Barton pot

Production of leady oxide. Pure lead ingots are subjected simultaneously to abrasion and surface oxidation in a ball mill, or are melted in a Barton pot and oxidized in an air atmosphere [2]. A 70-85% oxidized lead powder (called leady oxide ) is obtained with a characteristic grain size-distribution. The same leady oxide is used for the production of both positive and negative plates. 

It has been reported that silver decreases the rate of oxidation of lead, particularly in the Barton-pot process [25], by up to 10%. In the active materials, silver increases oxygen evolution (at the positive plate) more than it does to hydrogen evolution (at the negative plate). The promotion of gassing by silver, however, does not appear to be as serious a problem as was once thought, at least for materials with silver contents up to 0.01 wt.% [25]. 

Both the methods (Barton pot and ball-mill) produced partially oxidised lead oxide containing between 20% and 40% free lead. Hence, this oxide was called leady oxide . The production time of this oxide was reduced substantially, which gave a strong impetus to the development of the lead—acid battery industry after 1926. Nowadays, these two processes are still the dominating methods for leady oxide production. 

Leady oxide manufacture. Pure lead ingots are subjected to simultaneous grinding and surface oxidation (ball-mill method) or are melted and oxidized in humidified air (Barton pot method). A 60—80% oxidized lead powder (leady oxide) is obtained with a corresponding particle size distribution. 

Barton Pot Method of Leady Oxide Production with Moderate Temperature Oxidation of Lead... 

The influence of some of the Barton pot process parameters on the structure and properties of the obtained leady oxide can be summarised as follows ... 

About 75% of the total leady oxide production is realised by the Barton pot method. To bring the Barton pot process into operation at the desired reaction temperatures requires some 30 min each day. The required power for oxide manufacture is approximately 65 kW per ton of leady oxide. 

Figure 5.5a and b presents scanning electron microscopic (SEM) images of Barton pot oxide particles and Fig. 5.5c and d shows micrographs of these particles mounted in resin and polished in cross-section [13]. Particles of two sizes can be identified in the pictures fine lead oxide particles and coarse agglomerates of roughly spherical shape. When these particles are mounted in resin and polished, the unoxidized lead becomes visible. These are the large-sized particles obtained by solidification of the lead droplets and by surface oxidation of flie lead particles. The pure lead oxide particles are small and fairly equal in size. 

The energy consumption for operation of the whole ball mill system is about 200 kW per ton of leady oxide. This is about three times the energy consumed by a Barton pot production unit of the same capacity [16]. 

Comparison of Barton Pot and ball mill Leady Oxides... 

After the above brief description of the two methods of leady oxide production the question arises logically as to which of the two processes is better. Table 5.1 compares the characteristics of the leady oxides produced by the Barton pot and ball mill processes [17]. 

Table 5.1 Comparison of Barton pot and ball mill oxides [17]. 

Investment costs. Barton pot systems are significantly cheaper than the ball mill equipment, which makes them strong favourites in this respect, too. The lower price, the higher productivity and the lower operating and maintenance costs of Barton reactors have lead to a boom in their application by numerous battery companies worldwide after the 1960s. 

Reactivity of ball mill and barton pot leady oxides [21]. 

The acid absorption of the leady oxide is determined by a method similar to that applied for determining the water absorption, but in this case sulfuric acid with 1.10 relative density is used instead of water. Depending on the method of leady oxide production and on the equipment used, the acid absorption value varies. Figure 5.10 presents the acid absorption (in mg H2SO4 per g oxide) as a function of the BET surface area for leady oxides produced by the Barton pot and ball mill methods [21]. 

The specific surface of leady oxide is determined by both particle size and shape. The leady oxide powder produced by the Barton pot process consists of spherical particles. So, in order to... 

Most appropriate for determining the specific surface of powder materials of the above types is the adsorption method, or BET process. The average specific surface of leady oxide measured by BET is 0.7—1.4 m g for the Barton type and 2.4—2.8 m g for the ball mill type, respectively. It has been established that the BET surface area depends on the content of p-PbO in the leady oxide [21]. A maximum area is obtained at 15 wt% P-PbO level. It could be expected that the latter leady oxide would have the highest reactivity as well. The percent content of the P-PbO crystal modification can be controlled by varying the temperature of the Barton pot. Process temperature of about 450 °C yields the leady oxide with approximately 15 wt% P-PbO. 

These methods differ mainly by the technique used for packing (pressing) the powder into a vessel of a given volume and weight. The typical packed density of Barton pot oxide is about... 

Logarithmic plots of the particle size distribution by diameter for ball mill and Barton pot leady oxides are presented in Fig. 5.12 [22]. The two curves differ significantly, indicating considerably higher percentage of particles with diameters less than 1 pm in the ball mill oxide as compared to the Barton pot oxide. This particle size distribution is responsible for the higher reactivity and the acid absorption of ball mill leady oxide, as well as for its lower apparent density. 

Particle size distribution curves for ball mill and Barton pot leady oxides. Logarithmic plots [22]. 

Table 5.7 Typical properties and composition of the effluent gas stream from lead oxide ball mill and Barton pot processes [ 1 ].

Lead oxide is the main component of the active material for both the positive and negative electrodes. Lead oxide is made by oxidizing lead by using either the Barton pot process or the Ball mill process. 

The Barton pot process (also called the Barton-like process) is a process that melts lead ingots and feeds them into a vessel or pot. The molten lead is rapidly stirred and atomized into very small droplets via a rotating paddle in proximity to the bottom of the vessel. The droplets of molten lead are then oxidized by oxygen in the air to produce an oxide coating around the droplet. Figure 7.7 shows a flowchart for the Barton pot process. 

The lead oxidation process is exothermic and the generated heat is essential for sustaining a continuous reaction as more lead is introduced. The process temperature is critical for determining the degree of oxidation and crystal morphology of the lead oxide. The Barton pot process typically produces a product containing lead oxide with 15% to 30% free lead, which exists as the core of the lead oxide spherically shaped particles. Figure 7.8 shows a Barton pot. 

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