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A process known as the Cronak process is used to create zinc chromate for use in industry. This process is done by putting zinc or a zinc plated metal in a solution of sodium dichromate and sulfuric acid for a few seconds. [6] Zinc chromate can also be synthesized by using neutral potassium chromate (K 2 CrO 4) and zinc sulfate (ZnSO 4), which ...
The Cronak process is a conventional chromate conversion coating process developed in 1933 by The New Jersey Zinc Company. [1] It involves immersing a zinc or zinc-plated article for 5 to 15 seconds in a chromate solution, typically prepared from sodium dichromate and sulfuric acid. [2]
The chromate coating acts as paint does, protecting the zinc from white corrosion, thus making the part considerably more durable, depending on the chromate layer's thickness. [8] [9] [10] The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black.
There are many variations to this process, depending on the type of substrate being plated. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric, and sulfuric acids. Ferric chloride is also popular for the etching of nimonic alloys. Sometimes the component enters the chrome plating vat while electrically live.
Aluminium chromate conversion coatings are amorphous in structure with a gel-like composition hydrated with water. [18] Chromate conversion is a common way of passivating not only aluminium, but also zinc, cadmium, copper, silver, magnesium, and tin alloys. Anodizing is an electrolytic process that forms a thicker oxide layer.
The process steps can typically involve chromate conversion coating the entire component, followed by a masking of the surface in areas where the chromate coating must remain intact. Beyond that, the chromate coating is then dissolved in unmasked areas. The component can then be anodized, with anodizing taking to the unmasked areas.
Galvanization (also spelled galvanisation) [1] is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are coated by submerging them in a bath of hot, molten zinc. [citation needed]
The process takes advantage of the low solubility of phosphates at medium or high pH. The bath is a solution of phosphoric acid (H 3 PO 4), containing the desired iron, zinc or manganese cations and other additives. [10] The acid reacts with the iron metal producing hydrogen and iron cations: Fe + 2 H 3 O + → Fe 2+ + H 2 + 2 H 2 O