The destruction of CH + ions in collisions with H atoms has been studied in a temperature-variable 22 pole ion trap (22PT) combined with a cold effusive H-atom beam. The stored ions are relaxed to temperatures of T 22PT 12 K. The hydrogen atoms, produced in a radio frequency discharge, are slowed down to various temperatures of T ACC 7 K. They are formed into an effusive beam. The effective density of the hydrogen atoms in the trap as well as the H 2 background are determined in situ using chemical probing with CO 2 +. The experimental arrangement allows us not only to measure thermal rate coefficients (T 22PT = T ACC), but also to extract state-specific rate coefficients k(J,T t) at selected translational temperatures T t and for the CH + rotational states J = 0, 1, and 2. The measured thermal rate coefficients have a maximum at 60 K, k = (1.2 ± 0.5)×10 −9 cm 3 s −1. Toward higher temperatures, they fall off in accordance with previous measurements and the trend predicted by phase space theory. Toward lower temperatures, the rate coefficients decrease significantly, especially if the rotation of the ions is cooled. At the coldest conditions achieved (beam: 7.3 K; trap: 12.2 K), a value as low as (5 ± 4) × 10 −11 cm 3 s −1 has been measured. This leads to the conclusion that non-rotating CH + is protected against attacks of H atoms. This surprising result is not yet understood. It is most probably due to quantum-dynamical effects already occurring at large distances.
The novel alloying concept of high-entropy alloys (HEAs) has been the focus of many recent investigations revealing an interesting combination of properties. Alloying with aluminium and titanium showed strong influence on microstructure and phase composition. However, detailed investigations on the influence of titanium are lacking. In this study, the influence of titanium in the alloy system AlCoCrFeNiTi x was studied in a wide range (molar ratios x = 0.0; 0.2; 0.5; 0.8; 1.0; 1.5). Detailed studies investigating the microstructure, chemical composition, phase composition, solidification behaviour, and wear behaviour were carried out. Alloying with titanium showed strong influence on the resulting microstructure and lead to an increase of microstructural heterogeneity. Phase analyses revealed the formation of one body-centred cubic (bcc) phase for the alloy without titanium, whereas alloying with titanium caused the formation of two different bcc phases as main phases. Additional phases were detected for alloys with increased titanium content. For x ≥ 0.5, a minor phase with face-centred cubic (fcc) structure was formed. Further addition of titanium led to the formation of complex phases. Investigation of wear behaviour revealed a superior wear resistance of the alloy AlCoCrFeNiTi 0.5 as compared to a bearing steel sample.
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