预处理对镁合金镧转化膜及耐腐蚀性能的影响

为了提高镁合金镧转化膜的耐腐蚀性能,通过容量法和电化学方法研究了预处理对镁合金AX91D镧转化膜在5%NaCl溶液中腐蚀行为的影响.利用扫描电子显微镜(SEM)和能量色散谱仪(EDS)研究了膜层表面形貌及其组成,通过电极电位的跟踪测试研究了镧转化膜的成膜过程.结果表明:预处理不改变镧转化成膜过程的基本规律,但有助于镧的氧化物沉积;提高了镁合金镧转化膜的耐腐蚀性能,浸泡30 h其耐腐蚀性能与传统的封闭的铬酸盐转化膜相当.     

电镀锌层稀土转化膜成膜动力学研究

通过测量稀土转化膜生长微观形貌、稀土转化膜生长曲线、成膜反应表观活化能、成膜电位时间曲线及Tafel曲线,研究电镀锌稀土转化膜成膜动力学。结果表明:稀土转化膜的生长分为快速生长、缓慢生长、平稳生长3个阶段,3个阶段生长速率与单位面积转化膜质量均呈抛物线关系,形成具有保护性能的膜层;其中第一、二阶段成膜反应的活化能分别为18.17,28.93 kJ.mol-1,具有较快的反应速率,第三阶段成膜反应的活化能为42.41 kJ.mol-1,反应速率相对较慢。此外,成膜反应还与外因成膜温度和成膜时间有关,升高温度可缩短转化膜成膜的时间,有利于转化膜的形成,成膜温度在25~35℃之间,成膜时间在120~180 s之间,膜层具有较好的耐蚀性能。     

Galfan镀层镧盐转化膜的制备和耐蚀性能研究

将热浸镀Galfan钢板浸入含有20 g·L-1La(NO3)3·6H2O,10 m L·L-1H2O2,0.1 g·L-1Na F的处理液中,在70℃下处理10 s~30 min,从而在其表面获得镧盐转化膜。采用扫描电子显微镜(SEM)观察膜层的微观形貌,能谱仪(EDS)分析膜层的化学成分。采用中性盐雾试验和电化学极化曲线来研究膜层的耐蚀性能。结果表明,镧盐转化膜在晶界或相界等活性区域优先成膜并迅速生长,膜层形成不均匀。随着处理时间的延长,镧盐转化膜逐渐增厚,膜层的裂纹变多、扩大并脱落;膜层主要由Zn,Al,O和La元素组成。与未处理的热浸镀Galfan镀层相比,镧盐转化膜的腐蚀电流密度显著降低,极化电阻显著提高,基体耐腐蚀性能明显提高。     

镁合金表面镧、钐稀土防护膜研究

利用化学转化处理在AZ31镁合金表面制备两种非铈稀土防护膜--镧膜和钐膜.采用电化学阻抗谱(EIS)方法评定膜层的防护效果,采用扫描电子显微镜(SEM)和能量色散谱(EDS)表征膜层的表面形貌及组成.结果表明:镁合金表面镧、钐转化膜均由相应的稀土氢氧化物/氧化物及基体金属氢氧化物/氧化物组成;镧转化膜均匀、致密,对基体金属防护效果好,而钐转化膜呈碎片状,部分覆盖基体表面,防护作用很弱.初步探讨了成膜机制.     

铝合金在铈盐溶液中成膜过程的电化学阻抗谱研究

应用电化学阻抗谱(EIS)研究B95铝合金在0.01 mol.L-1CeCl3溶液中铈盐转化膜的形成过程和机制。结果表明:EIS变化可以清楚地显示B95铝合金在铈盐溶液中成膜的动态过程,稀土转化膜的成膜过程可以分成形成、成长和稳定平衡3个阶段;形成阶段以Al合金的溶解为主;在成长阶段随着时间的增加,转化膜不断增厚,铝合金基体的溶解已经被抑制;稳定平衡阶段,膜的成长与溶解已经达到平衡,通过EIS解析表明自然条件下生成的转化膜不致密,该阶段阻抗谱图等效电路与成长阶段相同,但阻抗谱包含两个时间常数;在成膜三阶段基础上提出了稀土转化膜的成膜模型;同时给出各阶段阻抗谱图等效电路及其阻抗表达式。     

电化学阻抗谱研究铈盐转化膜形成过程中的影响因素

应用电化学阻抗谱(EIS)连续测试B95铝合金在0.01 mol·L-1CeCl3溶液中铈盐转化膜的形成过程,通过成膜过程中交流阻抗值的变化研究了温度,溶解氧O2的变化对B95铝合金稀土转化膜成膜过程的影响机制,采用等效电路的方式对测试的EIS进行了解析.结果表明:温度在20,25,30 ℃时B95铝合金在0.01 mol·L-1CeCl3溶液中的阻抗谱等效电路与成膜形成阶段的相同;温度为35,40,45℃B95铝合金的阻抗谱与成膜成长阶段的等效电路相同,表明升高温度缩短了稀土膜形成阶段的时间,铝合金基体溶解迅速被抑制;升高温度有利于铈盐氧化膜的形成;通O2对稀土Ce转化膜的形成无明显促进作用,O2参与的反应不是Ce转化膜形成的决速步骤.     

镁合金铈转化膜的形成及表征

采用X射线光电子能谱（XPS）、原子力显微镜（AFM）、电化学方法等对AZ31镁合金铈转化膜的组成、形貌结构及耐蚀性能进行了表征,并结合成膜动力学研究探讨了膜的形成机制。结果表明,镁合金铈转化膜的主要成分为铈的氧化物/氢氧化物,铈在膜中以三价和四价两种价态存在。膜可以分为两层,内、外层膜由不同的微结构组成,这种微结构的差异使内、外层膜之间结合力较弱,成为限制膜耐蚀性能提高的根本原因之一。成膜过程中,成膜溶液pH值升高,使Ce3＋发生水解反应沉积析出铈的氢氧化物/氧化物。铈转化膜的生长动力学遵循抛物线规律。     

石墨纤维增强铝基复合材料表面稀土转化膜微观结构

石墨纤维表面和铝基体表面均有稀土膜层存在，EDS面扫描结果认定Ce含量达47．48％，Ce，O，Al，Si是组成膜的主要元素。Ce转化膜在成膜初期微裂纹不明显，但这一阶段成膜较薄，10min时膜层开始出现明显微裂纹。稀土膜层衍射斑点中存在连续的衍射环，也有大量的衍射斑点里不连续的环状排布，说明稀土膜层的晶体结构为纳米微晶，同时存在部分非晶体。由于Ce化合物十分复杂尚未能标定出它的具体晶体结构。Gr（f）／Al复合材料表面稀土膜层是由纳米微晶和非晶体的混合物颗粒堆积而成的，颗粒堆积留下的微孔在成膜初期不明显，但随成膜时间延长，堆积产生的微孔效应越来越明显，由此产生了稀土膜的微裂纹；加之成膜过程的不均匀性，膜层内应力增加以及膜层水分散失等原因也会导致微裂纹的形成。     

聚苯胺在聚酰亚胺膜基体表面的原位沉积成膜机理

采用分散聚合方法,在聚酰亚胺(PI)膜基体表面原位成膜,制备聚苯胺-聚酰亚胺-聚苯胺(PANI-PI-PANI)导电复合膜.通过反应历程跟踪、扫描电镜(SEM)及静滴接触角-界面张力测量仪研究了PANI在PI基体表面原位成膜的过程及其驱动力.结果表明,PANI在PI基体表面的成膜过程有3个阶段:含苯胺的结构单元(包括An盐酸盐、An阳离子自由基及低聚物)在PI表面吸附成核阶段、膜快速增长阶段和增长完成阶段;PANI膜由PANI小颗粒逐渐堆积而成,直至覆盖整个PI膜表面;PANI成膜的主要驱动力来自亲水-疏水相互作用.     

耐超高温连续SiC纤维制备过程中纤维结构和取向演变

以聚铝碳硅烷(PACS)为先驱体, 采用先驱体转化技术制备出耐超高温的连续SiC纤维. 研究了制备过程中纤维结构和取向的演变及其对纤维性能的影响. 研究结果表明, 耐超高温连续SiC纤维制备过程中纤维结构的演变随温度变化分为分子间交联(≤600 ℃)、基本无机化(600—800 ℃)、完全无机化(800—1300 ℃)和结晶重排(1300—1800 ℃) 四个阶段; 纤维的取向随着结构的演变而改变, 连续PACS纤维沿轴向具有的微弱取向, 经热分解后演变到1300 ℃的产物中, 1300 ℃后随着结晶重排的发生, 纤维由各向异性转变为各向同性; 结构和取向的转变对于纤维性能具有很大的影响.     

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%.     

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.     

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.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

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.     

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.