Spectroscopic analysis of carbon dioxide and nitrogen mixed gas hydrates in silica gel for CO2 separation

In this study solid-state NMR spectroscopy was used to identify structure and guest distribution of the mixed N₂ + CO₂ hydrates. These results show that it is possible to recover CO₂ from flue gas by forming a mixed hydrate that removes CO₂ preferentially from CO₂/N₂ gas mixture. Hydrate phase equilibria for the ternary CO₂–N₂–water system in silica gel pores were measured, which show that the three-phase H–L_w–V equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO₂ in the vapor phase decreased. ¹³C cross-polarization (CP) NMR spectra of the mixed hydrates at gas compositions of more than 10 mol% CO₂ with the balance N₂ identified that the crystal structure of mixed hydrates as structure I, and that the CO₂ molecules occupy mainly the abundant 5¹²6² cages. This makes it possible to achieve concentrations of more than 96 mol% CO₂ gas in the product after three cycles of hydrate formation and dissociation.     

铝硅混合凝胶对刚玉-莫来石制品性能的影响

按莫来石骨料占65%(质量分数),刚玉和黏土组成的混合粉占35%(质量分数)配料,分别外加占原料总质量4%的水、硅溶胶、铝硅混合凝胶作结合剂,研究了结合剂种类对刚玉-莫来石材料经1 100、1 400和1 600℃分别保温3 h烧后的性能及显微结构的影响,并在此基础上研究了铝硅混合凝胶加入量(分别为1%、2%、3%、4%)及配比(m(Al2O3):m(SiO2)分别为8:2、7:3、4:6)对刚玉-莫来石制品常温性能的影响.结果表明:以铝硅混合凝胶为结合剂的刚玉-莫来石试样,经1 400、1 600℃烧后的常温、高温抗折强度和抗热震性均比仅加硅溶胶或水的好,但显气孔率偏大;当铝硅混合凝胶加入量为2%且m(Al2O3):m(SiO2)=7:3时,烧后试样的常温强度最高.     

Enhanced Pt utilization in electrocatalysts by covering of colloidal silica nanoparticles

This work aims at enhancing Pt utilization in electrocatalysts by covering of preformed silica nanoparticles. Pt/C electrocatalysts were prepared by reductive deposition of Pt by citrate at moderate temperatures on silica nanoparticles with varying atomic silica to Pt ratios (1.7:1 and 3.3:1) to study the effects of silica to Pt ratio. Considerable voidages were created by inter-situated 10–20 nm silica nanoparticles between support carbon particulates to facilitate mass transfer of reactants and products. This particular method of catalyst preparation increases the Pt metal utilization, and generates a large amount of accessible voidage in the interpenetrating particle network of carbon and silica to support the facile transport of reactants and products. Electrochemical hydrogen adsorption/desorption has shown an increase in electrochemically active surface area by this approach. Methanol electro-oxidation was used as a test reaction to evaluate the catalytic activity. It was found that the Pt catalyst modified with silica at silica:Pt = 1.7:1 atomic ratio was more active than a catalyst prepared when silica to Pt ratio increased to 3.3:1.     

Comparison of experimental and simulation results on catalytic HI decomposition in a silica-based ceramic membrane reactor

In this study, the catalytic decomposition of hydrogen iodide was theoretically and experimentally investigated in a silica-based ceramic membrane reactor to assess the reactor's suitability for thermochemical hydrogen production. The silica membranes were fabricated by depositing a thin silica layer onto the surface of porous alumina ceramic support tubes via counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. The performance of the silica-based ceramic membrane reactor was evaluated by exploring important operating parameters such as the flow rates of the hydrogen iodide feed and the nitrogen sweep gas. The influence of the flow rates on the hydrogen iodide decomposition conversion was investigated in the lower range of the investigated feed flow rates and in the higher range of the sweep-gas flow rates. The experimental data agreed with the simulation results reasonably well, and both highlighted the possibility of achieving a conversion greater than 0.70 at decomposition temperature of 400 °C. Therefore, the developed silica-based ceramic membrane reactor could enhance the total thermal efficiency of the thermochemical process.     

Electrospun nanofiber composites with micro-/nano-particles for thermal insulation

Polyacrylonitrile (PAN) nanofiber and silica aerogel (SAG) laminated composites were prepared via electrospinning for thermal insulation. Conventional single nozzle and co-axial electrospinning were used to increase the fraction of aerogel particles in the composite sheets while maintaining the mechanical strength of the sheet. When the core-shell electrospinning technique with co-axial nozzle was applied, the proportion of aerogel particles increased two fold without a deterioration of the mechanical properties. The average thermal conductivity of the laminated composite sheet was reduced by approximately 12.5% as compared to the nanofiber composite prepared using the single-nozzle electrospinning technique. For additional reduction in thermal conductivity, hollow glass microspheres (HGM) was inserted between the interlayer spacing of the electrospun sheets to increase the interlayer spacing. When HGM particles were inserted, it was observed that the thermal conductivity decreased by approximately 20% compared to that of the specimen without particles.     

Effect of partial replacement of geopolymer binder materials on the fresh and mechanical properties: A review

The growth of demand for concrete raises concerns about the consumption of natural resources and ordinary Portland cement. Geopolymer composites show promise as a sustainable alternative for conventional cement concrete. Considering the wide range of potential geopolymer composites applications (including suitability for transportation infrastructure, underwater applications, repair and rehabilitation of structures as well as recent developments in 3D printing), the desired fresh and mechanical properties of the geopolymer composite may vary between applications: for example, rapid setting can be a merit for certain applications and a demerit for others. Therefore, the desired fresh and mechanical properties (e.g., workability, setting time, compressive strength, etc.) can be controlled for a given geopolymer source material through its partial substitution by natural or by-product materials. Recognizing the critical role of various replacement materials in enhancing the potential applications of geopolymer composites, the present review was undertaken to quantify and understand the effect of partial replacement by fly ash, metakaolin, kaolin, red mud, slag, ordinary Portland cement, and silica fume on the setting time, workability, compressive strength and flexural strength of various source materials addressed in the literature. The review also provides insights into research gaps in the field to promote future research.     

Structural Analysis of silica aerogels for the interlayer dielectric in semiconductor devices

As semiconductor devices have become miniaturized and highly integrated, interconnection problems such as RC delays, power dissipation, and crosstalk appear. To alleviate these problems, materials with a low dielectric constant should be used for the interlayer dielectric in nanoscale semiconductor devices. Silica aerogel as a porous structure composed of silica and air can be used as the interlayer dielectric material to achieve a very low dielectric constant. However, the problem of its low stiffness needs to be resolved for the endurance required in planarization. The purpose of this study is to discover the geometric effect of the electrical and mechanical properties of silica aerogel. The effects of porosity, the distribution of pores, the number of pores on the dielectric constant, and elastic modulus were analyzed using FEM. The results suggest that the porosity of silica aerogel is the main parameter that determines the dielectric constant and it should be at least 0.76 to have a very low dielectric constant of 1.5. Additionally, while maintaining the porosity of 0.76, the silica aerogel needs to be designed in an ordered open pores structure (OOPS) containing 64 or more pores positioned in a simple cubic lattice point to endure in planarization, which requires an elastic modulus of 8 GPa to prevent delamination.     

白炭黑/炭黑复合填充对NR性能的影响

在白炭黑和炭黑填料总量一定的情况下,研究了不同白炭黑/炭黑配比对NR性能的影响。结果表明,白炭黑用量增加,NR硫化速率下降,体系中炭黑填料网络被破坏且白炭黑-橡胶间较弱的相互作用也会对NR硫化胶力学性能产生一系列影响。DMA结果表明,加入20~25份白炭黑对提高硫化胶的抗湿滑性和降低滚动阻力最为有效。     

石英砂热膨胀性的研究

以大林砂、围场砂、平潭砂等为研究对象,采用自制的铸造用砂热膨胀性测定仪,分别对不同产地的铸造用砂的随温热膨胀和等温热膨胀进行了测试,对其热膨胀特性进行了研究.结果发现,石英砂的膨胀以热膨胀为主,相变膨胀为辅.膨胀量受加热温度、砂子粒度以及SiO2含量的影响.经700 ℃热再生的石英砂的热膨胀性低于同类新砂.