New insight into the formation and oxygen barrier mechanism of carbonaceous oxide interlayer in a multicomponent carbide

Early transition metal carbides are considered to be superior candidate materials for oxidizing environments at temperatures exceeding 2000°C. Generally, the remarkable oxidation resistance is largely attributed to a carbonaceous oxide interlayer (eg, Hf–O–C, Zr–O–C, and Ta–O–C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and TaC), acting as the primary oxygen barrier. However, the oxygen barrier mechanism of the carbonaceous oxide interlayer remains unclear. Herein, through studying the oxidation behavior of a novel multicomponent carbide Hf_0.5Zr_0.3Ti_0.2C in oxidizing environments up to 2500°C, the oxygen barrier mechanism of the carbonaceous oxide was recently revealed. We found that the oxygen barrier resulted from the slow oxygen diffusion through the inner grains of Hf-Zr–Ti–O due to the presence of carbon formed at the grain boundaries because of the existence of compact external oxide layer, beneath which the Hf–Zr–Ti–O–C interlayer possesses much lower oxygen activity and temperature that allow carbon to exist stably. This as-formed carbon strongly retarded the fast diffusion of oxygen along the grain boundaries of oxides. Additionally, desirable synergisms of the designed multicomponent system, particularly, the outward short-circuit diffusion of Ti, lead to the self-healing of the external oxide layer, evidently enhancing integral protection performance against oxidizing environments.     

Preparation of Docosahexaenoic Acid-Rich Diacylglycerol-Rich Oil by Lipase-Catalyzed Glycerolysis of Microbial Oil from Schizochytrium sp. in a Solvent-Free System

Docosahexaenoic acid (DHA)-rich diacylglycerol (DAG)-rich oil was prepared by lipase-catalyzed glycerolysis of microbial oil from Schizochytrium sp. in a solvent-free system. The reaction parameters including lipase type, substrate molar ratio, temperature, lipase concentration, and reaction time were screened. The selected conditions were determined as follows: Novozym® 435 (Novozymes A/S, Bagsvaerd, Denmark) as biocatalyst at 8 wt%, substrate ratio (DHA-rich microbial TAG/glycerol) of 1:1 mol/mol, temperature of 50 °C, and reaction time of 12 hours. Under these conditions, the triacylglycerol (TAG), DAG, and monoacylglycerol (MAG) contents in the product were 36.4%, 48.2%, and 15.4%, respectively. The lipase was reused successively for 18 cycles without significant loss of activity under the conditions given above. Fatty acid composition analysis of the final product showed that the contents of DHA in TAG, DAG, and MAG were 53.9%, 44.9%, and 34.8%, respectively. DHA-rich DAG has the potential to be used as an ingredient in infant formula to increase the bioavailability of DHA.     

石墨炉原子吸收光谱法测定水中钒、钴、钼

本文主要介绍石墨炉原子吸收法测定水中钒、钴、钼的方法。本方法采用美国PE公司配有自动进样器的5100ZL塞曼光谱石墨炉原子吸收分光光度仪。在测定浓度范围内,V、Co、Mo的峰面积和质量浓度呈线性关系,相关系数均大于0.99,回收率在91%-104%之间,相对标准偏差在3.4%-7.0%之间。     

彩色沥青混合料的生产

将现行彩色沥青混合料的生产工艺与传统生产工艺进行对比,介绍自行设计的彩色沥青混合料生产设备组成及结构特点,总结了彩色沥青混合料的生产经验。     

BP神经网络在工程机械液压系统故障诊断中的应用研究

将BP神经网络理论应用于工程机械液压系统故障诊断中进行研究,通过系统数据的采集、特征向量的提取和分类器的构造,在对网络进行训练的基础上,建立了学习算法,通过试验可以看出神经网络能给出的满意结果。     

羟丙基甲基纤维素增韧水泥胶浆的配合比试验研究

羟丙基甲基纤维素溶液作为一种改性剂,掺入水泥胶浆中用于改善其韧性.采用正交试验研究了水胶比、纤维素溶液浓度和掺量对水泥胶浆的抗折强度、抗压强度及折压比的影响,并获得了最佳配合比.用单因素分析研究了减水剂和纤维素对强度和折压比的影响,以及纤维素对凝结时间的影响.最终结果表明羟丙基甲基纤维素可以改善水泥胶浆的韧性并对凝结时...     

锰酸锂的制备及其在中性电解液中的电容性能

用高温固相法合成尖晶石型锰酸锂(LiMn2O4)电极材料.X射线衍射结果表明:800 ℃下得到纯的尖晶石型LiMn2O4样品.利用恒流充放电、循环伏安和交流阻抗等测试方法研究LiMn2O4在2 mol/L(NH4)2SO4溶液中的电容性能.结果表明:LiMn2O4电极材料在中性电解液中有较好的电容性能,电极的充放电曲线基本呈线性关系,比容量可达90F/g.电极经500次循环后容量并无衰减,具有极好稳定性.交流阻抗结果显示:LiMn2O4电极材料在2mol/L(NH4)2SO4溶液中内阻仅为0.3Ω.     

X60管线钢再结晶和过冷奥氏体连续冷却相变行为的研究

利用双道次压缩试验,在Gleeble-1500热模拟机上测定了X60管线钢的静态再结晶曲线.利用膨胀法,结合金相法,测定了X60不同冷却速度下连续冷却转变的膨胀曲线,获得了该钢的连续冷却转变曲线(动态CCT曲线);研究了X60管线钢的连续冷却过程中奥氏体转变过程及转变产物的组织;另外,通过对再结晶和CCT曲线的分析,为现场的控轧控冷工艺的制定提供了参考依据.     

城市滨水地区特色的规划探索--以台州市黄岩区西江河滨水地区城市设计为例

台州市黄岩区西江河滨水地区城市设计功能定位为体现黄岩当地风土人情的历史文化长廊、城市休闲活动的载体等.规划确立"历史的环""现实的环"两个主题,通过强调滨水空间的共享性与渗透性、历史文化遗迹的保护和再现、水的利用与多样化的岸线设计,以及市政道路的线型调整等实现滨水地区的复兴.     

论构筑我国城市总体规划改革的法制化框架

近几年来,"概念规划""战略规划"等规划类型在我国各城市中不断出现,由此引发了规划界对城市总体规划改革的探讨.应从加强城市规划和管理的法制化、树立法律意识的角度,构筑城市总体规划改革的法制化框架,即基于已有法律,尽快对区域规划进行立法,将"概念规划""战略规划"等规划类型纳入法制轨道,建立信息反馈、法律监督评价和责任追究机制.