Analyses of the reasons for the decreased service time of CrN-coated die for aluminy hot extrusion – a case study

Presented study shows that considerable reserves still exist for increasing the service times (lifetimes) of CrN – coated dies for Al hot extrusion. The main reasons for the decreased service times are revealed and explained regarding the selected CrN - coated die for hot extrusion, i.e. why the service time of the coated-die is not in accordance with the wear resistance of the CrN - coating. The shaping of the bearing surface and presence of the scratches, size and amount of nonmetalic inclusions in the die steel, nodular defects in the CrN - coating, as well as thicknesses uniformity of CrN - coatings along the bearing surface, are relevant influential parameters

Characterization of an enzymatic packed-bed microreactor: Experiments and modeling

A micro packed-bed reactor (µPBR) based on two-parallel-plates configuration with immobilized Candida antarctica lipase B in the form of porous particles (Novozym® 435) was theoretically and experimentally characterized. A residence time distribution (RTD) within µPBRs comprising various random distributions of particles placed in one layer was computationally predicted by a mesoscopic lattice Boltzmann (LB) method. Numerical simulations were compared with measurements of RTD, obtained by stimulus-response experiment with a pulse input using glucose as a tracer, monitored by an electrochemical glucose oxidase microbiosensor integrated with the reactor. The model was validated by a good agreement between the experimental data and predictions of LB model at different conditions. The developed µPBR was scaled-up in length and width comprising either a single or two layers of Novozym® 435 particles and compared regarding the selected enzyme-catalyzed transesterification. A linear increase in the productivity with the increase in all dimensions of the µPBR between two-plates demonstrated very efficient and simple approach for the capacity rise. Further characterization of µPBRs of various sizes using the piezoresistive pressure sensor revealed very low pressure drops as compared to their conventional counterparts and thereby great applicability for production systems based on numbering-up approach

Microfluidic flow injection immunoassay system for algal toxins determination: a case of study

A novel flow injection microfluidic immunoassay system for continuous monitoring of saxitoxin, a lethal biotoxin, in seawater samples is presented in this article. The system consists of a preimmobilized G protein immunoaffinity column connected in line with a lab-on-chip setup. The detection of saxitoxin in seawater was carried out in two steps: an offline incubation step (competition reaction) performed between the analyte of interest (saxitoxin or Ag, as standard or seawater sample) and a tracer (an enzyme-conjugated antigen or Ag*) toward a specific polyclonal antibody. Then, the mixture was injected through a "loop" of a few mu L using a six-way injection valve into a bioreactor, in line with the valve. The bioreactor consisted of a small glass column, manually filled with resin upon which G protein has been immobilized. When the mixture flowed through the bioreactor, all the antibody-antigen complex, formed during the competition step, is retained by the G protein. The tracer molecules that do not interact with the capture antibody and protein G are eluted out of the column, collected, and mixed with an enzymatic substrate directly within the microfluidic chip, via the use of two peristaltic pumps. When Ag* was present, a color change (absorbance variation, Delta Abs) of the solution is detected at a fixed wavelength (655 nm) by an optical chip docking system and registered by a computer. The amount of saxitoxin, present in the sample (or standard), that generates the variation of the intensity of the color, will be directly proportional to the concentration of the analyte in the analyzed solution. Indeed, the absorbance response increased proportionally to the enzymatic product and to the concentration of saxitoxin in the range of 3.5 x 10(-7)-2 x 10(-5) ng ml(-1) with a detection limit of 1 x 10(-7) ng ml(-1) (RSD% 15, S N-1 equal to 3). The immunoanalytical system has been characterized, optimized, and tested with seawater samples. This analytical approach, combined with the transportable and small-sized instrumentation, allows for easy in situ monitoring of marine water contaminations

The morphological and compositional changes of bimetallic Ti/Al thin film induced by ultra-short laser pulses

Results regarding morphological and compositional changes of bimetallic thin film (BMTF), composed of aluminium (Al) and titanium (Ti) nano-layers, by single fs laser pulses, are presented. Laser irradiation was conducted in the air with focused, linearly polarized laser pulses, the duration being 300 fs, wavelength 515 nm, and pulse energy up to 1.2μJ. Effects of the variations of the pulse energy on the changes were studied. In the experiment, single pulse energy values from 0.03 to 0.08 μ J caused ablation–photomechanical spallation of the upper part of BMTF layer from the Si substrate, without ablation of the whole film. Irradiation at higher pulse energies gradually removed the whole BMTF and even a part of the Si substrate. We explained the influence of different electron–phonon dynamics, in the case of multilayered thin films composed of Al and Ti, on BMTF ablation. Damage/ablation threshold, which is minimal pulse energy/fluence sufficient for starting ablation, was calculated. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature

Microstructure Analysis of Thermally Etched Alumina Ceramics

U radu je opisan postupak pripreme aluminij-oksidne (Al2O3) keramike visoko čiste, oblikovane hladnim izostatičkim prešanjem. Mikrostruktura pripravljene keramike analizirana je optičkim mikroskopom (OM), pretražnim elektronskim mikroskopom (SEM) te mikroskopom atomskih sila (AFM). Na poliranom uzorku određen je udjel pora, a nakon toplinskog nagrizanja određena je veličina zrna. Prosječni promjer zrna određen je metodom kruga, metodom crte te analizom slike.Ceramography is the art and science of preparation, examination, and evaluation of ceramic microstructures. Microstructure is the structure level approximately 0.1 to 100 μ m between the wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, microcracks, hardness microindentations. Investigation and evaluation of ceramic microstructure is very important because a number of mechanical, optical, thermal, electrical and other properties of ceramics are significantly affected by the microstructure. The techniques for ceramographic preparation are divided into five parts: sawing, mounting, grinding, polishing and etching. In this paper a method for preparation of a cold isostatically pressed high purity alumina ceramics (α-Al2O3) is described. Microstructure analysis of prepared ceramics was performed by means of optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Porosity is determined on the polished sample; grain size is measured after thermal etching. The mean grain diameter is determined by means of lineal-intercept method, circular-intercept method and image analysis

Modification of multilayered TiAlN/TiN coating by nanosecond and picosecond laser pulses

A multilayered TiAlN/TiN coating deposited on H11 work-steel was irradiated by a TEA CO(2) laser (ns pulses) and a Nd:YAG laser (ps pulses), and the effects compared. The coating was 2.17 mu m thick and consisted of 45 layers. The laser-induced modifications showed dependence on laser pulse duration, pulse count and laser wavelength. The conditions for coating ablation in both cases were determined. The experiment has revealed laser-induced periodic surface structures (LPSS) on nanometre and micrometre scales, depending on the laser wavelength used. Sample surfaces were characterized before and after laser irradiation by an optical microscope, scanning electron microscope (SEM), focused ion beam (FIB) microscope and profilometry