Enhanced electrical properties related to structural distortion of CaBi2Nb2O9-based piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high Curie temperature piezoelectric ceramics with formula Ca_0.8-xSr_x(Li_0.5Ce_0.15Bi_0.35)_0.2Bi₂Nb_1.94Ta_0.04W_0.02O₉ were prepared by conventional solid-state reaction method. The effects of strontium substitution for calcium in CBN pseudo-perovskite structure A-site were systematically studied. Results showed that the addition of Sr²⁺ ions lead to an improvement of the tetragonality of lattice structure, which resulted in an enhancement of piezoelectric and ferroelectric properties together with high Curie temperature T_C and good resistance to thermal depolarization. The analysis of dielectric spectrums revealed that the space charge polarization induced an additional dielectric anomaly occurred below T_C. The composition with x = 0.025 showed good integrated performance, the piezoelectric coefficient d₃₃ and T_C were ~17.5 pC/N and ~917°C, respectively. Even though the as-studied ceramics underwent high depolarizing temperature reached up to 875°C, d₃₃ decreased by 8% merely. The remanent polarization 2P_r and the resistivity ρ at 650°C were on the order of ~10 μC/cm² and 3 × 10⁵ Ω cm, respectively.     

杂卤石溶解动力学

杂卤石中含丰富的钾资源,由于其化学上的难溶性和埋藏较深,尚未合理开发利用.已有研究表明,杂卤石矿层具备溶浸开采的地质基本条件.矿石中钾的溶解是杂卤石资源合理利用的技术关键.利用CaCl2水溶液为溶剂,通过测定溶浸液中钾、钙离子的浓度,考察了溶浸剂浓度、矿石粒度、温度对杂卤石表观溶解动力学过程的影响.实验条件下,矿石中钾的溶解率随粒度的降低明显升高.矿石粒度在0.149～1 mm之间,钾的溶解率可达80%以上.该溶解反应为一级反应（对CaCl₂而言）.计算实验条件下溶浸过程表观动力学速率常数,得溶解反应表观活化能为8.34 kJ•mol^-1,实验结果初步表明杂卤石溶解过程受内扩散控制,溶解动力学方程符合未反应核收缩模型,实验结论对地浸法提取钾具有理论参考意义.     

球形碳酸钙的控制合成研究

以硼酸为控制剂,氯化钙和碳酸钠为原料,采用共沉淀法制备了方解石型碳酸钙球形晶体。研究了控制剂浓度、反应温度、反应时间、反应物浓度等因素对碳酸钙粒径和形貌的影响。结果表明：在硼酸浓度为0.4 mol/L、氯化钙浓度为0.1 mol/L、20 ℃饱和碳酸钠溶液滴速为4.9 mL/min、反应时间为60 min、陈化时间为60 min、反应温度为50 ℃、氯化钙与碳酸钠物质的量比为1∶1条件下,制备的球形碳酸钙颗粒大小均匀,平均粒径为1.57 μm。     

Porous polyurethane film fabricated via the breath figure approach for sustained drug release

The breath figure (BF) method is an effective process for fabricating porous polymeric films. In this study, we fabricated porous polymer films from thermoplastic polyurethane (PU) through static BF with CHCl₃ as a solvent under 55–80% relative humidity. The porous PU films were prepared within various pore structures and sizes, which were adjustable, depending on the fabrication conditions. The humidity and exposure time were examined as variable parameters affecting the surface morphology, wettability, and cytotoxicity. Atorvastatin calcium, a hyperlipidemic agent, was loaded into the porous films during the casting process, and the drug-loading and drug-releasing behaviors of the porous PU membranes were evaluated. Approximately 60–80% of the drug was released in 14 days. The films exhibited sustained drug-release performances because of the hydrophobicity and nonbiodegradable nature of PU for perivascular drug administration. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47658.     

Heat propagation in thermally conductive polymers of PA6 and hexagonal boron nitride

Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant.     

Scaling of the bubble/slug length of Taylor flow in a meandering microchannel

In order to reduce or avoid the fluctuations from interface breakup, a meandering microchannel with curved multi-bends (44 turns) is fabricated, and investigations of scaling bubble/slug length in Taylor flow in a rectangular meandering microchannel are systematically conducted. Based on considerable experimental data, quantitative analyses for the influences of two important characteristic times, liquid phase physical properties and aspect ratio are made on the prediction criteria for the bubble/slug length of Taylor flow in a meandering microchannel. A simple principle is suggested to predict the bubble formation period by using the information of Rayleigh time and capillary time for six gas-liquid systems with average deviation of 10.96%. Considering physical properties of the liquid phase and cross-section configuration of the rectangular mcirochannel, revised scaling laws for bubble length are established by introducing Ca, We, Re and W/h whether for the squeezing-driven or shearing-driven of bubble break. In addition, a simple principle in terms of Garstecki-type model and bubble formation period is set-up to predict slug lengths. A total of 107 sets of experimental data are correlated with the meandering microchannel and operating range:0.001 < Ca_TP < 0.05, 0.06 < We_TP < 9.0, 18 < Re_TP < 460 using the bubble/slug length prediction equation from current work. The average deviation between the correlated data and the experimental data for bubble length and slug length is about 9.42% and 9.95%, respectively.     

Morphology of Palladium Thin Film Deposited on a Two-Dimensional Bilayer Aluminosilicate

Topics in Catalysis - The morphology of a thin palladium film deposited on bilayer Al0.35Si0.65O2/Ru(0001), previously proposed as a two-dimensional zeolite model, is investigated using a set of...     

表面活性剂改性磁性氧化石墨烯共价固定脂肪酶CRL

采用化学共沉淀法制备磁性氧化石墨烯（MGO）,直接在反应体系中加入Span系列表面活性剂,一锅法制备得到表面活性剂改性磁性氧化石墨烯（SMGO）。X射线衍射仪（XRD）、扫描电镜（SEM）和傅里叶变换红外光谱（FTIR）表征结果表明SMGO制备成功,且具有良好的磁分离性能。以1,5-戊二醛（GA）为交联剂,褶皱假丝酵母脂肪酶（CRL）为模型酶,共价固定CRL于SMGO载体上。Span40 MGO固定化酶酶活回收率为116.5%±1.7%,为MGO固定化酶的6倍;比活可达32.5U/mg,为游离酶的1.6倍;k_cat/K_m也有较大的提升,高于游离酶50%。储存稳定性及热稳定性得到提高,用于水解反应6批次后仍然保留73.6%的相对酶活力。初步分析认为MGO经改性后表面从亲水性转为强疏水性,使得共价固定化过程中同时发生疏水性界面活化,这是酶活性提高的原因之一。文章所报道的改性策略可为类似载体改性提供新思路。     

燃煤循环流化床锅炉急冷脱硫底渣作为水泥混合材的性能

针对循环流化床锅炉（CFB）底渣利用率偏低的问题,提出一种新的底渣处理应用方案——对底渣进行急冷处理后,将其作为脱硫剂或水泥混合材进行综合利用。本文通过搭建CFB锅炉底渣急冷实验系统,制备了不同渣温下的急冷底渣样品;然后选取亿利底渣和42.5标号的水泥作为研究对象,探讨了急冷底渣作混合材对水泥性能的影响。实验结果表明：急冷会破坏底渣颗粒形状,导致外壳成分发生变化。急冷处理不仅造成CaSO₄峰值显著降低,而且使得Ca(OH)₂的特征峰变强。在相同的CFB底渣掺比下,与原始底渣相比,急冷底渣作为水泥混合材时,虽然无助于提高抗折抗压强度,但能缩短凝结时间,减少安定性值。同时,还能减少水泥标准稠度需水量,提升水泥的密实程度,对水泥的力学性能和抗侵蚀性有着一定的积极作用。