C - Chemistry – Metallurgy – 23 – C
Patent
C - Chemistry, Metallurgy
23
C
C23C 22/38 (2006.01)
Patent
CA 2066026
The resistance of chromated zinc surfaced steel objects, particularly plates and sheets, to extraction of hexavalent chromium by alkaline degreasing solutions used on the chromated objects, can be substantially increased by utilizing an aqueous acidic liquid chromating composition containing (A) about 9.6 to about 96 g/L, expressed as its stoichiometric equivalent as chromic acid, of total chromium; (B) about 2 to about 35 g/L of trivalent chromium ions; (C) about 1 to about 128 g/L of phosphate ions; and (D) about 0.3 to about 4 g/L of fluorozirconate ions, with the chromium ratio in the aqueous acidic liquid composition being about 0.41 to about 0.70, the chromic acid/fluorozirconate weight ratio being about 10 to about 40, and the PO4/Cr +3 ratio being greater than about 0.03, greater than or equal to about {(9.2)(the chromium ratio)- 4.0}, and less than or equal to about {(9.2)(the chromium ratio) -1.2}. The corrosion resistance of the coatings formed can be further improved if the chromating composition also contains about 0.1 to about 200 g/L of dispersed silica.
La résistance d'articles - notamment plaques et tôles - en acier avec surface de zinc chromaté, à l'extraction du chrome hexavalent par les solutions alcalines de dégraissage appliquées sur les objets chromés, peut être sensiblement améliorée à l'aide d'une composition acide aqueuse de chromatation, renfermant : A) 96 g/L de chrome total, exprimé sous la forme de son équivalent stoechiométrique en acide chromique; B) environ 2 à 35 g/L d'ions chrome trivalent ; C) environ 1 à 128 g/L d'ions phosphate; D) environ 0,3 à 4 g/L d'ions fluorozirconate; le taux de chrome (chrome trivalent/chrome total) dans la composition aqueuse acide est d'environ 0,41 à 0,70, le rapport massique acide chromique/fluorozirconate est d'environ 10 à 40, et le rapport PO4/Cr+3 est supérieur à 0,03, supérieur ou égal à environ ¢(9,2)(taux de chrome) - 4,0!, et inférieur ou égal à environ ¢(9,2)(taux de chrome) - 1,2!. La résistance des revêtements à la corrosion se trouve encore davantage améliorée si la composition de chromatation renferme également environ 0,1 à 200 g/L de silice dispersée.
Saeki Kenshi
Yoshitake Noriaki
Fetherstonhaugh & Co.
Henkel Corporation
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