Preece test (copper-sulphate dip) for zinc coatings

Abstract

The Preece test is in common use for inspection purposes to determine the uniformity of galvanized coatings, even though the results are sometimes erratic.An experimental study made with wires with different types of zinc coating and with wires consisting of commercially pure zinc and iron indicates that the pH value of the copper sulphate solution, the rate of solution of the zinc coating, and the cleanness of the test specimens are important factors in the Preece test. The use of cupric hydroxide instead of cupric oxide for neutralizing the copper sulphate solution is recommended, since a stable pH is much more quickly reached by its use.Electroplated and sprayed zinc coatings dissolve more rapidly in the copper sulphate solution than do hot-dipped or galvannealed coatings. Pure zinc coatings showed, during their solution, a "potential minimum" (with respect to a copper wire) which was practically absent with coatings that contain iron, such as on galvannealed wires and the inner layer of hot-dipped galvanized wires. This minimum may be caused by the delayed coagulation of basic zinc compounds which coagulation may be accelerated by the presence of iron. The causes and remedies of premature and delayed endpoints are explained. A method for measuring the thickness-distribution of the zinc coating by the use of a suitably acidified copper sulphate solution is suggested.

Corrosion-protective value of electrodeposited zinc and cadmium coatings on steel

“…The Preece test (immersion in neutral copper sulphate) is a measure of the variations in t.he thickness of zinc coatings, which is used in spite of its admitted shortcomings [15]. Many of these objections do not apply to plated coatings, which are practically pure zinc, with no layer of zinc-iron alloy.…”

INFLUÊNCIA DA VELOCIDADE DE GALVANIZAÇÃO NA MORFOLOGIA DAS CAMADAS DE Zn E Fe-Zn

“…A uniformidade da camada total de zinco formada no arame galvanizado é constantemente requerida pela indústria, principalmente nos segmentos de distribuição de energia elétrica. De acordo com Campanher [1] [2] comparam a perda de zinco em cinco diferentes tipos de material/recobrimento: Arame de zinco, Eletrodeposição, Galvanizado à fogo, Galvanizado e recozido e Spray de zinco. Em cada um dos recobrimentos foi encontrada uma taxa de perda de zinco diferente.…”

Influência Das Variáveis De Processo E Medição No Ensaio De Preece Em Arames Galvanizados (Classe B)

“…Os demais fatores não foram detalhados nesse trabalho. Groesbeck e Walkup[4] avaliaram o efeito do tipo de camada de zinco na taxa de remoção do zinco da camada durante o ensaio de preece conforme Tabela 2.No processo de Galvanização à fogo, o zinco aquecido é arrastado pelo arame e também reage com o metal base formando uma camada intermetálica denominada Fe-Zn. Vemos que neste caso, a taxa de perda de massa por imersão foi de 49 g/m², sendo menor que no processo de eletrodeposição.…”