Microwave assisted green synthesis of α, ά- bis (substituted- benzylidene) alkanones by the crossed- aldol condensation reaction of substituted aryl aldehydes with ketones in the presence of catalytic amount of NbCl5 in good to excellent yields. This reaction is carried out under solvent-free conditions. The results showed that aldehydes bearing electron–donating substituent's on phenyl-ring fa...

The use of liquid-liquid extraction for the separation of tantalum from niobium was demonstrated. Tantalum and niobium spectrographically free of each other were prepared in quantity on a continuous basis.

We report on a 850 GHz SIS heterodyne receiver employing a RF tuned niobium tunnel junction with a current density of 14kA/cm2, fabricated on a 1 μm Si3N4 supporting membrane. Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2 /h ≈ 690 GHz), special care has been taken to minimize niobium transmission line losses. Both Fourier Transform Spectro...

Metallic niobium powder was produced for applications in electric capacitors via calciothermic reduction of niobium hydroxide in molten CaCl2. Sub-micrometer spherical metallic particles with coral-like morphologies reflected the particle size of the starting oxide powder. A fine powder was obtained from the mixtures of niobium hydroxide and CaO or Ca(OH)2, respectively. Sintered pellets of the...

A method for bonding a niobium wire to a niobium thin film i s described The bonds are to be used as superconducting connections between wire-wound gradiometers and thin-film coupling coils on oc SOUIOS. The method is characterized by two steps. Firstly. the hardness of the niobium wire is reduced by a heat treatment. Secondly, the niobium film is covered with a thin layer of palladium to preve...

Group 3-15 metal chlorides (Lewis acids) were classified on the basis of activity and aldehyde- and aldimine-selectivity in an addition reaction of a silyl enol ether. Based on the experimental results, metal chlorides (Lewis acids) were classified as follows: A, active; B, weak; C, inactive for the activation of the aldehyde and/or aldimines. Groups A and B were further divided into A-1 or B-1...

Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride ...

The growth of niobium carbide in austenite involves the diffusion of both niobium and carbon. These elements diffuse at very different rates. A model is presented for the overall transformation kinetics of niobium carbide precipitation in austenite that takes into account the multicomponent nature of the diffusion process while at the same time allows for the curvature of the transformation fro...

The obtained Q0 value of a superconducting niobium cavity is known to depend on various factors like the RRR of the Niobium material, crystallinity, chemical treatment history, the high-pressure rinsing process, or effectiveness of the magnetic shielding. We have observed that spatial thermal gradients over the cavity length during cool-down appear to contribute to a degradation of Q0. Measurem...