri~
valent terbium-activated cerium magnesium aluminate~ A
metal wire 7, which is connec-ted -to a metal container 8
located behind the elec-trodes is welded to one o* the
30 current supply wires of electrode 4. The wall portion near
said container (the *oot 9 of the stem 2~ is provided
with an amalgam. Said amalgam is applied by means o* a
methocl in accordance with the inventionO The amalgam is
provided in a cool spot, w~ich is advantageous ~or the
35 con-trol of the mercury vapour pressura in the discharge
vessel, behind the electrode 4.
During the production o* the lamp the in-terior
wall o* a tube is ~irst coated by means o* a known method
"~
PIIN 10.009 - 7_ 1-12 - I981
wi-tn a luminescent layer, whereafter the stems are connected
in a vacuum-tight manner to the wall o~ the tube. ~aid
s-tems~have a closed metal con-tainer 8 which conta;ns an
amalgam. Thereafter the discharge vessel is exhausted (by
means of an exhaust tube 10 connected to one of the stems),
the rare gas atmosphere is established and the discharge
vessel is closed in a vacuum-tigh-t manner by sealing the
exhaust tube. Not until thereafter is the metal con-tainer
8 opened by directing a focussed laser beam onto the wall
of the con;tainer so as to make an opening therein. At least
a portion of the amalgam leaves the container through the
opening as a syrupy liquid and moves to the foot 9 of the
stem, where it adheres.
Fig. 2 shows one end of a discharge vessel at the
moment at which all operations on the lamps except the
release of the amalgarn have been finished. Said amalgam is
in the container 8 which is still in the closed condition.
The container 8 is formed by two sheet metal portions 8a
and 8b (for example consisting of iron or nickel) which are
welded together, 8b having been provided with a recess in
which an amalgam 11 consisting of indium, bismuth and
mercury is provided. The amalgam is obtained by heating a
small sphere of bismuth which is enclosed by a quantity
of a ductile alloy of indium and mercury~ It has been found
that the bismuth is then very rapidly absorbed by the alloy
and ~orms a homogeneous/somewhat liquid compound. The metal
portions 8a and 8b fi-t around arnalgam 11 in such a way
that no unwanted gasses are trapped in the container~ The
container 8 is opened by means of a laser arranged ou-tside
the discharge vessel. An opening is drilled in a portion 12
of 8a by ~ocussing the laser beam. The -temperature then in-
craases to such a value that a portion of the amalgarn
flows from the contair~er 8.
In a practical embodiment, the wall portion 9
wh~re a portion of the amalgam arrives is located at only
a few mm (~or example 2mm) ~rom portion 12. The use of a
converging laser beam to form the opening has the advantage
that the further portions (~or exarnple 1 and 2) o~ the
PHN 10.009 ~ 12-1981
glass wall of -the disoharge vessel are not attacked by
the laser light. Moreover~ the energy of the laser light
can be concentrated such -that even amalgam-~orming com-
ponents having a low vapour pressure (such as indium or
bismuth) become syrupy when -the opening is formed.
In an alternative embodiment the container is
inductively hea-ted, a wecik spot having been provided in
the container wall ~lere -the container is opened.
A practical embodiment o~ a lamp shown in ~ig. 1
produced by means of a method in accordance with the in-
vention contained 26.8 mg Bi, 13.2 mg In and 3.0 mg Hg
(in wt.7b 62.30/o Bi~ 30.7%' In, 7% Hg). The container was
formed of two metal portions which are welded together
and one o~ ~hich is provided with a recess, An opening
(diameter 0.~7 mmj was formed in the container ~y means
o~ a pulsed Nd-YAG laser (pulse energy appro~imately 2 J).
~t an applied power o~ 13 W -the lamp (having argon, 267
Pa, as rare gas filling~ had a luminous flux of approxima~
tely 900 Lumen.
