Activated flux tig welding of stainless-steel pipes

In this work, the presence of TiO2 nanoparticle-based activated flux combined with orbital welding of seamless thick-walled pipes of stainless steel and low-cycle pulse current was done, representing a novel combination of welding processes parameters. Control specimens were welded without flux and consumable material, and without flux with the consumable material. Experimental welding with different welding parameters was done. Special attention was given to characterize the flux by zetasizer method, representing a new approach, versus the conventional approach where the nominal oxide particle size is reported. The obtained welds were visually tested, macroanalyzed, their microstructures examined, and their tensile and bending properties determined. The results show that the flux influences a significant increase in penetration depth, up to full penetration, which has a positive effect on the increase in the tensile and bending properties of the weld metal. Material beahvior model was developed, based on microstructural features of the near weld-line. Without the flux, grain enlargement occurred near the surface, while with flux, it occurred under the weld, which can be attributed to recrystallization and a reversed Marangoni convection

Suppressing the Use of Critical Raw Materials in Joining of AISI 304 Stainless Steel Using Activated Tungsten Inert Gas Welding

The aim of this study was to study the influence of TiO2 coating for its efficacy during the activated-tungsten inert gas (TIG) welding and to suppress the use of consumables that are rich in critical raw materials. Post-welding penetration depth, particle size distribution, microstructure, and microhardness of welded samples were assessed. Based on these results, it was found that there is no direct correlation between the weld metal surface area and the coating. The particle size in the coating, although, seemed to have played an important role, e.g., nanoparticles resulted in an increased penetration depth and depth/width (D/W) ratio as opposed to the submicron-sized particles. The most optimal welding condition resulted when a mixture of submicron-sized and nanometric-sized particles were used. It was demonstrated by the Zeta analyser results that the micron particles rub the nanoparticles due to mechanical friction resulting in smaller oxide particle formation in the coating. Finally, the presence of Marangoni convection in TIG and reversed Marangoni convection in the activated TIG (A-TIG) process were proven by means of the microstructure analysis and measurement, which were found to be positively correlate

Structural, morphological and luminescence properties of nanocrystalline up-converting Y1.89Yb0.1Er0.01O3 phosphor particles synthesized through aerosol route

Nanocrystalline up-converting Y₂ O₃Yb³⁺ Er³⁺ phosphor particles were processed in a dispersed system-aerosol, generated ultrasonically at 1.3 MHz from common nitrate precursor solution having fixed ytterbium-to-erbium concentration ratio. The appropriate process parameters: residence time 21 s, carrier gas (air) flow rate 1.6 dm3/min, synthesis temperature 900 °C, led to the formation of un-agglomerated spherical nanostructured secondary particles, having mean particle size of approx 450 nm, composed of primary nanoscaled (20 nm) subunits. In order to reach targeting phase crystallinity, the as-prepared particles were additionally annealed at 1100 °C in air for 12, 24 and 48 h, respectively. Particle structure, morphology and purity were analyzed by X-ray powder diffraction (XRPD), scanning electron microscopy (FESEM/SEM), analytical and high resolution transmission electron microscopy (TEM/HRTEM) in combination with energy dispersive X-ray analysis and Fourier Transform Infrared Spectroscopy (FTIR). All samples crystallized in a cubic bixbyte-structure, space group Ia-3. The crystallite size changed with annealing time from 30 nm in as-prepared sample to 135 nm in sample annealed for 48 h, respectively. Emission spectra were assigned to the following trivalent erbium f–f electronic transitions: ²H₉/₂ → ⁴I₁₅/₂ (blue: 407–420 nm), (²H₁₁/₂̦ ⁴S₃/₂) → ⁴I₁₅/₂ (green: 510–590 nm), and ⁴F₉/₂ → ⁴I₁₅/₂ (red: 640–720 nm). The significant improvement of the emission decay times were observed after thermal treatment and this effect is correlated further with the structural and morphological particles characteristics. For the anneal-ing time of 12 h a quite high emission decay times were achieved (blue: 0.14 ms, green: 0.32 ms and red: 0.39 ms).This research is financially supported through the Project #172035 of the Ministry of Science and Education of the Republic of Serbia. OM especially acknowledge the University Carlos III, Madrid, Spain-Santander Bank Chairs of Excellence program and JSPS 2011/2012 fellowship, Japan.Publicad

Structure and enhanced antimicrobial activity of mechanically activated nano TiO2

Titanium dioxide is a photocatalyst, known not only for its ability to oxidize organic contaminants, but also for its antimicrobial properties. In this article, significant enhancement of the antimicrobial activity of TiO2 (up to 32 times) was demonstrated after its activation by ball milling. The antimicrobial activity was analyzed for one fungal and 13 bacterial ATCC strains using the microdilution method and recording the minimum inhibitory concentration (MIC) values. In order to further investigate the correlation between the mechanical activation of TiO2 and its antimicrobial activity, the structure, morphology and phase composition of the material were studied by means of Electron Microscopy, X-ray diffraction and nitrogen adsorption-desorption measurements. UV-Vis diffuse reflectance spectra were recorded and the Kubelka-Munk function was applied to convert reflectance into the equivalent band gap energy (E-g) and, consequently, to investigate changes in the E-g value. X-ray photoelectron spectroscopy was used to analyze the influence of mechanical activation on the Ti 2p and O 1s spectra. The presented results are expected to enable the development of more sustainable and effective advanced TiO2-based materials with antimicrobial properties that could be used in numerous green technology applications

Antibacterial potential of electrochemically exfoliated graphene sheets

Electrochemically exfoliated graphene is functionalized graphene with potential application in biomedicine. Two most relevant biological features of this material are its electrical conductivity and excellent water dispersibility. In this study we have tried to establish the correlation between graphene structure and its antibacterial properties. The exfoliation process was performed in a two electrode-highly oriented pyrolytic graphite electrochemical cell. Solution of ammonium persulfate was used as an electrolyte. Exfoliated graphene sheets were dispersed in aqueous media and characterized by atomic force microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X photoelectron spectroscopy, X-ray diffraction, electron paramagnetic resonance, zeta potential, contact angle measurements and surface energy. Antibacterial assays have shown lack of the significant antibacterial activity. Major effect on bacteria was slight change of bacteria morphology. Membrane remained intact despite significant change of chemical content of membrane components.This is the peer reviewed version of the paper: Marković, Z. M., Matijašević, D. M., Pavlović, V. B., Jovanović, S. P., Holclajtner-Antunović, I. D., Špitalský, Z., Mičušik, M., Dramićanin, M. D., Milivojević, D. D., Nikšić, M. P., & Todorović Marković, B. M. (2017). Antibacterial potential of electrochemically exfoliated graphene sheets. Journal of Colloid and Interface Science, 500, 30–43. [https://doi.org/10.1016/j.jcis.2017.03.110][https://www.sciencedirect.com/science/article/abs/pii/S0021979717303776?via%3Dihub

Conduction of Heat in Inhomgeneous Solids

In this letter we present a method for calculation of linear heat flow in inhomogeneous solids. The method is based on the evaluation of transfer matrices for each layer in a multilayered structure from the Laplace transformation of the partial differential equation of heat conduction. The multilayered structure is then described by a matrix obtained as a chain of products of individual layer transfer matrices and corresponding boundary thermal resistivity matrices. The analytic expression for the nth power of the multilayered transfer matrix is found, describing a periodic multilayered structure composed of n equal multilayered structures. The application of the presented method for calculation of photothermal signals is also shown. Dispersion relation for the thermal waves in inhomogeneous solids is obtained from the matrix elements of the transfer matrix. Finally, from the dispersion relation explicit expressions for the effective values of thermal diffusivity and conductivity of both the discontinuously and continuously inhomogeneous solids are evaluated