Apple has used aluminum and stainless-steel cellphone frames because the iPhone 2G’s introduction in 2007. Nonetheless, final yr’s iPhone 15 Professional received one thing new. A light-weight metallic utilized in every little thing from spacecraft to surgical implants with unimaginable power and sturdiness: Mighty Titanium!

Does titanium’s sturdiness make the iPhone 15 Professional much less prone to breaking? There’s some debate—JerryRigEverything was capable of crack the back glass of a Professional Max with a single bend, although the identical mannequin survived 100 rides within the Client Stories drop tumbler. Time will inform if the titanium body is related to fewer repairs. 

However our ears perked up at “titanium” for an additional motive that has nothing to do with restore: titanium will be anodized to create superior colours and patterns. Apple provides the iPhone 15 Professional in 4 finishes, however we’re going so as to add our personal customized flashy colours. To do that we’re going to combine water, electrical energy, and a few caustic chemical substances. How thrilling! Earlier than persevering with, we don’t advocate attempting this at residence except you understand precisely what you’re doing.

The Science Behind Titanium Anodizing

Anodizing is an electrolytic course of that grows a protecting oxide layer on a metallic floor. In less complicated phrases, the metallic floor is corroded in a managed method and the layer of corrosion protects the underlying metallic. The oxide layer is grown by submerging the half in an electrolyte bathtub and passing a present by means of it. Anodizing titanium grows a layer of titanium dioxide on the metallic’s floor, which takes on a wide selection of colours. 

Nonetheless, not all metals are as amenable to anodization as a result of the method is incompatible, or the pure oxide doesn’t present any safety. For instance, the stainless-steel body used on earlier iPhones can’t be anodized as a result of it already has a protecting chromium oxide layer that might simply dissolve.

The colourful colours consequence from the interplay between incoming mild waves and the oxide layer by means of a phenomenon known as thin-film interference. When mild strikes a floor with a movie on it (for anodizing, the skinny movie is the oxide layer), the sunshine waves mirrored on the higher and decrease boundaries of the movie intervene with one another. The interference is both constructive or harmful relying on the movie’s refractive index, thickness, and the wavelength of the incoming mild. Because of this, sure wavelengths are intensified whereas others are diminished. If you happen to’ve ever witnessed swirly colours in a cleaning soap bubble or rainbow splotches on a moist highway from oil stains, that’s thin-film interference in motion. 

Cleaning soap bubble by Brocken Inaglory from Wikipedia

Skinny Movies and Mild Defined

Most often, mild initially travels by means of the air after which the movie. A number of the incoming mild is mirrored on the movie’s floor and a few continues by means of the movie. For titanium anodizing, the “movie” is a skinny layer of titanium dioxide about thirty nanometers to a number of hundred nanometers thick. If the movie’s refractive index is larger than that of the medium it was initially touring in, the sunshine mirrored on the floor will bear a 180° part shift. Air has a refractive index of about one and titanium has a refractive index of about 2.8 so the sunshine mirrored on the floor will bear a part shift.

Mild waves that journey by means of the titanium dioxide layer and mirror off the decrease boundary will intervene with waves mirrored on the floor, both constructively or destructively, relying on the thickness of the layer. This occurs as a result of the wavelength and velocity of sunshine change when touring from one medium to a different. When touring from air to titanium dioxide, the wavelength and velocity of sunshine lower as a result of the refractive index is larger than air. The lower in wavelength introduces a part shift to the mirrored mild on the decrease boundary, which causes constructive or harmful interference.

If you would like an much more in-depth rationalization about thin-film interference, try this video from Khan Academy. Need a extra interactive expertise? Take a look at this cool thin-film interference simulator from oPhysics.

How Titanium Anodizing Works In Observe

That’s all the idea, however how is titanium really anodized? 

The titanium dioxide layer is grown electrochemically by both submerging a titanium half in an electrolyte answer and passing an electrical present by means of it, or by spot anodizing. Spot anodizing makes use of a sponge or brush soaked within the electrolyte answer related to an influence provide. This enables the anodizing to be “painted” onto the floor. The principle profit is that the titanium half doesn’t need to be submerged in any respect.

Another technique to develop the oxide layer is to easily warmth the titanium to a number of hundred levels Celsius. Whereas this isn’t technically anodizing as a result of it’s not an electrochemical course of, comparable outcomes will be achieved. This is so simple as grabbing a blowtorch and blasting the titanium till you’ve received the specified shade. Nonetheless, shade consistency and management is troublesome except you’ve received some critical blowtorch abilities. Anodizing is the popular technique as a result of the oxide layer thickness, and consequently the colour, is immediately associated to utilized voltage. 

Floor preparation is essential as a result of any earlier oxides, smudges, or contamination will have an effect on the vibrancy and end of the anodized shade. A weak hydrofluoric acid answer or a sizzling answer of ammonium persulfate and sodium fluoride is usually used to scrub and etch titanium. 

Hazard: Acid and Electrical energy!

Hydrofluoric acid is nasty harmful stuff even in small concentrations. It may possibly trigger extreme tissue harm and pull the calcium out of your bones. Protected to say, you don’t wish to get any on your self. But it surely works nice as a titanium etchant and is available. As for electrolyte options, they’re a bit of safer. Sulfuric acid, trisodium phosphate, and borax are generally used, however most ionic solutions will work

The optimistic or anode wire is related to the titanium half (therefore why it’s known as anodization) and the destructive or cathode wire is related to a different piece of metallic within the electrolyte answer. For spot anodizing, the destructive electrode is related to an electrolyte-soaked sponge or brush. The ability provide voltage is assorted from about 10 to 100 volts DC to develop the oxide layer. Mixing electrical energy and water is harmful, and the electrolyte answer’s elevated conductivity makes issues extra perilous. Carrying insulating gloves, dealing with the electrodes with care, and cleansing any electrolyte spills are vital to forestall shocks. 

Anodizing Time

As a lot enjoyable as it could be to get a model new iPhone 15 Professional and dunk it in an electrolyte tank or blast it with a blowtorch, we needed to give you a recreation plan first. (Observe: For these interested by what occurs when an iPhone 15 Professional (Max) will get blow-torched, our good friend JerryRigEverything did simply that.)

Our first step was disassembling the cellphone right down to the body to see what we have been working with. Wanting on the naked body, the internal aluminum subframe is clearly seen together with a number of plastic elements bonded to it that create the antenna bands. These bands are electrically remoted from one another and should be anodized individually.

To keep away from corroding the internal aluminum subframe or anything necessary, we’re not going to present the body a hydrofluoric acid or electrolyte bathtub. As a substitute, we’re going to etch the body by wiping it down with an acid-soaked material and use the spot anodizing technique to reduce any electrolyte splashes. It’s in all probability attainable to etch and spot-anodize the body with out full disassembly, however we didn’t wish to danger corroding or frying something necessary.

A naked iPhone 15 Professional body (Entrance)
A naked iPhone 15 Professional body (Again)

Subsequent up is eradicating the Blue Titanium PVD (bodily vapor deposition) end already on the body. Sanding the body with a 320 grit sanding block simply eliminated the blue PVD coating, leaving a pleasant shiny titanium floor. If we had a Pure Titanium iPhone 15 readily available, there can be no must sand off the end as a result of its floor is already conductive. 

Sanding off the blue PVD coating

Now onto floor etching prep, so the anodized colours will prove extra vibrant. 

That is probably the most harmful a part of the experiment as a result of we’re going to make use of hydrofluoric acid. Our acid supply is Whink rust remover which has a focus of about 2%. This can’t be understated sufficient: hydrofluoric acid is extremely harmful even in small concentrations and will solely be used if correct security precautions are taken!

To remain protected, we labored in a well-ventilated space, donned goggles and a face defend, and wore two units of nitrile gloves. Entry to a provide of calcium gluconate gel is a should. Within the occasion of pores and skin publicity, the gel binds with the toxic fluoride ion to neutralize it. 

Continuing with warning, we wiped down the outer titanium body with an acid-soaked material. Instantly after this, the body was dunked in a baking soda answer to neutralize the acid. The gloves and material have been soaked within the baking soda answer previous to disposal as effectively.

Lastly, it’s anodizing time. The anodizing setup consisted of an influence provide, some check leads, a little bit of sponge, and a trisodium phosphate answer for the electrolyte. Trisodium phosphate or TSP is a robust base and might trigger burns, so we goggled and gloved up for security. A small piece of kitchen sponge was related to the ability provide’s destructive terminal to make use of as an anodizing brush. The optimistic terminal was related to the body. A 100mA present restrict was set so issues wouldn’t get too thrilling. The sponge electrode and electrolyte answer should be dealt with with care when anodizing to forestall shocks. We wore nitrile gloves to insulate ourselves from the circuit and held the sponge aspect by the wire insulation to reduce shock danger. However please, don’t do this at residence.

Don’t do this at residence.

— Us. And we nearly by no means inform you that, so you understand we imply it.

The antenna bands divide the body into 4 sections that don’t share continuity. This implies every part will be anodized individually to create some enjoyable mismatched colours. Initially, we set the ability provide to round 25V aiming for an iFixit blue, and wiped the TSP-soaked sponge throughout the underside. Whereas not a real iFixit blue, it was fairly shut, with some discoloration close to the USB-C port cutout. 

This consequence excited us a lot, we instantly anodized the opposite edges. Turning as much as 50V for yellow and wiping the sponge throughout the proper aspect, we have been greeted with an exquisite straw gold at first. Sadly, the decrease proper aspect had some scratches and pitting, which didn’t look fairly. This was in all probability attributable to inadequate etching or floor contamination. However, we have been nonetheless stoked to create some superior colours. 

iPhone 15 Professional IKEA Version

Turning the voltage up much more—to 70V—to get purple yielded some very nice outcomes. Curiously, the realm close to the quantity and motion button cutouts remained yellow after a number of sponge passes. This could be attributable to a unique present density across the cutouts, or not sufficient electrolyte current within the sponge. Though we have been aiming for purple, the colour gradient between yellow and purple was cool-looking and a fan favourite across the workplace. Combine-matching and swirling colours is one thing we’ll positively strive if we do that once more. 

Anodized body

The First Anodized iPhone 15 Professional

Placing the cellphone again collectively makes the colours pop much more and has us eagerly ready to anodize one other cellphone. You could be questioning why the buttons nonetheless have the unique end. We tried anodizing them in a earlier experiment, however they wouldn’t take a shade. They’re doubtless stainless-steel and ended up including a pleasant distinction to the anodized body. 

What about sturdiness? The unique PVD coating might be extra scratch and fingerprint-resistant. 

Typical PVD coatings vary in thickness from about 1 micrometer to 5 micrometers which is a number of thousand occasions the thickness of the anodized oxide layer. Fingerprints and smudges are extra seen on the anodized floor as a result of the oil in your pores and skin acts as a further skinny movie layer that impacts the mirrored colours. The sturdiness and scratch resistance could possibly be improved by overlaying the anodized layer with a transparent protecting coating. One thing like a ceramic coating for automobiles would possibly work effectively. 

Anodizing Forward

Apple in all probability doesn’t approve of anodizing your shiny new iPhone. However you got it, you personal it, and that possession ought to include the liberty to make it uniquely yours. Restore it, hack it, or customise it with some fancy anodized colours (assuming you’re snug anodizing and have all the protection tools, after all). 

This experiment was a complete success, and we’re itching to do extra and refine it. We have already got some concepts about what to do subsequent. Some extra shade mixing and mixing would create a novel chromatic cellphone. Including masks over the body to anodize patterns or textual content can be superior too. Determining find out how to anodize with no full disassembly can be a recreation changer, so the manufacturing unit water resistance gained’t be compromised. We’re gonna do some extra testing, so keep tuned for extra anodizing adventures!

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