Search

Developing siloxane‐based coatings with excellent water vapor barrier ability is of great importance due to their wide applications for various optical‐related fields. To improve the water vapor barrier ability of polysilsesquioxane coatings, this research proposes a strategy of introducing carbon quantum dots (CQDs) into organic‐bridged polysilsesquioxane coatings to enhance their water vapor barrier property. The CQDs are prepared by the pyrolysis of citric acid and then the composite coatings are prepared by thioether‐ester‐bridged silsesquioxane precursor in situ hydrolysis and condensation in the presence of CQDs. The experimental results show that the CQDs disperse well in the polysilsesquioxane matrix which is conducive to provide long diffusion pathway of water vapor molecules and also introduce individual "bubble pores" into the composite coatings. Thus‐obtained composite coatings not only show fivefold enhancement in water vapor barrier ability compared to the polysilsesquioxane coating without CQDs, but also perform good light transparence and good UV radiation‐resistant property, which would satisfy the requirements of optical‐related moisture‐resistant application fields. [ABSTRACT FROM AUTHOR]

Magnesium–lithium alloy is the lightest metal alloy material so far, and the ultra-thin plate is also one of the main trends in the future development of Mg-Li alloy. In order to explore how to prepare LZ91 ultra-thin Mg-Li alloy, this topic adopts the combination of the finite element method (FEM) and visco-plastic self-consistent (VPSC) calculation, electron back-scattered diffraction (EBSD) and tensile experiment, and uses the asymmetric warm rolling process to realize the processing of ultra-thin LZ91 Mg-Li alloy plate with a thickness of 0.25 mm. The experimental results show that the maximum basal texture strengths of 1 mm initial plate and 0.25 mm ultra-thin rolled plate are 36.02 mud and 29.19 mud, respectively. The asymmetric warm rolling process not only reduces the basal texture strength but also significantly refines the grains. The tensile strength and yield strength of 0.25 mm ultra-thin rolled plate along the rolling direction reached 206.8 MPa and 138.4 MPa, respectively. This has a positive effect on the mechanical properties of subsequent materials. VPSC results show that the base slip is the main factor in Mg-Li alloy asymmetric warm rolling, and a large number of tensile twinning are initiated due to the coordinated deformation of the body-centered cubic (BCC) phase, which is beneficial to improve the plastic deformation capacity of Mg-Li alloy. [ABSTRACT FROM AUTHOR]

The AA7075/AZ31/AA7075 laminated composites were fabricated by hot roll bonding. The effects of pretreatment of Mg plate by severe plastic deformation (SPD) and heat treatment on its interface, microstructure and mechanical properties were studied. The diffusion layer is formed at the interface between Al and Mg layers, which is composed of the hard and brittle intermetallic phases β -Al 3 Mg 2 and γ -Al 1 2 Mg 1 7 , and become the weak zone of the laminated composites where the crack is first-generated and propagated to cause the delamination at the interface of the laminated composites. The hardness of laminated composites at the interface reaches 300–400 HV. Meanwhile, Mg plate pretreatment can increase the plastic matching and the deformation compatibility of the Al and Mg layers, and can effectively improve the mechanical properties of the laminated composites to a certain extent. The bending strength of the laminated composites with pretreated Mg plates are 1080 MPa. [ABSTRACT FROM AUTHOR]

[Display omitted] • In the prefabricated concrete industry, electric curing has lower energy consumption than steam curing. • Electric curing can not only improve the early strength of cement samples, but also the energy consumption is only 4% of that of steam-cured samples. • Sodium citrate can improve the durability of electric-cured cement pastes. Faced with the increasingly severe energy crisis, it is very important to seek a low-energy-consumption accelerated curing method for prefabricated concrete element to save energy in the construction industry. In this research, direct electric curing (DEC) was used to produce high early-strength cement sample, and sodium citrate was used to improve the durability of the paste. Meanwhile, the effects of DEC and traditional accelerated curing methods on the early-age strength of paste and the corresponding energy consumption were compared and discussed. The results indicate that the DEC makes the early-age strength of cement paste higher than that of steam-cured sample, but its energy consumption is only 4% of that of steam curing. Although DEC increases the early-ages strength of the cement sample without reducing its long-term strength, it increases the water absorption and drying shrinkage deformation of the sample. Meanwhile, incorporating sodium citrate to the electric-cured paste can effectively improve its durability by refining the pore structure. The reduction in energy consumption also means a reduction in production costs and carbon emissions. This means that DEC can replace traditional accelerated maintenance methods and improve production & energy efficiency, which may bring a technological change to the modern construction industry. [ABSTRACT FROM AUTHOR]

Abstract One-part geopolymers prepared by powder activators, similar to Portland cement in cast-in-situ application, are promising building materials due to the relatively slighter embodied environmental impact. There are three types of commercial sodium metasilicate powders in the China market, and they are Na 2 SiO 3 -anhydrous/NS0, Na 2 SiO 3 ·5H 2 O/NS5 and Na 2 SiO 3 ·9H 2 O/NS9, respectively. This study employed ultra-fine fly ash sinking beads (FASB) and ground granulated blast furnace slag (GGBS) as precursor materials to analyze the influences of NS0, NS5 and NS9 on the properties, microstructure and environmental impact of one-part geopolymer by measuring and characterizing compressive strength, porosity, reaction heat release, geopolymerization products and carbon dioxide equivalent (CO 2 -e) emission. The experimental results indicate that NS0 has the most rapid and effective activated effect in both single GGBS and GGBS-FASB composites. The strength of geopolymer activated with NS0 is the highest, followed by that with NS9, and followed by that with NS5. The products are mainly gelatinous phases, and the gels in NS0 and NS9 activated geopolymers are better geopolymerized than those in NS5 activated geopolymer, which is proved to be responsible for the difference in macro-performance. The evaluations of the cost and CO 2 -e emission per MPa of one-part geopolymer demonstrate that NS0 and NS9 are much cheaper and cleaner than NS5 for preparing one-part geopolymer. The embodied CO 2 indexes of NS0 and NS9 activated single GGBS are only about 26.5% and 34.0% of that of ordinary Portland cement. This study not only partially explains the reasons for the different properties of one-part geopolymer activated by different types of sodium metasilicate, but also provides a guidance for preparing one-part geopolymer with reasonable cost and slight environmental impact. Highlights • Properties of one-part geopolymer activated by three Na 2 SiO 3 ·nH 2 O powders were studied. • Influence of the type of Na 2 SiO 3 ·nH 2 O on hydration products and microstructure was analyzed. • Advantages of one-part geopolymer in environmental impact and economic efficiency were confirmed. [ABSTRACT FROM AUTHOR]

Hierarchically flowerlike Ag microstructure with uniform silver nanosheets as building blocks has been facilely prepared on a composite film surface via in situ reduction of Ag by a polyaniline component. The morphology of the as-prepared Ag microstructure is determined by the reaction duration, not the concentration of Ag in the reaction process. The complex geometry, rough surface, and interlaced nanosheets of the hierarchical Ag microstructure create interstitial sites and thus result in enhanced Raman signals. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) prepared by using magnesium chloride and light calcined magnesia has been widely used as decorative materials, refractory materials and adsorbing materials. But its poor water resistance restricts the application in construction and building. More importantly, the disposition of abundant waste gypsums is becoming a social issue, even a political issue in China. This study employs flue gas desulfurization gypsum (FGDG) and phosphogypsum (PG) to modify MOC, aiming to reduce the environmental hazards and production costs and improve the MOC properties. Effects of high content of FGDG and PG on the MOC properties and the mechanisms were systematically studied by a series of test and characterization experiments. The results demonstrated that the presence of FGDG and PG prolongs the setting time to some extent, and decreases the compressive strength to varying degrees. Compressive strength for FGDG-incorporated and PG-incorporated mixtures varies from 73 MPa to 62 MPa and from 73 MPa to 55 MPa, respectively, at curing age of 60 days. And the water resistance and volume stability of MOC are improved gradually with increasing the FGDG and PG contents. After adding FGDG and PG, no new hydration products were detected, while the formation of 5MgO ⋅ MgCl 2 ⋅ 8H 2 O was reduced. However, the presence of FGDG and PG slightly increased the large harmful pores among the air curing groups and decreased the total porosity after water immersion. And, the microstructure analysis is in agreement with the results of comprehensive strength and the 5 phase products can bond gypsum particles together to form a dense structure. Moreover, the generation amount expansive brucite decreases, which is beneficial to the volume stability. The superior compatibility between waste gypsums and MOC not only provides an efficient method to utilize FGDG and PG and solidify heavy metals contained in them, but also improves the durability of MOC and decreases the production cost which will inevitably promote the large-scale application of MOC in constructional engineering. The flue gas desulfurization gypsum (FGDG) and phosphogypsum (PG) are employed to modified magnesium oxychloride cement (MOC). High FGDG addition (the mass ratio of FGDG and light burnt magnesia is 1:1 in MF100) decreases the compressive strength by only about 10%, and that in MOC with high content of PG is nearly 25%. XRD and TG-DTG analysis reveal that the main hydration products including 5MgO ⋅ MgCl 2 ⋅ 8H 2 O (phase 5) and magnesium hydrate decrease significantly in pastes MF100 and MP100. Accordingly, the porosities of MF100 and MP100 are also much higher than MOC without waste gypsums. It is found that the decrease in compressive strength does not match the change in the amount of hydration products and porosity. More importantly, the water resistance and volume stability of MF100 and MP100 are much better. This indicates that high content of FGDG or PG can improve the durability significantly with a slight decrease in compressive strength. Physical functions including strong bonding effect and filling or skeleton effect can be responsible for these phenomena. [Display omitted] • Flue gas desulfurization gypsum (FGDG) and phosphogypsum (PG) were introduced into magnesium oxychloride cement (MOC). • Great improvement in durability of MOC with high content of FGDG or PG is confirmed with sacrificing very few strengths. • Mechanisms of FGDG or PG are mainly physical functions including strong bonding effect and filling or skeleton effect. [ABSTRACT FROM AUTHOR]

The AlNbTiZr medium-entropy alloy (MEA) coatings with different Al contents were prepared on N36 zirconium alloy substrates by RF magnetron co-sputtering. The morphology, microstructure, mechanical properties, surface wettability and corrosion resistance of the AlNbTiZr MEA coatings were studied to evaluate the surface protection behavior of zirconium alloy cladding under operation conditions of a pressurized water reactor. The results showed that all the coatings were composite structures with amorphous and bcc-structured nanocrystals. With the increase of Al content, both the elastic modulus and hardness decreased first and then increased. The hydrophobicity of the coatings was enhanced compared with that of the substrate. The 10.2 at.% Al AlNbTiZr coating had the best corrosion resistance and the minimum oxygen penetration depth, which originated from the formation of a denser oxide layer consisting of Nb2Zr6O17 and ZrO2. This study provides an improved idea for the design and development of Al-containing MEA coating materials for accident tolerant fuel. [ABSTRACT FROM AUTHOR]

The introduction of metakaolin into magnesium phosphate cement (MPC) can improve the compressive strength, volume stability, water resistance and freeze-thaw resistance significantly. Two possible reasons were proposed in this study. Firstly, metakaolin decreases the total porosity of MPC and improves the pore structure which is directly related to the mechanical properties. Secondly, part of metakaolin can dissolve in MPC and take part in hydration, even though no new hydration products can be observed in XRD patterns. This study not only gives a compressive evaluation on the application of metakaolin in magnesium phosphate cement, but also explains the possible reason for the improvement of the properties of magnesium phosphate cement. • Strength and durability of MPC incorporating metakaolin were systematically studied. • Possible mechanism of metakaolin influencing MPC was proposed by multi-analysis. • The more homogeneous microstructure in metakaolin modified MPC can explain the property improvement. Metakaolin has been generally used as a filler in Portland cement-based materials, and it was proved to be able to enhance the performance of magnesium phosphate cement composites. In this research, metakaolin was introduced into MPC, and compressive strength, tensile bonding strength, porosity and durability of MPC were measured. The microstructure of MPC before and after water immersion was evaluated. The experimental results indicate that the presence of metakaolin can lead to higher plastic viscosity of fresh MPC mortar, 28-day compressive strength, higher tensile bonding strength, better freeze-thaw resistance, better water resistance, lower drying shrinkage and better optimized microstructure. Physical effects of metakaolin including filling effect and inducing effect play the leading role in MPC. Metakaolin particles can fill in the pores or cracks, resulting in the decrease in porosity. In addition, metakaolin particles can provide lots of sites for crystallization of hydration products, inducing in the generation of more homogeneous microstructure. Finally, the dissolution and chemical reaction of metakaolin particles were confirmed by BSE analysis. [ABSTRACT FROM AUTHOR]

Highlights • The surface permeability of steam-cured concrete is higher than that of standard-cured concrete. • The subsequent curing condition has great influence on the surface permeability of concrete. • The subsequent water-soaking and elevated temperature curing decrease the performance of concrete. Abstract Steam curing is commonly used to produce the prefabricated elements to meet the requirement of the high early strength. However, this curing regime was proved to lead to the thermal damage on the microstructure and properties of concrete. And the subsequent curing after initial steam curing is critical to the development of performances of steam-cured concrete. In this study, four typical subsequent curing conditions simulating the extreme service environments were employed on the curing of steam-cured concrete. And the surface permeability indexes involving water and air permeations and compressive strength were measured to analyze the effects of subsequent curing condition on performance of steam-cured concrete. The results indicate that the surface permeability and strength development of steam-cured concrete are remarkably influenced by the subsequent curing condition. The subsequent curing such as long-term water-soaking curing at 20 °C or oven-dry curing at 60 °C deteriorates the performances of steam-cured concrete. Their surface permeability indexes are 75.1% and 88.0% higher than that of standard-cured concrete at 90 days, respectively. The continuous dissolution of calcium hydroxide is considered the main reason for deterioration of impermeability and strength of steam-cured concrete. [ABSTRACT FROM AUTHOR]

Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products. [ABSTRACT FROM AUTHOR]

• Small amount of CPCM can accelerate the early hydration of steam-cured cement paste. • Both paraffin and carriers in CPCMs jointly promote the hydration of cement. • The combination of two carriers promotes cement hydration better than single carrier. • The phase compositions of steam-cured cement paste are almost not affected. The application of phase change materials (PCMs) in building materials has attracted more and more attention. However, there is little information on the interactions between PCMs and cementitious material during hydration process. This study investigates the influence of PCMs on cement hydration behavior under steam curing condition. Three kinds of composite phase change material (CPCM) are synthesized, denoted by D/P, EG/P and D/EG/P, respectively. The thermal stability and crystalline phase of PCMs are characterized. The effects of above PCMs on hydration process of cement are evaluated by several testing methods, including isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Results indicate that CPCMs exhibit good thermal stability compared with single paraffin when the operating range is less than 200 °C. The time to reach the heat release rate peak of binders containing paraffin, D/P, EG/P and D/EG/P is 20 min, 20 min, 20 min and 30 min earlier than the cement pastes without PCM at 60 °C isothermal condition, respectively. The addition of a small amount of CPCM can accelerate the early hydration of steam-cured cement paste due to the combined action of paraffin and carriers with high surface area that can provide nucleation sites. Moreover, the combination of two carriers promotes cement hydration better than the single carrier. However, the number of hydration products and phase compositions of steam-cured cement paste are almost not affected by the addition of CPCM. [ABSTRACT FROM AUTHOR]

• Water curing causes the higher crystallinity degree of products and coarser microstructure in one-part geopolymer. • Composite activator including sodium carbonate can improve the water resistance of one-part geopolymer. • The difference in early-term hydration products and pore distribution of one-part geopolymer explain the mechanisms. The commonly used curing regime in one-part AAFSS is air curing or sealed standard curing. In this research, one-part alkali-activated fly ash sinking beads and slag (AAFSS) was prepared by using composite activators. The difference between standard curing and water curing was investigated, and the influencing mechanism of water curing was also studied. Experimental results indicate that the strength after 28 days of water curing stops increasing, and even decreases to some extent. The use of ultra-fine fly ash sinking beads (FASB) and Na 2 CO 3 can ameliorate the water resistance index defined as the ratio of compressive strength of specimens after the same days of standard curing and water curing. And the acid resistance of water-curing AAFSS is poorer than that of standard-curing AAFSS. The mechanical properties and durability of one-part AAFSS after water curing are affected by ions leaching and destruction of microstructure. XRD and TG-DTG analysis reveal that 28 days of water curing does not change the types of hydration products, but decreases the number of gelatinous products and calcite. An interesting finding is that the intensity of diffraction peaks of gelatinous products of specimens under water curing is higher than that under standard curing. Water curing makes the microstructure much coarser, and large microfracture could be found in SEM images. The use of FASB and Na 2 CO 3 can improve the microstructure of one-part AAFSS after water curing. [ABSTRACT FROM AUTHOR]

• Small amount of CPCM slightly reduces 28-day flexural and compressive strength of steam-cured mortar. • The presence of small amount of CPCM greatly improves the water absorption resistance of steam-cured mortar. • D/P is considered as optimum CPCM used in steam-cured mortar. Steam curing is a common method used in the production of precast concrete components. However, the formation of microcracks and large pores during steam curing process are very detrimental to the long-term performance of cement-based materials. The use of phase change materials may be a potential method for improving disadvantages caused by steam curing. Phase change composites are prepared by implanting paraffin into diatomite, expanded graphite, and mixture of diatomite and expanded graphite. They are represented by D/P, EG/P and D/EG/P in turn. The thermal properties and static water contact angle of phase change composite (CPCM) are tested. The mechanical and water absorption properties of steam-cured mortars with CPCM are investigated. Results indicate that the latent heat values of EG/P, D/P and D/EG/P are 80%, 30% and 36% of the values for pure paraffin, respectively. The CPCMs exhibit hydrophobic properties due to the roughness of solid surface. The presence of CPCM greatly improve the water resistance of steam-cured mortar without sacrificing mechanical properties, and steam-cured mortar with 1 vol% D/P has the best performance. The possible reason is that D/P reduces the porosity and improves porous microstructure of steam-cured mortar. The cracks and holes in the mortar matrix can be covered and filled with paraffin from D/P by SEM analysis. There is no interfacial gap between D/P and the mortar matrix through SEM analysis, which promotes the formation of a dense and strong mortar matrix. Therefore, the addition of an appropriate CPCM is helpful to improve the durability of the steam-cured cementitious materials. [ABSTRACT FROM AUTHOR]

• Metakaolin improves the mechanical properties and durability of MPC. • Metakaolin decreases the early-term hydration heat of MPC and the total porosity. • Mechanisms of metakaolin in MPC include providing nucleation cites, filling effect and pozzolanic effect. Different particle sizes of metakaolin were employed to replace magnesia partially, and it goes MK1, MK2 and MK3 in order of the specific surface area. Experimental results indicate that the presence of metakaolin indeed improves the compressive strength, tensile bonding strength and water resistance of MPC mortar through sacrificing the workability to some extent, and 30% MK2 blended MPC mortar has the best performances except fluidity. Metakaolin decreases the porosity and improves the pore structure of MPC mortar, especially for specimens after water immersion. The dissolution and reaction of metakaolin in MPC are confirmed by BSE analysis. Nevertheless, no new hydration products can be detected in MPC paste with metakaolin through XRD and TG-DTG analysis. The condensation of intermediate products, crystallization and crystal growth occurring on the surface of metakaolin promote the formation of the more compacted and homogeneous microstructure, which is the physical mechanism of metakaolin improving the properties of MPC. [ABSTRACT FROM AUTHOR]