Abstract:
A topical skin protectant formulation containing a barrier cream and an active moiety for protecting warfighters and civilians against all types of harmful chemicals, specifically chemical warfare agents (CWAs). The topical skin protectant offers a barrier property and an active moiety that serves to neutralize chemical warfare agents into less toxic agents.

Description:
PRIORITY INFORMATION 
     This application claims the benefit of priority of U.S. Provisional Application No. 60/209,337 filed Jun. 2, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to active topical skin protectants. More specifically, the invention relates to an active barrier cream for protection against all types of harmful chemicals, specifically chemical warfare agents (CWAs). The active barrier cream is applied prior to exposure on the skin of persons at risk of exposure to harmful chemicals to provide a protective barrier for the skin. The active barrier cream chemically or physically reacts with harmful chemicals such as CWAs (vesicants and nerve agents) to neutralize these harmful chemicals while the barrier properties of the cream prevent penetration of harmful chemicals through the cream to the skin. 
     2. Description of Related Art 
     The concept of applying a topical protectant to vulnerable skin surfaces before entry into a chemical combat arena has been proposed as a protective measure against percutaneous CWA toxicity since the first use of CWAs in World War I. The protectant was applied to vulnerable skin surfaces prior to entry into a chemical combat area. Topical protectants should augment the protection afforded by the protective overgarments and/or redefine the circumstances requiring mission oriented protective posture (MOPP) levels. The rapid action of vesicating agents, also known as blistering agents, such as sulfur mustard (HD) and lewisite (L), require a pre-exposure skin protection system or a contamination avoidance approach that may preclude the percutaneous toxicity of these agents. These approaches also reduce the risk of exposure to organophosphorus (OP) chemical agents (nerve agents), which unlike the vesicating agents, are lethal in droplet amounts. 
     An organic molecule, S-330, that reacts with CWAs was incorporated in a product and fielded as the M-5 ointment kit at the end of World War II (formula 1).                           
     However, the unacceptable barrier properties and the undesirable cosmetic properties (specifically foul odor and sticky texture) caused a recall of this product. 
     Two non-active topical skin protectant (TSP) formulations were developed at the United States Army Medical Research Institute of Chemical Defense (USAMRICD) and were transferred to advanced development following a Milestone Zero (MS 0 ) Review in October 1990. The timeline of the approval of the TSP continued with MSI in 1993, a Investigational New Drug (IND) filed with the FDA in 1994, MSII in 1995, and culminated with New Drug Application (NDA) approval in February, 2000. Upon approval by the FDA, the TSP was designated Skin Exposure Reduction Paste Against Chemical Warfare Agents (SERPACWA). SERPACWA is a 50:50 (wt/wt) mixture of perfluoropolyether oil (Fomblin® Y25 from Ausimont) and poly(tetrafluoroethylene) (polymist® F5a powder from Ausimont). The formulation described in McCreery U.S. Pat. No. 5,607,979 is directed to a topical skin protectant cream that acts as a barrier to CWAs. 
     Although SERPACWA extends the protection afforded by MOPP and allows a longer window for decontamination, it does not completely remove the possibility for contamination because the CWA is not neutralized. To avoid contamination of other areas of the battlefield and to preclude the future percutaneous absorption of the CWA, decontamination is still required. Furthermore, although the McCreery formulation provides excellent protection against GD and HD liquid, its protection against HD vapor is minimal. 
     To overcome these deficiencies, there is a need for a new TSP that contains an active component. This active Topical Skin Protectant (active TSP) was developed within the following criteria. First, the active TSP should neutralize CWAs including but not limited to sulfur mustard (HD), soman (GD), and VX. Second, the barrier properties of the TSP should be maintained or increased. Third, the protection against HD vapor should increase. And fourth, the cosmetic characteristics (i. e. odor, texture) of the TSP should be maintained. 
     This invention meets the above criteria and solves the problems associated with the past TSP&#39;s by providing an active topical skin protectant that increases effectiveness of the TSP barrier quality and neutralizes CWAs into less harmful products. 
     It is therefore, an objective of the present invention to provide an active topical skin protectant that prevents the percutaneous absorption of CWAs and converts these toxic materials into less harmful products. 
     It is a further objective of the present invention to provide an active topical skin protectant that maintains desirable cosmetic properties making it acceptable to the user. Specifically, the active TSP should not be sticky, should be without offensive odor, and should be nonirritating to the skin. 
     It is still a further object of the invention to provide an active topical skin protectant that is practical for field operations. Specifically, the active TSP should have a stable shelf life, not be easily washed off with water, and should not react with insecticides or camouflage paint. 
     SUMMARY OF THE INVENTION 
     A topical skin protectant formulation for neutralizing chemical warfare agents into less toxic products comprising: a barrier base cream and one or more active moieties. The base cream comprises poly(tetrafluoroethylene) resins dispersed in perfluorinated polyether oils. The active moieties that have been found to be effective with the base cream are listed in Table 1. The active barrier cream is applied to the skin prior to exposure of persons at risk of exposure to harmful chemicals to provide an active barrier to protect the skin. The active barrier cream chemically or physically reacts with harmful chemicals such as CWAs to neutralize these harmful chemicals while the barrier properties of the cream prevent penetration of harmful chemicals through the cream to the skin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram of the active TSP Decision Tree Network for efficacy evaluation. 
    
    
     DETAILED DESCRIPTION 
     Candidate Active Moieties 
     The types of materials that neutralize harmful agents use three main modes of action: oxidation, reduction or hydrolysis. 
     The selection of the active materials, however, is restricted by operating criteria. Thus, the active moiety must not irritate the skin, react with insecticides or camouflage paints or be unstable. This restriction eliminates many of the most active species. Furthermore, the active moiety must be incorporated into a highly fluorinated environment that is not amenable to many reaction pathways. 
     Table 1 is a list of active moieties that are acceptable for use in the present invention: 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 LIST OF ACTIVE COMPOUNDS AND EXAMPLE FORMULATIONS FOR 
               
               
                 ACTIVE TOPICAL SKIN PROTECTANTS 
               
             
          
           
               
                 Example Formulation 
                   
               
             
          
           
               
                 ICD # 
                 Active Moiety(ICD#) 
                 % Active 
                 % other 
                 % PFPE 
                 % PTFE 
               
               
                   
               
             
          
           
               
                 2851 
                 Mg 2 NiH 2  + propylene glycol butyl 
                 10 
                 (2289) 10 
                   
                 40 
               
               
                   
                 ether 
                   
                 (2853) 40 
               
               
                 2944 
                 TiFeMn(Fine) 
                 10 
                 (2289) 10 
                   
                 40 
               
               
                   
                   
                   
                 (2853) 40 
               
               
                 2945 
                 TiFeMn(Fine) 
                 10 
                 Water 10 
                   
                 35 
               
               
                   
                   
                   
                 (2289) 10 
               
               
                   
                   
                   
                 (2853) 35 
               
               
                 2948 
                 CaNi 5 H 3  + perfluoropropene reaction 
                 10 
                 (2289) 10 
                   
                 40 
               
               
                   
                 product coating 
                   
                 (2853) 40 
               
               
                 2949 
                 CaNi5H3 + perfluoropropene 
                 10 
                 Water 10 
                   
                 35 
               
               
                   
                 reaction product coating 
                   
                 (2289) 10 
               
               
                   
                   
                   
                 (2853) 35 
               
               
                 2950 
                 CaNi 5 H 3  powder 
                 10 
                 (2289) 10 
                   
                 40 
               
               
                   
                   
                   
                 (2853) 40 
               
               
                 2952 
                 Mg 2 NiH 2  + propylene glycol butyl 
                 10 
                 Water 10 
                   
                 35 
               
               
                   
                 ether 
                   
                 (2289) 10 
               
               
                   
                   
                   
                 (2853) 35 
               
               
                 2953 
                 slightly hydrided Mg 2 Ni powder 
                 10 
                 (2853) 60 
                   
                 30 
               
               
                 2954 
                 slightly hydrided Mg 2 Ni powder 
                 10 
                 (2853) 50 
                   
                 40 
               
               
                 3107 
                 slightly hydrided Mg 2 Ni powder 
                 10 
                   
                 50 
                 40 
               
               
                 3109 
                 TiFeMn(Fine) with 
                 10 
                   
                 50 
                 40 
               
               
                   
                 methylmethacrylate 
               
               
                 3109 
                 TiFeMn(Fine) with 
                 10 
                   
                 50 
                 40 
               
               
                   
                 methylmethacrylate 
               
               
                 3110 
                 CaNi 5 H 3  + perfluoropropene reaction 
                 10 
                   
                 50 
                 40 
               
               
                   
                 product coating 
               
               
                 3111 
                 TiFeMn(Fine) 
                 10 
                   
                 50 
                 40 
               
               
                 3112 
                 CaNi 5 H 3  powder 
                 10 
                   
                 50 
                 40 
               
               
                 3265 
                 (TiFe 0.9 Mn 0.1  + methyl methacrylate) 
                 9 
                 H 2 O 1 
                 47 
                 43 
               
               
                 3266 
                 (ZrNi 0.95 M 0.05  + methyl methacrylate) 
                 10 
                 H 2 O 1 
                 47 
                 42 
               
               
                 3267 
                 (ZrNi 0.95 M 0.05  + 
                 10 
                 H 2 O 1 
                 47 
                 42 
               
               
                   
                 2(dimethylamino)ethyl methacrylate) 
               
               
                 3268 
                 (TiFe 0.9 Mn 0.1  + styrene) 
                 10 
                 H 2 O 1 
                 46 
                 43 
               
               
                 3294 
                 (TiFe 0.9 Mn 0.1  + methyl methacrylate) 
                 10 
                   
                 50 
                 40 
               
               
                 3295 
                 (TiFe 0.9 Mn 0.1  + styrene) 
                 9 
                   
                 50 
                 41 
               
               
                 3296 
                 (ZrNi 0.95 M 0.05  + methyl methacrylate) 
                 10 
                   
                 50 
                 40 
               
               
                 3297 
                 (ZrNi 0.95 M 0.05  + 
                 10 
                   
                 50 
                 40 
               
               
                   
                 2(dimethylamino)ethyl methacrylate) 
               
               
                 3317 
                 Ti/Mn alloy 
                 10 
                   
                 90 
               
               
                 3367 
                 (TiFe 0.9 Mn 0.1  + methyl methacrylate) 
                 10 
                   
                 50 
                 40 
               
               
                   
               
               
                 Abbreviations:  
               
               
                 PTFE: poly(tetrafluoroethylene) available as F5A powder from Ausimont, Morristown, NJ  
               
               
                 PFPE: perfluoropolyether available as FOMBLIM ™ Y25 oil from Ausimont, Morristown, NJ  
               
               
                 ICD2853 light PFPE Surfactant, Dupont, Wilmington, DE  
               
               
                 ICD2289 SERPACWA, Skin Exposure Reduction Past Against Chemical Warfare Agents, 50% PTFE, 50% PFPE  
               
               
                 M mischmetal - mixture of lanthanides, primarily Ce, La, Nd, and Pr.  
               
               
                 ICD3367 same formulation as ICD3294; made a different time  
               
               
                 Percents are given in weight percents.  
               
             
          
         
       
     
     The percent values assigned to the above listed components of the example skin protectant formulations are given for example only. These values may be adjusted up or down and still embody the spirit of the invention if the herein described qualities of efficacy and composition of the present invention are met. 
     All active moieties listed above are useful for both liquid and vapor challenges. The amount of each varies with each formulation. The preparation of the active polymer coated metal alloys is covered in a patent filed by Back et al (U.S. Pat. No. 6,136,373, 2000). The object is to optimize the quantity of active moiety in the base cream without loosing the barrier properties of the base cream. The amount of active moiety can vary from about 1-20 wt. %. The amount of perfluorinated polyether oil can vary from about 40 to 60 wt. %. The amount of poly(tetrafluoroethylene) can vary from about 30 to 50 wt. %. One criterion for selection of the active materials is increased efficacy against HD and/or GD vapor. Formulation aTSP ICD 3267 ([ZrNi 0.95 M 0.05 ][2-(dimethylamino)ethylmethacrylate)], M=various lanthanides has significantly (P=0.05) increased protection compared to SERPACWA (ICD 3004) in the penetration cell model against HD. 
     The polymer coated metal alloy (PCMA) must also be incorporated into the TSP matrix without degradation of the barrier properties. The PCMA are prepared with the following monomers                           
     Monomers used in the preparation of polymer coated metal alloys. 
     The metals incorporated are listed in Table 1 and vary from alkali earth metals (i. e. Ca) to transition metals (Zr, Mn, Ni) and lanthanides (M, a mischmetal, a mixture of Ce, La, Nd, and Pr). 
     These materials were incorporated into the cream as solids. Typically they are dispersed into the perfluorinated oil followed by sequential addition of the appropriate amount of F5A PTFE. 
     SERPACWA (ICD3004) consists of fine particles of poly(tetrafluoroethylene) resin dispersed in perfluorinated polyether oil. The excellent barrier properties of this high molecular weight polymer formulation are related to the low solubility of most materials in it. Only highly fluorinated solvents like Freon® have been observed to show appreciable solubility. This aprotic non-polar polymer mixture provides a unique medium for active moieties of the invention. Reaction mechanisms that do not involve charged transition states should be favored in this chemical environment. 
     Base creams formed from about 35-50% fine particulates of certain poly(tetrafluoroethylene) PTFE resins dispersed in perfluorinated polyether oils (PFPE) having viscosities from about 20 cSt to about 500 cSt afford good protection against chemical warfare agents such as HD, L, sulfur mustard/Lewisite mixtures (HL), pinacolyl methylphosphonofluoridate (soman or GD), thickened soman (TGD) and O-ethyl S-(2-diisopropylaminoethyl)methylphosphonothiolate (VX). PTFE and PFPE are available commercially from Ausimont (Morristown, N.J.) and Dupont (Wilmington, Del.). 
     The base creams used in the invention are suspensions of 35-50% finely divided PTFE having a surface area below about 6 m 2 /g in a perfluorinated polyether base oil prepared from poly(perfluoropropylene oxide), which has a viscosity between about 20 and about 500 cSt. More preferred compositions comprise from about 35% to about 50% of finely divided PTFE having an average particle size from about 0.1 μm to about 10 μm and a surface area below about 4 m 2 /g in a perfluorinated polyether base oil from 40% to 60% having a viscosity between about 20 and about 500 cSt. 
     Suitable perfluorinated polyether oils are Fomblin® HC- and Y-oils (Ausimont) and Krytox® oils (Dupont). The Fomblin® oils are mixtures of linear polymers based on perfluoropropylene oxide having the following chain structure: CF 3 —[(OCF(CF 3 )CF 2 ) n —(OCF 2 CF 2 )m]OCF 3 . The Krytox® oils are mixtures of linear polymers also based on perfluoropropylene oxide and have the chemical structure F—[(CF(CF 3 )CF 2 O)] m CF 2 CF 3 . Fomblin® Z oils having the formula: CF 3 —[(OCF 2 CF 2 ) n —(OCF 2 ) m ]—OCF 3 , may also be useful in the practice of the invention. The indices n and m indicate the average number of repeating polymeric subunits in the oil molecules. The oils may have a viscosity of about 20 cSt to about 500 cSt or more. The creams were generally prepared according to U.S. Pat. No. 5,607,979, incorporated herein in its entirety. 
     Other additives to the base cream may be water and surfactant or other chemicals necessary to maintain activity. The surfactant facilitates the mixing of the water with the base cream. An example of a typical surfactant is perfluoropolyalkylether (Krytox® CAS # 60164-51-4 from Dupont). Additional materials may also be incorporated as long as they do not reduce effectiveness of the topical protectant, such as stabilizers, camouflage paints, and sunscreens. 
     A further understanding of the composition of the topical protectant of the invention can be obtained by reference to certain specific example formulations set forth in Table 1. These examples are provided herein for purposes of illustration only and are not intended to be limiting. 
     Temperature and mixing sheer should be monitored to maintain the base cream at the desired consistency and quality. The active TSPs are typically prepared at ambient temperature using mechanical mixing. Depending on the oxygen sensitivity of the active material, some of the PCMAs may be added to the perfluorinated oil under an inert (i. e. nitrogen) atmosphere. Mixing times of 10-20 minutes are usually sufficient for dispersal of metal alloys into the SERPACWA matrix. A typical procedure for the preparation of an active aTSP with a metal alloy is presented below: 
     In a polypropylene container is added the appropriate amount of metal alloy, Y25 (50-55% by weight) perfluorinated oil, and other additives (i. e. water). The suspension is mixed with a mechanical stirrer at ambient temperature for 5 to 15 minutes of with a magnetic stirrer for 10 to 20 hours. To the suspension is added F5A poly(tetrafluoroethylene) in three portions with vigorous mechanical stirring of 5 to 10 minutes between each addition. After final addition the container is tightly capped and sealed with Parafilm®. 
     Multilayer Approach 
     Although an active TSP can be generally the application of a powder that is a POM/RNP sprinkled on the skin, or an active moiety in a base cream wherein the cream is spread on the skin, a multilayering approach can also be used. The multilayer approach would be to use the active TSP as the first layer and a solid active moiety powder as the second layer. The second layer would be a thin coating of the solid active moiety powder sprinkled over the active TSP cream. This approach would provide a concentrated decontamination material at the surface of the barrier cream, which would accelerate the neutralization process of CWA&#39;s coming in contact with the surface. Alternatively, the first layer can be a thin coating of the solid active moiety powder followed by a second layer of the active TSP. 
     Testing 
     Evaluation of formulations was conducted with a decision tree network (DTN) that describes the path that active TSPs follow during evaluation (FIG.  1 ). 
     The DTN is divided into two pathways: one for vesicants and the other for nerve agents. Within these pathways there are three blocks each with a decision point. The first block consists of a series of three mechanical (in vitro) modules used to determine the initial efficacy of candidate formulations and to eliminate non-effective candidates before animal testing, the second block consists of in vivo modules and the third block consists of an advanced animal module to determine the influence of time, water and interactions with other products. 
     The M8 paper test is used to evaluate the barrier resistance of liquid CWA challenges, including HD, pinacolyl methylphosphonofluoridate (soman, GD), and O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate (VX). In this test a 0.15 mm layer of active TSP is placed over a well-defined area of M8 chemical detection paper and challenged with an 8 ul droplet of CWA. When agent penetrates the active TSP barrier and reaches the M8 paper, a colored spot develops on the paper. The test assemblies are observed for 6 hr and the breakthrough time is reported for each sample. A total of nine replicates are run for each test, and a standard reference compound is included each day for quality control. 
     The penetration cell test is used to evaluate the barrier properties against both liquid and vapor CWA challenges (Braue, E. H. Jr.  Journal of Applied Toxicology,  1999, 19(S), S47-S53). In this test the lower half of a Reifenrath diffusion cell (Reifenrath Consulting and Research, Richmond, Calif.) is used. A 0.15 mm thick layer of active TSP is supported by nitrocellulose paper on top of the cell. The active TSP layer is challenged with a 10-μl liquid droplet of HD or an 8 μl droplet of GD, or a saturated vapor cup of HD or GD. Breakthrough of CWA into the lower chamber of the diffusion cell is monitored using a miniature continuous air monitoring system (MINICAMS, CMS Research, Birmingham, Ala.). This system has been automated to allow continuous monitoring of five cells in a 40-min cycle. The test runs for 20 hr and the accumulated amounts of agent that break through the active TSP barrier are calculated. From these data, we obtained two values: the cumulative amount of CWA that penetrates through the active TSP, and the time at which a “breakthrough” occurs. We defined “breakthrough” values at the minimum amount of HD (1000 ng) and GD (1000 ng) that results in a physiological response. Minimal amount of HD for vesication=1000 ng. See F. R. Sidell, J. S. Urbanetti, W. J. Smith, and C. G. Hurst in  Textbook of Military Medicine, Medical Aspects of Chemical and Biological Warfare , edited by F. R. Sidell, E. T.Takafuji, and D. R. Franz (Office of the Surgeon General at TMM Publications, Washington, D.C. 1997) p 201. LD 50  for soman (GD)=350 mg/70 kg man. See F. R. Sidell in  Textbook of Military Medicine, Medical Aspects of Chemical and Biological Warfare , edited by F. R. Sidell, E. T. Takafuji, and D. R. Franz (Office of the Surgeon General at TMM Publications, Washington, D.C. 1997) p 141. These two values allow us to rank the active TSP formulations and to select the appropriate component for advanced development. 
     The proof-of-neutralization test is used to verify that active TSP formulations actually neutralize CWAs into less toxic materials. This test uses the headspace solid phase microextraction (HS-SPME) technique for the collection of CWAs. Samples collected on the extraction filament are analyzed by gas chromatography/mass spectroscopy. 100mg of active TSP formulation are challenged with 0.1 μl of neat CWA (HD, GD, or VX) in a small vial. The headspace above the mixture is sampled periodically to determine the amount of CWA remaining in the flask. Efficacy is determined by the % loss of CWA. Other analytical techniques such as Nuclear Magnetic Resonance (NMR) and Fourier-Transform Infrared Spectrometry (FTIR) have also been used in this module. 
     Formulations that pass this initial set of screens are moved into the second phase of testing using animal models. The weanling pig test for HD vapor evaluates a 0.10 to 0.20 mm thick layer of active TSP spread on the depilated dorsa. The standard saturated vapor cup is used for a 15-60 min challenge. The effectiveness of the active TSP is determined by measuring the degree of erythema that developed on the skin exposure site. Erythema is measured objectively using a reflectance calorimeter (see Braue, E. H. Jr.  Journal of Applied Toxicology,  1999, 19(S), S47-S53). 
     The rabbit lesion area ratio (LAR) test is used to evaluate a challenge by HD liquid. In this test, a 0.10 mm layer of active TSP spread on the clipped dorsa is challenged with 1.0 μl of liquid HD. The effectiveness of the active TSP is determined by measuring the lesion areas of protected and non-protected sites. 
     The rabbit acetyl cholinesterase (ACHE) inhibition test is performed by applying a 0.10 mm thick layer of active TSP on the clipped dorsa of rabbit followed by a fixed dose of GD (1 LD 50 ), TGD (1 LD 50 ), or VX (20 LD 50 ). The effectiveness of the active TSP is determined by lethality and also by measuring the erythrocyte acetyl cholinesterase activity 0.5, 1, 2, and 24 hr following exposure. 
     Candidate formulations that pass the in vivo test modules move into advanced animal testing. These tests are similar to the initial animal tests with the addition of stresses for wear-time and washing with water. Interactions with other products that a soldier might use are also evaluated. These products include camouflage paints, sunscreens and insecticides. 
     Results 
     The polymer coated metal alloys (PMCAs) are effective active moieties reducing the amount of HD vapor by up to 58% relative to the TSP alone. Although the exact mechanism for HD neutralization is not clear, the HD may react either by reduction or dehydrohalogenation (Scheme 1).                           
     In this reaction scheme, hydrophobic coating of the polymer alloy “pulls” the hydrophobic sulfur mustard to the metal surface. At that point, either the dehydrohalogenation or the reduction occurs. The reduction of HD requires that the “active hydrogen” incorporated in the preparation of the polymer coated alloys be available for the neutralization. Finally, a physical adsorption of HD by the polymer coating may also account for the increased protection. 
     The increase in protection, the polymer-coated metal allows, was remarkable against HD vapor as demonstrated in the increase in the time needed for 1000 ng of HD vapor to penetrate the active TSP as compared to SERPACWA (ICD 3004) (Chart 1). 
     
       
         
               
             
           
               
                 CHART 1 
               
               
                   
               
               
                 Time for 1000 ng HD to penetrate active TSPs containing PCMAs. 
               
               
                   
               
             
             
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                   
               
             
          
         
       
     
     A comparison of the cumulative amount of HD vapor that penetrates the active TSP over 20 hours also shows the increase in protection. 
     
       
         
               
             
           
               
                 CHART 2 
               
               
                   
               
               
                 Amount of HD vapor after 20 hours that penetrates an PCMA TSPs. 
               
               
                   
               
             
             
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
               
               
                   
               
             
          
         
       
     
     In fact, as few as 1200 ng of HD vapor penetrated through the active TSP over 20 hours with active TSP ICD 3267 ([ZrNi 0.95 M 0.05 ][2-(dimethylamino)ethylmethacrylate)], M=mischmetal−mixture lanthanides, primarily Ce, La, Nd, and Pr.). 
     Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.