Influence of limestone content, fineness, and composition on the properties and microstructure of alkali-activated slag cement

© 2016 Elsevier LtdThe influence of the fineness, concentration, and chemico-mineralogical composition of limestone on the workability, reaction kinetics, compressive strength, microstructure, and binder gel characteristics of sodium carbonate–based waste-activated waste slag cement pastes was investigated in this work. Alkali-activated slag cements incorporated with limestone, containing 33–100% of calcite, at a content of up to 60% with a 28-day compressive strength of 26.2–48.8 MPa were proposed. The main reaction products of hardened alkali-activated cement pastes and those incorporated with limestone are [Formula presented], CaCO3, Na2Ca(CO3)2·5H2O, and Na2CaSiO4. “Physically active” limestone does not chemically react with the binder gel but it can improve the physical structure. The higher packing density of mixed cement, without an increase in the water demand, the satisfactory binding strength of limestone with the binder gel lead to the improvement in the physical structure and compressive strength of alkali-activated slag paste

Electrosynthesis of gold nanoparticles mediated by methylviologen using a gold anode in single compartment cell

© 2017Methylviologen mediated reduction of AuI ions generated in situ by dissolution of a gold anode in single compartment cell has been used for the electrosynthesis of spherical gold nanoparticles (Au-NPs) stabilized by poly(N-vinylpyrrolidone). The size of Au-NPs was from 15±6 to 27±9 nm, depending on the electrosynthesis conditions. Au-NPs were characterized by cyclic voltammetry, UV-VIS spectroscopy, dynamic light scattering, scanning and transmission electron microscopy

Mechanism of solidification of simulated borate liquid wastes with sodium silicate activated slag cements

© 2017 Elsevier LtdIn this study the mineral matrix based on hydrous sodium metasilicate (NSH5) activated slag cement (AASC) was found to be suitable for solidification of borate solutions with pH 8.5–10.5 and concentration up to 200 g/L. Parameters such as setting times and compressive strength of the waste forms based on AASC and borate wastes can be influenced by the ratio of NSH5 and H3BO3 content. The dosage of 7% Na2O in the alkali activator per slag provides acceptable setting times and 28-day compressive strength of the waste forms in the range 49.7–56.1 MPa depending on pH of the borate solutions. Lowering the pH of borate solutions results in a reduced rate of setting of the fresh AASC paste, retardation in the structural formation of the hardened AASC paste, a reduced degree of hydration, and a reduction in the amount of calcium silicate hydrates and hydrotalcite. The product of AASC-based mineral matrix and simulated borate wastes interaction is ulexite (NaCaB5O6(OH)6(H2O)5)

Molecular oxygen as a mediator in the electrosynthesis of gold nanoparticles in DMF

© 2016 Elsevier B.V.The possibility of using of molecular oxygen as a mediator in electrosynthesis of metal nanoparticles by reduction of their ions and complexes in aprotic media was demonstrated by the example of electrosynthesis of gold nanoparticles by reduction of Au(I) in DMF

Fullerene mediated electrosynthesis of Au/C<inf>60</inf>nanocomposite

© 2017 The Electrochemical Society. All rights reserved. C 60 fullerene mediated electroreduction of Au(I) at potentials of the C 60 /C 60 •− redox couple was used to perform the electrosynthesis of an AuNP/C 60 nanocomposite in DCB-DMF (2:1)/0.1 M Bu 4 NCl medium. The nanocomposite consists of separate gold nanoparticles with various shapes and a mean size of ~27 ± 14 nm, as well as larger nanoaggregates of such particles, isolated in a fullerene matrix. The mean size of metal crystallites is 9–14 nm. The electrolysis occurs efficiently, and Au(I) is quantitatively reduced to Au(0) upon consumption of the theoretical amount of electricity. The resulting metal nanoparticles and the nanocomposite are not deposited on the electrode and are completely stabilized in the solution bulk. All the particles were characterized by electron microscopy methods (SEM, HR TEM) and X-ray powder diffraction (XRPD)

Solidification of nitrate solutions with alkali-activated slag and slag-metakaolin cements

© 2014 Elsevier B.V. All rights reserved. The solidification of nitrate solutions with alkali-activated slag (AASC) and slag-metakaolin cements (AASMC) and the resulting setting times, compressive strengths, dimensional stability, water resistance, hydration products, microstructures, and macroporous network structures were evaluated. The influences of the alkali activator concentration, mineral composition of metakaolin, ratio of slag to slag + metakaolin, and concentration of NaNO3 on the cement performance were all evaluated in detail. The compressive strength of cemented nitrate solutions with AASC and AASMC aged for 28 days was from 13.4 to 42 MPa depending on the NaNO3 concentration. X-ray diffractometer, differential thermal analyzer, and electron microscope analyses suggested that NaNO3 crystallizes in cementitious matrices without reacting with the hydration products of AASC and AASMC. X-ray microtomography showed that the solidified NaNO3 solution with a salt concentration of 700 g/l and AASC had a denser microstructure without shrinkage microcracks, a smaller macropore volume, and smaller macropore sizes than hardened AASC-based paste mixed with water

Raman spectra observation of silver nanoparticles in porous silicon fabricated by ion implantation

© 2015, Pleiades Publishing, Ltd. Porous silicon layers fabricated by the low-energy high-dose Ag+-ion implantation of crystalline silicon with doses from 7.5 × 1016 to 1.5 × 1017 ion/cm2 are studied by Raman spectroscopy. Pores with sizes from ∼100–180 nm formed on irradiated silicon surface are controlled by scanning electron microcopy. Synthesized silver nanoparticles are observed in the structure of porous silicon. The sizes of pour and nanoparticles are increased with an increase in implantation dose. Acoustic vibrations generated by laser irradiation in silver nanoparticles of various sizes are registered by low-temperature Raman spectra of composite material

Methylviologen mediated electrochemical reduction of AgCl - A new route to produce a silica core/Ag shell nanocomposite material in solution

© 2015 Elsevier B.V. All rights reserved. Methylviologen mediated electrochemical reduction of AgCl precipitate to Ag0 in the presence of alkylamino-modified silica nanoparticles (SiO2-NHR) in an aqueous medium was performed. The main products of reduction at potentials of the MV2 +/MV•+ redox couple are spherical SiO2-NHR/Ag core/shell nanoparticles (size range 120-160 nm) in solution

A diffraction grating created in diamond substrate by boron ion implantation

© 2017, Pleiades Publishing, Ltd.This work is devoted to new method of manufacturing of diffractive optical elements (gratings). A grating was formed in a diamond substrate by implantation with boron ions through a mask. Ion implantation led to the graphitization of diamond in unmasked regions and resulted in swelling of the irradiated layer. The formation of periodic graphitized surface microstructures on the diamond substrate was confirmed by optical, electron, and atomic force microscopy. The efficiency of operation of the obtained diffractive optical element was demonstrated by probing with He–Ne laser radiation

Methylviologen-mediated electrochemical synthesis of platinum nanoparticles in solution bulk

© 2017, Pleiades Publishing, Ltd.Platinum nanoparticles (PtNPs) are synthesized by methylviologen-mediated reduction of PtCl2 at the potentials of the MV2+/MV•+ redox couple in 40% aqueous DMF solution. In the absence of stabilizing agents and in the presence of a stabilizer in the form of spherical silica NPs or alkylamine-modified silica NPs (SiO2-NHR), a part of PtNPs (14–18%) are deposited on the electrode while the rest of particles remain in solution to form coarse aggregates which precipitate. In the latter case, PtNPs are also partly bound to form individual ultrafine NPs (3 ± 2 nm) on the SiO2-NHR surface. In the presence of polyvinylpyrrolidone (PVP), the generated PtNPs (18 ± 9 nm) neither aggregate nor deposit on the cathode but are completely stabilized in solution being encapsulated within the PVP matrix. The obtained PtNPs are characterized by the methods of dynamic light-scattering and electron microscopy