Preparation and Electrochemical Lithium Intercalation Performance of Segmented Carbon Nanofibers

以泡沫镍为催化剂 ,在 6 0 0和 70 0℃下 ,以CVD法热解乙炔气体制备大量的纳米碳纤维 .随着制备温度增加 ,纳米碳纤维直径变小 ,竹节状含量减少 ,d0 0 2 值减小 ,微晶片层平面Lc 和La 值增大 ,碳材料的可逆容量则下降 .分别用透射电镜、X射线衍射和拉曼光谱观察和测定了纳米碳纤维的形貌、微结构 ,发现在不同条件下生长的纳米碳纤维有不同的形貌和结构 .对纳米碳纤维的电化学嵌锂性能的研究表明 ,纳米碳纤维的结构对其电化学嵌锂容量和充放电循环寿命起重要影响 ,制备温度越低 ,纳米碳纤维的石墨化程度越差 ,可逆嵌锂容量相应要高一些Segmented carbon nanofibers were prepared by pyrolysis of acetylene on foam Ni at 600 and 700℃ in a fixed bed flowed-reactor. The morphology, microstructure and lithium insertion properties of these carbon nanofibers were investigated by TEM, XRD, Raman and electrochemical methods. Through TEM observations, it was found that this kind of carbon nanofibers was composed of lens-like segments with nearly equal separation stacking along the nanofiber axis. When the reaction temperature was 600℃, segmented carbon nanofibers were the major production. However, when the reaction temperature increased to 700 ℃, the content of segmented carbon filaments decreased and their diameter became smaller. The crystallite size d 002 and L c were determined by the 002 carbon Bragg peak of XRD patterns using the Bragg and Scherrer formulas. The intensity ratios of the 1350 cm -1 line and the 1580 cm -1 line (R=I D/I G) was used to evaluate the L a value, which was inversely proportional to the effective crystallite size in the direction of the graphite plane (L a). With the reaction temperature increased, the d 002 value decreased, L a and L c values increased, which indicated the degree of crystallinity increased. Segmented carbon nanofibers were used as positive electrodes of C/Li cells. The first charge capacities of C/Li cells were 480 and 300 mAh/g for samples produced at 600 and 700℃, respectively. The samples at 600℃ showed capacities higher than the theoretical value of graphite, which was attributed to accommodation of more lithium at the edge of graphene layers and on the surface of graphene layers according to the mechanisms of lithium insertion in carbons prepared by low-temperature pyrolysis of hydrocarbons. As confirmed by the XRD and Raman spectra, the samples at 700℃ had larger L a and L c, which led to the capacity decreasing.国家自然科学基金 (6 0 2 710 0 9);; 浙江省自然科学基金 (5 0 110 9,2 0 0 0 5 3)资助项

Preparation and electrochemical lithium intercalation performance of segmented carbon nanofibers

Segmented carbon nanofibers were prepared by pyrolysis of acetylene on foam Ni at 600 and 700degreesC in a fixed bed flowed-reactor. The morphology, microstructure and lithium insertion properties of these carbon nanofibers were investigated by TEM, XRD, Raman and electrochemical methods. Through TEM observations, it was found that this kind of carbon nanofibers was composed of lens-like segments with nearly equal separation stacking along the nanofiber axis. When the reaction temperature was 600degreesC, segmented carbon nanofibers were the major production. However, when the reaction temperature increased to 700degreesC, the content of segmented carbon filaments decreased and their diameter became smaller. The crystallite size d(002) and L-c were determined by the 002 carbon Bragg peak of XRD patterns using the Bragg and Scherrer formulas. The intensity ratios of the 1350 cm(-1) line and the 1580 cm(-1) line (R =I-D/I-G) was used to evaluate the L-a value, which was inversely proportional to the effective crystallite size in the direction of the graphite plane (L-a). With the reaction temperature increased, the d(002) value decreased, L-a and L-c values increased, which indicated the degree of crystallinity increased. Segmented carbon nanofibers were used as positive electrodes of C/Li cells. The first charge capacities of C/Li cells were 480 and 300 mAh/g for samples produced at 600 and 700degreesC, respectively. The samples at 600degreesC showed capacities higher than the theoretical value of graphite, which was attributed to accommodation of more. lithium at the edge of graphene layers and on the surface of graphene layers according to the mechanisms of lithium insertion in carbons prepared by low-temperature pyrolysis of hydrocarbons. As confirmed by the XRD and Raman spectra, the samples at 700degreesC had larger L-a and L-c, which led to the capacity decreasing

太阳能平移式喷灌机行走驱动系统配置与性能研究

对太阳能平移式喷灌机的行走驱动系统进行方案设计与理论计算，比较不同工况下喷灌机行走所需驱 动功率，确定机组在不同工况下的驱动电机选型与光伏配置。该研究以一日累计作业时间为太阳能驱动平移式喷灌 机的技术评价指标，预测陕西关中及宁夏地区晴天和阴天或雾霾天气下的机组续航能力；并得到各工况下喷灌机行 走速度和行走坡度与一日累计工作时间的关系：一日累计作业时间随机组运行速度的提高与爬坡角度的增大而降 低；相同工况下，晴天一日累计作业时间为阴天或雾霾天气的１．５倍。研究结果表明，以独立光伏发电系统作为平移 式喷灌机的驱动能源是可行的，能够满足机组日常行走作业的需求。该研究结果可为太阳能平移式喷灌机行走驱动 系统方案设计提供参考。</p

PARTICLE DYNAMICS IN THE EUPHOTIC ZONE Ⅵ.THE UTILITY OF TRACER ~(234)Th FOR STUDYING PARTICLE DYNAMICS IN THE UPPER WATER COLUMN OF THE NORTHEASTERN SOUTH CHINA SEA

利用234Th－238U不平衡研究南海东北部海域3个站位上层水体中的颗粒动力学性质，测定了水往中溶解态及颗粒态234Th的比活度，具体讨论各相中234Th／238U）AR（放射性活度比）比值的垂直分布情况及其与水化学要素间的关系。运用稿态箱式模型计算出各站位不同水层中溶解态234Th相对于清除至颗粒物的平均停留时间和颗粒态234Th相对于迁出作用的停留时间。由模型得出的参数表明3个站位的真光层具有两种不同的层化图像，这一情形与我们在南沙群岛海域得到的结果相一致。结合POC／PTh比值，估算出3个站位从真光层输出的颗粒有机碳（POC）通量分别为4.025.0和5．4mmolC·m－3－d-1。文中进一步讨论了234Th与POC两者停留时间的关系。 【英文摘要】 The disequilibrium between the particle -reactive tracer 234 Th (T1/2=24. 1d)and its soluble parent, 238U, was used to study the particle dynamics at three stations in the northeastern South China Sea. Profiles of dissolved and particulate 234Th in the upper 500m and a steady state box model were used to quantify dissolved 234Th scavenging and particle removal rates. Some valuable biogeochemical information have been gained by combination with the profiles of nutrients (NO-3 NO-2, SiO2-3,PO3-2), S, T, DO, T...国家自然科学基金!4945600l,4937627

THE DISTRIBUTION OF ~(226)Ra IN THE SURFACE WATER OF THE NORTHEASTERN SOUTH CHINA SEA

报道1994航次南海东北部的226Ra。利用Mn－纤维富集海水中的Ra同位素，采用Mn－纤维直接射气法测量226Ra的比活度，228Ra的比活度采用228Ac的β计数法测量。研究海区226Ra的放射性比活度范围为0．62－1．17Bq·m-3,228Ra／226Ra）A.R介于2.78－4.59。226Ra的表层比活度分布大致表现为该海区东北部较高，中南部也有一较大值，表明陆源物质对这两个区域水体中的226Ra的贡献很大，其它区域分布较均匀。表层228Ra／226Ra）AR分布为靠近珠江口和西南区较高。此外，还将本航次的结果与该海区1992年春季航次的结果进行了比较。 【英文摘要】 226Ra in the northeastern South China Sea during a crinse in 1994 has been reported in this paper. Radium isotopes in seawater were concentrated by Mn-fibre. 226 Ra activity was measured by Mn-fibre direct emanation while 228 Ac β-counting method was applied to determine are Ra activity. ase Ra radioactivity in the studied area ranged from 0.62 to 1.17 Bq - m-3 with 228 Ra /226Ra )A R between 2.78 and 4.59. The distribution of 226 Ra specific activities in surface waters approalmately show that there are h...国家自然科学基金!49456001;;高等学校博士学科点专项科研基

A STUDY ON HORIZONTAL EDDY DIFFUSION IN THE SURFACE WATER OF THE NORTHEASTERN SOUTH CHINA SEA BASED ON ~(228)Ra TRACER

研究了1994年8－9月南海东北部表层海水中228Ra的分布特征。采用Mn－纤维富集海水中的Ra同位素，通过其子体228Ac的β计数法来测量228Ra。表层海水中228Ra的放射性比活度从2．48Bq·m－3变化到4.47Bq·m－3，平均值为3.24Bq·m－3。228Ra的水平分布表现为调查海区东北部比活度较高，这与该航次的226Ra的分布特征相一致。根据各断面的228Ra放射性比活度与离岸距离之间的负相关关系，计算了它们所对应的水平涡动扩散系数，并讨论海域的地貌特征对228Ra比活度分布的影响。这些研究结果对表层水体的混合、交换，尤其是可溶性污染物的迁移、扩散以及海域的自净作用的研究都具有实际意义。 【英文摘要】 The distribution of 228 Ra in the surface water of the northeastern South China Sea during 1994 cruise was studied. Mn-fibre was used to concentrate radium isotopes from the sea water and are Ra activity was measured through β-counting of 228Ac. 228Ra specific activity in the surface water varied from 2.48 to 4.47 Bq' m-3,averaging 3.24 Bq' m-3. The horizontal distribution of 228 Ra showed that greater specific activity appeared in the northeastern part of this studied area, which is similar to that of 226 ...国家自然科学基金!49456001;;高等学校博士学科点专项科研基

铁路灯光信号显示的一些研究

&lt;正&gt; 铁路色灯信号不论在白天或夜间都指挥着列车的运行,其显示好坏直接关系到列车的安全和效率。影响色灯信号显示的因素很多,如光源参数,光系统结构,灯光散角,天气好坏等。而色灯信号的颜色,观察距离(或视张角)以及亮对比度是人对信号识别的三个较重要因素,所以我们想从这三个方面来讨论信号灯光显示问题。</p