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Polystyrene foamed plastic wastes are a kind of environmental pollutant. It could be recycled in cement industry as a chemical agent. In this paper, the effects of sodium polystyrene sulfonate (SPS) on the hydration and microstructure of blended cement were investigated by calorimetry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). SPS slightly delayed the hydration of alite and decreased its hydration degree. SPS did not change the phase compositions during hydration. SPS changed the morphology of ettringite (AFt) and decreased the pore volumes and the sizes of pores.

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]

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]

An expansive high early strength alite–ye’elimite clinker containing 4.8% ye’elimite was synthesised by annealing without addition of mineralizer into the raw meal. The reformation of ye’elimite was achieved by C 3 A reacting with C$ in clinker. The microstructure of the paste was characterised by SEM, MIP and N 2 adsorption/desorption. DSC-TG and XRD were used to investigate the hydration products of the paste. Mortar tests on the clinker yielded values of 30.0 MPa, 42.3 MPa and 55.8 MPa at 1, 3 and 28 days, respectively. Due to the presence of AFt in the hydrated paste, the expansive behaviour resulted in a reduction in the total pore volume by 29–62% (0.01–10 μm), but there were more mesopores (2–50 nm) due to the crystalisation of AFt. The linear expansion converged after ∼150 days with maximum expansion of 0.136%. [ABSTRACT FROM AUTHOR]

Abstract: Resorcinol–formaldehyde/silica composite (RF/SiO2) aerogel was synthesized by sol–gel process followed by supercritical drying (SCD). Monolithic SiC aerogel was obtained from RF/SiO2 aerogel after carbothermal reduction. The evolution of physical property, crystal structure, morphology and pore structure from RF/SiO2 to SiC aerogel was investigated by different methods, such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption/desorption. The as-synthesized SiC aerogel presented typical mesoporous structure and possessed high porosity (91.8%), high surface area (328m2/g) and large pore volume (2.28cm3/g). Carbothermal reduction mechanism was also discussed based on the experiment and characterization results. [Copyright &y& Elsevier]

Abstract: This paper presents a systemic study on the effect of α-calcium sulfate hemihydrate (α-hemihydrate) particle characteristics on the performance of calcium sulfate-based materials (CSBM) that widely used in the medical field. The hydration performance and water requirement for normal consistency of α-hemihydrate were investigated. The mechanical strength, microstructure, and pore structure of the hardened CSBM were also examined. The performance of CSBM was greatly affected by the α-hemihydrate crystal properties. α-Hemihydrate crystals with good gradation and a length/diameter ratio of 1–3:1 tended to have perfect fluidity, lower water requirement for normal consistency, and low crystallization velocity. Moreover, in the hardened CSBM hydrated from such α-hemihydrate crystals, the crystal size of the dehydrate was large, and the crystals were interconnected. The strength of the hardened CSBM was sufficient because of low porosity, small pore diameter, and dihydrate crystals firmly in contact. This study serves as a foundation for preparing high performance for CSBM medical applications. [Copyright &y& Elsevier]

(La0.67Mg0.33)1− x Ti x Ni2.75Co0.25 ( x = 0, 0.05, 0.10, 0.15 and 0.20, at%) alloys were synthesized by arc melting and subsequent heat solid-liquid diffusing method. The structure, electrochemical properties and kinetic characteristics of the alloys were investigated systematically. The results showed that all the alloys mainly consisted of the (La, Mg)Ni3, LaNi5 phases, and the lattice parameters and the cell volumes of the (La, Mg)Ni3 and LaNi5 phases decreased with increasing Ti content. The alloy electrodes could be activated to reach their maximum discharge capacity within five cycles. The cycle life after 100 charge/discharge cycles ( C 100/ C max) and the high-rate dischargeability at a discharge current density of 1200 mA/g first increased and then decreased. All the results showed that low-Ti content in AB3-type hydrogen storage alloys was beneficial to improvements of the overall electrochemical properties, and the optimum overall electrochemical performance of the alloy electrodes was obtained when x = 0.05. [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]

• THEED can be used as accelerator agent to shorten the Portland cement. • THEED has the advantages of TEA and TIPA, increasing the early compressive strength and late compressive strength. • THEED can promote the transformation of AFt into AFm, and change the morphology of AFt and C-S-H. N,N,N',N'-Tetrakis-(2-hydroxyethyl)ethylenediamine (C 10 H 24 N 2 O 4 ,THEED) is a different type of alkanolamine. In this work, the physical and chemical effects of small amounts of THEED added to Portland cement were investigated. THEED can be used as an accelerator for the setting of Portland cement. The compressive strengths of standard test mortars moist-cured for 1, 3, 28 and 90 days were enhanced in some cases by the addition of THEED. THEED promoted conversion of ettringite (AFt) to monosulfoaluminate (AFm). THEED had notable effects on the morphology of AFt and C-S-H at the early age, especially on the growth direction of portlandite(Ca(OH) 2) crystals. [ABSTRACT FROM AUTHOR]

• Silica aerogel (SA) with high specific surface area (903 m2/g) and pore volume (6.81 cm3/g). • SA is thermally stabile at 1000 °C within 120 min. • SA is thermally stabile at 1200 °C within 30 min. • The research provides new insights into the resistance of silica aerogels to high temperature. Silica aerogel (SA) with high specific surface area (903 m2/g) and pore volume (6.81 cm3/g) was synthesized via base-catalyzed one-step sol–gel process. Thermal stability of SA under high temperature was estimated from structure evolution with temperature and time. The results demonstrate that the SA is thermally stabile at 1000 °C within 120 min (leaving specific surface area of 286 m2/g and pore volume of 1.46 cm3/g) and 1200 °C within 30 min (leaving specific surface area of 129 m2/g and pore volume of 0.59 cm3/g). The research provides new insights into the resistance of silica aerogels to high temperature, which is significant for application under harsh conditions. [ABSTRACT FROM AUTHOR]

The high-polymeric degree or molecular-weight of self-made polyethoxydisiloxane (PEDS) was successfully used to synthesize aerogels with several advantageous mechanical characteristics, compared with those based on conventional tetraethylorthosilicate (TEOS) aerogel preparation methods. The first advantage is their lower initial values of bulk modulus ( K 0 ), compared with those prepared via the two - step method; this is due to release of internal stress during the shrinkage of wet gel. Secondly, a collapse index n of −0.125 is obtained by the collapse law; this implies a new buckling destruction model. This is different from those prepared via the two - step method, and suggests that a hierarchical filament structure, formed by the connection of nano-particles, constitutes the solid skeleton of pores. In this paper, average aerogel pore sizes between 16.0 and 39.3 nm are analyzed by the combination of Mercury Intrusion Porosimetry (MIP) and Nitrogen Adsorption–Desorption (NAD). The microstructure and morphology of the aerogels are demonstrated by Transmission Electron Microscopy (TEM) and Field Emission Scan Electron Microscopy (FE-SEM). [ABSTRACT FROM AUTHOR]

Highlights • Hydration behaviors of the CSP-OPC binary system are investigated comprehensively. • CSP can retard the conversion of AFt to AFm. • CSP can optimize the pore structure of the hardened cement paste at long term curing period. • CSP with 5% can contribute to the early compressive strength of cement mortar. Abstract This study presents the influence of coral sand powder (CSP) on the hydration and mechanical behaviours of Portland cement paste at the curing ages from 1 day to 90 days. The early hydration kinetics of Portland cement incorporated with CSP is studied by isothermal calorimetry test. The hydrates and pore structures of cement paste are determined by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP), respectively. Experimental results show that CSP can promote acceleration period to end in advance. XRD results imply that CSP can react with tricalcium aluminate (C 3 A) to form monocarbonate (Mc) and hemicarbonate (Hc), which can suppress the conversion of Al-phase products, viz. from AFt to AFm. From the MIP results, the addition of CSP can refine the pore structure of Portland cement paste at long-term curing age, although negative effect of CSP on the total porosity can be observed. Low replacement level of CSP (5 wt%) improves the compressive strength of cement mortar at ages from 1 day to 7 days. However, from 28 days to 90 days, the addition of CSP decreases the strength of cement mortar regardless of replacement levels. [ABSTRACT FROM AUTHOR]

To develop a high emissivity, high-temperature-resistant coating for a reusable thermal protection system, a metal silicide–glass hybrid coating was prepared on fibrous ZrO 2 ceramic by rapid sintering method, which comprises a Ta Si O glass layer and a dense MoSi 2 –TaSi 2 –glass layer and exhibits improved oxidation behavior at 1773 K in air for 50 h. During oxidation, the total emissivity in 0.3–2.5 μm slightly fluctuates around 0.9 without obvious degradation. The emissive mechanism was identified as electron transition in interband of metal silicides and in impurity states of amorphous SiO 2 and lattice vibration of crystalline SiO 2 . [ABSTRACT FROM AUTHOR]

The service life and durability of concrete structures strongly depend on the transport properties of the concrete. These transport properties are highly related to their microstructure, especially the pore structure of the hydrated cement paste. In this paper the microstructure development of cement paste and cement paste blended with fly ash is investigated, from solid phase to pore phase, at a long-term curing period up to 3 years. The solid phases are observed by environmental scanning electron microscope. The pore structure of blended cement paste is determined by mercury intrusion porosimetry. The results indicate that the addition of fly ash increases the total porosity of cement paste, not only at early ages, even at curing age of 3 years. The voids in hollow fly ash particles act as ink-bottle pores with progress of the pozzolanic reaction of fly ash, resulting in the increase of the total porosity of blended cement paste. [ABSTRACT FROM AUTHOR]

Diethanol-isopropanolamine (DEIPA) is a tertiary alkanolamine used in the formulation of cement grinding-aid additives and concrete early-strength agents. In this research, isothermal calorimetry was used to study the hydration kinetics of Portland cement with DEIPA. A combination of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC)–thermogravimetric (TG) analysis and micro-Raman spectroscopy was used to investigate the phase development in the process of hydration. Mercury intrusion porosimetry was used to study the pore size distribution and porosity. The results indicate that DEIPA promotes the formation of ettringite (AFt) and enhances the second hydration rate of the aluminate and ferrite phases, the transformation of AFt into monosulfoaluminate (AFm) and the formation of microcrystalline portlandite (CH) at early stages. At later stages, DEIPA accelerates the hydration of alite and reduces the pore size and porosity. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and electrochemical hydrogen storage characteristics of La0.7Mg0.3−x Ca x Ni2.8Co0.5 (x =0, 0.05 and 0.10) alloys prepared by arc-melting and subsequent powder sintering method are investigated. The electrochemical measurement results show that the cycle stability after 100 charge/discharge cycles first increases from 46.4% (x =0) to 54.3% (x =0.05), then decreases to 43.2% (x =0.10), and the high rate dischargeability increases from 64.5% (x =0) to 68.5% (x =0.10) at the discharge current density of 1200mA/g. The electrochemical impedance spectroscopy analysis indicates that the electrochemical kinetics of the alloy electrodes is improved by increasing Ca. The entire results exhibit that a suitable content of Ca (x =0.05) can improve the overall electrochemical hydrogen storage characteristics of the alloys. [Copyright &y& Elsevier]

Abstract: The microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33−x Ca x Ni2.75Co0.25 (x = 0, 0.05, 0.10 and 0.15) alloys are investigated. The results show that all alloys mainly consist of (La, Mg)Ni3 and LaNi5 phases, besides a small amount of (La, Mg)2Ni7 phase. The cycle stability (S 80) after 80 charge/discharge cycles of all alloy electrodes first increases from 60.1% (x = 0) to 64.2% (x = 0.05), then decreases to 45.9% (x = 0.15). The high rate dischargeability of all alloy electrodes first increases from 52.6% (x = 0) to 61.4% (x = 0.10), then decreases to 57.2% (x = 0.15). Moreover, the charge-transfer resistance (R ct) first decreases from 168.2 mΩ (x = 0) to 125.7 mΩ (x = 0.10), then increases to 136.6 mΩ (x = 0.15). All the results indicate that the substitution of Mg with a certain amount of Ca can improve the overall electrochemical characteristics. [Copyright &y& Elsevier]

Abstract: Surface treatment by the fluorination treatment with an aqueous solution of KF and HF with a little addition of KBH4 followed by electroless Ni–P plating has been carried out to modify the surface structure and electrochemical properties of the La–Ni–Al hydrogen storage alloy. The results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) show that a Ni-rich and Al-poor layer forms after fluorination treatment. The electroless plating results in the precipitation of the nanometer-scale Ni–P particles with homogeneous distribution on the alloy surface. Both the treatments contribute to an increase in exchange current density, a decrease in charge-transfer resistance and the facility of hydrogen diffusion within the bulk alloy, leading to significant improvements on high rate dischargeability (HRD) of the alloy. The alloy treated by the composite treatment of the fluorination treatment and the following electroless plating possesses best overall electrode performance. [Copyright &y& Elsevier]

• Ye'elimite affected the early hydration but did not affect greatly on the later hydration kinetics. • The minor ye'elimite reacted rapidly within the first 1.5 h to form a large amount of ettringite. • The precipitation of ettringite from the hydration of ye'elimite resulted in a reduction of the microporosity. This paper presents the hydration kinetics, products and microstructure of an alite-ye'elimite clinker containing 4 wt% of ye'elimite to boost the early strength development. Isothermal calorimetry, X-ray diffraction, backscattered scanning electron microscopy and mercury intrusion porosimetry were used to study the hydration processes. The results showed that the ye'elimite phase hydrated very rapidly, before the main hydration of alite, forming ettringite as main hydration product. The ye'elimite hydration products precipitated throughout the pore space and reduced the microporosity of the hardened paste at early age. The presence of ye'elimite strongly affected the early hydration before 24 h of hydration, but did not show a significant effect on the hydration kinetics or products at later ages. [ABSTRACT FROM AUTHOR]

• Hydration and mechanical properties of CSP-CSA system are studied up to 90 days. • CSP can promote the formation of AFt and inhibit the formation of AFm. • The conversion from Hc to Mc does not happen in CSP-CSA binary system. • CSP can accelerate the carbonation of AFt. • CSP can optimize the pore structure of the hardened cement paste in the long term. Recently, the studies on the application of coral reef debris to construction attracted wide attention and interest of researchers, especially in China. Coral reef debris and its powder can be used as fine aggregate and mineral admixture in concrete, respectively. The main component of coral reef debris is calcium carbonate (CaCO 3), up to 90%. In our previous research, the effects of coral sand powder on the hydration behavior and mechanical properties of Portland cement are well investigated. It is well known that calcium sulfoaluminate cement, with low production energy, reduced CO 2 emissions, fast bonding and rapid strength development, etc. has been used for decades in concrete. This paper will give a detailed fundamental research on the hydration kinetics, microstructure development and mechanical properties of the coral sand powder-calcium sulfoaluminate cement binary system up to 90 days of curing. Isothermal calorimetry test, X-ray diffraction analysis, thermogravimetric analysis, mercury intrusion porosimetry and compressive strength tests are used to evaluate the properties of the calcium sulfoaluminate cement incorporated with different contents of coral sand powder (5%, 15% and 25%). The obtained results show that coral sand powder reacts with ye'elimite to generate hemicarboaluminate. Coral sand powder optimizes the pore structure of calcium sulfoaluminate cement at long time curing. [ABSTRACT FROM AUTHOR]

The corrosion behavior and discharge characteristics of Al-0.5Mg-0.1Sn-0.05Ga (wt.%) alloys with different grain sizes in 4 M NaOH solution were investigated by collecting hydrogen, electrochemical measurement, discharge test, and microstructure analysis. The results reveal that the coarse-grained microstructure has a lower corrosion rate than the fine-grained one. As the annealing temperature increases, the grain size becomes larger, and more Sn-rich phases are solid-dissolved into the matrix, which results in less hydrogen evolution corrosion. The coarse-grained sample (6532 μm) produced by the directional solidification technique in combination with the rolling process and subsequent annealing at 600 °C has outstanding discharge performance. Its peak energy density reaches approximately 3743.9 Wh·kg−1 (at 40 mA cm−2), which exceeds the reported Al–Mg–Sn–In/Bi, Al–Mg-Ga-Sn-In, Al–Zn–In, Al–Bi–Pb-Ga, and Al–Sn/In/Ga anodes. Also, the anode efficiency and peak energy density of the sample at 40 mA cm−2 is 23.4% and 33.2% higher than that of the as-cast ones, respectively. • Discharge properties of Al–Mg–Sn-Ga anodes were investigated. • Self-corrosion rate (SCR) = 7.9d −1/2 + 0.08 (d is the average grain size). • Peak energy density of the anode reaches about 3743.9 Wh·kg−1 (at 40 mA cm−2). [ABSTRACT FROM AUTHOR]

• TiO 2 @SiO 2 nanoparticles can better improve compressive strength of cement than nano-TiO 2 did. • Nano-TiO 2 particles formed microscale agglomerates in the hardened cement matrix. • TiO 2 @SiO 2 can limit the agglomeration of TiO 2 nanoparticles in cement matrix. • TiO 2 @SiO 2 nanoparticles resulted in a considerable improvement in the microstructure of cement matrix. This paper presented the contribution of core/shell TiO 2 @SiO 2 nanoparticles to the hydration properties of Portland cement and the contribution was compared with that of nano-TiO 2. Both nanoparticles were used to partially replace cement at 1 wt%. The mechanical property and microstructure of the cement pastes were experimentally characterized using compressive strength and scanning electron microscope (SEM), respectively. Specially, thermodynamic modeling was also applied to predict the phase assemblages and calculate the corresponding volumes. The results showed that the paste with 1 wt% TiO 2 @SiO 2 developed a much higher compressive strength than the paste with or without nano-TiO 2 added at each curing age. Both SEM and mapping analyses showed that obvious agglomeration of nano-TiO 2 could be observed in nano-TiO 2 modified cement paste, which decreased its efficiency in the cement paste. However, nano-TiO 2 was well distributed when TiO 2 @SiO 2 was added because of its limiting effect on the agglomeration of nano-TiO 2 , further densifying the microstructure. The calculated hydrates volumes by thermodynamic modeling also indicated that TiO 2 @SiO 2 would result in producing most hydrates of all the pastes, thus contributing to a denser microstructure and a much higher compressive strength development. [ABSTRACT FROM AUTHOR]