1,721,147 research outputs found
The vibrational spectroscopy of minerals
No full textThis thesis focuses on the vibrational spectroscopy of the aragonite and\ud
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vivianite arsenate minerals (erythrite, annabergite and hörnesite), specifically the\ud
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assignment of the spectra. The infrared and Raman spectra of cerussite have been\ud
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assigned according to the vibrational symmetry species. The assignment of satellite\ud
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bands to 18O isotopes has been discussed with respect to the use of these bands to the\ud
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quantification of the isotopes. Overtone and combination bands have been assigned\ud
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according to symmetry species and their corresponding fundamental vibrations. The\ud
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vibrational spectra of cerussite have been compared with other aragonite group\ud
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minerals and the differences explained on the basis of differing chemistry and crystal\ud
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structures of these minerals.\ud
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The single crystal spectra of natural erythrite has been reported and compared\ud
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with the synthetic equivalent. The symmetry species of the vibrations have been\ud
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assigned according to single crystal and factor group considerations. Deuteration\ud
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experiments have allowed the assignment of water vibrational freque ncies to discrete\ud
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water molecules in the crystal structure. Differences in the spectra of other vivianite\ud
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arsenates, namely annabergite and hörnesite, have been explained by consideration of\ud
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their differing chemistry and crystal structures.\ud
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A novel approach to the assignment of site occupancy of ions in the erythrite -\ud
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annabergite solid solution has been reported. This approach has utilised vibrational\ud
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spectroscopy, in conjunction with careful consideration of the crystal structures of the\ud
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minerals. It has been shown that in the erythrite - annabergite solid solution Coprefers metal site 2 contrasting nickel which prefers site 1. This study in conjunction\ud
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with other studies has yielded the trend that the more electronegative metal prefers to\ud
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occupy site 1, with the least electronegative metal preferring to occupy site 2.\ud
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Fundamentally this thesis has increased the knowledge base of the\ud
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spectroscopic properties of the aragonite and the vivianite minerals. The site\ud
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occupancy of metal ion substitutions in solid solution series of the vivianite group of\ud
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minerals has been further enhanced, with novel method of studying the site occupancy\ud
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of ions in solid solutions has been developed. A detailed knowledge and\ud
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understanding of factor group analysis applied to the study of minerals has been\ud
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achieved
A Raman and infrared spectroscopic study of the uranyl silicates-weeksite, soddyite and haiweeite
No full textRaman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including weeksite K2\[(UO2)2(Si5O13)].H2O, soddyite \[(UO2)2SiO4.2H2O] and haiweeite Ca\[(UO2)2(Si5O12(OH)2](H2O)3 with UO22+/SiO2 molar ratio 2:1 or 2:5 .Raman spectra clearly show well resolved bands in the 750 to 800 cm-1 region and in the 950 to 1000 cm-1 region assigned to the ν1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example soddyite is characterised by Raman bands at 828.0, 808.6, 801.8 cm-1 (UO2)2+ (￮1), 909.6 and 898.0 cm-1 (UO2)2+ (￮3), 268.2 cm-1 and 257.8 and 246.9 cm-1are assigned to the ￮2 (￤) (UO2)2+. Coincidences of the ￮1 (UO2)2+ and the ￮1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1, 966.3 cm-1 are attributed to the ￮3 (SiO4)4-.Sets of Raman bands in the 200 to 300 cm-1 region are assigned to ν2 δ (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of ν2 δ (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470 to 550 cm-1 and in the 390 to 420 cm-1 region. These bands are attributed to the ν4 and ν2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900 to 3500 cm-1 and 3600 to 3700 cm-1
Raman spectroscopy of synthetic erythrite, partially dehydrated erythrite and hydrothermally synthesized dehydrated erythrite
No full textThe Raman spectra of the mono, di and octa (commonly known as the mineral erythrite) hydrates of cobalt(II) arsenate synthesized using hydrothermal techniques were obtained. The hydrates can be distinguished by their water hydroxyl stretching bands. Splitting of the AsO stretching vibrations is observed in the 77 K spectrum. The band at 852 cm−1 is assigned to the ν1 symmetric stretching vibration and the band at 790 cm−1 to the ν3 antisymmetric stretching vibration. The low-wavenumber region was used to identify bands attributable to the ν4 and ν2 modes
Using Raman spectroscopy to identify mixite minerals
No full textRaman spectroscopy has been used to identify whether or not a selection of minerals labelled as mixites (formula BiCu6(AsO4)3(OH)6.3H2O) are correctly marked. Of the four samples, two samples are shown to be potentially mixites because of the presence of the characteristic Raman spectra of (AsO4)3- units and (HAsO4)- units, characterised by bands at around 803 and 833 cm-1. Two of the minerals are shown to be predominantly carbonates. Bands are observed at 3473.9 and 3470.3 \ud
cm-1 for the two mixite samples. Bands observed in the region 880 to 910 cm-1 and in the 867 to 870 cm-1 region are assigned to the AsO stretching vibrations of (HAsO4)2- and (H2AsO4)- units. Whilst bands at around 803 and 833 cm-1 are assigned to the stretching vibrations of uncomplexed (AsO4)3- units. Intense bands are observed at 473.7 and 475.4 cm-1 are assigned to the ν4 bending mode of AsO4 units. Bands observed at around 386.5, 395.3 and 423.1 cm-1 are assigned to the ν2 bending modes of the HAsO4 (434 and 400 cm-1) and the AsO4 groups (324 cm-1). Raman spectroscopy lends itself to the identification of minerals on host matrices and is especially useful for the identification of mixites
Modification of Kaolinite Surfaces through Intercalation with Deuterated Dimethylsulfoxide
No full textThe surfaces of kaolinite have been modified through intercalation with deuterated dimethylsulfoxide (d-DMSO). X-ray diffraction shows the kaolinite to be expanded from 7.2 to 11.19 Å. Modification of the surface has been explored through (a) changes to the hydroxyl surfaces of the kaolinite and (b) through changes to the d-dimethylsulfoxide inserting molecule. Upon intercalation of the kaolinite with d-DMSO, additional infrared bands at 3660, 3538, and 3502 cm-1 and additional Raman bands at 3660, 3537, 3507, and 3480 cm-1 are observed. The first band at 3660 cm-1 is attributed to the inner-surface hydroxyls hydrogen bonded to the d-DMSO and the other bands to water hydroxyl-stretching modes. Both infrared and Raman spectroscopy shows that significant changes in the molecular structure of the d-DMSO occur upon intercalation. First, the CD stretching modes observed for d-DMSO at 2125 and 2249 cm-1 in the DRIFT spectrum lose the degeneracy and split into 2140 and 2127 cm-1 and 2267, 2250, and 2238 cm-1. The Raman spectrum shows this loss of degeneracy through the bands observed at 2272, 2267, 2263, and 2251 cm-1 for the antisymmetric CD stretching vibration and at 2129 and 2141 cm-1 for the symmetric stretching vibrations. Upon intercalation with d-DMSO, the S=O stretching region shows bands at 1066, 1023, and 1010 cm-1. The 1066 cm-1 band is assigned to the free monomeric S=O group and the 1023 and 1010 cm-1 bands to two different polymeric S=O groups. Bands attributed to the CS stretching vibrations, the in-plane and out-of-plane S=O bending and the CSC symmetric bends all move to higher frequencies upon intercalation with d-DMSO. It is proposed that intercalation depends on the presence of water and that the additional bands at 3536 and 3501 cm-1 are due to the presence of water. The precise positions of the hydroxyl stretching modes of water at these positions suggest that water is in a well-defined position within the intercalation structure
Absorption of the selenite anion from aqueous solutions by thermally activated layered double hydroxide
No full textThe presence of selenite or selenate in potable water is a health hazard especially when consumed over a long period of time. Its removal from potable water is of importance. This paper reports technology for the removal of selenite from water through the use of thermally activated layered double hydroxides.\ud
Mg/Al hydrotalcites with selenite in the interlayer were prepared at different times from 0.5 to 20 hours through ion exchange. X-ray diffraction of the MgAlSeO3 hydrotalcites indicates that the selenite anion entered the interlayer spacing of Mg/Al hydrotalcite and MgAlSeO3 hydrotalcite was formed. Raman spectra proved the presence of selenite anion in the hydrotalcite interlayer as the counter anion. The band intensity and width of MgAlSeO3 hydrotalcite in the region of 3800 to 3000 cm-1 increases with the adsorption of selenite by the Mg/Al hydrotalcite. The characteristic bands of free selenite anions in the MgAlSeO3 hydrotalcites are located between the region between 850 and 800 cm-1. The Raman spectra of the lower wavenumber region of 550 to 500 cm-1 show a shift toward higher wavenumbers with adsorption of the selenite. Thermally activated LDHs provide a mechanism for removing selenite anions from aqueous solutions. \u
Characterisation of conichalcite by SEM, FTIR, Raman and electronic reflectance spectroscopy
No full textThe mineral conichalcite from Bagdad mine- West of, Bagdad, Eureka District, Yavapai Co., Arizona, USA has been characterised by electronic, Near-IR, Raman and infrared spectroscopy. SEM micrographs show the mineral consists of bundles of fibres. Calculations of the EDX analyses on the stoichiometric basis show the substitution of arsenate by 12 wt % of phosphate in the mineral. Raman and infrared bands are assigned in terms of the fundamental modes of AsO43- and PO43- molecules and are related to the mineral structure. Near-IR reflectance spectroscopy shows the presence of adsorbed water and hydroxyl units in the mineral. The Cu(II) coordination polyhedron in conichalcite can have at best pseudo-tetragonal geometry. The crystal field and tetragonal field parameters of Cu(II) complex were calculated and found to agree well with the values reported for known tetragonal distortion octahedral complexes
Thermal analysis of halotrichites
Full text linkFour halotrichites from different origins were analysed by thermogravimetric and differential thermogravimetric analysis. The halotrichites were analysed by powder X-ray diffraction and were phase pure. The chemical composition was analysed using EDX techniques. The formula of the halotrichite minerals were determined as halotrichite (Fe0.752+,Mg0.25)SO4.Al2(SO4)3.22H2O,apjohnite (Mn0.642+,Mg0.28,Zn0.08)SO4.Al2(SO4)3.22H2O, pickeringite (Fe0.222+,Mg0.78)SO4.Al2(SO4)3.22H2O, wupatkiite as (Co0.45,Fe0.552+)SO4.Al2(SO4)3.22H2O. Three low temperature decomposition steps a) between 0 and 44°C, 50 and 76°C, 72 and 88°C were attributed to dehydration. An additional dehydration step at around 317 to 330°C was confirmed by in-situ mass spectrometry. The higher temperature decomposition steps between 516 and 738°C are attributed to the decomposition of sulphate to sulphur dioxide and oxygen as confirmed by mass spectrometry. A comparison of the thermal decomposition of jarosites is made
Synthetic deuterated erythrite-a vibrational spectroscopic study
No full textA comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm. The band at 3442 cm is attributed to weakly hydrogen bonded water and the band at 3039 cm to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm. The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm. Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm and new bands are observed at 692, 648 and 617 cm. These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers
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