The present invention provides an aqueous passivation composition for the treatment of zinc or zinc alloy coatings, comprising: i) phosphoric acid; ii) at least one water-soluble polyphosphonic acid or a water-soluble salt thereof, iii) at least one divalent metal cation (M.sup.2+); and, iv) at least one water-soluble or water-dispersible fluoroacid or a salt thereof, wherein said fluoroacid is defined by the following general empirical formula (II):

H.sub.pT.sub.qF.sub.rO.sub.s   (II)

wherein: each of q and r represents an integer from 1 to 10; each of p and s represents an integer from 0 to 10; and, T represents an element selected from the group consisting of Ti, Zr, Hf, Si, Sn, Al, Ge, and B.

The present invention provides an aqueous passivation composition for the treatment of zinc or zinc alloy coatings, comprising: i) phosphoric acid; ii) at least one water-soluble polyphosphonic acid or a water-soluble salt thereof, iii) at least one divalent metal cation (M.sup.2+); and, iv) at least one water-soluble or water-dispersible fluoroacid or a salt thereof, wherein said fluoroacid is defined by the following general empirical formula (II):

H.sub.pT.sub.qF.sub.rO.sub.s   (II)

wherein: each of q and r represents an integer from 1 to 10; each of p and s represents an integer from 0 to 10; and, T represents an element selected from the group consisting of Ti, Zr, Hf, Si, Sn, Al, Ge, and B.

A steel sheet has a hot-dip Zn—Al—Mg-based coating film, the coating film containing 1 mass % to 22 mass % of Al and 0.1 mass % to 10 mass % of Mg on a surface of the steel sheet, in which an X-ray diffraction peak intensity ratio of a Mg—Zn compound phase in the coating film, that is, MgZn.sub.2/Mg.sub.2Zn.sub.11, is 0.2 or less.

Provided are an insulating-coated oriented magnetic steel sheet having an insulating coating of excellent heat resistance, and a method for manufacturing the same. This insulating-coated oriented magnetic steel sheet has an oriented magnetic steel sheet, and an insulating coating arranged on the surface of the oriented magnetic steel sheet. The insulating coating contains Si, P, and O, and at least one element selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al, and Mn, the K-absorption edge of the P in the insulating coating having an XAFS spectrum that exhibits three absorption peaks from 2156 eV to 2180 eV.

Provided are an insulating-coated oriented magnetic steel sheet having an insulating coating of excellent heat resistance, and a method for manufacturing the same. This insulating-coated oriented magnetic steel sheet has an oriented magnetic steel sheet, and an insulating coating arranged on the surface of the oriented magnetic steel sheet. The insulating coating contains Si, P, and O, and at least one element selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al, and Mn, the K-absorption edge of the P in the insulating coating having an XAFS spectrum that exhibits three absorption peaks from 2156 eV to 2180 eV.

Provided is a surface treated steel sheet for a fuel tank, the surface treated steel sheet including: a Zn plated layer or a ZnNi alloy plated layer which is formed on at least a surface of the steel sheet to be an inner surface of the fuel tank; and a chromate-free chemical conversion coating layer containing a water-and-oil repellent, the chromate-free chemical conversion coating layer being placed over the Zn plated layer or the ZnNi alloy plated layer on the surface to be the inner surface of the fuel tank. A water contact angle on a surface of the chromate-free chemical conversion coating layer is more than or equal to 70 degrees and an n-hexadecane contact angle on the surface of the chromate-free chemical conversion coating layer is more than or equal to 30 degrees and less than or equal to 70 degrees.

Provided is a surface treated steel sheet for a fuel tank, the surface treated steel sheet including: a Zn plated layer or a ZnNi alloy plated layer which is formed on at least a surface of the steel sheet to be an inner surface of the fuel tank; and a chromate-free chemical conversion coating layer containing a water-and-oil repellent, the chromate-free chemical conversion coating layer being placed over the Zn plated layer or the ZnNi alloy plated layer on the surface to be the inner surface of the fuel tank. A water contact angle on a surface of the chromate-free chemical conversion coating layer is more than or equal to 70 degrees and an n-hexadecane contact angle on the surface of the chromate-free chemical conversion coating layer is more than or equal to 30 degrees and less than or equal to 70 degrees.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

A surface treatment solution composition for forming an inorganic film, comprising: 10 to 30% by weight of a trivalent chromium compound containing chromium phosphate (A) and chromium nitrate (B) and satisfying a content ratio A/(A+B) of 0.3 to 0.6; 5 to 50% by weight of a silane compound; 0.2 to 3% by weight of a vanadium-based rust-inhibiting and corrosion-resisting agent; 0.5 to 5% by weight of a cobalt-based rust-inhibiting and corrosion-resisting agent; and 12 to 84.3% by weight of water, an alloyed hot-dip galvanized steel sheet surface-treated using the composition, and a method for manufacturing the alloyed hot-dip galvanized steel sheet, are provided, and the surface treatment solution composition containing the trivalent chromium compound has an excellent effect on corrosion resistance, blackening resistance, fuel resistance, weldability, and alkali resistance.