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Alite(C3S)-Ye'elimite(C4A3$) cement is a high cementitious material that incorporates a precise proportion of ye'elimite into the ordinary Portland cement. The synthesis and hydration behavior of Alite-Ye'elimite clinker with different lime saturation factors were investigated. The clinkers were synthesized using a secondary thermal treatment process, and their compositions were characterized. The hydrated pastes were analyzed for their hydration products, pore structure, mechanical strength, and microstructure. The clinkers and hydration products were characterized using XRD, TG-DSC, SEM, and MIP analysis. The results showed that the Alite-Ye'elimite cement clinker with a lime saturation factor (KH) of 0.93, prepared through secondary heat treatment, contained 64.88% C3S and 2.06% C4A3$. At this composition, the Alite-Ye'elimite cement clinker demonstrated the highest 28-day strength. The addition of SO3 to the clinkers decreased the content of tricalcium aluminate (C3A) and the ratio of Alite/Belite (C3S/C2S), resulting in a preference for belite formation. The pore structure of the hydrated pastes was also investigated, revealing a distribution of pore sizes ranging from 0.01 to 10 μm, with two peaks on each differential distribution curve corresponding to micron and sub-micron pores. The pore volume decreased from 0.22 ± 0.03 to 0.15 ± 0.18 cm3 g−1, and the main peak of pore distribution shifted towards smaller sizes with increasing hydration time. [ABSTRACT FROM AUTHOR]

The physical properties of Ti6Al4V powder affect the spreadability of the powder and uniformity of the powder bed, which had a great impact on the performance of built parts made by powder bed fusion technology. Micro-computed tomography is a well-established technique used to analyze the non-destructivity of the objects' interior. Ti6Al4V powders were scanned with micro-CT to show the internal and external information of all the particles. The morphology, particle size distribution, hollow particle ratio, density, inclusion, and specific surface area of the powder samples were quantitatively characterized, and the relationship of flowability with these physical properties was analyzed in this work. The research results of this article showed that micro-CT is an effective way to characterize these items, and can be developed as a standard method of powder physical properties in the future. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) has attracted increasing attention all over the world. As an important parameter, hatch spacing, which is the distance between scan lines, however, still needs a more systematic study. In this paper, the relationship between hatch spacing and mechanical properties, including microhardness, wear resistance, and porous density, was studied. The testing results revealed that when hatch spacing decreased, the overlapping rate increased which resulted in an increase in the convection in the molten pool. It led to the formation of pores in the molten pool. However, when hatch spacing was too large, the overlapping zone decreased, while the strength between each welding line was not strong enough. It caused a decrease in the quality of printed parts. Combined with the testing results gained in this work, it can be seen that a 0.06 mm hatch spacing was considered as a relatively optimal condition for part formation under 0.05 μm. Comparison of the morphology of the samples printed under different hatch spacing also confirmed the phenomenon observed here. [ABSTRACT FROM AUTHOR]

A systematic study was conducted to investigate the distinct mechanisms involved in the formation of the inner surfaces of cylindrical and parallelepipedic-shaped structures. The surface roughness, flatness, and sinking distance were used as key indices to measure the quality of overhanging surfaces, while the surface flatness and roughness were used to evaluate the quality of the side and bottom surfaces of the inner hole. The inner surface morphology was observed using a scanning electron microscope and a white light interferometer. The test results show that the quality of the overhanging surface had a significant impact on the quality of the parallelepipedic-shaped inner hole. In contrast, the cylindrical-shaped inner hole had a shorter but more uniformly distributed overhanging surface, resulting in a different behavior of the overhanging and side surface quality. An improved model of the overhanging surface was established by combining all of the above results and comparing them with the traditional Euler Bernoulli beam model. The factors affecting the quality of the overhanging surface were analyzed, and measures for improving the quality of the overhanging surface during the SLM manufacturing process were proposed. [ABSTRACT FROM AUTHOR]

Steel slag (SS) has been largely discharged but little utilized, causing an environmental problem in China. In this paper, SS-based composite cementitious materials with high strength were prepared by the high volume of SS (≥40%), granulated blast-furnace slag (GBFS), fly ash (FA), flue gas desulfurization gypsum (FGDG) and cement to promote the effective utilization of SS. The hydration and hardening properties were studied through setting time, compressive strength, length change, isothermal calorimetry (IC), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) tests. The results show that SS-based composite cementitious material exhibited a lower hydration heat release, an appropriate setting time, and volume stability. The SS cementitious material with 40% SS could obtain high strength of over 65 MPa at 28 days and 80 MPa at 90 days. The strength value of > 60 MPa is present in the binder, with 50% SS at 56 days. GBFS promotes hydration reactions and the formation of AFt and C-(A)-S-H gel, thus enhancing compressive strength. FA has a beneficial effect on later strength. The small and fine pore structures contribute to the development of strength. The main hydration products of SS composite cementitious materials are C-(A)-S-H gel, and ettringite (AFt), with less Ca(OH)2. The C-(A)-S-H gel with a lower Ca/Si ratio and a higher Al/Ca ratio in cementitious material, promotes mechanical properties. [ABSTRACT FROM AUTHOR]

Dye wastewater has caused great harm to the environment, which is an urgent problem to be solved. As typical three-dimensional porous materials, aerogels have attracted great interest in dye wastewater treatment. In this work, spherical attapulgite/silica (ATP/SiO2) gels were initially prepared by easily scalable sol-gel dripping methods and then dried to aerogels with three drying techniques, namely, supercritical CO2 drying (SCD), freeze-drying (FD), and ambient pressure drying (APD). The effect of the drying techniques and heat-treated temperature on the physical characteristic, morphological properties, microstructure, and chemical structure of the spherical ATP/SiO2 aerogels were investigated. The macroscopic morphology of the spherical ATP/SiO2 aerogels was homogeneous and integrated without local cracking. The average pore diameter and specific surface area of the spherical ATP/SiO2 aerogels prepared by the three drying techniques were in the range of 6.8–8.6 nm and 218.5–267.4 m2/g, respectively. The heat treatment temperature had a significant effect on the pore structure and the wetting properties of the aerogels. The 600 °C heat-treated aerogels were subjected to adsorption tests in methylene blue (MB) solution (60 mg/g, 100 mL), which exhibited a great adsorption capacity of 102.50 mg/g. Therefore, the resulting spherical ATP/SiO2 aerogels possessed multipath preparation and exhibited an efficient adsorption performance, with the potential to be applied as an adsorbent for dye wastewater. [ABSTRACT FROM AUTHOR]

Aerogels have interconnected networks and preeminent pore structures. When used as the catalysts for oxygen reduction reaction (ORR), they can facilitate the mass transfer and expose more active sites. Here, we synthesized the Fe-doped titanium oxide-based aerogels (TA/Fes) by the sol–gel method combined with thermal treatment. The specific surface areas of the TA/Fes ranged from 475 to 774 m2·g−1, and the pore volumes varied from 0.96 to 1.72 cm3·g−1. The doping effect of the Fe ions and the oxygen vacancies in anatase enhance the electrical conductivity, leading to the low Rct (313.3–828.2 Ω). All samples showed excellent stability (2.0–4.5 mV) and 4e− pathway. The limiting current density of TA/Fe3 reached 5.34 mA·cm−2, which was comparable to that of commercial Pt/C. The preparation method is inspiring and the as-prepared aerogel catalysts have potential in promoting the scale of fuel cells. [ABSTRACT FROM AUTHOR]

To investigate the effects of limestone powder and gypsum on the early hydration of ye'elimite, the hydration behavior of C4A3 S ¯ -LP-CaSO4·2H2O-H2O systems are researched. The hydration behavior of systems are researched by employing isothermal calorimetry, XRD technique and chemical shrinkage. The thermodynamic modelling method is employed to predict the equilibrium phase assemblages. The results show that the system with 5 wt.% LP has a comparable hydration heat evolution to limestone powder-free systems. Limestone powder can take part in the reaction to produce monocarboaluminate in the system with M-value (molar ratio of gypsum to ye'elimite) of 1, but monocarboaluminate is not found in the system with M-value of 2. The level off time of chemical shrinkage shortens with the increase of limestone powder dosage. Thermodynamic modelling results show that monocarboaluminate is no longer formed in all systems when M-value exceeds 1.27, which corresponds to the XRD results. This study can provide theoretical guidance for the rational utilization of limestone powder in calcium sulphoaluminate cement. [ABSTRACT FROM AUTHOR]

Extrusion-based ceramic printing is fast and convenient, but the green body strength is too low, and the application prospect is not high. An extrusion-based printing method of alumina ceramics toughened by short carbon fiber is reported in this paper. The bending strength and fracture toughness of 3D-printed alumina ceramics were improved by adding short carbon fiber. The toughening effects of four carbon fiber lengths (100 μm, 300 μm, 700 μm, and 1000 μm) and six carbon fiber contents (1, 2, 3, 4, 5, and 6 wt%) on ceramics were compared. The experimental results show that when the length of carbon fiber is 700 μm, and carbon fiber is 5 wt%, the toughening effect of fiber is the best, and the uniform distribution of fiber is an effective toughening method. Its bending strength reaches 33.426 ± 1.027 MPa, and its fracture toughness reaches 4.53 ± 0.46 MPa·m1/2. Compared with extrusion-based printed alumina ceramics without fiber, the bending strength and fracture toughness increase by 55.38% and 47.56%, respectively. [ABSTRACT FROM AUTHOR]

The utilization of coral waste is an economical way of using concrete in coastal and offshore constructions. Coral waste with more than 96% CaCO3 can be ground to fines and combined with supplementary cementitious materials (SCMs) such as fly ash, silica fume, granulated blast furnace slag in replacing Portland cement to promote the properties of cement concrete. The effects of coral sand powder (CSP) compared to limestone powder (LSP) blended with SCMs on hydration and microstructure of mortar were investigated. The result shows CSP has higher activity than LSP when participating in the chemical reaction. The chemical effect among CSP, SCMs, and ordinary Portland cement (OPC) results in the appearance of the third hydration peak, facilitating the production of carboaluminate. CSP-SCMs mortar has smaller interconnected pores on account of the porous character of CSP as well as the filler and chemical effect. The dilution effect of CSP leads to the reduction of compressive strength of OPC-CSP and OPC-CSP-SCMs mortars. The synergic effects of CSP with slag and silica fume facilitate the development of compressive strength and lead to a compacted isolation and transfer zone (ITZ) in mortar. [ABSTRACT FROM AUTHOR]