Gas mantle technology

A gas mantle has an operating color temperature of about 2300K and consists essentially of from about one percent to ten percent by weight of ceria and from about ninety percent to ninety-nine percent by weight of erbia.

This invention relates to gas mantle technology and more particularly to 
mantle structures for use with fuel burning devices such as portable 
fuel-burning devices to provide visible radiation. 
Incandescent gas mantles were products of major commercial importance in 
the latter part of the nineteenth century and into the early part of the 
twentieth century. Early mantles, made of oxides of calcium, magnesium, 
zirconium, lanthanum, yttrium and the like, provided inadequate lighting 
power. Thorium oxide-cerium oxide mantles (with minor additives) became 
the standard for gas light illumination. Those mantles, however, have poor 
strength and durability, and also involve problems in both manufacturing 
and use. Thorium compounds are radioactive and require special handling 
precautions which makes those manufacturing procedures complex, difficult 
and costly. Also, those mantles are relatively fragile after they have 
been fired. Thoria mantles of greater strength and durability have 
recently been described, as has an yttrium oxide-cerium oxide mantle which 
is alleged to retain its mechanical strength better than commercial thoria 
mantles. 
In accordance with one aspect of the invention, there is provided an 
improved gas mantle structure comprising a self-supporting erbia-ceria 
structure that has golden white color (a color temperature of about 
2300.degree. K.) when energized. The erbia-ceria structure preferably 
contains from about one percent to ten percent by weight of cerium oxide 
and preferably has a shock resistance figure of merit of at least three 
g-meters. In a particular embodiment, the mantle structure is composed of 
erbia-ceria filaments that are five-ten micrometers in diameter and that 
include a significant number of grains of dimensions in the order of one 
to two micrometers. The mantle structures are efficient in converting 
thermal energy to radiation energy in the visible spectrum (radiation in 
the 400-700 nanometer range). 
In preferred mantles, the erbia-ceria structure is fabric-like, for 
example, in woven, braided, or knitted form, and formed so as to provide a 
self-supporting dome of erbia-ceria filaments which is heated to 
incandescence by a gas flame. This dome of erbia-ceria filaments can be 
distorted to a large degree by an external force; in such distortion the 
filaments bend or twist elastically, and when the force is removed they 
regain their original shape, restoring the initial configuration of the 
mantle. Mantles in accordance with this aspect of the invention are able 
to undergo large elastic distortions without fracture. 
Mantle shock resistance depends upon such factors as mantle size and shape, 
characteristics of the precursor substrate used in manufacture (such as 
yarn size, type of weave, open area), processing conditions and mantle 
support. A useful shock resistance figure of merit for a cantilever 
supported mantle whose length and diameter dimensions are similar is 
provided, to a first order approximation, by the product of the shock load 
(in g's) that the mantle withstands and the unsupported length (in meters) 
of the mantle. The shock load is the force experienced by the unsupported 
mantle as a consequence of rapid deceleration on impact of the support 
tube against a stop; this load is commonly expressed in g's, where g is 
the acceleration due to gravity. Impact loads can involve deceleration 
forces substantially in excess of the force of gravity. Mantle structures 
in accordance with this aspect of the invention preferably have a shock 
resistance figure of merit of at least three g-meters. 
The choice of processing conditions depends on the shape and chemical 
composition of the organic fabric and on the cerium and erbium compounds 
employed in the embodiment. A preferred organic material for use in 
producing mantles of the invention is low-twist rayon yarn. However, other 
materials that absorb adequate amounts of the imbibing solution and that 
thermally decompose without melting, such as cotton, wool, silk and 
certain synthetic materials may also be used. 
Preferred erbium and cerium compounds are nitrates. The erbium and cerium 
compounds can be imbibed into the organic material (uniformly distributed 
within the fibrils) by any of several methods. In particular processes, 
the fabric is imbibed in an aqueous solution of nitrate salts that have a 
molar concentration of less than 1.4, preferably in the range of 0.8-1.1 
molar, particular compositions containing erbium nitrate and cerium 
nitrate in concentrations such that the final sintered product contains 
ceria in the amount of 3.0-4.0 weight percent. Minor amounts of other 
materials may also be included. 
The elementary erbia-ceria fibers of preferred mantles have a cross section 
dimension of less than ten micrometers and the mantle fabric has open area 
of greater than fifty percent. In a dome configuration that defines a 
volume of about 0.1 cubic centimeter and with a skirt portion shrink 
secured to a heat resistant support tube, the mantle withstands shock 
loads in excess of 600 g's. 
In preferred embodiments, the mantle filaments contain erbium oxide in an 
amount in the range from 90 percent to 99 percent by weight (more 
preferably in the range from 96 percent to 97 percent by weight); and the 
mantle filaments contain cerium oxide in an amount in the range from one 
percent to ten percent by weight (more preferably in the range from three 
percent to four percent by weight). The metal oxide filaments of such a 
mantle, after heating in an isobutane flame, have a microstructure 
including a significant number of grains of dimensions in the order of one 
to two micrometers, and are efficient in converting thermal energy to 
luminous energy in the visible spectrum. The flexibility, or ability of 
the mantle fabric to undergo considerable elastic distortion without 
fracture, is evidence of the strength of this improved mantle. 
In accordance with another aspect of the invention, there is provided a gas 
mantle manufacturing process that includes steps of imbibing a fabric of 
organic material with nonradioactive erbium and cerium nitrate compounds, 
increasing the temperature of the imbibed organic fabric in a controlled 
atmosphere at a controlled rate to a temperature sufficiently high to 
thermally decompose the erbium and cerium nitrate compounds as a step in 
the conversion of the erbium and cerium nitrate compounds to erbia and 
ceria, the erbium and cerium nitrate compounds and organic substrate 
material having interaction characteristics such that (in a suitable 
processing sequence in accordance with the invention) the erbium and 
cerium nitrate compounds undergo thermal conversion to a skeletal replica 
(with healable fissures or rifts) before thermal decomposition of the 
organic material is completed; further heating the imbibed fabric to 
decompose and remove the organic material from the imbibed fabric (the 
resulting further gaseous decomposition products of the organic substrate 
being removed from the replica through the rifts) and to complete the 
conversion of the erbium and cerium nitrate compounds to erbia and ceria 
such that an erbia-ceria replica of the organic fabric remains; and 
further heating the erbia-ceria replica to sinter and densify the 
erbia-ceria replica such that the densified erbia-ceria replica that has a 
strength (shock resistance figure of merit of at least three g-meters, 
which strength is retained after the erbia-ceria replica has been heated 
to 1500.degree. C. 
In a particular process, an imbibing mixture is made by dissolving 
nonradioactive nitrates of erbium and cerium in distilled water and mixing 
the salt solutions. An organic multifiber fabric in the form of a tubular 
sleeve is immersed in the imbibing mixture and gently agitated to promote 
penetration of the imbibing solution into the organic fibers. After 
imbibition, the sleeve is removed from the solution and compressed and 
then centrifuged to remove surface liquid, tied off and formed into a 
mantle sock, and dried. The shiny white imbibed mantle sock fabric is then 
thermally processed under controlled conditions. Initially, the 
temperature of the fabric is gradually increased in an atmosphere that 
contains a reduced amount of oxygen (preferably an oxygen partial pressure 
of less than 100 mmHg). A quite vigorous reaction, which occurs when the 
mantle fabric has reached a temperature of 130.degree.-170.degree. C., 
involves an interaction (termed herein "nitrate burn") between the 
nitrates and the cellulosic fabric, which reaction is visually evidenced 
by a color change that starts at some location in the fabric and produces 
a front which separates a tan color from the shiny white color and 
advances through the fabric in a few seconds. This "nitrate burn" reaction 
involves a partial oxidation of the cellulose of the fabric by the 
decomposition products of the nitrate ions--the gases produced by the 
thermal decomposition of the nitrates being strongly oxidizing in reacting 
with the cellulose. The fabric is then further processed in an atmosphere 
containing an increased amount of oxygen (for example, in a heat soak 
interval at about 300.degree. C.) during which the remaining cellulose is 
pyrolyzed and the residual carbon is removed by oxidation. During this 
continued thermal processing, an intermediate compound, 
ErO(NO.sub.2).sub.2, if present, is transformed to Er.sub.2 O.sub.3 ; the 
gas evolution slows, but continues until the replica is essentially erbium 
oxide, with a minor amount of cerium oxide. The temperature is further 
increased to densify and sinter the erbia-ceria replica. Beneficial 
sintering and densification of the erbia-ceria replica continues to occur 
until temperatures of at least about 1500.degree. C. are reached. The 
resulting erbia-ceria mantle has substantial strength and light output in 
the visible spectrum. 
Erbia-ceria mantles of the invention, in visual appearance, retain 
characteristic physical shapes of their organic precursors, although they 
are substantially reduced in dimension. Those erbia-ceria structures are 
characterized by relatively high density, strength (preferably a shock 
resistance figure of merit of at least three g-meters) and flexibility, 
and in preferred mantle configurations are efficient radiation sources (a 
luminous efficiency of at least one-half lumen per watt and an output of 
at least ten lumens with a one gram per hour isobutane flow rate).

DESCRIPTION OF TICULAR EMBODIMENTS 
Shown in FIG. 1 is mantle 10 and its support tube 12 as viewed in section 
through the axis of tube 12. Support tube 12 is of mullite and has a 
length of about twenty five millimeters, an outer diameter of about five 
millimeters and an inner diameter about three millimeters. Mantle 10 is 
self-supporting erbia-ceria fabric structure that defines a hollow chamber 
of about seventy cubic millimeters volume with its tip 14 extending about 
one-half centimeter beyond the end 16 of support tube 12. The skirt 18 of 
the mantle fabric (about one-half centimeter in length) is firmly secured 
to the outer surface of support tube 12. The shape of the outer surface of 
support tube 12 may be varied to achieve desired mantle configurations, 
for example, a fluted mantle sidewall shape. Auxiliary means such as an 
inorganic cement or a annular recess can optionally used to enhance the 
securing of mantle 10 to tube 12. 
The mantle fabric, a portion of which is shown enlarged generally at 20 in 
FIG. 1A, is formed of erbia-ceria multifilament strands 22 in an open knit 
array with openings 24 such that the open area of the fabric is about 
sixty percent. Cross-sectional dimensions of the individual fibers of 
strands 22 are in the range of 5-10 micrometers and the strands 22 have 
cross-sectional dimensions in the order of about 0.1 millimeter with 
openings 24 having dimensions of about one-half millimeter. 
The erbia-ceria mantle 10 can be made generally as follows. An imbibing 
mixture is made by dissolving salts of erbium and cerium in distilled 
water and mixing the salt solutions. Multifibril organic yarn fabric in 
the form of tubular sleeves are immersed in the imbibing mixture at room 
temperature and gently agitated to promote penetration of the imbibing 
solution into the organic fibers. After imbibition the sleeves are removed 
from the solution and compressed and then centrifuged to remove surface 
liquid. The resulting damp imbibed sleeves are tied at one end to form 
mantle socks and the formed socks are dried in a flow of warm air and then 
hung on a support for firing. A firing process converts the cellulosic 
mantle socks imbibed with erbium and cerium compounds into mechanically 
strong mantles that are composed substantially entirely of erbia and ceria 
and that emit radiation in the visible spectrum. 
EXAMPLE 1 
Knit-braided rayon hose (14 needle, 150 denier/60 filament) was soaked for 
ten minutes at room temperature in an aqueous imbibing mixture containing 
0.952M Er(NO.sub.3).sub.3 and 0.048M Ce(NO.sub.3).sub.3, made by mixing 
ten cubic centimeters of a 1.0M solution of reagent grade hydrated erbium 
nitrate (Er(NO.sub.3).sub.3.4H.sub.2 O) and 0.5 cubic centimeters of a 
1.0M solution of reagent grade hydrated cerium nitrate 
(Ce(NO.sub.3).sub.3.6H.sub.2 O). The imbibed hose was pressed and then 
centrifuged for about ten minutes at about 200 g's to remove excess 
liquid. 
Lengths of the damp imbibed hose were then formed into mantle socks by 
tying, shaping on a preform and drying using a flow of warm air (about 
90.degree. C.), and then placed on a fixture comprising a series of 
upstanding mullite posts spaced at intervals of about three centimeters on 
a mullite base. Each mullite post was about three millimeters in diameter 
and about 3.7 centimeters long and receives a support tube and spacer, the 
top of each support tube being spaced about five millimeters below the top 
of the post. Optionally a ring of sodium silicate that has been pretreated 
by heating the tube to about 300.degree. C. can be carried by the tube. 
The fixture with knitted imbibed formed socks hung over the support tubes 
on the posts was then subjected to a firing procedure to convert the 
erbium nitrate and cerium nitrate imbibed cellulosic mantle socks into 
light emitting and mechanically strong mantles. 
In the processing sequence diagrammed in FIG. 2, the fixture with the socks 
was placed in a fifty-two millimeter inner diameter quartz tube furnace 
(Thermolyne Model F-21125). At ambient temperature (about 20.degree. C.; 
indicated at point 30 in FIG. 2), carbon dioxide at a flow rate of sixty 
cubic centimeters per minute was flowed through the furnace. With this 
atmosphere in the furnace, the furnace temperature was then increased at a 
rate of 8.9.degree. C. per minute as indicated at line 32. The mantle 
fabric underwent "nitrate burn" at about 136.degree. C. (point 34). At 
this point the fabric color changed rapidly from white to golden tan. 
Heating was continued at a rate of about 7.8.degree. C. per minute as 
indicated by line 36 to a temperature of about 300.degree. C. (point 38). 
During this time the color continuously changed from golden tan to dark 
brown or black with modest shrinkage (about 10%) of the fabric, indicating 
additional decomposition of the organic material. Air at a flow rate about 
250 cubic centimeters per minute was then flowed through the furnace while 
the temperature was being raised at about 0.4.degree. C. per minute, as 
indicated at line 40, to about 340.degree. C., where the furnace 
temperature was held for about two hours sufficient to permit the mantles 
to turn from black to light gray or white. During this soaking interval in 
air the remaining carbon was oxidized and driven off and each dimension of 
the mantle shrank to about one-third of its original dimension so that the 
skirt portion was shrunk onto its support tube. At the end of the soaking 
interval (point 42) the furnace temperature was increased rapidly, at 
37.degree. C. per minute, as indicated at line 44, to a temperature of 
about 900.degree. C. (point 46). The furnace heater was then turned off 
and the furnace allowed to cool to ambient temperature. 
After cooling, each mantle subassembly was removed from its post and 
exposed to a burning mixture of isobutane and air at an estimated 
temperature of about 1600.degree. C. for five minutes to further shrink 
and densify the metal oxide fabric. 
Mantles 10 formed and shrink fitted to support tubes 12 in this manner were 
evaluated for shock strength using a L A B Automatic Drop Shock Tester 
(Model SD-10-66-30, available from Material Technology Incorporated) which 
is used with a Type 5520.5.85 Decelerating Device (pulse pad) for shock 
loads of up to about 600 g's and with a Type 5520.5.28 Decelerating Device 
(pulse pad) for shock loads in the range of 600 g's to 1600 g's. Mantles, 
made as described in this example, survived drop tests at shock loads in 
excess of 900 g's (range 900-1150 g's) and, when activated with an 
isobutane flame, yielded luminous efficiencies of about 0.9 lumens/watt 
(range 0.86-0.99 lumens/watt) at a color temperature of about 2265.degree. 
K. (range 2220.degree.-2340.degree. K.). 
EXAMPLE 2 
In this example, knit-braided hose was imbibed, and imbibed socks were 
shaped, dried, and hung on a fixture as described above for Example 1. 
Then the socks were subjected to a firing procedure as follows. 
In the processing sequence diagrammed in FIG. 3, the fixture with the socks 
was placed in the quartz tube furnace. At ambient temperature (about 
20.degree. C.; indicated at point 50 in FIG. 3), a mixture of air at a 
flow rate of fifty cubic centimeters per minute and carbon dioxide at a 
flow rate of sixty cubic centimeters per minute (the mixture containing 
about 9% O.sub.2). This flow was continued as the furnace temperature was 
increased at a rate of 11.3.degree. C. per minute as indicated at line 52. 
The mantle fabric undergoes a nitrate burn at about 136.degree. C. (point 
54). At this point the fabric color changes rapidly from white to golden 
tan. Heating was continued at a rate of about 9.5.degree. C. per minute to 
a temperature of about 300.degree. C. (point 56). During this time the 
color continuously changed from golden tan to dark brown or black with 
modest shrinkage (about 10%) of the fabric, indicating additional 
decomposition of the organic material. Air was then flowed through the 
furnace at a rate about 250 cubic centimeters per minute as the 
temperature was raised at about 0.4.degree. C. per minute, as indicated at 
line 58, to about 340.degree. C., so that it was held in the range 
300.degree. C.-340.degree. C. for a time (about two hours) sufficient to 
permit the mantles to turn from black to light gray or white. During this 
soaking interval in air, the remaining carbon was oxidized and driven off 
and each dimension of the mantle shrank to about 1/3 its original value so 
that its skirt portion was shrunk onto the support tube. At the end of the 
soaking interval (point 60) the furnace temperature was increased rapidly, 
at 37.degree. C. per minute, as indicated at line 62, to a temperature of 
about 900.degree. C. (point 64). The furnace heater was then turned off 
and the furnace allowed to cool to ambient temperature. 
After cooling, each mantle subassembly 10, 12 was removed from its post and 
exposed to a burning mixture of isobutane and air at an estimated 
temperature of about 1600.degree. C. for five minutes to further shrink 
and densify the metal oxide fabric. 
Mantles 10 formed and shrink fitted to support tubes 12 in this manner were 
evaluated for shock strength as described above for Example 1. Mantles 
made as described in this example produced a luminous efficiency activated 
with isobutane at ten scc of about one lumen/watt (range 0.96-1.01 
lumens/watt) at a color temperature of about 2250.degree. K. (range 
2230.degree.-2360.degree. K.), and survived drop tests at shock loads in 
excess of about 1000 g's (range 750-1350 g's). 
FURTHER EXAMPLES 
Further erbia-ceria mantles according to the invention were made using 
imbibing solutions having various concentrations and various molar ratios 
of erbium and cerium, and the mantles so made were tested for luminous 
efficiency and color temperature. 
Erbium nitrate (99.9% pure) and cerous nitrate (A.C.S. grade) were each 
dissolved in distilled water at the following molar concentrations: 0.6M, 
0.8M, 1.0M, 1.2M, and 1.5M. These aqueous solutions of erbium nitrate and 
cerous nitrate were mixed in various proportions to yield imbibing 
mixtures having cerium:erbium atom ratios ranging from 0.02 to 0.15. Nine 
different such imbibing mixtures were prepared at each molar 
concentration. 
Lengths of braided rayon sleeves were imbibed with erbium and cerous 
nitrate solutions by immersing them in imbibing mixtures of aqueous erbium 
and cerous nitrates prepared as described above for thirty minutes and 
then dried and tied to form mantle socks. The dried preformed mantle socks 
were placed over support tubes 12 and thermally processed with a 
propane/air flame to provide erbia-ceria mantles 10 on support tubes 12. 
Each mantle-tube assembly was operated with a constant supply of isobutane 
(ten scc/minute), the isobutane vapor being delivered through a 0.001 inch 
diameter orifice located in the throat of a venturi so that primary 
combustion air was entrained with the isobutane vapor. The isobutane flow 
rate was measured using a Hastings H-10 mass flow transducer and an ALL-10 
readout. The air inlet to the venturi had an adjustable restriction so 
that the entrained air could be adjusted for maximum light output from the 
mantle. 
The luminous output of each operating mantle was measured with a Model 
450-1 EG&G, Inc. radiometer/photometer, having a silicon photodiode type 
detector with a photopic filter. Readings were taken at distances (about 
25 centimeters) from the mantle that were large compared to the mantle 
dimension. For purposes of calculating luminous efficiency, it was assumed 
that such a mantle acts like a point source (this assumption being 
approximately verified in an integrating sphere). The lux reading from the 
photometer was converted to lumens and the luminous efficiency obtained by 
dividing the lumen reading by the gross heat of combustion of the fuel 
burned. Color temperatures were measured with a Minolta Color Meter II. 
The luminous efficiencies and color temperatures of mantles made using 
imbibing solutions over the entire range of ceria/erbia ratios were 
measured, and at each cerium:erbium atom ratio, mantles made using 
imbibing solutions at the various concentrations showed no significant 
differences in resulting luminous efficiency and color temperature. 
As indicated in FIG. 4, the luminous efficiency was greatest for mantles 
made using a Ce:Er atom ratio of 0.04, was progressively less at ratios of 
0.06, 0.1, and 0.15, and was also less at a ratio of 0.02. In the range of 
atom ratios tested, for mantles with an isobutane flow rate of ten 
scc/min, the color temperatures, as indicated in FIG. 5, was highest 
(about 2320.degree. K.) for mantles made using a Ce:Er atom ratio of 0.02 
and was progressively less at higher atom ratios about 2265.degree. K. for 
a Ce:Er atom ratio of 0.04 to about 2050.degree. K. for a Ce:Er atom ratio 
of 0.15. 
A mantle with a ceria/erbia weight ratio of about 0.035. was operated over 
a range of isobutane fuel burn rates from five scc/minute to fourteen 
scc/minute, and luminous efficiencies were measured, as indicated in FIG. 
6. At lower fuel burn rates inadequate thermal energy was transferred to 
the luminous mantle and the mantle ran at cooler temperatures, resulting 
in lower luminous efficiencies. At higher fuel burn rates, the flame 
lifted off the mantle so that less heat was transferred to the mantle, 
resulting in lower luminous efficiencies. The optimum operating point was 
at a fuel burn rate about eleven to twelve scc/minute, where the luminous 
efficiency was in excess of about 1.1 lumens/watt. 
While particular embodiments of the invention have been shown and 
described, various modification thereof will be apparent to those skilled 
in the art, and therefor, it is not intended that the invention be limited 
to the disclosed embodiments or to details thereof, and departures may be 
made therefrom within the spirit and scope of the invention.