Chemico-structural properties and biomineralization of hydroxyapatite coatings produced by high power laminar plasma spray process.

U ovom radu je izvršeno nanošenje hidroksiapatitnih (HA) prevlaka primenom visokoenergetskog laminarnog plazma sprej postupka. Glavni ciljevi rada su bili: (i) da se ispita uticaj nekoliko parametara procesa nanošenja na hemijska, strukturna i morfološka svojstva HA prevlaka i (ii) da se ispita uticaj ljudskih proteina albumin i gama globulin na početni stadijum procesa biomineralizacije koji se javlja na površini dobijenih HA prevlaka u modifikovanim Kokubo rastvorima (simulirane telesne tečnosti) u kojima je vrednost pH bila aktivno regulisana pomoću CO2...In the present work, hydroxyapatite coatings (HACs) were deposited by using the high power laminar plasma spray process. Major objectives were: (i) to estimate effects of several deposition parameters on chemical, structural, and morphological properties of HACs and (ii) to evaluate effects of human proteins albumin and gamma globulin on the early stage of the biomineralization process on the surface of HACs in modified Kokubo solutions (simulated body fluids) in which the pH value was actively regulated using CO2

Simulated Body Fluids Prepared with Natural Buffers and System for Active pH Regulation

The current study focuses on creating an initial highly alkaline simulated body fluid whose pH can be decreased to a physiological range by adding CO2 (protein-free simulated body fluid) or a combination of CO2 and human proteins (protein-containing simulated body fluid). The effects of dissolved human proteins, Ca2+ ions, and immersed plasma-sprayed hydroxyapatite coatings on the pH and chemical instability of prepared simulated body fluids were investigated. The physiological concentration of dissolved human proteins decreased the pH instability in prepared simulated body fluids by 60% and the physiological concentration of dissolved Ca2+ ions by 15%. The effect of immersing the hydroxyapatite coatings was negligible. In terms of chemical instability, the dissolution of Ca2+ ions caused the blurring of protein-free simulated body fluids after 0.6-1.0 h. In protein-containing simulated body fluids, this phenomenon was undetectable due to their opacity. The effects of human protein presence on the carbonated-apatite-forming ability on the surfaces of immersed hydroxyapatite coatings in the prepared simulated body fluids were also assessed. The experiments validated the bioactivity of plasma-sprayed hydroxyapatite coatings in the prepared simulated body fluids, regardless of protein presence. On the other hand, under the different experimental conditions (unregulated or regulated pH), the human protein presence had an inhibitory (unregulated pH) or indifferent/promoting (regulated pH) influence on the carbonated-apatite-forming ability. The results of the present study are discussed, as well as the strengths and shortcomings of the prepared simulated body fluids, and are compared to those of previous relevant investigations

Influence of cold rolling and annealing on the mechanical and corrosion properties of an AA5182 Al-Mg alloy

In this study we investigated the effect of cold rolling reductions and different annealing conditions, on the mechanical properties and corrosion resistance of an AA5182 type Al-Mg alloy. Material was industrially produced and supplied as hot rolled 12 mm thick plates. Further lab-processing included cold rolling with 40-85% reduction in thickness, and 2h of annealing in the range of temperatures from 300-350°C. Annealed specimens were used for room temperature tensile testing while corrosion testing was performed on the annealed and sensitized specimens. Intergranular corrosion (IGC) susceptibility was determined by nitric acid mass loss test (NAMLT) for the selected states. The results showed that corrosion resistance, tensile strength and yield point elongation were mostly affected by a degree of cold deformation. It was found that increasing in cold rolling reduction from 40-85% before annealing causes an improved strength level due to grain size refinement. However, yield point elongation became more pronounced and a tendency towards Lüdering as undesirable surface appearance was increased. NAMLT testing showed that the material was corrosion resistant in as-annealed condition while it became susceptible to intergranular corrosion after sensitization treatment. IGC susceptibility of sensitized specimens increases with cold rolling reduction and a grain size refinement

Otpornost prema koroziji aluminijumske legure serije 7000 posle novog dvostepenog termičkog taloženja

Corrosion properties of an aluminium alloy 7000 series were investigated by different electrochemical methods. The alloy was subjected to the one-step and to a new two-step precipitation hardening. Polarization measurements in the 3.5 wt. % NaCl solution have shown a more positive value of the pitting potential (Epit) and a higher corrosion resistance for the two-step aged alloy. The electrochemical impedance spectroscopy (EIS) has also shown that the two-step aged alloy has better corrosion properties (higher value of polarization resistance, Rp, and lower value of double-layer capacitance, Cdl) comparing to the one-step aged alloy.Otpornost prema koroziji aluminijumske legure serije 7000 ispitivana je primenom različitih elektrohemijskih metoda. Legura je bila podvrgnuta jednostepenom i novom dvostepenom termičkom taloženju. Polarizaciona merenja u 3,5 mas.% NaCl su pokazala da legura posle dvostepenog termičkog taloženja ima pozitivniju vrednost potencijala pitinga (Epit) i veću otpornost prema koroziji. Spektroskopija elektrohemijske impedancije (SEI) je takođe pokazala da legura posle dvostepenog termičkog taloženja ima bolju otpornost prema koroziji (veću vrednost polarizacione otpornosti, Rp i manju vrednost kapacitivnosti dvojnog sloja, Cdl) u poređenju sa legurom posle jednostepenog termičkog taloženja

PLASTIC DEFORMATION AND HEAT TREATMENT OF THIN WALLED CENTRIFUGALLY CAST HIGH STRENGTH CrMoNb STEEL TUBES

This work deals with effects of hot plastic deformation process and subsequent heat treatment on structure and mechanical properties of centrifugally cast (CC) high strength CrMoNb steel tubes. Plate samples, taken from CC tubes, were homogenized and subsequently hot rolled. One serie of samples was soft-annealed (SA) and other series oil-quenched and tempered (QT) between 373-923 K. Primary and secondary structures, non-metallic inclusions in radial direction and prior austenite grain size were analyzed using bright-field and polarized light microsopy. Experimental mechanical properties of SA and QT samples were modeled by means of polynomial functions and correlated with structure properties

Certain aspects of provoding use of police units in actions of protection and rescuing in case of natural disasters

Police officers represent significant and very respectable force of the system for protection and rescue of people, material and cultural values from consequences caused by natural disasters. Effectiveness and efficiency of police forces depend on various factors, such as degree of abruptness, type, scale, intensity, phase and consequences of natural disaster, quality of training and equipping police officers, availability of response action plans and stable financial resources. However, experiences of the police in protection and rescue actions during the floods in May 2014, led to importance of exploring visibly present but not sufficiently explained theoretical aspects of the use of police units during natural disasters of catastrophic proportions. Regarding this, the paper elaborates the issues concerning organization and functioning of telecommunications and geo topographic ensuring use of police units in actions of protection and rescue during catastrophic floods on examples from Obrenovac and Šabac. At the end of the paper, the concrete suggestions for improving the treated issues are given

Analysis of floating-head heat exchanger bolts failure

As-received floating-head heat exchanger bolts were broken (BB) and deposite-coated. The aim was to estimate a cause of their failure. The new bolts of the same material were used as a reference material (reference bolt – RB). After visual and radiographic examination, their chemical composition, structure and room-temperature mechanical properties were determined and compared. Comparison was made with the values set by standard, as well. Afterwards, fractography was performed on fractured surfaces of tensile specimens and originally (during exploitation) BBs to try to get an impression about bolts failure mechanism. Qualitative analysis of deposite was employed in order to confirm was there any possible influence of surroundings during their failure in terms of corrosion-assisted cracking. Chemical composition of RB and BB materials was analyzed by use of spectrophotometry and structure properties with light optical microscope (LOM). Fractured surfaces of tensile specimens and of BBs, as well as deposite chemistry, were analyzed by use of Scanning Electron Microscopy with Energy Dispersive System (SEM-EDS). BBs had an approximately three times higher sulphur content and lesser manganese content, lower ductility and higher strength values comparing to those of the RBs. Generally, fracture surfaces of both, RB and BB tensile specimens have a similar rosette-like macro-appearance. The only difference is that the radial marks in the case of the RBs are rougher. The surface has a more fibrous area and shear lip presence. Fracture mode can be characterized as dimple rupture and micromechanism as microvoid coalescence. In the case of BB tensile specimens, the mixed presence of dimples and cleavage facets was noticed. The macrofractography of originally broken surfaces shows a rough and complex topography of fracture surfaces indicating on a possibility that bolts failure has been a result of complex loading conditions. Presence of sulphur- and chlorine-containing particles on the fracture surfaces of BBs and in deposite reveals a possibility that failure was environmentally-assisted

Hemijsko-strukturna svojstva i biomineralizacija hidroksiapatitnih prevlaka dobijenih visokoenergetskim laminarnim plazma sper postupkom

In the present work, hydroxyapatite coatings (HACs) were deposited by using the high power laminar plasma spray process. Major objectives were: (i) to estimate effects of several deposition parameters on chemical, structural, and morphological properties of HACs and (ii) to evaluate effects of human proteins albumin and gamma globulin on the early stage of the biomineralization process on the surface of HACs in modified Kokubo solutions (simulated body fluids) in which the pH value was actively regulated using CO2.U ovom radu je izvršeno nanošenje hidroksiapatitnih (HA) prevlaka primenom visokoenergetskog laminarnog plazma sprej postupka. Glavni ciljevi rada su bili: (i) da se ispita uticaj nekoliko parametara procesa nanošenja na hemijska, strukturna i morfološka svojstva HA prevlaka i (ii) da se ispita uticaj ljudskih proteina albumin i gama globulin na početni stadijum procesa biomineralizacije koji se javlja na površini dobijenih HA prevlaka u modifikovanim Kokubo rastvorima (simulirane telesne tečnosti) u kojima je vrednost pH bila aktivno regulisana pomoću CO2..

Chemico-structural properties and biomineralization of hydroxyapatite coatings produced by high power laminar plasma spray process.

U ovom radu je izvršeno nanošenje hidroksiapatitnih (HA) prevlaka primenom visokoenergetskog laminarnog plazma sprej postupka. Glavni ciljevi rada su bili: (i) da se ispita uticaj nekoliko parametara procesa nanošenja na hemijska, strukturna i morfološka svojstva HA prevlaka i (ii) da se ispita uticaj ljudskih proteina albumin i gama globulin na početni stadijum procesa biomineralizacije koji se javlja na površini dobijenih HA prevlaka u modifikovanim Kokubo rastvorima (simulirane telesne tečnosti) u kojima je vrednost pH bila aktivno regulisana pomoću CO2...In the present work, hydroxyapatite coatings (HACs) were deposited by using the high power laminar plasma spray process. Major objectives were: (i) to estimate effects of several deposition parameters on chemical, structural, and morphological properties of HACs and (ii) to evaluate effects of human proteins albumin and gamma globulin on the early stage of the biomineralization process on the surface of HACs in modified Kokubo solutions (simulated body fluids) in which the pH value was actively regulated using CO2