Spectroscopic properties of CrOx/Al2O3 nanopowders synthesized by cw CO2 laser vaporization

Nanosized 5.0 wt% Cr/nano-Al2O3 powders with the particle size of ca. 15 nm were synthesized via laser vaporization using irradiation by a cw CO2 laser in different gas atmospheres – Ar, Ar+O2, Ar+H2. All the investigated nanopowders were studied by XRF, XRD, TEM, UV-vis DRS and PL spectroscopy methods. The nanopowders were found to contain the Cr6+ ions located on the surface of Al2O3 nanoparticles and two types of Cr3+ sites. One type is Cr3+ ions located in the bulk (Cr3+ b-sites) of Al2O3 matrix in a strong crystal field. The second type is represented by Cr3+ sites residing near the surface (Cr3+ s-sites) of CrOx/Al2O3 nanoparticles in a weak crystal field. It was shown that varying the composition of the buffer gas (Ar, Ar+O2, Ar+H2) during laser vaporization makes it possible to control the properties of the obtained 5.0 wt% Cr/nano-Al2O3 nanopowders with a change in Cr6+/Cr3+ ratio in the bulk and on the surface of alumina support.

CO2 LASER-DRIVEN REACTIONS IN PURE ACETYLENE FLOW

We show that multiple-photon absorption of radiation from a 10.56 μm cw CO2 laser by intermediates (ethylene, vinylidene) generated in pure acetylene flow makes them decompose to carbon dimers and excited hydrogen. The latter associates with downstream acetylene to feedback those laser absorbing intermediates thus making the reactions self-sustained in the absence of oxygen. This process is different from acetylene self-decomposition that may occur at higher temperature and pressure. The results of our work may be useful for understanding the generation of various carbon allotropes and interstellar dust from acetylene.

Study on the Quality of Quasi-Isotropic Composite Laminates Containing a Circular Hole

Composite structures used in modern engineering applications are often subjected to circular holes in order to join with metal components via riveting, bolting or pinning joints. These design based holes will interrupt the force flux in the direction of the fibers and create high stress concentrations near the notched area. Objective of the project is to understand the quality of the quasi-isotropic composite laminates ([45°, -45°, 0°, 90°]S) containing circular hole. To achieve this objective, a 3-phase portal milling machine and a 5kW continuous wave (cw) CO2 laser system were used to produce the circular holes in the composite laminates. The processing parameters for both the processes are varied to understand its influence. The quality of the circular hole produced by these methods are further investigated and compared in order to arrive at the optimum processing parameters for the given quasi-isotropic composite laminates.The hole qualities were evaluated by means of delamination factor caused by milling; cone angle, matrix evaporation for cw-CO2 laser system. For further comparisons, the optimal parameter combinations of both methods were selected for a tensile test according to the standard ASTM D5766-2002.