Tungsten-halogen lamp with organic and inorganic getters

A tungsten halogen lamp which utilizes a quantity, in combination, of an organic getter and inorganic getter for the purposes of substantially eliminating contaminants contained within the lamp and substantially reducing filament sag. In particular, the organic getter may be in the form of a carbon-containing halide, such as methyl bromide, and the inorganic getter may be in the form of a phosphorus-based gaseous getter, such as phosphine.

CROSS REFERENCE TO CO-PENDING APPLICATIONS 
In co-pending Application having Ser. No. 700,361 ("Tungsten-Halogen Lamp 
with Means for Reducing Filament Embrittlement"), there is defined a lamp 
having two substances for example a carbon-containing compound and a 
phosphorus-based compound, in a preferred ratio of quantities for the 
purpose of substantially reducing filament embrittlement leading to 
reduced lamp life. This Application is filed concurrently herewith and is 
assigned to the same assignee as the instant invention. 
In co-pending Application having Ser. No. 321,994 ("Electric Lamp Including 
Oxygen Getter"), there is defined a lamp containing phosphine (PH.sub.3) 
gas for the purpose of serving as an oxygen getter. This Application was 
filed on Nov. 16, 1981 and was assigned to the same assignee as the 
instant invention. 
TECHNICAL FIELD 
This invention relates to incandescent lamps and more particularly to 
tungsten-halogen incandescent lamps. Still more particularly, it relates 
to lamps of the latter variety having means, incorporated therein, for 
substantially eliminating contaminants contained within and for preventing 
filament sag. 
BACKGROUND OF THE INVENTION 
The majority of incandescent lamps today use a filament made from tungsten 
wire which can be of the single or coiled coil design. When initially 
energized to incandescence, the filament will both metallurgically 
recrystallize and physically sag under gravitational attraction. Coiled 
coil filaments, for the most part, have a tendency of sagging more than do 
single coil filaments and fine wire has a tendency of sagging more than 
does heavy wire. 
In the vertical position, sag is characterized by a collapsing of turns 
with open turns at the top and compression at the bottom. Sag in the 
horizontal position is characterized by the formation of one or more 
catenaries depending on the number of filament support wires. 
The preliminary sag in tungsten filaments has never been completely 
eliminated. However, it can be significantly reduced by utilizing a 
controlled heating process at the time of initial light-up. Flashing is 
one particular process known for doing this and is now in common use. 
Briefly, flashing is a method of stabilizing a filament. It is usually 
done after the coil is mounted in the lamp and can be performed either 
before or after tip-off. Since the filament as received is not brittle, it 
does not require hand mounting and, therefore, can be mounted 
inexpensively via high speed automatic equipment. Initial light-up under 
these conditions results in more preliminary sag than on a pre-stabilized 
coil. 
Unfortunately, the filament in an incandescent lamp will continue to sag 
during subsequent lamp operation in spite of flashing. This is generally 
attributed to a slippage at the grain boundaries. The condition is known 
to be aggravated by the presence of oxygen in the vapor state. This 
accounts for a higher degree of sag in halogen lamps because the halogen 
regenerative cycle retains a higher percentage of oxygen in the vapor 
state than there is in a non-halogen incandescent lamp. Generally, the sag 
in non-halogen incandescent lamps is not severe because most of the 
residual oxygen is tied up on the bulb wall as tungsten oxide, a colorless 
solid condensate. Thus, a sufficient quantity of oxygen is not available 
in the vapor state to promote sagging. 
However, in halogen lamps secondary sag and contamination can be a serious 
problem due to the fact that any oxides present can be reduced by the 
halogen or halide additive (HBr in this case) which promotes the presence 
of free oxygen in the vapor state. Also, chemical corrosion of the wire in 
the cooler sections of the filament results in a significant reduction in 
life as caused by thinning and premature arcing. This is more pronounced 
in fine wire than it is in heavy wire. 
There are numerous techniques now in use attempting to solve the problem of 
the existence of contaminants within the halogen lamp and sag of the 
filament in lamps of this type. Most of these techniques introduce new 
problems which force a compromise with respect to lamp performance. For 
the purposes of clarity, some of the more widely used techniques are 
briefly described here. 
Reduced Halogen Content--It has been shown by tests that a reduction in 
halogen content in the fill gas will give rise to corresponding reduction 
in filament sag and corrosion. Unfortunately, it will also result in an 
increase in the percentage of lamps which will turn black prematurely due 
to failure of the halogen regenerative cycle. Lamp blackening of any 
halogen lamp constitutes lamp failure even if the filament continues to 
burn. 
Other Halides--The halide additive often used is Hydrogen Bromide (HBr). It 
is considered by some lamp manufacturers to be too corrosive and, 
therefore, less desirable than the carbonaceous halides. Tests run fail to 
show any advantage to using this latter type of halide (CH.sub.2 Br.sub.2, 
for example). Also, a serious defect arises when using this gas. The 
result is a significant attenuation of light output which is caused by a 
carbon layer deposited on the inner bulb wall during initial light-up when 
the CH.sub.2 Br.sub.2 is decomposed into a more elemental form. 
It is believed, therefore, that a tungsten-halogen lamp that provides for 
means for substantially eliminating contaminants from within the lamp and 
substantially reduces filament sagging would constitute an advancement in 
the art. 
DISCLOSURE OF THE INVENTION 
It is, therefore, a primary objective of this invention to overcome the 
advantages of the prior art devices such as mentioned above. 
It is another object of this invention to provide a lamp with means to 
eliminate the contaminants contained therein, which attack the supports or 
lead wires and the filament, that will enhance the performance of such a 
lamp. 
Still another object of this invention is to substantially eliminate the 
possibility of filament sag in tungsten-halogen lamps. 
In accordance with one aspect of the present invention, there is provided a 
tungsten-halogen incandescent lamp comprising a light-transmitting, 
hermetically sealed envelope and a pair of lead-in wires press sealed in 
the envelope and extending internally and externally of the envelope. In 
addition, the lamp includes a tungsten filament attached between the 
internal ends of the lead-in wires and a fill gas within the envelope 
consisting of an inert gas and a halogen or halide. Furthermore, the lamp 
includes means for gettering oxygen contained within the envelope which 
comprises an organic getter in combination with an inorganic getter. More 
specifically, the organic getter comprises a carbon-containing gaseous 
compound, and the inorganic getter comprises a phosphorus-based gaseous 
compound.

BEST MODE FOR CARRYING OUT THE INVENTION 
For a better understanding of the present invention, together with other 
and further objects, advantages, and capabilities thereof, reference is 
made to the following disclosure the appended claims in conjunction with 
the above described drawing. 
Referring now to the drawing with greater particularity, the FIGURE shows a 
tungsten-halogen lamp 10 made in accordance with the teachings of the 
present invention. It is to be understood that lamp 10 is representative 
of only one of several varieties of electric lamps capable of successfully 
utilizing the gettering combination of the instant invention. Accordingly, 
the scope of the invention is not to be limited to the particular lamp 10 
as shown and described herein below. 
Lamp 10 has a tubular envelope 12 made of a suitable light-transmitting 
material such as quartz or a borosilicate or aluminosilicate glass. A pair 
of lead-in wires 14 and 16 are press sealed in envelope 12 at press seal 
18. Lead-in wires 14 and 16 are formed from a material, such as 
molybdenum, which will form a relatively strain-free hermetic seal with 
glass envelope 12. Further, as illustrated, lead-in wires 14 and 16 may 
include respective foil portions 14a and 16a within press 18 to facilitate 
such a seal. A tungsten filament structure 20, such as a coiled coil 
designed, for example, for 50-watt, 120-volt operation, is attached to the 
internal ends of lead-in wires 14 and 16. Envelope 12 is filled with a 
fill gas comprising an inert gas and a halogen or halide. Suitable 
examples of such an inert gas include argon and nitrogen. The halogen or 
halide additive, e.g., iodine or an iodide, which is in the gaseous state 
under the heat of lamp operation or may be incorporated as part of a 
gaseous compound, functions to reduce the coloration of the lamp envelope. 
Lamps of the above variety are known today and examples of other halogen 
that have been used within the lamp envelope include bromine and chlorine, 
or respective halides thereof. Typically, the halogen or halide gases 
sealed in the lamp reduce envelope blackening and maintain the color 
temperature for the life of the lamp. In operation, tungsten particles 
from filament structure 20 evaporate and collide with the halogen gas 
particles, resulting in a chemical combination and formation of a halide. 
The halide in turn disassociates at high temperatures in the vicinity of 
the filament. Accordingly, tungsten particles are deposited on the 
filament and the halogen gas released to subsequently effect once again 
the described combination. The result of the above activity is a 
self-cleaning lamp which never darkens and yet produces maximum light 
output over its entire life. The described operation of tungsten-halogen 
lamps is well known in the art and further description, is, therefore, not 
believed necessary. 
In an example of a preferred embodiment of the present invention, the 
manner of substantially eliminating the contaminants contained within a 
50-watt lamp, and preventing filament sag, consisted of introducing an 
organic and an inorganic getter, in combination, into envelope 12. The 
combination found to be most suitable, and to give a surprising result, 
was that of a carbon-containing gaseous getter and a phosphorus-based 
gaseous getter, respectively. In particular, it was discovered that the 
interaction of carbon and phosphorus together provided superior gettering 
qualities than either of the two substances used alone. The 
carbon-containing gaseous getter was introduced into the lamp as methyl 
bromide (CH.sub.3 Br), in an amount of about 0.12%. Methyl bromide, 
halide, also served as the source of halogen needed for lamp 10. The 
phosphorus-based gaseous getter was introduced into lamp 10 in the form of 
phosphine gas (PH.sub.3). The phosphine gas may be introduced in 
combination with the fill gas of the lamp so that upon normal phosphorus 
disassociation from the hydrogen (during lamp operation) an amount of 
phosphorus of about 1 to 10 micrograms will result. 
The quantity of carbon and phosphorus required in a particular lamp may 
vary depending on the diameter of the filament wire and the volume of the 
lamp vessel used, but should be of such quantity that is sufficient to 
provide an effective gettering action within the particular lamp. The 
total dose would increase as a lamp's volume increased. As wattage 
increases, so must the carbon to phosphorus ratio. In the present 
invention, the carbon to phosphorus mass ratio is in the range of from 
about 4:1 to about 1:1. The quantity of carbon is about 4 to 10 
micrograms; while the quantity of phosphorus is about 1 to 10 micrograms. 
The type of phosphorus preferred here is of the yellow phosphorus variety. 
In addition, the filament used here had a diameter in the range of about 
0.005 inch to 0.020 inch. The aforementioned embodiment should serve only 
to clarify the manner in which the invention operates and not to limit its 
application to other lamps. 
In gettering oxygen the carbon is most efficient at high temperatures 
(greater than 1000.degree. Kelvin) and the phosphorus is more efficient at 
low temperatures (less than 1000.degree. K.). This allows for more 
effective oxygen gettering over a large range of temperatures. Lamps made 
in the past not incorporating the aforementioned getters have exhibited 
early signs of failure or have been unable to reach lifetimes of four to 
five thousand hours. Lamps presently made with the carbon and phosphorus 
getters have not exhibited signs of early failure, have achieved lives of 
over four thousand hours and have produced lamps of superior quality. 
Thus, there has been shown and described a tungsten halogen lamp having 
means incorporated therein for substantially eliminating the contaminants 
contained within the lamp and substantially reducing filament sag when the 
lamp is subjected to the process of flashing. More particularly, a 
combination of organic and inorganic getters is provided, in the form of a 
carbon-containing gaseous getter (e.g., methyl bromide (CH.sub.3 Br)) and 
a phosphorus-based gaseous getter (or phosphine (PH.sub.3)), to 
effectively getter oxygen contained within the lamp. 
While there have been shown what are at present to be the preferred 
embodiments of the invention, it will be apparent to those skilled in the 
art that various changes and modifications can be made therein without 
departing from the scope of the invention as defined in the appended 
claims.