Stannous tins

An electrorefining plant may operate with either an acid or an alkaline bath. The acid bath contains stannous sulfate, cresolsulfonic or phenolsulfonic acids (to retard the oxidation of the stannous tin in the solution), and free sulfuric acid with P-naphthol and glue as addition agents to prevent tree-like deposits on the cathode which may short-circuit the cells. The concentration of these addition agents must be carefliUy controlled. The acid electrolyte operates at room temperature with a current density of ca 86—108 A/m, cell voltage of 0.3 V, and an efficiency of 85%. Anodes (95 wt % tin) have a life of 21 d, whereas the cathode sheets have a life of 7 d. Anode slimes may be a problem if the lead content of the anodes is high the anodes are removed at frequent intervals and scmbbed with revolving bmshes to remove the slime (7). 

In the field, cassiterite ore is usually recognized by its high density (7.04 g/cm ), low solubiUty in acid and alkaline solutions, and extreme hardness. Tin in solution is detected by the white precipitate formed with mercuric chloride. Stannous tin in solution gives a red precipitate with toluene-3,4-dithiol. 

Stannous Chloride. Stannous chloride is available in two forms anhydrous stannous chloride, SnCl2, and stannous chloride dihydrate [10025-69-1], SnCl2 2H20, also called tin crystals or tin salts. These forms are sometimes used interchangeably however, where stabiUty, concentration, and adaptabihty are important, anhydrous stannous chloride is preferred. Even after long storage, changes in the stannous tin content of anhydrous stannous chloride are extremely low. Physical properties of the tin chlorides are Hsted in Table 1. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

Tin Nitrate. Stannic nitrate, Sn(N03)4, has been reported, but its existence is questionable. A soln contg stannic tin (Sn4+) can be made by dissolving Sn in nitric acid. It decomps on aging, heating or dilution. The existence of stannous nitrate, Sn(N03)2, must also be questioned. A soln of stannous tin (Sn +) in nitric acid can be made which must be kept cold. It is unstable to heat, dilution and aging (Ref 3)... 

Carnallite, KCl-MgCh-6H20.—A similar salt is to be expected with ammonium, rubidium, or cesium replacing potassium, zinc, cadmium, iron, nickel, cobalt, or stannous tin, replacing magnesium and bromine and occasionally iodine replacing chlorine. Many of these are known but not all. (Mellor, II, 430.)... 

Raw materials for PC board manufacture that contain metals include the following o Copper foil (encasing the board) o Etchants chromic acid, cupric chloride, ferric chloride o Catalysts stannous tin, palladium chloride o Electroless copper bath copper sulfate... 

Tin in ambient waters may exist as divalent cationic (positively charged) ions (Sn ) or as quadrivalent ions (Sn +). Stannous tin (Sn ) dominates in reduced (oxygen-poor) water, and will readily precipitate as a sulfide (SnS) or as a hydroxide (Sn(OH)2) in alkaline water. Stannic tin (Sn ) readily hydrolyzes, and can precipitate as a hydroxide (Wedepohl et al. 1978). The solubility product of Sn(OH)4 has been measured as approximately 10 g/L at 25°C (Wedepohl et al. 1978). 

Tin, having valence of +2 and +4, forms stannous (tin(II)) compounds and stannic (tin(IV)) compounds. Tin compounds include inorganic tin(II) and tin(IV) compounds complex stannites, MSnX3, and stannates, M2SnX5, and coordination complexes, organic tin salts where the tin is not bonded through carbon, and organotin compounds, which contain one-to-four carbon atoms bonded direcdy to tin. 

It is clear that some of the Sn cations in the B-site Sn04 groups are reduced but no one has determined the extent of such reduction. It is apparent that only a small fraction of such groups are affected. Otherwise the lattice structure would not be maintained. Note that a significant difference in ionic radius occurs when stannic tin is reduced to stannous tin. X-ray analj is shows no difference between the air-fired and the reduced phosphors. K. Th. Wilke studied this phenomenon in 1957 and proposed the following mechanism, given as 3.1.90. on the next page. 

Recently stereocomplexes of PLA appeared on the market and lead to promising applications in durable devices (see below PLA applications). The stereocomplexes are defined as the association of polymers with different tacticity or conformation. Three synthesis routes are used to produce a PLA stereocomplex, either in solution or in melt state during pol)nnerization or hydrolysis. The complexe formation is possible with (i) two monomers (L-lactide and D-lactide), (ii) polymer and monomer or (iii) two polymers (PLLA and PDLA). This synthesis is often performed with stannous tin and 1-dodecanol (lauryl alcohol) as initiator or co-initiator of the reaction [36-38]. According to Tsuji et al. [38], some other parameters affect the formation of stereocomplexes ... 

Copper(I) or cuprous, copper(II) or cupric Mercury(I) or mercurous, mercury(II) or mercuric Gold(I) or aurous, gold(III) or auric Iron(II) or ferrous, iron(III) or ferric Cobalt(II) or cobaltous, cobalt(III) or cobaltic Tin(II) or stannous, tin(IV) or stannic Lead(II) or plumbous, lead(IV) or plumbic Nickel(II) or nickelous, nickel(IV) or nickelic... 

An excellent account of the effect of tin catalysts on the physical properties of cellular urethanes is given by Mack (1964), who found that stannous tin catalysts are extremely sensitive to exposure to air, and to contamination by ferrous iron these result in chemical oxidation of stannous to stannic tin carboxylate, which in itself was found to be a very poor gelation catalyst. 

Solutions of stannous (+2) tin are common in any inorganic analytical laboratory. Stannous chloride, for exaniple, is a very effective reducing agent for a large number of species. Stannous tin may be prepared quite easily, and the reduction of Sn to Sn with iron or nickel metal is a usual preliminary step in the most common analytical method for quantitative determination of tin volumetric titration with a standard iodine solution. 

Unfortunately, stannous tin solutions are quite unstable and, if left in... 

Stannous tin (Sn ) behaves very much like Sn in its aqueous hydrolytic, reactions. When Sn solutions are neutralized with alkali carbonate or... 

Sn,(OH) and SnOH are formed to a lesser extent. Stannous tin is a power-... 

Stannous tin also reacts with halide ions to form complexes. The weak chlorostannite complexes SnCl, SnClI, and SnCl. have been reported,... 

In another iodide system, Irving and Rossotti state that stannous tin... 

As , Sb , Sn" ) in 26 different aqueous media. Stannous tin behaves as a cation and migrates toward the cathode in most of the.solutions used, but in several solutions (0. IN oxalate, citrate, iodide, tartrate, and EDTA — 0.1 1. NH OH) it behaves as an anion and moves in the opposite direction. The moat useful behavior, however, seems to be in 0. IM KI or 0. IM oxalic acid, where Sn migrates toward the anode, As toward the cathode, and Sb stands still. 

J. L. Garnett and L, C. Lock "The Use of Naphthalene Derivatives in Inorganic Analysis. Part IV. The Nitronaphthylamines as Fluorlmetric Reagents for Stannous Tin" Anal. Chim. Acta 1 7, 574-78 (1957). 

There has been occasional use of stannous tin compounds, such as the readily available stannous octoate, in place of, or in conjunction with zinc. In such cases, antioxidant protection is needed to prevent oxidation to tin(iv). 

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