Thermogravimetric analysis, PXRD, EDX and XPS study of chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O : structural implications

Frost, Ray L., Xi, Yunfei, & Wood, Barry J. (2012) Thermogravimetric analysis, PXRD, EDX and XPS study of chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O : structural implications. Thermochimica Acta, 545, pp. 157-162.

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Abstract

Selected chrysocolla mineral samples from different origins have been studied by using PXRD, SEM, EDX and XPS. The XRD patterns show that the chrysocolla mineral samples are non-diffracting and no other phases are present in the minerals, thus showing the chrysocolla samples are pure. SEM analyses show the chrysocolla surfaces are featureless. EDX analyses enable the formulae of the chrysocolla samples to be calculated. The thermal decomposition of the mineral chrysocolla has been studied using a combination of thermogravimetric analysis and derivative thermogravimetric analysis. Five thermal decomposition mass loss steps are observed for the chrysocolla from Arizona (a) at 125 ◦C with the loss of water, (b) at 340 ◦C with the loss of hydroxyl units, (c) at 468.5 ◦C with a further loss of hydroxyls, (d) at 821 ◦C with oxygen loss and (e) at 895 ◦C with a further loss of oxygen. The thermal analysis of the chrysocolla from Congo shows mass losses at 125, 275.3, 805.6 and 877.4 ◦C and for the Nevada chrysocolla, mass loss steps at 268, 333, 463, 786.0 and 817.7 ◦C are observed. The thermal analysis of spertiniite is very different from that of chrysocolla and thermally decomposes at around 160 ◦C. XPS shows that there are two different copper species present, one which is bonded to oxygen and one to a hydroxyl unit. The O 1s is broad and very symmetrical suggesting two O species of equal number. The bond energy of 102.9 eV for the Si 2p suggests that it is in the form of a silicate. The bond energy is much higher for silicas around ∼103.5 eV. The reported value for silica gel has Si 2p at 103.4 eV. The combination of TG, PXRD, EDX and XPS adds to our fundamental knowledge of the structure of chrysocolla.

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ID Code: 58122
Item Type: Journal Article
Refereed: Yes
Keywords: Chrysocolla, Copper silicate, Spertiniite, Thermal analysis, PXRD, EDX, XPS
DOI: 10.1016/j.tca.2012.07.011
ISSN: 0040-6031
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > PHYSICAL CHEMISTRY (INCL. STRUCTURAL) (030600) > Structural Chemistry and Spectroscopy (030606)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: © 2012 Elsevier B.V. All rights reserved.
Deposited On: 13 Mar 2013 00:27
Last Modified: 13 Mar 2013 00:30

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