Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INCANDESCENT MANTLE~
RELATED APPLI t:~ATION
This application is a continuation in part of application
Serial Number 07/292,767 filed on January 3, 1989
entitled: INCANDESCENT M~TLES.
FIELD OF T~E INVENTION
This invention relates in general to incandescent
mantles used in lamps burning fuels in gas or liquid form,
and in particular to mantles used in portable lamps of
this ~ype.
BACKGROUND OF THE I NVENTI ON
Incandescent mantles became a commercially
practicable produc~ following the introduction by Carl
Auer Von Welsbach in 1893 of a mantle having a composition
of about 99% thorium o~ide and about 1% cerium oxide.
This composition was determined by e~perimentation
covering a wide range of metal o~ides including rare earth
elements.
Thorium is a natural}y occurring radioactive metal.
Its decay products include alpha and beta radiation,
radium isotopes, and thoron gas, which is an isotope of
radon gas. Thorium is listed by US government agencies as
carcinogenic, and its processing is kept under strict
governmental licensing and control.
Thorium mantles are very fragile and the shocks
induced by normal usage cause rapid disintegration
requiring frequent replaceme~t. Each time a mantle is
changed and the old mantle discard~d, about 0.3 grams of
thorium o~ide, which is soft and powdery, is released into
the environment in an uncontrolled manner~ e~posing the
user and others to a potential health hazard.
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Early attempts to provide alternatives to the
thorium/cerium composition were focussed on a desire to
circumvent the Welsbach patents rather than to eliminate
thorium o~ide, but once these patents expired the
thorium/cerium composition was universally adopted and,
e~cept for minor proprietary ~ariations by various
manufacturers, this composition has remained virtually
unchanged, since no ef~ective alternative was considered
possible or even necessary. Now, however, a need e~ists
to reduce, or preferably eliminate, the unnecessary
release of radioactive material into the global
environment.
Further, a more robust incandescent mantle than the
conventional thorium/cerium mantle heretofore provided
would enhance the reliability and reduce the maintenance
expenses of incandescent lanterns and gaslights, and
permit che development of new forms of such devices, not
possible with the fragile thorium mantle.
Although it has been recognized that zirconium o~ide
would be a stronger and non-radioactive alternative to
thorium o~ide as a material for incandescent mantles, a
method for the practical production of mantles based on
zirconium o~ide has been wanting.
Encyclopedia Britanica l describes in some detail
the early history of the incandescent mantle. On page 656
it is noted that zirconia, and yttria, were possible
alternatives to thorium o~ide, but they were considered
unsuitable because of their fragility. Zirconia was also
rejected on the basis of shrinkage and slow volatilization.
The earliest mantles were of upright form, in which
the mantle was supported over a non-luminous flame by
means of a wire frame. Although obsolete, this type of
mantle is still manufactured for decorative purposes, see
Mantle E~amples Item D.
The problem of fragility was addressed in Voelker
U.S. Pat. No. 546,792 which proposed an incandescent
7227
mantle fashioned from filaments of porcelanous material
impregnated with solutions of rare earth salts, or with
rare earth o~ides incorporated in the porcelain base
material. There is no record in the literature to
indicate that such incandescent mantles were ever a
co~nercial success.
A more recent attempt to address the fragility of
thorium o~ide mantles is disclosed in Reid et al U.S. Pat.
~o. 3,738,793, which has a layer of thorium and cerium
oxides deposited on the outer surface of the porous
ceramic element of a gas burner operating on the surface
combustion principle.
The described manufacturing process is comple~, it
requires the deposition of several layers of metal o~ides
15 (column 2 line 29 through column 3 line 49~ onto a special
substrate followed by a heat treatment process, all
conducted under carefully controlled conditions. There is
no indication that incandescent lighting devices according
to Patent 3,738,793 have ever been produced on a
commercial basis.
Gas Appliance and Space Conditioning Newsletter,
March 1987, reviews the status of incandescent mantles and
provides a reference that mantle compositions other than
thorium/cerium were inferior to it in light output. Also
reviewed is the device disclosed in the above mentioned
25 Patent 3,738,793 which, also, attempts to coat
thorium/cerium oxide mi~tures onto substrates of silicon
carbide or zirconia, which are described as being the most
promising materials because of excellent high temperature
strength and thermal shock resistance, but these attempts
are recorded as having poor success and that a sintering
process instead of coating was to be tried. There is no
indication in this document that the substrate materials
were themselves to be used as the incandescent light
emitting body.
Nernst U.S. Pat. No. 685,730~ describes electric
lamp glowers composed of 85% zirconia and 15% of yttria or
7~7
- 4 -
other r~re earth o~ides. Nernst U.S. Pat. No. 685,732
describes electric lamp glow~rs composed of 80% zirconia,
10% yttria, and lO~ erbia. Nernst U.S. Pat. No. 685,733
describes electric lamp glowers co~posed of zirconia
5 combined with rare earth o~ides derived from yttrium
containing minerals in their natural-state proportions.
However, to date, neither Nernst nor anyone else has
described the u~e of zirconia, yttria and erbia in a gas
mantle.
In each of the above Nernst patents, the materials
were to be mi~ed with binding agents, compressed into bars
or tubes, and fired in a furnace to produce ceramic
elements termed glowers for use in Nernst lamps (see
Encyclopedia Britannica, p. 669). The resulting glowers
15 typically have thicknesses of about 1-2 mm, much greater
than those of the fibers employed in gas mantles. These
lamps made use of the property possessed by certain
ceramic materials to be good electrical insulators when
cold but good conductors when hot. After pre-heating to
20 initiate conduction, the glower element was raised to, and
maintained at, the required temperature by passage of an
electric current thus rendering the element an
incandescent light emitter.
Intended as an intermediate light source between the
25 powerful carbon arc li9ht and the weak Edison carbon
filament lamp, the Nernst light was rendered obsolete by
the introduction of the tungsten filament lamp, although
Nernst glowars are still produced in small quantities as
spectroscopic light sources. While the light emitting
30 property of the Nernst glower does not depend on the
passage of electric current, and in theory any suitable
heat source can be employed to cause the materials of the
glower to incandesce, use in conjunction with a gas flame
is not known.
"Making Ceramics Tougher" (July 27, 1987~ MACHINE
DESIGN, pp. 84-89, discusses a new variety of ceramic
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materials based on metal o~ides such as alumina, zirconia,
and magnesia. These are termed transformation-toughened,
or stabilised, ceramics in which a hase oxide is alloyed
or doped with a small percentage of other metal o~ides
S which strengthen and stabilize the structure by reducing
the metal o~ide grain size, so increasing resistance to
fracture.
One variety of transformation toughened ceramic is
yttria-stabilized tetragonal zirconia polycrystal ~Y-ZTP),
10 which is zirconium oxide with the addition of a small
percentage of yttrium o~ide (8-10% for example). This
ceramic has desirable strength properties, which may be
improved further by the addition of a second stabilizing
rare earth o~ide to eliminate certain temperature
15 degradation phenomena.
It will be noted that the composition of the Y-ZTP
materials bears a close resemblance to the Nernst glower
materials described above, but also, that these materials
have not been suggested for use in gas mantles. Another
20 form of toughened ceramic utilizes al~-minum o~ide
toughened with a small percentage of zirconium oxide
and/or chromium oxide.
Ceramic fibers are of special value as heat
insulating and refractory materials, but their preparation
25 has been difficult due to the brittleness and high melting
point of the appropriate materials. Hamling US Patent No.
3,385,915 discloses a process by which a host structure
composed of a cellulosic material, such as a woven fabric,
is used as a precursor to absorb dissolved metallic
30 compounds after prior dilation of the woven fibers with
plain water. The dissolved compounds enter into spaces
within the microscopic crystallite structure of the
dilated cellulosic fibers. A su~sequent heat treatment,
in an o~ygen-controlled atmosphere within a special
35 furnace, pyrolyses the organic fiber and leaves an
amorphous refractory metal o~ide structure in the shape of
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the host cellulosic material. The product ceramic fibers
ha~e tensile strength and flexibility. However~ the heat
treatment requires close control over temperature and the
oxygen content of the atmosphere surrounding the fibers.
5 It is emphasized in the
disclosure, Column 7 line 23 through Column 8 line 5 that
direct ignition of the impregnated material must be
avoided because the product then becomes weak and
brittle. The process of this disclosure is usually
10 referred to as the precursor process for producing ceramic
fibers.
E~ample 7 of the above disclosure, Column 14, line
67 through Column 15, line 19, describes application of
the sub~ect process to a thorium/cerium incandescent
15 mantle commercially manufactured for use in gasoline
lanterns. The resulting product was a thoria fiber
structure having the desirable properties of strength and
fle~ibility, which should render it suitable for
incandescent mantle applications. However, discussion of
20 this e~ample with patentee Hamling indicated that when
tested as an incandescent mantle, the light output was
less than that obtained from a regular mantle, and after a
period of use the amorphous structure of the thoria fibers
reverted to the same crystallized form produced in a
25 regular mantle when it is installed on a lantern burner
and ignited prior to admission of fuel to the burner, as
described on the mantle package.
The Zircar Product Brochure describes an end product
of the precursor process which is commercially
30 manufactured under the trade name of Zircar. One version
of this utilizes zirconium and yttrium compounds, with
hafnium as a second stabilizing agent, to reduce ceramic
fibers. Incandescent mantles are not among the producks
offered by the manufacturers of Zircar.
Levy, S. I., Pitman's Common Commodi~ies and
Industries; "Incandescent Lighting", Sir Isaac Pitman and
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Sons Ltd.: London (1922), pages 75 through 91, describes
in some detail the actual processes of incandescent mantle
manufacture, which is itself a form of precursor process.
A cellulosic yarn, usually rayon, is knitted into the form
5 of a tubular webbing which is cut in sections to form
precursor mantles. These sections are closed by stitching
at one end, leaving the other end open. They are then
impregnated by immersion in a solution of salts of thorium
and cerium, usually the nitrates. Excess solution is
10 removed and the sections are dried.
At this stage the mantle manufacture may be
completed in several different ways. For use as a soft or
tie-on inverted mantle for portable gasoline and similar
lanterns (see Mantle Examples Item A), the open end is
15 threaded with a length of heat resisting yarn by which
means the mantle may be tied to the burner nozzle of the
lantern. For use, the mantle is ignited without the fuel
gas flowing. This pyrolysis burns away the rayon base
yarn and converts the thorium and cerium nitrates into
20 o~ides, so forming an oxide skeleton of the original
knitted structure. This o~ide skeleton is very delicate
and easily damaged. When the pyrolysis is complete, the
fuel gas is admitted to the burner and ignited, so
rendering the mantle incandescent, this also consolidates
25 the o~ide skeleton and shapes it to fit the gas flame.
For use on the burners of other types of lights, the
soft mantle described above is attached to a ceramic ring
provided with internal lugs which engage with projections
on the nozzle of the gaslight burner. The initial
30 pyrolysis procedure is performed on the yaslight e~actly
as described above for a gasoline lantern (see Mantle
Examples Item B).
Another variation of inverted mantle manufacture is
based on the soft mantle and ceramic ring assembly
35 described above, but the pyrolysis is performed during
manufacture. The resulting mantle, termed a hard or
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pre-formed mantle, is intended for use on fi~ed gaslights,
but since the o~ide skeleton is very fragile it is dipped
in a collodion (nitro cellulose) solution and dried. The
nitro-cellulose so deposited strengthens the o~ide
5 structure for transportation. The collodion deposit is
burned off at the consumers lamp prior to ignition of the
fuel gas ~see Mantle Examples Item C). Knitted fabrics
are particularly suitable for the fabrication of
incandescent mantles since they can be produced directly
10 in one-piece tubular form, and they possess elasticity in
both the vertical and horizontal directions, which
property aids the shrinking and forming process during
pyrolysis, and which property is virtually absent from
woven fabrics.
There are various forms of comple~ knit stitch used
in mantle manufacture which are intended to enhance the
strength of the o~ide structure. Also, plain loop knit,
also termed jersey knit, or stoc~inette knit, is used for
some soft mantles. This form of knit uses interlinking
20 loops, each loop is identical to every other loop both
horizontally and vertically. However, the great
friability of thorium o~ide precludes substantial strength
improvemen~s based on structural modifications. "The
Formation of Loops and Construction of I,ooped Fahrics"
25 TECHNICS Volume 1, pg 499, George ~ewnes Ltd (London 1904)
describes in some detail the structure and properties of
plain knit textiles.
SI~MARY OF THE INVENTIQN
The present invention provides an improved
incandescent mantle which is stronger than mantles
produced in the past as well as free of radioactive
materials. The present invention provides a mantle
comprised of zirconia, yttria and erbia which produces a
35 resulting light output and color comparable for practical
purposes to that of traditional thorium mantles. Although
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the present invention is particularly adapted to mantles
of inverted form, it is also applicable tu other forms.
DE~RIPTION OF THE DRAWING
5 The invention will be more fully described in the
following detailed description, in conjunction with the
drawing, the single figure of which is a graph indicating
the preferred percent range of zirconium content and the
preferred range of erbium to yttrium ratios before
10 pyrolization of the mantle of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A fabric precursor mantle structure is prepared from
rayon yarn. A preferred form is a tubular webbing
15 comprised of knitted loops. Because considerable
shrinkage occurs during subsequent processing, the webbing
is fabricated so as to have appro~imately twice the
diameter of the desired finished mantle after conversion
to ceramic filament form. This shrinkage is desirable
20 since it helps to compact and sinter the ceramic filaments
during their formation. A precursor mantle is prepared
from a section cut from the knitted tubing~ Again because
of shrinkage, the selected length of tubing is about twice
the length of the desired finished mantle. This precursor
25 tubing section may be tied or sewn if required so as to
producs mantles of a form suitable for a particularly
intended variety of lamp.
In preparation for the process of imbibition of the
desired metal salts, the precursor mantle is soaked in
30 plain distilled water. This has the effect of swelling or
dilating the cellulosic fibers so as to pr~mote the
imbibition of the metal salts solution into the
crystallite structure of the fibers.
The initial water soaking is extended over
approximately 2 hours at room temperature, at the end of
which the precursor mantle is remoYed from the water bath
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and the excess water removed by centrifugation, blotting,
or other convenient means.
In the alternative, the precursor mantle may be
initially placed i~l a bath of an aqueous solution of the
5 desired metal salts without first presoaking the mantle as
described above. The len~th of time of imprsgnation is
appro~imately 10-15 minutes at a solution temperature of
120F. A most preferred solution is comprised of zirconyl
chloride, erbium chloride and yttrium chloride. The
10 acceptable ranges of the percentages by weight before
pyrolysis are shown in the drawing. Acceptable ranges of
percentages of zirconyl chloride vary from about 60% to
66% zirconyl chloride with the remaining percentage to be
made up of a combination of erbium chloride and yttrium
15 chloride at a ratio which varies from about 2.20 to 1 to
2.40 to 1 erkium chloride to yttrium chloride. A most
preferred range is comprised of about 62% to 64% zirconyl
chloride with the remaining percentage to be made up of a
combination o erbium chloride and yttrium chloride at a
20 ratio of about 2.25 to 1 to 2.35 to 1 er~ium chloride to
yttrium chloride.
The presence of erbium in the product mantle is
considered desirable since it is believed to act as a
second stabilizing age~t in the resulting yttrium
25 toughened zirconium o~ide ceramic filaments, and it is
also believed to behave as an activating agent which
enhances the light output beyond that obtained from a
formulation of zirconia and yttria alone.
After removal of the precursor mantle from the
30 irnpregnation bath, surplus solution is removed by a
process such as centrifugation, and the structure is
rapidly dried with warm air, or other convenient means.
The dried precursor mantle is then reacted with
ammonia gas. The reaction converts the metal chlorides ~o
35 their corresponding hyroxides, that is, to zirconium
hydro~ide, eroium hydro~ide and yttrium hydro~ide This
~, ~3 ~ !7 2 2 7
step serves several functions. First, it neutralizes the
acidity of the various salts. Second, it preserves the
integrity of the mantle fabric as the acidity of the metal
salts may cause the mantle fabric to deteriorate.
5 Thirdly, it may assist pyrolysis during the subsequent
formation 9f o$ide filamentsO Finally, it appears to
promote the spreading apart of individual filaments making
up rayon yarn thereby increasing e~posure to flame and
enhancing light output.
At this point the precursor mantle is provided with
a means of attachment to a burner nozzle, such as a length
of heat resistant yarn stitched around the open end.
Additional reinforcement of the mantle where it is
attached to the burner nozzle of the lamp is usually
15 required with a thorium mantle. ~owever, the mantle of
the present invention does not require added reinforcement
except in special situations. This reinforcement may be
achieved by impregnation of this zone of the mantle with a
metal salt solution which will form additional o~ide
20 deposits. The reinforcing solution does not need to have
the same illuminating properties as those used in the
light emitting area of the mantle.
The precursor mantle is a~tached to a burner nozzle
and converted to ceramic filament form by the ignition of
25 a fuel/air mixture such as the one normally used to
produce incandescence. This combustion pyrolyzes the
rayon abric to form carbon, which is then consumed and
dissipated as carbon dioxide, while the metallic salts are
converted into o~ide ceramic filaments to form a skeletal
30 replica of the original cellulosic precursor, but
approximately half its size.
Alloying between the various component o~id~s occurs
during this process, so imparting the desired properties
by the formation of yttrium/erbium stabilized zirconia.
EXAMPLE
An inverted precursor mantle, measuring about 2-1/2
~3~7~7
inches long and 2 inches in diameter, was prepared in
accordance with this invention, using webbing knitted in
plain loop stitches from 600 de~ier rayon yarn. The
precursor mantle was then impregnated for 15 minutes at
5 120F with an aqueous solution composed of zirconyl
chloride in the ra~ge of about 62%-64~ with the remaining
percentage of the solution composed of an erbium~yttrium
chloride ratio of about 2.25-2O35 to 1. Excess fluid was
removsd by centrifugation and the sample was dried with
10 warm air.
A length of heat resistant yarn was threaded through
the fabric forming the open end of the mantle and the
mantle was then tied to the burner nozzle of a Coleman
propane lantern type 5107C. After propane fuel gas was
15 ignited, the mantle carbonized, turning black. It then
became red hot, and converted to a white ceramic filament
form. The mantle became incandescent, emitting a light
very similar to the pale yellow/white color of a
commercial thorium mantle.
Shrinkage during this operation reduced the mantle
to about 52% of its ormer size.
The light output when the lantern was burning was
comparable for practical purposes to that of a thorium
mantle. The mantle of this invention was removed from the
25 lantern and sample strips of the ceramic filament fabric
were prepared for tensile tests by cementing small
sections of thin card as supports at the ends of the
strip. The fabric folded flat upon itself on the
horizontal a~is easily and without breakage, and the rows
30 of knitted filament loops moved vertically over each other
without breakage.
Vibration tests on the pyrolized mantle showed the
mantle of the present invention to be about S times
stronger than that of a thorium mantle.
It will be recognized that, although the present
disclosure represents the preferred embodiment of the
12 2 7
invention with a certain degree of particularity, changes
in the composition and structure can be resorted to
without departing from the spirit and scope of the
invention hereinafter claimed.
