Anisotropic ordered structures of silicon and silicon carbide by chemical vapor deposition

Anisotropic ordered structures of silicon and silicon carbide were prepared by chemical vapor deposition (CVD) technique using dichlorosilane (DCS), CCl₄, and CF₂Cl₅ and nitrogen gas as the components of starting gaseous mixtures. It has been shown that nitrogen molecules react at the active sites of substrate surface formed upon its etching with the 7.5% DCS + 7.5% CCl₄ + 85% N₂ gaseous mixture.     

Microhand With Internal Visual System

A pneumatically operated four-fingered micromanipulator (a ldquomicrohandrdquo) with a fiber-based internal visual system is developed using microelectromechanical systems fabrication techniques. This ldquoseeingrdquo microhand transfers images generated by the optical system equipped at the palm of the microhand to an operator via an optical fiber bundle to provide the shape and distal information of objects of interest. The use of illuminating fibers along with the optical bundle enables the microhand's operation even in light-deficient environments. Such visual information informs the accurate relative location of the device and the status of manipulation to the operator in real time, who will take subsequent actions accordingly with an increased accuracy and efficiency. Embedding the fiber-based optical system inside the manipulator, instead of using an external camera setup for overall system monitoring, greatly reduces the size of the manipulator and helps increase maneuverability, particularly when operating in a space-limited work area. Tests have been conducted to verify the performance of the visually aided microhand to manipulate millimeter-sized objects in real time. Building on the ability of the UCLA microhand to gently handle irregular-shaped objects, this vision-enabled microhand is expected to provide more accurate manipulations and widen the window of applications.     

Kinetics and Mechanism of Thermal Decomposition of Dinitramide

Kinetics of the thermal decomposition of dinitramide (HDN) in aqueous solutions and of NH₄N(NO₂)₂ (ADN) and KN(NO₂)₂ (KDN) in sulfuric acid, nitric acid and anhydrous acetic acid solutions was studied. The species N(NO₂)₋₂, HN(NO₂)₂ and H₂N(NO₂) were established to take part in the decomposition over a wide range of the medium acidity. Kinetic regularities of their thermal decomposition were determined. The role of the decomposition of dinitramide at the initial and self-acceleration stages of the decomposition of ADN was determined. The most likely mechanism of the decomposition of dinitramide, N(NO₂)₋₂ and H₂N(NO₂)₊₂ was proposed.     

Flame propagation in mixtures of monogermane and oxygen. II. Peculiarities of flame propagation and the structure of combustion waves

Different flame propagation regimes, including a two-wave regime, are studied in a closed pipe with single ignition of GeH₄−O₂ mixtures. It is shown that, depending on the initial conditions and, in particular, on the composition of the initial mixtures, spatially separated chemical reaction waves for oxidation and decomposition of monogermane are observed in certain parts of the reaction vessel which lead to the formation of a two-layer deposit of GeO/Ge. The temporal sequence of the separated combustion wave and wave from which layers of solid products are deposited, as well as the location of the deposition zones in the reaction vessel, are determined by two interacting chain processes—the oxidation and decomposition of monogermane. The thermal relaxation kinetics of the reactive mixture after passage of the combustion waves is determined by the rate of conductive heat transfer from heated solid particles (reaction products) to the gaseous phase. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 77–84, January–February 1999.     

Effect of Chemically Active Additives on the Detonation Wave Velocity and Detonation Limit in Rich Mixtures

On the basis of the Zel’dovich-von Neumann-Doering detonation theory with allowance for heat losses, as well as the theory of chain processes through, the example of the oxidation of hydrogen-rich mixtures in the presence of an inhibitor, it is shown that taking into account inhibition reactions and the trimolecular chain termination has the consequence that there are not only heat losses but also “chemical” losses. It is demonstrated that the presence of only “chemical” losses alone can ensure that there is a concentration limit of detonation and that the combustion wave near the limit is supersonic. Theoretical estimates agree qualitatively with the experimental data on the inhibition of a developed detonation wave in H₂-air mixtures with additives of a propane-butane mixture (0.5–4%) at a pressure of 1 atm.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 295–302.Original Russian Text Copyright © 2005 by Rubtsov.     

Unsteady-state radiative heat transfer between two opaque bodies of finite dimensions

The unsteady-state radiative interaction of two opaque gray bodies according to the Stefan-Boltzmann law is considered. The problem is reduced to a non-linear Volterra integral equation for the net radiation density. A solution is obtained for a linear approximation. The general case and the short-time behavior are discussed.