Yttrium-base sprayed coating and making method

Abstract

An yttrium-base sprayed coating is obtained by thermally spraying yttrium oxide, yttrium fluoride or yttrium oxyfluoride onto a substrate to form a coating of 10-500 μm thick, and chemically cleaning the coating with a cleaning liquid of organic acid, inorganic acid or a mixture thereof until the population of particles with a size of up to 300 nm becomes no more than 5 particles/mm 2 of the coating surface. The yttrium-base sprayed coating exhibits high corrosion resistance even in a halogen gas plasma atmosphere and prevents yttrium-base particles from spalling off during etching treatment.

1 . An yttrium-base sprayed coating comprising at least one compound selected from the group consisting of yttrium oxide, yttrium fluoride, and yttrium oxyfluoride and having a thickness of 10 to 500 μm, wherein particles with a size of up to 300 nm are present on a coating surface in a population of no more than 5 particles per square millimeters. 
     
     
         2 . The yttrium-base sprayed coating of  claim 1  having a thickness of 80 to 400 μm. 
     
     
         3 . The yttrium-base sprayed coating of  claim 1  which is sprayed onto a surface of a substrate of metallic aluminum, aluminum oxide or metallic silicon. 
     
     
         4 . A method for preparing a yttrium-base sprayed coating, comprising the steps of:
 thermally spraying a particulate spray material comprising at least one compound selected from the group consisting of yttrium oxide, yttrium fluoride, and yttrium oxyfluoride to form a yttrium-base sprayed coating having a thickness of 10 to 500 μm and   chemically cleaning a surface of the coating with a cleaning liquid which is an organic acid aqueous solution, inorganic acid aqueous solution or organic acid/inorganic acid aqueous solution until a population of particles with a size of up to 300 nm is no more than 5 particles per square millimeters of the coating surface.   
     
     
         5 . The method of  claim 4  wherein the cleaning liquid is an aqueous solution of an acid selected from the group consisting of a monofunctional carboxylic acid, difunctional carboxylic acid, trifunctional carboxylic acid, hydroxy acid, sulfonic acid, nitric acid, sulfuric acid, carbonic acid, hydrofluoric acid, and acidic ammonium fluoride or a mixture thereof. 
     
     
         6 . The method of  claim 5  wherein in the cleaning liquid, the monofunctional carboxylic acid is formic acid or acetic acid, the difunctional carboxylic acid is maleic acid, tartaric acid or phthalic acid, the trifunctional carboxylic acid is citric acid, the hydroxy acid is lactic acid, and the sulfonic acid is methanesulfonic acid. 
     
     
         7 . The method of  claim 4  wherein the chemical, cleaning step includes immersing the yttrium-base sprayed coating in the cleaning liquid to dissolve the coating to a depth of at least 0.01 μm from its surface for thereby removing particles with a size of up to 300 nm on the coating surface.