Plate cured positive

Tank formation means that the cured positive and negative raw plates are inserted alternately in special tanks filled with fairly dilute sulfuric acid (generally in the range 1.1 to 1.15gcm 3) and positive and negative plates are connected, a number of each, in parallel with a rectifier. The formation process means that the active material of the plates is electrochemically transformed into the final stage, namely ... 

Curing is the process of exposing plates pasted positive and negative to a regime of (a) controlled time (minimum 32h), (b) temperature (30-35°C), and (c) relative humidity (>90%). This process converts the free lead into lead oxide, using oxygen from the surrounding air. The plates are allowed to cure for a minimum of 32 h. Care is also taken to ensure that the maximum temperature of the plate does not exceed 60°C. The cured plates are then parted. 

Fig. 3.5. Changes in chemical composition of cured positive plates during soaking in 1.05, 1.15, or 1.25 rel. dens. H2SO4 [6].

Fig. 9.6 Profile of sound velocity V as a function of position d inside an epoxy plate cured and post-cured in a Silgel cuvette. The left and right sides of the graph correspond to the top and bottom of the horizontal cuvette, respectively.

Fig. 9.10 Sound velocity profiles v(d) for the RT-cured and for the post-cured state of two independently prepared EP plates on polished Cu alloy (open squares and triangles) as well as for an EP plate cured on polished Al alloy at ambient temperature (black squares). The metal is positioned at d = 0 mm.

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... 

Positive plates need much more time to form than negatives. The reason for this is the dielectric behaviour of the cured positive paste. Oxidation of the bivalent lead compounds in the paste and formation of the Pb02 positive active mass passes through a number of chemical reactions, some of which proceed at a low rate, which retards the technological process of formation of the positive plate. In an attempt to accelerate the formation process, additives to the positive paste have been looked for, which are characterised by electro-conductive properties and stability in sulfuric acid. These additives create an electro-conductive network in the paste and the process of oxidation proceeds simultaneously within a large paste volume, thus accelerating plate formation. 

Cured positive plates are treated with ozone gas in a chamber, as a result of which PbO is oxidized to Pb02, which forms a thin coating on the surface of unformed plates. During formation, the lead dioxide layers on the two plate surfaces grow simultaneously towards the plate s interior. Consequently, the formation time and the energy input are reduced substantially. However, this method is too expensive and requires special corrosion-resistant chambers. 

For progress control of the processes of plate curing and drying, a plate should be taken from the most unfavourable position in the stack and from the center of the pallet, where air and... 

Table 8.3 illustrates the influence of curing conditions on the physico-chemical parameters and the capacity of positive plates cured by three different air curing methods [30]. 

The above results provide an evidence of the influence of positive plate curing schedule on battery performance characteristics. 

The tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

The production of tubular positive plates is in principle similar to that of pasted plates. A number of manufacturers use the same gray oxide as the basic filling substance. Sometimes the share or red lead or minium (Pb304) is increased above 25 or even to 100wt.%. The latter is more economic when the manufacturer runs his own minium plant then the expense of the chemical oxidation of lead oxide (PbO) to minium (Pb304) may be compensated by reduced formation cost. Furthermore, curing is not required, because of the high oxidation state, and the battery starts with full capacity when formed. 

When a sample was placed in the rheometer at the rest position (i.e., no flow), we observed that the plates were pulled together which, we believe, is attributable to the shrinkage of the material during cure. The normal force (F) measured was used to calculate using the expression 11 " 22 ... 

Positive and negative active-mass formation. The cured pastes of both positive and negative plates comprise identical mixtures of bivalent lead compounds (3BS, 4BS, PbO), which cannot create electromotive forces when the pasted plates are assembled into cells. The purpose of the formation step is to convert the cured pastes into electrochemically active porous materials — Pb02 in the positive plates and Pb in the negative plates — which are connected mechanically and electrically to the grids. The process of formation can be conducted via two basic schemes, as shown in Fig. 3.1. 

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