Positive plates, formation

Positive-plate formation. As discussed earlier (Figs. 3.16 and 3.17), zonal processes occur during formation of the positive plates. In the case of the positive-plate... 

These processes depend strongly on the local conditions at a given site within the plate and lead to the formation of different macrostructures. That is why a more complex algorithm is needed for the current and voltage of formation of the positive plates. Hence, the overall battery (formation tank) algorithm should be based mainly on that required for positive-plate formation. The individual stages in this algorithm will be outlined below. 

Table 4.3. Effect of barium plumbate on positive-plate formation [11] (reproduced by...

Red lead blended with leady oxide in the paste for the production of positive battery plates has two beneficial effects (1) shortens the time for positive plate formation, which is, a rule, longer than the formation time of the negatives and (2) increases the initial capacity of the batteries. 

The reactions that proceed during positive-plate formation have been identified by the accompanying changes in phase and chemical composition of die plates, as well as by the changes in bofli open-circuit and charge potentials of the plates. The phase composition is determined by X-ray diffraction analysis (XRD) and the chemical composition through conventional analytical methods the potentials are measured vs. a Hg Hg2S04 reference electrode. 

Influence ofPb02 Crystal Modifications on the Capacity of Positive Plates. Formation Parameters that Affect the a/fi-Pb02 Proportion... 

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. 

Sulfuric acid is added to the assembled batteries and the plates are formed within the batteries by applying electric voltage. The formation process oxidizes the lead oxide in the positive plates to lead peroxide and reduces the lead oxide in the negative plates to metallic lead. The charging process produces an acid mist that contains small amounts of lead particulate, which is released without emission controls. 

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. 

Fig. 2. Plate format for siRNA library screening. A 384-well daughter plate contains library siRNA as well as wells for positive and negative control siRNA and additional controls as needed for each specific assay. Reference wells are designafed.

At the same time, the bioanalysis of LOR and DCL in rat, rabbit, mouse, and dog plasma was reported by others [64]. In order to get more rehable toxicology data, the bioanalysis in these four preclinical species is done simultaneously instead of on separate days. The sample pretreatment was SPE in a 96-well plate format, using a Tomtec Quadra hquid handling system and an Empore Cig 96-well extraction disk plate. Fom-channel parallel LC was done with four 100x2-mm-lD Cg colunms (5 pm) and a mobile phase of 85% methanol in 25 mmol/1 aqueous AmOAc (adjusted to pH 3.5). The mobile phase was delivered at a flow-rate of 800 pl/min and split into 200 pl/min over each of the four colunms. A multi-injector system was apphed with four injection needles. A post-column spht was applied to deliver 60 pEmin per column to a four-channel multiplexed ESI source (Ch. 5.5.3). The interspray step time was 50 ms. Positive-ion ESI-MS was performed in SRM mode with a dwell time of 50 ms for each of the four transitions, i.e., LOR, DCL, and their [DJ-ILIS, with 20 ms interchannel delay. The total cycle time was thus 1.24 s. The LOQ was 1 ng/ml for both analytes. QC samples showed precision ranging from 1 to 16% and accuracy from -8.44 to 10.5%. The interspray crosstalk was less than 0.08% at concentrations as high as 1000 ng/ml. 

High-throughput quantitation of the soy isoflavones genistein, daidzein, and equol in blood from human and animal studies was developed by Twaddle et al. [74] using positive-ion LC-ESI-MS in SIM or SRM mode. Samples were processed in 96-well plate format protein precipitation, enzymatic deconjugation by H. pomatia... 

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. 

The electrochemical reactions that proceed during the formation of positive plates can be represented by the following equations. Eh represents the equilibrium potential for the reaction at 298.15 K. 

Zonal processes are slow processes. They are responsible for the long duration of plate formation. Hence, it is important to find methods to by-pass the zonal processes. In order to accelerate the formation of positive plates, some conductive additives have been added to the positive pastes [28]. These additives increase the conductivity of the cured paste and formation proceeds almost uniformly throughout the whole plate volume as the electric current flows along the conductive additive network. The additives should be chemically stable in H2SO4 solution. Data have been reported about successful attempts to reduce the duration of the formation procedure to 8 h. 

Glass fibres coated with Sn02 have been developed and used in lead-acid battery positive plates with the aim to improve the process of plate formation and the performance of the plate. 

In positive-plate manufacture, 3BS and 4BS phases are never used alone. They are always in combination with PbO, which improves the connection between the basic lead sulfate crystals and hence facilitates the formation of a mechanically strong porous mass or skeleton. The ratio between the basic lead sulfates and the PbO in the pastes exerts an influence on the initial capacity and the cycle-life performance of the battery, namely the higher the PbO content in the paste, the lower is the initial capacity of the positive plates (Fig. 3.33). 

C and 3BS crystals are converted into 4BS crystals of irregular shape (Fig. 3.38), with good connection between themselves and with the current-collector. Formation of such pastes takes more than 48 h. This technology is used for the production of all types of positive plates. If the time of steam treatment is extended to 8-10 h and the temperature of the plate is higher than 90°C, the resulting 4BS crystals are very thick and the formation of such pastes requires several days. When this method is applied to the manufacture of positive plates for stationary batteries, service lives of over 15 years are achieved. 

Selection of a particular method for the production of 4BS pastes depends on the type of battery application, the time of plate formation and the planned service life of the battery. 4BS pastes are gaining an ever-increasing share in the production of positive plates for lead-acid batteries. 

It has been established that on cycling of tubular positive plates with die-cut strap grids (SGTP) or of positive plates with expanded grids with flat ribs, a rapid capacity loss is observed (the PCL-1 effect, see Section 2.3, Chapter 2 and Chapter 9) [54]. The reason for this capacity loss is the formation of groups of PbS04 crystals in the layer of the PAM that contacts the current-collector (Fig. 3.39). These PbS04... 

Fig. 3.4L Capacity curves for strap grid tubular positive plates (SGTP) (a) cast strap grids with smooth surface (b) die-cut strap grids with smooth surface (PCL-1 effect) (c) die-cut strap grids with rough surface obtained after reverse-current treatment prior to formation proper [54].

Fig. 3.58. Schematic of cross-section through structure of positive plate during formation.

The processes that occur during each of these stages should be taken into account when establishing the current (voltage) algorithm for formation of positive plates. The specific current and voltage values for the different formation stages are discussed below in Section 3.5.3. 

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