Materials Science Forum Vol. 956

Abstract: A series of mesoporous silica materials (SBA-15, MCM-41, KIT-6) with different pore structures and properties were synthesized and characterized by means of small angle X-ray scattering, transmission electron microscopy, infrared spectroscopy and nitrogen adsorption-desorption. The adsorption properties of three mesoporous silica materials for chlorine ions in aqueous solution were investigated. The results show that SBA-15, MCM-41 with two-dimensional hexagonal structure has a better adsorption effect on chloride ion than KIT-6 With cubic core structure, and MCM-41 with larger specific surface area and smaller pore size has better adsorption effect on chloride ion than on SBA-15. The specific surface area of MCM-41 is 1036 m²/g, and the The adsorption kinetics accords with the pseudo-second-order kinetic model, and the adsorption isotherm is more consistent with the Langmuir isotherm model. The optimum operating conditions for MCM-41 to adsorb chloride ions are as follows: temperature 55 °C, pH 6, adsorption time 2 h, Cl^- concentration 0.01 mol/L (584 mg/L) and adsorbent concentration 1.0 g/L. Under these conditions, the adsorption capacity of MCM-41 to chloride ions is greatly enhanced, and the maximum adsorption capacity is 188.18 mg/g.

Abstract: Using magnesium nitrate, nickel nitrate and aluminum nitrate as raw materials and urea as precipitant, magnesium nickel aluminum ternary hydrotalcites with large specific surface area were prepared by hydrothermal method. The prepared samples were characterized by SEM、XRD、BET and EDS etc., respectively. The adsorption properties of MgNiAl-LDHs, MgAl-LDHs and their calcined products (MgNiAl-LDOs, MgAl-LDOs) for chloride ions in solution were investigated. The results show that MgNiAl-LDHs are cubic with rod-like structure, with a specific surface area of 197.62 m²/g, which is much larger than that of MgAl-LDHs (102.82 m²/g). Under the same adsorption conditions, the saturated adsorption capacities of MgNiAl-LDHs and MgAl-LDHs for chloride ions are 130.06mg/g and 110.02 mg/g respectively. MgNiAl-LDOs showed better adsorption ability for chloride ions. By simulating the adsorption data, the results show that the adsorption kinetics and the adsorption isotherm are in accordance with the quasi-second-order kinetic model and the Langmuir isotherm model, respectively.

Abstract: Magnesium-aluminum hydrotalcite and carbon nanotube composites (CNTs/MgAl-LDHs) were prepared by one-step hydrothermal method using magnesium nitrate, aluminum nitrate and carbon nanotubes as raw materials and urea as precipitant. The samples were characterized by SEM, XRD, BET and other methods. The adsorption properties of CNTs/MgAl-LDHs on chloride ions and the factors affecting the adsorption of chloride ions were studied. The results show that the prepared CNTs/MgAl-LDHs exhibit a three-dimensional honeycomb structure with a specific surface area of 103.019 m²/g, which is larger than the specific surface area of MgAl-LDHs of 84.344 m²/g. The results showed that the optimal adsorption conditions were: adsorption temperature was 45°C, the pH value was 8, the adsorption time was 100 min, the Cl^- concentration was 0.01 M (584 mg/L), and the adsorbent concentration was 1.0 g/L. CNTs/MgAl-LDHs has the best adsorption performance for chloride ions. The maximum adsorption capacity is 75.58 mg/g. The adsorption isotherms and adsorption kinetics are consistent with the Langmuir isotherm model and the quasi-secondary kinetic model.

Abstract: In this paper, the CW epoxy resin grouting material produced by Changjiang River Scientific Research Institute was choosed as the research object. By testing the viscosity, surface tension and contact angle of the epoxy grouting material, the change law of the viscosity and affinity of the curing process was investigated. The results show that the viscosity, surface tension and contact angle of the slurry decreased with the time increased. The surface tension value of slurry is the maximum when its viscosity is the minimum. The trend of the surface tension change showed a rapid growth and then tended to be stable. When the curve is stable, the surface tension value is the equilibrium surface tension of the slurry. Through the calculation and analysis, the mathematical model of viscosity and affinity of CW epoxy resin was established.

Abstract: Based on the particle size distribution test of 6 kinds of limestone powder, the fractal dimension of particle size distribution was calculated, and its influence on the surface area, median grain diameter and RR-B value was studied. In addition, 20% of the total mass of cement was replaced with limestone powder, and the effect of fractal dimension on fluidity of cement paste and 3, 7, 28d strength of mortar was investigated. The results showed that fractal dimension for limestone powder specific surface area has a good linear relationship with median grain diameter and RR-B value. The fractal dimension showed a quadratic function with the degree of the fluidity, and the maximum value was between 2.1-2.2. Mortar strength at the age of 3, 7, 28d value displayed a linear relationship with fractal dimension L4 had the greatest effect on strength. L1-L4 had more influence on the strength at the age of 3d and 7d than that of 28d. While the influence of L5-L7 on the strength at 3d, 7d and 28d was essentially similar to each other.

Abstract: The performance prediction of C-S-H gel is critical to the theoretical research of cement-based materials. In the light of recent computational material technology, modeling from nano-scale to micro-scale to predict mechanical properties of structure has become research hotspots. This paper aims to find the inter-linkages between the monolithic "glouble" C-S-H at nano-scale and the low/high density C-S-H at the micro-scale by step to step method, and to find a reliable experimental verification method. Above all, the basic structure of tobermorite and the "glouble" C-S-H model at nano-scale are discussed. At this scale, a "glouble" C-S-H structure of about 5.5 nm3 was established based on the 11Å tobermorite crystal, and the elastic modulus ​​of the isotropic "glouble" is obtained by simulation. Besides, by considering the effect of porosity on the low/high density of the gel morphology, the C-S-H phase at micro-scale can be reversely characterized by the "glouble". By setting different porosities and using Self-Consistent and Mori-Tanaka schemes, elastic moduli of the low density and high density C-S-H ​​from that of "glouble" are predicted, which are used to compare with the experimental values of the outer and inner C-S-H. Moreover, the nanoindentation simulation is carried out, where the simulated P-h curve is in good agreement with the accurate experimental curve in nanoindentation experiment by the regional indentation technique(RET), thus the rationality of the "glouble" structure modeled is verified and the feasibility of Jennings model is proved. Finally, the studies from the obtained ideal "glouble" model to the C-S-H phase performance has realized the mechanical properties prediction of the C-S-H structure from nano-scale to micro-scale, which has great theoretical significance for the C-S-H structural strengthening research.

Abstract: Magnesia inorganic lightweight material was prepared by using magnesium cementitious materials as raw materials, sodium silicate solution as modifier, hydrogen peroxide solution as foaming agent, manganese dioxide as activator, calcium stearate as stabilizer and polyacrylamide as thickener in this paper. The effects of sodium silicate addition on the apparent density, mechanical strength, pore structure, crystalline phase and water resistance of magnesia inorganic lightweight material were discussed. The results show that when the content of sodium silicate is 7.5‰, the pore structure presents better morphology and the crystallization contains more 5·1·8 phases (strength phase). At this moment, the compressive strength and bending strength of the composite reached 10.35 MPa and 2.22 MPa, respectively. When the addition of sodium silicate exceeded 7.5‰, SEM and EDS presented that a large amount of sodium silicate and perforation appeared in the pores, meanwhile large number of perforations occurred between pores. XRD showed that the 5·1·8 phases and 3·1·8 phases in the materials changed into Mg (OH)₂ crystals. These results in a significant decrease in material properties. Keywords: Magnesium cementitious material; Sodium silicate; Inorganic light materials; Pore structure

Abstract: Separate and combined effects of sodium hex metaphosphate (SHMP) and polycarboxylate superplasticizer (PCS) of different dosages (0.5%, 1%, 1.5%, and 2%) on the dispersion stability of nanoSiO₂ (NS) were studied. The effect of the dispersant was characterized by the change of absorbance. When SHMP and PCS were used separately and in combination, the stability of nanoSiO₂ dispersions was compared and the optimal amount of dispersant for different dosage of nanoSiO₂ dispersions were summarized. Finally, the mechanism of dispersant compounding was discussed. The results show that with the increase of the concentration, the optimal amount of SHMP increases significantly while the optimal amount of PCS dispersant is lower and better than SHMP. A clear linear relationship between the optimal dosage of SHMP and the concentration of NS could be found. If SHMP is used combined with PCS, the stability of the dispersed NS will increase and the dosages of both dispersants will be reduced.