Zinc molybdate
| Zinc molybdate[1] | ||
|---|---|---|
| Identifiers | ||
| CAS number | 13767-32-3  | |
| PubChem | 16213780 | |
| Properties | ||
| Molecular formula | ZnMoO4 | |
| Molar mass | 225.33 g/mol | |
| Appearance | white tetragonal crystals | |
| Density | 4.3 g/cm³, solid | |
| Melting point | 900°C | |
| Solubility in water | insoluble | |
| Structure | ||
| Crystal structure | tetragonal | |
| Hazards | ||
| EU classification | not listed | |
| NFPA 704 |
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(verify) (what is: / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa) | ||
| Infobox references | ||
Zinc molybdate (ZnMoO4) is an inorganic material found in nature with two different types of crystalline phases: α-triclinic and β-monoclinic. In the α-ZnMoO4 triclinic structure, all zinc (Zn) atoms are bonded to six oxygen (O) atoms, forming the distorted octahedral [ZnO6] clusters. The molybdenum (Mo) atoms are coordinated to four O atoms, resulting in the tetrahedral [MoO4] clusters [1,2]. On the other hand, the β-ZnMoO4 monoclinic structure has both Zn and Mo atoms bonded to six O atoms, which promote the origin of distorted octahedral [ZnO6]/[MoO6] clusters, respectively [3]. Moreover, ZnMoO4 is an inorganic chemical compound. It is white to light-gray in color, which can be used as a corrosion inhibitor in paints and adhesives. While highly soluble molybdates (e.g. sodium molybdate) are toxic in high doses, zinc molybdate is essentially non-toxic because of its insolubility in water. Molybdates possess a lower toxicity than chromates or lead salts and are therefore seen as an interesting alternative to these salts for corrosion inhibition. One of the most common methods used to synthesize zinc molybdate is by mixing aqueous solutions of sodium molybdate and zinc chloride: the insoluble zinc molybdate will crystallize from this mixture. A less common procedure used is blending solid molybdenum trioxide powder with zinc oxide powder and then heating the mixture to above 600°C.
Fourier-transform Raman/infrared spectroscopies: Theoretical and experimental analyses of β-ZnMoO4 crystals
According to the group theory calculations and symmetry [4], β-ZnMoO4 crystals with a wolframite-type monoclinic structure present 3N = 36 degrees of freedom. Therefore, there are N = 12 atoms within the unit monoclinic cell. In case, β-ZnMoO4 crystals have 36 distinct vibrational modes (Raman and infrared) as indicated in Eq. (1) [5]:
Γ(Raman + Infrared) = 8Ag + 10Bg + 8Au + 10Bu........................(1)
where the Ag and Bg are Raman-active modes, and Au and Bu are active vibrational modes in the infrared spectrum; the A and B modes are nondegenerate. The terms ‘‘g and u’’ subscripts indicate the parity under inversion in centrosymmetric β-ZnMoO4 crystals. Therefore, only 18 active vibrational modes are expected in Raman spectra of b-ZnMoO4 crystals as represented by Eq. (2) below:
Γ(Raman + Infrared) = 8Ag + 10Bg.....................................(2)
(ZnMoO4)
References
[1] S.C. Abrahams, J. Chem. Phys. 46 (1967) 2052–2063.
[2] W. Reichelt, T. Weber, T. Söhnel, S. Däbritz, Z. Anorg. Allg. Chem. 626 (2000) 2020–2027.
[3] K. Pavani, A. Ramanan, Eur. J. Inorg. Chem. 2005 (2005) 3080–3087.
[4] L.S. Cavalcante, J.C. Sczancoski, M. Siu Li, E. Longo, J.A. Varela, Colloids and Surf. A. 396 (2012) 346–351.
[5] L.S. Cavalcante, E. Moraes, M.A.P. Almeida, C.J. Dalmaschio, N.C. Batista, J.A. Varela, E. Longo, M. Siu Li, J. Andrés, A. Beltrán, Polyhedron 54 (2013) 13–25.
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