纳米掺杂W型钡铁氧体的制备与性能研究

纳米钡铁氧体因为其优越的磁性能,被广泛应用在微波吸收材料等领域.近年来,对高效吸波材料开发和研究已经成为国内外学术界的热点.按照正交实验表的要求,采用溶胶-凝胶法制备了纳米掺杂W型钡铁氧体,采用TEM、XRD和VSM等检测手段进行了研究,得到了纳米掺杂W型钡铁氧体最佳的制备条件:pH值为7、柠檬酸物与金属离子的物质的量比为1∶1、焙烧温度为1100℃、焙烧时间为4.5 h.     

稀土氧化物对Ni-Zn铁氧体/泡沫铝吸波性能的影响

为研究掺杂稀土氧化物对Ni-Zn铁氧体/泡沫铝材料吸波性能,在泡沫铝表面涂覆了单一 Ni-zn铁氧体(记作CFe)和掺杂质量分数为1%的稀土氧化物的Ni-Zn铁氧体复合粉(记作CFe'),利用CJB 2038-94"雷达吸波材料反射率测试方法"中的雷达截面(RCS)法对材料微波反射率进行了测量,扫描电镜(SEM)和X射线衍射仪(xRD)对吸波剂的形貌和物相进行了分析.结果表明,在12～18 GHz频段内,泡沫铝表面涂敷单一的铁氧体其吸收量为1.8 dB,加人稀土氧化物后,其吸波值由1.8 dB增至2.65 dB,在26.5～40 GHz频段内时,添加稀土氧化物后,吸收量有较大的提高,从11 dB增加到15 dB,10 dB带宽扩展近6倍.因此掺杂稀土氧化物是提高吸波材料性能的一种途径.     

稀土Z型铁氧体Ba3-xCexCo2Fe24O41的制备及其微波吸收性能

采用溶胶-凝胶法合成了掺杂Ce的磁铅石型系列Z型钡铁氧体(Ba3-xCexCo2Fe24O41,x=0.00～0.40).结果表明,Z型钡铁氧体的最佳成相条件为1250 ℃/5 h;测试不同烧结温度下Ba3Co2Fe24O41的吸波特性,发现经1300 ℃/5 h烧结后所得试样对微波的吸收特性最为优良,最大衰减量可达35.012 dB.经1300 ℃/5 h下得到的Ba3-xCexCo2Fe24O41(x=0.00～0.40)的吸波特性分析表明,适量掺杂Ce可以提高Z型钡铁氧体的吸波特性,当x=0.3时有最大衰减量47.575 dB.     

掺La3+纳米钴铁氧体的制备、表征、磁性及其Peg-20000复合物的导电性研究

纳米铁氧体材料的许多电磁性质和光学性质已经有了一些研究[1]。为了改善其性能,有研究者将稀土Ce3 掺入铁氧体材料进行改性,发现其磁导率有明显改变[2]。纳米CoFe2O4因为具有较高的矫顽力、适中的饱和磁化强度、适中的机械强度和化学性质稳定而作为硬磁材料[3]。有研究表明,在CoFe2O4体系中掺入过渡金属离子可以改变其磁性[4],加入稀土Yb3 ,La3 可以使晶格发生畸变,增强磁光效应[5]。因此,本工作研究CoFe2O4体系中掺入La3 引起磁性的变化。磁性纳米粒子掺杂到导电聚合物中可制备高性能吸波材料[6]。因为单一的铁氧体在吸波过程中虽无…     

纳米级钡铁氧体的原子力显微镜分析及微波性能的研究

采用溶胶-凝胶法制备掺杂钡离子的纳米六角晶型铁氧体.采用X衍射仪对其物相进行鉴定,利用原子力显微镜对不同方法制得的试样粒径进行了分析研究,最后用网络分析仪对铁氧体在1～6 GHz范围内的微波性能进行分析,结果表明:实验制得粉体为M型钡铁氧体,利用乙醇分散的稀浓度的试样能在原子力显微镜下很好地观察到颗粒的粒径,其平均粒径为52.68 nm左右,并且实验制得的纳米M型钡铁氧体具有较大的介电损耗和磁损耗,具有良好的吸波性能.     

稀土元素对磁损耗型CoFeZrRE合金微波特性的作用

采用机械合金化工艺(MA)制备了在微波频段具有较高磁损耗的CoFeZrRE材料。在工艺条件对所合成材料性能影响的研究基础上，主要研究了材料组分中掺杂稀土元素对合成材料微波磁导率的影响。结果表明，稀土元素的掺入能有效调整材料的微波磁导率及其频响特性；加入适量的Tb，有利于获得高的微波磁导率和大的磁损耗。还用数值计算模拟方法得到了2～18GHz该材料的反射率曲线，结果表明该材料有可能应用于吸波材料的设计和制备中。     

脉冲激光法连续制备纳米钴乙醇溶胶的研究

纳米钴因其优异的磁性能在磁记录材料 [1]、超顺磁材料 [2 ]、巨磁材料 [3 ]和雷达吸波 [4 ]方面具有重要应用 .金属钴有面心立方、密排六方和非晶态 3种结构 [5] .目前 ,用等离子加热及碳电弧法制备的纳米钴粉基本上都是面心立方结构 [6] .Gibson等 [7]用超声化学方法获得了密     

纳米微孔NixZn(1-x)Fe2O4的水热合成研究

０引言尖晶石型铁酸盐是一类重要的磁性材料，它可用于防止电磁波辐射设备以及隐身材料中的吸波剂犤１，２犦，具有价格低廉、吸波性能优良的特点。同时尖晶石型铁酸盐也是一类重要的催化剂，９０年代初又发现了氧缺位的该类化合物具有将CO２还原为C的优良催化性能犤３犦。因此，有关铁酸盐的制备及性能研究一直是化学工作者和材料科学工作者感兴趣的领域。随着新的合成方法的不断涌现，对传统铁氧体材料进行结构改造以提高其性能是一个重要的研究发展方向，本文采用模板剂造孔技术，首次在NixZn（１－x）Fe２O４水热合成中选用模板剂，…     

柔性复合吸波材料研究进展

吸波材料在隐身技术、电磁兼容、安全保护、微波暗室中的应用十分广泛,因而备受关注。然而传统吸波材料的功能单一,不能同时满足重量轻、涂层薄、柔性、环境适应性等多种需求,限制了其在柔性、可折叠和可穿戴设备中的应用。柔性复合吸波材料一般采用导电损耗、介电损耗和磁损耗等多种吸波机制联用,吸波效率高达99.99%以上,而且具备可折叠、可弯曲、可扭曲变形的特点,为吸波材料在未来人工智能、机器人及可穿戴设备领域的应用提供了重要思路。本文重点介绍碳基、聚合物基、超材料基等柔性复合吸波材料的一些重要研究进展,并对柔性复合吸波材料当前的挑战进行了总结,并对未来的发展趋势进行了展望。     

蓝光剂CaS∶Cu+、Cl-的制备及其光致发光特性

随着农膜光能转换材料[1,2]研究的不断深入,利用碱土金属硫化物为基质材料掺杂稀土元素,制成光转换材料用于农膜的研究已越来越受到人们的重视.文献[1,3,4]相继报道了CaS∶Eu的制备方法、材料结构及其光谱特性,并进行了农田应用试验.本文应用高温固相反应法合成了CaS∶Cu+、Cl 蓝光剂,并探讨了激活剂用量、反应气氛、温度、反应时间等对产品性能的影响.光谱特性研究表明CaS∶Cu+、Cl 适于用作农膜改性的蓝光剂.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.