Papers by Author: Wilfried Wunderlich

Abstract: The needs for advanced functional materials are expected to provide a boost in powder metallurgy, where impurities on powder surfaces are incorporated as grain boundary segregation. This paper has three aims. After the consistency check, we analyze whether the reported data of Ni and Fe hosts can be correlated to the Mendeleev number of chemical elements. The data of the solvents were analyzed using the software R for principal component analysis (PCA). We grouped and correlated the data to Mendeleev number. The third aim is correlation with other element data such as solubility. As a result, we found that the embrittlement depends strongly on the chemical bonding. Surprisingly, the geometry of the grain boundary type such as interlayer distances, and local atomic volumes has only a minor influence.

Abstract: Global warming is the driving force for developing new functional thermoelectric generators based on new materials which contain at least one of the elements Si, Se, or Sn. We describe four processing methods and their characterization by SEM and thermoelectric properties. The earth-abundant Mg₂Si requires the method of cyclic hydrogen loading, which has two advantages: It suppresses the oxide formation, and promotes the driving force for formation of the intermetallic phase. While the clathrate BaCuSi and the Half-Heusler alloy (TiZr)NiSn, as most intermetallic alloys, can economically be produced by arc-melting, the Se-alloys CuTiSe and CuFeSe need to be processed by the powder-in-tube method and their Seebeck-voltage measurements up to +/- 0.04 mV/K and output power of 4 μW at ΔT= 400 K are reported here for the first time.

Abstract: The aim of this research is, to clarify which route the sol-gel-process is taking in the case of a Al-Mg-spinel slurry, in particular, whether the hydrolysis reaction or the spinel formation is faster and which of the intermediate hydroxide phases Al(OH)3, and Mg(OH)2, or MgO and Al2O3 or MgAl2O4
H2O are formed during the spinel formation. The spinel-alloy was produced using the polymeric route during wet chemical processing. Aluminium-isopropoxide was hydrolyzed in order to form the boehmite-sol and then the same amount of magnesia was added and mixed. This sol precipitated as boehmite (AlOOH) and brucite (Mg(OH)2) after ageing for 12h as confirmed by differential thermal analysis (DTA), and differential thermal gravity (DTG) measurements. After that, the powders were subsequently annealed at 900oC for 3h in air and observed by TEM. Calculations using thermodynamic enthalpy data are in good agreement with the experiments and can be used to predict reaction paths in other system as well.