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  • Author or Editor: R. Naumann x
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Abstract  

Scanning calorimetric methods permit determination of heat capacities at high temperatures up to 1600C. For disk systems with power compensation application limits are in order of 700C, and for cylindrical systems with electrical calibration up to 1000C. For the high temperature range above 1000C DSC plates and a cylindrical calorimetric systems based on the CALVET principle ('MULTI HTC’) are known. For cylindrical calorimetric systems the precision of the Cp data is between 2 and 5% even at high temperatures without any requirements on the kind and shape of samples. These results are better than data provided by DSC plate systems.

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The decomposition of magnesium chloride hexahydrate was followed by differential thermal analysis and thermogravimetry in combination with evolved gas analysis. The examinations were carried out by means of a Q-derivatograph (temperature range 20–400°; pressure 1 bar) under quasiisothermal and dynamic heating conditions, with variation of the crucible type. The temperatures of the stepwise decomposition of H2O and HCl are influenced by the partial pressures of H2O and HCl. Depending on the conditions, it is possible to remove 2 moles of water from solid MgCl2 · 6 H2O or from a melt in a nonisothermal step. Under quasiisobaric conditions MgCl2 · 4 H2O is transformed in isothermal steps to MgCl2 · 2 H2O and stable basic magnesium chlorides.

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Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)2·8H2O and Sr(OH)2·8H2O are promising latent heat storage materials.

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The thermal behaviour of sodium acetate trihydrate (NaAc · 3H2O) was investigated by DTA, Q-TG and measurements of the solubility properties. The nucleation efficiency of Na4P2O7 · 10H2O for the crystallization of NaAc · 3H2O melts is not stable over long periods. Stratification can be ascribed to the formation of anhydrous sodium acetate in the supercooled melts. Under static heat storage conditions, NaAc · 3H2O and Na4P2O7 · 10H2O do not exhibit stable behaviour.

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Abstract  

Optical absorption spectra of radical cations of n-C7-to n-C16-alkanes, cyclohexane and methylcyclohexane were observed in electron-irradiated liquid alkanes. Spectral properties of these radical cations their fragmentation pattern and electron transfer reactions are discussed.

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Abstract  

Standard entropies of adsorption (Δs 0) of CO on different materials (Cu catalysts, Au catalysts, ZnO and to TiO2) are obtained from static adsorption microcalorimetry, adsorption isobars and temperature-programmed desorption, based on the thermodynamics of adsorption on energetically heterogeneous surfaces. Vibrational entropies of the surfaces s vib α are normally between the rotational and the standard translational entropy of CO in gas phase, and decrease with increasing adsorption energy, which agrees with the explanation of statistical thermodynamics. Δs 0 reflects both the mobility of adsorbates and the specific adsorbate-adsorbent interaction. Limits for reasonable values of the entropy of adsorption are proposed.

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