by e i dupont de nemours amp co inc of wilmington del the silicon carbide sic filler is a crystalline material sold under the registered trade designation carborundum by carborundum co of niagara falls n y the wetting agent is a nonionic surfactant sold under the trade designation igepal co 610 by antara chemicals of new york n y the butyl latex binder is one sold under the trade designation emd603a by burke palmason chemical company of pompano beach fla the preferred thickner is one sold under the trade designation paragum 131 by para chem inc of philadelphia this above described particle coated web 12a can be comprised of inorganic refractory particles of amounts totaling greater than 70 of the total web weight in addition to the embodiment described above other materials suitable for use as substrate 12 can be open structured organic or inorganic woven or nonwoven material e g asbestos cloth glass web nonwoven polyester and nonwoven nylon substrate 12 may have a thickness of from about 5 to 20 mils and a basis weight in the range of about 25 to 200 g m 2 the fillers can along with other forms of silicon carbide be ceramic powder iron oxide or aluminum powder the particle size may vary from 100 800 mesh alternate binders may be used for both the oxidizing or inert atmosphere environment as long as good adhesion with the filler is maintained at high filler.