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Aerogel materials have broad application prospects in the market of building thermal insulation materials because of their high porosity, strong compression resistance and low thermal conductivity. In this paper, Al2O3-SiO2 aerogel composite thermal insulation materials with different SiO2 content were prepared by sol-gel method using tetraethyl orthosilicate and sec butanol aluminum as raw materials. The effects of SiO2 doping amount on the crystal structure, micro morphology, mechanical properties and thermal conductivity of composite aerogels were studied. The results showed that Al2O3-SiO2 aerogel was mainly composed of polycrystalline boehmite. SiO2 doping inhibited the formation of γ-Al2O3 phase and hindered the occurrence of hydroxyl condensation reaction. H in AlO—H group was replaced by Si, forming a more stable Al—O—Si bond. Al2O3-SiO2 aerogel showed an open porous structure, and the doping of SiO2 improved the pore orientation of the aerogel, reducing the pore size and distributing evenly. With the increase of SiO2 doping, the compressive strength and specific surface area of Al2O3-SiO2 aerogel first increased and then slightly decreased, and the thermal conductivity first decreased and then increased. When the doping amount of SiO2 was 9 mol %, the maximum compressive strength of the aerogel was 40.92 MPa, which was 58.97% higher than that of the undoped aerogel. The maximum specific surface area was 257.33 m²/g, the lowest thermal conductivity was 0.022 W/（m·K）, and the thermal insulation performance was the best. In summary, the optimal doping amount of SiO2 was 9 mol%. [ABSTRACT FROM AUTHOR]

Aiming at the problems of insufficient flexural strength and low durability of cement concrete, this paper prepared concrete with different content of epoxy resin（0%, 3 wt%, 6 wt%, 9 wt%） by using epoxy resin as doping phase, and analyzed the influence of epoxy resin on the mechanical properties, micro appearance and durability of cement concrete. The results show that the doping of epoxy resin accelerates the hydration reaction, reduces the number of cracks and pores, and improves the density of concrete. The compressive strength and flexural strength both increased first and then decreased with the increase of resin doping. The compressive strength and flexural strength of the concrete with 6 wt% epoxy resin doping reached the maximum values of 43.8 and 7.9 Mpa respectively when cured for 28 d, which increased by 18.70% and 29.51% respectively compared with the concrete without resin doping. The chloride ion diffusion coefficient of concrete decreases first and then increases with the increase of resin doping amount. The chloride ion diffusion coefficient of concrete with 6 wt% epoxy resin doping content for 28 d is the lowest of 7.7×10-8 cm/s, and the chloride ion corrosion resistance is the best. When the number of freeze-thaw cycles reaches 80, the concrete with 6 wt% epoxy resin doping has the lowest mass loss rate of-0.13%, the highest relative dynamic elastic modulus of 94.86%, the lowest wear amount of 0.66 kg/m², and the wear amount reduction rate of 46.77%. It has excellent durability. [ABSTRACT FROM AUTHOR]

In this paper, modified cementitious powders with different doping amounts of calcium carbide slag (0,0.5 wt%,1.0 wt% and 1.5 wt%) were prepared with 32.5 grade ordinary portland cement, II grade fly ash and mirabilite as raw materials and industrial waste calcium carbide slag as additive materials. The effects of calcium carbide slag doping on the crystal structure, micro morphology, mechanical properties, setting time and combined water content of modified cementitious powder were analyzed.The results show that the doping of carbide slag doesn’t produce new products, but accelerates the consumption of C2S and C3S and improves the rate of hydration reaction.When the doping amount of carbide slag is 1.0 wt%, the hydration products are most closely combined.With the increase of calcium carbide slag doping, the setting time of the modified cementitious powder gradually decreases, and the compressive strength and chemical binding water content at 28 d first increase and then decrease.When the doping amount of carbide slag is 1.0 wt%, the compressive strength and chemical binding water content at 28 d reach the maximum, which are 2.98 MPa and 6.8% respectively.This is because the addition of appropriate amount of calcium carbide slag accelerates the hydration reaction of cementitious powder, increases its structural compactness, and improves the mechanical properties of cementitious powder.It can be seen that the optimum doping amount of carbide slag is 1.0 wt%. [ABSTRACT FROM AUTHOR]

Al-based particle-reinforced composites have become the focus research around the world due to their unique quality, economic and performance advantages. Powder metallurgy method has the advantages of flexible selection of reinforced particles, accurate and controllable content, and strong designability, which is one of the commonly used methods for preparing particle reinforced Al matrix composites and is favored by many scholars. The present paper firstly gives a brief introduction to the development of Al matrix composites. Secondly, the densification molding technology and sintering process in powder metallurgy process are summarized. Subsequently, the composition design, such as reinforcement type, content, particle size, distribution, etc., interface wettability and its control, the relationship between microstructure characteristics and mechanical properties, and the strengthening mechanism were mainly discussed. Finally, it analyses the problems and challenges faced by powder metallurgical particle-reinforced Al matrix composites and looks forward to their development. [ABSTRACT FROM AUTHOR]

In view of the current research status that the experimental methods to study the effect of solute rare earth on the mechanical properties of steel has not achieved satisfactory results, in this paper, a system research was carried out by means of simulation calculation, and first-principles calculation method based on density functional theory was used to reveal the solid solution mechanism of Ce atoms in α-Fe by solvation energy, geometric structure, electronic structure, and Bader charge. And the mechanical properties of Fe-Ce doped system were calculated in detail. The calculation results of the solvation energy show that Ce can occupy the α-Fe matrix by replacing Fe atoms. In Fe-Ce doped system, Ce atoms lose electrons, resulting in a reduction in the radius of Ce atoms and a polarization effect, which is conducive to the solid solution of Ce in Fe. The calculation results of the mechanical properties of pure Fe and Fe-Ce doped system show that Ce doping reduces the incompressibility, shear strain resistance, rigidity, and Vickers hardness of the system, but improves the toughness and workability of the system. Ce doping leads to a decrease in the strength of the metallic bond of the system, which is the main reason for the decrease in the incompressibility, rigidity and hardness of Fe-Ce doped system. On the other hand, the doping of Ce increases the density of the electron cloud in the system, which is conducive to the improvement of the toughness of the doped system. [ABSTRACT FROM AUTHOR]

Graphene (G)/graphene oxide (GO) has shown promising applications in improving the mechanics and functionality of cement materials with its excellent mechanical, electrical, and thermal conductivity properties. However, these nanomate rials are difficult to disperse in cement-based materials, which limits their practical application in cement-based composites. Tn recent years, researchers have begun to mix fibers with these nanomaterials into cement-based materials, and its dispersion performance has been greatly improved. Tn this paper, the influence of graphene, GO and other fiber mixture on cement-based composite materials is systematically described from five aspects of material dispersion in cement, cement hydration process, mechanical properties, functionality and durability, which has a guiding role in improving the performance of cement-based composite materials in the future. [ABSTRACT FROM AUTHOR]