Leady oxide pastes prepared from

Figure 6.17c shows that, when a mixture of 50% tet-PbO plus 50% orthorhomb-PbO is used, 3BS forms within the first couple of minutes already, while formation of 4BS starts after the 5th min of paste stirring. After 20 min, the content of 4BS is as high as 65% against 20% in the paste prepared from tet-PbO alone. Our investigations have proved that the maximum rate of 4BS formation is achieved when the leady oxide mix contains 75 to 80% tet-PbO. The recommended proportion of the two PbO modifications in the initial lead powder for preparation of 4BS pastes is 20% orthorhomb-PbO + 80% tet-PbO. 

The basic components of the paste are crystal phases of 3BS or 4BS, small amounts of orthorhomb-PbO, tet-PbO and Pb. These are detected by X-ray diffraction methods. If a paste is prepared from crystal phases of 3BS and tet-PbO in the same proportion as in the paste prepared from leady oxide and H2SO4, and then grids are pasted with this paste and set to curing and formation, the obtained PAM is mechanically unstable and difficult to form, and hence the plates have low capacity. Valeriote has found that one of the reasons for the low energetic characteristics of positive plates is the lack of amorphous components in the paste [17]. The content of amorphous phases should amount to 15—10%. Such amorphous components in the paste are most often hydroxides. Some of the amorphous hydroxides are obtained as a result of oxidation of Pb in the leady oxide during paste preparation and plate curing. And the content... 

Pastes Prepared From Leady Oxide and Pbs04... 

It has been established from the battery practice that, in order to obtain pastes with densities from 3.90 to 4.40 g cm, the total volume of H2SO4 solution and water should be between 180 and 216 mL kg LO. Let us assume the upper limit value (216 mL kg LO) as the base volume of H2SO4 + H2O for paste preparation (denoted as Vq). The following method for 4BS preparation from semi-suspension has been developed [34,35]. First, leady oxide is loaded into the paste mixer. Then the total amount of H2SO4 solution and water, pre-heated to a temperature higher than 70 °C, is added under stirring for a few minutes. The heat released by the chemical reaction between PbO and H2SO4 causes further temperature rise to 88—92 °C and the semi-suspension is stirred at this temperature for about 15 min. Then, vacuum is applied as a result of which the paste density increases and the temperature drops down to 30 °C. Water is removed from the semi-suspension in an amount as to obtain a paste of the desired density. 

Paste preparation starts with the introduction of fibres or (fibres + 4BS nucleants) in the paste mixer. Then water is added and the suspension is mixed for 1 min. The next step is to add the leady oxide (LO) and mix for another 3—4 min until a homogenous mass is obtained. Then the sulphuric acid solution is added slowly, for about 10—12 min. The temperature is monitored continuously and kept below 50 °C. If needed, the cooling system of the paste mixer is activated. After adding the whole amount of H2SO4 solution, the paste is mixed for 15 more minutes to allow the 3BS crystals to grow. Finally, samples are taken from the paste to measure its density and consistency. If these parameters meet the technological requirements, the paste... 

G. Liptay and Sors [7] mixed a given amount of leady oxide with increasing amounts of H2SO4. They determined continuously the phase composition of the obtained pastes until a stoichiometric ratio of H2S04/Pb0 = 1 was reached. The phase composition of the paste was determined immediately after its preparation and 24 h later. Based on the data presented in [7], the dependence of phase composition of the paste as a function of the increasing H2SO4/ PbO ratio (from 3 to 100%) is plotted (Fig. 9.22). 

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