Protective internal coatings for porous substrates

Abstract

A material contains open pores in which the channels and pores that are internally coated with at least one layer of phosphorus-containing alumina. Such material is formed by infiltrating a porous material one or more times with a non-colloidal, low-viscosity liquid coating precursor, drying, and curing the coating precursor to form a phosphorus-containing alumina layer within pores of the material.

1 . A material comprising a porous substrate containing open pores and channels and comprising interconnected mesopores and micropores, in which the pores and channels are internally coated with at least one layer of phosphorus-containing alumina. 
     
     
         2 . A material of  claim 1  in which the internal coating layer is at least 5 nm thick. 
     
     
         3 . A material of  claim 1  in which open porosity of a coated substrate is at least 40% of the open porosity of an uncoated substrate. 
     
     
         4 . A material of  claim 1  in which density an internally coated substrate is increased by no more than 10% over an uncoated substrate. 
     
     
         5 . A material of  claim 1  in which pore or channel constrictions within the porous substrate are blocked. 
     
     
         6 . A material of  claim 1  in which the internal coating remains stable at 1000° C. 
     
     
         7 . A material of  claim 1  in which the internal coating layer contains at least two sublayers. 
     
     
         8 . A material of  claim 7  in which each sublayer does not cover all of total surface area within the internal open pores and channels. 
     
     
         9 . A material of  claim 1  in which the phosphorus-containing alumina has aluminum to phosphorus atomic ratios of 2:1 to 15:1. 
     
     
         10 . A material of  claim 1  in which the porous substrate comprises a ceramic material or coating, a ceramic matrix composite, or a metal or metal alloy. 
     
     
         11 . A material of  claim 1  in which the porous substrate comprises a ceramic thermal barrier coating bonded to a metal. 
     
     
         12 . A material of  claim 1  in which the porous substrate comprises a plasma spray coating, electron beam physical vapor deposition coating, metallurgical overlay coating, or a slurry coating bonded to metal or ceramic or ceramic composite. 
     
     
         13 . A material of  claim 1  in which the porous substrate comprises graphite; a silicon carbide; a carbon-carbon composite, a carbon-silicon carbide composite, or a silicon carbide-silicon carbide composite; or a ceramic refractory or tile. 
     
     
         14 . A material of  claim 1  bonded to a turbine blade, a vane, or a shroud. 
     
     
         15 . A method to form a material having an internally coated porous substrate surface comprising:
 a) contacting a porous substrate containing open pores and channels and comprising interconnected mesopores and micropores with a non-colloidal, low viscosity solution, having a viscosity lower than 100 centistokes, of a phosphorus-containing alumina coating precursor, formed by combining solutions of an aluminum salt and a phosphate ester, such that the coating precursor infiltrates and internally coats the open pores and channels; and   b) drying and curing the phosphorus-containing alumina coating precursor to form a layer of phosphorus-containing alumina onto internal surfaces of the pores.   
     
     
         16 . A method of  claim 15  in which a pressure differential is applied to the porous substrate by placing the substrate under vacuum conditions before contacting with the coating solution. 
     
     
         17 . A method of  claim 15  in which the alcohol is methanol, ethanol, or a mixture thereof. 
     
     
         18 . A method of  claim 15  in which steps a) and b) are repeated at least twice. 
     
     
         19 . A method of  claim 15  in which phosphorus-containing alumina has an aluminum to phosphorus atomic ratio of 4 to 10. 
     
     
         20 . A method to protect a porous substrate surface containing open pores from environmental conditions comprising:
 a) contacting a porous substrate containing open pores and channels and comprising interconnected mesopores and micropores under external pressure conditions with a non-colloidal, low viscosity solution of a phosphorus-containing alumina coating precursor, formed by combining solutions of an aluminum salt and a phosphate ester, such that the coating precursor infiltrates and internally coats the open pores; and   b) drying and curing the phosphorus-containing alumina coating precursor to form a continuous layer of phosphorus-containing alumina onto internal surfaces of the pores.