Addition Of SiO2 Research Articles

Effect of microstructure on thermal and mechanical properties of solid solutions Al2TiO5 - MgTi2O5

Aluminium titanate - tialite belongs to the compounds with pseudobrookite structure. The polycrystals made of tialite show valuable useful thermal properties: low thermal expansion, very low thermal conductivity and high resistance to thermal shock. These properties result from the cracks present in the microstructure, resulting from significant differences in the lattice coefficients of aluminium titanate. The basic disadvantage of tialite consist in a thermal decomposition occurring at the temperatures of about 750–1280 °C. This decomposition can be limited by structural and microstructural stabilization. The addition of cations, e.g. magnesium or iron, leads to the formation of stable solid solutions, while the addition of SiO2 or ZrO2 leads to the formation of secondary phases - diffusion barriers occurring at intergranular boundaries. Most often these additives are introduced simultaneously and at the reaction sintering stage. Stable solid solutions are usually produced by a classical solid phase reaction between the initial oxides: Al2O3, TiO2 and MgO. In this work, an innovative synthesis was applied to produce solid solutions, involving a heterogeneous isostructural nucleation with magnesium titanate. The polycrystals obtained in this way, at a much lower temperature, with a high content of solid solutions (95–96 %), high density, homogeneous microstructure with necessary microcracks were obtained. As a result, the obtained polycrystals exhibit the typical pseudobrookite structure behaviour as a function of temperature.

Enhancement of color quality and luminous flux for remote-phosphor LEDs with red-emitting CaMgSi2O6:Eu2+,Mn2+

Abstract SiO2 particles and red-emitting CaMgSi2O6:Eu2+,Mn2+ phosphor have been added into a yellow phosphor compound YAG:Ce3+ to enhance the optical efficiency of white light LEDs whose average correlated color temperature (CCT) is in the range of 5600 K ÷ 8500 K. It was observed that altering CaMgSi2O6:Eu2+,Mn2+ concentration from 2 % to 30 % while maintaining 5 % of the SiO2 strongly influenced the color rendering index (CRI), color quality scale (CQS), and lumen efficiency of the compound. Besides, through the application of Monte Carlo simulation and Mie-scattering theory, it was possible to improve the optical properties by CaMgSi2O6:Eu2+,Mn2+ and SiO2 addition. The results provided a practical approach to achieve higher luminous efficiency and better color uniformity in remote-phosphor white LEDs (RP-WLEDs).

Electrical Behavior against Current Impulse in ZnO Varistor Ceramics with SiO2 Addition

SiO2 addition effect on electrical behaviour against current impulse in the ZnO varistors was investigated. SiO2 acts as a controller in ZnO grain growth, decreasing the grain size of ZnO from 8.87 to 5.86 μm, which in turn results in an increase in breakdown voltage E1mA from 192.77 to 252.57 V/mm. SiO2 has a significant influence on the current energy withstand capability and impulse aging characteristics. The results indicated that the SiO2 content was optimized at 1.5 mol%, exhibiting the best energy withstand capability of 332.03J/cm3 and clamping ratio of 1.71.

Production of greener energy in microbial fuel cell with ceramic separator fabricated using native soils: Effect of lattice and porous SiO2

In this study, ceramic membranes with different compositions have been fabricated and used as a separator in two-chambers microbial fuel cells (MFCs). MFCs performance has been affected by properties of the clayware separator such as porosity, proton exchange, and electrical conductivity as well as the structure of the membrane. To study the effect of SiO2 on the composition of ceramic membrane soil, adding different amounts of SiO2 to two soil samples of Kalporgan and leached Kalporgan’s soil for fabricated ceramic membrane was investigated. The sintering phenomenon in the leaching process was reduced significantly and the membrane acted as an ideal substrate. The addition of SiO2 to the leached soil caused the melting point decreases and the sintering process increases slightly, thus have not a positive effect on the MFCs performance. However, when 30% SiO2 has been added to non-leached soil without proper support, its porous structure had a dominant effect on reducing the melting point, results in better performance of MFCs, decreasing the internal resistance from 977.36 to 115.96 Ω, growing up the current density from 102.00 to 769.23 mA/m2, increasing the power density by approximately 15-fold and gaining colombic efficiency from 27 to 79%.

Effect of SiO2 Addition on Chromium Transitions in Borate Glasses

Melt-quenching technique was used to prepare borosilicate glasses of composition xSiO2- (75-x) B2O3–24.7Li2O-0.3Cr2O3 (x = 0, 10, 20, 30, 40 and 50 mol%). With increasing the former content, both Cr6+ and Cr3+ optical transitions undergo strong intensity variations. The crystal field strength (10Dq) is increased, while Racah parameters (C,B) are decreased with increasing SiO2 content. The ratio estimated Dq/B values confirmed a weak crystal field environment for Cr3+ions, and further suggest a more covalent bond character. The ESR results revealed that Si-contained samples exhibit a strong microwave absorption signal, and justified the presence of both Cr3+ and Cr6+(charge transfer into 3d0 2p6+ = 3d1Cr5+) oxidation states. The fingerprints of borate and silicate relevant structural groups were clearly identified from FTIR spectroscopy.

Cyclic thermal shock resistance of h-BN composite ceramics with La2O3–Al2O3–SiO2 addition

The effects of La2O3–Al2O3–SiO2 addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La2O3–Al2O3 and 20 vol% SiO2 addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La2O3–Al2O3–SiO2 system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock.

DC bias characteristics of BaTi0.65Zr0.35O3 with additives (Gd2O3, SiO2, MgO) for multilayer ceramic capacitors

In this study, BaTi0.65Zr0.35O3-2 mol% MgO ceramics with various amounts of Gd2O3 and SiO2 additives were prepared via a solid-state reaction method. The densification temperature of the BaTi0.65Zr0.35O3-2 mol%, MgO-2 mol%, and SiO2 ceramic was 1275 °C, with the addition of less than 2.0 mol% Gd2O3. The Gd3+ ions preferentially replaced the A-site ions. The densification temperature was reduced to 1225 °C, and the grain size of the ceramics was grown significantly up to 2.96 μm for 2 mol% Gd2O3, in addition to the formation of a trace amount of Ba2GdZrO5.5. There was a significant decline in the value of tanδ, and the electrical resistivity was increased by almost an order of magnitude due to the decrease in the VO•• concentration and the larger grain size. When the Gd2O3 content exceeded 2 mol%, the Gd3+ ions entered the B-site positions. For 5 mol% Gd2O3, the densification temperature is increased to over 1350 °C, the grain size reduced to 0.84 μm, and the value of tanδ is increased and the electrical resistivity is decreased as a result of the increasing VO•• concentration. The temperature coefficient of capacitance curves shows a nearly linear relationship between temperature and negative temperature coefficient and rotate counter-clockwise with an increase in Gd2O3 and SiO2 content. The BaTi0.65Zr0.35O3-2 mol% MgO-2 mol% SiO2 ceramics had a dielectric constant of 871 at room temperature, which decreased to 417 for 5 mol% Gd2O3. The dielectric constant of the BaTi0.65Zr0.35O3-2 mol% MgO ceramics, with and without the 2 mol% SiO2 additive, steadily declined by 10.2% at a bias field of 2.5 KV/mm. The magnitude of change in the dielectric constant has reduced significantly to 1.33% for the 5 mol% Gd2O3 additive.

Properties of ZnO:Al, ZnO:Al–SiO2 Films Obtained in Sol Gel Process from Coating Solutions

The paper deals with ZnO, ZnO:Al 5 wt.% and ZnO:Al 5 wt.% – SiO2 5 wt.% thin films obtained on glass substrates by the sol gel process from film-forming solutions Zn[C6H4OHCOO]NO3, Al(NO3)3·9H2O and Si(OC2H5)4. The film properties such as transmission in the visible region, surface resistance and photocatalysis are investigated. It is shown that the aluminum addition has no effect on the ZnO film transmission in the visible region, but improves the film conductivity through the decrease in the surface resistance down to 107 Ohm. The ZnO:Al – SiO2 film has the highest transmission of 95%. The addition of SiO2 has no effect on the ZnO:Al film transmission. The maximum photocatalytic activity is observed in the ZnO:Al film. The photodecomposition velocity of methyl orange is 1.47 ∙10–2 min–1, that is by one order higher as compared to that in the presence of Degussa P25 adsorptive photocatalyst. The SiO2 addition lowers the degree of crystallinity of the ZnO:Al film and its photocatalytic activity.

Preparation of high-strength β-CaSiO3 bioceramic with B2O3 and SiO2 sintering additives

Calcium silicate (CS) bioceramic is a promising candidate in bone tissue engineering due to its excellent bioactivity and biodegradability. However, the deficient mechanical properties make it challengeable in hard bone tissue replacement. In this work, high-strength β-CS bioceramics were prepared with low melting-point B2O3–SiO2 sintering additives using liquid phase sintering mechanism via a versatile milling-pressing-pressureless sintering route. The results showed that the addition of B2O3–SiO2 could significantly promote densification and induce the in-situ growth of β-CS rod-like grains. β-CS ceramics with 5 wt% addition of B2O3/SiO2 with mass ratio of 92.5:7.5 sintered at 1000 °C for 2 h exhibited a relatively high flexural strength of 228.14 MPa, increased by 340% compared to that of pure β-CS ceramic (52.08 MPa) prepared under the same conditions. The elevated strength fully qualified the strength requirement of cortical bone (135–193 MPa), indicating β-CS ceramic reinforced with B2O3–SiO2 additives had great potential in load-bearing bone repair.

Studies on the synthesis of ZSM-5 by interzeolite transformation from zeolite Y without using organic structure directing agents

Abstract In this work, a study of the interzeolite transformation from a parent zeolite Y (FAU topology) into zeolite ZSM-5 (MFI topology) was carried out, without using organic structure directing agents, by addition of SiO2 to adjust the composition of the starting gel. Depending on the SiO2/Al2O3 molar ratio, zeolite Y can be present in amounts equivalent to those of seed-assisted syntheses. Zeolite Y was successfully transformed in ZSM-5, but a rigorous control of OH−/SiO2 and Na+/SiO2 molar ratios is necessary to avoid incomplete transformation and/or contamination by layered silicates, such as magadiite and kenyaite. For hydrothermal treatment duration lesser than 12 h, the phase dissolution of the Y zeolite is observed, resulting in amorphous phase after 24 h. From 48 h, nucleation and growth of ZSM-5 crystals, with increasing crystallinity up to 120 h, is observed. During the interzeolite transformation, FTIR spectra show the disappearance of the band at 568 cm−1 and the appearance of a band at 545 cm−1, assigned to the 5-membered double rings of ZSM-5. Scanning electron microscopy images suggest that the crystallites of zeolite Y condense and absorb silicate species from solution to form larger aggregates of ZSM-5 zeolite. These structural and morphological changes are accompanied by textural changes detected in nitrogen adsorption isotherms. These results suggested that a combined solution mediated and solid-state transformation mechanism is probably occurring. Since these zeolites do not possess any other structural features in common, RBU approach seems to be more adequate to describe this specific interzeolite transformation.

Physical, dielectric and biodegradation studies of PVC/silica nanocomposites based on traditional and environmentally friendly plasticizers

PVC/nano-SiO2 nanocomposites based on a bio-based plasticiser (castor oil) and dioctyl phthalate (DOP) were prepared using solution casting method. Castor oil (CO) was used as a complete alternate plasticiser of dioctyl phthalate (DOP) in PVC. The prepared films were characterised by different techniques. In addition, the biodegradation of the films was tested by soil burial, hydrolytic and enzymatic degradation tests. The presence of CO facilitates the dispersion of SiO2 in PVC matrix and enhances the thermal stability. Besides, it has a significant contribution in reduction of HCl emission during the decomposition of PVC nanocomposites. FTIR spectra of the nanocomposite films showed a considerable change in the intensity of the characteristic peaks of the functional group by addition of SiO2 and after proceeding hydrolytic and enzymatic degradation as well. Additionally, the presence of SiO2 plays a dominant role in improving the migration stability and volatility of the plasticiser. Further, the permittivity (ε’), loss factor (tanδ), electric modulus (M’) and conductivity (σ) of PVC were also investigated. It is found that the values of ε’ and σ of PVC/CO/SiO2 nanocomposites are higher compared to those of PVC/DOP/SiO2 nanocomposites. Moreover, electric modulus (M’) demonstrates two dielectric relaxation processes. The conductivity values revealed that PVC nanocomposites can perform as antistatic materials. This makes them a good choice for electronic components packaging.

Influence of CaO and SiO2 additives on the sintering behavior of Cr,Ca:YAG ceramics prepared by solid-state reaction sintering

Yttrium aluminum garnet optical ceramics (Y3−xCaxAl4.95Cr0.05O12) doped with 0.1 at.% of chromium ions and 0.5, 0.8 and 1.2 at.% of calcium ions were prepared by reactive sintering in vacuum at 1750°C. The influence of SiO2 and CaO sintering aids on optical properties and microstructure of Cr,Ca:YAG ceramics was investigated. A decrease in CaO concentration led to a reduction of the Cr,Ca:YAG ceramics transparency from 81 to 0% at 1064 nm, moreover, samples with a lower concentration of CaO had abnormal grains and high-level porosity. The obtained features were attributed to the interactions between silica and calcium oxide during vacuum sintering of Cr,Ca:YAG ceramics. We propose and discuss two possible ways in which CaO and SiO2 influence the formation of Ca,Cr:YAG ceramics. The first one involves the appearance of a liquid phase thanks to the CaO–SiO2 interaction during the heating stage of ceramics sintering which results in abnormal growth of ceramics grains. The second mechanism consists on the mutual consumption of Si4+ and Ca2+ ions during the isothermal stage of ceramic sintering, which leads to a decrease in Cr4+ concentration. Both mechanisms have a negative effect on the optical and laser properties of the ceramics.

Ag-diffusion inhibition mechanism in SiO2-added glass-ceramics for 5G antenna applications

Glass-ceramics for low-temperature co-fired-ceramic 5G wireless devices exhibit excellent microwave properties. However, silver diffusion and interdiffusion of the electrode decreases the high-frequency conductivity. In this work, the inhibition of the silver diffusion mechanism in CaO-MgO-SiO2 glass-ceramics was investigated. Specimens without SiO2 were found to exhibit both Ag diffusion and Zn, Mg, and Ca interdiffusion. In contrast, samples with SiO2 show much less diffusion and a Ag6O2 phase at the diffusive boundary layer, indicating that the SiO2 addition inhibits Ag diffusion and interdiffusion. Elemental mapping indicated the presence of a concentration gradient-reaction between the SiO2 particles and the glass-ceramic. This reaction enhances the glass viscosity and inhibits Ag diffusion and interdiffusion. SiO2-added glass-ceramics co-fired with an Ag electrode show improved 5G-patch-antenna microwave characteristics, with an enhanced conductivity at ~8.2 GHz and a return loss of S11 = -23 dB at ~28.3 GHz.

Preparation of PMMA/SiO2 PCM microcapsules and its thermal regulation performance on denim fabric

PurposeThis study aims to evaluate the thermal performance of phase change materials (PCMs) microcapsules (MCs) attached using SiO2 microspheres and investigate the thermal regulation effect on the coated denim fabric.Design/methodology/approachThe PCM microcapsule was prepared by in situ polymerization using a mixture of solid paraffin and butyl stearate as core material (CM) and methyl methacrylate as a monomer. The SiO2 microparticles were attached to the outer layer of the membrane to enhance the thermal performance of MCs. The morphology, chemical structure, latent heat storage and thermal resistance of MCs were characterized. PCM MCs were coated on the denim fabric and thermo-gravimetric analysis was conducted; thermal insulation and thermal infrared imaging performance of the coated fabrics were also investigated.FindingsThe diameters of SiO2 particles and PCMs MCs were 300-500 nm and 1 μm, respectively. SiO2 was wrapped on single-wall PCMs MCs with the mass ratio of 1:5. With the addition of SiO2, the phase transition temperature range of MCs increased from 34°C to 39°C, and the endothermic and exothermic latent heat decreased by 5.35 J/g and 10.07 J/g, respectively. The degradation rate of MCs was significantly slowed down at high temperature. The denim fabric coated with MCs revealed thermal regulation property. After absorbing heat, the MCs slowed down the rate of heat loss and extended the heat release time.Research limitations/implicationsThe phase transition temperature of the composite CM was wide, and the latent heat storage was reduced. The addition of SiO2 particles can significantly slow down the rate of heat loss, but it further reduces the latent heat storage performance.Practical implicationsThe method developed provided a simple and practical solution to improve the thermal regulation performance of fabrics.Originality/valueThe method of adjusting the phase transition temperature range of the composite CM is novel and many applications could be found in preparation of PCMs and thermal management.

Heterostructured TiO2/SiO2/γ-Fe2O3/rGO Coating with Highly Efficient Visible-Light-Induced Self-Cleaning Properties for Metallic Artifacts.

A novel nanohybrid composite of TiO2, SiO2, γ-Fe2O3, and reduced graphene oxide (TiO2@Si:Fe:rGO) is fabricated by the sol–gel method. The properties of the coated film were examined by structural and self-cleaning analyses using simulated discoloration/soiling and roofing tests. The fabricated transparent TiO2@Si:Fe:rGO composite showed excellent photoactivity and wettability, behaving well in self-cleaning applications. The addition of SiO2 improved the crystalline structure and surface hydroxylation of TiO2 nanoparticles. γ-Fe2O3 decreased the recombination rate of e–/h+ pairs, and significantly improved photocatalytic activity under visible light. Moreover, rGO sheets as excellent electron acceptors and transporters also reduced recombination, as well as affected wettability, achieving superhydrophilicity under irradiation. The coated substrate showed excellent resistance to simulated acid rain and significantly preserved the substrate from soiling in roofing tests.

Linking Mineralogy to Lithogeochemistry in the Highland Valley Copper District: Implications for Porphyry Copper Footprints

Abstract The Highland Valley Copper porphyry deposits, hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera, are unusual in that some of them formed at depths of at least 4 to 5 km in cogenetic host rocks. Enrichments in ore and pathfinder elements are generally limited to a few hundred meters beyond the pit areas, and the peripheral alteration is restricted to narrow (1–3 cm) halos around a low density of prehnite and/or epidote veinlets. It is, therefore, challenging to recognize the alteration footprint peripheral to the porphyry Cu systems. Here, we document a workflow to maximize the use of lithogeochemical data in measuring changes in mineralogy and material transfer related to porphyry formation by linking whole-rock analyses to observed alteration mineralogy at the hand specimen and deposit scale. Alteration facies and domains were determined from mapping, feldspar staining, and shortwave infrared imaging and include (1) K-feldspar halos (potassic alteration), (2) epidote veins with K-feldspar–destructive albite halos (sodic-calcic alteration), (3) quartz and coarse-grained muscovite veins and halos and fine-grained white-mica–chlorite veins and halos (white-mica–chlorite alteration), and two subfacies of propylitic alteration comprising (4) prehnite veinlets with white-mica–chlorite-prehnite halos, and (5) veins of epidote ± prehnite with halos of chlorite and patchy K-feldspar. Well-developed, feldspar-destructive, white-mica alteration is indicated by (2[Ca-C] + N + K)/Al values <0.85, depletion in CaO and Na2O, enrichment in K2O, and localized SiO2 addition and is spatially limited to within ~200 m of porphyry Cu mineralization. Localized K2O, Fe2O3, and depletion in Cu, and some enrichment in Na2O and CaO, occurs in sodic-calcic domains that form a large (~34 km2) nonconcentric footprint outboard of well-mineralized and proximal zones enriched in K. Water and magmatic CO2-rich propylitic and sodic-calcic–altered rocks form the largest lithogeochemical footprint to the mineralization in the Highland Valley Copper district (~60 km2). Calcite in the footprint is interpreted to have formed via phase separation of CO2 from a late-stage magmatic volatile phase. Several observations from this study are transferable to other porphyry systems and have implications for porphyry Cu exploration. Feldspar staining and shortwave infrared imaging highlight weak and cryptic alteration that did not cause sufficient material transfer to be confidently distinguished from protolith lithogeochemical compositions. Prehnite can be a key mineral phase in propylitic alteration related to porphyry genesis, and its presence can be predicted based on host-rock composition. Sodic-calcic alteration depletes the protolith in Fe (and magnetite) and, therefore, will impact petrophysical and geophysical characteristics of the system. Whole-rock loss on ignition and C and S analyses can be used to map enrichment in water and CO2 in altered rocks, and together these form a large porphyry footprint that extends beyond domains of enrichment in ore and pathfinder elements and of pronounced alkali metasomatism.

Elucidating the Roles of SiO2 and MnO upon Decarburization During Submerged Arc Welding: A Thermodynamic Study into EH36 Shipbuilding Steel

By employing CaF2-SiO2 and CaF2-SiO2-MnO system fluxes, the roles of SiO2 and MnO in decarburization behaviors during submerged arc welding of EH36 shipbuilding steel have been quantified and evaluated. All possible reactions associated with C transfer and interfaces at which these reactions occur are systematically discussed. It is concluded that the addition of SiO2 and MnO exerts synergistic effects on the extent of decarburization due to increased partial pressures of O2 and SiO gases in the plasma, improved O level in the weld pool, and higher activities of the oxides, such as SiO2, MnO, and FeO, at the slag–metal interface. The investigation over the macrographic detached slag surfaces shows that the possibility of bubble nucleation is highly influenced by flux formula. The effect of heat input on decarburization is discussed, and the optimal flux compositions expected in the present study are analyzed.

Energy analysis using carbon and metallic oxides-based nanomaterials inside a solar collector

The effectiveness of a flat-plate solar collector was studied by using SiO2, Al2O3, Graphene, and graphene nanoplatelets nanofluids with distilled water as the working fluids. The energy efficiency was theoretically compared using MATLAB programming. The prepared carbon and metallic oxides nanomaterials were structurally and morphologically characterized via field emission scanning electron microscope. The study was conducted under different operating conditions such as different volume fractions (0.25%, 0.5%, 0.75% and 1%), fluid mass flow rate (0.0085, 0.017, and 0.0255 kg/s), input temperatures (30, 40, and 50 °C), and solar irradiance (500, 750, and 1000 W/m2). Nanofluids showed better thermophysical properties compared to standard working fluids. With the addition of the nanofluids SiO2, Al2O3, Gr and GNPs to the FPSC the highest efficiency of 64.45%, 67.03%, 72.45%, and 76.56% respectively was reached. The results suggested that nanofluids made from carbon nanostructures and metallic oxides can be used in solar collectors to increase the parameters of heat absorbed/loss compared to water only usage.

Comparative impact of SiO2 and TiO2 nanofillers on the performance of thin‐film nanocomposite membranes

AbstractNanoparticle (NP) additions can substantially improve the performance of reverse osmosis and nanofiltration polyamide (PA) membranes. However, the relative impacts of leading additives are poorly understood. In this study, we compare the effects of TiO2 and SiO2 NPs as nanofillers in PA membranes with respect to permeate flux and the rejection of organic matter (OM) and salts. Thin‐film nanocomposite (TFN) PA membranes were fabricated using similarly sized TiO2 15 nm and SiO2 (10 – 20 nm) NPs, introduced at four different NP concentrations (0.01, 0.05, 0.2, and 0.5% w/v). Compared with PA membranes fabricated without NPs, membranes fabricated with nanofillers improved membranes hydrophilicity, membrane porosity, and consequently the permeability. Permeability was increased by 24 and 58% with the addition of TiO2 and SiO2, respectively. Rejection performance and fouling behavior of the membranes were examined with salt (MgSO4 and NaCl) and OM (humic acid [HA] and tannic acid [TA]). The addition of TiO2 and SiO2 nanofillers to the PA membranes improved the permeability of these membranes and also increased the rejection of MgSO4, especially for TiO2 membranes. The addition of TiO2 and SiO2 to the membranes exhibited a higher flux and lower flux decline ratio than the control membrane in OM solution filtration. TFN membranes' HA and TA rejections were at least 77 and 71%, respectively. The surface change properties of NPs appear to play a dominant role in determining their effects as nanofillers in the composite membrane matrix through a balance of changes produced in membrane pore size and membrane hydrophilicity.

Influence of nano SiO2 and nano CaCO3 particles on strength, workability, and microstructural properties of fly ash‐based geopolymer

AbstractThe influence of nano SiO2(NS) and CaCO3(NC) particles on the properties of class F fly ash based geopolymer mortar activated with different sodium ion concentrations have been investigated. Mortar mixture proportions were 1:3:0.3 for binder, sand, and water, respectively. Nano SiO2 and CaCO3 particles were replaced with a binder by weight basis at the ratios of 1, 2, and 3% in the mixtures. Sodium concentrations amount used were 8, 10, and 12% Na+ of binder content. Geopolymer mortar samples were cured at 60, 75, and 90°C in a furnace for 24, 48, and 72 hr. After the heat curing process, flexural, and compressive strength tests were performed. The changes in the microstructure of geopolymer due to influence of nanoparticles were examined by utilizing isothermal calorimetric studies on geopolymer paste, and field‐emission scanning electron microscopy (FESEM). Based on laboratory work results, it was concluded that for all sodium ion concentrations, the addition of nano SiO2 and CaCO3 particles improved the flexural and compressive strengths after 24 hr heat curing. However, the favorable effects of nanoparticles on strength properties tend to disappear after 48 and 72 hr heat curing. The results of isothermal calorimetric studies showed that nano SiO2 and CaCO3 particles accelerated the geopolymeric reactions at an early age. FESEM results showed that additions of nanoparticles made the microstructure of geopolymer products more intense and compact.