Nanosilica Sol Research Articles

Quantitative Relationship Between Strength and Porosity of Nano-Silica-Modified Mortar Based on Fractal Theory

Nano-silica (NS) is an ideal modifier for mortar materials, and exploring the evolution of the fractal dimension of the pore structure in NS-modified mortar is crucial for elucidating the mechanism by which NS enhances mortar strength. In this study, NS reinforced mortar was prepared using an NS sol solution, which inhibited the aggregation of NS particles. The relationship between the strength and pore structure of NS-modified mortar was quantitatively analyzed based on fractal dimension theory and gray correlation degree. The experimental system evaluated the mortar strength, pore structure distribution, and micro-morphology. Based on this evaluation, the fractal dimension of the mortar pore volume was calculated in detail. Subsequently, models for mortar strength and NS content were further established using grey analysis. The results indicate that NS significantly enhances the strength of mortar while also increasing its porosity due to reduced fluidity. NS can improve the compressive strength of mortar by up to 35%. The curve fitting of volume fractal dimension and box dimension is effective and can accurately reflect the complexity of the pore structure. The calculation of the grey correlation analysis model shows that the impact of varying silica content on the mechanical properties of mortar specimens is not linear; the distribution and quantity of bubbles are the main factors affecting the strength of the specimen.

Fabrication of PVA-Silica Sol Wood Composites via Delignification and Freezing Pretreatment.

The efficient exploitation of planted fast-growing wood is crucial for enhancing wood resource utilization. In this study, the fast-growing poplar wood was modified by in situ impregnation through vacuum impregnation with polyvinyl alcohol and nano-silica sol as impregnation modifiers, combined with delignification-freezing pretreatment. The samples were characterized by FTIR, XRD, SEM, and the universal mechanical testing machine. The results showed that the wrinkle deformation and cracking of the wood blocks were greatly alleviated after the delignification-freezing pretreatment and the polyvinyl alcohol and nano-silica sol were successfully integrated into the wood. The resulting polyvinyl alcohol-silica sol poplar composites exhibited about 216%, 80% and 43% higher compressive strength with respect to delignified wood, natural wood and impregnated natural wood, respectively, thereby demonstrating superior mechanical properties and potential opportunities for value-added and efficient utilization of low-quality wood.

Experimental Study on the Gelling Properties of Nano-Silica Sol and Its Spontaneous Imbibition Grouting Mudstone

The low-permeability argillaceous rock mass is an unfavorable geological body commonly found in the construction process of underground engineering conditions such as roadways and tunnels. Due to the compact structure and low permeability of the rock mass, grouting with conventional materials cannot effectively seal the micro-cracks of the rock mass. Based on the low efficiency of high-pressure grouting of nano-silica sol, this paper preliminarily explores the regularities and mechanism of grouting and pore sealing of low-permeability rock mass under the action of silica sol imbibition from the aspects of gelling properties of silica sol, core pore structure, imbibition law, and pore sealing characteristics. The results show the following: (1) The increase in particle size during the gel process reduced the injectability and wettability of the silica sol. The imbibition properties of silica sol were time-varying, and the deterioration inflection points of injectability and wettability appeared at 10 h and 9 h, respectively. (2) Catalyst, temperature, gel process, and rock mass permeability will affect the law of core imbibition, and the injectability and capillary force of the grouting material and rock mass will jointly affect the imbibition process of silica sol. (3) Silica sol imbibition changed the pore size distribution of the core, the pore volume above 50 nm decreased, and the pore volume below 50 nm increased. Silica sol has multiple effects such as filling, adsorption, and percolation in the imbibition process of the micro-pores of rock mass, and the adsorption and percolation of silica are related to the nano micro-pores.

Analysis of the Influence Mechanism of Nanomaterials on Spontaneous Imbibition of Chang 7 Tight Reservoir Core

This study investigates the impact of nanomaterials on different surfactant solutions. By measuring the parameters (including emulsification property, zeta potential, DLS, CA, IFT, etc.) of imbibition liquid system with nanoparticles and without nanoparticles, combining with imbibition experiments, the law and mechanism of improving the imbibition recovery of nanomaterials were obtained. The findings demonstrate that the nano-silica sol enhances the emulsification and dispersion of crude oil in the surfactant system, resulting in smaller and more uniform particle sizes for emulsified oil droplets. Non-ionic surfactant AEO-7 has the best effect under the synergistic action of nanomaterials. Zeta potential and DLS tests also showed that AEO-7 exhibits smaller particle sizes due to their insignificant electrostatic interaction with nanoparticles. Furthermore, the addition of nanomaterials enhances the hydrophilicity of core and reduces the interfacial tension. Under the synergistic action of nanoparticles, AEO-7 still showed the best enhanced core hydrophilicity (CA 0.61° after imbibition) and the lowest interfacial tension (0.1750 mN·m−1). In the imbibition experiment, the imbibition recovery of the system with nanomaterials is higher than that of the non-nanomaterials. The mixed system of AEO-7 and nano-silica sol ZZ-1 has the highest imbibition recovery (49.27%). Combined with the experiments above, it shows that nanomaterials have a good effect on enhancing the recovery rate of tight core, and the synergistic effect of non-ionic surfactant AEO-7 with nanomaterials is the best. Moreover, nanomaterials reduce adhesion work within the system while improving spontaneous imbibition recovery. These findings provide theoretical guidance for better understanding the mechanism behind nanomaterial-induced imbibition enhancement as well as improving tight oil’s imbibition recovery.

Use of nano-silica sol in concrete: Performance and influence mechanisms

Nano-silica sol (NSS) is an aqueous liquid containing colloidal nano-silica in dispersed state. It has been reported to offer better effects to the cement-based materials compared with nano-silica powder, which is by far the most widely studied nanomaterial for concrete applications. To identify the optimal type of NSS (acidic/ neutral/ alkaline) for use in cement-based materials, its effects on the performances and the influence mechanisms, a three-staged research program for testing the workability, strength, durability and chemo-physical properties of mixes with various types and contents of NSS at various ages has been completed. Generally, the addition of NSS decreased the workability and increased the strength and durability of concrete. It was found that alkaline NSS was the desirable type from the viewpoint of highest workability and strength. X-ray diffraction patterns, wet packing density, scanning electronic microscope images and mercury intrusion porosimetry tests verified the pozzolanic reaction effect, nucleation effect, densification effect and pore modification effect brought about by NSS. In-depth analysis revealed that the NSS induced nucleation effect at early age and pozzolanic reaction effect at later age, densified the microstructure and reduced both volume and size of pores. These effects explained the improvement of strength and durability of concrete by using NSS.

Effect of nano-silica sol dosage on the properties of 3D-printed concrete

Extruded laminate-based 3D printing (3DP) of concrete does not require formwork support during construction and can be used to construct buildings with different appearances. However, 3DP requires strict control over the setting time and mechanical and deformation properties of concrete materials. In this paper, we designed and formulated 3DP concrete with different nanosilica sol (NSS) admixtures to investigate how NSS modified the fluidity, extrudability, setting time, mechanical properties, and microstructure of 3DP concrete. The results showed that NSS thickened the admixture, shortened the setting time, and changed the thixotropy of the 3DP concrete. The dosage of NSS should not exceed 1.5 %, above which the workability range decreased significantly. In addition, an appropriate amount of NSS greatly improved the seven-day early strength of 3DP concrete when the dosage was controlled within the range of 0.5–1.5 %. Under the optimal dosage of 1 %, the compressive flexural strength was improved by 10 %. Scanning electron microscopy (SEM) was used to observe the microscopic pore structure, and the hydration products were analyzed using X-ray diffraction (XRD). The results demonstrated that the pore structure became denser after mixing NSS, and the main hydration products were Ca(OH)2 (CH) and CaCO3. It can be assumed that NSS accelerated the hydration reaction, which produced more CH and CaCO3. Therefore, the flocculation rate of the mixture was increased, and the reduced porosity increased the structural density.

Basic consolidation and impermeability laws for nano-silica-sol grouted mudstone

The engineering characteristic of the water absorption, swelling, softening, and disintegration of muddy soft rocks can cause long-term large deformation and instability in muddy tunnels. Due to the poor injectability of conventional cement slurry into rock microcracks and insufficient reinforcement and anti-seepage effects on mudstone, this research performed tests on the modification and reinforcement with silica sol. Taking nano-silica sol as the research subject, this study analyzed the injectability of the slurry, the anti-seepage performance of the gel, and the macro and micro characteristics of the pore closure of consolidated mudstone. Ultimately, the basic laws of silica sol grouting and anti-seepage reinforcement for mudstone are obtained. Besides, the impact of silica sol consolidation on grouting is examined, with its performance being compared with traditional slurries. Research indicates that the silica sol slurry exhibits superior injectability and permeability, with its gel demonstrating enduring volume stability and a compact structure. When applied to mudstone, silica sol grouting markedly diminishes both porosity (by 1.68–1.88%) and permeability, reaching an ultra-low level of 10-9 cm/s. NMR tests further elucidate that silica sol is more efficacious in sealing medium and large pores (with T2 > 10 ms, >0.1 μm) compared to smaller ones (with T2 < 10 ms, below 0.1 μm). Therefore, silica sol is a prime candidate for grouting and sealing applications in micro-cracked mudstones of coal mine tunnels, particularly in muddy tunnel projects necessitating extended maintenance and anti-seepage measures. The research is expected to provide solutions to the anti-seepage and reinforcement of mudstone.

Preparation of dense modified nanosilica superhydrophilic coatings on aluminum alloy surfaces by adjusting amino groups

In this work, a uniform superhydrophilic coating was prepared by grafting N-(2-aminoethyl)-3-aminopropyltriethoxysilane oligomers(AEAOS) onto nanosilica by using silane coupling agent modification and coated on the surface of aluminum alloys to reduce water droplet generation. The grafting and dispersibility of modified nanosilica and aminosilane oligomers were characterised using Fourier transform infrared (FTIR) and dynamic light scattering (DLS). The surface state, composition, and roughness of the coatings were characterised with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and optical profilometer. The hydroxyl and organic content of modified nanosilica was analyzed by Thermogravimetric Analysis (TGA). The compactness of the coating film is analyzed by an electrochemical impedance. The hydrophilicity and adhesion of the coating films were evaluated by contact angle and adhesion testing. By adjusting the concentration of amino groups in the nanosilica sol, the results show that the amino groups promote the silane grafting on the surface of nanosilica. The 10% addition of AEAOS gives the modified silica film a contact angle of <5° with superhydrophilic properties. The polarization resistance of the superhydrophilic coating film is about 10 times higher than that of the original aluminum alloy. The surface of the coated films is homogeneous and dense, showing high resistance to polarization and good corrosion resistance.

Effects and mechanisms of anion and cation on the gelation of nanosilica sol by all-atom molecular dynamics simulation: promotion or inhibition?

Nanosilica sol (NSS) is prone to gelation due to the condensation of silicon hydroxyl at normal temperature and pressure, which is further exacerbated by the addition of electrolytes during production. Therefore, the effects of ions and the mechanism of gelation of NSS are crucial for its stability. Herein, all-atom molecular dynamics (AAMD) was carried out to explore the effects and mechanisms of cations (K+, Na+, Ca2+) and anions (Cl-, NO3-, SO42-, PO43-) on the sol-gel transition. Results indicated that highly electrophilic cations (e.g., Ca2+) and anions with slightly stronger nucleophilicity than Si(OH)3O- (e.g., NO3-) could inhibit gelation by preventing Si(OH)4 and Si(OH)3O- from approaching the silica surface. Such inhibition is more pronounced in NSS with larger particle sizes. Our findings offer some critical insights into the effects of ions on the gel stability of NSS, which also contributes significantly to screening suitable electrolytes for the production of NSS.

Spreading and penetration dynamics of nanosilica sol droplets impacting on porous rocks

Spreading and penetration dynamics of nanosilica sol droplets impacting on porous rocks

Investigation on flow resistance reduction and EOR mechanisms by activated silica nanofluids: Merging microfluidic experimental and CFD modeling approaches

Activated silica nanofluids (ASN) flooding has been proven to be an effective method to enhance oil recovery. However, due to the variety of nanoparticles and surfactants used for ASN synthesis, the main mechanisms of flow resistance reduction and oil recovery enhancement by ASN are still unclear, and most studies are based on physical experiments, which are too cumbersome and inefficient. In this study, the ASN flooding experiment and CFD modeling are combined based on microscopic visualization experiments. Firstly, three kinds of ASN with different hydrodynamic diameters were synthesized by BS-12 and nano-silica sol, and the basic properties were tested to obtain the modeling parameters. Surface flow experiments were also carried out. Then, a microscopic model based on the real pore-throat size was developed, and combined with image processing technology, the quantitative study and EOR mechanism analysis of the ASN flooding process was carried out. Finally, CFD modeling was carried out based on microscopic visualization experiments to predict the recovery improvement after improving ASN performance. The results show that at the optimal concentration of 1%, the ASN with a smaller hydrodynamic diameter performs better in wettability alteration and reducing interfacial tension and viscosity ratio. ASN can significantly reduce the flow resistance coefficient by 30.36% to 95.43%. The reduction of micro-resistances is the important EOR mechanism of ASN. The results of the microscopic visualization experiment and CFD simulation are compared, and errors ranged from 3.9% to 5.22% for recovery factors in various injection scenarios. The prediction results by CFD simulation show that the viscosity reduction ability has the most significant effect on the recovery factor. The best performance parameters of ASN under the highest recovery factor are also predicted. Simulation results guide the selection of surfactants and nanoparticles in the subsequent ASN synthesis process, which has the advantages of high efficiency and low cost.

Study on preparation and strengthening mechanism of new surface treatment agent of concrete at multi-scale

Concrete is susceptible to external erosion during service, the life of which was thus shortened due to the deterioration from the surface to the inside. In this study, the concrete surface treatment agent at multi-scale was innovatively proposed, which compounded of nano-silica sol–gel, micron-scale lithium silicate and sodium silicate. The physical properties and mechanical properties were investigated. Moreover, the mechanism of the new surface treatment agent was revealed in terms of pore structure and hydration products by XRD, TG, NMR, iMicro, and SEM. The results show that the Mohs hardness, flexural strength, and hydration degree are increased (by 260%, 78.7%, 12.1%), and porosity is reduced by 22% after the surface treatment. The mechanism is that pores can be repaired by particles of multi-scale. In addition, pretreatment of Ca2+ can further promote the pozzolanic reaction. The extra of EDTA-2Na can promote not only the pozzolanic reaction but also secondary hydration reaction.

Reinforcement of ultra-low dosage of polycarboxylate ether (PCE) grafted nano-silica sol to the mechanical and durable properties of cement mortar

How good dispersion of nano-SiO2 (NS) plays a great influence on how strong reinforcing efficiency to cement-based materials. In this study, a novel nanohybrid of polycarboxylate ether (PCE) grafted nano-silica sol (PCE@NSS) was prepared by sol–gel methods to chemically adsorb PCE onto NSS. The developed nanohybrid showed a higher ultraviolet–visible (UV–Vis) absorbance and slower sedimentation in alkaline solutions, indicating the better dispersion and stability of PCE@NSS than that of untreated NSS. By this way, only 0.05 wt.% addition of PCE@NSS was helpful to refine the capillary pore size and reduce the total porosity of cement mortar, which in turn improved the compressive and flexural strength of cement mortar by 18.34% and 10.5% at 28 days, respectively. In addition, a reinforcing index (R index) with the ratio of strength enhancement % to dosage % was proposed, indicating that the R index of PCE@NSS showed 10 times higher than that of other NS-based nanomaterials reported in literatures, addressing the highly reinforcing efficiency of PCE@NSS to cement mortar. Furthermore, water absorption coefficient of cement mortar was therefore reduced by 12.7% with 0.2 wt.% addition of PCE@NSS. In conclusion, such an ultra-low dosage of PCE@NSS with better dispersion and stability exhibited great potential to reinforce cement-based materials with highly efficiency, lower cost and reduced carbon emissions.

Study on the Pore-throat structure characterization and nano grouting law of the Low-permeability mudstone based on NMR-RSM methods

Mudstone, a common sedimentary rock in coal measure strata, sees the softening and disintegration of its clay minerals such as kaolinite owing to groundwater, water accumulation in goaf, and high in-situ stress, resulting in serious deformation and shrinkage of roadway space. However, it can hardly be reinforced by grouting because of other factors such as dense occurrence and poor permeability. In view of this, the silica sol, a nano-sized grouting material featured with controllable solidification and colloidal compactness, may be able to grout the low-permeability mudstone. In this paper, using the response surface methodology (RSM) and low-field nuclear magnetic resonance (NMR), we designed a two-factor orthogonal experiment and proposed a new data coupling test method integrating the processes of design, monitoring, and analysis, thus illustrating the pore throat distribution characteristics and grouting feasibility of low-permeability mudstone and revealing the diffusion law of nano silica sol in this kind of rock under the dual influences of pressure and permeability. On this basis, the optimal grouting parameters as well as the critical value of injectability were eventually determined. Experimental results proved that low-permeability rocks primarily contained pore throats in the size of 0.1 μm; and as these rocks became less permeable, a larger proportion of throats narrower than this size were developed, accounting for 48.39% in 1 mD samples. The low-permeability mudstone, which was highly matched with the silica sol solution in the particle size of 6.23 nm, could be modified and reinforced. Based on a calculation model for response values, the experimental data were successively classified by permeability and grouting pressure, from which the following pore-sealing rates were obtained: A (60 ∼ 100 mD): 33.74%, B (30 ∼ 60 mD): 24.61%, C (0 ∼ 30 mD): 0.41%, D (2 ∼ 3 MPa): 0.75%, E (1 ∼ 2 MPa): 38.92%, and F (0 ∼ 1 MPa): 28.02%. This indicated that the grouting effect was proportional to permeability; and it first increased and then decreased under rising pressure. According to the response to these rates, the low-permeability mudstone had better be grouted with nano silica sol under the pressure of 0.804 MPa, with the critical value of injectable permeability being about 40.42 mD.

Preparation and properties of modified poplar impregnated with PVA-nano silica sol composite dispersion system

The dilemma of insufficient wood resources and poor properties of fast-growing wood necessitates a breakthrough in the expansion and efficient utilization of wood resources to meet the real needs. With the aim of enhancing the properties of fast-growing poplar wood, a combination of PVA and nano-silica sol impregnation treatment was carried out to develop a novel functional wood material with good dimensional stability, compressive strength and thermal stability, while fully exploiting the unique structural properties of the wood itself. In this work, PVA-nano-silica sol composite wood was prepared by in-situ impregnation of poplar fast-growing wood via ultrasound-assisted and vacuum impregnation methods. Firstly, the effects of different treatments on the impregnation effect and strengthening effect of modified wood were explored. The results showed that the PVA-nano-silica sol dispersion system had no negative effect on the impregnation modification, and the compressive strength of modified wood was obviously improved compared with natural wood. Among them, the most effective modification was achieved under the condition of vacuum-assisted impregnation. The effect of compound impregnation modification on the structure of poplar fast-growing wood was analyzed by FTIR, XRD, SEM, and EDS, in which PVA and nano-silica sol can form a certain cross-linking system and form chemical bonds such as Si-O-C and Si-O-Si, enabling them to enter the structure of wood and react with wood cell walls effectively. The compressive strength of modified poplar wood was increased by 72.29% compared with natural poplar wood. According to the thermogravimetric analysis, the thermal stability of the modified poplar wood was improved to some extent. In view of all the results, the method proposed in this study provides an opportunity for the high value utilization of low quality wood, and this modified wood can be considered as a candidate for new lightweight and high performance materials in the construction field.

Effects of Graphene Oxide Encapsulated Silica Fume and Its Mixing with Nano-Silica Sol on Properties of Fly Ash-Mixed Cement Composites

In the present research work, the ternary effects of varying dosages of graphene oxide encapsulated silica fume (GOSF), nano-silica sol (SS), and fly ash (FA) on the rheological properties, compressive strength, the content and crystal size of calcium hydroxide (CH), porosity, water absorption, and microstructure of cement were studied. The results showed that the incorporation of SF improved the dispersion of GO in the cement matrix. GOSF was prepared through electrostatic attraction between the positively charged SF and negatively charged GO. The ternary mixture of GOSF, SS, and FA had a synergistic effect that improved the performance of cement. When the curing age of cement reached 28 days, the compressive strength reached a peak of 86.5 MPa, the minimum values of content and crystal size of CH were 11.55% and 45.69 nm, respectively, and the minimum values of water absorption and porosity were 0.0011 cm/s0.5 and 13.56%, respectively. In terms of microstructure, the denser structure of C-S-H gel and the regular arrangement of CH were noticed.

Numerical Simulation of Nanosilica Sol Grouting for Deep Tunnels Based on the Multifield Coupling Mechanism

Grouting is an effective technical way for the construction of deep tunnels in unfavorable geological conditions. The fluid-solid-chemical coupling mechanism of grouting process is analyzed from the following three aspects: influence of physical properties of silica sol on permeability coefficient, dynamic changes of porosity and permeability of geotechnical media with seepage pressure, and governing equations for flow and mass transfer characteristics. A dynamically changing model for nanosilica sol grouting in deep tunnels is established, considering the changing physical properties of grout and surrounding rock. Based on the Xianglushan Tunnel of Yunnan Water Diversion Project, the temporal and spatial evolution of silica sol grout is studied. The effect characteristics of grouting pressure and initial permeability are clarified. The rationality of this model is verified by classical Newtonian fluid grouting theory. The main conclusions: with the molar concentration as the index, the grout range can be divided into the raw grout region and the transition region; with the decrease of the grouting pressure, the growth rate of the normal grouting radius and the axial grouting radius will gradually decrease; due to the mechanical dispersion and molecular diffusion, the range of the transition region will gradually increase with time. The ratio of the transition region to grouting radius fluctuates slightly with time under the initial permeability of 5 D. The fluctuation increases with the decrease of initial permeability, and the average ratio increases with the decrease of grouting pressure. This study can provide theoretical guidance for grouting design of deep tunnel engineering.

Study on the Influence of Nanosilica Sol on the Hydration Process of Different Kinds of Cement and Mortar Properties.

Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar.

Development of low-calcium fly ash-based geopolymer mortar using nanosilica and hybrid fibers

Fly ash has been widely explored in alkali-activated concrete technology as a precursor; however, it suffers sudden brittle failure and requires heat activation for early-strength development. Previous studies have demonstrated that these shortcomings can be overcome by adding nanosilica and various types of fibers. However, they were mainly focused on improving the mechanical properties, but there is no clear understanding of the durability and microstructural changes. Therefore, this study systematically addresses the effects of nanosilica sol and hybrid fibers (steel and polypropylene fibers) on the workability, porosity, flexural/compressive strength development, flexural toughness, crack resistance, and durability (subjected to sulfuric acid of pH = 1, 5% sodium sulfate, and 3.5% seawater attacks) of fly ash-based mortars cured at ambient environments. The results demonstrate that nanosilica and hybrid fibers have acceptable simultaneous effects on the properties of mortar. Although they both reduce fluidity, nanosilica improves the pore enlargement caused by fiber materials; thus, it greatly improves the mechanical properties of mortar. The flexural toughness of the mortar with nanosilica and hybrid fibers was approximately 200% higher than that of the pure-fly ash. Only approximately 58.25 mm2 microcracks were observed during the early crack detection, and the residual strength also improved under chemical solution attack. The microstructures were studied by field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction/Rietveld method, and nanoscale 3D X-ray microscopy. The nanosilica enhanced the reactivity of the precursors and refined the pore structure of the mortar due to the changes in the crystalline and amorphous phases, and the hybrid fibers produced composites with good internal characteristics and strong fiber/matrix interfacial bonding.

Improvement of Mechanical, Hydrophobicity and Thermal Properties of Chinese Fir Wood by Impregnation of Nano Silica Sol.

In this paper, a wood-SiO2 composite material was prepared via in-situ polymerization using vacuum/pressure impregnation technology using commercial scale nano silica sol and Chinese Fir (Cunninghamia lanceolate (Lamb.) Hook.). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), and water contact angle were used to study the changes in the microstructure and physical and mechanical properties of this composite. The results showed that silica sol can penetrate and distribute into the wood cell cavities and surface of cell walls and hence combine with the substances of wood materials. FTIR results indicated that the –OH groups of wood can polycondense in-situ with silica sol to form Si–O–C covalent bonds, and amorphous SiO2 formed from Si–O–Si bonds between the –OH groups of silica sol did not change the crystalline structure of wood cell walls. This in-situ formulating composite significantly improved the compact microstructure, thermal and mechanical properties, and hydrophobicity of the composites.