Negative plates, formation

Negative-plate formation. The stages in the formation of negative plates have been determined in terms of the zonal processes as presented in Fig. 3.45. The reactions involved in each of the formation stages are presented schematically in Figs. 3.43 and 3.44, and are summarized in Fig. 3.59. The formation can be divided into the following stages. 

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. 

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 ... 

A standard Lowry-based protein assay has been adjusted to the special conditions encountered with skin [126], Basically, proteins reduce an alkaline solution of Cu(II)-tartrate to Cu(I) in a concentration-dependent manner. Then, the formation of a blue complex between Folin-Ciocalteau reagent (a solution of complex polymeric ions formed from phosphomolybdic and phosphotungstic heteropoly acids) and Cu(I) can be measured spectrophotometrically at 750 nm. A calibration curve can be obtained by dissolving known amounts of stratum corneum in 1 M sodium hydroxide. A piece of tape that has not been in contact with skin is subjected to an identical procedure and serves as negative control. The method was recently adapted to a 96-well plate format, notably reducing analysis times [129],... 

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.

The EV range is obviously affected by the level of selfdischarge. The latter is mainly due to the reduction of Pb02 by lead of the grid and to the formation of anodic oxidation products (e.g., of Sb) which diffuse to the negative plate. Their deposition decreases the hydrogen overpotential and results in corrosion of... 

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. 

In this Chapter, the discussion is confined to the processes that occur during soaking and formation of the positive and negative plates, as well as to the structures of the two types of active mass obtained as a result of the formation procedure. These steps are identified in the dashed-line frame in Fig. 3.1. 

The reaction between the ions of the solution and the initial solid porous phases proceeds in a reaction layer, which is located between the zone of the initial phases and the zone occupied by the reaction products. The reaction layer shifts in space and penetrates the volume of the initial phase zone. Thus, the volume of the zone occupied by the reaction products grows at the expense of the initial phase zone. The direction in which the reaction product zone grows depends on the transport hindrances experienced by the ions on their way from the solution volume to the reaction layer and/or on the transport difficulties met by the ions formed in the reaction layer on their way to the solution volume. On soaking and formation of the positive and negative plates, some zonal processes occur. During soaking, only chemical reactions proceed in the reaction layer (i.e., chemical zonal processes). 

The electrochemical reactions that proceed during formation of negative plates can be represented by the following equations. represents the equilibrium potential... 

Fig. 3.42. Changes in phase compositions of paste and active mass of negative plates during formation [55].

Fig. 3.45. Photographs of cross-section of negative plate during formation (a) prior to formation (b)-(d) during different formation stages, dark regions are Pb- -PbS04 zones (e) completely formed plate [56], Plate thickness is 1.8 mm. This is a vertical cross-section of the plate.

Fig. 3.47. Scanning electron micrograph of crystals within Pb + PbS04 zone during first stage of formation of negative plate [55].

The secondary lead structure of the completely formed plates with or without expander is shown in Fig. 3.57. In NAM without expander, the secondary lead structure covers the skeleton in the form of a smooth layer, whereas the secondary lead structure in the NAM of expander-containing plates comprises individual Pb crystals which are located over the skeleton structure. Hence, organic expanders regulate the processes involved in the formation of both types of structure in the lead active-mass during the formation of negative plates. 

Fig. 3.55. Polarization curves during second hour (first stage — I) and seventh hour (second stage — II) of formation of negative plates with or without expander [66].

Fig. 3.59. Schematic of cross-section through structure of negative plate during the formation stage when Pb- -PbS04 zones have covered the whole plate surface.

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