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Abstract  

Conventional thermogravimetric analysis (TG) uses constant heating rates to determine decomposition rates of a material and compositional analysis. Often, the decomposition steps can not be separated clearly enough due to parallel or consecutive reactions. If the reaction rates and the respective activation energies are enough different the TG resolution can be much enhanced by lowering the heating rate during the decomposition steps. The automated discrete adjustment of the heating rate is controlled by a set of parameters, such as threshold values, waiting times and rate factors. This technique, called MaxRes, allows for faster compositional analysis without loss of resolution. The same technique is also applicable to thermomechanical analysis (TMA) if time/temperature dependent events such as softening are to be separated.

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Abstract  

The DSC curve of succinonitrile shows a melting peak at approximately 60°C with the very small heat of fusion of 47 J/g. Further investigations in the low temperature range result in an additional exotherm at −60°C. On heating there are the two corresponding endotherms repeatably. We postulate a so called plastic crystalline mesophase between the two thermal effects.

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Abstract  

After a brief introduction of the terms supercooling, amorphous solid state, glass transition and devitrification, the known ways of production of amorphous solid water are discussed. DSC experiments with quench cooled aqueous solutions show the phenomenon of glass transition and devitrification.

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Abstract  

The thermal behavior of a drawn PET fiber has been investigated by thermomechanical analysis, TMA, and by differential scanning calorimetry, DSC. Above the glass transition temperature of 79°C, the fiber shrinks to a maximum of 8% of the initial length. Temperature modulated TMA enabled the separation of the thermal expansion from the overlapping shrinkage during the first heating and to calculate the expansivity, e and the shrinkage coefficient, s, independent of each other. Young's modulus, E, was measured by TMA with modulation of the tensile stress. Hence, it was possible to record the behavior of e, s and E during the structural changes by combining both modulations in a single measurement.A new technique was developed to calibrate the sample temperature. With this, accurate control of the modulated temperature of the specimen was achieved, independent of the changing heating rate.

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Abstract  

A characteristic index for the oxidation stability this is the oxidation induction time (OIT) which is defined by the time between the start of oxygen exposure and the onset of oxidation. Pressure DSC is required to increase oxygen concentration in order to achieve faster reactions at lower temperatures. OIT measurements of reference engine oils have been used to study the influence of oxygen pressure in the range from 0.1 to 10 MPa. A power law relationship was derived to describe this correlation between OIT and oxygen pressure. From this a quantitation factor is proposed to represent the influence of stabilizer. The exponent describes the sensitivity of the oxidation reaction of the oil towards the oxygen pressure and the term 'inherent stability' is proposed for that.. This relationship characterizes in more details the oxidation behavior. Extrapolation to higher pressures indicates, that the stabilization effects of additives can be overcome by the inherent stability. This signifies, that the ranking of the oils can be affected by the oxygen pressure.

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A thermogravimetric unit is described having horizontal furnace arrangement, a temperature range of up to 1100°C and unsurpassed dynamic weighing range from 0 to 2 g at 0.1 μg resolution. Options of the system are sample robot, gas controller, high temperature furnace and hyphenated EGA techniques.

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Abstract  

DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change.

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Abstract  

ADSC with its periodical temperature programs combines the features of DSC measured at high heating rate (high sensitivity) with those at low heating rate (high temperature resolution). In addition, the “reversing” cp effects can be separated from the “non-reversing” latent heat effects. Various periodical temperature programs can be applied. This paper compares the different possible temperature programs and their algorithms for the cp determination for metal, metal oxide and polymer of various properties. Simulated and measured results for various wave shapes and samples are presented. The relevant sample properties and their influence on the measurements are identified and guiding rules for the proper choice of the various experimental parameters are given. Measurements with different samples, performed with the new METTLER TOLEDO STARe-System, are shown and compared with the simulation results. The simulations and the measurements clearly show that the alternating techniques can yield new information about sample properties, but are susceptible to the proper choice of the various experimental parameters.

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Abstract

Simultaneous thermogravimetry and thermomicroscopy were performed on Ca-oxalates which play an important role in the appearance of oxalate films connected with lichens superficially growing on human artefacts. Ca-oxalate exists in two well-described modifications: as the more stable monoclinic monohydrate whewellite and the less stable tetragonal dihydrate weddelite. Weddelite serves for lichens as a water absorbing and accumulating substrate which transforms to whewellite when humidity drops. To follow these morphological changes optically and the water loss gravimetrically at the same time, a combination of thermomicroscopy and thermogravimétric analysis was constructed, The reflection light microscope was connected to a video camera and computer so that the morphological changes and the thermogravimetric curves could be shown simultaneously on the screen as function of time and temperature.

Lichens — double organisms composed of algae and fungi — form surface layers not only on natural organic and inorganic material but also on human artefacts. In calcareous artefacts such as the famous Chinese terracotta soldiers or Egyptian epigraphs they lead to a destruction of the surface by forming Ca-oxalate layers and thus to a deterioration of the historian work of art. But in places where the surface is covered by some blue colours (Egyptian and Chinese Blue, Chinese Purple) the growth of lichens is inhibited and the artefacts are well preserved. The copper ion contained in the pigments is responsible for this effect since copper is a strong poison for microorganism.

As lichens exhibit an extremely slow growth under natural and laboratory conditions the two lichen components: algae and fungi were investigated separately. The three mentioned ancient pigments have very low solubility products and thus do not act on the quickly growing fungi. But under special experimental conditions Egyptian Blue formed clear halos on the growth plates of the algaeChlorella minutissima andTrebouxia glomerata. These halos were compared with those of the easily soluble copper sulphate as a standard.

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