CA1097991A - Metal oxide coating in halogen incandescent lamps - Google Patents
Metal oxide coating in halogen incandescent lampsInfo
- Publication number
- CA1097991A CA1097991A CA269,431A CA269431A CA1097991A CA 1097991 A CA1097991 A CA 1097991A CA 269431 A CA269431 A CA 269431A CA 1097991 A CA1097991 A CA 1097991A
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- CA
- Canada
- Prior art keywords
- coating
- lamp
- oxide
- halogen
- solution
- 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
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K1/00—Details
- H01K1/28—Envelopes; Vessels
- H01K1/32—Envelopes; Vessels provided with coatings on the walls; Vessels or coatings thereon characterised by the material thereof
Abstract
ABSTRACT OF THE DISCLOSURE:
The invention relates to electric incandescent lamps having a gas fill containing halogen. The internal surface of hte lamp envelope and optionally also the exposed surface of internal components of the lamp are protected from attack by halogens including flourine by a continuos imperforate coating composed of a metal oxide resistant to halogen attack.
In order to achieve the necessary degree of continuity of hte coating the oxide is formed in situ from a compound of the metal deposited as a solution on the surface. The preferred oxidee is alumina, the other oxides of polyvalent and transition metals, including metals of the lanthanide series may be used.
The coatings are preferably formed from solutions of halides of the metals in polar organic solvents such as methanol. The invention prolongs the life of lamps provided with the protective coating and enable such resistant and possibly cheaper materials to be employed for certain lamp components.
The invention relates to electric incandescent lamps having a gas fill containing halogen. The internal surface of hte lamp envelope and optionally also the exposed surface of internal components of the lamp are protected from attack by halogens including flourine by a continuos imperforate coating composed of a metal oxide resistant to halogen attack.
In order to achieve the necessary degree of continuity of hte coating the oxide is formed in situ from a compound of the metal deposited as a solution on the surface. The preferred oxidee is alumina, the other oxides of polyvalent and transition metals, including metals of the lanthanide series may be used.
The coatings are preferably formed from solutions of halides of the metals in polar organic solvents such as methanol. The invention prolongs the life of lamps provided with the protective coating and enable such resistant and possibly cheaper materials to be employed for certain lamp components.
Description
~37~
This in-~ention relates to electric inca~descent lamps, and mor~ especially to incc~descent lamps operating by a halogen Gycle.
I~ any incandescent twugsten fila~ent lamp co.~tainin~
a reactive fill such as halogen or hali.de, the choi.ce of material for the internal components and ellvelope is usually very restricted. ~or lalrlps having iodin2, bromine or chlorine in the ~ill the envelope is preferably fused quartæ or a high silica co~ten~ glass a~d the lead-in wire, filament supportst internal re~lectors, shields and other internal componellts are substantially composed of molybdenum or tungstenO If less e~ensi~e~ common materials such as nickel, iron, copper, alum ni~ and alloys containing these are used they react ~Jith the halogens to form halides which can cau~e ~ilament em-brittlementg and/or a halogen deficiency, both resulting inseverel~ reduced filament life~ Also, if soft glass~ such as soda li~e silicate, is used for the e~elope, apart from the obvious difficulties of the low softenin~ temperature and hlgh water content~ the alkali metals can react wi.th the halogen ox halides, again reducing filament li~e.
In ope~ation, tungsten-halogen la~ps normally contai.n a non-reactive gas filling such as ~2~ ~rg Kr or X.e together with iodine, bromine or chlorine vapour whiGh combin.es with the evaporated tungste~. escaping from the inca~descent fi7ament. A~ equilibr.ium concentration i.s attained by the gaseous species within the lamp between the 1:emperattlre limits defined by the i.ncandescent filament and col~est spot on the .~
.
.
7~
lamp envelope. ~he cold spot temperature must be suffi~
ciently high to prevent an-g tun~sten hali(le from condensing t and provided that this condition i5 met a continuous t~ngs~er trc~sport cycle operates which keeps t-he e~velope ~xee from tungsten~ The minimum envelope tempera-ture depends upon the halo~en ox halogens taki.ng part in the cycleO However, the maxi'num envelope temperature is usually well above the acceptable limit for soft glass, and for this reason tun~sten-halogen lamp envelopes are usually made from vitreous fus0d silica or high silica content glasses.
The return o~ tungsten to the filament does not in itself increase filament life since tungsten iodides, bromldes and chlorides dissociate well below normal filament operatin~
. temperatures. Radio-chemical tracers have shown that evaporated tungsten is redistribu.ted during the life of the lamp so that the cooler parts of the filament collect -tungsten at a ~reater rate than the hotter partsO ~ilament failure usually occurs quite normally by the subseque.nt burn~out of a 'hot spot'. '~he improvement in life of tungsten-halo~en lamps . 20 in comparison with conventional incandescent lamps is for quite a differeLlt reason~ The absence of envelope blackening coupled with the requiremen.t for a well-defined minimum envelope temperature dictates tha-t the envelope must be . su~stantially smaller than that of a conventional courlterpart.
In fact, tungsten-halo~en lamp envelopes are usually small and mechanicall~r strong and in consequence can be safely gas-. filled to several a-tmospheres pressure. ~'his increased.~as : -3-7~
filling pressure accounts for the gain in life.
If f;lament 'hot spots' could be healed or prevented a further extension in filament life would be possible. This is feasible with a tungsten-fluorine transport cycle because in this case the most stable tungsten fluoride dissociates at a temperature above 3000C, and tungsten is returned to the incandescent filament surface. Again, this has been substantiated by radiochemical tracer experiments, which show that tungsten vapour returned from the region of the envelope is evenly distributed along the incandescent part of the filament. Technological difficulties have prevented the further development of tungsten-fluorine lamps, the principal problem being that free fluorine reacts rapidly with solid tungsten below about 2000C, the cold parts of the filament, the lead wires and the supports being rapidly eroded, and that the fluorides formed (e.g. tungsten fluorides) react with the silica contained in the envelope material to form SiF4, depositing tungsten on the tube wall. This uses up the free fluorine in a very short time. Various methods have been proposed for protecting the envelope and tungsten components but these have been unsuccessful because of the inability to produce a continuous thin layer of protective material free from pin-holes and minor defects.
In our Canadian Patents Nos. 986,980 of April 6, 1976 and 1,050,605 of March 13, 1979, both of which are assigned to Thorn Lighting Limited, we describe the use of glassy coatings for the internal surfaces of halogen-containing electric lamps, and describe a process for ~ 9~
the form?~tion cf defect~free coatin~s by deposition of a solutio~l of compounds of the metal and phosphorus or arsesiG, followed by e~aporation of the solven-t and bakin~ of the resultin~ layer~
5 United States Patent ~o, 3,067,356 describes a fluores-cent lamp havin~ an inter:rlal barrier layer of, inter alia, aluminilun oxide i.ntended to reduce darkenin~ of the lamp by reaction of mercury in the gas fill with alkali in the glass of the lam~ tube. ~ot only is the use of this coati~g different from that required for this invention, but the layer in the Patent re~erred to is ~ormed by applying the particu-late oxide in a lacquer vehicle, follcwed bg- drying G~nd baking~
and such a layer does not provide effective protection against a hi~hl~ reactive gas such as fluorine.
r~he presellt invention now provides an alternative or improved. protective layer for the exposed internal surfaces oi' incandescent lamps which tend to react with the f-ill in -the lamp en-velope, particularly where -this includes a halogen~
and more especially fluorine or a fluorine-contai.nil~g compound,
This in-~ention relates to electric inca~descent lamps, and mor~ especially to incc~descent lamps operating by a halogen Gycle.
I~ any incandescent twugsten fila~ent lamp co.~tainin~
a reactive fill such as halogen or hali.de, the choi.ce of material for the internal components and ellvelope is usually very restricted. ~or lalrlps having iodin2, bromine or chlorine in the ~ill the envelope is preferably fused quartæ or a high silica co~ten~ glass a~d the lead-in wire, filament supportst internal re~lectors, shields and other internal componellts are substantially composed of molybdenum or tungstenO If less e~ensi~e~ common materials such as nickel, iron, copper, alum ni~ and alloys containing these are used they react ~Jith the halogens to form halides which can cau~e ~ilament em-brittlementg and/or a halogen deficiency, both resulting inseverel~ reduced filament life~ Also, if soft glass~ such as soda li~e silicate, is used for the e~elope, apart from the obvious difficulties of the low softenin~ temperature and hlgh water content~ the alkali metals can react wi.th the halogen ox halides, again reducing filament li~e.
In ope~ation, tungsten-halogen la~ps normally contai.n a non-reactive gas filling such as ~2~ ~rg Kr or X.e together with iodine, bromine or chlorine vapour whiGh combin.es with the evaporated tungste~. escaping from the inca~descent fi7ament. A~ equilibr.ium concentration i.s attained by the gaseous species within the lamp between the 1:emperattlre limits defined by the i.ncandescent filament and col~est spot on the .~
.
.
7~
lamp envelope. ~he cold spot temperature must be suffi~
ciently high to prevent an-g tun~sten hali(le from condensing t and provided that this condition i5 met a continuous t~ngs~er trc~sport cycle operates which keeps t-he e~velope ~xee from tungsten~ The minimum envelope tempera-ture depends upon the halo~en ox halogens taki.ng part in the cycleO However, the maxi'num envelope temperature is usually well above the acceptable limit for soft glass, and for this reason tun~sten-halogen lamp envelopes are usually made from vitreous fus0d silica or high silica content glasses.
The return o~ tungsten to the filament does not in itself increase filament life since tungsten iodides, bromldes and chlorides dissociate well below normal filament operatin~
. temperatures. Radio-chemical tracers have shown that evaporated tungsten is redistribu.ted during the life of the lamp so that the cooler parts of the filament collect -tungsten at a ~reater rate than the hotter partsO ~ilament failure usually occurs quite normally by the subseque.nt burn~out of a 'hot spot'. '~he improvement in life of tungsten-halo~en lamps . 20 in comparison with conventional incandescent lamps is for quite a differeLlt reason~ The absence of envelope blackening coupled with the requiremen.t for a well-defined minimum envelope temperature dictates tha-t the envelope must be . su~stantially smaller than that of a conventional courlterpart.
In fact, tungsten-halo~en lamp envelopes are usually small and mechanicall~r strong and in consequence can be safely gas-. filled to several a-tmospheres pressure. ~'his increased.~as : -3-7~
filling pressure accounts for the gain in life.
If f;lament 'hot spots' could be healed or prevented a further extension in filament life would be possible. This is feasible with a tungsten-fluorine transport cycle because in this case the most stable tungsten fluoride dissociates at a temperature above 3000C, and tungsten is returned to the incandescent filament surface. Again, this has been substantiated by radiochemical tracer experiments, which show that tungsten vapour returned from the region of the envelope is evenly distributed along the incandescent part of the filament. Technological difficulties have prevented the further development of tungsten-fluorine lamps, the principal problem being that free fluorine reacts rapidly with solid tungsten below about 2000C, the cold parts of the filament, the lead wires and the supports being rapidly eroded, and that the fluorides formed (e.g. tungsten fluorides) react with the silica contained in the envelope material to form SiF4, depositing tungsten on the tube wall. This uses up the free fluorine in a very short time. Various methods have been proposed for protecting the envelope and tungsten components but these have been unsuccessful because of the inability to produce a continuous thin layer of protective material free from pin-holes and minor defects.
In our Canadian Patents Nos. 986,980 of April 6, 1976 and 1,050,605 of March 13, 1979, both of which are assigned to Thorn Lighting Limited, we describe the use of glassy coatings for the internal surfaces of halogen-containing electric lamps, and describe a process for ~ 9~
the form?~tion cf defect~free coatin~s by deposition of a solutio~l of compounds of the metal and phosphorus or arsesiG, followed by e~aporation of the solven-t and bakin~ of the resultin~ layer~
5 United States Patent ~o, 3,067,356 describes a fluores-cent lamp havin~ an inter:rlal barrier layer of, inter alia, aluminilun oxide i.ntended to reduce darkenin~ of the lamp by reaction of mercury in the gas fill with alkali in the glass of the lam~ tube. ~ot only is the use of this coati~g different from that required for this invention, but the layer in the Patent re~erred to is ~ormed by applying the particu-late oxide in a lacquer vehicle, follcwed bg- drying G~nd baking~
and such a layer does not provide effective protection against a hi~hl~ reactive gas such as fluorine.
r~he presellt invention now provides an alternative or improved. protective layer for the exposed internal surfaces oi' incandescent lamps which tend to react with the f-ill in -the lamp en-velope, particularly where -this includes a halogen~
and more especially fluorine or a fluorine-contai.nil~g compound,
2~ Xn accordance with this invention at least those ; portions of the i.nterna]. surface of -the en~el.ope o~ a halogen cycle incandescen-t lamp, and preferably also the exposed sur~aces of inter~al components which tend to react wi-th the - fill in the envelope during operation of the lamp are coated.
with a continuous i~perforate coating substanti.ally consistirlg of a me~al oxide resistant to halogen attack ~nd derived from a compound of the said metal deposited on such surfaces from solution~
i7~
~ urther in accord.~nce with.-t~is in~ention there is provided a ~ethod of making a halogen cycle incandescerlt lamp which comprises coat-ing at least those portlons of the i~-ternal surface of the envelope and tne exposed surfaces of 5 internal components which tend to react with halogen during operation of the lamp with a solution of a metal compoun.d capable of generating on being heated a halogen~-resistant oxide o~ the metal, and heating the resulting coating -to form on the surface a coating of the said oxide.
~he pre~erred metal o~ide ~or the formation of the coating is aluminium oxide, but other halo~en-resistan-t oxides, more especially of polyvalent or transition metals such as cerium, thorium and yttrium, and others of the lanthanide series, may be used. All~inium oxide has an especial adva~
tage in -that coatings formed thereby are both colourless and ~ranspalent. The coatings are preferably formed ~rom solutions of halides of the metals in polar organic solvents such as methanol~
Preferred solvents for the preparation of -the coating solution a.re oxygen~containing organlc solvents such as alcohols, estexs, ketones, aldehydes, nitro-compounds and ethers, or miætures thereof. Particwlarly preferred are nliphati~. alcohols, especially lower molecular weight . alcohols containin~ 1 to 4 carbon atoms, for example methanol, : ~5 ethanol, n- o:r iso-propanol or substituted alcohols such as methoxy- or ethoxy-ethallol. A wide variet~ of compound.s of the me-tals can be used, provi.aed they are solllble :in the `-99~
chosen solvent and generate on bei.ng heated the desired oxide without substantial contamination by other elements Simple inor~anic salts of the metals are preferred, especially the halides, but org~nic salts such as acetates ~!ay also be used. ~he sa.lt may form in ~olution a complex with molecules of the solvent.
~ 'he coated surfaces in the la~ps of this invention may include the internal surface of the envelope, the filament tails or lead-in wires or the filament supports~
depending on t~e nature of the fill gas employed and on the materials from which the envelope and the internal components are fabricated. Part or al.l of the filament or filaments may be initially provided with a coating, for examAple ~here the coating technique according to the invention ca~no-t conven-iently avoid this, but the coating on the filament will be remove~ when the fi.lament is heated to incandescence.
~ he protective coatin~s provided in accordance wi.ththis invention may be applied to conventional materials used for the fabrication of lamp components, for exa~lple to :20 protect them from hi.ghly reactive fill substances~ or they - ~ay enable cheaper and more readily available mclteria].s to be substituted for conventionally used materials wlthou-t unacceptable loss in performance or life~
- ~he oxide coating should be continuous and free from pin-holes or other de~ect or imperfection ~rhich might cause it to bre~ down durin~ operation of the lamp. Suitable coati.n~s are glass-like in appearallce but may have a micro~
c.rystalline stl~cture. They preferably have a thickness in the range 0~001 - 1 micron. Alt~rnatively, the coati.ng weigh-t may be 0~ - 1000 microgram per cm2.
In one preferred method of makin~ lamps according to this invention, the desired portions of the internal surface of the envelope and the surfaces of in-ternal components which are exposed in the finished lamp are coated either separately or after assembly with an organic solveIlt solution of c~n aluminium compound or complex capabl~ of ~enerating aluminium oxide, and subsequently heated to evaporate the solvent and cure the composition to form a defect-free alumi.nium oxide coatingO It has been found valua~ie in the producti.on of d.efect-free coatings to allow the applied liquid coating composition to drain thoroughly and thereafter -to bake initially a-t a relatively low temperature to remove the solve~t and subsequently at a controlled higher temperature to complete the formation of the protective coa-ting The preferred baking temperatures vary with the particular com-position en~ployed to generate the aluminium oxide, but c~m be determined by experiment.
One example of this techni~ue wi1l now be described with reference to the accompanying drawing which shows dia~
grammatical:Ly a tungsten-halogexl lamp assembly ln the course of manufacture.
As shown i~ the drawin~, a 12V. 55W. tungsten-halogen lamp, o~ the type commonly used i.~ projector and motor ~ehicle lighting applications, comprises a fused quartz g~
envelope 1 in whiGh is sealed a tungsten filament 2 supported on filament tails o.r lead-in wires ~ and is ; provided with an exhaust tube 4. '~he lamp is -to be providecl with an aluminil~-n oxide barxier layer covering the inside surface of the envelope 1, the filament 2 and filament tails A liquid CQating composition capable of generating the aluminium oxide is dlspensed ~rom a h~podermic syringe through the lamp exhaust -tube 4 by inserting the needle of the syringe, discharging the liquid composition and then almost immedlately drawing it back into the syringe, lecaving only a thin layer adhering to the inside surfaces of the lamp struc~
turer At this stage the lamp is inverted to drain, and then heated in a vacuum or sui-tably inert atmosphere, for example at approx.imately 100C for an hour in the case of a methanolic composition. ~he aluminium oxide coating is finally formed by bakillg at a higher tempera-ture, for example at 500C in a vacuum or suitably inert atmosphere ~or about 5 minutes~ The final b~e can be e~fectively incorporated in 20 subsequent lamp processing.
The initial heating cycle is chosen to substantially remove the solvent and the time, temperature and atmo~phere will depend upon the solvent selectedO '~he temperature of the subse~uent bake depends on ths particula.r formulation used, but will in general be below 1000C.
The lamp i.s then processed in the noI~lal ma~ner lor tungsten--halogen lamps. Wherl the filament is first ener~.ised _9~
~13~9~
the aluminium oxide layer on the incandescent filament surface and part of the filament tail adjacent to the filament is removed, leaving a protective barrier on the envelope surface and cold parts of the filament tails or lead-on wires.
In accordance with one aspect of this invention it has been found that when such lamps are provided with a fluorine-containing fill they can be operate~ with less or even substantially no attack on the filament tails, the filament or the envelope surface by fluorine or fluorides. The fluorine can be added as the element, or more conveniently as WF6 within the pressure range of 1 to 10 Torr, or as NF3 or SF6 or a solid such as NF4SbF6, NF4AsF6, XeF4SbF6, XeF4AsF6, TeF4SbF5 or SeF4SbF5. Solids may also be added in solution in suitable solvents as disclosed in the specification of our United States Patent No. 3,898,500.
An alternative source of fluorine is described in our Canadian Patent No. 1,069,576 of January 8, 1980, namely a soluble fluorocarbon polymer, which can be metered into the lamp envelope in solution in, for example, a fluorinated organic solvent.
In accordance with another aspect of this invention r cheaper or more easily obtainable or workable materials are used for the envelope or internal components of halogen cycle lamps by providing on the exposed surfaces of such parts of the structure a coating of aluminium oxide as described above.
In certain established tungsten-halogen lamps (eAg.
-`10--t~ri~l filament car lamps) a molybdemlm ~rame or wires is or are used both as lead~in conductors and as a member to carr~-a molybdenum ~or tungsten) shield~ There is some evidence to suggest that there is a limited chemical reaction b~tween -these components and the fill, ~nd in such a case it is advantageous to coa-t them with a halogen or halide-resistant la~ex of the aluminium oxide. However 5 as an alternative, the refractory me-tal i~ these components can be replaced by a less expensive and easier to work metal, such as iron or nickel, coated with the aforementioned layer~
- A further possibility is to use a glass en~elope coated with a halogen- or halide-resistant layer o~ alwninium oxide in place of the fused quartz conventionally ernployed for such envelopes. This may involve a direct xeplacement of fused ~uartz ~y a hard glass, such as borosilicate or aluminc silicate, or the use o~ inexpensive soda-lime silicate soft glass. In the latter case the en~elope dimensions should be carefully chosen so that the hottest part is below the glass strain temperature and the coldest part i5 above the well establ~ished minim~ for the par-ticular tungsten-halogen cycle to function. ~his also would reduce material and mallu~actur~
in~ costs~ lt should be noted that aluminosilicate glass is used for the envelope material of certain tungsten-halogen lamps but Camlot be considered as a replacement for fused ~uartz. It will thus be apparent -that individual components or all the internal surfaces wi-thin the l~p may be coa-ted~
The following ~re specifjc examples of the practical . ' .
:
7~
application of ~he present irvention and the production of tu~gsten-halogen lamps.
_ample 1 A liquid aluminium oxide coa-ting cornposition was prepared by dissol~ing anhydro1ls aluminlu~ chloride (3O95 g.) in methanol (396.05 g.). A tungsten filament lamp assembly was coated internally with this composition by the technique described above and the coated assembly thoroughly drained~
heated at 100C in vacuo for one hour, and baked at 500C for 5 minutes also i vacuo~ q'he lamp was subsequently filled with ~ atm~ argon and 4 ~orr ~16 and finished in the usual way.
~ he lamp was rated at 12V. 100W~ in operation and was successfull~ run at a filamerl~ temperature of 3200C for mo~e -than 25 hours without bre~down of the coa-ting. In contrast, similar lamps withou-t the coating of this invention showed extremel~ rapid loss of fluorine due to reaction with the lamp components a~d had a useful li.fe of only a few minutes~
Ex~m~le 2 , I,amps were made as described ln ~xample 1 excep-t tha-t 4 '~orr of S~6 was used instead of the ~6. The lamp was e~ually successfu1.
La~ps were made as described in EY.ample 1, except that the coating compositiorl consisted of ~5 ~. CeriU~l chloride ~CeC13) dissolved in ~6~5 gO methanol, any precipit~te separatirlg out being filtered off befoxe use~ ~he larnps .
~. .. . .
- were b~ed at ~700C ~or 5 minutes ~n vacuo and showed similar performance.
Examples_~ to 10 ~he followi..ng are further examples of coating compositions employing different metals, whi.ch may be u~ed for the purposes o~ this invention:
E~ample 4: 6.2 gl Ce(N03)3~20 dissolved in 93~8 g~ m~th.~ol (and filtered).
ExaDlple 5: 4.4 g~ SnClL~ ydrous, dissol-ved in 95~6 g~
methanolO
Example 6: 5.9 gO SnGl~,~5H20 dis~olvecl in 94~1 g. me-thanol.
Ex~lple 7: 7.0 gO ZrOCl2.~H20 dissolved in 93O0 gO methanolO
~xample 8: ~.9 g. Sn(N0~3 h~drate~ dissolved in 96,1 gO
methanvl~
Exa~ple 90 '~.4 g~ YCl3 hydrate, clissolved in 95.6 ~. methanol~
Example 10: 392 g~ ThC14 h~drate, dissolved in 9608 g-methanol.
The salts used we:re of technical grade. Yn the case of Fxample 4 some precipitate formed on s-tandin~ ~nd this wa5 filtered off~ In the other 'æx~nples no t`~ltration w~s necessa, y~
~13
with a continuous i~perforate coating substanti.ally consistirlg of a me~al oxide resistant to halogen attack ~nd derived from a compound of the said metal deposited on such surfaces from solution~
i7~
~ urther in accord.~nce with.-t~is in~ention there is provided a ~ethod of making a halogen cycle incandescerlt lamp which comprises coat-ing at least those portlons of the i~-ternal surface of the envelope and tne exposed surfaces of 5 internal components which tend to react with halogen during operation of the lamp with a solution of a metal compoun.d capable of generating on being heated a halogen~-resistant oxide o~ the metal, and heating the resulting coating -to form on the surface a coating of the said oxide.
~he pre~erred metal o~ide ~or the formation of the coating is aluminium oxide, but other halo~en-resistan-t oxides, more especially of polyvalent or transition metals such as cerium, thorium and yttrium, and others of the lanthanide series, may be used. All~inium oxide has an especial adva~
tage in -that coatings formed thereby are both colourless and ~ranspalent. The coatings are preferably formed ~rom solutions of halides of the metals in polar organic solvents such as methanol~
Preferred solvents for the preparation of -the coating solution a.re oxygen~containing organlc solvents such as alcohols, estexs, ketones, aldehydes, nitro-compounds and ethers, or miætures thereof. Particwlarly preferred are nliphati~. alcohols, especially lower molecular weight . alcohols containin~ 1 to 4 carbon atoms, for example methanol, : ~5 ethanol, n- o:r iso-propanol or substituted alcohols such as methoxy- or ethoxy-ethallol. A wide variet~ of compound.s of the me-tals can be used, provi.aed they are solllble :in the `-99~
chosen solvent and generate on bei.ng heated the desired oxide without substantial contamination by other elements Simple inor~anic salts of the metals are preferred, especially the halides, but org~nic salts such as acetates ~!ay also be used. ~he sa.lt may form in ~olution a complex with molecules of the solvent.
~ 'he coated surfaces in the la~ps of this invention may include the internal surface of the envelope, the filament tails or lead-in wires or the filament supports~
depending on t~e nature of the fill gas employed and on the materials from which the envelope and the internal components are fabricated. Part or al.l of the filament or filaments may be initially provided with a coating, for examAple ~here the coating technique according to the invention ca~no-t conven-iently avoid this, but the coating on the filament will be remove~ when the fi.lament is heated to incandescence.
~ he protective coatin~s provided in accordance wi.ththis invention may be applied to conventional materials used for the fabrication of lamp components, for exa~lple to :20 protect them from hi.ghly reactive fill substances~ or they - ~ay enable cheaper and more readily available mclteria].s to be substituted for conventionally used materials wlthou-t unacceptable loss in performance or life~
- ~he oxide coating should be continuous and free from pin-holes or other de~ect or imperfection ~rhich might cause it to bre~ down durin~ operation of the lamp. Suitable coati.n~s are glass-like in appearallce but may have a micro~
c.rystalline stl~cture. They preferably have a thickness in the range 0~001 - 1 micron. Alt~rnatively, the coati.ng weigh-t may be 0~ - 1000 microgram per cm2.
In one preferred method of makin~ lamps according to this invention, the desired portions of the internal surface of the envelope and the surfaces of in-ternal components which are exposed in the finished lamp are coated either separately or after assembly with an organic solveIlt solution of c~n aluminium compound or complex capabl~ of ~enerating aluminium oxide, and subsequently heated to evaporate the solvent and cure the composition to form a defect-free alumi.nium oxide coatingO It has been found valua~ie in the producti.on of d.efect-free coatings to allow the applied liquid coating composition to drain thoroughly and thereafter -to bake initially a-t a relatively low temperature to remove the solve~t and subsequently at a controlled higher temperature to complete the formation of the protective coa-ting The preferred baking temperatures vary with the particular com-position en~ployed to generate the aluminium oxide, but c~m be determined by experiment.
One example of this techni~ue wi1l now be described with reference to the accompanying drawing which shows dia~
grammatical:Ly a tungsten-halogexl lamp assembly ln the course of manufacture.
As shown i~ the drawin~, a 12V. 55W. tungsten-halogen lamp, o~ the type commonly used i.~ projector and motor ~ehicle lighting applications, comprises a fused quartz g~
envelope 1 in whiGh is sealed a tungsten filament 2 supported on filament tails o.r lead-in wires ~ and is ; provided with an exhaust tube 4. '~he lamp is -to be providecl with an aluminil~-n oxide barxier layer covering the inside surface of the envelope 1, the filament 2 and filament tails A liquid CQating composition capable of generating the aluminium oxide is dlspensed ~rom a h~podermic syringe through the lamp exhaust -tube 4 by inserting the needle of the syringe, discharging the liquid composition and then almost immedlately drawing it back into the syringe, lecaving only a thin layer adhering to the inside surfaces of the lamp struc~
turer At this stage the lamp is inverted to drain, and then heated in a vacuum or sui-tably inert atmosphere, for example at approx.imately 100C for an hour in the case of a methanolic composition. ~he aluminium oxide coating is finally formed by bakillg at a higher tempera-ture, for example at 500C in a vacuum or suitably inert atmosphere ~or about 5 minutes~ The final b~e can be e~fectively incorporated in 20 subsequent lamp processing.
The initial heating cycle is chosen to substantially remove the solvent and the time, temperature and atmo~phere will depend upon the solvent selectedO '~he temperature of the subse~uent bake depends on ths particula.r formulation used, but will in general be below 1000C.
The lamp i.s then processed in the noI~lal ma~ner lor tungsten--halogen lamps. Wherl the filament is first ener~.ised _9~
~13~9~
the aluminium oxide layer on the incandescent filament surface and part of the filament tail adjacent to the filament is removed, leaving a protective barrier on the envelope surface and cold parts of the filament tails or lead-on wires.
In accordance with one aspect of this invention it has been found that when such lamps are provided with a fluorine-containing fill they can be operate~ with less or even substantially no attack on the filament tails, the filament or the envelope surface by fluorine or fluorides. The fluorine can be added as the element, or more conveniently as WF6 within the pressure range of 1 to 10 Torr, or as NF3 or SF6 or a solid such as NF4SbF6, NF4AsF6, XeF4SbF6, XeF4AsF6, TeF4SbF5 or SeF4SbF5. Solids may also be added in solution in suitable solvents as disclosed in the specification of our United States Patent No. 3,898,500.
An alternative source of fluorine is described in our Canadian Patent No. 1,069,576 of January 8, 1980, namely a soluble fluorocarbon polymer, which can be metered into the lamp envelope in solution in, for example, a fluorinated organic solvent.
In accordance with another aspect of this invention r cheaper or more easily obtainable or workable materials are used for the envelope or internal components of halogen cycle lamps by providing on the exposed surfaces of such parts of the structure a coating of aluminium oxide as described above.
In certain established tungsten-halogen lamps (eAg.
-`10--t~ri~l filament car lamps) a molybdemlm ~rame or wires is or are used both as lead~in conductors and as a member to carr~-a molybdenum ~or tungsten) shield~ There is some evidence to suggest that there is a limited chemical reaction b~tween -these components and the fill, ~nd in such a case it is advantageous to coa-t them with a halogen or halide-resistant la~ex of the aluminium oxide. However 5 as an alternative, the refractory me-tal i~ these components can be replaced by a less expensive and easier to work metal, such as iron or nickel, coated with the aforementioned layer~
- A further possibility is to use a glass en~elope coated with a halogen- or halide-resistant layer o~ alwninium oxide in place of the fused quartz conventionally ernployed for such envelopes. This may involve a direct xeplacement of fused ~uartz ~y a hard glass, such as borosilicate or aluminc silicate, or the use o~ inexpensive soda-lime silicate soft glass. In the latter case the en~elope dimensions should be carefully chosen so that the hottest part is below the glass strain temperature and the coldest part i5 above the well establ~ished minim~ for the par-ticular tungsten-halogen cycle to function. ~his also would reduce material and mallu~actur~
in~ costs~ lt should be noted that aluminosilicate glass is used for the envelope material of certain tungsten-halogen lamps but Camlot be considered as a replacement for fused ~uartz. It will thus be apparent -that individual components or all the internal surfaces wi-thin the l~p may be coa-ted~
The following ~re specifjc examples of the practical . ' .
:
7~
application of ~he present irvention and the production of tu~gsten-halogen lamps.
_ample 1 A liquid aluminium oxide coa-ting cornposition was prepared by dissol~ing anhydro1ls aluminlu~ chloride (3O95 g.) in methanol (396.05 g.). A tungsten filament lamp assembly was coated internally with this composition by the technique described above and the coated assembly thoroughly drained~
heated at 100C in vacuo for one hour, and baked at 500C for 5 minutes also i vacuo~ q'he lamp was subsequently filled with ~ atm~ argon and 4 ~orr ~16 and finished in the usual way.
~ he lamp was rated at 12V. 100W~ in operation and was successfull~ run at a filamerl~ temperature of 3200C for mo~e -than 25 hours without bre~down of the coa-ting. In contrast, similar lamps withou-t the coating of this invention showed extremel~ rapid loss of fluorine due to reaction with the lamp components a~d had a useful li.fe of only a few minutes~
Ex~m~le 2 , I,amps were made as described ln ~xample 1 excep-t tha-t 4 '~orr of S~6 was used instead of the ~6. The lamp was e~ually successfu1.
La~ps were made as described in EY.ample 1, except that the coating compositiorl consisted of ~5 ~. CeriU~l chloride ~CeC13) dissolved in ~6~5 gO methanol, any precipit~te separatirlg out being filtered off befoxe use~ ~he larnps .
~. .. . .
- were b~ed at ~700C ~or 5 minutes ~n vacuo and showed similar performance.
Examples_~ to 10 ~he followi..ng are further examples of coating compositions employing different metals, whi.ch may be u~ed for the purposes o~ this invention:
E~ample 4: 6.2 gl Ce(N03)3~20 dissolved in 93~8 g~ m~th.~ol (and filtered).
ExaDlple 5: 4.4 g~ SnClL~ ydrous, dissol-ved in 95~6 g~
methanolO
Example 6: 5.9 gO SnGl~,~5H20 dis~olvecl in 94~1 g. me-thanol.
Ex~lple 7: 7.0 gO ZrOCl2.~H20 dissolved in 93O0 gO methanolO
~xample 8: ~.9 g. Sn(N0~3 h~drate~ dissolved in 96,1 gO
methanvl~
Exa~ple 90 '~.4 g~ YCl3 hydrate, clissolved in 95.6 ~. methanol~
Example 10: 392 g~ ThC14 h~drate, dissolved in 9608 g-methanol.
The salts used we:re of technical grade. Yn the case of Fxample 4 some precipitate formed on s-tandin~ ~nd this wa5 filtered off~ In the other 'æx~nples no t`~ltration w~s necessa, y~
~13
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an electrical incandescent lamp comprising an envelope having a gas fill containing halogen, the improvement comprising:
a continuous imperforate coating on the internal surface of said envelope, said coating consisting essentially of a metal oxide resistant to halogen attack and being derived from a compound of said metal deposited on said surface from solution.
a continuous imperforate coating on the internal surface of said envelope, said coating consisting essentially of a metal oxide resistant to halogen attack and being derived from a compound of said metal deposited on said surface from solution.
2. A lamp according to claim 1 wherein said coating consists essentially of aluminium oxide.
3. A lamp according to claim 1 wherein the thickness of said coating is in the range 0.001 to 1 micron.
4. A lamp according to claim 1 including internal components having surfaces exposed to said gas fill, said exposed surfaces also having a continuous imperforate coating of said oxide.
5. A method of protecting the internal surface of a lamp envelope from attack by halogen in the gas fill of the lamp which comprises the steps of :
preparing a solution of a compound of a metal which on heating will generate an oxide of said metal resistant to halogen attack;
depositing a coating of said solution on said internal surface;
drying said solution coating to form a substantially uniform coating on said surface;
and heating said coated surface to form thereon a continuous imperforate coating of said oxide.
preparing a solution of a compound of a metal which on heating will generate an oxide of said metal resistant to halogen attack;
depositing a coating of said solution on said internal surface;
drying said solution coating to form a substantially uniform coating on said surface;
and heating said coated surface to form thereon a continuous imperforate coating of said oxide.
6. A method according to claim 5 wherein said metal compound is a compound of aluminum.
7. A method according to claim 5 wherein said solution is prepared by dissolving a halide of said metal in a polar organic solvent.
8. A method according to claim 5 including the addi-tional steps of:
coating the surfaces of internal components of said lamp with said solution;
and drying and heating said coated surface to form a protective coating of said oxide thereon.
coating the surfaces of internal components of said lamp with said solution;
and drying and heating said coated surface to form a protective coating of said oxide thereon.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1045/76 | 1976-01-12 | ||
| GB104576A GB1571194A (en) | 1976-01-12 | 1976-01-12 | Internal protective coating for incandescent lamps |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1097991A true CA1097991A (en) | 1981-03-24 |
Family
ID=9715212
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA269,431A Expired CA1097991A (en) | 1976-01-12 | 1977-01-11 | Metal oxide coating in halogen incandescent lamps |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS52101881A (en) |
| AU (1) | AU507484B2 (en) |
| BE (1) | BE850296A (en) |
| CA (1) | CA1097991A (en) |
| DE (1) | DE2701051A1 (en) |
| DK (1) | DK11577A (en) |
| FR (1) | FR2337939A1 (en) |
| GB (1) | GB1571194A (en) |
| IE (1) | IE44478B1 (en) |
| IT (1) | IT1075605B (en) |
| LU (1) | LU76555A1 (en) |
| NL (1) | NL185881C (en) |
| SE (1) | SE437743B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD143980A1 (en) * | 1979-07-13 | 1980-09-17 | Hasso Meinert | LIGHT BULB WITH A FLUOR CIRCULAR PROCESS |
| DE3139294A1 (en) * | 1981-10-02 | 1983-04-21 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH, 8000 München | HALOGEN BULB AND METHOD FOR PROTECTING YOUR INTERIOR SURFACE |
| JPS5958753A (en) * | 1982-09-28 | 1984-04-04 | 株式会社東芝 | Incandescent bulb |
| GB8428881D0 (en) * | 1984-11-15 | 1984-12-27 | Atomic Energy Authority Uk | Light scattering coatings |
| DE102008061776A1 (en) | 2008-12-11 | 2010-06-17 | Osram Gesellschaft mit beschränkter Haftung | halogen bulb |
| DE102010042557A1 (en) | 2009-10-21 | 2011-04-28 | Osram Gesellschaft mit beschränkter Haftung | halogen bulb |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT175628B (en) * | 1950-07-12 | 1953-07-25 | Egyesuelt Izzolampa | Incandescent lamp and process for making same |
| FR1139217A (en) * | 1954-02-26 | 1957-06-26 | Philips Nv | Incandescent lamp |
| FR1375567A (en) * | 1963-11-27 | 1964-10-16 | Philips Nv | Gas-filled incandescent lamp |
| HU162781B (en) * | 1971-12-22 | 1973-04-28 |
-
1976
- 1976-01-12 GB GB104576A patent/GB1571194A/en not_active Expired
-
1977
- 1977-01-07 NL NL7700150A patent/NL185881C/en not_active IP Right Cessation
- 1977-01-11 IT IT1916677A patent/IT1075605B/en active
- 1977-01-11 CA CA269,431A patent/CA1097991A/en not_active Expired
- 1977-01-12 IE IE5277A patent/IE44478B1/en unknown
- 1977-01-12 BE BE174002A patent/BE850296A/en not_active IP Right Cessation
- 1977-01-12 SE SE7700252A patent/SE437743B/en not_active IP Right Cessation
- 1977-01-12 DE DE19772701051 patent/DE2701051A1/en active Granted
- 1977-01-12 FR FR7700792A patent/FR2337939A1/en active Granted
- 1977-01-12 LU LU76555A patent/LU76555A1/xx unknown
- 1977-01-12 DK DK11577A patent/DK11577A/en not_active Application Discontinuation
- 1977-01-12 AU AU21269/77A patent/AU507484B2/en not_active Expired
- 1977-01-12 JP JP281177A patent/JPS52101881A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| IT1075605B (en) | 1985-04-22 |
| SE437743B (en) | 1985-03-11 |
| IE44478B1 (en) | 1981-12-16 |
| DE2701051C2 (en) | 1988-08-11 |
| DE2701051A1 (en) | 1977-07-21 |
| JPS52101881A (en) | 1977-08-26 |
| FR2337939B1 (en) | 1980-09-05 |
| GB1571194A (en) | 1980-07-09 |
| FR2337939A1 (en) | 1977-08-05 |
| AU2126977A (en) | 1978-07-20 |
| DK11577A (en) | 1977-07-13 |
| IE44478L (en) | 1977-07-12 |
| AU507484B2 (en) | 1980-02-14 |
| NL7700150A (en) | 1977-07-14 |
| SE7700252L (en) | 1977-07-13 |
| NL185881C (en) | 1990-08-01 |
| BE850296A (en) | 1977-07-12 |
| NL185881B (en) | 1990-03-01 |
| LU76555A1 (en) | 1977-06-17 |
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