The layer of Doped Tin Oxide is applied by painting on a fixed ratio solution of Tin and dopant compounds that are thermally decomposed into the Oxides. A layer of Alpha Lead Dioxide is plated next using an alkali Lead salt bath or perhaps a Lead Nitrate bath at a high current density. Next and lastly a Beta layer of Lead Dioxide is plated on top using a Lead Nitrate plating bath. The Alpha layer has better adherent properties that the Beta. It is also smoother and levels better. The Beta is better for exposure to the (Per)Chlorate electrolyte.
The substrate can be a drilled flat sheet of Ti. Mesh should be OK. Another possible alternative is to obtain a quantity of Ti welding rods. They can be got from you local welding supplier as a special order or as a sample. You can then 'weave' the rods together to form a mesh with, say, 0.5 cm square holes, he mesh being the size of the anode you want. You can weave more/less dense as you think fit. The Ti that is horizontal will play no part in taking current to the anode, it all being done by the vertical rods.
The Ti must be surface treated before any coatings are applied by degreasing, etching and (if possible) sandblasting.
Note:
Titanium does not permit films to be prepared at higher temperatures that 500C because the interface undergoes a sort of swelling and the over-layer becomes fragile and scales.
From J. Applied Electrochem 4 (1974) 57

It should be noted that certain Tin and Antimony compounds are toxic. This is especially true if you attempt to make your own compounds from Tin and Antimony metals + acids.

Some useful symbols Element Symbol Atomic weight Titanium Ti 204.4 Tin Sn 118.69 Antimony Sb 121.75 Oxygen O 16 Chlorine Cl 35.45

Some useful formula Name Name Formula Molecular Weight % actual Metal Stannic Chloride Tin(IV) Chloride SnCl4 260.5 45.5% Sn Stannic Chloride Pentahydrate Tin(IV) Chloride SnCl4:5H2O 350.5 33.9% Sn Stannous Chloride Tin(II) Chloride SnCl2 189.59 62.6% Sn Stannous Chloride Dihydrate Tin(II)Chloride SnCl2:2H2O 225.6 52.6% Sn Tin Oxide Tin(IV) Oxide SnO2 150.7 78.76% Sn Antimony Trichloride Antimony(III) Chloride SbCl3 228.1 53.4% Sb Antimony Trioxide Antimony(III) Oxide Sb2O3 291.5 83.5% Sb

The picture below shows an anode made with a drilled 1mm thick Ti substrate. The small depressions on the surface give an indication of the spacing of the holes which were 2.5mm diameter. The anode measures 5 cm by 30 cm. (In relation to the anode) The process that I finally settled upon is a bit laborious but I have had pretty consistent results: I used Ti sheet of about 1mm thickness because that is what I had at the time. A little thicker would probably be better. The first step involves drilling the solid sheet full of small holes. I used a piece of perforated stainless as a drilling guide/pattern. The holes then need to be de-burred or slightly countersunk to get rid of the ragged edges left by the drilling step; I just used a larger diameter drill bit to do this. The substrate should then be sandblasted, (to help the PbO2 adhere to it. The holes are needed for the same reason) degreased with dish-washing soap, thoroughly rinsed in clean water and dried. Next, a semiconducting coat of Sb doped SnO2 was applied by painting on a solution of SnCl4 + SbCl3 in water + Butanol, drying, and then heating to 500 degrees Celsius or so in an oxidizing atmosphere i.e. air. This step was repeated five to ten times to give a suitable coating thickness. Then a thin (about 0.1mm) layer of alpha PbO2 was plated onto the substrate from an alkaline lead tartrate bath. The final coat of beta PbO2 was then plated over top of this from a lead nitrate bath. This layer was about 2mm thick. The anode performed well in a perchlorate cell. The anode above was only used for two batches of perchlorate, starting from NaClO3, which means that it has seen about 200 hours of use at a current of 35-40 A. It still looks pretty much exactly the same. I have made other anodes (using the same process) that I've used in chlorate cells for hundreds of hours with no visible signs of wear. The alpha PbO2 layer was added in order to improve adhesion + uniformity of the final beta PbO2 layer. See US5683567 for a description of a very similar anode. I used to always try and cut corners but after accumulating a whole lot of hazardous waste from failed attempts I've come to realize that it is easier to do it properly, even if it is more work. I chose the SnO2/Sb2O3 system because it is easy to apply and the raw materials are easy to come by and above all cheap. SnO2 also has a higher oxygen overvoltage than PbO2 which supposedly means that any exposed SnO2 will not interfere with the anodic formation of Perchlorate.

Some Patents that are relevant to the Ti substrate LD Anode are:
United States Patent 4040939 Tin + Antimony Oxides on Ti + Lead Dioxide.
United States Patent 5683567 Tin metal layer converted to conductive Tin Oxide Layer + Lead Dioxide.
United States Patent 5545306 Uses a Lead metal layer on top of Ti. This Lead Layer is oxidized to Alpha then plated with Beta in a Lead Nitrate bath.
United States Patent 3627669 SnO2 + Sb2O3 coated electrode for brine electrolysis.

GB Patent 850,380 Massive anode using Ta as the plating substrate. See also JES February 1958 in further reading section for similar scheme.

Making Antimony Trichloride
Making Stannic Chloride

Test for DTO coating

Set up a power supply to give an open circuit voltage of 8 volts and a short circuit current of approximately 40mA per square cm on the anode to be tested. If your supply cannot output enough current then only test a small piece of the end of the anode.
Place the anode into a concentrated solution of Sodium Chloride with the anode well surrounded with cathode approx. one inch from anode.
Connect to power. At the start of the test the voltage across the cell with be approx. 4.8 volts. It will soon rise up about 0.2 volts and remain constant for at least 10 hours. The current shall be 40mA per square cm on the anode surface though out the test period. That's my test, perhaps it is a sensible test, perhaps not. Don't test a device that is going to be coated further. Only test an experimental anode in order to see if you are having success. You will then be able to judge a good coating by experience (color, texture, processing etc).

Solvents tried for making DTO solution precursor were Methanol, Ethanol, IsoProply Alcohol and also a mixture of water and Methanol. It would appear that the solvent used is not critical. Too much water may cause the Antimony Trichloride to Oxidize and precipitate. The patents usually use Butanol (Butyl Alcohol).

Attempts were made to form a DTO coating using SnCl2:2H2O (Tin(ii) Chloride, Stannous Chloride, or Tin Mordant) via pyrolysis. Little success was had, with the DTO coating failing from zero to 30 minutes after being placed in a test cell.
An attempt was make to convert SnCl2:2H2O to SnCl4 in solution. Stannous Chloride was dissolved in Methanol with some HCl. H2O2 was then very slowly added with cooling to increase the oxidation state of the Stannous to Stannic Chloride. When the Antimony Trichloride was added it immediately oxidized. If the Antimony Trichloride was added first it then oxidized when the H2O2 was added. This avenue was not explored further. If it worked it would be useful as all ingredients are easily available. If low Sb content is used it may help.
US Pat 3713884 uses SnCl2 to obtain an ATO coating on glass via a very exacting procedure.
US Pat 4873352 & 4924017 use Tin Oxalates to obtain an ATO coating. Tin Oxalates are not very easy to obtain.
An ATO coating is outlined in, Desalination 115 (1998) 295-302, using a Sol-Gel procedure using SnCl2. It is somewhat complicated.
ATO coatings using the Oxidative-soak procedure is outlined in, JOURNAL OF MATERIALS SCIENCE LETTERS 22, 2003, 1359 – 1361 & 21, 2002, 1241 – 1243. These coating may be suitable for anodes though an attempt to put ATO onto Co Oxide failed as the SnCl2 reacted with the Cobalt Oxide. It would probably be OK on Ti but the coatings are very thin.

Etching Titanium

The grades of Ti that are alloyed with Al (usually 6Al4V, meaning 6% Al & 4% Vanadium) is easy to etch in HCl at room temperature once you start it off by sandpapering the Ti. Grade one is more difficult with the HCl needing to be at a minimum of 85C. Heat the acid first and then put Ti into it. If the acid is heated from room temperature with the Ti in the acid it will not etch. If the Ti is sandpapered before going into acid this will guarantee as start to etching. Grade four is very difficult with hot HCl having no effect. It can be etched using molten NaOH or HF acid ( BOTH DANGEROUS). A product which may be useful for etching Ti is a paste sold in welding shops for cleaning Stainless Steel after it is welded. It contains HF & Nitric Acid. It may be called CromeBrite or some such.

Drilling Titanium

How easy Ti is to drill will depend on grade. Grade one is easy (for small holes anyways) and can be drilled with ordinary steel drill bits, Grade 4 is difficult.
Quote:
CP titanium won't start out very hard, but it will work harden rapidly, faster than 304 or 316 stainless steel. I'd recommend a high speed center drill, especially if you do not have a drill press or milling machine. Carbide will just break up if you try to drill by hand. Drill speed should be 800-1200 rpm for a 1/8" hole, 1/16 would be twice that, 1/4 would be 400-600. Scale accordingly. Use heavy feed and don't hesitate, as each turn of the drill should peel up a chip at least 0.004 thick. Otherwise the material will harden under the drill point.