Anwendungsbeispiele der Gaschromatographie in der industriellen Praxis

Ohne Zusammenfassung     

A Calixarene‐Based Metal–Organic Framework for Highly Selective NO2 Detection

A calixarene‐based metal–organic framework (Zr‐cal, [Zr₆O₄(OH)₄(FA)₆]₂(cal)₃], FA=formate, cal=1,3‐alt‐25,26,27,28‐tetrakis[(carboxy)methoxy]calixarene) was synthesized and characterized by single‐crystal X‐ray diffraction. The three‐dimensional framework is a 4,6‐connected network of gar topology and exhibits two equal but nonintersecting three‐dimensional pore systems. It has a specific BET surface area of 670 m² g^?1, and the calixarene cavities are accessible through the pore systems. The exposed calixarenes can be used for the visual detection and encapsulation of NO₂ through the formation of deeply colored charge–transfer complexes inside the MOF. The highly selective complexation was analyzed by UV/Vis and IR spectroscopy, and the stability of the material was confirmed by powder X‐ray diffraction and ¹H NMR spectroscopy. Finally, the MOF was used as a sensor material in a home‐made sensor cell and showed high sensitivity for NO₂.     

Elastooptic investigations in functional allyl polymer lightguides

Planar waveguides of the allyl polymer poly-(terephthal acid diallyl ester) (PDATP) exhibiting a particular high stress optical coefficient are investigated. Internal mechanical stress may be introduced in the wave-guides by the in-diffusion of small vapour molecules or by the activation of a piezoelectric transducer in the substrate. Based on the induced stress the feasibility of gas sensors or electro acousto optic phase shifters (V =180 V) with these waveguides is discussed.     

OH-radical formation by ultrasound in aqueous solution--Part II: Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield

Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg-1, the total yield [G(.OH) + 2 G(H2O2)], equals 16 x 10(-10) mol J-1. This represents the total of .OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, the lower the H2O2 production as more of the OH free radicals are scavenged, in competition with their recombination. Fricke dosimetry, in the absence and presence of Cu2+ ions, shows that the yield of H atom reaching the liquid phase is much lower, with G(H.) of the order of 3 x 10(-10) mol J-1. These sonolytic yields are smaller in solutions that are at the point of gas saturation, and increase to an optimum as the initial sonication-induced degassing and effervescence subsides. The probing of the sonic field has shown that the rate of sonolytic free-radical formation may vary across the sonicated volume depending on frequency and power input.     

Nearest neighbor effect on capture cross sections measured in IR phototransients on Si:In

The extrinsic photoconductive decay at T=20–100 K is analyzed in FZ-grown Si: In material after pulsed irradiation by a PbSSe infrared laser (=4 m). Trapping time constants (=10 ns-100 s) are resolved for the prevalent In acceptor (N _In=10¹⁶–10¹⁷ cm^–3) and for additional shallow acceptors B, Al, and the X(In)-center present at low concentrations (N=10¹²–10¹⁴ cm^–3). Hole capture cross sections determined for the acceptor levels show a large scatter over up to 4 orders of magnitude. It is shown that the capture cross section is dependent on all the dopant concentrations present in the sample due to nearest neighbor interaction. Due to the formation of donor-acceptor dipoles, the capture cross section assumes low values. A model calculation of the interaction based on only fundamental parameters of Si is in accordance with the experimental data within the experimental error. The hole capture cross sections for isolated acceptors are _p=1×10^–12, 1×10^–14, 1×10^–13, 2.5×10^–13 cm² for indium, X-center, aluminum, and boron at the temperatures T=95 K, 100 K, 70 K, 45 K, respectively.