Analytik rund ums Holi‐Pulver

These days, people use starch‐containing, coloured powder to throw it at each other during Holi parties – events based on a Hindu ritual. Fire departments warn that sparks, for example from cigarettes, could lead to dust explosions. The explosiveness of dusts depends on a number of parameters. Composition, water content and particle size are important ones. This study examines these parameters for Holi powders from a German and an Indian provider. Composition proves to be the main influence on explosiveness. The “Indian” Holi powder is made up from over 90 % combustible (corn‐)starch. The “German” product is more balanced containing starch and inert substances. Model mixtures are used to determine explosiveness. Mixtures with a starch content of over 90 % turn out to be highly explosive. All experiments are conducted with a low‐cost Hartmann apparatus.     

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO_2?x) powders and CeO_2?x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce³⁺ species to hydrogen, which results in the formation of Ce⁴⁺, and thus in oxidation of ceria.