Effect of the nature of the support on the activity of palladium catalysts for oxidation of carbon monoxide

We have studied the catalytic activity of TiN_0.65, TiO₂, Al₂O₃, and palladium catalysts supported on them in the oxidation of carbon monoxide. The order in which the activities of the supported catalysts vary, Pd/Al₂O₃>Pd/TiO₂>Pd/TiN_0.65, is the reverse of the activity series for the supports. This is explained by the effect of transfer of electron density from the palladium to the substrate. Taras Shevchenko Kiev University, 64 Vladimirskaya ul., Kiev 252033, Ukraine, G. V. Kurdyumov Institute of the Physics of Metals, National Academy of Sciences of Ukraine, 36 Akademika Vernadskogo bul’var, Kiev-142 252642, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 118–121, March–April, 1998.     

Influence of high-temperature annealing on the orientation of the unipolarity vector in lead zirconate titanate thin films

The factors responsible for the change in the orientation of the natural unipolarity vector due to heating to the Curie temperature of a Pt/PZT/Pt thin-film capacitor (PZT—lead zirconate titanate) formed on a TiO₂/SiO₂/Si substrate have been considered. Lead zirconate titanate thin layers containing a small excess of lead oxide have been formed ex situ using high-frequency magnetron sputtering with a variation in the annealing temperature (crystallization of the perovskite phase) in the range from 580 to 650°C. It has been assumed that the reorientation of the unipolarity vector in the PZT layer is caused by the change in the mechanism of crystallization of the perovskite phase with an increase in the annealing temperature.     

Phase-to-phase perovskite growth transformation in thin PZT films

The structure and dielectric properties of thin lead zirconate titanate films grown ex situ on Pt/SiO₂/Si substrates were studied. It was shown that with a crystallization temperature increase in the range of 540 to 580°C, the mechanism of perovskite phase growth changes and the ferroelectric parameters change according to this transformation.     

Compositional studies of near-room-temperature thermal CVD poly(chloro-p-xylylene)/SiO2 nanocomposites

Chemical-vapor-deposited (CVD) nanostructured thin films have been recently developed to overcome the limitations of thin films from one material class. In particular polymer/SiO₂ nanocomposite thin films have been developed to reduce power consumption, cross-talk, and RC delay in the next generation of ultralarge-scale integrated devices. Since polymers mainly possess electronic polarization they inherently have a low dielectric constant. However, they often suffer from poor dielectric anisotropy, low elastic and shear moduli, and have poor resistance to metallic diffusion. As a proof of concept, poly(chloro-p-xylylene)/SiO₂ thermal CVD nanocomposites have been developed to overcome such material deficiencies. Additionally, the CVD process allows for high manufacturing throughput and compositional control in situ, both potentially advantageous for IC fabrication. The study here focuses on the polymeric phase of the nanocomposite, which as a homopolymer can possess ≈60% crystallinity and a positive optical birefringence of 0.034, both post-deposition-annealed just before the polymer’s melting point. With increasing volume percent of SiO₂, the percent crystallinity is reduced, the thin film becomes more isotropic and the index of refraction can be varied depending on the volume percent SiO₂. Received: 15 December 1999 / Accepted: 7 January 2000 / Published online: 5 April 2000     

Deposition of silver coatings onto sodium borosilicate glass microspheres

A technique for preparation of silver coatings on the surface of sodium borosilicate microspheres was examined. The strength and stability of the coatings were studied as influenced by pre-irradiated titanium(IV) tetrabutoxide employed as surface modifier.     

Method of meridional sections in problems of a three-dimensional boundary layer

The difficulties and clumsiness of problems of calculating the heat transfer distribution over the surface of a body in a three-dimensional flow are well known. It is shown that this problem can be considerably simplified where the influence of the three-dimensionality of the flow, which in certain applications it is important to take into account, is only weak. In this case the three-dimensional problem can be reduced to a set of two-dimensional problems along the lines of meridional sections of the body. This has been demonstrated in detail with reference to the method of effective length or local similarity, which is widely used in engineering practice and is particularly justified in the the case of turbulent heat transfer law. However, in the three-dimensional case it is complicated by the need to calculate the distribution of the streamlines over the surface of the body [1–4]. In the presence of slight asymmetry of the flow the problem can be substantially simplified, mainly as a result of the demonstrated possibility of replacing (with quadratic accuracy) the streamlines by the lines of meridional sections. The possibility of an independent solution of the exact boundary layer equations along each meridional plane is demonstrated for the above-mentioned approximation (rule of meridional sections).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 67–73, May–June, 1986.     

Thermal and environmental stability of poly(4-ethynyl-p-xylylene-co-p-xylylene) thin films

The aim of this paper was to test the thermal and environmental stability of poly(4-ethynyl-p-xylyleneco-p-xylylene) thin films prepared by chemical vapor deposition(CVD) and to optimize the reaction conditions of the polymer.Fourier transformed infrared spectroscopy(FTIR),thermogravimetric analysis(TGA) and fluorescence microscopy were employed to investigate the stability of the reactive polymer coatings in various environmental conditions.Chemical reactivity of the thin films were then tested by Huisgen 1,3-dipolar cycloaddition reaction(‘‘click' reaction).The alkyne functional groups on poly(4-ethynyl-p-xylylene-co-p-xylylene) thin films were found to be stable under ambient storage conditions and thermally stable up to 100 8C when annealed at 0.08 Torr in argon.We also optimized the click reaction conditions of azide-functionalized molecules with poly(4-ethynyl-p-xylylene-co-p-xylylene).The best reaction result was achieved,when copper concentration was 0.5 mmol/L,sodium ascorbate concentration to copper concentration was 5:1.In contrast,the azide concentration and temperature had no obvious effect on the surface reaction.     

Theoretical organic chemistry

It is shown that the structures of X-ray photoelectron spectra of Cu₃Au and CuAu₃ in the disordered state differ from those in the ordered state. It enables us to conclude that the energy spectra of valence electrons in ordered and disordered states are slightly different.