Method for depositing a corrosion-protection coating

Abstract

The use of a cement in a process for pack cementation deposition on a substrate having cavities of minimum equivalent diameter e cm , characterized in that the cement consists of spherical particles each having a diameter d such that d≦e cm /10.

1 - 19 . (canceled) 
     
     
         20 . The use of a cement in a process for pack cementation deposition on a substrate having cavities of minimum equivalent diameter e cm , characterized in that the cement consists of spherical particles each having a diameter d such that d≦e cm /10. 
     
     
         21 . The use of  claim 20 , wherein at least some of the spherical particles are comprised of a precursor of the element to be deposited, at least some of the spherical particles are comprised of an activating agent and some of the spherical particles are comprised of an inert diluent. 
     
     
         22 . The use of  claim 21 , wherein:
 the precursor of the element to be deposited comprises a metallic powder;   10% to 60% of the spherical particles are comprised of the metallic powder;   5% to 40% of the spherical particles are comprised of the activating agent, and   a balance of the spherical particles are comprised of the inert diluent.   
     
     
         23 . The use of  claim 22 , wherein the metallic powder consists of aluminum or a mixture of aluminum with Ni x Al y  particles or Al x Cr y particles. 
     
     
         24 . The use of  claim 20 , wherein:
 at least some of the spherical particles are comprised of a precursor of the element to be deposited;   at least some of the spherical particles are comprised of a pickling flux; and   at least some of the spherical particles are comprised of an inert diluent.   
     
     
         25 . The use of  claim 20 , wherein at least some of the spherical particles are comprised of an organic or inorganic binder. 
     
     
         26 . The use of  claim 20 , wherein the substrate is a metallic heat exchanger. 
     
     
         27 . A process for depositing a coating by pack cementation on a substrate having cavities of minimum equivalent diameter e cm , comprising the following successive steps:
 a) preparing a cement consisting of three types of spherical particles, a first of the three types being comprised of an activating agent, a second of the three types being comprised of an inert diluents, a third of the three types being comprised of a metallic powder, each of said three types of spherical particles having a diameter d such that d≦e cm /10;   b) the prepared cement is introduced into the cavities of the substrate by a vibrating system to produce a substrate-cement assembly;   c) the produced substrate-cement assembly is heated at a temperature below a melting point of the metallic powder for a duration of at least 6 h at around 650° C. for aluminum;   d) the substrate-cement assembly is cooled to ambient temperature;   e) the cement is subjected to a vibration step so as to eliminate the cement residue;   f) the substrate-cement assembly is heated at a temperature of between 900° C. and 1150° C., preferably above 980° C.; and   g) a substrate having a coating over its entirety is recovered.   
     
     
         28 . The process of  claim 27 , wherein the metal of the metallic powder is aluminum. 
     
     
         29 . The process of  claim 28 , wherein the temperature, at which the produced substrate-cement assembly is heated, is around 650° C. 
     
     
         30 . The process of  claim 27 , wherein the temperature, at which the substrate-cement assembly is heated, is between 900° C. and 1150° C. 
     
     
         31 . The process of  claim 30 , wherein the temperature, at which the substrate-cement assembly is heated, is above 980° C. 
     
     
         32 . The deposition process of  claim 27 , wherein the particles of the cement prepared in step a) are preactivated by mechanosynthesis. 
     
     
         33 . The deposition process of  claim 27 , wherein the coating recovered in step g) comprises NiAl. 
     
     
         34 . The deposition process of  claim 27 , wherein the coating recovered in step g) has a thickness of between 15 and 25 μm. 
     
     
         35 . The process of  claim 27 , wherein the substrate is a metallic heat exchanger. 
     
     
         36 . A process for depositing a coating by pack cementation on a substrate having cavities of minimum equivalent diameter e cm , comprising the following successive steps:
 a) preparing a cement consisting of a pickling flux, spherical particles of an inert diluent and spherical particles of a metallic powder, each of the spherical particles of inert diluents and metallic powder having a diameter d such that d≦e cm /10;   b) introducing the prepared cement into the cavities of the substrate by a vibrating system to prepare substrate-cement;   c) heating the prepared substrate-cement assembly to a temperature above a melting point of the pickling flux, under either a low vacuum or under an inert atmosphere (Ar), for a duration of between 10 min and 2 hr, to thereby produce a substrate-cement assembly having a coating of cement residue;   d) cooling the coated substrate-cement assembly to ambient temperature;   e) subjecting the coated substrate-cement assembly to a washing step so as to eliminate a cement residue such that an entirety of the coating is recovered from the substrate-cement assembly.   
     
     
         37 . The process of  claim 36 , wherein the washing step e) is carried out using an acidified aqueous solution. 
     
     
         38 . The process of  claim 36 , wherein the coating recovered in step f) comprises NiAl 3 . 
     
     
         39 . The process of  claim 36 , wherein said process comprises, before step e) and after step d), a step of heating the coated substrate-cement assembly at a temperature of between 900° C. and 1150° C. 
     
     
         40 . The process of  claim 39 , wherein the coated substrate-cement assembly is heated to a temperature above 980° C. 
     
     
         41 . The process of  claim 39 , wherein the coating recovered in step f) comprises NiAl. 
     
     
         42 . The process of  claim 36 , wherein the coating recovered in step f) has a thickness of between 5 μm and 200 μm, preferably between 5 μm and 80 μm.