Sulfuric electrolytes

In valve-regulated batteries the sulfuric electrolyte is reacting with the electrodes, too, so that here also the same dilution of the electrolyte takes place. But in contrast to flooded batteries, because of the solidified electrolyte, the lead ions are hindered from diffusion into the cell. Thus the concentration of lead ions near the plate surface increases extremely, so that because of the solution equilibrium a further solution of lead is prevented. Therefore the electrolyte cannot become saturated with lead ions and no precipitation of lead dendrites takes place. 

Electrophoretic deposition (EPD) is anotlier metliod of casting slurries. EPD is accomplished tlirough tire controlled migration of charged particles under an applied electric field. During EPD, ceramic particles typically deposit on a mandrel to fonn coatings of limited tliickness, or tliin tubular shapes such as solid (3 " - AI2O2 electrolytes for sodium-sulfur batteries. 

Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world s selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. 

The amount of sulfur in aromatic monomers can be determined by differential pulse polarography. Standard solutions are prepared for analysis by dissolving 1.000 mb of the purified monomer in 25.00 mb of an electrolytic solvent, adding a known amount of S, deaerating, and measuring the peak current. The following results were obtained for a set of calibration standards... 

Ionic conductivity is used in oxygen sensors and in batteries (qv). Stabilized zirconia, Zr Ca 02 has a very large number of oxygen vacancies and very high conductivity. P-Alurnina/72(9(9j5 -4< -(y, NaAl O y, is an excellent cation conductor because of the high mobiUty of Na" ions. Ceramics of P-alurnina are used as the electrolyte in sodium-sulfur batteries. 

Lithium Fluorobora.te, Lithium fluoroborate is used in a number of batteries (qv) as an electrolyte, for example in the hthium—sulfur battery... 

The electrolytic processes for commercial production of hydrogen peroxide are based on (/) the oxidation of sulfuric acid or sulfates to peroxydisulfuric acid [13445-49-3] (peroxydisulfates) with the formation of hydrogen and (2) the double hydrolysis of the peroxydisulfuric acid (peroxydisulfates) to Caro s acid and then hydrogen peroxide. To avoid electrolysis of water, smooth platinum electrodes are used because of the high oxygen overvoltage. The overall reaction is... 

Inorganic Methods. Before the development of electrolytic processes, hydrogen peroxide was manufactured solely from metal peroxides. Eady methods based on barium peroxide, obtained by air-roasting barium oxide, used dilute sulfuric or phosphoric acid to form hydrogen peroxide in 3—8% concentration and the corresponding insoluble barium salt. Mote recent patents propose acidification with carbon dioxide and calcination of the by-product barium carbonate to the oxide for recycle. 

Production. Indium is recovered from fumes, dusts, slags, residues, and alloys from zinc or lead—zinc smelting. The source material itself, a reduction bullion, flue dust, or electrolytic slime intermediate, is leached with sulfuric or hydrochloric acid, the solutions are concentrated, if necessary, and cmde indium is recovered as 99+% metal. This impure indium is then refined to 99.99%, 99.999%, 99.9999%, or higher grades by a variety of classical chemical and electrochemical processes. 

Pure iron is a silvery white, relatively soft metal and is rarely used commercially. Typical properties are Hsted in Table 1. Electrolytic (99.9% pure) iron is used for magnetic cores (2) (see Magnetic materials, bulk). Native metallic iron is rarely found in nature because iron which commonly exhibits valences of +2 and +3 combines readily with oxygen and sulfur. Iron oxides are the most prevalent form of iron (see Iron compounds). Generally, these iron oxides (iron ores) are reduced to iron and melted in a blast furnace. The hot metal (pig iron) from the blast furnace is refined in steelmaking furnaces to make steel... 

It is easy to reduce anhydrous rare-earth hatides to the metal by reaction of mote electropositive metals such as calcium, lithium, sodium, potassium, and aluminum. Electrolytic reduction is an alternative in the production of the light lanthanide metals, including didymium, a Nd—Pt mixture. The rare-earth metals have a great affinity for oxygen, sulfur, nitrogen, carbon, silicon, boron, phosphoms, and hydrogen at elevated temperature and remove these elements from most other metals. 

Electrowinning from Aqueous Solutions. Electrowinriing is the recovery of a metal by electrochemical reduction of one of its compounds dissolved in a suitable electrolyte. Various types of solutions can be used, but sulfuric acid and sulfate solutions are preferred because these are less corrosive than others and the reagents are fairly cheap. From an electrochemical viewpoint, the high mobiUty of the hydrogen ion leads to high conductivity and low ohmic losses, and the sulfate ion is electrochemicaHy inert under normal conditions. 

The zinc electrolyte contains ca 60 kg/m zinc as sulfate and ca 100 kg/m free sulfuric acid. It is electrolyzed between electrodes suspended vertically in lead or plastic-lined, eg, poly(vinyl chloride), concrete tanks. The insoluble anodes are made of lead with small amounts of silver. The anodic... 

Nickel Sulfamate. Nickel sulfamate [13770-89-3] Ni(S02NH2)2 4H2O, commonly is used as an electrolyte ia nickel electroforming systems, where low stress deposits are required. As a crystalline entity for commercial purposes, nickel sulfamate never is isolated from its reaction mixture. It is prepared by the reaction of fine nickel powder or black nickel oxide with sulfamic acid ia hot water solution. Care must be exercised ia its preparation, and the reaction should be completed rapidly because sulfamic acid hydrolyzes readily to form sulfuric acid (57). 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Electrolytic reductions generally caimot compete economically with chemical reductions of nitro compounds to amines, but they have been appHed in some specific reactions, such as the preparation of aminophenols (qv) from aromatic nitro compounds. For example, in the presence of sulfuric acid, cathodic reduction of aromatic nitro compounds with a free para-position leads to -aminophenol [123-30-8] hy rearrangement of the intermediate N-phenyl-hydroxylamine [100-65-2] (61). 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Sulfur concretes are used in many specialty areas where Porfland cement concretes are not completely satisfactory. Because SC can be formulated to resist deterioration and failure from mineral acid and salt solutions, it is used for constmction of tanks, electrolytic cells, thickeners, industrial flooring, pipe, and others. In addition, SC is under investigation for many other prospective uses (58,59) (see Cement). 

Specifications for sulfuric acid vary rather widely. Exceptions include the federal specifications for "Sulfuric Acid, Technical" and "Sulfuric Acid, Electrolyte (for storage batteries)" and the Food Chemicals Codex specification for sulfuric acid, frequentiy called food-grade acid (although industrywide, "food-grade" is nonspecific). Very Httie has been done to estabUsh industry-wide analytical standards in the United States, except for development of the ASTM analytical methods, designated as E223-88 and summarized in Table 12. 

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