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Formation of titanium carbide on the titanium surface using laser ablation in n-heptane and investigating its corrosion resistance
摘要： Laser ablation of titanium in liquid (LAL) using a fiber laser was studied. Firstly, LAL was carried out in toluene, n-hexane, n-heptane, and acetone as liquid media at the same irradiation conditions. Samples were characterized by different diagnostic techniques X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). It was found that titanium carbide (TiC) structure has been generated on the surface of laser ablated samples in toluene, n-hexane, and n-heptane. Also, titanium dioxide was formed on the surface of laser ablated sample in acetone along with TiC. After that, n-heptane was chosen as the adequate liquid medium. LAL process was repeated in n-heptane for different ablation process times at the same irradiation conditions. Samples were investigated by XRD, Raman spectroscopy, EDS, nuclear reaction analysis (NRA), and cross sectional FESEM. It was concluded that the ablation process time of about 30 s is threshold time to form detectable TiC structure by XRD. Additionally, it was deduced that the amount of the carbon (in two forms of amorphous and carbidic) on the surface of the irradiated titanium for about 2 min (S8 sample) is more than other samples. The corrosion behavior of samples was studied by electrochemical impedance spectrometry (EIS) tests. The EIS plots obtained after 24, 48, 72, and 96 h immersion time showed the corrosion resistance of S8 sample enhancement in Ringer's solution compared with the other samples, and the corrosion resistance of this sample increased by rising the immersion time up to 96 h.
关键词： EIS.,titanium carbide,Ringer's solution,n-heptane,laser ablation,titanium
更新于2025-09-19 17:15:36
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Thermodynamic analysis of Organic Rankine cycle driven by reversed absorber hybrid photovoltaic thermal compound parabolic concentrator system
摘要： In current study, an effort is made to improve the overall performance of the solar powered organic Rankine system to meet increasing energy demand and mitigate the resulting menace caused by environmental imbalance. Hourly performance evaluation of Solar powered Organic Rankine Cycle (ORC) system is done for varying concentration ratio in terms of collector output temperature, heat gain in evaporator, combined thermal and exergetic efficiency. The Heptane/R245fa is used as working fluid at fixed (0.1/0.9) fractional mass component. Organic Rankine system is coupled with reversed absorber hybrid photovoltaic thermal compound parabolic concentrator (PVTCPC). The highest collector outlet temperature 125.45 (cid:1)C, heat gain 3.21 (cid:3) 105 W, combined thermal efficiency 7.8%, and exergetic efficiency 14.38% is observed at 13:00 h for 6 concentration ratio of the concentrator. This study establishes the utility of low-grade renewable heat source conversion into solar electrification, solar irrigation, solar cooling and solar water purification.
关键词： Concentration ratio,Heptane /R245fa,Reversed absorber,Zeotropic mixture,Organic Rankine cycle
更新于2025-09-16 10:30:52
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Structure and Permeability of Porous Silicon Investigated by Self-Diffusion NMR Measurements of Ethanol and Heptane
摘要： The adsorption and phase transitions of con?ned ?uids in nanoporous materials have been studied intensely because of both their fundamental interest and their crucial role in many technologies. Questions relating to the in?uence of the con?nement of ?uids, and the disorder or elastic deformation of porous solids on the liquid-gas phase transition are still under debate. Model systems are needed to understand the adsorption phenomenon. In this context, Porous Silicon (PoSi), which is a single crystal obtained by etching a (100) silicon wafer is an excellent candidate. Indeed, it consists of non-connected tubular pores running parallel to the [100] axis perpendicular to the wafer surface, with transverse sections with a polygonal shape of nanometric size whose areas are widely distributed. Once detached from the wafer, free PoSi membranes can be considered a nanoscale disordered honeycomb. Adsorption/desorption experiments have been performed to characterize the structure: they have shown that evaporation occurs collectively, an intriguing observation generally associated with a disordered pore structure with many interconnections through narrow necks. The characterization of ?uid mobility inside the pores should give complementary information about the pore structure and topology. This paper focuses on the dynamics of a ?uid con?ned inside the structure of porous silicon, and in particular the self-diffusion measurements (pulsed ?eld gradient spin echo Nuclear Magnetic Resonance (NMR)). The results show a strong anisotropy of the self-diffusion tensor, as expected in this highly anisotropic structure. However, a non-zero self-diffusion in the directions perpendicular to the pore axis is observed. In order to interpret these puzzling results, molecular and Brownian dynamics calculations are underway.
关键词： Ethanol,Porous Silicon,Permeability,Heptane,Self-Diffusion NMR
更新于2025-09-09 09:28:46
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Cavity-enhanced absorption sensor for carbon monoxide in a rapid compression machine
摘要： A sensor based on cavity-enhanced absorption spectroscopy (CEAS) was implemented for the first time in a rapid compression machine (RCM) for carbon monoxide concentration measurements. The sensor consisted of a pulsed quantum cascade laser (QCL) coupled to a low-finesse cavity in the RCM using an off-axis alignment. The QCL was tuned near 4.89 μm to probe the P(23) ro-vibrational line of CO. The pulsed mode operation resulted in rapid frequency down-chirp (6.52 cm ?1 / μs) within the pulse as well as a high time resolution (10 μs). The combination of rapid frequency down-chirp and off-axis cavity alignment enabled a near complete suppression of the cavity coupling noise. A CEAS gain factor of 133 was demonstrated in experiments, resulting in a much lower noise-equivalent detection limit than a single-pass arrangement. The sensor thus presents many opportunities for measuring CO formation at low temperatures and for studying kinetics using dilute reactive environments; one such application is demonstrated in this work using dilute n-heptane/air mixtures in the RCM. The formation of CO during first-stage ignition of n-heptane was measured over 802–899 K at a nominal pressure of 10 bar. These conditions correspond to the NTC region of n-heptane and such results provide useful metrics to test and compare the predictions of low-temperature heat release by different kinetic models.
关键词： n-heptane,Low-temperature heat release,Cavity-enhanced absorption spectroscopy,Rapid compression machine,Carbon monoxide
更新于2025-09-04 15:30:14