Optimization of coal tar gas chromatography conditions using probabilistic-deterministic design of experiment

The development of physicochemical methods for the analysis of objects of complex composition requires the application of methods of mathematical experiment design. This article investigates the possibility of using probabilistic-deterministic design of experiment (PDDoE) for obtaining a mathematical model of the chromatographic separation process of coal tar hydrogenation products on an Agilent 7890A device with an Rxi-5ms column. It is shown that the relationship between the column heating rate and the carrier gas pressure with the values averaged for the entire chromatogram can be established with a high accuracy. It is noted that the accuracy of modeling the individual characteristics of the mixture components’ peaks is less, but remains sufficient for many practical needs. Nonlinear multiple correlation coefficients (NMC) for the dependence of the average retention time and average intensity on the considered factors are more than 0.99; they are more than 0.98 for the average peak width. NMC for the dependence of the resolution with the relation to the peaks of naphthalene and 2-ethylphenol is more than 0.8 at a significant level that sufficient for practice. The quality of the mathematical model was checked by triple registration of the chromatogram at the values of the column heating rate and carrier gas pressure that were not used in the training experiment. The measurement results are excellent squared with those calculated using the obtained generalized equations. The PDDoE method can be recommended as a method for mathematical design of an optimization experiment in gas chromatography.

A coupled multiphase Lagrangian-Eulerian fluid-dynamics framework for numerical simulation of Laser Metal Deposition process

We present a Computational Fluid Dynamics (CFD) framework for the numerical simulation of the Laser Metal Deposition (LMD) process in 3D printing. Such a framework, comprehensive of both numerical formulations and solvers, aims at providing an exhaustive scenario of the process, where the carrier gas, modeled as an Eulerian incompressible fluid, transports metal powders, tracked as Langrangian discrete particles, within the 3D printing chamber. On the basis of heat sources coming from the laser beam and the heated substrate, the particle model is developed to interact with the carrier gas also by heat transfer and to evolve in a melted phase according to a growth law of the particle liquid mass fraction. Enhanced numerical solvers, characterized by a modified Netwon-Raphson scheme and a parallel algorithm for tracking particles, are employed to obtain both e ffi ciency and accuracy of the numerical strategy. In the perspective of investigating optimal design of the whole LMD process, we propose a sensitivity analysis specifically addressed to assess the influence of inflow rates, laser beams intensity, and nozzle channel geometry. Such a numerical campaign is performed with an in-house C++ code developed with the deal.II open source Finite Element library.

Zn diffusion technology for InP-InGaAs avalanche photodiodes

This paper presents a study of Zn diffusion process into InP and InGaAs/InP epitaxial heterostructures grown by molecular beam epitaxy. It was found that both diffusion systems: a resistively heated quartz reactor with a solid-state Zn vapor source placed inside and hydrogen or nitrogen as the carrier gas and MOCVD reactor with hydrogen as the carrier gas allow achieving similar dopant concentration above 2*10e18 cm-3. The depth of the diffusion front in the InP layer is located from 2 to 3.5 μm depending on the temperature and time of the diffusion process. The diffusion of Zn into InP through the intermediate InGaAs layer provides better surface quality comparing with direct zinc diffusion into InP surface.

Carrier-Gas Induced Changes in the Structural, Stoichiometric and Photocatalytic Characteristics of Gallium Oxide Nanostructures

Ga2O3/ITO/glass photoelectrodes prepared by the CVD method has rarely been tested in the electrochemical cell for water splitting. In this study, we investigate the photoelectrolytic performance of Ga2O3/ITO-glass photocatalysts produced by the high-temperature CVD route. The changing of N2 carrier gas flow rate from 0 to 1800 seem induces change in the materials properties. XRD signal strength of the produced bi-phase Ga2O3 is observed to deteriorate, while diffraction line width broadens with increasing N2 supply. Films show a combination of nanoclumps and nanostrips morphology. Ga/O ratio decreases, while the optical bandgap gradually increases from 4.37 to 4.42 eV with increasing O content and crystallite size. Photoluminescence measurements show UV, blue, green and red emissions, respectively. Linear sweep voltammetry of the electrodes in 0.1 M KOH electrolyte shows improvement in photocurrent density from 160 to 257 μA/cm2 versus Ag/AgCl at 1 V bias, and a maximum photon-to-current conversion efficiency 0.06%.

The influence of gas purification and addition of macro amounts of metal-carbonyl complexes on the formation of single-atom metal-carbonyl-complexes

Using the Fast On-line Reaction Apparatus (FORA), the influence of various gas-purification columns onto the formation of metal carbonyl complexes (MCCs) under single-atom chemistry conditions was investigated. MCCs were synthesized from single atoms of Mo, Tc, Ru and Rh being produced by the spontaneous fission of 252Cf and recoiling into a CO-gas containing carrier gas atmosphere. The in-situ synthesized MCCs were volatile enough to be transported by the carrier gas to a charcoal trap where they were adsorbed and their subsequent decay was registered by γ-spectrometry. It was found that the type and combination of purification columns used to clean the applied CO-gas strongly influences the obtained formation and transport yields for all MCCs. With the exception of Rh-carbonyl, intense gas-purification strategies resulted in reduced formation and transport yields for MCCs in comparison with less efficient or even completely missing purification setups. It was postulated that the observed reduction in yield might depend on the content of Fe(CO)5 and Ni(CO)4, as well as potentially other MCCs, in the CO-gas, being formed by the interaction between CO and the steel-surfaces of FORA as well as from impurities in the used charcoal traps. Subsequently, it was shown that macro amounts of Fe(CO)5, Ni(CO)4, Mo(CO)6 and Re2(CO)10 added to the used process gas indeed increase significantly the overall yields for MCCs produced by 252Cf fission products. Ni(CO)4 appeared the most potent to increase the yield. Therefore, it was used in more detailed investigations. Using isothermal chromatography, it was shown that Ni(CO)4 does not affect the speciation of carbonyl species produced by the 252Cf fission product 104Mo. For 107Tc, 110Ru and 111Rh a speciation change cannot be excluded. For 111Rh a speciation change cannot be excluded. An inter-carbonyl transfer mechanism is suggested boosting the formation of MCCs. The current discovery might allow for new opportunities in various research fields, which are currently restricted by the low overall yields for MCCs produced under single-atom chemistry conditions. Examples are the chemical investigation of transactinides or the generation of radioactive ion beams from refractory metals at accelerators.