University of belgrade faculty of technology and metallurgy

P6
Electrophoretic HAP/Lig Coatings: Biomimetic Approach
S. Eraković¹, Đ. Veljović¹, P. Diouf², T. Stevanović², M. Mitrić³, Đ. Janaćković¹, I. Matić⁴, Z. Juranić⁴, V. Mišković-Stanković^1
1Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia

²Département des sciences du bois et de la forêt, Université Laval, Québec, Canada

³ Vinča Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia

⁴Institute for Oncology and Radiology of Serbia, Pasterova 14, Belgrade, Serbia
New composite ceramic/polymer coatings were investigated in the past few years in order to obtain bone-substitute materials. Composite coatings have shown to be more effective for enhancement of both mechanical properties and bioactivity, compared to pure ceramic and polymer coatings. Synthetic hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) are frequently applied as a ceramic coated material, due to its chemical composition similarity to the main bone mineral. HAP nanoparticles were obtained by a modified chemical precipitation method. Lignin (Lig), as a poliphenolic natural polymer used in this study, is Alcell lignin obtained from organosolv pulping of mixed hardwoods. Therefore, biocomposite HAP/Lig coatings were produced from ethanol suspension of HAP and Lig powders by electrophoretic deposition on titanium at constant voltage of 60 V for 45 s, at room temperature. The aim of this work was to investigate the effect of lignin concentration on morphology and phase composition of obtained biocomposite HAP/Lig coatings. MTT test has been conducted in order to determine the cytotoxicity of coatings. It was shown that coatings can be sintered at a significantly lower sintering temperature.


P7
Electrochemically Synthesized Ag/PVP Nanocomposites for Medical Applications
I. Jevremović, Ž. Jovanović, J. Stojkovska, B. Obradović, M. Vukašinović-Sekulić, A. Perić-Grujić, M. Ristić, V. Mišković-Stanković
Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia
Innovative approaches to polymer/metal nanocomposites synthesis have been increasingly studied due to unique and novel properties of these nanosystems. Silver nanoparticles have potential for utilization in photonic, electronic, chemical, and biomedical areas. These specific properties could be attributed to their large specific surface area. In this study silver/poly(N-vinyl-2-pyrrolidone) (Ag/PVP) nanocomposites were obtained by electrochemical reduction of Ag⁺ ions in polymer matrix. The formation of the silver nanoparticles was monitored using UV-Vis absorption spectroscopy. Mechanical properties of Ag/PVP nanocomposites were characterized in bioreactor conditions, and swelling degree was investigated in simulated body fluid. Release of silver ions from Ag/PVP nanocomposites was determined by atomic absorption spectroscopy, while antibacterial activity was measured by Kirby-Bauer method. Results of this work suggest that Ag/PVP nanocomposites can preserve the sterility of the material, by conserving certain part of Ag nanoparticles even after 4 weeks. The results of tests performed in the bioreactor with mechanical stimulation have shown that mechanical properties of material are improved by silver nanoparticles. The swelling degree of Ag/PVP nanocomposites indicates that silver nanoparticles in PVP network are expanding the size of cavities in polymer network, increasing the diffusion coefficient. The antibacterial activity of silver nanoparticles is confirmed for bacteria S. aureus.

P8
The Influence of Porosity on the Corrosion Protection of Aluminium by Vinyltriethoxysilane Films
Željka Jovanović¹, Jelena Bajat¹, Ingrid Milošev², Radmila Jančić-Heinemann¹, Marija Dimitrijević¹, Vesna Mišković-Stanković^1
1Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia, ² Jožef Stefan Institute, Department of Physical and Organic Chemistry, Jamova c. 39, 1000 Ljubljana, Slovenia
Efficiency of adhesion promotion and corrosion protection of metallic surfaces by nano-sized silane films significantly depends on deposition parameters. Silane solution concentration and curing time are the most important variables affecting thickness, porosity and, consequently, barrier properties of the silane film. Vinyltriethoxysilane (VTES) films were deposited from 2 and 5 % solutions, and cured for 10 and 30 min at 100 ^oC, forming dense siloxane structure by simultaneous polymerization and crosslinking of silane monomers. VTES films were analyzed by Auger electron spectroscopy coupled with depth profiling, optical microscopy coupled with image analysis and electrochemical impedance spectroscopy. VTES films deposited from 2 % VTES solution were very thin: 4-30 nm, and films deposited from 5 % solution were 230-280 nm thick. VTES films deposited from less concentrated solution exhibited two times higher porosity (dry films), and also significantly greater corroded area after the exposure to 3 % NaCl (wet films) compared to VTES films deposited from 5 % solution. Longer curing time caused the decrease in both, film thickness and film porosity. However, porosity seams to be more influencing factor in the corrosion protection: VTES films cured for 10 min, eventhough thicker, exhibited lower corrosion stability, regardless the silane solution concentration.

P9
Creep and oxidation resistance of rare-earth doped Si₃N₄ based composite
P. Tatarko¹, M. Kašiarová¹, J. Morgiel², J. Dusza¹, P. Šajgalík^3
1Institute of Materials Research, Slovak Academy of Sciences, Košice, Slovak Republic

²Institute of Metallurgy and Materials Science, Polish Academy of Sciences, Kraków, Poland

³Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic
Creep and oxidation resistance of silicon nitride/silicon carbide micro/nano composites with various rare-earth oxide sintering additives (La₂O₃, Y₂O₃, Yb₂O₃, Lu₂O₃) has been investigated. The materials were prepared by hot-pressing method and the SiC particles were produced by carbothermal reduction of SiO₂ during sintering. Similarly, the set of four reference monolithic materials with the same oxide additives were prepared. Creep measurement was carried out in four-point bending mode in air atmosphere at temperatures between 1250°C and 1400°C with outer stresses from 50 to 150 MPa. The oxidation resistance was estimated on the crept samples. Beneficial effect of sintering additives with smaller ionic radius of rare-earth element on the creep and oxidation resistance was observed. Positive effect of SiC particles on the creep resistance was not observed in the composite containing La because the SiC particles were intragranularly located rather than intergranularly between the grains in this material. The SiC particles located on the grain boundary of Si₃N₄ hinder the grain boundary sliding and hence improve the creep resistance of Yb-, Y- or Lu-containing composites. Viscosity of the secondary glassy phase increases with decreasing ionic radius of RE³⁺ what is the reason for improved oxidation and creep resistance of those materials.

P10
Morphological factor in corrosion of nanocrystalline Zn-Mn electrodeposits
M.Bučko^a, J.Rogan^a, S.I.Stevanović^b, J.B.Bajat ^a
aFaculty of Technology and Metallurgy, University of Belgrade, P.O.Box 3503, YU-11120 Belgrade, Serbia, ^bICTM – IEC, P.O. Box 473, 11001 Belgrade, Serbia
Corrosion protection of steel substrate by electrodeposited Zn-Mn alloy coatings mostly depends on Zn-Mn alloy phase composition and coating morphology. The XRD patterns of Zn-Mn alloy coatings with 4.7 and 11.6 at % of Mn revealed the mixture of the two crystalline phases: ε-ZnMn phase and η-ZnMn phase, both having hexagonal close packed (HCP) structure. The content of ε-phase increased with the increase of Mn percentage, so in the Zn-Mn alloy with 4.7 at % of Mn the main phase was η-phase, whereas the other alloy was made up mostly of the ε-phase. The grain size of the coatings, determined from X-ray diffraction patterns, was 29 nm for alloy with 4.7 and 19 nm for alloy containing 11.6 at.% of Mn. Surface morphology studies, based on AFM measurements, showed that Zn-Mn coating with 4.7 at.% of Mn was more compact and possessed more homogeneous structure (more uniform agglomeration size). Besides, coating with 11.6 at % of Mn possessed cavities about 400 nm wide, with the shape of chutes, where the coating was significantly thinner. Electrochemical impedance spectroscopy was used to investigate corrosion behaviour of the two coatings. It showed that alloy with 4.7 at.% of Mn possessed significantly higher corrosion stability compared to the coating with higher Mn content. According to literature data, the increase in ε-phase content in Zn-Mn alloy promotes better corrosion protection of the coating. Since it was not the case in this work, it was concluded that the difference in surface morphology had the most important influence on the difference in corrosion stability of the coatings.

P11
Surface Characterization of Polyurethane Nanocomposites Based on Renewable Resources
Ivan S. Ristić¹, Pavol Hvizdoš², Nevena R. Vukić¹, Vesna B. Simendić^1
1Faculty of Technology, University of Novi Sad, Novi Sad, Serbia

²Institute of Materials Research of the Slovak Academy of Sciences, Košice, Slovak Republic
Due to presence of hydroxyl groups castor oil is suitable for polyurethanes preparation. In recent years, composites prepared from renewable resources have become a special interest in many areas. For sample preparation different NCO/OH ratios, r, were used (1; 1.15; 0.92). For nanocomposites r value was 1 and they were prepared by premixing the filler particles with the castor oil polyol before reaction in glass wassel with toluene diisocyanate at 120°C for 15 minutes. Samples were obtained in metal molds (heated in oven at 120°C for 12h). Different contents of titanium(IV)oxide nano particles were added to polymer matrix (0.5; 1; and 2 wt%) for composites preparation. Surface characterization of obtained materials was performed by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (TM-AFM). From SEM images good dispersion of nano filler in polymer matrix was noticed. TM-AFM method clearly showed topology of nano fillers in polymer matrix and confirmed its good homogenization.

P12
Dynamic Mechanical Properties of Polyurethanes Reinforced by Titanium(IV)Oxide Nanoparticles
Ivan Krakovsky¹, Ivan S. Ristić², Nevena R. Vukić², Vesna B. Simendić², Radmila Ž. Radičević^2
1Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic

²Faculty of Technology, University of Novi Sad, Novi Sad, Serbia
Polymer composites based on polyurethanes are used in a wide range of application areas, such as aerospace, military, construction, electrical and electronics, medicine, marine, transportation. The goal of this work was to investigate the influence of titanium(IV)oxide nanoparticles on dynamic mechanical properties of polyurethane nanocomposites. Different contents of titanium(IV)oxide nanoparticles were added to polyol component before synthesis. Glass transition temperatures (Tg) determined by DSC method were in range from -13 to 0°C. It was estimated that Tg of samples decreases with increasing nanofillers content, due to changes of segmental mobility influenced by interaction between titanium(IV)oxides and polymer chains. Dynamic mechanical measurements were performed on a DMA Tritec 2000 (Triton Technology Ltd.) in temperature range from -50°C to 100°C at five different frequencies f (0.31 Hz; 1 Hz; 3.1 Hz; 10 Hz; 31 Hz). It was concluded that addition of nanofiller to samples with the stoichiometric ratio (r=1) influenced decrease of Tg.

P13
Sintering behavior of different hydroxyapatite nanopowders
M. Lukić¹, Z. Stojanović¹, Lj. Veselinović¹, S. Marković¹, S. D. Škapin², I. Bračko² and D. Uskoković^1
1Institute of Technical Sciences of the SASA, Belgrade, Serbia

²Institute Jožef Stefan, Ljubljana, Slovenia
Among the large number of ceramic biometerials, dense hydroxyapatite (HAp) bioceramics belong to the most promising candidates for reconstruction of bone tissue large defects due to its combined biocompatibility and bioactivity. Final quality of this material, like mechanical properties and biological response, depend on many parameters related to the powder synthesis procedure and sintering cycle employed, so it is very important to understand the connection of powder characteristics and properties of sintered materials.

In this study, different HAp nanopowders were synthesized via chemical precipitation and hydrothermal processing of precipitate. Their sintering behavior is investigated through various sintering cycles. Characteristics of starting material and sintered bioceramics are investigated through XRD, BET, FE SEM, TEM measurements. The influence of starting nanopowders characteristics on microstructural properties, density, average grain size and uniformity, is discussed.

P14
Synthesis of Nanostructural Solid Solution of MgAl₂O₄ Spinel
M. Posarac¹, T. Volkov- Husovic², B. Matovic^1
1 Institute for nuclear science ‘’Vinca’’, Belgrade, Serbia

² Faculty of Technology and Metallurgy, University of Belgrade, Serbia

Spinel, MgAl₂O₄, offer desirable combination of mechanical, chemical and thermal properties both at ambient and elevated temperatures. Nanometric powders of solid solution of magnesium aluminate spinel, MgAl_1.94Y_0.06O₄, were obtained by a glycine nitrate procedure and modified glycine nitrate procedure. The glycine nitrate procedure, a self-combustion method for powder synthesis, uses amino acetic acid (glycine) as a fuel and metal nitrate of the composition to be synthesized, as an oxidant. This method producing very fine, very pure, nanometric powders in a very short time, with the yield of 98–99%. Modification of glycine nitrate procedure was done by partial replacement of nitrates by acetates.

P15
The effect of grain size on the biocompatibility of microwave sintered HAP bioceramics
Dj. Veljović¹, E. Palcevskis², M.Čolić³, Z. Kojić⁴, V. Kojić⁵, G. Bogdanović⁵, A. Banjac⁶, R. Petrović¹, Dj. Janaćković^1
1Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

²Institute of Inorganic Chemistry, Riga Technical University, Miera 34, Salaspils, LV-2169, Riga, Latvia

³Institute for Medical Research, Military Medical Academy, Crnotravska 17, 11002 Belgrade, Serbia

⁴Institute of Medical Physiology, School of Medicine, Dr Subotića 8, 11000 Belgrade, Serbia

⁵Institute of Oncology Sremska Kamenica, Institutski put 4, 21204 Sremska Kamenica, Serbia

⁶University of Belgrade, Studentski trg 1, 11000 Belgrade, Serbia
The aim of this study was to investigate the effect of decreasing the grain size from micro to nano level on the biocompatibility and mechanical properties of microwave sintered monophase HAP bioceramic materials. For that purpose, nanosized stoichiometric hydroxyapatite powder was isostatically pressed at 400 MPa and sintered in microwave furnace at 900 ºC and 1200 ºC for 15 min. HAP samples sintered at 1200 ºC had following properties: average grain size of 3 µm, 99 % of the theoretical density, hardness of 5.0 GPa and fracture toughness of 0.87 MPa m^1/2. The mean grain size decreased from micro to nano level with decreasing of temperature to 900 ºC. The decrease in the grain size from 3 μm to 100 nm led to an increase in the fracture toughness from 0.87 MPa m^1/2 to 1.34 MPa m^1/2. In vitro cytotoxicity investigation with L929 and human MRC-5 fibroblast cells showed non-essential cytotoxic effects for micro- and nanostructured HAP bioceramics. Relative cell proliferation rate, cell attachment and metabolic activity of fibroblast cells were improved with decreasing of the grain size. In vivo investigation of biocompatibility using primary cutaneous irritation test showed that micro and nanostructured HAP materials exhibit no irritation properties.

P16
Processing of fine grained HAP and HAP/TCP bioceramics using microwave sintering
Dj. Veljović¹, I. Zalite², E. Palcevskis², I. Smiciklas³, R. Petrović¹, Dj. Janaćković^1
1Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

²Institute of Inorganic Chemistry, Riga Technical University, Miera 34, Salaspils, LV-2169, Riga, Latvia

³Vinca Institute of Nuclear Science, 11000 Belgrade, Serbia
The processing of dense fine grained bioceramics, monophase hydroxyapatite (HAP) and biphasic HAP/tricalcium phosphate (TCP) materials, using microwave sintering process, starting from nanosized HAP powders was the aim of this study. The effects of processing conditions of microwave sintering on microstructure, phase composition and mechanical properties of obtained dense biomaterials, and comparing of results obtained by microwave sintering with results obtained by conventional sintering, are also investigate. The synthesized calcium deficient and stoichiometric nanosized HAP powders was uniaxially pressed, resulting into uniform green compacts, which were microwave sintered at 900 ºC, 1000 ºC, 1100 ºC and 1200 ºC in air atmosphere for 15 min and conventionally sintered at 900 ºC and 1000 ºC for 2h. The samples obtained by microwave sintering have dense and uniform microstructures, with an average grain size ranging from 130 nm to 1 m. The fracture toughness and hardness of the pure HAP bioceramics obtained by microwave sintering were certainly higher than those of the HAP ceramics obtained by conventional sintering. The monophase fine grained HAP bioceramics had appreciably higher values of the fracture toughness than the biphasic HAP/TCP bioceramics. Through the optimization of sintering process, dense pure HAP ceramics with high density, fine grains and good mechanical properties (MH = 3.5-4.85 GPa; Kic = 0.85-1.30 MPa m^1/2) were prepared using microwave sintering technique.

P17
Spark plasma sintering (SPS) of nanostructured HAP and HAP/CNT bioceramics
Dj. Veljović¹, G. Vuković¹, I. Stamenkovic¹ , E. Palcevskis², I. Steins², P. Uskoković¹, R. Petrović¹, Dj. Janaćković^1
1Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade, Serbia

²Institute of Inorganic Chemistry, Riga Technical University, Miera 34, Salaspils, LV-2169, Riga, Latvia
The aim of this study was to obtained nanostructured composite materials, with dense and uniform nanostructure, based on HAP and carbon nanotubes (CNTs) by spark plasma sintering method. The joint effect of the addition of oxidizes CNTs and decreasing of the grain size of HAP matrix to the nano level, on the microstructure and mechanical properties of the obtained nanocomposites was also investigated. For that purpose nanosized hydroxyapatite was obtained by modified precipitation method. Multi-walled CNTs (MWCNT, Sigma-Aldrich) were oxidized in order to introduce oxygen containing functional groups, enhance their dispersibility and eventual bonding to the HAP matrix. The pure HAP powder was sintered in the spark plasma furnace, Dr.Sinter SPS System-825.C, in the range of temperatures 900 ºC-1200 ºC, and applied pressure of 40 MPa during the sintering. The obtained mixtures of HAP/o-MWCNTs powders were SPS sintered at 900 C for 5 min. Monophase HAP samples SPS at 1200 ºC were characterized with non-homogeneous microstructures, with a presence of cracks and average grain size of 20 µm, due to relative high temperature for this tip of processing. With decreasing the sintering temperature to 900 ºC, the grain size of HAP compacts decreased from micro to nano level, and average grain size was around 100 nm. The temperature of 900 ºC was applied for processing of HAP/o-MWCNTs compacts, due to the nano dimensions of the grain size of HAP matrix. The presence of the o-MWCNTs was certainly improved the conductivity of HAP matrix and had the positive effect on the densification process. The SEM analysis of the HAP/o-MWCNTs nanocomposites showed that the o-MWCNTs were distributed homogenously with the HAP matrix and that dense nanostructured materials with improved mechanical properties were processed.


P18
Hydrothermal syntesis of hydroxyapatite powders doped with (Ag⁺, Cu²⁺, Zn²⁺), heating, characterization and antimicrobial testing
Ž. Radovanović, B. Jokić, S. Dimitrijević, Dj. Veljović, R. Petrović, Dj. Janaćković
Faculty of Technology and Metallurgy, University of Belgrade, 11001 Belgrade, Serbia
In order to obtain multifunctional materials with good biocompatibility and antimicrobial effect, it was carried out hydrothermal synthesis of hydroxyapatite doped with Ag⁺, Cu²⁺ and Zn²⁺; at 160  C. Doping was carried out with two concentrations: 0.2 % and 0.4 % according to the formula (M / (M + Ca)) x 100, with a constant atomic ratio (Ca + M) / P = 1.67 (M = Ag⁺, Cu²⁺ and Zn²⁺). Previous characterization of doped powders and powders heated at 1200 ° C was performed with SEM, EDS, XRD. Antimicrobial effects of powders, dried and heated, was examined in relation to Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans in liquid medium. The results of the antimicrobial tests showed that the obtained powders have good antimicrobial activity, especially powders doped with Ag⁺ ions.

P19
Iron- modified sepiolite for Ni²⁺ sorption from aqueous solution
S. Lazarević¹, I. Janković-Častvan¹, V. Djokić¹, Ž. Radovanović¹, Dj.Janaćković¹, R. Petrović^1
1Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Serbia

Sepiolite was used for the synthesis of the sepiolite-iron oxide system in order to obtain a sorbent suitable for the removal of Ni²⁺ from aqueous solution. The modified material, Fe-sepiolite, was characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, DTA/TG thermal analyses and point of zero charge (pH_pzc) determination. The sorption experiments were performed as a function of the initial metal concentration, equilibration time and temperature using the batch method. The Fe-sepiolite had a higher sorption capacity than the natural sepiolite sample due to a higher specific sorption and a higher ion exchange with Mg²⁺ ions from the sepiolite surface. Thermodynamic parameters, such as enthalpy, Gibbs energy and entropy, were calculated from the temperature dependent sorption isotherms and these values showed that the sorption of Ni²⁺ onto sepiolites was endothermic. Pseudo-second order kinetic models provide the best correlation of the experimental kinetic data.