Mo基复合金属氧化物催化丙烷氧化制丙烯醛

制备了Mo基复合金属氧化物(MoMxOn,M=C r,Co,Zn,Mn,Nb,Ce)催化剂,评价了不同金属含量的MoMxOn催化剂在不同温度下对丙烷选择性氧化制备丙烯醛反应的催化性能。在所研究的各种MoMxOn催化剂中,MoCo0.1On催化剂在773 K时的催化性能最佳,丙烯醛的收率为9.3%。Raman光谱和X射线衍射表征结果表明,除MoNbxOn催化剂外,其他各种MoMxOn催化剂中的主要物相是MoO3,说明MoO3可能对催化活性起重要作用。增加Co含量使MoO3衍射峰的相对强度发生改变,可能是引起MoCoxOn催化剂氧化性能下降的原因。     

Selective de-alloying of NiTi by oxochloridation

The systematic modification of a nickel–titanium-alloy by annealing in a complex gas atmosphere was investigated. A mixture of HCl and H₂O in inert argon was chosen. The reaction kinetics was investigated at 600 °C, 700 °C and 800 °C. The reaction kinetics displayed a significant dependence on the temperature. It was monitored by means of a thermogravimetric balance that showed a quasi-parabolic scale growth at 600 °C, a paralinear or so called Tedmon kinetic at 700 °C with a distinct weight maximum after about 35 h, and finally a linear evaporation kinetic at 800 °C. This behaviour is attributed to the concurrent reactions of oxidation, chloridation and evaporation of corrosion products. The kinetics of these reactions is different for the two alloying elements and with respect to the equiatomic composition they are coupled to each other. Cross sections prove that a stochiometric titanium depletion is achieved leading to the formation of a Ni₃Ti layer (d = 50 μm) which is in turn covered by a pure titanium oxide layer (d = 40 μm). The applicability of this technique for tailored surfaces with a high degree of biocompatibility is discussed.     

Reversible addition fragmentation chain transfer copolymerization: influence of the RAFT process on the copolymer composition

Reversible addition fragmentation chain transfer (RAFT) mediated and conventional copolymerizations at low monomer conversions have been carried out for the systems methyl methacrylate (MMA)-styrene, methyl acrylate (MA)-styrene and methyl methacrylate-butyl acrylate (BA). The polymer samples have been analyzed via ¹H-NMR spectroscopy to obtain the copolymer composition and the terminal model reactivity ratios. In the RAFT mediated copolymerizations, the polymer mole fraction of the monomer with the larger reactivity ratio is increased compared to the conventional copolymerization. Simulations have been carried out using the program package PREDICI^® to examine possible explanations for the experimental findings. The simulations demonstrate that the RAFT process itself may alter the macroradical populations and the copolymer composition by offering additional reaction pathways. Further, the rate coefficients for the initiation reaction and the pre-equilibrium play an important role in determining the copolymer composition. The rate coefficients governing the main equilibrium of the RAFT process have only a minor impact on the copolymer composition.     

Permittivity of modified polyimide layers on LTCC

In this work, the permittivity of a tailored compound material was investigated consisting of a polyimide matrix in which hollow glass microspheres with a mean diameter of 30 μm are implemented as filler material. Choosing this approach the dielectric constant compared to that of the pure polyimide material is further decreased due to the enclosed air targeted to improve the high-frequency performance of patch antennas operated in the GHz range. Furthermore, the thickness of one single layer can be increased substantially from a maximum of about 10 μm for pure polyimide films to values above 80 μm by simply adding this type of filler material to the liquid polyimide precursor so that cavities in LTCC (low temperature co-fired ceramics) substrates can be filled more reliable. Two different variations of this compound material with filler to polymer ratios of 1:7.5 and 1:10 are realized. Basically, the film thickness depends on the spin coating speed and the microsphere content, respectively. The high initial surface roughness can be decreased to an average value of about 3 μm by applying additional layers of pure polyimide on top enabling thin film technology. The dielectric constant of the complete substrate comprising the LTCC and the compound material is measured using a ring resonator in microstrip configuration. From the resonances occurring in the transmission S-parameter |S₂₁| spectrum between 1 and 10 GHz, the relative dielectric constant can be determined. Using 820 μm thick LTCC substrates the permittivity can be reduced from originally ε_r = 7.8-6.6. By applying numerical calculations, a reduced permittivity of the pure polymer film from ε_r = 3.3 to about 2.9 can be determined when adding the glass microspheres.     

Electrochemical production of nanopore arrays in a nickel aluminium alloy

Directional solidification of a eutectic is a novel route for the production of nanostructures. This method was applied to the quasibinary NiAl-Re system. Re as the minor phase forms fibers, which are parallel aligned in the NiAl matrix. At a temperature of 1690 ± 10 °C using a thermal gradient of 40 °C cm⁻¹ and a growth rate of 30 mm h⁻¹, the fibers formed had a diameter of about 400 nm. An electrochemical method is presented here that simultaneously passivates the NiAl matrix and selectively electrodissolves the Re. In this manner, it was possible to form an array of nanopores each with the same diameter of 400 nm. The mechanisms behind this procedure, as well as the potential of this method for the production of nanoelectrode arrays or nanofilters are discussed.     

Stabilizability of systems with exponential dichotomy

In this paper we introduce the concept of controllability into a closed subspace for time-varying linear systems. Various characterizations are given and the dual relation is discussed. This concept is used to present a necessary and sufficient condition for the stabilizability of systems with exponential dichotomy.