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Abstract  

Nickel sulphide (NiS) was characterised using X-ray diffraction, thermal gravimetric analysis (TG) and differential scanning calorimetry (DSC). The 'as received' Millerite, stoichiometric NiS, observed to be slightly nickel deficient, was found to readily decompose in a nitrogen atmosphere at elevated temperatures (450C max.) to the sulphur deficient Godlevskite, Ni7S6. DSC and X-ray measurements demonstrated that the high temperature form of the Godlevskite was readily stabilised at room temperature. The kinetics of the α-β re-transformation in Godlevskite were then investigated using DSC and were observed to be first order.

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Present study demonstrated the isolation of most promising β-galactosidase producing bacterial strain SB from soil. Morphological, biochemical, and 16s rRNA sequence analysis identified the bacterial strain as Arthrobacter oxydans. Several chemicals, including SDS, Triton X-100, Tween 20, isoamyl alcohol, and toluene-acetone mixture, were applied for extraction of intracellular β-galactosidase from the bacterial strain Arthrobacter oxydans. Among these, Tween 20 was recorded to be most effective. Role of pH, temperature, and shaker speed on production of β-galactosidase was evaluated using Box-Behnken design of response surface methodology. According to Box-Behnken analysis, optimum production of β-galactosidase (21.38 U (mg–1 protein)) is predicted at pH 6.76, temperature 36.1 °C, and shaker speed 121.37 r.p.m. The parameters are validated with the nearest value.

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Abstract  

The dehydration of samples of a Coober Pedy, South Australian sedimentary white opal, displaying play of colour, was investigated using TMA by heating the samples of the specimen to a range of temperatures between room temperature and 1000 at 200C intervals followed by cooling to room temperature. Etched fracture surfaces of the samples were then examined using SEM. The samples showed the typical expansion at low temperature up to 210C before contraction was observed. The contraction of the opals was ascribed to both sintering, supported by morphological change observed in the SEM micrographs, and dehydroxylation of the silanol groups producing silicon-oxygen-silicon bridges resulting in a more dense silica network.

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Abstract  

A model developed for the estimation of the diffusion coefficient based on Fickian diffusion is applied to the dehydration of a Coober Pedy white play of colour (precious) opal using thermogravimetric analysis (TG). The model was originally applied to bulk and powdered opal (opal with no bulk). In this paper the opal was graded prior to TG analysis. The diffusion coefficient was calculated and is reported up to the critical point of water.

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Abstract  

The dehydration of an opal specimen was investigated by thermogravimetric analysis (TG) in powder and bulk forms. The change in geometry resulted in a significant difference in the temperature range in which dehydration occurred with peak temperatures in the differential TG (DTG) curve for the hand ground opal at 203°C and for the bulk opal at 340°C. This difference was attributed to time taken for diffusion of free water in the bulk opal to the specimen surface prior to evolution as a registered mass loss. A model was proposed to account for the diffusion of water and was used to estimate the diffusion coefficient.

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Abstract  

There has been a significant research effort on the development of an oil industry based on Australian oil shales. However, to date the research has been based mainly on the processing aspects of oil shale. The thermal analyses of oil shales, while having been the subject of many studies, have been limited to some extent by instrumentation and analytical techniques. This paper reports on thermal analysis studies utilising traditional thermogravimetry/differential thermal analysis (TG/DTA) and differential scanning calorimetry (DSC). The application of modern thermal analysis techniques such as high resolution TG (HRTG) and modulated differential scanning calorimetry (MDSC) is also examined and compared to the traditional methods.

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Abstract  

Toughened glass panels used as a glazing material in multistorey buildings are known to fracture prematurely when they contain nickel sulfide inclusions as a result of the α-β phase recrystallisation in nickel sulfide. The kinetics of this recrystallisation were studied by differential scanning calorimetry (DSC) under isothermal and non-isothermal conditions. The recrystallisation was observed to be a two-step process with an induction period followed by the phase change. A two-stage kinetic model was used to estimate the recrystallisation time under ambient conditions. These values were found to correlate well with the observed time to failure for glass panels installed in multistorey buildings.

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Abstract  

Naturally occurring opals from three different regions in Australia were studied for their thermal characteristics. All the opals showed initial expansion followed by contraction in thermomechanical analysis (TMA) although the temperature at which the change from expansion to contraction occurred depended on their provenance. Thermogravimetric analysis (TG) revealed different rates and temperatures of dehydration for these opals. A general correlation between the temperature at which there was a zero thermal expansion and that of the maximum rate of dehydration was observed. A dehydration–sintering mechanism is proposed with the effect of sintering being more pronounced following total dehydration.

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Abstract  

Thermal analysis has been employed in a study of the degradation of heritage Sydney sandstone used in St Mary’s Cathedral in Sydney, Australia. TG and DSC have been used to characterise the clay components removed from weathered and unweathered sandstone. Two types of kaolin clays — kaolinite and its polymorph, dickite — have been identified. A higher amount of dickite present in the clay of weathered sandstone indicates that a kaolinite-to-dickite transformation occurs upon weathering. XRD hot stage analysis was also used to demonstrate the presence of a more thermally stable polymorph of the kaolinite.

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