Lead, red

Red lead (Pb304) has a brilliant red-orange color, is quite resistant to light, and finds extensive use as a priming coat for structural steel because it possesses corrosion-inhibiting properties. 

Red lead [1314-41-6], Pb304, Mr 685.57, crystallizes in the tetragonal system and is a red powder with a density of 9.1 g/cm3. It decomposes at ca. 500 °C at atmospheric pressure. For standard specifications, see Table 1. 

Red lead should be regarded as the lead salt of orthoplumbic acid, H4Pb04, i.e., it is lead(II) orthoplumbate, Pb2Pb04, in which PbOe octahedra are linked by Pb(II) ions [5.146]. 

Red lead is produced industrially by oxidizing lead monoxide (PbO) at ca. 460 480 °C with agitation in a stream of air for 15-24 h. Most red lead is used in the glass, ceramic, and accumulator industries where an apparent density of 2 g/mL is adequate. For the paint industry, however, highly dispersed red lead is normally necessary, with a sieve residue of 0.1 % on a 0.063 mm sieve (ISO 787, part 18) and an apparent density of 1.3-2.0 g/mL (ISO 510, DIN 55 516). 

The electrochemical action of red lead results from the fact that lead has valencies of 2 and 4 in lead orthoplumbate Pb(IV) compounds are reduced to Pb(II) in the cathodic region [5.147]. The chemical anticorrosive effect is a result of lead soaps that are formed when fatty acids in the binder react with the red lead. The lead soaps permeate the paint film as lamellae, and give good mechanical strength, water resistance, and adhesion to the steel surface. Furthermore, the corrosion-promoting chloride and sulfate ions are precipitated by lead(II) ions [5.148]. 

Possible combinations of red lead with various binder systems are listed in Table 39 [5.114]. Red lead is still used for heavy-duty anticorrosion applications, especially for surfaces bearing residual traces of rust. In waterborne paints, red lead has no advantages over zinc phosphate [5.149]. 

Why could not lead dioxide be prepared equally well by treating a solution of lead chloride with chlorine  

Compare the reaction of lead dioxide and of lead monoxide with hydrochloric acid. 

Compare the action of lead dioxide with that of manganese dioxide upon hydrochloric acid. 

Why should not lead dioxide and manganese dioxide dissolve in dilute nitric acid as well as in hydrochloric add  

The following procedures should yield a product of nearly the composition Pb304. This substance, under the commercial name of minium, finds use as a red pigment. 

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Trilead tetroxide, Pb304, red lead and other intermediate phases, e.g. Pb70i, and Pb203 are formed by heating PbO or Pb02- Uses... 

Finely divided lead, when heated in air, forms first the lead(II) oxide, litharge , PbO, and then on further heating in an ample supply of air, dilead(II) lead(IV) oxide, red lead , Pb304. Lead, in a very finely divided state, when allowed to fall through air, ignites and a shower of sparks is produced. Sueh finely divided powder is said to be pyrophoric . It can be prepared by carefully heating lead tartrate. 

Lead(IV) oxide is also obtained when red lead , Pb304 (see below), is treated with dilute nitric acid ... 

Red lead is a brilliant red powder obtained by heating lead monoxide in air to about 800 K. This reaction is reversible, for if heated, red lead evolves oxygen at temperatures above 850 K. 

Red lead is insoluble in water. Like lead(II) oxide it can readily be reduced to lead. The structure of the solid, as the systematic name suggests, consists of two interpenetrating oxide structures, in which each Pb atom is surrounded octahedrally by six oxygen atoms, and each Pb" by three (pyramidal) oxygen atoms, the oxygen atoms being shared between these two units of structure. With dilute nitric acid the lead(ll) part dissolves, and the lead(IV) part precipitates as lead(IV) oxide ... 

Red lead is a useful ingredient of anti-rusting paints, in which it is mixed with linseed oil. If glycerol is added to this mixture, a cement suitable for luting (i.e. making airtight or watertight) joints in iron pipes or vessels is obtained. 

Lead tetracetate. Red lead is warmed with acetic acid in the presence of sufficient acetic anhydride to combine with the water formed ... 

Realgar, see di-Arsenic disulfide Red lead, see Lead(II,IV) oxide Rhodochrosite, see Manganese carbonate... 

Lead Tetroxide. Lead tetroxide (red lead minium lead orthoplumbite), Pb O, is a brilliant orange-red pigment which accounted for U.S. shipments of 17,780 t ia 1977, mainly to the ceramics and storage battery iadustries (40). U.S. shipments ia 1993 amounted to approximately 12,000 t. The decrease ia usage siace 1973 (19,000 t) is attributable to discontinued use ia the paint and coatings (qv) iadustry, and alterations ia mbber and ceramics (qv) markets. It is iasoluble ia water and alcohol, and dissolves ia acetic acid or hot hydrochloric acid. Red lead is manufactured by heating lead monoxide ia a reverberatory furnace ia the preseace of air at 450—500°C uatil the desired oxidative composition is obtaiaed. 

Paste Mixing. The active materials for both positive and negative plates are made from the identical base materials. Lead oxide, fibers, water, and a dilute solution of sulfuric acid are combined in an agitated batch mixer or reactor to form a pastelike mixture of lead sulfates, the normal, tribasic, and tetrabasic sulfates, plus PbO, water, and free lead. The positive and negative pastes differ only in additives to the base mixture. Organic expanders, barium sulfate [7727-43-7] BaSO carbon, and occasionally mineral oil are added to the negative paste. Red lead [1314-41 -6] or minium, Pb O, is sometimes added to the positive mix. The paste for both electrodes is characterized by cube weight or density, penetration, and raw plate density. 

The tubular positive plate uses rigid, porous fiber glass tubes covered with a perforated plastic foil as the active material retainer (Fig. 2). Dry lead oxide, PbO, and red lead, Pb O, are typically shaken into the tubes which are threaded over the grid spines. The open end is then sealed by a polyethylene bar. Patents describe a procedure for making a type of tube for the tubular positive plate (90) and a method for filling tubular plates of lead—acid batteries (91). Tubular positive plates are pickled by soaking in a sulfate solution and are then cured. Some proceed directiy to formation and do not requite the curing procedure. 

Chromium was first isolated and identified as a metal in 1789 by Vauquelin who was working with a rare mineral, Siberian red lead or crocoite [14654-05-08] PbCrO (3). The name chromium comes from the Greek word chroma color and resulted from the wide variety of brilliant colors... 

Zinc yellow became an important corrosion-inhibiting pigment for aircraft during World War II. However, the war production rate of 11,000 t/yr has not since been reached. Now, 2inc yellow is widely used for corrosion inhibition on auto bodies, light metals, and steel, and in combination with red lead and ferric oxide for stmctural steel painting. 

The common acid acceptors, red lead oxide and barium carbonate, are both toxic when inhaled or ingested. They are, and should be, used in industry as dispersions in EPDM and ECO. SuppHers of red lead oxide include Polymeries, Inc., Rhein Chemie Corp., and Akrochem Co., Akron, Ohio. Barium carbonate in an ECO binder is available from Rhein Chemie Corp. and Synthetic Products Co. 

A frequently cited example of protection from atmospheric corrosion is the Eiffel Tower. The narrow and, for that age, thin sections required a good priming of red lead for protection against corrosion. The top coat was linseed oil with white lead, and later coatings of ochre, iron oxide, and micaceous iron oxide were added. Since its constmction the coating has been renewed several times [29]. Modern atmospheric corrosion protection uses quick-drying nitrocellulose, synthetic resins, and reaction resins (two-component mixes). The chemist Leo Baekeland discovered the synthetic material named after him, Bakelite, in 1907. Three years later the first synthetic resin (phenol formaldehyde) proved itself in a protective paint. A new materials era had dawned. 

About 5 minutes later, the liquid contents of the beaker are poured cautiously into a 2-1. glass beaker, and this is tipped and rotated slowly so as to spread the congealing mass in a thin film on the beaker walls. When the material in the beakers has cooled, a total of 11. of water is poured into the beakers and the water is stirred well for at least 1 hour (Note 5). The cold suspension is filtered with suction to separate 200-210 g. of an insoluble mixture of lead monoxide and red lead, which is washed on the filter with six 50-ml. portions of water. 

Application of protective paints consists of surface preparation of steel, priming coat and finishing coats. Wherever possible, steel should be blast-cleaned before painting. Primers thoroughly wet the metal to promote adhesion of finishing paints and carry inhibitive pigments. For example, red lead oxide will minimize the spread of rust on metal surfaces. The total thickness of fmishing coats must be at least 0.125 mm for adequate protection and life. Four coats of paint usually are necessary to achieve this. 

Red lead (Pb304) is manufactured on the 20000-tonne scale annually and is used primarily as a surface coating to prevent corrosion of iron and steel (check oxidation-reduction potentials). It is also used in the production of leaded glasses and ceramic glazes and. very substantially, as an activator, vulcanizing agent and pigment in natural and artificial rubbers and plastics. 

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