Lead Dioxide

Lead Dioxide has two crystal structures, (polymorphic), Alpha and Beta. The Beta structure is the structure best able to stand up to the (Per)Chlorate cell conditions and it is what is mainly electro deposited from the acidic Lead Nitrate bath when current densitys of less than 40mA per square cm is used for deposition.
The Alpha structure is not good at standing up to the (Per)Chlorate cell electrolyte. The Alpha form has better adhesion properties and can be used to give a more uniform, smoother coating of LD. The Alpha structure is electro deposited from alkaline baths and is used in US PATENT No. 4,064,035 where it is electro deposited alternatively with Beta to eliminate stress in the Lead Dioxide. The Alpha form has no internal stress, unlike the Beta form. The Alpha can also be deposited from an acid Lead Nitrate bath when a high (70mA per square cm) current density is used, according to RPW.
The diagram shows the structure of Alpha and Beta Lead Dioxide.

[IMAGE OF ALPHA AND BETA LEAD DIOXIDE CRYSTAL STRUCTURE]

Lead Dioxide is highly conductive and is more conductive than most metals. This is because of the deficiency of Oxygen atoms in its crystal lattice which leave charged carriers available in the crystal lattice.
Lead Dioxide is not stoichiometric. It formula could more accurately be described as PbO1.98

The Alpha Lead Dioxide is slightly more conductive that the Beta,the resistivity of Alpha being 10^-3 and Beta being 4 * 10-3 Ohm cm.

Some properties of Lead Dioxide
Molecular weight 239.21
Density 9.37g/cm2
Melting point Decomposes
Decomposition point 290C
Solubility in water Insoluble
Solubility in HCl Soluble
Solubility in nitric acid + H2O2 Soluble

[DIAGRAM OF ALPHA LEAD DIOXIDE DIFFRACTION PATTERN]

Figure 1 is an x-ray diffraction pattern indicating the structure of electro deposited Lead Dioxide. Most of the Lead Dioxide deposited from the Lead Nitrate bath is Beta Lead Dioxide.
[DIAGRAM OF ALPHA AND BETA LEAD DIOXIDE DIFFRACTION PATTERN]

Figure 2 is an x-ray diffraction pattern indicating the structure of Lead Dioxide that was deposited by the soaking and oxidising process (See US PATENT No.4,008,144)

[DIAGRAM OF ALPHA AND BETA LEAD DIOXIDE DIFFRACTION PATTERN]

The above diagram shows the stability of Lead ion in sulphate for a range of pH's.

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