Reactivity of Intermetallic Compounds:  A Solid State Approach to Direct Reactions of Silicon

Abstract

The present work is focused on a new approach to describe, quantify, and compare the reactivity of various transition metal silicide phases toward hydrogen chloride. Thermodynamic and kinetic parameters are obtained from isothermal calorimetric studies of these reactions. The reactivity of the silicide phases is discussed in terms of reaction start temperatures, rate constants, and apparent activation energies. Negative apparent activation energies are observed at low temperatures and are attributed to an initial stage of reaction where chlorine is chemisorbed and then incorporated into the silicide lattice near the surface. At a later time, a chlorine-containing reaction layer is formed having a composition and reactivity remarkably different from that of the bulk phase. On the basis of solid-state investigations, a diffusion model of the microscopic structure of these layers is presented, where a displacement of nickel atoms occurs followed by the occupation of nickel sites by chlorine. A model is suggested in which the electron level of the reaction layer is adjusted by the chlorine content of this layer, resulting in a electronic stabilization of silylenoide species at the surface. The model is applied to explain product distribution in the induction period during the direct reaction of silicon and methyl chloride.

Thermodynamic assessment of the copper catalyzed direct synthesis of methylchlorosilanes

“…It has already shown for the hydrochlorination of silicon, that the composition of the considered silicide phase is practically not changed during the reaction. On the other hand, the composition of the gaseous reaction products can undergo dramatic changes by variation of the transition metal and the metal-to-silicon ratio [31]. In the absence of any reactant excess, hints about the ongoing reaction due to solid phase depletion, processes at the initial or final period of reaction, or possible local equilibrium can be derived.…”

“…silylenes) or a chemical surface modification (e.g. the formation of a surface reaction layer [31]) established during the induction period act as a kinetic barrier of C-H bond cleavage.…”

Studies of the Induction Phase of the Hydrochlorination of Metallurgical Silicon

“…Ob sich die metallurgischen Si-Chargen in ihrem Zündverhalten unterscheiden, ist bis jetzt nicht bekannt. Weiterhin wurde über das Phänomen der Induktionsphase, die Phase bis zur tatsächlichen Reaktionszün-dung, bis jetzt sehr wenig berichtet [7]. Einer der Gründe dafür ist die benötigte, extrem hohe Zeitauflösung der verwendeten analytischen Methoden, mit denen die Messungen durchgeführt werden sollen.…”

High Temperature Chlorosilane Corrosion of AISI 316L

“…24,25 They proposed several reactions in the metal-chlorosilane system that can take place to form metal silicides. The first is the direct reaction of a metal with STC to form a silicon rich metal silicide as modeled by Equation 1.…”