水质硒质量控制用标准样品的研制

依据国家标准样品工作导则要求,制备硒标准样品。采用原子荧光法对样品进行均匀性和稳定性研究。以多个实验室协作分析定值的统计结果确定标准值,并进行不确定度评估。结果表明,硒标准样品均匀性良好,稳定性可达24个月以上;样品量值准确,与美国同种标准物质进行比对具有可比性。研制的硒标准样品符合国家标准样品的技术要求,标准编号为GSB 07—3172—2014,可用于水质硒元素检测的质量控制、分析方法研究以及分析实验室能力验证等方面。     

Controlled Synthesis of Polyions of Heavy Main-Group Elements in Ionic Liquids

Ionic liquids (ILs) have been proven to be valuable reaction media for the synthesis of inorganic materials among an abundance of other applications in different fields of chemistry. Up to now, the syntheses have remained mostly “black boxes”; and researchers have to resort to trial-and-error in order to establish a new synthetic route to a specific compound. This review comprises decisive reaction parameters and techniques for the directed synthesis of polyions of heavy main-group elements (fourth period and beyond) in ILs. Several families of compounds are presented ranging from polyhalides over carbonyl complexes and selenidostannates to homo and heteropolycations.     

Formation mechanism and microhardness characterization of the ultrasonic hardening layer in cementitious materials

Ultrasonic surface treatment (UST) is a novel treatment method to improve the durability of cementitious materials, resulting in the formation of an ultrasonic hardening layer (UHL). The UHL acts as an effective natural coating, offering penetration and erosion protection. However, the formation mechanism and the quantitative characterization of the UHL have not been studied, and the validity of the UST on the top and side surfaces of cementitious materials is still unknown. Therefore, in this study, we investigated and proposed a formation mechanism for the UHL, and defined a transition layer between the UHL and the matrix. We also utilized HV microhardness testing to provide an effective quantitative characterization method for the UHL. Finally, using a set of custom-designed ultrasonic molds, we confirmed the validity of the UST on the top and side surfaces of the cementitious materials.     

A Moisture Transfer Model for Isothermal Drying of Plant Cellular Materials Based on the Pore Network Approach

Plant materials with cellular structure, like fruits and vegetables, are often viewed as porous media in terms of model building of the drying process, on the basis of a hypothesis that all of the moisture of a plant tissue is trapped in a continuous and connected pore network system. However, most of the moisture in the plant tissue is contained naturally in enclosed cells. In the course of drying, the trapped moisture has to cross the cell membranes and then migrates in the extracellular space. Based on this concept, a pore network model for isothermal drying of plant materials was developed in which two stages of moisture movement—transmembrane transfer and extracellular transfer in the pore network—were considered. Finally, the isothermal convective air-drying processes of a potato slice were simulated. The calculated results were validated by the experiments conducted under the simulation conditions.     

Surface hierarchical porosity in poly (ɛ-caprolactone) membranes with potential applications in tissue engineering prepared by foaming in supercritical carbon dioxide

This article describes the preparation of porous poly (ɛ-caprolactone), PCL, membranes by supercritical CO₂ (SCCO₂) foaming, displaying surface hierarchical macroporosity which could be tailored by careful control of the pressure, in the range of 150–250 bar, and depressurization processes in several steps, showing also pore interconnectivity between both membrane faces. The membranes exhibited two distinct types of surface macroporosity, the larger with diameter sizes of 300–500 μm were surrounded by and also composed of smaller pores of 15–50 μm (same size as inner pores). Membranes were prepared by solvent casting and submitted to different SCCO₂ foaming. Parameters such as membrane thickness, CO₂ flow, foaming time, pressure, temperature and the depressurization processes (rate and profiles), were varied to determine their influence on final porosity and to decipher which parameters were the most critical ones in terms of surface hierarchical pore organization. No remarkable changes in PCL crystallinity were found when membranes were processed under SCCO₂. Finally, biological evaluation of the porous membranes was achieved by seeding human skin fibroblasts on the prepared membranes. The results, in terms of cell adhesion, spreading, proliferation and metabolic activity indicate that these membranes could hold promise for the fabrication of meshes with controlled porosity for tissue engineering applications.     

Strawberry‐like Core–Shell Ag@Polydopamine@BaTiO3 Hybrid Nanoparticles for High‐k Polymer Nanocomposites with High Energy Density and Low Dielectric Loss

Flexible nanocomposites comprising of polymer and high‐dielectric‐constant (high‐k) ceramic nanoparticles are becoming increasingly attractive for dielectric and energy storage applications in modern electronic and electric industry. However, a huge challenge still remains. Namely, the increase of dielectric constant usually at the cost of significant decrease of breakdown strength of the nanocomposites because of the electric field distortion and concentration induced by the high‐k filler. To address this long‐standing problem, by using nano‐Ag decorated core–shell polydopamine (PDA) coated BaTiO₃ (BT) hybrid nanoparticles, a new strategy is developed to prepare high‐k polymer nanocomposites with high breakdown strength. The strawberry‐like BT‐PDA‐Ag based ferroelectric polymer [i.e., poly(vinylideneflyoride‐co‐hexafluroro propylene), P(VDF‐HFP)] nanocomposites exhibit greatly enhanced energy density and significantly suppressed dielectric loss as well as leakage current density in comparison with the nanocomposites with the core–shell structured BT‐PDA. Coulomb‐blockade effect of super‐small nano‐Ag is used to explain the observed performance enhancement of the nanocomposites. The simplicity and scalability of the described approach provide a promising route to polymer nanocomposites for dielectric and energy storage applications.     

FINITE ELEMENT MODELLING OF INTERNALLY PRESSURIZED CLOSED CELL COMPOSITES

Composites composed of closed solid wall cells enclosing a fluid are examined in this paper. The analysis of their stiffness in compression includes the effects of fluids in the cell interiors. A specialized finite element program is developed to account for the internal pressure. Both two-dimensional and three-dimensional geometries are considered. The finite element calculations are then used to predict the compressive stiffness of fluid filled metal cell composites.     

钌基析氢电催化剂的研究进展

能源消耗持续增长以及化石燃料燃烧带来的能源安全与环保问题日益突出,开发安全、清洁、高效的新能源是人类可持续发展的重要课题。氢气具有能量密度高、无污染、资源丰富的优点,被视为最具发展潜力的石油与天然气的替代清洁能源。制氢最常用的方法是电解水,为实现高效制氢,通常需要添加催化剂（钌及钌基材料）提高析氢效果。本文详细介绍了铂（Pt）族元素中最便宜的金属元素钌（Ru）和钌基材料作为高效电催化剂的制备方法,阐明了析氢促进机理以及析氢效果,并提出了钌基析氢电催化剂的未来发展方向。     

氮化硅陶瓷微波烧结几何参数对电磁场分布影响规律的研究

在微波烧结过程中,烧结试样内部电场分布情况对试样烧结过程起决定性的作用。采用HFSS仿真软件,对一种加载氮化硅试样的5馈口微波烧结腔进行模拟仿真。同时,研究了试样的半径、高度及放置位置对微波电场的影响规律。模拟结果表明：当试样半径在42—44 mm左右时,内部电磁场分布均匀;随着试样高度的增加,电场的均匀性先下降后上升到最大值后又下降,试样高度在92—94 mm处附近时内部电磁场分布较为均匀、场强梯度小;随着放置高度的增加,试样内均匀性上升,但超过一定高度后电磁场均匀性下降;经比较研究,得出电磁场分布均匀、符合烧结要求的最佳烧结试样尺寸为高度93 mm、半径44mm、放置高度215 mm。     

超细晶/纳米晶钨材料制备技术的研究进展

晶粒细化可显著提高超细晶/纳米晶钨材料的性能,介绍了超细晶/纳米晶钨材料制备技术的最新研究进展,包括粉末冶金法和深度塑性变形法,粉末冶金法的烧结工艺主要包括热等静压烧结、超高压通电烧结、放电等离子体烧结、微波烧结等;深度塑性变形法包括高压扭转、等通道挤压、表面机械研磨处理和累积轧制等。由于超细晶/纳米晶钨材料存在大量的晶界可有效提高材料的力学性能和抗辐照性能,因此有望解决纯钨材料作为核聚变堆面向等离子体材料存在的问题,对超细晶/纳米晶钨材料的发展提出了建议。