Stannates

It is amphoteric it gives tin(II) salts with dilute acids and hydroxo stannates(II) with alkalis, for example ... 

Stannate(II) ions are powerful reducing agents. Since, for tin, the stability of oxidation state -b4 is greater than that of oxidation state -b2, tin(II) always has reducing properties, but these are greater in alkaline conditions than in acid (an example of the effect of pH on the redox potential, p. 101). 

Tin(IV) oxide is insoluble in water, but if fused with sodium hydroxide and the mass extracted with water, sodium hexahydroxo-stannate(IV) is formed in solution ... 

This reaction proceeds slowly in aqueous solution, so that the basic salt. Sn(OH)Cl, is slowly precipitated. Addition of excess hydrochloric acid gives the acids of formulae HSnCl3 and H2SnCl4. Salts of these acids containing the ions SnCl J and SnCl (chloro-stannates(II)) are known. 

HjSnCl, with which the aniline forms a salt, aniline chlorostannate (C4HjNH )i,H SnCl4, similar in type to aniline chloroplatinate (p. 448). The crude product is therefore made strongly alkaline with sodium hydroxide, which liberates the base with the formation of sodium stannate, and the aniline can (C4H NH,),H,SnCl, + SNaOH = 2C,H,NH, + Na.SnO, +6NaCl + sHjO then be removed by steam-distillation. 

Synergists. The effect of antimony oxide on the flammabiUty of unsaturated polyesters that contain chlorine is shown in Table 11. A similar effect on the flammabiUty of unsaturated polyester containing 2inc stannates and bromine instead of chlorine is given in Table 12. 

The niter and fresh caustic soda, required to maintain the fluidity of the salt bath in the reactor chamber, are added gradually. When the color of the saturated salts turns from a dark gray to white, the impurity metals are at their highest state of oxidation, and the lead content of the spent salts is very low. In a modification, the arsenic and tin are selectively removed as sodium arsenate and sodium stannate, followed by the removal of antimony as sodium antimonate. 

Wet Process. The sodium arsenate and stannate slag are treated by a leach and precipitation process to produce calcium arsenate, calcium stannate, and a sodium hydroxide solution for recycle. The sodium antimonate filtercake containing selenium, tellurium, and indium is treated in a special metals refinery to recover indium and tellurium. 

Dilute solutions of ammonium hydroxide and sodium carbonate have Httle effect on tin, but strong alkaline solutions of sodium or potassium hydroxide, cold and dilute, dissolve tin to form stannates. 

If tin and sulfur are heated, a vigorous reaction takes place with the formation of tin sulfides. At 100—400°C, hydrogen sulfide reacts with tin, forming stannous sulfide however, at ordinary temperatures no reaction occurs. Stannous sulfide also forms from the reaction of tin with an aqueous solution of sulfur dioxide. Molten tin reacts with phosphoms, forming a phosphide. Aqueous solutions of the hydroxides and carbonates of sodium and potassium, especially when warm, attack tin. Stannates are produced by the action of strong sodium hydroxide and potassium hydroxide solutions on tin. Oxidizing agents, eg, sodium or potassium nitrate or nitrite, are used to prevent the formation of stannites and to promote the reactions. 

Stannic and stannous chloride are best prepared by the reaction of chlorine with tin metal. Stannous salts are generally prepared by double decomposition reactions of stannous chloride, stannous oxide, or stannous hydroxide with the appropriate reagents. MetaUic stannates are prepared either by direct double decomposition or by fusion of stannic oxide with the desired metal hydroxide or carbonate. Approximately 80% of inorganic tin chemicals consumption is accounted for by tin chlorides and tin oxides. 

Stannous Oxide Hydrate. Stannous oxide hydrate [12026-24-3] SnO H2O (sometimes erroneously called stannous hydroxide or stannous acid), mol wt 152.7, is obtained as a white amorphous crystalline product on treatment of stannous chloride solutions with alkaH. It dissolves in alkaH solutions, forming stannites. The stannite solutions, which decompose readily to alkaH-metal stannates and tin, have been used industrially for immersion tinning. 

Hydrated Stannic Oxide. Hydrated stannic oxide of variable water content is obtained by the hydrolysis of stannates. Acidification of a sodium stannate solution precipitates the hydrate as a flocculent white mass. The colloidal solution, which is obtained by washing the mass free of water-soluble ions and peptization with potassium hydroxide, is stable below 50°C and forms the basis for the patented Tin Sol process for replenishing tin in staimate tin-plating baths. A similar type of solution (Staimasol A and B) is prepared by the direct electrolysis of concentrated potassium staimate solutions (26). 

Potassium staimate, K2Sn(OH) (mol wt 298.93), and sodium stannate [12058-66-17, Na2Sn(OH), mol wt 266.71, are colorless crystals and are soluble in water. The solubiUty of potassium stannate in water is 110.5 g/100 mL water at 15°C and that of sodium stannate is 61.5 g/100 mL water at 15°C. The solubihty of sodium stannate decreases with increasing temperature, whereas the solubiUty of potassium stannate increases with increasing temperature. The solubihty of either sodium or potassium stannate decreases as the concentration of the respective free caustic increases. Hydrolysis of stannates yields hydrated stannic oxides and is the basis of the Tin Sol solution, which is used to replenish tin in stannate tin-plating baths (28,29). 

Other. Insoluble alkaline-earth metal and heavy metal stannates are prepared by the metathetic reaction of a soluble salt of the metal with a soluble alkah—metal stannate. They are used as additives to ceramic dielectric bodies (32). The use of bismuth stannate [12777-45-6] Bi2(Sn02)3 5H20, with barium titanate produces a ceramic capacitor body of uniform dielectric constant over a substantial temperature range (33). Ceramic and dielectric properties of individual stannates are given in Reference 34. Other typical commercially available stannates are barium stannate [12009-18-6] BaSnO calcium stannate [12013 6-6] CaSnO magnesium stannate [12032-29-0], MgSnO and strontium stannate [12143-34-9], SrSnO. ... 

Certain anhydrous stannates are effective as smoke suppressants in glass-reinforced polyester, especially Na2Sn(OH)g [12058-66-1] and ZnSnO ... 

Electronic Ceramic Stannates Technical Data Sheet CER-322, M T Chemicals, Inc., Rahway, N.., 1969. 

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