Electrochemical system and method for electropolishing superconductive radio frequency cavities

Abstract

A method and system for electrochemically machining a hollow body of a metal or a metal alloy. An electrode is positioned within a hollow body including a metal or metal alloy, where the hollow body has a variable internal diameter. The hollow body is oriented vertically, with the electrode oriented vertically therein. The hollow body is at least partially filled with an aqueous, acidic electrolyte solution, the electrolyte solution being devoid of hydrofluoric acid and having a viscosity less than 15 cP. An electric current is passed between the hollow body and the electrode, where the electric current includes a plurality of anodic pulses and a plurality of cathodic pulses, and where the cathodic pulses are interposed between at least some of the anodic pulses.

What is claimed is: 
     
         1 - 20 . (canceled) 
     
     
         21 . A method for electrochemically machining a hollow body of a metal or metal alloy, the method comprising:
 positioning an electrode within a hollow body comprising a metal or metal alloy, wherein the hollow body has a variable internal diameter;   orienting the hollow body vertically, with the electrode oriented vertically therein;   at least partially filling the hollow body with a hydrofluoric acid free electrolyte solution having a viscosity less than 15 cP; and   passing an electric current between the hollow body and the electrode, wherein the electric current is comprised of a plurality of anodic pulses and a plurality of cathodic pulses, and wherein the cathodic pulses are interposed between at least some of the anodic pulses.   
     
     
         22 . The method of  claim 21 , wherein the electrolyte solution has a viscosity less than about 4 cP. 
     
     
         23 . The method of  claim 22 , wherein the electrolyte solution has a conductivity greater than about 200 mS/cm. 
     
     
         24 . The method of  claim 23 , wherein the voltage and on time of the anodic pulses are adjusted to polish the hollow body while limiting the formation of passivating metal oxide to a thickness that can be removed effectively by the cathodic pulse. 
     
     
         25 . The method of  claim 24 , wherein the cathodic pulse voltage is greater than 4 V. 
     
     
         26 . The method of  claim 21 , wherein the metal or metal alloy forms a strongly-bonded passivation layer during the anodic pulses of the passing an electric current step. 
     
     
         27 . The method of  claim 26 , wherein the metal or metal alloy of the hollow body is selected from the group consisting of niobium and niobium alloys, titanium and titanium alloys, zirconium and zirconium alloys, hafnium and hafnium alloys, tantalum and tantalum alloys, molybdenum and molybdenum alloys, tungsten and tungsten alloys, and chromium cobalt alloys. 
     
     
         28 . The method of  claim 27 , wherein said hollow body comprises niobium or niobium alloy. 
     
     
         29 . The method of  claim 21 , wherein the electrolyte contains at least about 10% water. 
     
     
         30 . The method of  claim 21 , wherein the hollow body does not rotate during the passing an electric current step. 
     
     
         31 . A method for electrochemically machining a hollow body of a metal or metal alloy, the method comprising:
 positioning an electrode within a hollow body comprising a metal or metal alloy, wherein the hollow body has a variable internal diameter;   orienting the hollow body vertically, with the electrode oriented vertically therein;   at least partially filling the hollow body with an aqueous electrolyte solution having a viscosity less than 15 cP; and   passing an electric current between the hollow body and the electrode, wherein the electric current is comprised of a plurality of anodic pulses and a plurality of cathodic pulses, and wherein the cathodic pulses are interposed between at least some of the anodic pulses.   
     
     
         32 . The method of  claim 31 , wherein the electrolyte solution has a viscosity less than about 4 cP. 
     
     
         33 . The method of  claim 32 , wherein the electrolyte solution has a conductivity greater than about 200 mS/cm. 
     
     
         34 . The method of  claim 33 , wherein the voltage and on time of the anodic pulses are adjusted to polish the hollow body while limiting the formation of passivating metal oxide to a thickness that can be removed effectively by the cathodic pulse. 
     
     
         35 . The method of  claim 34 , wherein the cathodic pulse voltage is greater than 4 V. 
     
     
         36 . The method of  claim 31 , wherein the metal or metal alloy forms a strongly-bonded passivation layer during the anodic pulses of the passing an electric current step. 
     
     
         37 . The method of  claim 36 , wherein the metal or metal alloy of the hollow body is selected from the group consisting of niobium and niobium alloys, titanium and titanium alloys, zirconium and zirconium alloys, hafnium and hafnium alloys, tantalum and tantalum alloys, molybdenum and molybdenum alloys, tungsten and tungsten alloys, and chromium cobalt alloys. 
     
     
         38 . The method of  claim 37 , wherein said hollow body comprises niobium or niobium alloy. 
     
     
         39 . The method of  claim 31 , wherein the electrolyte contains at least about 10% water. 
     
     
         40 . The method of  claim 31 , wherein the hollow body does not rotate during the passing an electric current step.