|Publication number||US3536946 A|
|Publication date||Oct 27, 1970|
|Filing date||Dec 7, 1967|
|Priority date||Dec 7, 1967|
|Publication number||US 3536946 A, US 3536946A, US-A-3536946, US3536946 A, US3536946A|
|Inventors||Kopelman Bernard, Kulberg Marshall E|
|Original Assignee||Sylvania Electric Prod|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (15), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Oct. 27, 1970 B. K OP ELIMAN ET AL 3,533I9Z TEMPERATURE-RESISTANT REFLECTIVE COATING FOR QUARTZ ENVELOPE Filed Dec. 7, 1967 BERNARD KOPELMAN MARSHALL E. KULBERG INVENTORS BY m A TORNEY FIG.2
United States Patent "ice US. Cl. 313-113 Claims ABSTRACT OF THE DISCLOSURE A diffusely-reflecting coating on quartz is made of a silico-phosphate. It can be used on a tubular quartz envelope to increase the effective size of an incandescent filament coil for optical purposes. The coating can be applied as a mixture of phosphoric and silicic acids with some ammonium bifluoride added, and then heated to a temperature of about 1125 C. A porous and adhesive white-coating is formed on the glass. Heating to 1150 C. will fuse the mixture to the quartz as a clear coating and cause cracking due to unequal coeflicients of expansion. The coating can also be used on the quartz envelope of an electric discharge tube such as a high pressure mercury vapor lamp, and the coating can be used for other purposes. The coating can be made thin for diffusion or heavy for reflection.
This invention relates to a diffusing coating suitable for use on quartz and high silica glasses. In particular, it relates to a lamp in a quartz envelope having such a coating over at least part of its surface.
Lamps having extended area planar type filaments, such as the so-called C13 and C13D filaments, have found wide use in slide projector equipment and in fixtures used in television and motion picture studios. These planar filaments often called monoplane or biplane filaments, depending on whether the multiplicity of parallel filament coils of which they are composed is arranged in a single plane or in two slightly-spaced parallel planes, are usually made in soft or hard glass envelopes.
While it is possible to use coil configurations in quartz lamps at wattages of 1000 w. or less, the larger wattages with their larger coil configurations require such large diameter quartz tubes as to be economically unattractive. It appears, however, that if a single coil is surrounded partially by a substantially opaque diffusely-reflecting coating, then the coating itself behaves as a spread-out filament and simulates the behavior of the C13 coil, due to reflection of light from the coating. Such a coating on a quartz tube will allow a single coil to behave like a C13 coil and allow tungsten-halogen lamps to be competitive with soft and hard glass incandescent lamps in existing fixtures.
The quartz envelope of the tungsten-halogen almp operates at very high temperatures, often well above 600 C., and ordinary coatings are unsatisfactory, because they will either crack the quartz, because of its much lower expansion coeificient, or they will burn off.
We have discovered, however, that a coating of a silicophosphate can be used on the quartz without such cracking or burn-off and with very effective results.
When phosphoric acid, silicic acid and ammonium bifluoride (NH,HF are mixed, applied to quartz and properly heated, a white reflective coating results, and seems to have a porous nature and firm adhesion to the quartz.
The application of the mixture to the enevlope is quite critical. After being applied to the quartz as a paste, it is heated slowly; at about 300 C., the liquids having 3,536,946 Patented Oct. 27, 1970 mostly evaporated, it has the appearance of a grey frozen slush. At about 1000 C. it begins to sinter to a porous but cohesive mix, and shows the beginning of adhesion to the quartz at about 1125 C. However, the mixture will fuse to a clear glass coating at about 1150 C. and the quartz envelope will eventually crack. Accordingly, the final temperature of the coating during manufacture must be below 1150 C., and about 1125 C. being effective, and the temperature during subsequent operation must be less than 1150 C. The latter limitation is not a disadavntage, however, since the tungsten halogen lamp generally operates well below that temperature.
The silico-phosphate is the only coating we have found that can be made to adhere to quartz throughout the thermal cycling and recycling normal to the operation of the lamp. It appears to do this by a combination of relatively low thermal expansion coeflicient, only two or three times that of quartz itself, and a porous structure which takes up any stresses involved.
In order to adhere satisfactorily to the quartz, the
, silico-phosphate should contain an addition such as ammonium bifluoride, which appears to etch the quartz surface so that a better bond is achieved between the quartz and the silico-phosphate. Without such an additive, the coating will flake ofli. Other fluorides can :be used.
When ammonium bifluoride is used, it breaks down on heating to become ammonium fluoride and hydrofluoric acid, the latter apparently etching the glass at the same time the coating is sintered, thereby forming a good bond.
In order to prevent cracking, the coating must not be heated to the point of complete fusion, but should be heated only to sintering or semi-fusion.
Other objects, features and advantages of the invention will be apparent from the following specification taken in connection with the accompanying drawings in which:
FIG. 1 is a perspective view of a lamp according to the invention; and
FIG. 2 is a cross-sectional view, showing the filament coils.
In FIG. 1, the tubular quartz envelope 1 has the pressed seal 2 at one end and the sealed exhaust tube 3 at the other end. The external lead-in wires 4, 5' extend into the press seal 1, where each is attached in the usual manner to the thin molybdenum ribbons 6, 7 and act also as support wires for the coiled-coil filament 10 shown in FIG. 2, but obscured in FIG. 1 by the coating 11 on the outside of envelope 1.
The coiled-coil tungsten wire filament 10 is mounted axially in the tubular envelope 1, the longitudinal axis of the coil being substantially on the longitudinal axis of the tubular envelope 1, the coil 10 being supported by the lead-in wires 8, 9, which are joined together a short distance above the seal 1 by the corrugated quartz bead 12. An additional support wire 13 extends to hold the middle portion of the filament coil 10, as shown more fully in FIG. 2
The lead-in and support wire 8 extends into the exhaust tube 3 to aid in centering and supporting the filament coil 10. Support wire 14 is wrapped around the upwardly-extending end 15 of wire 8 and extends from there in a bight 16 having an upwardly-extending end 17, which engages the singly-coiled end of the coiledcoil filament 10. The lead-in wire 9 extends upwardly and laterally, terminating in the downwardly-extending portion 18 to which an end 19 of filament coil '10 is affixed.
The filament structure and mounting can be shown in a copending application :Ser. No. 683,755 of L. S. Huston, Jr., filed Oct. 31, 1967, for an Incandescent Lamp and the bead 12 can be shown in a copending application Ser. No. 681,519 filed on Nov. 8, 1967, now Pat. No.
3 3,466,489, by Emery G. Audesse and L. S. Huston, Jr., with small coils around the lead-in wire inside the bead 12, if desired. Each of these applications has a common assignee with the present application.
The coating 11 can be applied to the quartz as a mixture of 20 grams of syrupy phosphoric acid, grams of silicic acid having a bulk-density of about 6.0 grams per cubic centimeter, and 2 grams of ammonium bifiuoride, results in a paste which can be applied in a layer. The coating is then slowly heated to 300 C., cooled, a second layer applied and heated similarly and then a third. A bubbly white coating results. It is then heated to 1125 C. If heated for minutes, the coating remains a bubbly white with excellent adhesion and good reflectance. If heated for A of an hour, the material sinteres to an advanced sintered state, 'which could be called semi-fused. Adhesion is excellent and no cracking of the quartz occurs.
The resultant lamp should not be operated at a temperature of 1100 C. or above, because at such temperatures the silico-phosphate coating will eventually change to a clear glaze and lose its reflecting power. Three layers of silico-phosphate, each about 3 millimeters thick, form a very effective coating.
Varioius modifications will be apparent from the foregoing specification without departing from the spirit and scope of the inevntion, which is limited only by the claims.
What we claim is:
1. An electric lamp comprising a tubular quartz envelope, a light source inside said envelope, and a porous semi-fused silico-phosphate coating on said quartz envelope, said light source is a compact incandescent filament and said coating is on a portion of the circumference of said envelope in register with said filament and covers an area substantially greater than the area correspending to the product of the length-and outside diameter of said filament, whereby the effective size of the light source is increased by reflection from the coating.
2. The lamp of claim 1, in which the coating is confined to the portion of the envelope adjacent the filament.
3. The lamp of claim 2, in which the compact incan-- descent filament is a single coiled-coil filamentvs'ubstan tially axial of the envelope.
4. The combination of claim 1 in which the silicophosphate coating contains a fluoride to improve the References Cited UNITED STATES PATENTS 2,144,438 1/1939 Birdseye 313-113 2,568,459 9/1951 Noel 313220 2,806,968 1/ 1957 Thorington et a1. 313-116 X 2,877,139 3/1959 Hyde 3l3l16 X 3,325,662 6/1967 Cook 313-113 X JAMES W. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner U.S. Cl. X.R.
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|U.S. Classification||313/113, 313/578, 427/108, 313/635, 427/106, 427/374.2|
|International Classification||H01J5/02, H01J5/08|