Interaction of a CO<Subscript>2</Subscript> laser beam with free-falling liquid drops during modification of dissolved biomolecules

Nonstationary processes involved in the interaction of a CO₂ laser beam with a free-falling drop of water were numerically simulated by calculating the gasdynamic streamlining of the drop by air, the temperature field in the drop, and the two-phase transformations on the liquid surface. Validity of the model and the results of calculations were checked in experiment. The study was aimed at explaining the effects related to degradation of large polysaccharide molecules in a drops of aqueous solution under the action of laser radiation.     

Temperature dynamics in a multicharge ion plasma generated by CO<Subscript>2</Subscript> laser pulses

Time evolution of the X-ray spectrum of a lead ion plasma generated by CO₂ laser pulses with an energy of 100 J and a duration of 15 ns was measured using an X-ray polychromator with six channels covering the quantum energy range from 180 to 1850 eV. The plasma temperature was determined by comparing the results of measurements with the calculated X-ray emission spectra. The electron temperature measured well agrees with the calculated data.     

Keyhole depth instability in case of CW CO<Subscript>2</Subscript> laser beam welding of mild steel

The study of keyhole (KH) instability in deep penetration laser beam welding (LBW) is essential to understand welding process and appearance of weld seam defects. The main cause of keyhole collapse is the instability in KH dynamics during the LBW process. This is mainly due to the surface tension forces associated with the KH collapse and the stabilizing action of vapour pressure. A deep penetration high power CW CO₂ laser was used to generate KH in mild steel (MS) in two different welding conditions i.e. ambient atmospheric welding (AAW) and under water welding (UWW). KH, formed in case of under water welding, was deeper and narrower than keyhole formed in ambient and atmospheric condition. The number and dimensions of irregular humps increased in case of ambient and under water condition due to larger and rapid keyhole collapse also studied. The thermocapillary convection is considered to explain KH instability, which in turn gives rise to irregular humps.     

Solid-state reactions in the system Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

The formation mechanisms of Li _x Na_{1 ?x} Ta _y Nb_{1 ? y} O₃ perovskite solid solutions in the Li₂CO₃-Na₂CO₃-Nb₂O₅-Ta₂O₅ system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions is proposed.     

Aging of ITO anodes treated by supercritical CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O<Subscript>2</Subscript> fluids for OLEDs

The aging behaviors of indium tin oxide (ITO) anodes treated by supercritical CO₂/H₂O₂ (SCCO₂/H₂O₂) fluids were investigated. As the SCCO₂/H₂O₂-treated ITO anodes were aged, the contact angle and surface energy were analyzed and compared with those of the ITO anodes treated by oxygen plasma. The SCCO₂/H₂O₂ pretreatment yielded a stable polar component of the ITO surfaces after 48 h of aging. The energy reduction in the polar component of the oxygen-plasma-treated ITO due to aging was 20 %, as compared with the 1.1 % decrease in ITO treated with the SCCO₂/H₂O₂ fluids at 4000 psi for 15 min. The X-ray photoelectron spectroscopy analysis revealed that the oxygen content of the ITO surfaces with the SCCO₂/H₂O₂ pretreatment was significantly higher than that of the ITO treated by oxygen plasma. This could result from the formation of hydroxyl products that functioned as a stable buffer layer against further contamination during aging. In addition, the correlated dependence of the OLED performance on the aged ITO anodes was also studied. The OLEDs with the SCCO₂/H₂O₂ pretreatment showed an improved degradation of I–V characteristics and brightness in comparison with those of the devices treated with oxygen plasma after aging the treated ITO anodes for 6 and 12 h. The obtained results suggested that the ITO anodes treated by the SCCO₂/H₂O₂ fluids exhibited a stable surface chemistry and could be useful for OLED applications.     

Physicochemical simulation of fusion processes of basalt and diabase with Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> and Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> + CaO

Fusion processes of basalt and diabase with sodium carbonate and its mixture with calcium oxide are investigated by methods of physicochemical simulation. Equilibrium compositions of the Si-Al-Fe-Ca-Mg-Na system are calculated at various ratios Na₂CO₃: basalt (diabase) and (Na₂CO₃ + CaO): basalt (diabase) in the temperature range of 1270–1470 K. It is shown that, on fusion with sodium carbonate, depending on conditions, the main components of fusion products are sodium metasilicate (Na₂SiO₃) and sodium metaaluminate (NaAlO₂), magnesium orthosilicate (CaMgSiO₄), sodium ferrite(III) (NaFeO₂), iron(III) oxide (Fe₂O₃), and sodium-aluminum orthosilicate (Na₂AlSiO₄). On fusion with the mixture of sodium carbonate and calcium oxide, respectively, the products are sodium metaaluminate, calcium pyrosilicate (Ca₃Si₂O₇), calcium-magnesium orthosilicate, and calcium ferrite (CaFe₂O₄).     

Scalable fabrication of SnO<Subscript>2</Subscript>/eo-GO nanocomposites for the photoreduction of CO<Subscript>2</Subscript> to CH<Subscript>4</Subscript>

Artificial photosynthesis uses a catalyst to convert CO₂ into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO₂) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO₂ reduction compared to SnO₂ and commercialized TiO₂ (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.

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Online mass-spectrometric monitoring of O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> during anesthesia

It is suggested to determine the breathing cycle duration during anesthesia by the online method based on synchronous mass-spectrometric monitoring of the concentrations of an inert gas (not involved in metabolism), CO₂, and O₂. Comparative results of determining the temporal boundaries of the breathing cycle using the proposed method with argon (Ar) and krypton (Kr) are presented. The concentrations of CO₂, O₂, and Ar (or Kr) were measured using an electron-impact ionization mass spectrometer. The gas mixture was sampled directly from the breathing circuit of an anesthesia machine during low-flow balanced inhalation anesthesia. The obtained results show the possibility of using mass-spectrometric monitoring of the CO₂/O₂ metabolism in order to assess online the adequacy of anesthesia with respect to surgical invasion during anesthesia.     

Experimental evaluation of interactions in supercritical CO<Subscript>2</Subscript>/water/rock minerals system under geologic CO<Subscript>2</Subscript> sequestration conditions

The hydrothermal autoclave experiments were conducted to simulate the interactions in the scCO₂/water/rock minerals (quartz, biotite and granite) reaction systems using a Hastelloy C reaction cell at 100 °C. The dissolution characteristics of rock minerals and their surface texture alternation after hydrothermal treatment were examined by ICP-AES and SEM/EDX investigation, respectively. The results suggested that the hydrolysis of plagioclase phase should be mainly responsible for the elements dissolved from the Iidate granite samples. The dissolution was encouraged by the introduction of CO₂ in the water/granite system, and generated an unknown aluminosilicate. No distinct chemical alternations occurred in the water-free scCO₂/granite system, which indicated that rock minerals should be chemically stable in the water-free scCO₂ fluids under the current mild experimental conditions. Both the highest concentration of Ca existing in the scCO₂/vapor/granite system and the SEM observation results of calcite deposit, suggested that a meaningful CO₂ minerals trapping process should be potential in the CO₂-rich field during a short physicochemical interaction period.     

An experimental study on drilling of titanium alloy using CO<Subscript>2</Subscript> laser

Laser drilling is a popular method as it eliminates the problem of chatter and vibration due to the absence of physical contact between the tool and workpiece. Tool breakage, a common phenomenon that occurs due to bending of the tool in making of slender holes using conventional drilling, can also be avoided. However, quality of the hole measured in terms of circularity, taper and spatter area is the major concern during laser drilling. The present investigation attempts to find out the optimum parametric setting during drilling of Ti6Al4V using CO₂ laser in order to achieve quality holes. Experiments have been conducted to assess the influence of machining parameters, viz. flushing pressure, laser power and pulse frequency, on the performance characteristics such as taper of kerf, heat-affected zone (HAZ) and spatter area. Taguchi’s L₉ orthogonal array has been used to design the experimental layout as it reduces the experimental cost and time. Analysis of variance has been performed to assess the effect of machining parameter on the performance characteristics. It has been observed that laser power has significant influence on taper of kerf, HAZ and spatter area. Based on desirability approach, the study suggests that all the performance characteristics can be simultaneously optimized at flushing pressure of 40 Pa, laser power of 2250 W and pulse frequency of 1600 Hz. The study also presents a numerical model to simulate the laser drilling process. Since comparison of experimental and numerical model shows a relative error within 10%, adequacy of the numerical model for assessment of quality characteristics of laser drilled holes is justified.     

Phase modification induced drying shrinkage reduction on Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> activated slag by incorporating Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>

This paper aims to study the phase modification, reaction kinetics, mechanical properties and drying shrinkage of sodium carbonate activated slag by incorporating sodium sulfate in the activator. The results show that the reaction process is firstly controlled by CO₃ ^2? anions, and later runs similar to that of sodium sulfate activation. Besides, the relatively unstable phase gaylussite, commonly found in the sodium carbonate activation, is not observed in the reaction products upon hybrid activation, and monosulfoaluminate rather than ettringite is identified, probably caused by the reduced aluminate-to-sulfate ratio and increased pH value. The drying shrinkage is considerably reduced by up to 41% when replacing 50 wt% sodium carbonate by sodium sulfate, most possibly attributed to the induced phase modification. Furthermore, the relationships between the phase modification and drying shrinkage, and the potentially involved chemical reaction are discussed.     

Photocatalytic reduction of CO<Subscript>2</Subscript> with H<Subscript>2</Subscript>O over modified TiO<Subscript>2</Subscript> nanofibers: Understanding the reduction pathway

Nanosized metal (Pt or Pd)-decorated TiO₂ nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO₂ NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO₂ under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO₂ NFs were found to exhibit enhanced performance compared to Pt-decorated TiO₂ NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO₂ NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg^?1·h^?1 methanol. The CO₂ photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.

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Ni-doped ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> atomic layers to boost the selectivity in solar-driven reduction of CO<Subscript>2</Subscript>

Regulating the selectivity of CO₂ photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the selectivity of CO₂ photoreduction. Prototypical ZnCo₂O₄ atomic layers with/without Ni-doping were first synthesized. Density functional theory calculations reveal that introducing Ni atoms creates several new energy levels and increases the density-of-states at the conduction band minimum. Synchrotron radiation photoemission spectroscopy demonstrates that the band structures are suitable for CO₂ photoreduction, while the surface photovoltage spectra demonstrate that Ni doping increases the carrier separation efficiency. In situ diffuse reflectance Fourier transform infrared spectra disclose that the CO₂^·? radical is the main intermediate, while temperature-programed desorption curves reveal that the ZnCo₂O₄ atomic layers with/without Ni doping favor the respective CO and CH₄ desorption. The Ni-doped ZnCo₂O₄ atomic layers exhibit a 3.5-time higher CO selectivity than the ZnCo₂O₄ atomic layers. This work establishes a clear correlation between elemental doping and selectivity regulation for CO₂ photoreduction, opening new possibilities for tailoring solar-driven photocatalytic behaviors.

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Structural-defect formation in CeO<Subscript>2</Subscript> nanoparticles upon laser ablation

Cerium-dioxide nanoparticles are prepared by laser ablation, and their structure is studied by transmission electron microscopy and X-ray-diffraction analysis. The semiquantitative elemental composition is determined by electron energy-loss spectroscopy. Based on the spectral data obtained before and after annealing of particles, the significant oxygen-vacancy concentration in the structure of ablated CeO₂ nanoparticles is established.     

The effect of nanosecond ionization on the characteristics of a fast-flow CO<Subscript>2</Subscript> laser with self-sustained discharge

We studied the possibility of increasing the electric discharge stability, efficiency, and working range of a technological continuous-wave electric-discharge CO₂ laser at the expense of an additional pulsed ionization produced by nanosecond high-voltage pulses.     

Hydriding Pd cocatalysts: An approach to giant enhancement on photocatalytic CO<Subscript>2</Subscript> reduction into CH<Subscript>4</Subscript>

Photocatalytic reduction of CO2 into high value-added CH4 is a promising solution for energy and environmental crises.Integrating semiconductors with cocatalysts can improve the activities for photocatalytic CO2 reduction;however,most metal cocatalysts mainly produce CO and H2.Herein,we report a cocatalyst hydridation approach for significantly enhancing the photocatalytic reduction of CO2 into CH4.Hydriding Pd cocatalysts into PdH0.43 played a dual role in performance enhancement.As revealed by our isotopic labeling experiments,the PdH0.43 hydride cocatalysts reduced H2 evolution,which suppressed the H2 production and facilitated the conversion of the CO intermediate into the final product:CH4.Meanwhile,hydridation promoted the electron trapping on the cocatalysts,improving the charge separation.This approach increased the photocatalytic selectivity in CH4 production from 3.2％ to 63.6％ on Pd{100} and from 15.6％ to 73.4％ on Pd{111}.The results provide insights into photocatalytic mechanism studies and introduce new opportunities for designing materials towards photocatalytic CO2 conversion.     

Glass formation in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO system

The physicochemical properties of BaO-Bi₂O₃-B₂O₃ glasses have been studied. The effect of KBF₄ additions on the properties of the glasses has been examined. The transmission of the glasses has been correlated with their local structure and composition.     

Effect of the precipitation sequence on phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied phase formation processes during heat treatment of precipitates in the ZrO₂-Al₂O₃ and ZrO₂-CeO₂-Al₂O₃ systems. During heat treatment of powders prepared by coprecipitation of precursors to ZrO₂, CeO₂, and Al₂O₃, α-Al₂O₃ is formed at higher temperatures, which is due to the formation and decomposition of T-ZrO₂ and metastable Al₂O₃ phases. The precipitation sequence in the ZrO₂-CeO₂-Al₂O₃ system influences the lattice parameters of the forming T-ZrO₂-based solid solutions because of the different degrees of Ce⁴⁺ and Al³⁺ substitutions for Zr⁴⁺.     

Steady-state O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> diffusion in carbonated mortars produced with blended cements

The diffusion coefficient \(D_{{{\text{O}}_{2} }}\), the porosity and the pore structure of mortars produced with a Portland cement and a range of blended cements containing limestone powder, microsilica, portlandite or slag were measured in the non-carbonated and the carbonated state. Additionally, the setup for measuring O₂ diffusion was adapted to measure also the CO₂ diffusion of the carbonated mortars. The diffusion coefficient \(D_{{{\text{O}}_{2} }}\) and the total porosity were increased in the mortars containing microsilica and slag, while they were decreased in the other mortars due to carbonation. Invariably, the pore structure became coarser in all samples. The relationship between diffusion coefficients \(D_{{{\text{O}}_{2} }}\) and \(D_{{{\text{CO}}_{2} }}\) in the carbonated mortars was always linear, with \(D_{{{\text{O}}_{2} }}\) systematically higher by factor of 1.37. As this factor broadly agrees with what was found in the scant literature about CO₂ diffusion, it could be used for estimating \(D_{{{\text{CO}}_{2} }}\) of carbonated mortar and concrete based on measurements of O₂ diffusion.