Electroless plating of ruthenium and ruthenium-plated products

Abstract

An electroless plating Ru bath for the deposition of Ru on the surface of a substrate comprises a Ru stock solution and hydrazine as a reducing reagent. Ru layers may be applied, for example, for use in membranes for the separation of hydrogen gas from mixtures of gases or to protect materials from corrosion. An example Ru stock solution comprises Ru chloride, hydrochloric acid, ammonia, nitrite salt, alkali hydroxide, and deionized water. The electroless plating bath may be applied to deposit ruthenium layers onto palladium layers to prepare Pd—Ru composite or alloy membranes or multilayer Pd—Ru composite or alloy membranes. Such membranes have example application to the separation of hydrogen from mixtures of gases.

What is claimed is: 
     
         1 . A method for depositing Ru onto a surface of a substrate, the method comprising:
 preparing an electroless plating bath having a pH of at least 13 comprising:
 a Ru stock solution; and 
 a hydrazine reducing reagent; and 
   contacting the substrate with the electroless plating bath.   
     
     
         2 . A method according to  claim 1 , wherein the Ru stock solution comprises:
 a source of Ru ions; and   a water soluble nitrite salt.   
     
     
         3 . A method according to  claim 2 , wherein the electroless plating bath further comprises one or more of:
 hydrochloric acid;   a complexing reagent; and   an alkali hydroxide.   
     
     
         4 . A method according to  claim 3 , wherein the source of Ru ions comprises a chloride or nitrate of Ru. 
     
     
         5 . A method according to  claim 3 , wherein the complexing reagent comprises ammonia. 
     
     
         6 . A method according to  claim 5 , wherein the molar ratio of ammonia/Ru is at least 150. 
     
     
         7 . A method according to  claim 6 , wherein the molar ratio of ammonia/Ru is at least 200. 
     
     
         8 . A method according to  claim 7 , wherein the alkali hydroxide comprises sodium hydroxide or potassium hydroxide. 
     
     
         9 . A method according to  claim 2 , wherein the water soluble nitrite salt comprises sodium nitrite or potassium nitrite. 
     
     
         10 . A method according to  claim 2 , wherein the molar ratio of nitrite/Ru is at least 1. 
     
     
         11 . A method according to  claim 2 , wherein the molar ratio of nitrite/Ru is in the range of 3 to 5. 
     
     
         12 . A method according to  claim 1 , wherein the molar ratio of hydrazine/Ru is at least 2. 
     
     
         13 . A method according to  claim 12 , wherein the molar ratio of hydrazine/Ru is in the range of 5 to 20. 
     
     
         14 . A method according to  claim 1 , wherein the pH of the electroless plating of the bath is in the range of 13 to 14. 
     
     
         15 . A method according to  claim 14 , wherein the pH is in the range of 13.3 to 13.7. 
     
     
         16 . A method according to  claim 1 , comprising maintaining a temperature of the electroless plating bath at a temperature of at least 50° C. 
     
     
         17 . A method according to  claim 16 , comprising maintaining a temperature of the electroless plating bath at a temperature of at least 60° C. 
     
     
         18 . A method according to  claim 1 , wherein the Ru stock solution comprises an aqueous solution of:
 1.0×10 −3  M to 2.0×10 −1  M RuCl 3 .×H 2 O (Ru mass, 38%);   4.0×10 −2  M to 4.0×10 −1  M HCl;   1.0 M to 21 M NH 3 .H 2 O (28%);   1.0×10 −1  M to 1.0 M NaOH; and   4.0×10 −2  M to 4.5×10 −1  M NaNO 2 .   
     
     
         19 . A method according to  claim 1 , wherein the Ru stock solution comprises an aqueous solution of:
 0.10% weight to 0.51% weight Ru;   0.15% weight to 1.46% weight HCl;   1.7% weight to 35.7% weight NH 3 ;   0.4% weight to 4% weight NaOH;   0.28% weight to 3.11% weight NaNO 2 .   
     
     
         20 . A method according to  claim 19 , wherein the substrate comprises stainless steel. 
     
     
         21 . A method according to  claim 19 , wherein the substrate comprises a ceramic. 
     
     
         22 . A method according to  claim 21 , wherein the substrate is porous. 
     
     
         23 . A method according to  claim 19 , comprising activating the substrate with a metal catalyst before contacting the substrate with the electroless plating bath. 
     
     
         24 . A method according to  claim 23 , wherein the metal catalyst comprises Pd. 
     
     
         25 . A method according to  claim 1  applied for preparing a Pd—Ru composite membrane, the method comprising:
 prior to contacting the substrate with the electroless plating bath, plating a surface of a substrate with Pd using electroless plating; 
 wherein the electroless plating bath has a pH of at least 13. 
 
     
     
         26 . A method according to  claim 25 , wherein the electroless plating bath comprises:
 a source of Ru ions; and   a water soluble nitrite salt.   
     
     
         27 . A method according to  claim 26 , wherein the electroless plating bath comprises:
 hydrochloric acid;   a complexing reagent; and   an alkali hydroxide.