A Sn-plated steel sheet according to the present invention includes a steel sheet, a Sn-plated layer that is provided on at least one surface of the steel sheet, and a film that is provided on a surface of the Sn-plated layer and includes zirconium oxide and tin oxide, in which an amount of the zirconium oxide in the film is 0.2 mg/m.sup.2 to 50 mg/m.sup.2 in terms of metal Zr amount, in a depth direction analysis by X-ray photoelectron spectroscopy, a depth position A at which an element concentration of Zr present as the zirconium oxide is maximum is positioned closer to a surface of the film than a depth position B at which an element concentration of Sn present as the tin oxide is maximum, and a distance between the depth position A and the depth position B in a depth direction is 0.5 nm or more.

Described herein is an aqueous composition including tin ions and at least one compound of formula I

##STR00001##

where X.sup.1, X.sup.2 are independently selected from a linear or branched C.sub.1-C.sub.12 alkanediyl, R.sup.11 is a monovalent group of formula (OCH.sub.2CHR.sup.41).sub.mOR.sup.42, R.sup.12, R.sup.13, R.sup.14 are independently selected from H, R.sup.11, and R.sup.40; R.sup.15 is selected from H, R.sup.11, R.sup.40 and X.sup.4N(R.sup.21).sub.2, X.sup.4 is a divalent group selected from (a) a linear or branched C.sub.1 to C.sub.12 alkanediyl, and (b) formula (OCH.sub.2CHR.sup.41).sub.o, R.sup.21 is selected from R.sup.11 and R.sup.40, R.sup.40 is a linear or branched C.sub.1-C.sub.20 alkyl, R.sup.41 is selected from H and a linear or branched C.sub.1 to C.sub.5 alkyl, R.sup.42 is selected from H and a linear or branched C.sub.1-C.sub.20 alkyl, n is an integer of from 1 to 6, m is an integer of from 2 to 250, and o is an integer of from 1 to 250.

Described herein is an aqueous composition including tin ions and at least one compound of formula I

##STR00001##

where X.sup.1, X.sup.2 are independently selected from a linear or branched C.sub.1-C.sub.12 alkanediyl, R.sup.11 is a monovalent group of formula (OCH.sub.2CHR.sup.41).sub.mOR.sup.42, R.sup.12, R.sup.13, R.sup.14 are independently selected from H, R.sup.11, and R.sup.40; R.sup.15 is selected from H, R.sup.11, R.sup.40 and X.sup.4N(R.sup.21).sub.2, X.sup.4 is a divalent group selected from (a) a linear or branched C.sub.1 to C.sub.12 alkanediyl, and (b) formula (OCH.sub.2CHR.sup.41).sub.o, R.sup.21 is selected from R.sup.11 and R.sup.40, R.sup.40 is a linear or branched C.sub.1-C.sub.20 alkyl, R.sup.41 is selected from H and a linear or branched C.sub.1 to C.sub.5 alkyl, R.sup.42 is selected from H and a linear or branched C.sub.1-C.sub.20 alkyl, n is an integer of from 1 to 6, m is an integer of from 2 to 250, and o is an integer of from 1 to 250.

The Sn-plated steel sheet of the disclosure is an Sn-plated steel sheet including: a steel sheet; an Sn plating layer formed on at least one side of the steel sheet and containing, based on % by mass, from 0.1 g/m.sup.2 to 15 g/m.sup.2 of metal Sn; and a coating layer formed on the surface of the Sn plating layer and containing zirconium oxide and tin oxide; in which the content of the zirconium oxide in the coating layer is from 0.2 mg/m.sup.2 to 50 mg/m.sup.2 in terms of metal Zr amount, and the peak position of binding energy of Sn3d.sub.5/2 according to X-ray photoelectron spectroscopy of the tin oxide in the coating layer is 1.6 eV or higher than the peak position of binding energy of the metal Sn.

The purpose of the present invention is to provide a stannous oxide, which has excellent solubility and resistance to oxidation, from a stannous oxide powder comprising a stannous oxide and inevitable impurities, the stannous oxide powder having a stannous oxide content of 99.99 mass % or more in dry mass, a specific surface area of less than 0.5 m.sup.2/g, a D50 particle size of 20 to 60 m, and a half width of the particle size distribution of 5 to 30 m.

The purpose of the present invention is to provide a stannous oxide, which has excellent solubility and resistance to oxidation, from a stannous oxide powder comprising a stannous oxide and inevitable impurities, the stannous oxide powder having a stannous oxide content of 99.99 mass % or more in dry mass, a specific surface area of less than 0.5 m.sup.2/g, a D50 particle size of 20 to 60 m, and a half width of the particle size distribution of 5 to 30 m.

This tin or tin-alloy plating liquid contains (A) a soluble salt including at least a stannous salt; (B) an acid selected from an organic acid and an inorganic acid, or a salt thereof; (C) a surfactant; (D) a leveling agent; and (E) an additive, wherein the surfactant is a compound (C1) represented by Formula (1) and/or a compound (C2) represented by Formula (2).

##STR00001##

In Formulas (1) and (2), R is an alkyl group having 7 to 13 carbon atoms, m is 5 to 11, n is 1 to 3, and m and n are different from each other.

This tin or tin-alloy plating liquid contains (A) a soluble salt including at least a stannous salt; (B) an acid selected from an organic acid and an inorganic acid, or a salt thereof; (C) a surfactant; (D) a leveling agent; and (E) an additive, wherein the surfactant is a compound (C1) represented by Formula (1) and/or a compound (C2) represented by Formula (2).

##STR00001##

In Formulas (1) and (2), R is an alkyl group having 7 to 13 carbon atoms, m is 5 to 11, n is 1 to 3, and m and n are different from each other.

This tin or tin alloy plating solution includes a soluble salt including at least a stannous salt (A), an acid selected from an organic acid and an inorganic acid or a salt thereof (B), a surfactant (C), benzalacetone (D), and a solvent (E), wherein the plating solution is used to form a pattern in which bump diameters are different from each other on a base material, an amount of the benzalacetone (D) is 0.05 g/L to 0.2 g/L, a mass ratio (C/D) of the surfactant (C) to the benzalacetone (D) is 10 to 200, and a mass ratio (E/D) of the solvent (E) to the benzalacetone (D) is 10 or more.

This tin or tin alloy plating solution includes a soluble salt including at least a stannous salt (A), an acid selected from an organic acid and an inorganic acid or a salt thereof (B), a surfactant (C), benzalacetone (D), and a solvent (E), wherein the plating solution is used to form a pattern in which bump diameters are different from each other on a base material, an amount of the benzalacetone (D) is 0.05 g/L to 0.2 g/L, a mass ratio (C/D) of the surfactant (C) to the benzalacetone (D) is 10 to 200, and a mass ratio (E/D) of the solvent (E) to the benzalacetone (D) is 10 or more.