Lead Dioxide Plating baths

There are two types of Lead Dioxide, Alpha and Beta. The Beta is the type needed at the surface of the anode as it withstands the Chlorate and Perchlorate cell conditions better than Alpha. Alpha (according to patents) is good at relieving stress in the anode and has better adherence properties to most substrates. For example, it is best to use Alpha when plating onto Tin/Sb Oxide coat according to US Pat. 5,683,567, as it's crystal structure is more compatible with theses substances that Beta . Alpha cannot be plated onto Graphite. You must start with a Beta and end with a Beta.
Beta (mainly) Lead Dioxide is deposited from acidic Lead Nitrate baths (if current density is below 40mA per square cm) and Fluoroboric baths. Theses baths are considered to be the best for depositing Beta Lead Dioxide.
The Lead Nitrate bath mainly plates Beta Lead Dioxide (the type we want on the outside of the anode). The amount of Beta or Alpha that is plated can be controlled by current density on the anode according to one source I have communicated with. High current density (70mA per square cm) giving the Alpha, 40mA (or below) per square cm giving the Beta. Alpha gives better adhesion to Ti substrates ( and possible others excluding graphite). Some articles I have read have used a high current density at the start of plating to create a large amount of PbO2 nucleation sights on the substrate to improve adhesion. The sights were probably Alpha PbO2. The different crystal structure of Alpha makes it more adherent to Ti and doped Tin Oxide and most substrates. It also gives a more uniform coating. The first coating of Alpha is very thin in some of the patents, at 1 to 10 micron.
Alpha Lead Dioxide is deposited from alkali baths.
The size of bath in relation to the size of the anode (amount of Lead Dioxide to be deposited) being made should be as big as possible. US 4064035 uses a 5 liter (Nitrate) bath for an anode that measures 50 by 20 by 0.3mm piece of Ti. They also used a continuous system where Lead ion was constantly supplied to the bath to replenish Lead ion and neutralize Nitric acid formed.
Since Alpha layers are usually very thin (small amount of Lead Dioxide being deposited), large baths may not be needed.
The Cathode area next to the Anode should be of similar surface area as to the Anode and should surround it. Too big or too small a Cathode may cause problems.

Two Lead Nitrate baths

Lead Nitrate at least 200g/liter (up to 800 is used)
Temperature 50 to 70 C.
Current density 10 to 40mA/cm squared (for Beta)
(from US Pat. 5,683,567)

800 g/liter of Lead Nitrate having suspended therein 1% a Tantalum Oxide powder having particle sizes of from 0.1 to 10 micro m
Temperature of 65 C.
Current density of 40 mA/cm squared for 4 hours, whereby a Beta Lead Dioxide layer having dispersed therein the Tantalum Oxide powder. (Reduces stress)
(from US Pat. 5,545,306)

At the very minimum the Lead Nitrate concentration must be kept above 200g/liter during the plating process. A tank that is big enough for the plating job should be employed. Estimate the amount of Lead Dioxide that you intend to plate at one sitting and employ a volume of plating solution that will not be depleted much in Lead ion as the plating progresses. The bigger the tank the better. The Lead Ion will vary less and the pH will vary less. This is desirable. If you are adding Lead ion (Carbonate, Hydroxide, Litharge) using two tanks then then perhaps smaller tanks can be used.
Keep temperature constant.

See US Pat. No. 4,236,978 for Fluroboric bath. The Fluoboric bath is claimed to be as good as the Nitrate bath.

There are no figures available for the minimum Lead Ion concentration in the Alkali baths below. Keep the bath as big as you pocket can afford (within reason). Alkali baths suitable for deposition of Alpha Lead Dioxide are
Sodium (and K) Plumbate bath
Lead Tartrate bath
Lead Acetate bath

Four Sodium Plumbate baths (Alpha)

It should be noted that attempts to use these Plumbate baths resulted in no coating of Lead Dioxide. The reason is unknown. Perhaps the Plumbate bath is very sensitive to impurities? Since high grade chemicals were not used they may have included enough imputities to stop plating from proceeding?

The Sodium Plumbate bath is made with Lead ion and Sodium Hydroxide

80 Grams per liter NaOH
30 Grams per liter PbO
Room temperature at 0.3 ampere per square inch (46.5 milliamperes/cm squared)
(from US Pat. 4,040,939)

Litharge (30 to 40 g/liter) [dissolve until saturation] in an aqueous solution of about 20% sodium hydroxide
20 to 50.degree. C. and a current density of from 0.1 to 10 A/dm²
(from US Pat. 5,683,567)

80 g of lead hydroxide in 2 liters of an aqueous 5N caustic soda solution.
Approx. current density 25mA/cm squared
Temperature 50C
Substrate was 5 by 2 by 0.3cm
Cathodes were 2 pieces of SS of similar size to anode
Bath size was 2 liter with 0.2mm Alpha deposited after 3 hours. (From US Pat. 4,064,035)

Excess amount of lead oxide in 5 liters of an aqueous 4N caustic soda.
Current density 25 mA/cm squared.
Temperature at 40 C
Substrate was 5 by 15cm
Cathode was two Cu sheets of similar size to anode
Deposition for 2 hours give 0.2mm Alpha. (From US Pat. 4,064,035)

Baths from JES Feb. 1958

Available in further reading section BTW

Alkaline Lead Tartrate (Alpha Lead Dioxide bath)
100g Potassium Sodium Tartrate, KNaC4H4 O6.4H2O 50g Sodium Hydroxide, NaOH 96g Lead Oxide, PbO Dissolve in the order listed in distilled water to make 2 liters of solution. Heat to 60C to complete solution of Lead Oxide. Cool and filter through sintered glass. Bath pH is about 13.
Lead Perchlorate (Beta Lead Dioxide bath)
108ml of 60% Perchloric acid (100g HCl04) 167ml distilled water 111.0g Lead Oxide, PbO Dissolve the Lead Oxide in the diluted Perchloric acid. Make up to 2 liters with distilled water. Heat to boiling for 2-3 minutes to dissolve any white precipitate. Cool and use. Bath pH is about 5. See GB 850,380 (below) for discussion regarding this bath.
Lead Nitrate (Beta Lead Dioxide)
269ml of 69.9% nitric acid (266.5g HNO3) 1000ml distilled water 472g Lead Oxide, PbO Add the Lead Oxide slowly to the diluted Nitric acid with stirring. Dilute to 2 liters and heat to 75C with stirring. Cool and filter through sintered glass. To this bath add: 0.75g per liter Copper Nitrate, Cu(NO3)2 .3H2O 0.75g per liter Igepal CO-880 (surface active agent) The bath pH is about 3.5

Lead Perchlorate bath (Alpha)

See US 2,872,405 for more on this bath.

Lead Tartrate bath (Alpha)

This bath is from GB 850,380
There is a discussion regarding the Tartarate bath, Lead Nitrate bath and Lead Perchlorate baths in this patent.

A Lead Tartrate bath is prepared by dissolving in one litre of distilled water, at 40 to 60C, 50 grams of Sodium Potassium Tartrate (NaKC4H4O6.4H20), 25 grams of Sodium Hydroxide (NaOH) and 48 grams of Lead Oxide (PbO). (dissolve in that order). The bath has a pH of 13.5.

A substantially oxide free Tantalum sheet 1" x 5" x 0.0125" thick is immersed in the bath and is connected as anode to a suitable source of current.
A Carbon rod is also immersed in the bath and connected as cathode to the same current source.
The bath is heated to 70C. and the circuit is completed with an anode current density of 0.7 amperes per square foot.
A glossy, dark grey deposit of Lead Dioxide forms on the Tantalum sheet.

From US 2846378. As above, current density was 1 amp per square foot (1.5mA per square cm), cell temperature was 64 to 68C. One half mil (0.5 mil) was deposited in 2 hours. A Nickle sheet was being used to make a massive anode.

See US 2,872,405 for more on the Tartrate bath.

Lead Acetate bath (Alpha)

This bath is from JAE 18 (1988) P 314
KOH 4M solution saturated with Lead Acetate and filtered.
Temperature 20 to 30C.
Mild stirring was essential.
Current density initially 50mA per cm squared for two minutes then decreased to 10mA until required thickness obtained.
Cathode was mild steel of about 20 times the surface area of anode.
Since the solubility of Lead Acetate in KOH (4M) is only about 40g/l a fairly large quantity of electrolyte (one liter per 8cm squared of electrode) was required to deposit a 1.5mm thick coating to minimize the depletion of Plumbite ion during the coating operation.
It was noted in the article that the current efficiency for the deposition of Alpha(60%) is lower than Beta (95%).
Note: NaOH could probably be used instead of KOH.
This path deposits Alpha Lead Dioxide

An alternative method of obtaining a layer of Alpha Lead Dioxide is discussed in US 5545306
In another method of forming the Alpha Lead Dioxide layer, by electrolyzing using the Sulfuric acid bath for forming Lead Sulfate described above as an electrolyte and using the core material having formed thereon and the Lead plating layer as the anode at a current density of about from 1 to 10 A/dm^2, the surface portion of the foregoing Lead plating layer is oxidized to form the Alpha Lead Dioxide layer. Usually, Beta Lead Dioxide is formed in the acid, however, almost complete Alpha Lead Dioxide is obtained by this method although the reason has not yet been clarified.

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