Flow equations for electron-phonon interactions: phonon damping

We report Nuclear Magnetic Resonance studies of CeAuAl₃ and LaAuAl₃ at frequencies between 1.30 and 76.91 MHz and at temperatures from up to . CeAuAl₃ is a new heavy-electron compound which orders antiferromagnetically at . For the two inequivalent Al sites of CeAuAl₃, the transferred hyperfine couplings and are relatively small compared to those in other Ce compounds. The nuclear quadrupolar coupling constants e2qQ / h are 2.9 MHz and 7.8 MHz, respectively. We suggest that the magnetic structure of the ordered state below is of a simple spiral type with the ordered Ce moments arranged ferromagnetically within the ( ab ) planes of the tetragonal crystal lattice. Based on this magnetic structure we estimate a 25% reduction of the Ce moments, most likely due to Kondo screening. At high temperatures, in the paramagnetic state of CeAuAl₃, the spin-lattice relaxation rate T1 ^-1 is dominated by the fluctuations of the localised Ce moments. At , T1 ^-1 is , more than two orders of magnitude larger than for the reference compound LaAuAl₃. For temperatures lower than T1 ^-1 decreases as a function of ( T / H ) and below , displays a linear-in-T behaviour, strongly enhanced compared to the reference compound LaAuAl₃. Received: 5 May 1998 / Received in final form: 16 July 1998 / Accepted: 20 July 1998     

The effect of anions in the coordination spherè of Mg complexes ofN-acetyldehydrophenylalanyl-(S)-valine on the diastereoselectivity of hydrogenation

Diastereoselective hydrogenation in ethanol over Pd/C ofN-acetyldehydrophenylalanyl-(S)-valine (1) as complexes with Mg salts of strong acids gives predominantlyN-acetyl-(S)-phenylalanyl-(S)-valine (de up to 60%). In the case of complexes of1 with Mg salts of weak acids, the sign of asymmetric induction changes. Data of¹⁹F NMR spectroscopy ofN-acetyldehydro(p-fluorophenylalanyl)-(S)-valine indicate that in the former case, the anion of a strong acid does not enter the coordination sphere of the complex, whereas in the larter case, the anion of the weak acid does. The nature of the solvent also influences the reaction stereoselectivity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1704–1706, September, 1999.     

MgAl2O4尖晶石的合成及作为甲烷部分氧化反应的良好催化剂载体

γ-Al2O3 has been intensively studied as a catalyst support in alkane conversion due to its large surface area. However, it is susceptible to crystal phase transition and favors catalyst sintering while the operaing temperature is higher than 700℃. Therefore, its application in industrial reactions is limited.     

NiO对镁铝尖晶石反应烧结性能的影响

本文以高纯电熔镁砂和煅烧活性氧化铝粉为原料,以氧化亚镍(NiO)为添加剂,通过传统固相烧结法制备镁铝尖晶石材料。将MgO和Al₂O₃粉按理论摩尔比1∶1进行配料,在体系中分别引入质量分数为0%、0.5%、1.0%、1.5%、2.0%的NiO。利用X射线衍射(XRD)仪、扫描电子显微镜(SEM)和能谱仪(EDS)对烧结后试样进行分析,研究了NiO的添加对MgAl₂O₄材料烧结性能、物相组成及显微结构的影响。结果表明:引入适量的NiO可以显著促进MgAl₂O₄相的形成以及晶粒的发育长大;在1 600 ℃时,当NiO含量低于1.5%时,NiO能完全溶入MgAl₂O₄晶格并优先取代Al³⁺,提高了MgAl₂O₄晶体内部的缺陷浓度,活化了晶格,从而促进MgAl₂O₄的烧结。当NiO含量高于1.5%时,其内部开始出现较多第二相NiO,阻碍了物质的迁移和传输,反而不利于MgAl₂O₄烧结性能的提高。     

盐卤硼酸盐化学——Ⅲ.盐卤在动态蒸发条件下硼酸镁的极限溶解度

首先将含硼盐卤日晒蒸发到不同浓度,分别取硫酸镁析出阶段卤水和水氯镁石析出阶段卤水加入芒硝使全部回溶。利用硫酸钠和氯化镁在水溶液中存在交互反应,将芒硝回溶后卤水进行天然蒸发浓缩到硼酸盐开始结晶析出,测得盐卤在动态蒸发过程中硼酸镁的最大极限溶解度为7.36～7.50%MgB₄O₇,室温放置10年后的平衡溶解度为0.94%MgB₄O₇。     

氧化镁对聚丙烯/聚氯乙烯脱氯行为的影响

对废旧塑料的回收利用是近年来人们一直关注和不断研究的一个重要课题。将废塑料热裂解为燃料油或单体被认为是最具前景的处理方法之一[1]。当含有PVC的废旧塑料裂解时产生氯化氢气体,严重腐蚀设备;同时也会产生含氯的有机化合物,从而使其裂解生成的液体作为燃料使用时会生成有     

超音速火焰喷涂含铝或锌中间层的YSZ热障涂层

在镁合金基底表面直接制备热障涂层,涂层的耐蚀性较差。采用超音速火焰喷涂法在镁合金基底和热障涂层之间分别制备了Al涂层和Zn涂层。通过XRD,SEM和EDS对涂层进行物相、微观结构和点扫描元素分析,采用电化学工作站对Al涂层试样和Zn涂层试样进行耐腐蚀性分析,同时研究了含Al中间层和含Zn中间层的热障涂层的抗热震性能。结果表明:Al涂层表面粗糙度(10.237±0.527μm)大于Zn涂层表面粗糙度(7.171±0.488μm),且喷涂过程中仅有轻微氧化。Al涂层试样的耐腐蚀性优于Zn涂层试样。含Zn中间层的热障涂层具有更好的抗热震性能。     

快速凝固过共晶铝硅合金的微观组织特征及耐磨性研究

利用单辊旋淬快速凝固法制备Al-21Si和Al-30Si过共晶铝硅合金,采用扫描电镜、透射电镜及XRD技术对所制备合金的组织形貌和相结构进行表征.结果表明:快速凝固合金形成微纳米晶组织,晶粒明显细化.Al-21Si过共晶合金凝固组织由羽毛针状(α-Al+β-Si)共晶体和雪花状α-Al相组成;快速凝固有效抑制初生硅相的形核与生长,α-Al相领先共晶形核生长,形成微纳米级亚共晶组织.Al-30Si高硅过共晶合金初生硅相细小钝化,初晶Si相显微结构为孪晶形貌,呈典型的过共晶组织特征.快速凝固显著提高了合金的显微度和耐磨性,快速凝固Al-21Si合金的耐磨性是传统铸造合金的5倍.     

网纹型表面微结构对Ti-6Al-4V水润滑摩擦学特性的影响

研究了Ti-6Al-4V合金表面网纹型微结构与Si3N4小球对摩时的水润滑摩擦学性能.利用电火花加工技术在Ti-6Al-4V合金表面加工出不同尺寸的网纹结构,运用正交试验设计方法分析了网纹宽度、深度、间宽比和网纹角度对Ti-6Al-4V合金水润滑摩擦学性能的影响.结果表明:具有合适几何参数的网纹结构能够降低摩擦副在水润滑条件下的摩擦系数和磨损量.当网纹角度在45°时,摩擦副的摩擦系数和磨损量能同时降低.网纹宽度对稳态摩擦系数的影响最大,而网纹深度和夹角对摩擦副材料的磨损影响最大.     

CaX分子筛负载过氯酸镁催化剂的制备及其催化性能

微波辐射;乙氧基化;CaX分子筛负载过氯酸镁催化剂的制备及其催化性能