1,720,972 research outputs found
The morphology and structure of intercalated and pillared clays
No full textThis thesis is submitted in a format of published papers by the candidate. Advanced methods of electron microscopy and X-ray spectroscopy have been used to study the relationship between the pillars and the silicate structure ranging from Al13 and Ga13 complexes to the final products Al- and Ga-pillared clays. The Al13 and Ga13 pillared montmorillonites have been prepared by conventional and ultrasonic methods. The ultrasonic method has been proven to be effective and showed very good catalytically activity. Transmission electron microscopy combined with elemental mapping by EDS showed the distribution of the Ga and Al pillars in the clay structure. The use of gallium allowed the independent observation of the Ga pillar distribution from the Al distribution in the clay structure.\ud
XPS spectra of the Ga13 pillared montmorillonites showed that the pillars has been changed from the original Keggin structure with a 7+ charge to something more stable with a lower charge upon intercalation. No direct evidence of the inverted silicon tetrahedron structure bonding to the pillar structure, as suggested by Plee in his original thesis, was observed. For comparative reasons the major aluminium hydroxide minerals in bauxite (gibbsite, bayerite and (pseudo-) boehmite) were studied. \ud
Detailed information about the Al13 structure was obtained by studying the basic sulphate and nitrate salts with XPS. The XPS results of a set of starting clays in comparison to the pillared clays indicated that small changes in the binding energy could explain the changes in the pillar structure and the formation of chemical bonds to the clay tetrahedral sheets during the calcination leading to the final products
Raman microscopy of selected tungstate minerals
No full textA series of tungstate bearing minerals including scheelite, stolzite ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analysed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The ￮1(Ag) band is observed at 909 cm-1 and although the corresponding ￮1(Bu) vibration should be inactive a minor band is observed around 894 cm-1. The bands at 790 and 881 cm-1 are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695 cm-1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The ￮4(Eg) band was absent for scheelite. The bands at 353 and 401 cm-1 are assigned as either deformation modes or as r(Bg) and ￤(Ag) modes of terminal WO2. The band at \ud
462 cm-1 has an equivalent band in the infrared at 455 cm-1 assigned as ￤as(Au) of the (W2O4)n chain. The band at 508 cm-1 is assigned as ￮sym(Bg) of the (W2O4)n chain
Identification of mixite minerals – an SEM and Raman spectroscopic analysis
No full textTwo mixites from Boss Tweed Mine, Tintic District, Juab Vounty, Utah and Tin Stope, Majuba Hill, Pershing Co., Nevada have been analysed by SEM with EDX analysis and by Raman spectroscopy. The SEM images show the mixite crystals to be elongated fibres up to 200 μm in length and 2 μm in width. Detailed images of the mixite crystals show the mineral to be composed of bundles of fibres The EDX analyses depend on the crystal studied, however the Majuba mixite gave analyses which matched the formula BiCu6(AsO4)3(OH)6.3H2O). Raman 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 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 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
XPS study of basic aluminum sulphate and basic aluminium nitrate
No full textBasic aluminium sulphate and nitrate crystals were prepared by forced hydrolysis of aluminium salt solution followed by precipitation with a sulphate solution or by evaporation for the basic aluminium nitrate. X-ray Photoelectron Spectroscopy (XPS) confirms the chemical composition determined by ICP-AES in earlier work. High resolution XPS scans of the individual elements allow the identification of both the central (AlO4)-Al-IV group and the 12 aluminium octahedra in the [IVAlO4AlVI(OH)(24)(H2O)(12)] building unit by two Al 2p transitions with binding energies of 73.7 and 74.2 eV in both the basic aluminium sulphate and nitrate. Four different types of oxygen atoms were identified in the basic aluminium sulphate associated with the central AlO4, OH, H2O and SO4 groups in the crystal structure with transitions at 529.4, 530.1, 530.7 and 531.8 eV, respectively. (c) 2005 Elsevier B.V. All rights reserved
A review of the synthesis and characterization of pillared clays and related porous materials for cracking of vegetable oil to produce biofuels
No full textThis paper presents an overview of the modification of clay minerals by propping apart the clay layers with an inorganic complex. This expanded material is converted into a permanent two-dimensional structure, known as pillared clay or shortly <i>PILC</i>, by thermal treatment. The resulting material exhibits a two-dimensional porous structure with acidic properties comparable to that of zeolites. Synthetic as well as natural smectites serve as precursors for the synthesis of <i>Al, Zr, Ti, Fe, Cr, Ga, V, Si</i> and other pillared clays as well as mixed <i>Fe/Al, Ga/Al, Si/Al, Zr/Al</i> and other mixed metal pillared clays. Biofuels form an interesting renewable energy source, where these porous catalytically active materials can play an important role in the conversion of vegetable oils, such as canola oil, into biodiesel. Transesterification of vegetable oil is currently the method of choice for conversion to biofuel. The second part of this review focuses on the catalysts and cracking reaction conditions used for the production of biofuel. A distinction has been made in three different vegetable oils as starting materials: canola oil, palm oil and sunflower oil
Use of environmental scanning electron microscopy to study uncoated minerals
No full textWe have explored the possibilities offered by the Environmental SEM to study minerals under a variety of conditions. Low voltage SEM can be used to study minerals without coating with gold or carbon, thereby allowing the researcher to use other analytical techniques on the same sample. Changes in pressure and temperature can be used to study mineral reactions such as wetting and drying but also the thermal behaviour such dehydration, dehydroxation or decarbonation. The general principles shown are not limited to the study of minerals but can be applied to a range of materials
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Identification by Raman microscopy of magnesian vivianite formed from Fe2+, Mg, Mn2+ and PO43- leached from metal and bone fragments in a Roman camp near Fort Vechten, Utrecht, The Netherlands
No full textThe presence of a magnesian vivianite (Fe2+)2.5(Mg,Mn,Ca)0.5(PO4)2.8H2O, has been identified in a soil sample from a Roman camp near Fort Vechten, The Netherlands, using a combination of Raman microscopy and scanning electron microscopy. An unsubstituted vivianite and bariĿite were characterised for comparative reasons. The split phosphate-stretching mode is recognised around 1115, 1062 and 1015 cm-1, while the corresponding bending modes are found around 591, 519, 471 and 422 cm-1. The substitution of Mg and Mn for Fe2+ in the crystal structure causes a shift towards higher wavenumbers compared to pure vivianite. As shown by the bariĿite sample substitution causes a broadening of the bands. The observed broadening however is larger than can be explained by substitution alone. The low intensity of the water bands, especially in the OH-stretching region between 2700 and 3700 cm-1 indicates that the magnesian vivianite is partially dehydrated, which explains the much larger broadening than the observed broadening caused by substitution of Mg and Mn in vivianite and bariĿite
Short communication: near- and mid-infrared spectroscopy of the lithium-bearing amphibole holmquistite from Barraute, Canada
No full textThe mid- and near-infrared spectra of holmquistite, a lithium-containing orthorhombic amphibole, from Barraute (Quebec, Canada) has been measured The OH-stretching region is characterised by bands around 3660, 3645, 3629 and 3613 cm-1 assigned to (3Mg)-OH, (2Mg + Fe2+)-OH, (Mg + 2Fe2+)-OH and (3Fe2+)-OH, respectively. Based on the ratio between the 3645 and 3660 cm-1 bands Fe2+/(Fe2+ + Mg2+) ratios in the M1 and M3 sites were determined to be in the range between 0.35 and 0.45. In the near-infrared region two times four bands were observed associated with the four possible combination modes of the four M-OH stretching and bending modes around 4029, 4193, 4323 and 4400 cm-1 and with the four overtones of M-OH stretching modes around 7055, 7091, 7123 and 7155 cm-1
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