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

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

Thermal Stability of Azurite and Malachite in Relation to the Formation of Mediaeval Glass and Glazes

Azurite and malachite have been extensively used as pigments in ancient and medieval manuscripts, glasses and glazes. The thermal stability of naturally occurring azurite and malachite was determined using a combination of controlled rate thermal analysis combined with mass spectrometry and infrared emission spectroscopy. Both azurite and malachite thermally decompose in six overlapping stages but the behaviour is different for the two minerals. These stages occur around 282, 328, 350, 369, 384 and 840 degrees Celsius for azurite and 250, 321, 332, 345, 362 and 842 degrees Celsius for malachite. The first two stages are associated with the loss of water, whereas stages 3 and 4 result from the simultaneous loss of water and carbon dioxide. The sixth stage is associated with reduction of cupric oxide to cuprous oxide and finally to copper. Infrared emission spectroscopy shows that dehydroxylation occurs before the loss of carbonate and that the thermal decomposition is complete by 375 degrees Celsius. The implication of this research is that in the preparation of glass or glazes using these two hydroxy-carbonate minerals of copper the samples will decompose at low temperatures and any colour formation in the glass is not due to azurite or malachite

Infrared Spectroscopy of Organoclays Synthesized with the Surfactant Octadecyltrimethylammonium Bormide

Infrared spectroscopy using a smart endurance single bounce diamond ATR cell has been used to study the changes in the spectra of the surfactant octadecyltrimethylammonium bromide upon intercalation into a sodium montmorillonite. The wavenumbers of bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant measured in terms of the cation exchange capacity (CEC) up to 1.0 CEC. After this point the bands increase approaching a value the same as that of the surfactant. Significant changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surfac

Molecular Assembly in Synthesized Hydrotalcites of Formula CuxZn6-xA12(OH)16(CO3).4H2O-A Vibrational Spectroscopic Study

Infrared and Raman spectroscopy have been used to characterize synthetic hydrotalcites of formula CuxZn6-xAl2(OH)16(CO3).4H2O . The spectra have been used to assess the molecular assembly of the cations in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based (a) upon the carbonate anion (b) the hydroxyl units (c) water units. The Raman spectra of the hydroxyl-stretching region enable bands to be assigned to the CuOH, ZnOH and AlOH units. It is proposed that in the hydrotalcites with minimal cationic replacement that the cations are arranged in a regular array. For the CuxZn6-xAl2(OH)16(CO3).4H2O hydrotalcites, spectroscopic evidence suggests that 'islands' of cations arte formed in the structure. In a similar fashion the bands assigned to the interlayer water suggest that the water molecules are also in a regular well-structured arrangement. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of water are identified (a) water hydrogen bonded to the interlayer carbonate ion (b) water hydrogen bonded to the hydrotalcite hydroxyl surface and (c) interlamellar water. It is proposed that the water is highly structured in the hydrotalcite as it is hydrogen bonded to both the carbonate anion and the hydroxyl surface

Graph Analysis Using a GPU-based Parallel Algorithm: Quantum Clustering

The article introduces a new method for applying Quantum Clustering to graph structures. Quantum Clustering (QC) is a novel density-based unsupervised learning method that determines cluster centers by constructing a potential function. In this method, we use the Graph Gradient Descent algorithm to find the centers of clusters. GPU parallelization is utilized for computing potential values. We also conducted experiments on five widely used datasets and evaluated using four indicators. The results show superior performance of the method. Finally, we discuss the influence of $\sigma$ on the experimental results