1.1. Current Production of Nano-Silica
Keywords: Olivine; Nano-Silica; CO2 Reduction; Environmentally Friendly; Concrete
. Energy generation during the olivine nano-silica process.
There are two main routes for the productions of synthetic amorphous silica: the thermal route and the wet route . In the thermal route, also called flame hydrolysis, highly dispersed silicas are formed from the gas phase at high temperatures. Silicon tetrachloride, which is the usual raw material, is continuously vaporized, mixed with dry air, then, with hydrogen and finally fed to a burner where it is hydrolyzed in an oxygen-hydrogen flame. The flame temperature depends on the properties of the burner and the desired characteristics of nano-silica. Moore patented a cooled plug burner to produce py-
possible to obtain the desired slump class. Therefore, when the specific surface area of the mix was raised by addition of nano-silica, more SP was required to maintain the same slump class. This is a clear disadvantage of the use of nano-silica, and it needs to be addressed in the future in order to find the type of SP that works efficiently with olivine nano-silica. Another possible solution for this problem could be to tailor the properties of olivine nano-silica to get lower specific surface areas and more spherical particles.
. Initial conditions of the nano-silica production experiments.
It was found that the thermaloxidation rate of the silicon nanowires was significantly enhanced bythe presence of the gold thin film, which fully converted the siliconinto silicon dioxide.
Subsequent thermal treatmentresulted in the fragmentation of the gold nanowire into a uniformlyspaced array of gold nanoparticles encapsulated by a silicon dioxideshell, which was observed by in situ annealing in transmission electronmicroscopy.
. TEM picture (89 kx) of the olivine nano-silica NS- 7 .
Before beginning this section, it is necessary to clarify the difference between olivine and dunite for readers unacquainted with geology terms. Olivine refers to the mineral (Mg,Fe)2SiO4 and dunite refers to a rock where 90% of the volume is made up of olivine. The remaining 10% present in dunite ores can consist of pyroxenes, amphiboles, micas, carbonates, serpentines, etc. In many weathering and dissolution studies, pure olivines were used [12-14], but in this study, and our previous work , dunite had been used because we focused on the commercial production of olivine nano-silica.
Because of the pozzolanic reaction, micro-silica can replace cement (1 part silica instead of 3 to 4 parts cement) for medium-strength concrete, while the strength is unaffected by the replacement . Considering that the main difference between nano-silica and micro-silica is their particle sizes—assuming pozzolanic behaviors in each are similar—nano-silica will react faster with the cement due to its smaller particles. Therefore, the replacement of cement by nano-silica should considerably reduce the CO2 emissions of the concrete. That is important because the cement industry is one of the industrial sectors that releases large amounts of CO2 into the environment accounting for 8% of global CO2 emissions . In addition to this interesting application, the largest use of micro-silica is for producing concrete with enhanced properties, such as high early strength or low permeability.
3.2. Olivine Nano-Silica Using Greek Dunite
. Characteristics of commercial and olivine nano-sililcas.
Dang, Hongyi, and Mark T. Swihart, “Computational Modeling of Silicon Nanoparticle Formation”, , 2 (7), 255-266 (2006).
. Chemical analysis of commercial and olivine nano-sililcas.
. Properties of olivine nano-silica produced using beneficiated waste dunite (NS-GM-4, -8 and -10).
3.4. Pozzolanic Activity of Olivine Nano-Silica
. Chemical analysis of olivine nano-silica produced using beneficiated waste dunite.
3.5. Application of Olivine Nano-Silica in Concrete
Yong, Ken-Tye, Yudhisthira Sahoo, Mark T. Swihart, and Paras , “Synthesis and Plasmonic Properties of Silver and Gold Nanoshells on Polystyrene Cores of Different Size and of Gold-Silver Core-Shell Nanostructures”, , 290, 89-105 (2006).()
Silica | Nanoparticle | Silicon Dioxide
Aerosol (gas-phase) methods of nanoparticle synthesis have some important advantages, including high throughput, production of bare (not surfactant-coated) particles, and elimination of solvents that must be disposed of and that often bring impurities. In a gas-phase process, particles that collide invariably stick together. If they are sufficiently hot (have sufficient energy) they will sinter (partially or completely) to form a larger particle or hard agglomerate of small particles. This is usually undesirable. In order to produce unagglomerated nanoparticles, one must prevent them from colliding until they are sufficiently cool and unreactive that they will not sinter or form hard agglomerates. This requires that either the collision rate be reduced, usually by reducing the particle concentration, or that the residence time during which the particles are hot (reactive) is reduced. Decreasing the residence time for coagulation thus increases the maximum concentration at which particles can be produced. By using a laser to heat a precursor gas, without heating the reactor walls or surrounding gas, we can achieve very rapid heating and cooling rates, and residence times of about a millisecond in the '"reaction zone" where the laser interacts with the gas. This laser-driven synthesis is the first step in our strategy for preparing silicon quantum dots, described at the top of this page. We have also used it to produce nanoparticles of other materials, including nickel, as illustrated here.
in a mesoporous silica nanoparticle
Nano-silica, one of the substances boosting the field of nanomaterials, can be produced by dissolving olivine in acid. The dissolution of olivine is a convenient alternative route to the existing methods of nano-silica production (neutralization of sodium silicate and flame hydrolysis) because the olivine dissolution is a low temperature process making this method cheaper and greener. Furthermore, this process can use waste olivine materials for the production of nano-silica. The produced nano-silica has a specific surface area between 100 and 400 m2/g; a primary particle size between 10 and 25 nm, which is agglomerated in clusters; and an impurity content below 5 wt.%. In addition, olivine nano-silica can be classified as a pozzolanic material with an activity index of 101%. The optimum replacement level of olivine nano-silica in conventional vibrated concrete is around 5% by volume resulting in: 1) a compressive strength increase of 20%; 2) a CO2 emission reduction of 3%. Therefore, the use of the olivine nano-silica in CVC does not only improve the compressive strength but also reduce the CO2 emissions.
What exactly are silicon dioxide nanoparticles (SiO2 nanoparticles)
Downloading of the abstract is permitted for personal use only.A lithography-free method for producing freestanding one-dimensionalgold nanoparticle arrays encapsulated within silicon dioxide nanowiresis reported.