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- Frost, Ray L., et al.
(författare)
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Combination bands in the infrared spectroscopy of kaolins : a drift spectroscopic study
- 1998
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Ingår i: Clays and clay minerals. - 0009-8604 .- 1552-8367. ; 46:4, s. 466-477
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Tidskriftsartikel (refereegranskat)abstract
- Kaolinites with varying degrees of defect structures have been studied by both mid-infrared (IR) and near-IR diffuse reflectance spectroscopy (DRIFT). Difference bands were observed in the 2650to 2750-cm-1 region. This region coincides with the kaolinite-deuterated hydroxyl stretching region. Summation bands were observed in the near-IR spectra in the 4500- to 4650-cm-1 and in the 7050- to 7250cm-1 region. Each of the spectral regions of the summation and difference bands is both kaolin polytype and sample dependent. It is proposed that each of these sets of bands arises from the combination of the hydroxyl stretching frequencies and the hydroxyl deformation frequencies and, to a lesser extent, the silicon-oxygen symmetric stretching vibration of the siloxane layer. Additional difference bands of very low intensity were also observed at 2930 and 2856 cm-1. Combination bands were observed in all kaolinites at 2137 and 2227 cm-1. Each of the 3 major combination spectral regions was composed of 5 component bands corresponding to the 4 IR active and the 1 Raman active kaolinite hydroxyl stretching frequencies. Combination bands were also observed at ∼1932 and 1821 cm-1.
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- Frost, Ray L., et al.
(författare)
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Raman spectroscopy at temperatures between 298 and 423 K and at 77 K of kaolinites intercalated with formamide
- 1998
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Ingår i: Journal of Raman Spectroscopy. - 0377-0486 .- 1097-4555. ; 29:12, s. 1065-1069
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectra of kaolinite and of the formamide-intercalated kaolinite were obtained at both 298 and 77 K using a Raman microprobe equipped with a thermal stage. Upon cooling to 77 K, the band attributed to the inner hydroxyl shifts by 5 cm-1 to lower wavenumbers and the bands assigned to the inner surface hydroxyls move to higher wavenumbers. Upon intercalation of the kaolinite with formamide, an additional Raman band attributed to the formation of a hydrogen-bonded complex between the inner surface hydroxyls and the carbonyl group of the formamide is observed at 3627 cm-1 at 298 K and at 3631 cm-1 at 77 K. Raman spectra of the deintercalation of the formamide-intercalated kaolinite are obtained by using the thermal stage to heat the intercalated kaolinite in situ. A decrease in intensity of the bands formed through intercalation and at the same time an increase in intensity of the inner surface hydroxyl bands are observed. A loss of intensity of the low-wavenumber region of the formamide-intercalated kaolinite is also observed.
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- Johansson, U., et al.
(författare)
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Adsorption of silane coupling agents onto kaolinite surfaces
- 1999
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Ingår i: Clay minerals. - : Mineralogical Society. - 0009-8558 .- 1471-8030. ; 34:2, s. 239-246
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of the silane coupling agents N-(2-amino-ethyl)-3-aminopropyltrimethoxysilane (Z-6020), N-(2-(vinylbenzyl-amino)-ethyl)-3-amino-propyl-trimethoxysilane (Z-6032) and 3-glycidoxy-propyl-trimethoxysilane (Z-6040) onto the surface of kaolinite has been studied using the solvents water and ethanol. The adsorbed silanes were analysed using diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy and FT-Raman spectroscopy. When the silane coupling agents are dissolved in water, silanol groups are formed. Raman spectra of aqueous solutions of the silanes show that condensation of the silanols into oligomers occurred. The peak at 1000 cm(-1) assigned to Si-O-Si vibrations indicates that polymerization has occurred. A similar behaviour is observed when the silanes are dissolved in ethanol. The DRIFT spect-ra show that the silane coupling agents adsorb onto the surface of kaolinite, It is proposed that the oligomers are bonded to the kaolinite surface only by hydrogen bondings with no covalent bonds formed.
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- Johansson, Ursula, et al.
(författare)
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Isotopic exchange of kaolinite hydroxyl protons: a diffuse reflectance infrared Fourier transform spectroscopy study
- 1998
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Ingår i: The Analyst. - 0003-2654 .- 1364-5528. ; 123:4, s. 641-645
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Tidskriftsartikel (refereegranskat)abstract
- Specific surface reactions on kaolinite were investigated by deuterium exchange of the hydroxyl protons of kaolinite, The kaolinite samples were reacted with deuterium oxide for 48 h and 2.5 and 5 weeks, at various pH values (3, natural and 8) and at different temperatures (ambient, and 30, 60 and 100 degrees C), Analyses were performed using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The spectral results show that it is very difficult at room temperature to exchange the hydroxyl protons isotopically with deuterons at the surface of kaolinite, The temperature and the reaction time must be increased for successful exchange. It was found that the most suitable temperature for isotopic exchange was 60 degrees C. The pH did not significantly influence the deuteration, Only at high pH were changes of the OD bands in the DRIFT spectra observed, This study shows that it is possible to deuterate kaolinite without using intercalation. All three types of hydroxyl protons from the inner, inner surface and edge were exchanged.
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- Johansson, Ursula, et al.
(författare)
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Raman spectroscopy of the kaolinite hydroxyls at 77 K
- 1998
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 52:10, s. 1277-1282
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy of two types of kaolinites has been obtained at liquid nitrogen temperature (77 K) with the use of a Raman microprobe and a thermal stage. The Raman spectrum is characterized by the combination of the frequencies of the inner hydroxyl and the inner surface hydroxyl groups. The inner hydroxyl frequency is reduced, and the outer hydroxyl frequencies move to higher frequencies upon cooling to 77 K. The inner hydroxyl frequency shifts from 3620 cm-1 at 298 K to 3615 cm-1 at 77 K. The two in-phase inner surface hydroxyl frequencies move from 3684 and 3689 cm-1 at 298 K to 3690 and 3699 cm-1 at 77 K. The two out-of-phase vibrations shift from 3650 and 3668 cm-1 to 3656 and 3675 cm-1. The bandwidth of the inner hydroxyl frequency decreases from 3.7 to 2.1 cm-1 at 77 K. The bandwidth of the inner surface hydroxyl frequency (upsilon 1) increases upon cooling from 17.4 to 19.2 cm-1. It is proposed that the increased resolution at low temperature enabled an additional inner surface hydroxyl frequency to be observed.
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