Semi‐theoretical prediction of volumetric mass transfer coefficients in bubble columns with organic liquids at ambient and elevated temperatures

A semi‐theoretical approach for predicting k_La values (referred to liquid volume) in 18 organic liquids [acetone, aniline, 1‐butanol, benzene, cyclohexane, decalin, 1,2‐dichloroethane, 1,4‐dioxane, ethanol (96%), ethylacetate, ethylbenzene, ligroin, methanol, nitrobenzene, 2‐propanol, tetralin, toluene, and xylene] at various operating conditions (including elevated temperatures and pressures) was developed. It was found that the approach is applicable regardless of the hydrodynamic regime (at u_G ≤ 0.1 m/s). Temperatures up to 353 K and pressures up to 0.5 MPa were tested. Two different distributors (multiple‐hole and single‐hole type) were employed. The liquid‐phase mass transfer coefficient k_L was calculated theoretically from the penetration theory on the basis of original definition of gas–liquid contact time. The interfacial area a was defined with respect to the liquid volume. It was found that their product k_La must be multiplied by some correction factor in order to take account of the non‐spherical (ellipsoidal) shape of the bubbles. When the correction term is correlated to both the Eötvös number (Eo) and the dimensionless temperature ratio, 198 experimental k_La values can be fitted reasonably well (average relative error 9.3%).     

More on the microstructural characterization of dense particle gels

A systematic study of the microstructure of densely packed coagulated colloidal particle gels is important for understanding their macroscopic, in particular, mechanical properties. It was previously shown that heterogeneous gels exhibit higher elastic properties and yield strengths than their homogeneous counterparts at the same solids loading. This was explained by the newly developed straight path method.¹ However, this macroscopic behaviour can be also explained by classical and conceptually simpler methods of spatial statistics, in particular, the pair-correlation function and the related K-function. Additionally, the structural differences of homogeneous and heterogeneous gels can be described by the contact distributions, which characterize the pore space and are of relevance for certain transport properties. The understanding of the structural differences is completed by presenting a benchmark model, which is in some sense ‘between’ the homogeneous and heterogeneous case.     

Surface treatment with ultraviolet laser for adhesive bonding of polymeric materials

We demonstrated an efficient surface pretreatment with excimer laser at 193 nm, which could be successfully used as a surface preparation tool to improve the adhesion and mechanical properties of bonded polymer joints. The effect of the ultraviolet (UV) light can be used both as a method for increasing the specific surface area improving the mechanical adhesion and as a method for activating the polymer surface improving the physical adhesion. Mechanical tests and studies on the failure of bonded polycarbonate (PC) and polyetheretherketone (PEEK) samples showed a significant increase in the quality of bonded connections by using pretreatment with UV laser. As a result of the studies, the bond strength of the PC samples was increased by about 32% using a PB437 UV curing adhesive. By using Loctite 9466 applied to PEEK samples, a strength increase of about 36% was achieved.     

High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment

Improved activity and durability performance of a two-cell (86 cm²) proton exchange membrane water electrolyzer (PEMWE) stack is reported for the first time. Both membrane electrode assemblies (MEAs) contain one order of magnitude lower platinum group metal (PGM) loadings compared to the state-of-the-art PEMWEs and incorporate novel Pt recombination layers. The high-performance and cost-effective MEAs are fabricated by the unique reactive spray deposition technology (RSDT). This advanced methodology allows for one-step fabrication of MEAs and ensures precise control and distribution of the catalyst composition and loading. The RSDT-fabricated MEAs contain only 0.2 and 0.3 mg_PGM cm^?2 loading in the cathode and anode electrodes, respectively, and demonstrate excellent activity and durability for over 3000 h of operation at industrially-relevant operating conditions without showing significant loss in performance. This novel work shows that a significant cost reduction for PEMWEs is achieved while maintaining excellent durability, high catalysts activities, and low hydrogen cross-over.     

Bio hydrometallurgical recovery of metals from Fine Shredder Residues

The leaching step of an integrated hydrometallurgical process for the selective recovery of metals from polymetallic concentrates has been investigated. This concentrate has been produced by physical treatment of Fine Shredder Residues derived from a shredding plant processing a mixed feed of metallic scraps, waste electric equipments and end-of-life vehicles. Bacterially assisted leaching experiments have been carried out using a copper-adapted consortium of mesophilic bacterial strains. The influence of various operating conditions such as stirring speed, temperature (25-50 °C), pulp solids density (5-20%) and initial iron concentration (0-15 g/L) has been studied. Temperature and stirring speed have proved to be the most influential parameter regarding copper dissolution kinetics, while pulp solids density and initial iron concentration have been found to have a subordinate importance. In optimum conditions, 95% extractions of zinc and copper were achieved within 48 h. Bacterial presence has been found beneficial in terms of catalysing copper dissolution.     

Mathematical Modeling of the Control of Dynamics of Thick Elastic Plates. I. Control Under Continuous Desired State

The authors formulate and solve control problems for the dynamics of the three-dimensional field of transverse dynamic displacements of elastic plates of finite thickness coordinated with the mean square fixed continuous desired condition. The control factors are superficially distributed external-dynamic loads, initial and boundary disturbing factors taken individually, in pairs, and all three together. The features of the solution of these problems are described for the case where some of the initial and boundary disturbances are not important. The conditions of the accuracy and uniqueness of the solutions are analyzed.     

The Time-resolution Limit of Photodetection Using Single-frequency Oscillations Excited by Secondary Electrons

Abstract

Analytical estimates for the limiting temporal resolution of the photoreceiving system based on the spectral analysis of the interference signal from single-frequency decayed oscillations excited by the secondary electron train are given. It is shown that the resolution limit is defined by the r.m.s. fluctuations of the photoemission time and time-jitter of the secondary electron packets divided by the square root of the number of photoelectrons within the resolution cell at arbitrary intensities, and does not depend on the time-broadening of the electron packets excited by individual photoelectrons. Numerical estimates show the possibility of obtaining resolutions of the order of 10^?12–10^?14 s. The achieving of such resolutions is due to the interference of a great number of oscillations with phase differences smaller than π giving a resultant signal of very small phase variance. The product of the limiting resolution interval and the square root of the signal energy is a constant, depending on the device fluctuation parameters. It is shown that the resolution limit may be achieved in the low frequency range, while the resolution of the Fourier method is limited by the maximum attainable frequency. The estimates show the possibility of realizing a new type of photoreceiving device with the following main advantages—high resolution (better than 1 ps for a standard gating technique), use of the full signal energy at arbitrary intensities and a sensitivity close to that of the photon detectors.     

High‐Pressure Investigation in the System SiO2–GeO2: Mutual Solubility of Si and Ge in Quartz,Coesite and Rutile Phases

Mutual solubilities in crystalline phases in the system SiO₂–GeO₂ have been investigated up to 10 GPa pressure and 1500°C temperature, using a bulk composition of 50 mol% GeO₂. Solid solution of up to 40 mol% GeO₂ into the mineral quartz has been confirmed as well as solubility of Si into GeO₂ rutile (argutite) and Ge into SiO₂ rutile (stishovite) phases and limited Ge into coesite. Solubility of Ge in quartz is very high, and decreases with pressure, with the univariant quartz‐out reaction occurring near 3.4 GPa at 1200°C. The solubility of GeO₂ in coesite is highest at 3.4 GPa (about 8 mol%) and decreases with increasing pressure. Significantly more extensive solubility than previously reported for the rutile phases has been found and measured in detail as a function of pressure and temperature. Extensive solubility of SiO₂ in GeO₂ is found in argutite at 1200°C, increasing strongly with pressure and reaching a maximum of 25.2 mol% SiO₂ in GeO₂ at 9 GPa. At this point coesite (ss) plus argutite (ss) react to form a stishovite phase with 18 mol% GeO₂, and the mutual solubility in both phases decreases above this pressure. At 1500°C, similar solubilities are observed but the maximum SiO₂ solubility in argutite of just over 25 mol% occurs near 10 GPa. All these solid solutions can be recovered to ambient temperature and pressure. Phase diagrams and unit cell information of the phases are presented here. Based on these results, a useful and industrially relevant, application for accurately measuring high pressure is suggested.     

3D Printing by Multiphase Silicone/Water Capillary Inks

3D printing of polymers is accomplished easily with thermoplastics as the extruded hot melt solidifies rapidly during the printing process. Printing with liquid polymer precursors is more challenging due to their longer curing times. One curable liquid polymer of specific interest is polydimethylsiloxane (PDMS). This study demonstrates a new efficient technique for 3D printing with PDMS by using a capillary suspension ink containing PDMS in the form of both precured microbeads and uncured liquid precursor, dispersed in water as continuous medium. The PDMS microbeads are held together in thixotropic granular paste by capillary attraction induced by the liquid precursor. These capillary suspensions possess high storage moduli and yield stresses that are needed for direct ink writing. They could be 3D printed and cured both in air and under water. The resulting PDMS structures are remarkably elastic, flexible, and extensible. As the ink is made of porous, biocompatible silicone that can be printed directly inside aqueous medium, it can be used in 3D printed biomedical products, or in applications such as direct printing of bioscaffolds on live tissue. This study demonstrates a number of examples using the high softness, elasticity, and resilience of these 3D printed structures.