Kinetics of Fe_3O_4 formation by air oxidation

1　INTRODUCTIONFe3O4 hasanumberofnovelpropertiesandper formances ,itsuniquemagnetic ,thermalandtribolog icalpropertiesmakeitanewtypeofmaterialspromis inginvariousapplicationssuchaspigment,toner ,in formationstorage ,ferrofluids ,bioprocessing ,elec tronicsandcatalyst[1,2 ] .Owingtothewideapplica tion ,majorityofresearchersfocusedontheprepara tionmethodsofmagnetite[310 ] ,however ,themech anismandkineticsofFe3O4 formationwerescarcelystudied .Thekineticsandmechanismofoxyhydrox idesformatio…     

底液对石灰水法制备氢氧化镁沉降性能的影响

以氯化镁为镁源,石灰水为沉淀剂,分别采用正向、反向、双向和双向底液4种滴定方式制备氢氧化镁,其中双向底液合成方式最佳.研究了氯化钙底液浓度、体积对氢氧化镁沉降性能的影响.研究表明,氯化钙溶液质量分数为15 ％、溶液体积为50mL时,氢氧化镁沉降性能最佳.研究了不同反应体系活度积对氢氧化镁沉降性能的影响,结果表明,氯化钙溶液质量分数和体积的增加都有利于反应体系过饱和度的降低.     

核电反应堆厂房钢穹顶预制测量定位

钢衬里穹顶为不等半径弧形结构,由分块板块拼装成型,结构位置控制是难点,通过场地中心点设置、建立平面（高程）加密控制网、后方交会设站、测量检查点位三维坐标、反算等技术综合运用,并利用计算器编程换算,有效保证了穹顶钢衬里位置的精度,解决了复杂立体结构施工测量中的定位问题。     

腐蚀监测用探头的研究

研制了Ａｇ／ＡｇＣｌ固体参比电极,并讨论了影响电极稳定性和温度系数的因素,同时制备了以固体参比电极为基础,中心嵌入与研究对象同材质的金属电极作为研究电极,外层以不锈钢作辅助电极的腐蚀监测探头。该探头可用于低阻和高阻介质的电化学测量。     

Asymmetric synthesis of 3β-acetoxy-17,17-ethylendioxy-15β,16β-methylene-5-androsten-7β-ol

3β-acetoxy-17,17-ethylendioxy-15β,16β-methylene-5-androsten-7β-ol( Ⅰ ) was prepared by 3 steps from 3β-acetoxy-15β,16β-methylene-5-androsten-17-one ( Ⅱ ) with overall yield of 52.7%. Thus, interaction of ethylene glycol and material ( Ⅱ ) gave 3β-acetoxy- 17,17-ethylendioxy-15β,16β-methylene-5-androsten ( Ⅲ ) which was subsequently oxidated and stereoselectively reduced to produce compound( Ⅰ ). The normal influencing factors, such as the types of oxidants and reductives, the mole ratio of reactants, the reaction temperature, and the addition ways of reactants, in oxidation and reduction were discussed. The results show that the oxidation rate order is CrO3-C5 H5 N (1: 1, mole fraction)＞CrO3-C5H5 N(1: 2)＞ (C5H5NH)2 Cr2O7 in terms of the oxidant, the yield of the oxidation becomes higher with increasing the oxidant stoichiometry and raising the reaction temperature. And the optimum condition is that the reaction temperature is at 30 ℃, and n(Ⅲ)/n(CrO3-C5H5N(1: 2))=1: 20. The yield of the -7β alcohol order with Li[Al(OC(CH3)3)3H] (e. G. 78. 6%) is more than that with NaBH4 (e. G. 14. 5%) in terms of the reductive agent and the reduction rate decreases in the course of reaction. The compound (Ⅰ) is characterized by 1R and MS.     

载Ag白炭黑抗菌剂的制备及性能研究

以AgNO₃为原料,沉淀白炭黑为载体,采用浸渍法制备载Ag白炭黑抗菌剂,以大肠杆菌为例测试了样品的抗菌性能,并对其抗菌过程进行初步分析。利用单因素实验讨论了银离子浓度、反应温度、反应时间和搅拌速度对载Ag白炭黑抗菌率的影响,确定最优制备条件为：银离子浓度0.2mol/L,反应温度80℃,反应时间1.5h,搅拌速度400r/min。在此条件下制备的载Ag白炭黑具有超过99%的抗菌率,银负载量可达3.0%。采用X射线衍射(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)和激光粒度仪对载Ag白炭黑的物相结构、形貌特征、化合价和粒度分布进行了表征。结果表明：载银白炭黑为蓬松的、多孔的无定型结构,平均粒径为9.9μm,其中,银以纳米Ag单质的形式存在,均匀负载在二氧化硅表面和孔道上。     

Preparation of cobalt-modified magnetite and its magnetic properties

Magnetite was modified by reaction with alkaline solution containing Co^2 and Fe^2 to obtain a cobalt ferrite layer on the surface of particles. The influences of modification conditions on the properties were investigated. The as-prepared particles were characterized by X-ray diffraction(XRD) and transmission electron microscope(TEM). The results show that pH value influences the particles composition directly, the desirable CoFe2O4 is obtained as pH value is 12. The coercivity of particles increases with the increase of cobalt content, and the cobalt efficiency reaches a maximum value at cobalt content of 2.71% (mass fraction). With cobalt modification, the magnetite particles have the similar lattice constant and structure to that without cobalt modification, and the squareness ratio is almost 0.5. The increase of the coercivity is attributed to the uniaxial magnetic anisotropy and magnetocrystalline anisotropy of cobalt-ferrite itself.     

Li-Mn-Ti复合氧化物的结构及其在酸介质中的稳定性

采用固相法合成系列Li-Mn-Ti复合氧化物(理论化学式为LiTi<,x>Mn<,2-x>p<,4>,0≤x≤1);利用热重-差示扫描量热法(TG-DSC)、X射线衍射(XRD)和扫描电子显微镜(SEM)等对其结构和形貌进行表征,并通过酸浸实验考察其在弱酸性介质中的稳定性.结果表明:当x≤0.5时,Ti能完全地纳入尖晶石晶格,并使晶胞参数增大、晶粒变小;Li-Mn-Ti复合氧化物酸浸前、后能够保持尖晶石的结构和形貌,具有结构稳定性,但其化学稳定性还有待进一步提高.     

以海底多金属锰结核制备三元正极材料前驱体Ni0.5Co0.2Mn0.3(OH)2

以海底多金属结核资源为原料,采用硫酸浸出-净化除杂-配合沉淀的工艺制备三元正极材料前驱体Ni_0.5Co_0.2Mn_0.3(OH)₂。在硫酸浸出过程中,考察温度、液固比、硫酸浓度、浸出时间对镍、钴、锰浸出率的影响,探究镍、钴、锰元素浸出动力学。结果表明:在温度200℃、液固比6:1、硫酸浓度350 g/L、浸出时间90 min条件下,镍、钴浸出率达到95%以上,锰浸出率仅为6.43%,实现镍、钴与少部分锰的浸出。当温度在120～200℃之间时,锰浸出过程受扩散控制,表观活化能为10.64k J/mol;镍、钴浸出过程受混合控制,表观活化能分别为27.60和38.16 kJ/mol。浸出液经黄钠铁矾法除铁、硫化锰除铜、碳酸氢铵水解沉淀除铝、P204萃取除钙后,采用P204萃取镍、钴、锰,得到硫酸镍、硫酸钴和硫酸锰的混合液,经调节镍钴锰比例后,用氨水-氢氧化钠配合共沉淀法制备得到球形的Ni_0.5Co_0.2Mn_0.3(OH)₂