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Studies of selected minerals, mineral surfaces and their colloidal dispersions
No full textThis thesis is about the molecular structure of minerals, their surface modification and the dispersion of selected minerals of a ceramic nature as sols and gels. The\ud
theme that permeates through this work and connects the different elements of the work is the search for fundamental knowledge and understanding of mineral structure\ud
and mineral surface structure. The underlying principal is that of molecular structure of surfaces and the changes in that molecular structure through modification of the\ud
surfaces.\ud
\ud
There are seven research divisions of study reported in this thesis:\ud
(A) Molecular structure and spectroscopy ofkaolinite\ud
(B) Molecular surface structure modified through intercalation with polar\ud
molecules\ud
(C) Molecular surface structure modified through intercalation with potassium and\ud
cesium acetates\ud
(D) Structure and spectroscopy of alumina phases and colloids\ud
(E) Structure and spectroscopy of titania and zirconia colloids\ud
(F) Synthesis, characterisation and spectroscopy of double layered hydroxides\ud
(hydrotalcites)\ud
(G) Spectroscopic and molecular structural studies of selected minerals of interes
Raman microscopy of selected chromate minerals
No full textA series of related chromate bearing minerals including crocoite,\ud
phoenicocroite, hemihedrite, iranite, macquartite, fornacite and vauquelinite have\ud
been analysed by Raman microscopy. These minerals are closely related and often\ud
have related paragenesis. Raman microscopy enables the selection of individual\ud
crystals of these minerals for Raman spectroscopic analysis. This is of importance as\ud
often the crystals are found adjacent to each other in the same matrix through\ud
paragenetic relationships. The Raman spectrum of crocoite shows three bands in the\ud
CrO4 stretching region at 856, 841 and 825 cm-1, phoenicocroite at 856, 848, 839 and\ud
826 cm-1, hemihedrite at 847, 837 and 824 cm-1, iranite bands at 865, 846 and 818\ud
cm-1, macquartite at 857, 840 and 814 cm-1. The Raman spectra of fornacite and\ud
vauquelinite are complicated by the presence or AsO4 and PO4 units in the structure\ud
and often the spectra are broad and vary with chemical composition. A comparison of\ud
the spectra of these minerals is made with that of the hexavalent chromate mineral\ud
edoylerite. Raman microscopy is a powerful and underutilized technique in terms of\ud
mineralogy for the study of closely related minerals such as these chromate minerals
Raman microscopy study of tyrolite : a multi-anion arsenate mineral
No full textThe Raman spectrum of tyrolite, CaCu5(AsO4)2(CO3)(OH) 4.6H2O, from Brixlegg, Tyrol, Austria, is reported. Comparison with copper hydroxy-arsenate and basic carbonates was used to achieve assignments of the observed bands. The AsO43- group is characterized by two υ4 modes around 433 and 480 cm-1 plus a broad band around 840 cm-1 as the υ overlapping with the υ. The υ3 mode is observed as a single band around 355 cm -1. The CO32- υ1 mode is observed around 1035 and 1088 cm-1, although this assignment is difficult because of the in-plane OH bending vibrations at similar frequencies. Two υ4 modes are assigned to the 717 and 755 cm-1 bands. The υ3 mode is present as three bands at 1431, 1463, and 1498 cm-1. A large split caused by bridging carbonates may explain the band at 1370 cm -1. The H2O bending region shows two bands at 1635 and 1667 cm-1 together with stretching modes around 3204 and 3303 cm-1, the first associated with adsorbed H2O, while the second indicates more strongly bonded H2O. Three bands around 3534, 3438, and 3379 cm -1 are assigned to OH stretching modes of the OH groups in the crystal structure. The 202, 262, 301, 524, and 534 cm-1 bands are assigned to Cu-OH bending and stretching modes, whereas the bands around 179, 202, and 217 cm-1 are ascribed to O-(Ca, Cu)-O(H) with the O(H) at much greater distance from the cation. The bands around 503, 570, and 598 cm-1 are ascribed to the Cu-O stretching modes
Raman and infrared spectroscopy of arsenates of the roselite and fairfieldite mineral subgroups
No full textRaman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of the roselite arsenate minerals of the roselite and fairfieldite subgroups of formula Ca2B(AsO4)2.2H2O (where B may be Co, Fe2+, Mg, Mn, Ni, Zn). The Raman arsenate (AsO4)2- stretching region shows strong differences between the roselite arsenate minerals which is attributed to the cation substitution for calcium in the structure. In the infrared spectra complexity exists with multiple (AsO4)2- antisymmetric stretching vibrations observed, indicating a reduction of the tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong Raman bands around 450 cm-1 are assigned to ν4 bending modes. Multiple bands in the 300 to 350 cm-1 region assigned to ν2 bending modes provide evidence of symmetry reduction of the arsenate anion. Three broad bands for roselite are found at 3450, 3208 and 3042 cm-1 and are assigned to OH stretching bands. By using a Libowitzky empirical equation hydrogen bond distances of 2.75 and 2.67 Å are estimated. Vibrational spectra enable the molecular structure of the roselite minerals to be determined and whilst similarities exist in the spectral patterns, sufficient differences exist to be able to determine the identification of the minerals
Characterisation of bauxite and seawater neutralised bauxite residue using XRD and vibrational spectroscopic techniques
No full textRaman spectroscopy of natural oxalates
No full textOxalates are markers or indicators of environmental events. Oxalates are readily determined by Raman spectroscopy. Thus deterioration of works of art, biogeochemical cycles, plant metal complexation, the presence of pigments and minerals formed in caves can be analysed. A comparative study of a suite of natural oxalates including weddellite, whewellite, moolooite, humboldtine, glushinskite, natroxalate and oxammite has been undertaken using Raman spectroscopy. The minerals are characterised by the wavenumber of the CO stretching vibration which is cation sensitive. The band is observed at 1468 cm-1 for weddellite, 1489 cm-1 for moolooite, 1471 cm-1 for glushinskite and 1456 cm-1 for natroxalate. Except for oxammite, the infrared and Raman spectra are mutually exclusive indicating that the minerals are bidentate. Differences are also observed in the wavenumber of the water OH stretching bands of the minerals. The significance of this work rests with the ability of Raman spectroscopy to identify oxalates which often occur as films on a host rocks or works of art
An infrared and Raman spectroscopic study of the uranyl micas
No full textVibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or ½(HAl) and X is As, or P. Included in these minerals are autunite, metautunite, torbernite, metatorbernite, metazeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm-1, attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation
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