Controlled Rate Thermal Analysis and Differential Scanning Calorimetry of Sepiolites and Palygorskites

A series of sepiolites, palygorskites and "Rocky Mountain Leather" clay minerals have been analysed by controlled rate thermal analysis and differential scanning calorimetry. Eight weight loss steps are observed and are structure and composition dependent. Three dehydration steps and five dehydroxylation steps are observed. The mass spectrometric curve mimicked the differential thermogravimetric (DTGA) curve enabling the detailed determination of the dehydration and dehydroxylation step

Thermal Activation of Copper Oxide Based upon the Copper Hydrotalcites of the Type CuxZn6-xCr2(OH)16(CO3).4H2O

A combination of DSC and high resolution DTG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a series of Cu/Zn hydrotalcites of formulae CuxZn6-xAl2(OH)16(CO3).4H2O where x varied from 6 to 0. The effect of increased Zn composition results in the increase of the endotherms and weight loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps. The interlayer carbonate anion is lost simultaneously with hydroxyl units. The endotherms and differential weight loss steps were both cation and mole ratio dependent

Acetylation of Raw Cotton for Oil Spill Cleanup Application: an FTIR and 13-C MAS NMR Spectroscopic Investigation

Fourier transform infrared (FTIR) and 13C MAS NMR spectroscopy have been used to investigate the acetylation of raw cotton samples with acetic anhydride without solvents in the presence of different amounts of 4-dimethylaminopyridine (DMAP) catalyst. This is a continuation of our previous investigation of acetylation of commercial cotton in an effort to develop hydrophobic, biodegradable, cellulosic sorbent materials for cleaning up oil spills. The FTIR data have again provided a clear evidence for successful acetylation. The NMR results further confirm the successful acetylation. The extent of acetylation was quantitatively determined using the weight percent gain (WPG) due to acetylation and by calculating the ratio R between the intensity of the acetyl C=O stretching band at 1740-1745 cm-1 and the intensity of C-O stretching vibration of the cellulose backbone at about 1020-1040 cm-1. The FTIR technique was found to be highly sensitive and reliable for the determination of the extent of acetylation. The level of acetylation of the raw cotton samples was found to be much higher than that of cotton fabrics and the previously studied commercial cotton. The variation of the R and WPG with reaction time, amount of DMAP catalyst and different samples of raw cotton is discusse

Synthesis and vibrational spectroscopic characterisation of synthetic hydrozincite and smithsonite

Hydrozincite and smithsonite were synthesised by controlling the partial pressure of CO2 . Previous crystallographic studies concluded that the structure of hydrozincite was a simple one. However both Raman and infrared spectroscopy show that this conclusion is questionable. Multiple bands are observed in both the Raman and infrared spectra in the (CO3)2-antisymmetric stretching and bending regions of hydrozincite showing that the symmetry of the carbonate anion is reduced and in all probability the carbonate anions are not equivalent in the hydrozincite structure. Multiple OH stretching vibrations centred in both the Raman and infrared spectra show that the OH units in the hydrozincite structure are non-equivalent. The Raman spectrum of synthetic smithsonite is a simple spectrum characteristic of carbonate with Raman bands observed at 1408, 1092 and 730 cm-1. The symmetry of the carbonate anion in hydrozincite is C2v or Cs. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band of hydrozincite at 1062 cm-1 is assigned to the ν1 (CO3)2- symmetric stretching mode. Three Raman bands assigned to the ν3 (CO3)2- antisymmetric stretching modes are observed for hydrozincite at 1545, 1532 and 1380 cm-1. Multiple infrared or Raman bands are observed in 800 to 850 cm-1 and 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion symmetry in the hydrozincite structure. A Raman band for hydrozincite at 980 cm-1 is attributed to the δ OH deformation mode

Raman Microscopy of Selected Autunite Minerals

Raman spectroscopy at ambient and liquid nitrogen temperature has been used to determine the molecular structure of selected minerals from the autunite and meta-autunite groups. Six hydroxyl stretching bands for autunite are observed of which three are highly polarised. The hydroxyl stretching vibrations are related to the strength of hydrogen bonding of the water units. Bands in the Raman spectrum of autunite at 998, 842 and 820 cm–1 are highly polarised. Low intensity band at 915 cm–1 is attributed to the 3 antisymmetric stretching vibration of (UO2)2+ units. The band at 820 cm–1 is attributed to the 1 symmetric stretching mode of the (UO2)2+ units. The (UO2)2+ bending modes are found at 295 and 222 cm–1. The presence of phosphate and arsenate anions and their isomorphic substitution are readily determined by Raman spectroscopy. The collection of Raman spectra at 77 K enables excellent band separation

Hydrated Double Carbonates - A Raman and Infrared Spectroscopic Study

The Raman spectra of selected double carbonates including pirssonite, gaylussite, shortite and quintinite complemented with infrared spectra have been used to characterise the structure of these carbonate minerals. By using a Libowitzky type function hydrogen bond distances for these minerals of 2.669 to 2.766 Å are estimated. The variation in the hydrogen bond distances contributed to the stability of the mineral. The Raman spectrum of pirssonite shows a single band at 1080 cm-1 attributed to the (CO3)2- symmetric stretching mode, in contrast to shortite and quintinite where two bands are observed. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of pirssonite and gaylussite

Effect of Ionic Surfactants on Bauxite Residues Suspensions Viscosity

Measurement of the rheological property of bauxite residue sample received from an Australian alumina refinery, treated with a number of cationic and anionic surfactant in laboratory has been carried out using a Brookfield viscometer for the assessment of the effect of surfactants on the residue viscosity. It was found that sodium laurate, prepared with an excess of sodium hydroxide was found to be effective while direct addition of anionic surfactants (lauric acid and sodium laureth sulphate) and cationic (cetyl trimethyl ammonium bromide) produce only moderate effect on the red mud suspension apparent viscosity at 65 oC. The experimental data appear to confirm the crucial role of the cation sodium in the process of adsorption of anionic surfactants on the flocculated red mud particles

Thermal Analysis of Goethite - Relevance to Australian Indigenous Art

Differential scanning calorimetry shows two endotherms at 75 and 225 degrees Celsius for synthetic goethite. The latter endotherm is strongly asymmetric on the low temperature side. The endotherms were attributed to the loss of water and the dehydroxylation of the goethite. The temperature of the endotherms and the enthalpy of the phase change were found to be linear functions of the % of aluminium substitution into the goethite. High-resolution thermogravimetric analysis of goethite showed three weight loss steps, occurring at ~ 175, 196 and 263 degrees Celsius. The temperatures of these weight loss steps and the % weight loss were also linearly related to the degree of Al substitution. The use of infrared emission spectroscopy confirmed the temperature of dehydroxylation. The observation of the low temperature dehydroxylation of goethite and its relation to ancient aboriginal cave art is discussed

Raman Spectroscopic Study of the Molybdate Mineral Szenicsite and Comparison with Other Paragenetically Related Molybdate Minerals

The molybdate-bearing mineral szenicsite, Cu3(MoO4)(OH)4, has been studied by Raman and infrared spectroscopy. A comparison of the Raman spectra is made with those of the closely related molybdate-bearing minerals, wulfenite, powellite, lindgrenite, and iriginite, which show common paragenesis. The Raman spectrum of szenicsite displays an intense, sharp band at 898 cm-1, attributed to the 1 symmetric stretching vibration of the MoO4 units. The position of this particular band may be compared with the values of 871 cm-1 for wulfenite and scheelite and 879 cm-1 for powellite. Two Raman bands are observed at 827 and 801 cm-1 for szenicsite, which are assigned to the 3(Eg) vibrational mode of the molybdate anion. The two MO4 2 modes are observed at 349 (Bg) and 308 cm-1 (Ag). The Raman band at 408 cm-1 for szenicsite is assigned to the 4(Eg) band. The Raman spectra are assigned according to a factor group analysis and are related to the structure of the minerals. The various minerals mentioned have characteristically different Raman spectra