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 (328 m2/g) and large pore volume (2.28 cm3/g). Carbothermal reduction mechanism was also discussed based on the experiment and characterization results.

The effect of the electronic structures of α′L-, β-, and γ-dicalcium silicate (α′L-, β- and γ-C2S, C = CaO, S = SiO2) on hydration reactivity have been investigated by first-principles calculations. Active O atoms with larger charge densities are found in α′L- and β-C2S, while they are absent in γ-C2S. The local density of states of valence band maximum in α′L- and β-C2S is highly localized around active O atoms, whereas that in γ-C2S is homogeneously dispersed. For the active O-2p orbital in α′L- and β-C2S, the highest orbital energy in the partial density of states is about 0.31 eV higher than that of the inactive O in γ-C2S. These differences make the active O atoms of α′L- and β-C2S more susceptible to electrophilic attack and result in higher hydration reactivity for α′L- and β-C2S.

•Borax was introduced as an activator to change the polymorph of belite from β to α'.•Hydration heat of activated HBSC was 382 J/g, while that of inactive HBSC was 311 J/g.•Fly ash in cement was increased from 5 % (β-C2S-C4A3$) to 12 % (α'-C2S-C4A3$).This study focuses on the activation of belite to promote the addition of solid industrial waste, such as fly ash (FA), as the supplementary component in high belite–sulfoaluminate cement (HBSC). The results indicate that the polymorph of belite, which transforms from β to α′, principally depends on the concentration of sodium tetraborate. The incorporation of FA into inactivated HBSC is very slow because the inactivated belite is unable to participate in the early hydration process to release calcium hydroxide (CH) and break the glass structure of FA. Compared with the inactivated belite, considerable hydration heat is released during the early hydration process in activated HBSC, in which a large amount of CH is present to promote the pozzolanic reaction of FA. In addition, (Na,Ca)8(Si,Al)12O24(SO4)2 is formed in the presence of sodium, which is a tectosilicate mineral with a bulk modulus that contributes to the compressive strength of the later period. The highest total content of FA in the activated HBSC, compared to inactive HBSC, improved from 5% to 12%. Thus, FA promotes the use of solid industrial waste and reduces the consumption of HBSC. Furthermore, the long term strength development with a large amount of FA can meet the requirements for engineering projects.

•Crystalline TiO2 aerogel (TA) was prepared by a one-step sol-gel process followed by supercritical ethanol drying.•TA presented excellent thermal stability in air.•TA possessed high surface area and large porosity.TiO2 aerogel (TA) was directly prepared by supercritical ethanol drying of TiO2 gel which was synthesized by a simple one-step sol–gel process. High temperature of the supercritical ethanol drying led to the decomposition of most of the organic groups in the TiO2 gel and formation of anatase TiO2. Thermogravimetric (TG) revealed that the resulting TA was anatase TiO2 with a small amount of organic groups. X-ray diffraction (XRD), scanning electron microscope (SEM) and N2 isothermal adsorption/desorption tests indicated that the crystalline structure (crystalline size and phase) and pore structure of TA were very stable after thermal treatment below 700 °C.

Resorcinol–formaldehyde/alumina composite (RF/Al2O3) gels were initially prepared by using sol–gel techniques, and then dried to aerogels with supercritical fluid CO2. After thermal treatment in argon atmosphere, RF/Al2O3 aerogels were successfully converted to monolithic carbon/alumina composite (C/Al2O3) aerogels. The samples were characterized by BET, SEM, TEM and XRD, and the compressive strengths were measured. The experimental results showed that the C/Al2O3 aerogels exhibited an interpenetrating framework with high mesoporosity. The as-synthesized C/Al2O3 aerogels consisted of spherical carbon particles and alumina (fibrous or columnar), which had high BET surface area (576–831 m2/g) and showed high compressive strength (5.4–9.1 MPa) and Young’s modulus (286.95–476.71 MPa). These novel C/Al2O3 aerogels could possibly be used as thermal isolates, catalysts and adsorbents.Graphical abstractHighlights► A simple route was used to synthesize the RF/Al2O3 aerogels (sol–gel, RT). ► High surface area of 831 m2/g was achieved after thermal treatment of 1400 °C/5 h. ► Sample exhibited high compressive strength and Young’s modulus (9.1 and 476.7 MPa). ► The C/Al2O3 aerogels had high-temperature resistance properties.

Electrochemical redox mechanism and cycling stability are two important points for the research of the anode of alkaline rechargeable Ni/Co batteries. Herein, we report an amorphous Co–B–H anode material, which shows a multistep reaction in the initial discharge and the reaction of Co/Co(OH)2 in the subsequent cycles instead of hydrogen storage. The severe capacity decay of the anode caused by the dissolution during cycling is substantially limited by a novel electrolyte additive of NaS2O3, which is also beneficial to achieving a long term store of Ni/Co batteries and thus markedly boost the application of the battery.

Alite-ye'elimite cement is an alternative cement that combines desirable characteristics of calcium sulfoaluminate cements and Portland cement in that it shows improved strength development at early age while retaining high portlandite contents. The key problem in the clinkering process is to produce the alite-ye'elimite phase assemblage so that both phases can co-exist. In this study, a new synthesis method is proposed to achieve the coexistence of alite and ye'elimite consisting of a secondary heat treatment step at 1250 °C after regular Portland clinker firing at 1450 °C. Quantitative X-ray powder diffraction and electron microscopy were used to analyze the phase composition of clinker before and after the secondary heat treatment. The results show that ye'elimite develops during secondary heat treatment of calcium sulphate enriched clinker by reaction of C3A and sulphate phases. Additional ferrite is formed as result of rejection of Fe originally in solid solution with C3A during ye'elimite formation.

Resorcinol–formaldehyde/silica composite (RF/SiO2) gels were synthesized in one pot using a facile process. RF/SiO2 aerogels were obtained after supercritical carbon dioxide fluid drying. Monolithic mesoporous silicon carbide (SiC aerogels) was prepared from RF/SiO2 aerogels after carbothermal reduction and calcination. The as-prepared SiC products exhibited monolithic mesoporous morphology and possessed a BET specific surface area of 251 m2/g and a pore volume of 0.965 cm3/g. X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrated that the resulting SiC aerogels were composed of α-SiC nanocrystals. The bulk density and skeleton density of SiC products is 0.288 g/cm3 and 3.12 g/cm3, respectively. The porosity of SiC products is 90.8%. The SiC aerogels were stable up to temperatures near 650 °C.Highlights► A facile sol–gel process of synthesizing RF/SiO2 aerogels was presented. ► Monolithic mesoporous silicon carbide with a surface area of 251 m2/g was formed. ► The as-synthesized mesoporous SiC is consist of α-SiC nanocrystals.

A novel graft copolymer solid electrolyte with a relatively high ionic conductivity, 10−3.9 S cm−1 at 30 °C and 10−3.1 S cm−1 at 80 °C, is prepared by free radical polymerization in this study. The polymer consists of methacrylate as the backbone and a mixture of hexadecal (C16)–methoxyl terminated oligo(ethylene oxide) at a certain ratio as side chains. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) analysis reveal that non-polar unit (C16) end-modification not only greatly increases the mobility of the ethylene oxide (EO) chains, but also suppresses their local crystallization behavior by interrupting the regular arrangement, therefore improving the conductivity of the obtained electrolyte.

The Ni/Co battery is a new electrochemical energy storage system for alkaline rechargeable batteries that has been attracting much attention due to its high energy density. This review presents the current R&D status of Co-based materials with a particular focus on Ni/Co batteries, including their underlying principles and the recent progress in Co-based materials (e.g., cobalt oxides and hydroxides, Co-based alloys, and some composites). It emphasizes the relationship of the composition, phase structure and electrochemical properties of Co-based materials that show promise in practical application due to their good electrode performance. The synthesis of novel Co-based materials in nanoscale and low dissolution of active materials into the alkaline solution during cycling are two essential factors favouring the application of this environmentally-friendly battery.

Li2CoTiO4 as a new titanate cathode material for Li-ion batteries was successfully synthesized by a sol–gel process. It had a cation disordered rock salt structure and showed an excellent cycle stability at room temperature. After coating with carbon, the Li2CoTiO4 possessed a high discharge capacity of 144.3 mAh g−1. The poor conductivity and lithium ion diffusion coefficient of pure Li2CoTiO4 are the main reasons for the limited electrochemical performance of the lithium batteries. The irreversible capacity loss during the first cycle was assigned to the irreversibility of the structural changes.

A crystalline Ti2Ni alloy was mechanically milled and subsequently annealed to form a non-equilibrium Ti2Ni alloy. This non-equilibrium structure could restrain the formation of irreversible metal hydride during charging. Consequently, we demonstrated that the alloy had a discharge capacity of 336 mAh g−1, which was much higher than those of other Ti2Ni alloys reported in the literature and also higher than that of the commercial LaNi5–based alloy. An electrochemical hydrogen absorption–desorption mechanism of the alloy during cycling is also presented.

Elemental substitution of part Ti by Zr has been carried out for Ti2Ni alloy to form Ti2−xZrxNi (x = 0, 0.2, 0.4) alloys. Mechanical milling and subsequent heat treatment have been used to prepare non-equilibrium Ti–Zr–Ni alloys. The effects of Zr addition on the structure and discharge properties of Ti2Ni alloy were investigated. The addition of Zr could enhance the discharge capacity of the non-equilibrium Ti2Ni alloy at electrolyte temperatures of 313 and 333 K. For instance, the non-equlibrium Ti1.6Zr0.4Ni alloy had a stable discharge capacity of about 210 mAh/g at 313 K. However, the protective surface layer formed during heat treatment was destroyed at a high electrolyte temperature of 333 K, and thus a severe capacity loss during cycling.Highlights► Successful synthesis of non-equilibrium A2B-type Ti–Zr–Ni alloys. ► Zr could effectively enhance the stable discharge capacity of the non-equilibrium alloy. ► We present the electrochemical hydrogen absorption/desorption mechanism of the alloys. ► The capacity loss could be attributed to the damage of surface layer and subsequent corrosion.

Resorcinol–formaldehyde/silica composite (RF/SiO2) gels were synthesized in one pot by simply mixing the monomers and dried under supercritical carbon dioxide to form RF/SiO2 aerogels. Carbon/silica composite (C/SiO2) and carbon/silicon carbide composite (C/SiC) aerogels were formed from the RF/SiO2 aerogels after carbonization and carbothermal reduction. The as-prepared C/SiC products exhibited a preserved monolithic morphology similar to the original templates and were composed of carbon particles and α-SiC nanocrystals. The C/SiC specimen possessed a BET surface area of 892 m2/g and a porosity of 94.8%, both of which were significantly higher than the BET surface area and porosity of C/SiO2 and RF/SiO2 aerogels. The resulting C/SiC monolith was stable up to temperatures near 550 °C, which is almost 150 °C higher than what C/SiO2 aerogels can tolerate.Highlights► A novel and simple route to synthesize RF/SiO2 aerogels was presented. ► The monolithic C/SiO2 and C/SiC aerogels were formed from RF/SiO2 aerogels after carbonization and carbothermal reduction. ► The as-synthesized C/SiC aerogels showed mesostructures with high surface area and high pore volume. ► The C/SiC products exhibited good anti-oxidation properties.

The design of experiments (DoE) was adjusted in cement clinker chemistry, with alite polymorphisms in the clinker taken into account. The additions of SO3, MgO, as well as two other factors, sintering temperature and time, were included to study clinker formation and alite polymorphisms. XRD quantitative analyses and thermal analysis (DSC–TG) were used to collect quantitative data from the samples and to investigate the clinkerization of the raw meal. The central composition design was used to design the experiments and the response surface methodology was used to evaluate the results. The addition of SO3 inhibited the formation of alite in the clinker, while MgO compensated for any negative effects caused by the SO3. A contour plot interpreted the combination effects of these four factors. The amount of C4AF was then increased with a likewise increasing SO3 content. MgO favored the formation of M3 type alites, while SO3 stabilized the M1. Alite modification, which is related to hydration properties, could be helpful for efficient use of high MgO content calcite in cement production.Highlights► Design of experiments (DoE) was adjusted in the cement clinker chemistry. ► Combination effects come from the interactions of SO3 with MgO and temperature, which can demonstrate in the contour plot. ► MgO favors the formation of M3 type alite while SO3 stabilizes M1. ► Temperature and sintering time have little effect on the crystal modifications of alite. ► The amount of C4AF is increased with likewise increasing SO3 content.

An amine-modified SiO2 aerogel (AMSA) was prepared using the sol–gel method and supercritical drying technology. CO2 adsorption tests were conducted under different conditions. High adsorption capacities were achieved in the presence of water vapor, with the highest CO2 adsorption capacity of 6.97 mmol/g-sorbent at 25 °C. A novel adsorption mechanism associated with the CO2 sorption process is proposed. The test results indicate that AMSA is a promising CO2 adsorbent.

Cu2O/Cu composite particles were synthesized by a novel and facile chemical reduction method without any template or surfactant. X-ray diffraction (XRD) results showed that the product mainly consisted of the Cu2O phase coexisting with a few Cu phases. Typical FE-SEM images indicated that the particles with an octahedral shape were Cu2O. In addition, the electrochemical performance of the Cu2O/Cu particles as the working electrode material in alkaline solution was systematically investigated. The particles showed a maximum discharge capacity of 222.9 mAh g−1 at a discharge current density of 60 mA g−1 and a high value of 109.1 mAh g−1 after 50 charge–discharge cycles. The results of cyclic voltammetry demonstrated that the reaction between Cu2O and Cu is the major electrochemical reaction during the charging and discharging process. The results of electrochemical impedance spectroscopy indicated that the formation of Cu2O on the surface of Cu particles significantly increased the contact resistance and the charge transfer resistance of the electrode during the discharging process.Highlights► A novel and simple chemical precipitation route was used to synthesize octahedral Cu2O particles. ► The electrochemical behavior of the Cu2O electrode in alkaline solution was investigated systematically.

The crystal structure and electrochemical properties of the La2MgMn0.3Ni8.7−x(Co0.5Al0.5)x (x = 0, 1.0, 2.0 and 3.0, at%) hydrogen storage alloys are investigated systematically. The results show that all the alloys consist of (La, Mg)Ni3 and LaNi5 phases, the cyclic stability S60 increases from 61.2% (x = 0) to 78.7% (x = 3.0) after 60 charge/discharge cycles, and the peak high rate dischargeability (HRD) at the discharge current density of 1200 mA/g appears at the alloy of x = 2.0 with the value of 68.3%. Moreover, the electrochemical kinetic properties of the alloys are also improved at different extent with increasing x. All the results indicate that the substitution of Co and Al for Ni in AB3-type hydrogen storage alloys is effective to improving the overall electrochemical properties, and the optimum content is x = 2.0.

The microstructure and electrochemical hydrogen storage characteristics of (La0.7Mg0.3)1−xCexNi2.8Co0.5 (x = 0, 0.05, 0.10, 0.15 and 0.20) alloys have been investigated. The results show that all alloys consist of (La, Mg)Ni3 and LaNi5 phases. The cyclic stability (S100) of the alloy electrodes increases from 58.7% (x = 0) to 69.8% (x = 0.20) after 100 charge/discharge cycles. The high rate dischargeability (HRD) increases from 66.8% (x = 0) to 69.6% (x = 0.10), then decreases to 65.1% (x = 0.20) at the discharge current density of 1200 mA/g. Moreover, the electrochemical kinetic characteristics of the alloy electrodes are also improved by increasing Ce content.

AbstractThe effectiveness of cement additives with and without chloride on the fluidity and the strength development of Portland cement was compared by using statistical full factorial design. The experimental results show that the cement additive containing CaCl2 and Ca(NO3)2 can enhance early strength of cement significantly. However, Ca(NO3)2 is less effective than CaCl2 even if it is combined with other organic chemicals such as alkanolamine and saccharide. No significant difference is found between CaCl2 and Ca(NO3)2 influencing the fluidity and 28 d strength of cement. The fluidity is determined by saccharide and its interaction with triisopropanolamine. The 28 d strength enhancement is determined by triisopropanolamine. The fluidity as well as the mechanical performance of treated cement can be significantly improved by combining Ca(NO3)2 with TIPA and saccharide.

Modeling the kinetics of the preparing process is necessary to produce a product with the appropriate particle properties and minimum production cost. Owing to the lackness of crystal size distributor (CSD) information, however, solvent-mediated phase transformation encounters difficulty in modeling the kinetics as compared to solution crystallization. Consequently, a model was established by making the product CSD to move along by horizontal translation to obtain the CSDs of the stable phase in the process of transformation. Then the moment method was used to solve the popular balance equation, and the least square nonlinear regression method was applied to estimate the kinetics parameters. The model has been successfully used to simulate the transformation of CaSO4·2H2O to α-CaSO4·1/2H2O in an isothermal seeded batch crystallizer with different stirring speeds, and it is beneficial to producing high performance α-CaSO4·1/2H2O crystals which have the right particle characteristics.

AbstractThe statistical tools such as descriptive statistics, full factorial design and analysis of source of variation were used to identify the potential factors that impact the validity of testing method for determining the strength of cement. The results showed that personal error impacted both accuracy and precision of test greatly. Experimental time associated with temperature fluctuation resulted in strength variation but did not impact the precision of test in all curing ages. Different compactions did not impact the precision of test but resulted in the strength variation on 3 d and 28 d significantly. Different methods for the initial moist air curing significantly impacted the precision of testing method and resulted in the strength variation of cement on 1 d.

An amorphous Ti2Ni alloy, prepared by mechanical milling of a crystalline Ti2Ni alloy, was heat-treated at several temperatures. The crystalline behavior of the amorphous alloy was studied , relative to a multi-stage crystallization mode, using X-ray diffraction, differential scanning calorimetry, and electron diffraction. X-Ray photoelectron spectroscopy was performed to analyze the surface structure of the alloys. The alloy that was heat-treated at 693 K, with a non-equilibrium bulk structure and a protective surface layer, has a high discharge capacity and good cycling stability. The issue of severe capacity loss of Ti2Ni-based alloys, which has caused problems for many years, has been significantly improved.

The electrochemical charge and discharge behavior of Co powders has been investigated by using X-ray diffraction (XRD), charge and discharge testing, and electrochemical impedance spectroscopy (EIS) at room temperature. Mechanical milling (MM) has been used to treat the Co powders for a comparative experiment. Mechanical milling induces a phase transition of fcc phase to hcp phase, an increase in particle size, and a decrease in grain size. The results of the XRD indicate a reversible reaction between Co and Co(OH)2. The non-milled Co has a higher discharge capacity at a current density of 60 mA g−1 as compared to the milled one. However, the milled Co presents a better HRD, in spite of the discrepancy in particle size. The results of EIS show that the electrochemical reaction process of Co powders consists of three steps, that is the charge-transfer of Co/Co(OH)2 or Co/CoHx, the mass-transfer of HCoO2−, and hydrogen diffusion within Co, depending on the depth of discharge.

The AB5 alloy and Co powders have been mixed at various weight ratios to form AB5–Co composite electrodes. The discharge properties such as discharge capacity, discharge plateau, and cycling stability are investigated by charge and discharge testing using Arbin battery testing equipment. Synergistic effects in the composite electrodes contribute to significant improvements of the discharge behavior. For instance, the composite AB5–25%Co electrode shows a high discharge capacity of 395.1 mAh/g, which is significantly higher than that of AB5 or Co electrode, and good cycling stability. The discharge process is also characterized by electrochemical impedance spectroscopy. Moreover, the electrochemical discharge mechanism is discussed.

Mechanical alloying has been carried out to synthesize a hydrogen storage alloy by milling titanium hydride and nickel. The structure and electrochemical properties such as discharge capacity, charge-transfer, and hydrogen diffusion of the milled powders were investigated. The results of X-ray diffraction showed that an amorphous phase was formed after ball milling. The electrode potentials of the milled powders were −0.989, −0.878 and −0.941 V (vs. Hg/HgO) in the electrolyte of 6 M KOH when the milling periods were 20, 40, and 60 h, respectively. The Ti–Ni–H powders milled for 60 h had a maximum discharge capacity of 102.2 mAh/g at a discharge current density of 60 mA/g. The results of the linear polarization showed that the exchange current density decreased as the hydrogen concentration within the powders decreased. The electrochemical impedance spectroscopy (EIS) demonstrated the same consequence and presented that the hydrogen diffusion decreased by decreasing the hydrogen concentration.

The structure, morphology, and electrochemical hydrogenation behavior of Ti2Ni alloy, prepared by an induction melting method, have been systematically investigated. The results of X-ray diffraction showed that hydrogen absorption led to a significant inelastic lattice expansion of the alloy. The alloy had a maximum discharge capacity of 235.5 mAh/g at a current density of 60 mA/g and a high rate dischargeability of 73.3% at 300 mA/g. The increase in the electrolyte temperature induced a decrease in discharge capacity, a decay of cycle life, an increase and subsequently a decrease in exchange current density, and an enhancement of hydrogen diffusion. Moreover, the alloy with a smaller particle size showed a higher discharge capacity. The mechanism for the capacity loss of the alloy during charge and discharge cycling was studied. The apparent activation energy for hydrogen diffusion within the bulk alloy was 10.7 kJ/mol.

Mechanical milling (MM) has been used to treat the crystalline Ti2Ni alloy prepared by solid-state sintering. Changes of the structure, morphology, and electrochemical properties were investigated. The particle size of the alloy decreases first and then increases after the milling. Moreover, MM contributes to a decrease in grain size and the formation and increase of the amorphous phase by increasing the milling time, resulting in improvements of the antipulverization ability and cycle life after the milling. The result of linear polarization indicates that the exchange current density, determined by the competition between the specific surface area and amorphous phase, increases first and then decreases. The amorphous phase is beneficial to hydrogen diffusion according to the result of potential-step measurement. The electrochemical properties of Ti2Ni alloy are significantly improved by the non-equilibrium processing technology.

The surface organic modification of Fe3O4 nanoparticles with silane coupling reagent KH570 was studied. The modified and unmodified nanoparticles were characterized by FT-IR, XPS and TEM. The spectra of FT-IR and XPS revealed that KH570 was coated onto the surface of Fe3O4 nanoparticles to get Fe-OSi bond and an organic coating layer also was formed. Fe3O4 nanoparticles were spheres partly with mean size of 18.8 nm studied by TEM, which was consistent with the result 17.9 nm calculated by Scherrer’s equation. KH570 was adsorbed on surface and formed chemistry bond to be steric hindrance repulsion which prevented nanoparticles from reuniting. Then glycol-based Fe3O4 magnetic liquids dispersed stably was gained.

A novel graft copolymer solid electrolyte with a relatively high ionic conductivity, 10−3.9 S cm−1 at 30 °C and 10−3.1 S cm−1 at 80 °C, is prepared by free radical polymerization in this study. The polymer consists of methacrylate as the backbone and a mixture of hexadecal (C16)–methoxyl terminated oligo(ethylene oxide) at a certain ratio as side chains. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) analysis reveal that non-polar unit (C16) end-modification not only greatly increases the mobility of the ethylene oxide (EO) chains, but also suppresses their local crystallization behavior by interrupting the regular arrangement, therefore improving the conductivity of the obtained electrolyte.

Li2CoTiO4 as a new titanate cathode material for Li-ion batteries was successfully synthesized by a sol–gel process. It had a cation disordered rock salt structure and showed an excellent cycle stability at room temperature. After coating with carbon, the Li2CoTiO4 possessed a high discharge capacity of 144.3 mAh g−1. The poor conductivity and lithium ion diffusion coefficient of pure Li2CoTiO4 are the main reasons for the limited electrochemical performance of the lithium batteries. The irreversible capacity loss during the first cycle was assigned to the irreversibility of the structural changes.