Latest ArticlesImmersion solutions at different salt ratios and concentrations were prepared based on the seawater salt composition in Shenzhen ports, China. The effect of immersion solution on the deterioration of the mortar and the chloride diffusion coefficient were investigated. The results show that the influence of sulfate ions on the diffusion of chloride ions is related to the salt concentration in multi-ion solutions. The diffusion of chloride ions is inhibited by high-concentrated sulfate and magnesium ions in the early stage and promoted in the later stage. This phenomenon is not consistent with the effect of multi-ion interactions in the marine environment. The low concentration of sulfate and magnesium ions in seawater does not inhibit and even slightly promote the diffusion of chloride ions in the mortar.
The influence of adding crystalline silica and silica fume on the mineral composition and physical-mechanical properties of the set-cement was investigated. The results show that optimizing the particle size distribution of cement dry blend can improve the 7-d compressive strength. Increasing the total silica addition can enhance the 30-d compressive strength. At 30-d curing, two optimized systems have an average compressive strength of greater than 40 MPa and a water permeability of lower than 2×10-6 μm2. The physical, mechanical, mineral and microstructual property evolution of the two systems within 30 d were analyzed. It is indicated that there are little changes in the mineral compositions and their crystallinity during 7-30 d. However, apparent microstructure coarsening occurs, leading to the decline in compressive strength and modulus of elasticity as well as the almost linear increase in water permeability of the set cement as a function of time.
A series of cationic sacrificial agents (CSA) were synthesized via free radical copolymerization of unsaturated quaternary ammonium salt monomer and unsaturated nonionic (anion) monomer. The effect of sacrificial agent on the dispersion of polycarboxylate superplasticizer in cement mixed with montmorillonite (MMT) was evaluated via the fluidity of cement paste. Also, the effects of monomer polymerization ratio, quaternary ammonium salt monomer type and nonionic (anionic) monomer type on the action effect of the sacrificial agent were investigated by organic carbon analysis, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Trimethyl allyl ammonium bromide-acrylamide (ATMA-AM 2∶1) was determined as an optimum structure, and its action mechanism was also analyzed. The fluidity of PCE in cement paste mixed with MMT increases from 156 mm to 225 mm at 1.0% of ATMA-AM (2∶1). The adsorption capacity of PCE on MMT and the holes on the surface of MMT all reduce, thus effectively preventing the polyether side chain of PCE molecule from entering the interlayer of MMT and enhancing MMT effect on the dispersion property of PCE.
The hardened cement mortar samples with different water-cement ratios were prepared and subjected to salt freezing experiment (CDF freeze-thaw). The microscopic images and three-dimensional pore structure of hardened cement mortar with different freeze-thaw cycles were investigated by X-ray tomography. The evolution process and mechanism of meso-structure in freezing-thawing cycle were analyzed. The variation law of pore parameters of hardened cement mortar under the action of CDF freeze-thaw cycle and the influence of water-cement ratio on the freeze-resistance of mortar sample were investigated. The results show that the freezing-thawing microcracks develop along the porous interface between cement aggregate and fine aggregate, and the reduction of water-cement ratio can reduce the interfacial porosity, thus improving the frost resistance of cement-based materials. The cement mortar with a water-cement ratio of 0.30 has a stronger frost resistance. The freeze-thaw damage evolution and crushing process of cement mortar can be characterized by fractal dimension curve.
Improving the dispersion of polycarboxylate superplasticizer (PCE) in cementitious materials containing clays has attracted recent research attentions. Using novel technologies to investigate the interaction between PCE and clay has made a significant breakthrough in recent years. A variety of approaches to improve the dispersibility of PCE in clay-containing cement paste were also emerged. This review summarized recent work on the improvement of clay tolerance of PCE, including the interaction mechanism between PCE and montmorillonite, the preparation of clay-tolerance PCEs, and clay-tolerance sacrificial agents. In addition, the future research direction in this aspect was also discussed.
Ultra-long MnOOH nanowire was prepared by a simple hydrothermal process using KMnO4 and ammonium acetate without additional template agents. MnOOH sample was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, amperometry, constant current charge/discharge characterization and electrochemical impedance spectroscopy. The results show that the length of MnOOH nanowires is more than 10 μm, and the diameter is approximately 20 nm. The specific capacitance is 285 F/g at current density of 1 A/g in 1.0 mol/L Na2SO4 electrolyte, and it can still keep a good cycling stability after 4 000 cycles. The post-capacitance retention rate reaches 96.2%. The MnOOH nanowire as an electrode material has an excellent electron transmission channel, exhibiting a superior ultracapacitor performance, which can have broad application prospects as an electrode material for supercapacitors.
A nanoporous carbon material was prepared via high-temperature heat treatment with lignite as raw material and KOH as an activating agent in inertia atmosphere. The results show that nanoporous carbon has massive mesopores and micropores with an average pore size of 2 nm, and the specific surface area can reach 3 135 m2/g. The specific capacitance of the symmetrical capacitor assembled with nanoporous carbon as an electrode is up to 267 F/g. A significant capacity retention of 95% is obtained after 1 000 cycles. The electrosorption capacity of the salt ions can reach 18.9 mg/g with a good adsorption and desorption cycle performance.
A Li1.167Ni0.167Co0.167Mn0.5O2 cathode material was synthesized by a co-precipitation method, and then a composite material with a uniform AlPO4 coating on its particle surfaces was prepared by a pH-controlled chemical deposition process with Al(NO3)3·6H2O, K2HPO4 and hexamethylenetetramine as reagents and citric acid-sodium citrate as a buffer solution. The effect of AlPO4 coating amount on the electrochemical performance of Li1.167Ni0.167Co0.167Mn0.5O2 cathode materials was investigated. The results show that 1% (in mass fraction) AlPO4 coated material exhibits a high initial discharge capacity (i.e., 265.9 mA·h/g at 0.1 C) and an excellent capacity retention (i.e., 88% retention rate after 150 cycles at 0.5 C). The superior electrochemical performance can be attributed to the AlPO4 coating preventing a direct contact between the electrolyte and the electrode material, accelerating the lithium ion diffusion and reducing the electrochemical resistance. As a result, Li+ diffusion rate increases from 3.17×10-15 cm2/s to 9.07×10-15 cm2/s, and the electrochemical impedance value decreases from 152.92 Ω to 62.27 Ω.
Recent research work of solid-state thin film batteries mainly focus on the construction of electrode/electrolyte interfaces with a low impedance and the development of solid electrolytes with a high ionic conductivity. In this review, the structure design and ion transport mechanism of solid-state thin film battery were introduced. The research progress of anode film, cathode film and solid electrolyte film were represented. In addition, some problems of electrode/electrolyte interfaces and their improvement strategies were also summarized.
This review summarized recent studies on the structures and thermal behavior of tobermorite, especially the different structures and thermal behaviors of several polymorphs of tobermorite. Also, the influences of raw materials and synthetic condition on the formation of tobermorite polymorphs were represented, and the corresponding mechanism was analyzed. In addition, some future work on tobermorite was also given.
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