活性MgO、La(OH)_3的表征及去除水中F~-的吸附性能研究

实验采用活性MgO和La(OH)3为吸附剂,对其去除水中氟离子的性能进行了研究.采用BET、XRD、TEM、SEM、FTIR等现代化手段对活性MgO和La(OH)3进行表征.探讨了pH、吸附时间、初始浓度、吸附剂投加量以及共存离子等因素对这两种吸附剂吸附性能的影响.影响因素的研究表明,活性MgO吸附剂最适宜的吸附条件为pH=6~7,温度20~25℃,吸附剂投加量约为1g/L;La(OH)3的最适宜条件为pH=4,温度20~25℃,吸附剂投加量约为1g/L.活性MgO的吸附容量约为55mg/g,La(OH)3的吸附容量约为7.2mg/g.     

CuO-Bi_2O_3/SiO_2-MgO催化合成1,4-丁炔二醇工艺条件研究

采用溶胶—凝胶结合超临界干燥技术制备了一系列不同Mg含量的SiO2-MgO气凝胶载体,负载铜铋后应用于甲醛乙炔化制1,4-丁炔二醇反应,考察了工艺条件对催化反应性能的影响。结果表明,载体中Mg的引入可有效提高催化剂的反应性能,在Mg含量18%时甲醛转化率和1,4-丁炔二醇收率均达到最大值。在优选的工艺条件为5 g催化剂/100 mL甲醛溶液,反应时间25 h条件下,分别为92%和78%。催化剂表现出优异的使用稳定性。     

Effects of Y2O3/MgO ratio on mechanical properties and thermal conductivity of silicon nitride ceramics

In this work, the effects of Y₂O₃/MgO ratio on the densification behavior, phase transformation, microstructure evolution, mechanical properties, and thermal conductivity of Si₃N₄ ceramics were investigated. Densified samples with bimodal microstructure could be obtained by adjusting the ratio of Y₂O₃/MgO. It was found that a low Y₂O₃/MgO ratio facilitated the densification of Si₃N₄ ceramics while a high Y₂O₃/MgO ratio benefited the phase transformation of Si₃N₄ ceramics. Best mechanical properties (flexural strength of 875 MPa, and fracture toughness of 8.25 MPa·m^1/2, respectively) and optimal thermal conductivity of 98.04W/(m·K) were achieved in the sample fabricated with Y₂O₃/MgO ratio of 3:4 by sintering at 1900°C for 4 h.     

Dislocation reactions,plastic anisotropy and forest strengthening in MgO at high temperature

The collective properties of dislocations in MgO are investigated in the high temperature regime and at constant strain rate with 3D Dislocation Dynamics simulations. Intersections between slip systems 1/2〈1 1 0〉{1 1 0} and 1/2〈1 1 0〉{1 0 0} allow essentially two types of junction reactions. These junctions are energetically stable and are expected to promote strong forest strengthening at high temperature. Large-scale DD simulations show that MgO strain hardening at high temperature may be dominated by forest reactions. Important parameters for dislocation density based modeling of MgO plasticity are finally calculated and verified to be consistent with experimental observations.     

‘Beautiful’ unconventional synthesis and processing technologies of superconductors and some other materials

Abstract

Superconducting materials have contributed significantly to the development of modern materials science and engineering. Specific technological solutions for their synthesis and processing helped in understanding the principles and approaches to the design, fabrication and application of many other materials. In this review, we explore the bidirectional relationship between the general and particular synthesis concepts. The analysis is mostly based on our studies where some unconventional technologies were applied to different superconductors and some other materials. These technologies include spray-frozen freeze-drying, fast pyrolysis, field-assisted sintering (or spark plasma sintering), nanoblasting, processing in high magnetic fields, methods of control of supersaturation and migration during film growth, and mechanical treatments of composite wires. The analysis provides future research directions and some key elements to define the concept of ‘beautiful’ technology in materials science. It also reconfirms the key position and importance of superconductors in the development of new materials and unconventional synthesis approaches.     

Study on the Possibility of Using ZnO to Increase the Desulfurization Potential of Blast Furnace Slag and Sulfide Capacities

Zinc oxide has recently been suggested to be a potential material for hot metal desulfurization. The present work was carried out to examine whether ZnO could help the remaining blast furnace (BF) slag to capture sulfur. For this purpose, slags prepared with relatively high ZnO content was equilibrated with either liquid silver or liquid copper under controlled oxygen potential at 1773 K. It was found that most of the ZnO escaped during the experiment, indicating thereby that ZnO could not increase the desulfurization potential of the BF slag in the case of hot metal. The experimental data were used to evaluate the sulfide capacities of the studied slags. In some of the slags equilibrated with silver, the MgO activities were evaluated.     

Impact of preheating on the mechanical performance of different MgO–C bricks - Low temperature range

This work complements an initial study regarding the mechanical behavior of MgO–C bricks at 1000 °C. In this case, two bricks bonded with phenolic resin, one of them containing aluminum, were treated at 600 °C and mechanically tested at RT and 600 °C. The thermal treatments attempt to simulate the in-service steelmaking ladle preheating process. At low temperatures, the binder pyrolysis is one of the main transformations and the Al melting neither its chemical reactions occur on a large scale yet. To evaluate the effects as the pyrolysis progresses, the soaking time at 600 °C was varied from 1 to 3 h. Although without significant chemical activity, the presence of Al affected the mechanical behavior of the tested bricks. The consolidation of the C–C network coming from the binder pyrolysis was identified as the main factor responsible for counterbalancing the material's degradation by microcracking. The heating combined with the low compressive pre-load applied on the tested specimens appears to close the microcracks and pores.     

Effect of sol–gel MgO spin-coating on the performance of TiO2-based dye-sensitized solar cells

This paper is concerned with the improvement of dye-sensitized solar cell (DSSC) efficiency upon MgO post-treatment of the TiO₂ electrode. A simple sol–gel technique, involving magnesium acetate as precursor, ethanol as solvent and nitric acid as stabilizer, is applied to prepare a solution of suspended MgO nanoparticles. A single drop of MgO sol at 0.1 M precursor concentration was spin-coated at 3000 rpm for 30 s onto the TiO₂ electrode and sintered at 500 K for 1 h. Dye-loading using N3-dye was applied for 6 h. An increase in the average efficiency of the DSSC from 2.5% to 3.9% (over 50% enhancement) was recorded. Measurements of the dark I–V characteristics, the open circuit voltage decays, the SEM images and the dye absorbance spectra, for both uncoated and MgO-coated electrodes were examined. The improvement of the DSSC efficiency was attributed to an upward shift of the TiO₂ flat band energy and a reduction of the rate of back-transport and recombination.     

Influence of nucleation seeding on the performance of carbonated MgO formulations

The continuation of the hydration and carbonation reactions within reactive MgO cement formulations is inhibited by the formation of hydrate and carbonate phases around MgO particles, resulting in a low MgO utility and limited mechanical performance. This study introduces carbonate seeds into the pore space of MgO-based concrete mixes to enable the nucleation and growth of carbonates on the seed surfaces. The influence of seeds on the hydration and carbonation capability, mechanical performance and microstructural development was evaluated through isothermal calorimetry, water absorption and compressive strength measurements, along with TGA, XRD and SEM analyses. The introduction of ≤1% seed within the initial mix design increased the carbonate phase content and improved carbonation degree by up to 96% by increasing the availability of Mg(OH)₂ for carbonation. The dense formation of carbonates in seeded samples enabled improved microstructures and 28-day strengths of 64 MPa, which were 33% higher than unseeded samples.