化学气相沉积低温热解炭的微观组织结构与沉积模型

利用扫描电子显微镜(SEM),透射电子显微镜(TEM)结合选取电子衍射(SAED)研究了化学气相沉积低温热解炭的微观组织结构。结果表明:低温热解炭是由直径小于2μm的球形颗粒状炭组成,该球形颗粒状炭的核心是炭黑颗粒,外层为中织构热解炭。其沉积过程主要经历了:微小炭黑颗粒的萌生,炭黑颗粒外层的生长,炭颗粒表面热解炭的沉积和炭颗粒的聚集长大四个过程。     

化学气相沉积与渗透过程中热解炭织态结构生成机理研究

为研究热解炭织态结构的生成规律，采用不同压强的甲烷为碳源，在1100℃条件下进行了化学气相沉积和化学气相渗透实验。化学气相沉积以具有不同表面积／自由体积比（[A／V]值）的直通方形多孔陶瓷为基体；化学气相渗透实验在直径为1mm细直孔内表面沉积和对炭纤维体积分数为7％的炭毡进行致密化。借助正交偏光显微镜（消光角）和透射电子显微镜（定向角）对在不同实验条件下制备的热解炭进行分析和定量表征。研究发现：热解炭的织态结构可以在两种不同的沉积条件下形成。当甲烷压强较低时为化学生长阶段；当甲烷压强较高时为物理形核阶段。在化学生长控制阶段，热解炭的织态结构可以利用之前提出的“颗粒填充模型（P-F模型）”加以解释。该模型假设高织构热解炭的沉积一定对应于气相中存在具有合适比例的芳香化合物（例如苯）和线性小分子（主要是C2H2），当二者的浓度比偏离该最优比（或者偏大，或者偏小），均将导致中织构甚至低织构热解炭的生成。在化学生成控制阶段，化学气相沉积和化学气相渗透对热解炭织态结构影响的差别，除了[A／V]值而外，还有氢气的作用。在化学气相渗透过程中，基体内部生成的氢气快速扩散至基体表面，使内外沉积速率和织态结构均发生较大变化。     

化学气相沉积低温各向同性热解炭微观结构及沉积机制

为了研究低温各向同性热解炭（LTIC）的微观结构及沉积机制,采用不同体积分数的丙烷为碳源,在不同的沉积温度下进行稳态流化床化学气相沉积实验制备LTIC,借助SEM和TEM对不同沉积条件下制备的LTIC微观结构进行表征和分析。结果表明:不同沉积条件下制备的LTIC由类球形颗粒状和片层状炭结构组成,沉积温度升高,降低了热解炭在气相中的形核势垒,LTIC中类球形颗粒数量增多,尺寸变小,且类球形颗粒内包围炭黑颗粒的炭层织构逐渐降低;丙烷体积分数升高,热解炭沉积过程逐渐由以表面生长机制为主转变为以气相形核机制为主,所制备的LTIC中类球形颗粒形貌越来越明显,而片层状炭结构逐渐减少甚至完全消失。      

Fe催化PAN炭纤维原位生长纳米炭纤维

为了研究气相生长纳米炭纤维在炭／炭复合材料制备中的应用，采用均热式化学气相沉积技术，以针刺PAN炭纤维薄毡为基体，二茂铁为催化剂前驱体，丙烯为炭源，氮气为载气，在炉压1．0kPa-1.3kPa，沉积温度880℃、920℃下进行了Fe催化PAN炭纤维原位生长纳米炭纤维的实验。经不同时间沉积后的样品在扫描电镜（SEM）下进行观察，发现880℃时沉积4h后在PAN炭纤维周围生成大量的原位生长纳米炭纤维，而在920℃时因催化剂失效导致热解炭对Fe催化剂颗粒包覆，形成颗粒状热解炭。     

丙烯热解炭过程的气相产物分析和动力学研究(英文)

以丙烯为碳源,在700℃～1200℃进行化学气相沉积热解炭。采用气相色谱和质谱联用对反应过程中的气体产物进行定性和半定量分析,采用磁悬浮天平实时称量反应过程中的固相产物进行动力学研究,在此基础上提出丙烯分解形成热解炭的机理。气相产物的分析结果表明:丙烯热解过程产生30多种芳香化合物,随着温度的升高,主要反应生成物由萘转变为苯;动力学研究结果表明,800℃～1000℃的活化能为137±25kJ/mol,生成乙炔的基元反应控制固相产物的形成。当温度高于1000℃时,沉积行为由气相分子通过边界向固相表面扩散和气相成核共同控制,形成热解炭的主要物质逐渐由苯转变为不饱和碳氢化合物如乙烃,乙烯等。     

乙酰丙酮铁为催化剂源在碳纤维表面生长碳纳米管的工艺研究

以乙酰丙酮铁为催化剂源,三甘醇为溶剂,通过溶剂热法在碳纤维表面负载催化剂前驱体,在H2与N2中一定温度下进行还原,采用化学气相沉积法在碳纤维表面生长碳纳米管。研究了催化剂的负载条件和碳纳米管的生长条件,采用XRD、FTIR、RAMAN对乙酰丙酮铁在三甘醇中反应在碳纤维表面负载催化剂前驱体产物进行分析,用SEM、TEM对催化剂前驱体粒子及碳纳米管的形貌进行表征。结果表明:催化剂前驱体为粒径30nm左右的Fe3O4颗粒,当催化剂的还原温度为415℃、还原时间为60min时,Fe3O4颗粒还原成纳米Fe颗粒;当碳纳米管的生长温度为750℃、生长时间为30min、气流体积比为V(N2)∶V(H2)∶V(C2H2)=50∶10∶10时能在碳纤维表面生长出形貌均一、管径为30~60nm的碳纳米管。     

溴插层热解炭的制备

采用液相法对化学气相沉积热解炭进行溴插层,插层工艺为溴炭质量比6:1,反应温度20℃,反应时间48h.采用XRD、SEM和XPS手段对制备的产物进行分析表征.结果表明:插层后,热解炭的XRD图谱有新的衍射峰出现,表明有新物质生成;SEM图显示溴元素以非单质状态均匀分布在热解炭中;XPS结果进一步证实热解炭中溴元素和碳元素为化学键键合.     

以丙烯为碳源气的热解炭的制备及其沉积机理分析

以等温法进行化学气相沉积(CVD),研究了过程参数(反应温度、碳源气浓度以及炉内气体的滞留时间)对热解炭结构的影响.实验表明,以丙烯为碳源气,保持炉内气体的流动为层流运动方式,在中等温度(880℃)、中等滞留时间(2.19s)以及碳源气与载气体积比为1:3时,能得到粗糙层(RL)结构的热解炭;碳源气裂解为小分子后,在气相中通过加成、聚合、脱氢环化等反应生成苯及含有六元环的芳香烃,才能沉积得到结构较好的热解炭.     

人工心瓣热解炭涂层的密度和孔隙结构研究

研究了人工心瓣热解炭涂层的密度和孔隙结构。采用准稳态流化床化学气相沉积工艺制备出人工心瓣用高密度各向同性热解炭涂层,利用密度计、扫描电镜、透射电镜、压汞仪等分析了热解炭涂层的密度和孔隙结构。结果表明:高密度各向同性热解炭的孔隙主要是由类球形生长特性间0.83μm左右的较大孔隙和62nm左右的中等孔隙以及类球形生长特性内缠结体结构所形成的微孔隙构成,缠结体之间形成的微孔隙能够导致热解炭密度的降低,热解炭类球形颗粒的多少也会对高密度各向同性热解炭的密度造成影响。     

纳米球形炭的无催化化学气相沉积制备及其机理研究（英文）

以天然气为碳源,氢气为载气,通过无催化化学气相沉积的方法,合成不同粒径的球形炭。研究了沉积温度、压力和气体比例对化学气相沉积球形炭的影响。用X射线衍射、扫描电子显微镜和透射电子显微镜对实验结果进行表征。研究结果表明制备纳米球形炭(50~100 nm)的优化工艺为沉积温度1150℃、沉积压力5kPa和天然气/氢气(气体流量比)1∶4。本研究对球形炭的气相沉积机理进行了详细的研究。沉积温度对球形炭的尺寸和微结构影响较小,沉积压力对炭核的碰撞几率影响较大。另外,氢在炭形核过程中起来很重要的作用,氢的存在有效的较少了炭核的碰撞几率。     

铁矿石中全铁含量的测定-EDTA滴定法

本文提出用EDTA络合滴定法取代经典的K2Cr2O7法测定铁矿石中全铁含量.避免因经典法加入饱和HgCl2溶液而造成环境污染.有害人的健康。本文报道的测定方法操作简便,结果准确。     

Computer model simulation study of nanocrystalline iron

This paper provides a computer modelling technique, associated with the molecular statics relaxation method, for the study of nanostructured crystals. Atomistic simulations have been carried out to study the structural features of nanocrystals, such as the reduced mass density, the boundary component proportion, the excess lattice parameter, the excess atomic volume and the radial distribution function. The energy and elastic properties also have been investigated. The simulated results have shown considerable agreement with the experimental results, which implies that the present modelling method is suitable to be used to study the structures and properties of nanocrystals.     

Design of a neutral electro-Fenton system with Fe@Fe(2)O(3)/ACF composite cathode for wastewater treatment

The narrow pH range limits the wide application of Fenton reaction in the wastewater treatment. It is of great importance to widen working pH range of Fenton reaction from strong acidic condition to neutral, even basic ones. In this study, for the first time nanostructured Fe@Fe(2)O(3) was loaded on active carbon fiber (ACF) as an oxygen diffusion cathode to be used in a heterogeneous electro-Fenton (E-Fenton) oxidation system. This novel Fe@Fe(2)O(3)/ACF composite cathode was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and element mapping. On the degradation of dye pollutant rhodamine B in water, this heterogeneous E-Fenton system with the Fe@Fe(2)O(3)/ACF cathode showed much higher activity than other E-Fenton systems with commercial zero valent iron powders (Fe(0)) and ferrous ions (Fe(2+)) under neutral pH. On the basis of experimental results, we proposed a possible pathway of rhodamine B degradation in this heterogeneous Fe@Fe(2)O(3)/ACF E-Fenton process. This heterogeneous E-Fenton system is very promising to remove organic pollutants in water at neutral pH.     

Triton X-100-5-Br-PADAP分光光度法选择性测定乳粉中微量铁

报道了以2-(5-溴-吡啶偶氮)-5-二乙氨基酚(5-Br-PADAP)为显色剂,应用分光光度法高选择性测定铁(Ⅲ)的新方法。实验结果表明,在pH4.0的乙醇介质中和Triton X—100、盐酸羟氨存在下,以746nm为测定波长,可选择性测定铁(Ⅲ)含量。本法线性范围为0～1.3μg/ml,表观摩尔吸收系数为2.94×10~4L·mol~(-1)·cm~(-1),批内和批间精密度cv%分别为1.2%、2.3%,平均回收率为98.9%。已用于乳粉中微量铁的直接测定,常见共存成分对测定无干扰。     

Research and Prospects of Iron‐Based Superconductors

The discovery of a new superconductor, LaFeAsO_1?xF_x with a superconducting critical temperatureT,_c, of 26 K in 2008, has quickly renewed interest in the exploration of iron‐based superconductors. More than 70 new superconductors have been discovered within several months, with the highest T_c of up to 55 K being observed in the SmFeAsO_1?x compound. High T_cs have previously only been observed in cuprates; these new iron‐based superconductors have been added as second members of the high‐T_c family. The crystal structure of these compounds contains an almost 2D Fe–As layer formed by FeAs₄ tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe–As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100–200 K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high‐T_c materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron‐based high‐T_c family.     

Fabrication of Lotus‐Structured Porous Iron by Unidirectional Solidification under Nitrogen Gas

A novel technique has been developed to fabricate lotus‐structured porous iron in which long cylindrical pores are aligned in one direction. The iron is melted and unidirectionally solidified in a pressurized gas mixture of nitrogen and argon. The process involves the dissolution of nitrogen in molten iron and the evolution of nitrogen pores due to the decrease in solubility of nitrogen during solidification. The porosity is controlled by adjusting the partial pressures of nitrogen and argon during melting and solidification. The nitrogen concentration in solid iron increases with increasing partial pressure of nitrogen at a given total pressure, leading to improvement of the mechanical properties of the porous iron.     

FeCuCrC粉末冶金材料性能研究

在烧结铁基材料FTG70Cu3 3 5的基础上 ,以铬铁合金粉的形式引入铬元素 ,制备了FeCuCrC材料。考察了铬元素含量及烧结温度对该材料力学性能、密度的影响 ,并探讨了其强化机理