低温热处理对α-Fe/Sm2Fe17Cx纳米复合永磁合金结构和磁性能的影响

采用X射线衍射分析、振动样品磁强计和差热分析研究了低温退火处理对Sm5Fe80Cu1Si5B3C2．5Zr3．5非晶合金晶化后纳米复合永磁体的组织结构、磁性能及晶化动力学的影响。结果表明,经400℃低温热处理后纳米复合合金中α-Fe相和Sm2（Fe,Si）17Cx相的组织结构均产生了明显改变,晶粒尺寸分别从原始态（未经处理）的50．6nm（α—Fe相）和20．6nm（Sm2（Fe,si）17Cx相）改变为36．5和24．4nm;体积分数分别从71．1％（α-Fe相）和28．9％（Sm2（Fe,si）17Cx相）改变为76．7％和23．3％;同时磁耦合性能明显增强。晶化动力学分析发现,低温热处理增大了非晶合金的短程有序范围,改变了原始态非晶合金中α—Fe相和Sm2（Fe,Si）17Cx相的晶化行为,这是优化α—Fe／Sm2（Fe,Si）17Cx复合纳米晶结构和提高磁耦合性能的根本原因。     

HDDR过程中三元和多元Nd-Fe-B合金磁畴结构的MFM研究

用磁力显微镜研究了三元Nd-Fe-B合金在HDDR过程的不同阶段(铸态、不充分吸氢歧化、充分吸氢歧化和脱氢再复合)的破畴结构。在铸态样品表面清楚地观察到了易磁化轴互相垂直的柱状晶表面的两类磁畴图型。当样品不充分吸氢歧化和充分吸氢歧化时，破畴结构明显发生变化，反映了Nd-Fe-B的分解产物NdH2，α-Fe和Fe2B及其微晶结构的变化。脱氢再复合后形成的微晶的磁畴结构则表明样品保留了铸态样品柱状晶的构型。此外，还对比研究了多元Nd-Fe-B合金在HDDR过程中的磁畴结构，并根据微磁结构分析，指出过量的Ga元素添加可抑制Nd2(Fe，M)14B相的吸氢歧化，从而导致相应HDDR粘结磁体性能降低。     

Nd60Fe20Al8Co10B2大块非晶合金晶化过程中的结构及磁性能变化

利用吸铸的方法制备了Nd60Fe20Al8Co10B2大块非晶合金。采用示差扫描量热法(DSC)，X射线衍射(XRD)，扫描电子显微镜(SEM)和振动样品磁强计(VSM)研究了Nd60Fe20Al8Co10B2大块非晶合金在晶化过程中的微观结构及磁性能的变化情况。Nd60Fe20Al8Co10B2大块非晶合金在低于723K退火时，富Nd相和富Fe相的析出对于合金的矫顽力影响不大。但是，富Fe相的长大使合金的饱和磁化强度和剩磁下降明显。合金完全晶化后，硬磁性迅速消失。     

混合稀土对共晶Al-2％Fe合金组织形态的影响

研究了富La混合稀土对共晶Al-2％Fe合金组织形态的影响。当混合稀土加入量较少时，合金中的α—Al相为明显的胞状枝晶；随着混合稀土加入量的增加，α-Al枝晶优先形核生长得到抑制，共晶Al3Fe相得到细化；当稀土加入量增至0．6％(质量分数)共晶Al3Fe相尺寸逐渐增大。并对混合稀土对共晶Al-2％Fe合金组织形态的影响机制进行了探讨。     

LaNi_(5-x)M_x高温氢化的歧化行为

采用X射线衍射、差热分析及电化学方法 ,研究了吸氢合金LaNi5-xMx(M =Mn ,Co,Fe,Cr,Al)在高温氢化反应时的歧化行为及其反应产物的电化学性能。LaNi5-xMx 在 2 5MPa氢压和 550℃以上保温一定时间后可发生明显的歧化反应 ,并析出纳米相镍。歧化反应的程度与加热温度、时间、第三组元M及合金的生成焓关系密切。电化学交换电流密度测定表明 ,经歧化反应得到的含纳米相镍的复相组织与原始合金组织相比具有较高的吸放氢电催化活性。     

高钐含量SmCo磁记录薄膜材料的研究

SmCo合金具有极高的单轴磁晶各向异性,成为未来高密度磁记录介质的候选材料之一.本文采用磁控溅射方法,在玻璃基片上制备了Cr(100nm)/SmCo(50 nm)/Cr(20 nm)结构的Smco薄膜,SmCo层中Sm含量为35%(原子分数).利用综合物性测试系统(PPMS)和X射线衍射(XRD)对薄膜的磁性能和晶体学结构进行了测试.结果表明,通过550℃退火20 min可以获得很好的硬磁性能,矫顽力R.达到了3183kA·m-1,XRD结果表明薄膜中同时存在磁性相SmCo5和非磁性相SmCo2等.高Sm古量的SmCo薄膜在退火温度为450℃时开始晶化,退火温度达到550℃时,晶化进行的比较完全.     

Sm2Fe17N3晶体的价电子结构分析和结合能、最强键能计算

由EET理论直接建立了Sm2Fe17N3晶体的价电子结构,同时计算并筛选了晶体的结合能和最强键能,分别为EC^0=14716.8±13.7kJ·mol^-1和Eα=110.1311 kJ·mol^-1。分析计算结果表明:Sm2Fe17N3晶体内共价电子数主要分布在12对由Fe(c1),Fe(c2)和Fe(c3)参与形成的最强键能的键上,由这3种Fe晶位原子形成的共价键键距普遍小于0.3 nm,共价键较强对晶体结合能作主要贡献;并且其结合能相比Sm2Fe17晶体的小得多,解释了Sm2Fe17合金在低温和非真空状态条件下易氧化而经过渗氮后得到的Sm2Fe17N3则表现出常温下结构稳定、化学性能好的特性;计算出N原子参与形成的成键原子对的理论键能值普遍在1 kJ·mol^-1左右,反映出Sm2Fe17N3化合物内在渗氮特性,分析了制备钐铁氮永磁材料过程中Sm2Fe17合金较低温渗氮难、渗氮不稳定和渗氮不均匀的缺陷。     

还原扩散法制备钐铁氮磁性材料的组织结构与性能研究

研究了还原扩散法制备Sm2Fe17Nx(x≈3)磁性材料的组织结构与性能。用DTA方法测定了Sm2Fe17Nx的热稳定性,用VSM测定了本实验所制Sm2Fe17Nx磁体的磁滞回线和退磁曲线;用TEM及高分辨电镜分析了渗氮前后Sm2Fe17合金及Sm2Fe17Nx结构。结果表明:Sm2Fe17Nx的分解温度为841 K,用还原扩散法制备的Sm2Fe17Nx磁粉做成粘结磁体后各向异性不是很强烈,性能偏低。Sm2Fe17Nx磁粉磁性的好差与渗氮层的厚度有密切的关系,渗氮后的Sm2Fe17Nx确实有体积膨胀的现象,而且属非晶结构。     

添加镝的Nd-Fe-B纳米晶单相合金的微结构与磁性能研究

采用单辊快淬法制备了Nd12.3-xDyxFe79.7Zr0.8Nb0.8Cu0.4B6.0(x=0,0.5,1.5,2.5)合金纳米晶单相永磁薄带,研究了合金薄带晶化处理后,成分、组织结构与磁性能之间的关系.X射线衍射分析(XRD)表明,淬态合金主要由非晶相和Nd2Fe14B相组成,完全晶化后由Nd2Fe14B相和少量α-Fe组成.高分辨透射电镜(HRTEM)分析表明,经充分退火后,Nd2Fe14B晶体完整,晶粒间几乎没有边界相.随着Dy含量增加,晶粒尺寸细化,矫顽力大幅提高.x=0.5合金综合磁性能最佳,经过700℃晶化处理10min后,其磁性能为Jr=1.09 T,Hci=1048kA·m-1,(BH)max=169.5 kJ·m-3.     

Ca-Sm2O3-Fe体系生成Sm2Fe17的研究

对由Ca-Sm2O3-Fe体系通过还原扩散反应生成Sm2Fe17合金的过程进行热力学和动力学分析; 研究了产物Sm2Fe17合金的收率及Sm和残余CaO的含量. 结果表明 还原扩散法制备Sm2Fe17合金的收率较高, 均大于80%, 且残余CaO的含量极低, 均小于0.55%; 随着温度的上升和反应时间的延长, Sm2Fe17合金的收率和Sm2Fe17合金中Sm的含量均增大. 收缩核模型处理结果表明 液态Sm和固态Fe之间的包晶反应为整个还原扩散反应过程的控速步骤; 还原扩散反应的表观活化能为73.74 kJ·mol-1, 指前因子为7.79×10-3.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.