Modelling of arc welding: The importance of including the arc plasma in the computational domain

We present results of computational simulations of tungsten-inert-gas and metal-inert-gas welding. The arc plasma and the electrodes (including the molten weld pool when necessary) are included self-consistently in the computational domain. It is shown, using three examples, that it would be impossible to accurately estimate the boundary conditions on the weld-pool surface without including the arc plasma in the computational domain. First, we show that the shielding gas composition strongly affects the properties of the arc that influence the weld pool: heat flux density, current density, shear stress and arc pressure at the weld-pool surface. Demixing is found to be important in some cases. Second, the vaporization of the weld-pool metal and the diffusion of the metal vapour into the arc plasma are found to decrease the heat flux density and current density to the weld pool. Finally, we show that the shape of the wire electrode in metal-inert-gas welding has a strong influence on flow velocities in the arc and the pressure and shear stress at the weld-pool surface. In each case, we present evidence that the geometry and depth of the weld pool depend strongly on the properties of the arc.     

Stress field at the boundary of a wedge-shaped twin

A model is proposed to calculate the stress field at the boundary of a wedge-shaped twin which can allow for its degree of coherence. It is shown that the stress field decreases exponentially with increasing distance from the twinning boundary. Pis’ma Zh. Tekh. Fiz. 23, 1–6 (November 26, 1997)     

Effect of hydrophilicity of carbon nanotube arrays on the release rate and activity of recombinant human bone morphogenetic protein-2

Novel nanostructures such as vertically aligned carbon nanotube (CNT) arrays have received increasing interest as drug delivery carriers. In the present study, two CNT arrays with extreme surface wettabilities are fabricated and their effects on the release of recombinant human bone morphogenetic protein-2 (rhBMP-2) are investigated. It is found that the superhydrophilic arrays retained a larger amount of rhBMP-2 than the superhydrophobic ones. Further use of a poloxamer diffusion layer delayed the initial burst and resulted in a greater total amount of rhBMP-2 released from both surfaces. In addition, rhBMP-2 bound to the superhydrophilic CNT arrays remained bioactive while they denatured on the superhydrophobic surfaces. These results are related to the combined effects of rhBMP-2 molecules interacting with poloxamer and the surface, which could be essential in the development of advanced carriers with tailored surface functionalities.     

Manufacturing of greases based on deep-cleaned spent mineral and synthetic motor oils

The possibility of increasing the efficiency of utilization of spent motor oils as the dispersion medium of lubricating greases has been explored. It has been established that the removal of resins, asphaltenes, carbenes, and carboids from used mineral and synthetic motor oils makes it possible to obtain a base stock close to commercial base oils in the main characteristics. It has been proposed to use carbamide or monoethanolamine in a mixture with isopropanol. It has been found that more than 90% of the contaminants are removed from used engine oils by refining according to the methods proposed. The re-refined oils have a high margin of performance. The composition of Litol-24 and Solidol Zh grease analogues based on refined waste motor oils has been determined. The corrosion-preventing, adhesion, and strength properties of the lubricant compositions are considered. The results of bench testing of lubricant compositions in rolling bearings, which confirm their high performance properties, are presented.     

Structure, bonding state and in-vitro study of Ca–P–Ti film deposited on Ti6Al4V by RF magnetron sputtering

Experimental investigation of functionally graded calcium phosphate-based bio-active films on Ti–6Al–4V orthopaedic alloy prepared in an RF magnetron sputtering plasma reactor is reported. The technique involves concurrent sputtering of Hydroxyapatite (HA) and Ti targets, which results in remarkably enhanced adhesion of the film to the substrate and stability of the interface. The films have been characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XPS data show that the films are composed of O, Ca, P and Ti, and reveal the formation of O=P groups and hybridization of O–Ca–P. The XRD pattern shows that the Ca–P thin films are of crystalline calcium oxide phosphate (4CaO·P₂O₅) with preferred orientation varying with processing parameters. High-resolution optical emission spectra show that the emission of CaO is dominant. The CaO, PO and CaPO species are strongly influenced by deposition conditions. The introduction of Ti element during deposition provides a stable interface between bio-inert substrates Ti–6Al–4V and bioactive HA coating. In-vitro cell culturing tests suggest excellent biocompatibility of the Ca–P–Ti films.     

Function-Targeted Lanthanide-Anchored Polyoxometalate–Cyclodextrin Assembly: Discriminative Sensing of Inorganic Phosphate and Organophosphate

Polyoxometalate (POM) clusters containing lanthanide ion (LnPOM) possess excellent luminescence features, but the envisaged applications are hindered by the challenges in integration into functional architectures. Herein, a novel cross-linked cyclodextrin (CL-CD) and LnPOM composite is developed and applied for discriminative detection of inorganic and organic phosphate phases. For inorganic phosphates, a ratiometric fluorescence response is demonstrated with excellent selectivity, and anti-interference ability in complex analyte mixtures. The outstanding performance is attributed to the high affinity of POM and distinct interactions between La³⁺ and Eu³⁺ with the phosphate. For organophosphates, a “signal-off” fluorescence response for p-nitrophenyl-substituted organophosphates is discovered due to the encapsulation of nitrophenyl group into the hydrophobic cavity of CD that enhances the interactions between POM and p-nitrophenyl phosphate. The discriminative responses of CL-CD–LnPOM to inorganic phosphates and organophosphates bring new insights into POM-based fluorescence probes for the detection of inorganic and organic phases based on the intrinsic structural difference between the phosphate analogs.