Lead, spongy

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

A third type of problem, that is often mistakenly confused with dendrite formation, is due to the presence of a reaction-product layer upon the growth interface if the electrode and electrolyte are not stable in the presence of each other. This leads to filamentary or hairy growth, and the deposit often appears to have a spongy character. During a subsequent discharge step the filaments often become disconnected from the underlying metal, so that they cannot participate in the electrochemical reaction, and the rechargeable capacity of the electrode is reduced. 

Osteoporosis is a common condition, in which bone density is decreased as a consequence of an imbalance between bone formation (osteoblast) and bone loss (osteoclast). This leads to fragile bones, which are at an increased risk for fractures. The term porosis means spongy, which describes the large holes seen in these bones. 

A cell in this type of battery has electrodes made of lead and spongy lead impregnated with Pb02. Sulfuric acid is the electrolyte, and the cell voltage is approximately 2.0 V. Depending on the number of cells linked in series, the overall voltage can be 6 or 12 (the more common type of battery). 

Other leukodystrophies are associated with the lysosomal and peroxisomal disorders in which specific lipids or other substances accumulate due to a deficiency in a catabolic enzyme - for example Krabbe s disease, meta-chromatic leukodystrophy (MLD) and adrenoleuko-dystrophy (ALD) [1,2]. (These are discussed in detail in Ch. 40.) Similarly, disorders of amino acid metabolism can lead to hypomyelination - for example phenylketonuria and Canavan s disease (spongy degeneration) [1, 2, 25] (Ch. 40). The composition of myelin in the genetically... 

Both half-cell reactions are fully electro-reversible. In practice, there are two types of lead the collector electrode is made of lead alloy mesh in order to give it greater structural strength, and is made with about 5 per cent antimony. Spongy lead (Pb + Pb02) is introduced into the holes of the mesh. 

Spongy lead has a higher surface area than normal lead. 

Cadmium also may be recovered from zinc ores and separated from other metals present as impurities by fractional distillation. Alternatively, the cadmium dust obtained from the roasting of zinc ore is mixed with sulfuric acid. Zinc dust is added in small quantities to precipitate out copper and other impurities. The metal impurities are removed by filtration. An excess amount of zinc dust is added to the solution. A spongy cadmium-rich precipitate is formed which may he oxidized and dissolved in dilute sulfuric acid. Cadmium sulfate solution is then electrolyzed using aluminum cathodes and lead anodes. The metal is deposited at the cathode, stripped out regularly, washed and melted in an iron retort in the presence of caustic soda, and drawn into desired shapes. More than half of the world s production of cadmium is obtained by elecrolytic processes. 

Lead is widely used in storage batteries. Each cell consists of a spongy lead plate as cathode and lead dioxide as anode immersed in the electrolyte sulfuric acid. The overall chemical reaction in the cell during discharge is as follows ... 

Secondary cells are voltaic cells that can be recharged repeatedly. The lead storage battery and nickel-cadmium cell are examples of secondary cells. The lead storage battery consists of six voltaic cells. Its electrodes are lead alloy plates, which take the form of a grill, filled with spongy lead metal. The cathode consists of another group of plates filled with lead (IV) oxide, P6O2. Dilute sulfuric acid is the electrolyte of the cell. When the battery delivers a current, the lead is oxidized to lead ions, which combine with sulfate fS0 7 ions of the electrolyte to cover the lead electrode. 

Positive plates grids filled Negative plates with PbO grids filled with spongy lead... 

Lead grid packed with with PbCri (cathode) spongy lead (anode)... 

J. Tafel electrolyzed a soln. of 0-4 grm. of nitric acid and 20 c.c. of 50 per cent, sulphuric acid, using 10 sq. ems. of cathode surface and 2-4 amps, at 0°. The product of the reduction is largely dependent on the nature of the metal used as electrode. Some results are indicated in Table XXVII. With platinum, no ammonia or hydroxylamine was formed, and with palladium the reduction is extremely slow. Hie chief products of the reduction are hydroxylamine and ammonia. The largest proportion of the hydroxylamine is formed when mercury is used as cathode, and the conversion of the nitric acid into this can be carried out almost quantitatively. With lead electrodes, about 40 per cent, of the nitric acid is converted into hydroxylamine, and with copper electrodes only about 15 per cent. if the copper be in the form of a spongy mass, only about one per cent, of the acid is transformed into hydroxylamine, the remainder being reduced to ammonia. When... 

C. i1. Burgess1 and C. Hambuechen, in 1903, investigated the various conditions requisite for the electrolytic production of a good white lead. They found that a two-compart-ment cell is necessary to obtain a pure product. When lead anodes and sodium nitrate solution are employed a certain quantity of basic lead salt is produced, and there is not therefore a 100 per cent, formation of pure lead nitrate. The reduction of sodium nitrate at copper cathodes cannot be prevented so that a certain amount of ammonia is formed, and the solution being alkaline after a time, plumbates are formed and a layer of spongy lead is deposited on the cathode. If, therefore, the cathode compartment be not separated from the anode, the loosely-deposited cathodic lead will fall into the white lead which is collecting at the bottom of the cell. 

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