CA1192942A - Discharge lamp arc tubes - Google Patents
Discharge lamp arc tubesInfo
- Publication number
- CA1192942A CA1192942A CA000411384A CA411384A CA1192942A CA 1192942 A CA1192942 A CA 1192942A CA 000411384 A CA000411384 A CA 000411384A CA 411384 A CA411384 A CA 411384A CA 1192942 A CA1192942 A CA 1192942A
- Authority
- CA
- Canada
- Prior art keywords
- arc tube
- producing
- discharge lamp
- end closure
- closure member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
: 10 :
ABSTRACT OF THE DISCLOSURE
A method of making an arc tube for a discharge is disclosed together with sealing compositions used in the method. The method consists of assembling together an incompletely fired or green state end closure member (complete with electrode etc.) and an arc tube also in the incompletely fired or green state. Applying a sealing composition selected from the disclosed range and firing this assembly so that the end closure member forms a hermetic seal with the arc tube. Separate steps for producing a completely fired end closure and arc tube and the subsequent step of sealing these two items together is thus avoided. A ternary phase diagram defining preferred compositions is disclosed.
ABSTRACT OF THE DISCLOSURE
A method of making an arc tube for a discharge is disclosed together with sealing compositions used in the method. The method consists of assembling together an incompletely fired or green state end closure member (complete with electrode etc.) and an arc tube also in the incompletely fired or green state. Applying a sealing composition selected from the disclosed range and firing this assembly so that the end closure member forms a hermetic seal with the arc tube. Separate steps for producing a completely fired end closure and arc tube and the subsequent step of sealing these two items together is thus avoided. A ternary phase diagram defining preferred compositions is disclosed.
Description
~ ~c DISC~A~GE L~MP ~RC TUBES
This inven~ion relates to discharge lamp arc tubes and ln particular to such tubes which comprise envelopes of polycrystalline alumina, sapphire or a spinel and one or more cer~et end closure members sealed thereto and to a method for their production. Such tubes are useful in the construction of discharge lamps containing metal vapours, such as sodium or tin or a wide range of metal halide ~apours such as sodium chloride, sodium bromide, aluminium chloride, tin chloride, scandium iodide, rare earth halides, mercuric chlorides and iodides and the like. The envelopes mentioned above are well ~nown in the art and cermet end closures t~erefor are described and claimed in our British sp0clfication No. 1571084 and Canadian Serial No~3638~6. These cermet end closures are of value because they can be produced from materials ~Jhich result in a product having a co~efficient of linear expansion which is intermediate between the materials comprising on the one hand, the arc tube envelope and on the other hand, the generally metallic electrode. A wide range of cermet materials can be produced, depending on the particular co-efficient of linear expansion which is required.
Particularly preferred types of cermet are those comprising alumina and tungsten or alumina and molybdenum. These may suitably contain a volume fraction of metal of from 0.045 to 0.2 where volume fraction is defined as the ratio of the volume : 2 o~ the metal to the total volume of the ceramlc and metal and will normally have a co-eff:icient o~ linear expansion from 50 to 85.10 7 per C over a range o~ 1 ao to 1000 CO
The above arc tubas are normally produced by sealing the sintered ceramic arc tube and the sintered cermet end closure together by means of a composition such as that disclosed in our Canadian Serial No. 363816.
It is an object of the present application to provide an alternative method of producing such discharge lamp arc tubes.
Accordingl-y we provide a method of producing a discharge l~mp arc tube whlch method comprises forming an assem~ly of one sintered cermet end closure member hermetically sealed to a ceramic arc tube of polycrystalline alumina, sapphire or a spinel by means of the follo~ing steps:~
providing an arc tube in the incompletely fired stats, providing a cermet end closure member in the incompletely fired state complete with an electrode assembled thereto 3 applying a layer of sealing composition between said end closure member and said arc tube and sintering the assembled arc tubs and cermet end closure member complete with electrode at a temperature of ~rom 1800 -1900 C in a vacuum, inert gas or in a hydrogen atmosphere.
According to a preferred method of the invention the sealing composition comprises silica, alumina and magnesia in proportions such that the composition falls within the area BCDEFXY~PQ on the accompa~ying ternary phase diagram.
.
The method o~ the :inventlon has the advantage th~t Lt eliminates the need to make a first end seal by an operatio~
separate ~rom the firing o~ the arc tube and closure member.
That is to say it eliminates the necessity to manufacture a completely fired cermet, a completely fired arc tube and then join them together.
The sealing compositions within the said area BCDEFXYZPQ
have relatively high melting points, generally in excess of 1700 C and are thus suited for use in a sintering operation which as stated abova, is carried out at a temperature of from 1800 to 1900C.
Certain o~ the sealing compositions have an alumina content of less than 45% by weight and speci~ic examples o~ these, together with their melting points are shown in the ~ollowing Table 1:-No. MgO A123 SiO2 B23 -2-5 MELTING POINT
1 15.242.0 42.8 _ _ 1700
This inven~ion relates to discharge lamp arc tubes and ln particular to such tubes which comprise envelopes of polycrystalline alumina, sapphire or a spinel and one or more cer~et end closure members sealed thereto and to a method for their production. Such tubes are useful in the construction of discharge lamps containing metal vapours, such as sodium or tin or a wide range of metal halide ~apours such as sodium chloride, sodium bromide, aluminium chloride, tin chloride, scandium iodide, rare earth halides, mercuric chlorides and iodides and the like. The envelopes mentioned above are well ~nown in the art and cermet end closures t~erefor are described and claimed in our British sp0clfication No. 1571084 and Canadian Serial No~3638~6. These cermet end closures are of value because they can be produced from materials ~Jhich result in a product having a co~efficient of linear expansion which is intermediate between the materials comprising on the one hand, the arc tube envelope and on the other hand, the generally metallic electrode. A wide range of cermet materials can be produced, depending on the particular co-efficient of linear expansion which is required.
Particularly preferred types of cermet are those comprising alumina and tungsten or alumina and molybdenum. These may suitably contain a volume fraction of metal of from 0.045 to 0.2 where volume fraction is defined as the ratio of the volume : 2 o~ the metal to the total volume of the ceramlc and metal and will normally have a co-eff:icient o~ linear expansion from 50 to 85.10 7 per C over a range o~ 1 ao to 1000 CO
The above arc tubas are normally produced by sealing the sintered ceramic arc tube and the sintered cermet end closure together by means of a composition such as that disclosed in our Canadian Serial No. 363816.
It is an object of the present application to provide an alternative method of producing such discharge lamp arc tubes.
Accordingl-y we provide a method of producing a discharge l~mp arc tube whlch method comprises forming an assem~ly of one sintered cermet end closure member hermetically sealed to a ceramic arc tube of polycrystalline alumina, sapphire or a spinel by means of the follo~ing steps:~
providing an arc tube in the incompletely fired stats, providing a cermet end closure member in the incompletely fired state complete with an electrode assembled thereto 3 applying a layer of sealing composition between said end closure member and said arc tube and sintering the assembled arc tubs and cermet end closure member complete with electrode at a temperature of ~rom 1800 -1900 C in a vacuum, inert gas or in a hydrogen atmosphere.
According to a preferred method of the invention the sealing composition comprises silica, alumina and magnesia in proportions such that the composition falls within the area BCDEFXY~PQ on the accompa~ying ternary phase diagram.
.
The method o~ the :inventlon has the advantage th~t Lt eliminates the need to make a first end seal by an operatio~
separate ~rom the firing o~ the arc tube and closure member.
That is to say it eliminates the necessity to manufacture a completely fired cermet, a completely fired arc tube and then join them together.
The sealing compositions within the said area BCDEFXYZPQ
have relatively high melting points, generally in excess of 1700 C and are thus suited for use in a sintering operation which as stated abova, is carried out at a temperature of from 1800 to 1900C.
Certain o~ the sealing compositions have an alumina content of less than 45% by weight and speci~ic examples o~ these, together with their melting points are shown in the ~ollowing Table 1:-No. MgO A123 SiO2 B23 -2-5 MELTING POINT
1 15.242.0 42.8 _ _ 1700
2 15.0~2.0 43.0 - - 1700 20 3 43.022.0 35.0 - - 1800 4 23.035.0 38.0 3.0 1.0 1800 27.035~0 38.0 _ _ 1850 6 63.0 - 37.0 - - 1890 7 56.016.0 28.0 - - 1890 We also have found that certain compositlons having 70'~ by weight or more of alwnina can be used and examples o~ these are set out in Table 2:-No. MgO Al203 ~i2 1 - 71.8 28.2 2 2.0 71~8 26.2
3 4 71~8 2~.2
4 6.0 71.8 22.2 8.o 70.0 22.0 6 10.0 70.0 22.0 In addition to the main constituents, the sealing composition may contain small amounts of nucleating agents such as phosphorous pentoxide (up to 5% by weight); rare earth oxides, titania, zirconia or c'nromia can be included in the starting materials which are helpful in controlling the size and extent of the crystalline phase during in-situ sealing operation. It has also been ~ound that up to 5~ by weight of boric oxide can be incorporated in the composition to improve the flow characteristics o~ the sealing compounds without any adverse e~fect on seal per~ormance. Also up to 10% by weight of rare earth oxides such as Y203, Yb203, La203, Dy203, Eu203, H~02 can be included in the compositions which improve the thermal and mechanical properties of the 2~
joints. Gene~ally speaking the seaLing composit-ions utilised in the invention may be obtained by talcing the starting ingredients in the form of fine powders and tumbler mi~ing ~or about 1 hour~ The appropriate amount o~ the major oxide components may be added in the form of a precursor soluble salt such as a nitrate, a sulphate or an oxalate. The minor constituents may likewise be added either in the form of the oxide or, preferably, as a soluble salt. The mixture is then fused at about 200 C in a high purity aluminium crucible for about 2 hours to homogeni7e the mixture, followad by calcination at a temperature of up to 1200 C for about 7 hours in air or an inert atmosphere. The calcined oxides are then crushed and sieved through a 250 micro mesh. An alternative method to homogenize the components is to melt the mixture at about 1650 C in air or in a controlled atmosphere in a crucible made from platinum containing 10% rhodium or in an irridium crucible for materials with melting points higher than 1650 C. This melt is then stirred for several hours and the resulting glass quenched in distilled water. The mixture is then dried and milled to form a fine glass powder, which may then be formed into suitable annular discs or frits~ Up to 2% by weight o~ a binder such as polyvinyl alcohol may be added which assists in the automatic pressing of the annular discs or frits. This binder has to be removed prior to sealing by preheating or premelting.
The invention will now be described by way of example only and with re~erence to the accompanying drawings in which:
Figure 1 is a ternary phase diagram in terms of weight per cent de~ining compositions use~ul in the practice o~ t,he invention.
Figure 2 is an illustrat:ion of an end closure member, sealed to one end of a lamp in one version of the invention.
Figure 3 is an illustration of an end closure member sealed to one end of a lamp in another version of the invention.
In Figure 2 an incompletely fired tube 10 of alumina material has an incompletely fired alumina plug 10a attached to it by smearing with an alumina slurry and partial sintering or by direct partial sintering without the use of slurry, the slurry being useful to hold the plug in position. It should be ap?reciated that this assembly is not completely sintered but is prefired merely to a stage where it can be handled for subsequent processing. An end closure member 11 of cermet material produced by pressing or machining is provided complete with conducting members 20 and 18 and with conductor 18 having an electrode 17 attached thereto. This end closure member 11 is also in an incompletely fired state similar to that of the arc tube 10 and plus 10a. An initially annular disc of sealing material selected from Table 1 is interposed between the surfaces of the end closure member 11 and the arc tube. The sealing composition has the property such that at the sintering temperature of around 1800 C the sealing composition will wet the surfaces of the closure member and the end surfaces of the arc tube and will thus be capable of forming a hermetic seal of the shape shown at 22. If the composition chosen has a melting ~/
: 7 temperature ot` above 1800 C, the slnter:ing temperature should be :increased accordin~ly. This assembly ls then fired until complete sintering takes place resulting in the hermetic seal being ~ormed. It is useful i~ the top end of the tube 10 projects beyond the outer surface of t~le plug 10a as this forms an enclosure ~or the sealing material to flow into as shown.
A variation as shown in Figure 3. In Figure 3 the tube 10 and plug 10a are trlmmed off to provide a ~lush outer sur~ace.
An end closure member 11 is attached as before by means of sealing composition 22. In thls case the end closure member is substantially the same overall diameter as the tube 10. It will be appreciated that in Figures 2 a;:rl , the seal~ng composition 22 is shown much exaggerated for the purposes of the description~ It wili be appreciated the above method steps will be carried out in a vacuum, inert gas or hydrogen atmosphere a3 pre~erred.
In place of She annular disc o~ sealing material, a powder (glass or calcined oxide) of the material may be used.
joints. Gene~ally speaking the seaLing composit-ions utilised in the invention may be obtained by talcing the starting ingredients in the form of fine powders and tumbler mi~ing ~or about 1 hour~ The appropriate amount o~ the major oxide components may be added in the form of a precursor soluble salt such as a nitrate, a sulphate or an oxalate. The minor constituents may likewise be added either in the form of the oxide or, preferably, as a soluble salt. The mixture is then fused at about 200 C in a high purity aluminium crucible for about 2 hours to homogeni7e the mixture, followad by calcination at a temperature of up to 1200 C for about 7 hours in air or an inert atmosphere. The calcined oxides are then crushed and sieved through a 250 micro mesh. An alternative method to homogenize the components is to melt the mixture at about 1650 C in air or in a controlled atmosphere in a crucible made from platinum containing 10% rhodium or in an irridium crucible for materials with melting points higher than 1650 C. This melt is then stirred for several hours and the resulting glass quenched in distilled water. The mixture is then dried and milled to form a fine glass powder, which may then be formed into suitable annular discs or frits~ Up to 2% by weight o~ a binder such as polyvinyl alcohol may be added which assists in the automatic pressing of the annular discs or frits. This binder has to be removed prior to sealing by preheating or premelting.
The invention will now be described by way of example only and with re~erence to the accompanying drawings in which:
Figure 1 is a ternary phase diagram in terms of weight per cent de~ining compositions use~ul in the practice o~ t,he invention.
Figure 2 is an illustrat:ion of an end closure member, sealed to one end of a lamp in one version of the invention.
Figure 3 is an illustration of an end closure member sealed to one end of a lamp in another version of the invention.
In Figure 2 an incompletely fired tube 10 of alumina material has an incompletely fired alumina plug 10a attached to it by smearing with an alumina slurry and partial sintering or by direct partial sintering without the use of slurry, the slurry being useful to hold the plug in position. It should be ap?reciated that this assembly is not completely sintered but is prefired merely to a stage where it can be handled for subsequent processing. An end closure member 11 of cermet material produced by pressing or machining is provided complete with conducting members 20 and 18 and with conductor 18 having an electrode 17 attached thereto. This end closure member 11 is also in an incompletely fired state similar to that of the arc tube 10 and plus 10a. An initially annular disc of sealing material selected from Table 1 is interposed between the surfaces of the end closure member 11 and the arc tube. The sealing composition has the property such that at the sintering temperature of around 1800 C the sealing composition will wet the surfaces of the closure member and the end surfaces of the arc tube and will thus be capable of forming a hermetic seal of the shape shown at 22. If the composition chosen has a melting ~/
: 7 temperature ot` above 1800 C, the slnter:ing temperature should be :increased accordin~ly. This assembly ls then fired until complete sintering takes place resulting in the hermetic seal being ~ormed. It is useful i~ the top end of the tube 10 projects beyond the outer surface of t~le plug 10a as this forms an enclosure ~or the sealing material to flow into as shown.
A variation as shown in Figure 3. In Figure 3 the tube 10 and plug 10a are trlmmed off to provide a ~lush outer sur~ace.
An end closure member 11 is attached as before by means of sealing composition 22. In thls case the end closure member is substantially the same overall diameter as the tube 10. It will be appreciated that in Figures 2 a;:rl , the seal~ng composition 22 is shown much exaggerated for the purposes of the description~ It wili be appreciated the above method steps will be carried out in a vacuum, inert gas or hydrogen atmosphere a3 pre~erred.
In place of She annular disc o~ sealing material, a powder (glass or calcined oxide) of the material may be used.
Claims (9)
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A method of producing an arc tube for a discharge lamp which method comprises forming an assembly of one sintered cermet end closure member hermetically sealed to a ceramic arc tube of polycrystalline alumina, sapphire or a spinel by means of the following steps:
providing an arc tube in the incompletely fired state, providing an end closure member in the incompletely fired state complete with an electrode assembled thereto, applying a layer of sealing composition between said end closure member and said arc tube and sintering the assembled are tube and end closure complete with electrode at a temperature of from 1800°C to 1900°C in a vacuum, inert gas or a hydrogen atmosphere.
providing an arc tube in the incompletely fired state, providing an end closure member in the incompletely fired state complete with an electrode assembled thereto, applying a layer of sealing composition between said end closure member and said arc tube and sintering the assembled are tube and end closure complete with electrode at a temperature of from 1800°C to 1900°C in a vacuum, inert gas or a hydrogen atmosphere.
2. A method according to claim 1 wherein the sealing composition comprises silica, alumina and magnesia in proportions such that said composition falls between the area BCDEFXYZPQ on the accompanying ternary phase diagram.
3. A method of producing an arc tube according to claim 1 wherein said sealing composition includes minor additions of nucleating agents selected from phosphorus pentoxide, titania, zirconia or chromia.
4. A method of producing an arc tube for a discharge lamp according to claim 3 wherein said nucleating agent is added in an amount up to about 5% by weight.
: 9 :
: 9 :
5. A method of producing an arc tube for a discharge lamp according to claim 1 wherein said sealing composition includes up to about 5% by weight of boric oxide.
6. A method of producing an arc tube for a discharge lamp according to claim 1 wherein said sealing composition includes up to about 10% by weight of rare earth oxides.
7. A method of producing an arc tube for a discharge lamp according to claim 6 wherein said rare earth oxides are selected from Y2O3, Yb2O3, La2O3, D Y2O3, Eu2O3 and Hfo2.
8. A method of producing an arc tube for a discharge lamp according to claim 1 wherein the volume fraction of the cermet material is between 0.045 to 0.2.
9. A method of producing an arc tube for a discharge lamp according to claim 1 wherein the cermet material comprises alumina and tungsten or alumina and molybdenum.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411384A CA1192942A (en) | 1982-09-14 | 1982-09-14 | Discharge lamp arc tubes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000411384A CA1192942A (en) | 1982-09-14 | 1982-09-14 | Discharge lamp arc tubes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1192942A true CA1192942A (en) | 1985-09-03 |
Family
ID=4123585
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000411384A Expired CA1192942A (en) | 1982-09-14 | 1982-09-14 | Discharge lamp arc tubes |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1192942A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8125133B2 (en) | 2004-08-02 | 2012-02-28 | Osram Ag | Lamp comprising a base that is mounted without cement |
-
1982
- 1982-09-14 CA CA000411384A patent/CA1192942A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8125133B2 (en) | 2004-08-02 | 2012-02-28 | Osram Ag | Lamp comprising a base that is mounted without cement |
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Legal Events
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|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |