Sol-Gel Synthesis of Silica-Poly (Vinylpyrrolidone) Hybrids with Prooxidant Activity and Antibacterial Properties.

The present work deals with the sol-gel synthesis of silica-poly (vinylpyrrolidone) hybrid materials. The nanohybrids (Si-PVP) have been prepared using an acidic catalyst at ambient temperature. Tetramethyl ortosilane (TMOS) was used as a silica precursor. Poly (vinylpyrrolidone) (PVP) was introduced into the reaction mixture as a solution in ethanol with a concentration of 20%. The XRD established that the as-prepared material is amorphous. The IR and 29Si MAS NMR spectra proved the formation of a polymerized silica network as well as the hydrogen bonding interactions between the silica matrix and OH hydrogens of the silanol groups. The TEM showed spherical particle formation along with increased agglomeration tendency. The efficacy of SiO2/PVP nanoparticles as a potential antimicrobial agent against a wide range of bacteria was evaluated as bacteriostatic, using agar diffusion and spot tests. Combined effects of hybrid nanomaterial and antibiotics could significantly reduce the bactericidal concentrations of both the antibiotic and the particles, and they could also eliminate the antibiotic resistance of the pathogen. The registered prooxidant activity of the newly synthesized material was confirmative and explicatory for the antibacterial properties of the tested substance and its synergetic combination with antibiotics. The effect of new hybrid material on Crustacea Daphnia magna was also estimated as harmless under concentration of 0.1 mg/mL.

Effect of Cu as a Minority Alloying Element on the Corrosion Behaviour of Amorphous and Crystalline Al-Ni-Si Alloy.

The effect of copper as a minority alloying element on the corrosion behaviour of amorphous and crystalline Al74Ni16Si10 and Al74Ni15Si9Cu2 alloys was investigated in this study. Amorphous alloys were produced as rapidly solidified ribbons using the Chill Block Melt Spinning (CBMS) method and subsequently annealed to complete crystallisation. The corrosion rate of alloys was obtained through continuous immersion tests in 3.5% NaCl at 25 °C and 50 °C for 360 h. The electrochemical parameters corrosion current density (Jcorr) and corrosion potential (Ecorr) were determined via the potentiodynamic polarisation test. The results showed better corrosion characteristics of amorphous alloys. The addition of 2 at.% copper to the Al74Ni16Si10 alloy improved pitting corrosion resistance without significant effect on the corrosion current and potential. In immersion tests at 25 °C, the presence of copper resulted in an increase in the corrosion rate of about 300% for both amorphous and crystalline alloys. At a temperature of 50 °C, this increase is on average 130%. The apparent difference between the results of the two test methods is discussed in terms of the imperfections on the surface of rapidly solidified ribbons. The results of this study will contribute to a more complex understanding of the nature of amorphous alloys and their application.

Thermal decomposition of pyrometallurgical copper slag by oxidation in synthetic air.

The purpose of this study was to investigate the possibility of separating pyrometallurgical copper (fayalite) slag by oxidation in a synthetic air atmosphere into ferrous and silicate phases suitable for resources to be recovered from them. Isothermal oxidation kinetics and the most probable reaction models are studied in the temperature range of 773 to 1173 K using thermogravimetric analysis data and the classical Johnson-Mehl-Avrami-Yerofeev-Kolmogorov (JMAYK) equation. Depending on the model applied, the activation energies of fayalite slag oxidation in the temperature range of 773-973 K were: D1: 37.55 kJ mol(-1); D2: 43.27 kJ mol(-1); D3: 50.52 kJ mol(-1); and D4: 45.65 kJ mol(-1). Depending on the model applied, the activation energies of fayalite slag oxidation in the temperature range of 1073-1173 K were: F1: 20.48 kJ mol(-1); R2: 20.45 kJ mol(-1); R3: 20.18 kJ mol(-1); A2: 21.54 kJ mol( -1) and A3: 22.34 kJ mol(-1). The transformation of fayalite to hematite and amorphous silica was completed after 1435, 1350 and 1080 s at temperatures of 1073, 1123 and 1173 K, respectively. The following oxidation products were identified by X-ray diffraction: (1) fayalite, hematite and magnesioferrite (Fe(2)MgO(4)) in the temperature range 773 to 973 K; and (2) hematite and magnesium iron oxide (Mg(1.55)Fe( 1.6)O(4)) in the temperature range of 1073 to 1173 K.