The oxides of lead

The crystal structure of tetragonal PbO (and SnO). The small shaded circles represent metal atoms. The arrangement of bonds from a metal atom is shown at the right, where the two dots represent the inert pair of electrons (see p. 937). 

The crystal structure of Pb304 (and ZnSb204). (a) Portion of the structure outlined in the projection (b) showing the chains of PblVOg octahedra joined by pyramidally 

The usual maroon form of this oxide has the rutile structure, the mean distance of Pb to the six octahedral neighbours being 218 A. At 300 under 40 kbar pressure this converts to a black orthorhombic polymorph, the structure of which has been described in the discussion of close-packed structures in Chapter 4. 

Qosely related to Pb02 are some complex oxides in which Pb(iv) is octahedrally coordinated. In Sr2Pb04 there are rutile-like chains which are joined through 7-coordinated Sr ions (instead of Pb in Pb304), while Ba2Pb04 has the K2NIF4 (layer) structure (p. 171) which accommodates the larger Ba ions in positions of 9-coordination  

In contrast to the octahedral coordination of M(iv) in these compounds there is 5-coordinatlon in the hygroscopic oxides K2M 03 (M = Zr, Sn, Pb). These contain the unusual MX3 chain of Fig. 12.16 in which M has a tetragonal pyramidal arrangement of 5 0 neighbours (one closer than the other four), the M atom lying above the base of the pyramid. The detailed structure of the Pb compound was not determined in K2Sn03 bond lengths are Sn-0, 1-93 A, Sn-2 0, 2-03 A, and Sn-2 0, 2-21 A. Note the numerous examples of isostructural compounds of Sn(iv) and Pb(iv). 

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Lead borate moaohydrate [14720-53-7] (lead metaborate), Pb(B02)2 H20, mol wt 310.82, d = 5.6g/cm (anhydrous) is a white crystalline powder. The metaborate loses water of crystallization at 160°C and melts at 500°C. It is iasoluble ia water and alkaHes, but readily soluble ia nitric and hot acetic acid. Lead metaborate may be produced by a fusion of boric acid with lead carbonate or litharge. It also may be formed as a precipitate when a concentrated solution of lead nitrate is mixed with an excess of borax. The oxides of lead and boron are miscible and form clear lead-borate glasses in the range of 21 to 73 mol % PbO. 

Lead zirconate [12060-01 -4] PbZrO, mol wt 346.41, has two colorless crystal stmctures a cubic perovskite form above 230°C (Curie point) and a pseudotetragonal or orthorhombic form below 230°C. It is insoluble in water and aqueous alkaUes, but soluble in strong mineral acids. Lead zirconate is usually prepared by heating together the oxides of lead and zirconium in the proper proportion. It readily forms soHd solutions with other compounds with the ABO stmcture, such as barium zirconate or lead titanate. Mixed lead titanate-zirconates have particularly high piezoelectric properties. They are used in high power acoustic-radiating transducers, hydrophones, and specialty instmments (146). 

Much confusion exists concerning the number, composition, and structure of the oxides of lead. PbO exists as a red tetragonal form (litharge) stable at room temperature and a yellow orthorhombic form (massicot) stable above 488°C. Litharge (mp 897°, d 9.355 gcm ) is not only the most important oxide of Pb, it is also the most widely used inorganic compound of Pb (see Panel on p. 386) it is made by reacting molten Pb with air or O2 above 600° and has the SnO structure (p. 383, Pb-O 230 pm). Massicot (d 9.642 gcm ) has... 

Curve A in Fig. 1 corresponds to the oxidation of lead to its divalent ion, described by the reaction... 

The losses of lead as litharge (PbO) can be minimized if the impurity elements could be oxidized at an oxygen potential lower than that which causes the oxidation of lead. This can be achieved if the activities of the oxides of the impurity elements in the slag are decreased, for example, by the addition of an oxide which reacts very much more strongly with the oxides of the impurities than it does with lead oxide. Sodium hydroxide is a useful reagent for this purpose and sodium nitrate can be used as the source of oxygen. The reaction involved in this process, known as the Harris process, can be formally written as... 

We shall not discuss here oxygen interaction with nickel since, although it is one of the most extensively studied systems (59), there is still considerable ambiguity and confusion regarding possible models. Two systems that, however, have lent themselves to investigation by XPS are the oxidation of lead (60, 60a) and aluminum surfaces (10). In both cases substantial shifts were observed in the metal core levels, which as emphasized previously is more the exception than the rule. 

LiH+Hg=LiHg+iH2. The hydrides are strong reducing agents—the oxides of lead, copper, etc., are reduced to the metallic state. Lithium hydride slowly decomposes absolute alcohol, forming the alcoholate and hydrogen the hydrated alcohol is vigorously decomposed. The alkali hydrides are insoluble in ether and benzene. 

The oxide of lead which is used in the manufacture of crystal, is sot the protoxide commonly known as massicot, and represented by the formula Pb O, but minium, which is a sesquioxide, Pba 0 for, as Bahru el remarks, one may depend on tho latter net being mixed with metallic lead, which almost necessarily happens with the massicot of commerce. The object of employing oxide of lead in this kind of glass is to increase the density, and, consequently, tho refractive power, which gives the glass a peculiar lustre or brilliancy. 

When the coloring oxides employed are such that they are not injuriously affected by the oxides of lead and of bismuth, the flux is usually composed of the following ingredients —... 

The ores of lead are numerous, but are found in very unequal proportions that from which the metal is extracted being for the most part galena, or bisulphide of load. The most important of them are the oxide of lead or massicot, chloride of lead, bisulphide of lead or galena, carbonate, phosphate, sulphate, arseniate, and chromate of lead. 

Codein is a very powerful base it turns red litmus paper blue, and precipitates the oxides of lead, iron, cobalt, and nickel from their solutions. It is precipi. tated from the solutions of its salts by potassa and by ammonia in the latter case, however, It does not fall immediately, but is slowly deposited as small transparent crystals. ... 

In 1852 J. Bn am deis took a patent for removing lead from sugar by animal charcoal, thus being able to use lead to purify sugar. The Editor believes that the destruction of the animal charcoal soon follows. The oxide of lead, on heating, melts in the pores. This, although possible, would be very expensive. 

The glaze or enamel is composed of quartz-sand, soda, common salt, and a mixture of calcined tin and lead. The two metals are more easily oxidizad when mixed the oxide of tin produced—Sn 0,—acting the part of nn acid to the oxide of lead—PbO. The mixture is prepared by placing tho lead with about one-fourth of tin in a special fumuoe, where it is exposed ta heat and a curroiit of air. A yellowish ash of tin and lead is formed, which is carefully calcined to oxidize thoroughly all the metallic particles. This metallic ash is mixed -to form tho enamel in the following proportions —. 

More recently, Chadwick and Christie reported evidence for oxygen spillover in the oxidation of lead monolayers on copper (756). Polycrystalline copper or single crystal (111) or (210) surfaces were covered by less than a monolayer of lead. 02 reacts with Pb to give PbO. If a complete monolayer of Pb was formed on Cu, the rate of oxidation of Pb decreased. Now H2S reacts with Cu but not with Pb. If H2S was adsorbed at saturation on Cu containing less than a monolayer of Pb (which does not adsorb H2S), the oxidation of Pb again decreased. These results were explained by the spillover of oxygen from Cu to Pb (and its oxidation into PbO). Oxygen was therefore adsorbed on a free surface of Cu, not covered either by Pb or by H2S, and then spilled over to Pb. 

O into the vessel L, and from there is drawn into tin can9 The oxide of lead... 

A recent report by Haver et al. (H16) described the recovery of lead and. sulfur from a lead sulfide concentrate using ferric sulfate as the leaching reagent. Elemental sulfur was produced during the oxidation of lead sulfide to lead sulfate by hot ferric sulfate solution. The lead sulfate in the re.sidue was changed to acid-soluble lead carbonate by treatment with ammonium carbonate, and ammonium sulfate was a by-product. Hydro-fluosilicic acid dissolved the lead carbonate and an electrolysis step regenerated the HjSiF and deposited 99.9% pure lead metal. The recovery for lead was about 90% and for sulfur, 67%, half as elemental sulfur and the other half as ammonium sulfate. 

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