Zincate

In chemistry the term zincate may refer to

• a salt containing Zn(OH)₄²⁻,also called the tetrahydroxozincate ion. It is an ore of Zinc. Examples include calcium zincate CaZn(OH)₄.2H₂O ^[1] or Na₂Zn(OH)₄^[2] or the polymeric anion [Zn(OH)₃⁻] in for example NaZn(OH)₃· H₂O ^[3]
• an alkali solution prepared from dissolving zinc metal, zinc hydroxide or zinc oxide which contains various anionic species such as Zn(OH)₄²⁻. Such solutions are used in the plating industry.
• an oxide containing zinc and a less electronegative element e.g. Na₂ZnO₂,^[4](see -ate complex).
• a commercially available zinc supplement formulated as zinc sulfate.

Zincate - plating processes

In industry it can refer to the alkaline solutions used in a dipping (immersion) process to plate aluminium with zinc prior to electrolytic or electroless nickel plating. This immersion process is electroless (i.e. not electroplating) and involves the displacement of zinc from zincate by aluminum:^[5]

3 Zn(OH)₄²⁻ + 2 Al → 3 Zn + 2 Al(OH)₄⁻ + 4 OH⁻

It can also refer to alkaline solutions used in electroplating of e.g. steel with zinc.^[6]

Inorganic compound nomenclature

In the naming of inorganic compounds zincate is a suffix that indicates that a polyatomic anion contains a central zinc atom. Examples include tetrachlorozincate, ZnCl₄²⁻, the tetrahydroxozincate, Zn(OH)₄²⁻ and tetranitratozincate, Zn(NO₃)₄²⁻. More recent recommendations (2005), that are not widely used, would call the first two ions tetrachloridozincate(2−) and tetrahydroxidozincate(2−) respectively.

Zincates aqueous chemistry

It is now generally accepted that the ionic species in alkali solutions of ZnO or Zn(OH)₂ contain Zn(OH)₄²⁻.^[7] Earlier Raman studies had been interpreted as indicating the existence of linear ZnO₂²⁻ ions.^[8]

References

1. Sharma, Ram A. (1986). "Physico-Chemical Properties of Calcium Zincate". Journal of the Electrochemical Society. 133 (11): 2215. doi:10.1149/1.2108376.
2. Stahl, R.; Niewa, R.; Jacobs, H. (1999). "Synthese und Kristallstruktur von Na2Zn(OH)4". Zeitschrift für anorganische und allgemeine Chemie. 625: 48. doi:10.1002/(SICI)1521-3749(199901)625:1<48::AID-ZAAC48>3.0.CO;2-L.
3. R. Stahl; H. Jacobs (1998). "Synthese und Kristallstruktur von NaZn(OH)₃· H₂O und NaZn(OH)₃". Zeitschrift für anorganische und allgemeine Chemie. 624 (1): 25–29. doi:10.1002/(SICI)1521-3749(199801)624:1<25::AID-ZAAC25>3.0.CO;2-8.
4. D. Trinschek; M. Jansen (1996). "Na₂ZnO₂, ein neues Natriumzinkat". Z. Naturforsch. 51 b: 711–4.
5. Glenn O. Mallory, Juan B. Hajdu (1990), Electroless Plating: Fundamentals and Applications, American Electroplaters and Surface Finishers Society, , William Andrew Inc., ISBN 0-936569-07-7
6. Porter, Frank C. (1991). Zinc Handbook. CRC Press. ISBN 978-0-8247-8340-2.
7. Kaumudi I. Pandya; Andrea E. Russell; J. Mc Breen; W. E. O' Grady (1995). "EXAFS Investigations of Zn(II) in Concentrated Aqueous Hydroxide Solutions". The Journal of Physical Chemistry. 99 (31): 11967. doi:10.1021/j100031a026.
8. Sharma, Shiv Kumar (1973). "Raman study of aqueous zinc oxide-alkali metal hydroxide system". The Journal of Chemical Physics. 58 (4): 1626. Bibcode:1973JChPh..58.1626S. doi:10.1063/1.1679405.