Can I Color Titanium in an Oven?

March 22, 2011

Kathleen asked:

Is it possible to color titanium in an oven (to control the temperature)? If so, what temperature does the oven have to have?

Assuming a kitchen oven, the answer is, No.

If you have a laboratory oven, a kiln, or some such, then the answer is, “Probably”.

Titanium colors by heat are controlled by temperature much like anodized color is controlled by voltage. The temperature at which you should start seeing the lowest tan/bronze is about 640°F. This is easy to reach with a direct flame, but not in a household oven.

I have not found a color/temperature scale, but would love to publish one. If anyone with a lab oven wants to play with this, please share your results.

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Black or Gray Titanium

March 4, 2011

John Asks:

I’m trying to get a black or dark gray finish on the face of a titanium driver head. What voltage achieves that color?

Sorry, John. Anodizing produces a particular spectrum of colors limited by the first two octaves of optical interference. I explain it here.

Black and gray are shades, not colors. One cannot make titanium black by anodizing.

So, how is black titanium made? Everyone who does it is keeping the actual process a tight secret. But my  educated guess is that it is produced by implanting nitrogen into the titanium using an industrial vacuum effusion furnace. This produces a relatively thick layer of titanium nitride in a similar chemical manner that titanium dioxide is made by anodizing. But nitrogen implanting cannot be done in an oxygen rich environment, like air or water. Air is 21% oxygen by volume, and water is 33% oxygen by atoms, or 88% by weight.


Anode vs. Cathode Terminology

January 25, 2011

A reader named Scott suggested that I may have made an error:

“On your Anodizing page,  point #3 & #4 are backwards. The anode is negative and the cathode is positive. The work goes on the negative side (the anode) and we are ‘anode-izing’

“Just the first few words of each line are backwards.”

His contention is that the “Anode” should be the negative side. I guess that he is familiar with batteries or sacrificial anodes, where the polarity is opposite that of the electrolytic process that I use.

Rather than just calling him “wrong”, I thought that I would explain it here, in case it comes up again:


The anode is the side of an ion exchange that supplies positive ions.

In the case of an electromotive source (like a galvanic cell, “battery”) you would be correct. The immersed source of positive ions into the solution (anode) produces the negative voltage by pumping electrons around the circuit to balance the positive ions lost to the solution. So in a battery, the anode is the negative side.

But in an electrolytic cell, like an anodizing or plating bath, the anode is where the positive external voltage pumps positive ions into the solution. So the anode is the positive side.

For my purposes, I need to bond oxygen to titanium. Oxygen is a negative ion (2-), pulled toward the positive electrode by the external power source.  The anode simply absorbs electrons from the solution and oxygen is split from the water to keep the accounts balanced. Titanium loves oxygen, so sucks it up as long as there is current. Hydrogen (+) bubbles off at the cathode (negative electrode).

Here’s the Wikipedia article on Anodes, if you want to corroborate what I’m saying and follow to even more authoritative sources.


Programmable Voltage Supply?

December 19, 2010

John asked:

Is there any value in a programmable(manual or C/C++) power supply for anodizing?

Say Vout=20+(110*N/(255)); // N=0,1,2,3,4,…255

Giving {20,20.4, 20.8,21.2…129.6, 130}

I can also make this power limited to approximately 13W(0.10A at 130VDC)

I am not selling anything! I am just wondering if this is a worth while adventure.

As a fellow electrical and programming geek, I see the appeal of the project. But practically speaking in terms of anodizing titanium, no. The color is determined by the final voltage, and the faster you get there, the better.

Also, I use down to 8 volts on occasion. And the lower voltages are more color sensitive than the higher, so it should either be 16 bit linear, or have exponential or quadratic output, as in

vOut = (((N/64)^2 + N) *120/255) + 5 // N={0…255}

But if you were to rig an x-y table to such a supply, one could then “print” in anodized colors. However, there is a limited palette. And also one would have trouble with certain adjacent colors, and have to adjust the lateral speed to be proportional to voltage, and maybe fluid flow through the dielectric cathode, and several other engineering considerations.

As such, it becomes fun and useful. But a lot more work. Then you would be able to share it on HackADay.com or Makezine.tv or some such.

In order to make such a project marketable, one would have to write the CADD end to prevent unfulfillable designs. Artists have to have limits imposed.


Is TSP/90 as Good as TSP for Anodizing?

December 13, 2010
TSP90
TSP 

James asked, “Will the TSP/90 Phosphate Free products work as well as the standard TSP brands?”

An excellent question. My first impulse is, “I doubt it.” But I am not sure. The folks at ReactiveMetals.com might have some insight (that I would share here if passed along).

TSP/90 is made with Sodium metasilicate and pentahydrate. So it is an alkali electrolyte with plenty of oxygen carriers in it. So far, so good. But as a cleanser it appears to suffer from leaving behind a film; a bad sign.

If you are concerned about the potential harm of artificial phosphates in the environment, anodizing is not a significant supply. I have been using the same 8 oz. box of actual TSP for the last dozen years. That’s equivalent to a few weeks of laundry. The same batch of electrolyte can keep on going for months, by adding distilled water (the part that is used up) and an occasional pinch of TSP crystals (to keep up the concentration from the drops removed by pulling out pieces). Occasionally, I filter out the dust and bring it to a boil to make sure it stays sterile.

If you want to be even more environmentally correct, use ammonium phosphate (lawn fertilizer) and then dispose of your old electrolyte by spraying it on your lawn. I used a box of this through the 1980’s and 1990’s.

One of these days, I’ll probably expound why the lingering phosphate meme of the 1970’s was somewhat misguided in the first place.


Why add a capacitor to the Anodizer?

August 6, 2008

I received the following question:

I have a variac and full wave rectifier but no cap.
What is the reason behind adding a capasitor to the anodizer? I know it will reduce electrical ripple but what will it mean to the anodize process or final results?

In principle, the smoother, ripple-reduced output allows more even anodizing starting at the initial surge. Whether this is truly useful, I don’t really know. My experience is almost exclusively with a smoothed DC supply. But I have a switch on my main anodizer to disconnect the capacitor for those occasions when I feel like it.

RMS vs Peak Voltage The voltage will read wrong with ripple. The anodized color depends on the peak voltage. But a rippled current shows on a meter as the rms voltage, that is somewhat lower. So the color is less predictable, and the time spent at that voltage is more critical to watch.

Also, once you reach your final voltage (or at least asymptotically close enough), the smooth DC current is stopped. But a rippling supply still produces a trickle of  current as the piece you are anodizing acts as a capacitor. If you wait long enough, you can see the color continues to rise at a fixed ripply voltage.

This latter point is more important if you mask and do a succession of lower voltages for multiple colors. With ripple, the higher voltage colors will creep as you anodize the lower voltage areas.

Another note is that AC is more dangerous than DC. Edison (General Electric) made sure that the first electric chair used the AC current promoted by his rival Tesla (Westinghouse), to popularize that point. (source) But I doubt it makes much difference in any practical sense of anodizer safety.


Epoxy Resin and Allergic Contact Dermatitis/Eczema

May 13, 2008

Titanium and Niobium cannot be soldered, so I am told.

So, short of Fusion Welding, Jewelers 2-part Epoxy seems to be the only alternative for bonding these elements.

There are 2 concerns regarding Epoxy Resin.

First, and foremost, is the fact that Epoxy Resin is an allergen causing agent in itself. Although not everyone suffers from Allergic Contact Dermatitis/Eczema, those of us who do, seem to be prone to react to a specified list of items. Epoxy Resin is one of them.

This means, in jewelry design, it is important that no Epoxy touch the skin. Although it is acceptable under governmental code (even in California), to label a pierced earring “hypo-allergenic” if at least, the post itself contains no allergen causing agents, the fact is, it’s not just the post that comes into “contact” with our skin.

Second, it is difficult to adhere Titanium and Niobium with Epoxy Resin. But I have found that attention to certain details seems to be the answer for success.

* The larger the two surfaces to be bonded, the more secure the bond.

* Etch the two surfaces well. Epoxy needs nooks and crannies to create a place to bond. I usually do this with needle files, in a cross hatch fashion. Filing in both directions creates an etching effect, as opposed to filing in one direction which creates a buffed effect.

* Remove all dirt, debre, and skin oils from the surfaces to be adhered. Rubbing alcohol works fine for this.

* 2-part Epoxies contain Resin, and Hardener. It’s important to use equal amounts of each. I use a paper plate and squeeze equal sized drops of each, next to one and other. Give it a moment to make sure that the two liquids (which are different in consistency to each other) are actually equal. Then I mix well with a toothpick, and apply evenly to one of the surfaces.

* I then have 5 minutes to set the second surface, press into place, and remove any excess (with a dampened cloth.

* I usually let this cure under a lamp for 12 hours. Then test the adhesion by trying to remove the two components from one and other. If it doesn’t come apart, I consider it a success. If it does come apart, it usually means that I didn’t etch the surfaces well enough.

Follow up care to the finished piece should include the following considerations. Don’t soak the piece for any length of time. Don’t use harsh chemicals on the piece. Both of these actions can loosen the epoxy.