Catalytic denitrification: direct and indirect removal of nitrates from potable water

A nitrate removal process that drastically reduces salt consumption and waste discharge has been developed on a bench scale. Nitrate is removed by chloride ion exchange, and the strong-base anion resin is completely regenerated at mild reaction conditions (i.e., ambient temperature, atmospheric pressure) in a closed circuit containing a single-flow fixed-bed reactor packed with a Pd–Cu/γ-Al₂O₃ catalyst. The combined treatment system avoids direct contact between the denitrification reactor and the water to be treated, and minimizes operational problems associated with each separate technique. No dissolution of Pd and Cu metallic-phases was observed at the given operating conditions.     

The Mechanochemical Synthesis of NaNbO3 Using Different Ball-Impact Energies

We studied the mechanochemical synthesis of NaNbO₃ from a starting-powder mixture of sodium carbonate and Nb₂O₅ using ball-impact energies of 15 and 370 mJ/hit. Based on the results of a quantitative phase analysis we propose a mechanism for the mechanochemical synthesis of NaNbO₃. During milling a condition is established, where the amounts of perovskite, X-ray diffraction -amorphous phase and residual carbonate in the mixture do not change with increasing milling time. Similarly, the NaNbO₃ crystallite size and the quantity of microstrains reach final values that are independent of the applied ball-impact energy.     

Preparation, characterization and catalytic properties of carbon nanofiber-supported Pt, Pd, Ru monometallic particles in aqueous-phase reactions

Carbon nanofibers (CNF) synthesized by catalytic chemical vapor deposition (CVD) method were used to prepare supported platinum, palladium and ruthenium monometallic (2.0 wt.%) catalysts by means of incipient-wetness impregnation method. The CNF support and catalysts were characterized by X-ray powder diffraction (XRD), nitrogen adsorption/desorption isotherms, volumetric chemisorption of hydrogen, temperature-programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). Solids were tested in catalytic wet-air oxidation (CWAO) of phenol aqueous solution (180–240 °C and 10.0 bar of oxygen partial pressure) carried out in a continuous-flow trickle-bed reactor. Trends of phenol and total organic carbon (TOC) conversion demonstrate that the CNF support and CNF-Pt catalyst did not exhibit constant activity for CWAO of phenol. A decrease of catalyst activity, detection of carbon dioxide in the off-gas stream while examining catalyst stability and significant textural changes observed, provide an evidence that under net oxidizing reaction conditions gasification of the CNF support occurs. The prepared catalysts were also tested in liquid-phase thermal decarboxylation of formic acid in inert atmosphere (60–220 °C). Among solids examined, the CNF-Pd exhibited the highest activity. At the employed conditions, no decomposition of the CNF support was observed during the thermal decarboxylation of formic acid.     

A structural and corrosion study of triethoxysilyl and perfluorooctyl functionalized polyhedral silsesquioxane nanocomposite films on AA 2024 alloy

A tri-functional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R_xR_yR_z(SiO_3/2)_n (x + y + z = n = 6, 8, 10, ….) bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl, isooctyl and perfluoropropyl groups was synthesized and investigated as corrosion protective coating for AA 2024 alloy. Infrared reflection-absorption (IR RA) combined with X-ray photoelectron spectroscopy and atomic force microscopy provided information about partial self-assembling of coatings having a fluorine enriched upper layer with a low surface energy (γ^tot = 12.37 mN/m). The structural changes that accompanied corrosion produced under chronocoulometrical conditions were assessed from ex-situ IR RA spectra. A new band at 1690-1700 cm^− 1 appeared above the corrosion potential, and was assigned to the formation of amidonium ions and consequent relaxation of urea-urea associations.     

Influence of Laser Remelting Process Parameters on Residual Stresses in Nodular Cast Iron 500 - 7

The measurement of residual stresses is very important in dynamically loaded precision machine parts which have been subjected to different kinds of heat treatment. Designers very frequently demand the presence of compressive residual stresses after heat treatment and finish grinding of the surface, since this increases the fatigue strength of the material and reduces the danger of fracture. In this investigation of the residual stresses after laser surface remelting, the size and variation of residual stresses were measured as a function of the modified layer depth on flat samples of nodular cast iron. Optimal laser remelting conditions were chosen, while the way of guiding the laser beam over the surface of flat samples was varied. To measure residual stresses, the relaxation method was used, including gradual electrochemical removal of the modified layer in which the deformation of the specimen was measured by resistance strain gauges.     

The Influence of Retained Austenite on Residual Stresses in Laser Remelted Cast Iron

The presence and amount of residual stresses is very important in dynamically loaded automotive machine parts. In this investigation, the residual stresses after laser surface remelting were measured as a function of the modified layer depth on flat specimens from nodular cast iron. The results of the measured residual stresses confirm that the stresses strongly depend on the presence and quantity of the microstructure constituents in the surface remelted layer. Residual stresses have a characteristic profile in the modified surface layer. In the surface remelted layer, tensile residual stresses were found in a range between +70 and +200 MPa. The change from tensile into compressive residual stresses takes place in the lower part of the remelted layer. Maximum compressive residual stress values were found in the middle of the hardened layer in a range between −25 and −80 MPa.     

The Effect of Phase Composition on the Mechanical Properties of LTCC Material

For the fabrication of complex, micro‐electromechanical systems (MEMS) devices based on low‐temperature co‐fired ceramic (LTCC), higher firing temperatures and longer times than those proposed by the LTCC producer are needed. These changes to the thermal budget may influence the material properties and consequently its functional properties. The effect of the firing conditions on the LTCC DuPont 951 and thus on the phase composition, that is, the alumina/anorthite ratio and porosity, on the mechanical properties is presented. The samples fired at low temperatures (800°C) had a high porosity (7%), which significantly contributed to the low elastic modulus (100 GPa) and the low mechanical strength of the LTCC (140 MPa). The samples fired at 850°C, which had only 1% of porosity, resulted in an elastic modulus of 122 GPa and a flexural strength of 224 MPa. A further increase in the temperature contributed to a slight decrease in the elastic modulus, while no significant difference in the flexural strength could be observed. The enhancement of the flexural strength with an increasing firing temperature was mainly related to a decrease in the porosity and to a lesser extent to the different ratio of the alumina/anorthite phases. The effect of firing time on the phase composition at selected temperatures (i.e., 100 h at 700 and 800°C) is also discussed.     

A new method for defining the measurement-uncertainty model of CNC laser-triangulation scanner

This article examines the measurement uncertainty in terms of the incident angle, the object colour and the measurement distance for a Computer Numerical Control (CNC) laser-scanning process. It describes a new method for predicting the measurement uncertainty that simultaneously considers all three parameters. A set of measurements with different values for these parameters was made in order to describe the measurement uncertainty for the whole measuring range of the laser-scanning device. The final result of this research is an equation model that allows an accurate prediction of the measurement uncertainty within the investigated measurement field while the results of the extrapolated measurement field give an accuracy of the prediction that is better than 15%. In general, the model can also be useful as a measuring guideline for any other laser-triangulation measuring device, although the values would need to be adapted to each particular device. The, thus, obtained equation model could then be implemented into automatic inspection/control lines or used for self-adaptive measuring CNC paths to perform measurements in the optimal measuring range for a particular surface.