Disclosed is a system for maintaining a pretreatment bath containing a pretreatment comprising a Group IVB metal. The system comprises an aqueous reducing agent comprising a metal cation and a latent source of sulfate which, upon reaction with a contaminant in the pretreatment bath, forms a metal sulfate. The contaminant comprises a nitrite source. The metal sulfate salt has a pKsp of 4.5 to 11 at a temperature of 25° C. Also disclosed is a method for maintaining a pretreatment bath containing a pretreatment composition comprising a Group IVB metal. The method comprises supplying the reducing agent to the pretreatment bath in an amount sufficient to reduce a pollution ratio of the pretreatment bath to less than 1:1. Also disclosed are substrates with a pretreatment bath maintained according to the system and method.

Disclosed is a stainless steel for a fuel cell separator, more specifically, a stainless steel for a fuel cell separator having a low contact resistance. According to an embodiment of the stainless steel for a fuel cell separator disclosed herein, an arithmetic mean summit curvature Ssc of the surface defined according to the ISO 25178 standard is at least 6.0 μm.sup.−1, a root mean square surface slope Sdq is at least 23, and a contact resistance is at most 10 mΩ.Math.cm.sup.2.

A method for producing a diaphragm for an ultrasonic sensor. In the method, a diaphragm body made of metal material is first provided. Next, an external surface region of the diaphragm body is degreased. The external surface region of the diaphragm body is then pickled. To pre-activate the subsequently applied second passivation layer, a first passivation layer is also deposited on the external surface region as a first layer.

A method for producing a diaphragm for an ultrasonic sensor. In the method, a diaphragm body made of metal material is first provided. Next, an external surface region of the diaphragm body is degreased. The external surface region of the diaphragm body is then pickled. To pre-activate the subsequently applied second passivation layer, a first passivation layer is also deposited on the external surface region as a first layer.

Provided is a method of performing pre-paint treatment of an automobile body including a high-tensile steel sheet, in which desirable corrosion resistance can be obtained after painting. A method of performing pre-paint treatment of an automobile body, the method including performing an alkaline degreasing step, a first water-washing step, a chemical conversion treatment step, a second water-washing step, and a cationic electrodeposition painting step, in this order, wherein the chemical conversion treatment step is performed using an chemical conversion treatment agent including zirconium (A), free fluorine ions (B), an allylamine-diallylamine copolymer (C), aluminum ions (D), nitrate ions (E) each at a predetermined concentration; the allylamine-diallylamine copolymer (C) forms an acid addition salt having an anionic counter ion, and the pKa of an acid thereof falls within the range of −3.7 to 4.8; and the content percentage of diallylamine is 80 mol % or more and 98 mol % or less.

Provided is a method of performing pre-paint treatment of an automobile body including a high-tensile steel sheet, in which desirable corrosion resistance can be obtained after painting. A method of performing pre-paint treatment of an automobile body, the method including performing an alkaline degreasing step, a first water-washing step, a chemical conversion treatment step, a second water-washing step, and a cationic electrodeposition painting step, in this order, wherein the chemical conversion treatment step is performed using an chemical conversion treatment agent including zirconium (A), free fluorine ions (B), an allylamine-diallylamine copolymer (C), aluminum ions (D), nitrate ions (E) each at a predetermined concentration; the allylamine-diallylamine copolymer (C) forms an acid addition salt having an anionic counter ion, and the pKa of an acid thereof falls within the range of −3.7 to 4.8; and the content percentage of diallylamine is 80 mol % or more and 98 mol % or less.

The invention relates to use of an adhesion promoting organic compound comprising at least one tertiary amine group, bonded via a bridge-constituting divalent radical, with the carbonyl carbon atom of an amide group, wherein the bridge-constituting divalent radical comprises two carbon atoms as bridge atoms, for anticorrosion pretreatment of metallic materials before painting and to aqueous compositions containing the adhesion promoting organic compound which generate conversion layers based on the elements Zr, Ti and/or Si. The present invention further comprises a process for anticorrosion coating of components at least partly manufactured from metallic materials comprising a pretreatment using acidic aqueous compositions according to the invention and subsequent painting. In a further aspect, the invention relates to a metallic substrate having a mixed organic/inorganic coating consisting of oxides, hydroxides and/or oxyfluorides of the elements Zr, Ti and/or Si and of the adhesion promoting organic compounds.

The invention relates to use of an adhesion promoting organic compound comprising at least one tertiary amine group, bonded via a bridge-constituting divalent radical, with the carbonyl carbon atom of an amide group, wherein the bridge-constituting divalent radical comprises two carbon atoms as bridge atoms, for anticorrosion pretreatment of metallic materials before painting and to aqueous compositions containing the adhesion promoting organic compound which generate conversion layers based on the elements Zr, Ti and/or Si. The present invention further comprises a process for anticorrosion coating of components at least partly manufactured from metallic materials comprising a pretreatment using acidic aqueous compositions according to the invention and subsequent painting. In a further aspect, the invention relates to a metallic substrate having a mixed organic/inorganic coating consisting of oxides, hydroxides and/or oxyfluorides of the elements Zr, Ti and/or Si and of the adhesion promoting organic compounds.

Disclosed is a composite coating for eliminating pollution by chromium and VOCs from a source, the coating comprising a conversion film layer and a coating surface layer. The conversion film layer is made of a surface pretreatment liquid, and the surface pretreatment liquid comprises the following components: an organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof, or a hydrate thereof; an ionic compound B containing zirconium and/or titanium and fluorine; a mixed solution C containing manganese fluoride; and an inorganic salt D containing potassium ions or sodium ions. The coating surface layer is an FEVE-type fluorocarbon powder coating layer. Also disclosed is a preparation method for the described composite coating.

Disclosed is a composite coating for eliminating pollution by chromium and VOCs from a source, the coating comprising a conversion film layer and a coating surface layer. The conversion film layer is made of a surface pretreatment liquid, and the surface pretreatment liquid comprises the following components: an organic compound A having an aromatic ring and at least two phenolic hydroxyl groups in the molecule thereof, or a hydrate thereof; an ionic compound B containing zirconium and/or titanium and fluorine; a mixed solution C containing manganese fluoride; and an inorganic salt D containing potassium ions or sodium ions. The coating surface layer is an FEVE-type fluorocarbon powder coating layer. Also disclosed is a preparation method for the described composite coating.