掺合料对超高性能水泥基装饰材料性能的影响

将重钙粉与偏高岭土以不同的比例混合并替代白水泥，制备超高性能水泥基装饰材料,研究两者掺入比例变化对超高性能水泥基装饰材料工作性能、力学性能及自收缩的影响，采用SEM扫描电镜观察28 d龄期后试件内部微观形貌，研究表明，随着重钙粉与偏高岭土比例的增大，试件的致密程度和强度先增后减，其中B9-9的28 d抗压与抗折强度可以达到120.6 MPa与42.9 MPa，且工作性、收缩性能良好、内部结构致密。     

Graphene Adsorption and Separation Functional Materials

Graphene and its derivatives have been considered intensively in the development and application of new types of adsorption and separation functional materials, due to its unique structure and superior performance. A comprehensive review on recent studies on adsorption and separation functional materials is given, including graphene, graphene oxide, graphene gel, graphene‐based sponge, graphene separation membrane as well as graphene continuous oil absorption and separation materials. Moreover, the preparation methods and application prospects are mainly utilized to illustrate the research progress. Especially, it is predicted that layered graphene membrane and graphene continuous oil absorption and separation materials may be the most research worthy.     

DC conductivity and AC impedance of Mn doped magnesia alumina spinel (MgAl2-2xMn2xO4) over a large temperature range

MgAl_2-2xMn_2xO₄ (MAMO) with x = 0-0.12 was synthesized in a single-phase form by solid-state reaction. XRD analysis showed that the samples had the cubic center structure of the Fd-3 m space group. Electrical properties of the samples were studied over the temperature range of 300 K∼1073 K. The results showed that the DC conductivity (σ_DC) increased from 10⁻¹¹S/cm at 300 K (MAMO, x = 0) to 10^-3S/cm at 1073 K (MAMO, x = 0.12). The equivalent circuit of the complex impedance spectra suggested that the relaxation of charge carriers was of non-Debye type. The conduction was mainly caused by grain boundaries and the capacitance was mainly attributed to polarization. The complex permittivity values (ε’ and ε’’) were increased by two orders of magnitude with the increase in Mn content and temperature over the measured frequency range (1 Hz-1 MHz). Therefore, doping with Mn could be applied to modify the electrical properties of MAMO at high temperature.     

Effect of Ni/tubular g-C3N4 on hydrogen storage properties of MgH2

Additive doping is one of the effective methods to overcome the shortcomings of MgH₂ on the aspect of relatively high operating temperatures and slow desorption kinetics. In this paper, hollow g-C₃N₄ (TCN) tubes with a diameter of 2 μm are synthesized through the hydrothermal and high-temperature pyrolysis methods, and then nickel is chemically reduced onto TCN to form Ni/TCN composite at 278 K. Ni/TCN is then introduced into the MgH₂/Mg system by means of hydriding combustion and ball milling. The MgH₂–Ni/TCN composite starts to release hydrogen at 535 K, which is 116 K lower than the as-milled MgH₂ (651 K). The MgH₂–Ni/TCN composite absorbs 5.24 wt% H₂ within 3500 s at 423 K, and takes up 3.56 wt% H₂ within 3500 s, even at a temperature as low as 373 K. The apparent activation energy (E_a) of the MgH₂ decreases from 161.1 to 82.6 kJ/mol by the addition of Ni/TCN. Moreover, the MgH₂–Ni/TCN sample shows excellent cycle stability, with a dehydrogenation capacity retention rate of 98.0% after 10 cycles. The carbon material enhances sorption kinetics by dispersing and stabilizating MgH₂. Otherwise, the phase transformation between Mg₂NiH₄ and Mg₂NiH_0.3 accelerates the re/dehydrogenation reaction of the composite.     

Surface structure and quenching effects in BiFeO3-BaTiO3 ceramics

The structure and properties of Mn-doped 0.67BiFeO₃-0.33BaTiO₃ ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air-quenching induces a change in crystal structure from pseudo-cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well-defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature-dependent relative permittivity for the as-sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature-stability of piezoelectric properties. It is proposed that the formation of defect clusters by A-site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.     

Corrosion of Li-ion battery cathode materials on mullite insulation materials during calcination

A specially designed experimental device was used in laboratory to investigate the corrosion of mullite during the calcination of Li(Ni_xCo_yMn_z)O₂ (LNCM) materials. The anti-corrosion tests were carried out at 1000, 1100, 1200 and 1300 °C, and characterized with X-ray diffraction and scanning electron microscopy. The influence of temperature on the interactions between mullite insulation materials and LNCM materials was determined. In addition, the high-temperature creep properties of the mullite insulation materials before and after corrosion were tested. The laboratory scale tests, thermodynamic and kinetic calculations allowed a more comprehensive understanding of the evolution of the mullite insulation materials during serving for the roasting process of LNCM materials. Through this research, it is suggested that the upgrading of the kiln lining in the lithium battery industry should select materials with excellent resistance to alkali corrosion, especially excellent resistance to Li⁺ corrosion.     

土木工程施工课程线上平台教学实践

土木工程施工课程作为土木工程及工程管理专业的学科基础课和核心专业课程,在疫情防控期间"停课不停教""停课不停学"的要求下,通过线上平台进行授课。由于土木工程施工课程内容庞杂、综合性强、实践性强,且章节之间关联性较弱,探究既能使学生快速适应,又能保证教学质量的在线教学方法至关重要。以华南某高校土木工程施工课程为例,基于中国大学MOOC、建筑云课、腾讯课堂、QQ群等线上平台讲授教学内容,并运用问卷调查对课程线上教学效果进行评价。结果表明,线上教学为学生提供了丰富灵活的学习方式,显著提高了学生的自主学习能力,扩大了学生的知识面,达到了较好的学习效果。     

Joining zirconia with nickel-based superalloys for extreme applications by using a pressure-free high-temperature resistant adhesive

In order to meet the high demand for joining ceramic/superalloy composite structure in extreme environments, a novel high-temperature resistant adhesion technique was developed for joining ZrO₂ and Inconel 625 by applying an aluminum phosphate emulsion/zirconium sol based adhesive. With increasing temperature, a series of reactions occurred in adhesive, and its high-temperature bonding was attributed to the formation of a composite structure containing various ceramics and intermetallics. The adhesive after RT curing could find direct applications in extreme environments, and provide bonding strength no less than 2.5 MPa in the temperature range of RT-1100 °C. The bonding strength was higher than 4 MPa in the temperature range of 800–1000 °C, which was further attributed to the formation of an effective CTE-gradient relationship among ZrO₂, adhesive and Inconel 625, as well as the interfacial reactions between the two substrates. The work broadened the application of adhesion technique and brought new ideas for joining dissimilar engineering materials.     

The effects of the modification of the BST-system solid solutions with rare earth elements

The conditions for the preparation of the solid solutions of a binary system of barium-strontium titanates with the substitutions in the A-sublattice with the rare-earth elements (REE), including the solid-phase synthesis, mechanical activation and sintering of dispersed-crystalline products by the conventional ceramic technology, were optimized. The presence (absence) of the impurity phases was established depending on the size effect of the REE. The precision X-ray diffraction analysis revealed the features of the phase formation in the studied solid solutions and showed that the “behavior” of the structural characteristics of the solid solutions with the participation of the REE is determined by the limiting conditions of the isomorphism and anion excess of the media under study. An assumption is made about the nature of the formation of a fine-grained landscape of the modified solid solutions, associated with the multicluster structure of the crystallite structure and the formation of the ballast phases during their synthesis. The dependences of the dielectric properties of the solid-state solution on the external influences – temperature, frequency of an alternating electric field and strength of a constant field – have been established. The possibility of choosing on the basis of the obtained data, promising for practical applications of the compositions is shown.     

Characterization of anisotropic gas permeability and thermomechanical properties of highly textured porous alumina

Porous alumina with a highly textured microstructure was fabricated by pulse electric current sintering (PECS) using alumina platelets. Highly oriented porous alumina with a porosity of 3%–50% was obtained by a pressure-controlled method of PECS. The properties of the highly textured porous alumina were measured in two directions. The nitrogen gas permeance and thermal conductivity at room temperature were higher in the direction along the platelet length due to the higher continuity of pores and the connectivity of alumina platelets, respectively. The anisotropy of the thermal conductivity at room temperature was investigated and explained by the effect of grain size of platelets as well as morphology and orientation of pores. The bending strength was higher with the loading direction along the platelet thickness. The thermal shock strength was clearly different in the two directions. The difference in the thermal shock strength was investigated by the measurement of properties and thermal stress analysis.