CA2047227A1 - Incandescent mantles - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

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 resulting light output and color comparable for practical purposes to that of traditional thorium mantles. Although the invention is particularly adapted to mantles of inverted form, it is also applicable to other forms.

Description

~,~3~72~7 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.

~0~22~

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 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 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 ~,~3'~7227 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 ~7~

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 ~0~7227 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 ~3~72~

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 ~ ~3 ~ r~ 2 2 ~

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 ~3~ 2~7 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 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.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A precursor mantle for incandescent gas lamps comprising:
a substrate impregnated with a solution of salts of zirconium, yttrium and erbium which when pyrolized, form corresponding oxides.

2. The precursor mantle of claim 1 wherein the percentage of zirconium salt in said solution ranges from 60% to 66%.

3. The precursor mantle of claim 2 wherein the ratio of erbium to yttrium salts in said solution ranges from 2.20-2.40 to 1.

4. The precursor mantle of claim 1 wherein the percentage of zirconium salt in said solution ranges from 62% to 64%.

5. The precursor mantle of claim 4 wherein the ratio of erbium to yttrium salts in said solution ranges from 2.25-2.35 to 1.

6. The precursor mantle of claim 1 wherein said substrate is a cellulosic fabric substrate.

7. The precursor mantle of claim 6 wherein said cellulosic fabric substrate is rayon.

8. The precursor mantle of claim 1 wherein said substrate is a fabric having tubular webbing comprised of knitted loops.

9. A precursor mantle for incandescent gas lamps comprising:

a substrate containing salts of zirconium, yttrium and erbium which when pyrolized, form corresponding oxides.

10. A mantle for incandescent gas lamps comprised of zirconium oxide, erbium oxide, and yttrium oxide.

11. The mantle of claim 10 wherein said oxides are in proportions resulting from a salt of zirconium in a range from about 60% to 66%, and from salts of erbium and yttrium in an erbium/yttrium ratio of 2.20-2.40 to 1.

12. The mantle of claim 10 wherein said oxides are in proportions resulting from a salt of zirconium in a range from about 62% to 64%, and from salts of erbium and yttrium in an erbium/yttrium ratio of 2.25-2.35 to 1.

13. A process for the preparation of a mantle for incandescent gas lamps comprising the steps of:
impregnating a combustible substrate with a solution of salts of zirconium, erbium and yttrium;
withdrawing said combustible substrate from said solution; and drying said combustible substrate.

14. The process for the preparation of a mantle for incandescent gas lamps of claim 13 wherein said solution is comprised of a zirconium salt in a percentage which ranges from about 60% to 66% and the remaining percentage of said solution is comprised of a ratio of erbium/yttrium salts of about 2.20-2.40 to 1.

15. The process for the preparation of a mantle for incandescent gas lamps of claim 13 wherein said solution is comprised of a zirconium salt in a percentage which ranges from about 62% to 64% and the remaining percentage of said solution is comprised of a ratio of erbium/yttrium salts of about 2.25 2.35 to 1.

16. The process for the preparation of a mantle for incandescent gas lamps of claim 13 further comprising:
pyrolizing said combustible substrate impregnated with said solution.

17. A mantle for incandescent gas lamps prepared by the process of claim 13.

18. A mantle for incandescent gas lamps prepared by the process of claim 14.

19. A mantle for incandescent gas lamps prepared by the process of claim 15.