Mercury-cadmium cells

Figure 8.2 Operating characteristics tbr 0.6 A h mercury-cadmium cell at various temperatures. Hourly discharge rate is 2 % of capacity, i.e. C/50 (Courtesy of Cromplort-Parkinson)...

Operating characteristics for a 0.6 A h mercury-cadmium cell are shown in Figure 55.5. 

Varta supply 0.9V, 3200 and 2000mAh mercury-cadmium cells (types 4910 and 4911 respectively). 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

Basol BB, Tseng ES (1986) Mercury cadmium telluiide solar cell with 10.6% efficiency. Appl Phys Lett 48 946-948... 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Cadmium (Cd) anode cells are at present manufactured based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples. Thus wastewater streams from cadmium-based battery industries carry toxic metals cadmium, nickel, silver, and mercury, of which Cd is regarded the most hazardous. It is estimated that globally, manufacturing activities add about 3-10 times more Cd to the atmosphere than from natural resources such as forest fire and volcanic emissions. As a matter of fact, some studies have shown that NiCd batteries contribute almost 80% of cadmium to the environment,4,23 while the atmosphere is contaminated when cadmium is smelted and released as vapor into the atmosphere4 Consequently, terrestrial, aquatic, and atmospheric environments become contaminated with cadmium and remain reservoirs for human cadmium poisoning. 

FTIR Microspectroscopy.3 A microscope accessory coupled to a liquid-nitrogen-cooled mercury-cadmium-telluride (MCT) detector can be used to obtain an IR spectrum. This is possible in both the transmission and reflectance modes. Several beads are spread on an IR-transparent window (NaCl, KBr, diamond) and possibly flattened via a hand-press or a compression cell. The IR beam is focused on a single bead using the view mode of the microscope. The blank area surrounding the bead is isolated using an adjustable aperture, and a spectrum is recorded using 32 scans (<1 min). A nearby blank area of the same size on the IR transparent window is recorded as the background. 

Marcott, C., Reeder, R. C., Paschalis, E. P., Talakis, D. N., Boskey, A. L. and Mendelsohn, R. (1998) Infrared microspectroscopic imaging of biomineralized tissues using a mercury-cadmium-telluride focal-plane array detector. Cell. Mol. Biol. 44, 109-115. 

It is well known that a large number of chemical substances, including toxic metals and metalloids such as arsenic, cadmium, lead, and mercury, cause cell injury in the kidney. With metal-induced neurotoxicity, factors such as metal-binding proteins, inclusion bodies, and cell-specific receptor-like proteins seem to influence renal injury in animals and humans. It is of interest to note that certain renal cell populations become the targets for metal toxicity, while others do not. In fact, the target cell populations handle the organic and common inorganic nephrotoxicants differently. ... 

The properties of the dual-film electrode were characterized by in situ Fourier transform infrared (FTIR) reflection absorption spectroscopy [3]. The FTIR spectrometer used was a Shimadzu FTIR-8100M equipped with a wide-band mercury cadmium teluride (MCT) detector cooled with liquid nitrogen. In situ FTIR measurements were carried out in a spectroelectro-chemical cell in which the dual-film electrode was pushed against an IR transparent silicon window to form a thin layer of solution. A total of 100 interferometric scans was accumulated with the electrode polarized at a given potential. The potential was then shifted to the cathodic side, and a new spectrum with the same number of scans was assembled. The reference electrode used in this experiment was an Ag I AgCl I saturated KCl electrode. The IR spectra are represented as AR/R in the normalized form, where AR=R-R(E ), and R and R(E ) are the reflected intensity measured at a desired potential and a base potential, respectively. 

The infrared-electrochemical cell, originally designed by Bewick and his coworkers, was partly modified to introduce an electrode from the upper part of the cell. The front side of the cell is attached with a CaFg optical window, and the backside with a glass syringe which pushes the electrode against the window. The Fourier transform infrared measurements were conducted at 0 °C for Cu electrodes and at ambient temperature for Ni and Fe electrodes by JIR-6000 (Nihon Densi, Co. Ltd.) externally equipped with an MCT (mercury-cadmium-telluride) detector. Infrared spectra were acquired by the subtraction of two spectra reflected from the electrode at different potentials (SNIFTIRS). The other details were described previously. [9]... 

Specific legislation relating to batteries includes the Toxic and Dangerous Waste Directive which gives priority consideration to mercury, cadmium and lead. This directive is being replaced by a Directive on Hazardous Waste which specifically includes batteries and other electrical cells. Additional metals to be covered include nickel, cobalt, silver, zinc and lithium. Thus, all commonly used batteries will be covered by this directive. 

Individual countries within the European Community handle the battery waste problem differently. For example, in Switzerland all used consumer batteries are considered hazardous waste and must be collected separately from ordinary household waste. Batteries must be recycled or stored in warehouses, not landfilled. A tax is collected on all new battery purchases to help defray the cost of recycling. In Italy, spent dry batteries are considered as hazardous waste and must be collected separately. In Sweden (10), the environmental issues relatii to waste batteries are addressed in the Control of Chemicals Bill and in the Decree on Environmentally Hazardous Batteries. All used batteries containing cadmium or mercury are collected separately under government control. The cadmium is then recycled. Regulations are in place for the manufacture of nickel/cadmium cells, limiting the exposure of workers and the emission of toxic materials. 

The development of new products with less or without dangerous substances must be a future goal of priority to avoid hazards to the environment. Good examples are lithium primary and secondary cells and the mercury-free rechargeable alkaline manganese dioxide cell, which is produced at a pilot plant in Canada [57]. But also the nickel-metalhydride cell will be a favourite to supplement and partly substitute nickel-cadmium cells. 

Most of the commercial battery systems, e.g. zinc-carbon, manganese dioxide-zinc, nickel-cadmium, lead-acid and mercury button cells contain toxic substances. Strong efforts have been made to recycle these batteries, to lower the concentration of their toxic substances or to replace them with alternative systems. Nevertheless, battery production processes as well as disposal or recycling activities of spent batteries are responsible for the infiltration of a few toxic substances in our environment. The following chapters describe the toxicology of mercury, cadmium and lead, which are the most toxic components found in different battery systems. 

Clark cell A type of cell formerly used as a standard source of e.m.f. It consists of a mercury cathode coated with mercury sulfate, and a zinc anode. The electrolyte is zinc sulfate solution. The e.m.f. produced is 1.4345 volts at 15°C. The Clark cell has been superseded as a standard by the Weston (Trademark) cadmium cell. The cell is named for the English engineer Josiah Latimer Clark (1822-98). 

Weston cadmium cell A standard cell that produces a constant e.m.f. of 1.0186 volts at 20°C. It consists of an H-shaped glass vessel containing a negative cadmium-mercury amalgam electrode in one leg and a positive mercury electrode in the other. The electrolyte - saturated cadmium sulfate solution - fills the horizontal bar of the vessel to connect the two electrodes. The e.m.f. of the cell varies very little with temperature, being given by the equation = 1.0186 - 0.000 037 (T - 293), where T is the thermodynamic temperature. 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

Phases formed on semiconductor surfaces can change the electrical properties in an uncontrolled, deleterious fashion. Oxide passivation layers on compound semiconductors (e.g., mercury cadmium telluride IR detectors or gallium arsenide solar cells) can be grown to impart protection to the surfaces and to stabilize electrical properties by preventing uncontrolled reactions. 

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