Electropolishing - indico.cern.ch · electropolishing, the working parameters must be so that it allows to smoothen, polish, deburr and clean metal surfaces. History's first reference

Electropolishing (applied to Copper, Niobium, Titanium…)

L. Ferreira TE-VSC-SCC

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 2

OUTLINE

- What is electropolishing - How it works - Advantages/disadvantages - Common uses

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 3

What is

ele

ctro

polis

hin

g

It’s an electrochemical treatment that removes material from metal objects surface. In order to be defined as electropolishing, the working parameters must be so that it allows to smoothen, polish, deburr and clean metal surfaces.

History's first reference to electropolishing seems to have occurred in 1910 when Germany issued a patent for the finishing of silver in a cyanide solution ( Spitalsky, Germ. Pat. Nr. 225873).

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 4

How

it work

s

Usually highly corrosive

and toxic chemical solutions

The metal is immersed in an electrolyte and subjected to direct

current. The metal part to be treated is made anodic and under

certain conditions, a controlled dissolution of the metal is

achieved.

DC Power supply

Cath

ode

Anode (Part to be

electropolished)

A

V

+

-

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 5

DC Power supply

Cath

ode

Anode

A

V

1 µm

If we go to the µm level

How

it work

s

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 6

How

it work

s

0

50

100

150

200

250

300

0 2 4 6 8 10

Cu

rren

t D

en

sit

y

(A

/m

2)

Overpotential (V)

Cathode

R R

Primary current distribution Secondary current distribution

j = f(η(Overpotential))

j = f( T, Qv, Sc/Sa, bath composition)

Quite straightforward?

For complex shapes and accurate

thickness removal, process simulation

becomes very helpfull.

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 7

It works for all metals?

In literature/patents, it’s possible to find processes for:

- Aluminium; - Beryllium; - Bismuth; - Cadmium - Cobalt; - Copper; - Gold; - Indium; - Iron (Stainless Steel); - Lead; - Molybdenum; - Nickel; - Niobium; - Silver; - Tantalum; - Titanium (CERN formulation); - Tin; - Zinc;

- Suitable for large surfaces

- Ra within the nm scale

- Works at room temperature

How

it work

s

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 8

Advanta

ges

Electropolishing / Mechanical based polishing

• No contact: Stress relief • Superior corrosion resistance (less stress, equipotential surface) • Clean surfaces (no recontamination) • No direction lines • Low-resistance, contaminants free welding surface • Suitable for complex shapes

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 9

Advanta

ges

Base metal

Impurities and/or alloy

elements

Organic base coating

Grease/lubricant

Pencil/Pen/ink

Voids or inclusions

Oxide/ scale

10 to 200

µm

Clean surfaces: How clean is clean?

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 10

Advanta

ges

Base metal

Impurities and/or alloy

elements

Voids or inclusions

Oxide/ scale

10 to 200

µm

Clean surfaces: How clean is clean?

After chemical degreasing (detergent/solvent)

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 11

Dis

advanta

ges

Electropolishing / Mechanical based polishing

• Final roughness is function of initial surface finishing and removed thickness • Usually highly corrosive and/or toxic solutions

- Handling; - Process equipment; - Installation to process extracted fumes; - Installation to process waste water.

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 12

At CERN

Copper and Niobium components:

Radio Frequency structures

Goal:

- surface cleaning (200 µm thick)

- smoth surface (high fields)

Titanium and alloys components:

High Voltage electrodes

12 µm 12 µm

Ti electropolished Ti mechanical polished

Applic

atio

ns

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 13

Applic

atio

ns

…Elsewhere

• Heavy industry:

•Deburring; •Oxides removing;

• Textile industry:

• Deburring; • Smooth surface; • Oxides removal.

• Semiconductor:

• Clean surfaces; • Flat surfaces; • Easy to clean.

• Pharmaceutical and food processing:

• Clean surfaces; • Easy to clean; • Lower bacteria yield.

• Chemical Industry:

• Clean and Smooth surfaces; • Improved passivation; • Improved corrosion resistance.

Vacuum, Surfaces & Coatings Group

Technology Department 19 November 2013 L. Ferreira 14

Thank you!

Questions?