棒状LiZnPO4的低温合成与表征

LiZnPO₄的性能与其形貌密切相关,其合成常用的固相法和水热法均无控制其微观形貌的优势。 本文采用改进的沉淀法成功合成了具有棒状结构的LiZnPO₄。 利用热重-差热分析仪(TG-DSC)、X射线衍射仪(XRD)、傅里叶变换红外光谱(FTIR)以及场发射扫描电子显微镜(FE-SEM)等技术研究了LiZnPO₄形成过程、晶相组成、微观结构和形貌。 同时探究了合成方法、煅烧温度、煅烧时间、酸的种类对LiZnPO₄形貌的影响。 结果表明,相比较于固相法,以醋酸为原料的改进沉淀法不仅可以有效降低LiZnPO₄的合成温度至500 ℃,而且很容易控制棒状LiZnPO₄的形成。 在600 ℃下煅烧2 h后可以获得分散性良好、横截面为矩形、直径约为2 μm的规则棒状LiZnPO₄。 此外,对比颗粒状LiZnPO₄和棒状LiZnPO₄的光响应能力,发现棒状LiZnPO₄的光响应能力明显增强。     

大豆脲酶诱导碳酸钙沉淀的多因素影响分析

本文探究了多个影响因素对大豆脲酶诱导碳酸钙沉淀(SICP)的影响,以优选出主要影响因素并提供其最佳范围。首先分析了脲酶浓度和温度对脲酶活性的影响;之后通过正交实验设计,进行25种工况的SICP水溶液实验,研究不同因素组合下Ca²⁺利用率的变化规律;最后借助扫描电子显微镜观测不同工况下生成碳酸钙的形态。结果表明:低温有利于脲酶的保存及活性发挥,5 ℃时脲酶活性能保持21 d以上;同一温度下,脲酶浓度越大,脲酶初始活性越高,脲酶完全失活所需时间越短。pH值、脲酶与胶结液体积比是影响Ca²⁺利用率的主要因素。为达到较高的Ca²⁺利用率,脲酶和胶结液最佳体积比为1,氯化钙与尿素最佳浓度比为1.5,Ca²⁺最佳浓度为1 mol/L。当脲酶浓度较低时生成的六面体状碳酸钙较多;随着脲酶浓度的增大,所沉淀的碳酸钙向球形转变。大豆中富含的天冬氨酸是控制碳酸钙形态的重要因素。     

用硝酸银溶液沉淀及分步沉淀卤素离子的数字化实验研究*

卤化银难溶电解质的沉淀溶解平衡是中学化学教学的重要知识点。应用本项目组研制的MXLab21先进数字化实验系统,结合银硫离子电极,测定AgNO₃溶液沉淀Cl^-,Br^-,I^-及其混合离子的沉淀曲线,即电动势(E)随AgNO₃溶液体积(V)变化的关系曲线。3种单一离子的沉淀曲线可以直观体现出滴定的电动势突跃范围与相应沉淀的溶度积大小的关系及其规律性变化。通过混合离子的沉淀曲线分析3种离子两两混合或3者混合时分步沉淀的可行性。Cl^-,Br^-,I^-的沉淀及分步沉淀的动态E-V曲线的建立,对中学化学教学具有重要作用,对化学学科核心素养的发展和培养具有重要价值。     

基于曲线问题情境的信息化教学尝试*——以“沉淀溶解平衡”为例

基于高中生对实验曲线理解困难的现状,为挖掘实验曲线的教学价值,以沉淀溶解平衡为例,结合课堂演示实验和教学软件,设计了“宏观微观符号曲线”多重表征教学为一体的实验探究课。根据沉淀溶解平衡实验证据,绘制实验曲线,构建微观模型和图像,从而培养学生的证据收集与应用意识,提高学生对曲线的分析和理解能力,领会各种变化曲线的来源。在曲线理解的基础上建立“溶解平衡转化”思维模型,以此为开展“曲线融入式”的问题引导型实验教学提供参考案例。     

Polymethylmethacrylate derivatives Eudragit E100 and L100: Interactions and complexation with surfactants

Precipitation or coprecipitation of polyelectrolytes has been largely investigated. However, the precipitation of polyelectrolytes via addition of charged and non‐charged surfactants has not been systematically studied and reported. Consequently, the aim of this work is to investigate the effect of different surfactants (anionic, cationic, non‐charged and zwitterionic) on the precipitation of cationic and anionic polymethylmethacrylate polymers (Eudragit). The surfactants effect has been investigated as a function of their concentration. Special attention has been dedicated to the CMC range and to the colloidal characterization of the formed dispersions. Moreover, the effect of salt (NaCl) and pH was also addressed. It is pointed out that non‐ionic and zwitterionic surfactants do not interact with charged Eudragit E100 and L100. For oppositely charged Eudragit E100/SDS and Eudragit L100/CTAB, precipitation occurs, and the obtained dispersions have been characterized in terms of particle size distribution and zeta potential. It was established that the binding of SDS molecules to Eudragit E100 polymer chains is made through the negative charges of the surfactant heads under the CMC value whereas binding of CTAB to Eudragit L100 chains is made at a CTAB concentration 5 times above its CMC. For Eudragit E100/SDS system, a more acidic medium induces aggregation. A same result was observed for the Eudragit L100/CTAB at a more basic pH. Moreover, it was observed that increasing salt concentration (higher than 100 mM) led to aggregation as generally observed for polycations/anionic surfactant systems.     

Influence of thermal annealing on the structural and optical properties of maghemite (γ‐Fe2O3) nanoparticle thin films

In this study, maghemite (γ‐Fe₂O₃) nanoparticles were initially synthesized via chemical co‐precipitation and then deposited by spray pyrolysis as thin films on white glass substrates. The thin films were annealed for 8 h at 400, 450, 500, 550, and 600 °C in an oven. The structural studies of maghemite nanoparticles were carried out using X‐ray diffractometer. Structural properties that we investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, SEM, and Energy dispersive X‐ray analysis (EDS). Optical properties of the samples were also investigated by ultraviolet‐visible (UV–vis) spectroscopy. The results showed that maghemite nanoparticles have crystalline structure with domain that increases in size with increasing annealing temperature. The optical band gap values were found to reduce from 2.9 to 2.4 eV with increase in annealing temperature. Copyright © 2015 John Wiley & Sons, Ltd.     

“蜡烛火焰划分”实验的局限成因分析及改进研究

人教版初中化学首个探究性实验"蜡烛及其燃烧"明确指出火焰的划分方法，但在实际教学中肉眼观察法和火柴梗燃烧法对蜡烛火焰的划分存在一定的局限性。采用文献研究法和实验验证法分析其局限性的成因——燃料的析炭能力强弱、材料结构的不同等，并提出相应的改进建议。     

Stable H and O isotope-based investigation of moisture sources and their role in river and groundwater recharge in the NE Carpathian Mountains,East-Central Europe†

The region situated between the mountain area and the lowlands in NE Romania (East-Central Europe) is experiencing increased competition for water resources triggered by a growing population, intensification of agriculture, and industrial development. To better understand hydrological cycling processes in the region, a study was conducted using stable isotopes of water and atmospheric trajectory data to characterize regional precipitation and vapour sources derived from the Atlantic Ocean, Mediterranean and Black Seas, as well as recycled continental moisture, and to assess and partition these contributions to recharge of surface and groundwater. Atmospheric moisture in the lowlands is found to be predominantly delivered along easterly trajectories, while mountainous areas appear to be dominated by North Atlantic Ocean sources, with moisture transported along mid-latitude, westerly storm tracks. Large-scale circulation patterns affect moisture delivery, the North Atlantic Oscillation being particularly influential in winter and the East Atlantic pattern in summer. Winter precipitation is the main contributor to river discharge and aquifer recharge. As winter precipitation amounts are projected to decrease over the next decades, and water abstraction is expected to steadily increase, a general reduction in water availability is projected for the region.     

Dislocation driven chromium precipitation in Fe-9Cr binary alloy: a positron lifetime study

The influence of initial heat treatment on anomalous Cr precipitation within high temperature solubility region of the Fe–9Cr alloy has been investigated using positron lifetime studies. Air-quenched samples with pre-existing dislocations exhibited a distinct annealing stage in positron lifetime between 800 and 1100?K corresponding to Cr-precipitation. During this stage, Transmission Electron Microscopy showed fine precipitates of average size 4 nm, dispersed throughout the sample and from Energy-dispersive X-ray spectroscopy (EDS) analysis they are found to be Cr-enriched. The presence of dislocations is found to be responsible for Cr precipitation.