High temperature amorphous composition based on aluminum phosphate

Abstract

A composition providing thermal, corrosion, and oxidation protection at high temperatures is based on a synthetic aluminum phosphate, in which the molar content of aluminum is greater than phosphorus. The composition is annealed and is metastable at temperatures up to 1400° C.

1 . A high temperature stable composition comprising aluminum phosphate wherein the ratio of aluminum to phosphorus is greater than one-to-one, said composition characterized by containing at least 50 percent by weight of an amorphous content, said composition being metastable of temperatures from ambient up to 1400° C.  
     
     
         2 . The composition of  claim 1  additionally comprising a substrate, said composition being a coating on said substrate.  
     
     
         3 . The composition of  claim 1  wherein said composition is in the form of a fiber.  
     
     
         4 . The composition of  claim 2  wherein said coating protects said substrate from oxidation at elevated temperatures.  
     
     
         5 . The composition of  claim 2  wherein said coating protects said substrate from corrosion at elevated temperatures.  
     
     
         6 . The composition of  claim 1  comprising an additional metal.  
     
     
         7 . An aluminum phosphate composition, said composition comprising aluminum phosphate wherein the amount of aluminum relative to phosphorus in said composition exceeds five percent, said composition being metastable at temperatures up to 1400° C.  
     
     
         8 . A method for protecting a substrate from corrosion and oxidation at elevated temperatures, said method comprising the steps of applying a precursor solution to said substrate, said precursor solution comprising phosphorus pentoxide and an aluminum salt, wherein the ratio of aluminum to phosphorus is greater than one to one, and thereafter drying annealing said solution on said substrate.  
     
     
         9 . A metastable material comprising an aluminum phosphate composition having the formula Al 1+x PO 4+3x/2 , wherein x is about 0 to about 1.5, said composition having structural components absorbing radiation in the infra red spectrum at about 795 cm −1  to about 850 cm −1 , said components present at temperatures of at least about 1000° C.  
     
     
         10 . The material of  claim 9  wherein x is about 0.  
     
     
         11 . The material of  claim 10  wherein x is about 0.1 to about 1.0.  
     
     
         12 . The material of  claim 11  wherein said material is substantially amorphous.  
     
     
         13 . The material of  claim 11  wherein said material is metastable at temperatures at least about 1200° C.  
     
     
         14 . The material of  claim 11  further including crystalline particles.  
     
     
         15 . The material of  claim 14  wherein said crystalline particles are ErPO 4 .  
     
     
         16 . A method of using an aluminum phosphate composition to enhance substrate oxidation resistance, said method comprising: 
 providing an aluminum phosphate composition, said composition having the formula Al 1+x PO 4+3x/2 , wherein x is about 0 to about 1.5; and    applying said composition to a substrate.    
     
     
         17 . The method of  claim 16  wherein said composition is annealed prior to said application.  
     
     
         18 . The method of  claim 16  wherein said composition is annealed after said application.  
     
     
         19 . The method of  claim 16  wherein said composition is dip-coated onto a substrate.  
     
     
         20 . The method of  claim 16  wherein said composition is plasma-sprayed on a substrate.  
     
     
         21 . The method of  claim 16  wherein said composition is aerosol-sprayed onto a substrate.  
     
     
         22 . The method of  claim 16  wherein said composition is a slurry in a solution of a compositional precursor.  
     
     
         23 . A method of using the aluminum content of an aluminum phosphate material to affect the metastability of said material, said method providing an aluminum phosphate material using an aluminum salt precursor compound, said material having an aluminum content corresponding to the aluminum content of said precursor compound, said precursor compound and said material aluminum content sufficient to provide a material metastability.  
     
     
         24 . The method of  claim 23  wherein said material aluminum content is stoichoimetric.  
     
     
         25 . The method of  claim 23  wherein said material aluminum content is greater than stoichoimetric.  
     
     
         26 . The method of  claim 23  further including a second component selected from the group consisting of silicon, lanthanum and zirconium.  
     
     
         27 . An aluminum phosphate product having Al—O—Al structural moieties absorbing radiation in the infra red spectrum at about 795 cm −1  to about 850 cm −1 , said product obtainable by mixing an alcoholic solution of phosphorus pentoxide with a solution of an aluminum salt, and heating the admixture.  
     
     
         28 . The product of  claim 27  wherein said product is substantially amorphous.  
     
     
         29 . The product of  claim 27  further including crystalline particles.  
     
     
         30 . The product of  claim 29  wherein said particles are crystalline ErPO 4  inclusions prepared by incorporating an erbium salt with said aluminum salt solution.  
     
     
         31 . The product of  claim 27  further including metal oxide particles, said particles selected from the group consisting of Group IIIA and IIIB-VIB metal oxides, said particles in an amount sufficient to modify the thermal expansion coefficient of said product.