Cadmium system

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

Because the nickel—iron cell system has a low cell voltage and high cost compared to those of the lead—acid battery, lead—acid became the dorninant automotive and industrial battery system except for heavy-duty appHcations. Renewed interest in the nickel—iron and nickel—cadmium systems, for electric vehicles started in the mid-1980s using other cell geometries. 

Figure 8. Ideal discharge characteristic, and discharge characteristic of a nickel/cadmium system.

The nominal capacity of every system is defined by a specific value of C for example, for the nickel-cadmium system, it is Cj20. By discharging with a higher current, the final capacity obtainable becomes lower. 

Figure 9. Dependence of the cell voltage on the charge capacity for three different currents in the nickel/cadmium system.

Although one of the most common storage batteries is called the nickel/cadmium system ( NiCad ), correctly written (-)Cd/KOH/NiO(OH)(+), cadmium is not usually applied as a metal to form a battery anode. The same can be said with regard to the silver/cadmium [(-) Cd / KOH / AgO (+)] and the MerCad battery [(-)Cd/KOH/HgO(+)]. The metallic negative in these cases may be formed starting with cadmium hydroxide, incorporated in the pore system of a sintered nickel plate or pressed upon a nickel-plated steel current collector (pocket plates), which is subsequently converted to cadmium metal by electrochemical reduction inside the cell (type AB2C2). This operation is done by the customers when they start the application of these (storage)... 

The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, as it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems, while in contrast to Pb and Cd, magnesium is inexpensive, environmentally friendly, and safe to handle. However, the development of Mg-ion batteries has so far been limited by the kinetics of Mg " " diffusion and the lack of suitable electrolytes. Actually, in spite of an expected general similarity between the processes of Li and Mg ion insertion into inorganic host materials, most of the compounds that exhibit fast and reversible Li ion insertion perform very poorly in Mg " ions. Hence, there... 

The iron-nickel oxide alkaline battery system has many features in common with the nickel-cadmium system discussed above. It was first developed by Edison in the USA at the turn of the century and was patented in the same year as Jungner s first nickel-cadmium US patent, 1901. Iron can be regarded as a favourable active battery material because of its low cost, high theoretical specific capacity (twice that of cadmium) and non-toxic, pollution-free characteristics. However, because its reduction potential is below that of hydrogen, and since hydrogen overvoltage is low on iron, charge retention is poor and efficiency is low. 

Batteries based on the iron-nickel oxide system are now being developed for electric vehicle applications. These use fibre-plaque electrodes, as described above for the nickel-cadmium system, and incorporate electrolyte circulation systems to permit removal of gases evolved during charge... 

Replacing zinc with cadmium reduces the OCV by approximately 0.4 V, but increases the cycle life of the system considerably. This cell is very similar to the nickel-cadmium system, but has an energy density higher by about a third. The cost of the system has restricted its application to small button cells. 

Two 67Zn (natural abundance = 4.12% / = f) n.m.r. studies have been reported.9,10 The chemical shift of 67Zn (4.81 MHz at 1.807 Tesla) in aqueous zinc chloride, bromide, and iodide solutions was found to be strongly concentration dependent, while no such dependence was noted in solutions of the perchlorate, nitrate, or sulphate. This behaviour resembles that found for analogous cadmium systems, and is attributed to the formation of mono- and poly-halogeno- complexes even at low salt concentrations. In addition, the zinc halide solutions show an anomalous shift to higher frequencies for their solutions in D20, compared with those in H20. The perchlorate, nitrate and sulphate show no solvent isotope effect. 

The technique requires the measurement of some property which is proportional to a product concentration—e.g., pH, color, or electrical conductivity. In the cerium-cadmium system the cadmium vapor pressure is one such measurable property. 

Much of our work has been on the cerium-cadmium system. In Figure 1 the width of each CeCd 6 and CeCd 4i5 line above room temperature indicates the true stable range of the compound (including microphases). 

Figure 1. Collected phase information for cerium-cadmium system...

Collected Phase Information for Cerium-Cadmium Alloys. A partial phase diagram for the cerium-cadmium system is presented in Figure 1. The room temperature results are based on x-ray studies by Iandelli and Ferro (9), who studied slowly cooled samples. However, their CeCd6 is shown as a dashed line because nuclear magnetic resonance studies by Jackson and the authors (10) have shown that the compound is unstable at room temperature and can decompose to metallic cadmium and CeCd 4i5. Because of probable kinetic barriers, the absence of compounds intermediate between cadmium and CeCd 6 does not indicate that these intermediates are unstable at room temperature. 

Since we do not have cadmium vapor pressure across the whole cerium-cadmium system, some standard state other than the pure metal would have to be used for cerium. 

The silver-cadmium system has been investigated in considerable detail and the results of these studies are summarized in the equilibrium diagram of fig. 13.10, which refers to room temperature. It will... 

Fig. 13.10. The equilibrium diagram of the silver-cadmium system at room temperature.

Fig. 13.11. Clinographic projections of the unit cells of the structures of the phases in the silver-cadmium system.

The simpler of these two structures is the caesium chloride arrangement, found in the phases LiHg, LiTl, MgTl, CaTl and SrTl. This is, of course, also the structure of the / phase in the silver-cadmium system and in other electron compounds (fig. 13.11), and for this reason the systems just mentioned are sometimes quoted as exceptions to Hume-Rothery s rule. Apart from this geometrical resemblance, however, these systems have little in common with the electron compounds, and it seems preferable to regard the Hume-Rothery rule as applicable only to alloys of the T2-B1 type. 

To meet the difficulties presented by metal systems, various wider definitions of chemical combination in terms of crystal structure have been proposed. For example, it has been suggested that we should regard an ideal chemical compound as one in which structurally equivalent positions are occupied by chemically identical atoms, and an ideal solid solution as a structure in which all atoms are structurally equivalent. It is clear that such a definition of chemical combination embraces all the generally accepted compounds, but it is not without objection when applied to metal systems. Thus, to take only one example, the ft phase in the silver-cadmium system already discussed has, in its ordered state, the simple caesium chloride structure and must therefore... 

Figure 6.11 Theoretical energy density of various Li/intercalation couples in comparison with the lead-acid and nickel-cadmium systems.

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