US3041862A - Flash lamp and ignition means therefor - Google Patents

Description

July 3, 1962 M. ANDERSON ETAL 3,041,862

FLASH LAMP AND IGNITION MEANS THEREFOR Filed July 5, 1960 lnven tors: lQoberb M. Andevson Louis A.DTT1ChOCl ,JTT

Their fi ter-neg United States Patent 3,041,862 FLASH LAMP AND IGNITION MEANS THEREFUR Robert M. Anderson, Euclid, and Louis A. Demchock, Jr., Cleveland, Ohio, assignors to General Electric Company, a corporation of New York Filed July 5, 1960, Ser. No. 40,716 Claims. (Cl. 67-31) Our invention relates in general to flash lamps of the type used for photographic purposes and comprising a sealed radiation-transmitting bulb in which is enclosed a readily combustible metallic material, together with suitable ignition means therefor, including a primer or fulminating substance, and a combustion-supporting gas filling which, upon ignition of the lamp, enters into a reaction with the combustible material with the resulting emission of a momentary flash of actinic light of high intensity. More particularly, our invention relates to an ignition means for such type flash lamps, and in particular to the composition of the fulminating or primer material thereof. The invention is especially applicable to flash lamps of the type employing, as the combustible lightproducing material thereof, metallic filamentary material in the form of wire or ribbon such as the so-called shredded foil and consisting essentially of zirconium.

Flashlamps of the type employing filamentary combustible material composed essentially of zirconium inherently are much more susceptible to accidental flashouts by electrostatic charges than corresponding type flash lamps that are provided with the more common forms of combustible materials such as aluminum or aluminum-magnesium alloys, for instance. This is particularly true in the case of extremely small size flash lamps such as are in general use at present and having a bulb of less than 10 cc. internal volume. Thus, such small size zirconium combustible material type flash lamps, when of substantially the same construction as that previously employed for corresponding aluminum combustible material type flash lamps, are apt to be flashed by the electrostatic charge which is produced on the bulb surface when the lamp is merely brushed against the clothing of one handling the lamp, as when being placed in a photographers coat pocket, for instance. In fact, entire packing sleeves and hampers of such lamps have been accidentally set oif by electrostatic charges. As a consequence, it has been necessary heretofore, in the manufacture of such extremely small size zirconium-filled flash lamps, to exercise the utmost safety precautions, including the wearing by manufacturing personnel of special apparel not conductive to the production of electrostatic charges, in order to prevent the occurrence of any such accidental flashouts of the lamps by electristatic charges with resulting likelihood of sustaining burns or other bodily injury.

We have observed that the degree of susceptibility of such zirconium combustible material type flash lamps to electrostatic charge-produced flash-outs appears to be related primarily to the presence in the lamp bulb of loose particles of the primer or fulminating material which is normally employed in flash lamps to initiate the combustion of the filamentary combustible material therein. Such primer or fulminating material conventionally consists of an admixture of a readily ignitable metallic powder such as zirconium and an oxidating powder such as potassium perchlorate bonded together by a suitable binder such as nitrocellulose, for instance. Whenever minute particles of such a primer material are loose withcalled electrostatic flashouts is thereby reduced to a degree such that the lamps, even though of extremely small size, are substantially free of such failing.

The presence of loose particles of the primer material within the lamp bulb is assumedly due to the lack of sufficient adherence of the particles in the primer beads of coatings conventionally provided on the inner ends of the lead-in wires within the lamp bulb. As a result, minute particles of the primer material are apt :to flake off or be dislodged from the surface of the primer beads or coatings during fabrication and use of the lamp, most likely by being abraded or scraped off the primer bead surface during the insertion of the lamp mount into the bulb in preparation for sealing thereinto. During the mountinsertion operation, the primer beads or coatings on the lead-in wires of the lamp mount are forced or pushed through the mass of filamentary combustible material within the bulb, as a result of which the combustible material then acts much in the same manner as a wad of steel wool to abrade or scrape the surface of the primer beads and thereby dislodge or scrape therefrom any particles that may be insecurely attached thereto. The likelihood of such primer particle dislodgement occurring by the abrasive action of the combustible material, either during the insertion of the lamp mount into the bulb or by the shifting of the combustible material about the interior of the bulb during the subsequent fabrication and handling of the lamp, is particularly prevalent in the case of Zirconium combustible material type flash lamps because of the appreciably stiffer character of the zirconium filamentary combustible material as compared to the aluminium or aluminium-magnesium alloy filamentary combustible material customarily employed in flash lamps. However, whatever may be the true reason for the presence of such loose particles of primer material within the lamp bulb, the presumption is that their actual presence within the lamp bulb conceivably could be avoided by assuring that the powder particles of the primer beads or coatings are adhered or held together by a binder with sufficient firrn ness to preclude their flaking off, or being scraped or jarred off the surface of the primer beads during the fabrication and handling of the flash lamp.

It is an object of our invention, therefore, to provide a flash lamp of the type provided with filamentary combustible material consisting essentially of zirconium and which, even though of extremely small bulb size, is nevertheless substantially unsusceptible to premature accidental flash-out by the electrostatic charges to which the lamp may be normally subjected during manufacture and use.

Another object of our invention is to provide an improved primer composition for the ignition means of a flash lamp which primer composition is elfective to render the lamp substantially nonsusceptible to premature accidental flash-out by electrostatic charges applied thereto without in any way adversely afliecting the flash performance characteristics of the lamp.

Still another object of our invention is to provide an improved primer composition for flash lamps possessing increased primer particle interadherence without adversely affecting the flash performance characteristics of the lamp. A further object of our invention is to provide an improved primer paste material for application to the ignition mount of a flash lamp which primer paste contains a considerably higher percentage of nitrocellulose resin content than heretofore present in primer paste compositions while nevertheless possessing the same workable consistency as before.

Briefly stated, in accordance with one aspect 'of our invention, we have found that by employing as the binder for the powder ingredients of flash lamp primer compositions, a nitrocellulose resin of lower nitration, and of considerably shorter molecular chain length than heretofore employed for such binder purposes, it is possible, without adversely affecting the flash performance characteristics of the flash lamp, to obtain increased nitrocellulose binder concentrations in the flash lamp primer coatings with resultant increased adherence of the powder ingredients thereof such as to substantially prevent the flaking or scraping of minute particles off the primer coatings during the subsequent manufacturing and handling of the flash lamp and to thereby render the lamp, even though of extremely small size and provided with zirconium type combustible filamentary material, substantially nonsusceptible to flash-out by the electrostatic charges to which the lamp may be normally subjected during manufacture and use.

In accordance with a further aspect of our invention, the binder for the powder ingredients of a primer composition for flash lamps is composed of a nitrocellulose resin having a nitrogen content approximately between 11.8- 12.2% and an average molecular chain length between approximately 175-300 mers, and in the case of a flash lamp of the type provided with zirconium type filamentary combustible material, the binder for the primer composition is formed from a solution containing from approximately 6-10% of such type nitrocellulose resin.

Further objects and advantages of our invention will appear from the following detailed description of species thereof and from the accompanying drawing.

In the drawing:

FIG. 1 is an elevation, partly in section, of a flash lamp comprising our invention, and

FIG. 2 is an enlarged view of the flash lamp ignition means comprising our invention.

Referring to FIG. 1, the invention is there shown as embodied in a miniature type flash lamp such as disclosed and claimed in copending application Serial No. 808,981, R. M. Anderson, filed April 27, 1959 and assigned to the assignee of the present invention now US. Patent No. 2,982,119, and comprising a very small size sealed glass envelope or bulb 1 approximately of tubular shape and consisting of a short length of drawn glass tubing closed at one end by an integral flattened external stem press 2 protruding axially from the bulb, and necked down and closed at its other end by an end wall portion 3 terminating in an exhaust tip 4. The particular bulb 1 illustrated has an internal volume of less than 2 cc. and preferably of the order of 1.2 cc., and the tubular portion of the bulb (i.e., the bulb proper) has an outside diameter of the order of 5 inch and a length of the order of inch. The opposite sides 5 of the stern press 2 are formed as flat surfaces preferably disposed approximately parallel to each other and to the axis of the bulb. As shown, the said flat sides 5 of the stem press 2 are provided with transversely extending guide channelways or grooves 6 for sliding engagement with cooperating guide track means of a lamp-holding magazine or feeding chamber (not shown) of a lamp flashing apparatus.

The bulb 1 contains a loosely distributed filling of a readily combustible metallic material 7 in filamentary form and consisting essentially of zirconium or an alloy essentially composed of zirconium, or of any material having a relatively low heat-energy ignition characteristic substantially corresponding to that of zirconium. The filamentary combustible material 7 preferably is in the form of fine cut strands of a thin foil of the above-men tioned composition, the said fine cut strands ,being such as that commercially known as shredded foil and produced by the method and apparatus described and claimed in U.S. Patents 2,297,368 and 2,331,230, Rippl et al., such shredded foil strands having a width ranging from approximately 0.5 to 1.5 mils and a thickness likewise ranging from approximately 0.5 to 1.5 mils. In the case of the preferred form of flash lamp according to the invention, employing a bulb 1 having a volume of approximately 1.2 cc., the bulb is filled with around 24 milligrams of 4 zirconium shredded foil the individual strands of which have a thickness of about 0.0008 inch and a width of about .0012 inch.

The envelope or bulb 1 also contains a filling of a suitable combustion-supporting gas such as oxygen or an oxygen-containing gas at a suitable pressure for supporting the combustion of the combustible material. The oxygen or other combustion-supporting gas is introduced into the bulb 1 through a glass exhaust tubulation at the top end 3 of the bulb which tubulation, after the evacuation of the bulb therethrough and the introduction of the oxygen or other combustion-supporting gas into the bulb, is then tipped off as indicated at 4 to hermetically seal the bulb. In the case of the preferred form of flash lamp according to the invention, the bulb is filled with oxygen at a pressure of at least approximately 5 atmospheres and preferably ranging between 5 to 6 atmospheres. The bulb 1 is coated on its outer surface with a protective lacquer coating 8 such as cellulose acetate to thereby strengthen the bulb and to render it substantially shatterproof.

Sealed into the stem press end 2 of the bulb 1 is a lamp ignition mount 9 comprising a pair of lead-in wires 10 which, in the manufacture of the lamp, are sealed into the stem press 2 so as to extend therethrough and into the bulb 1 in a direction approximately longitudinally of the bulb and in more or less side-by-side closely spaced relation. Outwardly' of the stem press 2, the lead-in wires 10 are bent or looped back upon themselves, with their free ends re-entered and sealed in the glass of the stem press 2, to thereby form loop-shaped wire terminal contact members 11 which are respectively bent around the end of the stem press to extend alongside the opposite fiat sides 5 thereof but terminating short of the guide channelways 6 therein. Interiorly of the bulb 1, the leadin wires 10 are rigidly tied together and held in place by a support bead 12 of glass or other suitable insulating material in which the lead-in wires are embedded.

Mounted on and connected across the inner ends of the lead-in Wires 10, within effective ignition range of the combustible material 7 in the bulb, is a lamp ignition filament 13 preferably consisting of a short straight length of fine tungsten wire having a diameter preferably of the order of 0.7 mil. The inner ends of the lead-in wires 10, and the portions of the ignition filament 13 at the points of connection thereof to the lead-in wires 10, are coated with a layer of fulminating substance or primer material 14 of a composition according to the invention to form beads of such material which become ignited when the ignition filament 13 is energized and heated. The fulminating or primer material 14 is applied to the lead-in wires 10 and filament 13 in the form of a paste consisting, in general, of a powder admixture of one or more extremely sensitive metal powders and suitable? powdered oxidizing material suspended in a binder ac-. cording to our invention and comprising a resin dissolved in a solvent. The subsequent volatilization of the sol-, vent in the binder solution then leaves a hardened residue 14 composed of the powder admixture ingredients bonded or adhered together by the residual resin solids of the binder solution remaining in the hardened residue after completion of the lamp fabrication operations.

The binder heretofore most commonly employed for adhering or holding together the powder particles of the primer beads or coatings of flash lamps has been ahigh or fully nitrated type of nitrocellulose resin (commonly known in the trade as guncotton or dynamite grade nitrocellulose) containing from approximately 12.2 up to around 14% of nitrogen, and having a very long average molecular chain length of around 3000 mers or thereabouts. However, the use of such highly-nitrated long average chain length nitrocellulose resins for flash lamp primer binder purposes places a limitation on the amount of nitrocellulose resin solids content that can be incorporated in binder solutions thereof used for suspending the powder admixture of the flash lamp primer while still maintaining the desired viscosity or workable consistency of the primer paste suspension for satisfactory use thereof with the present conventional manufacturing procedures employed to form the primer beads or coatings 14 on the lead-in wires of flash lamp mounts 9. Thus, with such highly-nitrated long average chain length nitrocellulose resins, only comparatively small amounts of the nitrocellulose resin up to a maximum of around 4% can be employed in binder solutions for use as suspending mediums for the powder admixture ingredients of a flash lamp primer composition, while still retaining the required workable consistency of the resulting primer suspension for satisfactory use thereof with present conventional primer bead manufacturing procedures.

In accordance with the invention, we have found that greatly improved adherence or holding together of the powder ingredients of the primer beads 14 such as to substantially prevent flaking or scraping of minute particles off the surfaces of the primer coatings or beads 14,

during the subsequent manufacturing or handling of the flash lamp, can be obtained by employing, as the binder for the primer powder ingredients, a comparatively low nitrated type of nitrocellulose having a nitrogen content approximately between 11.8 to 12.2% and having a relatively short average molecular chain length between 175 to 300 mers. With such lower nitrated short average chain length nitrocellulose resins, considerably greater amounts thereof than heretofore possible with the highnitrated long average chain length nitrocellulose resins previously used for primer binders, may be readily incorporated in binder solutions employed as the suspending medium for the primer powder admixture, while at the same time maintaining the same workable consistency or viscosity for the primer coating suspension as before in order to be satisfactorily utilizable with present conventional flash lamp primer bead manufacturing procedures. Thus, we have found that solutions containing from 6% up to as high as 10% of such lower nitrated short average chain length nitrocellulose resin can be satisfactorily employed as a binder solution for flash lamp primer compositions while maintaining the required viscosity of the primer coating suspension.

The primer material 14 according to the invention therefore comprises, in general, a powder admixture of one or more readily ignitable metal powders such as zirconium, and a finely divided oxidizing agent such as potassium perchlorate, bonded together by a binder of nitrocellulose having a nitrogen content by weight between 11.8 to 12.2% and an average molecular chain length between 175-300 mers. In the case of a flash lamp of the type employing combustible material consisting essentially of zirconium, the primer material 14 is constituted by the dried residue of a suspension of the aforementioned powder admixture in a binder solution containing from 6 to 10% and preferably around 8%, by weight, of the above type nitrocellulose resin dissolved in a suitable solvent therefor such as amyl acetate.

The powder admixture of the primer material according to the invention may desirably be of the composition disclosed and claimed in U.S. Patent 2,756,577, R. M. Anderson, and comprising an admixture of zirconium, magnesium and potassium perchlorate powders in the approximate proportions, by weight, of 60-90% zirconium, 18% magnesium and 935% potassium perchlorate. In the case of a flash lamp such as illustrated, employing filamentary combustible material consisting essentially of zirconium, the powder admixture of the primer material may be of the particular composition disclosed and claimed in our copending U.S. application Serial No. 25,626, filed April 29, 1960 and comprising an admixture of zirconium, magnesium and potassium perchlorate powders containing, in addition, a definite amount of one or more inert materials such as marble flour for the purpose of retarding the peak time of the light flash produced by the lamp. Such a primer admixture may be of the following composition, by weight:

In preparing the primer paste suspension according to the invention for application to the lead-in wires 10 of the lamp mount 9, enough binder solution is added to the primer powder admixture to impart the desired consistency or viscosity to the resulting primer paste suspension in order to produce the required size primer beads 14 on the inner lead-in wire tips for a given manufacturing application procedure. Using a binder according to the invention consisting of an approximately 8% solution in amyl acetate of a nitrocellulose containing around 11.8 to 12.2% of nitrogen and having an average molecular chain length of around mers, the amount of binder solution employed for suspending a powder admixture such as specified above for zirconium type flash lamps, and having a marble flour addition incorporated therein, will generally amount to around 18% by weight of the primer paste composition. A specific example of a primer paste composition according to the invention which has been found to be particularly satisfactory for use in a zirconium combustible material type flash lamp such as illustrated is as follows:

Zirconium powder grams 33 Magnesium powder do 4 Potassium perchlorate powder do 15 Marble flour do 13 8% Nitrocellulose solution in amyl acetate cc 18 proportion to the amount of resin present in the primer coatings or beads 14, the increased content of nitrocellulose remaining in the dried primer coatings or beads 14 resulting from the use of the particular lower nitrated, short average chain length type of nitrocellulose resin according to the invention therefore results in greatly increased interadherence of the primer particles in the primer coatings or beads 14, as compared to that obtained heretofore. Because of such materially increased primer particle interadherence, the possibility of minute particles of the primer coatings 14 being flaked or scraped off the surfaces of the primer beads 14, during either the subsequent lamp manufacturing operations or the handling of the lamp, is substantially prevented.

Since, as stated previously, the susceptibility of a flash V lamp, particularly one of the zirconium combustible material type, to premature accidental flash-out by electrostatic charges to which the lamp may be subjected during manufacture and use, is related to the presence of loose particles of the primer material 14 within the lamp bulb, the effectiveness therefore of the primer composi tion according to the invention in substantially preventing the flaking or scraping of any loose particles off the surfaces of the primer beads 14 consequently acts to render the flash lamp substantially nonsusceptible to flashout by any such electrostatic charges. Thus, With zirconium combustible material type flash lamps of the character illustrated herein, we have found that whereas with the use of the primer compositions heretofore employed for the primer beads or coatings 14 the number of premature accidental lamp flash-outs resulting from electrostatic charges applied to the lamps, by means of a standard 300,000 volt Van De Graaf generator, amounted to as high as 75% or thereabouts, the use instead in such flash lamps of a primer composition according to the invention is effective to reduce the number of such lamp flash-outs from such electrostatic charges to as low as and less. By our invention, therefore, the manufacture and use of zirconium combustible material type flash lamps, even in the extremely small sizes such as illustrated herein, is made practical from the standpoint of their susceptibility to premature flash-out by electrostatic charges. Moreover, the imparting to such type flash lamps of substantial immunity to accidental flash-out by electrostatic charges, through the use of our invention, is achieved without in any way adversely affecting the performance characteristics of the lamps.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A primer composition for flash lamps comprising an admixture of a readily ignitable metallic powder and a finely divided oxidizing agent, said admixture powder ingredients being bonded together by a binder of nitrocellulose having a nitrogen content, by weight, between 11.8-12.2% and an average molecular chain length between 175-300 mers.

2. A primer composition for flash lamps comprising a powder admixture of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between l-8% of magnesium, 60-90% of zirconium, and 9-35% of potassium perchlorate, said admixture ingredients being bonded together by a binder of nitrocellulose having a nitrogen content between 11.8- 12.2% and an average molecular chain length between 175-300 mers.

3. A primer composition for flash lamps comprising a powder admixture of magnesium, zirconium, potassium perchlorate and marble flour in the approximate proportions by weight of between 05-75% of magnesium, 40-85% of zirconium, 5-33% of potassium perchlorate powder and 5-35 of marble flour, said admixture ingredients being bonded together by a binder of nitrocellulose having a nitrogen contentbetween 11.8-12.2% and an average molecular chain length between 175-300 mers.

4. A primer paste composition for flash lamps comprising an admixture of a readily ignitable metallic powder and a finely divided oxidizing agent suspended in a binder solution consisting of nitrocellulose dissolved in a solvent and containing around 8% by weight of nitrocellulose, said nitrocellulose having a nitrogen content between 11.8-12.2% and an average molecular chain length between 175-300 mers.

5. A primer paste composition for flash lamps comprising a powder admixture of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between 1-8% of magnesium, 60-90% of zirconium, and 9-35% of potassium perchlorate, said admixture ingredients being suspended in a binder solution consisting of nitrocellulose dissolved in amyl acetate containing around 8% by weight of nitrocellulose, said nitrocellulose having a nitrogen content between 11.8-12.2% and an average molecular chain length between 150-300 mers.

6. A primer paste composition for flash lamps comprising a powder admixture of magnesium, zirconium, potassium perchlorate and marble flour in the approximate proportions by weight of between 0.5-7.5 of magnesium, 40-85% of zirconium, 5-33% of potassium perchlorate and 535% of marble flour, said admixture ingredients being suspended in a binder solution consisting of nitrocellulose dissolved in amyl acetate and containing around 8% by weight of nitrocellulose, said nitrocellulose having a nitrogen content between 11.8-12.2% and an average molecular chain length between -300 mers.

7. A flash lamp comprising a sealed envelope having an oxidizing atmosphere therein, a quantity of readily combustible material loosely arranged within said envelope and consisting essentially of zirconium, and ignition means disposed in said envelope within effective ignition range of said combustible material, said ignition means comprising a fulminating substance comprising an admixture of a readily ignitable metallic powder and a finely divided oxidizing agent, said admixture ingredients being bonded together by a binder of nitrocellulose having a nitrogen content between 11.8-12.2% and an average molecular chain length between 175-300 mers.

8. A flash lamp comprising a sealed envelope having an oxidizing atmosphere therein, a quantity of readily combustible filamentary material loosely arranged within said envelope and consisting essentially of zirconium, and ignition means disposed in said envelope within eflective ignition range of said combustible material, said lgnmon means comprising an electric energy translation element at least a portion of which is coated with a fulminating substance, said fulminating substance comprising a powder admixture of magnesium, zirconium, and potassium perchlorate in the approximate proportions by weight of between 1-8% of magnesium, 6090% of zirconium, and 9-35% of potassium perchlorate, said admixture ingredients being bonded together by a binder of nitrocellulose having a nitrogen content between 11.812.2% and an average molecular chain length between 175-300 mers.

9. A flash lamp comprising a sealed envelope having an oxidizing atmosphere therein, a quantity of readily combustible filamentary material loosely arranged within said envelope and consisting essentially of zirconium, and ignition means disposed in said envelope within eflective ignition range of said combustible material, said ignition means comprising a filament connected across 'a pair of lead-in wires and coatings of a fulminating substance on said lead-in wires and embedding portions of said filament, said fulminating substance comprising a powder admixture of magnesium, zirconium, potassium perchlorate and marble flour in the approximate proportions by weight of between 05-75% of magnesium, 40-85% of zirconium, 5-33% of potassium perchlorate and 5-35% of marble flour, said admixture ingredients being bonded together by a binder of nitrocellulose having a nitrogen content between l1.8-12.2% and an average molecular chain length between 175-300 mers.

10. An igniter for flash lamps comprising a filament connected across a pair of lead-in wires, and coatings of a primer material on said lead-in wires and embedding portions of said filament, said primer material comprising an admixture of a readily ignitable metallic powder and a finely divided oxidizing agent, said admixture ingredients being bonded together by a binder of nitrocellulose havand an ing a nitrogen content between 11.8-l2.2% average molecular chain length between 175-300 mers.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 9. A FLASH LAMP COMPRISING A SEALED ENVELOPE HAVING AN OXIDIZING ATMOSPHERE THEREIN, A QUANTITY OF READILY COMBUSTIBLE FILAMENTARY MATERIAL LOOSELY ARRANGED WITHIN SAID ENVELOPE AND CONSISTING ESSENTIALLY OF ZIRCONIUM, AND IGNITION MEANS DISPOSED IN SAID ENVELOPE WITHIN EFFECTIVE IGNITION RANGE OF SAID COMBUSTIBLE MATERIAL, SAID IGNITION MEANS COMPRISING A FILAMENT CONNECTED ACROSS A PAIR OF LEAD-IN WIRES AND COATINGS OF A FULMINATING SUBSTANCE ON SAID LEAD-IN WIRES AND EMBEDDING PORTIONS OF SAID FILAMENT, SAID FULMINATING SUBSTANCE COMPRISING A POWDER ADMIXTURE OF MAGNESIUM, ZIRCONIUM, POTASSIUM PERCHLORATE AND MARBLE FLOUR IN THE APPROXIMATE PROPORTIONS BY WEIGHT OF BETWEEN 0.5-7.5% OF MAGNESIUM, 40-85% OF ZIRCONIUM, 5-33% OF POTASSIUM PERCHLORATE AND 5-35% OF MARBLE FLOUR, SAID ADMIXTURE INGREDIENTS BEING BONDED TOGETHER BY A BINDER OF NITROCELLULOSE HAVING A NITROGEN CONTENT BETWEEN 11.8-12.2% AND AN AVERAGE MOLECULAR CHAIN LENGTH BETWEEN 175-300 MERS.

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