Process of determining the zinc content of phosphating baths

Details Process of determining the zinc content of phosphating baths Process of determining the zinc content of phosphating baths

1988-04-06

1990-01-30

Kaplan, G. L.

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

148262, 204 1T, 204405, 436 81, C23F 708

Patent

active

048971286

ABSTRACT:
Described is a process for determining the zinc content of an acid aqueous phosphating bath. A bath sample is titrated at a pH value between 1.2 and 1.7 in the presence of ethylenediaminetetraacetic acid, hexamethylenetetramine and alkalihexacyanoferrate (III) with an alkalihexacyanoferrate(II) until the potential at an oxidation-reduction electrode immersed into the bath sample reaches an inflection point.
Any content of nitrite and/or iron(II) ions must be removed by an addition of nitrite-destroying substances and by an oxidation to iron(III) ions at a pH value above 8.
The process is particularly suitable for determining the zinc concentration of phosphating baths which contain 0.4 to 2.0 g/l Zn. The presence in phosphating baths of additional cations such as manganese and/or calcium and/or nickel and/or magnesium does not interfere with the process. The analysis can be automatic and may directly be used to control a metering device for supplying make-up concentrates to the phosphating bath.

REFERENCES:
patent: 3479152 (1969-11-01), Overbeck et al.
patent: 4597806 (1986-07-01), Hauffe
"On-line-Titratoren for die Prozessanalytik vor Ort", Dipl.-Ing. F. Muller, Chemie-Technik, 15, Jahrgang (1986) Nr. 9, pp. 139-141.
Phosphating and Metal Pre-treatment, D. B. Freeman, Woodhead-Faulkner Cambridge in association with Pyrene Chemical Services Ltd., pp. 143 & 144, (1986).

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