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《中国稀土学报(英文版)》2019,37(7):760-766
A novel process of calcification-leaching for bastnaesite concentrate(REFCO_3) was proposed. The prior calcification was carried out in the system of NaOH-CaO-H_2O and the lgC-pH pattern for Ce-F-Ca-C-H_2O system was drawn. The thermodynamics result indicates that decomposition for bastnaesite requires certain alkaline condition, but excessive alkalinity also causes decomposition of CaF_2. XRD and SEM-EDS analyses on the calcification-leaching process reveal that bastnaesite first decomposes into RE(OH)_3 and CaF_2. Then, by HCl leaching rare earths were extracted,while CaF_2 was left in the leaching residue. In addition, effects of temperature, time, NaOH and CaO on the calcification were investigated. The results show that the leaching rate of rare earths(REs)reaches 72.5 wt%, at the same time 99.2 wt% of F is left in leaching residue with 20 wt% NaOH and 38 wt% CaO at 493 K for 180 min. 相似文献
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研究了一种宽阻抗带宽和宽圆极化轴比带宽的缝隙螺旋天线。天线印制在由FR4介质基板构建的方形柱状结构的内外表面,两组长短不同的缝隙螺旋臂印制在介质基板外表面并延伸至天线顶部;一条弯折的微带线作为馈电网络印制在介质基板内表面,通过对各缝隙耦合馈电,实现天线宽阻抗带宽和轴比带宽。实测结果表明:天线尺寸为0.111λ0×0.111λ0×0.221λ0(λ0为北斗B2中心频率1.207 GHz对应的自由空间波长),S11≤-10 dB的阻抗带宽为1.158~1.778 GHz,轴比≤3 dB的圆极化带宽为1.133~1.918 GHz。该天线采用缝隙螺旋结构,通过简易的馈电网络实现天线小型化和宽频带特性,在卫星导航系统中具有较好的应用前景。 相似文献
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在连续导通模式下,图腾柱无桥拓扑结构功率因数校正器(PFC)的损耗非常大,导致拓扑结构的效率降低,在输入电压过零点处电流容易发生畸变。针对此问题,提出了一种改进的过零点控制方法。将输入电压过零时段划分为两个控制阶段,即高频桥臂主开关管完成软启动,采用双极控制方法有效校正输入电流,使其跟随输入电压。搭建一台1 kW实验样机,并利用DSP开发板进行实验验证。测试结果表明,当开关频率为100 kHz时,功率因数为0.99,PFC模块效率最大可达98.5%,总谐波失真在输出功率大于200 W时小于3%。 相似文献
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提出一种快速、简便、高效的眼底血管分割方法。分析眼底图像的灰度值分布和对比度变化,利用匹配滤波克服背景干扰,消除噪声影响,达到灰度均衡,实现眼底图像的亮度归一化。估计眼底图像中背景像素所占比例,利用直方图自动选择阈值,完成对眼底图像中血管的有效分割。在公开的眼底图像数据库上进行测试,该方法对眼底血管分割具有较好的性能指标。实验表明,提出的基于匹配滤波和阈值优化的眼底血管分割方法,准确率高、复杂度低,对眼科疾病的计算机辅助诊断有一定的实用价值。 相似文献
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Kai Shen Mingxiang Jiang Xinwei Yang Weizhong Zhou Qiguang Dai Xingyi Wang Li Wang Yun Guo Yanglong Guo Wangcheng Zhan 《中国稀土学报(英文版)》2023,41(4):523-530
The cerium-based catalysts were investigated for the catalytic co mbustion of trichlo roethylene(TCE) and exhibit a surprising catalytic activity.MnOx was doped into CeO2 by a citric acid(CA) sol-gel method,and the effect of Mn content on the physicochemical properties and catalytic activities of MnOx-CeO2 mixed oxides was investigated systemically.The introduction of MnOx into CeO2 can evidently improve the catalytic activity and... 相似文献
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《International Journal of Hydrogen Energy》2019,44(47):26076-26099
Being a clean source of energy, hydrogen gas is in high demand in various industrial and commercial applications. However, the explosive nature of H2 gas above 4% concentration makes it highly dangerous to store, transport and use. Further, the small size gas molecules of H2 are prone to leak through the smallest possible holes and cracks. Hence, the detection of H2 gas becomes essential even at trace levels. This article reviews various gas sensing strategies including methods, materials, and integrated systems available for the sensitive detection of H2 gas for a bunch of different applications. The article also reviews some approaches which are available in the literature to detect parts per billion (ppb) level of H2 gas concentrations. This review article aims at explaining the different aspects of H2 gas sensing technology in a simple yet exhaustive manner. 相似文献
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《International Journal of Hydrogen Energy》2020,45(53):28437-28446
Exploiting efficient and stable noble metal-free hydrogen evolution catalysts for water splitting is of great importance. In this work, NixCo1-xO@C/CdS hybrid is successfully fabricated through an electrostatic interaction of oppositely charged nanoparticles on their surfaces. The resulting NixCo1-xO@C nanoboxes cocatalysts which were derived from NiCo-LDH@ZIF-67 with Ni–Co layered double hydroxides (LDH) decorated with ZIF-67 precursor exhibited improved hydrogen production rate compared with bare CdS semiconductor from 0.7 mmol g−1 h−1 to 56 mmol g−1 h−1. It is demonstrated that the electrostatic interaction between the two surface charged nanoparticles of NixCo1-xO@C and CdS play an important role in migrating and separating of photogenerated charge carriers. The synthesized NixCo1-xO@C as excellent candidates for cost-effective cocatalysts is aimed to substitute for noble metals in photocatalytic H2 evolution. 相似文献
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The Pd and PdBi nanoparticles dispersed on the reduced graphene oxide (Pd/rGO and PdBi/rGO) have been synthesized through one-pot reaction under the irradiation of microwave and the obtained composites have been characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and their electrocatalytic activities have also been evaluated. It is found that the PdBi0.05/rGO catalyst exhibits higher activity and better stability toward formic acid electrooxidation compared with Pd/C and Pd/rGO. The excellent electrocatalytic performance indicates that the addition of appropriate amount of Bi can greatly enhance the activity and stability of Pd catalysts for the formic acid oxidation. 相似文献