Anodizing

Transcription

Anodizing

Anodizing
Supinya Wongsriruksa
Division of Materials Science
(Gems and Jewelry)
Faculty of Science
Srinakharinwirot University
What is Anodizing?
z Anodizing is a method of coloring metals by coating the
surface with an electrically deposited oxide. Refractory
metals exhibit color due to the refractive properties of
the oxide.
z Anodizing was first used to wonderful effect in the early
1970s.
z It has become a popular way of introducing vibrant
colors into jewelry.
z The process is relatively inexpensive and quick to do.
z It is so dangerous because of the chemicals.
z Should work by specialize jewelers.
GJ474 Plating II ---- Anodizing
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Anodizing procedure (1)
z Anodizing most closely resembles standard electroplating.
z A reactive metal is suspended in an electrolytic bath as an
anode(+)
z Current is passed through the bath, oxygen is produced
at the anode surface.
z This oxygen reacts with the metal to form a thin oxide
film that generates colors.
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z The transparent oxide increases in thickness in relation
to the amount of voltage applied.
z At any given voltage the oxide will grow to a specific
thickness (i.e. color) and stop, having reached a stage
where current will no longer pass.
z This phenomenon of voltage controlled growth means
that the color is also voltage controlled.
4
Which voltage should be done 1st?
z An area of oxide produced with a high voltage will not
pass current from a lower voltage.
z An area anodized at 60 volts will not need masking when
an adjacent area is anodized to 40 volts.
z It follows that multiple anodizing processes should
proceed in decreasing voltages. Working in descending
order will save masking and generate fewer errors.
5
z While oxygen is generated at the anode(+), hydrogen is
formed at the cathode(-).
z Titanium and stainless steel make most convenient
cathodes.
z This process does not have much throwing power and it
is necessary to have a cathode equal to or larger than
the anode.
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Electrolytic solution
z The electrolytic solution can be almost any liquid capable
of carrying current, such as sulfuric acid (H2SO4),
ammonium sulfate ((NH4)2SO4 ), magnesium sulfate
(MgSO4 ), trisodium phosphate (Na3PO4)
z Recommended here is a solution of 3 to 10% by weight
Na3PO4 in solution with distilled water.
z The percentage of chemicals in the solution will
determine to some extent the length of time for the
desired reaction to be completed.
z Slowing the reaction can be achieved by lowering the
concentration of chemical in solution.
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Tools and Materials (1)
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Tools and Materials (2)
z A variable transformer or rectifier, 3 – 120 V
z A non-glass container for the HF acid.
z A glass vessel to hold 50% lactic acid.
z A glass vessel to hold a solution of ammonium sulfate:
1 oz. : 1 quart
z plastic tweezers
z Ti wires for the anode and cathode
z Strong rubber gloves
z Safety goggles.
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Power supplies
z The power supply required for anodizing has a much
greater range of voltage control and lower range of
current capabilities than plating rectifiers.
z The requirements are 0-150 volts DC variable in one volt
increments and from 2-5 amps.
z Larger capacity power supplies may be necessary for
work larger than jewelry and in high volume production.
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Anodizing techniques
z Anodizing techniques;
{ Bath anodizing
{ Anodic painting
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Bath anodizing (1)
z This technique is best for one color, rainbow and mass
produced work.
z You will need,
1)
2)
3)
4)
5)
a power supply
a plastic or glass container
electrolyte
a cathode
titanium clips, holders or hooks to hold the work.
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Bath anodizing (2)
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Bath anodizing (3)
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Bath anodizing procedure
1) Place the pieces to be anodized in the bath.
2) Turn the power ON and slowly increase the voltage.
(You may see small bubbles appear on the surface of the
anode. That means the anodizing is taking place.)
3) The colors will continue to change as the voltage increases.
If you do not like the color, increase the voltage and
produce a new color. You can never bring the color back
down once it is passed.
4) Turn the power OFF, remove the piece, rinse and wipe dry.
Only then will you see the true color.
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Anodic painting (1)
z We use the metal ferrule of paint brushes (applicators) for
this technique.
z Metals and conductive materials should be covered with
electrical tape or coated with a plastic coating.
z This technique brings the electrolyte to the work.
z Applicators can be made by soldering an insulated wire on
to the metal ferrule of an artist's brush or clipping on to a
sponge with the cathode lead wire.
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Anodic painting (2)
Sponge tool
Pen tool
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Anodic painting procedure (1)
z Connect the anode(+) lead from the power supply to a
reactive metal workpiece.
z Connect your applicator to the cathode(-) output of the
power supply.
z Moisten the applicator in electrolyte.
z Turn on the power supply and set the voltage to the
desired level.
z Touch the applicator to the surface and the colors will
begin to appear.
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Anodic painting procedure (2)
z Always wear rubber gloves.
z This is where the real graphic potential of this process
comes into play.
z If the applicator is held in one position the colors will
slowly radiate out from the point of contact.
z With excess electrolyte and constant movement, even
large areas can be evenly colored.
z Fine detail work can be produced with an almost dry
brush.
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Applications for anodic painting
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Anodizing refractory metals (1)
z Anodizing the refractory metals (Ti, Nb, Ta) produces a
range of colors over the surface that is similar to the colors
formed when oil floats on water.
z The effect is achieved by applying electric current through
a solution to form a layer of hard, TP oxides on metal.
z The thickness of oxide layer is determined by the area,
time, and voltage.
z The colors are called diffraction colors.
z Each color consists of a specific wave length of light.
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z White light (light that carries all colors) penetrates
through the oxide layer and is refracted, reflected, and
then diffracted through the oxide layer.
z Some elements of white light are cancelled out, some are
amplified to produce vibrant shades.
z The rougher the surface of the metal, the color is more
intense.
z High-voltage colors should be put on 1st because it will
be masked against the lower voltage colors.
z Apply a ‘stop out’ resist (varnish) to the area that need
protecting against a higher voltage.
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z It must be completely dry before the metal is immersed in
the anodizing bath.
z We can remove the varnish with a suitable solvent and
re-anodize the metal at a lower voltage.
z Ti can have patterns etched on it with HF acid.
z Ta and Nb anodize in the same way as Ti, and if the
metals are combined and anodized at the same voltage,
different colors will be produced as they produce different
colors at different voltage.
z Anodized metal can be engraved or abraded and then reanodized.
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Natural colours
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Anodizing Titanium and Niobium
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Anodizing Niobium
(1)
(3)
(2)
(5)
(4)
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Anodized Colors
Picture of anodized jewelry
Niobium & Sterling Silver Brooch
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Anodizing Goods
Hardcoat anodizing
Color anodizing
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Safety Procedure (1)
z The chemicals used in anodizing are dangerous.
z The most dangerous of all is HF acid, which will cause
serious burn when contact with skin.
z
z HF acid has to be kept in double-skinned plastic containers.
z HF is used for etching glass and it must away from children
and animals.
z The other chemicals used in the process are lactic acid and
ammonium sulfate.
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Safety Procedure (2)
z If you carry out anodizing yourself, you must:
1) wear safety glasses or goggles
2) heavy-duty gloves
3) cover all your body
4) mix and use the chemicals outdoors or in fume hood
5) make sure that you are working in a well-ventilated
room
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Anodizing Titanium (1)
z Etch the Ti by immersing it for 10 sec in a solution of
HF : water =
1 : 10
z Do this outdoors or in a very well-ventilated room.
z When you cut Ti, leave a long, thin piece from one corner
for holding and can be wired to the anode.
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z Procedure
Step 1: - Rinse the Ti well in the water for 5 sec.
- For normal anodizing, proceed to Step 3
Step 2: - For the high-voltage colors (magenta, turquoise,
and green), you will have to use lactic acid.
- Transfer the Ti to the lactic acid to stabilize it.
- Electricity does not use in lactic acid.
Step 3: - Rinse the piece in water again.
- Place the metal in the ammonium sulfate
solution for anodizing.
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Step 4: - The cathode wire is attached to a piece of
stainless steel or to titanium.
Step 5: - Alternatively, use the metal end of paintbrush as the
cathode, and can be used to paint the surface of the titanium
anode with the ammonium sulfate.
- the voltage in the paintbrush (or cathode) will allow
you to create some unusual colors.
Step 6: - Backgrounds that blend from one color into another
color can be created by lifting a piece out of the anodizing bath,
with increasing the voltage in proportion to the area applied.
- in this way you can create the effects of sky, sunset,
sea, and so on.
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Colored anodized titanium rings (1)
• The angle of viewing and type of light source
will also influence color.
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It can re-anodize the rings
the same or different color.
36
z The anodize process passes an electrical current through
the titanium in a conductive bath.
z A transparent titanium-oxide layer was produced on the
ring's surface.
z The applied voltage determines the oxide thickness,
which creates the color.
z The iridescent colors are formed by the refraction of
light off of, and through this transparent oxide layer,
essentially a 50 to 200 nanometer thick prism.
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Titanium Rings
Purple
Natural
Black
Dark blue
Bronze
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Anodized Jewelry
anodized aluminium, sterling silver,
brass, niobium, stainless steel necklace
Sterling silver & anodized titanium
bracelet
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Anodized Ornaments
Anodized aluminum hat
anodized aluminium, copper, leather, acrylic hat
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Anodized Aluminum
Anodized aluminum and fabric
Anodized aluminum, sterling silver
and gold plate
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Anodized Aluminum
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Anodizing Aluminum
z Aluninum can be anodized.
z Anodizing will protect the aluminum parts by making the
surface much harder than natural aluminum.
z Aluminum oxide (Al2O3) is grown out of the surface
during anodizing and it is extremely hard.
z The porous nature of the anodized layer allows the
product to be dyed any color that is required.
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Anodizing Aluminum
z Anodizing is done at room temperature will give an
anodized layer of 0.005 – 0.025 mm.
z Hard coat anodizing is done at much colder temperatures
and at higher current densities and can reach thickness of
0.05 mm.
z Hard coat anodized surfaces can only be dyed black or
dark green due to the denser pore size.
z It is possible to do two tone or multi color anodizing
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Anodizing Aluminum
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Basic steps for anodizing
z Not all steps are needed such as etch and deox.
z Basic steps for anodizing;
1) Submerse part in 60 C cleaner for 5 min, rinse.
2) Etch part in R.T. caustic solution 10-30 sec or longer if
matte finish is desired, rinse.
3) Deox part at R.T. for 1-3 min if previously etched, rinse.
4) Anodise part at the required current densities at R.T.,
rinse, rinse again.
5) Dye part in 60 C dye for 15 sec to 15 min, rinse.
6) seal part in 80 C nickel acetate sealer for 20 min, rinse and
hang to dry.
46
Basic steps for anodizing
47
Preparing the parts before anodizing
z The rule is “what you see is what you get after the part
is anodized”
z However, anodizing tend to slightly magnify the surface
texture so lean toward a smoother finish when preparing
the part.
z A small amount of the gloss will be lost after the part is
anodized.
z For a bright glossy surface on the anodized part, polish it
with a buffing wheel using tripoli compound.
48
z Use vibratory tumblers with different grades of media for
sanding and polishing the parts before anodizing.
z This allows a large quantity of parts to be done easily.
49
z Use buffing on a polishing wheel using tripoli compound
is the quickest way.
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Stripping the anodized layer
z You can strip off the existing anodized layer from any
anodized part by placing the part in a caustic solution for
an hour or longer.
z caustic solution : a few tablespoons of NaOH and water.
z Anodize coatings can be stripped using a dilute aqueous
solution of phosphoric and chromic acid
z Caution!! “Wear eye protection and rubber gloves
for this procedure”
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Stripping the anodized layer
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Solution for anodizing aluminum
z There are 5 types of the solution;
1) 10% by vol. sulfuric acid (H2SO4)
2) 15% by vol. sulfuric acid
3) 10% vol. sulfuric acid + 5% wt. oxalic acid (H2C2O4)
4) 5% wt. chromic acid (H2C2O7)
5) 10% wt. chromic acid
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Anodizing Aluminum
z Rings, anodised aluminium.
z Cloak pins; sterling silver &
anodized aluminium
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Anodizing Aluminum
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Anodizing Aluminum
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End of Anodizing

Anodizing

Transcription

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