Consequences of different cutting regimes on regrowth and nutrient stoichiometry of Sparganium erectum L. and Potamogeton natans L.

Aquatic vegetation forms an essential component in freshwater ecosystems but due to changed environmental and anthropogenic conditions often needs management to reduce nuisance for human land‐use. In this paper, the authors looked at the regrowth of two macrophyte species (Potamogeton natans and Sparganium erectum) in two lowland rivers under different cutting treatments. After an initial cross‐sectional transect was manually removed from bank to bank at the beginning of the growth season, a monthly repetitive removal of biomass in plots on that transect was done during the rest of the growth season (testing frequency of mowing). Additional new transects were also cut in subsequent months (testing timing of mowing). Finally, biomass was repetitively removed in plots in those additional transects too (testing frequency of mowing × timing of mowing). The biomass at the end of the growth season was analysed for C, N, P, and Si. It was demonstrated that timing and frequency of vegetation cutting has an important effect on the capacity and rate of species' recovery and therefore on the efficiency of the applied management. Nutrient stoichiometry of the regrown biomass was directly affected by cutting. Caused by differences in the applied timing and frequency of the cutting, C/N and N/P ratios and BSi concentrations were highly variable. Yet, overall, there was a clear tendency towards a higher C/N ratio and BSi concentration and lower N/P ratio in biomass that recovered after cutting. This human impact on the quantity and quality of autochthonous organic matter may have knock‐on effects on the decomposers food web and mineralization process.     

Solubility of Si3N4 in Liquid SiO2

The nitrogen solubility in the SiO₂-rich liquid in the metastable binary SiO₂-Si₃N₄ system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N₂. A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si₃N₄ and to adjust the computed phase diagram. The solubility of Si₃N₄ in fused SiO₂ is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si₃N₄ without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si₃N₄-SiO₂ interface that leads to amorphous regions of higher N content.     

Mechanical Properties of Alumina/Silicon Carbide Whisker Composites

The improvement of mechanical properties of Al₂O₃/SiC whisker composites has been studied with emphasis on the effects of the whisker content and of the hot-pressing temperature. Mechanical properties such as fracture toughness and fracture strength increased with increasing whisker content up to 40 wt%. In the case of the high SiC whisker content of 40 wt%, fracture toughness of the sample hot-pressed at 1900° decreased significantly, in spite of densification, compared with one hot-pressed at 1850°. Fracture toughness strongly depended on the microstructure, especially the distribution of SiC whiskers rather than the grain size of the Al₂O₃ matrix.     

Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors

Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me₃Si)_0.80((CH₂=CH)MeSi)_1.0(MeHSi)_0.35] _n (VPS) or [MeHSiCH₂] _n (MPCS) with [R₂AlNH₂]₃, where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et₂AlNH₂]₃. In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu₂AlNH₂]₃ yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed.     

氢氧化镁中微量元素硼硅铝的测定

以盐湖高镁卤水为原料生产的氢氧化镁产品纯度不高,含有部分无机杂质离子,为提高产品质量,改进产品性能,通过实验确定了氢氧化镁中微量元素硼、硅、铝的分光光度测定方法。此方法准确度与精密度较高,测定样品中的硼、硅、铝加标回收率分别为98.3%-101.5%,96.0%-99.3%,96.5%-97.3%,相对标准偏差（n=6）分别为2.06%,2.27%,2.39%,快速、简便、成本低,可作为企业生产的常规检测方法使用。     

Side-Surface Structure of a Commercial β-Silicon Carbide Whisker

The side surfaces of a commercial β-SiC whisker were analyzed by calculating the surface energy and observing the microstructure of the whiskers. The results indicated that the side surfaces displayed a type of zigzag structure and were composed of {111}, {110}, and {100} crystal planes.     

Binder effect on cycling performance of silicon/carbon composite anodes for lithium ion batteries

The cycling performance of a silicon/carbon composite anode has been significantly enhanced by using acrylic adhesive and modified acrylic adhesive as binder to fabricate the electrodes for lithium ion batteries. The capacity retentions of Si/C composite electrodes bound by acrylic adhesive and modified acrylic adhesive are 79% and 90% after 50 cycles, respectively. These two binders are electrochemically stable in the organic electrolyte in the working window. They also show larger adhesion strength between the coating and the Cu current collector as well as smaller solvent absorption in the electrolyte solvent than polyvinylidene fluoride (PVDF). Furthermore, sodium carboxyl methyl cellulose (CMC) plays an important role on improving the properties of acrylic adhesive, which increases the adhesive strength of acrylic adhesive and improves the activation of the electrodes.     

氮化硅反应烧结的研究进展

氮化硅作为高温功能陶瓷性能优越，但将其制备成陶瓷零件比较困难，目前一般用反应烧结法制备氮化硅陶瓷零件。此外，反应烧结制备氮化硅陶瓷还具有成本低、烧结温度低、产品成型好、陶瓷高温性能好等优点。综述了氮化硅陶瓷反应烧结工艺流程和工艺的优缺点，着重介绍了氮化硅反应烧结在成型工艺、烧结工艺、原材料影响、后处理和陶瓷增韧等方面所取得的进展。     

硅通孔化学机械平坦化中铜去除的电化学与选择性研究

利用极化曲线测量法研究了甘氨酸和过氧化氢浓度及pH对硅通孔(TSV)化学机械平坦化(CMP)中铜腐蚀的影响。结果表明:甘氨酸对铜的腐蚀随其浓度增大而增强;随着过氧化氢浓度增大,铜腐蚀电位逐渐增大;在p H为10时铜的腐蚀效果最佳。CMP实验表明,在不同浓度的甘氨酸和过氧化氢之下,抛光速率可调,达1.9~5.8μm/min,铜表面粗糙度为5~29 nm,铜钽去除速率比为20~50。     

用粉煤灰稳定抗生素废水处理剩余污泥的研究

利用粉煤灰稳定抗生素废水处理过程中产生的剩余污泥的试验表明:粉煤灰与剩余污泥按一定比例混合搅拌后,混合物的重金属离子浓度和病原菌的含量均低于农用规定的浓度。在粉煤灰对重金属离子的固定机制中,表面络合作用在较宽的pH值范围内,尤其是在较低pH值时起主要作用,氢氧化物沉淀作用在较高pH值时是主要作用机制;粉煤灰的强碱性是杀死剩余污泥中微生物的主要原因。